JP2018054943A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of suppressing the occurrence of streak-like wrinkles on a recording medium after passing through a fixing nip and to provide an image forming apparatus.SOLUTION: The fixing device includes a separation member such as a separation auxiliary member 48 which is arranged in a position not in contact with a pressure member such as a pressure roller 45 through a fixing belt 43 on the downstream side of a nip forming member such as a fixing roller 41 in the moving direction of the recording medium and comes into contact with the inner peripheral surface of the fixing belt 43, to make the curvature of the fixing belt 43 large. A pressing member 49 which comes into contact with the inner peripheral surface of the fixing belt 43, to press the fixing belt 43 is arranged between the nip forming member and the separation member in the moving direction of the recording medium. The fixing device includes contact/separation means such as a pressurizing and depressurizing mechanism which brings/separates the pressure member into contact with/from the fixing belt 43. The operation condition of a pre-heating operation for thermally expanding the pressure roller is changed on the basis of an environmental temperature.SELECTED DRAWING: Figure 2

Description

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

  2. Description of the Related Art Image forming apparatuses such as copying machines, facsimile machines, and printers using electrophotographic technology are provided with a fixing device that fixes an unfixed toner image formed on a recording medium such as paper on the recording medium. The fixing device includes, for example, a fixing belt that is heated by a heating unit such as a heater and is stretched around a plurality of stretching members. A nip such as a fixing nip is formed by the fixing belt and a pressure member such as a pressure roller that rotates while being pressed against a nip forming member such as a fixing roller, which is one of the stretching members, via the fixing belt. A system is known in which a recording medium carrying a toner image is passed through the nip to fix the toner image on the recording medium.

  Japanese Patent Application Laid-Open No. 2004-151858 describes a fixing device provided with a separation mechanism for separating the recording medium that has passed through the nip from the fixing belt as the fixing device. Specifically, it has a separation claw that faces the outer peripheral surface of the fixing belt with a predetermined gap on the downstream side of the nip in the recording medium conveyance direction. In addition, a separation member that abuts on the inner peripheral surface of the fixing belt and increases the curvature of the portion of the fixing belt facing the separation claw (decreasing the curvature radius) is provided. The separation member is disposed at a position separated from the pressure member from a contact position where the pressure member contacts the fixing belt.

  However, the fixing device described in Patent Document 1 has a problem that streaks are formed on the recording medium after passing through the fixing nip.

  In order to solve the above problems, the present invention provides an endless fixing belt that is stretched around a plurality of stretching members, a nip forming member that is one of the plurality of stretching members, and the nip forming member. A pressure member that forms a nip through the fixing belt, and a heat source that heats the fixing belt, and is separated from the pressure member downstream of the nip forming member in the moving direction of the fixing belt. And a separation member that stretches the fixing belt, and is disposed between the outlet of the nip and the upstream end of the separation member in the movement direction of the fixing belt. A pressing member that contacts the inner peripheral surface and presses the fixing belt; contacting / separating means that contacts and separates the pressing member from the fixing belt; and after the fixing operation, the pressing member is moved by the contacting / separating means. Above A control unit for controlling the belt to be separated from the belt, and a temperature detection unit for detecting an ambient temperature of the apparatus. The control unit is configured to control the fixing belt based on a detection result of the temperature detection unit. The pressure member is brought into contact with the fixing belt during a start-up operation for heating to a temperature, and a pre-heating operation for heating the pressure member is performed.

  According to the present invention, it is possible to suppress the occurrence of streak-like wrinkles on the recording medium after passing through the fixing nip.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 2 is a schematic sectional view of a fixing device. FIG. 6 is an enlarged view showing the vicinity of a fixing nip outlet of a conventional fixing device. The figure which shows an example of the recording sheet which the wrinkle-like wrinkle produced. FIG. 3 is an enlarged view showing the vicinity of a fixing nip outlet of the fixing device of the present embodiment. The figure explaining the modification of a pressing member. The figure explaining the 2nd modification of a pressing member. The figure explaining the 3rd modification of a pressing member. The figure explaining the 4th modification of a pressing member. The perspective view explaining a moving mechanism. The figure which shows the state which has located the pressing member in the contact position. The figure which shows the state which put the pressing member in the cancellation | release position. The schematic block diagram which shows a pressure depressurization mechanism. 6 is a graph showing the temperature of a fixing belt and the temperature of a pressure roller when a printing operation is performed immediately after power-on in the related art. 6 is a graph showing a fixing belt temperature and a pressure roller temperature when a printing operation is performed after waiting for a long period of time in the past. 6 is a graph showing the temperature of the fixing belt and the temperature of the pressure roller when a printing operation is performed immediately after the power is turned on in the present embodiment. 6 is a graph showing the temperature of the fixing belt and the temperature of the pressure roller when a printing operation is performed after waiting for a long time in the present embodiment. The figure explaining arrangement | positioning of the temperature sensor which is a temperature detection means to detect environmental temperature. The block diagram explaining an example of the control system of this embodiment. FIG. 6 is a block diagram illustrating an example of a control system according to a second embodiment.

An embodiment of an electrophotographic printer will be described below as an image forming apparatus to which the present invention is applied.
FIG. 1 is a schematic configuration diagram illustrating a printer according to an embodiment. In this figure, the printer includes four image forming units 2Y, 2M, 2C, and 2K for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. ing. The four image forming units 2Y, 2M, 2C, and 2K have a so-called tandem configuration in which an intermediate transfer belt 61 as an image bearing belt described later is arranged along the endless movement direction.

  The printer includes a paper feed path 30, a pre-transfer conveyance path 31, a manual paper feed path 32, a manual feed tray 33, a registration roller pair 34, a conveyance belt unit 35, a fixing device 40, a conveyance switching device 50, a paper discharge path 51, a discharge path 51, and a paper discharge path 51. A paper roller pair 52, a paper discharge tray 53, and the like are also provided. Further, two optical writing units 1YM and 1CK, a primary transfer unit 60, a secondary transfer unit 78, a first paper feed cassette 101, a second paper feed cassette 102, and the like are also provided.

  The image forming units 2Y, 2M, 2C, and 2K have drum-shaped photoconductors 3Y, 3M, 3C, and 3K that are latent image carriers. Each of the first paper feed cassette 101 and the second paper feed cassette 102 accommodates a bundle of recording sheets P therein. Then, the uppermost recording sheet P in the sheet bundle is sent out toward the paper feed path 30 by the rotational driving of the feed rollers 101 a and 102 a.

  A manual feed tray 33 is disposed on the side surface of the printer housing so as to be openable and closable with respect to the housing, and a sheet bundle is manually fed to the upper surface of the tray while being opened with respect to the housing. The uppermost recording sheet P in the manually fed sheet bundle is sent out toward the paper feed path 30 by the feed roller of the manual feed tray 33.

  The two optical writing units 1YM and 1CK each have a laser diode, a polygon mirror, various lenses, and the like. Then, based on image information read by a scanner outside the printer or image information sent from a personal computer, the laser diode is driven, and the photoreceptors 3Y, 3M of the image forming units 2Y, 2M, 2C, 2K. , 3C, 3K are optically scanned. Specifically, the photoreceptors 3Y, 3M, 3C, and 3K of the image forming units 2Y, 2M, 2C, and 2K are rotationally driven in the counterclockwise direction in the drawing by the driving unit. The optical writing unit 1YM performs an optical scanning process by irradiating the driven photoconductors 3Y and 3M while deflecting laser light in the direction of the rotation axis. Thereby, electrostatic latent images based on the Y and M image information are formed on the photoreceptors 3Y and 3M. Further, the optical writing unit 1CK performs an optical scanning process by irradiating the driven photoconductors 3C and 3K while deflecting laser light in the rotation axis direction. Thereby, electrostatic latent images based on the C and K image information are formed on the photoreceptors 3C and 3K.

  Each of the image forming units 2Y, 2M, 2C, and 2K serves as a common support using the photosensitive members 3Y, 3M, 3C, and 3K as latent image carriers and various devices arranged around the photosensitive members 3Y, 3M, 3C, and 3K as one unit. In a supported state, they are integrally attached to and detached from the printer casing. These image forming units have the same configuration except that the colors of the toners used are different from each other. Taking the image forming unit 2Y for Y as an example, this has a developing device 4Y for developing an electrostatic latent image formed on the surface of the photoreceptor 3Y into a Y toner image in addition to the photoreceptor 3Y. Further, the transfer residual toner attached to the surface of the photoreceptor 3Y after passing through a primary transfer nip for Y, which will be described later, or a charging device 5Y that uniformly charges the surface of the photoreceptor 3Y that is driven to rotate. A drum cleaning device 6Y is also provided.

  The photoreceptor 3Y has a drum shape in which a photosensitive layer is formed on a base tube made of aluminum or the like by applying a photosensitive organic photosensitive material. An endless belt-shaped belt may be used instead of the drum-shaped belt.

  The developing device 4Y includes a rotatable developing sleeve made of a non-magnetic pipe, and a magnet roller disposed in the hollow so as not to rotate with the sleeve. Then, an electrostatic latent image on the photoreceptor 3Y is obtained by a two-component developer (hereinafter simply referred to as a developer) containing a magnetic carrier carried on the surface of the developing sleeve by the magnetic force generated by the magnet roller and non-magnetic Y toner. Develop. At this time, the developing potential is applied to the Y toner facing the electrostatic latent image on the developing sleeve by the potential difference between the developing bias applied to the developing sleeve and the electrostatic latent image on the photoreceptor 3Y. On the other hand, the background potential is applied to the Y toner facing the background portion of the photoreceptor 3Y on the developing sleeve due to the potential difference between the developing bias and the background portion of the photoreceptor 3Y. Due to these potentials, the Y toner on the developing sleeve is selectively attached only to the electrostatic latent image of the electrostatic latent image and the background portion of the photoreceptor 3Y to develop the electrostatic latent image.

  The Y toner in the Y toner bottle 103Y is appropriately supplied to the developing device 4Y by the Y toner supply device. In the developing device 4Y, a toner concentration sensor is provided as a toner concentration detecting means. The toner concentration sensor detects the magnetic permeability of the developer caused by the carrier that is a magnetic material. The main control unit, which will be described later, controls the driving of the Y toner replenishing device based on the comparison between the output value from the toner density sensor and the output target value from the sensor that is the toner density target value, thereby developing the developer. Is set within a certain range (for example, 4 wt% to 9 wt%). The same toner replenishment control is performed for the developing devices 4M, 4C, and 4K.

  The drum cleaning device 6Y is of a type that scrapes off transfer residual toner from the surface of the photoreceptor 3Y by a polyurethane rubber cleaning blade in contact with the photoreceptor 3Y. Instead of this method, another method may be used. In order to improve the cleaning property, the drum cleaning device 6Y has a rotatable fur brush in contact with the photosensitive member 3Y in addition to the cleaning blade. This fur brush also serves to apply the lubricant to the surface of the photoreceptor 3Y while scraping the lubricant from the solid lubricant to make a fine powder.

  A static elimination lamp is disposed above the photoreceptor 3Y, and this static elimination lamp is also a part of the image forming unit 2Y. The neutralization lamp neutralizes the surface of the photoreceptor 3Y after passing through the drum cleaning device 6Y by light irradiation. The surface of the photoreceptor 3Y that has been neutralized is uniformly charged by the charging device 5Y, and then subjected to optical scanning by the optical writing unit 1YM described above. The charging device 5Y is driven to rotate while receiving a charging bias from a power source. Instead of such a system, a scorotron charger system that performs a non-contact charging process on the photoreceptor 3Y may be employed.

  The image forming unit 2Y for Y has been described, but the image forming units 2M, 2C, and 2K for M, C, and K have the same configuration as the image forming unit 2Y for Y.

  A primary transfer unit 60 is disposed below the four image forming units 2Y, 2M, 2C, and 2K. The primary transfer unit 60 is driven by the rotational drive of any one of the rollers while bringing the intermediate transfer belt 61, which is an image carrier stretched by a plurality of rollers, into contact with the photoreceptors 3Y, 3M, 3C, 3K. It is moved endlessly in the clockwise direction in the figure. As a result, primary transfer nips for Y, M, C, and K in which the photoreceptors 3Y, 3M, 3C, and 3K abut on the intermediate transfer belt 61 are formed.

  In the vicinity of the primary transfer nips for Y, M, C, and K, the intermediate transfer belt 61 is moved to the photoreceptors 3Y, 3M, 3C, and 3K by primary transfer rollers 62Y, 62M, 62C, and 62K disposed inside the belt loop. It is pushing toward. A primary transfer bias is applied to the primary transfer rollers 62Y, 62M, 62C, and 62K by a primary transfer power source. As a result, a primary transfer electric field for electrostatically moving the toner images on the photoreceptors 3Y, 3M, 3C, and 3K toward the intermediate transfer belt 61 is formed in the primary transfer nips for Y, M, C, and K. Yes.

  In the figure, on the front surface of the intermediate transfer belt 61 that sequentially passes through the primary transfer nips for Y, M, C, and K along with the endless movement in the clockwise direction, the Y toner image, the M toner image, and the C The toner image and the K toner image are sequentially superimposed and primarily transferred. By this superimposing primary transfer, a four-color superimposed toner image is formed on the front surface of the intermediate transfer belt 61.

  A secondary transfer unit 78 is disposed below the intermediate transfer belt 61 in the drawing. The secondary transfer unit 78 includes an endless secondary transfer belt 77, a ground driven roller 72, a driving roller, a secondary belt cleaning device 76, a toner adhesion amount detection sensor 64, and the like. The secondary transfer belt 77 is endlessly moved in the counterclockwise direction in the figure as the driving roller rotates while being tensioned by the ground driven roller 72 disposed inside the loop and the driving roller. .

  The secondary transfer belt 77 of the secondary transfer unit 78 has its place where the belt is driven with respect to the ground driven roller 72 abutted with the place where the intermediate transfer belt 61 of the primary transfer unit 60 is applied to the secondary transfer bias roller 68. A secondary transfer nip is formed. A secondary transfer bias output from a secondary transfer power source, which will be described later, is applied to a secondary transfer bias roller 68 inside the loop of the intermediate transfer belt 61, whereas a ground driven roller inside the loop of the secondary transfer belt 77. 72 is grounded. As a result, a secondary transfer electric field is formed in the secondary transfer nip.

  A registration roller pair 34 is disposed on the right side of the secondary transfer nip in the drawing, and the recording sheet P sandwiched between the rollers can be synchronized with the four-color superimposed toner image on the intermediate transfer belt 61. Send to the secondary transfer nip. In the secondary transfer nip, the four-color toner image on the intermediate transfer belt 61 is secondarily transferred onto the recording sheet P under the influence of the secondary transfer electric field and the nip pressure, and becomes a full color image combined with the white color of the recording sheet P.

  The secondary transfer residual toner adheres to the front surface of the intermediate transfer belt 61 after passing through the secondary transfer nip. The secondary transfer residual toner is removed from the surface of the intermediate transfer belt 61 by the primary belt cleaning device 75 of the primary transfer unit 60.

  The recording sheet P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 61 and the secondary transfer belt 77 and transferred to the transport belt unit 35. The conveyor belt unit 35 moves the endless conveyor belt 36 endlessly in the counterclockwise direction in the figure by the rotational driving of the driving roller 37 while being stretched by the driving roller 37 and the driven roller 38. Then, the recording sheet P delivered from the secondary transfer nip is conveyed along with the endless movement of the belt while being held on the belt upper tension surface, and delivered to the fixing device 40.

  The recording sheet P sent into the fixing device 40 is sandwiched between fixing nips by contact between an endless fixing belt and a pressure roller. Then, the toner image is fixed on the surface by the action of pressure or heating.

  The recording sheet P on which the toner image is transferred to the first surface at the secondary transfer nip and the toner image is fixed on the first surface by the fixing device 40 is sent out toward the conveyance switching device 50. In this printer, the transfer switching device 50, the retransmission path 54, the switchback path 55, the post-switchback transfer path 56, and the like constitute a retransmission means. The conveyance switching device 50 switches the subsequent conveyance destination of the recording sheet P received from the fixing device 40 between the paper discharge path 51 and the retransmission path 54.

  Specifically, when a single-sided mode print job for forming an image only on the first side of the recording sheet P is executed, the conveyance destination is set to the paper discharge path 51. As a result, the recording sheet P on which an image is formed only on the first surface is sent to the discharge roller pair 52 via the discharge path 51 and discharged onto the discharge tray 53 outside the apparatus. Further, when executing a print job in a duplex mode in which images are formed on both sides of the recording sheet P, when the recording sheet P having images fixed on both sides is received from the fixing device 40, the transport destination is also set. The paper discharge path 51 is set. As a result, the recording sheet P with images formed on both sides is discharged onto a discharge tray 53 outside the apparatus.

  On the other hand, when a recording sheet P having an image fixed only on the first side is received from the fixing device 40 during execution of the double-side mode print job, the transport destination is set to the retransmission path 54. A switchback path 55 is connected to the retransmission path 54, and the recording sheet P sent to the retransmission path 54 enters the switchback path 55. When the entire area in the conveyance direction of the recording sheet P enters the switchback path 55, the conveyance direction of the recording sheet P is reversed and the recording sheet P is switched back. In addition to the retransmission path 54, a post-switchback conveyance path 56 is connected to the switchback path 55, and the recording sheet P that has been switched back enters the post-switchback conveyance path 56. At this time, the upper and lower sides of the recording sheet P are reversed. Then, the recording sheet P that is turned upside down is retransmitted to the secondary transfer nip via the post-switchback conveyance path 56 and the sheet feeding path 30 described above. The recording sheet P on which the toner image is also transferred to the second surface at the secondary transfer nip is fixed on the second surface via the fixing device 40, and then the conveyance switching device 50 and the paper discharge path. The paper is discharged onto a paper discharge tray 53 via 51 and a paper discharge roller pair 52.

FIG. 2 is a schematic sectional view of the fixing device 40.
The fixing device 40 according to the present embodiment is a belt fixing method, and includes a fixing belt 43 and a pressure roller 45 as a pressure member that is rotatably provided facing the fixing belt 43. The fixing belt 43 is stretched by a fixing roller 41, a heating roller 42, a tension roller 47, and the like. The fixing roller 41, the pressure roller 45, and the heating roller 42 are pivotally supported so as to be rotatable in the longitudinal direction of the casing of the fixing device 40.

  The fixing belt 43 is an endless belt formed of a PI (polyimide) layer, and has an outer peripheral surface coated with an offset preventing agent such as a PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) film. . The fixing roller 41 and the pressure roller 45 are rubber rollers. When the pressure roller 45 is pressed toward the center of the fixing roller 41 through the fixing belt 43, the pressure roller 45 and the fixing belt 43 are interposed. Thus, the fixing nip N1 is formed. The tension roller 47 applies tension to the fixing belt 43 and is formed of a cylindrical aluminum tube.

  The pressure roller 45 is provided so as to be able to come into contact with and separate from the fixing belt 43. When the paper is passed (fixed), the pressure roller 45 presses the fixing belt 43 and fixes it by a pressure depressurization mechanism. A nip N1 is formed. On the other hand, during standby (non-fixing), the pressure is released and the pressure roller 45 is separated from the fixing belt 43.

  The heating roller 42 is a hollow roller made of aluminum or iron and has a heat source 44 including a heater such as a halogen heater inside. The heat source 44 may be an induction heating mechanism. A thermistor 11 that is a temperature sensor element is disposed at a position that opposes the heating roller 42 and the fixing belt 43, and the heat source 44 is controlled based on the temperature detection of the thermistor 11 so that the fixing belt reaches a set temperature. doing.

  The fixing roller 41 is connected to driving means constituted by a motor, a reduction gear train, and the like, and is driven to rotate in the direction of the arrow in the figure by this driving means. Due to the rotation of the fixing roller, the pressure roller 45 and the fixing belt 43 that are in pressure contact with the fixing roller 41 rotate at the same speed in the direction of the arrow shown in FIG. The rotation of the fixing roller 41 causes the pressure roller 45 and the fixing belt 43 that are in pressure contact with the fixing roller 41 to rotate at the same speed in the direction of the arrow shown in the drawing. Alternatively, the pressure roller 45 may be rotationally driven by a driving unit, and the fixing belt 43 and the fixing roller 41 that are in pressure contact with the pressure roller 45 may be driven to rotate.

  Further, between the tension roller 47 and the heating roller 42, a polishing device 10 for polishing the outer peripheral surface of the fixing belt 43 is disposed. The polishing apparatus 10 includes a polishing roller 10 a that contacts the outer peripheral surface of the fixing belt 43, and a counter roller 10 b that faces the polishing roller 10 a with the fixing belt 43 interposed therebetween. The polishing roller 10a is pressed against the fixing belt 43 by a pressure spring 10c. The polishing roller 10a and the counter roller 10b are provided so as to be able to contact and separate from the fixing belt 43. When it is not necessary to polish the fixing belt 43, the polishing roller 10a and the counter roller 10b are separated from the fixing belt 43. . Thereby, the life of the fixing belt 43 can be increased.

  When the recording sheet P passes through the fixing nip N1, the surface of the fixing belt 43 is worn by the cutting burr of the recording sheet P. Therefore, in the fixing belt 43, the wear at the portion corresponding to the width of the recording sheet P that is frequently used differs from the wear at the outer portion. As a result, there is a problem that when an image is output using a recording sheet having a width wider than that of a frequently used recording sheet, a worn portion on the fixing belt appears in the image. In the present embodiment, the polishing apparatus 10 is provided and the outer peripheral surface of the fixing belt 43 is polished by the polishing roller 10a, so that the wear of the fixing belt 43 is made uniform in the width direction, and the occurrence of the above problem is suppressed. Yes.

  A separation assisting member 48 as a separation member is provided inside the fixing belt 43 and downstream of the fixing nip N1 in the movement direction of the fixing belt surface. The separation assisting member 48 is a block member formed of a metal such as SUS or a rigid body such as a resin and having a substantially arc-shaped cross section. The separation assisting member 48 contacts the inner peripheral surface of the fixing belt 43 on the downstream side of the fixing nip N1 in the moving direction of the fixing belt, stretches the fixing belt 43 in a direction away from the fixing roller 41, and fixes the fixing belt 43. The direction of travel is changing rapidly. By abruptly changing the advancing direction of the fixing belt 43, the curvature of the fixing belt 43 can be increased (the radius of curvature is decreased), and the recording sheet P can be separated by this curvature, thereby improving the separation performance. it can.

  In the present embodiment, since the contact surface of the separation assisting member 48 with the fixing belt 43 has an arc shape, the fixing belt 43 can be moved smoothly along the arc-shaped contact surface.

  In addition, the surface of the separation assisting member 48 facing the fixing roller 41 is also formed in an arc shape along the surface of the fixing roller 41. Thereby, the separation assisting member 48 can be disposed in a narrow space without contacting the fixing roller 41.

  The separation assisting member 48 is provided over the entire axial direction of the fixing roller 41, and both ends thereof are fixed to the side surface of the casing of the fixing device 40. Further, the separation assisting member 48 is disposed at a position where it does not come into contact with the pressure roller 45, and is configured to prevent the durability of the pressure roller 45 and the motor torque from increasing.

  A separation plate 46 as a second separation member is disposed so as to face the separation assisting member 48 with the fixing belt 43 interposed therebetween. The front end of the separation plate 46 is disposed so as to have a minute gap with the fixing belt 43. The tip of the separation plate 46 is tapered and has a tapered shape. In this embodiment, a pressing member 49 is provided between the fixing nip and the separation assisting member 48 so as to contact the inner peripheral surface of the fixing belt 43 and to contact the fixing belt 43 to the pressure roller 45. Yes.

Hereinafter, the basic operation of the fixing device 40 of the present embodiment will be described.
The recording sheet P on which the toner image is formed is conveyed to the fixing nip N1, and the toner image on the recording sheet is heated and melted at the fixing nip N1, whereby the toner image is fixed. Thereafter, the recording sheet P is separated from the fixing belt 43 by the separation plate 46 after the nip exit and discharged from the fixing device 40. In order to confirm that the recording sheet P has passed at a predetermined timing, a paper discharge sensor is disposed at the exit of the fixing device 40. Then, when the recording sheet P is not discharged at a predetermined timing, the processing shifts to a jam processing mode such as notifying the user that a paper jam has occurred.

Next, the characteristic part of this embodiment is demonstrated.
FIG. 3 is an enlarged view showing the vicinity of the exit of the fixing nip N1 of the conventional fixing device.
The separation plate 46 mainly separates the recording sheet P from the fixing belt 43 by bringing the leading end of the recording sheet P, which is difficult to separate due to the curvature of the fixing belt 43, into contact with the leading end of the separation plate 46. It takes on the function. Further, when the tip of the separation plate 46 comes into contact with the fixing belt 43, the fixing belt 43 is scraped by the separation plate 46 and the life of the fixing belt 43 is reduced. As described above, in order to ensure that the leading end of the separation plate 46 does not contact the fixing belt 43 and the thin paper is surely brought into contact with the separation plate 46, the gap d (about approximately) between the fixing belt 43 and the separation plate 46. 0.2 mm) must be managed with high accuracy.

  Therefore, the separation assisting member 48 facing the separation plate 46 via the fixing belt 43 is formed of a rigid body, and fluctuations in the gap d between the fixing belt 43 and the separation plate 46 due to deformation of the separation assisting member 48 are suppressed. Further, when the rigid separation auxiliary member 48 is configured to contact the pressure roller 45 via the fixing belt 43, the separation auxiliary member 48 is elastically deformed by the pressure of the pressure roller 45 and separated from the fixing belt 43. There is a risk that the gap d with the plate 46 will fluctuate. There is also a problem that the durability of the pressure roller 45 is lowered. As shown in Table 1 below, when the separation assisting member 48 is retracted 2 mm from the pressure roller 45, the lifespan of the pressure roller 45 and the fixing belt 43 can be increased approximately twice.

However, by providing the separation assisting member 48 at a position separated from the pressure roller 45, pressure is applied to the recording sheet P attached to the fixing belt 43 from the fixing nip N1 to the separation portion where the leading end of the separation plate 46 faces. Will not be applied. When the recording sheet P is heated in the fixing nip N1, moisture contained in the recording sheet P is vaporized to become water vapor. The fixing nip N1 is pressurized with a strong surface pressure of about 40 [N / cm ² ], so that no water vapor is released from the recording sheet P. However, since there is no pressure on the recording sheet P that has exited the fixing nip N1, water vapor is released from the recording sheet P.

  As shown in FIG. 3, the gap between the fixing belt 43 and the pressure roller 45 at the fixing nip exit is narrower than when the fixing belt 43 is wound around the fixing roller 41. Therefore, heat is easily generated in the narrow region, the temperature of the recording sheet does not decrease, and a lot of water vapor is released. The water vapor is mainly released from the surface (back surface) of the recording sheet P facing the pressure roller 45. In addition, the recording sheet that has exited the fixing nip N1 is conveyed to a separation unit that is opposed to the front end of the separation plate 46 while being attached to the fixing belt 43. Since the non-image portion of the recording sheet P is lower than the image portion on which the toner image is formed, a gap is formed between the fixing belt 43 and the non-image portion, and water vapor is also released into this gap. Is done. When the water vapor is released, the fibers of the recording sheet P are dried and the undulation is generated.

  Further, water vapor mainly released from the surface (back surface) of the recording sheet P facing the pressure roller 45 stays in this narrow gap, and is again absorbed by the recording sheet and wets the recording sheet. Further, the water vapor released between the fixing belt 43 and the non-image portion remains in the gap, and is absorbed again by the recording sheet and wets the recording sheet. When the recording sheet P gets wet, the fibers extend and the recording sheet is wavy.

  In the conventional configuration shown in FIG. 3, during the period from when the recording sheet P is conveyed from the fixing nip N1 to the separation portion where the leading edge of the separation plate 46 faces, drying due to release of water vapor or wetting due to reabsorption of water vapor. Expansion and contraction occur in the fibers of the recording sheet P, and the recording sheet P is wavy during this time. Then, the wrinkles S are generated on the recording sheet P as shown in FIG.

  Therefore, in the present embodiment, a pressing member 49 that contacts the inner peripheral surface of the fixing belt 43 between the fixing roller 41 and the separation assisting member 48 and presses the fixing belt is provided.

FIG. 5 is an enlarged view showing the vicinity of the exit of the fixing nip N1 of the fixing device of the present embodiment.
In this embodiment, a pressing member 49 is disposed between the fixing roller 41 and the separation assisting member 48 inside the fixing belt 43. The pressing member 49 is a plate-like member having a thickness of about 0.2 mm formed of a metal such as SUS. One end is supported by the support plate 24, and extends from the support plate 24 to the pressure roller side. Thus, the plate spring is bent toward the fixing nip N1. In this way, by bending in the middle, the pressing portion 49b that makes contact with the inner peripheral surface of the fixing belt 43 and makes the fixing belt 43 contact with the pressure roller 45, and the surface movement direction of the fixing belt 43 rather than the pressing portion 49b. A bent peeling portion 49a is formed on the downstream side.

  The pressing member 49 is provided so as to bite 0.4 mm into the pressure roller 45 and is installed so as to be elastically deformed and press the fixing belt 43 against the pressure roller 45 with a predetermined load. As a result, a post nip portion N2 is formed by the pressing member 49 downstream of the fixing nip N1 in the recording sheet conveyance direction.

  Further, the shape of the pressing portion 49 b of the pressing member 49 is made to conform to the surface shape of the pressure roller 45, and the fixing belt 43 is uniformly pressed against the pressure roller 45. Further, at the outlet of the post nip portion N2, the moving direction of the fixing belt 43 is suddenly changed along the bending of the peeling portion 49a of the pressing member 49. Thereby, the curvature of the fixing belt 43 at the exit of the post nip portion N2 can be increased (the radius of curvature is decreased). In the present embodiment, the peeling portion 49a of the pressing member 49 is configured so that the radius of curvature of the fixing belt 43 at the exit of the post nip portion N2 is 6 mm.

  In the present embodiment, the recording sheet P that has exited the fixing nip N1 is conveyed while receiving pressure at the post nip portion N2. Since the pressure at the post nip portion N2 is lower than that at the fixing nip N1, water vapor is discharged from the recording sheet at the post nip portion N2. By releasing water vapor from such a recording medium, the fiber of the paper dries and shrinks, but the recording sheet is pressed by the pressing roller 49 by the pressing member 49 via the fixing belt 43. The fibers are not shrunk and the undulation of the recording sheet due to the release of water vapor is suppressed.

  Further, the water vapor released from the post nip portion N2 remains as bubbles between the recording sheet P and the fixing belt 43, and is absorbed again by the recording sheet P to wet the recording sheet P. However, during the absorption of water vapor, the recording sheet P is pressed by the pressing roller 45 by the pressing member 49 via the fixing belt 43. Accordingly, paper fibers are wetted by the absorption of water vapor and the paper fibers tend to stretch. However, since the recording sheet P is pressed by the pressure roller 45 by the pressing member 49 via the fixing belt 43, the fibers can stretch. Accordingly, the undulation of the recording sheet P due to the absorption of water vapor is suppressed.

  In this way, by suppressing the undulation of the recording sheet, when the recording sheet after passing through the fixing nip is nipped and conveyed by the pair of paper discharge rollers, the recording sheet is as shown in FIG. Generation of streak-like wrinkles can be suppressed.

  In this embodiment, the recording sheet may be pressed so that the fibers of the recording sheet do not expand or contract due to the release or absorption of water vapor, and the pressure may be sufficiently lower than the pressure in the fixing nip. In the present embodiment, the pressure of the post nip portion N2 may be about 5 [N]. Further, the waviness of the recording sheet may be suppressed to such an extent that no streak-like wrinkles as shown in FIG. Therefore, the fixing belt 43 may be pressed by the pressing member 49 so as to be close to the pressure roller, and there may be a slight gap between the fixing belt 43 and the pressure roller 45. In this case, the recording sheet P that has exited the nip N1 hits the pressure roller 45 and the fixing belt when the undulation is caused by the release or absorption of water vapor, and further undulation is suppressed. Therefore, even if there is a slight gap between the fixing belt 43 and the pressure roller 45 by pressing the fixing belt 43 with the pressing member 49 so as to be close to the pressure roller, the undulation can be suppressed. Further, when the fixing belt 43 is not brought into contact with the pressure roller 45 by the pressing member 49, if the gap described above is the thickness of the recording sheet P, the recording sheet exiting the fixing nip N1 is pressed against the fixing belt. Since the sheet is conveyed while being sandwiched between the rollers, it is possible to more effectively suppress the undulation of the recording sheet.

  Further, at the exit of the post nip portion N2, the fixing belt 43 is rapidly changed in the moving direction along the bending of the peeling portion 49a of the pressing member 49. As a result, the recording sheet P is separated from the fixing belt 43 by the curvature separation at the exit of the post nip portion N2. In addition, the recording sheet P having a weak stiffness such as thin paper and the recording sheet P on which an image is formed up to the leading end portion of the recording sheet P are not separated in curvature at the exit of the post nip portion N2, and are attached to the fixing belt 43. It is conveyed to the separation unit. However, the water vapor generated in the fixing nip N1 has already been released in the post nip portion N2. Therefore, there is almost no water vapor released until it moves to the separation part. Further, the gap between the fixing belt 43 and the pressure roller 45 at the exit of the post nip portion N2 is wider than that in FIG. Accordingly, the heat is not released near the exit of the post nip portion N2, but is released to the surroundings. Therefore, the recording sheet is heated by the heat in the vicinity of the outlet of the post nip portion N2 until it moves to the separation portion, and almost no water vapor is released. Therefore, there is almost no undulation caused by drying due to the discharge of water vapor between the post-nip portion N2 and the separation portion.

  Further, water vapor that has not been reabsorbed by the recording sheet at the post nip portion N2 is discharged to the periphery at the outlet of the post nip portion N2. However, since the gap between the fixing belt 43 and the pressure roller 45 at the exit of the post nip portion N2 is wider than that in FIG. 3, it does not stay near the exit of the post nip portion N2. Therefore, reabsorption of water vapor hardly occurs between the post nip portion N2 and the separation portion. Therefore, there is almost no undulation due to wetting due to reabsorption of water vapor between the post-nip portion N2 and the separation portion.

  Further, when the fixing belt 43 is pressed by the pressing member 49, a region where the fixing belt 43 is not stretched and is in a free state is between the outlet of the post nip portion N2 and the separation assisting member 48. Compared to FIG. The free region can be narrowed.

  Further, by making the pressing member 49 a plate-like member, the heat capacity can be reduced and the temperature loss due to the pressing member 49 can be suppressed as compared with the case where the pressing member 49 is a block-like member. As a result, the waiting time until the temperature of the fixing belt 43 is raised to a necessary temperature can be shortened as compared with the case where the pressing member 49 is a block-shaped member. Moreover, compared with the case where the pressing member 49 is a block-shaped member, an increase in power consumption can be suppressed and energy saving can be achieved.

  Also, by using the pressing member 49 as an elastic member, it is possible to make it easier to follow the pressure roller 45 than when the pressing member 49 is a rigid body. Accordingly, the fixing belt can be pressed uniformly against the pressure roller with a predetermined load.

  In the present embodiment, the recording sheet P has three separation portions that can be separated from the fixing belt 43. That is, there are three portions: the curvature portion of the fixing belt at the exit of the post nip portion N2 formed by the peeling portion 49a of the pressing member 49, the curvature portion of the fixing belt 43 formed by the separation auxiliary member, and the tip of the separation plate 46. . Thereby, the recording sheet P can be reliably separated from the fixing belt 43, and the occurrence of paper jam can be suppressed satisfactorily.

  In addition, the configuration of the pressing member 49 is not limited to the above-described configuration, and for example, as illustrated in FIG. 6, a portion of the pressing member 49 that extends from the support plate 24 toward the pressure roller may be bent. With such a configuration, the pressing member 49 is easily elastically deformed, the followability to the pressure roller 45 can be increased, and the durability of the pressure roller 45 can be increased.

  In addition, as shown in FIG. 7, the peeling portion 49 a may have a shape protruding toward the downstream side in the conveyance direction of the recording sheet P. With this configuration, the curvature of the fixing belt 43 at the exit of the post nip portion N2 formed by the peeling portion 49a can be increased (the radius of curvature is decreased), and the separation property of the recording sheet P at the exit of the post nip portion N2 can be improved. it can.

  Further, as shown in FIGS. 8 and 9, an opening 49 c may be provided in the pressing portion 49 b of the pressing member 49. With this configuration, the heat capacity of the pressing member 49 can be further reduced, the waiting time until the fixing belt 43 is heated to a necessary temperature can be shortened, and energy saving can be achieved. Can do.

  In addition, it is preferable to arrange the tip of the pressing portion 49 b of the pressing member 49 as close to the fixing roller 41 as possible. As shown in FIG. 5, this is pressed by the member from the inside between the post nip portion N2 pressed against the pressure roller 45 by the pressing portion 49b of the pressing member 49 and the fixing nip N1. An unbounded boundary region N2s is generated. The contact pressure to the pressure roller 45 in the boundary region N2s is lower than the contact pressure of the post nip portion N2. As described above, when there is a portion where the contact pressure on the upstream side in the recording sheet conveyance direction is lower than that on the downstream side, the following problem occurs. That is, since the pressure in the boundary region N2s is lower than that of the fixing nip N1, as described above, water vapor is released from the recording sheet, and bubbles are generated between the recording sheet and the fixing belt. Also, air in the toner image leaks due to thermal expansion, and bubbles are generated between the recording sheet and the fixing belt. When the recording sheet enters the post nip portion N2 having a pressure higher than that of the boundary region N2s, the bubbles are pushed out by the pressing force of the pressing member 49 and move on the surface of the recording sheet P. The toner image on the recording sheet is immediately after exiting the fixing nip N1, and is not completely solidified. The toner image is disturbed by the movement of bubbles on the surface of the recording sheet, and an abnormal image such as uneven glossiness is generated.

  Therefore, it is preferable that the fixing belt 43 is pressed to the vicinity of the fixing nip N1 by the pressing member 49 to narrow the boundary region N2s. By narrowing the boundary region N2s, it is possible to suppress the generation of bubbles in the boundary region. For this reason, in this embodiment, the pressing member 49 is configured to extend from the fixed end fixed to the support plate 24 to the pressure roller side and bend to the fixing nip N1 side in the middle. The upstream end in the direction was defined as a free end. As a result, the pressing member 49 can be disposed near the fixing nip N1 as compared with the case where the end on the downstream side in the recording sheet conveyance direction is bent to the side opposite to the fixing nip side and the free end. The boundary region N2s can be narrowed.

  For the same reason, the pressing force of the pressing member 49 to the fixing belt is also uniform or decreased as it goes downstream in the recording sheet conveyance direction, so that the downstream pressing force is higher than the upstream pressing force. It is preferable not to become. Thereby, it is possible to prevent the bubbles of the released water vapor from being pushed out and moved on the surface of the recording sheet at the post nip portion N2. Thereby, it is possible to suppress the occurrence of abnormal images such as uneven gloss in the post nip portion N2.

  Table 2 below shows the results of an evaluation test for the width of the boundary region N2s.

In the evaluation test in Table 2, the surface pressure of the fixing nip N1 is 40 [N / cm ² ], and the surface pressure of the post nip N2 is 2.84 [N / cm ² ] (0.29 [kg / cm ² ]). A solid image was created on A3 paper, and the created image was visually evaluated for uneven gloss. Each surface pressure was measured using ISCAN. The case where gloss unevenness could not be confirmed was designated as “OK level”, and the case where gloss unevenness was confirmed was designated as “NG level (bad level)”. The surface pressure of the boundary region N2s is an average surface pressure from the fixing nip outlet to the upstream end of the pressing member, and the surface pressure of the post nip N2 is downstream from the upstream end of the pressing member in the fixing belt moving direction. Average surface pressure to the side edge. The surface pressure of the post nip portion N2 is monotonously decreased from the upstream side toward the downstream side in the fixing belt moving direction, and the surface pressure at the upstream end portion of the post nip portion N2 is about 8 [N / cm ² ].

  As can be seen from Table 2, by setting the width of the boundary region N2s to 2.8 mm or less, it is possible to suppress the generation of bubbles in the boundary region N2s, and the surface of the recording sheet is pushed out by the post nip portion N2. It can suppress moving. As a result, it is considered that gloss unevenness did not occur and the gloss unevenness could be set to “OK level”.

  As shown in FIG. 5, it is preferable that the angle θ formed between the tangent line X1 of the pressure roller 45 and the tangent line X2 of the fixing roller 41 at the exit of the fixing nip N1 is 45 ° or more. The applicant conducted an evaluation test when the angle θ was 13 ° and when the angle θ was 45 °. When the angle θ was 13 °, uneven gloss occurred, and the angle θ was 45. When it was °, no gloss unevenness occurred. This is because when the angle θ is 13 °, the distance between the recording sheet P and the fixing roller 41 near the exit of the fixing nip N1 is short. Therefore, the recording sheet P1 exiting the fixing nip N1 is affected by the heat of the fixing roller 41. As a result, the release of water vapor in the boundary region N2s and the thermal expansion of air in the toner image increase, and the bubbles generated in the boundary region N2s tend to increase. As a result, even if the difference between the surface pressure of the boundary region N2s and the surface pressure of the post nip portion N2 is small, the volume of the air bubbles is large, so that the expansion of the air bubbles when being crushed at the post nip portion N2 increases. It is thought that unevenness occurred. On the other hand, by setting the angle θ to 45 ° or more, the influence of the heat of the fixing roller 41 received by the recording sheet P in the boundary region N2s can be reduced. Thereby, in the boundary region N2s, the release of water vapor from the recording sheet P and the thermal expansion of the air in the toner can be suppressed, and the bubble can be prevented from becoming large. As a result, it is considered that the expansion of the bubbles when the bubbles are crushed in the post nip portion is suppressed, and the level of gloss unevenness cannot be confirmed.

  Further, if the fixing belt 43 is always brought into contact with the pressure roller 45 by the pressing member 49, the pressing force of the pressing member 49 is constantly applied to the pressure roller 45 and the fixing belt 43, and the pressure roller 45 and the fixing belt 43 are fixed. There is a risk of reducing the life of the belt 43. Further, when the fixing belt 43 is brought into contact with the pressure roller 45 by the pressing member 49 at the time of rotational driving other than the paper passing time such as warm-up, the friction between the fixing belt inner peripheral surface and the pressing member 49 is caused. As a result, the fixing belt 43 is worn early. For this reason, it is preferable to release the contact of the pressing member 49 when the sheet is not passed or when a recording sheet such as thick paper or OHP which hardly generates undulation due to the release or absorption of water vapor. In the case of thick paper, the leading end of the thick paper collides with the free end of the pressing member 49, the pressing member 49 bends downstream in the recording sheet conveyance direction, or the fixing belt 43 is placed between the leading end of the thick paper and the free end of the pressing member 49. The fixing belt 43 may be damaged due to being pinched. Therefore, when the recording sheet is thick paper, it is preferable to position the pressing member at the release position.

FIG. 10 is a perspective view illustrating a moving mechanism that moves the pressing member 49 between a contact position where the fixing belt 43 contacts the pressure roller 45 and a release position where the contact is released.
As shown in FIG. 10, the moving mechanism 20 includes a bent support plate 24 to which the pressing member 49 is fixed and supported. The holding member 49 is screwed to the lower end portion of the support plate 24. Arm members 23 and guide members 21 are provided on both ends of the support plate 24 in the axial direction of the fixing roller. A connecting member 22 connected to a driving means constituted by a cam or the like is fixed to the tip of the arm member 23. The connection member 22 is held in an arc-shaped slot that is centered on the rotation center of the fixing roller provided on the side surface of the fixing device casing.

FIG. 11 is a diagram illustrating a state in which the pressing member 49 is positioned at a contact position where the fixing belt 43 contacts the pressure roller. FIG. 12 illustrates the pressing member 49 in the pressure roller of the fixing belt 43. It is a figure which shows the state located in the cancellation | release position which cancel | released contact | abutting to 45. FIG.
As shown in FIGS. 11 and 12, the guide member 21 is attached to the cored bar portion 41 a of the fixing roller 41. When the recording sheet P conveyed to the fixing nip N1 is a recording sheet that is unlikely to be wavy, the pressing member 49 is positioned at the release position. Examples of the recording sheet in which undulation is unlikely to occur include a strong recording sheet such as cardboard and a recording sheet that does not contain moisture such as OHP. In a strong recording sheet such as cardboard, even if the recording sheet is dried by the release of water vapor or absorbs the water vapor, it is difficult for the paper to be wavy due to its own elasticity. A recording sheet that does not contain water such as OHP does not generate water vapor and absorbs water in the first place.

  When the pressing member 49 is positioned at the release position, the connecting member 22 is pushed upward in the figure by the driving means. Then, the moving mechanism 20 rotates in the direction of the arrow A in the figure with the center of the fixing roller being guided by the guide member 21. Then, as shown in FIG. 12, the pressing member 49 moves in a direction away from the pressure roller 45, the pressing member is separated from the fixing belt, and the contact with the pressure roller is released.

  As described above, when the recording sheet conveyed to the fixing nip N1 is a recording sheet such as thick paper or OHP that is unlikely to be undulated, the pressing roller 49 and the fixing belt 43 are disposed by positioning the pressing member 49 at the release position. , And the life of the pressure roller 45 and the fixing belt 43 can be extended. Further, friction between the fixing belt 43 and the pressing member 49 can be reduced. In particular, in the present embodiment, when the pressing member 49 is located at the release position, the pressing member 49 is separated from the inner peripheral surface of the fixing belt 43. For this reason, when it is positioned at the release position, friction between the inner peripheral surface of the fixing belt 43 and the pressing member 49 does not occur, and wear of the fixing belt 43 can be further suppressed.

  In particular, by positioning the pressing member 49 at the release position for thick paper, the free end of the pressing member 49 does not collide with the leading end in the transport direction of the thick paper, and the life of the fixing belt 43 and the pressing member 49 can be extended. .

  Further, even when the recording sheet is not passed through the fixing device, the pressing member 49 is positioned at the release position, so that wear of the pressure roller 45 and the fixing belt 43 can be suppressed. The life of the pressure roller 45 and the fixing belt 43 can be extended. Specifically, at the time of standby, the pressing member 49 is positioned at the release position, for example, the recording member is moved from the release position to the contact position at the timing when the recording sheet passes through the secondary transfer nip, and the recording sheet is moved to the fixing device. Prior to entering, the pressing member is positioned at the contact position. When the recording sheet is discharged from the fixing device, the pressing member 49 is moved to the release position and separated from the fixing belt. As a result, it is possible to reduce the load caused by pressing the fixing member of the fixing belt or the pressure roller.

FIG. 13 is a schematic configuration diagram showing the pressurization / decompression mechanism 201.
As shown in FIG. 13, there is a pressure arm 201a that is in contact with the core of the pressure roller 45 and is rotatably supported at one end side, and a pressure cam 201b that is in contact with the other end side of the pressure arm 201a. doing. Further, the pressure cam 201b is rotated by driving means 201c such as a motor to displace the pressure arm 201a in contact with the pressure cam 201b, and the pressure roller 45 is displaced accordingly. The pressure release / pressure contact state of the roller 45 can be switched. The driving unit 201c is connected to the control unit 202, and the control unit 202 controls the driving of the driving unit 201c. In this embodiment, after the fixing operation is completed, the pressure cam 201b is driven to shift from a pressure contact state where the pressure roller 45 is pressed against the fixing belt 43 to a pressure release state where the pressure roller 45 is separated from the fixing belt 43. To do. As a result, the load on the pressure roller, the fixing belt, and the fixing roller can be reduced, and the durability can be improved.

  In the double-side mode, when the image formed on the second surface of the recording sheet is fixed, the pressure roller is separated from the fixing belt when the fixing operation is completed. That is, in the double-sided mode, after the image is fixed on one side of the recording sheet, the pressure roller is not separated from the fixing belt. In continuous printing, when the fixing operation is performed on the image of the last recording sheet, the pressure roller is separated from the fixing belt when the fixing operation is completed.

  When the pressure roller is separated after the fixing operation, the following problem may occur. That is, there is a problem in that gloss unevenness may occur in an image formed by an image forming operation after the standby mode continues for a long period of time or an image formed by the first image forming operation after the power is turned on. Hereinafter, the problem will be specifically described.

FIG. 14 is a graph showing the temperature of the fixing belt 43 and the temperature of the pressure roller 45 when the conventional printing operation is performed immediately after the power is turned on.
As shown in FIG. 14, when the power is turned on, the warm-up operation is started in a state where the pressure roller 45 is separated from the fixing belt 43, and the temperature of the fixing belt 43 rises to the standby temperature t1. If an image forming signal is received during the warm-up operation, the operation proceeds to the pre-sheet passing operation without shifting to the standby mode. When the pre-passage operation is started, the fixing belt 43 is heated to the fixing temperature t2 corresponding to the recording sheet to be passed with the pressure roller 45 being separated from the fixing belt 43. When the temperature is raised to the fixing temperature t2, sheet feeding of the recording sheet is started. The pressure roller 45 is brought into contact with the fixing belt 43 at a predetermined timing after the recording sheet starts to be fed until the recording sheet reaches the fixing nip.

  After the power is turned on, the temperature of the pressure roller 45 is lowered. For this reason, even if the pressure roller 45 is brought into contact with the fixing belt 43 at a predetermined timing after the recording sheet feeding is started until the recording sheet reaches the fixing nip, The application of heat is insufficient, heat is not sufficiently stored in the pressure roller 45, and is not sufficiently expanded. As a result, the amount of elastic deformation of the pressing member 49 decreases, the tip of the pressing member 49 moves away from the fixing nip N1, and the width of the boundary region N2s exceeds 2.8 mm. As a result, it is considered that uneven gloss occurred in the image formed first after the power was turned on.

FIG. 15 is a graph showing the temperature of the fixing belt 43 and the temperature of the pressure roller 45 when a printing operation is performed after waiting for a long period of time in the related art.
Even during standby for a long period of time, as shown in FIG. 15, the temperature of the pressure roller 45 is lowered. Therefore, even if the pressure roller 45 is brought into contact with the fixing belt 43 at a predetermined timing from when the recording sheet feeding is started until it reaches the fixing nip N1, heat is sufficiently accumulated in the pressure roller 45. Not enough thermal expansion. As a result, the amount of elastic deformation of the pressing member 49 decreases, the tip of the pressing member 49 moves away from the fixing nip N1, and the length in the sheet conveyance direction of the boundary region N2s exceeds 2.8 mm. As a result, gloss unevenness also occurs in an image formed after waiting for a long time.

  Therefore, in the present embodiment, the pressure roller 45 is brought into contact with the fixing belt 43 during the pre-sheet feeding operation so that the pressure roller 45 is preheated.

FIG. 16 is a graph showing the temperature of the fixing belt 43 and the temperature of the pressure roller 45 when the printing operation is performed immediately after the power is turned on in the present embodiment.
As shown in FIG. 16, in the warm-up operation, the temperature of the fixing belt 43 is raised to the standby temperature t1. If an image forming signal is received during the warm-up operation, the operation proceeds to the pre-sheet passing operation after the warm-up operation is completed. After shifting to the pre-sheet passing operation, a pre-heating operation for bringing the pressure roller 45 into contact with the fixing belt for a predetermined time is executed. As a result, heat is transferred from the fixing belt 43 to the pressure roller 45, heat is stored in the pressure roller 45, and the pressure roller 45 is thermally expanded. When the predetermined time has elapsed, the pressure roller 45 is separated from the fixing belt 43. In this way, when the predetermined time has elapsed, the pressure roller 45 is separated from the fixing belt 43, and thereafter, the fixing belt 43 is passed through the pressure roller 45 without the heat of the fixing belt 43 being taken away. It is possible to quickly raise the temperature to the fixing temperature t2 corresponding to the recording sheet to be recorded. Thereby, it is possible to suppress an increase in the operation time before passing paper. When the fixing belt 43 rises to the fixing temperature t2 corresponding to the recording sheet to be passed, the feeding of the recording sheet is started, and the pressure roller 45 is turned on at a predetermined timing before the recording sheet reaches the fixing nip. It is brought into contact with the fixing belt 43.

FIG. 17 is a graph showing the temperature of the fixing belt 43 and the temperature of the pressure roller 45 when the printing operation is performed after waiting for a long time in the present embodiment.
When the image forming signal is received, the operation shifts from the standby mode to the pre-passage operation, and the temperature is raised to the fixing temperature t2 corresponding to the recording sheet passing through the fixing belt 43. Also, a preheating operation is executed simultaneously with the pre-sheet passing operation, the pressure roller 45 is brought into contact with the fixing belt 43, and the pressure roller 45 is preheated for a predetermined time. The pressure roller 45 is heated to the temperature t3 by this preheating. Then, after preheating for a predetermined time, the pressure roller 45 is separated from the fixing belt 43, and the pressure roller 45 is brought into contact with the fixing belt 43 again at a predetermined timing after feeding of the recording sheet is started.

  Table 3 below shows the length in the sheet conveyance direction of the boundary region N2s when the pressure roller 45 is brought into contact with the fixing belt 43 without performing the preheating operation, and the pressure roller 45 that has performed the preheating operation. This shows the width (the length in the sheet conveying direction) of the boundary region N2s when it is brought into contact with the fixing belt 43.

By performing the pre-heating operation and sufficiently expanding the pressure roller, the width of the boundary region N2s can be reduced by 0.7 mm compared to the case where the pre-heating operation is not performed and the pressure roller is not thermally expanded. it can. As shown in FIG. 5, the gap between the fixing member 49 and the peeling portion 49 a is inclined so that the pressing member peeling portion 49 a is positioned closer to the fixing nip than the fixing end in the sheet conveyance direction. Yes. If the pressing amount of the pressing member 49 by the pressure roller 45 increases due to the thermal expansion of the pressing roller 45, the space between the fixed end of the pressing member 49 and the peeling portion is such that the peeling portion 49a approaches the fixing nip. Elastically deforms. As a result, the free end of the pressing member 49 approaches the fixing nip, and the boundary region N2s is narrowed. Further, the thermal expansion of the pressure roller widens the fixing nip width and narrows the width of the boundary region N2s.
Even when the pressure roller is not thermally expanded, if the width of the boundary region N2s is 2.8 mm or less, it is considered that the preheating operation is not required. However, depending on the configuration of the apparatus and the like, if the width of the boundary region N2s when the pressure roller 45 is not thermally expanded is set to 2.8 mm or less, when the pressure roller 45 thermally expands, There is a possibility that the free end comes into contact with the fixing roller 41. This will be specifically described below.

  The gap between the fixing roller 41 and the inner peripheral surface of the fixing belt 43 after exiting the fixing nip N1 is a rust-like gap that gradually widens from the outlet of the fixing nip N1 (see, for example, FIG. 5). ). As a result, the gap between the fixing roller 41 near the fixing nip exit and the inner peripheral surface of the fixing belt 43 becomes narrower than the thickness of the plate-shaped pressing member 49. If the pressing member 49 is disposed in a wedge-shaped gap at a position narrower than the thickness of the plate-shaped pressing member 49 near the exit of the fixing nip, the pressing member 49 comes into contact with the surface of the fixing roller 41. When the pressing member 49 comes into contact with the surface of the fixing roller 41, the surface of the fixing roller 41 is damaged by the tip of the pressing member 49. Accordingly, in order to prevent the pressing member 49 from coming into contact with the fixing roller 41, a certain boundary region N2s is inevitably required. The larger the outer diameter of the fixing roller 41, the longer the range narrower than the thickness of the plate-like pressing member 49 near the fixing nip exit. As a result, the width of the boundary region N2s when the pressing member 49 is prevented from contacting the fixing roller 41 is widened.

  In addition, there are errors in component tolerances, assembly errors, thermal expansion amount of the pressure roller, and thermal expansion amount of the fixing roller for each apparatus. Therefore, when the pressure roller thermal expansion is set so that the free end of the pressing member 49 does not contact the fixing roller, there is a possibility that the free end of the pressing member 49 contacts the fixing roller due to the above error. Therefore, in order to ensure that the free end of the pressing member does not contact the fixing roller during the thermal expansion of the pressure roller, the width of the boundary region N2s is further increased. For this reason, depending on the configuration of the apparatus, it is necessary to set the boundary region N2s to be 2.2 mm or more during the thermal expansion of the pressure roller, and the pressure roller is inevitably thermally expanded. The width of the boundary region N2s when not present may exceed 2.8 mm.

  However, in this embodiment, as can be seen from Table 3, when the pressure roller is not thermally expanded, the preheating operation is performed on the pressing member 49 even when the boundary region is set to exceed 3 mm. The pushing amount can be 2.8 mm or less, and the occurrence of uneven gloss can be suppressed. In addition, it is possible to ensure that the free end of the pressing member does not contact the fixing roller during thermal expansion of the pressure roller.

  The pre-heating operation is particularly effective when a so-called reverse crown-shaped pressure roller having an outer diameter that increases from the center to the end in the axial direction is used to suppress the occurrence of vertical wrinkles on the recording sheet. It is valid. When the pressure roller 45 has an inverted crown shape, the pressing amount of the pressure roller 45 at the center from the end in the axial direction with respect to the pressing member 49 is reduced. As a result, the amount of elastic deformation at the center in the axial direction of the push-in member 49 becomes less than that at the end, and the width at the center in the axial direction of the boundary region N2s becomes wider than at the end. As a result, even when the pressure roller 45 is not thermally expanded at the axial end, even if the width of the axial end of the boundary region N2s can be 2.8 mm or less, 2.8 mm is reduced at the center. May exceed. Therefore, it is conceivable that the pressing portion 49b of the pressing member is recessed on the pressure roller side so as to conform to the outer diameter shape of the pressing roller, but in this case, the processing of the pressing member becomes complicated and the manufacturing cost is increased. The problem of improvement and processing accuracy also occurs.

  In the reverse crown-shaped pressure roller 45, since the thermal expansion amount at the center is larger than the thermal expansion amount at the end, it is known that when heated, the difference in outer diameter between the end and the center becomes small. . Therefore, by performing the preheating operation, the width of the boundary region N2s in the axial center is narrower than that of the end portion, and the boundary region N2s in the axial center can be surely made 2.8 mm or less.

  Further, the speed until the pressure roller 45 sufficiently expands varies depending on the environmental temperature that is the temperature around the fixing device. When the environmental temperature is low, the temperature of the pressure roller 45 is low and heat easily escapes to the surroundings, so that the pressure roller 45 is difficult to thermally expand. On the other hand, when the environmental temperature is high, the pressure roller 45 is high in temperature and the heat hardly escapes to the surroundings, so the pressure roller 45 is likely to thermally expand. Therefore, it is preferable to change the operating conditions of the preheating operation according to the environmental temperature.

FIG. 18 is a diagram for explaining the arrangement of temperature sensors as temperature detection means for detecting the environmental temperature.
As shown in FIG. 18, the printer is provided with three temperature sensors 80a, 80b, and 80c for detecting the environmental temperature. The first temperature sensor 80a is provided in the Y-color developing device 4Y, the second temperature sensor 80b is provided in the K-color developing device 4K, and the third temperature sensor 80c is the first temperature sensor 80c. Provided in the paper feed cassette 101. In the present embodiment, the third temperature sensor 80 c is provided in the first paper feed cassette 101, but may be provided in the second paper feed cassette 102.

  In this embodiment, temperature control is performed for the three temperature sensors 80a, 80b, and 80c, and the lowest temperature is adopted as the environmental temperature. Not only this but the average value of the temperature which three temperature sensors detected is good also as environmental temperature. Further, the arrangement position of each temperature sensor is not limited to the example shown in FIG. 18, and may be determined as appropriate according to the layout of the apparatus. Further, the number of temperature sensors is not limited to the above, and may be determined as appropriate depending on the configuration of the apparatus.

FIG. 19 is a block diagram illustrating an example of a control system of the present embodiment.
The control unit 202 includes a CPU (Central Processing Unit), a read-only memory (ROM) that stores a control program, a readable / writable memory (RAM) that temporarily stores data, a nonvolatile flash memory, and the like. Yes.
Then, various arithmetic processes are executed, various drive system devices included in each device connected as shown in FIG. 19 are driven, and communication with various sensors is performed.

  Further, the control unit 202 adopts the lowest temperature among the temperatures detected by the temperature sensors 80a, 80b, and 80c as the environmental temperature, and changes the operating condition of the preheating operation based on the environmental temperature. The operating conditions to be changed according to the environmental temperature include the amount of heat generated per unit time of the heat source 44, the preheating operation time, the rotation speed of the pressure roller, the pressure contact position of the pressure roller 45 with the fixing belt 43, etc. Can be mentioned. One of the plurality of operating conditions listed above may be changed based on the environmental temperature, or a plurality of these operating conditions may be changed based on the environmental temperature. Hereinafter, the operating conditions to be changed based on the environmental temperature will be described as examples.

[Example 1]
Hereinafter, an example in which the operating condition to be changed according to the environmental temperature is set to the lighting rate of the heat source 44 composed of a heater such as a halogen heater (time ratio during which electric power is applied to the heat source 44) will be described as Example 1. . Table 4 below shows an example of the lighting rate of the heat source 44 during the preheating operation at each environmental temperature. Table 4 below is an example, and may be set as appropriate depending on the configuration of the apparatus.

  As shown in Table 4, when the environmental temperature is a low temperature of 17 ° C. or less, the temperature of the pressure roller 45 is low, and the heat stored in the pressure roller 45 easily escapes to the surroundings. Difficult to thermally expand. Therefore, even if the pressure roller 45 is brought into contact with the fixing belt 43 for a specified time, the pressure roller 45 may not be sufficiently expanded. Therefore, as shown in Table 4, in Example 1, when the environmental temperature is a low temperature of 17 ° C. or lower, the lighting rate of the heat source 44 is increased, and the amount of heat applied to the fixing belt 43 per unit time is determined as the environmental temperature. Is higher than that at normal temperature (18 ° C. to 29 ° C.). As a result, in the preheating operation, the amount of heat supplied from the fixing belt 43 to the pressure roller 45 increases, and the pressure roller 45 can be sufficiently thermally expanded even when the environmental temperature is low. Therefore, even when the environmental temperature is low, the boundary region N2s can be 2.8 mm or less, and the occurrence of uneven gloss can be suppressed.

  Further, as shown in Table 4, when the environmental temperature is a high temperature of 30 ° C. or higher, the lighting rate of the heat source 44 is reduced as compared with the normal temperature (18 ° C. to 29 ° C.). When the environmental temperature is high, the temperature of the fixing belt 43 and the pressure roller 45 is also high and the heat that escapes to the surroundings is small, so that the pressure roller 45 can be sufficiently thermally expanded with a small amount of heat. Therefore, when the environmental temperature is a high temperature of 30 ° C. or higher, the pressure roller 45 is sufficiently expanded within the preheating operation time even if the lighting rate of the heat source 44 is reduced from that at room temperature (18 ° C. to 29 ° C.). Can be made. Moreover, power consumption can be suppressed by reducing the lighting rate.

[Example 2]
Hereinafter, an example in which the operating condition of the preheating operation changed according to the environmental temperature is the preheating operation time will be described as a second embodiment. Table 5 below shows an example of the preheating operation time at each environmental temperature. Table 5 below is an example and may be set as appropriate depending on the configuration of the apparatus.

  As shown in Table 5, the amount of heat applied to the pressure roller 45 can be increased by increasing the preheating operation time when the environmental temperature is low than when it is normal temperature, and when the environmental temperature is low However, the pressure roller 45 can be sufficiently thermally expanded. Thereby, even if environmental temperature is low temperature, the width | variety of boundary area | region N2s can be 2.8 mm or less, and it can suppress that gloss unevenness generate | occur | produces. Further, when the environmental temperature is a high temperature of 30 ° C. or higher, as described above, the pressure roller 45 can be sufficiently thermally expanded even when the amount of heat applied to the pressure roller 45 is small. To shorten the preheating operation time. Accordingly, the pressure roller 45 can be separated from the fixing belt 43 at an early stage, and the temperature can be quickly raised to the fixing temperature t2 corresponding to the recording sheet to which the fixing belt 43 is passed. Thereby, it is possible to suppress an increase in the operation time before passing paper.

[Example 3]
Hereinafter, an example in which the operating condition of the preheating operation to be changed according to the environmental temperature is set as the rotation speed of the pressure roller 45 will be described as a third embodiment. Table 6 below shows an example of the rotation speed of the pressure roller during the preheating operation at each environmental temperature. Table 6 below is also an example, and may be set as appropriate depending on the configuration of the apparatus.

  As shown in Table 6, the rotation speed of the pressure roller 45 when the environmental temperature is low is made faster than that at room temperature. In the present embodiment, the pressure roller 45 is driven to rotate with respect to the fixing belt 43. Therefore, in order to increase the rotation speed of the pressure roller 45, the rotation speed of the fixing belt 43 is increased. . Specifically, the control unit 202 controls the motor of the belt driving unit 203 (configured by a drive transmission member such as a motor and a gear) for rotating the fixing belt to increase the rotation speed of the fixing belt 43 and pressurize it. Increase the rotation speed of the roller.

  By increasing the rotation speed of the pressure roller 45, the portion of the pressure roller that has received a heat from the fixing belt at the fixing nip N1 and has risen in temperature quickly passes through the fixing nip. Thereby, the heat transfer efficiency from the fixing belt 43 to the pressure roller 45 can be increased, and a sufficient amount of heat can be imparted to the pressure roller 45 within the preheating operation time. As a result, the pressure roller 45 can be sufficiently thermally expanded, and even when the environmental temperature is low, the width of the boundary region N2s can be 2.8 mm or less, and the occurrence of uneven gloss is suppressed. can do.

  Further, when the environmental temperature is a high temperature of 30 ° C. or higher, the pressure roller 45 can be sufficiently thermally expanded even if the heat transfer efficiency from the fixing belt 43 to the pressure roller 45 is low. Therefore, when the environmental temperature is a high temperature of 30 ° C. or higher, the rotation speed of the pressure roller is made slower than that at normal temperature. By reducing the rotation speed of the pressure roller, it is possible to suppress wear of a drive transmission member such as a gear constituting the belt driving unit 203 (see FIG. 20), and to improve durability of the belt driving unit 203. it can.

[Example 4]
Hereinafter, an example in which the operating condition of the preheating operation that is changed according to the environmental temperature is set to the pressure contact position of the pressure roller 45 with the fixing belt 43 will be described as a fourth embodiment. Table 7 below shows an example of the pressure contact position of the pressure roller with the fixing belt 43 at each environmental temperature. Table 7 below is also an example, and may be set as appropriate depending on the configuration of the apparatus.

  In this embodiment, the pressure contact position of the pressure roller 45 with the fixing belt 43 can be adjusted in four stages. One stage is located at the position farthest from the fixing roller 41, the pressure applied to the fixing belt 43 is the lowest, and the fourth stage is located closest to the fixing roller 41, and the pressure applied to the fixing belt 43 is the highest. In the present embodiment, the reference pressure contact position is “3”. For example, if the image to be recorded on the recording sheet is a large amount of toner on the recording sheet such as a full-color image, a large amount of heat is required to obtain good fixability. Therefore, for example, when the amount of toner adhering to the recording sheet is large, the pressure contact position is set to “4”, the fixing nip width is increased, and the amount of heat applied at the fixing nip is increased. Further, when the recording sheet has a paper thickness such as an envelope or a thick paper, for example, the pressure contact position is set to “1”, and the pressure applied to the fixing belt 43 by the pressure roller 45 is lowered. In this way, good fixability is maintained by setting the pressure contact position of the pressure roller 45 and changing the fixing nip width based on the amount of toner on the recording sheet to be passed and the type of paper. can do.

  As shown in Table 7, when the environmental temperature is low, the pressure contact position of the pressure roller 45 during the preheating operation is set to “4”. By setting the pressure contact position of the pressure roller 45 to “4”, the width of the fixing nip N1 is widened. Thereby, an area for transferring heat from the fixing belt 43 to the pressure roller 45 is increased, and heat transfer efficiency can be increased. As a result, even if the environmental temperature is low, the pressure roller 45 can be sufficiently thermally expanded within the preheating operation time.

  In the above description, the preheating operation is an operation for ending the preheating operation at a predetermined time. However, a temperature sensor for detecting the temperature of the pressure roller 45 is provided, and the temperature of the pressure roller 45 is the target. When the temperature is reached, the preheating operation may be terminated. With such an operation, when the temperature of the pressure roller 45 before the operation before paper passing is high, the preheating operation time is shortened, and the time for the operation before paper passing can be shortened.

  Then, when the preheating operation is performed to end the operation when the temperature of the pressure roller 45 reaches the target temperature, the target temperature of the pressure roller 45 is changed as the preheating operation condition to be changed according to the environmental temperature. It may be. Table 8 below shows an example of the target temperature of the pressure roller 45 at each environmental temperature.

  As shown in Table 8, when the environmental temperature is low, the target temperature of the pressure roller 45 is raised more than when the environmental temperature is normal temperature. When the ambient temperature is low, the preheating operation is terminated and the pressure roller 45 is separated from the fixing belt 43 until the pressure roller 45 is brought into contact with the fixing belt 43 again. A large amount of heat escapes from the roller 45 to the surroundings. For this reason, there is a possibility that the amount of thermal expansion of the pressure roller 45 is significantly reduced after the preheating operation is finished and before the pressure roller 45 is brought into contact with the fixing belt 43 again. Furthermore, when the environmental temperature is low, the temperature of the recording sheet is also low, and the amount of heat of the pressure roller taken away by the recording sheet when the paper is passed increases. As a result, the thermal expansion of the pressure roller 45 is greatly reduced until the recording sheet passes through the fixing nip, and the width of the boundary region N2s may not be maintained at 2.8 mm or less. Further, as a result of a significant decrease in the thermal expansion of the pressure roller 45, the width of the fixing nip decreases, and a sufficient amount of heat cannot be applied from the fixing belt to the toner image on the recording sheet, which may cause a fixing failure.

  Therefore, when the environmental temperature is low, the target temperature of the pressure roller 45 is increased, and the amount of heat stored in the pressure roller 45 is increased in the preheating operation. As a result, even if the heat escapes after the preheating operation is finished and before the pressure roller 45 is brought into contact with the fixing belt 43 again, the pressure roller 45 can maintain a sufficiently thermally expanded state. . Further, even if the recording sheet is low in temperature and the amount of heat taken away by the recording sheet is large, the thermal expansion of the pressure roller 45 can be maintained, and even if the environmental temperature is low, the width of the boundary region N2s is set to 2. It can be maintained at 8 mm or less. Thereby, generation | occurrence | production of gloss unevenness can be suppressed.

  Further, when the environmental temperature is high, the target temperature of the pressure roller 45 is lowered than when the environmental temperature is normal temperature. When the environmental temperature is high, the heat that escapes from the pressure roller 45 to the periphery after the preheating operation is completed and before the pressure roller is brought into contact with the fixing belt again is reduced. Also, since the temperature of the recording sheet is high, less heat is taken away by the recording sheet when the sheet is passed. Therefore, even if the heat accumulated in the pressure roller 45 by the preheating operation is small, the thermal expansion amount of the pressure roller 45 can be sufficiently maintained. Therefore, when the environmental temperature is high, the target temperature of the pressure roller 45 is lowered than when the environmental temperature is normal temperature. When the environmental temperature is high, by lowering the target temperature of the pressure roller 45 than when the environmental temperature is normal temperature, the pressure roller 45 can be set to the target temperature at an early stage, and the preheating operation time can be shortened. As a result, it is possible to shorten the time for the pre-sheet passing operation.

  In addition, when the temperature of the pressure roller is high, the amount of heat stored in the pressure roller is sufficient, so it is not a preheating operation corresponding to the environmental temperature in which the preheating operation condition is changed based on the environmental temperature described above, A normal preheating operation may be performed. Table 9 below is an example showing whether or not the preheating operation corresponding to the environmental temperature at the temperature of the pressure roller 45 can be performed.

  A temperature sensor such as a thermistor for detecting the temperature of the pressure roller 45 is provided, and the control unit 202 measures the temperature of the pressure roller with this temperature sensor before the preheating operation. When the temperature of the pressure roller 45 is 120 ° C. or higher, the pressure roller is sufficiently stored, and even if the environmental temperature is low, it can be sufficiently expanded by a normal preheating operation. . Therefore, when the temperature of the pressure roller 45 is 120 ° C. or higher, the normal preheating operation shown in FIGS. 16 and 17 is executed.

  On the other hand, when the temperature of the pressure roller 45 is 119 ° C. or less, if the environmental temperature is low, the pressure roller may not be sufficiently thermally expanded in a normal preheating operation. Therefore, when the temperature of the pressure roller 45 is 119 ° C. or less, a preheating operation corresponding to the environmental temperature is performed in which the preheating operation condition is changed based on the environmental temperature described above. Thereby, even if environmental temperature is low temperature, a pressure roller can fully be thermally expanded and the width | variety of boundary area | region N2s can be 2.8 mm or less.

  Further, it is preferable to change the standby temperature t1 (see FIGS. 16 and 17), which is the temperature of the fixing belt 43 during standby, according to the environmental temperature. Table 10 below shows an example of the standby temperature t1 of the fixing belt 43 at each environmental temperature.

  As described with reference to FIGS. 16 and 17, the preheating operation is performed after the fixing belt is raised to the standby temperature t1 by the warm-up operation or from the standby state in which the fixing belt is maintained at the standby temperature t1. It is something to do. When the temperature of the fixing belt 43 is higher at the start of the preheating operation, the amount of heat transferred from the fixing belt 43 to the pressure roller 45 increases accordingly. Accordingly, in an environment where the environmental temperature is low, the pressure roller 45 is low temperature, and the heat of the pressure roller 45 easily escapes to the surroundings, the standby temperature t1 of the fixing belt 43 is set to the normal temperature. Increase compared to. Thereby, the pressure roller 45 can be sufficiently thermally expanded in a specified preheating operation time. In addition, when the preheating operation is an operation that ends when the pressure roller 45 reaches the target temperature, the preheating operation time can be shortened.

  In addition, when the environmental temperature is low, the temperature of the fixing belt 43 hardly increases. Accordingly, by increasing the standby temperature t1 of the fixing belt when the environmental temperature is low, the time for raising the temperature to the fixing temperature t2 corresponding to the recording sheet that passes the fixing belt 43 when the environmental temperature is low. It can suppress extending. Thereby, it is possible to suppress an increase in the pre-sheet passing operation.

  Further, when the environmental temperature is high, the pressure roller 45 can be sufficiently thermally expanded even if the amount of heat applied to the pressure roller 45 is small. Therefore, as shown in Table 9, the environmental temperature is high. In this case, the standby temperature t1 of the fixing belt 43 is lowered as compared with the normal temperature. As a result, power consumption during standby can be reduced. Also, the warm-up operation time can be shortened.

  The control for changing the standby temperature t1 based on the environmental temperature is executed when the temperature of the pressure roller 45 is equal to or lower than a specified temperature (for example, 119 ° C.). For example, when the temperature is 120 ° C. or higher, the control for changing the standby temperature t1 based on the environmental temperature may not be performed.

  In addition to the pre-sheet passing operation for raising the temperature of the fixing belt 43 to the fixing temperature t2, an operation of heating the pressure roller 45 at a predetermined timing may be executed when the fixing device is in a standby state. It is determined whether or not the pressure roller heating operation executed at a predetermined timing in the standby state is executed according to the environmental temperature. Table 11 below shows an example of whether or not to perform a heating operation that is executed at a predetermined timing in a standby state at each environmental temperature.

  The control unit 202 operates a timer when the standby state is reached, and grasps the environmental temperature based on the temperatures detected by the plurality of temperature sensors 80a, 80b, and 80c when the timer reaches a predetermined time. And as shown in Table 11, when environmental temperature is low temperature, heating operation is performed. When the environmental temperature is low, the heat of the pressure roller 45 tends to escape to the surroundings, and the temperature of the pressure roller 45 tends to decrease. Therefore, when the environmental temperature is low, the heating operation is executed at a predetermined timing in the standby state, so that the temperature drop of the pressure roller 45 can be suppressed, and the pressure is applied during the preheating operation time during the paper passing operation. The roller 45 can be sufficiently thermally expanded. In the operation in which the preheating operation is finished when the pressure roller 45 is heated to the target temperature, the preheating operation time when the environmental temperature is low can be shortened.

  On the other hand, when the environmental temperature is equal to or higher than normal temperature, the temperature drop of the pressure roller 45 in the standby state can be suppressed. Therefore, even if the heating operation is not performed at a predetermined timing in the standby state, the pressure roller 45 can be sufficiently thermally expanded within the preheating operation time during the paper passing operation. In the operation in which the preheating operation is finished when the pressure roller 45 is heated to the target temperature, the pressure roller 45 can be quickly heated to the target temperature. Therefore, when the environmental temperature is equal to or higher than room temperature, the heating operation is not performed at a predetermined timing in the standby state. Thus, when the environmental temperature is equal to or higher than normal temperature, power consumption can be suppressed by not performing the heating operation at a predetermined timing in the standby state.

  Even if the environmental temperature is low, if the pressure roller 45 is high (for example, 120 ° C. or higher), the heat storage amount of the pressure roller is sufficient. The heating operation may not be performed.

  Further, when the environmental temperature is low, the temperature of the toner is also low. For this reason, the temperature of the toner image on the recording sheet is low, the temperature of the toner image on the recording sheet cannot be raised to a specified temperature, and there is a possibility that fixing failure may occur. Further, in order to prevent such a fixing failure, when the fixing temperature t2 when the environmental temperature is low is set higher than that at the normal temperature, the fixing failure can be suppressed, but the toner image is lost. The amount of heat generated is so large that the temperature of the fixing belt cannot be maintained, and the melting degree of the toner on the leading end side in the sheet conveying direction is different from the melting degree of the toner on the trailing end side.

  Therefore, it is preferable to change the toner adhesion amount per unit area of the toner image according to the environmental temperature. Table 11 below shows an example of the toner adhesion amount at each environmental temperature.

  As shown in Table 11, the toner adhesion amount per unit area of the toner image when the environmental temperature is low is reduced by 10% with respect to the toner adhesion amount when the environmental temperature is normal temperature. The control unit 202 controls the image forming unit and the optical writing unit to adjust the developing bias, the exposure amount, and the like, thereby reducing the toner adhesion amount per unit area of the toner image. By reducing the toner adhesion amount by 10%, the amount of heat necessary to satisfactorily fix the toner image on the recording sheet is reduced. As a result, even when the environmental temperature is low and the temperature of the toner image is low, the toner image can be satisfactorily fixed on the recording sheet. Also, by reducing the toner adhesion amount, the amount of heat taken by the toner image is reduced, and the temperature of the fixing belt can be maintained. Thereby, it can suppress that gloss unevenness arises.

  When the environmental temperature is low, the pressure contact position of the pressure roller 45 with the fixing belt 43 when the recording sheet is passed is set to “4” so that the width of the fixing nip is larger than that when the environmental temperature is normal temperature. You may make it expand. As a result, the range in which heat is transferred from the fixing belt 43 to the toner image is increased, and heat transfer efficiency can be increased. As a result, good fixability can be obtained even when the environmental temperature is low and the temperature of the toner image is low.

  As described above, when the environmental temperature is low, the temperature of the recording sheet is also low, so that the heat of the pressure roller is deprived more than at normal temperature. Between the sheets, the pressure roller directly contacts the fixing belt, and heat is supplied from the fixing belt, whereby the heat accumulation of the pressure roller is recovered. However, as described above, when the environmental temperature is low, more heat is taken from the pressure roller than at normal temperature, so recovery is not in time between the same paper as normal temperature, and the heat storage amount of the pressure roller is reduced. As a result, the amount of thermal expansion decreases. Eventually, the thermal expansion of the pressure roller cannot be maintained, the width of the boundary region N2s exceeds 2.8 mm, and uneven glossiness may occur in a certain number of images in continuous paper feeding. There is.

  Therefore, when the environmental temperature is low, the space between the papers entering the fixing nip N1 during continuous paper feeding may be wider than that between normal temperatures. As an example, the gap between papers when the environmental temperature is low is widened by 10% compared to the gap between papers at normal temperature. Thereby, even if the environmental temperature is low and the temperature of the recording sheet is low and the heat of the pressure roller taken away by the recording sheet is higher than that at normal temperature, the heat storage amount of the pressure roller can be recovered between the sheets. As a result, even if the ambient temperature is low and continuous paper feeding is performed, the thermal expansion of the pressure roller can be maintained, and the occurrence of uneven gloss can be suppressed.

[Embodiment 2]
Next, Embodiment 2 will be described.

  In an environment where an image forming apparatus such as a printer is installed, the input power input to the image forming apparatus may be lower than a prescribed power. For example, when the image forming apparatus is used in a country where power supply is unstable, such as when the infrastructure is not sufficiently developed, the input power input to the image forming apparatus may be lower than the prescribed power. . In addition, when the image forming apparatus is disposed at a location away from the power source, a wire for inputting power from the power source to the image forming apparatus becomes long, and there is a case where the prescribed power is not input due to a voltage drop.

  In the image forming apparatus of the present embodiment, when specified power is not input, the power supplied to each electrical device in the image forming apparatus is limited based on the input power input to the image forming apparatus. Accordingly, it is possible to prevent each electric device in the image forming apparatus from functioning and perform an image forming operation. In particular, in a large-sized image forming apparatus provided with a large number of electrical devices in the apparatus, the power supplied to the heat source 44 of the fixing apparatus may be limited by 30% at the maximum. When the power supplied to the heat source 44 is limited, the fixing failure is suppressed by reducing the recording sheet conveyance speed. In addition, the amount of adhesion per unit area of the toner image may be reduced, and the amount of heat necessary for fixing the toner image may be reduced to suppress the occurrence of fixing failure.

  As described above, when the prescribed power is not input to the image forming apparatus, the power supplied to the heat source 44 is limited based on the input power to the image forming apparatus, and the heat generation amount of the heat source 44 is reduced. As a result, there is a possibility that the pressure roller cannot be sufficiently thermally expanded within the preheating operation time. Therefore, in the second embodiment, the preheating operation condition is changed according to the power supplied to the heat source 44 of the fixing device. The preheating operation conditions to be changed according to the supplied power include the lighting rate of the heat source 44, the preheating operation time, the rotation speed of the pressure roller, the pressure contact position of the pressure roller 45 with the fixing belt 43, and the like. be able to. When the preheating operation is finished when the pressure roller reaches the target temperature, the preheating operation condition changed according to the supplied power may be set as the target temperature of the pressure roller. One of the plurality of operating conditions listed above may be changed based on the supplied power, or a plurality of these operating conditions may be changed based on the supplied power.

FIG. 20 is a block diagram illustrating an example of a control system according to the second embodiment.
As shown in FIG. 20, the power detection unit 81 is connected to the control unit 202.
The power detection unit 81 detects power information input to the image forming apparatus, and is provided in a power supply control circuit for supplying power to each electrical device in the image forming apparatus. As the power information, a voltage input to the image forming apparatus, a current input to the image forming apparatus, and the like can be raised. In the present embodiment, the power supply control circuit supplies an AC power supply board that controls an AC voltage supplied to an electric device driven by an AC voltage, such as a heat source 44, and an electric device driven by a DC voltage such as a fan or a motor. And a DC power supply board for controlling the DC voltage. In the present embodiment, a power detector 81 is disposed on the AC power supply board. The AC power supply board controls the power supplied to the heat source 44 based on the power information detected by the power detection unit 81. Specifically, when the input power input to the image forming apparatus is lower than the rating, the power supplied to the heat source 44 is limited based on the input power.

  Based on the power supplied to the heat source 44, the control unit 202 controls the lighting rate of the heat source 44, the pressure depressurization mechanism 201, the belt driving unit 203 that rotationally drives the fixing belt, and the like, and the operation of the preheating operation. Change the condition. Hereinafter, the operation conditions to be changed based on the supplied power will be described as Example A to Example E.

[Example A]
Example A is an example in which the operating condition to be changed according to the supplied power is the lighting rate of the heat source 44 composed of a heater such as a halogen heater. Table 13 below shows an example of the lighting rate of the heat source 44 during the pre-heating operation for each supply power. Table 13 below shows the ratio of the supplied power to the supplied power when the rated power is input to the image forming apparatus. The supplied power “70%” is limited to the supplied power to the heat source 44 by 30%. ing. Table 13 below is an example, and may be set as appropriate depending on the configuration of the apparatus.

  As the power supplied to the heat source 44 is limited, the output of the heat source 44 decreases and the amount of heat generated by the heat source 44 decreases. As a result, as the power supply is limited, heat cannot be sufficiently supplied to the pressure roller 45 within the preheating time, and the pressure roller 45 cannot be sufficiently expanded. Therefore, as shown in Table 13, the lighting rate, which is the time ratio of applying power to the heat source 44, is increased in accordance with the decrease in the supplied power. Thereby, the fall of the emitted-heat amount of the heat source by the fall of supplied electric power can be suppressed. As a result, even when the supplied power is reduced, the pressure roller can be sufficiently thermally expanded within the preheating operation time, and the boundary region N2s can be 2.8 mm or less. As a result, the occurrence of uneven gloss can be suppressed.

[Example B]
In Example B, the operating condition of the preheating operation changed according to the supplied power is set as the preheating operation time. Table 14 below shows an example of the preheating operation time for each supply power. Table 14 below is an example and may be set as appropriate depending on the configuration of the apparatus.

  Even if the power supply is reduced and the amount of heat generated by the heat source 44 is reduced, the pressure roller 45 can sufficiently store heat by increasing the preheating operation time. It can be thermally expanded. Thereby, even when the supplied power is reduced, the boundary region N2s can be 2.8 mm or less, and the occurrence of uneven gloss can be suppressed.

[Example C]
In Example C, the operating condition of the preheating operation that is changed according to the supplied power is the rotational speed of the pressure roller 45. Table 15 below shows an example of the rotation speed of the pressure roller during the preheating operation for each supply power. Table 15 below is also an example and may be set as appropriate depending on the configuration of the apparatus.

  As shown in Table 15, the lower the supply power, the faster the rotation speed of the pressure roller. Since the pressure roller 45 is driven to rotate with respect to the fixing belt 43, in order to increase the rotation speed of the pressure roller 45, the rotation speed of the fixing belt 43 is increased. By increasing the rotation speed of the pressure roller 45, the heat transfer efficiency from the fixing belt 43 to the pressure roller 45 can be increased. Thereby, even if the calorific value of the heat source 44 is reduced due to a decrease in the supplied power, the pressure transfer roller can be sufficiently thermally expanded within the preheating operation time by increasing the heat transfer efficiency. Thereby, the boundary region N2s can be made 2.8 mm or less, and the occurrence of uneven gloss can be suppressed.

[Example D]
In Example D, the operating condition of the preheating operation that is changed according to the supplied power is set to the pressure contact position of the pressure roller 45 with the fixing belt 43. Table 15 below shows an example of a pressure contact position of the pressure roller 45 with the fixing belt 43 at each supply power. Table 15 below is also an example and may be set as appropriate depending on the configuration of the apparatus.

  In the second embodiment, the pressure contact position of the pressure roller 45 with the fixing belt 43 can be adjusted in four stages. As shown in Table 15, when the supplied power is less than 100%, the pressure contact position of the pressure roller 45 during the preheating operation is set to “4”, and the pressure applied to the fixing belt 43 is the highest. To position. As a result, the width of the fixing nip N1 is widened, the area for transferring heat from the fixing belt 43 to the pressure roller 45 is increased, and the heat transfer efficiency can be increased. As a result, even if the heat generation amount of the heat source decreases due to a decrease in supply power, the pressure roller 45 can be sufficiently thermally expanded within the preheating operation time.

[Example E]
In Example E, a temperature sensor that detects the temperature of the pressure roller 45 is provided, and in the preheating operation that ends when the temperature of the pressure roller 45 reaches the target temperature, the preheating operation condition is changed according to the supplied power. The target temperature of the pressure roller 45 is changed. Table 17 below shows an example of the target temperature of the pressure roller 45 at each supply voltage.

As described above, after the preheating operation is completed, the pressure roller is once separated from the fixing belt 43, and the pressure roller is brought into contact with the fixing belt again before the recording sheet reaches the fixing nip.
As shown in FIGS. 16 and 17, the heat is supplied from the fixing belt 43 until the recording sheet reaches the fixing nip N1 after the pressure roller is brought into contact with the fixing belt again. The pressure roller is further heated, and the temperature of the heating roller rises. Due to this heating, heat is further stored in the pressure roller. When there is no decrease in the power supply, even when the recording sheet passes through the fixing nip, even if the heat of the pressure roller 45 is taken away by the recording sheet, the specified thermal expansion amount is maintained, and the boundary region N2s It does not exceed 2.8 mm. However, in a state where the supplied power is reduced and the heat generation amount of the heat source 44 is reduced, the pressure is applied after the pressure roller is brought into contact with the fixing belt again until the recording sheet reaches the fixing nip N1. The amount of heat supplied to the pressure roller 45 decreases. As a result, heat is not sufficiently stored in the pressure roller in the meantime, and if the heat of the pressure roller 45 is taken away by the recording sheet passing through the fixing nip, the amount of thermal expansion of the pressure roller cannot be maintained, There is a possibility that the boundary region N2s exceeds 2.8 mm. As a result, gloss unevenness may occur.

  Therefore, in Example E, as shown in Table 17, the target temperature of the pressure roller 45 is increased according to the amount of decrease in the supplied power. As a result, in the preheating operation, the amount of heat supplied to the pressure roller 45 is reduced after the pressure roller due to a decrease in power supply is brought into contact with the fixing belt again until the recording sheet reaches the fixing nip N1. Can be supplemented. As a result, even when the supplied power is reduced, the prescribed thermal expansion amount can be maintained in the fixing operation, and the boundary region N2s can be prevented from exceeding 2.8 mm. As a result, occurrence of uneven gloss can be suppressed.

  Also in the second embodiment, when the temperature of the pressure roller 45 is high before the preheating operation, it is not a preheating operation corresponding to supply power in which the preheating operation condition is changed based on the supply power described above, A normal preheating operation may be performed. Table 18 below is an example showing whether or not the preheating operation corresponding to the supply power at the temperature of the pressure roller 45 can be performed.

  The control unit 202 measures the temperature of the pressure roller 45 before the preheating operation. When the temperature of the pressure roller 45 is 120 ° C. or higher, the heat storage of the pressure roller is sufficient, and even if the amount of heat supplied to the pressure roller 45 decreases due to a decrease in supply power, a normal preheating operation is performed. It can be sufficiently thermally expanded. Therefore, when the temperature of the pressure roller 45 is 120 ° C. or higher, the normal preheating operation shown in FIGS. 16 and 17 is executed.

  On the other hand, when the temperature of the pressure roller 45 is 119 ° C. or less, the pressure roller may not be sufficiently thermally expanded in a normal preheating operation. Therefore, when the temperature of the pressure roller 45 is 119 ° C. or lower, the preheating operation corresponding to the supply voltage for changing the preheating operation condition based on the above-described supply power is executed. Even when the supply voltage decreases, the pressure roller can be sufficiently thermally expanded, and the width of the boundary region N2s can be reduced to 2.8 mm or less.

  Further, the interval between continuous sheets may be changed based on the supplied power. As described above, when the recording sheet passes through the fixing nip N1, the heat of the pressure roller is taken away by the recording medium, and the heat storage amount of the pressure roller is reduced. This reduced amount of stored heat is recovered by supplying heat from the fixing belt to the pressure roller between the sheets where the pressure roller is in direct contact with the fixing belt. However, if the amount of heat generated by the heat source decreases due to a decrease in the power supply, the amount of heat supplied from the fixing belt to the pressure roller between the sheets decreases, and the amount of heat stored in the pressure roller 45 cannot be sufficiently recovered. As a result, in continuous paper passing, the amount of thermal expansion of the pressure roller gradually decreases, and finally the width of the boundary region N2s exceeds 2.8 mm, which may cause uneven gloss. Therefore, when the supply power is limited and the supply power is reduced, the fixing belt can be interposed between the papers even if the supply power is reduced and the heat generation amount of the heat source 44 is reduced by widening the space between continuous papers. The amount of heat supplied to the pressure roller can be suppressed from decreasing. Thereby, the heat storage amount of the pressure roller 45 can be recovered satisfactorily, and the thermal expansion of the pressure roller can be maintained in continuous paper passing. As a result, it is possible to suppress the width of the boundary region N2s from exceeding 2.8 mm.

  Further, the operating condition of the preheating operation may be changed based on the supplied power and the environmental temperature.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
(Aspect 1)
An endless fixing belt 43 stretched between a plurality of stretching members, a nip forming member such as a fixing roller 41 that is one of the plurality of stretching members, and the nip forming member facing the nip forming member. A pressure member such as a pressure roller 45 that forms a nip via the belt 43, a heat source 44 that heats the fixing belt 43, and the heating belt downstream of the fixing belt 43 in the moving direction of the fixing belt 43. In a fixing device 40 that is disposed at a position spaced apart from the pressure member and includes a separation member such as a separation auxiliary member 48 that stretches the fixing belt 43, the fixing belt 43 is moved downstream of the nip outlet. A pressing member 49 for bringing the fixing belt 43 into contact with the pressure member; contact / separation means such as a pressure / decompression mechanism 201 for bringing the pressure member into and out of contact with the fixing belt; After the operation is completed, a control unit such as a control unit 202 that controls the pressing member to be separated from the fixing belt by the contact / separation unit, and temperature sensors 80a, 80b, and 80c that detect the ambient temperature of the fixing device. Temperature detecting means, and the control means abuts the pressure member against the fixing belt during a start-up operation for heating the fixing belt to a predetermined temperature based on a detection result of the temperature detecting means. Then, a preheating operation for heating the pressure member is performed.
In Patent Document 1, streaky wrinkles of the recording medium after passing through the fixing nip are generated when the recording medium after passing through the fixing nip is wavy, and the recording medium in which the waviness is conveyed is conveyed to a pair of paper discharge rollers. To occur. The undulation of the recording medium after passing through the fixing nip occurs until the recording medium that has exited the nip such as the fixing nip N1 moves to the separation position of the separation member. This occurs for the following reasons. That is, in the fixing device described in Patent Document 1 described above, the surface of the recording medium on which the toner image is formed is heated while being pressed against the fixing belt at the nip, whereby the toner melts and the toner image is formed on the recording medium. It is fixed. The recording medium exiting the nip is conveyed to the separation position of the separation member in a state where the toner melted at the nip adheres to the fixing belt, and is separated from the fixing belt at the separation position. When the recording medium is heated in the fixing nip, the moisture contained in the recording medium is vaporized to become water vapor. However, in the nip, since the recording medium is pressed with a high nip pressure, the water vapor is removed from the recording medium. Hard to be released. However, while the toner image on the recording medium from the nip to the separation position is conveyed while being attached to the fixing belt, no pressure is applied to the recording medium. Cheap. The water vapor is mainly released from the surface opposite to the surface on the fixing belt side of the recording medium. Further, the height is lower than the image portion on which the toner image is formed, and a gap is formed between the fixing belt and the non-image portion, and water vapor is also released into this gap. When the water vapor is released, the fibers of the recording medium are dried and the undulation is generated.
Further, the water vapor released into the gap between the fixing belt and the non-image portion remains in the gap and is again absorbed by the recording medium. The water vapor released by itself is reabsorbed, so that the recording medium is wetted and the fibers are extended, and the recording medium is wavy.
Thus, until the recording medium exiting the nip moves to the separation position, the fibers of the recording medium expand and contract due to drying due to the release of water vapor and wetting due to the reabsorption of water vapor. The undulations occur.
In contrast, in the first aspect, the recording medium that has come out of the nip is conveyed to the separation position of the separation member while being pressed by the pressure member via the fixing belt by the pressing member. As a result, even when water vapor is released from the recording medium during the movement to the separation position, the water vapor is released in a state where the recording medium is pressed by the pressure member via the fixing belt by the pressing member. become. Thereby, the fibers of the recording medium try to shrink due to the release of water vapor, but the fibers cannot be shrunk because the entire surface of the recording medium is pressed against the pressing member by the pressing force of the pressing member. As a result, the undulation of the recording medium due to the release of water vapor between the nip and the separating member is suppressed.
Further, even if reabsorption of the released water vapor occurs between the nip and the separating member, the water vapor is reabsorbed while the recording medium is pressed by the pressure member via the fixing belt by the pressing member. . As a result, even if the fibers of the recording medium are about to stretch due to the absorption of water vapor, the fibers cannot be stretched because the entire surface of the recording medium is pressed against the pressure member by the pressing force of the pressing member. As a result, the undulation of the recording medium due to the reabsorption of water vapor is also suppressed between the nip and the separating member.
Thereby, it is possible to suppress the occurrence of undulations in the recording medium between the nip and the separation position.
In the first aspect, the pressure member is separated from the fixing belt after the fixing operation is completed by providing contact / separation means such as a pressure depressurization mechanism 201 that contacts and separates the pressure member with respect to the fixing belt. be able to. Thereby, it can suppress that the wrinkle of the shape which carried out the elastic deformation at the time of the said nip formation on a pressurization member etc., and can improve durability.
In addition, the pressing member is arranged as close as possible to the nip forming member such as the fixing roller, and the fixing belt between the nip forming member and the pressing member is not pressed by the pressure member in the non-pressing area such as the boundary area N2s. The length in the sheet conveying direction needs to be a predetermined length (2.8 mm in this embodiment) or less. As described above, when the thickness exceeds 2.8 mm, water vapor or the like is generated in the non-pressing area, and the bubbles are generated by a pressing member such as the post nip portion N2 downstream of the non-pressing area in the recording medium conveyance direction. This is because moving the surface of the recording medium in such a manner that it is pushed out by the pressing force in the pressing area disturbs the toner image that is not sufficiently solidified and may cause a fixing failure such as uneven gloss. However, the temperature of the pressure member is lowered after waiting for a long time. Even if heat is applied from the fixing belt by bringing the pressure member into contact with the fixing belt at a predetermined timing from when the recording medium is fed until the recording medium reaches the nip, the pressure member Sufficient heat is not stored, and it is not sufficiently expanded. As a result, the amount of elastic deformation of the pressing member 49 is reduced, the tip of the pressing member 49 is separated from the nip N1, and the length in the sheet conveying direction of the non-pressing area may exceed a predetermined length. . As a result, gloss unevenness may occur in an image formed by the first image forming operation after waiting for a long time.
Therefore, in the aspect 1, the preheating operation is performed at the start-up operation such as the pre-sheet passing operation to heat the pressure member. Accordingly, the recording medium can be passed through in a state where the pressure member is thermally expanded. As a result, the pressing member 49 can be elastically deformed satisfactorily by the pressing member, and the length in the sheet conveying direction of the non-pressing area can be made a predetermined length or less. Therefore, it is possible to suppress the occurrence of uneven glossiness in the image formed by the first image forming operation after waiting for a long time.
In addition, when the ambient temperature of the device such as the environmental temperature is low, the heat escapes to the surroundings, so that the pressure member may not be sufficiently thermally expanded. Therefore, in the aspect 1, by performing the preheating operation based on the detection result of the temperature detection unit that detects the ambient temperature of the apparatus, the pressure member can be sufficiently thermally expanded even when the ambient temperature is low. .

(Aspect 2)
In the aspect 1, the control means such as the control unit 202 determines the amount of heat per unit time of the heat source 44 during the preheating operation based on the detection result (environment temperature) of the temperature detection means such as the temperature sensors 80a, 80b, and 80c. (In this embodiment, the amount of heat per unit time is set according to the lighting rate of the heat source 44.)
According to this, as described in the first embodiment, the pressure member such as the pressure roller can be sufficiently thermally expanded by the preheating operation regardless of the ambient temperature of the fixing device such as the environmental temperature.

(Aspect 3)
In the aspect 1 or 2, the preheating operation is an operation of raising the pressure member such as the pressure roller 45 to the target temperature, and the control unit such as the control unit 202 detects the temperature detection unit such as the temperature sensor. A target temperature is set based on the result.
According to this, as described in the embodiment, until the pressure member such as the pressure roller 45 is brought into contact with the fixing belt 43 again after the preheating operation is finished depending on the ambient temperature of the fixing device such as the environmental temperature. The amount of heat that is stored in the pressurizing member during this period is dissipated to the surroundings. Further, the temperature of a recording medium such as a recording sheet passing through a nip such as the fixing nip N1 varies depending on the ambient temperature of the fixing device, and the amount of heat transferred from the pressure member to the recording medium during passage through the nip also varies. Therefore, depending on the ambient temperature of the fixing device, the thermal expansion of the pressure member may not be sufficient, and the boundary region N2s may exceed a specified range (2.8 mm or less in this embodiment), resulting in gloss unevenness. There is.
Therefore, in aspect 3, the amount of heat stored in the pressure member is changed according to the ambient temperature of the fixing device by setting the target temperature based on the detection result of the temperature detection means such as the temperature sensor. As a result, the amount of heat radiated between the end of the preheating operation and the time when the pressure member such as the pressure roller 45 is brought into contact with the fixing belt 43 again, and the amount of heat taken by the recording medium passing through the nip are taken into account. Thus, the pressure member can be heated by the preheating operation. Accordingly, the thermal expansion of the pressure member can be maintained regardless of the ambient temperature of the fixing device, and the boundary region N2s is prevented from exceeding a specified range (2.8 mm or less in the present embodiment). be able to.

(Aspect 4)
In the aspect 1 or 2, the control unit such as the control unit 202 sets the operation time of the preheating operation based on the detection result of the temperature detection unit such as the temperature sensors 80a, 80b, and 80c.
According to this, as described in the second embodiment, the amount of heat stored in the pressure member such as the pressure roller 45 varies depending on the operation time of the preheating operation. Therefore, by setting the operation time of the preheating operation based on the ambient temperature of the fixing device such as the environmental temperature detected by the temperature detection means, the amount of heat corresponding to the ambient temperature of the fixing device is increased by the preheating operation. It can be applied to the member. Accordingly, the pressure member such as the pressure roller 45 can be sufficiently thermally expanded by the preheating operation regardless of the ambient temperature of the fixing device.

(Aspect 5)
In any one of the first to fourth aspects, the control unit such as the control unit 202 is a pressure member such as the pressure roller 45 during the preheating operation based on the detection result of the temperature detection unit such as the temperature sensors 80a, 80b, and 80c. Set the rotation speed.
According to this, as described in the third embodiment, if the rotation speed of the pressure member such as the pressure roller 45 is high, a portion on the surface of the pressure member transfers heat from the fixing belt to the pressure member. The time spent in the nip such as the fixing nip N1 is shortened. As a result, the temperature-increased portion where the heat is transferred from the fixing belt quickly passes through the nip, and the portion where the pressure member has a low temperature quickly moves to the nip. Therefore, as the rotation speed of the pressure member of the pressure roller increases, the heat transfer efficiency from the fixing belt to the pressure member increases, and the pressure member can be heated quickly. Therefore, the amount of heat applied to the pressure member by the preheating operation varies depending on the rotation speed of the pressure member. Therefore, by setting the rotation speed of the pressure member based on the ambient temperature of the fixing device detected by the temperature detecting means, a heat amount corresponding to the ambient temperature of the fixing device is applied to the pressure member by the preheating operation. be able to. Accordingly, the pressure member such as the pressure roller 45 can be sufficiently thermally expanded by the preheating operation regardless of the ambient temperature of the fixing device.

(Aspect 6)
In any one of the first to fifth aspects, the control unit such as the control unit 202 is a pressure member such as the pressure roller 45 during the preheating operation based on the detection result of the temperature detection unit such as the temperature sensors 80a, 80b, and 80c. The pressure position to the fixing belt 43 is set.
According to this, as described in the fourth embodiment, the width of the nip such as the fixing nip N1 (the length in the conveyance direction of the recording sheet) depends on the pressing position of the pressure member such as the pressure roller 45 to the fixing belt 43. Is changed. As the nip width increases, the area where heat is transferred from the fixing belt to the pressure member increases, and heat transfer efficiency can be increased. Accordingly, the amount of heat applied to the pressure member by the pre-heating operation differs depending on the position where the pressure member is applied to the fixing belt 43. Therefore, by setting the pressure position based on the ambient temperature of the fixing device detected by the temperature detection means, the amount of heat corresponding to the ambient temperature of the fixing device can be applied to the pressure member by the preheating operation. it can. Accordingly, the pressure member such as the pressure roller 45 can be sufficiently thermally expanded by the preheating operation regardless of the ambient temperature of the fixing device.

(Aspect 7)
In the fixing device according to any one of the first to sixth aspects, the control unit such as the control unit 202 sets the temperature of the fixing belt during standby based on the detection result of the temperature detection unit such as the temperature sensors 80a, 80b, and 80c. To do.
According to this, as described in the embodiment, the higher the temperature of the fixing belt during standby, such as the standby temperature t1, the higher the temperature of the fixing belt when starting the preheating operation, and the temperature during the preheating operation increases. The amount of heat applied to the pressure member increases. Accordingly, the amount of heat applied to the pressure member by the preheating operation differs depending on the temperature of the fixing belt during standby. Therefore, by setting the temperature of the fixing belt during standby based on the ambient temperature of the fixing device detected by the temperature detecting means, a heat amount corresponding to the ambient temperature of the fixing device is applied to the pressure member by the preheating operation. can do. Accordingly, the pressure member such as the pressure roller 45 can be sufficiently thermally expanded by the preheating operation regardless of the ambient temperature of the fixing device.

(Aspect 8)
In any one of the first to seventh aspects, the control unit such as the control unit 202 heats the pressure member at a predetermined timing during standby based on the detection result of the temperature detection unit such as the temperature sensors 80a, 80b, and 80c. Decide whether to perform the heating operation during standby.
As described in the embodiment, the lower the temperature of the pressure member such as the pressure roller 45, the greater the amount of heat required to sufficiently expand the pressure member, which is applied to the pressure member by the preheating operation. With the amount of heat, the pressure member may not be sufficiently thermally expanded. The lower the temperature around the fixing device such as the environmental temperature, the more heat escapes from the pressure roller to the surroundings during standby, and the temperature of the pressure member decreases. As described above, the temperature drop of the pressure member in the predetermined period during standby differs depending on the ambient temperature of the fixing device, and as a result, the pressure member may not be sufficiently thermally expanded by the preheating operation. There is. Therefore, in aspect 8, it is determined whether or not to perform the standby heating operation for heating the pressure member at a predetermined timing during standby based on the ambient temperature of the fixing device. Thereby, it can suppress that the temperature of a pressurization member falls at the time of preheating operation, and can fully expand a pressurization member by preheating motion.

(Aspect 9)
In any one of the first to eighth aspects, the control unit such as the control unit 202 may be a recording sheet that passes through a nip such as the fixing nip N1 based on the detection result of the temperature detection unit such as the temperature sensors 80a, 80b, and 80c. Set the paper spacing of the recording medium.
As described in the embodiment, the temperature of the recording medium such as the recording sheet conveyed to the nip varies depending on the ambient temperature of the fixing device such as the environmental temperature. As described above, the amount of heat of the pressure member taken by the recording medium varies depending on the temperature of the recording medium passing through the nip. Between the sheets, the pressure member directly contacts the fixing belt, and heat is supplied from the fixing belt to recover the amount of heat taken away by the recording medium, but the amount of heat taken away from the pressure member by the recording medium is low. If the amount is too large, the amount of heat is not recovered between the papers, the thermal expansion of the pressure member cannot be maintained, and the boundary region N2s may spread beyond the specified range.
In the ninth aspect, the amount of heat taken by the recording medium can be recovered between the sheets by setting the sheet interval of the recording medium based on the ambient temperature of the fixing temperature. Thereby, the thermal expansion of the pressurizing member can be maintained, and the boundary region N2s can be suppressed from spreading beyond the regulation.

(Aspect 10)
In any one of the first to ninth aspects, the control unit such as the control unit 202 determines the heat storage amount of the pressure member such as the pressure roller 45 (in this embodiment, the heat storage amount of the pressure member from the temperature of the pressure roller 45). Or the preheating operation based on the detection result of the temperature detection means or the preheating operation not based on the detection result of the temperature detection means is selected.
According to this, as described in the embodiment, the heat storage amount of the pressure member such as the pressure roller 45 is insufficient, and the amount of thermal expansion of the pressure member due to the preheating operation is around the fixing device such as the environmental temperature. When there is a risk of being influenced by the temperature, a preheating operation based on the detection result of the temperature detection means can be performed.

(Aspect 11)
An endless fixing belt 43 stretched between a plurality of stretching members, a nip forming member such as a fixing roller 41 that is one of the plurality of stretching members, and the nip forming member facing the nip forming member. A pressure member such as a pressure roller 45 that forms a nip via the belt 43, a heat source 44 that heats the fixing belt 43, and the heating belt downstream of the fixing belt 43 in the moving direction of the fixing belt 43. In a fixing device 40 that is disposed at a position spaced apart from the pressure member and includes a separation member such as a separation auxiliary member 48 that stretches the fixing belt 43, the fixing belt 43 is moved downstream of the nip outlet. A pressing member 49 for bringing the fixing belt 43 into contact with the pressure member; contact / separation means such as a pressure / decompression mechanism 201 for bringing the pressure member into and out of contact with the fixing belt; And a control unit such as a control unit 202 for controlling the pressing member to be separated from the fixing belt by the contact / separation unit after the operation is completed, and the control unit includes power information supplied to the fixing device. Based on this, during the start-up operation for heating the fixing belt to a predetermined temperature, the pressure member is brought into contact with the fixing belt, and a pre-heating operation for heating the pressure member for a predetermined time is performed.
In Patent Document 1, streaky wrinkles of the recording medium after passing through the fixing nip are generated when the recording medium after passing through the fixing nip is wavy, and the recording medium in which the waviness is conveyed is conveyed to a pair of paper discharge rollers. To occur. The undulation of the recording medium after passing through the fixing nip occurs until the recording medium that has exited the nip such as the fixing nip N1 moves to the separation position of the separation member. This occurs for the following reasons. That is, in the fixing device described in Patent Document 1 described above, the surface of the recording medium on which the toner image is formed is heated while being pressed against the fixing belt at the nip, whereby the toner melts and the toner image is formed on the recording medium. It is fixed. The recording medium exiting the nip is conveyed to the separation position of the separation member in a state where the toner melted at the nip adheres to the fixing belt, and is separated from the fixing belt at the separation position. When the recording medium is heated in the fixing nip, the moisture contained in the recording medium is vaporized to become water vapor. However, in the nip, since the recording medium is pressed with a high nip pressure, the water vapor is removed from the recording medium. Hard to be released. However, while the toner image on the recording medium from the nip to the separation position is conveyed while being attached to the fixing belt, no pressure is applied to the recording medium. Cheap. The water vapor is mainly released from the surface opposite to the surface on the fixing belt side of the recording medium. Further, the height is lower than the image portion on which the toner image is formed, and a gap is formed between the fixing belt and the non-image portion, and water vapor is also released into this gap. When the water vapor is released, the fibers of the recording medium are dried and the undulation is generated.
Further, the water vapor released into the gap between the fixing belt and the non-image portion remains in the gap and is again absorbed by the recording medium. The water vapor released by itself is reabsorbed, so that the recording medium is wetted and the fibers are extended, and the recording medium is wavy.
Thus, until the recording medium exiting the nip moves to the separation position, the fibers of the recording medium expand and contract due to drying due to the release of water vapor and wetting due to the reabsorption of water vapor. The undulations occur.
On the other hand, in aspect 11, the fixing belt is moved so that the recording medium that has come out of the nip is conveyed in a state of being sandwiched between the fixing belt and the pressure member, or in a state where there is almost no gap between the pressure member and the pressure member. By pressing with the pressing member, the following advantages are obtained. That is, while the recording medium moves to the separation position, if the recording medium undulates by drying due to the release of water vapor from the recording medium, the recording medium hits the fixing belt or the pressure member and the undulation is inhibited. As a result, the undulation of the recording medium due to the release of water vapor between the nip and the separating member is suppressed.
Further, even when the released water vapor is reabsorbed between the nip and the separating member to cause the recording medium to undulate, the waving is inhibited by the fixing belt and the pressure member. As a result, the undulation of the recording medium due to the reabsorption of water vapor is also suppressed between the nip and the separating member.
In this way, by suppressing the undulation of the recording medium after passing through the nip, the recording medium in which the undulation has occurred can be suppressed from being conveyed by the discharge roller pair, and the recording medium after passing through the fixing nip. It is possible to suppress the generation of streak-like wrinkles.
Further, in the aspect 11, by providing contact / separation means such as a pressure depressurization mechanism 201 that contacts and separates the pressure member with respect to the fixing belt, the pressure member is separated from the fixing belt after completion of the fixing operation. be able to. Thereby, it can suppress that the wrinkle of the shape which carried out the elastic deformation at the time of the said nip formation on a pressurization member etc., and can improve durability.
In addition, the pressing member is arranged as close as possible to the nip forming member such as the fixing roller, and the fixing belt between the nip forming member and the pressing member is not pressed by the pressure member in the non-pressing area such as the boundary area N2s. The length in the sheet conveying direction needs to be a predetermined length (2.8 mm in this embodiment) or less. As described above, when the thickness exceeds 2.8 mm, water vapor or the like is generated in the non-pressing area, and the bubbles are pressed in the pressing area by the pressing member downstream in the recording medium transport direction from the non-pressing area. This is because by moving the surface of the recording medium in such a manner that it is pushed out by pressure, a toner image that is not sufficiently solidified may be disturbed and fixing defects such as uneven gloss may occur. However, the temperature of the pressure member is lowered after waiting for a long time. Even if heat is applied from the fixing belt by bringing the pressure member into contact with the fixing belt at a predetermined timing from when the recording medium is fed until the recording medium reaches the nip, the pressure member Sufficient heat is not stored, and it is not sufficiently expanded. As a result, the amount of elastic deformation of the pressing member 49 is reduced, the tip of the pressing member 49 is separated from the nip N1, and the length in the sheet conveying direction of the non-pressing area may exceed a predetermined length. . As a result, gloss unevenness may occur in an image formed by the first image forming operation after waiting for a long time.
Therefore, also in the aspect 11, the preheating operation is performed at the start-up operation such as the pre-sheet passing operation to heat the pressure member. Thereby, the recording medium can be passed through in a state where the pressure member is sufficiently thermally expanded. As a result, the pressing member 49 can be elastically deformed satisfactorily by the pressing member, and the length in the sheet conveying direction of the non-pressing area can be made a predetermined length or less. Therefore, it is possible to suppress the occurrence of uneven glossiness in the image formed by the first image forming operation after waiting for a long time.
Further, the power supplied to the heat source 44 of the fixing device fluctuates due to fluctuations in the power input to an apparatus such as an image forming apparatus in which the fixing device is mounted, and the amount of heat generated by the heat source 44 fluctuates. As the amount of heat generated by the heat source 44 varies, the amount of heat supplied to the pressure member in the preheating operation varies. Therefore, in the aspect 11, by performing the preheating operation based on the power information supplied to the fixing device, it is possible to apply a specified amount of heat to the pressure member, and sufficiently expand the pressure member. be able to.

(Aspect 12)
In the aspect 11, the control means such as the control unit 202 sets the operation time of the heat source 44 during the preheating operation based on the power information (in this embodiment, the operation time is set by the lighting rate of the heat source 44. ing).
According to this, as described in the embodiment A, even if there is a fluctuation in the power supplied to an apparatus such as an image forming apparatus, a predetermined amount of heat can be applied to the pressure member by the preheating operation. The pressure member can be sufficiently thermally expanded.

(Aspect 13)
In the aspect 11 or 12, the preheating operation is an operation of raising a pressure member such as a pressure roller to a target temperature, and a control unit such as a control unit 202 is configured to control the target based on the power information. Set the temperature.
According to this, as described in Example E, after the preheating operation is finished, the pressure member is once separated from the fixing belt 43, and the pressure member is fixed again before the recording sheet reaches the fixing nip. Make contact with the belt. Heat is supplied from the fixing belt 43 until the recording medium such as a recording sheet reaches the fixing nip N1 after the pressure member is brought into contact with the fixing belt again, and heat is stored in the pressure member. The amount of heat stored in the pressurizing member fluctuates due to fluctuations in the power supplied to the heat source. As a result, when the recording medium passes through a nip such as the fixing nip N1, the heat of the pressure member is taken by the recording sheet, and the prescribed heat storage amount cannot be maintained, and the thermal expansion of the pressure member cannot be maintained. There is a fear.
Thus, by setting the target temperature based on the power information, the amount of heat stored in the pressure member is changed according to the power information. As a result, the amount of heat supplied to the pressure roller, which fluctuates depending on the power supplied to the fixing device, between the end of the preheating operation and the time when the pressure member such as the pressure roller 45 is brought into contact with the fixing belt 43 again. In consideration of the above, the amount of heat applied to the pressure member can be set by the preheating operation. Thereby, the thermal expansion of the pressure member can be maintained, and the boundary region N2s can be prevented from exceeding a specified range (2.8 mm or less in the present embodiment).

(Aspect 14)
In the aspect 11 or 12, control means, such as the control part 202, sets the operation time of the preheating operation based on the power information.
According to this, as described in Example B, even if the heat generation amount of the heat source fluctuates due to fluctuations in the supply power supplied to the apparatus, a prescribed amount of heat is applied to the pressure member by the preheating operation. And the pressure member can be sufficiently thermally expanded.

(Aspect 15)
In any of the aspects 11 to 14, the control means such as the control unit 202 sets the rotation speed of the pressure member such as the pressure roller 45 during the preheating operation based on the power information.
According to this, as described in the embodiment C, if the rotation speed of the pressure member such as the pressure roller 45 is high, a portion on the surface of the pressure member transfers heat from the fixing belt to the pressure member. The time spent in the nip such as the fixing nip N1 is shortened. As a result, the temperature-increased portion where the heat is transferred from the fixing belt quickly passes through the nip, and the portion where the pressure member has a low temperature quickly moves to the nip. Therefore, the heat transfer efficiency from the fixing belt 43 to the pressure member can be increased as the rotation speed of the pressure member increases. Therefore, by setting the rotation speed of the pressure member based on the power information, even if the heat generation amount of the heat source 44 decreases due to a decrease in the supplied power, the heat transfer efficiency to the pressure member correspondingly decreases. It is possible to increase the pressure, and a predetermined amount of heat can be applied to the pressure member. Thereby, a pressurization member can fully be thermally expanded.

(Aspect 16)
In any one of the aspects 11 to 15, the control unit such as the control unit 202 sets the pressure position of the pressure member such as the pressure roller during the preheating operation to the fixing belt based on the power information.
According to this, as described in the embodiment D, the width of the nip such as the fixing nip N1 (the length in the conveyance direction of the recording sheet) depends on the pressing position of the pressure member such as the pressure roller 45 to the fixing belt 43. Is changed. As the nip width increases, the area where heat is transferred from the fixing belt to the pressure member increases, and heat transfer efficiency can be increased. Therefore, by setting the pressurization position based on the power information, even if the heat generation amount of the heat source 44 decreases due to fluctuations in the supplied power, the heat transfer efficiency to the pressurization member is correspondingly increased. And a prescribed amount of heat can be applied to the pressure member. As a result, the pressure member can be sufficiently thermally expanded.

(Aspect 17)
In any one of aspects 11 to 16, the control means such as the control unit 202 performs preheating based on the power information based on the heat storage amount of the pressurizing member (in the embodiment, grasped based on the temperature of the pressurizing member). Select whether to perform an operation or to perform a pre-heating operation that is not based on power information.
According to this, as described in the second embodiment, the heat storage amount of the pressure member such as the pressure roller 45 is insufficient, and the thermal expansion amount of the pressure member due to the preheating operation may be influenced by the supplied power. When there is a preheating operation based on the power information can be performed.

(Aspect 18)
A latent image carrier such as a photoreceptor 3, toner image forming means (comprising charging device 5, optical writing unit 1, developing device 4, etc.) for forming a toner image on the latent image carrier; Transfer means (consisting of a primary transfer unit and a secondary transfer unit) for transferring onto the recording medium from the latent image carrier, and a fixing means for fixing the toner image transferred onto the recording material to the recording material; The fixing device according to any one of aspects 1 to 17 is used as the fixing unit.
According to this, it is possible to suppress the generation of streak-like wrinkles on the output recording medium.

(Aspect 19)
Aspect 18 includes temperature detection means such as temperature sensors 80a, 80b, and 80c for detecting the ambient temperature of the fixing device, and is formed on a latent image carrier such as the photoreceptor 3 based on the detection result of the temperature detection means. The toner adhesion amount per unit area of the toner image to be set is set.
According to this, as described in the embodiment, the amount of heat necessary to satisfactorily fix the toner image on the recording medium such as the recording sheet is changed according to the ambient temperature of the fixing device such as the environmental temperature. Can do. As a result, when the ambient temperature of the fixing device is low and the toner temperature of the toner image is low, it is possible to reduce the amount of toner adhesion, and good fixability can be obtained even when the ambient temperature of the fixing device is low. it can.

1: Optical writing unit 2: Image forming unit 3: Photoconductor 4: Developing device 5: Charging device 10: Polishing device 11: Thermistor 20: Moving mechanism 21: Guide member 22: Connection member 23: Arm member 24: Support plate 40: fixing device 41: fixing roller 41a: cored bar part 42: heating roller 43: fixing belt 44: heat source 45: pressure roller 46: separation plate 47: tension roller 48: separation auxiliary member 49: pressing member 49a: peeling part 49b: Presser 60: Primary transfer unit 78: Secondary transfer units 80a, 80b, 80c: Temperature sensor 81: Power detection unit 201: Pressurization / decompression mechanism 201a: Pressurization arm 201b: Pressurization cam 201c: Driving means 202 : Control unit 203: Belt driving means N 1: Fixing nip N 2: Post nip portion N 2 s: Boundary area P: Recording sheet

Japanese Patent Laying-Open No. 2015-18906

Claims (19)

An endless fixing belt stretched over a plurality of stretch members;
A nip forming member that is one of the plurality of stretching members;
A pressure member that forms a nip through the fixing belt opposite the nip forming member;
A heat source for heating the fixing belt;
A fixing device including a separation member that is disposed downstream of the nip forming member in the moving direction of the fixing belt and spaced from the pressure member, and stretches the fixing belt;
A pressing member that contacts the inner peripheral surface of the fixing belt and presses the fixing belt between the outlet of the nip and the upstream end of the separation member in the fixing belt moving direction;
Contacting / separating means for contacting and separating the pressure member with respect to the fixing belt;
Control means for controlling the pressing member to be separated from the fixing belt by the contact / separation means after the fixing operation is completed;
Temperature detecting means for detecting the ambient temperature of the device,
The controller is configured to bring the pressure member into contact with the fixing belt during a start-up operation for heating the fixing belt to a predetermined temperature based on a detection result of the temperature detection unit. A fixing device that performs a preheating operation for heating. The fixing device according to claim 1,
The fixing device is characterized in that the control means sets a heat amount per unit time of the heat source during a preheating operation based on a detection result of the temperature detection means. The fixing device according to claim 1 or 2,
The preheating operation is an operation of raising the pressure member to a target temperature,
The fixing device, wherein the control unit sets the target temperature based on a detection result of the temperature detection unit. In the fixing device according to claim 1 or 2,
The fixing device, wherein the control unit sets an operation time of the preheating operation based on a detection result of the temperature detection unit. The fixing device according to claim 1,
The fixing device, wherein the control unit sets a rotation speed of the pressure member during a preheating operation based on a detection result of the temperature detection unit. The fixing device according to claim 1,
The fixing device sets the pressure position of the pressure member to the fixing belt during the preheating operation based on the detection result of the temperature detection means. The fixing device according to claim 1,
The fixing unit is characterized in that the control unit sets a fixing belt temperature during standby based on a detection result of the temperature detection unit. The fixing device according to any one of claims 1 to 7,
The fixing device determines whether or not to perform a standby heating operation for heating the pressure member at a predetermined timing during standby based on a detection result of the temperature detection unit. The fixing device according to claim 1,
The fixing device is characterized in that the control unit sets a sheet interval of a recording medium to be passed through the nip based on a detection result of the temperature detection unit. The fixing device according to any one of claims 1 to 9,
The control means selects whether to perform a preheating operation based on the detection result of the temperature detection means or a preheating operation not based on the detection result of the temperature detection means, based on the heat storage amount of the pressure member. A fixing device. An endless fixing belt stretched over a plurality of stretch members;
A nip forming member that is one of the plurality of stretching members;
A pressure member that forms a nip through the fixing belt opposite the nip forming member;
A heat source for heating the fixing belt;
A fixing device including a separation member that is disposed downstream of the nip forming member in the moving direction of the fixing belt and spaced from the pressure member, and stretches the fixing belt;
A pressing member that contacts the inner peripheral surface of the fixing belt and presses the fixing belt between the outlet of the nip and the upstream end of the separation member in the fixing belt moving direction;
Contacting / separating means for contacting and separating the pressure member with respect to the fixing belt;
Control means for controlling the pressing member to be separated from the fixing belt by the contact / separation means after completion of the fixing operation;
The control means causes the pressure member to abut on the fixing belt during a start-up operation for heating the fixing belt to a predetermined temperature based on power information supplied to the fixing device, and for a predetermined time. A fixing device that performs a preheating operation for heating a pressure member. The fixing device according to claim 11.
The fixing device, wherein the control unit sets an operation time of the heat source during a preheating operation based on the power information. The fixing device according to claim 11 or 12,
The preheating operation is an operation of raising the pressure member to a target temperature,
The fixing device, wherein the control unit sets the target temperature based on the power information. The fixing device according to claim 11 or 12,
The fixing device, wherein the control unit sets an operation time of the preheating operation based on the power information. The fixing device according to claim 11,
The fixing device, wherein the control unit sets a rotation speed of the pressure member during a preheating operation based on the power information. The fixing device according to any one of claims 11 to 15, wherein
The fixing device is configured to set a pressure position of the pressure member to the fixing belt during a preheating operation based on the power information. The fixing device according to claim 11,
The fixing device selects whether to perform a preheating operation based on the power information or a preheating operation not based on the power information, based on a heat storage amount of the pressure member. A latent image carrier;
Toner image forming means for forming a toner image on the latent image carrier;
Transfer means for transferring the toner image from the latent image carrier onto a recording medium;
A fixing unit that fixes the toner image transferred onto the recording material to the recording medium;
An image forming apparatus using the fixing device according to claim 1 as the fixing unit. The image forming apparatus according to claim 18.
Temperature detecting means for detecting the ambient temperature of the fixing device,
An image forming apparatus, wherein a toner adhesion amount per unit area of a toner image formed on the latent image carrier is set based on a detection result of the temperature detection means.

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