Image forming apparatus

Abstract

To provide an image forming apparatus capable of setting a developing bias corresponding to a temperature and humidity environment.SOLUTION: The control unit 100 of the image forming apparatus 1 executes a developing bias setting process of setting a developing bias at which the density of the patch image becomes a predetermined target density based on the density of the patch image formed on the transfer belt 73 by applying the first developing bias to the developing roller 55 and the density of the patch image formed on the transfer belt 73 by applying the second developing bias larger than the first developing bias by a predetermined value to the developing roller 55. In the developing bias setting process, the controller 100 can execute a patch bias setting process of setting a first developing bias and a second developing bias for forming a patch image on the transfer belt 73. In the patch bias setting process, the controller 100 sets the first developing bias and the second developing bias in accordance with the temperature and humidity detected by the temperature and humidity sensor 14 while maintaining the difference between the first developing bias and the second developing bias at a predetermined value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus. [Background technology]

[0002] A conventional image forming apparatus is known that forms a patch image on a belt and sets a development bias based on the density of the formed patch image (Patent Document 1). In this technology, a gradient coefficient of density relative to the development bias is obtained based on the density of a patch image formed by applying a low test bias to the development roller and the density of a patch image formed by applying a high test bias to the development roller, and a development bias corresponding to a target density is set. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-125432 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the gradient of the density of the patch image relative to the developing bias changes depending on the temperature and humidity environment. Therefore, it is desirable to be able to set the development bias in accordance with the temperature and humidity environment. [Means for solving the problem]

[0005] In a first disclosure of the present application, an image forming apparatus includes an image forming unit, a density sensor, a temperature and humidity sensor, and a control unit. The image forming unit has a developing roller and is capable of forming a toner patch image on a transfer target. The density sensor is capable of measuring the density of a patch image formed on a transfer target. The temperature and humidity sensor detects the temperature and humidity. The control unit executes a developing bias setting process for setting a developing bias to be applied to the developing roller during printing. The developing bias setting process includes the following processes. A process in which a first developing bias is applied to a developing roller to form a patch image on a transfer target, and a second developing bias that is a predetermined value greater than the first developing bias is applied to the developing roller to form a patch image on the transfer target. A process in which the density of a patch image formed on a transfer target is measured by a density sensor. A process of setting a development bias based on the density of a patch image formed by applying a first development bias to a development roller and the density of a patch image formed by applying a second development bias to a development roller, so that the density of the patch image becomes a predetermined target density. In the developing bias setting process, the control unit can execute a patch bias setting process for setting a first developing bias and a second developing bias for forming a patch image on a transfer target. In the patch bias setting process, the control unit sets the first and second developing biases in accordance with the temperature and humidity detected by the temperature and humidity sensor while maintaining the difference between the first and second developing biases at a predetermined value.

[0006] In the patch bias setting process, the control unit sets the first and second developing biases in accordance with the temperature and humidity detected by the temperature and humidity sensor while keeping the difference between the first and second developing biases at a predetermined value, thereby making it possible to set the first and second developing biases to appropriate values ​​in accordance with the temperature and humidity. This makes it possible to set the developing bias in accordance with the temperature and humidity environment.

[0007] In the second disclosure of the present application, in the image forming apparatus of the first disclosure, when executing a patch bias setting process, the control unit sets the magnitude of the first development bias and the magnitude of the second development bias to predetermined magnitudes when the first environment is one in which the temperature and humidity detected by the temperature and humidity sensor are within a predetermined first temperature and humidity range. When executing the patch bias setting process, the control unit reduces the magnitude of the first developing bias and the magnitude of the second developing bias compared to that in the first environment when the second environment is one in which at least one of the temperature and humidity detected by the temperature and humidity sensor is in a second temperature and humidity range higher than the first temperature and humidity range.

[0008] In the second environment, the magnitude of the first developing bias and the magnitude of the second developing bias are made smaller than those in the first environment, thereby making it possible to set an appropriate developing bias according to the second environment in which at least one of the temperature and humidity is higher than that in the first environment.

[0009] In the third disclosure of the present application, in the image forming apparatus of the second disclosure, when executing a patch bias setting process, the control unit increases the magnitude of the first development bias and the magnitude of the second development bias compared to the first environment when the third environment is one in which at least one of the temperature and humidity detected by the temperature and humidity sensor is in a third temperature and humidity range that is lower than the first temperature and humidity range.

[0010] In the third environment, the magnitude of the first developing bias and the magnitude of the second developing bias are made larger than those in the first environment, so that an appropriate developing bias can be set according to the third environment in which at least one of the temperature and humidity is lower than that in the first environment.

[0011] In the fourth disclosure of the present application, in the image forming apparatus of the second disclosure, when executing a patch bias setting process, the control unit reduces the magnitude of the first developing bias and the magnitude of the second developing bias compared to the second environment when the fourth environment is one in which at least one of the temperature and humidity detected by the temperature and humidity sensor is in a fourth temperature and humidity range that is higher than the second temperature and humidity range.

[0012] In the fourth environment, the magnitude of the first developing bias and the magnitude of the second developing bias are made smaller than those in the second environment, thereby making it possible to set an appropriate developing bias according to the fourth environment in which at least one of the temperature and humidity is higher than that in the second environment.

[0013] In the fifth disclosure of the present application, in the image forming apparatus of the third disclosure, when executing a patch bias setting process, the control unit increases the magnitude of the first developing bias and the magnitude of the second developing bias compared to the third environment when the fifth environment is one in which at least one of the temperature and humidity detected by the temperature and humidity sensor is in a fifth temperature and humidity range lower than the third temperature and humidity range.

[0014] In the fifth environment, the magnitude of the first developing bias and the magnitude of the second developing bias are made larger than those in the third environment, so that an appropriate developing bias can be set according to the fifth environment in which at least one of the temperature and humidity is lower than that in the third environment.

[0015] In the sixth disclosure of the present application, in the image forming apparatus of the third disclosure, when executing a patch bias setting process, the control unit reduces the magnitude of the first developing bias and the magnitude of the second developing bias by a first magnitude in the second environment compared to the first environment. When executing the patch bias setting process, the control unit increases the magnitude of the first developing bias and the magnitude of the second developing bias in the third environment by a second magnitude compared to the magnitude in the first environment.

[0016] In a seventh disclosure of the present application, in the image forming apparatus of the sixth disclosure, the first size and the second size are the same value.

[0017] In an eighth disclosure of the present application, in the image forming apparatus of the seventh disclosure, the first size and the second size are half the predetermined value.

[0018] In a ninth disclosure of the present application, in the image forming apparatus of the first disclosure, the image forming apparatus includes a device main body and a toner cartridge that contains toner and is detachably attachable to the device main body. The control unit executes the patch bias setting process in the first developing bias setting process, which is the first developing bias setting process executed after determining that a new toner cartridge has been installed in the device main body.

[0019] By executing the patch bias setting process in the first developing bias setting process, which is the first developing bias setting process, it is possible to set the developing bias according to the temperature and humidity environment in the first developing bias setting process.

[0020] In the tenth disclosure of the present application, in the image forming apparatus of the ninth disclosure, in the second developing bias setting process, which is the second or subsequent developing bias setting process executed after the first developing bias setting process has been executed, the control unit sets the magnitude of the first developing bias to a value smaller than the magnitude of the reference bias, using the developing bias used in the immediately previous printing as the reference bias, and sets the magnitude of the second developing bias to a value larger than the magnitude of the reference bias and larger than the first developing bias by a predetermined value.

[0021] In the second developing bias setting process, which is the second or subsequent developing bias setting process, the developing bias used in the immediately preceding printing is used as the reference bias, so that an appropriate developing bias can be set.

[0022] In an eleventh disclosure of the present application, in the image forming apparatus of the first disclosure, the image forming apparatus includes an endless belt as a transfer object. [Effects of the Invention]

[0023] The developing bias can be set according to the temperature and humidity environment. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a cross-sectional view showing an image forming apparatus. [Figure 2] FIG. 2 is a perspective view showing a transfer unit and a density sensor. [Figure 3] FIG. 10 is a diagram illustrating a developing bias setting process. [Figure 4] FIG. 4 is a diagram showing an example of a table for setting a second bias according to the first embodiment. [Figure 5] 10A to 10C are diagrams illustrating a first patch bias setting process according to the first embodiment. [Figure 6]10A to 10C are diagrams illustrating a first patch bias setting process according to the first embodiment. [Figure 7] 10 is a flowchart illustrating an example of the operation of a control unit. [Figure 8] 10 is a flowchart illustrating an example of a test bias setting process. [Figure 9] FIG. 10 is a diagram showing an example of a table for setting a second bias according to the second embodiment. [Figure 10] 10A to 10C are diagrams illustrating a first patch bias setting process according to the second embodiment. [Figure 11] 10A to 10C are diagrams illustrating a first patch bias setting process according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] Next, a first embodiment will be described. As shown in FIG. 1, the image forming device 1 is a color printer and includes a device main body 10, a cover 11, a sheet supply unit 20, an image forming unit 30, a sheet discharge unit 90, a concentration sensor 13, a temperature and humidity sensor 14, and a control unit 100.

[0026] The device body 10 has an opening 10A. The cover 11 opens and closes the opening 10A. The cover 11 is movable between a closed position where the opening 10A is closed and an open position where the opening 10A is open. Specifically, the cover 11 is rotatable between the closed position and the open position.

[0027] The sheet supply unit 20 includes a sheet tray 21 and a sheet supply mechanism 22. The sheet tray 21 stores sheets S. The sheet supply mechanism 22 supplies the sheets S in the sheet tray 21 to the image forming unit 30.

[0028] The image forming section 30 includes four exposure units 40, four process cartridges 50, a transfer unit 70, and a fixing unit 80.

[0029] The exposure unit 40 has a plurality of LEDs. The exposure unit 40 exposes the photosensitive drum 53 to light emitted from the LEDs. The exposure unit 40 is held by the cover 11.

[0030] The process cartridges 50 include a process cartridge 50Y corresponding to yellow, a process cartridge 50M corresponding to magenta, a process cartridge 50C corresponding to cyan, and a process cartridge 50K corresponding to black.

[0031] The process cartridges 50 are arranged in the order of process cartridges 50Y, 50M, 50C, and 50K from upstream to downstream in the conveying direction of the sheet S. In this specification and drawings, when distinguishing between the colors yellow, magenta, cyan, and black, Y, M, C, and K are added to the reference symbols.

[0032] Each process cartridge 50 includes a drum cartridge 51 and a developing cartridge 52. The developing cartridge 52 is detachable from the drum cartridge 51. The developing cartridge 52 is an example of a "toner cartridge."

[0033] The drum cartridges 51 include drum cartridge 51Y, drum cartridge 51M, drum cartridge 51C, and drum cartridge 51K. Each drum cartridge 51 has a photosensitive drum 53 and a charger 54. The photosensitive drums 53 include photosensitive drum 53Y on which a yellow toner image is formed, photosensitive drum 53M on which a magenta toner image is formed, photosensitive drum 53C on which a cyan toner image is formed, and photosensitive drum 53K on which a black toner image is formed.

[0034] The developing cartridges 52 include a developing cartridge 52Y that contains yellow toner, a developing cartridge 52M that contains magenta toner, a developing cartridge 52C that contains cyan toner, and a developing cartridge 52K that contains black toner. Each developing cartridge 52 has a developing roller 55 and a toner storage section 56 that stores toner.

[0035] The developing rollers 55 include a developing roller 55Y that carries yellow toner, a developing roller 55M that carries magenta toner, a developing roller 55C that carries cyan toner, and a developing roller 55K that carries black toner.

[0036] The process cartridge 50 is detachably attached to the apparatus main body 10. Specifically, the process cartridge 50 is detachably attached to the apparatus main body 10 through the opening 10A with the cover 11 open. The developing cartridge 52 is detachably attached to the apparatus main body 10 with the developing cartridge 52 attached to the drum cartridge 51.

[0037] The transfer unit 70 includes a drive roller 71, a driven roller 72, a transfer belt 73 as a transfer object, and four transfer rollers 74. The drive roller 71 is a roller that rotates the transfer belt 73. The transfer belt 73 is stretched between the drive roller 71 and the driven roller 72. The transfer belt 73 is an endless belt that transports the sheet S between the transfer belt 73 and the photosensitive drum 53. The outer peripheral surface of the transfer belt 73 is in contact with the photosensitive drum 53. The transfer roller 74 sandwiches the transfer belt 73 between itself and the photosensitive drum 53.

[0038] The fixing unit 80 includes a heating roller 81 and a pressure roller 82. The heating roller 81 includes a heater 81A therein. The pressure roller 82 sandwiches the sheet S between itself and the heating roller 81.

[0039] When printing is performed, the charger 54 charges the surface of the rotating photosensitive drum 53. The exposure unit 40 exposes the surface of the charged photosensitive drum 53 to light. As a result, an electrostatic latent image is formed on the photosensitive drum 53. The developing roller 55 supplies toner to the photosensitive drum 53. As a result, a toner image is formed on the photosensitive drum 53.

[0040] The photosensitive drum 53 and the transfer roller 74 transport the sheet S supplied from the sheet supply unit 20. At this time, the transfer roller 74 transfers the toner image formed on the photosensitive drum 53 onto the sheet S. The heating roller 81 and the pressure roller 82 fix the toner image onto the sheet S while transporting the sheet S onto which the toner image has been transferred. In this way, an image is formed on the sheet S.

[0041] The sheet discharge section 90 conveys the sheet S on which the image has been formed toward the outside of the apparatus body 10. The sheet discharge section 90 includes a conveying roller 91 and a discharge roller 92. The conveying roller 91 conveys the sheet S toward the discharge roller 92. The discharge roller 92 discharges the sheet S onto the discharge tray 12.

[0042] As shown in FIGS. 1 and 2, the density sensor 13 can measure the density of a toner patch image P formed on the transfer belt 73. The patch image P is a test toner image for correcting the density of the toner image. The density sensor 13 faces the surface of the transfer belt 73. As an example, the density sensor 13 is an optical sensor having a light-emitting element and a light-receiving element. The light-emitting element emits light toward the transfer belt 73. The light-receiving element receives reflected light of the light emitted from the light-emitting element.

[0043] The image forming unit 30 is capable of forming a patch image P on the transfer belt 73. When forming the patch image P, the image forming unit 30 transfers a toner image formed on the photosensitive drum 53 to the transfer belt 73 by the transfer roller 74. The image forming unit 30 is capable of forming patch images PY, PM, PC, and PK corresponding to the respective colors of yellow, magenta, cyan, and black on the transfer belt 73. The patch images P formed on the transfer belt 73 are collected by the belt cleaner 75 after the density is measured by the density sensor 13.

[0044] The temperature and humidity sensor 14 detects temperature and humidity. In this embodiment, the temperature and humidity sensor 14 detects the temperature and humidity inside the device main body 10. The temperature and humidity sensor 14 may also detect the temperature and humidity outside the device main body 10. The temperature and humidity sensor 14 may also be configured to detect both temperature and humidity, or may be configured to include a temperature sensor that detects temperature and a humidity sensor that detects humidity separately.

[0045] The control unit 100 includes a CPU, RAM, ROM, input / output circuits, etc. The control unit 100 executes control by performing arithmetic processing based on programs and data stored in the ROM, etc. The control unit 100 executes a developing bias setting process.

[0046] The developing bias setting process is a process for setting the developing bias Vb to be applied to the developing roller 55 during printing. The control unit 100 can execute the developing bias setting process for each of the developing rollers 55Y, 55M, 55C, and 55K, and sets the developing biases VbY, VbM, VbC, and VbK.

[0047] The developing bias setting process includes a test bias setting process, a patch image forming process, a density measurement process, and a print bias setting process. In other words, the control unit 100 can execute the test bias setting process, the patch image forming process, the density measurement process, and the print bias setting process in the developing bias setting process. In this embodiment, the toner is a positively charged dry toner, and the developing bias Vb is a positive bias.

[0048] 3, in the test bias setting process, the control unit 100 sets a first developing bias Vr1 and a second developing bias Vr2 for forming a patch image P on the transfer belt 73 in the patch image forming process. The second developing bias Vr2 is a developing bias that is larger than the first developing bias Vr1 by a predetermined value ΔV. In the first embodiment, the predetermined value ΔV is, for example, 100 V.

[0049] In the patch image forming process, the control unit 100 forms a patch image P on the transfer belt 73. More specifically, the control unit 100 applies a first developing bias Vr1 to the developing roller 55 to form the patch image P on the transfer belt 73. The control unit 100 also applies a second developing bias Vr2 to the developing roller 55 to form the patch image P on the transfer belt 73.

[0050] In the density measurement process, the control unit 100 measures the density of the patch image P formed on the transfer belt 73 using the density sensor 13. In this embodiment, the control unit 100 acquires a first density Dm1 and a second density Dm2. The first density Dm1 is the density of the patch image P formed by applying a first developing bias Vr1 to the developing roller 55. The second density Dm2 is the density of the patch image P formed by applying a second developing bias Vr2 to the developing roller 55.

[0051] In the print bias setting process, control unit 100 sets development bias Vb based on the measured density of patch image P. In this embodiment, control unit 100 sets development bias Vb based on a first density Dm1 and a second density Dm2. Specifically, control unit 100 calculates a straight line L from the first development bias Vr1 and the first density Dm1, and the second development bias Vr2 and the second density Dm2. Then, control unit 100 sets development bias Vb from the calculated straight line L so that the density of patch image P becomes a predetermined target density Dr.

[0052] In the developing bias setting process, the first developing bias Vr1 may be applied to the developing roller 55 to form a patch image P, the density Dm1 of this patch image P may be measured by the density sensor 13, and then the second developing bias Vr2 may be applied to the developing roller 55 to form the patch image P. Alternatively, the first developing bias Vr1 may be applied to the developing roller 55 to form a patch image P, and then the second developing bias Vr2 may be applied to the developing roller 55 to form the patch image P, and then the densities Dm1 and Dm2 of the patch image P may be measured by the density sensor 13. Alternatively, the second developing bias Vr2 may be applied to the developing roller 55 first to form the patch image P, and then the first developing bias Vr1 may be applied to the developing roller 55 to form the patch image P.

[0053] The control unit 100 can execute a first developing bias setting process and a second developing bias setting process as the developing bias setting process. The first developing bias setting process is the first developing bias setting process that is executed after it is determined that a new developing cartridge 52 has been installed in the apparatus main body 10. The second developing bias setting process is the second or subsequent developing bias setting process that is executed after the first developing bias setting process has been executed.

[0054] As an example, after executing the first developing bias setting process, the control unit 100 executes the second developing bias setting process every time printing is executed on a predetermined number (e.g., 1000 sheets) of sheets S. Furthermore, after executing the first developing bias setting process, the control unit 100 executes the second developing bias setting process when the user performs an operation to instruct setting of the developing bias Vb.

[0055] The test bias setting process includes a first patch bias setting process and a second patch bias setting process. The first patch bias setting process corresponds to a "patch bias setting process." When executing the first developing bias setting process, the control unit 100 executes the first patch bias setting process as the test bias setting process. When executing the second developing bias setting process, the control unit 100 executes the second patch bias setting process as the test bias setting process.

[0056] In the first patch bias setting process, the control unit 100 sets the first developing bias Vr1 and the second developing bias Vr2 according to the temperature and humidity detected by the temperature and humidity sensor 14, while maintaining the difference between the first developing bias Vr1 and the second developing bias Vr2 at a predetermined value ΔV.

[0057] In the first embodiment, when the control unit 100 executes the first patch bias setting process, it sets the first developing bias Vr1 and the second developing bias Vr2 according to the following equations (1) and (2). Vr1=V0+V1-V2 (1) Vr2=V0+V1+V2 (2)

[0058] In equations (1) and (2), V0 is a reference bias. The reference bias V0 is a bias that serves as a reference between the first developing bias Vr1 and the second developing bias Vr2. In the first patch bias setting process, the control unit 100 sets the reference bias V0 to an initial reference bias Va. The control unit 100 stores the initial reference bias Va in advance for each color: yellow, magenta, cyan, and black. As an example, the initial reference bias Va is equal to or greater than 250 [V] and equal to or less than 350 [V].

[0059] V1 is a first bias. The first bias V1 is a shift amount for shifting the reference bias V0 to a smaller or larger value in the first patch bias setting process. In the first patch bias setting process, the control unit 100 sets the first bias V1 based on the temperature and humidity detected by the temperature and humidity sensor 14 and a pre-stored table such as that shown in FIG.

[0060] V2 is the second bias. The second bias V2 is a bias difference for determining the first developing bias Vr1 by reducing the reference bias (V0+V1 taking into account the temperature and humidity environment in the first embodiment) and for determining the second developing bias Vr2 by increasing it. In the first embodiment, the second bias V2 is a fixed value. The second bias V2 is half the magnitude of the predetermined value ΔV. In the first embodiment, the second bias V2 is, for example, 50 [V].

[0061] 4, the table has preset first temperature and humidity ranges R1, R2, R3, R4, and R5. In the first temperature and humidity range R1, the first bias V1 is set to 0 V.

[0062] The second temperature and humidity region R2 is a region where at least one of the temperature and humidity is higher than that of the first temperature and humidity region R1, and the first bias V1 is set to -20 V. The third temperature and humidity region R3 is a region where at least one of the temperature and humidity is lower than that of the first temperature and humidity region R1, and the first bias V1 is set to 20 V.

[0063] The fourth temperature and humidity region R4 is a region where at least one of the temperature and humidity is higher than the second temperature and humidity region R2, and the first bias V1 is set to -50 V. The fifth temperature and humidity region R5 is a region where at least one of the temperature and humidity is lower than the third temperature and humidity region R3, and the first bias V1 is set to 50 V.

[0064] In the table, a temperature of "up to 15°C" indicates that the temperature is 15°C or lower. A temperature of "up to 18°C" indicates that the temperature is higher than 15°C but lower than 18°C. A temperature of "over 42°C" indicates that the temperature is higher than 42°C. Similarly, a humidity of "up to 9%" indicates that the humidity is 9% or lower. A humidity of "up to 14%" indicates that the humidity is higher than 9% but lower than 14%. A humidity of "over 89%" indicates that the humidity is higher than 89%.

[0065] For example, when the temperature detected by the temperature and humidity sensor 14 is 25°C and the humidity detected by the temperature and humidity sensor 14 is 50%, the control unit 100 refers to the table and sets the first bias V1 to 0 [V]. When the temperature detected by the temperature and humidity sensor 14 is 35°C and the humidity detected by the temperature and humidity sensor 14 is 70%, the control unit 100 refers to the table and sets the first bias V1 to -50 [V].

[0066] 3, in a normal temperature and normal humidity environment where the temperature and humidity detected by the temperature and humidity sensor 14 are within the first temperature and humidity range R1, the control unit 100 sets the magnitude of the first developing bias Vr1 (Vr11) and the magnitude of the second developing bias Vr2 (Vr21) to predetermined magnitudes. The normal temperature and normal humidity environment corresponds to the "first environment."

[0067] Specifically, when the temperature and humidity detected by the temperature and humidity sensor 14 are within the first temperature and humidity region R1 of the table, the control unit 100 sets the first bias V1 to 0 [V]. Next, the control unit 100 sets the first developing bias Vr11 to (V0-50) [V] and sets the second developing bias Vr21 to (V0+50) [V]. The difference between the first developing bias Vr11 and the second developing bias Vr21 is a predetermined value ΔV.

[0068] 5, in a first high-temperature, high-humidity environment in which the temperature and humidity detected by the temperature and humidity sensor 14 are in the second temperature and humidity range R2, the control unit 100 reduces the magnitude of the first developing bias Vr1 (Vr12) and the magnitude of the second developing bias Vr2 (Vr22) compared to a normal-temperature, normal-humidity environment. The first high-temperature, high-humidity environment corresponds to the "second environment."

[0069] Specifically, in the first high-temperature, high-humidity environment, the control unit 100 reduces the magnitude of the first developing bias Vr12 by a first magnitude A1 compared to the magnitude of the first developing bias Vr11 in the normal-temperature, normal-humidity environment. Also, the control unit 100 reduces the magnitude of the second developing bias Vr22 by the first magnitude A1 compared to the magnitude of the second developing bias Vr21 in the normal-temperature, normal-humidity environment. In the first embodiment, the first magnitude A1 is 20 V.

[0070] Specifically, when the temperature and humidity detected by the temperature and humidity sensor 14 are in the second temperature and humidity region R2 of the table (see FIG. 4), the control unit 100 sets the first bias V1 to -20 [V]. Next, the control unit 100 sets the first developing bias Vr12 to (V0-20-50) [V] and sets the second developing bias Vr22 to (V0-20+50) [V]. The difference between the first developing bias Vr12 and the second developing bias Vr22 is a predetermined value ΔV.

[0071] In the second high-temperature, high-humidity environment where the temperature and humidity detected by the temperature and humidity sensor 14 are in the fourth temperature and humidity range R4, the control unit 100 reduces the magnitude of the first developing bias Vr1 (Vr14) and the magnitude of the second developing bias Vr2 (Vr24) compared to the first high-temperature, high-humidity environment. The second high-temperature, high-humidity environment corresponds to the "fourth environment."

[0072] Specifically, in the second high-temperature, high-humidity environment, the control unit 100 reduces the magnitude of the first developing bias Vr14 by a third magnitude A3 compared to the magnitude of the first developing bias Vr11 in the normal-temperature, normal-humidity environment. Also, the control unit 100 reduces the magnitude of the second developing bias Vr24 by a third magnitude A3 compared to the magnitude of the second developing bias Vr21 in the normal-temperature, normal-humidity environment. In the first embodiment, the third magnitude A3 is 50 V.

[0073] Specifically, when the temperature and humidity detected by the temperature and humidity sensor 14 are in the fourth temperature and humidity region R4 of the table (see FIG. 4), the control unit 100 sets the first bias V1 to -50 [V]. Next, the control unit 100 sets the first developing bias Vr14 to (V0-50-50) [V] and sets the second developing bias Vr24 to (V0-50+50) [V]. The second developing bias Vr24 is equal to the reference bias V0. The difference between the first developing bias Vr14 and the second developing bias Vr24 is a predetermined value ΔV.

[0074] 6, in a first low-temperature, low-humidity environment in which the temperature and humidity detected by the temperature and humidity sensor 14 are in the third temperature and humidity range R3, the control unit 100 increases the magnitude of the first developing bias Vr1 (Vr13) and the magnitude of the second developing bias Vr2 (Vr23) compared to a normal-temperature, normal-humidity environment. The first low-temperature, low-humidity environment corresponds to the "third environment."

[0075] Specifically, in the first low-temperature, low-humidity environment, the control unit 100 increases the magnitude of the first developing bias Vr13 by a second magnitude A2 compared to the magnitude of the first developing bias Vr11 in the normal-temperature, normal-humidity environment. Also, the control unit 100 increases the magnitude of the second developing bias Vr23 by the second magnitude A2 compared to the magnitude of the second developing bias Vr21 in the normal-temperature, normal-humidity environment. In the first embodiment, the second magnitude A2 is 20 [V]. The first magnitude A1 (see FIG. 5) and the second magnitude A2 are the same value (20 [V]).

[0076] Specifically, when the temperature and humidity detected by the temperature and humidity sensor 14 are in the third temperature and humidity region R3 of the table (see FIG. 4), the control unit 100 sets the first bias V1 to 20 [V]. Next, the control unit 100 sets the first developing bias Vr13 to (V0 + 20 - 50) [V] and sets the second developing bias Vr23 to (V0 + 20 + 50) [V]. The difference between the first developing bias Vr13 and the second developing bias Vr23 is a predetermined value ΔV.

[0077] When the temperature and humidity detected by the temperature and humidity sensor 14 are in the second low-temperature, low-humidity environment in the fifth temperature and humidity range R5, the control unit 100 increases the magnitude of the first developing bias Vr1 and the magnitude of the second developing bias Vr2 compared to the first low-temperature, low-humidity environment. The second low-temperature, low-humidity environment corresponds to the "fifth environment."

[0078] Specifically, in the second low-temperature, low-humidity environment, the control unit 100 increases the magnitude of the first developing bias Vr15 by a fourth magnitude A4 compared to the magnitude of the first developing bias Vr11 in the normal-temperature, normal-humidity environment. Also, the control unit 100 increases the magnitude of the second developing bias Vr25 by a fourth magnitude A4 compared to the magnitude of the second developing bias Vr21 in the normal-temperature, normal-humidity environment. In the first embodiment, the fourth magnitude A4 is 50 [V]. The third magnitude A3 (see FIG. 5) and the 24th magnitude A4 are the same value (50 [V]).

[0079] Specifically, when the temperature and humidity detected by the temperature and humidity sensor 14 are in the fifth temperature and humidity region R5 of the table (see FIG. 4), the control unit 100 sets the first bias V1 to 50 [V]. Next, the control unit 100 sets the first developing bias Vr15 to (V0 + 50 - 50) [V] and sets the second developing bias Vr25 to (V0 + 50 + 50) [V]. The first developing bias Vr15 is equal to the reference bias V0. The difference between the first developing bias Vr15 and the second developing bias Vr25 is a predetermined value ΔV.

[0080] In the second patch bias setting process executed in the second or subsequent development bias setting process (second development bias setting process), the control unit 100 sets the first development bias Vr1 and the second development bias Vr2 using the above formulas (1) and (2). In the second patch bias setting process, the control unit 100 sets the development bias Vb used in the immediately preceding printing as the reference bias V0. In addition, in the second patch bias setting process, the control unit 100 sets the first bias V1 to 0 [V]. The second bias V2 is 50 [V].

[0081] In the second patch bias setting process, the control unit 100 sets the magnitude of the first developing bias Vr1 to a value smaller than the magnitude of the reference bias V0. The control unit 100 also sets the magnitude of the second developing bias Vr2 to a value larger than the magnitude of the reference bias V0. Specifically, the control unit 100 sets the first developing bias Vr1 to (V0-50) [V] and sets the second developing bias Vr2 to (V0+50) [V]. The second developing bias Vr2 is a value larger than the first developing bias Vr1 by a predetermined value ΔV.

[0082] Next, an example of the operation of the control unit 100 will be described with reference to a flowchart. As shown in FIG. 7, in the developing bias setting process, the control unit 100 first executes a test bias setting process to set a first developing bias Vr1 and a second developing bias Vr2 (S10).

[0083] Next, the control unit 100 applies the first developing bias Vr1 set in the test bias setting process to the developing roller 55 to form a patch image P on the transfer belt 73 (S11). Then, the control unit 100 measures the density of the patch image P formed on the transfer belt 73 with the density sensor 13 to obtain a first density Dm1 (S12).

[0084] Furthermore, the control unit 100 applies the second developing bias Vr2 set in the test bias setting process to the developing roller 55 to form a patch image P on the transfer belt 73 (S13). Then, the control unit 100 measures the density of the patch image P formed on the transfer belt 73 with the density sensor 13 to obtain a second density Dm2 (S14).

[0085] Thereafter, the control unit 100 calculates a straight line L (see FIG. 3) based on the first developing bias Vr1, the first density Dm1, the second developing bias Vr2, and the second density Dm2, and sets a developing bias Vb from the straight line L such that the density of the patch image P becomes the target density Dr (S15). After setting the developing bias Vb, the control unit 100 ends the developing bias setting process.

[0086] As shown in FIG. 8, in the test bias setting process (S10), the control unit 100 determines whether the developing bias setting process being executed is the first developing bias setting process (S101).

[0087] If the developing bias setting process being executed is the first developing bias setting process (S101, Yes), the control unit 100 sets the reference bias V0 to a pre-stored initial reference bias Va (S102). The control unit 100 also detects the temperature and humidity using the temperature and humidity sensor 14 (S103). Then, the control unit 100 sets the first bias V1 based on the detected temperature and humidity and a table (see FIG. 4) (S104).

[0088] In step S101, if the developing bias setting process being executed is the second developing bias setting process (No), the control unit 100 sets the reference bias V0 to the developing bias Vb used in the immediately previous printing, and sets the first bias V1 to 0 [V] (S105).

[0089] After setting the reference bias V0 and the first bias V1, the control unit 100 sets the first developing bias Vr1 and the second developing bias Vr2 based on the set reference bias V0 and the first bias V1 and the pre-stored second bias V2 (50 [V]) (S106). After setting the first developing bias Vr1 and the second developing bias Vr2, the control unit 100 ends the test bias setting process.

[0090] Next, the effects of the first embodiment will be described. In the first patch bias setting process, the control unit 100 sets the first developing bias Vr1 and the second developing bias Vr2 in accordance with the temperature and humidity detected by the temperature and humidity sensor 14 while keeping the difference between the first developing bias Vr1 and the second developing bias Vr2 at a predetermined value ΔV, thereby making it possible to set the first developing bias Vr1 and the second developing bias Vr2 to appropriate values ​​in accordance with the temperature and humidity. This makes it possible to set the developing bias Vb in accordance with the temperature and humidity environment.

[0091] In the first high-temperature, high-humidity environment, the magnitude of the first developing bias Vr1 and the magnitude of the second developing bias Vr2 are made smaller than those in the normal temperature, normal humidity environment, thereby making it possible to set an appropriate developing bias Vb according to the first high-temperature, high-humidity environment in which at least one of the temperature and humidity is higher than that in the normal temperature, normal humidity environment.

[0092] In the first low-temperature, low-humidity environment, the magnitude of the first developing bias Vr1 and the magnitude of the second developing bias Vr2 are made larger than those in the normal temperature, normal humidity environment, thereby making it possible to set an appropriate developing bias Vb according to the first low-temperature, low-humidity environment in which at least one of the temperature and humidity is lower than that in the normal temperature, normal humidity environment.

[0093] In the second high-temperature, high-humidity environment, the magnitude of the first developing bias Vr1 and the magnitude of the second developing bias Vr2 are made smaller than those in the first high-temperature, high-humidity environment, thereby making it possible to set an appropriate developing bias Vb according to the second high-temperature, high-humidity environment in which at least one of the temperature and humidity is higher than that in the first high-temperature, high-humidity environment.

[0094] In the second low-temperature, low-humidity environment, the magnitude of the first developing bias Vr1 and the magnitude of the second developing bias Vr2 are made larger than those in the first low-temperature, low-humidity environment, thereby making it possible to set an appropriate developing bias Vb according to the second low-temperature, low-humidity environment in which at least one of the temperature and humidity is lower than that in the first low-temperature, low-humidity environment.

[0095] In the first developing bias setting process, which is the first developing bias setting process, the first patch bias setting process is executed, so that the developing bias Vb according to the temperature and humidity environment can be set in the first developing bias setting process.

[0096] In the second developing bias setting process, which is the second or subsequent developing bias setting process, the developing bias Vb used in the immediately preceding printing is set as the reference bias V0, thereby making it possible to set an appropriate developing bias Vb.

[0097] Next, a second embodiment will be described. The following description will focus on the differences from the first embodiment. The same elements will be denoted by the same reference numerals and the description will be omitted.

[0098] In the first patch bias setting process, the control unit 100 sets the first developing bias Vr1 and the second developing bias Vr2 in accordance with the temperature and humidity detected by the temperature and humidity sensor 14, while keeping the difference between the first developing bias Vr1 and the second developing bias Vr2 at a predetermined value ΔV. In the second embodiment, the predetermined value ΔV is, for example, 120 [V].

[0099] When executing the first patch bias setting process, the control unit 100 sets the first developing bias Vr1 and the second developing bias Vr2 according to the above formulas (1) and (2). In the second embodiment, the second bias V2 is, for example, 60 V.

[0100] In the first patch bias setting process, the control unit 100 sets the first bias V1 based on the temperature and humidity detected by the temperature and humidity sensor 14 and a pre-stored table such as that shown in FIG.

[0101] 9, the table has a first temperature and humidity region R1, a second temperature and humidity region R2, and a third temperature and humidity region R3, which are preset. In the first temperature and humidity region R1, the first bias V1 is set to 0 [V].

[0102] The second temperature and humidity region R2 is a region where at least one of the temperature and humidity is higher than that of the first temperature and humidity region R1, and the first bias V1 is set to -60 V. The third temperature and humidity region R3 is a region where at least one of the temperature and humidity is lower than that of the first temperature and humidity region R1, and the first bias V1 is set to 60 V.

[0103] 10, in a normal temperature and normal humidity environment where the temperature and humidity detected by the temperature and humidity sensor 14 are within the first temperature and humidity range R1, the control unit 100 sets the magnitude of the first developing bias Vr1 (Vr11) and the magnitude of the second developing bias Vr2 (Vr21) to predetermined magnitudes. The normal temperature and normal humidity environment corresponds to the "first environment."

[0104] Specifically, when the temperature and humidity detected by the temperature and humidity sensor 14 are within the first temperature and humidity region R1 of the table, the control unit 100 sets the first bias V1 to 0 [V]. Next, the control unit 100 sets the first developing bias Vr11 to (V0-60) [V] and sets the second developing bias Vr21 to (V0+60) [V]. The difference between the first developing bias Vr11 and the second developing bias Vr21 is a predetermined value ΔV.

[0105] In a high-temperature, high-humidity environment where the temperature and humidity detected by the temperature and humidity sensor 14 are in the second temperature and humidity range R2, the control unit 100 reduces the magnitude of the first developing bias Vr1 (Vr12) and the magnitude of the second developing bias Vr2 (Vr22) compared to a normal-temperature, normal-humidity environment. The high-temperature, high-humidity environment corresponds to the "second environment."

[0106] Specifically, in a high-temperature, high-humidity environment, the control unit 100 reduces the magnitude of the first developing bias Vr12 by a first magnitude A1 compared to the magnitude of the first developing bias Vr11 in a normal-temperature, normal-humidity environment. Also, the control unit 100 reduces the magnitude of the second developing bias Vr22 by the first magnitude A1 compared to the magnitude of the second developing bias Vr21 in a normal-temperature, normal-humidity environment. In the second embodiment, the first magnitude A1 is 60 V.

[0107] Specifically, when the temperature and humidity detected by the temperature and humidity sensor 14 are in the second temperature and humidity region R2 of the table (see FIG. 9), the control unit 100 sets the first bias V1 to -60 [V]. Next, the control unit 100 sets the first developing bias Vr12 to (V0-60-60) [V] and the second developing bias Vr22 to (V0-60+60) [V], i.e., the reference bias V0. The difference between the first developing bias Vr12 and the second developing bias Vr22 is a predetermined value ΔV.

[0108] 11, in a low-temperature, low-humidity environment where the temperature and humidity detected by the temperature and humidity sensor 14 are in the third temperature and humidity range R3, the control unit 100 increases the magnitude of the first developing bias Vr1 (Vr13) and the magnitude of the second developing bias Vr2 (Vr23) compared to a normal-temperature, normal-humidity environment. The low-temperature, low-humidity environment corresponds to the "third environment."

[0109] Specifically, in a low-temperature, low-humidity environment, the control unit 100 increases the magnitude of the first developing bias Vr13 by a second magnitude A2 greater than the magnitude of the first developing bias Vr11 in a normal-temperature, normal-humidity environment. Also, the control unit 100 increases the magnitude of the second developing bias Vr23 by the second magnitude A2 greater than the magnitude of the second developing bias Vr21 in a normal-temperature, normal-humidity environment. In the second embodiment, the second magnitude A2 is 60 V.

[0110] The first magnitude A1 (see FIG. 10) and the second magnitude A2 are the same value (60 [V]). The first magnitude A1 and the second magnitude A2 are half the predetermined value ΔV (120 [V]).

[0111] When the temperature and humidity detected by the temperature and humidity sensor 14 are in the third temperature and humidity region R3 of the table (see FIG. 9), the control unit 100 sets the first bias V1 to 60 [V]. Next, the control unit 100 sets the first developing bias Vr13 to (V0 + 60 - 60) [V], i.e., the reference bias V0, and sets the second developing bias Vr23 to (V0 + 60 + 60) [V]. The difference between the first developing bias Vr13 and the second developing bias Vr23 is a predetermined value ΔV.

[0112] In the second patch bias setting process, the control unit 100 sets the first developing bias Vr1 and the second developing bias Vr2 according to the above formulas (1) and (2). In the second patch bias setting process, the control unit 100 sets the developing bias Vb used in the immediately preceding printing as the reference bias V0. In addition, in the second patch bias setting process, the control unit 100 sets the first bias V1 to 0 [V]. The second bias V2 is 60 [V].

[0113] In the second patch bias setting process, the control unit 100 sets the magnitude of the first developing bias Vr1 to a value smaller than the magnitude of the reference bias V0. The control unit 100 also sets the magnitude of the second developing bias Vr2 to a value larger than the magnitude of the reference bias V0. Specifically, the control unit 100 sets the first developing bias Vr1 to (V0-60) [V] and sets the second developing bias Vr2 to (V0+60) [V]. The second developing bias Vr2 is a value larger than the first developing bias Vr1 by a predetermined value ΔV.

[0114] Next, the effects of the second embodiment will be described. In the first patch bias setting process, the control unit 100 sets the first developing bias Vr1 and the second developing bias Vr2 in accordance with the temperature and humidity detected by the temperature and humidity sensor 14 while keeping the difference between the first developing bias Vr1 and the second developing bias Vr2 at a predetermined value ΔV, thereby making it possible to set the first developing bias Vr1 and the second developing bias Vr2 to appropriate values ​​in accordance with the temperature and humidity. This makes it possible to set the developing bias Vb in accordance with the temperature and humidity environment.

[0115] In a high-temperature, high-humidity environment, the magnitude of the first developing bias Vr1 and the magnitude of the second developing bias Vr2 are set smaller than those in a normal-temperature, normal-humidity environment, thereby making it possible to set an appropriate developing bias Vb for the high-temperature, high-humidity environment.

[0116] In a low-temperature, low-humidity environment, the magnitude of the first developing bias Vr1 and the magnitude of the second developing bias Vr2 are set to be larger than those in a normal-temperature, normal-humidity environment, thereby making it possible to set an appropriate developing bias Vb for the low-temperature, low-humidity environment.

[0117] In the first developing bias setting process, by executing the first patch bias setting process, the developing bias Vb can be set according to the temperature and humidity environment in the first developing bias setting process.

[0118] In the second developing bias setting process, the developing bias Vb used in the immediately preceding printing is set as the reference bias V0, thereby making it possible to set an appropriate developing bias Vb.

[0119] Although the embodiment has been described above, the image forming apparatus can be modified as appropriate as exemplified below.

[0120] For example, when executing the patch bias setting process, if the environment is one in which at least one of the detected temperature and humidity is higher than the fourth temperature and humidity range, the control unit may reduce the magnitude of the first developing bias and the magnitude of the second developing bias compared to the fourth environment. Also, for example, when executing the patch bias setting process, if the environment is one in which at least one of the detected temperature and humidity is lower than the fifth temperature and humidity range, the control unit may increase the magnitude of the first developing bias and the magnitude of the second developing bias compared to the fifth environment.

[0121] In the above-described embodiment, the first magnitude A1 and the second magnitude A2 are the same value, but for example, the first magnitude and the second magnitude may be different values. The same applies to the third magnitude and the fourth magnitude.

[0122] In the above-described embodiment, the control unit 100 increases the magnitude of the first developing bias Vr1 and the magnitude of the second developing bias Vr2 in the low-temperature, low-humidity environment (third environment) compared to the normal-temperature, normal-humidity environment (first environment). However, for example, the control unit may set the magnitude of the first developing bias Vr1 and the magnitude of the second developing bias in the third environment to the same as in the first environment.

[0123] In the above-described embodiment, in the second developing bias setting process, the patch bias setting process is not performed, and the first developing bias Vr1 and the second developing bias Vr2 are set, which do not change depending on the temperature and humidity detected by the temperature and humidity sensor 14. However, for example, in the second developing bias setting process, a patch bias setting process may be performed to set the first developing bias and the second developing bias depending on the temperature and humidity detected by the temperature and humidity sensor.

[0124] In the above embodiment, the first developing bias setting process, which is the initial developing bias setting process, is executed when new toner is used, but the first developing bias setting process may also be executed when, for example, the developing roller is new.Furthermore, the first developing bias setting process may also be executed when, for example, the photosensitive drum is new.

[0125] In the above embodiment, the developer cartridge 52 having the developer roller 55 is exemplified as the toner cartridge that contains toner, but for example, the toner cartridge may be a cartridge that does not have a developer roller. Also, for example, the toner cartridge may be a cartridge that has a photosensitive drum and a developer roller.

[0126] In the above embodiment, the transfer belt 73 that transports the sheet S between the photosensitive drum 53 and the endless belt is exemplified, but the endless belt may be, for example, an intermediate transfer belt.

[0127] In the above-described embodiment, an endless belt is exemplified as the transfer object, but the transfer object may also be, for example, a sheet S. That is, the image forming apparatus may form a patch image P on the sheet S, measure the density of the patch image P formed on the sheet S, and set the development bias Vb based on the measured density of the patch image P.

[0128] In the above-described embodiment, the exposure unit 40 of the image forming section 30 exposes the photosensitive drum 53 with light emitted from an LED, but for example, the exposure unit may expose the photosensitive drum with a beam emitted from a semiconductor laser or the like. Also, in the above-described embodiment, the fixing unit 80 of the image forming section 30 includes the heating roller 81 and the pressure roller 82, but for example, the fixing unit may be a belt fixing type fixing unit in which at least one of the heating section and the pressure section has an endless belt.

[0129] In the above embodiment, the image forming apparatus 1 is a printer, but the image forming apparatus may be, for example, a copying machine or a multifunction peripheral.

[0130] In the above embodiment, the image forming apparatus 1 uses a positively charged toner, but the image forming apparatus may use a negatively charged toner, for example. In addition, when the image forming apparatus uses a negatively charged toner, the positive and negative of the developing bias are reversed from those in the above embodiment.

[0131] The elements described in the above-described embodiment and modifications may be implemented in any combination. [Explanation of symbols]

[0132] 1. Image forming device 13 Concentration sensor 14 Temperature and humidity sensor 30 Image forming unit 55 Developing roller 73 Transfer belt 100 control section P patch image

Claims

1. an image forming unit having a developing roller and capable of forming a toner patch image on a transfer target; a density sensor capable of measuring the density of a patch image formed on a transfer target; a temperature and humidity sensor for detecting temperature and humidity; a control unit, The control unit A developing bias setting process for setting a developing bias to be applied to the developing roller during printing, a process of applying a first developing bias to the developing roller to form a patch image on a transfer object, and applying a second developing bias to the developing roller that is larger than the first developing bias by a predetermined value to form the patch image on the transfer object; a process of measuring the density of the patch image formed on the transfer target by the density sensor; a process of setting a developing bias based on the density of a patch image formed by applying a first developing bias to the developing roller and the density of a patch image formed by applying a second developing bias to the developing roller, so that the density of the patch image becomes a predetermined target density; An image forming apparatus characterized in that, in the development bias setting process, a patch bias setting process is performed in which a first development bias and a second development bias are set to form a patch image on a transfer object, and the patch bias setting process is performed in which the difference between the first development bias and the second development bias remains at the predetermined value, and the first development bias and the second development bias are set according to the temperature and humidity detected by the temperature and humidity sensor.

2. When the control unit executes the patch bias setting process, When the temperature and humidity detected by the temperature and humidity sensor are in a first environment within a first temperature and humidity range set in advance, the magnitude of the first developing bias and the magnitude of the second developing bias are set to predetermined magnitudes; 2. The image forming apparatus according to claim 1, wherein, in a second environment in which at least one of the temperature and humidity detected by the temperature and humidity sensor is in a second temperature and humidity range higher than the first temperature and humidity range, the magnitude of the first developing bias and the magnitude of the second developing bias are made smaller than in the first environment.

3. When the control unit executes the patch bias setting process, 3. An image forming apparatus according to claim 2, wherein when a third environment is present in which at least one of the temperature and humidity detected by the temperature and humidity sensor is in a third temperature and humidity range that is lower than the first temperature and humidity range, the magnitude of the first developing bias and the magnitude of the second developing bias are made larger than those in the first environment.

4. When the control unit executes the patch bias setting process, 3. The image forming apparatus according to claim 2, wherein when the fourth environment is one in which at least one of the temperature and humidity detected by the temperature and humidity sensor is in a fourth temperature and humidity range higher than the second temperature and humidity range, the magnitude of the first developing bias and the magnitude of the second developing bias are made smaller than those in the second environment.

5. When the control unit executes the patch bias setting process, An image forming apparatus as described in claim 3, characterized in that in a fifth environment in which at least one of the temperature and humidity detected by the temperature and humidity sensor is in a fifth temperature and humidity range lower than the third temperature and humidity range, the magnitude of the first developing bias and the magnitude of the second developing bias are made larger than in the third environment.

6. When the control unit executes the patch bias setting process, In the second environment, the magnitude of the first developing bias and the magnitude of the second developing bias are made smaller by a first magnitude than in the first environment; 4. The image forming apparatus according to claim 3, wherein in the third environment, the magnitude of the first developing bias and the magnitude of the second developing bias are increased by a second magnitude compared to the magnitude in the first environment.

7. 7. The image forming apparatus according to claim 6, wherein the first size and the second size are the same value.

8. 8. The image forming apparatus according to claim 7, wherein the first size and the second size are half the predetermined value.

9. A device body, a toner cartridge that contains toner and is detachably mountable to the device body; The image forming apparatus according to claim 1, characterized in that the control unit executes the patch bias setting process in a first developing bias setting process, which is the first developing bias setting process executed after determining that a new toner cartridge has been installed in the device main body.

10. The image forming apparatus according to claim 9, characterized in that in the second developing bias setting process, which is the second or subsequent developing bias setting process executed after the first developing bias setting process, the control unit sets the magnitude of the first developing bias to a value smaller than the magnitude of the reference bias, using the developing bias used in the immediately previous printing as a reference bias, and sets the magnitude of the second developing bias to a value larger than the magnitude of the reference bias and larger than the first developing bias by the predetermined value.

11. 2. The image forming apparatus according to claim 1, further comprising an endless belt as the transfer object.

Images