Control of multiple degree of freedom fast tool stages for noncircular turning process

There are many cases in the industrial control area where the reference and/or disturbance signals are periodic. To utilize this specific characteristic of the periodic signal in control system design, a variety of repetitive controllers has been developed and applied to several applications. One of the manufacturing applications is the noncircular turning process.; The goal of the proposed research is to extend the capability of the noncircular turning process. The major work of this research can be divided into three sections: (1) A prototype variable rake angle mechanism has been developed and controlled. The objective of the variable rake angle mechanism is to provide another degree of freedom to the conventional noncircular turning process, so we can change the tool angle as well as the tool position. Kinematics, dynamics, and design of the mechanism are discussed. The equations of motion are derived and numerically analyzed. Experimental results on the variable rake angle mechanism support the design concept and control approach. (2) A robust repetitive controller is designed for a dual stage actuator system and it demonstrates the tracking performance improvement through a dual stage actuator system. The dual stage actuator system has a piezoelectric actuator inside of the hollow piston of an electrohydraulic actuator system, so it has another degree of freedom in addition to the main tool motion. Cascading two SISO control loops results in the squaring effect on the overall sensitivity function and improves the tracking performance. Experimental and simulation results show the effectiveness of the dual stage actuator system for the noncircular turning process. (3) A new discrete-time robust repetitive controller design with improved performance is proposed. The basic idea is to achieve the squaring effect on the sensitivity function. A modified q( z,z−1) filter structure is used to achieve its goal. It is shown that this design method improves not only tracking performance but also robustness for small variations in the period of the periodic signal. A systematic controller design methodology is presented to guarantee the robust stability. Experimental and simulation results from an electrohydraulic actuator system validate this approach.