| 摘要 |
PURPOSE:To attain stable running at an extremely low speed, by detecting the feeding speed of a magnetic tape, detecting the speed error digitally, using an output of speed error detection as a pluse width modulation wave, and pulse- driving a magnetic tape driving means. CONSTITUTION:A capstan 11 is driven with a DC motor 13 and a disc 14 with slits is fixed externally. The DC motor 13 generates a rotating torque T toward the arrow C when an input signal of a driving circuit 23 is at high level, and does not produce the torque T when the level is low. The rotary angle of the capstan 11, i.e., the amount of progress of a magnetic tape 10 is detected at the disc 14 with slits, a light emitting device 15 and a photodetector 16. A light outputted from the light emitting device 15 is intermitted with the revolution of the disc 4, inputted to the photodetector 16 and a pulse signal is outputted. The progressing speed of the magnetic tape 10 is measured by measuring the period of the pulse signal. |
