Reduction of control input variance of feed drive systems using sliding-mode control with non-linear sliding surface

Ball-screw drives have been widely used in industrial applications delivering high precision motion in work machines, such as machine tools, where both high speed and positioning accuracy are required. Most of control schemes used in industrial application have a constant damping ratio leads to make a tradeoff between the low overshoot and small settling time of the system. This paper presents a novel sliding-mode controller with a non-linear sliding surface to improve the machining accuracy of ball-screw feed drive systems. Unlike the conventional sliding-mode control design, the proposed non-linear sliding surface varies due to the output so that the damping ratio of the system changes from its initial low value to its final high value as the output changes from its initial value to the reference point. Hence, the proposed algorithm allows a closed-loop system to simultaneously achieve low overshoot and a small settling time, resulting in a smaller error and control input variance. Computer simulation and experimental results for a ball-screw feed drive system show that the proposed approach reduces the control input variance by an average of 19.1% than using the conventional linear sliding surface.