JP2001301158A - Ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem such that power for driving a head is substantially consumed to generate heat in a circuit for driving an ink jet actuator and generated heat gives an adverse effect on the ink and causes unstable operation. SOLUTION: A drive section of an actuator is separated into an analog switch circuit and a drive pulse generating circuit and output impedance of the drive pulse generating circuit is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an ink jet recording apparatus in which a large number of channels having ink flow paths connected to nozzles are formed separated by a plurality of side walls made of a piezoelectric material.

[0002]

2. Description of the Related Art Various types of ink jet heads have been proposed, one of which is a shear mode ink jet head. FIGS. 1 and 2 are Japanese Patent Application Laid-Open No. 10-27277.
FIG. 1 is a diagram illustrating an example of a shear mode inkjet head (hereinafter simply referred to as a head) described in Japanese Patent Publication No. 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. 4M, which are ink flow paths, are formed by side walls 50, 51, 52,... 5N separating the channels, the cover plate 6, and the substrate 8 as shown in FIG.

FIG. 1 shows a cross-sectional view of one channel having one nozzle. In an actual shear mode ink jet head, as shown in FIG. A plurality of side walls 50, 51, 52,.
Channels 40, 41, 42,... 4M separated by 5N
Are formed in large numbers. In the figure, 2 of channels 40 and 41
Only the channels are shown. One end of the channel 40 is connected to the nozzle 3 formed on the nozzle forming member 2, and the other end is connected to the ink tank (not shown) by the ink tube 1 via the supply port 7. Then, for example, electrodes 101 and 103 closely attached to the side wall 50 and electrodes 102 and 104 closely attached to the side wall 51 are provided, respectively. Similarly, electrodes are formed in close contact with the respective side walls.

FIG. 3 is a diagram showing a waveform of a driving pulse applied to the electrodes. As shown in FIG.
01 and 102 are connected to ground, and the electrodes 103 and 10 are connected.
By applying a rectangular wave pulse having a peak value V as shown in FIG. 3A to 4, an ink droplet is made to fly from the nozzle 3 by the operation described below, and is made to fly on a recording material to record an image.

The side wall 50 is composed of side walls 50A and 50B made of two piezoelectric materials having different polarization directions as shown by arrows in FIG. 2A, and operates as an actuator which is deformed by applying a pulse. . Electrode 103
2 (a) when no drive pulse is applied to
Although the side walls 50 and 51 are not deformed as described above, when the drive pulse having the above-described waveform is applied between the electrodes 103 and 104 and the ground (see FIG. 2B), the direction perpendicular to the polarization direction of the piezoelectric material is obtained. Electric field is generated, and shear deformation occurs in the joining surfaces of the side walls 50A and 50B, and also the side walls 51A and 51B similarly cause shear deformation in the opposite direction, and as shown in FIG. 2B, the side walls 50A and 50B And the side walls 51A and 51B are deformed outward from each other, and in this example, the volume of the channel 40 is increased. Next, the drive pulse falls, and the electrodes 103 and 104 and the electrodes 101 and 102 have the same potential, and the side walls 50A and 50B and 51A and 51B are shown in FIG.
Return to the state of (a). At this time, the volume of the channel 40 is rapidly reduced, and a change in the pressure in the channel 40 causes ink droplets 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.

[0006]

A drive circuit for driving an actuator which is a side wall made of a piezoelectric material is a capacitive load as an electric load. FIG. 3B shows an equivalent circuit of a one-channel drive circuit. Show.

The energy E used for driving the ink flying is well known, assuming that the capacity of the actuator is C, the pulse voltage is V, the frequency of the driving pulse applied is f _d , and the number of nozzles is N (CV). ^{From 2} ) / 2, the energy E generated by charging / discharging the capacity is E = CV ² · f _d ·
N.

[0008] A part of this energy E is used to fly ink, but most of the energy is converted into Joule heat in the circuit to generate heat. So, for example,
In the case of driving with a pulse having a repetition frequency of about 20 kHz, there is a problem in that the heat generation increases, and the heat generation of the head increases as the number of channels increases.

FIG. 4 shows an example of a conventional driving circuit for driving a head. Although only two-channel driving circuits are shown in the figure, there are actually many N-channel driving circuits, and a voltage V applied to the electrodes of the actuators C1 and C2 is, for example, n.
It is generated from switch circuits S1 and S2 in which CMOS and pCMOS FETs are complementarily combined. Switch circuit S
1, S2 is individually controlled by a drive pulse formed based on an image signal to perform a switching operation.

As described above, the switch circuits S1 and S2 perform the switching operation based on the image signal, drive the actuator, cause the ink to fly from the nozzles, and make the ink fly on the recording material to form an image.

Normally, the drive circuit of FIG. 4 is integrated as a driver IC chip 21a. Then, the head having the driver IC 21a, the actuators C1 and C2, and the ink manifold are connected to the head unit 23a.
Is configured. Most of the heat generated by the drive power is generated in the head unit 23a, that is, the drive circuit. And a head unit 23a including the driving circuit.
Is difficult to dissipate heat because of high integration.

Further, there is a problem that the heat generated by the head unit 23a has an effect such as a change in the viscosity of the ink, and the flying (ejection) characteristics of the ink are changed to be unstable. Further, there is a problem that heat is also exerted on a head driving circuit mounted on the head unit.

An object of the present invention is to solve the problem of heat generation in the head unit and to provide an ink jet recording apparatus which operates stably.

[0014]

The object of the present invention is achieved by the following invention.

1. A plurality of channels each including an ink flow path and a nozzle connected to the ink flow path are provided separated by a plurality of side walls made of a piezoelectric material, and the ink is ejected from the nozzles by driving an actuator formed of the side walls. An ink jet recording apparatus that forms an image by causing ink to fly on a recording material, wherein a driving unit of the actuator includes a driving pulse generation circuit that drives the actuator, and an analog switch that selectively passes a driving pulse. Wherein the drive pulse generation circuit is separated from a head unit including the analog switch and the actuator, and an output impedance of the drive pulse generation circuit is larger than an impedance of the head unit. Inkjet recording apparatus.

2. The frequency of the natural vibration of the actuator is f, and the drive pulse generation circuit has an output impedance such that the time constant of a drive circuit system including the actuator is substantially 1 / (2f). 2. The ink jet recording apparatus according to 1.

3. 3. The ink jet recording apparatus according to 1 or 2, wherein the output impedance is adjusted by a resistor provided at an output section of the drive pulse generation circuit.

4. The inkjet according to any one of claims 1 to 3, wherein the actuator and the analog switch are provided on the head unit, and the drive pulse generating circuit is provided on a circuit board other than the hand unit. Recording device.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Even though the amount of heat generated by the entire drive system for driving an actuator is determined, the place where heat is generated differs depending on the impedance of each part.

In the embodiment of the present invention, the above-mentioned problem due to heat generation is eliminated by separating the circuit configuration concentrated on the head unit and reducing the ratio of the heat generation amount in the head unit to the total heat generation amount. Solved.

That is, the drive section for driving the actuator for ejecting ink is separated into an analog switch and a drive pulse generation circuit, and the effective output impedance of the drive pulse generation circuit is made larger than the impedance of the head unit including the analog switch. This suppresses heat generation in the head unit provided with the analog switch.

FIG. 5 is a circuit diagram of a driving section of the actuator according to the embodiment of the present invention. In FIG. 5, a circuit for driving four channels is shown as an example. However, in an actual ink jet printing apparatus, many channels are provided, and in the following description, it is assumed that there is a circuit for driving up to N channels. .

In FIG. 5, the drive unit has a drive pulse generation circuit 20, analog switches S1, S2,... SN and an image signal circuit 22, and the drive pulse generation circuit 20 and the image signal generation circuit 21 are a head unit. 23b is provided on a motherboard 24 which is a separated circuit board.
The drive IC 21b and the actuators C1, C2,... CN constituting the analog switches S1, S2,.
Is provided in the head unit 23b. The drive pulse generation circuit 20 generates a drive pulse having a constant repetition period and a constant voltage V, inputs the drive pulse to a drive IC 21b indicated by a broken line, and outputs analog switches S1, S corresponding to each channel.
2, S3, S4,... SN are input to signal terminals. The outputs of the analog switches S1, S2,... SN are the actuators C1, C2, C3, C4 of the respective channels.
..Connected to CN and each analog switch S1, S
2,... SN ground terminals are commonly connected to ground to form a drive unit. Analog switch S1,
S2,... SN selectively transmit the drive pulse of the drive pulse generation circuit 20 to the actuators C1, C2,. -Drive CN.

Hereinafter, analog switches S1, S2,.
A case where the signal terminal of the SN is switched to the ON state will be described as ON, and a case where the signal terminal is switched to the ground terminal will be described as OFF. Then, based on the control signal from the image signal circuit 22, only the switch corresponding to the control signal among the analog switches S1, S2,... SN is operated and turned on, and the drive pulse is turned on to the actuators C1, C2,. Drive the corresponding CN to fly the ink and fly the recording material to form an image; Further, the drive IC 21b is provided on the head unit 23b shown by the dotted line in FIG. 5, and is integrally formed. The drive pulse generation circuit 20 and the image signal circuit 22 are provided on the motherboard 24 separated from the head unit 23b. .

FIG. 6A shows that the frequency f of the natural vibration is 1 MHz.
z, the actuator C1 (or C2,... C)
9 is a graph in which the change in the flying speed of the ink droplet is measured when N) is driven by a drive pulse having a constant voltage V and a constant pulse width W, and the rise time ΔT of the drive pulse is changed. FIG. 6B shows the waveform of the drive pulse of the δT drive pulse in which the rise time is ΔT and the fall time is ΔT. Normally, the rise and fall are determined by the time constant.
T and δT are the same value.

In FIG. 6A, the horizontal axis indicates the rise time ΔT (fall time δT) (μsec), and the vertical axis indicates the flying speed (m / sec) of the ink droplet. From this graph, the flying speed of the ink droplet does not change at approximately 8 m / sec until the rising time ΔT (falling time δT) is 0.5 μsec. I understand. Therefore, if the output impedance of the drive pulse generation circuit 20 in FIG. 5 is made larger than the impedance of the head unit 23b when ΔT is within the range of 0.5 μsec,
Most of the heat is generated by the motherboard 24, which easily radiates heat, without lowering the flying speed of the ink droplets. If the output impedance of the drive pulse generation circuit 20 is smaller than the impedance of the head unit 23b, the amount of heat generated in the head unit 23b is large. But,
If the impedance of the driving pulse generation circuit 20 is too large, the time constant determined by the product of the driving capacitance and the load capacitance becomes long, and the pulse waveform becomes dull. The allowable bluntness of the pulse waveform is due to the actuators C1, C
2,... Are determined by the frequency f of the natural vibration of the CN.
.. Cannot follow a drive pulse having a frequency equal to or higher than the frequency f of the natural vibration of the actuators C1, C2,. For example, actuators C1, C2,... CN
Assuming that the natural frequency f is 1 MHz, 0.5 is required between the application of the driving pulse and the actual displacement of the side wall.
A time of about μsec is required. That is, even if the rising edge of the driving pulse is dull by about 0.5 μsec, there is almost no difference in the actual driving operation.

FIG. 7 is a diagram showing an equivalent circuit of the drive circuit of FIG. The output impedance of the driving pulse generation circuit 20 is rd, and the head unit 23 b
The resistance of the wiring up to is rw, the resistance when one analog switch is turned on is ron, and the wiring resistance to the actuator is ra.

For example, ron is 50Ω, ra is 20Ω,
rw is 0.5Ω, the capacitance of the actuator of one channel is 1 nF, the number N of channels is 128, and the time constant is
That is, when C × R is set to 0.5 μsec, the driving pulse generation circuit 20 and the analog switch S1 are connected in the system shown in FIG.
(Or S2,... SN), the impedance R of the entire circuit system including the image signal circuit 22 and the actuator C1 (or C2,... CN) is R = 3.9Ω, and rd is
rd = 3.9− (50 + 20) /128=3.4Ω. That is, 3.4 / 3.9 generates heat on the motherboard 24. For this reason, even if the rise and fall times of the drive pulse are slowed down in the range of 0.5 μsec, the flying speed of the ink droplet is hardly affected, and heat generation can be effectively suppressed.

Therefore, the time constant of the entire circuit system is set to 1 / (2
It can be said that setting to about f) is a desirable state in terms of balance between heat generation and ink ejection characteristics.

Next, a description will be given of a different example of the drive pulse generation circuit 20 formed on the motherboard 24 from the above. FIG. 8 shows these circuit diagrams.

The circuit shown in FIG. 8A is, for example, an nCMO
The drive pulse generation circuit 20 is constituted by a switch circuit in which S and pCMOS FETs are complementarily combined. A pulse having a constant period is input to the gate of the FET, and the voltage V applied to the actuator is switched and output. Then, a load resistor R1 for increasing the output impedance and appropriately dulling the rise and fall of the output (drive) pulse waveform is inserted into the output section of the drive pulse generation circuit 20, and the output voltage of the head unit 23b is reduced. The data is input to the drive IC 21b and used. In this case, the time constant greatly changes depending on the number of actuators driven simultaneously, that is, a change in load capacity. As the number of actuators increases along with the number of nozzles, the load capacity increases, the heat generation also increases, and the viscosity of the ink decreases, so that the volume of flying ink droplets also increases. However, in this circuit, when the load capacity increases, the pulse waveform rises,
There is an effect that the fall of the fall becomes large and the heat generation tends to decrease automatically.

The drive pulse generation circuit 20 shown in FIG.
5, a trapezoidal wave pulse whose pulse waveform rises and falls slowly is generated in advance from the trapezoidal wave generation circuit 25, and the pulse is input to a current amplification circuit composed of an operational amplifier OP, and the output is used to drive the head unit 23b of FIG. Input to IC 21b for use.

Originally, the operational amplifier OP is a circuit having a small output impedance, but since the input waveform is dull,
The effective output impedance always increases, and the entire heat generation can be considerably shared by this circuit portion.

[0034]

According to the first aspect of the present invention, the amount of heat generated in the head unit of the ink jet head can be controlled.

According to the second aspect of the present invention, it is possible to satisfactorily control the heat generation of the ink jet head while preventing the flying speed of the ink from decreasing.

According to the third aspect of the present invention, the heat generation of the ink jet head can be favorably controlled with a simple circuit configuration.

According to the fourth aspect of the present invention, the heat generation in the ink jet head can be satisfactorily controlled by transferring the heat generating portion of the drive circuit of the ink jet head to the separated circuit board.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view along an ink flow path of an inkjet head.

FIG. 2 is a sectional view traversing an ink flow path of the inkjet head.

FIG. 3 is a diagram showing a drive pulse waveform and an equivalent circuit.

FIG. 4 is a diagram showing a drive circuit of a conventional actuator.

FIG. 5 is a diagram showing a drive circuit of the actuator according to the embodiment of the present invention.

FIG. 6 is a graph showing a relationship between a rising time of a driving pulse and an ink flying speed.

FIG. 7 is a diagram showing an equivalent circuit of a drive circuit of the actuator according to the embodiment of the present invention.

FIG. 8 is a diagram showing another example of the drive circuit of the actuator according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ink tube 3 Nozzle 40, 41 Channel 50, 51, 52, 53 Side wall 101-104 Electrode 21b Driving IC 22 Image signal circuit 23a, 23b Head unit 24 Motherboard

Claims (4)

[Claims] 1. A plurality of channels each having an ink flow path and a nozzle connected to the ink flow path are provided separated by a plurality of side walls made of a piezoelectric material, and an actuator formed by the side walls is driven to drive the actuator. An ink jet recording apparatus that forms an image by causing ink to fly from a nozzle and causing the ink to fly on a recording material, wherein the driving unit of the actuator selectively drives a driving pulse generating circuit that drives the actuator. And the drive pulse generation circuit is separated from the head unit including the analog switch and the actuator, and
An ink jet recording apparatus, wherein an output impedance of the driving pulse generation circuit is larger than an impedance of the head unit. 2. The driving pulse generating circuit according to claim 2, wherein a frequency of a natural vibration of the actuator is f, and an output impedance of the driving circuit system including the actuator is substantially 1 / (2f). The inkjet recording apparatus according to claim 1, wherein: 3. The ink jet recording apparatus according to claim 1, wherein the output impedance is adjusted by a resistor provided at an output section of the drive pulse generation circuit. 4. The apparatus according to claim 1, wherein the actuator and the analog switch are provided on the head unit, and the drive pulse generating circuit is provided on a circuit board other than the head unit. Item 6. The ink jet recording apparatus according to item 1.