Reibadaptive Gleitführungen für Vorschubantriebssysteme

Abstract

The precision of feed drive systems depends strongly on the frictional behaviour of the bearing elements. Friction has two effects onto the feed drive system, on the one hand it improves the damping and reduces vibrations and on the other hand it induces nonlinear effects that affect the motion quality in terms of precision and smoothness. In this thesis, an idea is investigated that uses the good damping properties of sliding bearings and improves their frictional behaviour using high frequency oscillations. The phenomenon that friction is reduced in the presence of high-frequency oscillations was observed in various experiments since the 1950’s and found its way into industrial applications such as ultrasonic deep drawing, drilling, grinding and cutting. However, the idea to use this effect to come up with new bearing elements has not been investigated yet. The goal of this thesis is to develop a systematic design for sliding bearings that allow high-frequency oscillations. The theory of friction in the presence of vibrations is used to investigate the influence of vibration and motion parameters such as longitudinal, transversal, angluar and higher harmonic vibrations onto the friction force. Chapter 4 introduces the basic setup of high-frequency sliding bearings containing a vibration module with actuator resonator and sliding elements. Basic design principles for the different components are developed in Chapter 5. The design of the resonator plays a key role in transmitting the vibrations from the actuator to the sliding elements. The design is based either on a two-mass model or as an waveguide depending on the dimension of the bearing. An demonstrator is developed in Chapter 6 using FEM to optimize the stiffness an vibration characteristics of the bearing. Chapter 7 presents the results of experimental investigations of the vibrational and frictional properties of the developed bearing elements. It is shown, that the sliding and static friction can be reduced significantly and that the frictional force can be controlled using the acutator voltage and frequency. Thus, it is possible to actively design the frictional behaviour of the bearing element, giving the possibility to linearize the friction and thereby changing the damping and linearity properties of the bearing. Using this effects, experiments are made that show that the friction control allows to minimize and even eleminate the appearing of stick-slip during movement.