ELECTRIC MICROMOTOR DYNAMICS

This paper describes dynamic measurements in rotary, variable-capacitance, radial-gap (side-drive) micromotors using a stroboscopic dynamometry technique. This technique has allowed, for the first time, the capture of detailed micromotor transients. The combination of the data from these experiments with parameter estimation techniques has resulted in the first determination of micromotor friction parameters and drive torque amplitude, independent of a simulated drive torque amplitude reference. The dynamometry technique uses a strobe flash which is triggered from a phase excitation signal after a known time delay. This acts essentially as a video shutter allowing the position of the rotor as a function of the time delay to be recorded and measured. A dynamic model is developed that includes an electrostatic drive term, a velocity-dependent viscous drag term, and a Coulomb friction term that is dependent on the square of the drive voltage and the sign of the velocity. From the position-versus-time data, coefficients for this model are estimated using nonlinear least square error estimation. It is shown that both viscous drag and Coulomb friction terms are required if the model is to closely fit all the experimental data. A constant friction term is shown to be negligible compared to the voltage-dependent term. Further, the relative importance of friction due to lateral forces on the rotor and friction due to substrate attractive forces is examined. The motor dynamics are shown to have a weak, if any, dependence on the rotor-bushing apparent area of contact.