| 摘要 |
In a reel-to-reel web transport (such as a magnetic tape recorder), apparatus is provided for accurately positioning a takeup reel to receive the lead end of a web. The takeup reel is rotated in web supply and takeup directions by a brushless direct current (DC) motor. A magnetic hysteresis brake is coupled to the takeup reel when the reel is rotated in a web supply direction. The rotational position of the takeup reel to receive the lead end of a web is coincident with a stable torque equilibrium position of the DC motor. A control circuit is provided (1) for commutating the DC motor in a supply direction to couple said brake to said takeup reel, until a position sensor associated with the reel is actuated; (2) for commutating the motor for one more cycle in the same direction to bring the motor to rest at a position past the predetermined position; and (3) for commutating the DC motor for one cycle in the reverse direction, to uncouple the brake from the takeup reel and to bring the motor to rest at the stable equilibrium position which is coincident with the web receiving position of the takeup reel.
|
