JP2010064389A - Inkjet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a difference in image quality between images recorded by means of inkjet recording heads with nozzle faces having different vertical levels in a small recorder. <P>SOLUTION: A first back pressure generating mechanism 61 generates a back pressure in ink supplied to a first inkjet recording head 41 by virtue of a hydraulic head difference between a nozzle face 41A and the liquid level of an ink reservoir 53. A second back pressure generating mechanism 62 generates a back pressure in ink supplied to a second inkjet recording head 42 by virtue of a capillary force of a felt 56 instead of the hydraulic head difference to the liquid level of the ink reservoir 53. Accordingly, the pressure difference is reduced to be lower than the pressure difference in the case where the back pressure is generated in the ink supplied to the first inkjet recording head 41 and the ink supplied to the second inkjet recording head 42 by virtue of the hydraulic head difference to the liquid level of the ink reservoir 53, thereby reducing a difference in image quality between images. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ink jet recording apparatus.

  As an ink jet recording apparatus, an ink jet recording apparatus disclosed in Patent Document 1 is known. The ink jet recording apparatus disclosed in Patent Document 1 includes a plurality of ink jet recording heads having different nozzle surface heights, and ink tanks provided for the respective ink jet recording heads.

Ink is supplied from each ink tank to each ink jet recording head, and the back pressure applied to the ink is generated by a water head difference between the liquid level of each ink tank and the nozzle surface of each ink jet recording head.
JP 2000-510780 Gazette

  It is an object of the present invention to reduce the difference in image quality between images recorded by inkjet recording heads having different nozzle surface heights with a small apparatus.

  An ink jet recording apparatus according to a first aspect of the present invention includes a first ink jet recording head having a nozzle surface on which nozzles for ejecting ink droplets are formed, and a second surface having a nozzle surface disposed at a position lower than the nozzle surface. Inkjet recording head, one ink reservoir for storing ink, a first supply path for supplying ink from the ink reservoir to the first inkjet recording head, and ink from the ink reservoir to the second inkjet recording head A second supply path for supplying, a first back pressure generating mechanism for generating a back pressure with respect to the ink supplied to the first inkjet recording head, the ink supplied to the first inkjet recording head, and the second Back pressure is generated for the ink supplied to the ink jet recording head due to the water head difference from the liquid level of the ink reservoir. As the pressure difference than the pressure difference becomes small in a case where allowed, and a, a second back pressure generating mechanism that generates a back pressure against the ink supplied to said second ink jet recording head.

  An ink jet recording apparatus according to a second aspect of the present invention is the ink jet recording apparatus according to the first aspect, wherein the first back pressure generating mechanism is a liquid surface of the ink reservoir with respect to the ink supplied to the first ink jet recording head. The second back pressure generation mechanism has a porous member, and the back pressure is generated by the capillary force of the porous member with respect to the ink supplied to the second inkjet recording head. Generate pressure.

  An ink jet recording apparatus according to a third aspect of the present invention is the ink jet recording apparatus according to the first aspect, wherein the first back pressure generating mechanism has a porous member and supplies ink to the first ink jet recording head. Back pressure is generated by the capillary force of the porous member, and the second back pressure generating mechanism has a porous member, and the capillary of the porous member with respect to the ink supplied to the second inkjet recording head Back pressure is generated by force.

  An ink jet recording apparatus according to a fourth aspect of the present invention is the ink jet recording apparatus according to the third aspect, wherein the ink reservoir is a sealed structure that is not open to the atmosphere.

  An ink jet recording apparatus according to a fifth aspect of the present invention is the ink jet recording apparatus according to any one of the second to fourth aspects, wherein the ink is supplied from the ink reservoir to the first ink jet recording head and the second ink jet recording head. A detour circuit for detouring the ink so that the ink does not pass through the porous member, and a return path for returning the ink supplied to the first inkjet recording head and the second inkjet recording head to the ink reservoir. And a circulation means for circulating the ink between the first ink jet recording head, the second ink jet recording head, and the ink reservoir, by circulating the ink through the bypass and the return path. .

  An ink jet recording apparatus according to a sixth aspect of the present invention is the ink jet recording apparatus according to the first aspect, wherein the first back pressure generating mechanism is a liquid surface of the ink reservoir with respect to the ink supplied to the first ink jet recording head. The second back pressure generating mechanism generates a back pressure due to a water head difference between the ink supplied to the second inkjet recording head and the liquid level of the ink reservoir. In addition, the flow path resistance of the second supply path is made larger than that of the first supply path.

  According to a seventh aspect of the present invention, in the configuration of the sixth aspect, the back pressure generated by the first back pressure generation mechanism at the maximum flow rate of the ink flowing through the first supply path, and the first The flow path resistance is set so that the back pressure generated by the second back pressure generating mechanism is the same at the maximum flow rate of the ink flowing through the two supply paths.

  According to the configuration of the first aspect of the present invention, as compared with the configuration including a plurality of ink storage units, the image quality difference of the image recorded by the inkjet recording head having a different nozzle surface height is reduced with a small device. can do.

  According to the configuration of the second aspect of the present invention, the image quality difference of the image recorded by the inkjet recording head having a different nozzle surface height can be reduced with a small device as compared with the configuration including a plurality of ink storage units. can do.

  According to the configuration of the third aspect of the present invention, the first inkjet is compared with the configuration in which the back pressure is generated by the water head difference between the ink supplied to the first inkjet recording head and the liquid level of the ink reservoir. There may be a small difference in height between the recording head and the ink reservoir.

  According to the configuration of the fourth aspect of the present invention, it is not necessary to dispose the ink reservoir below the first ink jet recording head and the second ink jet recording head.

  According to the configuration of the fifth aspect of the present invention, the ink can be circulated even when the porous member is provided.

  According to the configuration of the sixth aspect of the present invention, the image quality difference of the image recorded by the inkjet recording head having a different nozzle surface height is reduced with a small device as compared with the configuration including a plurality of ink storage portions. can do.

  According to the configuration of the seventh aspect of the present invention, in the case where the density of the image recorded by the first inkjet recording head and the second inkjet recording head is high compared to the case where the configuration is not provided, the density difference Can be reduced.

Below, an example of an embodiment concerning the present invention is described based on a drawing.
(Configuration of inkjet recording apparatus according to this embodiment)
First, the configuration of the ink jet recording apparatus according to the present embodiment will be described. FIG. 1 is a schematic diagram illustrating a configuration of an ink jet recording apparatus according to the present embodiment. In FIG. 1, the vertical direction (vertical direction) of the apparatus is indicated by arrows.

  As shown in FIG. 1, the ink jet recording apparatus 10 according to the present embodiment includes an apparatus housing 12 that houses each component. The apparatus housing 12 is provided with an image recording mechanism 14 that records an image on a recording medium P such as paper.

  The inkjet recording apparatus 10 may further include an image reading mechanism that reads an image of a document. In the case of this configuration, the image recording mechanism 14 may record an image based on the image read by the image reading mechanism.

  The image recording mechanism 14 includes a recording medium accommodating unit 16 that accommodates a recording medium P such as paper, a recording medium conveying unit 18 that conveys the recording medium P accommodated in the recording medium accommodating unit 16, and a recording medium conveying unit 18. An image recording unit 20 capable of recording an image on the recording medium P conveyed to the recording medium, and a recording medium discharging unit 22 from which the recording medium P conveyed by the recording medium conveying unit 18 is discharged.

  The recording medium storage unit 16 includes a table 24 on which the recording medium P is placed. When the recording medium P is placed on the table 24, the recording medium P is accommodated in the recording medium accommodation unit 16.

  The recording medium transport unit 18 includes a feed roll 26 that sends out the recording medium P stored in the recording medium storage unit 16 from the recording medium storage unit 16. A separation mechanism 28 that separates the recording media P delivered from the recording medium storage unit 16 one by one is disposed on the downstream side of the delivery roll 26. The separation mechanism 28 applies a conveyance resistance from the front side to the recording medium P fed to the sending roll 26 and a feeding roll 30 that applies a feeding force from the front side to the recording medium P sent to the sending roll 26. And a separation pad 32 to be applied.

  Thereby, when a plurality of recording media P are sent out from the recording medium accommodating portion 16 in an overlapping manner, the conveying roll 30 applies a conveying force to the upper recording medium P (first recording medium P), The lower recording medium P (second and subsequent recording media P) is given a transport resistance by the separation pad 32, and the recording medium P is separated. In this way, the overlapping recording media P are rolled and fed one by one by the delivery roll 26 and the separation pad 32.

  In the recording medium transport unit 18, a U-shaped transport path 34 for transporting the recording medium P separated by the separation mechanism 28 to the recording medium discharge unit 22 is formed. In the transport path 34, a plurality of transport rolls 36 that transport the recording medium P and a discharge roll 38 that discharges the recording medium P to the recording medium discharge unit 22 are arranged.

  The recording medium discharge unit 22 includes a table 40 on which the recording medium P discharged by the discharge roll 38 is placed. The recording medium P discharged by the discharge roll 38 is placed on the table 40 and discharged from the recording medium. Housed in the part 22.

  On the other hand, the image recording unit 20 includes a first inkjet recording head 41 and a second inkjet recording head 42 that record ink images on a recording medium by ejecting ink droplets from nozzles 45 (see FIG. 2). The first inkjet recording head 41 records an image by ejecting ink droplets onto a recording medium P conveyed to an image recording position below the first inkjet recording head 41.

  The first ink jet recording head 41 and the second ink jet recording head 42 have a recordable area that is equal to or larger than the maximum width of the recording medium P on which image recording with the ink jet recording apparatus 10 is assumed. .

  The first inkjet recording head 41 and the second inkjet recording head 42 are configured by integrally providing a plurality of colors such as yellow (Y), magenta (M), cyan (C), and black (K). Yes. The ink droplets corresponding to the respective colors are ejected from a plurality of nozzles by a piezoelectric method to record an image. In the first inkjet recording head 41 and the second inkjet recording head 42, the configuration for ejecting ink droplets may be a configuration for ejecting by another method such as a thermal method.

The recording medium P on which the image is recorded on the surface by the first inkjet recording head 41 is reversed by the conveyance path 34 and conveyed to the image recording position below the second inkjet recording head 42.
The second inkjet recording head 42 ejects ink droplets onto the recording medium P transported to the image recording position below the second inkjet recording head 42 to record an image on the back surface. The recording medium P on which images are recorded on both sides in this way is discharged to the recording medium discharge unit 22 by the discharge roll 38.

  A maintenance member 44 for maintaining the first ink jet recording head 41 and the second ink jet recording head 42 is provided below the first ink jet recording head 41 and the second ink jet recording head 42 on each of the nozzle surfaces 41A and 42A. It is provided facing. Each maintenance member 44 includes a cap that covers the nozzle surface, a cleaning member that cleans the nozzle surface, and a suction device that sucks ink in the nozzle.

(Image recording unit 20 and supply mechanism for supplying ink to image recording unit 20)
Next, the supply mechanism for supplying ink to the image recording unit 20 and the image recording unit 20 will be described. FIG. 2 is a schematic diagram illustrating the configuration of the image recording unit 20 and a supply mechanism that supplies ink to the image recording unit 20.

  The ink jet recording apparatus 10 according to this embodiment includes an image recording unit 20 and a supply mechanism 50 that supplies ink to the image recording unit 20. The image recording unit 20 includes the first inkjet recording head 41 and the second inkjet recording head 42 as described above.

  The first inkjet recording head 41 has a nozzle surface 41A on which nozzles 45 for ejecting ink droplets are formed, and the second inkjet recording head 42 has a nozzle surface 42A on which nozzles 45 for ejecting ink droplets are formed. is doing.

  The nozzle surface 42 </ b> A of the second inkjet recording head 42 is disposed at a position lower than the nozzle surface 41 </ b> A of the first inkjet recording head 41.

  The supply mechanism 50 includes an ink storage unit 53 for storing ink supplied to the first inkjet recording head 41 and the second inkjet recording head 42. In addition, the dot part in a figure has shown the ink.

  Only one ink reservoir 53 is provided for the first inkjet recording head 41 and the second inkjet recording head 42, that is, for two inkjet recording heads. The ink reservoir 53 is open to the atmosphere with an opening 53A formed at the top. Further, the ink reservoir 53 is disposed below the first inkjet recording head 41 and the second inkjet recording head 42, and from the nozzle surface 41 </ b> A of the first inkjet recording head 41 and the nozzle surface 42 </ b> A of the second inkjet recording head 42. The liquid level is located below.

  In addition, the supply mechanism 50 includes an ink common path 54 connected to the ink reservoir 53 and a branch path that branches from the ink common path 54 and is connected to each of the first inkjet recording head 41 and the second inkjet recording head 42. 54A, 54B.

  The first supply path 51 that supplies the ink in the ink storage unit 53 to the first inkjet recording head 41 includes an ink common path 54 and a branch path 54A. The second supply path 52 that supplies the ink in the ink reservoir 53 to the second inkjet recording head 42 is configured by an ink common path 54 and a branch path 54B. The first supply path 51 and the second supply path 52 are formed of tubes such as tubes.

  The first supply path 51 and the second supply path 52 are partially shared by the ink common path 54, but may be configured as separate and independent flow paths.

  Further, the supply mechanism 50 includes a first back pressure generating mechanism 61 that generates a back pressure for the ink supplied to the first ink jet recording head 41 and a back for the ink supplied to the second ink jet recording head 42. And a second back pressure generating mechanism 62 that generates pressure.

  In the present embodiment, the first back pressure generation mechanism 61 generates a back pressure for the ink supplied to the first ink jet recording head 41 due to a water head difference between the nozzle surface 41 </ b> A and the liquid surface of the ink storage unit 53. Is. That is, the first back pressure generating mechanism 61 is specifically configured to include an ink storage unit 53 that is disposed below the first ink jet recording head 41 to cause a water head difference.

  When the ink in the ink storage unit 53 is consumed and the remaining amount of ink in the ink storage unit 53 changes, the water head difference changes. For example, the change in the water head difference falls within the allowable range. The width (area in the horizontal direction) is set. By setting the area of the ink reservoir 53 wide, even when ink is consumed, the fluctuation of the liquid level is reduced, and the fluctuation of the water head difference is suppressed.

  Further, as shown in FIG. 3, an adjustment mechanism 55 that adjusts the liquid level may be provided in the ink reservoir 53. The adjustment mechanism 55 includes a sensor 55 </ b> A that detects the liquid level of the ink reservoir 53, and a raiseable bottom plate 55 </ b> B disposed in the ink reservoir 53. In this configuration, the sensor 55A detects the liquid level, and when the liquid level falls below a predetermined value, the bottom plate 55B is raised so that the liquid level is set to an appropriate height.

  On the other hand, the second back pressure generating mechanism 62 is driven by the head difference between the ink supplied to the first ink jet recording head 41 and the ink supplied to the second ink jet recording head 42 with the liquid surface of the ink reservoir 53. The back pressure is generated so that the pressure difference becomes smaller than the pressure difference when the pressure is generated.

  Here, since the nozzle surface 41A of the first ink jet recording head 41 and the nozzle surface 42A of the second ink jet recording head 42 have different heights, the back pressure under the same condition is caused by the difference in water head from the liquid surface of the ink reservoir 53. Is generated, a pressure difference is generated in the back pressure by the different height. The second back pressure generation mechanism 62 generates a back pressure for the ink supplied to the second inkjet recording head 42 so that the pressure difference becomes smaller than the pressure difference.

  Specifically, the second back pressure generating mechanism 62 includes a felt 56 as an example of a porous member. The felt 56 is disposed between the second supply path 52 and the second ink jet recording head 42, and is accommodated in a casing 58 having an opening 58A. The felt 56 is opened to the atmosphere through the opening 58A.

  The felt 56 may be provided integrally with the second inkjet recording head 42. Further, the felt 56 may be disposed in the second supply path 52.

  The second back pressure generation mechanism 62 generates a back pressure on the ink supplied to the second ink jet recording head 42 by the capillary force of the felt 56, not by the water head difference from the liquid level of the ink reservoir 53. This back pressure is set to be approximately the same as the back pressure generated by the first back pressure generating mechanism 61 by adjusting the porous hole diameter of the felt 56, for example.

  Further, the capillary force of the felt 56 is smaller than the capillary force of the nozzle 45, and when the ink of the nozzle 45 is consumed, the ink is filled from the felt 56 into the second inkjet recording head 42. When the ink is filled in the second inkjet recording head 42 from the felt 56 and the ink in the felt 56 is consumed, the ink is supplied from the ink reservoir 53 to the felt 56 by the capillary force of the felt 56.

  4 and 5, the ink jet recording apparatus 10 includes a circulation mechanism 70 for circulating ink between the first ink jet recording head 41 and the second ink jet recording head 42 and the ink reservoir 53. The structure provided may be sufficient.

  In the circulation mechanism 70, a pump 74 as an example of a circulation unit that circulates ink between the first inkjet recording head 41, the second inkjet recording head 42, and the ink reservoir 53 is disposed in the ink common path 54. .

  The pump 74 is configured by, for example, a tube pump when the flow path is formed by a tube. The tube pump is wound around the outer periphery of the tube pump in a squeezed state. The tube pump rotates with the tube crushed, and squeezes the tube to send ink downstream. Since the tube pump is in a state where the tube is crushed, the ink does not circulate in the ink common path 54 when the tube pump is not driven to rotate.

  The ink common path 54 is connected to a bypass circuit 78 that bypasses the pump 74. The bypass circuit 78 has one end (upstream end) connected to the ink common path 54 on the upstream side of the pump 74, and the other end (downstream end) connected to the ink common path 54 on the downstream side of the pump 74. Yes.

  In the bypass 78, an on-off valve 76A for opening and closing the flow path is disposed. When the opening / closing valve 76A opens the flow path, ink can flow in the bypass circuit 78, and when the opening / closing valve 76A closes the flow path, ink cannot flow in the bypass circuit 78.

  When the pump 74 is not driven and the pump 74 is configured to allow ink to flow, the bypass circuit 78 and the on-off valve 76A are unnecessary.

  In addition, the circulation mechanism 70 includes a bypass circuit 73 that bypasses the ink so that the ink supplied from the ink storage unit 53 to the first inkjet recording head 41 and the second inkjet recording head 42 does not pass through the felt 56, and the first inkjet A first return path 71 for returning ink supplied to the recording head 41 to the ink reservoir 53 and a return path 72 for returning ink supplied to the second inkjet recording head 42 to the ink reservoir 53 are provided. ing.

  The bypass 73 has one end (upstream end) connected to the ink common path 54 upstream of the felt 56 and the other end (downstream end) connected to the branch path 54B downstream of the felt 56. Yes. In the bypass 73, an on-off valve 76A for opening and closing the flow path is disposed.

  In the circulation mechanism 70, the felt 56 is disposed in the branch path 54B. In the branch path 54B, an opening / closing valve 76C for opening / closing the flow path is disposed on the upstream side of the felt 56, and an opening / closing valve 76D for opening / closing the flow path is disposed on the downstream side of the felt 56.

  Specifically, the opening / closing valve 76C is located between the felt 56 and the connection portion between the upstream end of the bypass 73 and the ink common path 54, and the opening / closing valve 76D branches from the downstream end of the bypass 73. It is located between the connection part with the path 54B and the felt 56. An opening / closing valve 76E that opens and closes the flow path is also disposed in the branch path 54A.

  The first return path 71 has an upstream end connected to the first ink jet recording head 41 and a downstream end disposed in the opening 53 </ b> A of the ink reservoir 53. The ink flowing through the first return path 71 falls into the ink storage unit 53. In addition, an opening / closing valve 76F for opening and closing the flow path is disposed in the first return path 71.

  The second return path 72 has an upstream end connected to the second inkjet recording head 42 and a downstream end disposed in the opening 53 </ b> A of the ink reservoir 53. The ink that has flowed through the second return path 72 falls into the ink reservoir 53. The second return path 72 is provided with an opening / closing valve 76G that opens and closes the flow path.

  When the ink is circulated in the circulation mechanism 70, as shown in FIG. 4, the on-off valve 76A, the on-off valve 76C, and the on-off valve 76D are closed, and the on-off valve 76B, the on-off valve 76E, the on-off valve 76F, and the on-off valve 76G are closed. Open. Then, the pump 74 is driven to circulate ink between the first ink jet recording head 41, the second ink jet recording head 42, and the ink reservoir 53.

  Ink from the ink reservoir 53 passes through the ink common path 54 and the branch path 54A, reaches the first inkjet recording head 41, and passes from the first inkjet recording head 41 through the first return path 71 to the ink reservoir 53. To reach.

  Further, the ink from the ink reservoir 53 reaches the second ink jet recording head 42 through the ink common path 54, the detour path 73, and the branch path 54B, and passes through the second return path 72 from the second ink jet recording head 42. It passes through and reaches the ink reservoir 53.

  At the time of ink ejection, as shown in FIG. 5, the on-off valve 76B, the on-off valve 76F, and the on-off valve 76G are closed, and the on-off valve 76A, the on-off valve 76C, the on-off valve 76D, and the on-off valve 76E are opened. Ink is supplied from the ink reservoir 53 to the first inkjet recording head 41 and the second inkjet recording head 42 by the capillary force of the nozzle 45 and the felt 56 without driving the pump 74.

(First Modification of Supply Mechanism 50)
Next, a first modification of the supply mechanism 50 will be described. FIG. 6 is a diagram illustrating a configuration of a supply mechanism according to a first modification. In addition, the same code | symbol is attached | subjected to the part same as said embodiment, and description is abbreviate | omitted.

  As shown in FIG. 6, the supply mechanism 150 according to the first modification includes a first back pressure generation mechanism 161 that generates a back pressure for the ink supplied to the first inkjet recording head 41.

  The first back pressure generating mechanism 161 includes a felt 156 as an example of a porous member. The felt 156 is disposed between the first supply path 51 and the first inkjet recording head 41, and is accommodated in a casing 158 having an opening 158A. The felt 156 is open to the atmosphere through the opening 158A.

  The felt 156 may be provided integrally with the first ink jet recording head 41. Further, the felt 156 may be disposed in the first supply path 51.

  In the first back pressure generation mechanism 161, back pressure is generated for the ink supplied to the first inkjet recording head 41 by the capillary force of the felt 156, not by the water head difference from the liquid level of the ink reservoir 53. This back pressure is adjusted, for example, by adjusting the porous pore diameter of the felt 156 and the like.

  Similar to the supply mechanism 50, the supply mechanism 150 according to the first modification includes a second back pressure generation mechanism 62. The back pressure generated by the second back pressure generation mechanism 62 is approximately the same as the back pressure generated by the first back pressure generation mechanism 161 by adjusting, for example, the porous hole diameter of the felt 56. .

  As shown in FIG. 7, the ink reservoir 53 is not opened to the atmosphere but may be a sealed ink reservoir 153. In this case, air A is sealed in the ink reservoir 153 at a pressure equal to or higher than the bubble point pressure.

  Here, the bubble point pressure is a pressure at which the surface tension against the force acts when the meniscus of the liquid formed in the micropores is pushed by the air, but the air is overcome by overcoming this surface tension. .

  In this configuration, even when the height of the ink reservoir 153 is changed, the pressure applied to the ink supplied to the first inkjet recording head 41 and the second inkjet recording head 42 does not vary. For this reason, it is not necessary to dispose the ink reservoir 153 below the first inkjet recording head 41 and the second inkjet recording head 42.

  Note that the ink jet recording apparatus 10 also circulates ink between the first ink jet recording head 41 and the second ink jet recording head 42 and the ink reservoir 53 in the supply mechanism 150 according to the first modification, as described above. The structure provided with the circulation mechanism for making it may be sufficient. In this case, it is configured in the same manner as the circulation mechanism 70 and bypasses the ink so that the ink supplied from the ink reservoir 53 to the first inkjet recording head 41 and the second inkjet recording head 42 does not pass through the felt 56 and the felt 156. A detour to be made is arranged.

(Second Modification of Supply Mechanism 50)
Next, a second modification of the supply mechanism 50 will be described. FIG. 8 is a diagram illustrating a configuration of a supply mechanism according to a second modification. In addition, the same code | symbol is attached | subjected to the part same as said embodiment, and description is abbreviate | omitted.

  As shown in FIG. 8, the supply mechanism 250 according to the second modification includes a first back pressure generation mechanism 61, similar to the supply mechanism 50.

  The supply mechanism 250 according to the second modification includes a second back pressure generation mechanism 262 that generates a back pressure with respect to the ink supplied to the second inkjet recording head 42.

  Similar to the second back pressure generation mechanism 62, the second back pressure generation mechanism 262 has an ink storage section for the ink supplied to the first inkjet recording head 41 and the ink supplied to the second inkjet recording head 42. The back pressure is generated so that the pressure difference becomes smaller than the pressure difference when the back pressure is generated by the water head difference from the liquid level of 53.

  Specifically, the second back pressure generating mechanism 262 is similar to the first back pressure generating mechanism 61 in that the water head difference between the ink supplied to the second ink jet recording head 42 and the liquid level of the ink reservoir 53 is the same. This generates back pressure. That is, the second back pressure generation mechanism 262 is specifically configured to include an ink storage unit 53 that causes a water head difference by being disposed below the second inkjet recording head 42.

  The second back pressure generating mechanism 262 adjusts the generated back pressure by making the flow path resistance of the second supply path 52 larger than the flow path resistance of the first supply path 51. Specifically, the second back pressure generating mechanism 262 is configured to include a second supply path 252 having a flow path width narrower than that of the first supply path 51 and a flow path resistance increased.

  When the 1st supply path 51 and the 2nd supply path 252 are constituted by tubes, such as a tube, the diameter of the pipe which constitutes the 1st supply path 51 is the tube of the pipe which constitutes the 2nd supply path 252 It is thinner than the diameter. Similar to the second supply path 52, the second supply path 252 includes an ink common path 54 and a branch path 54B.

  Note that as the adjusting means for adjusting the channel resistance, not only the tube diameter but also a tube length of the tube or a filter disposed in the channel may be used. If the pipe length of the pipe is increased, the flow path resistance is increased accordingly. Further, if a filter is arranged in the flow path, the flow path resistance is increased accordingly. Furthermore, the flow path resistance is increased by reducing the hole diameter of the filter hole disposed in the flow path.

  Further, the back pressure generated by the first back pressure generating mechanism 61 at the maximum flow rate of the ink ejected by the first inkjet recording head 41 and the second back pressure at the maximum flow rate of the ink ejected by the second inkjet recording head 42. The channel resistance is set so that the back pressure generated by the generating mechanism 262 is the same (see FIGS. 9 and 10).

  As a result, the negative pressure difference at the high image density portion is eliminated, and the density difference at the high image density portion is reduced.

  The maximum flow rate is a flow rate when all the nozzles are driven almost simultaneously. Note that when the nozzles to be driven are limited during ink ejection, the flow rate is when all the unrestricted nozzles are driven almost simultaneously.

  The case where the driven nozzle is limited is, for example, in order to reduce the amount of ink adhering to the recording medium P and suppress curling of the recording medium P when recording images on both sides of the recording medium P. The image density (coverage) may be reduced, and usable nozzles may be reduced as compared with the case where an image is recorded on one side of the recording medium P. 9 shows the case where the maximum ink flow rate is obtained when the image density (coverage) is 100%, and FIG. 10 shows the maximum ink flow rate when the image density (coverage) is 50%. Show the case.

  As shown in FIG. 11, the back pressure generated by the first back pressure generating mechanism 61 at the maximum ink flow rate ejected by the first ink jet recording head 41 and the maximum ink ejected by the second ink jet recording head 42 are shown. The back pressure generated by the second back pressure generation mechanism 262 at the time of the flow rate may be different. In the example shown in FIG. 11, the slope θ1 with respect to the flow rate of the negative pressure generated by the second back pressure generating mechanism 262 is smaller than the slope θ2 in the case shown in FIG.

  In addition, as shown in FIGS. 12 and 13, the inkjet recording apparatus 10 includes the first inkjet recording head 41, the second inkjet recording head 42, and the ink storage unit 53 in the supply mechanism 250 according to the second modification. A configuration provided with a circulation mechanism 170 for circulating ink between them may be used.

  In the circulation mechanism 170, a pump 174 as an example of a circulation unit that circulates ink between the first inkjet recording head 41 and the second inkjet recording head 42 and the ink reservoir 53 is disposed in the ink common path 54. .

  The pump 174 is constituted by, for example, a tube pump when the flow path is formed by a tube. The tube pump is wound around the outer periphery of the tube pump in a squeezed state. The tube pump rotates with the tube crushed, and squeezes the tube to send ink downstream. Since the tube pump is in a state where the tube is crushed, the ink does not circulate in the ink common path 54 when the tube pump is not driven to rotate.

  Further, a bypass circuit 178 that bypasses the pump 174 is connected to the ink common path 54. The bypass circuit 178 has one end (upstream end) connected to the ink common path 54 on the upstream side of the pump 174, and the other end (downstream end) connected to the ink common path 54 on the downstream side of the pump 174. Yes.

  The bypass circuit 178 is provided with an on-off valve 176A that opens and closes the flow path. When the opening / closing valve 176A opens the flow path, ink can flow in the bypass circuit 178, and when the opening / closing valve 176A closes the flow path, ink cannot flow in the bypass circuit 178.

  When the pump 174 is not driven and the pump 174 is configured to allow ink to flow, the bypass 178 and the on-off valve 176A are not necessary.

  In the circulation mechanism 170, an on-off valve 176B that opens and closes the flow path is disposed in the branch path 54A, and an on-off valve 176C that opens and closes the flow path is disposed in the branch path 54B.

  The circulation mechanism 170 also supplies a first return path 171 for returning the ink supplied to the first inkjet recording head 41 to the ink storage unit 53 and the ink supplied to the second inkjet recording head 42 to the ink storage unit 53. And a return path 172 for returning to the back.

  The first return path 171 has an upstream end connected to the first ink jet recording head 41 and a downstream end disposed in the opening 53 </ b> A of the ink reservoir 53. The ink that has flowed through the first return path 171 falls into the ink reservoir 53. The first return path 171 is provided with an on-off valve 176D that opens and closes the flow path.

  The second return path 172 has an upstream end connected to the second inkjet recording head 42 and a downstream end disposed in the opening 53 </ b> A of the ink reservoir 53. The ink flowing through the second return path 172 falls into the ink storage unit 53. In the second return path 172, an on-off valve 176E that opens and closes the flow path is disposed.

  When the ink is circulated in the circulation mechanism 170, as shown in FIG. 12, the on-off valve 176A is closed, and the on-off valve 176B, on-off valve 176C, on-off valve 176D, and on-off valve 176E are opened. Then, the pump 174 is driven to circulate ink between the first ink jet recording head 41 and the second ink jet recording head 42 and the ink reservoir 53.

  The ink from the ink reservoir 53 passes through the ink common path 54 and the branch path 54A, reaches the first inkjet recording head 41, and passes from the first inkjet recording head 41 through the first return path 171 to the ink reservoir 53. To reach.

  Further, the ink from the ink storage unit 53 reaches the second inkjet recording head 42 through the ink common path 54 and the branch path 54B, and stores the ink from the second inkjet recording head 42 through the second return path 172. The unit 53 is reached.

  At the time of ink discharge, as shown in FIG. 13, the on-off valve 176D and the on-off valve 176E are closed, and the on-off valve 176A, the on-off valve 176B, and the on-off valve 176C are opened. Ink is supplied from the ink reservoir 53 to the first inkjet recording head 41 and the second inkjet recording head 42 by the capillary force of the nozzle 45 without driving the pump 174.

  The present invention is not limited to the above-described embodiment, and various modifications, changes, and improvements can be made.

FIG. 1 is a schematic diagram showing the overall configuration of the ink jet recording apparatus according to the present embodiment. FIG. 2 is a schematic diagram illustrating a configuration of an image recording unit and a supply mechanism that supplies ink to the image recording unit. FIG. 3 is a schematic diagram illustrating a configuration in which an adjustment mechanism that adjusts the liquid level is provided in the ink storage unit in the supply mechanism according to the present embodiment. FIG. 4 is a schematic diagram showing a configuration including a circulation mechanism according to the present embodiment, and shows a state during ink circulation. FIG. 5 is a schematic diagram illustrating a configuration including the circulation mechanism according to the present embodiment, and illustrates a state during ink ejection. FIG. 6 is a schematic diagram illustrating a configuration of a supply mechanism according to a first modification. FIG. 7 is a schematic diagram illustrating a configuration using a sealed ink storage unit in the configuration of the supply mechanism according to the first modification. FIG. 8 is a schematic diagram illustrating a configuration of a supply mechanism according to a second modification. FIG. 9 shows the back pressure generated by the first back pressure generating mechanism at the maximum ink flow rate discharged from the first ink jet recording head and the second back pressure generation at the maximum ink flow rate discharged by the second ink jet recording head. 6 is a graph showing the relationship between the ink flow rate and the negative pressure when the flow path resistance is set so that the back pressure generated by the mechanism is the same. FIG. 10 shows the back pressure generated by the first back pressure generation mechanism at the maximum ink flow rate discharged from the first ink jet recording head and the second back pressure generation at the maximum ink flow rate discharged by the second ink jet recording head. It is a graph showing the relationship between the ink flow rate and the negative pressure when the flow path resistance is set so that the back pressure generated by the mechanism is the same, and when the image density (coverage) is 50%, The case where the maximum ink flow rate is shown. FIG. 11 shows the back pressure generated by the first back pressure generating mechanism at the maximum ink flow rate ejected by the first ink jet recording head and the second back pressure generation at the maximum ink flow rate ejected by the second ink jet recording head. 6 is a graph showing the relationship between the ink flow rate and the negative pressure when the channel resistance is set so that the back pressure generated by the mechanism is different. FIG. 12 is a schematic diagram showing a configuration in which a circulation mechanism is applied in the supply mechanism according to the second modification, and shows a state during ink circulation. FIG. 13 is a schematic diagram illustrating a configuration in which a circulation mechanism is applied in the supply mechanism according to the second modification, and illustrates a state during ink ejection.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inkjet recording device 41 1st inkjet recording head 41A Nozzle surface 42 2nd inkjet recording head 42A Nozzle surface 45 Nozzle 51 1st supply path 52 2nd supply path 53 Ink storage part 56 Felt (porous member)
61 First back pressure generating mechanism 62 Second back pressure generating mechanism 71 First return path 72 Second return path 73 Detour path 74 Pump (circulation means)
252 Second supply path 153 Ink reservoir 156 Felt (porous member)
161 First back pressure generation mechanism

Claims (7)

A first inkjet recording head having a nozzle surface on which nozzles for discharging ink droplets are formed;
A second inkjet recording head having a nozzle surface disposed at a position lower than the nozzle surface;
One ink reservoir for storing ink;
A first supply path for supplying ink in the ink reservoir to the first inkjet recording head;
A second supply path for supplying ink from the ink reservoir to a second inkjet recording head;
A first back pressure generating mechanism for generating a back pressure for the ink supplied to the first ink jet recording head;
More than the pressure difference in the case where back pressure is generated by the water head difference between the ink supplied to the first ink jet recording head and the ink supplied to the second ink jet recording head from the liquid surface of the ink reservoir. A second back pressure generating mechanism for generating a back pressure with respect to the ink supplied to the second ink jet recording head so as to reduce a pressure difference;
An ink jet recording apparatus comprising: The first back pressure generation mechanism generates a back pressure due to a water head difference with respect to a liquid surface of the ink storage unit with respect to the ink supplied to the first inkjet recording head,
2. The inkjet according to claim 1, wherein the second back pressure generation mechanism includes a porous member, and generates a back pressure by the capillary force of the porous member with respect to the ink supplied to the second inkjet recording head. Recording device. The first back pressure generating mechanism has a porous member, and generates a back pressure by the capillary force of the porous member for the ink supplied to the first inkjet recording head,
2. The inkjet according to claim 1, wherein the second back pressure generation mechanism includes a porous member, and generates a back pressure by the capillary force of the porous member with respect to the ink supplied to the second inkjet recording head. Recording device.   The ink jet recording apparatus according to claim 3, wherein the ink storage unit has a sealed structure that is not open to the atmosphere. A detour that bypasses the ink so that the ink supplied from the ink reservoir to the first inkjet recording head and the second inkjet recording head does not pass through the porous member;
A return path for returning the ink supplied to the first inkjet recording head and the second inkjet recording head to the ink reservoir;
Circulating means for circulating the ink in the bypass and the return path, and circulating the ink between the first inkjet recording head, the second inkjet recording head, and the ink reservoir;
An inkjet recording apparatus according to any one of claims 2 to 4, further comprising: The first back pressure generation mechanism generates a back pressure due to a water head difference with respect to a liquid surface of the ink storage unit with respect to the ink supplied to the first inkjet recording head,
The second back pressure generation mechanism generates a back pressure for the ink supplied to the second ink jet recording head due to a water head difference from the liquid level of the ink reservoir, and more than the first supply path. The inkjet recording apparatus according to claim 1, wherein the flow path resistance of the second supply path is increased.   The back pressure generated by the first back pressure generating mechanism at the maximum flow rate of ink flowing through the first supply path, and the second back pressure generating mechanism at the maximum flow rate of ink flowing through the second supply path. The inkjet recording apparatus according to claim 6, wherein the flow path resistance is set so that the back pressure to be generated is the same.

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