System identification and robust control of a high-precision computer numerical controlled machine

Modeling a feed axis of a Computer Numerical Controlled (CNC) machine is a challenging problem due to its time-varying dynamics and parametric uncertainties. A simple but practical system identification method was proposed in this thesis and combined with the Hinfinity technique to design a robust controller for a high-precision CNC milling machine. The ballscrew driven worktable of a Southwestern Industries 2OP Mill was modeled by means of a standard frequency response test. The model was linearized around the first axial resonance, and then used to synthesize an Hinfinity controller based on the linear matrix inequality approach. The simulated closed-loop system was subjected to disturbances and to a reference tool path to test its disturbance rejection and command following capabilities. Another simulated closed-loop system based on the machine's actual Proportional-Integral-Derivative (PID) controller was created and subjected to the same tests in order to compare the performance of the two controllers. In all simulations, the Hinfinity controller displayed better performance than the PID controller.