Limits for controller settings with electric linear direct drives

In considerations of machine tool feed axes directly driven by linear motor s, 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 int ent to improve control behavior, mechanical oscillations occur. Thus, the m echanical structure itself represents the oscillatory system. In fact, even high natural frequencies can be stimulated due to the stiff anchoring of t he linear motor with the high control bandwidth. In this paper the complex interactions between control and mechanical struc ture are theoretically derived and verified by measurements and investigati ons on a test bench. (C) 2000 Elsevier Science Ltd. All rights reserved.