Positioning system with backlash compensation by twin motor cooperative control (Evaluation of rectilinear motion mechanism installed planetary gear speed reducer)

Abstract

Backlash occurs in gear drive systems that are used with machine tools and transport mechanisms. The problem with backlash is that it reduces positioning accuracy and tends to cause vibrations. In this paper, a twin-motor drive method that compensates for backlash by master-slave control is adopted. In full-closed loop control of master motor, the position is controlled by using a linear scale mounted externally which detects the machine position directly and feeds it back, whereas in semi-closed loop control of slave motor, the position is determined by using a rotary encoder mounted inside the motor which detects the motor position directly and feeds it back. An integral control factor on the master motor is required to minimized positioning errors when using a combination of semi-closed loop control (slave motor) and full-closed loop control (master motor), and a P ( proportional ) control system without I ( integral ) control factor neither on position nor velocity control is adopted as the slave motor's semi-closed loop control system, allowing the slave motor for a follow-up control after the master motor and to compensate for and eliminate mechanical backlash. We confirmed the effectiveness of this control method by simulation and experiment. Slave motor locates itself and master motor into final position by automatically adjusting the gap between itself and the master motor. At final positioning, the phase between main motor and slave motor is automatically controlled to compensate for the backlash upon positioning. It is shown that this method improves the positioning accuracy of the system.