Fundamental study on micro ultrasonic motor

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For reduction of the size of ultrasonic motor down to mm order in its major size, piezoelectric material and the friction drive condition are the most important factor. We tried to improve the hydro thermal method to deposit the PZT thin film on titanium base material. Then, the fiction drive condition of nm order ultrasonic vibration has been investigated and obtained interesting results.The improved way of depositing the PZT film on titanium is a single process. The process temperature, density of material in the solution and the KOH density were examined to optimize the reaction. Hence the process is single, the control of the reaction was rather easy. The PZT film was successfully deposited on titanium directory. The improve piezoelectric film has superior performance to make micro ultrasonic motor. At 5V driving voltage, the output torque was 7 muNm. It was 40 times lager than previous one.The friction drive condition was investigated using 10 MHz surface acoustic wave linear motor. At the optimum condition to obtain larger output force, the force density was more than 100 N/nm^2. The actual output force was about 0.45 N by 6mm x 6mm slider.By using higher driving frequency, high contact pressure and improved PZT thin film, micro ultrasonic motor down to sub mm size will be available.