JPH02220850A - Driving circuit for impact dot head - Google Patents

Abstract

PURPOSE:To eliminate an increase in energy consumption due to the heating of a Zener diode and to improve energy converting efficiency and the stability of a current waveform by allowing a driving signal generator to vary the leading edge of a coil current in two stages. CONSTITUTION:In the driving signal generator 10, a current flowing into the coil gradually increases according to the time constant of the coil 3 and that of a driving circuit as the current waveform (i) of the coil 3 shows, when a PNP transistor 5 and an NPN transistor 4 are simultaneously turned on. After first predetermined time t0 has passed, the NPN transistor 4 is turned off. Counter-electromotive force generated in this instance is effectively used as a trailing edge current circulating a coil 5 via the turned on PNP transistor 5 and a diode 7. After second set time t1 has passed, the PNP transistor 5 is turned off, and the counter-electromotive force of the coil 3 is quickly absorbed to a high voltage power line V1 from an unstabilized power source voltage V2 via a counter-electromotive force absorbing diode 8.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention reduces heat generation in the current switching element and continuous power absorption element of the coil in driving a high-response frequency multi-bin wire dot head, thereby improving power efficiency. The present invention relates to a drive circuit for a wire dot head that is inexpensive and has a stable one-fall waveform.

[Conventional technology]

Among printers that print characters or bit images using a dot matrix, serial type printers that use a wire as a print head are widely used because they can produce copies and have excellent cost performance.

An example of a conventional wire drive circuit is a patent advertisement published in 1986.
2-261432, and is driven by the drive timing shown in FIGS. 6(a) and 6(b) by the circuit configuration shown in FIG. 5. In FIG. 5, 14 is an NPN transistor which is a switch for driving a coil, 15 is a PNP transistor which is a switch for absorbing back electromotive force, and 16 is a Zener diode for absorbing back electromotive force. As shown in FIG. 6, the NPN transistor 14 is turned off by the 81 signal.
NL, current begins to accumulate in the coil, S1 signal OF F I
The PNP transistor is turned on by the nS2 signal.
, the back electromotive force is absorbed as a current circulating through the coil 3, and then the S2 signal is turned off and the back electromotive force is returned to the power supply via the Zener diode 16.
As shown in Figure (d), a surge occurs when the signals Sl and 82 are switched, and the coil current changes rapidly as shown in Figure (C). Further, when the Zener diode operates, the back electromotive force becomes heat generation in the Zener diode and is consumed. Figure 7 shows another example of the conventional patent publication No. 63-25407.
With the circuit configuration as shown in FIG. 7, 35.8 in FIG. 38. Driven by S7 signal. 7th
In the figure, 18° and 19 are coil drive switches N.
A PN transistor, 20 is a PNP transistor which is a switch for controlling the voltage drop, and 13 is a Zener diode for absorbing back electromotive force. 35.3 as shown in Figure 8
6.37 signal causes said NPN l-transistor, PN
The P transistor turns ON at the same time, current begins to flow to the coil, and after the S5 signal turns OFF, power flows to the coil via the flywheel diode 21, and then after the 86 signal turns OFF, a back electromotive force flows to the power source via the diode 22 and the Zener diode. Absorbed. If the Zener diode is not connected, the 86 signal is OFF as shown in Figure 8.
If the subsequent fall of the coil current becomes gradual and the energization cycle to the coil is short, the back electromotive force cannot be absorbed completely within one cycle, and other coils/coils 8 whose one end is commonly connected to the coil 3 When the coil 3 is driven, as shown by the broken line and the hatched part of the current waveform 11 in FIG. 8, when the coil 3 is not activated, the current swells and the printing ribbon gets caught, reducing the reliability of the operation.

Therefore, in order to make the wire pin respond quickly, the Zener diode had to be added.

[Problem to be solved by the invention]

First, the conventional drive circuits shown in Figures 5 and 7 require a Zener diode to absorb the back electromotive force, and when driving an impact dot head with a high response frequency and multiple bins, the heat generation This method has disadvantages such as increased energy consumption and a significant decrease in conversion efficiency, as well as an increase in the cost of the drive circuit. Second, in the case of the conventional drive signal as shown in FIG. 6, there was another drawback in that the coil current suddenly changed when No. 18 was switched.

[Means to solve the problem]

The impact head drive circuit of the present invention is a drive circuit that controls the fall of the current flowing through the coil.One end of the coil is connected to one side of the power supply line via the drive switch 4, and the other end of the coil is connected to the power supply voltage. The connection point between the drive switch 4 and the coil is connected to the power supply line of the stabilized voltage v2, and the power supply voltage before the power supply voltage stabilization is output from the power supply smoothing circuit via the back electromotive force absorption diode 8. Is the voltage v1 higher than v2? ! The first feature is that the connection point is connected to the power supply line of the voltage v2 via a switch 5 and a diode 7 for switching back electromotive force absorption circuit, and In the drive circuit configuration having the following characteristics, the drive signal generator 10 simultaneously turns on the drive switches 4 and 5 when driving the wire pin.
L After the first set time has elapsed, the drive switch 4 is turned OFF.
The second feature is that a timing signal is generated to turn off the drive switch 5 after a second set time has elapsed, and the falling current of the coil 3 is changed in two stages. Furthermore, as another drive circuit for controlling the fall of the current flowing through the coil of the wire pin, one end of the coil is connected to one side of the power supply line via the drive switch 9, and the other end of the coil is connected via the drive switch 4. The connection point between the drive switch 9 and the coil is connected to the other power supply line to which the drive switch 9 is not connected via a back electromotive force absorption diode 11, and the drive switch 9 is connected to the other power supply line. 4
The connection point between the coil 3 and the coil 3 is connected to a power line having a higher voltage than the power supply voltage before stabilization, which is output from the power supply smoothing circuit via the back electromotive force absorption diode 12. This is a characteristic feature.

[Effect]

As described above, according to the drive circuit configuration and drive timing of the impact dot head of the present invention, when driving an impact dot head with multiple bins of high response frequency, increase in energy consumption due to heat generation of the Zener diode can be eliminated, and the drive circuit can be It becomes possible to drive an impact dot head with low cost, high energy conversion efficiency, and good current waveform stability.

〔Example〕

An embodiment of the head drive circuit for an impact dot printer according to the present invention will be described below.

FIG. 1 is a drive circuit diagram. One end of the coil is a driving NP
Connected to the ground line of the power supply line via the N transistor 4,
The other end of the coil is connected to the power line of the voltage v2 after the power supply voltage has been stabilized, and the connection point between the drive NPN transistor 4 and the coil is connected to the power output from the power supply smoothing circuit via the back electromotive force absorption diode 8. The above power supply voltage before voltage stabilization■
The connection point is further connected to the power line of the power supply voltage v2 via a PNP transistor 5 and a diode 7 for switching back electromotive force absorption circuit. FIG. 2 shows the drive timing and the drive current flowing through the coil 3. In response to a print command signal generated by software or hardware, the drive signal generator 10 connects the PNP transistor 5 and the NPN l-
When the transistors 4 are turned on at the same time, the current flowing through the coil is as shown in the 199m type i of the coil 3 in Fig. 2.
and gradually increases according to the time constant of the drive circuit.

Then, when the first set time to set in advance has elapsed, the NPN transistor 4 is turned off. The back electromotive force generated at this moment is ONI.

It is effectively consumed as a falling current flowing back through the coil 5 through the PNP l-transistor 5 and the diode 7. Further, since the back electromotive force circulates through the PNPI transistor 5 which is already turned on, there is no sudden change in the falling current waveform. After that, P.N.
P) The transistor 5 is turned off after the second set time t1 shown in FIG. It is quickly absorbed into the power supply line (1) which has a higher voltage than the power supply voltage (2).

FIG. 3 shows a case where the above embodiment is implemented to drive a plurality of coils. The rumor is that it is a mixed current blocking diode,
This is provided to control the currents of the coils 3 and 23 separately. The PNP transistor 5 and diode 7 for switching the back electromotive force absorption circuit, and the back electromotive force absorption diode 8 are used in common for a plurality of coils within the range permitted by their electrical ratings. In the embodiment shown in FIG. 3, two coils are connected.

Another embodiment is shown in FIG. 4, one end of the coil 3 is for driving N.
The other end of the coil 3 is connected to the power line of the voltage v2 output from the power supply voltage stabilizing circuit through the driving PNP transistor 9, and the PNP Transistor 9 and coil 3
The connection point between the NPN transistor 4 and the coil 3 is connected to the ground line via a back electromotive force absorption diode 11, and the connection point between the NPN transistor 4 and the coil 3 is outputted from the power supply smoothing circuit via a back electromotive force absorption diode 12. It is connected to a power supply line with a voltage v1 of 1 fli [volts] lower than the power supply voltage v2 before the power supply voltage is stabilized. As shown in the first flow in the drive timing and drive ' flowing through the coil 3 in FIG. S4
When a signal is generated, the PNP transistor 9 and the NPN
Transistor 4 turns on at the same time. The current flowing through the coil 3 gradually increases according to the time constant of the coil 3 and the drive circuit, as shown in the current waveform 1 of the coil 3 in FIG.
Then, when the first set time to set in advance has elapsed, the PNP l-transistor 9 is QFFed. The back electromotive force generated at this moment is effectively consumed as a falling current flowing back through the coil 3 via the NPN transistor 4 and diode 11. Then, the NP
The N transistor 4 is turned off after the second set time t1 has elapsed, and the back electromotive force of the coil 3 is absorbed by the back electromotive force absorbing diode 12.
It is quickly absorbed into the power supply line v1, which has a higher voltage than the power supply voltage v2 before the power supply voltage stabilization, which is outputted from the power supply smoothing circuit via the power supply voltage smoothing circuit.

It is obvious that semiconductor elements such as FETs and thyristors can be used as the drive switch of the present invention in place of the transistors in the embodiments.

〔Effect of the invention〕

As described above, according to the drive circuit configuration and drive timing of the impact dot head of the present invention, when driving an impact dot head with multiple bins of high response frequency, increase in energy consumption due to heat generation of the Zener diode can be eliminated, and the drive circuit can be It becomes possible to drive a wire dot head with low cost, high energy conversion efficiency, and good current waveform stability.

[Brief explanation of the drawing]

FIG. 1 is a driving circuit diagram of the impact dot head of the present invention, FIG. 2 is an explanatory diagram of its timing signal, FIG. 3 is another driving circuit diagram of the impact dot head of the present invention, and FIG. 4 is a diagram of the driving circuit of the impact dot head of the present invention. Still another driving circuit diagram of the impact dot head and an explanatory diagram of the timing signal. FIG. 5 is a diagram of the driving circuit of the conventional impact dot head, and FIG. 6 is a first diagram of the timing signal. 1.2... Smoothing capacitors and above Applicant Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki and 1 other person Figure 2 Figure 3 Figure 51゜

Claims (3)

[Claims] (1) In a dot matrix printer in which wire pins are selectively driven by a print command to print characters or bit images, one end of the coil is used as a drive circuit to control the fall of the current flowing through the coil of the wire pin. It is connected to one side of the power supply line via the drive switch (4), and the other end of the coil is connected to the power supply line of the voltage V2 after the power supply voltage has been stabilized, and the first drive switch (4) and the The connection point of the coil is connected to a voltage (V
1), and the connection point is further connected to the power supply line of the power supply voltage (V2) via a second switch (5) for switching back electromotive force absorption circuit. Impact dot head drive circuit. (2) When driving the wire pin, the drive signal generator (10) turns on the first and second drive switches (4, 5) at the same time.
N, generates a timing signal to turn off the first drive switch (4) after a first set time elapses, and then turns off the second drive switch (5) after a second set time elapses; The impact dot head drive circuit according to claim 1, further comprising a drive signal generator (10) that changes the falling current of the coil (3) in two stages. (3) As a drive circuit that controls the fall of the current flowing through the coil of the wire pin, one end of the coil is connected to one side of the power supply line via the drive switch (9), and the other end of the coil is connected to the drive switch (4). ), and the connection point between the drive switch (9) and the coil is connected to the other power supply line to which the drive switch (9) is not connected, and a back electromotive force absorption diode (11 ), and the connection point between the drive switch (4) and the coil (3) is connected to the power supply voltage before stabilization, which is output from the power supply smoothing circuit via the back electromotive force absorption diode (12). A drive circuit for an impact dot head, characterized in that the drive circuit is connected to a power supply line having a voltage higher than the power supply voltage (V2).