Image forming apparatus

Abstract

To prevent a reduction in image quality due to deterioration of toner.SOLUTION: An image forming apparatus comprises: a photoconductor drum 1; a developing unit 5 that has a developing roller 6 carrying toner to the photoconductor drum 1, and a toner storage section 17 storing the toner; a toner cartridge 13 that stores the toner supplied to the toner storage section 17; and a control section 220 that performs image forming processing, toner discharge processing of discharging the toner to the photoconductor drum 1, and calculation of the average printing rate in the image forming processing on a predetermined number of recording materials. The control section 220 performs control so that the toner discharge amount when the total initial toner amount obtained by adding up the amount of toner stored in the developing unit 5 in an unused state and the amount of toner stored in the toner cartridge 13 in an unused state is larger than a reference toner amount and the average printing rate is a first printing rate lower than a predetermined printing rate, is larger than the toner discharge amount when the total initial toner amount is smaller than the reference toner amount and the average printing rate is the first printing rate (S104-S115).SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to an electrophotographic image forming apparatus such as a laser printer, a copying machine, and a facsimile machine.

Background Art

[0002] In image forming apparatuses such as copying machines, printers, and facsimiles that form an image on a recording material using the electrophotographic method (electrophotographic process), in the image forming process, an electrostatic latent image is formed on a photoreceptor, and the formed electrostatic latent image is developed using a developer (toner) to form a visible image. A developing container (developer) responsible for the developing process in the image forming process is configured to be detachable from the image forming apparatus as an independent unit or as part of a process cartridge. The developing container is also called a developing container or the like, and has a frame body that houses the toner as the developer, and a developing roller that is rotatably disposed at the opening of the frame body and carries and conveys the toner from the inside of the frame body to the outside by rotating. Further, the developing container has a toner supply roller that is a supply member for supplying toner to the developing roller, and a developing blade that is a regulating member that contacts the surface of the developing roller to regulate the amount of toner carried on the developing roller and passing through the opening.

[0003] As a toner replenishment method in such an image forming apparatus, for example, Patent Document 1 discloses a developing container in which a replenishment container containing developer can be attached and detached. Such a toner replenishment method is widely used because it reduces the number of replacement parts after the toner is used up and offers excellent usability. Furthermore, the toner carried on the developing roller is constantly rubbed against the developing blade, toner supply roller, and photosensitive drum as the number of image forming cycles of the developing container increases. This rubbing causes the toner to become loose or embedded in external additives added to the toner. As a result, the toner may not be able to maintain the desired amount of charge, which can lead to image defects. This phenomenon in which the toner cannot maintain the desired amount of charge is called toner degradation. For example, Patent Document 2 discloses the following control to suppress the decline in image quality due to toner degradation and maintain high image quality. That is, a control is disclosed that performs a developing operation of the degraded toner into the non-image area (hereinafter referred to as toner ejection) at an appropriate timing only when low-print-rate printing, in which toner degradation becomes significant, is performed continuously. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-117421 [Patent Document 2] Japanese Patent Publication No. 2004-125829 [Overview of the project] [Problems that the invention aims to solve]

[0005] Traditionally, when low-print density printing is performed continuously, the toner on the developing roller is not consumed and continues to move around on the roller, rubbing against the developing blade and photosensitive drum, which accelerates toner degradation. Therefore, toner degradation is suppressed by periodically ejecting the toner from the developing roller and replacing the toner coated on the developing roller, depending on the toner consumption status and the rotation time of the developing roller. In recent years, with the increasing need for longer process cartridge lifespans, toner replenishment methods that offer superior usability and only require the replacement of the toner replenishment container have become widespread. In such configurations, even when printing with the same image pattern, variations in the tolerance of the amount of toner filled in the developing container and toner replenishment container can lead to differences in toner degradation. Generally, the remaining amount of toner in the developing container is detected by a toner remaining amount detection means, and the replacement time is determined based on the detected toner remaining amount. Therefore, if printing continues at the same print density using a developer container manufactured with toner at the lower tolerance limit and a developer container manufactured at the upper tolerance limit, the developer container with less toner (lower tolerance limit) will reach its replacement time sooner than the developer container with more toner (upper tolerance limit). From the perspective of toner degradation, the developer container with more toner (upper tolerance limit) has more time for the toner to circulate around the developer roller than the developer container with less toner (lower tolerance limit). As a result, toner degradation progresses, leading to problems such as toner fogging and ghosting.

[0006] This invention was made under such circumstances and aims to prevent a decrease in image quality due to toner degradation. [Means for solving the problem]

[0007] To solve the above-mentioned problems, the present invention has the following configuration.

[0008] (1) A control unit that can perform an image forming process for supplying toner to the photosensitive drum and forming a toner image on the photosensitive drum for transferring to a recording material, and a toner discharge process for discharging toner from the developing roller to the photosensitive drum, wherein the control unit performs the toner discharge process each time the image forming process is performed on a predetermined number of recording materials, and the acquisition unit acquires the average print density in the image forming process of the predetermined number of recording materials performed immediately before the toner discharge process. In an image forming apparatus, the total initial toner amount is defined as the sum of a first initial toner amount contained in the unused developing unit and a second initial toner amount contained in the unused toner cartridge, and the toner discharge amount is defined as the toner discharge amount discharged from the developing roller to the photosensitive drum in the toner discharge process. The control unit controls the first toner discharge amount, which is the toner discharge amount when the total initial toner amount is greater than the reference toner amount and the average print rate is lower than a predetermined print rate, to be greater than the second toner discharge amount, which is the toner discharge amount when the total initial toner amount is less than the reference toner amount and the average print rate is lower than the first print rate. [Effects of the Invention]

[0009] According to the present invention, it is possible to prevent a decrease in image quality due to toner degradation. [Brief explanation of the drawing]

[0010] [Figure 1] Cross-sectional view showing the schematic configuration of the image forming apparatus in the embodiment. [Figure 2] Perspective view illustrating the configuration of the developing unit and toner cartridge in the embodiment. [Figure 3] Cross-sectional view illustrating the configuration of the developing unit and toner cartridge in the embodiment. [Figure 4]Control block diagram illustrating the configuration of the control unit of the image forming apparatus in the embodiment. [Figure 5] Graph showing the relationship between toner level and number of printed pages in the example. [Figure 6] Flowchart of toner ejection control in the embodiment [Figure 7] Graph showing the relationship between toner level and number of printed pages in the example. [Figure 8] Graph showing the relationship between toner level and number of printed pages in the example. [Figure 9] Graph showing the relationship between toner level and number of printed pages in the example. [Figure 10] Graph showing the relationship between the number of toner strokes and the number of printed pages in the example. [Figure 11] Graph showing the relationship between the number of toner strokes and the number of printed pages in the example. [Figure 12] Graph showing the relationship between the number of toner strokes and the number of printed pages in the example. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described in detail below with reference to the drawings. [Examples]

[0012] [Overall configuration of the image forming apparatus] FIG. 1 is a cross-sectional view showing a schematic configuration of an electrophotographic image forming apparatus 100. As shown in FIG. 1, in the image forming apparatus 100, a process cartridge 70, which is a detachable image forming unit, is mounted by a mounting member (not shown). In the process cartridge 70, a photosensitive drum 1, which is an image carrier, and a charging roller 2, a developing roller 6, a cleaning member 30, etc. are integrally arranged around the photosensitive drum 1. The charging roller 2 charges the surface of the photosensitive drum 1 to a uniform potential, and the developing roller 6 develops the electrostatic latent image formed on the photosensitive drum 1 by attaching toner, which is a developer, thereto, thereby forming a visible toner image. Then, when the toner image formed on the photosensitive drum 1 (on the photosensitive drum) is transferred to a sheet 19, which is a recording medium, the cleaning member 30 removes the toner remaining on the photosensitive drum 1. Also, in the figure, above the process cartridge 70, a scanner unit 3 is provided that exposes the photosensitive drum 1 by irradiating it with laser light according to the on / off of an image signal based on image information, thereby forming an electrostatic latent image on the photosensitive drum 1. On the other hand, in the figure, a cassette 15 storing the sheet 19 is mounted at the lower part of the image forming apparatus 100. Then, during image formation, the sheet 19 is conveyed by a pickup roller 10, passes through a transfer roller 11 and a fixing unit 12, and is conveyed upward of the image forming apparatus 100.

[0013] During image formation, the process cartridge 70 rotates the photosensitive drum 1, and the surface of the photosensitive drum 1 is charged to a uniform potential by the charging roller 2. The scanner unit 3 then exposes the photosensitive drum 1 according to the image information, forming an electrostatic latent image on the photosensitive drum 1. The formed electrostatic latent image is developed by the development roller 6, which deposits toner, forming a toner image on the photosensitive drum 1. Synchronized with image formation in the process cartridge 70, the pickup roller 10 transports the paper 19 from the cassette 15 to the transfer roller 11. A transfer voltage is then applied to the transfer roller 11, transferring the toner image formed on the photosensitive drum 1 to the paper 19. The paper 19 with the transferred toner image is heated and pressurized in the fixing unit 12, fixing the toner image to the paper 19. After that, the paper 19 is discharged by the discharge roller 16 to the discharge unit located at the top of the image forming apparatus 100. The controller 201 that controls the image forming apparatus 100 will be described later.

[0014] [Cleaning Unit Configuration] Next, the configuration of the process cartridge 70 will be described. As shown in FIG. 1, the process cartridge 70 is composed of a cleaning unit 23 and a developing unit 5. The cleaning unit 23 has a photosensitive drum 1, a charging roller 2, and a cleaning member 30, and the charging roller 2 and the cleaning member 30 are arranged on the circumference of the photosensitive drum 1. The cleaning member 30 is composed of an elastic member formed of a rubber blade and a cleaning support member. The tip of the rubber blade of the cleaning member 30 is disposed so as to abut in a direction opposite to the rotation direction of the photosensitive drum 1 (clockwise in FIG. 1). Then, the toner remaining on the surface of the photosensitive drum 1 without being transferred to the paper 19 is removed by the cleaning member 30 and collected in the waste toner collection container 31. The driving force of the main body drive motor (not shown), which is a drive source, is transmitted to the cleaning unit 23, and the photosensitive drum 1 is rotationally driven according to the image forming operation. The charging roller 2 is rotatably attached to the cleaning unit 23 via a charging roller bearing (not shown), and is pressed in the direction of the photosensitive drum 1 by a pressing member (not shown) and rotates in a driven manner with the photosensitive drum 1.

[0015] [Configuration of Developing Unit] On the other hand, as shown in Figure 1, the developing unit 5 consists of a developing roller 6 that rotates in contact with the photosensitive drum 1, and a developing frame 32 that supports the developing roller 6. The developing roller 6 is rotatably supported by the developing frame 32 via a pre-developing bearing (not shown) and a post-developing bearing (not shown) attached to both sides of the developing frame 32. Also, a toner supply roller 4 that rotates in contact with the developing roller 6 and a developing blade 7 for regulating the toner layer on the developing roller 6 are arranged around the circumference of the developing roller 6. When the toner supplied from the toner supply roller 4 to the developing roller 6 passes through the developing blade 7, the amount of toner coating on the developing roller 6 is regulated and charged by the developing blade 7. In this embodiment, the developing blade 7 is a metal SUS blade, and the contact pressure and contact width with the developing roller 6 are adjusted so that the toner obtains the desired charge level. This results in the formation of an optimal toner coating for developing the electrostatic latent image formed on the photosensitive drum 1.

[0016] The developing roller 6 and the photosensitive drum 1 rotate in the same direction (from top to bottom in Figure 1) at the opposing section (also called the developing section). In this embodiment, the toner, which has been charged to a negative potential by frictional charging with the developing blade 7, is transferred in the developing section only to the bright potential areas on the photosensitive drum 1 exposed by the scanner unit 3 when a predetermined DC voltage is applied to the developing roller 6. As a result, the electrostatic latent image is revealed by the toner, and a toner image is formed. Furthermore, the toner storage section 17 of the developing frame 32 is provided with a toner transport member 8 that agitates the stored toner and transports the toner to the toner supply roller 4. As shown in Figure 1, the toner transport member 8 consists of an agitation shaft 8a (see Figure 3) that is rotated by an external driving force, and a sheet member 8b (see Figure 3) that is attached to the agitation shaft 8a and rotates together with the agitation shaft 8a. In addition, the toner used in this embodiment is a non-magnetic one-component toner.

[0017] [Toner cartridge configuration] The process cartridge 70 in this embodiment is detachable from the toner storage section 17 of the developing unit 5 and has a toner cartridge 13, which is a replenishment container for supplying toner to the toner storage section 17. Figure 2 is a schematic perspective view illustrating the configuration of the developing unit 5. As shown in Figure 2, the developing unit 5 is used in a configuration in which the toner cartridge 13 is mounted on the developing frame 32. As shown in Figure 1, the developing unit 5 and the toner cartridge 13 are detachable from the main body of the image forming apparatus 100.

[0018] The toner cartridge 13, like the toner storage unit 17, has a stirring member 9 which consists of a stirring shaft 9a (see Figure 3) that is rotated by an external driving force, and a sheet member 9b (see Figure 3) that is attached to the stirring shaft 9a and rotates together with the stirring shaft 9a. By driving the stirring member 9, the toner inside the toner cartridge 13 is stirred, and toner is supplied to the toner storage unit 17 through the toner supply port 13a (shown as a dashed line in the figure), which is an opening.

[0019] In this embodiment, the toner storage unit 17 has a toner supply port 17a which is the same shape as the toner supply port 13a of the toner cartridge 13. When the toner cartridge 13 is installed in the developing unit 5, the toner supply port 17a of the toner storage unit 17 and the toner supply port 13a of the toner cartridge 13 are installed with their openings aligned. Furthermore, when the toner cartridge 13 is attached or detached, a shutter member (not shown) closes the toner supply port 17a of the toner storage unit 17 and the toner supply port 13a of the toner cartridge 13.

[0020] As shown in Figure 1, when the process cartridge 70 is installed in the image forming apparatus 100, the toner cartridge 13 is positioned diagonally above the toner storage unit 17 in Figure 1. This configuration facilitates the supply of toner from the toner cartridge 13 to the toner storage unit 17.

[0021] [Toner level detection] Next, the detection of the remaining toner amount in the toner storage section 17 of the developing unit 5 will be explained. Figure 3 is a schematic cross-sectional view illustrating the internal configuration of the developing unit 5 and the toner cartridge 13 shown in Figure 2. As described above, the toner in the toner storage section 17 is agitated by a sheet member 8b attached to the agitation shaft 8a and rotating together with the agitation shaft 8a in the direction of the arrow in the figure (clockwise). Similarly, the toner in the toner cartridge 13 is agitated by a sheet member 9b attached to the agitation shaft 9a and rotating together with the agitation shaft 9a in the direction of the arrow in the figure (clockwise), and is supplied to the toner storage section 17 via the toner supply port 13a. The developing unit 5 also has a non-volatile memory 50 which is a developing memory, and the toner cartridge 13 has a non-volatile memory 51 which is a toner cartridge memory. The non-volatile memories 50 and 51 will be described later.

[0022] As shown in Figure 3, the toner storage section 17 of the developing unit 5 is provided with a light guide member 42 for detecting the amount of toner inside the toner storage section 17. In this embodiment, the light guide member 42 is composed of a light-emitting guide member 40 and a light-receiving guide member 41. The light guide member 42 is provided on the developer receiving section 43 of the toner transport member 8, which has a convex shape in the direction toward the outside of the rotation radius of the stirring shaft 8a.

[0023] The developer receiving section 43 is a box-shaped space provided on the wall surface of the toner storage section 17, downstream of the toner supply port 17a and upstream of the bottom of the toner storage section 17, in the rotation direction of the stirring member 8 (clockwise in the figure). Furthermore, the developer receiving section 43 is provided approximately in the center of the longitudinal direction (depth direction in the figure) of the toner storage section 17. In this embodiment, the light guide member 42 is formed integrally with the developer receiving section 43, with the light emission guide member 40 and the light receiving guide member 41 being integrated. That is, the light emission guide member 40 and the light receiving guide member 41 communicate with the inside of the toner storage section 17 through an opening (not shown) provided in the developer receiving section 43.

[0024] Detection light L (indicated by the dotted arrow in the figure) emitted from a light-emitting element (not shown), such as an LED, attached to the image forming apparatus 100 is introduced into the light-emitting guide member 40. The detection light L introduced into the light-emitting guide member 40 is polarized by the reflective surface 40a of the light-emitting guide member 40 toward the inside of the developer receiving section 43, which is also the inside of the toner storage section 17. The polarized detection light L is further deflected by the reflective surface 40b and guided into the inside of the developer receiving section 43 through a light-emitting window (not shown). The detection light irradiated from the light-emitting window (not shown) passes through the developer receiving section 43, which is also the inside of the toner storage section 17, and is introduced into a light-receiving window (not shown) provided on a light-receiving guide member 41, which is positioned opposite the light-emitting window (not shown). Subsequently, the detection light L that has passed through the light-receiving window (not shown) is deflected by the reflective surfaces 41b and 41a of the light-receiving guide member 41 and emitted from the light-receiving guide member 41 to the outside of the developing unit 5. The detection light L emitted to the outside of the developing unit 5 is guided to a light-receiving section (not shown) which is equipped with a light-receiving element such as a phototransistor and is attached to the image forming apparatus 100, and the detection light L is detected by the light-receiving section.

[0025] As described above, the developer receiving section 43 and the toner storage section 17 are in communication with each other, and the toner transported by the sheet member 8b of the toner transport member 8 flows from the toner storage section 17 into the developer receiving section 43. At this time, the space between the light-emitting window (not shown) of the light-emitting guide member 40 and the light-receiving window (not shown) of the light-receiving guide member 41, which are located inside the developer receiving section 43, is filled with the toner transported by the sheet member 8b. Then, depending on the amount of toner remaining (stored) inside the toner storage section 17, the detection light L emitted from the light-emitting window (not shown) of the light-emitting guide member 40 is blocked by the toner transported by the sheet member 8b. In this case, the detection light L emitted from the light-emitting window (not shown) of the light-emitting guide member 40 does not reach the light-receiving window (not shown), and as a result is not detected by the light-receiving unit (not shown) attached to the image forming apparatus 100 or the like. On the other hand, when the sheet member 8b passes through the developer receiving section 43 and toner flows out from the developer receiving section 43, the detection light L emitted from the light-emitting window (not shown) of the light-emitting guide member 40 is not blocked by the toner and reaches the light-receiving window (not shown). In this case, the detection light L emitted from the light-emitting window (not shown) of the light-emitting guide member 40 passes through the inside of the developer receiving section 43, through the light-receiving window (not shown), and through the light-receiving guide member 41, and is detected by the light-receiving unit (not shown) attached to the image forming apparatus 100. In this way, the reception time of the detection light that passes through the inside of the developer receiving section 43 and is received by the light-receiving unit (not shown) attached to the image forming apparatus 100 is measured during one rotation of the sheet member 8b. Based on the reception time of the detection light measured by the light-receiving unit, the controller 201 can detect the remaining amount of toner stored inside the toner storage section 17.

[0026] Furthermore, the toner cartridge 13 does not have a toner level detection unit to detect the amount of toner contained in the cartridge 13. In addition, the controller 201 notifies the user to replace the toner cartridge 13 if the amount of toner detected in the toner storage unit 17 falls below a predetermined toner level.

[0027] [Control unit of the image forming apparatus] Figure 4 is a control block diagram illustrating the configuration of the controller 201, which is the control unit that controls the image forming apparatus 100 shown in Figure 1. The controller 201 shown in Figure 4 has a control unit 220 that controls the image forming apparatus 100, a memory 221 such as ROM and RAM, and an input / output interface 222 that performs input / output with peripheral devices. The RAM of the memory 221 temporarily stores data necessary for the operation of the image forming apparatus 100. The ROM of the memory 221 stores control programs that control the image forming apparatus 100, such as the toner ejection control program and the toner level detection program, which will be described later, as well as control data necessary for the operation of the image forming apparatus 100.

[0028] The control unit 220 is a control means that comprehensively controls the operation of the image forming apparatus 100. It is connected to each device that is the target of control in the image forming apparatus 100 via the input / output I / F 222, and controls the transmission and reception of various signals, the timing of driving motors, etc. The motor drive unit 223 is a motor that is the power source for rotating the scanner motor, photosensitive drum 1, developing roller 6, etc., located inside the scanner unit 3, and operates based on control signals from the control unit 220. The high-voltage power supply 224 is a power supply that supplies high voltage to the photosensitive drum 1, charging roller 2, developing roller 6 of the developing unit 5, transfer roller 11, fixing unit 12, etc. In addition, the non-volatile memory 50 provided in the developing unit 5 and the non-volatile memory 51 provided in the toner cartridge 13 are connected to the controller 201 via the memory communication unit 225. The control unit 220 can read and write information stored in the non-volatile memories 50 and 51 via the memory communication unit 225. In this embodiment, a non-contact non-volatile memory is used as the storage means, but it is not limited to non-contact non-volatile memory. As the storage means, for example, a contact-type non-volatile memory, a non-contact non-volatile memory, or a volatile memory with a backup power supply may be used as appropriate.

[0029] In this embodiment, the control unit 220 is capable of performing a rotation speed counting function and an image dot counting function. The rotation speed counting function counts the rotation speed of the developing roller 6 in order to calculate the lifespan of the developing unit 5 and the toner ejection timing. The image dot counting function counts the number of pixels for which the image signal that irradiates the photosensitive drum 1 with laser light from the scanner unit 3 is on, in order to calculate the print rate of the image formed on the paper 19. This counts the number of image dots (pixels) formed on the photosensitive drum 1. The rotation speed counting function and the image dot counting function are performed by the control unit 220 during the image formation process in which an image is formed on the recording material. The control unit 220, which is the acquisition unit, acquires the counting results and stores the acquired coefficient results in the RAM of the non-volatile memory 50, 51 or memory 221, which will be described later. The print rate is the ratio obtained by dividing the number of pixels that form an image on the paper by the number of pixels that can form an image on the paper. In other words, the print density is also the ratio of the number of pixels with an image signal turned on to the total number of pixels in the image formed on the recording material.

[0030] [Information stored in non-volatile memory] In this embodiment, the non-volatile memory 50 of the developing unit 5 and the non-volatile memory 51 of the toner cartridge 13 store information regarding the amount of toner filled in the toner storage section 17 and the toner cartridge 13, respectively. When filling the developing unit 5 and the toner cartridge 13 with toner during manufacturing, manufacturing variations (tolerances for the amount of toner filled during manufacturing) inevitably occur. The amount of manufacturing variation that occurs during manufacturing can be determined by comparing the amount of toner actually filled during manufacturing with the center value of the manufacturing variation. The amount of toner actually filled during manufacturing is also the amount of toner when new or unused. The center value of the manufacturing variation is the manufacturing center value that includes the tolerance for the amount of toner filled during manufacturing, and the center value of the tolerance when filling the toner (filling tolerance center value). In this embodiment, the non-volatile memory 50 of the developing unit 5 stores the standard filled toner amount Dc, which is the filling tolerance center value, and the actual amount of toner filled during manufacturing Dr. On the other hand, the non-volatile memory 51 of the toner cartridge 13 stores the standard toner amount Tc, which is the center value of the filling tolerance, and the actual toner amount Tr that was filled during manufacturing. Details of the toner amounts Dc, Dr, Tc, and Tr will be described later.

[0031] In addition to the toner amounts Dc and Dr mentioned above, the non-volatile memory 50 stores the following information as unique information of the developing unit 5. Specifically, the non-volatile memory 50 stores the cumulative rotational speed of the developing roller 6 counted by the rotational speed counting function mentioned above, the cumulative value of the number of image dots counted by the image dot counting function, and a system program for controlling the image forming apparatus 100. Furthermore, the non-volatile memory 50 stores system data such as the number of sheets of paper on which images have been formed, information regarding the lifespan of the developing unit 5, information regarding the remaining toner amount, various adjustment values, the serial number of the developing unit 5, and the manufacturing date.

[0032] Similarly, in addition to the toner amounts Tc and Tr mentioned above, the non-volatile memory 51 stores the following information as unique information for the toner cartridge 13. Specifically, the non-volatile memory 51 stores the cumulative value of the number of image dots counted by the image dot counting function, the number of sheets of paper on which images were formed, information regarding the lifespan of the toner cartridge 13, information regarding the remaining toner amount, and various adjustment values. Furthermore, the non-volatile memory 51 also stores system data such as the serial number and manufacturing date of the toner cartridge 13.

[0033] [Toner refill amount information] Next, we will explain the information regarding the toner filling amount stored in the non-volatile memory 50 of the developing unit 5 and the non-volatile memory 51 of the toner cartridge 13. In this embodiment, in the initial state when the user starts using the developing unit 5 (new and unused), the developing unit 5 is filled with 40g ± 5g of toner. Here, "40g" is the standard toner filling amount (standard toner amount), which is the center value of the filling tolerance, and "±5g" indicates that the upper limit of the tolerance for variation in the amount of toner filled during manufacturing is +5g, and the lower limit is -5g. Variation in the amount of toner filled during manufacturing inevitably occurs due to device errors in the toner filling device, differences in the fluidity of each toner manufacturing lot, etc.

[0034] The non-volatile memory 50 of the developing unit 5 stores individual data regarding the amount of toner filled. In this embodiment, the standard toner filled amount Dc and the actual toner filled amount Dr, which is the first initial amount of toner contained in the developing unit 5 when unused, are stored. For example, if the actual amount of toner filled at the time of manufacture was 43g, then the standard toner filled amount Dc = 40g and the actual toner filled amount Dr = 43g are stored in the non-volatile memory 50. Also, for example, if the actual amount of toner filled at the time of manufacture was 39g, then the standard toner filled amount Dc = 40g and the actual toner filled amount Dr = 39g are stored in the non-volatile memory 50.

[0035] Similarly, the toner cartridge 13 stores individual-specific data regarding the amount of toner filled. In this embodiment, the reference toner filled amount Tc and the actual toner filled amount Tr, which is the first initial amount of toner contained in the unused toner cartridge 13, are stored. In this embodiment, when the user starts using the toner cartridge 13, the toner cartridge 13 is filled with 60g ± 5g of toner. Here, "60g" is the reference toner filled amount (reference toner amount), which is the center value of the filling tolerance, and "±5g" indicates that the upper limit of the tolerance for variation in the amount of toner filled at the time of manufacture is +5g, and the lower limit is -5g. For example, if the actual amount of toner filled in the toner cartridge 13 at the time of manufacture was 65g, then the reference toner filled amount Tc = 60g and the actual toner filled amount Tr = 65 are stored in the non-volatile memory 51.

[0036] In this embodiment, the standard toner filling amount and the actual amount of toner filled are stored in non-volatile memory, but this is not the only way to do so. For example, it is also preferable to store the difference between the standard toner filling amount and the actual amount of toner filled. What is important in this embodiment is that the degree of variation between the standard toner filling amount and the actual amount of toner filled can be determined for each individual developing unit 5 and toner cartridge 13.

[0037] [Trends in toner refill volume] This section describes the changes in the remaining toner levels in the developing unit 5 and toner cartridge 13 of the image forming apparatus 100 in this embodiment. Figure 5 is a graph showing the relationship between the remaining toner levels in the developing unit 5 and toner cartridge 13 and the number of printed sheets. The vertical axis of Figure 5 represents the total remaining toner levels in the developing unit 5 and toner cartridge 13 (in grams), and the horizontal axis represents the number of printed sheets (in sheets).

[0038] For example, let's assume that the standard toner filling amount Dc = 40g stored in the non-volatile memory 50 of the developing unit 5, the actual toner filling amount Dr = 40g, and the toner variation amount is 0g. Also, let's assume that the standard toner filling amount Tc = 60g stored in the non-volatile memory 51 of the toner cartridge 13, the actual toner filling amount Tr = 60g, and the toner variation amount is 0g. When the standard toner filling amount and the actual toner filling amount are the same, the remaining toner amount when the number of printed pages is 0 before printing begins will be 100g (=40g + 60g) (circled number 1 in the figure). In Figure 5, the graph shown by the solid line shows the change in the remaining toner amount when printing is performed at an average print density of 5% under these conditions.

[0039] In this embodiment, the control unit 220 notifies the user to replace the toner cartridge 13 if the remaining amount of toner stored in the toner storage section 17 of the developing unit 5, as detected using the light guide member 42 described above, falls below a preset threshold. In this embodiment, the toner cartridge 13 is replaced when the remaining amount of toner stored in the toner storage section 17 of the developing unit 5 reaches 30g. Therefore, when printing is performed at a print density of 5%, the toner cartridge 13 is replaced at the timing when 5000 sheets of paper have been printed (circled number 2 in the figure), as shown in Figure 5. When the toner cartridge 13 is replaced, toner is supplied from the replaced toner cartridge 13 to the toner storage section 17 of the developing unit 5. For example, if the actual amount of toner filled in the replaced toner cartridge 13 is Tr = 60g, the remaining amount of toner immediately after replacing the toner cartridge 13 will be 90g (= 30g + 60g) (circled number 3 in the figure).

[0040] In Figure 5, the dotted line graph (labeled "Lower Tolerance Limit" in the figure) shows the change in remaining toner when the actual amount of toner filled in the developer unit 5 and toner cartridge 13 is at the lower tolerance limit (-5g) of the standard toner amount. For example, the developer unit 5 has a standard toner amount Dc=40g, but the actual amount of toner filled Dr=35g, and the toner cartridge 13 has a standard toner amount Tc=60g, but the actual amount of toner filled Tr=55g. In this case, the remaining toner when the number of printed pages is 0, before printing begins, is 90g (=35g + 55g). The dotted line graph in Figure 5 shows the change in remaining toner when printing at a print density of 5% in this state.

[0041] On the other hand, in Figure 5, the dashed line graph (labeled "Tolerance Limit" in the figure) shows the change in remaining toner when the actual amount of toner filled in the developer unit 5 and toner cartridge 13 is within the tolerance limit (+5g) of the standard toner amount. For example, the developer unit 5 has a standard toner amount Dc=40g, but the actual amount of toner filled Dr=45g, and the toner cartridge 13 has a standard toner amount Tc=60g, but the actual amount of toner filled Tr=65g. In this case, the remaining toner when the number of printed pages is 0, before printing begins, is 110g (=45g + 65g). The dashed line graph in Figure 5 shows the change in remaining toner when printing at a print density of 5% in this state.

[0042] In Figure 5, as shown by the dotted line graph, the number of printable pages before replacing the toner cartridge 13 is 4285 when the toner filling amount is at the lower tolerance limit of the standard toner filling amount (circled number 2' in the figure). On the other hand, as shown by the dashed line graph, the number of printable pages before replacing the toner cartridge 13 is 5714 when the toner filling amount is at the upper tolerance limit of the standard toner filling amount (circled number 2'' in the figure). Thus, when printing continues at the same print density, the number of printable pages before replacing the toner cartridge 13 differs depending on the tolerance variation of the toner filling amount contained in the developing unit 5 and the toner cartridge 13.

[0043] [Toner ejection control] Next, the toner ejection control in this embodiment will be described. Figure 6 is a flowchart showing the control sequence of toner ejection control in this embodiment. The process shown in Figure 6 is started when a print job is received from an external computer or the like, and is executed by the control unit 220 of the controller 201. In this embodiment, the amount of toner ejected is determined based on the following information. Specifically, a feature of this embodiment is that the amount of toner ejected is calculated based on the average print density during the period of printing a predetermined number of sheets (250 sheets in this embodiment) and the toner filling amount information stored in the non-volatile memory of the developing unit 5 and the toner cartridge 13. In this embodiment, the control unit 220 counts the number of printed sheets, and the toner ejection process (also called the toner discharge process) of this embodiment is performed each time a predetermined number of sheets (250 sheets in this embodiment) are printed. When the toner ejection process is performed, the count of the number of printed sheets is reset. If the number of printed sheets exceeds the predetermined number due to continuous printing, the toner ejection process of this embodiment is performed when the continuous printing job is completed. Furthermore, the average print density is calculated by the control unit 220 based on the number of dots in the image formed, which is counted by the stroke count dot counting function described above, and the number of printed sheets of paper. In this embodiment, the control unit 220 obtains the average print density in the image forming process of a predetermined number of sheets of paper performed immediately before the toner ejection process described later.

[0044] In this embodiment, when the image forming operation is completed and a predetermined number of sheets of paper have been printed, toner ejection control is executed, and the toner on the developing roller 6 is developed to form a toner image for toner ejection on the photosensitive drum 1. The toner image for ejection formed on the photosensitive drum 1 is then removed by the cleaning member 30 and collected in the waste toner collection container 31. This makes it possible to refresh the deteriorated toner that has been carried around on the developing roller 6, and suppresses the occurrence of image defects such as toner fogging and ghost images.

[0045] In step (hereinafter referred to as S) 101, the control unit 220 executes the received print job. In S102, the control unit 220 determines whether the print job has finished. If the control unit 220 determines that the print job has finished, it proceeds to S103; if it determines that the print job has not finished, it returns to S102.

[0046] In S103, the control unit 220 determines whether it is time to perform toner ejection, based on the value of a counter that counts the number of printed sheets, which indicates that a predetermined number of sheets have been printed or more. In this embodiment, the timing for toner ejection is when the count value of a counter that counts the number of sheets printed since the last toner ejection process is 250 or more, which is a predetermined number. The average print rate is the print rate during the period from the last toner ejection process until 250 or more sheets of paper have been printed. If the control unit 220 determines that it is time to perform toner ejection, it proceeds to S104; otherwise, it terminates the process.

[0047] In S104, the control unit 220 resets the value of the counter that counts the number of printed sheets of paper, and obtains the reference toner filling amount Dc and the actual toner filling amount Dr from the non-volatile memory 50 provided in the developing unit 5 via the memory communication unit 225. In S105, the control unit 220 subtracts the reference toner filling amount Dc from the obtained actual toner filling amount Dr to calculate the variation amount a (=Dr-Dc) of the toner filling amount in the developing unit 5.

[0048] In S106, the control unit 220 obtains the reference toner filling amount Tc and the actual toner filling amount Tr from the non-volatile memory 51 provided in the toner cartridge 13 via the memory communication unit 225. In S107, the control unit 220 calculates the variation amount b (=Tr-Tc) of the toner filling amount in the toner cartridge 13 from the obtained reference toner filling amount Tc and the actual toner filling amount Tr.

[0049] Here, each time the toner ejection process is executed, the variation amount a of the toner filling amount in the developing unit 5 and the variation amount b of the toner filling amount in the toner cartridge 13 are calculated. For example, when the developing unit 5 and the toner cartridge 13 are installed in the image forming apparatus 100, the standard toner filling amount and the actually filled toner filling amount are obtained from the non-volatile memory 50 of the developing unit 5 and the non-volatile memory 51 of the toner cartridge 13. Then, based on the obtained standard toner filling amount and the actually filled toner filling amount of the developing unit 5 and the toner cartridge 13, the variation amounts a and b are calculated and stored in the memory 221 of the controller 201. These can then be read when the toner ejection process is executed.

[0050] In S108, the control unit 220 determines whether the actual toner filling amount is greater than the standard toner filling amount (a+b>0?) based on the variation amounts a and b of the toner filling amounts in the developing unit 5 and the toner cartridge 13. If the control unit 220 determines that the actual toner filling amount is greater than the standard toner filling amount (a+b>0), it proceeds to S109. On the other hand, if the control unit 220 determines that the actual toner filling amount is the same as the standard toner filling amount or less than the standard toner filling amount (a+b≦0), it proceeds to S112.

[0051] In steps S105 and S107, the variation in toner filling amount is calculated separately for the developer unit 5 and the toner cartridge 13. In step S108, the variation in toner filling amount calculated separately for the developer unit 5 and the toner cartridge 13 is added together to determine whether the total variation in toner filling amount for the developer unit 5 and the toner cartridge 13 is positive or negative. For example, the variation in toner filling amount for the developer unit 5 and the toner cartridge 13 can be calculated by taking the total initial toner amount as the sum of the toner actually filled in the developer unit 5 and the toner cartridge 13. Then, the difference can be calculated by subtracting the sum of the standard toner filling amounts for the developer unit 5 and the toner cartridge 13 from the calculated sum of the toner actually filled in the developer unit 5 and the toner cartridge 13.

[0052] In S109, the control unit 220 determines whether the average print rate in the section where a predetermined number of sheets (250 sheets in this embodiment) are printed is less than a predetermined print rate of 2% (print rate < 2%). If the control unit 220 determines that the average print rate is less than 2% (first print rate), it proceeds to S110; if it determines that the average print rate is 2% or more (second print rate), it proceeds to S111.

[0053] In S110, the control unit 220 calculates the toner discharge amount Pα when the actual toner charge is greater than the standard toner charge and the average print coverage is less than 2%, and proceeds to S115. The first toner discharge amount Pα is the sum of the toner amount corresponding to the difference between the actual toner charge and the standard toner charge, and the toner amount consumed to make the average print coverage equal to the predetermined print coverage of 2%. The difference between the actual toner charge and the standard toner charge is the difference obtained by subtracting the sum of the standard toner charge amounts for the developer unit 5 and toner cartridge 13 from the sum of the toner amounts charged in the unused developer unit 5 and toner cartridge 13. The toner amount consumed to make the average print coverage equal to the predetermined print coverage of 2% refers to the following toner amounts. In other words, it is the difference between the amount of toner consumed when printing a predetermined number of pages at a predetermined print density of 2% and the amount of toner consumed when printing a predetermined number of pages at a first print density. The method for calculating the ejected toner amount Pα will be described later.

[0054] In S111, the control unit 220 calculates the ejected toner amount Pβ, which is the toner discharge amount when the actual toner filling amount is greater than the standard toner filling amount and the average print density is 2% or more, and proceeds to S115. The ejected toner amount Pβ, which is the third toner discharge amount, is the amount of toner corresponding to the difference between the actual toner filling amount and the standard toner filling amount. Here, the difference between the actual toner filling amount and the standard toner filling amount is the difference obtained by subtracting the sum of the standard toner filling amounts of the developer unit 5 and toner cartridge 13 from the sum of the toner amounts filled in the developer unit 5 and toner cartridge 13 in an unused state. The method for calculating the ejected toner amount Pβ will be described later.

[0055] In S112, the control unit 220 determines whether the average print rate in the section where a predetermined number of sheets of paper are printed is less than 2% (print rate < 2%). If the control unit 220 determines that the average print rate is less than 2% (first print rate), it proceeds to S113; if it determines that the average print rate is 2% or more (second print rate), it terminates the process.

[0056] In S113, the control unit 220 calculates the toner discharge amount Pγ when the actual toner filling amount is the same as or less than the standard toner filling amount (less than or equal to the standard toner amount) and the average print rate is less than 2%, and proceeds to S114. The second toner discharge amount Pγ is the sum of the toner amount corresponding to the difference between the actual toner filling amount and the standard toner filling amount, and the toner amount consumed to make the average print rate equal to the predetermined print rate of 2%. Here, the difference between the actual toner filling amount and the standard toner filling amount is the difference obtained by subtracting the sum of the standard toner filling amounts of the developer unit 5 and toner cartridge 13 from the sum of the toner amounts filled in the developer unit 5 and toner cartridge 13 in an unused state. The toner amount consumed to make the average print rate equal to the predetermined print rate of 2% refers to the following toner amounts. In other words, it is the difference between the amount of toner consumed when printing a predetermined number of pages at a predetermined print density of 2% and the amount of toner consumed when printing a predetermined number of pages at a first print density. In this case, since the actual amount of toner filled is the same as or less than the standard amount of toner filled, the amount of toner corresponding to the difference between the actual amount of toner filled and the standard amount of toner filled will be 0 or less. Therefore, the ejected toner amount Pγ can be positive, 0, or negative. The method for calculating the ejected toner amount Pγ will be described later.

[0057] In S114, the control unit 220 determines whether the toner output amount Pγ calculated in S112 is a positive value (Pγ>0?). If the control unit 220 determines that the toner output amount Pγ is a positive value and there is toner to be output, it proceeds to S115. On the other hand, if the control unit 220 determines that the toner output amount Pγ is 0 or a negative value and there is no toner to be output, it terminates the process.

[0058] In S115, the control unit 220 executes a toner ejection process to eject the calculated amount of toner. Since the amount of toner per pixel (dot) that makes up the toner image is known in advance, the control unit 220 calculates the number of pixels (dots) required for the amount of toner to be ejected by dividing the amount of toner to be ejected by the amount of toner per pixel (dot). Next, the control unit 220 controls the scanner unit 3 to output an ON image signal that irradiates the photosensitive drum 1 with laser light for the number of pixels required for the amount of toner to be ejected, thereby forming an electrostatic latent image on the photosensitive drum 1. Then, similar to the image formation operation on paper, the control unit 220 applies toner from the developing roller 6 to the electrostatic latent image formed on the photosensitive drum 1, forming a toner image for the toner ejection process on the photosensitive drum 1. The toner image for ejection formed on the photosensitive drum 1 is removed by the cleaning member 30 without being transferred to the paper and is collected in the waste toner collection container 31, thus consuming the calculated amount of toner to be ejected. The control unit 220 terminates the process once the toner ejection process described above is completed. When the toner ejection process is performed, no paper is fed, and the photosensitive drum 1 and the transfer roller 11 are separated.

[0059] [Method for calculating toner output] In this embodiment, the amount of toner ejected during the toner ejection process is calculated by adding the amount of toner ejected relative to the tolerance of the toner filling amount to the amount of toner ejected corresponding to the actual toner consumption. On the other hand, in conventional toner ejection processes, the amount of toner ejected is the amount of toner ejected corresponding to the actual toner consumption, and the tolerance of the toner filling amount in the developing unit 5 and the toner cartridge 13 is not taken into consideration when calculating the amount of toner ejected. Therefore, a toner cartridge 13 with a small amount of filled toner at the lower tolerance limit will reach its replacement time sooner than a toner cartridge 13 with a large amount of filled toner at the upper tolerance limit. On the other hand, from the perspective of toner degradation, a toner cartridge 13 with a large amount of filled toner at the upper tolerance limit will have more time for the toner to be carried around by the developing roller 6 than a toner cartridge 13 with a small amount of filled toner at the lower tolerance limit. Therefore, toner degradation progresses, and image defects such as toner fogging and ghost images are more likely to occur.

[0060] Next, we will explain how to calculate the toner discharge amounts Pα, Pβ, and Pγ mentioned above. The toner discharge amounts Pα, Pβ, and Pγ are calculated using the following equations (Equation 1), (Equation 2), and (Equation 3), respectively. Toner output Pα = ((a+b) / (Y / X)) + d(1-f / e)··(Equation 1) Toner output Pβ = ((a+b) / (Y / X)) ··(Equation 2) Toner output Pγ = ((a+b) / (Y / X)) + d(1-f / e)··(Equation 3) The parameters in (Equation 1) to (Equation 3) are as follows: a: Variation in the toner filling amount of the developing unit 5 (=Dr-Dc) b: Variation in the filling amount of toner cartridge 13 (=Tr-Tc) X: The number of pages printed that will trigger the toner ejection process (250 pages in this example). Y: Number of prints corresponding to the lifespan of toner cartridge 13 d: Toner consumption when printing X pages on A4 size paper at a print density of 2% (predetermined standard value) e: The total number of image pixels / dots when printing X sheets of A4 paper at a print density of 2% (a predetermined standard value). f: Total number of image pixels / dots when printed on X sheets of A4 paper.

[0061] In equations (1) to (3) described above, the term ((a+b) / (Y / X)) calculates the amount of toner ejected relative to the tolerance of the toner filling amount in the toner ejection process, which is a characteristic of this embodiment. Specifically, (a+b) calculates the total tolerance of the toner filling amounts of the developing unit 5 and the toner cartridge 13, and (Y / X) calculates the number of times the toner ejection process (performed every X pages) will be performed until the lifespan of the toner cartridge 13 reaches Y pages. Furthermore, the term d(1-f / e) calculates the amount of toner ejected per toner ejection process, according to the actual toner consumption when the print coverage is 2% or less.

[0062] Next, we will explain the calculation examples of the ejected toner amounts Pα, Pβ, and Pγ mentioned above. First, we will explain the calculation examples of ejected toner amounts Pα and Pβ when the actual toner filling amount is greater than the standard toner filling amount. Here, we assume that the toner filling amount error a of the developing unit 5 = 5000 mg, the filling amount error b of the toner cartridge 13 = 5000 mg, the number of pages per toner ejection interval X = 250 pages, and the lifespan of the toner cartridge 13 Y = 2000 pages. Furthermore, we assume that the toner consumption d when printing X pages = 1250 mg, and the ratio of the total number of image pixel dots e when printing X pages to the total number of image pixel dots f when actually printing X pages = 2:1. Substituting the values ​​of each parameter mentioned above into (Equation 1), the amount of toner ejected Pα is ((5000mg + 5000mg) / (2000 sheets / 250 sheets)) + 1250mg × (1 - 1 / 2) = 1250mg + 625mg = 1875mg. Similarly, substituting the values ​​of each parameter mentioned above into (Equation 2), the amount of toner ejected Pβ is ((5000mg + 5000mg) / (2000 sheets / 250 sheets)) = 1250mg.

[0063] Next, we will explain an example of calculating the ejected toner amount Pγ when the actual toner filling amount is the same as or less than the standard toner filling amount. Here, we assume that the toner filling amount error a of the developing unit 5 is -5000mg, the filling amount error b of the toner cartridge 13 is -5000mg, the number of pages X for toner ejection execution interval is 250 pages, and the lifespan of the toner cartridge 13 is Y is 2000 pages. Furthermore, we assume that the toner consumption d when printing X pages is 1250mg, and the ratio of the total number of image pixel dots e when printing X pages to the total number of image pixel dots f when actually printing X pages is 2:1. Substituting the values ​​of each parameter mentioned above into (Equation 3), the ejected toner amount Pα is ((-5000mg-5000mg) / (2000 pages / 250 pages))+1250mg×(1-1 / 2)=-1250mg+625mg=-625mg. In this case, since the toner ejection amount Pγ is a negative value, the toner ejection process is not performed.

[0064] As explained above, the amount of toner ejected Pα is controlled to be greater than the amount of toner ejected Pβ. Furthermore, the amount of toner ejected Pα is controlled to be greater than the amount of toner ejected Pγ.

[0065] [Evaluation of toner ejection performance] To verify the effectiveness of the toner ejection performance in this embodiment, a comparative study was conducted comparing the toner ejection performance of this embodiment, which uses the toner ejection process described above, with that of a comparative example using a conventional toner ejection process. As described above, the amount of toner ejected in this embodiment is calculated by adding the amount of toner ejected relative to the tolerance of the toner filling amount to the amount of toner ejected corresponding to the actual toner consumption. On the other hand, the amount of toner ejected in the comparative example is the amount of toner ejected corresponding to the actual toner consumption, and the tolerance of the toner filling amount in the developing unit 5 and the toner cartridge 13 is not considered in the calculation of the amount of toner ejected.

[0066] (1) Changes in remaining toner when the actual amount of toner filled is greater than the standard amount of toner filled, and the average print density is less than 2%. In this embodiment, when the actual toner filling amount is greater than the standard toner filling amount, and the average print density is less than 2%, an example of the change in the remaining toner amount when toner ejection is performed will be explained using Figure 7. The vertical axis of Figure 7 shows the total amount of toner contained in the developing unit 5 and the toner cartridge 13 (unit: g), and the horizontal axis shows the number of printed pages (unit: pages).

[0067] Here, since the actual amount of toner filled is greater than the standard amount of toner filled, the standard amount of toner filled in the developer unit 5, Dc = 40g, and the actual amount of toner filled, Dr = 45g, are stored in the non-volatile memory 50 of the developer unit 5. Similarly, the standard amount of toner filled in the toner cartridge 13, Tc = 60g, and the actual amount of toner filled, Tr = 65g, are stored in the non-volatile memory 51 of the toner cartridge 13. When the tolerance for toner amounts is at the upper limit, the remaining toner amount when the number of printed pages is 0 is 110g (= 45g + 65g). In Figure 7, the graph shown by the solid line shows the change in the remaining toner amount when printing is performed under these conditions while maintaining a low print density of 1%.

[0068] Next, we will explain the toner level change in the comparative example where the toner level is 110g when the number of printed pages is 0. In conventional toner ejection control, if printing is performed continuously at a predetermined print density or lower, toner ejection control is performed so that the toner consumption corresponds to the predetermined print density. In this comparative example, when the print density is less than 2%, toner ejection is performed periodically to bring the print density to 2%. In Figure 7, the graph shown by the dashed line shows the toner level change in the comparative example.

[0069] Next, we will explain the change in the remaining toner amount in this embodiment when the remaining toner amount is 110g when the number of printed pages is 0. In the toner ejection control of this embodiment, in addition to the toner ejection amount based on the print rate in the comparative example described above, toner ejection is performed taking into account the toner filling tolerance in the developing unit 5 and the toner cartridge 13. In this embodiment, toner ejection is performed every 250 printed pages to refresh the toner on the developing roller 6. Therefore, the ejected toner amount Pα is ((5000mg + 5000mg) / (2000 pages / 250 pages)) + 1250mg × (1 - 1 / 2) = 1875mg from (Equation 1), which is 1250mg more than in the comparative example. Then, the toner ejection process of 1875mg of toner is performed. In Figure 7, the graph shown by the dotted line shows the change in the remaining toner amount in this embodiment.

[0070] In this embodiment and comparative example, the toner cartridge 13 is replaced when the toner level reaches 30g. As shown in Figure 7, this embodiment dispenses a larger amount of toner than the comparative example. Therefore, the toner cartridge 13 is replaced earlier in this embodiment than in the comparative example.

[0071] (2) Changes in remaining toner when the actual amount of toner filled is greater than the standard amount of toner filled, and the average print density is 2% In this embodiment, when the actual toner filling amount is greater than the standard toner filling amount, and the average print density is 2%, an example of the change in the remaining toner amount when toner ejection is performed will be explained using Figure 8. The vertical axis of Figure 8 shows the total amount of toner contained in the developing unit 5 and the toner cartridge 13 (unit: g), and the horizontal axis shows the number of printed pages (unit: pages).

[0072] Here, since the actual amount of toner filled is greater than the standard amount of toner filled, the standard amount of toner filled in the developer unit 5, Dc = 40g, and the actual amount of toner filled, Dr = 45g, are stored in the non-volatile memory 50 of the developer unit 5. Similarly, the standard amount of toner filled in the toner cartridge 13, Tc = 60g, and the actual amount of toner filled, Tr = 65g, are stored in the non-volatile memory 51 of the toner cartridge 13. When the tolerance for toner amounts is at the upper limit, the remaining toner amount when the number of printed pages is 0 is 110g (= 45g + 65g). In Figure 8, the graph shown by the solid line shows the change in the remaining toner amount when printing is performed while maintaining a low print density of 2%.

[0073] Next, we will explain the toner level change in the comparative example where the toner level is 110g when the number of printed pages is 0. In conventional toner ejection control, if printing is performed continuously at a predetermined print density or lower, toner ejection control is performed so that the toner consumption corresponds to the predetermined print density. In this comparative example, when the print density is 2% or less, toner ejection processing is performed periodically to bring the print density to 2%. However, since the print density in this case is 2%, toner ejection control is not performed. Therefore, the toner level change in the comparative example is the same as the graph shown by the solid line in Figure 8.

[0074] Next, we will explain the change in the remaining toner amount in this embodiment when the remaining toner amount is 110g when the number of printed pages is 0. In the toner ejection control of this embodiment, since the print coverage rate is 2%, toner ejection is not performed according to the print coverage rate, but rather toner ejection is performed considering the toner filling tolerance in the developing unit 5 and the toner cartridge 13. In this embodiment, the toner on the developing roller 6 is refreshed every 250 printed pages. Therefore, the ejected toner amount Pβ is ((5000mg + 5000mg) / (2000 pages / 250 pages)) = 1250mg, which is 1250mg more than in the comparative example. Then, the toner ejection process of 1250mg of toner is performed. In Figure 8, the graph shown by the dotted line shows the change in the remaining toner amount in this embodiment.

[0075] In this embodiment and comparative example, the toner cartridge 13 is replaced when the toner level reaches 30g. As shown in Figure 8, this embodiment dispenses a larger amount of toner than the comparative example. Therefore, the toner cartridge 13 is replaced earlier in this embodiment than in the comparative example.

[0076] (3) Changes in remaining toner when the actual amount of toner filled is less than the standard amount of toner filled and the average print rate is less than 2% In this embodiment, when the actual toner filling amount is less than the standard toner filling amount and the average print density is less than 2%, an example of the change in the remaining toner amount when toner ejection is performed will be explained using Figure 9. The vertical axis of Figure 9 shows the total amount of toner contained in the developing unit 5 and the toner cartridge 13 (unit: g), and the horizontal axis shows the number of printed pages (unit: pages).

[0077] Here, since the actual toner filling amount is less than the standard toner filling amount, the standard toner filling amount Dc = 40g and the actual toner filling amount Dr = 35g are stored in the non-volatile memory 50 of the developing unit 5. Similarly, the standard toner filling amount Tc = 60g and the actual toner filling amount Tr = 55g are stored in the non-volatile memory 51 of the toner cartridge 13. When the tolerance for toner amounts is at the lower limit, the remaining toner amount when the number of printed pages is 0 is 90g (= 35g + 55g). The graph shown by the solid line in Figure 9 shows the change in the remaining toner amount when printing is performed under these conditions, while maintaining a low print density of 1%.

[0078] Next, we will explain the toner level change in the comparative example where the toner level is 90g when the number of printed pages is 0. In conventional toner ejection control, if printing is performed continuously at a predetermined print density or lower, toner ejection control is performed so that the toner consumption corresponds to the predetermined print density. In this comparative example, when the print density is less than 2%, toner ejection is performed periodically to bring the print density to 2%. In Figure 9, the dotted line graph shows the toner level change in the comparative example.

[0079] Next, we will explain the change in the remaining toner amount in this embodiment when the remaining toner amount is 90g when the number of printed pages is 0. In the toner ejection control of this embodiment, in addition to the toner ejection amount based on the print rate in the comparative example described above, toner ejection is performed taking into account the toner filling tolerance in the developing unit 5 and the toner cartridge 13. In this embodiment, toner ejection is performed every 250 printed pages to refresh the toner on the developing roller 6. Therefore, the ejected toner amount Pγ is ((-5000mg-5000mg) / (2000 pages / 250 pages))+1250mg×(1-1 / 2)=-625mg from (Equation 3), and since the ejected toner amount is a negative number, the toner ejection process is not performed. In Figure 9, the graph shown by the dashed line shows the change in the remaining toner amount in this embodiment.

[0080] In this case, since the toner ejection amount Pγ calculated by (Equation 3) is a negative number, the toner ejection process is not performed. However, if, for example, the toner ejection amount Pγ is a positive number, the toner ejection process for the calculated toner ejection amount Pγ will be performed.

[0081] In this embodiment and comparative example, the toner cartridge 13 is replaced when the remaining toner level reaches 30g. As shown in Figure 9, in this embodiment, toner consumption due to the toner ejection process is reduced compared to the comparative example. Therefore, since the comparative example ejects more toner than this embodiment, it can be seen that the toner cartridge 13 needs to be replaced earlier in the comparative example than in this embodiment.

[0082] Furthermore, the above example described the case where the filled toner amount is at the lower or upper tolerance limit. Regarding the filled toner amount, for example, the amount of toner filled in the developing unit 5 may be at the lower tolerance limit and the amount of toner filled in the toner cartridge 13 may be at the upper tolerance limit, or vice versa. In addition, the filled toner amount may be within the range of the standard filled toner amount and the lower or upper tolerance limit. In each case, the corresponding ejected toner amounts Pα, Pβ, and Pγ described above should be calculated and the toner ejection process should be performed.

[0083] [Evaluation of toner degradation suppression] Next, in order to verify the effect of this embodiment on suppressing toner degradation, a comparative study was conducted comparing the effect of this embodiment, which uses the toner ejection process described above, with a comparative example that uses a conventional toner ejection process. For the comparative study, the degree of toner degradation D was calculated based on the calculation method described below, and the effect of suppressing toner degradation in this embodiment and the comparative example was compared based on the calculated degree of toner degradation D. In this embodiment, in order to simplify the explanation, the degree of toner degradation D was calculated every time two sheets of paper as a recording medium were printed, but it is not necessarily required to calculate it every two sheets. For example, it may be calculated for each print job, every predetermined number of printed sheets, or every predetermined distance traveled by the developing roller 6.

[0084] In this embodiment, the toner degradation degree Dn is calculated using the following equations (4) and (5). Dn=(j / (k-1))+j×log((k-1) / (kn))...(Equation 4) Here, j = t / s, k = T0 / s... (Equation 5) The parameters in (Equation 4) and (Equation 5) are as follows: Dn: Toner degradation level at the end of development roller 6's operation after printing the nth sheet of paper. t: Toner weight per unit area on the developing roller 6 (mg / cm²) 2 ) × Toner coating width (cm) on developing roller 6 × Rotation distance of the developing roller 6 when printing one sheet of paper (cm) s: Toner consumption (g) T0: Toner refill amount (g)

[0085] The toner degradation degree Dn calculated by (Equation 4) and (Equation 5) indicates the number of times the toner coated on the developing roller 6 is rubbed against the developing blade 7, which is a developer regulating member. The toner degrades as it is repeatedly rubbed against the developing blade 7, causing the external additives added to the toner to be released or embedded. The degree of toner degradation is proportional to the amount of toner in the developing unit 5. When there is a large amount of toner remaining in the developing unit 5, the proportion of toner coated on the developing roller 6 is small, so the toner does not degrade. On the other hand, as the amount of toner remaining in the developing unit 5 decreases, the proportion of toner coated on the developing roller 6 increases, thus accelerating the degree of toner degradation. Furthermore, the toner degradation degree Dn is also proportional to the printing speed of the image forming apparatus 100. As the printing speed increases, the rotation speed of the photosensitive drum 1 increases, and consequently, the rotation speed of the developing roller 6 also increases. As a result, even if the amount of toner remaining in the developing unit 5 is the same, the frequency of friction of the toner coated on the developing roller 6 increases or decreases depending on the rotation speed of the developing roller 6, causing a difference in the toner degradation degree Dn. In this embodiment, the inventors have confirmed that when the toner degradation degree Dn exceeds 140, toner fogging occurs on the image.

[0086] Therefore, in this embodiment, toner ejection control is implemented so that the toner degradation level Dn remains below 140 times throughout the product life of the developing unit 5. Furthermore, when the actual amount of toner filled is less than the standard toner filling amount, and the tolerance of the toner filling amount remains at the lower limit, the toner ejection control may eject excessive toner. Therefore, in this embodiment, when there is a margin for the increase in toner degradation level Dn, the control is characterized by reducing the amount of toner ejected or not ejecting toner at all.

[0087] In the following section, similar to the comparison of toner ejection performance in this embodiment and the comparative example described above, we will compare the toner filling tolerance and the degree of toner degradation according to the average print density in this embodiment and the comparative example.

[0088] (1) Comparison of toner degradation when the actual toner filling amount is greater than the standard toner filling amount and the average print density is less than 2%. In the comparative example, without considering the tolerance of the toner filling amount, when printing at a low print density of less than 2%, toner ejection control is performed sequentially so that the print density becomes the predetermined print density of 2%. On the other hand, in the toner ejection control of this embodiment, the amount of toner ejected according to the tolerance of the toner filling amount is added to the amount of toner ejected according to the actual toner consumption. Figure 10 is a graph showing the calculation results calculated based on the graphs of this embodiment and the comparative example shown in Figure 7 above. In Figure 10, the horizontal axis shows the number of printed sheets (unit: sheets), and the vertical axis shows the number of toner rubbings (unit: times). In Figure 10, the graph shown with a solid line shows the relationship between the number of printed sheets and the number of toner rubbings in this embodiment, and the graph shown with a dashed line shows the relationship between the number of printed sheets and the number of toner rubbings in the comparative example.

[0089] As shown in Figure 10, in this embodiment, the number of toner strokes is reduced compared to the comparative example. In the image forming apparatus 100 of this embodiment, if the number of toner strokes exceeds 140, image defects occur due to toner fogging caused by toner deterioration. In the toner ejection control of the comparative example, the amount of toner ejected on the developing roller 6 is insufficient, and the number of toner strokes may exceed 140, resulting in image defects. On the other hand, in this embodiment, no image defects occurred until the end of the product life of the developing unit 5 (50,000 prints in this embodiment). Thus, by performing toner ejection control that takes into account the actual amount of toner filled in the developing unit 5 and the toner cartridge 13, the occurrence of image defects can be suppressed.

[0090] (2) Comparison of toner degradation when the actual toner filling amount is greater than the standard toner filling amount and the average print density is 2% In the comparative example, without considering the tolerance of the toner filling amount, toner ejection control is performed sequentially to bring the print density to a predetermined print density of 2% during low print density printing of less than 2%, but when the average print density is 2%, toner ejection control is not performed. On the other hand, in the toner ejection control of this embodiment, toner ejection is not performed according to the actual toner consumption, but rather toner ejection is performed according to the toner ejection amount according to the tolerance of the toner filling amount. Figure 11 is a graph showing the calculation results calculated based on the graphs of this embodiment and the comparative example shown in Figure 8 above. In Figure 11, the horizontal axis shows the number of printed sheets (unit: sheets), and the vertical axis shows the number of toner strokes (unit: strokes). In Figure 11, the graph shown with a solid line shows the relationship between the number of printed sheets and the number of toner strokes in this embodiment, and the graph shown with a dashed line shows the relationship between the number of printed sheets and the number of toner strokes in the comparative example.

[0091] As shown in Figure 11, in this embodiment, the number of toner strokes is reduced compared to the comparative example. In the image forming apparatus 100 of this embodiment, if the number of toner strokes exceeds 140, image defects occur due to toner fogging caused by toner deterioration. In the toner ejection control of the comparative example, the amount of toner ejected on the developing roller 6 is insufficient, and the number of toner strokes may exceed 140, resulting in image defects. On the other hand, in this embodiment, no image defects occurred until the end of the product life of the developing unit 5 (50,000 prints in this embodiment). Thus, by performing toner ejection control that takes into account the actual amount of toner filled in the developing unit 5 and the toner cartridge 13, the occurrence of image defects can be suppressed.

[0092] (3) Comparison of toner degradation when the actual toner filling amount is less than the standard toner filling amount and the average print density is less than 2% In the comparative example, without considering the tolerance of the toner filling amount, when printing at a low print density of less than 2%, toner ejection control is performed sequentially so that the print density becomes the predetermined print density of 2%. However, if the actual toner filling amount is less than the standard toner filling amount, performing the toner ejection process constitutes excessive toner ejection control. On the other hand, in the toner ejection control of this embodiment, if the toner ejection amount, which is the sum of the toner ejection amount according to the actual toner consumption and the toner ejection amount according to the tolerance of the toner filling amount, is 0 or less, the toner ejection process is not performed. Figure 12 is a graph showing the calculation results calculated based on the graphs of this embodiment and the comparative example shown in Figure 9 above. In Figure 12, the horizontal axis shows the number of printed sheets (unit: sheets), and the vertical axis shows the number of toner rubbings (unit: times). In Figure 12, the graph shown with a solid line shows the relationship between the number of printed sheets and the number of toner rubbings in this embodiment, and the graph shown with a dashed line shows the relationship between the number of printed sheets and the number of toner rubbings in the comparative example.

[0093] As shown in Figure 12, in this embodiment, the amount of toner ejected is less than in the comparative example, resulting in an increase in the number of toner rubbings. However, the number of toner rubbings does not exceed 140, which is the degradation limit value at which toner degradation causes image defects due to toner fogging. Therefore, no image defects occur. In this way, by controlling the toner ejection while considering the actual amount of toner filled in the developing unit 5 and the toner cartridge 13, the occurrence of image defects can be suppressed.

[0094] As described above, in this embodiment, the manufacturing tolerance of the amount of toner filled in the developing unit 5 of the process cartridge 70 and the toner cartridge 13, as well as toner ejection control according to the user's usage, are considered. As a result, compared to conventional examples that do not consider the manufacturing tolerance of the filled toner amount, when ejecting toner to suppress toner degradation, the filling tolerance during manufacturing is taken into consideration, and toner ejection is performed with a more accurate amount of toner ejection, thereby efficiently suppressing toner degradation. Consequently, in this embodiment, the occurrence of image defects due to toner fogging caused by toner degradation can be suppressed, and if the amount of toner ejected is excessive, toner ejection can be suppressed, thereby making effective use of the filled toner.

[0095] Furthermore, in this embodiment, the toner cartridge 13 that replenishes toner to the developing unit 5 of the image forming apparatus 100 of a monochrome printer was described using an example that can be installed in the developing unit 5. For example, in a color printer, toner replenishment cartridges are arranged corresponding to the process cartridges of each toner color, and a toner transport device transports and replenishes toner from the toner replenishment cartridges in accordance with the toner consumption in the process cartridges. This embodiment can also be applied to toner replenishment cartridges that have a memory that stores information about the standard toner filling amount and the actual amount of toner filled, even in such a configuration.

[0096] As explained above, this embodiment makes it possible to prevent a decrease in image quality due to toner degradation. [Explanation of Symbols]

[0097] 1 Photosensitive drum 5. Developing Unit 6. Developing roller 13 Toner Cartridges 17 Toner storage section 220 Control Unit

Claims

1. Photosensitive drum and A developing unit including a developing roller that carries toner for supplying toner to the photosensitive drum and a toner storage section that houses the toner, A toner cartridge containing toner for replenishment in the toner storage section, A control unit capable of performing an image forming process for supplying toner from the developing roller to the photosensitive drum and forming a toner image on the photosensitive drum for transfer to recording material, and a toner discharge process for discharging toner from the developing roller to the photosensitive drum, wherein the control unit performs the toner discharge process each time the image forming process is performed on a predetermined number of recording materials, An acquisition unit that acquires the average print density in the image forming process of a predetermined number of recording materials performed immediately before the toner discharge process, In an image forming apparatus comprising, If the total amount of toner is defined as the sum of the first initial toner amount contained in the unused developing unit and the second initial toner amount contained in the unused toner cartridge, and the amount of toner discharged from the developing roller to the photosensitive drum during the toner discharge process is defined as the toner discharge amount, The control unit controls the first toner discharge, which is the toner discharge when the total initial toner amount is greater than the reference toner amount and the average print rate is lower than a predetermined print rate, so that the first toner discharge is greater than the second toner discharge, which is the toner discharge when the total initial toner amount is less than the reference toner amount and the average print rate is lower than the first print rate.

2. The image forming apparatus according to claim 1, characterized in that the first toner discharge amount is the sum of the following toner amounts: the difference obtained by subtracting the standard toner amount from the total initial toner amount, divided by the number of printed pages corresponding to the lifespan of the toner cartridge divided by the predetermined number of pages; and the difference obtained by subtracting the toner amount consumed when printing the predetermined number of pages at a first printing rate from the amount of toner consumed when printing the predetermined number of pages at a predetermined printing rate.

3. The image forming apparatus according to claim 1, characterized in that the second toner discharge amount is the sum of the difference obtained by subtracting the standard toner amount from the total initial toner amount, divided by the value obtained by dividing the number of printed pages corresponding to the lifespan of the toner cartridge by the predetermined number of pages, and the difference obtained by subtracting the amount of toner consumed when printing the predetermined number of pages at the first printing rate from the amount of toner consumed when printing the predetermined number of pages at the predetermined printing rate.

4. The image forming apparatus according to any one of claims 1 to 3, characterized in that the control unit controls the first toner discharge to be greater than the third toner discharge, which is the toner discharge when the total initial toner amount is greater than the reference toner amount and the average print rate is higher than the predetermined print rate.

5. The image forming apparatus according to claim 4, characterized in that the third toner discharge amount is the difference obtained by subtracting the standard toner amount from the total initial toner amount, divided by the number of printed pages corresponding to the lifespan of the toner cartridge divided by the predetermined number of pages.

6. The image forming apparatus according to any one of claims 1 to 5, characterized in that the toner discharge process is not performed when the total initial toner amount is less than the standard toner amount and the average print rate is higher than the predetermined print rate (second print rate).

7. The system comprises: an exposure means for exposing the photosensitive drum to form an electrostatic latent image on the photosensitive drum in accordance with the on / off status of an image signal based on image information; and a counting means for counting the number of pixels in which the image signal is on. The image forming apparatus according to any one of claims 1 to 6, characterized in that the printing ratio is the ratio of the number of pixels in which the image signal is turned on to the total number of pixels in the image formed on the recording material.

8. The image forming apparatus according to claim 7, characterized in that the control unit outputs the image signal to the exposure means, in order to discharge toner corresponding to the toner discharge amount from the developing roller to the photosensitive drum in the toner discharge process, the number of ONs corresponding to the toner discharge amount, and to form the electrostatic latent image on the photosensitive drum.

9. The developing unit and the toner cartridge are detachable from the main body of the device, which includes the control unit and the acquisition unit. The developing unit has a developing memory that stores the first initial toner amount, The toner cartridge has a toner cartridge memory that stores a second initial amount of toner. The image forming apparatus according to any one of claims 1 to 8.

10. The image forming apparatus according to claim 9, characterized in that the toner cartridge is detachable from the developing unit.

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