Magnetic and optical-fluorescence position sensing for planar linear motors

Planar linear motors, e.g. Sawyer motors, operate in an open-loop stepping manner. This mode of operation makes them i) susceptible to loss of steps, ii) unable to reject external disturbances, iii) unable to provide controlled forces, and iv) unable to provide high sti ness. These limitations, in turn, restrict their usefulness in a wide range of robotic applications. Suitable position sensing and control technology, when added to such motors, can to a large degree eliminate these problems. In this paper we present two new sensor technologies for planar motor systems: one uses an ac magnetic technique, the other uses an optical uorescence technique. The magnetic sensor has achieved 1 m position resolution and is compact and easy to fabricate. The optical uorescence sensor has the advantage of complete insensitivity to nearby motor elds. Either technology has the potential to greatly improve future robotic systems that are based on planar linear motors.