Digital tracking control for machine tool feed drives

High speed machining is an emerging technology which will increase manufacturing productivity. For the full benefits of other developments in high-speed machining to be realized, servo control of feed drive systems must also be improved. Consequently, three aspects of tracking control in machine tool feed drives are examined.; Over the past 10 years the use of feedforward control to improve tracking performance has become commonplace in many applications. A typical approach to the development of such controllers involves fitting a transfer function model to measured frequency response data. An new approach is to use the frequency response data to directly design a feedforward filter, eliminating errors induced by imperfect model fits. Designing the feedforward controller utilizing information from an uncertainty bound for the system further improves performance. Experimental results on a single axis electro-hydraulic direct drive support these techniques.; Accuracy in multi-axis machining is best measured in contour error, so improved performance is obtained by a controller specifically designed to reduce that error. A receding horizon linear quadratic optimal control approach is formulated to address this. The formulation leads to a solution of time varying state feedback and finite preview gains that combines both tracking and contour tracking control. Stability for the system is proven for the linear trajectory case. Experimental and simulation results from 2 axis motion control show the benefits of this control method.; The use of linear motor direct drives as feed drives enables higher feed rates and accelerations, eliminates problems with backlash, and reduces power waste due to friction. Servo controller design of those feed drives becomes more challenging due to dynamic interaction between the servo control and cutting process. A simplified end milling cutting process model is used in a structured singular value based uncertainty analysis to predict the cutting conditions for which the machining process will remain stable. Experimental results from machining aluminum on a linear motor X-Y table validate this approach.