Image forming apparatus

Abstract

To provide a technique to suitably remove a toner attached to an electrifying roller, in an image forming apparatus of a drum cleaner-less system.SOLUTION: An image forming apparatus has an image carrier, an electrifying member, a developing member, a transfer member, and a control unit. A toner image on a surface of the image carrier is transferred by the transfer member to a transfer target body, and subsequently a residual toner on the surface of the image carrier is recovered by the developing member. The control unit can execute an image forming operation, a first cleaning operation, and a second cleaning operation. In the first cleaning operation, a toner attached to the electrifying member is recovered by the developing member, and in the second cleaning operation, the toner attached to the electrifying member is discharged to the transfer target body passing through the transfer member.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] Image forming devices, such as copiers and laser printers, have been used for forming images using an electrophotographic process and have a photosensitive drum. One cleaning method for such image forming devices is a drum cleanerless system, which does not require a dedicated toner cleaning device for the photosensitive drum. In a drum cleanerless image forming device, the developing device also serves as a recovery device for recovering residual toner remaining on the photosensitive drum after transfer. The residual toner recovered by the developing device is reused for development. Therefore, the drum cleanerless system does not require a dedicated toner cleaning device or a container for storing the recovered residual toner, allowing for the miniaturization and cost reduction of the image forming device.

[0003] In a drum cleanerless image forming apparatus, if a large amount of residual toner remains on the photosensitive drum, it may adhere to the charging roller that charges the photosensitive drum. This may result in poor charging, making it impossible to control the potential difference between the surface potential of the photosensitive drum and the potential of the developing member to an appropriate value. As a result, the developing unit may not be able to properly collect the residual toner, or the developing unit may not be able to properly collect the toner, resulting in poor image quality due to unintended toner development.

[0004] Patent Document 1 discloses a technology for cleaning the charging roller by charging the toner adhering to the charging roller to the normal polarity, transferring the charged toner from the charging roller to a photosensitive drum, and then recovering the toner from the photosensitive drum to a developing member, thereby suppressing charging defects on the surface of the photosensitive drum and suppressing image defects. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2022-129271 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the toner deteriorates toward the end of its life, a large amount of toner charged to the normal polarity may adhere to the developing member. In such cases, the potential difference between the developing member and the surface of the photosensitive drum facing it cannot be properly controlled, and a large amount of toner continues to be expelled from the developing member onto the photosensitive drum. In such cases, the cleaning effect of the charging roller using the method disclosed in Patent Document 1 may be insufficient.

[0007] The present invention has been made in view of the above-mentioned problems, and its object is to provide a technique for suitably removing toner adhering to a charging roller in a drum cleanerless type image forming apparatus. [Means for solving the problem]

[0008] The present invention employs the following configuration: a rotatable image carrier; a charging member that contacts the image carrier to form a charging portion and charges the surface of the image carrier in the charging portion; A developing section is formed in contact with the image carrier, and toner charged to the normal polarity is supplied to the surface of the image carrier in the developing section, thereby forming a toner image on the surface of the image carrier based on image information. a rotatable developing member for developing the electrostatic latent image formed thereon to form a toner image; a transfer member that faces the image carrier, forms a transfer section between itself and the image carrier, and transfers the toner image from the image carrier to a transfer target in the transfer section; a charging voltage applying means for applying a charging voltage to the charging member; a developing voltage applying means for applying a developing voltage to the developing member; a transfer voltage applying means for applying a transfer voltage to the transfer member; a control unit that controls the charging voltage application means, the developing voltage application means, and the transfer voltage application means; and After the toner image formed on the surface of the image carrier in the transfer section is transferred to the transferee, the toner remaining on the surface of the image carrier is collected by the developing member, the control unit is capable of performing an image forming operation of forming the toner image developed from the electrostatic latent image on the transfer medium, and a cleaning operation of cleaning the charging member, the cleaning operation includes a first cleaning operation and a second cleaning operation, and is performed at a timing when a non-image forming operation different from the image forming operation is performed; In the first cleaning operation, the toner adhering to the charging member is collected by the developing member, In the second cleaning operation, the toner adhering to the charging member is discharged onto the transfer object passing through the transfer unit. The image forming apparatus is characterized by the above. [Effects of the Invention]

[0009] According to the present invention, toner adhering to a charging roller can be suitably removed in a drum cleanerless image forming apparatus. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view of an image forming apparatus according to a first embodiment of the present invention; [Figure 2] Schematic diagram of a brush member in Example 1 [Figure 3] Control block diagram in the first embodiment [Figure 4] FIG. 1 is a diagram illustrating the potential relationship in the development unit in the first embodiment. [Figure 5] FIG. 1 is a diagram illustrating poor charging due to toner contamination of the charging roller in the first embodiment. [Figure 6] FIG. 1 is a diagram illustrating poor charging due to toner contamination of the charging roller in the first embodiment. [Figure 7]FIG. 10 is a diagram illustrating the cleaning operation of the charging roller in the first embodiment. [Figure 8] FIG. 10 is a diagram illustrating the relationship between the amount of transfer residual toner and the transfer voltage in the first embodiment. [Figure 9] FIG. 10 is a diagram illustrating image defects caused by toner contamination of the charging roller in the first embodiment. [Figure 10] FIG. 10 is an explanatory diagram of an image forming apparatus according to a second embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the following embodiments may be changed as appropriate depending on the configuration of the device to which the present invention is applied and various conditions. Therefore, unless otherwise specified, the scope of the present invention is not intended to be limited to these.

[0012] [Example 1] <1. Image forming device> 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 of this embodiment is a monochrome laser beam printer that employs a cleanerless system and a contact charging system.

[0013] The image forming apparatus 100 is provided with a photosensitive drum 1 (image carrier). A charging roller 2 (charging means, charging member) and a developing device 3 (developing means) are provided around the photosensitive drum 1. In addition, an exposure device 4 (exposure means, exposure unit) is provided between the charging roller 2 and the developing device 3 in the rotation direction R of the photosensitive drum 1 in FIG. 1. In addition, a transfer roller 5 (transfer means, transfer member) is pressed against the photosensitive drum 1.

[0014] The photosensitive drum 1 in this embodiment is a cylindrical, negatively charged organic photosensitive member. The photosensitive drum 1 has a photosensitive layer on a drum-shaped aluminum substrate. The photosensitive drum 1 is driven to rotate in a rotation direction R at a predetermined process speed by a drive motor 110 (driving means) shown in FIG. 3. The process speed in this embodiment corresponds to the peripheral speed (surface movement speed) of the photosensitive drum 1, which is 140 mm / sec. The outer diameter of the photosensitive drum 1 is 24 mm.

[0015] The charging roller 2 contacts the photosensitive drum 1 with a predetermined pressure, forming a charging portion G. A desired charging voltage Vc (charging bias) is applied to the charging roller 2 by a charging power source E1 (charging voltage application means). This causes the charging roller 2 to uniformly charge the surface of the photosensitive drum 1 to a predetermined potential. In this embodiment, the charging power source E1 applies a negative DC voltage as the charging voltage Vc to the charging roller 2. This causes the charging roller 2 to charge the surface of the photosensitive drum 1 to a negative polarity. In this embodiment, the charging voltage Vc is set to -1300 V. This charging process causes the surface of the photosensitive drum 1 to have a uniform dark potential Vd of -700 V.

[0016] More specifically, the charging roller 2 charges the surface of the photosensitive drum 1 by discharge occurring in at least one of the minute gaps formed between the charging roller 2 and the photosensitive drum 1 on the upstream and downstream sides of the contact point with the photosensitive drum 1 with respect to the rotation direction R of the photosensitive drum 1. However, in the following description, it is assumed that the contact point between the charging roller 2 and the photosensitive drum 1 is the charging portion G.

[0017] The exposure device 4 in this embodiment is a laser scanner device. The exposure device 4 irradiates the surface of the photosensitive drum 1 with laser light corresponding to image information input from an external device such as a host computer, thereby performing scanning exposure. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1. In this embodiment, of the dark area potential Vd (-700 V) on the surface of the photosensitive drum 1 formed by uniform charging processing, the absolute value of the potential in the portion exposed by the exposure device 4 decreases to a light area potential Vl (-100 V).

[0018] Hereinafter, the portion of the surface of the photosensitive drum 1 that is exposed by the exposure device 4 will be referred to as the exposure section. The exposure section is the "image forming section" where an image (electrostatic latent image) is formed. On the other hand, the portion that is not exposed will be the "non-image forming section." Note that the exposure device 4 is not limited to a laser scanner device, and may be, for example, an LED array in which multiple LEDs are arranged along the longitudinal direction of the photosensitive drum 1.

[0019] In this embodiment, a contact development method is used as the development method. The development device 3 (developing means) includes a development roller 31 (developer carrier, developing member), a supply roller 32 (developer supply means), a toner storage chamber 33 that stores toner (developer), and a development blade 34.

[0020] The supply roller 32 supplies toner from a toner storage chamber 33 to the developing roller 31. The supplied toner is charged to a predetermined polarity as it passes through a blade nip Nb, which is the contact point between the developing roller 31 and the developing blade 34. The toner carried on the developing roller 31 moves from the developing roller 31 to the photosensitive drum 1 in accordance with the electrostatic latent image. Here, the contact point between the developing roller 31 and the photosensitive drum 1 is assumed to be the developing unit H.

[0021] The developing roller 31 in this embodiment is driven to rotate in a rotation direction P. At the contact point between the photosensitive drum 1 and the developing roller 31, the photosensitive drum 1 and the developing roller 31 move forward. Note that the driving means for the developing roller 31 may be a common driving motor 110 for the photosensitive drum 1. Alternatively, the photosensitive drum 1 and the developing roller 31 may be driven by separate driving motors.

[0022] During development, a predetermined development voltage Vf (development bias) is applied to the development roller 31 by a development power supply E2 (development voltage application means). In this embodiment, the development power supply E2 applies a negative DC voltage as the development voltage Vf to the development roller 31, and the value of this voltage is -380V. As described above, in the image forming portion on the photosensitive drum 1, the absolute value of the potential is reduced by exposure (from -700V to -100V). Toner charged with the same polarity as the charge polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to this image forming portion. This development method is called a reversal development method. In this embodiment, the normal polarity, which is the charge polarity of the toner during development, is negative polarity.

[0023] Although the present embodiment employs a one-component non-magnetic contact development method, the present invention is not limited to this embodiment, and two-component non-magnetic contact development, non-contact development, magnetic development, and other methods may also be employed. The two-component non-magnetic contact development method uses a two-component developer comprising a non-magnetic toner and a magnetic carrier, and develops by bringing the developer carried on a developer carrier into contact with the photosensitive drum 1. The non-contact development method involves scattering toner from a developer carrier disposed opposite the photosensitive drum in a non-contact manner onto the photosensitive drum. The magnetic development method involves magnetically supporting magnetic toner on a developer carrier containing a magnet as a magnetic field generating means, disposed opposite the photosensitive drum in a contact or non-contact manner. In the present embodiment, toner with a mean particle diameter of 6 μm and a normal negative charge polarity is used.

[0024] The transfer roller 5 is preferably made of an elastic material such as sponge rubber made of polyurethane rubber, EPDM (ethylene propylene diene rubber), NBR (nitrile butadiene rubber), etc. The transfer roller 5 is pressed against the photosensitive drum 1, forming a transfer portion J where the photosensitive drum 1 and the transfer roller 5 are in pressure contact.

[0025] During transfer, a predetermined transfer voltage Vt (transfer bias) is applied to the transfer roller 5 by a transfer power supply E3 (transfer voltage application means). In this embodiment, the transfer power supply E3 applies a DC voltage of +1000 V, which is opposite in polarity to the normal polarity of the toner (positive in this embodiment), to the transfer roller 5 as the transfer voltage Vt. Then, the toner image is electrostatically transferred from the photosensitive drum 1 to the transfer material S due to the action of the electric field formed between the transfer roller 5 and the photosensitive drum 1.

[0026] The toner image formed on the photosensitive drum 1 is transferred to the transfer section J at the same time. A transfer material S as a recording material stored in a set 6 is fed by a paper feed unit 7, passes through a pair of registration rollers 8, and is conveyed to a transfer section J. The toner image formed on the photosensitive drum 1 is The toner image is transferred onto the transfer material S by a transfer roller 5 to which a predetermined transfer voltage Vt is applied by a transfer high voltage power supply.

[0027] After the toner image has been transferred, the transfer material S is transported to a fixing device 9. The fixing device 9 is a film heating type fixing device that includes a fixing film 91 that incorporates a fixing heater (not shown) and a thermistor (not shown) that measures the temperature of the fixing heater, and a pressure roller 92 that presses against the fixing film 91. The toner image is fixed to the transfer material S by the heat and pressure applied by the fixing device 9. Thereafter, a pair of paper discharge rollers 10 discharges the transfer material S outside the device.

[0028] Here, toner that is not used in image formation, such as transfer residual toner that is not transferred to the transfer material S and remains on the photosensitive drum 1, is removed in the following process.

[0029] The residual toner remaining on the photosensitive drum 1 is a mixture of toner charged with a positive polarity opposite to the normal polarity, and toner charged with a negative polarity but not enough charge. The toner is sufficiently charged to a negative polarity by discharge caused by the potential difference formed between the charging roller 2 and the photosensitive drum 1. As a result, electrostatic repulsion is generated between the charging roller 2 to which a negative charging voltage Vc is applied, and the toner passes through the charging section without adhering to the charging roller 2.

[0030] In addition, some of the toner that was not sufficiently charged to negative polarity by the discharge in the charging section G The toner adheres to the charging roller 2. However, the toner adhered to the charging roller 2 is again charged to negative polarity due to friction between the charging roller 2 and the photosensitive drum 1 and the application of the charging voltage Vc. Then, the adhering toner is transferred from the charging roller 2 onto the photosensitive drum 1 due to the electrostatic repulsion between the charging roller 2 and the charging roller 2 to which the negative charging voltage Vc is applied.

[0031] The residual toner on the photosensitive drum 1, which has been negatively charged by the charging roller 2, reaches the developing section H as the photosensitive drum 1 rotates, and is then processed as follows.

[0032] FIG. 4 shows the surface potential (dark potential) formed on the photosensitive drum 1 in the developing section H in Example 1. The graph shows the relationship between the potential Vd (light area potential Vl) and the developing voltage Vf. The horizontal axis schematically shows the position on the surface of the photosensitive drum 1, and the vertical axis shows the potential. In non-image forming areas where an electrostatic latent image is not formed, the developing voltage Vf is relatively more positive than the surface potential (dark area potential Vd) of the photosensitive drum 1. Due to this potential relationship, the negatively charged residual toner on the photosensitive drum 1 is transferred from the photosensitive drum 1 to the developing roller 31, and then collected in the toner storage chamber 33. The toner collected in the toner storage chamber 33 is reused for image formation.

[0033] Here, a description will be given of a preferable setting of the value of back contrast (Vback), which is the absolute value of the potential difference between the surface potential (dark potential Vd) of the photosensitive drum 1 and the development voltage (Vf) in the non-image forming portion shown in Fig. 4. In order to collect the negatively charged toner on the photosensitive drum 1 onto the development roller 31, it is preferable to ensure a sufficient Vback in the development portion H. It is preferable to set Vback to a value that can prevent the toner carried on the developing roller 31 from being unintentionally developed on the surface of the photosensitive drum 1 (i.e., the occurrence of "fog toner" described later). Specifically, it is preferable to set Vback to about 100V to 500V.

[0034] If Vback is less than 100 V, there is a possibility that the recovery of negatively charged toner adhering to the surface of the photosensitive drum 1 cannot be sufficiently ensured. Furthermore, a phenomenon (fog toner) in which negatively charged toner on the developing roller 31 is unintentionally developed on the photosensitive drum 1 is likely to occur. On the other hand, if Vback is greater than 500 V, there is a possibility that the toner on the developing roller 31 will be positively charged due to discharge occurring between the developing roller 31 and the photosensitive drum 1. As a result, toner is transferred from the developing roller 31 to the photosensitive drum 1, making it more likely that fog toner will occur. Therefore, in Example 1, the dark area potential Vd of the photosensitive drum 1 was set to −600 V, the developing voltage Vf was set to −300 V, and Vback was set to 300 V.

[0035] As shown in FIG. 4, the image forming unit in which the electrostatic latent image is formed in the developing unit H is The light area potential Vl is the light area potential Vf. The relationship between the light area potential Vl and the development voltage Vf is such that negatively charged toner is supplied from the development roller 31 to the photosensitive drum 1 for development. This potential relationship is called the development contrast (Vcont). As a result, the negatively charged toner on the photosensitive drum 1 is used as a toner image as is, and the electrostatic latent image is developed into a toner image by supplying toner from the development roller 31. The formed toner image is then transferred to the transfer material S at the transfer section J.

[0036] As shown in FIG. 1, between the transfer portion J and the charging portion G in the rotation direction R of the photosensitive drum 1, A pre-exposure device 12 (discharging means) is provided to eliminate the charge potential of the photosensitive drum 1. Discharging using the pre-exposure device 12 can even out unevenness in the surface potential of the photosensitive drum 1 caused by transfer, so that discharge at the charging section G is stabilized and a uniform charge potential can be obtained. .

[0037] The photosensitive drum 1, charging roller 2, etc. may be assembled in a housing to form a cartridge that is detachable from the main body of the image forming apparatus 100. The developing device 3 may also be formed as a cartridge that is detachable from the main body of the image forming apparatus 100. The photosensitive drum 1, charging roller 2, and developing device 3 may all be formed as a cartridge that is detachable from the main body of the image forming apparatus 100. The image forming apparatus 100 is not limited to a monochrome system, and may also be a color printing system using toner of multiple colors (for example, four colors).

[0038] Next, the paper dust removal mechanism in this embodiment will be described. As shown in FIG. 1, the image forming apparatus 100 has a brush member 11 (collection member). The brush member 11 is a paper dust removal mechanism and is a contact member with the photosensitive drum 1. In this embodiment, the brush member 11 is disposed downstream of the transfer unit J and upstream of the charging unit G in the rotation direction R of the photosensitive drum 1. The brush member 11 contacts the surface of the photosensitive drum 1 to form a brush contact portion.

[0039] 2(A) is a schematic diagram of the brush member 11 in a standalone state, viewed along its longitudinal direction (substantially parallel to the rotational axis direction of the photosensitive drum 1). Also, FIG. 2(B) is a schematic diagram of the brush member 11 in contact with the photosensitive drum 1, viewed along its longitudinal direction. The brush member 11 is arranged so that its longitudinal direction is substantially parallel to the rotational axis direction of the photosensitive drum 1.

[0040] The brush member 11 is composed of a fixed, conductive brush. The brush member 11 is composed of conductive nylon pile yarns 11a and a base cloth 11b that supports the pile yarns 11a. The pile yarns 11a are made of a plurality of bristles that rub against the surface of the photosensitive drum 1. For example, the brush member 11 may be configured by weaving conductive pile yarns 11a (conductive yarns) made of nylon fibers blended with a conductive material into a base cloth 11b made of synthetic fibers containing carbon as a conductive agent. The pile yarns 11a may be made of nylon, rayon, acrylic, polyester, or the like, in addition to nylon.

[0041] As shown in Figure 2(A), when the brush member 11 is in a standalone state, i.e., when no external force is being applied to bend the pile yarns 11a, the distance from the base fabric 11b to the tip of the pile yarns 11a is defined as L1. In this embodiment, L1 is 6.5 mm. The base fabric 11b of the brush member 11 is fixed to a support member (not shown) installed at a predetermined position in the image forming apparatus 100 by a fixing means such as double-sided tape.

[0042] The brush member 11 is fixed so that the tip of the pile yarn 11a penetrates into the photosensitive drum 1. Here, "penetration" refers to a state in which the tip of the pile yarn 11a is bent by contact with the photosensitive drum 1 and becomes shorter than its natural length, as shown in FIG. 2(B). In this embodiment, the clearance between the support member and the photosensitive drum 1 is fixed. The shortest distance from the base fabric 11b of the brush member 11 fixed to the support member to the photosensitive drum 1 is defined as L2. In this embodiment, the difference between L2 and L1 is defined as the penetration amount of the brush member 11 into the photosensitive drum 1. In this embodiment, the penetration amount of the brush member 11 into the photosensitive drum 1 is 1 mm.

[0043] In this embodiment, the brush member 11 is rotated around the photosensitive drum 1 in the state shown in FIG. The length L3 in the short direction (hereinafter referred to as the "transverse direction") of the brush member 11 is 5 mm. In this embodiment, the length in the longitudinal direction of the brush member 11 is 216 mm. This allows the brush member 11 to come into contact with the entire image forming area (area where a toner image can be formed) on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. With this configuration, the brush member 11 can rub against the surface of the photosensitive drum 1 as the photosensitive drum 1 rotates. The brush member 11 collects (recovers) deposits such as paper dust transferred from the transfer material S onto the photosensitive drum 1 in the transfer section, and collects the deposits from the charging section G and the photosensitive drum 1 in the movement direction of the photosensitive drum 1. This also reduces the amount of paper dust that moves to the developing section H.

[0044] The length of the brush member 11 in the short-side direction of the photosensitive drum 1 is not limited to the above example, and may be changed as appropriate depending on the lifespan of the image forming apparatus 100, the photosensitive drum 1, etc. The longer the length of the brush member 11 in the short-side direction, the longer the period for which paper dust can be collected. Furthermore, the length of the brush member 11 in the long-side direction is not limited to the above example, and may be changed as appropriate depending on the maximum paper passing width of the image forming apparatus.

[0045] A brush power supply E4 serving as a brush voltage application means is connected to the brush member 11. During image formation, a predetermined brush voltage (brush bias) is applied to the brush member 11 by the brush power supply E4. In this embodiment, during image formation, a negative DC voltage is applied to the brush member 11 as the brush voltage. In this embodiment, the brush voltage is −350 V.

[0046] <2. Control mode> FIG. 3 is a schematic block diagram showing the control mode of the main parts of the image forming apparatus 100 of this embodiment. The control unit 150 has a CPU 151 (arithmetic and control means) and a memory 152 (storage means, storage element) such as a ROM or RAM, and receives signals from each component connected to the control unit 150 and transmits control signals. In the memory 152, the RAM stores sensor detection results, calculation results, etc., and the ROM stores control programs, pre-determined data tables, etc. The control unit 150 is a control means that comprehensively controls the operation of the image forming apparatus 100. The control unit 150 controls the exchange of various electrical information signals, drive timing, etc., to execute a predetermined image formation sequence. Each part of the image forming apparatus 100 is connected to the control unit 150.

[0047] <3. Image output operation> An image output operation (job) is a series of operations in which the image forming apparatus 100 forms an image on a transfer material S in accordance with instructions from an external device such as a personal computer or a user. The image output operation generally includes an image forming process (printing process), a pre-rotation process, an inter-sheet process when forming images on multiple transfer materials S, and a post-rotation process.

[0048] The image formation process is a period during which an electrostatic latent image is formed on the photosensitive drum 1, the electrostatic latent image is developed (formed a toner image), the toner image is transferred, and the toner image is fixed, and "image formation" generally refers to this process. The pre-rotation process is a period during which preparatory operations are performed before the image formation process. The sheet interval process is a period corresponding to the interval between transfer materials S when the image formation process is performed continuously on multiple transfer materials S (continuous image formation). The post-rotation process is a period during which an organizing operation (preparatory operation) is performed after the image formation process. "Non-image formation" refers to a period other than image formation, and includes the pre-rotation process, sheet interval process, post-rotation process, and the pre-multiple rotation process, which is a preparatory operation when the image forming apparatus 100 is turned on or when it returns from a sleep state.

[0049] <4. Cleaning of charging members> After transfer, if there is a large amount of residual toner on the photosensitive drum 1, the photosensitive drum In some cases, the negative polarity conversion process of the residual toner on charging roller 1 may be insufficient, and in such a case, the positively charged toner will adhere to charging roller 2, causing toner stains to accumulate on charging roller 2.

[0050] In particular, when printing in a high-temperature, high-humidity environment, when printing on paper containing a large amount of talc as a filler (talc paper), when a jam occurs, etc., a large amount of residual toner remains on the photosensitive drum 1 after transfer. In these cases, a large amount of toner stains due to toner with reduced chargeability occur, and toner stains may accumulate on the charging roller 2.

[0051] FIG. 5 shows the relationship between the surface potential of the photosensitive drum 1 and the developing voltage Vf when a large amount of toner contamination has accumulated on the charging roller 2. As shown in FIG. 5, on the photosensitive drum 1, regions of the charging roller 2 that correspond to the toner-contaminated areas are insufficiently charged, resulting in insufficient charging. In these insufficiently charged areas, Vback is small (Vback_d). This is because the resistance increases as toner adheres to the surface of the charging roller 2, making it impossible to achieve the desired discharge.

[0052] In particular, when Vback is smaller than 100V, as mentioned above, the residual toner charged to negative polarity on the photosensitive drum 1 in the non-image forming portion will not be properly collected by the developing roller 31. Furthermore, there is a risk of fog toner being generated on the photosensitive drum 1. The residual toner and fog toner on the photosensitive drum 1 that have not been collected will adhere to the charging roller 2 as toner stains, further exacerbating the charging failure. When the amount of discharge at the charging portion G decreases due to the toner stains on the charging roller 2, the absolute value of the surface potential of the photosensitive drum 1 will decrease. Furthermore, As the discharge amount decreases, Vback becomes smaller, and the amount of fog toner increases.

[0053] Figure 6 shows the surface potential of the photosensitive drum 1 when toner contamination continues to progress as described above. When toner contamination progresses to the state shown in Figure 6, it becomes almost impossible to charge the photosensitive drum 1 at the insufficiently charged portion of the charging roller 2 corresponding to the toner-contaminated portion. Furthermore, some of the toner developed at the insufficiently charged portion of the photosensitive drum 1 due to the toner contamination of the charging roller 2 is transferred onto the transfer material S, resulting in an image defect due to the toner contamination.

[0054] Such image defects are eliminated by a cleaning operation of the charging roller 2 (first cleaning operation, hereinafter referred to as "cleaning operation 1") as shown in the background art. In summary, cleaning operation 1 involves rotating the photosensitive drum 1, charging roller 2, and developing roller 31 with the charging voltage Vc set to negative polarity and below the discharge start voltage, and the developing voltage Vf set to positive polarity (opposite polarity to the normal polarity). By the above operation, the positive toner adhering to the charging roller 2 becomes negative polarity, moves to the photosensitive drum 1, and is collected in the toner storage chamber 33 via the developing roller 31. Note that the first cleaning operation (first cleaning operation) and the second cleaning operation (described later) are also performed. The cleaning operation (second cleaning operation) is performed at a timing different from that of the image forming operation. This is executed at the timing of the image forming operation.

[0055] Here, when the toner has deteriorated at the end of the product life, a phenomenon called development filming (or simply "filming") may occur, in which a large amount of toner charged to the normal polarity adheres to the developing roller 31.

[0056] The developer filming will be explained in detail. When the toner is not deteriorated, after toner is supplied to the developing roller 31 downstream of the contact portion between the supply roller 32 and the developing roller 31 during image formation or non-image formation, the toner on the developing roller 31 is regulated by the developing blade 34. This removes excess toner from the developing roller 31. Therefore, when the developing roller 31 contacts the photosensitive drum 1, a certain amount of toner is always held on it. After contacting the photosensitive drum 1, the toner on the developing roller 31 is removed from the developing roller 31 upstream of the contact portion between the supply roller 32 and the developing roller 31.

[0057] On the other hand, if the toner has deteriorated, some of the toner supplied to the developing roller 31 at the downstream portion of the contact area between the supply roller 32 and the developing roller 31 will adhere strongly to the developing roller 31. This adhered toner may not be completely removed even by the control of the developing blade 34. Furthermore, after contacting the photosensitive drum 1, the adhered toner may not be completely removed even at the upstream portion of the contact area between the supply roller 32 and the developing roller 31. Furthermore, the deteriorated toner that adheres on top of it will gradually adhere. This phenomenon in which a large amount of toner adheres to the developing roller 31 due to repeated toner adhesion is called development filming.

[0058] When development filming occurs and a large amount of toner charged to the normal polarity (negative polarity) adheres to the development roller 31, the potential on the outermost surface of the development roller 31 shifts toward the normal polarity side relative to the potential of the development voltage Vf applied to the development roller 31. This occurs because the normal polarity toner adheres to the surface of the development roller 31, causing the surface of the development roller 31 to have a more negative potential than the core metal portion of the development roller 31. This makes it impossible to ensure a sufficient back contrast Vback between the photosensitive drum 1 and the development roller 31 in the non-image forming area. As a result, a large amount of toner adheres to the photosensitive drum 1 even in the non-image forming area.

[0059] If paper is passed through in this state, a part of the large amount of adhering toner is transferred onto the transfer material S, causing image defects such as a solid black image. Sometimes, a portion of the toner that is not transferred to the paper adheres to the charging roller 2, causing poor charging. The toner that does not adhere to the charging roller 2 then reaches the developing section H again. As mentioned above, since Vback cannot be secured sufficiently, this toner is actively transferred to the developing section H. As a result, a large amount of toner continues to accumulate on the photosensitive drum 1 and the developing roller 31 in the area where the development filming occurs.

[0060] When development filming occurs, even if cleaning operation 1 is performed, the cleaning effect of charging roller 2 may be insufficient due to the following phenomena (1) to (3), making it impossible to prevent charging defects and resulting image defects. First, in (1), toner expelled from developing roller 31 onto photosensitive drum 1 may adhere to charging roller 2. Second, in (2), the presence of toner expelled from developing roller 31 onto photosensitive drum 1 facing charging roller 2 reduces the friction between charging roller 2 and photosensitive drum 1, inhibiting the toner from being charged to the correct polarity, making it difficult for toner to transfer from charging roller 2 to photosensitive drum 1. Finally, in (3), toner transferred from charging roller 2 to photosensitive drum 1 may remain on photosensitive drum 1 without being collected by developing roller 31 due to improper control of the potential difference between developing roller 31 and the opposing photosensitive drum 1.

[0061] Therefore, in this embodiment, by performing the cleaning operation of the charging roller 2 as described below (a second cleaning operation, referred to as "cleaning operation 2"), even when a large amount of toner charged to the normal polarity adheres to the developing roller 31, the toner adhering to the charging roller 2 is suitably removed, thereby suppressing poor charging of the surface of the photosensitive drum 1 and reducing image defects.

[0062] 7 is a timing chart illustrating cleaning operation 2 for toner stains on charging roller 2 when development filming occurs in Example 1. Here, the trigger for performing cleaning operation 2 may be a mode selection by the user, or may be when a situation in which development filming is expected to occur is detected in a usage situation in which this situation is expected to occur. Examples of detection timing include timing when a user gives an instruction after viewing a formed image, or timing when detection is performed by a sensor. It may also be performed when the device operating time or the number of sheets passed reaches a predetermined number.

[0063] At timing T1 in FIG. 7, the charging power source E1 applies a charging voltage Vc to the charging roller 2. Power supply E2 applies a development voltage Vf to development roller 31, and transfer power supply E3 applies a transfer voltage Vt to transfer roller 5. The control unit 150 also turns on the pre-exposure device 12. In this embodiment, the charging voltage Vc is set to -500V, the developing voltage Vf to +200V, and the transfer voltage Vt to +500V. The charging voltage Vc is set to a voltage equal to or lower than the discharge start voltage. In this embodiment, the discharge start voltage is -550V.

[0064] After the charging voltage Vc, the developing voltage Vf, and the transfer voltage Vt have risen sufficiently, the control unit 150 starts driving the photosensitive drum 1 at timing T2. After that, during the period from t1 to t2 (paper passing period), the paper passes through the transfer unit J. At timing T3 after the paper has passed, The drive of the photosensitive drum 1 is turned off. Then, at timing T4, the charging voltage Vc, developing voltage Vf, transfer voltage Vt, and exposure by the pre-exposure device 12 are turned off almost simultaneously. During the period from timing T1 to T4, the developing roller 31 and charging roller 2 are in contact with the photosensitive drum 1. Also, timings T3 and T4 may be simultaneous.

[0065] As an example of controlling the transfer voltage Vt, it is possible to set the voltage to negative polarity until the paper starts to pass, and then set the voltage to positive polarity as described above after the paper starts to pass. This is because, among the toner transported from the developing roller 31, negatively charged toner is not transferred to the transfer roller 5 until the paper starts to pass, and positively charged toner is allowed to transfer to the transfer roller 5. Then, by controlling the voltage to positive polarity after the paper starts to pass, both the negatively charged toner on the photosensitive drum 1 and the positively charged toner on the transfer roller 5 are transferred to the transfer material S.

[0066] When development filming occurs, a large amount of negatively charged toner, which is the normal polarity, adheres to the surface of the development roller 31, so even if the development voltage Vf is set to positive, it is not possible to create a sufficient potential difference with the photosensitive drum 1. As a result, a large amount of negatively charged toner continues to be expelled onto the photosensitive drum 1, and some of this toner adheres to the charging roller 2. In this situation, if a positive voltage is applied to the transfer roller 5 and paper is passed through, the negatively charged toner on the photosensitive drum 1 can be collected onto the paper. Then, the surface of the photosensitive drum 1 from which the toner has been removed reaches the charging section G, thereby suppressing toner adhesion to the charging roller 2.

[0067] Furthermore, the surface of the photosensitive drum 1 from which the toner has been removed rubs against the charging roller 2, thereby charging toner of positive polarity or toner that does not have a sufficient negative charge to negative polarity that is attached to the charging roller 2. Then, the electrostatic repulsion between the negative toner and the charging roller 2 causes the toner to be transferred from the charging roller 2 onto the photosensitive drum 1.

[0068] Furthermore, the negatively charged toner transferred from the charging roller 2 to the photosensitive drum 1 is transferred to paper at the transfer section J to which a positive transfer voltage Vt is applied via paper, and then discharged outside the machine. In this way, the toner adhering to the charging roller 2 can be removed.

[0069] In this embodiment, the charging voltage Vc, the developing voltage Vf, and the transfer voltage Vt are all started at the same timing. Also, the pre-exposure device 12 is turned on. However, although the charging voltage Vc and the developing voltage Vf need to be started before the drive motor 110 is driven, the transfer voltage Vt only needs to be turned on before the paper reaches the transfer section. Also, the pre-exposure device 12 is turned on when the photosensitive drum 1 that formed the development section H is stopped. The exposure may start when the surface of the drum 1 reaches the opposite surface of the pre-exposure device 12, i.e., the pre-exposure section that exposes the surface of the photosensitive drum 1. The exposure may start when the surface of the drum 1 reaches the pre-exposure section that exposes the surface of the photosensitive drum 1. The reason for turning on the pre-exposure device 12 is to take into consideration the possibility that the photosensitive drum potential may be charged from 0 V to the negative side due to injection charging via the toner when a charging voltage of -500 V is applied.

[0070] Regarding the length of the paper (transfer material S) passing through the transfer section J in the cleaning operation 2, First, in order to remove the toner on the surface of the photosensitive drum 1, at least the length of the paper is required to rotate the photosensitive drum 1 once. Furthermore, in addition to that length, when considering the transfer of toner from the charging roller 2 to the photosensitive drum 1, there may also be a length in the transport direction of the photosensitive drum 1 that the charging roller 2 faces as it rotates once.

[0071] The transfer of the toner discharged onto the photosensitive drum 1 by the development filming to the transfer material S starts when the transfer material S starts to pass through the transfer portion J (=t1). At the time t1, the surface of the photosensitive drum 1 forming the transfer portion J reaches the charging portion G, and then the surface of the charging roller 2 rotates. The transfer material S continues to exist in the transfer portion J until the surface of the photosensitive drum 1 that has been rubbed against the transfer material S again completes the transfer portion J. Of course, the length of the transfer material S in the transport direction may be longer than this, or multiple sheets of paper may be fed continuously.

[0072] The length in the longitudinal direction of the transfer material S passing through the transfer section J is at least It is preferable that the length of the developing opening, through which toner is supplied, in the longitudinal direction of the developing roller 31 is 221.6 mm, or longer, so as to cover the portion corresponding to the longitudinal position where the developing opening is located. As an example, if the length of the developing opening through which toner is supplied in the longitudinal direction of the developing roller 31 is 221.6 mm, it is preferable that the length of the transfer material S in the longitudinal direction be equal to or longer than that. Furthermore, in order to maximize the cleaning effect, it is more preferable to pass the transfer material S with the maximum paper passing width.

[0073] The type of transfer material S used in cleaning operation 2 may be plain paper, glossy paper, or the like. Alternatively, it does not have to be paper as long as it does not interfere with transport from the paper feed section to the paper discharge section and can suitably collect toner on the photosensitive drum 1 in the transfer section. In this embodiment, Xerox Vitality Multipurpose Printer Paper (trade name, basis weight 75 g / m), which is letter-size (215.9 mm width x 279.4 mm length) plain paper, is used. 2 ) was passed through one sheet.

[0074] The relationship between the transfer voltage Vt during cleaning operation 2 and the transfer voltage Vt during normal paper passage will be explained using Figure 8. The horizontal axis in Figure 8 is the transfer voltage Vt. The vertical axis simply indicates the amount of transfer residual toner remaining on the photosensitive drum 1 when the transfer voltage Vt is changed. It is assumed that the surface potential of the opposing photosensitive drum 1 is 0V. The amount of transfer residual toner that is positively charged is transfer residual (+), and the amount of transfer residual toner that is negatively charged is transfer residual (-), and the total amount of transfer residual toner combined is transfer residual (total amount). Vt_CLN is the transfer voltage during cleaning operation 2, V0 is the discharge start voltage, and Vt_normal is the transfer voltage when paper is passing. As an example, Vt_CLN may be +500V, V0 may be +550V, and Vt_normal may be +1000V.

[0075] It is also preferable to control the brush voltage applied from the brush power supply E4 to the brush member 11 during the cleaning operation. For example, the control unit 150 may control the brush voltage to be lower than the discharge voltage and positive with respect to the drum potential (0 V). With this potential relationship, normal polarity toner is collected inside the brush member 11, and positive polarity toner is expelled. By expelling positive polarity toner in advance in this way, it is possible to prevent the charging roller 2, which is located downstream of the brush member 11 and to which a negative polarity voltage is applied during paper passing, from being soiled when paper is passed after the cleaning operation is completed.

[0076] From FIG. 8, it can be seen that the amount of positively charged residual toner increases due to discharge at the transfer portion J when the transfer voltage Vt is equal to or higher than the discharge start voltage V0. On the other hand, the amount of negatively charged residual toner increases due to discharge at the transfer portion J. The transfer voltage Vt is increased to reduce the transfer error.

[0077] During normal paper feed, not during cleaning operation, it is necessary to reliably transfer the negatively charged toner developed on the photosensitive drum 1 onto the transfer material S. For this reason, it is desirable to set the transfer voltage Vt_normal as high as possible. However, as the transfer voltage Vt is increased, the amount of positively charged toner remaining after transfer increases, as shown in Figure 8. This positively charged toner accumulates on the charging roller 2 and causes image defects, but this can be tolerated to a certain extent because it can be removed by performing periodic cleaning operation 1.

[0078] On the other hand, the transfer voltage Vt_CLN during cleaning operation 2 is preferably set to a value lower than V0. Vt_CLN must be greater than the surface potential of the photosensitive drum 1 at the transfer station J to ensure electrostatic repulsion between the photosensitive drum 1 and the negatively charged toner. The higher VCLN, the more negatively charged toner can be transferred from the photosensitive drum 1 to paper. However, if VCLN is higher than V0, discharge at the transfer station J generates positively charged residual toner. When positively charged residual toner reaches the charging roller 2, it is electrically attracted to the charging roller 2. When development filming occurs and this cleaning operation is performed, it is necessary to remove as much toner as possible from the charging roller 2 during the paper feed period. To achieve this, it is important to minimize the amount of positively charged residual toner attracted to the charging roller 2, even if it means allowing negatively charged residual toner that is less likely to adhere to the charging roller 2. Therefore, VCLN is a positive voltage, opposite to the normal polarity of the toner, and is preferably greater than 0 and less than V0 in absolute value.

[0079] This embodiment can also be applied when an intermediate transfer body is used instead of the transfer material S as the transfer target body. That is, a cleaning operation similar to this embodiment can be performed when an electrostatic transfer belt system or intermediate transfer belt system, which is used in color laser beam printers as the intermediate transfer body, is used. In this case, the "transfer material S" described above corresponds to the "electrostatic transfer belt" or "intermediate transfer belt." This achieves the same cleaning effect on the charging roller 2 as in this embodiment. However, the toner transferred to the electrostatic transfer belt or intermediate transfer belt is stored in a waste toner container or the like without being discharged outside the machine. Because there is a limit to the capacity that can be stored in the waste toner container, this point must be taken into consideration when performing a charging member cleaning operation like this embodiment, especially in models with a long lifespan.

[0080] <5. Checking the effectiveness of cleaning operation> To confirm the effectiveness of the cleaning operation, the following experiment was conducted. Using the image forming apparatus 100 of this embodiment, printing was repeatedly performed every two sheets in a high-temperature, high-humidity environment with a temperature of 32.5°C and humidity of 90%. The image forming apparatus 100 was brand new, with 50 g of toner filled in the toner chamber 33. A character image pattern with a 5% print coverage was used. Talc paper was used as the transfer material S, and CenturyStar paper (manufactured by CENTURY PULP AND PAPER) was used. 10,000 sheets were printed, and the presence or absence of image defects was confirmed. Image defects were confirmed by printing a blank image (solid white image) and evaluating whether unintended toner particles appeared on the paper. Note that when the talc contained in the talc paper gets mixed into the developing device 3 and mixes with the toner, it removes electrons from the toner and becomes negatively charged. As a result, the toner becomes less likely to be charged by friction and more likely to adhere to the developing roller 31, which increases the risk of developing filming.

[0081] As a result, the occurrence of development filming was confirmed, and toner stains of different densities were confirmed in the areas where development filming occurred and areas where development filming did not occur. Figure 9(A) shows a typical example of an image defect occurring on the transfer material S. Reference numeral 108a indicates an area where development filming did not occur (corresponding to a solid white image). In this area, toner adheres to the charging roller 2, and the photosensitive drum 1 cannot be sufficiently charged, and sufficient Vback cannot be secured in the development section. As a result, toner is transferred from the development roller 31 to the photosensitive drum 1 and then transferred to the transfer material S in the transfer section, causing dark half-tone-like toner stains.

[0082] Furthermore, reference numeral 108b denotes a portion where development filming occurs. Due to development filming, a large amount of toner is developed even in a non-image forming portion. Then, when paper is passed through, part of this toner is transferred to the transfer material S, resulting in a defective image such as a solid black.

[0083] Therefore, cleaning operation 2 was performed, and the image defect was improved. Figure 9(B) shows a typical example of an image after the image defect was improved. In the area corresponding to reference numeral 108a, the dark halftone-like image defect disappeared. This is the result of the positive toner adhering to the charging roller 2 in the area where development filming did not occur becoming negative, moving to the photosensitive drum 1, and being collected by the developing roller 31, thereby effectively cleaning the charging roller 2.

[0084] In addition, in the portion corresponding to the reference numeral 108b, the solid black image defect disappeared. This is because, in the portion where the development filming occurred, the clean surface of the photosensitive drum 1 on which the toner was transferred onto the transfer material S reached the charging portion G, the charging roller 2 was not soiled during the cleaning operation, and the band This is because the toner adhering to the charging roller 2 can be recharged and easily transferred to the photosensitive drum 1, and the toner transferred from the charging roller 2 to the photosensitive drum 1 can be collected with paper. By performing cleaning operation 2 in this way, the charging roller 2 is cleaned appropriately, and good images can be obtained in the subsequent job. When cleaning operation 2 is performed, the toner remaining on the developing roller 31 without adhering is expelled onto the transfer material S via the photosensitive drum 1. As a result, the layer of adhered toner is exposed, and the adhered toner is gradually removed by regulation by the developing blade 34 and contact with the supply roller 32, which also has the effect of eliminating development filming.

[0085] As described above, by carrying out the cleaning operation 2 of the charging member according to this embodiment, it is possible to effectively remove toner adhering to the charging roller 2 even when development filming occurs. As a result, it was shown that it is possible to suppress charging defects on the surface of the photosensitive drum 1 and reduce image defects caused by charging defects. Note that this cleaning operation is effective even when development filming does not occur.

[0086] Note that development filming, a phenomenon in which a large amount of toner charged to the normal polarity adheres to the development roller 31, can occur for reasons other than toner deterioration due to durability. For example, development filming can occur when a different type of toner than the toner originally contained in the development container is mistakenly added. In this case, cleaning operation 2 of this embodiment is also effective.

[0087] In addition, various operations including normal paper passing, cleaning operation 1, cleaning operation 2, and other cleaning operations should be performed appropriately depending on the configuration and various conditions of the device to which the present invention is applied, and these can also be performed in any combination.

[0088] For example, by performing cleaning operation 1 and then performing image judgment using normal paper passing to determine whether cleaning operation 2 is necessary, and controlling to perform cleaning operation 2 if necessary, paper consumption can be reduced when cleaning operation 2 is not necessary.

[0089] [Example 2] A second embodiment of the present invention will be described. The basic configuration and operation of an image forming apparatus 200 of this embodiment are the same as those of the first embodiment. Therefore, elements that are the same as or correspond to the configurations and functions of the image forming apparatus 100 of the first embodiment are given the same reference numerals as those of the first embodiment, and detailed descriptions thereof will be omitted.

[0090] The image forming apparatus 200 in this embodiment does not have any replaceable parts other than the toner, and is configured so that the user replenishes toner depending on the amount of remaining toner. In this embodiment, performing cleaning operation 2 after the replenishment timing is expected to have the effect of eliminating development filming in addition to cleaning the charging roller 2. This can prevent toner contamination of the charging roller 2, thereby suppressing the occurrence of image defects. In addition, the frequency of cleaning operations for the charging roller 2 can be reduced.

[0091] <1. Image forming device> As shown in FIG. 10 , the image forming apparatus 200 of this embodiment is equipped with a toner supply mechanism 40 for the toner storage chamber 33. The user can use the toner supply mechanism 40 to supply new toner to the toner storage chamber 33 at any time. A toner pack 41 (toner supply container) is attached to the toner supply mechanism 40. The toner pack 41 is a container that is detachable from the image forming apparatus 200. While the toner pack 41 is attached to the image forming apparatus 200 in this embodiment, it may be attached directly to the toner storage chamber 33. The toner supply container is not limited to the toner pack 41 and may be shaped like a toner bottle. As long as the toner can be replenished, the shape, configuration, and connection location of the toner supply container are not important. In this embodiment, after replenishment is complete, the toner pack 41 is removed and image formation is performed. However, the configuration may also be such that image formation can be performed with the toner pack 41 attached.

[0092] In this embodiment, a method (direct replenishment method) is adopted in which the user replenishes toner from a toner pack 41 filled with replenishment toner. Therefore, when the amount of toner remaining in the toner storage chamber 33 becomes low, the work of replacing the toner storage chamber 33, which serves as a developing container, is not required, thereby improving usability. The image forming device 200 and the toner pack 41 constitute an image forming system.

[0093] <2. Cleaning of charging members> In this embodiment, when development filming occurs, toner is replenished and then cleaning operation 2 is performed. This not only cleans the charging roller 2 but also eliminates development filming, as will be explained below.

[0094] In cleaning operation 2, toner on the photosensitive drum 1 is removed by passing paper through the transfer section J. The surface of the photosensitive drum 1 from which the toner has been removed then reaches the charging section G and is attached to the charging roller 2. The toner particles adhering to the developing roller 31 are charged to negative polarity and then collected on the photosensitive drum 1. Furthermore, in the developing section H, the toner particles adhering in large amounts to the developing roller 31 and causing development filming are collected. The toner is transferred to the photosensitive drum 1. This exposes the toner adhering to the developing roller 31. The adhering toner can then be removed by the control of the developing blade 34 and the rubbing between the supply roller 32 and the developing roller 31. These operations eliminate the development filming. In this way, by performing cleaning operation 2 after toner replenishment, the development filming and toner stains on the charging roller 2 can be eliminated.

[0095] In a situation where development filming occurs, even if cleaning operation 2 is performed before toner replenishment, the development filming will not be eliminated. Here, if cleaning operation 2 is performed before toner replenishment, a large amount of toner will adhere to the developing roller 31 in the developing section H, causing development filming. The toner causing the filming is transferred onto the photosensitive drum 1. This exposes the toner adhering to the developing roller 31, and the adhering toner is removed by the control of the developing blade 34 and the rubbing between the supply roller 32 and the developing roller 31. However, before the toner is replenished, a large amount of toner that has deteriorated and is likely to adhere to the developing roller 31 remains in the toner storage chamber 33. As a result, an amount of toner that exceeds the amount of toner removed by cleaning operation 2 adheres to the developing roller 31, and the development filming cannot be eliminated.

[0096] On the other hand, after toner replenishment, a large amount of new toner is supplied into the toner storage chamber 33, and the proportion of degraded toner is significantly reduced. Therefore, when cleaning operation 2 is performed, toner that has adhered to the developing roller 31 can be removed, and further adhesion of toner to the developing roller 31 (=development filming) can be suppressed.

[0097] As described above in each embodiment, in a drum cleanerless image forming apparatus, a transfer material S such as paper is passed through the transfer section during the cleaning operation of the charging roller 2. This makes it possible to effectively remove toner adhering to the charging roller 2, even when a large amount of toner charged to the normal polarity is adhering to the developing roller 31. As a result, poor charging of the surface of the photosensitive drum 1 can be suppressed, and image defects resulting from this can be reduced.

[0098] [Configuration 1] a rotatable image carrier; a charging member that contacts the image carrier to form a charging portion and charges the surface of the image carrier in the charging portion; a rotatable developing member that contacts the image carrier to form a developing section, and that supplies toner charged to a normal polarity to the surface of the image carrier in the developing section, thereby developing an electrostatic latent image formed on the surface of the image carrier based on image information, thereby forming a toner image; a transfer member that faces the image carrier, forms a transfer section between itself and the image carrier, and transfers the toner image from the image carrier to a transfer target in the transfer section; a charging voltage applying means for applying a charging voltage to the charging member; a developing voltage applying means for applying a developing voltage to the developing member; a transfer voltage applying means for applying a transfer voltage to the transfer member; a control unit that controls the charging voltage application means, the developing voltage application means, and the transfer voltage application means; and After the toner image formed on the surface of the image carrier in the transfer section is transferred to the transferee, the toner remaining on the surface of the image carrier is collected by the developing member, the control unit is capable of performing an image forming operation of forming the toner image developed from the electrostatic latent image on the transfer medium, and a cleaning operation of cleaning the charging member, the cleaning operation includes a first cleaning operation and a second cleaning operation, and is performed at a timing when a non-image forming operation different from the image forming operation is performed; In the first cleaning operation, the toner adhering to the charging member is collected by the developing member, In the second cleaning operation, the toner adhering to the charging member is discharged onto the transfer object passing through the transfer unit. An image forming apparatus characterized by: [Configuration 2] The control unit During the first cleaning operation, control is performed so that the developing voltage has a polarity opposite to the normal polarity and the charging voltage has the normal polarity and is equal to or lower than a discharge start voltage; During the second cleaning operation, control is performed so that the developing voltage has a polarity opposite to the normal polarity, the transfer voltage has a polarity opposite to the normal polarity, and the charging voltage has the normal polarity. 2. The image forming apparatus according to claim 1, [Configuration 3] The control unit controls the transfer voltage in the second cleaning operation so that the transfer voltage is lower than a discharge start voltage. 3. The image forming apparatus according to claim 1, wherein: [Configuration 4] a charge removing member disposed downstream of the transfer unit and upstream of the charging unit in a rotation direction of the image carrier, the charge removing member removing charge from the surface of the image carrier; The control unit controls the charge removal member to remove charge from the surface of the image carrier during the cleaning operation. 4. The image forming apparatus according to any one of configurations 1 to 3. [Configuration 5] the developing member further has a toner storage section that stores toner to be supplied to the developing section, The toner storage section is supplied with toner from a toner supply container, The control unit controls the cleaning operation to be performed when toner is replenished from the toner supply container to the toner storage unit. 5. The image forming apparatus according to any one of configurations 1 to 4. [Configuration 6] 6. The image forming apparatus according to any one of configurations 1 to 5, wherein the object to be transferred is a transfer material that is discharged from the image forming apparatus after an image has been transferred thereon. [Configuration 7] The transfer medium is an intermediate transfer medium. 6. The image forming apparatus according to any one of configurations 1 to 5. [Explanation of symbols]

[0099] 1: photosensitive drum, 2: charging roller, 31: developing roller, 5: transfer roller, 105: control unit

Claims

1. a rotatable image carrier; a charging member that contacts the image carrier to form a charging portion and charges the surface of the image carrier in the charging portion; a rotatable developing member that contacts the image carrier to form a developing section, and that supplies toner charged to a normal polarity to the surface of the image carrier in the developing section, thereby developing an electrostatic latent image formed on the surface of the image carrier based on image information, thereby forming a toner image; a transfer member that faces the image carrier, forms a transfer section between itself and the image carrier, and transfers the toner image from the image carrier to a transfer target in the transfer section; a charging voltage applying means for applying a charging voltage to the charging member; a developing voltage applying means for applying a developing voltage to the developing member; a transfer voltage applying means for applying a transfer voltage to the transfer member; a control unit that controls the charging voltage application means, the developing voltage application means, and the transfer voltage application means; and After the toner image formed on the surface of the image carrier in the transfer section is transferred to the transferee, the toner remaining on the surface of the image carrier is collected by the developing member, the control unit is capable of performing an image forming operation of forming the toner image developed from the electrostatic latent image on the transfer medium, and a cleaning operation of cleaning the charging member, the cleaning operation includes a first cleaning operation and a second cleaning operation, and is performed at a timing when a non-image forming operation different from the image forming operation is performed; In the first cleaning operation, the toner adhering to the charging member is collected by the developing member, In the second cleaning operation, the toner adhering to the charging member is discharged onto the transfer object passing through the transfer section. An image forming apparatus characterized by:

2. The control unit During the first cleaning operation, control is performed so that the developing voltage has a polarity opposite to the normal polarity and the charging voltage has the normal polarity and is equal to or lower than a discharge start voltage; During the second cleaning operation, control is performed so that the developing voltage has a polarity opposite to the normal polarity, the transfer voltage has a polarity opposite to the normal polarity, and the charging voltage has the normal polarity.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. The control unit controls the transfer voltage in the second cleaning operation so that the transfer voltage is lower than a discharge start voltage.

3. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. a charge removing member disposed downstream of the transfer unit and upstream of the charging unit in a rotation direction of the image carrier, the charge removing member removing charge from the surface of the image carrier; The control unit controls the charge removal member to remove charge from the surface of the image carrier during the cleaning operation.

3. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. the developing member further has a toner storage section that stores toner to be supplied to the developing section, The toner storage section is supplied with toner from a toner supply container, The control unit controls the cleaning operation to be performed when toner is replenished from the toner supply container to the toner storage unit.

3. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. 3. The image forming apparatus according to claim 1, wherein the object is a transfer material that is discharged from the image forming apparatus after an image is transferred thereon.

7. The transfer medium is an intermediate transfer medium.

3. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

Images