Image forming device

Abstract

To make a density difference in a width direction in a toner image less likely to occur, the toner image formed on a surface of a photoreceptor even when a cleanerless method and a contact electrification method are employed.SOLUTION: An image forming apparatus is provided with an electrifying roller 22 that is in contact with a photoreceptor drum 21 to electrify a surface of the photoreceptor drum 21, a developing device 26 that forms a toner image on the surface of the photoreceptor drum 21 and recovers an untransferred toner attached to the surface of the photoreceptor drum 21, and detection means 30, 81 that can detect that the electrifying roller 22 is a new article. When the detection means 30, 81 detect that the electrifying roller 22 is the new article, before a printing operation is started, the image forming apparatus executes a control mode (idling mode) for forming, with the developing device 26, a toner image pattern TP over an image area M on the surface of the photoreceptor drum 21, and attaching toner GP onto an outer peripheral surface of the electrifying roller 22 with the toner image pattern TP over a circumferential direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a combination machine thereof. [Background technology]

[0002] Conventionally, among image forming devices such as copiers and printers, cleanerless types have been known that do not include a cleaning device for cleaning untransferred toner adhering to the surface of a photosensitive member (photosensitive drum) (see, for example, Patent Document 1). In such cleanerless image forming devices, untransferred toner adhering to the surface of the photosensitive member is collected by a developing device. In addition, in image forming devices such as copiers and printers, a contact charging system has been known in which the surface of a photosensitive member (photosensitive drum) is charged by a charging roller that contacts the surface of the photosensitive member (see, for example, Patent Document 1).

[0003] On the other hand, Patent Document 1 discloses a technology in which, in a cleanerless, contact charging image forming apparatus, when an abnormal stop occurs during development due to a jam or the like, the charging roller is contaminated with toner, thereby preventing a problem of reduced charging performance. In this case, the toner adhering to the photosensitive member is temporarily collected by the charging roller, and then the toner collected by the charging roller is expelled onto the photosensitive member. Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional image forming devices, when a cleanerless system and a contact charging system are adopted, a portion of the charging roller in the width direction becomes locally contaminated with toner, resulting in a difference in density in the width direction of the toner image formed on the surface of the photosensitive member.

[0005] The present invention has been made to solve the above-mentioned problems, and aims to provide an image forming apparatus in which density differences in the width direction are unlikely to occur in the toner image formed on the surface of the photosensitive member, even when a cleanerless system and a contact charging system are adopted. [Means for solving the problem]

[0006] The image forming apparatus of the present invention includes a photosensitive member, a charging roller that contacts the photosensitive member and charges the surface of the photosensitive member, a developing device that develops a latent image formed on the surface of the photosensitive member to form a toner image and collects untransferred toner that has adhered to the surface of the photosensitive member, and a detection means that can detect that the charging roller is new, and when the detection means detects that the charging roller is new, a control mode is executed in which, before a printing operation is started, the developing device forms a toner image pattern over an image area on the surface of the photosensitive member and the toner image pattern causes toner to adhere to the outer peripheral surface of the charging roller in a circumferential direction. and when it is determined that the amount of toner adhering to the charging roller exceeds a threshold, a cleaning mode is executed in which the toner adhering to the charging roller is caused to adhere to the surface of the photosensitive body and is collected by the developing device, and after the cleaning mode is executed, a leveling mode is executed in which a second toner image pattern is formed on the surface of the photosensitive body over an image area by the developing device, and the toner adhering to the charging roller is leveled across the width direction by the second toner image pattern. It is something. [Effects of the Invention]

[0007] According to the present invention, an image forming apparatus can be provided in which, even when a cleanerless system and a contact charging system are adopted, density differences in the width direction are unlikely to occur in the toner image formed on the surface of the photosensitive member. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. [Figure 3] 1A and 1B are a top view and a side view, respectively, showing how toner adheres to a charging roller due to a toner image pattern on a photosensitive drum. [Figure 4] 10 is a flowchart showing an example of control when an idle drive mode (control mode) is executed. [Figure 5]10 is a table showing the relationship between the amount of toner adhered to the charging roller and the density unevenness in the width direction of the toner image. [Figure 6] FIG. 10 is a side view showing a state in which part of the toner adhering to the charging roller is discharged onto the photosensitive drum in a cleaning mode in the image forming apparatus as the first modified example. [Figure 7] 10 is a flowchart showing control after printing starts in Modification 1. [Figure 8] 10 is a graph showing the relationship between the amount of toner input onto the photosensitive drum and the amount of toner adhered onto the charging roller. [Figure 9] 10 is a flowchart showing control after the start of printing according to Modification 2. [Figure 10] FIG. 11 is a cross-sectional view showing an imaging unit according to a third modified example. [Figure 11] 10 is a graph showing the relationship between the amount of toner input onto the photosensitive drum and the amount of toner adhered onto the charging roller in Modification 3. [Figure 12] 10 is a flowchart showing control after the start of printing according to a fourth modified example. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be appropriately simplified or omitted.

[0010] First, the overall configuration and operation of an image forming apparatus 1 will be described with reference to FIG. The image forming apparatus 1 in this embodiment is a tandem color image forming apparatus in which a plurality of process cartridges 20Y, 20M, 20C, and 20BK are arranged side by side so as to face an intermediate transfer belt 40. In addition, a developing device 26 (see FIG. 2) is installed so as to face the photosensitive drums 21 of the plurality of process cartridges 20Y, 20M, 20C, and 20BK.

[0011] In Figure 1, 1 indicates the main body of a color copier as an image forming device, 2 indicates a document transport unit that transports a document to a document reading unit 3, 3 indicates a document reading unit that reads image information from the document, and 4 indicates a writing unit (exposure unit) that emits laser light L (see Figure 2) based on input image information. Also, 20Y, 20M, 20C, and 20BK indicate process cartridges corresponding to the respective colors (yellow, magenta, cyan, and black), and 40 indicates an intermediate transfer belt onto which toner images of multiple colors are transferred in an overlapping manner. Also, 61 denotes a paper feed device in which sheets P such as paper are stored, 65 denotes a secondary transfer roller that transfers a toner image formed on an intermediate transfer belt 40 as an intermediate transfer body onto the sheet P, 66 denotes a fixing device that fixes an unfixed image on the sheet P, and 70 denotes a toner container for replenishing toner of each color to each developing device 26 corresponding to the multiple process cartridges 20Y, 20M, 20C, and 20BK.

[0012] 2, each of the process cartridges 20Y, 20M, 20C, and 20BK is an integrated unit of a photosensitive drum 21 (image carrier) as a photosensitive member and a charging roller 22. Each of the process cartridges 20Y, 20M, 20C, and 20BK is replaced with a new one in the image forming apparatus main body 1 when it reaches the end of its life. Each developing device 26 is disposed opposite the photosensitive drum 21 (photosensitive member) of each process cartridge 20Y, 20M, 20C, and 20BK. When the developing device 26 reaches the end of its life, it is replaced with a new one in the image forming apparatus main body 1. The operation of attaching and detaching the developing device 26 to and from the image forming apparatus main body 1 and the operation of attaching and detaching the process cartridges 20Y, 20M, 20C, and 20BK to and from the image forming apparatus main body 1 can be performed separately and independently. A toner image of each color (yellow, magenta, cyan, black) is formed on the photosensitive drum 21 (photosensitive member) of each of the process cartridges 20Y, 20M, 20C, and 20BK.

[0013] Hereinafter, the operation (printing operation) of the image forming apparatus during normal color image formation will be described. First, the document is transported from the document table by the transport rollers of the document transport unit 2 and placed on the contact glass of the document reading unit 3. Then, the document reading unit 3 optically reads the image information of the document placed on the contact glass. Then, the image information for each color of yellow, magenta, cyan, and black is sent to the writing unit 4. Then, from the writing unit 4, laser light L (exposure light) based on the image information for each color is irradiated onto the surface of the photosensitive drum 21 (see FIG. 2) of the corresponding process cartridge 20Y, 20M, 20C, 20BK.

[0014] Meanwhile, the photosensitive drums 21, which serve as photosensitive bodies, are each driven and rotated clockwise in FIG. 2 by a drive motor 90. First, the surface of the photosensitive drum 21 is uniformly charged at a position facing the charging roller 22 (charging step). In this way, a charging potential is formed on the photosensitive drum 21. Thereafter, the charged surface of the photosensitive drum 21 reaches a position where the laser light L is irradiated by each writing unit 4, and an electrostatic latent image based on image information is formed at that position (exposure step).

[0015] The laser light corresponding to the yellow component is irradiated onto the surface of the photosensitive drum 21 of the first process cartridge 20Y from the left side of the drawing. At this time, the laser light of the yellow component is scanned in the direction of the rotation axis (main scanning direction) of the photosensitive drum 21 by a polygon mirror rotating at high speed. In this way, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 21 after it has been charged by the charging roller 22. Similarly, the cyan laser light is irradiated onto the surface of the photosensitive drum 21 of the process cartridge 20C, which is the second from the left on the paper, and an electrostatic latent image of the cyan component is formed. The magenta laser light is irradiated onto the surface of the photosensitive drum 21 of the process cartridge 20M, which is the third from the left on the paper, and an electrostatic latent image of the magenta component is formed. The black laser light is irradiated onto the surface of the photosensitive drum 21 of the process cartridge 20BK, which is the fourth from the left on the paper, and an electrostatic latent image of the black component is formed.

[0016] Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent image of each color is formed reaches a position facing the developing device 26. Then, toner of each color is supplied from each developing device 26 onto the photosensitive drum 21, and the latent image on the photosensitive drum 21 is developed (this is the developing process). Thereafter, the surfaces of the photosensitive drums 21 after the development process reach positions facing the intermediate transfer belt 40. Here, primary transfer rollers 24 serving as transfer devices are installed at each of the facing positions so as to abut against the inner circumferential surface of the intermediate transfer belt 40. Then, at the positions of the primary transfer rollers 24, the toner images of each color formed on the photosensitive drums 21 are transferred onto the intermediate transfer belt 40 in order, superimposed on top of each other (this is the primary transfer process). A predetermined transfer bias (a voltage with a positive polarity different from the polarity of the toner) is applied to the primary transfer rollers 24 (transfer device) from a transfer power source 96.

[0017] After that, the surface of the photosensitive drum 21 after the primary transfer process is neutralized by a neutralization device (not shown). Thereafter, the surfaces of the photosensitive drums 21 reach positions facing the developing devices 26. Then, the developing devices 26 collect untransferred toner remaining on the photosensitive drums 21 (cleaning process). In this manner, the developing devices 26 in this embodiment are configured to be able to collect untransferred toner remaining on the surfaces of the photosensitive drums 21 (photosensitive bodies). That is, the image forming apparatus 1 in this embodiment employs a cleanerless system. Thus, a series of image forming processes on the photosensitive drum 21 is completed.

[0018] Meanwhile, the surface of intermediate transfer belt 40, which serves as an intermediate transfer body onto which the images of each color on photosensitive drum 21 are transferred in a superimposed manner, travels in the direction of the arrow in the figure and reaches the position of secondary transfer roller 65. Then, at the position of secondary transfer roller 65, the full-color image on intermediate transfer belt 40 is secondarily transferred onto sheet P (secondary transfer process). Thereafter, the surface of the intermediate transfer belt 40 reaches the position of the intermediate transfer belt cleaning device, and the untransferred toner on the intermediate transfer belt 40 is collected by the intermediate transfer belt cleaning device, completing the series of transfer processes on the intermediate transfer belt 40.

[0019] Here, the sheet P conveyed to the position of the secondary transfer roller 65 is conveyed from the paper feeder 61 via the registration roller 64 and the like. More specifically, a sheet P fed by a paper feed roller 62 from a paper feed device 61 that stores sheets P passes through a conveyance path and is then guided to the position of a registration roller 64. The sheet P that has reached the position of the registration roller 64 is conveyed toward the position of a secondary transfer roller 65 in synchronization with the toner image on the intermediate transfer belt 40.

[0020] Thereafter, the sheet P onto which the full-color image has been transferred is guided to the position of the fixing device 20. Then, in the fixing device 20, the color image is fixed onto the sheet P at the nip between a fixing roller and a pressure roller. After the fixing process, the sheet P is discharged as an output image outside the apparatus main body 1 by a discharge roller 69, and then stacked on the discharge tray 5, completing a series of image forming processes (printing operations).

[0021] Next, the image forming unit of the image forming apparatus will be described in detail with reference to FIG. The four image forming units installed in the image forming apparatus main body 1 have almost the same structure except for the color of the toner used in the image forming process, so they are illustrated without the alphabetical symbols (Y, M, C, BK) for components such as process cartridges and developing devices.

[0022] As shown in FIG. 2, the process cartridge 20 mainly includes a photosensitive drum 21 as a photosensitive member and a charging roller 22 housed integrally in a case. As explained above, the image forming unit in this embodiment is a cleanerless type image forming unit, and does not have a dedicated cleaning device (cleaning blade) for cleaning untransferred toner (residual toner) on the photosensitive drum 21, and the function of such a cleaning device is performed by the developing device 26.

[0023] The photosensitive drum 21 as a photosensitive member is a negatively charged organic photosensitive member, and is formed by providing a photosensitive layer and the like on a drum-shaped conductive support. The charging roller 22 is a roller member made of a conductive core metal and a medium-resistance elastic layer coated on the outer periphery thereof. A predetermined charging bias is applied to the charging roller 22 from a charging power source 95, thereby uniformly charging the surface of the opposing photosensitive drum 21. The charging roller 22 in this embodiment is configured to come into contact with the surface of the photosensitive drum 21 (photosensitive member). That is, the image forming apparatus 1 in this embodiment employs a contact charging system.

[0024] 2, the developing device 26 is mainly arranged so that the developing roller 26a, which serves as a developer carrier, comes into contact with the photosensitive drum 21 with a predetermined pressure. Toner (a non-magnetic or magnetic one-component developer) is contained within the developing device 26. An electric field (developing electric field) is formed between the developing roller 26a and the photosensitive drum 21 (developing region), which develops the electrostatic latent image formed on the surface of the photosensitive drum 21 (forming a toner image). The electric field in the development area is formed by a predetermined development bias applied to the development roller 26a by the development power supply 91 and a surface potential (latent image potential) formed on the surface of the photosensitive drum 21 by the charging process and the exposure process.

[0025] The structure and operation of the developing device 26 will be described in more detail below. 2, the developing device 26 in this embodiment is a developing device of a contact single-component development type, and is installed separately from the process cartridge 20 so as to be detachable (replaceable) from the image forming apparatus main body 1. As shown in FIG. 2, the developing device 26 is made up of a developing roller 26a as a developer carrier, a supply roller 26b as a supply rotor, a doctor blade 26c as a developer regulating member, and the like.

[0026] The developing roller 26a, which serves as a developer carrier, carries toner T (developer) on its surface and rotates in a predetermined direction (counterclockwise in FIG. 2) to supply the toner T to the electrostatic latent image formed on the photosensitive drum 21. In this embodiment, the developing roller 26a is disposed so as to contact the photosensitive drum 21. The developing roller 26a may be one having a roller portion made of a conductive elastic material mounted on a rotating shaft portion (core metal) made of a conductive metal material such as stainless steel.

[0027] The supply roller 26b is in contact with the developing roller 26a. The supply roller 26b rotates in the opposite direction (clockwise in FIG. 2) to the rotation direction of the developing roller 26a to supply the toner T to the developing roller 26a. In other words, the supply roller 26b is a roller member that supplies the toner T to the developing roller 26a while rotating in the co-rotating direction with the rotation direction of the developing roller 26a.

[0028] The supply roller 26b is made of a metal core and has a conductive foamed polyurethane layer (electrical resistance value: 10 3 ~10 14 Ω or so.) can be used as a laminate. Although not shown, gears are provided on the shafts of the developing roller 26a and the supply roller 26b, and the gears are configured to mesh with each other. A driving force is input to these gear trains from a drive motor 90, and the developing roller 26a and the supply roller 26b are each driven to rotate in the directions of the arrows in FIG. 2.

[0029] The doctor blade 26c is a thin plate-like member made of a metal material such as stainless steel, and is in contact with the photosensitive drum 21 downstream of the supply roller 26b and upstream of the development area. The doctor blade 26c regulates the amount of toner on the developing roller 26a to an appropriate amount. That is, the amount of toner (toner layer) supplied from the supply roller 26b onto the developing roller 26a is thinned at the position of the doctor blade 26c.

[0030] The developing device 26 configured as above operates as follows during a normal developing process. First, a portion of the toner T contained in the developing device 26 is drawn up (carried) onto the supply roller 26b. Then, the toner T carried on the supply roller 26b is supplied onto the developing roller 26a in a frictionally charged state. The toner carried on the developing roller 26a is then thinned by the doctor blade 26c and reaches a position (developing area) facing the photosensitive drum 21. At this position, the toner is attracted to the electrostatic latent image formed on the photosensitive drum 21 by an electric field (developing electric field) formed in the developing area. In this way, a desired toner image (image) is formed on the photosensitive drum 21. At this time, the untransferred toner carried on the photosensitive drum 21 is collected onto the developing roller 26a. That is, after passing through the development area, the surface of the developing roller 26a carries the untransferred toner carried on the photosensitive drum 21 and the toner that did not move onto the photosensitive drum 21 in the development process (undeveloped toner). Then, the toner carried on the developing roller 26a is returned into the developing device 26. In addition, in the developing device 26 of this embodiment, a scraping member for scraping off undeveloped toner and untransferred toner carried on the developing roller 26a, and a stirring member for stirring the toner so that it does not aggregate within the developing device 26, can also be provided. In this embodiment, non-magnetic toner with a circularity of approximately 0.932 is used as the toner (developer) contained in the developing device 26. In addition, non-spherical pulverized toner or polymerized toner can be used as the toner.

[0031] The following describes the characteristic configuration and operation of the image forming apparatus 1 according to this embodiment. 2 and other figures, the image forming apparatus 1 is of a cleanerless type and employs a contact charging type. That is, the image forming apparatus 1 is provided with a contact-type charging roller 22 that contacts the photosensitive drum 21 serving as a photosensitive member to charge the surface of the photosensitive drum 21, and a developing device 26 that develops a latent image formed on the surface of the photosensitive drum 21 to form a toner image and collects untransferred toner adhering to the surface of the photosensitive drum 21.

[0032] Referring now to FIG. 2, image forming apparatus 1 in this embodiment is provided with ID chip 30 and reader 81 as detection means capable of detecting whether charging roller 22 is new. More specifically, in this embodiment, the charging roller 22 and the photosensitive drum 21 are integrated as a process cartridge 20. The ID chip 30 and the reading device 81 serving as the detection means are configured to be able to detect that the process cartridge 20 (charging roller 22) is new. That is, the detection means detects whether the photosensitive drum 21 is new as well as the charging roller 22.

[0033] Specifically, the ID chip 30 (information storage medium) is installed in the case (exterior part) of the process cartridge 20. The ID chip 30 records (stores) various information about the process cartridge 20, such as the serial number, destination, etc., in addition to information about whether the process cartridge 20 is new or not (for example, information about the usage history). On the other hand, the reading device 81 is installed in the image forming apparatus main body 1. When the process cartridge 20 is attached to the image forming apparatus main body 1, the reading device 81 facing the ID chip 30 reads the information recorded on the ID chip 30, and the information is sent to the control unit 80. As a result, when the charging roller 22 (process cartridge 20) is attached to the image forming apparatus main body 1, the control unit 80 determines whether the charging roller 22 (process cartridge 20) is new or not. In this way, the reading device 81, the ID chip 30 (and the control unit 80) function as a detection means for detecting whether the charging roller 22 (process cartridge 20) is new or not. In this embodiment, the reader 81 is configured to be able to write information stored (recorded) in the control unit 80 (for example, updated information on the usage history) into the ID chip 30.

[0034] In this specification and the like, the state in which the charging roller 22 or the process cartridge 20 is "new" is defined as a state in which no toner is attached to the outer peripheral surface of the charging roller 22. Specifically, when the charging roller 22 or the process cartridge 20 has not yet been used in the image forming apparatus 1 (when it is about to be used) (mainly when it is delivered or when it is replaced), the charging roller 22 or the process cartridge 20 is treated as being "new." In addition, in this embodiment, the ID chip 30 and the reading device 81 are used as detection means for detecting whether the charging roller 22 (process cartridge 20) is new or not, but the detection means is not limited to this and any known means (for example, a fuse that breaks when first installed in the image forming device 1) can be used.

[0035] 3, in this embodiment, when the detection means (reader 81, ID chip 30) detects that the charging roller 22 (process cartridge 20) is new, before the printing operation is started, the developing device 26 forms a toner image pattern TP (a dummy image that is not intended to be printed on the sheet P) on the surface of the photosensitive drum 21 over an image area M (the maximum range in the width direction in which an image can be formed), and the toner image pattern TP causes toner GP to adhere to the outer peripheral surface of the charging roller 22 in the circumferential direction, in a "control mode." Note that hereinafter, such a control mode will be referred to as an "idle drive mode" where appropriate. That is, when the charging roller 22 (process cartridge 20) is new, the photosensitive drum 21 is idled to form a toner image pattern TP on the photosensitive drum 21 without performing a normal printing operation, and a predetermined amount or more of toner adheres to the entire outer periphery of the outer surface of the image area M of the charging roller 22, and this state is maintained thereafter. Hereinafter, the toner adhered to the charging roller 22 in this way in the idle drive mode (control mode) will be referred to as "adhered toner GP" as appropriate.

[0036] The reason for this control (idle drive mode) is that in the cleanerless and contact charging image forming apparatus 1, when images are continuously formed locally at the same position in the width direction (the direction perpendicular to the paper surface in FIGS. 2 and 3(B), and the left-right direction in FIG. 3(A)), only a portion of the width direction of the charging roller 22 becomes locally contaminated with toner. When a portion of the width direction of the charging roller 22 becomes locally contaminated with toner in this way, the charging potential of only that portion changes, resulting in a difference in density in the width direction of the toner image formed on the surface of the photosensitive drum 21 during printing. In contrast to this, in this embodiment, when the charging roller 22 is new and has a clean surface, the idle drive mode (control mode) is executed before printing starts to uniformly deposit toner GP in the width and circumferential directions of the charging roller 22, which reduces the likelihood of the charging roller 22 becoming locally soiled with toner in only a portion of its width direction during subsequent printing. This also reduces the likelihood of the toner image (image) formed on the surface of the photosensitive drum 21 during printing having a density difference in the width direction.

[0037] In this embodiment, the toner image pattern TP formed on the photosensitive drum 21 in the idle drive mode is a solid image. More specifically, in the idle drive mode, a substantially rectangular solid image (having an image area M as its length in the main scanning direction (width direction) and a length N in the sub-scanning direction) is formed as a toner image pattern TP on the photosensitive drum 21 by the image creation process previously described with reference to Figures 1 and 2, and a layer of adhered toner GP is formed on the charging roller 22. The "length N in the sub-scanning direction" of the toner image pattern TP at this time corresponds to at least the outer circumferential length of the charging roller 22 (one revolution or more). In this embodiment, when the main power supply (main switch) of the image forming apparatus 1 is switched from the off state to the on state, the reading device 81 (detection means) detects whether the cartridge is new, and when the new cartridge is detected, the idle drive mode is executed. This is because the main power supply of the image forming apparatus 1 is turned on and off when the process cartridge 20 (charging roller 22) is delivered or replaced.

[0038] In this embodiment, when the idle drive mode (control mode) is executed, the image forming conditions are adjusted so that the toner image pattern TP formed on the surface of the photosensitive drum 21 easily adheres to the charging roller 22. That is, the image creation conditions in the image creation process are optimized so that a desired amount of adhered toner GP is efficiently carried in a short time on the new charging roller 22. In other words, the image creation conditions are adjusted so that the adhesion rate (transfer rate) of the toner GP to the charging roller 22 is maximized.

[0039] In detail, in this embodiment, the idle drive mode (control mode) is executed in at least one of the following states: a state in which the absolute value of the development bias applied to the development roller 26a (developer carrier) is increased compared to that during normal printing (a state in which the development potential is increased); a state in which the polarity of the transfer bias applied to the primary transfer roller 24 as a transfer device is the opposite polarity (negative polarity) to that during normal printing; and a state in which the polarity of the charging bias applied to the charging roller 22 is the opposite polarity (positive polarity) to that during normal printing. When the developing bias is adjusted to be larger by controlling the developing power supply 91 by the control unit 80, the image density (toner adhesion amount, toner input amount) of the toner image pattern TP formed on the photosensitive drum 21 becomes denser, and the amount of toner GP adhering to the charging roller 22 per unit area also increases. Furthermore, when the control unit 80 controls the transfer power supply 96 to adjust the polarity of the transfer bias to the opposite polarity, the toner image pattern TP formed on the photosensitive drum 21 becomes less likely to electrostatically adhere (move) to the intermediate transfer belt 40, and therefore the image density of the toner image pattern TP at the position of the charging roller 22 also becomes higher, and the amount of adhering toner GP adhering to the charging roller 22 also increases. Furthermore, when the polarity of the charging bias is adjusted to be the opposite polarity by controlling the charging power source 95 by the control unit 80, the rate at which the toner image pattern TP formed on the photosensitive drum 21 adheres to the charging roller 22 (adhesion rate, transfer rate) increases, and the amount of adhering toner GP adhering to the charging roller 22 increases. The image forming conditions adjusted in this way are returned to their original values ​​after the idle drive mode ends.

[0040] In this embodiment, the time T1 during which the idle drive mode (control mode) is executed is set so that the amount of adhering toner GP on the charging roller 22 becomes equal to or greater than a desired value. Specifically, the amount of toner adhesion per unit area of ​​the toner GP on the charging roller 22 is X (mg / cm 2), the image area M (development width) is M (cm), the outer diameter of the charging roller 22 is F (cm), and the toner adhesion amount (toner input amount) per unit area of ​​the toner image pattern TP on the photosensitive drum 21 is W (mg / cm 2 ), the length (discharge length) of the toner image pattern TP in the sub-scanning direction is N (cm), and the adhesion rate (transfer rate) to the charging roller 22 is Z (%), then X M F = W M N Z / 100 Therefore, the length N (discharge length) of the toner image pattern TP in the sub-scanning direction is N=X·F·100 / (W·Z) Therefore, when the linear velocity (process linear velocity) of the photosensitive drum 21 is V (cm / sec), the time T1 for executing the idle drive mode (control mode) is T1=N / V This can be obtained by: In this embodiment, a solid image is formed as the toner image pattern TP, so W and N in the above formula are small, and the execution time T1 of the idle drive mode is also short. Therefore, the waiting time in the idle drive mode is also short, and the load on the components involved in the image formation process is also small.

[0041] An example of control when the idle drive mode (control mode) is executed will be described below with reference to FIG. As shown in FIG. 4, first, when the main power supply of the image forming apparatus 1 is turned on (step S1), a start-up process (a warm-up operation such as adjusting image forming conditions) of the image forming apparatus 1 is performed (step S2). Then, the detection means (reader 81, ID chip 30) determines whether the charging roller 22 (process cartridge 20) is new (step S3). If it is determined that the charging roller 22 is not new, it is determined that the toner GP is carried on the charging roller 22 and no difference in image density occurs in the width direction, and the flow ends. On the other hand, if it is determined in step S3 that the charging roller 22 is new, it is determined that there is a possibility that a difference in image density in the width direction will occur during printing if left as is, and so the idle drive mode is executed for a predetermined time T1 (steps S4 and S5). That is, a predetermined amount or more of adhered toner GP is carried on the charging roller 22. Then, after the shutdown process (for example, an operation to return the image formation conditions adjusted in the idle drive mode to their original state) is completed (step S6), this flow ends.

[0042] It is preferable that the amount of adhered toner GP carried on the charging roller 22 in the idle driving mode exceeds a target value. Figure 5 shows the results of visually checking the degree of image density unevenness in the width direction in a gradation image (halftone image) after using the image forming apparatus 1 of this embodiment to vary the amount of toner GP adhering to the charging roller 22 (toner adhesion amount) between four levels and printing a localized image (vertical band image) for each level. As shown in FIG. 5, the amount of toner adhered per unit area on the charging roller 22 is 0.50 (mg / cm 2 ) or more, no unevenness in image density occurs (determined as "◯"), and if it is below that, unacceptable unevenness in image density occurs (determined as "X"). In this way, by carrying an amount of adhered toner GP exceeding a predetermined value on the charging roller 22 in the idle driving mode, it is possible to stably reduce the occurrence of uneven image density.

[0043] <Variation 1> Referring to Figure 6, when the image forming device 1 in variant example 1 determines that the amount of toner adhering to the charging roller 22 (amount of adhering toner GP) exceeds the threshold value R, it executes a "cleaning mode" in which the toner adhering to the charging roller 22 is deposited on the surface of the photosensitive drum 21 and collected by the developing device 26. Specifically, when the cumulative dot count value of the toner image formed on the surface of the photosensitive drum 21 reaches a predetermined value A, it is determined that the amount of toner adhering to the charging roller 22 has exceeded the threshold value R. Then, the excess adhering toner GP that exceeds the threshold value R is discharged onto the photosensitive drum 21 as discharge toner CP. The above-mentioned "cumulative dot count value" is approximately proportional to the cumulative amount of toner used to form an image on the photosensitive drum 21, and can be grasped by the control unit 80 based on the cumulative number of written pixels in the writing unit 4. The reason for this control is that if too much toner GP adheres to the charging roller 22, the toner may fall off the charging roller 22 onto the photosensitive drum 21, or the charging performance of the charging roller 22 may deteriorate, resulting in poor charging and causing abnormal images.As shown in Figure 8, this phenomenon becomes more noticeable as the printing operation is repeated and the cumulative number of printed sheets (operating time) increases (as the amount of toner input onto the photosensitive drum 21 increases), the amount of toner GP adhered to the charging roller 22 (toner adhesion amount) increases. Therefore, in the first modified example, when the number of printed sheets increases, the cumulative dot count value becomes equal to or exceeds the predetermined value A, and the toner adhesion amount X per unit area on the charging roller 22 becomes equal to or exceeds the threshold value R (for example, 0.8 mg / cm 2 When it is determined that the toner level on the charging roller 22 has reached or exceeded this level, the cleaning mode is executed, and the excess toner on the charging roller 22 is expelled onto the photosensitive drum 21 as discharged toner CP, and the discharged toner CP is then collected into the developing device 26. Specifically, the cleaning mode is executed at a timing different from that at which normal printing operations are performed (for example, a timing corresponding to the interval between sheets when continuous paper is fed or a timing at which a series of printing operations is completed), and under image creation conditions that make it easier for toner to migrate from the charging roller 22 to the photosensitive drum 21 than during normal printing (for example, the absolute value of the negative polarity charging bias is set larger than during normal printing). The cumulative dot count value is also reset each time the cleaning mode is executed. The above-mentioned predetermined value A is set so that the amount of toner GP adhered to the charging roller 22 that is reduced by executing the cleaning mode once is equal to the amount of toner GP adhered to the charging roller 22 that is increased by the cumulative dot count value.

[0044] An example of control when the cleaning mode is executed in Modification 1 will be described below with reference to FIG. 7, when printing starts (step S11), it is determined whether the cumulative dot count value related to printing up to now is equal to or greater than a predetermined value A (step S12). As a result, if it is determined that the cumulative dot count value is not equal to or greater than the predetermined value A, it is determined that the amount of toner adhesion on charging roller 22 has not reached threshold value R, and the flow ends. On the other hand, if it is determined in step S12 that the cumulative dot count value is equal to or greater than the predetermined value A, it is determined that the amount of toner adhered to the charging roller 22 has reached the threshold value R, and there is a possibility that an abnormal image may be produced, so the cleaning mode is executed for a predetermined time T2 (steps S13 and S14). Then, after the shutdown process (for example, an operation to adjust the image forming conditions after printing) is completed (step S15), this flow ends. In the first modification, the cleaning mode is executed before the shutdown process, but the cleaning mode can also be executed during the shutdown process after printing is completed. In such a case, the cleaning mode is executed during printing, which prevents problems such as a decrease in printing productivity.

[0045] <Variation 2> Referring to Figure 9, after the cleaning mode described in Variation 1 is executed, the image forming device 1 in Variation 2 executes a "leveling mode" in which the developing device 26 forms a second toner image pattern (for example, similar to the toner image pattern PT described earlier using Figure 3, etc.) on the surface of the photosensitive drum 21 across the image area M, and then uses the second toner image pattern to level the toner adhering to the charging roller 22 across the width. The reason for this control is that after the cleaning mode is executed, there is a possibility that the amount of toner adhered to the charging roller 22 may become uneven across the width. If the amount of toner adhered to the charging roller 22 becomes uneven across the width, the distribution of the charging potential formed on the photosensitive drum 21 also becomes uneven across the width, resulting in uneven image density. In order to alleviate such problems, in variant example 2, after the cleaning mode, toner is adhered to the charging roller 22 using a second toner image pattern (e.g., a solid image) formed on the surface of the photosensitive drum 21, so that the amount of toner adhered to the charging roller 22 is uniform in the width direction. In addition, in variant example 2, the "predetermined value A" for the cumulative dot count value is set so that the amount of toner that is reduced by executing the cleaning mode once is equal to the sum of the amount of increase in the amount of toner GP that is adhered to the charging roller 22 due to the cumulative dot count value and the amount of increase in the amount of toner GP that is adhered to the charging roller 22 due to the smoothing mode. An example of control when the smoothing mode is executed in Modification 2 will be described below with reference to FIG. 9, when printing starts (step S11), the flow of steps S11 to S14 is performed similarly to that of Modification Example 1. Then, after the cleaning mode ends, the smoothing mode S20 is executed for a predetermined time T3 (steps S20, S21). Then, after the smoothing mode ends, this flow ends.

[0046] <Variation 3> 10, the image forming apparatus 1 in the third modification is provided with a cleaning roller 23 as a cleaning member that cleans the surface of the charging roller 22. As the cleaning roller 23, a known one can be used. In this way, by providing the cleaning roller 23 (cleaning member), even if the amount of toner input onto the photosensitive drum 21 increases with the increase in printing time, the amount of toner GP adhering to the charging roller 22 does not increase proportionally as in Figure 8, but rather increases gradually as shown in Figure 11. Therefore, compared to the first and second modifications, the number of times the cleaning mode is executed can be reduced.

[0047] <Variation 4> Referring to Figure 12, in the image forming apparatus 1 of variant example 4, when a toner image (for example, a vertical band image formed in the center of the width direction) is formed locally at a predetermined position on the photosensitive drum 21 in the width direction continuously for more than a predetermined number of times D, the developing device 26 forms a second toner image pattern (for example, similar to the toner image pattern PT described earlier using Figure 3, etc.) on the surface of the photosensitive drum 21 across the image area M, and executes a "leveling mode" in which the second toner image pattern levels the toner adhering to the charging roller 22 across the width direction. The reason for this control is that if a toner image is repeatedly formed locally at a predetermined position in the width direction of the photosensitive drum 21, the amount of toner adhesion at the position on the charging roller 22 corresponding to that predetermined position in the width direction may become greater than at other positions. If the amount of toner adhesion on the charging roller 22 becomes uneven in the width direction in this way, the distribution of the charging potential formed on the photosensitive drum 21 in the width direction will also become uneven, resulting in uneven image density. To alleviate such problems, in variant 4, when a toner image is formed locally at a predetermined position in the width direction continuously more than a predetermined number D (for example, 500 times (sheets)), a leveling mode (similar to that in variant 2) is used to make the amount of toner adhered to the charging roller 22 uniform in the width direction. An example of control when the smoothing mode is executed in the second modification will be described below with reference to FIG. 12, when printing starts (step S11), it is determined whether the toner image involved in the printing is localized (step S30). If it is determined that the toner image is localized, it is further determined whether such printing has occurred a predetermined number of times D or more (step S31). If it has occurred a predetermined number of times D or more, it is determined that there is a possibility of image density unevenness occurring, and the smoothing mode is executed (step S32). Then, this flow ends. On the other hand, if it is determined in step S30 that the toner image is not a localized toner image, or if it is determined in step S31 that the number of times that a localized toner image has been formed is less than the predetermined number D, the flow ends.

[0048] As described above, the image forming apparatus 1 in this embodiment includes the photosensitive drum 21 (photosensitive element), the charging roller 22 that contacts the photosensitive drum 21 to charge the surface of the photosensitive drum 21, the developing device 26 that develops the latent image formed on the surface of the photosensitive drum 21 to form a toner image and collects untransferred toner adhering to the surface of the photosensitive drum 21, and detection means (reader 81, ID chip 30) that can detect that the charging roller 22 is new. If the detection means detects that the charging roller 22 is new, the developing device 26 forms a toner image pattern TP on the surface of the photosensitive drum 21 across the image area M before a printing operation is started, and a control mode (idle drive mode) is executed in which the toner image pattern TP causes toner GP to adhere circumferentially to the outer peripheral surface of the charging roller 22. As a result, even when a cleanerless system and a contact charging system are employed, it is possible to make it difficult for density differences to occur in the width direction of the toner image formed on the surface of the photosensitive drum 21.

[0049] In the present embodiment, the developing device 26 is not a component of the process cartridge 20, but is a unit that can be attached to and detached from the image forming apparatus main body 1 independently. However, the developing device 26 can also be one of the components of the process cartridge 20, and configured to be attached and detached from the image forming apparatus main body 1 as a process cartridge. In such a case, the same effect as that of this embodiment can be obtained. In this application, a "process cartridge" is defined as a unit that integrates at least one of a charging device that charges an image carrier and a developing device that develops a latent image formed on the image carrier, and an image carrier, and is configured to be detachable from the image forming apparatus main body.

[0050] In this embodiment, the present invention is applied to an image forming apparatus 1 equipped with a developing device 26 of a contact one-component development type configured so that the developing roller 26a (developer carrier) abuts against the photosensitive drum 21 (photosensitive body). However, the present invention can also be applied to an image forming apparatus equipped with a developing device of a non-contact one-component development type configured so that the developing roller 26a (developer carrier) faces the photosensitive drum 21 (photosensitive body) with a small gap therebetween, or an image forming apparatus equipped with a developing device of a two-component development type. Furthermore, in this embodiment, the present invention is applied to an image forming apparatus 1 equipped with a transfer device (primary transfer roller 24) that transfers a toner image formed on the surface of photosensitive drum 21 (photosensitive body) to intermediate transfer belt 40 (intermediate transfer body). However, the present invention can also be applied to an apparatus that does not have an intermediate transfer body such as an intermediate transfer belt or intermediate transfer drum, but instead has a photosensitive drum (photosensitive body) on which a toner image developed by a developing device is formed, and a transfer device such as a transfer roller or transfer belt for transferring the toner image on the photosensitive drum to a sheet transported to the position of the photosensitive drum, that is, a so-called direct transfer type image forming apparatus. In such cases, the same effect as that of this embodiment can be obtained.

[0051] It is clear that the present invention is not limited to the present embodiment, and that within the scope of the technical concept of the present invention, each embodiment may be appropriately modified in addition to what is suggested in each embodiment. Furthermore, the number, position, shape, etc. of the components are not limited to the present embodiment, and the number, position, shape, etc. of the components may be any number, position, shape, etc. that is suitable for implementing the present invention. [Explanation of symbols]

[0052] 1 Image forming apparatus (image forming apparatus main body), 20, 20Y, 20M, 20C, 20BK process cartridges, 21 Photosensitive drum (photosensitive body, image carrier), 22 charging roller (charging device), 23 cleaning roller (cleaning member), 24 Primary transfer roller (transfer device), 26 developing device, 26a developing roller (developer carrier), 26b supply roller, 26c Doctor blade (developer control member), 30 ID chip (detection means), 40 Intermediate transfer belt (intermediate transfer body), 81 Reading device (detection means), M image area, TP toner image pattern, GP adhesion toner, CP discharge toner. [Prior art documents] [Patent documents]

[0053] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-209277

Claims

1. A photoreceptor; a charging roller that contacts the photoreceptor and charges the surface of the photoreceptor; a developing device that develops the latent image formed on the surface of the photosensitive member to form a toner image and collects untransferred toner adhering to the surface of the photosensitive member; a detection means for detecting whether the charging roller is new; Equipped with When the detection means detects that the charging roller is new, a control mode is executed in which, before a printing operation is started, a toner image pattern is formed on the surface of the photosensitive member over an image area, and toner is adhered to the outer peripheral surface of the charging roller in a circumferential direction by the toner image pattern. When it is determined that the amount of toner adhering to the charging roller exceeds a threshold, a cleaning mode is executed in which the toner adhering to the charging roller is caused to adhere to the surface of the photosensitive member and is collected by the developing device; an image forming apparatus characterized in that, after the cleaning mode is executed, the developing device forms a second toner image pattern across an image area on the surface of the photosensitive member, and executes a leveling mode in which the second toner image pattern levels the toner adhering to the charging roller across the width direction.

2. 2. The image forming apparatus according to claim 1, wherein, when the control mode is executed, image forming conditions are adjusted so that the toner image pattern formed on the surface of the photosensitive member easily adheres to the charging roller.

3. a transfer device that transfers the toner image formed on the surface of the photoreceptor to an intermediate transfer body or a sheet; the developing device includes a developer carrier that contacts or faces the photosensitive member, 3. The image forming apparatus according to claim 2, wherein the control mode is executed in at least one of the following states: a state in which the absolute value of the development bias applied to the developer carrier is increased compared to that during normal printing; a state in which the polarity of the transfer bias applied to the transfer device is reversed relative to that during normal printing; and a state in which the polarity of the charging bias applied to the charging roller is reversed relative to that during normal printing.

4. An image forming apparatus as described in any one of claims 1 to 3, characterized in that when the cumulative dot count value of the toner image formed on the surface of the photosensitive body reaches a predetermined value, it is determined that the amount of toner adhering to the charging roller exceeds the threshold value.

5. An image forming apparatus as described in any one of claims 1 to 3, characterized in that the smoothing mode is executed when the toner image is formed continuously more than a predetermined number of times locally at a predetermined position in the width direction of the photosensitive body.

6. An image forming apparatus according to claim 1, wherein the toner image pattern is a solid image.

7. An image forming apparatus as described in any one of claims 1 to 6, characterized in that it is provided with a cleaning member that cleans the surface of the charging roller.

8. A process cartridge is provided in which at least the photosensitive member and the charging roller are integrated, 8. The image forming apparatus according to claim 1, wherein the detecting means is capable of detecting that the process cartridge is new.

Images