Patent Publication Number: US-8983350-B2

Title: Fixing device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2009-250238 filed Oct. 30, 2009. The entire content of the priority application is incorporated herein by reference. The present application closely relates to a co-pending US patent application (based on Japanese patent application No. 2009-250235 filed Oct. 30, 2009) which is incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a fixing device that thermally fixes a transferred developing agent image to a sheet. 
     BACKGROUND 
     A conventional fixing device includes a fusing film, a heater, a pressure roller, a heating plate (nip plate) defining a nip portion relative to the pressure roller through the fusing film, and a reflection plate for reflecting radiant heat from the heater to the nip plate. 
     SUMMARY 
     The heater such as a halogen heater includes a glass tube body in which a heat source and a gas are sealingly disposed. For the gas sealing, a tip portion protrudes radially outwardly from the glass tube body. The inventors of the present application found that the orientation of the tip portion is one of important factors for the fusing performance and size of the fixing device, since the orientation may have an impact on positions and size of the reflection plate and the nip plate. In view of the foregoing, it is an object of the invention to provide a compact fixing device capable of improving fusing performance. 
     In order to attain the above and other objects, the present invention provides a fixing device for thermally fixing a developing agent image to a sheet fed in a sheet feeding direction including: a tubular flexible fusing member; a nip plate; a heater; a reflection plate; and a backup member. The tubular flexible fusing member has an inner peripheral surface defining an internal space and an axis defining an axial direction. The nip plate is disposed in the internal space. The inner peripheral surface is in sliding contact with the nip plate. The heater is disposed in the internal space and confronts the nip plate in a confronting direction. The heater includes a glass tube, a heat source provided in the glass tube, and a gas sealed in the glass tube. The glass tube includes a glass tube body and a tip portion protruding radially outwardly from the glass tube body for sealing the gas in the glass tube body. The tip portion protrudes in a predetermined direction to define a cross-sectional length of the glass tube in the confronting direction smaller than a cross-sectional length of the glass tube in a perpendicular direction extending perpendicular to the confronting direction and the axial direction, and the cross-section includes the tip portion. The reflection plate is configured to reflect a radiant heat from the heater toward the nip plate. The backup member is configured to provide a nip region in cooperation with the nip plate for nipping the fusing member between the backup member and the nip plate. 
     According to another aspect, the present invention provides a fixing device for thermally fixing a developing agent image to a sheet fed in a sheet feeding direction including: a tubular fusing film; a nip member; and a heater. The tubular fusing film has an inner peripheral surface defining an internal space and an axis defining an axial direction. The nip member is disposed in the internal space. The inner peripheral surface is in sliding contact with the nip member. The heater is disposed in the internal space and confronts the nip member in a confronting direction. The heater includes a heating body and a projection protruding outwardly from the heating body in a perpendicular direction extending perpendicular to the confronting direction and the axial direction. The heater has a first length in the confronting direction and a second length in the perpendicular direction. The first length is smaller than the second length. 
     According to still another aspect, the present invention provides a fixing device for thermally fixing a developing agent image to a sheet fed in a sheet feeding direction including: a tubular fusing film; a nip member; and a heater. The tubular fusing film has an inner peripheral surface defining an internal space and an axis defining an axial direction. The nip member is disposed in the internal space. The inner peripheral surface is in sliding contact with the nip member. The heater is disposed in the internal space and confronts the nip member in a confronting direction. The heater includes a glass tube, a heat source provided in the glass tube, and a gas sealed in the glass tube. The glass tube includes a glass tube body and a tip portion protruding radially outwardly from the glass tube body for sealing the gas in the glass tube body. The heater has a first length in the confronting direction and a second length in a perpendicular direction extending perpendicular to the confronting direction and the axial direction. The first length is smaller than the second length. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a schematic cross-sectional view showing a structure of a laser printer having a fixing device according to one embodiment of the present invention; 
         FIG. 2  is a schematic cross-sectional view showing a structure of the fixing device according to the embodiment; 
         FIG. 3  is an exploded perspective view showing a halogen lamp, a nip plate, a reflection plate, and a stay; 
         FIG. 4  is a rear view showing an assembled state of the nip plate, the reflection plate and the stay; 
         FIG. 5A  is a schematic cross-sectional view of the fixing device in which a tip portion of the halogen lamp protrudes in a direction obliquely upward and frontward; 
         FIG. 5B  is a schematic cross-sectional view of the fixing device in which the tip portion of the halogen lamp protrudes horizontally rearward; and 
         FIG. 5C  is a schematic cross-sectional view of the fixing device in which two halogen lamps are juxtaposed with each other in a horizontal direction. 
     
    
    
     DETAILED DESCRIPTION 
     Next, a general structure of a laser printer as an image forming device according to one embodiment of the present invention will be described with reference to  FIG. 1 . The laser printer  1  shown in  FIG. 1  is provided with a fixing device  100  according to the embodiment of the present invention. A detailed structure of the fixing device  100  will be described later while referring to  FIGS. 2 to 5C . 
     &lt;General Structure of Laser Printer&gt; 
     As shown in  FIG. 1 , the laser printer  1  includes a main frame  2  with a movable front cover  21 . Within the main frame  2 , a sheet supply unit  3  for supplying a sheet P, an exposure unit  4 , a process cartridge  5  for transferring a toner image (developing agent image) on the sheet P, and the fixing device  100  for thermally fixing the toner image onto the sheet P are provided. 
     Throughout the specification, the terms “above”, “below”, “right”, “left”, “front”, “rear” and the like will be used assuming that the laser printer  1  is disposed in an orientation in which it is intended to be used. More specifically, in  FIG. 1 , a left side and a right side are a rear side and a front side, respectively. 
     The sheet supply unit  3  is disposed at a lower portion of the main frame  2 . The sheet supply unit  3  includes a sheet supply tray  31  for accommodating the sheet P, a lifter plate  32  for lifting up a front side of the sheet P, a sheet supply roller  33 , a sheet supply pad  34 , paper dust removing rollers  35 ,  36 , and registration rollers  37 . Each sheet P accommodated in the sheet supply tray  31  is directed upward to the sheet supply roller  33  by the lifter plate  32 , separated by the sheet supply roller  33  and the sheet supply pad  34 , and conveyed toward the process cartridge  5  passing through the paper dust removing rollers  35 ,  36 , and the registration rollers  37 . 
     The exposure unit  4  is disposed at an upper portion of the main frame  2 . The exposure unit  4  includes a laser emission unit (not shown), a polygon mirror  41 , lenses  42 ,  43 , and reflection mirrors  44 ,  45 ,  46 . In the exposure unit  4 , the laser emission unit is adapted to project a laser beam (indicated by a dotted line in  FIG. 1 ) based on image data so that the laser beam is deflected by or passes through the polygon mirror  41 , the lens  42 , the reflection mirrors  44 ,  45 , the lens  43 , and the reflection mirror  46  in this order. A surface of a photosensitive drum  61  is subjected to high speed scan of the laser beam. 
     The process cartridge  5  is disposed below the exposure unit  4 . The process cartridge  5  is detachable or attachable relative to the main frame  2  through a front opening defined by the front cover  21  at an open position. The process cartridge  5  includes a drum unit  6  and a developing unit  7 . 
     The drum unit  6  includes the photosensitive drum  61 , a charger  62 , and a transfer roller  63 . The developing unit  7  is detachably mounted to the drum unit  6 . The developing unit  7  includes a developing roller  71 , a toner supply roller  72 , a regulation blade  73 , and a toner accommodating portion  74  in which toner (developing agent) is accommodated. 
     In the process cartridge  5 , after the surface of the photosensitive drum  61  has been uniformly charged by the charger  62 , the surface is subjected to high speed scan of the laser beam from the exposure unit  4 . An electrostatic latent image based on the image data is thereby formed on the surface of the photosensitive drum  61 . The toner accommodated in the toner accommodating portion  74  is supplied to the developing roller  71  via the toner supply roller  72 . The toner is conveyed between the developing roller  71  and the regulation blade  73  so as to be deposited on the developing roller  71  as a thin layer having a uniform thickness. 
     The toner deposited on the developing roller  71  is supplied to the electrostatic latent image formed on the photosensitive drum  61 . Hence, a visible toner image corresponding to the electrostatic latent image is formed on the photosensitive drum  61 . Then, the sheet P is conveyed between the photosensitive drum  61  and the transfer roller  63 , so that the toner image formed on the photosensitive drum  61  is transferred onto the sheet P. 
     The fixing device  100  is disposed rearward of the process cartridge  5 . The toner image (toner) transferred onto the sheet P is thermally fixed on the sheet P while the sheet P passes through the fixing device  100 . The sheet P on which the toner image is thermally fixed is conveyed by conveying rollers  23  and  24  so as to be discharged on a discharge tray  22 . 
     &lt;Detailed Structure of Fixing Device&gt; 
     As shown in  FIG. 2 , the fixing device  100  includes a flexible tubular fusing member such as a tube or film  110 , a halogen lamp (halogen heater)  120 , a nip plate (nip member)  130 , a reflection plate  140 , a pressure roller  150  as a backup member, and a stay  160 . 
     In the following description, a frontward/rearward direction will be simply referred to as a sheet feeding direction; a widthwise direction of the sheet P (a lateral or rightward/leftward direction) will be simply referred to as a widthwise direction; and a direction such that the nip plate  130  confronts the halogen lamp  120  (a vertical direction) will be simply referred to as a confronting direction. 
     The fusing film  110  is of a tubular configuration having heat resistivity and flexibility. Each widthwise end portion of the fusing film  110  is guided by a guide member (not shown) fixed to a casing (not shown) of the fixing device  100  so that the fusing film  110  is circularly movable. 
     The halogen lamp  120  is a heater to heat the nip plate  130  and the fusing film  110  for heating toner on the sheet P. The halogen lamp  120  is positioned at an internal space of the fusing film  110  and is spaced away from an inner surface of the nip plate  130  by a predetermined distance. The halogen lamp  120  includes a glass tube (heating body)  121 , and a filament  122  as a heat source disposed at an internal space of the glass tube  121 . Halogen gas  123  is sealed in the glass tube  121 . 
     The glass tube  121  has a glass tube body  121 ′ and a tip portion (projection)  124  protruding radially outwardly from the glass tube body  121 ′. The tip portion  124  is inevitably formed for sealing the halogen gas  123  in the glass tube  121 . The glass tube  121  is oriented such that the tip portion  124  protrudes frontward (upstream of the glass tube body  121 ′ in the sheet feeding direction), so that a combination of the glass tube body  121 ′ and the tip portion  124  defines a vertical cross-sectional length L 1  in the confronting direction smaller than a cross-sectional length L 2  in the sheet feeding direction. 
     The nip plate  130  is adapted for receiving pressure from the pressure roller  150  and for transmitting radiant heat from the halogen lamp  120  to the toner on the sheet P through the fusing film  110 . To this effect, the nip plate  130  is stationarily positioned such that an inner peripheral surface of the fusing film  110  is moved slidably therewith through grease. 
     The nip plate  130  has a generally U-shaped cross-section made from a material such as aluminum having a thermal conductivity higher than that of the stay  160  (described later) made from steel. More specifically, for fabricating the nip plate  130 , an aluminum plate is bent into U-shape to provide a base portion  131  and upwardly folded portions  132 . 
     The base portion  131  has a center portion  131 A in the sheet feeding direction and end portions  131 B. The center portion  131 A is protruding toward the pressure roller  150 , and has an inner surface painted with a black color or provided with a heat absorbing member so as to efficiently absorb radiant heat from the halogen lamp  120 . One of the end portions  131 B provided at a position frontward of the center portion  131 A has a length in the sheet feeding direction greater than remaining one of the end portions  131 B provided at a position rearward of the center portion  131 A. With this arrangement, preheating to the fusing film  110  described later can be attained. 
     As shown in  FIG. 3 , the nip plate  130  has a right end portion provided with an insertion portion  133  extending flat, and a left end portion provided with an engagement portion  134 . The engagement portion  134  has U-shaped configuration as viewed from a left side including side wall portions  134 A extending upward and formed with engagement holes  134 B. 
     The reflection plate  140  is adapted to reflect radiant heat radiating in the frontward/rearward direction and the upper direction from the halogen lamp  120  toward the nip plate  130  (toward the inner surface of the base portion  131 ). As shown in  FIG. 2 , the reflection plate  140  is positioned within the fusing film  110  and surrounds the halogen lamp  120 , with a predetermined distance therefrom. Thus, radiant heat from the halogen lamp  120  can be efficiently concentrated onto the nip plate  130  to promptly heat the nip plate  130  and the fusing film  110 . 
     Because of the above-described difference in length L 1  and L 2 , a top wall  141 B of the reflection plate  140  and a top wall  166  of the stay  160  as well as the nip plate  130  can be positioned as close as possible to the surface of the glass tube body  121 ′. Thus, a compact halogen lamp  120  in the upward/downward direction can be provided, which leads to a compact fixing device  100  in the upward/downward direction. 
     Further, the tip portion  124  protrudes horizontally frontward. To this effect, the nip plate  130  has a front elongated portion (front end portion  131 B) extending frontward from the nip region N 1 . The front elongated portion can function as a preheat portion in contact with the inner peripheral surface of the fusing film  110  for preheating a portion of the fusing film  110 , the portion being immediately upstream of the nip region N 1 . 
     Here, the nip region N 1  nips the sheet P between the nip plate  130  (more specifically, the fusing film  110 ) and the pressure roller  150  to transfer heat of the fusing film to the sheet P. The center of the nip region N 1  in the sheet feeding direction is positioned in alignment with the axis of the glass tube body  121 ′ and the axis of the pressure roller  150 . Thus, the halogen lamp  120  can efficiently heat the nip region N 1 . Since the tip portion  124  is provided at a position frontward of the glass tube body  121 ′, the front elongated portion of the nip plate  130  extends frontward from the nip region N 1 . Hence, preheating to the fusing film  110  can be attained by the front elongated portion, thereby improving image-fixing performance. 
     The reflection plate  140  is configured into U-shape in cross-section and is made from a material such as aluminum having high reflection ratio regarding infrared ray and far infrared ray. The reflection plate  140  has a U-shaped reflection portion  141  including front and rear side walls  141 A, the top portion  141 B, and a flange portion  142  extending from each end portion of the reflection portion  141  in the sheet feeding direction. The reflection plate  140  has a vertical cross-sectional length L 3  in the confronting direction, that is, a vertical length defined between the top portion  141 B and the flange portion  142 , and a horizontal cross-sectional length L 4  in the sheet feeding direction, that is a horizontal length defined between the front and rear side walls  141 A. The vertical cross-sectional length L 3  is smaller than the horizontal cross-sectional length L 4 . A mirror surface finishing is available on the surface of the aluminum reflection plate  140  for specular reflection in order to enhance heat reflection ratio. As shown in  FIG. 3 , two engagement sections  143  are provided at each widthwise end of the reflection plate  140 . Each engagement section  143  is positioned higher than the flange portion  142 . 
     The pressure roller  150  is positioned below the nip plate  130  and nips the fusing film  110  in cooperation with the nip plate  130  to provide a nip region N 1  for nipping the sheet P between the pressure roller  150  and the fusing film  110 . In other words, the pressure roller  150  presses the nip plate  130  through the fusing film  110  for providing the nip region N 1  between the pressure roller  150  and the fusing film  110 . 
     The pressure roller  150  is rotationally driven by a drive motor (not shown) disposed in the main frame  2 . By the rotation of the pressure roller  150 , the fusing film  110  is circularly moved along the nip plate  130  because of a friction force generated therebetween or between the sheet P and the fusing film  110 . A toner image on the sheet P can be thermally fixed thereto by heat and pressure during passage of the sheet P at the nip region N 1  between the pressure roller  150  and the fusing film  110 . 
     The stay  160  is adapted to support the end portions  131 B of the nip plate  130  for maintaining rigidity of the nip plate  130 . The stay  160  has a U-shape configuration in conformity with the outer shape of the reflection portion  141  covering the reflection plate  140 . For fabricating the stay  160 , a highly rigid member such as a steel plate is folded into U-shape to have a top wall  166 , a front wall  161  and a rear wall  162 . As shown in  FIG. 3 , each of the front wall  161  and the rear wall  162  has a lower end portion provided with comb-like contact portions  163 . 
     As a result of assembly of the nip plate  130  together with the reflection plate  140  and the stay  160 , the comb-like contact portions  163  are nipped between the right and left engagement sections  143 . That is, the right engagement section  143  is in contact with the rightmost contact portion  163 A, and the left engagement section  143  is in contact with the leftmost contact portion  163 A. As a result, displacement of the reflection plate  140  in the widthwise direction due to vibration caused by operation of the fixing device  100  can be restrained by the engagement between the engagement sections  143  and the comb-like contact portions  163 A. 
     The front and rear walls  161 ,  162  have right end portions provided with L shaped engagement legs  165  each extending downward and then leftward. The insertion portion  133  of the nip plate  130  is insertable into a space between the confronting engagement legs  165  and  165 . Further, each end portion  131 B of the base portion  131  is abuttable on each engagement leg  165  as a result of the insertion. 
     The top wall  166  has a left end portion provided with a retainer  167  having U-shaped configuration. The retainer  167  has a pair of retaining walls  167 A whose inner surfaces are provided with engagement bosses  167 B each being engageable with each engagement hole  134 B. 
     As shown in  FIGS. 2 and 3 , each widthwise end portion of each of the front wall  161  and the rear wall  162  has an inner surface provided with two abutment bosses  168  protruding inward in abutment with front and rear side walls of the reflection plate  140  in the sheet feeding direction. Therefore, displacement of the reflection plate  140  in the sheet feeding direction due to vibration caused by operation of the fixing device  100  can be restrained because of the abutment of the reflection portion  141  with the bosses  168 . 
     Assembling procedure of the reflection plate  140  and the nip plate  130  to the stay  160  will be described. First, the reflection plate  140  is temporarily assembled to the stay  160  by the abutment of the outer surface of the reflection portion  141  on the abutment bosses  168 . In this case, the engagement sections  143  are in contact with the widthwise endmost contact portions  163 A. 
     Then, as shown in  FIG. 4 , the insertion portion  133  is inserted between the engagement legs  165  and  165 , so that the base portion  131  can be brought into engagement with the engagement legs  165 . Thereafter, the engagement bosses  167 B are engaged with the engagement holes  134 B. By this engagement, each flange portion  142  is sandwiched between the nip plate  130  and the stay  160 . Thus, the nip plate  130  and the reflection plate  140  are held to the stay  160 . 
     Vertical displacement of the reflection plate  140  due to vibration caused by operation of the fixing device  100  can be restrained, since the flange portions  142  are held between the nip plate  130  and the stay  160  as shown in  FIG. 2 . Thus, position of the reflection plate  140  relative to the nip plate  130  can be fixed. 
     Incidentally, the stay  160  holding the nip plate  130  and the reflection plate  140  and the halogen lamp  120  are held to the guide member (not shown) that guides circular movement of the fusing film  110 . The guide member is fixed to the main casing (not shown) of the fixing device  100 . Thus, the fusing film  110 , the halogen lamp  120 , the nip plate  130 , the reflection plate  140 , and the stay  160  are held to the main casing of the fixing device  100 . 
     Various modifications are conceivable. For example, in the above-described embodiment, the tip portion  124  protrudes horizontally frontward or is positioned upstream of the glass tube body  121 ′ in the sheet feeding direction. However, protruding direction of the tip portion  124  is not limited to the depicted embodiment. For example, the tip portion  124  can protrude in a direction obliquely upward and frontward as shown in  FIG. 5A , or horizontally rearward as shown in  FIG. 5B , i.e., is positioned downstream of the glass tube body  121 ′ in the sheet feeding direction, as long as the relationship L 1 &lt;L 2  is satisfied. In  FIG. 5A , the tip portion has a portion not overlapping with the glass tube body as viewed in the confronting direction. The tip portion also has a portion not overlapping with the glass tube body as viewed in the sheet feeding direction. 
     Further, as shown in  FIG. 5C , two halogen lamps  120  can be juxtaposed with each other in the vertical direction (confronting direction) so as to accelerate heating to the nip plate  130 . In this case, a tip portion  124  of one of the halogen lamps  120  protrudes rearward or is positioned downstream of the glass tube body  121 ′ in the sheet feeding direction, and another tip portion  124  of remaining one of the halogen lamps  120  protrudes frontward or is positioned upstream of the glass tube body  121 ′ in the sheet feeding direction. With this arrangement, the halogen lamps  120  can be vertically closer to each other in comparison with a case where two halogen lamps  120  are juxtaposed such that a glass tube body  121 ′ of one of the halogen lamps  120  is vertically aligned with another glass tube body  121 ′ of remaining one of the halogen lamps  120 . Hence, heating performance can be improved without enlarging the fixing device  100 . 
     The fusing film  110  can be formed of resin or metal. Alternatively, the fusing film  110  can be provided with an outer rubber layer. 
     In the depicted embodiment, the stay  160  can be dispensed with. Further, an infrared ray heater or a carbon heater is available instead of the halogen lamp  120 . 
     In the depicted embodiment, the pressure roller  150  is employed as a backup member. However, a belt like pressure member is also available. Further, in the depicted embodiment, the nip region N 1  is provided by the pressure contact of the backup member (pressure roller  150 ) against the nip plate  130 . However, the nip region N 1  can also be provided by a pressure contact of the nip plate  130  against the backup member. 
     Further, the sheet P can be an OHP sheet instead of plain paper and a postcard. 
     Further, in the depicted embodiment, the image forming device is the monochromatic laser printer. However, a color laser printer, an LED printer, a copying machine, and a multifunction device are also available. 
     While the invention has been described in detail with reference to the embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention.