JP3852263B2 - Ink jet head driving method and ink jet recording apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inkjet head driving method and an inkjet recording apparatus in which ink is ejected by an actuator composed of a piezoelectric material.
[0002]
[Prior art]
Various types of ink-jet heads have been proposed. One of them is a shear-mode ink-jet head. FIGS. FIG. In FIG. 1, 1 is an ink tube, 2 is a nozzle forming member, 3 is a nozzle, 50 is a side wall, 6 is a cover plate, 7 is an ink supply port, and 8 is a substrate. As shown in FIG. 2, the channels 40, 41,... 4M, which are ink flow paths, are formed by side walls 50, 51, 52,. FIG. 1 shows a cross-sectional view of one channel having one nozzle, but in an actual shear mode inkjet head, a plurality of gaps are provided between the cover plate 6 and the substrate 8 as shown in FIG. .. 4M are formed by a plurality of channels 40, 41, 42,... 4M separated by side walls 50, 51, 52,. In the figure, only two channels 40 and 41 are shown. One end of the channel 40 is connected to the nozzle 3 formed in the nozzle forming member 2, and the other end is connected to an ink tank (not shown) by the ink tube 1 through the supply port 7. For example, electrodes 101 and 103 formed in close contact with the side wall 50 and electrodes 102 and 104 in close contact with the side wall 51 are provided. Similarly, electrodes are formed in close contact with each side wall.
[0003]
FIG. 3 is a diagram showing a waveform of a drive pulse applied to the electrode. As shown in FIG. 2B, the electrodes 101 and 102 are connected to the ground, and a positive square wave pulse of + V as shown in FIG. By continuously applying the wave pulse, ink droplets are ejected from the nozzle 3 by the operation described below, and are recorded on the recording material to record an image.
[0004]
The side wall 50 includes side walls 50A and 50B made of two piezoelectric materials having different polarization directions as indicated by arrows in FIG. 2A, and operates as an actuator that is deformed by applying a pulse. When the drive pulse is not applied to the electrodes 103 and 104, the side walls 50 and 51 are not deformed as shown in FIG. 2A, but when the drive pulse having the above waveform is applied between the electrodes 103 and 104 and the ground ( During the application of the positive voltage pulse, an electric field in a direction perpendicular to the polarization direction of the piezoelectric material is generated, and the side walls 50A and 50B are deformed in the joint surface between the side walls 51A. , 51B are also deformed in the opposite direction, and as shown in FIG. 2B, the side walls 50A, 50B and the side walls 51A, 51B are deformed outward, and in this example, the volume of the channel 40 is increased. . Next, as shown in FIG. 2C, while the negative voltage pulse is applied, the side walls 50A, 50B and 51A, 51B are deformed in opposite directions, and the volume of the channel 40 is rapidly reduced. As a result, the pressure in the channel 40 changes to cause an ink droplet due to a part of the ink filling the channel 40 to fly from the nozzle 3. The space D is a space provided so that adjacent channel operations do not affect each other. In the channel 41, ink droplets are ejected by the same operation.
[0005]
[Problems to be solved by the invention]
The electrical load of the circuit that drives the actuator, which is a side wall made of a piezoelectric material, is a capacitive load, and FIG. 4 shows an equivalent circuit of a one-channel drive circuit.
[0006]
The energy used to drive the actuator that causes ink to fly is well known (CV ² ), where C is the actuator capacity, V is the pulse voltage, f _{d is} the repetition frequency of the drive pulse, and N is the number of nozzles. / 2, in the case of a simple rectangular wave pulse with a voltage of only + V, the energy E1 generated by charging / discharging the capacity is E1 = CV ² f _d N. However, as shown in FIG. 3A, the energy E2 when driven by a drive pulse having a waveform having a rising edge P1 of + V and a falling edge P2 of −V is (CV ² ) / 2 at P1, [C (2V) ² ] / 2 at P2, and (CV ² ) / 2 at P3. Therefore, the energy E2 by this pulse waveform becomes (1/2 + 4/2 + 1/2) CV ² f _d N, and becomes 3CV ² f _d N, which is 1.5 times the rectangular wave pulse and 2 pulses. is there.
[0007]
A part of this energy E2 is used to drive the ink flight, but most of the energy is generated as Joule heat in the circuit. Therefore, for example, when driving with a pulse having a repetition frequency of about 20 kHz, the amount of heat generation increases, and as the number of channels N increases, the amount of heat generation increases and becomes a problem.
[0008]
The head drive circuit is mounted on the head unit 20 integrated with the head and supplies driving power, so that most of the heat is generated by the head unit. Since the unit 20 is highly integrated, heat dissipation is difficult.
[0009]
Further, the heat generated by the head unit 20 has an effect such as a change in the viscosity of the ink, thereby changing the flying characteristics of the ink to make it unstable.
[0010]
Furthermore, there is a problem that the head driving circuit mounted on the head unit 20 also has an effect of heat generation.
[0011]
An object of the present invention is to solve the above problems by suppressing the amount of heat generated in the head unit 20 and to provide an ink jet recording apparatus that operates stably.
[0012]
[Means for Solving the Problems]
The object of the present invention is achieved by the following invention.
[0013]
1. A plurality of channels each having an ink flow path and a nozzle connected to the ink flow path are provided by being separated by a plurality of side walls, and the side walls are made of a piezoelectric material to form an actuator. An inkjet head driving method in which ink is ejected from the nozzle by driving with a driving pulse having a positive pulse for expanding the volume of the channel and a negative pulse for reducing the volume of the channel ;
The actuator is driven with the driving pulse provided with a delay time between the falling of the positive pulse and the falling of the negative pulse ,
An inkjet head driving method , wherein f is a natural vibration frequency of the actuator, and the delay time is 1 / (2f) or less .
[0014]
2. A plurality of channels each having an ink flow path and a nozzle connected to the ink flow path are provided by being separated by a plurality of side walls, and the side walls are made of a piezoelectric material to form an actuator. An inkjet head driving method in which ink is ejected from the nozzle by driving with a driving pulse having a positive pulse for reducing the volume of the channel and a negative pulse for expanding the volume of the channel ;
The actuator is driven with the driving pulse provided with a delay time during the transition from the rising edge of the negative pulse to the rising edge of the positive pulse ,
An inkjet head driving method , wherein f is a natural vibration frequency of the actuator, and the delay time is 1 / (2f) or less .
[0015]
3. The one or driving method for an inkjet head according to the 2 absolute value of the pulse voltage of the negative side of the voltage of the positive pulse is characterized by different of Rukoto.
[0016]
4). 4. The method of driving an inkjet head according to any one of items 1 to 3, wherein the delay time is provided in a portion having a substantially intermediate potential between the highest voltage and the lowest voltage of the drive pulse.
[0017]
5). A plurality of channels each having an ink flow path and a nozzle connected to the ink flow path are provided by being separated by a plurality of side walls, and the volume of the actuator and the channel formed of the piezoelectric material is increased. A drive pulse having a positive pulse and a negative pulse for reducing the volume of the channel is output, and has a drive pulse output means for driving the actuator, and the actuator is driven by the drive pulse to operate. An ink jet recording apparatus for causing ink to fly from the nozzle and landing on a recording material,
The drive pulse output means outputs the drive pulse with a delay time between the fall of the positive pulse and the fall of the negative pulse ,
The inkjet recording apparatus , wherein the delay time is 1 / (2f) or less, where f is the natural vibration frequency of the actuator .
[0018]
6). A plurality of channels each having an ink flow path and a nozzle connected to the ink flow path are provided by being separated by a plurality of side walls, and the volume of the actuator and the channel is made of the side wall made of piezoelectric material . Drive pulse output means for driving the actuator by outputting a drive pulse having a positive pulse and a negative pulse for expanding the volume of the channel, and the actuator is driven by the drive pulse to operate, An ink jet recording apparatus for causing ink to fly from the nozzle and landing on a recording material,
The drive pulse output means outputs the drive pulse with a delay time between the rise of the negative pulse and the rise of the positive pulse ,
The inkjet recording apparatus , wherein the delay time is 1 / (2f) or less, where f is the natural vibration frequency of the actuator .
[0019]
7). Absolute value inkjet recording device to the 5 or the 6, characterized in different of Rukoto absolute value and the pulse of the voltage of the negative side of the voltage of the positive pulse.
[0020]
8). 8. The ink jet recording apparatus according to any one of 5 to 7, wherein the delay time is provided in a substantially intermediate potential portion between the highest voltage and the lowest voltage of the drive pulse.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
As described above, the drive energy E2 when the actuator is driven with the drive pulse of FIG. 3A is 3 CV ² fN.
[0022]
On the other hand, in the embodiment of the present invention, the drive pulse is shifted by a delay time Δt between a positive (+) side pulse and a negative (−) side pulse as shown in FIG. By driving the actuator, the drive energy is kept low and the problem due to heat generation in the head unit is solved.
[0023]
Next, the effect of suppressing the heat generation of the head unit in the embodiment of the present invention will be described. When the delay time Δt is set to a time at which the discharge of the positive (+) waveform portion ends, the energy E3 when driven by the pulse having the waveform shown in FIG. 3B is ² CV ² fN, The driving energy E2 is reduced from the energy 3CV ² fN when driven by the driving pulse having the waveform shown in a). However, if the delay time Δt is too long, the ink flying efficiency is deteriorated. On the other hand, the waveform of the drive pulse shown in FIG. 3B actually has a time constant due to the capacitor of the drive circuit system, so that the rise and fall times as shown in FIG. It is desirable to determine the delay time Δt in consideration of this dullness.
[0024]
FIG. 5 shows the change in the flying speed of an ink droplet when an actuator having a natural vibration frequency f of 1 MHz is driven by a drive pulse having the waveform of FIG. 3C and the delay time Δt of the drive pulse is changed. It is a graph. In the graph, the horizontal axis represents time Δt (μsec), and the vertical axis represents the flying speed of ink droplets (m / sec). From this graph, it can be seen that the flying speed of the ink droplet does not change at about 8 m / sec until the delay time Δt is 0.5 μsec, and that the flying speed of the ink droplet rapidly decreases as Δt further increases. When the preferable range of Δt is expressed by the natural frequency f of the actuator, even if the delay time Δt is increased to time 1 / (2f), the ink flying is not actually adversely affected.
[0025]
After all, providing the delay time Δt between the positive (+) side pulse and the negative (−) side pulse of the drive pulse in the range of Δt ≦ 1 / (2f) does not decrease the flying speed of the ink droplet. It is preferable for reducing energy required for driving and suppressing heat generation of the head unit.
[0026]
FIG. 3 shows an example in which the first pulse is driven first and then the negative pulse is driven, but first the negative pulse is driven first, and then the positive pulse is driven. It is also possible to adopt a method, and in this case as well, it is effective to interpose the delay time Δt.
[0027]
FIG. 6 is a circuit diagram showing an example of an actuator drive circuit according to the embodiment of the present invention. Circuits using other analog switches are also effective, and are not limited to these circuits.
[0028]
In FIG. 6, a circuit for driving three channels is shown as an example, but it is assumed that there is actually a circuit configured with a large number of channels and driving up to N channels. 6, the supply voltage + V, the voltage −V, and the ground terminal G are switched by analog switch circuits S1, S2, S3,... SN as drive pulse output means, and the drive pulse having the waveform shown in FIG. The outputs are connected to the actuators C1, C2, C3,... CN of the respective channels to drive the actuators C1, C2, C3,. The switch circuit is formed as an IC as a head drive IC and is mounted on the head unit 20.
[0029]
Based on the image signal GS, the control signal CS is output from the control signal circuit 21 with a delay time Δt between a positive pulse and a negative pulse, and corresponds to the image signal GS among the switches S1 to SN. Only the switch is operated to form the drive pulse shown in FIG. 3B, the corresponding one of the actuators C1, C2,... Is driven to fly the ink, and the ink is made to land on the recording material to make the image. Is recorded.
[0030]
Although the above description is based on the case of driving with the drive pulse having the waveform shown in FIG. 3C, it is also possible to use a drive pulse in which the positive (+) side voltage and the negative (−) side voltage are not necessarily the same. This is possible, and the amount of heat generated in this case will be described.
[0031]
In the drive pulse, the positive (+) side voltage and the negative (−) side voltage do not necessarily have the same absolute voltage value. An example is shown in FIG. The pulse waveform shown in FIG. 7A differs from the pulse waveform shown in FIG. 3 in that the voltage rising to the positive side is + 2V, the voltage falling to the negative side is −V, and the negative side voltage is positive in absolute value. ½ of the side voltage. In the case of driving with such a pulse waveform, as shown in FIG. 7B, the voltage during the delay time Δt is preferably set to +0.5 V from the ground potential. In this way, the portion that contributes to actual driving on both the positive side and the negative side of the pulse is 1.5 V in absolute voltage value, and the term of energy CV ² is C × (1.5) ^2. Take the minimum value. As shown in FIG. 7B, by providing a delay time Δt at a potential approximately in the middle between the highest potential and the lowest potential of the drive pulse, various types of drive pulses having various positive and negative values are used. Efficient energy suppression is possible.
[0032]
【The invention's effect】
According to the first, second, fifth, or sixth invention, it becomes possible to reduce the amount of heat generated in the drive circuit of the ink-jet head as compared with the prior art, and the heat generation in the head unit is suppressed satisfactorily.
[0033]
According to the invention of claim 3 or 7, it is possible to satisfactorily suppress heating in the head unit while preventing a drop in ink droplet flying speed.
[0034]
According to the invention of claim 4 or 8, it is possible to efficiently reduce the driving energy in the driving pulse of various waveforms, and to effectively suppress the heat generation in various types of ink jet heads. Become.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view taken along an ink flow path of an inkjet head.
FIG. 2 is a cross-sectional view across an ink flow path of an inkjet head.
FIG. 3 is a diagram showing waveforms of an example of a driving pulse in a conventional driving method and a driving pulse used in an embodiment of the present invention.
FIG. 4 is a diagram of an equivalent circuit of a drive circuit.
FIG. 5 is a graph showing a relationship between a delay time provided for a drive pulse and an ink flying speed.
FIG. 6 is a diagram showing an example of an actuator drive circuit according to an embodiment of the present invention.
FIG. 7 is a diagram showing another waveform of the drive pulse used in the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ink tube 3 Nozzle 7 Ink supply port 8 Board | substrate 20 Head unit 21 Control signal circuit 40, 41 Channel 50, 51, 52, 53 Side wall 101-104 Electrode

Claims (8)

A plurality of channels each having an ink flow path and a nozzle connected to the ink flow path are provided by being separated by a plurality of side walls, and the side walls are made of a piezoelectric material to form an actuator. An inkjet head driving method in which ink is ejected from the nozzle by driving with a driving pulse having a positive pulse for expanding the volume of the channel and a negative pulse for reducing the volume of the channel ;
The actuator is driven with the driving pulse provided with a delay time between the falling of the positive pulse and the falling of the negative pulse ,
An inkjet head driving method , wherein f is a natural vibration frequency of the actuator, and the delay time is 1 / (2f) or less . A plurality of channels each having an ink flow path and a nozzle connected to the ink flow path are provided by being separated by a plurality of side walls, and the side walls are made of a piezoelectric material to form an actuator. An inkjet head driving method in which ink is ejected from the nozzle by driving with a driving pulse having a positive pulse for reducing the volume of the channel and a negative pulse for expanding the volume of the channel ;
The actuator is driven with the driving pulse provided with a delay time during the transition from the rising edge of the negative pulse to the rising edge of the positive pulse ,
An inkjet head driving method , wherein f is a natural vibration frequency of the actuator, and the delay time is 1 / (2f) or less . Absolute value and the driving method for an inkjet head according to claim 1 or claim 2 absolute value of the pulse voltage of the negative side is characterized by different of Rukoto voltage of the positive pulse.   4. The method of driving an ink jet head according to claim 1, wherein the delay time is provided in a portion having a substantially intermediate potential between the highest voltage and the lowest voltage of the drive pulse. A plurality of channels each having an ink flow path and a nozzle connected to the ink flow path are provided by being separated by a plurality of side walls, and the volume of the actuator and the channel formed of the piezoelectric material is increased. A drive pulse having a positive pulse and a negative pulse for reducing the volume of the channel is output, and has a drive pulse output means for driving the actuator, and the actuator is driven by the drive pulse to operate. An ink jet recording apparatus for causing ink to fly from the nozzle and landing on a recording material,
The drive pulse output means outputs the drive pulse with a delay time between the fall of the positive pulse and the fall of the negative pulse ,
The inkjet recording apparatus , wherein the delay time is 1 / (2f) or less, where f is the natural vibration frequency of the actuator . A plurality of channels each having an ink flow path and a nozzle connected to the ink flow path are provided by being separated by a plurality of side walls, and the volume of the actuator and the channel is made of the side wall made of piezoelectric material . Drive pulse output means for driving the actuator by outputting a drive pulse having a positive pulse and a negative pulse for expanding the volume of the channel, and the actuator is driven by the drive pulse to operate, An ink jet recording apparatus for causing ink to fly from the nozzle and landing on a recording material,
The drive pulse output means outputs the drive pulse with a delay time between the rise of the negative pulse and the rise of the positive pulse ,
The inkjet recording apparatus , wherein the delay time is 1 / (2f) or less, where f is the natural vibration frequency of the actuator . Absolute value and the absolute value of the ink-jet recording apparatus in claim 5 or claim 6, characterized in different of Rukoto pulse voltage of the negative side of the voltage of the positive pulse.   The ink jet recording apparatus according to claim 5, wherein the delay time is provided in a portion at a substantially intermediate potential from the highest voltage to the lowest voltage of the drive pulse.

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