GB1416295A - Ribbon control in electromechanical printers - Google Patents

Abstract

1416295 Drive arrangement for print ribbon INTERNATIONAL STANDARD ELECTRIC CORP 10 Oct 1974 [22 Oct 1973] 43912/74 Heading H2J An electromechanical printer has first and second motors providing drive respectively for each of the printer ribbon spools such that when one motor is being driven, the other motor is being dragged, and has first and second circuits respectively associated with the first and second motors each circuit providing one electrical logic state when its corresponding motor is being driven and a different logic state when its motor is being dragged, means responsive to a change in the logic state of the circuit associated with the motor being dragged during a printing operation such that the source of energy to the driving motor is switched to the motor being dragged. Motors M1 and M2 having coils L11, L12; L21, L22 are powered with A.C. across points A, B and switch S1, which is controlled by flip-flop JK supplies power to one of the motors, e.g. Ml. Whilst Ml is being driven, M2 will act as a generator and rectified A.C. will pass through the diode of optical isolator OP2 and cause point P of Darlington pair T2, which is normally high, to be grounded. An identical circuit arrangement is associated with motor M1 and the outputs of the circuits are connected to inputs 1, 2 of a gate and Schmidt trigger ST, the input 3 being connected to an external logic circuit to indicate a "print" command. The output from the gate is designed to be "high" in all events except where the end of the ribbon is reached during a printing operation, whereby the motor being dragged will be stopped and the voltage generated thereby will fall causing the input at ST to go "high" and the output to go to "low" and trigger flip-flop JK. In an alternative embodiment, Fig. 3 (not shown), the motor generated voltages are applied to respective comparators which produce square wave outputs in phase with their inputs. The coupled outputs are then used to trigger a monostable such that when the idling motor is moving normally, a constant output from the monostable is obtained, but when it slows when the end of the ribbon is reached, a change of output, which triggers the flip-flop via a gate and Schmidt triggers, occurs. A counter to count the number of reversals in any one print operation may be provided and an alarm activated if this exceeds a particular number.