JPH07125195A - Drive method for ink jet head - Google Patents

Abstract

PURPOSE:To obtain an inexpensive drive circuit capable of high-speed printing by reducing a peak total current value to drive piezoelectric devices of a head and eliminating malfunction caused by noise. CONSTITUTION:Piezoelectric devices, as energizing portions to jet ink drops, are driven, lagging by a delay time td for each channel. Peak charge and discharge current values are made lower than when the devices are driven simultaneously by making the delay time td equal to a rise time tr as determined by, for example, an electrostatic capacity Cp and a charge resistance rab, by preventing a peak charge current value consumed during the rise time tr and a peak discharge current value at a fall time from being overlapped.

Description

Detailed Description of the Invention

[0003]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving an inkjet head, and more specifically, in an on-demand type inkjet recording apparatus using a piezoelectric element as a driving source, peak currents when driving the piezoelectric element of the head do not overlap. Thus, the present invention relates to a method for driving an inkjet head that eliminates malfunction due to noise and is driven with low power.

[0004]

2. Description of the Related Art An ink jet recording apparatus having a head for driving a piezoelectric element by a pulse output according to an image signal to generate a pressure wave in a flow path containing ink to eject ink droplets for recording The structure is simple and high quality recorded images can be obtained. The piezoelectric element of the actual inkjet recording apparatus head is driven as follows.

FIG. 12 shows a normal drive block circuit for driving the head. A CPU (central processing unit) 42 and a power source 43 are incorporated in the control board 41, and a control signal output based on image information, that is, a print signal, is transmitted through a control signal line 47 by a furnace line (FPC) to a drive board 44. A piezoelectric element (eg, P
ZT: lead zirconate titanate) drive circuit 45. On the other hand, the piezoelectric element (PZT) drive circuit 45 is connected to the power source 43 via the high voltage line 48 and the ground line 49.
Is applied. The piezoelectric element 46 is divided into a plurality of grooves so as to drive a plurality of flow paths corresponding to the flow paths, thereby forming a multi-channel piezoelectric element 46. The multi-channel piezoelectric element 46 is driven by applying a voltage pulse corresponding to the control signal. The drive board 44 is
The head is mounted on a carriage.

FIG. 13 is a diagram showing a voltage waveform (FIG. 13 (a)) and a current waveform (FIG. 13 (b)) for driving the piezoelectric element. Piezoelectric elements have high resistance and electrostatic capacitance between electrodes,
When the drive pulse is a rectangular pulse due to the charging resistance,
As shown in FIG. 13B, a transient charging current Ipa flows when the pulse rises, and a discharge current Ipb flows when the pulse falls. Therefore, the voltage waveform also changes as shown in FIG. 13 (a), and a time delay occurs in the fall and rise.

Therefore, in a head having N nozzles, if all N channels are simultaneously driven, N × Ipa, N
Since a peak current of × Ipb flows, a power supply with a large current capacity is required. Further, at this time, a large current flows between the high voltage line 48 and the ground line 49 for charging and discharging the piezoelectric element, which becomes a noise source of the control signal, which may cause a malfunction. Alternatively, the circuit pattern may be damaged due to electrical migration. In this way, when all channels are driven simultaneously,
Since a large current flows, a method of shifting the driving timing between adjacent channels can be considered.

For example, in the "ink jet recording apparatus" according to Japanese Examined Patent Publication No. 59-33117, as shown in FIG. 14, each channel is pulse-driven with a phase shift so that the pulses of each channel do not overlap.

FIG. 14 is a time chart of a drive pulse for driving the piezoelectric element for each channel of the conventional ink jet recording apparatus, which shows the case where the number of channels is 3 and the pulse interval (repeating cycle) T is the first. The driving pulses e ₂ and e ₃ of the _second and _third channels are controlled to be inserted at equal intervals during the pulse interval T with respect to the driving pulse e ₁ of the second channel.

However, in the case of a head having a multi-nozzle with the number N of nozzles, the repeating cycle T is restricted to the delay time td × the number N of nozzles as shown in FIG. 14, which is disadvantageous for high-speed printing. Becomes

Further, the embodiment shown in FIG. 15 is disclosed in the "multi-head ink jet recording apparatus" disclosed in JP-A-55-63278.

FIG. 15 is a time chart of drive pulses for driving the piezoelectric elements for each channel in the conventional multi-head ink jet recording apparatus. The pulses output from the pulse generator are sequentially shifted by the clock pulse Cl. Pulse P that is shifted by 1 clock pulse τ
₀ , P ₁ ... P ₄ are output and ₁ according to the pulses P ₀ , P 1
Piezoelectric element drive pulse f whose phase is different only by the clock pulse
p ₁ , fp ₂ ... Are output.

However, in the time charts of FIGS. 14 and 15, no specific study is made from the viewpoint of the peak current generated by driving the piezoelectric element by the drive pulse.

[0014]

[Object] The present invention has been made in view of the above-mentioned circumstances, and by reducing the peak value of the total current for driving a piezoelectric element as an energy acting portion, high-speed printing is possible and an inexpensive drive circuit is provided. It is provided for the purpose of preventing noise and enhancing reliability of the circuit pattern.

[0015]

In order to achieve the above object, the present invention provides (1)
A plurality of parallel flow paths for accommodating the recording liquid to be introduced, a piezoelectric element attached to the flow paths, for generating a pressure wave in the flow paths by applying a pulse, and arranged in each of the flow paths. ,
A plurality of droplet ejection channels including an orifice for ejecting droplets by the pressure wave, a common liquid chamber for introducing the recording liquid into the flow path, and recording liquid introducing means for supplying the recording liquid to the common liquid chamber. In the method of driving an inkjet head having the above-mentioned, the peak value of the charging current or the discharging current for charging or discharging the piezoelectric element should not be overlapped at least partially between arbitrary channels, or (2) Introduction A plurality of parallel flow passages containing the recording liquid, a piezoelectric element attached to the flow passages, for generating a pressure wave in the flow passages by applying a pulse, and arranged in each of the flow passages, A plurality of liquids including an orifice for ejecting liquid droplets by the pressure wave, a common liquid chamber for introducing the recording liquid into the flow path, and a recording liquid introducing unit for supplying the recording liquid to the common liquid chamber. In a method of driving an inkjet head having an ejection channel, when the piezoelectric element is driven by a plurality of pulses, each of the plurality of pulses discharges the charged piezoelectric element at the timing of rising of a pulse for charging the piezoelectric element. At least a part of the pulse falling timing should not be overlapped between arbitrary channels, or (3) a plurality of parallel flow paths for accommodating the recording liquid to be introduced and the flow paths attached to the flow paths. And a piezoelectric element that generates a pressure wave in the flow channel by applying a pulse, an orifice that is disposed in each of the flow channels and that ejects a droplet by the pressure wave, and the recording liquid in the flow channel. An inkjet head having a plurality of liquid droplet ejection channels including a common liquid chamber to be introduced and recording liquid introducing means for supplying the recording liquid to the common liquid chamber. In the driving method, when driving the piezoelectric element in a plurality of pulses, it is matched only timing of the launch of each pulse,
At least a part of the timing of the fall should not be overlapped between arbitrary channels, or (4) a plurality of parallel flow paths for accommodating the recording liquid to be introduced, and attached to the flow paths, A piezoelectric element that generates a pressure wave in the flow channel by applying a pulse, an orifice that is provided in each of the flow channels and that ejects a droplet by the pressure wave, and the recording liquid is introduced into the flow channel. In a method of driving an inkjet head having a plurality of liquid droplet ejection channels including a common liquid chamber and recording liquid introducing means for supplying a recording liquid to the common liquid chamber, between arbitrary channels when the plurality of channels are divided and driven. The pulse delay time of td,
When the rise time of the driving pulse is set to tr, the delay time td is set to 0 <td ≦ tr, or (5) a plurality of parallel flow paths containing the recording liquid to be introduced and the flow A piezoelectric element that is attached to the passage and generates a pressure wave in the passage by applying a pulse;
An orifice that is provided in each of the flow channels and that ejects a droplet by the pressure wave, a common liquid chamber that introduces the recording liquid into the flow channel, and a recording liquid introduction that supplies the recording liquid to the common liquid chamber. In the method of driving an inkjet head having a plurality of droplet ejection channels, the droplet ejection minimum repetition time is Tmin, the total number of channels is N, and the number of simultaneous driving channels is m. When (m ≧ 0),

[0016]

[Equation 2]

It is characterized in that Hereinafter, description will be given based on examples of the present invention. First, a drive device and drive circuit for an inkjet head according to the present invention will be described.

FIGS. 1 (a) and 1 (b) are configuration diagrams for explaining an ink jet head driving device according to the present invention.
1A is a cross-sectional view, and FIG. 1B is BB of FIG. 1A.
It is a line arrow enlarged view. In the figure, 1 is a substrate, 2 is a piezoelectric element,
2a is a non-driving piezoelectric element, 2b is a driving piezoelectric element, 3 is a flow path plate, 3a is an ink flow path, 3b is a wall portion, 4 is a common liquid chamber constituent member, 4a is a common liquid chamber, 5 is an ink supply pipe, 6 is a nozzle plate, 6a is a nozzle, 7 is a drive circuit printed board (PBC), 8 is a lead wire, 9 is a drive electrode, 10 is a groove, 11 is a protective plate, 12 is a fluid resistance, 13 and 14 are internal electrodes. , 15 are upper partition walls.

In the integrated head, the internal electrode 1
The laminated piezoelectric element 2 having 3, 14 is subjected to groove processing in the direction of the flow path 3a corresponding to the flow path 3a.
It is divided into a driving piezoelectric element 2b and a non-driving piezoelectric element 2a.
A filling material is enclosed in the groove 10. The flow path plate 3 is bonded to the grooved piezoelectric element 2 through the upper partition wall 15. That is, the upper partition wall 15 is the non-driving piezoelectric element 2
It is supported by a and a wall portion 3b that separates the adjacent flow path. The width of the driving piezoelectric element 2a is slightly narrower than the width of the flow path 3a,
When a pulsed signal voltage is applied to the driving piezoelectric element 2b selected by the driving circuit on the driving circuit printed board (PCB), the driving piezoelectric element 2b is displaced in the thickness direction, and the flow path 3a is passed through the upper partition wall 15. Changes, and as a result, ink droplets are ejected from the nozzles 6a of the nozzle plate 6.

FIG. 2 is a block diagram of a head drive circuit according to the present invention. Piezoelectric elements Cp ₁ and C 4 of a 4-channel head are shown.
This is for driving p ₂ ... Cp ₄ .

The 4-bit shift register has a clock C.
LK and DAT are input, a pulse shifted with a predetermined phase difference is output and latched by the 4-bit latch circuit 21, and the latch signal is used as one input signal of the AND circuit 22. Image signal EN corresponding to each channel
, ENA2, ..., ENA4 are input to the other input terminals of the AND circuit 22. The output of the AND circuit 22 is a pulse signal according to the image signal, and the output terminals out of the drive circuits Dr ₁ , Dr ₂ , ..., Dr ₄ having the inverter circuit 23 and the booster output circuit to which the power supply voltage Vp is applied. ₁ , o
The piezoelectric elements Cp ₁ , Cp ₂ ... Cp ₄ are driven via ut ₂ ... Out ₄ .

The piezoelectric element of each channel has a power supply voltage Vp.
However, the startup time constant tr is determined by the electrostatic capacitance Cp of the piezoelectric element of each channel × charging resistance rab. Further, as shown in FIG. 2, when the charging resistance and the discharging resistance are common, the falling time constant tf is substantially equal to the rising time constant tr.

FIG. 3 is a diagram showing an example of piezoelectric element drive waveforms in the method of driving an ink jet head according to the present invention. The output terminals out ₁ , out ₂ ... Of the drive circuits Dr ₁ , Dr ₂ ... Dr ₄ in FIG.
The voltage waveform of out ₄ is shown.

Since the driving voltage corresponding to the channel 1 indicated by ch ₁ has the electrostatic capacitance Cp of the piezoelectric element × the rising time constant tr of the charging resistor rab, this should be equal to the falling time constant tf. The charging resistors rab are made equal. The drive voltage ch ₂ of the channel ₂ is obtained by delaying the drive timing with respect to the drive voltage ch ₁ by a time td equal to the rising time constant tr. As described above, in channels 3 and 4, as shown by ch ₃ and ch ₄ , the driving waveforms are sequentially delayed by 2td and 3td within the repeating cycle T.

FIG. 4 shows the charge and discharge waveforms of FIG. 3. The charge current and discharge current of each channel have a peak value every time td within the repeating cycle T,
Since they do not overlap, the peak current is reduced to 1/4 as compared with the case of simultaneous driving (td = 0). In FIG. 4, the case of four channels has been described. However, even if the number of channels is different, peaks of currents generated during charging or discharging of each channel within the repeating period T do not overlap between arbitrary channels. A delay time td between channels can be provided.

FIG. 5 is a diagram for explaining the charging peak current reduction rate according to the method of driving an ink jet head according to the present invention. Specifically, in the case of four channels, the delay time td between the channels and the startup time constant t
It is a figure showing how the reduction rate of the charging peak current when each channel is driven simultaneously changes depending on the relationship of r. In the figure, Ipa ₀ is the peak current value when the delay time td = 0, Ipa is the peak current value at the delay time td, and the drive voltage waveform and the charging current waveform when td / tr = 1 where the delay time td and the rising time constant tr are equal are shown in FIGS. 3 and 4. As shown in the figure, even if td / tr> 1, the peak current reduction rate does not change from that when td = tr. Even if the peak current reduction rate is td / tr <1, the effect is sufficient. The peak current reduction rate is td / tr = 0.25,
The current waveform is as shown in FIG. 6, and although it partially overlaps, the reduction rate is about 50%.

As described above, the peak current reduction rate is td>
If tr is set to N and the number of channels is N, the peak current can be reduced to 1 / N. However, in order to increase the repetition frequency, td = tr, which is the limit for increasing the peak current reduction rate, is set. Is the best. Further, if the peak current reduction rate is sufficient, the peak current reduction rate is td 0 <
The frequency can be increased by setting td <tr.

FIGS. 7 and 8 are diagrams showing drive voltage waveforms when one pixel is formed by arbitrary plural pulses according to the present invention. In order to form dots on the paper surface with one or more ink droplets, FIG. , Between any channels, for example, ch ₁ ,
at least 1 for each pulse on ch ₂ , ch ₃ , ch ₄
One or more start-up timings or fall-down timings are repeated and shifted in the cycle T. In this case as well, the start-up charge current or the fall current does not flow simultaneously in all channels, so it is sufficiently effective. is there.

In FIG. 7, the pulse width of the pulse of the channel ch ₂ is made shorter than that of the pulse of the channel ch ₁ , so that the falling timing of the pulse and the rising and falling timing of the pulse can be shifted. . Also, as shown in channel ch ₃ ,
Pulse ,, pulse width of channel ch ₁ pulse,
,, and by shifting the phase, pulse ,,
It is possible to shift the start and stop timings of the. Channel ch _4, by varying the time delay between the pulse and the time delay between the channel ch ₁ pulse, the channel ch ₁ and ch ₄ pulses launched, it is possible to shift the falling timing.

In FIG. 8, each channel ch ₁ , ch ₂ ,
..., it is obtained by output with a sequential delay time td for each channel at the same pulse period in the repetition period T of the pulse ,, equal same waveform peak value and pulse width from ch _4. At this time, ch ₁ , ch ₂ , ..., ch ₄
The delay time td is set equal to the rising time constant tr or the falling time constant tf of the pulse. Further, not only in the case of a plurality of pulses having the same peak value, but in the case of a pulse group having different peak values, it is possible to efficiently reduce the peak current by shifting the rising and falling timings of the pulse having the highest peak value.

In the above-described embodiment, the push drive method in which the ink droplet is ejected by the pressure wave that presses the flow path by the piezoelectric element that is deformed by the rise of the drive voltage pulse is used, but the drive pulse is negative. This is also applicable to the Pull-Push driving method in which the ink meniscus in the nozzle is attracted by the pulse fall of the negative pulse and the ink droplet is ejected at the rise.

FIG. 9 shows a pulse waveform in which the discharge current has a plurality of discharge currents during the rise and fall times. For example, FIG.
As shown in FIG. 9 (b), the peak currents 1, 2, 3 correspond to the pulse rise and fall, as shown in FIG. 9 (b). , 4,5 occur. If such a driving pulse exists in any channel, the peak current is 1, 2, ... 5
The overall peak current can be reduced by slightly shifting the timing of the occurrence of the noise.

10 (a) and 10 (b) are drive pulse waveforms for explaining still another embodiment of the method for driving an ink jet head according to the present invention. FIG. 10 (a) is a push drive method, and FIG. 10 (b) is an example of the Pull-Push driving method, in which the rising timings of the pulses of the same crest value of channels ch ₁ , ch ₂ , and ch _{3 in} the repeating cycle T are the same, and the falling time is Each is a method of shifting. In this case, since the droplet discharge process is performed during the start-up time,
There is no dot position deviation between channels, and only the peak current can be reduced to almost half. In addition, Pu of FIG.
In the case of the ll-Push driving method, the meniscus is sucked at the time of pulse falling, but the droplet discharge process is performed during the rising time. Therefore, similarly, within the repeating cycle T, ch ₁ ,
ch _2, ch ₃ of the fall may be shifted only the timing of the time of the pulse ,,.

FIG. 11 is a drive voltage waveform for explaining still another embodiment according to the present invention, which is an example of an 8-division drive method in an 8-channel head. Channel Ch ₁ , C
When the equal division delay drive is performed within the minimum droplet discharge repetition time Tmin of h ₂ ... Ch ₈ , the delay time td is td = T
It becomes min / 8. At this time, if the rise time tr of the drive pulse is tr = td or tr <td, the peak current at the time of driving all channels can be reduced to 1/8.

However, if tr <td, the droplet discharge repetition time T is restricted to T ≧ 8td, which is disadvantageous for high frequency driving. Therefore, in the case of the head having the number of channels N, when the equal division delay drive is performed, the droplet ejection minimum turn-around time is Tmin and the number of simultaneously driven channels (m ≧ 0)
Is m,

[0036]

[Equation 3]

It is preferable to have the relationship of Figure 10 above
Although 11 is an example of a single pulse, it can be similarly applied to a plurality of pulse groups.

[0038]

As is apparent from the above description, the present invention has the following effects. (1) Effect corresponding to claim 1: In an arbitrary piezoelectric element drive voltage waveform, the peak of the current waveform does not overlap with other channels, so the peak value of the total current is reduced. Therefore, the capacity of the power supply can be small, so that the cost of the drive circuit can be reduced, the noise can be prevented, and the reliability of the circuit pattern can be improved. (2) Effect corresponding to claim 2: In the pulse drive voltage waveform, the same effect as (1) can be obtained. (3) Effect corresponding to claim 3: Since the pulse rising timings are the same, there is no dot position deviation on the image, and the falling timings are shifted to reduce the peak value of the total current. it can. (4) Effect corresponding to claim 4: Pulse rising time t
Since the delay time td is shorter than r, high-speed printing is possible and the peak current can be reduced. (5) Effect corresponding to claim 5: In split driving, when an equal division delay time is provided, all peak currents are reduced to 1 / N.
/ m, and high-speed printing becomes possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an inkjet head driving device according to the present invention.

FIG. 2 is a block diagram of a head drive circuit according to the present invention.

FIG. 3 is a diagram showing an example of a piezoelectric element drive waveform in an inkjet head drive method according to the present invention.

FIG. 4 shows the charge and discharge waveforms of FIG.

FIG. 5 is a diagram for explaining a charging peak current reduction rate according to the inkjet head driving method of the present invention.

FIG. 6 is a diagram showing a current waveform when td / tr = 0.25.

FIG. 7 is a diagram showing a drive voltage waveform when one pixel according to the present invention is formed by arbitrary plural pulses.

FIG. 8 is a diagram showing a drive voltage waveform when one pixel according to the present invention is formed by arbitrary plural pulses.

FIG. 9 is a pulse waveform in which a discharge current is generated a plurality of times during the rise and fall times.

FIG. 10 is a drive pulse waveform for explaining still another embodiment of the method for driving an inkjet head according to the present invention.

FIG. 11 is a drive voltage waveform for explaining yet another embodiment according to the present invention.

FIG. 12 is a normal drive block circuit for driving a head.

FIG. 13 is a diagram showing a voltage waveform and a current waveform for driving the piezoelectric element.

FIG. 14 is a diagram showing a time chart of drive pulses for driving the piezoelectric element for each channel of the conventional inkjet recording apparatus.

FIG. 15 is a time chart of drive pulses for driving a piezoelectric element for each channel by a conventional multi-head inkjet recording apparatus.

[Explanation of symbols]

1 ... Substrate, 2 ... Piezoelectric element, 2a ... Non-driving piezoelectric element, 2b
... Drive piezoelectric element, 3 ... Flow path plate, 3a ... Ink flow path, 3b
... Wall part, 4 ... Common liquid chamber constituent member, 4a ... Common liquid chamber, 5 ...
Ink supply pipe, 6 ... Nozzle plate, 6a ... Nozzle, 7 ... Drive circuit printed board (PBC), 8 ... Lead wire, 9 ... Drive electrode, 10 ... Groove, 11 ... Protective plate, 12 ... Fluid resistance, 13, 14 ... Internal electrodes, 15 ... Upper partition wall.

Claims (5)

[Claims] 1. A plurality of parallel flow passages for accommodating a recording liquid to be introduced, a piezoelectric element attached to the flow passages for generating a pressure wave in the flow passages by applying a pulse, Each of the orifices is provided with an orifice for ejecting droplets by the pressure wave, a common liquid chamber for introducing the recording liquid into the flow path, and a recording liquid introducing unit for supplying the recording liquid to the common liquid chamber. In a method of driving an inkjet head having a plurality of droplet ejection channels, it is preferable that peak values of a charging current or a discharging current for charging or discharging the piezoelectric element do not at least partially overlap between arbitrary channels. A characteristic method of driving an inkjet head. 2. A plurality of parallel flow passages for accommodating the recording liquid to be introduced, a piezoelectric element attached to the flow passages for generating a pressure wave in the flow passages by applying a pulse, Each of the orifices is provided with an orifice for ejecting droplets by the pressure wave, a common liquid chamber for introducing the recording liquid into the flow path, and a recording liquid introducing unit for supplying the recording liquid to the common liquid chamber. In a method of driving an inkjet head having a plurality of liquid droplet ejection channels, when the piezoelectric element is driven by a plurality of pulses, each of the plurality of pulses charges the piezoelectric element at the timing of rising of a pulse or the charged piezoelectric element. A method for driving an inkjet head, characterized in that at least part of the timing of falling of a pulse for discharging an element does not overlap between arbitrary channels. 3. A plurality of parallel flow passages for accommodating the recording liquid to be introduced, a piezoelectric element attached to the flow passages for generating a pressure wave in the flow passages by applying a pulse, Each of the orifices is provided with an orifice for ejecting droplets by the pressure wave, a common liquid chamber for introducing the recording liquid into the flow path, and a recording liquid introducing unit for supplying the recording liquid to the common liquid chamber. In a method of driving an inkjet head having a plurality of droplet ejection channels, when the piezoelectric element is driven by a plurality of pulses, only the rising timing of each pulse is made coincident and at least a part of the falling timing is arbitrary. A method for driving an inkjet head, characterized in that the channels do not overlap each other. 4. A plurality of parallel flow passages for accommodating the recording liquid to be introduced, a piezoelectric element attached to the flow passages, for generating a pressure wave in the flow passages by applying a pulse, Each of the orifices is provided with an orifice for ejecting droplets by the pressure wave, a common liquid chamber for introducing the recording liquid into the flow path, and a recording liquid introducing unit for supplying the recording liquid to the common liquid chamber. In a method of driving an inkjet head having a plurality of droplet ejection channels, a pulse delay time between arbitrary channels when the plurality of channels are divided and driven is td, and a rising time of a driving pulse is td.
When r, the delay time td is set to 0 <td ≦ tr. 5. A plurality of parallel flow passages for accommodating the recording liquid to be introduced, a piezoelectric element attached to the flow passages for generating a pressure wave in the flow passages by applying a pulse, Each of the orifices is provided with an orifice for ejecting droplets by the pressure wave, a common liquid chamber for introducing the recording liquid into the flow path, and a recording liquid introducing unit for supplying the recording liquid to the common liquid chamber. In a method of driving an inkjet head having a plurality of droplet ejection channels, the minimum droplet ejection repetition time is T
min, N for all channels, m for simultaneous drive channels
When (m ≧ 0), [0001] A method of driving an ink jet head, characterized in that