Enhanced transfer efficiency of ultrasonic motors with polyimide based frictional materials and surface texture

In order to improve the transfer efficiency of the travelling wave ultrasonic motor (TRUM), the advanced polyimide-based (PI) frictional materials with high friction coefficient and elastic modulus were designed and prepared by hot press sintering. The friction coefficient of PI composite sliding against phosphor bronze was investigated by a flat-on-flat pattern tribo-meter simulated the running conditions of the TRUM. Besides, the micro-dimples with diameter of 300 mu m and area density of 7.06% were fabricated on the surface of PI composites by laser ablation. The friction coefficient of the textured PI interface further increased compared to the smooth PI or polytetrafluoroethylene (PTFE) interface. Therefore, the mechanical output torque, rotational speed and transfer efficiency of the TURM with new frictional materials and surface texture were correspondingly improved. The enhancement mechanisms were discussed by analyzing the changes in friction coefficient and contact sate of the tribo-pairs. (C) 2019 Elsevier B.V. All rights reserved.