Image forming apparatus

Abstract

To provide an image forming apparatus that can prevent the occurrence of printing failure.SOLUTION: An image forming apparatus 1 comprises: a body housing 2; a photoconductor drum 61; an exposure unit 4 that emits light for exposing the photoconductor drum 61; a developing cartridge 7 that has a developing roller 71; a developing memory 76 that stores the cumulative number of printed sheets on which printing is performed by using the developing cartridge 7; and a control section 10. When a first condition is satisfied in which the cumulative number of printed sheets is equal to or more than a first threshold and equal to or less than a second threshold larger than the first threshold, and the number of rotations of the developing roller 71, from the start of a printing operation after the lapse of predetermined time from the completion of the previous printing operation, becomes a third threshold or more, the control section 10 executes image quality improvement control. In the image quality improvement control, the magnitude of developing voltage to be applied to the developing roller 71 when a toner image is formed on the photoconductor drum 61, is made larger than that when the toner image is formed on the photoconductor drum 61 during printing immediately before the first condition is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, an image forming apparatus is known that includes a photosensitive drum and a developing roller to which a developing bias is applied when toner is supplied to the photosensitive drum (Patent Document 1). In this technology, the developing bias applied to the developing roller is reduced in a linear function fashion as the number of printed sheets increases. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-292475 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, toner deteriorates as the image forming device performs printing operations. As toner deterioration progresses, the toner aggregates, which can result in a larger amount of toner remaining on the developing roller than usual. When the amount of toner on the developing roller increases, for example, it becomes difficult for toner particles to be frictionally charged, making it difficult for the toner on the developing roller to move to the photosensitive drum, which can result in print defects such as faded images.

[0005] Therefore, it is desirable to be able to suppress the occurrence of printing defects. [Means for solving the problem]

[0006] The image forming apparatus according to the first disclosure of the present application includes a main body housing, a photosensitive drum, an exposure unit, a developing device, a memory, and a control unit. The exposure unit emits light that exposes the photosensitive drum. The developing unit has a developing roller. The memory stores the cumulative number of pages printed using the developing device or the cumulative number of rotations of the developing roller. The control unit executes image quality improvement control when a first condition is satisfied in which the cumulative number of printed sheets or cumulative number of rotations is equal to or greater than a first threshold value and equal to or less than a second threshold value that is greater than the first threshold value, and the number of printed sheets printed using the developing device from the time the printing operation was started after a predetermined time had elapsed since the printing operation was finished, or the number of rotations of the developing roller from the time the printing operation was started after a predetermined time had elapsed since the printing operation was finished, is equal to or greater than a third threshold value. In the image quality improvement control, when forming a toner image on a photosensitive drum, the magnitude of the development voltage applied to the development roller, the size of the dots of the electrostatic latent image formed on the photosensitive drum, or the intensity of the light emitted by the exposure unit is made larger than when the toner image was formed on the photosensitive drum during printing immediately before the first condition was satisfied.

[0007] According to the first disclosure, even if the toner on the developing roller is difficult to move to the photosensitive drum, by executing image quality improvement control, the toner on the developing roller can be made to move more easily to the photosensitive drum, thereby suppressing the occurrence of printing defects.

[0008] A second disclosure of the present application is the image forming apparatus of the first disclosure, wherein the developing device may be a developing cartridge having a memory and detachable from the main body housing.

[0009] According to the second disclosure, the developing unit is a developing cartridge having a memory for storing the cumulative number of printed sheets or the cumulative number of rotations, so that even if the developing cartridge is removed from the main body housing and then re-installed in the main body housing, or even if it is installed in the main body housing of another image forming device, the cumulative number of printed sheets or the cumulative number of rotations can continue to be used for control, thereby enabling accurate execution of image quality improvement control.

[0010] A third disclosure of the present application is the image forming apparatus of the first disclosure, which may further include a humidity sensor for detecting humidity. The control unit may execute the image quality improvement control when, in addition to the first condition, a condition that the humidity detected by the humidity sensor is equal to or higher than a predetermined humidity is further satisfied.

[0011] According to the third disclosure, by executing image quality improvement control when the condition that humidity is equal to or higher than a predetermined humidity is met in addition to the first condition, image quality improvement control can be executed in a high humidity environment where printing defects are more likely to occur.

[0012] A fourth disclosure of the present application is the image forming apparatus of the first disclosure, wherein the developing device may be a developing cartridge that has a developing memory that can store a flag and is detachable from the main body casing. The control unit may execute image quality improvement control when, in addition to the first condition, a condition that a flag is stored in the development memory is further satisfied.

[0013] According to the fourth disclosure, the developer is a developer cartridge having a development memory capable of storing flags, so by associating the flag with conditions under which printing defects are likely to occur, image quality improvement control can be performed under conditions under which printing defects are likely to occur.

[0014] A fifth disclosure of the present application is the image forming apparatus of the fourth disclosure, wherein the developing cartridge may have a toner containing portion capable of containing toner. The development memory may store a flag when the toner contained in the toner container is pulverized toner.

[0015] According to the fifth disclosure, the development memory stores a flag when the toner contained in the toner storage unit is pulverized toner, thereby enabling image quality improvement control to be performed when the toner storage unit contains toner that is prone to causing printing defects.

[0016] A sixth disclosure of the present application is the image forming apparatus of the fourth disclosure, wherein the development memory may store a flag when the surface roughness of the development roller is equal to or greater than a predetermined surface roughness.

[0017] According to the sixth disclosure, the development memory stores a flag when the surface roughness of the development roller is equal to or greater than a predetermined surface roughness, thereby enabling image quality improvement control to be performed when the development roller is prone to print defects.

[0018] A seventh disclosure of the present application is the image forming apparatus of the fourth disclosure, wherein the developing cartridge may have a supply roller that supplies toner to the developing roller. The development memory may store a flag when the outer diameter of the supply roller is equal to or smaller than a predetermined outer diameter, or when the hardness of the supply roller is equal to or smaller than a predetermined hardness.

[0019] According to the seventh disclosure, the development memory stores a flag when the outer diameter of the supply roller is equal to or smaller than a predetermined outer diameter or when the hardness of the supply roller is equal to or smaller than a predetermined hardness, thereby enabling image quality improvement control to be performed when the supply roller is prone to printing defects.

[0020] An eighth disclosure of the present application is the image forming apparatus of the fourth disclosure, wherein the development memory may store a flag when the development cartridge is a recycled product.

[0021] According to the eighth disclosure, when the developer cartridge is a recycled product, the development memory stores a flag, so that image quality improvement control can be executed when the developer cartridge is prone to producing printing defects.

[0022] A ninth disclosure of the present application may be the image forming apparatus of the first disclosure, further comprising a fixing device that thermally fixes a toner image transferred from the photosensitive drum onto a sheet. If the temperature of the fixing unit is equal to or lower than a predetermined temperature, the control unit may determine that a predetermined time has elapsed since the printing operation ended.

[0023] The tenth disclosure of the present application is the image forming apparatus of the first disclosure, wherein when the control unit executes image quality improvement control, the control unit may increase the magnitude of the development voltage applied to the development roller, the size of the dots of the electrostatic latent image formed on the photosensitive drum, or the intensity of the light emitted by the exposure unit as the number of printed sheets increases.

[0024] According to the 10th disclosure, when image quality improvement control is performed, the magnitude of the development voltage, etc., is increased as the number of printed sheets increases, thereby suppressing the occurrence of printing defects and suppressing sudden changes in the color tone of the image formed on the sheet.

[0025] An eleventh disclosure of the present application is the image forming apparatus of the tenth disclosure, wherein when executing image quality improvement control, the control unit may set the magnitude of the developing voltage applied to the developing roller to a predetermined upper limit value or less. [Effects of the Invention]

[0026] This can prevent printing defects from occurring. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram illustrating an image forming apparatus. [Figure 2] FIG. 10 is a diagram illustrating an image of control of a development voltage. [Figure 3] 5 is a flowchart showing the operation of the control unit of the first embodiment. [Figure 4] 4 is a timing chart showing the timing of executing image quality improvement control in the first embodiment. [Figure 5] 10 is a flowchart showing the operation of a control unit in the second embodiment. [Figure 6] 10 is a flowchart showing the operation of a control unit in the third embodiment. [Figure 7] 10 is a timing chart showing the timing at which image quality improvement control is executed in the fourth embodiment. [Figure 8] 10A and 10B are diagrams illustrating an image of control of a development voltage in a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0028] Next, a first embodiment will be described. 1, the image forming apparatus 1 is a printer capable of forming a monochrome image on a sheet S such as paper. The image forming apparatus 1 includes a main body housing 2, a cover 2C, a sheet supply unit 3, an exposure unit 4, a process cartridge 5, a fixing unit 8, a discharge roller 9, a control unit 10, a humidity sensor 11, and a main body memory 16.

[0029] The main body housing 2 has an opening 2A. The cover 2C opens and closes the opening 2A of the main body housing 2.

[0030] The sheet supply unit 3 includes a sheet tray 31 , a pressure plate 32 , and a sheet supply roller 33 . The sheet tray 31 accommodates the sheets S. The pressure plate 32 pushes up the sheets S in the sheet tray 31 . The sheet supply roller 33 supplies the sheet S pushed up by the pressure plate 32 to the process cartridge 5.

[0031] The exposure unit 4 includes a light source, a deflector, a lens, a mirror, etc. The exposure unit 4 emits a light beam as shown by the imaginary line. The light beam is light that exposes the photosensitive drum 61.

[0032] With the cover 2C open, the process cartridge 5 is detachable from the main body casing 2 through the opening 2A. The process cartridge 5 includes a drum cartridge 6 and a developing cartridge 7 as a developing device.

[0033] The drum cartridge 6 is detachably attached to the main body 2. The drum cartridge 6 includes a photosensitive drum 61, a charger 62, and a transfer roller 63. A toner image is formed on the surface of the photosensitive drum 61 .

[0034] The developing cartridge 7 is detachable from the main body housing 2. More specifically, the developing cartridge 7 is detachable from the drum cartridge 6. The developing cartridge 7 is detachable from the main body housing 2 together with the drum cartridge 6 while attached to the drum cartridge 6.

[0035] The developing cartridge 7 includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, an agitator 74, a toner storage section 75, and a developing memory 76 as a memory. The toner storage section 75 is capable of storing toner.

[0036] The agitator 74 agitates the toner in the toner storage unit 75. The agitator 74 also supplies the toner to the supply roller 72. The supply roller 72 supplies the toner to the developing roller 71 . The layer thickness regulating blade 73 comes into contact with the surface of the developing roller 71 to regulate the thickness of the toner on the developing roller 71 to a constant thickness.

[0037] The fixing unit 8 includes a heating roller 81 , a pressure roller 82 , and a temperature sensor 83 . The heating roller 81 heats the sheet S. The pressure roller 82 presses the sheet S against the heating roller 81 . The temperature sensor 83 is a sensor that detects the temperature of the fixing unit 8. In this embodiment, the temperature sensor 83 detects the temperature of the heating roller 81. The temperature sensor 83 outputs the detected temperature T to the control unit .

[0038] The charger 62 charges the surface of the photosensitive drum 61 . The exposure unit 4 irradiates the surface of the charged photosensitive drum 61 with a light beam, thereby forming an electrostatic latent image on the photosensitive drum 61 based on image data.

[0039] When a predetermined developing voltage Vb is applied to the developing roller 71, the developing roller 71 supplies toner to the surface of the exposed photosensitive drum 61. As a result, a toner image is formed on the photosensitive drum 61. The transfer roller 63 transfers the toner image formed on the photosensitive drum 61 onto the sheet S by conveying the sheet S supplied from the sheet supply unit 3 between the photosensitive drum 61 and the transfer roller 63.

[0040] The fixing device 8 thermally fixes the toner image transferred from the photosensitive drum 61 onto the sheet S by conveying the sheet S onto which the toner image has been transferred between the heating roller 81 and the pressure roller 82. Discharge rollers 9 discharge the sheet S onto which the toner image has been thermally fixed onto a discharge tray 2B.

[0041] The image forming apparatus 1 includes a main motor such as a DC motor. The pressure roller 82 rotates as the main motor is driven. The photosensitive drum 61 and the developing roller 71 also rotate as the main motor is driven. The control unit 10 controls the driving of the main motor.

[0042] The image forming apparatus 1 includes an interface such as a USB interface, a LAN interface, etc. The image forming apparatus 1 is connected to an external terminal such as a personal computer via the interface. The external terminal inputs a print job to the image forming apparatus 1.

[0043] The humidity sensor 11 is a sensor that detects humidity H. As an example, the humidity H is relative humidity. The humidity sensor 11 may be a sensor that detects humidity H inside the main body housing 2, or may be a sensor that detects humidity H outside the main body housing 2. The humidity sensor 11 outputs the detected humidity H to the control unit 10.

[0044] The developing memory 76 stores a first parameter. The first parameter is a parameter that increases as the developing roller 71 rotates from a state in which the developing roller 71 is brand new. In this embodiment, the first parameter is the cumulative number of pages printed using the developing cartridge 7. In other words, the first parameter is the cumulative number of pages printed from a state in which the developing roller 71 is brand new (hereinafter, simply referred to as the "cumulative number of pages printed"). The cumulative number of pages printed is the cumulative number of pages printed since a brand new developing cartridge 7 was installed in the main body housing 2.

[0045] The development memory 76 stores the cumulative number of printed sheets. The control unit 10 counts the cumulative number of printed sheets. The control unit 10 stores the counted cumulative number of printed sheets in the development memory 76.

[0046] Furthermore, the development memory 76 can store a flag F. Specifically, if the toner contained in the toner storage unit 75 is pulverized toner, the development memory 76 stores the flag F in advance. If the toner contained in the toner storage unit 75 is not pulverized toner, the development memory 76 does not store the flag F. For example, if the toner contained in the toner storage unit 75 is polymerized toner, the development memory 76 does not store the flag F.

[0047] In the embodiment, "storing flag F" refers to a state in which 1 is stored in the storage area for flag F in the development memory 76 (F=1). Furthermore, "not storing flag F" refers to a state in which 0 is stored in the storage area for flag F in the development memory 76 (F=0).

[0048] Furthermore, the development memory 76 stores a flag F (F=1) in advance when the surface roughness of the development roller 71 is equal to or greater than a predetermined surface roughness. The development memory 76 does not store a flag F (F=0) when the surface roughness of the development roller 71 is less than the predetermined surface roughness.

[0049] Here, the developing roller 71 has a shaft 71A and a roller body 71B made of rubber or the like. The surface roughness of the developing roller 71 is the surface roughness of the outer circumferential surface of the roller body 71B of the developing roller 71. The surface roughness of the developing roller 71 is, for example, the arithmetic mean roughness (Ra).

[0050] Furthermore, the development memory 76 stores a flag F (F=1) in advance when the outer diameter of the supply roller 72 is equal to or smaller than a predetermined outer diameter. The development memory 76 does not store a flag F (F=0) when the outer diameter of the supply roller 72 is larger than the predetermined outer diameter.

[0051] Here, supply roller 72 has shaft 72A and roller body 72B made of sponge etc. The outer diameter of supply roller 72 is the outer diameter of roller body 72B of supply roller 72.

[0052] Furthermore, the development memory 76 stores a flag F (F=1) in advance when the hardness of the supply roller 72 is equal to or less than a predetermined hardness. The development memory 76 does not store a flag F (F=0) when the hardness of the supply roller 72 is greater than the predetermined hardness.

[0053] Here, the hardness of the supply roller 72 is the hardness of the roller body 72B of the supply roller 72. The hardness of the supply roller 72 is, for example, Asker F hardness.

[0054] Furthermore, if the developer cartridge 7 is a recycled product, the development memory 76 stores a flag F (F=1) in advance. If the developer cartridge 7 is not a recycled product, the development memory 76 does not store a flag F (F=0).

[0055] The main memory 16 is a non-volatile memory capable of storing information. The main memory 16 is located inside the main body housing 2. The main memory 16 stores a second parameter. The second parameter is a parameter that increases with the rotation of the developing roller 71 from the time when the printing operation is started after a predetermined time has elapsed since the printing operation was completed. In this embodiment, the second parameter is the number of rotations of the developing roller 71 from the time when the printing operation is started after a predetermined time has elapsed since the printing operation was completed (hereinafter referred to as the "first number of rotations").

[0056] The control unit 10 counts the first number of rotations. The control unit 10 counts the first number of rotations in conjunction with the control of the main motor. The control unit 10 stores the counted first number of rotations in the main body memory 16. If the temperature T of the fixing unit 8 detected by the temperature sensor 83 is equal to or lower than a predetermined temperature Tth, the control unit 10 determines that a predetermined time has passed since the end of the printing operation. The control unit 10 also determines that a predetermined time has passed since the end of the printing operation when it determines that the developing cartridge 7 has been replaced with a new one.

[0057] In this embodiment, when the control unit 10 determines that a predetermined time has elapsed since the printing operation ended, it resets the first number of rotations stored in the main body memory 16. After resetting the first number of rotations, when a printing operation is started by inputting a new print job to the image forming apparatus 1, the control unit 10 starts counting the first number of rotations.

[0058] The control unit 10 holds the first rotation number at the time when the printing operation was completed until a predetermined time has elapsed since the printing operation was completed. If a new print job is input to the image forming apparatus 1 and the printing operation is started before the predetermined time has elapsed since the printing operation was completed, the control unit 10 restarts counting from the first rotation number that was held.

[0059] The control unit 10 includes a CPU, RAM, ROM, input / output circuits, etc. The control unit 10 executes a printing operation by performing arithmetic processing based on programs and data stored in the ROM, etc. The printing operation is an operation of forming an image on a sheet S. The control unit 10 executes the printing operation by controlling the exposure unit 4, the process cartridge 5, the fixing unit 8, etc. The control unit 10 can read information from the main body memory 16 and the developing memory 76, and write information to the main body memory 16 and the developing memory 76.

[0060] As shown in FIG. 2, the control unit 10 controls the developing voltage Vb applied to the developing roller 71 during printing. The image forming apparatus 1 includes a power supply circuit that applies the developing voltage Vb to the developing roller 71. The control unit 10 applies the developing voltage Vb to the developing roller 71 using the power supply circuit. In this embodiment, the developing voltage Vb is a positive voltage. The control unit 10 normally applies a reference voltage V0 to the developing roller 71 as the developing voltage Vb. In this embodiment, the control unit 10 controls the reference voltage V0 to be a constant voltage regardless of an increase in the cumulative number of printed sheets.

[0061] The control unit 10 can execute image quality improvement control while a printing operation is being performed. The control unit 10 executes image quality improvement control when a first condition is met: the cumulative number of printed sheets is equal to or greater than a first threshold value TH1 and equal to or less than a second threshold value TH2, and the first number of rotations is equal to or greater than a third threshold value TH3. More specifically, the control unit 10 executes image quality improvement control when the first condition is met: the cumulative number of printed sheets is equal to or greater than the first threshold value TH1 and equal to or less than the second threshold value TH2, and the first number of rotations is equal to or greater than the third threshold value TH3.

[0062] The second threshold TH2 is greater than the first threshold TH1. As an example, the first threshold TH1 is 500 sheets, and the second threshold TH2 is 1500 sheets. The third threshold TH3 is the number of rotations of the developing roller 71 that is required to form images on a predetermined number of sheets S. As an example, the predetermined number is 30 to 100 sheets.

[0063] In the image quality improvement control, the control unit 10 increases the magnitude of the developing voltage Vb applied to the developing roller 71 when forming a toner image on the photosensitive drum 61 compared to when the toner image was formed on the photosensitive drum 61 during the printing immediately before the first condition was satisfied. In this embodiment, in the image quality improvement control, the control unit 10 sets the developing voltage Vb to a voltage obtained by adding a positive additional value V1 to a reference voltage V0. The control unit 10 sets the developing voltage Vb for each sheet S.

[0064] The control unit 10 reads the cumulative number of printed sheets from the development memory 76 and the first number of rotations from the main memory 16. The control unit 10 executes image quality improvement control on the condition that a first condition is satisfied: the cumulative number of printed sheets stored in the development memory 76 is equal to or greater than a first threshold value TH1 and equal to or less than a second threshold value TH2, and the first number of rotations stored in the main memory 16 is equal to or greater than a third threshold value TH3.

[0065] The control unit 10 executes the image quality improvement control when, in addition to the first condition, a second condition is satisfied, that is, the humidity H detected by the humidity sensor 11 is equal to or higher than a predetermined humidity Hth. More specifically, the control unit 10 executes the image quality improvement control when, in addition to the first condition, the second condition is satisfied.

[0066] The control unit 10 reads the information of flag F from the development memory 76. The control unit 10 executes image quality improvement control when, in addition to the first condition, a third condition is met, that is, the development memory 76 stores flag F (F=1). More specifically, the control unit 10 executes image quality improvement control when, in addition to the first condition, the third condition is met.

[0067] In the embodiment, the control unit 10 executes image quality improvement control when all of the first condition, the second condition, and the third condition are satisfied.

[0068] As described above, when a printing operation is started after a predetermined time has elapsed since the end of the printing operation, the control unit 10 starts counting the first number of rotations. If the number of first rotations counted by the control unit 10 becomes equal to or greater than the third threshold value TH3 and the cumulative number of printed sheets stored in the development memory 76 is equal to or greater than the first threshold value TH1 and equal to or less than the second threshold value TH2, the following phenomenon may occur.

[0069] That is, the toner in the toner storage portion 75 of the developer cartridge 7 deteriorates and aggregates. When the aggregated toner is supplied to the developer roller 71, the amount of toner on the developer roller 71 increases. When the amount of toner on the developer roller 71 increases, it becomes difficult for the toner particles to be frictionally charged, and it becomes difficult for the toner on the developer roller 71 to move to the photosensitive drum 61.

[0070] In this embodiment, the control unit 10 executes image quality improvement control when at least the first condition is satisfied. Specifically, the control unit 10 sets the development voltage Vb to a voltage obtained by adding a positive additional value V1 to the reference voltage V0, and applies the voltage to the development roller 71. As a result of the image quality improvement control, the voltage corresponding to the positive additional value V1 is added to the reference voltage V0, which makes it easier for the toner on the development roller 71 to move to the photosensitive drum 61.

[0071] Next, the operation of the control unit 10 in the first embodiment will be described with reference to a flowchart. Specifically, the setting of the development voltage Vb will be described. During the printing operation, the control unit 10 executes the development voltage setting process shown in FIG. 3 for each sheet S.

[0072] 3, the control unit 10 determines whether the humidity H is equal to or greater than a predetermined humidity Hth (S11). If the humidity H is less than the predetermined humidity Hth (S11, No), the control unit 10 sets the development voltage Vb to the reference voltage V0 (S51).

[0073] In step S11, if the humidity H is equal to or higher than the predetermined humidity Hth (Yes), the control unit 10 determines whether the development memory 76 stores a flag F (whether the flag F=1) (S21). If the flag F=0 (S21, No), the control unit 10 sets the development voltage Vb to the reference voltage V0 (S51).

[0074] In step S21, if flag F=1 (Yes), the control unit 10 determines whether the first rotation count, which is the number of rotations of the developing roller 71 from the start of the printing operation after a predetermined time has elapsed since the end of the printing operation, is equal to or greater than a third threshold value TH3 (S31). If the first rotation count is less than the third threshold value TH3 (S31, No), the control unit 10 sets the developing voltage Vb to the reference voltage V0 (S51).

[0075] In step S31, if the first rotation count is equal to or greater than the third threshold value TH3 (Yes), the control unit 10 determines whether the cumulative number of printed sheets is equal to or greater than the first threshold value TH1 (S41). If the cumulative number of printed sheets is less than the first threshold value TH1 (S41, No), the control unit 10 sets the development voltage Vb to the reference voltage V0 (S51).

[0076] In step S41, if the cumulative number of printed sheets is equal to or greater than the first threshold value TH1 (Yes), the control unit 10 determines whether the cumulative number of printed sheets is equal to or less than the second threshold value TH2 (S42). If the cumulative number of printed sheets is greater than the second threshold value TH2 (S42, No), the control unit 10 sets the development voltage Vb to the reference voltage V0 (S51).

[0077] In step S42, if the cumulative number of printed sheets is equal to or less than the second threshold value TH2 (Yes), the control unit 10 sets the development voltage Vb to a voltage obtained by adding the additional value V1 to the reference voltage V0 (S52).

[0078] Next, the timing for executing the image quality improvement control will be described with reference to a timing chart. Here, it is assumed that the second condition (humidity condition), the third condition (flag condition), and the condition that the cumulative number of printed sheets is equal to or greater than the first threshold value TH1 and equal to or less than the second threshold value TH2 are satisfied.

[0079] As shown in FIG. 4, when the control unit 10 determines that a predetermined time has elapsed at time t1 since the previous printing operation ended, it resets the number of rotations of the developing roller 71 (first number of rotations) stored in the main body memory 16.

[0080] After that, when a print job is input at time t2, the control unit 10 starts the printing operation (printing operation ON). When the printing operation starts, the control unit 10 counts the first number of rotations. If the first number of rotations is less than the third threshold value TH3, the control unit 10 sets the developing voltage Vb applied to the developing roller 71 to the reference voltage V0 and forms an image on the sheet S.

[0081] If the first rotation count becomes equal to or greater than the third threshold value TH3 at time t3 during the printing operation, the control unit 10 executes image quality improvement control. Specifically, the control unit 10 sets the developing voltage Vb applied to the developing roller 71 to a voltage obtained by adding an additional value V1 to the reference voltage V0, and forms an image on the sheet S. Thereafter, the control unit 10 forms an image on the sheet S by setting the developing voltage Vb applied to the developing roller 71 to a voltage obtained by adding an additional value V1 to the reference voltage V0, until the printing operation is completed (times t3 to t4).

[0082] When the printing operation ends at time t4, the control unit 10 stops counting the first number of rotations. When the next print job is input at time t5, before it is determined that a predetermined time has passed since the printing operation ended at time t4, the control unit 10 starts the printing operation. When the printing operation starts, the control unit 10 resumes counting the first number of rotations. In this case, since the first number of rotations is equal to or greater than the third threshold value TH3, the control unit 10 executes image quality improvement control from the beginning. That is, until the printing operation ends, the control unit 10 forms an image on the sheet S by setting the development voltage Vb applied to the development roller 71 to a voltage obtained by adding the additional value V1 to the reference voltage V0 (times t5 to t6).

[0083] When the control unit 10 determines that a predetermined time has passed at time t7 since the printing operation ended at time t6, it resets the first rotation count stored in the main body memory 16. Time t7 is the time when a predetermined time has passed since the printing operation ended.

[0084] Next, the effects of the first embodiment will be described. In a state where the toner on the developing roller 71 is difficult to move to the photosensitive drum 61, the magnitude of the developing voltage Vb is increased by executing image quality improvement control. As a result, the toner on the developing roller 71 is more likely to move to the photosensitive drum 61, thereby suppressing the occurrence of printing defects such as blurring.

[0085] Since the developer cartridge 7 has a development memory 76 that stores the cumulative number of printed pages, the cumulative number of printed pages can be continuously used for control even if the developer cartridge 7 is removed from the main body housing 2 and then re-attached to the main body housing 2, or is attached to the main body housing 2 of another image forming apparatus 1. This allows for accurate image quality improvement control.

[0086] By executing image quality improvement control when the second condition that humidity H is equal to or higher than a predetermined humidity Hth is satisfied in addition to the first condition, image quality improvement control can be executed in a high humidity environment where printing defects are more likely to occur.

[0087] Since the developer cartridge 7 has a developer memory 76 capable of storing the flag F, by associating the flag F with the conditions under which printing defects are likely to occur, it is possible to execute image quality improvement control under the conditions under which printing defects are likely to occur.

[0088] Specifically, when the toner contained in the toner storage section 75 is pulverized toner, the development memory 76 stores flag F, thereby enabling image quality improvement control to be performed when the toner storage section 75 contains toner that is prone to causing printing defects.

[0089] Furthermore, by storing flag F in the development memory 76 when the surface roughness of the development roller 71 is equal to or greater than a predetermined surface roughness, image quality improvement control can be performed when the development roller 71 is prone to print defects.

[0090] Furthermore, the development memory 76 stores flag F when the outer diameter of the supply roller 72 is equal to or smaller than a predetermined outer diameter or when the hardness of the supply roller 72 is equal to or smaller than a predetermined hardness, thereby enabling image quality improvement control to be performed when the supply roller 72 is prone to print defects.

[0091] Furthermore, if the developing cartridge 7 is a recycled product, the developing memory 76 stores flag F, so that image quality improvement control can be executed when the developing cartridge 7 is prone to print defects.

[0092] 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. In the second embodiment, the control unit 10 does not change the development voltage Vb from the reference voltage V0 during image quality improvement control.

[0093] In the second embodiment, the control unit 10, in image quality improvement control, increases the size of the dots of the electrostatic latent image formed on the photosensitive drum 61 when forming a toner image on the photosensitive drum 61 compared to when the toner image was formed on the photosensitive drum 61 during printing immediately before satisfying the first condition. The control unit 10 forms an electrostatic latent image on the photosensitive drum 61 using the exposure unit 4. Specifically, in image quality improvement control, the control unit 10 sets the exposure time TE per dot of the electrostatic latent image to a time obtained by multiplying a reference time T0 by a first coefficient C1. The first coefficient C1 is greater than 1. As an example, the first coefficient C1 is 1.05.

[0094] Next, the operation of the control unit 10 in the second embodiment will be described with reference to a flowchart. Specifically, the setting of the exposure time TE will be described. In the printing operation, the control unit 10 executes the dot size setting process shown in FIG. 5 for each sheet S.

[0095] As shown in FIG. 5, if the humidity H is less than the predetermined humidity Hth (No) in step S11, the control unit 10 sets the exposure time TE to the reference time T0 (S53). If the flag F=0 in step S21 (No), the control unit 10 sets the exposure time TE to the reference time T0 (S53).

[0096] In step S31, if the first rotation count, which is the number of rotations of the developing roller 71 since the printing operation started after a predetermined time has elapsed since the printing operation ended, is less than the third threshold value TH3 (No), the control unit 10 sets the exposure time TE to the reference time T0 (S53). If the cumulative number of printed sheets is less than the first threshold value TH1 (No) in step S41, the control unit 10 sets the exposure time TE to the reference time T0 (S53).

[0097] If the cumulative number of printed sheets is greater than the second threshold value TH2 in step S42 (No), the control unit 10 sets the exposure time TE to the reference time T0 (S53). If the cumulative number of printed sheets is equal to or less than the second threshold value TH2 in step S42 (Yes), the control unit 10 sets the exposure time TE to the reference time T0 multiplied by the first coefficient C1 (S54).

[0098] In the second embodiment, even if the toner on the developing roller 71 is difficult to move to the photosensitive drum 61, by executing image quality improvement control to increase the size of the dots of the electrostatic latent image, the toner on the developing roller 71 becomes more likely to move to the photosensitive drum 61, thereby suppressing the occurrence of printing defects such as blurring.

[0099] Next, a third embodiment will be described. In the third embodiment, the control unit 10 does not change the development voltage Vb from the reference voltage V0 during image quality improvement control. Also, the control unit 10 does not change the exposure time TE per dot of the electrostatic latent image from the reference time T0 during image quality improvement control.

[0100] In the third embodiment, the control unit 10, in image quality improvement control, increases the intensity LI of the light beam emitted by the exposure unit 4 when forming a toner image on the photosensitive drum 61 compared to when the toner image was formed on the photosensitive drum 61 during printing immediately before the first condition was satisfied. Specifically, in image quality improvement control, the control unit 10 sets the intensity LI of the light beam to an intensity obtained by multiplying the reference intensity L0 by a second coefficient C2. The second coefficient C2 is greater than 1. As an example, the second coefficient C2 is 1.1.

[0101] Next, the operation of the control unit 10 in the third embodiment will be described with reference to a flowchart. Specifically, the setting of the intensity LI of the light beam will be described. In the printing operation, the control unit 10 executes the light intensity setting process shown in FIG. 6 for each sheet S.

[0102] As shown in FIG. 6, if the humidity H is less than the predetermined humidity Hth (No) in step S11, the control unit 10 sets the intensity LI of the light beam to the reference intensity L0 (S55). If the flag F=0 in step S21 (No), the control unit 10 sets the intensity LI of the light beam to the reference intensity L0 (S55).

[0103] In step S31, if the first rotation count, which is the number of rotations of the developing roller 71 since the printing operation started after a predetermined time has elapsed since the printing operation ended, is less than the third threshold value TH3 (No), the control unit 10 sets the intensity LI of the light beam to the reference intensity L0 (S55). If the cumulative number of printed sheets is less than the first threshold value TH1 in step S41 (No), the control unit 10 sets the intensity LI of the light beam to the reference intensity L0 (S55).

[0104] If the cumulative number of printed sheets is greater than the second threshold value TH2 in step S42 (No), the control unit 10 sets the intensity LI of the light beam to the reference intensity L0 (S55). If the cumulative number of printed sheets is equal to or less than the second threshold value TH2 in step S42 (Yes), the control unit 10 sets the intensity LI of the light beam to the reference intensity L0 multiplied by the second coefficient C2 (S56).

[0105] In the third embodiment, by executing image quality improvement control and increasing the intensity LI of the light beam, the magnitude of the potential at the portion of the photosensitive drum 61 exposed by the light beam decreases, and therefore it is possible to increase the potential difference between the developing roller 71 and the portion of the photosensitive drum 61 exposed by the light beam. As a result, even if the toner on the developing roller 71 is in a state where it is difficult for the toner to move to the photosensitive drum 61, by executing image quality improvement control, the toner on the developing roller 71 can move more easily to the photosensitive drum 61, thereby suppressing the occurrence of printing defects such as blurring.

[0106] Next, a fourth embodiment will be described. In the fourth embodiment, when the control unit 10 executes the image quality improvement control, the control unit 10 increases the magnitude of the developing voltage Vb as the number of printed sheets increases. Also, when the control unit 10 executes the image quality improvement control, the control unit 10 sets the magnitude of the developing voltage Vb to a predetermined upper limit value or less.

[0107] Next, the fourth embodiment will be described in detail with reference to a timing chart. Here, it is assumed that the second condition (humidity condition), the third condition (flag condition), and the condition that the cumulative number of printed sheets is equal to or greater than the first threshold value TH1 and equal to or less than the second threshold value TH2 are satisfied.

[0108] As shown in FIG. 7, when the control unit 10 determines that a predetermined time has elapsed at time t1 since the previous printing operation ended, it resets the number of rotations of the developing roller 71 (first number of rotations) stored in the main body memory 16.

[0109] After that, when a print job is input at time t2, the control unit 10 starts the printing operation. When the printing operation starts, the control unit 10 counts the first number of rotations. If the first number of rotations is less than the third threshold value TH3, the control unit 10 sets the developing voltage Vb applied to the developing roller 71 to the reference voltage V0 and forms an image on the sheet S.

[0110] When the first rotation count becomes equal to or greater than the third threshold value TH3 at time t3 during the printing operation, the control unit 10 executes image quality improvement control. In the fourth embodiment, when executing image quality improvement control, the control unit 10 sets the development voltage Vb for each sheet S in principle based on the following formula (1). Vb = V0 + A1 × (NR - NR1) (1)

[0111] In equation (1), A1 is a predetermined voltage increase rate. The control unit 10 increases the development voltage Vb by A1 every time the development roller 71 rotates a number of times corresponding to one sheet S. A1 is a preset positive value.

[0112] NR is the number of rotations of the developing roller 71, which corresponds to the number of pages printed using the developing cartridge 7 from the time the printing operation was started after a predetermined time had elapsed since the end of the printing operation. Here, NR is the number of rotations of the developing roller 71, which corresponds to the number of pages printed from time t2.

[0113] NR1 is the number of rotations of the developing roller 71, which corresponds to the number of pages printed using the developing cartridge 7 from when the printing operation is started after a predetermined time has elapsed since the end of the printing operation until before the image quality improvement control is executed. Here, NR1 is the number of rotations of the developing roller 71, which corresponds to the number of pages printed from time t2 to time t3.

[0114] When the control unit 10 starts image quality improvement control at time t3, it sets the developing voltage Vb based on equation (1). As a result, the magnitude of the developing voltage Vb increases stepwise as the number of printed sheets increases (times t3 to t31).

[0115] If the developing voltage Vb set based on equation (1) is equal to or greater than a predetermined upper limit, the control unit 10 sets the developing voltage Vb to the upper limit. In this embodiment, the upper limit is V0+V1. That is, the control unit 10 sets the developing voltage Vb so that it does not exceed the upper limit (V0+V1). After time t31, the control unit 10 forms an image on the sheet S by setting the developing voltage Vb applied to the developing roller 71 to the upper limit (V0+V1) until the printing operation is completed (times t31 to t4).

[0116] When the printing operation ends at time t4, the control unit 10 stops counting the first number of rotations. When the next print job is input at time t5, before it is determined that a predetermined time has passed since the printing operation ended at time t4, the control unit 10 starts the printing operation. When the control unit 10 starts the printing operation, it resumes counting the first number of rotations.

[0117] In this case, since the first rotation count is equal to or greater than the third threshold value TH3, the control unit 10 executes image quality improvement control from the beginning. In the fourth embodiment, when executing this image quality improvement control, the control unit 10 sets an initial value Vb0 of the development voltage Vb to be applied to the development roller 71 based on the following equation (2), in principle. Vb0(Vb)=Vb n-1 -B1×(ts-tf) (2)

[0118] In equation (2), Vbn-1 is the development voltage that was set when the previous printing operation was completed. Here, Vb n-1 is the development voltage (V0+V1) set at time t4.

[0119] B1 is a predetermined voltage reduction rate. The control unit 10 sets the initial value Vb0 of the developing voltage Vb n-1 The value is set to a value obtained by decreasing the value by B1 per predetermined unit time from the value of B1, where B1 is a preset positive value. tf is the time when the immediately preceding printing operation ends. In this example, time tf is time t4. ts is the time when the current printing operation starts. In this embodiment, ts is the time when the print job for the current printing operation is input. In this example, time ts is time t5.

[0120] If the initial value Vb0 of the development voltage Vb set based on equation (2) is equal to or less than a predetermined lower limit, the control unit 10 sets the initial value Vb0 of the development voltage Vb to the lower limit. In this embodiment, the lower limit is V0. That is, the control unit 10 sets the initial value Vb0 of the development voltage Vb so that it does not become equal to or less than the lower limit (V0).

[0121] When the control unit 10 starts the printing operation at time t5, it sets the initial value Vb0 of the developing voltage Vb based on equation (2). That is, the control unit 10 starts the printing operation at time t5, sets the developing voltage Vb applied to the developing roller 71 to the initial value Vb0 for the first sheet S, and forms an image on this sheet S.

[0122] Thereafter, the control unit 10 sets the development voltage Vb to be applied to the development roller 71, in principle, based on the following equation (3). Vb = Vb0 + A1 × (NR - NR2) (3) In equation (3), NR is the number of rotations of the developing roller 71, which corresponds to the number of printed sheets from time t2.

[0123] NR2 is the number of rotations of the developing roller 71, which corresponds to the number of pages printed using the developing cartridge 7 from the start of a printing operation a predetermined time after the end of the previous printing operation until the start of the current printing operation. Here, NR2 is the number of rotations of the developing roller 71, which corresponds to the number of pages printed from time t2 to time t5.

[0124] When the printing operation starts at time t5, the control unit 10 sets the developing voltage Vb based on equation (3) for the second and subsequent sheets S. As a result, the magnitude of the developing voltage Vb increases stepwise as the number of printed sheets increases (times t5 to t51).

[0125] If the developing voltage Vb set based on equation (3) is equal to or greater than a predetermined upper limit (V0+V1), the control unit 10 sets the developing voltage Vb to the upper limit (V0+V1). After time t51, the control unit 10 forms an image on the sheet S by setting the developing voltage Vb applied to the developing roller 71 to the upper limit (V0+V1) until the printing operation is completed (times t51 to t6).

[0126] When the control unit 10 determines that a predetermined time has passed at time t7 since the printing operation ended at time t6, the control unit 10 resets the first rotation number stored in the main body memory 16.

[0127] Next, the effects of the fourth embodiment will be described. In the fourth embodiment, when performing image quality improvement control, the control unit 10 increases the magnitude of the developing voltage Vb as the number of printed sheets increases. Specifically, the control unit 10 increases the developing voltage Vb by A1 each time the developing roller 71 is rotated a number of times equivalent to one sheet S, thereby forming an image on the sheet S.

[0128] The reason for performing image quality improvement control as in the fourth embodiment is as follows: That is, the state in which it becomes difficult for toner on the developing roller 71 to move to the photosensitive drum 61 gradually occurs as the image forming apparatus 1 performs the printing operation. In other words, the state in which it becomes difficult for toner on the developing roller 71 to move to the photosensitive drum 61 gradually progresses as the printing operation is performed and the number of printed sheets increases.

[0129] Therefore, in the fourth embodiment, the developing voltage Vb is increased by A1 each time the developing roller 71 is rotated a number of times equivalent to one sheet S. This makes it easier for the toner on the developing roller 71 to move to the photosensitive drum 61, thereby suppressing the occurrence of printing defects such as blurring, and by gradually increasing the developing voltage Vb, it is possible to suppress abrupt changes in the color tone of the image formed on the sheet S.

[0130] Furthermore, in the fourth embodiment, the control unit 10 sets the initial value Vb0 of the development voltage Vb when image quality improvement control is resumed, based on the length of time from time t4 to time t5, based on equation (2). As the time during which no new print job is input to the image forming apparatus 1 (the time from time t4 to time t5) becomes longer, the condition in which it is difficult for toner on the development roller 71 to move to the photosensitive drum 61 is gradually improved.

[0131] Therefore, by setting the initial value Vb0 of the developing voltage Vb according to the length of time from time t4 to time t5 based on equation (2), it is possible to prevent the initial value Vb0 of the developing voltage Vb in the image quality improvement control from becoming larger than necessary, thereby preventing, for example, deterioration of the toner, the developing roller 71, etc.

[0132] In the fourth embodiment, when image quality improvement control is performed, the magnitude of the developing voltage Vb is increased as the number of printed sheets increases. However, for example, when image quality improvement control is performed, the control unit 10 may increase the size of the dots of the electrostatic latent image (exposure time TE) as the number of printed sheets increases. Also, for example, when image quality improvement control is performed, the control unit 10 may increase the light intensity LI as the number of printed sheets increases.

[0133] Although the embodiment has been described above, the image forming apparatus can be modified as appropriate as exemplified below.

[0134] In the above-described embodiment, the control unit 10 controls the reference voltage V0 to be a constant voltage regardless of the increase in the cumulative number of printed sheets, as shown in Fig. 2. However, for example, as shown in Fig. 8, the control unit 10 may control the reference voltage V0 to decrease in a linear function manner as the cumulative number of printed sheets increases.

[0135] In the above-described embodiment, in the image quality improvement control, one of the magnitude of the development voltage Vb, the size of the electrostatic latent image dots (exposure time TE), and the light intensity LI is increased, but for example, two or more elements may be increased. Furthermore, the element to be increased or the combination of elements to be increased may be changed depending on the conditions that are met.

[0136] The first parameter may be, for example, the cumulative number of rotations of the developing roller 71. In other words, the first parameter may be the cumulative number of rotations of the developing roller 71 since the developing roller 71 was brand new (hereinafter simply referred to as the "cumulative number of rotations"). In this case, the developing memory 76 stores the cumulative number of rotations. The control unit 10 executes image quality improvement control when, for example, a first condition is satisfied in which the cumulative number of rotations is equal to or greater than a first threshold value and equal to or less than a second threshold value that is greater than the first threshold value, and the first number of rotations is equal to or greater than a third threshold value TH3.

[0137] The second parameter may be, for example, the number of pages printed using the developing cartridge 7 from the start of a printing operation after a predetermined time has elapsed since the end of the printing operation (hereinafter referred to as the "first number of pages printed"). In this case, the control unit 10 executes image quality improvement control when a first condition is met, for example, that the cumulative number of pages printed or the cumulative number of rotations is equal to or greater than a first threshold value and equal to or less than a second threshold value, and the first number of pages printed is equal to or greater than a third threshold value.

[0138] The first parameter may be, for example, the cumulative number of rotations of the supply roller 72 or the cumulative number of rotations of the agitator 74. The second parameter may be, for example, the number of rotations of the supply roller 72 from when the printing operation started after a predetermined time has elapsed since the printing operation ended. The second parameter may be, for example, the number of rotations of the agitator 74 from when the printing operation started after a predetermined time has elapsed since the printing operation ended.

[0139] The first parameter may be stored in the main memory 16. In other words, the memory that stores the cumulative number of prints or cumulative number of rotations may be the main memory 16, not the development memory 76.

[0140] For example, the control unit 10 may actually count the time from the time the printing operation is completed, and if the counted time is equal to or greater than a predetermined time, determine that the predetermined time has passed since the printing operation was completed. Alternatively, the control unit 10 may determine that the printing operation is completed when the main motor stops.

[0141] The conditions under which the development memory 76 stores the flag F may be some of the conditions described in the above embodiment. For example, the development memory 76 may store a flag only when the outer diameter of the supply roller 72 is equal to or smaller than a predetermined outer diameter, or may store a flag only when the hardness of the supply roller 72 is equal to or smaller than a predetermined hardness.

[0142] Also, for example, the development memory 76 may store flag F only when the toner contained in the toner container 75 is pulverized toner, or may store flag F only when the development cartridge 7 is a recycled product. Also, the memory does not have to be capable of storing flags. The development cartridge 7 does not have to have a memory.

[0143] The control unit 10 may execute the image quality improvement control when, for example, the first condition and the condition that the humidity is equal to or higher than a predetermined humidity are satisfied, even if the condition that the memory stores a flag are not satisfied. The control unit 10 may also execute the image quality improvement control when, for example, the first condition and the condition that the memory stores a flag are satisfied, even if the condition that the humidity is equal to or higher than a predetermined humidity are not satisfied. The control unit 10 may also execute the image quality improvement control when the first condition is satisfied, even if the second and third conditions are not satisfied.

[0144] In the above-described embodiment, the exposure unit 4 is configured to emit a light beam to expose the photosensitive drum 61, but for example, the exposure unit 4 may be configured to emit LED light to expose the photosensitive drum 61.

[0145] In the above-described embodiment, the image forming apparatus 1 is a printer, but the image forming apparatus may be, for example, a copier, a multifunction peripheral, etc. The image forming apparatus does not need to be equipped with the humidity sensor 11. The developing voltage may be a negative voltage.

[0146] The elements described in the above-described embodiment and modifications may be implemented in any combination. [Explanation of symbols]

[0147] 1. Image forming device 2 Main unit housing 4 Exposure Unit 7 Developer cartridge 8 Fixing unit 10 Control Unit 11 Humidity sensor 61 Photosensitive drum 71 Developing roller 72 Supply roller 75 Toner storage compartment 76 Development Memory

Claims

1. A main body housing; A photosensitive drum; an exposure unit that emits light to expose the photosensitive drum; a developing unit having a developing roller; a memory for storing the cumulative number of prints made using the developing device or the cumulative number of rotations of the developing roller; a control unit, The control unit The cumulative number of printed sheets or the cumulative number of rotations is equal to or greater than a first threshold value and equal to or less than a second threshold value that is greater than the first threshold value, and When a first condition is satisfied that the number of printed sheets printed using the developing device from the time when the printing operation was started after a predetermined time has elapsed since the printing operation was completed, or the number of rotations of the developing roller from the time when the printing operation was started after a predetermined time has elapsed since the printing operation was completed, is equal to or greater than a third threshold value, When a toner image is formed on the photosensitive drum, the magnitude of the development voltage applied to the development roller; The size of the dots of the electrostatic latent image formed on the photosensitive drum, or the intensity of the light emitted by the exposure unit; the toner image formed on the photosensitive drum during printing immediately before the first condition is satisfied.

2. 2. The image forming apparatus according to claim 1, wherein the developing unit is a developing cartridge that has the memory and is detachable from the main body casing.

3. Further comprising a humidity sensor for detecting humidity, 2. The image forming apparatus according to claim 1, wherein the control unit executes the image quality improvement control when, in addition to the first condition, a further condition is satisfied in which the humidity detected by the humidity sensor is equal to or higher than a predetermined humidity.

4. the developing unit is a developing cartridge that has a developing memory that can store a flag and is detachable from the main body housing; 2. The image forming apparatus according to claim 1, wherein the control unit executes the image quality improvement control when, in addition to the first condition, a condition that the development memory stores the flag is further satisfied.

5. the developing cartridge has a toner storage portion capable of storing toner, 5. The image forming apparatus according to claim 4, wherein the development memory stores the flag when the toner contained in the toner container is pulverized toner.

6. 5. The image forming apparatus according to claim 4, wherein the development memory stores the flag when the surface roughness of the developing roller is equal to or greater than a predetermined surface roughness.

7. the developing cartridge has a supply roller that supplies toner to the developing roller, 5. The image forming apparatus according to claim 4, wherein the development memory stores the flag when the outer diameter of the supply roller is equal to or smaller than a predetermined outer diameter or when the hardness of the supply roller is equal to or smaller than a predetermined hardness.

8. 5. The image forming apparatus according to claim 4, wherein the development memory stores the flag when the development cartridge is a recycled product.

9. a fixing device that thermally fixes the toner image transferred from the photosensitive drum to the sheet, 2. The image forming apparatus according to claim 1, wherein the control unit determines that a predetermined time has elapsed since the end of a printing operation when the temperature of the fixing unit is equal to or lower than a predetermined temperature.

10. The control unit When the image quality improvement control is executed, the magnitude of the development voltage applied to the development roller; The size of the dots of the electrostatic latent image formed on the photosensitive drum, or the intensity of the light emitted by the exposure unit; 2. The image forming apparatus according to claim 1, wherein the number of prints increases as the number of prints increases.

11. 11. The image forming apparatus according to claim 10, wherein the control unit sets the magnitude of the developing voltage applied to the developing roller to a predetermined upper limit value or less when the image quality improvement control is executed.

Images