Fixing apparatus and image forming apparatus

Abstract

Compared to a fixing device where the pressure in the upstream nip does not continuously increase from the upstream end to the downstream end in the rotational direction of the rotating body, this device suppresses the occurrence of wrinkles in the paper passing through the upstream and downstream nip. [Solution] A fixing device comprising: a rotating body having a heat source; a tubular belt that rotates in contact with the outer circumferential surface of the rotating body; an opposing member disposed on the inner circumferential surface side of the belt and having an opposing surface facing the outer circumferential surface of the rotating body; a raised portion that is raised at the end of the opposing surface that is downstream in the direction of rotation of the rotating body, and presses the belt against the outer circumferential surface of the rotating body to form a downstream nip N1; and an elastic member that is attached to the opposing surface in contact with the side surface of the raised portion, and presses the belt against the outer circumferential surface of the rotating body to form an upstream nip N2, wherein the pressure of the upstream nip N2 is configured to increase continuously from the upstream end N2j to the downstream end N2k in the direction of rotation.

Description

Technical Field

[0001] The present invention relates to a fixing device and an image forming apparatus.

Background Art

[0002] The following fixing device described in Patent Document 1 below sandwiches a transfer material in a nip portion and heat-presses and fixes an unfixed toner image. The fixing device has a high-pressure portion higher than a preset threshold value and a low-pressure portion lower than the preset threshold value in the nip. In addition, the fixing device is configured to vary the area ratio between the high-pressure portion and the low-pressure portion.

[0003] The following fixing device provided with a heating portion, a pressure-contact portion, and a pressurizing portion is described in Patent Document 2 below. The pressure-contact portion forms the heating portion and the nip portion, and is a portion for pressing a sheet against the heating portion. The pressurizing portion applies a pressing force to the sheet via the heating portion, and is a portion for forming a nip portion between the heating portion and the pressure-contact portion. The heating portion is configured to apply a higher pressing force than the central portion of the nip portion to the upstream portion and the downstream portion of the nip portion in the sheet conveyance direction. Further, the heating portion is configured to apply a higher pressing force to the downstream portion of the nip portion than the upstream portion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention aims to suppress the occurrence of wrinkles in the paper passing through the upstream and downstream nip in a fixing device, compared to a device in which the pressure of the upstream nip does not continuously increase from the upstream end to the downstream end in the rotational direction of the rotating body. [Means for solving the problem]

[0006] A first aspect of the present invention is: A rotating body having a heat source, A tubular belt that rotates in contact with the outer surface of the rotating body, An opposing member is positioned on the inner circumferential surface side of the belt and has an opposing surface facing the outer circumferential surface of the rotating body, A raised portion is formed at the end of the opposing surface that is on the downstream side in the direction of rotation of the rotating body, pressing the belt against the outer circumferential surface of the rotating body to form a downstream nip, An elastic member is attached to the opposing surface in contact with the side surface of the raised portion, and presses the belt against the outer circumferential surface of the rotating body to form an upstream nip, Equipped with, The upstream nip is a fixing device configured such that the pressure continuously increases from the upstream end to the downstream end in the direction of rotation.

[0007] A second aspect of the present invention is the fixing device of the first aspect described above, This fixing device is characterized by a pressure at the downstream end of the upstream nip that is close to the pressure at the downstream nip.

[0008] A third aspect of the present invention is the fixing device of the first aspect described above, The opposing surface is a surface in which the distance between it and the outer circumferential surface of the rotating body continuously narrows from the upstream end to the downstream end in the direction of rotation. The elastic member is a fixing device in which a member of constant thickness is pressed against the outer circumferential surface of the rotating body via the belt by the opposing surface and maintained in an elastically deformed state.

[0009] A fourth aspect of the present invention is the fixing device of the first aspect described above, The opposing surface is a surface whose distance from the outer circumferential surface of the rotating body is constant from the upstream side to the downstream side in the direction of rotation. The elastic member is a fixing device whose thickness continuously increases from the upstream end to the downstream end in the rotational direction, and is pressed against the outer circumferential surface of the rotating body via the belt by the opposing surface, and is maintained in an elastically deformed state.

[0010] A fifth aspect of the present invention is an image forming apparatus equipped with a fixing device according to any of the first to fourth aspects described above. [Effects of the Invention]

[0011] According to the fixing device of the first embodiment described above, wrinkles can be suppressed in the paper passing through the upstream and downstream nip, compared to a case where the pressure of the upstream nip does not increase continuously from the upstream end to the downstream end in the rotational direction of the rotating body.

[0012] According to the fixing device of the second embodiment described above, wrinkles can be suppressed in the paper passing through the upstream and downstream nip, compared to the case where the pressure at the downstream end of the upstream nip is significantly less than the pressure at the downstream nip.

[0013] According to the fixing device of the third embodiment described above, it is possible to suppress the occurrence of wrinkles in the paper passing through the upstream nip and the downstream nip without adjusting the thickness of the elastic member.

[0014] According to the fixing device of the fourth embodiment described above, wrinkles can be prevented from occurring in the paper passing through the upstream nip and the downstream nip without adjusting the distance between the opposing surface of the opposing member and the outer surface of the rotating body.

[0015] According to the image forming apparatus of the fifth aspect, in the fixing device, compared with the case where the pressure of the upstream nip does not continuously increase from the upstream end to the downstream end in the rotation direction of the rotating body, it is possible to suppress the occurrence of wrinkles in the paper passing through the upstream nip and the downstream nip, and it is also possible to suppress the occurrence of fixing defects and image quality defects caused by the occurrence of such wrinkles.

Brief Description of Drawings

[0016] [Figure 1] It is a schematic diagram of an image forming apparatus provided with a fixing device according to Embodiment 1. [Figure 2] It is a schematic cross-sectional view of a fixing device according to Embodiments 1 and 2. [Figure 3] It is an enlarged schematic cross-sectional view of a part of the fixing device according to Embodiment 1. [Figure 4] (A) is a schematic cross-sectional view of a facing member in the fixing device of FIG. 3, and (B) is a schematic perspective view of a part of the facing member of (A). [Figure 5] (A) is a schematic cross-sectional view of a facing member and an elastic member in the fixing device of FIG. 3, and (B) is a schematic explanatory view showing the state of an upstream nip formed by the facing member and the elastic member of (A). [Figure 6] It is a graph showing the pressure distributions of the upstream nip and the downstream nip in the fixing device of FIG. 3 and the like. [Figure 7] It is an enlarged schematic cross-sectional view of a part of the fixing device according to Embodiment 2. [Figure 8] (A) is a schematic cross-sectional view of a facing member and an elastic member in the fixing device of FIG. 7, and (B) is a schematic explanatory view showing the state of an upstream nip formed by the facing member and the elastic member of (A). [Figure 9] (A) is an enlarged schematic cross-sectional view of a part of a fixing device for comparison, and (B) is a schematic cross-sectional view of a facing member and an elastic member in the fixing device of (A). [Figure 10] It is a graph showing the pressure distributions of the upstream nip and the downstream nip in the fixing device of FIG. 9.

Embodiments for Carrying Out the Invention

[0017] The following describes embodiments for carrying out the present invention.

[0018] Embodiment 1. Figure 1 shows an image forming apparatus 10 equipped with a fixing device 5 according to Embodiment 1. Figure 2 shows a fixing device 5 according to Embodiment 1.

[0019] In this specification and the drawings, substantially identical components are denoted by the same reference numerals. Furthermore, redundant descriptions of these identical components are omitted in this specification. In Figure 1, etc., the arrow +X indicates the right direction when viewed from the front of the image forming apparatus 10, and the arrow -X indicates the left direction. Also, the arrow +Y indicates the upward direction of the image forming apparatus 10, and the arrow -Y indicates the downward direction. Furthermore, the symbol +Z indicates the depth direction when viewed from the front of the image forming apparatus 10, and the symbol -Z indicates the forward direction. In addition, the symbol with a "×" inside a "○" in Figure 1, etc., indicates the direction from the front to the back of the drawing. The symbol with a "·" inside a "○" indicates the direction from the back to the front of the drawing.

[0020] (1) Image forming apparatus The image forming apparatus 10 is a device that forms a predetermined image on a sheet of paper 19. An image is a representation that includes visible information such as characters, figures, photographs, and patterns. The image forming apparatus 10 has the image forming apparatus 20, paper feeding apparatus 40, fixing apparatus 5, etc., arranged in the internal space of the housing 11. Furthermore, a power supply device, a rotary drive device, a control device, etc. (not shown) are also arranged inside the housing 11. An operation panel, etc. (not shown) is located outside the housing 11.

[0021] The enclosure 11 is a box-shaped structure having a predetermined external shape and internal space. The enclosure 11 is composed of, for example, a frame, plates, exterior materials, etc. The housing 11 is provided with an output and storage section 12 at its top for ejecting and storing the paper 19 on which the image has been formed. In addition, an output port 13 is provided on the side portion that forms part of the output and storage section 12 for passing the paper 19 through and ejecting it.

[0022] The image forming apparatus 20 is a device capable of forming an unfixed image on the paper 19. As the image forming apparatus 20, for example, an apparatus employing an image forming method such as electrophotography is used. In this case, the image forming apparatus 20 includes an image holder, a charging device, an image exposure device, a developing device, a transfer device, a cleaning device, etc., which are not shown. Furthermore, this image forming apparatus 20 may be either a device that forms a monochrome (e.g., black) image or a device that forms a multicolor (color) image.

[0023] The image holder is a rotating structure, such as a photosensitive drum, that has an image-holding surface capable of holding an image. The charging device is a device that charges the image-holding surface of the image holder. The image exposure apparatus is a device that forms an electrostatic latent image by exposing the charged image-holding surface of an image holder to image information. The image information is information about an image that is input to the image forming apparatus 10 from an external source. A developing device is a device that develops the electrostatic latent image formed on the image-holding surface of an image holder using a developer to create an unfixed image. The unfixed image is, for example, the toner image obtained by development.

[0024] The transfer device is a device that transfers an unfixed image formed on an image holder onto a sheet of paper 19. The transfer device used may be either a direct transfer method or an intermediate transfer method. The direct transfer method is a method in which the unfixed image is directly transferred to the paper 19. The intermediate transfer method is a method in which the unfixed image is first transferred to an intermediate transfer medium and then secondarily transferred to the paper 19. In Figure 1, the portion that transfers the unfixed image to the paper 19 is shown as the transfer section 30. The transfer section 30 has a transfer position TP that transfers the unfixed image by passing it through the paper 19. The cleaning device is used to clean the image-holding surface of the image holder and the image-holding surface of the intermediate transfer body.

[0025] The paper supply device 40 is a device that stores a predetermined amount of paper 19 and supplies it to the image forming apparatus 20. The paper supply device 40 includes a container 41 for holding the paper 19, a feeder 43 for feeding the paper 19 one sheet at a time from the container 41, and the like. The container 41 and the feeder 43 are not limited to one set as illustrated in Figure 1, but may be provided in multiple sets. The paper 19 is a recording medium that can be transported inside the housing 11 and used to transfer unfixed images in the image forming apparatus 20. The paper 19 is mainly a sheet-shaped recording medium of a predetermined size.

[0026] The fixing device 5 is a device that fixes the unfixed image formed by the image forming device 20 onto the paper 19. The fixing device 5 is configured by arranging a heating roll 51, which is an example of a rotating body for heating, and a belt 53, which is an example of a rotating body for pressurizing, inside the fixing housing 50. In the fixing device 5, the contact area where the heating roll 51 and the belt 53 come into contact becomes the fixing position FP, where the paper 19 is passed through and the fixing process is performed. Details of the fixing device 5 will be described later.

[0027] A paper transport path 45, illustrated by a dashed line in Figure 1, is arranged within the internal space of the housing 11. The paper transport path 45 has a main transport path from the paper supply device 40 through the image forming device 20 and the fuser device 5 to the discharge port 13. Along this main transport path, the paper 19 is transported so as to pass through the transfer position TP of the image forming device 20 and the fixing position FP of the fuser device 5. The paper transport path 45 is composed of a predetermined number of pairs of transport rolls 46a, 46e and transport guide members (not shown).

[0028] (2) Image formation process The following image forming operations are performed in the image forming apparatus 10. Here, we will explain assuming that a monochrome image is formed in the image forming apparatus 20.

[0029] When a control device (not shown) receives a command to perform an image forming operation, the image forming apparatus 10 starts up the image forming apparatus 20, paper supply device 40, fixing device 5, etc.

[0030] At this time, the image carrier in the image forming apparatus 20 begins to rotate in a predetermined direction. The image forming apparatus 20 also performs charging, exposure, development, transfer, and cleaning operations on the rotating image carrier. Furthermore, the paper supply device 40 and the paper transport path 45 perform paper feeding operations in accordance with the timing of the transfer operation.

[0031] As a result, an unfixed image is formed on the image holder in the image forming apparatus 20. In addition, a predetermined sheet of paper 19, fed from the paper supply device 40, is supplied to the transfer section 30 of the image forming apparatus 20 via the paper transport path 45. Then, in the image forming apparatus 20, the unfixed image on the image holder is transferred to the paper 19 at the transfer position TP of the transfer unit 30.

[0032] In the fixing device 5, the heating roll 51 and the belt 53 begin to rotate. Also in the fixing device 5, the heating roll 51 is heated to a temperature at which fixing operation is possible. In the fixing device 5, the fixing operation is performed after the heating roll 51 reaches a temperature at which fixing is possible.

[0033] Then, in the fixing device 5, the paper 19 on which the unfixed image has been transferred is introduced into the fixing housing 50 and passed through the fixing position FP. As a result, in the fixing device 5, the unfixed image on the paper 19 is heated under pressure as it passes through the fixing position FP and fixed to the paper 19.

[0034] Finally, in the image forming apparatus 10, the paper 19 that has been fixed by the fixing device 5 is transported to the discharge port 13 via the paper transport path 45. The fixed paper 19 is then discharged from the discharge port 13 by a pair of transport rolls 46e and stored in the discharge storage section 12.

[0035] As a result of the above series of actions, the basic image formation process of forming an image on one side of a single sheet of paper 19 is completed.

[0036] (3) Fixing device The fixing device 5 has a fixing housing 50 (see Figure 2). Furthermore, the fixing device 5 is equipped with a heating roll 51, a belt 53, an opposing member 56A, an elastic member 59A, and the like inside the fixing housing 50.

[0037] The fixing housing 50 is a box-shaped structure having a predetermined external shape and internal space. The fixing enclosure 50 has a paper input 50a and an output 50b for the paper 19. The fixing housing 50 has an internal space in which an input guide member 50c, an output guide member 50d, and the like are arranged. In addition, a temperature sensor (not shown) for detecting the surface temperature of the heating roll 51 is also arranged inside the fixing housing 50. The fixing housing 50 is then fixed in a predetermined position within the housing 11 of the image forming apparatus 10.

[0038] The heated roll 51 is a roll with a structure in which necessary layers, such as a release layer, are laminated on the outer surface of a cylindrical roll base made of metal or the like. Furthermore, the heating roll 51 is rotatably mounted to the fixing housing 50 via bearings or the like at both ends in its axial direction J (see Figure 4(B)). The axial direction J is aligned with the depth direction Z of the image forming apparatus 10. Furthermore, the heating roll 51 receives power from a rotational drive device (not shown) via a passive gear (not shown) mounted on its far end in the axial direction J. As a result, when it is time for operation such as fixing, the heating roll 51 rotates in the direction indicated by arrow A.

[0039] Furthermore, a halogen heater lamp 52, which is an example of a heat source, is placed in the internal space of the heating roll 51. The halogen heater lamp 52 is positioned within the internal space of the heating roll 51 and fixed along the axial direction J of the heating roll 51. The halogen heater lamp 52 receives a predetermined power supply from a power supply device (not shown) and generates heat, thereby heating the heating roll 51.

[0040] The belt 53 is a tubular member that rotates in contact with the outer surface of the heating roll 51. The belt 53 is a component in which the necessary layers are formed on the outer surface of a cylindrical belt base material. The belt base material is made of a material such as polyimide resin. The necessary layers are, for example, heat-resistant release layers.

[0041] Furthermore, the belt 53 is rotatably held by a belt holding member 54, an opposing member 56A, an elastic member 59A, etc., which are arranged on its inner circumferential surface side.

[0042] The belt holding member 54 is a member positioned on the inner circumferential surface side of the belt 53, extending along the axial direction J of the heating roll 51. The belt holding member 54 has a belt holding surface 54a and a pressing surface 54b (see Figure 2). The belt holding surface 54a is a curved surface that slidably holds the inner circumferential surface of the belt 53 from below. The pressing surface 54b is a substantially flat surface that contacts a part of the opposing member 56A and pushes the opposing member 56A. The part of the opposing member 56A becomes the pressing receiving surface 56a, which will be described later.

[0043] Furthermore, the belt holding member 54 is attached to the pressurizing mechanism 55 via the support member 551 (see Figure 2).

[0044] The support member 551 supports the belt holding member 54 and transmits the pressurizing action of the pressurizing mechanism 55 to the belt holding member 54. The support member 551 is a plate material that extends along the axial direction J of the heating roll 51. In Embodiment 1, the support member 551 is made of a metal plate material with a bent upper section.

[0045] The support member 551 is attached such that its bent upper portion is located inside the belt holding member 54 and fixed in place. The lower portion (bottom edge) of the support member 551 is fitted into the insertion groove 56e (see Figure 3) provided in the opposing member 56A. Furthermore, both ends of the support member 551 in the longitudinal direction are attached to the swing arms 55a of the pressurizing mechanism 55, which will be described later.

[0046] The pressurizing mechanism 55 is a mechanism that includes a swinging arm 55a, pressurizing components (not shown), etc. The oscillating arm 55a is a member that oscillates around the support shaft 55c as a pivot point, and to which both ends of the support member 551 are attached. The oscillating arm 55a is a pair of arms positioned so as to straddle both ends of the heating roll 51 from above. The support shaft 55c is fixed, for example, to a part of the fixing housing 50. The pressurizing component is a component that applies a predetermined pressure F1 (see Figure 2) to cause the oscillating arm 55a to oscillate in a direction that brings it closer to the heating roll 51. The pressurizing component can be one or a combination of tension springs, compression springs, cams, etc.

[0047] The belt holding member 54 receives a predetermined pressure F1 generated by the pressurizing mechanism 55 through the support member 551. As a result, the belt holding member 54 presses against the opposing member 56A by its pressing surface 54b contacting the opposing member 56A's pressing receiving surface 56a. At this time, the support member 551 directly applies pressure from the pressurizing mechanism 55 to the insertion groove 56e of the opposing member 56A. As a result, the belt holding member 54 works in cooperation with the support member 551 to press the opposing member 56A in a direction that brings it closer to the heating roll 51.

[0048] The opposing member 56A is positioned on the inner circumferential side of the belt 53 and faces the outer circumferential surface of the heating roll 51. The opposing member 56A is configured as a plate-shaped member having a raised portion 58 and an opposing surface 57A. The opposing member 56A is also a member having a pressing receiving surface 56a, a belt guiding portion 56b, and an insertion groove 56e.

[0049] The opposing member 56A is obtained, for example, by molding it using a material such as synthetic resin. Furthermore, the opposing member 56A is attached to the fixing housing 50 at both of its longitudinal ends in a displaceable manner. In other words, the opposing member 56A is in a state where the opposing surface 57A and the raised portion 58 can be displaced in directions toward and toward the outer circumferential surface of the heating roll 51.

[0050] The raised portion 58 on the opposing member 56A is the raised portion at the end of the opposing surface 57A that is downstream in the rotation direction A of the heating roll 51. Furthermore, the raised portion 58 is also the part that presses the belt 53 against the outer surface of the heating roll 51 to form a downstream nip N1 (see Figure 2). The nip is the part that makes contact under pressure.

[0051] The raised portion 58 rises from the opposing surface 57A of the opposing member 56A toward the heating roll 51 at a predetermined height. Furthermore, the raised portion 58 is provided in a manner that is aligned with the axial direction J of the heating roll 51. Furthermore, the raised portion 58 has a roughly rectangular cross-section.

[0052] Furthermore, the raised portion 58 has a top surface 58a, an upstream side surface 58b, a downstream side surface 58c, and so on. The top surface 58a is the surface that presses the belt 53 against the outer circumferential surface of the heating roll 51, and is also the surface that forms the downstream nip N1. The top surface 58a is formed as a curved surface that is convex in the direction of elevation. The elevation portion 58 forms the downstream nip N1 when the top surface 58a contacts the heating roll 51 in the rotational direction A with a nip width Wn (see Figure 3). The upstream side surface 58b is the surface extending from the upstream end of the top surface 58a to the opposing surface 57A. The downstream side surface 58c is the surface extending from the downstream end of the top surface 58a to the downstream end of the opposing member 56A.

[0053] The opposing surface 57A of the opposing member 56A is the surface that faces the outer circumferential surface of the heating roll 51 with a predetermined distance S between them. The opposing surface 57A is formed to extend from the raised portion 58 of the opposing member 56A to the upstream side in the rotation direction A of the heating roll 51. Furthermore, the opposing surface 57A is formed as a curved surface that curves substantially along the outer circumferential surface of the heating roll 51.

[0054] The pressing surface 56a of the opposing member 56A is the surface that comes into contact with the pressing surface 54b of the belt holding member 54. The pressing surface 56a is formed on the portion of the opposing member 56A opposite to the opposing surface 57A. Furthermore, the pressing surface 56a is formed as a planar surface that is substantially parallel to and facing the pressing surface 54b of the belt holding member 54.

[0055] The belt guide portion 56b in the opposing member 56A is the part that guides the rotating belt 53 to approach the heating roll 51 at a predetermined position. The belt guide portion 56b is formed to extend upstream in the rotational direction A from the portion of the opposing surface 57A to which the elastic member 59A is attached. As a result, the belt guide unit 56b guides the portion of the belt 53 that has passed the belt holding member 54 to approach the heating roll 51. At this time, the belt 53 is guided to approach the heating roll 51 at a position just before the upstream nip N2, which will be described later.

[0056] The insertion groove 56e in the opposing member 56A is a groove into which the lower part of the support member 551 is fitted. The insertion groove 56e is formed on the opposite side of the opposing member 56A from the raised portion 58. Furthermore, the insertion groove 56e is formed as a groove that extends linearly along the axial direction J of the heating roll 51. As a result, the insertion groove 56e exists on both the front and back surfaces of the opposing member 56A in a state that aligns with the raised portion 58.

[0057] The elastic member 59A is an elastically deformable member that is attached to the opposing surface 57A of the opposing member 56A. Furthermore, the elastic member 59A also serves to press the belt 53 against the outer surface of the heating roll 51 to form the upstream nip N2 (see Figure 2).

[0058] The elastic member 59A is a plate-like member with a substantially rectangular cross-section having a predetermined thickness (height) and width Wa, and extending for a predetermined length. Furthermore, the elastic member 59A is positioned such that its longitudinal direction lies along the axial direction J of the heating roll 51. The width Wa of the elastic member 59A is a dimension that aligns with the rotation direction A of the heating roll 51 (see Figure 3). The width Wa of this elastic member 59A is set to match the required dimension as the width of the upstream nip N2. As the elastic member 59A, an elastic material such as a silicone sponge is used.

[0059] The elastic member 59A is attached to the opposing surface 57A of the opposing member 56A by means of double-sided adhesive tape, adhesive, or the like. At this time, the elastic member 59A is attached with one end in contact with the upstream side surface 58b of the raised portion 58 (see Figure 3).

[0060] The fixing device 5 receives pressure from the belt holding member 54 and the support member 551 due to the pressurizing action of the pressurizing mechanism 55, causing the opposing member 56A to be subjected to pressure. In other words, in the fixing device 5, the pressure F1 generated by the pressurizing mechanism 55 is transmitted to the opposing member 56A via the belt holding member 54 and the support member 551. As a result, in the fixing device 5, the opposing member 56A is subjected to pressure in a direction that moves it toward the outer surface of the heating roll 51.

[0061] At this time, the raised portion 58 of the opposing member 56A is kept pressed against the outer surface of the heating roll 51 with the belt 53 in between. In other words, the raised portion 58 at this time is mainly pressed down by the support member 551. As a result, the raised portion 58 is pressed against the outer surface of the heating roll 51 with a predetermined pressure F2 (see Figure 2).

[0062] As a result, the raised portion 58 forms a downstream nip N1 between itself and the outer surface of the heating roll 51 with the belt 53 in between. The downstream nip N1 is formed by the raised portion 58 with a nip width Wn. The downstream nip N1, due to the raised portion 58, is the area that applies pressure F2 to the paper 19 and the unfixed image with a nip width Wn.

[0063] At this time, the elastic member 59A is kept pressed against the outer surface of the heating roll 51 with the belt 53 in between. In other words, at this time, the elastic member 59A is pressed against the outer surface of the heating roll 51 by the opposing surface 57A of the opposing member 56A. As a result, the elastic member 59A is pressed against the outer surface of the heating roll 51 via the belt 53, causing it to undergo elastic deformation. Therefore, the elastic member 59A is used in a state where its thickness is thinner than that of the fixing device 5 before assembly (when unloaded).

[0064] As a result, the elastic member 59A forms an upstream nip N2 between itself and the outer surface of the heating roll 51 with the belt 53 in between. The upstream nip N2 is formed with a nip width that is approximately equivalent to the width Wa of the elastic member 59A. The upstream nip N2 is formed by an elastically deformable elastic member 59A. Therefore, the upstream nip N2 is the part that applies a smaller pressure to the paper 19 and the unfixed image than the pressure F2 at the downstream nip N1. On the other hand, the upstream nip N2 has a wider nip width (effective width Wa) than the downstream nip N1's nip width Wn. The nip width of the upstream nip N2 should be, for example, three times or more the nip width Wn of the downstream nip N1. Therefore, the upstream nip N2 is the part that applies heat and weak pressure to the paper 19 and the unfixed image for a longer period of time than the downstream nip N1.

[0065] (4) Fixing operation When the fixing device 5 receives a fixing command, the heating roll 51 begins to rotate in the rotation direction A. At this time, the belt 53 receives the rotational force of the heating roll 51 at the upstream nip N2 and the downstream nip N1 and rotates in the direction indicated by arrow B. The driven rotating belt 53 is held by the belt holding member 54 and guided by the belt guiding portion 56b of the opposing member 56A. The driven rotating belt 53 moves in a circulating manner, contacting the outer circumferential surface of the heating roll 51 and passing through the upstream nip N2 and the downstream nip N1. At this time, the heating roll 51 is heated to a predetermined temperature by the heating action of the halogen heater lamp 52. The heated heating roll 51 prepares the upstream nip N2 and downstream nip N1 that it passes through for heating.

[0066] When the fixing device 5 is ready for fixing, it accepts the paper 19 on which the unfixed image It (see Figure 2) has been transferred into the fixing housing 50. At this time, the paper 19 is brought in with the side on which the unfixed image It has been transferred facing the heating roll 51. At this time, the paper 19 is guided by the loading guide member 50c to a position where the heating roll 51 and the belt 53 begin to come into contact.

[0067] The paper 19 is then transported while sandwiched between the rotating heated roll 51 and the belt 53. In other words, the paper 19 is transported in such a way that it passes through the upstream nip N2 and the downstream nip N1 in that order.

[0068] As a result, the paper 19 on which the unfixed image It has been transferred is heated under pressure as it passes through the upstream nip N2 and the downstream nip N1. As a result, the unfixed image It is heated and melted and fixed to the paper 19.

[0069] At this time, the unfixed image It and the paper 19 are subjected to relatively weak pressure at the upstream nip N2. Subsequently, the unfixed image It and the paper 19 are subjected to relatively strong pressure (F2) at the downstream nip N1. Therefore, the fixing device 5 performs preliminary fixing at the upstream nip N2, and then performs the main fixing at the downstream nip N1.

[0070] In the fixing device 5, the paper 19 after the fixing process is completed is guided by the discharge guide member 50d and discharged to the outside of the fixing housing 50. At this point, the paper 19 is peeled off the heated roll 51 and discharged after passing through the downstream nip N1.

[0071] As a result of the above series of operations, the fixing operation of the fixing device 5 on one sheet of paper 19 is completed.

[0072] (5) Defects In the comparative fixing device exemplified in Figure 9(A), the following problems may occur.

[0073] The comparison fixing device employs the opposing member 56X and elastic member 59X shown in Figure 9(B). The opposing member 56X is a member having an opposing surface 57X ​​as shown in Figure 9(B). The opposing surface 57X ​​is a surface that has a constant distance Sx from the outer peripheral surface of the heating roll 51 from the upstream side 57Xj to the downstream side 57Xk in the rotation direction A. Incidentally, the opposing surface 57X ​​is approximately equivalent to the opposing surface 57B of the opposing member 56B in Embodiment 2, which will be described later. The constant spacing Sx of the opposing surfaces 57X may be the same as or different from the constant spacing S5 of the opposing surfaces 57B (see Figure 8(A)), which will be described later.

[0074] Furthermore, the elastic member 59X is a plate-shaped member having a constant thickness Dx and width Wx as shown in Figure 9(B). Incidentally, the elastic member 59X is roughly equivalent to the elastic member 59A in this embodiment 1. The constant thickness Dx and width Wx of the elastic member 59X may be the same as or different from the constant thickness D1 and thickness Wa of the elastic member 59A (see Figure 5(A)), which will be described later.

[0075] As a result, the comparison fixing device is configured such that the pressure at the upstream nip N2 is as shown in Figure 10. In other words, the pressure at the upstream nip N2 is configured to be constant from the upstream end N2j to the downstream end N2k in the rotation direction A. In Figure 10, the symbol F2x indicates a constant pressure at the upstream nip N2. Furthermore, the symbol F1m in Figure 10 indicates the maximum pressure at the downstream nip N1. Additionally, the symbol N1k in Figure 10 indicates the downstream end (location) of the downstream nip N1.

[0076] However, in this comparative fixing device, the upstream nip N2 can sometimes exhibit an unexpected pressure distribution, as illustrated by the dashed line +δ in Figure 10. This unexpected pressure distribution shows a tendency for the pressure to gradually decrease from the upstream end N2j to the downstream end N2k. This unexpected pressure distribution results in a relationship where the pressure at the upstream end N2j is greater than the pressure at the downstream end N2k. Furthermore, this unexpected pressure distribution tends to occur due to factors such as component tolerances and variations in assembly precision.

[0077] In a fixing device with this unexpected pressure distribution, wrinkles are more likely to occur in the paper 19 that has passed through the upstream nip N2 and the downstream nip N1. It is presumed that the cause of these wrinkles is the fluctuation in the pressure the paper 19 experiences as it passes through the upstream nip N2 and the downstream nip N1. This pressure fluctuation is a decrease followed by an increase. It is presumed that this pressure fluctuation causes the speed at which the paper 19 is transported to fluctuate, resulting in the paper 19 expanding and contracting in the transport direction.

[0078] (6) Additional configuration of the fixing device Therefore, the fixing device 5 is configured so that the pressure of the upstream nip N2 increases as shown by the solid line in Figure 6. In other words, the pressure at the upstream nip N2 is configured to increase continuously from the upstream end N2j to the downstream end N2k. As a result, the upstream nip N2 becomes a region where the pressure continuously increases monotonically from the upstream end N2j to the downstream end N2k. The pressure shown in Figure 6, etc., is also called the applied pressure.

[0079] It is preferable that the pressure in the upstream nip N2 increases at a constant rate. The pressure F2j at the upstream end N2j of the upstream nip N2, and the aforementioned constant increase rate, can be set arbitrarily.

[0080] Furthermore, the difference between the pressure F2j at the upstream end N2j of the upstream nip N2 and the pressure F2k at the downstream end N2k is determined from the following perspectives. The difference is such that, even if the above-mentioned unexpected pressure distribution occurs at the upstream nip N2, the pressure F2j at the upstream end N2j does not exceed the pressure F2k at the downstream end N2k. As a result, even if an unexpected pressure distribution occurs, the upstream nip N2 will not have a distribution where the upstream pressure F2j exceeds the downstream pressure F2k. The unexpected pressure distribution in this case is illustrated by the dashed line +δ in Figure 6.

[0081] Furthermore, it is preferable to set the pressure F2k at the downstream end N2k of the upstream nip N2 within the following range. In other words, the pressure F2k should be set within the range of 0 ≤ F2k ≤ 0.5·F1m, where F1m is the maximum pressure at the downstream nip N1.

[0082] The fixing device 5 employs the following configuration for the opposing member 56A and the elastic member 59A.

[0083] The opposing member 56A employs an opposing surface 57A in which the distance S between it and the outer surface of the heating roll 51 continuously narrows from the upstream end to the downstream end in the rotational direction A. Figure 4(A) shows four representative spacings S1, S2, S3, and S4 as the spacing S between the opposing surfaces 57A. Spacing S1 is the distance between the upstream ends 57Aj of the opposing surfaces 57A. Spacing S4 is the distance between the downstream ends 57Ak of ​​the opposing surfaces 57A. Spacings S2 and S3 are the distances between the two middle points when the distance between the upstream end 57Aj and the downstream end 57Ak of ​​the opposing surfaces 57A is divided into three equal parts. The intervals S1, S2, S3, and S4 have a hierarchical relationship of S1 > S2 > S3 > S4. This hierarchical relationship narrows at a constant rate of decrease.

[0084] As shown in Figure 5(A), the elastic member 59A is made of a member with a constant thickness D1. The width of the elastic member 59A is the width Wa described above. The constant thickness D1 of the elastic member 59A is greater than the distance S1 between the upstream ends 57Aj of the opposing surfaces 57A.

[0085] This elastic member 59A, having a constant thickness D1, is attached to the opposing surface 57A of the opposing member 56A, which has the above-mentioned spacing S. Furthermore, the elastic member 59A is pressed against the outer surface of the heating roll 51 via the belt 53 during the assembly of the fixing device 5. As a result, the elastic member 59A is kept in an elastically deformed state. Furthermore, this causes the elastic member 59A to press the belt 53 against the outer surface of the heating roll 51, thereby forming the upstream nip N2. In this case, the upstream end N2j of the upstream nip N2 is almost entirely formed by the upstream end 59Aj of the elastic member 59A (see Figure 5(B)). Also, the downstream end N2k of the upstream nip N2 is almost entirely formed by the downstream end 59Ak of ​​the elastic member 59A (see Figure 5(B)).

[0086] At this time, the elastic member 59A is in a state where the amount of elastic deformation is relatively small at the distance S1 between the upstream end 57Aj of the opposing surface 57A. Furthermore, the elastic member 59A experiences the greatest amount of elastic deformation at the interval S4 between the downstream end 57Ak of ​​the opposing surface 57A.

[0087] In the fixing device 5 according to Embodiment 1, the pressure of the upstream nip N2 continuously increases from the upstream end N2j to the downstream end N2k (see Figure 6). Therefore, in the fixing device 5, the pressure that the paper 19 receives as it passes through at least the upstream nip N2 does not fluctuate to decrease along the way or fluctuate multiple times.

[0088] Therefore, in this fixing device 5, compared to the case where the pressure of the upstream nip N2 does not increase continuously as described above, the occurrence of wrinkles in the paper 19 passing through the upstream nip N2 and the downstream nip N1 is suppressed. Cases where the pressure does not increase continuously as described above include, for example, cases where the pressure increases while also decreasing, or cases where it increases gradually over multiple stages. Furthermore, this fixing device 5 can suppress the occurrence of wrinkles in the paper 19 without adjusting the thickness of the elastic member 59A.

[0089] Furthermore, in an image forming apparatus 10 equipped with a fixing device 5, the fixing device 5 suppresses the occurrence of wrinkles on the paper 19. Therefore, the image forming apparatus 10 also suppresses the occurrence of fixing failures and image quality defects caused by the formation of wrinkles.

[0090] Embodiment 2. Figure 7 shows a part of the fixing device according to Embodiment 2. The fixing device 5 according to Embodiment 2 differs from the fixing device 5 according to Embodiment 1 in that the opposing member 56B and the elastic member 59B have been changed, but otherwise they are the same.

[0091] The opposing member 56B has an opposing surface 57B in which the distance S from the outer circumferential surface of the heating roll 51 is constant from the upstream end 57Bj to the downstream end 57Bk in the rotational direction A. Figure 8(A) shows three representative spacings S5, S5, and S5 for the spacing S of the opposing surfaces 57B. The most upstream spacing S5 is the spacing at the upstream end 57Bj of the opposing surfaces 57B. The most downstream spacing S5 is the spacing at the downstream end 57Bk of the opposing surfaces 57B. These three intervals, S5, and S5, are all the same size. Incidentally, the spacing S5 may be the same dimension as or different from the spacing S1 of the opposing surfaces 57A in Embodiment 1 (see Figure 4(A)).

[0092] The elastic member 59B is a member whose thickness D increases continuously from the upstream end 59Bj to the downstream end 59Bk in the rotational direction A (see Figure 8(A)). The width of the elastic member 59B is Wa, the same as in the case of the elastic member 59A in Embodiment 1. The elastic member 59B has its thinnest thickness D2 at the upstream end 59Bj and its thickest thickness D3 at the downstream end 59Bk. Furthermore, the thickness D of the elastic member 59B increases monotonically from the upstream end 59Bj to the downstream end 59Bk. The thickness D2 at the upstream end of the elastic member 59B is greater than the distance S5 at the upstream ends of the opposing surfaces 57B. Furthermore, the elastic member 59B has a trapezoidal cross-sectional shape when laid on its side.

[0093] The elastic member 59B, whose thickness D increases continuously, is attached to the opposing surface 57B of the opposing member 56B, which is spaced at a constant interval S5. At this time, the elastic member 59B is attached, for example, with its lower surface 59Bc (see Figure 8(A)), which is not an inclined surface, in contact with the opposing surface 57B. Furthermore, the elastic member 59B is pressed against the outer surface of the heating roll 51 via the belt 53 during the assembly of the fixing device 5. As a result, the elastic member 59B is kept in an elastically deformed state. Furthermore, this causes the elastic member 59B to press the belt 53 against the outer surface of the heating roll 51, thereby forming the upstream nip N2. In this case, the upstream end N2j of the upstream nip N2 is almost entirely formed by the upstream end 59Bj of the elastic member 59B (see Figure 8(B)). The downstream end N2k of the upstream nip N2 is almost entirely formed by the downstream end 59Bk of the elastic member 59B (see Figure 8(B)).

[0094] At this time, the elastic member 59B is in a state where the amount of elastic deformation is relatively small at the portion of thickness D2 at the upstream end 59Bj. Furthermore, at this time, the elastic member 59B experiences the greatest amount of elastic deformation at the portion of its downstream end 59Bk with a thickness of D3.

[0095] In the fixing device 5 according to Embodiment 2, the pressure of the upstream nip N2 continuously increases from the upstream end N2j to the downstream end N2k (see Figure 6). Therefore, in the fixing device 5, compared to the case where the pressure of the upstream nip N2 does not increase continuously as described above, the occurrence of wrinkles in the paper 19 passing through the upstream nip N2 and the downstream nip N1 is suppressed. Furthermore, this fixing device 5 can suppress the occurrence of wrinkles in the paper 19 without adjusting the distance S between the opposing surfaces 57B.

[0096] In the image forming apparatus 10 equipped with this fixing device 5, fixing failures and image quality defects caused by wrinkles forming on the paper 19 by the fixing device 5 are also suppressed.

[0097] Variant expression. The present invention is not limited to the configuration examples illustrated in the above embodiments. The present invention can be modified as necessary, as long as the gist of the invention described as a means of solving the problem is not altered. Therefore, the present invention also includes modifications as illustrated below.

[0098] The heating roll 51 may use a heat source other than the halogen heater lamp 52. Examples of other heat sources include a heat-resistant layer, an electromagnetic induction heating layer, and an external heating device.

[0099] The fixing device 5 may use a rotating heating element consisting of a belt supported by multiple rolls instead of the heating roll 51.

[0100] (Note) (((1))) A rotating body having a heat source, A tubular belt that rotates in contact with the outer surface of the rotating body, An opposing member is positioned on the inner circumferential surface side of the belt and has an opposing surface facing the outer circumferential surface of the rotating body, A raised portion is formed at the end of the opposing surface that is on the downstream side in the direction of rotation of the rotating body, pressing the belt against the outer circumferential surface of the rotating body to form a downstream nip, An elastic member is attached to the opposing surface in contact with the side surface of the raised portion, and presses the belt against the outer circumferential surface of the rotating body to form an upstream nip, Equipped with, The upstream nip is a fixing device configured such that the pressure increases continuously from the upstream end to the downstream end in the direction of rotation. (((2))) The fixing device according to (((1))), wherein the pressure at the downstream end of the upstream nip is a pressure that approaches the pressure of the downstream nip. (((3))) The opposing surface is a surface in which the distance between it and the outer circumferential surface of the rotating body continuously narrows from the upstream end to the downstream end in the direction of rotation. The fixing device according to (((1))) or (((2))), wherein the elastic member is a member of constant thickness and is pressed against the outer circumferential surface of the rotating body via the belt by the opposing surface and kept in an elastically deformed state. (((4))) The opposing surface is a surface whose distance from the outer circumferential surface of the rotating body is constant from the upstream end to the downstream end in the direction of rotation. The fixing device according to (((1))) or (((2))), wherein the elastic member is a member whose thickness continuously increases from the upstream end to the downstream end in the rotational direction, and is pressed against the outer circumferential surface of the rotating body via the belt by the opposing surface and kept in an elastically deformed state. (((5))) An image forming apparatus equipped with a fixing device as described in any of (((1))) to (((4))).

[0101] According to the fixing device described in (((1))), wrinkles can be suppressed in the paper passing through the upstream and downstream nip, compared to a case where the pressure of the upstream nip does not increase continuously from the upstream end to the downstream end in the rotational direction of the rotating body. According to the fixing device described in (((2))), wrinkles in the paper passing through the upstream and downstream nip can be suppressed compared to the case where the pressure at the downstream end of the upstream nip is significantly less than the pressure at the downstream nip. According to the fixing device described in (((3))), wrinkles can be prevented from forming on the paper passing through the upstream and downstream nip without adjusting the thickness of the elastic member. According to the fixing device described in (((4))), wrinkles can be prevented from forming on the paper passing through the upstream and downstream nip without adjusting the distance between the opposing surface of the opposing member and the outer surface of the rotating body. According to the image forming apparatus described in (((5))), compared to a fixing apparatus in which the pressure of the upstream nip does not continuously increase from the upstream end to the downstream end in the rotational direction of the rotating body, it is possible to suppress the occurrence of wrinkles in the paper passing through the upstream and downstream nip, and to suppress the occurrence of fixing failures and image quality defects caused by the occurrence of such wrinkles. [Explanation of symbols]

[0102] 5. Fixing device 10…Image forming apparatus 51…Heated roller (an example of a rotating body) 52…Halogen heater lamp (an example of a heat source) 53... Belt 56A, 56B… Opposing members 57A, 57B…Opposite surface 57Aj,57Bj...Upstream end 57Ak,57Bk…Downstream end 58...Protuberance 58b... Upstream side (an example of the side facing the opposite side) 59A, 59B… Elastic members A...direction of rotation D, D1, D2, D3, Dx... thickness J…Axis direction N1... Downstream nip N2... Upstream nip N2j... Upstream end N2k... Downstream end S,S1,S2,S3,S4,S5,Sx…interval

Claims

1. A rotating body having a heat source, A tubular belt that rotates in contact with the outer surface of the rotating body, An opposing member is positioned on the inner circumferential surface side of the belt and has an opposing surface facing the outer circumferential surface of the rotating body, A raised portion is formed at the end of the opposing surface that is on the downstream side in the direction of rotation of the rotating body, pressing the belt against the outer circumferential surface of the rotating body to form a downstream nip, An elastic member is attached to the opposing surface in contact with the side surface of the raised portion, and presses the belt against the outer circumferential surface of the rotating body to form an upstream nip, Equipped with, The upstream nip is a fixing device configured such that the pressure increases continuously from the upstream end to the downstream end in the direction of rotation.

2. The fixing device according to claim 1, wherein the pressure at the downstream end of the upstream nip is a pressure that approaches the pressure of the downstream nip.

3. The opposing surface is a surface in which the distance between it and the outer circumferential surface of the rotating body continuously narrows from the upstream end to the downstream end in the direction of rotation. The fixing device according to claim 1, wherein the elastic member is a member of constant thickness and is pressed against the outer circumferential surface of the rotating body via the belt by the opposing surface and kept in an elastically deformed state.

4. The opposing surface is a surface whose distance from the outer circumferential surface of the rotating body is constant from the upstream end to the downstream end in the direction of rotation. The fixing device according to claim 1, wherein the elastic member is a member whose thickness continuously increases from the upstream end to the downstream end in the rotational direction, and is pressed against the outer circumferential surface of the rotating body via the belt by the opposing surface and kept in an elastically deformed state.

5. An image forming apparatus comprising a fixing device according to any one of claims 1 to 4.

Images