A sensitivity optimization approach to design of a disturbance observer in digital motion control systems

This paper is concerned with a digital design methodology for the disturbance observer. The controller (disturbance observer) is designed such that the system sensitivity function is made to match a chosen target sensitivity function by numerical optimization. One advantage of the proposed design method is that the tradeoff between command following, disturbance suppression, and measurement noise rejection is made transparent in the process of the control system design. This allows the system designer to bypass the effort of obtaining a highly accurate system model. Another aim of this research, relative to previous works, is to study how the design specifications can be best structured in the digital filter (a main component of the disturbance observer) for easy implementation. The robust feedback controller, designed in the velocity loop, is used in conjunction with a feedback controller located in the position loop and a feedforward controller acting on the desired output to construct a control structure for high-speed/high-accuracy motion control. Simulation and experiments applied to a high-speed XY table designed for micro positioning demonstrate the effectiveness of the proposed controller.