| 摘要 |
PURPOSE:To permit quick and sure adjustment of the position of a photodetector with respect to a light beam by displaying whether the light beam scans the end of the photodetector or scans the central part by using the results of the detection by photodetecting elements. CONSTITUTION:After detection outputs 21, 22 of the photodetecting elements 12, 13 are converted to voltage signals by corresponding current/voltage converters 23, 24, the signals are inputted to a comparator 25. The comparison output thereof is a synchronizing signal 26 for starting scanning and is outputted from a terminal 27 to the circuit. On the other hand, the 3rd and 4th photodetecting elements 14, 15 are respectively disposed at both ends distanced from the ideal positions where a laser beam is ought to be scanned. The detection outputs 28, 29 of the photodetecting elements 14, 15 are converted to voltage signals by current/voltage converters 31, 32 and are supplied to an error detecting circuit 33. An error signal 34 indicating that there is a positional deviation is outputted when the laser beam is detected by the circuit 33. A light emitting diode 35 emits light in this state to display the positional deviation. Easy setting of the photodetector is thereby permitted.
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