| 摘要 |
PURPOSE:To read a bar code accurately with a sufficient quantity of light at any time by forming the opening part of an aperture plate in a shape which is based upon an ellipse or diamond while set to a short-axis diameter according to the minimum bar width of a bar code image. CONSTITUTION:A light image formed by reflected light obtained by irradiating a readout object surface 1 where the bar code BC is recorded with light from a light source 2 is photodetected by a photoelectric converting element 5 through an image forming lens 3 and the aperture plate 4. When the opening part of the aperture plate 4 is elliptic and respective bars of the bar codes BC are perpendicular, the diameter on the short axis of the ellipse is equalized to the minimum bar width of the bar code image BC' projected on the aperture plate 4. More transmitted light than when the opening part 43 is circle is obtained and when the bar code image BC' slants, the opening part 43 reaches either of adjacent bar parts and a readout error is eliminated.
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