A hydraulic control system for controlling at least one load (1; 30, 40), the respective load pressure as a load-sensing signal via a respective load-sensing line (LS - that as a means for influencing a load-sensing signal, a compensator (10) is present, a corrected load sensing signal (LS - that the compensator (10) consists of a compensation valve (11) and a shut-off valve (12), - that the compensation valve (11) comprises a pressure applied to it load-sensing pressure (p - that the shut-off valve (12) shuts the compensator (10) when at the compensation valve (11) pending load-sensing pressure (p

A hydraulic control system

In this paper, aimed at the problem of control accuracy when the traditional position-based impedance control is applied in the hydraulic drive unit (HDU) of legged robot, a kind of nonlinear model-based variable impedance parameters controller (MVIPC) is designed. First, the mathematical model of position-based impedance control for HDU is given. Second, the performance of traditional position-based impedance control is tested on the HDU performance test platform under different working conditions, and the experimental results show that the control accuracy of this control method needs to be improved greatly. Thirdly, the control idea of MVIPC is described, and the theoretical derivation is deduced. MVIPC considers the high-order dynamic characteristics of servo valve, pressure-flow nonlinearity of servo valve, oil compressibility and load characteristics. Finally, the control performance of MVIPC is verified on the HDU performance test platform. The experimental results show that MVIPC can significantly improve the performance of traditional position-based impedance control, and have an excellent adaptability under different working conditions. This research can provide an underlying control method of hydraulic systems during the robot locomotion.

A Nonlinear Model-based Variable Impedance Parameters Control for Position-based Impedance Control System of Hydraulic Drive Unit

Since the emergence of digital hydraulic technology, it has achieved good results in intelligence, integration, energy saving, etc. After decades of development, and it has also attracted wide attention in the industry. However, for many years, the definition of digital hydraulic technology has differed between researchers, and there is no uniform definition. Such a situation affects the development of it to a certain extent. Therefore, this paper gives the exact definition of digital hydraulic technology based on a large number of researches on it. At the same time, the paper analyzes the research status and developmental process of the such a technology, and we forecast the development trend of it.

Review and Development Trend of Digital Hydraulic Technology

Intelligent Impedance Control using Wavelet Neural Network for dynamic contact force tracking in unknown varying environments

In order to solve the leg dragging,sliding and impingement against the ground of a quadruped walking robot,a low contact impact gait planning method with particular attention on foot motion trajectory is proposed.After analyzing the leg phases of a four-legged mammal in walking,the foot trajectory generation method is used for a single leg.By applying it to four legs of the hydraulically actuated bionic quadruped robot that has been designed according typical gaits of mammals,a walking pattern generator is constructed.Joint angle functions are solved by inverse kinematics employing legs phases in typical gaits and the displacement for rods of hydraulic cylinders by mechanism.Thereby,gaits of prototype robot could be driven by there lengths.Simulation experiments show that the robot walks stably at the speed up to 0.8 m/s on the even surface,the foot trajectories are smooth and the undulation of body has small amplitude.

Strategy of Foot Trajectory Generation for Hydraulic Quadruped Robots Gait Planning

In this paper, the hydraulic drive unit (HDU) driving the joint motion of the legged robot is the research object. Through the experiment on HDU, it is observed that the control accuracy of the traditional position-based impedance control is not high enough. The further analysis researches the serial-parallel composition on dynamic compliances from both position control inner and impedance outer loop. Then, the two reasons affecting control accuracy are found out. Therefore, aimed at the first reason, a compliance-eliminated controller with multiple serial branches is designed. Aimed at the second reason, a feedforward compensation controller is designed. Finally, the dynamic compliance composition is rearranged. The results of experiments conducted indicate that the proposed method significantly improves the control accuracy compared to that of traditional position-based impedance control.

The position-based impedance control combined with compliance-eliminated and feedforward compensation for HDU of legged robot

In this paper, the dynamic compliance analysis for position-based impedance control is studied. First, the leg hydraulic drive system (LHDS) of legged robots is studied and the mathematical model of hydraulic drive unit (HDU) position control system is built. Then, combined with kinematics, statics and dynamics of the leg mechanical structure, the position-based impedance control method is applied to LHDS. Moreover, the serial–parallel composition of the dynamic compliance of position-based impedance control is analyzed and the three key factors influencing the impedance control accuracy are found, which is the main contribution of this paper. Finally, the key factors proposed in this paper are verified experimentally by using both LHDS and HDU performance test platform. The theories and experiments proposed in this paper provide a theoretical foundation for the compensation of position-based impedance control.

Dynamic Compliance Analysis for LHDS of Legged Robot, Part A: Position-Based Impedance Control

Each joint of hydraulic drive legged robot adopts highly integrated electro-hydraulic servo system, and the system has two common forms, namely, valve-controlled cylinder system and pump-controlled cylinder system. The former has a large energy loss, which restricts the endurance of the legged robot in the field. Although the latter has the advantages of energy saving and high efficiency, the overall response ability of control system is unsatisfied. In this paper, a novel pump-valve compound drive system (PCDS) is designed. It combines the advantages of pump-controlled cylinder system and valve-controlled cylinder system, which can not only effectively reduce the energy loss of the system, but also ensure the electro-hydraulic servo system of the robot joint has the ideal response ability. This paper consists of three parts. In the first part, the mathematical model of nonlinear force control of PCDS is established, which takes into account the pressure-flow nonlinearity of servo valve, the asymmetry of servo cylinder and the complexity and variability of load. So this model has a high accuracy. In the second part, On the basis of the above model, a force control method combining tracking error compensation and load compensation control is designed. And this control method can improve the control precision of the robot. In the third part, the performance of the designed control method is verified by experiments. The experiments show that the designed force control method can effectively reduce the influence of external position disturbance on the tracking accuracy of the force control system and improve the control accuracy of the robot joint movement.

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Zhengguo Jin

Papers

A Nonlinear Model-based Variable Impedance Parameters Control for Position-based Impedance Control System of Hydraulic Drive Unit

Review and Development Trend of Digital Hydraulic Technology

The position-based impedance control combined with compliance-eliminated and feedforward compensation for HDU of legged robot

Dynamic Compliance Analysis for LHDS of Legged Robot, Part A: Position-Based Impedance Control

Design, Mathematical Modeling and Force Control for Electro-Hydraulic Servo System With Pump-Valve Compound Drive