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EP-3913440-B1 - IMAGE FORMING APPARATUS

EP3913440B1EP 3913440 B1EP3913440 B1EP 3913440B1EP-3913440-B1

Inventors

  • IWASAKI, HISANORI

Dates

Publication Date
20260506
Application Date
20210416

Claims (12)

  1. An image forming apparatus (100) comprising: an image bearing member (506) configured to bear a toner image; transfer means (57) including a transfer nip (N2) in which a sheet (S) is nipped and fed and configured to transfer the toner image from said image bearing member (506) onto the sheet (S) nipped in the transfer nip; fixing means (58) including a fixing nip (N) in which the sheet (S) is nipped and fed and configured to fix the toner image, on the sheet (S), transferred by said transfer means (57); first feeding means (10) including a first belt portion for having a first endless belt (101) with air permeability, which is forming a first feeding surface (10A) on which the sheet (S) is fed, a first stretching member (102, 103, 104, 105) for rotatably stretching said first belt portion, and a first air sucking portion (106) capable of attracting the sheet (S) to said first feeding surface (10A) by sucking air through said first belt portion, and configured to feed the sheet (S) from said transfer means (57) toward said fixing means (58) by rotating said first endless belt (101); second feeding means (20) including a second belt portion for having a second endless belt (201) with air permeability, which is forming a second feeding surface (20A) on which the sheet (S) is fed, a second stretching member (202, 203, 204, 205) for rotatably stretching said second belt portion, and a second air sucking portion (206) capable of attracting the sheet (S) to said second feeding surface (20A) by sucking air through said second belt portion, wherein said second feeding means is provided downstream of said first feeding means (10) with respect to a sheet feeding direction (FD) and is configured to feed the sheet (S), fed by said first feeding means (10), toward said fixing means (58) by rotating said second endless belt; characterized by detecting means (30) configured to output a signal depending on a distance between said first feeding surface (10A) and the sheet (S) at a detecting position where said detecting means (30) overlaps with said first feeding means (10) as viewed in a widthwise direction (W) of the sheet (S) perpendicular to the sheet feeding direction (FD); wherein the detecting means (30) is provided in said first feeding means (10) and provided downstream of a center of said first feeding surface (10A) with respect to the sheet feeding direction (FD); and a controller (305) configured to receive the signal outputted from said detecting means (30) and to control said fixing means (58).
  2. An image forming apparatus (100) according to claim 1, wherein said detecting means (30) includes: a flag member (301) displaceable depending on the distance between said first feeding surface (10A) and the sheet (S), fed through said first belt portion, and being displaceable between a first position where the sheet (S) is separated from said first feeding surface (10A) and is in a stretched state while being nipped in the transfer nip (N2) and in the fixing nip (N), a second position where the sheet (S) is separated from said first feeding surface (10A) and is in a loosened state while being nipped by the transfer nip (N2) and the fixing nip (N), and a third position where the distance between said first feeding surface (10A) and the sheet (S) is closer to said first feeding surface (10A) than the second position is; and a first sensor (302) and a second sensor (303) which are switchable between a light-transmission state and a light-blocking state depending on the position of said flag member (301), wherein said detecting means (30) outputs a first signal, a second signal and a third signal when said flag member (301) is in the first position, the second position and the third position, respectively, wherein said controller (305) is capable of controlling said transfer means (57) and starts feeding of the sheet (S) from said transfer means (57) toward said fixing means (58) in a state in which a feeding speed of the sheet (S) by said transfer means (57) is a first speed, wherein in a state in which the sheet (S) is nipped in the transfer nip (N2) and in the fixing nip (N), in a case that the first signal is outputted from said detecting means (30), said controller (305) changes a feeding speed of the sheet (S) by said fixing means (58) to a second speed lower than the first speed, in a case that the third signal is outputted from said detecting means (30), said controller (305) changes the feeding speed of the sheet (S) by said fixing means (58) to a third speed higher than the first speed, and in a case that the second signal is outputted from said detecting means (30), said controller (305) continues the feeding of the sheet (S) without changing the feeding speed of the sheet by said fixing means (58).
  3. An image forming apparatus (100) according to claim 1 or 2, wherein said controller (305) is capable of controlling said second feeding means (20), and wherein in a case that a leading end of the sheet (S) reaches the fixing nip (N) in a state in which the sheet (S) is nipped in the transfer nip (N2), said controller (305) switches a suction force of air by said second air sucking portion (206) from a first suction force for sucking the sheet (S) to said second feeding surface (20A) to a second suction force smaller than the first suction force.
  4. An image forming apparatus (100) according to claim 3, wherein in a case that a trailing end of the sheet (S) nipped in the transfer nip (N2) and in the fixing nip (N) passes through the fixing nip in a state in which said controller (305) switches the suction force of the air by said second air sucking portion (206) to the second suction force, said controller (305) switches the suction force of the air by said second air sucking portion (206) from the second suction force to the first suction force.
  5. An image forming apparatus (100) according to any one of claims 1 to 4, wherein as viewed in the widthwise direction (W) of the sheet (S) perpendicular to the sheet feeding direction (FD), the first feeding surface (10A) is disposed at a position lower than the transfer nip (N2) and the second feeding surface (20A) is disposed at a position lower than the fixing nip (N), and a downstream end of said first feeding surface (10A) with respect to the sheet feeding direction (FD) is positioned above an upstream end of said second feeding surface (20A) with respect to the sheet feeding direction (FD).
  6. An image forming apparatus (100) according to any one of claims 1 to 5, wherein said first belt portion includes a third endless belt (101c, 101d) which has air permeability and which is provided with a gap from said first endless belt (101a, 101b) with respect to the widthwise direction (W) of the sheet (S) perpendicular to the sheet feeding direction (FD), and wherein the detecting position (PL) of said detecting means (30) is between said first endless belt (101a, 101b) and said third endless belt (101c, 101d) in said first belt portion with respect to the widthwise direction (W) of the sheet (S).
  7. An image forming apparatus (100) according to any one of claims 1 to 6, wherein a center of said second air sucking portion (206) with respect to the sheet feeding direction (FD) is positioned downstream of a center of said second belt portion with respect to the sheet feeding direction (FD).
  8. An image forming apparatus (100) according to any one of claims 1 to 7, wherein said controller (305) acquires information on a size of the sheet (S) fed from said transfer means (57) toward said fixing means (58) and adjusts a feeding speed of the sheet (S) by said fixing means (58) in a case that a length of the sheet (S) with respect to the sheet feeding direction (FD) is longer than a length from said transfer nip (N2) to said fixing nip (N) with respect to the sheet feeding direction (FD).
  9. An image forming apparatus (100) according to any one of claims 1 to 8, wherein said fixing means (58) including a heating roller (582) for heating the sheet (S) and an opposite roller (583) for forming said fixing nip (N) in contact with said heating roller (582), and wherein a phantom line extended from said second feeding surface (20A) toward a downstream side with respect to the sheet feeding direction (FD) crosses a nip line, which is a tangential line of said fixing nip (N) contacting said heating roller (582) and said opposite roller (583), on a side downstream of said fixing nip (N) with respect to the sheet feeding direction (FD).
  10. An image forming apparatus (100) according to claim 9, further comprising a guiding member (581) which crosses the phantom line on a side downstream of said second belt portion as viewed in the widthwise direction (W) of the sheet (S) perpendicular to the sheet feeding direction (FD) and which has a guiding surface (581A) on which a leading end of the sheet (S) fed on said second feeding surface (20A) is guided toward said fixing nip (N).
  11. An image forming apparatus (100) according to any one of claims 1 to 10, wherein said first feeding surface (10A) is positioned higher than said second feeding surface (20A) as viewed in the widthwise direction (W) of the sheet (S) perpendicular to the sheet feeding direction (FD).
  12. An image forming apparatus (100) according to claim 8, wherein the length between said transfer nip (N2) and said fixing nip (N) is designed so as to be 19 inches (483 mm) or more.

Description

The present invention relates to an image forming apparatus according to the preamble of the independent claims for forming an image on a sheet. Conventionally, an image forming apparatus of an electrophotographic type includes a transfer portion where the image is transferred onto the sheet and includes a fixing portion where the image transferred on the sheet is fixed on the sheet. Further, as disclosed in JP 2012-083416 A, there is a constitution in which a feeding means for sucking and feeding the sheet on a belt is provided between the transfer portion and the fixing portion with respect to a sheet feeding direction. Further, as disclosed in JP 2014-044232 A, there is a constitution in which a loop detecting means is provided between the transfer portion and the fixing portion and a sheet feeding speed by the fixing portion is controlled on the basis of a detection result of a height of the loop. However, in recent years, in order to realize a high image quality and high productivity, devices of the transfer portion and a fixing portion are upsized, and correspondingly, a distance in which the sheet is fed by a feeding means between the transfer portion and the fixing portion becomes long. In this constitution, for example, in the case where an elongated sheet longer than the distance between the transfer portion and the fixing portion is subjected to loop control, a sheet feeding distance with respect to the sheet feeding direction between a transfer nip and a fixing nip in which the sheet is nipped becomes long, so that there is a liability that behavior such that the sheet is looped cannot be stabilized and thus the loop control cannot be carried out. US 2012/087687 A1 shows a generic image forming apparatus according to the preamble of the independent claim 1. Another image forming apparatuses according to the prior art are shown in JP 2012-083415 A and US 2010/196036 A1. SUMMARY OF THE INVENTION It is the object of the present invention to further develop an image forming apparatus according to the preamble of the independent claim 1, in which an elongated sheet is subjected to loop control between a transfer portion and a fixing portion, capable of improving a sheet feeding performance. The object of the present invention is achieved by the image forming apparatus as defined in the independent claim 1. Further advantageous developments of the present invention are defined in the dependent claims. Further features, advantages and effects of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic structural view of an image forming apparatus of an embodiment 1 of the present invention.Figure 2 is a sectional view showing a secondary transfer portion, a belt feeding unit and a fixing potion in the embodiment 1.Figure 3 is a perspective view of the belt feeding unit in the embodiment 1.Figure 4 is a perspective view of the belt feeding unit in a state in which a belt is dismounted in the embodiment 1.Figure 5 is a block diagram showing a control constitution of the image forming apparatus of the embodiment 1.Figure 6 is a flowchart showing a flow of an operation for feeding a sheet by the belt feeding unit in the embodiment 1. DESCRIPTION OF THE EMBODIMENTS In the following, an embodiment for carrying out the present invention will be described by making reference to the drawings. Figure 1 is a schematic structural view of an image forming apparatus 100 of an embodiment 1. First, with reference to Figure 1, a structure of the image forming apparatus 100 will be described. The image forming apparatus 100 includes a feeding portion 100B for feeding a sheet and a height feeding (conveying) portion 100d for feeding (conveying) the sheet fed by the feeding portion 100B. Further, the image forming apparatus 100 includes an image forming portion 513 for forming a toner image on the sheet, a secondary transfer portion 57 where the toner image is transferred onto the sheet, and a belt feeding unit 100E for feeding the sheet, on which the toner image is transferred, to a fixing portion 58. Further, the image forming apparatus 100 includes a post-feeding portion 59 for feeding the sheet on which the toner image is fixed by the fixing portion 58. The feeding portion 100B includes a sheet cassette 51 in which sheets are stacked on a life-up device 52 and includes a sheet feeding means 53 for sending (feeding) a sheet S stacked in the sheet cassette 51. As a sheet feeding method by the sheet feeding means 53, for example, a friction-separation type by a roller and a separation attraction type by the air exist, but in Figure 1, an example using the separation attraction type by the air is shown. Incidentally, in the image forming apparatus 100, a constitution in which the sheet is fed by the friction-separation type by the roller may also be employed. The sheet fed from the f