JP7786155B2 - Image forming device - Google Patents

Description

This disclosure relates to an image forming apparatus.

JP 2004-321978 A (Patent Document 1) discloses a droplet ejection device having an ejection head that ejects a functional liquid from a nozzle and a mounting plate with openings in which multiple ejection heads are arranged. The multiple ejection heads are arranged in the openings at the mounting positions under the same temperature conditions as when the functional liquid is ejected.

Japanese Patent Application Laid-Open No. 2004-321978

In image forming devices that form images by ejecting ink from multiple heads, the temperature of the holding unit that holds the multiple heads can change due to heat generated during image formation and changes in the ambient temperature. If the positional relationship between the heads changes due to thermal deformation of the holding unit, ink may not be supplied from each head to the target position, resulting in reduced image quality.

This disclosure proposes an image forming apparatus that can form high-quality images even if the temperature of the holding section changes during image formation.

The image forming apparatus according to the present disclosure includes multiple heads that eject ink onto an image forming body to form an image on the image forming body, a holding unit that holds the multiple heads, a temperature determination unit that determines the temperature of the holding unit, and an adjustment unit that adjusts the position of the image formed on the image forming body by the ink ejected from each head in accordance with the temperature of the holding unit determined by the temperature determination unit.

In the above-mentioned image forming device, the adjustment unit may change the position of each head in the holding unit depending on the temperature of the holding unit.

In the above image forming device, each head may include multiple nozzles, and ink may be ejected from some of the multiple nozzles, and the adjustment unit may change the nozzles in each head that eject ink depending on the temperature of the holding unit.

In the above image forming device, the adjustment unit may change the timing at which ink is ejected from each head onto the image forming body depending on the temperature of the holding unit.

In the above-mentioned image forming device, the temperature determination unit may have multiple temperature sensors provided in the holding unit.

In the above-mentioned image forming device, the temperature determination unit may estimate the temperature of the holding unit based on the amount of ink ejected from each head.

In the above image forming device, the temperature determination unit may determine the temperature distribution of the holding unit, and the adjustment unit may adjust the position of the image formed by each head in accordance with the temperature distribution of the holding unit.

In the above-mentioned image forming device, the multiple heads may include heads that eject inks of different colors.

In the above image forming apparatus, the ink may be water-based ink.

The image forming apparatus disclosed herein can form high-quality images even if the temperature of the holding unit changes during image formation.

FIG. 1 is a schematic diagram showing a schematic configuration of an image forming apparatus according to an embodiment. FIG. 2 is a schematic diagram illustrating the configuration of the inkjet head shown in FIG. 1 . FIG. 10 is a diagram for explaining another example of the temperature determination unit. FIG. 10 is a schematic diagram showing a state in which the holding portion is thermally deformed. FIG. 2 is a schematic diagram illustrating a first example of an adjustment unit. FIG. 10 is a schematic diagram showing a second example of the adjustment unit. FIG. 10 is a first schematic diagram showing a third example of the adjustment unit. FIG. 10 is a second schematic diagram showing a third example of the adjustment unit. FIG. 10 is a third schematic diagram showing a third example of the adjustment unit.

Embodiments of an image forming apparatus according to the present disclosure will be described below with reference to the drawings. In the following description, identical parts and components are designated by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions of these will not be repeated.

[Configuration of image forming apparatus 1]
1 is a schematic diagram showing the general configuration of an image forming apparatus 1 according to an embodiment. The image forming apparatus 1 is, for example, an inkjet recording apparatus that forms an ink image on a recording medium as an image forming body.

As shown in FIG. 1, the image forming apparatus 1 mainly comprises a conveying unit 10, an image forming unit 30, and an ink drying unit 60.

The transport unit 10 transports the recording medium. The transport unit 10 has a pay-out roller 11, take-up rollers 12 and 13, and a transport belt 14. The pay-out roller 11 is a roller that pays out the recording medium. The take-up rollers 12 and 13 are rollers that take up the recording medium. The transport belt 14 is stretched between the pay-out roller 11 and the take-up rollers 12 and 13 and transports the recording medium. The recording medium is transported on the transport belt 14 from the pay-out roller 11 toward the take-up rollers 12 and 13 along the transport direction DR indicated by the arrow in Figure 1.

Plain paper can be used as the recording medium. The plain paper may be roll paper, which is a long piece of paper wound into a roll, or may be sheets cut to a specified size. The recording medium may also be a resin film. The resin film may be, for example, a PET film, a PP film, or a PE film. The recording medium may also be metal, a wooden board, cloth, etc.

The image forming unit 30 ejects ink onto the recording medium transported on the transport belt 14. The image forming unit 30 is of an aqueous inkjet type. The image forming unit 30 has multiple inkjet heads 31. Each inkjet head 31 supplies ink of a corresponding color to the recording medium. For example, inkjet head 31Y supplies Y (yellow) ink. Inkjet head 31M supplies M (magenta) ink. Inkjet head 31C supplies C (cyan) ink. Inkjet head 31K supplies K (black) ink. The ink ejected from each inkjet head 31 is applied to the recording medium, forming an ink image on the recording medium.

The ink drying unit 60 heats the recording medium to dry and fix the ink image on the recording medium. The ink drying unit 60 may heat the recording medium from the front side on which the ink image is formed, or from the back side on which the ink image is not formed. The ink drying unit 60 may be equipped with any of the known heaters selected as needed, such as an infrared heater, electric heating wire, ultraviolet lamp, gas, or hot air dryer. From the standpoints of safety and energy efficiency, heating using an electric heating wire or infrared heater is preferred.

<Ink>
The inks used are of various colors including cyan, magenta, yellow, and black (CMYK). By using one or more inks of these colors selected from the group consisting of CMYK, primary colors, multi-colors, or halftones can be formed for each of the many unit areas that make up an image. The inks can contain various components such as colorants, resins, aqueous media, surfactants, and other additives.

(Colorant)
The coloring material contained in the ink may be a pigment or a dye.

Pigments that can be used include any conventionally known pigment, including water-dispersible pigments and solvent-dispersible pigments. For example, organic pigments such as insoluble pigments and lake pigments, and inorganic pigments such as carbon black are preferably used.

It is preferable to use a dye having an anionic group. Specific examples of dyes include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone dyes.

Of these, the colorant is preferably a pigment, and more preferably a resin-dispersible pigment.

(resin)
Examples of resins contained in the ink include acrylic, styrene acrylic, acrylonitrile-acrylic, vinyl acetate acrylic, polyurethane, and polyester.

Such resins may be obtained by polymerizing a monomer having an acid group. Examples of such monomers include radical copolymerization of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and acid derivatives of styrene. They may also be copolymerized with other monomers as needed.

The amount of ink-soluble resin varies depending on the degree of polymerization of the resin, but is preferably 2-10% of the total ink mass, and more preferably 3-6%. If the amount of resin is too small, the effects of the present invention will not be achieved, while if the amount is too large, abnormalities will occur in the inkjet ejection performance and storage stability. Furthermore, multiple resins may be present, or they may be present as a copolymer, or they may be dispersed in an emulsion state.

The ink solvent that dissolves and disperses the above solutes preferably contains, in addition to water, a solvent component that dissolves in water, for purposes such as improving ejection performance and adjusting the ink's physical properties. There are no particular restrictions on the type of solvent, as long as it does not impair the effects of the present invention.

(aqueous medium)
The ink may be a water-based ink containing water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. Deionized water or ion-exchanged water is preferably used as the water. The water content (mass %) in the ink is preferably 20% to 95% by mass, based on the total mass of the ink. Furthermore, the water-soluble organic solvent content (mass %) in the ink is preferably 3% to 50% by mass, based on the total mass of the ink.

(Surfactant)
The surfactant to be used may be any of cationic, anionic, amphoteric, and nonionic. The surfactant or solvent may be used alone or in combination.

(Other additives)
Depending on the purpose of improving ejection stability, compatibility with print heads and ink cartridges, storage stability, image storage stability, and other performances, various known additives, such as polysaccharides, viscosity modifiers, resistivity modifiers, film-forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, anti-mold agents, and anti-rust agents, can be appropriately selected and used.

[Configuration of inkjet head 31]
FIG. 2 is a schematic diagram showing the configuration of the inkjet head 31 shown in FIG. 1. The inkjet head 31 for each color includes multiple heads. While FIG. 2 exemplarily shows a first head 311, a second head 312, and a third head 313, the inkjet head 31 may include four or more heads. The multiple heads are arranged in a staggered pattern. The inkjet head 31 includes a holder 33 that holds the multiple heads. The holder 33 may hold a head group consisting of multiple heads that eject ink of one color, or may hold a multiple head group that each ejects ink of a different color.

The transport direction DR of the recording medium, also shown in Figure 1, is the vertical direction in Figure 2. The direction perpendicular to the transport direction DR will be referred to as the width direction below. The width direction is the horizontal direction in Figure 2. In the transport direction DR, the first head 311 and the second head 312 are arranged downstream, and the third head 313 is arranged upstream. The first head 311 and the second head 312 are arranged side by side in the width direction. In the width direction, the third head 313 is arranged between the first head 311 and the second head 312. In the width direction, a portion of the first head 311 and a portion of the third head 313 overlap. In the width direction, a portion of the second head 312 and a portion of the third head 313 overlap.

Each inkjet head 31 has multiple nozzles. Nozzles 321 shown in FIG. 2 are a schematic representation of the multiple nozzles of the first head 311, shown as straight lines. Nozzles 321 include multiple nozzles arranged side by side in the width direction. Nozzles 322 shown in FIG. 2 are a schematic representation of the multiple nozzles of the second head 312, shown as straight lines. Nozzles 323 shown in FIG. 2 are a schematic representation of the multiple nozzles of the third head 313, shown as straight lines. Nozzles 322 and 323 each include multiple nozzles arranged side by side in the width direction.

The inkjet head 31 further includes multiple temperature sensors 34, 35. The temperature sensors 34, 35 are provided in the holding portion 33 and measure the temperature of the holding portion 33. The temperature sensors 34, 35 are an example of a temperature determination portion that determines the temperature of the holding portion 33. The temperature sensors 34, 35 are arranged apart in the width direction. Each temperature sensor 34, 35 measures the temperature of the holding portion 33 at a different position, and by interpolating the temperature of the holding portion 33 at a position between the temperature sensors 34, 35, the temperature distribution of the holding portion 33 can be determined.

Figure 3 is a diagram illustrating another example of a temperature determination unit. While Figure 3 shows the first head 311 as a representative example, the other heads also have a similar configuration. As mentioned above, the nozzle 321 includes multiple nozzles arranged in the width direction (the left-right direction in Figure 3).

Each nozzle 321 is connected to a cavity 321C. Ink is stored in the cavity 321C. A piezoelectric element 321P is installed adjacent to the cavity 321C. The piezoelectric element 321P deforms when a voltage is applied from a drive circuit (not shown). When the piezoelectric element 321P deforms, the cavity 321C also deforms, and the volume of the cavity 321C decreases, forcing some of the ink in the cavity 321C out of the cavity 321C. An ink droplet D is then ejected from the nozzle 321.

Heat is generated each time the piezo element 321P is driven. Each time an ink droplet D is ejected from a nozzle 321, the piezo element 321P corresponding to that nozzle 321 is driven, generating heat. For nozzles 321 that eject ink continuously, the amount of heat generated by the piezo element 321P increases. The area around the nozzle 321 that ejects ink continuously generates heat, causing a localized temperature rise. As a result, a high-temperature area A1, which is an area with a relatively high temperature, and a low-temperature area A2, which is an area with a relatively low temperature, are formed within the inkjet head 31.

A controller (not shown) receives input of an ink image to be formed on a recording medium by the image forming apparatus 1. Based on the input ink image, the controller sets which of the multiple heads will eject ink and which of the multiple nozzles in that head will eject ink. The controller outputs a control signal to the drive circuit of that piezo element, instructing it to drive the piezo element corresponding to the nozzle set to eject ink. The amount of heat generated around nozzles where a large amount of ink is ejected and the piezo element is continuously driven increases, causing the temperature of the holding unit 33 to rise. The controller can estimate the temperature rise of the holding unit 33 based on the amount of ink ejected from each head. Therefore, the controller that controls the image forming apparatus 1 can function as a temperature determination unit that determines the temperature of the holding unit 33.

[Thermal deformation of the holding portion 33]
Fig. 4 is a schematic diagram showing a state in which the holding unit 33 has been thermally deformed. In the image forming apparatus 1, the temperature of the holding unit 33 that holds the multiple heads may change due to heat generated during image formation and changes in the environmental temperature. The temperature of the holding unit 33 shown in Fig. 4 has risen compared to the state in Fig. 2, and the holding unit 33 has thermally expanded as indicated by the diagonal arrow in Fig. 4.

The dashed lines in Figure 4 indicate the positions of the heads before the holding portion 33 shown in Figure 2 was thermally deformed. The thermal expansion of the holding portion 33 has caused the positions of each head to change. The widthwise spacing between the first head 311 and the second head 312 has increased. The distance in the transport direction DR between the first head 311 and the second head 312 and the third head 313 has increased. The position of the third head 313 has also shifted in the widthwise direction. As the positions of the first head 311, the second head 312, and the third head 313 change, the positions of the nozzles 321, 322, and 323 also change. The positions of the nozzles 321, 322, and 323 have changed in both the transport direction DR and the widthwise direction.

Figure 4 shows the holding portion 33 thermally expanded, but the holding portion 33 may also thermally contract due to changes in environmental temperature. In this case, the positions of the first head 311, second head 312, and third head 313 change, and the positions of the nozzles 321, 322, and 323 also change.

[Adjustment section]
The image forming apparatus 1 of the embodiment is provided with an adjustment unit so that ink can be supplied from each head to a target position even if the positional relationship between the heads changes due to thermal deformation of the holding unit 33. The adjustment unit adjusts the position of an image formed on a recording medium by ink ejected from each head in accordance with the temperature of the holding unit 33.

<First Example of Adjustment Unit>
5 is a schematic diagram showing a first example of the adjustment unit. In the example shown in Fig. 5, the first head 311 is representatively illustrated, and a mechanical mechanism for moving the first head 311 in the width direction is also illustrated.

Specifically, a stepping motor 361 is attached to the holding unit 33. An external thread 363 is provided on the output shaft 362 of the stepping motor 361. The external thread 363 may be formed by threading the outer circumferential surface of the output shaft 362, or the external thread 363 may be formed by fastening an externally threaded member to the output shaft 362. A swinging member 364 is engaged with and coupled to the external thread 363. The swinging member 364 is provided with an internal thread. The output shaft 362 and external thread 363 rotate relative to the holding unit 33 when driven by the stepping motor 361. On the other hand, the swinging member 364 is configured to be unable to rotate relative to the holding unit 33.

A biasing spring 366 is disposed at a position opposite the swinging member 364 in the width direction. The biasing spring 366 is attached to a support plate 365. The support plate 365 is fixed to the holding portion 33. The biasing spring 366 is disposed so that it can expand and contract in the width direction, and one end of the biasing spring 366 is supported by the support plate 365. The support plate 365 supports one end of the biasing spring 366 so that it cannot be displaced or is nearly unable to be displaced.

The first head 311, shown representatively in Figure 5, is held between a swinging member 364 and a biasing spring 366. One end of the first head 311, which extends in the width direction, receives a widthwise biasing force from the biasing spring 366, and the other end of the first head 311 is pressed against the swinging member 364. The swinging member 364 and the biasing spring 366 position the first head 311 in the width direction.

When the stepping motor 361 is driven, the male screw 363 rotates in accordance with the rotation of the output shaft 362. Because the oscillating member 364 does not rotate, the male screw 363 rotates relative to the female screw formed on the oscillating member 364. This causes stress to act in the width direction on the oscillating member 364. By driving the stepping motor 361 to rotate in both directions, the oscillating member 364 can be moved back and forth in the width direction. When the oscillating member 364 is moved in a direction approaching the support plate 365, the first head 311, pressed by the oscillating member 364, also moves in a direction approaching the support plate 365. When the oscillating member 364 is moved in a direction away from the support plate 365, the first head 311 is subjected to the biasing force of the biasing spring 366 and also moves in a direction away from the support plate 365.

Referring to Figures 2 and 4 together, the first head 311, which has been displaced in the width direction due to thermal expansion of the holding unit 33, can be displaced in the width direction by driving the stepping motor 361. By appropriately controlling the drive amount of the stepping motor 361 in accordance with the temperature of the holding unit 33, the displaced first head 311 shown in Figure 4 can be displaced in the width direction to its original position shown in Figure 2.

Figure 5 shows a mechanical mechanism that displaces the first head 311 in the width direction, but a mechanical mechanism that displaces the first head 311 in the transport direction DR is also provided. By appropriately controlling the mechanical mechanism, the first head 311 can be displaced in both the transport direction DR and the width direction, returning the first head 311 to the position shown in Figure 2.

The second head 312, the third head 313, and other heads are similarly provided with mechanical mechanisms that displace each head in the transport direction DR and the width direction. By appropriately controlling each mechanical mechanism and using the mechanical mechanisms to move the heads to correct any misalignment of the heads due to thermal deformation of the holding unit 33, all heads can be positioned in the positions they would be in when the holding unit 33 is not thermally deformed, as shown in Figure 2. Even if the temperature of the holding unit 33 changes and the holding unit 33 is thermally deformed, the amount of head misalignment can be predicted from the temperature of the holding unit 33 and the heads can be displaced a distance corresponding to that misalignment, thereby positioning each head in the positions they would be in when the holding unit 33 is not thermally deformed. This allows ink to be supplied from each head to the target position, enabling the image forming device 1 to form high-quality images.

<Second Example of Adjustment Unit>
Fig. 6 is a schematic diagram showing a second example of the adjustment unit. Fig. 6 shows a timing chart, with the horizontal axis representing time. Time T01 represents the timing at which ink is ejected from the first head 311 and the second head 312, which are disposed downstream in the transport direction DR, of the inkjet head 31 before thermal deformation shown in Fig. 2. Time T02 represents the timing at which ink is ejected from the third head 313, which is disposed upstream in the transport direction DR, of the inkjet head 31 before thermal deformation shown in Fig. 2.

As shown in Figure 4, the thermal expansion of the holding unit 33 causes the nozzles 321, 322, and 323 to shift in position in the transport direction DR. Due to the thermal expansion of the holding unit 33, the recording medium arrives at the first head 311 and the second head 312 later. Due to the thermal expansion of the holding unit 33, the recording medium arrives at the third head 313 earlier.

Therefore, the timing for ejecting ink from the first head 311 and the second head 312 is set to time T1, which is later than time T01. The timing for ejecting ink from the third head 313 is set to time T2, which is earlier than time T02.

By predicting the amount of head misalignment based on the temperature of the holding unit 33 and changing the timing at which each head ejects ink onto the recording medium, ink can be supplied from each head to the target position in the transport direction DR. This allows the image forming device 1 to form high-quality images.

<Third Example of Adjustment Unit>
Fig. 7 is a first schematic diagram showing a third example of the adjustment unit. Fig. 7 and the subsequent Figs. 8 and 9 representatively show the first head 311 and the third head 313 out of the multiple heads of the inkjet head 31. As already described, the nozzles 321 of the first head 311 include multiple nozzles arranged side by side in the width direction. The nozzles 323 of the third head 313 include multiple nozzles arranged side by side in the width direction.

Each head is controlled to eject ink from only some of its nozzles. The nozzles 321 of the first head 311 include idle nozzles 3210, which do not eject ink and are shown in white in the figure, and operating nozzles 3211, which do eject ink and are shown in hatched in the figure. The nozzles 323 of the third head 313 include idle nozzles 3230, which do not eject ink and are shown in white in the figure, and operating nozzles 3231, which do eject ink and are shown in hatched in the figure.

In the width direction, the range over which the nozzles 321 of the first head 311 extend overlaps the range over which the nozzles 323 of the third head 313 extend. More specifically, the operating nozzles 3211 of the first head 311 overlap with the idle nozzles 3230 of the third head 313, and the operating nozzles 3231 of the third head 313 overlap with the idle nozzles 3210 of the first head 311. The operating nozzles 3211 of the first head 311 do not overlap with the operating nozzles 3231 of the third head 313.

As shown in FIG. 7, the rightmost nozzle of the operating nozzles 3211 of the first head 311 and the leftmost nozzle of the operating nozzles 3231 of the third head 313 are adjacent to each other in the width direction. In the width direction, there are no idle nozzles 3210, 3230 between the rightmost nozzle of the operating nozzles 3211 and the leftmost nozzle of the operating nozzles 3231. This allows the desired image to be formed by ink ejection from the operating nozzles 3211, 3231.

Figure 8 is a second schematic diagram showing a third example of the adjustment unit. Figure 8 shows the holding unit 33 thermally expanded as indicated by the diagonal arrow. As the holding unit 33 thermally expands, the positions of the first head 311 and the third head 313 change in the width direction. The overlap in the width direction between the range in which the nozzles 321 extend and the range in which the nozzles 323 extend becomes smaller. Specifically, in the example shown in Figure 7, six nozzles are arranged in a range in which they overlap each other in the width direction, whereas in Figure 8, only two nozzles are arranged in a range in which they overlap each other in the width direction.

In the inkjet head 31 shown in Figure 8 in which the holding portion 33 has thermally expanded, the positions of the nozzles that eject ink have been changed. In the example shown in Figure 7, there are three inactive nozzles 3210 to the right and left of the operating nozzle 3211. There are three inactive nozzles 3230 to the right and left of the operating nozzle 3231. In contrast, in Figure 8, there is one inactive nozzle 3210 to the right of the operating nozzle 3211 and five inactive nozzles 3210 to the left. There are five inactive nozzles 3230 to the right of the operating nozzle 3231 and one inactive nozzle 3230 to the left.

As a result of changing the positions of the operating nozzles 3211 and 3231 that eject ink, the positions of the operating nozzles 3211 and 3231 are the same before thermal deformation as shown in Figure 7 and after thermal deformation as shown in Figure 8.

Figure 9 is a third schematic diagram showing a third example of the adjustment unit. Figure 9 shows the holding unit 33 thermally shrunk, as indicated by the diagonal arrow. As the holding unit 33 thermally shrinks, the positions of the first head 311 and the third head 313 change in the width direction. The overlap in the width direction between the range in which the nozzles 321 extend and the range in which the nozzles 323 extend becomes larger. Specifically, in the example shown in Figure 7, six nozzles are arranged in an overlapping range in the width direction, whereas in Figure 9, eight nozzles are arranged in an overlapping range in the width direction.

In the inkjet head 31 shown in Figure 9, where the holding portion 33 has been thermally shrunk, the positions of the nozzles that eject ink have been changed. In Figure 9, there are four idle nozzles 3210 to the right of the operating nozzle 3211 and two idle nozzles 3210 to the left. There are two idle nozzles 3230 to the right of the operating nozzle 3231 and four idle nozzles 3230 to the left.

As a result of changing the positions of the operating nozzles 3211 and 3231 that eject ink, the positions of the operating nozzles 3211 and 3231 are the same before thermal deformation as shown in Figure 7 and after thermal deformation as shown in Figure 9.

By predicting the amount of head misalignment based on the temperature of the holding unit 33 and changing the position of the nozzles that eject ink from each head onto the recording medium, ink can be supplied from each head to the targeted position in the width direction. This allows the image forming device 1 to form high-quality images.

[Action and effect]
Although some of the description overlaps with the above description, the characteristic configuration and effects of the image forming apparatus 1 of the embodiment can be summarized as follows.

As shown in Figures 5 to 9, the image forming device 1 adjusts the position of the image formed on the recording medium by ink ejected from each head in accordance with the temperature of the holding unit 33. Even if the temperature of the holding unit 33 changes and the position of the head changes due to thermal deformation of the holding unit 33, the amount of change in head position is predicted from the temperature of the holding unit 33, and the position of the image formed on the recording medium by each head is adjusted for each head based on the amount of change in head position, thereby allowing ink to be supplied to the target position from each head. Therefore, the image forming device 1 can form high-quality images.

As shown in Figure 5, the position of each head in the holding unit 33 may be changed depending on the temperature of the holding unit 33. By changing the position of the head, it is possible to appropriately adjust the position of the image in the transport direction DR and the width direction, and ink can be supplied from each head to the target position. By making the head position changeable, it is possible to reduce the overlap of the ranges in which the nozzles extend in the width direction, and therefore the number of nozzles in each head can be reduced.

As shown in Figures 7 to 9, the nozzles that eject ink in each head may be changed depending on the temperature of the holding unit 33. By changing the position of the nozzles used, the position of the image in the width direction can be appropriately adjusted, and ink can be supplied to the target position from each head. Compared to the example shown in Figure 5, in which the head position is changed, there is no need to include a stepping motor 361, etc., so the image position can be adjusted with a simple configuration.

As shown in Figure 6, the timing at which ink is ejected from each head onto the recording medium may be changed depending on the temperature of the holding unit 33. By changing the timing at which ink is ejected, the position of the image in the transport direction DR can be appropriately adjusted, and ink can be supplied to the target position from each head. Compared to the example shown in Figure 5, in which the head position is changed, there is no need to include a stepping motor 361, etc., so the image position can be adjusted with a simple configuration.

As shown in Figure 2, the holding unit 33 may be provided with multiple temperature sensors 34, 35 that measure the temperature of the holding unit 33. In this way, the temperature distribution of the holding unit 33 can be determined based on the measurement results of the temperature sensors, allowing the position of the image to be adjusted accurately according to the temperature of the holding unit 33.

As shown in Figure 3, the temperature of the holding unit 33 may be estimated based on the amount of ink ejected from each head. Since the temperature of the holding unit 33 can be estimated through processing by the controller that controls the image forming device 1, the temperature of the holding unit 33 can be determined without having to provide multiple temperature sensors.

The position of the image formed by each head can be adjusted according to the temperature distribution of the holding unit 33. The adjustment amount can be increased for heads in high-temperature positions and decreased for heads in low-temperature positions. The image position can be appropriately adjusted for each head according to temperature changes in the holding unit 33, and ink can be supplied from each head to the target position with precision.

As shown in FIG. 1, the inkjet head 31 may include inkjet heads 31Y, 31M, 31C, and 31K that eject ink of different colors. The adjustment of the image position according to the temperature of the holding unit 33 in this embodiment can also be applied to color printers.

The ink ejected from each head may be water-based ink. In an image forming device 1 using water-based ink, temperature management of the ink is not required, so there is no temperature adjustment mechanism within the device, and the temperature of the holding unit 33 in standby mode follows the ambient temperature. When image formation begins, the head generates heat as ink is ejected from the nozzles, causing the temperature of the surrounding holding unit 33 to rise, resulting in thermal expansion of the holding unit 33. In this way, by applying the configuration of an embodiment in which the position of the image formed by each head on the recording medium is adjusted for each head in accordance with the temperature of the holding unit 33 to an image forming device 1 using water-based ink, which has large temperature changes in the holding unit 33, the image forming device 1 can form high-quality images.

The image forming apparatus shown in Figure 1 is configured to directly form an ink image on a recording medium, using the recording medium as the image forming body. The image forming apparatus is not limited to this configuration, and may be configured to eject ink from the image forming unit 30 onto an intermediate transfer body, form an ink image on the intermediate transfer body as the image forming body, and then transfer the image from the intermediate transfer body to the recording medium.

The embodiments have been described above, but configurations described in the embodiments that can be combined with each other may be combined as appropriate. Furthermore, the embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

1 Image forming apparatus, 10 Conveying section, 11 Payout roller, 12, 13 Take-up roller, 14 Conveying belt, 30 Image forming section, 31, 31C, 31K, 31M, 31Y Inkjet head, 33 Holding section, 34, 35 Temperature sensor, 60 Ink drying section, 311 First head, 312 Second head, 313 Third head, 321, 322, 323 Nozzle, 321C Cavity, 321P Piezo element, 361 Stepping motor, 362 Output shaft, 363 Male screw, 364 Swinging member, 365 Support plate, 366 Spring, 3210, 3230 Inactive nozzle, 3211, 3231 Operating nozzle, A1 High temperature area, A2 Low temperature area, D Droplet, DR Transport direction, T01, T1, T2, T02 time.

Claims (8)

a plurality of heads that eject ink onto an image forming body to form an image on the image forming body;
a holding unit that holds a plurality of the heads;
a temperature determination unit that determines the temperature of the holding unit;
an adjustment unit that adjusts a position of an image formed on the image forming body by ink ejected from each of the heads in accordance with the temperature of the holding unit determined by the temperature determination unit,
Each of the heads includes a plurality of nozzles arranged side by side in a width direction perpendicular to the conveyance direction of the image forming body, and ejects ink from some of the plurality of nozzles that are in operation and some of the plurality of nozzles that are inactive, without ejecting ink;
the adjustment unit changes positions of the operating nozzles and the idle nozzles in each of the heads in accordance with the temperature of the holding unit;
Each of the heads is controlled so as to eject ink from only some of the nozzles of the plurality of nozzles of each head,
an inactive nozzle is located on the right and left sides of the active nozzle in the width direction ; The image forming apparatus of claim 1, wherein the adjustment unit changes the position of each of the heads in the holding unit depending on the temperature of the holding unit. The image forming apparatus of claim 1 or claim 2, wherein the adjustment unit changes the timing at which ink is ejected from each of the heads onto the image forming body depending on the temperature of the holding unit. An image forming apparatus according to any one of claims 1 to 3, wherein the temperature determination unit has multiple temperature sensors provided in the holding unit. An image forming apparatus according to any one of claims 1 to 3, wherein the temperature determination unit estimates the temperature of the holding unit based on the amount of ink ejected from each of the heads. the temperature determination unit determines a temperature distribution of the holding unit,
6. The image forming apparatus according to claim 4, wherein the adjustment section adjusts the position of the image formed by each of the heads in accordance with the temperature distribution of the holding section. An image forming apparatus according to any one of claims 1 to 6, wherein the multiple heads include heads that eject inks of different colors. An image forming apparatus according to any one of claims 1 to 7, wherein the ink is a water-based ink.