EP4186701A1

EP4186701A1 - Image forming apparatus

Info

Publication number: EP4186701A1
Application number: EP22207815.6A
Authority: EP
Inventors: Shinya Naoi
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 2021-11-25
Filing date: 2022-11-16
Publication date: 2023-05-31
Also published as: JP2023077566A

Abstract

There is provided an image forming apparatus (1) capable of forming a high-quality image even when a temperature of a holding unit (33) holding a plurality of heads (311, 312, and 313) changes during image formation.

An image forming apparatus (1) includes a plurality of heads (311, 312, and 313) that ejects ink onto an image forming body to form an image on the image forming body, a holding unit (33) that holds the plurality of heads (311, 312, and 313), a temperature determination unit that determines a temperature of the holding unit (33), and an adjustment unit that adjusts a position of an image formed on the image forming body by the ink ejected from each of the heads (311, 312, and 313) according to the temperature of the holding unit (33) determined by the temperature determination unit.

Description

Background

Technological Field

The present disclosure relates to an image forming apparatus.

Description of the Related art

JP 2004-321978 A discloses a droplet ejection device including ejection heads that eject functional liquid from a nozzle, and a mounting plate having an opening in which a plurality of ejection heads is disposed. The plurality of ejection heads is disposed in the opening at an attachment position under the same temperature condition as when the functional liquid is ejected.
In an image forming apparatus that forms an image by ejecting ink from a plurality of heads, the temperature of a holding unit that holds the plurality of heads may change due to heat generation during image formation, a change in environmental temperature, and the like. When the positional relationship of each head changes due to thermal deformation of the holding unit, ink cannot be supplied from each head to a target position, and image quality may deteriorate.

Summary

The present disclosure proposes an image forming apparatus capable of forming a high-quality image even when the temperature of a holding unit changes during image formation.
To achieve the abovementioned object, according to an aspect of the present invention, an image forming apparatus reflecting one aspect of the present invention comprises: a plurality of heads that ejects ink onto an image forming body to form an image on the image forming body; a holding unit that holds the plurality of heads ; a temperature determination unit that determines a temperature of the holding unit; and an adjustment unit that adjusts a position of the image formed on the image forming body by the ink ejected from each of the heads according to the temperature of the holding unit determined by the temperature determination unit.

Brief Description of the Drawings

The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention:

Fig. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment;
Fig. 2 is a schematic view illustrating a configuration of an inkjet head illustrated in Fig. 1;
Fig. 3 is a diagram for explaining another example of a temperature determination unit;
Fig. 4 is a schematic view illustrating a state in which a holding unit is thermally deformed;
Fig. 5 is a schematic diagram illustrating a first example of an adjustment unit;
Fig. 6 is a schematic diagram illustrating a second example of the adjustment unit;
Fig. 7 is a first schematic diagram illustrating a third example of the adjustment unit;
Fig. 8 is a second schematic diagram illustrating a third example of the adjustment unit; and
Fig. 9 is a third schematic diagram illustrating a third example of the adjustment unit.

Detailed Description of Embodiments

Hereinafter, one or more embodiments of an image forming apparatus according to the present disclosure will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. In the following description, the same parts and components are designated by the same reference numerals. Their names and functions are the same. Therefore, detailed descriptions thereof will not be repeated.

[Configuration of Image Forming Apparatus 1]

Fig. 1 is a schematic diagram illustrating a schematic configuration of an image forming apparatus 1 according to the 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 illustrated in Fig. 1, the image forming apparatus 1 mainly includes a conveyance unit 10, an image former 30, and an ink dryer 60.
The conveyance unit 10 conveys a recording medium. The conveyance unit 10 includes a feeding roller 11, winding rollers 12 and 13, and a conveyance belt 14. The feeding roller 11 is a roller that feeds the recording medium. The winding rollers 12 and 13 are rollers for winding a recording medium. The conveyance belt 14 is stretched between the feeding roller 11 and the winding rollers 12 and 13, and conveys the recording medium. The recording medium is conveyed on the conveyance belt 14 from the feeding roller 11 toward the winding rollers 12 and 13 along a conveyance direction DR indicated by an arrow in Fig. 1.
As the recording medium, plain paper can be used. The plain paper may be roll paper in which long paper is wound in a roll shape, or may be a sheet paper cut into a predetermined size. The recording medium may be a resin film. The resin film may be, for example, a PET film, a PP film, a PE film, or the like. The recording medium may be a metal, a wood plate, cloth, or the like.
The image former 30 ejects ink onto the recording medium conveyed on the conveyance belt 14. The image former 30 is of an aqueous inkjet type. The image former 30 includes a plurality of inkjet heads 31. Each inkjet head 31 supplies ink of each color to the recording medium. For example, the inkjet head 31Y supplies yellow (Y) ink. The inkjet head 31M supplies magenta (M) ink. The inkjet head 31C supplies cyan (C) ink. The inkjet head 31K supplies black (K) ink. The ink ejected from each inkjet head 31 is applied to the recording medium to form an ink image on the recording medium.
The ink dryer 60 heats the recording medium to dry and fix the ink image on the recording medium. The ink dryer 60 may heat the recording medium from a front surface on which the ink image is formed, or may heat the recording medium from a back surface on which the ink image is not formed. The ink dryer 60 may include a necessary heater selected from known heaters such as an infrared heater, an electric heating wire, an ultraviolet lamp, a gas, and a hot air dryer. From the viewpoint of safety and energy efficiency, heating by an electric heating wire or an infrared heater is preferable.

<Ink>

The ink is used as inks of respective colors including cyan, magenta, yellow, and black (CMYK). By using an ink of one color or inks of two or more colors selected from a group constituted of CMYK, a primary color, a multi-order color, or a halftone can be formed for each of a large number of unit regions constituting an image. The ink can include components such as colorants, resins, aqueous media, surfactants and other additives.

(Coloring material)

As a coloring material contained in the ink, a pigment or a dye can be used.
As the pigment that can be used, conventionally known pigments can be used without particular limitation, and any of water dispersible pigments, solvent dispersible pigments, and the like can be used. For example, organic pigments such as insoluble pigments and lake pigments, and inorganic pigments such as carbon black can be preferably used.
As the dye, a dye having an anionic group is preferably used. Specific examples of the dye include dyes such as azo, triphenylmethane, (aza) phthalocyanine, xanthene, and anthrapyridone.
Among them, the coloring material is preferably a pigment, and more preferably a resin dispersible pigment.

(Resin)

Examples of the resin contained in the ink can include acrylic-based, styrene-acrylic-based, acrylonitrileacrylic-based, vinyl acetate-acrylic-based, polyurethane-based, polyester-based resins, and the like.
Such a resin may be obtained by polymerizing a monomer having an acid group. Examples of such a monomer include those obtained by radically copolymerizing acid derivatives of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, styrene, and the like. Further, it may be copolymerized with another monomer as necessary.
The amount of ink soluble resin varies depending on the polymerization degree of the resin, but is preferably 2 to 10%, more preferably 3 to 6% of the total ink mass. When the amount of the resin is small, the effect of the embodiment of the present invention cannot be obtained, and conversely, when the amount is large, the ejection property and storage stability of the inkjet are abnormal. In addition, a plurality of resins may be contained, or a resin may be contained as a copolymer or dispersed in an emulsion state.
The solvent for the ink that dissolves and disperses the solutes preferably contains, in addition to water, a solvent component that dissolves in water for the purpose of improving ejection performance, adjusting ink physical properties, and the like. The type of the solvent is not particularly limited as long as the effect of the embodiment of the present invention is not impaired.

(Aqueous medium)

The ink may be an aqueous ink containing water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As the water, deionized water or ion-exchanged water is preferably used. The content (mass%) of water in the ink is preferably 20 mass% or more to 95 mass% or less based on the total mass of the ink. Further, the content (mass%) of the water-soluble organic solvent in the ink is preferably 3 mass% or more to 50 mass% or less with respect to the total mass of the ink.

(Surfactant)

As the surfactant to be used, any of cationic, anionic, amphoteric, and nonionic surfactants can be used. A surfactant or a solvent may be used alone or in combination.

(Other Additives)

Various known additives, for example, a polysaccharide, a viscosity modifier, a specific resistance modifier, a film forming agent, an ultraviolet absorber, an antioxidant, a discoloration inhibitor, an antifungal agent, a rust inhibitor, and the like can be appropriately selected and used according to the purpose of emission stability, print head and ink cartridge compatibility, storage stability, image storability, and other performance improvement.

[Configuration of Inkjet Head 31]

Fig. 2 is a schematic view illustrating a configuration of an inkjet head 31 illustrated in Fig. 1. The inkjet head 31 of respective colors includes a plurality of heads. Although a first head 311, a second head 312, and a third head 313 are exemplarily illustrated in Fig. 2, the inkjet head 31 may include four or more heads. The plurality of heads is disposed in a staggered manner. The inkjet head 31 includes a holding unit 33 that holds a plurality of heads. The holding unit 33 may hold a head group including a plurality of heads that eject ink of one color, or may hold a plurality of head groups that respectively ejects inks of different colors.
The conveyance direction DR of the recording medium illustrated in Fig. 1 is a vertical direction in Fig. 2. A direction orthogonal to the conveyance direction DR is hereinafter referred to as a width direction. The width direction is a horizontal direction in Fig. 2. In the conveyance direction DR, the first head 311 and the second head 312 are disposed on the downstream side, and the third head 313 is disposed on the upstream side. The first head 311 and the second head 312 are disposed side by side in the width direction. In the width direction, the third head 313 is disposed at a position between the first head 311 and the second head 312. A part of the first head 311 and a part of the third head 313 overlap in the width direction. In the width direction, a part of the second head 312 and a part of the third head 313 overlap each other.
Each inkjet head 31 has a plurality of nozzles. A nozzle 321 illustrated in Fig. 2 schematically illustrates a plurality of nozzles of the first head 311 by a straight line. The nozzle 321 includes a plurality of nozzles disposed side by side in the width direction. A nozzle 322 illustrated in Fig. 2 schematically illustrates a plurality of nozzles of the second head 312 by a straight line. A nozzle 323 illustrated in Fig. 2 schematically illustrates a plurality of nozzles of the third head 313 by a straight line. Each of the nozzles 322 and 323 includes a plurality of nozzles disposed side by side in the width direction.
The inkjet head 31 further includes a plurality of temperature sensors 34 and 35. The temperature sensors 34 and 35 are provided on the holding unit 33 and measure the temperature of the holding unit 33. The temperature sensors 34 and 35 are an example of a temperature determination unit that determines the temperature of the holding unit 33. The temperature sensors 34 and 35 are disposed apart from each other in the width direction. Each of the temperature sensors 34 and 35 is configured to measure the temperature of the holding unit 33 at different positions, and interpolate the temperature of the holding unit 33 at the position between the temperature sensors 34 and 35, so that the temperature distribution of the holding unit 33 can be determined.
Fig. 3 is a diagram for explaining another example of the temperature determination unit. Although the first head 311 is representatively illustrated in Fig. 3, other heads similar configurations. As described above, the nozzle 321 includes a plurality of nozzles disposed side by side in the width direction (in Fig. 3, a horizontal direction in the drawing).
Each nozzle 321 communicates with 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 is deformed by application of a voltage from a drive circuit which is not illustrated. When the piezoelectric element 321P is deformed, the cavity 321C is also deformed, and the volume of the cavity 321C is reduced, so that a part of the ink in the cavity 321C is pushed out of the cavity 321C. Then, ink droplets D are ejected from the nozzles 321.
Heat is generated every time the piezoelectric element 321P is driven. Every time the ink droplet D is ejected from the nozzle 321, the piezoelectric element 321P corresponding to the nozzle 321 is driven to generate heat. In the nozzle 321 that continuously ejects the ink, the calorific value of the piezoelectric element 321P increases. The periphery of the nozzle 321 performing continuous ejection generates heat, and the temperature locally rises. Thus, a high temperature region A1, which is a relatively high temperature region, and a low temperature region A2, which is a relatively low temperature region, are formed in the inkjet head 31.
A controller which is not illustrated receives an input of an ink image formed on a recording medium by the image forming apparatus 1. On the basis of the input ink image, the controller sets which head among the plurality of heads to eject the ink and which nozzle among the plurality of nozzles of the head to eject the ink. The controller outputs a control signal instructing to drive the piezoelectric element corresponding to the nozzle set to eject the ink to a drive circuit of the piezoelectric element. The amount of ink to be ejected is large and the calorific value increases around the nozzle where the piezoelectric element is continuously driven, thereby causing the temperature of the holding unit 33 to rise. The controller can estimate the temperature rise of the holding unit 33 on the basis of the amount of ink ejected from each head. Therefore, the controller that controls the image forming apparatus 1 can have a function as the temperature determination unit that determines the temperature of the holding unit 33.
[Thermal Deformation of holding unit 33] Fig. 4 is a schematic diagram illustrating a state in which the holding unit 33 is thermally deformed. In the image forming apparatus 1, the temperature of the holding unit 33 holding the plurality of heads may change due to heat generation during image formation, a change in environmental temperature, or the like. The holding unit 33 illustrated in Fig. 4 is increased in temperature as compared with the state in Fig. 2, and thermally expanded as indicated by an oblique arrow in Fig. 4.
A dashed line in Fig. 4 indicates the position of the head before the holding unit 33 illustrated in Fig. 2 is thermally deformed. The position of each head is changed by the thermal expansion of the holding unit 33. The gap between the first head 311 and the second head 312 in the width direction increases. The gap between the first head 311 and the second head 312 and the third head 313 in the conveyance direction DR increases. The third head 313 is also displaced in the width 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 change in both the conveyance direction DR and the width direction.
Although the thermally expanded holding unit 33 is illustrated in Fig. 4, the holding unit 33 may be thermally contracted due to a change in environmental temperature, and even in this case, the positions of the first head 311, the second head 312, and the third head 313 change, and the positions of the nozzles 321, 322, and 323 also change.

[Adjustment unit]

The image forming apparatus 1 of the embodiment includes an adjustment unit in order to supply ink from each head to the target position even if the positional relationship of respective heads change due to thermal deformation of the holding unit 33. The adjustment unit adjusts the position of the image formed on the recording medium by the ink ejected from each head according to the temperature of the holding unit 33.

Fig. 5 is a schematic diagram illustrating a first example of the adjustment unit. In the example illustrated in Fig. 5, the first head 311 is representatively illustrated, and a mechanism that moves the first head 311 in the width direction is illustrated.
Specifically, a stepping motor 361 is attached to the holding unit 33. An output shaft 362 of the stepping motor 361 is provided with a male screw 363. An outer peripheral surface of the output shaft 362 may be threaded to form the male screw 363, or the male screw 363 may be configured by fixing a male screw member to the output shaft 362. A swing member 364 is engaged with and coupled to the male screw 363. The swing member 364 is internally threaded. The output shaft 362 and the male screw 363 rotate relative to the holding unit 33 by driving of the stepping motor 361. On the other hand, the swing member 364 is configured to be relatively non-rotatable with respect to the holding unit 33.
A biasing spring 366 is disposed at a position facing the swing 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 unit 33. The biasing spring 366 is disposed to be stretchable in the width direction, and one end thereof is supported by the support plate 365. The support plate 365 supports one end of the biasing spring 366 in a non-displaceable or substantially non-displaceable manner.
The first head 311 representatively illustrated in Fig. 5 is held between the swing member 364 and the biasing spring 366. One end of the first head 311 extending in the width direction receives a biasing force in the width direction from the biasing spring 366, and the other end of the first head 311 is pressed against the swing member 364. The first head 311 is positioned in the width direction by the swing member 364 and the biasing spring 366.
When the stepping motor 361 is driven, the male screw 363 rotates according to the rotation of the output shaft 362. Since the swing member 364 does not rotate, the male screw 363 rotates relative to the internal thread formed in the swing member 364. Consequently, stress in the width direction acts on the swing member 364. By rotationally driving the stepping motor 361 in both directions, the swing member 364 can be reciprocated in the width direction. When the swing member 364 is moved in the direction of approaching the support plate 365, the first head 311 pressed by the swing member 364 also moves in a direction of approaching the support plate 365. When the swing member 364 is moved in a direction away from the support plate 365, the first head 311 also moves in the direction away from the support plate 365 under the biasing force of the biasing spring 366.
Referring also to Figs. 2 and 4, the first head 311 displaced in the width direction by the thermal expansion of the holding unit 33 can be displaced in the width direction by driving the stepping motor 361. By appropriately controlling the driving amount of the stepping motor 361 according to the temperature of the holding unit 33, the first head 311 displaced in position illustrated in Fig. 4 can be displaced in the width direction to the original position illustrated in Fig. 2.
In Fig. 5, a mechanism for displacing the first head 311 in the width direction is illustrated, but a mechanism for displacing the first head 311 in the conveyance direction DR is also provided. By appropriately controlling the mechanisms, the first head 311 can be displaced in both the conveyance direction DR and the width direction to return the first head 311 to the position of Fig. 2.
Similarly, the second head 312, the third head 313, and the other heads are provided with a mechanism that displaces each head in the conveyance direction DR and the width direction. By appropriately controlling each mechanism and correcting the amount of displacement of the position of the head due to the thermal deformation of the holding unit 33 by moving the head with the mechanism, all the heads can be disposed at the positions when the holding unit 33 illustrated in Fig. 2 is not thermally deformed. Even if the temperature of the holding unit 33 changes and the holding unit 33 is thermally deformed, the positional displacement amount of the head is predicted from the temperature of the holding unit 33, and the head is displaced by a distance corresponding to the positional displacement amount. Thus, each head can be disposed at a position when the holding unit 33 is not thermally deformed. Thus, the ink can be supplied from each head to the target position, so that the image forming apparatus 1 can form a high-quality image.

Fig. 6 is a schematic diagram illustrating a second example of the adjustment unit. Fig. 6 illustrates a timing chart, and a horizontal axis indicates time. Time T01 indicates timing of ejecting the ink from the first head 311 and the second head 312 disposed on the downstream side in the conveyance direction DR in the inkjet head 31 before the thermal deformation illustrated in Fig. 2. Time T02 indicates timing of ejecting the ink from the third head 313 disposed on the upstream side in the conveyance direction DR in the inkjet head 31 before the thermal deformation illustrated in Fig. 2.
As illustrated in Fig. 4, the positions of the nozzles 321, 322, and 323 in the conveyance direction DR are shifted due to the thermal expansion of the holding unit 33. As the holding unit 33 is thermally expanded, the recording medium reaches the first head 311 and the second head 312 with a delay. The recording medium reaches the third head 313 earlier by the thermal expansion of the holding unit 33.
Thus, the timing of ejecting the ink from the first head 311 and the second head 312 is set to time T1 later than time T01. The timing of ejecting the ink from the third head 313 is set to time T2 earlier than time T02.
By predicting the positional displacement amount of the head according to the temperature of the holding unit 33 and changing the timing of ejecting the ink from each head to the recording medium, the ink can be supplied from each head to the target position in the conveyance direction DR. Therefore, the image forming apparatus 1 can form a high-quality image.

Fig. 7 is a first schematic diagram illustrating a third example of the adjustment unit. In Fig. 7 and subsequent Figs. 8 and 9, a first head 311 and a third head 313 among the plurality of heads of the inkjet head 31 are representatively illustrated. As described above, the nozzles 321 of the first head 311 include a plurality of nozzles disposed side by side in the width direction. The nozzle 323 of the third head 313 includes a plurality of nozzles disposed side by side in the width direction.
Each head is controlled to eject ink from only a part of the plurality of nozzles of each head. The nozzle 321 of the first head 311 includes idle nozzles 3210 that do not eject ink indicated by white in the drawing, and operating nozzles 3211 that eject ink indicated by hatching in the drawing. The nozzle 323 of the third head 313 includes idle nozzles 3230 that do not eject ink indicated by white in the drawing, and operating nozzles 3231 that eject ink indicated by hatching in the drawing.
A range in which the nozzle 321 of the first head 311 extends and a range in which the nozzle 323 of the third head 313 extends overlap each other in the width direction. More specifically, the operating nozzles 3211 in the first head 311 and the idle nozzles 3230 in the third head 313 overlap, and the operating nozzles 3231 in the third head 313 and the idle nozzles 3210 in the first head 311 overlap. The operating nozzles 3211 in the first head 311 and the operating nozzles 3231 in the third head 313 do not overlap.
The nozzle at the right end in the drawing among the operating nozzles 3211 of the first head 311 and the nozzle at the left end in the drawing among the operating nozzles 3231 of the third head 313 illustrated in Fig. 7 are adjacent to each other in the width direction. In the width direction, the idle nozzles 3210 and 3230 are not disposed between the nozzle at the right end of the operating nozzles 3211 and the nozzle at the left end of the operating nozzles 3231. Thus, a desired image can be formed by ink ejection from the operating nozzles 3211 and 3231.
Fig. 8 is a second schematic diagram illustrating a third example of the adjustment unit. Fig. 8 illustrates the thermally expanded holding unit 33 as indicated by an oblique arrow. As the holding unit 33 is thermally expanded, the positions of the first head 311 and the third head 313 are changed in the width direction. The overlap between the range in which the nozzle 321 extends and the range in which the nozzle 323 extends in the width direction is smaller. Specifically, in the example illustrated in Fig. 7, six nozzles in the width direction are disposed in the range overlapping each other, whereas in Fig. 8, two nozzles in the width direction are disposed in the range overlapping each other.
In the inkjet head 31 in which the holding unit 33 illustrated in Fig. 8 is thermally expanded, the positions of the nozzles that eject ink are changed. In the example illustrated in Fig. 7, there are three idle nozzles 3210 on each of the right and left sides of the operating nozzles 3211. There are three idle nozzles 3230 on each of the right and left sides of the operating nozzles 3231. On the other hand, in Fig. 8, one idle nozzle 3210 is provided on the right side of the operating nozzles 3211, and five idle nozzles 3210 are provided on the left side. There are five idle nozzles 3230 on the right side of the operating nozzles 3231 and one idle nozzle 3230 on the left side.
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 the thermal deformation illustrated in Fig. 7 and after the thermal deformation illustrated in Fig. 8.
Fig. 9 is a third schematic diagram illustrating a third example of the adjustment unit. Fig. 9 illustrates the holding unit 33 that is thermally contracted as indicated by oblique arrows. As the holding unit 33 thermally contracts, the positions of the first head 311 and the third head 313 are changed in the width direction. The overlap between the range in which the nozzle 321 extends and the range in which the nozzle 323 extends in the width direction is larger. Specifically, in the example illustrated in Fig. 7, six nozzles in the width direction are disposed in the range overlapping each other, whereas in Fig. 9, eight nozzles in the width direction are disposed in the range overlapping each other.
In the inkjet head 31 in which the holding unit 33 illustrated in Fig. 9 is thermally contracted, the positions of the nozzles that eject ink are changed. In Fig. 9, four idle nozzles 3210 are provided on the right side of the operating nozzles 3211, and two idle nozzles 3210 are provided on the left side. There are two idle nozzles 3230 on the right side of the operating nozzles 3231 and four idle nozzles 3230 on the left side.
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 the thermal deformation illustrated in Fig. 7 and after the thermal deformation illustrated in Fig. 9.
By predicting the positional displacement amount of the head according to the temperature of the holding unit 33 and changing the position of the nozzle that ejects ink from each head to the recording medium, the ink can be supplied from each head to the target position in the width direction. Therefore, the image forming apparatus 1 can form a high-quality image.

[Operation and Effect]

Although there is a description partially overlapping with the above description, the characteristic configuration and operation and effect of the image forming apparatus 1 of the embodiment will be collectively described as follows.
As illustrated in Figs. 5 to 9, the image forming apparatus 1 adjusts the position of the image formed on the recording medium by the ink ejected from each head according to 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 the position of the head 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 on the basis of the amount of change in the position of the head. Thus, ink can be supplied from each head to the target position. Therefore, the image forming apparatus 1 can form a high-quality image.
As illustrated in Fig. 5, the position of each head in the holding unit 33 may be changed according to the temperature of the holding unit 33. By changing the position of the head, the position of the image in the conveyance direction DR and the width direction can be appropriately adjusted, and the ink can be supplied from each head to the target position. Since the overlapping of the ranges in which the nozzles extend in the width direction can be reduced by enabling the position of the head to be changed, the number of nozzles included in each head can be reduced.
As illustrated in Figs. 7 to 9, the nozzles that eject the ink in each head may be changed according to the temperature of the holding unit 33. By changing the position of the nozzle to be used, the position of the image in the width direction can be appropriately adjusted, and the ink can be supplied from each head to the target position. As compared with the example illustrated in Fig. 5 in which the position of the head is changed, it is not necessary to provide the stepping motor 361 and the like, so that the position of the image can be adjusted with a simple configuration.
As illustrated in Fig. 6, the timing of ejecting ink from each head to the recording medium may be changed according to the temperature of the holding unit 33. By changing the timing of ejecting the ink, the position of the image in the conveyance direction DR can be appropriately adjusted, and the ink can be supplied from each head to the target position. As compared with the example illustrated in Fig. 5 in which the position of the head is changed, it is not necessary to provide the stepping motor 361 and the like, so that the position of the image can be adjusted with a simple configuration.
As illustrated in Fig. 2, the holding unit 33 may be provided with a plurality of temperature sensors 34 and 35 that measure the temperature of the holding unit 33. In this manner, the temperature distribution of the holding unit 33 can be grasped on the basis of measurement results of the temperature sensors, and thus it is possible to accurately adjust the position of the image according to the temperature of the holding unit 33.
As illustrated in Fig. 3, the temperature of the holding unit 33 may be estimated on the basis of the amount of ink ejected from each head. The temperature of the holding unit 33 can be estimated by processing of the controller that controls the image forming apparatus 1, and thus the temperature of the holding unit 33 can be determined without providing a large number of 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 of the head at the position where the temperature is high can be increased, and the adjustment amount of the head at the position where the temperature is low can be decreased. The position of the image can be appropriately adjusted according to the temperature change of the holding unit 33 for each head, and the ink can be accurately supplied from each head to the target position.
As illustrated in Fig. 1, the inkjet head 31 may include inkjet heads 31Y, 31M, 31C, and 31K that eject inks of different colors. The adjustment of the position of the image according to the temperature of the holding unit 33 of the present embodiment can also be applied to a color printer.
The ink ejected from each head may be a water-based ink. In the image forming apparatus 1 using the aqueous ink, temperature management of the ink is unnecessary and thus there is no mechanism for temperature adjustment in the apparatus, and the temperature of the holding unit 33 in a standby state is a temperature following the environmental temperature. When image formation is started, the head generates heat by ejection of ink from the nozzle, and the temperature of the surrounding holding unit 33 rises, thereby causing the holding unit 33 to thermally expand. As described above, the configuration of the embodiment in which the position of the image formed on the recording medium by each head is adjusted for each head according to the temperature of the holding unit 33 is applied to the image forming apparatus 1 using the aqueous ink having a large temperature change of the holding unit 33, and thus the image forming apparatus 1 can form a high-quality image.
The image forming apparatus illustrated in Fig. 1 has a configuration in which a recording medium is an image forming body, and an ink image is directly formed on the recording medium. The image forming apparatus is not limited to such a configuration, and may be configured to eject ink from the image former 30 to an intermediate transfer body, form an ink image on the intermediate transfer body as the image forming body, and transfer the image from the intermediate transfer body to the recording medium.
Although embodiments of the present invention have been described and illustrated in detail, configurations that can be combined with each other among the configurations described in the embodiment may be appropriately combined, and the disclosed embodiments are made for purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims, and it is intended that all modifications are included in the meaning and scope equivalent to the claims.

Claims

An image forming apparatus (1), comprising:
a plurality of heads (311, 312, and 313) that ejects ink onto an image forming body to form an image on the image forming body;

a holding unit (33) that holds the plurality of heads (311, 312, and 313);

a temperature determination unit that determines a temperature of the holding unit (33); and

an adjustment unit that adjusts a position of the image formed on the image forming body by the ink ejected from each of the heads (311, 312, and 313) according to the temperature of the holding unit (33) determined by the temperature determination unit.
The image forming apparatus (1) according to claim 1, wherein the adjustment unit changes a position of each of the heads (311, 312, and 313) in the holding unit (33) according to the temperature of the holding unit (33).
The image forming apparatus (1) according to claim 1 or 2, wherein
each of the heads (311, 312, and 313) includes a plurality of nozzles (321, 322, and 323) and ejects ink from a part of the plurality of nozzles (321, 322, and 323), and

the adjustment unit changes a nozzle that ejects ink in each of the heads (311, 312, and 313) according to the temperature of the holding unit (33).
The image forming apparatus (1) according to any one of claims 1 to 3, wherein the adjustment unit changes timing of ejecting ink from each of the heads (311, 312, and 313) to the image forming body according to the temperature of the holding unit (33).
The image forming apparatus (1) according to any one of claims 1 to 4, wherein the temperature determination unit includes a plurality of temperature sensors (34 and 35) provided in the holding unit (33).
The image forming apparatus (1) according to any one of claims 1 to 4, wherein the temperature determination unit estimates the temperature of the holding unit (33) on a basis of an amount of ink ejected from each of the heads (311, 312, and 313).
The image forming apparatus (1) according to claim 5 or 6, wherein
the temperature determination unit determines a temperature distribution of the holding unit (33), and

the adjustment unit adjusts a position of an image formed by each of the heads (311, 312, and 313) according to the temperature distribution of the holding unit (33).
The image forming apparatus (1) according to any one of claims 1 to 7, wherein the plurality of heads (311, 312, and 313) includes heads (31Y, 31M, 31C, and 31K) that eject inks of different colors.
The image forming apparatus (1) according to any one of claims 1 to 8, wherein the ink is a water-based ink.