変位センサの傾斜設置に起因するアライメント誤差の抑制

Abstract

In the field of semiconductor manufacturing equipments, acceleration signals from servo-type accelerometers are widely used. In order to apply direct velocity and displacement feedback (DVDFB), it is preferable to use seismo-type absolute displacement sensors which can simultaneously detect acceleration, velocity, and displacement signals. However, the displacement signal includes offset output due to alignment errors of the sensor, even if a PI compensator is utilized. This is because of mechanical and electrical factors. Specifically, the sensor has a mechanical pendulum as well as the servo-type accelerometer, and we have simply implemented electrical circuits of the PI compensator. In this paper, the offset output is modeled by considering input voltage and current offsets of operational amplifiers. In addition, leak currents and dielectric absorbers of capacitors are also considered. Using the models, the alignment errors are calculated and simulated. As a result, it is revealed that the input offset current of the operational amplifier will mainly influence to the offset output.