Abstract
A feedforward controller which respects the underlying hybrid nature of digital control systems, i.e. continuous-time plant and discrete-time feedback loop, is proposed for high speed/high precision motion systems. The feedforward controller combines the shift(q) and the delta (δ) operators such that uncancellable discrete-time zeros caused by sampling the continuous-time plant at high rates, which make the mathematical inverse unstable, are handled in a natural way. The controller is optimized by tuning two parameters in a pre-filter of the feedforward controller. The optimization problem is generalized to an H∞ problem. Convex minimization techniques are used to find the solution to the optimization problem. Experiments are carried out on a Matsuura Vertical Machining Center. The performance of the proposed optimal hybrid feedforward controller is compared with that of the zero phase error tracking controller. Some improvements have been observed from the experimental results.
