JP5322507B2 - Fixing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent temperature from rising in a region where no paper sheet passes, to make temperature distribution of a fixing film nearly uniform, and to prevent a fixing offset from occurring. <P>SOLUTION: A fixing apparatus 16 has: a fixing film 202; a cooling fan 301 for cooling the region of the fixing film 202 where no paper sheet passes; a ventilation guide 302 that guides, from a ventilation hole to the region where no paper sheet passes, an air sent from the cooling fan 301; and a shutter 303 that opens and closes the ventilation hole. An opening area of the ventilation hole is determined by opening or closing the shutter 303 based on the size of a recording sheet, and the blast volume of the cooling fan 301 is determined based on the resultant opening area. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for heating an image on a recording sheet and an image forming apparatus including the fixing device, which are used in an image forming apparatus employing an electrophotographic method or an electrostatic recording method such as a copying machine, a printer, and a facsimile. .

  In an electrophotographic image forming apparatus, as a fixing method for fixing an unfixed toner image on a recording paper, heat fixing that heats the unfixed toner image and melts and fixes it on the recording paper from the viewpoint of safety and good fixability. A scheme is generally used.

  As one of the thermal fixing methods, heating fixing in which a recording sheet is nipped and conveyed to a fixing area (fixing nip portion) where a heating rotating member and a pressure rotating member are pressed against each other, and an unfixed toner image is heated and pressed to be thermally fixed. There is a method. In the heat fixing method, a ceramic surface heater (hereinafter referred to as a surface heater) or the like is used as a heat source.

  In recent image forming apparatuses, for example, recording paper of various sizes from a relatively large size recording paper such as A3 size to a normally used small size recording paper such as A4R or B5 size can be used. Diversification to enable paper is progressing. For this reason, it is necessary to configure the axial lengths of the heating rotary member and the pressure rotary member to correspond to a relatively large size such as A3 size, for example.

  At this time, when a small size recording paper such as A4R or B5 passes through the fixing device, the non-sheet passing area through which the recording paper does not pass increases in the effective fixing area of the heating rotating member. In addition, when a small size recording paper is continuously passed, the surface temperature of the non-sheet passing area is changed to the sheet passing area because the recording paper does not remove heat from the surface of the heating rotating member corresponding to the non-sheet passing area. On the other hand, a so-called non-paper passing region temperature rise phenomenon is generated.

  If the heater temperature is biased due to the temperature rise phenomenon of the non-sheet passing area, it becomes an image defect or a heater failure factor. Specific examples include fixing offset due to temperature difference and heater cracking.

  As a technique for preventing such a non-sheet-passing region temperature rise phenomenon, a temperature detection element for detecting the temperature of the non-sheet-passing region is provided, and the fan is turned on / off according to a signal from the temperature detection element. A technique for controlling the temperature of the non-sheet passing area is proposed (for example, see Patent Document 1).

Further, in order to change the air blowing area according to the width of the recording paper passing through the fixing nip portion, a technique having a shutter for adjusting the length of the air blowing opening in the opening width direction has been proposed (for example, Patent Documents). 2). Specifically, the shutter is initially opened at a position corresponding to the paper size, and is moved by a certain distance in the direction of closing the shutter every time a predetermined number of sheets are passed.
Japanese Patent Application Laid-Open No. 60-136779 Japanese Unexamined Patent Publication No. 2007-187816 (Example 2)

  However, the conventional technology described in Patent Document 1 controls the blower fan according to the temperature of the fixing region. However, since the opening width of the blower port is constant, the non-sheet passing region and the opening width of the blower port do not match. Thus, temperature unevenness occurs at the interface between paper passing and non-paper passing.

  In the prior art described in Patent Document 2, the temperature decreases in the sheet passing area by the wind flowing around the sheet passing area of the heating rotating member up to a predetermined number of sheets that drive the shutter.

  Also, since the shutter is moved in the closing direction when the predetermined number of sheets has been passed, the temperature drop in the sheet passing area can be solved, but no wind hits the boundary between the sheet passing area and the non-sheet passing area. This will cause a temperature rise at the boundary. Therefore, when the recording paper size is changed from a small size paper to a recording paper having a larger area, a fixing offset may be generated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device and an image forming apparatus that can prevent a temperature rise in a non-sheet-passing region of a heating rotation unit and can make the temperature distribution of the heating rotation unit close to uniform and prevent occurrence of fixing offset. It is to provide.

In order to achieve the above object, the fixing device according to claim 1 is a heating rotation unit that applies heat to a recording sheet to be passed to melt and fix an unfixed image on the recording sheet on the recording sheet. A blowing means for cooling the non-sheet passing area of the heating rotation means; a guiding means for guiding the wind sent from the blowing means to the non-sheet passing area from the blowing opening; and the blowing opening of the guiding means by moving. and closing means for opening and closing the to determine the opening area of the blower opening of the guide means according to the size of the recording sheet, and control means for moving said closing means in response to the opening area that is the determined, the Detecting means for detecting a movement amount of the opening / closing means, and the control means determines a necessary air blowing amount according to the movement amount of the opening / closing means detected by the detecting means , and the determined necessary air blowing amount Turkey controls the air blowing means in response to The features.

  According to the present invention, there is provided a fixing device and an image forming apparatus that can prevent a temperature increase in a non-sheet passing region of the heating rotation unit and can make the temperature distribution of the heating rotation unit uniform and can prevent occurrence of a fixing offset. Can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

  The image forming apparatus shown in FIG. 1 is a color image forming apparatus having an electrophotographic tandem type intermediate transfer belt.

  The image forming apparatus includes an image forming unit 1Y that forms a yellow image, an image forming unit 1M that forms a magenta image, an image forming unit 1C that forms a cyan image, and a black image. The image forming unit 1Bk to be formed includes four image forming units.

  These four image forming units 1Y, 1M, 1C, and 1Bk are arranged in a line at regular intervals. Further, a paper feeding unit 17 and a manual feed tray 20 are disposed below, a recording paper conveyance path 18 is disposed vertically, and a fixing device 16 is provided above the paper path.

  Each of the image forming units 1Y, 1M, 1C, and 1Bk is provided with drum-type electrophotographic photosensitive members (hereinafter referred to as photosensitive drums) 2a, 2b, 2c, and 2d as image carriers.

  Around each photosensitive drum 2a, 2b, 2c, 2d, there are primary chargers 3a, 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d, and a drum cleaner device 6a. , 6b, 6c, 6d are arranged.

  A laser exposure device 7 is installed below the primary chargers 3a, 3b, 3c, and 3d and the developing devices 4a, 4b, 4c, and 4d.

  Each of the photosensitive drums 2a, 2b, 2c, and 2d is a negatively charged OPC photosensitive member having a photoconductive layer on an aluminum drum base, and a predetermined process speed in a clockwise direction by a driving device (not shown). Is driven to rotate.

  The primary chargers 3a, 3b, 3c, and 3d uniformly charge the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d to a predetermined negative potential by a charging bias applied from a charging bias power source (not shown). .

  The laser exposure device 7 disposed below the photosensitive drum 2 includes laser light emitting means that emits light corresponding to time-series electric digital pixel signals of given image information, a polygon lens, a reflection mirror, and the like.

  The laser exposure device 7 exposes the photosensitive drums 2a, 2b, 2c, and 2d to expose the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d charged by the primary chargers 3a, 3b, 3c, and 3d. Then, an electrostatic latent image of each color corresponding to the image information is formed. The detailed configuration of the laser exposure apparatus 7 will be described later.

  Each of the developing devices 4a, 4b, 4c, and 4d stores yellow toner, cyan toner, magenta toner, and black toner, respectively. Each developing device 4a, 4b, 4c, 4d attaches each color toner to each electrostatic latent image formed on each photosensitive drum 2a, 2b, 2c, 2d, thereby converting each electrostatic latent image into a toner image. To develop (visualize).

  The transfer rollers 5a, 5b, 5c, and 5d are disposed so as to be in contact with the photosensitive drums 2a, 2b, 2c, and 2d via the intermediate transfer belt 8 at the primary transfer portions 32a to 32d. The toner images on the respective photosensitive drums 2 are sequentially transferred onto the intermediate transfer belt 8 and superimposed, whereby a full color toner image is transferred (formed) onto the intermediate transfer belt 8.

  The drum cleaners 6a, 6b, 6c, and 6d are constituted by a cleaning blade or the like, and scrape off residual transfer toner remaining on the photosensitive drum 2 during the primary transfer from the photosensitive drum 2 to clean the surface of the drum.

  The intermediate transfer belt 8 is disposed on the upper surface side of each of the photosensitive drums 2a, 2b, 2c, and 2d, and is stretched between the secondary transfer counter roller 10 and the tension roller 11. Further, the secondary transfer counter roller 10 is disposed in the secondary transfer portion 34 so as to be in contact with the secondary transfer roller 12 via the intermediate transfer belt 8.

  The intermediate transfer belt 8 is made of a dielectric resin such as polycarbonate, polyethylene terephthalate resin film, polyvinylidene fluoride resin film, or the like. The image (toner image) transferred to the intermediate transfer belt 8 is transported from the paper supply unit 17 and transferred onto the recording paper in the secondary transfer section 34.

  The paper feed unit includes a paper feed unit 17 for storing the recording paper P, a manual feed tray 20, and a pickup roller for feeding the recording paper P one by one from the paper feed unit 17 or from the manual feed tray 20.

  In addition, the paper feeding unit supplies the recording paper P to the secondary in accordance with the image forming timing of the paper feeding roller, the transport path 18 and the image forming unit 1 for transporting the recording paper P delivered from each pickup roller to the registration rollers. A registration roller 19 for feeding to the transfer area is provided.

  The fixing device 16 includes a cylindrical fixing film 202 provided with a heat source such as an alumina heater inside, and a pressure roller 203 that pressurizes the fixing film 202 (the pressure roller 203 may be provided with a heat source). . Further, on the downstream side of the fixing device 16, an outer paper discharge roller 21 for guiding the recording paper P discharged from the fixing device 16 to the outside of the device and a paper discharge tray 22 are disposed.

  FIG. 2 is a schematic configuration diagram of the fixing device 16 in FIG.

  In FIG. 2, a fixing device 16 includes a surface heater (ceramic heater) 201, a cylindrical fixing film 202, a pressure roller 203, a U-shaped sheet metal 211, a temperature detection thermistor 212, a holder 213, and a self-bias circuit 214. Is provided.

  By passing a recording paper carrying an unfixed image (toner image) through a fixing nip, which is a contact portion between the fixing film 202 as a heating rotation means and the pressure roller 203, the image is melt-fixed on the recording paper. To do.

  The surface heater 201 disposed in the fixing film 202 is a heater having a heat generation pattern printed on ceramic, and is a highly responsive heater that rises in temperature by about 50 ° C. per second.

  The fixing film 202 is a film in which a rubber layer having a thickness of about 300 μm is provided on a metal and a fluorine surface treatment is performed on the rubber layer. The heat capacity is extremely small, and only the nip portion heats the surface heater 201. Tell.

  The pressure roller 203 is a roller having a hardness of about 60 ° and frictionally drives the fixing film 202. The U-shaped metal plate 211 presses the fixing film 202 against the pressure roller 203 from the inside, and the applied pressure is about 180N. A thermistor 212 for detecting the temperature of the surface heater 201 is disposed in the center of the surface heater 201 for fixing temperature control.

  FIG. 3 is a schematic configuration diagram of a cooling mechanism 305 that cools the non-sheet passing region 307 of the fixing device 16 of FIG.

  In FIG. 3, a cooling mechanism 305 for cooling the non-sheet passing regions 307 at both ends in the axial direction of the fixing film 202 is provided above the fixing film 202 of the fixing device 16. Reference numeral 308 indicates a paper passing area. The cooling mechanism 305 also constitutes the fixing device of the present invention.

  In the cooling mechanism 305, a centrifugal fan such as a sirocco fan or an axial fan is used as the cooling fan 301 as a blowing means. Further, below the cooling fan 301, a blowing guide 302 is provided as a guide means for limiting the blowing location to the non-sheet passing area 307.

  Furthermore, a shutter 303 as an opening / closing means for opening and closing the air outlet of the air guide 302 is provided on the fixing film 202 side (air outlet side) of the air guide 302. The shutter 303 moves to a predetermined position with respect to the size of the recording paper P to be passed, so that air can be blown with an optimum opening area of the air blowing opening of the air blowing guide 302 corresponding to each recording paper size.

  FIG. 4 is a control circuit diagram of the cooling mechanism 305 of FIG.

  When the size of the recording paper to be subjected to the fixing operation is determined by the fixing device 16, the CPU 407 as a control unit moves the shutter 303 to a predetermined position. The shutter 303 is driven by a shutter drive motor 402. When the shutter drive motor 402 rotates forward, the shutter 303 moves in the opening direction, and when it rotates backward, the shutter 303 moves in the closing direction.

  The shutter 303 is provided with a variable resistor 403 for detecting the movement amount (open / close amount). The variable resistor 403 changes the resistance value from 0 to 10 kΩ according to the movement amount of the shutter 303. At this time, the CPU 407 can detect the movement amount of the shutter 303 from the divided voltage of the resistor 401 and the variable resistor 403.

  In the present embodiment, the opening length is a fixed length of 50 mm, and the opening width is, for example, 40 mm when the size of the recording paper passed through is B5.

  By multiplying this opening area by the air flow per unit area required to keep the non-paper passing region 307 of the fixing device 16 and the paper passing region 308 at a uniform temperature, the air blowing amount of the cooling fan 301 is reduced. Can be determined.

  When the air flow rate is determined, the rotational speed of the cooling fan 301 that is proportional to the air flow rate is determined. At this time, it is necessary to supply a driving voltage corresponding to the rotational speed to the fan motor 406 that drives the cooling fan 301. The drive voltage is controlled by the transistors 404 and 405, and the fan drive voltage can be varied by a D / A converter built in the CPU 407.

  Specifically, when the maximum drive voltage of the cooling fan 301 is 24 V, the rotation speed at that time is 2000 rPm, and the required rotation speed is 1000 rPm, the drive voltage and the rotation speed are in a proportional relationship. The drive voltage is 12V. Thereby, the rotation speed can be controlled.

  FIG. 5 is a flowchart showing the procedure of the cooling control process for the non-sheet passing area executed by the cooling mechanism 305 in FIG.

  This flowchart is executed under the control of the CPU 407 in FIG.

  When the image forming apparatus starts operation, the recording paper size is determined by the formed image (step S501). At this time, the CPU 407 determines whether or not the non-sheet passing area 307 exists on the fixing film 202 according to the recording paper size (step S502).

  If the non-sheet passing area 307 does not exist, the CPU 407 stops driving the cooling fan 301 because it is not necessary to perform cooling (step S503). If the non-sheet passing area 307 exists, the CPU 407 determines the opening area of the air blowing opening of the air blowing guide 302 according to the recording paper size (step S504). Note that determining the opening area of the air outlet of the air guide 302 means determining the amount of movement of the shutter 303.

  Then, the CPU 407 moves the shutter 303 to a predetermined position by driving the shutter drive motor 402 according to the opening area of the air outlet of the air guide 302 (step S505). At this time, the CPU 407 calculates the amount of air necessary for cooling from the amount of movement due to the movement of the shutter 303 (step S506).

  Then, the CPU 407 determines the rotational speed of the cooling fan 301 according to the amount of air necessary for cooling (step S507), and drives and controls the fan motor 406 based on the determined rotational speed (step S508). Then, this process ends.

  Further, in order to accurately control the air flow rate, the air flow rate meter 304 is provided in the air flow guide 302. By comparing the air flow detected by the air flow meter 304 with the required air flow and controlling the rotational speed of the cooling fan 301 so that there is no difference, the air flow per unit area can be controlled with high accuracy.

  FIG. 6 is a table showing the relationship between the rotational speed of the cooling fan 301 and the air flow rate in FIG.

  By measuring the generated air flow rate with respect to the rotational speed of the cooling fan 301 in advance and holding the value in the CPU 407 as a table, the air flow rate of the cooling fan 301 can be reduced as in the case of using the air flow meter 304. It can be controlled with high accuracy.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a fixing device 16 in FIG. 1. FIG. 3 is a schematic configuration diagram of a cooling mechanism 305 that cools a non-sheet passing region 307 of the fixing device 16 of FIG. 2. FIG. 4 is a control circuit diagram of the cooling mechanism 305 in FIG. 3. FIG. 5 is a flowchart showing a procedure of cooling control processing for a non-sheet passing area executed by the cooling mechanism 305 of FIG. 4. FIG. It is a figure which shows the table showing the relationship between the rotational speed of the cooling fan 301 in FIG. 3, and ventilation volume.

Explanation of symbols

201 Surface heater 202 Fixing film 203 Pressure roller 301 Cooling fan 302 Blower guide 303 Shutter 304 Blow meter 305 Cooling mechanism 307 Non-sheet passing area 308 Sheet passing area 402 Shutter drive motor 406 Fan motor 407 CPU

Claims (4)

A heating and rotating means for applying heat to the recording paper to be passed and melting and fixing an unfixed image on the recording paper on the recording paper;
Air blowing means for cooling the non-sheet passing area of the heating rotation means;
Guiding means for guiding the wind sent from the blowing means to the non-sheet passing area from the blowing port;
Opening and closing means for moving and opening and closing the air outlet of the guide means;
And control means for moving said closing means in response to the opening area determining the opening area of the blower opening of said guide means, which is the determined in accordance with the size of the recording paper,
Detecting means for detecting the amount of movement of the opening and closing means,
The control means determines a required air volume in accordance with the amount of movement of said detected closing means by said detecting means, and wherein the benzalkonium controls said air blowing means according to the required air volume which is the determined Fixing device to do. Comprising a detecting means for detecting the blowing amount of the blowing means;
The control means according to claim 1 Symbol mounting of the fixing device and controls said air blowing means according to the required air volume of the determined and sensed air volume from the detection means. The control means has a table representing the relationship between the rotation speed of the air blowing means and the air blowing amount,
The control means according to claim 1 Symbol mounting of the fixing device and controls the rotational speed of said blower means in response to the required air blowing amount of the determined and the table. An image forming apparatus comprising: a fixing device according to any one of claims 1-3.

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