JP2005075500A - Sheet transport device and image forming apparatus including it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet transport device, surely transporting a sheet to a fixing part regardless of the size of the sheet, and preventing transport failure due to scattered toner. <P>SOLUTION: An endless sheet transport means 4a is disposed between a transfer part 3 for transferring a toner image formed on an image bearing member 1 to the sheet S, and a pair of fixing rollers for fixing the transferred toner image to the sheet S, and air is sucked by two or more suction means 4b, thereby transporting the sheet S to which the toner image is transferred to the paired fixing rollers 5 while sucking the same to the sheet transport means 4a. In transporting the sheet S, sucking force generated by the two or more suction means 4b is varied according to the type of the sheet S by a control means 30. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus equipped with the sheet conveying apparatus, and in particular, conveys a sheet onto which a toner image has been transferred in a transfer unit while adhering to an endless sheet conveying unit to a fixing unit. About.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a printer, or a facsimile machine, the distance between a fixing unit and a transfer unit is made shorter than, for example, a length in a sheet conveying direction in order to reduce the size of the main body. There is something that was configured. A sheet conveying device that conveys the sheet onto which the toner image has been transferred to the fixing unit while adsorbing the sheet onto which the toner image has been transferred is provided between the fixing unit and the transfer unit. Some include a roller for driving the conveyance belt, a fan for adsorbing the sheet onto the conveyance belt, and the like.

  Here, in the image forming apparatus configured such that the distance between the fixing unit and the transfer unit is shorter than the length in the sheet conveyance direction, the sheet onto which the toner image has been transferred constitutes the fixing unit. When reaching the fixing roller pair, the latter half of the sheet is still in the transfer portion. In this state, in order to fix the transferred image, if rotation unevenness occurs in the fixing roller pair that conveys the sheet while applying a high pressure, the rotation unevenness reaches the transfer portion through the sheet. There arises a problem that a transfer image on a certain sheet is disturbed to cause unevenness.

  On the other hand, in the case of a sheet whose length in the conveyance direction is shorter than the distance between the fixing unit and the transfer unit, when the sheet reaches the fixing unit, the latter half of the sheet is detached from the transfer unit, so the fixing unit Even if rotation unevenness occurs in the (fixing roller pair), there is no problem that the transferred image is disturbed, but the sheet must be pushed into the nip (hereinafter referred to as the fixing nip) of the fixing roller pair only by the conveying force of the sheet conveying device. Therefore, the sheet conveying device needs to have a certain pushing force. If the pressing force is insufficient and the sheet cannot be pressed into the fixing nip, a sheet conveyance problem that the sheet stops at the fixing nip occurs.

  Here, as a countermeasure against such problems, apart from the viewpoint of how to minimize the disturbance generated by the fixing unit, it is based on the viewpoint of how to suppress the arrival of disturbance from the fixing unit to the transfer unit. As such a method, for example, a method is adopted in which the conveyance path between the fixing unit and the transfer unit is convex downward or waved up and down to make it difficult to transmit sheet disturbance. It has been.

  In addition, the sheet conveyance speed on the fixing unit side is slower than the sheet conveyance speed on the transfer unit side, or the height of the sheet guide provided immediately before the fixing unit is increased, so that the fixing unit to transfer A method is also adopted in which the sheet is slackened between the parts, and the sheet itself absorbs vibration due to the disturbance of the sheet.

  Here, for example, when the sheet conveyance speed on the fixing unit side is made slower than the sheet conveyance speed on the transfer means side, the sheet S has a conveyance speed on the fixing unit side as shown in FIG. Since the transfer speed of the transfer unit 3 constituted by the body drum 1 and the transfer separation charger 2 is lower than the transfer speed of the transfer belt 4A rotating at the same speed, first, a downward convex shape along the shape of the sheet guide 7 become.

  Furthermore, after this, when the sheet S is conveyed, the sheet S is further bent into a downward convex shape, but when the deflection is increased in this way, the sheet S cannot fully absorb slack in the downward convex shape, As shown in FIG. 8 (b), it rises upward to form a convex shape. Then, when the sheet S has an upward convex shape in this way, even if the sheet S is further conveyed thereafter, the sheet will not be stretched between the transfer unit and the fixing unit. The disturbance of 5) is not transmitted.

  In general, the fixing roller pair 5 includes a pressure roller 5a and a heating roller 5b. The fixing roller pair 5 includes a pressure roller 5a and a heating roller 5b. By using one or both of them as an elastic body such as rubber, a nip is formed between the pressure-contacted rollers.

  By the way, the configuration in which the distance between the fixing unit and the transfer unit is shorter than the length of the sheet in the conveyance direction is not only an image forming apparatus that forms a black and white image but also an image forming apparatus that forms a color image. Is also adopted.

  Here, in an image forming apparatus that forms such a color image, a larger amount of heat is required to fix the color image than to fix the black and white image. Therefore, conventionally, for example, the heating distance is extended by increasing the pressure contact force of the pair of fixing rollers to increase the formation distance of the fixing nip. Furthermore, when fixing an image on thick paper or the like that requires a larger amount of heat, a method of increasing the amount of heat given per unit time by slowing the fixing speed of the fixing unit (fixing roller pair) is employed.

  However, if the formation distance of the fixing nip is increased or the fixing speed is decreased in this way, the conveyance force required to allow a small-size sheet, such as a postcard, in the sheet conveyance direction to enter the fixing nip. Therefore, when the conveyance force is not sufficient, a small-size sheet cannot be pushed into the fixing nip, and a sheet conveyance problem that the sheet stops at the fixing nip occurs.

  Therefore, as a method for pushing such a small-sized sheet into the fixing nip, for example, an uneven portion is provided on the surface of the conveyance belt formed of rubber or the like, a suction means is provided below the conveyance belt, and the sheet is formed on the uneven portion. A method of attracting and adsorbing the sheet to the conveying belt by suction means, or a method of electrostatically adsorbing the sheet by forming the conveying belt of PET material and applying an electric charge to the conveying belt is used.

  Alternatively, as shown in FIG. 8C, a method of pressing the sheet S by providing the suction means 4B inside the conveying belt 4A and adsorbing and conveying the sheet S to the conveying belt 4A is adopted. (See Patent Document 1).

  On the other hand, in an image forming apparatus for forming a color image, a color image is usually formed using four color toners. Therefore, when a color image is transferred to a sheet, or the sheet on which the color image is transferred is transferred to a fixing unit. When transported, the amount of toner scattering increases. When the amount of scattered toner increases in this way, the scattered toner adheres to the conveying belt 4A or the driving member that drives the belt, and as a result, slip occurs between the driving member and the conveying belt 4A. This causes a problem that it is impossible to obtain a correct image.

  Therefore, as a method for solving such a problem, there is a method of absorbing the scattered toner by providing an air suction duct and a fan in the transfer unit so that the scattered toner does not fall on the sheet conveying device. It has been taken.

JP 2000-47503 A

  By the way, in such a conventional sheet conveying apparatus and an image forming apparatus provided with the same, particularly an image forming apparatus for forming a color image, not only compactness and high image quality but also high speed are achieved. As the speed increases, the amount of scattered toner increases more and more.

  In addition, when the pressure applied to the fixing unit increases and the conveyance speed of the fixing unit increases as the speed increases, the disturbance generated by the fixing unit increases, and as a result, the disturbance transmitted through the sheet increases.

  Here, in order to prevent the disturbance of the fixing unit (fixing roller pair) from being transmitted to the transfer unit side, it is necessary to give the sheet a slack as described above so that the sheet has an upwardly convex shape. However, in the case of such a configuration, as described above, the pushing force is insufficient, so that the small size sheet cannot be pushed into the fixing nip.

  On the other hand, if the sheet is conveyed while being adsorbed to the conveyance belt as described above so that the small size sheet can be pushed into the fixing nip, the sheet is adsorbed to the conveyance belt when conveying the large size sheet. Therefore, it becomes difficult to make the sheet convex upward. Note that if the suction force of the conveyance belt is weakened, a small-sized sheet cannot enter the fixing nip.

  Therefore, the present invention has been made in view of such a current situation, and can reliably convey a sheet to a fixing unit regardless of the size of the sheet, and can prevent conveyance failure due to scattered toner toner. An object of the present invention is to provide a sheet conveying apparatus capable of performing the above and an image forming apparatus including the sheet conveying apparatus.

  The present invention provides a sheet conveying apparatus that conveys a sheet on which a toner image formed on an image carrier is transferred by a transfer unit to a fixing unit that fixes the transferred toner image. An endless sheet conveying unit disposed between the sheet and having the toner image transferred thereon is conveyed to the fixing unit; and the sheet having the toner image transferred thereto is sucked into the endless sheet conveying unit. It is characterized by comprising a plurality of suction means for suction, and a control means for changing the suction force generated by the plurality of suction means according to the type of the sheet.

  In the invention, it is preferable that the control unit changes the suction force generated by the plurality of suction units according to the size and thickness of the sheet or the number of toner colors forming the toner image. It is.

  As described above, as in the present invention, the sheet onto which the toner image has been transferred is conveyed to the fixing unit while being adsorbed to the endless sheet conveying unit by the adsorption force generated by the plurality of adsorption units. By changing the suction force generated by the suction means according to the type of the sheet, the sheet can be reliably conveyed to the fixing unit while suppressing the influence of disturbance due to the increase in speed. Further, by conveying the driving of the driving member to the sheet conveying means via the convex part on the driving member side and the convex part on the sheet conveying means side, it is possible to prevent conveyance failure due to scattered toner.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus including a sheet conveying device according to an embodiment of the present invention. In FIG. 1, reference numeral 100 denotes an image forming apparatus, and 101 denotes an image forming apparatus main body (hereinafter referred to as an apparatus main body). The image forming apparatus 100 includes an image reading unit 102 provided on the upper part of the apparatus main body 101, and an image reading apparatus. An image forming unit 103 disposed below the unit 102 and a sheet feeding device 104 that feeds the sheet S to the image forming unit 103 are provided.

  Here, the image reading unit 102 irradiates light to the automatic document feeder 57 that sequentially conveys the original G set on the original table 58 to the reading position 59 one by one and the original conveyed to the reading position 59. A light source (not shown), and an optical system having an image reading element 63 such as a CCD that guides reflected light after being reflected from the original G through the folding mirrors 60 to 62.

  The image forming unit 103 includes a photosensitive drum 1 that is a rotatable image carrier, a primary charger 12 that uniformly charges the surface of the photosensitive drum, and a laser for forming an electrostatic latent image on the photosensitive drum. A scanner 50A, a developing device 14 that develops an electrostatic latent image formed on the photosensitive drum with toner to form a toner image on the photosensitive drum, a static elimination charger 15 that neutralizes the toner image, and a photosensitive drum. A transfer separation charger 2 for transferring the formed toner image to the sheet S is provided. Reference numeral 6 denotes a cleaner device that removes transfer residual toner on the photosensitive drum 1.

  The sheet feeding device 104 includes a sheet feeding roller 40 that feeds sheets S stored in the sheet feeding cassette 39, a feed roller 41 and a retard roller for separating the sheets S fed by the sheet feeding roller 40 one by one. And a separation portion constituted by 42.

  Next, an image forming operation in the image forming apparatus 100 having such a configuration will be described.

  When an image is formed on the sheet S, first, the document G is set on the document table 58 of the automatic document feeder 57, and after that, when the copy button is pressed, the document G is moved to the reading position 59 by the automatic document feeder 57. Be transported. The original G is irradiated with light from a light source (not shown), and the reflected light is guided to the image reading element 63 through the folding mirrors 60 to 62, and then converted into an image signal by the image reading element 63. This image signal is transferred to the laser scanner 50 </ b> A of the image forming unit 103.

  The laser scanner 50A includes a laser oscillator (not shown) and a polygon mirror 50. When an image signal from the image reading element 63 is input, laser light is emitted from the laser oscillator corresponding to the image signal. The emitted laser beam is reflected by the rotating polygon mirror 50 and is further turned back by the reflecting mirror 51 to be irradiated onto the photosensitive drum.

  Then, the photosensitive drum 1 whose surface is uniformly charged by the primary charger 12 is scanned by the laser light emitted from the laser scanner 50A in this way, and an electrostatic latent image is formed on the photosensitive drum. . Thereafter, the electrostatic latent image is developed by the developing device 14 and visualized as a toner image. Thereafter, the toner image is neutralized by the neutralization charger 15.

  Further, in parallel with such a toner image forming operation, the sheet feeding roller 40 rotates to feed out the sheet S, and thereafter, the sheet S is fed one by one by the separation unit constituted by the feed roller 41 and the retard roller 42. After the separation, registration correction is performed by the registration roller pair 43.

  Thereafter, the sheet S subjected to the registration correction by the registration roller pair 43 in this way is conveyed to the transfer unit 3 constituted by the photosensitive drum 1 and the transfer separation charger 2, and the toner image is transferred to the transfer unit 3. Is transcribed.

  Next, the sheet S to which the toner image has been transferred is conveyed to a fixing roller pair 5 constituting a fixing unit, and the sheet S is heated and pressed by the fixing roller pair 5 to permanently fix the toner image on the sheet. . Then, after fixing the toner image in this manner, for example, in the case of single-sided copying in which an image is formed only on the first surface, a top discharge unit formed between the image forming unit 103 and the image reading unit 102 To 48. Further, the transfer residual toner on the photosensitive drum 1 is removed by the cleaner device 6.

  By the way, in the image forming apparatus 100 of this embodiment, the transfer unit 3 and the fixing roller pair 5 convey the sheet S having the longest distance in the conveyance direction among the sheets S on which the image is formed. The sheet is arranged so as to be shorter than the length in the direction, and the sheet conveyance speed of the fixing roller pair 5 is configured to be lower than the sheet conveyance speed in the transfer unit 3.

  A sheet conveying device 4 that adsorbs and conveys the sheet S at the same speed as the sheet conveying speed in the transfer unit 3 is disposed between the fixing roller pair 5 and the transfer unit 3. A sheet guide 7 is disposed between the roller pair 5.

  Here, as shown in FIG. 2, the sheet conveying apparatus 4 includes a driving roller 41 that is a driving member, a conveying belt 4a that is an endless sheet conveying means stretched around three rollers 42, and a conveying belt 4a. In addition to being provided inside, there is provided a suction fan 4b as suction means for sucking air (air) and sucking the sheet S onto the transport belt 4a.

  Then, the sheet S after the toner image is transferred is conveyed to the fixing roller pair 5 at the same speed as the sheet conveyance speed in the transfer unit 3 while being adsorbed to the conveyance belt 4a by the suction fan 4b.

  The suction force generated by the suction fan 4b is pushed into the fixing roller pair 5 due to the difference in conveying speed after the sheet S is sent to the fixing roller pair 5, and then lifts upward with the rigidity of the sheet S. It is controlled to a predetermined size that can be shaped. In this way, since the sheet S is not stretched between the transfer portion and the fixing portion, the disturbance of the fixing portion (fixing roller pair 5) is not transmitted to the transfer portion side.

  FIG. 3 shows a state in which the sheet S passes through the transfer unit 3 and is conveyed to the fixing roller pair 5 while being attracted to the conveying belt 4a by the suction fan 4b. FIG. It shows a state of being bitten by the pair 5 and transported for a while. Further, (b) shows a state when the sheet S is further fed and pushed in. The sheet S jumps up due to the rigidity and becomes an upward convex shape, and by forming such a shape, the transfer portion to the fixing portion are shown. It is transported without stretching between the sections.

  By the way, in the present embodiment, as shown in FIG. 2, the air sucked by the suction fan 4b is guided from below the sheet conveying device 4 to below the fixing roller pair 5 through the blowing duct 21. ing. In addition, by guiding the air to the lower side of the fixing roller pair 5 by the duct 21 in this way, it is possible to prevent the blown-out air from flowing back to the image forming unit 103, and stains near the image forming unit due to toner or the like. It can be reduced. Further, by guiding the warm air below the fixing roller pair 5, it is possible to prevent the ambient temperature around the fixing roller pair from being lowered, which is also effective in terms of energy saving.

  On the other hand, FIG. 4 shows a case where a small-size sheet S having a shorter length in the conveyance direction than the distance between the transfer unit 3 and the fixing roller pair 5 is conveyed. In this case, since the sheet S is detached from the transfer unit 3, even if a disturbance from the fixing roller pair 5 occurs, the image being transferred is not affected. However, as described above, since the conveying force from the transfer unit 3 cannot be expected, the sheet S must be pushed into the nip of the fixing roller pair 5 only by the conveying force of the sheet conveying device 4.

  Here, when the sheet S is thick, a larger pushing force is required. In addition, when the image forming apparatus forms a color image and the fixing speed is low, the conveyance speed of the sheet S is low. A large pushing force is required.

  Therefore, in order to obtain such a large pushing force, as shown in FIG. 5, a plurality of suction fans 4b, four in this embodiment, are arranged between the conveyor belts 4a. When the sheet S needs to be conveyed by suction with the maximum suction force, for example, a postcard on which a color image is transferred, the sheet S is surely pushed into the fixing nip by driving the four suction fans 4b. To be able to. In this embodiment, an axial fan is used as the suction fan 4b. However, the suction fan 4b need not be limited to this type as long as it has a suction function.

  By the way, the four suction fans 4b are selectively driven according to the type of sheet, for example, size, thickness, basis weight, and the like by the control means 30 provided at a predetermined position of the apparatus main body 101 shown in FIG. It has come to be.

  For example, in the case of a small and thick sheet, the four suction fans 4b are operated so as to obtain the maximum suction force. Further, in the case of a sheet that does not need to be adsorbed with the maximum adsorbing force, for example, a large-size sheet, the number of the adsorbing fans 4b to be operated is reduced, thereby reducing power consumption.

  Furthermore, even a small size sheet can easily enter the fixing nip, so there is no need to maximize the suction force, and a color mode for forming an image using four colors of toner on a thick sheet and a single color toner. Since the speed of the fixing unit is different from that in the monochrome mode in which an image is formed using the image, the suction force is reduced in the monochrome mode.

  FIG. 6 shows the relationship between the size of the sheet S (length in the sheet conveyance direction), the image mode (one-color monochrome mode and four-color mode), the thickness of the sheet, and the magnitude of the suction force. As shown in the figure, by controlling the suction force according to the size of the sheet S and the like, reliable sheet conveyance and energy saving can be achieved at the same time.

  Thus, when the sheet S is conveyed, by selectively operating the plurality of suction fans 4b according to the type of the sheet S, the sheet can be reliably conveyed to the fixing unit and disturbance from the fixing unit. It is possible to suppress the disturbance of the transferred image in the transfer portion 3 due to the above. Thereby, a favorable image can be obtained, and improvement in thermal efficiency and power saving can be achieved.

  In the description so far, the number of suction fans 4b to be operated is controlled in order to change the suction force generated by the plurality of suction fans 4b in accordance with the type of the sheet S. For example, the suction force can be changed by reducing the applied voltage of the suction fan 4b according to the type of the sheet S, for example.

  FIG. 7 is a diagram showing the configuration of the conveyor belt 4a and the drive roller 41 that drives the conveyor belt 4a. As shown in FIG. 7, air is fed to the conveyor belt 4a by the suction fan 4b (see FIG. 2). A large number of vent holes 4c are formed so that they can be taken in.

  Here, as described above, when the amount of scattered toner increases due to the increase in color and speed, the back surface of the conveying belt 4a is contaminated with toner through the vent hole 4c, and slip occurs between the conveying belt 4a and the driving roller 41. , Cause paper clogging.

  Therefore, in the present embodiment, the convex portion 22 extending in the width direction orthogonal to the sheet conveying direction on the back surface side of the conveying belt 4a that contacts the driving roller 41 and the surface of the driving roller 41 that contacts the conveying belt 4a, 23 are formed continuously. Then, the convex portions 23, 23 are continuously formed on both the back surface of the transport belt 4a and the front surface of the drive roller 41 in this way, so that the drive roller 41 is driven by the convex portion 23 on the drive roller side and the transport belt side. Thus, it is possible to prevent slippage between the transport belt 4a and the driving roller 41 due to scattered toner.

  When the convex portions 22 and 23 are continuously formed on both the conveying belt 4a and the driving roller 41 as described above, the convex portions interfere with each other if the intervals between the convex portions 22 and 23 are the same. As a result, the conveying belt 4a meanders in the vertical direction and the width direction, which causes sheet skew. For this reason, in the present embodiment, for example, the interval T between the convex portions 23 on the drive roller side is made larger than the interval t between the convex portions 22 of the conveying belt 4a, thereby preventing interference between the convex portions. And can prevent sheet skew.

1 is a diagram illustrating a schematic configuration of an image forming apparatus including a sheet conveying device according to an embodiment of the present invention. FIG. 3 is a side cross-sectional view illustrating a configuration of a sheet conveying unit of the image forming apparatus. The figure explaining a mode that the large sized sheet | seat of the said sheet | seat conveyance part is conveyed. The figure explaining a mode that the small size sheet | seat of the said sheet | seat conveyance part is conveyed. The perspective view explaining the structure of the said sheet conveyance part. A table showing a relationship between a sheet size, an image mode, a sheet thickness, and a suction force of the sheet conveying unit. FIG. 3 is a perspective view illustrating the structure of a conveyance belt and a driving roller of the sheet conveyance unit. The figure explaining a mode that the sheet | seat of the conventional sheet conveyance part is conveyed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 Apparatus main body 103 Image forming part 1 Photosensitive drum 2 Transfer separation charger 3 Transfer part 4 Sheet conveying apparatus 4a Conveying belt 4b Adsorption fan 5 Fixing roller pair 7 Sheet guide 21 Blowing duct 23 Convex part on driving roller side 24 Convex part 30 on transport belt side Control means 41 Driving roller S Sheet T Spacing part of driving roller side t Spacing part of conveyor belt

Claims (8)

In a sheet conveying apparatus that conveys a sheet on which a toner image formed on an image carrier is transferred by a transfer unit to a fixing unit that fixes the transferred toner image.
An endless sheet transporting unit disposed between the fixing unit and the transfer unit and configured to transport the sheet onto which the toner image has been transferred to the fixing unit;
A plurality of suction means for sucking air and sucking the sheet on which the toner image is transferred to the endless sheet conveying means;
Control means for changing the suction force generated by the plurality of suction means according to the type of the sheet;
A sheet conveying apparatus comprising:   2. The sheet according to claim 1, wherein the control means changes the suction force generated by the plurality of suction means in accordance with the size and thickness of the sheet or the number of toner colors forming the toner image. Conveying device.   The control unit is configured to control the plurality of sheets so that the suction force is maximized when the sheet has a length in the sheet conveyance direction shorter than a distance between the fixing unit and the transfer unit. The sheet conveying apparatus according to claim 2, wherein the suction force generated by the suction means is changed.   4. The control device according to claim 1, wherein the control unit changes the suction force by selectively operating the plurality of suction units according to the type of the sheet. 5. Sheet conveying device.   4. The apparatus according to claim 1, wherein the control unit changes the suction force by changing an air suction force of the plurality of suction units in accordance with a type of the sheet. 5. Sheet transport device.   6. The sheet conveying apparatus according to claim 1, wherein air sucked by the plurality of adsorbing units is blown out from below the sheet conveying unit toward the fixing unit. A driving member that contacts the sheet conveying means and drives the sheet conveying means;
Convex portions extending in a direction perpendicular to the sheet conveying direction and having different intervals in the sheet conveying direction are formed on the surface of the sheet conveying unit that contacts the driving member and the surface of the driving member that contacts the sheet conveying unit. 2. The driving member according to claim 1, wherein the driving members are continuously formed, and the driving of the driving member is transmitted to the sheet conveying unit via the convex part on the driving member side and the convex part on the sheet conveying unit side. The sheet conveying apparatus according to any one of 1 to 6. A transfer unit that transfers the toner image formed on the image carrier to a sheet, a fixing unit that fixes the transferred toner image to the sheet, and a sheet on which the toner image is transferred by the transfer unit to the fixing unit. An image forming apparatus comprising: the sheet conveying apparatus according to claim 1 that conveys the sheet conveying apparatus.

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