Image forming apparatus

Abstract

To provide an image forming apparatus that, when toner images are formed on surfaces of a plurality of image carriers by a plurality of toner carriers applied with common developing voltage, efficiently forms a plurality of test toner images different in conditions for the developing voltage on a surface of an intermediate transfer body.SOLUTION: A control unit 8 causes an image forming unit 4x to execute test output processing of sequentially forming a plurality of test toner images different in conditions for developing voltage on surfaces of a plurality of image carriers 41 and transferring the test toner images to an intermediate transfer body 441. The control unit 8 causes the image forming unit 4x to execute the test output processing of sequentially selecting a plurality of target image carriers arranged distant from the plurality of image carriers 41 by an arrangement interval between the plurality of image carriers or longer, so that, every time the plurality of target image carriers are selected, the plurality of test toner images for the plurality of target image carriers are transferred into an area with a length corresponding to the interval between the plurality of target image carriers on a surface of the intermediate transfer body 441.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that forms a plurality of test toner images on the surface of an intermediate transfer member and adjusts an image forming section in accordance with the densities of the plurality of test toner images. [Background technology]

[0002] In an electrophotographic image forming apparatus, various conditions such as the charge amount of toner affect the density of an output image.

[0003] It is known that the image forming apparatus forms a plurality of types of gradation patterns on the surface of a transfer belt and detects the densities of the plurality of types of gradation patterns using an optical sensor (see, for example, Patent Document 1). The image forming apparatus controls image density according to the detected densities of the plurality of types of gradation patterns. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-18212 Summary of the Invention [Problem to be solved by the invention]

[0005] In the image forming apparatus, the image forming unit may include a plurality of image carriers and a plurality of toner carriers to which a common developing voltage is applied, and the image forming unit forms a toner image of each of a plurality of developing colors on the surface of each of the plurality of image carriers using toner supplied from each of the plurality of toner carriers.

[0006] The image forming apparatus may sequentially form a plurality of test toner images, each having a different developing voltage condition, on the surface of each of the plurality of image carriers, and transfer the plurality of test toner images to the surface of an intermediate transfer body. The image forming apparatus may detect the densities of the plurality of test toner images with a sensor and adjust the image forming unit in accordance with the detected densities.

[0007] The change in the development voltage takes a predetermined time. It is desirable that the image forming apparatus be able to efficiently form the plurality of test toner images with different development voltage conditions on the surface of the intermediate transfer member.

[0008] An object of the present invention is to provide an image forming apparatus that can efficiently form multiple test toner images with different developing voltage conditions on the surface of an intermediate transfer body when toner images are formed on the surfaces of multiple image carriers by multiple toner carriers to which a common developing voltage is applied. [Means for solving the problem]

[0009] According to one aspect of the present invention, an image forming apparatus includes an image forming unit, a transfer device, a density detection unit, and a control unit. The image forming unit includes a plurality of image carriers arranged at intervals and a plurality of toner carriers arranged corresponding to the plurality of image carriers and applied with a common development voltage. The image forming unit forms a toner image of each of a plurality of developing colors on the surface of each of the plurality of image carriers using toner supplied from each of the plurality of toner carriers. The transfer device includes an intermediate transfer body and transfers the toner images on the surfaces of the plurality of image carriers to the intermediate transfer body, and then transfers the toner images transferred to the intermediate transfer body to a sheet. The density detection unit detects the density of the toner image formed on the surface of the intermediate transfer body. The control unit causes the image forming unit to execute a test output process in which a plurality of test toner images, each with different development voltage conditions, are sequentially formed on the surfaces of the plurality of image carriers and transferred to the intermediate transfer body, and adjusts the image forming unit according to the densities of the plurality of test toner images detected by the density detection unit. The control unit sequentially selects a plurality of target image carriers from the plurality of image carriers that are arranged at a distance greater than the arrangement interval of the plurality of image carriers, and causes the image forming unit to execute the test output process so that each time a plurality of target image carriers is selected, the plurality of test toner images for each of the plurality of target image carriers are transferred within an area on the surface of the intermediate transfer body whose length corresponds to the interval between the plurality of target image carriers.

[0010] According to another aspect of the present invention, an image forming apparatus includes the image forming unit, the transfer device, the density detection unit, and a control unit. The control unit causes the image forming unit to perform a test output process in which multiple test toner images, each having a different development voltage condition, are sequentially formed on the surface of each of the multiple image carriers and transferred to the intermediate transfer body, and adjusts the image forming unit in accordance with the densities of the multiple test toner images detected by the density detection unit. The control unit causes the image forming unit to perform the test output process so that the multiple test toner images for each of the multiple image carriers are transferred within an area on the surface of the intermediate transfer body that has a length corresponding to an arrangement interval between the multiple image carriers. [Effects of the Invention]

[0011] According to the present invention, when toner images are formed on the surfaces of multiple image carriers by multiple toner carriers to which a common development voltage is applied, it is possible to provide an image forming apparatus that can efficiently form multiple test toner images with different development voltage conditions on the surface of an intermediate transfer body. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a configuration diagram of a developing device in the image forming apparatus according to the embodiment. [Figure 3] FIG. 3 is a block diagram showing the configuration of a control device in the image forming apparatus according to the embodiment. [Figure 4] FIG. 4 is a flowchart showing a first example of a procedure for test output control in the image forming apparatus according to the embodiment. [Figure 5] FIG. 5 is a flowchart showing an example of the procedure of the development parameter adjustment process in the image forming apparatus according to the embodiment. [Figure 6] FIG. 6 is a diagram showing a state in which the first test output is performed for the first target photosensitive member in the first example of the procedure for test output control in the image forming apparatus according to the embodiment. [Figure 7] FIG. 7 is a diagram showing a situation in which the second test output is performed for the first target photosensitive member in the first example of the procedure for test output control in the image forming apparatus according to the embodiment. [Figure 8] FIG. 8 is a diagram showing a situation in which the third test output is performed for the first target photosensitive member in the first example of the procedure for test output control in the image forming apparatus according to the embodiment. [Figure 9] FIG. 9 is a diagram showing a state in which the first test output is performed for the second target photosensitive member in the first example of the procedure for test output control in the image forming apparatus according to the embodiment. [Figure 10]FIG. 10 is a diagram showing a situation in which the third test output is performed for the second target photosensitive member in the first example of the procedure for test output control in the image forming apparatus according to the embodiment. [Figure 11] FIG. 11 is a flowchart showing a second example of the procedure for test output control in the image forming apparatus according to the embodiment. [Figure 12] FIG. 12 is a diagram showing a situation in which the first test output is performed in the second example of the procedure for test output control in the image forming apparatus according to the embodiment. [Figure 13] FIG. 13 is a diagram showing a situation in which the third test output is performed in the second example of the procedure for test output control in the image forming apparatus according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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.

[0014] [Configuration of image forming apparatus 10] The image forming apparatus 10 according to the embodiment is capable of performing a print process by electrophotography. The print 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 resin sheet.

[0015] 1 is a printer. However, the image forming apparatus 10 may also be a copying machine, a facsimile machine, a multifunction machine, or the like.

[0016] As shown in FIG. 1, the image forming apparatus 10 includes a main housing 1, a sheet storage unit 2, a conveying device 3, a printing device 4, a toner supplying device 5, a control device 8, an operating device 801, and a display device 802.

[0017] The main housing 1 is a housing that houses the transport device 3, the printing device 4, the toner supply device 5, and the control device 8. Inside the main housing 1, a transport path 300 that is a passage for the sheet 9 is provided.

[0018] The conveying device 3 includes a sheet feeding mechanism 30 and a plurality of pairs of conveying rollers 31. The sheet feeding mechanism 30 sends out the sheets 9 stored in the sheet storage unit 2 to a conveying path 300 one by one.

[0019] The plurality of pairs of transport rollers 31 transport the sheet 9 along the transport path 300. One of the plurality of pairs of transport rollers 31 discharges the sheet 9, on which an image has been formed by the printing device 4, from the transport path 300 onto the discharge tray 1x.

[0020] The printing device 4 performs the printing process on the sheet 9 conveyed along the conveying path 300. In the example shown in Fig. 1, the printing device 4 performs the printing process by an electrophotographic method. The printing device 4 is a tandem color printing device.

[0021] The printing device 4 includes an image forming section 4x, a transfer device 44, and a fixing device 46. The image forming section 4x includes an exposure device 4a, a plurality of unit image forming sections 40 corresponding to a plurality of developing colors, and a voltage output circuit 4b.

[0022] In this embodiment, the image forming section 4x includes four unit image forming sections 40 corresponding to the developing colors of yellow, magenta, cyan, and black.

[0023] Each unit image forming section 40 includes a photoconductor 41, a charging device 42, a developing device 43, and a drum cleaning device 45. That is, image forming section 4x includes four photoconductors 41, four charging devices 42, four developing devices 43, and four drum cleaning devices 45.

[0024] The four photoconductors 41 are arranged at intervals along a portion of the intermediate transfer belt 441. In this embodiment, the four photoconductors 41 are arranged at equal intervals.

[0025] The four photoconductors 41 rotate, and the four charging devices 42 charge the surfaces of the four photoconductors 41. The exposure device 4a scans the surface of each charged photoconductor 41 with a laser beam, thereby forming an electrostatic latent image on the surface of each photoconductor 41.

[0026] The developing device 43 supplies toner to the surface of the photoreceptor 41 to develop the electrostatic latent image into a toner image.

[0027] 2, each of the developing devices 43 includes a developer container 430 and a developing roller 431. That is, the image forming unit 4x includes four developer containers 430 and four developing rollers 431 corresponding to the four developing colors.

[0028] The four developer containers 430 and the four developing rollers 431 are arranged corresponding to the four photoconductors 41, respectively. Each developer container 430 contains a two-component developer. The two-component developer contains a magnetic carrier and the toner supplied from the toner supply device 5.

[0029] The voltage output circuit 4b outputs a common developing voltage to the four developing rollers 431. The developing voltage is a bias voltage applied to each of the developing rollers 431 with the potential of each of the photoconductors 41 as a reference.

[0030] The four developing rollers 431 are an example of a plurality of toner carriers to which the common developing voltage is applied. Each of the developing rollers 431 carries the toner in each of the developer containers 430.

[0031] Each developing roller 431 supplies the toner to the surface of each photoreceptor 41, thereby developing the electrostatic latent image into the toner image.

[0032] That is, the image forming unit 4x forms the toner image of each of the multiple developing colors on the surface of each of the four photoconductors 41 using the toner supplied from each of the four developing rollers 431. The four photoconductors 41 are an example of multiple image carriers that each carry a toner image.

[0033] Furthermore, each developing device 43 includes a developer transport member 433 and a remaining amount detection unit 434. The developer transport member 433 rotates in the developer accommodating unit 430. The developer transport member 433 transports the two-component developer in the developer accommodating unit 430 while stirring it.

[0034] The remaining amount detection unit 434 detects the remaining amount of toner in the developer accommodating unit 430. In this embodiment, the remaining amount detection unit 434 is a magnetic permeability sensor that detects the magnetic permeability in the developer accommodating unit 430. A high magnetic permeability in the developer accommodating unit 430 indicates that the remaining amount of toner in the developer accommodating unit 430 is low.

[0035] The transfer device 44 transfers the toner image on the surface of the photoreceptor 41 onto the sheet 9 being transported along the transport path 300 .

[0036] The transfer device 44 includes an intermediate transfer belt 441, four primary transfer devices 442, a secondary transfer device 443, and a belt cleaning device 444. The four primary transfer devices 442 are provided corresponding to the four photosensitive members 41.

[0037] The intermediate transfer belt 441 rotates with a portion thereof aligned with the four photoconductors 41. The longitudinal direction of each photoconductor 41 is the main scanning direction D1, and the direction perpendicular to the main scanning direction D1 is the sub-scanning direction D2 (see FIG. 1).

[0038] The four photoconductors 41 are arranged along the sub-scanning direction D2. A belt movement direction D21, which is the movement direction of the portion of the intermediate transfer belt 441 that moves along the four photoconductors 41, is a direction from one side to the other side of the sub-scanning direction D2 (see FIG. 1).

[0039] The four primary transfer devices 442 transfer the toner images on the surfaces of the four photosensitive members 41 onto the surface of the intermediate transfer belt 441. As a result, a color toner image, which is a composite of the toner images of multiple colors, is formed on the surface of the intermediate transfer belt 441.

[0040] The secondary transfer device 443 transfers the color toner image on the surface of the intermediate transfer belt 441 to the sheet 9. That is, the transfer device 44 transfers the toner images on the surfaces of the four photosensitive members 41 to the surface of the intermediate transfer belt 441, and further transfers the toner images transferred to the surface of the intermediate transfer belt 441 to the sheet 9. The intermediate transfer belt 441 is an example of an intermediate transfer body.

[0041] The fixing device 46 fixes the toner image on the sheet 9 by applying heat and pressure to the toner image on the sheet 9 .

[0042] The toner supply device 5 supplies four color toners to the four developer containers 430, respectively. The toner supply device 5 includes four toner containers 51 and a toner sending mechanism 52.

[0043] The four toner containers 51 each contain toner of a different developing color. A toner sending mechanism 52 sends the toner contained in each toner container 51 to the four developer containers 430. Each toner container 51 is removably attached to the main housing 1.

[0044] The operation device 801 is a device that accepts operations by a person, and includes, for example, one or both of a touch panel and operation buttons.

[0045] The display device 802 is capable of displaying various types of information. For example, the display device 802 is a panel display device such as a liquid crystal display device. The control device 8 controls various electrical devices included in the image forming apparatus 10.

[0046] As shown in FIG. 3, the control device 8 includes a central processing unit (CPU) 80, a random access memory (RAM) 81, a secondary storage device 82, a signal interface 83, a communication device 84, and the like.

[0047] The CPU 80 is an example of a processor that executes computer programs to perform various control and data processing operations. The RAM 81 temporarily stores the computer programs executed by the CPU 80 and various data.

[0048] 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 may be used as the secondary storage device 82.

[0049] The signal interface 83 converts the detection signals of the various sensors into digital detection data, which is then transmitted to the CPU 80.

[0050] The communication device 84 communicates with a plurality of external devices, including one or more host devices, via a network. The CPU 80 communicates with each of the external devices through the communication device 84. The host device is an information processing device that requests the image forming apparatus 10 to perform the print processing.

[0051] The CPU 80 includes a plurality of processing modules that are realized by executing the computer programs, including a main control unit 8a, a supply control unit 8b, and a print control unit 8c (see FIG. 2).

[0052] The main control unit 8a receives various requests and controls other modules to execute processes according to the requests. For example, the main control unit 8a receives a print request through the operation device 801 or the communication device 84. The main control unit 8a then causes the print control unit 8c to execute processes according to the print request.

[0053] The supply control unit 8 b controls the toner supply device 5 to thereby control the supply of toner from the toner supply device 5 to the printing device 4 .

[0054] In this embodiment, the supply control unit 8b controls the amount of toner supplied by the toner supply device 5 to the developing device 43 in accordance with the difference between the remaining amount detected by the remaining amount detection unit 434 and a preset target remaining amount.

[0055] The print control unit 8c controls the conveying device 3 and the printing device 4. The print control unit 8c causes the conveying device 3 to convey the sheet 9, while causing the printing device 4 to execute the printing process.

[0056] The image forming unit 4x of the image forming apparatus 10 includes a plurality of photoconductors 41 and a plurality of developing rollers 431 to which the common developing voltage is applied. As described above, the image forming unit 4x forms the toner image of each of the plurality of developing colors on the surface of each of the plurality of photoconductors 41 by using the toner supplied from each of the plurality of developing rollers 431.

[0057] The image forming apparatus 10 executes a test output control, which will be described later (see FIGS. 4 and 11). In the test output control, the image forming apparatus 10 sequentially forms a plurality of test toner images, each having a different developing voltage condition, on the surface of each of the plurality of photoconductors 41, and transfers the plurality of test toner images onto the surface of the intermediate transfer belt 441.

[0058] Furthermore, the image forming apparatus 10 executes a development parameter adjustment process (described later) in parallel with the test output control (see FIG. 5). The image forming apparatus 10 further includes a density detection unit 6 (see FIG. 1) used in the development parameter adjustment process. The density detection unit 6 detects the density of the toner image formed on the surface of the intermediate transfer belt 441.

[0059] For example, the density detection unit 6 is a reflective photosensor. In this case, the density detection unit 6 irradiates the surface of the intermediate transfer belt 441 with light and detects the amount of diffused light reflected by the surface of the intermediate transfer belt 441.

[0060] The image forming apparatus 10 can detect the densities of the plurality of test toner images using the density detection unit 6, and adjust the image forming unit 4x in accordance with the detected densities.

[0061] It takes a predetermined time for the voltage output circuit 4b to change the developing voltage. In the image forming apparatus 10, it is desirable that the plurality of test toner images with different developing voltage conditions can be efficiently formed on the surface of the intermediate transfer belt 441.

[0062] The plurality of processing modules of the CPU 80 include an adjustment unit 8d that executes the test output control and the development parameter adjustment process (see FIG. 3).

[0063] In the test output control, the adjustment unit 8d causes the printing device 4 to execute a test output process in which the plurality of test toner images with different developing voltage conditions are formed on the surface of the intermediate transfer belt 441. Each of the plurality of test toner images is a uniform solid image, a shaded image, an image with a uniform pattern, or the like.

[0064] The adjustment section 8d executes the test output control and the development parameter adjustment process every time the adjustment conditions are met.

[0065] For example, the adjustment condition may be that the number of prints reaches a predetermined number. Alternatively, the adjustment condition may be that the cumulative number of pixels drawn for each development color in the print process reaches a predetermined number.

[0066] The CPU 80 including the adjustment unit 8d is an example of a processor that executes the test output control and the development parameter adjustment process. The control device 8 including the supply control unit 8b, the print control unit 8c, and the adjustment unit 8d is an example of a control unit that controls the image forming apparatus 10.

[0067] [First example of test output control] The procedure of the first example of the test output control will be described below with reference to the flowchart shown in FIG.

[0068] In the following description, S101, S102, ... represent identification codes of a plurality of steps in the first example of test output control. In the first example of test output control, the processing of step S101 is executed first.

[0069] <Process S101> In step S101, the adjustment unit 8d selects two target photoconductors that are part of the four photoconductors 41.

[0070] The two target photoconductors are two of the four photoconductors 41 that are arranged farther apart than the arrangement interval SP1 of the four photoconductors 41 (see FIGS. 6 to 10). That is, the two target photoconductors are other than the two adjacent photoconductors among the four photoconductors 41.

[0071] The four photoconductors 41 include a first photoconductor 41a, a second photoconductor 41b, a third photoconductor 41c, and a fourth photoconductor 41d arranged in this order from the downstream side in the belt movement direction D21 (see FIGS. 6 to 10).

[0072] For example, the adjustment unit 8d selects the first photoconductor 41a and the third photoconductor 41c as the two target photoconductors for the first time. That is, in the first step S101, the adjustment unit 8d selects the two target image carriers that are arranged first and third in the arrangement direction of the four photoconductors 41 among the four photoconductors 41.

[0073] When the first photoconductor 41a and the third photoconductor 41c are selected as the two target photoconductors, the interval between the two target photoconductors is twice the arrangement interval SP1.

[0074] After performing the process of step S101, the adjustment unit 8d performs the process of step S102.

[0075] <Process S102> In step S102, the adjustment unit 8d sets a number i that identifies the plurality of conditions of the development voltage. In this embodiment, the number i is selected from three numbers 1 to 3. In the first step S102, the number i is set to 1.

[0076] After executing the process of step S102, the adjustment unit 8d executes the process of step S103.

[0077] <Process S103> In step S103, the adjustment unit 8d sets the output voltage of the voltage output circuit 4b to the ith developing voltage, which is one of a plurality of candidate voltages. As a result, the set developing voltage is applied to the four developing rollers 431.

[0078] After executing the process of step S103, the adjustment unit 8d executes the process of step S104.

[0079] <Process S104> In step S104, the adjustment unit 8d causes the image forming unit 4x to execute the ith test output process. The ith test output process in the first example is a process of forming an ith test toner image on the surface of each of the two target photoconductors and transferring the ith test toner image to the surface of the intermediate transfer belt 441.

[0080] The i-th test toner image is one of the plurality of test toner images, and is formed under a condition where the i-th developing voltage is applied to four developing rollers 431.

[0081] After executing the process of step S104, the adjustment unit 8d executes the process of step S105.

[0082] <Process S105> In step S105, the adjustment unit 8d selects the next process depending on whether or not all of the plurality of test toner images for the two target photosensitive members selected in step S101 have been output.

[0083] Here, it is assumed that the total number of conditions of the developing voltages corresponding to the plurality of test toner images is N. In step S105, the adjustment unit 8d selects the next process depending on whether the Nth test output process has been executed or not.

[0084] If any of the N test toner images for the two target photoconductors has not yet been output, the adjustment unit 8d repeats the processes from step S102 onwards.

[0085] That is, the adjustment unit 8d counts up the number i in step S102 and then repeats the processes of steps S103 and S104 until all of the N test toner images for the two target photoconductors are output.

[0086] On the other hand, when all of the N test toner images for the two target photoconductors have been output, the adjustment unit 8d executes the process of step S106.

[0087] <Process S106> In step S106, the adjustment unit 8d selects the next process depending on whether all of the four photoconductors 41 have been selected as the two target photoconductors.

[0088] In the first example, if any of the four photoconductors 41 has not yet been selected as the two target photoconductors, the adjustment unit 8d repeats the processes from step S101 onwards.

[0089] In the first example, in the first step S101, the adjustment unit 8d selects the first photoconductor 41a and the third photoconductor 41c, which are arranged first and third among the four photoconductors 41, as the two target photoconductors.

[0090] Furthermore, in the second step S101, the adjustment unit 8d selects the second photoconductor 41b and the fourth photoconductor 41d, which are arranged second and fourth among the four photoconductors 41, as the two target photoconductors.

[0091] That is, in step S101, the adjustment unit 8d sequentially selects the two target photosensitive elements that are arranged first and third in the arrangement direction of the four photosensitive elements 41, and the remaining two target image carriers.

[0092] Even when the second photoconductor 41b and the fourth photoconductor 41d are selected as the two target photoconductors, the interval between the two target photoconductors is twice the arrangement interval SP1.

[0093] Each time two target photosensitive bodies are selected, the adjustment unit 8d causes the image forming unit 4x to execute the test output processes from the first to the Nth so that the N test toner images for each of the two target photosensitive bodies are transferred within an area on the surface of the intermediate transfer belt 441 whose length corresponds to the distance between the two target photosensitive bodies.

[0094] In the first example, each time two target photosensitive bodies are selected, the adjustment unit 8d causes the image forming unit 4x to execute the test output processes from the first to the Nth so that the N test toner images for each of the two target photosensitive bodies are transferred within an area having a length equivalent to twice the arrangement interval SP1 (see Figures 6 to 10).

[0095] In step S106, if all of the four photoconductors 41 have been selected as the two target photoconductors, the adjustment unit 8d ends the test output control.

[0096] 6 to 10 show the process of forming three test toner images on each of the four photoconductors 41 by the first example of the test output control when N, which is the number of conditions of the development voltage, is three.

[0097] 6 to 8 show a state in which the processing of steps S104 is performed for the first to third times when the first photoconductor 41a and the third photoconductor 41c are selected as the two target photoconductors in the first step S101.

[0098] FIG. 6 shows a situation in which a first test toner image G1a for the first photosensitive member 41a and a first test toner image G1c for the third photosensitive member 41c are simultaneously transferred onto the intermediate transfer belt 441 in the first step S104.

[0099] The first test toner images G1a and G1c are one of the three test toner images for the first photoconductor 41a and the third photoconductor 41c, and are toner images formed under the first developing voltage.

[0100] FIG. 7 shows a situation in which the second test toner image G2a for the first photoconductor 41a and the second test toner image G2c for the third photoconductor 41c are simultaneously transferred onto the intermediate transfer belt 441 in the second step S104.

[0101] The second test toner images G2a and G2c are one of the three test toner images for the first photoconductor 41a and the third photoconductor 41c, and are toner images formed under the second developing voltage.

[0102] FIG. 8 shows a situation in which a third test toner image G3a for the first photoconductor 41a and a third test toner image G3c for the third photoconductor 41c are simultaneously transferred onto the intermediate transfer belt 441 in the third step S104.

[0103] The third test toner images G3a and G3c are one of the three test toner images for the first photoconductor 41a and the third photoconductor 41c, and are toner images formed under the third developing voltage.

[0104] 9 and 10 show a situation in which the processing of step S104 is performed for the first and third times when the second photoconductor 41b and the fourth photoconductor 41d are selected as the two target photoconductors in step S101 for the second time.

[0105] FIG. 9 shows a situation in which a first test toner image G1b for the second photoconductor 41b and a first test toner image G1d for the fourth photoconductor 41d are simultaneously transferred onto the intermediate transfer belt 441 in the first step S104.

[0106] The first test toner images G1b and G1d are one of the three test toner images for the second photoconductor 41b and the fourth photoconductor 41d, and are toner images formed under the first developing voltage.

[0107] In FIG. 10, second test toner images G2b and G2d are one of three test toner images for the second photoconductor 41b and the fourth photoconductor 41d, and are toner images formed under the second developing voltage.

[0108] FIG. 10 shows a situation in which a third test toner image G3b for the second photosensitive member 41b and a third test toner image G3d for the fourth photosensitive member 41d are simultaneously transferred onto the intermediate transfer belt 441 in the third step S104.

[0109] The third test toner images G3b and G3d are one of the three test toner images for the second photoconductor 41b and the fourth photoconductor 41d, and are toner images formed under the third developing voltage.

[0110] As shown in Figures 6 to 10, when the number of conditions for the development voltage is three, each time two target photosensitive bodies are selected, the adjustment unit 8d causes the image forming unit 4x to execute the first to third test output processes so that three test toner images for each of the two target photosensitive bodies are transferred within an area with a length equivalent to twice the arrangement interval SP1.

[0111] By adopting the first example of the test output control, it is possible to efficiently form N test toner images while ensuring the length of the area on the surface of the intermediate transfer belt 441 where the N test toner images are formed.

[0112] The first example of the test output control is particularly effective when the voltage output circuit 4b takes a relatively long time to change the development voltage.

[0113] [Development Parameter Adjustment Process] Next, an example of the procedure for the development parameter adjustment process will be described with reference to the flowchart shown in FIG.

[0114] The adjustment section 8d executes the development parameter adjustment process in parallel with the test output control.

[0115] In the following description, S201, S202, ... represent identification codes of a plurality of steps in the development parameter adjustment processing. In the development parameter adjustment processing, the processing of step S201 is executed first.

[0116] <Process S201> In step S201, the adjustment unit 8d waits until the detection timing arrives, and when the detection timing arrives, executes the process of step S202.

[0117] The detection timing is the timing when any one of the N test toner images for each of the four photoconductors 41 passes a position facing the density detection unit 6. In the following description, one of the N test toner images for each of the four photoconductors 41 that passes a position facing the density detection unit 6 is referred to as a target toner image.

[0118] <Process S202> In step S202, the adjusting unit 8d acquires information on the detected density of the target toner image from the density detecting unit 6, and stores the information on the detected density.

[0119] After executing the process of step S202, the adjustment unit 8d executes the process of step S203.

[0120] <Process S203> In step S203, the adjustment unit 8d selects the next process depending on whether or not the information on the detected densities of all of the N test toner images for each of the four photoconductors 41 has been acquired.

[0121] If the adjustment unit 8d has not completed obtaining the information on the detected densities of all of the N test toner images for each of the four photoconductors 41, the adjustment unit 8d repeats the processes of steps S201 to S203.

[0122] On the other hand, when the acquisition of the information on the detected densities of all of the N test toner images for each of the four photoconductors 41 is completed, the adjusting unit 8d executes the process of step S204.

[0123] <Process S204> In step S204, the adjustment unit 8d adjusts the development parameters for each development color in accordance with the detected densities of the N test toner images for each development color.

[0124] For example, the development parameters may include a correction value for the development voltage for each of a plurality of densities of the output image. The development parameters may also include a correction value for the exposure intensity of the exposure device 4a for each of a plurality of densities of the output image.

[0125] After executing the process of step S204, the adjustment section 8d ends the development parameter adjustment process.

[0126] The development parameter adjustment process is an example of a process for adjusting the image forming unit 4x in accordance with the densities detected by the density detection unit 6 of the plurality of test toner images.

[0127] [Second example of test image output control] Next, the procedure of the second example of the test output control will be described with reference to the flowchart shown in FIG.

[0128] In the following description, S301, S302, ... represent identification symbols of a plurality of steps in the second example of test output control. In the second example of test output control, the processing of step S301 is executed first.

[0129] <Process S301> In step S301, the adjustment unit 8d sets a number i that identifies a plurality of conditions of the development voltage. The number i is selected from N numbers ranging from 1 to N. In the first step S301, the number i is set to 1.

[0130] After executing the process of step S301, the adjustment unit 8d executes the process of step S302.

[0131] <Process S302> In step S302, the adjustment unit 8d sets the output voltage of the voltage output circuit 4b to the ith developing voltage, which is one of a plurality of candidate voltages. As a result, the set developing voltage is applied to the four developing rollers 431.

[0132] After executing the process of step S302, the adjustment unit 8d executes the process of step S303.

[0133] <Process S303> In step S303, the adjustment unit 8d causes the image forming unit 4x to execute the ith test output process. The ith test output process in the second example is a process of forming an ith test toner image on the surface of each of the four photoconductors 41 and transferring the ith test toner image to the surface of the intermediate transfer belt 441.

[0134] The i-th test toner image is one of the plurality of test toner images, and is formed under a condition where the i-th developing voltage is applied to four developing rollers 431.

[0135] After executing the process of step S303, the adjustment unit 8d executes the process of step S304.

[0136] <Process S304> In step S304, the adjustment unit 8d selects the next process depending on whether or not all of the plurality of test toner images for the four photoconductors 41 have been output.

[0137] Here, it is assumed that the total number of conditions of the developing voltage corresponding to the plurality of test toner images is N. In step S304, the adjustment unit 8d selects the next process depending on whether the Nth test output process has been executed or not.

[0138] If any of the N test toner images for the four photoconductors 41 has not yet been output, the adjustment unit 8d repeats the processes from step S301 onwards.

[0139] That is, the adjustment unit 8d counts up the number i in step S301 and then repeats the processes of steps S302 and S303 until all of the N test toner images for the four photoconductors 41 are output.

[0140] On the other hand, when all of the N test toner images for the four photoconductors 41 have been output, the adjustment unit 8d ends the test image output control.

[0141] The adjustment section 8d also executes the development parameter adjustment process shown in FIG. 5 when the second example of the test image output control is executed.

[0142] In the second example, the adjustment unit 8d causes the image forming unit 4x to execute test output processes from the first to the Nth so that the N test toner images for each of the four photosensitive elements 41 are transferred within an area of length corresponding to the arrangement interval SP1 on the surface of the intermediate transfer belt 441 (see Figures 12 and 13).

[0143] 12 and 13 show the process of forming three test toner images for each of the four photoconductors 41 by the second example of the test output control when N, which is the number of conditions of the development voltage, is three.

[0144] FIG. 12 shows a situation in which four first test toner images G1a, G1b, G1c, and G1d for four photoconductors 41 are simultaneously transferred onto the intermediate transfer belt 441 in the first step S303.

[0145] FIG. 13 shows a situation in which four third test toner images G3a, G3b, G3c, and G3d for four photoconductors 41 are simultaneously transferred onto the intermediate transfer belt 441 in the third step S303.

[0146] As shown in Figures 12 and 13, when the number of conditions for the development voltage is three, the adjustment unit 8d causes the image forming unit 4x to execute the first to third test output processes so that three test toner images for each of the four photosensitive drums 41 are transferred within an area of a length corresponding to the arrangement interval SP1.

[0147] By adopting the second example of the test output control, N test toner images can be efficiently formed on the surface of the intermediate transfer belt 441.

[0148] The second example of the test output control is effective when the time required for the voltage output circuit 4b to change the development voltage is relatively short.

[0149] [Notes on the Invention] The following is a summary of the invention extracted from the above-described embodiment. Note that the configurations and processing functions described in the following supplementary notes can be selected and combined as desired.

[0150] <Appendix 1> an image forming unit including a plurality of image carriers arranged at intervals and a plurality of toner carriers arranged corresponding to the plurality of image carriers and to which a common developing voltage is applied, and forming a toner image of each of a plurality of developing colors on the surface of each of the plurality of image carriers by toner supplied from each of the plurality of toner carriers; a transfer device including an intermediate transfer body, which transfers the toner images on the surfaces of the plurality of image carriers to the intermediate transfer body, and further transfers the toner images transferred to the intermediate transfer body to a sheet; a density detection unit that detects the density of a toner image formed on the surface of the intermediate transfer body; a control unit that causes the image forming unit to execute a test output process in which a plurality of test toner images, each having a different developing voltage condition, are sequentially formed on the surface of each of the plurality of image carriers and transferred to the intermediate transfer body, and adjusts the image forming unit in accordance with the densities of the plurality of test toner images detected by the density detection unit, the control unit sequentially selects, from the plurality of image carriers, a plurality of target image carriers that are arranged at a distance greater than the arrangement interval of the plurality of image carriers, and causes the image forming unit to execute the test output process so that, each time one of the plurality of target image carriers is selected, the plurality of test toner images for each of the plurality of target image carriers are transferred within an area on the surface of the intermediate transfer body whose length corresponds to the interval between the plurality of target image carriers.

[0151] <Appendix 2> the image forming unit includes four image carriers and four toner carriers corresponding to four developing colors, The image forming apparatus described in Appendix 1, wherein the control unit sequentially selects the two target image carriers that are arranged first and third in the arrangement direction of the four image carriers, and the remaining two target image carriers.

[0152] <Appendix 3> an image forming unit including a plurality of image carriers arranged at intervals and a plurality of toner carriers arranged corresponding to the plurality of image carriers and to which a common developing voltage is applied, and forming a toner image of each of a plurality of developing colors on the surface of each of the plurality of image carriers by toner supplied from each of the plurality of toner carriers; a transfer device including an intermediate transfer body, which transfers the toner images on the surfaces of the plurality of image carriers to the intermediate transfer body, and further transfers the toner images transferred to the intermediate transfer body to a sheet; a density detection unit that detects the density of a toner image formed on the surface of the intermediate transfer body; a control unit that causes the image forming unit to execute a test output process in which a plurality of test toner images, each having a different developing voltage condition, are sequentially formed on the surface of each of the plurality of image carriers and transferred to the intermediate transfer body, and adjusts the image forming unit in accordance with the densities of the plurality of test toner images detected by the density detection unit, the control unit causes the image forming unit to execute the test output process so that the multiple test toner images for each of the multiple image carriers are transferred within an area having a length corresponding to an arrangement interval of the multiple image carriers on the surface of the intermediate transfer body.

[0153] <Appendix 4> 4. The image forming apparatus according to claim 3, wherein the image forming unit includes four image carriers and four toner carriers corresponding to four developing colors. [Explanation of symbols]

[0154] 4: Printing device 4a: exposure device 4b: Voltage output circuit 4x: Image forming section 6: Concentration detection unit 8: Control device (control unit) 10: Image forming device 40: Unit image forming unit 41: Photoreceptor 42: Charging device 43: Developing device 44: Transcription device 45: Drum cleaning device 46: Fixing device 441: Intermediate transfer belt (intermediate transfer body) 442: Primary transfer device 443: Secondary transfer device

Claims

1. an image forming unit including a plurality of image carriers arranged at intervals and a plurality of toner carriers arranged corresponding to the plurality of image carriers and to which a common developing voltage is applied, and forming a toner image of each of a plurality of developing colors on the surface of each of the plurality of image carriers by toner supplied from each of the plurality of toner carriers; a transfer device including an intermediate transfer body, which transfers the toner images on the surfaces of the plurality of image carriers to the intermediate transfer body, and further transfers the toner images transferred to the intermediate transfer body to a sheet; a density detection unit that detects the density of a toner image formed on the surface of the intermediate transfer body; a control unit that causes the image forming unit to execute a test output process in which a plurality of test toner images, each having a different developing voltage condition, are sequentially formed on the surface of each of the plurality of image carriers and transferred to the intermediate transfer body, and adjusts the image forming unit in accordance with the densities of the plurality of test toner images detected by the density detection unit, the control unit sequentially selects, from the plurality of image carriers, a plurality of target image carriers that are arranged at a distance greater than the arrangement interval of the plurality of image carriers, and causes the image forming unit to execute the test output process so that, each time one of the plurality of target image carriers is selected, the plurality of test toner images for each of the plurality of target image carriers are transferred within an area on the surface of the intermediate transfer body whose length corresponds to the interval between the plurality of target image carriers.

2. the image forming unit includes four image carriers and four toner carriers corresponding to four developing colors, 2. The image forming apparatus according to claim 1, wherein the control unit sequentially selects the two target image carriers that are arranged first and third in the arrangement direction of the four image carriers and the remaining two target image carriers.

3. an image forming unit including a plurality of image carriers arranged at intervals and a plurality of toner carriers arranged corresponding to the plurality of image carriers and to which a common developing voltage is applied, and forming a toner image of each of a plurality of developing colors on the surface of each of the plurality of image carriers by toner supplied from each of the plurality of toner carriers; a transfer device including an intermediate transfer body, which transfers the toner images on the surfaces of the plurality of image carriers to the intermediate transfer body, and further transfers the toner images transferred to the intermediate transfer body to a sheet; a density detection unit that detects the density of a toner image formed on the surface of the intermediate transfer body; a control unit that causes the image forming unit to execute a test output process in which a plurality of test toner images, each having a different developing voltage condition, are sequentially formed on the surface of each of the plurality of image carriers and transferred to the intermediate transfer body, and adjusts the image forming unit in accordance with the densities of the plurality of test toner images detected by the density detection unit, the control unit causes the image forming unit to execute the test output process so that the multiple test toner images for each of the multiple image carriers are transferred within an area having a length corresponding to an arrangement interval of the multiple image carriers on the surface of the intermediate transfer body.

4. 4. The image forming apparatus according to claim 3, wherein said image forming section includes four image carriers and four toner carriers corresponding to four developing colors.

Images