Friction compensation design for velocity-controlled feed drive motions of CNC machines

Feedforward friction torque compensation structure is usually used for friction compensation on the basis of the given position commands, velocity commands, and an integrated friction model. However, for mechanical systems that are actuated by velocity-controlled servomotor packs, the torque compensation structure cannot be applied directly to reduce the effects of friction, and thus a velocity-based friction compensator is required in the motion control design. In this study, a new velocity-based friction compensation structure with an additional velocity input was developed to overcome the adverse effects induced by friction to an extent. A number of circle motion tests with different federates were carried out on a three-axis CNC milling machine and the experimental results indicate that a maximum reduction of 58.71% is achieved in the absolute contouring errors during circular motions by the friction compensation structure developed in this study.