Droplet ejection device and droplet ejection method

Abstract

Provided are a liquid droplet discharging device and a liquid droplet discharging method with which scattering of liquid droplets of a preliminary discharge can be effectively suppressed. The liquid droplet discharging device comprises: a liquid droplet discharging unit provided with a nozzle for discharging a liquid droplet having volatility; and a control means that controls a liquid droplet discharge operation from the nozzle by the liquid droplet discharging unit. The control means performs preliminary discharge control in which a first liquid droplet is discharged from the nozzle onto a three-dimensional recording medium for maintenance of the nozzle, and image formation control in which, on the basis of image data of an image to be formed, a second liquid droplet is discharged from the nozzle onto the three-dimensional recording medium so as to form an image on the three-dimensional recording medium. In the preliminary discharge control, the discharge operation is controlled so that the volume of the first liquid droplet is equal to or less than the volume of the second liquid droplet and the velocity of the first liquid droplet is faster than the velocity of the second liquid droplet.

Description

[Technical Field]

[0001] The present invention relates to a droplet ejection device and a droplet ejection method. [Background technology]

[0002] Conventionally, there is a droplet ejection device that ejects droplets onto a recording medium from a droplet ejection unit provided with a nozzle that ejects droplets, thereby forming an image on the recording medium. The nozzle of the droplet ejection device is supplied and filled with a liquid (e.g., ink) to be ejected as droplets. When the liquid comes into contact with air at the nozzle opening while droplets are not being ejected, a portion of the liquid near the opening vaporizes, changing the properties of the liquid. As a result, it gradually becomes impossible to perform the droplet ejection operation properly, resulting in a problem of deterioration in image quality.

[0003] In response to this, conventionally, there is known a technique for maintaining nozzles by suppressing changes in the properties of the liquid inside the nozzles by preliminarily ejecting droplets from the nozzles when no image is being formed (for example, Patent Documents 1 and 2). It is also known to perform such preliminarily ejecting droplets onto a recording medium for nozzle maintenance.

[0004] Furthermore, some droplet ejection devices are capable of ejecting droplets onto a three-dimensional recording medium to form an image. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-299219 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-181972 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the recording medium is three-dimensional, a large clearance (spacing) between the droplet ejection unit and the recording medium tends to be maintained to ensure contact between the droplet ejection unit and the recording medium, which can result in a long droplet flight distance to the recording medium. Therefore, when performing preliminary ejection on a three-dimensional recording medium, the preliminary ejected droplets are prone to scattering due to various factors, which can lead to problems such as adhesion to the nozzle surface, resulting in ejection failure, or contamination of the device. For example, if droplets are made small to reduce ink consumption during preliminary ejection, they are likely to scatter while flying long distances. Furthermore, near the edges of a three-dimensional object where preliminary ejection is often performed, air currents generated by the shape of the three-dimensional object can easily sweep the droplets away and scatter them. Furthermore, because droplets are not ejected during periods when the nozzle is not facing the three-dimensional recording medium, the droplet ejection direction during preliminary ejection is likely to deviate from the desired direction due to the influence of liquid vaporization during these non-ejection periods, leading to droplet scattering.

[0007] An object of the present invention is to provide a droplet ejection device and a liquid delivery method that can effectively prevent droplets from scattering during preliminary ejection. [Means for solving the problem]

[0008] In order to achieve the above object, the invention of the droplet ejection device described in claim 1 is as follows: a droplet ejection unit provided with a nozzle for ejecting volatile droplets; a control unit for controlling the droplet ejection operation from the nozzle by the droplet ejection unit; Equipped with The control means preliminary ejection control for ejecting first droplets from the nozzles onto a three-dimensional recording medium for maintenance of the nozzles; image formation control that ejects second droplets from the nozzles onto the three-dimensional recording medium based on image data of an image to be formed, and forms the image on the three-dimensional recording medium; and In the preliminary ejection control, The ejection operation is controlled so that the volume of the first droplet is equal to or less than the volume of the second droplet, and the velocity of the first droplet is faster than the velocity of the second droplet. death , Furthermore, the velocity of the first droplet is adjusted within a range faster than the velocity of the second droplet, and the ejection operation is controlled so that the velocity of the first droplet increases as the volume of the first droplet decreases. .

[0009] The invention described in claim 2 is the droplet ejection device described in claim 1, In the preliminary ejection control, the control means controls the ejection operation so that the volume of the first droplet is less than the volume of the second droplet.

[0010] The invention described in claim 3 is the droplet ejection device described in claim 1 or 2, The control means performs the ejection operation by the preliminary ejection control within the period during which the image is formed by the image formation control, and in the preliminary ejection control, disperses and ejects a plurality of the first droplets within an area that overlaps with at least a portion of the formation area of ​​the image by the image formation control.

[0011] The invention described in claim 4 is the droplet ejection device described in claim 3, When the image formed in the image formation control includes characters, the control means controls the ejection operation in the preliminary ejection control so that the volume of the first droplet becomes smaller as the characters become smaller.

[0012] The invention described in claim 5 is the droplet ejection device described in claim 3 or 4, In the preliminary ejection control, the control means controls the ejection operation so that the volume of the first droplet has a value according to the material of the surface of the three-dimensional recording medium on which the droplet lands.

[0013] The invention described in claim 6 is the droplet ejection device described in any one of claims 1 to 5, The surface material of the three-dimensional recording medium includes fiber.

[0014] The invention described in claim 7 is the droplet ejection device described in any one of claims 1 to 5, The three-dimensional recording medium is cardboard.

[0015] The invention described in claim 8 is the droplet ejection device described in any one of claims 1 to 7, a mounting member having a mounting surface on which the three-dimensional recording medium is placed, the three-dimensional recording medium has a height of 5 mm or more from the placement surface; The droplet discharge unit is disposed at a position where, when discharging droplets onto the three-dimensional recording medium placed on the placement surface, the distance between the three-dimensional recording medium and the opening of the nozzle is 5 mm or more.

[0016] The invention described in claim 9 is the droplet ejection device described in any one of claims 1 to 8, the droplet ejection unit has a plurality of the nozzles arranged in a predetermined arrangement direction, The arrangement direction has a vertical component.

[0017] In order to achieve the above object, the invention of a droplet ejection method as set forth in claim 10 comprises: A droplet ejection method for a droplet ejection device including a droplet ejection unit provided with a nozzle for ejecting volatile droplets, comprising: a preliminary ejection step of ejecting a first droplet from the nozzle onto a three-dimensional recording medium for maintenance of the nozzle; an image forming step of ejecting second droplets from the nozzles onto the three-dimensional recording medium based on image data of an image to be formed, thereby forming the image on the three-dimensional recording medium; Including, In the preliminary ejection step, The droplet ejection unit controls the ejection of the droplets from the nozzle so that the volume of the first droplet is equal to or less than the volume of the second droplet and the velocity of the first droplet is faster than the velocity of the second droplet. death , Furthermore, the velocity of the first droplet is adjusted within a range faster than the velocity of the second droplet, and the ejection operation is controlled so that the velocity of the first droplet increases as the volume of the first droplet decreases. . [Effects of the Invention]

[0018] According to the present invention, scattering of droplets during preliminary ejection can be effectively suppressed. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of a droplet ejection device. [Figure 2] FIG. 2 is a diagram showing the configuration of a first head unit. [Figure 3] FIG. 2 is a diagram showing the configuration of a second head unit. [Figure 4] FIG. 2 is a schematic diagram showing the positional relationship between a first head unit, a second head unit, and a recording medium. [Figure 5] FIG. 2 is a block diagram showing a main functional configuration of the droplet ejection device. [Figure 6] 10A and 10B are diagrams illustrating an example of a preliminary ejection operation by the first head unit. [Figure 7] 10A and 10B are diagrams illustrating an example of a preliminary ejection operation by the second head unit. [Figure 8] 10A and 10B are diagrams illustrating an example in which dispersed ejection is performed as a preliminary ejection operation by the first head unit. [Figure 9] 10A and 10B are diagrams illustrating an example in which dispersed ejection is performed as a preliminary ejection operation by the second head unit. [Figure 10] 10 is a flowchart showing a control procedure for image forming processing. [Figure 11] 10A and 10B are diagrams showing the contents and results of an experiment conducted to confirm the effects of the embodiment. [Figure 12] 10A and 10B are schematic diagrams showing ejection states during preliminary ejection and image formation in an experiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0021] <Configuration of droplet ejection device> FIG. 1 is a diagram showing a schematic configuration of a droplet ejection device 1. As shown in FIG. The droplet ejection device 1 includes a transport unit 20, a medium detection unit 30, a first head unit 40 (droplet ejection unit), and a second head unit 50 (droplet ejection unit). The droplet ejection device 1 of this embodiment is an inkjet recording device that ejects droplets of ink as a liquid onto a three-dimensional recording medium M to form an image.

[0022] The transport unit 20 includes a drive roller 21 and a driven roller 22 that rotate around a rotation axis extending in the X direction in FIG. 1 , a ring-shaped transport belt 23 whose inner side is supported by the drive roller 21 and the driven roller 22, a transport motor 24 that rotates the drive roller 21, a rotary encoder 25 attached to the drive roller 21, and a transport control unit 26 (see FIG. 5 ) that controls the operation of the transport motor 24. The drive roller 21 rotates around its rotation axis by being driven by the transport motor 24. The transport belt 23 is a ring-shaped belt whose inner side is supported by the drive roller 21 and the driven roller 22, and moves in a circular motion as the drive roller 21 rotates. The driven roller 22 rotates around a rotation axis parallel to the rotation axis of the drive roller 21 as the transport belt 23 moves in a circular motion. The transport belt 23 is made of a material that flexes flexibly at the contact surface between the drive roller 21 and the driven roller 22 and reliably supports the recording medium M. For example, a resin belt such as rubber, or a steel belt can be used. The conveyor belt 23 has a material and / or a configuration that allows the recording medium M to be adsorbed, thereby enabling the recording medium M to be more stably placed on the conveyor belt 23. The outer peripheral surface of the conveyor belt 23 is a placement surface 23a on which the three-dimensional recording medium M is placed, and the conveyor belt 23 is an example of a placement member having a placement surface.

[0023] In this embodiment, the three-dimensional recording medium M is an object whose maximum height from the mounting surface 23a of the conveyor belt 23 is 5 mm or more. The three-dimensional recording medium M may have a surface that intersects with the mounting surface 23a when placed on the mounting surface 23a of the conveyor belt 23. The normal direction of this surface is different from the normal direction of the mounting surface 23a, and the surface has an area on which ink droplets ejected from the first head unit 40 or the second head unit 50 can land. The three-dimensional recording medium M may also have a surface at a position that is 5 mm or more high from the mounting surface 23a, and the surface may have an area on which ink droplets can land. An example of the three-dimensional recording medium M is cardboard. The cardboard may be pre-assembled or may not be assembled. In this embodiment, cardboard assembled into a rectangular parallelepiped shape is used as the recording medium M. The droplet ejection device 1 can also form images on non-three-dimensional recording media, such as sheet-like recording media such as paper.

[0024] The transport motor 24 rotates the drive roller 21 at a rotation speed corresponding to a control signal from the transport control unit 26. With the recording medium M placed on the placement surface 23a of the transport belt 23, the transport belt 23 moves in a circular motion at a speed corresponding to the rotation speed of the drive roller 21, thereby transporting the recording medium M in the movement direction of the transport belt 23 (transport direction: Y direction in FIG. 1).

[0025] The rotary encoder 25 is attached to the drive roller 21 and outputs a pulse signal (detection signal) to the control unit 10 and the head control unit 42 (see FIG. 5 ) each time the drive roller 21 rotates a predetermined angle. Therefore, the amount of movement of the conveyor belt 23 and the recording medium M can be determined based on the number of pulse signals from the rotary encoder 25. The configuration of the rotary encoder 25 is not particularly limited, but it can be configured to include, for example, a code wheel having a plurality of slits arranged on a predetermined circumference and rotating together with the drive roller 21, a light-emitting unit that irradiates light onto the slits of the code wheel, and a light-receiving unit that detects light emitted from the light-emitting unit and passed through the slits, and to output a pulse signal based on the light detection result by the light-receiving unit to the control unit 10 and the head control unit 42.

[0026] The medium detection unit 30 is provided upstream of the first head unit 40 and the second head unit 50 in the transport direction. The medium detection unit 30 detects the recording medium M using a sensor and outputs a signal related to the detection result to the control unit 10. The configuration of the sensor is not particularly limited, but in this embodiment, a sensor including an emission unit that emits laser light in the X direction at a predetermined height from the placement surface 23a, and a detection unit that detects the laser light on the opposite side of the placement surface 23a in the width direction to detect blocking of the laser light by the recording medium M is used. The position of the recording medium M can be identified by counting pulse signals from the rotary encoder 25, starting from the timing when the recording medium M is detected by the medium detection unit 30.

[0027] The first head unit 40 and the second head unit 50 have a plurality of nozzles N that eject ink droplets. The first head unit 40 and the second head unit 50 form an image on the recording medium M that is transported by the transport unit 20 by ejecting ink droplets from the nozzles N at a timing based on a control signal from the control unit 10 or the like.

[0028] The first head unit 40 ejects ink vertically downward (in the -Z direction) onto, for example, the upper surface of the rectangular parallelepiped recording medium M (one of the two surfaces parallel to the mounting surface 23a, the surface opposite the surface facing the mounting surface 23a). The first head unit 40 is also called a "horizontally placed head" because the arrangement direction of the nozzles N is the lateral direction (horizontal direction).

[0029] The second head unit 50 ejects ink in a horizontal direction (-X direction in FIG. 1) onto, for example, the side surface (surface adjacent to the top surface and perpendicular to the top surface) of the recording medium M, which has a rectangular parallelepiped shape. The second head unit 50 is also called a "vertically mounted head" because the arrangement direction of the nozzles N is the vertical direction. Note that while only one second head unit 50 is depicted in FIG. 1, two or more second head units 50 may be provided to eject ink onto two or more of the four side surfaces of the recording medium M, which has a rectangular parallelepiped shape.

[0030] The positions of the first head unit 40 and the second head unit 50 in the X, Y, and Z directions can be adjusted by a head unit movement mechanism (not shown). This allows ink to be ejected from an appropriate position according to the shape of the recording medium M.

[0031] 1 depicts one first head unit 40 and one second head unit 50 that eject ink of a single color (for example, black (K)), but a configuration that allows color images to be formed may also be provided in which multiple first head units 40 and / or multiple second head units 50 that eject ink of different colors are provided. For example, four first head units 40 and / or four second head units 50 corresponding respectively to ink of four colors, yellow (Y), magenta (M), cyan (C), and black (K), may be arranged at predetermined intervals in the order of Y, M, C, and K from the upstream side in the transport direction of the recording medium M.

[0032] FIG. 2 is a diagram showing the configuration of the first head unit 40, and is a plan view of the first head unit 40 as seen from the -Z direction. The first head unit 40 includes a plurality of (six in this embodiment) droplet ejection heads 41, each having a plurality of nozzles N. The first head unit 40 includes a plate-shaped support portion 40a parallel to the XY plane, and six droplet ejection heads 41 fixed to the support portion 40a while fitting into through holes provided in the support portion 40a. The droplet ejection heads 41 are fixed to the support portion 40a with their nozzle opening surfaces 41a, on which the openings of the nozzles N are provided, exposed from the through holes in the support portion 40a in the -Z direction. Therefore, the nozzle opening surfaces 41a of the droplet ejection heads 41 face vertically downward, and the nozzles N of the droplet ejection heads 41 eject ink droplets vertically downward.

[0033] In the droplet ejection head 41, a plurality of nozzles N are arranged at equal intervals in an arrangement direction that intersects with the transport direction of the recording medium M (in FIG. 2, the X direction that is perpendicular to the transport direction), forming nozzle rows. In this embodiment, each droplet ejection head 41 has four nozzle rows. The positions of these nozzle rows in the X direction are shifted from each other so that the positions of the nozzles N in the X direction do not overlap. Note that the number of nozzle rows that the droplet ejection head 41 has is not limited to four, and may be three or less, or five or more.

[0034] The six droplet ejection heads 41 in the first head unit 40 are arranged in a staggered pattern so that the arrangement range of the nozzles N in the X direction is continuous. The arrangement range in the X direction of the nozzles N included in the first head unit 40 covers the width in the X direction of an area on the upper surface of the recording medium M transported by the transport belt 23, on which an image can be formed. The number of droplet ejection heads 41 may be changed depending on the recording width of the image, etc. The first head unit 40 is used in a fixed position when forming an image, and forms an image by a single pass method by ejecting ink from the nozzles N to each position at predetermined intervals in the transport direction (transport direction intervals) as the recording medium M is transported.

[0035] FIG. 3 is a diagram showing the configuration of the second head unit 50, and is a plan view of the second head unit 50 as seen from the −X direction. The second head unit 50 includes a plurality of droplet ejection heads 51 (four in this embodiment), each having a plurality of nozzles N. The second head unit 50 includes a plate-shaped support portion 50a parallel to the YZ plane, and four droplet ejection heads 51 fixed to the support portion 50a while fitting into through-holes formed in the support portion 50a. The droplet ejection heads 51 are fixed to the support portion 50a with their nozzle opening surfaces 51a, on which the openings of the nozzles N are formed, exposed from the through-holes in the support portion 50a toward the -X direction. Therefore, the nozzle opening surfaces 51a of the droplet ejection heads 51 shown in FIGS. 1 and 3 face horizontally (the X direction), and the nozzles N of the droplet ejection heads 51 eject ink droplets toward the -X direction. The arrangement of the nozzles N in the droplet ejection head 51 is the same as that of the droplet ejection head 41.

[0036] In the droplet ejection head 51, a plurality of nozzles N are arranged at equal intervals in an arrangement direction (Z direction in FIG. 3) that intersects with the transport direction of the recording medium M, forming a nozzle row. That is, the arrangement direction of the nozzles N in the nozzle row has a vertical component. In this embodiment, each droplet ejection head 51 has four nozzle rows. The positions of these nozzle rows in the Z direction are shifted from each other so that the positions of the nozzles N in the Z direction do not overlap. Note that the number of nozzle rows that the droplet ejection head 51 has is not limited to four, and may be three or less, or five or more.

[0037] The four droplet ejection heads 51 in the second head unit 50 are arranged in a staggered pattern so that the arrangement range of the nozzles N in the Z direction is continuous. The arrangement range in the Z direction of the nozzles N included in the second head unit 50 covers the width in the Z direction of an area on the side of the recording medium M transported by the transport belt 23 where an image can be formed. The number of droplet ejection heads 51 may be changed depending on the recording width of the image, etc. The second head unit 50 is used in a fixed position when forming an image, and forms an image by a single pass method by ejecting ink from the nozzles N to each position at predetermined intervals in the transport direction (transport direction intervals) as the recording medium M is transported.

[0038] FIG. 4 is a schematic diagram showing the positional relationship between the first head unit 40, the second head unit 50, and the recording medium M. As shown in FIG. The first head unit 40 is disposed at a position where, when the opening of the nozzle N faces the upper surface of the recording medium M, the distance d1 between the opening of the nozzle N and the recording medium M (i.e., the distance d1 between the nozzle opening surface 41 a and the recording medium M) is secured to be equal to or greater than a predetermined reference distance. The second head unit 50 is disposed at a position where, when the opening of the nozzle N faces the side surface of the recording medium M, the distance d2 between the opening of the nozzle N and the recording medium M (i.e., the distance d2 between the nozzle opening surface 51 a and the recording medium M) is secured to be equal to or greater than a predetermined reference distance. In this embodiment, the above-mentioned reference distances are both 5 mm, and the distances d1 and d2 are both 5 mm or greater. In other words, the first head unit 40 and the second head unit 50 eject ink droplets from the nozzles N onto the recording medium M while securing a clearance of 5 mm or greater from the surface of the recording medium M. These distances d1 and d2 are greater than the distance between the recording medium and the head unit when the recording medium is in sheet form. This takes into consideration the fact that when the recording medium M is three-dimensional, the three-dimensional recording medium M is prone to shaking and deformation due to the influence of vibrations and air currents during transport. In other words, even if the surface position of the three-dimensional recording medium M fluctuates during transport, contact between the nozzle opening surface 41a of the first head unit 40 and the recording medium M, and contact between the nozzle opening surface 51a of the second head unit 50 and the recording medium M can be reliably avoided. Also, as mentioned above, the height h of the three-dimensional recording medium M shown in FIG. 4 is 5 mm or more.

[0039] The ink ejection mechanism provided in the droplet ejection head 41 and the droplet ejection head 51 for ejecting ink from the nozzle N is not particularly limited, but a piezo-type mechanism using a piezoelectric element can be used. Known piezo-type ink ejection mechanisms include shear mode and vent mode. A shear mode ink ejection mechanism generates a shear mode type displacement in a piezoelectric element on the wall of a pressure chamber communicating with the nozzle N in response to a drive signal, thereby varying the pressure of the ink in the pressure chamber. A vent mode ink ejection mechanism ejects ink by varying the pressure of the ink in the pressure chamber by deforming a piezoelectric element fixed to a diaphragm that forms the wall of the pressure chamber in response to a drive signal.

[0040] In this embodiment, aqueous ink is used as the ink ejected from the droplet ejection head 41 and the droplet ejection head 51. The aqueous ink contains, for example, water as a dispersion medium and a pigment or dye as a colorant, and may also contain various water-soluble organic solvents, hydrophobic polymers, and the like. Note that the ink ejected from the droplet ejection head 41 is not limited to aqueous ink, and may be solvent ink using an organic solvent as a dispersion medium. These aqueous inks and solvent inks are volatile because the water or organic solvent that serves as the dispersion medium can evaporate.

[0041] FIG. 5 is a block diagram showing the main functional configuration of the droplet ejection device 1. As shown in FIG. The droplet discharge device 1 includes a control unit 10 (control means), a transport unit 20 having a transport motor 24, a rotary encoder 25, and a transport control unit 26, a medium detection unit 30, a first head unit 40 having a droplet discharge head 41 and a head control unit 42, a second head unit 50 having a droplet discharge head 51 and a head control unit 52, an operation display unit 61, a communication unit 62, a bus 63, etc. In the following, explanations of the configuration that has already been explained will be omitted.

[0042] The control unit 10 has a CPU 11 (Central Processing Unit), a RAM 12 (Random Access Memory), a ROM 13 (Read Only Memory), and a storage unit 14. The control unit 10 controls the overall operation of each unit of the droplet ejection device 1 by the CPU 11 executing various processes in accordance with a program 131.

[0043] The CPU 11 reads out various control programs 131 and setting data stored in the ROM 13, stores them in the RAM 12, and executes the programs to perform various arithmetic processing.

[0044] The RAM 12 provides a working memory space for the CPU 11 and stores temporary data. The RAM 12 may include a non-volatile memory.

[0045] The ROM 13 is a non-transitory recording medium readable by the CPU 11 as a computer, and stores various control programs 131 and setting data executed by the CPU 11. Note that the ROM 13 may be replaced by a rewritable non-volatile memory such as a flash memory.

[0046] The storage unit 14 is a non-transitory recording medium readable by the CPU 11 as a computer, and stores a print job (image recording command) input from an external device via the communication unit 62 and image data of an image to be formed in the print job (hereinafter referred to as "formation image data"), etc. As the storage unit 14, for example, an HDD (Hard Disk Drive) or the like is used.

[0047] The conveying control unit 26 supplies a conveying drive signal to the conveying motor 24 based on a control signal supplied from the control unit 10, causing the drive roller 21 to rotate at a predetermined rotational speed, thereby moving the conveying belt 23 at a predetermined moving speed.

[0048] The head control unit 42 outputs a drive signal (a voltage signal of a drive waveform) for driving the ink ejection mechanism to the droplet ejection head 41 at an appropriate timing based on the control signal and image data sent from the control unit 10, and the pulse signal sent from the rotary encoder 25. The configuration of the head control unit 42 is not particularly limited, but can be configured to include, for example, a drive waveform generation unit that generates a drive waveform pattern in accordance with the control signal and image data sent from the control unit 10, a DAC that converts the drive waveform pattern into an analog drive waveform, and an amplifier circuit that amplifies the analog drive waveform to generate a drive signal.

[0049] The droplet ejection head 41 performs an ejection operation to eject ink droplets from the nozzle N by supplying a drive signal to the ink ejection mechanism of the nozzle N to be ejected based on the image data, based on the drive signal transmitted from the head control unit 42 and image data transmitted from the control unit 10 or the head control unit 42. Here, if the image data is formation image data, an image to be formed is formed on the recording medium M by the ejection operation. Furthermore, if the image data is preliminary ejection image data for performing preliminary ejection, which will be described later, preliminary ejection is performed at a specified timing by the nozzle N specified by the preliminary ejection image data. The volume (droplet amount) and velocity of the ink droplets ejected from the nozzle N during the ejection operation are determined by the drive waveform pattern and / or the magnitude of the voltage signal of the supplied drive signal. In other words, the control unit 10 and the head control unit 42 can cause the nozzle N to eject ink droplets of a desired volume and velocity by transmitting a drive signal to the droplet ejection head 41. The method for adjusting the volume of an ink droplet may be a method for adjusting the size of a single droplet ejected from a nozzle N, or a method for adjusting the number of droplets ejected consecutively and / or the volume of each droplet in an ejection method in which two or more ink droplets are ejected consecutively from a nozzle N and combined in flight.

[0050] The operation of the head control unit 52 and the droplet ejection head 51 is the same as the operation of the head control unit 42 and the droplet ejection head 41 except for the ink ejection direction, so a description thereof will be omitted. Hereinafter, when referring to either the head control unit 42 or the head control unit 52, it will be referred to as the "head control unit" without a reference number.

[0051] In this embodiment, for the first head unit 40, the control unit 10 and the head control unit 42 constitute a "control means" that controls the ejection operation. Also, for the second head unit 50, the control unit 10 and the head control unit 42 constitute a "control means" that controls the ejection operation. In this way, the control means may have two or more separate hardware processors (ICs, etc.). Note that the configuration of the control means is not limited to that exemplified in this embodiment; for example, the control means may be constituted by only the control unit 10, or the control means may be constituted by a single hardware processor.

[0052] The operation display unit 61 includes a display device such as a liquid crystal display, and an input device such as operation keys and a touch panel overlaid on the screen of the display device. The operation display unit 61 displays various information on the display device, and converts user input operations on the input device into operation signals and outputs them to the control unit 10.

[0053] The communication unit 62 is a communication interface that controls data communication with external devices. The communication interface may include one or more devices that support various communication protocols, such as a LAN board or LAN card. The communication unit 62 acquires image data and setting data (job data) related to a print job from an external device under the control of the control unit 10, and also transmits status information and the like to the external device.

[0054] The bus 63 is a path for transmitting and receiving signals between the control unit 10 and other components.

[0055] <Operation of the droplet ejection device> Next, the operation of the droplet ejection device 1 will be described, focusing on the operation relating to the preliminary ejection for maintenance of the nozzles N.

[0056] The nozzles N of the droplet ejection device 1 are filled with ink. When ink comes into contact with air at the openings of the nozzles N while no ink droplets are being ejected, some of the ink near the openings evaporates, causing changes in the ink's properties (e.g., viscosity and specific gravity). As a result, ejection defects (problems with the ink ejection operation) occur, in which the flight direction, flight speed, and amount of ink ejected from the nozzles N deviate from their original settings, leading to a deterioration in image quality. In particular, in the droplet ejection device 1 of this embodiment, large distances d1 and d2 are ensured between the first head unit 40 and the second head unit 50 and the recording medium M, so even slight deviations in the flight direction or flight speed of the ink can easily lead to large deviations in the landing position, easily degrading image quality.

[0057] To avoid this problem, the droplet ejection device 1 of this embodiment performs preliminary ejection, in which ink is preliminarily ejected from the nozzle N onto the three-dimensional recording medium M being transported for nozzle maintenance. Hereinafter, the control by the control unit 10 and head control unit as control means to preliminarily eject droplets from the nozzle N onto the three-dimensional recording medium M for nozzle N maintenance will be referred to as "preliminary ejection control." Furthermore, the ink droplets ejected from the nozzle N by preliminary ejection control will be referred to as "preliminary ejection droplets." Furthermore, the control by the control unit 10 and head control unit as control means to eject droplets from the nozzle N onto the three-dimensional recording medium M based on the formation image data of the image to be formed, thereby forming an image on the three-dimensional recording medium M, will be referred to as "image formation control." Furthermore, the ink droplets ejected from the nozzle N by image formation control will be referred to as "image formation droplets." The preliminary ejection droplets and image formation droplets may be multiple droplets continuously ejected from the nozzle N that coalesce in flight. The pre-ejected droplets correspond to the "first droplets," and the image-forming droplets correspond to the "second droplets." Hereinafter, the volume of the pre-ejected droplets will also be referred to as the "first volume," and the volume of the image-forming droplets will also be referred to as the "second volume." In addition, the velocity of the pre-ejected droplets will also be referred to as the "first velocity," and the velocity of the image-forming droplets will also be referred to as the "second velocity."

[0058] Furthermore, in this embodiment, large distances d1 and d2 are ensured between the first head unit 40 and the second head unit 50 and the three-dimensional recording medium M, so the flight distance of droplets ejected from the nozzles N to the recording medium M is long. For this reason, when preliminary ejection is performed onto the three-dimensional recording medium M, the preliminary ejected droplets are likely to scatter due to various factors.

[0059] For example, if the first volume of the preliminary ejection droplets is set to be less than the second volume of the image-forming droplets for the purpose of reducing ink consumption during preliminary ejection, the flight stability of the preliminary ejection droplets decreases, and the flight direction is more likely to change due to the influence of air currents. As a result, the preliminary ejection droplets are more likely to scatter while flying long distances. Furthermore, air currents are more likely to occur near the edges of the three-dimensional recording medium M due to the three-dimensional shape. Therefore, when forming a discharge zone 71 (see FIGS. 6 and 7) near the edges of the recording medium M (described later), the preliminary ejection droplets are more likely to be blown away by the air currents and scattered. Furthermore, even when performing image formation or preliminary ejection on multiple three-dimensional recording media M consecutively, droplets are not ejected during periods when the nozzle N is not facing the three-dimensional recording media M. Therefore, during preliminary ejection, the droplet ejection direction is more likely to deviate from the desired direction due to the influence of ink vaporization during these non-ejection periods, and the droplets are more likely to scatter.

[0060] If the scattered preliminary ejection droplets adhere to the nozzle opening surfaces 41a and 51a and solidify, blocking part of the nozzle opening of the nozzle N, this can lead to defective ejection of ink droplets from the nozzle N. Furthermore, the scattered preliminary ejection droplets can also adhere to various components of the droplet ejection device 1, causing damage and soiling. In particular, if the preliminary ejection droplets ejected horizontally from the vertically-mounted second head unit 50 scatter without landing on the recording medium M, they scatter over a wide area without landing on the mounting surface 23a of the conveyor belt 23, which can lead to significant damage and soiling. Furthermore, when the preliminary ejection droplets are ejected from the nozzle N, minute mist-like droplets (hereinafter referred to as "microdroplets") may be generated along with the main droplets. These microdroplets may scatter and adhere to the interior of the device, causing defective ejection of the nozzle N and soiling of the device. Hereinafter, the scattered preliminary ejection droplets (including microdroplets) without landing on the recording medium M will also be referred to as "ink mist."

[0061] Therefore, in the present embodiment, the control unit 10 and the head control unit control the preliminary ejection operation so that the first speed of the preliminary ejection droplets is faster than the second speed of the image-forming droplets. This increases the stability of the flight of the preliminary ejection droplets, allowing them to land more reliably on the surface of the recording medium M. This makes it possible to suppress the scattering of the preliminary ejection droplets. Furthermore, by increasing the speed of the main droplets of the preliminary ejection droplets, the speed and volume of the accompanying microdroplets increase. This also increases the stability of the flight of the microdroplets, and suppresses problems caused by the microdroplets scattering as ink mist.

[0062] A specific example of the preliminary ejection operation performed by the droplet ejection device 1 will be described below. 6 is a diagram illustrating an example of a preliminary ejection operation by the first head unit 40. In FIG. 6, the second head unit 50 is omitted from the illustration. In FIG. 6 , the control unit 10 and the head control unit 42 perform image formation control to eject image-forming droplets from the nozzles N of the first head unit 40 onto the upper surface S1 of the recording medium M being transported in the Y direction, thereby forming an image 80 related to a print job. Prior to the formation of the image 80, the control unit 10 and the head control unit 42 also perform preliminary ejection control to perform preliminary ejection from each nozzle N near the edge of the upper surface S1 on the +Y direction side, thereby forming a strip-like spit-out band 71 that is long in the X direction. The spit-out band 71 is formed by ejecting preliminary ejection droplets a predetermined number of times from all nozzles N of the first head unit 40 toward the formation position of the spit-out band 71. This preliminary ejection performed outside the formation region of the image 80 is also referred to as “spit-out.” Spit-out is preferably performed on the downstream side of the formation region of the image 80 in the transport direction of the recording medium M on which the image 80 is to be formed. This allows the image 80 to be formed using the nozzles N immediately after preliminary ejection, thereby effectively suppressing degradation in image quality due to ink evaporation.

[0063] 7 is a diagram illustrating an example of a preliminary ejection operation by the second head unit 50. In FIG. 7, the first head unit 40 is omitted from the illustration. 7, the control unit 10 and the head control unit 52 perform image formation control, causing the nozzles N of the second head unit 50 to eject image forming droplets onto the side surface S2 of the recording medium M being transported in the Y direction, thereby forming an image 80 related to the print job. Furthermore, at a timing prior to the formation of this image 80, the control unit 10 and the head control unit 52 perform preliminary ejection control, causing each nozzle N to perform preliminary ejection near the end of the side surface S2 on the +Y direction side, thereby forming a strip-shaped discharge band 71 that is long in the Z direction. In this way, preliminary ejection can also be performed using the side surface S2 of the recording medium M with the second head unit 50 that is vertically installed.

[0064] The first volume of the preliminary ejection droplets when forming the discharge zone 71 is set to be equal to or less than the second volume of the image formation droplets. In particular, by setting the first volume to be less than the second volume, the amount of ink consumed in the preliminary ejection control can be reduced. Note that, when a plurality of image formation droplets with different volumes are used in the image formation control, the first volume of the preliminary ejection droplets is set to be equal to or less than the smallest volume of the image formation droplets.

[0065] Furthermore, the first velocity of the pre-ejected droplets when forming the spit-away zone 71 is set to be faster than the second velocity of the image-forming droplets, thereby increasing the stability of the flight of the pre-ejected droplets and making them less susceptible to the influence of air currents that tend to occur near the edges of the three-dimensional recording medium M.

[0066] FIG. 8 is a diagram illustrating an example in which the first head unit 40 performs dispersed ejection as a preliminary ejection operation. In FIG. 8, an image 80 is formed on the upper surface S1, as in FIG. 6. The control unit 10 and the head control unit 42 also perform a discharge operation under preliminary discharge control during a period in which the image 80 is formed under image formation control, discharging a plurality of preliminary discharge droplets in a dispersed manner within an area overlapping at least a portion of the formation area of ​​the image 80. As a result, a plurality of dispersed dots 72 are formed on the upper surface S1. Each dispersed dot 72 is formed by a preliminary discharge droplet discharged from one nozzle N. Here, the formation area of ​​the image 80 is an area corresponding to the image data used to form the image 80, and if the image 80 includes a non-discharge area (white area), the non-discharge area is also included. In FIG. 8, preliminary discharge droplets are dispersedly discharged over substantially the entire surface of the upper surface S1, including the formation area of ​​the image 80, to form dispersed dots 72. Distributing preliminary discharge droplets in a dispersed manner within an area overlapping at least a portion of the formation area of ​​the image to be formed according to the print job is also referred to as "distributed discharge." In dispersed ejection, preliminary ejection droplets may be ejected from all nozzles N, or may be ejected only from nozzles N that do not eject image-forming droplets. Dispersed dots 72 formed by dispersed ejection are less visible than the discarded bands 71. Therefore, dispersed ejection can make it even less visible that preliminary ejection is being performed.

[0067] FIG. 9 is a diagram illustrating an example in which the second head unit 50 performs dispersed ejection as a preliminary ejection operation. 9, an image 80 is formed on the side surface S2, as in FIG. 7. Furthermore, the control unit 10 and the head control unit 52 perform a discharge operation by preliminary discharge control within a period in which the image 80 is formed by image formation control, and cause a plurality of preliminary discharge droplets to be dispersed and discharged within an area that overlaps with at least a portion of the formation area of ​​the image 80. As a result, a plurality of dispersed dots 72 are formed on the side surface S2. In FIG. 9, preliminary discharge droplets are dispersed and discharged over substantially the entire surface of the side surface S2, including the formation area of ​​the image 80, and dispersed dots 72 are formed. In this way, the vertically oriented second head unit 50 can also perform dispersed discharge using the side surface S2 of the recording medium M.

[0068] Even when dispersed ejection is performed, the first volume of the preliminary ejection droplets is set to be equal to or less than the second volume of the image-forming droplets. In particular, by setting the first volume to be less than the second volume, the amount of ink consumed in preliminary ejection control can be reduced.

[0069] 8 and 9, when an image 80 includes characters, the smaller the characters, the more likely the dispersed dots 72 will reduce the visibility of the characters, and the more likely the dispersed dots 72 will be visible. Therefore, when an image formed in image formation control includes characters, the control unit 10 and the head control unit may control the ejection operation from the nozzle N in preliminary ejection control so that the smaller the characters, the smaller the volume of the preliminary ejection droplets. Here, characters include numbers and symbols. Furthermore, when image 80 includes multiple characters of different sizes, the volume of the preliminary ejection droplets may be set according to the size of the smallest character among them.

[0070] Furthermore, the visibility of the dispersed dots 72 varies depending on the material of the surface on which the preliminary ejection droplets land of the three-dimensional recording medium M. For this reason, the volume of the preliminary ejection droplets may be set to a predetermined value that makes them less visible depending on the material of the surface on which the preliminary ejection droplets land. For example, if the surface of the recording medium M is made of fabric, for example, and the surface material contains fibers, the landed preliminary ejection droplets (dispersed dots 72) are less visible, so the volume of the preliminary ejection droplets may be larger than when the surface material does not contain fibers.

[0071] The volume of the preliminary ejection droplets may be set according to how easily the droplets dry after landing, so that they dry and become fixed within a predetermined time after landing. The ease with which the droplets dry is affected by the material of the surface on which they land, the temperature, the humidity, etc. For example, the volume of the preliminary ejection droplets may be made smaller as they become more difficult to dry after landing.

[0072] Furthermore, even when dispersed ejection is performed, the first velocity of the preliminary ejection droplets is set to be faster than the second velocity of the image-forming droplets, which makes it possible to minimize deviation in the ejection direction even in a state where the ejection direction of the droplets is likely to be deviated due to the influence of vaporization of ink in the nozzle N during periods when no droplets are ejected.

[0073] As for whether to perform the preliminary ejection as the discharge, the setting of either the discharge-dropping or the dispersed ejection may be fixed, or the user may be able to select and set either one by a predetermined operation. When the method of preliminary ejection is selectable, setting data specifying the preliminary ejection method may be stored in the storage unit 14, and when preliminary ejection control is executed, the control unit 10 may select either the discharge-dropping or the dispersed ejection in accordance with this setting data. Furthermore, for one recording medium M, the preliminary ejection onto the top surface S1 shown in FIG. 6 or 8 and the preliminary ejection onto the side surface S2 shown in FIG. 7 or 9 may be performed in parallel.

[0074] The first velocity of the prefired droplets may be further adjusted to be greater than the second velocity of the imaging droplets. For example, the smaller the first volume of the pre-ejected droplets is, the higher the first velocity may be, which effectively prevents the pre-ejected droplets with a small volume, which tend to lose flight stability, from scattering. Furthermore, the first velocity may be increased as the ejection position of the preliminary ejection droplets is closer to the edge of the three-dimensional recording medium M. This makes it possible to effectively suppress scattering due to the influence of air currents that tend to occur near the edge of the three-dimensional recording medium M. Furthermore, the first velocity may be increased as the non-ejection period of ink droplets from the nozzle N becomes longer. This makes it possible to effectively suppress deviations in the ejection direction and ejection amount caused by changes in the ink characteristics during the non-ejection period.

[0075] Next, a control procedure for the image forming process for carrying out the above-mentioned preliminary ejection control and image forming control will be described. FIG. 10 is a flowchart showing a control procedure for the image forming process. The image forming process is executed when the control unit 10 receives a print job from an external device via the communication unit 62.

[0076] When the image formation process is started, the control unit 10 determines whether it is time to perform a preset preliminary ejection (step S101). The timing to perform the preliminary ejection can be determined arbitrarily, but may be, for example, when a predetermined time has elapsed since the last preliminary ejection, or when image formation has been performed on a predetermined number of recording media M since the last preliminary ejection. Alternatively, the preliminary ejection may be performed on all recording media M every time.

[0077] If it is determined that it is time to perform preliminary ejection ("YES" in step S101), the control unit 10 refers to the setting data in the memory unit 14 and determines whether the preliminary ejection method is set to dispersed ejection (step S102).

[0078] If it is determined that the preliminary ejection method is set to dispersed ejection ("YES" in step S102), the control unit 10 identifies the surface material of the three-dimensional recording medium M specified in the print job, and sets a first volume of the preliminary ejection droplets according to the material (step S103). The method for setting the first volume in this step is not particularly limited, but can be, for example, a method in which table data (not shown) in which a first volume is associated with each material is referenced, and the first volume corresponding to the material is selected and set.

[0079] The control unit 10 determines whether the image to be formed specified by the print job includes text (step S104). If it is determined that the image to be formed includes text ("YES" in step S104), the control unit 10 adjusts the setting of the first volume of the preliminary ejection droplets according to the size of the text included in the image to be formed (step S105). The method for setting the first volume in this step is not particularly limited, but may be, for example, a method in which table data (not shown) in which a first volume is associated with each character size is referenced, and the first volume corresponding to the size of the text in the image to be formed is selected and set. Alternatively, the table data may associate a reduction rate of the first volume with the first volume instead of the first volume itself, and the setting may be adjusted by multiplying the reduction rate by the current setting value of the first volume. Alternatively, if the first volume has already been adjusted according to the material in step S103, the smaller of the adjusted first volumes determined in steps S103 and S105 may be selected as the setting value.

[0080] When the processing of step S105 is completed, or when it is determined in step S104 that the formed image does not include text ("NO" in step S104), the control unit 10 and the head control unit form an image on the three-dimensional recording medium M based on the formation image data, and perform dispersed ejection on the recording medium M (step S106: preliminary ejection step, image formation step). That is, the control unit 10 and the head control unit eject image formation droplets of a second volume and a second speed from the nozzle N based on the formation image data at the timing when the image formation position on the three-dimensional recording medium M faces the nozzle N, and form an image on the recording medium M. Furthermore, in parallel with the formation of the image, the control unit 10 and the head control unit eject preliminary ejection droplets of a first volume and a first speed from the nozzle N into an area overlapping at least a part of the image formation area, and perform dispersed ejection (step S106). Here, for example, image formation droplets and / or preliminary ejection droplets may be ejected from each nozzle N based on composite image data that combines formation image data and preliminary ejection image data for forming dispersed dots 72.

[0081] In step S102, when it is determined that the preliminary ejection method is not set to dispersed ejection (i.e., the preliminary ejection method is set to discard) (“NO” in step S102), the control unit 10 and the head control unit perform preliminary ejection by a method that forms the discard zone 71. That is, the control unit 10 and the head control unit cause the nozzle N to eject preliminary ejection droplets of a first volume and a first speed based on the preliminary ejection image data of the discard zone 71 at the timing when the image formation position on the three-dimensional recording medium M faces the nozzle N, thereby forming the discard zone 71 (step S107: preliminary ejection step). Note that instead of performing the ejection operation based on the preliminary ejection image data of the discard zone 71, the discard zone 71 may be formed by supplying a drive signal to all nozzles without based on image data.

[0082] After the formation of the discharge zone 71, the control unit 10 and the head control unit, when the image formation position on the three-dimensional recording medium M faces the nozzle N, eject image formation droplets of a second volume and a second speed from the nozzle N based on the formation image data to form an image on the recording medium M (step S108: image formation step).

[0083] When step S106 or step S108 is completed, the control unit 10 determines whether or not all image formation specified in the print job has been completed (step S109). If it is determined that all image formation has not been completed ("NO" in step S109), the control unit 10 returns the process to step S101 and executes the processes of steps S101 to S109 for the next recording medium M. If it is determined that all image formation has been completed ("YES" in step S109), the control unit 10 ends the image formation process.

[0084] <Example> Next, an experiment conducted to confirm the effects of the above embodiment will be described. FIG. 11 shows the details and results of the experiment. FIG. 12 is a schematic diagram showing the ejection state during preliminary ejection and image formation in the experiment. A total of four experiments were conducted: an example corresponding to the above embodiment and three comparative examples 1 to 3. In the example and comparative examples 1 to 3, preliminary ejection was performed under different conditions using the first head unit 40, and then image formation was performed under common conditions in each experiment using the first head unit 40. Furthermore, the stability of preliminary ejection and the stability of image formation were evaluated for each experiment. Regarding the stability of preliminary ejection, the presence or absence of scattering of preliminary ejected droplets was evaluated based on whether or not the main droplets and microdroplets of the ejected preliminary ejected droplets adhered to the nozzle opening surface 41a. Regarding the stability of image formation, the presence or absence of deviation in the landing position of the droplets was evaluated.

[0085] In all of the image formations in Example and Comparative Examples 1 to 3, the second volume of the image-forming droplets D2 was set to 25 pl and the second velocity was set to 8 m / s.

[0086] In this example, the first volume of the preliminary ejection droplets D1 was set to 5 pL, and the first velocity was set to 9 m / s. That is, the first velocity was set to be faster than the second velocity. Furthermore, preliminary ejection was performed onto the surface of the three-dimensional recording medium M. In Comparative Example 1, image formation was performed without performing preliminary ejection. In Comparative Example 2, the first volume of the preliminary ejection droplets D1 was 5 pL, and the first velocity was 7 m / s. That is, the first velocity was slower than the second velocity. Furthermore, preliminary ejection was performed onto the surface of a three-dimensional recording medium M. Comparative Example 2 corresponds to Example 2 in which the first velocity of the preliminary ejection droplets was slowed. In Comparative Example 3, the first volume of the preliminary ejection droplets D1 was 5 pL, and the first velocity was 9 m / s. The preliminary ejection droplets were not landed on the three-dimensional recording medium M, but on the surface of the conveyor belt 23. Comparative Example 3 corresponds to the example in which the target of the preliminary ejection droplets was changed to the conveyor belt 23.

[0087] In the example, no adhesion of the pre-ejected droplets to the nozzle opening surface 41a was observed, and the stability of the pre-ejection was evaluated as "good." Furthermore, no deviation in the landing position was observed during image formation, and the stability of the image formation was also evaluated as "good."

[0088] In Comparative Example 1, a change in ink characteristics occurred in nozzle N, which had a low usage rate, due to the lack of preliminary ejection. As a result, as shown in the lower part of Figure 12, ejection disturbances and landing deviations of image formation droplets D2 from that nozzle N were confirmed during image formation. As a result, as shown in Figure 11, the stability of image formation was evaluated as "X".

[0089] In Comparative Example 2, due to the slow speed of the preliminary ejection droplets D1, the main droplets and minute droplets of the preliminary ejection droplets D1 scattered as ink mist and adhered to the nozzle opening surface 41a, as shown in the upper part of FIG. 12. As a result, the preliminary ejection stability was evaluated as "X", as shown in FIG. 11. Furthermore, during image formation, as shown in the lower part of FIG. 12, droplet bending and landing deviation of the image formation droplets D2 were confirmed due to the ink In (solidified ink mist) adhering to the nozzle opening surface 41a. As a result, the image formation stability was evaluated as "X", as shown in FIG. 11.

[0090] In Comparative Example 3, as shown in the upper part of FIG. 12, the preliminary ejection droplets D1 scattered as ink mist while flying the long distance to the conveyor belt 23 and adhered to the nozzle opening surface 41a. As a result, as shown in FIG. 11, the preliminary ejection stability was evaluated as "X". Furthermore, during image formation, as shown in the lower part of FIG. 12, droplet bending and landing deviation of the image formation droplets D2 were confirmed due to the ink In adhering to the nozzle opening surface 41a. As a result, as shown in FIG. 11, the image formation stability was evaluated as "X".

[0091] From the above experiments, it was confirmed that scattering of the preliminary ejection droplets D1 can be suppressed when the first volume of the preliminary ejection droplets D1 is less than the second volume of the image formation droplets D2, the first speed of the preliminary ejection droplets D1 is less than the second speed of the image formation droplets D2, and preliminary ejection is performed onto a three-dimensional recording medium M (Example).

[0092] <Effects> As described above, the droplet ejection device 1 according to this embodiment includes a first head unit 40 provided with nozzles N that eject droplets of volatile ink, and a control unit 10 and a head control unit 42 that serve as control means for controlling the ejection of droplets from the nozzles N by the first head unit 40. The control unit 10 and the head control unit 42 perform preliminary ejection control, which ejects preliminary ejection droplets as first droplets from the nozzles N onto a three-dimensional recording medium M for maintenance of the nozzles N. The control unit 10 and the head control unit 42 also perform image formation control, which ejects image formation droplets as second droplets from the nozzles N onto the three-dimensional recording medium M based on image data of an image to be formed, to form an image on the three-dimensional recording medium M. In the preliminary ejection control, the control unit 10 and the head control unit 42 control the ejection operation so that the volume of the preliminary ejection droplets is equal to or smaller than the volume of the image formation droplets and so that the speed of the preliminary ejection droplets is faster than the speed of the image formation droplets. By making the speed of the preliminary ejection droplets faster than the speed of the image-forming droplets, the flight stability of the preliminary ejection droplets is improved, allowing them to land more reliably on the surface of the recording medium M. This reduces the scattering of the preliminary ejection droplets. Furthermore, increasing the speed of the main droplets of the preliminary ejection droplets increases the speed and volume of the accompanying microdroplets. This improves the flight stability of the microdroplets and reduces the scattering of the microdroplets. As a result of reducing the scattering of the preliminary ejection droplets, a decrease in ejection stability or ejection failure due to the preliminary ejection droplets adhering to the nozzle opening surface 41a is less likely to occur, thereby reducing degradation of image quality. Furthermore, by reducing the contamination of the device, the frequency of maintenance can be reduced, improving productivity. Furthermore, by performing preliminary ejection on a three-dimensional recording medium M, maintenance of the nozzles N can be performed without, for example, providing a special mechanism for ejecting the preliminary ejection droplets into a dedicated ink receiving unit.

[0093] Furthermore, in the preliminary ejection control, the ejection operation is controlled so that the volume of the preliminary ejection droplets is less than the volume of the image-forming droplets, thereby reducing the amount of ink consumed in the preliminary ejection control. Even when the volume of the preliminary ejection droplets is reduced in this way, scattering of the preliminary ejection droplets can be suppressed by increasing the speed of the preliminary ejection droplets.

[0094] Furthermore, the control unit 10 and the head control unit 42 perform a discharge operation by preliminary discharge control during the period of image formation by image formation control, and in the preliminary discharge control, a plurality of preliminary discharge droplets are dispersed and discharged within an area that overlaps with at least a part of the area where the image is formed by image formation control. By performing such dispersed discharge, it is possible to make it difficult to visually recognize that preliminary discharge is being performed.

[0095] Furthermore, when an image formed in the image formation control includes characters, the control unit 10 and the head control unit 42 control the preliminary discharge control so that the volume of the preliminary discharged droplets decreases as the characters become smaller. This makes it possible to suppress a decrease in the visibility of the characters due to the dispersed dots 72 and to make the dispersed dots 72 less visible.

[0096] Furthermore, in the preliminary ejection control, the control unit 10 and the head control unit 42 control the ejection operation so that the volume of the preliminary ejected droplets becomes a value according to the material of the surface on which the droplets land of the three-dimensional recording medium M. This makes it possible to make the dispersed dots 72 less visible.

[0097] Furthermore, if the surface material of the three-dimensional recording medium M contains fibers, the preliminary ejection can be performed in a manner that is difficult to see.

[0098] Furthermore, the three-dimensional recording medium M may be cardboard. In this case, the preliminary ejection onto the cardboard can be performed while suppressing the scattering of the preliminary ejected droplets.

[0099] The droplet ejection device 1 also includes a conveyor belt 23 having a mounting surface 23a on which a three-dimensional recording medium M is placed. The three-dimensional recording medium M is at a height of 5 mm or more from the mounting surface 23a. The first head unit 40 is positioned so that the distance between the three-dimensional recording medium M and the opening of the nozzle N is 5 mm or more when ejecting droplets onto the three-dimensional recording medium M placed on the mounting surface 23a. When the distance between the opening of the nozzle N and the recording medium M is 5 mm or more, the ejected droplets tend to scatter as ink mist due to air resistance. However, the configuration of the above embodiment can suppress the scattering of preliminary ejected droplets. When the height of the three-dimensional recording medium M is 5 mm or more, the distance from the nozzle N to the mounting surface 23a is 10 mm or more, which increases the impact of scattering if the preliminary ejected droplets do not land on the recording medium M. However, the configuration of the above embodiment can increase the stability of the flight of the preliminary ejected droplets, allowing them to land on the recording medium M.

[0100] Furthermore, the second head unit 50 has a plurality of nozzles N arranged in a predetermined arrangement direction, which has a vertical component. If the preliminary ejection droplets from such a vertically-mounted second head unit 50 scatter without landing on the three-dimensional recording medium M, they will scatter over a wide area without landing on the mounting surface 23a of the conveyor belt 23, which can easily cause problems such as soiling, but the configuration of the above embodiment makes it possible to make this problem less likely to occur.

[0101] The droplet ejection method according to this embodiment also includes a preliminary ejection step of ejecting preliminary ejection droplets from the nozzles N onto a three-dimensional recording medium M for maintenance of the nozzles N, and an image formation step of ejecting image formation droplets from the nozzles N onto the three-dimensional recording medium M based on image data of the image to be formed, thereby forming an image on the three-dimensional recording medium M. In addition, in the preliminary ejection step, the ejection operation of droplets from the nozzles N by the first head unit 40 is controlled so that the volume of the preliminary ejection droplets is equal to or less than the volume of the image formation droplets and the speed of the preliminary ejection droplets is faster than the speed of the image formation droplets. By making the speed of the preliminary ejection droplets faster than the speed of the image formation droplets in this way, the flight stability of the preliminary ejection droplets is improved, allowing them to land more reliably on the surface of the recording medium M. This makes it possible to suppress scattering of the preliminary ejection droplets.

[0102] In addition, in the above description of the effects, the same effects are achieved even if the "first head unit 40," "head control unit 42," and "nozzle opening surface 41a" are replaced with the "second head unit 50," "head control unit 52," and "nozzle opening surface 51a," respectively.

[0103] <Other> The present invention is not limited to the above-described embodiment and modifications, and various modifications are possible. For example, the first head unit 40 and the second head unit 50 may eject a liquid other than ink, such as a functional liquid for forming a circuit pattern or the like on a recording medium.

[0104] In the above embodiment, the first volume of the preliminary ejection droplets is set to be less than the second volume of the image-forming droplets, but the first volume may be set to be the same as the second volume. In this case, too, by setting the first velocity of the preliminary ejection droplets to be faster than the second velocity of the image-forming droplets, the effect of increasing the stability of the flight of the preliminary ejection droplets and suppressing scattering can be obtained.

[0105] Furthermore, in the above example, a method of forming the spit-out band 71 is used when spit-out is performed as preliminary ejection, but the pattern formed by spit-out is not limited to the spit-out band 71 and can be any pattern.

[0106] Furthermore, although the droplet ejection section is exemplified as having a horizontally placed first head unit 40 and a vertically placed second head unit 50, this is not limited to this, and the droplet ejection section may be configured to have, for example, either the first head unit 40 or the second head unit 50.

[0107] Furthermore, a line head (first head unit 40, second head unit 50) in which multiple droplet ejection heads 41, 51 are arranged has been given as an example of the droplet ejection section, but this is not limited to this, and the droplet ejection section may also be composed of a single droplet ejection head 41, 51.

[0108] Furthermore, although the single-pass type droplet ejection device 1 has been described as an example, the present invention may also be applied to a droplet ejection device that records an image while scanning a head unit or a droplet ejection head.

[0109] Although several embodiments of the present invention have been described, the scope of the present invention is not limited to the above-described embodiments, but includes the scope of the invention described in the claims and its equivalents. [Industrial Applicability]

[0110] The present invention can be used in a droplet ejection device and a droplet ejection method. [Explanation of symbols]

[0111] 1 Droplet discharge device 10 Control unit (control means) 11 CPU 12 RAM 13 ROM 131 Programs 14 Storage section 20 Conveying section 21 Drive roller 22 driven roller 23 Conveyor belt (loading member) 23a Placement surface 24 Transport motor 25 rotary encoder 26 Transport control unit 30 Medium detection unit 40 First head unit (droplet ejection unit) 50 Second head unit (droplet ejection unit) 40a, 50a support part 41, 51 Droplet ejection head 41a, 51a Nozzle opening surface 42, 52 Head control unit (control means) 61 Operation display section 62 Communications Department Bus 63 71 Spit Belt 72 Dispersed Dots 80 images D1 Pre-ejected droplet (first droplet) D2 Image-forming droplet (second droplet) Ink M Recording medium N nozzle S1 top S2 side

Claims

1. a droplet ejection unit provided with a nozzle for ejecting volatile droplets; a control unit for controlling the droplet ejection operation from the nozzle by the droplet ejection unit; Equipped with The control means preliminary ejection control for ejecting first droplets from the nozzles onto a three-dimensional recording medium for maintenance of the nozzles; image formation control that ejects second droplets from the nozzles onto the three-dimensional recording medium based on image data of an image to be formed, and forms the image on the three-dimensional recording medium; and In the preliminary ejection control, controlling the ejection operation so that the volume of the first droplet is equal to or less than the volume of the second droplet and the velocity of the first droplet is faster than the velocity of the second droplet; The droplet ejection device further adjusts the velocity of the first droplet within a range faster than the velocity of the second droplet, and controls the ejection operation so that the velocity of the first droplet increases as the volume of the first droplet decreases.

2. 2. The droplet ejection device according to claim 1, wherein the control means controls the ejection operation in the preliminary ejection control so that the volume of the first droplet is less than the volume of the second droplet.

3. 3. The droplet ejection device according to claim 1, wherein the control means performs the ejection operation by the preliminary ejection control within a period during which the image is formed by the image formation control, and in the preliminary ejection control, the control means ejects a plurality of the first droplets in a dispersed manner within an area that overlaps with at least a portion of the area during which the image is formed by the image formation control.

4. 4. The droplet ejection device according to claim 3, wherein, when the image formed in the image formation control includes characters, the control means controls the ejection operation in the preliminary ejection control so that the volume of the first droplet becomes smaller as the characters become smaller.

5. 5. The droplet ejection device according to claim 3, wherein the control means controls the ejection operation in preliminary ejection control so that the volume of the first droplet becomes a value corresponding to the material of the surface on which the droplet lands of the three-dimensional recording medium.

6. 6. The droplet ejection device according to claim 1, wherein the material of the surface of the three-dimensional recording medium includes fiber.

7. 6. The droplet ejection device according to claim 1, wherein the three-dimensional recording medium is cardboard.

8. a mounting member having a mounting surface on which the three-dimensional recording medium is placed, the three-dimensional recording medium has a height of 5 mm or more from the placement surface; The droplet ejection device according to any one of claims 1 to 7, wherein the droplet ejection unit is positioned at a position where, when ejecting droplets onto the three-dimensional recording medium placed on the placement surface, the distance between the three-dimensional recording medium and the opening of the nozzle is 5 mm or more.

9. the droplet ejection unit has a plurality of the nozzles arranged in a predetermined arrangement direction, 9. The droplet ejection device according to claim 1, wherein the arrangement direction has a vertical component.

10. A droplet ejection method for a droplet ejection device including a droplet ejection unit provided with a nozzle for ejecting volatile droplets, comprising: a preliminary ejection step of ejecting a first droplet from the nozzle onto a three-dimensional recording medium for maintenance of the nozzle; an image forming step of ejecting second droplets from the nozzles onto the three-dimensional recording medium based on image data of an image to be formed, thereby forming the image on the three-dimensional recording medium; Including, In the preliminary ejection step, controlling the discharge operation of the droplets from the nozzle by the droplet discharge unit so that the volume of the first droplet is equal to or less than the volume of the second droplet and the velocity of the first droplet is faster than the velocity of the second droplet; Furthermore, the droplet ejection method adjusts the velocity of the first droplet within a range faster than the velocity of the second droplet, and controls the ejection operation so that the velocity of the first droplet increases as the volume of the first droplet decreases.

Images