Yousheng Yang

HyQ - Hydraulically actuated quadruped robot: Hopping leg prototype

This paper describes the concept, specifications and design of the biologically inspired quadruped robot HyQ, with special focus on the leg design. The main scope of this new robotic platform is to study highly dynamic tasks such as running and jumping. To meet the specifications in terms of performance and dimensions, hydraulic actuation has been chosen due to its high power to weight ratio and fast response. Guidelines on how to choose the design parameters of the hydraulic cylinders including lever length are reported. A two DOF leg prototype has been designed and constructed. The experimental test setup for the leg prototype is explained and the results of first hopping experiments are reported.

Research on low cavitation in water hydraulic two-stage throttle poppet valve:

Abstract Cavitation has important effects on the performances and lifespan of water hydraulic control valve, such as degrading efficiency, intense noise, and severe vibration. Two-stage throttle valve is a practicable configuration to mitigate cavitation, which is extensively used in water hydraulic pressure relief valves and throttle valves. The pressure distribution inside a medium chamber located between two throttles of a two-stage throttle valve is investigated through numerical simulations. The effects of the passage area ratio of the two throttles and the inlet and outlet pressures on the pressure inside the medium chamber are examined. The simulation results indicate that (a) the pressure inside the medium chamber is not constant, (b) the locations of maximum and minimum pressures inside the medium chamber are both fixed, which will not vary with the passage area ratio or the inlet and outlet pressures, and (c) the ratio of the pressure drop across the front throttle to the total pressure drop across the two-stage throttle valve is nearly constant. The critical cavitation index of the two-stage throttle valve is then established. A semiempirical design criterion is obtained for the water hydraulic two-stage throttle valve. The correlation between the critical cavitation index and the passage area ratio of the two throttles is investigated. Relevant validation experiments are conducted at a custom-manufactured testing apparatus. The experimental results are consistent with the simulated ones. Further analyses indicate that (a) the large backpressure can improve not only the anti-cavitation capability but also the total load rigidity of the water hydraulic two-stage throttle valve, (b) an appropriate passage area ratio will be beneficial for improving the anti-cavitation capability of the water hydraulic two-stage throttle valve, and (c) the water hydraulic two-stage throttle valve with a passage area ratio of 0.6 would have the best anti-cavitation performance with the lowest risk of cavitation.

Control of a hydraulically-actuated quadruped robot leg

This paper is focussed on the modelling and control of a hydraulically-driven biologically-inspired robotic leg. The study is part of a larger project aiming at the development of an autonomous quadruped robot (hyQ) for outdoor operations. The leg has two hydraulically-actuated degrees of freedom (DOF), the hip and knee joints. The actuation system is composed of proportional valves and asymmetric cylinders. After a brief description of the prototype leg, the paper shows the development of a comprehensive model of the leg where critical parameters have been experimentally identified. Subsequently the leg control design is presented. The core of this work is the experimental assessment of the pros and cons of single-input single-output (SISO) vs. multiple-input multiple-output (MIMO) and linear vs. nonlinear control algorithms in this application (the leg is a coupled multivariable system driven by nonlinear actuators). The control schemes developed are a conventional PID (linear SISO), a Linear Quadratic Regulator (LQR) controller (linear MIMO) and a Feedback Linearisation (FL) controller (nonlinear MIMO). LQR performs well at low frequency but its behaviour worsens at higher frequencies. FL produces the fastest response in simulation, but when implemented is sensitive to parameters uncertainty and needs to be properly modified to achieve equally good performance also in the practical implementation.

Energy Efficient Fluid Power in Autonomous Legged Robotics

This paper is concerned with the application of fluid power in autonomous robotics where high power density and energy efficiency are key requirements. A hydraulic drive for a bioinspired quadruped robot leg is studied. The performance of a classical valve-controlled (“resistive-type”) and of an energy saving (“switching-control mode”) hydraulic actuation system are compared. After describing the bio-inspired leg design and prototyping, models for both drives are developed and energy efficiency assessments are carried out. It is shown through simulation that the switching-control mode hydraulic actuation can meet the challenge of legged robotic locomotion in terms of energy efficiency with respect to improving robot power-autonomy. An energy saving of about 75% is achieved. Limitations of the current system are identified and suggestions for improvements are outlined.Copyright

Reaction thrust of submerged water jets

Abstract Reaction thrusts of submerged water jets for different cylindrical nozzles are investigated numerically and experimentally. Simplified models of the pressure distribution on the interior walls of high-pressure chambers, the reaction thrust of water jets and the thrust coefficients are all established on the basis of the general characteristics of the isobaric surface near the inlet of the nozzle, respectively. Simulation studies on the reaction thrust are also conducted through a commercial computational fluid dynamics (CFD) software package called FLUENT. In particular, the effects of the inlet conditions as well as the nozzle dimensions on the reaction thrust of the water jet are addressed. Comparison analyses are also performed on the results of the simplified models, the CFD simulation and the experiments. It is concluded from the results that: (a) the model results and the CFD simulation results are in excellent agreement with the experimental results; (b) the nozzle diameter and the inlet conditions exert a significant influence on the reaction thrust of the water jet; and (c) the reaction thrust coefficient is almost a constant, ranging from 1.1 to 1.3. The related conclusions are extended to the study of the water hydraulic flapper-nozzle a servo valve.

Water vs. oil hydraulic actuation for a robot leg

The significant competitive advantage of hydraulics (high power density, large output force/torque and wide range of speeds) together with the properties of water (low compressibility, high thermal conductivity, low solubility of air, non-flammability and no environmental hazard) make water hydraulic actuation very suitable for systems such as legged robots. This paper addresses the comparison between a water and an oil hydraulically actuated robot leg. The mechanism and operation principle of a two degree of freedom leg are presented. In details, numerical studies have been carried out to investigate accuracy, responses, required flow, pressure in the actuator chambers and efficiency of the two actuation means.

Modeling of a novel 3-way rotary type electro-hydraulic valve

Hydraulic actuation is characterized by fast dynamics, high power density, high stiffness, large output force/torque, and in recent years it has become an increasing attractive form of robot actuation. Hydraulic control valves that not only provide the interface between hydraulic power element and actuators, but also receive feedback signal and adjust the system output accordingly, are key components of hydraulic actuation systems. This paper presents a novel 3-way rotary type electro-hydraulic valve which is driven by a DC motor. The valve is mainly composed of a rotary spool, a bush and a body. The operating principle is presented in details and a mathematical model is developed. In particular, the drag torque that majorly affects the valve performance is analyzed based on the theory of fluid mechanics.

Leg mechanisms for hydraulically actuated robots

The performance of highly dynamic robotic machines is directly associated with both the actuation means and the specific mechanical properties/configuration of the system. Hydraulic actuation demonstrates significant competitive advantages when minimum weight and volume, large forces and wide range of speeds are required and this makes it very suitable for systems such as legged robots. The geometry and design of leg mechanisms have great effect on the actuation system performance such as the required flow, which directly determines the size/weight and power density, in turn affecting the performance of the robot. This paper describes the mechanism and operation principle of two 2-DOF legs considered for HyQ, a hydraulically actuated quadruped robot [1]. Numerical studies have been done to investigate the required flow, the pressure in the actuator chambers and the efficiency of the two leg mechanisms. The results show that the second leg design reduces the required flow significantly with less pressure-jump in the actuator and higher efficiency.

Water hydraulics - A novel design of spool-type valves for enhanced dynamic performance

Hydraulic systems provide the most powerful actuators available. In the last decades however, their use in mechatronic systems has decreased, mainly because of two factors: the nature of the actuators themselves (such as noise, cleanliness, size) and the ease of use of electric systems. Water hydraulics, which use water instead of oil as working medium, have several advantages and could not only improve the system performance but also the general acceptance of hydraulics. This paper addresses the flow force inside water hydraulic spool valves, which directly controls the dynamic performance of the entire system. Simulations have been carried out to study the efflux angles (strongly related to flow force) and anti-cavitation ability of different spool valves. In details, the effects of the geometry, opening width and the pressure drop on the efflux angles have been analyzed. The results show that: 1) the geometry and opening width exert significant influence on the efflux angles, while the pressure drop and cavitation have little effect; 2) The arc spool valve has good anti-cavitation ability, and it can increase the efflux angles greatly, thus improving performance. The results provide a basis for developing high performance, light weight and compact water hydraulic control valves for robot actuation systems.

Flow characteristics of throttle valve with sharp-edged seat

A throttle valve, of which the flow characteristics is one of the important factors, is a typical hydraulic element for controlling pressure or flow in hydraulic actuation systems. This paper represents a new method to investigate the flow characteristics of water hydraulic poppet valve with sharp-edged seat. Based on previous studies of pressure field inside poppet valve, a simplified model is developed to describe the pressure distribution on the spool conical surface. The static flow force acting on the spool is investigated by utilizing the pressure distribution and the momentum theorem. The flow-pressure equation and the flow coefficient are modeled based on the equivalence of the two methods. Experimental studies are carried out to investigate the flow characteristics and comparison analyses are made between the models and the experiments. The results show that the flow characteristics of poppet valve is highly affected by the inlet/outlet conditions, openings and spool taper angles and can be expressed considerably by the models.