JP2012230293A - Fixing device and image forming apparatus having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device which suppresses dissipation of heat from a fixing roller, and after fixing, eliminates a temperature difference between a central part and an end part in an axial direction of the fixing roller easily in a short time and an image forming device having the same.SOLUTION: A fixing device 5 comprises: a reflection member 65 which is provided oppositely to an outer peripheral surface 18a of a fixing roller 18 and reflects radiation heat from the fixing roller 18; a drive mechanism 65 for moving the reflection member 65 to a separating position separated from the outer peripheral surface 18a of the fixing roller 18 at a predetermined interval and a contact position in contact with the outer peripheral surface 18a of the fixing roller 18; and a thermister 71 for detecting each temperature of a central part and an end part in an axial direction of the fixing roller 18. When a fixing process is performed, the reflection member 61 is located at the separating position. Meanwhile, when the temperature difference between the central part and end part of the fixing roller 18 after the fixing process is larger than a predetermined value, the reflection member 61 is located at the contact position.

Description

  The present invention relates to a fixing device that performs fixing processing of a recording medium used in a copying machine, a printer, a facsimile machine, a multi-function machine thereof, and the like, and an image forming apparatus including the fixing device.

  2. Description of the Related Art Conventionally, in image forming apparatuses such as copying machines and printers, fixing devices that fix a toner image carried on a recording medium to the recording medium by heating and pressurizing are widely used. With the recent increase in awareness of energy saving, there is a demand for lower power consumption of image forming apparatuses, and in particular, there is a particular demand for higher efficiency of fixing devices that consume more power in the image forming apparatus.

  Specifically, the fixing device includes a fixing roller and a pressure roller, the fixing roller includes a heat source such as a halogen lamp, and is attached in a state where the pressure roller is in pressure contact with the fixing roller. The toner image carried on the recording medium is thermally melted and fixed on the recording medium when the recording medium passes through a fixing nip portion between the fixing roller and the pressure roller. In order to increase the efficiency of the fixing device, it has become important to prevent the heat generated from the fixing device from flowing out of the fixing device.

  For example, the fixing device disclosed in Patent Document 1 includes a heat reflecting plate provided along the outer periphery of the fixing roller, and a plurality of recesses formed in a lattice shape on one surface, and the heat reflecting plate covers the recesses. And a support member to which is attached. With this configuration, an air layer having low thermal conductivity can be formed in a large number of recesses, heat insulation is improved, and heat is prevented from flowing out of the fixing device. Further, since the heat reflecting plate reflects the radiant heat of the fixing roller toward the outer peripheral surface of the fixing roller, the heat divergence from the fixing roller is suppressed.

  Usually, the fixing device performs fixing processing of various paper sizes. When a recording medium having a width smaller than the maximum printable recording medium is printed, a temperature difference occurs between the paper passing area and the non-paper passing area. This is because heat consumption is performed for the fixing process in the paper passing area of the recording medium, while no heat is consumed in the non-paper passing area, so that there is a temperature difference between the paper passing area and the non-paper passing area. By expanding.

  In order to eliminate such a temperature difference between the sheet passing area and the non-sheet passing area, in the fixing device of Patent Document 2, a fan is provided in a transport unit that transports a recording medium toward the fixing device. Are arranged over the entire width corresponding to the sheet passing area and the non-sheet passing areas on both sides thereof. When fixing a recording medium having a width smaller than the maximum width, the two fans corresponding to the non-sheet passing area are driven so that the temperature of the non-sheet passing area does not rise. Is kept uniform in the axial direction.

Japanese Patent Laid-Open No. 6-222697 (paragraphs [0010] to [0012], FIG. 2) JP 2007-219032 ([0027] to [0029], FIG. 1)

  However, in Patent Document 1 described above, heat dissipation from the fixing roller can be suppressed. However, after fixing a recording medium with a small width, the heat reflecting plate and the heat insulating air layer in the recesses prevent the paper passing area from passing through. There is a problem that it takes time until the temperature of the fixing nip portion becomes uniform in the axial direction because the temperature is kept with a temperature difference from the paper region.

  In Patent Document 2, in order to make the temperature of the fixing nip portion uniform in the axial direction, three fans are arranged over the entire width corresponding to the sheet passing area and the non-sheet passing area. In addition, there is a problem that the apparatus becomes large.

  The present invention has been made in order to solve the above-described problems, and suppresses the heat dissipation of the fixing roller, and after the fixing process, the temperature difference between the central portion and the end portion in the axial direction of the fixing roller. An object of the present invention is to provide a fixing device and an image forming apparatus provided with the fixing device that can easily solve the problem in a short time.

  In order to achieve the above object, a first invention has a fixing member heated by a heating means and a pressure member that presses the fixing member, and a nip portion where the fixing member and the pressing member are pressed. In the fixing device for fixing the toner image carried on the recording medium to the recording medium, a reflecting member provided facing the outer peripheral surface of the fixing member and reflecting radiant heat of the fixing member, and an outer periphery of the fixing member A driving mechanism that moves the reflecting member to a separation position that is separated from the surface by a predetermined distance and a contact position that contacts an outer peripheral surface of the fixing member; and an axially central portion and an end portion of the fixing member. A temperature detection member that detects each temperature, and when the fixing process is performed, the reflective member is disposed at the separated position, and a temperature difference between an axial center and an end of the fixing member after the fixing process. Before is greater than or equal to the specified value The reflection member is characterized in that disposed in the contact position.

  According to a second aspect of the present invention, in the fixing device, the heating unit includes a central heating unit that heats the axial center portion of the fixing member and an end that heats both axial ends of the fixing member. Part heating means, and the reflection member comprises a central reflection member disposed to face the central heating means and end reflection members respectively disposed to face the end heating means, In the fixing process of a recording medium having a size exceeding the width of the central heating unit, the central heating unit and the end heating unit are energized, and after the fixing process, the temperature difference between the central part and the end part in the axial direction of the fixing member is When it is equal to or greater than a predetermined value, the central reflection member and the end reflection member are arranged at the contact position, while in the fixing process of the recording medium smaller than the width of the central heating unit, the central heating unit is energized, After the fixing process, the central reflection member is It is characterized by placing the contact position.

  According to a third aspect of the present invention, in the fixing device, the central reflecting member and the end reflecting member are arranged side by side with a gap in the axial direction of the fixing member, and the end reflecting member has the gap. An extending portion is formed so as to cover the surface of the central reflecting member opposite to the reflecting surface so as to cover the surface.

  According to a fourth aspect of the present invention, in the above fixing device, the reflecting member is made of an aluminum plate.

  According to a fifth aspect of the invention, there is provided an image forming apparatus comprising the fixing device having the above-described configuration and a control unit that controls the heating unit and the driving mechanism based on the temperature detected by the temperature detection member.

  According to the first aspect, when the fixing process is performed, the reflecting member is arranged at a predetermined interval with respect to the outer peripheral surface of the fixing member, and heat dissipation from the fixing member is suppressed. After the fixing process, when the temperature difference between the central portion and the end portion in the axial direction of the fixing member is a predetermined value or more, the reflecting member is arranged so as to contact the outer peripheral surface of the fixing member. Is transmitted in the axial direction from the high temperature side to the low temperature side through the reflecting member, and the surface temperature difference between the central portion and the end portion of the fixing member is eliminated in a short time. In addition, with a simple configuration in which the reflecting member is moved to a position where it is away from the outer peripheral surface of the fixing member and a position where it is in contact with the fixing member, heat dissipation from the fixing member is suppressed, and the surface temperature difference of the fixing member can be reduced in a short time. Can be resolved.

1 is a diagram illustrating a schematic configuration of an image forming apparatus including a fixing device according to a first embodiment of the present invention. 1 is a schematic cross-sectional view of a fixing device according to a first embodiment and its surroundings as viewed from an axial direction. Schematic sectional view of a fixing device according to a second embodiment of the present invention as viewed from a direction perpendicular to the axial direction.

  Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. Further, the use of the invention and the terms shown here are not limited thereto.

(First embodiment)
FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus including a fixing device according to an embodiment of the present invention. The image forming apparatus 1 includes a sheet feeding unit 2 disposed in a lower portion thereof, a sheet conveying unit 3 disposed on the right side of the sheet feeding unit 2, and an image disposed on the upper side of the sheet conveying unit 3. The image forming unit 4 includes a forming unit 4, a fixing device 5 disposed on the discharge side of the image forming unit 4, and an image reading unit 6 disposed on the image forming unit 4 and the fixing device 5.

  The paper feed unit 2 includes a plurality of paper feed cassettes 7 that store paper 9 that is a recording medium. The paper 9 is sent to the paper transport unit 3 one by one.

  The paper 9 sent to the paper transport unit 3 is transported toward the image forming unit 4 via the paper transport path 10. The image forming unit 4 forms a toner image on the paper 9 by an electrophotographic process, and a photosensitive member 11 that can rotate in the direction of an arrow, and a charging device around the photosensitive member 11 along the rotating direction. A unit 12, an exposure unit 13, a developing device 14, a transfer unit 15, a cleaning unit 16, and a charge removal unit 17.

  The charging unit 12 includes a charging wire to which a high voltage is applied. When a predetermined potential is applied to the surface of the photoconductor 11 by corona discharge from the charging wire, the surface of the photoconductor 11 is uniformly charged. Then, when light based on the image data of the original read by the image reading unit 6 is irradiated to the photoconductor 11 by the exposure unit 13, the surface potential of the photoconductor 11 is selectively attenuated, and the surface of the photoconductor 11 is irradiated. An electrostatic latent image is formed.

  Next, the developing device 14 develops the electrostatic latent image on the surface of the photoconductor 11, and a toner image is formed on the surface of the photoconductor 11. This toner image is transferred by the transfer unit 15 to the paper 9 supplied between the photoconductor 11 and the transfer unit 15.

  The sheet 9 on which the toner image has been transferred is conveyed toward the fixing device 5 disposed downstream of the image forming unit 4 in the sheet conveying direction. In the fixing device 5, the paper 9 is heated and pressed by the fixing roller 18 and the pressure roller 19, and the toner image is melted and fixed on the paper 9. Next, the sheet 9 on which the toner image is fixed is discharged onto the discharge tray 21 by the discharge roller pair 20.

  After the transfer by the transfer unit 15, the toner remaining on the surface of the photoconductor 11 is removed by the cleaning unit 16, and the residual charge on the surface of the photoconductor 11 is removed by the charge eliminating unit 17. Then, the photosensitive member 11 is charged again by the charging unit 12, and image formation is performed in the same manner.

  FIG. 2 is a schematic sectional view of the fixing device 5 used in the above-described image forming apparatus 1 as seen from the axial direction.

  The fixing device 5 is a roller fixing method, and includes a fixing roller 18 as a fixing member, a pressure roller 19 as a pressure member, a heater 43 as a heating means, a thermistor 71 as a temperature detection member, A side frame 55, an upper frame 56, and a reflection member 61 are provided. Further, a drive mechanism 65 and a control unit 81 are provided around the fixing device 5.

  As the fixing roller 18, a cylindrical cored bar made of a metal such as aluminum or iron having excellent thermal conductivity is coated with a fluororesin coating or a tube. A heater 43 such as a halogen lamp or a xenon lamp is provided inside the cored bar of the fixing roller 18.

  The pressure roller 19 is formed by forming an elastic layer such as silicon rubber on a cylindrical base material made of synthetic resin, metal or other material, and coating the surface of this elastic layer with a fluororesin coat. .

  The pressure roller 19 is brought into pressure contact with the fixing roller 18 with a predetermined pressure, and when the pressure roller 19 is rotationally driven, the fixing roller 18 is driven to rotate. A nip portion N is formed at a portion where the fixing roller 18 and the pressure roller 19 come into contact with each other while rotating in reverse.

  The lower frame 55 constitutes a part of the outer frame of the fixing device 5 and supports the pressure roller 19 rotatably. Further, an upstream conveyance guide 40 and a downstream conveyance guide 41 are attached to the lower frame 55 so as to face the pressure roller 19, respectively. The upstream conveyance guide 40 guides the sheet 9 to the nip N, and the downstream conveyance guide 41 guides the sheet 9 fixed at the nip N to a predetermined position outside the fixing device 5. is there.

  The upper frame 56 constitutes a part of the outer frame of the fixing device 5 and supports the fixing roller 18 rotatably. A separation claw 51 is attached to the upper frame body 56. The separation claw 51 separates the sheet 9 after the fixing process from the surface of the fixing roller 18, and is arranged on the downstream side in the rotation direction of the fixing roller 18 with respect to the nip portion N, and the leading end thereof is the fixing roller. 18 is arranged in contact with or close to the surface of 18. A plurality of separation claws 51 are provided side by side in the axial direction of the fixing roller 18.

  The thermistor 71 detects the surface temperature of the fixing roller 18, and is disposed in the vicinity of the outer peripheral surface 18 a of the fixing roller 18 and in the vicinity of the upstream side of the fixing nip portion N in the sheet conveyance direction. Further, the thermistor 71 is disposed on the center and end sides in the axial direction of the fixing roller 18 and detects the surface temperatures of the center and end sides of the fixing roller 18. As a result, the surface temperature of the fixing roller 18 can be controlled to a temperature necessary for image formation.

  The sheet 9 is guided to the upstream conveyance guide 40 and conveyed to the nip portion N, and the powder state on the sheet 9 is heated and pressed by the fixing roller 18 and the pressure roller 19 in the nip portion N. The toner is melted and fixed. After the fixing process, the sheet 9 is separated from the surface of the fixing roller 18 by the separation claw 51 and then guided to a predetermined position outside the fixing device 5 by the downstream side conveyance guide 41.

  The reflecting member 61 reflects the radiant heat from the fixing roller 18 toward the fixing roller 18, and a material having good heat reflection characteristics and heat conductivity, for example, an aluminum plate is used. Further, the reflection member 61 is formed in an arc shape in a side view so as to have substantially the same curvature as the outer peripheral surface 18 a of the fixing roller 18, a separation position spaced apart from the outer peripheral surface 18 a of the fixing roller 18 by a predetermined interval, and the fixing roller 18. It is supported by the drive mechanism 65 mentioned later so that a movement is possible at the contact position which contacts the outer peripheral surface 18a.

  By configuring the reflecting member 61 with an aluminum material, when the reflecting member 61 is arranged at a predetermined interval with respect to the outer peripheral surface 18a of the fixing roller 18, the radiant heat of the fixing roller 18 is efficiently reflected and fixed. Heat dissipation from the roller 18 can be suppressed. Further, when the surface temperature of the fixing roller 18 is different in the axial direction, when the reflecting member 61 comes into contact with the outer peripheral surface 18 a of the fixing roller 18, the temperature of the outer peripheral surface 18 a of the fixing roller 18 is lowered from the high temperature side through the reflecting member 61. The surface temperature difference of the fixing roller 18 is eliminated in a short time.

  The drive mechanism 65 includes an eccentric cam 66, a pair of spring members 67, and a motor 68, and moves the reflection member 61 to a separation position and a contact position with respect to the outer peripheral surface 18 a of the fixing roller 18.

  The pair of spring members 67 are tension coil springs, one end of which is fixed to the upper frame body 56 and the other end is fixed to the reflecting member 61, so that the reflecting member 61 is removed from the outer peripheral surface 18 a of the fixing roller 18. It is energizing in the direction of separating.

  The eccentric cam 66 is rotatably supported by the upper frame 56 and is always in contact with the outer surface of the reflecting member 61 (the surface opposite to the reflecting surface of the reflecting member 61) by the biasing force of the spring member 67. . In the state of the eccentric cam 66 shown in FIG. 2, the reflecting member 61 is in the separated position, and when the eccentric cam 66 rotates 180 degrees from the state shown in FIG. 2, the reflecting member 61 moves to the contact position. The spring member 67 is composed of a compression coil spring, the reflecting member 61 is urged by the spring member 67 in a direction in contact with the outer peripheral surface 18 a of the fixing roller 18, and the eccentric cam 66 is further moved to the reflecting surface side of the reflecting member 61. You may comprise so that it may always contact | abut.

  The motor 68 is connected to the eccentric cam 66 through a gear or the like, and rotates the eccentric cam 66. By the rotational drive of the motor 68 every 180 degrees, the contact position of the eccentric cam 66 with respect to the reflection member 61 is changed, and the reflection member 61 can be moved to the separation position and the contact position. In place of the motor 68, a solenoid may be used. The reflecting member 61 can be moved to the separated position and the contact position by pushing and pulling the solenoid.

  The motor 68 is connected to the control unit 81. The control unit 81 is connected to the thermistor 71 and the power source 69 in addition to the motor 68. The control unit 81 includes a microcomputer, a storage element such as a RAM and a ROM, and the like. The control unit 81 controls the rotation driving of the motor 68 every 180 degrees based on the temperature-related information detected by the thermistor 71, and from the power source 69 to the heater. The on / off of energization to 43 is controlled.

  That is, based on the surface temperature of the fixing roller 18 detected by the thermistor 71, the control unit 81 supplies power to the heater 43 from the power source 69 when the temperature is equal to or lower than the first temperature necessary for the fixing process. If the temperature of the fixing roller 18 is exceeded, the energization from the power source 69 to the heater 43 is cut off, and the surface temperature of the fixing roller 18 is controlled to a temperature necessary for fixing processing.

  When the fixing process is performed, the motor 68 is driven so that the reflecting member 61 is disposed at the separated position. In this state, the reflecting member 61 efficiently reflects the radiant heat of the fixing roller 18 toward the fixing roller 18, and can suppress the divergence of heat from the fixing roller 18.

  Further, the control unit 81 controls the drive of the motor 68 based on the surface temperature of the fixing roller 18 detected by the thermistor 71 after the fixing process.

  That is, the thermistor 71 detects the temperatures of the central portion and the end portion side of the fixing roller 18 in the axial direction. The control unit 81 does not drive the motor 68 when the temperature difference between the center portion and the end portion detected by the thermistor 71 does not exceed a predetermined value. Accordingly, the reflecting member 61 is held at the separated position. This is the case, for example, when the maximum width of paper P that can be fixed is fixed. In this case, since a significant temperature difference does not occur between the central portion and the end portion of the fixing roller 18 in the axial direction, the fixing roller 18 is immediately uniformed in the axial direction by heating the fixing roller 18 with the heater 43 after fixing. Surface temperature.

  On the other hand, when the paper P having a width smaller than the maximum width of the paper P that can be fixed is fixed, the paper passing area (the central part in the axial direction) and the non-paper passing area (the end in the axial direction) after the fixing process. A temperature difference occurs between In the sheet passing area, heat is conducted to the fixed paper P, and the sheet passing area is at a lower temperature than the non-sheet passing area. When the temperature difference between the central portion and the end portion detected by the thermistor 71 is equal to or larger than a predetermined value, the control portion 81 drives the motor 68 so as to move the reflecting member 61 to the contact position. When the reflecting member 61 comes into contact with the outer peripheral surface 18 a of the fixing roller 18, the heat on the end side of the fixing roller 18 is conducted to the reflecting member 61, and the heat on the end side through the reflecting member 61 is relatively low. Is conducted to the central portion of the fixing roller 18. The thermistor 71 always detects the surface temperatures of the center portion and the end portion side of the fixing roller 18 in the axial direction. When the temperature difference between the central portion and the end portion detected by the thermistor 71 becomes small and the temperature difference reaches a predetermined threshold, the control unit 81 drives the motor 68 to move the reflecting member 61 from the contact position to the separated position. Move. If the temperature difference between the central portion and the end portion becomes smaller than a predetermined threshold value, a predetermined time elapses after the reflecting member 61 moves to the contact position instead of moving the reflecting member 61 from the contact position to the separated position. Then, the motor 68 may be controlled so as to move from the contact position to the separated position.

  As described above, when the temperature difference between the central portion and the end portion in the axial direction of the fixing roller 18 is equal to or larger than a predetermined value, the reflecting member 61 comes into contact with the outer peripheral surface 18 a of the fixing roller 18, thereby fixing the fixing roller. The temperature difference between the 18 axial central portions and the end portions is eliminated in a short time.

(Second Embodiment)
FIG. 3 is a schematic cross-sectional view of the fixing device according to the second embodiment viewed from a direction perpendicular to the axial direction. The second embodiment is a configuration in which the reflecting member is divided and arranged in the axial direction, and the divided reflecting member and its peripheral configuration, which are different from the first embodiment, will be described. Hereinafter, the same parts as the first embodiment The description of is omitted.

  Inside the fixing roller 18, a central heater 44 that heats the axial center of the fixing roller 18 and an end heater 45 that heats both axial ends of the fixing roller 18 are disposed. Each of the heaters 44 and 45 is a heater such as a halogen lamp or a xenon lamp.

  Thermistors 71 a and 71 b are disposed in the vicinity of the outer peripheral surface 18 a of the fixing roller 18. The thermistor 71 a is disposed in the central portion of the fixing roller 18 in the axial direction, and detects the surface temperature of the central portion of the fixing roller 18. The thermistor 71 b is disposed on the end side in the axial direction of the fixing roller 18 and detects the surface temperature on the end side of the fixing roller 18.

  On the outer peripheral surface 18 a side of the fixing roller 18, a central reflection member 62 and an end reflection member 63 that are formed in an arc shape so as to have substantially the same curvature as the outer peripheral surface 18 a are disposed. The central reflection member 62 and the end reflection member 63 are formed of a material having good heat reflection characteristics and heat conductivity, for example, an aluminum plate.

  The central reflection member 62 is disposed in the central portion in the axial direction of the fixing roller 18 so as to face the central heater 44, while the end reflection member 63 is opposed to the end heater 45 in the axial direction of the fixing roller 18. It is arrange | positioned at the both-ends side.

  The central reflecting member 62 and the end reflecting member 63 are supported so as to be movable between a separation position spaced apart from the outer peripheral surface 18a of the fixing roller 18 by a predetermined distance and a contact position that contacts the outer peripheral surface 18a of the fixing roller 18. The The central reflection member 62 and the end reflection member 63 are arranged in parallel with a gap in the axial direction so that the central reflection member 62 and the end reflection member 63 can move independently.

  The end reflection member 63 has an extending portion 63a. The extending portion 63 a is provided to extend to the outer surface on the opposite side of the reflecting surface of the central reflecting member 62 so as to cover the axial gap between the central reflecting member 62 and the end reflecting member 63. When the center reflecting member 62 and the end reflecting member 63 are disposed at the contact positions, the extending portion 63 a is configured to contact the outer surface of the center reflecting member 62.

  With this configuration, when the central reflection member 62 and the end reflection member 63 are disposed at the separated positions, the radiant heat of the fixing roller 18 can be prevented from being radiated from the gap, and the radiant heat of the fixing roller 18 is fixed. Reflecting efficiently toward the roller 18, heat divergence from the fixing roller 18 can be suppressed.

  The central reflecting member 62 is moved between the separated position and the contact position by the drive mechanism 65a. The end reflection member 63 is moved between the separation position and the contact position by the drive mechanism 65b. As the drive mechanisms 65a and 65b, the drive mechanism 65 of the first embodiment is used.

  The control unit 81 performs on / off control of energization from the power source 69 to the heaters 44 and 45 during the fixing process and drive control of the drive mechanisms (motors) 65a and 65b after the fixing process according to the size of the paper to be printed. Make it different.

  When fixing the paper P having a size exceeding the width of the central heater 44, the control unit 81 supplies power to the central heater 44 and the end heater 45 from the power source 69. The thermistors 71 a and 71 b detect the surface temperature of the fixing roller 18. When the surface temperature of the fixing roller 18 detected by the thermistors 71a and 71b is equal to or lower than the first temperature required for the fixing process, the control unit 81 supplies power to the central heater 44 and the end heater 45 from the power source 69. Hold. On the other hand, when the surface temperature of the fixing roller 18 detected by the thermistors 71a and 71b exceeds the first temperature, the power supply 69 is cut off from the central heater 44 and the end heater 45, and the surface temperature of the fixing roller 18 is exceeded. Is controlled to a temperature required for the fixing process.

  When the fixing process is performed, the driving mechanisms 65a and 65b are driven so that the central reflecting member 62 and the end reflecting member 63 are arranged at the separated positions. In this state, the central reflecting member 62 and the end reflecting member 63 efficiently reflect the radiant heat of the fixing roller 18 toward the fixing roller 18, and can suppress the divergence of heat from the fixing roller 18.

  After the fixing process, the thermistors 71a and 71b detect the temperatures at the central portion and the end side in the axial direction of the fixing roller 18, respectively. The control unit 81 does not drive the driving mechanisms 65a and 65b when the temperature difference between the central portion and the end portion detected by the thermistors 71a and 71b does not exceed a predetermined value. Therefore, the central reflecting member 62 and the end reflecting member 63 are held at the separated positions.

  The control unit 81 is driven so that the central reflection member 62 and the end reflection member 63 move to the contact position when the temperature difference between the center and the end detected by the thermistors 71a and 71b is equal to or greater than a predetermined value. The mechanisms 65a and 65b are driven. Accordingly, the central reflecting member 62 and the end reflecting member 63 come into contact with the outer peripheral surface 18 a of the fixing roller 18. Due to the contact of the center reflecting member 62 and the end reflecting member 63 with the outer peripheral surface 18 a of the fixing roller 18, the heat on the end side of the fixing roller 18 is conducted to the end reflecting member 63 and further from the end reflecting member 63 to the center. The heat is conducted to the reflecting member 62, and the heat on the end side is conducted through the central reflecting member 62 to the central portion of the fixing roller 18 having a relatively low temperature. As a result, the temperature difference between the central portion and the end portion of the fixing roller 18 in the axial direction is eliminated in a short time.

  On the other hand, when fixing the paper P smaller than the width of the central heater 44, the control unit 81 cuts off the power supply from the power source 69 to the end heater 45 and supplies the power to the central heater 44. The thermistors 71 a and 71 b detect the surface temperature of the fixing roller 18. When the surface temperature of the fixing roller 18 detected by the thermistor 71a is equal to or lower than the first temperature necessary for the fixing process, the control unit 81 maintains energization from the power source 69 to the central heater 44. On the other hand, when the surface temperature of the fixing roller 18 detected by the thermistor 71a exceeds the first temperature, power supply from the power source 69 to the central heater 44 is cut off, and the surface temperature of the fixing roller 18 is set to a temperature necessary for the fixing process. Control.

  When the fixing process is performed, the driving mechanisms 65a and 65b are driven so that the central reflecting member 62 and the end reflecting member 63 are arranged at the separated positions. In this state, the central reflecting member 62 and the end reflecting member 63 efficiently reflect the radiant heat of the fixing roller 18 toward the fixing roller 18, and can suppress the divergence of heat from the fixing roller 18.

  After the fixing process, the control unit 81 drives the drive mechanism 65a but does not drive the drive mechanism 65b. As a result, the central reflecting member 62 moves to the contact position, while the end reflecting member 63 is held at the separated position. The end reflecting member 63 is held at the separated position because the surface temperature of the fixing roller 18 facing the end reflecting member 63 is higher than the surface temperature of the central portion (paper passing area) of the fixing roller 18. by. When the central reflecting member 62 contacts the outer peripheral surface 18 a of the fixing roller 18, the heat of the fixing roller 18 facing the end portion side of the central reflecting member 62 is conducted to the central reflecting member 62, and further, the central reflecting member 62 is passed through the central reflecting member 62. To the central portion of the fixing roller 18 having a relatively low temperature. As a result, the temperature difference between the central portion and the end portion of the fixing roller 18 in the axial direction is eliminated in a short time.

  In the first and second embodiments, the configuration in which the reflecting member 61 (62, 63) is opposed to the roller fixing type fixing roller 18 is not limited to this, and the fixing roller and the heating roller are not limited thereto. In the belt fixing system including the heating belt stretched by the belt and the pressure roller that presses the fixing roller via the heating belt, the reflecting member 61 (62, 63) may be configured to face the heating belt. . In this case, the heating roller may be heated by a heater such as a halogen lamp or a xenon lamp or electromagnetic induction. In this case as well, the same effects as in the above embodiment can be obtained.

  The present invention can be used in an image forming apparatus that performs fixing processing of a recording medium used in a copying machine, a printer, a facsimile machine, or a multifunction machine thereof.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 5 Fixing apparatus 18 Fixing roller (fixing member)
18a outer peripheral surface 19 pressure roller (pressure member)
43 Heater (heating means)
44 Central heater (central heating means)
45 End heater (end heating means)
55 Lower frame 56 Upper frame 61 Reflective member 62 Central reflective member 63 End reflective member 63a Extension portion 65 Drive mechanism 66 Eccentric cam (drive mechanism)
67 Spring member (drive mechanism)
68 Motor (drive mechanism)
69 Power supply 71 Thermistor (temperature detection member)
81 Control part N Nip part

Claims (5)

A fixing member heated by a heating unit and a pressing member that presses the fixing member are recorded, and a toner image carried on a recording medium is recorded at a nip portion where the fixing member and the pressing member are pressed. In a fixing device for fixing to a medium,
A reflecting member provided opposite to the outer peripheral surface of the fixing member and reflecting radiant heat of the fixing member;
A drive mechanism that moves the reflecting member to a separation position spaced apart from the outer peripheral surface of the fixing member by a predetermined distance and a contact position that contacts the outer peripheral surface of the fixing member;
A temperature detection member for detecting each temperature of the central portion and the end portion in the axial direction of the fixing member,
When the fixing process is performed, the reflective member is disposed at the separation position, and when the temperature difference between the central portion and the end in the axial direction of the fixing member is equal to or greater than a predetermined value after the fixing process, the reflective member is A fixing device arranged at a contact position. The heating means includes a central heating means for heating the axial center part side of the fixing member, and an end heating means for heating both axial side ends of the fixing member,
The reflective member is composed of a central reflective member disposed to face the central heating means and end reflective members respectively disposed to face the end heating means,
In the fixing process of the recording medium having a size exceeding the width of the central heating unit, the central heating unit and the end heating unit are energized, and the temperature difference between the central part and the end in the axial direction of the fixing member after the fixing process. Is equal to or greater than a predetermined value, the central reflection member and the end reflection member are disposed at the contact position, while in the fixing process of the recording medium smaller than the width of the central heating unit, the central heating unit is energized. The fixing device according to claim 1, wherein the central reflection member is disposed at the contact position after the fixing process.   The central reflecting member and the end reflecting member are arranged side by side with a gap in the axial direction of the fixing member, and the end reflecting member is opposite to the reflecting surface of the central reflecting member so as to cover the gap. The fixing device according to claim 2, wherein an extending portion that overlaps the surface of the fixing device is formed.   The fixing device according to claim 1, wherein the reflecting member is made of an aluminum plate material.   An image forming apparatus comprising: the fixing device according to claim 1; and a control unit that controls the heating unit and the driving mechanism based on a temperature detected by the temperature detection member.