| 摘要 |
<p>Spindles driving film or tape recorder reels are individually driven by dc electric motors fed from a system giving the voltage and current required for best combination of speed and tension of the film or tape. A gear train couples the motor to the reel spindle. A ferromagnetic disc mounted on the spindle via splines is free to slide along the spindle and is normally held away from the electromagnetic brake, mounted coaxially with the spindle, by a spring. When the spindle drive motor supply is interrupted the electric supply to the electromagnetic brake is imitated, drawing the braking disc along the spindle and into contact with the stationary part of the brake. The braking force may be varied by variation of the electromagnet supply which is dc with a superposed 100Hz component to provide extra hysteresis braking and to ensure no residual magnetism when the brake is released.</p> |
