Image forming apparatus

Abstract

An image forming apparatus includes a main body housing, a photosensitive drum, an exposure unit, a developer having a developing roller, a memory storing a cumulative number of printed sheets or a cumulative number of rotations of the developing roller, and a control unit. The accumulated number of printed sheets or the accumulated number of rotations is greater than or equal to a first threshold value and less than or equal to a second threshold value. The first condition is that the number of printed sheets to be printed using the developer from the start of the printing operation after a predetermined time elapses from the end of the printing operation, or the number of rotations of the developing roller from the start of the printing operation after the predetermined time elapses from the end of the printing operation is equal to or greater than a third threshold value. The control unit performs image quality improvement control such that the magnitude of the developing voltage applied to the developing roller when the toner image is formed in the photosensitive drum, the size of the dot of the electrostatic latent image formed in the photosensitive drum, or the intensity of the light emitted by the exposure unit becomes larger than when the toner image is formed in the photosensitive drum during printing immediately before the first condition is satisfied.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus. Background Art

[0002] Conventionally, as an image forming apparatus, there is known a structure having a photosensitive drum and a developing roller for applying a developing bias when supplying toner to the photosensitive drum (Patent Document 1). In this technology, as the number of printed sheets increases, the developing bias applied to the developing roller is reduced linearly as a function.

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2005-292475

[0004] However, toner degrades during printing operations in image forming apparatuses. As toner degradation progresses, toner aggregates, sometimes resulting in a larger amount of toner on the developing roller than usual. If the amount of toner on the developing roller increases, for example, it becomes difficult for the toner to be triboelectrically charged, making it difficult for the toner on the developing roller to move to the photosensitive drum. This can lead to printing defects such as blurred images. Summary of the Invention

[0005] Therefore, it is desired to suppress the occurrence of printing defects.

[0006] An image forming apparatus according to a first aspect of the present application includes a main body casing, a photosensitive drum, an exposure unit, a developer, a memory, and a control section.

[0007] The exposure unit emits light to expose the photosensitive drum.

[0008] The developer includes a developing roller.

[0009] The memory stores the cumulative number of printed sheets printed using the developer or the cumulative number of rotations of the developing roller.

[0010] The control unit performs image quality improvement control when a first condition is met, which is the following condition: the cumulative number of printed sheets or the cumulative number of rotations is greater than a first threshold and less than a second threshold that is greater than the first threshold, and the number of printed sheets printed using the developer from the time the printing action is started after a specified time has passed since the end of the printing action, or the number of rotations of the developing roller from the time the printing action is started after a specified time has passed since the end of the printing action, is greater than a third threshold.

[0011] In image quality improvement control, the size of the developing voltage applied to the developing roller when forming a toner image on the photosensitive drum, the size of the dots of the electrostatic latent image formed on the photosensitive drum, or the intensity of light emitted by the exposure unit are increased compared to when forming a toner image on the photosensitive drum during printing just before the first condition is met.

[0012] According to the first invention, even when the toner on the developing roller is difficult to move to the photosensitive drum, the toner on the developing roller can be easily moved to the photosensitive drum by executing the image quality improvement control, thereby suppressing the occurrence of printing defects.

[0013] A second invention of the present application may be the image forming apparatus of the first invention, wherein the developing device includes a memory and is a developing cartridge that is attachable to and detachable from the main body casing.

[0014] According to the second invention, since the developer is a developing cartridge having a memory for storing the cumulative number of printed sheets or the cumulative number of rotations, even if the developing cartridge is removed from the main body housing and reinstalled therein, or is installed in the main body housing of another image forming apparatus, the cumulative number of printed sheets or the cumulative number of rotations can continue to be used for control. This allows for highly accurate image quality improvement control.

[0015] A third invention of the present application may be the image forming apparatus of the first invention, further comprising a humidity sensor that detects humidity.

[0016] The control unit may execute the image quality improvement control when, in addition to the first condition, a condition is satisfied that the humidity detected by the humidity sensor is equal to or higher than a predetermined humidity.

[0017] According to the third invention, by executing image quality improvement control when the humidity is equal to or higher than the predetermined humidity in addition to the first condition, image quality improvement control can be executed in a high humidity environment where printing defects are likely to occur.

[0018] A fourth invention of the present application may be the image forming apparatus of the first invention, wherein the developing device includes a developing memory capable of storing a flag, and is a developing cartridge detachable from the main body casing.

[0019] The control unit may execute the image quality improvement control when, in addition to the first condition, a condition that a flag is stored in the development memory is satisfied.

[0020] According to the fourth invention, since the developer is a developer cartridge having a developer memory capable of storing a flag, by associating the flag with a condition where printing defects are likely to occur, image quality improvement control can be performed under the condition where printing defects are likely to occur.

[0021] A fifth invention of the present application may be that, in the image forming apparatus according to the fourth invention, the developing cartridge includes a toner containing portion capable of containing toner.

[0022] The developing memory may store a flag when the toner stored in the toner storing portion is pulverized toner.

[0023] According to the fifth invention, when the toner stored in the toner storing portion is pulverized toner, the developer memory stores the flag, thereby enabling image quality improvement control to be executed when toner that is likely to cause printing defects is stored in the toner storing portion.

[0024] According to a sixth aspect of the present application, in the image forming apparatus according to the fourth aspect, the developing memory may store a flag when the surface roughness of the developing roller is equal to or greater than a predetermined surface roughness.

[0025] According to the sixth aspect of the present invention, when the surface roughness of the developing roller is equal to or greater than a predetermined surface roughness, the developing memory stores a flag, thereby enabling image quality improvement control to be executed even when a developing roller prone to printing defects is present.

[0026] A seventh invention of the present application may be that, in the image forming apparatus according to the fourth invention, the developing cartridge includes a supply roller that supplies toner to the developing roller.

[0027] The developing memory may store 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.

[0028] According to the seventh invention, when the outer diameter of the supply roller is less than a specified outer diameter, or when the hardness of the supply roller is less than a specified hardness, the developer memory stores a flag, thereby enabling image quality improvement control to be performed in the case of a supply roller that is prone to poor printing.

[0029] According to an eighth aspect of the present application, in the image forming apparatus according to the fourth aspect, when the developing cartridge is a reusable product, the developing memory may store the flag.

[0030] According to the eighth aspect of the present invention, when the developer cartridge is a reused product, the developer memory stores the flag, thereby enabling image quality improvement control to be executed in the case of a developer cartridge in which printing defects are likely to occur.

[0031] A ninth invention of the present application may be the image forming apparatus of the first invention, further comprising a fixing device that thermally fixes the toner image transferred from the photosensitive drum to the sheet to the sheet.

[0032] When 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 was completed.

[0033] The tenth invention of the present application may also be that, in the image forming device of the first invention, the control unit, when performing image quality improvement control, increases the size of the developing voltage applied to the developing 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.

[0034] According to the tenth invention, when executing image quality improvement control, the magnitude of the developing voltage is increased as the number of printed sheets increases, thereby suppressing the occurrence of printing defects and suppressing abrupt changes in the color tone of the image formed on the sheet.

[0035] According to an eleventh invention of the present application, in the image forming apparatus according to the tenth invention, the control unit may set the magnitude of the development voltage applied to the developing roller to be equal to or less than a predetermined upper limit value when executing the image quality improvement control.

[0036] The occurrence of printing defects can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a diagram showing an image forming apparatus.

[0038] Figure 2 It is a diagram showing an image of control of the development voltage.

[0039] Figure 3 This is a flowchart showing the operation of the control unit in the first embodiment.

[0040] Figure 4 This is a timing chart showing the timing of executing the image quality improvement control in the first embodiment.

[0041] Figure 5 This is a flowchart showing the operation of the control unit according to the second embodiment.

[0042] Figure 6 This is a flowchart showing the operation of the control unit according to the third embodiment.

[0043] Figure 7 This is a timing chart showing the timing of executing the image quality improvement control in the fourth embodiment.

[0044] Figure 8 1 and 2 are diagrams showing images of control of the development voltage in a modified example. DETAILED DESCRIPTION

[0045] Next, a first embodiment will be described.

[0046] like Figure 1 As shown, image forming apparatus 1 is a printer capable of forming a monochrome image on a sheet S such as paper. Image forming apparatus 1 includes a main body housing 2, a cover 2C, a sheet feeding 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.

[0047] The main body housing 2 has an opening 2A.

[0048] The cover 2C opens and closes the opening 2A of the main body casing 2 .

[0049] The sheet feeding section 3 includes a sheet tray 31 , a pressing plate 32 , and a sheet feeding roller 33 .

[0050] The sheet tray 31 stores sheets S.

[0051] The pressing plate 32 pushes up the sheets S in the sheet tray 31 .

[0052] The sheet feeding roller 33 feeds the sheet S pushed up by the pressing plate 32 to the process cartridge 5 .

[0053] The exposure unit 4 includes a light source, a deflector, a lens, a reflector, etc. The exposure unit 4 emits a light beam as shown by an imaginary line. The light beam is light for exposing the photosensitive drum 61.

[0054] In a state where the cover 2C is opened, the process cartridge 5 is attachable to and 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.

[0055] The drum cartridge 6 is attachable to and detachable from the main body casing 2 . The drum cartridge 6 includes a photosensitive drum 61 , a charger 62 , and a transfer roller 63 .

[0056] The photosensitive drum 61 has a toner image formed on its surface.

[0057] The developer cartridge 7 is attachable to and detachable from the main body casing 2. Specifically, the developer cartridge 7 is attachable to and detachable from the drum cartridge 6. The developer cartridge 7 is attachable to and detachable from the main body casing 2 together with the drum cartridge 6 in a state in which the developer cartridge 7 is mounted.

[0058] The developing cartridge 7 includes a developing roller 71 , a supply roller 72 , a layer thickness regulating plate 73 , an agitator 74 , a toner storage portion 75 , and a developing storage 76 serving as a storage.

[0059] The toner storage portion 75 can store toner.

[0060] The agitator 74 agitates the toner in the toner storage portion 75 . The agitator 74 also supplies the toner to the supply roller 72 .

[0061] The supply roller 72 supplies toner to the developing roller 71 .

[0062] The layer thickness regulating plate 73 is in contact with the surface of the developing roller 71 and regulates the thickness of the toner on the developing roller 71 to a constant thickness.

[0063] The fixing device 8 includes a heating roller 81 , a pressure roller 82 , and a temperature sensor 83 .

[0064] The heating roller 81 heats the sheet S.

[0065] The pressure roller 82 presses the sheet S against the heating roller 81 .

[0066] The temperature sensor 83 is a sensor that detects the temperature of the fixing device 8. In the 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 10.

[0067] The charger 62 charges the surface of the photosensitive drum 61 .

[0068] The exposure unit 4 irradiates the charged surface of the photosensitive drum 61 with a light beam, thereby forming an electrostatic latent image based on image data on the photosensitive drum 61 .

[0069] The developing roller 71 is applied with a predetermined developing voltage Vb to supply toner to the exposed surface of the photosensitive drum 61 , thereby forming a toner image on the photosensitive drum 61 .

[0070] The transfer roller 63 transfers the toner image formed on the photosensitive drum 61 to 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 .

[0071] The fixing device 8 thermally fixes the toner image transferred from the photosensitive drum 61 to the sheet S by conveying the sheet S to which the toner image has been transferred between the heating roller 81 and the pressure roller 82 .

[0072] The discharge roller 9 discharges the sheet S with the thermally fixed toner image to the discharge tray 2B.

[0073] 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.

[0074] The image forming apparatus 1 has interfaces such as a USB interface and a LAN interface. 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 into the image forming apparatus 1 .

[0075] The humidity sensor 11 is a sensor that detects humidity H. For example, the humidity H is relative humidity. The humidity sensor 11 may detect humidity H inside the main body housing 2 or outside the main body housing 2. The humidity sensor 11 outputs the detected humidity H to the control unit 10.

[0076] The developer memory 76 stores a first parameter. The first parameter increases as the developer roller 71 rotates, starting from the time the developer roller 71 is brand new. In the embodiment, the first parameter is the cumulative number of printed sheets using the developer cartridge 7. In other words, the first parameter is the cumulative number of printed sheets since the developer roller 71 was brand new (hereinafter referred to as the "cumulative number of printed sheets"). The cumulative number of printed sheets is the cumulative number of printed sheets since the new developer cartridge 7 was installed in the main body housing 2.

[0077] The developing 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 developing memory 76.

[0078] The developer memory 76 can also store a flag F. Specifically, when the toner stored in the toner storage portion 75 is crushed toner, the developer memory 76 stores the flag F in advance. When the toner stored in the toner storage portion 75 is not crushed toner, the developer memory 76 does not store the flag F. For example, when the toner stored in the toner storage portion 75 is polymerized toner, the developer memory 76 does not store the flag F.

[0079] In the embodiment, storing the flag F means that 1 is stored in the flag F storage area of ​​the development memory 76 (F=1). Not storing the flag F means that 0 is stored in the flag F storage area of ​​the development memory 76 (F=0).

[0080] The developing memory 76 stores a flag F (F=1) when the surface roughness of the developing roller 71 is greater than or equal to a predetermined surface roughness. The developing memory 76 does not store the flag F (F=0) when the surface roughness of the developing roller 71 is less than the predetermined surface roughness.

[0081] Here, the developing roller 71 includes a shaft 71A and a roller body 71B made of rubber, etc. The surface roughness of the developing roller 71 is the surface roughness of the outer peripheral 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).

[0082] When the outer diameter of the supply roller 72 is smaller than a predetermined diameter, the developing memory 76 stores a flag F (F=1). When the outer diameter of the supply roller 72 is larger than the predetermined diameter, the developing memory 76 does not store the flag F (F=0).

[0083] Here, the supply roller 72 includes a shaft 72A and a roller body 72B made of sponge, etc. The outer diameter of the supply roller 72 is the outer diameter of the roller body 72B of the supply roller 72 .

[0084] When the hardness of the supply roller 72 is below a predetermined hardness, the developing memory 76 stores a flag F (F=1). When the hardness of the supply roller 72 is greater than a predetermined hardness, the developing memory 76 does not store the flag F (F=0).

[0085] Here, the hardness of the supply roller 72 refers to 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.

[0086] In addition, when the developer cartridge 7 is a reused product, the developer memory 76 stores the flag F (F=1) in advance. When the developer cartridge 7 is not a reused product, the developer memory 76 does not store the flag F (F=0).

[0087] The main body memory 16 is a non-volatile memory capable of storing information. It is located within the main body housing 2. The main body memory 16 stores a second parameter. The second parameter increases as the developing roller 71 rotates, starting when printing is resumed after a predetermined time has elapsed from the end of printing. In the embodiment, the second parameter is the number of rotations of the developing roller 71 (hereinafter referred to as the "first number of rotations"), starting when printing is resumed after a predetermined time has elapsed from the end of printing.

[0088] The control unit 10 counts the first number of rotations. The control unit 10 counts the first number of rotations as it controls 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 fuser 8 detected by the temperature sensor 83 is below a predetermined temperature Tth, the control unit 10 determines that a predetermined time has elapsed since the end of the printing operation. Furthermore, if it is determined that the developer cartridge 7 has been replaced with a new one, the control unit 10 also determines that a predetermined time has elapsed since the end of the printing operation.

[0089] In the embodiment, when the control unit 10 determines that a predetermined time has elapsed since the end of the printing operation, the control unit 10 resets the first rotation count stored in the main body memory 16. After resetting the first rotation count, the control unit 10 starts counting the first rotation count when a new print job is input to the image forming apparatus 1 to start the printing operation.

[0090] The control unit 10 holds the first rotation count at the time the printing operation ends until a predetermined time has passed since the printing operation ended. If the printing operation is started by inputting a new print job to the image forming apparatus 1 before the predetermined time has passed since the printing operation ended, the control unit 10 restarts counting from the held first rotation count.

[0091] The control unit 10 includes a CPU, RAM, ROM, input / output circuits, and other components. The control unit 10 performs operations based on programs and data stored in the ROM, etc., to execute printing operations. Printing operations form images on sheet S. The control unit 10 executes printing operations by controlling the exposure unit 4, process cartridge 5, fuser 8, and other components. The control unit 10 can read information from and write information to the main memory 16 and developer memory 76.

[0092] like Figure 2 As shown, 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 for applying the developing voltage Vb to the developing roller 71. The control unit 10 uses the power supply circuit to apply the developing voltage Vb to the developing roller 71. In the 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 the embodiment, the control unit 10 controls the reference voltage V0 to be constant regardless of the increase in the cumulative number of printed sheets.

[0093] The control unit 10 can execute image quality improvement control during printing. The control unit 10 executes image quality improvement control when a first condition is satisfied: the cumulative number of printed sheets is greater than a first threshold value TH1 and less than a second threshold value TH2, and the first number of rotations is greater than a third threshold value TH3. Specifically, the control unit 10 executes image quality improvement control when the first condition is satisfied: the cumulative number of printed sheets is greater than a first threshold value TH1 and less than a second threshold value TH2, and the first number of rotations is greater than a third threshold value TH3.

[0094] The second threshold TH2 is greater than the first threshold TH1. For 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 required to form an image on a predetermined number of sheets S. For example, the predetermined number of sheets is 30 or more and 100 or less.

[0095] During image quality improvement control, the control unit 10 increases the magnitude of the development voltage Vb applied to the developing roller 71 when forming a toner image on the photosensitive drum 61, compared to the magnitude of the development voltage Vb applied when forming a toner image on the photosensitive drum 61 during printing immediately before the first condition is satisfied. In the embodiment, during image quality improvement control, the control unit 10 sets the development voltage Vb to a voltage obtained by adding a positive added value V1 to a reference voltage V0. The control unit 10 sets the development voltage Vb for each sheet S.

[0096] The control unit 10 reads the cumulative number of printed sheets from the developer memory 76 and reads the first number of rotations from the main body memory 16. The control unit 10 executes the image quality improvement control under the first condition that the cumulative number of printed sheets stored in the developer memory 76 is greater than or equal to the first threshold value TH1 and less than or equal to the second threshold value TH2, and the first number of rotations stored in the main body memory 16 is greater than or equal to the third threshold value TH3.

[0097] The control unit 10 executes the image quality improvement control when, in addition to the first condition, a second condition is satisfied: the humidity H detected by the humidity sensor 11 is equal to or greater than a predetermined humidity Hth. Specifically, the control unit 10 executes the image quality improvement control when, in addition to the first condition, the second condition is satisfied.

[0098] The control unit 10 reads the information of the flag F from the development memory 76. The control unit 10 executes the image quality improvement control if, in addition to the first condition, a third condition is satisfied, namely, that the flag F (F=1) is stored in the development memory 76. Specifically, the control unit 10 executes the image quality improvement control if, in addition to the first condition, the third condition is satisfied.

[0099] In the embodiment, the control unit 10 executes the image quality improvement control when all of the first condition, the second condition, and the third condition are satisfied.

[0100] As described above, the control unit 10 starts counting the first number of rotations when the printing operation is started after a predetermined time has elapsed from the end of the printing operation. If the first number of rotations counted by the control unit 10 is greater than or equal to the third threshold value TH3, and the cumulative number of printed sheets stored in the developer memory 76 is greater than or equal to the first threshold value TH1 and less than or equal to the second threshold value TH2, the following phenomenon may occur.

[0101] Specifically, as the toner in the toner container 75 of the developer cartridge 7 deteriorates, the toner aggregates. The aggregated toner is supplied to the developing roller 71, increasing the amount of toner on the developing roller 71. When the amount of toner on the developing roller 71 increases, the toner becomes less likely to be triboelectrically charged, making it difficult for the toner on the developing roller 71 to move toward the photosensitive drum 61.

[0102] In the 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 addition of the positive additional value V1 to the reference voltage V0 facilitates the transfer of toner on the development roller 71 to the photosensitive drum 61.

[0103] Next, the operation of the control unit 10 of the first embodiment will be described with reference to the flowchart. Specifically, the setting of the developing voltage Vb will be described. The control unit 10 executes the following operation for each sheet S during the printing operation: Figure 3 The process of setting the developing voltage is shown.

[0104] like Figure 3 As shown, the control unit 10 determines whether the humidity H is equal to or higher than the predetermined humidity Hth (S11). If the humidity H is lower than the predetermined humidity Hth (S11: No), the control unit 10 sets the development voltage Vb to the reference voltage V0 (S51).

[0105] 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 flag F is stored in the development memory 76 (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).

[0106] In step S21, if flag F = 1 (Yes), the control unit 10 determines whether the number of rotations of the developing roller 71, i.e., the first number of rotations, from the time the printing operation is started after a predetermined time has elapsed since the end of the printing operation is greater than or equal to a third threshold value TH3 (S31). If the first number of rotations 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).

[0107] In step S31, if the first number of rotations is greater than or equal to the third threshold value TH3 (Yes), the control unit 10 determines whether the cumulative number of printed sheets is greater than or equal to 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 developing voltage Vb to the reference voltage V0 (S51).

[0108] In step S41, if the cumulative number of printed sheets is greater than or equal to the first threshold value TH1 (Yes), the control unit 10 determines whether the cumulative number of printed sheets is less than or equal to 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).

[0109] In step S42 , when the cumulative number of printed sheets is equal to or smaller than the second threshold value TH2 (Yes), the control unit 10 sets the developing voltage Vb to a voltage obtained by adding the additional value V1 to the reference voltage V0 ( S52 ).

[0110] Next, the timing for executing image quality improvement control will be described with reference to a timing chart. It is assumed here that the second condition (humidity condition), the third condition (flag condition), and the cumulative number of printed sheets being greater than or equal to the first threshold TH1 and less than or equal to the second threshold TH2 are satisfied.

[0111] like Figure 4 As shown, when the control unit 10 determines that a predetermined time has elapsed at time t1 since the end of the previous printing operation, it resets the number of rotations of the developing roller 71 (the first number of rotations) stored in the main body memory 16 .

[0112] Subsequently, when a print job is input at time t2, the control unit 10 starts the printing operation (print 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.

[0113] At time t3 during the printing operation, if the first rotation count exceeds the third threshold value TH3, 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 the additional value V1 to the reference voltage V0, thereby forming an image on the sheet S. Subsequently, the control unit 10 sets the developing voltage Vb applied to the developing roller 71 to a voltage obtained by adding the additional value V1 to the reference voltage V0, thereby forming an image on the sheet S until the printing operation ends (times t3 to t4).

[0114] 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 restarts counting the first number of rotations. In this case, since the first number of rotations is greater than the third threshold value TH3, the control unit 10 performs image quality improvement control from the beginning. That is, the control unit 10 sets the developing voltage Vb applied to the developing roller 71 to a voltage obtained by adding the added value V1 to the reference voltage V0 and forms an image on the sheet S until the printing operation ends (time t5 to t6).

[0115] When the control unit 10 determines that a predetermined time has elapsed at time t7 since the printing operation ended at time t6, the control unit 10 resets the first rotation count stored in the main body memory 16. Time t7 indicates that a predetermined time has elapsed since the printing operation ended.

[0116] Next, the effects of the first embodiment will be described.

[0117] When the toner on the developing roller 71 is difficult to move toward the photosensitive drum 61, the image quality improvement control is executed to increase the development voltage Vb. As a result, the toner on the developing roller 71 is easily moved toward the photosensitive drum 61, thereby suppressing the occurrence of printing defects such as blurring.

[0118] Since the developer cartridge 7 includes the developer memory 76 for storing the cumulative number of printed sheets, the cumulative number of printed sheets can continue to be used for control even if the developer cartridge 7 is removed from the main body casing 2 and then reinstalled therein, or is installed in the main body casing 2 of another image forming apparatus 1. This allows for highly accurate image quality improvement control.

[0119] By executing the image quality improvement control when the second condition that the humidity H is equal to or higher than the predetermined humidity Hth is satisfied in addition to the first condition, the image quality improvement control can be executed in a high humidity environment where printing defects are likely to occur.

[0120] Since the developing cartridge 7 includes the developing memory 76 capable of storing the flag F, by associating the flag F with a condition where printing defects are likely to occur, image quality improvement control can be executed under the condition where printing defects are likely to occur.

[0121] Specifically, when the toner stored in the toner storage portion 75 is pulverized toner, the development memory 76 stores the flag F, thereby enabling image quality improvement control to be executed when toner that is likely to cause printing defects is stored in the toner storage portion 75 .

[0122] Furthermore, when the surface roughness of the developing roller 71 is equal to or greater than a predetermined surface roughness, the developing memory 76 stores a flag F, thereby enabling image quality improvement control to be executed in the case of a developing roller 71 that is prone to printing defects.

[0123] In addition, when the outer diameter of the supply roller 72 is less than a specified outer diameter, or when the hardness of the supply roller 72 is less than a specified hardness, the developing memory 76 stores a flag F, thereby enabling image quality improvement control to be performed in the case of a supply roller 72 that is prone to printing defects.

[0124] Furthermore, when the developer cartridge 7 is a reused product, the developer memory 76 stores the flag F, thereby enabling image quality improvement control to be executed in the case of the developer cartridge 7 that is prone to printing defects.

[0125] Next, the second embodiment will be described. The following description will focus on the differences from the first embodiment. For similarities, the same reference numerals are used for the same elements, and descriptions thereof will be omitted.

[0126] In the second embodiment, the control section 10 does not change the development voltage Vb from the reference voltage V0 during the image quality improvement control.

[0127] In the second embodiment, during image quality improvement control, the control unit 10 increases the dot size of the electrostatic latent image formed on the photosensitive drum 61 when forming a toner image on the photosensitive drum 61, compared to the dot size when the toner image was formed on the photosensitive drum 61 during printing immediately before the first condition was satisfied. The control unit 10 forms the electrostatic latent image on the photosensitive drum 61 using the exposure unit 4. Specifically, during image quality improvement control, the control unit 10 sets the exposure time TE for each dot of the electrostatic latent image to the time multiplied by the first coefficient C1, the reference time T0. The first coefficient C1 is greater than 1. As an example, the first coefficient C1 is 1.05.

[0128] Next, the operation of the control unit 10 of the second embodiment will be described with reference to the flowchart. Specifically, the setting of the exposure time TE will be described. The control unit 10 executes the following operation for each sheet S during the printing operation: Figure 5 The process of setting the dot size is shown.

[0129] like Figure 5 As shown, in step S11 , when the humidity H is lower than the predetermined humidity Hth (No), the control unit 10 sets the exposure time TE to the reference time T0 ( S53 ).

[0130] In step S21 , when the flag F=0 (No), the control unit 10 sets the exposure time TE as the reference time T0 ( S53 ).

[0131] In step S31 , if the first rotation number of the developing roller 71 from the start of printing after a predetermined time has elapsed from the end of printing is less than the third threshold value TH3 (No), the control unit 10 sets the exposure time TE to the reference time T0 ( S53 ).

[0132] In step S41 , when the cumulative number of printed sheets is smaller than the first threshold value TH1 (No), the control unit 10 sets the exposure time TE as the reference time T0 ( S53 ).

[0133] In step S42 , when the cumulative number of printed sheets is greater than the second threshold value TH2 (No), the control unit 10 sets the exposure time TE as the reference time T0 ( S53 ).

[0134] In step S42 , when the cumulative number of printed sheets is equal to or less than the second threshold value TH2 (Yes), the control unit 10 sets the exposure time TE to a time obtained by multiplying the reference time T0 by the first coefficient C1 ( S54 ).

[0135] In the second embodiment, even when the toner on the developing roller 71 is difficult to move toward the photosensitive drum 61, the size of the dots of the electrostatic latent image is increased by performing image quality improvement control, and the toner on the developing roller 71 is easy to move toward the photosensitive drum 61, thereby suppressing the occurrence of printing defects such as blurring.

[0136] Next, a third embodiment will be described.

[0137] In the third embodiment, the control unit 10 does not change the development voltage Vb from the reference voltage V0 during the image quality improvement control. Also, the control unit 10 does not change the exposure time TE of the electrostatic latent image or each dot from the reference time T0 during the image quality improvement control.

[0138] In the third embodiment, during image quality improvement control, the control unit 10 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 the intensity when forming a toner image on the photosensitive drum 61 during printing immediately before the first condition is satisfied. Specifically, during image quality improvement control, the control unit 10 sets the intensity LI of the light beam to an intensity obtained by multiplying a 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.

[0139] Next, the operation of the control unit 10 of the third embodiment will be described with reference to the flowchart. Specifically, the setting of the intensity LI of the light beam will be described. The control unit 10 executes the following operation for each sheet S during the printing operation: Figure 6 The process of setting the light intensity is shown.

[0140] like Figure 6 As shown, in step S11 , when the humidity H is lower than the predetermined humidity Hth (No), the control unit 10 sets the intensity LI of the light beam to the reference intensity L0 ( S55 ).

[0141] In step S21 , when the flag F=0 (No), the control unit 10 sets the intensity LI of the light beam to the reference intensity L0 ( S55 ).

[0142] In step S31, if the first number of rotations of the developing roller 71 from the start of printing after a predetermined time has passed since the end of printing 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).

[0143] In step S41 , when the cumulative number of printed sheets is less than the first threshold value TH1 (No), the control unit 10 sets the intensity LI of the light beam to the reference intensity L0 ( S55 ).

[0144] In step S42 , when the cumulative number of printed sheets is greater than the second threshold value TH2 (No), the control unit 10 sets the intensity LI of the light beam to the reference intensity L0 ( S55 ).

[0145] In step S42 , when the cumulative number of printed sheets is equal to or less than the second threshold value TH2 (Yes), the control unit 10 sets the intensity LI of the light beam to an intensity obtained by multiplying the reference intensity L0 by the second coefficient C2 ( S56 ).

[0146] In the third embodiment, by executing image quality improvement control to increase the intensity LI of the light beam, the potential of the portion of the photosensitive drum 61 exposed by the light beam decreases, thereby increasing the potential difference between the developing roller 71 and the portion of the photosensitive drum 61 exposed by the light beam. Consequently, even when toner on the developing roller 71 is difficult to transfer to the photosensitive drum 61, executing image quality improvement control facilitates the transfer of toner on the developing roller 71 to the photosensitive drum 61, thereby suppressing the occurrence of print defects such as blurring.

[0147] Next, a fourth embodiment will be described.

[0148] In the fourth embodiment, the control unit 10 increases the developing voltage Vb as the number of printed sheets increases when executing image quality improvement control. Furthermore, the control unit 10 sets the developing voltage Vb to a predetermined upper limit or less when executing image quality improvement control.

[0149] Here, it is assumed that the second condition (humidity condition), the third condition (flag condition), and the cumulative number of printed sheets being greater than or equal to the first threshold TH1 and less than or equal to the second threshold TH2 are satisfied.

[0150] like Figure 7 As shown, when it is determined that a predetermined time has elapsed at time t1 since the end of the previous printing operation, the control unit 10 resets the number of rotations of the developing roller 71 (the first number of rotations) stored in the main body memory 16 .

[0151] Subsequently, when a print job is input at time t2, the control unit 10 starts the printing operation. When starting the printing operation, 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.

[0152] At time t3 during the printing operation, when the first number of rotations becomes equal to or greater than the third threshold value TH3, 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 developing voltage Vb for each sheet S based on the following equation (1) in principle.

[0153] Vb=V0+A1× (NR-NR1) … (1)

[0154] In the formula (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.

[0155] NR is the number of rotations of the developing roller 71 corresponding to the number of printed sheets from the time the printing operation is started after a predetermined time has passed since the end of the printing operation using the developing cartridge 7. Here, NR is the number of rotations of the developing roller 71 corresponding to the number of printed sheets from time t2.

[0156] NR1 is the number of rotations of the developing roller 71 corresponding to the number of sheets printed using the developing cartridge 7 from the time the printing operation is restarted after a predetermined time has elapsed from the end of the printing operation until the image quality improvement control is executed. Here, NR1 is the number of rotations of the developing roller 71 corresponding to the number of sheets printed from time t2 to time t3.

[0157] When the image quality improvement control starts at time t3, the control unit 10 sets the development voltage Vb based on equation (1). As a result, the magnitude of the development voltage Vb increases stepwise as the number of printed sheets increases (time t3 to t31).

[0158] When the development voltage Vb set based on equation (1) is greater than or equal to a predetermined upper limit, the control unit 10 sets the development voltage Vb to the upper limit. In the embodiment, the upper limit is V0 + V1. That is, the control unit 10 sets the development voltage Vb so that it does not exceed the upper limit (V0 + V1). After time t31, the control unit 10 sets the development voltage Vb applied to the developing roller 71 to the upper limit (V0 + V1) and forms an image on the sheet S until the printing operation ends (times t31 to t4).

[0159] 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 determining that a predetermined time has elapsed since the printing operation ended at time t4, the control unit 10 restarts the printing operation. When the printing operation starts, the control unit 10 restarts counting the first number of rotations.

[0160] In this case, since the first number of rotations is greater than or equal to the third threshold value TH3, the control unit 10 executes the image quality improvement control from the beginning. In the fourth embodiment, when executing the image quality improvement control, the control unit 10 sets the initial value Vb0 of the development voltage Vb applied to the development roller 71 based on the following formula (2) in principle.

[0161] Vb0(Vb)=Vb n－1 -B1× (ts-tf) … (2)

[0162] In formula (2), Vb n-1 It is the developing voltage set at the end of the previous printing action. n-1 This is the development voltage (V0+V1) set at time t4.

[0163] B1 is a predetermined voltage reduction rate. The control unit 10 sets the initial value Vb0 of the development voltage Vb to be increased from the development voltage Vb to the initial value Vb0 per predetermined unit time. n-1 Decrease the value of B1. B1 is a preset positive value.

[0164] tf is the time when the previous printing operation ends. Here, time tf is time t4.

[0165] ts is the time when the current printing operation is started. In the embodiment, ts is the time when the print job of the current printing operation is input. Here, time ts is time t5.

[0166] When the initial value Vb0 of the development voltage Vb set based on equation (2) is below a predetermined lower limit, the control unit 10 sets the initial value Vb0 of the development voltage Vb to the lower limit. In the 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 fall below the lower limit (V0).

[0167] 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, when the control unit 10 starts the printing operation at time t5, the developing voltage Vb applied to the developing roller 71 is set to the initial value Vb0 for the first sheet S, and an image is formed on the sheet S.

[0168] Then, the control section 10 sets the development voltage Vb applied to the development roller 71 based on the following equation (3) in principle.

[0169] Vb=Vb0+A1× (NR-NR2) … (3)

[0170] In the formula (3), NR is the number of rotations of the developing roller 71 corresponding to the number of printed sheets from time t2.

[0171] NR2 is the number of rotations of the developing roller 71 corresponding to the number of sheets printed using the developing cartridge 7 from the time the printing operation is restarted after a predetermined time has elapsed from the end of the printing operation to the start of the current printing operation. Here, NR2 is the number of rotations of the developing roller 71 corresponding to the number of sheets printed from time t2 to time t5.

[0172] When the control unit 10 starts the printing operation at time t5, it sets the development voltage Vb based on equation (3) for the second and subsequent sheets S. Thus, the magnitude of the development voltage Vb increases stepwise as the number of printed sheets increases (time t5 to t51).

[0173] When the development voltage Vb set based on equation (3) is equal to or greater than the predetermined upper limit (V0 + V1), the control unit 10 sets the development voltage Vb to the upper limit (V0 + V1). After time t51, the control unit 10 sets the development voltage Vb applied to the developing roller 71 to the upper limit (V0 + V1) and forms an image on the sheet S until the printing operation is completed (times t51 to t6).

[0174] When the control unit 10 determines that a predetermined time has elapsed at time t7 since the printing operation ended at time t6 , the control unit 10 resets the first number of rotations stored in the main body memory 16 .

[0175] Next, the effects of the fourth embodiment will be described.

[0176] In the fourth embodiment, the control unit 10 increases the developing voltage Vb as the number of printed sheets increases when executing image quality improvement control. Specifically, the control unit 10 increases the developing voltage Vb by A1 every time the developing roller 71 rotates a number of times corresponding to one sheet S, thereby forming an image on the sheet S.

[0177] The reason for executing the image quality improvement control described in the fourth embodiment is as follows. Specifically, the condition in which the toner on the developing roller 71 has difficulty transferring to the photosensitive drum 61 gradually develops as the image forming apparatus 1 performs a printing operation. In other words, the condition in which the toner on the developing roller 71 has difficulty transferring to the photosensitive drum 61 gradually progresses as the printing operation continues and the number of printed sheets increases.

[0178] Therefore, in the fourth embodiment, the developing voltage Vb is increased by A1 every time the developing roller 71 rotates a number of times corresponding to one sheet S. This facilitates the transfer of toner on the developing roller 71 to the photosensitive drum 61, thereby suppressing the occurrence of printing defects such as blurring. Furthermore, 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.

[0179] In the fourth embodiment, the control unit 10 sets the initial value Vb0 of the developing voltage Vb when resuming the image quality improvement control 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) increases, the condition in which the toner on the developing roller 71 is difficult to transfer to the photosensitive drum 61 gradually improves.

[0180] 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 from becoming excessive during the image quality improvement control. This can, for example, prevent deterioration of the toner, developing roller 71, and the like.

[0181] Furthermore, in the fourth embodiment, while image quality improvement control is being executed, the development voltage Vb is increased as the number of printed sheets increases. However, for example, the control unit 10 may also increase the size of the electrostatic latent image dots (exposure time TE) as the number of printed sheets increases while image quality improvement control is being executed. Furthermore, for example, the control unit 10 may also increase the light intensity LI as the number of printed sheets increases while image quality improvement control is being executed.

[0182] Although the embodiment has been described above, the image forming apparatus can be implemented in various appropriately modified forms as exemplified below.

[0183] In the above embodiment, if Figure 2 As shown, 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. Figure 8 As shown, the control unit 10 may also perform control so as to reduce the reference voltage V0 in a linear function as the cumulative number of printed sheets increases.

[0184] In the above embodiment, the image quality improvement control increases one of the development voltage Vb, the electrostatic latent image dot size (exposure time TE), and the light intensity LI. However, for example, two or more of these factors may be increased. Furthermore, the increased factor or combination of increased factors may be changed depending on the conditions satisfied.

[0185] 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 new (hereinafter referred to as the "cumulative number of rotations"). In this case, the developing memory 76 stores the cumulative number of rotations. For example, if a first condition is satisfied, that the cumulative number of rotations is greater than a first threshold value and less than a second threshold value greater than the first threshold value, and the first number of rotations is greater than a third threshold value TH3, the control unit 10 executes image quality improvement control.

[0186] The second parameter may be, for example, the number of printed sheets printed using the developing cartridge 7 from the time the printing operation is started after a predetermined time has passed since the end of the printing operation (hereinafter referred to as the "first number of printed sheets"). In this case, the control unit 10 executes the image quality improvement control when, for example, a first condition is satisfied in which the cumulative number of printed sheets or the cumulative number of rotations is greater than or equal to a first threshold value and less than or equal to a second threshold value, and the first number of printed sheets is greater than or equal to a third threshold value.

[0187] 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. Furthermore, the second parameter may be, for example, the number of rotations of the supply roller 72 from the time the printing operation is restarted after a predetermined time has elapsed since the printing operation ended. Furthermore, the second parameter may be, for example, the number of rotations of the agitator 74 from the time the printing operation is restarted after a predetermined time has elapsed since the printing operation ended.

[0188] The first parameter may be stored in the main body memory 16. In other words, the main body memory 16 may be used instead of the developing memory 76 to store the cumulative number of printed sheets or the cumulative number of rotations.

[0189] For example, the control unit 10 may actually count the time since the printing operation ended, and if the counted time is greater than a predetermined time, determine that the predetermined time has elapsed since the printing operation ended. Alternatively, the control unit 10 may determine that the printing operation ended when the main motor stopped, for example.

[0190] The conditions under which the developer memory 76 stores the flag F may be some of the conditions described in the above-mentioned embodiment. For example, the developer memory 76 may store the flag only when the outer diameter of the supply roller 72 is less than a predetermined outer diameter, or may store the flag only when the hardness of the supply roller 72 is less than a predetermined hardness.

[0191] Furthermore, for example, the developer memory 76 may store the flag F only when the toner stored in the toner storage portion 75 is crushed toner, or may store the flag F only when the developer cartridge 7 is a reusable product. Furthermore, the memory may not store any flags. The developer cartridge 7 may not have a memory.

[0192] Even if the condition for the flag stored in the memory is not met, the control unit 10 may, for example, execute image quality improvement control if the first condition and the humidity being at or above a predetermined humidity are met. Furthermore, even if the humidity being at or above the predetermined humidity is not met, the control unit 10 may, for example, execute image quality improvement control if the first condition and the condition for the flag being stored in the memory are met. Furthermore, even if the second and third conditions are not met, the control unit 10 may execute image quality improvement control if the first condition is met.

[0193] In the above embodiment, the exposure unit 4 is configured to emit a light beam to expose the photosensitive drum 61 . However, for example, the exposure unit 4 may be configured to emit LED light to expose the photosensitive drum 61 .

[0194] In the above 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 may not include the humidity sensor 11. The development voltage may be a negative voltage.

[0195] The respective elements described in the above-mentioned embodiment and modified examples may be arbitrarily combined and implemented.

Claims

1. An image forming apparatus, characterized in that: have: Main body shell; Photosensitive drum; an exposure unit that emits light for exposing the photosensitive drum; a developer having a developing roller; a memory storing a cumulative number of printed sheets printed using the developer or a cumulative number of rotations of the developing roller; as well as Control Department, The control unit performs image quality improvement control when a first condition is satisfied. The first condition is a condition in which the cumulative number of printed sheets or the cumulative number of rotations is greater than or equal to a first threshold value and less than or equal to a second threshold value which is greater than the first threshold value, and the number of printed sheets printed using the developer from the time the printing operation is started after a predetermined time has elapsed from the end of the printing operation, or the number of rotations of the developing roller from the time the printing operation is started after a predetermined time has elapsed from the end of the printing operation, is greater than or equal to a third threshold value. In the image quality improvement control, the size of the development voltage applied to the developing roller when the toner image is formed on the photosensitive drum, 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 are made larger than when the toner image is formed on the photosensitive drum during printing just before the first condition is met.

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

3. The image forming apparatus according to claim 1, wherein It also has a humidity sensor that detects humidity. The control unit executes the image quality improvement control when, in addition to the first condition, a condition is satisfied that the humidity detected by the humidity sensor is equal to or higher than a predetermined humidity.

4. The image forming apparatus according to claim 1, wherein The developer has a developer memory capable of storing a flag, and is a developer cartridge that can be attached to and detached from the main body housing. The control unit executes the image quality improvement control when, in addition to the first condition, a condition that the flag is stored in the development memory is satisfied.

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

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

7. The image forming apparatus according to claim 4, wherein: The developing box has a supply roller that supplies toner to the developing roller. The developing 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. The image forming apparatus according to claim 4, wherein The developing memory stores the flag when the developing cartridge is a reused product.

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

10. The image forming apparatus according to claim 1, wherein When the control unit executes the image quality improvement control, The magnitude of the development voltage applied to the developing 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 increased as the number of printed sheets increases.

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

Images