JPS5936403B2 - Drive circuit for electromagnetic coil in printer hammer drive magnet - Google Patents

Description

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

[Prior art]

Magnets are 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, such a type has not yet been realized that fully satisfies the driving conditions of the electromagnetic coil of the hammer drive magnet in a high-speed printer. For example, Japanese Utility Model Publication No. 52-22179 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 transistor is turned on and off, and it is not possible to supply continuous current to the electromagnetic coil as in an analog circuit. The drive circuit of the hammer drive magnet of an impact-type high-speed printer, for example in the analog drive circuit disclosed in Japanese Patent Laid-Open No. 52-48926, changes the current level of the electromagnetic coil over time from the initial stage of the drive. Must be able to be controlled smoothly. However, the aforementioned Jikosho 5
The prior art of No. 2-22179 does not give any consideration to digital coil current level control, let alone smooth control of the electromagnetic coil current level. Another requirement that the electromagnetic coil drive circuit must have is:
The purpose is to quickly raise the coil current at the beginning of driving, and quickly attenuate the coil current at the end of driving.

[Purpose of the invention]

The present invention was developed in view of the above-mentioned circumstances, and uses a digital signal to supply an uninterrupted continuous current to an electromagnetic coil with smooth level control. An object of the present invention is to provide a drive circuit for an electromagnetic coil for driving a hammer of a printer, which enables a rapid fall.

[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 supply via a transistor 2, which is a first switch element.

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 end of the electromagnetic coil 1 via a resistor 4 which is a resistive impedance element. connected to. The collector of the transistor 5, which is the second switch element connected in parallel with the resistor 4, is connected to the non-grounded end of the power supply +Vs.
connected to. The emitter of transistor 5 is connected to the other end of the electromagnetic coil. Transistor 2 is OR gate 6
It is driven by a pulse train signal D supplied through the circuit and turns on and off continuously. This pulse train signal D is a pulse signal B given from the outside through an AND gate 7.
This is an OR signal between C and the single pulse C output from the one-shot multipipulator 8. The signal A is a timing pulse that becomes high level during the driving period of the transistor 2, in other words, the driving period of the electromagnetic coil 1, and the opening/closing control of the AND gate 7 and the triggering of the one-shot multivibrator 8 are performed by the timing pulse A. It is done. Also, the transistor 5 also receives the timing pulse A.
It is turned on and off by. Next, referring to Figure 2,
The operation of the diagram will be explained.

When the timing pulse A rises, the transistor 5 turns on, and at the same time, the output pulse C of the one-shot multipipulator 8 rises and the transistor 2 turns on. Therefore, the electromagnetic coil 1 is substantially directly connected to the power supply, and the coil current I rapidly rises along a time constant curve determined by the inductance of the electromagnetic coil 1, internal resistance, and the power supply voltage (+Vs). When the pulse C is deenergized after T time has elapsed, the transistor 2 is continuously turned on and off by the pulse signal B.

When the transistor 2 turns off, the diode 3 turns on due to the back electromotive force of the electromagnetic coil 1. At this time, since the transistor 5 is also on, the back electromotive force of the electromagnetic coil 1 is fed back to the electromagnetic coil 1 through a low impedance path of the diode 3 and the transistor 5 with low loss. Because of this current feedback, the coil current I is not cut off rapidly even during the off period of the transistor 2, and when the transistor 2 is turned on again after it has decreased to a certain level, the coil current I increases again. In this way, the coil current I 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, due to the effect of highly efficient current feedback, the coil current I becomes a substantially continuous current, and the coil current is not intermittent in a pulsed manner as in the conventional switching type electromagnetic coil drive circuit. As mentioned above, the level of the coil current I is determined by the on/off duty cycle of transistor 2.
In other words, control can be performed according to the duty cycle of the drive pulse train signal D. When the timing pulse A that determines the drive period of the transistor 2 is deactivated, the AND gate T 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 I rapidly attenuates. Note that the 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, there is provided a switching type electromagnetic coil that allows continuous current to flow through the electromagnetic coil, allows smooth control of this current level by a digital signal, and allows steep rise and fall. A drive circuit can be provided.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
FIG. 3 is a timing diagram for the illustrated embodiment; 1... Electromagnetic coil, 2, 5... Transistor, 3... Diode, 4...
Resistor, 6...OR gate, T...and gate, 8...inverter.

Claims (1)

[Claims] 1. A driving circuit for an electromagnetic coil in a hammer drive magnet of a printer, wherein one end of the electromagnetic coil is connected to one end of a power source via a first switch element, and the other end of the electromagnetic coil is connected to a second end of the electromagnetic coil. A resistive impedance is connected to the other end of the power supply via a switch element, and a one-way conductive element is connected to both ends of the electromagnetic coil with a polarity that is non-conductive with respect to the polarity of the power supply voltage applied to the electromagnetic coil. connected in parallel through elements, a connection point between the one-way conductive element and the impedance element is connected to the other end of the power supply, and the first switching element is turned on and off by a pulse train having a predetermined duty cycle; A drive circuit for an electromagnetic coil, wherein the second switch element is turned on during a period in which the first switch element is turned on and off by a pulse train. 2. The electromagnetic coil drive circuit according to claim 1, wherein at least the first switch element among the first and second switch elements is constituted by a transistor.