| 摘要 |
A system includes a plurality of photo detectors, which generate signals proportional to incident light. The system further includes an optical barrier adjacent to a surface and includes a control circuit. The optical barrier partially obstructs reflected light from reaching the plurality of photo detectors to produce a spatially dependent reflectance pattern that is dependent on a position of an object relative to a substrate. The control circuit determines a position of the object during a reflectance measurement cycle using each of the plurality of photo detectors by calibrating to ambient light conditions, measuring ambient plus reflected light, determining the reflected light and detecting the position of the object based on a ratio of the reflected light received by at least two of the plurality of photo detectors.
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