Vibration Control to Avoid Stick-Slip Motion

Friction-induced self-sustained oscillations result in a very robust limit cycle that characterizes stick-slip motion. This type of motion should be avoided under any circumstances because it creates noise, wear, and damage. In this paper we show, by simple models, how stick-slip motion can be avoided. Effective methods are: (i) appropriate increase of internal damping that compensates the negative damping induced by a friction characteristic, which decreases with increasing sliding speed; (ii) external excitation that breaks up the limit cycle (however, this often leads to chaotic motion); (iii) passive vibration control by fluctuating normal forces. The last mentioned mechanism is new and will be investigated in detail. The stick-slip oscillator is extended by an additional degree of freedom, which couples the slipping motion to the normal force. The dynamic behavior of the system has been worked out by analytical investigations and numerical integration. Scanning a broad range of values, parameters of the additional system, called the dynamic vibration absorber, have been found that prevent stick-slip and minimize the amplitude of the residual limit cycle. For this task the evaluation of the system behavior has been achieved by observing its energy content. The feasibility of the proposed dynamic vibration absorber is demonstrated by an experiment.