JP2018169467A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dissipate heat of a fixing member to an end portion of a heat transfer assisting member in contact with the fixing member, so that the temperature of the end portion of the fixing member is lowered and the fixing property of the end portion of a recording medium is deteriorated. SOLUTION: A nip portion is formed between a fixing member, a heating member for heating the fixing member, a nip member provided inside the fixing member, and a fixing member sandwiched between the nip members. A fixing device having a pressurized rotating body, the nip member includes a heat transfer assisting member that comes into contact with the inner surface of the fixing member, and a nip forming member that supports the heat transfer assisting member from the opposite side of the fixing member. The heating member has an end heating member that heats the longitudinal end region of the fixing member, and the fixing device further has an end temperature detection that detects the temperature of the fixing member heated by the end heating member. Regarding the heat capacity in the longitudinal direction of the heat transfer assisting member having the member, the first region including the longitudinal position detected by the end temperature detecting member is the second end side in the longitudinal direction with respect to the first region. Larger than the area of. [Selection diagram] Fig. 6

Description

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

  In recent years, market demands for energy saving and high speed have been increasing for image forming apparatuses such as printers, copiers, and facsimiles.

  In an image forming apparatus, an unfixed toner image is transferred to a recording material sheet, printing paper, photosensitive paper, electrostatic recording paper, etc. by an image transfer method or a direct method by an image forming process such as electrophotographic recording, electrostatic recording, and magnetic recording. Formed on recording material. As a fixing device for fixing an unfixed toner image, a contact heating method fixing device such as a heat roller method, a film heating method, and an electromagnetic induction heating method is widely used.

  As an example of such a fixing device, a belt-type fixing device (for example, Patent Document 1), a fixing device using a ceramic heater (for example, Patent Document 2), and directly heating a fixing belt with a halogen heater can save energy. A fixing device (for example, Patent Document 3) is disclosed. Further, Patent Document 3 has a nip forming member and a heat transfer assisting support member having better heat conduction than the nip forming member on the side sliding with the fixing belt, and the heat transfer assisting member equalizes heat in the longitudinal direction. Thus, it is described that the excessive temperature rise of the non-sheet passing portion that occurs when the small size paper is passed is prevented.

  However, when the heat transfer auxiliary member that slides with the fixing belt is arranged, the heat generated by the heat source is dissipated to the longitudinal end portion of the heat transfer auxiliary member, and the heat transfer auxiliary member contacts the heat transfer auxiliary member. The end temperature of the will also decrease. As a result, the fixability of the end portion of the recording medium is deteriorated.

  In order to solve the above-mentioned problem, the invention according to claim 1 is a rotating endless fixing member, a heating member for heating the fixing member, a nip member provided inside the fixing member, A fixing rotator for fixing a toner image on a recording medium at the nip portion, the pressure rotator forming a nip portion between the fixing member and the nip member. The nip member includes a heat transfer auxiliary member that contacts an inner surface of the fixing member, and a nip forming member that is supported by the heat transfer auxiliary member from the opposite side of the fixing member, and the heating member includes the fixing member. An end heating member that heats the longitudinal end region of the member, and the fixing device further includes an end temperature detection member that detects the temperature of the fixing member heated by the end heating member, In the longitudinal direction of the heat transfer assisting member. Capacity, the first region including the longitudinal position of the end portion temperature detection member is detected, a larger fixing device as compared to the second region and the a first longitudinal end side than the region of.

  According to the present invention, it is possible to provide a fixing device having good fixing properties up to the end in the width direction of the recording medium.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic cross-sectional configuration diagram illustrating a first embodiment of a fixing device. It is a control block diagram for controlling the fixing device. FIG. 3 is a schematic cross-sectional configuration diagram illustrating a second embodiment of a fixing device. FIG. 3 is a schematic perspective view showing one end portion of the fixing device. It is a disassembled perspective view which shows 1st embodiment of the nip formation member and heat transfer auxiliary member which comprise a nip member. It is the figure which expand | deployed the heat transfer auxiliary member. It is a disassembled perspective view which shows 2nd embodiment of the nip formation member and heat transfer auxiliary member which comprise a nip member. It is a schematic diagram which shows the heat generating area | region of a heating member, and the positional relationship of a sensor. It is a schematic diagram in which the heat from a heating member is transmitted to a heat transfer auxiliary member via a fixing member. 3 is a graph showing a temperature distribution in a longitudinal direction of a fixing member.

  The configuration of the image forming apparatus according to the embodiment of the present invention will be described below with reference to FIG. The image forming apparatus 100 shown in FIG. 1 is a color printer called a tandem system in which image forming units that form a plurality of color images are arranged side by side along the rotation direction of a rotating belt.

  The image forming apparatus 100 arranges photoconductor drums 20Y, 20C, 20M, and 20Bk as image carriers that can form images as images corresponding to colors separated into yellow, cyan, magenta, and black, respectively. The tandem structure is adopted.

  Although the tandem color printer has been described as an example of the image forming apparatus, the present invention is not limited to this method. It is also possible to target not only printers but also copying machines and facsimile machines.

  In the image forming apparatus 100, an intermediate transfer member (hereinafter referred to as an endless belt) in which a visible image formed on each of the photosensitive drums 20Y, 20C, 20M, and 20Bk can move in the direction of arrow A1 while facing the respective photosensitive drums. (Referred to as a transfer belt) 11. By executing the primary transfer process, images of the respective colors are superimposed and transferred, and then transferred in a batch by executing the secondary transfer process on the recording material S as a recording medium on which a recording sheet or the like is used. .

  Around each photosensitive drum, an apparatus for performing image forming processing according to the rotation of the photosensitive drum is arranged to constitute an image forming unit. The image forming unit will be described with the photosensitive drum 20Bk that performs black image formation as a representative. The charging device 30Bk that performs image forming processing along the rotation direction of the photosensitive drum 20Bk, the developing device 40Bk, the primary transfer roller 12Bk, and the cleaning. A device 50Bk is arranged. The optical writing device 8 is used for writing using the writing light Lb performed after charging.

  In the superimposing transfer on the transfer belt 11, the visible image formed on each of the photosensitive drums 20 </ b> Y, 20 </ b> C, 20 </ b> M, and 20 </ b> Bk is transferred to the same position on the transfer belt 11 while the transfer belt 11 moves in the A1 direction. Is done. For this reason, the transfer is performed in the A1 direction by applying a voltage from the primary transfer rollers 12Y, 12C, 12M, and 12Bk disposed opposite to the photosensitive drums 20Y, 20C, 20M, and 20Bk with the transfer belt 11 interposed therebetween. The timing is shifted from the upstream side toward the downstream side.

  The photosensitive drums 20Y, 20C, 20M, and 20Bk are arranged in this order from the upstream side in the A1 direction. Each of the photosensitive drums 20Y, 20C, 20M, and 20Bk is provided in an image forming unit for forming yellow, cyan, magenta, and black images.

  The image forming apparatus 100 is arranged to face four image forming units that perform image forming processing for each color and above each of the photosensitive drums 20Y, 20C, 20M, and 20Bk, and includes a transfer belt 11 and a primary transfer roller. A transfer belt unit 10 having 12Y, 12C, 12M, and 12Bk; a secondary transfer roller 5 that is disposed to face the transfer belt 11 and is driven by the transfer belt 11; A belt cleaning device 13 is provided for cleaning the transfer belt 11, and an optical writing device 8 is provided so as to face the lower side of these four image forming units.

  The optical writing device 8 is equipped with a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a folding mirror, a rotating polygon mirror as a polarizing means, and the like. The optical writing device 8 emits writing light Lb corresponding to each color to each of the photosensitive drums 20Y, 20C, 20M, and 20Bk to form an electrostatic latent image on the photosensitive drums 20Y, 20C, 20M, and 20Bk. It is configured as follows. In FIG. 1, for the sake of convenience, the writing light Lb is labeled only for the black image forming unit, but the same applies to the other image forming units.

  The image forming apparatus 100 is provided with a sheet feeding device 61 as a paper feeding cassette on which recording materials S conveyed between the secondary transfer roller 5 and the transfer belt 11 are stacked. Further, the recording material S conveyed from the sheet feeding device 61 is transferred to the transfer portion between the secondary transfer roller 5 and the transfer belt 11 at a predetermined timing in accordance with the toner image formation timing by the image forming unit. A pair of registration rollers 4 that is fed out is provided. The fact that the leading edge of the recording material S has reached the registration roller pair 4 is detected by a known sensor.

  Further, the image forming apparatus 100 includes a fixing device 200 as a roller fixing type fixing unit for fixing the toner image to the recording material S to which the toner image is transferred, and the recording material S that has been fixed. A discharge roller 7 is provided for discharging to the outside of the main body. In addition, a discharge tray 17 on which the recording material S discharged to the outside of the main body of the image forming apparatus 100 by the discharge roller pair 7 is stacked is provided at the upper part of the main body of the image forming apparatus 100. Further, toner bottles 9Y, 9C, 9M, and 9Bk filled with yellow, cyan, magenta, and black toners are provided below the paper discharge tray 17.

  The transfer belt unit 10 includes a drive roller 72 and a driven roller 73 around which the transfer belt 11 is wound, in addition to the transfer belt 11 and the primary transfer rollers 12Y, 12C, 12M, and 12Bk.

  The driven roller 73 also has a function as a tension urging unit for the transfer belt 11. For this reason, the driven roller 73 is provided with an urging unit using a spring or the like. Such a transfer belt unit 10, the primary transfer rollers 12Y, 12C, 12M, and 12Bk, the secondary transfer roller 5, and the belt cleaning device 13 constitute a transfer device 71.

  The sheet feeding device 61 is disposed at the lower part of the main body of the image forming apparatus 100, and has a feeding roller 3 that contacts the upper surface of the uppermost recording material S. The uppermost recording material S is fed toward the registration roller pair 4 by rotating the feeding roller 3 counterclockwise in the drawing.

  The belt cleaning device 13 provided in the transfer device 71 includes a cleaning brush and a cleaning blade disposed so as to face and contact the transfer belt 11. The belt cleaning device 13 cleans the transfer belt 11 by scraping and removing foreign matters such as residual toner on the transfer belt 11 with a cleaning brush and a cleaning blade.

  The belt cleaning device 13 also has discharge means for carrying out and discarding the residual toner removed from the transfer belt 11.

  FIG. 2 is a schematic configuration diagram illustrating the fixing device according to the present embodiment. The fixing device 200 includes a fixing belt 201 as an example of a rotatable fixing member, and a pressure roller 203 as an example of a pressure member that is disposed opposite to the fixing belt 201 and is rotatable. Each of the fixing belt 201 and the pressure roller 203 has a shape extending longer than the width of the recording material S in a direction perpendicular to the rotation axis, that is, in a direction perpendicular to the paper surface in FIG. 2, with the recording material S interposed therebetween. Can be transported. In addition, the fixing device 200 includes a heater 202 as an example of a heating member. The heater 202 has a central heater 202A and an end heater 202B, and each directly heats the fixing belt 201 from the inner peripheral side by radiant heat. As will be described later, each has a different heat generating region in the direction of the rotation axis of the fixing belt 201, and different regions of the fixing belt 201 are heated. As an example of the heater 202, a halogen heater is used. However, the heater 202 is not limited to this, and may be a ceramic heater that is heated by being brought into contact with the fixing member, or an IH (Induction Heating) heater that is heated from the inside of the fixing member using electromagnetic induction.

  Further, the fixing device 200 includes a temperature sensor 230 as an example of a temperature detection member in order to detect the temperature of the fixing belt 201. As an example of the temperature sensor 230, a non-contact thermopile is used, but is not limited thereto. As will be described later, the temperature sensor 230 includes a center temperature sensor 230A and an end temperature sensor 230B, which are two temperature sensors having different detection positions in the rotation axis direction of the fixing belt 201, and the outer surface temperature of the fixing belt 201 is determined. Detected. As will be described later, the control unit 18 controls the lighting rate of the heater 202 according to the temperature detected by the temperature sensor 230, and controls the temperature of the fixing belt 201 to a desired temperature.

  At this time, a nip member including a nip forming member 206 and a heat transfer auxiliary member 216 is provided inside the fixing belt 201 in FIG. The nip member forms a nip portion (N shown in FIG. 2) with the pressure roller 203 via the fixing belt 201. That is, the fixing belt 201 is sandwiched between the nip member and the pressure roller 203, and a nip portion is formed between the fixing belt 201 and the pressure roller 203. At this nip portion, the toner image on the recording material S is fixed to the recording material by applying sufficient heat and pressure for fixing. The nip forming member 206 is in contact with the heat transfer auxiliary member 216, and the surface of the heat transfer auxiliary member 216 opposite to the surface in contact with the nip forming member 206 is in contact with the inner surface of the fixing belt 201. The fixing belt 201 rotates in contact with the heat transfer auxiliary member 216 in the direction of the arrow in the figure.

  FIG. 3 is a control block diagram of the temperature control described above. The control unit 18 includes a known microcomputer having a CPU (Central Processing Unit), a ROM (Read-Only Memory), a RAM (Random Access Memory), and the like. The control unit 18 can control energization to the heater 202 based on the temperature detection result from the temperature sensor 230. That is, based on the temperature information from each of the central temperature sensor 230A and the end temperature sensor 230B, the energization control is performed on each of the central heater 202A and the end heater 202B, which are halogen heaters, through a known triac or the like. So-called feedback control is performed to adjust the rate. The control unit 18 is provided in the apparatus main body of the image forming apparatus 100 as an example, and can also control members other than the fixing device 200 in the image forming apparatus 100 and control communication between the image forming apparatus and the outside. The control unit 18 may be provided in the fixing device 200 or may be provided outside the image forming apparatus 100.

  As shown in FIG. 2, the surface on the pressure roller 203 side of the heat transfer assisting member 216 is flat. The surface may not be flat, but may be a concave shape along the outer peripheral surface of the pressure roller 203 or other shapes. When the nip portion has a concave shape, the direction in which the leading edge of the recording material S is discharged is closer to the pressure roller, so that the separability is improved and the occurrence of jam is suppressed.

  Inside the fixing belt 201, a nip forming member 206 disposed to face the pressure roller 203, a heat transfer auxiliary member 216 that covers a surface of the nip forming member 206 facing the inner surface of the fixing belt 201, and a nip forming member And a stay member 207 that holds 206 against the pressure applied by the pressure roller 203. The nip forming member 206, the heat transfer assisting member 216, and the stay member 207 all have lengths that extend in the rotation axis direction of the fixing belt 201 (hereinafter may be referred to as “longitudinal direction”). Each of the recording materials S has a length necessary for forming the nip portion in the direction in which the recording material S is conveyed at a substantially right angle with respect to the rotation axis (hereinafter sometimes referred to as “short direction”). .

  The heat transfer assisting member 216 is provided to prevent the heat of the fixing belt 201 from staying locally and to actively move the heat in the longitudinal direction to reduce the temperature non-uniformity in the longitudinal direction. For this reason, the heat transfer auxiliary member 216 is preferably a material that can transfer heat in a short time, and for example, a metal material such as copper, aluminum, or silver having high thermal conductivity is preferable. In view of cost, availability, thermal conductivity characteristics, and workability, it is most desirable to use copper.

  In the present embodiment, the surface of the heat transfer assisting member 216 that faces the inner surface of the fixing belt 201 is a surface at least part of which directly contacts the inner surface of the fixing belt 201 and serves as a nip forming surface.

  The fixing belt 201 is composed of an endless belt or a film using a metal such as nickel or SUS (stainless steel) or a resin material such as polyimide. The surface layer of the fixing belt 201 is formed of a PFA (polytetrafluoroethylene perfluoroalkyl vinyl ether copolymer) or PTFE (polytetrafluoroethylene) layer so that toner does not adhere. There may be an elastic layer formed of a silicone rubber layer or the like between the base material of the fixing belt 201 and the PFA or PTFE layer. If the elastic layer is not provided, the heat capacity is reduced and the fixability is improved. However, when the unfixed image is crushed and fixed, minute irregularities on the belt surface are transferred to the image, leaving uneven gloss on the solid portion of the image. This can cause problems. In order to improve this, it is necessary to provide an elastic layer of 100 [μm] or more. Due to the deformation of the elastic layer, minute unevenness is absorbed and uneven glossiness of the image is improved.

  The stay member 207 has an upright portion that stands on the opposite side of the nip N side. The standing portion is arranged at a position separating the central heater 202A and the end heater 202B as fixing heat sources. The fixing belt 201 is directly heated by radiant heat from the inner surface side by the central heater 202A and the end heater 202B.

  Inside the fixing belt 201, a nip forming member 206 and a stay member 207 as a supporting member for supporting the nip portion N are provided, and the bending of the nip forming member 206 that receives pressure by the pressure roller 203 is prevented. So that a uniform nip width can be obtained. The nip forming member 206 has a protrusion 206a on the stay member 207 side. The protrusions 206a are arranged in two rows in the longitudinal direction, and two end portions are shown in FIG. When the stay member 207 and the nip forming member 206 come into contact with each other, heat is accumulated and the nip forming member 206 may be deformed. In the present embodiment, since both are in contact with each other at the protrusion 206a, heat accumulation is prevented. Further, the nip forming member 206 has a boss 206b. The nip forming member 206 and the stay member 207 can determine the positions of each other through a boss hole provided in the stay member 207.

  The nip forming member 206 has a high mechanical strength and is preferably a heat resistant resin, for example, as a material having a heat resistance of 200 ° C. or higher. Examples of the heat resistant resin include polyimide (PI) resin, polyether ether ketone (PEEK) resin and the like, and those reinforced with glass fibers can be used.

  The stay member 207 is held and positioned at both ends by a flange 209 as a holding member described later. In addition, a reflective member 208 is provided between the heater 202 and the stay member 207. Thereby, useless energy consumption caused by the stay member 207 being heated by the radiant heat from the heater 202 is suppressed. Here, instead of providing the reflecting member 208, the same effect can be obtained even if the surface of the stay member 207 is heat-insulated or mirror-finished. The stay member 207 is preferably made of a material having high mechanical strength in order to support the nip forming member 206 and prevent the nip forming member 206 from bending. For example, metal materials such as stainless steel and iron are preferable, but they may be made of resin.

  The pressure roller 203 has an elastic rubber layer 204 formed around a cored bar 205. A release layer (for example, a PFA or PTFE layer) is provided on the surface of the elastic rubber 204 in order to obtain release properties. The pressure roller 203 is rotated by a driving force transmitted from a driving source such as a motor provided in the image forming apparatus via a gear. The pressure roller 203 is pressed against the fixing belt 201 by a spring or the like, and the elastic rubber layer 204 is crushed and deformed to maintain a predetermined nip width. The pressure roller 203 may be a hollow roller, and the pressure roller 203 may have a heating source such as a halogen heater. The elastic rubber layer 204 may be solid rubber, but if there is no heater inside the pressure roller 203, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is increased and heat of the fixing belt 201 is less likely to be taken away.

  The fixing belt 201 rotates along with the pressure roller 203. In the case of FIG. 2, the pressure roller 203 is rotated by a driving source, and the driving force is transmitted to the fixing belt 201 at the nip portion N, whereby the fixing belt 201 rotates. The fixing belt 201 is sandwiched and rotated at the nip portion N, and travels by being guided by flanges 209 described later at both ends other than the nip portion.

  With the above configuration, it is possible to realize a fixing device that is inexpensive and has a fast warm-up.

  Here, the axial length of the heat transfer assisting member 216 in the fixing device of FIG. 2 will be described. The length of the pressure roller 203 in the longitudinal direction is designed to be longer than the maximum sheet passing width (for example, 320 mm width) of the fixing device in consideration of the shift of the sheet setting position of the user. Further, the heat transfer auxiliary member 216 is designed to be longer in the longitudinal direction than the pressure roller 203. This is because if the heat transfer assisting member 216 is shorter than the pressure roller 203, the fixing belt 201 may be bent at the end portion in the longitudinal direction of the heat transfer assisting member 216 at the nip portion, and the fixing belt 201 may be damaged. . For this reason, the heat transfer assisting member 216 is designed to be longer than the pressure roller 203 in consideration of manufacturing tolerance of each member and providing play necessary for assembly. As a result, the heat transfer assisting member 216 is designed to be considerably longer than the maximum sheet passing width of the fixing device, and as an example, it is designed to be approximately 20 mm longer on both sides.

  FIG. 4 shows the configuration of the fixing device 200 according to the second embodiment. The same components as those in FIG. 2 are denoted by the same reference numerals. In FIG. 2, the central heater 202A and the end heater 202B are arranged at positions sandwiching the stay member 207. However, in this embodiment, both of the two heaters are in the rotation direction of the fixing belt 201 at the nip portion. Arranged upstream.

  In the configuration in which the stay member 207 is sandwiched as shown in FIG. 2, the radiant heat from the two halogen heaters is blocked by the stay member 207, so that the heat radiated from one halogen heater is the glass constituting the other halogen heater. There is little energy loss caused by being absorbed by a member such as a tube. As shown in FIG. 4, if the halogen heater is located upstream of the nip portion, energy that is dissipated while the portion heated by the halogen heater moves to the nip portion as the heat of the fixing belt 201 moves with rotation. Loss can be reduced. As described above, the fixing device can be variously modified.

  FIG. 5 is a schematic perspective view showing one end portion of the fixing device 200 in the longitudinal direction. Flange 209 is provided at both ends of fixing belt 201. FIG. 5 shows one side thereof.

  The flange 209 has a hollow shape that is open on both sides in the longitudinal direction, and integrally includes a receiving portion 209a extending in the longitudinal direction and a jaw portion 209b protruding in the radial direction from the receiving portion 209a. The receiving portion 209a is formed in a partial cylindrical shape having a notch 209c in a partial region in the circumferential direction. The nip forming member 206 and the heat transfer assisting member 216 are inserted into the space formed by the notch 209c.

  The receiving portion 209 a comes into contact with the end portion of the fixing belt 201 when the belt shift occurs in the longitudinal direction of the fixing belt 201, and restricts the movement of the fixing belt 201 in the longitudinal direction. The jaw 209 b is held on the main body side plate of the fixing device 200. Further, a ring-shaped plate made of a material having good sliding property with respect to the fixing belt 201 may be further provided between the end portion of the fixing belt 201 and the receiving portion 209a.

  FIG. 6 is an exploded perspective view showing a first embodiment of a nip forming member and a heat transfer auxiliary member constituting the nip member. Dotted lines indicate positions in the longitudinal direction (rotational axis direction) of the fixing belt 201 at which the center temperature sensor 230A and the end temperature sensor 230B detect the temperature of the surface of the fixing belt 201, respectively.

  Specifically, when the nip forming member 206 and the heat transfer assisting member 216 are assembled to the fixing device 200 and the fixing device 200 is operated, the fixing is performed with the rotation of the fixing belt 201 as shown in FIGS. The inner peripheral surface of the belt 201 comes into contact with the heat transfer auxiliary member 216. A one-dot chain line on the heat transfer auxiliary member 216 in FIG. 6 indicates that the portion corresponding to the back surface of the fixing belt 201 detected by each of the temperature sensors 230A and 230B passes through and contacts with the rotation of the fixing belt 201. The longitudinal position on the member 216 is shown.

  Here, when the center temperature sensor 230A and the end temperature sensor 230B have detection ranges of areas A and B indicated by circles in the drawing as an example, the width of the dotted line is centered on the alternate long and short dash line as the fixing belt 201 rotates. The surface of the fixing belt 201 is detected, and the back surface corresponding to the width of the fixing belt 201 comes into contact with the heat transfer assisting member 216 as the fixing belt 201 rotates. In addition, although the dashed-dotted line in a figure has shown the longitudinal direction detection position of each temperature sensor as above-mentioned, the installation position does not necessarily correspond with a dashed-dotted line. In particular, if it is a non-contact sensor, it can be installed at a position deviating from the detection position, for example, due to the layout in the apparatus.

  The heat transfer assisting member 216 has a nip forming portion 216a and a bent portion 216b, and is formed so as to cover the nip portion side of the nip forming member 206 in the longitudinal direction. The nip forming portion 216a is formed along the outer surface of the nip forming member 206 and faces the nip portion of the nip forming member 206 when viewed in a cross section perpendicular to the longitudinal direction as shown in FIGS. It is the part that touches the side. The surface of the nip forming portion 216 a opposite to the surface in contact with the nip forming member 206 is in contact with the fixing belt 201.

  The bent portion 216b is bent at a substantially right angle from the nip forming portion 216a. As the fixing belt 201 rotates, friction between the fixing belt 201 and the heat transfer assisting member 216 causes a shift in the recording material S conveyance direction between the nip forming member 206 and the heat transfer assisting member 216. Power may work. At that time, the contact between the nip forming member 206 and the bent portion 216b prevents the nip forming member 206 and the heat transfer assisting member 216 from being displaced in the recording material S transport direction, and the mutual positions are set. Can be maintained.

  The heat transfer assisting member 216 further includes a first extension 216c and a second extension 216d. The first extension portion 216c and the second extension portion 216d constitute a convex portion that protrudes in a direction perpendicular to the longitudinal direction in the central region in the longitudinal direction of the bent portion 216b. As shown in FIG. 7, the first extension 216c and the second extension 216d protrude in the short direction in the central region in the longitudinal direction of the bent portion 216b when the heat transfer assisting member 216 is deployed in a flat state. It can also be said that a convex part is constituted.

  The first extension portion 216c and the second extension portion 216d in the present embodiment have the same width in the longitudinal direction, and protrude from a region including the position in the longitudinal direction detected by the end temperature sensor 230B. The convex portion is a region including a longitudinal position detected by the end temperature sensor 230B from the center in the longitudinal direction of the heat transfer auxiliary member 216 toward the end on the side where the end temperature sensor 230B is installed. Further, the heat capacity is provided to be larger than that of the end side region. As an example, a convex portion is provided from the position (one-dot chain line) where the end temperature sensor 230B is installed to a position 10 mm away from the end. On the other hand, toward the opposite end, a region that is substantially symmetric with respect to the longitudinal center of the fixing belt 201 in the longitudinal direction of the region including the position detected by the end temperature sensor 230B is a further end portion of the region. It is wide so that the heat capacity is larger than that of the side region. As an example, the heat transfer assisting member 216 is provided with a convex portion up to a position that is substantially symmetric with respect to the longitudinal center of the heat transfer assisting member 216.

  As described above, when the nip forming member 206 is covered with the heat transfer assisting member 216 and attached to the fixing device 200, the outer peripheral length of the cross section perpendicular to the longitudinal direction of the heat transfer assisting member 216 is the first extension portion. The vicinity of the center portion is longer than the vicinity of the end portion by the sum of 216c and the second extension portion 216d. In other words, the heat transfer assisting member 216 is designed to have a shape in which the end portion in the longitudinal direction is notched in the extending direction of the extension portion so that the outer peripheral length of the vertical section in the longitudinal direction is shorter than that in other regions. ing.

  Here, in order to increase the outer peripheral length of the cross section perpendicular to the longitudinal direction, it is also possible to increase the thickness of the plate-like heat transfer auxiliary member 216. That is, in the present embodiment, since the thickness of the heat transfer auxiliary member 216 is substantially constant, if the length of the extension portion in the extension direction is increased, the outer peripheral length is increased correspondingly, and the cross-sectional area is increased. Therefore, as a result of an increase in volume per unit length in the longitudinal direction, the heat capacity is increased. Further, even if the thickness of the plate-like heat transfer auxiliary member 216 is increased, the cross-sectional area is increased. Therefore, as another embodiment, the heat capacity can be changed depending on the position in the longitudinal direction by changing the thickness of the plate-like heat transfer assisting member 216 depending on the position in the longitudinal direction.

  The first extension portion 216c is bent along the nip forming member 206 in a direction opposite to the pressure roller 203 forming the nip portion or the nip portion via the fixing belt. The second extension portion 216d is further bent inward from the first extension portion 216c and extends substantially in parallel with the surface of the nip forming member 206 forming the nip N, that is, in a substantially short direction. At this time, the second extension 216d extends to the extent that it contacts the protrusion 206a. The heat transfer auxiliary member 216 covers the nip forming member 206 by the first extension portion 216c and the second extension portion 216d, and has a shape capable of locking the back surface, in other words, the surface opposite to the surface forming the nip portion. It has become.

  FIG. 8 is an exploded perspective view showing a second embodiment of the nip forming member and the heat transfer auxiliary member constituting the nip member. The same members as those in FIG. 6 are denoted by the same reference numerals. In the present embodiment, in a state where the heat transfer auxiliary member 216 is attached to the nip forming member 206, the first extension portion 216c is within a range of 10 mm on both sides centering on the position where the end temperature sensor 230B is installed in the longitudinal direction. In addition, by providing the second extension 216d and increasing the length of the vertical cross section in the longitudinal direction of the heat transfer auxiliary member 216, the heat capacity is increased as compared with other portions. The end on the opposite side is not provided with an end sensor, but a first extension 216c and a second extension 216d are provided so as to be symmetrical in the longitudinal direction, and the end and the other portions are long. The outer peripheral length of the vertical section is different from the direction.

  Compared with the first embodiment, the center portion in the longitudinal direction of the heat transfer auxiliary member 216 is shorter than the portion where the first extension 216c and the second extension 216d are formed. By doing so, the heat capacity of the heat transfer assisting member 216 becomes smaller as the center portion is shorter, so that the heat transfer assisting member 216 is warmed up faster and the warm-up time can be shortened. Moreover, compared with 1st embodiment, the length of the 2nd extension part 216d is extended longer. Accordingly, as shown in FIG. 8, it is also possible to change the portion where 216d is extended to a configuration in which the protruding portion 206a is not provided. It is possible to extend the projection 206a so as to avoid the projection 206a while the projection 206a is provided.

  A first example of the above heat capacity comparison will be described with reference to FIG. A range of 10 mm on both sides from the position of the end temperature sensor 230B, that is, a substantially rectangular shape in the range of 20 mm in the longitudinal direction in which the extensions 216c and 216d are formed, is a first region as a longitudinal direction region including the end temperature sensor 230B. To do. If the same 20 mm range as the first region is extracted at the end in the longitudinal direction as the second region, the first region has a larger heat capacity than the second region by the extensions 216c and 216d.

  Another example of the comparison of the heat capacity using FIG. 8 will be described. A range of 5 mm on both sides from the position of the end temperature sensor 230B, that is, a range of 10 mm in the longitudinal direction is set as a first region as a longitudinal region including the end temperature sensor 230B. If the same area of 10 mm as the first region is extracted from the end in the longitudinal direction as the second region, the first region is not formed by the extension portions 216c and 216d. The heat capacity of the region is greater. The range of 10 mm as the second region can be selected continuously in the longitudinal direction within the longitudinal direction end side region from the first region, but can be extracted including the portion without the extension portions 216c and 216d. As long as the heat capacity of the first region is increased accordingly, the effect of the present embodiment can be obtained.

  In the embodiment described in FIGS. 6 and 8, the convex portion is formed over the length in the longitudinal direction so as to cover the entire longitudinal direction of the detection region B. However, the present invention is not limited to this, and a part of the detection region B is formed. It may be covered. Further, the extension portions 216c and 216d may be provided on both the upstream side and the downstream side of the nip portion, or only one side may be provided.

  Further, the length of the extension of the heat transfer auxiliary member 216 around the end temperature sensor 230B is changed as compared with the end of the heat transfer auxiliary member 216, but the thickness of the heat transfer auxiliary member 216 is partially reduced as described above. It is possible to change the heat capacity according to the position in the longitudinal direction by changing the position or by partially providing holes. That is, a hole is provided only at the end of the heat transfer assisting member 216, or a hole is provided at both the end and the periphery of the end temperature sensor 230B. The density and size of the hole are larger at the end. To.

  Further, another member can be attached to the region where the heat capacity is desired to be increased in the longitudinal direction, that is, the peripheral region of the end temperature sensor 230B here, and the heat capacity can be increased accordingly. With this method of pasting another member, there is a possibility that the heat transfer speed will change depending on the contact state of the surfaces of each other, but the method of changing the thickness and length with the same member can expect stable heat transfer, and processing Due to accuracy, assembly accuracy, etc., there is little variation in image quality for each fixing device.

  The effect of the nip member shown as an example in each of FIGS. 6 and 8 will be described with reference to FIGS. 9, 10, and 11.

  FIG. 9 is a schematic diagram showing the positional relationship between the heat generation region of the heating member and the temperature sensor. Central part heating member, central part heater 202A as an example of an end part heating member, end part heater 202B, central part temperature detection member, central part temperature sensor 203A as an example of an end part temperature detection member, and end part temperature sensor 203B The positional relationship is shown. The longitudinal direction of the fixing belt 201 is the left-right direction in FIG. 9, and each heater 202A, 202B has a shape extending in the longitudinal direction of the fixing belt 201. The heat generation area of each of the heaters 202A and 202B is indicated by a wavy portion in the figure. The wavy portion represents a state in which a filament that generates heat when energized is wound more densely than other portions. The densely wound portion has a larger amount of heat generation than the other portions, and that portion functions as a heat generation region. A halogen heater is used as a heating member in which the filament wound in a dense manner is enclosed with a halogen gas in a cylindrical transparent glass tube. Note that the fixing belt 201 is not shown for easy understanding of the positional relationship between each heater and each temperature sensor.

  A central heater 202A and an end heater 202B as examples of the central heating member and the end heating member will be described. The central heater 202A generates heat in a paper size and an area corresponding to an A4T (A4 length) width of 210 mm. The end heater 202B is designed to generate heat in an area corresponding to a paper size and an A3 width of 320 mm by adding to the heat generating area of 202A. By heating with the center heater 202A and the end heater 202B, a heating region corresponding to the A3 nobi width which is the maximum sheet passing width is obtained. The central heater 202 </ b> A has a heat generation area in the central portion, and is provided in the fixing device 200 so as to heat the central portion in the longitudinal direction of the fixing belt 201. On the other hand, the end heater 202 </ b> B has heat generation regions at both ends, and is provided in the fixing device 200 so that the heat generation regions at both ends are substantially symmetrical with respect to the center of the fixing belt 201.

  A central temperature sensor 230A and an end temperature sensor 230B as examples of the central temperature detection member and the end temperature detection member will be described. The central temperature sensor 230A is installed at a position for detecting the surface of the fixing belt 201 that is substantially in the center of the A4T width. The end temperature sensor 230B is installed so as to detect the approximate center between the A4T width end and the A3 nobi width end.

  FIG. 10 shows the flow of heat transmitted from the end heater 202B to the heat transfer assisting member 216 via the fixing belt 201 as an example of the nip member of FIG. In order to make the explanation easy to understand, the fixing belt 201 is not shown. The nip forming member 206 and the heat transfer assisting member 216 have substantially the same length in the longitudinal direction, but either one may be longer.

  The heat radiated from the end heater 202B is transmitted to the heat transfer assisting member 216 via the fixing belt 201. As described above, the heat transfer assisting member 216 is made longer than the maximum sheet passing width (substantially corresponding to the heat generation area in which the center heater 202A and the end heater 202B are turned on). At this time, the energy transmitted to the outside of the maximum sheet passing width represented by Q1 in FIG. 10 is dissipated without being used for fixing. Therefore, the end temperature of the fixing belt 201 is lowered by the energy Q1 dissipated to the end of the heat transfer assisting member 216 at the end of the maximum sheet passing width.

  At this time, in the region of the fixing belt 201 corresponding to the detection position of the end temperature sensor 230B, feedback control is performed so as to maintain the target temperature, so that a sufficient fixing temperature can be maintained. On the other hand, in the region outside the detection position of the end temperature sensor 230B, even if the temperature decreases, it cannot be detected by the end temperature sensor 230B, so feedback control is not performed to maintain the target temperature. As a result, even if a sufficient fixing temperature has been reached at the detection position of the end temperature sensor 230B, the sheet is dissipated through the heat transfer auxiliary member 216 without being used for heat fixing of the paper as it goes to the end from there. The temperature at the end position within the maximum sheet passing width is reduced by energy Q1, and fixing failure occurs.

  In the heat transfer assisting member 216 in FIGS. 6 and 8, the outer peripheral length of the longitudinal cross section of the heat transfer assisting member 216 in the longitudinal direction is increased around the detection position of the end temperature sensor 230B as viewed in the longitudinal direction, and the heat capacity accordingly. Has increased. Therefore, heat is transferred to the extensions 216c and 216d of the heat transfer auxiliary member 216 by energy Q2, and is dissipated through the nip forming member 206 without being used for heat fixing. As a result, the temperature at that position decreases by the amount of energy Q2 being deprived, compared to when it is not deprived. Here, since the lighting rate of the end heater 202B is adjusted by detecting the temperature of the fixing belt 201 at the position of the end temperature sensor 230B, in order to maintain the target temperature, it is more than when there is no energy Q2. Will light up. As a result, more heating from the end heater 202B is received also on the end side than the detection position of the end temperature sensor 230B.

  Therefore, by adjusting the energy Q1 and the energy Q2 in FIG. 10, the energy taken from the fixing belt 201 is made substantially the same in the longitudinal direction, the temperature uniformity of the fixing belt 201 is improved, and the end temperature is prevented from being lowered. Can do. That is, the length of the fixing belt 201 is adjusted by adjusting the amount dissipated from the end portion in the longitudinal direction of the heat transfer assisting member 216 and the amount dissipated to the extension portion of the heat transfer assisting member 216 at the position of the end temperature sensor 230B. Adjust the directional temperature. As a result, as shown in FIG. 11, when the temperature reaches a desired temperature by the control based on the detection result of the end temperature sensor 230B, the temperature at the end position of the maximum sheet passing width W becomes higher than the conventional temperature. Thus, the fixing strength can be secured up to the edge of the maximum paper.

  Further, the end heater 202B also has a heat generation region at the end opposite to the longitudinal direction, heats both ends of the end heater 202B and the center heater 202A, and the recording material S is fixed to the longitudinal direction of the fixing belt 201. Fixing is possible by conveying the approximate center of the direction and the approximate center of the recording material S to the nip portion. At this time, the end of the heat transfer assisting member 216 on the side where the end temperature sensor 230 </ b> B is not provided is also provided with an extension so as to be symmetric with respect to the substantially longitudinal center of the fixing belt 201. That is, similarly to the region including the position detected by the end temperature sensor 230B, the region substantially symmetric with respect to the center in the longitudinal direction of the fixing belt 201 in the region including the position detected by the end temperature sensor 230B is also substantially symmetric. The outer peripheral length of the vertical cross section in the longitudinal direction of the heat transfer assisting member 216 is made longer so that the heat capacity becomes larger than the end side region of the region. Accordingly, the above-described energy adjustment is performed substantially equally at both ends, and the fixing strength can be ensured up to both ends of the maximum sheet.

  As described above, when the heat transfer assisting member 216 is brought into contact with the fixing belt 201, the heat held by the fixing belt 201 is dissipated to the heat transfer assisting member 216 made of a good heat conductive material by contact heat transfer. It dissipates to the nip forming member 206 that is in contact with the heat transfer auxiliary member 216 and transfers heat. The end of the fixing belt 201 is deprived of heat as much as heat is dissipated to the end of the heat transfer assisting member 216, and the temperature drops.

  That is, the length in the longitudinal direction of the heat transfer assisting member 216 must be designed to be longer than the maximum sheet passing width that can be passed by the fixing device 200 in consideration of various variations. In particular, immediately after the warm-up in which the temperature of the entire fixing device 200 is low and the temperature easily dissipates, the energy generated by the heat source is easily dissipated to the end portion in the longitudinal direction of the heat transfer assisting member 216 and contacts the heat transfer assisting member 216 The end temperature of the fixing belt 201 that conducts heat also decreases. Therefore, the fixing property at the end in the longitudinal direction is deteriorated, and an abnormal image such as an offset is generated.

  On the other hand, in this embodiment, as an example, the outer peripheral length of the cross section perpendicular to the longitudinal direction of the fixing member is long around the longitudinal position where the end temperature sensor 230B is located, and short around the end of the fixing belt 201. Thus, the heat capacity of the heat transfer assisting member 216 is varied in the longitudinal direction so as to balance with the energy dissipated to the extreme end of the heat transfer assisting member 216.

  By doing this, the energy dissipated to the extreme end of the heat transfer assisting member 216 and the energy dissipated to the portion where the heat capacity is increased are made the same, and as a result, the energy of the fixing belt 201 is aligned in the longitudinal direction, thereby warming up. It is possible to align the temperature up to the end portion of the fixing belt 201 immediately after that and prevent the end portion temperature from decreasing.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 200 Fixing apparatus 201 Fixing belt 202 Heater 202A Center heater 202B End heater 203 Pressure roller 206 Nip forming member 216 Heat transfer auxiliary member 216a Nip forming part 216b Bending part 216c First extension part 216d Second Extension part 230A Central part temperature sensor 230B End part temperature sensor W Maximum sheet passing width

JP 2004-286922 A Japanese Patent No. 2861280 Japanese Patent Laying-Open No. 2015-099352

Claims (11)

A rotatable endless fixing member;
A heating member for heating the fixing member;
A nip member provided inside the fixing member;
A pressure rotator that sandwiches the fixing member with the nip member and forms a nip portion with the fixing member;
A fixing device for fixing a toner image on a recording medium at the nip portion;
The nip member is
A heat transfer auxiliary member in contact with the inner surface of the fixing member;
A nip forming member that supports the heat transfer auxiliary member from the opposite side of the fixing member;
The heating member is
An end heating member for heating the longitudinal end region of the fixing member;
The fixing device further includes:
An end temperature detecting member that detects the temperature of the fixing member heated by the end heating member;
The heat capacity in the longitudinal direction of the heat transfer assisting member is a second region in which the first region including the longitudinal position detected by the end temperature detecting member is closer to the end in the longitudinal direction than the first region. Larger fixing device. The fixing device according to claim 1, wherein a cross-sectional area in a direction perpendicular to a longitudinal direction of the heat transfer assisting member is larger in the first area than in the second area. The fixing device according to claim 1, wherein an outer peripheral length of a cross section in a direction perpendicular to a longitudinal direction of the heat transfer assisting member is longer in the first region than in the second region. The end heating member further heats the other end region that is symmetrical with respect to the longitudinal center of the fixing member,
The heat capacity in the longitudinal direction of the heat transfer assisting member is:
4. The device according to claim 1, wherein a region that is symmetric with respect to the center in the longitudinal direction of the first region and the fixing member is larger than a region that is on the end side in the longitudinal direction with respect to the symmetric region. Fixing device. The outer peripheral length of the cross section perpendicular to the longitudinal direction of the heat transfer assisting member is:
The fixing device according to claim 4, wherein the symmetric region is longer than a region that is closer to a longitudinal end side than the symmetric end region. In addition to the end heating member, the heating member has a center heating member that heats the longitudinal center of the fixing member,
In at least a part of the heating region of the central heating member,
The fixing device according to claim 4, wherein an outer peripheral length of a cross section in a direction perpendicular to a longitudinal direction of the heat transfer assisting member is shorter than the first region and the symmetrical end region. The width in the longitudinal direction of the center heating member and the region heated by the end heating member corresponds to the maximum paper passing width in the longitudinal direction when the fixing device can pass a plurality of types of paper widths. The fixing device according to claim 6. The fixing device according to claim 1, wherein the nip forming member is a resin. The fixing device according to claim 1, wherein the heat transfer auxiliary member is a metal plate. A fixing device that heat-fixes a toner image on a recording medium by a nip member provided inside a rotatable endless fixing member,
The inside of the sheet passing width of the fixing member is heated so as to maintain the target temperature according to the temperature detected by the temperature detecting member,
The nip member is
A heat transfer auxiliary member in contact with the inner surface of the fixing member;
A nip forming member that supports the heat transfer auxiliary member from the opposite side of the fixing member;
The heat capacity of the heat transfer auxiliary member is a fixing device in which a detection area detected by the temperature detection member is larger than an area outside the sheet passing width. An image forming apparatus comprising the fixing device according to claim 1.

Images