Optimisation of servo control for highly dynamic axes for ultra precision freeform machining

Components in optical industry like lenses and mirrors with freeform geometry are becoming more and more complex and require sophisticated production techniques. One alternative to machine a broad spectrum of geometries is the ultra-precision turning process, where diamonds are used as cutting tools. With a highly dynamic infeed of the diamond tool even freeform geometries with a moderate clearance angle of 20 deg turn out to be manufacturable. This article shows the design of a highly dynamic axis for the production of asymmetric geometries and freeform shapes in optical quality with the focus on the control and feedback control system as well as the output stage in the servo amplifier. After a brief survey of the mechanics of the axis - an electromagnetic actor with a static permanent magnet and a voice coil - the article deals with an electro-mechanical drive system and the impacts of the requirements from the process to the design of the servo amplifier and the control loop with a short discussion of the axis's area of operation in the frequency range. The article ends with a discussion of measurement results showing the performance of the axis.