| 摘要 |
PROBLEM TO BE SOLVED: To improve the reliability and the detection precision without problems with respect to cost. SOLUTION: Intervals of light emitters of a light emitter group 12 are set to 10 mm and are made narrower than intervals of 15 mm of light receivers of a light receiver group 22. In order to secure a required signal level, a lower limit value is set for light reception areas of light receivers, and 15 mm intervals are required as intervals of light receivers. Meanwhile, light emitters don't require so much dimensions as light receivers, and intervals of light emitters can be made narrow up to 10 mm. Thus, intervals of light emitters are made narrower than those of light receivers to increase the density of detection beams, and the detection precision is improved. Further, intervals of light emitters are allowed to be made wider than 15 mm, and the reliability is improved.
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