Design, Analysis and Test of A Long Stroke Fast Tool Servo

Abstract

Fast Tool Servo (FTS) is an ultra-precision machining method used to manufacture surfaces with complex microstructures and arrays. Compared to the traditional machining method, it has high efficiency and machining accuracy. The FTS is an independent tool holder system that can realise the cutting tool's high frequency reciprocating motion. Appropriate design should be achieved for the mechanical and control systems according to the system motion characteristics. In the mechanical system, to ensure sufficient dynamic driving force in both dynamic and static condition, the moving mass and the friction should be reduced as much as possible. A reliable control system is required for high control accuracy under high working frequency. Besides, the system inertia force needs to be balanced by a well-designed counterbalance. This thesis presents a complete and systematic design method for a long stroke FTS system driven by a voice coil motor. System motion analysis, motor selection, design and manufacture analysis of different components, the air bearing simulation and performance tests, and some engineering problems in system assembly processes were covered in the mechanical design. Besides, the research on the simulation and the dynamic performances of the whole mechanical system was conducted, and the relationship between the system working bandwidth and air bearing stiffness was established. A closed loop control system was built based on the chosen control hardware in the control system design. The control system simulation and the system identification were conducted. Different control algorithms were tested on the designed system. Most importantly, a novel hybrid control algorithm was proposed based on PID control, sliding mode control, and feedforward control. The hybrid control algorithm helped the FTS system achieve less than 1% tracking error. The rapidity, accuracy and robustness of the hybrid control algorithms were also verified. A back-to-back counterbalance design was adopted in this thesis. This design can suppress system vibration effectively and benefit the tracking accuracy. A series of machining experiments were designed and conducted to verify the counterbalance design. In the machining experiments, the machine tool axis tracking error, the FTS system's motion profile, and the machined surface accuracy were analysed. Finally, improvements and future work were given according to issues found in the machining experiments.