Magnetic and optical-fluorescence position sensing for planar linear motors

Abstract

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 stiffness. 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 fluorescence technique. The magnetic sensor has achieved 1 μm position resolution and is compact and easy to fabricate. The optical fluorescence sensor has the advantage of complete insensitivity to nearby motor fields. Either technology has the potential to greatly improve future robotic systems that are based on planar linear motors.