Image forming apparatus

Abstract

To provide an image forming apparatus that can maintain a uniform surface potential of an image carrier to obtain a stable image.SOLUTION: An image forming apparatus comprises an image carrier, a charging device, an exposure device, a developing device, a transfer unit, and a cleaning blade. The image carrier has a photosensitive layer on its surface and is driven to rotate, and the charging device electrostatically charges the surface of the image carrier. The exposure device exposes the surface of the electrostatically charged image carrier to form an electrostatic latent image, and the developing device develops the electrostatic latent image into a toner image. The transfer unit transfers the toner image on the image carrier to a recording medium, and an image is formed on the recording medium. The cleaning blade scrapes off a toner remaining on the image carrier. The image forming apparatus detects the amount of charging current on the image carrier, and when the integrated current amount obtained by integrating the amount of charging current within a predetermined time is lower than a predetermined threshold, performs aging processing of driving to rotate the image carrier in an electrostatically charged state.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus using an electrophotographic process, and more particularly to uniforming the surface potential of an image bearing member. [Background technology]

[0002] Patent Document 1 discloses an electrophotographic image forming apparatus. This image forming apparatus includes an image carrier (photoconductor), a charging unit, an LSU, a developing unit, and a fixing unit. When an image formation command is input, the cylindrical image carrier rotates, and the charging unit charges the surface of the image carrier. An electrostatic latent image is formed on the charged surface of the image carrier by exposure to light from the LSU, and the electrostatic latent image is developed into a toner image by the developing unit. The toner image formed on the surface of the image carrier is transferred to paper via an intermediate transfer belt, and the image is fixed on the paper by the fixing unit. Any toner remaining on the image carrier is scraped off by a blade.

[0003] At this time, the amount of film scraping on the surface of the image carrier is calculated at regular intervals based on the drive time and charging current of the image carrier, and the charging bias is shifted accordingly, thereby making it possible to form high quality images over a long period of time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-128345 A (pages 6 to 14, Figure 7) Summary of the Invention [Problem to be solved by the invention]

[0005] In the conventional image forming apparatus described above, if the blade does not sufficiently scrape off the film of the image carrier, the deposits on the surface of the image carrier cannot be removed, and there is a risk of image defects such as white spots and color spots or breakdowns occurring. In particular, in the initial stage when the film thickness of the photosensitive layer on the surface of the image carrier is thick, the surface of the image carrier is difficult to scrape off.

[0006] For this reason, if an insulating foreign substance remains on a part of the surface of the image carrier, the surface potential of that part becomes high. As a result, it is not possible to accurately calculate the film scraping on the surface of the image carrier based on the charging current, and it is not possible to form a uniform image.

[0007] SUMMARY OF THE PRESENT EMBODIMENT In view of the above problems, an object of the present invention is to provide an image forming apparatus which is capable of preventing image defects and breakdowns and obtaining uniform images. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides an image forming apparatus including an image carrier, a charging device, an exposure device, a developing device, a transfer section, and a cleaning blade. The image carrier has a photosensitive layer on its surface and is driven to rotate, and the surface of the image carrier is charged by the charging device. The exposure device exposes the charged surface of the image carrier to light to form an electrostatic latent image, and the developing device develops the electrostatic latent image into a toner image. The toner image on the image carrier is transferred to a recording medium by the transfer section, and an image is formed on the recording medium. The cleaning blade scrapes off toner remaining on the image carrier. The image forming apparatus detects the amount of charging current of the image carrier, and when the integrated current amount obtained by integrating the amount of charging current over a predetermined time is lower than a predetermined threshold value, an aging process is performed in which the image carrier is driven to rotate in a charged state. Effect of the Invention

[0009] According to the present invention, since the aging process is performed when the integrated current amount for a predetermined period of time is lower than a threshold value, the surface of the image carrier can be scraped reliably, and a uniform image can be obtained. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram illustrating an internal configuration of an image forming apparatus according to an embodiment of the present invention. [Diagram 2] Enlarged view of the image forming section in Figure 1 [Diagram 3] FIG. 2 is a block diagram showing an example of a control path of the image forming apparatus according to the embodiment of the present invention. [Figure 4]FIG. 13 is a diagram showing the change in the total thickness of the photosensitive layer of the photosensitive drum and the amount of charging current depending on the number of printed sheets. [Diagram 5] A flowchart showing a printing operation including an aging process of an image forming apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic diagram showing a configuration of an image forming apparatus 100 according to an embodiment of the present invention, and Fig. 2 is an enlarged view of the vicinity of an image forming section Pa in Fig. 1.

[0012] The image forming apparatus 100 shown in Fig. 1 is a so-called tandem type color printer, and has the following configuration: Within the main body of the image forming apparatus 100, four image forming sections Pa, Pb, Pc, and Pd are arranged in this order from the upstream side in the transport direction (the left side in Fig. 1). These image forming sections Pa to Pd are provided corresponding to images of four different colors (yellow, cyan, magenta, and black), and sequentially form images of yellow, cyan, magenta, and black through the processes of charging, exposing, developing, and transferring, respectively.

[0013] These image forming stations Pa to Pd are provided with photoconductor drums 1a, 1b, 1c, and 1d (image carriers) that carry visible images (toner images) of each color. The photoconductor drums 1a to 1d are formed of positively charged single-layer organic photoconductors and have a photosensitive layer on their surfaces. Furthermore, an intermediate transfer belt 8 that rotates counterclockwise in FIG. 1 is provided adjacent to each of the image forming stations Pa to Pd. The toner images formed on these photoconductor drums 1a to 1d are sequentially transferred onto the intermediate transfer belt 8 that moves while contacting each of the photoconductor drums 1a to 1d.

[0014] Thereafter, the toner image on the intermediate transfer belt 8 is transferred onto a sheet S, which is an example of a recording medium, by a secondary transfer roller 9. After the toner image is fixed onto the sheet S in a fixing unit 13, the sheet S is discharged from the main body of the image forming apparatus 100. An image forming process is performed on each of the photoconductor drums 1a to 1d while the photoconductor drums 1a to 1d are rotated clockwise in FIG.

[0015] The paper S onto which the toner image is transferred is stored in a paper cassette 16 at the bottom of the main body of the image forming apparatus 100, and is transported to a secondary transfer roller 9 via a paper feed roller 12a and a pair of registration rollers 12b. A seamless belt is generally used as the intermediate transfer belt 8.

[0016] Next, the image forming units Pa to Pd will be described. The image forming unit Pa will be described in detail below, but the image forming units Pb to Pd will not be described because they have basically the same configuration. As shown in FIG. 2, a charging device 2a, a developing device 3a, and a cleaning device 7a are arranged around the photosensitive drum 1a along the drum rotation direction (clockwise direction in FIG. 2), and a primary transfer roller 6a is arranged with an intermediate transfer belt 8 sandwiched between them. In addition, a belt cleaning unit 19 is arranged upstream of the photosensitive drum 1a in the rotation direction of the intermediate transfer belt 8. The belt cleaning unit 19 faces a tension roller 11 with the intermediate transfer belt 8 sandwiched between them.

[0017] An exposure device 5 is disposed below the image forming units Pa to Pd. The exposure device 5 is configured with a laser scanning unit (LSU) and includes a light source such as a semiconductor laser, a scanning mirror such as a polygon mirror, and optical components such as lenses. The light beam emitted from the light source scans the photoconductor drums 1a to 1d, respectively.

[0018] Next, an image forming procedure in the image forming apparatus 100 will be described. When a user inputs a command to start image formation, the photoconductor drums 1a to 1d are rotated and driven by the main motor 61 (see FIG. 3). The surfaces of the rotating photoconductor drums 1a to 1d are uniformly charged by the charging rollers 20 of the charging devices 2a to 2d. Next, the surfaces of the photoconductor drums 1a to 1d are scanned and irradiated with a beam of light (laser light) emitted from the exposure device 5. As a result, an electrostatic latent image is formed on each of the photoconductor drums 1a to 1d, the charge of which is attenuated in accordance with the image signal.

[0019] The developing devices 3a to 3d are filled with a predetermined amount of toner of each color, yellow, cyan, magenta, and black. When the ratio of toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of a toner image described later, toner is replenished from the toner containers 4a to 4d to each developing device 3a to 3d. The toner in the developer is supplied onto the photoconductor drums 1a to 1d by the developing rollers 21 of the developing devices 3a to 3d and electrostatically adheres to the photoconductor drums 1a to 1d. As a result, a toner image is formed according to the electrostatic latent image formed by exposure of the exposure device 5.

[0020] Then, the primary transfer rollers 6a-6d apply an electric field with a predetermined transfer voltage between the primary transfer rollers 6a-6d and the photosensitive drums 1a-1d, and the yellow, cyan, magenta, and black toner images on the photosensitive drums 1a-1d are primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a-1d is rubbed off and removed by the cleaning blades 22 and rubbing rollers 23 of the cleaning devices 7a-7d. This prepares the photosensitive drums 1a-1d for the subsequent formation of a new electrostatic latent image.

[0021] As the drive roller 10 is rotated by the belt drive motor 63 (see FIG. 3), the intermediate transfer belt 8 starts to rotate counterclockwise. As the intermediate transfer belt 8 rotates, the paper S is transported at a predetermined timing from the pair of registration rollers 12b to a secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8. A full-color toner image is transferred onto the paper S by the secondary transfer roller 9. Therefore, the primary transfer rollers 6a-6d, the intermediate transfer belt 8, and the secondary transfer roller 9 constitute a transfer section that transfers the toner images on the photoconductor drums 1a-1d onto the recording medium (paper S).

[0022] The paper S onto which the toner image has been transferred is transported to the fixing unit 13. Any toner remaining on the surface of the intermediate transfer belt 8 is removed by a belt cleaning unit 19. The paper S transported to the fixing unit 13 is heated and pressed by a pair of fixing rollers 13a to fix the toner image onto the surface, and a predetermined full-color image is formed. The paper S on which the full-color image has been formed is then directed to a branching unit 14, which branches into multiple directions, and the direction of transport is determined depending on whether or not double-sided printing is to be performed. The paper S is either directly conveyed or sent to a double-sided conveying path 18 to be printed on both sides, and then discharged by a pair of discharge rollers 15 onto a discharge tray 17.

[0023] 3 is a block diagram showing an example of a control path of the image forming apparatus 100 of this embodiment. Note that, since various controls are performed on each part of the image forming apparatus 100 when the image forming apparatus 100 is used, the control path of the entire image forming apparatus 100 becomes complicated. Therefore, the following description will focus on the parts of the control path that are necessary for implementing the present invention.

[0024] The control unit 90 includes a CPU 91 as a central processing unit, a ROM 92 which is a read-only storage unit, a RAM 93 which is a readable and writable storage unit, a temporary storage unit 94 which temporarily stores image data and the like, a counter 95, and a plurality of (here, two) I / Fs (interfaces) 96 which transmit control signals to each device in the image forming apparatus 100 and receive input signals from the operation unit 80. The control unit 90 can be disposed at any location inside the main body of the image forming apparatus 100.

[0025] ROM 92 stores data such as a control program for image forming apparatus 100, numerical values ​​necessary for control, and data that will not be changed while image forming apparatus 100 is in use. RAM 93 stores data necessary that is generated during the control of image forming apparatus 100, data temporarily necessary for the control of image forming apparatus 100, and the like. Counter 95 accumulates and counts the number of printed sheets.

[0026] Furthermore, the control unit 90 transmits control signals from the CPU 91 through the I / F 96 to each part and device in the image forming apparatus 100. Furthermore, signals indicating the state and input signals are transmitted from each part and device to the CPU 91 through the I / F 96. Examples of each part and device controlled by the control unit 90 include image forming units Pa to Pd, the main motor 61, the belt drive motor 63, the image input unit 70, the voltage control circuit 71, and the operation unit 80.

[0027] The image input unit 70 is a receiving unit that receives image data transmitted from a device such as a personal computer to the image forming apparatus 100. The image signal input from the image input unit 70 is converted into a digital signal and then sent to the temporary storage unit 94.

[0028] The voltage control circuit 71 is connected to the charging voltage power supply 72, the developing voltage power supply 73, and the transfer voltage power supply 74, and operates each of these power supplies according to an output signal from the control unit 90. The charging voltage power supply 72 applies a predetermined charging voltage to the charging rollers 20 in the charging devices 2a to 2d according to a control signal from the voltage control circuit 71. The developing voltage power supply 73 applies a predetermined developing voltage, which is a DC voltage superimposed on an AC voltage, to the developing rollers 21 in the developing devices 3a to 3d according to a control signal from the voltage control circuit 71. The transfer voltage power supply 74 applies a predetermined transfer voltage to the primary transfer rollers 6a to 6d and the secondary transfer roller 9, respectively, according to a control signal from the voltage control circuit 71.

[0029] The operation unit 80 is provided with a liquid crystal display unit 81 and LEDs 82 that indicate various states. The user operates the stop / clear button on the operation unit 80 to stop image formation, and operates the reset button to reset various settings of the image forming apparatus 100 to their default states. The liquid crystal display unit 81 indicates the state of the image forming apparatus 100, as well as the image formation status and the number of copies to be printed. Various settings of the image forming apparatus 100 are set from a printer driver on the personal computer.

[0030] The aging process of the image forming apparatus 100 will be described below. Fig. 4 is a diagram showing the change in the total thickness of the photosensitive layers of the photosensitive drums 1a-1d and the amount of charging current i of the photosensitive drums 1a-1d with respect to the number of sheets printed by the image forming apparatus. The vertical axis represents the total thickness (unit: μm) and the amount of charging current i (unit: μA), and the horizontal axis represents the number of sheets printed (unit: sheets). In the figure, the dashed line represents the total thickness, and the solid line represents the amount of charging current i.

[0031] According to the figure, the total thickness of the photosensitive layer decreases with an increase in the number of printed sheets, but the earlier the photosensitive drums 1a-1d are in use, the smaller the degree of reduction in the total thickness of the photosensitive layer. That is, the larger the total thickness of the photosensitive layer of the photosensitive drums 1a-1d, the less likely it is to be scraped off. Also, the larger the total thickness of the photosensitive layer, the smaller the amount of charging current required to apply a certain surface potential. Therefore, the photosensitive drums 1a-1d are less likely to be scraped off during a period when the charging current amount i is low. For this reason, the aging process is performed during a period when the charging current amount i is low, so that the surfaces of the photosensitive drums 1a-1d are sufficiently scraped off.

[0032] 5 is a flowchart showing a printing operation including an aging process of the image forming apparatus 100. When a print command is received from the image input unit 70 (see FIG. 4), measurement of the drive time t (unit: sec) and the charging current amount i (unit: μA) of the photoconductor drums 1a-1d that are driven to rotate is started in step S11. In step S12, printing is performed.

[0033] In step S13, it is determined whether the print job is complete. If the print job is not complete, steps S12 and S13 are repeated, and if the print job is complete, the process proceeds to step S14.

[0034] In step S14, the integrated time Σt obtained by integrating the drive time t and the integrated current amount Σi obtained by integrating the charging current amount i within the integrated time Σt are stored in the RAM 93. The integrated time Σt is the same as the drive time t when the first job is completed, but when multiple jobs are performed, it is the sum of the drive times t of each job.

[0035] In step S15, it is determined whether the cumulative time Σt has reached a predetermined time. Here, the predetermined time is, for example, 10 minutes (600 seconds). If the cumulative time Σt is 10 minutes or more, the process proceeds to step S16, and if the cumulative time Σt has not reached 10 minutes, the process proceeds to step S20.

[0036] In step S20, it is determined whether or not there is a next job, and if there is a next job, the process proceeds to step S12. Then, steps S12 to S15 and S20 are repeated until the integrated time Σt becomes 10 minutes or more.

[0037] When the cumulative time Σt due to one or more jobs exceeds 10 minutes, step S16 determines whether the cumulative current amount Σi within the cumulative time Σt is lower than a predetermined threshold A. Here, threshold A is 30,000 μC as described below. If the cumulative current amount Σi is lower than threshold A, the process proceeds to step S17.

[0038] In step S17, an aging process is performed for a predetermined time (e.g., 60 seconds) in which the photoconductor drums 1a-1d are rotated while being charged. When the integrated current amount Σi is lower than the threshold A, the charging current amount i is low and the photoconductor drums 1a-1d are not easily scraped. Therefore, by performing the aging process, the surfaces of the photoconductor drums 1a-1d are sufficiently scraped, and the deposits can be reliably removed.

[0039] The charging current amount i temporarily decreases when the control unit 90 is intentionally controlling the surface potential of the photosensitive drum to be lowered. Therefore, by comparing the charging current amount i with the threshold value using the integrated current amount Σi, it is possible to avoid the aging process being performed due to the charging current amount i being temporarily low.

[0040] If it is determined in step S16 that the integrated current amount Σi is equal to or greater than the threshold value A, the film abrasion of the photoconductor drums 1a to 1d is large, so the process proceeds to step S18 without carrying out the aging process. In step S18, the integrated time Σt and the integrated current amount Σi stored in the RAM 93 are reset, and the process ends.

[0041] Next, Table 1 shows the test results for determining threshold A. The test conditions were photoconductor drums with charging current amounts i of 30 μA, 50 μA, and 70 μA, and a comparison was made between printing without aging treatment and printing after aging treatment for 60 seconds. In the table, "○" indicates a state in which no white or colored dots were generated in the image, and "×" indicates a state in which white or colored dots were generated in the image.

[0042] [Table 1]

[0043] According to Table 1, when the charging current amount is low at 30 μA, white spots appear on the image without aging, and the potential of the photoconductor drum is not kept constant. However, when the charging current amount i is 50 μA or 70 μA, white or colored spots do not appear on the image even without aging, and the potential of the photoconductor drum is kept constant. Therefore, aging is not required at least when the charging current amount i is 50 μA or more, that is, when the integrated current amount Σi for an integrated time Σt of 10 minutes is 30,000 μC or more. Therefore, in the image forming apparatus 100 of this embodiment, the threshold A is set to 30,000 μC.

[0044] According to this embodiment, the aging process is performed when the integrated current amount Σi for a predetermined time is lower than the threshold A, so that the surfaces of the photosensitive drums 1a to 1d (image carriers) can be reliably scraped to obtain uniform images.

[0045] Furthermore, when the job is completed, it is determined whether the integrated time Σt has reached a predetermined time (10 minutes), and if the predetermined time has not been reached, the next job is performed. Furthermore, when the predetermined time has been reached, it is determined whether the integrated current amount Σi is lower than the threshold A, and the integrated time Σt and the integrated current amount Σi are reset. This makes it easy to realize an image forming apparatus 100 that determines whether to perform an aging process based on the integrated current amount Σi within a predetermined integrated time Σt.

[0046] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, the present invention is not limited to the tandem color printer shown in FIG. 1, but can be applied to various image forming apparatuses such as monochrome printers, monochrome copiers, digital multifunction machines, color copiers, and color multifunction machines. [Industrial Applicability]

[0047] The present invention can be used in an image forming apparatus using an electrophotographic process. [Explanation of symbols]

[0048] 1a to 1d Photoconductor drum (image carrier) 2a~2d Charging device 3a~3d developing device 5 Exposure equipment 6a~6d Primary transfer roller 7a~7d Cleaning device 8 Intermediate transfer belt 9 Secondary transfer roller 10 Drive roller 11 Tension roller 12a Paper feed roller 12b Registration roller pair 13 Fixing section 13a Fixing roller pair 14 Branch 15 Discharge Roller Pair 16 Paper Cassette 17 Output Tray 18-sided conveyor 19 Belt cleaning unit 20 Charging roller 21 Developing roller 22 Cleaning blade 23 Rubbing roller 61 Main motor 63 Belt drive motor 70 Image input section 71 Voltage control circuit 72 Charge voltage power supply 73 Development voltage power supply 74 Transfer voltage power supply 80 Control section 81 LCD display section 82 LED 90 Control section 91 CPU 92 ROM 93 RAM 94 Temporary storage 95 Counter 100 Image forming device Pa~Pd Image forming section S Paper (recording medium)

Claims

1. An image forming apparatus comprising: an image carrier having a photosensitive layer on its surface and driven to rotate; a charging device for charging the surface of the image carrier; an exposure device for exposing the surface of the image carrier charged by the charging device to light to form an electrostatic latent image; a developing device for developing the electrostatic latent image into a toner image; a transfer section for transferring the toner image onto a recording medium; and a cleaning blade for scraping off toner remaining on the image carrier, An image forming apparatus characterized in that an amount of charging current of the image carrier is detected, and if an integrated current amount obtained by integrating the amount of charging current over a predetermined period of time is lower than a predetermined threshold value, an aging process is performed in which the image carrier is rotated in a charged state.

2. 2. The image forming apparatus according to claim 1, further comprising: a determining unit that determines, when a job is completed, whether or not an accumulated time obtained by accumulating the driving time of the image carrier has reached the predetermined time; if the predetermined time has not been reached, a next job is performed; and if the predetermined time has been reached, a determining unit that determines whether or not the accumulated current amount has exceeded the threshold value, and resets the accumulated time and the accumulated current amount.

3. 3. The image forming apparatus according to claim 1, wherein the image carrier is a positively charged organic photoconductor.

Images