JPH03216349A - Impact wire dot head drive circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit for a high-response frequency multi-pin impact wire dot head.

[Conventional technology]

Among printers that print characters or bit images in a dot matrix, serial type printers that use wire pins in the print head are widely used because they can produce copies and have excellent cost performance. An example of a conventional wire drive circuit is disclosed in Japanese Patent Application Laid-Open No. 63-2540-76. FIG. 3 is a drive circuit diagram, and FIG. 4 is a diagram of the drive timing relationship. In Fig. 3, Mi is a drive coil (j=1, 2, 3...), Qi is an individual drive transistor, Qcb is a common line drive transistor, ZDi is an individual Zener diode, DC is a common line diode, and Di is a common line diode. It is an individual diode. As shown in the drive timing relationship diagram in Figure 4, first, in the period T1, the common line drive transistor and the selected individual drive transistor are turned on, and current I begins to flow through the drive coil and increases according to the time constant of the circuit. After the tlc time has elapsed, the common line driving transistor is turned off and the current becomes M.
Circulating the root of i −+ Q i −+ D c, t
After 1 b time has elapsed, the individual driving transistors are turned off and the generated back electromotive force is consumed as a current that circulates through Mi-+Di→ZDi→power supply. When the common line driving transistor is turned on again in the subsequent printing cycle T2, the back electromotive voltage of the drive coil driven in the previous T1 cycle is always less than the Zener voltage, so the current curve ■ in Figure 4 is indicated by a broken line. Loop X of the harmful current Mi+Di→ZDi-+Qcb
It is possible to prevent the backflow at the wire pin and enable good driving of the wire pin.

[Problem to be solved by the invention]

After the drive coil is energized, power generation occurs due to the residual magnetic flux of the head magnetic circuit and the drive coil.

For this reason, when a circuit including a drive coil is formed, a current flows through the drive coil when it is not driven, and if this current is generated when the wire pin returns, the return of the wire pin will be delayed.
This causes printing defects such as ribbon catching. In the conventional drive circuit configuration and drive timing, the circulation circuit for the generated harmful current is opened and closed by a Zener diode connected to each drive coil via a diode.

For this reason, if the drive cycle is shortened, the common line drive transistor is turned on during the on period of the Zener diode, generating harmful current, and the drive cycle is shortened in anticipation of the back electromotive force absorption time due to variations in Zener breakdown voltage. The drawback was that it required setting. Another drawback was that most of the back electromotive force was absorbed by the heat generated by the Zener diode, resulting in a reduction in input energy conversion efficiency.

[Means to solve the problem]

In the present invention, one end of the coil that drives the wire pin is connected to a power line via a common line drive switch and to a ground line via a unidirectional element as a drive circuit that controls the fall of the current flowing through the coil. , the other end of the coil is connected to the ground line via an individual drive switch, and to the power line via an induced current path opening/closing switch that is commonly connected to the unidirectional element and other coils. The first feature is
When the common line drive switch is on, the induced current path opening/closing switch is off, and when the common line driving switch is off, the induced current path opening/closing switch is on. This is the second feature.

[Effect]

As described above, if the impact wire dot head drive circuit of the present invention is used, generation of harmful current on the circuit can be prevented when driving a wire dot head with multiple bins with a high response frequency, and printing defects such as ribbon catching can be avoided. Good wire pin drive is possible.

〔Example〕

Hereinafter, the present invention will be explained according to one embodiment.

FIG. 1 is a drive circuit diagram in an embodiment. One end of the drive coil 10 is connected to a PNP transistor 2, which is a common line drive switch, and a common diode 3, which is a unidirectional element, and the other end is connected to an NPN transistor 4, which is an individual drive switch, and an individual diode, which is a unidirectional element. It is connected via a diode 6 to a PNP I-transistor 2 which is a switch for opening and closing the induced current path. The common line driving PNP l-transistor 1 and the induced current path opening/closing PNP l-transistor 2 are further connected to a power supply high voltage line Va, and the individual driving NPN transistor 4 is connected to a power supply ground line. Numerals 8 and 9 are NPN transistors for level conversion of drive signals, which convert the voltage levels of the drive signals Sc and *SC, respectively, to connect the common line drive PNP transistor 1 and the induced current path opening/closing PNP transistor 2. is driving. PNP for common drive Transistor 1, common diode 3, and PNP for switching induced current }-The number of coils driven by transistor 2 can be set arbitrarily within the range allowed by the element standard, so the number of coils is not limited in the figure. .

The operation of the circuit shown in FIG. 1 will be explained with reference to the drive timing relation diagram shown in FIG. By the print command that drives the wire, the common line driving PNP }-drive signal Sc of the transistor 1, the drive signal Si of the individual driving NPN transistor (i=1, 2
, 3...), PNP transistor 2 for switching induced current path
A drive signal *Sc is generated. In the period T1, first the common line driving PNP I-transistor 1 and the individual driving NPN transistor 4 are turned on, and the current flowing through the driving coil 10 gradually increases according to the time constant of the circuit, as shown at 11 in FIG. At this time, P for opening and closing the induced current path
NPI-transistor 2 is off. After Ta time has elapsed, the common line drive PNP h transistor 1 is turned off, and the current due to the back electromotive force is transferred to the drive coil 10 indicated by the broken line in FIG.
→Individual drive NPN} - transistor 4 → power supply ground line → common line diode 3 Circulate through the lube p. At this time, the induced current path opening/closing PNP transistor 2 is in the on state. The circulating current gradually decreases and after Tb time elapses,
The individual driving NPN transistor 4 is turned off, and the current due to the back electromotive force flows through the driving coil 10 shown by the dashed line in FIG.
→Individual diode 6→PNP for switching induced current path l-Loop m of transistor 2→power supply→common line diode 3
circulate. In the case of the conventional circuit configuration shown in FIG. 3, the back electromotive force during the Tc period is absorbed by the heat generated by the Zener diode, and the circulating current suddenly falls as shown by the broken line of curve 11 in FIG. According to the example, the input energy conversion efficiency is improved because it gradually falls as shown by the solid line while being used to drive the drive coil.

In this T1 period, changes in the magnetic flux closely related to the driving force of the wire are as shown by φ1 in FIG. 2. Tal
, during the Tb period, the magnetic flux gradually increases and decreases like the drive current jl, but after the Tc period, the magnetic flux decreases as residual magnetic flux T due to the hysteresis characteristics of the magnetic circuit that constitutes the head.
It decreases slowly compared to the al and Tb periods. In the case of the conventional circuit configuration shown in FIG. 3, 11 of the Tc period
Due to the sudden drop in φ1, φ1 decreases more rapidly as shown by the broken line than the change shown by the solid line according to the embodiment of the present invention, but the change after the current 11 becomes 0 is almost the same.

Continuation (In the period T2, the cantering coil 11, which was not driven in the previous period T1 and is commonly connected to the drive coil 10, is driven. First, the common line driving PNP transistor 1 and the individual driving NPN transistor 5 are is turned on, and then the second
It is driven by a current as shown at 12 in the figure. This T2
During the Ta2 period of the cycle, the induced current path opening/closing PNP
Since the transistor 2 is off, the drive coil 10 shown by the two-dot chain line in FIG. 1 → the individual diode 6 → the induced current path switching transistor 2 → the common line driving transistor 1
The circuit loop n including the drive coil is not formed, and the circulation of harmful current due to the power generation effect of the residual magnetic flux φ1 in FIG. 2 is prevented.

As mentioned above, the circuit configuration in Figure 1 and the common line driving P
By controlling the ON and OFF states of the NP}-transistor 1 and the PNP transistor 2 for opening/closing the induced current path, high-speed response of the wire pin without generation of harmful current can be realized.

In the embodiments of the present invention, transistors and diodes are used as circuit components, but switching elements such as FETs and thyristors that can achieve the same effect can also be used.

〔Effect of the invention〕

As described above, if the impact wire dot head drive circuit of the present invention is used, it is possible to prevent the generation of harmful current on the circuit when driving a high response frequency multi-bin wire dot head, and to achieve a good result with high input energy conversion efficiency. Wire pin drive is possible.

[Brief explanation of drawings]

Figure 1 is a drive circuit diagram of one embodiment of the present invention, and Figure 2 is a drive circuit diagram of an embodiment of the present invention.
FIG. 3 is a conventional drive circuit diagram, and FIG. 4 is a drive timing diagram of FIG. 3. that's all

Claims (2)

[Claims] (1) In a dot matrix printer where wire pins are selectively driven by a print command to print characters or bit images, one end of the coil that drives the wire pins is driven by a common line as a drive circuit that controls the fall of the current flowing through the coil. The other end of the coil is connected to the power line via a switch for driving, and to the ground line via a unidirectional element, and the other end of the coil is connected to the ground line via an individual drive switch, and is also common to the unidirectional element and other coils. A drive circuit for an impact wire dot head, characterized in that the drive circuit is connected to a power supply line via an induced current path opening/closing switch connected to a power supply line. (2) When the common line drive switch is on, the induced current path opening/closing switch is off; when the common line driving switch is off, the induced current path opening/closing switch is on. An impact wire dot head drive circuit characterized by: