| 摘要 |
<p>PURPOSE:To avoid malfunction produced with the reduction in the amount of photo reception due to dust, etc. in the optical path, by coding the light irradiated from the light illumination section of column with the addition of modulation and detecting the tape loop position through the reception of it at each photodetector. CONSTITUTION:In the magnetic tape unit having the vacuum buffer column, the photodetectors S1, S2 are placed corresponding to the light illumination sections L1, L2 at the column C1, the light irradiated from the light illuminating sections L1, L2 is flickered and coded in different period by driving the light illumination sections L1, L2 with the controlling circuit 11. Since the detected signal of the photodetectors S1, S2 is inputted to the logic circuit 14 per each frequency component with the band pass filter 13 after amplification, the tape loop position can be detected with the fequency of detected signal independently of the amount of light received, allowing to avoid the influence of reduction in the light received due to dust and the like.</p> |
