| 摘要 |
PROBLEM TO BE SOLVED: To simplify the constitution of a control part by detecting wavelengths of signals changing in accordance with revolving speeds of respective hubs of a take-up and a supply and by changing over a take-up speed from a high speed to a normal speed when the difference between wavelengths reaches a predetermined reference value. SOLUTION: First and second photosensors 20, 22 transmit alternating signals whose revolving speeds are changed in accordance with revolving speeds of first and second hubs 24, 26 to a control part 16 by receiving reflected lights from black-and-white patterns of respective reflection plates 18 provided at first and second rotary shafts 10, 12. In a rewind operation, a motor 14 is revolved at a fixed high speed and a magnetic tape 30 is wound up from the second hub 26 to the first hub 24 with this motor. A control part 16 detects wavelengths of alternating signals from the first and second photosensors 20, 22 by respectively sampling them. Since the revolving speed is rised as the residual amount of the tape becomes smaller at the side of the second hub 26, the cycle of the alternating signal from the second photosensot 22 becomes shorter. Then, it is judged that the residual amount of the tape of the side of the second hub 26 became a few by the difference between the cycle from the sensors 22 and the cycle from the sensor 20.
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