Fixing device and image forming apparatus

Abstract

To achieve suppression of the slipping between a fixing belt and a pressing roller and reduction in the heating time of the fixing belt, without adding another roller.SOLUTION: A fixing device includes: a fixing belt that is heated by a heat source and rotates; a pressing roller that rotates forms a nip part at a spot where the pressing roller is in contact with the fixing belt, the pressing roller rotating; and a load adjustment mechanism that obtains a belt temperature of the fixing belt and adjusts a load at the nip part according to a state of the belt temperature relative to a predetermined temperature.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Patent document 1 discloses a technology for driving a fixing belt with a driving member that drives the fixing belt from its outer surface outside the contact nip area, in order to provide a belt nip type fixing device that ensures both the glossiness of a toner image by ensuring pressure in the contact nip area between the fixing belt and heating roller, and stabilizing belt transport performance by preventing belt slippage. Furthermore, Patent Document 2 discloses a technology for suppressing the advance load applied to the nip forming member when the pressure member performs an advance movement operation, in order to prevent a shortening of the lifespan of the fixed member as a component by reducing the load applied to the fixed member. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-300986 A [Patent Document 2] JP 2007-121407 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in the fixing device used in the image forming apparatus, a fixing process is performed using a fixing belt tensioned by multiple rolls and a pressure roll in contact with a pad portion with the fixing belt sandwiched between them. In this technique, the fixing belt rotates together with the pressure roll as the temperature of the fixing belt rises. In this technology, the temperature of the fixing belt may not be fully increased, and the pressure roll may rotate in a state where the fixing belt is still embossed. When the fixing belt is embossed in this way, the drive torque for rotating the fixing belt increases, and a difference in rotation speed occurs between the fixing belt and the pressure roll. When a difference in rotation speed occurs between the fixing belt and the pressure roll, slippage occurs, and the surfaces of the fixing belt and the pressure roll are damaged. In order to suppress this slippage, for example, if a new drive roll is provided externally, the fixing device becomes larger and more expensive. An object of the present invention is to suppress slippage between a fixing belt and a pressure roll and to shorten the heating time of the fixing belt without adding a new roll. [Means for solving the problem]

[0005] The invention described in claim 1 is a fixing device characterized by comprising a fixing belt that is heated and rotated by a heat source, a rotating pressure roll that forms a nip portion at a point of contact with the fixing belt, and a load adjustment mechanism that acquires the belt temperature of the fixing belt and adjusts the load of the nip portion depending on the state of the belt temperature relative to a predetermined temperature. The invention described in claim 2 is the fixing device described in claim 1, characterized in that the load adjustment mechanism increases the load at the nip portion compared to during printing when the belt temperature is below a predetermined temperature. The invention described in claim 3 is the fixing device described in claim 2, characterized in that when the belt temperature reaches a predetermined temperature with the load of the nip portion increased compared to during printing, the load adjustment mechanism reduces the load of the nip portion compared to during printing. The invention described in claim 4 is the fixing device described in claim 3, characterized in that the load adjustment mechanism increases the load of the nip portion from a state lowered compared to the load during printing to the load during printing when printing begins. The invention described in claim 5 is the fixing device described in claim 1, characterized in that the load adjustment mechanism reduces the load at the nip portion compared to when printing is occurring when the belt temperature is above a predetermined temperature and no printing is occurring. The invention described in claim 6 is the fixing device described in claim 5, characterized in that the load adjustment mechanism increases the load of the nip portion from a state lowered compared to the load during printing to the load during printing when printing begins. The invention described in claim 7 is the fixing device described in claim 1, characterized in that the load adjustment mechanism switches the load of the nip portion when the fixing device is raised. An eighth aspect of the present invention is the fixing device according to the seventh aspect, characterized in that the load at the nip portion is switched from a load greater than the load during printing to a load smaller than the load during printing. The invention described in claim 9 is the fixing device described in claim 1, characterized in that the predetermined temperature is a temperature determined to relieve mold on the fixing belt. The invention described in claim 10 is the fixing device described in claim 1, characterized in that the nip portion is formed by a pad that presses the paper together with the pressure roll, and the load adjustment mechanism adjusts the load of the nip portion formed by the pad and the pressure roll with the fixing belt sandwiched therebetween. The invention described in claim 11 is the fixing device described in claim 1, characterized in that it is provided with a temperature sensor that detects the belt temperature of the fixing belt before it enters the nip portion, and the load adjustment mechanism adjusts the load of the nip portion according to the state of the belt temperature detected by the temperature sensor. The invention described in claim 12 is an image forming apparatus comprising: a developing unit that develops an electrostatic latent image on a photosensitive member; a transfer unit that transfers the developed image to paper; a fixing belt that is heated by a heat source and rotates; a pressure roll that rotates and forms a nip portion at a point of contact with the fixing belt; and a load adjustment mechanism that acquires the belt temperature of the fixing belt and adjusts the load of the nip portion depending on the state of the belt temperature relative to a predetermined temperature, and a fixing device that fixes the paper to which the developed image has been transferred. Effect of the Invention

[0006] According to the first aspect of the present invention, slippage between the fixing belt and the pressure roll can be suppressed and the heating time of the fixing belt can be shortened without adding a new roll. According to the invention described in claim 2, for example, slippage between the fixing belt and the pressure roll caused when the pressure roll rotates in a state where the fixing belt has a pattern attached thereto is suppressed. According to the invention described in claim 3, the efficiency of heat conduction from the heating source to the belt temperature is improved, compared to the case where the load at the nip portion is not reduced compared to during printing. According to the invention described in claim 4, the load at the nip portion can be adjusted to the load during printing when starting printing, in a state in which the efficiency of heat conduction from the heating source to the belt temperature is improved. According to the invention as set forth in claim 5, the nip width of the nip portion can be reduced to increase the efficiency of heat conduction to the belt, and the warm-up time can be shortened. According to the sixth aspect of the present invention, printing can be started in a state where the efficiency of heat conduction to the belt is increased. According to the seventh aspect of the present invention, slippage between the fixing belt and the pressure roll can be suppressed when the fixing device is started up. According to the eighth aspect of the present invention, after slippage between the fixing belt and the pressure roll is suppressed when the fixing device is started up, the efficiency of heat conduction to the belt can be increased until printing begins. According to the ninth aspect of the present invention, slippage between the fixing belt and the pressure roll can be suppressed. According to the tenth aspect of the invention, a load can be applied stably to the pressure roll. According to the invention as set forth in claim 11, the belt temperature in the nip portion between the fixing belt and the pressure roll can be grasped, and slippage caused by the fixing belt and the pressure roll can be suppressed. According to the twelfth aspect of the present invention, slippage between the fixing belt and the pressure roll can be suppressed without adding a new roll, and the heating time of the fixing belt can be shortened. [Brief description of the drawings]

[0007] [Figure 1]FIG. 1 is a diagram illustrating an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram illustrating a fixing device according to the present embodiment. [Diagram 3] 6(a) and 6(b) are diagrams illustrating a procedure for adjusting the load by the load adjustment mechanism in accordance with the belt temperature state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. [Description of Image Forming Apparatus] FIG. 1 is a diagram illustrating an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 according to the present embodiment includes a paper feed unit 1A, a printing unit 1B, and a paper discharge unit 1C. The paper feed unit 1A includes a first paper storage section 11 to a fourth paper storage section 14 for storing paper P as an example of a recording medium. The paper feed unit 1A also has feed rolls 15-18 that correspond to the first paper storage section 11 to the fourth paper storage section 14, respectively, and feed the paper P stored in each paper storage section to a transport path connected to the printing unit 1B.

[0009] The printing unit 1B includes an image forming section 20 that forms an image on a sheet P. The printing unit 1B also includes a control section 21 that controls each section of the image forming apparatus 1. The printing unit 1B also includes an image processing section 22. The image processing section 22 performs image processing on image data transmitted from the image reading device 4 and the personal computer (PC) 5. The printing unit 1B is also provided with a UI (User Interface) 23, which is configured with a touch panel or the like and notifies the user of information and receives information input from the user.

[0010] The image forming section 20 is provided with six image forming units 30T, 30P, 30Y, 30M, 30C, and 30K (hereinafter, sometimes simply referred to as "image forming units 30") that are arranged in parallel at regular intervals. Each image forming unit 30 includes a photosensitive drum 31 on which an electrostatic latent image is formed while rotating in the direction of arrow A, a charging roll 32 which charges the surface of the photosensitive drum 31, a developing device 33 which develops the electrostatic latent image formed on the photosensitive drum 31, and a drum cleaner 34 which removes toner and the like from the surface of the photosensitive drum 31.

[0011] The image forming section 20 is also provided with an exposure device 26 that exposes the photoconductor drum 31 of each image forming unit 30 to laser light. The exposure of the photoconductor drum 31 by the exposure device 26 is not limited to using laser light. For example, a light source such as an LED (Light Emitting Diode) may be provided for each image forming unit 30, and the photoconductor drum 31 may be exposed to light emitted from the light source.

[0012] Each image forming unit 30 is configured similarly, except for the toner contained in the developer 33. The image forming units 30Y, 30M, 30C, and 30K form toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Further, the image forming units 30T and 30P form toner images using toner corresponding to a corporate color, foaming toner for Braille, fluorescent color toner, toner for improving gloss, etc. In other words, the image forming units 30T and 30P form toner images using toner of a special color.

[0013] The image forming section 20 is also provided with an intermediate transfer belt 41 onto which the toner images of each color formed on the photosensitive drums 31 of the image forming units 30 are transferred. The image forming section 20 is also provided with a primary transfer roll 42 that transfers the respective color toner images of the respective image forming units 30 onto the intermediate transfer belt 41 at the primary transfer portion P1. The image forming section 20 is also provided with a secondary transfer roll 40 that transfers the toner image transferred onto the intermediate transfer belt 41 onto the paper P at a secondary transfer section P2. Furthermore, the image forming section 20 is provided with a belt cleaner 45 that removes toner and the like from the surface of the intermediate transfer belt 41, and a fixing device 100 that fixes the secondarily transferred image onto the paper P.

[0014] The image forming unit 20 performs an image forming operation based on a control signal from the control unit 21 . Specifically, in the image forming unit 20, first, image processing is performed on the image data input from the image reading device 4 or the PC 5 by the image processing unit 22, and the image data after image processing is supplied to the exposure device 26. Then, for example, in a magenta (M) image forming unit 30M, the surface of the photosensitive drum 31 is charged by the charging roll 32, and then the exposure device 26 irradiates the photosensitive drum 31 with laser light modulated by image data obtained from the image processing unit 22.

[0015] As a result, an electrostatic latent image is formed on the photoconductor drum 31 . The formed electrostatic latent image is developed by the developing unit 33, and a magenta toner image is formed on the photosensitive drum 31. Similarly, yellow, cyan and black toner images are formed in the image forming units 30Y, 30C and 30K, and special color toner images are formed in the image forming units 30T and 30P.

[0016] The respective color toner images formed in each image forming unit 30 are electrostatically transferred in sequence by a primary transfer roll 42 onto an intermediate transfer belt 41 rotating in the direction of arrow B in Figure 1, and superimposed toner images are formed on the intermediate transfer belt 41. The superimposed toner image formed on the intermediate transfer belt 41 is transported to a secondary transfer portion P2 constituted by a secondary transfer roll 40 and a backup roll 49 as the intermediate transfer belt 41 moves.

[0017] On the other hand, the paper P is taken out from the first paper storage unit 11 by, for example, the delivery roll 15, and then transported to the position of the registration roll 74 via the transport path. When the superimposed toner image is transported to the secondary transfer portion P2, the paper P is supplied from the registration roll 74 to the secondary transfer portion P2 in accordance with the timing. Then, at the secondary transfer portion P2, the superimposed toner images are electrostatically transferred onto the paper P all at once by the action of a transfer electric field formed between the secondary transfer roll 40 and the backup roll 49.

[0018] Thereafter, the paper P onto which the superimposed toner images have been electrostatically transferred is conveyed to a fixing device 100. In the fixing device 100, the sheet P on which the unfixed toner image has been formed is pressurized and heated under the control of the control unit 21, and the toner image is fixed to the sheet P. Then, the sheet P on which the fixing process has been performed passes through a curl correction section 81 provided in the sheet discharge unit 1C, and is then conveyed to a sheet stacking section (not shown).

[0019] [Description of Fixing Device 100] Fig. 2 is a diagram for explaining the fixing device 100 in the present embodiment, and is an enlarged view of the fixing device 100 shown in Fig. 1. As shown in Fig. 2, the fixing device 100 includes a fixing belt 110 that is heated by a heat source and rotates, a pressure roll 120 that forms a nip portion N at a point where it contacts the fixing belt 110 and presses the paper P, and a load adjustment mechanism 130 that adjusts the load of the nip portion N by moving the pressure roll 120 in the vertical direction. Note that the upward direction is the direction in which the pressure roll 120 is brought closer to the fixing belt 110, and the downward direction is the direction in which the pressure roll 120 is moved away from the fixing belt 110. Furthermore, the fixing device 100 includes a pad 140 which forms a nip portion N together with the pressure roll 120 with the fixing belt 110 sandwiched therebetween and presses the paper P together with the pressure roll 120, a heat roll 150 which is an example of a heat source and heats the fixing belt 110, and a steering roll 160 which applies tension to the fixing belt 110. The fixing device 100 also includes a temperature sensor 170 which detects the belt temperature T of the fixing belt 110 before it enters the nip portion N.

[0020] The pressure roll 120 is configured to rotate in the transport direction of the paper P by a motor (not shown) (direction "C" in FIG. 2). The rotation of the pressure roll 120 in direction C causes the fixing belt 110 to rotate in response (direction "D" in FIG. 2). The pressure roll 120 rotates together with the fixing belt 110, thereby transporting the paper P on which the unfixed toner image has been formed, one after another, to the nip portion N. Then, at the nip portion N, the unfixed toner image is fixed to the paper P by heating the fixing belt 110 and applying pressure from the pressure roll 120 and pad 140.

[0021] The load adjustment mechanism 130 acquires the belt temperature T from the temperature sensor 170. For example, the belt temperature T is the surface temperature of the fixing belt 110. The load adjustment mechanism 130 is controlled by the control unit 21 described in FIG. 1. The belt temperature T detected by the temperature sensor 170 is sent to the control unit 21, and the control unit 21 adjusts the load of the nip portion N by the load adjustment mechanism 130 according to the state of the belt temperature T sent thereto.

[0022] The load adjustment mechanism 130 adjusts the load at the nip portion N by moving the pressure roll 120 in the vertical direction. For example, the load adjustment mechanism 130 increases the load at the nip portion N by moving the pressure roll 120 in the upward direction, which is a direction that brings the pressure roll 120 closer to the fixing belt 110, and decreases the load at the nip portion N by moving the pressure roll 120 in the downward direction, which is a direction that moves the pressure roll 120 away from the fixing belt. The load adjustment mechanism 130 is configured by combining, for example, a motor and an eccentric cam structure.

[0023] The nip width of the nip portion N is a contact area between the pressure roll 120 and the fixing belt 110, and is a width that expands in the conveying direction of the paper P at the location where the pad 140 is provided. The surface shape of the pressure roll 120 is composed of an elastic layer, and the nip width changes depending on the load of the nip portion N. For example, when the load adjustment mechanism 130 moves the pressure roll 120 in an upward direction that brings the pressure roll 120 closer to the fixing belt 110 and increases the load of the nip portion N, the nip width of the nip portion N becomes wider. Also, for example, when the load adjustment mechanism 130 moves the pressure roll 120 in a downward direction that moves the pressure roll 120 away from the fixing belt and decreases the load of the nip portion N, the nip width of the nip portion N becomes narrower.

[0024] [Load Adjustment Mechanism 130 Adjusts Load According to Belt Temperature T] Next, the load adjustment by the load adjustment mechanism 130 according to the state of the belt temperature T will be described with reference to FIGS. 3(a) and (b) are diagrams illustrating the procedure of load adjustment by the load adjustment mechanism 130 in this embodiment according to the state of the belt temperature T. Fig. 3(a) is a diagram showing the change in load by the load adjustment mechanism 130, and Fig. 3(b) is a diagram showing the temperature change of the belt temperature T.

[0025] The vertical axis of FIG. 3(a) indicates the load applied to the nip N by the load adjustment mechanism 130, and the horizontal axis indicates time. Also, N1 to N3 on the vertical axis indicate predetermined loads applied to the nip N. The horizontal axis indicates time, which includes start-up from when the power is turned on until the first print is performed, printing from start-up until the first print is performed, standby after that while waiting for printing, next printing, and next standby. This start-up is divided into a first start-up (1) at which the rotation of the pressure roll 120 and the driven rotation of the fixing belt 110 start, and a second start-up (2) after this start-up (1) until the first print is performed. Note that FIG. 3(a) shows a state after a certain time has passed since the first start-up (1).

[0026] Among N1 to N3 on the vertical axis, N1 is a low load determined to suppress a drop in temperature without preventing the temperature rise of the fixing belt 110. N2 is a load determined to fix an unfixed toner image on the paper P. N3 is a load determined to increase the grip force of the pressure roll 120 to the fixing belt 110. By increasing the grip force using the load of N3, slippage between the fixing belt 110 and the pressure roll 120 is suppressed. Considering N2, which is the load when actually fixing an unfixed toner image, as the center, N1 can be set to a load of about 1 / 4 to 2 / 3 times N2, and N3 can be set to a load of about 5 / 4 to 2 times N2. As the actual loads of N1 to N3, for example, N1 is set to 30 Newtons (30N), N2 is set to 50 Newtons (50N), and N3 is set to 80 Newtons (80N), etc. are selected.

[0027] The vertical axis of FIG. 3(b) indicates the belt temperature T, and the horizontal axis indicates time. The start-up, printing, and standby shown in FIG. 3(b) correspond to those shown in FIG. 3(a). T1 to T3 shown on the vertical axis indicate the state of the belt temperature T. T1 indicates the belt temperature after a certain time has elapsed from the initial temperature at the first start-up (1), which is, for example, room temperature. T2 is a preset temperature, which indicates the temperature at which the first start-up (1) is switched to the second start-up (2). This preset temperature is a temperature that is preset to ease the mold attached to the fixing belt 110, and when the belt temperature T reaches T2, the influence of slip caused by the mold attached to the fixing belt 110 is eliminated or reduced, and the rise in the belt temperature is allowed to take priority. Then, the control unit 21 recognizes that the belt temperature T has reached T2, and causes the load adjustment mechanism 130 to reduce the load at the nip portion N from N3 to N1. The load on the nip portion N is reduced, suppressing heat dissipation and shortening the start-up time. T3 is the heating temperature when fixing an unfixed toner image to paper P, and represents the temperature during printing. The temperature T3 during printing is, for example, 150°C to 200°C, and T2 can be set to about 1 / 2 of T3, for example, 100°C.

[0028] Next, adjustment of the load by the load adjustment mechanism 130 in accordance with the state of the belt temperature T will be described with reference to FIGS.

[0029] First, the first start-up (1) will be described. As shown in FIG. 3(b), the first start-up (1) is a state in which the belt temperature T is equal to or lower than the set temperature T2. In this first start-up (1), the shape of the belt is not relaxed. When the belt temperature T is equal to or lower than the set temperature T2, the load adjustment mechanism 130 described in FIG. 2 moves the pressure roll 120 upward to increase the load at the nip N. As shown in FIG. 3(a), in the first start-up (1), the load at the nip N is N3, which is higher than the load N2 during printing. When the load at the nip N becomes N3, the grip force of the pressure roll 120 on the fixing belt 110 increases. As a result, even if the shape of the belt is not relaxed, slippage between the fixing belt 110 and the pressure roll 120 is suppressed.

[0030] The transition from the first start-up time (1) to the second start-up time (2) will be described. As shown in FIG. 3(b), when the belt temperature T further rises from the first start-up time (1), the belt temperature T becomes the set temperature T2. This set temperature T2 is a temperature that is determined in advance to ease the marks on the fixing belt 110. When the belt temperature T reaches the set temperature T2, the load adjustment mechanism 130 described in FIG. 2 moves the pressure roll 120 downward to reduce the load on the nip N. As a result, as shown in FIG. 3(a), the load on the nip N becomes N1 from N3, which is lower than the load N2 during printing. In this way, in this embodiment, the load on the nip N is switched when the fixing device 100 is started up.

[0031] The second start-up time (2) will be described. The second start-up time (2) is a warm-up time during which the belt temperature T rises from T2 to T3, which is a temperature at which printing is possible. During the second start-up time (2), the load at the nip portion N is reduced from N3 to N1 by the load adjustment mechanism 130, that is, the load is switched from N3, which is a load greater than the load N2 during printing, to N1, which is a load smaller than the load N2 during printing. As a result, the nip width of the nip portion N is narrower than during the first start-up time (1), and the thermal conduction efficiency of the belt temperature T is improved during the second start-up time (2) compared to during the first start-up time (1). In other words, during the second start-up time (2), heat dissipation is suppressed from T2 to T3, which is a temperature at which printing is possible, making it easier to raise the belt temperature T, and shortening the start-up time.

[0032] Next, the transition from the second start-up time (2) to the printing time will be described. At the second start-up time (2), the belt temperature T rises to T3, and printing of the paper P is started. Then, when the transition from the second start-up time (2) to the printing time occurs, the load adjustment mechanism 130 described in FIG. 2 moves the pressure roll 120 upward, and increases the load at the nip portion N until it reaches the load at the printing time. As shown in FIG. 3(a), the load at the nip portion N rises from N1 to N2, which is the load at the printing time. Then, in FIGS. 3(a) and (b), the state of the belt temperature T and the load at the nip portion N transitions from the start-up time to the printing time. At the printing time, the belt temperature T is maintained at T2, and the load at the nip portion N is maintained at N2.

[0033] Next, the standby state will be described. During standby when no printing is being performed, as shown in FIG. 3(b), the belt temperature T is equal to or higher than the set temperature T2. During this standby state, the load adjustment mechanism 130 moves the pressure roll 120 downward to reduce the load at the nip portion N compared to that during printing. As shown in FIG. 3(a), when moving from printing to standby, the load at the nip portion N is reduced from N2, which is the load during printing, to N1. In this way, by reducing the load at the nip portion N, during standby, the improved thermal conduction efficiency of the belt temperature T can be maintained until the next printing.

[0034] At the next printing time, the load adjustment mechanism 130 moves the pressure roll 120 upward to increase the load at the nip portion N from a state lower than that at the time of printing to the load at the time of printing. As shown in FIG. 3(a), the load at the nip portion N increases from N1 to N2, which is the load at the time of printing.

[0035] In this manner, in the present embodiment, by adjusting the load at the nip portion N according to the state of the belt temperature T, slippage between the fixing belt and the pressure roll during start-up is suppressed, and the heating time of the fixing belt is also shortened.

[0036] Although the present embodiment has been described above, the present invention is not limited to these embodiments. For example, the load of the nip portion N may be increased by moving the pad 140 in the vertical direction. In addition, the load of the nip portion N can be adjusted more finely.

[0037] <Additional Notes> (((1))) a fixing belt that is heated and rotated by a heat source; a pressure roll that rotates and forms a nip portion at a position where the pressure roll contacts the fixing belt; a load adjustment mechanism that acquires a belt temperature of the fixing belt and adjusts a load at the nip portion in accordance with a state of the belt temperature relative to a predetermined temperature; A fixing device comprising: (((2))) The fixing device according to (((1))), wherein the load adjustment mechanism increases the load at the nip portion compared to during printing when the belt temperature is equal to or lower than a predetermined temperature. (((3))) The fixing device described in (((2))) is characterized in that when the belt temperature reaches a predetermined temperature with the load at the nip portion increased compared to that during printing, the load adjustment mechanism reduces the load at the nip portion compared to that during printing. (((4))) The fixing device described in any one of ((2))) to (((4))), characterized in that, when starting printing, the load adjustment mechanism increases the load of the nip portion from a state lowered compared to the load during printing to the load during printing. (((5))) The fixing device described in (((1))) is characterized in that the load adjustment mechanism reduces the load at the nip portion compared to when printing is occurring when the belt temperature is at or above a predetermined temperature and printing is not occurring. (((6))) The fixing device described in (((5))) is characterized in that, when starting printing, the load adjustment mechanism increases the load at the nip portion from a state lowered compared to the load during printing to the load during printing. (((7))) The fixing device according to any one of ((1))) to (((6))), wherein the load adjustment mechanism switches the load on the nip portion when the fixing device is started up. (((8))) The fixing device according to any one of ((1))) to (((7))), wherein the load at the nip portion is switched from a load greater than the load during printing to a load smaller than the load during printing. (((9))) The fixing device according to any one of ((1)) to ((8)) above, wherein the predetermined temperature is a temperature determined to relax the mold on the fixing belt. (((10))) The nip portion is formed by a pad that presses the paper together with the pressure roll, The fixing device according to (((1))), wherein the load adjustment mechanism adjusts the load of the nip portion formed by the pad and the pressure roll with the fixing belt sandwiched therebetween. (((11))) a temperature sensor for detecting a belt temperature of the fixing belt before the fixing belt enters the nip portion; The fixing device according to (((1))), wherein the load adjustment mechanism adjusts the load at the nip portion in accordance with the state of the belt temperature detected by the temperature sensor. (((12))) a developer for developing the electrostatic latent image on the photoconductor; a transfer section for transferring the developed image onto a sheet of paper; a fixing belt that is heated and rotated by a heat source; a pressure roll that rotates and forms a nip portion at a position where the pressure roll contacts the fixing belt; a load adjustment mechanism that acquires a belt temperature of the fixing belt and adjusts a load at the nip portion in accordance with a state of the belt temperature relative to a predetermined temperature; and a fixing device that fixes the paper onto which the developed image has been transferred. An image forming apparatus comprising:

[0038] According to the fixing device of (((1))), slippage between the fixing belt and the pressure roll can be suppressed and the heating time of the fixing belt can be shortened without adding a new roll. According to the fixing device of (((2))), for example, slippage between the fixing belt and the pressure roll caused by the pressure roll rotating with the fixing belt having a pattern attached thereto is suppressed. According to the fixing device of (((3))), the efficiency of heat conduction from the heat source to the belt temperature is improved, compared to a case in which the load at the nip portion is not reduced compared to during printing. According to the fixing device of (((4))), the load of the nip portion can be adjusted to the load during printing when starting printing, while improving the efficiency of thermal conduction from the heat source to the belt temperature. According to the fixing device of (((5))), the nip width of the nip portion is reduced to increase the efficiency of heat conduction to the belt, and the warm-up time can be shortened. According to the fixing device of (((6))), it is possible to start printing in a state where the efficiency of heat conduction to the belt is increased. According to the fixing device of (((7))), slippage between the fixing belt and the pressure roll can be suppressed when the fixing device is started up. According to the fixing device of (((8))), after slippage between the fixing belt and the pressure roll is suppressed when the fixing device is started up, the efficiency of heat conduction to the belt can be increased until printing begins. According to the fixing device of (((9))), slippage between the fixing belt and the pressure roll can be suppressed. According to the fixing device of (((10))), a stable load can be applied to the pressure roll. According to the fixing device of (((11))), the belt temperature in the nip portion between the fixing belt and the pressure roll can be grasped, and slippage between the fixing belt and the pressure roll can be suppressed. According to the image forming apparatus of (((12))), slippage between the fixing belt and the pressure roll can be suppressed and the heating time of the fixing belt can be shortened without adding a new roll. [Explanation of symbols]

[0039] 100... fixing device, 110... fixing belt, 120... pressure roll, 130... load adjustment mechanism

Claims

1. a fixing belt that is heated and rotated by a heat source; a pressure roll that rotates and forms a nip portion at a position where the pressure roll contacts the fixing belt; a load adjustment mechanism that acquires a belt temperature of the fixing belt and adjusts a load at the nip portion in accordance with a state of the belt temperature relative to a predetermined temperature; A fixing device comprising:

2. 2. The fixing device according to claim 1, wherein the load adjustment mechanism increases the load at the nip portion compared to during printing when the belt temperature is equal to or lower than a predetermined temperature.

3. 3. The fixing device according to claim 2, wherein the load adjustment mechanism reduces the load at the nip portion compared to that during printing when the belt temperature reaches a predetermined temperature with the load at the nip portion increased compared to that during printing.

4. 4. The fixing device according to claim 3, wherein the load adjustment mechanism increases the load at the nip portion from a state lowered compared to the state during printing to the load during printing when starting printing.

5. 2. The fixing device according to claim 1, wherein the load adjustment mechanism reduces the load at the nip portion compared to when printing is in progress when the belt temperature is equal to or higher than a predetermined temperature and printing is not in progress.

6. 6. The fixing device according to claim 5, wherein the load adjustment mechanism increases the load at the nip portion from a state lowered compared to the state during printing to the load during printing when starting printing.

7. 2. The fixing device according to claim 1, wherein the load adjustment mechanism switches the load applied to the nip portion when the fixing device is started up.

8. 8. The fixing device according to claim 7, wherein the load at the nip portion is switched from a load larger than the load during printing to a load smaller than the load during printing.

9. 2. The fixing device according to claim 1, wherein the predetermined temperature is a temperature determined to relax a mold attached to the fixing belt.

10. The nip portion is formed by a pad that presses the paper together with the pressure roll, 2. The fixing device according to claim 1, wherein the load adjustment mechanism adjusts a load at the nip portion formed by the pad and the pressure roll with the fixing belt sandwiched therebetween.

11. a temperature sensor for detecting a belt temperature of the fixing belt before the fixing belt enters the nip portion; 2. The fixing device according to claim 1, wherein the load adjustment mechanism adjusts the load at the nip portion in accordance with the state of the belt temperature detected by the temperature sensor.

12. a developer for developing the electrostatic latent image on the photoconductor; a transfer section for transferring the developed image onto a sheet of paper; a fixing belt that is heated and rotated by a heat source; a pressure roll that rotates and forms a nip portion at a position where the pressure roll contacts the fixing belt; a load adjustment mechanism that acquires a belt temperature of the fixing belt and adjusts a load at the nip portion in accordance with a state of the belt temperature relative to a predetermined temperature; and a fixing device that fixes the paper onto which the developed image has been transferred. An image forming apparatus comprising:

Images