An investigation of stick-slip friction in capstan drives at very low velocities

The capstan drives are widely used in precision machines for it is easily constructed, maintained and it can, in comparison with the conventional leadscrew system, effectively minimize the backlash in servo system. However, the non-linear phenomena induced by stick-slip friction in capstan drive are frequently observed in the system when moving at very low velocities. This will limit the achievable positioning accuracy of capstan drive at low velocities. To investigate the stick-slip in capstan drives at very low velocities so as to minimize the nonlinearities and improve the positioning accuracy, two types of capstan drives are designed and tested. The responses of system in frequency domain and time domain showed that the improved air-lubricated capstan drive system could significantly reduce the stick-slip by getting rid of unnecessary friction force. In comparison to the double-roller type capstan drive, very minor stick-slip was detected on the improved air-lubricated capstan drive system when moving at velocity of 10nm/sec.