Photodiode position sensors for integrated feedback control of a long-range micropositioner

The demonstration of a photodiode-based position sensing mechanism for integrated feedback control of a long-range micropositioner is reported. Interdigitated aluminum-silicon photodiodes with a responsivity of 0.2 A/W have been integrated into a linear electrostatic micromotor supported on microball bearings. Using photodiode signals as feedback and implementing a proportional control law, closed-loop excitation of the device has been achieved. The microball bearings provide continuous long-range motion, while the feedback sensors and control scheme overcome the random nature of microscale rolling friction, leading to a robust positioning system with a range of 4 mm and a resolution of 120 mum. Accurate and reliable operation has been demonstrated, including referenced positioning from a device-defined origin and autonomous response to external disturbances. This is the first demonstration of position sensing and feedback control in a ball bearing supported MEMS device.