Design Of Gradient Friction Material For Ultrasonic Motor And Matching Behavior

Ultrasonic motor (USM) is a new type of motor which is driven by friction force. It has many unique advantages and is paied wide attention on aerospace, missile guidance, precision positioning, etc. Because of special driving principle of USM, wear and fatigue of friction material (FM) in the contact friction interface are inevitable, and advantages characteristic of USM are restricted. However, as one of key materials for improving the performance of USM, FM's design and tribological behavior are still lack of deep understanding. Consequently, it is necessary to study the friction and wear behavior between contact interfaces of USM deeply. Researches on breaking the traditional design theory for FM and studying friction controllable high performance FMs have theoretical and practical significance, either for improving the performance life and reliability of USM, or for promoting development and application of USM.Based on operation principle and wear characteristics of USM, an equivalent wear experimental method was proposed, and relationships between wear of FM and performance of USM were established. The effect of wear on output performance of USM, contact state between stator and rotor, friction coefficient between contact interfaces and wear morphology of contact surfaces were experimental investigated. Based on a simplified contact model of USM, variations of some critical contact parameters of USM were studied with wear of FM. In order to improve the performance of USM further, the special requirements for friction material on contact properties, tribological properties and construction properties were discussed preliminary. Some special design principles for FM of USM were achieved. And the view of FM should be one kind of gradient friction material (GFM) with special gradient properties was proposed.Considering effect of wear and equivalent wear method, design principle of GFM for USM was established. According to the role of different parts of FM during the whole life, the whole structure of GFM was designed. In normal, when the contact width is kept in stable state, the variations of elastic modulus of GFM were obtained. In tangential, when the friction force generated between contact interfaces maintained in stable state, the variations of friction coefficient between contact interfaces were designed. For life of USM, when the wear rate of contact interface maintained in stable state, the variations of hardness of GFM were gained. A gradient design theoretical method of FM for USM was obtained. This could provide theoretical foundation for design high performance FM for USM.Taking epoxy resin as the base of GFM, curing agent, diluents and friction modifier as the performance modifier. According the design principle of GFM, one kind of gradient coating friction material which made up of three coating layers was prepared by cohering technology. Elastic modulus, friction coefficient and hardness of gradient coating friction material were tested. Contact state, load properties and wear properties were studied on experimental prototyped USM. And the experimental results were compared with single homogeneous friction material. The results show that ultrasonic motors with GFM could obtain better contact properties and output performance. The design principle of gradient friction material for USM was verified basically by experimental date. Thus a new field is opened up for choosing and researching FM for ultrasonic motors.Combining with contact model, equivalent wear method and wear prediction model of FM, the performance prediction model was established and verified by experimental results. Variations of preload, distribution of contact force and load properties of USM with running time and life of USM with some fixed load could be predicted. In order to obtain the control evidence for using properties of GFM on performance of USM, the control principles of elastic modulus, friction coefficient and hardness of GFM on contact state between stator and rotor, output performance and life of USM were studied, respectively. The results could provide active control foundation for USM.In order to develop the properties advantages of GFM, it is necessary to study the matching behavior of friction material on stator and rotor. Based on a single homogeneous friction material, friction coefficient and dynamic force between contact interfaces were studied. Effect of load and wear properties of USM were also studied between different matching modes on two prototyped USMs. Matching principles of FM on stator and rotor were discussed. The research conclusions could provide guidance for reasonable application of GFM for USM.