Damping Feed-forward Closed-loop Control for Voice-coil Fast Servo Actuator without Velocity Sensor

Abstract:

Low damping and large overshoot of voice-coil fast servoactuator (VCA) were its natural openloop characteristics. In order to improve the dynamic performance and steady accuracy of VCA, a double closed-loop feedback control structure was used with a velocity loop and a position loop in classical control strategy. It was inevitable to add complexity and bring additional noise to fast tool servo (FTS) system for the use of velocity sensor. Based on the timeoptimal control idea of the two order integrator series system, the damping feedforward control method was put forward. The output damping could be improved by modulating the damping of input signal or the controlling signal through a time-optimal process (TOP) with no use of velocity sensor. The corresponding controlling projects were designed, dynamic performances were tested and typical microlens array was fabricated. The testing and experimental results indicated that the proposed damping feed forward control method could improve the system damping effectively, the overshoot of square wave exciting response was 4% and the setting time was only 3ms. The machined workpiece had better form accuracy and surface finish. The PV value of form error was only 0.228λ and the Ra of surface finish was less than 15nm.