JP4558455B2 - Charging device - Google Patents

Description

  The present invention relates to a charging device including a charging roller for charging a photosensitive member.

  In general, in an image forming apparatus such as a copying machine, a printer apparatus, and a facsimile apparatus using an electrophotographic method, the surface of a photoconductor as an image carrier is uniformly charged by a charging device, and then is read by an image reading unit. Light based on the read image is irradiated on the surface of the photoreceptor by the exposure device to form an electrostatic latent image of the image, and then a toner is attached to the electrostatic latent image by the developing device to form a toner image. It is formed.

  As one of the methods used in the charging device, a corotron charging device is generally used. This corotron charging device extends a discharge wire facing a photoconductor in a shield case, and charges the surface of the photoconductor by applying a high voltage to the discharge wire. is there.

However, although the corotron method is effective as a means for uniformly charging the surface of the photoreceptor, it is necessary to apply a high voltage to charge the photoreceptor to a predetermined potential, and the charging operation is repeated. Then, the discharging wire provided in the charging device becomes dirty due to toner scattering, paper dust, and the like. Further, for example, there is a problem that silica (SiO ₂ ) is generated due to a reaction between silicon contained in toner or grease and ozone generated in the air by discharge, and this adheres to the discharge wire. If such stains are left unattended, uneven discharge due to changes in image density, etc. occur, and the surface of the photoconductor becomes non-uniform, resulting in poor copy image quality and a short charging device life. The problem of becoming will arise.

  Therefore, in order to reduce the applied voltage necessary for charging the photosensitive member and reduce the generation of ozone, the charging roller is brought into contact with the photosensitive member instead of the corotron method, and a bias voltage is applied to the charging roller. A charging device to be applied has been proposed.

  In the charging device using such a charging roller system, the configuration of the charging roller used can be roughly classified into two types. That is, a “solid type” in which a conductive elastic body (for example, rubber) is coated around a conductive shaft, and a conductive elastic body (for example, a foamed body such as a sponge) is coated around the shaft. In addition, a “tube type” in which a conductive tube is placed around a conductive member is known.

  Both types of charging rollers are arranged to face the photosensitive member, and the surface of the charging roller is exposed by urging both ends in the longitudinal direction of the charging roller using, for example, a pressing member such as a spring. It is configured to press against the surface of the body and bring the surface of the charging roller into contact with the surface of the photoreceptor. Then, the surface of the photoconductor is charged to a predetermined potential by rotating the charging roller by following the rotation of the photoconductor and applying a predetermined charging voltage to the shaft.

  Here, in the above-mentioned “tube type” charging roller, since the conductive elastic body and the conductive tube can be selected separately, they are preferably used when designing a charging roller having excellent charging properties. In addition, by using a foam such as sponge as the conductive elastic body, it is possible to reduce the hardness of the charging roller, so that stable contact with the surface of the photoreceptor can be ensured and a bias voltage is applied. There is an advantage that charging noise can be prevented.

  However, the “tube type” charging roller generally has a high material cost and a large number of processing steps. Therefore, there is a problem that the manufacturing cost is higher than that of the above-described corotron charging device. Further, when the conductive elastic body and the conductive tube are in close contact in the recycling process of the used charging roller, when the conductive tube is separated from the conductive elastic body (that is, when the conductive tube is replaced). The conductive elastic body may be damaged. Therefore, there are problems that it is difficult to recycle the used charging roller and that it takes time to separate and collect in the recycling process.

Therefore, a charging device for avoiding these disadvantages has been proposed. More specifically, there has been proposed a charging device provided with an inexpensive charging roller in which the amount of material used is reduced by providing a conductive elastic body or a conductive shaft only in the vicinity of both ends of the charging roller. Yes. Further, in the charging device, the conductive elastic body can be inserted into and removed from the conductive tube having an inner diameter larger than the outer diameter of the conductive elastic body without closely contacting the conductive elastic body and the conductive tube. Accordingly, the processing cost is reduced, and recycling of the used charging roller and separation and collection in the recycling process are facilitated (see, for example, Patent Document 1).
JP 2000-235294 A

  Here, in the conventional charging device, as described above, since the conductive tube has an inner diameter larger than the outer diameter of the conductive elastic body, the conductive tube and the conductive tube are driven by the rotation of the photosensitive member. When the elastic body is rotated, the conductive tube is thrust-moved in the axial direction. As a result, the conductive elastic body directly comes into contact with the surface of the photoconductor, the surface of the photoconductor may be damaged, and pinholes or the like may be generated in the photoconductor. Therefore, the conventional charging device is configured to avoid the occurrence of the inconvenience by providing a stopper made of an insulating resin piece outside the both ends of the conductive tube.

  However, when such a stopper is provided, there is a problem that the configuration of the charging roller is complicated and the cost is increased. In addition, since the stopper is in direct contact with the photoconductor, the contact between the charging roller and the photoconductor is not uniform, or when the stopper is in contact with the cut surface of the conductive tube, The cut surface of the conductive tube may be damaged by friction, and the contact area between the photoreceptor and the conductive tube may be reduced. Therefore, there is a possibility that uneven charging in the longitudinal direction of the photosensitive member may occur.

  Accordingly, the present invention has been made in view of the above-described problems, and prevents damage to the surface of the photoreceptor due to the conductive member with an inexpensive and simple configuration without providing a separate member such as a stopper. An object of the present invention is to provide a charging device that avoids the occurrence of uneven charging of the photoconductor.

In order to achieve the above object, according to the first aspect of the present invention, the shaft rotatably supported by the bearing portion, the conductive member coated around the shaft, and the conductive member are covered. In a charging device including a charging roller that is disposed opposite to the photoconductor and is driven to rotate as the photoconductor rotates, the inner diameter of the main body of the conductive tube is made conductive. The outer diameter of the conductive tube is set to be larger than the outer diameter of the conductive tube, and the inner diameter of the conductive tube is set to be smaller than the outer diameter of the conductive member. The portion can be in contact with the bearing portion , and the inner diameter of the other end of the conductive tube is set to be larger than the outer diameter of the conductive member .

  According to the first aspect of the present invention, it is possible to prevent the conductive tube from moving in the longitudinal direction of the charging roller even when the charging roller is driven to rotate as the photosensitive member rotates. become. Accordingly, it is possible to prevent damage to the surface of the photosensitive member due to the conductive member with a low cost and simple configuration without providing a separate member such as a stopper. In addition, it is possible to avoid the occurrence of uneven charging in the longitudinal direction of the photosensitive member due to the contact between the stopper and the photosensitive member. Furthermore, it is possible to avoid the occurrence of uneven charging in the longitudinal direction of the photoreceptor due to the contact between the stopper and the conductive tube.

Further , the conductive tube can be easily detached from the conductive member in a state where the charging roller is removed from the bearing portion. As a result, the used charging roller can be easily recycled and separated and collected in the recycling process.

According to a second aspect of the present invention, in the charging device according to the first aspect, one end of the conductive tube is formed in a tapered shape in which the outer diameter gradually decreases from the inner side to the outer side in the longitudinal direction of the charging roller. It is characterized by.

According to the second aspect of the present invention, the surface of the photosensitive member can be prevented from being damaged by the conductive member only by performing a simple processing on one end of the conductive tube, and the photosensitive member. The occurrence of uneven charging in the longitudinal direction can be avoided.

  According to the present invention, damage to the surface of the photoreceptor due to the conductive member can be prevented with an inexpensive and simple configuration. Further, the occurrence of uneven charging in the longitudinal direction of the photoconductor can be avoided.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 1 is a digital copying machine, and is arranged at a lower side of the image forming apparatus main body 1a and at a side and an upper side of the paper feeding unit 2. A sheet conveyance unit 3 is provided, an image forming unit 4 disposed on the right side of the sheet conveyance unit 3, and an image reading unit 5 disposed above the image forming apparatus main body 1a.

  The paper feed unit 2 includes a paper feed cassette 6 in which paper is accommodated, and the paper is fed from the paper feed cassette 6 to the paper transport unit 3 side by the rotation operation of the paper feed roller 7 so that one sheet of paper is fed. Each sheet is surely fed to the sheet conveying unit 3 one by one. The paper feed cassette 6 is configured to be detachable from the image forming apparatus main body 1a.

  The paper feed unit 2 is provided with a manual paper feed device 8, and the manual paper feed device 8 includes a manual paper feed tray 9 and a paper feed roller 10. The paper placed on the manual paper feed tray 9 is sent out from the manual paper feed tray 9 to the paper supply transport path 11 by the rotation operation of the paper feed roller 10, and the paper is fed one by one to the paper transport unit 3. It is configured to be.

  The paper fed to the paper supply transport path 11 is transported toward the image forming unit 4 via the paper transport unit 3. The image forming unit 4 forms a predetermined toner image on a sheet by an electrophotographic process, and is a photosensitive member that is an image carrier that is rotatably supported in a predetermined direction (in the direction of arrow R in the figure). A charging roller 13, a developing device 14, a transfer roller 15 as a transfer device (or transfer member), a cleaning device 16, and a charge eliminating device 17 are provided around the photoconductor 12 and along the rotation direction of the photoconductor 12. Yes.

  Then, by applying a predetermined potential to the charging roller 13, the surface of the photoconductor 12 is uniformly charged, and then a laser scanning unit (LSU) based on the image data of the original read by the image reading unit 5. An electrostatic latent image is formed on the photoreceptor 12 by the laser beam from 18. Next, toner is attached to the electrostatic latent image by the developing device 14 to form a toner image on the surface of the photoconductor 12, and the toner image on the surface of the photoconductor 12 is transferred to the photoconductor 12 by the transfer roller 15. The image is transferred to a sheet supplied between the rollers 15.

  A sheet on which the toner image is transferred (hereinafter referred to as “transfer sheet”) is conveyed from the image forming unit 4 toward the fixing roller pair 19. The fixing roller pair 19 is arranged on the downstream side of the image forming unit 4 in the sheet conveying direction, and the transfer paper is sandwiched between a heating roller constituting the fixing roller pair 19 and a pressure roller pressed against the heating roller. At the same time, the toner image is fixed on the transfer paper.

  Next, the transfer paper on which the image is formed by the fixing roller pair 19 from the image forming unit 4 is discharged to the paper discharge unit 21 provided in the cylinder of the image forming apparatus main body 1a by the discharge roller pair 20 which is a discharge unit. The paper is loaded on the paper discharge unit 21. On the other hand, after the transfer, the toner remaining on the surface of the photoconductor 12 is removed by the cleaning device 16, and the residual charge on the surface of the photoconductor 12 is removed by the static eliminator 17. The photosensitive member 12 is charged again by the charging roller 13, and image formation is performed in the same manner.

  Next, the charging device of this embodiment will be described with reference to the drawings. FIG. 2 is a perspective view for explaining a schematic configuration around the charging device according to the embodiment of the present invention, and FIG. 3 is a diagram for explaining the configuration of the charging roller in the charging device according to the embodiment of the present invention. It is sectional drawing.

  As shown in FIG. 2, the charging device 22 of the present embodiment is disposed to face the surface of the photosensitive member 12 that is a surface to be charged, and includes a charging roller 13 for charging the surface of the photosensitive member 12, and a charging device. And a power supply 50 for applying a predetermined voltage to the roller 13.

  2 and 3, the charging roller 13 includes a conductive shaft 23 and an elastic body (hereinafter referred to as “conductive elastic body”) that is a conductive member coated around the shaft 23. 24) and a conductive tube 25 placed around the conductive elastic body 24.

  Here, the shaft 23 is made of, for example, a metal having conductivity such as iron, copper, stainless steel, and aluminum, and the shaft 23 is arranged in parallel with the shaft core 12 a of the photoreceptor 12. The conductive elastic body 24 is formed of a foamed body made of, for example, sponge or EPDM (ethylene / propylene rubber). Further, the conductive tube 25 is made of nylon, for example, and the thickness thereof is set to 50 to 300 μm. In the longitudinal direction X of the charging roller 13, the conductive tube 25 is set longer than the conductive elastic body 24, and is configured so that the conductive elastic body 24 is not exposed.

  Further, as shown in FIG. 3, both ends of the shaft 23 are supported by bearings 26 and 27, and the charging roller 13 is rotatably supported. The charging roller 13 is driven to rotate as the photosensitive member 12 rotates in the direction of arrow R. Further, both left and right end portions of the shaft 23 are urged toward the surface of the photosensitive member 12 by elastic members 28 and 29 such as springs via bearing portions 26 and 27. The surface is in contact with the surface of the photoreceptor 12.

  The power source 50 is connected to the shaft 23 of the charging roller 13, and a DC voltage and an AC voltage are applied to the shaft 23 by the power source 50 in order to charge the surface of the photoconductor 12 to a predetermined potential. The superimposed voltage is applied.

  As shown in FIG. 3, the shaft 23 and the conductive elastic body 24 are in close contact with each other, but the inner diameter of the main body portion 25 b and the other end portion 25 c of the conductive tube 25 is the outer diameter of the conductive elastic body 24. The conductive elastic body 24 is provided so as to be detachable with respect to the conductive tube 25 in the direction of the shaft 23. In the present embodiment, the difference between the inner diameter of the main body portion 25b and the other end portion 25c of the conductive tube 25 and the outer shape of the conductive elastic body 24 is set to about 0.5 to 1 mm. Further, the inner diameter of the main body portion 25b of the conductive tube 25 and the inner diameter of the other end portion 25c are set to be substantially the same.

  Here, the present embodiment is characterized by the shape of the one end portion 25a of the conductive tube 25. That is, in the present embodiment, the one end portion 25 a of the conductive tube 25 is thermally contracted, and the inner diameter of the one end portion 25 a of the conductive tube 25 is set smaller than the outer diameter of the conductive elastic body 24. It is said. More specifically, as shown in FIG. 3, one end portion 25 a of the conductive tube 25 is formed in a tapered shape whose outer diameter gradually decreases from the inner side to the outer side in the longitudinal direction X of the charging roller 13.

  In this configuration, when the photoconductor 12 is rotated, the charging roller 13 is driven to rotate as the photoconductor 12 rotates. At this time, the charging roller 13 tries to move in the longitudinal direction X. As described above, the shaft 23 and the conductive elastic body 24 are in close contact, and both ends of the shaft 23 are supported by the bearing portions 26 and 27. Therefore, the shaft 23 and the conductive elastic body 24 hardly move in the longitudinal direction X.

  Further, as described above, the inner diameters of the main body portion 25b and the other end portion 25c of the conductive tube 25 are set larger than the outer diameter of the conductive elastic body 24, so that the conductive tube 25 is connected to the charging roller 13. It tries to move in the longitudinal direction X.

  However, as described above, the inner diameter of the one end portion 25 a of the conductive tube 25 is set smaller than the outer diameter of the conductive elastic body 24. Therefore, when the conductive tube 25 is to move in the right direction (that is, the direction of the arrow Xa in the drawing) in the longitudinal direction X, the inner peripheral surface of the one end portion 25a and the conductive elastic body 24 are Since the contact is made at the portion A in the figure, the conductive tube 25 can be prevented from moving in the direction of the arrow Xa.

  As shown in FIG. 3, when the charging roller 13 rotates, one end portion 25 a of the conductive tube 25 (more specifically, a cut surface of the one end portion 25 a) can come into contact with the bearing portion 26. It has a configuration. Therefore, when the conductive tube 25 is to move leftward in the longitudinal direction X (that is, in the direction of the arrow Xb in the drawing), the one end portion 25a and the bearing portion 26 are part B in the drawing. Therefore, the conductive tube 25 can be prevented from moving in the direction of the arrow Xb.

  With the above configuration, even when the charging roller 13 is driven to rotate as the photosensitive member 12 rotates, it is possible to prevent the conductive tube 25 from moving in the longitudinal direction X of the charging roller 13. Become. Therefore, it is possible to prevent the surface of the photosensitive member 12 from being damaged by the conductive elastic body 24 with an inexpensive and simple configuration without providing a separate member such as a stopper. In addition, it is possible to avoid the occurrence of uneven charging in the longitudinal direction of the photoconductor 12 due to the contact between the stopper and the photoconductor 12. Furthermore, it is possible to avoid the occurrence of uneven charging in the longitudinal direction of the photoconductor 12 due to the contact between the stopper and the conductive tube 25.

  In the present embodiment, since the one end portion 25a of the conductive tube 25 can come into contact with the bearing portion 26 when the charging roller 13 rotates, the one end portion 25a of the conductive tube 25 is worn by friction. However, since the one end portion 25a is a portion that does not come into contact with the surface of the photoconductor 12, even when it is worn, the charging of the photoconductor 12 is not adversely affected (that is, charging unevenness is not caused). .

  In the present embodiment, only one end portion 25 a of the conductive tube 25 is thermally contracted, and the inner diameter of the other end portion 25 c is set larger than the outer diameter of the conductive elastic body 24. Accordingly, the conductive tube 25 can be easily detached from the conductive elastic body 24 in a state where the charging roller 13 is removed from the bearing portions 26 and 27. As a result, the used charging roller 13 can be easily recycled and can be separated and collected in the recycling process.

  In addition, one end portion 25 a of the conductive tube 25 is formed in a tapered shape in which the outer diameter gradually decreases from the inner side to the outer side in the longitudinal direction X of the charging roller 13. Therefore, the surface of the photoconductor 12 can be prevented from being damaged by the conductive elastic body 24 only by performing simple processing on the one end portion 25a, and charging unevenness in the longitudinal direction of the photoconductor 12 can be prevented. Occurrence can be avoided.

  In addition, the said embodiment is only an explanatory example, The scope of the present invention is not limited to the said embodiment, Based on the meaning of this invention, the shape, dimension, material, etc. of each component are changed. It is possible that they are not excluded from the scope of the present invention.

  For example, in the above embodiment, the one end portion 25a of the conductive tube 25 is formed in a tapered shape with the outer diameter gradually decreasing from the inner side to the outer side in the longitudinal direction X of the charging roller 13, but the one end portion 25a It is good also as a structure which provides a level | step difference in the boundary part with the main-body part 25b.

  In the above-described embodiment, the charging roller 13 is driven to rotate as the photosensitive member 12 rotates. For example, the charging roller 13 is driven to rotate by a unique driving unit such as a motor. Also good.

  Furthermore, in the above embodiment, a digital copying machine is shown as an example of an image forming apparatus, but it goes without saying that other image forming apparatuses such as a facsimile and a printer may be used.

  As an application example of the present invention, there is a charging device provided with a charging roller for charging a photosensitive member.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. It is a perspective view for demonstrating schematic structure of the periphery of the charging device which concerns on embodiment of this invention. It is sectional drawing for demonstrating the structure of the charging roller in the charging device which concerns on embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 1a ... Image forming apparatus main body, 2 ... Paper feed part, 3 ... Paper conveyance part, 4 ... Image forming part, 5 ... Image reading part, 12 ... Photoconductor, 13 ... Charging roller, 22 ... Charging Device 23 ... Shaft 24 ... Conductive elastic body 25 ... Conductive tube 25a ... One end part 25b ... Main body part 25c ... Other end part 26 ... Bearing part 27 ... Bearing part 28 ... Elastic member, 29 ... elastic member, 50 ... power source, X ... longitudinal direction

Claims (2)

A shaft that is rotatably supported by the bearing portion, a conductive member that is coated around the shaft, and a conductive tube that is covered around the conductive member, and is disposed to face the photoreceptor. In addition, in a charging device including a charging roller that rotates following rotation of the photosensitive member,
The inner diameter of the main body portion of the conductive tube is set larger than the outer diameter of the conductive member, and the inner diameter of one end portion of the conductive tube is set smaller than the outer diameter of the conductive member. And
When the charging roller rotates, one end portion of the conductive tube can come into contact with the bearing portion , and an inner diameter of the other end portion of the conductive tube is larger than an outer diameter of the conductive member. The charging device is characterized in that it is also set large . 2. The charging device according to claim 1 , wherein one end portion of the conductive tube is formed in a tapered shape in which an outer diameter gradually decreases from an inner side to an outer side in a longitudinal direction of the charging roller.

Images