Active compensation of dynamic vibrations in precision machining

For metal cutting with machine tools the high frequency dynamic change of the relative distance between cutting tool and work piece due to machine component vibrations and spindle error motion is a substantial error factor. A compensating infeed of the tool was realised with a high dynamic piezo actuator. A non-contacting distance sensor as well as a force sensor were used to measure the disturbances. Because the propagation delay time of the measuring and actuator system is large compared with the typical vibration period of the disturbances, prediction of the dynamic behaviour is necessary. This cannot be achieved with conventional control systems. Predictive algorithms were therefore adopted at IPT, as already familiar in the field of telecommunications. With this powerful method it is possible to improve the manufacturing quality of machine tools substantially. With active compensation, it was found possible to reduce the surface roughness R(a) by 50 per cent with significantly les s roundness error. It is possible to adapt the position of actuator and sensor to various machine set-ups.