High-Gain Control of Linear Motor Feed Drive Table by Introducing a Virtual Friction

Abstract

This paper proposes a novel friction compensation method for achieving higher system stability and responsiveness by actively utilizing the friction force of feed drive systems driven by a linear motor. The proposed method is applied to general feedback position control system combined with the proposed compensator. The proposed compensator replaces the real friction characteristics of feed drive mechanism by the virtual friction characteristics that provide higher damping characteristics. In the compensator design, first, the precise nonlinear friction characteristics of linear roller guides are mathematically modeled for use in the proposed compensator. Then, To evaluate the proposed friction model, step responses under various conditions were measured and simulated. As the results, it was confirmed that the proposed nonlinear friction model can express the actual behaviors. Next, the virtual friction model was designed by using the proposed friction model that provides the feed drive system with higher damping characteristic as compared with the real one. To evaluate the proposed compensation method, the positioning performances of a linear motor servo system using the proposed compensator were simulated and measured. The results confirmed that the proposed compensator corrects for the decrease in stability of the control system and enables higher servo gains, leading to high responsiveness.