Mark Versteyhe

A Nanometre-precision, Ultra-stiff Plezostepper Stage for ELID-grinding

Abstract The extremely high machine stiffnesses required for a successful Implementation of ELectrolytic in-process Dressing (ELID) grinding cannot be obtained win conventional technologies. In this paper, an Innovative drive concept is presented, where the actuation and guiding functions in three degrees of freedom are combined in one functional unit, using an original plezo-stepping technology. The stage is actively positioned by a set of six ‘feet’ giving it an infinite static stiffness in all six degrees of freedom. The drive motions in x-, y- and C-directions are obtained by rolling the feet over the base surface in a three-by-three feet gait pattern. The stepping resolution can be as low as 2.5 nm. Hammering is avoided by force-controlled stepping. The x and y stage positions are interferometrically measured. Thermal errors are minimised by a symmetrical design.

Hybrid force-position control of clamping with a piezo-stepper

The demands concerning shape accuracy, surface roughness, and subsurface damage on machined parts are continuously increasing. Traditionally, the production process of accurate and smooth surfaces consists of some roughing steps, like turning, and subsequent finishing steps, like polishing or precision grinding. Two new grinding processes, however, electrolytic in-process dressing (ELID), and high-speed chipping (HSC), can combine high removal rates with high surface quality through a mechanism of submicron chip removal. For the successful application of these processes, very stiff, ultra-precision positioning systems are needed. Classical solutions, based on traditional guide way technology, cannot meet the requirements of these new machining processes. The piezo-stepper solution presented in this paper can provide accurate motion, combined with high stiffness, through the use of piezo-electric actuators with high resolution. High passive stiffness is provided thanks to the integration of the driving, bearing and transmission functions. The same actuators can provide an extremely high active stiffness by referring the position of the positioning stage with respect to an absolute reference frame. In contrast with existing (position-controlled) piezo-steppers, this paper presents a way to provide smooth stepping by avoiding hammering through hybrid force-position controlled clamping and by rolling traction.