Reduction of Electrical Energy Consumed by Feed-Drive Systems Using Sliding-Mode Control With a Nonlinear Sliding Surface

The large amount of energy consumed in machining by feed-drive systems has become an important issue in recent years because machine tools are extensively used worldwide. This paper presents a novel sliding-mode controller with a nonlinear sliding surface (NLSS) to improve the machining accuracy of ball-screw feed-drive systems. Unlike the conventional sliding-mode control design, the proposed NLSS varies according to the output (controlled variable) 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. Experiments to verify the effectiveness of the proposed approach are carried out for a ball-screw feed-drive system for two perspectives. The first perspective is to show the effectiveness of the proposed NLSS in reducing the tracking error, while the second one is to verify the ability of the proposed approach to reduce the consumed energy and control input variation. For the first case, sliding-mode controllers with and without the nonlinear term are compared under the same parameters. The mean of the tracking error magnitude was reduced by 35% without additional electrical energy or control input variation in the controller with NLSS. In the second case, the linear gain is increased for the controller with the linear surface to obtain similar tracking performance. By using the controller with an NLSS, the consumed energy and control input variation were reduced by about 12.9% and 19.1%, respectively.