JPS6149856A - Magnet drive circuit for printer - Google Patents

Abstract

PURPOSE:To obtain the drive conditions of an electromagnetic coil in the magnet for driving hammers by controlling the current of the electromagnetic coil by digital signals and also by controlling the drive circuit of the electromagnetic coil by a switching method. CONSTITUTION:A transistor 2 is operated in a continuous ON-OFF manner by pulse train signals D. When timing pulse A in a signal A rises, coil current I in an electromagnetic coil 1 rapidly rises. When the pulse C is weakened after the lapse of time T, the transistor 2 is turned ON-OFF by pulse signal B. When the transistor 2 is turned off, a diode 3 goes on by the counter electromotive force of the coil 1. The coil current I becomes continuous current by current returning actions with high efficiency, and the level of the current can be controlled according to the duty cycle of the pulse train signal D. In the ending period of the drive, the coil current I is quickly damped by the resistor 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a drive circuit for an electromagnetic coil in a printing magnet of a printer.

[Prior art]

Magnet i. is widely used to drive hammers in printers. In the past, when controlling the acting force of the electromagnetic coil of this type of magnet, an analog method was mainly used in which the coil current was controlled by changing the voltage applied to the electromagnetic coil. However, in recent years, there has been a trend toward digitization of many electronic devices, control devices, etc., and it has come to be desired that driving circuits for electromagnetic coils be of a switching type and can be controlled digitally. However, a similar type of magnet that fully satisfies the drive conditions for the electromagnetic coil of the hammer drive magnet in high-speed printers has not yet been realized.

For example, Japanese Utility Model Publication No. 52-221'79 discloses an electromagnet drive device configured to turn on and off a transistor connected in series with an electromagnetic coil. However, in this device, the current in the electromagnetic coil is intermittent as the transistors turn on and off, and it is not possible to supply continuous current to the electromagnetic coil as in analog circuits. The drive circuit for the hammer drive magnet of an impact-type high-speed printer is, for example, disclosed in Japanese Patent Application Laid-open No. 52
As in the analog type drive circuit disclosed in Japanese Patent No. 48926, it is necessary to be able to smoothly control the current of the electric culm coil over time from the initial stage of the drive. However, the prior art disclosed in Japanese Utility Model Publication No. 52 =2.2179 does not give any consideration to digital level control of the coil current, let alone the smooth control of one level of the electromagnetic coil current.

Furthermore, another requirement that the electromagnetic coil drive circuit must have is that the coil current should be quickly raised in the initial stage of driving, and that the coil current should be quickly attenuated in the final stage of driving.

[Purpose of the invention]

The present invention was developed in view of the above circumstances, and uses a digital signal to supply an uninterrupted continuous current to an electromagnetic coil whose level can be smoothly controlled. The object of the present invention is to provide a drive circuit for a printing magnet 1 of a printer.

[Structure of the invention]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 shows signal waveforms at various parts to explain its operation.

In FIG. 1, reference numeral 1 denotes an electromagnetic coil of a hammer drive magnet of a printer, one end of which is connected to the ground terminal of a power source via a first switch element, ie, a hemistatic resistor 2. In FIG. The connection point between the electromagnetic coil 1 and the transistor 2 is connected to the anode of a diode 3 which is a one-way conductive element, and the cathode of the diode 3 is connected to the other electromagnetic coil 1 through a resistor 4 which is a resistive impedance element. connected to the end. A second switch element connected in parallel with the resistor 4 is connected to the non-ground terminal 5 of the power supply. The emitter of the 1-herald transistor 5 is connected to the other end of the electromagnetic coil 1.

Transistor 2 is driven by a pulse train signal supplied via OR gate 6 and is turned on and off continuously. This pulse train signal is an OR signal of the pulse train signal B applied from the pulse train generating circuit 9 through the analogues 1 to 7 and the single pulse C output from the one-shot multivibrator 8. The signal A is a timing pulse that becomes high 1 during the drive period of the transistor 2, in other words, the drive period of the electromagnetic coil I, and is used to control the opening and closing of the anti-games 1 to 7, as well as the triggers of the one-shikotsu 1- and the multi-bye break 8. Fast timing pulse A
carried out by The 1-transistor 5 is also turned on and off by the timing pulse A.

Next, the operation shown in FIG. 1 will be explained with reference to FIG.

When timing pulse 8 rises, transistor 1-transistor 5 turns on and at the same time, output pulse C of one-sided multivibrator 8 rises. turns on. Therefore, the electromagnetic coil 1 is substantially directly connected to the power supply, and the coil power supply quickly rises along a time constant curve determined by the inductance of the electromagnetic coil 1, the internal resistance, and the power supply voltage (ys).

When the pulse C is deactivated after T time has elapsed, the 1-transistor 2 is continuously turned on and off by the pulse signal B. When the transistor 2 turns off, the back electromotive force of the electromagnetic coil 1 turns on the diode 3. At this time, the transistor 5 is also on, so the back electromotive force of the electromagnetic coil 1 is transferred to the diode 3,
It is fed back to the electromagnetic coil 1 through the low impedance path of the transistor 5 with low loss.

Because of this current feedback, the coil current ■ does not cut off suddenly even during the off period of the transistor 2, and when the transistor 2 turns on again after it has decreased to a certain level, the coil current ■
increases again. In this way, the coil current (2) gradually attenuates and stabilizes while oscillating in a certain width toward a certain level determined by the duty cycle of the pulse signal B. In other words, the coil current I becomes a substantially continuous current due to the effect of the high-efficiency current feedback, and the coil current does not intermittent in a pulsed manner as in conventional switching type electromagnetic coil drive circuits. As described above, the level of the coil current (2) can be controlled according to the on/off duty cycle of the transistor 2, that is, the duty cycle of the drive pulse train signal.

When the timing pulse 8 determining the drive period of the 1-transistor 2 is deactivated, the AND gate 7 is closed and the supply of the pulse signal B is stopped, and the transistor 2 is kept in an off state. At this time, since the transistor 5 is also turned off, the back electromotive force of the electromagnetic coil 1 is fed back to the electromagnetic coil 1 through the path of the diode 3 and the resistor 4. In this way, at the end of the drive, the feedback of the back electromotive force is suppressed by the resistor 4 of the current feedback circuit, so the coil current 2 rapidly attenuates.

Note that the single-bar resistor 4 in FIG. 1 can be replaced with another element that can achieve the desired effect as a resistive impedance, such as a Zener diode.

〔Effect of the invention〕

As described above, according to the present invention, a continuous current is passed through the electromagnetic coil of the printing magnet l- of the printer, and the level of this current can be smoothly controlled by a digital signal, and the coil current can be controlled at the initial stage of driving. A quick start-up is possible.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a timing diagram of the embodiment of FIG. 1... Electromagnetic coil, 2, 5... Transistor, 3
...Diode, 4...Resistor, 6...OR gate, 7...And gate, 8...One-shot multi, 9...Pulse train generation circuit.

Claims (1)

[Claims] (1) In the printer's printing magnet drive circuit,
pulse train generating means for generating a pulse train having a predetermined cycle; single pulse generating means for generating a single pulse having a pulse width greater than the pulse width of at least one pulse of the pulse train; and an output signal of the pulse train generating means; A printing magnet drive circuit for a printer, comprising a signal synthesizing means for OR-combining the output signal of the single pulse generating means, and the signal synthesizing means drives an electromagnetic coil of the printing magnet.