Image density measuring method and image forming apparatus

Abstract

To appropriately derive the density of a test toner image even when periodic density unevenness occurs in the test toner image.SOLUTION: A processor 81 derives a plurality of unit density values that are average values of the densities detected by a density detection unit for a plurality of unit areas obtained by dividing a test toner image by unit length (S3). The processor 81 derives the weighted average value of the plurality of unit density values to derive a test image density used for adjustment of a control parameter in a print unit 4 (S5). The unit length is the greatest common measure of two target lengths corresponding to the peripheral lengths of two types of target rotating bodies of a plurality of rotating bodies. When the number of the plurality of unit areas is defined as n, n is a value obtained by subtracting 1 from an added value of a first constant and a second constant. The first constant and the second constant are values obtained by dividing each of the two target lengths by the unit length.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to an image density measuring method for measuring the density of a test toner image used to adjust control parameters, and to an image forming apparatus. [Background technology]

[0002] An image forming apparatus may include an electrophotographic printing unit, which forms a toner image on the surface of an image carrier and transfers the toner image to a sheet.

[0003] When the image forming apparatus is a tandem color image forming apparatus, the image carrier includes a photoconductor and an intermediate transfer belt, and in this case, an electrostatic latent image is formed on the surface of the photoconductor and developed into the toner image.

[0004] Furthermore, the toner image formed on the surface of the photosensitive member is transferred to the surface of the intermediate transfer belt, and further, the toner image formed on the surface of the intermediate transfer belt is transferred to the sheet.

[0005] In some cases, the image forming apparatus further includes a density detection unit that detects the density of toner on the surface of the intermediate transfer belt. For example, the density detection unit detects the density of toner on the surface of the intermediate transfer belt at a portion that has passed the transfer position.

[0006] For example, it is known that when a patch image is formed on the surface of the intermediate transfer belt and the patch image is transferred to the sheet, a lookup table for gradation correction is corrected according to the density detected by the density detection unit (see, for example, Patent Document 1).

[0007] The lookup table is an example of a control parameter in the printing unit, and the patch image is an example of a test toner image used to adjust the control parameter. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-93488 Summary of the Invention [Problem to be solved by the invention]

[0009] The electrophotographic printing unit includes a plurality of rotating bodies involved in forming a toner image, such as the drum-shaped photosensitive body, a charging roller, and a developing roller.

[0010] Variations in the surface characteristics of the plurality of rotating bodies may cause periodic density unevenness in the sub-scanning direction of the toner image, which may adversely affect the adjustment of the control parameters.

[0011] That is, the density detection unit sequentially detects the density of the portion of the test toner image that passes through the detection position, and therefore the detected density of the density detection unit fluctuates in accordance with the periodic density unevenness.

[0012] Furthermore, it is possible that the length of the test toner image in the sub-scanning direction is not a common multiple of the circumferential lengths of the plurality of rotating bodies, and in this case, the average value of the detected density by the density detection unit may change each time the test toner image is formed, regardless of the control parameter.

[0013] If the density of the test toner image derived based on the density detected by the density detection unit changes due to the periodic density unevenness, there is a risk that the control parameters will be adjusted inappropriately.

[0014] An object of the present invention is to provide an image density measurement method and an image forming apparatus that can appropriately derive the density of a test toner image even when periodic density unevenness occurs in the test toner image formed by an electrophotographic printing unit. [Means for solving the problem]

[0015] According to one aspect of the present invention, an image density measurement method is implemented in an image forming apparatus. The image forming apparatus includes a print unit and a density detection unit. The print unit includes multiple rotating bodies involved in toner image formation and is capable of forming a test toner image on the surface of a photosensitive body. The density detection unit is capable of sequentially detecting the image density of portions of the test toner image passing through predetermined detection positions. The image density measurement method includes a processor deriving multiple unit density values, which are the average values ​​of the densities detected by the density detection unit for multiple unit areas divided into unit lengths in the sub-scanning direction in the test toner image. The image density measurement method further includes the processor deriving a test image density used to adjust control parameters in the print unit by deriving a weighted average value of the multiple unit density values. The unit length is the greatest common divisor of two target lengths corresponding to the circumferential lengths of two target rotating bodies among the multiple rotating bodies. When the number of the multiple unit areas is n, n is a value obtained by subtracting 1 from the sum of a first constant and a second constant. The first constant is a value obtained by dividing the shorter of the two target lengths by the unit length, and the second constant is a value obtained by dividing the longer of the two target lengths by the unit length.

[0016] An image forming apparatus according to another aspect of the present invention includes the print unit, the density detection unit, and the processor that implements the image density measurement method. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an image density measurement method and an image forming apparatus that can appropriately derive the density of a test toner image even when periodic density unevenness occurs in the test toner image formed by an electrophotographic printing unit. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing the configuration of an image forming apparatus according to the first embodiment. [Figure 2] FIG. 2 is a block diagram showing the configuration of a control device in the image forming apparatus according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing the intermediate transfer belt on which a print image and a test image are formed in the image forming apparatus according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing the relationship between a plurality of unit areas and periodic components of density unevenness in a test image formed by the image forming apparatus according to the first embodiment. [Figure 5] FIG. 5 is a diagram showing the relationship between a plurality of unit regions and a plurality of evaluation regions in a test image. [Figure 6] FIG. 6 is a diagram showing a specific example of the relationship between a plurality of unit regions, a plurality of evaluation regions, and periodic components of density unevenness in a test image. [Figure 7] FIG. 7 is an explanatory diagram relating to a specific example of a method for deriving the test image density in the image forming apparatus according to the first embodiment. [Figure 8] FIG. 8 is a flowchart showing an example of the procedure of the control parameter adjustment process in the image forming apparatus according to the first embodiment. [Figure 9] FIG. 9 is a diagram showing the configuration of an image forming apparatus according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] 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 does not limit the technical scope of the present invention.

[0020] [First embodiment] The image forming apparatus 10 according to the embodiment is an apparatus that performs a printing process using an electrophotographic method. 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.

[0021] [Configuration of image forming apparatus 10] 1, the image forming apparatus 10 includes a sheet storage unit 2, a conveying path 30, a conveying device 3, and a printing device 4. The image forming apparatus 10 further includes an operation device 801, a display device 802, and a control device 8.

[0022] The transport path 30, the transport device 3, the printing device 4, and the control device 8 are housed in a housing 1.

[0023] The sheet storage unit 2 stores the sheet 9. The conveying device 3 sends the sheet 9 from the sheet storage unit 2 to the conveying path 30, and further conveys the sheet 9 along the conveying path 30. The conveying device 3 further discharges the sheet 9 from the conveying path 30 onto the discharge tray 101.

[0024] The printing device 4 performs the printing process on the sheet 9 conveyed along the conveying path 30. In this embodiment, the printing device 4 is a tandem color printing device.

[0025] The printing device 4 forms a toner image on the sheet 9 conveyed along the conveying path 30. The toner image is an image made of toner as a developer. The toner is an example of the granular developer.

[0026] The printing device 4 includes a plurality of image forming units 4x, an optical scanning device 40, a transfer device 44, and a fixing device 46. In this embodiment, the printing device 4 includes four image forming units 4x corresponding to four colors: yellow, cyan, magenta, and black.

[0027] Each image forming unit 4x includes a drum-shaped photosensitive member 41, a charging device 42, a developing device 43, a drum cleaning device 45, and the like.

[0028] In each image forming unit 4x, a photoconductor 41 rotates, and a charging device 42 charges the surface of the photoconductor 41. Furthermore, an optical scanning device 40 forms an electrostatic latent image on the surface of the rotating photoconductor 41 by scanning with a light beam.

[0029] The optical scanning device 40 is an example of a latent image forming unit that forms the electrostatic latent image on the surface of the charged photosensitive member 41 .

[0030] 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 developing device 43 supplies the toner to the photoconductor 41 at a development position on the outer periphery of the photoconductor 41.

[0031] The charging device 42 includes a charging roller 421 and a charging voltage output device 422. The charging roller 421 is disposed opposite to the photoconductor 41 and rotates. The charging voltage output device 422 supplies a charging voltage to the charging roller 421.

[0032] The charging voltage is supplied from the charging voltage output device 422 to the photoconductor 41 through the charging roller 421. As a result, the surface of the photoconductor 41 is charged.

[0033] The developing device 43 includes a developing roller 431 and a bias output device 432. The developing roller 431 is disposed at the developing position so as to face the photoconductor 41. The developing roller 431 carries toner and rotates.

[0034] Developing device 43 further includes a spacing member 430. Spacing member 430 is configured integrally with developing roller 431. Spacing member 430 rotates while in contact with the surface of photoreceptor 41, thereby maintaining the gap between photoreceptor 41 and developing roller 431.

[0035] The bias output device 432 supplies a development bias voltage to the development roller 431. In this embodiment, the bias output device 432 supplies to the development roller 431 the development bias voltage in which an AC voltage is superimposed on a DC voltage.

[0036] The developing roller 431 rotates while carrying toner, and at the developing position supplies the toner to the surface of the photoreceptor 41. The toner carried by the developing roller 431 transfers to the portion of the electrostatic latent image on the surface of the photoreceptor 41. As a result, the electrostatic latent image is developed into the toner image.

[0037] The transfer device 44 includes an intermediate transfer belt 441, four primary transfer devices 442 corresponding to the four image forming units 4x, a secondary transfer device 443, and a belt cleaning device 444.

[0038] The intermediate transfer belt 441 is supported by a plurality of support rollers 400. One of the plurality of support rollers 400 is rotated by power received from a motor (not shown), thereby rotating the intermediate transfer belt 441.

[0039] In the transfer device 44, the primary transfer device 442 transfers the toner image formed on the surface of the photosensitive member 41 onto the surface of the intermediate transfer belt 441. As a result, the toner images of multiple colors are formed on the surface of the intermediate transfer belt 441.

[0040] The primary transfer device 442 includes a primary transfer roller 4421 and a primary current output device 4422. The primary transfer roller 4421 is disposed opposite the photosensitive member 41 with the intermediate transfer belt 441 interposed therebetween, and rotates.

[0041] The primary current output device 4422 supplies a primary transfer current to the primary transfer roller 4421. The toner image formed on the surface of the photosensitive member 41 is transferred onto the surface of the intermediate transfer belt 441 by an electric field generated between the photosensitive member 41 and the primary transfer roller 4421.

[0042] As described above, the printing device 4 forms the toner images on the surfaces of the four photoconductors 41. Furthermore, the printing device 4 transfers the toner images formed on the surfaces of the four photoconductors 41 onto the surface of the intermediate transfer belt 441.

[0043] The secondary transfer device 443 transfers the toner image formed on the intermediate transfer belt 441 onto the sheet 9. In the following description, the toner image transferred onto the sheet 9 will be referred to as a print toner image G10 (see FIG. 3).

[0044] The secondary transfer device 443 includes a secondary transfer member 4431 and a secondary current output device 4432. The secondary transfer member 4431 is in contact with the intermediate transfer belt 441. The sheet 9 passes between the intermediate transfer belt 441 and the secondary transfer member 4431.

[0045] A secondary current output device 4432 supplies a secondary transfer current to the secondary transfer member 4431. The print toner image G10 formed on the surface of the intermediate transfer belt 441 is transferred to the sheet 9 by an electric field generated between the intermediate transfer belt 441 and the secondary transfer member 4431.

[0046] As described above, the transfer device 44 transfers the print toner image G10 formed on the surface of the four photosensitive members 41 onto the sheet 9 via the intermediate transfer belt 441.

[0047] The drum cleaning device 45 removes waste toner remaining on the surface of the photosensitive member 41. The belt cleaning device 444 removes the waste toner remaining on the intermediate transfer belt 441. The waste toner is generated in the printing device 4 as the toner image is formed.

[0048] The fixing device 46 applies heat and pressure to the printed toner image G10 on the sheet 9. In this way, the fixing device 46 fixes the printed toner image G10 to the sheet 9.

[0049] The printing device 4 is an example of a printing unit capable of forming a toner image on the surface of the photosensitive member 41. The photosensitive member 41, the charging roller 421, the spacing member 430, the developing roller 431, and the primary transfer roller 4421 are each an example of a rotating body involved in the formation of the toner image.

[0050] The operation device 801 is a device that accepts operations by a person, and includes, for example, operation buttons and a touch panel.

[0051] The display device 802 is a device that displays information, and includes, for example, a panel display device such as a liquid crystal display unit.

[0052] [Configuration of control device 8] As shown in FIG. 2, the control device 8 includes a central processing unit (CPU) 81, a random access memory (RAM) 82, a secondary storage device 83, a signal interface 84, a communication device 85, and the like.

[0053] The secondary storage device 83 is a computer-readable non-volatile storage device. The secondary storage device 83 can store and update computer programs and various data. For example, a flash memory or a hard disk drive, or both, may be used as the secondary storage device 83.

[0054] The signal interface 84 converts signals output by various sensors into digital data and transmits the converted digital data to the CPU 81. Furthermore, the signal interface 84 converts control commands output by the CPU 81 into control signals and transmits the control signals to the devices to be controlled.

[0055] The communication device 85 executes communication with other devices such as a host device (not shown). The CPU 81 communicates with the other devices through the communication device 85.

[0056] The CPU 81 is a processor that executes the computer program to perform various data processing and control operations. The control device 8 including the CPU 81 controls the conveying device 3, the printing device 4, the display device 802, the communication device 85, and the like.

[0057] The RAM 82 is a computer-readable volatile storage device that temporarily stores the computer programs executed by the CPU 81 and data that is output and referenced by the CPU 81 in the course of executing various processes.

[0058] The CPU 81 includes a plurality of processing modules that are realized by executing the computer programs, including a main processing unit 8a, a job control unit 8b, and an adjustment unit 8c.

[0059] The main processing unit 8a executes processes to start various processes in response to operations on the operation device 801, controls the display device 802, and the like.

[0060] The job control unit 8b controls the conveying device 3. In this way, the job control unit 8b controls the feeding of the sheet 9 from the sheet storage unit 2 and the conveyance of the sheet 9 in the conveying path 30.

[0061] Furthermore, the job control unit 8b controls the printing device 4. In synchronization with the conveyance of the sheet 9 by the conveyance device 3, the job control unit 8b causes the printing device 4 to execute the printing process.

[0062] The printing process includes a process of forming a print toner image G10 on the surface of each photoconductor 41. The printing process further includes a process of transferring the print toner image G10 from the surface of each photoconductor 41 to a sheet 9 via an intermediate transfer belt 441.

[0063] Furthermore, the job control unit 8b can cause the printing device 4 to execute a process of forming a test toner image G1 (see FIG. 3). That is, the printing device 4 can form the test toner image G1 on the surface of the photosensitive member 41.

[0064] The test toner image G1 is a toner image used to adjust the control parameters in the printing device 4. For example, the test toner image G1 is a pattern image of a predetermined intermediate tone. For convenience, the test toner image G1 is painted black in Figures 3 to 7. The adjustment of the control parameters will be described later.

[0065] The image forming apparatus 10 further includes a density sensor 5 (see FIG. 1). The density sensor 5 is capable of sequentially detecting the image density of portions of the test toner image G1 that pass through predetermined detection positions. The density sensor 5 is an example of a density detection unit.

[0066] Specifically, the density sensor 5 sequentially detects the image density of the linear stripe areas along the main scanning direction D1 in the test toner image G1 while the test toner image G1 passes through the detection position.

[0067] In the following description, the density detected by the density sensor 5 in the line stripe region of the test toner image G1 will be referred to as the line detected density.

[0068] In this embodiment, the detection position is a position downstream of the secondary transfer position in the rotation direction of the intermediate transfer belt 441. For example, the density sensor 5 is a CIS (Contact Image Sensor).

[0069] In the image forming apparatus 10, the width direction of the photosensitive member 41 and the intermediate transfer belt 441 is the main scanning direction D1 (see FIG. 3), and the direction along the movement direction of the surfaces of the rotating photosensitive member 41 and the intermediate transfer belt 411 is the sub-scanning direction D2 (see FIG. 3).

[0070] The printing device 4 forms a print toner image G10 in a print area R1 in the main scanning direction D1 on the surface of each photosensitive member 41. The print area R1 is an area corresponding to the width of the sheet 9.

[0071] For example, the print area R1 is an area in the main scanning direction D1 occupied by a secondary transfer member 4431 that transfers a print toner image G10 onto the sheet 9 (see FIG. 3).

[0072] In this embodiment, the printing device 4 can form a test toner image G1 in an outer region R2 on the surface of each photosensitive element 41 when forming a print toner image G10 in a print region R1 on the surface of each photosensitive element 41 (see Figure 3).

[0073] The outer region R2 is a region different from the print region R1, that is, the outer region R2 is a region on the outer side of the print region R1 in the main scanning direction D1.

[0074] That is, the printing device 4 forms the print toner image G10 and the test toner image G1 in different areas in the main scanning direction D1 on the surface of each photoconductor 41. In this case, the printing device 4 can execute the process of forming the print toner image G10 and the process of forming the test toner image G1 in parallel.

[0075] More specifically, the printing device 4 executes a parallel development process when executing a page print process for forming an image on one page of a sheet 9. The parallel development process is a process for forming a print toner image G10 for one page of the sheet 9 in the print region R1 of each of the four photoconductors 41, and for forming a test toner image G1 in the outer region R2 of one of the target photoconductors.

[0076] The target photoconductor is one of the four photoconductors 41, and is selected sequentially from the four photoconductors 41 each time the page print process is executed.

[0077] When the job control unit 8b causes the printing device 4 to execute the page print process, it selects the target photoconductor and then causes the printing device 4 to execute the parallel development process.

[0078] The print toner image G10 is transferred from the print area R1 on the surface of each photoconductor 41 to the print area R1 on the surface of the intermediate transfer belt 411. Furthermore, the print toner image G10 is transferred from the print area R1 on the surface of the intermediate transfer belt 411 to the sheet 9.

[0079] Meanwhile, the test toner image G1 is transferred from the outer region R2 on the surface of each photoconductor 41 to the outer region R2 on the surface of the intermediate transfer belt 411. Thereafter, the test toner image G1, while being carried on the outer region R2 on the surface of the intermediate transfer belt 411, passes through the detection position and reaches the belt cleaning device 444.

[0080] The intermediate transfer belt 441 is an example of an intermediate transfer member onto which the test toner image G1 is transferred from the photosensitive member 41.

[0081] The belt cleaning device 444 removes the test toner image G1 and the waste toner remaining in the print area R1 from the surface of the intermediate transfer belt 411.

[0082] The adjusting unit 8c adjusts the control parameters so that the difference between the density of the test toner image G1 detected by the density sensor 5 and the target density becomes smaller.

[0083] For example, the control parameters include one or more of the charging voltage of the charging device 42 , the developing bias voltage of the developing device 43 , and the light amount of the beam of light of the optical scanning device 40 .

[0084] The electrophotographic printing device 4 includes a plurality of rotating bodies involved in the formation of the toner image. In this embodiment, the plurality of rotating bodies include a photosensitive member 41, a charging roller 421, a spacing member 430, a developing roller 431, and a primary transfer roller 4421.

[0085] Variations in the surface characteristics of the multiple rotating bodies may cause periodic density unevenness in the toner image in the sub-scanning direction D2. If the periodic density unevenness occurs in the test toner image G1, it may adversely affect the adjustment of the control parameters.

[0086] That is, the density sensor 5 sequentially detects the density of the portion of the test toner image G1 that passes through the detection position. Therefore, the detected density of the density sensor 5 fluctuates in accordance with the periodic density unevenness.

[0087] Furthermore, it is possible that the length of the test toner image G1 in the sub-scanning direction D2 is not a common multiple of the circumferential lengths of the multiple rotating bodies. In this case, the average value of the density detected by the density sensor 5 may change each time the test toner image G1 is formed, regardless of the control parameters.

[0088] If the density of the test toner image G1 derived based on the density detected by the density sensor 5 changes due to the periodic density unevenness, the control parameters may be adjusted inappropriately.

[0089] In this embodiment, the print toner image G10 and the test toner image G1 are formed side by side in the main scanning direction D1 (see FIG. 3). In this case, the test toner image G1 is formed with a length equal to or shorter than the length of the sheet 9 in the sub-scanning direction D2.

[0090] Therefore, if the common multiple of the circumferential lengths of the plurality of rotating bodies exceeds the length of the sheet 9, the test toner image G1 cannot be formed with a length that is a common multiple of the circumferential lengths of the plurality of rotating bodies, which can cause a problem that the control parameters are inappropriately adjusted due to the periodic density unevenness.

[0091] Meanwhile, in a control parameter adjustment process described later, the adjustment unit 8c derives a test image density based on the density detected by the density sensor 5. The test image density represents the density of the test toner image G1 and is used to adjust the control parameters.

[0092] The adjusting unit 8c can appropriately derive the density of the test toner image G1 even when the test toner image G1 formed by the printing device 4 has the periodic density unevenness.

[0093] Hereinafter, a method for deriving the density of the test toner image G1 based on the density detected by the density sensor 5 will be described with reference to FIGS.

[0094] 4 shows that the test toner image G1 includes a plurality of unit areas A1 divided into unit lengths L1 in the sub-scanning direction D2. In FIG. 4, an identification number i identifies each of the plurality of unit areas A1. The identification number i is an integer equal to or greater than 1.

[0095] The unit length L1 is the greatest common divisor of two target lengths corresponding to the circumferential lengths of two types of target rotating bodies among the plurality of rotating bodies. Two values ​​that are respectively approximate to the circumferential lengths of the two types of target rotating bodies are set in advance as the two target lengths.

[0096] The shorter of the two target lengths is referred to as a first target length, and the longer of the two target lengths is referred to as a second target length. The two target rotation bodies include a first target rotation body corresponding to the first target length and a second target rotation body corresponding to the second target length.

[0097] The two types of target rotating bodies are, for example, photosensitive body 41 and spacing member 430 of developing device 43. Below, a specific example of unit length L1 when the two types of target rotating bodies are photosensitive body 41 and spacing member 430 will be shown.

[0098] For example, when the circumferential length of the spacing member 430 is approximately 65 mm, the first target length may be set to 64.4 mm. When the circumferential length of the photosensitive member 41 is approximately 94 mm, the second target length may be set to 92.0 mm.

[0099] 64.4 mm is an example of a length that approximates the circumferential length of the spacing member 430, and 92.0 mm is an example of a length that approximates the circumferential length of the photosensitive member 41.

[0100] The greatest common divisor of 64.4 mm and 92.0 mm is 9.2 mm. Therefore, if the two target lengths are 64.4 mm and 92.0 mm, the unit length L1 is 9.2 mm.

[0101] Furthermore, a value obtained by dividing the first target length by the unit length L1 is defined as a first constant a, and a value obtained by dividing the second target length by the unit length L1 is defined as a second constant b.

[0102] The first constant a is an integer greater than or equal to 1. The second constant b is an integer greater than the first constant a.

[0103] In other words, the first target length is a times the unit length L1, and the second target length is b times the unit length L1. In the above example where the unit length L1 is 9.2 mm, the first constant a is 7 and the second constant b is 10.

[0104] Here, a+b-1=n, where n is the value obtained by subtracting 1 from the sum of the first constant a and the second constant b.

[0105] The test toner image G1 is formed to have a length equal to or greater than the reference length L2 in the sub-scanning direction D2. The reference length L2 is n times the unit length L1 (see FIG. 4). The test toner image G1 includes n unit areas A1 divided in the sub-scanning direction D2.

[0106] In the following description, the circumferential lengths of the two types of symmetric rotating bodies are considered to be approximately equal to the two symmetric lengths, respectively.

[0107] The density of unit regions A1(1) to A1(a) in test toner image G1 includes first periodic components F1(1) to F(a) resulting from the circumferential characteristic distribution of the first symmetric rotating body (see FIG. 4). Similarly, the density of unit regions A1(1) to A1(b) includes second periodic components F2(1) to F(b) resulting from the circumferential characteristic distribution of the second symmetric rotating body (see FIG. 4).

[0108] Furthermore, the i-th first period component F1(i) and the (i+a)-th first period component F1(i+a) are the same component. Similarly, the i-th second period component F2(i) and the (i+b)-th second period component F2(i+b) are the same component.

[0109] When the test toner image G1 is formed with a length that is a common multiple of the two target lengths, the density distribution of the test toner image G1 equally includes the first periodic components F1(1) to F(a) and the second periodic components F2(1) to F(b).

[0110] However, if the test toner image G1 is formed with a length that is a common multiple of the two target lengths, the length of the test toner image G1 may exceed the length of the sheet 9. In this case, the length of the test toner image G1 exceeds the upper limit length of the test toner image G1 that can be formed by the parallel development process.

[0111] When the length of the test toner image G1 is shorter than the common multiple of the two target lengths, the density distribution of the test toner image G1 includes the first periodic components F1(1) to F(a) and the second periodic components F2(1) to F(b) unevenly.

[0112] Here, unit area A1(1) to A1(b) is group area A2(1), unit area A1(2) to A1(b+1) is group area A2(2), and unit area A1(j) to unit area A1(j+b-1) is group area A2(j) (see FIG. 5), where j is an integer equal to or greater than 1.

[0113] The n unit areas A1(1) to A1(n) are classified into a group areas A2(1) to A2(a) (see FIG. 5). Some of the n unit areas A1(1) to A1(n) overlap and belong to the a group areas A2(1) to A2(a).

[0114] The a group regions A2(1) to A2(a) each include one of the second periodic components F2(1) to F(b) (see FIG. 5).

[0115] Here, the average densities of the n unit areas A1(1) to A1(n) in the test toner image G1 are defined as unit density values ​​ID(1) to ID(n). The n unit density values ​​ID(1) to ID(n) are the average values ​​of the densities detected by the density sensor 5 for each of the multiple unit areas A1.

[0116] Furthermore, the totals of the b unit density values ​​ID(j) to ID(j+b-1) in each of the a group regions A2(1) to A2(a) are defined as group totals IDg(1) to IDg(a).

[0117] Each of the a group totals IDg(1) to IDg(a) is a value that reflects one of the second period components F2(1) to F(b) (see FIG. 5). However, each of the a group totals IDg(1) to IDg(a) is a value that reflects the first period components F1(1) to F(a) unevenly.

[0118] FIG. 7 shows an example in which seven unit areas A1(1) to A1(7) of the test toner image G1 are classified into three group areas A2(1) to A2(3) when a=3, b=5, and N=7.

[0119] Furthermore, FIGS. 7 and 8 show the correspondence between the three group regions A2(1) to A2(3), the three first period components F1(1) to F1(3), and the five second period components F2(1) to F2(5).

[0120] 8, the three group regions A2(1) to A2(3) as a whole include five of each of the three types of first period components F1(1) to F2(3). Furthermore, the three group regions A2(1) to A2(3) as a whole include three of each of the five types of second period components F2(1) to F2(5).

[0121] That is, the total sum of the three group total values ​​IDg(1) to IDg(3) corresponding to the three group regions A2(1) to A2(3) is a value that equally reflects the three types of first period components F1(1) to F2(3) and the five types of second period components F2(1) to F2(5).

[0122] On the other hand, the three group areas A2(1) to A2(3) as a whole include one unit area A1(1), two unit areas A1(2), three unit areas A1(3), three unit areas A1(4), three unit areas A1(5), two unit areas A1(6), and one unit area A1(7).

[0123] The three group areas A2(1) to A2(3) as a whole include N unit areas A1(i), where N is the value obtained by multiplying a and b.

[0124] Therefore, it is conceivable to derive the test image density as a weighted average of n unit density values ​​ID(1) to ID(n) based on a predetermined weighting coefficient, where the weighting coefficient is the ratio of the number of each of the n unit areas A1(1) to A1(n) included in all three group areas A2(1) to A2(3) to N.

[0125] The following equation (1) for deriving the test image density is a calculation formula that generalizes what has been shown above.

[0126]

number

[0127] In equation (1), IDT is the test image density. n is the number of unit areas A1. i is the identification number of the unit areas A1. ID(i) is the density value corresponding to the i-th unit area A1(i) among the n unit density values. a is a first constant, and b is a second constant greater than the first constant a.

[0128] As described above, the first constant a is a value obtained by dividing the first target length by the unit length L1, and the second constant b is a value obtained by dividing the second target length by the unit length L1.

[0129] Equation (1) is an example of a calculation formula for deriving the weighted average value of n unit density values ​​ID(1) to ID(n) as the test image density.

[0130] The test image density may also be derived based on the following equation (2): Equation (2) is an example of an alternative equation equivalent to equation (1).

[0131]

number

[0132] It should be noted that IDT, a, b, and N in equation (2) are the same as IDT, a, b, and N in equation (1), respectively.

[0133] By employing equation (1) or (2), the weighted average value of n unit density values ​​ID(1) to ID(n) is derived as the test image density, so that the multiple first periodic components F1 and the multiple second periodic components F2 are each equally reflected in the test image density.

[0134] Furthermore, the two target lengths are similar to the circumferential lengths of the two types of target rotating bodies, so that the difference between the two target lengths and the circumferential lengths of the two types of target rotating bodies has little effect on the test image density.

[0135] Therefore, even if the periodic density unevenness occurs in the test toner image G1, the influence of the periodic density unevenness on the test image density is small.

[0136] Furthermore, among the plurality of rotating bodies, members with relatively short circumferential lengths have little effect on the non-uniformity of the plurality of periodic components in the test toner image G1.

[0137] Therefore, among the plurality of rotating bodies, those with relatively long circumferential lengths and likely to cause the periodic density unevenness are selected as the two types of target rotating bodies. Photoconductor 41 and spacing member 430 have relatively long circumferential lengths among the plurality of rotating bodies.

[0138] In addition, some specific members of the multiple rotating bodies may have a circumferential length that is close to the length obtained by dividing the reference length L2 by an integer. Such specific members also have a small effect on the non-uniformity of the multiple periodic components in the test toner image G1.

[0139] [Control parameter adjustment processing] In this embodiment, the adjustment unit 8c executes the control parameter adjustment process every time the page print process is executed.

[0140] As described above, every time the page print process is executed, a test toner image G1 is formed in the outer region R2 on the surface of the target photosensitive member.

[0141] An example of the procedure for the control parameter adjustment process will be described below with reference to the flowchart shown in Fig. 4. The control parameter adjustment process includes a process for realizing an image density measurement method.

[0142] In the following description, S1, S2, ... represent identification symbols of a plurality of steps in the control parameter adjustment process. In the control parameter adjustment process, step S1 is executed first.

[0143] <Process S1> In step S1, the adjustment unit 8c counts up the identification number i. When the process of step S1 is executed for the first time, i after the count up is 1.

[0144] After performing the process of step S1, the adjustment unit 8c shifts the process to step S2.

[0145] <Process S2> In step S2, the adjusting unit 8c acquires the plurality of line detection densities corresponding to the i-th unit area A1(i) from the density sensor 5. The adjusting unit 8c executes the process of step S2 when the test toner image G1 passes the detection position.

[0146] After performing the process of step S2, the adjustment unit 8c shifts the process to step S3.

[0147] <Process S3> In step S3, the adjusting unit 8c derives the i-th unit density value DI(i), which is the average value of the plurality of line detection densities for the i-th unit area A1(i).

[0148] After performing the process of step S3, the adjuster 8c shifts the process to step S4.

[0149] <Process S4> In step S4, the adjusting section 8c determines whether or not n unit density values ​​DI(1) to DI(n) have been derived.

[0150] When the adjusting unit 8c determines that n unit concentration values ​​DI(1) to DI(n) have not yet been derived, the adjusting unit 8c shifts the process to step S1, whereby the adjusting unit 8c repeats the processes of steps S1 to S3 n times.

[0151] Therefore, the adjusting unit 8c derives n unit concentration values ​​DI(1) to DI(n) which are the average values ​​of the concentrations detected by the concentration sensor 5 for the n unit areas A1(1) to A2(n) (step S3).

[0152] On the other hand, when the adjusting section 8c determines that n unit concentration values ​​DI(1) to DI(n) have been derived, it shifts the processing to step S5.

[0153] <Process S5> In step S5, the adjusting unit 8c derives the test image density DIT based on the n unit density values ​​DI(1) to DI(n).

[0154] Specifically, the adjusting unit 8c derives the test image density DIT by applying the n unit density values ​​DI(1) to DI(n) to the equation (1) or (2) (step S5).

[0155] The process of step S5 is an example of a process for deriving the test image density DIT by deriving a weighted average value of n unit density values ​​DI(1) to DI(n). The processes of steps S1 to S5 are also an example of a process for realizing an image density measurement method in the image forming apparatus 10.

[0156] After performing the process of step S5, the adjuster 8c shifts the process to step S6.

[0157] <Process S6> In step S6, if the test image density DIT is outside the predetermined target range, the adjusting section 8c shifts the process to step S7.

[0158] On the other hand, if the test image density DIT falls within the target range, the adjusting section 8c ends the control parameter adjusting process.

[0159] <Process S7> In step S7, the adjusting unit 8c adjusts the control parameters in accordance with the density difference, which is the difference between the test image density DIT and the target range.

[0160] For example, the control parameters to be adjusted include one or more of the charging voltage of the charging device 42 , the light beam amount of the optical scanning device 40 , and the developing bias of the developing device 43 .

[0161] The control parameters adjusted in step S7 are parameters corresponding to the target photoconductor selected each time the page print process is executed.

[0162] After executing the process of step S7, the adjuster 8c ends the control parameter adjustment process.

[0163] By employing the control parameter adjustment process, it is possible to appropriately derive the density of the test toner image G1 even when the periodic density unevenness occurs in the test toner image G1.

[0164] Furthermore, the reference length L2 of the test toner image G1 is shorter than the least common multiple of the two target lengths, so the control parameter adjustment process can be adopted in many cases where the length of the test toner image G1 is limited.

[0165] [Second embodiment] Next, an image forming apparatus 10A according to a second embodiment will be described with reference to FIG.

[0166] In Fig. 9, the same components as those shown in Fig. 1 are denoted by the same reference numerals. Below, differences between image forming apparatus 10A and image forming apparatus 10 will be described.

[0167] The image forming apparatus 10A includes a printing device 4A that can form only monochrome images. The printing device 4A has a configuration in which the four image forming units 4x and transfer device 44 in the printing device 4 of the image forming apparatus 10 are replaced with a single image forming unit 4x and transfer device 44X.

[0168] One image forming unit 4x forms the electrostatic latent image on the surface of the photoreceptor 41 and develops the electrostatic latent image into the toner image.

[0169] The transfer device 44X transfers the toner image formed on the surface of the photoreceptor 41 onto the sheet 9. The transfer device 44X is an example of a transfer section that transfers the toner image from the image carrier onto the sheet 9.

[0170] In the image forming apparatus 10A, the density sensor 5 detects the density of the test toner image G1 formed on the surface of the photoconductor 41 in the outer region R2.

[0171] The detection position in the image forming apparatus 10A is a position downstream of the position of the transfer device 44X on the outer periphery of the photosensitive member 41 in the rotation direction of the photosensitive member 41.

[0172] The adjustment unit 8c of the image forming apparatus 10A also executes the control parameter adjustment process (see FIG. 8). However, in the image forming apparatus 10A, the image forming unit 4x includes one photoconductor 41. Therefore, in the image forming apparatus 10A, the process of selecting the target photoconductor is omitted.

[0173] When the image forming apparatus 10A is employed, the same effects as when the image forming apparatus 10 is employed can be obtained. [Explanation of symbols]

[0174] 4, 4A: Printing device 4x: Image forming section 5: Concentration sensor (concentration detection part) 8: Control device 10, 10A: Image forming apparatus 40: Optical scanning device 41: Photoreceptor 42: Charging device 43: Developing device 44, 44X: Transfer device 46: Fixing device 81: CPU (processor) 411: Intermediate transfer belt 421: Charging roller 422: Charge voltage output device 430: Spacing member 431: Developing roller 432: Bias output device 441: Intermediate transfer belt 442: Primary transfer device 443: Secondary transfer device A1: Unit area A2: Group Area

Claims

1. a printing unit including a plurality of rotating bodies for forming a toner image and capable of forming a test toner image on the surface of a photosensitive member; a density detection unit capable of sequentially detecting image densities of portions of the test toner image passing through a predetermined detection position, a processor deriving a plurality of unit density values ​​which are average values ​​of the densities detected by the density detection unit for each of a plurality of unit areas divided into unit lengths in the sub-scanning direction in the test toner image; the processor deriving a test image density used to adjust control parameters in the printing unit by deriving a weighted average of the plurality of unit density values; the unit length is a greatest common divisor of two target lengths corresponding to circumferential lengths of two types of target rotating bodies among the plurality of rotating bodies, When the number of the plurality of unit areas is n, n is a value obtained by subtracting 1 from the sum of the first constant and the second constant, The image density measuring method, wherein the first constant and the second constant are values ​​obtained by dividing each of the two target lengths by the unit length.

2. the processor derives the test image density by applying the plurality of unit density values ​​to the following formula or an alternative formula equivalent to the following formula: [Equation 1] 2. The image density measurement method according to claim 1, wherein, in the calculation formula, IDT is the test image density, i is an identification number of the plurality of unit areas, ID(i) is a density value corresponding to the i-th unit area among the plurality of unit density values, a is the first constant obtained by dividing a shorter of the two target lengths by the unit length, and b is the second constant obtained by dividing a longer of the two target lengths by the unit length.

3. The printing unit a developing roller that supplies toner to the surface of the photoreceptor; a spacing member that is integral with the developing roller and rotates while in contact with the surface of the photosensitive member to maintain a spacing between the photosensitive member and the developing roller; an intermediate transfer member onto which the test toner image is transferred from the photosensitive member, 3. The image density measuring method according to claim 1, wherein the two types of target rotating bodies are the photosensitive body and the spacing member.

4. a printing unit including a plurality of rotating bodies for forming a toner image and capable of forming a test toner image on the surface of a photosensitive member; a density detection unit capable of sequentially detecting image densities of portions of the test toner image passing through a predetermined detection position; An image forming apparatus comprising: a processor that implements the image density measuring method according to any one of claims 1 to 3.

5. 5. The image forming apparatus according to claim 4, wherein the printing unit is capable of forming the test toner image in an outer area different from the printing area on the surface of the photosensitive body when forming a print toner image to be transferred to the sheet in a printing area on the surface of the photosensitive body corresponding to the width of the sheet.

Images