Belt unit and image forming apparatus

Abstract

To suppress damage to the endless means compared to when the endless means starts rotating with the same contact pressure as during use. [Solution] A belt unit (F) comprising: an opposing means (Fp) positioned opposite a support means (4) with an endless means (1) in between and in contact with the endless means (1) at a first contact pressure; a heating means (2a) for heating the endless means (4); and a control means (C) that, when the rotation of the endless means (1) begins, starts heating with the heating means (2a) and controls at least one of the support means (4) and the opposing means (Fp) to control the contact pressure between the endless means (1) and the opposing means (Fp) to a second contact pressure higher than the first contact pressure.

Description

Technical Field

[0001] The present invention relates to a belt unit and an image forming apparatus.

Background Art

[0002] Regarding a fixing device that heats and fixes an unfixed image on the surface of a medium in an image forming apparatus, the techniques described in the following Patent Documents 1-3 are known. Japanese Unexamined Patent Application Publication No. 2008-165102 as Patent Document 1 describes a fixing device having a heating roller (10) and a pressure belt (20). In the configuration described in Patent Document 1, a pressing member (5) and a grip portion (G1) having a high coefficient of friction outside the paper passing range are provided inside the pressure belt (20). When the rotation of the heating roller (10) starts, the pressure belt (20) is surely driven by the high coefficient of friction of the grip portion (G1).

[0003] Japanese Unexamined Patent Application Publication No. 2009-069220 as Patent Document 2 describes a fixing device having a fixing roller (60) and a pressure roller (70). In Patent Document 2, an endless belt (83) is in contact with the fixing roller (60), and the endless belt (83) is heated in a state of being stretched by heater lamps (86, 87). The endless belt (83) varies the tension before fixing to relax the shape (curl) attached to the endless belt (83) and suppresses the rotation failure of the endless belt (83).

[0004] Japanese Unexamined Patent Application Publication No. 2001-075385 as Patent Document 3 describes a fixing device having a fixing belt (110) and a pressure roller (120). In Patent Document 3, high grip members (G) are fixed to both ends in the width direction of the outer periphery of the fixing belt (110). The high grip member (G) is configured to be able to absorb the oil applied to the surface of the fixing belt (110) or flow it in the circumferential direction. By providing the high grip member (G), the grip force between the fixing belt (110) and the pressure roller (120) is ensured.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2008-165102 ("0008"-"0010", "0056"-"0074", Figures 2-4) [Patent Document 2] Japanese Patent Publication No. 2009-069220 ("0008"-"0014", "0064"-"0085", Figure 3, Figures 5-7) [Patent Document 3] Japanese Patent Publication No. 2001-075385 ("0014"-"0016", Figure 2) [Overview of the project] [Problems that the invention aims to solve]

[0006] The technical objective of this invention is to suppress damage to the endless means compared to the case where the endless means starts rotating with the same contact pressure as during use. [Means for solving the problem]

[0007] To solve the aforementioned technical problems, the belt unit of the invention described in claim 1 is: A rotating endless means, Support means for supporting the endless means, An opposing means is positioned opposite the support means with the endless means in between, and contacts the endless means with a predetermined first contact pressure, A heating means for heating the endless means, When the rotation of the endless means is started, the heating means starts heating and controls at least one of the support means and the opposing means to control the contact pressure between the endless means and the opposing means to a second contact pressure higher than the first contact pressure, It is characterized by having the following features.

[0008] The invention described in claim 2 is the belt unit described in claim 1, The support means that supports the endless means and is non-rotating, It is characterized by having the following features.

[0009] The invention described in claim 3 is the belt unit described in claim 2, At the end of the support means downstream of the rotational direction of the endless means, the support means supports the endless means in a bent position. It is characterized by having the following features.

[0010] The invention described in claim 4 is the belt unit described in claim 1, The heating means is positioned at a location separate from the support means. It is characterized by having the following features.

[0011] The invention described in claim 5 is the belt unit described in claim 4, A rotating means that incorporates the heating means and rotates while supporting the endless means, It is characterized by having the following features.

[0012] The invention described in claim 6 is the belt unit described in claim 1, The control means returns the contact pressure from the second contact pressure to the first contact pressure after one rotation of the endless means, It is characterized by having the following features.

[0013] The invention described in claim 7 is the belt unit described in claim 1, The control means controls the second contact pressure for the period from when the endless means started rotating until the surface portion of the endless means that was in contact with the heating means reaches the position opposite the opposing means. It is characterized by having the following features.

[0014] The invention described in claim 8 is the belt unit described in claim 1, The support means is supported so as to be movable in a direction approaching or moving away from the opposing means, When controlling the second contact pressure, a control means for moving the support means in a direction approaching the opposing means more than in the case of the first contact pressure, characterized by comprising the same.

[0015] The invention according to claim 9 is the belt unit according to claim 1, an opposing means supported so as to be movable in a direction approaching or separating from the support means, When controlling the second contact pressure, a control means for moving the opposing means in a direction approaching the support means more than in the case of the first contact pressure, characterized by comprising the same.

[0016] The invention according to claim 10 is the belt unit according to claim 1, a control means for controlling the contact pressure to the second contact pressure at the start of rotation of the endless means when power is turned on, characterized by comprising the same.

[0017] The invention according to claim 11 is the belt unit according to claim 1, a measuring means for measuring the elapsed time since the endless means stopped rotating, a control means for controlling the contact pressure to the second contact pressure when the elapsed time measured by the measuring means reaches a predetermined first time, characterized by comprising the same.

[0018] The invention according to claim 12 is the belt unit according to claim 1, a temperature detecting means for detecting the temperature of the endless means, a control means for controlling the contact pressure to the second contact pressure when the temperature detected by the temperature detecting means is lower than a predetermined first temperature, characterized by comprising the same.

[0019] The invention according to claim 13 is the belt unit according to claim 1, During the period in which the second contact pressure is controlled, the control means controls the rotational speed of the endless means to be lower than the rotational speed during the period in which the first contact pressure is controlled. It is characterized by having the following features.

[0020] The invention described in claim 14 relates to the belt unit described in any one of claims 1 to 13, The fixing device is configured such that, as the medium passes between the endless means and the opposing means, the unfixed image on the surface of the medium is fixed by the heat of the heating means and the contact pressure between the endless means and the opposing means. It is characterized by the following:

[0021] To solve the aforementioned technical problems, the image forming apparatus of the invention described in claim 15 is Image holding means for holding an image on the surface, A transfer means for transferring the image of the image holding means onto a medium, A belt unit according to claim 14 for fixing an image transferred to the aforementioned medium, It is characterized by having the following features. [Effects of the Invention]

[0022] According to the invention described in claim 1, 15, damage to the endless means can be suppressed compared to the case where the endless means starts rotating with the same contact pressure as during use. According to the invention described in claim 2, even if the rotational resistance of the endless means increases compared to the case of a rotating support means, rotation is initiated by the second contact pressure, and damage to the endless means can be suppressed. According to the invention described in claim 3, even if the rotational resistance of the endless means increases compared to the case where the endless means is not bent, rotation is initiated by the second contact pressure, and damage to the endless means can be suppressed.

[0023] According to the invention described in claim 4, even if heating of the endless means in the opposing region between the support means and the opposing means is not possible at the start of rotation, damage to the endless means can be suppressed. According to the invention described in claim 5, the endless means can be heated by a heating means built into the rotating means. According to the invention described in claim 6, after one rotation in which the entire circumference of the endless means is heated and slippage between the endless means and the opposing means is less likely to occur, the contact pressure is returned from the second to the first contact pressure, thereby enabling rapid fixing while suppressing damage to the endless means. According to the invention described in claim 7, the second contact pressure is controlled until the heated surface portion, which is less prone to slippage, reaches the opposing position, thereby enabling rapid fixing while suppressing damage to the endless means.

[0024] According to the invention described in claim 8, compared to the case where the opposing means moves relative to the support means, a reduction in the cost of the configuration for moving the support means can be expected. According to the invention described in claim 9, the influence on the posture of the endless means can be suppressed compared to the case where the support means moves relative to the opposing means. According to the invention described in claim 10, compared to the case where the contact pressure is not controlled to a second level when the power is turned on, damage to the endless means when the power is turned on is suppressed. According to the invention described in claim 11, compared to the case where the contact pressure is controlled to a second contact pressure when the elapsed time does not reach a first time, unnecessary contact pressure control processing can be reduced. According to the invention described in claim 12, compared to the case where the contact pressure is controlled to a second level when the temperature of the endless means reaches a first level, unnecessary contact pressure control processing can be reduced. According to the invention described in claim 13, damage to the endless means can be suppressed compared to a case where the rotational speed of the endless means is not lower than the rotational speed during the period when it is controlled by the first contact pressure, even when it is controlled by the second contact pressure. According to the invention described in claim 14, compared to not applying a second contact pressure when the endless means starts rotating, poor fixing due to damage to the endless means can be suppressed. [Brief explanation of the drawing]

[0025] [Figure 1] Figure 1 is an overall explanatory diagram of the image forming apparatus of Embodiment 1 of the present invention. [Figure 2] Figure 2 is an enlarged view of the fixing device of Example 1, with Figure 2A being an explanatory diagram of the state when it has moved to the first contact position, and Figure 2B being an explanatory diagram of the state when it has moved to the second contact position. [Figure 3] Figure 3 is a functional block diagram of the control unit of Embodiment 1. [Modes for carrying out the invention]

[0026] Next, with reference to the drawings, examples of embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. For the sake of easier understanding of the following explanation, in the drawings, the front-to-back direction is the X-axis direction, the left-to-right direction is the Y-axis direction, and the up-to-down direction is the Z-axis direction. The directions or sides indicated by the arrows X, -X, Y, -Y, Z, and -Z are defined as front, rear, right, left, up, down, or front side, rear side, right side, left side, up side, and down side, respectively. Furthermore, in the diagram, a circle with a "·" inside represents an arrow pointing from the back to the front of the paper, and a circle with an "×" inside represents an arrow pointing from the front to the back of the paper. In the following explanation using diagrams, diagrams of components other than those necessary for the explanation have been omitted as appropriate for ease of understanding. [Examples]

[0027] Figure 1 is an overall explanatory diagram of the image forming apparatus of Embodiment 1 of the present invention. In Figure 1, a copier U, as an example of an image forming apparatus, includes a user interface UI as an example of an operating unit, a scanner U1 as an example of an image reading device, a paper feeder U2, a printer U3 as an example of an image recording means, and a paper ejection unit U4.

[0028] The user interface UI includes, as an example of an input unit, a power button, a copy start key, a copy count setting key, a numeric keypad, and a display unit. The scanner device U1 reads a document (not shown), converts it into image information, and inputs it into the printer unit U3. The paper feeder U2 has multiple paper feed trays TR1, TR2, TR3, and TR4, which are examples of paper feed sections. Recording paper S, which is an example of a medium, is contained in each of the paper feed trays TR1 to TR4. A paper feed path SH1, which is an example of a medium transport path, extends from each of the paper feed trays TR1 to TR4 toward the printer section U3.

[0029] In Figure 1, the printer unit U3 includes a control unit C as an example of a control means, and a power supply circuit E that supplies power to each component of the printer unit U3. The control unit C receives image information of the original document scanned by the scanner device U1 and image information transmitted from a personal computer, which is an example of an information transmission device (not shown) connected to the copier U. The control unit C processes the received image information into printing information for Y: yellow, M: magenta, C: cyan, and K: black, and outputs it to a laser drive circuit D, which is an example of a drive circuit for a latent image writing device. The laser drive circuit D outputs the laser drive signal input from the control unit C to exposure devices ROSy, ROSm, ROSc, and ROSk, which are examples of latent image forming means for each color, at a predetermined time.

[0030] Below each exposure unit ROSy~ROSk, the image holding units Uy, Um, Uc, and Uk are positioned as Y, M, C, and K. In Figure 1, the black image-holding unit Uk (K) includes a photoreceptor drum Pk as an example of an image-holding means, a charging corotron CCk as an example of a charging means, and a photoreceptor cleaner CLk as an example of a cleaning means for the image-holding means. The image-holding units Uy, Um, and Uc (Y, M, C) also include photoreceptor drums Py, Pm, and Pc, charging corotrons CCy, CCm, and CCc, and photoreceptor cleaners CLy, CLm, and CLc. In Example 1, the K-colored photoreceptor drum Pk, which is frequently used and experiences significant surface wear, is configured with a larger diameter compared to the other colored photoreceptor drums Py, Pm, and Pc, enabling high-speed rotation and extending its lifespan.

[0031] The photoreceptor drums Py to Pk are uniformly charged by the charging corotron CCy to CCk, and then electrostatic latent images are formed on the surface of the photoreceptor drums Py to Pk by the laser beams Ly, Lm, Lc, and Lk, which are examples of latent image writing light output from the exposure device ROSy to ROSk. The electrostatic latent images on the surface of the photoreceptor drums Py to Pk are then developed into toner images of the respective colors Y: yellow, M: magenta, C: cyan, and K: black by the developing device Gy, Gm, Gc, and Gk, which are examples of developing means.

[0032] The toner images on the surface of the photoreceptor drums Py~Pk are sequentially transferred in the primary transfer region Q3 by primary transfer rolls T1y, T1m, T1c, T1k, which are an example of primary transfer means, onto an intermediate transfer belt B, which is an example of an intermediate transfer means and an example of an image holding means, thereby forming a multicolor image, or so-called color image, on the intermediate transfer belt B. The color image formed on the intermediate transfer belt B is then transported to the secondary transfer region Q4. In the case of black image data only, only the black photoreceptor drum Pk and developer Gk are used, and only a black toner image is formed. After the primary transfer, any residual toner remaining on the surface of the photoconductor drums Py to Pk is cleaned by the photoconductor cleaners CLy to CLk. The aforementioned image-holding units Uy to Uk and developing devices Gy to Gk constitute a toner image-forming member, which is an example of an image-forming means.

[0033] A toner dispenser U3a, as an example of a supply mechanism, is located at the top of the printer unit U3. Toner cartridges Ky, Km, Kc, and Kk, as an example of a developer storage mechanism, are detachably mounted on the toner dispenser U3a. When toner is consumed in the developer units Gy to Gk during image formation, toner is supplied from each toner cartridge Ky to Kk to each developer unit Gy to Gk.

[0034] The intermediate transfer belt B, positioned below the photoreceptor drums Py~Pk, is stretched by an intermediate drive roll Rd as an example of a driving means for the intermediate transfer means, an intermediate tension roll Rt as an example of a tensioning means for applying tension to the intermediate transfer belt B, an intermediate steering roll Rw as an example of a first deviation correction means for correcting deviation and meandering of the intermediate transfer belt B, a plurality of intermediate idler rolls Rf as an example of a driven means, and a backup roll T2a as an example of a counter means for the secondary transfer region. The intermediate transfer belt B is supported so as to be rotatable in the direction of arrow Ya by the drive of the intermediate drive roll Rd. The belt module BM, as an example of an intermediate transfer device, is composed of the aforementioned intermediate drive roll Rd, intermediate tension roll Rt, intermediate steering roll Rw, intermediate idler roll Rf, backup roll T2a, primary transfer rolls T1y~T1k, intermediate transfer belt B, etc. In Example 1, the belt module BM is composed of a unit that can be attached to and replaced with the printer unit U3.

[0035] Below the backup roll T2a, a secondary transfer unit Ut is positioned as an example of a transfer transport means. The secondary transfer unit Ut has a secondary transfer roll T2b as an example of a transfer member. The secondary transfer roll T2b is positioned opposite the backup roll T2a. The region where the secondary transfer roll T2b faces the intermediate transfer belt B constitutes a secondary transfer region Q4. In addition, a contact roll T2c, as an example of a contact means for voltage application, is in contact with the backup roll T2a. A secondary transfer voltage with the same polarity as the charging polarity of the toner is applied to the contact roll T2c at a preset time from a power supply circuit E controlled by the control unit C. The aforementioned rolls T2a to T2c constitute a secondary transfer unit T2, which is an example of a secondary transfer means. Furthermore, the intermediate transfer belt B, primary transfer rolls T1y to T1k, secondary transfer unit T2, etc. constitute a transfer apparatus B+T1+T2, which is an example of a transfer means.

[0036] A paper transport path SH2 is located below the belt module BM. The recording paper S fed from the paper feed path SH1 of the paper feed device U2 is transported to the paper transport path SH2 by a transport roll Ra, which is an example of a transport means. The recording paper S in the paper transport path SH2 is fed out by a register roll Rr, which is an example of a delivery means, in accordance with the timing when the toner image is transported to the secondary transfer area Q4, and is guided by paper guides SG1 and SG2, which are examples of media guiding means, and transported to the secondary transfer area Q4. The toner image on the intermediate transfer belt B is transferred to the recording paper S by the secondary transfer unit T2 as it passes through the secondary transfer region Q4. In the case of a color image, the toner image that was primary transferred onto the surface of the intermediate transfer belt B is transferred to the recording paper S all at once. After secondary transfer, the intermediate transfer belt B is cleaned using a belt cleaner CLB, which is an example of a cleaning means for the intermediate transfer means.

[0037] The recording paper S on which the toner image has been secondarily transferred is sent to a media transport belt BH, which is an example of a transport means. The media transport belt BH transports the recording paper S to a fixing device F, which is an example of a belt unit and an example of a fixing means. The fixing device F has a heating unit Fh, which is an example of a heating means, and a pressure roll Fp, which is an example of a pressure means. A fixing region Q5 is formed by the region where the heating unit Fh and the pressure roll Fp face each other and are in contact. The toner image on the recording paper S is heated and fixed by the fuser unit F as it passes through the fuser area Q5. The recording paper S, with the toner image fixed by the fuser unit F, is discharged into the discharge tray TRh, which is an example of a discharge unit. The paper transport path SH is composed of the aforementioned symbols SH1, SH2, etc. Furthermore, the paper transport device SU is composed of the aforementioned symbols SH, Ra, Rr, SG1, SG2, BH, etc.

[0038] (Explanation of the fixing device) Figure 2 is an enlarged view of the fixing device of Example 1, with Figure 2A being an explanatory diagram of the state when it has moved to the first contact position, and Figure 2B being an explanatory diagram of the state when it has moved to the second contact position. In Figure 1, the heating unit Fh of the fixing device F of Embodiment 1 has a fixing belt 1 as an example of an endless means. The fixing belt 1 is stretched by a heating roll 2 as an example of a rotating means, a steering roll 3 as an example of a bias correction means, and a heating pad 4 as an example of a support means. The fixing belt 1 can be made of any conventionally known material, but the base material is preferably made of a highly rigid polyimide-based material. Furthermore, the surface layer of the fixing belt 1 is preferably made of a material such as a fluororesin that has high release properties for molten toner, paper dust, etc.

[0039] The heating roll 2 in Example 1 has a heater 2a built inside as an example of a heating means. The heating roll 2, heated by the heater 2a, heats the fixing belt 1 that it contacts. The steering roll 3 corrects any meandering or misalignment of the anchor belt 1.

[0040] The heating pad 4 is positioned opposite the pressure roll Fp, which is an example of an opposing means. The fixing region Q5 is formed in the area between the fixing belt 1, which is supported by the heating pad 4, and the pressure roll Fp. Therefore, the unfixed image on the recording paper S passing through the fixing region Q5 is heated and pressurized and fixed to the recording paper S. In Example 1, the heating pad 4 is supported so as to be movable toward and toward the pressure roll Fp. The heating pad 4 moves toward or toward the pressure roll Fp as the eccentric cam 6, which is an example of an actuation means, rotates. The heating pad 4 in Example 1 is movable between a fixed position, which is an example of a first contact position shown in Figure 2A, and a high-pressure position, which is an example of a second contact position shown in Figure 2B. In the fixed position shown in Figure 2A, the heating pad 4 brings the fixing belt 1 into contact with the pressure roll Fp at a predetermined first contact pressure. In the high-pressure position shown in Figure 2B, the heating pad 4 moves to a position closer to the center of the pressure roll Fp than in the fixed position. Therefore, in the high-pressure position, the fixing belt 1 is in contact with the pressure roll Fp at a second contact pressure that is higher than the first contact pressure.

[0041] In Example 1, the heating pad 4 is shown as being moved toward or toward the pressure roll Fp to switch between the first and second contact pressures, but the invention is not limited to this. It is also possible to make the pressure roll Fp movable toward or toward the heating pad 4, and to make it possible to switch between the first and second contact pressures. Moving the pressure roll Fp eliminates the need to move the heating pad 4, resulting in less impact on the posture of the fixing belt 1 and making it easier to stabilize the posture of the fixing belt 1. On the other hand, in the case where the heating pad 4 is moved, only the heating pad 4, which is smaller than the pressure roll Fp, needs to be moved, and less force and load is required for movement.

[0042] In Example 1, unlike the heating roll 2 and steering roll 3, the heating pad 4 is positioned in a non-rotating state relative to the fixing belt 1. Furthermore, the heating pad 4 of Example 1 has different shapes at its downstream end 4a and upstream end 4b in the rotational direction of the fixing belt 1. The upstream end 4b has a smaller angle with respect to the paper transport direction than the downstream end 4a, in order to guide the recording paper S into the fixing area Q5. The downstream end 4a has a larger angle with respect to the paper transport direction, in order to improve the release between the recording paper S that has passed through the fixing area Q5 and the fixing belt 1. The fixing belt 1 is supported in a bent position at the downstream end 4a. In other words, the radius of curvature of the fixing belt 1 at the downstream end 4a is smaller than the radius of curvature of the upstream end 4b. Therefore, the posture of the fixing belt 1 changes at a sharp angle at the downstream end 4a. Furthermore, the heating pad 4 in Example 1 is positioned separately from the heating roll 2 that heats the fixing belt 1.

[0043] (Description of the control unit in Example 1) Figure 3 is a functional block diagram of the control unit of Embodiment 1. In Figure 3, the control unit (controller) C of the copier U has an input / output interface (I / O) for inputting and outputting signals to and from the outside. The control unit C also has a ROM (read-only memory) where programs and information for necessary processing are stored. Furthermore, the control unit C has a RAM (random-access memory) for temporarily storing necessary data. Finally, the control unit C has a CPU (central processing unit) that performs processing according to the programs stored in the ROM, etc. Therefore, the control unit C in Embodiment 1 is composed of a small information processing device, a so-called microcomputer. Thus, the control unit C can realize various functions by executing programs stored in the ROM, etc. In Embodiment 1, the control unit C receives a signal from the signal output element and outputs a signal to the controlled element to control it.

[0044] (Description of signal output elements) The control unit C receives signals from signal output elements such as the user interface UI, a temperature sensor SN1 as an example of a temperature detection means, and other sensors (not shown). The user interface (UI) inputs the information entered by the user or worker into the control unit (C). The temperature sensor SN1 detects the temperature of the fixing belt 1 and outputs the detection result to the control unit C.

[0045] (Description of controlled elements) The control unit C outputs signals to the power supply circuit E, the fixing motor drive circuit D1, the contact pressure motor drive circuit D2, and other controlled elements (not shown). The power supply circuit E controls the charging bias of the charging rollers Cry~CRk, the developing bias of the developing unit Gy~Gk, the primary transfer bias of the primary transfer rolls T1y~T1k, the secondary transfer bias of the secondary transfer roll T2b, and the power supply to the heater of the fixing unit F. The fixing motor drive circuit D1 controls the fixing motor M1 to rotate the pressure roll Fp, causing the fixing belt 1 to rotate in a driven manner. The contact pressure motor drive circuit D2 controls the contact pressure motor M2 to actuate the eccentric cam 6 and move the heating pad 4.

[0046] (Functions of Control Unit C) The control unit C of Example 1 has the following functional means (functional module, program module). The job control means C1 controls the job, which is an image forming operation. When a job starts, it controls the photoreceptor drums Py~Pk, the power supply circuit E, etc., to form an image on the recording paper S. The fixing control means C2 includes a fixing temperature detection means C21, a fixing temperature control means C22, a rotation control means C23, a contact pressure switching timer TM1, an elapsed time measurement means TM2, and a contact pressure control means C24. The fixing control means C2 controls the operation and stopping of the fixing device F. The fixing temperature detection means C21 detects the temperature of the fixing belt 1 based on the detection result of the temperature sensor SN1.

[0047] The fixing temperature control means C22 controls the on / off state of the heater 2a to maintain the temperature of the fixing belt 1 at a predetermined fixing temperature, based on the detection result of the fixing temperature detection means C21. When the job starts, the fixing temperature control means C22 starts controlling the heater 2a to reach the fixing temperature. The rotation control means C23 controls the fixing motor M1 to control the rotation of the pressure roll Fp. The rotation of the driven fixing belt 1 is also indirectly controlled in conjunction with the control of the pressure roll Fp's rotation. In Embodiment 1, the rotation control means C23 drives the fixing motor M1 when a job starts and stops it when the job ends. In addition to the start of a job, the fixing motor M1 is also driven and stopped in predetermined cases, such as when the power is turned on or during maintenance. Furthermore, in Embodiment 1, the rotation control means C23 controls the rotation speed of the fixing belt 1 to a lower speed than when the contact pressure in the fixing area Q5 is controlled to the first contact pressure during the period when the contact pressure is controlled to the second contact pressure. In other words, during the period when the contact pressure is controlled to the first contact pressure, the fixing belt 1 rotates at the fixing speed to fix the passing recording paper S. On the other hand, during the period when the contact pressure is controlled to the second contact pressure, the recording paper S is not fixed, so the belt is controlled to rotate at a lower speed. While it is preferable to rotate at a low speed during the period controlled by the second contact pressure, it is also possible to rotate at the same speed as during the period controlled by the first contact pressure.

[0048] The contact pressure switching timer TM1 measures the timing for switching the contact pressure in the fixing area Q5 from the second contact pressure to the first contact pressure. In Example 1, the timing for switching is set to the time when the fixing belt 1 completes one rotation (one revolution) after the fixing belt 1 starts rotating. In Example 1, even after the fixing belt 1 completes one revolution from the start of the job, the first sheet of paper S that is fed does not reach the fixing area Q5. In other words, the timing for switching the contact pressure is set to the time before the first sheet of paper S reaches the fixing area Q5. The elapsed time measuring means TM2 measures the time elapsed since the fixing belt 1 stopped rotating.

[0049] The contact pressure control means C24 controls the contact pressure between the fixing belt 1 and the pressure roll Fp. In Embodiment 1, the contact pressure control means C24 acts on the eccentric cam 6 via the contact pressure motor M2 to move the heating pad 4 between the fixing position and the high-pressure position. When the job starts and the fixing belt 1 starts rotating, the contact pressure control means C24 moves the heating pad 4 to the high-pressure position. That is, the contact pressure in the fixing region Q5 becomes the high-pressure second contact pressure. Then, when the contact pressure switching timer TM1 determines that it is time to switch the contact pressure, it moves the heating pad 4 from the high-pressure position to the fixing position. Thus, the contact pressure in the fixing region Q5 becomes the first contact pressure for fixing. The recording paper S passes through the fixing region Q5 with the first contact pressure and is heated and fixed.

[0050] In Embodiment 1, the contact pressure control means C24 controls the contact pressure between the first and second contact pressures not only at the start of the job but also when the power is turned on. That is, when the fixing belt 1 rotates during the trial operation, also known as the warm-up or initialization operation, when the power is turned on, the contact pressure is controlled. Therefore, when the fixing belt 1 starts rotating when the power is turned on, the contact pressure is controlled to the second contact pressure, and then switched back to the first contact pressure when it is time to switch.

[0051] Furthermore, while the first embodiment is configured to control the contact pressure at the start of each job, it is not limited to this. For example, when the elapsed time measured by the elapsed time measuring means TM2 reaches a predetermined first time, the contact pressure can be controlled to a second contact pressure when the fixing belt 1 starts rotating. That is, if the elapsed time since the end of the previous job is short (less than the first time), the fixing belt 1 can be rotated with the first contact pressure for fixing without changing to the high-pressure second contact pressure, and if the elapsed time since the end of the previous job is long (first time or longer), the contact pressure can be changed to the high-pressure second contact pressure. Therefore, if there is no need to change to the second contact pressure, the first contact pressure can be kept, thereby suppressing unnecessary operation and wear of materials. The first time can be set to 5 minutes as an example, but it can be changed as appropriate according to the design and specifications.

[0052] Furthermore, if the temperature of the fixing belt 1 at the start of a job has not reached a predetermined first temperature, the contact pressure can also be controlled to a second contact pressure. That is, if a long time has elapsed since the end of the previous job and the temperature of the fixing belt 1 has fallen below the first temperature, the control is performed to change to a high-pressure second contact pressure. On the other hand, if a short time has elapsed since the end of the previous job and the temperature of the fixing belt 1 has not fallen much below the fixing temperature, the fixing belt 1 is rotated at the first contact pressure for fixing without changing to a high-pressure second contact pressure. Therefore, by keeping the contact pressure at the first level when there is no need to change to the second contact pressure, unnecessary operation and wear of components can be suppressed. The first temperature can be set to, for example, 80% of the fixing temperature, but it can be changed as appropriate according to the design and specifications.

[0053] (Effect of Example 1) In the copier U of Embodiment 1, which has the above configuration, when an image forming operation (job) is started, the image on the recording paper S is transferred in the secondary transfer area Q4 and sent to the fixing area Q5. In the fixing device F, the fixing belt 1 is heated, and as the recording paper S passes through the fixing area Q5, the developer on the surface of the recording paper S is heated, melted, and fixed. After the job is completed, the fixing belt 1 is not heated and cools naturally, causing its temperature to drop. The fixing belt 1, once its temperature has dropped, tends to become harder. Therefore, if the fixing belt 1 is held in the position supported by the heating roll 2, steering roll 3, and heating pad 4 for a long time, it is prone to developing kinks and shapes. When the fixing belt 1 develops kinks or shapes, the rotational resistance when the fixing belt 1 starts to rotate increases. In particular, in Embodiment 1, the heating pad 4 is in a non-rotating state relative to the fixing belt 1, which tends to increase rotational resistance. Furthermore, in Example 1, the heating pad 4 has a bent position at the downstream end 4a where the fixing belt 1 is bent, making it prone to kinks and other deformations, and the rotational resistance tends to be higher compared to when the shape of the downstream end 4a is gentler.

[0054] Therefore, when the fixing belt 1 is driven to rotate by the pressure roll Fp, the surface of the fixing belt 1 becomes more prone to slipping relative to the pressure roll Fp. If slipping occurs, there is a risk of damage such as abrasions on the surface of the fixing belt 1. If the fixing belt 1 is damaged, there is a risk of reduced image quality due to poor fixing and a reduction in product lifespan. In the configuration with a grip member as described in the patent document, the grip member functions not only when slip countermeasures are needed, but also at all times, including during steady rotation. Therefore, there are issues such as the grip member becoming a rotational resistance and the grip member wearing out quickly. Therefore, there are issues such as the need for a large-capacity motor that takes rotational resistance into account, and the increased frequency of replacement of the fixing device including the grip member, which leads to an increase in overall costs.

[0055] In contrast, in Example 1, when the rotation of the fixing belt 1 is started, the contact pressure between the fixing belt 1 and the pressure roll Fp is controlled to a high second contact pressure. Therefore, compared to when rotation is started with the first contact pressure, slippage of the fixing belt 1 at the start of rotation is suppressed. Thus, damage such as abrasion to the fixing belt 1 is suppressed. In Example 1, the anchoring belt 1 is rotated at a low speed during the period when the contact pressure is controlled to the second level. Therefore, the occurrence of slippage is suppressed compared to the case where it is not rotated at a low speed. In particular, in the fixing device F of Example 1, the heating pad 4 is not rotating, and the fixing belt 1 is held in a bent position at the downstream end 4a, which tends to increase rotational resistance. In contrast, in Example 1, the fixing belt 1 starts rotating at the second contact pressure, which helps to suppress slippage.

[0056] Furthermore, in Example 1, the heater 2a is located at a position separate from the fixing region Q5. In a fixing device in which the heater is built into a heating pad facing the fixing region Q5, it is conceivable, for example, to heat the heater before rotation starts to reduce the hardness of the fixing belt 1 in the fixing region Q5 and suppress rotational resistance. However, in Example 1, the heater 2a is located on the heating roll 2 at a position separate from the fixing region Q5. The fixing belt 1 is then heated as the heating roll 2 rotates. In the fixing device F of Example 1, if one attempts to heat the fixing belt 1 before rotation starts, it is necessary to wait for the fixing belt 1 to heat up through heat conduction. In this case, there is a problem that it takes time for the fixing belt 1 to heat up completely. In contrast, in Example 1, the fixing belt 1 is rotated by applying a second contact pressure without waiting for the fixing belt 1 to heat up. Therefore, in Example 1, the start-up time is shortened while slip and abrasion are suppressed.

[0057] In Example 1, after the fixing belt 1 starts rotating, the contact pressure is switched from the second to the first after one rotation of the fixing belt 1. That is, when the fixing belt 1 is heated by the heating roll 2 and its hardness decreases, making slippage less likely, the contact pressure is switched to the first contact pressure for fixing. The recording paper S does not reach the fixing area Q5 before the fixing belt 1 completes one rotation. Therefore, the recording paper S reaches the fixing area Q5 after the contact pressure is switched to the first and is fixed under predetermined fixing conditions (fixing temperature, fixing pressure (first contact pressure)).

[0058] Furthermore, in Example 1, the contact pressure is controlled to the second level not only at the start of the job but also when the fixing belt 1 starts rotating upon power-up. Therefore, slippage and damage to the fixing belt 1 during trial operation upon power-up are suppressed.

[0059] (Example of change) Although embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the gist of the present invention as described in the claims. Examples of modifications to the present invention (H01) to (H07) are shown below. (H01) In the above embodiment, a copier U was given as an example of an image forming apparatus, but the apparatus is not limited to this, and can also be configured with, for example, a fax machine, a printer, or a multifunction device. (H02) In the above embodiment, a configuration in which four colors of developer are used as the image forming apparatus was illustrated, but the invention is not limited to this, and can also be applied to, for example, a single-color image forming apparatus or a multi-color image forming apparatus with three or fewer colors or five or more colors.

[0060] (H03) In the above embodiment, the timing of the switchover was exemplified as the time it takes for the fixing belt 1 to complete one rotation, but it is not limited to this. It is also possible to set it to less than one rotation. For example, it is also possible to set the switching timing as the period from when the surface portion of the fixing belt 1 that was in contact with the heating roll 2 at the start of the fixing belt 1's rotation reaches the fixing area Q5. That is, it is possible to set the switching timing as the elapsed time corresponding to the distance L1 in Figure 2 for the distance the fixing belt 1 has rotated. Alternatively, the switching timing can be set as the time when the fixing temperature reaches a predetermined temperature. Furthermore, depending on the design and specifications, it is also possible to set the switching timing as the time when the belt has rotated two or more times. However, in Embodiment 1, the switching timing is set at a time when the job has started but before the fed recording paper S reaches the fixing device F.

[0061] (H04) In the above embodiment, it is preferable that the heating pad 4 is non-rotating, but it can also be a rotatable roll-shaped member or a belt-shaped member. Furthermore, the shape of the downstream end 4a and the upstream end 4b of the heating pad 4 are not limited to the shapes exemplified in the embodiment. The downstream end 4a can also be the same shape as the upstream end 4b. Conversely, the upstream end 4b can also be the same shape as the downstream end 4a. (H05) In the above embodiment, the heater 2a, which is the heating means, is shown to be built into the heating roll 2 as an example, but the embodiment is not limited to this. It is also possible to build it into the heating pad 4.

[0062] (H06) In the above embodiment, the fixing device F was exemplified as the belt unit, but it is not limited to this. For example, it can be applied to any belt unit having a belt, such as an intermediate transfer belt, a photoreceptor belt, a transfer transport belt, or a secondary transfer belt, where abrasion is a problem. (H07) In the above embodiment, a configuration in which the pressure roll Fp is driven and the fixing belt 1 is driven to rotate was illustrated, but the invention is not limited thereto. It is also applicable to a configuration in which the fixing belt 1 is driven and the pressure roll Fp is driven to rotate. Furthermore, it is also applicable when the pressure roll Fp is a pressure belt configuration.

[0063] (Note) (((1))) A rotating endless means, Support means for supporting the endless means, An opposing means is positioned opposite the support means with the endless means in between, and contacts the endless means with a predetermined first contact pressure, A heating means for heating the endless means, When the rotation of the endless means is started, the heating means starts heating and controls at least one of the support means and the opposing means to control the contact pressure between the endless means and the opposing means to a second contact pressure higher than the first contact pressure, A belt unit characterized by having the following features. (((2))) The support means that supports the endless means and is non-rotating, The belt unit according to (((1))) characterized by comprising the above. (((3))) At the end of the support means downstream of the rotational direction of the endless means, the support means supports the endless means in a bent position. The belt unit according to (((2))) characterized by comprising (((4))) The heating means is positioned at a location separate from the support means. A belt unit according to any one of (((1))) to (((3))) characterized by comprising: (((5))) A rotating means that incorporates the heating means and rotates while supporting the endless means, The belt unit according to (((4))) characterized by having the following: (((6))) The control means returns the contact pressure from the second contact pressure to the first contact pressure after one rotation of the endless means, A belt unit according to any one of (((1))) to (((5))) characterized by comprising: (((7))) The control means controls the second contact pressure for the period from when the endless means started rotating until the surface portion of the endless means that was in contact with the heating means reaches the position opposite the opposing means. A belt unit according to any one of (((1))) to (((5))) characterized by comprising: (((8))) The support means is supported so as to be movable in a direction approaching or moving away from the opposing means, When controlling to the second contact pressure, the control means moves the support means in a direction closer to the opposing means than in the case of the first contact pressure, A belt unit according to any one of (((1))) to (((7))) characterized by comprising the above. (((9))) The opposing means is supported so as to be movable in a direction toward or toward the support means, When controlling to the second contact pressure, the control means moves the opposing means in a direction closer to the support means than in the case of the first contact pressure, A belt unit according to any one of (((1))) to (((8))) characterized by comprising the above. (((10))) The control means controls the contact pressure to the second contact pressure when the endless means starts rotating upon power-up. A belt unit according to any one of (((1))) to (((9))) characterized by comprising: (((11))) A measuring means for measuring the elapsed time since the endless means stopped rotating, When the elapsed time measured by the measuring means reaches a predetermined first time, the control means controls the contact pressure to the second contact pressure, A belt unit according to any one of (((1))) to (((10))) characterized by being equipped with the above. (((12))) A temperature detection means for detecting the temperature of the endless means, The control means controls the contact pressure to the second contact pressure if the temperature detected by the temperature detection means does not reach a predetermined first temperature, A belt unit according to any one of (((1))) to (((11))) characterized by comprising the above. (((13))) During the period in which the second contact pressure is controlled, the control means controls the rotational speed of the endless means to be lower than the rotational speed during the period in which the first contact pressure is controlled. A belt unit according to any one of (((1))) to (((12))) characterized by comprising the above. (((14))) The fixing device is configured such that, as the medium passes between the endless means and the opposing means, the unfixed image on the surface of the medium is fixed by the heat of the heating means and the contact pressure between the endless means and the opposing means. A belt unit according to any one of (((1))) to (((13))) characterized by the above. (((15))) Image holding means for holding an image on the surface, A transfer means for transferring the image of the image holding means onto a medium, A belt unit described in (((14))) for fixing the image transferred to the aforementioned medium, An image forming apparatus characterized by comprising the following:

[0064] According to the belt unit described in (((1))), damage to the endless means can be suppressed compared to the case where the endless means starts rotating with the same contact pressure as during use. According to the belt unit of (((2))), even if the rotational resistance of the endless means increases compared to the case of a rotating support means, rotation is initiated by the second contact pressure, and damage to the endless means can be suppressed. According to the belt unit of (((3))), even if the rotational resistance of the endless means increases compared to the case where the endless means is not bent, rotation is initiated by the second contact pressure, and damage to the endless means can be suppressed. According to the belt unit of (((4))), even if heating of the endless means in the opposing region between the support means and the opposing means is not possible at the start of rotation, damage to the endless means can be suppressed. According to the belt unit of (((5))), the endless means can be heated by a heating means built into the rotating means. According to the belt unit of (((6))), after one rotation in which the entire circumference of the endless means is heated and slippage between the endless means and the opposing means becomes less likely, the contact pressure is returned from the second to the first contact pressure, thereby enabling rapid fixing while suppressing damage to the endless means. According to the belt unit of (((7))), the second contact pressure is controlled until the heated surface portion, which is less prone to slippage, reaches the opposing position, thereby enabling rapid fixing while suppressing damage to the endless means. According to the belt unit of (((8))), it is expected that the cost of the configuration for moving the support means can be reduced compared to the case where the opposing means moves relative to the support means. According to the belt unit of (((9))), the influence on the posture of the endless means can be suppressed compared to the case where the support means moves relative to the opposing means. According to the belt unit of (((10))), damage to the endless means when power is turned on is suppressed compared to when the contact pressure is not controlled to a second level when power is turned on. The belt unit relating to (((11))) can reduce unnecessary contact pressure control processing compared to the case where the contact pressure is controlled to a second level when the elapsed time does not reach a first level. According to the belt unit of (((12))), compared to the case where the contact pressure is controlled to a second level when the temperature of the endless means reaches a first level, unnecessary contact pressure control processing can be reduced. According to the belt unit of (((13))), damage to the endless means can be suppressed compared to a case where the rotational speed of the endless means is not lower than the rotational speed during the period when it is controlled by the first contact pressure, even when it is controlled by the second contact pressure. According to the belt unit of (((14))), compared to not applying a second contact pressure when the rotation of the endless means starts, poor fixing due to damage to the endless means can be suppressed. According to the image forming apparatus described in (((15))), damage to the endless means can be suppressed compared to the case where the endless means starts rotating with the same contact pressure as during use. [Explanation of Symbols]

[0065] 1...Endless means, 2... means of rotation, 2a...Heating means, 4...support means, B+T1+T2...Transfer method, C... control means, F... Belt unit, fixing device, Fp... Countermeasure, Py, Pm, Pc, Pk...image holding means, Q5... Opposite position S...medium, SN1...Temperature detection means, TM2...Method of measurement, U...Image forming apparatus.

Claims

1. A rotating endless means, Support means for supporting the endless means, An opposing means is positioned opposite the support means with the endless means in between, and contacts the endless means with a predetermined first contact pressure, A heating means for heating the endless means, When the rotation of the endless means is started, the heating means starts heating and controls at least one of the support means and the opposing means to control the contact pressure between the endless means and the opposing means to a second contact pressure higher than the first contact pressure, A belt unit characterized by having the following features.

2. The support means that supports the endless means and is non-rotating, The belt unit according to claim 1, characterized by comprising the following:

3. At the end of the support means downstream of the rotational direction of the endless means, the support means supports the endless means in a bent position. The belt unit according to claim 2, characterized by comprising:

4. The heating means is positioned at a location separate from the support means. The belt unit according to claim 1, characterized by comprising the following:

5. A rotating means that incorporates the heating means and rotates while supporting the endless means, The belt unit according to claim 4, characterized by comprising the above.

6. The control means returns the contact pressure from the second contact pressure to the first contact pressure after one rotation of the endless means, The belt unit according to claim 1, characterized by comprising the following:

7. The control means controls the second contact pressure for the period from when the endless means started rotating until the surface portion of the endless means that was in contact with the heating means reaches the position opposite the opposing means. The belt unit according to claim 1, characterized by comprising the following:

8. The support means is supported so as to be movable in a direction approaching or moving away from the opposing means, When controlling to the second contact pressure, the control means moves the support means in a direction closer to the opposing means than in the case of the first contact pressure, The belt unit according to claim 1, characterized by comprising the following:

9. The opposing means is supported so as to be movable in a direction toward or toward the support means, When controlling to the second contact pressure, the control means moves the opposing means in a direction closer to the support means than in the case of the first contact pressure, The belt unit according to claim 1, characterized by comprising:

10. When the power is turned on and the endless means starts to rotate, the control means controls the contact pressure to the second contact pressure. The belt unit according to claim 1, characterized by comprising:

11. A measuring means for measuring the elapsed time since the endless means stopped rotating, When the elapsed time measured by the measuring means reaches a predetermined first time, the control means controls the contact pressure to the second contact pressure, The belt unit according to claim 1, characterized by comprising:

12. A temperature detection means for detecting the temperature of the endless means, If the temperature detected by the temperature detection means does not reach a predetermined first temperature, the control means controls the contact pressure to the second contact pressure, The belt unit according to claim 1, characterized by comprising:

13. During the period in which the second contact pressure is controlled, the control means controls the rotational speed of the endless means to be lower than the rotational speed during the period in which the first contact pressure is controlled. The belt unit according to claim 1, characterized by comprising:

14. The fixing device is configured such that, as the medium passes between the endless means and the opposing means, the unfixed image on the surface of the medium is fixed by the heat of the heating means and the contact pressure between the endless means and the opposing means. A belt unit according to any one of features 1 to 13.

15. Image holding means for holding an image on the surface, A transfer means for transferring the image of the image holding means onto a medium, A belt unit according to claim 14 for fixing an image transferred to the medium, An image forming apparatus characterized by comprising the following:

Images