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

This figure showed the improvement of the energy transfer efficiency of USM by designing new types of polyimide composite and surface texture. [Display omitted] •The new polyimide composite as frictional materials of USM was designed.•USM with PI composites had higher energy transfer efficiency that that with PTFE composites.•Fabricating micro-dimples on the surface of PI composites can further improve the efficiency of USM.•Processing the same surface texture on the stator made a reverse effect on the transfer efficiency of USM. 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 μm 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.