New developments in capacitive encoders for servo drives

Speed and position encoders are essential components in electrical drives. High resolution encoders are necessary to obtain acceptable speed control behaviour. Therefore optical encoders are mainly used in servo drives as position (and speed) feedback. Optical encoders, however, do not provide a robustness comparable to electrical motors - hard environmental influences like mechanical shock and/or vibrations often damage the optical disc inside the encoder. Using resolvers provides better mechanical robustness - their resolution, however, is not sufficient for good speed control behaviour. Capacitive (electrcial) encoders are an attempt to combine good robustness with high resolution. Technical results obtained with a first commercial product encourage to proceed with further research and development in this area.