Limits for controller settings with electric linear direct drives

Abstract In considerations of machine tool feed axes directly driven by linear motors, the machine structure has been assumed to be ideal stiff up to now. The reason is the lack of mechanical transfer elements (ball screw for instance) which create the first dominant natural drive frequency. Raising the controller settings with electric linear direct drives with intent to improve control behavior, mechanical oscillations occur. Thus, the mechanical structure itself represents the oscillatory system. In fact, even high natural frequencies can be stimulated due to the stiff anchoring of the linear motor with the high control bandwidth. In this paper the complex interactions between control and mechanical structure are theoretically derived and verified by measurements and investigations on a test bench.