Patent Description:
<CIT> 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.

<CIT> discloses an inkjet recording apparatus that changes the adjustment temperature of a recording head depending on the number of recording media so that a favorable recording result can be maintained for any number of recording media and a time required for the recording can be reduced. Different adjustment temperatures are used depending on the number of recording media. When the number of recording media is relatively small, the adjustment temperature is determined to be low and, when the number of recording media is relatively large, then the adjustment temperature is determined to be high. When the recording is started, when the head temperature is lower than the determined adjustment temperature, then ink is heated by a sub heater. Depending on the determined temperature, an interval with which a preliminary ejection is performed is changed.

<CIT> discloses an ink-jet print method of coloring each pixel array on a substrate by using an ink-jet head having a plurality of ink discharging nozzles while changing the ink discharging nozzle used to color one line for every scanning operation, including discharging the inks discharged in the plurality of scanning operations such that the inks are arranged at equal intervals within each pixel array. Such an ink-jet print method can uniformly distribute inks within each pixel array when a color filter is to be colored in a plurality of scanning operations.

<CIT> discloses an image forming apparatus that includes: a recording head having plural sub-heads, the sub-heads each including plural nozzles, each of the plural nozzles within a sub-head ejecting liquid droplets at the same time with respect to a medium on which an image is drawn, and the sub-heads being arranged in a width direction of the medium; a setting unit; and a rotation unit. The setting unit uses a timing when a predetermined sub-head of the plural sub-heads ejects liquid droplets as a reference to set timings when sub-heads other than the predetermined sub-head eject liquid droplets. The rotation unit uses a predetermined axis as a spindle to rotate and position the recording head in a plane parallel to a plane of the medium.

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.

According to a first aspect the present invention provides an image forming apparatus in accordance with independent claim <NUM>. Further aspects are set forth in the dependent claims, the drawings, and the following description.

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 a predicted amount of change in position of each of the heads, that is due to thermal deformation of the holding unit at the temperature of the holding unit determined by the temperature determination unit.

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:.

Hereinafter, one or more embodiments of an image forming apparatus according to the present disclosure will be described with reference to the drawings. 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.

<FIG> is a schematic diagram illustrating a schematic configuration of an image forming apparatus <NUM> according to the embodiment. The image forming apparatus <NUM> 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>, the image forming apparatus <NUM> mainly includes a conveyance unit <NUM>, an image former <NUM>, and an ink dryer <NUM>.

The conveyance unit <NUM> conveys a recording medium. The conveyance unit <NUM> includes a feeding roller <NUM>, winding rollers <NUM> and <NUM>, and a conveyance belt <NUM>. The feeding roller <NUM> is a roller that feeds the recording medium. The winding rollers <NUM> and <NUM> are rollers for winding a recording medium. The conveyance belt <NUM> is stretched between the feeding roller <NUM> and the winding rollers <NUM> and <NUM>, and conveys the recording medium. The recording medium is conveyed on the conveyance belt <NUM> from the feeding roller <NUM> toward the winding rollers <NUM> and <NUM> along a conveyance direction DR indicated by an arrow in <FIG>.

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 <NUM> ejects ink onto the recording medium conveyed on the conveyance belt <NUM>. The image former <NUM> is of an aqueous inkjet type. The image former <NUM> includes a plurality of inkjet heads <NUM>. Each inkjet head <NUM> supplies ink of each color to the recording medium. For example, the inkjet head 31Y supplies yellow (Y) ink. The inkjet head <NUM> supplies magenta (M) ink. The inkjet head 31C supplies cyan (C) ink. The inkjet head <NUM> supplies black (K) ink. The ink ejected from each inkjet head <NUM> is applied to the recording medium to form an ink image on the recording medium.

The ink dryer <NUM> heats the recording medium to dry and fix the ink image on the recording medium. The ink dryer <NUM> 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 <NUM> 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.

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.

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.

Examples of the resin contained in the ink can include acrylic-based, styrene-acrylic-based, acrylonitrile-acrylic-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 <NUM> to <NUM>%, more preferably <NUM> to <NUM>% 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.

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 <NUM> mass% or more to <NUM> 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 <NUM> mass% or more to <NUM> mass% or less with respect to the total mass of the ink.

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.

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.

<FIG> is a schematic view illustrating a configuration of an inkjet head <NUM> illustrated in <FIG>. The inkjet head <NUM> of respective colors includes a plurality of heads. Although a first head <NUM>, a second head <NUM>, and a third head <NUM> are exemplarily illustrated in <FIG>, the inkjet head <NUM> may include four or more heads. The plurality of heads is disposed in a staggered manner. The inkjet head <NUM> includes a holding unit <NUM> that holds a plurality of heads. The holding unit <NUM> 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> is a vertical direction in <FIG>. 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>. In the conveyance direction DR, the first head <NUM> and the second head <NUM> are disposed on the downstream side, and the third head <NUM> is disposed on the upstream side. The first head <NUM> and the second head <NUM> are disposed side by side in the width direction. In the width direction, the third head <NUM> is disposed at a position between the first head <NUM> and the second head <NUM>. A part of the first head <NUM> and a part of the third head <NUM> overlap in the width direction. In the width direction, a part of the second head <NUM> and a part of the third head <NUM> overlap each other.

Each inkjet head <NUM> has a plurality of nozzles. A nozzle <NUM> illustrated in <FIG> schematically illustrates a plurality of nozzles of the first head <NUM> by a straight line. The nozzle <NUM> includes a plurality of nozzles disposed side by side in the width direction. A nozzle <NUM> illustrated in <FIG> schematically illustrates a plurality of nozzles of the second head <NUM> by a straight line. A nozzle <NUM> illustrated in <FIG> schematically illustrates a plurality of nozzles of the third head <NUM> by a straight line. Each of the nozzles <NUM> and <NUM> includes a plurality of nozzles disposed side by side in the width direction.

The inkjet head <NUM> further includes a plurality of temperature sensors <NUM> and <NUM>. The temperature sensors <NUM> and <NUM> are provided on the holding unit <NUM> and measure the temperature of the holding unit <NUM>. The temperature sensors <NUM> and <NUM> are an example of a temperature determination unit that determines the temperature of the holding unit <NUM>. The temperature sensors <NUM> and <NUM> are disposed apart from each other in the width direction. Each of the temperature sensors <NUM> and <NUM> is configured to measure the temperature of the holding unit <NUM> at different positions, and interpolate the temperature of the holding unit <NUM> at the position between the temperature sensors <NUM> and <NUM>, so that the temperature distribution of the holding unit <NUM> can be determined.

<FIG> is a diagram for explaining another example of the temperature determination unit. Although the first head <NUM> is representatively illustrated in <FIG>, other heads similar configurations. As described above, the nozzle <NUM> includes a plurality of nozzles disposed side by side in the width direction (in <FIG>, a horizontal direction in the drawing).

Each nozzle <NUM> 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 <NUM>.

Heat is generated every time the piezoelectric element 321P is driven. Every time the ink droplet D is ejected from the nozzle <NUM>, the piezoelectric element 321P corresponding to the nozzle <NUM> is driven to generate heat. In the nozzle <NUM> that continuously ejects the ink, the calorific value of the piezoelectric element 321P increases. The periphery of the nozzle <NUM> 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 <NUM>.

A controller which is not illustrated receives an input of an ink image formed on a recording medium by the image forming apparatus <NUM>. 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 <NUM> to rise. The controller can estimate the temperature rise of the holding unit <NUM> on the basis of the amount of ink ejected from each head. Therefore, the controller that controls the image forming apparatus <NUM> can have a function as the temperature determination unit that determines the temperature of the holding unit <NUM>.

<FIG> is a schematic diagram illustrating a state in which the holding unit <NUM> is thermally deformed. In the image forming apparatus <NUM>, the temperature of the holding unit <NUM> 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 <NUM> illustrated in <FIG> is increased in temperature as compared with the state in <FIG>, and thermally expanded as indicated by an oblique arrow in <FIG>.

A dashed line in <FIG> indicates the position of the head before the holding unit <NUM> illustrated in <FIG> is thermally deformed. The position of each head is changed by the thermal expansion of the holding unit <NUM>. The gap between the first head <NUM> and the second head <NUM> in the width direction increases. The gap between the first head <NUM> and the second head <NUM> and the third head <NUM> in the conveyance direction DR increases. The third head <NUM> is also displaced in the width direction. As the positions of the first head <NUM>, the second head <NUM>, and the third head <NUM> change, the positions of the nozzles <NUM>, <NUM>, and <NUM> also change. The positions of the nozzles <NUM>, <NUM>, and <NUM> change in both the conveyance direction DR and the width direction.

Although the thermally expanded holding unit <NUM> is illustrated in <FIG>, the holding unit <NUM> may be thermally contracted due to a change in environmental temperature, and even in this case, the positions of the first head <NUM>, the second head <NUM>, and the third head <NUM> change, and the positions of the nozzles <NUM>, <NUM>, and <NUM> also change.

The image forming apparatus <NUM> 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 <NUM>. 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 <NUM>.

<FIG> is a schematic diagram illustrating a first example of the adjustment unit. In the example illustrated in <FIG>, the first head <NUM> is representatively illustrated, and a mechanism that moves the first head <NUM> in the width direction is illustrated.

Specifically, a stepping motor <NUM> is attached to the holding unit <NUM>. An output shaft <NUM> of the stepping motor <NUM> is provided with a male screw <NUM>. An outer peripheral surface of the output shaft <NUM> may be threaded to form the male screw <NUM>, or the male screw <NUM> may be configured by fixing a male screw member to the output shaft <NUM>. A swing member <NUM> is engaged with and coupled to the male screw <NUM>. The swing member <NUM> is internally threaded. The output shaft <NUM> and the male screw <NUM> rotate relative to the holding unit <NUM> by driving of the stepping motor <NUM>. On the other hand, the swing member <NUM> is configured to be relatively non-rotatable with respect to the holding unit <NUM>.

A biasing spring <NUM> is disposed at a position facing the swing member <NUM> in the width direction. The biasing spring <NUM> is attached to a support plate <NUM>. The support plate <NUM> is fixed to the holding unit <NUM>. The biasing spring <NUM> is disposed to be stretchable in the width direction, and one end thereof is supported by the support plate <NUM>. The support plate <NUM> supports one end of the biasing spring <NUM> in a non-displaceable or substantially non-displaceable manner.

The first head <NUM> representatively illustrated in <FIG> is held between the swing member <NUM> and the biasing spring <NUM>. One end of the first head <NUM> extending in the width direction receives a biasing force in the width direction from the biasing spring <NUM>, and the other end of the first head <NUM> is pressed against the swing member <NUM>. The first head <NUM> is positioned in the width direction by the swing member <NUM> and the biasing spring <NUM>.

When the stepping motor <NUM> is driven, the male screw <NUM> rotates according to the rotation of the output shaft <NUM>. Since the swing member <NUM> does not rotate, the male screw <NUM> rotates relative to the internal thread formed in the swing member <NUM>. Consequently, stress in the width direction acts on the swing member <NUM>. By rotationally driving the stepping motor <NUM> in both directions, the swing member <NUM> can be reciprocated in the width direction. When the swing member <NUM> is moved in the direction of approaching the support plate <NUM>, the first head <NUM> pressed by the swing member <NUM> also moves in a direction of approaching the support plate <NUM>. When the swing member <NUM> is moved in a direction away from the support plate <NUM>, the first head <NUM> also moves in the direction away from the support plate <NUM> under the biasing force of the biasing spring <NUM>.

Referring also to <FIG>, the first head <NUM> displaced in the width direction by the thermal expansion of the holding unit <NUM> can be displaced in the width direction by driving the stepping motor <NUM>. By appropriately controlling the driving amount of the stepping motor <NUM> according to the temperature of the holding unit <NUM>, the first head <NUM> displaced in position illustrated in <FIG> can be displaced in the width direction to the original position illustrated in <FIG>.

In <FIG>, a mechanism for displacing the first head <NUM> in the width direction is illustrated, but a mechanism for displacing the first head <NUM> in the conveyance direction DR is also provided. By appropriately controlling the mechanisms, the first head <NUM> can be displaced in both the conveyance direction DR and the width direction to return the first head <NUM> to the position of <FIG>.

Similarly, the second head <NUM>, the third head <NUM>, 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 <NUM> by moving the head with the mechanism, all the heads can be disposed at the positions when the holding unit <NUM> illustrated in <FIG> is not thermally deformed. Even if the temperature of the holding unit <NUM> changes and the holding unit <NUM> is thermally deformed, the positional displacement amount of the head is predicted from the temperature of the holding unit <NUM>, 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 <NUM> is not thermally deformed. Thus, the ink can be supplied from each head to the target position, so that the image forming apparatus <NUM> can form a high-quality image.

<FIG> is a schematic diagram illustrating a second example of the adjustment unit. <FIG> illustrates a timing chart, and a horizontal axis indicates time. Time T01 indicates timing of ejecting the ink from the first head <NUM> and the second head <NUM> disposed on the downstream side in the conveyance direction DR in the inkjet head <NUM> before the thermal deformation illustrated in <FIG>. Time T02 indicates timing of ejecting the ink from the third head <NUM> disposed on the upstream side in the conveyance direction DR in the inkjet head <NUM> before the thermal deformation illustrated in <FIG>.

As illustrated in <FIG>, the positions of the nozzles <NUM>, <NUM>, and <NUM> in the conveyance direction DR are shifted due to the thermal expansion of the holding unit <NUM>. As the holding unit <NUM> is thermally expanded, the recording medium reaches the first head <NUM> and the second head <NUM> with a delay. The recording medium reaches the third head <NUM> earlier by the thermal expansion of the holding unit <NUM>.

Thus, the timing of ejecting the ink from the first head <NUM> and the second head <NUM> is set to time T1 later than time T01. The timing of ejecting the ink from the third head <NUM> 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 <NUM> 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 <NUM> can form a high-quality image.

<FIG> is a first schematic diagram illustrating a third example of the adjustment unit. In <FIG> and subsequent <FIG>, a first head <NUM> and a third head <NUM> among the plurality of heads of the inkjet head <NUM> are representatively illustrated. As described above, the nozzles <NUM> of the first head <NUM> include a plurality of nozzles disposed side by side in the width direction. The nozzle <NUM> of the third head <NUM> 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 <NUM> of the first head <NUM> includes idle nozzles <NUM> that do not eject ink indicated by white in the drawing, and operating nozzles <NUM> that eject ink indicated by hatching in the drawing. The nozzle <NUM> of the third head <NUM> includes idle nozzles <NUM> that do not eject ink indicated by white in the drawing, and operating nozzles <NUM> that eject ink indicated by hatching in the drawing.

A range in which the nozzle <NUM> of the first head <NUM> extends and a range in which the nozzle <NUM> of the third head <NUM> extends overlap each other in the width direction. More specifically, the operating nozzles <NUM> in the first head <NUM> and the idle nozzles <NUM> in the third head <NUM> overlap, and the operating nozzles <NUM> in the third head <NUM> and the idle nozzles <NUM> in the first head <NUM> overlap. The operating nozzles <NUM> in the first head <NUM> and the operating nozzles <NUM> in the third head <NUM> do not overlap.

The nozzle at the right end in the drawing among the operating nozzles <NUM> of the first head <NUM> and the nozzle at the left end in the drawing among the operating nozzles <NUM> of the third head <NUM> illustrated in <FIG> are adjacent to each other in the width direction. In the width direction, the idle nozzles <NUM> and <NUM> are not disposed between the nozzle at the right end of the operating nozzles <NUM> and the nozzle at the left end of the operating nozzles <NUM>. Thus, a desired image can be formed by ink ejection from the operating nozzles <NUM> and <NUM>.

<FIG> is a second schematic diagram illustrating a third example of the adjustment unit. <FIG> illustrates the thermally expanded holding unit <NUM> as indicated by an oblique arrow. As the holding unit <NUM> is thermally expanded, the positions of the first head <NUM> and the third head <NUM> are changed in the width direction. The overlap between the range in which the nozzle <NUM> extends and the range in which the nozzle <NUM> extends in the width direction is smaller. Specifically, in the example illustrated in <FIG>, six nozzles in the width direction are disposed in the range overlapping each other, whereas in <FIG>, two nozzles in the width direction are disposed in the range overlapping each other.

In the inkjet head <NUM> in which the holding unit <NUM> illustrated in <FIG> is thermally expanded, the positions of the nozzles that eject ink are changed. In the example illustrated in <FIG>, there are three idle nozzles <NUM> on each of the right and left sides of the operating nozzles <NUM>. There are three idle nozzles <NUM> on each of the right and left sides of the operating nozzles <NUM>. On the other hand, in <FIG>, one idle nozzle <NUM> is provided on the right side of the operating nozzles <NUM>, and five idle nozzles <NUM> are provided on the left side. There are five idle nozzles <NUM> on the right side of the operating nozzles <NUM> and one idle nozzle <NUM> on the left side.

As a result of changing the positions of the operating nozzles <NUM> and <NUM> that eject ink, the positions of the operating nozzles <NUM> and <NUM> are the same before the thermal deformation illustrated in <FIG> and after the thermal deformation illustrated in <FIG>.

<FIG> is a third schematic diagram illustrating a third example of the adjustment unit. <FIG> illustrates the holding unit <NUM> that is thermally contracted as indicated by oblique arrows. As the holding unit <NUM> thermally contracts, the positions of the first head <NUM> and the third head <NUM> are changed in the width direction. The overlap between the range in which the nozzle <NUM> extends and the range in which the nozzle <NUM> extends in the width direction is larger. Specifically, in the example illustrated in <FIG>, six nozzles in the width direction are disposed in the range overlapping each other, whereas in <FIG>, eight nozzles in the width direction are disposed in the range overlapping each other.

In the inkjet head <NUM> in which the holding unit <NUM> illustrated in <FIG> is thermally contracted, the positions of the nozzles that eject ink are changed. In <FIG>, four idle nozzles <NUM> are provided on the right side of the operating nozzles <NUM>, and two idle nozzles <NUM> are provided on the left side. There are two idle nozzles <NUM> on the right side of the operating nozzles <NUM> and four idle nozzles <NUM> on the left side.

By predicting the positional displacement amount of the head according to the temperature of the holding unit <NUM> 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 <NUM> can form a high-quality image.

Although there is a description partially overlapping with the above description, the characteristic configuration and operation and effect of the image forming apparatus <NUM> of the embodiment will be collectively described as follows.

As illustrated in <FIG>, the image forming apparatus <NUM> 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 <NUM>. Even if the temperature of the holding unit <NUM> changes and the position of the head changes due to thermal deformation of the holding unit <NUM>, the amount of change in the position of the head is predicted from the temperature of the holding unit <NUM>, 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 <NUM> can form a high-quality image.

As illustrated in <FIG>, the position of each head in the holding unit <NUM> may be changed according to the temperature of the holding unit <NUM>. 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 <FIG>, the nozzles that eject the ink in each head may be changed according to the temperature of the holding unit <NUM>. 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> in which the position of the head is changed, it is not necessary to provide the stepping motor <NUM> and the like, so that the position of the image can be adjusted with a simple configuration.

As illustrated in <FIG>, the timing of ejecting ink from each head to the recording medium may be changed according to the temperature of the holding unit <NUM>. 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> in which the position of the head is changed, it is not necessary to provide the stepping motor <NUM> and the like, so that the position of the image can be adjusted with a simple configuration.

As illustrated in <FIG>, the holding unit <NUM> may be provided with a plurality of temperature sensors <NUM> and <NUM> that measure the temperature of the holding unit <NUM>. In this manner, the temperature distribution of the holding unit <NUM> 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 <NUM>.

As illustrated in <FIG>, the temperature of the holding unit <NUM> may be estimated on the basis of the amount of ink ejected from each head. The temperature of the holding unit <NUM> can be estimated by processing of the controller that controls the image forming apparatus <NUM>, and thus the temperature of the holding unit <NUM> 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 <NUM>. 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 <NUM> for each head, and the ink can be accurately supplied from each head to the target position.

As illustrated in <FIG>, the inkjet head <NUM> may include inkjet heads 31Y, <NUM>, 31C, and <NUM> that eject inks of different colors. The adjustment of the position of the image according to the temperature of the holding unit <NUM> 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 <NUM> 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 <NUM> 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 <NUM> rises, thereby causing the holding unit <NUM> 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 <NUM> is applied to the image forming apparatus <NUM> using the aqueous ink having a large temperature change of the holding unit <NUM>, and thus the image forming apparatus <NUM> can form a high-quality image.

The image forming apparatus illustrated in <FIG> 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 <NUM> 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.

Claim 1:
An image forming apparatus (<NUM>), comprising:
a plurality of heads (<NUM>, <NUM>, and <NUM>) configured to eject ink onto an image forming body to form an image on the image forming body;
a holding unit (<NUM>) that holds the plurality of heads (<NUM>, <NUM>, and <NUM>);
a temperature determination unit configured to determine a temperature of the holding unit (<NUM>); and
an adjustment unit
characterised in that
the adjustment unit is configured to adjust a position of the image formed on the image forming body by the ink ejected from each of the heads (<NUM>, <NUM>, and <NUM>) according to a predicted amount of change in position of each of the heads (<NUM>, <NUM>, and <NUM>), that is due to thermal deformation of the holding unit (<NUM>) at the temperature of the holding unit (<NUM>) determined by the temperature determination unit.