JP3120812B2 - Drive circuit for inkjet print head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a print head driving circuit used in an ink jet printer.

[0002]

2. Description of the Related Art A drive circuit of a conventional ink jet print head will be described with reference to FIG. FIG. 11 shows one drive circuit for driving one electrostrictive element 600. Here, the transistor 601 and the transistor 602 selectively charge and discharge the electrostrictive element 600 by the drive signal generation means of the transistor 607, and the resistors 604 and 605 determine the charge and discharge speed. By selectively performing such charge / discharge, the electrostrictive element is extended, and ink droplets are ejected and recorded.

However, FIG. 11 shows one piezoelectric element.
However, there is a problem that the number of elements is large and the cost is high. To solve these problems,
As can be seen in JP-A-2-164544, one terminal is
Multiple electrostrictive elements connected in common and connected to a drive signal source
A switching element is connected to the other terminal of each
An ink jet recording head drive circuit has been proposed.

[0004]

According to this, a switch is provided.
One that can reduce the number of chining elements as much as possible
When a voltage waveform that changes rapidly during discharge is required
Requires a switching element with a large rating.
Problems such as increased costs. The present invention
It is made in view of such a problem, and the purpose and
Where switching elements with relatively low ratings
It is another object of the present invention to provide a drive circuit for an ink-jet printing head which allows a large current to flow during discharging .

[0005]

Means for Solving the Problems] In the present invention in order to solve the above problems, an ink jet print head selectively driven according electrostrictive element kicked set corresponding to the plurality of nozzles to a recording signal Drive circuit , one of the poles
Time-varying signal and time towards the other pole
To the one terminal of the electrostrictive element
Scanning voltage generating means, and the other terminal of the electrostrictive element.
Connected and timed towards said one pole and the other pole
Switching element capable of conducting signals that change
And the switching element and the switching element are connected in parallel.
Always conductive only for signals changing towards the other pole
And a diode for maintaining the state.

[0006]

FIG. 1 shows an embodiment of a drive circuit for an ink jet print head according to the present invention. In FIG. 1, 1 is a scanning voltage generating circuit, 2 is a shift clock, 3 is a recording signal,
4 is a latch signal. Also, 10, 11, 12, ...
Are transistors, 20, 31, 22,... Are transistors, 30, 31, 32,.
,... Are latches, 50, 51, 52,.
Is a shift register.

FIG. 2 shows an example of the scanning voltage generating circuit 1.
101 to 103 are PNP transistors, 104 to 107 are NPN transistors, 108 to 110 are resistors, 111 is capacitors, 112 and 113 are control signals, and 114 is a scanning voltage output.

The scanning voltage generating circuit shown in FIG. 2 will be described with reference to a time chart shown in FIG.

(A) When the NPN transistor 104 is turned on by setting the control signal 112 to High level, the PNP transistor 101 flows a constant current Ir until the voltage of the capacitor 111 reaches the power supply voltage VH. When the power supply voltage VH is reached, Ir becomes zero. At this time, the PNP transistor 102 serves to limit the current.

(B) Next, the control signal 112 is set to a low level, and the control signal 113 is set to a high level. NP
N-type transistor 105 allows constant current If to flow until the voltage of capacitor 111 reaches GND. At this time, the NPN transistor 106 serves to limit the current. At this time N
PN transistor 107 and PNP transistor 10
3 compensates for the current drive capability during charging and discharging.

The above operation outputs the scanning voltage output 114 shown in FIG. At this time, the rising time constant Tr of the scanning voltage output 114 is obtained by the following equation when the resistance value of the resistor 108 is Rr, the capacitance of the capacitor 111 is C, and the base-emitter voltage of the PNP transistor 101 is VBE.

Ir = VBE ÷ Rr (1) Tr = C × VH ÷ Ir (2) Similarly, the falling time constant Tf of the scanning voltage output 114
The resistance value of the resistor 110 is Rf, the capacitance of the capacitor is C,
Assuming that the base-emitter voltage of the NPN transistor 106 is VBE, it can be obtained by the following equation.

If = VBE ÷ Rr (3) Tf = C × VH ÷ If (4) where the capacitance C of the capacitor 111 is 10 [pF] ≦ C ≦ 1
0 [nF] is desirable. Hereinafter, the driving method of the present invention will be described. A scanning voltage output 114 shown in FIG. 4 is generated by one example of the scanning voltage circuit 1 described above, and within one scanning period of this scanning voltage, the recording signal 3 is shifted by the shift clock 2 into the shift registers 50, 51, 52,. Are transferred sequentially, and after a predetermined number of transfers, the latch signal 4
0, 41, 42,...

By the transfer of the recording signal, the latch 40,
The signals output from 41, 42,...
t40, 41, 42,... In the case of recording (Fig. 4
, Lout 40, 41, 42,... Are at the High level) are NPN transistors 20, 21, 22,.
Are turned on, and the piezoelectric elements 10, 11, 12,.
According to the waveform of the scanning voltage output 114 shown in FIG.
The voltages of Vpzt 10, 11, 12,... Shown in FIG.

The piezoelectric elements 10, 11, 12,... Expand in accordance with the applied voltage waveform Vpzt10, 11,.
Ink droplets are ejected from the nozzles by the dynamic pressure of the ink generated at this time to form dots on the recording medium.

The ink discharging operation will be described in detail using a part of a print head as shown in FIG. 201 is a nozzle, 202 is a nozzle plate, 203 is ink, 20
4 is an elastic plate, 205 is a piezoelectric element, and 206 is a base.

(A) In a standby state, no voltage is applied to the piezoelectric element 205. (B) As the scanning voltage waveform 114 rises, the piezoelectric element 205 contracts, and the elastic plate 204 becomes the nozzle plate 202.
And sucks ink from an ink channel (not shown).

(C) Next, as the scanning voltage output 114 falls, the piezoelectric element 205 expands, the elastic plate 204 is pushed in the direction of the nozzle plate 202, presses the ink 203, and ejects ink droplets from the nozzle 201. .

In this case, the charge / discharge current is determined by the transistor 20 during charging (rising of the scanning voltage output 114).
, 22 (FIG. 1), flows in the forward direction, and discharges (falls of the scanning voltage output 114).
Flow in the forward direction of 0, 31, 32 (FIG. 1),.

In the case of non-recording (Lout 40 in FIG. 4,
Are low, the NPN transistors 20, 21, 22,... Are off, and no voltage is applied to the piezoelectric elements 10, 11, 12,.

The embodiment of the present invention shown in FIG. 1 has been described above.
On resistance Zo of transistors 20, 21, 22,...
n is the rising time constant Tr of the scanning voltage waveform, considering the delay time of the voltage waveform actually applied to the piezoelectric element, and taking the capacitance of the piezoelectric element as Cp, 0.2 × Tr> Cp × Zon ( 5) Required. Further, in consideration of IC integration, if the maximum driving cycle of the piezoelectric element is f and the number of piezoelectric elements that can be driven by one IC is N, the power consumption of the IC is P
Ip = Cp × VH ÷ Tr (6) P = Zon × Ip × Ip × Tr × f × N (7) In general, when the heat radiation mechanism of the IC is not provided, Zo is set so that the maximum value of P is 0.5 to 1 [W] or less.
Determine n. If a heat dissipation mechanism for IC is provided,
Radiating mechanism and Zo
Determine n.

The transistors 20, 21, 22,...
The off-state resistance Zoff is determined by the following equation: Zoff> 100 × Tr （Cp (8)

The diodes 30, 31, 32,...
Is obtained by the following equation: Id <0.1 × Cp × VH ÷ Tr (9)

Although a laminated piezoelectric element is used as the piezoelectric element 205 used in the example of the print head shown in FIG. 5, sufficient discharge can be obtained when the applied voltage VH is 40 V or less in such a laminated piezoelectric element. Can be

The NPN transistors 20, 21, 2
2,... Are FETs (field effect transistors), SCRs
It is obvious that the same effect can be obtained by replacing the element with a (silicon control sizing element) or the like.

In this embodiment, the control is performed by the combination of the NPN transistor and the diode. However, the same effect can be obtained by using a bidirectional current control element such as a transfer miss gate (analog switch). It is obvious.

When the IC is formed, all components except the scanning voltage circuit 1 and the piezoelectric elements 10, 11, 12,... Shown in FIG. The print head and its vicinity can be mounted in a space-saving manner, and can be controlled only by connecting a few control signals.

In this embodiment, the piezoelectric element 10, the diode 31, and the transistor 20 constitute one set, and the connection between the output 114 of each set of scanning voltage generating means and the piezoelectric elements 10, 11,. Possible impact. Therefore, the PNP transistor 107 shown in FIG.
The output impedance of the current amplifier circuit (or the output impedance of the scanning voltage generating means) constituted by the N-type transistor 103 is set as follows.

The maximum output voltage and output impedance of the current amplifier circuit are VH and Zout, and the current flowing through
Assuming that p and the number of sets connected to the common electrode are n (n is a natural number of 2 or more), Zout ≦ VH ÷ (n × Ip) × m (10) where m ≦ 1 is a margin in consideration of variation ( m
= 0.5 is desirable).

FIG. 6A shows another embodiment of the scanning voltage circuit 1. 301 to 305 are PNP transistors, 3
06 to 309 are NPN transistors, 310 is a diode, 311 is a capacitor, 312 to 317 are resistors, 318 and 319 are control signals, and 320 is a scanning voltage output.

[0031] FIG 6 (a) is illustrated by the time chart of FIG. 6 (b).

(A) When the control signal 318 is set to Low level and the PNP transistor 302 is turned on,
PNP transistor 302 allows constant current Ir to flow until the voltage of capacitor 311 reaches power supply voltage Vcc. At this time, the piezoelectric element usually loses the piezoelectric effect when a reverse electric field is applied. Therefore, the diode 310 protects the piezoelectric element from increasing the voltage above the GND level. At this time, PN
P-type transistor 301 serves to limit the current.

(B) Next, when the control signal 318 is set to the high level, the control signal 319 is set to the low level, and the PNP transistor 303 is turned on, the voltage of the capacitor 311 is changed to the power supply voltage VH- by the NPN transistor 307. The constant current If is allowed to flow until the current reaches. At this time, the NPN transistor 306 serves to limit the current. At this time, the NPN transistors 308 and 309 and the PNP transistors 304 and 305 compensate for the current driving capability at the time of charging and discharging.

With the above operation, the scanning voltage output 320 shown in FIG. 7 is output. When the scanning voltage output 320 is used in the embodiment of the present invention shown in FIG. 1, similar to the above-described operation, in the case of recording (Lout 40, 41, 42,... In FIG.
Level) are NPN transistors 20, 21, 2
Are turned on, and the piezoelectric elements 10, 11, 1
7, the voltages Vpzt 10, 11, 12,... Shown in FIG. 7 are applied in accordance with the waveform of the scanning voltage output 320 shown in FIG. Piezoelectric elements 10, 11, 12, ...
Extends in accordance with the applied voltage waveform, and ejects ink droplets from nozzles by the dynamic pressure of ink generated at this time to form dots on the recording medium.

The ink discharging operation will be described in detail using a part of a print head as shown in FIG.

FIG. 7A shows a state in which the piezoelectric element 205 is contracted in a standby state because a voltage is applied to the piezoelectric element 205, and the elastic plate 204 is pulled in a direction opposite to the nozzle plate 202 to suck ink from an ink flow path (not shown). ing.

In (b), as the scanning voltage output 320 rises, the piezoelectric element 205 expands, the elastic plate 204 is pushed in the direction of the nozzle plate 202, presses the ink 203, and ejects ink droplets from the nozzle 201. Next, when the scanning voltage output 320 falls, the piezoelectric element 205 contracts.

The process returns to the standby state (c).

In this case, the charge / discharge current is set at the time of charging (rising of the scanning voltage output 320) by the diodes 30, 3
1, 32,... Flows in the forward direction, and when discharging (falling of the scanning voltage output 114), the NPN transistor 2
Flow in the forward direction of 0, 21, 22,.

In the case of non-recording (Lout 40 in FIG. 8,
Are low levels, the NPN transistors 20, 21, 22,... Are turned off, and the piezoelectric elements 10, 11, 12,. Is applied with the power supply voltage VH-.

Further, as described in the scanning voltage circuit of FIG. 2, the equations (1), (2), (3), (4) and (10) are similarly applied.

The charging / discharging means of the embodiment of the present invention is shown in FIG.
Although the description has been made with reference to the scanning voltage generating means of FIG. 6, a similar effect can be obtained by the charge / discharge circuit as shown in FIG.

In FIG. 9, 501 and 502 are resistors, and 503 is N
A PN transistor, 504 is a capacitor, 505 is a control signal, and 506 is an output signal.

The resistance values of the resistors 501 and 502 are represented by R1 and R2.
R1 >> R2 (11) When the control signal 505 turns on the NPN transistor 503, the output signal 506 becomes GN.
It becomes D level.

Next, when the NPN transistor 503 is turned off by the control signal 505, the potential V of the output signal 506 becomes higher.
Assuming that the power supply voltage is VH and the capacitance of the piezoelectric element is C, out1 is as follows: Vout1 = VH × (1−exp (−t1 ÷ R1 ÷ C)) (12), and the piezoelectric element is charged. Here, t1 is the time since the NPN transistor 503 was turned off.

Next, when the NPN transistor 503 is turned on, the potential Vout2 of the output signal 506 becomes Vout2 = VH × exp (-t2 ÷ R2 ÷ C) (13), and the piezoelectric element is discharged.

The above-described charge / discharge operation results in a waveform as shown in FIG. FIG. 10 shows the control signal 505 and the output signal 50.
6 is shown.

Further, the capacitor 504 is for preventing the capacitance C from largely changing according to the number of selected piezoelectric elements, and for reducing the variation in the time constant of charging and discharging.

[0049]

In the present invention, as described above, according to the present invention,
The recording signal is sent to the electrostrictive elements provided corresponding to the multiple nozzles.
Ink-jet print head selectively driven according to
Change in time toward one pole
Signal and a time-varying signal towards the other pole
Scanning voltage generating means for supplying to one terminal of the electrostrictive element,
Connected to the other terminal of the electrostrictive element, one pole, and the other
Can conduct time-varying signals toward the
Switching element and a parallel connection with the switching element.
For signals that follow and change towards the other pole
Since it has a diode that always keeps the conduction state,
Without the need for large rated switching elements,
Drive by increasing the current capacity of the signal changing to the other pole
Signal delay and distortion can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a drive circuit of an ink jet print head of the present invention.

FIG. 2 is a diagram showing an example of a scanning voltage circuit of the present invention.

FIG. 3 is a time chart of an example of a scanning voltage generation circuit.

FIG. 4 is a time chart of the embodiment of the present invention.

FIG. 5 is a diagram showing an operation example of the print head of the present invention.

FIG. 6 is a diagram showing another embodiment of the scanning voltage generation circuit and a time chart.

FIG. 7 is a time chart of another embodiment of the present invention.

FIG. 8 is a diagram showing another operation example of the print head.

FIG. 9 is a diagram showing another example of the charging / discharging means.

FIG. 10 is a time chart of another example of the charging / discharging means.

FIG. 11 is a diagram showing a conventional example of a drive circuit of an ink jet print head.

[Explanation of symbols]

 Reference Signs List 1 scanning voltage generating circuit 3 recording signal 10, 11, 12 piezoelectric element 20, 21, 22 NPN transistor 30, 31, 32 diode 112, 113 control signal 114 scanning voltage output 201 nozzle 202 nozzle plate 203 ink 204 elastic plate 205 piezoelectric element

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/045 B41J 2/01 B41J 2/055

Claims (1)

(57) [Claims] In the driving circuit of claim 1] Inkjet <br/> preparative printheads to the electrostrictive element kicked set corresponding to the plurality of nozzles selectively driven according to recording signals, towards the one pole Time-varying signal and the other pole
And a signal that changes over time with one of the electrostrictive elements.
Scanning voltage generating means for supplying a terminal, the one terminal connected to the other terminal of the electrostrictive element,
And conducting a time-varying signal towards the other pole
A switching element, which is connected in parallel with the switching element, and
Only for signals that change toward the
A drive circuit for an ink jet print head comprising a diode to be maintained .