JP7367778B2 - Inkjet recording device and recording operation driving method - Google Patents

Description

The present invention relates to an inkjet printing apparatus and a printing operation driving method.

2. Description of the Related Art Conventionally, inkjet devices are known that circulate ink through an inkjet head and eject the ink from nozzles of the inkjet head.
Generally, an inkjet recording apparatus is equipped with an inkjet head in which a large number of nozzles are arranged to eject minute ink droplets.
Since these nozzles eject ink from ejection ports with minute diameters, the state of the meniscus formed in the nozzle before ejection significantly affects the flying state of droplets, that is, it is related to the image quality of printed matter. Improving the stability of droplets ejected from inkjet head nozzles is an important issue because it is related to the image quality of printed matter.

On the other hand, it has been realized that a multi-drive signal including a plurality of drive pulses is generated to eject relatively large droplets.
However, when ejection and non-ejection are repeated, the state and position of the meniscus before ejection also changes. Therefore, during ejection after the non-ejection period, there is a high possibility that ejection becomes unstable due to non-ejection of droplets or deflection of flight.

The invention described in Patent Document 1 supplies an inkjet head with a non-ejection driving voltage that moves a meniscus to the outside of a non-ejecting nozzle in order to prevent ejection abnormalities caused by foreign matter attached to the edge of a nozzle. At this time, the relationship between the diameter dn of the non-discharge nozzle and the meniscus diameter dm moved to the outside of the non-discharge nozzle is made to satisfy 1.1≦dm/dn≦1.4.

JP2013-199021A

However, the invention described in Patent Document 1 aims to prevent ejection abnormalities due to adhesion of foreign matter, and the meniscus formed by the non-ejection drive voltage is static.
Even by forming a static meniscus during non-ejection as in the invention described in Patent Document 1, it is not possible to eliminate instability that causes droplet non-ejection or flight deflection during subsequent ejection. .

The present invention has been made in view of the above-mentioned problems in the prior art, and an object of the present invention is to stably eject large droplets using an inkjet recording device.

One aspect of the present invention includes an inkjet head having a pressure chamber communicating with a nozzle and ejecting ink in the pressure chamber from the nozzle;
a head drive unit that drives a recording operation by the inkjet head,
The head driving section includes:
A drive pulse voltage that expands and contracts the pressure chamber, and includes an ejection drive pulse that causes ink to be ejected from the nozzle, and a non-ejection drive pulse that causes a meniscus formed in the nozzle to behave without ejecting ink from the nozzle. The drive pulse is enabled to be applied,
During the ink ejection period for forming one dot during the recording operation, ejection drive pulses are applied a number of times with the upper limit of the number of gradations n to each dot that lands on the recording medium, and dots are ejected according to the number of times. Executes a discharge drive that changes the diameter,
During the ink non-ejection period during the recording operation, m times of non-ejection drive pulses, which are equal to the number of gradations n, are applied for a period equal to the ink ejection period for forming one dot. The present invention is an inkjet recording apparatus that performs non-ejection driving that causes the meniscus to behave.

One aspect of the present invention is a recording operation driving method for driving a recording operation by an inkjet head having a pressure chamber communicating with a nozzle and ejecting ink in the pressure chamber from the nozzle, the method comprising:
A drive pulse voltage that expands and contracts the pressure chamber, and includes an ejection drive pulse that causes ink to be ejected from the nozzle, and a non-ejection drive pulse that causes a meniscus formed in the nozzle to behave without ejecting ink from the nozzle. Using a driving pulse,
During the ink ejection period for forming one dot during the recording operation, ejection drive pulses are applied a number of times with the upper limit of the number of gradations n to each dot that lands on the recording medium, and dots are ejected according to the number of times. Executes a discharge drive that changes the diameter,
During the ink non-ejection period during the recording operation, m times of non-ejection drive pulses, which are equal to the number of gradations n, are applied for a period equal to the ink ejection period for forming one dot. This is a recording operation driving method that executes non-ejection driving that causes the meniscus to behave.

According to the present invention, large droplets can be stably ejected by an inkjet recording device.

1 is a block diagram showing a functional configuration of an inkjet recording apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a pressure chamber and a nozzle viewed in the axial direction of the nozzle, showing changes in the pressure chamber in response to drive pulse voltage. FIG. 3 is a schematic diagram showing the operation of ink droplets ejected from a nozzle. FIG. 3 is a drive signal waveform diagram showing an example of a drive pulse voltage according to an embodiment of the present invention. FIG. 7 is a drive signal waveform diagram showing a drive pulse voltage according to a comparative example. FIG. 3 is a cross-sectional view of the nozzle and meniscus in static steady state. FIG. 3 is a cross-sectional view of a nozzle and a meniscus after continuous discharge.

An embodiment of the present invention will be described below with reference to the drawings. The following is one embodiment of the present invention and is not intended to limit the present invention.

The inkjet recording apparatus 1 includes a transport section 10, a recording operation section 20, a cleaning section 30, a control section 40, a storage section 50, a communication section 70, an operation reception section 81, a display section 82, and a power supply section. 90 etc.

The conveyance section 10 moves a recording medium on which an image is to be recorded so as to face a recording range by the recording operation section 20 . The transport unit 10 includes, for example, a transport motor 14 that pulls out a long recording medium wound up into a roll at a predetermined speed. The recording medium is, for example, cloth, but may be made of other materials such as paper.

The recording operation section 20 performs an operation of recording an image by discharging ink onto a recording medium. The recording operation unit 20 includes a large number of nozzles 27 arranged in a predetermined pattern to eject ink, and a piezoelectric element that deforms an ink flow path (pressure chamber) that supplies ink to the nozzles 27 to apply pressure fluctuations to the ink. 26, a head drive unit 25 that outputs a drive pulse voltage that deforms each piezoelectric element 26, and the like.
By applying a driving pulse voltage P to the piezoelectric element 26 as shown in FIG. 2, the side wall 29 of the pressure chamber 28 communicating with the nozzle 27 is deformed, and a pressure chamber 28 is formed near the discharge opening of the nozzle 27 as shown in FIG. The ink droplets 23 are separated from the meniscus 22 and ejected by shaking the meniscus 22.

The cleaning unit 30 includes a wiping member 32 that removes ink and its solidified matter adhering to the nozzle surface where the openings of the nozzles 27 are arranged, a drive unit 31 that operates the wiping member 32, and the like. The wiping member 32 is, for example, a non-woven fabric that sucks ink, a resin member on a blade that scrapes off solids, etc., although it is not particularly limited.

The control unit 40 is a processor that centrally controls the overall operation of the inkjet recording apparatus 1. The control unit 40 includes, for example, a CPU 41 (Central Processing Unit) and a RAM 42 (Random Access Memory). The CPU 41 performs arithmetic operations and performs various control processes. The RAM 42 provides a working memory space for the CPU 41 and stores temporary data.

The storage unit 50 stores image data to be recorded and its processed data, as well as other setting data and programs. The image data may be stored in, for example, a DRAM that can temporarily store large amounts of data and output at high speed. Further, setting data, programs, and the like are stored in a nonvolatile memory such as a flash memory that can be stored even when power supply to the inkjet recording apparatus 1 is stopped, and/or an HDD (Hard Disk Drive).

The communication unit 70 controls data transmission and reception with external devices according to a predetermined communication standard (eg, TCP/IP). The communication unit 70 may be connected to a LAN (Local Area Network) or the like, and may be connectable to the external Internet via a router or the like, or directly connectable to peripheral devices via a USB cable connected to a USB terminal. It may be.
The power supply unit 90 supplies power to the inkjet recording apparatus 1 from a power source.

Next, the driving of the recording operation will be explained.
The head drive unit 25 applies a drive pulse voltage P to the piezoelectric element 26 to expand and contract the pressure chamber 28 . As the drive pulse voltage P, two types (Pa, Pb) shown in FIG. 4 are used. The head drive unit 25 applies an ejection drive pulse Pa that causes ink to be ejected from the nozzle 27 and a non-ejection drive pulse Pb that causes the meniscus 22 formed in the nozzle 27 to behave without causing the nozzle 27 to eject ink. is made possible.
It is assumed that the voltage value of the ejection drive pulse Pa is Va, the pulse width (time from the rise of the pulse to the start of the fall) is Pwa, the voltage value of the non-ejection drive pulse Pb is Vb, and the pulse width is Pwb.

During the ink ejection period Ta (=period T) for forming one dot during the recording operation, the head drive unit 25 performs ejection drive a number of times with the upper limit of the number of gradations n for one dot to land on the recording medium. A pulse is applied to perform ejection driving in which the dot diameter is changed according to the number of times.
In this embodiment, n=8.
In the example shown in FIG. 4, eight ejection drive pulses Pa are applied in period T to form the largest dot diameter.
By applying the ejection drive pulse Pa pulse by pulse, ink droplets are ejected as shown in FIG. 3 and land on the recording medium.
By selecting the number of ejection drive pulses Pa, the number of droplets to be ejected is selected and the dot diameter is changed. The inkjet recording apparatus 1 employs a recording method that expresses gradation using this method.

During the ink non-ejection period Tb (=period T) during the recording operation, the head drive unit 25 applies the non-ejection drive pulse Pb m times, which is equal to or greater than the number of gradations n, to drive the meniscus 22. Execute non-discharge drive to make the device behave. Note that the non-ejection period Tb is equal to the ink ejection period Ta for forming one dot, and corresponds to the period T. Further, in this embodiment, n=m=8.
The voltage value Vb of the non-ejection drive pulse Pb is set lower than the voltage value Va of the ejection drive pulse Pa. Further, the pulse width Pwb of the non-ejection drive pulse Pb is set narrower than the pulse width Pwa of the ejection drive pulse Pa. This is to prevent ink from being ejected due to the application of the non-ejection drive pulse Pb. Although the condition is that no ink is ejected due to the application of the non-ejection drive pulse Pb, the setting is made so that the meniscus 22 can be caused to behave largely to the extent that it is close to the time of ejection. Therefore, the pulse width preferably satisfies the condition of 0.6Pwa<Pwb≦Pwa. Further, the voltage value preferably satisfies the condition of 0.3<Vb/Va<0.5.
Note that either one of the voltage value Vb and the pulse width Pwb of the non-ejection drive pulse Pb may be made equal to the ejection drive pulse Pa, or the other may be adjusted so that no ink is ejected.
The ink ejection period Ta and the ink non-ejection period Tb during the recording operation are for each nozzle. When a certain nozzle is in the ink ejection period Ta, another nozzle may be in the ink non-ejection period Tb, so the ink ejection period Ta or the ink non-ejection period Tb is not determined for the entire apparatus.

FIG. 5 shows drive pulses of a comparative example.
This comparative example differs in that no pulse voltage is applied during the ink non-ejection period Tb, and the rest is the same as the drive pulse of the present embodiment shown in FIG. 4.
In a static stable state before the drive pulse is applied, the meniscus 22a is maintained in a concave shape almost at the ejection opening position of the nozzle 27, as shown in FIG.
When there is continuous ejection, especially continuous ejection of large droplets (n=8), the meniscus gradually retreats to the back of the nozzle 27. When the ink non-discharge period Tb starts after continuous discharge, the meniscus 22b is located at the back of the nozzle 27 as shown in FIG. approaches. However, when no pulse voltage is applied during the ink non-ejection period Tb, the position and swing state of the meniscus 22b are unstable and vary at the start of the ink ejection period Ta following the ink non-ejection period Tb. Furthermore, during continuous ejection, the state shown in FIG. 6 and the state shown in FIG. 7 are repeated, resulting in an unstable state of the meniscus. As a result, during the ink ejection period Ta after the ink non-ejection period Tb, there is a high possibility that ejection becomes unstable due to non-ejection of droplets or flight deflection.

In a demonstration experiment of a comparative example in which the drive was performed in the repeating pattern shown in Figure 5 with period T = 175.4 μs and Pwa = 1.2AL, it was confirmed that droplets did not eject when the droplet velocity reached 7.6 m/s. did it.
On the other hand, in a demonstration experiment of the example of the present invention in which the period T = 175.4 μs and Pwa = Pwb = 1.2 AL were driven in the repeating pattern shown in Fig. 4, even when the droplet velocity reached 9.1 m/s, It was confirmed that the ink could be stably ejected without any non-ejection of droplets.
In the example of the present invention, during the ink non-ejection period Tb, a constant fluctuation of the meniscus occurs with a frequency and amplitude that are close to those of the ink ejection period Ta, and the behavior is dynamically stable and similar to that of the ink ejection period Ta.
Therefore, the ink ejection period Ta following the ink non-ejection period Tb has conditions close to the ink ejection period Ta before the ink ejection period Tb, and the ink ejection is as stable as in the case of continuous ejection.
In order to obtain the above effects, it is preferable that m≧n. In particular, it is preferable that m=n as in this embodiment. During the ink non-ejection period Tb, the meniscus can be shaken the same number of times as the ink ejection period Ta, and the ink ejection becomes stable in the next ink ejection period Ta.

In order to effectively obtain the above effects, it is further carried out under the following conditions.
The condition of 20 μm<dn<50 μm is satisfied, where the discharge opening diameter of the nozzle 27 is dn. More preferably, the condition of 30 μm<dn<50 μm is satisfied.
Apply an ink with a specific gravity greater than 1.
The condition 1AL≦Pwa≦1.4AL is satisfied. More preferably, 1.2AL≦Pwa≦1.4AL is satisfied. Note that AL is one half of the natural vibration period of the pressure chamber 28.

As described above, according to this embodiment, large droplets can be stably ejected by the inkjet recording apparatus.

INDUSTRIAL APPLICATION This invention can be utilized for an inkjet recording device.

1 Inkjet recording device 20 Recording operation section 21 Inkjet head 22 Meniscus 23 Ink droplet 25 Head drive section 27 Nozzle 28 Pressure chamber 40 Control section P Drive pulse voltage T Period

Claims (16)

an inkjet head having a pressure chamber communicating with a nozzle and ejecting ink in the pressure chamber from the nozzle;
a head drive unit that drives a recording operation by the inkjet head,
The head driving section includes:
A drive pulse voltage that expands and contracts the pressure chamber, and includes an ejection drive pulse that causes ink to be ejected from the nozzle, and a non-ejection drive pulse that causes a meniscus formed in the nozzle to behave without ejecting ink from the nozzle. The drive pulse is enabled to be applied,
During the ink ejection period for forming one dot during the recording operation, ejection drive pulses are applied a number of times with the upper limit of the number of gradations n to each dot that lands on the recording medium, and dots are ejected according to the number of times. Executes a discharge drive that changes the diameter,
During the ink non-ejection period during the recording operation, m times of non-ejection drive pulses, which are equal to the number of gradations n, are applied for a period equal to the ink ejection period for forming one dot. An inkjet recording apparatus that executes non-ejection driving that causes the meniscus to behave. The inkjet recording apparatus according to claim 1, wherein 0.6Pwa<Pwb≦Pwa is satisfied, where Pwa is the pulse width of the ejection drive pulse and Pwb is the pulse width of the non-ejection drive pulse. 3. The inkjet recording apparatus according to claim 1, wherein 0.3<Vb/Va<0.5 is satisfied, where Va is the voltage value of the ejection drive pulse and Vb is the voltage value of the non-ejection drive pulse. The inkjet recording apparatus according to any one of claims 1 to 3 , which satisfies 20 μm<dn<50 μm, where dn is the discharge opening diameter of the nozzle. The inkjet recording apparatus according to any one of claims 1 to 3 , which satisfies 30 μm<dn<50 μm, where dn is an ejection opening diameter of the nozzle. The inkjet recording apparatus according to any one of claims 1 to 5 , wherein the ink has a specific gravity greater than 1. 7. The method according to claim 1, wherein 1AL≦Pwa≦1.4AL is satisfied, where Pwa is the pulse width of the ejection drive pulse, and AL is 1/2 of the natural vibration period of the pressure chamber. Inkjet recording device. According to any one of claims 1 to 6 , where 1.2AL≦Pwa≦1.4AL is satisfied, where Pwa is the pulse width of the ejection drive pulse, and AL is 1/2 of the natural vibration period of the pressure chamber. The inkjet recording device described above. A recording operation driving method for driving a recording operation by an inkjet head having a pressure chamber communicating with a nozzle and ejecting ink in the pressure chamber from the nozzle, the method comprising:
A drive pulse voltage that expands and contracts the pressure chamber, and includes an ejection drive pulse that causes ink to be ejected from the nozzle, and a non-ejection drive pulse that causes a meniscus formed in the nozzle to behave without ejecting ink from the nozzle. Using a driving pulse,
During the ink ejection period for forming one dot during the recording operation, ejection drive pulses are applied a number of times with the upper limit of the number of gradations n to each dot that lands on the recording medium, and dots are ejected according to the number of times. Executes a discharge drive that changes the diameter,
During the ink non-ejection period during the recording operation, m times of non-ejection drive pulses, which are equal to the number of gradations n, are applied for a period equal to the ink ejection period for forming one dot. A recording operation driving method for performing non-ejection driving that causes the meniscus to behave. 10. The recording operation driving method according to claim 9 , wherein 0.6 Pwa<Pwb≦Pwa is satisfied, where Pwa is the pulse width of the ejection drive pulse and Pwb is the pulse width of the non-ejection drive pulse. 11. The recording operation driving method according to claim 9 , wherein 0.3<Vb/Va<0.5 is satisfied, where Va is the voltage value of the ejection drive pulse and Vb is the voltage value of the non-ejection drive pulse. The recording operation driving method according to any one of claims 9 to 11 , which satisfies 20 μm<dn<50 μm, where dn is the discharge opening diameter of the nozzle. The recording operation driving method according to any one of claims 9 to 11 , which satisfies 30 μm<dn<50 μm, where dn is the discharge opening diameter of the nozzle. 14. The recording operation driving method according to claim 9 , wherein the specific gravity of the ink is greater than 1. 15. The method according to claim 9 , wherein 1AL≦Pwa≦1.4AL is satisfied, where Pwa is the pulse width of the ejection drive pulse, and AL is half the natural vibration period of the pressure chamber. Recording operation driving method. Any one of claims 9 to 14 that satisfies 1.2AL≦Pwa≦1.4AL, where Pwa is the pulse width of the ejection drive pulse, and AL is half the natural vibration period of the pressure chamber. The recording operation driving method described.

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