Effects of back electromotive force in an absolute displacement sensor and improvement using current-feedback-type driver

An absolute displacement sensor, which can simultaneously detect acceleration, velocity, and displacement signals, has been proposed for vibration control of semiconductor manufacturing equipments. Based on state feedback, a control model of the sensor is previously designed in order to calculate the feedback gains using optimal regulator. However, characteristics in simulations have been different from experiments in low frequency region. This difference is due to modeling of a driver circuit. In this paper, a voltage-feedback-type driver is replaced by a current-feedback-type driver in actual circuits of the sensor. The latter driver can ignore the effect of back electromotive force from a forcer coil. After the driver and the force are remodeled, simulation parameters are identified. As a result, the simulations are corresponding to the experiments.