Patent Publication Number: US-6911625-B2

Title: Heating roller

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention relates to a heater apparatus for a heating roller of a fixing device provided in an image forming apparatus such as an electrophotographic type printer, copying machine and the like. 
   DESCRIPTION OF RELATED ART 
   In an image forming apparatus such as a printer, a copying machine and the like that uses an electrophotographic process, a fixing device for fixing a unfixed toner image held on a recording material such as a recording paper sheet, an OHP sheet and the like is provided. For the fixing device, a so-called heating roller is widely used as means for fixing the toner on the paper sheet. 
   Such a heating roller type fixing device will be explained below, referring to FIG.  5 . 
   In  FIG. 5 , the fixing device has a heating roller  1  with which a pressure roller  2  is in contact under pressure. A recording paper sheet P, that is, a toner transferred material holding a unfixed toner image T o  passes through a contact area between the heating roller  1  and the pressure roller  2  so that the toner on the recording paper sheet P is fixed by the heat and pressure. 
   As shown in  FIGS. 5 and 6 , for example, two heating lamps are provided inside a cylindrical roller body  10  of the heating roller  1 , which is made of metal or aluminum so that the tube axis directions of the lamps are in parallel to each other. These two heater lamps are, for example, a fixing heater lamp  21  and an auxiliary heater lamp  22  which are filament lamps in which necessary inert gas and halogen gas are included. Tungsten is used as a material of the filaments in such a heater lamp. The tungsten in which about 50-90 ppm potassium is doped, that is, so called doped tungsten, consists of more than 99.9% tungsten. Such a heater lamp in which the tungsten filaments are used as heating elements has excellent heat response capability and heat-impact resistance capability. As a result, it is possible to obtain an excellent heating roller for the fixing device. 
   Out of the heaters, the fixing heater lamp  21  operates solely as a heat source for heating the heating roller  1  when fixing the unfixed toner T o  on the recording paper sheet P. 
   On the other hand, the auxiliary heater lamp  22  is a auxiliary heat source which is turned on only in an initial operation of the fixing device to shorten period to reach a predetermined temperature of the roller body  10 , that is, to shorten a rising time of the heating roller. 
   SUMMARY OF THE INVENTION 
   However, the heat apparatuses having such a structure have problems described below. 
   Since the filament of the heater lamp is made of tungsten, rush current which is more than 10 times the amount of current in the steady state flows at the same time voltage from a power supply is applied to the heater lamp instantaneously. The resistivity value of the tungsten at the target temperature of the heart roller (160° C.) is thirteen to sixteen times the value of that at room temperature. Since the tungsten filaments of the heater lamps have such a characteristic, the resistivity value of the tungsten filaments changes due to temperature change. 
   In view of the above problems, the heater lamp may be turned on by saving power to be applied thereto. However, it takes long time to reach a predetermined temperature of the heating roller since output of the heater lamp is not sufficient. That is, a long rising time of heating roller is necessary. Since a controlling circuit for reducing rush current needs to be provided in the power supply device, the cost of the power supply device increases and the power supply device also grows in size. 
   In the heater lamp of the fixing device, there is a problem that the circuit of the device is vulnerable to a rush current since the heater lamp is turned on with maximum input power that is usually close to rated consumption electric power thereby easily causing a break in the circuit. See Japanese Laid Open Patent No. 2002-258646. 
   In view of the above problems, it is an object of the present invention to provide a heater roller capable of reducing rush current at the start of power distribution. 
   It is another object of the present invention to provide a heater roller of a fixing device with a simple structure which is capable of reducing rush current at the start power. 
   A heating roller comprises a first heater lamp having a first filament made of tungsten, and a second heater lamp having a second filament, wherein the second filament is a heating element whose resistivity value is greater than that of tungsten at a room temperature. 
   The second heater lamp may be an auxiliary heater lamp. The auxiliary heater lamp may be turned on at an initial power distribution period. 
   Further, the first filament of the first heater lamp may have at least one first lighting portion and at least one first non-lighting portion, and the second filament of the second heater lamp may have at least one second lighting portion and at least one second non-lighting portion. 
   Furthermore, the at least one first lighting portion may face the at least one second non-lighting portion and the at least one first non-lighting portion may face the at least one second lighting portion. 

   
     DESCRIPTION OF THE DRAWINGS 
     The embodiments of the present invention will be described referring to  FIGS. 1-6 . 
       FIG. 1  is a diagram explaining the structure of heating roller according to the present invention; 
       FIG. 2  is a diagram explaining an operation of on/off switching; 
       FIG. 3  is a diagram explaining the structure of heater lamp in a heater lamp according to a second embodiment; 
       FIG. 4A  shows a rising characteristic of a heating roller according to the present invention; 
       FIG. 4B  shows a rising characteristic of a heating a comparative example; 
       FIG. 5  is a schematic view of a fixing device; and  FIG. 6  is a schematic view of a heating roller. 
   

   The present invention will become more apparent from the following detailed description of the embodiments and examples of the present invention. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Description of a heating roller of a first embodiment according to the present invention will be given below referring to FIG.  1 . 
   In  FIG. 1 , a heating roller  1  has for example, a roller body  10 , a fixing heater lamp  21  that operates as a main heating source of the roller body  10  in a fixing device at a fixing device operating time, and an auxiliary heater lamp  22  which is turned on only at an initial period of lighting, that is, time when power of the fixing device is on. 
   Valves  31  and  32  of the heater lamps  21  and  22 are a quartz glass tube. At each end of each of the valves, a pinch seal portion is formed. Each end of a filament  210  is connected to a metallic foils  41  contained in the pinch seal via an internal lead. An outside lead  51  is connected to each of the metallic foils  41  and derived to the outside of the heating roller  1 . Each end of a filament  220  is connected to a metallic foils  42  contained in the pinch seal via an internal lead. Furthermore, an outside lead  52  is connected to each of the metallic foils  42  and derived to the outside of the heating roller  1 . Furthermore, each of the outside leads  51  and  52  is connected to a power supply (not shown in  FIG. 1 ) via a lead and the like (not shown). 
   The filament  210  of the fixing heater lamp  21  is made of tungsten, specifically, doped tungsten in which 50 to 90 ppm potassium is doped. Necessary inactive gas and Halogen gas are included inside the valve  31 . 
   The filament  220  of the auxiliary heater lamp  22  is a heating element whose resistivity value at room temperature is greater than that of tungsten. The inside of the valve  32  of the auxiliary heater lamp  22  may be held with vacuum or in the atmosphere, or filled with inactive gas depending on the heating element, that is, filament  220 . Furthermore, it may not be necessary to form the pinch seal portions. 
   The “heating element having the resistivity value at the room temperature greater than that of tungsten” means a heating element having the resistivity value at the room temperature or temperature near the room temperature (25° C.±5° C.) greater than the resistivity value of tungsten (5.5(Ω·cm)(20° C.)), specifically, a heating element made of nickel-chromium alloy (hereinafter simply referred to as Nichrome), or iron-chromium-aluminium alloy (hereinafter referred to as Cantal), a tantalum heating element, a graphite heating element, a platinum heating element and the like. 
   Alloys containing tungsten as a main component and about a couple of percent to 50 percent of other metal such as molybdenum which is different from so-called pure tungsten or doped tungsten (made of more than 99.9% tungsten) have the resistivity value at room temperature much greater than that of tungsten (5.5(Ω·cm)(20° C.)). It depends on the percentage of molybdenum. Thus, it is possible to select a heating element made of such alloy and use it for the present invention. 
   Table 1 shows examples of the resistivity value at 20° C. of heating elements made of such materials. Of course, it is possible to use a heating elements other than these heating elements for the present invention if the resistivity value of thereof at room temperature (or temperature near the room temperature) is greater than that of tungsten. 
   
     
       
         
             
             
             
             
             
             
           
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
                 
                 
               Cantal 
                 
                 
             
             
                 
                 
               Nichrome 
               (Fe026Cr- 
             
             
                 
               Heating 
               (Ni-20Cr 
               7.5Al) 
             
             
                 
               Element 
               Heating 
               Heating 
               Tantalum 
               Platinum 
             
             
                 
               Material 
               Element) 
               Element) 
               (Ta) 
               (Pt) 
             
             
                 
                 
             
           
          
             
                 
             
          
         
         
             
             
             
             
             
             
          
             
                 
               Resistivity 
               110 
               160 
               12.5 
               10.6 
             
             
                 
               Value 
             
             
                 
               (20° C.) 
             
             
                 
               (μΩ · cm) 
             
             
                 
                 
             
          
         
       
     
   
   The fixing heater lamp  21  and the auxiliary heater lamp  22  are connected in parallel to an outside power supply apparatus (not shown). It is possible to supply power to both heater lamps  21  and  22  or only to the fixing heater lamp  22  by a switching unit (not shown). 
   Description of a switching operation will be given referring to FIG.  2 . 
     FIG. 2  is a timing chart to explaining the relationship between power application timing of the fixing heater lamp  21  and the auxiliary heater lamp  22 . At an initial fixing device rising time, almost maximum dissipation is applied to both heater lamps  21  and  22  so as to turn on them. When the roller body  10  reaches a predetermined temperature, the heating roller  10  is ready to operate and the auxiliary heater lamp  22  is turned off thereby turning on only the fixing heater lamp  21  so that the operation is changed to a normal lighting operation. 
   At the initial operation period of the fixing device, almost (fixing device rising device) maximum dissipation is applied to the fixing heater lamp  21  and the auxiliary heater lamp  22  to heat the roller body  10 . Since even at the initial operation period of the fixing device, the filament  220  of the auxiliary heater lamp  22  has the resistivity value at room temperature sufficiently greater than that of tungsten, it is possible to control the value of current flowing the auxiliary heater lamp to much lower than that in the conventional device thereby reducing rush current. 
   After the heating roller reaches the predetermined temperature so that the heating roller is warmed up, power is applied to the fixing heater lamp  21  only and power is not applied to the auxiliary heater lamp  22 . At this point, the filament  210  of the fixing heater lamp  21  is sufficiently warmed up, that is, the resistivity value of the tungsten is increased so that rush current does not flow. 
   As described above, since an auxiliary heater lamp  22  out of a plurality of heater lamps provided inside the roller body  10  has, as a heating element, the filament  220  whose resistivity value at room temperature is greater than that of tungsten, it is possible to reduce rush current at the initial operation of the fixing device. Further, since the filament  210  of the fixing heater lamp  21  is made of tungsten, it is possible to maintain excellent heat response capability of the heater lamp while the heating roller  1  operates. 
   Since if the filaments of the plurality of heater lamps provided inside the roller body  10  are made of only Nichrome or Cantal, the temperature rises slowly compared with the heater lamp  21  made of tungsten, the temperature rising speed of the roller body  10  is remarkably deteriorated so that requirements for temperature rising time of the heating roller in the market cannot be met. 
   Specifically, although the rising time is preferably less than 30 seconds, in case of Nichrom or Cantal filaments, it takes more than 60 seconds. 
   Therefore, it is possible to meet the requirements of the rising time of the surface temperature of the heating roller  1  by using at least one of the heater lamps which is made of tungsten and it is possible to delicately control the surface temperature of the heating roller  1 . Further, even though the heater lamps are turned on at a state where the filament temperature is low, current flowing through the circuit does not become excessive. Especially, it is preferred that the filament of a heater lamp which is turned on while the fixing device is operated is made of tungsten. 
   According to the above described structure of the embodiment described above, since the tungsten filament is used for the fixing heater lamp  21  and the filament  220  whose resistivity value at room temperature is greater than that of tungsten is used as a heating element for an auxiliary heater lamp  22 , it is possible to prevent the problem that the rush current becomes excessive, and it is possible to provide a heating roller  1  with excellent heat response capability while the fixing device is operated. 
   Description of a second embodiment according to the present invention will be given below referring to FIG.  3 . In  FIG. 3 , a roller body  10  shown in  FIG. 1  is omitted and only heater lamps are shown. For the same elements as those shown in  FIG. 1 , in  FIG. 3 , the same reference numerals are used and explanation therefore is omitted. 
   Difference between the first and the second embodiments is that the auxiliary heater lamp  24  is also operated at time other than the temperature rising time while the fixing device is operated. 
   As shown in  FIG. 3 , a fixing heater lamp  23  and the auxiliary heater lamp  24  are provided inside the roller body  10 . Both heater lamps  23  and  24  are inserted inside the roller body  10  so that the tube axes of the heater lamps  23  and  24  are parallel to the longitudinal direction of the heating roller  1 . 
   The fixing heater lamp  23  and the auxiliary heater lamp  24  have a light emitting portion(s) and a non-light emitting portion(s). A light emitting portion  231  of a filament  230  of the fixing heater lamp  23  faces a non-light emitting portion  242  of a filament  240  of the auxiliary heater lamp  24 . Lighting portions  241  of the filament  240  of the auxiliary heater lamp  24  faces non-lighting portions  232  of the filament  230  of the fixing heater lamp  23 . In the fixing heater lamp  23 , the filament  230  made of tungsten in which potassium is doped at about 100 ppm is provided. In the auxiliary heater lamp  24 , the filament  240  which is a heating element made of, for example, Nichrome or Cantal. The heating element of the auxiliary heater lamp  24  has the resisitivity at a room temperature greater than that of tungsten. 
   The non-light emitting portion includes one that emits heat so that, to uniformly heat the heating cylindrical body, the heat release value per unit length from the non-light emitting portion is smaller than that from the light emitting portion. The non-light emitting portion may emit no light. 
   The fixing heater lamp  23  has the light emitting portion  231  corresponding to a paper sheet passing through area L 2  for a predetermined size paper sheet which is smaller than a paper sheet passing through area L 1  for a maximum size paper sheet. By emission of the light emitting portion  231 , the paper sheet passing through area L 2  for the smaller paper sheet is heated. On the other hand, the auxiliary heater lamp  24  has light emitting portions  241  in areas L 3  which is located outside the paper sheet passing through area L 2  for the predetermined size paper sheet and inside the largest size paper sheet passing through area L 1 . By emission of the light emitting portion  241 , the areas L 3  outside the predetermined size paper sheet passing through area L 2  for a maximum size paper sheet is heated. Thus, it is possible to heat, on the heating roller  1 , only area where a paper sheet passes through. 
   In the heating roller described above, it is preferably changed to the fixing device operating state for a short time as well as the first embodiment. 
   In the initial lamp lighting period, all the heater lamps are turned on by applying thereto input power equal to rated consumption electric power so as to heat the roller body  10 . Since the filament  240  of the auxiliary heater lamp  24  is a heating element whose resisitivity is greater than that of tungsten, it is possible to control rush current flowing through the auxiliary heater lamp  24  even when high power is applied to all the heater lamps. 
   Accordingly, it is possible to reduce rush current flowing through the entire circuit thereby reducing rush current. The material of the heating element as a filament of the auxiliary heater lamp  24  is, for example, Nichrom, Cantal, Tantalum, platinum, or graphite. Of course, it is possible to use other alloys. In such a heating roller  1  having the auxiliary heater lamp  24 , after the roller body  10  is sufficiently heated the auxiliary heater lamp  24  is turned on and off (a switching operation takes place) in accordance with areas L 1  to L 3  where the paper sheet passes through. 
   The fixing heater lamp  23  in which the light emitting portion  231  is provided corresponding to a paper sheet passing through area L 2  for the predetermined paper sheet, is always turned on despite the size of the paper sheet so as to heat the roller body  10 . The filaments of these heater lamp are made of tungsten so that it is possible to provide a heating roller  1  with high heat response capability. 
   EXAMPLE 
   A heating roller according to the second embodiment was prepared in the following specification: 
   Roller Body  10   
   Material: Iron 
   External Diameter: 35 mm 
   Internal Diameter: 33 mm 
   Length: 350 mm 
   Fixing Heater Lamp  23   
   Entire Length: 390 mm 
   Valve Material: Quartz glass 
   Valve External Diameter: 6 mm 
   Valve Radial Thickness: 1 mm 
   Filament Material: 50 to 90 ppm potassium doped 
   tungsten (Tungsten: more than 99.9%) 
   Filament Diameter (Wire Diameter): φ0.29 mm 
   Length of Light Emitting Portion: (L 1 ): 195 mm 
   Applied Power: 600 W (Voltage: 100 V) 
   Auxiliary Heater Lamp  24   
   Lamp Length: 390 mm 
   Valve Material: Quartz glass 
   Valve External Diameter: 6 mm 
   Valve Radial Thickness: 1 mm 
   Material of Filament: Cantal 
   Filament Diameter (Wire Diameter): φ0.5 mm, 
   Length of light emitting portion (L 2 ): 335 mm 
   Applied Power: 600 W (Voltage: 100 V) 
   Comparative Example 
   Except that the filament of the auxiliary heater lamp  24  was made of tungsten with the wire diameter φ0.29, a conventional heating roller having the same structure as that of the above embodiment was used. 
   Lamp Current Characteristic 
   The lamp current characteristics of the heating roller according to the present invention and the conventional heating roller were examined. When the temperature of the filament was about 20° C. (a room temperature) and stable, AC 600 W (100 V) power is applied, at the same time, to the heating rollers according to the present invention and the comparative example and held until the heater lamps are stabilized, and then rush current at an initial operation period and lamp current in the steady state while the lamp is turned on are measured and compared with each other. 
     FIGS. 4A and 4B  show lamp current characteristic at a power applied initial period. In  FIG. 4A , the lamp current characteristic of the heat roller in the comparative example is shown.  FIG. 4B  shows the lamp current characteristic of the heating roller according to the embodiment. 
   As shown in  FIG. 4A , the maximum value of lamp current (the amount of rush current) at the initial lighting operation of the heating roller according to the comparative example reached 10 times the amount of the lamp current in the steady state. On the other hand, in the heating roller according to the present invention, as shown in  FIG. 4B , the maximum value of lamp current (the amount of rush current) could be controlled so as to be, at the initial lighting operation, approximately 4 times the amount of lamp current in the steady state. 
   Rising Characteristic 
   In the experiment of rising characteristic of the heating rollers according to the present invention and comparative example when each of the heating rollers were turned on in the condition of AC 600 W, 100 V, it took 19 seconds for the heating roller according to the present invention to reach 160° C. which is a target outer surface temperature of the roller body, and it took 27 seconds for the heating roller according to the comparative example to reach 160° C. which is the target outer surface temperature of the roller body. The heating roller according to the present invention and the heating roller according to the comparative example sufficiently meet the demand in the market that the rising time is less than 30 seconds. 
   Although, as described above, as to the rising characteristic, the rising time of the heating roller according to the comparative example is shorter than that according to the present invention, in the heating roller according to the comparative example, the circuit of the comparative example can be in excess current status so that the device may be broken or flicker may occur. Therefore, judging in a comprehensive manner, it is found that the heating roller according to the present invention has advantages over the heating roller according to the comparative example, since the heating roller according to the present invention can reduce rush current without a particular circuit, breakdowns of the circuit due to excess current and flickers, and/or shorten the rising time to a certain period. 
   Although the embodiments according to the present invention are described above referring to the figures, it is not limited to the embodiments and possible to change them in various ways. For example, the number of the heater lamps is not limited to two (2) and may be more than three (3). In the embodiments, Cantal is used as a material of the filament of the heating roller, the heating element that has resistivity value greater than that of tungsten at a room temperature may be used thereby obtaining similar effects. That is, it is possible to reduce rush current in comparison with rush current in the steady state of lighting and also control the rising time of the heater to a certain rage demanded in the market. 
   Also, the structure of the heater lamp and the roller body may be changed in various ways if necessary and the structure thereof is not limited to that described above. For example, it is possible to select gas included in the valve if necessary and change the structure of the valve if necessary. Some methods for processing the surface and some materials of the filament allow to use the heating rollers in the atmosphere without forming the pinch seal portions. 
   As described above, according to the heating roller of the present invention, it is possible to reduce rush current at the initial power distribution period in a fixing device with a relatively simple structure. 
   The disclosure of Japanese Patent Application No. 2002-300150 filed on Oct. 15, 2002 including specification, drawings and claims is incorporated herein by reference in its entirety. 
   Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciated that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.