Research on compound control algorithm for motion control system

Force of friction, which blocks tendency of object's motion or relative motion can easily lead to low tracking accuracy of manipulator arm driven by PMSM at low speed or in back-and-forth m ovement. During the robot positioning, the gravity torque changes all the time. The variation of it is difficult to measure, Which have influence on the control accuracy of the manipulator arm. The traditional friction compensation algorithm does not take the gravity torque of mechanical arm into account, so the friction model lacks accuracy. For those previous m ethods which treat friction as disturbance and use disturbance observer to estimate it, it is difficult to estimate the friction precisely in low speed due to the existence of strong nonlin earity at this stage. In this paper, to eliminate the effects of friction and disturbance on the system, a Stribeck friction model is used to eliminate the influence of friction on the system. At first, the q-axis current and rotation s peed are s ampled. Then the friction model parameters are identified via Lagrange interpolation polynomial and least square method after the gravity and friction to rques are separated. Considering the heavy torque of mechanical arm, the deviation of friction model when conditions are changing and the load torque as lumped disturbance, a sliding mode disturbance observer is designed for disturbance estimation. The estimate of friction and the observation of lumped disturbances are employed as feedforward compensation. Then combining the proportion feedback together, a com posite speed controller is obtained. Simulation results indicate that the com posite control method in this paper can effectively ameliorate “flat-top” phenomenon of positi on tracking and “chattering” phenomenon of speed tracking of the servo system, and improve the anti-disturbance ability of servo system.