Mechanical coupling and direct torque measurement of outer-rotor polysilicon micromotors

This paper presents preliminary results on investigation of involute and cycloidal tooth profiles with respect to their suitability for mechanical coupling of surface micromachined mechanisms, and results on direct measurement of the output torque of mechanically loaded polysilicon outer-rotor micromotors. Results have shown that although micromotors with involute and cycloidal shaped gear teeth successfully drive another micromotor, involute shaped teeth micromotors operate more consistently and more smoothly than those with cycloidal teeth. For torque measurement of outer-rotor micromotors, the micromotor is driven to bend a beam, the deflection of which is used to measure the output torque of the motor. In order to couple the micromotor torque to the beam, a partial rotor ring is attached to the free end of a cantilever beam. By measuring the maximum deflection that the micromotor can bend the beam during operation, the output force and torque of the micromotor can be calculated using beam theory. Results show that forces up to 1.04 μN, or torques up to 156 pN-m are available from outer-rotor micromotors with pitch radii from 75 μm to 150 μm