Robust Position Sensing and Control for Planar Linear Motors

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9523156 Hollis Planar linear motors, often called forcers, provide low friction motion in a large workspace with few moving parts. Because they operate as open loop steppers, they are: susceptible to losing steps, affected by external disturbances, and cannot provide controlled forces or high stiffness. Feedback control can compensate for these deficiencies if reliable and unobtrusive position sensors are available. This project will investigate two unobtrusive sensing techniques for planar motor systems with 1 micrometer positioning resolution. One proposed sensor uses the AC magnetic field drive flux to induce a field in a sensing tooth on the mounting platen. The other approach also uses platen teeth, but is based on optics. A when a tooth coated with a florescent dye material is illuminated by light of one wavelength, it emits light at a longer wavelength; the intensity of this secondary wavelength is function of position. Research issues for both sensors are spatial and temporal noise, cross talk, and sensor-forcer integration. Using these sensors, a model based and a variable structure robust control scheme will be designed to deal with nonlinear magnetic fields, payload effects and model uncertainties. This research will enable increases in speed and payload for planar linear motors, making them attractive as actuators for next generation machines and equipment that need one micrometer positioning over a large planar workspace. ***