Droplet discharge device

Abstract

The droplet discharge device includes a liquid flow path portion, a discharge portion and an adjustment portion. The liquid flow path portion is for liquid flow, the discharge portions are multiple and arranged along the direction of gravity to discharge droplets from the liquid flow path portion, and the adjustment portion adjusts the flow direction of the liquid in the liquid flow path portion so that the lower the position of each discharge portion in the flow direction, the more downstream it is.

Description

Technical Field

[0001] The present invention relates to a liquid droplet discharge device. Background Art

[0002] Conventionally, there is known an image forming apparatus (liquid droplet ejection apparatus) having a liquid droplet ejection head (recording head) with a plurality of nozzles (ejection units) arranged so as to form a height difference along the direction of gravity. For example, in the image forming apparatus described in Patent Document 1, either the number of pulses or the pulse width of a pulse signal applied to a pressure generating unit that generates pressure for ejecting liquid is adjusted based on the height difference between the plurality of nozzles.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-206086 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] However, when there are height differences between multiple nozzles, the position of the liquid surface (meniscus) fluctuates at each nozzle, potentially causing uneven droplet discharge performance across the droplet ejection device. The main factors determining the position of the meniscus are the difference in meniscus pressure due to the height difference and the reverberant vibrations generated by driving the droplet ejection device. However, the dominant factor varies depending on the range of the driving frequency. Therefore, even when adjusting the pulse signal based on a predetermined frequency, as in the configuration described in Patent Document 1, there is a risk that uneven discharge performance across the nozzles will still occur depending on the range of the driving frequency.

[0008] An object of the present invention is to provide a liquid droplet discharge device capable of suppressing variations in liquid droplet discharge performance among discharge sections.

[0009] Solutions to Problems

[0010] The liquid droplet discharge device of the present invention comprises a liquid flow path unit, a discharge unit, and an adjustment unit.

[0011] The liquid flow path portion is for liquid to flow,

[0012] The discharge portion is multiple and arranged along the gravity direction to discharge liquid droplets from the liquid flow path portion.

[0013] The adjusting portion adjusts the flow direction of the liquid in the liquid flow path portion so that the lower the position of each discharge portion in the flow direction, the more downstream it is.

[0014] According to the present invention, it is possible to suppress the occurrence of variations in droplet discharge performance among discharge portions. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

[0016] Figure 2 This is a diagram showing the image forming apparatus as viewed from the conveying direction.

[0017] Figure 3 This is a block diagram showing the main functional configuration of the image forming apparatus.

[0018] Figure 4A This is an enlarged view of the discharge surface portion of the recording head.

[0019] Figure 4B This is an enlarged view of the discharge surface portion of the recording head.

[0020] Figure 5 This is a diagram showing the discharge surface of the recording head. DETAILED DESCRIPTION

[0021] Hereinafter, embodiments of the present invention will be described in detail based on the drawings. Figure 1 1 is a diagram showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention. Figure 2 This is a diagram of the image forming apparatus 1 as viewed from the conveying direction.

[0022] like Figure 1 as well as Figure 2 As shown, image forming apparatus 1 is an inkjet image forming apparatus configured to form an image on, for example, a box-shaped recording medium P. Image forming apparatus 1 includes a belt conveyor 2, a first droplet ejection unit 3, a second droplet ejection unit 4, and the like. Image forming apparatus 1 corresponds to the "droplet ejection apparatus" of the present invention.

[0023] The belt conveyor 2 has an endless conveyor belt 21 of a predetermined width provided between drive rollers and driven roller frames (not shown) arranged parallel to each other at predetermined intervals. The upper surface of the conveyor belt 21 stretched between the drive rollers and driven rollers serves as a loading surface for the recording medium P.

[0024] The belt conveyor 21 is rotated by the driving roller of the belt conveyor 2. This movement conveys the recording medium P placed on the upper surface of the conveyor belt 21 in the conveying direction of arrow A (from right to left) in the figure.

[0025] The first droplet ejection unit 3 ejects droplets onto the upper surface of the recording medium P (in the direction of gravity) to record a desired image on the upper surface. The first droplet ejection unit 3 includes a first main tank 31 , a first supply unit 32 , a first recording head 33 , and a first recovery unit 34 .

[0026] The second droplet ejection unit 4 ejects droplets toward the side surface of the recording medium P (in the width direction of the recording medium P) to record an image on the side surface, and includes a second main tank 41 , a second supply unit 42 , a second recording head 43 , and a second recovery unit 44 .

[0027] In addition, in the following description, when the various components of the first droplet discharge unit 3 and the second droplet discharge unit 4 are not distinguished, they are only referred to as the droplet discharge units 3, 4, the main boxes 31, 41, the supply units 32, 42, the recording heads 33, 43 and the recovery units 34, 44.

[0028] The main tanks 31 and 41 are tanks that store liquid (ink) to be supplied to the recording heads 33 and 43 .

[0029] The supply units 32 and 42 suck liquid from the main tanks 31 and 41 and supply the liquid to the recording heads 33 and 43. Liquid infusion pumps 32A and 42A are provided in the flow paths connecting the supply units 32 and 42 and the main tanks 31 and 41.

[0030] The recording heads 33 and 43 include a plurality of inkjet heads and have liquid flow path sections 331 and 431 inside thereof through which the liquid supplied from the supply sections 32 and 42 flows.

[0031] The first recording head 33 is disposed at a position facing the upper surface of the recording medium P on the conveyor belt 21. The first liquid flow path 331 of the first recording head 33 extends, for example, in the width direction of the conveyor belt 21, and the supply port 331A and the recovery port 331B are provided at either end of the width direction.

[0032] The supply port 331A is an opening that connects the first supply section 32 and the first liquid flow path section 331. The recovery port 331B is an opening that connects the first recovery section 34 and the first liquid flow path section 331. The first liquid flow path section 331 is configured so that the liquid supplied from the supply port 331A flows in the width direction to the recovery port 331B.

[0033] The first recording head 33 has multiple nozzles (first discharge unit) located on the lower surface of the first liquid flow path 331. The droplet discharge surface 332A is positioned downward (in the direction of gravity). The first recording head 33 discharges droplets (ink) from the multiple nozzles, thereby recording an image on the upper surface of the recording medium P.

[0034] The second recording head 43 is disposed opposite the side surface of the recording medium P on the conveyor belt 21. The second liquid flow path 431 of the second recording head 43 extends in the direction of gravity and has a supply port 431A at the upper end and a recovery port 431B at the lower end.

[0035] The supply port 431A is an opening that connects the second supply unit 42 and the second liquid flow path unit 431. The recovery port 431B is an opening that connects the second recovery unit 44 and the second liquid flow path unit 431. The second liquid flow path unit 431 is configured so that the liquid supplied from the supply port 431A flows in a direction along the direction of gravity (from top to bottom) to the recovery port 431B.

[0036] The second recording head 43 has a side surface ( Figure 2 The second recording head 43 has multiple nozzles 432 (discharge unit and second discharge unit) on the right side of the recording medium P. The droplet discharge surface 432A is arranged so as to face the width direction (horizontal direction) of the recording medium P. The second recording head 43 discharges droplets (ink) from the multiple nozzles 432 to record an image on the side surface of the recording medium P.

[0037] The recovery units 34, 44 recover liquid from the recording heads 33, 43 and return the liquid to the main tanks 31, 41. The droplet ejection units 3, 4 recover liquid from the recording heads 33, 43 using the recovery units 34, 44, thereby circulating the liquid among the main tank, the supply unit, the recording heads, and the recovery units.

[0038] Figure 3 1 is a block diagram showing the main functional structure of the image forming apparatus 1. Figure 3 As shown, the image forming apparatus 1 includes a control unit 100 , a discharge drive unit 110 , a conveyance drive unit 120 , an input / output interface 130 , and an adjustment unit 140 .

[0039] The control unit 100 includes a CPU 101 (Central Processing Unit), a RAM 102 (Random Access Memory), a ROM 103 (Read Only Memory), and a storage unit 104 .

[0040] The CPU 101 reads various control programs and setting data stored in the ROM 103 and stores them in the RAM 102 , and executes the programs to perform various calculations. The CPU 101 also comprehensively controls the entire operation of the image forming apparatus 1 .

[0041] RAM 102 provides a storage space for work to CPU 101 and temporarily stores data. RAM 102 may also include a nonvolatile memory.

[0042] The ROM 103 stores various control programs, setting data, etc. executed by the CPU 101. Alternatively, a rewritable nonvolatile memory such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory may be used instead of the ROM 103.

[0043] The storage unit 104 stores print jobs (image recording commands) and image data for the print jobs input from the external device 6 via the input / output interface 130. For example, an HDD (Hard Disk Drive) is used as the storage unit 104, and a DRAM (Dynamic Random Access Memory) or the like may also be used.

[0044] Based on the control of the control unit 100, the discharge drive unit 110 supplies a drive signal corresponding to the image data to the pressure generating unit (not shown) at an appropriate time relative to the droplet discharge units 3 and 4, thereby discharging a quantity of liquid (ink) corresponding to the pixel value of the image data from the nozzles of the recording heads 33 and 43.

[0045] The conveyance drive unit 120 supplies a drive signal based on the control of the control unit 100 to drive the conveyance belt 21 for conveyance at a predetermined speed and timing.

[0046] The input / output interface 130 mediates data transmission and reception between the external device 6 and the control unit 100. The input / output interface 130 is configured by, for example, various serial interfaces and various parallel interfaces, or a combination of these interfaces.

[0047] The external device 6 is, for example, a personal computer, and supplies image recording commands (printing jobs), image data, and the like to the control unit 100 via the input / output interface 130 .

[0048] The adjustment unit 140 includes a vacuum pump, solenoid valve, pressure gauge, and buffer tank (not shown). Based on control by the control unit 100, it controls the pressure to circulate the liquid within the droplet ejection units 3 and 4. The adjustment unit 140 controls the hydraulic head value and pressure of the liquid within the supply units 32 and 42 and the recovery units 34 and 44, thereby controlling the pressure within the liquid flow path units 331 and 431 to cause the liquid to flow in the direction of the liquid flow. The adjustment unit 140 controls the pressure applied to the liquid at the supply ports 331A and 431A and the recovery ports 331B and 431B of the liquid flow path units 331 and 431, respectively. This causes the liquid within the liquid flow path units 331 and 431 to flow, and the liquid circulates within the droplet ejection units 3 and 4.

[0049] When a plurality of nozzles are arranged to generate a height difference in the gravity direction as in the second recording head 43 , the pressure for forming the meniscus of each nozzle (hereinafter referred to as meniscus pressure) varies according to the height difference.

[0050] Usually it is like Figure 4A As shown in FIG. 4 , the pressure in the liquid flow path portion 431 is controlled to be a relatively small negative pressure so that the meniscus W is slightly recessed relative to the discharge surface 432A of the nozzle 432. For example, Figure 2 As shown, in the case of a structure where the discharge surface of the droplets is parallel to the width direction as in the first recording head 33, the water level of the supply unit 32 and the water level of the recovery unit 34 and the water head of the discharge surface 332A are fixed at H1, so the meniscus pressure is constant in the width direction. Therefore, it can be easily set to Figure 4A As shown, each nozzle has a substantially fixed meniscus W.

[0051] In contrast, when a plurality of nozzles 432 are arranged with a height difference in the direction of gravity, as in the second recording head 43, the hydraulic head at the discharge position of each nozzle 432 varies. In other words, the lower the nozzle 432 is, the greater the hydraulic head, and consequently, the higher the meniscus pressure.

[0052] For example, Figure 2 As shown in FIG. 1 , the water head H3 corresponding to the lowest nozzle 432 is longer than the water head H2 corresponding to the highest nozzle 432 by the amount of the height difference in the liquid flow path 431. Figure 4B As shown, when the position of the nozzle 432 is lowered, the pressure in the liquid flow path becomes positive due to the meniscus pressure, and the meniscus W protrudes relative to the discharge surface 432A of the nozzle 432.

[0053] As described above, the meniscus pressure fluctuates according to the height difference of the nozzles, and therefore the discharge performance in the second recording head 43 varies depending on the position of the nozzles 432 .

[0054] On the other hand, in the second liquid flow path portion 431 , the pressure loss increases as the flow direction becomes downstream, so the pressure on the downstream side in the flow direction becomes lower than that on the upstream side in the flow direction.

[0055] In this embodiment, the adjustment unit 140 controls the pressure within the second liquid flow path 431 so that the liquid flows in the direction of gravity. In other words, the adjustment unit 140 adjusts the flow direction of the liquid in the second liquid flow path 431 so that the nozzle 432 is positioned more downstream as it moves lower in the flow direction.

[0056] Specifically, the adjustment unit 140 adjusts the pressure applied to the liquid at the supply port 431A (upstream end in the flow direction) in the second liquid flow path unit 431 and the amount of change in the pressure applied to the liquid at the recovery port 431B (downstream end in the flow direction).

[0057] Specifically, the adjustment unit 140 changes the flow rate of the liquid flowing from the supply port 431A of the second liquid flow path section 431 to the recovery port 431B based on the difference in the hydraulic heads at the plurality of nozzles 432 so that the meniscus W at all the nozzles 432 does not protrude from the discharge surface 432A. In other words, the adjustment unit 140 adjusts the pressure in the second liquid flow path section 431 so that the flow rate of the liquid exceeds a predetermined condition.

[0058] The predetermined condition can be set as a flow rate condition of a recording head having a plurality of nozzles arranged so as not to cause a step in the flow direction, such as the first recording head 33 , and can be set as appropriate.

[0059] More specifically, the adjustment unit 140 adjusts the pressure change in the second liquid flow path unit 431 to absorb the first pressure difference based on the difference in water heads between the multiple nozzles 432 by utilizing the second pressure difference based on the pressure loss in the flow direction of the liquid in the second liquid flow path unit 431.

[0060] For example, the first pressure difference can be calculated as a pressure based on the distance between the nozzles at both ends in the gravity direction and the horizontal direction (transport direction), the liquid density, and the gravitational acceleration.

[0061] In addition, the nozzle 432 is as Figure 5 As shown, they are arranged not only in the direction of gravity but also in the direction of transport. Figure 5 When nozzle 432 at the upper left end of the diagram is positioned most upstream in the flow direction, closest to supply port 431A, pressure loss also occurs as the nozzle moves to the right in the conveying direction. Specifically, at nozzle 432 located at the bottom, the pressure loss differs between nozzles 432 at the left end and nozzles 432 at the right end. Therefore, the first pressure difference is calculated by taking into account the component in the direction of gravity and the component in the conveying direction.

[0062] For example, the adjustment unit 140 adjusts the second pressure difference so that the sum of the square of the difference between the pressure difference based on the difference in water head between the nozzles and the pressure difference based on pressure loss in the horizontal direction component and the square of the difference between the pressure difference based on the difference in water head between the nozzles and the pressure difference based on pressure loss in the gravity direction component, that is, the square root of a based on the following formula (1) becomes the minimum value.

[0063] a={(ρ×ΔN d x×g)-ΔP d x}2 +{(ρ×ΔN d y×g)-ΔP d y} 2 ……(1)

[0064] ρ in formula (1) is the liquid density (kg / m 3 ), g is the acceleration due to gravity (m / s 2 ). ΔN d x is the distance between the nozzles at both ends in the x direction (m). The x direction is, for example, the conveying direction. ΔN d y is the distance between the nozzles at both ends in the y direction (m). The y direction is, for example, the direction of gravity. ΔP d x is the pressure loss between the nozzles at both ends in the x direction (N / m 2 ). ΔP d y is the pressure loss between the nozzles at both ends in the y direction (N / m 2 ).

[0065] ΔN d x and ΔN d y is a value based on the size of the second liquid flow path portion 431 used in the second recording head 43. ΔP d x and ΔP d y is a preset value based on actual measurements such as experiments. Figure 5 The pressure value obtained after the nozzle 432 at the four corners is broken by the negative pressure is set as ΔP d x and ΔP d y.

[0066] For example, the pressure difference between the supply port 331A and the recovery port 331B of the first liquid flow path portion 331 in the first recording head 33 is set to -5 kPa (prescribed condition). In this case, when the second pressure difference in the second recording head 43 is set to the same as the prescribed condition, the difference in meniscus pressure (first pressure difference) due to the height difference of the plurality of nozzles 432 will increase with the lower nozzles, resulting in more uneven discharge performance.

[0067] In contrast, in this embodiment, based on the above-described formula (1), the absolute value of the second pressure difference between the supply port 431A and the recovery port 431B of the second liquid flow path portion 431 in the second recording head 43 is made larger than a predetermined condition. For example, when the second pressure difference calculated using the above-described formula (1) is -15 kPa, the adjustment unit 140 controls the vacuum pump on the recovery unit 44 side to increase the negative pressure by -10 kPa.

[0068] Alternatively, the second pressure difference may be adjusted by controlling the vacuum pump on the supply unit 42 side. However, if the amount of negative pressure in the predetermined nozzle 432 is excessively large, Figure 4A The amount of depression of the meniscus W relative to the discharge surface 432A increases, which affects the discharge from the nozzle 432. Therefore, it is preferable to adjust the pressure in consideration of this depression.

[0069] By configuring in this manner, it is possible to suppress variation in droplet discharge performance among nozzles due to height differences among the plurality of nozzles.

[0070] The position of the meniscus is mainly determined by two factors: the difference in meniscus pressure due to the height difference of the meniscus and the reverberation vibration generated by driving the droplet ejection unit.

[0071] For example, in areas where the drive frequency of the droplet ejection unit is relatively slow, the difference in meniscus pressure caused by the height difference of the meniscus becomes the dominant factor. Conversely, in areas where the drive frequency of the droplet ejection unit is relatively fast, the reverberant vibration generated by the drive of the droplet ejection unit becomes the dominant factor.

[0072] Here, for example, if the structure is to adjust the pulse signal for driving the pressure generating unit in the droplet ejection unit, as described above, the dominant factor for determining the position of the curved liquid surface varies depending on the driving frequency, so the pulse signal needs to be adjusted according to the driving frequency.

[0073] In contrast, this embodiment utilizes the pressure differential (second pressure differential) generated by the flow in the liquid flow path to absorb the difference in meniscus pressure (first pressure differential) caused by nozzle height differences, thereby suppressing variations in meniscus position. This eliminates the need to adjust the pulse signal with respect to the drive frequency. As a result, variations in meniscus position are easily reduced, further suppressing variations in discharge performance between nozzles caused by height differences between the multiple nozzles.

[0074] Furthermore, the pressure in the liquid flow path portion 431 is controlled so that the meniscus of all nozzles 432 does not protrude from the discharge surface 432A, thereby suppressing discharge defects such as landing deviation in all of the plurality of nozzles.

[0075] Furthermore, in the above embodiment, the first droplet ejecting section 3 and the second droplet ejecting section 4 are provided. However, the present invention is not limited thereto, and a structure may be provided with only a droplet ejecting section similar to the second droplet ejecting section.

[0076] Alternatively, a configuration may be employed in which the position of one droplet discharge unit is moved by a moving mechanism (not shown) to discharge droplets in either the direction of gravity or the horizontal direction. In this configuration, for example, when the droplet discharge unit is caused to discharge droplets horizontally, the adjustment unit moves the droplet discharge unit to a position corresponding to the second droplet discharge unit to adjust the flow direction of the liquid flow path.

[0077] In the above embodiment, the pressure in the second liquid flow path section 431 is adjusted based on the above-mentioned equation (1), but the present invention is not limited thereto, and the pressure may be adjusted using a method other than equation (1).

[0078] Furthermore, in the above embodiment, the image forming apparatus 1 is exemplified as the liquid droplet discharge device. However, the present invention is not limited thereto, and the second liquid droplet discharge section itself may be used as the liquid droplet discharge device.

[0079] Furthermore, in the above embodiment, the control unit controls the adjustment unit, but the present invention is not limited thereto. The adjustment unit may include a CPU, RAM, ROM, etc., and adjust the pressure of the liquid flow path unit by itself.

[0080] Furthermore, in the above embodiment, the adjustment unit adjusts the liquid flow direction by adjusting the pressure within the recording head (in the liquid flow path), but the present invention is not limited to this. For example, the liquid flow direction may be adjusted by adjusting the pressure of the liquid circulation path outside the recording head or other parameters other than pressure.

[0081] In addition, the above embodiments are merely examples of specific implementations of the present invention and should not be used to limit the scope of protection of the present invention. That is, the present invention can be implemented in various forms without departing from the main purpose or key features of the present invention. For example, the shape, size, number, and materials of the various components described in the above embodiments are merely examples and can be appropriately modified to implement the present invention.

[0082] Description of Reference Numerals

[0083] 1. Image forming device; 2. Belt conveyor unit; 3. First liquid droplet discharge unit; 4. Second liquid droplet discharge unit; 21. Conveyor belt; 31. First main tank; 32. First supply unit; 33. First recording head; 34. First recovery unit; 41. Second main tank; 42. Second supply unit; 43. Second recording head; 44. Second recovery unit; 100. Control unit; 110. Discharge drive unit; 120. Conveyor drive unit; 130. Input / output interface; 140. Adjustment unit; 331. First liquid flow path unit; 331A. Supply port; 331B. Recovery port; 431. Second liquid flow path unit; 431A. Supply port; 431B. Recovery port; 432. Nozzle; 432A. Discharge surface.

Claims

1. A liquid droplet discharge device, wherein: The droplet discharge device includes a liquid flow path unit, an adjustment unit, and a plurality of discharge units. The liquid flow path portion is for liquid to flow, The plurality of discharge portions are arranged in a gravity direction and a horizontal direction to discharge liquid droplets from the liquid flow path portion. The adjusting portion adjusts the flow direction of the liquid in the liquid flow path portion so that each discharge portion is located on the downstream side as it is lower in the flow direction. The adjustment unit controls the pressure in the liquid flow path portion for causing the liquid to flow in the flow direction. The adjusting unit adjusts the amount of change in the pressure in the liquid flow path portion so that a first pressure difference based on the difference in the water heads at the plurality of discharge portions is absorbed by a second pressure difference based on the pressure loss of the liquid in the flow direction within the liquid flow path portion. The first pressure difference is calculated as pressure based on a component in the gravity direction and a component in the horizontal direction.

2. The liquid droplet discharge device according to claim 1, wherein: The adjustment unit adjusts a change in pressure applied to the liquid at an upstream end portion in the flow direction and a change in pressure applied to the liquid at a downstream end portion in the flow direction in the liquid flow path portion.

3. The liquid droplet discharge device according to claim 2, wherein: The adjustment unit adjusts the pressure in the liquid flow path unit so that the meniscus in all the discharge portions does not protrude from the discharge surface.

4. The liquid droplet discharge device according to claim 2 or 3, wherein: The liquid flow path portion includes a supply port and a recovery port, wherein the supply port is located at the upstream end portion in the flow direction and supplies the liquid, and the recovery port is located at the downstream end portion in the flow direction and recovers the liquid. The adjustment unit changes a flow rate of the liquid flowing from the supply port to the recovery port according to a difference in water heads at the plurality of discharge portions.

5. The liquid droplet discharge device according to claim 4, wherein: The adjustment unit adjusts the pressure in the liquid flow path unit so that the liquid flows from the supply port toward the recovery port.

6. The liquid droplet discharge device according to any one of claims 1 to 3, wherein: The second pressure difference is based on a preset value.

7. The liquid droplet discharge device according to any one of claims 1 to 3, wherein: The plurality of discharge units discharge the liquid droplets onto a recording medium to record an image.

8. The liquid droplet discharge device according to any one of claims 1 to 3, wherein: The liquid flow path portion extends along the gravity direction, The discharge surfaces of the plurality of discharge portions face the horizontal direction.

9. The liquid droplet discharge device according to any one of claims 1 to 3, wherein: The plurality of discharge units are configured to discharge liquid droplets in at least one of a gravity direction and a horizontal direction. When the discharge portion is caused to discharge the liquid droplets in the horizontal direction, the adjustment portion adjusts the flow direction so that each discharge portion is located further downstream as the position thereof decreases.

10. The liquid droplet discharge device according to claim 9, wherein: The plurality of discharge units include a first discharge unit that discharges the liquid droplets in the direction of gravity and a second discharge unit that discharges the liquid droplets in the horizontal direction.

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