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IN THIS VOLUME


2008;():1-8. doi:10.1115/DSCC2008-2100.

Time keeping devices have been designed, fabricated, and widely deployed throughout history to regulate daily functions including commerce and transportation. In addition, horology offers a catalog of mankind’s innovation and demonstrates important scientific and engineering concepts. The investigation and analysis of clock systems from a mechatronics perspective illustrates the evolution of gear systems, feedback control, and transformation of energy for time measurement. In this paper, the operational behavior of an eight day mechanical clock has been studied through mathematical models, numerical simulation, and computer animation. The classroom exploration of time keeping mechanisms offers practical applications of physical principles.

Commentary by Dr. Valentin Fuster
2008;():9-16. doi:10.1115/DSCC2008-2101.

A vibration suppression strategy based on passive damping is presented. Modal energy is shifted from low to high frequency modes where it will be rapidly dissipated. This is achieved through the repeated application and removal of constraints. Upon application of the constraint, part of the energy is transferred to the system modes in its new configuration while the remaining energy goes into the unmodeled, high frequency, flexible body modes where it is dissipated. When the constraint is removed, the remaining energy is transferred back to the modes of the unconstrained system. Removal of the constraint allows it to be applied again and the cycle to be repeated until the energy drains away completely. It is shown that the amount of energy lost during one cycle depends on the timing of the constraint application. Special cases where energy is conserved are considered. In one such case, energy is trapped in modes which are unaffected by the application of the constraint. These modes span an invariant subspace where energy remains trapped. Examples of linear systems are presented to illustrate this strategy.

Commentary by Dr. Valentin Fuster
2008;():17-23. doi:10.1115/DSCC2008-2102.

In this paper, modeling, simulation and experimental validation of a magnetic ball suspension system are presented. Non-linear empirical expressions for inductance and electromagnetic force are determined using experimental data. A simple PID controller and a Gain scheduling PID controller are designed based on the linearized model. The controllers are used in real time levitation and tracking of a steel ball. Numerical simulation is carried out using Simulink. The derived model is verified by comparing the simulation results with experimental results.

Commentary by Dr. Valentin Fuster
2008;():25-31. doi:10.1115/DSCC2008-2103.

The demand of hydraulic parallel motion system of space rendezvous and docking simulator to its hydraulic system is high flow and high performance. To achieve good motion simulation results and meet the requirements of precision control, a method of self-tuning parameters fuzzy PID control of proportional water valve opening has been employed to control oil temperature, a method of online vacuum degassing in a sealed system has been used to increase oil effective bulk modulus, and a device has been developed to measure oil bulk modulus online. Experimental research has been carried out on the hydraulic driving system of comprehensive test bed for docking mechanism. The experimental results show that precise control of oil temperature has been achieved and bulk modulus of oil has been increased obviously.

Commentary by Dr. Valentin Fuster
2008;():33-40. doi:10.1115/DSCC2008-2104.

The paper solves some control problems of mobile robots as both kinematics and dynamics are intertwined in the mathematical model. The problems of driving the vehicle to a desired configuration in a specified time and tracking a reference trajectory are considered. The control problems associated with motion in convoy and rigid formations of a group of vehicles are studied and some results are demonstrated by numerical examples.

Commentary by Dr. Valentin Fuster
2008;():41-48. doi:10.1115/DSCC2008-2105.

We explore the use of cable actuators for vibration suppression in space structures. The dynamics of the structure and cable-structure interaction are modeled using finite elements. It is found that the cable has two distinct effects on the structure. The first is a parametric effect, which changes the stiffness of the structure, and the second is a direct effect resulting from an external force on the structure. A general control scheme is designed using passivity analysis, where the input is the cable tension. The study is divided into two parts. In the first part, control by stiffness variation is investigated placing special emphasis on cable placement on the structure. In the second study, control by the direct force is examined and numerical and experimental results are presented.

Commentary by Dr. Valentin Fuster
2008;():49-55. doi:10.1115/DSCC2008-2106.

A Diesel Particulate Filter (DPF) is a necessary component on all modern Diesel vehicles in order to achieve the emission targets for particulate matter. A key problem in this context is the accurate real-time estimation of the soot in the DPF during or after a regeneration event. In this paper, a lumped parameter model for the regeneration regime of a Diesel Particulate Filter (DPF) is proposed which can be used as a starting point for the above purpose. Sensitivity of this model to various model parameters is discussed and significant parameters are identified. An observation problem is identified and a preliminary observability analysis is performed. Results of model performance and implications of the observability analysis are presented.

Commentary by Dr. Valentin Fuster
2008;():57-62. doi:10.1115/DSCC2008-2107.

In this paper we consider a simple model for systems with friction. The model includes differential equations with discontinuous right-hand side. We prove the existence and uniqueness of solution, and also discuss performance limitations caused by friction associated with tracking limitations.

Topics: Friction
Commentary by Dr. Valentin Fuster
2008;():63-70. doi:10.1115/DSCC2008-2108.

This paper presents a first step towards developing a physics-based two-zone model of a single cylinder HCCI engine. Previously control laws were derived by using single zone mathematical models of HCCI combustion; although certain multi-zone models were reported, they were found too complex and unwieldy for the development of fast and efficient controllers for HCCI engines. The present work outlines the modeling approach of a single-cylinder two-zone HCCI engine by incorporating the first law of thermodynamics and temperature and concentration inhomogeneities within the cylinder in order to better predict peak pressures and combustion timings. The results showed good conformity when compared with the computationally intensive multi-zone models. A comparative analysis between the single zone and two-zone models, in the context of predicting cylinder pressures, temperatures, ignition timing is also discussed. Moreover, the effect of external parameters such as speed, and EGR were also evaluated.

Commentary by Dr. Valentin Fuster
2008;():71-78. doi:10.1115/DSCC2008-2109.

A fault diagnosis method for a three mass torsion oscillator is considered which is subject to different additive faults. By using a bank of fault models three faults of different type are detected, isolated and identified in size and time of occurrence. The bank of fault models is formed by a model of each considered fault. Comparison of simulated fault model outputs and measured signals leads to fault isolation. Fault size and time of occurrence are identified by a parity equation approach and used as fault model parameters. The method is capable to perform the tasks with use of one actuator and one sensor signal. It is shown that common approaches for fault isolation can not be used due to the small number of measured signals.

Commentary by Dr. Valentin Fuster
2008;():79-86. doi:10.1115/DSCC2008-2110.

Freeze–form Extrusion Fabrication (FEF) is an additive manufacturing process that extrudes high solids loading aqueous ceramic pastes in a layer–by–layer fashion below the paste freezing temperature for component fabrication. Due to effects such as the air bubble release, agglomerate breakdown, change in paste properties during extrusion as a result of liquid phase migration, etc., the extrusion force is difficult to control. In this paper, an adaptive controller is proposed to regulate the extrusion force. Recursive Least Squares is used to estimate extrusion force model parameters during fabrication and a low–order control scheme capable of tracking general reference trajectories is designed and implemented to regulate the extrusion process. Several parts were fabricated with the adaptive extrusion force controller. These results illustrate the need for extrusion force control and that variable reference extrusion force profiles are required to fabricate complex features.

Commentary by Dr. Valentin Fuster
2008;():87-94. doi:10.1115/DSCC2008-2111.

In Friction Stir Welding (FSW) processes, force control can be used to achieve good welding quality. This paper presents the systematic design and implementation of a FSW path force controller. The path force is modeled as a nonlinear function of the FSW process parameters (i.e., plunge depth, tool traverse rate, and tool rotation speed). An equipment model, which includes a communication delay, is constructed to relate the commanded and measured tool rotation speed. Based on the dynamic process and equipment models, a feedback controller for the path force is designed using the Polynomial Pole Placement technique. The controller is implemented in a Smith Predictor–Corrector structure to compensate for the inherent equipment communication delay and the controller parameters are tuned to achieve the best closed loop response possible given equipment limitations. In the path force controller implementation, a constant path force is maintained, even in the presence of gaps, and wormhole generation during the welding process is eliminated by regulating the path force.

Commentary by Dr. Valentin Fuster
2008;():95-102. doi:10.1115/DSCC2008-2112.

This paper proposes a novel method, called Variable Powder Flow Rate Control (VPFRC), for the regulation of powder flow rate in laser metal deposition processes. The idea of VPFRC is to adjust the powder flow rate to maintain a uniform powder deposition per unit length even when disturbances occur (e.g., the motion system accelerates and decelerates). Dynamic models of the powder delivery system motor and the powder transport system (i.e., five–meter pipe, powder dispenser, and cladding head) are constructed. A general tracking controller is then designed to track variable powder flow rate references. Since the powder flow rate at the nozzle exit cannot be directly measured, it is estimated using the powder transport system model. The input to this model is the DC motor rotation speed, which is estimated on–line using a Kalman filter. Experiments are conducted to examine the performance of the proposed control methodology. The experimental results demonstrate that the VPFRC method is successful in maintaining a uniform track morphology, even when the motion system accelerates and decelerates.

Commentary by Dr. Valentin Fuster
2008;():103-110. doi:10.1115/DSCC2008-2113.

The distance from the center of gravity (CG) of the sprung mass to the roll axis, referred to as the relative CG height, is a critical parameter in vehicle roll motion. Although the nominal value of the relative CG height can be measured, its actual value generally varies due to different vehicle loading conditions. To facilitate the control of vehicle roll motion, this paper presents a model-based in-vehicle estimation of the relative CG height. The parameter estimation utilizes information measured by common in-vehicle sensors and employs an approach for the parameter estimation in stochastic gray-boxes models. An Extended Kalman Filter (EKF) is developed based on a linear vehicle yaw/lateral/roll model and the best estimate was solved by minimizing the EKF prediction error. A simplified estimation algorithm for in-vehicle implementation is also presented; the simplified algorithm limits the parameter space to a finite number of candidate parameters and the candidate that yields the smallest EKF innovation is identified as the best estimate. The estimation results with vehicle experimental data are included to verify the effectiveness of the proposed design.

Topics: Vehicles
Commentary by Dr. Valentin Fuster
2008;():111-113. doi:10.1115/DSCC2008-2114.

This paper presents the preliminary results of an ongoing computational and experimental study of common impact situations in mechanical systems involving both rigid and flexible bodies. It is demonstrated that a characterization diagram that shows the relationship of three non-dimensional parameters with the normalized maximum impact force, can be used to fully describe the impact response. The governing non-dimensional parameters can be obtained a priori by analytical, experimental, or computational means. Impact situations having the same non-dimensional parameters, have dynamic similarity and have the same non-dimensional response. Furthermore, they can be placed in appropriate dynamic regions in which simplified dynamic models can be used to predict the response. Therefore, the characterization methodology has the potential to identify the most suitable model for a given impact situation.

Commentary by Dr. Valentin Fuster
2008;():115-122. doi:10.1115/DSCC2008-2115.

In this paper, we present design, modeling analysis, and experimental study of a vibration-based energy harvester. The energy harvester is made of a composite cantilever of a single crystal relaxor ferroelectric material (PMN-PT), and a polydimethyl-siloxane (PDMS) base layer. A PDMS proof mass is constructed at the tip of the composite cantilever beam. The use of the PMN-PT piezo-material and an interdigited electrodes (IDE) design improves the energy conversion efficiency. The PDMS base layer prevents the possible damage to the fragile PMN-PT layer. A dynamic systems approach is employed to analyze the responses and the performance of the harvester design. The experiments have demonstrated that a prototype of the harvester with a size of 7.4 mm × 2 mm × 110 μm can produce a maximum output voltage of 10 V (0.3 mW power) under a vibration excitation with a peak-to-peak amplitude of 1 mm, and the power density can reach 4.15 mW/cm3 under short circuit conditions.

Commentary by Dr. Valentin Fuster
2008;():123-130. doi:10.1115/DSCC2008-2116.

A human wearing an exoskeleton-type assistive device results in a parallel control system that includes two controllers: the human brain and a digital exoskeleton controller. Unknown and complicated characteristics of the brain dynamically interact with the exoskeleton controller which makes the controller design challenging. In this paper, the motion control system of a human is regarded as a feedback control loop that consists of a brain, muscles and the dynamics of the extended human body. The brain is modeled as a control algorithm amplified by a fictitious variable gain. The variable gain compensates for characteristic changes in the muscle and dynamics. If a human is physically impaired or subjected to demanding work, the exoskeleton should generate proper assistive forces, which is equivalent to increasing the variable gain. In this paper, a control algorithm that realizes the fictitious variable gain is designed and its performance and robustness are discussed for single-input single-output cases. The control algorithm is then verified by simulation results.

Commentary by Dr. Valentin Fuster
2008;():131-138. doi:10.1115/DSCC2008-2117.

The performance of engine cooling systems can be improved by replacing the traditional mechanical driven radiator fan and water pump assemblies with computer controlled components. The power requirements for electric servo-motors increase with larger cooling demands which necessitate larger motors and/or a distributed configuration. One solution may be the use of hydraulic-based components due to their high power density and compact size. This paper investigates a thermal management system that features a computer controlled hydraulic actuated automotive fan and water pump. A mathematical model was derived for the hydraulic and thermal system components. To experimentally study the concept, a hydraulic driven fan and coolant pump were integrated with electric immersion heaters and radiator to emulate a vehicle cooling system. The dynamic model exhibited a strong correlation with the experimental test data. For a series of operating profiles, the servo-solenoid proportional control valves successfully tracked prescribed temperature set points to demonstrate that a hydraulic cooling system can maintain engine operating conditions.

Commentary by Dr. Valentin Fuster
2008;():139-146. doi:10.1115/DSCC2008-2118.

In this paper, we consider nonlinear control of a symmetric spacecraft about its axis of symmetry with two control torques. Using a computationally efficient ℋ∞ control design procedure, attitude regulation and trajectory tracking problems of the axi-symmetric spacecraft were solved. Resorting to higher order Lyapunov functions, the employed nonlinear ℋ∞ control approach reformulates the difficult Hamilton-Jacobian-Isaacs (HJI) inequalities as semi-definite optimization conditions. Sum-of-squares (SOS) programming techniques are then applied to obtain computationally tractable solutions, from which nonlinear control laws will be constructed. The proposed nonlinear ℋ∞ designs will be able to exploit the most suitable forms of Lyapunov function for spacecraft control and the resulting controllers will perform better than existing nonlinear control laws.

Topics: Space vehicles
Commentary by Dr. Valentin Fuster
2008;():147-154. doi:10.1115/DSCC2008-2119.

We propose a semi-autonomous teleoperation control framework for wheeled mobile robots with nonholonomic constraints and second-order Lagrangian dynamics over the Internet. The proposed control architecture consists of the two control-loops: 1) local autonomous formation control, which, residing in the common workspace of the robots, ensures rigid formation-keeping among the robots regardless of human-command, varying-delay/packet-loss of the Internet, and external disturbance without any holding-fixture (e.g. fixture-less cooperative grasping); and 2) teleoperation-loop, which enables a (remote or coexisting) human operator to stably tele-drive the overall team maneuver (e.g. grasped object’s centroid motion) over the Internet with haptic-feedback. Simulation is performed to validate/highlight properties of the proposed control framework.

Commentary by Dr. Valentin Fuster
2008;():155-162. doi:10.1115/DSCC2008-2121.

Just as environmental constraints lead nature to produce biological solutions that arise time and again in a variety of living organisms, industry market forces constrain the design of engineered systems. Using data driven dimensional analysis one can uncover these underlying design relationships for a class of dynamic systems. We apply this data driven dimensional analysis methodology to the class of 2-stage electrohydraulic servovalve systems. When the original servovalve design data does not present the expected dimensionless design relationships, we present a clean sheet of paper design which perturbs the servovalve parameters to maintain dynamic similarity and display dimensionless design relationships. These dimensionless design relationships can then be used to produce dynamically similar servovalves for entirely new parameter spaces.

Commentary by Dr. Valentin Fuster
2008;():163-170. doi:10.1115/DSCC2008-2122.

One of the challenges of condition monitoring and fault detection is to develop techniques that are sufficiently sensitive to faults without triggering false alarms. In this paper we develop and experimentally demonstrate an intelligent approach for detecting faults in a single-input, single-output active magnetic bearing. This technique uses an augmented linear model of the plant dynamics together with a Kalman filter to estimate fault states. A neural network is introduced to enhance the estimation accuracy and eliminate false alarms. This approach is validated experimentally for two types of fabricated faults: changes in suspended mass and coil resistance. The Kalman filter alone is shown to be incapable of identifying all fault cases due to modeling uncertainties. When an artificial neural network is trained to compensate for these uncertainties, however, all fault conditions are identified uniquely.

Commentary by Dr. Valentin Fuster
2008;():171-178. doi:10.1115/DSCC2008-2123.

MPC also known as moving or receding horizon control, is a feedback control scheme that has originated in industry as a real-time computer control algorithm to solve linear and nonlinear multi-variable problems that have constraints and time delays. Since disturbances can drive model predictive control into non-convexity and instability this problem has attracted many researchers. The stability studies in this paper are illustrated in presence of colored noise, error in delay estimation, unstable and non-minimum phase system by means of numerical example. The simulation is carried out using an example, which is the main contribution of the paper.

Commentary by Dr. Valentin Fuster
2008;():179-186. doi:10.1115/DSCC2008-2125.

Previous work by the authors developed a novel model reduction method, namely, importance analysis, that offered a unique set of properties: concurrent dynamic and kinematic reduction, applicability to nonlinear systems, preservation of realization, and trajectory dependence. This paper investigates the utility of importance analysis as a model reduction tool within the context of vehicle dynamics. To this end, a high-fidelity model of a High Mobility Multipurpose Wheeled Vehicle (HMMWV) is considered, and this model is reduced for three different scenarios. Reduction is achieved in both dynamics and kinematics while preserving the original definition and interpretation of state variables and parameters. Furthermore, the resulting reduced models are very different in terms of complexity, containing only what is necessary for their respective scenarios, and providing important insight and computational savings. The conclusion is that importance analysis can be an invaluable reduction tool in vehicle dynamics, offering the aforementioned unique set of properties.

Commentary by Dr. Valentin Fuster
2008;():187-194. doi:10.1115/DSCC2008-2126.

The problem of controlling the rectilinear motion of an open container without exceeding a prescribed liquid level and other constraints is considered using a recently-developed constrained sliding mode control design methodology based on invariant cylinders. A conventional sliding mode regulator is designed first to address nominal performance in the sliding mode. Then an robustly-invariant cylinder is constructed and used to describe the set of safe initial conditions from which the closed-loop controller can be operated without constraint violation. Simulations of a typical transfer illustrate the usefulness of the method in an industrial setting. Experimental results corresponding to a high-speed transfer validate the theory.

Commentary by Dr. Valentin Fuster
2008;():195-202. doi:10.1115/DSCC2008-2127.

A fixed full state feedback controller design approach is proposed for linear time invariant (LTI) systems with time delays. This approach enables the designer to use recently introduced “delay scheduling” procedure, which opens a new direction in control synthesis. “Delay scheduling” strategy suggests prolonging the existing (and unavoidable) delays in order to recover stability or to improve the control performance features. To be able to do this, however, system should have multiple stable operating zones in the domain of the delays. The main contribution of this paper is to develop a procedure for designing such a control law. It starts with a simple usage of LQR for non-delayed systems. This approach, nevertheless, imparts some complexities when delays are introduced. We handle them using a recent paradigm, called the Cluster Treatment of Characteristic Roots (CTCR). For an example to the ensuing design strategy, we use a fully actuated cart-pendulum system. Relevant simulations are carried out to show the viability of the proposed idea.

Commentary by Dr. Valentin Fuster
2008;():203-210. doi:10.1115/DSCC2008-2128.

Piezoelectric ceramic material, such as Lead Zirconate Titanate (PZT), has large stress and bandwidth, but its extremely small strain, i.e. only 0.1%, has been a major bottleneck for broad applications. We have proposed a “nested rhombus” multi-layer mechanism for PZT actuators, which increases strain exponentially through its hierarchical cellular structure, for over 20% effective strain. To drive a large load, however, care must be taken in the design of the strain amplification structure. Through kinematic and static analysis this paper addresses how the output force and displacement are attenuated by the joint stiffness and beam compliance involved in the strain amplification mechanism. An insightful lumped parameter model is developed to quantify the performance degradation and facilitate design tradeoffs. A prototype nested PZT cellular actuator that weighs only 15 g has produced 21% effective strain (2.49 mm displacement from 12 mm actuator length) and 1.7 N blocking force.

Topics: Actuators , Mechanisms
Commentary by Dr. Valentin Fuster
2008;():211-218. doi:10.1115/DSCC2008-2129.

Thickness and tension control in multi-stand cold rolling mills is a multivariable problem which in literature is typically solved with MIMO control approaches. Nevertheless due to the realization and commissioning effort SISO PI-control is often preferred for practical applications. In this article the coupling between strip thickness and interstand tension is analyzed in detail. Based on this analysis an assignment of controlled and manipulated variables is proposed for the design of SISO PI-control loops. A method for the controller design based on the Internal Model Control approach is presented and it will furthermore be shown how the SISO loops can be extended stepwise to a more complex MIMO controller. This results in a scalable control concept where performance and controller complexity are directly linked.

Commentary by Dr. Valentin Fuster
2008;():219-225. doi:10.1115/DSCC2008-2130.

Presented is a method for model based diagnostics of automotive three-way catalysts (TWC). The model relates measurable engine inputs (engine air mass (AM) and catalyst temperature), to a metric indicating oxygen storage capacity, KTWC . The model structure is identified using orthogonal least squares (OLS). The model coefficients are estimated via the instrumental variable four step (IV4) approach. TWC diagnostics is realized using an information synthesis (IS) technique. This diagnostics method is experimentally validated using data from federal test procedure (FTP) driving cycle for a healthy (full useful life, FUL) and failed (threshold) TWC.

Topics: Catalysts
Commentary by Dr. Valentin Fuster
2008;():227-234. doi:10.1115/DSCC2008-2131.

It is shown that delineation of output sensitivities with respect to model parameters in dynamic models can be enhanced in the time-scale domain. This enhanced differentiation of output sensitivities then provides the capacity to isolate regions of the time-scale plane wherein a single output sensitivity dominates the others. Due to this dominance, the prediction error can be attributed to the error of a single parameter at these regions so as to estimate each model parameter error separately. The proposed Parameter Signature Isolation Method (PARSIM) that uses these parameter error estimates for parameter adaptation has been found to have an adaptation precision comparable to that of the Gauss-Newton method for noise-free cases. PARSIM, however, appears to be less sensitive to input conditions, while offering the promise of more effective noise suppression by the capabilities available in the time-scale domain.

Commentary by Dr. Valentin Fuster
2008;():235-242. doi:10.1115/DSCC2008-2133.

Analytical engineering design is a global activity requiring efficient global distribution of analytical models of dynamic physical systems through computer networks. Finite Element Method (FEM) models are used globally to analyze the response of physical systems assembled from physical components. FEM models from different physical component suppliers often have geometrically incompatible meshes. This geometric incompatibility of mesh node placement typically requires component internal details in the assembly process. The modular model assembly introduced in this paper does not require such component internal details. It assembles incompatible finite element component models fast and with accuracy comparable to traditional reformulation. The proprietary geometry and material component details are not revealed during the assembly. Modular model assembly can be used to assemble distributed component models through the internet in global engineering design. Dynamic examples are provided.

Commentary by Dr. Valentin Fuster
2008;():243-251. doi:10.1115/DSCC2008-2134.

This paper presents two different control strategies for paper position control in printing devices. The first strategy is based on feedback linearization plus dynamic extension (dynamic feed-back linearization). Even though this controller is very simple to design, we show that it is not able to handle actuator multiplicative uncertainties, and therefore it fails when it is implemented on the experimental setup. The second strategy we present uses similar concepts, but it is more robust since feedback linearization is used only to linearize the kinematics of the system and internal loops are used to locally control the actuator’s positions and velocities. Not only do we prove the robustness of the second control strategy, but we also show its successful implementation.

Topics: Feedback , Mechanisms
Commentary by Dr. Valentin Fuster
2008;():253-258. doi:10.1115/DSCC2008-2136.

A transporting mechanism is designed for a micro total analysis system to move samples and reagents through microchannels that connect unit procedure components in the system. This study presents control design based on the 8051 microprocessor and implementation of biochip system comprising a pneumatic pumping actuator, feedback-signal photodiodes, and flowmeter. The new microfluid management technique successfully improved the efficiency of molecular biology reaction by increasing the velocity of the target nucleic acid molecules, which increases the effective collision into the probe molecules as the target molecules flow back and forth. Therefore, this hybridization chip is able to increase hybridization signal 6-fold and reduce non-specific target-probe binding and background noises within 30 minutes.

Commentary by Dr. Valentin Fuster
2008;():259-261. doi:10.1115/DSCC2008-2137.

A sequential application and removal of constraints can remove energy from vibrating systems. In this paper several optimization formulations are suggested, whereby maximum energy removal is achieved by selecting optimal strategies that identify where and when the constraints should be applied. The optimization process is illustrated by means of simple mass-spring and membrane systems and the corresponding problems are solved using a genetic algorithm.

Commentary by Dr. Valentin Fuster
2008;():263-270. doi:10.1115/DSCC2008-2139.

In the context of simulating the frictional contact dynamics of large systems of rigid bodies, this paper reviews a novel method for solving large cone complementarity problems by means of a fixed-point iteration algorithm. The method is an extension of the Gauss-Seidel and Gauss-Jacobi methods with overrelaxation for symmetric convex linear complementarity problems. Convergent under fairly standard assumptions, the method is implemented in a parallel framework by using a single instruction multiple data (SIMD) computation paradigm promoted by the Compute Unified Device Architecture (CUDA) library for graphical processing unit (GPU) programming. The framework is anticipated to become a viable tool for investigating the dynamics of complex systems such as ground vehicles running on sand, powder composites, and granular material flow.

Commentary by Dr. Valentin Fuster
2008;():271-277. doi:10.1115/DSCC2008-2140.

Modeling of three-way catalyst behavior in stoichiometric engines is a tovpic with significant depth of research which encompasses complex kinetics based models through highly simplified control-oriented models. For model based control design, one must consider the behavior of the catalyst in conjunction with the feedback oxygen sensors. These sensors have well known influences from exhaust gas species due to interaction with the catalyst which, if ignored, can cause significant difficulties in modeling and control. These effects have often been addressed by calibrating and validating catalyst models under simplified conditions in order to minimize errors. In this work, the root cause of many of these errors is investigated and experimental evidence presented. Additionally, ARMA and Hammerstein models are used to find a model capable of predicting the post-catalyst oxygen sensor response over realistic validation data.

Commentary by Dr. Valentin Fuster
2008;():279-286. doi:10.1115/DSCC2008-2141.

This paper presents a precise modeling framework for modal characterization and dynamic response analysis of nanomechanical cantilever Active Probes with geometrical discontinuities. An experimental setup consisting of a commercial NMC Active Probe from Veeco and a state-of-the-art microsystem analyzer, the MSA-400 from Polytec, for non-contact vibration measurement is developed to verify the theoretical derivations. Mode shapes and modal frequency response of system for the first three modes obtained from the proposed model are compared with those obtained from the experiment and commonly used theory for uniform beams. Results indicate that the uniform beam model fails to accurately predict the actual system response in multiple-mode operation, while the proposed discontinuous beam model demonstrates good agreement with the experimental data. The Active Probe is then utilized in an ultra small mass detection application. For this, a sensitivity analysis is carried out to measure the added mass at the most sensitive mode of operation. Results indicate detection of tip masses as small as a few hundreds of picograms.

Commentary by Dr. Valentin Fuster
2008;():287-294. doi:10.1115/DSCC2008-2142.

This paper presents the analysis and optimization of a series-elastic actuator (SEA) for jumping with an articulated leg. Analytical and simulation results are validated with experimental results from a prototype leg. Similar to the series-elastic elements in muscles, an SEA decouples the dynamic limitations of a DC actuator from the joint, allowing larger liftoff velocities than with a directly driven joint. Detailed analysis of the complex dynamic SEA response during the thrust phase yields insights into its performance. The maximum impulse occurs when the motor speed is approximately half the no-load speed at the moment of peak motor torque. This proposed criterion is used to develop a simple analytical design equation for an optimal SEA.

Commentary by Dr. Valentin Fuster
2008;():295-302. doi:10.1115/DSCC2008-2143.

This paper presents the development and implementation of a robust nonlinear control framework for piezoresistive nanomechanical cantilever (NMC)-based force tracking with applications to high-resolution imaging and nanomanipulation. Among varieties of nanoscale force sensing platforms, NMC is an attractive approach to measure and apply forces at this scale when compared with other previously reported configurations utilizing complicated MEMS devices or inconvenient-to-handle nanowires and nanotubes. More specifically, a piezoresistive layer is utilized here to measure nanoscale forces at the NMC’s tip instead of bulky laser-based feedback which is commonly used in Atomic Force Microscopy (AFM). In order to track a predefined force trajectory at the NMC’s tip, there is a need to model the piezoresistive NMC and design appropriate controller to move its base to provide the desired force. In previous publications of the authors, a new distributed-parameters modeling framework has been proposed to precisely predict the force acting on the microcantilever’s tip. In contrast to this approach and in an effort to ease the follow-up controller development, the NMC-based force sensor is modeled here as a lumped-parameters system. However, replacing the NMC with a linear mass-spring-damper trio, creates a variety of uncertainties and unmodeled dynamics that need to be addressed for a precise force sensor’s read-out. Moreover, the very slow response of NMC’s piezoresistive layer to force variations at the NMC’s tip, makes the tracking problem even more challenging. For this, a new controller is proposed to overcome these roadblocks. Using extensive numerical simulations and experimental results it is shown that utilizing the proposed controller instead of the commonly used PID controller can significantly enhance the controller’s stability and performance characteristics, and ultimately the imaging resolution and manipulation accuracy needed at this scale.

Commentary by Dr. Valentin Fuster
2008;():303-310. doi:10.1115/DSCC2008-2144.

Bilateral teleoperation across significant time delays has been extensively studied and is posed to provide remote control of orbiting robots. Unfortunately, most standard approaches assume an impedance controlled, backdrivable robot. In this work, we apply wave variable control to Ranger, a large, space-qualified, geared robot. We incorporate local feedback of contact forces into the control framework to achieve backdrivable operation. In particular, this control framework imitates an idealized point mass to respect Ranger’s dynamic capabilities. Beyond perceiving steady state contact forces, the user’s perception can be enhanced with high-frequency acceleration feedback of contact transients. Experimental results from controlling Ranger using network communications show stable operation in free space and contact.

Topics: Waves , Force feedback
Commentary by Dr. Valentin Fuster
2008;():311-314. doi:10.1115/DSCC2008-2145.

Aggregate modeling can approximate the convex hull of local matrices to nonlinear dynamics for any given accuracy. The authors use aggregate models to extend sufficient conditions for asymptotic stability of linear differential inclusions to nonlinear dynamics. An example illustrates the applicability of the proposed criteria to the analysis of nonlinear biochemical reaction chains.

Commentary by Dr. Valentin Fuster
2008;():315-321. doi:10.1115/DSCC2008-2146.

Feedforward A/F control in turbocharged gasoline engines with variable valve timing requires knowledge of exhaust manifold pressure, Pe . Physical conditions in the manifold make measurement costly, compelling manufacturers to implement some form of on-line estimation. Processor limitations and the calibration process, however, put constraints on estimator complexity. This paper assesses the feasibility of estimating Pe with an algorithm that is computationally efficient and relatively simple to calibrate. A traditional reduced order linear observer is found to perform well but has too many calibration parameters for practical implementation. Using the performance of the observer as a benchmark, static estimation is explored by parameterizing the equilibrium values of Pe with both the inputs and the outputs of the system. This nonlinear static estimate, combined with simple lead compensation, yields a practical observer implementation.

Commentary by Dr. Valentin Fuster
2008;():323-330. doi:10.1115/DSCC2008-2147.

A nonlinear adaptive framework for bounded-error tracking control of a class of non-minimum phase marine vehicles is presented. The control algorithm relies on a special set of tracking errors guaranteeing satisfactory tracking performance and stable internal dynamics. First, the design of a model-based nonlinear control law, providing asymptotic stability of the error dynamics, is presented. This control algorithm solves the tracking problem for the considered class of marine vehicles, assuming full knowledge of the system model. Then, the analysis of the zero dynamics is carried out, which illustrates the efficacy of the chosen set of tracking errors in stabilizing the internal dynamics. Finally, an indirect adaptive technique is used to address parametric uncertainties in the model. The resulting adaptive control algorithm guarantees Lyapunov stability of the tracking errors and of the parameter estimates, and convergence of the tracking errors to zero. Numerical simulations illustrate the performance of the adaptive algorithm.

Commentary by Dr. Valentin Fuster
2008;():331-338. doi:10.1115/DSCC2008-2148.

Electroslag Remelting (ESR) is used widely throughout the specialty metals industry. The process generally consists of a regularly shaped electrode that is immersed a small amount in liquid slag at a temperature higher than the melting temperature of the electrode. Melting droplets from the electrode fall through the lower density slag into a liquid pool constrained by a crucible and solidify into an ingot. High quality ingots require that electrode melt rate and immersion depth be controlled. This can be difficult when process conditions are such that the temperature distribution in the electrode is not at steady state. A new method of ESR control has been developed that incorporates an accurate, reduced-order melting model to continually estimate the temperature distribution in the electrode. The ESR process is highly nonlinear, noisy, and has coupled dynamics. An extended Kalman filter and an unscented Kalman filter were chosen as possible estimators and compared in the controller design. During the highly transient periods in melting, the unscented Kalman filter showed superior performance for estimating and controlling the system.

Topics: Kalman filters
Commentary by Dr. Valentin Fuster
2008;():339-344. doi:10.1115/DSCC2008-2149.

This paper presents a new approach to blind identification of a class of 2-channel infinite impulse response (IIR) systems describing the wave propagation dynamics. For these systems, this paper derives a blind identifiability condition and develops a blind identification algorithm, which is capable of uniquely determining both the numerator and denominator polynomials of the channel dynamics. The efficacy of the method is illustrated by a 2-sensor central cardiovascular monitoring application as an example, where the cardiovascular blood pressure wave propagation dynamics is identified and the aortic signals are reconstructed from blood pressure measurements at two distinct extremity locations. Experimental results using a swine subject illustrate how the new blind identification approach effectively identifies cardiovascular dynamics and reconstructs the aortic blood pressure and flow signals very accurately from two distinct peripheral blood pressure measurements under diverse physiologic conditions.

Commentary by Dr. Valentin Fuster
2008;():345-351. doi:10.1115/DSCC2008-2150.

An automated test driver (ATD) has been developed which is capable of executing dynamic test maneuvers with accuracy and repeatability beyond the ability of a human driver. This system enables any production car or light truck to follow a user-defined path or to perform specific steering sequences with excellent repeatability. Combined with an automated brake and throttle controller, capable of matching a desired velocity profile as well as providing specific test inputs with acceleration or other feedback, this system provides a powerful tool to improve vehicle dynamics testing.

Commentary by Dr. Valentin Fuster
2008;():353-360. doi:10.1115/DSCC2008-2151.

The equations of motion of planetary gear sets including pinion dynamics are derived using the Lagrange method. The Lagrange method provides a systematic procedure for derivation and yields a single set of equations that are valid for all gears and shifts for a given configuration. This procedure is applied to the coupled planetary gear set in GM Hydramatic 440 transmission. The planetary gear set equations along with a simplified engine, torque converter, friction elements and vehicle model are simulated for 2–3 and 3–4 shifts. The simulation results demonstrate that the equations derived for planetary gear sets can be used for studying shift quality.

Commentary by Dr. Valentin Fuster
2008;():361-368. doi:10.1115/DSCC2008-2152.

Lanekeeping assistance systems and stability control systems both seek to control the yaw behavior of the vehicle. However, lanekeeping systems are typically thought of as linear systems, while stability control systems are explicitly designed to work at the limits of handling. In order to bring these two systems together, there is a need to investigate lanekeeping up to and beyond the limits of handling. This paper presents a nonlinear tire model suitable for analyzing the behavior of a lanekeeping system at all points along the tire curve and a method for finding common quadratic Lyapunov functions to prove stability. The results show that the lanekeeping system is stable well into the nonlinear tire region. This stability holds even under changes in the lanekeeping gain and the understeering/oversteering characteristics of the vehicle. The results suggest that future safety systems could benefit from incorporating integrated lanekeeping and stability control functionality.

Topics: Stability , Functions
Commentary by Dr. Valentin Fuster
2008;():369-375. doi:10.1115/DSCC2008-2153.

AFM-based nanomanipulation is very challenging because of the complex mechanics in tip-sample interactions and the limitations in AFM visual sensing capabilities. In the present paper, we investigate the modeling of AFM-based nanomanipulation emphasizing the effects of the relevant interactions at the nanoscale. The major contribution of the present work is the use of a combined DMT-JKR interaction model in order to describe the complete collision process between the AFM tip and the sample. The coupling between the interactions and the friction at the nanoscale is emphasized. The efficacy of the proposed model to reproduce experimental data is demonstrated via numerical simulations.

Commentary by Dr. Valentin Fuster
2008;():377-384. doi:10.1115/DSCC2008-2154.

In this paper, we consider the fault Detection and isolation (FDI) problem for faulty linear parameter-varying (LPV) systems subject to disturbances and propose a observer-based solution by using multiobjective optimization techniques. To simply the design process, a general faulty LPV system will be constructed from standard LPV description by converting actuator/system component faults into sensor faults at first. Then a bank of LPV FDI filters will be designed to identify each fault. Each FDI filter could generate a residual signal to track individual fault with minimum error and suppressing the effects of disturbances and other fault signals. The design of FDI filters will be formulated as multiobjective optimization problems in terms of linear matrix inequalities (LMIs) and can be solved efficiently. Two numerical examples are also presented to demonstrate the proposed fault detection and isolation approach on both LPV and LTI systems.

Topics: Flaw detection
Commentary by Dr. Valentin Fuster
2008;():385-392. doi:10.1115/DSCC2008-2155.

We analyze the controllability and observability (C/O) of first principles-based numeric and reduced semi-analytic PEMFC models, with emphasis on the effects of model reduction on these analyses. The numeric model is a partial differential equation (PDE) based model approximated by difference equations, including both channels and both GDL of a PEMFC. The reduced model uses a semi-analytic solution (SAS) method, which is a combination of analytic and numeric solutions, gaining physical intuition at lower computational cost. The C/O analysis is based on linearizations around multiple operating points of the numeric and the semi-analytic models. The results indicate that stabilizability of the anode water states is possible.

Commentary by Dr. Valentin Fuster
2008;():393-401. doi:10.1115/DSCC2008-2156.

The permeability or crossover characteristics of a typical polymeric perfluorosulfonic acid membrane are used for the temporal and spatial estimation of nitrogen concentration along the anode channels of a fuel cell stack. The predicted nitrogen accumulation is then used to estimate the impact of local fuel starvation on stack voltage through the notion of apparent current density. Despite simplifying assumptions on membrane hydration levels, the calibrated model reasonably predicts the response of a 20-cell stack whenever there is no significant liquid water accumulation in the dead-ended anode. Specifically, the predicted voltage decay and estimated anode outlet gas composition are experimentally validated using stack-averaged voltage and a mass spectrometer. This work shows that the crossover of nitrogen and its accumulation in the anode can cause a considerable stack voltage decay and should be considered under high hydrogen utilization conditions.

Topics: Fuel cells , Nitrogen
Commentary by Dr. Valentin Fuster
2008;():403-408. doi:10.1115/DSCC2008-2157.

This paper reports the primary resonance of single mode forced, undamped, bending vibration of nonuniform sharp cantilevers of rectangular cross-section, constant width, and convex parabolic thickness variation. The case of nonlinear curvature, moderately large amplitudes, is considered. The method of multiple scales is applied directly to the nonlinear partial-differential equation of motion and boundary conditions. The frequency-response is analytically determined, and numerical results show a softening effect of the geometrical nonlinearities.

Commentary by Dr. Valentin Fuster
2008;():409-411. doi:10.1115/DSCC2008-2158.

Growing interest in robotic treatment of patients with neurological injury motivates the development of therapeutic robots for basic research into recovery. Though humans are the ultimate beneficiaries, basic research frequently involves rodent models of neurological injury, which motivates robotic devices that can interact with rats or mice. This paper proposes an overground therapeutic robot suitable for rodent studies of recovery after for spinal cord injury. Advantages and challenges of an overground machine are compared with treadmill-type machines. Design and implementation issues, including its kinematic configuration, control scheme, biomechanical coupling and partial body weight support system, are presented and discussed. Current development progress is reported along with possible future applications of the device.

Commentary by Dr. Valentin Fuster
2008;():413-415. doi:10.1115/DSCC2008-2159.

This preliminary work is concerned with low sample rate control of a residential Demand Response network. Residential Demand Response networks are very high order nonlinear stochastic systems. We provide a methodology for dealing with this complicated type of system. Then we examine the performance and robustness of potential controllers. To date, only sliding mode control has been examined, but further work will compare sliding mode control to other robust controllers.

Commentary by Dr. Valentin Fuster
2008;():417-424. doi:10.1115/DSCC2008-2160.

Nonlinear Programming (NLP) is for optimization of nonlinear cost functions. In applications of NLP for real-time optimization, however, the estimation of the gradient of the cost function remains as a challenge. On the other hand, the Extremum-Seeking Control (ESC) optimizes the cost function in real-time, but it involves a complicated design of filters in multi-dimensional cases. In this paper, a new method that optimizes an arbitrary multi-variable cost function in real-time is proposed. In the proposed method, the variables are updated as in NLP while the gradient of the cost function is continuously estimated by the amplitude modulation as in ESC. The proposed method does not require design of any complicated filters. The performance is verified by simulations on time-varying and noisy cost functions as well as automatic controller tuning applications.

Commentary by Dr. Valentin Fuster
2008;():425-432. doi:10.1115/DSCC2008-2161.

This work develops a probability broadcast feedback controller for an ensemble of stochastically behaving cellular units exhibiting hysteresis. Previous work has developed asymptotically stable control laws for ideal on-off cellular units without any hysteresis or time lag. This work extends previous results by developing an asymptotically stable control law for an ensemble of cells that experience an arbitrary refractory period after a change in output, during which time the cell output is fixed. This refractory period describes the behavior of hysteretic cells such as shape memory alloy (SMA) actuators or biological cell migration. Conditions for stability are obtained using a stochastic Lyapunov function. Simulation of SMA actuators demonstrates the application of the new control law to practical hysteresis loops.

Commentary by Dr. Valentin Fuster
2008;():433-438. doi:10.1115/DSCC2008-2162.

A closed loop system identification method is developed in which estimation bias from sensor noise and external disturbances is minimized. The method, based on the instrumental variables four step algorithm (IV4), uses three steps. The first step estimates a model using cross covariance calculations between the reference input signal and the control and measured output signals. The second step employs the prefilter identification process from the IV4 process. The third and final step uses the prefilter, the instrumental variables and the reference, control and output signals to estimate the final model. The method is demonstrated on a diesel engine where an open loop model relating fueling to engine speed is sought. The identification example is complicated by the presence of nonmeasurable external torque disturbances due to vehicle accessories.

Commentary by Dr. Valentin Fuster
2008;():439-446. doi:10.1115/DSCC2008-2163.

We address a dynamic configuration strategy for teams of Unmanned Air Vehicles (UAVs). A team is a collection of UAVs which may evolve through different organizations, called configurations. The team configuration may change with time to adapt to changes in the environment. To each configuration there corresponds a set of different properties for the UAVs in the team. The design for the configuration control problem involves a distributed hierarchical control architecture where the properties of the system can be formally analyzed. We do this in the framework of dynamic networks of hybrid automata. We present results from simulation to demonstrate these ideas.

Commentary by Dr. Valentin Fuster
2008;():447-454. doi:10.1115/DSCC2008-2164.

The potential for UAVs to benefit the civilian consumer is driving the demand for the integration of these vehicles into the national airspace. With UAV accidents occurring at a significantly higher rate than commercial airlines, the urgent issue becomes designing systems and protocols that can prevent UAV accidents, better train UAV operators and augment pilot performance. This paper presents three directions of research stemming from the goal of a UAV piloting and training system. Research direction one is the development of a research platform to assess UAV pilot skills and recreate the sensation of shared fate for UAV pilots. The second research direction looks at utilizing flight simulation packages to create virtual tools for training UAV pilots. The third direction covers the investigation of UAV’s in near earth environments as future applications will place UAVs in these areas.

Commentary by Dr. Valentin Fuster
2008;():455-462. doi:10.1115/DSCC2008-2165.

Many automotive transmissions, including automatic and hybrid transmissions, employ electro-hydraulics for gear shift, system cooling, and lubrication. Transmission oil budget refers to the process of dynamically distributing pressurized fluid from the pump into the sub-systems of the transmission. The oil budget will ultimately determine the transmission pump size and directly impact vehicle fuel economy. It will further affect the dynamic performance of the transmission. Due to large number of components, complex hydraulic circuits, and dynamic operating conditions, estimating transmission oil budget is extremely complex. To obtain a precise oil budget, we need to not only model each hydraulic component accurately, but also analyze the flow requirement in a dynamic fashion. This paper presents the modeling of the transmission hydraulic system and its application for oil budget analysis.

Commentary by Dr. Valentin Fuster
2008;():463-470. doi:10.1115/DSCC2008-2166.

Clutch fill control is critical for automotive transmission performance and fuel economy, including both automatic and hybrid transmissions. The traditional approach, by which the clutch fill pressure command is manually calibrated, has a couple of limitations. First, the pressure profile is not optimized to reduce the peak clutch fill flow demand. Moreover, it is not systematically designed to account for uncertainties in the system, such as variations of solenoid valve time delay and parameters of the clutch assembly. In this paper, we present a systematic approach to evaluate the clutch fill dynamics and synthesize the optimal pressure profile. First, a clutch fill dynamic model is constructed and analyzed. Second, the applicability of the conventional numerical Dynamic Programming (DP) algorithm to the clutch fill control problem is explored and shown to be ineffective. Thus we developed a new customized DP method to obtain the optimal and robust pressure profile subject to specified constraints. After a series of simulations and case studies, the new customized DP approach is demonstrated to be effective, efficient, and robust for solving the clutch fill optimal control problem.

Commentary by Dr. Valentin Fuster
2008;():471-476. doi:10.1115/DSCC2008-2167.

We prove global uniform asymptotic stability of adaptively controlled dynamics by constructing explicit global strict Lyapunov functions. We assume a persistency of excitation condition that implies both asymptotic tracking and parameter identification. We also construct input-to-state stable Lyapunov functions under an added growth assumption on the regressor, assuming that the unknown parameter vector is subject to suitably bounded time-varying uncertainties. This quantifies the effects of uncertainties on the tracking and parameter estimation. We demonstrate our results using the Rössler system.

Commentary by Dr. Valentin Fuster
2008;():477-479. doi:10.1115/DSCC2008-2168.

Using Anklebot, a therapeutic robot module, we perturbed human gait by applying external torque to the human ankle at various frequencies. We observed that with a properly designed perturbation, 8 subjects out of 10 exhibited entrained gaits: their gait frequencies were adapted to the frequency of mechanical perturbation, and they synchronized their ankle actuation with the external torque supplied by the robot. This preliminary result suggests that a limit-cycle oscillator, a plausible element of the coupled system of central nervous system and musculo-skeletal periphery, plays a significant role in the neuro-motor execution of human locomotion. The entrainment of human gait by periodic torque from a robotic aid may provide a novel approach to walking therapy that is uniquely supportive of normal biological function.

Commentary by Dr. Valentin Fuster
2008;():481-488. doi:10.1115/DSCC2008-2169.

In this article, a description of the kinetic energy partition values (or energy ratios) of serial chain mechanisms, as well as their rates of change, are presented. These energy ratios are indicators of the kinetic energy distribution within the system and they exploit the structure of the effective inertia matrix. The rates of change of the kinetic energy partition values with respect to the input parameters of the system indicate the sensitivity of change of the kinetic energy, meaning that a high value for the partition value rate of change together with a high operational state implies that the amount of kinetic energy flowing in the system is large further implying a loss of precision in the system due to large inertial torques applied about the joint axes. Two design criteria, one based on the kinetic energy partition values and another based on their rates of change, are presented. A two degree-of-freedom (DOF) mechanism is used to illustrate the solution of a multi-criteria design optimization problem where three design criteria are considered: a kinetic energy partition value criterion, a force capability criterion and an effective mass criterion. The design variables for the optimization problem are the transmission reduction ratios of the actuators. It is shown that the reduction ratios significantly influence the kinetic energy distribution within the system due to the high levels of kinetic energy in the rotary mass of the prime movers.

Commentary by Dr. Valentin Fuster
2008;():489-496. doi:10.1115/DSCC2008-2171.

A major portion of the frictional losses in internal combustion engines has been attributed to the piston-assembly. The current work examines the piston secondary motions and the relationships with which they interact with the lubricating oil film. This is done by developing a model that accounts for the rigid and flexible motions of the crank-slider mechanism of a single cylinder engine. The model considers the secondary motions of the piston and has a variable structure, which allows for the number of degrees of freedom of the system to vary depending on the nature of contact between the piston and the liner. The 3-D Reynolds’ equation is used to determine the instantaneous oil pressure, which is needed for the computation of the normal and the hydrodynamic friction forces exerted on the piston-assembly. The simulation results demonstrate the capability of the model in predicting the hydrodynamic friction force, the piston secondary motions, and the instantaneous oil film thickness.

Commentary by Dr. Valentin Fuster
2008;():497-503. doi:10.1115/DSCC2008-2172.

This paper proposes the use of electrochemical impedance spectroscopy (EIS) to estimate the cathode flow rate in a fuel cell system. Through experimental testing of an eight-cell, hydrogen-fueled polymer electrolyte stack, it shows that the ac impedance measurements are highly sensitive to the air flow rates at varying current densities. The ac impedance magnitude at 0.1Hz allows the distinction of air flow rates (stoichiometry of 1.5–3.0) at current densities as low as 0.1A/cm2 . Using experimental data and regression analysis, a simple algebraic equation that estimates the air flow rate using impedance measurements at a frequency of 0.1Hz is developed. The derivation of this equation is based on the operating cell voltage equation that accounts for all the irreversibilities.

Commentary by Dr. Valentin Fuster
2008;():505-512. doi:10.1115/DSCC2008-2173.

Characterization of the lubrication regimes and quantification of the frictional losses are very important factors for the design of durable IC engines with improved fuel economy. Therefore, the current work has focused on the development of a tribology test rig that allows for the direct measurement of the instantaneous piston-assembly friction force under motoring conditions. The test rig was used to examine the effects of oil viscosity and engine speed on both the lubrication regimes and the friction force of the piston-assembly. Furthermore, the experimental data served to generate Stribeck curves for the coefficient of friction at different points in the cycle. Tear-down experiments were conducted to assess the friction contribution of each component in the piston-assembly. The results demonstrated that the magnitude of the friction force decreases with increasing oil grade under both boundary and mixed lubrication regimes. However, it tends to increase with increasing oil viscosity under a hydrodynamic lubrication regime. Moreover, the engine speed above which the hydrodynamic lubrication regime becomes prevalent at the midpoint of the stroke tends to decrease with increasing oil viscosity.

Commentary by Dr. Valentin Fuster
2008;():513-520. doi:10.1115/DSCC2008-2174.

The increasing complexity of engineering systems has motivated continuing research on computational learning methods towards making autonomous intelligent systems that can learn how to improve their performance over time while interacting with their environment. These systems need not only to be able to sense their environment, but should also integrate information from the environment into all decision making. The evolution of such systems is modeled as an unknown controlled Markov chain. In previous research, the predictive optimal decision-making (POD) model was developed that aims to learn in real time the unknown transition probabilities and associated costs over a varying finite time horizon. In this paper, the convergence of POD to the stationary distribution of a Markov chain is proven, thus establishing POD as a robust model for making autonomous intelligent systems. The paper provides the conditions that POD can be valid, and an interpretation of its underlying structure.

Topics: Chain
Commentary by Dr. Valentin Fuster
2008;():521-528. doi:10.1115/DSCC2008-2175.

Variable displacement engines are a proven technology for improving fuel economy without sacrificing performance. To achieve the most benefit, variable displacement needs to be properly integrated into the vehicle system. A reverse tractive road load demand model, dynamic optimization methodology, and Matlab®/Simulink® based tool are developed to address the challenge of properly matching variable displacement engines and their control strategies to specific vehicle applications for improved overall vehicle system efficiency. Using a reverse model and a dynamic programming algorithm, optimal variable displacement control strategies considering the gear shift and torque converter clutch interaction effects for various drive cycles are developed virtually. The development of an optimal control strategy facilitates better integration of variable displacement into vehicle system designs.

Commentary by Dr. Valentin Fuster
2008;():529-536. doi:10.1115/DSCC2008-2176.

This paper considers the path following problem of underactuated marine vessels whose control imposes a challenging problem due to its under-actuated nature. The recently developed Dynamic Surface Control (DSC) design method is applied to overcome the problem of explosion of terms associated with the backstepping design procedure. We show that the exponential stability of the resulting closed loop dynamics can be proved using Lyapunov direct method. The feasibility of the proposed Dynamic Surface Controller is evaluated analytically and verified through computer simulations and experiments.

Topics: Vessels
Commentary by Dr. Valentin Fuster
2008;():537-544. doi:10.1115/DSCC2008-2177.

Since the initial conception in the late 1960’s, the field of active suspensions for automotive applications has seen numerous research investigations. While there has been a wealth of information previously published, relatively few of these works have incorporated the dynamics of the actuator in their analysis. Including the electrohydraulic actuator dynamics with the plant model introduces the additional effects of the coupling between the actuator and the vehicle body motion. Controller designs using the linearized actuator dynamics typically use a tracking framework. Electrohydraulic systems are limited in their ability to do force or position tracking control when interacting with an environment possessing dynamics such as the 1/4 car model. This paper introduces a novel framework that includes electrohydraulic actuator dynamics in which the tracking problem is replaced by a properly posed regulation problem. Both force regulation and position regulation frameworks are considered and the relative merits/drawbacks of each presented.

Commentary by Dr. Valentin Fuster
2008;():545-552. doi:10.1115/DSCC2008-2178.

Ship-board integrated power systems (IPS) play a crucial role in the all-electric ships (AES) initiative, where the power generation, conversion and distribution are done on a common electric platform. Along with many advantages of the IPS, its inter-connectivity presents a major opportunity as well a challenge for reconfiguration control. To ensure overall optimal performance while sustaining the critical ship service loads, the reconfiguration problem can be formulated as a trajectory optimization problem with the inputs to power sources as optimization variables. The high dimensional and nonlinear nature, along with the extended time horizon involved, makes many grid and gradient based methodologies infeasible for this application, especially when real-time requirements are considered. This paper, motivated by the IPS reconfiguration control, proposes strategies for improving the real-time computational efficiency of the IPS optimization by leveraging the time scale separation of its dynamics. The trade-offs between the computational efficiency and optimization accuracy are analyzed and a numerical example is provided to illustrate the effectiveness of the proposed algorithm.

Commentary by Dr. Valentin Fuster
2008;():553-560. doi:10.1115/DSCC2008-2179.

Control of Hybrid Electric Vehicles (HEVs) is an active research area. Much of the past research focused on one aspect of hybrid vehicle performance–fuel economy. While fuel economy is important for HEVs, reduction of emissions is another major performance of interest, due to ever-tightening emission regulations. Minimization of fuel consumption may have a trickle-down effect but does not guarantee reduced emissions. In fact, over-zealous pursuit of fuel consumption reduction may compromise emission. This paper investigates the emissions formation mechanism, develops an emission model that predicts tail-pipe emissions, and formulates a supervisory control problem of emissions reduction. The Dynamic Programming (DP) technique is employed to solve the optimal control problem of parallel HEVs for both emission reduction and fuel economy. The DP solution of the optimal control problem shows that tail-pipe emissions could be significantly reduced with negligible loss of fuel economy.

Commentary by Dr. Valentin Fuster
2008;():561-568. doi:10.1115/DSCC2008-2180.

In Iterative Learning Control (ILC), the lifted system is often used in design and analysis to determine convergence rate of the learning algorithm. Computation of the convergence rate in the lifted setting requires construction of large NxN matrices, where N is the number of data points in an iteration. The convergence rate computation is O(N2 ) and is typically limited to short iteration lengths because of computational memory constraints. In this article, we present an alternative method for calculating the convergence rate without the need of large matrix calculations. This method uses the implicitly restarted Arnoldi method and dynamic simulations to calculate the ILC norm, reducing the calculation to O(N). In addition to faster computation, we are able to calculate the convergence rate for long iteration lengths. This method is presented for multi-input multi-output, linear time-varying discrete-time systems.

Commentary by Dr. Valentin Fuster
2008;():569-576. doi:10.1115/DSCC2008-2182.

This paper proposes a new model for cogging forces of linear motor systems. Sinusoidal functions of positions are used to capture the largely periodic nature of cogging forces with respect to position effectively while B-spline functions are employed to account for the additional aperiodic part of cogging forces. This model is experimentally demonstrated to be able to capture both the periodic and non-periodic characteristics of cogging force while having a linear parametrization form which makes effective on-line adaptive compensation of cogging forces possible. A discontinuous projection based desired compensation adaptive robust controller (DCARC) is then constructed for linear motors, which makes full use of the proposed cogging force model for an improved cogging force compensation. Comparative experimental results are obtained on both axes of a linear motor driven Anorad industrial gantry having a linear encoder resolution of 0.5 μm. Experiments are done with each axis running separately to compare the three algorithms: DCARC without cogging force compensation, DCARC with sinusoidal cogging force model compensation, and DCARC with the proposed cogging force model compensation. The results show that DCARC with proposed model compensation achieves the best tracking performance among the three algorithms tested, validating the proposed cogging force model. The excellent tracking performances obtained in experiments also verify the effectiveness of the proposed ARC control algorithms in practical applications.

Commentary by Dr. Valentin Fuster
2008;():577-584. doi:10.1115/DSCC2008-2183.

The Precision Immobilization Technique (PIT) is a maneuver frequently used by the law enforcement to terminate a hazardous vehicle pursuit situation. The maneuver is performed by intentionally nudging the pursued vehicle sideways to create large yaw motion which renders the pursued vehicle out of control. This work investigates the behavior of vehicles involved in this maneuver, develops dynamics models for the pre-impact, impact, and post-impact stages. Simulation results provide guidelines for the effective execution of the maneuver. In addition, the case for the vehicle equipped with an active yaw control system, such as the Electronic Stability Control, in response to the PIT maneuver is also addressed.

Commentary by Dr. Valentin Fuster
2008;():585-590. doi:10.1115/DSCC2008-2184.

In this paper we explore parametric amplification of multidegree of freedom mechanical systems. We consider frequency conditions for modal interactions and determine stability conditions for three important cases. We develop conditions under which it is possible to sweep with direct and parametric excitation to produce a sweep response with amplified effective quality factor of resonances encountered during the sweep. With this technique it is possible to improve the measurement of resonance locations in swept devices, such as those that operate on resonance shifting. A numerical example motivated by a MEMS mass sensor is given in support of the analysis.

Commentary by Dr. Valentin Fuster
2008;():591-597. doi:10.1115/DSCC2008-2185.

This paper presents a proposed control method for controlling the foot positions of two robotic legs through direct operator inputs with haptic feedback. The robot consists of two 3-DoF legs driven by pneumatic actuators. A demonstration of the controller shows the tracking performance enhancements of the proposed force-based position controller over a simple differential pressure gain scheduler-based position controller. The proposed controller incorporates pressure feedback to create supplementary force control. Foot position tracking remains within 10% of the commanded reference position, even through the sharp disparities of loading conditions as the actuators are either lifting the weight of the legs or supporting the weight of the robot itself. An operator gives direct foot position commands to the controller through two PHANToM haptic devices. Bilateral teleoperation of the system provides directional force feedback to the operator as a function of foot position error. The proposed controller also decreases the ambient and false forces reflected to the operator while moving the legs through gait cycles.

Topics: Haptics , Feedback
Commentary by Dr. Valentin Fuster
2008;():599-606. doi:10.1115/DSCC2008-2186.

This paper describes a unique, computer-based, mechanism design strategy that takes into account both kinematic and dynamic performance criteria at the synthesis stage of the design process. The strategy can be used to investigate improvements in the design of any existing mechanism with geometric redundancy in its output path. By iteratively varying the form of this redundant portion of the output path, alternative potentially better mechanism designs can be generated using a traditional mechanism synthesis and kinematic analysis method. The generated designs with the most desirable kinematic characteristics can be selected and analyzed using a multi-body, dynamic modeling and analysis tool. Using forward and inverse dynamic analysis the quality of the designs can be quantified. This paper describes work done to apply the strategy to an existing mechanism. An alternative mechanism design was identified with superior dynamic qualities. Kinematic performance was not sacrificed.

Commentary by Dr. Valentin Fuster
2008;():607-614. doi:10.1115/DSCC2008-2187.

Many telerobotic systems require the use of a slave robot with large inertial and frictional properties. Using a force sensor on the end effector can hide the slave’s inertia and friction from the user providing a more accurate sense of the environment, but introduces dangers of system instability. Both the position and force scale directly affect the system loop gain and hence stability. This opens up the possibility of trading off between them based on the environment and task. In this paper we derive explicit limits for their product. In particular we consider varying environment stiffnesses, as well as distinguishing impact and contact phases. The theoretical limits closely align with experimental results using a large slave telerobotic system interacting with very soft to nearly rigid environments.

Topics: Force , Stability
Commentary by Dr. Valentin Fuster
2008;():615-621. doi:10.1115/DSCC2008-2188.

External perception based on vision plays a critical role in developing improved and robust localization algorithms for mobile robots, as well as in gaining important information about the vehicle and the traversed terrain. This paper presents two novel methods to improve mobility on rough terrains by using visual input. The first method consists of a stereovision algorithm for 6-DoF ego-motion estimation, which integrates image intensity information and 3D stereo data using an Iterative Closest Point (ICP) approach. The second method aims at estimating the wheel sinkage of a mobile robot on deformable soil, based on the visual input from an onboard monocular camera, and an edge detection strategy. Both methods were implemented and experimentally validated on an all-terrain mobile robot, showing that the proposed techniques can be successfully employed to improve the performance of ground vehicles operating in uncharted environments.

Topics: Mobile robots , Wheels
Commentary by Dr. Valentin Fuster
2008;():623-630. doi:10.1115/DSCC2008-2189.

It is well known that an autonomous dynamical system can have a stable periodic orbit, arising for example through a Hopf bifurcation. When a collection of such oscillators is coupled together, the system can display a number of phase-locked solutions which can be understood in the weak coupling limit by using a phase model. It is also well known that a stable periodic orbit can be found for a parametrically forced dynamical system, with the phase of the periodic orbit being locked to the forcing. Here we discuss the periodic solutions which occur for a collection of such parametrically forced oscillators that are weakly coupled together.

Commentary by Dr. Valentin Fuster
2008;():631-638. doi:10.1115/DSCC2008-2190.

A rule-based and a model predictive power management strategy are evaluated in experiments for power management of a fuel cell/ultracapacitor hybrid. The two degrees of freedom provided by use of two dc/dc convertors enable independent low-level control of the DC BUS voltage and the current split between the fuel cell and ultracapacitor. The high-level control objectives are to respond to rapid variations in load while minimizing damaging fluctuations in fuel cell current and maintaining the ultracapacitor charge (or voltage) within allowable bounds. Experiments show that both strategies can be tuned to meet these control objectives; however the predictive nature of the model predictive scheme coupled with its ability to aggressively push the ultracapacitor to its constraint line results in smoother fuel cell current transients.

Commentary by Dr. Valentin Fuster
2008;():639-645. doi:10.1115/DSCC2008-2191.

This article considers the state feedback controller design in the networked control systems (NCSs). The network-induced random time delays and packet dropout existing in sensor-to-controller (S-C) and controller-to-actuator (C-A) links are modeled by two Markov chains. The controller incorporates not only the current S-C delay but also the most recent C-A delay to exploit all available information. Then, the system is converted to be a special jump linear system. The sufficient and necessary conditions for stochastic stability are derived and the state feedback stabilization problem is formulated to be an optimization problem solved by the iterative linear matrix inequality (LMI) approach. A design example is given to illustrate the effectiveness of the proposed method.

Commentary by Dr. Valentin Fuster
2008;():647-652. doi:10.1115/DSCC2008-2192.

Deriving models of human body motion is important for prosthetics, rehabilitation and development of humanoids. We present a method that simplifies the derivation of equations of motion of human movements. We illustrate our approach by deriving motion models of a person riding in a moving bus. Our approach simplifies the derivation of dynamics as only open chain dynamics are to be derived. The kinematic constraints are then introduced to represent a complete system model in which the contact forces appear explicitly. We then constrain the contact forces based on the performance requirements to determine the feasibility of motions, which is difficult to determine with the traditional methods. Our model allows for the design and control analysis, specifically, the derivation of the relationship between the change in rider’s posture and the feasibility of motions.

Topics: Motion , Modeling , Robotics
Commentary by Dr. Valentin Fuster
2008;():653-660. doi:10.1115/DSCC2008-2193.

Articulated Wheeled Robotic (AWR) locomotion systems consist of chassis connected to a set of wheels through articulated linkages. Such articulated “leg-wheel systems” facilitate reconfigurability that has significant applications in many arenas, but also engender constraints that make the design, analysis and control difficult. We will study this class of systems in the context of design, analysis and control of a novel planar reconfigurable omnidirectional wheeled mobile platform. We first extend a twist based modeling approach to this class of AWRs. Our systematic symbolic implementation allows for rapid formulation of kinematic models for the general class of AWR. Two kinematic control schemes are developed which coordinate the motion of the articulated legs and wheels and resolve redundancy. Simulation results are presented to validate the control algorithm that can move the robot from one configuration to another while following a reference path. The development of two generations of prototypes is also presented briefly.

Commentary by Dr. Valentin Fuster
2008;():661-668. doi:10.1115/DSCC2008-2194.

In this paper, we present a decentralized dynamic control algorithm for a robot collective consisting of multiple nonholonomic wheeled mobile manipulators (NH-WMMs) capable of cooperatively transporting a common payload. In this algorithm, the high level controller deals with motion/force control of the payload, at the same time distributes the motion/force task into individual agents by grasp description matrix. In each individual agent, the low level controller decomposes the system dynamics into decoupled task space (end-effector motions/forces) and a dynamically-consistent null-space (internal motions/forces) component. The agent level control algorithm facilitates the prioritized operational task accomplishment with the end-effector impedance-mode controller and secondary null-space control. The scalability and modularity is guaranteed upon the decentralized control architecture. Numerical simulations are performed for a 2-NH-WMM system carrying a payload (with/without uncertainty) to validate this approach.

Commentary by Dr. Valentin Fuster
2008;():669-676. doi:10.1115/DSCC2008-2195.

The use of feedforward control is beneficial for high-performance trajectory tracking in many motion control systems. Three methods of designing and tuning feedforward control signals (Iterative Learning Control, Iterative Controller Tuning, and Adaptive Feedforward Control) for a wafer scanner system are presented and compared. For this application, the main sources of tracking error are due to phase mismatch and nonlinear force ripple disturbance. The objective is to compare the performance of these three methods in compensating for error arising from these sources. The methods are compared based on a set of metrics. Comparison is followed by a discussion on advantages and disadvantages of each method including ability to reduce error during acceleration or scan phases of the trajectory, necessary assumptions, effect of inaccurate modeling, and effect of noise.

Commentary by Dr. Valentin Fuster
2008;():677-683. doi:10.1115/DSCC2008-2196.

In this paper, the design of a controller is proposed for a multi-robot target search and retrieval system. Inspired by research in insect foraging and swarm robotics, we developed a transition mechanism for the multi-robot system. Environmental information and task performance obtained by the robot system are used to adjust individual robot’s parameters and guide environment exploration. The proposed control system is applicable in the solution of multi-target problem also where several robots may be needed to cooperate together to retrieve a large target. Simulations show that the task performance improves significantly with the proposed method by sharing information in parameter learning and environment exploration.

Commentary by Dr. Valentin Fuster
2008;():685-692. doi:10.1115/DSCC2008-2197.

This paper presents preliminary results for using dynamic systems models to describe cortisol responses to stressful events. Linear, single-input single-output discrete-time models are used. Choices that must be made regarding interpolation and input modeling are discussed in some detail. Results are presented that indicate an impulse model for the stressful input gives a better fit than no input, and that logarithmic transformation of the data before model fitting gives no better results than using the raw data. The issue of stability of the resulting models is discussed. In addition, the paper discusses how the resulting dynamic systems models can be used for statistical analysis, as well as for predicting future stress responses.

Commentary by Dr. Valentin Fuster
2008;():693-700. doi:10.1115/DSCC2008-2198.

This paper presents an overview of the state-of-the-art for underwater vehicle autopilots. We start by reviewing reference frames, vehicle states, typical control surfaces, equations of motion, the different coefficients and how they are obtained, and disturbance models as well. We then consider different possible configurations for the autopilot, including decoupled lateral and longitudinal loops, maneuver and waypoint control. Adaptive dynamic surface control of nonlinear tracking of a single underwater vehicle is designed with the corroboration with numerical simulations. Finally, we describe current hardware implementations for autonomous underwater vehicles.

Commentary by Dr. Valentin Fuster
2008;():701-708. doi:10.1115/DSCC2008-2199.

The paper presents a model-based tracking control strategy design for wheeled mobile systems (WMS). The strategy enables tracking a variety of WMS motions that come from task specifications and control or design requirements put on them. From the point of view of mechanics and derivation of equations of motion, the WMS belongs to one class of first order nonholonomic systems. From the perspective of nonlinear control theory, the WMS differ and may not be approached by the same control strategies and algorithms, e.g. some of them may be controlled at the kinematic level and the other at the dynamic level only. The strategy we propose is based on a modeling control oriented framework. It serves a unification of the WMS modeling and a subsequent controller design with no regard whether a specific WMS is fully actuated, underactuated, or constrained by the task constraints.

Commentary by Dr. Valentin Fuster
2008;():709-715. doi:10.1115/DSCC2008-2200.

This paper describes an approach that uses support vector machines (SVM) for path planning of mobile robots. The algorithm generates a collision free path for mobile robots running between two tracks or moving towards a known way point. This approach can negotiate tracks and avoid obstacles which may be initially unknown but are later perceived by the robot, and hence is suitable for use with onboard sensors which provides local information. The approach involves dividing the whole terrain into two different classes, classifying any new point obtained from sensors into either of the classes, and generating a track between both the classes as a path of the robot. SVM generates a non-linear class boundary on the principle of maximizing the margin. The boundary generated by this method is smooth, free of obstacles, and safe for a robot to navigate. The paper presents various case studies and simulation results. Future possibility to integrate this technique with other path planning techniques is also discussed.

Commentary by Dr. Valentin Fuster
2008;():717-724. doi:10.1115/DSCC2008-2201.

In this paper, we develop a sliding mode model reference adaptive control (MRAC) scheme for a class of nonlinear dynamic systems with multiple time-varying state delays which is robust with respect to unknown plant delays, to a nonlinear perturbation, and to an external disturbance with unknown bounds. An appropriate Lyapunov-Krasovskii type functional is introduced to design the adaptation algorithms, and to prove stability.

Commentary by Dr. Valentin Fuster
2008;():725-730. doi:10.1115/DSCC2008-2202.

The brake-by-wire units such as EMB (Electro-Mechanical Brake) will be applied to the intelligent vehicles because the brake-by-wire units are lighter in weights and have faster response compared to conventional hydraulic brake units. However, the brake-by-wire units such as EMB should be at least as reliable as the conventional hydraulic brake units. Because there are no mechanical links between the brake pedal and brake-by-wire actuators, FDI (Fault detection and isolation) is essential in implementing EMB units. In this study, a model-based fault diagnosis system is developed for monitoring the brake status utilizing the analytical redundancy method. The performance of the proposed model-based fault diagnosis system is verified in simulations in various faulty cases.

Commentary by Dr. Valentin Fuster
2008;():731-738. doi:10.1115/DSCC2008-2203.

This paper presents the design and testing of systems for autonomous tracking, payload pickup, and deployment of cargo via a UAV helicopter. The tracking system uses a visual servoing algorithm and is tested using open loop velocity control of a 3DOF gantry system with a camera mounted via a pan-tilt unit on the end effecter. The pickup system uses vision to control the camera pan tilt unit as well as a second pan tilt unit with a hook mounted on the end of the arm. The ability of the pickup system to hook a target is tested by mounting it on the gantry while recorded helicopter velocities are played back by the gantry. A preliminary semi-autonomous deployment system is field tested, where a manually controlled RC truck is transported by a UAV helicopter under computer control that is manually directed to GPS waypoints using a ground station.

Commentary by Dr. Valentin Fuster
2008;():739-745. doi:10.1115/DSCC2008-2204.

An adaptive nonlinear stabilizer is introduced for uncertain, voltage-controlled, microelectromechanical system (MEMS) relays. The control construction follows a Lyapunov approach, and is based on a nonlinear dynamic model applicable to the two types of MEMS relays—electrostatic and electromagnetic. The adaptive stabilizer compensates for parametric uncertainty in all mechanical parameters and selected electrical parameters while ensuring asymptotic regulation of the electrode opening and closing. Simulations demonstrate the performance of the adaptive control scheme in comparison to the typical open-loop operation of the MEMS relay.

Commentary by Dr. Valentin Fuster
2008;():747-753. doi:10.1115/DSCC2008-2205.

A graphical technique for finding all proportional integral derivative (PID) controllers that stabilize a given single-input-single-output (SISO) linear time-invariant (LTI) system of any order system with time delay has been solved. In this paper a method is introduced that finds all PID controllers that also satisfy an H∞ complementary sensitivity constraint. This problem can be solved by finding all PID controllers that simultaneously stabilize the closed-loop characteristic polynomial and satisfy constraints defined by a set of related complex polynomials. A key advantage of this procedure is the fact that it does not require the plant transfer function, only its frequency response.

Commentary by Dr. Valentin Fuster
2008;():755-762. doi:10.1115/DSCC2008-2206.

This paper describes the integration of thin film ZnO strain sensors onto hard disk drive suspensions for improved vibration suppression for tracking control. Sensor location was designed using an efficient optimization methodology based on linear quadratic gaussian (LQG) control. Sensors were fabricated directly onto steel wafers that were subsequently made into instrumented suspensions. Prototype instrumented suspensions were installed into commercial hard drives and tested. For the first time, a sensing signal was successfully obtained while the suspension was flying on a disk as in normal drive operation. Preliminary models were identified from experimental transfer functions. Nominal H2 control simulations demonstrated improved vibration suppression as a result of both the better resolution and higher sensing rate provided by the sensors.

Commentary by Dr. Valentin Fuster
2008;():763-769. doi:10.1115/DSCC2008-2207.

Two prominent models frequently used to explain targeted human movement are the stochastic optimized-submovement model and the minimum variance model. Both successfully explain the speed-accuracy tradeoff known as Fitts’ law, but neither is complete. The former cannot predict movement trajectory between the endpoints, while the latter is not congruent with the multiple movement segments often observed in human motion. In this paper, a new model is proposed in which an aimed movement consists of two submovements and a single feedback instant, with the trajectory of each submovement being individually optimized. Simulations using the proposed model show that the optimal transition between two submovements occurs at an early stage of the movement, and produces a sharp peak in the acceleration profile. This result is consistent with psychophysical data. Also observed in numerical simulation is the bell-shaped positional variance curve that is in agreement with psychophysical data.

Topics: Feedback
Commentary by Dr. Valentin Fuster
2008;():771-778. doi:10.1115/DSCC2008-2208.

It was shown recently that regions in the time-scale plane can be isolated wherein the prediction error can be attributed to the error of an individual model parameter. A necessary condition for this isolation capacity is the mutual (pairwise) identifiability of the model parameters. This paper presents conditions for mutual identifiability of parameters of linear models and refines these conditions for models that exhibit rank-1 dependency on the parameters.

Topics: Errors
Commentary by Dr. Valentin Fuster
2008;():779-786. doi:10.1115/DSCC2008-2209.

Preliminary design and analysis of a new concept for efficiently amplifying piezoelectric actuators are presented in this paper. Piezoelectric actuators, such as Lead Zirconate Titanate (PZT), have produced substantial stress at high bandwidth, but at very small strains on the order of 0.1%. This paper presents a new strain amplification design to be utilized as the first layer in the previously designed “nested rhombus” multi-layer mechanism. This mechanism produces substantial strain through exponentially increasing strain with each subsequent layer. However, the blocking force produced in previous designs is insufficient for many practical applications. Through static and kinematic analysis, this paper addresses how this new concept sufficiently amplifies strain, and presents numerous issues to consider in designing for greater blocking force. A prototype of this new concept provides 126 N of blocking force and displacement of 0.3 mm.

Commentary by Dr. Valentin Fuster
2008;():787-794. doi:10.1115/DSCC2008-2210.

The mining industry is introducing several autonomous mining operations, however the development of these algorithms is extremely expensive. This paper discusses the integration of a Hardware In the Loop (HIL) simulation to earthmoving equipment to aid in the development of autonomous mining operations. The benefit of this simulation is to save time and money for engineers developing the autonomous features. The hardware setup contained machine components that were connected to the Electronic Control Modules (ECMs). The ECMs used in the lab setup were the same as those on the actual tract type tractors. Those ECMs receive input signals based on which they command the solenoids. The HIL simulator converts the analog outputs into digital ones. Then the HIL sends out digital or simulated outputs to the ECMs such as pressure and fuel levels. The results of this work compare simulated data and real machine test data of an autonomous feature. A comparison is presented between the autonomous feature and a human operator. Finally potential of the HIL is demonstrated examining the autonomous feature with different soil conditions.

Commentary by Dr. Valentin Fuster
2008;():795-800. doi:10.1115/DSCC2008-2211.

In this paper, we study how to identify the model parameters of a plant with randomly missing output in a network environment. As a result of networked-induced time delays and packet loss, the identification is inevitable to be affected by data missing. We propose to online estimate the missing output measurements, and employ the Kalman filter to estimate system parameters recursively. Convergence analysis on parameter estimation and output estimation is carried out. Simulation results verify the effectiveness of the proposed algorithm.

Commentary by Dr. Valentin Fuster
2008;():801-807. doi:10.1115/DSCC2008-2212.

A MEMS actuator and its controller are jointly optimized, both sequentially and simultaneously. The sequential problem is formulated to account for controllability by means of a constraint on the actuator’s natural frequency. By varying the frequency constraint, sequential optimization generates a set of designs with significantly increased displacement, compared to the original non-optimized design, and with various settling times. In simultaneous optimization, a non-linearly weighted objective function combines the two objectives, and the relative weights are varied. The tradeoff between the two objectives shows that the use of the frequency constraint serves as an effective surrogate for controllability of the actuator.

Commentary by Dr. Valentin Fuster
2008;():809-816. doi:10.1115/DSCC2008-2213.

In vapor compression cycle (VCC) systems, it is desirable to effectively control the thermodynamic cycle. By controlling the thermodynamic states of the refrigerant with an inner-loop, supervisory algorithms can manage critical objectives such as maintaining superheat and maximizing the coefficient of performance, etc. In the HVAC industry, it is generally preferred to tune multiple single-input-single-output (SISO) control inner-loops rather than a single multiple-input-multiple-output (MIMO) control inner-loop. This paper presents a process by which a simplified feedback control structure amenable to a decoupled SISO control loop design may be identified. In particular, the many possible candidate input-output pairs for decentralized control are sorted via a decoupling metric, the relative gain array number. From a reduced set of promising candidate input-output pairs, engineering insight is applied to arrive at the final pairings successfully verified on a refrigeration test stand.

Commentary by Dr. Valentin Fuster
2008;():817-824. doi:10.1115/DSCC2008-2214.

Ch Control System Toolkit (CCST) is a software package for design and analysis of control systems. It is implemented as a class with member functions to run in the user-friendly C/C++ interpreter Ch. Based on the CCST, a Web-based Control System Design and Analysis System (WCDAS) has been developed. In this article, using CCST and WCDAS to teach automatic control of engineering systems is presented. Using CCST, students are able to write programs easily with a few lines of C/C++ code to solve practical engineering problems. By solving control system design and analysis problems in C/C++ , the programming skills gained in the course are applicable to other areas of engineering. CCST and WCDAS are open source. Students are able to examine the source code to understand the implementation of theories and algorithms in software. Based on CCST and WCDAS, the Web-based Controller/Compensator Design Module (WCCDM) has also been developed for teaching and student learning. Using these Web-based tools, students can perform design and analysis of control systems interactively through a Web browser remotely. The CCST, WCDAS, and WCCDM have been used to teach an undergraduate course on Automatic Control of Engineering Systems at the University of California, Davis. All software packages and teaching materials for this course are available on the internet. They can be downloaded and modified to teach similar courses with different requirements.

Commentary by Dr. Valentin Fuster
2008;():825-831. doi:10.1115/DSCC2008-2215.

This paper adds to the analytical work done in a companion paper [3]. In that work, the power analysis for a Parallel Force/Velocity Actuator was carried out. In this work, we present a force balance analysis of the same actuator. In so doing, we consider a link driven by a Parallel Force/Velocity Actuator and study the balance of static and inertial forces in this system. The results from this study include design maps for the PFVA including the effects listed above. We also present five specific design examples of the PFVA using commercial off-the-shelf components to illustrate our force balance analysis.

Commentary by Dr. Valentin Fuster
2008;():833-840. doi:10.1115/DSCC2008-2216.

We report a local minimum spanning tree (LMST)-based consensus control of multi-robot systems. Instead of using a potential function-based approach, we propose a safety region concept for distributed collision-free control system design. The safety region design also takes a consideration of the kinematics and dynamics constraints, namely, kinodynamic constraints of each robot. The network topology control among multiple robots is constructed by an LMST algorithm. The LMST-based topology control not only preserves the connectivity of multi-robot systems but also improves the energy consumption and network communication quality. Simulation results are presented to validate the proposed control system design.

Topics: Safety , Robots
Commentary by Dr. Valentin Fuster
2008;():841-849. doi:10.1115/DSCC2008-2217.

In order to handle increasingly complex engineering applications with highly nonlinear behaviors, various advanced system identification algorithms have been developed for control and diagnostic purposes. Since the performance of these algorithms depends significantly on the selection of input variables, a systematic input selection methodology is needed to identify the nonlinear relation between the input variables and system outputs, even in the presence of high correlation among the candidate input variables. The methodology proposed in this paper converts the problem of selecting appropriate input variables for the identification of a nonlinear dynamic system into one of a set of properly linearized models. In order to enable the approximation of the nonlinear system behavior with a set of linear models, a growing self-organizing map is employed to appropriately partition the system operating region into sub-regions via unsupervised learning. Evaluated based on the minimum description length principle, a model with its most related input variables is then selected using a genetic algorithm so that the computational burden can be reduced. The effectiveness of this methodology has been demonstrated with two simulation examples and a real-world example of modeling the air mass flow rate and intake manifold pressure in a diesel engine airflow system.

Commentary by Dr. Valentin Fuster
2008;():851-857. doi:10.1115/DSCC2008-2218.

Modal parameter estimation in terms of natural frequencies and mode shapes is studied using smooth orthogonal decomposition (SOD) for randomly excited vibration systems. This work shows that under certain conditions, the SOD eigenvalue problem formulated from white noise induced response data can be tied to the unforced structural eigenvalue problem, and thus can be used for modal parameter estimation. Using output response ensembles only, the generalized eigenvalue problem is formed to estimate modal frequencies and modal vectors for a sixteen-degree-of-freedom lightly damped vibratory system. The estimated frequencies are compared against system frequencies obtained from the structural eigenvalue problem and estimated modal vectors are checked using the modal assurance criterion. Simulations show that for light damping, satisfactory results are obtained for estimating both system frequencies and modal vectors even in presence of sensor noise.

Commentary by Dr. Valentin Fuster
2008;():859-866. doi:10.1115/DSCC2008-2220.

Considered in this paper is the question of for what type of multivariable systems is the generalized formulation effective in conditioning the SISO equivalent plants that are pivotal in MIMO QFT design. It is shown by example that for some plant cases there is no benefit to be gained by using the generalized formulation. However, this does not necessarily suggest that no such M and N matrices exist which give desirable SISO equivalent plants. The Smith-McMillan form is used to derive a result for a general nominal MIMO plant. We show that, for any nominal MIMO plant with no unstable blocking poles there exists a pair of M and N matrices such that the resulting conditioned plant yields stable equivalent SISO plants.

Commentary by Dr. Valentin Fuster
2008;():867-874. doi:10.1115/DSCC2008-2221.

Accurate modeling of physical devices is one of the keys to improving the realism of haptic simulations. This paper presents general, locally linear haptic force models to describe the feel of complex mechanical systems that exhibit nonlinear static and dynamic behavior. The parameters of these models are estimated from experimental data using moving ridge regression. Nonlinear variations of the locally linear model are presented and analyzed, and the goodness-of-fit of these models is compared. Initial results suggest that higher-order terms do little to improve the quality of this class of haptic models, and that reduced-order models should be further investigated.

Topics: Force , Haptics
Commentary by Dr. Valentin Fuster
2008;():875-882. doi:10.1115/DSCC2008-2222.

The objective in this paper is to control a robot as it transitions from a non-contact to a contact state with an unactuated viscoelastic mass-spring system such that the mass-spring is regulated to a desired final position. A nonlinear Hunt-Crossley model, which is physically consistent with the real behavior of the system at contact, is used to represent the viscoelastic contact dynamics. A Neural Network feedforward term is used in the controller to estimate the environment uncertainties, which are not linear-in-parameters. The NN Lyapunov based controller is shown to guarantee uniformly ultimately bounded regulation of the system despite parametric and nonparametric uncertainties in the robot and the viscoelastic environment respectively. The proposed controller only depends on the position and velocity terms, and hence, obviates the need for measuring the impact force and acceleration. Further, the controller is continuous, and can be used for both non-contact and contact conditions.

Commentary by Dr. Valentin Fuster
2008;():883-890. doi:10.1115/DSCC2008-2223.

A new, distributed control algorithm for multiple vehicles with limited sensing capability for each vehicle is developed in this paper. It is assumed that each vehicle can sense other vehicles in the group in only a limited region around it. Coordination of multiple vehicles in the presence of distance constraints is considered. The objective for each vehicle within the group is to reach a target point from any given initial location without any collisions. The notion of constraint forces is used to develop a distributed algorithm that is capable of achieving this objective. The distributed algorithm is scalable and allows for addition (removal) of vehicles to (from) the group. Simulation studies conducted on a number of examples show the effectiveness of the proposed distributed algorithm. A representative sample of the results from these studies is shown and discussed.

Commentary by Dr. Valentin Fuster
2008;():891-898. doi:10.1115/DSCC2008-2224.

This article presents a math model of a hypothetical driveline power-dividing unit. The use of this model and generalized vehicle parameters made it possible to synthesize a universal (generalized) model of the vehicle’s driveline system that can be used for modeling virtually all the currently known passive as well as active autonomously operated power-dividing units. The salient feature of the developed computational algorithm consists in its capability to autonomously switch the states of active power-dividing units from one to another, i.e., to control the performance of the power-dividing units. An algorithm for controlling the performance of autonomously operated driveline power-dividing units was also developed. The algorithm allows flexibly controlling the flow of power to the drive wheels and improving the AWD vehicle dynamics. As an illustration the article presents some results of simulating the motion of an AWD middle class SUV with three controlled power-dividing units, control of which provides the specified motion of the vehicle.

Commentary by Dr. Valentin Fuster
2008;():899-906. doi:10.1115/DSCC2008-2225.

Document scanners enjoy widespread use for converting hardcopy documents into digital images. Improving image quality is a key issue for scanner manufacturers. This paper proposes an ILC based step timing synthesis technique for reducing color registration error in stepper motor driven document scanners with no real-time feedback. To quantify color registration error, a line pattern image based technique is devised. Based on the measured color registration error signal, a single iteration convergent iterative learning control scheme is proposed to synthesize a stepper motor step timing command for the scan region. Reduction in color registration error is achieved by compensating for velocity fluctuations in the constant speed portion of the motion. Experimental results demonstrate the effectiveness of the proposed approach in reducing color registration error in scanned image.

Topics: Errors
Commentary by Dr. Valentin Fuster
2008;():907-914. doi:10.1115/DSCC2008-2226.

Traditional underwater vehicles are limited in speed due to dramatic friction drag on the hull. A supercavitating vehicle exploits supercavitation to induce a gaseous cavity that contains most part of the vehicle and separates the vehicle hull from its surrounding water. Thus friction drag is substantially reduced. A supercavitating underwater vehicle can achieve very high speed, but also poses technical challenges in stability, control, and maneuvering due to various characteristics such as instability in open-loop dynamics, nonlinearity, cavity memory effect, etc. Among the existing literature on the control design for supercavitating vehicles, the cavity memory effect is often neglected to simplify system dynamics. In this paper, we take into account the cavity memory effect and model the supercavitating vehicle as a time-delay Quasi-Linear-Parameter-Varying system. Then a robust controller is designed to handle the switched, time-delay dependent behavior of the vehicle. The uncertainties considered in the presented control design include both parameter and planing force modeling uncertainties.

Commentary by Dr. Valentin Fuster
2008;():915-921. doi:10.1115/DSCC2008-2228.

In this paper, we present two robust trajectory-tracking controllers for a differentially driven two-wheeled mobile robot using its kinematic and dynamic model in the presence of slip. The structure of the differential flatness-based controller, which is an integrated framework for planning and control, is extended in this paper to account for slip disturbances by adding a corrective control term. Simulation results for both kinematic and dynamic controllers are presented to demonstrate the effectiveness of the robust controllers. Experiments with the kinematic controller were conducted to validate the performance of the robust controller. The simulation and experimental results show that the robust controllers are very effective in the presence of slip.

Commentary by Dr. Valentin Fuster
2008;():923-930. doi:10.1115/DSCC2008-2229.

We have formulated and implemented a control system for levitation and motion control of a disk magnet using a planar array of electromagnetic coils and an optical localizer to provide real time position feedback. The significance of this work is that this is the first magnetic levitation system which controls the orientation and position of a levitated body throughout a workspace volume whose dimensions are multiples of those of the levitated body in all directions. Furthermore, the horizontal range of motion can be extended indefinitely by adding more coils to the planar array. The potential applications of this levitation system include any robotic manipulation and positioning tasks such as camera and antenna pointing, materials handling and processing, and haptic interaction. Analysis methods, implementation details, and experimental results are given for our current system with a 37.5 mm diameter and 12.5 mm height magnet and 10 actuator coils, providing an 80×60×30 mm range of motion.

Commentary by Dr. Valentin Fuster
2008;():931-938. doi:10.1115/DSCC2008-2230.

This paper addresses the issue of control design for rollover prevention of a multi-body ground vehicle with army applications. The novelty of the approach lies in expressing the traditional rollover index as a quadratic performance index in Linear-quadratic regulator (LQR) design thereby integrating the roll over index directly and explicitly in the optimization procedure. The control gain obtained based on rollover performance index is more effective for rollover prevention than the gain obtained based on standard LQR design in which there is much ambiguity and labor involved in assigning the weights. The control gain obtained based on the proposed rollover performance index outperforms the standard LQR design, essentially because it introduces a cross coupling term between the state and control variables in the modified performance index. Thus, the proposed rollover prevention technique effectively incorporates the physical nature of the vehicle dynamics in the problem formulation resulting in significantly improved performance.

Commentary by Dr. Valentin Fuster
2008;():939-946. doi:10.1115/DSCC2008-2231.

This paper presents a hierarchical approach to fault detection and isolation (FDI) of an automotive electrical power generation and storage (EPGS) system. In particular, this work focuses on a fault diagnosis strategy for the alternator and belt of the EPGS system. The proposed approach is able to detect and isolate the faults of the following components: the voltage regulator, the diodes and the belt. Preliminary evaluation results using an EPGS system test bench have shown the effectiveness of the algorithm.

Commentary by Dr. Valentin Fuster
2008;():947-954. doi:10.1115/DSCC2008-2232.

Throughout the history of the automobile there have been periods of intense interest in using ethanol as an alternative fuel to petroleum-based gasoline and diesel derivatives. Currently available flexible fuel vehicles (FFVs) can operate on a blend of gasoline and ethanol in any concentration of up to 85% ethanol. In all these FFVs, the engine management system relies on the estimation of the ethanol content in the fuel blend, which typically depends on the estimated changes in stoichiometry through an Exhaust Gas Oxygen (EGO) sensor. Since the output of the EGO sensor is used for the air-to-fuel ratio (AFR) regulation and the ethanol content estimation, several tuning and sensitivity problems arise. In this paper, we develop a simple phenomenological model of the AFR control process and a simple ethanol estimation law which can be representative of the currently practiced system in FFVs. Tuning difficulties and interactions of the two learning loops are then elucidated using classical control techniques. The sensitivity of the ethanol content estimation with respect to sensor and modeling errors is also demonstrated via simulations. The results point to an urgent need for model-based analysis and design of the AFR controller, the ethanol adaptation law and the fault detection issues in FFVs. Tuning and sensitivity issues are demonstrated via simulations and limitations are also discussed.

Commentary by Dr. Valentin Fuster
2008;():955-961. doi:10.1115/DSCC2008-2233.

Distributed sensing and actuation systems research has drawn a great attention in recent years from various research communities. These systems are usually deployed in wild fields using a wireless network for the communication. Due to the shortage of power supply and bandwidth, the less communication between system components is desired since it consumes much more power comparing with local computation and uses network bandwidth. In addition, the dynamics of the deployed environments requires distributed sensing and actuation systems being self-organized, scalable, and adaptable. To achieve these desirable characteristics, this paper proposes a mobile agent approach to reduce raw data transmission over a network and increase the flexibility of a distributed sensing and actuation system. The basic ideas of the proposed mobile agent method and the framework based on a mobile agent system called Mobile-C are introduced. Mobile-C is embedded into sensor nodes consisting of an embedded computer and several expansion boards for analog/digital signal input/output and wireless communication. The advantages of using mobile agent based wireless sensor networks for intelligent structure health monitoring are discussed, and a data analysis mobile agent example is given to demonstrate the capability of such a network to dynamically deploy data analysis algorithms and reduce raw data transmission.

Commentary by Dr. Valentin Fuster
2008;():963-970. doi:10.1115/DSCC2008-2234.

Two problems encountered in precision manufacturing are friction and flexibility. With regard to friction, Pulse-Width Control (PWC) has been shown to be exceptionally effective for rigid systems. When used to control flexible systems, however, residual vibrations often result, limiting speed and precision. In a previous related paper, an optimal pulse-width controller was developed that uses two pulses such that the second pulse cancels vibration induced by the first Based on a numerical process minimizing vibration attenuation time, optimal zero vibration (ZV) solutions for the first pulse width, the second pulse width, and the time between pulses were found. Trends in these numerical solutions were also identified that approached limiting values for short maneuvers. In the present paper, a theoretical foundation for these limiting values is derived. This derivation shows that for short maneuvers analytical expressions for pulse widths and timings are easily obtained. These analytical expressions are then used as the basis of an optimal pulse-width controller that is shown to function effectively in both simulation and experiment.

Commentary by Dr. Valentin Fuster
2008;():971-978. doi:10.1115/DSCC2008-2235.

This paper presented an H∞ -controller design to achieve active damping for a MEMS microphone system. The parametric uncertainties introduced by linearization process were modeled. The stability and performance of the closed-loop system were analyzed for the uncertain microphone model and both were shown to be robust. The nonlinear simulation further verifies that the controller offers the desired performance.

Commentary by Dr. Valentin Fuster
2008;():979-986. doi:10.1115/DSCC2008-2236.

This paper presents the application of Buckingham’s π theorem to scale the powertrain of a High Mobility Multipurpose Wheeled Vehicle (HMMWV) by deriving non dimensional ratios called π parameters. A Hardware In the Loop (HIL) setup is constructed and the resulting longitudinal dynamics of the scaled vehicle are validated against those of a full scale vehicle model. This is performed with the ultimate goal of testing cooperative collision avoidance algorithms on a testbed comprising a number of these scaled vehicles. This paper is based on “Development of a scaled vehicle with Longitudinal dynamics of a HMMWV for ITS testbed”, by Verma, R., Domitilla Del Vecchio, and Hosam K. Fathy which appeared in IEEE/ASME Transactions on Mechatronics, February 2008 and is being reprinted with permission from IEEE.

Commentary by Dr. Valentin Fuster
2008;():987-994. doi:10.1115/DSCC2008-2237.

In this paper, we solve the problem of output tracking for linear systems in presence of unknown actuator failures using discontinuous projection based output feedback adaptive robust control (ARC) scheme. The faulty actuators are characterized as unknown inputs stuck within certain bounds at unknown instants of time. This problem is of prime importance for safety critical missions like flight control system. Many existing techniques to solve this problem use model reference adaptive control (MRAC), which is not well suited for handling various disturbances and modeling errors inherent to any realistic system model. In comparison, the backstepping based output feedback ARC approach used here can effectively deal with such uncertainties. Simulation studies are carried out on a linearized Boeing 747 model, which shows the effectiveness of the proposed scheme. Furthermore, we compare our simulation results with that of MRAC in presence of disturbances, which clearly illustrates the superior performance of the proposed ARC based actuator fault compensation scheme.

Topics: Actuators
Commentary by Dr. Valentin Fuster
2008;():995-1002. doi:10.1115/DSCC2008-2238.

This paper is a continuation of the work on the model-based fault diagnosis for the automotive electric power generation system (EPGS) presented in [5]. Based on the previous work on the subject, a new and optimized fault diagnosis algorithm for the EPGS system is developed. In this paper, the thresholds for the diagnosis algorithm are selected and calibrated based on experimental data. The test bench used for the calibration and validation process is discussed. Finally the effectiveness of the fault diagnosis algorithm and threshold selection is validated using experimental data collected from the test bench.

Commentary by Dr. Valentin Fuster
2008;():1003-1010. doi:10.1115/DSCC2008-2239.

In this paper, we present a new algorithm for solving the LQG control problem with variance constraints which utilizes derivative information about the relevant ℋ2 costs to achieve quasi-Newton convergence. Using a lifting procedure, this algorithm is then generalized to work with linear periodically time-varying systems. This algorithm is then applied to the design of controllers for hard disk drives in order to assess the limits of performance of a particular setup. It is demonstrated that just by utilizing multirate sampling and actuation characteristics (i.e. without changing the hardware), the performance of this particular setup can improved by more than 39 %.

Commentary by Dr. Valentin Fuster
2008;():1011-1018. doi:10.1115/DSCC2008-2240.

For the heating, ventilating, and air conditioning (HVAC) systems for commercial buildings, there has been a greater demand for reducing energy consumption. The economizers have been developed as a class of energy-saving HVAC devices that may increase the energy efficiency by taking advantage of outdoor air during cool or cold weather. However, many economizers do not operate in the expected manner and waste even more energy than before installation, mostly due to the unreliable sensors and actuators in practice. Better control strategy is needed for optimal and robust operation. In this paper, an extremum seeking control (ESC) based self-optimizing strategy is proposed to minimize the energy consumption, with the feedback of chilled water supply command rather than the temperature and humidity measurements. The mechanical cooling load is minimized by seeking the optimal outdoor-air damper opening in real time. Such scheme does not need temperature and humidity sensors and depends much less on the knowledge of economizer model. Simulation was performed on a Modelica based transient model of a single-duct air-handling unit (AHU) developed with Dymola and AirConditioning Library. The simulation results demonstrated the potential of using ESC to achieve the minimal mechanical cooling load in a self-optimizing manner. In addition, an anti-windup ESC scheme is proposed to handle the ESC windup due to actuator (damper) saturation. The simulation results validated the effectiveness of the proposed anti-windup ESC.

Commentary by Dr. Valentin Fuster
2008;():1019-1026. doi:10.1115/DSCC2008-2241.

The plug-in hybrid electric vehicles (PHEV), utilizing more battery power, has become a next-generation HEV with great promise of higher fuel economy. Global optimization charge-depletion power management would be desirable. This has so far been hampered due to the a priori nature of the trip information and the almost prohibitive computational cost of global optimization techniques such as dynamic programming (DP). Combined with the Intelligent Transportation Systems (ITS), our previous work developed a two-scale dynamic programming approach as a nearly globally optimized charge-depletion strategy for PHEV power management. Trip model is obtained via GPS, GIS, real-time and historical traffic flow data and advanced traffic flow modeling. The main drawback was the dependency of external server for obtaining the macroscale SOC profile, which makes it difficult to handle the impromptu change of driving decision. In this paper, a computationally efficient strategy is proposed based on road segmentation and lookup table methods. Simulation results have shown its great potential for real-time implementation.

Commentary by Dr. Valentin Fuster
2008;():1027-1034. doi:10.1115/DSCC2008-2242.

This paper discusses the development of a linear quadratic optimal control algorithm for web guides, and implementation of the control algorithm using web lateral position feedback from a new, experimental fiber optic sensor. The lateral dynamic model of the web and the measurement characteristics of the fiber optic sensor are conducive for a linear quadratic regulator design. The performance of the optimal control algorithm with web lateral position feedback from the fiber optic edge sensor is evaluated by conducting experiments on a web platform. Experiments were also conducted using the same controller but with an existing industrial infrared sensor for web lateral position measurement. Results from a series of comparative experiments indicate that the optimal control algorithm with feedback from the fiber optic sensor provides accurate lateral position regulation in the presence of disturbances, at various web transport speeds, and with web materials with different mechanical, physical and geometric properties. Based on the analysis of the web lateral dynamic model, recommendations for proper guide operation and selection of appropriate web transport conditions for good guiding performance are also discussed.

Commentary by Dr. Valentin Fuster
2008;():1035-1042. doi:10.1115/DSCC2008-2243.

TOPL is a suite of software tools for specifying freeway operational improvement strategies, such as ramp metering, demand and incident management, and for quickly estimating the benefits of such improvements. TOPL is based on the macroscopic cell transmission model. The paper summarizes the theory of the cell transmission model and describes the procedure to carry out a TOPL application. The procedure is illustrated for the 26-mile long I-210W freeway in California, whose model is calibrated using loop detector measurements of volume and speed. The measurements show that congestion originates in a bottleneck and moves upstream, as predicted by the theory. The simulations show that appropriate ramp metering can dramatically reduce total congestion delay and mainline travel time.

Commentary by Dr. Valentin Fuster
2008;():1043-1050. doi:10.1115/DSCC2008-2244.

In practical applications, multi-robot systems may have to simultaneously deal with several tasks: collision-free maneuvers in dynamic environments; tracking certain desired trajectories; forming suitable patterns or geometrical shapes, and/or varying the pattern when necessary. The proposed formation control scheme in this paper addresses these issues. First a dynamic model for a nonholonomic robot prototype is developed. Tracking control is then realized by employing input-output feedback linearization. To achieve typical complex formation missions, a two-layer hierarchical architecture is proposed. At the upper layer, a null-space method is utilized to prioritize the tasks of the robot team and to generate reference trajectories for formation control. In the lower layer, the control scheme for each individual robot guarantees asymptotic tracking of the desired trajectories. Numerical simulations of a realistic case study illustrate the effectiveness of the proposed framework.

Commentary by Dr. Valentin Fuster
2008;():1051-1058. doi:10.1115/DSCC2008-2245.

We present and discuss a modular flight control system suitable for video tracking natural structures with Unmanned Air Vehicles (UAVs), like rivers, roads or canals. The control system is modeled in the framework of hybrid automata, where each state corresponds to different control algorithms. We implemented four nonlinear turn-rate control algorithms and compared them in a simulation environment to assess tracking performance.