JPH0418367A - Driving apparatus for wire dot print head - Google Patents

Abstract

PURPOSE:To absorb a fly-back current by providing a plurality of diodes short- circuiting both terminals of a printing wire driving coil and connecting a Zener diode to each of head driving transistors. CONSTITUTION:Since a FRY-BACK signal 50 becomes a low level during the period T3 of the operation time chart of the drive apparatus of a print head, a PNP transistor 30 is turned OFF and a HEAD #1 signal also becomes low. At this time, an NPN transistor 1 is turned OFF and the place to go to of the current flowing to a printing wire driving coil #1 is lost and extremely high counter-electromotive force is generated. When this counter-electromotive force becomes higher than the Zener voltage of a Zener diode 301, a base current is supplied to the NPN transistor 1 from the printing wire driving coil #1 through the Zener diode 301 and the NPN transistor 1 is turned On. As a result, a current ii1 flows to earth from power supply voltage Vcc through the printing wire driving coil #1 and the NPN transistor 1 and a fly-back current is absorbed by high Zener voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a drive device for a wire dot print head in a serial printer.

(Prior Art) Conventionally, printers using wire dot print heads have the advantage of having a high degree of freedom in printing media and being able to use copy paper, etc., and have been in high demand. Further, the wire dot print head drives the wire by a permanent magnet or a magnetic attraction force of a magnet.

The above printers are based on the wire dot print head model.
It can be divided into plunger type, spring charge type, and clapper type.

Among these, the spring-charged type has an armature to which the printing wire is fixed, which is swingably supported by a leaf spring for bias, and the armature is previously attached to the core by a permanent magnet against the elastic force of the temporary spring for bias. When printing, a coil wound around the core is excited to generate a magnetic flux in the opposite direction to the permanent magnet, and the armature is released.

In this case, a coil is disposed corresponding to each of the plurality of bins constituting the wire dot print head, and the wire dot print head is driven by passing a drive current through each coil via a drive device.

FIG. 3 is a circuit diagram of a conventional wire dot print head drive device.

Here, a 24-bin wire dot print head will be described.

In the figure, 11 is the first printing wire drive coil;
#2: second printing wire drive coil...112
4 indicates the 24th printing wire drive coil.

1.2. ..., 24, the collector side is the printing wire drive coil Ill 12. ...The emitter side is connected to ground in key 24! IP! l transistor, 3
0, the collector side is the printing wire drive coil I11.
+12. ...In #24, the emitter side is connected to the electric flvcc
is a PNP transistor connected to the PNP transistor. 31.
IOL 102. . . . 1124 is a flyback gouote, and 32 is a zener diode for flyback absorption. , 33, 34, and 201 are resistors, and 36 is an NPN transistor disposed between the base of the PNP transistor 30 and the ground.

At the base of the NPN transistor 36, there is a HEAD-OVD 40 that commonly overdrives each head.
is input, and I(EAI)# is input to the base of transistor 1 (NPN), which drives only the printing wire drive coil #l.
Il signal is input.

Although not shown, similarly, the HEAD2 signal is applied to the base of the NPN transistor 2, and the lEAfl13 signal is applied to the base of the NPN transistor 3.
NPN) At the base of transistor 24) IEADI
124 signals are input. In this case, a pull-up resistor similar to resistor 201 is connected to each NPN transistor 2.
．． 3..., connected to the 240 base.

Next, the operation of the wire dot print head drive device configured as described above will be explained.

FIG. 4 is an operation time chart of a conventional wire dot print head drive device.

In the figure, only the HEAD-OVD signal and HEAD#l signal are shown, but) IEAD#2. ...,
Similarly, the HEAD 1124 signal is the waveform of the current flowing through the print wire drive coil 11.

During TI, IIEAD-OV[l signal, HEAD#1
Since the signals are both at the low level, the PNP transistor 30 and the NPN transistor 1 are turned on, and the current 11 flows from the IT source voltage V Ce through the PNP transistor 30, the print wire drive coil #l, and the NPN transistor 1.

Since the HEAD-OVD signal is off during T,
NP transistor 30 is turned off. The current 11 flows to the print wire drive coil 1 via the print wire drive coil 11SNPN) transistor 1, ground (Ov), and diode 31.

Also, during T, )IEAD-OVD signal, )IEAD
Since both of the III signals are off, the PNP ) range meta 30. ．． Both IIIPII transistors 1 are turned off. At this time, the current i flows through the ground and the diode 31 to the power supply voltage Vcc. The other print wire drive coils #2 to #24 operate in the same manner.

In the wire dot print head drive device with the above configuration, since the current between T is large, the drive time of T is determined depending on conditions such as the number of printing wires driven simultaneously and the thickness of paper to be printed. lengthening or shortening.

(Problem M to be Solved by the Invention) However, in the conventional wire dot print head drive device described above, the length of the drive time of T is
Since it is determined by the ON time of the PNP transistor 3o commonly connected to each print wire drive coil 11-124, it is not possible to set different drive times for each print wire drive coil Ill-124.

To make this possible, as many PNP wires as there are printing wires.
) It is necessary to provide a transistor 30. In other words, in the above conventional example, 24 PNP transistors 30 are required, and the connection cord for the collector side of the PNP transistor 30, that is, the A part, cannot be shared, and the head cable, connector, etc. become larger, resulting in higher costs. It ends up.

The present invention solves the problems of the conventional wire dot print head drive device and sets the drive time of each of a plurality of print wire drive coils without increasing the number of transistors or increasing the size of cables and connectors. The object of the present invention is to provide a drive device for a wire dot print head that is capable of printing.

(Means for Solving the Problem) For this purpose, in the wire dot printing head drive device of the present invention, a plurality of printing wire driving coils are connected in parallel to the power supply, and a connection between the printing wire driving coil and the ground is provided. A plurality of head drive transistors are connected to each of the head drive transistors.

The head drive transistor is turned on and off by a head drive signal input to its base, and a common flyback transistor is connected to short-circuit both ends of each printing wire drive coil. It is turned on and off by a signal. A plurality of diodes are disposed between the fly-hack transistor and each of the print wire drive coils, and are connected in a direction to conduct current across the short circuit of the print wire drive coils.

A Zener diode is connected to each of the head drive transistors, which breaks down when a back electromotive force is generated by the current flowing through the print wire drive coil, and makes the head drive transistor conductive.

(Function) According to the present invention, as described above, a plurality of print wire drive coils are connected in parallel to itB, and a plurality of head drive coils are connected between each print wire drive coil and the ground. a transistor, a common flyback transistor connected to short-circuit both ends of each of the print wire drive coils, and a plurality of diodes that short-circuit both ends of the print wire drive coil; A Zener diode is connected to.

Therefore, FLY of the above flyback transistor
- When the BACK signal is turned on and the HEAD signal of the head driving transistor is turned on, the drive current rises. Subsequently, when the HEAD signal is turned off while the FLY-BACK signal remains on, a flyback current flows through the printing wire drive coil. Also, FLY-BAC
When both the K signal and the HEAD signal are turned off, the current flowing through the print wire drive coil has nowhere to go and a very high back emf is generated, and when this back emf becomes higher than the zener voltage of the zener diode. , the head drive transistor turns on and absorbs the flyhack current.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of a drive device for wire dot printing, etc., showing an embodiment of the present invention.

In the figure, 1, 2. ..., 24 is NPN) transistor, II, 12. ..., #24 is the NPN
) print wire drive coils connected to transistors 12, . . . , 24, respectively, forming 24 pairs. Each of these pairs is connected in parallel to the voltage Vcc.

101, 102. ..., 124 is a diode for fly hack current, PliP transistor 30
The anode is connected to the emitter side of the printing wire drive coil Ill, 12..., 1124 and NPN) transistor 1.2. ..., the cathode is connected to the 24 connection points. Further, the collector side of the PNP transistor 30 is connected to the printing wire drive coils 111, 112.・
..., connected to the other terminal of #24, and print wire drive coil Ill, 112. ..., 1124,
Diode 101.102. ..., 124 and PNP
Transistor 30 forms a flyback current loop. The above PNP) transistor 30 is connected to the above printing wire drive coil Ill, +12. ..., s2
4 and NPN transistor 1.2. . . , are commonly connected to each of the 24 pairs.

301, 302. ..., 324 is the above NPN
) This is a Zener diode disposed between the collector side and the base side of transistors 1, 2, . . . , 24.

Further, 36 is an NPN transistor for flowing a flyback current, and the collector side is connected to the above-mentioned P through the resistor 34.
NP) The emitter side is connected to the base of the transistor 30 and grounded. 33.201 is the NPN transistor 36 and the NPN transistors l, 2.・・・
・This is a pull-up resistor connected to the base side of 24.

Although not shown, a resistor 202 similar to the resistor 201.・
...224 is NPN) transistor 2. ..., 24
It is connected to the.

The FRY-BACK signal 50 for causing a flyback current to flow through the NPN) transistor 36 is input, and the NPN
N) The 1IEAll#l signal 4z for driving the print wire of the print head II is input to the transistor 1. Although not shown, HEAD#2. ...
, I (EAD 124 signal is NPN) transistor 2
..., 24, printing wire drive coil II,
112. ..., drives I24.

FIG. 2 is an operation time chart of the drive device for wire dot printing of the present invention.

FI? input to the base of the NPN l-transistor 36? Y-BA (J signal only needs to be at a high level during T2, for example, FI?Y- as shown in the figure).
The signal may be a BACK-1 signal, a FRY-BACK-2 signal, or a signal having a waveform intermediate therebetween.

HEADI during T1! 1 signal is at a high level, NPN) transistor 1 is turned on, and the current iI changes from the power supply voltage V Ce to the printing wire drive coil 11, NP
N Flows to ground via transistor l.

Next, during T2, Fl? Since the Y-BACK signal 50 is at high level and the HEADIII signal is at low level, P
The NP transistor 30 is turned on and the NPN transistor 1 is turned off.

As a result, the current i returns to the print wire drive coil 11, and the waveform of the current i becomes like the part Ilb.

Next, during T, the FRY-BACK signal 50 is at a low level, so the PNP) transistor 30 is turned off, and the FIEADIII signal is also at a low level. At this time N
PN') The transistor 1 is turned off, and the ti flowing to the printing wire drive coil j11 has nowhere to go, and a very high back electromotive voltage is generated. When this back electromotive voltage becomes higher than the Zener voltage of the Zener diode 301, the NP
N The base current is supplied to transistor 1, and the NPN
) Transistor 1 turns on. In other words, the Zener diode 301 and the NPN transistor 1 function as one large Zener diode.

As a result, a current f+ flows from the supply voltage Vcc through the print wire drive coil cloud 1, NPN) transistor 1 to ground. As mentioned above, in this case, the voltage between the collector and emitter of the NPN transistor 1 is ■.

is equal to the zener voltage of the zener diode 301,
Since the flyback current is absorbed by a high Zener voltage, the current waveform i becomes like the part II.

In other words, it decays rapidly.

In the case of this circuit, the Zener voltage of the Zener diode 301 is the power supply voltage ■. need to be sufficiently higher.

In the wire dot print head drive device with the above configuration, the drive time T is as shown in FIG.
It is only affected by the MDII signal.

Therefore, the drive time T, is from HEAD month to HEA
Different times can be set for the D124 signals.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

(Effects of the Invention) As described above in detail, according to the present invention, there are a plurality of printing wire drive coils each connected in parallel to the power supply, and a plurality of printing wire drive coils each connected between each printing wire drive coil and the ground. a plurality of head drive transistors, a common flyback transistor connected to short-circuit both ends of each of the print wire drive coils, and a plurality of diodes for short-circuit the print wire drive coils; A Zener diode is connected to each head drive transistor.

Therefore, FLY of the above flyback transistor
-Turn on the BACK signal and turn on the head drive transistor
When the EAD signal is turned on, the drive current rises and FLY
- When the BACK signal is turned on and the HEAD signal is turned off, a flyback current flows, and the FLY-BACK signal and H
Turning off both EAD signals will absorb the flyback current, and by controlling the HEAD signal, the drive time can be set to a different time for each print wire drive coil.

As a result, the drive time can be made variable for each printing wire drive coil depending on whether printing was performed in the previous column (at the previous printing timing), and printing quality can be improved.

Additionally, in the case of a serial wire dot printer, the platen is generally round and the distance between the print head pins and the print paper is long, so the drive time may need to be a little longer, but this can be easily accommodated.

Furthermore, by setting the drive time for each print wire drive coil depending on whether or not the adjacent print wire drive coil is being driven, it is possible to eliminate the influence of magnetic interference between the adjacent print wire drive coils.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a drive device for a wire dot print head showing an embodiment of the present invention, Fig. 2 is an operation time chart of the drive device for wire dot printing of the present invention, and Fig. 3 is a conventional wire dot print head. FIG. 4 is an operation time chart of the drive device for a conventional wire dot print head. 1.2. ..., 24.36...NPN transistor, 30...PNP) transistor, 33.3
4.201...Resistor, 41...HEAD111 signal, 50...FRY-BACK signal, 101.102.
..., 124... diode, 301.302.・
..., 324... Zener diode, 11.112.
..., #24... Printing wire drive coil. Patent Applicant Oki Electric Industry Co., Ltd. Agent Patent Attorney Makoto Kawai (1 other person) FLY-BA
CK-7. Unfired ψ 1 wire F7 Togato U' head, F life; d
, Shigetsugu Kui X Hand Figure 2 HEAD#1: Figure 4

Claims (1)

[Claims] (a) A plurality of print wire drive coils each connected in parallel to a power source; (b) A plurality of print wire drive coils each connected between each print wire drive coil and the ground, and turned on and off by a head drive signal. (c) a common flyback transistor connected to short-circuit both ends of each printing wire drive coil and turned on and off by a flyback signal; (d) the flyback a plurality of diodes connected in a direction to conduct the short-circuit current of the printing wire driving coil between the printing wire driving transistor and each of the printing wire driving coils; (e) connecting the printing wire driving transistor to each of the head driving transistors; 1. A drive device for a wire dot print head, characterized in that a Zener diode is connected for breaking down due to a back electromotive force generated by a coil and for making the head drive transistor conductive.