Disturbance Observer-based Repetitive Control with Application to Fast Tool Servo System

As the most potential precision manufacturing technology, the Fast Tool Servo (FTS) technology is widely employed to machine micro-nano structures. During the manufacturing process, the FTS system is commanded to track particularly periodic trajectory corresponding to the array arrangement of micro-nano structures. The tracking performance of the FTS system is full of challenge in presence of environmental vibrations, cutting-load variation as well as system parameter variations. By regarding these effects as the equivalent input disturbance, we propose a Disturbance Observer (DOB) based repetitive control structure for the piezo driven FTS system, such that the undesired amplification of non-periodic disturbances caused by the repetitive controller is compensated by the DOB. Considering the disturbance observe performance and robustness against of system uncertainties, the design of the DOB is transformed as an $\mathrm{H}\infty$ optimization problem. The developed control structure is finally implemented on the prototype of FTS system. Real time experimental results effectively verify tracking performance and disturbance rejection capability, as well as robustness against system uncertainties.