Variable structure control of double-motors-double-screws drive system

Abstract

Abstract —Double-motors-double-screws (DMDS) drive system is used in the feeding system of the high precision machine tool to improve the rigidity and to eliminate the effect of the backlash nonlinearity. The parameters in this system change with the working condition, the traditional control method cannot achieve the desirable performance. In this paper, we established the mathematical model of the DMDS drive systems. We employed the variable structure controller (VSC) to deal with the parameters uncertainties and external perturbation of the DMDS drive system. Simulation results show that the proposed method achieves better performance compared to the backstepping controller. Keywords—Double-motors-double-screws drive system; backlash nonlinearity; Parameter uncertainty; Variable structure control; backstepping control I. I NTRODUCTION Backlash nonlinearity is common phenomena in the mechanical transmission and motion control systems that use gears or screws [1]. The backlash nonlinearity causes the difficulty to achieve high precision tracking control [2]. There are two ways to decrease the effect of the backlash on the system performance. One way is to use the mechanical compensation usually accomplished by the complicated mechanism. The other way is to use the control strategy for the motor drive to compensate the backlash. The later way dominates in the field of the high precision motion control application [3,4]. Machine tool feeding system is a typical mechanical transmission and motion control system. A typical configuration of the feeding system consists of one expensive ball screw and motor. Another possible configuration is to use double motors and double low-cost screws to improve the stiffness of the feeding system and to eliminate the backlash nonlinearity. In the DMDS configuration, a bias torque can be applied to eliminate the backlash nonlinearity [5]. But the machine tool feeding system is subject to parameters uncertainty and external load perturbation. The conventional method without parameters adaption, such as PID or backstepping method, cannot achieve the desire tracking performance in the DMDS drive system. To solve this problem, the variable structure control method is proposed in this paper. A boundary layer is used to decrease the chattering of the control force. The performance of the proposed method is better than the backstepping control method. This paper is organized as follows, the mathematical model of the DMDS drive system including the backlash nonlinearity is built in section