2017 Fiscal Year Annual Research Report
Torque improvement of ultrasonic motor with polymer-based vibrator
| Project/Area Number |
17J05057
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
WU JIANG 東京工業大学, 総合理工学研究科, 特別研究員(DC2)
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| Project Period (FY) |
2017-04-26 – 2019-03-31
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| Keywords | Ultrasonic motor / Polymer / Functional materials / Acoustics |
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| Outline of Annual Research Achievements |
With the aim of improving the performance of polymer-based ultrasonic motors, we analyzed how the key dimensions of the vibrators affect the motor performance, particularly output torques, rotational speeds, and output torques, and discussed the optimal vibration modes for polymer-based motors. Owing to the low stiffness, the optimal design of polymer-based motors are greatly different from that of metal-based ones: The optimal thicknesses are much higher for polymer-based motors than for metal-based ones. However, thicker motors provide higher frictional loss, which restricts the output torques. Besides, when operated in the higher-order vibration modes, polymer-based motors exhibit higher electromechanical coupling factors, and consequently higher output powers. At the same time, polymer-based motors operated in the high-order vibration modes provide nodal lines on their outer surface; they make it easy to firmly fix the vibrators.
On the basis of the aforementioned conclusions, we have summarized the design process of polymer-based ultrasonic motors. We have published two journal papers and made several presentations to exchange ideas and experience with other researchers on international conferences.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Through the investigations on polymers-based ultrasonic motors, we have obtained several conclusions. 1. The reason for the low torques of polymer-based motors have been revealed: Owing to the low stiffness of polymers, polymer-based motors should be sufficiently thick. However, the frictional loss also become higher with increasing thickness, and consequently restrict the output torque. 2. A higher-order vibration mode, greatly different from the commonly-used mode for the metal-based motor, is optimal for the polymer-based motor as it provides higher electromechanical coupling factors. Besides, the motors operated in higher-order modes are easy to firmly fix. These properties indicate that polymer-based ultrasonic motors utilizing high-order vibration modes are practically applicable.
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| Strategy for Future Research Activity |
To further improve the motor performance, we would like to sandwich a thin ceramic disk between the polymer layer and the piezoelectric ceramic disk to compensate the vibrator stiffness. As the first step, the mechanical-loss characteristics of ceramics will be estimated for selecting materials. Then, the optimal structure of the triple-layered vibrator will be discussed for better performance.
On the other hand, we have found that the functional polymer that we are currently employing, namely poly phenylene sulfide (PPS) exhibits a lowered mechanical loss after thermal annealing owing to the increased degrees of crystallinity. Thus, to further reduce the mechanical loss, we would like to experimentally discuss how the annealing temperature and time period affect the mechanical loss.
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