Image forming apparatus

Abstract

To suppress occurrence of wrinkles when a sheet tip part abuts against a fixing section, while conveying a sheet that is absorbed on a belt.SOLUTION: A conveying unit 4 conveying a sheet from a secondary transfer section 47 toward a fixing section 50 has a first downstream fan 15a arranged on the most downstream in a conveyance direction FD, and a first upstream fan 15b arranged on an upstream of the first downstream fan 15a in the conveyance direction FD. A control section can execute any of a plurality of modes including a first mode for performing control such that when basis weight of the sheet is first basis weight, sucking force of the first downstream fan 15a is first sucking force in a state where a sheet tip reaches the fixing section 50, and a second mode for performing control such that when the basis weight of the sheet is second basis weight smaller than the first basis weight, the sucking force of the first downstream fan 15a is second sucking force smaller than the first sucking force in a state where the tip of the sheet reaches the fixing section 50.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus that forms an image on a sheet in a copying machine, a printer, a facsimile, a multifunction machine having a plurality of these functions, or the like. [Background technology]

[0002] When an image is formed on a sheet by an electrophotographic method, the sheet on which a toner image has been transferred by a transfer unit is transported to a fixing unit, where the toner image is fixed to the sheet. In order to transport the sheet from the transfer unit to the fixing unit, for example, a suction transport unit that sucks the sheet on a belt onto the belt and transports it is widely used (see Patent Document 1). In this suction transport unit, multiple suction fans are provided on the inner peripheral side of a single belt with many through holes formed therein. The sheet transported from the transfer unit is sucked by the suction fans on the belt and transported while in close contact with the belt without floating up. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-117666 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the suction transport unit described in the above-mentioned Patent Document 1, the suction force of the suction fan until the leading edge of the sheet enters the fixing nip is set to a strength that suppresses the sheet from floating up. Therefore, especially in the case of thin paper, when the leading edge of the sheet hits the fixing section, the suction force of the suction fan is strong, and the sheet that hits the fixing nip or its vicinity is stressed without being able to form a sufficient amount of loop, and there is a risk that wrinkles will occur at the leading edge of the sheet. On the other hand, if the suction force of the suction fan is too weak, the sheet will float up, and there is a risk of transport failure.

[0005] An object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of wrinkles when the leading edge of a sheet strikes a fixing unit, even when the sheet is transported in a state where the sheet is sucked by a belt. [Means for solving the problem]

[0006] One aspect of the present invention is a transfer unit having a transfer nip portion which holds and transports a sheet, and which transfers a toner image carried on an image carrier to the sheet held in the transfer nip portion; a fixing unit having a fixing nip portion which holds and transports a sheet, and which fixes the toner image transferred to the sheet by the transfer unit onto the sheet; and a transport unit which transports a sheet from the transfer unit to the fixing unit, the transport unit having an endless belt on which the sheet is placed and which has air permeability, a tension member which rotatably stretches the belt, and a plurality of suction units which can attract the sheet to the belt by sucking air through the belt; and a control unit which can change the suction force of the suction units, the control unit is capable of executing one of a plurality of modes including a first mode in which, when the basis weight of the sheet is a first basis weight, the suction force of the first suction unit is controlled to be a first suction force when the leading edge of the sheet reaches the fixing unit, and a second mode in which, when the basis weight of the sheet is a second basis weight which is smaller than the first basis weight, the suction force of the first suction unit is controlled to be a second suction force which is smaller than the first suction force when the leading edge of the sheet reaches the fixing unit.

[0007] One aspect of the present invention is an image forming apparatus comprising: a transfer unit having a transfer nip portion that clamps and transports a sheet, and transfers a toner image carried on an image carrier to the sheet clamped in the transfer nip portion; a fixing unit having a fixing nip portion that clamps and transports a sheet, and fixes the toner image transferred to the sheet by the transfer unit to the sheet; and a transport unit that transports the sheet from the transfer unit to the fixing unit, the transport unit having an endless belt on which the sheet is placed and which has breathability, a tension member that rotatably stretches the belt, and a plurality of suction units that can adsorb the sheet to the belt by sucking air through the belt, wherein the plurality of suction units include a first suction unit that is arranged most downstream in the sheet transport direction, and a second suction unit that is arranged upstream of the first suction unit in the sheet transport direction, and wherein when the leading edge of the sheet reaches the fixing unit, the suction force of the first suction unit is smaller than the suction force of the second suction unit. Effect of the Invention

[0008] According to the present invention, even when the sheet is transported in a state where it is sucked onto the belt, it is possible to suppress the occurrence of wrinkles when the leading edge of the sheet abuts against the fixing section. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing an image forming apparatus according to an embodiment. [Diagram 2] 2 is a cross-sectional view showing a transport unit from a secondary transfer unit to a fixing unit of the image forming apparatus according to the embodiment; [Diagram 3] FIG. 2 is a block diagram showing the configuration of a control system of the image forming apparatus according to the embodiment. [Figure 4] 4 is a cross-sectional view showing a state in which thin paper is transported by the transport unit according to the embodiment. FIG. [Diagram 5] 4 is a cross-sectional view showing a state in which thick paper is transported by a transport unit according to the embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the present embodiment will be described with reference to the drawings. First, a schematic configuration of an image forming apparatus according to the present embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view showing an image forming apparatus 1 according to the present embodiment.

[0011] [Image forming device] The image forming apparatus 1 includes a feeding section 2 that feeds a sheet S, an image forming section 3 that forms a toner image to be fixed on the sheet S fed by the feeding section 2, and a transport unit 4 that transports the sheet S onto which the toner image has been transferred to a fixing section 50 by a belt. The image forming apparatus 1 further includes a post-conveying section 5 that transports the sheet S onto which the toner image has been fixed by the fixing section 50.

[0012] The feeding section 2 includes a sheet cassette 41 that stores sheets S, a pickup roller 42 that picks up sheets S from the sheet cassette 41, and a separation device 43 that separates and feeds the sheets S picked up by the pickup roller 42. The feeding section 2 further includes a delivery roller 44 that conveys the sheets S in a feeding path 7 along which the sheets S separated and fed by the separation device 43 are conveyed, and a registration roller 45. The image forming section 3 is a so-called tandem type image forming section in which electrophotographic image forming stations 6Y, 6M, 6C, and 6K that form toner images of Y (yellow), M (magenta), C (cyan), and K (black) are arranged in series.

[0013] The image forming stations 6Y, 6M, 6C, and 6K have the same configuration except for the toner color. Therefore, the configuration of the image forming station 6Y will be described as an example, and the configurations of the image forming stations 6M, 6C, and 6K will not be described. The image forming station 6Y has a photosensitive drum 60Y, a charging device 61Y, an exposure device 62Y, a developing device 63Y, and a primary transfer roller 64Y. The image forming unit 3 has an intermediate transfer belt 65 as an example of an image carrier on which the toner image visualized by the image forming stations 6Y, 6M, 6C, and 6K is carried. The intermediate transfer belt 65 is supported in a state of being stretched over a drive roller 66, a tension roller 67, and a secondary transfer inner roller 68, and rotates in the direction of the arrow R2 in FIG. 1 by the drive of the drive roller 66.

[0014] The secondary transfer outer roller 46 is pressed against the intermediate transfer belt 65 supported from the inside of the intermediate transfer belt 65 by the secondary transfer inner roller 68 to form a secondary transfer nip portion N2 between the intermediate transfer belt 65 and the secondary transfer outer roller 46. The secondary transfer nip portion N2 is an example of a transfer nip portion that sandwiches and conveys the sheet S. The secondary transfer outer roller 46, the intermediate transfer belt 65, and the secondary transfer inner roller 68 form a secondary transfer section 47. The secondary transfer section 47 is an example of a transfer section that transfers a toner image carried on the intermediate transfer belt 65 to the sheet S sandwiched in the secondary transfer nip portion N2. The cleaning device 48 rubs a cleaning web against the intermediate transfer belt 65 to remove residual toner, paper powder, and the like remaining on the surface of the intermediate transfer belt 65 after passing through the secondary transfer nip portion N2.

[0015] Fixing section 50, which is disposed downstream of secondary transfer section 47 in the conveying direction FD (sheet conveying direction) of sheet S, fixes the toner image onto sheet S by heat and pressure. Fixing section 50 includes heating roller 52 with an internal heater, and opposing roller 53, which is disposed so as to be able to come into contact with heating roller 52 and forms fixing nip section N1 together with heating roller 52. That is, fixing section 50 has fixing nip section N1 which sandwiches and conveys sheet S, and fixes the toner image transferred onto sheet S by secondary transfer section 47 onto the sheet.

[0016] Heating roller 52 is an example of a first rotating body that heats sheet S, and opposing roller 53 is an example of a second rotating body that forms fixing nip portion N1 with heating roller 52. Fixing section 50 also includes a heating roller temperature sensor 54 that detects the surface temperature of heating roller 52, and an opposing roller temperature sensor 55 that detects the surface temperature of opposing roller 53. Heating roller temperature sensor 54 and opposing roller temperature sensor 55 are provided to maintain the temperatures of heating roller 52 and opposing roller 53 at appropriate temperatures, respectively.

[0017] A transport unit 4 is disposed between the secondary transfer section 47 and the fixing section 50 in the transport direction FD of the sheet S. The transport unit 4 is an example of a transport section that transports the sheet S from the secondary transfer section 47 toward the fixing section 50. The transport unit 4 is configured by disposing a first transport section 10, a second transport section 20, and a third transport section 30 in this order from the upstream side in the transport direction FD of the sheet S. The transport unit 4 will be described in detail later.

[0018] The post-conveying section 5 includes discharge rollers 71 that discharge the sheet S discharged from the fixing section 50 to the outside of the image forming apparatus 1. The post-conveying section 5 includes reversing rollers 72 that reverse and convey the sheet S, and a double-sided conveying path 73 that conveys the sheet S reversed by the reversing rollers 72 and merges it with the feeding path 7.

[0019] Next, a series of steps for forming an image on a sheet S in the image forming apparatus 1 will be described. Based on an image forming job input to the image forming apparatus 1, an exposure device 62Y of the image forming station 6Y exposes the photosensitive drum 60Y to form an electrostatic latent image on the surface of the photosensitive drum 60Y. The electrostatic latent image on the photosensitive drum 60Y is developed by a developing device 63Y and visualized as a toner image. The toner image carried on the surface of the photosensitive drum 60Y is primarily transferred onto the intermediate transfer belt 65 by a primary transfer roller 64Y. Similarly, for the other image forming stations 6M, 6C, and 6K, the toner images of each color are primarily transferred onto the intermediate transfer belt 65 in a sequential overlapping manner. The toner image primarily transferred onto the intermediate transfer belt 65 is secondarily transferred to the sheet S fed from the feeding unit 2 at a secondary transfer nip portion N2.

[0020] The registration roller 45 receives the sheet S while stopping rotation and keeps it waiting, and sends the sheet S toward the secondary transfer nip N2 in time with the toner image on the intermediate transfer belt 65. The sheet S carrying the toner image transferred at the secondary transfer nip N2 is conveyed from the secondary transfer nip N2 to the fixing unit 50 by the conveying unit 4. In the fixing unit 50, the sheet S is sandwiched at the fixing nip N1, and heat and pressure are applied to the unfixed toner image to fix the toner image to the sheet S. The sheet S sent out from the fixing unit 50 is discharged outside the image forming apparatus 1 by the discharge roller 71. When an image is formed on both sides of the sheet S, the sheet S sent out from the fixing unit 50 is conveyed to the reversing roller 72, and after being reversed by the reversing roller 72, is conveyed toward the double-sided conveying path 73. The sheet S is then conveyed again to the feeding path 7 via the double-sided conveying path 73, and a toner image is formed on the second side (back side) of the sheet S in the same manner as on the first side (front side).

[0021] [Transport unit] Next, the transport unit 4 and the configuration in the vicinity thereof will be described with reference to Fig. 2. Fig. 2 is a cross-sectional view showing the secondary transfer section 47, the transport unit 4, and the fixing section 50. The transport unit 4 used as a transport means includes a first transport section 10, a second transport section 20, and a third transport section 30. The first transport section 10, the second transport section 20, and the third transport section 30 are arranged in order from the fixing nip section N1 toward the secondary transfer nip section N2, that is, from downstream to upstream in the transport direction FD.

[0022] In the transport direction FD of the sheet S, between the transport unit 4 and the secondary transfer nip portion N2, there is provided a secondary post-transfer guide 91 that guides the sheet S transported from the secondary transfer nip portion N2 toward the transport unit 4. In addition, in the transport direction FD of the sheet S, between the transport unit 4 and the fixing nip portion N1, there is provided a pre-fixing guide 92 that guides the sheet S transported by the transport unit 4 to the fixing nip portion N1.

[0023] The first conveying section 10 includes a first conveying belt 11, a first driving roller 12a that rotatably stretches the first conveying belt 11, and first driven rollers 12b, 12b, and 12d. The first conveying belt 11 is an endless belt with a large number of holes formed therein, and is an example of a first belt made of a breathable material that allows air to pass through the holes between the inside and outside of the circumferential surface of the first conveying belt 11. The first driving roller 12a and the first driven rollers 12b, 12b, and 12d are an example of a tension member that rotatably stretches the first conveying belt 11. The first conveying section 10 includes a first driving motor 14 that rotates the first driving roller 12a to rotate the first conveying belt 11.

[0024] The second conveying section 20 includes a second conveying belt 21, a second driving roller 22a that rotatably stretches the second conveying belt 21, and second driven rollers 22b, 22c, and 22d. The second conveying belt 21 is an endless belt with a large number of holes formed therein, and is an example of a second belt made of a breathable material that allows air to pass through the holes between the inside and outside of the circumferential surface of the second conveying belt 21. The second conveying section 20 includes a second driving motor 24 that rotates the second driving roller 22a to rotate the second conveying belt 21.

[0025] The third conveying section 30 includes a third conveying belt 31, a third driving roller 32a that rotatably stretches the third conveying belt 31, and third driven rollers 32b, 32c, and 32d. The third conveying belt 31 is an endless belt with many holes formed therein, and is made of a breathable material that allows air to pass between the inside and outside of the circumferential surface of the third conveying belt 31 through the holes. The third conveying section 30 includes a third driving motor 34 that rotates the third driving roller 32a to rotate the third conveying belt 31.

[0026] The first conveying section 10 is disposed such that a sheet conveying surface 11a, which is an example of a sheet placement surface of the first conveying belt 11, is positioned vertically below the fixing nip N1. The third conveying section 30 is disposed such that a sheet conveying surface 31a of the third conveying belt 31 is positioned vertically below the secondary transfer nip N2. The second conveying section 20 is disposed such that an upstream portion of the sheet conveying surface 21a of the second conveying belt 21 is positioned lower than a downstream portion of the sheet conveying surface 31a of the third conveying section 30, and a downstream portion is positioned higher than an upstream portion of the sheet conveying surface 11a of the first conveying section 10. That is, the first conveying belt 11 is disposed furthest downstream in the conveying direction FD, and the second conveying belt 21 is disposed upstream of the first conveying belt 11 in the conveying direction FD.

[0027] In this embodiment, an imaginary line L1 extending from the sheet conveying surface 11a to the downstream side in the conveying direction FD when viewed from the width direction of the sheet S perpendicular to the conveying direction FD of the sheet S intersects with a nip line Ln of the fixing nip portion N1 downstream of the fixing nip portion N1 in the conveying direction FD. The nip line Ln of the fixing nip portion N1 refers to a tangent line of the fixing nip portion N1 that is in contact with the heating roller 52 and the counter roller 53. With this configuration, the sheet S conveyed through the first conveying section 10 is conveyed in a direction that intersects with the nip line Ln from below to above.

[0028] A pre-fixing guide 92 is provided between the first conveying section 10 and the fixing section 50 in the conveying direction FD. The pre-fixing guide 92 has a guide surface 92a that guides the leading edge of the sheet S conveyed on the sheet conveying surface 11a toward the fixing nip section N1. In this embodiment, the guide surface 92a guides the leading edge of the sheet S toward an upper portion of the opposing roller 53. That is, the pre-fixing guide 92 is an example of a guide member, and guides the leading edge of the sheet S conveyed downstream from the conveying unit 4 to the fixing nip section N1 by abutting it against the opposing roller 53.

[0029] The guide surface 92a of the pre-fixing guide 92 intersects with the imaginary line L1 of the sheet conveying surface 11a downstream of the first conveying section 10 and upstream of the fixing nip N1 when viewed from the width direction. That is, the guide surface 92a intersects with the imaginary line L1 when viewed from the width direction, the imaginary plane extending the sheet conveying surface 11a downstream in the conveying direction FD. With this configuration, the sheet S conveyed through the first conveying section 10 is guided by the pre-fixing guide 92 from the opposing roller 53 side to the fixing nip N1 in a state where the sheet S intersects with the nip line Ln from below to above.

[0030] In this way, the sheet S is transported to the fixing nip N1 in a state where it crosses the nip line Ln from below to above, so that it is possible to suppress contact of the heating roller 52 with the unfixed toner on the sheet S. Also, the pre-fixing guide 92 guides the leading edge of the sheet S to the fixing nip N1 so as to abut against the opposing roller 53. Therefore, even if the leading edge of the sheet S transported from the first transport section 10 faces slightly upward from the set transport path due to the tolerance of each part or the curvature of the sheet S, it is possible to prevent the leading edge of the sheet S from contacting the heating roller 52 above the fixing nip N1. This makes it possible to suppress the leading edge of the sheet S from contacting the heating roller 52 above the fixing nip N1, which would cause the sheet S to become wavy and lead to a deterioration in image quality.

[0031] A first downstream fan 15a, which is an example of a first suction section that adsorbs the sheet S to the sheet conveying surface 11a of the first conveying belt 11, and a first upstream fan 15b, which is an example of a second suction section, are arranged inside the first conveying belt 11. That is, the first conveying section 10 has the first downstream fan 15a and the first upstream fan 15b, which are examples of a plurality of suction sections that can adsorb the sheet S to the first conveying belt 11 by sucking air through the first conveying belt 11. The first downstream fan 15a is arranged most downstream in the conveying direction FD among the plurality of suction sections, and the first upstream fan 15b is arranged upstream of the first downstream fan 15a in the conveying direction FD. The first downstream fan 15a and the first upstream fan 15b suck air from the outside to the inside of the sheet conveying surface 11a through a number of holes formed in the first conveying belt 11, and apply a suction force necessary to convey the sheet S to the sheet conveying surface 11a.

[0032] A second downstream fan 25a and a second upstream fan 25b are disposed on the inner side of the second conveyor belt 21 to attract the sheet S to the sheet conveying surface 21a of the second conveyor belt 21. The second downstream fan 25a and the second upstream fan 25b suck air from the outside to the inside of the sheet conveying surface 21a through a large number of holes formed in the second conveyor belt 21, and apply a suction force necessary to convey the sheet S to the sheet conveying surface 21a.

[0033] A third fan 35 is disposed on the inner side of the third conveyor belt 31 to attract the sheet S to the sheet conveying surface 31a of the third conveyor belt 31. The third fan 35 sucks air from the outside to the inside of the sheet conveying surface 31a of the third conveyor belt 31 through a large number of holes formed in the third conveyor belt 31, thereby applying a suction force required to convey the sheet S to the sheet conveying surface 31a.

[0034] Each of the fans 15a, 15b, 25a, 25b, and 35 of the transport unit 4 can be set to a different air volume. In the first transport section 10 and the second transport section 20, it is possible to set a difference in suction force that attracts the sheet S between the upstream fan and the downstream fan in the same transport section.

[0035] [Control system] A block diagram showing the control system of this embodiment is shown in Fig. 3. The image forming apparatus 1 is provided with a control unit 8, which is connected to the control unit 8 so as to be able to control the motors and the like that drive each fan of the transport unit 4. The control unit 8 has hardware components such as a CPU, RAM, and ROM (not shown). In the control unit 8, these hardware components are configured to achieve various functions by programs and the like. When a sheet setting is input to the operation unit 9, the control unit 8 can change the air volume of each of the fans 15a, 15b, 25a, 25b, and 35 in accordance with the input sheet setting, thereby changing the suction power.

[0036] The control unit 8 can execute any one of a plurality of modes including a first mode, a second mode, and a third mode in which the suction force of the first downstream fan 15a is different. The first mode is a mode in which the suction force of the first downstream fan 15a is controlled to be a first suction force. The second mode is a mode in which the suction force of the first downstream fan 15a is controlled to be a second suction force that is smaller than the first suction force. The third mode is a mode in which the suction force of the first downstream fan 15a is controlled to be a third suction force that is smaller than the second suction force.

[0037] The first suction force here is, for example, the same as that of the first upstream fan 15b, and is, for example, about 75% to 100% of the maximum suction force. The second suction force is, for example, about 40% to 60% of the maximum suction force, and is 50% in this embodiment. The third suction force is, for example, about 20% to 30% of the maximum suction force, and is 25% in this embodiment. That is, when the second or third mode is performed, the suction force of the first downstream fan 15a is smaller than the suction force of the first upstream fan 15b when the leading edge of the sheet S has reached the fixing unit 50.

[0038] When the basis weight of the sheet S is the first basis weight, the control unit 8 executes the first mode so that the suction force of the first downstream fan 15a becomes the first suction force in a state in which the leading edge of the sheet S has reached the fixing unit 50. The first basis weight here is a basis weight equal to or greater than a predetermined basis weight, and if the predetermined basis weight is, for example, 200 gsm, it is a basis weight equal to or greater than that, and includes, for example, cardboard.

[0039] When the basis weight of the sheet S is a second basis weight smaller than the first basis weight, the control unit 8 executes the second mode so that the suction force of the first downstream fan 15a becomes the second suction force in a state in which the leading edge of the sheet S has reached the fixing unit 50. The second basis weight here is, for example, 100 gsm to 200 gsm, and includes, for example, thin paper.

[0040] When the basis weight of the sheet S is a third basis weight smaller than the second basis weight, the control unit 8 executes the third mode so that the suction force of the first downstream fan 15a becomes a third suction force in a state in which the leading edge of the sheet S has reached the fixing unit 50. The third basis weight here is, for example, 50 gsm to 100 gsm, and includes, for example, thin paper.

[0041] In this embodiment, the control unit 8 sets the suction force of the first downstream fan 15a at the time when the sheet S is transported from the secondary transfer unit 47, and executes one of the first to third modes. Then, the control unit 8 maintains the suction force of the first downstream fan 15a constant, and causes the sheet S to enter the fixing unit 50 with the same suction force. That is, when the control unit 8 is executing one of the multiple modes, it maintains the suction force of the first downstream fan 15a constant. Also, although specific numerical values ​​are shown for the basis weight, they are all examples and are not limited to them.

[0042] [Fan settings when transporting thin paper] The settings of the first downstream fan 15a and the first upstream fan 15b of the first conveying section 10 when conveying thin paper are shown in Fig. 4. In the first conveying section 10, the second conveying section 20, and the third conveying section 30, the fans need to generate a suction force F1 that causes the sheet S to stick to the first conveying belt 11, the second conveying belt 12, and the third conveying belt 13 so that the sheet S does not float up.

[0043] However, in the case of conveying thin paper, if the sheet S is strongly attracted to the first conveyor belt 11 when the leading edge of the sheet S enters the fixing nip portion N1, the suction force and the nip force of the fixing nip portion N1 act on the sheet S, and wrinkles may occur in the sheet S. Therefore, the first upstream fan 15b arranged inside the first conveyor portion 10 is operated with a suction force F1 that causes the sheet S to stick to the first conveyor belt 11. Furthermore, the first downstream fan 15a is operated with a minimum suction force F2 that allows the sheet to be conveyed, thereby making it possible to reduce the lifting of the sheet S and the occurrence of wrinkles in the sheet S. That is, the control unit 8 executes the second mode or the third mode. Moreover, the suction force F1 that causes the sheet S to stick to the first conveyor belt 11 and the minimum suction force F2 that allows the sheet S to be conveyed are changed according to the basis weight value input to the control unit 8 in the sheet setting. This enables high-speed sheet transport in the transport unit 4 between the secondary transfer section 47 and the fixing section 50 while reducing lifting of the sheet S during transport and wrinkles that may occur when the sheet S enters the fixing nip N1.

[0044] [Fan settings when transporting thick paper] FIG. 5 shows the settings of the first downstream fan 15a and the first upstream fan 15b of the first conveying section 10 when conveying thick paper. When conveying thick paper, if the sheet S is conveyed with the suction force set for conveying thin paper described above, the conveying force is insufficient, and it is difficult to convey the sheet S to the pre-fixing guide 92 that is inclined in the conveying direction FD. Therefore, when conveying thick paper, the first conveying section 10 also operates the first downstream fan 15a with the suction force F1 that causes the sheet S to stick to the belt, similar to the first upstream fan 15b. That is, the control section 8 executes the first mode. This makes it possible to secure a conveying force that allows the sheet S to pass through the pre-fixing guide 92. In addition, when conveying thick paper, the possibility of wrinkles occurring due to entering the fixing nip N1 is low, so the suction force of the first downstream fan 15a may be made equal to the suction force of the first upstream fan 15b. Further, the suction force F1 at which the sheet S sticks to the first conveyor belt 11 is changed according to the basis weight value input to the control unit 8 in the sheet setting.

[0045] As described above, according to the image forming apparatus 1 of the present embodiment, when the basis weight of the sheet S is small, the suction force of the first downstream fan 15a is made small. This makes it possible to reduce the lifting of the sheet S and the occurrence of wrinkles in the sheet S. This makes it possible to suppress the occurrence of wrinkles when the leading edge of the sheet S hits the fixing unit 50, even while the sheet S is transported in a state in which it is sucked by the first transport belt 11.

[0046] According to the image forming apparatus 1 of the present embodiment, any one of the three modes, the first mode, the second mode, and the third mode, can be executed, so that fine control is possible. Therefore, even when the sheet S is conveyed while being sucked by the first conveyor belt 11, it is possible to more effectively prevent the occurrence of wrinkles when the leading edge of the sheet S hits the fixing unit 50.

[0047] In the above embodiment, the suction force of the first downstream fan 15a is set when the sheet S is transported from the secondary transfer section 47, and the suction force of the first downstream fan 15a is maintained until the sheet S enters the fixing section 50. However, the present invention is not limited to this. For example, the suction force of the first downstream fan 15a may be changed based on the basis weight of the sheet S after the sheet S is transported from the secondary transfer section 47 and reaches the second transport section 20 or the first transport section 10. In this case, even when a plurality of sheets S are transported simultaneously by the transport unit 4, the suction force of the first downstream fan 15a can be appropriately set, so that the occurrence of wrinkles at the leading edge of the sheet S can be suppressed without reducing productivity.

[0048] In the above embodiment, the control unit 8 is described as being capable of executing one of the three modes, the first mode to the third mode, but is not limited to this. For example, the control unit 8 may have only the first mode and the second mode, or may have four or more modes. Furthermore, the basis weight and the suction force are not limited to being changed in stages, and may be changed in a linear relationship such that the suction force decreases as the basis weight decreases.

[0049] In the above embodiment, the first conveying section 10 has two fans 15a and 15b, but the present invention is not limited to this and may have three or more fans. In this case, the first downstream fan 15a is disposed at the most downstream position in the conveying direction FD among the three or more fans. In the above embodiment, the conveying unit 4 has three belts 11, 21, and 31, but the present invention is not limited to this and may have one belt, two belts, or four or more belts. In any case, the suction force of the first downstream fan 15a provided on the inside of the belt disposed at the most downstream position is changed.

[0050] The present technology can also be configured as follows. (1) a transfer section having a transfer nip section for nipping and conveying a sheet, and for transferring a toner image carried on an image carrier onto the sheet nipped in the transfer nip section; a fixing unit having a fixing nip portion that holds and conveys a sheet, and fixes the toner image transferred to the sheet by the transfer unit onto the sheet; a conveying section that conveys a sheet from the transfer section to the fixing section, the conveying section including: an endless belt on which the sheet is placed and which has air permeability; a tension member that rotatably stretches the belt; and a plurality of suction sections that can adsorb the sheet to the belt by sucking air through the belt; A control unit capable of changing the suction force of the suction unit, the plurality of suction units include a first suction unit disposed most downstream in a sheet transport direction, and a second suction unit disposed upstream of the first suction unit in the sheet transport direction, The control unit is a first mode in which, when the basis weight of the sheet is a first basis weight, the suction force of the first suction unit is controlled to be a first suction force when the leading edge of the sheet reaches the fixing unit; a second mode in which, when the basis weight of the sheet is a second basis weight smaller than the first basis weight, the suction force of the first suction unit is controlled to be a second suction force smaller than the first suction force when the leading edge of the sheet reaches the fixing unit; The present invention is capable of performing one of several modes, including Image forming device. (2) the plurality of modes include a third mode in which, when the basis weight of the sheet is a third basis weight that is smaller than the second basis weight, the control unit controls the suction force of the first suction unit to be a third suction force that is smaller than the second suction force when the leading edge of the sheet reaches the fixing unit. The image forming apparatus according to (1) above. (3) The control unit, when executing the first mode, makes the first suction force equal to the suction force of the second suction unit. The image forming apparatus according to (1) or (2). (4) The first basis weight is equal to or greater than a predetermined basis weight. The image forming apparatus according to any one of (1) to (3). (5) The control unit maintains a suction force of the first suction unit constant when any one of the plurality of modes is being executed. The image forming apparatus according to any one of (1) to (4). (6) the fixing section includes a first rotating body that heats a sheet, and a second rotating body that forms the fixing nip portion between the first rotating body and a second rotating body; a guide member that intersects with a virtual plane that extends a sheet placement surface of the belt downstream in the sheet conveying direction and guides a leading edge of the sheet conveyed downstream from the conveying section to the fixing nip section so as to abut against the second rotating body; The image forming apparatus according to any one of (1) to (5). (7) The belt is a first belt, the conveying section includes the first belt disposed most downstream in the sheet conveying direction, and a second belt disposed upstream of the first belt in the sheet conveying direction, The first suction portion and the second suction portion are disposed on the inner side of the first belt. The image forming apparatus according to any one of (1) to (6). (8) When the leading end of the sheet reaches the fixing unit, the suction force of the first suction unit is smaller than the suction force of the second suction unit. The image forming apparatus according to any one of (1) to (7). (9) a transfer section having a transfer nip section for nipping and conveying a sheet, and for transferring a toner image carried on an image carrier onto the sheet nipped in the transfer nip section; a fixing unit having a fixing nip portion that holds and conveys a sheet, and fixes the toner image transferred to the sheet by the transfer unit onto the sheet; a conveying section that conveys a sheet from the transfer section to the fixing section, the conveying section including: an endless belt on which the sheet is placed and which has air permeability; a tension member that rotatably stretches the belt; and a plurality of suction sections that can attract the sheet to the belt by sucking air through the belt; the plurality of suction units include a first suction unit disposed most downstream in a sheet transport direction, and a second suction unit disposed upstream of the first suction unit in the sheet transport direction, When the leading end of the sheet reaches the fixing unit, the suction force of the first suction unit is smaller than the suction force of the second suction unit. Image forming device. [Explanation of symbols]

[0051] 1...image forming apparatus, 4...conveying unit (conveying section), 8...control section, 11...first conveying belt (belt, first belt), 11a...sheet conveying surface (sheet placing surface), 12a...first driving roller (tensioning member), 12b, 12c, 12d...first driven roller (tensioning member), 21...second conveying belt (second belt), 47...secondary transfer section (transfer section), 50...fixing section, 52...heating roller (first rotating body), 53...opposing roller (second rotating body), 92...pre-fixing guide (guide member), FD...conveying direction (sheet conveying direction), L1...virtual line (virtual surface), N1...fixing nip section, N2...secondary transfer nip section (transfer nip section), S...sheet

Claims

1. a transfer section having a transfer nip section for nipping and conveying a sheet, and for transferring a toner image carried on an image carrier onto the sheet nipped in the transfer nip section; a fixing unit having a fixing nip portion that sandwiches and conveys a sheet, and that fixes the toner image transferred onto the sheet by the transfer unit; a conveying section that conveys a sheet from the transfer section toward the fixing section, the conveying section including: an endless belt having a conveying surface that conveys a sheet supported on the conveying surface; a first suction fan that sucks the sheet into a first region of the conveying surface; and a second suction fan that sucks the sheet into a second region of the conveying surface that is located upstream of the first region in the sheet conveying direction; a guide that guides the sheet conveyed by the belt to the fixing unit, the guide being arranged so as to intersect with a virtual plane that is an extension of the conveying surface of the belt when viewed from a sheet width direction that intersects with the sheet conveying direction; a control unit that controls the suction force of the first suction fan and the suction force of the second suction fan, the control unit controls the suction force of the first suction fan to be smaller than the suction force of the second suction fan when the sheet is transported from the transfer nip portion to the fixing nip portion. An image forming apparatus characterized by:

2. The conveying section has a first support roller that supports the belt, and a second support roller that is arranged downstream of the first support roller in the sheet conveying direction and supports the belt.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. The conveying surface of the belt is parallel to a common tangent to the first support roller and the second support roller.

3. The image forming apparatus according to claim 2, wherein the image forming apparatus is a recording medium.

4. The control unit changes the suction force of the first suction fan based on the basis weight of the sheet transported by the belt.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. The belt is a first belt, the conveying surface is a first conveying surface, the conveying section includes a second belt disposed upstream of the first belt in the sheet conveying direction, the sheet is supported on the second conveying surface of the second belt; a downstream end of the second conveying surface in the sheet conveying direction is disposed vertically higher than an upstream end of the first conveying surface in the sheet conveying direction; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. A transfer section having a transfer nip section that holds and transports a sheet, and that transfers a toner image carried on an image carrier onto the sheet held in the transfer nip section; a fixing unit having a fixing nip portion that sandwiches and conveys a sheet, and that fixes the toner image transferred onto the sheet by the transfer unit; a conveying unit that conveys a sheet from the transfer unit toward the fixing unit, an endless belt having a conveying surface for conveying a sheet supported on the conveying surface; a plurality of support parts that support the belt, the support parts having a first support part that is arranged at a highest position among the plurality of support parts and a second support part that is arranged at a second highest position among the plurality of support parts; a first suction fan disposed between the first support portion and the second support portion in the sheet conveying direction and configured to suck the sheet onto the conveying surface; a second suction fan that is disposed between the first support portion and the second support portion in the sheet conveying direction and upstream of the first suction fan in the sheet conveying direction, and that sucks the sheet onto the conveying surface; a conveying unit having a control unit that controls the suction force of the first suction fan and the suction force of the second suction fan, the control unit controls the suction force of the first suction fan to be smaller than the suction force of the second suction fan when the sheet is transported from the transfer nip portion to the fixing nip portion. An image forming apparatus characterized by:

7. The first support portion is a first support roller that supports the belt, the second support portion is a second support roller that is disposed downstream of the first support roller in the sheet conveying direction and supports the belt; 7. The image forming apparatus according to claim 6, wherein the image forming apparatus is a recording medium.

8. The conveying surface on which the first suction fan and the second suction fan suck the sheet is parallel to a common tangent line between the first support roller and the second support roller.

8. The image forming apparatus according to claim 7,

9. The control unit changes the suction force of the first suction fan based on the basis weight of the sheet transported by the belt.

8. The image forming apparatus according to claim 7,

10. The belt is a first belt, the conveying surface is a first conveying surface, the conveying section includes a second belt disposed upstream of the first belt in the sheet conveying direction, the sheet is supported on the second conveying surface of the second belt; a downstream end of the second conveying surface in the sheet conveying direction is disposed vertically higher than an upstream end of the first conveying surface in the sheet conveying direction; 8. The image forming apparatus according to claim 7,

11. A transfer section having a transfer nip section that holds and transports a sheet, and that transfers a toner image carried on an image carrier onto the sheet held in the transfer nip section; a fixing unit having a fixing nip portion that sandwiches and conveys a sheet, and that fixes the toner image transferred onto the sheet by the transfer unit; a conveying unit that conveys a sheet from the transfer unit toward the fixing unit, an endless belt having breathability and on which a sheet is placed; a tension member that rotatably stretches the belt; a plurality of suction units that suck air through the belt to adsorb the sheet onto the belt; a conveying unit having a control unit that controls the suction forces of the plurality of suction units, the plurality of suction units include a first suction unit disposed most downstream in a sheet conveying direction, and a second suction unit disposed upstream of the first suction unit in the sheet conveying direction, The control unit a first mode in which, when the basis weight of the sheet is a first basis weight, the suction force of the first suction unit is controlled to be a first suction force when the leading edge of the sheet reaches the fixing unit; a second mode in which, when the basis weight of the sheet is a second basis weight that is smaller than the first basis weight, the suction force of the first suction unit is controlled to be a second suction force that is smaller than the first suction force when the leading edge of the sheet reaches the fixing unit; The system is capable of performing one of several modes, including An image forming apparatus characterized by:

12. The plurality of modes include a third mode in which, when the basis weight of the sheet is a third basis weight which is smaller than the second basis weight, the control unit controls the first suction unit so that the suction force of the first suction unit becomes a third suction force which is smaller than the second suction force when the leading edge of the sheet reaches the fixing unit.

12. The image forming apparatus according to claim 11.

13. The control unit, when executing the first mode, makes the first suction force equal to the suction force of the second suction unit.

12. The image forming apparatus according to claim 11.

14. The first basis weight is a basis weight equal to or greater than a predetermined basis weight.

12. The image forming apparatus according to claim 11.

15. The control unit maintains the suction force of the first suction unit constant when any of the plurality of modes is being executed.

12. The image forming apparatus according to claim 11.

16. The fixing device further includes a guide that guides the sheet transported downstream in the sheet transport direction from the transport section to the fixing nip section, the fixing unit includes a first rotating body that heats the sheet and a second rotating body that forms the fixing nip portion between the first rotating body and the second rotating body; the guide intersects with an imaginary plane extending the conveying surface of the belt downstream in the sheet conveying direction, and guides the leading edge of the sheet conveyed downstream in the sheet conveying direction from the conveying unit to the fixing nip portion so as to abut against the second rotating body.

12. The image forming apparatus according to claim 11.

17. The conveying section is arranged so that the conveying surface of the belt is positioned vertically below the fixing nip section.

12. The image forming apparatus according to claim 11.

18. The conveying section is arranged so that, when viewed from the sheet width direction perpendicular to the sheet conveying direction, a virtual line extending from the conveying surface of the belt downstream in the sheet conveying direction intersects with the nip line of the fixing nip section at a position downstream of the fixing nip section in the sheet conveying direction.

12. The image forming apparatus according to claim 11.

19. The belt is a first belt arranged most downstream in the sheet conveying direction in the conveying section, the conveying section includes a second belt disposed upstream of the first belt in the sheet conveying direction, the first suction portion and the second suction portion are disposed on the inner peripheral side of the first belt, 12. The image forming apparatus according to claim 11.

20. The conveying section is arranged so that the upstream portion of the conveying surface of the first belt in the sheet conveying direction is located vertically lower than the downstream portion of the conveying surface of the second belt in the sheet conveying direction, and the conveying surface of the second belt is located vertically lower than the transfer nip portion.

20. The image forming apparatus according to claim 19.

21. When the leading edge of the sheet reaches the fixing section, the suction force of the first suction section is smaller than the suction force of the second suction section.

12. The image forming apparatus according to claim 11.

Images