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ASME Conference Presenter Attendance Policy and Archival Proceedings

2016;():V001T00A001. doi:10.1115/FPMC2016-NS.
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This online compilation of papers from the BATH/ASME 2016 Symposium on Fluid Power and Motion Control (FPMC2016) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Symposium on Fluid Power and Motion Control

2016;():V001T01A001. doi:10.1115/FPMC2016-1701.

Today’s available software packages that feature dedicated hydraulic system noise analysis capabilities focus on the Fluid-Borne Noise (FBN) prediction in frequency or time domain. However, some noise sensitive hydraulic installation areas, like light weight structures in aviation, drive the development of an extended toolbox that also covers the prediction of Structure-Borne Noise (SBN) and Fluid-Structure-Interaction (FSI) in hydraulic systems.

This conference contribution presents the concept and design of such a toolbox. It is implemented in a Matlab Simulink/ Simscape environment by FBN-, SBN- and FSI- model libraries. For a given study case a simulation model is generated using elements from these libraries. The simulation results are experimentally validated using a dedicated hydraulic system noise test rig. It features a rotary valve as FBN source and a pipe system equipped with dynamic pressure transducers for FBN detection and acceleration sensors for SBN detection.

The analysis capabilities of such a toolbox are considered beneficial in particular for future (pre-/re-) design projects in the aviation environment, which hold challenging application constraints for efficient hydraulic system noise reduction devices: Besides obligatory strong limits on component weight and size, the high safety and reliability standards demand simple and maintenance-free onboard devices. Hence solutions with minimum hardware efforts are preferred. In this context, the proposed toolbox can be used for a combined tuning of type and location of standard/simple FBN silencers together with type and location of SBN effecting pipe clamps in order to optimize the overall system noise pattern towards an increased equipment durability and passenger comfort.

Commentary by Dr. Valentin Fuster
2016;():V001T01A002. doi:10.1115/FPMC2016-1702.

The goal of this study is to develop a miniaturized artificial muscle in which a tiny compressor can be installed. Pneumatic actuators, such as pneumatic artificial rubber muscles (PARMs), have been widely used in many industrial and robotic research applications because they are compact and lightweight. However, the compressors driving such actuators are relatively large. To solve this problem, the authors have been researching soft actuators driven by gas-liquid phase changes (GLPCs).

In this study, a fixed chamber containing a constantan heater and fluorocarbon was used to generate pressure instead of a compressor. The pressure generation caused by the GLPC was confirmed, and a PARM contraction experiment was then conducted. Additionally, a PI control system was built to test the step and frequency responses of the actuator. A frequency response of up to 4.0 Hz was determined, and the corner frequency was found to be approximately 1.5 Hz.

The size of the actuator was reduced by removing the chamber and installing the heater in the rubber muscle. A PARM driving experiment was conducted, and the performance of the PARM was evaluated. The miniaturized actuator consumes less power than the original actuator.

Topics: Rubber , Actuators , Muscle
Commentary by Dr. Valentin Fuster
2016;():V001T01A003. doi:10.1115/FPMC2016-1705.

Fluid-structure interaction in a bent pipeline is investigated by modal methods. Measured frequency response functions between flow rate excitation and pressure response indicate a coupling effect near the third pipeline resonance. Using modal coordinates for the hydraulic and the mechanical subsystems, a two-degrees-of-freedom study of resonance coupling is carried out. An experimental modal analysis of the coupled hydraulic-mechanical system confirms the predicted resonance splitting; it illustrates the coupling mechanism and shows the relevant mechanical part. An analytical fluid-structure interaction model succeeds in reproducing the measured coupling effect. This model is also used for modification prediction; it demonstrates that an appropriate assembly of mass and damping on the pipeline can help to reduce hydraulic resonance amplitudes.

Commentary by Dr. Valentin Fuster
2016;():V001T01A004. doi:10.1115/FPMC2016-1706.

Pneumatic muscles have a high potential in industrial use, as they provide safety, high power over volume ratio, low price and wide range of pulling effort. Nevertheless, their control is quite hard to achieve due to the non linearity and hysteresis phenomena, plus the uncertainties in their behavior. This paper presents the modeling of a two degree of freedom platform actuated by three pneumatic muscles for control purposes. Three servovalves are used to supply airflow inside the muscles. The innovative concept is the modeling of each component including the static and dynamic muscle behavior. The model of the servovalve consists of a look-up table gathering the three variables: airflow, pressure and voltage applied to the servovalve. In addition, a thermodynamic and a mechanical study of the system complete the model. The result is a complete model design having as input the voltage applied to the three servovalves, and as outputs, the two angles of rotation. Simulated and experimental results permit to validate the complete model for high variation in static and dynamic conditions. These results will be helpful for nonlinear control synthesis.

Commentary by Dr. Valentin Fuster
2016;():V001T01A005. doi:10.1115/FPMC2016-1707.

A novel concept of an active pulsation damper is described that cancels parasitic flow pulsatility of peristaltic pumps and is able to inject desired pulsatility signatures such as physiological heart beat. Peristaltic pumps avoid contact between the moving parts of a pump and the operating fluid. They are used for clean or sterile fluids as well as for highly aggressive fluids, whenever it is important to isolate the fluid from the environment. The background application for the proposed active pulsation damper is the simulation of hemodynamic flow.

The paper presents a novel pulse damper concept that allows the use of roller or peristaltic pumps as primary pumps for hemodynamic flow loops. The problem with peristaltic pumps is that they exhibit a high parasitic pulsatility that needs to be canceled before a desired pulsatility can be injected. The active pulsation damper does this and is also used to superpose a desired flow pattern that resembles measured heart flow rate profiles. The nonlinear dynamic equations of a test system with active pulsation dampers are established and linearized to allow a first analysis of the achievable bandwidth. Simulation results of the closed loop system are presented based on the non-linear equations.

Commentary by Dr. Valentin Fuster
2016;():V001T01A006. doi:10.1115/FPMC2016-1708.

This paper proposes a design and control method of a supporting arm which reduces factory worker load. The supporting arm is a robot manipulator, which is driven by pneumatic cylinders, and is attached to the worker’s hip. In some situation, the factory worker is forced to work with an uncomfortable posture. By using the supporting arm, the worker leg loads are relaxed, and the worker posture is stabilized. To support 50 % weight of the worker, the link system of the supporting arm is designed, and the pneumatic cylinders for actuation are selected. There are two required specifications: (i) support force is sufficient for supporting target load, and (ii) desired stiffness characteristics in the hip height direction can be obtained. The support force is controlled by a two degrees of freedom control system to satisfy the required specifications. An experimental system of the supporting arm was developed, and its performance was evaluated by experiments. As a result, the experimental system shows capability of supporting the target weight and controllability of stiffness.

Topics: Stress , Design , Stiffness
Commentary by Dr. Valentin Fuster
2016;():V001T01A007. doi:10.1115/FPMC2016-1713.

For existing hydraulic hybrid excavators, the loss of energy is still too large and the energy recovery efficiency is not high enough. Concerning these issues, a new hydraulic hybrid excavator potential energy recovery system is proposed within this paper. The energy recovery system uses three-chamber cylinders (TCCs) and accumulators to recover the potential energy of mechanical arms and load of the excavator. The TCC consists of three chambers, including chamber with piston rod, chamber without piston rod and counterweight chamber. The counterweight chamber is connected to an accumulator, which provides average load force. The chamber with piston rod and the chamber without piston rod are connected to inlet and outlet of a variable pump respectively, constituting a pump controlled system together. The mathematical models of load, engine, pump, TCC and accumulator were established in this study. According to the mathematical model, the dynamic response was simulated and the dynamic characteristics of each components were analyzed. The parameter matching of accumulator was proposed as well. Besides, the simulation model was built and the simulation result was carried out. From the simulation, the dissipated energy of each cylinder was obtained and compared with the dissipated energy without potential energy recovery system. According to the comparison, the potential energy recovery system can reduce the dissipated energy of variable pumps by around 30∼60%, and reduce the dissipated energy of engine by around 50%.

Commentary by Dr. Valentin Fuster
2016;():V001T01A008. doi:10.1115/FPMC2016-1716.

Recent research has been used to identify efficiency improvements that may be obtained by utilizing on-off hydraulic valves in the place of traditional hydraulic valves. These efficiency improvements reduce throttling losses in the valve by using wide-open valve positions that are intermittently turned on and off. While this efficiency idea has emerged with great interest among some, there are still those who remain doubtful about the efficiency improvements that have been claimed and anecdotal concerns continue to be voiced at conferences and in hallway discussions within industry. This paper is being written to address the subject from a theoretical perspective. In the analysis of this paper, the efficiency equations for an on-off valve will be derived and compared to the efficiencies of valves that are employed in pressure relief systems, pressure compensating systems, and load sensing systems. In conclusion, it is shown that valves operating in load sensing systems are always the most efficient valves, while digital valves are often the next most efficient design except during low flow conditions when the valve in a pressure compensating system may occasionally be more efficient than the digital valve. It is shown in this research that valves used in pressure relief systems are always the most inefficient design.

Commentary by Dr. Valentin Fuster
2016;():V001T01A009. doi:10.1115/FPMC2016-1717.

When designing a hydraulic circuit, there are a number of ways to power each hydraulic function in the circuit. For instance, a single hydraulic function may be powered by its own dedicated pump; or, a hydraulic function may share a pump with additional functions in the circuit. The design question is this: “What is the optimal arrangement of pumps for a given circuit that will result in the lowest energy consumption and the smallest machine size?” This research documents an example study in which a duty cycle from the typical wheel loader is used to study the five possible pump-combinations that exist for powering the lift, tilt, and steering functions of the machine. It is shown that the lowest efficiency for the machine is observed when all three functions are powered by a single pump, and that a 15% efficiency increase may be realized over the single-pump design by giving each function its own dedicated pump. In order to achieve this efficiency increase, the original single pump is replaced by the following pump combination: 1) a pump 69% the size of the original pump for the Lift function, 2) a pump 86% the size of the original pump for the Tilt function, and 3) a pump 31% the size of the original pump for the Steering function. This solution increases the overall pump volume on the machine by 86%, nearly doubling the pump volume on the machine.

Commentary by Dr. Valentin Fuster
2016;():V001T01A010. doi:10.1115/FPMC2016-1721.

For the huge energy losses of the conventional hydraulic valve-controlled servo control system, a new Multi-level Pressure Switching Control System (MPSCS) was coined and proposed in this study to address this issue. First, the discrete force distribution and switching rules of MPSCS was designed for conducting the four-quadrant working principle. Second, the hybrid control strategy was designed and applied for a displacement control system with three-level pressure rails. Finally, an experiment rig was established to validate proposals above in this study. The experimental results approved the pump input power and throttling losses of MPSCS was decreased dramatically compared with the conventional displacement control system, but the response time, position jitter etc. were still challenges to MPSCS.

Commentary by Dr. Valentin Fuster
2016;():V001T01A011. doi:10.1115/FPMC2016-1722.

Traditionally, counterbalance valve (CBV) is widely used to counterbalance negative load of fluid power machinery. CBV introduces extra energy consumption and oscillation to hydraulic system especially for time varying system. The essence of its shortcoming is the inflexibility of the control architecture. In this article, a proportional orifice is adopted to counterbalance negative load, which makes the control strategy flexible. A load observer is proposed to demonstrate the load dynamically. A control algorithm based on back-stepping design is proposed in this paper afterwards, aiming at keeping the inlet chamber pressure of the actuator around a fairy small value. The control error is estimated, as well. A simulation for the process of the excavator booming down is carried out to verify the observer and control algorithm, which proves the energy-saving target achieved.

Topics: Stress
Commentary by Dr. Valentin Fuster
2016;():V001T01A012. doi:10.1115/FPMC2016-1723.

A numerical study in a mini trochoidal-gear pump based on an ingenious strategy to adapt the background mesh to the profiles shape and a new boundary condition is presented. The strategy achieves a final background mesh better adapted to the geometries and, additionally, the cells are more homogenous and less distorted when the trochodial-profiles are moved. The new boundary condition to simulate the multi-meshing contact points is applied at every time step by means of the viscous wall approach, a home-made ad-hoc code, which has been integrated in an OpenFOAM solver that also includes the dynamic mesh functionality by deforming the mesh following the trochoidal-gear rotation.

The presented numerical study establishes the basis that will allow simulating more realistic aspects of a new design of a mini trochoidal-gear pump once the need for a continuous fluid domain is overcome reproducing actual contacts between the rotors and will guide to a better understanding of the new design.

Topics: Gears , Pumps
Commentary by Dr. Valentin Fuster
2016;():V001T01A013. doi:10.1115/FPMC2016-1724.

When designing an actuator for a spool type directional control valve, axial forces acting on the spool have to be estimated. The steady-state flow force is the dominant axial force, which usually acts in the closing direction of the valve. However, many factors such as the valve geometry and the oil properties influence the flow force characteristics. Investigations regarding their effects on steady-state flow forces are described within this paper.

Different spool geometries of a test 2/2-way spool valve are used for steady-state flow force measurements at different oil temperatures. The measurement data are used for validation of CFD simulations, which are carried out to scrutinise the flow inside the valve. Besides the steady-state flow forces, the fluid flow angles at the inlet and the outlet of the spool chamber are analysed.

The results show that the spool geometry has a significant influence both on the flow rate and the steady-state flow force characteristics. Especially, the shape of the control edge has an impact on the flow patterns and on the magnitudes of steady-state flow forces. Moreover, the inlet and outlet fluid flow angles do not correlate with the expected values, which are commonly used for an analytical estimation of the flow forces. Furthermore, the oil temperature leads to quantitative deviations of the steady-state flow forces.

Commentary by Dr. Valentin Fuster
2016;():V001T01A014. doi:10.1115/FPMC2016-1725.

The four-point leveling hydraulic system (FLHS) is a key component of high-precision hydraulic press. To meet the development trend of leveling system of hydraulic press, such as large stroke, anti-bias load ability, big leveling torque, principle of passive FLHS with four axis synchronous controlling has been proposed, using four high-precision displacement sensors and four high-response servo-proportional valves (HSPV). Because the HSPV has a certain predictive opening, during the process of passive leveling operating, linearization of the mathematic model at operating point is necessary. In this paper, a simulation model of the system, which uses the average type synchronous control strategy, is built with ADAMS and MATLAB / Simulink, as well as the operational parameters of the model. The result of the simulation shows that the system using the average type synchronous control strategy is able to ensure the synchronization error among the four axis of the leveling system. It also suggests that the proposed leveling and the control strategy are reasonable, effective and feasible.

Commentary by Dr. Valentin Fuster
2016;():V001T01A015. doi:10.1115/FPMC2016-1734.

This paper presents a comprehensive study to estimate the total torque losses which contribute to the hydro-mechanical efficiency in external gear machines (EGMs). A study of these losses at different operating conditions is an important design factor in prototyping many positive displacement machines to achieve efficient and reliable designs.

Although semi-empirical models for the description of the steady-state behavior of positive displacement machines accounting for both volumetric and torque losses are available in literature, their fidelity is often based on the availability of reliable experimental data. In the case of EGMs, it is difficult to consider intricate operating features such as the micro-motion of the different components in these generic models. A numerical evaluation of these special features in an EGM using dedicated models for EGMs can potentially contribute to an accurate prediction of the hydro-mechanical efficiency of a given design.

In the present work, different sources of the torque losses are methodically determined for a reference EGM unit through various numerical models which were previously developed and validated in the authors’ research team. The cumulative predictions of the torque losses from the different simulation models are then validated against the corresponding measured experimental torque losses at various operating conditions for the reference EGM unit.

Topics: Machinery , Simulation , Gears
Commentary by Dr. Valentin Fuster
2016;():V001T01A016. doi:10.1115/FPMC2016-1735.

Pneumatic booster valve is widely used in local pressure boost circuit for energy saving, a new booster valve with energy recovery (short for BVER) was proposed in this paper in order to further improve the energy efficiency. Firstly, the principle of BVER was introduced by comparing with the traditional booster. Based on flow-rate characteristics equation, gas state equation, energy conservation equation, etc., the mathematics model of BVER was established, and the flow-rate characteristics, boost ratio, pressure in tank and energy efficiency were systematically analyzed by simulation. Lastly, the model was verified by experiments. This study shows that: firstly, the pressure decreased sharply with the flow-rate’s increasing, and the pressure in tank is much lower than in BVER. Secondly, the boost ratio was affected by supply pressure, regulator coefficient and the diameter of recovery chamber. Thirdly, the pressure fluctuation in tank decreases with the tank volume increasing, and the pressure fluctuation is less than 1% when tank volume is larger than 10L. Lastly, the energy efficiency will increase 5∼10 percent with the boost ratio increases 15∼25 percent under different supply pressure. This study proves that BVER has better performance than VBA for its high boost ratio and high energy efficiency, and it provides a reference for booster valve’s design and energy saving.

Commentary by Dr. Valentin Fuster
2016;():V001T01A017. doi:10.1115/FPMC2016-1738.

Water hydraulic system using tap water as working fluid is a new driving method which provides high speed, high-output control, while providing safety, hygiene, and ecofriendliness. Its applicable markets widely range from food, health, pharmaceuticals, cosmetics, semiconductors, beverages, to energy industries. Applications of the water hydraulic technology differ from those of its oil counterpart in heavy industries.

This paper is aimed at analytically considering the stability of systems that use tap water as the working fluid. We studied a comprehensive system, including a water hydraulic control valve, a cylinder, and piping for connecting these components, to determine the transfer function of the entire system that has three elements: a control valve; piping and cylinder; and a compensation circuit. Based on the determined function, we reviewed the relationship among natural frequencies of the system, including the control valve and piping, and examined the effect of the control valve and cylinder on the stability of the entire system according to the Hurwitz stability criterion. This gave us a design guideline about the compensation circuit that stabilizes the system by adjusting the natural frequency of the water hydraulic proportional control valve according to the natural frequencies of the piping and cylinder.

Commentary by Dr. Valentin Fuster
2016;():V001T01A018. doi:10.1115/FPMC2016-1739.

In the modelling of the leakage rate, friction force or contact pressure distribution of hydraulic seals is quite common to assume the mating surfaces to be characterized by a random isotropic roughness. However, due to different surface finishing methods, such as coating, grinding or polishing, roughness with anisotropic characteristics is often generated.

In this paper a first experimental investigation of the influence of such anisotropic surfaces on the sliding friction is provided. For this purpose, a test rig has been designed and set up to investigate a soft, lubricated line contact representative of a generic reciprocating hydraulic seal. In particular, an O-ring cord is squeezed into contact with a steady rotating rigid cylinder. In order to adopt a cylinder-on-flat configuration, the diameter of the rigid cylinder is chosen to be significantly larger than the O-ring (cross-section) diameter. Furthermore, three cylinders with different surfaces are used: One (sandblasted) isotropic surface and two anisotropic surfaces roughness, scratched perpendicularly or along the azimuthal direction. Therefore, under temperature control, Stribeck curves have been measured at different squeezing loads and surface roughness, showing a neat influence of the surface roughness characteristics on the friction force. Finally, the experimental results are compared with the predictions provided by a recent mean field theory of soft contact (e.g. rubber) lubrication.

Topics: Friction , Anisotropy
Commentary by Dr. Valentin Fuster
2016;():V001T01A019. doi:10.1115/FPMC2016-1740.

When hydraulic excavators lower their boom or brake the rotating upper structure, recoverable potential or kinetic energy is available. In recent years electric and hydraulic hybrid excavators have been developed to recover this energy that is lost through usually the throttle or relief valve. Although boom lowering motion occurs frequently, most commercial hybrid excavators only recover the swing braking energy. Some hybrid architectures to recover the boom potential energy have also been introduced, however, much of this energy is still lost as throttling losses when they save the energy into a storage device by using a recuperation scheme or they need many additional electric components.

This paper introduces a new regeneration scheme to recover the boom potential energy for hydraulic excavators. By directly connecting the head chambers of the boom cylinders to a variable displacement hydraulic motor installed on the engine shaft, the boom potential energy could be used to support the torque required to be delivered by the engine. The speed of boom lowering is controlled by adjusting the motor displacement. Also bypass into a tank is implemented to limit the size of the recovery motor. The simulation results show the average fuel consumption in leveling and 90deg truck loading tasks can be reduced by 10% and 7%, respectively.

Commentary by Dr. Valentin Fuster
2016;():V001T01A020. doi:10.1115/FPMC2016-1744.

Within the cluster of excellence “Tailor-made Fuels from Biomass” at RWTH Aachen University new biofuels are developed and investigated. Because common-rail injection pumps are generally lubricated by the fuel itself, the tribological characteristics of the fuel candidates is of interest. The lubricity and viscosity of the alternative fuels differ from diesel. Hence, a reliable function of the tribological contacts, which are designed for the operation with diesel, cannot be guaranteed. To achieve a reliable operation even for fuels with, for instance, a lower viscosity or worse lubricity an optimisation of the tribological contacts is necessary.

The focus of the investigations presented in this paper lies on the piston-cylinder-contact. Prior to the simulative study the losses in a pump operating with various fuel candidates are quantified by means of efficiency measurements. By these measurements the great impact of the fuel’s rheology on the pump performance is clarified.

Based on detailed EHD-simulations with various fuels under typical operating conditions, an optimisation of the piston-cylinder-contact is presented. The optimisation aims for the reduction of solid friction by changing the pressure field on the piston. The approaches can basically be separated into grooved and contoured pistons. The potential of the different approaches is discussed based on simulation results and effects, which occur in the lubricating film of the optimised contacts.

Commentary by Dr. Valentin Fuster
2016;():V001T01A021. doi:10.1115/FPMC2016-1745.

As an effort to develop more efficient system for an excavator, EH (Electro-Hydraulic) system has been widely adopted to take the advantage of the well-commercialized EH valves and its control technologies[1]. Utilizing the EH technology, an innovative IMV (Independent Metering Valve) control system for an excavator mechanism, which consists of high capacity EH valve blocks, an electric-controlled pump, and a main controller unit, has been developed by Hyundai Heavy Industries Co., Ltd. This IMV control system can provide tremendous flexibility to the control of cylinder movements and reduce the energy consumption of an excavator.

In this paper, we introduce the major features of the developed IMV control system and propose the novel control algorithm considering optimal power distribution and energy saving. Furthermore, the effectiveness of the proposed system and control algorithm is verified through various experiments conducted on an excavator equipped with the IMV control system. The results are compared with those of conventional machine. It was shown that IMV system could save the energy consumption more than 10% of an excavator.

Commentary by Dr. Valentin Fuster
2016;():V001T01A022. doi:10.1115/FPMC2016-1748.

This paper describes the design, simulation and testing of a high response servo-proportional valve. The purpose of this work is to study the possibilities, using a modeling technology, to increase the dynamic performance of a servo-proportional directional developing new algorithms for the digital control system.

The development of digital technology, introduced also in the control of proportional valves, have led to the reduction of the differences between the overall characteristics of proportional and servo valves so that the proportional ones can be a suitable solution in many applications, where servo-valves are traditionally used.

The mathematical model of the servo-proportional valve has been developed by using the commercial software AMESim® (Advanced Modeling and Simulation Environment for Systems Engineering). The model includes the proportional solenoid and the linear transducer.

Digital control of the proportional valve proposed in this paper, is a key part of this research. Its mathematical model and the control algorithm have been built using Matlab®. Both models have been run in co-simulation to improve the overall valve performance.

The experimental tests have been performed in the labs of Duplomatic Oleodinamica SpA and Continental Hydraulic Inc.

The data have been used to validate the simulation models.

Commentary by Dr. Valentin Fuster
2016;():V001T01A023. doi:10.1115/FPMC2016-1753.

In this work a Computational Fluid Dynamic (CFD) analysis was applied to the design and optimization of a novel concept roto-translating (RT) valve.

A Roto-Translating valve is a spool type valve assembled to a moving sleeve. The two parts are controlled by two independent actuators and are placed inside the valve body. The valve features both basic logic functions (AND, OR), and advanced control techniques. From the safety viewpoint it offers a fail-operational characteristic thanks to operational redundancy and functional diversity. Moreover the control flexibility allows to get rid of the need of a specific spool design for each different application. One of the goals of the valve is to enhance the speed and precision achievable by the use of two concurrent actuators; for this reason it is fundamental to study the flow forces effect that could adversely affect both rotating and linear motion.

In the field of hydraulic valves design the Flow Force, generated by the acceleration of fluid flow across the metering edges, is an important phenomenon to be considered for the study of the operation and dynamics of the valve. Differently from common spool valves, in this new kind of valve two types of reaction to fluid flow are present: the Flow Force and the Flow Torque.

The first is the well-known axial Flow Force which is generated from the variation of axial component of momentum of the fluid flow and was studied by several authors. The second type of reaction can be identified as a Flow Torque, a less investigated argument. Basically the Flow Torque, equivalently to Flow Force, is linked to the variation of the component of fluid momentum, but in this case in circumferential direction and effects the mutual rotation of the two metering elements.

A complete map of operative conditions, 5 angular positions and 5 linear displacements have been investigated, simulating all the combinations of 4 different pressure ranges. This approach generates a quite large matrix of 25 results for each of the 4 working pressure conditions. For each run the pressure and velocity gradients have been recorded and the flow and torques forces have been computed. These data allow the validation of the sizing of both electric valve actuators, in order to define the operational limits of the valve in terms of pressure drop and flow rate. This activity could also inspire new solutions for a further geometric optimization of the design.

Commentary by Dr. Valentin Fuster
2016;():V001T01A024. doi:10.1115/FPMC2016-1754.

The reliable and repeatable experimental testing of automotive components is a challenge, especially when human occupants are involved. In most circumstances full vehicle testing over a range of road conditions is used even though this is expensive, difficult and time-consuming. In this work an experimental platform that compensates for the vehicle motion using the principle of hardware-in-the-loop (HIL) simulation is developed using a multi-axis simulation table (MAST) available in the Center for Power Transmission and Motion Control (PTMC) laboratory at the University of Bath. The MAST was tested in both the time and frequency domains with a range of road profiles including a random and single bump in the low frequency range (0.5–25 Hz). Also, uncertainties in the vehicle suspension characteristics such as the damping coefficient, the stiffness rate and the vehicle mass are examined. The experimental results in the frequency and time domain show that the MAST can be used to reproduce the dynamic characteristics of a quarter vehicle model with an excellent degree of agreement with the simulated response.

Commentary by Dr. Valentin Fuster
2016;():V001T01A025. doi:10.1115/FPMC2016-1755.

The target application of this study is hydraulic excavators, which are one of the most common machines found at construction sites across the world. Road constructions and improvements, laying operation of cables or pipes and building can be seen in urban areas and digging and dumping operations of natural resource are done in country regions. For the construction site in urban areas, mini hydraulic excavators with operating weights up to 6 tons are often used and they make up more than 60% of the total hydraulic excavators market [1].

In recent years, a number of new system architectures for mobile hydraulic systems have been proposed. Examples of such improved architectures are displacement control, transformer systems and valve controlled systems with multiple pressure rails. For these systems, electronic controls are always used. Although these new methods are promising, they cannot be applied to mini-excavators, because today’s mini-hydraulic excavators do not use electronic controls as this would increase costs and make the system complex. Therefore, the goal of this study is to propose a fully hydro-mechanical valve controlled constant pressure system, which can be applied to mini-excavators in the future.

This paper begins by introducing the details of this novel hydraulic system and shows its advantages. Using a simulation model of an 18 ton excavator, it is confirmed that the novel system functions well and the energy efficiency is compared to a conventional Load Sensing system. The simulation results show that the novel system can save 22% and 24% of fuel in leveling and 90° dig-dump cycles respectively.

Commentary by Dr. Valentin Fuster
2016;():V001T01A026. doi:10.1115/FPMC2016-1756.

Hydraulic power units operated as constant supply pressure systems remain to be widely used in the industry, to supply valve controlled hydraulic drives etc., where the hydraulic power units are constituted by variable pumps with mechanical outlet pressure control, driven by induction motors. In the analysis of supplied drives, both linear and rotary, emphasis is commonly placed on the drives themselves and the related loads, and the supply system dynamics is often given only little attention, and usually neglected or taken into account in a simplified fashion. The simplified supply system dynamics used in such analyzes is often justified by short supply lines and/or the utilization of accumulators near valve inlets, accounting for the majority of possible supply pressure variations. Such considerations are reasonable in many test benches, where the supply pressure variations are small enough such that limited impact on the drive dynamics is observed. Such ideal properties however, are not necessarily present in industrial hydraulic applications for various reasons, with the most common being large volumes of supply lines. Long supply lines, hence large supply line volumes, between the supply system and drives will reduce the flow-to-pressure gain of the supply system, and hence increase the time constant of the supply pressure dynamics. A consequence of this may be large variations in the supply pressure, hence large variations in the pump shaft torque, and thereby the induction motor load torque, with possible excitation of the induction motor dynamics as a result. In such cases, the coupled dynamics of the pressure controlled pump and induction motor may influence the supply pressure significantly, possibly affecting the dynamics of the supplied drives, especially in cases where pilot operated valves with internal pilot supply are used. This paper is concerned with the analysis and characterization of the coupled pump-induction motor dynamics, confined to hydraulic power units constituted by an axial piston pump with mechanical outlet pressure control, driven by an induction motor operated at grid conditions. Furthermore, a simplified general model representation of the coupled dynamics is established, accounting for the entire dominating dynamics of the supply unit. Results demonstrate the accuracy of the simplified model representation.

Commentary by Dr. Valentin Fuster
2016;():V001T01A027. doi:10.1115/FPMC2016-1759.

The design and numerical simulation of a radial inflow turbine for a micromachining spindle is described. The spindle design specifications require the turbine stage to produce approximately 120W of power at a nominal design speed of 100,000 rpm. The aerodynamic and structural performance of the turbine stage is assessed using Computational Fluid Dynamics (CFD) and Finite Element (FE) simulations. A number of options to reduce rotor weight and inertia while maintaining high efficiency are investigated. Finally, as machine tool spindles are typically required to operate over a wide range of torque loads and speeds, the part-load aerodynamic performance of the turbine is also assessed.

Topics: Turbines
Commentary by Dr. Valentin Fuster
2016;():V001T01A028. doi:10.1115/FPMC2016-1760.

This paper describes an application of direct drive volume control (DDVC) to ship speed control. The DDVC fuel injection device consists of an AC servo motor, a fixed-displacement oil-hydraulic pump, and an oil-hydraulic cylinder. The cylinder piston pushes a fuel pump to pressurize fuel and an injection valve opens to inject fuel into a combustion chamber. Timing and the quantity of fuel injection can be controlled by the electric signal added to the AC servo motor. In this paper, the DDVC fuel injection device is applied to engine speed control of marine diesel engine and ship speed control. A simulation model is made including a model of the DDVC fuel injection device, propeller model, and hull motion model. Firstly, engine speed control system is proposed. Stop injection angle is automatically adjusted according to engine speed error signal. Secondarily, ship speed control is proposed. Propeller pitch angle is used to control ship speed. Simulation study of these control systems are presented to show the capability of the DDVC fuel injection device for marine diesel engine.

Topics: Fuels , Ships
Commentary by Dr. Valentin Fuster
2016;():V001T01A029. doi:10.1115/FPMC2016-1762.

The fluid-structure interaction (FSI) can be observed significantly in the axial vibration of the liquid-filled pipe system. When distributed friction was neglected, the model could be solved with an exact solution without numerical error, developed from the method of characteristics (MOC). Then time-line interpolations have been employed to reduce the high time cost and retain the accuracy, named as the improved exact solution. For the purpose of practical applications, series connection of double-pipes is discussed in this paper. And complex constraints, including elastic, damping and inertial effects at connections, are studied. Models and methods are validated by numerical cases.

Commentary by Dr. Valentin Fuster
2016;():V001T01A030. doi:10.1115/FPMC2016-1765.

Hydraulic pump health monitoring can give early notice of a catastrophic failure occurring within the pump, saving time and money on repairs. This work focuses on developing a system to monitor an axial piston pump’s volumetric efficiency, using state and parameter estimation techniques. A high order, nonlinear model has been utilized for the axial piston pump. Pressure measurements of the pump are used for a linear Kalman filter (KF) as well as an extended Kalman filter (EKF) to estimate the remaining states of pump model. Volumetric efficiency losses are tracked by the filters via estimation of two flow loss coefficients, low Reynolds and high Reynolds flow loss, which are allowed to vary within the model to track the changes. In a separate analysis, a third parameter, a disturbance torque, was applied to the load and its estimation in a similar process to the flow loss coefficients.

Both filters are able to estimate a single flow loss or load. However, the KF was unable to distinguish between two flow losses. The EKF is able to distinguish between low and high Reynolds number flows since it takes into account the nonlinearities in the system including the flow loss characteristics. The EKF shows promise in being able to estimate both flow losses and a load disturbance simultaneously. Both types of filters are found to have fast run times suggesting that the filters could be implemented using typical microcontroller hardware found on industrial and mobile hydraulic machinery.

Commentary by Dr. Valentin Fuster
2016;():V001T01A031. doi:10.1115/FPMC2016-1767.

The focus of this paper is the biphasic phenomena that occurs in a lubrication system of a CVT gearbox transmission of an agricultural tractor, in particular a Method of Analysis is outlined with the aim of mapping and assessing the behavior of the lubrication circuit.

The study of the lubrication in gearboxes is an important issue in the design of off-road machines because their reliability depends mostly on the lubrication performance, as well as the machine’s lifetime and overall energy efficiency of the transmission is strongly dependent on the lubrication system behavior. In fact the role of the lubrication system is twofold: firstly to remove the heat generated in the highly loaded rolling bearings and the gears found in the power and accessory gearboxes via heat exchangers; secondly to lubricate these parts. The trend in the development of gearbox transmissions has been towards lower consumption and higher power transmitted, consequently it is necessary to conceive more effective and efficient lubrication systems. Nonetheless the lubrication problem often relies on a trial and error approach and most available scientific literature is based on lumped element model dynamic simulation or one phase thermo-fluid dynamic simulations, overlooking the effects linked to cavitation and air inclusion.

One important phenomenon in lubrication systems is that of air suction. This can be seen in particular at high rotational speeds of shafts when the centrifugal force causes a positive pressure drop between inner lubrication pipes and outer radial conduits. In this case the air occupies part of the lubrication conduits, and since the domain is shared by the outflowing liquid phase and the air included, the monophase CFD simulation fails to predict the correct lubrication flow. If this effect is not carefully considered it could cause a lubrication unbalance among the various parts of the gearbox, creating a risk of transmission damage.

In this paper the methodology will be presented step by step until in final a complete map of operation condition is created. A preliminary analysis of the circuitry is an essential phase of the project since the tractor’s transmission is an extremely complex assembly composed by hundreds of components therefore the lubrication circuit appears as a large net of moving hydraulic connections and consumers. From this analysis a computational domain is obtained and appropriately meshed. After the pivotal choice of the proper turbulence model and boundary conditions, various runs at different rotating speeds corresponding to the different operating ranges will be performed. The result will be contextualized by commenting on the fluid dynamics phenomena involved and the influence parameters on flow rate distribution, finally evaluating the performances of the lubrication circuit, and in particular highlighting the most critical conditions in terms of speed condition and locating the most critical gearbox parts.

Commentary by Dr. Valentin Fuster
2016;():V001T01A032. doi:10.1115/FPMC2016-1768.

Reed valves are a type of check valve commonly found in a wide range of applications including air compressors, internal combustion engines, and even the human heart. While reed valves have been studied extensively in these applications, published research on the modeling and application of reed valves in hydraulic systems is severely lacking. Because the spring and mass components of a reed valve are contained in a single element, it is light and compact compared to traditional disc, poppet, or ball style check valves. These advantages make reed valves promising for use in high frequency applications such as piston pumps, switch-mode hydraulics, and digital hydraulics. Furthermore, the small size and fast response of reed valves provide an opportunity to design pumps capable of operating at higher speeds and with lower dead volumes, thus increasing efficiency and power density. In this paper, a modeling technique for reed valves is presented and validated in a hydraulic piston pump test bed. Excellent agreement between modeled and experimentally measured reed valve opening is demonstrated. Across the range of experimental conditions, the model predicts the pump delivery with an error typically less than 1% with a maximum error of 2.2%.

Topics: Modeling , Valves
Commentary by Dr. Valentin Fuster
2016;():V001T01A033. doi:10.1115/FPMC2016-1769.

Published theoretical work about fluid stiction between two separating plates was so far limited to a finite initial gap. It was shown that pressure and force evolution are well described by fluid film lubrication equations if cavitation is taken into account. The practically important case that plate separation starts from a mechanical contact condition was only studied by experiments. They showed that quite substantial negative pressures can occur in the gap for a very short time and that the peak forces are varying strongly even between consecutive experiments with equal test conditions. In this paper two models are presented which complement the Reynolds equations with dynamical bubble evolution equations. Initial gap height, bubble number density, and initial bubble radius are the three unknown parameters of these models. Initial gap height accounts for surface roughness, the two other parameters refer to the bubble nucleation of the fluid in the small roughness indentations of the gap. A first model employs the Rayleigh-Plesset bubble dynamic model. It requires that the bubbles stay small compared to the gap. Results show that its stiction force dynamics is two orders of magnitude faster than experimentally observed and that the bubble size condition is violated. The second model assumes that bubbles span over the whole gap height and that the flow of the liquid between the bubbles is guided by the Reynolds equation. This model can be brought into reasonable agreement with the experiments. Force variation from experiment to experiment can at least in part be reproduced by a random variation of the initial bubble sizes. The model exhibits a kind of boundary layer behavior close to the outer boundary. This layer represents the interaction zone between bubble growth dynamics, pressure distribution due to viscous flow, and the pressure boundary condition.

Topics: Fluids , Stiction
Commentary by Dr. Valentin Fuster
2016;():V001T01A034. doi:10.1115/FPMC2016-1770.

This paper presents a prototype powered ankle prosthesis which can operate passively in most of the gait cycle and provide assistance for toe push-off and subsequent foot dorsiflexion. The use of electrohydrostatic actuation (EHA) gives the ability to switch quickly and smoothly between passive and active modes. In this new powered ankle prosthesis, the motor-pump unit is integrated with the ankle joint and the battery and controller are held in a backpack. A 100W brushless DC motor is used driving a 0.45cc/rev gear pump. The motor runs in hydraulic fluid, pressurised to 60bar, avoiding the need for a pump shaft seal and a refeeding circuit for external leakage. A simulation model was developed to help analyse the performance characteristics of the EHA. The simulation results are compared with laboratory-based experiment results to validate the model. The compact prototype is suitable for prolonged testing with amputees, and an example set of results from amputee testing is presented.

Topics: Design , Prostheses , Testing
Commentary by Dr. Valentin Fuster
2016;():V001T01A035. doi:10.1115/FPMC2016-1771.

Energy efficiency improvements are forced by steadily increasing general performance and cost saving requirements, and for mobile machines mostly by stricter governmental emission laws. Such improvements can be realized by new system architectures, like hybrids or energy recovery systems, but also by optimizing existing systems. This publication discusses the reduction of systematic losses for an existing hydraulic Load Sensing System (LSS) used in mobile working machines, especially in compact excavators. Energy losses in a LSS are proportional to the pressure difference between pump and actuator in each section. These systematic losses are investigated and can be reduced by actuator adaptation or by splitting non-correlating sections. Energy losses along the hydraulic circuit, such as pump losses hydraulic line losses and actuator losses, which are affected by these adaptations indirectly, are neglected.

The investigations are founded on measurements of a 5 ton compact excavator and their systematic evaluation. The actuator adaptation can be realised by changing the excavator’s geometry and/or hydraulic specifications (cylinder areas, displacement volume). The focus of this paper is limited to the hydraulic domain. Mathematical models and operation scenarios verified by measurements were taken as the basis to find optimum system parameter configurations by mathematical optimization, employing evolutionary algorithm. This included also different groupings of LSS circuits. Boom, stick, bucket and swing were taken into account and results are shown for a one, two and three pump LSS. Considering the introduced methods an effective way for reducing systematic losses up to 40% is shown in this exemplary case.

Topics: Stress
Commentary by Dr. Valentin Fuster
2016;():V001T01A036. doi:10.1115/FPMC2016-1772.

In recent years, fuel consumption of vehicles has been remarkably improved by some cutting edge technologies (e.g., hybrid electric vehicles, non-idling systems). In-vehicle equipment is also required to improve efficiency. The vane pumps used to control power steering and transmissions must demonstrate maximum performance, even under high temperature conditions and with rich gases contained in hydraulic oil. Precise recognition of the dynamics of pump inner flow can help in the design and development of vane pumps.

In this study, the 3-dimensional CFD is adopted to analyze the characteristics of inner flow dynamics of vane pumps. Since the gases contained in hydraulic oil influence the characteristics of vane pumps, the two-phase flow model with cavitation is assumed in particular. First, this CFD was verified by comparison with experimental results which were carried out at higher rotational speeds and with oil containing a high level of gas; the results showed the error of the suction flow rate could be as little as 5% or less. Internal pressure in the vane chambers was then studied to identify the relationship between the cavitation model and the contained gas ratio of the oil. The simulation results further clarified that the gas clouds deformed by pump rotation could restrict the flow of the suction ports.

Topics: Gases , Pumps
Commentary by Dr. Valentin Fuster
2016;():V001T01A037. doi:10.1115/FPMC2016-1773.

An effective way for the testing of a large number of systems is using single and multi-axis shaking tables. Among the possible applications, the civil engineering field stands out for the testing of structures, or part of them, both on a reduced and on a full scale. However, design a high performance controller for a servo-hydraulic shaking table is a difficult problem due to its non-linarites and large friction forces. The goal of this paper is to develop and experimentally validate a robust numerical model that simulates the acceleration behavior of a uni-axial servo-hydraulic shaking table system with considering three friction models, the LuGre model, the modified LuGre model and the new modified LuGre model. First, a full system model of servo-hydraulic system is developed based on fluid mechanical expressions and then the friction force of hydraulic cylinder is modeled and validated on the real shaking table. Data of the experiment are gathered from input command valve, and the output acceleration and position of the table. All models are simulated by using MATLAB and SIMULINK computer program. The parameters of the system and the friction models are estimated by using least square method (LSM). Finally, the comparisons of simulated results with experimental ones show that the model of the system with considering third model of the friction can predict accurately the shaking table’s behaviors.

Commentary by Dr. Valentin Fuster
2016;():V001T01A038. doi:10.1115/FPMC2016-1775.

Hydrostatic or closed-circuit pump-controlled hydraulic systems are attractive due to their high energy efficiency; their lack of throttling losses and ability to recover energy onto the pump shaft have made them a common design choice in systems using rotary actuators such as ground drive transmissions. However, the natural asymmetrical flow of typical hydraulic cylinders have prevented the widespread adoption of closed-circuit systems for linear actuators. Some hydrostatic linear actuator systems have been developed, but these suffer from a large dead volume and reduced force if using a symmetrical dual rod cylinder, or increased cost and complexity if using a specialized cylinder geometry or flow balancing circuits. This paper presents a concept system which uses a pair of common single-rod hydraulic cylinders to achieve the efficiency of a pump-controlled hydrostatic system with the opportunity for energy recovery. The system’s available force is equal to a standard valve-controlled system with a greater maximum velocity. This is achieved using only commercially-available components. The paper will present an analysis of the theoretical energy recovery potential over a representative work cycle for a hydraulic excavator. It will also present a controller design analysis and experimental verification.

Commentary by Dr. Valentin Fuster
2016;():V001T01A039. doi:10.1115/FPMC2016-1777.

Traditionally, a typical hydraulic circuit utilized in stationary industrial applications is based on valve operated actuation. One realization of such a system is a constant pressure circuit employing a hydraulic accumulator as an energy reserve and pressure stabilizer. The pump is used to maintain the desired pressure level, for example by using a variable displacement pump that controls the displacement setting based on the pressure level.

The main benefit of this system architecture is its ability to produce high output powers with a very low response time. However, it is not the most energy efficient and in many cases, not the most space efficient solution. The efficiency of this system type is reduced mainly by the need to choke the pressure difference between the set system pressure and the actual pressure need in the actuator. By directly controlling the actuator via controlling the pump’s output flow with an electric servo motor, the throttling losses of the valve controlled system can be avoided. In addition, this enables the usage of closed circuits which in terms removes the need for a large reservoir.

In this study, the replacement of a valve controlled hydraulic system with a pump controlled system in an industrial stationary material handling machine is investigated. The machine’s work cycle consist of continuous consecutive lifting and lowering motions of one end of a platform pivoted at the opposite end. The study consist of designing the replacing circuit topology, of dimensioning the hydraulic components utilizing a created Simulink-based tool and of a simulation based analysis on the dynamic properties of the designed hydraulic system.

Topics: Pressure , Pumps , Valves
Commentary by Dr. Valentin Fuster
2016;():V001T01A040. doi:10.1115/FPMC2016-1779.

Switched Inertance Hydraulic Systems (SIHS) use inductive, capacitive, and switching elements to boost or buck a pressure from a source to a load in an ideally lossless manner. Real SIHS circuits suffer a variety of energy losses, with throttling of flow during transitions of the high-speed valve resulting in 44% of overall losses. These throttling energy losses can be mitigated by applying the analog of zero-voltage-switching, a soft switching strategy, adopted from power electronics. In the soft switching circuit, the flow that would otherwise be throttled across the transitioning valve is stored in a capacitive element and bypassed through check valves in parallel with the switching valves. To evaluate the effectiveness of soft switching in a boost converter SIHS, a lumped parameter model was constructed. The model demonstrates that soft switching can improve the efficiency of the circuit up to 42% and extend the power delivery capabilities of the circuit by 76%.

Commentary by Dr. Valentin Fuster
2016;():V001T01A041. doi:10.1115/FPMC2016-1780.

Many mobile hydraulic systems are fitted with over centre valves for safety measures. However, it is well known that over centre valves in combination with pressure compensated flow control valves may lead to oscillatory and even unstable system behaviour. The traditional solution to overcome this problem is to use an over centre valve with a sufficiently low pilot ratio and/or include various damping orifices in the system. Both of these solutions are energy consuming and may decrease the control performance. An alternative approach is to use (electronic) pressure feedback — also referred to as active damping — to stabilise the system and damp pressure pulsations. This is not a new method, but the effect and adjustment of the filters is often misunderstood leading to incorrectly adjusted filters and degraded system performance. The focus of the current paper is therefore to explain and derive a set of guidelines for how to properly adjust a standard pressure feedback in system with an over centre valve when also considering model uncertainties, un-modelled dynamics and parameter variations.

The paper takes its basis in a standard cylinder drive with an inertia load, over centre valve and a pressure compensated proportional valve. Based on a linearized model of the system, the system is analysed and it is shown that there is an optimal range for both the filter frequency and gain, which are closely linked. It is furthermore shown that these both closely affect the obtainable damping and dynamic response of the system. From the analysis a set of guidelines are derived for how to properly adjust the filter coefficients and the effect of different filter adjustments are shown and commented for the example system.

Topics: Pressure , Valves , Feedback
Commentary by Dr. Valentin Fuster
2016;():V001T01A042. doi:10.1115/FPMC2016-1781.

Bent axis hydraulic pumps and motors are extremely popular due to their high efficiency and large speed range. A number of different concepts exist with respect to kinematic restraints on the cylinder barrel motion. Some manufacturers rely upon a timing gear for precise synchronization of the shaft and barrel speeds while other companies have successfully introduced bent axis units without such a mechanism. The paper analyses the dynamics of bent axis machines with tapered pistons driving the cylinder barrel. A rotation of the pistons inside the corresponding bores is proposed to result in changing cylinder chamber to case drain leakages. The reported phenomenon is shown to have a significant effect on the low frequency part of pressure and flow pulsations. In this way, frequency components far below the fundamental frequency associated with the shaft revolution are generated.

Commentary by Dr. Valentin Fuster
2016;():V001T01A043. doi:10.1115/FPMC2016-1782.

Pressure ripples generated by a positive displacement pump in a hydraulic system can lead to severe noise and vibration problems. The source impedance of a positive displacement pump has a considerable impact on the generation of pressure ripples. It is, therefore, important to be able to predict the source impedance in order to design quiet hydraulic systems.

The source impedance of a positive displacement pump depends, amongst other things, on bulk modulus and volume. However, it is known that the mathematical model that takes into account the bulk modulus of hydraulic oil and the volume of a discharge room in the pump results in an estimated value of the source impedance that is greater than the measured value.

In this study, the factors which affect the source impedance of an external gear pump for an agricultural tractor have been investigated. In particular, the effect of the following factors has been investigated experimentally: the effective bulk modulus as determined by the components of the pump: leakage in the pump: the specific volume ratio of entrained air to hydraulic oil: and the volume of the tooth space of the pump. In addition, the effect of volumetric change of the discharge room by pumping action has been investigated using CFD with moving mesh technique.

Commentary by Dr. Valentin Fuster
2016;():V001T01A044. doi:10.1115/FPMC2016-1783.

Flow ripple is generally considered to be a negative attribute of positive displacement units as the resulting pressure ripple can cause unsteady behavior in the overall system as well as generate significant audible noise that can spread throughout the entire hydraulic system. Passive methods of attenuating pressure ripple have included both pump design and adding compliant elements such as pulsation dampers and Helmholtz-style resonators that are often limited in their effectiveness and introduce compromises with regards to system size and response time. Active techniques have also been investigated and typically seek to employ a secondary flow source to actively cancel the flow pulsations, often with the use of feedback sensors such as pressure transducers. Some techniques using speed variation of the pump have been investigated theoretically and pointed to the limitations of the technique when applied to piston pumps of a certain size.

This paper will discuss the theory and implementation of a feed-forward motor torque control algorithm to reduce flow ripple and therefore pressure ripple by influencing the speed of a relatively-high volumetric displacement low-inertia pump through open loop control of the driving motor torque. The application under consideration is that of a gerotor pump/motor in lockstep fluid communication with a compact hydraulic actuator. The commercial application for the compact hydraulic actuators used in this study is for use as localized force sources in a fully active suspension system of sedan-sized automobiles.

Commentary by Dr. Valentin Fuster
2016;():V001T01A045. doi:10.1115/FPMC2016-1786.

Significant usable energy is discarded as exhaust gas in most pneumatic processes. The ability to recycle this energy could lead to significant improvements in system efficiency. This paper presents a method of dynamically converting the exhaust gas energy of pneumatic systems to a higher pressure so that it may be reintroduced to the pressure supply and reused, boosting energy efficiency of industrial pneumatic systems. This is the pneumatic equivalent of a boost converter, an electrical system that supplies a greater voltage to a load than the power source can supply. Each component of the electrical system can be analogized to an equivalent pneumatic component. The most apparent of these comparisons is the method of storing and transforming energy. In the electrical system, the energy is stored in an inductor which is charged in a closed loop. In the pneumatic system, energy can be stored as momentum. When this stored energy is discharged, a spike in voltage or pressure will be observed in the electrical or pneumatic system, respectively. Similarly, every component of the electrical boost converter can be linked to a pneumatic counterpart. With these relationships fully understood, a device to perform the pneumatic boost conversion is modeled. Successful realization of this result will confirm the analogy between the electrical and pneumatic systems, which will allow for the development of more complex pneumatic systems based on various well understood electrical converters. This paper presents simulations of both electrical and pneumatic boost converters. Insights regarding the energy conversion and its efficiency are drawn from the pneumatic model as well as from the dynamically similar electrical model.

Topics: Exhaust systems
Commentary by Dr. Valentin Fuster
2016;():V001T01A046. doi:10.1115/FPMC2016-1788.

The characterization of the noise emitted by positive displacement machines serves as an important metric for the design of positive displacement machines and their corresponding systems. One method of characterizing the noise produced by positive displacement machines utilizes the two microphone-intensity probes at various locations surrounding the unit to approximate the total sound power generated by the machine in question.

This paper proposes a method of utilizing a robotic arm to perform automatic sound intensity measurements (ASIM). This paper will explain the various theoretical motivations and justifications for the basic design concept as well as the specific implementation.

All the necessary theoretical considerations and technical difficulties were accounted for in the successful design and manufacturing of an ASIM robot.

To highlight the usefulness of the automatic measurement procedure, three case studies was performed to evaluate the robotic ASIM’s ability to measure sound power. A total of 1086 measurement locations were taken in order for each grid study to quantify the convergence of the field non-uniformity.

Commentary by Dr. Valentin Fuster
2016;():V001T01A047. doi:10.1115/FPMC2016-1789.

This paper focuses on estimating the velocity and position of fast switching digital hydraulic valves actuated by electromagnetic moving coil actuators, based on measurements of the coil current and voltage. The velocity is estimated by a simple first-order sliding mode observer architecture and the position is estimated by integrating the estimated velocity. The binary operation of digi-valves enables limiting and resetting the position estimate since the moving member is switched between the mechanical end-stops of the valve. This enables accurate tracking since drifting effects due to measurement noise and integration of errors in the velocity estimate may be circumvented. The proposed observer architecture is presented along with stability proofs and initial experimental results. To reveal the optimal observer performance, an optimization of the observer parameters is carried out. Subsequently, the found observer parameters are perturbed to assess the robustness of the observer to parameter estimation errors. The proposed observer demonstrates accurate tracking of the valve movement when using experimentally obtained data from a moving coil actuated digi-valve prototype and observer parameters estimates in the vicinity of the optimized parameter values.

Topics: Actuators , Valves
Commentary by Dr. Valentin Fuster
2016;():V001T01A048. doi:10.1115/FPMC2016-1790.

A high power density is a crucial requirement to axial piston pumps. It is determined by the machines’ maximum pressure and speed. At high rotational speeds, cavitation leads to the partial filling of the cylinders with gas and causes a breakdown of the delivery flowrate. A further increase of the speed limit requires a deep understanding of these effects. Since they are very hard to capture metroligically, power density has not significantly increased over the past 20 years. Recently, the steadily increasing availability of computational power has made possible the simulation, visualisation and analysis of the flow effects inside the pumps by means of computational fluid dynamics. In this paper, a criterion and a method for the precise determination of the pumps’ speed limit are presented. The description of the experimental setup is followed by flow characteristics measured at varying suction and delivery pressures. Afterwards, a CFD model of the pump is presented. It is shown how the measured flow characteristics can be reproduced in the simulation. The flow phenomena causing the speed-limiting cavitation effects are identified by a detailed analysis of the CFD results. Eventually, constructive countermeasures allowing increased rotational speeds and thereby power densities are proposed.

Topics: Pistons
Commentary by Dr. Valentin Fuster
2016;():V001T01A049. doi:10.1115/FPMC2016-1792.

Smooth operation of heavy-duty forestry cranes is not an easy task for the operators with the current joystick-based control method that is complex and non-intuitive. Moreover, abrupt movements of the same joysticks provoke aggressive signals that can lead to oscillatory motions in the actuators and in the entire crane. These oscillations, not only contribute to wear of the joint actuators but also can cause damage to both the operators and the environment; therefore, they must be attenuated. The proposed approach in this paper uses the popular input shaping control technique combined with a practical switching logic to deal with different frequency payload oscillations induced by the motion of the inner boom actuator of a forwarder crane. The results show a significant improvement in terms of visible oscillation reduction monitored through their appearance in the torque signal computed from pressure measurements. Experiments performed on a down-sized forestry crane verifies the effectiveness of the approach.

Topics: Oscillations , Cranes
Commentary by Dr. Valentin Fuster
2016;():V001T01A050. doi:10.1115/FPMC2016-1793.

This paper deals with a novel independent metering valve system which is intended to be used in medium sized mobile machines. The system uses a mechanical pressure compensator to enable a very simple SISO control algorithm which does not need any feedback parameters to be adjusted. The algorithm is capable of handling resistive and pulling loads at a certain desired velocity and inlet chamber pressure level. The paper gives a brief summary of the systematic approach to deriving the valves structure and compares different control approaches for the complete hydraulic system comprising several actuators. Special emphasis is given to the preferred solution, which is verified on a laboratory test rig consisting of reasonably priced mobile machine components. Furthermore a linear model of system and control structure is constructed to give detailed information regarding the dynamic characteristics of the controlled drive. The energetic benefits of the novel system architecture in comparison to a standard coupled metering flow sharing system are investigated by means of a levelling movement performed on the test rig and a simulated synthetic high power digging cycle.

Topics: Stress
Commentary by Dr. Valentin Fuster

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