JP7740334B2 - Droplet ejection device and droplet ejection method - Google Patents

Description

The present invention relates to a droplet ejection device and a droplet ejection method.

Conventionally, there are droplet ejection devices that eject droplets onto a recording medium from a droplet ejection unit equipped with nozzles that eject droplets, forming an image on the recording medium. The nozzles of the droplet ejection device are supplied and filled with the 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, some of the liquid near the opening vaporizes, changing the properties of the liquid. As a result, the droplet ejection operation gradually becomes inappropriate, resulting in a problem of degraded image quality.

In response to this, conventional techniques for maintaining nozzles have been known, such as pre-ejecting droplets from the nozzles when no image is being formed, thereby suppressing changes in the properties of the liquid inside the nozzles and performing nozzle maintenance (see, for example, Patent Documents 1 and 2). It is also known to perform such pre-ejection onto a recording medium for nozzle maintenance.

In addition, some droplet ejection devices are capable of ejecting droplets onto a three-dimensional recording medium to form an image.

Japanese Patent Application Laid-Open No. 2004-299219 JP 2007-181972 A

However, when the recording medium is three-dimensional, a large clearance (spacing) between the droplet ejection unit and the recording medium is often maintained to ensure contact between them, resulting in a long droplet flight distance. Therefore, when performing preliminary ejection on a three-dimensional recording medium, the preliminary ejected droplets are prone to scattering due to various factors, resulting in problems such as adhesion to the nozzle surface, resulting in ejection failure, and device contamination. For example, if droplets are made small to reduce ink consumption during preliminary ejection, they are likely to scatter during their long flight. Furthermore, near the edges of a three-dimensional object, where preliminary ejection is often performed, air currents generated by the three-dimensional object's shape can easily carry 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 effects of liquid evaporation during these non-ejection periods, leading to droplet scattering.

The object of this invention is to provide a droplet ejection device and a liquid delivery method that can effectively suppress droplet scattering during preliminary ejection.

In order to achieve the above object, the invention of a droplet ejection device according to claim 1 comprises:
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 ;
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 .

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.

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.

A fourth aspect of the present invention provides the droplet ejection device according to the third aspect,
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.

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 will land.

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.

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.

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 ejection unit is disposed 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.

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.

In order to achieve the above object, the invention of a droplet ejection method according to 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,
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 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 .

According to the present invention, scattering of droplets during preliminary ejection can be effectively suppressed.

FIG. 1 is a diagram showing a schematic configuration of a droplet ejection device. FIG. 2 is a diagram illustrating a configuration of a first head unit. FIG. 2 is a diagram illustrating a configuration of a second head unit. FIG. 2 is a schematic diagram showing the positional relationship between a first head unit, a second head unit, and a recording medium. FIG. 2 is a block diagram showing a main functional configuration of the droplet ejection device. 10A and 10B are diagrams illustrating an example of a preliminary ejection operation by the first head unit. 10A and 10B are diagrams illustrating an example of a preliminary ejection operation by the second head unit. 10A and 10B are diagrams illustrating an example in which dispersed ejection is performed as a preliminary ejection operation by the first head unit. 10A and 10B are diagrams illustrating an example in which dispersed ejection is performed as a preliminary ejection operation by the second head unit. 10 is a flowchart showing a control procedure for image forming processing. 10A and 10B are diagrams showing the contents and results of an experiment conducted to confirm the effects of the embodiment. 10A and 10B are schematic diagrams showing ejection states during preliminary ejection and image formation in an experiment.

Below, an embodiment of the present invention is described based on the drawings.

<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 forms an image by ejecting droplets of ink as a liquid onto a three-dimensional recording medium M.

The conveying 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 conveying belt 23 whose inner side is supported by the drive roller 21 and driven roller 22, a conveying motor 24 that rotates the drive roller 21, a rotary encoder 25 attached to the drive roller 21, and a conveying control unit 26 (see FIG. 5) that controls the operation of the conveying motor 24. The drive roller 21 rotates around its rotation axis by being driven by the conveying motor 24. The conveying belt 23 is a ring-shaped belt whose inner side is supported by the drive roller 21 and 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 conveying belt 23 moves in a circular motion. The conveyor belt 23 is made of a material that can flex flexibly at the contact surfaces with the drive roller 21 and the driven roller 22 and can reliably support the recording medium M, and can be, for example, a belt made of a resin such as rubber, or a steel belt. The conveyor belt 23 has a material and/or a configuration that allows the recording medium M to be attracted, 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.

In this embodiment, the three-dimensional recording medium M is an object whose maximum height from the support surface 23a of the conveyor belt 23 is 5 mm or more. The three-dimensional recording medium M may have, for example, a surface that intersects with the support surface 23a when placed on the support surface 23a of the conveyor belt 23. The normal direction of this surface is different from the normal direction of the support 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 height of 5 mm or more from the support surface 23a, and the surface may have an area on which ink droplets can land. An example of a three-dimensional recording medium M is cardboard. The cardboard may be pre-assembled or pre-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.

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 loading 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 Figure 1).

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 Figure 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, for example, to include a code wheel with multiple slits arranged on a predetermined circumference that rotates 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 passing through the slits, and outputs a pulse signal to the control unit 10 and the head control unit 42 based on the light detection results by the light-receiving unit.

The medium detection unit 30 is located 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 sensor configuration is not particularly limited, but in this embodiment, a sensor equipped with an emission unit that emits laser light in the X direction at a predetermined height from the loading surface 23a, and a detection unit that detects the laser light on the opposite side of the loading surface 23a in the width direction to detect the 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.

The first head unit 40 and the second head unit 50 have multiple 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 transported by the transport unit 20 by ejecting ink droplets from the nozzles N at timing based on control signals, etc. from the control unit 10.

The first head unit 40 ejects ink vertically downward (in the -Z direction) onto the top surface of the recording medium M, which has a rectangular parallelepiped shape (the surface opposite the surface facing the mounting surface 23a, out of the two surfaces parallel to the mounting surface 23a). The first head unit 40 is also called a "horizontally mounted head" because the nozzles N are arranged in the horizontal direction.

The second head unit 50 ejects ink in a horizontal direction (the -X direction in Figure 1) onto the side surface (the surface adjacent to 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 nozzles N are arranged in the vertical direction. Note that while Figure 1 shows only one second head unit 50, 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, each of which ejects ink onto one of the four side surfaces.

The first head unit 40 and the second head unit 50 can be adjusted in position in the X, Y, and Z directions using 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.

While Figure 1 depicts one first head unit 40 and one second head unit 50 ejecting ink of a single color (e.g., black (K)), multiple first head units 40 and/or multiple second head units 50 ejecting ink of different colors may be provided to form a configuration capable of forming color images. For example, four first head units 40 and/or four second head units 50 corresponding to four ink colors, yellow (Y), magenta (M), cyan (C), and black (K), may be arranged at predetermined intervals from the upstream side in the transport direction of the recording medium M in the order of Y, M, C, and K.

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 droplet ejection heads 41 (six in this embodiment), 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 formed 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 formed, 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.

In the droplet ejection head 41, multiple nozzles N are arranged at equal intervals in an arrangement direction that intersects with the transport direction of the recording medium M (in Figure 2, the X direction that is perpendicular to the transport direction), forming a nozzle row. In this embodiment, each droplet ejection head 41 has four nozzle rows. The positions of these nozzle rows in the X direction are shifted relative to 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.

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 of the nozzles N included in the first head unit 40 in the X direction covers the X direction width of the area on the top surface of the recording medium M transported by the transport belt 23 where 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 using a single pass method by ejecting ink from the nozzles N to each position at a predetermined interval in the transport direction (transport direction interval) as the recording medium M is transported.

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.

In the droplet ejection head 51, multiple nozzles N are arranged at equal intervals in an arrangement direction (Z direction in Figure 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 relative to 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.

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 Z direction width of the 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 using a single pass method by ejecting ink from the nozzles N to each position at a predetermined interval in the transport direction (transport direction interval) as the recording medium M is transported.

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.
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. Furthermore, 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 41 a of the first head unit 40 and the recording medium M, and contact between the nozzle opening surface 51 a 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.

The ink ejection mechanism provided in droplet ejection head 41 and droplet ejection head 51 to eject ink from 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 the piezoelectric element on the wall of the pressure chamber communicating with nozzle N in response to a drive signal, thereby varying the pressure of the ink within the pressure chamber. A vent mode ink ejection mechanism ejects ink by varying the pressure of the ink within 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.

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. The ink ejected from the droplet ejection head 41 is not limited to aqueous ink, but may also be solvent ink using an organic solvent as a dispersion medium. These aqueous inks and solvent inks are volatile because the water and organic solvents that serve as dispersion media can evaporate.

FIG. 5 is a block diagram showing the main functional configuration of the droplet ejection device 1.
The droplet ejection 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 ejection head 41 and a head control unit 42, a second head unit 50 having a droplet ejection head 51 and a head control unit 52, an operation display unit 61, a communication unit 62, a bus 63, etc. In the following, a description of the configuration that has already been described will be omitted.

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

The CPU 11 reads 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 calculation processes.

RAM 12 provides working memory space for CPU 11 and stores temporary data. RAM 12 may include non-volatile memory.

ROM 13 is a non-transitory recording medium that can be read by CPU 11 as a computer, and stores various control programs 131 executed by CPU 11, setting data, etc. Note that rewritable non-volatile memory such as flash memory may be used instead of ROM 13.

The storage unit 14 is a non-transitory recording medium readable by the CPU 11 as a computer, and stores print jobs (image recording commands) input from an external device via the communication unit 62 and image data of the image to be formed in the print job (hereinafter referred to as "formation image data"). The storage unit 14 may be, for example, a hard disk drive (HDD).

The conveying control unit 26 supplies a conveying drive signal to the conveying motor 24 based on the 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.

The head control unit 42 outputs a drive signal (a voltage signal of a drive waveform) to the droplet ejection head 41 at an appropriate timing to drive the ink ejection mechanism 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 include, for example, a drive waveform generation unit that generates a drive waveform pattern in response to 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.

Based on the drive signal sent from the head control unit 42 and image data sent from the control unit 10 or the head control unit 42, the droplet ejection head 41 supplies a drive signal to the ink ejection mechanism of the nozzle N to be ejected according to the image data, thereby performing an ejection operation to eject ink droplets from the nozzle N. Here, if the image data is formation image data, the ejection operation forms the image to be formed on the recording medium M. Furthermore, if the image data is preliminary ejection image data for performing a preliminary ejection, as described below, preliminary ejection is performed at the specified timing by the nozzle N specified by the preliminary ejection image data. The volume (droplet amount) and speed 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, by sending a drive signal to the droplet ejection head 41, the control unit 10 and the head control unit 42 can cause the nozzle N to eject ink droplets of the desired volume and speed. 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 in succession and/or the volume of each droplet in an ejection method in which two or more ink droplets are ejected in succession from a nozzle N and combined during flight.

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 detailed explanation will be omitted. Below, when referring to either the head control unit 42 or the head control unit 52, the term "head control unit" will be used without a reference number.

In this embodiment, for the first head unit 40, the control unit 10 and 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 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.

The operation display unit 61 includes a display device such as an LCD 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.

The communication unit 62 is a communication interface that controls data communication with external devices. Examples of communication interfaces include one or more LAN boards, LAN cards, and other devices that support various communication protocols. The communication unit 62 acquires image data and print job setting data (job data) from external devices under the control of the control unit 10, and also transmits status information and the like to external devices.

Bus 63 is a path for sending and receiving signals between the control unit 10 and other components.

<Operation of 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.

Ink is supplied to and filled inside the nozzles N of the droplet ejection device 1. 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, changing the ink's properties (e.g., viscosity and specific gravity). This results in ejection defects (malfunctions in the ink ejection operation) in which the flight direction, flight speed, and amount of ink ejected from the nozzles N deviate from their original settings, leading to reduced image quality. In particular, in the droplet ejection device 1 of this embodiment, large distances d1 and d2 are maintained 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 significant deviations in the landing position, potentially reducing image quality.

To avoid this problem, the droplet ejection device 1 of this embodiment performs preliminary ejection, in which ink is preliminarily ejected from nozzle N onto a three-dimensional recording medium M during transport for nozzle maintenance. Hereinafter, the control by the control unit 10 and head control unit as control means to preliminarily eject droplets from nozzle N onto a three-dimensional recording medium M for nozzle N maintenance will be referred to as "preliminary ejection control." Furthermore, ink droplets ejected from nozzle N through 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 nozzle N onto a 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, ink droplets ejected from nozzle N through image formation control will be referred to as "image formation droplets." Preliminary ejection droplets and image formation droplets may be multiple droplets ejected continuously from 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."

In addition, in this embodiment, the distances d1 and d2 between the first head unit 40 and the second head unit 50 and the three-dimensional recording medium M are ensured to be large, so the flight distance of droplets ejected from the nozzles N to the recording medium M is long. Therefore, when performing preliminary ejection onto the three-dimensional recording medium M, the preliminary ejected droplets are prone to scattering due to various factors.

For example, if the first volume of the preliminary ejection droplets is set 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 their 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 its three-dimensional shape. Therefore, when forming a discharge zone 71 (see Figures 6 and 7) near the edges of the recording medium M, as described below, the preliminary ejection droplets are more likely to be swept 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 medium 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, leading to droplet scattering.

If scattered preliminary ejection droplets adhere to the nozzle opening surfaces 41a and 51a and solidify, partially blocking the nozzle N opening, this can lead to poor ink droplet ejection from the nozzle N. Furthermore, scattered preliminary ejection droplets can also adhere to various components of the droplet ejection device 1, causing contamination. In particular, if 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 contamination and other damage. Furthermore, when preliminary ejection droplets are ejected from the nozzle N, tiny mist-like droplets (hereinafter referred to as "microdroplets") may be generated along with the main droplets. These microdroplets may scatter and adhere to the device interior, causing poor ejection from the nozzle N and contamination of the device. Hereinafter, scattered preliminary ejection droplets (including microdroplets) without landing on the recording medium M will also be referred to as "ink mist."

In this embodiment, the control unit 10 and head control unit control the ejection operation in the preliminary ejection control 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 therefore 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 therefore increases the stability of the flight of the microdroplets, and also suppresses problems caused by the microdroplets scattering as ink mist.

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. Furthermore, prior to the formation of this image 80, the control unit 10 and the head control unit 42 perform preliminary ejection control to perform preliminary ejection from each nozzle N near the end of the upper surface S1 on the +Y direction side, thereby forming a strip-like discard band 71 that is long in the X direction. The discard 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 discard band 71. This preliminary ejection performed outside the formation region of the image 80 is also referred to as "discarding." Discarding 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.

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 to eject image forming droplets from the nozzles N of the second head unit 50 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 to perform preliminary ejection from each nozzle N near the end of the side surface S2 on the +Y direction side, thereby forming a long strip-shaped discharge band 71 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 installed vertically.

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 multiple 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.

In addition, the first speed of the pre-ejected droplets when forming the discharge zone 71 is set to be faster than the second speed of the image-forming droplets. This increases the stability of the flight of the pre-ejected droplets and makes them less susceptible to the effects of air currents that tend to occur near the edges of the three-dimensional recording medium M.

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 . Furthermore, the control unit 10 and the head control unit 42 perform a discharge operation under preliminary discharge control during a period in which the image 80 is formed under image formation control, thereby 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), this also includes the non-discharge area. In FIG. 8 , preliminary discharge droplets are dispersedly discharged over substantially the entire 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.

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 during the 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, dispersed discharge can also be performed using the side surface S2 of the recording medium M with the second head unit 50 in vertical orientation.

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 making the first volume less than the second volume, the amount of ink consumed in preliminary ejection control can be reduced.

As shown in Figures 8 and 9, when image 80 contains 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 the image formed in image formation control contains characters, the control unit 10 and head control unit may control the ejection operation from 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 contains 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.

Furthermore, the visibility of the dispersed dots 72 varies depending on the material of the surface of the three-dimensional recording medium M on which the preliminary ejection droplets land. 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.

The volume of the pre-ejected droplets may also be set according to how easily the pre-ejected droplets dry after landing, so that they dry and set 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, humidity, etc. For example, the volume may be smaller if the pre-ejected droplets are more difficult to dry after landing.

Also, when performing dispersed ejection, the first speed of the preliminary ejection droplets is set to be faster than the second speed of the image-forming droplets. This allows for the deviation of the ejection direction to be minimized even in a state where the droplet ejection direction is likely to be deviated due to the influence of ink vaporization in the nozzle N during periods when droplets are not being ejected.

Whether the preliminary ejection is to be performed as a discharge or dispersed ejection may be set to one of the two methods, or the user may be able to select either method through a predetermined operation. If the preliminary ejection method is selectable, setting data specifying the preliminary ejection method is stored in the memory unit 14, and when preliminary ejection control is executed, the control unit 10 selects either discharge or dispersed ejection according to this setting data. Furthermore, for one recording medium M, preliminary ejection onto the top surface S1 shown in FIG. 6 or FIG. 8 and preliminary ejection onto the side surface S2 shown in FIG. 7 or FIG. 9 may be performed in parallel.

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 greater 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.

Next, a control procedure for the image forming process for carrying out the above-mentioned preliminary ejection control and image formation control will be described.
FIG. 10 is a flowchart showing the control procedure of 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 .

When the image formation process starts, the control unit 10 determines whether it is time to perform a preset preliminary ejection (step S101). The timing for performing preliminary ejection can be set arbitrarily, but can be, for example, when a predetermined time has passed since the last preliminary ejection, or when images have been formed on a predetermined number of recording media M since the last preliminary ejection. Alternatively, preliminary ejection may be performed on all recording media M every time.

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).

If it is determined that the pre-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 the first volume of the pre-ejected droplets according to that material (step S103). The method for setting the first volume in this step is not particularly limited, but it can be, for example, a method in which table data (not shown) that associates a first volume with each material is referenced, and the first volume corresponding to the material is selected and set.

The control unit 10 determines whether the image specified in the print job contains text (step S104). If it is determined that the image contains 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 (step S105). The method for setting the first volume in this step is not particularly limited. For example, the control unit 10 may refer to table data (not shown) that associates a first volume with each character size, and select and set the first volume corresponding to the size of the text in the image. Alternatively, the table data may associate a reduction rate of the first volume instead of the first volume itself, and the setting may be adjusted by multiplying the current setting value of the first volume by the reduction rate. Furthermore, 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.

When the processing of step S105 is completed, or when it is determined in step S104 that the formed image does not contain text ("NO" in step S104), the control unit 10 and 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, when the image formation position on the three-dimensional recording medium M faces the nozzle N, the control unit 10 and head control unit eject image formation droplets from the nozzle N at a second volume and a second speed based on the formation image data to form an image on the recording medium M. Furthermore, in parallel with the formation of the image, the control unit 10 and head control unit eject preliminary ejection droplets from the nozzle N at a first volume and a first speed into an area overlapping at least a portion of the image formation area, performing dispersed ejection (step S106). Here, for example, image forming 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.

If it is determined in step S102 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 using a method that forms the discard zone 71. That is, when the image formation position on the three-dimensional recording medium M faces the nozzle N, 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 based on the preliminary ejection image data of the discard zone 71 to form 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.

After the discharge zone 71 is formed, 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 when the image formation position on the three-dimensional recording medium M faces the nozzle N, thereby forming an image on the recording medium M (step S108: image formation step).

When step S106 or step S108 is completed, the control unit 10 determines whether 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 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.

<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 41 a. Regarding the stability of image formation, the presence or absence of deviation in the landing position of the droplets was evaluated.

In all image formations in the examples and comparative examples 1 to 3, the second volume of the image-forming droplet D2 was 25 pl and the second speed was 8 m/s.

In this example, the first volume of the preliminary ejection droplet 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, the preliminary ejection was performed on 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 speed was 7 m/s. That is, the first speed was slower than the second speed. Furthermore, preliminary ejection was performed onto the surface of a three-dimensional recording medium M. Comparative Example 2 corresponds to Example 1, in which the first speed of the preliminary ejection droplets was slowed.
In Comparative Example 3, the first volume of the preliminary ejection droplets D1 was set to 5 pl, and the first velocity was set to 9 m/s. Furthermore, 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.

In the example, no adhesion of pre-ejected droplets to the nozzle opening surface 41a was observed, and the stability of the pre-ejection was evaluated as "Good." Furthermore, no misalignment of the droplets was observed during image formation, and the stability of the image formation was also evaluated as "Good."

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, irregular ejection of image-forming droplets D2 from that nozzle N and misaligned landing were confirmed during image formation. As a result, as shown in Figure 11, the image formation stability evaluation was "X."

In Comparative Example 2, due to the slow speed of the preliminary ejection droplets D1, the main droplets and microdroplets 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 Figure 12. As a result, the preliminary ejection stability was evaluated as "X", as shown in Figure 11. Furthermore, during image formation, as shown in the lower part of Figure 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 Figure 11.

In Comparative Example 3, as shown in the upper part of Figure 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 Figure 11, the preliminary ejection stability was evaluated as "X". Furthermore, during image formation, as shown in the lower part of Figure 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 Figure 11, the image formation stability was evaluated as "X".

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).

<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 operation 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 suppresses the scattering of the preliminary ejection droplets. Furthermore, by increasing the speed of the main droplets of the preliminary ejection droplets, the velocity and volume of the accompanying microdroplets are increased. This increases the flight stability of the microdroplets and suppresses the scattering of the microdroplets. As a result of suppressing the scattering of the preliminary ejection droplets, a decrease in ejection stability and ejection failures caused by the preliminary ejection droplets adhering to the nozzle opening surface 41a are less likely to occur, thereby suppressing degradation of image quality. Furthermore, by suppressing 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.

In addition, by controlling the ejection operation so that the volume of the preliminary ejection droplets is less than the volume of the image-forming droplets during preliminary ejection control, the amount of ink consumed during preliminary ejection control can be reduced. Even when the volume of the preliminary ejection droplets is reduced in this way, the scattering of the preliminary ejection droplets can be suppressed by increasing the speed of the preliminary ejection droplets.

The control unit 10 and the head control unit 42 also perform a discharge operation using preliminary discharge control during the period in which an image is formed using image formation control, and in the preliminary discharge control, multiple preliminary discharge droplets are dispersed and discharged within an area that overlaps with at least a portion of the area in which the image is formed using image formation control. By performing such dispersed discharge, it is possible to make it difficult to visually recognize that preliminary discharge is being performed.

Furthermore, when the image formed in the image formation control includes characters, the control unit 10 and the head control unit 42 control the ejection operation in the preliminary ejection control so that the volume of the preliminary ejection 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.

In addition, the control unit 10 and the head control unit 42 control the ejection operation in the preliminary ejection control so that the volume of the preliminary ejected droplets is a value that corresponds 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.

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

The three-dimensional recording medium M may also be cardboard. In this case, preliminary ejection onto the cardboard can be performed while suppressing the scattering of preliminary ejection droplets.

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. If the distance between the opening of the nozzle N and the recording medium M is 5 mm or more, the ejected droplets are likely to scatter as ink mist due to air resistance. However, the configuration of the above embodiment can suppress the scattering of preliminary ejection droplets. Furthermore, if 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 becomes 10 mm or more, which increases the impact of scattering if the preliminary ejection 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 ejection droplets, allowing them to land on the recording medium M.

The second head unit 50 also has multiple nozzles N arranged in a predetermined arrangement direction, which has a vertical component. If 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 loading surface 23a of the conveyor belt 23, which can lead to serious problems such as soiling. However, the configuration of the above embodiment can make this problem less likely to occur.

The droplet ejection method according to this embodiment also includes a preliminary ejection step in which preliminary ejection droplets are ejected from the nozzles N onto a three-dimensional recording medium M for nozzle N maintenance, and an image formation step in which image formation droplets are ejected 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 velocity of the preliminary ejection droplets is faster than the velocity of the image formation droplets. By making the velocity of the preliminary ejection droplets faster than the velocity 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 prevents the preliminary ejection droplets from scattering.

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.

<Others>
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.

In addition, in the above embodiment, an example was described in which the first volume of the preliminary ejection droplets was less than the second volume of the image formation droplets, but the first volume may be the same as the second volume. Even in this case, by making the first velocity of the preliminary ejection droplets faster than the second velocity of the image formation droplets, the effect of increasing the stability of the flight of the preliminary ejection droplets and suppressing scattering can be obtained.

Furthermore, although an example has been given of a method of forming a spitting-out zone 71 when spitting-out is performed as a preliminary ejection, the pattern formed by spitting-out is not limited to the spitting-out zone 71 and can be any pattern.

Furthermore, although the droplet ejection section is exemplified as having a horizontally-mounted first head unit 40 and a vertically-mounted second head unit 50, this is not limited to this, and the configuration may be, for example, having either the first head unit 40 or the second head unit 50.

Furthermore, a line head (first head unit 40, second head unit 50) with multiple droplet ejection heads 41, 51 arranged has been exemplified as 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.

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

While 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 their equivalents.

The present invention can be used in a droplet ejection device and a droplet ejection method.

1 Droplet ejection device 10 Control unit (control means)
11 CPU
12 RAM
13 ROM
131 Program 14 Storage unit 20 Conveying unit 21 Driving roller 22 Driven roller 23 Conveying 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 Supporting parts 41, 51 Droplet ejection heads 41a, 51a Nozzle opening surfaces 42, 52 Head control parts (control means)
61 Operation display unit 62 Communication unit 63 Bus 71 Discharge band 72 Dispersed dots 80 Image D1 Preliminary ejection droplets (first droplets)
D2: Image-forming droplet (second droplet)
In Ink M Recording medium N Nozzle S1 Top surface S2 Side surface

Claims (10)

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 . The droplet ejection device according to claim 1, wherein the control means controls the ejection operation during the preliminary ejection control so that the volume of the first droplet is less than the volume of the second droplet. The droplet ejection device according to claim 1 or 2, 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 first droplets are dispersed and ejected within an area that overlaps at least a portion of the area during which the image is formed by the image formation control. The droplet ejection device according to claim 3, wherein, when the image formed in the image formation control includes text, the control means controls the ejection operation in the preliminary ejection control so that the volume of the first droplet decreases as the text becomes smaller. The droplet ejection device according to claim 3 or 4, wherein the control means controls the ejection operation during preliminary ejection control so that the volume of the first droplet is a value corresponding to the material of the surface of the three-dimensional recording medium on which the droplet will land. The droplet ejection device described in any one of claims 1 to 5, wherein the surface material of the three-dimensional recording medium includes fiber. The droplet ejection device described in any one of claims 1 to 5, wherein the three-dimensional recording medium is cardboard. 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. 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. A droplet ejection method for a droplet ejection device having a droplet ejection unit provided with a nozzle that ejects 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 .