ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V003T00A001. doi:10.1115/DSCC2018-NS3.

This online compilation of papers from the ASME 2018 Dynamic Systems and Control Conference (DSCC2018) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Modeling and Validation

2018;():V003T29A001. doi:10.1115/DSCC2018-8943.

Two adjustable compliant mechanism load deflection test benches are presented in this study. Both test bench mechanisms enable testing the deflection of flexible links or mechanisms. The modularity of the designs provides to test various link forms such as fixed-fixed and pinned-pinned joints. The load deflection test benches consist of a linear actuator, an amplifier rod, a linear rail and a sliding car. The measurement setup is equipped with force and displacement sensors for the linear actuator, various clamps to attach the compliant member, and machine vision software to measure member deflection. A displacement-controlled loading using a linear actuator, rack-pinion attached to a motor, or step loading with a pulley can be applied as an input to the system.

There are several limitations involved in the design. First, the length of the test object should be kept between 5 cm to 30 cm. Second, a low cost linear actuator with a low extension velocity to obtain quasi static deflection curves of the compliant members is required. Finally, the design should also have the capability of providing various types of boundary conditions with interchangeable attachments. The force can be applied either parallel or perpendicular to the test object. Input load deflection is measured with the displacement sensor, and the resulting member displacement measured visually using machine vision software. This software synchronizes data from the displacement sensor and a calibrated camera image to automatically detect deflection using a pinhole camera model and known dimensions of the test apparatus.

The purpose of this study is to design and fabricate a load deflection test setup capable of testing flexible links and compliant mechanisms. Two different designs are proposed and explored in this study. The first design is the modification of a commercially available ECP Model 210 educational turnkey system favorably utilized in undergraduate level vibrations and control labs. By attaching the designed clamps on two carts, fixed-fixed and U shaped compliant link load deflection can be obtained. Four cases such as fixed-fixed buckling beam, U shaped beam buckling with one end sliding, already buckled beam loaded at its upper midpoint, and inverse U-shaped beam loaded at its apex to form deflected M beam (with design 2) are considered. In order to achieve buckled beam experiments in which the load is applied at the midpoint of the already buckled links, a new test bench consisting of a linear actuator, rigid links, rail and two sliding cars is designed.

Commentary by Dr. Valentin Fuster
2018;():V003T29A002. doi:10.1115/DSCC2018-8947.

Lithium-ion battery cycle- and calendar-life remain to be one of the greatest uncertainties for the advanced energy storage systems. Accurate characterization of battery aging has been crucial for battery state-of-health (SOH) estimation and the remaining useful life (RUL) prediction. The formation-and-growth of the solid-electrolyte interphase (SEI) has been widely recognized as one of the most prominent battery degradation mechanisms. It consumes the cyclable lithium within the cell and ultimately leads to the capacity fade which cannot be measured directly onboard. This study evaluates the multi-scale multi-physics battery models and their respective aging mechanisms as well as the corresponding characterization metrics. Then the reduced order single particle model (SPM) is selected in this study, given its parametric dependence on both electrochemical and physical parameters as well as its compatibility to the available measurements in vehicle for aging characterization. nLi, the total moles of cyclable lithium within the cell, is identified as a valid aging parameter that can effectively characterize the capacity fade through the interpretation of experimental aging data. This study also investigates into the potentially optimal testing profile and the sufficient amount of data required for the accurate aging characterization. Then the method of brute force nearest neighbor search (NNS) is applied to derive the long-term evolution trend of the aging parameter nLi, which can serve as a key benchmark for validating the in-vehicle implementable algorithms for battery state-of-health (SOH) estimation and as an important foundation for predicting the remaining useful life (RUL) of battery.

Commentary by Dr. Valentin Fuster
2018;():V003T29A003. doi:10.1115/DSCC2018-9000.

This paper proposes a hybrid multibody dynamics formalism with a symbolical multibody toolbox developed in MATLAB Environment. The toolbox can generate the dynamic model of a multibody system with hybrid and nonholonomic dynamic properties. The framework and software structure of the toolbox are briefly demonstrated. The paper discusses the recursive kinematics and modular modeling theories that help improve the modeling performance and offer accessibility into the dynamic elements. The formalism that offers a symbolic solution to nonholonomic and constrained dynamics is explained in detail. The toolbox also provides design tools and auto-compilation of hybrid automata. Two exemplary models and their simulations are presented to verify the feasibility of the formalism and demonstrate the performance of the toolbox.

Commentary by Dr. Valentin Fuster
2018;():V003T29A004. doi:10.1115/DSCC2018-9030.

The Furuta pendulum is a two degree of freedom mechanical system that serves as an excellent and simple device to check control strategies applied for strongly nonlinear mechanical structures. Stability results related to certain stationary motions of the Furuta pendulum are compared to experimental observations, and conclusions are obtained regarding some essential mechanical phenomena that are present in the experimental rig, but still not properly described in the standard mathematical model of the pendulum. The results call the attention for the importance of the identification of the Coulomb friction in the structure, which effect the control strategies to be implemented.

Commentary by Dr. Valentin Fuster
2018;():V003T29A005. doi:10.1115/DSCC2018-9100.

Ground testing of full-scale wind turbine nacelles has emerged as a highly favorable alternative to field testing of prototypes for design validation. Currently, there are several wind turbine nacelle test facilities with capabilities to perform repeated and accelerated testing of integrated turbine components under loads that the machine would experience during its nominal lifetime. To perform accurate and efficient testing, it is of significant interest to understand the interaction between coupled test rig/dynamometer and nacelle components, particularly when applying extreme loads. This paper presents a multi-body simulation model that is aimed at understanding the responses of a coupled test rig and nacelle system during specific tests. The validity of the model is demonstrated by comparing quasi-static and dynamic simulation responses of key components with experimental data obtained on an actual 7.5 MW test rig. A case study is conducted to analyze a transient grid-loss event; a Low Voltage Ride Through (LVRT) test on the dynamometer and drivetrain components. It is shown that the model provides an efficient way to predict responses of the coupled system during transient/dynamic tests before actual implementation. Recommendations for mitigating the impact of such tests on the test bench drive components are provided. Additionally, observations of differences between transient events in the field and ground based testing are made.

Commentary by Dr. Valentin Fuster
2018;():V003T29A006. doi:10.1115/DSCC2018-9206.

Developing controllers for powered prostheses is a daunting task that requires involvement from clinicians, patients and robotics experts. Difficulties arise for tuning prosthetic devices that perform in multiple conditions and provide more functionality to the user. For this reason, we propose the implementation of a simulation framework based on the open-source 3D simulation environment Gazebo, to reduce the burden of experimentation and aid in the early stages of development. In this study, we present a minimalist plugin for the simulator that allows the interfacing of a virtual model with the native prosthesis controller and renders the finding of impedance parameters as a pattern search problem. To demonstrate the functionality of this approach, we used the framework to obtain the parameters that offer the most similar joint trajectory to the respective biological counterpart during swing phase for ground level walking. The optimization results are compared against the response of a physical 2DOF knee-ankle prosthesis operating under the optimized parameters, showing congruence to our model-based results. We found that a simulation-based solution is capable of finding parameters that create an emerging behavior that approximates to the kinematic trajectory goals within a tolerance (mean absolute error ∼10%). This provides an appropriate method for development and evaluation of impedance-based controllers before deployment to the physical device.

Commentary by Dr. Valentin Fuster

Multi-Agent and Networked Systems

2018;():V003T30A001. doi:10.1115/DSCC2018-8926.

This work is concerned with stability analysis of stationary and time-varying equilibria in a class of mean-field games that relate to multi-agent control problems of flocking and swarming. The mean-field game framework is a non-cooperative model of distributed optimal control in large populations, and characterizes the optimal control for a representative agent in Nash-equilibrium with the population. A mean-field game model is described by a coupled PDE system of forward-in-time Fokker-Planck (FP) equation for density of agents, and a backward-in-time Hamilton-Jacobi-Bellman (HJB) equation for control. The linear stability analysis of fixed points of these equations typically proceeds via numerical computation of spectrum of the linearized MFG operator. We explore the Evans function approach that provides a geometric alternative to solving the characteristic equation.

Topics: Stability
Commentary by Dr. Valentin Fuster
2018;():V003T30A002. doi:10.1115/DSCC2018-8944.

The swashplate of a model helicopter consists of stationary and rotating plates separated by ball bearings. This mechanism enables the swashplate to tilt in all directions and move vertically as one unit. The lower stationary plate is mounted on the main rotor mast and connected to the cyclic and collective controls by a series of pushrods. There are similar pushrods known as pitch links connected to the upper rotating plate. These pitch links are connected to the pitch horns and control the pitch of individual blades. In this study, the pitch links of the model helicopter are replaced by a semi compliant mechanism. This mechanism is directly connected to the pitch horns to control the pitch of the individual blades. The actuation of the bars can be achieved by using high torque stepper or servo motors. These precise low and high amplitude outputs are specifically required for the cyclic and collective controls of the helicopter swashplate. The compliant swashplate mechanism can be fabricated as a single piece using an injection molding technique or by 3D printing. The mechanism is modeled by two similar vector loops in two different planes. The mathematical model of the plate motion and the forces on the mechanism links are developed and simulated using MATLAB and Simulink, and initial results are discussed in this paper. This mechanism would be applied to the helicopter directional control where the plate in the pitch-roll mechanism would serve as the swash plate of the helicopter.

Commentary by Dr. Valentin Fuster
2018;():V003T30A003. doi:10.1115/DSCC2018-8954.

In this paper, a novel switched systems approach is taken to enable the distributed coordination of a multi-agent system with intermittent communication. A mobile information service provider switches between various (follower) agents in the network to provide them with state feedback when they are within close proximity. The follower agents do not have navigational sensors but are still proven to converge to a desired goal through open-loop control with intermittent error correction by the leader. A switched systems stability analysis is performed to determine the maximum dwell-time the mobile information service provider can intermittently communicate information to the agents to ensure convergence to the desired goal. Simulation results are included to demonstrate the development.

Commentary by Dr. Valentin Fuster
2018;():V003T30A004. doi:10.1115/DSCC2018-8959.

In previous work, a (smooth) finite-time distributed control algorithm with time transformation was introduced for first-order multiagent systems, which guarantees convergence of the single state of agents to a time-varying leader at a-priori given, user-defined time T from any arbitrary initial conditions with bounded local control signals. In this paper, we present an extension of this previous work to second-order multiagent systems. Specifically, utilizing a user-defined finite-time interval of interest t ∈ [0, T), we time transform this class of multiagent systems subject to the considered (smooth) distributed control algorithm to an infinite-time interval s ∈ [0, ∞) with s being the stretched time. Based on a property of this time transformation, this results in finite-time convergence as the regular time t approaches to T from any arbitrary initial conditions with bounded local control and internal signals. Finally, two numerical examples illustrate the efficacy of the proposed algorithm.

Commentary by Dr. Valentin Fuster
2018;():V003T30A005. doi:10.1115/DSCC2018-9001.

The effectiveness of a network’s response to external stimuli depends on rapid distortion-free information transfer across the network. However, the rate of information transfer, when each agent aligns with information from its network neighbors, is limited by the update rate at which each individual can sense and process information. Moreover, such neighbor-based, diffusion-type information transfer does not predict the superfluid-like information transfer during swarming maneuvers observed in nature. The main contribution of this article is to propose a novel model that uses self reinforcement, where each individual augments its neighbor-averaged information update using its previous update, to (i) increase the information-transfer rate without requiring an increased, individual update-rate; and (ii) enable superfluid-like information transfer. Simulations results of example systems show substantial improvement, more than an order of magnitude increase, in the information transfer rate, without the need to increase the update rate. Moreover, results show that the DSR approach’s ability to enable superfluid-like, distortion-free information transfer results in maneuvers with smaller turn radius and improved cohesiveness.

Commentary by Dr. Valentin Fuster
2018;():V003T30A006. doi:10.1115/DSCC2018-9003.

A cooperative deterministic learning based state feedback control algorithm is proposed in this paper for joint tracking control and learning/identification for a group of identical nonholonomic vehicles. Specifically, this algorithm is able to model the unknown nonlinear dynamics of the nonholonomic vehicle, and use it for trajectory tracking control with cooperative deterministic learning (DL) theory. In addition, cooperative DL grants every vehicle in the system the ability of knowledge learning not only along the trajectory of its own, but also along the trajectories of all other vehicles as well. It is shown using Lyapunov stability theory that with cooperative DL, the closed-loop system is guaranteed to be stable, with all vehicles tracking its own reference trajectories, and the radial basis function (RBF) neural network (NN) weights of all agents converge to the same constants.

Commentary by Dr. Valentin Fuster
2018;():V003T30A007. doi:10.1115/DSCC2018-9038.

Modeling two-phase flow across orifices is critical in optimizing orifice design and fluid’s operation in countless architectures and machineries. While flow across different orifice geometries has been extensively studied for air-water flow, simulations and experiments on other two-phase flow combinations are limited. Since every fluid mixture has its own physical properties, such as densities, viscosities and surface tensions, the effect of these properties on the local pressure drops across the orifices may differ. This study aims to investigate the effect of different fluid combinations on the pressure drop across sharp-edged orifices with varying gas mass fractions, orifice thicknesses, and area ratios. A numerical model was developed and validated using experimental data for air-water flow. Then, the model was extended to include various gas-liquid flows including gasoil, argon-diesel and fuel oil. The local pressure drops were then estimated and compared with the existing empirical correlations. The developed model presents a unified approach to measure pressure drop across orifices for different fluid mixtures with different geometries and gas-liquid compositions, unlike existing empirical correlations which are applicable for specific orifice geometries. The results showed that Morris correlation, Simpson correlation, and Chisholm correlation are more appropriate for gasoil, argon-diesel and fuel oil mixtures, respectively. They also yielded that for all fluid combinations, increasing orifice thickness and area ratio led to a decrease in local pressure drop, while increasing gas mass fraction led to an increase in local pressure drop. This revealed that, despite having similar responses to changes in orifice geometries and gas fractions, unlike the assumption made by previous works on air-water flow, no empirical correlation is able to predict pressure drops for all flow mixtures, while the presented numerical model can efficiently determine the local pressure drop for all combinations of flow mixtures, orifice geometries and gas mass fractions.

Commentary by Dr. Valentin Fuster
2018;():V003T30A008. doi:10.1115/DSCC2018-9139.

In this paper, we explore a model of collective behavior using EUGENE, an algorithm for automated discovery of so-called “dynamical kinds”. Two systems are of the same dynamical kind if their underlying causal dynamics are similar, as defined using dynamical symmetry. We apply EUGENE to simulation data from a model capable of generating a range of qualitatively different collective behaviors, from aligned motion to circular milling. These behaviors are measured using both global and local order parameters, and this data is analyzed with EUGENE. We find that EUGENE is capable of differentiating between these systems when global order parameters are used, and can only identify more coarse characteristics when local order parameters are considered.

Commentary by Dr. Valentin Fuster
2018;():V003T30A009. doi:10.1115/DSCC2018-9146.

In this paper a periodic event-based repetitive controller with dynamic output feedback is designed for linear systems with exogenous disturbances. The periodic event mechanism is designed such that within any two event triggering instants, the dynamic output feedback controller is open which substantially reduces the control and communication burden when the output does not change significantly. First, by employing the input delay approach, the overall system consisting of the physical plant, the repetitive controller, and the dynamic output feedback controller with periodic event-triggering mechanism is modeled as a closed-loop time-varying delay system. Then, sufficient conditions in terms of linear matrix inequalities are derived to ensure that the closed-loop system is asymptotically stable with a prescribed H attenuation performance level. The controller gains are synthesized by using a matrix decomposition technique. A numerical example is provided to evaluate the proposed design approach.

Commentary by Dr. Valentin Fuster
2018;():V003T30A010. doi:10.1115/DSCC2018-9161.

This paper presents a human-robot trust integrated task allocation and motion planning framework for multi-robot systems (MRS) in performing a set of parallel subtasks. Parallel subtask specifications are conjuncted with MRS to synthesize a task allocation automaton. Each transition of the task allocation automaton is associated with the total trust value of human in corresponding robots. A dynamic Bayesian network (DBN) based human-robot trust model is constructed considering individual robot performance, safety coefficient, human cognitive workload and overall evaluation of task allocation. Hence, a task allocation path with maximum encoded human-robot trust can be searched based on the current trust value of each robot in the task allocation automaton. Symbolic motion planning (SMP) is implemented for each robot after they obtain the sequence of actions. The task allocation path can be intermittently updated with this DBN based trust model. The overall strategy is demonstrated by a simulation with 5 robots and 3 parallel subtask automata.

Topics: Robots , Path planning
Commentary by Dr. Valentin Fuster
2018;():V003T30A011. doi:10.1115/DSCC2018-9232.

Collective behavior emerges from local interactions in a group, has been observed in many natural systems, and is of significant interests for engineering applications. The Vicsek model is a mathematical tool to study collective alignment in a group of self-propelled particles based on local interaction, which has been well-studied in the literature for its simple algorithm and complex global behaviors. Several studies show that particles reach alignment faster when the directionality of particle interaction is restricted by an optimal view angle. This result seems counterintuitive, since each particle is expected to get more information through omnidirectional interaction. This work seeks to explore the possible causes of this optimal view angle by studying interaction dynamics in Vicsek model with restricted view angle through numerical simulation.

Commentary by Dr. Valentin Fuster

Path Planning and Motion Control

2018;():V003T32A001. doi:10.1115/DSCC2018-8949.

A majority of the routing algorithms for unmanned aerial or ground vehicles rely on Global Positioning System (GPS) information for localization. However, disruption of GPS signals, by intention or otherwise, can render these algorithms ineffective. This article provides a way to address this issue by utilizing landmarks to aid localization in GPS-denied environments. Specifically, given a number of vehicles and a set of targets, we formulate a joint routing and landmark placement problem as a combinatorial optimization problem: to compute paths for the vehicles that traverse every target at least once, and to place landmarks to aid the vehicles in localization while each of them traverses its route, such that the sum of the traveling cost and the landmark placement cost is minimized. A mixed-integer linear program is presented, and a set of algorithms and heuristics are proposed for different approaches to address certain issues not covered by the linear program. The performance of each proposed algorithm is evaluated and compared through extensive computational and simulation results.

Topics: Algorithms , Vehicles
Commentary by Dr. Valentin Fuster
2018;():V003T32A002. doi:10.1115/DSCC2018-8997.

Rapidly Exploring Random Trees (RRTs) have gained significant attention due to provable properties such as completeness and asymptotic optimality. However, offline methods are only useful when the entire problem landscape is known a priori. Furthermore, many real world applications have problem scopes that are orders of magnitude larger than typical mazes and bug traps that require large numbers of samples to match typical sample densities, resulting in high computational effort for reasonably low-cost trajectories. In this paper we propose an online trajectory optimization algorithm for uncertain large environments using RRTs, which we call Locally Adaptive Rapidly Exploring Random Tree (LARRT). This is achieved through two main contributions. We use an adaptive local sampling region and adaptive sampling scheme which depend on states of the dynamic system and observations of obstacles. We also propose a localized approach to planning and re-planning through fixing the root node to the current vehicle state and adding tree update functions. LARRT is designed to leverage local problem scope to reduce computational complexity and obtain a total lower-cost solution compared to a classical RRT of a similar number of nodes. Using this technique we can ensure that popular variants of RRT will remain online even for prohibitively large planning problems by transforming a large trajectory optimization approach to one that resembles receding horizon optimization. Finally, we demonstrate our approach in simulation and discuss various algorithmic trade-offs of the proposed approach.

Commentary by Dr. Valentin Fuster
2018;():V003T32A003. doi:10.1115/DSCC2018-9009.

Semi-autonomous steering promises to combine the best of human perception, planning, and manual control with the precision of automatic control. This paper presents an adaptive haptic shared control scheme using Markov Decision Process (MDP) to keep human drivers in the loop yet free attention and avoid automation pitfalls. Using MDP, algorithms are developed to support the negotiation of authority between the human driver and automation system.

Commentary by Dr. Valentin Fuster
2018;():V003T32A004. doi:10.1115/DSCC2018-9013.

We investigate the dynamics of a pair of spinning spheres or microrotors in a fluid at low Reynolds numbers. These microrotors are each approximated by a rotlet, a fundamental singularity of the Stokes equation. Singularities of Stokes flows serve as useful theoretical models for microswimmers and micro-robots. Rotlet models of microswimmers have received less attention since a rotlet cannot generate translation by itself if the only control input is the rate of spin or strength of the rotlet. However a pair of rotlets can interact and execute net motion. In an unbounded domain of fluid, the positions of a pair of rotlets are not fully controllable due to the existence of an invariant. However, in a confined domain, we show that the positions of the pair of spheres are small time locally controllable. We show how control inputs can be constructed based on combinations of Lie brackets to move the rotlets from one point to another in the domain.

Topics: Reynolds number
Commentary by Dr. Valentin Fuster
2018;():V003T32A005. doi:10.1115/DSCC2018-9022.

In this research, a scooping motion generation method is proposed to scoop the semi-liquid objects from different containers automatically for meal support purpose. A spoon equipped robot arm is used. Based on the pre-measured shape of the containers, the robot arm can move the spoon to trace the inner surface of containers continuously. We also control the rotation of the spoon to scoop more semi-liquid object every time by imitating human’s scooping motion. A scraping motion is also generated as the auxiliary operation to gather the remaining semi-liquid object, which can realize an increase in the scooping amount. In the experiment, we tested the generated scooping motion for two containers and four type of semi-liquid objects. The scooped amount and the scooping times are measured and compared. The result shows that about 85.9% object on average could be scooped out.

Topics: Robots
Commentary by Dr. Valentin Fuster
2018;():V003T32A006. doi:10.1115/DSCC2018-9040.

Citrus greening (Huanglongbing) has caused significant financial loss in many states of the United States and worldwide. In recent years, a heat therapy method has been investigated to prolong the production period of the diseased citrus trees after infection. One crucial step in this heat treatment process is to precisely align the truck with the diseased tree to reduce the operation time during deployment of the treatment tent. In this study, a binocular vision system is used to detect the position of the diseased tree relative to the truck, and a direct based path planning method is used to generate a nominal, optimal path for the truck to follow. A driver’s eye perception model is derived, simulating the distortion due to the human eye’s perception of objects on the computer screen, which will be used in the truck controller. A linear quadratic controller is then designed to compensate for the error coming from the eye perception mismatches and sensor and actuator noise. The studied human augmented driving control system can significantly reduce the operation time as the driver doesn’t have to constantly get out of the cab to check the truck-tree alignment. Simulation results show the effectiveness of the proposed system.

Commentary by Dr. Valentin Fuster
2018;():V003T32A007. doi:10.1115/DSCC2018-9042.

For a lately constructed disease detection field robot, the segregation of unhealthy leaves from strawberry plants is a major task. In field operations, the picking mechanism is actuated via three previously derived inverse kinematic algorithms and their performances are compared. Due to the high risk of rapid and unexpected deviation from the target position under field circumstances, some compensation is considered necessary. For this purpose, an image-based visual servoing method via the camera-in-hand configuration is activated when the end-effector is nearby to the target leaf subsequent to performing the inverse kinematics algorithms.

In this study, a bio-inspired trajectory optimization method is proposed for visual servoing and the method is constructed based on a prey-predator relationship observed in nature (“motion camouflage”). In this biological phenomenon, the predator constructs its path in a certain subspace while catching the prey. The proposed algorithm is tested both in simulations and in hardware experiments.

Commentary by Dr. Valentin Fuster
2018;():V003T32A008. doi:10.1115/DSCC2018-9048.

In recent years, self-balancing personal transportation devices have gained significant popularity, the most popular ones being the “Hoverboard” systems. These systems utilize the dynamics of an inverted pendulum to create stable lateral motion. In this paper, the dynamic behavior of a hoverboard system with an attached flexible beam is investigated. By introducing a flexible beam, the vibrational characteristics of the system created by both the rider and the environment can be measured and accounted for. The beam is a continuous system modeled as an n degree of freedom (DOF) inverted pendulum. The resulting system becomes an n+2 DOF (n DOF for the beam, one DOF for the rotation of the beam about the wheel axis, and one DOF for the horizontal motion of the system). A mathematical model is developed to simulate the vibrations of the beam when excited by a piezoelectric actuator at the base, and to simulate the horizontal motion necessary to balance the beam as it is excited.

Commentary by Dr. Valentin Fuster
2018;():V003T32A009. doi:10.1115/DSCC2018-9096.

In this work, we address the problem of deploying a multi-robot system for row crop phenotyping. We propose a sampling-based navigation algorithm for the team of robots to estimate the underlying spatial distribution in a field. We use Gaussian Process Models to predict the distribution of a scalar function in a field, and choose Mutual Information as a metric for selecting the future samples. With a row crop structure, we present a collision-free assignment and scheduling algorithm for the robots to reach the goal positions which minimizes the total traveling distance. The effectiveness of the proposed algorithm is demonstrated through simulations.

Topics: Robots , Navigation
Commentary by Dr. Valentin Fuster
2018;():V003T32A010. doi:10.1115/DSCC2018-9108.

Trajectory tracking robotic systems require complex control procedures that occupy less space and need less energy. For these reasons, the development of computerized and integrated control systems is crucial. Recently, developing reconfigurable Field Programmable Gate Arrays (FPGAs) give a prominence of the complete robotic control systems. Furthermore, it has been found in the literature that the model-based control methods are most efficient and cost-effective. This model must interpret how multiple moving parts interact with each other and with their environment. On the other hand, MultiBody Dynamic (MBD) approach is considered to solve these difficulties to attain the models accurately. However, the obtained equations of motion do not match the well-developed forms of control theory. In this paper, the MBD model of a mobile robot is established; and the equations of motion are reshaped into their control canonical form. Additionally, the Sliding Mode Control (SMC) theory is used to design the control law. The constraints’ manifold, which is available in the equations of the MBD system, are imposed systematically as the switching surface. SMC is applied because of its ability to address multiple-input/multiple-output nonlinear systems without resorting any approximations. Eventually, the experimental verification of the proposed algorithm is carried out using DaNI mobile robot in which, a Reconfigurable Input/Output (RIO) board is used to reorient the control design, so that can fit the required trajectory. The control law is implemented using LabVIEW software and NI-sbRIO-9631 with acceptable performance. It is obvious that the integration of MBD/SMC/FPGA can be used successfully to develop embedded systems for the applications of trajectory tracking robotics.

Commentary by Dr. Valentin Fuster
2018;():V003T32A011. doi:10.1115/DSCC2018-9115.

There has been a recent increase in research related to supernumerary robotic arms. A challenge with supernumerary robotic arms is how to operate them effectively. One solution is to use the foot to teleoperate the arm. That frees the person to use their arms for other tasks. However, unlike hand interfaces, it is not known how to create effective foot control for robotic teleoperation. This paper presents an experiment to compare position and rate control methods for foot interfaces. A foot interface is presented that can be used for both position and rate control. A human subject experiment uses 2D positioning tasks to evaluate the effectiveness of each control method. These same tasks are tested with a hand interface to provide a baseline for comparison. Results show that, similar to the hand, position control performs faster than rate control when using the foot.

Commentary by Dr. Valentin Fuster
2018;():V003T32A012. doi:10.1115/DSCC2018-9127.

In this paper, we address a visibility-based target tracking game for the scenario when the environment contains a circular obstacle. The game is originally formulated in four dimensions, but due to the symmetry of the environment, the dimension of the state space can be reduced to three. In the reduced state space, we formulate a game of degree. We use Isaacs techniques to obtain the locally optimal solution of the players. These solutions are extended back in the state space keeping in mind the geometry of the environment to obtain complete solution in the solution. Finally, we construct vector fields whose integral curves are the optimal solutions in the state space.

Topics: Dimensions , Geometry
Commentary by Dr. Valentin Fuster
2018;():V003T32A013. doi:10.1115/DSCC2018-9144.

Kinematic motion planning using geometric mechanics tends to prescribe a trajectory in a parameterization of a shape space and determine its displacement in a position space. Often this trajectory is called a gait. Previous works assumed that the shape space is Euclidean when often it is not, either because the robotic joints can spin around forever (i.e., has an 𝕊1 configuration space component, or its parameterization has an 𝕊1 dimension). Consider a shape space that is a torus; gaits that “wrap” around the full range of a shape variable and return to its starting configuration are valid gaits in the shape space yet appear as line segments in the parameterization. Since such a gait does not form a closed loop in the parameterization, existing geometric mechanics methods cannot properly consider them. By explicitly analyzing the topology of the underlying shape space, we derive geometric tools to consider systems with toroidal and cylindrical shape spaces.

Topics: Space , Path planning , Shapes
Commentary by Dr. Valentin Fuster
2018;():V003T32A014. doi:10.1115/DSCC2018-9174.

In this paper, we propose a trust-based runtime verification (RV) framework for deploying multiple quad-rotors with a human-in-the-loop (HIL). By bringing together approaches from runtime verification, trust-based decision-making, human-robot interaction (HRI), and hybrid systems, we develop a unified framework that is capable of integrating human cognitive skills with autonomous capabilities of multi-robot systems to improve system performance and maximize the intuitiveness of the human-robot-interaction. On top of the RV framework, we utilize a probabilistic trust inference model as the key component in forming the HRI, designed to maintain the system performance. A violation avoidance controller is designed to account for the unexpected/unmodeled environment behaviors e.g. collision with static/moving obstacles. We also use the automata theoretic approaches to generate motion plans for the quad-rotors working in a partially-known environment by automatic synthesis of controllers enforcing specifications given in temporal logic languages. Finally, we illustrated the effectiveness of this framework as well as its feasibility through a simulated case study.

Topics: Rotors , Path planning
Commentary by Dr. Valentin Fuster
2018;():V003T32A015. doi:10.1115/DSCC2018-9176.

Artificial Potential Field (APF) theory is a unique branch of robotic path planning, which could be capable of handling the need for high dimensional robotic obstacle avoidance. However, APF theories have general performance issues which often make them undesirable in application. This research analyzes the Secant Approach; an algorithm developed to follow the APF style of path planning, but which has guaranteed convergence and obstacle avoidance properties in n-dimensional space. Using a unique potential function, the Secant Approach can guarantee a global minimum at the target while provably eliminating local minimums at other locations. Also, a control scheme has been developed which has guaranteed convergence properties. The Secant Approach is therefore capable of guiding various forms of robotic applications to target positions in n-dimensional space, making the theory a powerful path planning tool. This analysis examines the structure of the Secant Approach and extends the theory to include variable radius, solid obstacles.

Commentary by Dr. Valentin Fuster
2018;():V003T32A016. doi:10.1115/DSCC2018-9179.

In recent years, gliding robotic fish have emerged as promising mobile platforms for underwater sensing and monitoring due to their notable energy efficiency and maneuverability. For sensing of aquatic environments, it is important to use efficient sampling strategies that incorporate previously observed data in deciding where to sample next so that the gained information is maximized. In this paper, we present an adaptive sampling strategy for mapping a scalar field in an underwater environment using a gliding robotic fish. An ergodic exploration framework is employed to compute optimal exploration trajectories. To effectively deal with the challenging complexity of finding optimum three-dimensional trajectories that are feasible for the gliding robotic fish, we propose a novel strategy that combines a unicycle model-based 2D trajectory optimization with spiral-enabled water column sampling. Gaussian process (GP) regression is used to infer the field values at unsampled locations, and to update a map of expected information density (EID) in the environment. The outputs of GP regression are then fed back to the ergodic exploration engine for trajectory optimization. We validate the proposed approach with simulation results and compare its performance with a uniform sampling grid.

Topics: Robotics , Water
Commentary by Dr. Valentin Fuster
2018;():V003T32A017. doi:10.1115/DSCC2018-9195.

The path planning problem for autonomous car parking has been widely studied. However, it is challenging to design a path planner that can cope with parking in tight environment for all common parking scenarios. The important practical concerns in design, including low computational costs and little human’s knowledge and intervention, make the problem even more difficult. In this work, a path planner is developed using a novel four-phase algorithm. By using some switching control laws to drive two virtual cars to a target line, a forward path and a reverse path are obtained. Then the two paths are connected along the target line. As illustrated by the simulation results, the proposed path planning algorithm is fast, highly autonomous, sufficiently general and can be used in tight environment.

Commentary by Dr. Valentin Fuster
2018;():V003T32A018. doi:10.1115/DSCC2018-9224.

This paper presents a strategy to integrate the planning and control for autonomous vehicles. The aim of this work is to provide a method that can yield controller feasible reference paths, i.e. paths that are not only dynamically feasible but are feasible under the action of a low-level feedback controller. The method is designed to find a control feasible parameterization of a collision-free path provided by a path generation scheme, e.g. rapidly-exploring random trees or one of its many variants. This parameterization is found such that the vehicle under the action of the low-level controller will be able to follow that path within a specified tolerance. The design is based on a feedback strategy with nested MPCs for planning and control. The results presented here are preliminary but hint at the benefits of such a strategy and suggest avenues for future work.

Topics: Vehicles
Commentary by Dr. Valentin Fuster

Tracking Control Systems

2018;():V003T35A001. doi:10.1115/DSCC2018-8987.

Thrust Vector Control (TVC) is one means of controlling air vehicles to follow a desired flight path where, in particular, those that are flexure jointed are currently the most commonly used. Often, dynamic modeling of such systems is for the case where a universal gimbal joint is present, which neglects uncertainties in the dynamics, such as vertical motion of the pivot point of nozzle and misalignment. This paper gives early results on a new approach to dynamic modeling of TVC systems that includes one more degree of freedom compared to previously reported models and also enables the flexure jointed structure to move along vertical direction on the flight axis. A Computed Torque Control Law (CTCL) is then designed for the new resulting model with the potential for higher tracking accuracy and lower feedback gains. A simulation based case study is given to demonstrate the new design.

Commentary by Dr. Valentin Fuster
2018;():V003T35A002. doi:10.1115/DSCC2018-9094.

A data driven control design approach in the frequency domain is used to design track following feedback controllers for dual-stage hard disk drives using multiple data measurements. The advantage of the data driven approach over model based approach is that, in the former approach the controllers are directly designed from frequency responses of the plant, hence avoiding any model mismatch. The feedback controller is considered to have a Sensitivity Decoupling Structure. The data driven approach utilizes H and H2 norms as the control objectives. The H norm is used to shape the closed loop transfer functions and ensure closed loop stability. The H2 norm is used to constrain and/or minimize the variance of the relevant signals in time domain. The control objectives are posed as a locally convex optimization problem. Two design strategies for the dual-stage hard disk drive are presented.

Topics: Design , Disks
Commentary by Dr. Valentin Fuster
2018;():V003T35A003. doi:10.1115/DSCC2018-9196.

This paper proposes a robust filtered basis functions approach for feedforward tracking of linear time invariant systems with dynamic uncertainties. Identical to the standard filtered basis functions (FBF) approach, the robust FBF approach expresses the control trajectory as a linear combination of user-defined basis functions with unknown coefficients. The basis functions are forward filtered using a model of the plant and their coefficients are selected to minimize tracking errors. The standard FBF and robust FBF approaches differ in the filtering process. The robust FBF approach uses an optimal robust filter which is based on minimization of a frequency domain based error cost function over the dynamic uncertainty, whereas, the standard FBF approach uses the nominal model. Simulation examples and experiments on a desktop 3D printer are used to demonstrate significantly more accurate tracking of uncertain plants using robust FBF compared with the standard FBF.

Commentary by Dr. Valentin Fuster
2018;():V003T35A004. doi:10.1115/DSCC2018-9200.

This paper presents a trajectory-tracking method using disturbance observer-based model predictive control (MPC) for small autonomous underwater vehicles (AUV). The goal of the work is to design a robust motion controller for AUVs under the system constraints and unknown disturbances such as hydrodynamics and ocean currents. Super-twisting-algorithm (STA) is employed to design the disturbance observer and its output is used and included in the feedback linearization law to compensate for the disturbances. The control inputs are generated using the MPC design with the nominal linearized model. Simulation results are included to validate the effectiveness of the control design and also compare with the traditional MPC motion control.

Commentary by Dr. Valentin Fuster

Unmanned Aerial Vehicles (UAVs) and Application

2018;():V003T36A001. doi:10.1115/DSCC2018-8950.

We employ a genetic algorithm approach to solving the persistent visitation problem for UAVs. The objective is to minimize the maximum weighted revisit time over all the sites in a cyclicly repeating walk. In general, the optimal length of the walk is not known, so this method (like the exact methods) assume some fixed length. Exact methods for solving the problem have recently been put forth, however, in the absence of additional heuristics, the exact method scales poorly for problems with more than 10 sites or so. By using a genetic algorithm, performance and computation time can be traded off depending on the application. The main contributions are a novel chromosome encoding scheme and genetic operators for cyclic walks which may visit sites more than once. Examples show that the performance is comparable to exact methods with better scalability.

Commentary by Dr. Valentin Fuster
2018;():V003T36A002. doi:10.1115/DSCC2018-9079.

We present a state estimator for a UAV operating in an environment equipped with ultra-wideband radio beacons. The beacons allow the UAV to measure distances to known positions in the world. The estimator additionally uses the vehicle’s rate gyroscope and accelerometer, and crucially does not rely on any knowledge of the vehicle’s dynamic properties (e.g. mass, mass moment of inertia, aerodynamic properties). This makes the estimator especially useful in situations where the exact system parameters are unknown (e.g. due to unknown payloads), or where the environment is unpredictable (e.g. wind gusts). Experimental results demonstrate the approach’s efficacy, and demonstrate that the estimator can run on low-cost microcontrollers with typical sensors.

Commentary by Dr. Valentin Fuster
2018;():V003T36A003. doi:10.1115/DSCC2018-9107.

In this paper, an image based visual servo (IBVS) scheme is developed for a hexacopter, equipped with a robotic soft grasper to perform autonomous object detection and grasping. The structural design of the hexacopter-soft grasper system is analyzed to study the soft grasper’s influence on the multirotor’s aerodynamics. The object detection, tracking and trajectory planning are implemented on a high-level computer which sends position and velocity setpoints to the flight controller. A soft robotic grasper is mounted on the UAV to enable the collection of various contaminants. The use of soft robotics removes excess weight associated with traditional rigid graspers, as well as simplifies the controls of the grasping mechanics. Collected experimental results demonstrate autonomous object detection, tracking and grasping. This pipeline would enable the system to autonomously collect solid and liquid contaminants in water canal based on GPS and multi-camera system. It can also be used for more complex aerial manipulation including in-flight grasping.

Topics: Design , Grasping
Commentary by Dr. Valentin Fuster
2018;():V003T36A004. doi:10.1115/DSCC2018-9123.

This paper presents a new approach for Unmanned Aerial Vehicle (UAV) attitude estimation using a cascade of nonlinear observer and linearized Kalman filter. The nonlinear observer is globally asymptotically stable and is designed using linear matrix inequalities (LMI). The exogenous signal from the nonlinear observer is used to generate a linearized model for the Kalman filter. The method is implemented for attitude estimation of a quadcopter. The nonlinear model is derived from the Newton-Euler equations. The nonlinear model is locally Lipschitz due to the cross and dot products between the angular and linear velocity vectors. The attitude estimation from the dynamical system presented in this paper can be used as a module for fault detection. Simulations in Gazebo on a PX4 using Software In The Loop (SITL) shows the proposed method is able to estimate the attitude of a quadcopter accurately.

Commentary by Dr. Valentin Fuster
2018;():V003T36A005. doi:10.1115/DSCC2018-9133.

This paper proposes an energy-efficient adaptive robust tracking control method for a class of fully actuated, thrust vectoring unmanned aerial vehicles (UAVs) with parametric uncertainties including unknown moment of inertia, mass and center of mass, which would occur in aerial maneuvering and manipulation. We consider a novel vector thrust UAV with all propellers able to tilt about two perpendicular axes, so that the thrust force generated by each propeller is a fully controllable vector in 3D space, based on which an adaptive robust control is designed for accurate trajectory tracking in the presence of inertial parametric uncertainties and uncertain nonlinearities. Theoretically, the resulting controller achieves a guaranteed transient performance and final tracking accuracy in the presence of both parametric uncertainties and uncertain nonlinearities. In addition, in the presence of only parametric uncertainties, the controller achieves asymptotic output tracking. To resolve the redundancy in actuation, a thrust force optimization problem minimizing power consumption while achieving the desired body force wrench is formulated, and is shown to be convex with linear equality constraints. Simulation results are also presented to verify the proposed solution.

Commentary by Dr. Valentin Fuster
2018;():V003T36A006. doi:10.1115/DSCC2018-9137.

In this paper, we address the decentralized collaborative trajectory planning and target surrounding of multiple Unmanned Air Vehicles (UAVs) in three-dimensional space using Partial Differential Equation (PDE) method. The mission objective is simultaneously arrival of UAVs with safe flight trajectory to a certain radius of an a – priori target. Then by reforming the configuration of swarm, UAVs would circle around the target. The assumption in this work is that the arrival time between the UAVs’ final and initial positions are defined a – priori. The constraints in this paper are (i) Three dimensional Dubins path and UAV dynamic constraints, (ii) Minimum separation distance between UAVs, and (iii) Collision-free trajectory throughout the flight. We define a novel concept of Prediction Set (PS) based on our previous study on PDE path planning method and then we apply the PDE PSs to the constraints of the problem (i.e., (i) to (iii)) and solve the optimization problem. Finally, the concept is demonstrated by numerical simulation and an experiment to represent the effectiveness of the solution.

Commentary by Dr. Valentin Fuster

Unmanned Ground and Aerial Vehicles

2018;():V003T37A001. doi:10.1115/DSCC2018-9039.

This article presents the design of a reinforcement learning method based flight controller to enhance the qualities of image taken from an octorotor platform. Concerning the effect of a low resolution and a high blur rate of target images on feature extraction and target detection, we started by analyzing the relationship between these two kinds of image qualities and altitude and velocity of the octorotor. This leads to the generation of corresponding control commands. We then applied a reinforcement learning technique to automatically design the altitude and velocity controllers of the octorotor. The image analysis and the control command generation algorithms are successfully tested on the octorotor platform, and the controllers demonstrate a satisfactory performance in simulations.

Topics: Flight
Commentary by Dr. Valentin Fuster
2018;():V003T37A002. doi:10.1115/DSCC2018-9053.

In this paper, we present a method to accurately predict the wheel speed limits at which mobile robots can operate without significant slipping. The method is based on an asymptotic solution of the nonlinear equations of motion. Using this approach, we can predict wheel slipping limits of both the inside and outside wheel when the robot is in a circular motion of any radius. The analytical results are supported by experiments which show that the inside wheel slipping limits for circular motions of various radii occur very close to the predicted values.

Topics: Mobile robots , Wheels
Commentary by Dr. Valentin Fuster
2018;():V003T37A003. doi:10.1115/DSCC2018-9078.

Unmanned Aerial Vehicle (UAV) mission success is highly dependent on the robust and reliable performance of individual UAVs. Therefore implementing fault tolerant control to prevent UAV catastrophic failure is critical. In this paper, a control strategy for a Quadrotor under actuator fault is considered. A Sliding Mode Controller (SMC) is used to control the quadrotor during nominal and fault conditions. The gains of the SMC are obtained through a Lyapunov stability analysis, and optimized through Particle Swarm Optimization (PSO). Simulations are presented to exhibit controller effectiveness during nominal and fault conditions.

Commentary by Dr. Valentin Fuster
2018;():V003T37A004. doi:10.1115/DSCC2018-9080.

This paper presents a new approach for the guidance and control of a UGV (Unmanned Ground Vehicle). An obstacle avoidance algorithm was developed using an integrated system involving proportional navigation (PN) and a nonlinear model predictive controller (NMPC). An obstacle avoidance variant of the classical proportional navigation law generates command lateral accelerations to avoid obstacles, while the NMPC is used to track the reference trajectory given by the PN. The NMPC utilizes a lateral vehicle dynamic model. Obstacle avoidance has become a popular area of research for both unmanned aerial vehicles and unmanned ground vehicles. In this application an obstacle avoidance algorithm can take over the control of a vehicle until the obstacle is no longer a threat. The performance of the obstacle avoidance algorithm is evaluated through simulation. Simulation results show a promising approach to conditionally implemented obstacle avoidance.

Commentary by Dr. Valentin Fuster
2018;():V003T37A005. doi:10.1115/DSCC2018-9095.

Road conditions are of critical importance for motion control problems of the autonomous vehicle. In the existing studies of Model Predictive Control (MPC), road condition is generally modeled with the system dynamics, sometimes simplified as common disturbances, or even ignored based on some assumptions. For most of such MPC formulations, the cost function is usually designed as fixed function and has no relations with the time-varying road conditions. In order to comprehensively deal with the uncertain road conditions and improve the overall control performance, a new model predictive control strategy based on a mechanism of adaptive cost function is proposed in this paper. The relation between the cost function and road conditions is established based on a set of priority policies which reflect the different cost requirements under different road grades and friction coefficients. The adaptive MPC strategy is applied to solve the longitudinal control problem of autonomous vehicles. Simulation studies are conducted on the MPC method with both the fixed cost function and the adaptive cost function. The results show that the proposed adaptive MPC approach can achieve a better overall control performance under different road conditions.

Commentary by Dr. Valentin Fuster
2018;():V003T37A006. doi:10.1115/DSCC2018-9140.

Robotic mapping and simultaneous localization and mapping (SLAM) typically rely on sensors that produce a large number of measurements at many locations in an environment to produce an accurate map and, in the case of SLAM, the pose of the robot in that map. However, with the advent of small, low-power robots with insect-scale features, there is a need for techniques that can produce useful maps using limited capability sensors and a small number of measurements. In this work, we focus on the use of compressive sensing to extract local environment reconstructions from ultrasonic sensor measurements. We first examine a simplistic setting where a square pulse is emitted and use the returned echoes in a compressive sensing scheme to reconstruct the locations of objects inside the sensing cone. We then extend this to the more practical setting, accounting for the wave nature of the acoustic signal and corresponding issues of interference, showing that these can be accounted for in designing the measurement matrix of the compressive sensing description of the problem. We demonstrate the performance of our approach though several simulations.

Commentary by Dr. Valentin Fuster
2018;():V003T37A007. doi:10.1115/DSCC2018-9148.

A car-like ground vehicle is a nonlinear and underactuated system subject to nonholonomic constraints. Trajectory tracking control of such systems is a challenging problem. To this end, a trajectory tracking controller based on nonlinear kinematics and dynamics model of a ground vehicle by Trajectory Tracking Control (TLC) is presented in our previous work. In this paper, we present hardware validation of TLC controller design with vehicle parameters determination for a Radio Controlled (RC) scaled model vehicle, experimental implementation, and tuning procedure. Hardware testing results are presented to demonstrate the effectiveness of our design. The design can be readily scaled-up to full-size vehicles and adapted to different types of autonomous ground vehicles with only knowledge of the vehicle model parameters.

Commentary by Dr. Valentin Fuster
2018;():V003T37A008. doi:10.1115/DSCC2018-9197.

In this paper, fault-tolerance characteristics of a reconfigurable tilt-rotor quadcopter upon a propeller failure are presented. Traditional quadcopters experience instability and asymmetry about yaw-axis upon a propeller failure but the design and control strategy presented here can handle a complete propeller failure during flight. Fault-tolerance is achieved by means of structural and flight controller reconfiguration. The concept involves conversion of a tilt-rotor UAV into a T-copter. The dynamics and control of the tilt-rotor quadcopter are presented for ideal flight condition and for the reconfigured system in case of propeller failure. Analytical solution for trim flight conditions yielding zero angular rates for the UAV is derived. It has been shown that the structurally reconfigured UAV is controllable and completes the flight mission without much compromise in flight performance. The controllability and observability analysis of the reconfigured system is shown by state space formulation. The flight controllers for both dynamic models are analyzed and the applicability of the proposed concept is presented by propeller failure simulation during the way-point navigation.

Topics: Rotors
Commentary by Dr. Valentin Fuster
2018;():V003T37A009. doi:10.1115/DSCC2018-9199.

Tilt-rotor quadcopters are a novel class of quadcopters with a servo motor attached on each arm that assist the quadcopter’s rotors to tilt to a desired angle thereby enabling thrust vectoring. Using these additional tilt angles, this type of a quadcopter can be used to achieve desired trajectories with faster maneuvering and can handle external disturbances better than a conventional quadcopter. In this paper, a non-linear controller has been designed using sliding mode technique for the pitch, roll, yaw motions and the servo motor tilt angles of the quadcopter. The dynamic model of the tilt-rotor quadcopter is presented, based on which sliding surfaces were designed to minimize the tracking errors. Using the control inputs derived from these sliding surfaces, the state variables converge to their desired values in finite-time. Further, the non-linear sliding surface coefficients are obtained by stability analysis. The robustness of this proposed sliding mode control technique is shown when a faulty motor scenario is introduced. The quadcopter transforms into a T-copter design upon motor failure thereby abetting the UAV to cope up with the instabilities experienced in yaw, pitch and roll axes and still completing the flight mission. The dynamics of the T-copter design and the derivation of the switching surface coefficients for this reconfigurable system are also presented.

Commentary by Dr. Valentin Fuster
2018;():V003T37A010. doi:10.1115/DSCC2018-9228.

For patients with amyotrophic lateral sclerosis (ALS), disease progression can cause a loss of motor function. As motor function declines, the dexterity needed to control a wheelchair’s joysticks can also be compromised. The objective of this work is to integrate user sensor inputs and wheelchair position measurements to improve the performance of wheelchair guidance, even in the presence of noisy inputs from the user. This work evaluates probabilistic, model-based methods for blending joystick and position inputs along a series of user-created trajectories, similar to those that a wheelchair user may follow in their day-to-day navigational routines. We answer three key questions in order to associate joystick inputs to path-keeping decisions: 1) What is a path? 2) When are paths different? 3) What is the probability of a particular destination along a path? The algorithmic answers to these questions are verified using experimental wheelchair joystick and position measurements. Using this approach, the goal is to safely guide a wheelchair’s trajectory even if the user is providing ambiguous inputs. This process enables better discrimination of user joystick inputs for navigation algorithms, resulting in improved wheelchair guidance, safety, and patient monitoring.

Commentary by Dr. Valentin Fuster
2018;():V003T37A011. doi:10.1115/DSCC2018-9231.

The objective of this work is to develop a negative obstacle detection algorithm for a robotic wheelchair. Negative obstacles — depressions in the surrounding terrain including descending stairwells, and curb drop-offs — present highly dangerous navigation scenarios because they exhibit wide characteristic variability, are perceptible only at close distances, and are difficult to detect at normal operating speeds. Negative obstacle detection on robotic wheelchairs could greatly increase the safety of the devices.

The approach presented in this paper uses measurements from a single-scan laser range-finder and a microprocessor to detect negative obstacles. A real-time algorithm was developed that monitors time-varying changes in the measured distances and functions through the assumption that sharp increases in this monitored value represented a detected negative obstacle.

It was found that LiDAR sensors with slight beam divergence and significant error produced impressive obstacle detection accuracy, detecting controlled examples of negative obstacles with 88% accuracy for 6 cm obstacles and above on a robotic development platform and 90% accuracy for 7.5 cm obstacles and above on a robotic wheelchair. The implementation of this algorithm could prevent life-changing injuries to robotic wheelchair users caused by negative obstacles.

Commentary by Dr. Valentin Fuster
2018;():V003T37A012. doi:10.1115/DSCC2018-9249.

Safety and efficiency are two key elements for planning and control in autonomous driving. Theoretically, model-based optimization methods, such as Model Predictive Control (MPC), can provide such optimal driving policies. Their computational complexity, however, grows exponentially with horizon length and number of surrounding vehicles. This makes them impractical for real-time implementation, particularly when nonlinear models are considered. To enable a fast and approximately optimal driving policy, we propose a safe imitation framework, which contains two hierarchical layers. The first layer, defined as the policy layer, is represented by a neural network that imitates a long-term expert driving policy via imitation learning. The second layer, called the execution layer, is a short-term model-based optimal controller that tracks and further fine-tunes the reference trajectories proposed by the policy layer with guaranteed short-term collision avoidance. Moreover, to reduce the distribution mismatch between the training set and the real world, Dataset Aggregation is utilized so that the performance of the policy layer can be improved from iteration to iteration. Several highway driving scenarios are demonstrated in simulations, and the results show that the proposed framework can achieve similar performance as sophisticated long-term optimization approaches but with significantly improved computational efficiency.

Commentary by Dr. Valentin Fuster

Vibration in Mechanical Systems

2018;():V003T39A001. doi:10.1115/DSCC2018-8906.

Anyone who has ever used a chalkboard is probably familiar with the phenomenon of “chalk hopping,” where the chalk unexpectedly skips across the chalkboard, leaving a dotted line in its wake. Such behavior is ubiquitous to mechanical systems with moving parts in contact, where it is almost always undesirable. It is widely believed that hopping behavior is a physical manifestation of either the classical Painlevé paradox or a related phenomenon called dynamical jam. The present paper poses the question of whether chalk hopping might be caused by a different, and much more recently discovered, instability called “reverse chatter,” in which two bodies initially in sustained contact can lose contact through a sequence of impacts with increasing amplitude. Previous simulations of reverse chatter have considered only constant external loads, which do not adequately model the forces exerted on a piece of chalk. The current work presents simulation results for a model system in the presence of a control algorithm that mimics the human hand by attempting to keep the chalk in contact with the chalkboard. The simulations reveal that there exist physically realistic parameter values for which a loss of contact occurs that cannot be attributed to either the classical Painlevé paradox or dynamical jam, but which can only be attributed to reverse chatter. Furthermore, the subsequent motion of the system after losing contact is found to be strikingly similar to that of chalk hopping on a chalkboard, to a hitherto unparalleled degree. These results show that neither the classical Painlevé paradox nor dynamical jam is necessary for hopping behavior, and suggest that reverse chatter may be the most plausible explanation for chalk hopping.

Topics: Chalk , Chatter
Commentary by Dr. Valentin Fuster
2018;():V003T39A002. doi:10.1115/DSCC2018-8933.

For wave propagation in periodic media with strong nonlinearity, steady-state solutions can be obtained by solving a corresponding nonlinear delay differential equation (DDE). Based on the periodicity, the steady-state response of a repeated particle or segment in the media contains the complete information of solutions for the wave equation. Considering the motion of the selected particle or segment as a variable, motions of its adjacent particles or segments can be described by the same variable function with different phases, which are delayed variables. Thus, the governing equation for wave propagation can be converted to a nonlinear DDE with multiple delays. A modified incremental harmonic balance (IHB) method is presented here to solve the nonlinear DDE by introducing a delay matrix operator, where a direct approach is used to efficiently and automatically construct the Jacobian matrix for the nonlinear residual in the IHB method. This method is presented by solving an example of a one-dimensional monatomic chain under a nonlinear Hertzian contact law. Results are well matched with those in previous work, while calculation time and derivation effort are significantly reduced. Also there is no additional derivation required to solve new wave systems with different governing equations.

Commentary by Dr. Valentin Fuster
2018;():V003T39A003. doi:10.1115/DSCC2018-8942.

Many flapping wing micro air vehicles (FWMAVs) utilize a flexible joint that allows the wing to passively rotate about the pitching axis. Generally, simple rigid body models are used to estimate the passive pitching dynamics. However, evidence suggests elastic wings increase aerodynamic force generation and expend less energy relative to rigid wings. As a result, elastic wings are becoming an integral part of FWMAV design. But, the effect of wing elasticity on passive pitching mechanics is unclear. To explore this, we develop a coupled model of an elastic wing attached to a flexible pitching joint. Aerodynamic moments are included through a simple blade element approach. The model is applied to an idealized insect forewing subject to prescribed roll rotation. The simulation results suggest (1) aerodynamic moments, not rigid body inertia or elastic forces, are primarily responsible for lift-generating passive pitch, (2) joint stiffness influences pitching mechanics more than wing elasticity does, and (3) flexible wings can increase net lift by as much as 20% if the pitching joint is mistuned. The framework developed in this paper can be used to design and optimize FWMAV systems in terms of both elastic wings and flexible passive pitch joints.

Topics: Wings
Commentary by Dr. Valentin Fuster
2018;():V003T39A004. doi:10.1115/DSCC2018-8964.

Machining thin-walled components involves continuous decrease in mass and stiffness of the parts being machined, causing increase in vibrations and instability. This leads to undesirable machining errors in dimensional and form tolerances as well as surface finish which adversely affects the quality of machined parts.

To track and quantify the changing dynamic behaviour of Aluminum 6061-T6 workpiece, first, numerical simulations are carried out in ANSYS Workbench 18.2 to extract its modal properties. To validate this, off-line modal hammer tests are carried out on a number of semi-machined fixtured components, representing intermediate stages of machining. The results of the numerical simulations match well with the experimental measurements. With thinning of the walls from 6mm to 4.5mm the natural frequencies and damping ratios are found to drop by a factor of 1.5 and the magnification factor is found to rise by 25% signifying rise in the vibration levels. This obviously would reflect in enhanced vibrations of the workpiece when subjected to dynamic forces during machining. In this paper, this problem is addressed by deploying strain gauge bridge in the feedback and thereby regulating clamping pressure by proportional hydraulic clamping mechanism in an on-line mode. The method is found to compensate the vibration level by 40% and can be integrated in the design of a smart fixtures.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2018;():V003T39A005. doi:10.1115/DSCC2018-9084.

Due to platform motions, floating offshore wind turbine loads are increased. Among proposed platform concepts, tension leg platform introduces least wind turbine load increase. To reduce wind turbine loads, extra actuators have been added to the platform to suppress the tension leg platform motion. For these actuators controller design, it is critical to derive a mathematical model of the platform-wind turbine-actuator system. In this paper, a reduced 13 DOFs model is derived using Lagrange equation and validated with simulation results from FAST. This reduced model is simple, but accurate enough to predict wind turbine and platform response under wind and wave disturbance. Based on the proposed model, an LQR controller is designed. One simulation case shows that the wind turbine tower load can be effectively reduced by actively controlled DVAs.

Commentary by Dr. Valentin Fuster

Vibrations and Control of Systems

2018;():V003T40A001. doi:10.1115/DSCC2018-8902.

The drilling industry has been suffering from huge monetary losses and non-productive time due to wear and fatigue of the drill string components. Vibration mitigation plays a pivotal role in extending the life of drill string components. The development of a comprehensive drill string vibration model will help in classifying the causes of drill string vibrations and helps in planning pro-active measures to suppress it. In the past, researchers have developed models based on factors like drill string length, axial compression load, lateral loads, shear deformation, rotary inertia and fluid damping. The four classical engineering vibration theories will be discussed in detail with the addition of fluid stiffness and fluid damping. This paper develops a drill string vibration model considering the effects of bending, translational inertia, rotary inertia, shear deformation, fluid stiffness and fluid damping. The drill string is considered as a cantilever beam of a circular cross-section immersed in water with equal pressure on both sides. The water is considered to be a spring and dash-pot model in parallel. It adopts a classical solution methodology based on D’Almbert’s principle. The eigen values, normalized mode shape, natural frequencies, orthogonality conditions and dynamic response equations are derived for all the theories. Natural Frequency and Dynamic response of the drill string are used to make informed decisions. Numerical simulation results show the influence of all the factors on vibration damping of the drill string. A critical understanding of the effects of all the above factors individually and in tandem will help in adopting a novel drilling strategy. To conclude, a complete step-by-step methodology for the proposed comprehensive drill string vibration model is put forth to determine the natural frequency and dynamic response of the drill string.

Commentary by Dr. Valentin Fuster
2018;():V003T40A002. doi:10.1115/DSCC2018-8918.

This paper proposes a novel dynamic model of a Reaction Wheel Assembly (RWA) based on the Two-Input Two-Output Port framework, already presented by the authors. This method allows the user to study a complex system with a sub-structured approach: each sub-element transfers its dynamic content to the other sub-elements through local attachment points with any set of boundary conditions. An RWA is modelled with this approach and it is then used to study the impact of typical reaction wheel perturbations on a flexible satellite in order to analyze the micro-vibration content for a high accuracy pointing mission. This formulation reveals the impact of any structural design parameter and highlights the need of passive isolators to reduce the micro-vibration issues. The frequency analysis of the transfer between the disturbance sources and the line-of-sight (LOS) jitter highlights the role of the reaction wheel speed on the flexible modes migration and suggests which control strategies can be considered to mitigate the residual micro-vibration content in order to fulfil the mission performances.

Commentary by Dr. Valentin Fuster
2018;():V003T40A003. doi:10.1115/DSCC2018-8967.

When lifting up a long slender beam from ground, the payload may slip or move suddenly in unintended and unpredictable ways. This occurs during crane operations when the movements of the overhead trolley and the hoist cable are not properly coordinated. Also, it is difficult to keep the centers of hook and payload mass aligned with the pivot point when the payload is lifted off the ground, resulting in undesired hook and payload swing. The payload’s unintended sliding or swing can potentially cause damage and reduce efficiency. This paper divides the lift-up process into two phases including a constrained phase and a free hanging phase, develops a combination of PID controller and speed envelope to prevent slip in the constrained phase, and presents an observer-based Linear Quadratic Regulator (LQR) control strategy to stabilize the double-pendulum oscillations in the free hanging phase. The robustness of the proposed observer-based LQR was analyzed. Lift-up experiments were carried out to verify the controller development.

Commentary by Dr. Valentin Fuster
2018;():V003T40A004. doi:10.1115/DSCC2018-8970.

In this paper, we consider the control design for manipulator handling a flexible payload in the presence of input constraints. The dynamics of the system is described by coupled ordinary differential equation and a partial differential equation. Considering actuators saturation, the proposed control law applies a smooth hyperbolic function to handle the effect of the input constraints. The asymptotic stability of the closed-loop system is proved by using semigroup theory and extended LaSalle’s Invariance Principle. Simulation results show that the proposed controller is effective.

Topics: Design , Manipulators
Commentary by Dr. Valentin Fuster
2018;():V003T40A005. doi:10.1115/DSCC2018-8992.

A faulty sensor may lead to degraded system performance, unstable system, or even a fatal accident. On the other hand, the increasing need for safety and reliability has motivated the development of fault-tolerant control (FTC) techniques. This paper proposes a robust fault-tolerant gain-scheduled noisy output-feedback controller (GSNOF) that guarantees system stability and performance in the presence of sensor aging under control input constraints, where the sensor performance degradation due to aging is modeled by its measurement noisy covariance. The closed-loop system stability and performance, in terms of numerical complexity, computation time, and ℋ2 performance, are studied. The proposed controller is compared in simulations with the published results, which shows that the proposed controller is capable of guaranteeing the stability, performance with reduced numerical complexity and computation load under gradual sensor performance degradation, and it is feasible for real-time control.

Topics: Sensors
Commentary by Dr. Valentin Fuster
2018;():V003T40A006. doi:10.1115/DSCC2018-9011.

This paper presents a many-objective optimal design of a four-degree-of-freedom passive suspension system with an inerter device. In the optimization process, four objectives are considered: passenger’s head acceleration (HA), crest factor (CF), suspension deflection (SD), and tire deflection (TD). The former two objectives are important for the health and comfort of the driver and the latter two quantify the suspension system performance. The spring ks and damping cs constants between the sprung mass and unsprung mass, the inertance coefficient B, and the tire spring constant ky are considered as design parameters. The non-dominated sorting genetic algorithm (NSGA-II) is used to solve this optimization problem. The results show that there are many optimal trade-offs among the design objectives that could be applicable to suspension design in the industry.

Commentary by Dr. Valentin Fuster
2018;():V003T40A007. doi:10.1115/DSCC2018-9037.

The Chaplygin beanie is a single-input robotic vehicle for which partial planar motion control can be achieved by exploiting a simple nonholonomic constraint. A previous paper suggested a strategy for such motion control. In the present paper, this strategy is validated experimentally and extended to the context of multi-vehicle coordination. It is then shown that when the plane on which two such vehicles operate is translationally compliant, energy transfer between the two can enable a mechanism whereby one (operating under control) may entrain the other (operating passively), partly coordinating their motion. As an extension to this result, it is further demonstrated that a pair of passive vehicles operating on a translationally compliant platform can eventually attain the same heading when released from their deformed configurations.

Topics: Motion control
Commentary by Dr. Valentin Fuster
2018;():V003T40A008. doi:10.1115/DSCC2018-9049.

We report a new non-raster scan method based on a rosette pattern for high-speed atomic force microscopy (AFM). In this method, the lateral axes of the scanner are driven by the sum of two sinusoids with identical amplitudes and different frequencies. We formulate the problem so as to generate the rosette pattern and calculate scan parameters and resolution. To achieve high performance tracking, a controller is designed based on the internal model principle. The controller includes the dynamic modes of the reference signals and higher harmonics to cope with the system nonlinearities. We conduct an experiment employing the proposed method and a two degree of freedom microelectromechanical system nanopositioner to scan a circular-shaped area with a diameter of 6μm in 0.2 sec. The steady state tracking error is less than 4.48nm, i.e. only 9% of the selected resolution. AFM scanning is performed in contact mode constant height and high quality images are obtained.

Commentary by Dr. Valentin Fuster
2018;():V003T40A009. doi:10.1115/DSCC2018-9052.

A control design and numerical study is presented for the problem of maneuvering a quadcopter with suspended load. An inverse shaper with a distributed time delay is applied to the feedback path in order to pre-compensate the oscillatory mode of the two-body system. As the first step, the mode to be targeted by the inverse shaper is determined, which is neither the oscillatory mode of the overall system dynamics, nor the oscillatory mode of the suspended load. Next, the established cascade control scheme for UAVs with slave PD pitch angle controller and master PID velocity controller is adopted and supplemented by the inverse shaper tuned to the isolated flexible mode. The numerical and simulation based analysis reveals the key design aspects and dynamics features — due to including the inverse shaper with time delays, the closed loop system becomes infinite dimensional. As the main result, the positive effects of including the inverse shaper in the loop feedback are demonstrated. First of all, the oscillatory mode is well compensated when excited by both the set-point and disturbance changes. Besides, it is shown that the mode compensation is preserved even when reaching the saturation limits at the control actions.

Topics: Stress , Design , Feedback
Commentary by Dr. Valentin Fuster
2018;():V003T40A010. doi:10.1115/DSCC2018-9093.

This paper presents an open-loop, minimum-energy control law for attitude maneuver of a solar-sail. The proposed control law utilizes the magnetic torques and reaction wheels to reorient the solar-sail for near-earth missions. Using the calculus of variations and Pontryagin’s minimum principle, the necessary and sufficient conditions were derived for the nonlinear model of the solar-sail. Then the optimal control problem was formulated as a two-point boundary-value problem and solved via the Shooting method. The computed control law can be utilized in a flight-computer and in a sampled-data feedback closed-loop system which can compensate for disturbance torques.

Topics: Solar energy , Wheels
Commentary by Dr. Valentin Fuster

Vibrations: Modeling, Analysis, and Control

2018;():V003T42A001. doi:10.1115/DSCC2018-9006.

In this paper, a control design for a flexible link co-robot with safety constraints is proposed. The safety constraints are converted to the constraints on the tip position and velocity. To handle this constrained control problem, a barrier Lyapunov function (BLF) is employed in the control design. The derivative of the logarithmic BLF is more complicated compared with the derivative of a quadratic Lyapunov function, which makes the problem of “explosion of terms” more serious. Thus, the dynamic surface control is used to deal with the problem. Furthermore, an extended state observer is adopted to estimate and compensate the uncertainty and disturbance in the system. The stability analysis via the singular perturbation theory shows the local practical exponential stability of the system. Simulation results indicate that the control performance is guaranteed without violation of the constraints.

Topics: Safety , Robots
Commentary by Dr. Valentin Fuster
2018;():V003T42A002. doi:10.1115/DSCC2018-9012.

The purpose of this paper is to investigate the nonlinear dynamics governing the behavior of electrostatically actuated micro electro mechanical systems (MEMS) cantilever undergoing parametric resonance. The MEMS consists of a cantilever parallel to a ground plate. The beam is actuated via an A/C voltage with excitation frequency near first natural frequency of the cantilever. The model includes damping, electrostatic, and Casimir (or van der Waals) forces. The electrostatic force is modeled to include the fringe effect. The amplitude-voltage response of the parametric resonance and the effects of varying the magnitudes of the fringe, Casimir (or Van der Waals), and damping forces along with varying the detuning parameter are reported. The response is obtained using two different methods, namely the method of multiple scales (MMS), and the homotopy analysis method (HAM). In this study approximations up to a 2nd order HAM are used. HAM is a deformation technique that begins with an initial guess and continuously deforms it to the exact answer. For the 1st Order HAM, a softening effect is reported. The 1st Order HAM matches the MMS results in low amplitude and begins to soften and deviate away from the MMS solution in higher amplitudes. For the 2nd Order HAM deformation the softening effect is slightly more pronounced with a slightly lower prediction of the maximum deflection of the cantilever tip. For the 2nd order deformation solution the stable branch of the amplitude-voltage response obtained by the HAM shifts leftward from the MMS solution with the unstable branches between the two methods continue to agree in low amplitudes and deviate in high amplitudes. As a remark, the higher order HAM solutions are obtained symbolically with the software Mathematica and numerically ran with the software Matlab.

Commentary by Dr. Valentin Fuster
2018;():V003T42A003. doi:10.1115/DSCC2018-9015.

This paper presents experimental and numerical analyses of a vibrating sandwich beam with a tip mass. The mathematical formulation is based on higher order sandwich panel theory (HSAPT) and the governing equations of motion and boundary conditions are obtained using Hamilton’s principle. General Differential Quadrature (GDQ) is employed to solve the system governing equations of motion. Experiments are carried out to validate the proposed formulation and the results show very good agreement. Parametric studies are conducted to investigate the influence of key design parameters on the natural frequency and vibration response of the system.

Commentary by Dr. Valentin Fuster
2018;():V003T42A004. doi:10.1115/DSCC2018-9050.

In this paper, the flexural-torsional vibrations of a segmented cantilever beam are considered both theoretically and experimentally under steady-state base rotation. While operating in this steady-state, a piezoelectric actuator is used to excite the beam at various test frequencies. Further, through preliminary investigations, it is demonstrated that accelerometer measurements are not suitable for such a testing apparatus, as these sensors add complex unmodeled dynamics and change the natural frequencies of vibration. The resulting unmodeled dynamics appear to be caused by a large initial deflection due to the added sensor mass, contradicting the conventional assumption that the beam is initially undeformed. This initial bending results in a Coriolis acceleration, and consequently produces a substantial deviation from the anticipated tip response. To further investigate the effect of base rotation on flexural vibrations, experiments were performed in the absence of piezoelectric excitation, both with and without the tip mass. For these conditions, the theory uniformly predicts no flexural or torsional vibrations, while the experimental results demonstrate significant vibrations in both cases. These discrepancies illuminate the presence of significant unmodeled dynamics that are neglected in the conventional mathematical modeling, potentially invalidating the classical simplifications when considering rotating beams.

Commentary by Dr. Valentin Fuster
2018;():V003T42A005. doi:10.1115/DSCC2018-9202.

Railway transportation has been increasingly significant for modern society in recent decades. To enable smart technology, such as health monitoring and electromagnetic braking for railway vehicles, a mechanical motion rectifier (MMR) based energy harvesting shock absorber (EHSA) has been proposed and proved to be capable of scavenging energy from the train suspension vibration. When installed on the train, MMR-EHSA works as a tunable damper in parallel with an inerter. This new suspension form brings great potential for further optimization of suspension dynamics but is rarely researched before. In this paper, the influence of the energy harvesting shock absorber (EHSA) on the railway vehicle dynamics performance is studied. A ten-degree of freedom vehicle model is established, with MMR shock absorber’s nonlinearity taken into account, with the purpose to analyze the influence of the EHSA on the ride comfort and wheel-rail vertical forces. Simulations are conducted by replacing the traditional shock absorber from train secondary suspension with the EHSA. Results show that EHSA could respectively harvest 180 W and 40 W average power at AAR 6th and 5th rail irregularity. In addition, compared with the traditional shock absorber, the MMR-EHSA can provide a higher ride comfort for passengers and slightly reduce the wheel-rail contact force.

Commentary by Dr. Valentin Fuster
2018;():V003T42A006. doi:10.1115/DSCC2018-9214.

This paper studies the vibration damping characteristics of a magnetorheological (MR) damper. A single-degree-of-freedom vibration isolation system with pedestal motion containing MR dampers has been experimentally investigated. Results show that the transmissibility at the resonance frequency does not constantly decrease as expected. It gradually decreases at the beginning, then increase unexpectedly as the input current increases. In addition, the resonant frequency of the system increases continuously. In order to explore the mechanism behind the experimental phenomenon, a centralized parameterized model of the MR damper is established. Hardening coefficient, a parameter that characterizes the dynamic characteristics of the MR damper is introduced, and the influence of the structural parameters and dynamic parameters of the MR damper on the hardening coefficient is analyzed. Simultaneously, a dynamic model of the MR damper is derived based on the Bingham model, and the damping characteristics of the MR damper are predicted and compared with the experimental results. Further, based on a simplified and equivalent dynamic model of the system, the relationship between transmissibility of the system and load mass, stiffness, and damping reveals the physical laws behind the experimental phenomenon. Finally, theoretical results are derived and compared with the experimental results, which demonstrates the rationality of the theoretical analysis.

Topics: Dampers , Damping , Vibration
Commentary by Dr. Valentin Fuster

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