An Automated Performance Testing System for Piezoelectric Micromotors

The performance of micro-scale piezoelectric motors is characterised primarily in terms of their torque, speed and efficiency. In order to be meaningful these parameters must be measured concurrently and an effective test system is therefore essential for design, development, device optimisation and assessment of reliability. At the micro-scale, conventional methods of testing rotary motors, such as pulley brakes, are not easy to implement due to size constraints and the difficulty in measuring small dynamic forces. An automated method of testing a 5 mm diameter flextensional ultrasonic motor has been created which derives performance measurements from the transient start up and stopping behaviour of the motor using a simple non-contact position encoder. The method gives full performance characteristics in less than a second and it is scaleable for use with other sizes and other types of motor. Furthermore, it provides a generic technique for non-contact measurements of position, angle or velocity that can be rapidly cycled as part of a development programme. The method has shown sufficient sensitivity, using basic components, to measure torque in the range 10-200 muNm and speed in the range from 0 to over 2000 rpm. The torque and speed ranges are only dependant on the sensitivity of encoder instrumentation, inertial load on the motor and data acquisition. This system is believed to be a significant improvement over previously-reported work and the test format has greater applicability for micro-motors that are used for their positioning capabilities.