Image forming apparatus

Abstract

To prevent occurrence of local reduction in the quality of an image.SOLUTION: A developer disposal operation performed by an image forming apparatus (1) includes: first disposal processing of forming a first electrostatic latent image for developer disposal with a first printing rate within a first range in a longitudinal direction of an image carrier (3), conveying developer in a developer storage unit (11) to form a first developer image for disposal corresponding to the first electrostatic latent image for developer disposal, and removing the first developer image for disposal; and second disposal processing of forming a second electrostatic latent image for developer disposal with a second printing rate higher than the first printing rate within one or more second ranges in the longitudinal direction of the image carrier (3), conveying developer in the developer storage unit (11) to form a second developer image for disposal corresponding to the second electrostatic latent image for developer disposal, and removing the second developer image for disposal. The total length in the longitudinal direction of the one or more second ranges is shorter than the length in the longitudinal direction of the first range.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] In an image forming apparatus using an electrophotographic method, a developer is supplied from a developer container that contains developer to an electrostatic latent image formed on the surface of a photosensitive drum as an image carrier by a developing roller, a developer image corresponding to the electrostatic latent image is formed, and the developer image is transferred to a recording medium to form an image on the recording medium (see, for example, Patent Document 1). When a printing operation is performed with a high printing duty (i.e., print rate) and a sufficient amount of developer is consumed, a large amount of deteriorated developer is also consumed, so that the deteriorated developer in the developer container does not increase too much. However, when a printing operation is performed repeatedly with a low printing duty and in which little developer is consumed, the deteriorated developer in the developer container is not consumed very much, so that the deteriorated developer in the developer container increases too much. Therefore, every time a predetermined developer disposal condition is satisfied, a developer disposal operation in the developer container is performed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-166732 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, there were cases where localized degradation of image quality was observed in a certain range (i.e., the stain occurrence location) in the longitudinal direction (i.e., the main scanning direction) of the image carrier. In this case, even if developer was discarded at a uniform printing rate over the entire longitudinal direction of the image carrier, the image quality was not satisfactory.

[0005] An object of the present disclosure is to provide an image forming apparatus that does not cause local degradation of image quality. [Means for solving the problem]

[0006] The image forming apparatus of the present disclosure includes an image carrier, an exposure head that forms an electrostatic latent image on a surface of the image carrier, a developer container that contains a developer, a developer carrier that transports the developer in the developer container to the surface of the image carrier to form a developer image corresponding to the electrostatic latent image, and a control unit that controls a printing operation that forms an image on a recording medium using the developer image and controls a developer disposal operation that discards the developer on the image carrier using the developer image, and the developer disposal operation forms a first electrostatic latent image for developer disposal having a first printing ratio in a first range in a longitudinal direction of the image carrier, and a control unit that controls a developer disposal operation that discards the developer on the image carrier using the developer image. a first disposal process of transporting the developer to form a first discarded developer image corresponding to the first developer discarded electrostatic latent image, and removing the first discarded developer image; and a second disposal process of forming a second developer discarded electrostatic latent image having a second printing rate higher than the first printing rate in one or more second ranges in the longitudinal direction of the image carrier, transporting the developer in the developer accommodating section to form a second developer discarded developer image corresponding to the second developer discarded electrostatic latent image, and removing the second discarded developer image, wherein a total of the longitudinal lengths of the one or more second ranges is shorter than a longitudinal length of the first range. Effect of the Invention

[0007] According to the present disclosure, it is possible to prevent local degradation of image quality. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus according to an embodiment. [Diagram 2] 2 is a block diagram illustrating a schematic configuration of a control system of the image forming apparatus according to the embodiment. FIG. [Diagram 3]13 is a diagram showing a toner potential when no contamination has occurred (amount of remaining toner is equal to or greater than a threshold value) and when contamination has occurred (amount of remaining toner is less than a threshold value). FIG. [Figure 4] 11 is a diagram showing the relationship between the level of contamination and the amount of toner remaining in a developer container. FIG. [Diagram 5] FIG. 1A is a diagram showing an example of a first toner discarding pattern, and FIG. 1B is a diagram showing an example of a second toner discarding pattern. [Figure 6] 4 is a flowchart showing an operation of the image forming apparatus according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an image forming apparatus according to an embodiment of the present disclosure will be described with reference to the drawings. The following embodiment is merely an example, and various modifications are possible within the scope of the present disclosure.

[0010] 1. Configuration 1 is a schematic cross-sectional view showing the configuration of an image forming apparatus 1 according to an embodiment. The image forming apparatus 1 is a printer capable of forming an image on a recording medium P such as paper using a toner as a developer by electrophotography. In this embodiment, an example will be described in which the image forming apparatus 1 is a color printer that prints a color image on the recording medium P using four color toners, but the image forming apparatus 1 may also be a monochrome printer.

[0011] The image forming apparatus 1 has an image forming section (also called a "developing section") 2, an LED (Light Emitting Diode) head 16 as an exposure head, a transfer roller 20 as a transfer member, a fixing unit 30, a paper feed tray 40, a hopping roller 41, a registration roller 42, and a discharge roller 43. The image forming section 2, the transfer roller 20, and the fixing unit 30 are configured to be detachable from the main body of the image forming apparatus 1. The LED head 16 is also called an "LED array head" or a "light emitting element array head."

[0012] The image forming unit 2 includes a photosensitive drum 3 as an image carrier, a developing roller 14 as a developer carrier, a charging roller 4 as a charging member, a cleaning unit 5 having a cleaning member such as a cleaning blade, a discharging unit 6 that irradiates the photosensitive drum 3 with discharging light, a toner container 11 as a developer container to which toner 10 is supplied from a toner supply body (also called a "developer cartridge" or a "toner cartridge (TC)") 7 as a developer supply body, a supply roller 8 as a developer supply member, a regulating blade 9 as a developer regulating member, and a toner sensor 12 as a developer sensor. The image forming units 2 (i.e., image forming units 2K, 2Y, 2M, and 2C) each have toner of black (K), yellow (Y), magenta (M), and cyan (C), and the toner is supplied to the toner container 11 from the corresponding toner supply body 7, and the toner in the toner container 11 is transported to an electrostatic latent image to form a toner image as a developer image corresponding to the electrostatic latent image. In addition, the image forming units 2K, 2Y, 2M, and 2C are arranged in a row in the transport direction of the recording medium P (from right to left in Figure 1) in this order, and the image forming unit 2C is located on the most downstream side in the transport direction of the recording medium P.

[0013] In the first embodiment, the image forming units 2K, 2Y, 2M, and 2C have the same configuration as one another except for the toner contained therein, so the configuration of the image forming unit 2K will be described as an example.

[0014] The photoconductor drum 3 has a conductor such as aluminum, a photosensitive layer coated on the outer periphery of the conductor, and a shaft supporting the conductor. A gear is provided at the end of the shaft, and the driving force from the drum drive motor is transmitted to the shaft via the gear. The photoconductor drum 3 is configured to be rotatable in the direction of the arrow in FIG. 1 by the driving force from the drum drive motor.

[0015] The charging roller 4 is a charging member that uniformly charges the surface of the photosensitive drum 3, and has, for example, a metal shaft such as stainless steel and a conductive elastic body that covers the outer periphery of the shaft. The charging roller 4 is disposed so as to rotate together with the photosensitive drum 3 while being in contact with the photosensitive drum 3.

[0016] The developing roller 14 conveys the toner 10 in the toner storage section 11 to the latent image pattern (i.e., electrostatic latent image) formed on the surface of the photosensitive drum 3, and forms a toner image as a developer image corresponding to the electrostatic latent image. The developing roller 14 is arranged so as to contact the surface of the photosensitive drum 3. The developing roller 14 has a metal shaft such as stainless steel, and a conductive elastic body such as urethane rubber or silicone rubber that covers the outer periphery of the shaft. A gear is provided at the end of the shaft of the developing roller 14, and a driving force for rotating the photosensitive drum 3 is transmitted to this gear. A supply roller 8 and a regulating blade 9 are arranged around the developing roller 14.

[0017] The cleaning unit 5 has a cleaning member that scrapes off deposits on the surface of the photosensitive drum 3, and a cleaning container that contains the scraped off deposits. The deposits include external additives that have adhered to the toner 10, weakly charged toner that has not been transferred in a printing operation, or waste toner that has adhered to the surface of the photosensitive drum 3 in a toner disposal operation as a developer disposal operation. The cleaning member is, for example, an elastic blade that uses an elastic body such as rubber. The elastic blade is disposed so as to come into contact with the surface of the photosensitive drum 3.

[0018] The static elimination unit 6 is a device for eliminating variations in the surface potential of the photosensitive drum 3. The static elimination unit 6 is, for example, a light irradiation device for uniformly exposing the surface of the photosensitive drum 3. The static elimination unit 6 has, for example, a plurality of LED chips arranged on a substrate, and the plurality of LED chips are disposed so as to face the photosensitive drum 3.

[0019] The toner supply unit 7 accommodates therein toner of a color corresponding to each of the image forming units 2K, 2Y, 2M, and 2C, and is a toner cartridge that is detachably attachable to the image forming units 2K, 2Y, 2M, and 2C.

[0020] The supply roller 8 supplies the toner 10 in the toner storage unit 11 onto the developing roller 14. The supply roller 8 has a metal shaft such as stainless steel, a foamed elastic body such as silicone that covers the outer periphery of the shaft, and a gear provided at the end of the shaft. The driving force from the developing roller 14 is transmitted to this gear, causing the supply roller 8 to rotate.

[0021] The regulating blade 9 regulates the amount of toner adhering to the developing roller 14. The regulating blade 9 is an elastic blade made of, for example, a thin stainless steel plate, one end of which is fixed to a part (for example, a holder) of the image forming unit 2. The other end of the regulating blade 9 is disposed so as to be pressed against the developing roller 14. The contact portion of the regulating blade 9 with the surface of the developing roller 14 has a structure that has been subjected to bending processing with a curvature radius of 0.2 [mm], and is disposed so that the linear pressure against the developing roller 14 is 30 [gf / cm].

[0022] The toner sensor 12 detects the remaining amount of toner in the toner storage unit 11. For example, the toner sensor 12 detects the remaining amount of toner based on the rotational operation of a stirring bar that stirs the toner in the toner storage unit 11. The method of detecting the remaining amount of toner by the toner sensor 12 is not limited to using a stirring bar. In addition, each of the image forming units 2K, 2Y, 2M, and 2C may be provided with a plurality of toner sensors 12. For example, each of the image forming units 2K, 2Y, 2M, and 2C may have, as the toner sensor 12, a first toner sensor that detects a first LOW level and a second toner sensor that detects a second LOW level that is lower than the first LOW level.

[0023] The LED head 16 is an exposure device for selectively exposing the uniformly charged surface of the photosensitive drum 3 in the axial direction (also called the "main scanning direction" or "longitudinal direction") to form a latent image pattern. The LED head 16 has multiple LED elements, an LED driving element (i.e., a driving circuit), and a lens array including multiple microlenses. The LED head 16 is disposed at a position where the light emitted from the multiple LED elements forms an image on the surface of the photosensitive drum 3.

[0024] The transfer roller 20 as a transfer section transfers the toner image formed on the surface of the photosensitive drum 3 onto a recording medium P or a transfer belt (not shown). The transfer roller 20 is made of, for example, a conductive foamed elastic body. The transfer roller 20 is disposed so as to face the photosensitive drum 3.

[0025] The fixing unit 30 has a heat roller 31 and a pressure roller 32, and fixes the toner image transferred onto the recording medium P to the recording medium P by applying pressure and heat. The heat roller 31 is provided with a halogen lamp (not shown) inside a tube as a heat source.

[0026] The paper feed tray 40 contains a plurality of recording media P. The hopping roller 41 feeds the recording media P one by one from the paper feed tray 40. The registration rollers (conveying rollers) 42 are a pair of rollers that correct skew of the recording media P fed by the hopping roller 41 and convey the recording media P.

[0027] The discharge rollers 43 convey the recording medium P on which the toner image has been fixed by the fixing device 30, and discharge it to the outside of the image forming apparatus 1.

[0028] 2 is a block diagram showing a schematic configuration of a control system of an image forming apparatus according to an embodiment. As shown in FIG. 2, the image forming apparatus 1 has an interface 50 for communicating with an external device, and a control unit 100 for controlling the overall operation of the image forming apparatus 1. The control unit 100 has a print operation control unit 101, a drive system control unit 102, an image formation control unit 103, a charging voltage control unit 130, a developing voltage control unit 131, a regulation voltage control unit 132, a supply voltage control unit 133, a head control unit 140, a toner waste count holding unit 150, a drum count measurement unit 160, a dot count measurement unit 170, a toner waste threshold holding unit 180, a toner waste count calculation unit 190, a toner remaining amount calculation unit 200 at the time of toner waste, a toner waste pattern change unit 210, and a toner waste pattern storage unit 220. The control unit 100 is, for example, a processing circuit (control circuit). The processing circuit may be composed of a storage device such as a memory that stores a program as software, and a processor such as a CPU (Central Processing Unit) that executes the program.

[0029] The drive system control unit 102 follows instructions from the printing operation control unit 101 and controls the conveying system drive motor 110, the fixing unit drive motor 111, and the drum drive motor 112 based on information such as the printing speed and the drive timing of each motor received from the printing operation control unit 101.

[0030] The conveying system drive motor 110 rotates the medium conveying rollers 120 at a predetermined timing and speed. The medium conveying rollers 120 are a collective term for rollers for conveying the recording medium P, and include the hopping roller 41, the registration rollers 42, the discharge rollers 43, and the like shown in FIG.

[0031] The fixing unit drive motor 111 rotates the heat roller 31 or the pressure roller 32 of the fixing unit 30 at a predetermined timing and speed.

[0032] The drum drive motor 112 rotates the photosensitive drum 3 at a predetermined timing and speed.

[0033] The image formation control unit 103 controls the charging voltage control unit 130 , the developing voltage control unit 131 , the regulating voltage control unit 132 , the supply voltage control unit 133 , and the head control unit 140 in accordance with instructions from the printing operation control unit 101 .

[0034] The charging voltage control unit 130 generates and stops the generation of a charging voltage to be applied to the charging roller 4 in accordance with instructions from the image formation control unit 103. The developing voltage control unit 131 generates and stops the generation of a charging voltage to be applied to the developing roller 14 in accordance with instructions from the image formation control unit 103. The regulating voltage control unit 132 generates and stops the generation of a charging voltage to be applied to the regulating blade 9 in accordance with instructions from the image formation control unit 103. The supply voltage control unit 133 generates and stops the generation of a charging voltage to be applied to the supply roller 8 in accordance with instructions from the image formation control unit 103.

[0035] The head control unit 140 follows instructions from the image formation control unit 103 to control the light emitting operation of each LED element of the LED head 16, such as the light emitting timing and the amount of light emitted.

[0036] The toner waste count storage unit 150 stores an integrated value accumulated until the current printing operation (that is, the current print job) is executed, that is, a toner waste count value (value K described below).

[0037] The drum count measurement unit 160 measures a drum count value (a value Dr described below) which is a numerical value corresponding to the number of rotations of the photosensitive drum 3 (that is, the drum rotation number) during a printing operation.

[0038] The dot count measurement unit 170 measures a dot count value (a value Dt described below) which is a numerical value corresponding to the number of light emitting dots of LEDs serving as light emitting elements in a printing operation.

[0039] The toner waste threshold value storage unit 180 stores a toner waste threshold value (a waste coefficient A described later) and a conversion coefficient B.

[0040] The toner waste count calculation unit 190 calculates a toner waste count value (value K described below) using the drum count value (value Dr described below) and dot count value (value Dt described below) during the printing operation measured by the drum count measurement unit 160 and the dot count measurement unit 170, and the toner waste threshold (waste coefficient A described below) and conversion coefficient B stored in the toner waste threshold storage unit 180, and sends the toner waste count value to the toner waste count storage unit 150.

[0041] The drum count value (value Dr described below) is measured by counting the number of drum rotations in a printing operation to print three A4-sized sheets, for example, as 3. The dot count value (value Dt described below) is the number of light-emitting dots divided by 8192, and a print rate of 5% on A4-sized paper is 792 counts.

[0042] The toner remaining amount calculation unit 200 in the toner storage unit 11 at the time of toner disposal determines whether the remaining amount of toner in the toner storage unit 11 is less than a preset remaining amount threshold (first threshold) (i.e., toner is LOW) at the timing of toner disposal.

[0043] The toner disposal pattern changing unit 210 switches the toner disposal pattern used in the toner disposal operation depending on whether the toner remaining amount calculating unit 200 in the toner storage unit 11 indicates that the toner is low or not low when the toner is disposed of.

[0044] The toner disposal pattern memory storage unit 220 stores different toner disposal patterns set by the toner disposal pattern changing unit 210 .

[0045] 2. Printing operation When a print command is input to the printing operation control unit 101 from a higher-level device (for example, a personal computer, etc.) via the interface 50, information on timing and printing speed generated by the printing operation control unit 101 is sent to the drive system control unit 102. Based on the received timing and printing speed information, the drive system control unit 102 rotates the conveyor system drive motor 110, the fuser drive motor 111, and the drum drive motor 112 at a predetermined timing and speed. The rotations of the conveyor system drive motor 110, the fuser drive motor 111, and the drum drive motor 112 are transmitted, and the medium conveying roller 120, the roller in the fuser 30, and the photosensitive drum 3 rotate. As a result, the recording media P are conveyed one by one.

[0046] Furthermore, the image formation control unit 103 provides information on the applied voltage and the voltage application timing to each of the charging voltage control unit 130, the developing voltage control unit 131, the regulating voltage control unit 132, and the supply voltage control unit 133. Based on the received voltage control conditions, these voltage control units 130 to 133 apply a predetermined negative voltage at a predetermined timing to each of the charging roller 4, the developing roller 14, the regulating blade 9, and the supply roller 8.

[0047] Furthermore, the image data received by the print operation control unit 101 is processed in the print operation control unit 101 and the image formation control unit 103, and is sent to the head control unit 140. The head control unit 140 lights up the LED elements of the LED head 16 based on the received image data to expose the surface of the photosensitive drum 3.

[0048] In the image forming unit 2, a charging roller 4 to which a charging voltage Vc is applied uniformly charges the surface of the photoconductor drum 3. The uniformly charged surface (i.e., the outer peripheral surface) of the photoconductor drum 3 is selectively exposed to light by an LED head 16 according to an image pattern, and an electrostatic latent image with a reduced potential is formed at the exposed locations. The electrostatic latent image faces a developing roller 14 to which a developing voltage is applied, and toner 10 is transported onto the electrostatic latent image by the electric field formed between the electrostatic latent image and the developing roller 14, and a toner image is formed on the outer peripheral surface of the photoconductor drum 3.

[0049] Prior to this step, the toner 10 is frictionally charged to a negative pole at the contact portion between the supply roller 8 and the development roller 14 and at the contact portion between the regulating blade 9 and the development roller 14. The frictionally charged toner 10 moves from the supply roller 8 to the development roller 14 and from the regulating blade 9 to the development roller 14 due to the electric field formed between the development roller 14 and the supply roller 8 and between the development roller 14 and the regulating blade 9. The regulating blade 9 also serves to regulate the amount of toner adhering to the surface (i.e., the outer peripheral surface) of the development roller 14 and to form a uniform thin layer of toner on the development roller 14. The developed toner image is transported to the photoconductor drum 3.

[0050] The toner image and recording medium P reach the contact point between the photosensitive drum 3 and transfer roller 20 at the same time, and at this time, a positive high voltage is applied to the transfer roller 20, so that the toner image on the photosensitive drum 3 is transferred onto the recording medium P by the electric field formed between the photosensitive drum 3 and the transfer roller 20. Even after this transfer process, a small amount of toner 10 remains on the photosensitive drum 3, but this is removed by the cleaning unit 5. Thereafter, the entire surface of the photosensitive drum 3 is uniformly exposed to the static elimination light, and the surface potential of the photosensitive drum 3 is reset.

[0051] The toner image transferred onto the recording medium P is transported to the fixing device 30 together with the recording medium P, and is fixed onto the recording medium P by heat and pressure. Thereafter, the recording medium P on which the toner image has been fixed is discharged to the outside of the image forming apparatus 1 by the discharge rollers 43, and the printing operation is completed.

[0052] When the image forming apparatus 1 is operated in a normal temperature and humidity environment using negatively charged toner, the applied voltages are, for example, −1200V for the charging voltage Vc of the charging roller 4, −300V for the developing voltage Vd of the developing roller 14, −420V for the supply voltage Vs of the supply roller 8, and −420V for the blade voltage Vb of the regulating blade 9. When a charging voltage of a predetermined value or more is applied to the charging roller 4, the surface of the photosensitive drum 3 is charged, and the surface potential Vo changes in proportion to the applied charging voltage. In this embodiment, when the charging voltage Vc is −1200V, the surface potential Vo of the photosensitive drum 3 is −600V. The latent image potential Vl of the photosensitive drum 3 usually approaches 0V as the driving time of the LED head 16 becomes longer (i.e., the exposure energy increases), and is saturated at around −50V. The toner 10 is reversely developed from the developing roller 14 into a latent image pattern by the electric field formed by the latent image potential Vl and the developing voltage Vd. In the above, the case where negatively charged toner is used has been described, but when positively charged toner is used, the applied voltages have the opposite polarities.

[0053] <3> Toner disposal operation Next, the toner disposal operation in this embodiment will be described. The quality of the image output from the image forming apparatus 1 varies over time. For this reason, the toner disposal operation is performed to prevent image defects (hereinafter also referred to as "stains") from occurring and to prevent a decrease in image quality. The cause of the stains is that, as printing is continued with a latent image pattern having a low printing rate (i.e., print duty), deteriorated developer (i.e., damaged toner) occupies a high proportion of the toner 10 in the toner storage unit 11 of the image forming unit 2, and the amount of toner remaining in the toner storage unit 11 in particular becomes low, causing the stains to occur.

[0054] FIG. 3 is a diagram showing the toner potential when no stain occurs (toner remaining amount is equal to or greater than a threshold) and when stain occurs (toner remaining amount is less than a threshold). As shown in FIG. 3, damaged toner accumulates locally in the longitudinal direction of the photosensitive drum 3 due to the configuration inside the toner storage unit 11, causing stains to occur near the middle between the end and center of the photosensitive drum 3 (i.e., the stain occurrence location). As a countermeasure against this, if a conventional toner disposal method is used, for example, control is used to discard toner at a uniform printing rate over the entire area of ​​the main scanning direction (i.e., the longitudinal direction) of the photosensitive drum 3, it is not possible to discard all of the locally accumulated damaged toner. In addition, if the amount of toner disposal is increased in order to discard all of the locally accumulated damaged toner, even good quality toner that does not need to be discarded will be discarded, resulting in more wasted toner consumption and a shorter period until the toner cartridge as the toner supply 7 is replaced.

[0055] Incidentally, when the toner consumption in the entire image forming apparatus 1 is excessively low, or when a specific color is selected to form a color image, the toner consumption in a specific image forming unit 2 may become excessively low. When the toner consumption becomes low, the toner continues to be stirred up in the toner storage unit 11, and the toner adhering to the developing roller 14 continues to be rubbed by the supply roller 8, the regulating blade 9, and the photosensitive drum 3. In this case, the toner on the developing roller 14 tends to be triboelectrically charged and has a high potential, and if the potential becomes too high, it may cause stains on the image.

[0056] Furthermore, when the toner is continuously rubbed, it is damaged, and the amount of damaged toner in which the external additives contained therein are peeled off from the toner surface increases. In such a case, the toner cannot be normally charged, which causes smudges, fogging, blurring, and the like, and causes the graininess to deteriorate.

[0057] In this way, if printing that consumes an excessively small amount of toner (i.e., printing with a low printing rate) continues, the toner cannot be charged normally, and image quality deteriorates due to the occurrence of smudges, fogging, blurring, and deterioration of graininess, etc. Therefore, in order to improve image quality, a certain amount of toner is discarded when printing that consumes a small amount of toner is repeated.

[0058] The image forming apparatus 1 according to the present embodiment controls the toner disposal operation in consideration of the above-mentioned factors that cause stains. In the toner disposal operation, toner is disposed of on the photosensitive drum 3 using a toner image (i.e., by forming a toner image on the photosensitive drum 3). In this embodiment, a print operation is executed after receiving a print instruction, and the toner disposal operation is executed after the print job is completed. The toner disposal operation is executed by illuminating the LED head 16 on the photosensitive drum 3 that is uniformly charged by the charging roller 4, forming an electrostatic latent image pattern on the surface of the photosensitive drum 3, and developing the toner with the developing roller 14. The amount of toner disposed of at one time is one count (printing rate of 5%) of a toner disposal count (value K described later). Here, the timing of the toner disposal operation is not limited to this, and may be when the power of the image forming apparatus 1 is turned on or when the cover of the image forming apparatus 1 is opened or closed, when various correction operations are performed, after the printing operation is completed, or at multiple timings. The amount of toner disposed of in the toner disposal operation is not limited to one count, and can be appropriately adjusted.

[0059] FIG. 4 is a diagram showing the relationship between the dirt level and the amount of toner remaining in the toner storage unit 11. FIG. 5(A) is a diagram showing an example of a first toner disposal pattern, and FIG. 5(B) is a diagram showing an example of a second toner disposal pattern. FIG. 5(A) shows an example in which the first toner disposal pattern as the first toner disposal electrostatic latent image includes the entire area in the longitudinal direction of the photoconductor drum 13. FIG. 5(B) shows an example in which the second toner disposal pattern as the second toner disposal electrostatic latent image includes two ranges in the longitudinal direction of the photoconductor drum 13 (two areas spaced apart from the end positions in the longitudinal direction and spaced apart from the central position in the longitudinal direction).

[0060] In a conventional image forming apparatus, when the print pattern has a small overall toner consumption, the toner is uniformly discarded in the main scanning direction as in the conventional first developer discarding pattern in Fig. 5(A). However, in this embodiment, depending on the configuration inside the toner storage unit 11 as in Fig. 3, damaged toner may accumulate locally in the main scanning direction, causing stains in that area.

[0061] Also, as shown in FIG. 4, it is known in advance that stains do not occur in the section SA, but stains occur in the section SB after toner LOW is detected. Therefore, in this embodiment, in the section SA as shown in FIG. 4 where stains do not occur, toner is discarded in the first developer discarding pattern as shown in FIG. 5(A) as in the conventional manner, and in the section SB as shown in FIG. 4 where stains may occur, the developer discarding pattern is switched to the second developer discarding pattern for stain relief as shown in FIG. 5(B) using the toner LOW detection as a trigger to relieve the stains, thereby increasing the amount of toner discarded at the position where stains occur, and forcibly disposing of a large amount of damaged toner that has accumulated locally. This makes it possible to switch the developer discarding pattern at an appropriate timing, so that initially, stains can be dealt with at a timing when stains may occur without impairing image quality as in the conventional manner.

[0062] In other words, in this embodiment, the following two types of disposal processes are used for the toner disposal operation.

[0063] The first disposal process is a process of forming a first toner disposal electrostatic latent image (first developer disposal electrostatic latent image) with a first printing rate (e.g., 50%) in a first range in the longitudinal direction of the photosensitive drum 3, transporting the toner in the toner storage section 11 to form a first disposal toner image (first disposal developer image) corresponding to the first toner disposal electrostatic latent image, and removing the first disposal toner image.

[0064] The second disposal process is a process of forming a second toner disposal electrostatic latent image (second developer disposal electrostatic latent image) with a second printing rate (e.g., 100%) higher than the first printing rate in one or more second ranges in the longitudinal direction of the photosensitive drum 3, transporting the toner in the toner storage section 11 to form a second disposal toner image (second disposal developer image) corresponding to the second toner disposal electrostatic latent image, and removing the second disposal toner image. Here, the total longitudinal length of the one or more second ranges is shorter than the longitudinal length of the first range (e.g., the entire longitudinal area).

[0065] Furthermore, the control unit 100 repeatedly executes the first disposal process at intervals. The first disposal process is executed when a predetermined condition is satisfied (for example, when K obtained by equation (1) described below becomes 1 or more). Furthermore, the control unit may be set to execute the first disposal process when the image forming apparatus 1 is powered on, when a cover (not shown) of the housing of the image forming apparatus 1 is opened or closed, when various correction operations are performed, and after a printing operation is completed, and the execution timing of the first disposal process can be adjusted as appropriate.

[0066] In addition, when the remaining amount of toner in the toner storage section 11 is less than a preset first threshold value (i.e., when toner is LOW), the control section 100 executes the second disposal process instead of the first disposal process when the conditions for executing the second disposal process are satisfied.

[0067] In this embodiment, the developer disposal pattern is switched using toner LOW as a trigger, but the setting of the trigger is not limited to toner LOW and can be appropriately adjusted based on the result of detection of the remaining toner amount by dot count or the like.

[0068] A method for calculating the toner waste count K in this embodiment will be described. The toner waste count K is 0 for a new image forming unit. The toner waste count K increases or decreases depending on the printing operation. The toner waste count K increases when a printing operation is performed in which the print rate is lower than a predetermined reference value, and decreases when a printing operation is performed in which the print rate is higher than the predetermined reference value.

[0069] When the count value corresponding to the number of rotations of the photosensitive drum 3 in the printing operation is Dr [count], a predetermined threshold coefficient is A, a threshold consumption amount that is the minimum toner consumption amount that does not increase the deteriorated developer (damaged toner) in the toner storage unit 11 by the printing operation corresponding to Dr [count] is A × Dr [dot], an actual developer consumption amount consumed by the printing operation corresponding to Dr [count] is Dt [dot], and a predetermined conversion coefficient is B, the control unit 100 executes the developer disposal operation every time the integrated value (A × Dr - Dt) / B obtained by subtracting Dt [dot] from A × Dr [dot] and dividing the value obtained by B, becomes equal to or greater than a preset deteriorated developer threshold value (for example, value 1). For example, B = 792. Also, A is, for example, the toner consumption amount when the printing rate (i.e., print density) is 1.5%.

[0070] This can be expressed mathematically as follows: K = K + (A × Dr - Dt) / B … (1)

[0071] When the control unit 100 executes the developer disposal operation, it performs a process of subtracting the first threshold value from the integrated value of (A×Dr−Dt) / B to obtain a value (K−1) as a new integrated value (i.e., toner disposal count K).

[0072] Next, a method for verifying the location where dirt has occurred will be described. Here, an example of a method for verifying whether the developer disposal pattern when the remaining amount of toner in the toner storage unit 11 is low is formed at the location where dirt has occurred will be described, in the case where the developer disposal pattern is changed between when the remaining amount of toner in the toner storage unit 11 is sufficiently large and when the remaining amount of toner in the toner storage unit 11 is low.

[0073] The method of verifying the location where dirt occurs is to reduce the difference between the charging voltage Vc and the developing voltage Vd, i.e., (Vc-Vd) by lowering the charging voltage Vc of the charging roller 4 (at this time, (Vo-Vd) also becomes smaller), and print a halftone. When the difference (Vc-Vd) is reduced, the density of the location where dirt occurs becomes higher, and the density of the area other than the dirty area remains almost the same as before the change in the charging voltage Vc. At this time, the density distribution is measured in the main scanning direction, and the peak of the density distribution and the density difference are obtained to identify the location where the density becomes higher. As an example, by lowering the charging voltage Vc by about 45 [V], high and low density areas appear in the halftone density distribution. It is possible to verify that the toner disposal pattern is formed at a position that corresponds to the location where dirt occurs shown in FIG. 3 by checking whether the high density area that appears by the above verification method matches the formation position of the toner disposal pattern when the remaining toner amount in the toner storage unit 11 is low.

[0074] Based on the above, the operation of the present embodiment will be described below. Fig. 6 is a flowchart showing the operation of the image forming apparatus 1 according to the present embodiment.

[0075] First, in the image forming apparatus 1 in which the toner waste count K is set to 0, a print instruction is received and it is confirmed whether printing has been started (steps S0 and S1).

[0076] When a print command is received and printing is started, the control unit 100 executes printing as is (step S2). After executing printing (step S2) and completing the print job, the control unit 100 checks the toner waste count storage unit 150 to see if the toner waste count K is K≧1 (step S3).

[0077] If K≧1 is not satisfied in step S3, the control unit 100 does not perform the toner disposal operation and advances the process to step S8.

[0078] If K≧1 is satisfied in step S3, the control unit 100 checks the remaining toner amount in the toner storage unit 11 using the remaining toner amount calculation unit 200 to check whether the toner is LOW (step S4).

[0079] If the toner is not LOW in step S4, a first developer disposal pattern for conventional fog relief is set (step S5), and if the toner is LOW in step S4, a second developer disposal pattern for dirt relief is set (step S6).

[0080] After the developer disposal patterns are set in steps S5 and S6, toner disposal is performed according to each developer disposal pattern, and one unit of toner is disposed of, so that the toner disposal count is decremented by one unit (step S7).

[0081] After the toner disposal operation is performed in step S7, the drum count measurement unit 160 and the dot count measurement unit 170 acquire the drum count Dr and the dot count Dt in the printing operation performed in step S2 (step S8).

[0082] After step S8, the toner waste count calculation unit 190 calculates the toner waste count using equation (1) based on the drum count Dr and dot count Dt during the printing operation measured by the drum count measurement unit 160 and the dot count measurement unit 170, the toner waste threshold held by the toner waste threshold holding unit 180, and the toner waste count conversion coefficient, and sends the toner waste count to the toner waste count holding unit 150.

[0083] 4. Effects According to this embodiment, when the remaining amount of toner in the toner storage unit 11 is large, a first toner disposal electrostatic latent image with a first printing ratio is formed in a first range covering the entire area in the longitudinal direction of the photosensitive drum 3, the toner in the toner storage unit 11 is transported to form a first disposal toner image (i.e., a first toner disposal pattern) corresponding to the first toner disposal electrostatic latent image, and a first disposal process is executed to remove the first disposal toner image. Therefore, when the remaining amount of toner in the toner storage unit 11 is large, it is possible to prevent the quality of the image from deteriorating.

[0084] According to this embodiment, when the remaining amount of toner in the toner storage section 11 is small, a second toner disposal electrostatic latent image with a second printing rate higher than the first printing rate is formed in a second range covering two narrow areas (i.e., stain occurrence areas) in the longitudinal direction of the photosensitive drum 3, a second disposal toner image (i.e., a second toner disposal pattern) corresponding to the second toner disposal electrostatic latent image is formed by conveying the toner in the toner storage section 11, and a second disposal process is performed to remove the second disposal toner image. Therefore, even when the remaining amount of toner in the toner storage section 11 is small, the quality of the image can be prevented from being deteriorated. In addition, since a second toner disposal electrostatic latent image with a second printing rate higher than the first printing rate is formed in a second range covering a narrow area in the longitudinal direction of the photosensitive drum 3, the damaged toner can be efficiently disposed of while suppressing an increase in the amount of toner to be disposed of.

[0085] 5. Variations The image forming apparatus 1 is not limited to a printer, but may be a copier, a facsimile, a multifunction peripheral (MFP), or the like.

[0086] Also, a plurality of types of second toner discarding electrostatic latent images (second toner discarding patterns) may be provided. [Explanation of symbols]

[0087] 1 image forming apparatus, 2, 2K, 2Y, 2M, 2C image forming section (developing section), 3 photosensitive drum (image carrier), 4 charging roller (charging member), 5 cleaning section, 7 toner supply body (developer supply body), 8 supply roller (developer supply body), 9 regulating blade (regulating member), 10 toner (developer), 11 toner storage section (developer storage section), 12 toner sensor (developer sensor), 14 developing roller (developer carrier), 16 LED head (exposure head), 30 fixing unit, 100 control section.

Claims

1. An image carrier; an exposure head for forming an electrostatic latent image on the surface of the image carrier; a developer storage unit that stores a developer; a developer carrier that transports the developer in the developer container to a surface of the image carrier and forms a developer image corresponding to the electrostatic latent image; a control unit that controls a printing operation for forming an image on a recording medium using the developer image, and also controls a developer disposal operation for disposing of the developer on the image carrier using the developer image; having The developer disposal operation includes: a first disposal process for forming a first electrostatic latent image for developer disposal having a first printing ratio in a first range in a longitudinal direction of the image carrier, transporting the developer in the developer accommodating section to form a first developer image for disposal corresponding to the first electrostatic latent image for developer disposal, and removing the first developer image for disposal; a second disposal process for forming a second electrostatic latent image for discarding the developer having a second printing rate higher than the first printing rate in one or more second ranges in the longitudinal direction of the image carrier, transporting the developer in the developer accommodating section to form a second electrostatic latent image for discarding the developer corresponding to the second electrostatic latent image for discarding the developer, and removing the second electrostatic latent image for discarding the developer; Including, The sum of the longitudinal lengths of the one or more second ranges is less than the longitudinal length of the first range.

1. An image forming apparatus comprising:

2. The image bearing member further includes a cleaning unit for removing deposits from the surface of the image bearing member.

2. The image forming apparatus according to claim 1,

3. The control unit is Repeating the first discarding process at intervals; When the remaining amount of the developer is less than a first threshold value set in advance, the second disposal process is executed instead of the first disposal process.

2. The image forming apparatus according to claim 1,

4. The control unit stores a printing operation and detects the remaining amount of the developer.

4. The image forming apparatus according to claim 3.

5. a developer sensor for detecting a remaining amount of the developer in the developer container, The control unit detects the remaining amount of the developer based on an output of the developer sensor.

4. The image forming apparatus according to claim 3.

6. the first range in which the first developer discarding electrostatic latent image is formed includes an entire area of ​​the image carrier in the longitudinal direction, The one or more second ranges in which the second developer waste electrostatic latent image is formed include two regions spaced apart from end positions in the longitudinal direction of the image carrier and spaced apart from a central position in the longitudinal direction.

6. The image forming apparatus according to claim 1, wherein the image forming apparatus is a multi-color image forming apparatus.

7. The second printing rate is 100%.

6. The image forming apparatus according to claim 1, wherein the image forming apparatus is a multi-color image forming apparatus.

8. A count value corresponding to the number of rotations of the image carrier during the printing operation is defined as Dr [count], Denote the predetermined threshold coefficient by A, A threshold consumption amount, which is a minimum developer consumption amount that does not increase the deteriorated developer in the developer accommodating portion by the printing operation corresponding to the Dr [count], is set to A×Dr [dots], The actual developer consumption amount consumed by the printing operation corresponding to the Dr [count] is defined as Dt [dot], When a given conversion coefficient is represented by B, The control unit executes the developer disposal operation every time an integrated value (A×Dr−Dt) / B obtained by subtracting Dt [dots] from A×Dr [dots] and dividing the resultant value by B becomes equal to or greater than a preset deteriorated developer threshold value.

6. The image forming apparatus according to claim 3, wherein the image forming apparatus is a multi-color image forming apparatus.

9. The control unit performs a process of subtracting the first threshold value from the integrated value of the value (A×Dr−Dt) / B as a new integrated value when the developer disposal operation is performed.

9. The image forming apparatus according to claim 8,

Images