Parameters Sensitivity Research On Hydraulic Actuator Force Servo System

The high-integration and high-performance hydraulic actuator has become a new idea for the study of the joint drive of legged robot.The force control of the joint which supports the phase has become an imperative requirement to improve the flexibility,environmental adaptability and terrain adaptability of the robot.But the output force control of the hydraulic actuator is the difficulty of hydraulic system,the output force control system itself has the small stability margin and fast changing output force,which greatly limit the gain of the control system.At the same time,the output force is sensitive to system parameters,and it is very easy to make the surplus force destroy the target force under the external disturbance.These factors lead to the slow response of the force servo,large oscillation and poor tracking accuracy,which can't meet the requirements of legged robots.Therefore,we study the parameter sensitivity of the joint drive hydraulic actuator servo system,and the sensitivity analysis theory is introduced to the nonlinear servo system of hydraulic actuator,it can quantitatively analyze the time-varying parameters of the system and understand the influence of each parameter sensitivity on the dynamic performance of the system,it lays a foundation for the research of system parameter optimization and control method,and has great significance to improve the overall performance of the robot.This paper studies the sensitivity of hydraulic actuator servo system parameters,two sensitivity analysis methods which are trajectory sensitivity and matrix sensitivity are used to quantitatively analyze the influence of system parameters on system output.Firstly,the mathematical model of the joint driven hydraulic actuator servo system for legged robot is established,and the state space equation,trajectory sensitivity equation and matrix sensitivity equation are derived to determine the relationship between system parameters and system output.Secondly,the trajectory sensitivity equation and matrix sensitivity equation programming are solved respectively for the system in the no load condition and loading condition.Then the time history curves of the two sensitivity analysis methods are obtained.And two sensitivity measures which are percentage sensitivity and integral sensitivity are proposed,the column chart is used to show the value of the two measurement methods in order to compare the influence of each parameter in the system sampling time on the system output to determine the secondary parameters of the main parameters that affect the output.Finally,according to the semi physical simulation test-bed of hydraulic actuator force servo system,the comparative analogy method is adopted.By changing the system integral coefficient,proportional coefficient,differential coefficient,flow gain of servo valve and other controllable parameters,we can calculate the values of these parameters in two sensitivity measures,contrast the sensitivity simulation analysis results,verify the feasibility and accuracy of sensitivity analysis method,and determine the system parameters of the system output impact size.