Spool driving and braking

摘要

In combination with a spool upon which elongated stock such as ribbon, wire, thread etc. is to be wound and from which the elongated stock is to be unwound; an electromagnet with cooperating armature and a yoke; the device is to be selectively used as a brake and as a clutch. This is accomplished by a permanent air gap from 0.1 to 1.5 mm between the yoke and the armature to remain effective in the energized state. On application of a relatively high voltage to the electromagnet positive coupling obtains between the electromagnet and the armature and, therefore between a shaft connected to the electromagnet and the armature as thereafter being connected to the spool; for positive common rotation of these parts. Upon application of a lower voltage to the electromagnet, a brake force becomes effective between the electromagnet on one hand, plus armature and the spool subassembly on the other hand.