Discrete Variable Structure Control With Its Implementation In A Linear Servo System

For the provision of linear mechanical energy, Linear motor has much more excellent performance than the traditional approach, especially in NC machining fields characterized by high speed and high precision. In order to improve the control performance of linear motor, more and more advanced control technologies are applied and fruitful results have been achiev ed up to now. Therefore, studying how to apply the advanced control technology into linear motor to improve control performance of linear servo systems is of great practical significance.In this paper, we focus on application feasibility of sliding mode variable control and repetitive control on the linear motors. The main work and achievements are as follows:1. For addressing the chattering problem of Gao's power reaching law, an idea called boundary layer is introduced to improve the reaching law and eliminate the chattering effectively, which makes the system switch between two different reaching laws.2. An method named ideal switch dynamic is proposed to design the variable controller of the uncertain system, i.e., disturbance rejection measure is embedded into the improved power reaching law as mentioned in part 1, and then the controller is designed according to this new reaching law. Theoretical analysis shows that there are three kinds of convergence layers in the system, such as the band of monotone descending region, the band of absolute attractive layer, and the band of quasi sliding mode.3. Linear motor often needs to perform some repetitive control tasks, so the uncertain of system shows obvious periodic. A discrete time sliding mode repetitive controller is proposed to achieve perfect tracking of periodic trajectories and complete rejection of periodic disturbance.4. In order to establish the characteristic model of linear motor, an identification experiment is designed in the paper. Our work mainly includes two following aspects: 1) prove the characteristic model of linear motor, i.e., it could be approximatively described by a slow varying second order difference equation(when the period satisfies some conditions, it could be described by a time invariant second order difference equation); 2) Collecting experimental data from DSP board, and calculating the coefficient of the system with Matlab. 5. Programming on the DSP board to implement the discrete time sliding mode repetitive controller, which is the position loop of servo system. Experimental results show that the designed controller can effectively improve the precision of linear servo system.