Image forming apparatus and image forming method

An image forming apparatus superimposes a plurality of color images each formed of a single-color developer to form a superimposed color image. The image forming apparatus includes a transfer belt and processing circuitry. The processing circuitry forms, as a correction pattern, combination patterns arranged along a conveyance direction of the color images and including a first pattern, a second pattern, and a third pattern. A formation interval of the first pattern constituting one combination pattern is shorter than a formation interval between one horizontal line of the first pattern constituting the one combination pattern and another horizontal line of the first pattern constituting another combination pattern. The one horizontal line is opposite the other horizontal line.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2020-116364, filed on Jul. 6, 2020 in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

Technical Field

Embodiments of the present disclosure relate to an image forming apparatus and an image forming method.

Related Art

As an electrophotographic image forming apparatus, there is known a tandem-type electrophotographic image forming apparatus. A tandem-type color image forming apparatus forms electrostatic latent images on photoconductive members corresponding to a plurality of color developing materials (toners) of different colors by using an optical writing control technique, and causes the color developing materials of the different colors to adhere to the electrostatic latent images to develop the electrostatic latent image, thus forming the different color images. The different color images are transferred onto a transfer body so as to be superimposed one on top of another to form a color image.

If a superimposed position of each color image is deviated in a tandem type color image forming apparatus, color registration deviation occurs in a final color image. For this reason, in recent years in which high-resolution and high-quality image formation is required, there is a demand for highly accurately restraining a deviation in the superimposed position of each color image, in other words, “positional deviation”.

Although there are many causes of positional deviation, a main cause is a physical configuration that operates to execute an image forming process including a transfer process of each color image. In other words, it is considered that the positional deviation occurs due to the fluctuation of the operation of, e.g., an intermediate transfer belt that transfers and superimposes the respective color images, for example, the speed fluctuation of the rotational driving. When the image forming process including the transfer process is performed, a large number of endless rotating bodies are used. Examples of the endless rotating bodies include a photoconductive member, a charging roller that charges the photoconductive member, an intermediate transfer belt serving as a transfer member, a transfer roller that transfers a color image formed on the intermediate transfer belt to a recording medium, and gears used in a drive mechanism for rotating the foregoing members. If the rotation operations (rotation timing and rotation speed) of such a large number of endless rotating bodies are all in an ideally adjusted state and such an ideal state is maintained, it is considered that the occurrence of positional deviation can be restrained. However, actually, there is “fluctuation” in the rotation operation of each endless rotating body and the rotation speed periodically fluctuates. For this reason, on the premise of the occurrence of the positional deviation due to the speed fluctuations of the endless rotating bodies, a technology for reducing the positional deviation is needed.

Hence, for the purpose of reducing positional deviation, for example, a technology has been used in which an image forming process is executed to form a detection pattern including a specific image pattern on a transfer body, and the control of an operation of transferring an actual image of each color is corrected based on a result of detection of the detection pattern by a sensor. In such a case, a detection pattern is formed over the entire length of the intermediate transfer belt to cancel out the influence of periodic speed fluctuations, and the detection results are averaged to calculate a correction value. In other words, the correction value is calculated after all the detection patterns formed on the intermediate transfer belt whose longest length corresponds to one cycle are detected. Accordingly, it takes time to calculate the correction value, and there is a disadvantage in terms of efficiency in the control for restraining the positional deviation.

SUMMARY

In an aspect of the present disclosure, there is provided an image forming apparatus to superimpose a plurality of color images each formed of a single-color developer to form a superimposed color image. The image forming apparatus includes a transfer belt and processing circuitry. The processing circuitry forms a correction pattern on the transfer belt. The correction pattern is for calculating a correction value used for a correction operation of correcting a positional deviation of each of the plurality of color images occurring when the plurality of color images are superimposed one on top of another onto the transfer belt. The transfer belt is at least one of endless rotating bodies used to superimposing processing of the plurality of color images. The processing circuitry detects the correction pattern formed on the transfer belt and calculate the correction value based on a detection result of the correction pattern. The processing circuitry forms, as the correction pattern, a plurality of combination patterns arranged along a conveyance direction of the plurality of color images, the plurality of combination patterns including a first pattern, a second pattern, and a third pattern. The first pattern includes horizontal lines arranged along the conveyance direction and parallel to a direction orthogonal to the conveyance direction, the second pattern includes horizontal lines arranged along the conveyance direction and parallel to the direction orthogonal to the conveyance direction, and the third pattern includes diagonal lines arranged along the conveyance direction and inclined with respect to the conveyance direction and the direction orthogonal to the conveyance direction, the third pattern having a same color as the second pattern. In each combination pattern of the plurality of combination patterns, one of a horizontal line of the second pattern and a diagonal line of the third pattern is placed between horizontal lines of the first pattern spaced away from each other in the conveyance direction. The other one of the horizontal line of the second pattern and the diagonal line of the third pattern is not included in one combination pattern of the plurality of combination patterns formed on the transfer belt and another combination pattern of the plurality of combination patterns formed ahead of or behind the one combination pattern in the conveyance direction and is placed between the one combination pattern and said another combination pattern. A formation interval of the first pattern constituting the one combination pattern is shorter than a formation interval between one horizontal line of the first pattern constituting the one combination pattern and another horizontal line of the first pattern constituting said another combination pattern, the one horizontal line being opposite said another horizontal line.

DETAILED DESCRIPTION

Hereinafter, embodiments of an image forming apparatus and an image forming method according to an embodiment of the present disclosure are described with reference to drawings. As an embodiment according to the present disclosure, a description is given below of a “method of forming a detection pattern” used for correcting a positional deviation at the time of superimposing color images in an image forming apparatus that superimposes the color images to form a composite color image. The detection pattern is an image formed on a transfer body through an optical writing process and is used to calculate a correction value for correcting a writing position in the optical writing process according to a result of detecting the detection pattern with the sensor. In other words, the image forming apparatus according to an embodiment the present disclosure has a function of highly accurately calculating a correction value for effectively reducing a positional deviation, using a detection pattern formed by a characteristic method.

Here, the “method of forming the detection pattern” refers to the shape, arrangement, color, and their combination of elements constituting the detection pattern in the formation of the detection pattern. In other words, the detection pattern is formed by a combination of a plurality of image elements. Therefore, the formation of the detection pattern means that image elements having different shapes or colors are formed based on a specific arrangement manner so that a correction value for effectively reducing the positional deviation can be calculated with high accuracy.

Outline of Detection Pattern

First, a description is given of an outline of a detection pattern formed in an image forming apparatus according to an embodiment of the present disclosure.FIG. 17is an illustration of an example of components of a correction pattern500as a detection pattern according to the present embodiment. The correction pattern500is formed by a combination of a plurality of line images.

The correction pattern500includes a reference pattern511, a horizontal line pattern512, and a diagonal line pattern513. The reference pattern511is a first pattern formed of straight lines (or horizontal lines) of a reference color. The straight lines extend in a main scanning direction as a direction orthogonal to a sub-scanning direction as a conveyance direction of a recording medium and arranged along the sub-scanning direction. The horizontal line pattern512is a second pattern formed of a straight line extending in the main scanning direction and having a color to be corrected. The diagonal line pattern513is a third pattern formed of a straight line (diagonal line) inclined with respect to the main scanning direction (and the sub-scanning direction) and has a color to be corrected.

A first combination pattern521and a second combination pattern522are distinguished based on how the first pattern, the second pattern, and the third pattern are combined. In the first combination pattern521, two horizontal lines of the reference pattern511as the first pattern and a horizontal line of the horizontal line pattern512as the second pattern are arranged along the sub-scanning direction as the conveyance direction. The horizontal line of the horizontal line pattern512as the second pattern is disposed between the two horizontal lines of the reference pattern511to constitute a set of detection patterns. Similarly, in the second combination pattern522, two horizontal lines of the reference pattern511as the first pattern and a diagonal line of the diagonal line pattern513as the third pattern are arranged along the sub-scanning direction. The diagonal line of the diagonal line pattern513as the third pattern is disposed between the two reference patterns511to constitute a set of detection patterns. The sets of detection patterns are appropriately arranged and formed along the sub-scanning direction.

In any of the first combination pattern521and the second combination pattern522, two horizontal lines of the reference pattern511are used. The color of a color developer used for forming the reference pattern511is a color set as a reference color. The reference color is, for example, black. In other words, the plurality of reference patterns511used for the first combination pattern521and the second combination pattern522are all formed in, for example, “black”.

The color of the color developer used when forming the horizontal line pattern512included in the first combination pattern521and the diagonal line pattern513included in the second combination pattern522is a color to be corrected, in other words, a correction target color. In the present embodiment, the color to be corrected is any one of yellow (Y), magenta (M), cyan (C), and black (K) used as the color of the color developer as described later. For example, in the case of the correction pattern500used for calculating the correction value for reducing the positional deviation related to the magenta color, the correction pattern includes a first combination pattern521in which a horizontal line pattern512of the correction target color (magenta color) is arranged between two horizontal lines of a reference pattern511of the reference color (black) and a second combination pattern522in which a diagonal line pattern513of the correction target color (magenta color) is arranged between other two horizontal lines of the reference pattern511of the reference color (black). Note that the first combination pattern521is a pattern in which three straight lines extending in the main scanning direction are formed side by side along the sub-scanning direction, and has a shape similar to the Chinese numeral “three”, which may be referred to as a “three-parallel-line pattern”. The second combination pattern522is a pattern in which straight lines extending in the main scanning direction are arranged at intervals in the sub-scanning direction and a diagonal line is arranged between the two straight lines, and may be referred to as a “Z pattern” since the pattern has a shape similar to the Roman character “Z”.

In the following description of the present embodiment, the second combination pattern522may be simply referred to as “Z pattern”. The first combination pattern521may be referred to as “three-parallel-line pattern”.

The horizontal line pattern512and the diagonal line pattern513illustrated inFIG. 15are drawn by broken lines used to express magenta color in this embodiment. Note that the reference pattern511is formed of a reference color and black is used as the reference color in the present embodiment. However, the reference color is not limited to black and may be any other color. In this embodiment, black is drawn by a straight line.

In the image forming apparatus according to the present embodiment, the alignment process can be repeatedly executed. Therefore, when attention is focused on a detection pattern used when one cycle of the alignment process, that is, one correction operation is executed, the reference pattern511is formed in the same color (reference color). The horizontal line pattern512and the diagonal line pattern513arranged between the reference patterns511are formed in the same correction target color.

The “one round of alignment process” refers to a pattern detection process for calculating a correction value for correcting a positional deviation and a pattern forming process performed using the calculated correction value. The color of the reference pattern511is set to the same color in one round of alignment. Such a configuration allows the phase component of the deviation of the formation position of the reference pattern511to be uniformed by the fluctuation of the rotation speed of the endless rotating body. Uniformizing the phase component of the deviation can enhance the alignment accuracy.

If the reference patterns511of two or more colors are used, it would be necessary to provide a pattern interval when the colors of the reference patterns511are switched. However, when the reference patterns511of the same color are used, it is not necessary to provide such an interval. Thus, the length (total pattern length) of the correction pattern500formed by a set of the first combination pattern521and the second combination pattern522can be shortened.

Image Forming Apparatus According to Embodiment

A description is given below of an image forming apparatus including an optical writing device according to an embodiment of the present disclosure.FIG. 1is a perspective view of a multifunction peripheral (MFP) as an image forming apparatus according to an embodiment of the present disclosure. As illustrated inFIG. 1, an MFP100as the image forming apparatus according to the present embodiment includes an intermediate transfer belt105and image forming units106. The intermediate transfer belt105is one of endless rotating bodies and is a transfer body to which color images of black (K), cyan (C), magenta (M), and yellow (Y) are transferred. The image forming units106as image forming devices or image forming means corresponding to the respective colors are arranged along the intermediate transfer belt105. The MFP100illustrated inFIG. 1is referred to as a tandem type. The intermediate transfer belt105is a conveyor or conveying means of a recording medium on which an image is formed. The rotation direction of the intermediate transfer belt105is a conveyance direction of a correction pattern500formed on the intermediate transfer belt105.

The image forming unit106is an electrophotographic process unit and has a configuration used for forming an image of each color. For example, the image forming apparatus includes a yellow image forming unit106Y to form a yellow (Y) image, a magenta image forming unit106M to form a magenta (M) image, a cyan image forming unit106C to form a cyan (C) image, and a black image forming unit106K to form a black (K) image. Hereinafter, these units are collectively referred to as image forming units106. The image forming units106are disposed along a rotation direction of rotation of the intermediate transfer belt105, in other words, a conveyance direction of a transferred image. The image forming unit106is different only in the color of a color developer (or toner) used for developing an electrostatic latent image, and has the same internal configuration.

Hereinafter, the yellow image forming unit106Y is described in detail. However, each component corresponding to any other color may be simply indicated by reference numerals distinguished by M, C, and K instead of Y attached to each component of the yellow image forming unit106Y in drawings.

The intermediate transfer belt105is an intermediate transfer unit or intermediate transfer means, and is an endless belt member, that is, an endless rotating body, stretched between a driving roller108and a driven roller107. Color images are transferred from the image forming units106onto the intermediate transfer belt105to form a full-color image. The driving roller108is rotationally driven by, e.g., a driving motor and a driving gear. The driven roller107is rotated by the intermediate transfer belt105rotated by the driving force of the driving roller108. The driving roller108, a driving motor that drives the driving roller108, and the driven roller107that rotates according to the driving of the driving roller108function as a driving device or driving means that rotates the intermediate transfer belt105.

A transfer roller119is disposed at a position opposite the driving roller108across the intermediate transfer belt105. The transfer roller119constitutes a secondary transfer device that applies pressure to press a sheet104, that is a recording medium, against the intermediate transfer belt105. The sheet104supplied from a sheet feed tray101is pressed against the intermediate transfer belt105by the pressure from the transfer roller119and conveyed, and the color image formed on the intermediate transfer belt105is transferred to the sheet104.

The yellow image forming unit106Y includes, for example, a photoconductive drum109Y serving as an image bearer, a charging roller110Y serving as a charging roller disposed around the photoconductive drum109Y, an optical writing control device111, a developing device112Y, a photoconductive drum cleaner, and a static eliminator113Y. The optical writing control device111irradiates the photoconductive drums109Y,109M,109C, and109K, which may be hereinafter collectively referred to as “photoconductive drums109”, corresponding to the respective colors with light.

Upon image formation, the outer peripheral surface of the photoconductive drum109Y is uniformly charged by the charging roller110Y in the dark, and writing is performed by light from a light source corresponding to a yellow image from the optical writing control device111. Thus, an electrostatic latent image are formed on the photoconductive drum109Y. The developing device112Y develops the electrostatic latent images into a visible image with yellow toner. Thus, a yellow toner image is formed on the photoconductive drum109Y.

The toner image is transferred to the intermediate transfer belt105by the action of the transfer device115Y at a position (transfer position) at which the photoconductive drum109Y and the intermediate transfer belt105are in contact with or closest to each other. Accordingly, the yellow toner image is transferred onto the intermediate transfer belt105. After the transfer of the toner image is completed, unnecessary toner remaining on the outer peripheral surface of the photoconductive drum109Y is wiped off by the photoconductive drum cleaner, and then the photoconductive drum109Y is destaticized by the static eliminator113Y to wait for the next image formation.

As described above, the yellow toner image is transferred onto the intermediate transfer belt105by the yellow image forming unit106Y and conveyed to the next magenta image forming unit106M by the roller drive of the intermediate transfer belt105. This conveyance direction is the sub-scanning direction. The width direction (depth direction inFIG. 1) of the intermediate transfer belt105orthogonal to the sub-scanning direction is the main scanning direction. In the magenta image forming unit106M, a magenta toner image is formed on the photoconductive drum109M by the same process as the image forming process in the yellow image forming unit106Y. The magenta toner image is transferred so as to be superimposed on the yellow toner image that has already been formed and transferred.

The toner images, in which the yellow toner image and the magenta toner image are transferred to the intermediate transfer belt105and superimposed one on another, are further conveyed to the cyan image forming unit106C and the black image forming unit106K. According to similar operations, the cyan toner image formed on the photoconductive drum109C and the black toner image formed on the photoconductive drum109K are superimposed on the already transferred toner images (in other words, the toner images in which yellow and magenta are superimposed). Thus, a color intermediate transfer image is formed on the intermediate transfer belt105.

The sheets104stored in the sheet feed tray101are fed in order from the uppermost sheet, stopped once by a registration roller pair103, and fed to a transfer position of the intermediate transfer image from the intermediate transfer belt105according to the timing of image formation in the image forming units106. The intermediate transfer image formed on the intermediate transfer belt105is transferred to the sheet104at a position where the conveyance path is in contact with or closest to the intermediate transfer belt105, thus forming a color image. The sheet104on which the image is formed is further conveyed, and after the image is fixed by the fixing device116, the sheet is ejected to the outside of the MFP100.

In the MFP100having the above-described configuration, the toner images of the respective colors, which are to be originally overlapped, do not overlap one on top of another, and positional deviation (color-registration-deviation) may occur between the respective colors due to, for example, an error in the distances between the axes of the photoconductive drums109Y,109M,109C, and109K, an error in the parallelism of the photoconductive drums109Y,109M,109C, and109K, an error in the installation of light emitting diode arrays (LEDA)130in the optical writing control device111, and an error in the timing of writing electrostatic latent images on the photoconductive drums109Y,109M,109C, and109K. Accordingly, due to the influence of the fluctuation in the rotation speed of the endless rotating member in the MFP100, the positional deviation of the superimposed position of the toner images may occur, and the color-registration deviation of the image formed on the recording medium may occur.

The MFP100includes pattern detection sensors117to detect a correction pattern500formed for correcting positional deviation. The pattern detection sensors117are, for example, optical sensors (TM sensors) using reflection of light. The pattern detection sensors117are sensors that read the correction pattern500transferred as a toner image onto the intermediate transfer belt105by the photoconductive drums109Y,109M,109C, and109K. Each of the pattern detection sensors117includes a light emitting element and a light receiving element. The light emitting element emits light to illuminate the correction pattern500drawn on the surface of the intermediate transfer belt105. The light receiving element receives reflected light from the correction pattern500. As illustrated inFIG. 1, the pattern detection sensors117are disposed downstream from the photoconductive drums109Y,109M,109C, and109K in the conveyance direction of the sheet104. The plurality of pattern detection sensors117are supported on the same board along a direction (so-called main scanning direction) orthogonal to the conveyance direction in which the sheet104is conveyed by the intermediate transfer belt105.

When the light emitted from the light emitting element is reflected by the surface of the intermediate transfer belt105, the light is received by the light receiving element and output as an output voltage in the pattern detection sensor117. The output voltage is higher than an output voltage based on the light reflected by the correction pattern500. Detecting the output voltages of the pattern detection sensors117allows detection of the formation position of the correction pattern500formed on the intermediate transfer belt105. On the other hand, the formation position of the correction pattern500on the intermediate transfer belt105can be specified based on the formation timing of the toner image in the optical writing control device111. Accordingly, comparing the detection result of the correction pattern500by the pattern detection sensors117with the formation position of the correction pattern500with respect to the intermediate transfer belt105allows the “positional deviation amount” to be calculated when the toner image of each color (each color image) is deviated from the ideal position. Based on the positional deviation amount, a correction value for correcting an operation of forming each color image in the optical writing control device111can be calculated in order to restrain the positional deviation. The correction operation of calculating a correction value and performing correction is performed at a predetermined timing. Details of the pattern detection sensors117and an aspect of positional-deviation correction are described later. Note that the MFP100includes a configuration for achieving information processing function such as a central processing unit (CPU)10described later, and operates under the control of such a configuration.

The MFP100includes a belt cleaner118to remove the toner of the correction pattern500drawn by the toner image transferred to the intermediate transfer belt105so that the sheet104conveyed by the intermediate transfer belt105is not contaminated with the toner. As illustrated inFIG. 1, the belt cleaner118is disposed downstream from the driving roller108and upstream from the photoconductive drums109in the conveyance direction of the sheet. The belt cleaner118is a cleaning blade pressed against the intermediate transfer belt105. The belt cleaner118is a developer remover that scrapes off the toner adhering to the surface of the intermediate transfer belt105.

Outline of Optical Writing Device

The optical writing control device111mounted on the MFP100according to the present embodiment is described below.FIG. 2is a diagram illustrating the relative positions between the optical writing control device111and the photoconductive drums109according to the present embodiment. As illustrated inFIG. 2, the irradiation light irradiated to each of the photoconductive drums109Y,109M,109C, and109K of the respective colors is irradiated from each of the LEDA130Y,130M,130C, and130K (hereinafter, collectively referred to as LEDA130) as light sources. In the optical writing control device111according to the present embodiment, a laser diode (LD) may be used as the light source. Accordingly, the type of the configuration used as the light source is not limited as long as the light source can cope with the optical writing control according to the present embodiment. In the LEDA130, light emitting diodes (LEDs) as light emitting elements are arranged in the main scanning direction of each of the photoconductive drums109. The controller included in the optical writing control device111controls the on/off state of each of the LEDs arranged in the main scanning direction for each main scanning line based on drawing data input from a controller20described later. Thus, the controller in the optical writing control device111selectively exposed the surfaces of the photoconductive drums109to form electrostatic latent images.

Hardware Configuration of Image Forming Apparatus

A hardware configuration constituting a control system of an image forming apparatus including an optical writing device according to an embodiment of the present disclosure is described below with reference toFIG. 3. The control system of the MFP100according to the present embodiment includes an image processing engine13that executes image formation in addition to a configuration similar to the configuration of a personal computer (PC) that is an information processing apparatus. For example, the MFP100according to the present embodiment includes a CPU10, a random access memory (RAM)11, a read only memory (ROM)12, an image processing engine13, a hard disk drive (HDD)14, and an interface (I/F)15that are connected via a system bus18. A liquid crystal display (LCD)16, an operation unit17, and a pattern detection sensor117are connected to the I/F15.

The CPU10is control means or processing circuitry and controls the operation of the entire MFP100. The RAM11is a volatile storage medium that allows reading and writing of data at a high speed and is used as a working area when the CPU10processes data. The ROM12is a non-volatile read only storage medium and stores programs such as firmware. The image processing engine13includes components that operate to actually perform image formation in the MFP100.

The HDD14is a nonvolatile storage medium that allows reading and writing of data, and stores, for example, an operating system (OS), various control programs, and application programs. The I/F15connects the system bus18to various hardware components or networks for control. The LCD16is a visual user interface for a user to confirm the state of the MFP100. The operation unit17is a user interface such as a keyboard or a mouse used by the user to input information to the MFP100.

In such a hardware configuration, the CPU10reads out a program stored in a recording medium such as the ROM12or the HDD14to the RAM11and performs an operation according to the program, thus configuring a software controller. A combination of the software controller configured as described above and hardware constitutes functional blocks that implement the functions of the MFP100according to the present embodiment. Note that the hardware configuration illustrated inFIG. 3is an example, and the hardware configuration of the MFP100according to the present embodiment is not limited to the configuration ofFIG. 3as long as the configuration of the hardware is capable of achieving the functional configuration described below.

Functional Configuration of Image Forming Apparatus

The functional configuration of the MFP100according to the present embodiment is described with reference toFIG. 4.FIG. 4is a block diagram illustrating a functional configuration of the MFP100according to the present embodiment. The MFP100includes a controller20, an auto document feeder (ADF)21, a scanner unit22, a sheet ejection tray23, a display panel24, a sheet feed table25, a printing engine26, a sheet ejection tray27, and a network I/F28.

The controller20includes a main control unit30, an engine control unit31, an input-and-output control unit32, an image processing unit33, and an operation display control unit34. The MFP100according to the present embodiment is a multifunction peripheral including the scanner unit22and the printing engine26. InFIG. 4, electrical connections are indicated by solid arrows, and the flow of a recording medium is indicated by broken arrows.

The display panel24is an output interface that visually displays the state of the MFP100and is also an input interface (operation unit) used as a touch panel when the user directly operates the MFP100or inputs information to the MFP100. The network I/F28is an interface for the MFP100to communicate with other devices via a network. For example, an Ethernet (registered trademark) or universal serial bus (USB) interface is used as the network I/F28.

The controller20is configured by a combination of software and hardware. For example, control programs stored in the ROM12, a non-volatile memory, and the HDD14are loaded onto a volatile memory (hereinafter referred to as a memory) such as the RAM11. The controller20is configured by a software controller implemented by computation of the CPU10according to the control programs and hardware such as integrated circuits. The controller20functions as a controller that controls the entire MFP100.

The main control unit30controls units included in the controller20and gives an instruction to each unit of the controller20. The engine control unit31serves as a driver hat controls or drives, for example, the printing engine26and the scanner unit22. The input-and-output control unit32inputs signals and commands input via the network I/F28to the main control unit30. The main control unit30controls the input-and-output control unit32to access other devices via the network I/F28.

The image processing unit33generates drawing data based on print data included in an input print job under the control of the main control unit30. The drawing data is data for drawing an image to be formed by the printing engine26serving as an image forming unit in an image forming operation. The print data included in the print job is image data converted in a format recognizable by the MFP100. The conversion of the image data is performed by, for example, a printer driver installed in an information processing apparatus such as a PC. The operation display control unit34displays information on the display panel24or notifies the main control unit30of data input via the display panel24.

When the MFP100operates as a printer, the input-and-output control unit32receives a print job via the network I/F28. The input-and-output control unit32transfers the received print job to the main control unit30. Upon receiving the print job, the main control unit30causes the image processing unit33to generate drawing data according to print data included in the print job.

When the drawing data is generated by the image processing unit33, the engine control unit31controls the printing engine26according to the generated drawing data and executes image formation on the recording medium conveyed from a sheet feed table25. In other words, the printing engine26serves as an image forming unit. The recording medium on which an image has been formed by the printing engine26is ejected to the sheet ejection tray27.

The image data generated by the image processing unit33is stored in, e.g., the HDD14as it is in accordance with an instruction of the user, or is transmitted to an external device via the input-and-output control unit32and the network I/F28. In other words, the ADF21and the engine control unit31serve as an image input unit.

When the MFP100operates as a copier, the image processing unit33generates drawing data according to the image data received by the engine control unit31from the scanner unit22or the image data generated by the image processing unit33. As in the case of the printer operation, the engine control unit31drives the printing engine26according to the drawing data.

Control Blocks of Optical Writing Device Control blocks of the optical writing control device111according to the present embodiment are described with reference toFIG. 5.FIG. 5is a diagram illustrating a functional configuration of the optical writing controller120that controls the optical writing control device111according to the present embodiment and the relations of the optical writing controller120with the LEDA130and the pattern detection sensor117.

As illustrated inFIG. 5, the optical writing controller120according to the present embodiment includes a light-emission control unit121, a counter122, a sensor control unit123, a correction-value calculation unit124, a reference-value storage unit125, and a correction-value storage unit126. The optical writing controller120functions as an optical writing control device that controls LEDAs130serving as light sources to form electrostatic latent images on the photoconductive drums.

Similarly to the controller20in the MFP100, the optical writing controller120is configured by loading a control program stored in the ROM12or the HDD14into the RAM11and operating according to arithmetic processing in the CPU10.

The light-emission control unit121is a light source control unit that controls the LEDAs130according to image data input from the engine control unit31of the controller20. In other words, the light-emission control unit121also functions as a pixel data acquisition unit. The light-emission control unit121causes the LEDAs130to emit light in a certain line cycle to achieve optical writing onto the photoconductive drums109.

The line cycle at which the light-emission control unit121controls the light emission of the LEDAs130is determined by the output resolution of the image forming apparatus.

However, as described above, in a case where the magnification is changed in the sub-scanning direction according to the ratio to the conveyance speed of a sheet, the light-emission control unit121adjusts the line cycle to change the magnification in the sub-scanning direction.

In addition to driving the LEDAs130according to the drawing data input from the engine control unit31, the light-emission control unit121controls light emission of the LEDAs130to draw the correction pattern500in the above-described drawing parameter correction processing.

As described inFIG. 2, the plurality of LEDAs130are provided corresponding to the respective colors. Accordingly, as illustrated inFIG. 5, a plurality of light-emission control units121are provided so as to correspond to the respective LEDAs130. In the drawing parameter correction processing, the correction value generated as a result of the positional-deviation correction processing as the positional-deviation correction operation is stored as a color positional-deviation correction value in the correction-value storage unit126illustrated inFIG. 5.

The light-emission control unit121corrects the timing of driving the LEDAs130according to the past color-registration-deviation correction values stored in the correction-value storage unit126. To correct the position of an image in the main scanning direction, when the light-emission control unit121causes the LEDA130to emit light based on the image data for each main scanning line, the light-emission control unit121adjusts the correspondence between each pixel data constituting the image data for one line and each LED element included in the LEDA130based on the color-registration-deviation correction values stored in the correction-value storage unit126.

The correction of the driving timing of the LEDA130by the light-emission control unit121is implemented by delaying the timing of the light emission driving of the LEDA130in the unit of line cycle based on the drawing data input from the engine control unit31, in other words, by shifting the line. On the other hand, since the drawing data is sequentially input from the engine control unit31in accordance with a predetermined cycle, the input drawing data are held and the reading timing is delayed to shift the line and delay the light emission timing

Accordingly, the light-emission control unit121has a line memory that is a storage medium to hold the drawing data input for each main scanning line. The light-emission control unit121stores the drawing data in the line memory to hold the drawing data input from the engine control unit31. As the correction of the drive timing of the LEDA130, fine adjustment of the light emission timing for each line cycle is performed in addition to the adjustment for each line cycle. The light-emission control unit121constitutes a pattern forming unit or pattern forming means.

In the color-registration-deviation correction processing, the counter122starts counting at the same time when the light-emission control unit121controls the LEDA130to start exposure of the photoconductive drum109K. The counter122acquires a detection signal output when the sensor control unit123detects the correction pattern500based on the output signal of the pattern detection sensor117. In other words, the counter122executes interrupt control based on the operation clock of the CPU10and acquires a detection signal (output voltage of the pattern detection sensor117) from the sensor control unit123. The counter122inputs the count value at the timing when the correction-value calculation unit124acquires the detection signal. In other words, the counter122functions as a detection timing acquisition unit that acquires the detection timing of the correction pattern500.

The sensor control unit123is a control unit that controls the pattern detection sensors117. As described above, based on the output signal of the pattern detection sensor117, the sensor control unit123determines that the positional-deviation correction pattern formed on the intermediate transfer belt105has reached the positions of the pattern detection sensors117, and outputs a detection signal. In other words, the sensor control unit123as a pattern detection unit or pattern detection means also functions as a detection signal acquisition unit that acquires pattern detection signals from the pattern detection sensors117.

In the density correction using the density correction pattern, the sensor control unit123acquires the signal intensities of the output signals of the pattern detection sensors117and inputs the signal intensities to the correction-value calculation unit124. The sensor control unit123adjusts the detection timing of the density correction pattern according to the detection result of the correction pattern500. The sensor control unit123constitutes a combination pattern detection unit or combination pattern detection means.

The correction-value calculation unit124calculates a correction value based on the reference value for positional-deviation correction and the reference value for density correction stored in the reference-value storage unit125, according to the count value acquired from the counter122and the signal intensities of the detection result of the density correction pattern acquired from the sensor control unit123. In other words, the correction-value calculation unit124functions as a reference-value acquisition unit and a correction-value calculation unit. The reference-value storage unit125stores a reference value used for such calculation. The correction value is calculated based on the “deviation direction” and the “deviation amount” of the positional-deviation correction pattern. The correction-value calculation unit124constitutes a correction value calculator or correction-value calculation means.

Brief Description of Periodic Speed Variation

A description is given below of an example of a cause of occurrence of a periodic rotational speed fluctuation due to an endless component, that is a problem to be solved, in an image forming apparatus according to an embodiment of the present disclosure. InFIG. 6, the intermediate transfer belt105is illustrated as an endless component (endless rotating body). However, the cause of the rotational speed fluctuation to be a problem is not limited to the intermediate transfer belt105. For example, in other components such as the photoconductive drums109, the rotational speed fluctuation is also a cause of the periodic speed fluctuation of the rotating body.

As illustrated inFIG. 6A, for example, assume that a part of the intermediate transfer belt105is cut and extended. Since the intermediate transfer belt105is made of a resin material (e.g., thermoplastic elastomers (TPE)), as illustrated inFIG. 6B, the surface of the intermediate transfer belt105is “twisted” or “curled”, and the intermediate transfer belt105is not flat over the entire length thereof. Accordingly, even when the intermediate transfer belt105is simply rotated as an endless rotating body, a uniform rotational speed is not obtained. If each color image is transferred to the surface of the intermediate transfer belt105whose rotation speed is not uniform, the intermediate transfer belt105returns to the same position as the transfer position before one rotation, when the intermediate transfer belt105makes one rotation. However, a positional deviation occurs at any local position while the intermediate transfer belt105makes one rotation. At such a local position, the current transfer position is different from the transfer position before one rotation. In other words, during one rotation of the intermediate transfer belt105, a “periodical positional deviation” locally occurs in which the current transfer position is different from the transfer position in the previous rotation.

FIG. 7is a graph illustrating the fluctuation of the rotation speed of the intermediate transfer belt105(the conveyance speed of the toner image) over the entire circumference of the intermediate transfer belt105. The origin of the graph ofFIG. 7is assumed to be an ideal rotation speed (target value V). To make the description easy to understand, the rotation speed of the intermediate transfer belt105varies so as to draw a sine curve with one cycle being the circumferential length of the intermediate transfer belt105. Since the intermediate transfer belt105continues to rotate in the image forming process, similar speed fluctuations occur repeatedly. Hereinafter, when referring to the fluctuation of the rotation speed, in particular, the fluctuation of the rotation speed around the intermediate transfer belt105by one circumference is referred to as “primary speed fluctuation”.

The following description focuses on the intermediate transfer belt105among the components (endless rotating bodies) that cause periodic speed fluctuations. Note that the intermediate transfer belt105may be replaced with another endless rotating member that is a power transmitter or power transmission means such as the photoconductive drum109, the transfer roller119, the driving roller108, the driven roller107, the charging roller, or a driving gear thereof.

First Comparative Example for Correction Pattern500

Here, a description is given of one of comparative examples for the correction pattern500before describing the outline of the positional-deviation correction operation according to the present embodiment. This example is a first comparative example.FIG. 8illustrates a comparative pattern400as a comparative example of detection pattern. Since the structure for detecting the pattern is also similar for the correction pattern500according to the present embodiment, the pattern detection operation is exemplified while describing the first comparative example. The comparative pattern400is a pattern image drawn on the intermediate transfer belt105by the LEDAs130controlled by the light-emission control unit121. For example, various pattern images are arranged in the sub-scanning direction to form an alignment pattern array401. In addition, a plurality of alignment pattern arrays401are arranged in the main scanning direction.

The comparative pattern400is constituted by line patterns corresponding to the respective colors. In the present specification, in expressing the difference in color between the line patterns, the dotted line indicates an image drawn by the photoconductive drum109Y. A solid line indicates an image drawn by the photoconductive drum109K. A broken line indicates an image drawn by the photoconductive drum109C. An alternate long and short dash line indicates an image drawn by the photoconductive drum109M. In other words, the dotted line indicates “yellow”, the solid line indicates “black”, the broken line indicates “cyan”, and the alternate long and short dash line indicates “magenta”.

The alignment pattern array401is drawn at a position passing through the detection range of each pattern detection sensor element170. When the line images constituting the alignment pattern array401enters the detection range of the pattern detection sensor element170, the output voltage of the pattern detection sensor element170drops. When the line pattern passes through the detection range, the output voltage of the pattern detection sensor element170rises. Based on the output voltage, the sensor control unit123acquires a detection signal output by detecting the positional-deviation correction pattern, and inputs a count value at the timing when the counter122acquires the detection signal, to the correction-value calculation unit124.

Thus, the optical writing controller120can detect the image constituting the detection pattern at a plurality of positions in the main scanning direction, and can correct the skew of the drawn image. Averaging the detection results based on the plurality of pattern detection sensor elements170allows the correction accuracy to be enhanced.

As illustrated inFIG. 8, the entire-position correction pattern411includes lines drawn by the photoconductive drum109Y and parallel to the main scanning direction. The entire-position correction pattern411includes a pattern drawn to obtain a count value for correcting the deviation of the entire image in the sub-scanning direction, in other words, the transfer position of the image to the sheet. The entire-position correction pattern411is also used for correcting detection timing when the sensor control unit123detects the drum-interval correction pattern412or a density correction pattern to be described later.

In the entire-position correction using the entire-position correction pattern411, the optical writing controller120performs the correction operation of the writing start timing based on the read signal of the entire-position correction pattern411by the pattern detection sensor117.

The drum-interval correction pattern412is a pattern that is drawn to obtain a count value for correcting a deviation in drawing timing on the photoconductive drums109of the respective colors, in other words, a superimposed position at which images of the respective colors are superimposed. As illustrated inFIG. 8, the drum-interval correction pattern412includes a horizontal line pattern413and a diagonal line pattern414. As illustrated inFIG. 8, in the drum-interval correction pattern412, horizontal line patterns413of the respective colors constituted by a set of four linear images in a direction orthogonal to the conveyance direction and diagonal line patterns414of the respective colors constituted by a set of four linear patterns inclined at a predetermined angle with respect to the conveyance direction are alternately repeated. A total of eight linear images of the four horizontal line patterns413and the four diagonal line patterns414are used as a set for calculating the correction value.

The optical writing controller120corrects the positional deviation in the sub-scanning direction of the writing start position with respect to each of the photoconductive drums109Y,109K,109M, and109C, based on the read signals of the horizontal line patterns413by the pattern detection sensors117. On the other hand, in the positional-deviation correction operation, the optical writing controller120corrects the positional deviation in the main scanning direction of the writing start position with respect to each of the photoconductive drums109Y,109K,109M, and109C based on the read signals of the diagonal line patterns414. The process of calculating the correction value for detecting the horizontal line images and correcting the deviation (registration deviation) of the writing start position in the sub-scanning direction and the process of calculating the correction value for detecting the diagonal line images and correcting the deviation (registration deviation) of the writing start position in the main scanning direction are also common to the present embodiment.

Second Comparative Example of Correction Pattern500

A description is given below of another comparative example with respect to the correction pattern500according to the present embodiment. The second comparative example is an example of one that has already been studied and filed by the applicant of the present application. In the second comparative example, the positional deviation is corrected by using the first combination pattern521and the second combination pattern522as detection patterns.FIGS. 9 and 10are diagrams illustrating a method of forming detection patterns according to the second comparative example.FIG. 11is a diagram illustrating detection patterns according to the second comparative example and an effect of canceling out the influence of the speed fluctuation by the detection patterns.

In the second comparative example, when one period of the speed fluctuation is divided by n, the interval until the same reference line is formed again is set to τ times, and the magnification parameter τ is used for the interval of the line pattern repeatedly formed.

As illustrated inFIG. 11, any of the variation of the formation position of the “Z pattern” and the “three-parallel-line pattern” and the periodic speed fluctuation in the second comparative example can also be expressed by a sine function with respect to the deviation of the formation positions of the detection patterns. The intensity component and the phase component are parameters of each order and are expressed as the total sum of the periodic deviations of the formation positions up to the first order, the second order, the third order, . . . , and the infinite order.

In the second comparative example, when attention is paid to a certain set of detection patterns, a “first calculation formula” can be considered in which a positional-deviation correction value is calculated using a reference line (similar to the reference pattern511) of a detection pattern formed before the set of detection patterns and a line (horizontal line or diagonal line) of a correction target color. In addition, a “second calculation formula” can be considered for calculating a positional-deviation correction value using a reference line (similar to the reference pattern511) of a detection pattern formed after the set of detection patterns of interest and a line (horizontal line or diagonal line) of the correction target color. Averaging the positional-deviation correction values calculated by the above-described two calculation formulas, a final positional-deviation correction value can be calculated. Performing the above-described calculation processes can “approximately” cancel the periodic deviation of the formation position occurring in one Z pattern (or three-parallel-line pattern). Accordingly, the positional deviation can be corrected without forming line patterns (corresponding to the correction pattern500) over the entire circumference of the intermediate transfer belt105.

Here, a description is given of the difference between the first comparative example and the second comparative example. The comparative second example is different from the first comparative example in that the effect is exhibited even if respective line patterns are not formed at the positions obtained by “dividing by an integer” the circumferential length of the intermediate transfer belt105. In other words, the effect can be exhibited even when respective line patterns are formed at the positions obtained by “dividing by a real number” the circumferential length of the intermediate transfer belt105. Accordingly, even if periodic deviations in the formation position occur at the same time due to a plurality of endless rotating bodies such as the photoconductive drum109and the transfer roller119, the second comparative example can effectively restrain the influence of the periodic deviations in the formation position in each line pattern when calculating the positional-deviation correction value.

In the first comparative example and the second comparative example described above, it is assumed that the speed fluctuation of the intermediate transfer belt105occurs in the same manner in a constant cycle. However, in the case of an endless rotating body such as the intermediate transfer belt105, in particular, in the case of a structure to which tension is applied when the endless rotating body rotates, the endless rotating body may expand and contract during the rotation. As illustrated inFIG. 12, the speed fluctuation occurring in a constant cycle may be irregular. For example, a driving gear for drive transmission is easily affected by minute speed fluctuations, and a speed fluctuation exceeding an assumed range may occur. If the influence of such an irregular speed fluctuation is not restrained, in particular, the positional alignment accuracy at the time of superimposing a plurality of color images is greatly affected. Accordingly, the correction accuracy of the writing start position deviation (registration deviation) may be deteriorated.

In the case of the second comparative example, the influence of the speed fluctuation between the colors generated in the endless rotating body is more complicated as the formation of the detection patterns is more distant. For example, a case of a correction pattern500formed with a magnification parameter τ of “2” as illustrated inFIG. 13is described below as an example. In such a case, the first combination pattern521and the second combination pattern522are formed at positions apart from each other by the number k of repeated formation. Accordingly, the first combination pattern521for correcting the positional deviation in the sub-scanning direction and the second combination pattern522for correcting the positional deviation in the main scanning direction are formed at positions where the running stability of the intermediate transfer belt105is greatly different. In addition, positional deviation components in the sub-scanning direction between the reference pattern511included in the pair of detection patterns and the diagonal line pattern513(magenta) as the pattern of the correction target color are not appropriately cancelled.

Accordingly, also in the second comparative example, it is difficult to improve the correction accuracy if deviations (registration deviations) in the main scanning direction and the sub-scanning direction are attempted to be simultaneously corrected.

Correction Pattern500According to First Embodiment

Based on the above situation, a method of forming the correction pattern500in the MFP100according to the present embodiment is described in detail.FIG. 14illustrates the correction pattern500according to an embodiment of the present disclosure.

As illustrated inFIG. 14, the correction pattern500according to the present embodiment is formed by alternately repeating a first combination pattern521and a second combination pattern522in the sub-scanning direction. In the correction pattern500according to the present embodiment, the formation interval of two horizontal lines of the reference pattern511constituting the first combination pattern521is different from the formation interval of two horizontal lines of the reference pattern511constituting the second combination pattern522. In other words, the formation interval of two horizontal lines of the reference pattern511constituting the first combination pattern521is shorter than the formation interval of two horizontal lines of the reference pattern511constituting the second combination pattern522. In any of the combination patterns, the sensor control unit123serving as a pattern detection unit or pattern detection means uses the reference pattern511as a reference position of the correction pattern500.

When the correction pattern500according to the present embodiment is formed in an ideal state in which the positional deviation of each color image due to the speed fluctuation of the endless rotating body does not occur (is absent), the formation position of the horizontal line pattern512or the diagonal line pattern513formed between two adjacent combination patterns is the center position of the two combination patterns in the conveyance direction. In other words, when the correction pattern500according to the present embodiment is formed in an ideal state in which the positional deviation of each color image due to the speed fluctuation of the endless rotating body does not occur (is absent), the formation interval of the combination patterns that are repeatedly formed becomes a constant interval.

As described in the description of the second comparative example, as the formation positions of the detection patterns are apart from each other (as the formation interval is increased), the influence of the speed fluctuation between colors is more complicated. Accordingly, it is advantageous that the formation positions of the detection patterns are closer to each other. Therefore, when the correction pattern500according to the present embodiment is formed, the magnitude of the “magnification parameter T” described in the second comparative example can be set to be small in the first combination pattern521and the second combination pattern522at the same time. Such a configuration can reduce the influence of speed fluctuation occurring between colors.

InFIG. 14, two horizontal lines of the reference pattern511and a horizontal line of the horizontal line pattern512drawn in a correction target color between the two horizontal lines of the reference pattern511constitute one set to form the first combination pattern521. A diagonal line of the diagonal line pattern513drawn with the correction target color is formed at a position interposed between the first combination patterns521repeatedly formed. Alternatively, two horizontal lines of the reference pattern511and a diagonal line of the diagonal line pattern513drawn with the correction target color between two horizontal lines of the reference pattern511may form a second combination pattern522as a set. A horizontal line of the horizontal line pattern512drawn with the correction target color may be formed at a position interposed between the second combination patterns522repeatedly formed.

AlthoughFIG. 14illustrates an example of forming the correction pattern500in which the correction target color is magenta, the correction target color may be replaced with yellow (Y) or cyan (C). In the present embodiment, black (K) is described as the reference color. However, a color other than black (K) may be used as the reference color. When the diagonal line pattern513is repeatedly formed to form the correction pattern500, the degree of inclination and the direction of inclination may not be the same but may be different.

Correction Pattern500According to Second Embodiment

Next, a description is given below of a method of forming a correction pattern500in the MFP100according to a second embodiment of the present disclosure. One advantage of the MFP100according to the present embodiment is that a writing start position deviation (registration deviation) can be corrected with high accuracy by one correction operation. Hence, as illustrated inFIG. 15, a description is given of a case where the correction pattern500is not formed of a single color but is formed while setting each color in turn as a correction target color. As illustrated inFIG. 15, forming the correction pattern500using each color as a correction target color allows efficient calculation of a correction value capable of correcting the writing start position deviation (registration deviation) of each color with high accuracy by one correction operation. Such a configuration can effectively restrain the positional deviation of each color image and exhibit high positioning accuracy by one correction operation.

Shortening the total length of the correction pattern500can reduce the downtime of the image forming process due to the process for reducing the positional deviation. Therefore, as illustrated inFIG. 15, the correction target color is set in accordance with the arrangement of the image forming stations of the respective colors from the upstream side in the rotation direction of the intermediate transfer belt105, thus allowing the downtime to be most effectively reduced.

Correction Pattern500According to Third Embodiment

A description is given below of a method of forming the correction pattern500in the MFP100according to a third embodiment of the present disclosure. A first advantage of the MFP100according to the present embodiment is that the writing start position deviation (registration deviation) can be corrected with high accuracy by one correction operation.

Therefore, as described in the second embodiment, it is more advantageous to form the correction pattern500not in a single color but sequentially using each color in turn as a correction target color.

In such a case, particularly in a configuration in which the pattern lengths (intervals between reference colors) of the three-parallel-line pattern and the Z pattern are different from each other when the detection patterns are sequentially formed, the restriction on the position at which the diagonal line pattern of the necessary reference color (Bk) is inserted is strict. Therefore, as illustrated inFIG. 16, after the correction pattern500corresponding to a certain correction target color is drawn on the intermediate transfer belt105, the black diagonal line pattern514as the reference color may be arranged before the correction pattern500corresponding to the next correction target color is drawn. Thus, the entire length of the correction pattern500can be further shortened.

In the third embodiment, the shape of the combination pattern for correcting the positional deviation is limited to the shape of the first combination pattern521. If the shape of the combination pattern is the shape of the second combination pattern522, the horizontal line pattern512is inserted while the correction target color is switched. Accordingly, there is no room for inserting the diagonal line pattern of the reference color (Bk).

Image Forming Method According to Embodiment

As an image forming method according to an embodiment of the present disclosure, a flow of an alignment process using the correction pattern500according to the present embodiment is described with reference to a flowchart ofFIG. 18.FIG. 18illustrates a flow of processing for forming a plurality of sets of correction patterns (correction patterns500) on the intermediate transfer belt105, detecting the correction patterns500with the pattern detection sensors117, and controlling the formation positions of the correction patterns500by the correction values calculated based on the detection results, in order to execute positional-deviation correction. Therefore, the processing flow illustrated inFIG. 18exemplifies the formation processing of the correction pattern (correction pattern500) formed when the alignment process is executed once (during the color matching operation).

First, calibration processing is executed so that the pattern detection sensors117can normally detect line patterns constituting the correction pattern500(step S1801). If the pattern detection sensors117are optical sensors, processing for adjusting the amount of irradiation, the gain of a detection signal, or the like is executed.

Next, it is determined whether the calibration process in step S1801has been normally executed (step S1802). When the calibration process of the pattern detection sensors117cannot be normally executed (NO in step S1802), the process is interrupted and abnormality is notified with an alert notification device or alert notification means provided in the MFP100(step S1806).

When the calibration process of the pattern detection sensors117is normally performed (YES in step S1802), a process of forming the correction pattern500is performed (step S1803). In this process, a detection pattern generation function provided by a dedicated application-specific integrated circuit (ASIC) that controls the operation of the optical writing control device111is used. Alternatively, image data for a detection pattern may be prepared in advance and used to form a detection pattern. The image data for the detection pattern is image data corresponding to the Z pattern and the three-parallel-line pattern constituting the correction pattern500.

Subsequently, the pattern detection sensors117detect the correction pattern500and notifies the correction-value calculating unit124of the calculation result via the sensor control unit123(step S1804).

Subsequently, the correction-value calculating unit124calculates the positional-deviation correction amount based on the detection results from the pattern detection sensors117and stores the calculated positional-deviation correction value in the correction-value storage unit126(step S1805). The MFP100including the optical writing control device111adjusts the image forming position using the positional-deviation correction values stored in the correction-value storage unit126when executing the image forming process.

The calibration process (step S1801) of the pattern detection sensor117may be periodically performed, and may not be performed every time the alignment process is performed. In such a case, when the calibration process (step S1801) is not performed, the process may be started from the pattern forming process (step S1803).

As described above, the correction pattern500is formed, the pattern detection sensors117perform pattern detection processing on the correction pattern500, and the correction-value calculation unit124is notified of the calculation result via the sensor control unit123. Subsequently, the correction-value calculation unit124calculates a positional-deviation correction amount based on the detection result from the pattern detection sensors117and stores the calculated positional-deviation correction value in the correction-value storage unit126. The MFP100including the optical writing control device111adjusts the image forming position using the positional-deviation correction values stored in the correction-value storage unit126when the image forming process is executed. Accordingly, the positional deviation of each color image can be accurately restrained by the correction pattern500formed at one time when the alignment process is executed once, in other words in one cycle of the correction operation.

Embodiments of the present disclosure are not limited to the above-described embodiments, and various modifications can be made without departing from the technical scope of the present disclosure. While the above-described embodiments illustrate examples, a person skilled in the art can realize various modifications from the disclosed content. Such modifications are also included in the technical scope of the present disclosure.