JP2005298181A - Image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device, in which transfer paper that is relatively hard is usable without vibrating or generating transfer defective even when it springs up at a rear end at the instant it passes a carrying roller (resist roller). <P>SOLUTION: This image forming device comprises a transfer part 44 where a toner image on an image carrier 1 is transferred to the transfer paper P, a the carrying roller 55 to feed the transfer paper to the transfer part, a first carrying guide 58 provided on the transfer part side between the carrying roller and the transfer part, and a second carrying guide 59 disposed to face the first carrying guide 58. It is composed in such a way as to set the minimum value θ' as 21° or less with a displacement angle θ formed by a first line m connecting a contact point D on the transfer part side to the transfer paper with a tip part of the first carrying guide 58 to a nip point B of the carrying roller and a second line n connecting a contact point A of the image carrier with the transfer paper in the transfer part to a desired point C on a guide surface of the second carrying guide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus of a type that transfers a toner image on an image carrier onto a transfer sheet, and more particularly to an image forming apparatus that can prevent transfer failure.

  A conventional electrophotographic image forming apparatus forms an image on a recording medium such as transfer paper as follows. First, the surface of an image carrier such as a photoconductor is charged, and a laser beam is scanned on the charged surface to form an electrostatic latent image. Next, toner is attached to the electrostatic latent image with a developing device to form a toner image. This toner image is transferred onto the transfer paper at the transfer portion. Since the toner image on the transfer paper is not fixed on the transfer paper, the toner image is heated by a fixing device to melt the toner, and the melted toner is pressurized and fixed on the transfer paper. Thereafter, the transfer paper is discharged out of the apparatus, but the toner is cooled and solidified after it leaves the fixing device and is discharged out of the apparatus.

  As described above, the toner image on the image carrier is transferred onto the transfer paper, but when transferring, the transfer paper is adjusted in posture so that the toner image is transferred to a predetermined position on the transfer paper. Together, it is supplied to the transfer section. This supply is performed by a conveyance roller called a registration roller.

  The conveyance path of the transfer paper from the conveyance roller to the transfer unit is curved rather than linear due to restrictions on the structure of the apparatus. In other words, the direction of feeding by the transport roller does not match the direction of entering the transfer section, and the transfer paper is curved and transported. Further, guide members for guiding the transport direction are provided in the transport path, but the transport path defined by these guide members is considerably widened. Therefore, when the transfer paper fed from the upstream conveyance roller enters the transfer section, the trailing edge of the transfer paper becomes free at the moment when the trailing edge of the transfer paper passes the nip point of the conveyance roller, Due to elasticity, it jumps in a straight direction from the curved state in the transport path and hits the transport guide. The state of jumping up so as to hit the conveyance guide in this way is called repellency. However, when the trailing edge of the transfer paper hits the conveyance guide, the transfer paper vibrates, causing transfer deviation or transfer failure.

  Patent Document 1 (Japanese Utility Model Laid-Open No. 58-69848) discloses that the position of a guide can be changed depending on the strength of the transfer paper when the transfer paper is fed from a conveying roller such as a registration roller to the transfer portion. Are known. This is because one or both of the conveyance guides provided on both sides of the transfer paper conveyance path between the conveyance roller and the transfer unit is supported by an elastic member, and the shape of the conveyance path can be changed by the strength of the waist of the transfer paper. It is what I did.

Further, there is Patent Document 2 (Japanese Patent No. 3386235) that eliminates the influence of repelling caused by the trailing edge of the transfer paper. In this case, a transfer guide member formed by bending a thermoplastic film is attached to the front end of the conveyance guide, and when the rear end of the transfer paper is flipped up, the transfer guide member can absorb the impact.
Japanese Utility Model Publication No. 58-69848 FIGS. 2 to 5 Japanese Patent No. 3386235 FIG.

  However, Patent Document 1 does not describe or suggest any repelling at the moment when the trailing edge of the transfer paper passes through the nip point of the conveyance roller. In Patent Document 2, it is difficult to prevent the transfer guide member from contacting the image carrier.

  The present invention has been conceived from the above facts, and when the transfer paper having a strong stiffness is used, even if the rear end of the transfer paper jumps up at the moment when it passes the transport roller, the transfer paper moves due to vibration or the like. Therefore, an object of the present invention is to provide an image forming apparatus that does not cause transfer defects.

  In order to achieve the above object, an image forming apparatus according to claim 1 of the present application includes a transfer unit that transfers a toner image on an image carrier to transfer paper, a conveyance roller that feeds the transfer paper to the transfer unit, In an image forming apparatus, comprising: a first conveyance guide provided on a transfer portion side of a conveyance path between the conveyance roller and the transfer portion; and a second conveyance guide disposed to face the first conveyance guide. , A first line connecting a contact point with the transfer paper at the front end portion of the first conveyance guide on the transfer unit side and a nip point of the conveyance roller, a contact point between the image carrier and the transfer sheet in the transfer unit, and the second line. The minimum value of the displacement angle formed by the second line connecting to an arbitrary point on the guide surface of the transport guide is set to 21 ° or less.

  The image forming apparatus according to claim 2 of the present application is characterized in that the minimum value of the displacement angle is an end portion of the guide surface on the conveying roller side.

  The image forming apparatus according to claim 3 of the present application is characterized in that the displacement angle increases as the second line moves away from the conveying roller on the guide surface.

  The image forming apparatus according to claim 4 of the present application is characterized in that the guide surface is a curved surface.

  The image forming apparatus according to claim 5 of the present application is characterized in that the conveyance guide is made of an elastic sheet, and a surface of the elastic sheet is the guide surface.

  In the image forming apparatus according to claim 6 of the present application, the conveyance guide has a configuration in which an elastic sheet is stacked on a rigid member, and the elastic sheet is attached to the rigid member at an end portion on the conveyance roller side of the conveyance guide. In the cantilever structure, the other side is a free end floating from the hard member, and the guide surface is the surface of the elastic sheet.

  In the image forming apparatus according to claim 7 of the present application, an angle formed by a tangent line of the image carrier drawn on a contact point between the image carrier and the transfer paper in the transfer unit and the first line is defined as an entrance angle. The approach angle is 40 ° or more.

  According to the first aspect of the present invention, at the moment when the trailing edge of the transfer sheet is fed out from the nip point of the conveying roller toward the transfer section, the trailing edge of the transfer sheet jumps up strongly if the transfer sheet is stiff. Although it collides with the conveyance guide, the displacement angle at which the trailing edge of the transfer paper jumps up is set to 21 ° or less, so that the impact at the time of jumping is reduced, the vibration of the transfer paper is reduced, and transfer defects do not occur. Has an effect.

  According to the second aspect, since the minimum value of the displacement angle is at the conveyance roller side end portion of the guide surface, the rear end of the transfer paper that has left the nip point is sequentially transferred from the conveyance roller side end portion of the guide surface. It is possible to slide on the guide surface toward the side end, and vibration can be reliably suppressed.

  According to the third aspect, the displacement angle increases as the trailing edge of the transfer sheet slides on the guide surface sequentially from the conveyance roller side end of the guide surface toward the transfer portion side end. Therefore, the jumping up of the trailing edge of the transfer paper when passing through the guide surface is reduced, and the vibration applied to the transfer paper is reduced, thereby preventing transfer deviation.

  According to claim 4, when the rear end of the transfer paper slides on the guide surface sequentially from the end of the guide surface toward the transfer roller side, the guide surface is a curved surface. It becomes easy to take a large displacement angle when the rear end passes through the guide surface.

  According to the fifth aspect, since the conveyance guide is made of an elastic sheet, it is possible to effectively suppress the vibration of the transfer paper edge by the elastic sheet.

  According to the sixth aspect, since the elastic sheet is deformed only until it hits a hard member, the deformation is reduced even if the elastic sheet is used for a long period of time.

  According to the seventh aspect of the present invention, the present invention is particularly effective for an image forming apparatus having an approach angle of 40 ° or more.

  Hereinafter, an optimum embodiment of the fixing device according to the present invention will be described with reference to the drawings. However, the present invention is not limited to this embodiment. FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus 10 according to the present invention.

  The image forming apparatus 10 is an example of a digital copying machine having a re-conveying means for automatic duplex copying. The apparatus main body is provided with an image processing unit 2, an image writing unit (exposure device 42), an image forming unit 4, a cassette paper feeding unit 5, a fixing device 6, and a paper discharge unit 7. 20 and an image reading unit 30 are mounted.

  A document (not shown) is placed on the document table 21 of the document transport unit 20 with the copy surface facing upward, and is sent to the transport path by the unloading unit pickup roller 25 of the automatic document reverse transport device 22. A document conveyance unit registration roller 26 is disposed at the final end of the conveyance path, and rotates in synchronization with the scanning timing of the image reading unit 30 to pass over the slit glass 27.

  The image reading unit 30 includes a light source L that irradiates an original through a slit glass 27 and a scanning unit 31 that includes a mirror, two mirrors 32 that guide reflected light, a lens 33, and an imaging element 34 such as a CCD.

  When the original passes through the slit glass 27 disposed on the upper part of the image reading unit 30, the original is read by the scanning unit 31 and imaged on the image sensor 34 through the two mirrors 32 and the lens 33. Image information of the read original is processed by the image processing unit 2, and digitized image information data is temporarily stored in a memory provided in the image processing unit 2.

  The image forming unit 4 includes an image carrier 1 made of a photoconductor on which a latent image is formed. The surface of the image carrier 1 is almost aligned with the outer peripheral surface of the image carrier 1 in the order of operation. A charging device 41 that uniformly charges, an exposure device 42 that writes an electrostatic latent image on the surface of the photoreceptor, and a toner image that is transferred to the latent image formed on the surface of the image carrier 1 to form a toner image Developing device 43, transfer unit 44 for transferring the toner image on the surface of the photoreceptor to transfer paper P, separation unit 46 for separating transfer paper P from image carrier 1 after transfer, and surface of image carrier 1 after transfer A cleaning device 45 is disposed for cleaning.

  On the other hand, the paper feed cassette 51 that accommodates the transfer paper P is provided with a movable plate 52 whose free end is always urged upward by an urging means such as a leaf spring, and the transfer paper placed thereon. The uppermost one of P is configured to contact the pickup roller 53. The transfer paper P in contact with the pickup roller 53 is discharged from the paper feed cassette 51 and separated one by one by a separation roller 53A, and then guided to a plurality of intermediate rollers 54 and conveyed to a conveyance roller 55 comprising registration rollers. The

  The transfer paper P is transported to the transfer unit 44 at a paper feed timing by the transport roller 55, and the toner images formed on the image carrier 1 are collectively transferred onto the transfer paper P in the transfer unit 44. The transfer paper P onto which the toner image has been transferred is separated from the image carrier 1 by the separation unit 46 and conveyed to the fixing device 6. The toner image on the transfer paper P is fixed by fixing rollers 61 and 62 of the fixing device 6. The fixed transfer paper P is nipped by a paper discharge roller 71 and discharged outside the apparatus, and is placed on a paper discharge table 72.

  2 is an enlarged view of the periphery of the image carrier 1 and the transport roller 55 in FIG. 1, and FIG. 3 is an enlarged view of the periphery of the transport roller 55. The conveyance roller 55 includes a conveyance roller 55a on the left side and a conveyance roller 55b on the right side of the drawing, and a conveyance path between the conveyance roller 55 and the transfer unit 44 includes a first conveyance guide 58 on the transfer unit 44 side, A second conveyance guide 59 is provided opposite to the second conveyance guide 59. These conveyance guides 58 and 59 are made of a hard material such as plastic or metal.

  The second conveyance guide 59 is integrally provided at the tip of a semicircular cover 56 that covers half of one conveyance roller 55a. On the other end side of the cover 56, a guide 57 that defines a conveyance path between the upstream side intermediate roller 54 and the upstream intermediate roller 54 is integrally provided. The guide surface 59a of the second transport guide 59 is shifted to the right side of the figure as compared with the conventional one, and is a curved surface such as an arc surface.

  The point at which the transfer paper P contacts the image carrier 1 in the transfer unit 44 is A, the nip point of the transport roller 55 is B, and any point on the guide surface 59a of the second transport guide 59 is C. A point where the transfer paper P at the tip of the guide 58 is pressed is defined as D. A point O indicates the center of the image carrier 1. A line connecting the point D and the point B is a first line m, a line connecting the point A and the point C is a second line n, and the first line m and the second line n are formed. The angle is defined as the displacement angle θ. The tangent line at the nip point B of the transport roller 55 is directed to the first transport guide 58, and the angle formed by the first line m is 4.7 °.

  When the rear end of the transfer paper P passes through the nip point B of the transport roller 55, if the back of the transfer paper P is strong, the rear end of the transfer paper P jumps up toward the second transport guide 59 to return straight. . This is received by the guide surface 59a, but the angle to be raised is limited to the minimum value θ ′ of θ. The minimum value of the displacement angle θ may be anywhere on the guide surface 59a, but in the embodiment shown in the figure, the minimum value θ ′ is obtained when the second line is n ′ at the point C ′ at the end of the guide surface 59a on the conveying roller 55 side. It is trying to become.

  The inventor examined various values of the minimum value θ ′ of the displacement angle θ, but it was found that when the minimum value is 21 ° or less, the occurrence of transfer deviation is eliminated. At that time, the minimum value was set at the point C ′ at the end of the guide surface 59a on the side of the conveying roller 55, but the distance between the point C ′ and the first line m was 3 mm. In addition, the guide surface 59a at the point C 'is set to be substantially parallel to the first line m.

  That is, at this angle or distance, even if the transfer paper P is stiff and the rear end of the transfer paper jumps up when passing the point B, the rear end of the transfer paper P is displaced by only 21 °. The impact received by the transfer paper P is reduced, and transfer deviation and transfer failure can be prevented. In addition, since the guide surface 59a at the point C 'and the first line m are substantially parallel, the end portion of the transfer paper P is not bent by being flipped up.

  Next, a tangent line of the image carrier 1 at point A is defined as t, and an angle formed by the tangent line t and the first line m is defined as an approach angle α. In this example, the approach angle α was 40 °. In the image forming apparatus having a small entry angle α, the angle at which the trailing edge of the transfer paper P is flipped up is small, so that problems such as transfer misalignment are relatively small. On the other hand, in the image forming apparatus in which the entrance angle α exceeds 40 °, the effect of preventing transfer deviation and transfer failure according to the present invention becomes remarkable.

  The guide surface 59a in the embodiment of FIG. 3 has an arc shape. The guide surface 59a may be a flat surface. However, depending on the shape and installation position of the guide surface 59a, when the transfer paper P passes through the guide surface 59a of the second transport guide 59, the rear end of the transfer paper P may jump up here to cause transfer displacement. . Therefore, when the guide surface 59a is a curved surface such as an arc shape, the displacement angle θ increases as the guide surface 59a approaches the leading end of the guide surface 59a. As a result, the impact applied to the transfer paper P can be reduced to prevent transfer misalignment.

  FIG. 4 is a diagram showing the main part of the second embodiment of the present invention. In this embodiment, an additional guide 59b is attached to a conventional second conveyance guide 59. The additional guide 59b may be the same material as the second transport guide 59 or a different material. The second transport guide 59 can be moved in the right direction in the figure by the thickness of the additional guide 59b, whereby the minimum value of the displacement angle θ can be made 21 ° or less.

  FIG. 5 is a diagram showing the main part of the third embodiment of the present invention. In this embodiment, an elastic sheet 59 d is attached to the second conveyance guide 59. The elastic sheet 59d is a thin plate made of metal or synthetic resin, and in this example, a PET sheet having a thickness of 0.1 mm was used. The elastic sheet 59d is fixed to one end of a hard member such as the second conveyance guide 59 with an adhesive or the like with a spacer 59c interposed therebetween, and has a cantilever structure. In the illustrated embodiment, the spacer 59c is provided at the end of the second transport guide 59 on the side of the transport roller 55, but is not limited to this position. If the cantilever structure is used as in the illustrated embodiment, the elastic sheet 59d can be elastically displaced toward the leading end, so that it is easy to absorb the impact of the trailing edge of the transfer paper P.

  In the embodiment of FIG. 5, the elastic sheet 59d is attached in a state of being close to the second conveyance guide 59 that is a hard member. Therefore, the elastic displacement of the elastic sheet 59d is limited to the position where it is in close contact with the second conveyance guide 59, and further elastic displacement is limited. With such a configuration, the amount of displacement of the elastic sheet 59d can be limited, so that contact with the image carrier 1 can be prevented, and the elastic sheet 59d can be prevented from being sagted or deformed.

  The elastic sheet 59d does not necessarily have to be lifted as a cantilever on the second conveyance guide 59 so as to be close to each other. The second conveyance guide 59 may be eliminated, and the elastic sheet 59d may be cantilevered at the tip of the cover 56. In this case, the trailing edge of the transfer paper P is bounced only by the elastic sheet 59d, and therefore, a material that is not easily bent and has an appropriate strength is selected.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to the present invention. FIG. 2 is an enlarged view of a periphery of an image carrier and a conveyance roller in FIG. 1. It is the figure which expanded the periphery of a conveyance roller. It is a figure which shows the principal part of 2nd Example of this invention. It is a figure which shows the principal part of 3rd Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image carrier 44 Transfer part 55 Conveyance roller 58 1st conveyance guide 59 2nd conveyance guide 59a Guide surface 59d Elastic sheet A Contact point B of image carrier and transfer paper Nip point C of conveyance roller Arbitrary point C on guide surface 'Conveyance roller side end D of guide surface Contact point with transfer paper at first conveyance guide tip m First line n Second line α Entrance angle θ Displacement angle

Claims (7)

A transfer unit that transfers the toner image on the image carrier onto transfer paper, a conveyance roller that feeds the transfer paper to the transfer unit, and a transfer unit side of the conveyance path between the conveyance roller and the transfer unit. In an image forming apparatus having a first conveyance guide and a second conveyance guide disposed to face the first conveyance guide,
A first line connecting a contact point between the transfer sheet and the transfer sheet at the front end of the first transfer guide on the transfer unit side, and a nip point of the transfer roller; a contact point between the image carrier and the transfer sheet in the transfer unit; An image forming apparatus characterized in that a minimum value of a displacement angle formed by a second line connecting an arbitrary point on the guide surface of the guide is set to 21 ° or less.   The image forming apparatus according to claim 1, wherein the minimum value of the displacement angle is an end portion of the guide surface on the side of the conveyance roller.   3. The image forming apparatus according to claim 1, wherein the displacement angle is increased as the second line moves away from the conveying roller on the guide surface.   The image forming apparatus according to claim 1, wherein the guide surface is a curved surface.   The image forming apparatus according to claim 1, wherein the conveyance guide is made of an elastic sheet, and a surface of the elastic sheet is the guide surface.   The conveyance guide has a configuration in which an elastic sheet is stacked on a rigid member, and the elastic sheet is attached to the rigid member at the conveyance roller side end of the conveyance guide, and the other side is a free end floating from the rigid member. 6. The image forming apparatus according to claim 1, wherein the guide surface is a surface of the elastic sheet in a cantilever structure.   When the angle formed by the first line and the tangent line of the image carrier drawn on the contact point between the image carrier and the transfer paper in the transfer portion is the entrance angle, the entrance angle is 40 ° or more. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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