JPH0118373Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ink ribbon drive device used in an impact printer that runs an ink ribbon at a constant speed and tension.

Conventionally, in order to control the tension of an ink ribbon whose ends are attached to a pair of spools driven by a pair of motors, a current is applied to the coil of the driven motor and the current value is controlled to approximately A constant tension of the ink ribbon was obtained.

This method requires a circuit to flow current to the driven motor in addition to the current flowing to the driving motor, and because current must be supplied to the driven motor in addition to the driving motor, the circuit The disadvantages are that it is physically complex and requires extra power.

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned conventional techniques and to realize a longer service life of the ink ribbon by controlling the tension of the ink ribbon to be approximately constant.

This invention focuses on the fact that an electromotive force is generated in each phase of the step motor on the driven side depending on the rotation speed, and by short-circuiting each phase with an appropriate impedance depending on the rotation speed, the step motor on the driven side This is an attempt to extend the life of the ink ribbon by causing the step motor to generate a braking force and controlling this braking force so that the tension of the ink ribbon is approximately constant.

The present invention will be described below with reference to the drawings.

In FIG. 1, a magnet 8 attached to a guide roller 7 turns on and off a reed switch 9, and a control circuit 5 detects the signal. The control circuit 5 controls the rotational speeds of the driving step motors 3 and 4 so that the cycle of the reed switch 9 on and off is substantially constant. As a result, the ink ribbon 6 is transported at a substantially constant speed.

Now, assuming that the left step motor 3 is the driving side and the right step motor 4 is the driven side, in FIG. 2, the flyback diodes 23 to 26 of the right step motor 4 are opened by the switches 11 and 12 in response to the diode switching signal. In addition, the flyback diodes 27 to 30 of the left step motor 3 are
It is connected by switches 13 and 14. and,
When the control clock is input, the phase control section 10 outputs a drive signal. At this time, the left motor gate signal is controlled to have a logical value of 1, and the right motor gate signal is controlled to have a logical value of 0. Therefore, the control transistors 51 to 54 are driven, and the control transistors 47 to 50 are not driven and remain off. This drives the left step motor 3. At this time, the right switch control signal controls the drag torque changeover switches 33 and 34 in the manner described below.

Assuming that the ink ribbon 6 is being transported at a constant speed, as the winding diameter of the ink ribbon of the left step motor 3 on the drive side gradually increases, the rotational speed decreases. On the other hand, the winding diameter of the ink ribbon of the right step motor 4, which is the driven side, gradually becomes smaller, so if the ink ribbon 6 is being transported at a constant speed, the rotational speed will increase. Therefore, the AC electromotive force generated in the right step motor 4 increases. Here, the decrease in the winding diameter of the ink ribbon on the driven side means that the tension of the ink ribbon 6 increases, and the increase in the AC electromotive force generated in the right step motor 4 also increases.
This is the direction in which the drag torque increases, that is, the tension of the ink ribbon 6 increases. Therefore, when the ink ribbon 6 is transported at a constant speed, the ink ribbon 6
The tension in is in the increasing direction. Therefore, in order to keep the tension of the ink ribbon 6 constant, the drag torque of the right step motor 4 must be controlled to be reduced.

Here, the drag torque on the driven side increases as the impedances 35 to 40 that short-circuit both ends of the coils 15 to 18 of the right step motor 4 become smaller. Therefore, as the winding diameter of the ink ribbon 6 on the drive side becomes larger and the rotational speed becomes smaller, the right switch control of the right step motor 4 needs to be controlled so that the drag torque decreases.

If the ink ribbon 6 is transported at a constant speed, the rotation speed of the left step motor 3 decreases. Once the rotational speed of the left step motor 3 is determined, the rotational speed of the right step motor 4 is also uniquely determined. Therefore, the rotational speed of the drive side step motor 3,
In other words, the number of driving pulses PPS (Pulse Per Second)
The drag torque of the right step motor 4 on the driven side is determined, and the drag torque resistances 35 to 37 and 38 to 40 are determined according to the drag torque.
Determine the overall impedance based on the combination of With this, when changing the rotational speed on the driving side to transfer at a constant speed, by changing the drag torque in accordance with the speed, a substantially constant ribbon tension can be obtained. If you want to increase the drag torque here, drag torque resistors 35 to 37 and 38
-40 combinations, the overall impedance is controlled to be small, and conversely, when drag torque is to be decreased, the overall impedance may be controlled to be large.

As described above, according to the present invention, the electromotive force generated in the coil of the step motor, which is the driven side, is generated by short-circuiting both ends of the coil with an appropriate impedance, thereby generating a drag force and varying the impedance. This makes it possible to vary the drag force and thereby apply a substantially constant tension to the ink ribbon, which improves the running stability of the ink ribbon, thereby making it possible to extend the life of the ink ribbon.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the device of the present invention;
FIG. 2 is a block circuit diagram showing an example of the control circuit. In the figure, 1 and 2 are spools, 3 and 4 are step motors, 5 is a control circuit, 6 is an ink ribbon,
7 is a speed detection roller, 8 is a magnet, 9 is a reed switch, 10 is a phase control unit, 11 to 14 are changeover switches, 15 to 22 are coils, 23 to 30 are flyback diodes, and 31 to 34 are drag torque changeover switches. , 35-46 are drag torque resistors, 47-54 are transistors, 5
5 to 62 are step motor control gates.

Claims (1)

[Claims for Utility Model Registration] In a printing device having an ink ribbon whose both ends are attached to a pair of spools and which travels back and forth in a printing position, the ink ribbon is attached to the pair of spools so as to drive the spools, and the ink ribbon is attached to the driving side alternately. and a pair of step motors on the driven side, an impedance for short-circuiting a coil of the step motor on the driven side, and a control means for controlling the value of the impedance in accordance with the rotational speed of the step motor on the driving side. Ink ribbon drive device.