Inkjet recording apparatus

Abstract

To provide an inkjet recording apparatus which can securely recover a thickened ink by properly oscillating a meniscus.SOLUTION: This inkjet recording apparatus comprises a plurality of nozzles 71, a plurality of compression chambers 91, a plurality of piezoelectric devices 93, and a voltage impressing part 99 which impresses voltage on the piezoelectric devices 93 on the basis of a drive waveform for discharging an ink to the recording medium out of the nozzles 71 and a fine drive waveform for giving a fine oscillation to the meniscus of the ink in the nozzles 71, where the voltage impressing part 99 impresses voltage on the piezoelectric devices 93 on the basis on the fine drive waveform on non-printing, and where the fine drive waveform has a voltage change time of less than Tc / 2 for drawing in the meniscus when the natural oscillation period of the meniscus is Tc, being formed so as to push out the meniscus for a time of Tc after an elapse of time from the voltage change start to Tc / 2 or more to Tc×3 / 2.SELECTED DRAWING: Figure 3B

Description

[Technical field]

[0001] The present invention relates to an inkjet recording apparatus. [Background technology]

[0002] An inkjet recording device is equipped with many nozzles that eject ink droplets to form dots on a recording medium. Depending on the image, some nozzles do not eject ink. In addition, there are nozzles that are not used for printing even during standby or between sheets of paper during continuous printing. In such cases, ink remains in the nozzle. Then, since the nozzle outlet is open to the atmosphere, the volatile components in the ink that remains in the nozzle evaporate, and the viscosity of the ink may increase. If the ink becomes viscous in this way, when ink is next ejected to form a dot, the volume of the ejected ink may decrease, the ejection speed may decrease, or the ejection direction may be bent, making it impossible to form dots accurately.

[0003] For this reason, inkjet recording devices are provided with a circulation flow path to collect the thickened ink. However, since ink generally thickens at the tip of the nozzle (near the ejection port) and the length of the nozzle is longer than the thickness of the thickened ink layer, it is difficult to reliably collect the thickened ink in the circulation flow path.

[0004] Therefore, a method has been proposed in which the ink meniscus inside the nozzle is vibrated to the extent that ink is not ejected from the nozzle when dots are not being formed, and the thickened ink is collected in a circulation flow path. This method requires that the drive waveform of the voltage applied to the piezoelectric element be set so that the meniscus can be efficiently drawn into the nozzle.

[0005] The liquid ejection unit described in Patent Document 1 switches the voltage change time for drawing in the meniscus and the voltage change time for pushing out the meniscus between drive waveform data for forming dots and micro-drive waveform data for applying micro-vibrations to the meniscus. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-116935 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the liquid ejection unit of Patent Document 1, the voltage change time required to draw in the meniscus is Tc / 2 (Tc is the natural vibration period of the meniscus), so the meniscus cannot be vibrated significantly, which may result in the thickened ink not being reliably collected.

[0008] SUMMARY OF THE PRESENTLY PREFERRED EMBODIMENTS In consideration of the above circumstances, an object of the present invention is to provide an inkjet recording apparatus capable of properly vibrating the meniscus and reliably recovering thickened ink. [Means for solving the problem]

[0009] In order to achieve the above object, an ink jet recording device of the present invention comprises a plurality of nozzles opening toward a recording medium, a plurality of pressure chambers communicating with each of the plurality of nozzles and containing ink therein, a piezoelectric element provided corresponding to each of the plurality of pressure chambers, which is flexibly deformed when a voltage is applied thereto to apply pressure to the ink in the pressure chamber to cause the ink to be ejected from the nozzle, and a voltage application unit which applies a voltage to the piezoelectric element based on a drive waveform for ejecting ink from the nozzle to the recording medium and a fine drive waveform for applying a fine vibration to a meniscus of the ink in the nozzle, the voltage application unit applies a voltage to the piezoelectric element based on the drive waveform during printing, and applies a voltage to the piezoelectric element based on the fine drive waveform during non-printing, the fine drive waveform being formed such that, when a natural vibration period of the meniscus is Tc, a voltage change time for pulling in the meniscus is less than Tc / 2, and the meniscus is pushed out over a period of Tc after a time period from Tc / 2 or more to Tc×3 / 2 has elapsed from the start of the voltage change.

[0010] The present invention may be characterized in that the ink ejection device further comprises a common supply flow path through which ink contained in the plurality of pressure chambers is supplied, and a common circulation path that communicates with the plurality of pressure chambers and through which ink circulates. Effect of the Invention

[0011] According to the present invention, the fluctuation of the meniscus can be increased, so that the thickened ink layer at the tip of the nozzle can be reliably recovered, and poor ink ejection caused by thickened ink can be prevented. [Brief description of the drawings]

[0012] [Figure 1] 1 is a front view showing a schematic diagram of an inkjet recording apparatus according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a plan view illustrating a head unit in the inkjet recording apparatus according to one embodiment of the present invention. [Figure 3A]1 is a plan view showing an ink ejection section of a print head in an inkjet printing apparatus according to an embodiment of the present invention; [Figure 3B] 1 is a cross-sectional view showing an ink ejection section of a print head in an inkjet printing apparatus according to an embodiment of the present invention. [Figure 4A] 4 is a graph showing a driving waveform during dot formation in an inkjet recording apparatus according to an embodiment of the present invention. [Figure 4B] 5 is a graph showing the meniscus speed during dot formation in an inkjet recording apparatus according to one embodiment of the present invention. [Figure 4C] 5 is a graph showing the amount of change in the meniscus when dots are formed in an inkjet recording apparatus according to one embodiment of the present invention. [Figure 5A] 11 is a graph showing a driving waveform when dots are not formed in a conventional inkjet recording apparatus. [Figure 5B] 11 is a graph showing the meniscus speed when dots are not formed in a conventional inkjet recording apparatus. [Figure 5C] 11 is a graph showing the amount of change in the meniscus when dots are not formed in a conventional inkjet recording apparatus. [Figure 6A] 4 is a graph showing a drive waveform when dots are not formed in a first example of the inkjet recording apparatus according to one embodiment of the present invention. [Figure 6B] 6 is a graph showing the meniscus speed when dots are not formed in a first example of the inkjet recording apparatus according to one embodiment of the present invention. [Figure 6C] 6 is a graph showing the amount of change in the meniscus when dots are not formed in a first example, in an inkjet recording apparatus according to an embodiment of the present invention. [Figure 7A] 13 is a graph showing a drive waveform when dots are not formed in a second example, in an inkjet recording apparatus according to an embodiment of the present invention. [Figure 7B]13 is a graph showing the meniscus speed when dots are not formed in a second example, in an inkjet recording apparatus according to an embodiment of the present invention. [Figure 7C] 13 is a graph showing the amount of change in the meniscus when dots are not formed in a second example, in an inkjet recording apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] An inkjet recording apparatus according to an embodiment of the present invention will now be described with reference to the drawings.

[0014] First, the configuration of an inkjet recording apparatus 1 will be described with reference to Fig. 1. Fig. 1 is a front view showing a schematic configuration of the inkjet recording apparatus 1.

[0015] The inkjet recording device 1 includes a paper feed unit 3, a printing unit 5, and a drying unit 7. First, the paper feed unit 3 will be described. The paper feed unit 3 includes a paper feed tray 11 that stores a stack of recording media, and a paper feed roller pair 13 that feeds the recording media from the paper feed tray 11 and transports them to the printing unit 5. The paper feed roller pair 13 includes a drive roller that comes into contact with the uppermost recording medium of the stack of recording media, and a driven roller that rotates in response to the drive roller.

[0016] Next, the printing unit 5 will be described. The printing unit 5 is disposed downstream of the paper feed unit 3 in the transport direction of the recording medium, and includes a first transport unit 17 and a head unit 19. The first transport unit 17 includes a first driving roller 21 disposed downstream in the transport direction, a first driven roller 23 disposed upstream, and a first transport belt 25 stretched over the first driving roller 21 and the first driven roller 23. The first transport belt 25 is, for example, a seamless belt made of a dielectric resin. The first driving roller 21 is driven to rotate in the clockwise direction in FIG. 1, so that the first transport belt 25 travels in a circular manner in the clockwise direction in FIG. 1. As a result, the recording medium fed by the paper feed unit 3 is transported in the transport direction by the first transport belt 25 traveling along the upper travel track. The upper surface of the first transport belt 25 traveling along the upper travel track is set as the transport surface.

[0017] Next, the head unit 19 will be described with reference to Fig. 2. Fig. 2 is a plan view showing the head unit 19. The head unit 19 includes a head housing 31 and four line heads 33C, 33M, 33Y, and 33K (collectively referred to as line heads 33) held by the head housing 31. These line heads 33 are supported at a height such that a predetermined gap (for example, 1 mm) is formed with respect to the conveying surface of the first conveyor belt 25.

[0018] The line head 33 has a plurality of (three in this example) recording heads 35 arranged in a staggered pattern along the width direction of the paper (the vertical direction in FIG. 2) perpendicular to the transport direction. The recording head 35 has a large number of nozzles 71 to which ink is supplied, and a piezoelectric element (not shown in FIG. 2) provided for each nozzle 71. The nozzles 71 have ejection openings that open on the bottom surface of the recording head 35. When the piezoelectric element is driven, the ink in the nozzles 71 is ejected downward from the ejection openings (details will be described later). The line head 33 has a recording area that is equal to or larger than the width of the recording medium being transported.

[0019] Based on image data input from an external computer or the like, the line head 33 (recording head 35) ejects ink downward from nozzles 71 onto the recording medium transported on the transport surface of the first transport belt 25. As a result, a color image is formed on the recording medium on the first transport belt 25 in which four colors of ink, cyan, magenta, yellow, and black, are superimposed.

[0020] Furthermore, purging is performed at a predetermined timing to eject viscous ink in order to prevent ink ejection problems caused by drying or clogging of the recording head 35. Purging is performed on the nozzles 71 of all recording heads 35 when printing starts after a long period of inactivity, and on the nozzles 71 of recording heads 35 whose ink ejection volume is below a specified value between printing operations.

[0021] Next, the drying unit 7 will be described with reference to FIG. 1 again. The drying unit 7 is disposed downstream of the printing unit 5 in the transport direction of the recording medium, and includes a second transport unit 41. The second transport unit 41 includes a second driving roller 43 disposed downstream in the transport direction, a second driven roller 45 disposed upstream, and a second transport belt 47 stretched over the second driving roller 43 and the second driven roller 45. The second driving roller 43 is driven to rotate in the clockwise direction in FIG. 1, so that the second transport belt 47 travels in a circular manner in the clockwise direction in the figure. As a result, the ink ejected onto the recording medium is dried while the recording medium is transported in the transport direction by the second transport belt 47 traveling along the upper travel track.

[0022] A maintenance unit 49 is disposed below the second transport unit 41. When performing the above-mentioned purge, the maintenance unit 49 moves below the printing unit 5, wipes off the ink ejected from the nozzles 71 of the recording head 35, and collects the wiped ink.

[0023] A pair of discharge rollers 51 that discharges the print medium on which an image has been printed is provided downstream of the drying unit 7 in the transport direction of the recording medium. The medium on which the image has been printed is loaded onto a discharge tray 53 by the pair of discharge rollers 51.

[0024] Next, the ink ejection section 35a of the recording head 35 will be described with reference to Figures 3A and 3B. Figure 3A is a plan view of the ink ejection section 35a seen from above, and Figure 3B is a cross-sectional view of the ink ejection section 35a. As shown in Figure 3B, the ink ejection section 35a is formed by laminating a nozzle plate 61, a flow path plate 63, and a pressure plate 65 in this order from the bottom.

[0025] The nozzle plate 61 has a large number of nozzles 71 formed at predetermined positions, penetrating the nozzle plate 61 in the vertical direction.

[0026] The flow path plate 63 is provided with a common supply flow path 81 and a common circulation flow path 83 that are common to the multiple nozzles 71, and a descending flow path 85 provided for each nozzle 71. A supply port 81a that communicates with a pressurizing chamber 91 (described later) is formed in the upper wall of the common supply flow path 81. The descending flow path 85 communicates with the nozzles 71, and also communicates with the common circulation flow path 83 via a circulation flow path 87.

[0027] The pressure plate 65 is provided with a pressure chamber 91 for each nozzle 71. The pressure chamber 91 communicates with the common supply flow path 81 via the above-mentioned supply port 81a, and also communicates with the downward flow path 85. A piezoelectric element 93 is disposed for each pressure chamber 91 on the upper surface of the pressure plate 65. The piezoelectric element 93 is provided with an individual electrode 95. When a voltage is applied between a common electrode 97 provided on the upper surface of the pressure plate 65 and the individual electrode 95, the piezoelectric element 93 is deflected and deformed. The individual electrode 95 and the common electrode 97 are connected to a voltage application unit 99.

[0028] A positive pressure is applied to the common supply flow channel 81 from the upstream side by a pump. A negative pressure is applied to the common circulation flow channel 83 from the downstream side by a pump. The pressures of both pumps are balanced so that an appropriate negative pressure for ejecting ink is also applied to the upstream side of the nozzle 71. When dots are being formed and when dots are not being formed, the above pressure is applied to all nozzles 71, so that ink always flows from the common supply flow channel 81 through the supply port 81a to the pressure chamber 91, and from the pressure chamber 91 through the downward flow channel 85 and the circulation flow channel 87 to the common circulation flow channel 83. This flow is called a circulation flow (see arrow A in FIG. 2B).

[0029] When forming dots, a voltage corresponding to a drive waveform is applied between the individual electrodes 95 and the common electrode 97 from a voltage application unit 99, causing the piezoelectric elements 93 to bend and deform. This generates pressure in the pressure chambers 91, and ink is ejected from the pressure chambers 91 through the nozzles 71. This flow is called an oscillatory flow (see arrow B in FIG. 2B). The pressure of the circulating flow A is set to a level that does not affect the oscillatory flow B.

[0030] Next, a description will be given of the driving waveform of the voltage applied between the individual electrode 95 and the common electrode 97. As described above, the circulating flow (see arrow A in FIG. 3B) is formed in order to recover ink that has thickened at the tip of the nozzle 71, but it is difficult to reliably recover the thickened ink using only this circulating flow. Therefore, in order to reliably place the thickened ink in the circulating flow, the piezoelectric element 93 is driven with a voltage corresponding to a micro-driving waveform that vibrates the ink so as to draw in the meniscus to such an extent that the ink is not ejected from the nozzle 71 during non-formation of dots.

[0031] A vibration flow of ink is generated in the nozzle 71 by the pressure generated in the pressure chamber 91 by the flexural deformation of the piezoelectric element 93. The vibration period of this vibration flow is specific to the physical properties of the nozzle plate 61, flow path plate 63, and pressure plate 65 constituting the ink ejection unit 35a, the shapes of each flow path, the physical properties of the ink, etc. This vibration period is referred to as the natural vibration period Tc.

[0032] First, the driving waveform of the voltage applied when forming dots will be described with reference to Figures 4A to 4C. Figure 4A shows the driving waveform when forming dots, Figure 4B shows the meniscus speed, and Figure 4C shows the meniscus change amount. The meniscus speed and meniscus change amount show the simulation results for the driving waveform.

[0033] The driving waveform of the voltage applied when forming dots is based on a pulse with a pulse width of approximately Tc / 2, and multiple such pulses are combined to form a waveform that ejects droplets of different volumes. Figure 4A shows a driving waveform with a pulse width of Tc / 2. In this case, the meniscus of the ink in the nozzle 71 changes over time as shown in Figures 4B and 4C. That is, when the driving voltage changes from the standby voltage to zero, the deflection deformation of the piezoelectric element 93 is released and the meniscus is retracted.

[0034] 4B, after half a period of the natural vibration period Tc, the meniscus velocity changes from negative to positive, and the meniscus changes from being drawn into the nozzle 71 to being pushed out of the nozzle 71. At this timing, the applied voltage is returned to the standby voltage, causing the piezoelectric element to bend and deform, pushing out the meniscus. In this way, the vibration velocity of the meniscus is accelerated, causing ink droplets to be ejected from the nozzle 71.

[0035] Incidentally, when a common circulation path is not provided, a voltage is applied with a slight drive waveform to a nozzle that has not formed a dot for a predetermined period of time before forming a dot, to oscillate the meniscus and diffuse the thickened ink. For example, as shown in Fig. 5A, when the drive voltage is changed from the standby voltage to zero over a time corresponding to approximately Tc, and then the drive voltage is returned from zero to the standby voltage over a time corresponding to approximately Tc (when the drive voltage change time for drawing in the meniscus is Tc / 2 or more), the meniscus speed and the amount of change in the meniscus are small, as shown in Figs. 5B and 5C.

[0036] On the other hand, when a common circulation flow path 83 is provided (see FIGS. 3A and 3B), the purpose of applying a voltage with a micro-driving waveform is to draw the thickened ink layer formed at the tip of the nozzle 71 as deeply as possible into the nozzle 71 and place it on the circulation flow A. To achieve this, it is necessary to increase the amount of meniscus change. However, if the amount of meniscus change is increased, there is a possibility that a droplet will be erroneously ejected from the nozzle 71. Therefore, it is necessary to form a micro-driving waveform that can increase the amount of meniscus change to the same amount as when forming dots and prevent erroneous ejection.

[0037] For this reason, in the present invention, the voltage change time for drawing in the meniscus is set to less than Tc / 2, and a drive waveform is used that pushes out the meniscus over a time period of approximately Tc after a time period between Tc / 2 and Tc×3 / 2 has elapsed from the start of the voltage change.

[0038] Figure 6A shows a drive waveform (first embodiment) in which the voltage change time for pulling in the meniscus is Tc x 0.15, and the meniscus is pushed out over a period of approximately Tc after Tc / 2 has elapsed since the start of the voltage change. Figures 6B and 6C show the meniscus speed and meniscus change amount in this case. As shown in each figure, the meniscus change amount is larger than in the case of Figure 5, and is equivalent to the case of dot formation shown in Figure 4.

[0039] FIG. 7A shows a drive waveform (second embodiment) in which the voltage change time for drawing in the meniscus is Tc×0.15, and the meniscus is pushed out over a period of approximately Tc after the time Tc has elapsed since the start of the voltage change. The meniscus speed and meniscus change amount in this case are shown in FIG. 7B and FIG. 7C. In this case as well, as shown in each figure, the meniscus change amount is larger than in the case of FIG. 5, and is equivalent to the case of dot formation shown in FIG. 4. Also, since the meniscus is pushed out over a period of approximately Tc, the meniscus speed is reduced. This prevents erroneous ejection.

[0040] As described above, according to the present invention, the voltage change time for drawing in the meniscus is made relatively short and the voltage change time for pushing out the meniscus is made relatively long, thereby making it possible to increase the fluctuation of the meniscus. Therefore, the thickened layer of ink at the tip of the nozzle 71 can be drawn into the nozzle 71 without erroneous ejection, put on the circulation flow (arrow A in FIG. 3B), and sent to the circulation common flow path 83. As a result, it is possible to reliably prevent ink ejection defects caused by thickened ink, and form a good image.

[0041] Although the operation of oscillating the meniscus with the above-mentioned micro-driving waveform is performed during non-dot formation, it may be performed only for nozzles for which the cumulative time of non-dot formation has reached a predetermined time. Alternatively, since the degree of ink viscosity increase differs depending on the surrounding environment, in an environment where ink viscosity is likely to increase (such as when humidity is low), a micro-driving waveform may be selected that causes greater fluctuations in the meniscus.

[0042] Although the present invention has been described with reference to specific embodiments, the present invention is not limited to the above embodiments, and those skilled in the art may modify the above embodiments without departing from the scope and spirit of the present invention. [Explanation of symbols]

[0043] 1 Inkjet recording device 71 Nozzle 81 Common Supply Route 83 Common Circulation Route 91 Pressurized chamber 93 Piezoelectric element 99 Voltage application section

Claims

1. A plurality of nozzles opening toward a recording medium; a plurality of pressure chambers each communicating with the plurality of nozzles and containing ink therein; a piezoelectric element provided corresponding to each of the plurality of pressure chambers, the piezoelectric element being deflected and deformed by application of a voltage to apply pressure to the ink in the pressure chamber to cause the ink to be ejected from the nozzle; a voltage application unit that applies a voltage to the piezoelectric element based on a drive waveform for ejecting ink from the nozzle onto a recording medium and a micro-drive waveform for applying micro-vibrations to a meniscus of ink in the nozzle, The voltage application unit is A voltage is applied to the piezoelectric element based on the drive waveform during printing, and a voltage is applied to the piezoelectric element based on the fine drive waveform during non-printing; An inkjet recording device characterized in that, when the natural vibration period of the meniscus is Tc, the micro-driving waveform is formed so that the voltage change time for pulling in the meniscus is less than Tc / 2, and so that the meniscus is pushed out over a time period of Tc after a time period from Tc / 2 or more to Tc x 3 / 2 has elapsed from the start of the voltage change.

2. a common supply flow channel through which ink contained in the plurality of pressure chambers is supplied; 2. The ink jet recording apparatus according to claim 1, further comprising a common circulation path communicating with the plurality of pressure chambers and through which ink circulates.

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