| 摘要 |
PROBLEM TO BE SOLVED: To detect a malfunction of an optical encoder caused by stains to slits of a scale plate. SOLUTION: A light-projecting part 12a, a light-detecting part 12b are set at opposite positions to a scale plate 11. In addition to photodetecting elements of an A-phase and a-B phase for detecting a transmission light from a light projector via the fixed slit plate, a photodetecting element of a C-phase which is the same phase as the A-phase is arranged. Since outputs of the A-phase and C-phase synchronize, an abnormal signal is detected by an exclusive OR circuit. An abnormal state caused by stains of slits can be detected accordingly.
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