An Algorithm for High-Speed Control of Machine Tools

Experiments are performed for end-milling aluminum at 15,000 RPM spindle speed (1,508 m/min cutting speed) and up to 3 m/min table feedspeed using an eexperimental machine tool control system. A digital feedforward controle for feed drive control is designed based on the zero phase error tracking controller (ZPETC), using a model derived from a frequency-weighted identifcation of the closed-loop plant. The controller achieves near-perfect (± 3 ¿m) tracking over a 26 mm trajectory with a maximum speed of 2 m/min. The maximum contouring error for a 26 mm diameter circle at this speed is less than 4 ¿m. Tracking and contouring experiments are conducted for table feedspeeds as high as 10 m/min. Frquency domain analysis demonstrates that the feedforward controller achieves a bandwidth of 10 Hz without phase distortion. In a direct comparison of machining accuracy, the experimental controller demonstrates a significant improvement over an industrial CNC, as measured by a coordinate measuring machine.