Active compensation of kinematic transmission errors in servo drives for machine tools and robots

Feed drives of machine tools and robots mostly consist of fast rotating motors and precision gears with high transmission ratios. A drawback of precision gears is the kinematic transmission error due to unavoidable manufacturing errors of the toothed elements. The result of a kinematic transmission error may be an inadmissible oscillation at the gear output shaft. Critical oscillations have to be expected, if a spectral line of the kinematic transmission error overlays the resonant range of the mechanical system. The paper introduces an identification and compensation scheme for the kinematic transmission errors of precision gears. The aim of the compensation scheme is a performance improvement of feed drives which are applied in contour welding processes with robots or surface grinding with machine tools. The compensation scheme extends the current, speed, and position controller structure. Based on a measurement of the motor position and the motor speed, a compensation signal is calculated and injected into the control scheme at the input of the current control loop