JP2016049700A - Ink jet printing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an increase in size of an ink jet printing device for applying a negative pressure to a nozzle of an ink jet head while circulating an ink by applying a pressure to an upstream tank and a downstream tank by an air pump.SOLUTION: A control section 5 of an ink jet printing device 1 performs control to send air from a downstream side sealed space to an upstream side sealed space by an air pump 16 while controlling an ink pump 15 and an ink replenishment section 4 so that a state in which the volume of the upstream side sealed space including an air layer 27 in an upstream tank 11 is equal to the volume of the downstream side sealed space including an air layer 30 in a downstream tank 13 is maintained during ink circulation. The ink jet printing device 1 is configured so that pressure loss in an upstream side flow passage 28 is larger than that in a downstream side flow passage 31.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ink circulation type ink jet printing apparatus.

  2. Description of the Related Art An ink circulation type inkjet printing apparatus that prints by ejecting ink from an inkjet head while circulating ink is known.

  Patent Document 1 discloses an ink jet printing apparatus that generates pressure for circulating ink by sending air from a downstream tank to an upstream tank by an air pump.

  In this ink jet printing apparatus, the air volume of the upstream tank is maintained larger than the volume of the air layer of the downstream tank, and air is sent from the downstream tank to the upstream tank by an air pump. As a result, the negative pressure in the downstream tank has a larger absolute value than the positive pressure in the upstream tank, and a negative pressure appropriate for ink ejection is applied to the nozzles of the inkjet head.

JP 2012-153004 A

  In the technique of Patent Document 1, the volume of the air layer in the upstream tank needs to be larger than the volume of the air layer in the downstream tank. For this reason, when an upstream tank needs to be enlarged, there exists a possibility that an inkjet printing apparatus may enlarge.

  The present invention has been made in view of the above, and in an inkjet printing apparatus that applies a negative pressure to the nozzles of an inkjet head while applying pressure to an upstream tank and a downstream tank by an air pump to circulate the ink, the apparatus is increased in size. The purpose is to suppress.

  In order to achieve the above object, a first feature of an ink jet printing apparatus according to the present invention is an ink jet head having a nozzle for discharging ink, an upstream tank for storing ink to be supplied to the ink jet head, and the ink jet head. A downstream tank that receives ink that has not been consumed; a first path that connects the upstream tank and the inkjet head; a circulation path that includes a second path that connects the inkjet head and the downstream tank; and the upstream tank An adjustment unit that adjusts the volume of the first sealed space including the first air layer on the ink in the inside and the volume of the second sealed space including the second air layer on the ink in the downstream tank; and the second sealed An air pump for sending air from the space to the first sealed space, and during ink circulation via the circulation path Air is sent from the second sealed space to the first sealed space by the air pump while controlling the adjusting unit so that the volume of the first sealed space is equal to the volume of the second sealed space. A pressure loss in a first flow path, which is a flow path of ink between the nozzle of the inkjet head and the upstream tank, between the nozzle of the inkjet head and the downstream tank. This is because the pressure loss in the second flow path, which is the flow path of the ink, is larger.

  A second feature of the ink jet printing apparatus according to the present invention is that the first path is longer than the second path, so that the pressure loss in the first flow path is larger than the pressure loss in the second flow path. There is to be.

  A third feature of the inkjet printing apparatus according to the present invention is that the first path and the second path are circular tubes, and the inner diameter of the first path is smaller than the inner diameter of the second path. The pressure loss in one flow path is larger than the pressure loss in the second flow path.

  A fourth feature of the ink jet printing apparatus according to the present invention is that the upstream tank and the downstream tank are arranged such that the liquid level of the ink inside is lower than the nozzle surface of the ink jet head. The volume of the air layer is larger than the volume of the first flow path, and the volume of the second air layer is larger than the volume of the second flow path.

  According to the first feature of the ink jet printing apparatus according to the present invention, the pressure loss in the first flow path is made larger than the pressure loss in the second flow path, whereby a negative pressure suitable for ink ejection can be applied to the nozzle. Thereby, since a negative pressure can be applied to the nozzle by the flow path design, an increase in the size of the apparatus can be suppressed.

  According to the second feature of the inkjet printing apparatus according to the present invention, the first path is longer than the second path, so that the pressure loss in the first flow path is larger than the pressure loss in the second flow path. For this reason, the flow path design for making the pressure loss in the first flow path larger than the pressure loss in the second flow path can be facilitated.

  According to the third feature of the inkjet printing apparatus according to the present invention, the pressure loss in the first flow path is larger than the pressure loss in the second flow path because the inner diameter of the first path is smaller than the inner diameter of the second path. It has become. For this reason, the flow path design for making the pressure loss in the first flow path larger than the pressure loss in the second flow path can be facilitated.

  According to the fourth feature of the ink jet printing apparatus of the present invention, the volume of the first air layer is larger than the volume of the first flow path, and the volume of the second air layer is larger than the volume of the second flow path. For this reason, even if the ink inside the first channel and the second channel flows down to the upstream tank and the downstream tank due to the impact, overflow of the upstream tank and the downstream tank can be avoided.

1 is a schematic configuration diagram of an inkjet printing apparatus according to an embodiment. 2 is a flowchart for explaining the operation of the inkjet printing apparatus shown in FIG. 1. It is explanatory drawing of liquid level maintenance control. It is a figure which shows the various design parameters in a specific example. It is a figure which shows the various setting values in a specific example. It is a figure which shows the various calculation values in a specific example. It is the schematic diagram which replaced the inkjet printing apparatus shown in FIG. 1 with the electric circuit. It is a figure which shows the various design parameters in the specific example in the modification 1. FIG. 10 is a diagram showing various set values in a specific example in Modification 1; It is a figure which shows the various calculation values in the specific example in the modification 1. It is a figure which shows the various design parameters in the specific example in the modification 2. It is a figure which shows the various setting values in the specific example in the modification 2. It is a figure which shows the various calculation values in the specific example in the modification 2.

  Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same or equivalent parts and components are denoted by the same or equivalent reference numerals. However, it should be noted that the drawings are schematic and different from the actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the embodiment described below exemplifies an apparatus or the like for embodying the technical idea of the present invention, and the technical idea of the present invention includes the material, shape, structure, The layout is not specified as follows. The technical idea of the present invention can be variously modified within the scope of the claims.

  FIG. 1 is a schematic configuration diagram of an inkjet printing apparatus according to an embodiment of the present invention. In the following description, the vertical direction is the vertical direction, and the vertical direction on the paper surface in FIG.

  As shown in FIG. 1, the inkjet printing apparatus 1 according to the present embodiment includes an inkjet head 2, an ink circulation unit 3, an ink supply unit 4, and a control unit 5.

  The ink jet head 2 ejects ink supplied by the ink circulation unit 3. The inkjet head 2 has a plurality of nozzles (not shown) and ejects ink from the nozzles. The ink jet head 2 has an input port (not shown) for connecting to an upstream ink conduit 17 described later, and an output port (not shown) for connecting to a downstream ink conduit 18 described later.

  The ink circulation unit 3 supplies ink to the inkjet head 2 while circulating the ink. The ink circulation unit 3 includes an upstream tank 11, an upstream tank atmosphere release valve 12, a downstream tank 13, a downstream tank atmosphere release valve 14, an ink pump 15, an air pump 16, an upstream ink conduit 17, and a downstream ink conduit. 18, an intermediate ink conduit 19, and air conduits 20-22.

  The upstream tank 11 stores ink to be supplied to the inkjet head 2. The ink in the upstream tank 11 is supplied to the inkjet head 2 via the upstream ink conduit 17.

  An upstream tank liquid level sensor 26 is provided in the upstream tank 11. The upstream tank liquid level sensor 26 is for detecting whether or not the ink level in the upstream tank 11 has reached a reference height. The upstream tank liquid level sensor 26 outputs a signal indicating “ON” when the liquid level of the ink in the upstream tank 11 is equal to or higher than the reference height, and sets “OFF” when it is lower than the reference height. The signal shown is output.

  The reference level of the liquid level in the upstream tank 11 is below the upper end of the upstream tank 11. That is, an air layer (corresponding to a first air layer in claims) 27 is formed in the upstream tank 11 on the ink surface.

  The upstream tank 11 is disposed so that the liquid level of the ink inside is lower (lower) than the nozzle surface (lower surface) of the inkjet head 2. That is, the position of the reference level of the liquid level in the upstream tank 11 is below the nozzle surface of the inkjet head 2.

  In the upstream tank 11, the volume of the air layer 27 is larger than the volume of the upstream flow path (corresponding to the first flow path in the claims) 28 that is an ink flow path between the upstream tank 11 and the nozzles of the inkjet head 2. It is formed to be large.

  The upstream flow path 28 includes a portion of the upstream ink conduit 17 exposed above the liquid level of the upstream tank 11 and a flow path between the input port of the inkjet head 2 and the nozzle.

  The upstream tank atmosphere release valve 12 switches the air flow path in the air conduit 20 in order to switch the upstream tank 11 between a sealed state (a state where the upstream tank 11 is shut off from the atmosphere) and an atmosphere open state (a state where the atmosphere is communicated with the atmosphere). Open and close. The upstream tank atmosphere release valve 12 is provided in the middle of the air conduit 20.

  The downstream tank 13 receives and stores ink that has not been consumed by the inkjet head 2. Further, the downstream tank 13 stores ink supplied from an ink cartridge 36 of the ink replenishing unit 4 described later.

  A downstream tank liquid level sensor 29 is provided in the downstream tank 13. The downstream tank liquid level sensor 29 is for detecting whether or not the liquid level of the ink in the downstream tank 13 has reached the reference height. The downstream tank liquid level sensor 29 outputs a signal indicating “ON” when the liquid level of the ink in the downstream tank 13 is equal to or higher than the reference height, and sets “OFF” when the ink level is lower than the reference height. The signal shown is output.

  The reference level of the liquid level in the downstream tank 13 is below the upper end of the downstream tank 13. That is, an air layer (corresponding to a second air layer in the claims) 30 is formed in the downstream tank 13 on the ink surface.

  The downstream tank 13 is arranged such that the position of the reference level of the internal liquid level is the same as the position of the reference level of the liquid level of the upstream tank 11.

  In the downstream tank 13, the volume of the air layer 30 is larger than the volume of the downstream flow path (corresponding to the second flow path in the claims) 31 that is a flow path of ink between the nozzles of the inkjet head 2 and the downstream tank 13. It is formed to be large.

  The downstream flow path 31 includes a flow path between the nozzle of the inkjet head 2 and the output port and a portion exposed above the liquid level of the downstream tank 13 of the downstream ink conduit 18.

  The downstream tank air release valve 14 opens and closes the air flow path in the air conduit 21 in order to switch the downstream tank 13 between a sealed state and an air open state. The downstream tank atmosphere release valve 14 is provided in the middle of the air conduit 21.

  The ink pump 15 sends ink from the downstream tank 13 to the upstream tank 11. The ink pump 15 is provided in the middle of the intermediate ink conduit 19.

  When ink is sent from the downstream tank 13 to the upstream tank 11 by the ink pump 15, the liquid levels of the upstream tank 11 and the downstream tank 13 change. Thereby, the volume of the air layer 27 in the upstream tank 11 and the air layer 30 in the downstream tank 13 fluctuate. Therefore, in the sealed state of the upstream tank 11 and the downstream tank 13, the upstream sealed space including the air layer 27 (corresponding to the first sealed space in the claims) and the downstream sealed space including the air layer 30 (claim) Corresponding to the second sealed space) fluctuates. Accordingly, the ink pump 15 has a function of adjusting the volumes of the upstream side sealed space and the downstream side sealed space. The ink pump 15 corresponds to a part of the adjustment unit.

  The upstream side sealed space is a space including the air layer 27 and a space communicating therewith in the sealed state of the upstream tank 11. Specifically, the upstream sealed space includes the air layer 27 in the upstream tank 11, the space in the air conduit 20 between the upstream tank 11 and the upstream tank atmosphere release valve 12, the upstream tank 11, and the air pump 16. And a space in the air conduit 22 between the two.

  The downstream-side sealed space is a space including the air layer 30 and a space communicating therewith in the sealed state of the downstream tank 13. Specifically, the downstream sealed space includes an air layer 30 in the downstream tank 13, a space in the air conduit 21 between the downstream tank 13 and the downstream tank atmosphere release valve 14, a downstream tank 13 and an air pump 16. And a space in the air conduit 22 between the two. The volume of the downstream sealed space when the liquid level of the downstream tank 13 is at the reference height is equal to the volume of the upstream sealed space when the liquid level of the upstream tank 11 is at the reference height.

  The air pump 16 sends air from the air layer 30 of the downstream tank 13 to the air layer 27 of the upstream tank 11. In other words, the air pump 16 sends air from the downstream sealed space to the upstream sealed space.

  The upstream ink conduit 17 connects the upstream tank 11 and the inkjet head 2. One end of the upstream ink conduit 17 is at a position lower than the reference height of the liquid level in the upstream tank 11. The other end of the upstream ink conduit 17 is connected to the input port of the inkjet head 2. Ink flows from the upstream tank 11 toward the inkjet head 2 through the upstream ink conduit 17. The upstream ink conduit 17 corresponds to the first path of the claims.

  The downstream ink conduit 18 connects the inkjet head 2 and the downstream tank 13. One end of the downstream ink conduit 18 is connected to the output port of the inkjet head 2. The other end of the downstream ink conduit 18 is at a position lower than the reference level of the liquid level in the downstream tank 13. Ink flows from the inkjet head 2 toward the downstream tank 13 through the downstream ink conduit 18. The downstream ink conduit 18 corresponds to the second path of the claims.

  The intermediate ink conduit 19 connects the upstream tank 11 and the downstream tank 13. Ink flows through the intermediate ink conduit 19 from the downstream tank 13 toward the upstream tank 11.

  The upstream ink conduit 17, the downstream ink conduit 18, and the intermediate ink conduit 19 constitute a circulation path for circulating ink between the upstream tank 11, the inkjet head 2, and the downstream tank 13.

  The air conduit 20 forms an air flow path for opening the upstream tank 11 to the atmosphere. The air conduit 20 has one end connected to the air layer 27 of the upstream tank 11 and the other end communicating with the atmosphere.

  The air conduit 21 forms an air flow path for opening the downstream tank 13 to the atmosphere. One end of the air conduit 21 is connected to the air layer 30 of the downstream tank 13 and the other end communicates with the atmosphere.

  The air conduit 22 forms a flow path for air sent from the downstream tank 13 to the upstream tank 11 by the air pump 16. One end of the air conduit 22 is connected to the air layer 27 of the upstream tank 11, and the other end is connected to the air layer 30 of the downstream tank 13.

  The ink circulation unit 3 is configured such that the pressure loss in the upstream channel 28 is larger than the pressure loss in the downstream channel 31. Specifically, since the upstream ink conduit 17 is longer than the downstream ink conduit 18, the pressure loss in the upstream channel 28 is larger than the pressure loss in the downstream channel 31.

  The pressure loss in the flow path is the product of the flow path resistance and the flow rate. In the ink jet printing apparatus 1, the upstream flow path 28 and the downstream flow path 31 have the same flow rate. Therefore, if the flow resistance of the upstream flow path 28 is greater than the flow resistance of the downstream flow path 31, the pressure loss in the upstream flow path 28 is greater than the pressure loss in the downstream flow path 31.

  The channel resistance R is expressed by the following formula (1) when the Reynolds number is small. In the present embodiment, the Reynolds number is sufficiently small.

R = 2 × k × (S ² / A ³ ) × L × μ (1)
Here, k is a pipe friction coefficient ratio. The pipe friction coefficient ratio k is determined by the cross-sectional shape of the pipe. S is the circumference of the pipeline. A is the cross-sectional area of the pipeline. L is the pipe length. μ is the viscosity of the ink.

  As can be seen from equation (1), if the pipe cross-sectional shape, pipe friction coefficient ratio k, and ink viscosity μ are the same, the flow path resistance R increases as the pipe length L increases.

  Therefore, in the inkjet printing apparatus 1, the upstream ink conduit 17 and the downstream ink conduit 18 have the same cross-sectional shape and the same pipe friction coefficient ratio k, and the upstream ink conduit 17 is made longer than the downstream ink conduit 18, so The channel resistance of the side channel 28 is set to be larger than that of the downstream channel 31. Thereby, the pressure loss in the upstream flow path 28 becomes larger than the pressure loss in the downstream flow path 31. The lengths of the upstream ink conduit 17 and the downstream ink conduit 18 are set so that the nozzle pressure of the inkjet head 2 becomes a negative pressure within an appropriate range during ink circulation.

  The ink supply unit 4 supplies ink to the downstream tank 13 of the ink circulation unit 3. The ink supply unit 4 includes an ink cartridge 36, an ink supply valve 37, and an ink supply pipe 38.

  The ink cartridge 36 contains ink used for printing by the inkjet head 2. The ink in the ink cartridge 36 is supplied to the downstream tank 13 via the ink supply pipe 38.

  The ink supply valve 37 opens and closes the ink flow path in the ink supply pipe 38. When ink is supplied to the downstream tank 13, the ink supply valve 37 is opened.

  The ink supply pipe 38 connects the ink cartridge 36 and the downstream tank 13. Ink flows from the ink cartridge 36 toward the downstream tank 13 through the ink supply pipe 38.

  When ink is supplied to the downstream tank 13 by the ink supply unit 4, the liquid level of the downstream tank 13 fluctuates. For this reason, the volume of the downstream sealed space including the air layer 30 varies. Thereby, the ink replenishing part 4 has a function of adjusting the volume of the downstream sealed space. The ink supply unit 4 corresponds to a part of the adjustment unit in the claims.

  The control unit 5 controls the operation of each unit of the inkjet printing apparatus 1. The control unit 5 includes a CPU, a RAM, a ROM, a hard disk, and the like.

  The control unit 5 controls the ink pump 15 and the ink replenishing unit 4 so that the volume of the upstream sealed space and the volume of the downstream sealed space are kept equal during the ink circulation, and the downstream sealed by the air pump 16. Control to send air from the space to the upstream sealed space. The control unit 5 controls the ink jet head 2 to print an image on a sheet while performing ink circulation.

  Next, the operation of the inkjet printing apparatus 1 will be described.

  FIG. 2 is a flowchart for explaining the operation of the inkjet printing apparatus 1. The process of the flowchart of FIG. 2 starts when a print job is input to the inkjet printing apparatus 1.

  In step S1 of FIG. 2, the control unit 5 starts the liquid level maintenance control. In the liquid level maintenance control, the ink pump 15 and the ink supply valve 37 corresponding to the liquid level heights of the upstream tank 11 and the downstream tank 13 are used to maintain the liquid levels of the upstream tank 11 and the downstream tank 13 near the reference height. Control. In other words, the liquid level maintenance control is control for maintaining a state where the volume of the upstream side sealed space and the volume of the downstream side sealed space are equal.

  Specifically, as shown in FIG. 3, when both the upstream tank liquid level sensor 26 and the downstream tank liquid level sensor 29 are on, the control unit 5 turns off the ink pump 15 and closes the ink supply valve 37. To do. Similarly, even when the upstream tank level sensor 26 is on and the downstream tank level sensor 29 is off, the control unit 5 turns off the ink pump 15 and closes the ink supply valve 37.

  When the upstream tank liquid level sensor 26 is off and the downstream tank liquid level sensor 29 is on, the control unit 5 turns on the ink pump 15 and closes the ink supply valve 37.

  When both the upstream tank liquid level sensor 26 and the downstream tank liquid level sensor 29 are off, the control unit 5 turns off the ink pump 15 and opens the ink supply valve 37.

  Returning to FIG. 2, following step S <b> 1, in step S <b> 2, the control unit 5 closes the upstream tank atmosphere release valve 12 and the downstream tank atmosphere release valve 14. Thereby, the upstream tank 11 and the downstream tank 13 will be in a sealed state. In the standby state of the inkjet printing apparatus 1, the upstream tank atmosphere release valve 12 and the downstream tank atmosphere release valve 14 are open.

  Next, in step S <b> 3, the control unit 5 starts driving the air pump 16. The controller 5 drives the air pump 16 at a rotational speed set so that the pressures in the upstream tank 11 and the downstream tank 13 become the specified values Pku and Pkd, respectively. As a result, a positive pressure of the specified value Pku is applied to the upstream tank 11 and a negative pressure of the specified value Pkd is applied to the downstream tank 13. With this pressure, ink flows from the upstream tank 11 to the downstream tank 13 and ink circulation is performed.

  The prescribed values Pku and Pkd of the pressure in the upstream tank 11 and the downstream tank 13 are set as values that ensure the necessary circulation flow rate and the nozzle pressure of the inkjet head 2 is a negative pressure within an appropriate range. is there.

  Here, the liquid level of the upstream tank 11 and the downstream tank 13 is maintained near the reference height by the liquid level maintenance control described above. As described above, the volume of the upstream sealed space when the liquid level of the upstream tank 11 is at the reference height, and the volume of the downstream sealed space when the liquid level of the downstream tank 13 is at the reference height, Are equal. For this reason, the absolute value of the positive pressure applied to the upstream tank 11 and the negative pressure applied to the downstream tank 13 when air is sent from the downstream tank 13 to the upstream tank 11 by the air pump 16 is equal. Therefore, the prescribed value Pku for the positive pressure in the upstream tank 11 and the prescribed value Pkd for the negative pressure in the downstream tank 13 are equal in absolute value.

  In the case where the positive pressure of the upstream tank 11 and the negative pressure of the downstream tank 13 have the same absolute value, when the pressure loss in the upstream flow path 28 and the pressure loss in the downstream flow path 31 are equal, the nozzle of the inkjet head 2 The pressure becomes atmospheric pressure (0 Pa). That is, the nozzle pressure does not become a negative pressure suitable for ink ejection. The pressure is expressed in gauge pressure.

  In contrast, in the inkjet printing apparatus 1, as described above, the upstream ink conduit 17 is made longer than the downstream ink conduit 18, so that the pressure loss in the upstream channel 28 is larger than the pressure loss in the downstream channel 31. It is comprised so that it may become. Thereby, the nozzle pressure of the inkjet head 2 becomes a negative pressure. As described above, since the lengths of the upstream ink conduit 17 and the downstream ink conduit 18 are set so that the nozzle pressure is within the appropriate range, the negative pressure within the appropriate range is applied to the nozzle during ink circulation. It will be in the state where was given.

  Subsequent to step S3, in step S4, the control unit 5 starts execution of the print job. Specifically, the controller 5 prints an image by ejecting ink from the inkjet head 2 based on the print job.

  During execution of the print job, ink is supplied from the upstream tank 11 to the inkjet head 2, and ink that has not been consumed by the inkjet head 2 is collected in the downstream tank 13. When the upstream tank liquid level sensor 26 is turned off and the downstream tank liquid level sensor 29 is turned on by the liquid level maintenance control, the ink pump 15 sends ink from the downstream tank 13 to the upstream tank 11. Further, when both the upstream tank liquid level sensor 26 and the downstream tank liquid level sensor 29 are turned off, the ink supply unit 4 supplies ink to the downstream tank 13. In this manner, the liquid level height of the upstream tank 11 and the downstream tank 13 is maintained, and printing is performed while the ink is circulated.

  Subsequent to step S4, in step S5, the control unit 5 determines whether or not the print job is completed. If it is determined that the print job has not ended (step S5: NO), the control unit 5 repeats step S5.

  When it is determined that the print job is completed (step S5: YES), the control unit 5 stops the air pump 16 in step S6.

  Next, in step S <b> 7, the control unit 5 opens the upstream tank atmosphere release valve 12 and the downstream tank atmosphere release valve 14. Thereby, the upstream tank 11 and the downstream tank 13 will be in an air release state.

  Next, in step S8, the control unit 5 ends the liquid level maintenance control. Thereby, a series of operation | movement is complete | finished and the inkjet printing apparatus 1 will be in a standby state.

  Next, the pressure loss in the upstream channel 28 and the downstream channel 31 will be described with specific numerical examples.

  FIG. 4 is a diagram showing various design parameters in this specific example. FIG. 5 is a diagram showing various set values in this specific example. FIG. 6 is a diagram showing various calculated values in this specific example. FIG. 7 is a schematic diagram in which the inkjet printing apparatus 1 is replaced with an electric circuit.

  In this specific example, the upstream ink conduit 17 and the downstream ink conduit 18 are assumed to be composed of a member such as a joint or a single circular tube without bending. In such a circular tube, the tube friction coefficient ratio k is 1. Therefore, as shown in FIG. 4, the tube friction coefficient ratio k of the upstream ink conduit 17 and the downstream ink conduit 18 is 1.

  Further, the upstream ink conduit 17 and the downstream ink conduit 18 have the same inner diameter d. Therefore, the upstream ink conduit 17 and the downstream ink conduit 18 have the same circumferential length S and cross-sectional area A. On the other hand, the pipe length L is longer in the upstream ink conduit 17 than in the downstream ink conduit 18. The pipe lengths L of the upstream ink conduit 17 and the downstream ink conduit 18 are the lengths of the portions of the upstream ink conduit 17 and the downstream ink conduit 18 that are exposed above the liquid levels of the upstream tank 11 and the downstream tank 13, respectively. The lengths of the upstream ink conduit 17 and the downstream ink conduit 18 below the ink surface are equal to each other.

  The channel resistance R / μ per viscosity shown in FIG. 4 is a value determined by the channel shape. In the upstream ink conduit 17 and the downstream ink conduit 18, the flow path resistance R / μ per viscosity is calculated by the following equation (2) obtained by modifying the above equation (1).

R / μ = 2 × k × (S ² / A ³ ) × L (2)
The channel resistance R / μ per viscosity in the inkjet head 2 is calculated based on the channel shape of the inkjet head 2. In the inkjet head 2, it is assumed that the flow path between the input port and the nozzle and the flow path between the nozzle and the output port have the same flow path shape.

  The applied pressure P shown in FIG. 5 is set based on the target flow rate. The absolute value of the specified value Pku of the pressure (positive pressure) of the upstream tank 11 and the specified value Pkd of the pressure (negative pressure) of the downstream tank 13 is half of the in pressure P. The ink viscosity μ shown in FIG. 5 is the viscosity at normal temperature of the ink used in the inkjet printing apparatus 1.

  The flow path resistance Rpu of the upstream ink conduit 17, the flow path resistance Rpd of the downstream ink conduit 18, and the flow path resistance Rh of the inkjet head 2 shown in FIGS. 6 and 7 are the flow resistance R per viscosity shown in FIG. 4. / Μ and the ink viscosity μ shown in FIG.

  The flow rate Q shown in FIGS. 6 and 7 is the flow rate of ink in the upstream flow path 28 and the downstream flow path 31, and is calculated by the following equation (3).

Q = P / (Rpu + Rpd + Rh) (3)
The pressure loss ΔPpu in the upstream ink conduit 17 shown in FIGS. 6 and 7 is the product of the flow resistance Rpu and the flow rate Q of the upstream ink conduit 17. Similarly, the pressure loss ΔPpd in the downstream ink conduit 18 is the product of the flow path resistance Rpd and the flow rate Q of the downstream ink conduit 18. The pressure loss ΔPh in the inkjet head 2 is the product of the flow path resistance Rh and the flow rate Q of the inkjet head 2.

  As described above, the flow path between the input port and the nozzle of the inkjet head 2 and the flow path between the nozzle and the output port have the same flow path shape. For this reason, the pressure loss in the flow path between the input port and the nozzle of the inkjet head 2 is equal to the pressure loss in the flow path between the nozzle and the output port, which is ΔPh / 2.

  For this reason, the pressure loss ΔPu in the upstream channel 28 and the pressure loss ΔPd in the downstream channel 31 shown in FIGS. 6 and 7 are calculated by the following equations (4) and (5), respectively.

ΔPu = ΔPpu + ΔPh / 2 (4)
ΔPd = ΔPpd + ΔPh / 2 (5)
As shown in FIG. 6, the pressure loss ΔPu in the upstream flow path 28 is larger than the pressure loss ΔPd in the downstream flow path 31.

  The nozzle pressure Pn shown in FIGS. 6 and 7 is calculated by the following formula (6) or formula (7). The calculation results of the nozzle pressure Pn by both formulas coincide.

Pn = Pku−ΔPu (6)
Pn = Pkd + ΔPd (7)
As shown in FIG. 6, the nozzle pressure Pn is −1366.3 Pa, which is a negative pressure suitable for ink ejection.

  Thus, by making the upstream ink conduit 17 longer than the downstream ink conduit 18, the pressure loss in the upstream flow path 28 can be made larger than the pressure loss in the downstream flow path 31. A negative pressure can be applied to the nozzles of the inkjet head 2.

  As described above, in the ink jet printing apparatus 1, the control unit 5 causes the ink pump 15 and the ink replenishing unit to maintain a state where the volume of the upstream sealed space and the volume of the downstream sealed space are equal during ink circulation. 4 is controlled such that air is sent from the downstream sealed space to the upstream sealed space by the air pump 16. As a result, positive pressure and negative pressure having the same absolute value are applied to the upstream tank 11 and the downstream tank 13, respectively.

  In the inkjet printing apparatus 1, the pressure loss in the upstream channel 28 is larger than the pressure loss in the downstream channel 31. For this reason, the negative pressure suitable for ink ejection can be applied to the nozzles even in such a control that the positive pressure of the upstream tank 11 and the negative pressure of the downstream tank 13 have the same absolute value as described above.

  Here, unlike the present embodiment, in a configuration in which the pressure loss in the upstream flow path 28 is equal to the pressure loss in the downstream flow path 31, the volume of the upstream sealed space is larger than the volume of the downstream sealed space. The negative pressure can be applied to the nozzle by controlling the air pump 16 to send air from the downstream sealed space to the upstream sealed space while maintaining the above.

  In this case, in order to realize a state where the volume of the upstream sealed space is larger than the volume of the downstream sealed space, the volume of the air layer 27 of the upstream tank 11 can be maintained larger than the volume 30 of the air layer of the downstream tank 13. Like that. In this case, since the upstream tank 11 needs to be enlarged, the apparatus may be enlarged.

  On the other hand, in the inkjet printing apparatus 1 according to the present embodiment, negative pressure can be applied to the nozzle by the flow path design, so that the enlargement of the apparatus can be suppressed.

  In the inkjet printing apparatus 1, the upstream ink conduit 17 is longer than the downstream ink conduit 18, so that the pressure loss in the upstream channel 28 is larger than the pressure loss in the downstream channel 31. For this reason, the flow path design for making the pressure loss in the upstream flow path 28 larger than the pressure loss in the downstream flow path 31 can be facilitated.

  In the inkjet printing apparatus 1, the volume of the air layer 27 in the upstream tank 11 is larger than the volume of the upstream flow path 28, and the volume of the air layer 30 in the downstream tank 13 is larger than the volume of the downstream flow path 31. For this reason, even if the meniscus of the nozzle of the inkjet head 2 is destroyed by the impact and the ink inside the upstream flow path 28 and the downstream flow path 31 flows down to the upstream tank 11 and the downstream tank 13 respectively, the upstream tank 11 and the downstream tank The overflow of the tank 13 can be avoided.

(Modification 1)
In the above-described embodiment, the upstream ink conduit 17 is longer than the downstream ink conduit 18, but the configuration in which the pressure loss in the upstream channel 28 is greater than the pressure loss in the downstream channel 31 is this. Not limited to.

  As can be seen from the above equation (1), the smaller the cross-sectional area A, the greater the flow path resistance R. Thus, in the first modification, the inner diameter of the upstream ink conduit 17 is made smaller than the inner diameter of the downstream ink conduit 18 so that the pressure loss in the upstream flow path 28 is larger than the pressure loss in the downstream flow path 31. . In the first modification, the upstream ink conduit 17 and the downstream ink conduit 18 are circular tubes. The inner diameters of the upstream ink conduit 17 and the downstream ink conduit 18 are set so that the nozzle pressure of the inkjet head 2 is a negative pressure within an appropriate range during ink circulation.

  Next, pressure loss in the upstream flow path 28 and the downstream flow path 31 of Modification 1 will be described with specific numerical examples.

  FIG. 8 is a diagram showing various design parameters in this specific example. FIG. 9 is a diagram showing various set values in this specific example. FIG. 10 is a diagram showing various calculated values in this specific example.

  Also in this specific example, the upstream ink conduit 17 and the downstream ink conduit 18 are composed of a single circular tube without a member such as a joint or a bending process, as in the specific example described in the above-described embodiment. To do. Accordingly, the tube friction coefficient ratio k of the upstream ink conduit 17 and the downstream ink conduit 18 is 1.

  As shown in FIG. 8, the upstream ink conduit 17 and the downstream ink conduit 18 have the same pipe length L. On the other hand, the inner diameter d is smaller in the upstream ink conduit 17 than in the downstream ink conduit 18. For this reason, the circumferential length S and the cross-sectional area A are also smaller in the upstream ink conduit 17 than in the downstream ink conduit 18.

  The set values such as the applied pressure P are as shown in FIG. The calculation method of various calculation values shown in FIG. 10 is the same as that described in the above embodiment.

  As shown in FIG. 10, the pressure loss ΔPu in the upstream flow path 28 is larger than the pressure loss ΔPd in the downstream flow path 31. The nozzle pressure Pn is −1428.5 Pa, which is a negative pressure suitable for ink ejection.

  Thus, by making the inner diameter of the upstream ink conduit 17 smaller than the inner diameter of the downstream ink conduit 18, the pressure loss in the upstream channel 28 can be made larger than the pressure loss in the downstream channel 31. A negative pressure can be applied to the nozzles of the inkjet head 2.

  According to the first modification, the flow path design for making the pressure loss in the upstream flow path 28 larger than the pressure loss in the downstream flow path 31 can be facilitated.

(Modification 2)
In the second modification, the upstream ink conduit 17 subjected to bending is used.

  The pipe friction coefficient ratio k is increased by bending such as L-shaped bending and U-shaped bending of the pipe. As the pipe friction coefficient ratio k increases, the flow path resistance R increases and the pressure loss increases. Therefore, in the second modification, the upstream ink conduit 17 is bent to increase the pressure loss in the upstream flow path 28. The upstream ink conduit 17 may be bent and has a larger flow resistance than the downstream ink conduit 18.

  Next, the pressure loss in the upstream flow path 28 and the downstream flow path 31 of Modification 2 will be described with specific numerical examples.

  FIG. 11 is a diagram showing various design parameters in this specific example. FIG. 12 is a diagram showing various set values in this specific example. FIG. 13 is a diagram showing various calculated values in this specific example.

  In this specific example, the upstream ink conduit 17 is composed of a circular tube that has been bent, and the tube friction coefficient ratio k is 1.15 as shown in FIG. The downstream ink conduit 18 is assumed to be composed of a member such as a joint or a single circular tube without bending. Therefore, the tube friction coefficient ratio k of the downstream ink conduit 18 is 1.

  The values of other design parameters are as shown in FIG. Here, the upstream ink conduit 17 and the downstream ink conduit 18 in this specific example are different from the upstream ink conduit 17 and the downstream ink conduit 18 in the specific example described with reference to FIGS. The pipe friction coefficient ratio k and the pipe length L of the ink conduit 17 are shown.

  The set values such as the applied pressure P are as shown in FIG. The calculation method of various calculation values shown in FIG. 13 is the same as that described in the above embodiment.

  As shown in FIG. 13, the pressure loss ΔPu in the upstream flow path 28 is larger than the pressure loss ΔPd in the downstream flow path 31. The nozzle pressure Pn is −1463.4 Pa, which is a negative pressure suitable for ink ejection.

  In the specific example of the second modification, the pipe length L of the upstream ink conduit 17 is increased by increasing the pipe friction coefficient ratio k as compared with the specific examples described with reference to FIGS. It has been shortened.

  Thus, according to the second modification, the upstream ink conduit 17 can be shortened by bending the upstream ink conduit 17. This facilitates the wiring arrangement of the ink conduit.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments. For example, some components may be deleted from all the components shown in the embodiment.

DESCRIPTION OF SYMBOLS 1 Inkjet printing apparatus 2 Inkjet head 3 Ink circulation part 4 Ink replenishment part 5 Control part 11 Upstream tank 12 Upstream tank atmosphere release valve 13 Downstream tank 14 Downstream tank atmosphere release valve 15 Ink pump 16 Air pump 17 Upstream ink conduit 18 Downstream ink conduit 19 Intermediate ink conduit 20-22 Air conduit 27, 30 Air layer 28 Upstream flow path 31 Downstream flow path 36 Ink cartridge 37 Ink supply valve 38 Ink supply pipe

Claims (4)

An inkjet head having a nozzle for ejecting ink;
An upstream tank for storing ink to be supplied to the inkjet head;
A downstream tank for receiving ink not consumed by the inkjet head;
A circulation path having a first path connecting the upstream tank and the inkjet head, and a second path connecting the inkjet head and the downstream tank;
An adjusting unit that adjusts the volume of the first sealed space including the first air layer on the ink in the upstream tank and the volume of the second sealed space including the second air layer on the ink in the downstream tank;
An air pump for sending air from the second sealed space to the first sealed space;
During the ink circulation through the circulation path, the second sealed space is controlled by the air pump while controlling the adjusting unit so that the volume of the first sealed space and the volume of the second sealed space are kept equal. And a control unit that controls to send air to the first sealed space from
The pressure loss in the first flow path, which is the ink flow path between the nozzle of the inkjet head and the upstream tank, is the ink flow path between the nozzle of the inkjet head and the downstream tank. An ink jet printing apparatus having a pressure loss greater than two flow paths.   2. The ink jet printing according to claim 1, wherein a pressure loss in the first flow path is larger than a pressure loss in the second flow path because the first path is longer than the second path. apparatus. The first path and the second path consist of circular tubes,
The pressure loss in the first flow path is larger than the pressure loss in the second flow path because the inner diameter of the first path is smaller than the inner diameter of the second path. The inkjet printing apparatus as described. The upstream tank and the downstream tank are arranged such that the liquid level of the ink inside is lower than the nozzle surface of the inkjet head,
4. The volume of the first air layer is larger than the volume of the first flow path, and the volume of the second air layer is larger than the volume of the second flow path. 5. The inkjet printing apparatus as described in any one of Claims 1-3.