| 摘要 |
PURPOSE:To improve the accuracy in detection by alleviating an influence of the light from the outside by connecting an optical fiber to a vacuum attraction means in a manner the fiber faces an attraction hole and letting a detecting light enter the optical fiber through the attraction hole. CONSTITUTION:An optical fiber 7 as a light waveguide is fixed on an upper end plane of a vacuum attraction means 1 with its edge plane inserted and fixed oppositely to an attraction hole 5 through a vacuum attraction path 3. If a pellet 6 has been attracted and held to the attraction hole 5 when the vacuum attraction means 1 is opposed to a light source 9, the light projected from the light source 9 is shielded by the pellet 6 and it does not enter through the attraction hole 5. Accordingly, the light is not transmitted by the optical fiber 7 and a quantity of the light received by a light receiving element 8 becomes nearly completely zero. Then, it is possible to judge whether the pellet 6 exists or not according to the existence of the received light.
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