Image density determination method, and image forming apparatus

Abstract

To determine the density of an image formed on a surface of a belt member without being affected by the eccentricity of a rotation shaft of a roller that supports the belt member.SOLUTION: A processor 80 acquires a plurality of belt detection densities obtained by a density sensor 6 in correspondence with a plurality of rotation positions of a specific roller 52b in a situation where an image is not formed on a belt member 51. The processor 80 specifies, from the plurality of belt detection densities, a plurality of singular densities falling outside a reference range. The processor 80 determines whether a plurality of singular positions corresponding to the plurality of singular densities, of the plurality of rotation positions, have periodicity corresponding to the rotation of the specific roller 52b. When the plurality of singular positions are determined to have the periodicity, the processor 80 compares each of the plurality of belt detection densities with a representative value of the plurality of belt detection densities to derive a plurality of density correction values corresponding to the plurality of rotation positions.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image density determining method and an image forming apparatus for determining image density based on the detection result of a density sensor disposed opposite to the surface of a rotating belt member. [Background technology]

[0002] An electrophotographic image forming apparatus includes an image forming section, a transfer device, and a fixing device. The image forming apparatus forms an image on a surface of an image carrier. The transfer device transfers the image on the surface of the image carrier to a sheet. The fixing device fixes the image to the sheet.

[0003] The transfer device may include a belt rotating mechanism, a primary transfer unit, and a secondary transfer unit. The belt rotating mechanism includes a belt member that is supported and rotated by a plurality of support rollers.

[0004] The primary transfer section transfers the image on the surface of the image carrier onto the surface of the belt member, and the secondary transfer section transfers the image on the surface of the belt member onto the sheet.

[0005] It is also known that the image forming apparatus includes an image sensor that reads the image formed on the surface of the belt member (see, for example, Patent Document 1). For example, the image density detected by the image sensor is used to adjust parameters for image output. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2007-187700 A Summary of the Invention [Problem to be solved by the invention]

[0007] Incidentally, there are cases where the rotation axis of a roller supporting a portion of the belt member facing the density sensor is eccentric, in which case the distance between the density sensor and the belt member varies with the rotation of the roller.

[0008] If the distance between the density sensor and the belt member varies, the density detected by the density sensor may vary regardless of the image density.

[0009] An object of the present invention is to provide an image density determination method and an image forming apparatus that can determine the density of an image formed on the surface of a belt member without being affected by the eccentricity of the rotation axis of a roller that supports the belt member. [Means for solving the problem]

[0010] An image density determination method according to one aspect of the present invention is a method for determining image density based on a detection result of the density sensor in an apparatus including a belt rotation mechanism and a density sensor. The belt rotation mechanism has a plurality of support rollers and a belt member supported by the plurality of support rollers and rotating in conjunction with the rotation of one of the plurality of support rollers. The density sensor is disposed opposite to a detection position that is a position of a surface of a portion of the belt member supported by a specific roller that is one of the plurality of support rollers, and detects the density of an image formed on the surface of the belt member. The image density determination method includes a processor acquiring a plurality of belt detection densities obtained by the density sensor corresponding to a plurality of rotation positions of the specific roller during a preparation period that exceeds a period during which the specific roller makes one rotation under a condition in which no image is formed on the belt member. The image density determination method further includes a process in which the processor executes a process of identifying a plurality of specific densities that fall outside a preset reference range from among the plurality of belt detection densities. The image density determination method further includes, when the plurality of peculiar densities are identified, determining whether or not a plurality of peculiar positions among the plurality of rotational positions corresponding to the plurality of peculiar densities have periodicity corresponding to the rotation of the specific roller. The image density determination method further includes, when the plurality of peculiar positions are determined to have periodicity, deriving a plurality of density correction values ​​corresponding to the plurality of rotational positions by comparing each of the plurality of belt detection densities with a representative value of the plurality of belt detection densities. The image density determination method further includes, when the plurality of peculiar positions are determined to have periodicity, obtaining a plurality of target detection densities obtained by the density sensor corresponding to the plurality of rotational positions under a condition in which an image is formed on the belt member. The image density determination method further includes, when the plurality of peculiar densities are identified, determining an image density based on the plurality of target detection densities after correction.

[0011] An image forming apparatus according to another aspect of the present invention includes an image carrier, a transfer device, and the processor that realizes the image density determination method. The image carrier is a member on whose surface an image is formed. The transfer device transfers the image formed on the surface of the image carrier to a sheet. The transfer device includes the multiple support rollers, the belt member, a primary transfer unit, a secondary transfer unit, and the density sensor. The primary transfer unit transfers the image formed on the surface of the image carrier to the surface of the belt member. The secondary transfer unit transfers the image transferred to the surface of the belt member to the sheet. Effect of the Invention

[0012] According to the present invention, it is possible to provide an image density determination method and an image forming apparatus that can determine the density of an image formed on the surface of a belt member without being affected by the eccentricity of the rotation axis of the roller that supports the belt member. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing the configuration of an image forming apparatus according to an embodiment. [Diagram 2] FIG. 2 is a block diagram showing the configuration of a control device in the image forming apparatus according to the embodiment. [Diagram 3] FIG. 3 is a diagram showing the configuration of the density sensor and its surroundings in the image forming apparatus according to the embodiment. [Figure 4] FIG. 4 is a flowchart showing an example of a procedure of the density adjustment process in the image forming apparatus according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the following embodiment is an example of the present invention, and is not intended to limit the technical scope of the present invention.

[0015] The image forming apparatus 10 according to the embodiment executes printing processing by electrophotography. For example, the image forming apparatus 10 is a printer, a copier, a facsimile machine, a multifunction machine, or the like.

[0016] [Configuration of image forming apparatus 10] 1, the image forming apparatus 10 includes a sheet transport device 3, a printing device 4, and a control device 8, which are provided in a main body 1. The image forming apparatus 10 further includes a user interface device 800.

[0017] The printing device 4 executes the printing process by electrophotography. The printing process is a process of forming an image on a sheet 9. The sheet 9 is an image forming medium such as paper or a sheet-like resin member.

[0018] The sheet transport device 3 includes a sheet sending device 30 and a plurality of transport roller pairs 31. The sheet sending device 30 sends out the sheet 9 stored in the sheet storage unit 2 to a transport path 300 in the main body 1. The transport path 300 forms a passage along which the sheet 9 is transported.

[0019] The plurality of transport roller pairs 31 are driven to rotate by a motor (not shown). The plurality of transport roller pairs 31 rotate to transport the sheet 9 along the transport path 300, and then discharge the sheet 9 onto the discharge tray 101.

[0020] The sheet 9 passes through a transfer position P1 and a fixing position P2 on the conveying path 300, and is discharged onto a discharge tray 101. The fixing position P2 is a position downstream of the transfer position P1 in the sheet conveying direction.

[0021] The printing device 4 forms a toner image on the sheet 9 transported along the transport path 300. The toner image is an image using toner as a developer. The toner is an example of the granular developer.

[0022] The printing device 4 includes one or more image forming units 4x, an optical scanning device 40, a transfer device 44, and a fixing device 46. The image forming unit 4x includes a drum-shaped photoconductor 41, a charging device 42, a developing device 43, a drum cleaning device 45, and the like.

[0023] 1 is a tandem color image forming apparatus, and the printing device 4 includes four image forming units 4x corresponding to the toners of the four colors, yellow, cyan, magenta, and black.

[0024] In the image forming unit 4x, the photoconductor 41 rotates, and the charging device 42 charges the surface of the photoconductor 41. Furthermore, the optical scanning device 40 writes an electrostatic latent image on the surface of the photoconductor 41 by scanning with a laser beam. The optical scanning device 40 is an example of an exposure device that forms the electrostatic latent image on the surface of the photoconductor 41 by exposing the surface of the photoconductor 41 to light.

[0025] Furthermore, the developing device 43 develops the electrostatic latent image into the toner image by supplying the toner to the surface of the photoconductor 41. The photoconductor 41 is an example of an image carrier on whose surface the toner image is formed.

[0026] The transfer device 44 transfers the toner image on the surface of the photoreceptor 41 onto a sheet 9. The transfer device 44 includes a belt rotating mechanism 5, four primary transfer units 441 corresponding to the four image forming units 4x, a secondary transfer unit 442, and a belt cleaning device 443.

[0027] The belt rotating mechanism 5 includes an intermediate transfer belt 51, a plurality of support rollers 52, and a driving mechanism 53. The intermediate transfer belt 51 is an endless belt member.

[0028] The intermediate transfer belt 51 is supported by a plurality of support rollers 52. One of the plurality of support rollers 52 is a drive roller 52a that is driven to rotate by a drive mechanism 53. The intermediate transfer belt 51 rotates in conjunction with the rotation of the drive roller 52a.

[0029] The primary transfer unit 441 transfers the toner image on the surface of the photoconductor 41 onto the surface of the intermediate transfer belt 51. As a result, a color toner image is formed on the surface of the intermediate transfer belt 51. For example, the primary transfer unit 441 includes a primary transfer roller to which a transfer voltage is applied.

[0030] The secondary transfer unit 442 transfers the toner image formed on the intermediate transfer belt 51 onto the sheet 9 at a transfer position P1 on the transport path 300. For example, the secondary transfer unit 442 includes a secondary transfer roller to which a transfer voltage is applied.

[0031] The drum cleaning device 45 removes the waste toner remaining on the surface of the photoconductor 41. The belt cleaning device 443 removes the waste toner remaining on the intermediate transfer belt 51.

[0032] The fixing device 46 applies heat and pressure to the toner image on the sheet 9 while transporting the sheet 9 at a fixing position P2 on the transport path 300. In this way, the fixing device 46 fixes the toner image on the sheet 9 to the sheet 9.

[0033] The user interface device 800 includes an operation unit that accepts user operations and a display unit that displays information. The control device 8 executes various data processing and controls various electric devices included in the image forming apparatus .

[0034] The control device 8 includes a central processing unit (CPU) 80, a random access memory (RAM) 81, a secondary storage device 82, a communication device 83, and a signal interface 84 (see FIG. 2).

[0035] The CPU 80 executes various control and data processing operations by executing computer programs. The RAM 81 temporarily stores the computer programs executed by the CPU 80 and various data.

[0036] The secondary storage device 82 is a computer-readable non-volatile storage device. The secondary storage device 82 stores the computer programs executed by the CPU 80 and various data. For example, one or both of a flash memory and a hard disk drive are adopted as the secondary storage device 82.

[0037] The communication device 83 executes communication with other devices such as a host device through a network. The CPU 80 executes communication with other devices through the communication device 83. The host device is an information processing device that requests the image forming apparatus 10 to perform a print process.

[0038] The signal interface 84 converts the detection signals of the various sensors into digital detection data. The detection data is transmitted to the CPU 80.

[0039] The CPU 80 includes a plurality of processing modules that are realized by executing the computer programs, including a main control unit 8a and a print control unit 8b (see FIG. 2).

[0040] The main control unit 8a executes a process of receiving various requests and a control for causing other modules to execute processes according to the requests.

[0041] For example, the main control unit 8a accepts a print request through the user interface device 800 or the communication device 83. Furthermore, the main control unit 8a causes the print control unit 8b to execute a process corresponding to the print request.

[0042] The print control unit 8b controls the sheet transport device 3 to control the supply and transport of the sheet 9. Furthermore, the print control unit 8b causes the printing device 4 to execute the print process in synchronization with the transport of the sheet 9.

[0043] The image forming apparatus 10 includes a density sensor 6 that detects the density of an image formed on the surface of the intermediate transfer belt 51. The image density detected by the density sensor 6 is used for adjusting parameters for image output, and the like.

[0044] The density sensor 6 is disposed to face a detection position P3 which is a portion of the surface of the intermediate transfer belt 51. The detection position P3 is a position of the surface of a portion of the intermediate transfer belt 51 which is supported by a specific roller 52b which is one of the multiple support rollers 52.

[0045] That is, the specific roller 52 b supports the portion of the intermediate transfer belt 51 that faces the density sensor 6 .

[0046] The concentration sensor 6 includes a light emitting unit 6a, a lens 6b, and a photoelectric conversion element 6c (see FIG. 3). The light emitting unit 6a emits light onto the surface of the intermediate transfer belt 51. The lens 6b collects the light reflected by the surface of the intermediate transfer belt 51 onto the light receiving unit of the photoelectric conversion element 6c.

[0047] The photoelectric conversion element 6c detects the amount of light reflected from the surface of the intermediate transfer belt 51, and outputs a detection signal. The detection signal is a signal that represents the image density.

[0048] The multiple support rollers 52 include a drive roller 52a, an opposing roller 52c that faces the secondary transfer unit 442, and multiple other tension rollers.

[0049] In this embodiment, the specific roller 52b is one of the plurality of tension rollers. The drive roller 52a may be the specific roller 52b.

[0050] The transfer device 44 further includes a support frame 54 that supports a rotation shaft 52x of the specific roller 52b and the density sensor 6 (see FIG. 3).

[0051] That is, the support frame 54 that supports the rotation shaft 52x also supports the concentration sensor 6. The support frame 54 is an example of a support member that supports the rotation shaft 52x and the concentration sensor 6.

[0052] Incidentally, there are cases where the rotation axis 52x of the specific roller 52b is eccentric. In such cases, the distance between the density sensor 6 and the intermediate transfer belt 51 varies in accordance with the rotation of the specific roller 52b.

[0053] If the distance between the density sensor 6 and the intermediate transfer belt 51 varies, the density detected by the density sensor 6 may vary regardless of the image density.

[0054] In this embodiment, the plurality of processing modules of the CPU 80 further includes a density adjustment unit 8c. The density adjustment unit 8c executes a density adjustment process, which will be described later. The density adjustment process includes a process for determining the density of the image formed on the surface of the intermediate transfer belt 51 without being affected by the eccentricity of the rotation shaft 52x of the specific roller 52b.

[0055] The belt rotation mechanism 5 further includes a rotary encoder 55 (see FIG. 3). The rotary encoder 55 detects the rotational position of the specific roller 52b.

[0056] The rotary encoder 55 outputs a pulse signal each time the specific roller 52b rotates by a predetermined unit angle. The concentration adjusting unit 8c counts the pulse signals and identifies the rotational position of the specific roller 52b according to the count value.

[0057] [Density adjustment processing] An example of the procedure of the density adjustment process will be described below with reference to the flowchart shown in FIG.

[0058] For example, when the main control unit 8a receives an adjustment execution request through the user interface device 800 or the communication device 83, it causes the concentration adjustment unit 8c to execute the concentration adjustment process.

[0059] The density adjustment process includes a process of determining the density of the image formed on the intermediate transfer belt 51 based on the detection result of the density sensor 6 (steps S1 to S9).

[0060] The density adjustment process is an example of a process for realizing an image density determination method. The CPU 80 including the density adjustment unit 8c is an example of a processor for realizing an image density determination method.

[0061] In the density adjustment process, step S1 is executed first. In the following description, S1, S2, ... represent identification codes of a plurality of steps in the density adjustment process.

[0062] <Process S1> In step S1, the density adjusting unit 8c acquires a plurality of belt detection densities obtained by the density sensor 6 during a preparatory period in which the specific roller 52b makes N rotations, where N is an integer of 1 or more.

[0063] The plurality of belt detection densities are a plurality of detection densities obtained by the density sensor 6 corresponding to a plurality of rotation positions of the specific roller 52b during the preparation period in a state where no image is formed on the intermediate transfer belt 51.

[0064] The plurality of belt detection densities are respectively associated with a plurality of rotation positions detected by the rotary encoder 55. The density adjusting unit 8c performs the process of step S1 and then performs the process of step S2.

[0065] <Process S2> In step S2, the density adjusting section 8c executes a peculiar density identifying process based on the plurality of belt detection densities obtained in step S1.

[0066] The peculiar concentration identifying process is a process for identifying a plurality of peculiar concentrations that are out of a predetermined reference range from among the plurality of belt detection densities. When the plurality of peculiar concentrations are identified, a plurality of peculiar positions corresponding to the plurality of peculiar concentrations from among the plurality of rotational positions are also identified.

[0067] The plurality of specific concentrations includes one or both of one or more low specific concentrations and one or more high specific concentrations, the low specific concentrations being concentrations below the reference range and the high specific concentrations being concentrations above the reference range.

[0068] The plurality of specific locations includes one or both of one or more low specific locations corresponding to the low specific concentration and one or more high specific locations corresponding to the high specific concentration.

[0069] When the rotation shaft 52x of the specific roller 52b is eccentric, the distance between the surface of the intermediate transfer belt 51 and the density sensor 6 varies. When the surface of the intermediate transfer belt 51 is closer to the density sensor 6 than the allowable distance range, the high specific density is identified. When the surface of the intermediate transfer belt 51 is farther from the density sensor 6 than the allowable distance range, the low specific density is identified.

[0070] The concentration adjustment unit 8c executes the process of step S3 when the plurality of peculiar concentrations are identified, and executes the process of step S6 when the plurality of peculiar concentrations are not identified.

[0071] <Process S3> In step S3, the concentration adjusting unit 8c judges whether or not the plurality of specific positions have a periodicity corresponding to the rotation of the specific roller 52b.

[0072] For example, when one or more low specific concentrations and one or more high specific concentrations are identified, the concentration adjustment unit 8c determines that the multiple specific concentrations have periodicity when a first periodicity condition is satisfied.

[0073] The first periodicity condition is a condition that the difference between the low singular position and the high singular position is equivalent to half a rotation of the specific roller 52b within a predetermined approximation range.

[0074] Furthermore, in a case where a plurality of low specific concentrations are identified, the concentration adjustment unit 8c determines that the plurality of low specific concentrations have periodicity when a second periodicity condition is satisfied.

[0075] The second periodicity condition is a condition that the plurality of low singular positions are equivalent rotational positions within a predetermined approximation range.

[0076] Furthermore, in a case where a plurality of high specific concentrations are identified, the concentration adjustment unit 8c determines that the plurality of high specific concentrations have periodicity when a third periodicity condition is satisfied.

[0077] The third periodicity condition is a condition that the multiple highly singular positions are equivalent rotational positions within a predetermined approximation range.

[0078] The density adjuster 8c executes the process of step S4 when it determines that the plurality of peculiar positions does not have periodicity, whereas the density adjuster 8c executes the process of step S5 when it determines that the plurality of peculiar positions has periodicity.

[0079] <Process S4> In step S4, the density adjusting unit 8c specifies each of the plurality of peculiar positions as an invalid position. As will be described later, the invalid position is a rotational position that is excluded from the target of the image density determination.

[0080] After performing the process of step S4, the concentration adjusting unit 8c performs the process of step S6.

[0081] <Process S5> In step S5, the density adjusting section 8c derives a plurality of density correction values ​​corresponding to the plurality of rotation positions by comparing each of the plurality of belt detection densities with a representative value of the plurality of belt detection densities.

[0082] For example, the density adjustment unit 8c derives the differences between each of the plurality of belt detection densities and the average value of the plurality of belt detection densities as the plurality of density correction values. The plurality of density correction values ​​may be derived according to a ratio between each of the plurality of belt detection densities and a representative value of the plurality of belt detection densities.

[0083] By the process of step S5, the plurality of density correction values ​​corresponding to the plurality of rotation positions of one rotation of the specific roller 52b are obtained. After performing the process of step S5, the density adjusting unit 8c performs the process of step S6.

[0084] <Process S6> In step S6, the density adjusting unit 8c causes the printing device 4 to execute a process of forming a test image. As a result, the test image is formed on the surface of the intermediate transfer belt 51. For example, the test image is a solid patch image.

[0085] In the process of forming the test image, a process of transferring the test image from the intermediate transfer belt 51 to the sheet 9 is not performed. As a result, the test image is removed from the surface of the intermediate transfer belt 51 by the belt cleaning device 443.

[0086] After performing the process of step S6, the concentration adjusting unit 8c performs the process of step S7.

[0087] <Process S7> In step S7, the density adjustment unit 8c obtains a plurality of test detection densities obtained by the density sensor 6 corresponding to the plurality of rotational positions when the test image passes through the detection position P3.

[0088] The plurality of test detection densities are a plurality of detection densities obtained by the density sensor 6 corresponding to a plurality of rotation positions of the specific roller 52b under a condition in which the test image is formed on the intermediate transfer belt 51.

[0089] The plurality of test detection densities are an example of a plurality of target detection densities used in determining the image density. After performing the process of step S7, the density adjusting section 8c performs the process of step S8.

[0090] <Process S8> In step S8, the density adjustment unit 8c corrects the test detection densities by the density correction values ​​according to the rotation positions. The process of step S8 is executed when the density correction values ​​are derived in step S5.

[0091] For example, the plurality of density correction values ​​may be values ​​obtained by subtracting the average value of the plurality of belt detection densities from each of the plurality of belt detection densities. In this case, the density adjustment unit 8c corrects each of the plurality of test detection densities by subtracting each of the plurality of corresponding density correction values ​​from each of the plurality of test detection densities.

[0092] After performing the process of step S8, the concentration adjusting unit 8c performs the process of step S9. If the process of step S5 has not been performed, the concentration adjusting unit 8c skips the process of step S8 and performs the process of step S9.

[0093] <Process S9> In step S9, the density adjusting section 8c determines the image density based on the plurality of test detection densities after correction. In this embodiment, the image density is the density of the test image.

[0094] For example, the density adjusting unit 8c derives, as the image density, a representative value of the test detection densities corresponding to a period during which the test image passes through the detection position P3. The representative value is, for example, an average value.

[0095] However, if the processes in steps S5 and S8 are not performed, the density adjusting section 8c determines the image density based on the plurality of test detection densities that have not been corrected.

[0096] In addition, when the invalid position is identified in step S4, the density adjustment unit 8c judges the image density based on the detection densities corresponding to the positions other than the invalid position among the plurality of test detection densities. That is, the detection densities corresponding to the invalid position among the plurality of test detection densities are excluded from the target of the image density judgment.

[0097] After performing the process of step S9, the concentration adjusting unit 8c performs the process of step S10.

[0098] <Process S10> In step S10, the density adjusting section 8c judges whether the image density obtained in step S9 is outside a preset target range or not.

[0099] The density adjusting unit 8c executes the process of step S11 when it determines that the image density is outside the target range, whereas the density adjusting unit 8c ends the density adjustment process when it determines that the image density is not outside the target range.

[0100] <Process S11> In step S11, the density adjusting section 8c corrects a control parameter relating to the density of the output image.

[0101] For example, the density adjusting unit 8c corrects the control parameters according to the difference between the image density and the target range. For example, the control parameters include parameters for setting the charging bias of the charging device 42 or the developing bias of the developing device 43.

[0102] After executing the process of step S11, the concentration adjusting section 8c ends the concentration adjustment process.

[0103] In the density adjustment process, steps S1 to S8 are performed, so that the influence of the eccentricity of the rotation shaft 52x of the specific roller 52b is removed in the plurality of test detection densities after correction.

[0104] Therefore, by performing the density adjustment process, it is possible to determine the density of the image formed on the surface of the intermediate transfer belt 51 without being affected by the eccentricity of the rotation shaft 52x of the specific roller 52b.

[0105] [Application example] The concentration adjusting unit 8c may specify the plurality of rotation positions of the specific roller 52b by measuring the elapsed time from a predetermined starting point when the specific roller 52b rotates at a constant speed.

[0106] In the example shown in FIG. 1, the state in which the specific roller 52b rotates at a constant speed is the state in which the rotating body of the drive mechanism 52a rotates at a constant speed. [Explanation of symbols]

[0107] 3: Sheet transport device 4: Printing device 4x: Image forming section 5: Belt rotation mechanism 6: Concentration sensor 8: Control device 10: Image forming device 40: Optical scanning device 41: Photoconductor (image carrier) 42: Charging device 43: Developing device 44: Transcription device 46: Fixing device 51: Intermediate transfer belt (belt member) 52: Support roller 52b: Specific roller 52x: Axis of a specific roller 53: Driving mechanism 54: Support frame 55: Rotary Encoder 80: CPU (processor)

Claims

1. a belt rotation mechanism including a plurality of support rollers and a belt member supported by the plurality of support rollers and rotating in conjunction with rotation of one of the plurality of support rollers; a density sensor disposed opposite a detection position that is a position on a surface of a portion of the belt member that is supported by a specific roller that is one of the plurality of support rollers, and that detects a density of an image formed on the surface of the belt member, the density sensor detecting the density of the image based on a detection result of the density sensor in an apparatus comprising the steps of: a processor acquires a plurality of belt detection densities obtained by the density sensor corresponding to a plurality of rotation positions of the specific roller during a preparation period that exceeds a period during which the specific roller makes one rotation under a condition in which no image is formed on the belt member; The processor executes a process of identifying a plurality of specific densities that are out of a preset reference range from among the plurality of belt detection densities; When the plurality of specific concentrations are identified, the processor determines whether a plurality of specific positions among the plurality of rotation positions corresponding to the plurality of specific concentrations have a periodicity corresponding to the rotation of the specific roller or not; when it is determined that the plurality of peculiar positions have periodicity, the processor derives a plurality of density correction values ​​corresponding to the plurality of rotational positions by comparing each of the plurality of belt detection densities with a representative value of the plurality of belt detection densities; the processor acquires a plurality of target detection densities obtained by the density sensor corresponding to the plurality of rotational positions under a condition in which an image is formed on the belt member; the processor correcting the plurality of object detection densities with the plurality of density correction values ​​according to the plurality of rotational positions; and determining an image density based on the corrected plurality of target detected densities by the processor.

2. The image density determination method according to claim 1 , wherein the processor derives a difference between each of the plurality of belt detection densities and an average value of the plurality of belt detection densities as the plurality of density correction values.

3. an image carrier on whose surface an image is formed; a transfer device that transfers the image formed on the surface of the image carrier onto a sheet; A processor for implementing the image density determination method according to claim 1 or 2, The transfer device is A plurality of support rollers; a belt member supported by the plurality of support rollers and rotating in conjunction with rotation of one of the plurality of support rollers; a primary transfer section that transfers an image formed on the surface of the image carrier onto the surface of the belt member; a secondary transfer section that transfers the image transferred onto the surface of the belt member onto the sheet; an image forming apparatus comprising: a density sensor that is disposed opposite a detection position, which is a surface position of a portion of the belt member that is supported by a specific roller that is one of the multiple support rollers, and detects the density of an image formed on the surface of the belt member.

4. The image forming apparatus according to claim 3 , wherein the transfer device further comprises a support member for supporting a rotation shaft of the specific roller and the density sensor.

Images