JP2005227453A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents a defective image from being formed by defective charging or the like due to the contamination of the surface of a electrifying roller by securing an excellent cleaning state of the surface of the electrifying roller for a long period of time or maintaining the surface of the electrifying roller in a favorable cleaning state for a long period of time, and for which the space is saved, the cost is reduced and benefits of a cleanerless method are made useful. <P>SOLUTION: The image forming apparatus comprises an image carrier, a contact electrifying means using a electrifying roller method which is in contact with the surface of the image carrier and charges the surface of the image carrier, an exposure means as an information writing means which forms an electrostatic latent image on a charged image carrier, a development means which supplies a developer to the electrostatic latent image and visualizes the electrostatic latent image and a transfer means which transfers a visualized developer image to transfer material, wherein the contact electrifying member has a electrifying roller holding member that holds the electrifying roller, and the electrifying roller holding member is freely rotatable in the image carrier contacting plane. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using a charging roller type contact charging device. More specifically, the developing roller (toner) remaining on the image carrier after the transfer process is removed and collected from the image carrier by development simultaneous cleaning in the developing device, and the cleaning device is discarded so as to be reused. The present invention relates to a cleanerless type image forming apparatus using the method.

  2. Description of the Related Art Conventionally, transfer-type image forming apparatuses such as copying machines, printers, and facsimiles using an electrophotographic system are photosensitive drums, which are general image bearing members of a rotating drum type, and the photosensitive drums are made to have a predetermined polarity and potential. Charging device (charging process) for charging processing, an exposure device (exposure process) as information writing means for forming an electrostatic latent image on the charged photosensitive member, and an electrostatic latent image formed on the photosensitive member A developing device (development process) that visualizes with toner as a developer, a transfer device (transfer process) that transfers the toner image onto a transfer material such as paper from the surface of the photoreceptor, and a little on the photoreceptor after the transfer process It consists of a cleaning device (cleaning process) that removes residual toner and cleans the surface of the photosensitive member, a fixing device (fixing step) that fixes the toner image on the transfer material, and the like. (Charging, exposure, development, transfer and cleaning) is applied is used for image formation.

  The toner remaining on the photoconductor after the transfer process is removed from the surface of the photoconductor by the cleaning device and accumulated in the cleaning device to become waste toner. However, such waste is used from the viewpoint of environmental conservation and effective use of resources. It is desirable that toner does not come out.

  Therefore, there is an image forming apparatus in which transfer residual toner collected by a cleaning device, so-called waste toner, is returned to the developing device and reused.

  Also, there is a cleanerless type image forming apparatus in which the cleaning device is eliminated, and the transfer residual toner on the surface of the photosensitive member after the transfer process is removed and collected from the photosensitive member by “development simultaneous cleaning” in the developing device and reused. is there.

  Simultaneous development cleaning is the process of developing the electrostatic latent image by transferring the residual toner on the photosensitive member after transfer to the subsequent development step, that is, continuously charging the photosensitive member and exposing it to light. Fog removal bias (fogging potential difference Vback, which is a potential difference between the DC voltage applied to the developing device and the surface potential of the photoconductor) during the process, exists on the surface of the photoconductor (non-image area) that should not be developed with toner. The transfer residual toner is collected by a developing device. According to this method, since the transfer residual toner is collected by the developing device and reused for developing the electrostatic latent image in the subsequent process, the waste toner is eliminated, and the trouble in the maintenance can be reduced. it can. Further, the cleanerless is advantageous for downsizing the image forming apparatus.

  However, in the cleanerless type image forming apparatus in which the transfer residual toner on the photoreceptor after the transfer process as described above is removed, collected, and reused, the charging polarity is originally opposite to the normal polarity. If there is toner that is reversed, or toner that has a charged polarity that is normal polarity, but has a toner whose polarity is reversed due to transfer bias, peeling discharge, etc., these toners are removed from the surface of the photoreceptor by the developing device. It may not be recovered / removed.

  Further, when the charging device is a contact charging device using a charging roller system in which the photosensitive member surface is charged by contacting the photosensitive member, the toner that rotates on the photosensitive member surface is a charging nip portion between the photosensitive member and the charging roller. When passing through the part, it adheres to the surface of the charging roller and causes toner contamination, which causes charging failure.

  In other words, in order to remove and collect the transfer residual toner on the photoconductor by the simultaneous development cleaning of the developing device, the charge polarity of the transfer residual toner on the photoconductor that passes through the charging unit and is carried to the developing unit is normal. It is necessary that the toner has a polarity and the charge amount is a charge amount of toner that can develop the electrostatic latent image on the photosensitive member by the developing device.

  Therefore, a toner charge amount control means for charging the transfer residual toner on the photoreceptor, which is located upstream from the contact charging device using the charging roller method and downstream from the transfer means, and upstream from the toner charge amount control means. There is provided a transfer residual toner equalizing unit that is located downstream of the unit and uniformizes the residual toner remaining on the photosensitive member after the toner image is transferred to the transfer material. This problem can be solved by applying a constant DC voltage to the uniformizing means.

  That is, after the transfer, the residual toner remaining on the surface of the photoconductor is made uniform by the transfer residual toner uniformizing unit, and the transfer residual toner on the homogenized photoconductor surface is charged to the normal polarity by the toner charge amount control unit. At the same time that the surface of the photosensitive member is charged by the charging roller, the transfer residual toner charged by the toner charge amount control means is charged to an appropriate charge amount to be removed and collected by the development simultaneous cleaning in the developing device. Collect with.

  However, even when the transfer residual toner on the photosensitive member is not rotated, the transfer residual toner adheres to the surface of the charging roller in a small amount when passing through the charging roller. In particular, when a continuous printing operation of an image with a high printing rate such as a photographic image is performed, the toner adhering to the surface of the charging roller gradually increases according to the number of prints and eventually causes a charging failure.

  As a method of removing this dirt, a method of bringing a cleaning member into contact with the surface of the charging roller has been used. There are two types of cleaning members according to their effects. One method is to use a soft and highly collective pad member such as sponge or fine fiber as a cleaning member in order to collect the toner adhering to the surface of the charging roller. As another method, a flexible organic polymer compound made of polyimide or the like is used to recharge the toner to a normal polarity by being rubbed with the toner adhering to the surface of the charging roller and then ejecting the toner onto the surface of the photoreceptor. It is the method of using this film as a cleaning member.

  However, even when the cleaning member as described above is used, in the contact charging device using the charging roller method, the contact pressure with respect to the photosensitive member is not uniform in the main scanning direction, and as a result, the surface of the charging roller surface If the speed is uneven in the main scanning direction and the surface of the charging roller is wrinkled or a minute gap is formed between it and the surface of the photoconductor, the toner will adhere to that part compared to other parts. It becomes easy. In particular, in the case of cleanerless, the transfer residual toner adheres to the surface of the charging roller in the image area, but the transfer residual toner does not adhere to the surface of the charging roller outside the image area. The frictional force at the contact nip between the charging roller and the photoconductor is different, the above-mentioned speed difference is more likely to occur, toner contamination on the charging roller surface is more likely to occur, and charging failure due to local toner contamination on the charging roller surface is likely to occur. A problem occurs.

  Therefore, the present invention has a contact charging device using a charging roller system, and removes and collects the transfer residual developer on the image carrier after the transfer process by simultaneous development cleaning and reuses it. In the image forming apparatus using the charging roller, the charging roller surface is ensured in a good cleaning state over a long period of time, or the charging roller surface is maintained in a substantially clean state for a long period of time. An object of the present invention is to provide an image forming apparatus that prevents image formation defects such as charging defects due to surface contamination and is space-saving and low-cost and that takes advantage of the cleanerless system.

  In order to achieve the above object, the present invention provides an image carrier, contact charging means using a charging roller system that contacts and charges the surface of the image carrier, and a charged image carrier. Exposure means as information writing means for forming an electrostatic latent image, developing means for supplying a developer to the electrostatic latent image to visualize the electrostatic latent image, and transfer means for transferring the visualized developer image to a transfer material The contact charging member has a charging roller holding member for holding a charging roller, and the charging roller holding member is freely rotatable in the plane in contact with the image carrier. To do.

  According to the present invention, in the cleanerless type image forming apparatus having the contact charging device that removes and collects the transfer residual developer on the image carrier after the transfer process by the simultaneous development cleaning and reuses the contact charging device, It has a charging roller holding member for holding the charging roller, and the charging roller holding member is free to rotate in the plane in contact with the image carrier, thereby preventing image formation failure such as charging failure due to contamination of the contact charging device. It is possible to provide an image forming apparatus that prevents the occurrence, is space-saving, is low-cost, and takes advantage of the cleanerless system.

  The image forming apparatus (image recording apparatus) according to the present embodiment will be described below.

FIG. 5 is a cross-sectional view of the main part of the image forming apparatus according to the embodiment of the present invention. The image forming apparatus of this example is an electrophotographic laser beam printer using a contact charging system, a reversal development system, and a cleanerless system.
(A) Image carrier 1 is a rotating drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. The photosensitive drum 1 is a negatively charged organic photoconductor (OPC) having an outer diameter of 60 mm, and is driven to rotate counterclockwise as indicated by an arrow with a process speed (peripheral speed) of 100 mm / sec centered on a central support shaft. Is done.

As shown in the layer configuration model diagram of FIG. 2, the photosensitive drum 1 has an undercoat layer 1b that suppresses light interference and improves the adhesion of an upper layer on the surface of an aluminum cylinder (conductive drum base) 1a. The photocharge generation layer 1c and the charge transport layer 1d are coated in order from the bottom.
(B) Charging means 2 is a contact charging device (contact charger) as a charging means for uniformly charging the peripheral surface of the photosensitive drum 1, and in this example, a charging roller (roller charger).

  The charging roller 2 is urged in the direction of the photosensitive drum and is brought into pressure contact with the surface of the photosensitive drum 1 with a predetermined pressing force, and is rotated by the rotation of the photosensitive drum 1. A pressure contact portion between the photosensitive drum 1 and the charging roller 2 is a charging portion (charging nip portion) a. A method for supporting the charging roller 2 will be described in detail later.

  A charging bias voltage of a predetermined condition is applied to the core metal 2a of the charging roller 2 from the power source S1, whereby the peripheral surface of the rotating photosensitive drum 1 is contact-charged to a predetermined polarity and potential. In this example, the charging bias voltage for the charging roller 2 is an oscillating voltage obtained by superimposing a DC voltage (Vdc) and an AC voltage (Vac). More specifically, DC voltage: −500 V, AC voltage; frequency f1 kHz, peak-to-peak voltage Vpp 1.5 kV, vibration voltage superimposed with a sine wave, and the peripheral surface of the photosensitive drum 1 is −500 V (dark potential Vd). Are uniformly charged by contact.

  The longitudinal length of the charging roller 2 is 320 mm, and a lower layer 2b, an intermediate layer 2c, and a surface layer 2d are sequentially arranged from the bottom on the outer periphery of the cored bar (support member) 2a as shown in the layer configuration model diagram of FIG. It is a laminated three-layer structure. The lower layer 2b is a foamed sponge layer for reducing charging noise, and the surface layer 2d is a protective layer provided to prevent leakage even if the photosensitive drum 1 has a defect such as a pinhole. .

  More specifically, the specification of the charging roller 2 of this example is as follows.

a. Cored bar 2a; stainless steel round bar 6mm in diameter b. Lower layer 2b: carbon dispersion foamed EPDM, specific gravity 0.5 g / cm ³ , volume resistivity 10 ² to 10 ⁹ Ωcm, layer thickness 3.0 mm, length 320 mm
c. Intermediate layer 2c: carbon-dispersed NBR rubber, volume resistivity 10 ² to 10 ⁵ Ωcm, layer thickness 700 μm
d. Surface layer 2d: tin oxide and carbon dispersed in resin resin of fluorine compound
Volume resistance 10 ⁷ to 10 ¹⁰ Ωcm, surface roughness (JIS standard 10-point average surface roughness Ra) 1.5 μm, layer thickness 10 μm
(C) Information writing means 3 is an exposure apparatus as information writing means for forming an electrostatic latent image on the surface of the charged photosensitive drum 1, and this example is a laser beam scanner using a semiconductor laser. A laser beam modulated in response to an image signal sent from a host process such as an image reading apparatus (not shown) to the printer side is output, and the uniformly charged surface of the rotating photosensitive drum 1 is laser-scanned and exposed at the exposure position b. L (image exposure). Due to the laser scanning exposure L, the potential of the surface of the photosensitive drum 1 irradiated with the laser light is lowered, so that electrostatic latent images corresponding to the scanned and exposed image information are sequentially formed on the surface of the rotating photosensitive drum 1. Go.
(D) Developing means 4 is a developing device (developing device) as developing means for supplying developer Z (toner) to the electrostatic latent image on the photosensitive drum 1 to visualize the electrostatic latent image. This is a reversal developing device of a component magnetic brush developing system.

  4a is a developing container. Reference numeral 4b denotes a non-magnetic developing sleeve, and the developing sleeve 4b is rotatably arranged in the developing container 4a with a part of its outer peripheral surface exposed to the outside. 4c is a non-rotating fixed magnet roller inserted in the developing sleeve 4b, 4d is a developer coating blade, 4e is a two-component developer contained in the developing container 4a, and 4f is disposed on the bottom side in the developing container 4a. The provided developer agitating member, 4g, is a toner hopper and contains replenishing toner.

The two-component developer 4e in the developing container 4a is a mixture of toner and a magnetic carrier and is stirred by the developer stirring member 4f. In this example, the resistance of the magnetic carrier is about 10 ¹³ Ωcm, and the particle size is 40 μm. The toner is triboelectrically charged to negative polarity by rubbing with the magnetic carrier.

  The developing sleeve 4b is disposed in close proximity to the photosensitive drum 1 while maintaining a closest distance (referred to as S-Dgap) to the photosensitive drum 1 at 350 μm. The facing portion between the photosensitive drum 1 and the developing sleeve 4a is a developer c. The developing sleeve 4b is rotationally driven in the direction opposite to the traveling direction of the photosensitive drum 1 in the developing unit c. This is advantageous for collecting the transfer residual toner on the photosensitive drum 1.

  A part of the two-component developer 4e in the developing container 4a is attracted and held as a magnetic brush layer on the outer peripheral surface of the developing sleeve 4b by the magnetic force of the magnet roller 4c in the sleeve, and is rotated and conveyed as the sleeve 4b rotates. Then, a predetermined thin layer is formed by the developer coating blade 4d, and in contact with the surface of the photosensitive drum 1 at the developing portion c, the surface of the photosensitive drum is rubbed appropriately. A predetermined developing bias is applied to the developing sleeve 4b from the power source S2. In this example, the developing bias voltage for the developing sleeve 4b is an oscillating voltage obtained by superimposing a DC voltage (Vdc) and an AC voltage (Vac). More specifically, a DC voltage; -350 V, an AC voltage; a frequency f8.0 kHz, a peak-to-peak voltage 1.8 kV, and an oscillating voltage in which a rectangular wave is superimposed.

  Thus, the toner in the developer coated as a thin layer on the surface of the rotating developing sleeve 4b and transported to the developing section c corresponds to the electrostatic latent image on the surface of the photosensitive drum 1 by the electric field due to the developing bias. By selectively adhering, the electrostatic latent image is developed as a toner image. In the case of this example, the toner adheres to the exposed bright portion of the surface of the photosensitive drum 1 and the electrostatic latent image is reversely developed.

  The developer thin layer on the developing sleeve 4b that has passed through the developing section c is returned to the developer reservoir in the developing container 4a with the subsequent rotation of the developing sleeve.

In order to maintain the toner concentration of the two-component developer 4e in the developing container 4a within a predetermined substantially constant range, the toner concentration of the two-component developer 4e in the developing container 4a is adjusted by, for example, an optical toner concentration sensor (not shown). The toner hopper 4g is driven and controlled according to the detected information, and the toner in the toner hopper is supplied to the two-component developer 4e in the developing container 4a. The toner supplied to the two-component developer 4e is stirred by the stirring member 4f.
(E) Transfer means / fixing means 5a is a transfer device, and this example is a transfer roller. The transfer roller 5a is brought into pressure contact with the photosensitive drum 1 with a predetermined pressing force, and the pressure nip portion is a transfer portion d. A transfer material (a member to be transferred, a recording material) P is fed to the transfer portion d from a paper feeding mechanism portion (not shown) at a predetermined control timing.

  The transfer material P fed to the transfer portion d is nipped and conveyed between the rotating photosensitive drum 1 and the transfer roller 5a. During this time, the transfer roller 5a has a negative polarity that is the normal charging polarity of the toner from the power source S3. In this example, a positive transfer bias of +2 kV is applied in this example, so that the toner image on the surface of the photosensitive drum 1 is sequentially electrostatically transferred onto the surface of the transfer material P that is nipped and conveyed by the transfer portion d. It will be done.

The transfer material P which has received the transfer of the toner image through the transfer portion d is sequentially separated from the surface of the rotary photosensitive drum 1 and is conveyed to the fixing device 6 (for example, a heat roller fixing device) to receive the toner image fixing process. Output as an image formed product (print, copy).
(F) Cleanerless auxiliary means 7 is a toner (developer) charge amount control means for aligning the charge polarity of the transfer residual toner with the negative polarity which is the normal polarity, and 8 is a uniform transfer residual toner on the photosensitive drum 1 This is a transfer residual toner (residual developer image) uniformizing means. Generally, the transfer residual toner remaining on the photosensitive drum 1 without being transferred to the transfer material P at the transfer portion d is a mixture of reversal toner and toner having an inappropriate charge amount. Image) The transfer residual toner is neutralized once by the homogenizing means 8, and the transfer residual toner is subjected to normal polarity charging again by the toner charge amount control means 7, thereby preventing the transfer residual toner from adhering to the charging roller 2. In addition, the removal and recovery by the developing device 4 can be performed effectively.

  The toner charge amount control means 7 and the transfer residual toner equalizing means 8 are brush-like members having appropriate conductivity, and are arranged such that the brush portion is in contact with the surface of the photosensitive drum 1. Reference numeral e denotes a contact portion between the toner charge amount control means 7 and the photosensitive drum 1 surface. f is a contact portion between the transfer residual toner uniformizing means 8 and the surface of the photosensitive drum 1.

  A negative DC voltage is applied from the power source S4 to the toner charge amount control means 7, and a positive DC voltage is applied from the power source S5 to the transfer residual toner equalizing means 8. Specifically, a DC voltage of −800 V is applied to the toner charge amount control means 7 and a +400 V DC voltage is applied to the transfer residual toner equalizing means 8.

  Next, the generation mechanism of the toner contamination on the surface of the charging roller will be described with reference to FIG.

  As shown in FIG. 3A, the charging roller 2 is generally pressed against the photosensitive drum 1 by a bearing member in which load springs are attached to the metal core portions at both ends. Although the charging roller 2 has a particularly high rigidity in the cored bar, the central part floats with respect to the photosensitive drum 1 by pressurizing the cored bar at both ends. The pressure applied to the charging roller 2 is the smallest at the center and tends to gradually increase toward both ends.

  For this reason, since the amount of crushing of the charging roller 2 increases in both end regions of the charging roller 2 in contact with the photosensitive drum 1, the rotation radius decreases, and the contact nip portion a between the charging roller 2 and the photosensitive drum 1. The frictional force at will also increase.

  On the other hand, in the central portion, the amount of crushing of the charging roller 2 in contact with the photosensitive drum 1 is small compared to the both end regions, so that the radius of rotation increases, and at the contact nip portion a between the charging roller 2 and the photosensitive drum 1. The frictional force is also reduced. Therefore, as shown in FIG. 3B, the surface speed of the surface of the charging roller 2 tends to be smaller in the both end portions of the charging roller 2 than in the central portion.

  As described above, when the surface speed of the charging roller 2 is different between both end portions and the central portion, as shown in FIG. 3C, the intermediate portion between the central portion and both end portions (1/4 portion, 3 Twist occurs on the surface of the charging roller 2 per / 4 part). When such a twist occurs, wrinkles are generated on the surface of the charging roller 2, and further, the rotation radius of the charging roller 2 at the twisted portion becomes small, so that the above-described contamination due to the toner tends to deteriorate around the twisted portion. is there.

  Furthermore, in the image forming apparatus using the cleanerless system as in the present embodiment, the transfer residual toner is steadily coming in the image area such as the central portion of the charging roller 2. The additive acts as a kind of lubricant which is a contact nip a between the charging roller 2 and the photosensitive drum 1.

  On the other hand, such transfer residual toner is not supplied to both ends of the charging roller 2 outside the maximum image area. Therefore, the difference between the friction force acting between the charging roller 2 and the photosensitive drum 1 between the central portion and both ends, and further, the difference in the surface speed of the charging roller 2 is further increased, and the charging roller 2 is twisted. Will increase.

  Therefore, in the present embodiment, a contact charging device of the charging roller 2 support system as shown in FIG. 4 is used. The charging roller 2 is held at both ends of a core metal 2a by a cylindrical member 2l made of polycarbonate having an inner diameter substantially the same as the diameter of the core metal 2a and good sliding properties. The cylindrical members 21 at both ends are respectively held by the first holding member 2i via the support member 2k. Furthermore, a cylindrical support member 2j is provided at the center in the longitudinal direction of the first holding member 2i, and is held by the second holding member 2h via the cylindrical support member 2j. Here, the cylindrical support member 2j can be freely rotated with respect to the second holding member 2h in the plane of contact with the photosensitive drum 1. The second holding member 2h is connected to a member fixed in the image forming apparatus or the image forming unit via a pressure spring 2e.

  Therefore, the charging roller 2 held by the above-described support method is urged in the direction of the photosensitive drum by the pressure spring 2e and is brought into pressure contact with the surface of the photosensitive drum 1 with a predetermined pressing force. Rotates following the rotation.

  A mechanism that can solve the above-described problem by using such a charging roller 2 supporting contact charging device will be described with reference to FIG.

  As shown in FIG. 6B, the bus of the normal charging roller 2 is parallel to the bus of the photosensitive drum. In such a case, as described above, the charging force on the photosensitive drum 1 at the end of the charging roller 2 is larger than the pressing force on the photosensitive drum 1 at the center of the charging roller 2. The surface speed of the roller 2 is different between the end portion of the charging roller 2 and the central portion of the charging roller 2.

  At this time, when the charging roller 2 is supported by a conventional supporting method, the surface of the charging roller 2 is twisted. In the present embodiment, the cylindrical support member 2j rotates within the tangential plane of the photosensitive drum 1. Since it can operate freely, as shown in FIG. 6C, it is stable in a state where the bus of the charging roller 2 and the bus of the photosensitive drum 1 have a certain angle (hereinafter referred to as “tolerance angle”). To do. The reason for this state is that the pressure on the photosensitive drum 1 at the end of the charging roller 2 is larger than that at the center of the charging roller 2, that is, the amount of penetration, so that it is separated from the photosensitive drum 1 so as to relieve it. The force to act. On the other hand, since the amount of penetration into the photosensitive drum 1 increases in the central portion of the charging roller 2, the pressure applied to the photosensitive drum 1 in the central portion of the charging roller 2 increases. As a result, the charging roller 2 is stable on the photosensitive drum 1 with a tolerance angle that equalizes the pressure applied to the photosensitive drum 1 in the longitudinal direction of the charging roller 2, and the surface speed of the charging roller 2 is the same in the longitudinal direction. become.

  The charging roller 2 supporting contact charging device of the present embodiment is similar to a method in which a certain tolerance angle is previously provided between the bus of the charging roller 2 and the bus of the photosensitive drum 1, but is a conventional method. In addition, it is not possible to absorb changes with time on the surfaces of the charging roller 2 and the photosensitive drum 1 and variations in design tolerances.

  On the other hand, in the charging roller 2 support type contact charging device of the present embodiment, the crossing angle is set so that the speed of the surface of the charging roller 2 is uniform in the longitudinal direction at any time under conditions such as change with time and fluctuation of each parameter. Is set.

  As described above, as shown in the present embodiment, a cleanerless image forming apparatus having a contact charging device that removes and collects the transfer residual developer on the image carrier after the transfer step by simultaneous development cleaning and reuses it. , The surface roughness outside the maximum image area of the charging roller 2 is made larger than the surface roughness inside the image area of the charging roller 2, thereby preventing the twisting phenomenon of the charging roller 2 caused by the difference in surface speed in the main scanning direction. An image forming apparatus that can prevent image formation defects such as charging defects due to partial toner contamination of the charging roller 2, is space-saving and low-cost, and takes advantage of the cleanerless system Can be provided.

  In the present invention, the developer (toner) remaining on the image carrier after the transfer process is removed and collected from the image carrier by the development simultaneous cleaning in the developing device, and the cleaning device is discarded so as to be reused. The applicability to a cleanerless type image forming apparatus using a roller type is high.

It is a schematic sectional view of a conventional image forming apparatus. It is a layer structure model figure of a photosensitive drum and a charging roller. FIG. 6 is a schematic diagram for explaining a cause of occurrence of a twist generated on the surface of the charging roller. 1 is a model diagram of a contact charging device of an image forming apparatus according to the present invention. 1 is a schematic cross-sectional view of a main part of an image forming apparatus according to the present invention. FIG. 6 is a schematic diagram illustrating the behavior of a charging roller when the contact charging device of the image forming apparatus according to the present invention is used.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging roller 3 Laser beam scanner 4 Developing device 5 Transfer device 6 Fixing device 7 Toner charge amount control means (Developer charge amount control means)
8 Transfer residual toner uniformizing means (residual developer uniformizing means)
S1 to S5 Bias voltage application power supply

Claims (3)

As an image carrier, contact charging means using a charging roller system that contacts and charges the surface of the image carrier, and information writing means for forming an electrostatic latent image on the charged image carrier An image forming apparatus including: an exposure unit; a developing unit that supplies a developer to the electrostatic latent image to visualize the electrostatic latent image; and a transfer unit that transfers the visualized developer image to a transfer material.
2. The image forming apparatus according to claim 1, wherein the contact charging member has a charging roller holding member for holding a charging roller, and the charging roller holding member is freely rotatable within a plane in contact with the image carrier.   The image forming apparatus according to claim 1, wherein the rotation operation of the charging roller holding member in a plane in contact with the image carrier operates with a central portion in the longitudinal direction of the charging roller holding member as a fulcrum.   3. The image forming apparatus according to claim 1, wherein a cleanerless system is used in which the developer remaining on the surface of the image carrier without being transferred by the transfer unit is collected by the developing device.

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