The Research On Speed Dead-zone And Compensation Method Of Variable Speed Electrostatic Hydraulic Actuator

Speed dead zone is an important factor affecting the control performance of variable speed electro-hydrostatic actuator(EHA),such as positioning adjustment time,tracking delay time and bandwidth.The flow dead zone of hydraulic pump causes speed dead zone of variable speed EHA to a large extent.On the premise of considering the leakage inside the hydraulic pump and the hydraulic contraction of the outlet chamber oil,this paper established the speed model of variable speed EHA,and analyses show that the essence of the speed dead-zone for variable speed EHA and its influencing factors are consistent with the flow dead-zone of the hydraulic pump,and the mathematical model of the flow dead-zone for the hydraulic pump was obtained.Based on the above research,the influence of several factors on the width of flow dead zone for the hydraulic pump is qualitatively analyzed theoretically.Taking gear pump,power component of EHA,as an example,the influence of various factors was analyzed quantificationally on flow dead zone for hydraulic pump using the Simulink-AMESim co-simulation model.The theoretical and simulation results show that the flow dead-zone width of hydraulic pump increases with the increase of the oil chamber at the outlet,load pressure,oil temperature and starting acceleration,and decreases with the increase of displacement of hydraulic pump.And the flow dead-zone width of hydraulic pump increases linearly with the increase of load pressure and starting acceleration,and increases exponentially with the increase of oil temperature.Furthermore,a variable speed EHA control system using ordinary PID control algorithm as controller is constructed.With the help of its Simulink-AMESim simulation model,the changes of system positioning and adjusting time,sinusoidal input response lag time and frequency bandwidth before and after adding the flow dead-zone of gear pump are compared and analyzed,so as to equivalently study the effect of variable speed EHA speed dead-zone on the above control performance.The results show that with the increase of flow dead-zone for gear pump,that is,variable speed EHA speed dead-zone,the positioning adjustment time and sinusoidal input response delay time of variable speed EHA control system increase gradually,while the bandwidth decreases gradually.Leakage coefficients k_a and k_b of hydraulic pumps are important parameters for calculating dead zone width of variable speed EHA,but it is difficult to measure them directly.In order to solve this problem,the generalized least squares algorithm and MATLAB platform are used for off-line identification to obtain k_a and k_b estimates.The deviations of leakage clearance S and?calculated by k_a and k_b estimation deviations are-9.09%and 5.55%respectively,while the total leakage varies slightly,which shows that the off-line identification accuracy of leakage coefficient k_a and k_b of hydraulic pump by using generalized least squares algorithm is within acceptable range.To solve the problem of time-varying characteristics of speed dead zone of the EHA caused by changes in oil temperature and load pressure,a method of compensation for the EHA speed dead-zone based on gear pump dynamic dead-zone inversion was proposed,considering that the dead-zone of EHA speed is essentially the same as that of hydraulic pump flow dead-zone.Aiming at linearizing step motor+gear pump link,the inverse model of gear pump flow dead-zone was deduced,and the dynamic dead-zone inverse compensation controller was designed based on the inverse model.A PID variable speed EHA control system without considering the flow dead-zone of gear pump is built.The gear pump module with flow dead-zone and the dynamic dead-zone inverse compensation controller was added to the above control system in turn.Simulink-AMESim platform is used to simulate and verify the compensation effect of the dynamic dead-zone inverse compensation controller on the flow dead-zone of gear pump.The experimental results show that the dynamic dead-zone inverse compensation controller can relatively reduce the step response adjustment time of the variable speed EHA control system with speed dead-zone by68.01%~99.42%when the load pressure is 3~21 MPa and the oil temperature is20~80?,reduced the time delay of sinusoidal input response by 84.56%and 86.00%at 50?and 80?oil temperature when the load pressure is 21 MPa,and increased the system bandwidth by 13.71%and 65.85%at 50?and 80?oil temperature when the load pressure is 21 MPa,respectively.