2-DOF Planar Motion Control System Using Model Reference Adaptive Control (MRAC) Algorithm

This paper reports the application of Model Reference Adaptive Control (MRAC) to an X-Y planar motion mechanism. A flexure-based 2-DOF planar motion platform is first developed for the wafer probing purpose and a planar Voice Coil Motor (VCM) is used for driving the mechanism and the flexural bearings. The dynamics of the motion platform is governed by a set of differential equations using the mass-spring-damper model and the Kirchhoff’s circuit laws. Due to the non-linearity of the force constant and the coupling effect of the VCM, a MRAC algorithm is proposed to implement on the motion control system so as to improve the system transient response. In order to guarantee the stability of the Model Reference Adaptive System (MRAS), Lyapunov Theory is adopted in the controller design. The control system performance is simulated using MATLAB /SIMULINK with the considerations of the motor non-linearity and the assembly variation of the flexural mechanism. On the other hand, a conventional PID controller is also constructed for control experiments to compare the transient responses between MRAC and PID control systems. Simulation results revealed that the proposed MRAS outperforms the PID controller for the 2 DOF planar motion system in the presence of sensor noise, disturbing force and parameter variation effects.