| 摘要 |
<p>PROBLEM TO BE SOLVED: To eliminate the influence of fluctuation in the transmittance of a substrate or the sensitivity of a light receiving section by comparing the quantity of light projected from a light projecting means with the quantity of light received by a light receiving means and detecting presence of a substrate based on the comparison results. SOLUTION: A light projecting section 1 and a light receiving section 2 are disposed, respectively, in the vicinity of pectinate base parts 5a, 5b in a housing. A wafer 3 is inserted between respective guides and the light projected from the light projecting section 1 is transmitted through the wafer 3 twice, i.e., between a projection reflector 6 and a first reflector 7 and between a second reflector 8 and a receiving reflector 9, before being received at the light receiving section 2. The quantity of light projected from the light projecting section 1 is then compared with the quantity of light received the light receiving section 2 at the subtracting section 10 of a decision means 12 and then a decision is made at a decision section 11 whether the wafer 3 is present or not based on the subtracted value.</p> |
