JP2008281841A - Charger and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging device having a simple configuration and capable of preventing failure in supply of power to a charging roller, improving durability of a bearing of the charging roller, and reducing time and effort required for maintenance such as component replacement, and to provide an image forming apparatus using the charging device. <P>SOLUTION: A charging section 22 includes: a charging roller 221 that applies a charging potential to a photoreceptor drum 21; a bearing 222 holding the charging roller 221; a conductive firm-contact member 224 disposed in firm contact with the shaft end 221a of the charging roller 221; a hold member 225 for holding the conductive firm-contact member 224; and a power source that applies a voltage to the hold member 225. In the charging section 22, the shaft end 221 of the charging roller 221 tapers toward the leading end in the direction of the axis of the charging roller 221. The conductive firm-contact member 224 is formed such that a face disposed in contact with at least the shaft end 221a is curved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a charging device and an image forming apparatus using the same, and more particularly to a charging device that charges a member to be charged using a charging roller, and an electrophotographic image forming apparatus using the charging device.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses such as copying machines, facsimiles, and printers are provided with a charging device that charges the surface of a photosensitive drum by applying a voltage to a charging member such as a charging roller. .

  As a method of applying to the charging roller in this charging device, a method is known in which a bearing that supports the shaft portion of the charging roller is formed of a conductive member, and a voltage is directly applied to the charging roller by this conductive bearing. Yes. However, in a configuration in which a voltage is directly applied to the charging roller via a conductive bearing that supports the shaft portion of the charging roller, foreign matter such as toner floating in the machine is caused between the conductive bearing and the shaft portion of the charging roller. There is a problem that charging failure occurs between them.

  Therefore, as a countermeasure for the above problem, for example, a plurality of protrusions are formed in the circumferential direction on the inner surface of the conductive bearing, and the shaft portion can be rotated by the protrusions so that foreign matter is not easily caught between the bearing and the shaft portion. A configuration configured as described above has been proposed (see Patent Document 1).

  However, according to such a configuration, since the bearing uses a conductive member to which a conductive substance is added, the mechanical strength is low and the durability is inferior. A new problem arises that rotation unevenness is likely to occur. For this reason, replacement is required in a short period of time, so maintenance must be performed frequently.

Therefore, in order to solve the above problem, as a conventional technique, a contact member for applying a voltage to the charging roller is configured separately from the bearing, and the contact member is fixed to a plate spring-like electrode plate. It is known that the contact member is brought into contact with the charging roller by the elastic force, and the voltage from the power supply unit is applied to the shaft portion of the charging roller through the contact member. For example, there has been proposed one in which power is supplied directly to the axial end surface of the rotating shaft of a rotatable charging roller (see Patent Document 2).
JP 2003-84543 A JP-A-4-320281

  However, in the case of a configuration in which a contact member is brought into contact with the charging roller and a voltage is applied, generally, an electrode plate provided with the contact member is formed of metal, and the contact member is used as a charging roller by utilizing the rigidity of the electrode plate. Since they are in contact with each other, there is a problem in that a metal part that comes into contact wears out and a power feeding failure occurs.

  The present invention has been made in view of conventional problems, and with a simple configuration, prevents power supply failure to the charging roller, improves durability of the bearing of the charging roller, and replaces parts. It is an object of the present invention to provide a charging device and an image forming apparatus using the same that can reduce the labor required for maintenance.

A charging device according to the present invention for solving the above-described problems and an image forming apparatus using the charging device are as follows.
The charging device according to claim 1, for example, a charging roller that applies a charging potential to a member to be charged, a bearing that holds the charging roller, a conductive pressure contact member that is in pressure contact with a shaft end portion of the charging roller, In a charging device including a holding member that holds the conductive pressure contact member and a voltage applying unit that applies a voltage to the holding member, the shaft end portion of the charging roller faces the tip along the axial direction of the charging roller. The taper is tapered, and the conductive pressure contact member is formed with a curved surface at least in contact with the shaft end.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, the holding member is formed using a leaf spring.

According to a third aspect of the present invention, in addition to the configuration of the second aspect of the present invention, the charging device has a force for pressing the conductive pressure contact member to the shaft end portion of 1.96 × 10 ^{−2 to} 4.9. × 10 ⁻² MPa (200 gf to 500 gf / cm ² ).

  According to a fourth aspect of the present invention, in addition to the configuration of the invention according to any one of the first to third aspects, the charging member is formed of stainless steel or phosphor bronze as a material. It is characterized by.

  A charging device according to a fifth aspect is characterized in that, in addition to the configuration of the invention according to any one of the first to fourth aspects, the bearing is formed using a fluorine-containing polyacetal resin as a material. It is what.

  According to a sixth aspect of the present invention, in addition to the configuration of the fifth aspect of the invention, the peripheral speed of the member to be charged is 350 mm / sec or more.

  According to a seventh aspect of the present invention, there is provided an image forming apparatus having an electrostatic latent image carrier on which an electrostatic latent image is formed, and a charging device for applying a charging potential to the electrostatic latent image carrier. An electrophotographic system based on print image information, and a developing section having a developing roller for transporting a developer charged by mixing two components of a chargeable toner and a magnetic carrier to the electrostatic latent image carrier 7. The image forming apparatus according to claim 1, wherein the electrostatic latent image formed on the electrostatic latent image carrier by the developer is visualized by the developer. The charging device described in the item is used.

  According to the first aspect of the present invention, a charging roller that applies a charging potential to the member to be charged, a bearing that holds the charging roller, a conductive pressure contact member that is in pressure contact with a shaft end of the charging roller, In a charging device including a holding member that holds a conductive pressure contact member and a voltage applying unit that applies a voltage to the holding member, the shaft end of the charging roller is tapered toward the tip along the axial direction of the charging roller. By forming the conductive pressure contact member with a curved surface at least in contact with the shaft end portion, the shaft end portion of the charging roller and the conductive pressure contact member can be widened with a simple structure. The contact between the charging roller and the conductive pressure contact member can be ensured and the durability can be improved. In addition, since the bearing of the charging roller and the conductive pressure contact member are configured separately, a resin having high mechanical strength can be used for the bearing, so that the life can be extended as compared with the conventional case. .

  According to the second aspect of the invention, in addition to the effect obtained by the first aspect of the invention, the holding member is formed by using a leaf spring, so that the charging roller and the conductive pressure contact can be formed with a simple structure. It is possible to secure a contact point with the member and apply an appropriate pressure contact force.

According to the third aspect of the present invention, in addition to the effect obtained by the second aspect of the present invention, the force for pressing the conductive pressure contact member to the shaft end is 1.96 × 10 ⁻² to 4. By setting it to .9 × 10 ⁻² MPa (200 gf to 500 gf / cm ² ), the conductive state can be stably maintained without greatly changing the shape of the conductive pressure contact member.

  According to the invention described in claim 4, in addition to the effect obtained by the invention according to any one of claims 1 to 3, by using stainless steel or phosphor bronze as the material of the holding member, A holding member having high mechanical strength and easy to process can be realized.

  According to the invention described in claim 5, in addition to the effect obtained by the invention described in any one of claims 1 to 4, by using a fluorine-containing polyacetal resin as a material of the bearing, It is possible to realize a bearing that is excellent in wear and has little change with time.

  According to the sixth aspect of the invention, in addition to the effect obtained by the fifth aspect of the invention, the wear of the bearing is increased rapidly by setting the peripheral speed of the member to be charged to 350 mm / sec or more. In the peripheral speed, the effect of durability and longer life can be exhibited compared with the conventional case.

  According to the invention described in claim 7, an image forming unit having an electrostatic latent image carrier on which an electrostatic latent image is formed, and a charging device that applies a charging potential to the electrostatic latent image carrier. An electrophotographic system based on print image information, and a developing section having a developing roller for transporting a developer charged by mixing two components of a chargeable toner and a magnetic carrier to the electrostatic latent image carrier 7. The image forming apparatus according to claim 1, wherein the electrostatic latent image formed on the electrostatic latent image carrier by the developer is visualized by the developer. By using the charging device described in the section, the charging roller and the conductive pressure contact member can be reliably brought into contact with each other with a simple structure by widely contacting the shaft end portion of the charging roller and the conductive pressure contact member. Can improve durability, and By forming the charging roller bearing and the conductive pressure contact member separately, it is possible to use a resin with high mechanical strength for the bearing. Can be realized.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a side view showing a configuration of an image forming apparatus employing a charging device according to the present invention.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment has a developer image (hereinafter, referred to as toner) formed by a developer (hereinafter referred to as toner) that matches each hue in accordance with color-separated image information. Hereinafter, the photosensitive drum 21 (21a, 21b, 21c, 21d) on which the toner image is formed, a charger (charging device) 22 for charging the photosensitive drum 21, and the photosensitive drum 21 A plurality of process printing units (image forming units) 20 (20a, 20b, 20c, 20d) including a developing device 23 (23a, 23b, 23c, 23d) for supplying the toner to the surface are provided, and further image information Based on the above, an exposure unit (optical scanning device) 10 for generating an electrostatic latent image by irradiating each photosensitive drum 21 with a laser beam (beam) for each color, and an endless conveyance for feeding the supplied recording paper The image forming apparatus includes a transfer belt unit 30 including a copying belt 31 and a fixing unit 27 that thermally fixes a toner image transferred onto a recording sheet by a heating roller 27a and a pressure roller 27b. An image forming apparatus 1 in which an electrostatic latent image formed on a photosensitive drum 21 is visualized by a developer, and the visualized toner image is transferred to a recording sheet and output. As the charger 22, a charging device according to the present invention is configured and mounted.

First, the overall configuration of the image forming apparatus 1 will be described.
An image forming apparatus 1 according to the present embodiment is a so-called digital color printer, which color-separates image information, forms an image for each hue, and outputs a color image, as shown in FIG. The image forming unit 108 and the sheet feeding unit 109 are roughly configured, and a multicolor image or a single color image is recorded on a recording sheet based on a print job from an information processing apparatus (not shown) such as a personal computer connected to the outside. Is formed.

  The image forming unit 108 uses an electrophotographic method to form a multicolor image using each color of yellow (Y), magenta (M), cyan (C), and black (BK). The unit 10, the process printing unit 20, the fixing unit 27, a transfer belt unit 30 as a transfer means including a transfer belt 31, a transfer roller 36, and a transfer belt cleaning unit 37 are configured.

  The schematic configuration of the image forming unit 108 is that a fixing unit 27 is disposed on the upper end of one end of the casing 1 a of the image forming apparatus 1, and is transferred below the fixing unit 27 from one end to the other end of the casing 1 a. A belt unit 30 is disposed, a process printing unit 20 is disposed below the transfer belt unit 30, and an exposure unit 10 is disposed below the process printing unit 20.

  A transfer belt cleaning unit 37 is provided on the other end side of the transfer belt unit 30. Further, a paper discharge tray 43 is provided adjacent to the fixing unit 27 above the image forming unit 108. A paper feeding unit 109 is configured below the image forming unit 108.

  In the present embodiment, four process printing units 20a, 20b, 20c, and 20d corresponding to the respective colors of black (BK), cyan (C), magenta (M), and yellow (Y) are transferred as the process printing unit 20. The belts 31 are sequentially provided along the belt 31.

  These process printing units 20 (20a, 20b, 20c, 20d) are arranged in parallel in a substantially horizontal direction (left-right direction in the figure) in the housing 1a, and a photosensitive drum 21 serving as an image carrier for each color. (21a, 21b, 21c, 21d), a charger (charging means) 22 (22a, 22b, 22c, 22d) for charging the photosensitive drum 21, and a developing device (developing means) 23 (23a, 23b, 23c, 23d) ), Cleaner units 24 (24a, 24b, 24c, 24d) and the like.

  Here, the symbols a, b, c, and d attached to the components corresponding to the respective colors correspond to the respective colors of black (BK), cyan (C), magenta (M), and yellow (Y). However, in the following description, the constituent elements provided for the respective colors are collectively shown in the photosensitive drum 21, except for the case where the constituent elements corresponding to a specific color are specified. The charger 22, the developing device 23, and the cleaner unit 24 are described.

  The photosensitive drum 21 is disposed such that a part of the outer peripheral surface thereof is in contact with the surface of the transfer belt 31, and the charger 22, the developing device 23, and the cleaner unit as an electric field generating unit along the outer peripheral surface of the drum. 24 are arranged close to each other.

  The charger 22 is a roller-type charger, and is disposed along the outer peripheral surface of the photosensitive drum 21 on the substantially opposite side to the position where the transfer belt unit 30 is disposed across the photosensitive drum 21.

  The developing device 23 stores toner of each color of black (BK), cyan (C), magenta (M), and yellow (Y) for each developing device 23a, 23b, 23c, and 23d. It is arranged downstream of the charger 22 in the drum rotation direction (the direction of arrow A in the figure).

  The developing devices 23a, 23b, 23c, and 23d include five toner replenishers 500a for replenishing toner to the developing devices 23a, 23b, 23c, and 23d in order to be capable of high-speed and high-volume printing. , 500b, 500c, and 500d, toner replenishing devices 100a, 100b, 100c, and 100d are provided, and developing rollers 231a, 231b, 231c, and 231d are disposed to face the photosensitive drums 21a, 21b, 21c, and 21d, respectively. Thus, each color toner is supplied to the electrostatic latent images formed on the outer peripheral surfaces of the photosensitive drums 21a, 21b, 21c, and 21d so as to be visualized.

As toner for replenishment, black (BK) toner is supplied to the toner replenishment unit 500a, cyan (C) toner is supplied to the toner replenishment unit 500b, magenta (M) toner is supplied to the toner replenishment unit 500c, and toner supply unit 500d is supplied. Contains yellow (Y) toner.
Note that two toner replenishing portions 500a for black (BK) toner are provided in parallel so that large-scale printing is possible in consideration of monochrome printing that is normally used.

  Each toner replenishing section 500 is disposed almost immediately above the developing device 23 that develops using the corresponding toner, and the toner replenishing passage body 612 (612a) is provided to each corresponding developing device 23. , 612b, 612c, 612d).

  The supply passage body 612a for supplying black (BK) toner is configured to supply toner from the two toner supply devices 100a and 100a together to the developing device 23a. .

  The cleaner unit 24 is disposed on the upstream side of the charger 22 in the rotation direction of the photosensitive drum. In addition, the cleaner unit 24 includes a cleaning blade 241, and the cleaning blade 241 is disposed in contact with the outer peripheral surface of the photoconductive drum 21 to scrape and collect residual toner on the photoconductive drum 21. Has been. Reference numeral 242 in the figure denotes a conveying screw that conveys the collected toner.

  Although the cleaning blade 241 is used in this embodiment, the present invention is not particularly limited to these configurations, and one or more cleaning blades may be used, or a fur brush or a magnetic brush may be used alone. A cleaning blade, a fur brush, and a magnetic brush may be used in combination. Any device configured to scrape and collect residual toner on the photosensitive drum 21 can be used.

  The exposure unit 10 mainly includes a box-shaped housing 10a, a laser scanning unit (LSU) 11 having a laser irradiation unit 11a disposed therein, a polygon mirror 12, and laser light for each color. Mirrors 13a, 13b, 13c, 13d, 14a, 14b, 14c and the like.

  Laser light emitted from the laser irradiation unit of the laser scanning unit 11 is color-separated by the polygon mirror 12 and the fθ lens, and then reflected by the reflection mirrors 13a to 13c, and the respective photosensitive drums 21a and 21b for each color. , 21c, 21d.

  The laser scanning unit 11 may be configured to use a writing head in which light emitting elements such as EL (Electro Luminescence) and LED (Light Emitting Diode) are arranged in an array instead of the laser irradiation unit, or a light source The liquid crystal shutter may be used, and any means capable of forming an electrostatic latent image on the photosensitive drum 21 can be used.

  As shown in FIG. 1, the transfer belt unit 30 mainly includes a transfer belt 31, a transfer belt drive roller 32, a transfer belt driven roller 33, and intermediate transfer rollers 35a, 35b, 35c, and 35d.

  In the following description, the intermediate transfer rollers 35a, 35b, 35c, and 35d are collectively referred to as the intermediate transfer roller 35 when used.

  The transfer belt 31 is endlessly formed using a film having a thickness of about 75 μm to 120 μm. As the material of the transfer belt 31, polyimide, polycarbonate, a thermoplastic elastomer alloy, or the like is mainly used.

  The transfer belt 31 is stretched by a transfer belt driving roller 32, a transfer belt driven roller 33, and an intermediate transfer roller 35 so that the surface thereof is in contact with the outer peripheral surface of the photosensitive drum 21, and the transfer belt driving roller 32. It is configured to move in the sub-scanning direction (in the direction of arrow B in the figure) by the driving force of.

  The transfer belt driving roller 32 is disposed on one end side of the housing 1a, drives the transfer belt 31 to convey the transfer belt 31, and transfers the transfer belt 31 in a state where the transfer belt 31 and the recording paper are overlapped. The recording paper is conveyed while being pressed between and pressed.

  The transfer belt driven roller 33 is disposed on the other end side of the housing 1a, and the transfer belt 31 and the transfer belt driving roller 32 are laid substantially horizontally from the fixing unit 27 side to the other end side of the housing 1a. In order to reduce the dimension in the width direction of the image forming apparatus 1 in FIG. 1 or to save the space in the so-called width direction, the transfer belt 31 together with the transfer belt drive roller 32 is mounted from the fixing unit 27 side. The other side of the body 1a can be inclined, and one of them can be provided with an appropriate arrangement, size, etc., such as a photoreceptor, development, laser irradiation unit, fixing, etc. It doesn't matter.

  The intermediate transfer roller 35 is disposed in the inner space of the transfer belt 31 that is wound from the transfer belt driving roller 32 to the transfer belt driven roller 33. The transfer belt 31 is disposed at a position shifted to the downstream side in the moving direction, presses the inner surface of the transfer belt 31, and the outer surface of the transfer belt 31 winds a part of the outer peripheral surface of the photosensitive drum 21. You may provide so that a predetermined | prescribed nip amount may be obtained.

  The intermediate transfer roller 35 includes a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm, and the outer peripheral surface of the metal shaft is coated with a conductive elastic material such as EPDM or urethane foam. It is not necessary to limit to these elastic materials.

  The intermediate transfer roller 35 configured as described above has a high voltage transfer bias for transferring the toner image formed on the photosensitive drum 21 to the transfer belt 31, that is, a polarity opposite to the charging polarity (−) of the toner. A high voltage (+) is applied, and the high voltage is uniformly applied to the transfer belt 31 by an elastic material.

  A visualized toner image (electrostatic image) corresponding to each hue on each of the above-described photosensitive drums 21 is laminated on the transfer belt 31 and becomes image information input to the apparatus. The stacked image information is transferred onto a recording sheet by a transfer roller 36 disposed at a contact position of the transfer belt 31.

  The transfer roller 36 constituting the transfer means constitutes a transfer means for transferring the toner image transferred to the transfer belt 31 onto a recording sheet, and is opposed to the transfer belt drive roller 32 in a substantially horizontal and parallel manner. The multi-color toner image formed on the transfer belt 31 is transferred onto a recording sheet and is arranged so as to come into pressure contact with the transfer belt 31 wound around the transfer belt driving roller 32 at a predetermined nip. Voltage, that is, a high voltage having a polarity (+) opposite to the charging polarity (−) of the toner is applied.

  Further, in order to obtain a nip between the transfer belt 31 and the transfer roller 36 steadily, either the transfer belt drive roller 32 or the transfer roller 36 is made of a hard material such as metal, and the other roller Is made of a soft material such as elastic rubber or foamable resin.

  A registration roller 26 is provided below the transfer belt driving roller 32 and the transfer roller 36. The registration roller 26 is configured to align the leading edge of the recording paper supplied from the paper feeding unit 109 and the leading edge of the toner image on the transfer belt 31 and convey the toner to the transfer roller 36 side.

  Further, as described above, the toner adhering to the transfer belt 31 due to contact with the photosensitive drum 21 or the toner remaining on the transfer belt 31 without being transferred onto the recording paper by the transfer roller 36 is mixed with toner in the next step. Therefore, the transfer belt cleaning unit 37 is set to be removed and collected.

  The transfer belt cleaning unit 37 is provided in the vicinity of the transfer belt driven roller 33 and disposed so as to be in contact (or sliding contact) with the transfer belt 31, and the residual on the transfer belt 31 by the cleaning blade 37a. A box-shaped toner collecting portion 37b that temporarily stores the toner (waste toner) that has been scraped off the toner, and scrapes and collects the residual toner on the transfer belt 31.

  Further, the transfer belt cleaning unit 37 is disposed in the vicinity of the process printing unit 20d on the upstream side of the process printing unit 20a in the moving direction of the transfer belt 31. The portion of the transfer belt 31 where the cleaning blade 37 a contacts the outer surface is supported by the transfer belt driven roller 33 on the inner surface.

  As shown in FIG. 1, the fixing unit 27 includes a pair of fixing rollers 271 configured by a heating roller 27a and a pressure roller 27b, and a conveying roller 27c above the fixing roller 271. It is carried in from below 271 and carried out above carrying roller 27c.

  Further, a paper discharge roller 28 is provided above the fixing unit 27, and the recording paper conveyed from the conveyance roller 27 c is discharged onto the paper discharge tray 43 by the paper discharge roller 28. .

  The fixing of the toner image by the fixing unit 27 is controlled by controlling heating means (not shown) such as a heater lamp provided inside or close to the heating roller 27a based on a detection value of a temperature detector (not shown). The heating roller 27a is maintained at a predetermined temperature (fixing temperature), and the recording paper on which the toner image has been transferred is heated and pressed while being rotated and conveyed by being sandwiched between the heating roller 27a and the pressure roller 27b. The toner image is thermally fixed.

  Adjacent to the fixing unit 27, a double-sided document conveying path S3 for double-sided printing is formed from the rear to the bottom of the fixing unit 27 to the vicinity of the paper feed unit 109, and is arranged in the vertical direction on the double-sided document conveying path S3. The recording paper is reversed toward the transfer roller 36 in a state where the recording paper is reversed by the provided conveying rollers 29a and 29b.

  Specifically, the transport roller 29a is disposed behind the fixing unit 27, and the transport roller 29b is disposed below the transport roller 29a in the vertical direction and is disposed at substantially the same position as the registration roller 26 in the lateral direction. Yes.

  In this embodiment, the heating roller 27a and the pressure roller 27b, which are heating means such as a heater lamp, are used. However, an induction heating method may be used or they may be used in combination. Further, any means may be used as long as it is an appropriate method capable of uniformly heat-fixing the toner image on the recording paper without disturbing the toner image without using a roller.

  The paper feed unit 109 includes a manual feed tray 41 and a paper feed cassette 42 for storing recording paper used for image formation. The image forming unit 108 feeds recording paper from the manual feed tray 41 and the paper feed cassette 42 one by one. To be supplied to.

  As shown in FIG. 1, the manual feed tray 41 is expanded to one side end (right side in the drawing) of the casing 1 a of the image forming apparatus 1. A small number (necessary number) of recording sheets of the type desired by the user are placed and taken into the housing 1a of the image forming apparatus 1 one by one.

A pickup roller 41a is provided on the side of the exposure unit 10 in the casing 1a of the image forming apparatus 1 on the downstream side of the paper feeding direction of the recording paper by the manual feed tray 41 (the direction of arrow C in the figure). A conveyance roller 41b is provided substantially horizontally on the downstream side in the paper direction. The pickup roller 41a comes into contact with the surface of one end portion of the recording paper fed from the manual feed tray 41 and reliably conveys the paper one by one by the frictional resistance of the roller.
The pickup roller 41a and the transport rollers 41b, 41c, 41d configured in this way constitute a recording paper transport path S1.

  On the other hand, the paper feed cassette 42 is provided below the image forming unit 108 and the exposure unit 10 in the housing 1a, and records a large amount of recording paper having a size defined by the specifications of the apparatus or a size predetermined by the user. Can be accommodated.

  A pickup roller 42a is provided on one end portion (left end portion in the figure) of the paper feed cassette 42, and a conveyance roller 42b is provided downstream of the pickup roller 42a in the recording paper conveyance direction.

  The pickup roller 42a contacts the surface of one end of the recording paper at the top of the recording paper set in the paper feeding cassette 42 in response to an output request, and reliably feeds out one by one by the frictional resistance of the roller. It is supposed to be.

  The conveyance roller 42b is configured to convey the recording sheet fed from the pickup roller 42a upward to the image forming unit 108 along the recording sheet conveyance path S2 formed on one end side in the housing 1a. .

Next, image output by the image forming apparatus 1 according to the present embodiment will be described.
The image forming apparatus 1 is configured to transfer the toner image on the photosensitive drum 21 onto the recording paper supplied from the paper supply unit 109 via the transfer belt 31 by a so-called intermediate transfer method (offset method). ing.

  First, the charger 22 uniformly charges the outer peripheral surface of the photosensitive drum 21 to a predetermined potential. By irradiating the charged photosensitive drum 21 with laser light from the exposure unit 10, an electrostatic latent image for each color is generated on the photosensitive drum 21 for each color.

  Next, toner is supplied from the developing device 23 (23a, 23b, 23c, 23d) to each outer peripheral surface of the photosensitive drum 21 (21a, 21b, 21c, 21d), and formed on the outer peripheral surface of the photosensitive drum 21. The electrostatic latent image thus made is visualized as a toner image with toner.

Then, the toner image generated on the photosensitive drum 21 is transferred to the transfer belt 31.
The transfer of the toner image from the photosensitive drum 21 to the transfer belt 31 is performed by applying a high voltage to the intermediate transfer roller 35 disposed in contact with the back side of the transfer belt 31.

  By applying a high voltage with a polarity (+) opposite to the toner charging polarity (-) to the intermediate transfer roller 35, the transfer belt 31 is uniformly applied with a high voltage by the intermediate transfer roller 35 and has a reverse polarity. (+). As a result, the toner image of the charged polarity (−) on the photosensitive drum 21 is transferred onto the transfer belt 31 when the photosensitive drum 21 is in rotational contact with the transfer belt 31.

  The toner images of the respective colors formed on the respective photoconductive drums 21 are yellow (Y), magenta (M), cyan (C), black as the transfer belt 31 moves and makes rotational contact with the respective photoconductive drums 21. The images are transferred in the order of (BK), and a color toner image is formed on the transfer belt 31.

  In this way, the electrostatic latent image visualized with toner on the photosensitive drum 21 for each color is laminated on the transfer belt 31, and the print image is reproduced on the transfer belt 31 as a multicolor toner image. The The multicolor toner image transferred onto the transfer belt 31 is transferred from the transfer belt 31 onto the recording paper by the transfer roller 36 at a position where the transfer belt 31 moves and the recording paper and the transfer belt 31 overlap. The

  When recording paper placed on the manual feed tray 41 is used, the recording paper is fed from the manual feed tray 41 by a pickup roller 41a at a timing controlled by an instruction on an operation panel (not shown) as shown in FIG. Are taken into the apparatus one by one. The recording sheet taken into the apparatus is conveyed to the image forming unit 108 along the recording sheet conveying path S1 by the conveying roller 41b.

  On the other hand, when recording paper stored in the paper feed cassette 42 is used, the recording paper is separated and fed one by one from the paper feed cassette 42 by the pickup roller 42a in response to an output request, and the recording paper is conveyed by the conveyance roller 42b. It is conveyed along the path S2 to the upper image forming unit.

  The recording paper transported from the manual feed tray 41 and the paper feed cassette 42 is transported to the transfer roller 36 side at the timing when the leading edge of the recording paper and the leading edge of the toner image on the transfer belt 31 are aligned by the registration roller 26. The toner image on the transfer belt 31 is transferred onto the recording paper.

  The recording sheet on which the toner image has been transferred is conveyed substantially vertically and reaches the fixing unit 27, where the toner image is thermally fixed on the recording sheet by the heating roller 27a and the pressure roller 27b. The recording paper that has passed through the fixing unit 27 is discharged face down onto the paper discharge tray 43 by the paper discharge roller 28 in the case of a single-sided print request.

  On the other hand, in the case of a double-sided printing request, after the recording paper is chucked by the paper discharge roller 28, the paper discharge roller 28 is rotated in the reverse direction to guide the recording paper to the double-sided document transport path S3. Transport to roller 26.

  At this time, the front side of the recording sheet is reversed while the surface to be transferred is reversed. That is, the end that becomes the start side during the first transfer is the end side during the back transfer, and the end that becomes the end side during the first transfer is the start side during the back transfer. After the toner image is transferred and thermally fixed on the back surface of the recording paper, it is discharged onto the paper discharge tray 43 by the paper discharge roller 28. In this way, the transfer operation to the recording paper is performed.

  Next, the characteristic charger 22 according to the present embodiment will be described in detail with reference to the drawings. FIG. 2 is a schematic explanatory view showing an example of the structure of a charger constituting the process printing unit of the image forming apparatus according to the present embodiment, FIG. 3 is an explanatory view showing the structure of the charger, and FIG. 4 shows the charger. FIG. 5 is a partial detailed explanatory view showing the structure of the charging roller and the conductive pressure contact member, FIG. 5 is a partial detailed explanatory view of FIG. 4 viewed from obliquely above, and FIG. 6A shows the structure of the conductive pressure contact member. FIG. 4B is a perspective view illustrating a configuration of a shaft end portion of the charging roller.

  A charging device (charging device) 22 according to the present embodiment constitutes a process printing unit 20 as shown in FIGS. 2, 4, and 5, and a charging roller 221 that applies a charging potential to the photosensitive drum 21; A bearing 222 that holds the charging roller 221, a bracket 223 that holds the bearing 222, a conductive pressure contact member 224 that presses against the shaft end 221 a of the charging roller 221, and a holding member 225 that holds the conductive pressure contact member 224. I have. Reference numeral 211 denotes a photosensitive drum drive motor.

As shown in FIG. 3, the charging roller 221 is disposed along the photosensitive drum 21 with its axial direction being substantially parallel to the axial direction of the photosensitive drum 21, and as shown in FIGS. The shaft end 221 a of the part is held by the bearing 222.
The tip 221b of the shaft end 221a is formed in a taper shape that tapers toward the tip along the axial direction of the charging roller 221 as shown in FIG. 6B. Specifically, the tip 221b is formed in a conical shape.

  The bearing 222 is formed using a fluorine-containing polyacetal resin as a material, and as shown in FIG. 2, a concave portion 222a whose side facing the photosensitive drum 21 is opened is formed, and a shaft end 221a is formed in the concave portion 222a. It comes to be installed. Specifically, the concave portion 222a has a substantially U-shaped concave shape, and its bottom portion is formed to have substantially the same size as the outer diameter of the shaft end portion 221a so that the shaft end portion 221a is positioned and held. It has become.

  As shown in FIG. 2, the bracket 223 is formed with a recess 223a whose side facing the photoconductor drum 21 is open, and a bearing 222 is mounted in the recess 223a. Specifically, the concave portion 223a has a substantially U-shaped concave shape, and is configured to be slidable while guiding both side surfaces of the bearing 222 disposed in the concave portion 223a. A compression coil spring 223b is disposed between the bottom side of the recess 223a and the bottom side of the bearing 222. The charging roller 221 attached to the bearing 222 is urged toward the photosensitive drum 21 by the compression coil spring 223b.

  Further, both end portions 223d and 223d on the opening 223c side of the recess 223a are formed to protrude toward the inside of the opening 223c. In other words, the gap between the two end portions 223d and 223d is formed to be narrower than the width of the bearing 222, and the bearing 222 attached to the concave portion 223a abuts against the both end portions 223d and 223d and does not come off from the opening 223c. . That is, both end portions 223d and 223d of the recess 223a also have a stopper function of the bearing 222.

  As shown in FIGS. 4 and 5, the conductive pressure contact member 224 is disposed to face the shaft end 221 a of the charging roller 221 in the axial direction, and is pressed against the shaft end 221 a by the holding member 225. The conductive pressure contact member 224 has at least a portion (hereinafter referred to as a “contact portion”) 224 a that faces and contacts the shaft end 221 a of the charging roller 221 with a curved surface. Specifically, as shown in FIG. 6 (a), the contact portion 224a is formed in a columnar shape with a part having an arcuate cross section, that is, in a so-called kamaboko shape in which a part is a curved surface.

  The contact portion 224a is disposed so that the columnar longitudinal direction of the contact portion 224a is substantially parallel to the sliding direction of the bearing 222 with respect to the recess 223a of the bracket 223, and the arc shape thereof. The curved surface protruding in the direction is in contact with the conical curved surface of the tip portion 221b of the charging roller 221.

  With this configuration, even when the charging roller 221 slides and moves along the recess 223a of the bracket 223, the conical curved surface of the tip 221b is displaced in the columnar longitudinal direction along the curved surface of the contact portion 224a. Therefore, the change of the contact state between curved surfaces can be reduced.

  The holding member 225 is formed by using a leaf spring using stainless steel or phosphor bronze as a material, and has a shape in which a plurality of portions are bent from one end 225a to the other end 225b. One end 225 a of the holding member 225 is attached to a bracket 226 attached to the main body side of the process printing unit 20, and a conductive pressure contact member 224 is attached to the other end 225 b. A voltage is applied from a power supply unit (voltage applying means) (not shown).

Further, the force by which the conductive pressure contact member 224 is pressed against the shaft end 221a by the holding member 225 is set to 1.96 × 10 ^{−2 to} 4.9 × 10 ⁻² MPa (200 gf to 500 gf / cm ² ). By setting in this way, it is possible to stably maintain the contact state (conductive state) between the conductive pressure contact member 224 and the shaft end 221a without greatly changing (deforming) the shape of the conductive pressure contact member 224. it can.

If the contact pressure by the holding member 225 is less than 1.96 × 10 ⁻² MPa (200 gf / cm ² ), the electrification failure may occur due to failure to follow the shake of the roller holder when the charging roller 221 rotates. There is. Moreover, when the contact pressure by the holding member 225 is set to a pressure exceeding 4.9 × 10 ⁻² MPa (500 gf / cm ² ), the wear of the conductive pressure contact member 224 may be accelerated.

  In the image forming apparatus 1 according to the present embodiment, the peripheral speed of the photosensitive drum 21 is set to 350 mm / sec or more to cope with high-speed image output.

Next, the operation of the charger 22 according to the present embodiment will be described in detail.
FIG. 7 is a schematic view showing a connection state between the charging roller and the conductive pressure contact member in the charger according to the present embodiment, and is a schematic view seen from the direction of arrow A in FIG.

In the charger 22, as shown in FIG. 7, the charging roller 221 is positioned and held rotatably by a bearing 222. The conductive pressure contact member 224 is pressed in the axial direction of the charging roller 221 by the holding member 225, and the contact portion 224a is in contact with the shaft end portion 221a of the charging roller 221.
That is, the conical curved surface of the tip end portion 221b of the shaft end portion 221a of the charging roller 221 and the semicircular curved surface of the contact portion 224a of the conductive pressure contact member 224 are in contact with each other.

  Specifically, the charging roller 221 and the conductive pressure contact member 224 are in contact with each other so that the top portion P1 of the front end portion 221b of the charging roller 221 and the top portion P2 of the contact portion 224a of the conductive pressure contact member 224 do not contact each other. In this embodiment, the tip portion 221b and the contact portion 224a come into contact with each other at a position where the top portion P1 of the tip portion 221b of the charging roller 221 is shifted upward from the top portion P2 of the contact portion 224a of the conductive pressure contact member 224 in FIG. ing. That is, the contact between the conductive pressure contact member 224 and a part of the conical curved surface of the front end portion 221b without contact between the top portion P1 of the front end portion 221b of the charging roller 221 and the top portion P2 of the contact portion 224a of the conductive pressure contact member 224. Part of the kamaboko-shaped curved surface of the portion 224a comes into contact.

  At this time, as shown in FIG. 7, the conductive pressure contact member 224 is pressed in the B direction against the tip portion 221 b of the charging roller 221 by the elastic force (spring force) of the holding member 225, and the contact portion P <b> 0 is Since it is shifted upward (a position lower than the top portion P2) in the drawing, it is pressed in the C direction against the conical curved surface of the tip portion 221b.

  With such a configuration, the contact portion between the charging roller 221 and the conductive pressure contact member 224 is not in contact with the top portions but in contact with the surfaces, so that it can be prevented from being concentrated and stable. The contact state can be maintained.

  Further, as shown in FIG. 2, the charging roller 221 is pressed against the photosensitive drum 21 by the spring force of the compression coil spring 223b. Further, the charging roller 221 can follow along the outer peripheral surface of the photosensitive drum 21 by slidable engagement between the bearing 222 and the bracket 223.

  At this time, in the contact portion 224a of the conductive pressure contact member 224, the tip end portion 221b of the shaft end portion 221a of the charging roller 221 is displaced along the columnar longitudinal direction of the cone-shaped curved surface of the contact portion 224a. It is like that. Thereby, the stable contact state can be maintained, without the contact state of the front-end | tip part 221b and the contact part 224a changing a lot.

Further, in the present embodiment, by using a fluorine-containing polyacetal resin as the material of the bearing 222 of the charger 22, a bearing having excellent wear resistance and little change with time is realized.
Below, the result verified about the lifetime by the material of the bearing 222 is demonstrated.
FIG. 8 is a table comparing wear states according to the material of the bearing used in the charger according to the present embodiment.

Here, in the image forming apparatus 1, a bearing using a carbon-containing conductive member generally used in the related art and a bearing using a fluorine-containing polyacetal resin according to the present invention are used, and φ8.02 is fitted to each bearing. An image was output using a charging roller having a shaft end portion with an outer diameter of φ8 corresponding to the fitting hole formed in the fitting hole, and the wear situation according to the number of output of each bearing was compared.
In this embodiment, Mulite (registered trademark) manufactured by Bando Chemical Co., Ltd. was used as the fluorine-containing polyacetal resin.

  As a result, as shown in FIG. 8, in the bearing using the carbon-containing conductive member, the size of the fitting hole after the 50K image output is changed from φ8.02 to φ8.12, and the image of 50K images is obtained. On the other hand, about 0.1 mm of wear occurs at the output, while with bearings using fluorine-containing polyacetal resin, the size of the fitting hole after image output of 300K sheets is changed from φ8.02 to φ8.03, 300K sheets It can be seen that the image output of only 0.02 mm causes only slight wear.

  Therefore, by using a fluorine-containing polyacetal resin as the material of the bearing, it is possible to realize a bearing that is remarkably excellent in wear resistance and less changed with time as compared with the conventional one.

In the present embodiment, by using the charger 22 having the above-described configuration, an image forming apparatus that can increase the peripheral speed of the photosensitive drum to 350 mm / sec or more is realized.
Hereinafter, the result of verifying the relationship between the process speed of the photosensitive drum and the wear of the bearing will be described.
FIG. 9 is a graph showing the relationship between the process speed and the amount of wear of a bearing in an image forming apparatus using a bearing using a carbon-containing conductive member and a bearing using a fluorine-containing polyacetal resin.

  Here, in the image forming apparatus 1, the amount of bearing wear when the process speed was increased from 50 mm / s to 50 mm / s was compared by printing 50,000 sheets of A4 size paper.

  As a result, as shown in FIG. 9, in the bearing using the carbon-containing conductive member, the wear amount of the bearing is 30 μm or less in the image forming apparatus 1 when the process speed is from 50 mm / s to 300 mm / s. It can be seen that the bearing starts to wear rapidly when the process speed exceeds 300 mm / s and the process speed exceeds 350 mm / s to 450 mm / s. However, in a bearing using a fluorine-containing polyacetal resin, the bearing will not be abruptly worn at 450 mm / s.

  Therefore, according to the structure of the bearing charger according to the present invention at a process speed of 350 mm / s or more, in which the conventional bearing is severely worn, the durability and the longer life can be achieved as compared with the conventional bearing. it can.

  With the configuration as described above, according to the present embodiment, the shaft end 221a of the charging roller 221 constituting the charger 22 in the image forming apparatus 1 is tapered toward the tip along the axial direction of the charging roller 221. The conductive pressure contact member 224 is formed in a tapered shape, and at least the contact surface 224a that comes into contact with the shaft end portion 221a is formed into a curved surface, so that the shaft end portion 221a of the charging roller 221 and the conductive pressure contact member have a simple structure. The contact between the charging roller 221 and the conductive pressure contact member 224 can be ensured by bringing the 224 into wide contact, and the durability can be improved.

  Further, according to the present embodiment, since the bearing 222 of the charging roller 221 and the conductive pressure contact member 224 are configured separately, a resin having high mechanical strength can be used for the bearing 222. As a result, the service life can be extended.

  In the present embodiment, the example in which the charger (charging device) 22 according to the present invention is applied to the image forming apparatus 1 as shown in FIG. 1 has been described. However, any image forming apparatus equipped with a charging device may be used. For example, the present invention may be applied to a copying machine 101 as shown in FIG.

As shown in FIG. 10, the copying machine 101 includes a charger 122 (122a, 122b, 122c, 122d) and a process printing unit 20 (20a, 20b, 122d) having substantially the same configuration as the image forming apparatus 1 according to the above-described embodiment. 20c, 20d) and below the image forming unit 108, a first paper feed cassette 142a, a second paper feed cassette 142b, a third paper feed cassette 142c, and a fourth paper feed cassette corresponding to a plurality of types of paper. 142d is arranged to automatically perform various kinds of mass printing. Reference numeral 120 in the figure denotes a waste toner box that collects waste toner.
Incidentally, in the copying machine 101, those having the same configuration as that of the image forming apparatus 1 according to the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In the copying machine 101 configured as described above, the charger 122 (122a, 122b, 122c, 122d) is configured in the same manner as the charger 22 described above, so that the same effects as those of the above-described embodiment can be obtained. .

  Furthermore, the present invention is not limited to the image forming apparatus and the copying machine having the above-described configuration as long as the image forming apparatus includes a charging device, and can be developed to other image forming apparatuses.

  As described above, the present invention is not limited to the above-described embodiments and examples, and various modifications can be made within the scope of the claims. That is, embodiments obtained by combining technical means appropriately changed within the scope not departing from the gist of the present invention are also included in the technical scope of the present invention.

1 is a side view showing a configuration of an image forming apparatus employing a charging device according to the present invention. FIG. 2 is a schematic explanatory diagram illustrating an example of a configuration of a charger that configures a process printing unit of the image forming apparatus. It is explanatory drawing which shows the structure of the said charger. It is a partial detailed explanatory view showing the configuration of a charging roller and a conductive pressure contact member constituting the charger. It is the partial detailed explanatory view which looked at FIG. 4 from diagonally upward. (A) is a perspective view showing a configuration of the conductive pressure contact member, (b) is a perspective view showing a configuration of a shaft end portion of the charging roller. FIG. 3 is a schematic diagram illustrating a connection state between a charging roller and a conductive pressure contact member in the charger according to the present embodiment, as viewed from an arrow A in FIG. 2. It is the table | surface which compared the abrasion state according to the material of the bearing used for the charger which concerns on this embodiment. 6 is a graph showing a relationship between a process speed and a bearing wear amount in the image forming apparatus according to the embodiment. It is explanatory drawing which shows the structure of the whole copying machine carrying the charging device which concerns on other embodiment of this invention.

Explanation of symbols

1 Image forming apparatus 20 Process printing unit (image forming unit)
21 Photosensitive drum (electrostatic latent image carrier)
22 Charger (Charging device)
23 Developing device (developing part)
221 Charging roller 221a Shaft end 221b Tip end 222 Bearing 222a Recess 223 Bracket 223a Recess 223b Compression coil spring 223c Opening 223d Both ends 224 Conductive pressure contact member 224a Contact portion 225 Holding member 225a One end 225b Other end 226 Bracket P0 Contact P1, P2 Top

Claims (7)

A charging roller that applies a charging potential to a member to be charged, a bearing that holds the charging roller, a conductive pressure member that presses against a shaft end of the charging roller, and a holding member that holds the conductive pressure member. In a charging device comprising a voltage applying means for applying a voltage to the holding member,
The shaft end of the charging roller is formed in a tapered shape that tapers toward the tip along the axial direction of the charging roller,
The charging device according to claim 1, wherein the conductive pressure contact member has a curved surface at least in contact with the shaft end portion.   The charging device according to claim 1, wherein the holding member is formed using a leaf spring. The force for press ^- contacting the conductive pressure-contact member to the shaft end portion is 1.96 × 10 ^{−2 to} 4.9 × 10 ⁻² MPa (200 gf to 500 gf / cm ² ). The charging device according to 1.   4. The charging device according to claim 1, wherein the holding member is formed using stainless steel or phosphor bronze as a material. 5.   The charging device according to any one of claims 1 to 4, wherein the bearing is formed using a fluorine-containing polyacetal resin as a material.   The charging device according to claim 5, wherein a peripheral speed of the member to be charged is 350 mm / sec or more. An image forming unit having an electrostatic latent image carrier on which an electrostatic latent image is formed, a charging device for applying a charging potential to the electrostatic latent image carrier, a chargeable toner, and a magnetic carrier. And a developing unit having a developing roller for conveying the mixed and charged developer to the electrostatic latent image carrier, and formed on the electrostatic latent image carrier by electrophotography based on print image information In the image forming apparatus in which the electrostatic latent image is visualized by the developer,
An image forming apparatus using the charging device according to claim 1 as the charging device.

Images