WO2021250906A1

WO2021250906A1 - Inkjet head, inkjet image forming device, and method for controlling inkjet head

Info

Publication number: WO2021250906A1
Application number: PCT/JP2020/023310
Authority: WO
Inventors: 聡一田中
Original assignee: コニカミノルタ株式会社
Priority date: 2020-06-12
Filing date: 2020-06-12
Publication date: 2021-12-16
Also published as: JPWO2021250906A1

Abstract

Provided are: an inkjet head that can suppress the pressure fluctuation of an ink inside a pressure chamber even when intervals between ink discharges are short; an inkjet image forming device; and a method for controlling the inkjet head. The inkjet head comprises: a first chamber having a nozzle that can discharge an ink; a first pressure application unit that applies a first pressure to the ink in the first chamber and discharges the ink from the nozzle; a second pressure application unit that applies a second pressure to the ink; and a control unit that determines the second pressure that assumes an application mode for cancelling a reverberant wave generated in the ink according to the application mode of the first pressure, and that controls the first and second pressure application units so as to simultaneously apply the first pressure and the second pressure to the ink.

Description

Inkjet head, inkjet image forming device and control method of inkjet head

The present invention relates to an inkjet head, an inkjet image forming apparatus, and a control method for the inkjet head.

Inkjet device In image formation, the inkjet head has a pressure chamber for storing ink and a nozzle for ejecting ink. When ejecting ink from the inkjet head, the ejection pressure is applied to the ink in the pressure chamber to eject the ink from the nozzle.

In Patent Document 1, in order to improve the control accuracy and responsiveness of the ink pressure in the pressure chamber, the pressure adjustment in which the liquid chamber and the gas chamber are partitioned by a flexible film on the supply port side or the discharge port side of the inkjet head. An inkjet image forming apparatus with a section is shown. In Patent Document 1, the ejection amount of ink is predicted, the elastic modulus of the flexible film is controlled according to the ejection amount, and the pressure (back pressure) of the liquid chamber is controlled. In this way, by controlling the elastic modulus of the flexible film and controlling the back pressure of the liquid chamber according to the ejection amount, it is possible to absorb the pressure fluctuation of the ink in the pressure chamber caused by the ink ejection.

Japanese Unexamined Patent Publication No. 2009-241426

The ejection pressure for ejecting the ink from the nozzle is applied to the ink in the pressure chamber of the inkjet head. At that time, the reverberation wave generated by the applied ejection pressure and the propagating wave thereof fluctuate the pressure of the ink in the pressure chamber, which may adversely affect the ink ejection after the pressure fluctuation. In particular, in the case of high-speed drive in which the ink ejection interval is short, the influence of reverberation waves and propagating waves on the ink ejection is unavoidable, so that there is a limit to the high-speed driving of ink ejection.

The technique described in Patent Document 1 is such that a flexible film absorbs fluctuations in pressure in the pressure chamber due to ink ejection. That is, when the pressure fluctuation occurs, the generated pressure fluctuation is passively absorbed by the flexible membrane. Therefore, it may not be possible to properly absorb the pressure fluctuation due to the response delay or the like for the reverberation wave generated by the applied discharge pressure and the propagating wave thereof. In particular, in the case of high-speed drive in which the ink ejection interval is short, it is difficult to absorb the pressure fluctuation because the flexible film cannot follow the pressure fluctuation.

An object of the present invention is to provide an inkjet head, an inkjet image forming apparatus, and a control method for an inkjet head that can suppress pressure fluctuations of ink in a pressure chamber even when the ink ejection interval is short.

The inkjet head according to the present invention is
The first chamber having a nozzle capable of ejecting ink, and
A first pressure applying unit that applies a first pressure to the ink in the first chamber and ejects the ink from the nozzle.
A second pressure applying portion that applies a second pressure to the ink,
The second pressure, which is an application mode for canceling the reverberation wave generated in the ink, is determined according to the application mode of the first pressure, and the second pressure is applied to the ink at the same time as the first pressure. A control unit that controls the first and second pressure application units, and
To prepare for.

The inkjet image forming apparatus according to the present invention is
The above-mentioned inkjet head is provided.

The method for controlling an inkjet head according to the present invention is as follows.
When the first pressure is applied to the ink in the first chamber from the first pressure application unit and the ink is ejected from the nozzle in the first chamber, the reverberation generated in the ink according to the application mode of the first pressure. A second pressure, which is an application mode for canceling waves, is determined, and at the same time as the first pressure, the second pressure is applied to the ink from the second pressure application unit.

According to the present invention, it is possible to suppress the pressure fluctuation of the ink in the pressure chamber even when the ink ejection interval is short.

It is a figure which shows schematically the inkjet image forming apparatus which concerns on embodiment of this invention. It is a block diagram which shows the main part of the control system of the inkjet image forming apparatus shown in FIG. It is a figure which shows schematic the head unit mounted on the inkjet image forming apparatus shown in FIG. 1. It is a perspective view which shows the inkjet head of the head unit shown in FIG. It is a perspective view which shows the tip part of the inkjet head shown in FIG. 4A. It is sectional drawing of the tip part of an inkjet head. It is a flowchart explaining the control method of the inkjet head carried out in the inkjet image forming apparatus shown in FIG. 1. It is a figure which shows the reverberation wave and the cancellation wave generated when the inkjet head is driven at high speed. It is a figure which shows the reverberation wave and the cancellation wave generated when the inkjet head is driven at a low speed. It is a graph which shows the speed fluctuation of the pressure wave in a pressure chamber when the drive frequency of an inkjet head is changed in the conventional inkjet image forming apparatus. It is a graph which shows the speed fluctuation of the pressure wave in a pressure chamber when the drive frequency of an inkjet head is changed in the inkjet image forming apparatus shown in FIG. 1.

Hereinafter, the inkjet head, the inkjet image forming apparatus, and the control method of the inkjet head according to the embodiment of the present invention will be described in detail with reference to the drawings.

[Inkjet image forming apparatus]
FIG. 1 is a diagram showing a schematic configuration of an inkjet image forming apparatus 1. The inkjet image forming apparatus 1 includes a feeding unit 10, an image forming unit 20, a paper ejection unit 30, a control unit 100 (see FIG. 2), and the like.

Under the control of the control unit 100, the inkjet image forming apparatus 1 conveys the recording medium P stored in the paper feeding unit 10 to the image forming unit 20, and the image forming unit 20 forms an image on the recording medium P to form an image. The recording medium P on which the is formed is conveyed to the paper ejection unit 30. As the recording medium P, in addition to paper such as plain paper and coated paper, various media such as cloth or sheet-shaped resin capable of fixing the ink landed on the surface can be used.

The paper feed unit 10 has a paper feed tray 11 for storing the recording medium P, and a medium supply unit 12 for transporting and supplying the recording medium P from the paper feed tray 11 to the image forming unit 20. The medium supply unit 12 includes a ring-shaped belt whose inside is supported by two rollers, and the recording medium P is transferred from the paper feed tray 11 by rotating the rollers with the recording medium P placed on the belt. It is conveyed to the image forming unit 20.

The image forming unit 20 includes a transport unit 21, a transfer unit 22, a heating unit 23, a fixing unit 24, a delivery unit 25, a head unit 50, and the like.

The transport unit 21 holds the recording medium P mounted on the transport surface 212 (mounting surface) of the cylindrical transport drum 211, and the transport drum 211 is centered on its rotation axis (cylindrical axis) in the direction of the arrow. The recording medium P on the transfer drum 211 is conveyed by rotating around the transfer drum 211.

The delivery unit 22 delivers the recording medium P conveyed by the medium supply unit 12 of the paper feed unit 10 to the transfer unit 21. The delivery section 22 is provided at a position between the medium supply section 12 and the transfer section 21 of the paper feed section 10, and one end of the recording medium P conveyed from the medium supply section 12 is held by the swing arm section 221 and picked up. , Handed over to the transport unit 21 via the delivery drum 222.

The heating unit 23 is provided between the arrangement position of the transfer drum 222 and the arrangement position of the head unit 50, and is the recording medium so that the recording medium P conveyed by the transfer unit 21 has a temperature within a predetermined temperature range. Heat P. The heating unit 23 has, for example, an infrared heater, and energizes the infrared heater based on a control signal supplied from the control unit 100 to generate heat of the infrared heater.

The head unit 50 ejects ink from a nozzle provided on the ink ejection surface facing the conveying surface 212 of the conveying drum 211 at an appropriate timing according to the rotation of the conveying drum 211 holding the recording medium P. An image is formed on the recording medium P. The head unit 50 is arranged so that the ink ejection surface and the transport surface 212 are separated by a predetermined distance. Here, four head units 50 corresponding to the four color inks of yellow (Y), magenta (M), cyan (C), and black (K) are Y, M, from the upstream side in the transport direction of the recording medium P. They are arranged so as to be arranged at predetermined intervals in the order of C and K colors. The configuration of the head unit 50 will be described later with reference to FIGS. 3 to 5.

The fixing unit 24 has a light emitting unit arranged over the width of the transport unit 21 (the width in the rotation axis direction of the transport drum 211), and the light emitting unit with respect to the recording medium P mounted on the transport unit 21. The ink ejected onto the recording medium P is cured and fixed by irradiating it with energy rays such as ultraviolet rays. The light emitting portion of the fixing portion 24 is arranged to face the transport surface 212 from the arrangement position of the head unit 50 to the arrangement position of the delivery drum 251 of the delivery unit 25 in the transfer direction.

The delivery unit 25 has a belt loop 252 having a ring-shaped belt whose inside is supported by two rollers, and a cylindrical transfer drum 251 that transfers the recording medium P from the transfer unit 21 to the belt loop 252. The delivery unit 25 conveys the recording medium P delivered from the transfer unit 21 onto the belt loop 252 by the transfer drum 251 by the belt loop 252 and sends it to the paper ejection unit 30.

The paper ejection unit 30 has a plate-shaped paper ejection tray 31 on which the recording medium P sent out from the image forming unit 20 by the delivery unit 25 is placed.

FIG. 2 is a block diagram showing a main part of the control system of the inkjet image forming apparatus 1. The inkjet image forming apparatus 1 includes a heating unit 23, a fixing unit 24, a head unit 50, a control unit 100, a transport drive unit 111, an input / output interface 112, and the like as main parts of the control system.

The control unit 100 includes a CPU (Central Processing Unit) 101, a RAM (RandomAccessMemory) 102, a ROM (ReadOnlyMemory) 103, a storage unit 104, and the like.

The CPU 101 reads out various control programs and setting data stored in the ROM 103, stores them in the RAM 102, executes the program, and performs various arithmetic processes. Further, the CPU 101 comprehensively controls the overall operation of the inkjet image forming apparatus 1.

The RAM 102 provides a memory space for work to the CPU 101 and stores temporary data. The RAM 102 may include a non-volatile memory.

The ROM 103 stores various control programs and setting data executed by the CPU 101. Instead of the ROM 103, a rewritable non-volatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory may be used.

The storage unit 104 stores a print job (image recording command) input from the external device 2 via the input / output interface 112 and image data related to the print job. As the storage unit 104, for example, an HDD (Hard Disk Drive) may be used, or a DRAM (Dynamic Random Access Memory) or the like may be used in combination.

The transfer drive unit 111 supplies a drive signal to the transfer drum motor of the transfer drum 211 based on the control signal supplied from the control unit 100. As a result, the transfer drive unit 111 rotates the transfer drum 211 at a predetermined speed and timing. Further, the transport drive unit 111 supplies a drive signal to the motor for operating the medium supply unit 12, the delivery unit 22, and the delivery unit 25 based on the control signal supplied from the control unit 100. As a result, the transport drive unit 111 supplies the recording medium P to the transport drum 211 and discharges the recording medium P from the transport drum 211.

The input / output interface 112 mediates the transmission / reception of data between the external device 2 and the control unit 100. The input / output interface 112 is composed of, for example, any of various serial interfaces, various parallel interfaces, or a combination thereof.

The external device 2 is, for example, a personal computer, and supplies an image recording command (print job), image data, and the like to the control unit 100 via the input / output interface 112.

As described above, the heating unit 23 has an infrared heater or the like. The heating unit 23 energizes the infrared heater to generate heat based on the control signal supplied from the control unit 100, and heats the recording medium P.

As described above, the fixing unit 24 has a light emitting unit. The fixing unit 24 causes the light emitting unit to emit light based on the control signal supplied from the control unit 100, and irradiates the recording medium P with energy rays such as ultraviolet rays to cure the ink ejected on the recording medium P. Let it settle.

The head unit 50 has a head drive unit 51, an inkjet head 90, and the like. The head drive unit 51 supplies a drive signal according to the image data to the inkjet head 90 at an appropriate timing based on the control of the control unit 100, so that the pixel value of the image data is obtained from the nozzle of the inkjet head 90. The amount of ink corresponding to is ejected.

[Head unit]
FIG. 3 is a diagram schematically showing a head unit 50 mounted on the inkjet image forming apparatus 1. FIG. 3 illustrates the corresponding main tank 40, along with the head unit 50 for one color of ink. The main tank 40 and the head unit 50 have the same configuration for other colors.

The main tank 40 stores ink (fluid) used for printing. The ink stored in the main tank 40 is supplied to the sub tank module 60 by using the supply pump 41.

The head unit 50 includes a sub tank module 60, a degassing module 70, a filtration module 80, an inkjet head 90, and the like. A degassing filtration unit composed of a degassing module 70 and a filtering module 80 is arranged at one end of the sub tank module 60, and the filtration module 80 is arranged between the sub tank module 60 and the degassing module 70. ..

The sub tank module 60 includes a first sub tank 61, a liquid feed pump 62, a second sub tank 63 (back pressure chamber), a back pressure pump 64, a liquid level sensor 65, a pressure sensor 66, and the like. The ink supplied from the main tank 40 by using the supply pump 41 is stored in the first sub tank 61. As will be described later, the ink returned from the inkjet head 90 is also stored in the first sub tank 61.

The ink stored in the first sub tank 61 is sucked by the liquid feeding pump 62 and is sent to the degassing module 70 and the filtration module 80.

The ink supplied to the degassing module 70 is degassed with gas (air) by the degassing module 70. The ink supplied to the filtration module 80 is filtered by the filtration module 80. As the degassing module 70, a known configuration can be applied if the ink can be degassed, and as the filtration module 80, a known configuration can be applied if the ink can be filtered. be.

The ink degassed by the degassing module 70 and filtered by the filtration module 80 is supplied to the second sub tank 63 by using the liquid feed pump 62. The second sub-tank 63 has a configuration in which the air pressure (back pressure) in the second sub-tank 63 can be adjusted by the back pressure pump 64, and the ink ejection from the nozzle of the inkjet head 90 is controlled by adjusting the air pressure. It is possible.

A liquid level sensor 65 is provided inside the second sub tank 63 to detect the height of the liquid level of the ink supplied to the second sub tank 63.

Further, a pressure sensor 66 is provided on the outlet side of the second sub tank 63 to detect the discharge pressure of the ink supplied from the second sub tank 63. The pressure sensor 66 is used for adjusting the air pressure in the second sub tank 63.

[Inkjet head]
The inkjet head 90 will be described with reference to FIGS. 4A, 4B, and 5 together with FIG. FIG. 4A is a perspective view showing the inkjet head 90. Further, FIG. 4B is a perspective view showing a tip portion of the inkjet head 90. Further, FIG. 5 is a cross-sectional view of the tip end portion of the inkjet head 90.

The inkjet head 90 includes an inlet 91, a head tip 92, a manifold 93, an outlet 94, a head drive unit 51 (see FIG. 2), and the like. The head drive unit 51 is arranged inside the cover 90a of the inkjet head 90, and the manifold 93 is arranged inside the housing 90b of the inkjet head 90. Although FIG. 3 illustrates a configuration in which two inkjet heads 90 are connected in series, one inkjet head 90 may be used, or three or more inkjet heads 90 may be connected in series.

The inlet 91 is connected to the manifold 93, and the ink from the second sub tank 63 is supplied to the manifold 93 via the inlet 91 (in FIG. 3, the inlet 91 of the inkjet head 90 on the upstream side).

The head tip 92 has a nozzle plate 921, a pressure chamber plate 922, and the like. A plurality of nozzles (not shown) are formed on the nozzle plate 921. Further, a plurality of pressure chambers 923 (first chamber) are formed in the pressure chamber plate 922, and a plurality of first piezoelectric elements 95 (first pressure application portion) are arranged. The first piezoelectric element 95 is driven by applying a voltage by the head drive unit 51.

One nozzle is provided for one pressure chamber 923, and although not shown, the nozzle is formed at the end of the pressure chamber 923 (lower end in FIG. 5). .. Further, one first piezoelectric element 95 is provided for one pressure chamber 923, and in the pressure chamber 923, an end portion opposite to the end portion on which the nozzle is arranged (upper end in FIG. 5). The first piezoelectric element 95 is arranged in the section). One pressure chamber 923 and one first piezoelectric element 95 form one set, and the inkjet head 90 is provided with a plurality of such sets.

The first piezoelectric element 95 is driven by the head drive unit 51, and by displacing the wall surface of the pressure chamber 923 in contact with the first piezoelectric element 95, the first pressure is applied to the ink in the pressure chamber 923. As a result, the ink in the pressure chamber 923 is ejected from the nozzles to form an image on the recording medium P.

The manifold 93 has a common liquid chamber 931 (second chamber) formed inside, and the common liquid chamber 931 communicates with a plurality of pressure chambers 923. The ink supplied to the common liquid chamber 931 is supplied to the individual pressure chambers 923.

The outlet 94 is connected to the manifold 93, and the ink that has not been used (discharged) is sent from the manifold 93 to the first sub tank 61 via the outlet 94 (in FIG. 3, the outlet 94 of the inkjet head 90 on the downstream side in FIG. 3). Returned to. In this way, the ink in the head unit 50 is circulated.

By the way, as described above, the first pressure for ejecting the ink from the nozzle is applied to the ink in the pressure chamber 923 of the inkjet head 90. At that time, the reverberation wave generated by the applied first pressure and the propagating wave thereof fluctuate the pressure of the ink in the pressure chamber 923, which may adversely affect the ink ejection after the pressure fluctuation. In particular, in the case of high-speed drive in which the ink ejection interval is short, the influence of reverberation waves and propagating waves on the ink ejection is unavoidable, so that there is a limit to the high-speed driving of ink ejection.

Therefore, in the present embodiment, as described above, the inkjet head 90 applies the first pressure to the pressure chamber 923 having the nozzle capable of ejecting ink and the ink in the pressure chamber 923 to eject the ink from the nozzles. A first piezoelectric element 95 for discharging is provided. In addition, the inkjet head 90 includes a second piezoelectric element 96a (second pressure applying portion) that applies a second pressure to the ink. Then, the control unit 100 determines a second pressure which is an application mode for canceling the reverberation wave generated in the ink according to the application mode of the first pressure, and applies the second pressure to the ink at the same time as the first pressure. The first piezoelectric element 95 and the second piezoelectric element 96a are controlled.

As shown in FIGS. 4B and 5, the second piezoelectric element 96a is provided on the outer surface of the upper wall surface 93a of the manifold 93, and extends along the flow direction of the ink flowing in the manifold 93 (common liquid chamber 931). Being present. The second piezoelectric element 96a is arranged at a position facing the pressure chamber 923 in the manifold 93.

The second piezoelectric element 96a is driven by applying a voltage by the head drive unit 51, and by displacing the upper wall surface 93a in contact with the second piezoelectric element 96a, a second pressure is applied to the ink in the common liquid chamber 931. Apply. At this time, the head drive unit 51 controls the second pressure by the above-mentioned second piezoelectric element 96a so as to cancel the reverberation wave generated in the ink by applying the first pressure.

The control of the second pressure by the second piezoelectric element 96a will be described with reference to FIG. FIG. 6 is a flowchart illustrating a control method of the inkjet head 90 implemented in the inkjet image forming apparatus 1.

The control unit 100 starts an image forming operation when, for example, a print job, image data, or the like is supplied from the external device 2 via the input / output interface 112.

(Step S11)
First, the control unit 100 performs image processing based on image data (for example, image processing of a raster image) to determine an ejection pattern for ejecting ink from the inkjet head 90. This determines each ejection pattern for each pressure chamber 923 (each nozzle) of each inkjet head 90.

(Step S12)
Next, the control unit 100 has a first application pattern (first application mode) of the first pressure applied for ink ejection by the first piezoelectric element 95 of the inkjet head 90 based on the determined ink ejection pattern. To determine. Again, for each pressure chamber 923 of each inkjet head 90, each first application pattern is determined.

(Step S13)
Next, the control unit 100 predicts the reverberation wave generated in the pressure chamber 923 by the application of the first pressure based on the first application pattern of the first pressure. The reverberation wave may include a pressure wave (a type of crosstalk) propagating to another pressure chamber 923 via the common liquid chamber 931. Here, the reverberation wave is predicted based on the first application pattern of the first pressure, but the reverberation wave corresponding to the first application pattern of the first pressure is acquired in advance, and the acquired reverberation wave is used. The reverberation wave corresponding to the first application pattern of the first pressure may be selected from the inside.

(Step S14)
Next, the control unit 100 determines a second application pattern (second application mode) of the second pressure that cancels the reverberation wave by the second piezoelectric element 96a based on the predicted reverberation wave. As described in step S13, when the reverberation wave corresponding to the first application pattern of the first pressure is selected, the reverberation wave is canceled by the second piezoelectric element 96a based on the selected reverberation wave. The second application pattern of the second pressure is determined.

Here, the reverberation wave and the cancellation wave, which is the second application pattern of the second pressure for canceling the reverberation wave, will be described with reference to FIGS. 7 and 8. FIG. 7 is a diagram showing a reverberation wave generated when the inkjet head 90 is driven at high speed and a cancellation wave thereof. Further, FIG. 8 is a diagram showing a reverberation wave generated when the inkjet head 90 is driven at a low speed and a cancellation wave thereof.

In the inkjet head 90, when the first piezoelectric element 95 is driven at high speed based on the ink ejection pattern and the first application pattern of the first pressure is applied to the ink, the fluctuation frequency of the reverberation wave is first applied. It increases according to the fluctuation frequency of the pattern. In this case, in order to cancel the reverberation wave having a high frequency (for example, several tens of KHz or more), the control unit 100 determines the cancellation wave of the high frequency having the opposite phase of the reverberation wave as the second application pattern of the second pressure (for example). See FIG. 7).

In the inkjet head 90, when the first piezoelectric element 95 is driven at a low speed based on the ink ejection pattern and the first application pattern of the first pressure is applied to the ink, the fluctuation frequency of the reverberation wave is first applied. It decreases according to the fluctuation frequency of the pattern. In this case as well, in order to cancel the low frequency reverberation wave, the control unit 100 determines the low frequency cancellation wave having the opposite phase of the reverberation wave as the second application pattern of the second pressure (see FIG. 8). ..

Note that, in FIGS. 7 and 8, a simple reverberation wave is illustrated for easy understanding, but the reverberation wave changes according to the first application pattern of the first pressure, for example, its frequency and amplitude. Even in such a case, the control unit 100 may determine the cancel wave having the opposite phase of the reverberation wave as the second application pattern of the second pressure.

(Step S15)
Next, the control unit 100 instructs the head drive unit 51 of the first application pattern of the first pressure to the first piezoelectric element 95 and the second application pattern of the second pressure to the second piezoelectric element 96a.

In response to a command from the control unit 100, the head drive unit 51 controls the first pressure with the first piezoelectric element 95 based on the first application pattern, and ejects an amount of ink from the nozzle according to the pixel value of the image data. Let me. At this time, the head drive unit 51 controls the second pressure with the second piezoelectric element 96a based on the second application pattern that cancels the reverberation wave generated in the ink by applying the first pressure.

In this way, by applying the second application pattern (cancellation wave) of the second pressure from the second piezoelectric element 96a to the reverberation wave generated in the pressure chamber 923 by the application of the first pressure by the first piezoelectric element 95. , The pressure fluctuation in the pressure chamber 923 can be suppressed. In other words, active seismic control is performed. In the present embodiment, the pressure fluctuation in the pressure chamber 923 can be suppressed even when the inkjet head 90 is driven at high speed, that is, even when the ink ejection interval is short.

FIG. 9 is a graph showing the speed fluctuation of the pressure wave in the pressure chamber when the drive frequency of the inkjet head is changed in the conventional inkjet image forming apparatus. Further, FIG. 10 is a graph showing the speed fluctuation of the pressure wave in the pressure chamber 923 when the drive frequency of the inkjet head 90 is changed in the inkjet image forming apparatus 1 of the present embodiment.

As shown in FIG. 9, in the conventional inkjet image forming apparatus, the fluctuation range of the speed fluctuation of the pressure wave in the pressure chamber tends to increase as the driving frequency increases. This indicates that the reverberation wave in the pressure chamber is large and the pressure fluctuation in the pressure chamber is large.

On the other hand, as shown in FIG. 10, in the inkjet image forming apparatus 1 of the present embodiment, the fluctuation range of the speed fluctuation of the pressure wave in the pressure chamber tends to increase as the driving frequency increases, but FIG. 9 Compared with, the fluctuation range is suppressed. This indicates that the reverberation wave in the pressure chamber is suppressed and the pressure fluctuation in the pressure chamber is suppressed. That is, the frequency characteristics of the inkjet head 90 are improved as compared with the conventional case.

(Step S16)
Finally, the control unit 100 determines whether or not the image forming operation continues. If the image forming operation continues (YES), the process returns to step S11, and if it does not continue (NO), a series of procedures is terminated. The control unit 100 determines, for example, whether or not a print job, image data, or the like is supplied from the external device 2, and determines whether or not the image forming operation is continued.

As described above, in the inkjet image forming apparatus 1, the inkjet head 90 applies a first pressure to the pressure chamber 923 having a nozzle capable of ejecting ink and the ink in the pressure chamber 923 to eject ink from the nozzles. A first piezoelectric element 95 for discharging is provided. In addition, the inkjet head 90 includes a second piezoelectric element 96a that applies a second pressure to the ink. Then, the control unit 100 determines a second pressure which is an application mode for canceling the reverberation wave generated in the ink according to the application mode of the first pressure, and applies the second pressure to the ink at the same time as the first pressure. The first piezoelectric element 95 and the second piezoelectric element 96a are controlled.

According to the inkjet image forming apparatus 1 configured in this way, the second piezoelectric element 96a is provided so that the second pressure cancels the reverberation wave according to the reverberation wave generated in the ink by the application of the first pressure. I'm in control. As a result, the pressure fluctuation in the pressure chamber 923 can be suppressed, and the pressure fluctuation in the pressure chamber 923 can be suppressed even when the ink ejection interval is short. As a result, the print quality can be improved.

Further, in the present embodiment, the second piezoelectric element 96a is controlled so that the reverberation wave is predicted before the application of the first pressure and the second pressure cancels the reverberation wave. That is, feedforward control is performed. When the ink ejection interval is short, that is, when the inkjet head 90 is driven at high speed, the reverberation wave becomes a periodic and constant high frequency fluctuation, but the response delay to such a reverberation wave is eliminated. , The pressure fluctuation in the pressure chamber 923 can be suppressed. As a result, the inkjet head 90 can be driven at a higher speed, and the printing speed and printing quality of the inkjet head 90 can be further improved.

In the present embodiment, the second piezoelectric element 96a is provided on the outer surface of the upper wall surface 93a of the manifold 93, but in addition to this, the second piezoelectric element 96b is provided on the outer surface of the side wall surface 93b of the manifold 93. It may be provided (see FIGS. 4B and 5). In this way, by providing the second

piezoelectric elements

96a and 96b and increasing the area in contact with the upper wall surface 93a and the side wall surface 93b, a cancel wave having a large amplitude is generated even when the amplitude of the reverberation wave is large. , The reverberation wave can be canceled.

Further, here, the second

piezoelectric elements

96a and 96b extend along the flow direction of the ink flowing in the manifold 93 (common liquid chamber 931), but these are divided into a plurality of parts in the flow direction. A second pressure may be applied to each of the divided parts. By dividing the second

piezoelectric element

96a and 96b into a plurality of parts in this way, a cancel wave is generated for each region in the flow direction and also for each individual pressure chamber 923 to cancel the reverberation wave. Can be done. Thereby, the pressure fluctuation can be suppressed in the flow direction of the manifold 93 (common liquid chamber 931), and the pressure distribution in the flow direction can be made uniform.

Further, in the present embodiment, in the case of an ink having a viscosity of 7 mPa · s or less and a sound velocity of 1400 m / s or more, that is, a water-based inkjet ink, the above effect can be obtained more effectively. Further, in the case of ink having a viscosity of 7 mPa · s or less and a sound velocity of 1400 m / s or more, the second

piezoelectric elements

96a and 96b can be driven at a high frequency of 20 KHz or more, and the frequency characteristics of the inkjet head 90 are also improved.

<Modification 1>
In the above embodiment, the inkjet head 90 is provided with the second

piezoelectric elements

96a and 96b, but in this modification, the second

piezoelectric elements

96a and 96b may not be provided. In this modification, the control unit 100 uses the first piezoelectric element 95 of the other pressure chamber 923, which does not eject the ink from the nozzle of the pressure chamber 923 when the ink is ejected from the nozzle of the pressure chamber 923, to be the second piezoelectric element 96a described above. , 96b. For example, when ejecting ink from a nozzle of a certain pressure chamber 923 and not ejecting ink from a nozzle of a pressure chamber 923 adjacent to the pressure chamber 923, the first piezoelectric element 95 of the adjacent pressure chamber 923 is used. , Used as the above-mentioned second

piezoelectric elements

96a and 96b.

Also in this case, the control unit 100 predicts the reverberation wave generated in the ink by applying the first pressure in the pressure chamber 923 that ejects the ink from the nozzle. Then, the control unit 100 controls the first piezoelectric element 95 so that the first pressure of the first piezoelectric element 95 of the other pressure chamber 923 that does not eject ink from the nozzle is an application mode that cancels the predicted reverberation wave. do. In this case, the control unit 100 controls the first piezoelectric element 95 so that the first pressure does not break the meniscus of the ink of the nozzle in another pressure chamber 923 that does not eject the ink from the nozzle.

As described above, in this modification, since the second

piezoelectric elements

96a and 96b do not have to be provided, the pressure fluctuation in the pressure chamber 923 can be suppressed without changing the configuration of the inkjet head 90 from the conventional configuration. Can be done.

<Modification 2>
In the above embodiment, the pressure fluctuation of the pressure chamber 923 is suppressed by the second

piezoelectric elements

96a and 96b, but the third pressure that suppresses the fluctuation of the back pressure applied by the second sub tank 63 is applied. It may be applied to the ink in the common liquid chamber 931.

In this case, the control unit 100 determines a third pressure, which is an application mode that cancels the fluctuation of the back pressure of the second sub tank 63 generated by ejecting ink from the nozzle of the pressure chamber 923. For example, the control unit 100 predicts the fluctuation of the back pressure of the second sub tank 63 generated by the ejection of the ink from the nozzle, and makes the application pattern of the opposite phase to the fluctuation of the back pressure of the second sub tank 63. 3 Determine the pressure.

Then, the control unit 100 controls the first piezoelectric element 95 and the second

piezoelectric elements

96a and 96b so that the third pressure is applied to the ink at the same time as the first pressure when the ink is ejected from the nozzle of the pressure chamber 923. ..

As described above, in this modification, the second

piezoelectric elements

96a and 96b are controlled so that the third pressure is an application mode that cancels the fluctuation of the back pressure of the second sub tank 63. As a result, the fluctuation of the back pressure applied by the second sub tank 63 is suppressed, so that the pressure fluctuation in the pressure chamber 923 can be further suppressed.

<Modification 3>
In the above embodiment, the pressure fluctuation of the pressure chamber 923 is suppressed by the second

piezoelectric elements

96a and 96b, but when it is desired to increase the amount of ink ejected from the nozzle of the pressure chamber 923, the first pressure is used. A fourth pressure may be applied to the ink in the pressure chamber 923 so as to be superimposed on the ink.

In this case, the control unit 100 determines the fourth pressure, which is an application mode in which the ink ejection amount is larger than that in the case where the ink is not superposed on the first pressure by superimposing the ink on the first pressure. For example, the fourth pressure is determined so that the application pattern has the same phase as the first application pattern of the first pressure.

piezoelectric elements

96a and 96b so that the fourth pressure is applied to the ink at the same time as the first pressure when the ink is ejected from the nozzle of the pressure chamber 923. Then, the fourth pressure is superimposed on the first pressure.

As described above, in this modification, the first pressure chamber is applied to the ink in the pressure chamber 923 by the first piezoelectric element 95, and the pressure chambers are applied to the second

piezoelectric elements

96a and 96b so as to be superimposed on the first pressure. A fourth pressure is applied to the ink in 923. As a result, the amount of ink ejected from the nozzle of the pressure chamber 923 can be increased as compared with the case where the fourth pressure is not superimposed on the first pressure.

Even in this case, the control unit 100 predicts the reverberation wave generated in the ink in the pressure chamber 923 due to the application of the first pressure and the fourth pressure. Then, the control unit 100 controls the second

piezoelectric elements

96a and 96b so that the second pressure newly applied after the ink is ejected cancels the reverberation wave. By doing so, the amount of ink ejected can be increased and the pressure fluctuation in the pressure chamber 923 can be suppressed.

The above-described embodiments and modifications 1 to 3 are merely examples of embodiment of the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. It is a thing. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

1 Inkjet image forming device 2 External device 10 Feeding part 20 Image forming part 30 Paper ejection part 50 Head unit 51 Head drive part 90 Inkjet head 92 Head tip 921 Nozzle plate 922 Pressure chamber plate 923 Pressure chamber 93 Manifold 931 Common liquid chamber 95 1st

piezoelectric element

96a, 96b 2nd piezoelectric element 100 Control unit

Claims

The first chamber having a nozzle capable of ejecting ink, and
A first pressure applying unit that applies a first pressure to the ink in the first chamber and ejects the ink from the nozzle.
A second pressure applying portion that applies a second pressure to the ink,
The second pressure, which is an application mode for canceling the reverberation wave generated in the ink, is determined according to the application mode of the first pressure, and the second pressure is applied to the ink at the same time as the first pressure. A control unit that controls the first and second pressure application units, and
Inkjet head with.
It has a second room that communicates with the first room.
The second pressure applying unit applies the second pressure to the ink in the second chamber.
The inkjet head according to claim 1.
The second pressure applying unit individually applies the second pressure in a plurality of regions in the ink flow direction of the second chamber.
The inkjet head according to claim 2.
A plurality of sets of the first chamber and the first pressure applying section,
A second room that communicates with the plurality of first rooms,
Equipped with
The second pressure applying unit is the first pressure applying unit of the first chamber that does not eject the ink when the ink is ejected from at least one nozzle of the first chamber.
The inkjet head according to claim 1.
A back pressure chamber for applying back pressure to the ink in the second chamber is provided.
The control unit determines a third pressure, which is an application mode for canceling the fluctuation of the back pressure generated by ejecting the ink from the nozzle of the first chamber, and at the same time as the first pressure, the third pressure. Controls the first and second pressure applying portions so as to apply the ink to the ink.
The inkjet head according to any one of claims 2 to 4.
When the ink is ejected from the nozzle of the first chamber, the control unit superimposes the ink on the first pressure so that the amount of the ink ejected is larger than that in the case where the ink is not superimposed on the first pressure. The first and second pressure application units are controlled so as to determine the fourth pressure to be the ink and apply the fourth pressure to the ink at the same time as the first pressure.
The inkjet head according to any one of claims 1 to 5.
The second pressure application unit is a piezoelectric element driven by applying a voltage.
The inkjet head according to any one of claims 1 to 6.
The ink is a water-based inkjet ink.
The inkjet head according to any one of claims 1 to 7.
An inkjet image forming apparatus including the inkjet head according to any one of claims 1 to 8.
When the first pressure is applied to the ink in the first chamber from the first pressure application unit and the ink is ejected from the nozzle in the first chamber, the reverberation generated in the ink according to the application mode of the first pressure. A second pressure, which is an application mode for canceling waves, is determined, and the second pressure is applied to the ink from the second pressure application unit at the same time as the first pressure.
Inkjet head control method.