Position acquisition for linear drives a comparison of optical and capacitive sensors

Long stator permanent magnet synchronous linear drives with passive, lightweight movers (vehicles) are proposed for material handling systems which require high dynamics. For high quality speed and position control of the vehicles, precise and fast position measurement is necessary. These passive vehicles present a restriction for the position acquisition system through the fact that neither energy nor information must be transmitted to the moving parts. The evaluation of two position acquisition systems which comply to this requirement will be presented in this paper: the first system is based on high resolution optical encoder and the second one uses a comparatively lower resolution capacitive sensor.