JP3852264B2 - Inkjet recording device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet recording apparatus in which a plurality of channels having ink flow paths connected to nozzles are separated by a plurality of side walls made 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,.
[0003]
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 formed between the cover plate 6 and the substrate 8 as shown in FIG. A number of channels 40, 41, 42,... 4M separated by the 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.
[0004]
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 rectangular wave pulse having a peak value V as shown in FIG. By the operation, ink droplets are ejected from the nozzles 3 and landed on the recording material to record an image.
[0005]
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 ( 2 (see FIG. 2B), 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 also deformed in the joint surfaces of the side walls, and the side walls 51A and 51B are also displaced in the opposite direction. 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 the volume of the channel 40 is increased in this example. Next, the drive pulse falls, 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 return to the state shown in FIG. At this time, the volume of the channel 40 is abruptly reduced, and an ink droplet due to a part of the ink filling the channel 40 is caused to fly from the nozzle 3 by changing the pressure in the channel 40. 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]
[Problems to be solved by the invention]
The drive circuit for driving the actuator which is the side wall made of the piezoelectric material is a capacitive load as an electrical load, and FIG. 3B shows an equivalent circuit of the one-channel drive circuit.
[0007]
The energy E used to drive the ink flight is well known (CV ² ) /, where C is the actuator capacity, V is the pulse voltage, f _d is the applied frequency frequency of the drive pulse, and N is the number of nozzles. 2, the energy E generated by charging and discharging the capacity is E = CV ² · f _d · N.
[0008]
A part of this energy E is used to fly the ink, but most of the energy is converted into Joule heat in the circuit to generate heat. Therefore, for example, when driving with pulses having a repetition frequency of about 20 kHz, there is a problem that the amount of heat generation increases, and the amount of heat generation of the head increases as the number of channels increases.
[0009]
An example of a conventional drive circuit for driving the head is shown in FIG. Although only a two-channel driving circuit is shown in the figure, there are actually a large number of N-channel switches, and the voltage V applied to the electrodes of the actuators C1 and C2 is, for example, a complementary combination of nCMOS and pCMOS FETs. Generated from the circuits S1 and S2. The switch circuits S1 and S2 are individually controlled by a drive pulse formed based on the image signal to perform a switch operation.
[0010]
In this manner, the switch circuits S1 and S2 perform a switch operation based on the image signal, drive the actuator, cause ink to fly from the nozzle, and make ink land on the recording material to form an image.
[0011]
Usually, the drive circuit of FIG. 4 is integrated as a driver IC chip 21a. The head having the driver IC 21a, the actuators C1 and C2, and the ink manifold constitute a head unit 23a. Most of the heat generated by the driving power is generated in the head unit 23a, that is, the driving circuit. Since the head unit 23a including the drive circuit is highly integrated, it is difficult to dissipate heat.
[0012]
Further, the heat generated in the head unit 23a has an effect such as a change in ink viscosity, which changes the flying (discharge) characteristics of the ink and makes it unstable. Furthermore, there is a problem that the head driving circuit mounted on the head unit also has an influence of heat generation.
[0013]
An object of the present invention is to solve the above-described heat generation problem in a head unit and provide an ink jet recording apparatus that operates stably.
[0014]
[Means for Solving the Problems]
The object of the present invention is achieved by the invention described below.
[0015]
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 made of a piezoelectric material, and an actuator made of the side walls is driven to eject ink from the nozzles. An ink jet recording apparatus for forming an image by landing ink on a recording material,
Driver of the actuator, a drive pulse generator for driving the actuator consists of a analog switch through a driving pulse Optionally, said drive pulse generating circuit and a head unit including the analog switch and the actuator separation a configurations, and the output impedance of the driving pulse generating circuit is much larger than the impedance of the head unit, and the frequency of natural vibration of the actuator is f, when the drive circuit system including the actuator An ink jet recording apparatus , wherein the drive pulse generating circuit has an output impedance such that a constant is substantially 1 / (2f) .
[0016]
2. The capacity of the actuator is C, the number of channels is N, the output impedance of the drive pulse generation circuit is rd, the resistance of the wiring from the drive pulse generation circuit to the head unit is rw, and one analog switch is turned on In the case where the resistance is ron and the wiring resistance to the actuator is ra, the time constant of the drive circuit system including the actuator is represented by C × (((ron + ra) / N) + rd). 2. The inkjet recording apparatus according to 1 above.
[0017]
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 unit of the drive pulse generating circuit.
[0018]
4). It provided in the actuator and the analog switch the head unit, the drive pulse generating circuit according to any one of the 1 to 3, characterized in that provided on the circuit board other than the F head unit Inkjet recording device.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Even if the heat generation amount of the entire drive system for driving the actuator is determined, the place where heat is generated differs depending on the impedance of each part.
[0020]
In the embodiment of the present invention, the above-described problem due to heat generation is solved by separating the circuit configuration concentrated on the head unit and reducing the ratio of the heat generation amount in the head unit of the total heat generation amount. Yes.
[0021]
In other words, by separating the drive unit that drives the actuator that causes ink to fly into an analog switch and a drive pulse generation circuit, and making the effective output impedance of the drive pulse generation circuit larger than the impedance of the head unit including the analog switch, Heat generation in the head unit provided with the analog switch is suppressed.
[0022]
FIG. 5 is a circuit diagram of the actuator drive unit according to the embodiment of the present invention. FIG. 5 shows an example of a circuit that drives four channels. However, in an actual inkjet recording apparatus, a number of channels are provided, and in the following description, there is a circuit that drives up to N channels. .
[0023]
In FIG. 5, the drive unit includes a drive pulse generation circuit 20, analog switches S1, S2,... SN and an image signal circuit 22. The drive pulse generation circuit 20 and the image signal generation circuit 21 are the head unit 23b. It is provided on the mother board 24 which is a separated circuit board. The drive IC 21b and the actuators C1, C2,... CN constituting the analog switches S1, S2,... SN are provided in the head unit 23b. The drive pulse generation circuit 20 generates a drive pulse having a constant voltage V and a constant voltage V, and inputs the drive pulse to the drive IC 21b indicated by a broken line. The analog switches S1, S2, S3, S4,. Input to the signal terminal. The outputs of the analog switches S1, S2,... SN are connected to the actuators C1, C2, C3, C4,... CN of the respective channels, and the ground terminals of the analog switches S1, S2,. Are commonly connected to ground to form a drive unit. The analog switches S1, S2,... SN selectively transmit the drive pulse of the drive pulse generation circuit 20 to the actuators C1, C2,... CN based on the control signal from the image signal circuit 22, and the actuator C1, C2,... CN are driven.
[0024]
In the following description, the case where the signal is switched to the signal terminal of the analog switches S1, S2,. 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 by the actuators C1, C2,. A corresponding one of CN is driven to eject ink and land on a recording material to form an image. The head unit 23b indicated by the dotted line in FIG. 5 is provided with the drive IC 21b so as to be integrated, and the drive pulse generation circuit 20 and the image signal circuit 22 are provided on a mother board 24 separated from the head unit 23b. .
[0025]
FIG. 6A shows an actuator C1 (or C2,... CN) having a natural vibration frequency f of 1 MHz driven by a drive pulse having a constant voltage V and a pulse width W, and the rise of the drive pulse. It is the graph which measured the change of the flying speed of the ink drop at the time of changing time (DELTA) T. FIG. 6B shows the waveform of the drive pulse with a rise time of ΔT and a fall time of δT drive pulse. Usually, since rise and fall are determined by a time constant, ΔT and δT are the same value.
[0026]
In FIG. 6A, the horizontal axis represents the rising time ΔT (falling time δT) (μsec), and the vertical axis represents the ink droplet flying speed (m / sec). From this graph, the flying speed of the ink droplet does not change at about 8 m / sec until the rising time ΔT (falling time δT) is 0.5 μsec, and the flying speed of the ink droplet rapidly decreases as ΔT is further increased. I understand. Accordingly, 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 within the range of ΔT of 0.5 μsec, most of the heat is generated without reducing the flying speed of the ink droplets. Is generated in the mother board 24 that easily dissipates heat. When 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. However, if the impedance of the drive pulse generation circuit 20 is increased too much, the time constant determined by the product of the load capacitance becomes longer, and the pulse waveform becomes dull. The allowable bluntness of the pulse waveform is determined by the natural vibration frequency f of the actuators C1, C2,. It is impossible to 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, if the natural vibration frequency f of the actuators C1, C2,... CN is 1 MHz, a time of about 0.5 μsec is required after the drive pulse is applied until the side wall is actually displaced. That is, even if there is a dullness of about 0.5 μsec at the rising edge of the drive pulse, there is almost no difference in the actual drive operation.
[0027]
FIG. 7 is a diagram showing an equivalent circuit of the drive circuit of FIG. The output impedance of the drive pulse generation circuit 20 is rd, the resistance of the wiring from the motherboard 24 to the head unit 23b is rw, the resistance when one analog switch is on is ron, and the wiring resistance to the actuator is ra. .
[0028]
For example, when ron is 50Ω, ra is 20Ω, rw is 0.5Ω, the capacity of one channel actuator is 1 nF, the number of channels N is 128, and the time constant, that is, C × R is 0.5 μsec. 7, the impedance R of the entire circuit system including the drive pulse generation circuit 20, the analog switch S1 (or S2,... SN), the image signal circuit 22, and the actuator C1 (or C2,... CN). Becomes R = 3.9Ω, and rd becomes rd = 3.9− (50 + 20) /128=3.4Ω. That is, 3.4 / 3.9 generates heat on the mother board 24. For this reason, even if the rise and fall times of the drive pulse are dulled in the range of 0.5 μsec, the flying speed of the ink droplet is hardly affected and the heat generation can be effectively suppressed.
[0029]
Therefore, it can be said that setting the time constant of the entire circuit system to about 1 / (2f) is desirable in terms of the balance between heat generation and ink ejection characteristics.
[0030]
Next, an example different from the above for the drive pulse generation circuit 20 configured on the mother board 24 will be described. FIG. 8 is a circuit diagram of these.
[0031]
In the circuit shown in FIG. 8A, for example, a drive pulse generation circuit 20 is configured by a switch circuit in which nCMOS and pCMOS FETs are complementarily combined, and a pulse with a constant period is input to the gate of the FET and applied to the actuator. Switch the voltage V to be output. Then, a load resistor R1 is inserted into the output section of the drive pulse generation circuit 20 to increase the output impedance and to moderate the rise and fall of the output (drive) pulse waveform. Used by inputting to the drive IC 21b. In this case, the time constant varies greatly depending on the number of actuators that are driven simultaneously, that is, the load capacity. As the number of actuators increases with the number of nozzles, the load capacity increases, heat generation increases, and the volume of ink droplets flying due to the decrease in ink viscosity increases. However, this circuit has the effect that when the load capacity increases, the rise and fall of the pulse waveform increases and the heat generation tends to decrease automatically.
[0032]
In the drive pulse generation circuit 20 shown in FIG. 8B, a trapezoidal wave pulse whose rise and fall of the pulse waveform have been blunted in advance is generated from the trapezoidal wave generation circuit 25 and input to a current amplification circuit composed of an operational amplifier OP. The output is input to the driving IC 21b of the head unit 23b in FIG.
[0033]
Originally, the operational amplifier OP is a circuit having a small output impedance, but since the input waveform is dull, the effective output impedance is always large, and the entire heat generation can be shared considerably by this circuit portion. .
[0034]
【The invention's effect】
The invention according to claim 1 makes it possible to control the amount of heat generated in the head unit of the inkjet head.
[0035]
According to the second aspect of the present invention, it is possible to favorably control the heat generation of the ink jet head while preventing a decrease in the flying speed of the ink.
[0036]
According to the invention of claim 3, the heat generation of the ink jet head can be controlled well with a simple circuit configuration.
[0037]
According to the invention of claim 4, the heat generation in the ink jet head can be favorably controlled by transferring the heat generating portion in 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 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 a drive pulse waveform and an equivalent circuit.
FIG. 4 is a diagram illustrating a driving circuit of a conventional actuator.
FIG. 5 is a diagram showing an actuator drive circuit according to an embodiment of the present invention.
FIG. 6 is a graph showing the relationship between the drive pulse rise time and the 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 actuator drive circuit according to the embodiment of the present invention.
[Explanation 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 circuits 23a and 23b Head unit 24 Motherboard

Claims (4)

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 made of piezoelectric material, and an actuator made of the side walls is driven to eject ink from the nozzles. An ink jet recording apparatus for forming an image by landing ink on a recording material,
Driver of the actuator, a drive pulse generator for driving the actuator consists of a analog switch through a driving pulse Optionally, said drive pulse generating circuit and a head unit including the analog switch and the actuator separation a configurations, and the output impedance of the driving pulse generating circuit is much larger than the impedance of the head unit, and the frequency of natural vibration of the actuator is f, when the drive circuit system including the actuator An ink jet recording apparatus , wherein the drive pulse generation circuit has an output impedance such that a constant is substantially 1 / (2f) . The capacity of the actuator is C, the number of channels is N, the output impedance of the drive pulse generation circuit is rd, the resistance of the wiring from the drive pulse generation circuit to the head unit is rw, and one analog switch is turned on In the case where the resistance is ron and the wiring resistance to the actuator is ra, the time constant of the drive circuit system including the actuator is represented by C × (((ron + ra) / N) + rd). The inkjet recording apparatus according to claim 1.   3. The ink jet recording apparatus according to claim 1, wherein the output impedance is adjusted by a resistor provided at an output portion of the drive pulse generation circuit.   The inkjet according to any one of claims 1 to 3, wherein the actuator and the analog switch are provided in the head unit, and the drive pulse generation circuit is provided on a circuit board other than the head unit. Recording device.

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