Planar linear motors, e.g. Sawyer motors, operate in an open-loop stepping-manner. This mode of operation makes them: 1) susceptible to loss of steps, 2) unable to reject external disturbances, 3) unable to provide controlled forces, and 4) 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 /spl mu/m 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.

Assembly accuracies of 0.05-0.1 mm, needed for electronic product manufacture, are attainable with current automated manufacturing equipment. Aggressive electronic system designs will require manufacturing accuracies in the range of 0.005-0.01 mm. A system and strategy is described here to fabricate circuit boards requiring alignment accuracies of 7.5 /spl mu/m using existing automation equipment with enhancements and typical manufacturing line fixtures. The system, configured as a pilot workcell, consisted of an IBM 7576 coarse positioning robot, a fine positioning manipulator, an optical sensing system and a unique bracing method to reduce environmental disturbances. The strategy was to use a coarse/fine placement technique with sensing to align, stack and bond individual test laminates with patterns of 100 /spl mu/m holes. The results showed that pairs of holes were consistently aligned to 2-5 /spl mu/m which surpasses the 7.5 /spl mu/m manufacturing requirement.>

Special-purpose sensors and hybrid mechanical systems have been developed to assemble advanced electronic circuits. State-of-the-art robot systems that are used for electronic assembly and accuracy requirements for the developing surface mount technology are reviewed, showing the need for improved robot positioning capability. Examples of laboratory experiments that demonstrated successful precision assembly or testing using an ordinary robot, a micropositioner, and an optical sensing system are given. These involve fiber-optic sensing, machine-vision endpoint sensing, and hybrid tactic-vision endpoint sensing.>