Pieter Van den Braembussche

Motion control and identification techniques for machine tool axes

The traditional indirect drive design for machine tool axes, a rotary motor and a ball-screw, is well known, but has some important drawbacks (like limited speed, acceleration, accuracy and lifetime). The use of linear motors can overcome these problems, but it also has its inherent drawbacks. In this direct drive design, all stiffness must result from the servo controller. This makes high demands upon the controller design. This paper presents some control techniques to achieve a good tracking behaviour for both types of axis design. The linear motor ripple results in significant tracking errors for the indirect drive design. A compensation technique is proposed based on an experimentally identified ripple model. The proposed technique is tested on three experimental set-ups: a rotary motor axis with ball-screw, a linear motor axis supported by air bearings and a linear motor axis supported by rolling element slideways.