Image forming apparatus

Abstract

To provide an image forming apparatus having a heat-and-pressure-type fixing device, in which a temperature difference in the axial direction, caused by the sheet passage area and the non-passage area of a pressing roller in the fixing device, is reduced by adjusting a load applied to the pressing roller.SOLUTION: An image forming apparatus includes: an image forming part that forms an unfixed image on a sheet; and a fixing device that fixes the unfixed image on the sheet, the fixing device including a fixing belt, a plurality of holding members that hold the fixing belt so as to allow the fixing belt to rotate, a pressing roller that presses the fixing belt from the outer circumferential surface side against one of the holding members to form a fixing processing part, heating means that heats the fixing belt, and a load adjustment mechanism that adjusts a load applied to the pressing roller and applies a fixing load during a fixing operation. At least at the end of the fixing operation of the fixing device, the load adjustment mechanism applies, as necessary, a low load, which is lower than the fixing load, to the pressing roller.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Patent Document 1, JP 2007-3998 A, describes an image forming apparatus equipped with a fixing device that fixes a toner image on a sheet of paper passing through the center of a nip between two rollers, at least one of which is heated by a heat source. Patent document 1 also describes that the fixing device is provided with a first temperature detection means for detecting the temperature at approximately the center of the width of the transportable area of ​​the two rollers in the width direction, and a second temperature detection means for detecting the temperature of a portion outside the paper passing range of the transportable area, and the heating state by the heat source is controlled based on the difference between the temperatures detected by the two temperature detection means. Furthermore, Patent Document 1 also describes that when the difference in the detected temperatures exceeds a preset temperature difference, the device transitions to a standby state, power to the heater, which is the heat source, is turned off, and the two rollers are controlled to rotate until the temperature difference decreases to a separately preset value.

[0003] Patent Document 2, JP 2014-178509 A, describes an image forming apparatus including a fixing device having a heating rotor, a pressure rotor, a heat source for heating the heating rotor, a cooling mechanism for cooling the pressure rotor, a pressurizing / depressurizing mechanism for moving the heating rotor and the pressure rotor closer together, a first temperature detection means for detecting the temperature in the axial central region of the heating rotor, a second temperature detection means for detecting the temperature in the axial end region of the pressure rotor, and a control unit for controlling the supply of electricity to the heat source and the cooling mechanism. Patent document 2 also describes that when the detection temperature of the first temperature detection means in the fixing device is A and the detection temperature of the second temperature detection means is B, during start-up before paper is passed, if detection temperature A>detection temperature B, cooling of the axial end region is performed by the cooling mechanism, and if detection temperature A≦detection temperature B, cooling of the axial end region is not performed by the cooling mechanism. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-3998 A (Claims 1-4, Figures 1-4) [Patent Document 2] JP 2014-178509 A (Claim 1, Figures 1 to 3) Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to reduce the axial temperature difference that occurs due to the pass and non-pass areas of the press roll in the fixing device in an image forming apparatus having a heat and pressure fixing device, by adjusting the load applied to the press roll. [Means for solving the problem]

[0006] The first aspect of the present invention is an image forming section for forming an unfixed image on a sheet of paper; a fixing device for fixing the unfixed image onto the paper; having the fixing device includes a fixing belt, a plurality of holding members for rotatably holding the fixing belt, a pressing roll for pressing the fixing belt from an outer circumferential surface side against one of the holding members to form a fixing processing section, a heating means for heating the fixing belt, and a load adjustment mechanism for adjusting a load applied to the pressing roll and applying a load for fixing during a fixing operation; In the image forming apparatus, the load adjustment mechanism may perform an operation of applying a low load, which is smaller than the load for fixing, to the pressing roll at least when the fixing operation of the fixing device is completed.

[0007] The second aspect of the present invention is the image forming apparatus according to the first aspect, The one holding member is an image forming apparatus in which a center portion of a portion where the fixing belt passes in contact with the one holding member is shaped to be closer to the pressing roll than an end portion of the portion where the fixing belt passes.

[0008] The third aspect of the present invention is the image forming apparatus according to the second aspect, The one holding member is an image forming device that is a contact member that is arranged so as to contact the inner circumferential surface of the fixing belt at a certain position.

[0009] The fourth aspect of the present invention is the image forming apparatus according to the first aspect, A temperature detection means is provided for detecting temperatures of a central portion and an end portion of the pressing roll in an axial direction, The image forming apparatus applies the low load when the temperature difference between the center and end portions in the axial direction of the pressing roll reaches or exceeds a predetermined temperature using information on the detected temperature from the temperature detection means.

[0010] The fifth aspect of the present invention is the image forming apparatus according to the fourth aspect, The low load is divided into a plurality of levels of low load, and the temperature difference is divided into a plurality of stages; The low loads applied to the image forming apparatus are changed in accordance with the temperature differences between the plurality of stages.

[0011] The sixth aspect of the present invention is the image forming apparatus according to the first aspect, a collection means for collecting information on at least the width and the number of consecutive sheets of the paper; The image forming apparatus applies the low load when the number of consecutive sheets of paper having a width narrower than the maximum width during transport among the sheets satisfies a predetermined condition using information collected by the collecting means.

[0012] The seventh aspect of the present invention is the image forming apparatus according to the sixth aspect, The low load is divided into a plurality of levels of low load, and the predetermined condition is divided into a plurality of combinations of conditions, The low loads of the plurality of levels are applied in an image forming apparatus while being changed according to the difference in the results when the plurality of combinations of conditions are satisfied. Effect of the Invention

[0013] According to the image forming apparatus of the first aspect, the temperature difference in the axial direction caused by the pass and non-pass areas of the press roll in the fixing device where the paper passes can be reduced by adjusting the load applied to the press roll.

[0014] According to the image forming apparatus of the second means described above, the axial temperature difference occurring in the pressing roll can be reduced by adjusting the load applied to the pressing roll, compared to a case in which the center and end portions of the portion of one holding member through which the fixing belt comes into contact are shaped to be at the same distance from the pressing roll.

[0015] According to the image forming apparatus of the third means described above, the axial temperature difference occurring in the pressing roll is more easily reduced by adjusting the load applied to the pressing roll, compared to a case in which one holding member is not a contact member arranged to contact the inner surface of the fixing belt at a fixed position.

[0016] According to the image forming apparatus of the fourth means described above, the axial temperature difference occurring in the pressing roll can be appropriately reduced by adjusting the load applied to the pressing roll when necessary in accordance with the actual state of the temperature difference.

[0017] According to the image forming apparatus of the fifth means described above, the axial temperature difference occurring in the pressing roll can be appropriately reduced by fine-tuning the load applied to the pressing roll, compared to a case in which the low load is not divided into multiple levels of low load and the temperature difference is not divided into multiple stages.

[0018] According to the image forming apparatus of the sixth means described above, the axial temperature difference occurring in the pressing roll can be appropriately reduced by adjusting the load applied to the pressing roll when necessary, assuming in advance the cases in which the temperature difference occurs.

[0019] According to the image forming apparatus of the seventh means, the axial temperature difference occurring in the pressing roll can be appropriately reduced by fine-tuning the load applied to the pressing roll, compared to a case where the low load is not divided into multiple levels of low load and the specified conditions are not divided into multiple combinations of conditions. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to a first embodiment. [Diagram 2] 2 is a schematic diagram of a fixing device included in the image forming apparatus in FIG. 1. [Diagram 3] 3A is a schematic diagram of a load adjustment mechanism and the like in the fixing device of FIG. 2, and FIG. 3B is a schematic side view of the load adjustment mechanism and the like in FIG. [Figure 4] FIG. 2A is a schematic side view showing one state of the pressure roll and the like when the fixing operation is not performed, and FIG. 2B is a schematic side view showing the state when the fixing operation is performed. [Diagram 5] 1 is a chart showing the combination relationship between the load level and the temperature difference of the pressure roll. [Figure 6] FIG. 11 is a flowchart showing a control operation for adjusting the load of the pressure roll. [Figure 7] FIG. 7 is a flow chart showing the remaining part of the control operation of FIG. 6. [Figure 8] 5A to 5C are schematic side views showing the states of a pressure roll, a fixing belt, and a contact member subjected to low loads of various levels. [Figure 9] 13 is a table showing combinations of load levels and pressure roll temperature differences used in a fixing device in an image forming apparatus according to a second embodiment. [Figure 10] FIG. 11 is a flow chart showing a control operation for adjusting the load of a pressure roll of a fixing device in a second embodiment. [Figure 11] FIG. 11 is a flow chart showing the remaining part of the control operation of FIG. [Figure 12]FIG. 1A is a side schematic diagram showing the state when performing a fixing operation on paper with a narrow transport width, and FIG. 1B is a graph showing an example of the temperature difference in the axial direction of the pressure roll that occurs after the fixing operation of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0022] Embodiment 1 FIG. 1 shows an image forming apparatus 1 according to a first embodiment of the present invention. In this specification and the drawings, the same reference numerals are used for substantially the same components. In this specification, duplicated explanations of the same components are omitted. Furthermore, in the drawings, in order to ensure ease of understanding, illustrations other than those necessary for the explanation are almost omitted.

[0023] (1) Configuration of Image Forming Apparatus The image forming apparatus 1 is an apparatus that forms an unfixed image corresponding to image information input from the outside on a sheet 9, which is an example of a recording medium. 1, the image forming apparatus 1 has a housing 11 having a desired external shape. The image forming apparatus 1 is configured by arranging an image forming section 2, a paper feeder 4, a fixing device 5, a control device 15, etc. in the internal space of the housing 11. 1 indicates a main transport path along which the paper 9 is transported by the paper transport device 45 within the housing 11.

[0024] The image forming section 2 is a section that forms a toner image made of toner as a developer and transfers it onto a sheet 9 . The image forming unit 2 in the first embodiment is configured as an electrophotographic image forming unit. The image forming unit 2 includes a photosensitive drum 21, a charging device 22, an exposure device 23, a developing device 24, a transfer device 25, a cleaning device 26, and other devices.

[0025] Among these, the photosensitive drum 21 is an example of an image carrying means, and is a photosensitive body having a drum shape with a photosensitive layer that becomes an image forming surface or an image carrying surface. The photosensitive drum 21 receives power from a driving device (not shown) and rotates in the direction indicated by the arrow A. The charging device 22 is a device that charges the outer peripheral surface (image forming surface) of the photosensitive drum 21 to a required surface potential. As the charging device 22, for example, a device equipped with a charging member in the form of a roll or the like that is brought into contact with the image forming surface of the outer peripheral surface of the photosensitive drum 21 and to which a charging current is supplied is used.

[0026] The exposure device 23 is a device that forms an electrostatic latent image by irradiating and exposing the charged outer peripheral surface of the photosensitive drum 21 with light corresponding to image information. The exposure device 23 operates by receiving an image signal that is generated by subjecting image information input from the outside to predetermined processing by an image processing means (not shown) or the like. The image information is, for example, information related to images such as characters, figures, photographs, and patterns. The developing device 24 is a device that develops the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 21 with a developer (toner) of a corresponding predetermined color (e.g., black) to visualize it as a toner image of the predetermined color. As the developer, for example, a two-component developer containing a toner and a carrier is used.

[0027] The transfer device 25 is a device that transfers the unfixed toner image formed on the outer peripheral surface of the photosensitive drum 21 onto the paper 9. As the transfer device 25, a device that includes a transfer member in the form of a roll or the like that is brought into contact with the outer peripheral surface of the photosensitive drum 21 and is supplied with a transfer current is used. The location where the transfer device 25 and the photosensitive drum 21 face each other is a transfer position TP where an unfixed toner image is transferred. The cleaning device 26 is a device that cleans the outer circumferential surface of the photosensitive drum 21 by removing unnecessary matter such as unnecessary toner and paper powder adhering to the outer circumferential surface of the photosensitive drum 21 .

[0028] The paper feeder 4 is a device that stores paper 9 to be fed to the transfer position TP in the image forming unit 2 and sends it out at a predetermined time. The paper feeder 4 includes a container 41 for storing the paper 9, a delivery device 43 for delivering the paper 9 one sheet at a time, and other devices. In the first embodiment, two containers 41A and 41B are used as the container 41, and two sending devices 43A and 43B are used as the sending device 43. Furthermore, container 41A stores paper 9A. Container 41B stores paper 9B. Paper 9A and paper 9B are, for example, different sizes.

[0029] The paper 9 may be any sheet-like recording medium that can be transported inside the housing 11 and onto which an unfixed toner image can be transferred and fixed. As long as the recording medium satisfies these conditions, there are no particular restrictions on the material, shape, etc., of the recording medium. In the image forming apparatus 1, as the paper 9, recording media such as plain paper cut to a predetermined size, coated paper, film, thick paper, and also recording media such as envelopes.

[0030] The paper transport device 45 is a device that transports the paper 9 within the housing 11 to a required location. The paper transport device 45 has a supply path, a relay path, a discharge path, etc. The supply path is a path that transports the paper 9 from the paper supply device 4 to the transfer position TP in the image forming unit 2. The relay path is a path that transports the paper 9 from the transfer position TP in the image forming unit 2 to the fixing device 5. The discharge path is a path that transports the paper 9 from the fixing device 5 to the discharge outlet 12 provided on a side portion or the like of the housing 11. Further, the paper transport device 45 is configured by combining a plurality of transport roll pairs 46, transport path members (not shown), etc. The transport roll pair 46 is a pair of transport rolls that sandwich and transport the paper 9. In the first embodiment, for example, six transport roll pairs 46a to 46e are used. The transport path members are members that form a transport space for the paper 9 and guide the paper 9 to its destination.

[0031] The fixing device 5 is a device that fixes the unfixed image onto the paper 9. The unfixed image is a toner image that is formed in the image forming unit 2 and transferred.

[0032] As shown in FIGS. 1 and 2, the fixing device 5 according to the first embodiment is configured by arranging devices such as a heating rotor 51 and a pressure rotor 61 in the internal space of a housing 50. The housing 50 is provided with an inlet 50a for introducing the paper 9 and an outlet 50b for discharging the paper 9 after fixing. The fixing device 5 is arranged so that the heating rotor 51 and the pressure rotor 61 rotate in contact with each other, and the contacting portion is configured as the fixing processing portion FN. The fixing processing portion FN is a portion that performs a fixing process by applying heat and pressure to the paper 9 and toner image passing therethrough, and is also called a fixing nip. The fixing device 5 will be described in detail later.

[0033] The control device 15 is a device that controls the overall operation of the image forming apparatus 1. The control device 15 is configured as a control circuit in which an arithmetic processing unit, a memory element, an input / output device, etc. The control device 15 is provided with a memory device as necessary.

[0034] The control device 15 is connected to various detectors, an operation panel, a communication unit, etc. (not shown), and receives necessary information through these. The control device 15 is also connected to various control circuits to be controlled, and outputs necessary control information through these. The control device 15 operates based on a control program stored in a memory device or the like, utilizing control data, detection data, and the like.

[0035] (2) Operation of the image forming device The image forming apparatus 1 forms a basic image as follows.

[0036] In image forming apparatus 1, when a control means (not shown) receives a command for an operation of forming an image, a charging operation, an exposure operation, a developing operation, and a transfer operation are performed in image forming unit 2. Also, in image forming apparatus 1, paper supply device 4 and paper transport device 45 perform a paper feed operation.

[0037] As a result, in the image forming unit 2, a toner image corresponding to the image information is formed on the image forming surface of the photosensitive drum 21 rotating in the direction indicated by the arrow A. Meanwhile, in the paper supply device 4, the desired paper 9 (9A, 9B) is sent out and supplied to the transfer position TP of the image forming unit 2 via the supply path of the paper transport device 45. Then, in the image forming unit 2, the toner image is transferred from the photosensitive drum 21 to the paper 9 (9A, 9B) at the transfer position TP.

[0038] Furthermore, in the image forming unit 2, the cleaning device 26 performs a cleaning operation while the photosensitive drum 21 is rotating. As a result, the image forming surface of the photosensitive drum 21 is cleaned by the cleaning device 26 at times including after the toner image has been transferred.

[0039] Next, in the image forming apparatus 1, the paper 9 onto which the toner image has been transferred is transported to the fixing device 5 via the relay path of the paper transport device 45. In the relay path, the paper 9 is sent out in a state of being sandwiched between the rotating photosensitive drum 21 and the transfer device 25.

[0040] In the fixing device 5, as shown in FIG. 2, a fixing operation is performed in which the paper 9 (9A, 9B) onto which the toner image 92 has been transferred is fixed in the fixing unit FN. As a result, in the fixing device 5, the unfixed toner image 92 on the paper 9 is introduced into the fixing processing section FN and heated under pressure as it passes through, thereby being fixed to the paper 9.

[0041] Next, in the image forming apparatus 1, the paper 9 after fixing is discharged from the housing 50 of the fixing device 5, and then conveyed to the discharge port 12 via the discharge path of the paper conveying device 45. As a result, the paper 9 is sent by the transport roll 46e to an ejected paper storage section (not shown) provided in a part of the housing 11 and stored therein.

[0042] Through the above series of operations, the basic image forming operation for forming a monochrome image on one side of one sheet of paper 9 is completed.

[0043] (3-1) Configuration of the Fixing Device Next, the fixing device 5 will be described in detail.

[0044] 2, the fixing device 5 uses a heating unit having a belt-nip configuration as the heating rotator 51. The fixing device 5 also uses a pressure roll 62, which is an example of a pressing roll having a roll configuration, as the pressure rotator 61.

[0045] The heating rotator 51 includes a fixing belt 52, three holding members 53, 54, and 55 that rotatably hold the fixing belt 52, a heating means 56 that heats the fixing belt 52, and the like. Of these, the three supporting members are a heating roll 53, a contact member 54, and a meandering correction roll 55. The fixing belt 52 is supported so as to rotate in the direction indicated by an arrow B (counterclockwise in FIG. 2).

[0046] The fixing belt 52 is an endless belt whose outer circumferential surface 52a comes into contact with the surface of the paper 9 onto which the toner image 92 has been transferred in the fixing unit FN to perform the fixing process. An endless belt having thermal conductivity, flexibility, and heat resistance is used as the fixing belt 52. In addition, as the fixing belt 52, for example, a belt having a laminated structure in which an elastic layer and a release layer are formed in this order on the outer peripheral surface of a cylindrical belt base material is used.

[0047] The belt substrate is a cylindrical member made of a synthetic resin such as polyimide or polyamide, the elastic layer is made of an elastic material such as silicone rubber, and the release layer is made of a resin material such as polytetrafluoroethylene.

[0048] The heating roll 53 is a rotating roll that is heated by a heating means 56 and also heats the fixing belt 52 . As the heating roll 53, a roll body having a structure in which a surface layer 532 is laminated on the outer peripheral surface of a cylindrical roll base material 531 is used.

[0049] The roll base 531 is a cylindrical body made of a metal material such as aluminum. The roll base 531 is rotatably attached to a part of the housing 50 via a bearing (not shown). The surface layer 532 is a layer that is non-conductive and has good thermal conductivity. As the heating means 56, for example, a plurality of electric heating lamps arranged in the internal space of the roll base material 531 are used.

[0050] The contact member 54 is a member that contacts the inner circumferential surface 52b of the fixing belt 52 at a certain position to hold the fixing belt 52. As shown in FIG. 4 and other figures, the contact member 54 is a structure in which a pad material 542 is provided on the lower surface of a cylindrical support 541. The support 541 is a structure made of a metal material such as aluminum. The support 541 is fixedly attached to a part of the housing 50. The pad material 542 is a member having heat resistance, elasticity, and the like.

[0051] The contact member 54 also includes a sliding sheet (not shown) disposed between the outer surface of the pad material 542 and the inner circumferential surface 52b of the fixing belt 52. One end of the sliding sheet is attached to the support 541. Furthermore, the corner of the contact member 54 on the side where the paper 9 to be fixed is introduced (the left side in FIG. 2) is raised, and the contact member 54 is disposed in a state in which it is inclined slightly backward as a whole.

[0052] The meandering correction roll 55 is a roll that corrects meandering of the fixing belt 52. As the meandering correction roll 55, for example, a steering roll is used, which corrects the meandering of the fixing belt 52 by temporarily tilting its rotation axis when the fixing belt 52 meanders and then returning to its original position.

[0053] The pressure roll 62 as the pressure rotating member 61 presses the fixing belt 52 from its outer circumferential surface 52a side against the contact member 54 to form the fixing processing section FN. 2, the pressure roll 62 has a roll structure in which an elastic release layer 64 is provided on the outer peripheral surface of a columnar or cylindrical roll substrate 63. Reference numeral 65 in FIG. 2 denotes shaft portions provided on both ends of the roll substrate 63.

[0054] During a fixing operation, the pressure roll 62 receives power from a driving device (not shown) and is driven to rotate in the direction indicated by an arrow C. Therefore, in the fixing device 5, the pressure roll 62 rotates in the direction indicated by the arrow C, whereby the fixing belt 52 is rotated in the direction indicated by the arrow B. The fixing device 5 may be configured such that the heating roll 53 receives power from a driving device (not shown) at a predetermined time and rotates in the direction indicated by the arrow B. The predetermined time is, for example, when the pressure roll 62 is separated from the fixing belt 52 and it is necessary to keep the fixing belt 52 heated by the heating roll 53.

[0055] The pressure roll 62 has a load adjustment mechanism 70 that adjusts and applies a predetermined load to the contact member 54 via the fixing belt 52 . As shown in FIG. 3, the load adjustment mechanism 70 includes a swing support frame 71, a cam 73, a drive unit 75, and the like.

[0056] The swing support frame 71 is a member that swings about a support shaft 72 with one end supported by the support shaft 72. The swing support frame 71 has a recess that holds the shaft portion 65 of the pressure roll 62. The shaft portion 65 of the pressure roll 62 is supported by the recess held by the swing support frame 71 via a bearing 66.

[0057] The cam 73 is a plate cam that is fixed to a rotating shaft 74 and operates. The cam 73 is disposed so as to contact the other end of the swaying support frame 71 from below. The cam 73 rotates about a rotation shaft 74 and operates to sway the swaying support frame 71 in directions D1 and D2 approaching and moving away from the contact member 54. By the operation of the cam 73, the pressure roll 62 is moved in a direction approaching and separating from the contact member 54.

[0058] The driving device 75 is a device that rotates the rotary shaft 74 of the cam 73 by a predetermined angle. The driving device 75 is composed of a motor, a reduction mechanism, and the like. The operation of the drive device 75 is controlled by a drive control device 76. The drive control device 76 controls the drive power supplied to the motor. The drive control device 76 is configured as a part of a control unit of the control device 15 of the image forming apparatus 1, but may be configured as a control circuit independent of the control device 15.

[0059] 4A, when no image forming operation, and therefore no fixing operation, is being performed, the load adjustment mechanism 70 is caused to swing in a direction D2 in which the swing support frame 71 moves away from the contact member 54. When a series of continuous fixing operations are being performed, the period when no fixing operation is being performed does not include the periods between each of the continuous fixing operations.

[0060] At this time, the swing support frame 71 swings due to the operation of the cam 73. At this time, the drive device 75 is operated under the control of the drive control device 76, and the cam 73 rotates by a predetermined angle in a predetermined direction. In this case, the load adjustment mechanism 70 separates the pressure roll 62 from the contact member 54 and the fixing belt 52. As a result, the load adjustment mechanism 70 sets the load F applied to the shaft portion 65 of the pressure roll 62 to 0 (zero). At this time, the pressure roll 62 does not receive heat from the heated fixing belt 52.

[0061] When the image forming operation, and in turn the fixing operation, is performed, the load adjustment mechanism 70 is caused to swing in a direction D1 in which the swing support frame 71 approaches the contact member 54 by the operation of the cam 73, as shown in FIG. 4B.

[0062] At this time, the swing support frame 71 swings due to the operation of the cam 73. The drive device 75 is operated under the control of the drive control device 76, and the cam 73 also rotates in a predetermined direction by a predetermined angle. In this case, the load adjustment mechanism 70 brings the pressure roll 62 close to the contact member 54 and into contact with it via the fixing belt 52. As a result, the load adjustment mechanism 70 sets the load F applied to the shaft portion 65 of the pressure roll 62 to the maximum load Fmax. The maximum load Fmax at this time becomes the fixing load, which is the minimum load required for the fixing operation.

[0063] (3-2) Temperature difference occurring in the pressure roll In the fixing device 5, as illustrated in Figure 12(A), when a fixing operation is performed on a sheet of paper 9 having a conveying width W narrower than the maximum conveying width Wmax (maximum width) used in the image forming device 1, the following temperature difference occurs in the pressure roll 62.

[0064] Here, the conveying width W is the dimension of the paper 9 in a direction perpendicular to the conveying direction when the paper 9 is conveyed (conveyed) within the image forming apparatus 1. Also, the paper 9 having the narrow conveying width W is assumed to be paper 9B. Furthermore, the paper 9 is conveyed by a method in which the center position of the conveying width W is guided to pass through the center position of the conveying path or the fixing processing unit FN, that is, a so-called center registration method.

[0065] That is, when the fixing operation is performed on the paper 9 of the transport width W, the surface temperature of the pass area E1 where the paper 9B comes into contact and passes through the pressure roll 62 temporarily drops below the fixing temperature because heat is absorbed by the paper 9B, etc. On the other hand, the surface temperature of the non-pass area E2, E3 where the paper 9B does not pass through the pressure roll 62 rises above the fixing temperature because heat is not absorbed by the paper 9B, etc. and the non-pass area E2, E3 where the paper 9B does not pass through continues to be heated. 12B, a temperature difference occurs in the axial direction of the pressure roll 62. This temperature difference tends to increase almost in proportion to the number of times the fixing operation is performed consecutively on the paper 9B.

[0066] Incidentally, the fixing temperature is the minimum temperature required in the fixing unit FN during the fixing operation. The symbol CA in Fig. 12(A) indicates the portion of the contact member 54 where the fixing belt 52 passes in contact. The area including the pass area E1 and the non-pass areas E2 and E3 corresponds to the dimension of the maximum conveying width Wmax of the paper 9. The pass area E1 corresponds to the conveying width W of the paper 9B.

[0067] When such a temperature difference occurs in the pressure roll 62, the following problems arise. In other words, when the fixing operation for sheet 9A, which has a wider transport width W than sheet 9B, is performed after the fixing operation for sheet 9B is completed, the temperature difference may cause uneven fixing or wrinkles in sheet 9A.

[0068] (3-3) Measures against temperature difference of pressure roll Therefore, the fixing device 5 is configured such that the load adjustment mechanism 70 may perform an operation of applying a low load, which is smaller than the load (Fmax) for fixing, to the pressure roll 62 at least at the end of the fixing operation.

[0069] As shown in FIG. 3, the fixing device 5 is provided with temperature sensors 67, which are an example of a temperature detection means for detecting the temperatures of the central portion and the ends of the pressure roll 62 in the axial direction. The temperature sensors 67 include a first temperature sensor 67a for detecting the center, a second temperature sensor 67b for detecting the rear end, and a third temperature sensor 67c for detecting the front end. The first temperature sensor 67a, the second temperature sensor 67b, and the third temperature sensor 67c are connected to the control device 15 so as to input detection information thereto.

[0070] The central portion of the pressure roll 62 is a portion through which the center of the width direction of the paper 9 passes within the contact area of ​​the pressure roll 62 with the paper 9 at the maximum conveying width Wmax. The end portion of the pressure roll 62 is a position through which both ends of the paper 9 pass within the contact area of ​​the pressure roll 62 with the paper 9 at the maximum conveying width Wmax, or a portion a certain amount inward from that position.

[0071] And in the fixing device 5, as shown in FIGS. 5 and 7, the operation of applying the low load is performed when the temperature difference ΔT between the central part and the end part in the axial direction of the pressure roll 62 becomes a predetermined temperature or higher using the detected temperature information from the temperature sensor 67. That is, the fixing device 5 performs the operation of applying the low load only when the temperature difference ΔT reaches a necessary predetermined temperature, and does not perform the operation when the temperature difference ΔT does not reach the predetermined temperature.

[0072] The temperature difference ΔT is an average value obtained by averaging a first temperature difference obtained by subtracting the detected temperature of the first temperature sensor 67a from the detected temperature of the second temperature sensor 67b and a second temperature difference obtained by subtracting the detected temperature of the first temperature sensor 67a from the detected temperature of the third temperature sensor 67c. Note that for the temperature difference ΔT, the higher one of the first temperature difference and the second temperature difference may be selected and used, or either one may be fixed and used.

[0073] Also, in the fixing device 5, as shown in FIG. 5, the low load is divided into a plurality of levels of low loads, and the temperature difference ΔT is divided into a plurality of stages. In the first embodiment, as shown in FIG. 5, the low load is divided into three levels (low loads f1 to f3), and the temperature difference ΔT is divided into four numerical ranges. The low loads f1 to f3 have a magnitude relationship of "0 < f1 < f2 < f3 < maximum load". In this case, the fixing device 5 is configured to change and apply a plurality of levels of low loads according to the differences in temperature differences at a plurality of stages, as shown in FIGS. 5 and 7.

[0074] Furthermore, in the fixing device 5, for the contact member 54, as shown in FIG. 4(A), the central part of the portion CA where the fixing belt 52 comes into contact and passes is bent so as to approach the pressure roll 62 side more than the end part of the portion CA through which it passes. This shape is the shape when the pressure roll 62 receives the maximum load and is not in contact with the contact member 54 via the fixing belt 52.

[0075] In Embodiment 1, the contact member 54 has a shape in which the lower surface portion 541a of the cylindrical support 541 is bent as described above. In FIG. 4(A), for the sake of easy understanding, the degree of bending of the lower surface portion 541a of the support 541 is illustrated with an excessive degree. In FIG. 4(A), the symbol La indicates the separation distance between the central portion of the contacting portion CA of the lower surface portion 541a of the support 541 and the pressure roll 62. The symbols Lb and Lc indicate the separation distances between the front and rear end portions of the contacting portion CA of the lower surface portion 541a of the support 541 and the pressure roll 62, respectively. The separation distances La, Lb, and Lc have a magnitude relationship of "La < Lb ≒ Lc".

[0076] During the fixing operation, the bent lower surface portion 541a of the support 541 becomes a substantially flat surface as illustrated in FIG. 4(B). At this time, the lower surface portion 541a of the support 541 is contacted by the pressure roll 62 that has received the maximum load via the fixing belt 52. As a result, the lower surface portion 541a of the support 541 is pressurized by the pressure roll 62, so that the bending temporarily disappears and it becomes a substantially flat surface.

[0077] (3-4) Operation of the load adjustment mechanism of the pressure roll Then, as shown in FIGS. 6 and 7, in the fixing device 5, the load adjustment mechanism 70 operates to adjust the load on the pressure roll 62.

[0078] In the fixing device 5, it is determined whether the control device 15 has received a request (command) for the fixing operation (step 10: S10). The request for the fixing operation is included in the request for the image forming operation received by the image forming device 1. Also, when waiting for the request for the fixing operation, since the fixing operation is not being performed in the fixing device 5, the load F applied to the shaft portion 65 of the pressure roll 62 in the load adjustment mechanism 70 is set to 0 (see FIG. 4(A)).

[0079] The load F is 0 when, for example, the image forming apparatus 1 is waiting for the first image forming operation request after power-on, or when the load F is 0 when a certain time has elapsed since the image forming operation ended and the image forming apparatus 1 is waiting for the next image forming operation request.

[0080] Next, when a request for a fixing operation is received, the load F applied to the shaft portion 65 of the pressure roll 62 is increased from 0 to the maximum load Fmax (S11). At this time, in the fixing device 5, the load adjustment mechanism 70 is operated under the control of the control device 15 to change the load F to the maximum load Fmax. The states of the load adjustment mechanism 70 and the pressure roll 62 at this time are as described above with reference to FIG. 4(B). As a result, in the fixing device 5, the pressure roll 62 applies a minimum load required for the fixing operation to the fixing part FN.

[0081] Thereafter, the fixing operation is performed by the fixing device 5 in accordance with the image forming operation by the image forming apparatus 1 (S12). The fixing operation at this time is performed in accordance with the conditions of the image forming operation, such as the size including the conveying width of the paper 9 to be used, the number of times the image forming operation is performed, and the like.

[0082] At this time, it is determined whether the fixing operation of the fixing device 5 for the paper 9 having the same conveying width W is completed (S13). Therefore, in the fixing device 5, the fixing operation continues until the fixing operation under the same conditions is completed.

[0083] Subsequently, when the fixing operation for the paper 9 having the same conveying width W is completed, the control device 15 judges whether or not there is a next fixing operation for a paper 9 having a wider width (S14). The next wider fixing operation means that the subsequent fixing operation is a fixing operation using paper 9A having a conveying width W wider than the conveying width W of paper 9B used in the preceding fixing operation.

[0084] If it is determined in step S14 that there is no next wide fixing operation, it is determined whether there is a next narrow fixing operation (S15). The next narrower fixing operation means that the subsequent fixing operation is a fixing operation using a sheet of paper 9 having a narrower conveying width W than the conveying width W of the sheet of paper 9B used in the preceding fixing operation.

[0085] If it is determined in step S15 that there is a next narrow fixing operation, the next fixing operation is executed (S12). In this case, since the conveying width W of the paper 9 is narrower than the preceding one, it is considered that there is no risk of the temperature difference ΔT of the pressure roll 62 inducing uneven fixing, etc. Therefore, the load F applied by the load adjustment mechanism 70 in the next fixing operation at this time remains at the maximum load Wmax, as in the preceding fixing operation.

[0086] If it is determined in step S14 that there is no next wide fixing operation, the load F applied to the shaft portion 65 of the pressure roll 62 is reduced from the maximum load Fmax to 0, as shown in FIG. 6 (S16). At this time, in the fixing device 5, the load adjustment mechanism 70 is operated under the control of the control device 15, and an operation is performed to change the load F from the maximum load Fmax to 0. The states of the load adjustment mechanism 70 and the pressure roll 62 at this time are as described above with reference to FIG. In this case, the control device 15 judges again whether or not there is a request for a next new fixing operation (S10).

[0087] On the other hand, if it is determined in step S14 that the next fixing operation is a wide fixing operation, the control device 15 determines whether the temperature difference ΔT (°C) of the pressure roll 62 is within the temperature range of "0≦ΔT<10" as shown in FIG. 7 (S20).

[0088] If it is determined in step S20 that the temperature difference ΔT of the pressure roll 62 is within the temperature range of "0≦ΔT<10", the next wide-range fixing operation is performed (S12). In this case, since the temperature difference ΔT of the pressure roll 62 is relatively small, it is considered that there is no risk of the temperature difference ΔT inducing defects such as uneven fixing in the next wide fixing operation. Therefore, the load F applied by the load adjustment mechanism 70 in this next wide fixing operation is kept at the maximum load Wmax, as in the preceding fixing operation. The load selection in this case corresponds to the selection of "maximum load" of the load levels shown in FIG.

[0089] Next, if it is determined in step S20 that the temperature difference ΔT of the pressure roll 62 is not within the temperature range of "0≦ΔT<10", the control device 15 determines what temperature range the temperature difference ΔT is in (S21).

[0090] If it is determined in step S21 that the temperature difference ΔT is within the temperature range of "ΔT≧30", the load F applied by the load adjustment mechanism 70 is set to the level of the low load f1 (S22). At this time, in the fixing device 5, the load adjustment mechanism 70 is operated under the control of the control device 15, and an operation is performed to change the load F from the maximum load Fmax to the lowest load f1.

[0091] 8A, the load adjustment mechanism 70 operates to relatively minimize the degree of contact between the pressure roll 62 and the contact member 54 and the fixing belt 52. In other words, the load adjustment mechanism 70 moves the pressure roll 62 in a direction farthest from the contact member 54 while still slightly contacting a portion of the fixing belt 52.

[0092] The reference symbol CP1 in FIG. 8A indicates a portion where the pressure roll 62 receiving the low load f1 at this time comes into contact with the contact member 54 and the fixing belt 52. This contact portion CP1 is limited to a central portion in the axial direction of the pressure roll 62, and is the narrowest portion in the first embodiment. In addition, this contact portion CP1 may be, for example, approximately the same dimension as the conveying width W of the paper 9B used in the preceding fixing operation, or approximately the same dimension as the minimum conveying width W of the paper 9 used in the image forming device 1.

[0093] As a result, the end of the pressure roll 62 at this time, other than the contact portion CP1, is not substantially in contact with the heated fixing belt 52, and is therefore in a state in which the heat of the fixing belt 52 is not easily transmitted. In other words, the end of the pressure roll 62 at this time, other than the contact portion CP1, is not heated or is not easily heated by the heated fixing belt 52. Meanwhile, the contact portion CP1 of the pressure roll 62 at this time continues to be heated by the heated fixing belt 52. The heated state at this time is illustrated in FIG. 8(A) in which the pressure roll 62 is shaded in black.

[0094] As a result, the pressure roll 62 is prevented from increasing in surface temperature at the end portion other than the portion CP1 that contacts the fixing belt 52, etc., and is reheated and restored even if the surface temperature of the contact portion CP1 drops. In other words, the temperature difference ΔT in the axial direction of the pressure roll 62 is reduced.

[0095] In this case, the control device 15 determines whether the temperature difference ΔT of the pressure roll 62 is within the temperature range of "0≦ΔT<10" (S25). That is, the load F in the fixing device 5 is maintained at the low load f1 until the temperature difference ΔT of the pressure roll 62 is reduced to an acceptable level.

[0096] If the temperature difference ΔT falls within the temperature range of "0≦ΔT<10" in step S25, the determination result is YES, and the next wide-range fixing operation is performed (S12). Note that until the determination result in step S25 becomes YES, the fixing operation by the fixing device 5 is temporarily interrupted and the next wide fixing operation is not started. This temporary interruption of the fixing operation is also the same when the subsequent low loads f2 and f3 are applied.

[0097] Therefore, according to the fixing device 5 at this time, the temperature difference ΔT in the axial direction occurring in the pressure roll 62 is reduced by adjusting the load applied to the pressure roll 62 .

[0098] Next, if it is determined in step S21 that the temperature difference ΔT is within the temperature range of "20≦ΔT<30", the load F applied by the load adjustment mechanism 70 is set to the level of the low load f2 (S23). At this time, in the fixing device 5, the load adjustment mechanism 70 is operated under the control of the control device 15, and an operation is performed to change the load F from the maximum load Fmax to a low load f2 that is an intermediate level among low loads.

[0099] 8B, the load adjustment mechanism 70 operates so that the degree of contact between the pressure roll 62 and the contact member 54 and the fixing belt 52 is relatively low at an intermediate level. That is, the load adjustment mechanism 70 moves the pressure roll 62 in a direction away from the contact member 54 at an intermediate level while keeping the pressure roll 62 in contact with a portion of the fixing belt 52 more than when the load f1 is low.

[0100] 8B indicates a portion where the pressure roll 62 receiving the low load f2 comes into contact with the contact member 54 and the fixing belt 52. This contact portion CP2 is wider than the contact portion CP1 at the time of the low load f1, but is limited to a portion on the central side in the axial direction of the pressure roll 62. In the first embodiment, it is a narrow portion at the intermediate level. Moreover, the contact portion CP2 only needs to be at least wider than the above-mentioned CP1.

[0101] As a result, the end of the pressure roll 62 at this time, other than the contact portion CP2, is not substantially in contact with the heated fixing belt 52, and is therefore in a state in which the heat of the fixing belt 52 is not easily transmitted. In other words, the end of the pressure roll 62 at this time, other than the contact portion CP2, is not heated or is not easily heated by the heated fixing belt 52. Meanwhile, the contact portion CP2 of the pressure roll 62 at this time continues to be heated by the heated fixing belt 52. This heated state is illustrated in FIG. 8(B) with the pressure roll 62 shaded in black, similar to the case of FIG. 8(A).

[0102] As a result, the pressure roll 62 is prevented from increasing in surface temperature at the end portion other than the portion CP2 that contacts the fixing belt 52, etc., and is restored even if the surface temperature at the contact portion CP2 drops. In other words, the temperature difference ΔT in the axial direction of the pressure roll 62 is reduced.

[0103] Also in this case, the control device 15 determines whether the temperature difference ΔT of the pressure roll 62 is within the temperature range of "0≦ΔT<10" (S25). If it is determined in step S25 that the temperature difference ΔT falls within the temperature range of "0≦ΔT<10", the next wide-range fixing operation is performed (S12).

[0104] Therefore, also in this fixing device 5, the temperature difference ΔT in the axial direction occurring in the pressure roll 62 is reduced by adjusting the load applied to the pressure roll 62.

[0105] Next, if it is determined in step S21 that the temperature difference ΔT is within the temperature range of "10≦ΔT<20," the load F applied by the load adjustment mechanism 70 is set to the level of a low load f3 (S24). At this time, in the fixing device 5, the load adjustment mechanism 70 is operated under the control of the control device 15, and an operation is performed to change the load F from the maximum load Fmax to a low load f3 that is the relatively largest level among the low loads.

[0106] 8C, the load adjustment mechanism 70 operates so that the degree of contact between the pressure roll 62 and the contact member 54 and the fixing belt 52 is at the relatively lowest level. That is, the load adjustment mechanism 70 moves the pressure roll 62 in the direction farthest from the contact member 54 while keeping the pressure roll 62 in contact with a portion of the fixing belt 52 more than when the load f2 is low.

[0107] Reference symbol CP3 in FIG. 8C indicates a portion where the pressure roll 62 receiving the low load f3 comes into contact with the contact member 54 and the fixing belt 52. This contact portion CP3 is wider than the contact portion CP2 at the time of the low load f2, but is limited to exclude parts of both ends in the axial direction of the pressure roll 62. In the first embodiment, this is the widest portion. Moreover, the contact portion CP3 is required to have a dimension at least larger than that of the contact portion CP2.

[0108] As a result, the end of the pressure roll 62 at this time, other than the contact portion CP3, is not substantially in contact with the heated fixing belt 52, and is therefore in a state in which the heat of the fixing belt 52 is not easily transmitted. In other words, the end of the pressure roll 62 at this time, other than the contact portion CP3, is not heated or is not easily heated by the heated fixing belt 52. Meanwhile, the contact portion CP3 of the pressure roll 62 at this time continues to be heated by the heated fixing belt 52. This heated state is illustrated in FIG. 8(C) with the pressure roll 62 shaded in black, similar to the case of FIG. 8(A).

[0109] As a result, the pressure roll 62 is prevented from increasing in surface temperature at the end portion other than the portion CP3 that contacts the fixing belt 52, etc., and is restored even if the surface temperature at the contact portion CP3 drops. In other words, the temperature difference ΔT in the axial direction of the pressure roll 62 is reduced.

[0110] Also in this case, the control device 15 determines whether the temperature difference ΔT of the pressure roll 62 is within the temperature range of "0≦ΔT<10" (S25). If it is determined in step S25 that the temperature difference ΔT falls within the temperature range of "0≦ΔT<10", the next wide-range fixing operation is performed (S12).

[0111] Therefore, also in this fixing device 5, the temperature difference ΔT in the axial direction occurring in the pressure roll 62 is reduced by adjusting the load applied to the pressure roll 62.

[0112] As described above, in the fixing device 5, even if a temperature difference ΔT occurs in the axial direction of the pressure roll 62, the temperature difference ΔT is reduced, thereby suppressing the induction of uneven fixing and wrinkles in the paper 9 caused by such temperature difference ΔT. Furthermore, in the image forming apparatus 1 equipped with the fixing device 5, the fixing device 5 can perform a satisfactory image forming operation without causing uneven fixing or wrinkles in the paper 9 due to the temperature difference ΔT.

[0113] In addition, in the fixing device 5, the central portion of the portion CA of the contact member 54 through which the fixing belt 52 passes in contact therewith is bent so as to be closer to the pressure roll 62 side than the ends of the portion CA through which the contact member 54 passes (see FIG. 4(A)). For this reason, in the fixing device 5, it is easier to adjust the range of the contact portion of the pressure roll 62 with the fixing belt 52, compared to a case in which the center and end portions of the contact member 54, where the fixing belt 52 passes in contact with the pressure roll 62, are shaped to be at the same distance as the pressure roll 62. As a result, according to the fixing device 5, the temperature difference ΔT in the axial direction generated in the pressure roll 62 can be easily reduced by adjusting the load applied to the pressure roll 62.

[0114] Furthermore, in the fixing device 5, the operation of applying a low load is configured to be performed when the temperature difference ΔT in the axial direction of the pressure roll 62 becomes equal to or greater than a predetermined temperature, using information on the detected temperature from the temperature sensor 67. Therefore, according to the fixing device 5, the axial temperature difference ΔT occurring in the pressure roll 62 can be appropriately reduced by adjusting the load F applied to the pressure roll 62 when necessary in accordance with the actual state of the temperature difference ΔT. In other words, when the temperature difference ΔT is such that there is no risk of causing problems such as uneven fixing due to the temperature difference ΔT, there is no need to adjust the load F applied to the pressure roll 62, and the next wide-width fixing operation can be performed quickly.

[0115] Furthermore, in the fixing device 5, the low load is divided into three levels of low load, f1, f2, and f3, and the temperature difference ΔT is divided into a plurality of temperature ranges as shown in FIG. Therefore, according to the fixing device 5, compared to a case where the low load is not divided into multiple levels of low load and the temperature difference is not divided into multiple stages, it is possible to appropriately reduce the temperature difference ΔT generated in the pressure roll 62 by fine-tuning the load F applied to the pressure roll 62.

[0116] Embodiment 2 FIG. 9 is a diagram showing a part of a fixing device in an image forming apparatus according to the second embodiment of the present invention. The image forming apparatus of embodiment 2 and the fixing device used therein have the same configuration as the image forming apparatus 1 of embodiment 1 and the fixing device 5 used therein, except that the information used for load adjustment of the load adjustment mechanism 70 of the fixing device is changed.

[0117] The fixing device in the image forming apparatus according to the second embodiment includes a collection unit 17 (see FIG. 3) for collecting information on the conveying width W of the paper 9 and the number of sheets used continuously. The number of sheets of paper 9 used continuously is information corresponding to the number of times when an image forming operation or fixing operation using paper 9 of the same conveying width W is requested (continuously) multiple times.

[0118] The collection means 17 may be, for example, an operation panel for selecting or setting information on the size of the paper 9 used in the image forming operation and the number of times the image forming operation will be performed (number of prints, etc.). In addition, examples of the collection means 17 include a communication unit or a control device 15 that receives information selected or set for the size of the paper 9 and the number of image forming operations on the setting screen of an external connection device connected to the image forming apparatus 1. Furthermore, as the collection means 17, when there is a size detection means for detecting the size of the paper 9 stored in the storage body 41 in the paper supply device 4, the size detection means may also be included.

[0119] In the fixing device according to the second embodiment, as shown in FIGS. 10 and 11, the operation of applying a low load by the load adjustment mechanism 70 is performed when the number of consecutive sheets of the paper 9 having a conveyance width W narrower than the maximum width Wmax during conveyance among the papers 9 satisfies a predetermined condition using the collection information of the collection means 17. In the second embodiment, as the predetermined condition of the above-described number of consecutive sheets, as shown in step S17 of FIG. 10, it is divided into a condition of whether or not the fixing operation of the same width has been performed N times or more.

[0120] In the fixing device according to the second embodiment, as shown in FIGS. 9 and 10, similar to the case of the first embodiment, the low load is divided into three levels of low loads (low loads f1 to f3), and the above-described predetermined condition is divided into a plurality of combined conditions. In the second embodiment, as shown in FIG. 9, for the conveyance width Wa of the paper 9 used in the fixing operation of the same width, as the conveyance width W other than the maximum width Wmax, it is divided into three conveyance widths Wmin, W2, and W3. The three conveyance widths Wmin, W2, and W3 are each a division of the conveyance width of the paper 9 used in the image forming apparatus. Also, the three conveyance widths Wmin, W2, and W3 have a magnitude relationship of "Wmin < W2 < W3 < Wmax".

[0121] In the second embodiment, a condition is set as to whether the conveying width Wa of the paper 9 used in the fixing operation of the same width is the maximum width Wmax, as shown in step S30 in Fig. 11. In the second embodiment, a condition is set as to whether the conveying width Wa of the paper 9 used in the fixing operation of the same width is the maximum width Wmax or any one of the above three conveying widths Wmin, W2, and W3, as shown in Figs. 9 and 11.

[0122] In this case, the fixing device determines the result when a condition is satisfied that combines the condition of the number of fixing operations of the same width (corresponding to the number of continuous uses) and the condition of the transport width Wa of the paper 9 used in the fixing operations of the same width, as shown in Figures 9 to 11. Next, the fixing device in this case is configured to apply a plurality of levels of low loads f1 to f3 in a manner that changes them according to the difference in the determination result.

[0123] In the fixing device in the second embodiment, as shown in FIGS. 10 and 11, the load adjustment mechanism 70 is operated to adjust the load on the pressure roll 62.

[0124] In this fixing device, the operation relating to the load adjustment of the pressure roll 62, that is, the operations from step S10 to step S16 in FIG. 10, are performed in the same manner as in the fixing device 5 in the first embodiment (see FIG. 6).

[0125] In particular, in this fixing device, when it is determined in step S14 that there is a next wide fixing operation, it is determined whether the number of fixing operations of the same width up to step S13 is N or more (S17). In this case, the number N of times can be appropriately set from the viewpoint of whether or not the load F applied to the pressure roll 62 needs to be changed to a lower load. The number N of times is set to, for example, 3 times.

[0126] If it is determined in step S15 that the number of fixing operations for the same width is less than N, the process proceeds to step S15 as shown in FIG. 10, and may proceed to step S16 in some cases. In this case, since the number of fixing operations for the same width is less than N times, it is not considered that the load F applied to the pressure roll 62 needs to be changed to a low load at this stage.

[0127] On the other hand, if it is determined in step S15 that the fixing operation of the same width has been performed N times or more, as shown in FIG. 11, it is determined whether the conveying width Wa of the paper 9 used in the preceding fixing operation of the same width is the maximum width Wmax (S30).

[0128] If it is determined in step S30 that the conveying width Wa is the maximum width Wmax, it is assumed that there is almost no temperature difference ΔT in the axial direction of the pressure roll 62, and the next wide fixing operation is performed (S12).

[0129] If it is determined in step S30 that the conveying width Wa is not the maximum width Wmax, it is determined what width the conveying width Wa is (S31).

[0130] If it is determined in step S31 that the conveying width Wa is Wmin, it is assumed that the temperature difference ΔT of the pressure roll 62 is at its largest, and the load F applied by the load adjustment mechanism 70 is set to the level of the low load f1 (S32). At this time, in the fixing device in the second embodiment, the load adjustment mechanism 70 is operated under the control of the control device 15, and an operation is performed to change the load F from the maximum load Fmax to the lowest load f1.

[0131] At this time, the load adjustment mechanism 70 operates to reduce the degree of contact between the contact member 54 of the pressure roll 62 and the fixing belt 52 to a relatively minimum, similar to when the low load f1 is applied in embodiment 1 (see Figure 8(A)).

[0132] 8A, the pressure roller 62 of the fixing device in the second embodiment is prevented from increasing in surface temperature at the end portion other than the portion CP1 that contacts the fixing belt 52, etc. On the other hand, even if the surface temperature of the contact portion CP1 of the pressure roller 62 drops, the pressure roller 62 is reheated and restored. As a result, the temperature difference ΔT in the axial direction of the pressure roll 62 at this time becomes small.

[0133] In this case, the control device 15 determines whether the elapsed time T after the change to application of a low load has reached a predetermined time Tx or more (S35).

[0134] The specified time Tx is set based on an estimate of the time at which the temperature difference ΔT in the axial direction of the pressure roll 62 after the application of a low load becomes small enough that there is no risk of causing defects such as uneven fixing due to the temperature difference ΔT. The predetermined time Tx can also be set to a time previously obtained through experiments that is small enough to prevent the occurrence of such a problem. The determination in step S35 may be the same as that in the fixing device 5 in the embodiment 1. That is, the determination in step S35 may be configured to determine whether the temperature difference ΔT of the pressure roll 62 is within the temperature range of "0≦ΔT<10" (see S25 in FIG. 7).

[0135] If the elapsed time T becomes equal to or exceeds the predetermined time Tx in step S35, the determination result becomes YES, and the next wide-width fixing operation is executed (S12). Incidentally, until the determination result in step S35 becomes YES, the fixing operation by the fixing device in the second embodiment is temporarily suspended without starting the next wide fixing operation. This temporary suspension of the fixing operation is also the same when the subsequent low loads f2 and f3 are applied.

[0136] Therefore, in this case, according to the fixing device in the second embodiment, the temperature difference ΔT in the axial direction occurring in the pressure roll 62 is reduced by adjusting the load applied to the pressure roll 62.

[0137] Next, if it is determined in step S31 that the conveying width Wa is W2, the temperature difference ΔT of the pressure roll 62 is deemed to be at an intermediate level, and the load F applied by the load adjustment mechanism 70 is set to the low load f2 level (S33). At this time, in the fixing device in the second embodiment, the load adjustment mechanism 70 is operated under the control of the control device 15 to change the load F from the maximum load Fmax to a low load f2 that is an intermediate level among low loads.

[0138] At this time, the load adjustment mechanism 70 operates in the same manner as in the fixing device 5 in the first embodiment so that the degree of contact between the contact member 54 of the pressure roll 62 and the fixing belt 52 is relatively low at an intermediate level. That is, the load adjustment mechanism 70 moves the pressure roll 62 in a direction away from the contact member 54 at an intermediate level while keeping the pressure roll 62 in contact with a part of the fixing belt 52 more than when the load f1 is low (see FIG. 8B).

[0139] This suppresses an increase in the surface temperature of the pressure roll 62 of the fixing device in the second embodiment at the end portion other than the portion CP2 that contacts the fixing belt 52, etc. On the other hand, even if the surface temperature of the contact portion CP2 of the pressure roll 62 drops, the pressure roll 62 is reheated and restored. As a result, the temperature difference ΔT in the axial direction of the pressure roll 62 at this time becomes small.

[0140] Also in this case, in the fixing device in the second embodiment, the control device 15 determines whether the elapsed time T is equal to or greater than the predetermined time Tx (S35). If it is determined in step S35 that the elapsed time T is equal to or greater than the predetermined time Tx, the next wide-width fixing operation is performed (S12).

[0141] Therefore, also in this fixing device 5, the temperature difference ΔT in the axial direction occurring in the pressure roll 62 is reduced by adjusting the load applied to the pressure roll 62.

[0142] Next, if it is determined in step S31 that the conveying width Wa is W3, it is assumed that the temperature difference ΔT of the pressure roll 62 is at its smallest, and the load F applied by the load adjustment mechanism 70 is set to the low load f3 level (S34). At this time, in the fixing device in the second embodiment, the load adjustment mechanism 70 is operated under the control of the control device 15 to change the load F from the maximum load Fmax to a low load f3, which is the highest level among the low loads.

[0143] At this time, the load adjustment mechanism 70 operates to relatively increase the degree of contact between the contact member 54 of the pressure roll 62 and the fixing belt 52, as in the case of the fixing device 5 in the first embodiment. That is, the load adjustment mechanism 70 moves the pressure roll 62 in a direction away from the contact member 54 at an intermediate level while keeping the pressure roll 62 in contact with a portion of the fixing belt 52 more than when the load f2 is low (see FIG. 8C).

[0144] 8C, the pressure roll 62 of the fixing device in the second embodiment is prevented from increasing in surface temperature at the end portion other than the portion CP3 that contacts the fixing belt 52, etc. On the other hand, even if the surface temperature of the contact portion CP3 of the pressure roll 62 drops, the pressure roll 62 is reheated and restored. As a result, the temperature difference ΔT in the axial direction of the pressure roll 62 at this time becomes small.

[0145] Also in this case, in the fixing device in the second embodiment, the control device 15 determines whether the elapsed time T is equal to or greater than the predetermined time Tx (S35). If it is determined in step S35 that the elapsed time T is equal to or greater than the predetermined time Tx, the next wide-width fixing operation is performed (S12).

[0146] Therefore, also in this fixing device 5, the temperature difference ΔT in the axial direction occurring in the pressure roll 62 is reduced by adjusting the load applied to the pressure roll 62.

[0147] As described above, in the fixing device of embodiment 2, even if a temperature difference ΔT occurs in the axial direction of the pressure roll 62, the temperature difference ΔT is reduced, and therefore, the induction of uneven fixing and wrinkles in the paper 9 caused by such temperature difference ΔT is also suppressed. Furthermore, in the image forming apparatus 1 including the fixing device in the second embodiment, good image forming operation is performed without uneven fixing or wrinkling of the paper 9 caused by the temperature difference ΔT in the fixing device.

[0148] Variations. The present invention is not limited to the configuration examples exemplified in the first and second embodiments, and may be modified as necessary, such as by combination, without departing from the spirit of the inventions described in the claims. Therefore, the present invention also includes, for example, the following modified examples.

[0149] In the first and second embodiments, a configuration may be adopted in which the low load is set to one level, and the temperature difference ΔT of the pressure roll 62 when the low load is applied is set to one value. In addition, in the first and second embodiments, a configuration may be adopted in which the low load is divided into two levels, and two values ​​of the temperature difference ΔT of the pressure roll 62 are prepared as the criterion for determining when to apply each of the two levels of low load. Furthermore, in the first and second embodiments, the low load may be subdivided into three or more levels, and three or more values ​​of the temperature difference ΔT of the pressure roll 62 may be prepared as the criterion for applying the low load of each of the subdivided levels.

[0150] In the second embodiment, the configuration example has been exemplified in which the presence or absence and level of the operation of applying a low load are adjusted and controlled in response to information relating to differences in the conveying width W of the paper 9 being used. In the second embodiment, other than this, for example, the adjustment and control may be performed in response to information relating to differences in thickness of the paper 9. In this case, the adjustment and control may be configured to combine information on the difference in thickness of the paper 9 and information on the difference in the conveying width W of the paper 9. Also, in this case, for example, since there is a tendency for a temperature difference to occur more easily in the axial direction of the pressure roll 62 as the thickness of the paper 9 increases, the adjustment and control may be configured to correspond to this.

[0151] In the first and second embodiments, a contact member 54 is exemplified which is fixed at a certain position as a retaining member for the fixing belt 52, and which is shaped so that the central portion of the portion CA through which the fixing belt 52 contacts is closer to the pressure roll 62 side than the ends of the portion CA through which the fixing belt 52 passes. However, the holding member having such a shape may be a rotating roll having such a shape (for example, a spindle shape or a crown shape).

[0152] The fixing device 5 may be modified in terms of the type and type of the heating means 56, the type and number of holding members other than the heating roll 53 that holds the fixing belt 52, and the like.

[0153] In addition, in the first embodiment and the like, a configuration example in which a monochrome image is formed is shown as the image forming apparatus 1, but the image forming apparatus of the present invention may be an apparatus that forms a multi-color image composed of a combination of toners of multiple colors. In addition, the image forming apparatus of the present invention is not particularly limited in terms of its image forming method, transfer method, and the like, so long as it employs a fixing device such as that exemplified in the first and second embodiments.

[0154] (Additional Note) (((1))) an image forming section for forming an unfixed image on a sheet of paper; a fixing device for fixing the unfixed image onto the paper; having the fixing device includes a fixing belt, a plurality of holding members for rotatably holding the fixing belt, a pressing roll for pressing the fixing belt from an outer circumferential surface side against one of the holding members to form a fixing processing section, a heating means for heating the fixing belt, and a load adjustment mechanism for adjusting a load applied to the pressing roll and applying a load for fixing during a fixing operation; In the image forming apparatus, the load adjustment mechanism may perform an operation of applying a low load, which is smaller than the load for fixing, to the pressing roll at least when the fixing operation of the fixing device is completed. (((2))) The image forming apparatus described in (((1))) has a shape in which the center of the portion through which the fixing belt passes in contact with the holding member is closer to the pressing roll than the ends of the portion through which the fixing belt passes. (((3))) The image forming apparatus according to (((2))), wherein the one holding member is a contact member that is arranged so as to come into contact with the inner circumferential surface of the fixing belt at a fixed position. (((4))) A temperature detection means is provided for detecting temperatures of a central portion and an end portion of the pressing roll in an axial direction, The operation of applying the low load is performed when the temperature difference between the center and end portions in the axial direction of the pressing roll becomes equal to or greater than a predetermined temperature using information on the detected temperature from the temperature detection means. (((5))) The low load is divided into a plurality of levels of low load, and the temperature difference is divided into a plurality of stages; The image forming apparatus according to (((4))), wherein the low loads of the plurality of levels are changed and applied in accordance with differences in the temperature differences of the plurality of stages. (((6))) a collection means for collecting information on at least the width and the number of consecutive sheets of the paper; The image forming apparatus described in any one of (((1))) to (((3))) above, wherein the operation of applying the low load is performed when the number of continuously used sheets of paper that are narrower than the maximum width during transport satisfies a predetermined condition using the collection information of the collection means. (((7))) The low load is divided into a plurality of levels of low load, and the predetermined condition is divided into a plurality of combinations of conditions, The image forming apparatus according to (((6))), wherein the low loads of the plurality of levels are applied while being changed according to differences in results when the plurality of combinations of conditions are satisfied.

[0155] According to the image forming apparatus of (((1))), the axial temperature difference that occurs due to the pass and non-pass areas of the press roll in the fixing device where the paper passes can be reduced by adjusting the load applied to the press roll. According to the image forming apparatus of (((2))), the axial temperature difference occurring in the pressing roll can be reduced by adjusting the load applied to the pressing roll, compared to a case in which the center and end portions of the portion of one holding member through which the fixing belt comes into contact are shaped to be at the same distance from the pressing roll. In the image forming apparatus of (((3))), the axial temperature difference occurring in the pressing roll can be easily reduced by adjusting the load applied to the pressing roll, compared to a case in which one holding member is not a contact member that is arranged so as to contact the inner surface of the fixing belt at a fixed position. According to the image forming apparatus of (((4))), the axial temperature difference occurring in the pressing roll can be appropriately reduced by adjusting the load applied to the pressing roll as necessary in accordance with the actual state of the temperature difference. According to the image forming apparatus of (((5))), the axial temperature difference occurring in the pressing roll can be appropriately reduced by fine-tuning the load applied to the pressing roll, compared to a case in which the low load is not divided into multiple levels of low load and the temperature difference is not divided into multiple stages. According to the image forming apparatus of (((6))), the axial temperature difference occurring in the pressing roll can be appropriately reduced by adjusting the load applied to the pressing roll when necessary, assuming in advance the cases in which the temperature difference will occur. According to the image forming apparatus of (((7))), the axial temperature difference occurring in the pressing roll can be appropriately reduced by fine-tuning the load applied to the pressing roll, compared to a case in which the low load is not divided into a plurality of levels of low load and the above-mentioned specified conditions are not divided into a plurality of combinations of conditions. [Explanation of symbols]

[0156] 1. Image forming device 2 … Image forming section 5. Fixing device 17…Collection means 52...Fuser belt 52b…Inner peripheral surface 53...heating roll (an example of a plurality of holding members) 54...contact member (one example of a plurality of holding members) 55...Meandering correction roll (an example of a plurality of holding members) 62...Pressure roll (an example of a pressing roll) 67...Temperature detection means 67a, 67b, 67c...Temperature sensors (an example of a temperature detection means) 70...Load adjustment mechanism FN: Fixing section CA: Contact area of ​​the fixing belt F...Load Fmax: Maximum load (an example of the load for fixing) f1,f2,f3…Low load

Claims

1. an image forming section for forming an unfixed image on a sheet of paper; a fixing device for fixing the unfixed image onto the paper; having the fixing device includes a fixing belt, a plurality of holding members for rotatably holding the fixing belt, a pressing roll for pressing the fixing belt from an outer circumferential surface side against one of the holding members to form a fixing processing section, a heating means for heating the fixing belt, and a load adjustment mechanism for adjusting a load applied to the pressing roll and applying a load for fixing during a fixing operation; In the image forming apparatus, the load adjustment mechanism may perform an operation of applying a low load, which is smaller than the load for fixing, to the pressing roll at least when the fixing operation of the fixing device is completed.

2. 2 . The image forming apparatus according to claim 1 , wherein the one holding member is shaped so that a center portion of the portion through which the fixing belt passes in contact with the one holding member is closer to the pressing roll than an end portion of the portion through which the fixing belt passes.

3. 3. The image forming apparatus according to claim 2, wherein the one holding member is a contact member arranged to contact the inner circumferential surface of the fixing belt at a fixed position.

4. A temperature detection means is provided for detecting temperatures of a central portion and an end portion of the pressing roll in an axial direction, 2. The image forming apparatus according to claim 1, wherein the operation of applying the low load is performed when a temperature difference between a center portion and an end portion in an axial direction of the pressing roll becomes equal to or exceeds a predetermined temperature using information on a detected temperature from the temperature detection means.

5. The low load is divided into a plurality of levels of low load, and the temperature difference is divided into a plurality of stages; 5. The image forming apparatus according to claim 4, wherein the low loads at the plurality of levels are changed and applied in accordance with differences in the temperature differences at the plurality of stages.

6. a collection means for collecting information on at least the width and the number of consecutive sheets of the paper; 2. The image forming apparatus according to claim 1, wherein the operation of applying the low load is performed when the number of consecutive sheets of paper having a width narrower than the maximum width during transport among the sheets satisfies a predetermined condition using the collected information of the collecting means.

7. The low load is divided into a plurality of levels of low load, and the predetermined condition is divided into a plurality of combinations of conditions, 7. The image forming apparatus according to claim 6, wherein the low loads of the plurality of levels are changed and applied in accordance with differences in results when the plurality of combinations of conditions are satisfied.

Images