Intelligent Guideways to Improve Servo Control Performance of NC Machine Tools

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1. Development of the contact-type Intelligent Guideway on a test stand of a two-axis feed drive The Intelligent Guideway is a roller guideway with brake shoes installed on the guide rail. By controlling the braking force, one can dynamically control the friction on the guideway. We developed a test stand of a two-axis feed drive with the proposed Intelligent Guideway to evaluate its effectiveness. A pneumatic actuator with using a high-speed electronic valve is used to control brakes. Particularly in latest high-speed, high-acceleration NC machine tools, the structural vibration is a critical issue that has a significant effect on the closed-loop stability and contouring accuracies. By employing the Intelligent Guideway in feed drive systems, the damping characteristics of such structural vibration can be improved. Experimental studies on the test stand validated the dynamic damping given by the Intelligent Guideway to low-frequency structural vibrations, and the significant improvement in the system's closed-loop response.2. Comparison studies of damping control schemes for feed drive systems In order to address vibration issues in feed drive systems such as the machine's structural vibration or the longitudinal vibration of the ball screw, various damping control schemes have been proposed. In particular, the effectiveness of the relative velocity feedback control scheme was mathematically analyzed and compared with different setups. Basically, this scheme implements an additional feedback loop of the difference between the linear velocity of the table and the rotational velocity of the servo motor. The relative velocity can be feedbacked to either the servo motor control system or directly to the table. In order to feedback the relative velocity directly to the table, the Intelligent Guideway can be used.Theoretical, simulation, and experimental comparison studies were conducted with various types of relative velocity control schemes.