ABSTRACT
Enhanced power versions of millimetre scale electrostatic wobble motors, developing gross motive torques of approximately 1 µNm, are presently under evaluation. To improve the output power to volume ratio of motors of this type, the surface area contained within the motor envelope has been maximised. A twin stator design has been fabricated to investigate the effect of concentric surface pairs. Synchronous control of the excitation signals is necessary to improve the operational efficiency, since asynchronous actuation disregards any loading or inertial effects on the true dynamic performance. Rotor positional information, necessary for synchronous control, is provided by segmenting the bearing, where the momentary continuity between adjacent segments is detected as the rotor rolls around the perimeter of the bearing. The prototype devices are 300 microns tall, with the rotor and stator fabricated separately and assembled manually. The stator outside diameter is 2600 microns and gear ratios of 225 and 113 and minimum rotor-stator air gaps of 5 and 10 microns have been produced. A complete dynamic model of the motor, incorporating analytic and finite element field predictions, has also been developed to determine the dynamic characteristics of the wobble motor.
