Investigation of control algorithm for long-stroke fast tool servo system

Fast tool servo (FTS) is an efficient and reliable method in precision machining for fabricating freeform surfaces or microarrays with sub-micrometric form accuracy. In this paper, a Lorentz force FTS is designed where the voice coil motor is located inside the slide, and four air bearings are used as support components. Three different control algorithms, namely conventional PID control, advanced PID control with velocity/acceleration feedforward (FF) and sliding mode control (SMC) are implemented in the system, and corresponding Simulink simulation models are built including for both mechanical and electrical systems. The results show that advanced PID and SMC can reduce phase error and overshoot, and tracking error can be controlled at 3.13% at 50 Hz. A new hybrid control algorithm (PID + SMC + FF) is developed, with system tracking error subsequently decreased to 0.871% at 50 Hz. In addition, with a suitable compensation method, the steady state tracking error is further decreased to 0.029%. Consistent results from testing with signals of different input frequency also indicate the general effectiveness of the algorithm.