Research On Force Control Of The Singled-rod Hydraulic Cylinder With P-Q Valve Towards The Legged Robots

Legged robot is an important kind of mobile robots. With the ability of uncontinuous supporting, selecting its footholds by itself and adapting to the complex environment, legged robot i s acting an important role in military fileds and wild research. With the increasing of legged robots’ load and power, the hydraulic system becomes an ideal choice. As the P-Q valve can release the reducant flow with its presser-feedback channel and the single-rod cylinder can fit for the structure requirements and load charateritics of the leged robot, there can be special advantages for choosing the P-Q valve and singled-rod cylinder as its acturactor for the legged robot. The control of the position and force of the acturactor is the basis of the moving performance. But the the hydraulic system is complex in itself, especially the influence of the external interference and the parameters changing on force control. On the other hand, force control is the basis of the impedance control of the legged robot, which can improve the performance of the supporting phase significantly. So the research of force servo control has become the key subject of the legged robot. This paper is mainly on the research the P-Q valve controlling the single-rod cylinder. The characteritics of the position control and force control of the system were studied by simulatons and experiments. In this paper, the feedforward-compensation method was raised on the force control after an in-depth reaearch and some simulations and experiments was made to prove the effectiveness of the algorithm. The method of impedance control of the robot’s single-leg was studied and experimented based on the force control algorithm of the hydraulic actuactor.Firstly, the model of position servo and force servo of P-Q valve controlling single-rod cylinder was established to study the characteritics of the system. The transfer function was established based on the principle on the valvem, getting the relationship between the output presser and the input current by simulations and experiments. The nonlinear model was made by Simulink on the position and force servo system and the equivalent stiffness of the closed-loop position servo system and the relationship between the control current and the cylinder output force of the force servo system was studies by mears of simulation and experiemnts based on the P-Q valve.Secondly, the algorithm of force servo of P-Q valve controlling single rod cylinder was studied. The reaserch on force servo with position interference and without position interference was made. The relation between output force and input current was accomplished by theory and the feedforward-compensation algorithm was put forward based on the theory. Simulations and experiments were made to prove the effectiveness on force tracking with different position interference.Lastly, the research on the impedance control of the robot’s single-leg was made based on the feedforward-compensation algorithm for force servo of the cylinder. The basic principle of the spring damper and the method of impedance control of the single hydraulic cylinder and robot’s leg was studied. The effectiveness of impedance control was prove by means of evaluating the performance of output force tracking target force. The esperiments on touching ground of the robot’s leg was made to prove the influence of the impedance control on the movement characteritics of the leg.