Compensation for servo drift in industrial robots

A control technique is proposed for compensating for servo drift due to a wide range of temperature fluctuation without any overshoot of the robot end-effector. The effect of servo drift on the position of the end-effector is estimated, and the compensation for servo drift is then based on the estimation. Thus, an integral action need not compensate for the whole servo drift but rather to compensate the difference between the servo drift and its estimation. Since this difference is very small compared with the magnitude of the drift, an integral with a small limiter, which prevents the integral wind-up, is enough to reduce the effect of servo drift on the end-effector position to null. An application of the proposed control to an industrial robot is illustrated, and the result is compared with that for a PD (proportional-derivative) control