Integrated servo-mechanical control systems design using Nyquist plots for high-performance mechatronics

In this paper, an integrated servo-mechanical control systems design method using Nyquist plots is proposed for high-performance mechatronic systems. The proposed technique is used to analyze stability, performance, and robustness of the control system, considering control and mechanical specifications under one unified framework. The desired stability and performance specifications such as gain and phase margins, infinity norm of sensitivity transfer function, mechanical characteristics, and robustness against plant uncertainties, etc., are transformed into disc regions in the developed technique. The proposed methodology is used to design and analyze a control system for a voice coil motor actuated hard disk drive (HDD) targeted to provide stronger disturbance rejection capabilities on the identified critical resonant mode at 9,146 Hz. The designed controller is implemented in a commercial HDD, and experimental results show that the disturbance at the frequency of critical resonant mode is attenuated by −7 dB for stronger vibration control.