| 摘要 |
PURPOSE:To discriminate the running direction of tapes by using only one photo interruptor, by making the output waveform of the photo interruptor at the time when passing through the light transmissive window section of an encoder plate asymmetric about the time axis. CONSTITUTION:To the outer periphery of an encoder 2 fitted to a rotary post member 1 plural light transmissive window sections 3 with steps asymmetric about radial lines from the center of the encoder are installed at the same pitch and one photo interruptor 4 is arranged. When the encoder 2 rotates, the electric power waveform generated in the photo interruptor 4 has a step-like form asymmetric about the time axis as shown in the figure because of the quantity of light passing through the window sections 3. The running direction of a tape is discriminated by detecting whether the position of the stepped part E of the output waveform is before or after the peak part F with a prescribed electric circuit. Therefore, the running direction of tapes can be discriminated with only one photo interruptor.
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