Image forming apparatus

Abstract

To prevent attachment of developer to a non-exposure portion of a photoreceptor drum even at the end of the life of a developing cartridge.SOLUTION: An image forming apparatus comprises: a body housing; a developing cartridge that is removably attached to the body housing; a photoreceptor drum; an electrifier that electrifies the photoreceptor drum; a voltage application unit that applies electrification voltage to the electrifier; a memory that stores the cumulative usage of the developing cartridge; and a control unit. When determining that a first predetermined time or longer has elapsed from when the photoreceptor drum or a developing roller is driven last (Yes, S2), the control unit applies a smaller electrification voltage as the cumulative usage read out from the memory is larger (S7).SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus capable of mounting a developing cartridge.

Background Art

[0002] Conventionally, an image forming apparatus capable of mounting a developing cartridge has been known (see Patent Document 1). In this image forming apparatus, in order to suppress the adhesion of the developer to the non-exposed portion of the photosensitive drum, when a predetermined time or more has elapsed since the previous image formation, a process of reducing the charging voltage is executed.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in recent years, with the increase in the service life of the developing cartridge, when only the charging voltage is reduced when a predetermined time or more has elapsed since the previous image formation, it has been difficult to suppress the adhesion of the developer to the non-exposed portion of the photosensitive drum at the end of the service life of the developing cartridge.

[0005] Therefore, an object of the present disclosure is to suppress the adhesion of the developer to the non-exposed portion of the photosensitive drum even at the end of the service life of the developing cartridge.

Means for Solving the Problems

[0006] An image forming apparatus for solving the above problems includes a main body housing, a developing cartridge, a photosensitive drum, a charger, a voltage application unit, a memory, and a control unit. The developing cartridge is detachable from the main body housing. The developing cartridge includes a developing roller and a casing capable of accommodating a developer. The charger charges the photosensitive drum. The voltage application unit applies a charging voltage to the charger. The memory stores the cumulative usage amount of the developing cartridge. When the control unit determines that the elapsed time since the photosensitive drum or the developing roller was last driven is equal to or greater than a first predetermined time, the smaller the charging voltage is applied as the cumulative usage amount read from the memory is larger.

[0007] When the elapsed time since the drive of the photosensitive drum or the developing roller was stopped is equal to or greater than the first predetermined time, the charging of the developer on the developing roller becomes insufficient, and more developer charged with the opposite polarity (hereinafter referred to as "reverse charging") also increases. Therefore, a phenomenon occurs in which the developer charged with the opposite polarity adheres to the non-exposed portion of the photosensitive drum. Further, when the cumulative usage amount of the developing cartridge is large, the amount of the developer charged with the opposite polarity further increases. On the other hand, when the control unit determines that the elapsed time since the photosensitive drum or the developing roller was last driven is equal to or greater than the first predetermined time, by applying a smaller charging voltage as the cumulative usage amount read from the memory is larger, it is possible to suppress the adhesion of the developer charged with the opposite polarity to the non-exposed portion of the photosensitive drum even at the end of the life of the developing cartridge.

[0008] Further, when the control unit does not determine that the elapsed time since the drive of the photosensitive drum or the developing roller was stopped is equal to or greater than the first predetermined time, the charging voltage for charging the charger may be set as the reference charging voltage. Then, when the control unit determines that the elapsed time since the drive of the photosensitive drum or the developing roller was stopped is equal to or greater than the first predetermined time, a correction process may be executed to make the absolute value of the charging voltage smaller than the absolute value of the reference charging voltage. Then, in the correction process, the control unit may increase the correction amount for reducing the absolute value of the charging voltage according to the cumulative usage amount.

[0009] In the correction process, the control unit increases the correction amount for reducing the absolute value of the charging voltage according to the cumulative usage amount of the developing cartridge, so that even at the end of the life of the developing cartridge, the adhesion of the developer to the non-exposed portion of the photosensitive drum can be suppressed.

[0010] Further, when the operation amount of the photosensitive drum or the developing roller after starting the correction process reaches a predetermined amount, the control unit may end the execution of the correction process and set the charging voltage as the reference charging voltage.

[0011] After starting the correction process, when the operation amount of the photosensitive drum or the developing roller reaches a predetermined amount, the triboelectric charging of the developer progresses, and the reversely charged developer decreases. When the operation amount of the photosensitive drum or the developing roller after starting the correction process reaches a predetermined amount, the control unit ends the execution of the correction process, so that the correction process is not performed more than necessary.

[0012] Further, when executing the correction process, the control unit may determine an initial charging voltage whose absolute value is smaller than the absolute value of the reference charging voltage after determining that the elapsed time since stopping the driving of the photosensitive drum or the developing roller is equal to or more than a first predetermined time. Then, when executing the correction process, the control unit may gradually decrease the correction amount according to the operation amount from the initial charging voltage toward the reference charging voltage.

[0013] When executing the correction process, the control unit gradually decreases the correction amount according to the operation amount from the initial charging voltage toward the reference charging voltage, so that the correction process according to the operation amount of the photosensitive drum or the developing roller can be performed.

[0014] Further, in the correction process, the control unit may decrease the absolute value of the initial charging voltage in proportion to the cumulative usage amount as the cumulative usage amount of the developing cartridge increases.

[0015] In the correction process, the control unit decreases the absolute value of the initial charging voltage in proportion to the cumulative usage amount as the cumulative usage amount of the developing cartridge increases, so that the charging voltage corresponding to the charging state of the developer can be applied.

[0016] Further, in the correction process, when the cumulative usage amount of the developing cartridge is less than the first threshold value, the control unit may set the initial charging voltage as the first voltage. And in the correction process, when the cumulative usage amount of the developing cartridge is equal to or more than the first threshold value, the control unit may set the initial charging voltage as a second voltage whose absolute value is smaller than that of the first voltage.

[0017] Since the control unit sets the initial charging voltage as a second voltage whose absolute value is smaller than that of the first voltage when the cumulative usage amount of the developing cartridge is equal to or more than the first threshold value in the correction process, a charging voltage corresponding to the charging state of the developer can be applied.

[0018] Also, the image forming apparatus may further include a temperature and humidity sensor capable of detecting temperature and humidity. And the control unit may be able to determine whether it is a high temperature and high humidity environment based on the temperature and humidity detected by the temperature and humidity sensor. And when the control unit determines that it is a high temperature and high humidity environment, it may execute the correction process, and when it does not determine that it is a high temperature and high humidity environment, it may not execute the correction process.

[0019] When it is not a high temperature and high humidity environment, the charging of the developer on the developing roller is less likely to be insufficient. Therefore, when the control unit does not determine that it is a high temperature and high humidity environment, by not executing the correction process, the correction process will not be performed more than necessary.

[0020] Also, the image forming apparatus may further include a motor disposed in the main body housing and driving the photosensitive drum and the developing roller. And the control unit may also execute the correction process when the motor has stopped for a second predetermined time or more.

[0021] By executing the correction process even when the motor has stopped for a second predetermined time or more, the control unit can more reliably suppress the adhesion of the developer to the non-exposed portion of the photosensitive drum at the end of the life of the developing cartridge.

[0022] Further, the image forming apparatus may further include a fixing device that thermally fixes the developer image on the sheet and a fixing temperature sensor that detects the temperature of the fixing device. Then, the control unit may execute the correction process even when the temperature of the fixing device is equal to or lower than the second temperature.

[0023] Even when the temperature detected by the fixing temperature sensor is equal to or lower than the second temperature, the control unit can more reliably suppress the adhesion of the developer to the non-exposed portion of the photosensitive drum at the end of the life of the developing cartridge by executing the correction process.

[0024] Further, the developing cartridge may further include a new product detection gear that identifies whether the developing cartridge is new, or a developing memory that stores information indicating whether it is new or used. Then, the control unit determines whether the developing cartridge is new based on the information stored in the new product detection gear or the developing memory, and may execute the correction process even when it is determined that the developing cartridge is new.

[0025] Even when it is determined that the developing cartridge is new, the control unit can more reliably suppress the adhesion of the developer to the non-exposed portion of the photosensitive drum at the end of the life of the developing cartridge by executing the correction process.

[0026] Further, the memory may be the developing memory included in the developing cartridge. Then, the developing memory may be able to store the cumulative usage amount of the developing cartridge. Then, the control unit may determine the correction amount according to the cumulative usage amount of the developing cartridge stored in the developing memory.

[0027] By the control unit determining the correction amount according to the cumulative usage amount of the developing cartridge stored in the developing memory, it is possible to more reliably suppress the adhesion of the developer to the non-exposed portion of the photosensitive drum at the end of the life of the developing cartridge.

[0028] Further, in the correction process, the control unit may also correct the developing voltage applied to the developing roller according to the charging voltage.

[0029] In the correction process, the control unit can correct the development voltage applied to the development roller according to the charging voltage, thereby making the printing density appropriate.

[0030] Further, the cumulative usage amount of the development cartridge may be configured to be calculated from at least any one of the number of rotations of the development roller, which is the number of rotations of the development roller, the number of printed sheets printed using the development roller, or the dot count printed using the development roller.

[0031] Further, the operation amount of the photosensitive drum may be configured to be calculated from at least any one of the number of rotations of the drum, which is the number of rotations of the photosensitive drum, or the number of drum printed sheets printed using the photosensitive drum. And the operation amount of the development roller may be configured to be calculated from at least any one of the number of rotations of the development roller, which is the number of rotations of the development roller, the number of printed sheets printed using the development roller, or the dot count printed using the development roller.

[0032] Further, the image forming apparatus may further include a drum cartridge that is detachable from the main body housing. And the drum cartridge may be configured to have a photosensitive drum, a charger, and a mounting portion to which the development cartridge is detachably attached.

Effect of the Invention

[0033] According to the image forming apparatus of the present disclosure, it is possible to suppress the adhesion of the developer to the non-exposed portion of the photosensitive drum even at the end of the life of the development cartridge.

Brief Description of the Drawings

[0034]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0035] Next, embodiments of the present disclosure will be described in detail with appropriate reference to the drawings. As shown in FIG. 1, the image forming apparatus 1 is a monochrome laser printer. The image forming apparatus 1 includes a main body housing 2, a feeder unit 3, an image forming unit 4, a control unit 100, and a main body memory 110 as an example of a memory.

[0036] The main body housing 2 is in the shape of a hollow case. The main body housing 2 has a pair of left and right side walls 21 and a front wall 22 connecting the side walls 21. The front wall 22 has a main body opening 22A. A front cover 23 for opening and closing the main body opening 22A is provided on the front wall 22.

[0037] The feeder unit 3 includes a supply tray 31 and a supply mechanism 32. The supply tray 31 is detachably attached to the lower part of the main body housing 2. The supply mechanism 32 supplies the sheet S in the supply tray 31 toward the image forming unit 4.

[0038] The image forming unit 4 includes a scanner unit 5, a fixing unit 7, a drum cartridge 8, and a developing cartridge 9.

[0039] The scanner unit 5 is provided at the upper part inside the main body housing 2. The scanner unit 5 includes a laser emitting unit (not shown), a polygon mirror, a lens, a reflecting mirror, and the like. In this scanner unit 5, a laser beam is irradiated onto the surface of a photosensitive drum 81 described later at high speed.

[0040] The control unit 100 includes, for example, a CPU, a RAM, a ROM, and input / output circuits, and executes print control by performing arithmetic processing based on information of the installed cartridge, programs and data stored in the ROM, and the like.

[0041] The main body memory 110 is a medium for storing information regarding the image forming apparatus 1.

[0042] The drum cartridge 8 is disposed between the feeder unit 3 and the scanner unit 5. The drum cartridge 8 is detachable from the main body housing 2. Specifically, the drum cartridge 8 is detachable from the main body housing 2 through the main body opening 22A.

[0043] The drum cartridge 8 has a frame 80, a photosensitive drum 81, a transfer roller 82, a charger 83, and a drum memory 85.

[0044] The frame 80 has a mounting portion 80A on which the developing cartridge 9 is detachably mounted. The photosensitive drum 81 is rotatably supported by the frame 80. The transfer roller 82 transfers the developer image carried on the photosensitive drum 81 to the sheet S. The charger 83 charges the photosensitive drum 81.

[0045] The drum memory 85 is a medium for storing information of the drum cartridge 8. The drum memory 85 can store the cumulative usage amount of the drum cartridge 8 and information indicating whether the drum cartridge 8 is new. The cumulative usage amount of the drum cartridge 8 refers to the cumulative usage amount of the drum cartridge 8 since it was new. Specifically, the cumulative usage amount of the drum cartridge 8 is calculated from at least either the number of drum rotations, which is the number of rotations of the photoreceptor drum 81, or the number of printed sheets S printed using the photoreceptor drum 81, which is the number of printed sheets.

[0046] The developing cartridge 9 is detachable from the drum cartridge 8. The developing cartridge 9 is detachable from the main body housing 2 when assembled to the drum cartridge 8.

[0047] The developing cartridge 9 has a casing 90, a developing roller 91, a supply roller 92, a blade 93, a developing memory 95, and a new product detection gear 98.

[0048] The casing 90 can accommodate the developer. The developing roller 91 supplies the developer to the photoreceptor drum 81. The supply roller 92 supplies the developer in the casing 90 to the developing roller 91. The blade 93 regulates the layer thickness of the developer supplied to the developing roller 91.

[0049] The developing memory 95 is a medium for storing information of the developing cartridge 9. The developing memory 95 can store the cumulative usage amount of the developing cartridge 9. The cumulative usage amount of the developing cartridge 9 refers to the cumulative usage amount of the developing cartridge 9 since it was new. Specifically, the cumulative usage amount of the developing cartridge 9 is calculated from at least either the number of rotations of the developing roller 91, which is the number of rotations of the developing roller 91, the number of printed sheets S printed using the developing roller 91, which is the number of printed sheets, or the dot count printed using the developing roller 91.

[0050] The new product detection gear 98 is a gear for identifying whether the developing cartridge 9 is new. The new product detection gear 98 rotates only when the developing cartridge 9 is new according to a known structure and does not rotate when it is not new.

[0051] In this drum cartridge 8, after the surface of the photosensitive drum 81 is uniformly charged by the charger 83, it is exposed by the scanning of the laser beam from the scanner unit 5. As a result, the potential of the exposed part decreases, and an electrostatic latent image based on the image data is formed on the surface of the photosensitive drum 81.

[0052] Next, the developer in the developing cartridge 9 is supplied to the electrostatic latent image on the photosensitive drum 81 by the rotationally driven developing roller 91, and a developer image is formed on the surface of the photosensitive drum 81. Then, when the sheet S is conveyed between the photosensitive drum 81 and the transfer roller 82, the developer image carried on the surface of the photosensitive drum 81 is transferred onto the sheet S.

[0053] The fixing device 7 includes a heating roller 71 and a pressure roller 72. The pressure roller 72 is positioned opposite to the heating roller 71. The pressure roller 72 presses the heating roller 71. The fixing device 7 thermally fixes the developer transferred onto the sheet S while the sheet S passes between the heating roller 71 and the pressure roller 72.

[0054] The sheet S thermally fixed by the fixing device 7 is conveyed to a paper discharge roller 24 disposed on the downstream side of the fixing device 7 and sent out onto a paper discharge tray 25 from this paper discharge roller 24.

[0055] As shown in FIG. 2, the image forming apparatus 1 further includes a charging application unit 210, a developing voltage application unit 220, a main motor 230, a process motor 240, a fixing temperature sensor 260, a temperature and humidity sensor 270, and a new product determination sensor 280. The main motor 230 is an example of a motor.

[0056] In this embodiment, a positively chargeable toner is used as the developer. Corresponding to the positively chargeable toner, a positive potential bias is applied to the charging application unit 210 and the developing voltage application unit 220.

[0057] The charging application unit 210 is a circuit for applying a charging voltage Vg to the charger 83. The charging voltage Vg of the charging application unit 210 is controlled by the control unit 100.

[0058] The developing voltage application unit 220 is a circuit for applying a developing voltage Vb to the developing roller 91. The developing voltage Vb of the developing voltage application unit 220 is controlled by the control unit 100.

[0059] The main motor 230 is disposed in the main body housing 2. The main motor 230 is a motor that supplies a driving force to a plurality of conveying rollers that convey the sheet S. The main motor 230 is controlled by the control unit 100.

[0060] The process motor 240 is disposed in the main body housing 2. The process motor 240 is a motor that supplies a driving force to the photosensitive drum 81. The process motor 240 is controlled by the control unit 100.

[0061] The fixing temperature sensor 260 is a sensor that detects the temperature of the fuser 7. The temperature of the fuser 7 detected by the fixing temperature sensor 260 is sent to the control unit 100.

[0062] The temperature and humidity sensor 270 is a sensor that detects the ambient temperature and ambient humidity. The temperature and humidity sensor 270 is located at a position away from the fuser 7. For example, the temperature and humidity sensor 270 is located on the front wall 22. Thereby, the temperature and humidity sensor 270 can detect a temperature and humidity close to the temperature and humidity outside the main body housing 2. The temperature and humidity detected by the temperature and humidity sensor 270 are sent to the control unit 100.

[0063] The new product determination sensor 280 is disposed in the main body housing 2. The new product determination sensor 280 can detect the rotation of the new product detection gear 98. When the new product determination sensor 280 detects the rotation of the new product detection gear 98, the control unit 100 determines that the developing cartridge 9 is a new product.

[0064] Next, in this embodiment, the process by which the control unit 100 determines the charging voltage Vg and the developing voltage Vb will be described.

[0065] When the control unit 100 determines that the elapsed time since the photoreceptor drum 81 was last driven is equal to or greater than a first predetermined time, the smaller the charging voltage applied is as the cumulative usage amount read from the development memory 95 is larger. When the control unit 100 determines that the elapsed time since the photoreceptor drum 81 was last driven is equal to or greater than a first predetermined time, it can be estimated that the charge amount of the developer has decreased. In this way, the state in which it is estimated that the charge amount of the developer has decreased is referred to as a "cold state".

[0066] In this embodiment, when the control unit 100 does not determine that it is in the cold state, the charging voltage Vg for charging the charger 83 is set to the reference charging voltage Vg1. When the control unit 100 determines that it is in the cold state, correction processing is executed to make the absolute value of the charging voltage Vg smaller than the absolute value of the reference charging voltage Vg1.

[0067] To determine whether the elapsed time since the photoreceptor drum 81 was last driven is equal to or greater than a first predetermined time, the control unit 100 counts the stop time of the process motor 240. The first predetermined time can be arbitrarily set, but can be, for example, 6 hours.

[0068] Here, the control unit 100 can determine whether it is a high-temperature and high-humidity environment based on the temperature and humidity detected by the temperature and humidity sensor 270. Specifically, the control unit 100 refers to the table in FIG. 6 to determine whether it is the first high-temperature and high-humidity environment (HH1) and the second high-temperature and high-humidity environment (HH2). Both the first high-temperature and high-humidity environment (HH1) and the second high-temperature and high-humidity environment (HH2) are high-temperature and high-humidity environments. The second high-temperature and high-humidity environment (HH2) is a more severe environment with at least a higher temperature or a higher humidity than the first high-temperature and high-humidity environment (HH1).

[0069] When the control unit 100 determines that it is a high-temperature and high-humidity environment, it executes correction processing in the cold state. However, when the control unit 100 does not determine that it is a high-temperature and high-humidity environment, it does not execute correction processing even in the cold state. When the control unit 100 determines that it is the second high-temperature and high-humidity environment (HH2), it increases the correction amount by the correction processing compared to when it determines that it is the first high-temperature and high-humidity environment (HH1).

[0070] When the control unit 100 calculates the charging voltage Vg, the control unit 100 determines the initial charging voltage Vg0. Then, the control unit 100 calculates the charging voltage Vg based on the initial charging voltage Vg0 and the operation amount (count value R) of the photoreceptor drum 81 or the developing roller 91 since the start of the correction processing. Specifically, it is calculated by the following formula. Vg = Vg0+(R / Rth)α

[0071] The initial charging voltage Vg0 is a value obtained by subtracting the initial correction amount α from the reference charging voltage Vg1 (Vg0 = Vg1 - α). The absolute value of the initial charging voltage Vg0 is smaller than the absolute value of the reference charging voltage Vg1.

[0072] The initial correction amount α is determined with reference to the table in FIG. 7. When not in a high-temperature and high-humidity environment (HH), the initial correction amount α is 0. The initial correction amount α is larger when in the second high-temperature and high-humidity environment (HH2) than when in the first high-temperature and high-humidity environment (HH1). Also, the initial correction amount α increases as the cumulative usage amount of the developing cartridge 9 increases. For example, in the HH1 environment, the correction amount α is larger when the cumulative number of printed sheets of the developing roller 91 is 1000 to 1999 than when it is 0 to 999.

[0073] In this embodiment, the control unit 100 counts the operation amount of the developing roller 91 after starting the correction process as the count value R. When the count value R is less than the threshold value Rth (R < Rth), the control unit 100 executes the correction process. When the count value R is greater than or equal to the threshold value Rth (R ≧ Rth), the control unit 100 does not execute the correction process.

[0074] The operation amount of the developing roller 91 is calculated from at least one of the number of rotations of the developing roller 91 which is the number of rotations the developing roller 91 has rotated, the number of printed sheets printed using the developing roller 91, or the dot count printed using the developing roller 91.

[0075] When the operation amount after starting the correction process reaches a predetermined amount, the control unit 100 ends the execution of the correction process and sets the charging voltage Vg to the reference charging voltage Vg1.

[0076] Specifically, the control unit 100 calculates the count value R from the number of printed sheets of the developing roller 91 after being determined to be in the cold state. Here, the count value R is set to the number of printed sheets of the developing roller 91 after being determined to be in the cold state, and the threshold value Rth is set to 300. That is, in this embodiment, the correction process is executed until 300 sheets are printed after starting the correction process, and when 300 sheets are printed after starting the correction process, the correction process ends.

[0077] Further, the control unit 100 determines a correction amount according to the cumulative usage amount of the developing cartridge 9 stored in the development memory 95. The correction amount in the correction process increases according to the cumulative usage amount of the developing cartridge 9. For this reason, in the correction process, as the cumulative usage amount of the developing cartridge 9 increases, the absolute value of the initial charging voltage Vg0 decreases. As shown in FIG. 7, in the present embodiment, the cumulative number of printed sheets of the developing roller 91 is used as the cumulative usage amount. Then, as the cumulative number of printed sheets of the developing roller 91 increases, the initial correction amount α increases.

[0078] As shown in FIG. 8(a), in the correction process in the first high-temperature and high-humidity environment (HH1), when the cumulative usage amount of the developing cartridge 9 is less than the first threshold value, the control unit 100 sets the initial charging voltage Vg0 to the first voltage Vg01. Here, the first threshold value is set to 1000 (sheets).

[0079] In the correction process in the first high-temperature and high-humidity environment (HH1), when the cumulative usage amount of the developing cartridge 9 is equal to or greater than the first threshold value and less than the second threshold value, the control unit 100 sets the initial charging voltage Vg0 to the second voltage Vg02 whose absolute value is smaller than that of the first voltage Vg01. Here, the second threshold value is set to 2000 (sheets).

[0080] In the correction process in the first high-temperature and high-humidity environment (HH1), when the cumulative usage amount of the developing cartridge 9 is equal to or greater than the second threshold value, the control unit 100 sets the initial charging voltage Vg0 to the third voltage Vg03 whose absolute value is smaller than that of the second voltage Vg02.

[0081] As shown in FIG. 8(b), in the correction process in the second high-temperature and high-humidity environment (HH2), when the cumulative usage amount of the developing cartridge 9 is less than the first threshold value, the control unit 100 sets the initial charging voltage Vg0 to the fourth voltage Vg04. Here, the first threshold value is set to 1000 (sheets). The fourth voltage Vg04 has an absolute value smaller than that of the first voltage Vg01.

[0082] In the correction process in the second high-temperature and high-humidity environment (HH2), when the cumulative usage amount of the developing cartridge 9 is equal to or greater than the first threshold value and less than the second threshold value, the control unit 100 sets the initial charging voltage Vg0 to a fifth voltage Vg05 whose absolute value is smaller than that of the fourth voltage Vg04. Here, the second threshold value is set to 2000 (sheets). The absolute value of the fifth voltage Vg05 is smaller than that of the second voltage Vg02.

[0083] In the correction process in the second high-temperature and high-humidity environment (HH2), when the cumulative usage amount of the developing cartridge 9 is equal to or greater than the second threshold value, the control unit 100 sets the initial charging voltage Vg0 to a sixth voltage Vg06 whose absolute value is smaller than that of the fifth voltage Vg05. The absolute value of the sixth voltage Vg06 is smaller than that of the third voltage Vg03.

[0084] As shown in FIGS. 8(a) and 8(b), when the control unit 100 executes the correction process, the correction amount is gradually decreased according to the operation amount from the initial charging voltage Vg0 toward the reference charging voltage Vg1. That is, as the count value R increases, the charging voltage Vg becomes a value closer to Vg1 from Vg0.

[0085] As described above, when the control unit 100 determines that the elapsed time since the last drive of the photosensitive drum 81 or the developing roller 91 is equal to or greater than the first predetermined time, it determines that it is in the cold state. However, even in cases other than those described above, it determines that it is in the cold state and executes the correction process.

[0086] First, when the main motor 230 stops for a second predetermined time or longer, the control unit 100 also determines that it is in the cold state and executes the correction process. The second predetermined time can be arbitrarily set, but for example, it can be set to 6 hours.

[0087] When the temperature detected by the fixing temperature sensor 260 is equal to or lower than the second temperature, the control unit 100 also determines that it is in the cold state and executes the correction process. The second temperature can be arbitrarily set, but for example, it can be set to 40°C.

[0088] Based on the information indicating whether the drum cartridge 8 stored in the drum memory 85 is new, even when it is determined that the drum cartridge 8 is new, the control unit 100 determines it to be in a cold state and executes correction processing. Based on the new product detection gear 98, even when it is determined that the developing cartridge 9 is new, the control unit 100 determines it to be in a cold state and executes correction processing.

[0089] In the correction processing, the control unit 100 corrects the developing voltage Vb according to the charging voltage Vg. In the correction processing, the developing voltage Vb is smaller than the correction amount of the charging voltage Vg. Specifically, Vb is calculated by the following formula. Vb0 = Vb1 - 0.2α Vb = Vb0 + 0.2(R / Rth)α In this embodiment, the correction coefficient for reducing the correction amount is set to 0.2, but this correction coefficient can be arbitrarily set according to the type of developer and the cartridge configuration.

[0090] In the image forming apparatus 1 configured as described above, an example of the process in which the control unit 100 determines the charging voltage Vg and the developing voltage Vb will be described with reference to the flowcharts of FIGS. 3 to 5.

[0091] As shown in FIG. 3, when it is determined that a job has been input (S1, Yes), the control unit 100 executes cold state determination processing (S2).

[0092] As shown in FIG. 4, in the cold state determination processing (S2), when the control unit 100 determines that 6 hours or more have elapsed since the main motor 230 stopped (S21, Yes), it determines that it is in a cold state (S28).

[0093] Also, in the cold state determination processing (S2), when the control unit 100 determines that 6 hours or more have elapsed since the photosensitive drum 81 stopped (S22, Yes), it determines that it is in a cold state (S28).

[0094] Also, in the cold state determination process (S2), when the control unit 100 determines that it is immediately after the power-on of the image forming apparatus 1 and the temperature detected by the fixing temperature sensor 260 is 40°C or lower (S24, Yes), it determines that it is in the cold state (S28).

[0095] Also, in the cold state determination process (S2), when the control unit 100 detects a new drum cartridge 8 (S25, Yes), it determines that it is in the cold state (S28).

[0096] Also, in the cold state determination process (S2), when the control unit 100 detects a new developing cartridge 9 (S26, Yes), it determines that it is in the cold state (S28).

[0097] Also, in the cold state determination process (S2), when the control unit 100 does not correspond to any of steps S21 to S26 (S21 to 26, No), it determines that it is not in the cold state (S27).

[0098] Returning to FIG. 3, after step S2, when the control unit 100 determines that it is in the cold state (S3, Yes), it sets the count value R to 0 (S4), and when it determines that it is not in the cold state (S3, No), it does not set the count value R to 0 and proceeds to step S5.

[0099] After step S4, the control unit 100 determines whether the count value R is less than the threshold value Rth (R < Rth?) (S5).

[0100] In step S5, when the control unit 100 does not determine that the count value R is less than the threshold value Rth (S5, No), it sets the charging voltage Vg to the reference charging voltage Vg1 (Vg = Vg1) and sets the developing voltage Vb to the reference developing voltage Vb1 (Vb = Vb1) (S6).

[0101] In step S5, when the control unit 100 determines that the count value R is less than the threshold value Rth (S5, Yes), it executes the correction process (S7).

[0102] As shown in FIG. 5, in the correction process, the control unit 100 determines whether it is in the HH1 environment or the HH2 environment (S71). Whether it is in the HH1 environment or the HH2 environment is determined with reference to the table in FIG. 6. The cold state in the first high temperature and high humidity environment (HH1) is referred to as the HH1 cold state (see also FIG. 8(a)). The cold state in the second high temperature and high humidity environment (HH2) is referred to as the HH2 cold state (see also FIG. 8(b)).

[0103] After step S71, the control unit 100 calculates the initial charging voltage Vg0 and the initial developing voltage Vb0 (S72). Vg0 and Vb0 are calculated from the following equations. Vg0 = Vg1 - α Vb0 = Vb1 - 0.2α The initial correction amount α is determined with reference to the table in FIG. 7.

[0104] After step S72, the control unit 100 calculates the charging voltage Vg and the developing voltage Vb from the initial charging voltage Vg0, the initial developing voltage Vb0, and the count value R (S73). Vg and Vb are calculated from the following equations. Vg = Vg0 + (R / Rth)α Vb = Vb0 + 0.2(R / Rth)α

[0105] Returning to FIG. 3, after step S6 or step S7, the control unit 100 applies the determined charging voltage Vg to the photoreceptor drum 81, applies the determined developing voltage Vb to the developing roller 91, and executes the input job (S8).

[0106] After step S8, the control unit 100 adds the count value R corresponding to the executed job and ends the process.

[0107] According to the image forming apparatus 1 of the present embodiment as described above, the following effects are obtained.

[0108] When the elapsed time since the driving of the photosensitive drum 81 is stopped is equal to or longer than a first predetermined time, the charging of the developer on the developing roller 91 becomes insufficient, and the amount of reversely charged developer also increases. Therefore, a phenomenon occurs in which the reversely charged developer adheres to the non-exposed portion of the photosensitive drum 81. Further, when the cumulative usage amount of the developing cartridge 9 is large, the amount of reversely charged developer further increases. On the other hand, in the image forming apparatus 1 of the present embodiment, when the control unit 100 determines that the elapsed time since the last driving of the photosensitive drum 81 is equal to or longer than a first predetermined time, the larger the cumulative usage amount of the developing cartridge 9 read from the development memory 95, the smaller the charging voltage is applied, so that even at the end of the life of the developing cartridge 9, it is possible to suppress the reversely charged developer from adhering to the non-exposed portion of the photosensitive drum 81.

[0109] Further, in the correction process, the control unit 100 increases the correction amount for reducing the absolute value of the charging voltage Vg according to the cumulative usage amount of the developing cartridge 9, so that even at the end of the life of the developing cartridge 9, it is possible to suppress the developer from adhering to the non-exposed portion of the photosensitive drum 81.

[0110] Further, after the start of the correction process, when the operation amount of the photosensitive drum 81 reaches a predetermined amount, the triboelectric charging of the developer progresses, and the amount of reversely charged developer decreases. On the other hand, when the operation amount of the photosensitive drum 81 or the developing roller 91 since the start of the correction process reaches a predetermined amount, the control unit 100 ends the execution of the correction process, so that the correction process is not performed more than necessary.

[0111] Further, when executing the correction process, the control unit 100 gradually reduces the correction amount according to the operation amount (count value R) from the initial charging voltage Vg0 toward the reference charging voltage Vg1, so that the correction process according to the operation amount of the photosensitive drum 81 can be performed.

[0112] Further, in the correction process, as the cumulative usage amount of the developing cartridge 9 increases, the control unit 100 reduces the absolute value of the initial charging voltage Vg0 in proportion to the cumulative usage amount, so that a charging voltage according to the charging state of the developer can be applied.

[0113] Further, when the cumulative usage amount of the developing cartridge 9 is equal to or greater than the first threshold value in the correction process by the control unit 100, the initial charging voltage Vg0 is set to the second voltage Vg02 whose absolute value is smaller than that of the first voltage Vg01, so that a charging voltage corresponding to the charging state of the developer can be applied.

[0114] Also, when it is not in a high-temperature and high-humidity environment, the charging of the developer on the developing roller 91 is less likely to be insufficient. Therefore, when the control unit 100 does not determine that it is in a high-temperature and high-humidity environment, the correction process is not executed, so that the correction process is not performed more than necessary. Further, when the control unit 100 determines that it is in the second high-temperature and high-humidity environment (HH2), in order to increase the correction amount by the correction process compared to the case where it is determined to be in the first high-temperature and high-humidity environment (HH1), even when the charged amount of the developer on the developing roller 91 is considerably low in a more severe environment, a charging voltage corresponding to the charged amount of the developer can be applied.

[0115] Also, when the main motor 230 stops for a second predetermined time or more, the control unit 100 also executes the correction process, so that at the end of the life of the developing cartridge 9, the adhesion of the developer to the non-exposed portion of the photosensitive drum 81 can be more reliably suppressed.

[0116] Also, when the temperature of the fuser 7 is equal to or lower than the second temperature, the control unit 100 also executes the correction process, so that the adhesion of the developer to the non-exposed portion of the photosensitive drum 81 can be suppressed even at the end of the life of the developing cartridge 9.

[0117] Also, when the control unit 100 determines that the developing cartridge 9 is new, the correction process is executed, so that at the end of the life of the developing cartridge 9, the adhesion of the developer to the non-exposed portion of the photosensitive drum 81 can be more reliably suppressed.

[0118] Further, in the correction process, the control unit 100 can optimize the printing density by correcting the developing voltage Vb applied to the developing roller 91 according to the charging voltage Vg.

[0119] Note that the present disclosure is not limited to the above-described embodiment and can be used in various forms as exemplified below.

[0120] In the above-described embodiment, in the correction process, when it is less than the first threshold value, the first voltage is used, and when it is equal to or greater than the first threshold value, the second voltage is used. However, in the correction process, the control unit may decrease the absolute value of the initial charging voltage in proportion to the cumulative usage amount as the cumulative usage amount of the developing cartridge 9 increases. Also in this configuration, similar to the above-described embodiment, an appropriate charging voltage can be applied even at the end of the life of the developing cartridge 9.

[0121] In the above-described embodiment, the operation amount of the developing roller 91 since the start of the correction process has been counted as the count value R. However, the operation amount of the photosensitive drum 81 since the start of the correction process may be counted as the count value R. In this case, the operation amount of the photosensitive drum 81 is calculated from at least one of the number of drum rotations, which is the number of rotations of the photosensitive drum 81, or the number of drum prints, which is the number of sheets S printed using the photosensitive drum 81.

[0122] In the above-described embodiment, the control unit 100 executes the correction process when it determines that the elapsed time since the last drive of the photosensitive drum 81 is equal to or greater than the first predetermined time. However, the control unit 100 may be configured to execute the correction process when it determines that the elapsed time since the last drive of the developing roller 91 is equal to or greater than the first predetermined time.

[0123] In the above-described embodiment, the cumulative usage amount of the developing cartridge 9 is stored in the developing memory 95, but it may be stored in the drum memory 85, the main body memory 110, or the like.

[0124] In the above-described embodiment, the control unit 100 determines whether the developing cartridge 9 is new by means of the new detection gear 98. However, it may also determine whether the developing cartridge 9 is new based on the information indicating whether the developing cartridge 9 stored in the developing memory 95 is new or not.

[0125] In the above-described embodiment, a positively charged toner is used as the developer. However, a negatively charged toner may also be used as the developer. In this case, the charging application unit 210 and the developing voltage application unit 220 may be configured to apply a negative potential voltage.

[0126] In the above-described embodiment, the developing cartridge 9 is detachable from the drum cartridge and is detachable from the main body housing 2 when assembled to the drum cartridge 8. However, the developing cartridge and the drum cartridge may each be independently detachable from the main body housing, or the developing cartridge and the drum cartridge may be an integrated cartridge.

[0127] In the above-described embodiment, a monochrome laser printer is exemplified as the image forming apparatus. However, the image forming apparatus may be a color laser printer, or may be a copier or a multifunction peripheral.

[0128] The elements described in the above-described embodiment and the modified examples can also be implemented by arbitrarily combining them.

Explanation of Reference Numerals

[0129] 1 Image forming apparatus 2 Main body housing 7 Fuser 8 Drum cartridge 81 Photoconductor drum 83 Charger 9 Developing cartridge 90 Casing 91 Developing roller 100 Control unit

Claims

1. A main body housing, a developing cartridge that is detachable from the main body housing and has a developing roller and a casing capable of accommodating a developer, a photosensitive drum, a charger for charging the photosensitive drum, a voltage application unit that applies a charging voltage to the charger, a memory that stores the cumulative usage amount of the developing cartridge, a control unit, and when the control unit determines that the elapsed time since the photosensitive drum or the developing roller was last driven is equal to or more than a first predetermined time, the smaller the charging voltage is applied as the cumulative usage amount read from the memory is larger. An image forming apparatus characterized by this.

2. The control unit when it is not determined that the elapsed time since the drive of the photosensitive drum or the developing roller was stopped is equal to or more than a first predetermined time, sets the charging voltage for charging the charger as a reference charging voltage, when it is determined that the elapsed time since the drive of the photosensitive drum or the developing roller was stopped is equal to or more than a first predetermined time, executes a correction process of making the absolute value of the charging voltage smaller than the absolute value of the reference charging voltage, In the correction process, the image forming apparatus according to claim 1, characterized in that a correction amount for making the absolute value of the charging voltage smaller is increased according to the cumulative usage amount.

3. When the operation amount of the photosensitive drum or the developing roller has reached a predetermined amount after the control unit starts the correction process, the control unit ends the execution of the correction process and sets the charging voltage as the reference charging voltage. The image forming apparatus according to claim 2, characterized by this.

4. When the control unit executes the correction process, after determining that the elapsed time since the drive of the photosensitive drum or the developing roller was stopped is equal to or more than a first predetermined time, determines an initial charging voltage whose absolute value is smaller than the absolute value of the reference charging voltage, The image forming apparatus according to claim 3, characterized in that the correction amount is gradually decreased according to the operation amount from the initial charging voltage toward the reference charging voltage.

5. In the correction process, the control unit makes the absolute value of the initial charging voltage smaller in proportion to the cumulative usage amount as the cumulative usage amount of the developing cartridge increases. The image forming apparatus according to claim 4, characterized by this.

6. The control unit, in the correction process, when the cumulative usage amount of the developing cartridge is less than a first threshold value, sets the initial charging voltage as a first voltage, The image forming apparatus according to claim 4, wherein when the cumulative usage amount of the developing cartridge is equal to or greater than the first threshold value, the initial charging voltage is set to a second voltage having an absolute value smaller than that of the first voltage.

7. further comprising a temperature and humidity sensor capable of detecting temperature and humidity, the control unit, is capable of determining whether it is a high temperature and high humidity environment based on the temperature and humidity detected by the temperature and humidity sensor, when it is determined that it is a high temperature and high humidity environment, the correction process is executed, The image forming apparatus according to claim 2, wherein when it is not determined that it is a high temperature and high humidity environment, the correction process is not executed.

8. further comprising a motor disposed in the main body housing and driving the photosensitive drum and the developing roller, The control unit executes the correction process even when the motor has stopped for a second predetermined time or more. The image forming apparatus according to claim 2.

9. a fixing device for thermally fixing the developer image on the sheet; and a fixing temperature sensor for detecting the temperature of the fixing device, The control unit executes the correction process even when the temperature detected by the fixing temperature sensor is equal to or lower than the second temperature. The image forming apparatus according to claim 2.

10. The developing cartridge further includes a new product detection gear for identifying whether the developing cartridge is new, or a developing memory in which information indicating whether it is new or used is stored, the control unit, determines whether the developing cartridge is new based on the information stored in the new product detection gear or the developing memory, The image forming apparatus according to claim 2, wherein when it is determined that the developing cartridge is new, the correction process is executed.

11. The memory is a developing memory included in the developing cartridge, the developing memory is capable of storing the cumulative usage amount of the developing cartridge, The control unit determines the correction amount according to the cumulative usage amount of the developing cartridge stored in the developing memory. The image forming apparatus according to claim 2.

12. The control unit corrects the developing voltage applied to the developing roller according to the charging voltage in the correction process. The image forming apparatus according to claim 2.

13. The cumulative usage amount of the developing cartridge is calculated from at least any one of the number of rotations of the developing roller which is the number of rotations of the developing roller, the number of printed sheets printed using the developing roller, or the dot count printed using the developing roller. The image forming apparatus according to claim 1, characterized in that.

14. The operation amount of the photosensitive drum is calculated from at least any one of the number of rotations of the drum which is the number of rotations of the photosensitive drum, or the number of drum printed sheets which is the number of sheets printed using the photosensitive drum. The operation amount of the developing roller is calculated from at least any one of the number of rotations of the developing roller which is the number of rotations of the developing roller, the number of printed sheets printed using the developing roller, or the dot count printed using the developing roller. The image forming apparatus according to claim 3, characterized in that.

15. The image forming apparatus further includes a drum cartridge detachable from the main body housing. The drum cartridge has the photosensitive drum, the charger, and a mounting portion to which the developing cartridge is detachably attached. The image forming apparatus according to claim 1, characterized in that.

Images