Research On Properties Of Ultrasonic Motor And Its Friction Material In Vacuum And Low Temperature

Ultrasonic motor (USM) has many unique advantages in its structure and driving characteristics, such as simple structure, light weight, high torque with low speed and non-electromagnetic interference, etc. Consequently, it is a promising acutator in aerospace field. Recently, research on USM under abnormal environment has become a focus of many researchers from domestic and abroad. However, research on USM and its friction material (FM) in vacuum and low temperature was still incomplete. Moreover, the problem of wear and life prediction of FM needs to solve urgently. Therefore, research on FM for USM and its life prediction in vacuum and low temperature has theorectial and practical significance, either for USM design in abnormal environment, or for its theory completeness and its property improvement.Firstly,according to the heat conduction problem of original stator in lab, a stator of USM which inner side was fixed to facilitate heat and cold conduction was designed. Finite element analysis method was used to simulate the effect of structure parameters of stator on its vibrating parameters. Based on the above studies, vacuum and low temperature environment testing system for USM was built up, which could simulate abnormal harsh environment and actual motor operating condition. It provided foundational platform for study on USM in vacuum and low temperature.In vacuum and low temperature, the influences of several structure parameters on properties of USM were also reviewed, such as adhesive, piezoelectric ceramic, bearing, FM and so on. The principle of USM design used for vacuum and low temperature was proposed, which was used to guide USM design in abnormal environment. Then, the USM was improved. Compared with another commercial USM, the tharacteristics of traveling wave USM (TWUSM) in vacuum and low temperature were studied. It provided reliable experimental device for FM study in vacuum and low temperature.Characteristics of FM for USM were investigated in vacuum and low temperature. Several domestic usual FMs were selected to test their ultrasonic driving characteristics and wear properties in vacuum and low temperature. According to large amount of USM experiments, their tribological behavior in abnormal environment was discussed. The design principle of FM for USM was proposed. This provided guidance for fabrication of FM for USM and prepared test datum for its life prediction.FM for USM used in vacuum and low temperature was developed. The conception of bending p-hydroxybenzoic acid (Ekonol) and polyfluortetraethylene (PTFE) as mother body of FM was proposed. According to their mechanical and tribological properties, two kinds of heat-resistant resin were used to modify Ekonol. The amounts of fillers were achieved by vast tests. Orthogonal experiment design method was used to design complex formulas and realize control between formulas and their properties. A satisfied FM for USM was developed. By comparison with domestic usual FMs and real motor tests in vacuum and low temperature, it was verified to have better driving characteristics. It was a high quality FM for USM under vacuum and low temperature environment.By analyzing the cause of wear of FM for TWUSM in microcosmic level, wear prediction of FM for USM was studied. Based on Archard wear equation, the effect of ultrasonic vibration on wear was considered. The function of normal pressure distribution and relative sliding speed were calculated. The wear prediction model of FM for TWUSM was established. In the model, not only the changes of FM thickness, stiffness and preload were considered, but the corresponding relationship between time and distance were also considered to analyze contact interval. The effects of vacuum and low temperature environment on material wear parameters were discussed, then the wear prediction model was modified. Wear and life tester of FM for TWUSM was developed which could simulate actual USM operating condition to investigate effects of working parameters on wear properties and life time of FM. Using this tester, the wear and life time of a FM for TWUSM were tested. Compared with test results, the wear prediction curve was consistent with the experiment which verified the validity of the prediction model.