Robust and Adaptive Sliding Mode Controller for Machine Tool with Varying Inertia

This thesis considers the problem of designing a robust controller that achieves highperformance positioning and reference tracking of a machine tool. Specifically, the machine tool is a XY-table used in high-accuracy/high speed milling applications. The XY-table consists of a DC motor drive connected to the load using a ball screw, and can be modelled as a two-mass system. However, the presence of friction and backlash requires nonlinear models and associated control designs. Moreover, the machine tool needs to operate under a wide variety of load conditions, which necessitates a robust design. The starting point of this thesis is a PID controller comprised of position and velocity feedback loops, velocity and acceleration feed-forward controls and a nonlinear friction compensator. With this controller as a baseline, we develop two advanced controllers of sliding mode type: one is based on disturbance observer theory, while the other uses adaptive methods. It turns out that the controller based on disturbance observer theory fails to improve the performance of the baseline PID solution. However, the controller based on adaptive methods achieves superior performance towards the PID controller