| 摘要 |
PURPOSE:To exactly catch changes in the light quantity caused by dust passing through a light flux region so as to reduce influences of outside light by covering a light emitting element and a light receiving element by translucent covers that diameters of their top faces, that face the inside of a dust suction duct, are the same as or smaller than that of the elements respectively. CONSTITUTION:Openings 3 and 4 are provided on a portion of a dust suction duct 2 that is molded in a body together with an operating handle 1, and a light emitting element 5 and a light receiving element 6 are arranged face-to-face in the openings. The diameters of the top faces 7a and 7b of translucent covers 7 and 8 are same as or smaller than that of the light emitting element 5 and the light receiving element 6 respectively. The inside diameters of element holders are nearly same as the outside diameters of the elements, and the inside surfaces of the holders are vertically formed against the top faces 7a and 8a respectively. Thereby, as the optical axes of the both elements are correctly met each other, the light passing through the transparent 7a forms a light flux having a large quantity of light that is cut by the outside diameter of the light emitting element 5, and the same light flux passes through the transparent top face 8a and reaches the light receiving element 6. |
