Controlling friction

Two different controlling methods are proposed to stabilize unstable continuous-sliding states of a dry-friction oscillator. Both methods are based on a delayed-feedback mechanism well known for stabilizing periodic orbits in deterministic chaos. The feedback variable is the elastic deformation. The control parameter is either the sliding velocity or the normal force. We calculate analytically stability boundaries in the space of control parameter and delay time. Furthermore, we show that our methods are able to turn stick-slip motion into continuous sliding. Controlling friction helps to get a better understanding of friction by measuring, e.g., velocity-weakening friction forces.