| 摘要 |
PURPOSE:To obtain a compact detector whose attachment position is determined with high accuracy, by using a light guiding prism having a projected part which interlocks with a cut part of a holder, and also partially locked with a loading reference pin of a cassette half. CONSTITUTION:A holder 3 contains an opening window 31 and a cut part 32 and stores a light emitting element 1 and a photodetector 2 independently of each other and with mutual cut-off of light. A light guiding prism 4 has a pro jected part 41 and a cassette half 6 is positioned by a loading reference pin 7. Then the prism 4 is locked with the pin 7 via the part 41 of the prism 4. Thus the relative position is decided with extremely high accuracy between the prism 4 and the cassette half 6. The window 31 is et opposite to a through hole 61 of the cassette half 6 loaded to the pin 7. Thus the light emitted from the element 1 is made incident on the prism 4 after crossing the driving surface of a tape 5 and reaches the photodetector 2 after applying flection by the reflec tion of two times inside the prism 4. The termination of the tape 5 is detected by a change of the transmitted light quantity of the magnetic surface of the tape and a leader tape respectively and in the form of the variance of the output signal of the photodetector.
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