Image forming apparatus

Abstract

The present invention provides an image forming apparatus using a two-component development method that can suppress the decrease in image density caused by carrier contamination at the start of use of the image forming apparatus. [Solution] The image forming apparatus comprises an image forming unit, a toner storage container, a control unit, and a storage unit. The control unit controls the supply of toner from the toner storage container to the developing unit based on the output value of a toner concentration sensor that detects the toner concentration in the two-component developer in the developing unit, and corrects the target value of toner concentration based on the cumulative toner consumption since the start of use of the developing unit. The storage unit stores a first cumulative consumption amount, which is the cumulative consumption amount in the first production line of the image forming apparatus. The control unit calculates a second cumulative consumption amount, which is the cumulative consumption amount due to the setup operation of the image forming apparatus and the image output operation after the start of use, and determines a correction value when correcting the target value of toner concentration using the sum of the first cumulative consumption amount and the second cumulative consumption amount.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer, which includes a developing device that uses a two-component developer composed of a magnetic carrier and toner.

Background Art

[0002] As a developing method using a dry toner in an image forming apparatus using an electrophotographic process, a two-component developing method is known in which a non-magnetic toner is charged using a magnetic carrier, and an electrostatic latent image on an image carrier (photosensitive member) is developed by a magnetic brush composed of toner and carrier formed on a developing roller.

[0003] In a developing device using a two-component developing method, the toner concentration (T / C; the ratio of toner to carrier in the developer) in the developing device is detected by a toner concentration sensor, and new toner is replenished only by the amount corresponding to the decrease due to printing or the like. However, if the output value of the toner concentration sensor changes due to factors other than the toner concentration fluctuation, the toner concentration cannot be correctly detected, and the measured value of the toner concentration may increase beyond the target toner concentration (reference concentration) due to an unintended toner replenishment operation.

[0004] For example, in a certain period at the initial stage of using the developer, a phenomenon occurs in which the carrier is contaminated by an external additive of the toner and the fluidity of the developer decreases. When the fluidity of the developer decreases, the bulk density of the developer decreases, and the output value of the toner concentration sensor is output higher than the actual toner concentration. As a result, toner replenishment is not performed in the developing device, and the toner concentration in the developing device shifts lower than the target value. When the toner concentration shifts lower, the toner charge amount (Q / M) becomes higher than the appropriate value. At this time, the developing voltage is set higher to suppress a decrease in image density, but there is a problem that a desired image density cannot be obtained when the developing voltage reaches the upper limit value. Therefore, a method of predicting carrier contamination from the integrated printing rate (toner consumption) and controlling the toner concentration to reach the target value so that the toner concentration does not shift lower can be considered.

[0005] As a technology for controlling an image forming apparatus based on toner consumption, for example, Patent Document 1 discloses an image forming apparatus in which a toner ejection mode is executed when the amount of toner used, which is added to and stored in memory, becomes equal to the amount of toner used until a toner ejection mode, which is pre-stored in memory, is executed. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2007-148122 [Overview of the project] [Problems that the invention aims to solve]

[0007] Conventionally, the amount of toner consumed on the manufacturing line of an image forming apparatus (cumulative print density) for image density adjustment, etc., was reset at the time of shipment. In other words, the amount of toner consumed on the manufacturing line was not taken into account when the user started using the apparatus. Therefore, if a method was adopted to predict carrier contamination from the cumulative print density, even if the actual cumulative print density reached the specified value and carrier contamination occurred, the toner density was not corrected, which could lead to a decrease in the toner density in the developing device and the resulting image density problem.

[0008] In view of the above problems, the present invention aims to provide an image forming apparatus using a two-component development method that can suppress the decrease in image density caused by carrier contamination at the start of use of the image forming apparatus. [Means for solving the problem]

[0009] To achieve the above objective, the first configuration of the present invention is an image forming apparatus comprising an image forming unit, a toner storage container, a control unit, and a storage unit. The image forming unit comprises an image carrier, a charging device, an exposure device, and a developing device. A photosensitive layer is formed on the surface of the image carrier. The charging device charges the surface of the image carrier. The exposure device exposes the surface of the image carrier, which has been charged by the charging device, to form an electrostatic latent image. The developing device comprises a developing container that contains a two-component developer including a carrier and toner, a developer carrier that is rotatably supported within the developing container and carries the two-component developer on its surface, and a toner concentration sensor that detects the toner concentration in the two-component developer in the developing container, and develops the electrostatic latent image into a toner image. The toner storage container contains toner to be supplied to the developing device. The control unit controls the supply of toner from the toner storage container to the developing device based on the output value of the toner concentration sensor, and corrects the target value of the toner concentration based on the cumulative amount of toner consumed since the start of use of the developing device. The memory unit stores the first cumulative consumption amount, which is the cumulative consumption amount in the first production line of the image forming apparatus. The control unit calculates the second cumulative consumption amount, which is the cumulative consumption amount due to the setup operation of the image forming apparatus and the image output operation after the start of use, and uses the sum of the first and second cumulative consumption amounts to determine the correction value when correcting the target value of toner density. [Effects of the Invention]

[0010] According to the first configuration of the present invention, a target value for toner concentration is set considering the cumulative toner consumption in the manufacturing line of the image forming apparatus. This makes it possible to accurately predict the increase in the output value of the toner concentration sensor due to carrier contamination and maintain a constant toner concentration in the developing apparatus. As a result, it is possible to suppress the decrease in image density during the initial use of the image forming apparatus. [Brief explanation of the drawing]

[0011] [Figure 1] Schematic diagram showing the overall configuration of an image forming apparatus 100 according to one embodiment of the present invention. [Figure 2] Side cross-sectional view of the developing device 3a mounted on the image forming apparatus 100 of this embodiment. [Figure 3] Enlarged view of the area around the image forming unit Pa, including the control path of the image forming unit Pa. [Figure 4] A graph showing the relationship between cumulative print coverage and the correction value used when setting the target value for toner density. [Figure 5] This graph shows examples of setting target toner concentrations, both with and without considering toner consumption on the manufacturing line. [Figure 6] A flowchart showing an example of setting and controlling the target value of toner concentration in the image forming apparatus 100 of this embodiment. [Figure 7] This graph shows an example of setting a target value for toner concentration in a conventional scenario where toner ejection is not performed in the developing devices 3a to 3d for supplying toner. [Figure 8] This graph shows an example of setting the target value for toner concentration in this embodiment, which is used when the toner ejection operation is performed in the developing devices 3a to 3d for supplying toner. [Figure 9] Graph showing the relationship between the cumulative drive time of photoreceptor drums 1a-1d and the correction amount of the charging voltage Vdc. [Modes for carrying out the invention]

[0012] [1. Overall configuration of the image forming apparatus] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a cross-sectional view showing the internal structure of an image forming apparatus 100 according to one embodiment of the present invention. Inside the main body of the image forming apparatus 100 (here, a color printer), four image forming units Pa, Pb, Pc, and Pd are arranged in order from the upstream side in the transport direction (left side in Figure 1). These image forming units Pa to Pd are provided to correspond to images of four different colors (cyan, magenta, yellow, and black), and each sequentially forms images of cyan, magenta, yellow, and black through the processes of charging, exposure, development, and transfer, respectively.

[0013] These image forming sections Pa to Pd are equipped with photoreceptor drums (image carriers) 1a, 1b, 1c, and 1d, which carry visible images (toner images) of each color. An OPC (organic photosensitive layer) is laminated as a photosensitive layer on the surface of the photoreceptor drums 1a to 1d. Furthermore, an intermediate transfer belt 8, which rotates counterclockwise in Figure 1 by a drive motor (not shown), is provided adjacent to each image forming section Pa to Pd.

[0014] The toner images formed on these photoreceptor drums 1a to 1d are sequentially transferred and superimposed onto an intermediate transfer belt 8 that moves in contact with each photoreceptor drum 1a to 1d. Subsequently, the toner images transferred onto the intermediate transfer belt 8 are secondarily transferred onto a transfer paper P, which is an example of a recording medium, by a secondary transfer roller 9. Furthermore, the transfer paper P on which the toner images have been secondarily transferred is discharged from the main body of the image forming apparatus 100 after the toner images have been fixed in the fixing unit 13. The image forming process for each photoreceptor drum 1a to 1d is performed while the photoreceptor drums 1a to 1d are rotated clockwise in Figure 1.

[0015] The transfer paper P on which the toner image is secondarily transferred is housed in a paper cassette 16 located at the bottom of the main body of the image forming apparatus 100. The transfer paper P is transported via the paper feed roller 12a and the pair of registration rollers 12b to the nip between the secondary transfer roller 9 and the drive roller 11 of the intermediate transfer belt 8. The intermediate transfer belt 8 is made of a dielectric resin sheet, and a seamless belt is mainly used. In addition, a blade-shaped belt cleaner 19 is positioned downstream of the secondary transfer roller 9 to remove toner and other residues remaining on the surface of the intermediate transfer belt 8.

[0016] Next, the image forming units Pa to Pd will be described. Around and below the rotatably arranged photosensitive drums 1a to 1d, there are charging devices 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d, an exposure device 5 for exposing the photosensitive drums 1a to 1d with image information, developing devices 3a, 3b, 3c, and 3d for forming toner images on the photosensitive drums 1a to 1d, and cleaning devices 7a, 7b, 7c, and 7d for removing the developer (toner) and the like remaining on the photosensitive drums 1a to 1d.

[0017] When image data is input from a host device such as a personal computer, first, the charging devices 2a to 2d uniformly charge the surfaces of the photosensitive drums 1a to 1d. Next, the exposure device 5 irradiates light according to the image data, and an electrostatic latent image corresponding to the image data is formed on each of the photosensitive drums 1a to 1d.

[0018] The developing devices 3a to 3d are each filled with a predetermined amount of a two-component developer containing cyan, magenta, yellow, and black toners of each color. When the ratio of the toner in the two-component developer filled in each of the developing devices 3a to 3d falls below a specified value due to the formation of the toner image described later, toner is replenished from the toner containers 4a to 4d to each of the developing devices 3a to 3d. The toner in this developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and adheres electrostatically. Thereby, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 5 is formed.

[0019] Then, an electric field is applied at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d by the primary transfer rollers 6a to 6d, and the cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are primarily transferred onto the intermediate transfer belt 8. These four-color images are formed with a predetermined positional relationship determined in advance for forming a predetermined full-color image. Thereafter, in preparation for the formation of a new electrostatic latent image that is subsequently performed, the toner and the like remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer are removed by the cleaning devices 7a to 7d.

[0020] The intermediate transfer belt 8 is stretched between the upstream driven roller 10 and the downstream drive roller 11. As the drive roller 11 rotates due to a drive motor (not shown), the intermediate transfer belt 8 begins to rotate counterclockwise, and the transfer paper P is transported from the resist roller pair 12b to the nip section (secondary transfer nip section) between the drive roller 11 and the secondary transfer roller 9 located adjacent to it at a predetermined timing. As the transfer paper P passes through the secondary transfer nip section, the toner image on the intermediate transfer belt 8 is secondarily transferred onto the transfer paper P. The transfer paper P with the secondarily transferred toner image is then transported to the fixing section 13.

[0021] The transfer paper P, transported to the fixing unit 13, is heated and pressurized by the fixing roller pair 13a, fixing the toner image to the surface of the transfer paper P and forming a predetermined full-color image. The transfer paper P on which the full-color image has been formed is then transported in a direction determined by the branching unit 14 which branches in multiple directions, and is discharged into the discharge tray 17 by the discharge roller pair 15 (or after being sent to the double-sided transport path 18 for double-sided printing).

[0022] An image density sensor 40 is positioned downstream of the image forming unit Pd and opposite the intermediate transfer belt 8. Generally, an optical sensor is used as the image density sensor 40, which includes a light-emitting element such as an LED and a light-receiving element such as a photodiode. When measuring the amount of toner deposited on the intermediate transfer belt 8, measurement light is irradiated from the light-emitting element onto each reference image formed on the intermediate transfer belt 8, and the measurement light is incident on the light-receiving element as light reflected by the toner and light reflected by the belt surface.

[0023] The light reflected from the toner and the belt surface includes specular and diffuse reflection. This specular and diffuse reflection is separated by a polarization separation prism and then incident on separate photodetectors. Each photodetector converts the received specular and diffuse reflection into photoelectric signals and outputs them to the main control unit 80 (see Figure 3). The amount of toner is then detected from the characteristic changes of the specular and diffuse reflection output signals, and density correction (calibration) is performed for each color by adjusting the characteristic values ​​of the development voltage, etc., by comparing it with a predetermined reference density.

[0024] [2. Configuration of the developing device] Figure 2 is a side cross-sectional view of the developing apparatus 3a mounted on the image forming apparatus 100 of this embodiment. In the following description, the developing apparatus 3a located in the image forming section Pa of Figure 1 is used as an example, but the configuration of the developing apparatuses 3b to 3d located in the image forming sections Pb to Pd is basically the same, so their description is omitted.

[0025] As shown in Figure 2, the developing apparatus 3a includes a developing container 20 in which a two-component developing agent (hereinafter simply referred to as "developing agent") containing a magnetic carrier and toner is stored. The developing container 20 is divided into an agitation and conveying chamber 21 and a supply and conveying chamber 22 by a partition wall 20a. Rotatable agitation and conveying screws 25a and 25b are installed in the agitation and conveying chamber 21 and the supply and conveying chamber 22, respectively, to mix and agitate the toner supplied from the toner container 4a (see Figure 1) with the magnetic carrier and charge it.

[0026] The developer is then agitated and transported axially (perpendicular to the plane of the paper in Figure 2) by the agitation and transport screw 25a and the supply and transport screw 25b, and circulates between the agitation and transport chamber 21 and the supply and transport chamber 22 through developer passages (not shown) formed at both ends of the partition wall 20a. In other words, a developer circulation path is formed within the developing container 20 by the agitation and transport chamber 21, the supply and transport chamber 22, and the developer passages.

[0027] The developing container 20 extends diagonally upward to the right in Figure 2, and within the developing container 20, the developing roller 30 is positioned diagonally upward to the right of the supply transport screw 25b. A portion of the outer surface of the developing roller 30 is exposed through the opening 20b of the developing container 20 and faces the photosensitive drum 1a. The developing roller 30 rotates counterclockwise in Figure 2.

[0028] The developing roller 30 consists of a cylindrical developing sleeve that rotates counterclockwise in Figure 2, and a magnet (not shown) with multiple magnetic poles fixed inside the developing sleeve. Here, a developing sleeve with a knurled surface is used, but developing sleeves with numerous dimples on the surface, blast-finished surfaces, or even those with knurling, dimple formation, blast finishing, or plating can also be used.

[0029] Furthermore, a regulating blade 27 is attached to the developing container 20 along the longitudinal direction of the developing roller 30 (the direction perpendicular to the plane of the paper in Figure 2). A small gap is formed between the tip of the regulating blade 27 and the surface of the developing roller 30.

[0030] The developing roller 30 is subjected to a developing voltage consisting of a direct current voltage Vslv (DC) and an alternating current voltage Vslv (AC) by a high-voltage generation circuit 43 (see Figure 3).

[0031] A toner concentration sensor 31 is positioned at the bottom of the stirring and conveying chamber 21, facing the stirring and conveying screw 25a. The toner concentration sensor 31 detects the ratio of toner to carriers in the developer (T / C), and for example, a permeability sensor that detects the permeability of the developer in the developing container 20 is used. When the permeability of the developer is detected by the toner concentration sensor 31, a voltage value corresponding to the detection result is output to the main control unit 80 (see Figure 3), which will be described later, and the toner concentration is determined by the main control unit 80 from the output value of the toner concentration sensor 31.

[0032] The sensor output value changes according to the toner concentration. As the toner concentration increases, the ratio of toner to carriers increases, and the proportion of toner that does not conduct magnetism increases, resulting in a lower output value. Conversely, as the toner concentration decreases, the ratio of toner to carriers decreases, and the proportion of carriers that conduct magnetism increases, resulting in a higher output value. The main control unit 80 transmits a control signal to the toner supply motor (not shown) according to the determined toner concentration, and a predetermined amount of toner is supplied from the toner container 4a (see Figure 1) to the agitation and transport chamber 21 via the toner supply port 20c.

[0033] An IC tag 32 is attached to the outer surface of the developing container 20. The IC tag 32 stores information regarding the amount of toner consumed (cumulative print rate) when toner ejection and image output operations are performed during the manufacturing of the image forming apparatus 100 and the developing apparatus 3a. The information stored in the IC tag 32 is read by a reader / writer module (not shown) of the main body of the image forming apparatus 100 and transmitted to the main control unit 80 (see Figure 3).

[0034] [3. Control paths for the image forming unit] Figure 3 is a magnified view of the area around the image forming unit Pa, including the control path. The following explanation describes the configuration and control path of the image forming unit Pa, but the same applies to the configuration and control paths of the image forming units Pb to Pd, so the explanation is omitted.

[0035] The developing roller 30 is connected to a high-voltage generation circuit 43 that generates an oscillating voltage in which a DC voltage and an AC voltage are superimposed. The high-voltage generation circuit 43 comprises an AC constant voltage power supply 43a and a DC constant voltage power supply 43b. The AC constant voltage power supply 43a outputs a sinusoidal AC voltage generated from a low-voltage DC voltage that has been pulsed-modulated using a step-up transformer (not shown). The DC constant voltage power supply 43b outputs a DC voltage obtained by rectifying the sinusoidal AC voltage generated from a low-voltage DC voltage that has been pulsed-modulated using a step-up transformer.

[0036] During image formation, the high-voltage generation circuit 43 outputs a developing voltage obtained by superimposing an AC voltage on a DC voltage from the AC constant voltage power supply 43a and the DC constant voltage power supply 43b.

[0037] Next, the control system of the image forming apparatus 100 will be described with reference to Figure 3. The image forming apparatus 100 is equipped with a main control unit 80, which consists of a CPU and the like. The main control unit 80 is connected to a storage unit 70, which consists of a ROM, RAM, and the like. The main control unit 80 controls each part of the image forming apparatus 100 (charging devices 2a to 2d, exposure device 5, developing devices 3a to 3d, primary transfer rollers 6a to 6d, cleaning devices 7a to 7d, fixing unit 13, high-voltage generation circuit 43, voltage control unit 45, etc.) based on control programs and control data stored in the storage unit 70.

[0038] The voltage control unit 45 controls the high-voltage generation circuit 43. The voltage control unit 45 may also consist of a control program stored in the memory unit 70. The external temperature sensor 50 detects the temperature outside the image forming apparatus 100 and is installed, for example, near the intake duct (not shown) on the side of the paper cassette 16 in Figure 1, where it is less affected by heat-generating parts. The internal temperature sensor 51 detects the temperature inside the image forming apparatus 100, particularly the temperature around the developing units 3a to 3d, and is placed near the image forming units Pa to Pd.

[0039] The main control unit 80 is connected to a liquid crystal display unit 90 and a transceiver unit 91. The liquid crystal display unit 90 functions as a touch panel for the user to make various settings of the image forming apparatus 100, and also displays the status of the image forming apparatus 100, the image forming status, the number of printed sheets, etc. The transceiver unit 91 communicates with the outside world using a telephone line or an internet line.

[0040] [4. Setting target toner density in the developing device using cumulative print rate] As mentioned above, there is a problem in that the carrier is contaminated by toner additives, which reduces the fluidity of the developer. In particular, when using a silicone-coated carrier whose surface is coated with silicone resin, the carrier surface is contaminated by toner additives during a certain initial period of developer use, reducing the fluidity provided by the silicone coating.

[0041] When the fluidity of the developer decreases, the bulk density of the developer decreases, and the output value of the toner density sensor 31 is output higher than the actual toner density. As a result, toner is not supplied from the toner containers 4a to 4d to the developing units 3a to 3d, and the toner density in the developing units 3a to 3d remains lower than the target value.

[0042] Therefore, in this invention, carrier contamination is predicted based on the toner consumption from the start of use of the developing devices 3a to 3d, and the toner concentration is controlled to reach a target value. Specifically, a correction value is determined when setting the target value of the toner concentration based on the cumulative printing rate from the start of use of the developing devices 3a to 3d.

[0043] Figure 4 is a graph showing the relationship between the cumulative print coverage and the correction value when setting the target toner density. As shown in Figure 4, the correction value when setting the target toner density increases as the cumulative print coverage from the start of use of the developing devices 3a to 3d increases. For example, if the target toner density is 6.5%, the correction value is 1.5% when the cumulative print coverage is 500%, so the target toner density needs to be corrected to 6.5 + 1.5 = 8%. When the cumulative print coverage is 1000%, the correction value is 2%, so the target toner density needs to be corrected to 6.5 + 2 = 8.5%. When the cumulative print coverage is 2000% or higher, the correction value becomes a constant value (2.5%), and the target toner density becomes 6.5 + 2.5 = 9%.

[0044] By correcting the target toner concentration using the relationship between the cumulative print density and the correction value shown in Figure 4, it is possible to suppress the decrease in toner concentration caused by the decrease in developer fluidity due to carrier contamination.

[0045] Meanwhile, in the manufacturing line (first manufacturing line) of the image forming apparatus 100, toner ejection from the developing units 3a to 3d and image output operations are performed. The toner ejection operation is performed to supply toner to the contact area between the photoreceptor drums 1a to 1d and the cleaning blades (not shown) of the cleaning units 7a to 7d. This reduces friction between the photoreceptor drums 1a to 1d and the cleaning blades, allowing the photoreceptor drums 1a to 1d to rotate smoothly. The image output operation is performed to adjust the overall image forming apparatus 100, such as adjusting the density and position of the toner images of each color.

[0046] Previously, the toner consumption (cumulative print rate) on the manufacturing line was reset when the image forming apparatus 100 was shipped. Therefore, the toner consumption (cumulative print rate) on the manufacturing line was not taken into consideration during the setup after the image forming apparatus 100 arrived at the user's location.

[0047] Figure 5 is a graph showing examples of setting target toner density values ​​with and without considering toner consumption on the manufacturing line. When toner consumption on the manufacturing line is considered (solid line in Figure 5), the cumulative print rate at the end of setup (start of use) is the cumulative print rate on the manufacturing line (toner ejection operation + image output operation = 1100%) + cumulative print rate during setup operation (1100%) = 2200%. Since the correction value when the cumulative print rate is 2200% is 2.5%, if the target toner density is 6.5%, the target toner density is corrected to 6.5 + 2.5 = 9%.

[0048] If toner consumption on the manufacturing line is not considered (dashed line in Figure 5), the cumulative print density at the end of setup (start of use) is only the cumulative print density during the setup operation (1100%). Since the correction value when the cumulative print density is 1100% is approximately 2%, if the target toner density is 6.5%, the target toner density will be corrected to 6.5 + 2 = 8.5%. In other words, the target toner density is set lower than when toner consumption on the manufacturing line is considered (9%), which leads to a decrease in image density.

[0049] In the image forming apparatus 100 of this embodiment, the cumulative printing rate (first cumulative consumption Σpn1) resulting from toner ejection and image output operations on the manufacturing line is stored in the IC tag 32, and the first cumulative consumption Σpn1 is not reset when the image forming apparatus 100 is set up.

[0050] Then, after the setup operation is completed and the image forming apparatus 100 is put into use, the integrated print rate (second integrated consumption Σpn2) based on the setup operation and the image output operation after the start of use is calculated. The main control unit 80 determines a correction value based on the sum of the first integrated consumption Σpn1 and the second integrated consumption Σpn2, and sets a target value for toner density.

[0051] In the example shown in Figure 5, the cumulative consumption (cumulative print density), which is the sum of the toner consumption during the setup operation (second cumulative consumption Σpn2) and the toner consumption during the manufacturing line (first cumulative consumption Σpn1), exceeds 2000%. Since the correction value becomes a constant value (2.5%) when the cumulative print density exceeds 2000%, correction of the target value of toner density is unnecessary after the image forming apparatus 100 is put into use. If the cumulative consumption (cumulative print density), which is the sum of the toner consumption during the setup operation and the first cumulative consumption Σpn1, is less than 2000%, the target value of toner density is corrected based on the cumulative consumption (second cumulative consumption Σpn2), which is the sum of the toner consumption during the image forming operation after the image forming apparatus 100 is put into use.

[0052] Figure 6 is a flowchart showing an example of setting a target value for toner density in the image forming apparatus 100 of this embodiment. The procedure for setting a target value for toner density based on the cumulative printing rate will be explained following the steps in Figure 6, referring to Figures 1 to 5 as needed.

[0053] First, the image forming apparatus 100 performs toner ejection from the developing devices 3a to 3d on its production line (step S1). Next, it performs image output (step S2). Then, the IC tags 32 of the developing devices 3a to 3d store the first cumulative consumption amount Σpn1, which is the toner consumed by the toner ejection and image output operations (step S3).

[0054] Subsequently, the image forming apparatus 100 is shipped from the factory, and a setup operation for the image forming apparatus 100 is performed at the installation site (step S4). After the setup operation is completed, the image forming apparatus 100 is put into use (step S5). The main control unit 80 calculates the second integrated consumption amount Σpn2, which is the toner consumption due to the setup operation and the image output operation after the start of use (step S6).

[0055] As shown in Figure 5, the main control unit 80 determines a correction value for setting the target value of toner density (T / C) based on the sum of the first cumulative consumption amount Σpn1 stored in the IC tag 32 in step S3 and the second cumulative consumption amount Σpn2 calculated in step S6, Σpn1+Σpn2 (step S7).

[0056] Next, the main control unit 80 determines whether Σpn1 + Σpn2 has reached a predetermined value (for example, 2000%) (step S8). If Σpn1 + Σpn2 has not reached the predetermined value (No in step S8), the process returns to step S6 and continues with the calculation of the second integrated consumption amount Σpn2 and the determination of a correction value based on Σpn1 + Σpn2 (steps S6, S7).

[0057] If Σpn1 + Σpn2 has reached a predetermined value (Yes in step S8), the correction value is maintained at a constant value (e.g., 2.5%) (step S9) and the control of setting the target value of the toner density is terminated.

[0058] According to the control described above, a target value for toner concentration is set considering the toner consumption in the manufacturing line of the image forming apparatus 100. This makes it possible to accurately predict the increase in the output value of the toner concentration sensor 31 due to carrier contamination, and to maintain a constant toner concentration in the developing devices 3a to 3d. As a result, it is possible to suppress the decrease in image density during the initial use of the image forming apparatus 100.

[0059] In the control described above, the cumulative toner consumption (first cumulative consumption Σpn1 and second cumulative consumption Σpn2) was calculated using the cumulative printing rate, but the cumulative toner consumption can also be calculated using other methods. Other methods include calculating the cumulative toner consumption based on the dot count when the electrostatic latent image is formed by the exposure device 5, and the amount of toner supplied from the toner containers 4a to 4d to the developing devices 3a to 3d.

[0060] Furthermore, in the above control system, the cumulative toner consumption (first cumulative consumption Σpn1 and second cumulative consumption Σpn2) is stored in the IC tags 32 attached to the developing devices 3a to 3d. However, the cumulative toner consumption can also be stored in the storage unit 70 (see Figure 3) of the main body of the image forming apparatus 100. However, if the developing devices 3a to 3d are replaced, the cumulative consumption stored in the storage unit 70 will no longer match the actual cumulative consumption. Therefore, a mechanism is provided to detect whether or not the developing devices 3a to 3d have been replaced, and if the developing devices 3a to 3d are replaced, control is required to rewrite the cumulative consumption stored in the storage unit 70.

[0061] Next, we will describe the supply (replacement) developing units 3a to 3d (replacement developing units) which are manufactured on a separate production line (second production line) from the main image forming apparatus 100. Figure 7 is a graph showing an example of setting a target value for toner density in a conventional manner, where the toner ejection operation is not performed in the supply developing units 3a to 3d. As shown in Figure 7, the supply developing units 3a to 3d only perform image output operations and do not perform toner ejection operations on the production line. That is, the first cumulative consumption amount Σpn1 of the supply developing units 3a to 3d is different from that of the developing units 3a to 3d already installed in the main image forming apparatus 100 (see Figure 5).

[0062] For example, if only developer unit 3a is replaced among the developer units 3a to 3d, the combined value of the first cumulative consumption Σpn1 and the second cumulative consumption Σpn2 exceeds a predetermined value for developer units 3b to 3d, and therefore the target value for toner density is set higher. In the example shown in Figure 5, the target value for toner density is set to 9% when the cumulative print coverage is 2000% or more.

[0063] On the other hand, since the toner ejection operation is not performed in the developer unit 3a after replacement, the sum of the first cumulative consumption amount Σpn1 and the second cumulative consumption amount Σpn2 does not reach the predetermined value (cumulative print density of 2000%) when installed in the main body of the image forming apparatus 100. As a result, if the target value of the toner density is set to 9%, as in the developer units 3b to 3d, the toner density becomes too high and the amount of toner charge decreases.

[0064] Figure 8 is a graph showing an example of setting the target value of toner concentration in this embodiment, when the toner ejection operation is performed in the supply developing units 3a to 3d. In this embodiment, the supply developing units 3a to 3d also perform the toner ejection operation after being installed in the image forming apparatus 100, and adjust to the same toner consumption as the already installed developing units 3a to 3d. Note that, similar to the developing units 3a to 3d already installed in the image forming apparatus 100, the cumulative printing rate (first cumulative consumption Σpn1) on the manufacturing line stored in the IC tag 32 installed in the supply developing units 3a to 3d is not reset when the developing units 3a to 3d are shipped.

[0065] This allows the toner consumption when the supply developing units 3a to 3d are installed in the image forming apparatus 100 and the setup operation is started to be matched with the developing units 3a to 3d already installed in the image forming apparatus 100. Therefore, regardless of whether the developing units 3a to 3d are replaced or not, the same correction value (2.5% in Figure 8) can be used to set the same target toner density (9% in Figure 8) for all developing units 3a to 3d, simplifying toner density correction control.

[0066] [5. Setting the target value of the charging voltage using the accumulated drive time of the photoreceptor drum] To maintain image quality, it is necessary to properly control the surface potential V0 of the photoreceptor drums 1a to 1d. To control the surface potential V0, it is necessary to determine the correction amount for the charging voltage Vdc applied to the charging rollers 35 (see Figure 3) of the charging devices 2a to 2d.

[0067] In the image forming apparatus 100 of this embodiment, the application time of the charging voltage Vdc and the cumulative rotation speed (cumulative drive time) of the photoreceptor drums 1a to 1d, which are used to determine the correction amount of the charging voltage Vdc, are not reset at the time of shipment of the image forming apparatus 100, similar to the toner consumption (cumulative print rate) of the developing devices 3a to 3d.

[0068] Figure 9 is a graph showing the relationship between the cumulative drive time of the photoreceptor drums 1a to 1d and the amount of correction for the charging voltage Vdc. As shown in Figure 9, the amount of correction for the charging voltage Vdc is not constant with respect to the drive time, and the amount of change is larger in the early stages of use when the thickness of the organic photosensitive layer of the photoreceptor drums 1a to 1d changes significantly.

[0069] Therefore, the accumulated drive time or accumulated drive distance (first accumulated drive amount) of the photoreceptor drums 1a to 1d on the manufacturing line is stored in the memory unit 70 (see Figure 3), and without resetting at the time of shipment, the correction amount is determined by adding it to the accumulated drive time or accumulated drive distance (second accumulated drive amount) after the start of image formation during the setup operation. This makes it possible to properly control the surface potential V0 in the initial stages of use of the image forming apparatus 100 and suppress the deterioration of image quality.

[0070] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, although the above embodiments described an image forming apparatus 100 equipped with a two-component developing apparatus 3a to 3d that includes a developing roller (developer carrier) 30 carrying a two-component developer, the present invention is not limited thereto. The present invention can be applied in exactly the same way to an image forming apparatus equipped with a developing apparatus that further includes a developer carrier such as a magnetic roller between the supply transport screw 25b and the developing roller 30, and after supplying the developer from the supply transport screw 25b to the magnetic roller, supplies only toner from the magnetic roller to the developing roller 30.

[0071] Furthermore, although the above embodiment described an image forming apparatus 100 using a color printer as an example as shown in Figure 1, the present invention is not limited to color printers and can be applied to image forming apparatuses equipped with a two-component developing apparatus, such as color copiers, color multifunction printers, monochrome printers, monochrome copiers, and monochrome multifunction printers. [Industrial applicability]

[0072] The present invention is applicable to image forming apparatus equipped with a developing device that uses a two-component developer. By using the present invention, it is possible to provide an image forming apparatus that can suppress the decrease in image density caused by carrier contamination at the start of use of the image forming apparatus. [Explanation of symbols]

[0073] Pa~Pd Image Forming Unit 1a~1d Photoreceptor drum (image carrier) 2a~2d Charging device 3a~3d developing device 5. Exposure apparatus 8. Intermediate transfer belt 20 developing containers 30. Developing roller (developer carrier) 31 Toner density sensor 32 IC tag (memory unit) 35 Electrostatic Roller 40 Image density sensor 43. High-voltage generation circuit (developing voltage power supply) 70 Memory section 80 Main control unit 100 Image forming apparatus

Claims

1. An image carrier having a photosensitive layer formed on its surface, A charging device for charging the surface of the image carrier, An exposure apparatus that exposes the surface of the image carrier, which has been charged by the charging device, to form an electrostatic latent image, A developing apparatus comprising: a developing container containing a two-component developer including a carrier and toner; a developer carrier rotatably supported within the developing container and bearing the two-component developer on its surface; and a toner concentration sensor for detecting the toner concentration in the two-component developer within the developing container, wherein the developing apparatus develops the electrostatic latent image into a toner image, An image forming unit having, A toner container for storing the toner to be supplied to the developing device, A control unit controls the supply of toner from the toner container to the developing device based on the output value of the toner concentration sensor, and corrects the target value of the toner concentration based on the cumulative amount of toner consumed since the start of use of the developing device. In an image forming apparatus equipped with, The image forming apparatus includes a storage unit that stores the first cumulative consumption amount, which is the cumulative consumption amount in the first production line of the image forming apparatus, The control unit calculates a second cumulative consumption amount, which is the cumulative consumption amount due to the setup operation of the image forming apparatus and the image output operation after the start of use, and determines a correction value for correcting the target value of the toner concentration using the sum of the first cumulative consumption amount and the second cumulative consumption amount.

2. The image forming apparatus according to claim 1, characterized in that the first cumulative consumption is the cumulative value of the printing rate due to the toner ejection operation from the developing device and the image output operation in the first manufacturing line.

3. The developing apparatus includes a replacement developing apparatus manufactured on a second production line separate from the first production line. The storage unit is installed in the replacement developing device and is capable of storing the cumulative amount of toner consumed in the second production line. The image forming apparatus according to claim 2, characterized in that the replacement developing device does not perform the toner ejection operation in the second production line, and the control unit performs the toner ejection operation of the replacement developing device after it is mounted on the image forming apparatus, thereby matching the first cumulative consumption of the replacement developing device with that of the developing device already mounted on the image forming apparatus.

4. The target value of the toner concentration becomes a constant value when the cumulative consumption reaches a predetermined value. The image forming apparatus according to any one of claims 1 to 3, characterized in that the cumulative consumption obtained by adding the toner consumption due to the setup operation to the first cumulative consumption is equal to or greater than the predetermined value.

5. The image forming apparatus according to any one of claims 1 to 3, characterized in that the surface of the carrier is coated with a silicone resin.

6. The image carrier has an organic photosensitive layer formed as the photosensitive layer. The control unit corrects the charging voltage applied to the charging device based on the accumulated driving time or accumulated driving distance from the start of use of the image carrier. The storage unit stores a first cumulative drive amount, which is the cumulative drive time or the cumulative drive distance in the first manufacturing line. The image forming apparatus according to claim 1, characterized in that the control unit calculates a second integrated drive amount, which is the integrated drive time or the integrated drive distance, based on the setup operation and the image output operation, and determines a correction amount for the charging voltage applied to the charging device using the sum of the first integrated drive amount and the second integrated drive amount.

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