Patent Publication Number: US-9405209-B2

Title: Image forming unit and image forming apparatus provided with same

Description:
INCORPORATION BY REFERENCE 
     This application claims priority to Japanese Patent Application No. 2014-252467 filed on Dec. 12, 2014, the entire contents of which are incorporated by reference herein. 
     BACKGROUND 
     This disclosure relates to an image forming unit and an image forming apparatus provided with such an image forming unit. 
     In an image forming apparatus such as a copier, a photoconductive drum as a toner image carrier and a charging roller are arranged in a manner such as to rotate in contact with each other. For example, shown is a mechanism of driving the photoconductive drum and the charging roller while pressing the charging roller against the photoconductive drum to form a nip part. In this image forming apparatus, to form the nip part, the charging roller needs to be fitted to a frame member pivotably supporting the photoconductive drum. 
     SUMMARY 
     As one aspect of this disclosure, a technology obtained by further improving the technology described above will be suggested. 
     An image forming unit according to one aspect of this disclosure includes: a photoconductive drum, a charging member, and a holding member. 
     The photoconductive drum is pivotably supported at a frame member. 
     The charging member extends in a direction along a rotary shaft of the photoconductive drum and charges a circumferential surface of the photoconductive drum while making contact with the circumferential surface. 
     The holding member is provided in the charging member and holds the charging member at the frame member. 
     While held at the frame member with the holding member in between, the charging member is arranged in parallel to the photoconductive drum in contact with the circumferential surface of the photoconductive drum with a rotary shaft of the charging member and the rotary shaft of the photoconductive drum in parallel to each other. 
     The holding member and the frame member respectively have interference-preventing-shaped parts which is provided at a tip part of the holding member in a direction in which the holding member is attached and at a position of the frame member receiving the holding member. The interference-preventing-shaped parts are capable of first making contact with each other upon attachment of the charging member to the frame member with the holding member in between to thereby prevent interference between the holding member and the photoconductive drum. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational cross section showing a structure of an image forming apparatus having image forming units according to one embodiment of this disclosure; 
         FIG. 2  is a side view showing a state in which a charging device is fitted to a unit frame in the image forming unit; 
         FIG. 3  is a perspective view showing the charging device; 
         FIG. 4  is a perspective view showing a bearing member; and 
         FIG. 5  is an enlarged view of mechanisms around the bearing member shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, image forming units and an image forming apparatus provided with such image forming units according to one embodiment of this disclosure will be described with reference to the drawings.  FIG. 1  is an elevational cross section showing a structure of the image forming apparatus having the image forming units according to one embodiment of this disclosure. 
     The image forming apparatus  1  according to one embodiment of this disclosure is a multifunction peripheral combining a plurality of functions such as, for example, a copy function, a printer function, a scanner function, and a facsimile function. The image forming apparatus  1  includes: in an apparatus main body  11 , an operation section  47 , an image formation section  12 , a fixing section  13 , a paper feed section  14 , a document feed section  6 , a document reading section  5 , etc. 
     The operation section  47  receives, from an operator for various kinds of operation and processing executable by the image forming apparatus  1 , instructions such as an image formation operation execution instruction and a document reading operation execution instruction. The operation section  47  includes a display section  473  which displays, for example, an operation guide to the operator. 
     To perform the document reading operation by the image forming apparatus  1 , an image of a document fed by the document feed section  6  or a document loaded on document loading glass  161  is optically read by the document reading section  5  to generate image data. The image data generated by the document reading section  5  is saved into, for example, a built-in HDD or a network-connected computer. 
     To perform the image formation operation by the image forming apparatus  1 , based on, for example, the image data generated through the document reading operation, the image data received from the network-connected computer, or the image data stored in the built-in HDD, the image formation section  12  forms a toner image on recording paper P as a recording medium fed from the paper feed section  14 . 
     A magenta image forming unit  12 M, a cyan image forming unit  12 C, an yellow image forming unit  12 Y, and a black image forming unit  12 B of the image formation section  12  each include: a photoconductive drum  121 , a developing device  122 , a charging device  123 , an exposure device  124 , and a primary transfer roller  126 . 
     To perform color printing, each of the magenta image forming unit  12 M, the cyan image forming unit  12 C, the yellow image forming unit  12 Y, and the black image forming unit  12 Bk of the image formation section  12 , based on an image formed of a respective color component forming the image data, forms a toner image onto the photoconductive drum  121  through charging, exposure, and development processes, and transfers the toner image onto an intermediate transfer belt  125  by the primary transfer roller  126 . 
     The toner images of the respective colors transferred onto the intermediate transfer belt  125  are superposed on one another on the intermediate transfer belt  125  through transfer timing adjustment, turning into a color toner image. A secondary transfer roller  210  transfers, at a nip part N formed between the secondary transfer roller  210  and a driving roller  125 A with the intermediate transfer belt  125  in between, the color toner image, which has been formed on a surface of the intermediate transfer belt  125 , onto recording paper P conveyed through a conveyance path  190  from the paper feed section  14 . Then the fixing section  13  fixes the toner image on the recording paper P thereon through thermal compression. The recording paper P on which the color toner image has already been formed and which has gone through fixing processing is discharged onto a discharge tray  151 . 
     The paper feed section  14  includes a plurality of paper feed cassettes. A control section (not shown) drives, into rotation, a pickup roller  145  of the paper feed cassette storing recording paper of a size specified by an operator&#39;s instruction to convey the recording paper P stored in the respective paper feed cassette towards the nip part N. 
     In the image forming apparatus  1 , to perform double face printing, the recording paper P on one side of which the image has been formed by the image formation section  12  is nipped with a discharge roller pair  159 , is then switched back by the discharge roller pair  159  and conveyed to an inverted conveyance path  195 , and is conveyed again by a conveyance roller pair  19  to a region upstream of the nip part N and the fixing section  13  in a direction in which the recording paper P is conveyed. As a result, an image is formed on another surface of the recording paper by the image formation section  12 . 
     Next, mechanisms around the photoconductive drums  121  and the charging devices  123  in the image forming units  12 M,  12 C,  12 Y, and  12 Bk will be described. The mechanisms around the photoconductive drums  121  and the charging devices  123  in the image forming units  12 M,  12 C,  12 Y, and  12 Bk are identical, and thus in the following description, the color of the image forming unit is not specified and numeral  12  will be provided for the description. 
       FIG. 2  is a side view showing a state in which the charging device  123  is fitted to a unit frame UF in the image forming unit  12 . In  FIG. 2 , a direction (X-X direction) along a rotary shaft of the photoconductive drum  121  is defined as a horizontal direction and a radial direction (Y-Y direction) orthogonal to this direction along the rotary shaft is defined as a vertical direction, and, in particular, an −X direction is defined as left, an +X direction is defined as right, a −Y direction is defined as bottom, and a +Y direction is defined as top. 
       FIG. 2  shows the state in which the charging device  123  is fitted to the unit frame UF, and in a state after the charging device  123  is fitted to the unit frame UF, while held at the unit frame UF with bearing members  24 R and  24 L in between, the charging roller  22  is arranged in parallel to the photoconductive drum  121  in contact with a circumferential surface of the photoconductive drum  121  with their rotary shafts in parallel to each other. 
     The image formation unit  12  is provided with the unit frame UF including a pair of side walls  66  and  68  opposing each other with a gap in between. To this unit frame UF, the photoconductive drum  121  and the charging device  123  are detachably attached. The photoconductive drum  121  is rotationally and pivotably supported between the side walls  66  and  68 . The unit frame UF is one example of a frame member in the scope of the claims. 
       FIG. 3  is a perspective view showing this charging device  123 . In  FIG. 3 , a direction (X-X direction) along rotary shafts of the charging roller  22  and a cleaning roller  23  is defined as a horizontal direction and a radial direction (Y-Y direction) orthogonal to this direction along the rotary shafts is defined as a vertical direction, and, in particular, an −X direction is defined as left, an +X direction is defined as right, a −Y direction is defined as bottom, and a +Y direction is defined as top. 
     The charging device  123  includes: a charging case  21 , the charging roller  22 , the cleaning roller  23 , and bearing members  24 L and  24 R. In the following, unless the bearing members  24 L and  24 R need to be discriminated from each other for a description, the bearing members  24 L and  24 R are simply referred to as bearing members  24 . The charging roller  22  is one example of a charging member in the scope of the claims. The bearing member  24  is one example of a holding member in the scope of the claims. 
     The charging case  21  is formed of, for example, non-conductive synthetic resin, includes: a bottom wall  82  longitudinally extending in a slim form of a given width; side walls  84  extending upwardly (in the +Y direction) from both sides of the bottom wall  82  in a manner such as to oppose each other; and a pair of end walls  86  and  88  extending upwardly (in the +Y direction) from both longitudinal ends of the bottom wall  82 , and, as a whole, is formed into a box shape with a top (the +Y direction) open. Arranged inside of the charging case  21  are: the charging roller  22 , the cleaning roller  23 , and the bearing members  24 . 
     The charging roller  22  is a roller which, in contact with the photoconductive drum  121 , applies charging bias to a drum surface to charge the surface of the photoconductive drum  121 . The charging roller  22  is formed by, for example, a conductive rubber layer. To the charging roller  22 , the bias is applied from a charging bias application section, not shown. 
     The cleaning roller  23  is a roller which cleans the charging roller  22 . The cleaning roller  23  is, for example, a sponge (foamed) roller. The cleaning roller  23  is arranged in a manner such as to abut the charging roller  22 , and, for example, has a circumferential surface rotating in the same direction as that of a circumferential surface of the charging roller  22  with a circumferential speed difference therebetween, thereby removing a contaminant adhering to the circumferential surface of the charging roller  22 . 
     The bearing members  24  are members which are formed of, for example, synthetic resin, and which pivotably support right and left end parts of the charging roller  22  and the cleaning roller  23 . The bearing members  24 L and  24 R pivotably supporting these left and right end parts have a common basic structure but partially have different shapes. In this embodiment, only on the bearing member  24 R, a projection  122  to be described later on is formed. 
       FIG. 4  is a perspective view showing the bearing member  24 R. In  FIG. 4 , an axial direction (X-X direction) of the bearing member  24 R is defined as a horizontal direction, a radial direction (Y-Y direction) orthogonal to this axial direction is defined as a vertical direction, and, in particular, an −X direction is defined as left, an +X direction is defined as right, a −Y direction is defined as bottom, and a +Y direction is defined as top. 
     The bearing member  24 R includes: a main body part  116  in a form of a rectangular plate; and an upper bearing part  118  and a lower bearing part  120  respectively formed at an upper end part and a lower end part of this main body part  116 . 
     The upper bearing part  118  rotationally and pivotably supports a rotary shaft of the charging roller  22 . The upper bearing part  118  is one example of a bearing part in the scope of the claims. The lower bearing part  120  rotationally and pivotably supports a rotary shaft of the cleaning roller  23 . 
     The upper bearing part  118  and the lower bearing part  120  are projected from both surfaces of the main body part  116  and extend in the horizontal direction (X-X direction). Formed on a right surface (one axial end surface) of the upper bearing part  118  is a projection  122  of a flanged shape protruding rightward (in the +X direction). This projection  122  is provided integrally with the upper bearing part  118 . The projection  122 , at an end part of the charging device  123  in the direction along the rotary shaft of the photoconductive drum  121 , extends in this direction along the rotary shaft to support the charging device  123  at the unit frame UF. 
     A first tapered part  224  is formed at this projection  122 . This first tapered part  224  has a shape whose vertical thickness (in the Y-Y direction) becomes increasingly smaller towards the right (in the +X direction), that is, towards the unit frame UF. Upon the fitting of the charging device  123  to the unit frame UF, the first tapered part  224  first makes contact with the unit frame UF. This prevents interference between the bearing member  24 R and the photoconductive drum  121 . To guide the charging device  123  to the unit frame UF while preventing this interference, it is preferable that a tip part of the projection  122  in a travel direction be increasingly thinner towards the unit frame UF. From this viewpoint, in this embodiment, the projection  122  is provided with the first tapered part  224  on its unit frame UF side. Moreover, the first tapered part  224  is formed at the projection  122  of the flanged shape protruding rightward (in the +X direction). Thus, in this embodiment, the first tapered part  224  can be brought into contact with the unit frame UF side earlier than the upper bearing part  118  upon the aforementioned fitting, which reliably prevent the interference between the bearing member  24 R and the photoconductive drum  121 . 
       FIG. 5  is an enlarged view of mechanisms around the bearing member  24  shown in  FIG. 2 . In  FIG. 5 , directions related to the photoconductive drum  121  are defined in the same manner as in  FIG. 2 . On the side wall  66  located below the photoconductive drum  121 , side walls  66 A and  66 B are formed. 
     This side wall  66 B is more recessed rightward (in an +X direction) than the side wall  66 A. Formed at a bottom end part of the side wall  66 A (in a −Y direction) is a second tapered part  201 . This second tapered part  201  is slidable on the first tapered part  224 . This second tapered part  201  has a shape with inclination such that its vertical thickness (in a Y-Y direction) becomes increasingly larger rightward (in the +X direction), that is, towards the side wall  66 B. Upon the fitting of the charging device  123  to the unit frame UF, the projection  122  of the bearing member  24 R first makes contact with the second tapered part  201 . This prevents the interference between the bearing member  24 R and the photoconductive drum  121 . To smoothly guide the charging device  123  to the unit frame UF while preventing this interference, it is preferable that the side wall  66 A to which the projection  122  travels in its travel direction have a shape whose thickness becomes increasingly larger towards the side wall  66 B. From this viewpoint, in this embodiment, the side wall  66 A is provided on its bearing member  24 R side with the second tapered part  201 . The first tapered part  224  and the second tapered part  201  are each one example of an interference-preventing shaped part in the scope of the claims. 
     The bearing member  24 R is provided with a compression spring  25 . The compression spring  25  is stored in a case body  26  together with the bearing member  24 . This compression spring  25  is provided originally for the purpose of absorbing error in accuracy of positioning between the photoconductive drum  121  and the charging roller  22  upon fitting of the charging roller  22  and the cleaning roller  23  to the unit frame UF. This compression spring  25  is bent vertically (in the Y-Y direction) thereby moving the bearing member  24 R vertically (in the Y-Y direction). Upon the fitting of the charging device  123  to the unit frame UF, contact between the first tapered part  224  of the projection  122  and the second tapered part  201  of the side wall  66 A results in impact of the second tapered part  201  on the first tapered part  224 , but this impact can be absorbed since the compression spring  25  is bent vertically (in the Y-Y direction) as described above. 
     Next, a mechanism of guiding the charging roller  22  to the unit frame UF by movement of the bearing member  24  upon the fitting of the charging roller  22  to the unit frame UF will be described. 
     In  FIG. 5 , upon the attachment of the charging roller  22  to the unit frame UF, a projection  26 A of the case body  26  is inserted into a hole  200  on a unit frame UF side. In this state, the charging device  123  is inclined with respect to the photoconductive drum  121  with its left end part arranged lower (in the −Y direction) than its right end part, and thus it is arranged in a region lower than the photoconductive drum  121 . In this state, the first tapered part  224  of the bearing member  24 R first makes contact with the second tapered part  201  of the side wall  66 A. That is, the projection  122  of the flanged shape projected rightward (outward) from the upper bearing part  118  first makes contact with the side wall  66 A. Therefore, this can prevent the upper bearing part  118  from first making contact with the photoconductive drum  121 . Furthermore, the first tapered part  224  slides on the second tapered part  201 , and thus upon the fitting of the charging roller  22  to the unit frame UF, the charging roller  22  can smoothly be guided to the unit frame UF. That is, the inclination of the second tapered part  201 , upon movement of the charging device  123  towards the unit frame UF while abutting the inclination of the first tapered part  224 , guides the projection  26 A to the hole  200 . 
     Then a person in charge of the attachment arranges the charging roller  22  in contact with the circumferential surface of the photoconductive drum  121  at a position where rotary shafts of these two are aligned in parallel to each other. 
     In a state in which the charging roller  22  is guided in the aforementioned manner, between the circumferential surface of the photoconductive drum  121  and the bearing member  24 , a vertical space S (in the Y-Y direction) is formed which can prevent the contact between them, preventing interference between the upper baring part  118  and the photoconductive drum  121 . By the first tapered part  224  formed at the projection  122  and the second tapered part  201  formed on the side wall  66 A, in the state in which the charging roller  22  is guided in the aforementioned manner, the bearing member  24  is guided to the unit frame UF in such a manner as to make the bearing member  24  escape from the photoconductive drum  121 . The space S in  FIG. 5  is one example of a space formed between the circumferential surface of the photoconductive drum  121  and the bearing member  24 , and indicates a space formed between the circumferential surface of the photoconductive drum  121  and a top surface of the upper bearing part  118 . 
     As described above, in this embodiment, in a state in which the charging roller  22  is guided in contact with the circumferential surface of the photoconductive drum  121  to the position where the rotary shafts of these two are aligned in parallel to each other, by the first tapered part  224  formed at the projection  122  and the second tapered part  201  formed on the side wall  66 A, it can be guided to the unit frame UF in such a manner as to make the bearing member  24  escape from the photoconductive drum  121 , which can therefore prevent the contact of the bearing member  24  with the surface of the photoconductive drum  121  upon the fitting of the charging device  123  to the unit frame UF. 
     A typical image forming apparatus faces a risk that, at time of fitting of a charge roller to a frame member, contact of a bearing pivotably supporting the charge roller with a circumferential surface of a photoconductive roller may damage this circumferential surface. Thus, an operator has to pay utmost attention to operation of fitting the charge roller to the frame member. On the contrary, in this embodiment, in a state in which the first tapered part  224  of the bearing member  24 R slides on the second tapered part  201  of the side wall  66 A, the radial space S capable of preventing the contact between the photoconductive drum  121  and the bearing member  24 R is formed between them, and thus by the first tapered part  224  formed at the projection  122  and the second tapered part  201  formed on the side wall  66 A, the operator can fit the charging device  123  to the unit frame UF without bringing the bearing member  24  into contact with the circumferential surface of the photoconductive drum  121 . 
     According to this embodiment, providing the tapered parts at the bearing member  24  and part of the side wall  66  of the unit frame UF can smoothly guide the bearing member  24  to the unit frame UF without preventing the movement of the bearing member  24  upon the fitting. 
     Therefore, this embodiment can reliably prevent the damage on the photoconductive drum upon the fitting of the charging member to the frame member at lower costs than conventional art. 
     Moreover, the configuration and processing shown in the embodiment above with reference to  FIGS. 1 to 5  are just one embodiment of this disclosure, and thus configuration and processing of this disclosure are not limited them. 
     Various modifications and alterations of this disclosure will be apparent to those skilled in the art without departing from the scope and spirit of this disclosure, and it should be understood that this disclosure is not limited to the illustrative embodiments set forth herein.