JP2008058686A - Electrifying device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrifying device equipped with constitution capable of preventing the occurrence of an abnormal image without causing cost rise with simple constitution. <P>SOLUTION: The electrifying device which uniformly electrifies an image carrier while coming in contact with the image carrier is provided with a flange part 24K2 at a driven member 24K1 rotating operatively connected with a driving means on the image carrier side, and a separation member 100 equipped with a large-diameter part 100A capable of abutting on the flange part 24K2 by energizing force acting on the electrifying roller 24K. By separating the electrifying roller 24K from the image carrier against energizing while the large-diameter part 100A abuts on the flange part 24K2, and rotating it when the large-diameter part 100A is dragged by the rotation of the driven member 24K1, the electrifying roller 24K is brought into contact with the image carrier by using such energizing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a charging device and an image forming apparatus, and more particularly to a contact state setting mechanism for a charging member.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus such as an electrostatic copying machine or an optical printer is provided with a device for charging a photosensitive member, which is a member to be charged, as a discharge product such as ozone or nitrogen oxidation. Instead of a non-contact method in which an object is generated, a contact method in which such a discharge product is not generated has been frequently used.

  For example, a contact-type charging device includes a charging roller that can be interlocked while being in contact with a photoconductor, and is configured to uniformly charge the photoconductor. However, the charging roller is always in contact with the photoconductor. If this is the case, an elastic body such as a conductive rubber used for the charging roller is pressed against the photoconductor by a predetermined pressure, and the surface of the photoconductor may be soiled by components that exude from the surface. For example, if the portion of the charging roller that contacts the photoreceptor is formed of conductive rubber such as EPDM (ethylene propylene diene terpolymer), it is in contact with the photoreceptor at a predetermined contact pressure. If the pressure contact state is continued for a long time, the softener (plasticizer) contained in the rubber material may ooze out and contaminate the surface of the photoreceptor.

The contamination on the surface of the photoconductor is almost invisible to the naked eye, but when developed, the toner image on the part to which the softening agent has adhered becomes less adhered to the toner than the other parts. When the image is transferred to the transfer paper, white streaks (white spots) appear periodically in the portion corresponding to the dirty portion, resulting in an image defect.
In addition, the charging roller that is always in contact with a certain amount of pressure may cause plastic deformation in the surface layer portion due to the pressure, and this deformed portion causes abnormal contact with the photosensitive member and causes uneven charging. As a result, an abnormal image is generated, and in particular, when a halftone image is obtained, the above-described streak-like image may be obtained.

Therefore, in order to solve such a problem, for example, in a standby state where the image forming operation is not performed (standby state), the charging roller (conductive roller) is separated from the drum-shaped photoconductor by the moving means and is not contacted. There has been proposed an image forming apparatus in which the contact time with the photoconductor is shortened by moving the photoconductor to the position of the photoconductor so that the contact portion of the photoconductor is not easily soiled (for example, Patent Document 1).
The above-mentioned Patent Document 1 uses a solenoid that sets the swinging position of a support member that swingably supports the charging roller as a driving source for contacting and separating the charging roller from the photoreceptor. There is.

  Therefore, for the purpose of reducing the cost, an image formation in which a charging roller is provided at the swing end of a swing lever whose swing direction is set according to the rotation direction of a drive gear used as a drive member, and the photosensitive member is driven. A configuration has been proposed in which the rotation direction of the drive gear is switched between when the apparatus is in operation and when it is stopped (for example, Patent Document 2).

JP-A-1-207768 Japanese Patent Laid-Open No. 7-23469

  In any of the configurations disclosed in the above-mentioned patent documents, the charging roller contact / separation control is performed for the case where the image forming process is performed after the image forming apparatus is installed at the place where the image forming apparatus is used and the case where the image forming process is not performed. Is assumed.

  However, the state in which the charging roller remains in contact with the photosensitive member for a long time is not only after the image forming apparatus is installed, but may be stored in a warehouse or the like after shipment from the factory until the installation. is there.

  Equipped with the above-described contact / separation mechanism only for the period up to factory shipment results in an exaggerated structure and increases costs. In other words, when it is only necessary to prevent the photosensitive member and the charging roller from contacting each other until the device is deferred after shipment from the factory, providing the mechanism having the contact and separation functions described above is intended for the intended operation. An extra function is included, which causes an increase in cost.

  The present invention provides a charging device and an image forming apparatus having a configuration capable of preventing the occurrence of an abnormal image without causing an increase in cost with a simple configuration in view of the problems in the conventional charging device and the image forming apparatus using the same. There is to do.

In order to achieve this object, the invention according to claim 1 is a charging device including a charging member that uniformly charges the image carrier by contacting and interlocking with the image carrier.
The charging member is provided so as to be interlocked with a rotatable charging roller urged toward the surface of the image carrier and a rotatable driving member provided on the image carrier, and the charging roller A driven member positioned coaxially with the rotating shaft of the charging roller, and a large-diameter portion provided coaxially with the rotating shaft of the charging roller and separating the charging roller from the image carrier against the biasing in the circumferential direction. And a separation member capable of abutting against the driven member, wherein the separation member separates the charging roller from the image carrier against the bias by the large diameter portion abutting against the driven member. When the driven member rotates, when the driven member rotates and the large-diameter portion is dragged and rotated, the urging force sets the charging roller in contact with the image carrier. It is a feature.

  According to a second aspect of the present invention, the spacing member is provided with a portion having a high friction coefficient and a portion having a low friction coefficient at the large diameter portion, and after the large diameter portion is dragged and rotated by the driven member, the friction coefficient is increased. The lower portion is in contact with the driven member.

  According to a third aspect of the present invention, the portion of the large-diameter portion that contacts the driven member after being dragged and rotated by the driven member has a smaller area than the portion that contacts the driven member due to the biasing. It is characterized by being.

  According to a fourth aspect of the present invention, the driven member includes a flange having a circumferential surface around the rotation axis of the driven member, and the large-diameter portion of the spacing member is brought into contact with the outer peripheral surface of the flange. It is characterized by that.

  According to a fifth aspect of the present invention, the large-diameter portion contacts the driven member until the drive member starts rotating for the first time after shipment from the factory, thereby separating the charging roller from the image carrier. It is characterized by setting the position.

  A sixth aspect of the invention is characterized in that the charging device according to any one of the first to fifth aspects is used for a process cartridge.

  A seventh aspect of the invention is characterized in that the charging device according to any one of the first to fifth aspects is used in an image forming apparatus.

  According to the present invention, the charging roller can be brought into contact with the image carrier main body by dragging the large-diameter portion of the separating member by utilizing the rotation of the driven member, so that a special contacting / separating mechanism or the like is required. The contact state of the charging roller can be set. In particular, the charging roller that is separated from the image carrier by the large-diameter portion of the separation member until the drive member starts rotating for the first time after shipment from the factory is rotated first after the shipment from the factory. Since the charging roller is brought into contact with the image carrier by the drag action of the driven member interlocked with the driving member at the time of starting, the charging roller contacts the image carrier for a long time after shipment from the factory. It is possible to prevent the occurrence of abnormal images due to contamination of the image carrier and composition deformation of the charging roller that occur when the contact state is maintained.

The best mode for carrying out the present invention will be described below with reference to the illustrated embodiments.
FIG. 1 shows an image forming apparatus to which a charging device according to the present invention is applied. The image forming apparatus shown in FIG. 1 includes an image forming unit capable of forming images of a plurality of colors by writing using a laser beam. Although the tandem color laser printers are arranged side by side, in the present invention, a copying machine, a facsimile machine, or a printing machine is also included in the image forming apparatus.

The configuration of the color laser printer shown in FIG. 1 will be described as follows.
In FIG. 1, a color laser printer 1 includes an image carrier (photosensitive drum) 21K that rotates at a constant speed for each color of black, cyan, magenta, and yellow (denoted by K, C, M, and Y). 21C, 21M, 21Y, an image forming unit having color developing units 22K, 22C, 22M, 22Y, and a transfer that holds the color image that has been superimposed and transferred developed by the image forming unit and is fed from the paper feeding unit 5 Further, an intermediate transfer member 41 (which may be an intermediate transfer belt, a transfer belt of the transfer material P, or a photosensitive belt) 41 that is further transferred to the material P is provided.
The transfer material P onto which the color image has been transferred is conveyed to the fixing unit 6 to fix the color image on the transfer material P, and is discharged to the discharge unit on the upper surface of the apparatus by the discharge roller 71. The four color developing devices and the image carrier are integrally formed for each color and are detachable from the printer main body.

Next, the configuration of each part of the image forming apparatus 1 will be described in detail.
The image carriers (photosensitive drums) 21K, 21C, 21M, and 21Y are configured integrally with the developing units 22K, 22C, 22M, and 22Y and the toner storage containers 23K, 23C, 23M, and 23Y, and the developing units 2K and 2C. 2M and 2Y are detachably held with respect to the printer main body, and are configured so that the units can be easily replaced according to toner consumption.

Image carriers (photosensitive drums) 21K, 21C, 21M, and 21Y shown in FIG. 1 are configured by applying an organic photoconductive layer to the outside of an aluminum cylinder, and image carriers (photosensitive drums) 21K, 21C, and 21M. , 21Y are rotatably supported by the developing units 2K, 2C, 2M, and 2Y via flanges, bearings, and shafts that are coaxially disposed at both ends of the image bearing member 21K, 21C, 21M, 21Y and the shaft are electrically connected.
Further, there is a drive transmission mechanism (for example, a helical gear) (not shown) coaxially with the image carriers (photosensitive drums) 21K, 21C, 21M, and 21Y, and rotates by obtaining power from a drive device (not shown). .

  The charging units 24K, 24C, 24M, and 24Y include a charging roller that can contact and interlock with the image carriers (photosensitive drums) 21K, 21C, 21M, and 21Y, and the image carriers (photosensitive drums) 21K and 21C. , 21M, 21Y to uniformly charge the surface.

  As described above, the link between the charging roller used in the charging units 24K, 24C, 24M, and 24Y and the image carriers (photosensitive drums) 21K, 21C, 21M, and 21Y is the image carrier (photosensitive drum) 21K, It is connected to a drive transmission mechanism (for example, a helical gear) provided coaxially with 21C, 21M, and 21Y, that is, via a gear meshing with the helical gear. The structure relating to this interlocking relationship will be described in detail in a contact / separation mechanism between (photosensitive drums) 21K, 21C, 21M, and 21Y and charging means 24K, 24C, 24M, and 24Y, which will be described later.

  Writing on the image carrier is performed by each color LD light (31K, 31C, 31M, 31Y) from the writing exposure device 3, and image carriers (photosensitive drums) 21K, 21C rotating at a constant speed. , 21M, and 21Y are selectively irradiated with laser light to perform exposure writing, thereby forming an electrostatic latent image on the image carrier.

  The developing means is composed of four developing units 22K, 22C, 22M, and 22Y that can develop black, cyan, magenta, and yellow colors in order to visualize the electrostatic latent image. The four color developing devices 22K, 22C, 22M and 22Y are image bearing members (photosensitive drums) 21K, 21C, 21M and 21Y, and developing rollers 25K, 25C, 25M and 25Y are image bearing members (photosensitive drums). 21K, 21C, 21M, and 21Y are arranged in contact with each other while rotating, and a visible image is formed on each of the image carriers (photosensitive drums) 21K, 21C, 21M, and 21Y with toner of each color.

  An intermediate transfer member (hereinafter referred to as an intermediate transfer belt) 41 multiplexes toner images of image carriers (photosensitive drums) 21K, 21C, 21M, and 21Y visualized by the developing units 2K, 2C, 2M, and 2Y during a color image forming operation. Rotates to transfer. The intermediate transfer member is mainly composed of an intermediate transfer belt 41, a drive roller 42 that transmits drive, and a tension roller 43 that stretches the intermediate transfer belt. The toner images formed by the image carriers (photosensitive drums) 21K, 21C, 21M, and 21Y are multiple transferred to the intermediate transfer belt 41. The intermediate transfer member (intermediate transfer belt) 41 that has undergone the multiple transfer collectively transfers the toner images of the respective colors onto the transfer material P in the secondary transfer unit 44.

  In addition, the sheet feeding device 5 that feeds the transfer material P from the sheet feeding cassette 51, the transport device 8 that transports the fed transfer material P, the fixing unit 6 that fixes the color images collectively transferred to the transfer material P, and the image A paper discharge unit 7 that transports the transfer material P that has been formed to a paper discharge port at the top of the apparatus, and a double-sided printing unit 9 that forms images on both sides of the transfer material P are provided.

  In a color laser printer having the above-described configuration, an image carrier (photosensitive drum) and an apparatus for performing each process of charging, developing, and cleaning are collectively stored in the unit to create an image of each color. A process cartridge in the image forming unit is configured. Therefore, the replacement work of the accommodated device can be performed only for the image forming unit of the target color, and unlike the case where the device or the member whose life is still remaining is replaced. It is possible to prevent the management cost from rising.

  On the other hand, the charging units 24K, 24C, 24M, and 24Y provided in each process cartridge are configured to come in contact with and separate from the image carriers (photosensitive drums) 21K, 21C, 21M, and 21Y. As the contact / separation operation, the charging means 24K is not until the image carriers (photosensitive drums) 21K, 21C, 21M, and 21Y start to rotate for the first time after the shipment from the factory, instead of when the color printer is in operation. , 24C, 24M, and 24Y are maintained apart from the image carriers (photosensitive drums) 21K, 21C, 21M, and 21Y, and the image carriers (photosensitive drums) start to rotate first. At this point, the charging roller is set in contact with the image carrier (photoreceptor drum), and the pressing state against the image carrier (photoreceptor drum) cannot be maintained carelessly. There is a Do not operate.

  FIG. 2 is a schematic diagram for explaining this contact / separation mechanism. In this figure, an image carrier (photosensitive drum) is provided on the rotating shaft of the charging roller used in the charging units 24K, 24C, 24M, and 24Y. A helical gear as a driven member that meshes with a helical gear that is the drive transmission means on the side (in FIG. 2, for convenience, the charging means 24K is indicated by reference numeral 24K1, but the other charging means 24C, 24M, and 24Y are also shown. (Similar structure) is rotatably provided.

  The helical gear 24K1 is provided with a flange portion 24K2 having a smaller diameter than the helical gear 24K1, and a part of the separation member 100 is in contact with the flange portion 24K2.

  The separation member 100 is a member for maintaining the state in which the charging roller is separated from the image carrier (photosensitive drum), and is supported on the same axis as the charging roller (shown by reference numeral 24K for convenience) in the circumferential direction. The rotating member is partially provided with a large diameter portion 100A.

  In FIG. 2B, a large diameter portion 100A is a lower side portion extended in the diameter direction of the charging roller 24K, and a tip portion is a side portion 100A1 in contact with the flange portion 24K2, and a direction perpendicular to the side portion 100A1. Then, the side portion 100B located on the rear side of the rotation direction of the helical gear 24K1 (the direction indicated by the symbol F in FIG. 2) extends in a direction perpendicular to the side 100B and is a side perpendicular to the diameter direction. A protrusion 100B1 having a smaller area than the portion 100A1 is provided.

  In the present embodiment, a relationship is set in which the friction coefficient between the side portion 100A1 and the projection portion 100B1 is larger than the friction coefficient of the projection portion 100B1. It is easy to maintain the state in contact with the outer peripheral surface of the flange portion 24K2 of the tooth gear 24K1.

The charging roller 24K is biased toward the image carrier (photoreceptor drum) by an elastic body 101 such as a spring, and the side portion 100A1 is applied to the flange portion 24K2 of the helical gear 24K1 by using this biasing. The state in which the charging roller 24K is separated from the image carrier (photosensitive drum) by the extension distance of the side portion 100A1 can be maintained by the frictional force generated when facing each other.
At this time, the image bearing member (photosensitive drum) does not rotate, which corresponds to storage during the period from the factory shipment until the user is installed, and during this time, the charging roller 24K passes through the elastic body 101. The state of being separated from the image carrier (photosensitive drum) is maintained against the biasing.

  Since the side member 100A1 is in frictional contact with the flange portion 24K2 of the helical gear 24K1, the separation member 100 can be dragged by the rotation of the flange portion 24K2, thereby centering on the rotation axis of the charging roller 24K. It is designed to rotate. When the separating member 100 rotates, as shown in FIG. 2 (C), the side portion 100A1 is dragged by the flange portion 24K2, and this causes the protrusion portion 100B1 to rotate to the outer peripheral surface of the flange portion 24K2. It comes to contact.

  The protruding portion 100B1 has a protruding amount that can prevent the side portion 100A1 from coming into contact with the flange portion 24K2. Further, since the friction coefficient is smaller than the side portion 100A1, the frictional force due to the contact is slight. When contacted with the flange portion 24K2, the side portion 100A1 is prevented from recontacting the flange portion 24K2, and the rotation of the helical gear 24K2 is prevented from being hindered by frictional resistance. It has become.

  As a configuration for setting the relationship of the friction coefficient, the surface of the inner surface of the mold corresponding to the side portion 100A1 when the surface roughness of the side portion 100A1 of the separating member 100 is increased or when a resin molded product is used. It is conceivable to roughen the roughness. In the case of a resin molded product, for example, polycarbonate resin, acrylonitrile butadiene styrene resin, acrylonitrile styrene resin, styrene resin, polyethylene resin, polyprene resin, polyamide resin, polyacetal resin, polyphenylene ether resin, polyphenylene oxide resin, polyphenylene oxide resin, Ether terephthalate resins and their alloy resins are used.

  In the state where the side portion 100A1 of the separating member 100 is in frictional contact with the flange portion 24K2, the contact pressure in the cleaning device having a member that contacts the image carrier (photosensitive drum) is acting. Since it is in a so-called brake state, even when the pressing force of the elastic body 101 is set to several N to several tens N and applied to the charging roller 24K, rotation on the image carrier (photosensitive drum) side is prevented, The helical gear 24K1 is prevented from rotating carelessly.

  Since the present embodiment is configured as described above, in the charging unit that is in the storage state after shipment from the factory, the side portion 100A1 of the separating member 100 contacts the flange portion 24K2 of the helical gear 24K1, thereby charging roller 24K. Is kept away from the image carrier (photosensitive drum).

  On the other hand, when the image carrier (photoreceptor drum) starts rotating for the first time after being shipped from the factory, the helical gear 24K1 on the charging roller 24K side rotates in conjunction with the rotation. Accordingly, since the side portion 100A1 of the separating member 100 is dragged and rotated, unlike the case where the side portion 100A1 is in contact, the charging roller 24K moves toward the image carrier (photosensitive drum) side. Contact. This contact is performed by urging the elastic body 101.

  According to the embodiment as described above, since the charging roller 24K is kept out of contact with the image carrier (photoreceptor drum) for a long period after factory shipment, the surface of the image carrier (photoreceptor drum) is maintained. The charging roller 24K can be prevented from fouling and plastic deformation of the charging roller 24K, and the transition from the separated state to the contacting state of the charging roller 24K can be performed only by using the rotation of the helical gear 24K1, so that a special contact / separation is required. Cost increase can be prevented without providing a mechanism. In addition, as for protrusion part 100B1, it is desirable to form a corner | angular part roundly in order to reduce resistance at the time of contact with flange part 24K2.

Next, another embodiment of the present invention will be described.
FIG. 3 is a view showing a modified example of the separation member 200. In FIG. 3, a convex portion 200A2 is provided on a side portion 200A1 corresponding to the side portion 100A1 shown in FIG. 2, and the convex portion 200A2 is a side portion. When 200A1 and the flange portion 24K2 face each other, they engage with a recess 24K3 formed in the flange portion 24K2. 3 is provided with a projection 200B1 corresponding to the projection 100B1 as in the case shown in FIG.

  Since the present embodiment is configured as described above, the convex portion 200A2 of the side portion 200A1 of the separation member 200 is engaged with the concave portion 24K3 of the flange portion 24K2 after factory shipment and before installation to the user. Is done. As a result, as in the case shown in FIG. 2, the charging roller 24K maintains a state where it is separated from the image carrier (photosensitive drum) against the urging of the elastic body 101.

  When the helical gear 24K1 starts rotating, the convex portion 200A2 of the separating member 200 is disengaged from the concave portion 24K3 as the side portion 200A1 is dragged and rotated by the flange portion 24K2, and the case shown in FIG. Similarly, the charging roller 24K can be brought into contact with the image carrier (photosensitive drum) by the urging of the elastic body 101.

  In the present embodiment, in addition to the frictional contact between the side portion 200A1 of the separation member 200 and the flange portion, the engagement between the convex portion 200A2 and the concave portion 24K3 is used to prevent inadvertent rotation of the separation member 200 and charging. The state where the roller 24K is separated from the image carrier (photosensitive drum) can be reliably maintained.

  In the above embodiment, the surface roughness is increased as a configuration for increasing the friction coefficient of the side portion 100A1, or 200A1, but a tape or material having a material having a high friction coefficient is integrated into the side portion. You may make it do.

  In addition, the present embodiment presents a configuration in which the charging roller is separated from the image carrier (photosensitive drum) for the period from factory shipment until installation to the user. For example, setting of image formation timing, etc. When the image formation is completed, the image carrier is slightly reversed at the end of image formation, and the helical gear on the charging roller side is rotated in reverse, so that the protruding portion of the separating member is dragged and moved so that the side portion faces the flange portion. It is impossible to make the charging roller contact / separate not only during factory shipment but also during operation and non-operation of the image forming apparatus after installation. I can say no.

1 is a schematic diagram illustrating an example of an image forming apparatus including a charging device according to the present invention. It is a figure which shows the principal part structure of the charging device by the Example of this invention. It is a figure which shows the modification of the principal part structure shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color laser printer 21K, 21C, 21M, 21Y Image carrier 24K, 24C, 24M, 24Y Charging means 24K1 Helical gear 24K2 Flange part 24K3 Recessed part 100,200 Separating member 100A Large diameter part 100A1 Side part 100B1 Protrusion Part 200A1 Convex part

Claims (7)

In a charging device including a charging member that uniformly charges the image carrier by contacting and interlocking with the image carrier,
The charging member includes a rotatable charging roller biased toward the surface of the image carrier,
A driven member provided to be capable of interlocking with a rotatable drive member provided on the image carrier side, and positioned coaxially with a rotation shaft of the charging roller;
A separation member provided coaxially with the rotation shaft of the charging roller and capable of abutting the driven member with a large-diameter portion that separates the charging roller from the image carrier against the biasing in the circumferential direction. Prepared,
When the driven member rotates, the separating member is in a state where the charging roller is separated from the image bearing member against the urging by the large diameter portion coming into contact with the driven member. A charging device characterized in that, when the large-diameter portion is dragged and rotated by a member, a state in which the charging roller is brought into contact with the image carrier by the biasing is set.   The spacing member is provided with a portion with a high friction coefficient and a portion with a low friction coefficient at the large diameter portion, and after the large diameter portion is dragged and rotated by the driven member, the portion with the low friction coefficient contacts the driven member. The charging device according to claim 1, wherein the charging device is in contact with the charging device.   Of the large-diameter portion, the portion that contacts the driven member after being rotated by being dragged by the driven member has a smaller area than the portion that contacts the driven member by the biasing. The charging device according to claim 1 or 2.   The said driven member is provided with the flange which has the circumferential surface centering on the rotating shaft of this driven member, and makes the large diameter part of the said separation member contact | abut on the outer peripheral surface of this flange, It is characterized by the above-mentioned. The charging device according to any one of 1 to 3.   The large-diameter portion is in contact with the driven member until the drive member starts rotating for the first time after shipment from the factory, and sets the state in which the charging roller is separated from the image carrier. The charging device according to any one of claims 1 to 4.   6. A process cartridge using the charging device according to claim 1.   An image forming apparatus using the charging device according to claim 1.

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