| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a flat object detector capable of accurately detecting the location of the object. SOLUTION: When a detector element 13 moves across a wafer 1, the light quantities received in a first and second photo detectors 13A, 13B constituting the detector element 13 increase and decreases as the photodetectors 13A, 13B approach to and leave the wafer 1, respectively. Because both photodetectors 13A, 13B are arrayed in the moving direction, the light quantity received by one photodetector is first higher than that of the other, but when the orientation flat 2 of the wafer 1 faces the centers of both photodetectors 13A, 13B, this relation is reversed. An AND circuit 20 outputs the lower one of both received light signals from both photodetectors 13A, 13B as is, and its output waveform becomes sharp at the peak. Based on whether the peak exceeds a prescribed reference, the existence and the position of the wafer 1 are detected.</p> |
