Effect of parameters perturbation on displacement control characteristics of hydraulic drive unit of quadruped robot

KONG Xiang-dong1，2， YU Bin3， QUAN Ling-xiao1，2， QIN Chun-yan3， WU Liu-jie3
（1. Advanced Manufacturing Technology and Equipment National Engineering Research Center for Local Joint， Yanshan University， Qinhuangdao 066004， China； 2. Hebei Provincial Key Laboratory of Heavy Machinery Fluid Power Transmission and Control， Yanshan University, Qinhuangdao 066004， China； 3. School of Mechanical Engineering， Yanshan University， Qinhuangdao 066004， China）

Abstract：The satisfying dynamic characteristics of hydraulic drive unit which can drive the joints of high-performance quadruped bionic robot are required. However，control characteristics of hydraulic drive unit are restricted in most cases by its parameters perturbation and inherent nonlinear factors. Aiming at hydraulic drive unit structure which corresponds to structure of symmetrical valve controlling symmetrical cylinder，nonlinear mathematical model of hydraulic drive unit was founded，then mathematical expressions of hydraulic natural frequency and damping ratio were derived. Influence factors， including saturation characteristics of controller，nonlinear relation of pressure-flow，differences of initial piston position of servo-cylinder， and coulomb friction，were considered in the nonlinear mathematical model above. The nonlinear simulation model of hydraulic drive unit was founded in Matlab/Simulink，and it was verified by comparing simulation curves and experimental curves in the same conditions. The performance test-platform of hydraulic drive unit was built. The acting mechanisms and influence rules of controller gain，oil supply pressure，initial piston position of servo-cylinder， load force，load mass and load stiffness on dynamic characteristics of hydraulic drive unit，were obtained by experiment and simulation analysis. The research indicates that nonlinear model is accurate and practical. The changes of parameters above influence displacement control characteristics of hydraulic drive unit and these influence rules can provide theoretical basis for the online optimization of controller parameters of hydraulic drive unit.
Key words：quadruped bionic robot； hydraulic drive unit； symmetrical valve controlling symmetrical cylinder； nonlinear mathematical model; displacement control characteristics