| 摘要 |
PROBLEM TO BE SOLVED: To prevent the occurrence of detection error even when the optical boundary to be detected is a circular arc by providing a comparator, etc., which output a difference between the output signals of photoelectric conversion elements at diagonal positions out of the respective positions corresponding to the vertexes of a square. SOLUTION: Comparators 2a and 2b output differencesαandβbetween the output signals from two pairs of photoelectric conversion elements 1a and 1c and 1b and 1d which are placed diagonal to each other, among four positions corresponding to the vertexes of a square. A selector 3 selects one pair thereof whose difference between the output signals from the comparators 2a and 2b is larger than that of the other. Amplifiers 4a and 4b amplify the output signal of the selected pair so that it may be at the same level to the same amount of incident light. An amplifier 4c amplifies the output signal from a photoelectric conversion element 1e at a position equivalent to the center so as to make it to be at two-fold level in the same amount of incident light. A computing device 5 subtracts the output of the amplifier 4c from a sum of outputs of the amplifiers 4a and 4b, and when the result becomes zero, it outputs a boundary detection signal G.
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