Microelectromechanical digital-to-analog converters of displacement for step motion actuators

This paper presents a novel micromechanism for precise positioning by using an N-bit digital code. The mechanism is an N-stage network of connected suspensions, in which an electrostatic actuator is attached to the longer suspensions of compliance 2C, and N of such unit structures are connected side by side with the shorter suspensions of compliance C. Each actuator is an electrostatic shuttle moving back and forth between the driving electrodes, and is operated by the corresponding digit of the input code. The N-bits of local displacement accumulate in the suspension network to synthesize an analog output, which is proportional to the analog value coded with the N-bit input. The output displacement is independent of the fluctuation of the driving voltage since the traveling distance of the shuttle is clipped by mechanical stoppers. We call the mechanism a microelectromechanical digital-to-analog converter (MEMDAC) since the function is equivalent to the electrical digital-to-analog converter known as the R-2R resistor network. Three different types of MEMDAC's are compared. Preliminary results of a silicon micromachined 4-bit MEMDAC successfully showed a total stroke of 5.8 /spl mu/m with a step of 0.38 /spl mu/m. The positioning resolution can be made finer by simply increasing the number of chained units.