| 摘要 |
PURPOSE:To enable the measurement of the outside diameter of a photosensitive substance without imparing a photosensitive layer, by making two laser light fluxes intercepted partly at the opposite ends of the outside diameter of the photosensitive substance and by measuring output voltages of two photodetectors on the occasion. CONSTITUTION:Two pairs of laser projector elements 2 and photodetector elements 3 are provided parallel and separately on the opposite sides of a photosensitive substance 1 so that laser light fluxes 4 are intercepted partly by the photosensitive substance 1. When it is assumed that photodiodes of the photodetector elements 3 output voltages V1 and V2 proportional to the quantity of received laser light respectively, the amount of variation of the sum of the two voltages DELTA(V1+V2) increases as the amount of variation of the outside diameter of the photosensitive substance 1, i.e., the degree of interception of the light fluxes increases. Accordingly, an unknown outside diameter can be determined by determining DELTA(V1+V2) in relation to V1+V2 in respect to the known outside diameter as a basis, and the value of DELTA(V1+V2) can be made proportional to the amount of variation of the outside diameter of the photosensitive substance 1 by making the laser light fluxes 4 linear.
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