JP2017203887A - Image forming apparatus and current suppressing member - Google Patents

Abstract

CONSTITUTION: An image forming apparatus (10) comprises: a transfer part that transfers a toner image from an image carrier (54) to a sheet; and current paths for grounding 76, 92 for suppressing charging of a metal member (86). The current paths for grounding are provided with a current suppressing member 100 that is formed of an insulating material into a sheet shape and include penetration parts 102 that penetrate in a thickness direction.EFFECT: An image forming apparatus and a current suppressing member can appropriately suppress flowing of a transfer current while suppressing charging of a metal member.SELECTED DRAWING: Figure 7

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus and a current suppressing member, and in particular, an image forming apparatus having, for example, an image carrier that carries a toner image and a transfer unit that transfers a toner image from the image carrier to paper. The present invention relates to a current suppressing member.

  An example of a conventional image forming apparatus is disclosed in Patent Document 1. The image forming apparatus disclosed in Patent Document 1 includes a paper feeding device having a detachable paper feeding tray (paper feeding cassette). The bottom plate of the paper feed tray is made of metal and can be rotated with a rotation fulcrum provided at an upstream portion in the paper conveyance direction as a fulcrum. When the paper feed tray is set in the image forming apparatus main body, the ground electrode portion of the paper feed tray is grounded via the image forming apparatus main body. As a result, it is possible to prevent static electricity generated by friction between sheets during sheet feeding from moving to the bottom plate of the sheet feeding tray and accumulating charges on the bottom plate.

  Another example of a conventional image forming apparatus is disclosed in Patent Document 2. The image forming apparatus of Patent Document 2 includes a guide unit provided between a transfer unit and a registration roller. The guide unit includes a conductive guide plate, an insulating support member that supports the guide plate, a connection member that is attached to the support member and electrically connected to the ground plate, and the guide plate and the connection member. And a non-linear element such as a varistor or a Zener diode electrically connected therebetween. The nonlinear element has a resistance value that decreases when a voltage of a predetermined value or more is applied between the guide plate and the ground plate.

JP 2011-131958 A JP 2007-298735 A

  With the technique of Patent Document 1, charging of the bottom plate (metal member) of the paper feed tray can be prevented. However, when the resistance value of the paper decreases in a high humidity environment, the transfer current in the transfer nip portion flows into the bottom plate of the paper feed tray through the paper (low resistance paper), and the image forming apparatus main body is There is a risk that it will come off. If a predetermined transfer electric field is not formed in the transfer nip portion, the toner image is not properly transferred to the paper, and transfer failure such as image omission occurs.

  On the other hand, in the technique of Patent Document 2, by providing a non-linear element such as a varistor or a Zener diode, it is possible to suppress the flow of the transfer current to the guide plate while suppressing the charging of the guide plate (metal member). Since a non-linear element is used, cost is increased.

  Therefore, a main object of the present invention is to provide a novel image forming apparatus and a current suppressing member.

  Another object of the present invention is to provide an image forming apparatus and a current suppressing member capable of appropriately suppressing a transfer current from being lost while suppressing charging of a metal member.

  A first invention is an image forming apparatus having an image carrier that carries a toner image, and a transfer unit that transfers the toner image from the image carrier to a sheet, for suppressing charging of a metal member The image forming apparatus includes a current suppressing member provided in a grounding current path, and the current suppressing member is formed in a sheet shape with an insulating material and has a through portion penetrating in the thickness direction.

  In the first invention, the image forming apparatus is an apparatus for forming an image on a sheet by an electrophotographic method, and an image carrier that carries a toner image, and a transfer that transfers the toner image from the image carrier to the sheet. Part. The image forming apparatus includes a current suppressing member provided in a grounding current path for suppressing charging of a metal member such as a bottom plate of the sheet feeding cassette or a guide member. This current suppressing member is formed in a sheet shape (thin plate shape) with an insulating material and has a penetrating portion that penetrates in the thickness direction, that is, communicates one surface with the other surface.

  According to the first aspect of the present invention, the current suppressing member that is formed into a sheet shape with an insulating material and has a through portion is provided for the grounding current path for suppressing charging of the metal member. While appropriately suppressing the charging of the member, it is possible to appropriately suppress the loss of the transfer current. Accordingly, it is possible to prevent transfer defects such as image omission. Further, since only the sheet-like current suppressing member is provided, the cost can be reduced.

  The second invention is an invention subordinate to the first invention. In the second invention, the grounding current path includes a current path from the metal bottom plate of the paper feed cassette to the metal main body frame. The current suppressing member is sandwiched between a first metal member such as a coil spring that constitutes a current path for grounding and a second metal member such as a main body frame, and is in contact with both the first metal member and the second metal member. To be provided. And a 1st metal member and a 2nd metal member oppose a predetermined interval through a penetration part.

  According to the second invention, it is possible to appropriately suppress the transfer current from being lost while appropriately suppressing the charging of the bottom plate of the sheet feeding cassette. Accordingly, it is possible to prevent the occurrence of transfer defects such as image omission while preventing double feeding of sheets.

  The third invention is an invention subordinate to the second invention. In the third invention, the first metal member is an elastic member such as a coil spring or a leaf spring provided in the paper feed cassette or the main body frame.

  According to the third aspect, since the one metal member brought into contact with the current suppressing member is an elastic member, the current suppressing member is stably inserted in the grounding current path.

  The fourth invention is an invention subordinate to the third invention. In the fourth invention, the elastic member is fixed by a fastening member such as a step screw fastened to the rotation fulcrum portion of the bottom plate. And a fastening member is provided rotatably with respect to the through-hole formed in the paper feed cassette.

  The fifth invention is an invention subordinate to the third or fourth invention. In the fifth invention, the elastic member is a coil spring, and the penetrating portion includes a plurality of elongated holes extending in parallel to the radial direction of the coil spring.

  The sixth invention is an invention subordinate to the third or fourth invention. In the sixth invention, the elastic member is a coil spring, and the penetrating portion includes a plurality of elongated holes extending radially from a position corresponding to the central portion of the coil spring.

  The seventh invention is an invention subordinate to the third or fourth invention. In 7th invention, an elastic member is a coil spring, Comprising: A penetration part contains the some hole arrange | positioned at random with respect to an electric current suppression member.

  The eighth invention is an invention subordinate to the third or fourth invention. In the eighth invention, the elastic member is a coil spring, and the penetrating portion includes a plurality of holes arranged along the tip portion of the coil spring.

  The ninth invention is an invention subordinate to any of the third to eighth inventions. In the ninth invention, the length or area of the portion where the elastic member contacts the current suppressing member is larger than the length or area of the portion where the elastic member faces the penetrating portion.

  According to the ninth aspect, contact between the elastic member, which is the first metal member, and the second metal member is appropriately prevented.

  The tenth invention is an invention subordinate to the first invention. In a tenth aspect of the invention, the grounding current path includes a current path from a metal guide member provided on the upstream side in the paper conveyance direction of the fixing unit for fixing the toner image on the paper to the metal main body frame, thereby suppressing current. The member is provided on a guide surface that guides the sheet of the guide member.

  According to the tenth aspect, it is possible to appropriately suppress the transfer current from being lost while appropriately suppressing the charging of the guide member. Therefore, it is possible to prevent the occurrence of transfer defects such as image omission while preventing the toner image on the paper from being disturbed.

  The eleventh invention is an invention subordinate to the tenth invention. In the eleventh invention, the current suppressing member includes a protruding portion that protrudes from the guide member toward the fixing portion and has flexibility.

  According to the eleventh aspect, it is possible to prevent the toner adhering to the paper from adhering to the front end portion of the guide member and accumulating.

  The twelfth invention is an invention subordinate to the tenth or eleventh invention. In a twelfth aspect, the penetrating portion includes a plurality of long holes extending along the paper transport direction.

  A thirteenth invention is a current suppressing member provided in a grounding current path for suppressing charging of a metal member provided in the image forming apparatus, and is formed in a sheet shape by an insulating material and penetrates in the thickness direction. This is a current suppressing member having a penetrating part.

  In a thirteenth invention, the current suppressing member is a sheet-like member provided in a grounding current path for suppressing charging of a metal member provided in the image forming apparatus, and is formed of an insulating material such as polyethylene terephthalate. And has a penetrating portion penetrating in the thickness direction.

  According to the thirteenth aspect, it is possible to appropriately suppress the transfer current from being lost while appropriately suppressing the charging of the metal member, and to prevent the occurrence of transfer defects such as image loss. Moreover, such a current suppressing member can be manufactured at low cost.

  According to the present invention, since the current suppressing member formed in a sheet shape with the insulating material and having the through portion is provided for the grounding current path for suppressing the charging of the metal member, While appropriately suppressing charging, it is possible to appropriately suppress transfer current loss. Accordingly, it is possible to prevent transfer defects such as image omission. Further, since only the sheet-like current suppressing member is provided, the cost can be reduced.

  The above object, other objects, features, and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

1 is an illustrative view showing a schematic configuration of an image forming apparatus according to a first embodiment of the present invention; FIG. 2 is a perspective view showing a main body frame and a paper feed cassette included in the image forming apparatus of FIG. 1. It is a top view which shows a paper feed cassette. FIG. 4 is an enlarged cross-sectional view illustrating a peripheral portion of a coil spring of a paper feed cassette. It is an illustration figure which shows a main body frame, (A) is a fragmentary sectional view of a main body frame, (B) is a front view of the electric current suppression member provided in a main body frame. FIG. 3 is an illustrative view showing a state when a paper feed cassette is attached to the image forming apparatus. It is an illustration for demonstrating the positional relationship of a coil spring and a current suppression member, Comprising: (A) is an illustration figure which shows a mode that the current suppression member was seen from the front side, (B) is (A). It is sectional drawing in the VII (B) -VII (B) line. It is a graph which shows the experimental result which investigated the electric charge accumulate | stored in the baseplate of a paper feed cassette. It is an illustration figure which shows an example of the electric current suppression member with which the image forming apparatus which is 2nd Example of this invention is provided. It is an illustration figure which shows another example of a current suppression member. It is an illustration figure which shows another example of a current suppression member. It is an illustration figure which shows another example of a current suppression member. It is an illustration figure which shows another example of a current suppression member. It is an illustration for demonstrating the positional relationship of a leaf | plate spring and an electric current suppression member, Comprising: (A) is an illustration figure which shows a mode that the electric current suppression member was seen from the front side, (B) is (A). It is sectional drawing in a XIV (B) -XIV (B) line. FIG. 6 is a cross-sectional view schematically showing a peripheral portion of a transfer portion and a fixing portion of an image forming apparatus according to a third embodiment of the present invention. FIG. 16 is an illustrative view showing a current suppressing member provided in the pre-fixing guide of FIG. 15.

[First embodiment]
Referring to FIGS. 1 and 2, an image forming apparatus 10 according to a first embodiment of the present invention is an apparatus for forming an image on a sheet by an electrophotographic method, and is an intermediate transfer belt (image) carrying a toner image. Carrier) 54, and a transfer portion for transferring the toner image from the intermediate transfer belt 54 to the paper.

  As will be described in detail later, the image forming apparatus 10 includes a paper feed cassette 48 that is detachably attached to the apparatus main body 12. A bottom plate (metal member) 86 of the paper feed cassette 48 is electrically connected to a metal main body frame 76 provided on the back side of the apparatus main body 12 via a coil spring 92 and is grounded through the main body frame 76. This suppresses charging. A current suppressing member 100 is provided in the grounding current path from the bottom plate 86 of the paper feed cassette 48 to the main body frame 76.

  First, the basic configuration of the image forming apparatus 10 will be schematically described. In the first embodiment, the image forming apparatus 10 is a multifunction peripheral (MFP) having a copying function, a printer function, a scanner function, a facsimile function, and the like.

  As shown in FIG. 1, the image forming apparatus 10 includes an apparatus main body 12 including an image forming unit 30, a paper feed cassette 48, and the like, and an image reading apparatus 14 disposed above the apparatus main body 12.

  The image reading device 14 includes a document placing table 16 formed of a transparent material. A document pressing cover 18 is attached above the document placing table 16 through a hinge or the like so as to be freely opened and closed. The document pressing cover 18 is provided with an ADF (automatic document feeder) 24 that automatically feeds the documents placed on the document placing tray 20 one by one to the image reading position 22. Although not shown, an operation unit such as a touch panel and operation buttons for receiving an input operation such as a print instruction by a user is provided on the front side of the document placing table 16.

  The image reading device 14 includes an image reading unit 26 including a light source, a plurality of mirrors, an imaging lens, a line sensor, and the like. The image reading unit 26 exposes the document surface with a light source, and guides the reflected light reflected from the document surface to the imaging lens by a plurality of mirrors. Then, the reflected light is imaged on the light receiving element of the line sensor by the imaging lens. The line sensor detects the luminance and chromaticity of the reflected light imaged on the light receiving element, and generates image data based on the image on the document surface. As the line sensor, a charge coupled device (CCD), a contact image sensor (CIS), or the like is used.

  The apparatus main body 12 includes a control unit 28 including a CPU and a memory, an image forming unit 30 and the like. The control unit 28 transmits a control signal to each part of the image forming apparatus 10 according to an input operation to an operation unit such as a touch panel, and causes the image forming apparatus 10 to execute various operations.

  The image forming unit 30 includes an exposure unit 32, a developing unit 34, a photosensitive drum 36, a cleaner unit 38, a charger 40, an intermediate transfer belt unit 42, a transfer roller 44, a fixing unit 46, and the like. An image is formed on a sheet conveyed from the manual sheet feed tray 50, and the image-formed sheet is discharged to a sheet discharge tray 52. As image data for forming an image on a sheet, image data read by the image reading unit 26 or image data transmitted from an external computer is used.

  The image data handled in the image forming apparatus 10 corresponds to four color images of black (K), cyan (C), magenta (M), and yellow (Y). For this reason, each of the developing device 34, the photosensitive drum 36, the cleaner unit 38, and the charging device 40 is provided so as to form four types of latent images corresponding to the respective colors, thereby providing four image stations. Composed.

  The photosensitive drum 36 is an image carrier in which a photosensitive layer is formed on the surface of a conductive cylindrical substrate. The charger 40 is a member that charges the surface of the photosensitive drum 36 to a predetermined potential. is there. Further, the exposure unit 32 is configured as a laser scanning unit (LSU) including a laser emitting portion and a reflection mirror, and exposes the surface of the charged photosensitive drum 36 so that an electrostatic latent image corresponding to image data is obtained. An image is formed on the surface of the photosensitive drum 36. The developing device 34 visualizes the electrostatic latent image formed on the surface of the photosensitive drum 36 with toner of four colors (YMCK). The cleaner unit 38 removes toner remaining on the surface of the photosensitive drum 36 after development and image transfer.

  The intermediate transfer belt unit 42 includes an intermediate transfer belt 54, a driving roller 56, a driven roller 58, four intermediate transfer rollers 60, and the like, and is disposed above the photosensitive drum 36.

  The intermediate transfer belt 54 is an endless belt having flexibility, and is formed of a synthetic resin or rubber appropriately blended with a conductive material such as carbon black. The intermediate transfer belt 54 is suspended by a driving roller 56 and a driven roller 58, and is arranged so that its outer peripheral surface (lower surface) abuts on the outer peripheral surface of the photosensitive drum 36. The intermediate transfer belt 54 rotates in a predetermined direction as the driving roller 56 rotates.

  The drive roller 56 is provided so as to be rotatable around its axis by a drive unit (not shown). The driven roller 58 rotates as the intermediate transfer belt 54 rotates and applies a constant tension to the intermediate transfer belt 54 to prevent the intermediate transfer belt 54 from loosening.

  The intermediate transfer roller 60 is disposed at a position facing each photosensitive drum 36 with the intermediate transfer belt 54 interposed therebetween. During image formation, a predetermined voltage (primary transfer voltage) is applied to the intermediate transfer roller 60, whereby a transfer electric field is formed between the photosensitive drum 36 and the intermediate transfer belt 54. The toner image formed on the outer peripheral surface of the photosensitive drum 36 is transferred to the outer peripheral surface of the intermediate transfer belt 54 by the action of the transfer electric field.

  The transfer roller 44 is provided so as to press the intermediate transfer belt 54 with the driving roller 56. During image formation, a predetermined voltage (secondary transfer voltage) is applied to the transfer roller 44, whereby a transfer electric field is formed between the intermediate transfer belt 54 and the transfer roller 44. Due to the action of the transfer electric field, the toner image formed on the outer peripheral surface of the intermediate transfer belt 54 is formed while the sheet passes through the transfer nip portion (transfer portion) between the intermediate transfer belt 54 and the transfer roller 44. Transferred (secondary transfer) onto the paper.

  The fixing unit 46 includes a heat roller 62 and a pressure roller 64 and is disposed above the transfer roller 44. The heat roller 62 is set to have a predetermined fixing temperature, and is transferred onto the paper when the paper passes through a fixing nip portion (fixing portion) between the heat roller 62 and the pressure roller 64. The toner image is melted, mixed, and pressed, and the toner image is thermally fixed to the paper.

  Further, a pre-fixing guide 70 for guiding the sheet on which the toner image is transferred to the fixing nip portion of the fixing unit 46 is provided on the upstream side of the fixing unit 46 in the sheet conveying direction. The pre-fixing guide 70 includes a pair of plate-shaped guide members arranged to face each other, and forms a part of the sheet conveyance path between the pair of guide members.

  Further, a paper feed cassette 48 that supplies paper to the image forming unit 30 is provided below the image forming unit 30. A plurality of sheets are stacked on a bottom plate (also referred to as a sheet stacking tray or a rotating plate) 86 of the sheet feeding cassette 48. 1 and 2 show only one paper feed cassette 48, the number of paper feed cassettes 48 provided in the image forming apparatus 10 is arbitrary. A specific configuration of the paper feed cassette 48 will be described later.

  A pickup roller 72 for taking out the uppermost sheet from the sheet feeding cassette 48 is provided above the downstream end of the sheet feeding cassette 48 in the sheet conveying direction. Further, on the downstream side of the pickup roller 72 in the paper conveyance direction, a paper feed roller 74 is provided that applies a driving force to the paper and prevents double feeding of the paper.

  In the apparatus main body 12, the first sheet for feeding the sheet conveyed from the sheet feeding cassette 48 or the manual sheet feeding tray 50 to the sheet discharge tray 52 via the registration roller 68, the transfer roller 44 and the fixing unit 46. A one-sheet conveyance path L1 is formed. Further, when performing double-sided printing on the paper, the paper after the single-sided printing is finished and passed through the fixing unit 46 is returned to the first paper transport path L1 on the upstream side of the transfer roller 44 in the paper transport direction. The second paper transport path L2 is formed. In the first paper transport path L1 and the second paper transport path L2, a plurality of transport rollers 66 are provided as appropriate to supplementarily apply a propulsive force to the paper.

  When performing single-sided printing (image formation) in the apparatus main body 12, the sheets are guided one by one from the sheet feeding cassette 48 or the manual sheet feeding tray 50 to the first sheet conveying path L 1, and the registration rollers 68 are conveyed by the conveying rollers 66. It is conveyed to. The registration roller 68 conveys the sheet to the transfer roller 44 (transfer nip portion) at a timing when the leading end of the sheet and the leading end of the image information on the intermediate transfer belt 54 are aligned, and the toner image is transferred onto the sheet. . Thereafter, when the toner passes through the fixing unit 46 (fixing nip portion), the unfixed toner on the paper is melted and fixed by heat, and the paper is discharged onto the paper discharge tray 52.

  On the other hand, when performing double-sided printing, when the trailing edge of the paper that has passed through the fixing unit 46 after single-sided printing has reached the transport roller 66 in the vicinity of the paper discharge tray 52, the transport roller 66 is reversely rotated. As a result, the sheet runs backward and is guided to the second sheet conveyance path L2. The paper guided to the second paper transport path L2 is transported through the second paper transport path L2 by the transport roller 66, and is guided to the first paper transport path L1 on the upstream side of the registration roller 68 in the paper transport direction. At this time, the front and back sides of the sheet are reversed, and thereafter, the sheet passes through the transfer roller 44 and the fixing unit 46, whereby printing is performed on the back side of the sheet.

  Next, the configuration of the paper feed cassette 48 will be described with reference to FIGS. The paper feed cassette 48 includes a cassette main body 80 formed in a box shape with an open top, and is detachably attached to the apparatus main body 12 from the front side. The cassette body 80 is provided with a pair of side guides 82, a sheet rear end pressing plate 84, a bottom plate 86, and the like.

  The side guide 82 regulates each of the paper edges in the direction (paper width direction) perpendicular to the paper conveyance direction of the paper stacked on the bottom plate 86, that is, both side edges of the paper, and one or both of them are paper. It is provided so as to be movable in the width direction. The sheet trailing edge pressing plate 84 regulates the trailing edge of the sheets stacked on the bottom plate 86 in the sheet conveying direction, and is provided to be movable in the front-rear direction in the sheet conveying direction. The cassette body 80, the side guide 82, and the paper trailing edge pressing plate 84 are formed of an insulating material such as a synthetic resin.

  The bottom plate 86 is a metal member such as a steel plate formed in a substantially rectangular flat plate shape, and is disposed at the bottom of the cassette body 80 on the pickup roller 72 side. On both sides of the bottom plate 86 on the upstream side in the sheet conveying direction, a rising portion that rises upward is formed, and a rotation fulcrum portion (bearing portion) 86a is formed on the rising portion. The rotation fulcrum portion 86a is fastened to the cassette body 80 by a fastening member 88 such as a step screw, and the bottom plate 86 is rotatably provided with the rotation fulcrum portion 86a and the fastening member 88 as fulcrums. In addition, the fastening member 88 fastened to the rotation fulcrum portion 86 a is rotatable about the axis with respect to the through hole 80 a formed in the cassette body 80 as the bottom plate 86 rotates. Further, the leading end portion of the bottom plate 86 on the downstream side in the sheet conveying direction is biased upward by a biasing member 90 (see FIG. 1), and the leading end of the uppermost sheet stacked on the bottom plate 86 is fed during paper feeding. The portion is pressed against the pickup roller 72.

  In such a sheet feeding cassette 48, since the bottom plate 86 is made of metal, static electricity generated by friction between sheets moves to the bottom plate 86, and as the number of fed sheets increases, the charge to the bottom plate 86 increases. Gradually accumulates. If the bottom plate 86 is excessively charged, problems such as double feeding of paper will occur.

  For this reason, as a conventional technique, a metal elastic member is provided in the periphery of the rotation fulcrum portion on the back side in the mounting direction of the sheet cassette on the bottom plate, and the bottom plate and the metal main body frame are electrically connected via this elastic member. In some cases, the bottom plate is grounded (grounded) to prevent charging.

  Also in the first embodiment, the bottom plate 86 and the main body frame 76 are electrically connected using a coil spring 92 as a metal elastic member, and a grounding current path for suppressing charging of the bottom plate 86 is formed. Thus, charging of the bottom plate 86 is prevented. Specifically, in the first embodiment, a coil spring 92 is attached to the cassette body 80 of the paper feed cassette 48 using a fastening member 88 fastened to the rotation fulcrum 86a of the bottom plate 86. In the state in which the paper feed cassette 48 is attached to the apparatus main body 12, a grounding current path from the bottom plate 86 to the main body frame 76 through the fastening member 88 and the coil spring 92 is formed.

  Here, if the bottom plate 86 is grounded, the bottom plate 86 is prevented from being charged. However, when the resistance value of the sheet decreases in a high humidity environment, the transfer current in the transfer nip portion is changed to the sheet ( There is a risk that it will flow into the bottom plate 86 through the low-resistance paper) and come out through the grounding current path. If a predetermined transfer electric field is not formed in the transfer nip portion, transfer defects such as image omission occur. That is, in order to eliminate problems such as double feeding, it is necessary to prevent excessive charging of the bottom plate 86, while it is necessary to appropriately suppress the transfer current from flowing out (outflow) through the bottom plate 86.

  Therefore, in the first embodiment, the current suppressing member 100 is inserted into the grounding current path from the bottom plate 86 of the paper feed cassette 48 to the main body frame 76, thereby suppressing the charging of the bottom plate 86 and the transfer. The current loss is appropriately suppressed. This will be specifically described below.

  As shown in FIGS. 5 and 6, the metal body frame 76 provided on the back side of the apparatus body 12 has a current suppressing member 100 at the position corresponding to the coil spring 92 of the sheet feeding cassette 48. Affixed using an adhesive or the like.

  The current suppressing member 100 is formed in a sheet shape (thin plate shape) from an insulating material such as a synthetic resin such as polyethylene terephthalate. And the electric current suppression member 100 has the penetration part 102 which penetrates in the thickness direction, ie, connects one surface and the other surface. In the first embodiment, the current suppressing member 100 is formed in a substantially rectangular sheet shape. The thickness of the current suppressing member 100 is, for example, 0.19 mm.

  The insulating material referred to in the present invention means a material having a resistivity [Ω · cm] of 10 8 or higher. In this first embodiment, the insulating material has a resistivity of 10 17. The current suppressing member 100 is formed using polyethylene terephthalate. However, the material for forming the current suppressing member 100 is not particularly limited as long as it is an insulating material having a resistivity of at least 10 8 or more, and thereby the effect of the present invention is exhibited. In addition, the current suppressing member 100 is partially cut out in a rectangular shape, but this is for avoiding interference with holes and protrusions formed in the main body frame 76. The shape of can be changed as appropriate.

  In the first embodiment, the through portion 102 formed in the current suppressing member 100 is configured by a plurality of long holes (slits) extending in parallel to the radial direction of the coil spring 92. Specifically, three elongated holes having a rounded rectangular shape extending in the horizontal direction when viewed from the front are formed so as to be aligned in the vertical direction. Moreover, the penetration part 102 is arrange | positioned so that the front-end | tip part of the coil spring 92 may straddle the penetration part 102 (refer FIG. 7 (A)). At this time, the length of the penetrating portion 102 in the longitudinal direction is larger than the diameter of the tip portion (contact portion) of the coil spring 92, and the length in the short direction is larger than the diameter of the tip portion of the coil spring 92. It is preferable to be formed to be small. The through portion 102 is formed so that the length or area of the portion where the coil spring 92 contacts the current suppressing member 100 is larger than the length or area of the portion where the coil spring 92 faces the through portion 102. It is preferable.

  As shown in FIG. 7, in a state where the paper feed cassette 48 is mounted on the apparatus main body 12, the current suppressing member 100 includes a coil spring (first metal member) 92 that constitutes a grounding current path of the bottom plate 86 and the main body. It is sandwiched between the frame (second metal member) 76 and contacts both the coil spring 92 and the main body frame 76. In addition, the coil spring 92 and the main body frame 76 are opposed to each other with a predetermined interval (that is, an interval corresponding to the thickness of the current suppressing member 100) through the penetrating portion 102.

  At this time, the length of the portion where the coil spring 92 contacts the current suppressing member 100 is set to be larger than the length of the portion where the coil spring 92 faces the penetrating portion 102. Is properly prevented. Further, the coil spring 92 is brought into contact with one surface of the current suppressing member 100 and the current suppressing member 100 is pressed by the coil spring 92, whereby the coil spring 92 and the current suppressing member 100 are stably in contact with each other. That is, the current suppressing member 100 is stably inserted into the grounding current path by using the one metal member brought into contact with the current suppressing member 100 as an elastic member.

  In such an image forming apparatus 10, charges gradually accumulate on the bottom plate 86 as the number of sheets fed from the sheet feeding cassette 48 increases. When a predetermined amount or more of electric charge accumulates in the bottom plate 86, it is discharged from the coil spring 92 to the main body frame 76 through the through portion 102, and the electric charge of the bottom plate 86 is released through the grounding current path. That is, in the bottom plate (metal member) 86 of the paper feed cassette 48, the charge is gradually accumulated and released gradually. Thus, the transfer current of the transfer nip portion (transfer roller 44) is prevented from being released all at once through the paper while preventing the paper from being fed from the paper feed cassette 48.

  FIG. 8 shows an experimental result in which the inventors of the present application examined the behavior when charges are accumulated on the bottom plate 86 of the paper feed cassette 48. As shown in FIG. 8, in the image forming apparatus 10 of the first example, a good result was confirmed that the electric charge was accumulated and released to near -2.2 kV with respect to the bottom plate 86.

  As described above, according to the first embodiment, the bottom plate 86 of the paper feed cassette 48 is formed into a sheet shape from the grounding current path from the bottom plate 86 to the main body frame 76 with an insulating material, and the through-hole 102 is formed. Since the current suppressing member 100 is provided, it is possible to appropriately suppress the transfer current from being lost while appropriately suppressing the charging of the bottom plate 86. Accordingly, it is possible to prevent the occurrence of transfer defects such as image omission while preventing double feeding of sheets.

  Moreover, since only the sheet-like current suppressing member 100 is provided, the cost can be reduced.

  In the first embodiment described above, the long holes constituting the penetrating portion 102 are formed so as to extend in the lateral direction when viewed from the front. However, the long holes are formed so as to extend in the vertical direction or the oblique direction. Also good. Further, the through portion 102 may be one long hole.

[Second Embodiment]
Next, an image forming apparatus 10 according to a second embodiment of the present invention will be described with reference to FIG. In this 2nd Example, the aspect of the penetration part 102 formed in the electric current suppression member 100 differs from the above-mentioned 1st Example. Since the configuration of the other parts is the same, parts common to the first embodiment described above are given the same reference numerals, and redundant descriptions are omitted or simplified.

  As shown in FIG. 9, the current suppressing member 100 included in the image forming apparatus 10 of the second embodiment is sandwiched between the coil spring 92 and the main body frame 76, and is sandwiched between the coil spring 92 and the main body frame 76. Provided in contact. The current suppressing member 100 is formed in a sheet shape with an insulating material, and has a through portion 102 penetrating in the thickness direction. And in this 2nd Example, the penetration part 102 is comprised by the some long hole radially extended from the position corresponding to the center part of the coil spring 92, and the front-end | tip part of the coil spring 92 straddles the penetration part 102, It is arranged to become.

  According to the second embodiment, similarly to the first embodiment, the transfer of the transfer current can be appropriately suppressed while appropriately suppressing the charging of the bottom plate 86. Accordingly, it is possible to prevent the occurrence of transfer defects such as image omission while preventing double feeding of sheets.

  Note that the number, shape, arrangement, and the like of the through portions 102 formed in the current suppressing member 100 are not limited to the modes shown in the first and second embodiments, and can be changed as appropriate.

  For example, as illustrated in FIG. 10, the through portion 102 may be a plurality of circular holes that are randomly arranged with respect to the current suppressing member 100. Further, for example, as shown in FIG. 11, the through portion 102 may be a plurality of circular holes arranged in a circular shape along the tip portion of the coil spring 92.

  Furthermore, in each of the above-described embodiments or modifications, the through portion 102 formed in the current suppressing member 100 is configured by a hole, but the through portion 102 may be a notch or a gap. That is, the penetrating portion 102 may be partially open at the periphery.

  For example, as shown in FIG. 12, the through portion 102 may be a plurality of substantially triangular notches or gaps formed at a predetermined interval in the peripheral portion of the current suppressing member 100. For example, as shown in FIG. 13, the penetrating portion 102 may be a plurality of substantially rectangular notches or gaps extending in the lateral direction when viewed from the front.

  Furthermore, the penetration part 102 can also be comprised combining suitably the aspect of the penetration part 102 shown in FIG. 5, FIG.

  In the embodiment or the modification shown in FIGS. 9 to 13, as in the first embodiment, the through portion 102 formed in the current suppressing member 100 is a portion where the coil spring 92 contacts the current suppressing member 100. It is preferable that the length or area be formed so that the coil spring 92 is larger than the length or area of the portion facing the penetrating portion 102.

  In each of the above-described embodiments, the coil spring 92 is used as the elastic member (first metal member) that constitutes a part of the grounding current path. However, the present invention is not limited to this. For example, as shown in FIG. 14, the elastic member may be a leaf spring 120. Even when the leaf spring 120 is used as the elastic member, the through portion 102 formed in the current suppressing member 100 has an area where the leaf spring 120 contacts the current suppressing member 100 so that the leaf spring 120 faces the through portion 102. It is preferable to be formed so as to be larger than the area of the portion.

  Further, in each of the above-described embodiments, the elastic member (coil spring 92) is provided in the paper feed cassette 48 and the current suppressing member 100 is provided in the main body frame 76, but this arrangement may be reversed. That is, the elastic member may be provided in the main body frame 76 and the current suppressing member 100 may be provided in the paper feed cassette 48. In this case, for example, a metal plate (sheet metal) electrically connected to the bottom plate 86 may be attached to the outer surface of the cassette main body 80 of the paper feed cassette 48, and the current suppressing member 100 may be attached to the metal plate.

[Third embodiment]
Next, with reference to FIGS. 15 and 16, an image forming apparatus 10 according to a third embodiment of the present invention will be described. The third embodiment is different from the first embodiment in that the current suppressing member 100 is provided in the grounding current path from the guide member 112 provided in the pre-fixing guide 70 to the main body frame 114. Since the configuration of the other parts is the same, parts common to the first embodiment described above are given the same reference numerals, and redundant descriptions are omitted or simplified.

  As shown in FIGS. 15 and 16, the image forming apparatus 10 according to the third embodiment includes a pre-fixing guide 70 provided on the upstream side of the fixing unit 46 (fixing nip portion) in the sheet conveying direction.

  The pre-fixing guide 70 is a guide member for guiding the paper, onto which the toner image has been transferred by the transfer roller 44 (transfer nip portion), to the fixing nip portion of the fixing unit 46, and is a pair of plate-like plates arranged opposite to each other. The guide members 110 and 112 are included. Each of the guide members 110 and 112 is made of metal. In addition, the guide member (metal member) 112 disposed on the back side of the paper is electrically connected to the metal main body frame 114 and grounded through the main body frame 114 to suppress charging. This is because if the guide member 112 is excessively charged due to friction with the paper or the like, spark discharge may occur between the paper and the guide member 112 and the toner image on the paper may be disturbed.

  Here, if the guide member 112 is grounded, charging of the guide member 112 is prevented. However, when the resistance value of the sheet is reduced in an environment with high humidity, the transfer nip portion (transfer portion) There is a possibility that the transfer current flows into the guide member 112 through the paper (low resistance paper) and escapes through the grounding current path. That is, in the guide member 112, it is necessary to prevent excessive charging, but it is necessary to appropriately prevent the transfer current from being lost via the guide member 112.

  Therefore, in the third embodiment, by providing the current suppressing member 100 with respect to the grounding current path from the guide member 112 to the main body frame 114, it is possible to appropriately prevent the transfer current from being lost while suppressing charging of the guide member 112. I try to suppress it.

  Specifically, the current suppressing member 100 is attached to the guide surface of the guide member 112, which is a metal member, using a double-sided tape or an adhesive. The current suppressing member 100 is provided so as to cover the guide surface that guides the paper of the guide member 112, and is provided at least in an area where the paper can contact among the entire surface area of the guide surface of the guide member 112.

  The current suppressing member 100 is formed in a sheet shape by an insulating material such as a synthetic resin such as polyethylene terephthalate, and has a through portion 102 penetrating in the thickness direction. In the third embodiment, the current suppressing member 100 is formed in a substantially rectangular sheet shape. The thickness of the current suppressing member 100 is, for example, 0.19 mm.

  Further, in the third embodiment, the through portion 102 formed in the current suppressing member 100 is constituted by a plurality of long holes (slits) extending along the paper transport direction. Specifically, six rectangular long holes extending in the paper transport direction are formed to be aligned in the paper width direction, which is a direction orthogonal to the paper transport direction. However, the shape, number, and arrangement of the penetrating portions 102 can be changed as appropriate. For example, holes such as circles may be arranged randomly or in a predetermined arrangement.

  Furthermore, in this third embodiment, the current suppressing member 100 has a protruding portion 112a that protrudes from the guide member 112 toward the fixing nip portion and has flexibility. At this time, the entire current suppressing member 100 may have flexibility, or at least the portion of the protruding portion 112a may have flexibility. The protruding length of the protruding portion 112a from the guide member 112 is, for example, 1 to 2 mm. Providing such a protruding portion 112 a on the current suppressing member 100 can prevent toner adhering to the back side of the sheet from adhering to the leading end of the guide member 112 and accumulating. That is, at the time of paper conveyance, the protrusion 112a of the current suppressing member 100 is bent along the paper or the first paper conveyance path L1 due to the contact pressure of the paper. For this reason, the sheet is not strongly squeezed by the protruding portion 112 a of the current suppressing member 100, so that the toner on the back surface of the sheet is difficult to adhere to the tip of the protruding portion 112 a of the current suppressing member 100. Even if the toner on the back surface of the paper adheres to the tip of the protruding portion 112a of the current suppressing member 100, since the current suppressing member 100 is thin, the amount of toner attached to the tip of the protruding portion 112a is small. Yes, when the protruding portion 112a returns to its original shape by its own elastic repulsive force, a small amount of toner attached to the tip portion of the protruding portion 112a is blown off.

  In the image forming apparatus 10 according to the third embodiment, even when the transfer current in the transfer nip portion flows into the pre-fixing guide 70 through the sheet (low resistance sheet), the current flowing from the sheet to the guide member 112 is Since the current is passed through the through portion 102 of the current suppressing member 100, the transfer current at the transfer nip portion is prevented from being released all at once via the sheet.

  According to the third embodiment, since the sheet-like current suppressing member 100 having the penetrating portion 102 with respect to the grounding current path from the guide member 112 of the pre-fixing guide 70 to the main body frame 114 is provided, the guide member 112 While appropriately suppressing charging, it is possible to appropriately suppress transfer current loss. Therefore, it is possible to prevent the occurrence of transfer defects such as image omission while preventing the toner image on the paper from being disturbed.

  In the third embodiment described above, the current suppressing member 100 is provided for the grounding current path from the guide member 112 of the pre-fixing guide 70 to the main body frame 114. However, the present invention is not limited to this. For example, the current suppressing member 100 can be provided for the grounding current path from the guide member of the pre-transfer guide provided between the transfer nip portion and the registration roller 68 to the main body frame.

  Further, in each of the above-described embodiments, the image forming apparatus 10 is exemplified by a multi-function apparatus in which a copier, a facsimile, and a printer are combined. However, the image forming apparatus 10 may be any one of a copier, a facsimile, a printer, and the like. A multifunction machine combining at least two of these may be used.

  In addition, although the change of the structure from 1st Example shown to the above-mentioned 2nd and 3rd Example was each demonstrated individually, each of the technical feature currently described in each Example or each modification is Can be combined with each other.

  Further, the specific numerical values, materials, shapes, and the like listed above are merely examples, and can be appropriately changed according to needs such as product specifications.

DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 30 ... Image forming part 44 ... Transfer roller 46 ... Fixing unit 48 ... Paper feed cassette 54 ... Intermediate transfer belt (image carrier)
70 ... Pre-fixing guide 76 ... Body frame (second metal member)
80 ... cassette body 86 ... bottom plate (metal member)
88 ... Fastening member 92 ... Coil spring (first metal member, elastic member)
DESCRIPTION OF SYMBOLS 100 ... Current suppression member 102 ... Through-hole 112 ... Guide member (metal member)
120 ... leaf spring (first metal member, elastic member)

Claims (13)

An image forming apparatus comprising: an image carrier that carries a toner image; and a transfer unit that transfers the toner image from the image carrier to paper.
A current suppressing member provided in a grounding current path for suppressing charging of the metal member;
The said current suppression member is an image forming apparatus which has a penetration part which is formed in the shape of a sheet with an insulating material, and penetrates in the thickness direction. The grounding current path includes a current path from the metal bottom plate of the paper feed cassette to the metal main body frame,
The current suppression member is sandwiched between a first metal member and a second metal member constituting the grounding current path, and is provided so as to contact both the first metal member and the second metal member. And
The image forming apparatus according to claim 1, wherein the first metal member and the second metal member are opposed to each other with a predetermined interval through the through portion.   The image forming apparatus according to claim 2, wherein the first metal member is an elastic member provided in the paper feed cassette or the main body frame. The elastic member is fixed by a fastening member fastened to a rotation fulcrum portion of the bottom plate,
The image forming apparatus according to claim 3, wherein the fastening member is provided to be rotatable with respect to a through hole formed in the paper feed cassette. The elastic member is a coil spring,
5. The image forming apparatus according to claim 3, wherein the penetrating portion includes a plurality of long holes extending in parallel to a radial direction of the coil spring. The elastic member is a coil spring,
5. The image forming apparatus according to claim 3, wherein the penetrating portion includes a plurality of long holes extending radially from a position corresponding to a central portion of the coil spring. The elastic member is a coil spring,
The image forming apparatus according to claim 3, wherein the penetrating portion includes a plurality of holes that are randomly arranged with respect to the current suppressing member. The elastic member is a coil spring,
5. The image forming apparatus according to claim 3, wherein the penetrating portion includes a plurality of holes arranged along a distal end portion of the coil spring.   9. The length or area of the portion where the elastic member contacts the current suppressing member is greater than the length or area of the portion where the elastic member faces the penetrating portion. Image forming apparatus. The grounding current path includes a current path from a metal guide member provided on the upstream side in the sheet conveyance direction of the fixing unit for fixing the toner image on the sheet to the metal main body frame,
The image forming apparatus according to claim 1, wherein the current suppressing member is provided on a guide surface that guides the sheet of the guide member.   The image forming apparatus according to claim 10, wherein the current suppressing member includes a protruding portion that protrudes from the guide member toward the fixing portion and has flexibility.   The image forming apparatus according to claim 10, wherein the penetrating portion includes a plurality of long holes extending along the paper conveyance direction. A current suppressing member provided in a grounding current path for suppressing charging of a metal member included in the image forming apparatus,
A current suppressing member that is formed in a sheet shape by an insulating material and has a through portion that penetrates in a thickness direction.

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