Ribbon tension control with dynamic braking and variable current

Details Ribbon tension control with dynamic braking and variable current Ribbon tension control with dynamic braking and variable current

1992-02-27

1996-02-13

Darling, John P.

Winding, tensioning, or guiding

Tension control or brake

Supply controlled

2424222, B65H 7700

Patent

active

054906385

ABSTRACT:
A pair of ribbon spools are independently operated by respective motors to rotate in one direction until the ribbon end and then in the opposite direction, and so forth. Spools alternately function as feed and take-up spools and motors as a drive and drag motors, respectively To eliminate excess drag motor cogging, a ribbon tension control system uses dynamic braking of the drag motor, and includes drag circuitry with rectifier bridge circuitry and a constant current sink settable for drawing predefined selectable levels of current from the windings of the drag motor. The motors are polyphase, permanent magnet, stepper motors which, when turned by the ribbon, generate alternating back emf signals in their windings. A full-wave rectifier bridge is connected to each winding of the drag motor with bridge outputs connected to a common sink which is an emitter follower circuit whose current level is set and maintained by an operational amplifier. The current level of the emitter follower circuit is set by adjusting the reference voltage of the amplifier using a resistive voltage divider network connected to a binary switch controlled by a microprocessor with a memory. The microprocessor monitors the back emf signals, periodically adjusts the rotational speed of the drive motor depending on distribution of ribbon, and adjusts the sink based on drag value tables stored in memory.

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IBM Technical Disclosure Bulletin, vol. 32, No. 6, Nov., 1989, "Switchable Stepper Motor Drag Control", by Burke et al.
IBM Technical Disclosure Bulletin, vol. 19, No. 11, Apr., 1977, "Use Of Stepper Motor As Variable Load", by Barnett.

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