JP2007272015A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely avoid transfer slippage arising in accordance with a timing when the leading end of a paper enters a fixing part by introducing not a fixed system, but a movable system to a transfer belt related to an apparatus, then, making a distance between a transfer area and a fixation nip variable in accordance with the type of a conveyed sheet and printing demand contents, etc. <P>SOLUTION: Bridge rollers 54 and 56 are separately attached to respective arm pieces 62 and 63 as the leading end side parts of a support body 60 having a base end part 61 that is positioned on the upstream side in a paper conveying direction (left side in Fig.) and that is rotatably supported by a support shaft 68. By vertically oscillating the support body 60 by taking the support shaft 68 as a center (by oscillating in a direction shown by a symbol R in Fig.3), a distance L1 between the bridge roller 54 attached to the upper arm piece 62 and the transfer position 14a of the photoreceptor drum 14 is changed, and thereby, the paper conveying distance between the fixation nip part N of a fixing unit 20 and the transfer position 14a of the photoreceptor drum 14 is changed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is an endless transfer belt disposed opposite to the photoconductor, a transfer unit in which a plurality of bridging rollers for bridging the transfer belt are disposed, and the transfer unit disposed on the downstream side in the sheet conveyance direction, The present invention relates to an image forming apparatus including a paper guide for guiding a conveyance sheet to a fixing nip portion of a fixing unit.

  In recent years, the image forming apparatus pursues compactness of the apparatus, and a fixing nip portion which is a pressure contact portion between a transfer region for transferring a developer image on an electrostatic latent image carrier (photosensitive member) onto a sheet and a fixing roller. And the distance is shortened. For this reason, when the leading edge of the conveyance sheet enters the fixing nip, the trailing edge of the sheet is often still in the transfer process.

  In such a state, an impact when the leading edge of the sheet enters the fixing nip portion affects the trailing edge of the sheet, which is a cause of occurrence of “transfer blur”.

  Therefore, techniques for avoiding such transfer blur have been conventionally proposed (see, for example, Patent Documents 1 and 2).

  In the image forming apparatus described in Patent Document 1, a transfer material (recording paper) is spread over each member by providing a speed difference in the transfer material conveyance speed between the upstream fixing device and the downstream timing roller. It is configured to avoid being pulled when being conveyed.

In addition, when the image forming apparatus described in Patent Document 2 drives each device in the image forming apparatus with one driving source, a driving force transmission path from the driving source is used as a carrier (photosensitive member) driving system, The developing unit driving system and the transfer material fixing / conveying unit driving system are divided into three types, and these three types of driving systems are separately divided from the position of the output shaft of the driving source.
JP 2003-150019 A JP-A-2-306256

  Each of the above-mentioned patent documents 1 and 2 is devised so that the impact when the leading edge of the sheet enters the fixing nip portion does not affect the trailing edge of the sheet by controlling the conveying speed of the conveying sheet. However, it is mechanically complex to individually control the sheet conveyance speed. In order to avoid an impact, if the transfer speed at the trailing edge of the paper in the transfer process is controlled to be slightly higher than the pull-in speed at the leading edge of the paper in the fixing process, the interval between the fixing process and the transfer process is reduced. Therefore, there is a possibility that a new problem will occur such that the paper is bent and this may cause a jam or the like. For this reason, it is extremely difficult to finely adjust the sheet conveyance speed so as not to cause such a problem. In other words, it is difficult to reliably avoid the transfer deviation at the rear end of the sheet only by fine adjustment of the sheet conveyance speed. Therefore, there has been a demand for a more reliable method in which the impact when the leading edge of the paper enters the fixing nip does not affect the transfer process of the trailing edge of the paper.

  The present invention has been developed in view of such circumstances, and its purpose is to focus on a transfer belt of a transfer unit arranged as a transfer mechanism, and the transfer belt is transported to a device instead of a fixed method. An image forming apparatus that can reliably avoid transfer blur that occurs at the timing when the leading edge of the paper enters the fixing portion by changing the distance between the transfer region and the fixing nip according to the paper size to be printed, the print request content, etc. Is to provide.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes an endless transfer belt disposed to face a photoreceptor, a transfer unit in which a plurality of crosslinking rollers that bridge the transfer belt are disposed, and the transfer unit. The image forming apparatus includes a paper guide that is disposed downstream of the unit in the paper conveyance direction and guides the conveyance paper to the fixing nip portion of the fixing unit. The bridging roller further includes control means for controlling the swinging motion of the bridging roller, and the control means changes the distance from the transfer position of the photoconductor to the paper guide in accordance with the print request contents. Is controlled to swing.

  Specifically, in the plurality of bridging rollers, a distal end side of a support body whose base end portion is rotatably supported by a support shaft is branched into bifurcated arm pieces, and a bridging roller is provided at each distal end portion of each arm piece. Is attached. The bridging roller swings up and down by swinging the support up and down around the support shaft. The support is disposed downstream in the transport direction from the transfer position of the photoconductor, and is disposed so that the tip of the support is downstream in the paper transport direction with respect to the support shaft. ing.

  In this case, if the relationship between the transfer position of the photoconductor, the position of the support shaft, and the position of the bridging roller attached to the front end of the support is appropriately set, the front end can be swung up and down. The distance between the bridging roller attached to the portion and the transfer position of the photosensitive member can be changed. Specifically, the transfer position of the photoconductor, the position of the support shaft, and the support body are set such that the distance between the bridge roller and the transfer position of the photoconductor is increased by swinging the support body downward. The relationship with the position of the bridging roller attached to the front end of is set.

  In this case, one arm piece is provided so as to be extendable and contracted, and is configured to be constantly urged in an extension direction by an elastic body provided therein. Thereby, since the tension of the transfer belt is kept constant, it is possible to maintain good transfer at the transfer position of the photosensitive member even if the bridging roller swings.

  On the other hand, the paper guide has its front end downstream in the paper conveyance direction fixed to a shaft so as to be rotatable in the vicinity of the fixing nip portion, and the rear end on the upstream side in the paper conveyance direction is held so as to swing up and down. Specifically, the rear end portion of the paper guide is in contact with the peripheral surface of the fixed eccentric cam, and the paper guide can be swung up and down by rotating the eccentric cam.

  In this case, the control means controls the swing operation of the paper guide in conjunction with the swing operation of the bridging roller. By interlocking, the position of the paper guide and the position of the transfer belt supported by the bridging roller are kept constant, so that the transfer paper is smoothly transferred from the transfer belt to the paper guide.

  Further, the paper guide may be provided so as to be extendable and contractable in the paper transport direction in accordance with the swinging operation. When both the bridging roller and the paper guide are swung downward, the gap between the transfer belt supported by the bridging roller and the paper guide may be increased, but by making the paper guide extendable, This gap can be made small (or almost constant). As a result, it is possible to prevent such a problem that the leading end portion of the transport sheet enters between the transfer belt and the paper guide.

  Here, the control means controls the swinging motion of the bridging roller and the paper guide based on the paper length selected by the print request and the print processing conditions on the paper. Specifically, when the leading edge of the transport paper enters the fixing nip portion, the bridging roller and the paper guide are swung so that the transfer area of the transport paper is not located at the transfer position of the photosensitive member. The distance from the portion to the transfer position of the photoconductor is changed.

  That is, even if the leading edge of the paper enters the fixing nip portion and an impact occurs, if the image information is not transferred onto the paper by the photosensitive member at that time (that is, if it is not the paper transfer area), Even if the trailing edge of the sheet is still in the transfer process, transfer deviation does not occur. The present invention pays attention to this point, constructs a mechanism structure that changes the sheet conveyance distance from the fixing nip portion to the transfer position of the photosensitive member, the timing at which the leading edge of the conveyance sheet enters the fixing nip portion, and the transfer By properly shifting the transfer timing in the process, it is possible to reliably prevent the occurrence of transfer deviation at the rear end of the sheet.

  The image forming apparatus according to the present invention constructs a mechanism structure that changes the sheet conveyance distance from the fixing nip portion to the transfer position of the photosensitive member, the timing at which the leading edge of the conveyance sheet enters the fixing nip portion, and the transfer in the transfer process. Since the timing is configured to be well shifted by changing the paper conveyance distance, it is possible to reliably prevent the occurrence of transfer deviation at the rear end of the paper.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a side view showing the overall configuration of the image forming apparatus according to the present embodiment.

  The image forming apparatus 1 of the present embodiment is a digital image forming apparatus having copy, printer, scanner, and fax modes, for example, and an operation panel 10 is provided on the front side.

  On the upper surface of the image forming apparatus 1, a manuscript table 11 made of a hard transparent glass body is arranged, an automatic manuscript feeder 12 is arranged above the manuscript table 11, and an optical unit 13 is arranged below the manuscript table 11. .

  Below the optical unit 13, a photosensitive drum 14 whose surface is made of a photoconductive material is rotatably supported. Around the photosensitive drum 14, a charger 15, a developing device 16, a transfer unit 17, and a cleaner 18 are disposed so as to face the peripheral surface of the photosensitive drum 14.

  In the image forming apparatus 1 configured as described above, when the start of the image forming process is instructed by operating the operation panel 10, the optical unit 13 scans the image surface of the document placed on the document table 11, and the inside of the optical unit 13 The light reflected from the copy lamp on the original image surface is irradiated onto the surface of the photosensitive drum 14.

  Prior to the irradiation of the reflected light from the original, the surface of the photosensitive drum 14 is uniformly charged with a single polarity charge by the charger 15, and the photoconductor is caused by the photoconductive action caused by the irradiation of the reflected light from the original. An electrostatic latent image is formed on the surface of the drum 14. Toner is supplied from the developing device 16 to the surface of the photosensitive drum 14 on which the electrostatic latent image is formed, and the electrostatic latent image is visualized as a developer image.

  A fixing unit 20 including a heating roller and a pressure roller is disposed on the downstream side of the photosensitive drum 14. A transfer belt 50 and a paper guide 19 of the transfer unit 17 are disposed between the fixing unit 20 and the photosensitive drum 14. The transfer belt 50 and the paper guide 19 allow the transfer belt 50 and the paper guide 19 to move from the photosensitive drum 14. A sheet conveyance path to the fixing unit 20 is formed.

  A sheet discharge tray 33 is provided on the side surface of the image forming apparatus 1, and a sheet discharge conveyance path 22 is formed between the fixing unit 20 and the sheet discharge tray 33. A part of the paper discharge conveyance path 22 branches through a branch gate 25 into a re-conveyance path 24 that is continuous with an automatic double-sided paper feeder 23 disposed below the photosensitive drum 14.

  Below the image forming apparatus 1, four paper feed cassettes 26 that are detachably mounted from the front side of the image forming apparatus 1 are provided. Each paper feed cassette 26 stores recording papers of different sizes, and the recording paper from one of the four paper feed cassettes 26 feeds the paper feed roller 27 prior to the rotation of the photosensitive drum 14. Is fed through. The fed recording paper is conveyed in the direction of the photosensitive drum 14 by the conveyance roller 29 via the common conveyance path 28, and the front end is brought into contact with the registration roller 30 and stopped.

  The registration roller 30 rotates in synchronization with the rotation of the photosensitive drum 14 and guides the recording sheet to an image forming area between the photosensitive drum 14 and the transfer unit 17. The recording paper guided to the image forming area is subjected to corona discharge from the transfer unit 17, and the developer image carried on the surface of the photosensitive drum 1 is transferred to the surface of the recording paper.

  The recording sheet on which the developer image has been transferred is transported to the fixing unit 20 along the transfer belt 50 and the paper guide 19, and is heated and pressurized in the fixing unit 20, and the developer image is melted on the surface of the recording sheet. To settle.

  In the single-sided copying mode in which an image is copied on one side of a recording sheet, the recording sheet that has passed through the fixing unit 20 is discharged from a discharge port 32 onto a discharge tray 33 by a discharge roller 31 via a discharge conveyance path 22. The

  In the double-sided copying mode in which images are copied on both sides of the recording paper, the branch gate 25 is exposed in a part of the paper discharge conveyance path 22, and the recording paper that has passed through the fixing unit 20 is re-conveyance path 24 provided with a conveyance roller 34. To the automatic duplex paper feeder 23. The recording paper transported to the automatic double-sided paper feeder 23 is fed in a state where the front and back are reversed by a refeed roller 35, and the front and back surfaces are reversed by a retransport roller 36 via a common transport path 28. It is again conveyed in the direction of the photosensitive drum 14.

  Next, the configuration of the control system of the image forming apparatus 1 will be described with reference to the block diagram shown in FIG.

  The central processing unit (control unit) 101 manages each drive mechanism unit constituting the image forming apparatus 1 such as the automatic document feeder 12, the optical unit 13, the image forming unit 102, and the recording paper conveyance system 103 by sequence control. At the same time, a control signal is output to each unit.

  An operation panel 10 is connected to the control unit 101 in a state where mutual communication is possible, and the operation of the operation panel 10 causes the image forming apparatus 1 to operate in accordance with print processing conditions set and input by the user. Yes.

  In addition, a memory 104 and an image data communication unit 105 are connected to the control unit 101. The memory 104 stores various control information necessary for controlling each drive mechanism unit constituting the image forming apparatus 1. The image data communication unit 105 is a communication unit provided for enabling information communication of image information and image control signals with other digital image devices.

  The control unit 101 performs print processing control according to print processing conditions input and set by the user by operating the operation panel 10. At this time, the transfer unit 50 and the paper of the transfer unit 17 are connected via the recording paper transport system 103. By swinging and controlling the guide 19, the sheet conveyance distance from the transfer position of the photosensitive drum 14 to the fixing nip portion of the fixing unit 20 is changed according to the printing processing conditions.

  FIG. 3 is a side view showing a more detailed structure of the transfer unit 17 and the paper guide 19.

  The transfer unit 17 includes an endless transfer belt 50. The transfer belt 50 includes a drive roller 51 disposed in the vicinity of the registration roller 30 side, a transfer roller 52 disposed opposite to the photosensitive drum 14, The tension roller 53 and the bridging rollers 54 and 55 are rotatably supported.

  The bridging rollers 54 and 55 are attached to the distal end side (downstream side in the paper conveyance direction) of the support body 60, the base end portion 61 which is upstream in the paper conveyance direction (right side in the drawing) supported rotatably by the support shaft 68. ing. That is, the front end side of the support body 60 is branched into bifurcated arm pieces 62 and 63, and bridging rollers 54 and 55 are rotatably attached to the front end portions of the arm pieces 62 and 63, respectively. Then, the bridging rollers 54 and 55 are configured to swing up and down by swinging the support 60 up and down around the support shaft 68 (swing in the direction R in FIG. 3). As can be seen from FIG. 3, the support 60 is disposed downstream in the transport direction from the transfer position 14 a of the photosensitive drum 14 (position where the transfer roller 52 faces), and with respect to the support shaft 68. Thus, the support member 60 is disposed so that the front end portion is on the downstream side in the sheet conveyance direction.

  In this case, if the relationship between the transfer position 14a of the photosensitive drum 14, the position of the support shaft 68, and the positions of the bridging rollers 54 and 55 attached to the front end of the support 60 is appropriately set, the support 60 is By swinging up and down, the distance L1 between the bridging roller 54 attached to the upper arm piece 62 and the transfer position 14a of the photosensitive drum 14 can be changed. In the present embodiment, the upper bridge roller 54 and the photosensitive drum are moved by swinging the support body 60 upward (R1 direction) from the home position position shown in FIG. 4A (see FIG. 4B). 14, the distance between the transfer position 14a and the transfer position 14a is short (L1-α), and the support 60 is swung downward (in the direction R2) (see FIG. 5C), so that the upper cross-linking roller 54 and the photosensitive member are exposed to light. It is attached to the transfer position 14a of the photosensitive drum 14, the position of the support shaft 68, and the arm pieces 62 and 63 of the support 60 so that the distance from the transfer position 14a of the body drum 14 is long (L1 + α). The relationship with the positions of the bridging rollers 54 and 55 is set.

  Here, in the present embodiment, the lower arm piece 63 has a stretchable structure. That is, as shown in a partial cross section in FIG. 4A, the arm piece 63 includes a cylindrical holding rod 63a formed integrally with the support 60, and a sliding portion 63b1 inserted into the holding rod 63a. It has a structure in which a coil spring 64 is inserted inside the holding rod 63a. As a result, the telescopic rod 63b to which the bridging roller 55 is attached is urged in a direction in which it is pushed into the holding rod 63a under the tension from the transfer belt 50. The repulsive force of the coil spring 64 against this urging force Since the expansion / contraction of the expansion / contraction bar 63b is adjusted, the transfer belt 50 is always maintained at a constant tension. That is, even if the shape viewed from the side surface of the transfer belt 50 changes due to the support 60 swinging up and down, the transfer belt 50 is always not affected by this change by adjusting the expansion and contraction of the expansion and contraction bar 63b. It will be kept at a certain tension.

  On the other hand, as shown in FIG. 3, the paper guide 19 includes a transport plate 91 and a support plate 92, and the transport plate 91 and the support plate 92 are formed in a substantially L shape in a side view. The leading end 91a of the transport plate 91 on the downstream side in the paper transport direction is rotatably fixed by the support shaft 71 in the vicinity of the fixing nip N of the fixing unit 20, and the support plate 92 on the upstream side in the paper transport direction. The lower end portion 92a is held so as to be vertically swingable. Specifically, the lower end 92a of the support plate 92 is in contact with the circumferential surface of an eccentric cam 77 rotatably supported by an apparatus frame (not shown), and the paper guide is rotated by rotating the eccentric cam 77. It is the structure which rocks 19 up and down. Note that the lower end portion 92 a of the support plate 92 is preferably formed in a slightly curved shape so as to easily contact the peripheral surface of the eccentric cam 77.

  The paper guide 19 can also be swung up and down as described above even when the shape of the transfer belt 50 is changed by the swinging operation of the bridging rollers 54 and 55, and is transported from the transfer belt 50 to the transport plate 91 of the paper guide 19. This is to smoothly transfer the paper. That is, the paper guide 19 is also swung up and down in accordance with the up and down swinging motion of the bridging rollers 54 and 55, so that the leading end of the transport paper is at the optimum position of the transport plate 91 (near the point P1 in FIG. This is to ensure that they are always in contact. Further, by swinging the paper guide 19 up and down in this way, the sheet conveyance distance L2 formed by the paper guide 19 is slightly changed, although not as much as the transfer belt 50. That is, as shown in FIG. 4, the paper conveyance distance formed by the paper guide 19 is shortened (L2-β) by swinging the paper guide 19 upward (in the S1 direction) (see FIG. 4B). Thus, the paper conveyance distance formed by the paper guide 19 is increased (L2 + β) by swinging the paper guide 19 downward (in the S2 direction) (see FIG. 4C).

  Therefore, the control unit 101 controls the swing operation of the paper guide 19 in conjunction with the swing operation of the bridging rollers 54 and 55.

  Here, control of the swinging operation of the bridging rollers 54 and 55 and the paper guide 19 by the control unit 101 will be described.

  Usually, the sheet conveyance distance (L1 + L2) from the transfer position 14a of the photosensitive drum 14 to the fixing nip portion N of the fixing unit 20 is almost equal to the sheet size of the A4 side when, for example, it is most frequently used in the A4 side. It is set together. That is, when the leading edge of the A4 side transport sheet enters the fixing nip N of the fixing unit 20, the rear end of the transport sheet is just passing through the transfer position 14a of the photosensitive drum 14, and The transcription is already over. Therefore, even if the leading end of the transport sheet collides with the fixing nip N and a slight impact is applied to the sheet, and the impact affects the trailing end of the sheet, the developer image on the surface of the photosensitive drum 1 is recorded on the recording sheet. There is no problem in the transcription of

  Here, consider a case where the user sets the paper as A4 and the printing direction as one of the print processing conditions. As shown in FIG. 5A, there is a difference in distance T1 between the paper trailing edge E1 when the paper is A4 horizontal and the paper trailing edge E2 when the paper is A4 vertical. In other words, when printing is performed in A4 portrait, when the leading edge of the A4 portrait transport paper enters the fixing nip N of the fixing unit 20, the rear end E2 of the transport media is still at the transfer position of the photosensitive drum 14. It is in front of (upstream side) 14a, and is still in a state where transfer onto the conveyance sheet is still continuing. Therefore, in this state, when the leading edge of the transport sheet collides with the fixing nip N and a slight impact is applied to the sheet, and the impact affects the trailing edge of the sheet, the photosensitive drum 1 is still on the trailing edge of the sheet. Since the transfer of the developer image to the recording paper is continued, there is a possibility that transfer deviation occurs.

  Therefore, in this embodiment, when A4 portrait is set as the print processing condition, the control unit 101 determines the sheet conveyance distance from the transfer position 14a of the photosensitive drum 14 to the fixing nip N of the fixing unit 20 as a distance T1. Therefore, both the support 60 and the paper guide 19 are swung downward (R2 direction and S2 direction in FIG. 4C), and the upper bridging roller 54 and the transfer position 14a of the photosensitive drum 14 are moved. Is increased (L1 + α), and the paper conveyance distance of the paper guide 19 is increased (L2 + β). At this time, the swing angle is controlled so that α + β = T1.

  As a result, when the leading end of the A4 vertical transport paper enters the fixing nip N of the fixing unit 20, the rear end of the transport paper is just passing through the transfer position 14a of the photosensitive drum 14, and the transport paper is transferred to the transport paper. Transcription of is already over. Therefore, even if the leading end of the transport sheet collides with the fixing nip N and a slight impact is applied to the sheet, and the impact affects the trailing end of the sheet, no problem occurs in the transfer process.

  Next, consider a case where A4 portrait is set as the print processing condition and right binding is set. In this case, as shown in FIG. 5B, it is necessary to leave a margin portion 82 of about 20 mm as a binding margin on the right side of the sheet. That is, the blank portion 82 does not become the transfer area 81. In this case, in consideration of the margin portion 82, the distance difference between the rear end E1 of the sheet in the case of the A4 width and the rear end portion 81a of the transfer area 81 in the case of the A4 vertical bag binding with respect to the sheet conveyance direction is T2 ( T2 <T1). Therefore, when the A4 vertical bag binding is set as the print processing condition, the control unit 101 increases the sheet conveyance distance from the transfer position 14a of the photosensitive drum 14 to the fixing nip N of the fixing unit 20 by the distance T2. In order to achieve this, both the support 60 and the paper guide 19 are swung downward (R2 direction and S2 direction in FIG. 4C), so that the upper bridge roller 54 and the transfer position 14a of the photosensitive drum 14 are between. Is increased (L1 + α), and the paper conveyance distance of the paper guide 19 is increased (L2 + β). At this time, the swing angle is controlled so that α + β = T2.

  Thus, when the leading end of the A4 vertical transport sheet enters the fixing nip N of the fixing unit 20, the rear end of the transport sheet is still at the transfer position 14a of the photosensitive drum 14, but the transfer region 81 is It has just come off and the transfer to the transport paper has already been completed. Therefore, even if the leading end of the transport sheet collides with the fixing nip N and a slight impact is applied to the sheet, and the impact affects the trailing end of the sheet, no problem occurs in the transfer process.

  Next, let us consider a case where B4 landscape is set as the print processing condition and 2-in-1 (B5 portrait images are printed on the left and right sides of the B4 landscape paper), respectively. When 2-in-1 is set, it is usually considered that the B4 paper is folded into two left and right for filing. Therefore, when printing, the central portion in the transport direction beside B4 serves as one reference. As shown in FIG. 5C, there is a distance T3 between the paper trailing edge E1 in the case of A4 side with respect to the paper transport direction and the center part E3 in the side of B4 in the case of 2-in-1 on the side of B4. There is a difference. That is, when printing is performed in the B4 side, when the leading edge of the B4 side transport paper enters the fixing nip N of the fixing unit 20, the transport direction central portion E3 of the transport paper is the transfer position of the photosensitive drum 14. There is a possibility that the image on the right side on the downstream side after passing through 14a has been transferred to the conveyance sheet. Therefore, in this state, when the leading end of the transport sheet collides with the fixing nip portion N and a slight impact is applied to the sheet, and the impact affects the trailing end side of the sheet, the following is performed by the photosensitive drum 1 on the trailing end side of the sheet. Since the transfer of the image has been started, there is a possibility that transfer deviation occurs.

  Accordingly, the control unit 101 sets the sheet conveyance distance from the transfer position 14a of the photosensitive drum 14 to the fixing nip N of the fixing unit 20 by the distance T3 when 2 in 1 is set beside B4 as the print processing condition. In order to shorten the length, both the support 60 and the paper guide 19 are swung upward (R1 direction and S1 direction in FIG. 4B), and the upper bridging roller 54 and the transfer position 14a of the photosensitive drum 14 are moved. The distance between them is shortened (L1-α), and the paper conveyance distance of the paper guide 19 is also shortened (L2-β). At this time, the swing angle is controlled so that α + β = T3.

  As a result, when the leading edge of the B4 horizontal transport paper enters the fixing nip N of the fixing unit 20, the transport paper center E3 just passes through the transfer position 14a of the photosensitive drum 14, and the transport is performed. No transfer to paper. For this reason, even if the leading end of the transport sheet collides with the fixing nip N and a slight impact is applied to the sheet, and the impact affects the trailing end of the sheet, no problem occurs in the next image transfer process.

  FIG. 6 shows another embodiment of the paper guide 19.

  That is, the paper guide 19 shown in FIGS. 3 and 4 only swings up and down around the support shaft 71, but in this embodiment, the transport plate 91 has a structure that can be expanded and contracted. That is, as shown in a partial cross section in FIG. 6A, the conveying plate 91 includes a sliding plate 94 having a sliding groove 93 formed integrally with the support plate 92, and sliding of the sliding plate 94. The holding plate 96 has a guide rod 95 inserted into the groove 93. At the rear end of the guide rod 95, a protrusion 95a for preventing slipping and for restricting sliding is formed. That is, the sliding plate 94 and the support plate 92 can reciprocate back and forth (Y direction in FIG. 6) while being guided by the guide rod 95 within the range of the length L11 of the sliding groove 93.

  Further, the lower end 92 a of the support plate 92 has a maximum curvature surface and a minimum curvature surface of the eccentric cam 77 so that the lower end 92 a does not come off from the circumferential surface of the eccentric cam 77 by sliding of the sliding plate 94. A wide contact member 97 having an intermediate curvature surface is provided.

  With such a configuration, when both the bridging rollers 54 and 55 and the paper guide 19 are swung downward, the gap between the transfer belt 50 and the paper guide 19 held by the bridging rollers 54 and 55 is large. However, the gap can be reduced by making the paper guide 19 an expandable structure.

  That is, the paper guide 19 is assumed to have the home position at the position shown in FIG. From this state, when the eccentric cam 77 is rotationally driven so that the minimum curved surface portion of the eccentric cam 77 faces upward, the paper guide 19 swings upward (in the S1 direction), as shown in FIG. The contact member 97 is placed on the minimum curved surface portion of the eccentric cam 77. Then, due to the interaction between the minimum curved surface portion of the eccentric cam 77 and the contact member 97, the sliding plate 94 slightly moves in the Y1 direction in the drawing, and the conveying plate 91 is slightly contracted. On the other hand, when the eccentric cam 77 is rotated 180 degrees from the state shown in FIG. 5B, the paper guide 19 swings downward (in the S2 direction), and as shown in FIG. It is shaped to ride on the bottom surface portion of the eccentric cam 77. Then, due to the interaction between the bottom surface portion of the eccentric cam 77 and the contact member 97 and the weight of the sliding plate 94, the sliding plate 94 slightly moves in the Y2 direction in the figure, and the conveying plate 91 extends slightly. Become.

  By such an expansion / contraction operation of the conveyance plate 91, the sheet conveyance distance L2 formed by the paper guide 19 is slightly changed, and the gap between the transfer belt 50 is also kept within a certain range. As a result, it is possible to prevent such a problem that the leading end portion of the transport paper enters between the transfer belt 50 and the paper guide 19.

  The image processing apparatus according to the present invention is suitably used for a digital multi-function machine having a copy mode, a printer mode, a scanner mode, and a fax mode and processing a large amount of printed matter at a high speed.

1 is a side view showing an overall configuration of an image forming apparatus of the present invention. 3 is a block diagram illustrating a configuration of a control system of the image forming apparatus of the present invention. FIG. It is a side view which shows the more detailed structure of a transfer unit and a paper guide. It is explanatory drawing which shows the shape change of the transfer belt by the rocking | fluctuation operation | movement of a bridge | crosslinking roller. It is explanatory drawing which shows the specific example of printing process conditions. It is a side view which shows the other Example of a paper guide. It is explanatory drawing which shows rocking | fluctuation operation | movement of the paper guide of another Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Operation panel 11 Document stand 12 Automatic document feeder 13 Optical unit 14 Photosensitive drum 14a Transfer position 15 Charger 16 Developer 17 Transfer unit 18 Cleaner 20 Fixing unit 22 Paper discharge conveyance path 23 Automatic duplex paper feeder 24 Re-feeding path 26 Paper feed cassette 30 Registration roller 50 Transfer belt 51 Drive roller 52 Transfer roller 53 Tension roller 54, 55 Bridge roller 60 Support body 61 Base end portion 62, 63 Arm piece 68 Support shaft 63a Holding rod 63b Extendable rod 63b1 Sliding portion 64 Coil spring 77 Eccentric cam 91 Conveying plate 91a Tip portion 92 Support plate 92a Lower end portion 93 Sliding groove 94 Sliding plate 95 Guide rod 95a Protruding portion 96 Holding plate 97 Contact member 101 Central processing unit (control portion)
DESCRIPTION OF SYMBOLS 102 Image formation part 103 Recording paper conveyance system 104 Memory 105 Image data communication unit

Claims (11)

An endless transfer belt arranged opposite to the photoconductor, a transfer unit having a plurality of bridging rollers for bridging the transfer belt, and a transfer unit arranged downstream of the transfer direction of the transfer unit to fix the transfer paper. In an image forming apparatus provided with a paper guide for guiding to a fixing nip portion of a unit,
The plurality of bridging rollers are provided so as to be able to swing up and down, and further provided with control means for controlling the swinging operation of the bridging rollers,
The image forming apparatus according to claim 1, wherein the control unit swings and controls the bridging roller so as to change a distance from the transfer position of the photoconductor to the paper guide in accordance with a print request content.   The plurality of bridging rollers are attached to a distal end portion of a support body whose base end portion is rotatably supported by a support shaft, and the bridging roller is swung up and down around the support shaft to thereby form the bridging roller. The image forming apparatus according to claim 1, wherein the roller swings up and down.   The image forming apparatus according to claim 2, wherein the support body is branched into bifurcated arm pieces at the front end side, and a bridging roller is attached to a front end portion of each arm piece.   The one arm piece is provided so as to be expandable and contractible, and the tension of the transfer belt is kept constant by being always urged in an extension direction by an elastic body provided therein. The image forming apparatus according to 3.   The support is disposed on the downstream side in the transport direction from the transfer position of the photoconductor, and the front end of the support is disposed on the downstream side in the paper transport direction with respect to the support shaft. The image forming apparatus according to claim 2.   The paper guide is characterized in that the front end portion on the downstream side in the paper transport direction is rotatably fixed in the vicinity of the fixing nip portion, and the rear end portion on the upstream side in the paper transport direction is held so as to swing up and down. The image forming apparatus according to claim 1.   The back end portion of the paper guide is in contact with a peripheral surface of a fixed eccentric cam, and the paper guide is swung up and down by rotating the eccentric cam. Image forming apparatus.   The image forming apparatus according to claim 6, wherein the paper guide is provided so as to be expandable and contractable in a paper transport direction according to the swinging operation.   The image forming apparatus according to claim 6, wherein the control unit controls the swinging operation of the paper guide in conjunction with the swinging operation of the bridging roller.   The control means controls swinging operations of the bridging roller and the paper guide based on a paper length selected by the print request and a print processing condition on the paper. The image forming apparatus described.   The control means swings the bridging roller and the paper guide so that the transfer area of the conveyance sheet is not positioned at the transfer position of the photosensitive member when the leading edge of the conveyance sheet enters the fixing nip portion. The image forming apparatus according to claim 10, wherein a distance from the fixing nip portion to a transfer position of the photosensitive member is changed.

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