Closed-loop control of a long-range micropositioner using integrated photodiode sensors

Closed-loop control of an electrostatically actuated micropositioner using integrated feedback sensors is reported. A photodiode-based position sensing mechanism has been incorporated into a variable-capacitance micromotor supported on microball bearings with a range of 4 mm and a resolution of 120 μm. Accurate and reliable positioning has been demonstrated using a proportional control law and the effect of the proportionality constant has been investigated for various stepping distances and actuation voltages. A minimum settling time of 0.1 s was achieved for a 1 mm step at 150 V. Closed-loop excitation has enabled sustained synchronous motion and a maximum speed of 20.4 mm/s. This is a noted improvement compared to open-loop excitation, which exhibits erratic motion and a maximum speed of 7.2 mm/s. Using feedback control, two critical functions for robust positioning have been demonstrated; the micropositioner can establish a necessary frame of reference and autonomously respond to arbitrary disturbances. The closed-loop position control system presented in this work illustrates the feasibility and functionality of smart microsystems using integrated feedback sensors.