Closed Loop Compensation of Linear Deviations in Ball Screw Drives

Traditionally ball screw feed drives for machine tools use collocated control for positioning purposes. Although a higher bandwidth can be achieved with collocated control respect to non-collocated control, the performance can be severely deteriorated by many factors related to the ball screw. Therefore, this work proposes a strategy that combines two particular control loops. First, a collocated sliding mode controller using a rotary encoder that reduces the induced errors from the dynamic effects of friction and backlash. Second, a control loop that uses a linear encoder, which compensates the screw cumulative geometric error and screw thermal-induced error. The complete controller was tuned to achieve safe stability margins for both nominal and non-nominal operational conditions. The experiments show that the linear error can be considerably reduced for the presented trajectory.