US Patent 7597187 Conveyor system

A conveyor system has an elongated guide defining a closed transport path extending through a plurality of treatment stations and a plurality of carriers movable on the guide along the path and each capable of holding a respective workpiece. At least one magnet is provided on each carrier, and an annular row of individually energizeable electromagnets extends along the path and is capable of exerting force on the magnets of the carriers so as to displace the respective carriers along the path. A plurality of sensors spaced along the path detect the carriers and generate outputs indicating positions and movement of the carriers along the path. At least some of the electromagnets at least intermittently form some of the sensors.