Abstract:
The work involved in replacing the fixing lamps in a printer is made easy, and the non-operational period of the printer associated with such maintenance work is shortened. A portion of a fixing lamp is formed in a lamp cartridge which includes a first lamp holder for holding one end of the fixing lamp; a second lamp holder for holding the other end of the fixing lamp; and a protective member holding portion for holding a lamp protective member which is attached depending on necessity. The protective member holding portion is arranged around a region where the lamp holding member is placed, and, thereby, all of the plurality of fixing lamps are capable of being attached to and removed from the heating roller as a unit from one end of the heating roller.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a fixing unit for fixing a toner image onto a print material, and to a lamp holder, a lamp cartridge using the lamp holder and a fixing unit using the lamp holder. 
     As fixing units of a printer, typical of a laser printer, a copier machine and the like, there is known a fixing unit in which print material holding a toner image is heated and pressed while it is being transferred between a heating roller and a pressing roller to fix the toner image onto the print material. Lamps operating as a heat source are located inside of the heating roller, and in general, the number of the lamps placed inside the heating roller is increased as the printing speed of the printer is increased. 
     In the use of such a heating roller having a plurality of lamps, when the heating roller is exchanged due to, for example, the expiration of the lifetime of the heating roller, the roller is replaced by a new heating roller by removing the lamps one by one and then removing the heating roller from the fixing unit. Therefore, the amount of work required to detach and attach the lamps from and to the heating roller is in proportion to the number of lamps, and, accordingly, the work efficiency of this maintenance task has been low. 
     A structure to solve such a problem is proposed, for example, in published Japanese PCT international publication for patent application No.5-504633(1997). According to Japanese PCT international publication for patent application No.5-504633, the disclosed structure is designed such that the lamps can be pulled off from the back side of the fixing unit in a state in which the heating roller remains attached to the fixing unit. 
     lamp used in a fixing unit of this kind has a long and slender shape with a diameter about 10 mm and a length above 600 mm. In the case of the structure disclosed in Japanese PCT international publication for patent application No.5-504633, because the attaching and removing of the lamps to and from the heating roller is performed in a state in which the lamps are exposed, there has been a problem in that the lamp surface is scratched or the lamps are broken due to contact between the lamps and the edge of the heating roller or between the lamps and other parts, when the lamps are being attached to or removed from the heating roller. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to make the work of replacing the fixing lamps easy and to shorten the non-operational time period of the printer associated with the maintenance work. 
     Further, another object of the present invention is to hold the fixing lamps attached inside the heating roller in a correct position without displacement in the heating roller. 
     The above object can be attained by a fixing unit comprising a heating roller having a plurality of fixing lamps inside; and a pressing roller arranged so as to be capable of pressing against the heating roller, a print material having a toner image being transferred between said heating roller and the pressing roller to fix the toner image onto the print material, wherein the fixing lamps are formed as a lamp cartridge which comprises a first lamp holder for holding one end of the fixing lamps; a second lamp holder for holding the other end of the fixing lamps; and a protective member holding portion for holding a lamp protective member which is attached to the heating roller depending on necessity. The protective member holding portion is arranged around a region where the lamp holding member is placed, whereby all of the plurality of fixing lamps are capable of being attached to and removed from the heating roller together from one end of the heating roller. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view showing the overall structure of an embodiment of a lamp cartridge in accordance with the present invention. 
     FIG. 2 is an exploded perspective view showing a first embodiment of a lamp cartridge in accordance with the present invention. 
     FIG. 3 is an exploded perspective view showing a second embodiment of a lamp cartridge in accordance with the present invention. 
     FIG. 4 is a rear view showing the first embodiment of the lamp cartridge. 
     FIG. 5 is a cross-sectional view showing an embodiment of a heating roller. 
     FIG. 6 is a cross-sectional view showing the heating roller in a state in which a lamp protective member is inserted into the heating roller. 
     FIG. 7 is a perspective view showing the overall structure of the lamp cartridge over which the lamp protective member is attached. 
     FIG. 8 is a diagrammatic view showing the overall construction of a printer. 
     FIG. 9 is a cross-sectional view showing another embodiment of a heating roller. 
     FIG. 10 is a cross-sectional view showing the heating roller in a state in which a lamp protective member is inserted into the heating roller. 
     FIG. 11 is a cross-sectional view showing the main portion of the heating roller in the state that a lamp protective member is inserted into the heating roller. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments in accordance with the present invention will be described below with reference to the accompanying drawings. 
     Initially, as an example of a printer to which the present invention is applied, a laser beam printer using electrophotography will be described with reference to FIG.  8 . 
     In FIG. 8, the reference character  1  is the laser beam printer, in which a photosensitive drum  21  is rotated in the direction shown by an arrow based on a print operation start signal from a controller  22 . The photosensitive drum  21  is rotated at a speed corresponding to a printing speed of the laser beam printer  1  and continues to be rotated until the print operation is completed. As rotation of the photosensitive drum  21  is started, a high voltage is applied to a corona charger  2  to uniformly charge the surface of the photosensitive drum  21 , for example, with positive charges. 
     A rotating polygon mirror  3  starts to rotate immediately after the switching on of the power to the laser beam printer  1 , and it is rotated at a constant speed with a high accuracy while the power is supplied. A light beam emitted from a light source  4 , such as a semiconductor laser, is reflected by the rotating polygon mirror  3 , which operates to irradiate and scan the beam on the surface of the photosensitive drum  21 , after the beam has passed through an fθ lens  5 . 
     As character data and pattern data converted into dot images are transmitted to the laser beam printer from the controller  22  as ON/OFF signals of the laser beam, portions irradiated by the laser beam and portions not irradiated by the laser beam are formed on the surface of the photosensitive drum  21  to form a so-called electrostatic latent image. When the area of the photosensitive drum holding the electrostatic latent image arrives at a position opposite to a developing unit  6 , toner is supplied onto the electrostatic latent image, and a toner image is formed on the surface of the photosensitive drum  21  by attracting the toner charged with, for example, positive charges to the positions on the surface of the photosensitive drum  21  where charges are eliminated by the irradiation of the laser beam. 
     A continuous paper sheet  7  contained in a paper hopper  11  is transported by a paper transport tractor  8  toward a gap between the photosensitive drum  21  and a transfer unit  10  in synchronism with a timing at which the toner image of the print data formed on the surface of the photosensitive drum  21  arrives at the transfer position. 
     The toner image formed on the surface of the photosensitive drum  21  is attracted to the paper sheet  7  by the operation of the transfer unit  10  applying charges having a polarity inverse to the polarity of charges of the toner image on the rear surface side of the paper sheet  7 . 
     As described above, the paper sheet  7  set in the paper hopper  11  is transported to a fixing unit  12  through the paper transport tractor  8 , the transfer unit  10 , a paper transport tractor  9  and a buffer plate  24 . The paper sheet  7  arriving at the fixing unit  12  is pre-heated by a per-heater  13 , and then driven between and transported by a nip portion constructed of a pair of fixing rollers composed of a heating roller  14  having a fixing lamp (hereinafter, referred to as “heater lamp”) and a pressing roller  15 , so that it is heated and pressed by the nip portion to melt-fix the toner image onto the paper sheet  7 . 
     The paper sheet  7  delivered by the heating roller  14  and the pressing roller  15  is dispensed to a stacker table  19  by a paper conveying roller  16 , and, alternatively, it is folded along the tear-off edge by a swinging operation of a swing fin  17 , and further the folding state of the paper sheet is prepared by rotating paddle  18  and stacked on the stacker table  19 . The area of the surface of the photosensitive drum  21  which has passed through the transfer position is cleaned by a cleaning unit  20  so as to be prepared for the next print operation. 
     In FIG. 8, the reference character  23  denotes a display screen for displaying information based on the state of the laser beam printer  1  during the print operation. The buffer plate  24  described above is used for absorbing the slack or the tension caused in the paper sheet  7  when a difference in the paper transporting speed occurs between the paper transport tractor  9  and the fixing rollers  14 ,  15 . The reference character  26  indicates a web member for cleaning the surface of the heating roller  14  and for applying an erasing agent onto the surface of the heating roller  14 , and the web member  26  is arranged so that it may contact the surface of the heating roller  14  and may be wound. 
     Referring to FIG. 1, the structure of the lamp cartridge which comprises the present invention will be described in detail below. 
     The lamp cartridge  27  is composed of a plurality of heater lamps  25  (four heater lamps in the present embodiment) of the type described with reference to FIG. 8, a first lamp holder  28  for holding one end of each of the heater lamps  25 , a second lamp holder  29  for holding the other end of each of the heater lamps  25 , and a protective member holding portion  30  arranged around the heater lamps  25  held by the first lamp holder  28 . The protective member holding portion  30  is provided for holding a lamp protective member, to be described later, when the protective member is attached, and the protective member holding portion  30  in the present embodiment is formed of a tapered surface, though the invention is not limited particularly to this structure. 
     As shown in FIG. 2, the first lamp holder  28  comprises holes  31 , into each of which one end of a heater lamp  25  is inserted; and a hole  32  for inserting a spacer  33  thereinto. All the holes  31  and the hole  32  are through-holes. Accordingly, when a heater lamp  25  is inserted into the hole  31 , a power supply wire provided for each of the heater lamps can be led to the outside through the hole  31  (refer to FIG.  5 ). The spacer  33  is fit into the hole  32 . 
     The heater lamps  25  are inserted into the holes  31 , and then the parts are fixed with a screw  37  by fastening the lamp holder  28  between a plate  34  and a plate  36 . In FIG. 2, the reference character  35  indicates springs. The springs  35  are placed in a groove formed in the rear side of the lamp holder  28  so that backlash and play of the heater lamps in the holes  31  are prevented by applying a pushing force between the two heater lamps in opposite directions to each other. 
     FIG. 4 shows the rear portion of the lamp holder  28  (a front view showing the lamp holder from the direction of the screw  37  in FIG.  2 ). In FIG. 4, the reference character  38  indicates the grooves for accommodating the springs  35 . The reference character  39  denotes a depressed portion formed in the front surface portion of the lamp holder  28 . The depressed portion  39  is provided in order to prevent the lamp cartridge attached to the heating roller from being turned. The position of the lamp cartridge  27  is restricted by fitting a stopping member  65  (refer to FIG.  9  and FIG. 10) arranged in the main body of the fixing unit into the depressed portion  39 , and the restriction of the circumferential position of the lamp cartridge  27  is released by drawing back the stopping member  65  from the depressed portion  39 . 
     On the other hand, as shown in FIG. 3, the second lamp holder  29  comprises holes  40 , into each of which the other end of a heater lamp  25  is inserted; and a hole  41  for inserting a spacer  42  thereinto. All the holes  31  and the hole  32  are through-holes similar to the first lamp holder  28 . Accordingly, when a heater lamp  25  is inserted into the hole  40 , a power supply wire  63  (refer to FIG.  5  and FIG. 9) provided for each of the heater lamps can be led to the outside through the hole  40 . The spacer  42  is fit into the hole  41 . 
     The heater lamps  25  are inserted into the holes  40 , and then the parts are fixed with a screw  45  by fastening the second lamp holder  29  between a plate  43  and a plate  44 . The second lamp holder  29  may be provided with springs similar to the first lamp holder  28 , if necessary. 
     Referring to FIG. 5, the construction around the heating roller in the state of mounting of the lamp cartridge will be described below. 
     The heating roller  14  is composed of a metallic base pipe  14   a  made of, for example, aluminum, and a surface layer  14   b  made of Teflon, silicon rubber or the like provided on the base pipe  14   a , and absorbers  14   c  for preventing heat dissipation are arranged in the inner end portions of the base pipe  14   a . Both ends of the base pipe  14   a  are supported on a frame  50  of the fixing unit through holding members  48 ,  49  having centering members  46 ,  47 , respectively. 
     A bearing  51  is arranged in the holding member  48 , and the bearing  51  is coupled with the heating roller  14  along with the centering member  46 . Further, the bearing  51  is disposed so that the thermal expansion of the heating roller  14  and deviations in dimensions of the surrounding supporting members can be absorbed using a plurality of springs  52  and a guide plate  53 . The holding member  48  is fixed to the frame  50  using wing screws  54 . On the other hand, a gear  55  for receiving a drive force from a drive motor (not shown) for driving the heating roller  14  is arranged in the holding member  49 , and the gear  55  is supported by two housings  58 ,  59  containing bearings  56 ,  57 . 
     A projection  60  is provided in each of the centering members  46 ,  47  in order to secure coupling with the heating roller  14 , and each projection  60  is engaged with one of the grooves  61  provided at both ends of the heating roller  14 . 
     Further, in order to prevent heat from flowing out from the heating roller  14  to the centering members  46 ,  47  and to prevent damage in the engaging portion of the projection  60  and the groove  61 , collars  62  made of a heat resistant plastic are inserted between both end portions of the heating roller  14  and the centering members  46 ,  47 . In FIG. 5, the lines led out from both end portions of the lamp cartridge  27 , indicated by the reference characters  63 , are the power supply wires of the heater lamps  25 . 
     In the construction described above, the lamp cartridge  27  is inserted through a hole  48   a  formed in the holding member  48  and is attached inside the heating roller  14 , as shown in FIG.  5 . The reason why the shape of the first lamp holder  28  is different from the shape of the second lamp holder  29  is to prevent erroneous insertion of the lamp cartridge  27 . 
     When the lamp cartridge  27  is to be pulled out of the heating roller  14 , an operator comes to the rear side (the side where the second lamp holder  29  exists) of the printer and inserts a cylindrical member  64  of a lamp protective member through a through hole  59   a  formed in the housing  59 , as shown in FIG.  6 . Then the operator pushes in the cylindrical member  64  until the inner front end peripheral surface of the cylindrical member  64  is held by the tapered surface  30  provided in the first lamp holder  28 . 
     After the setting of the cylindrical member  64  is completed, the operator moves to the front side of the printer and draws back the stopping member described above from the depressed portion  39  of the first lamp holder  28  to release the positional restriction of the lamp cartridge  27 . 
     As the lamp cartridge  27  in this state is drawn out, the lamp cartridge  27  and the cylindrical member  64  are drawn out together and removed to the outside in the state as shown in FIG.  7 . 
     Further, when the lamp cartridge  27  is inserted into the heating roller  14 , the lamp cartridge  27  in the state as shown in FIG. 7 is loaded from the front side of the printer, and the stopping member  65  is moved on the depressed portion  39  of the first lamp holder  28  to restrict the position of the lamp cartridge  27 . After that, the operator comes to the rear side of the printer and draws off the cylindrical member  64 , so that only the lamp cartridge  27  remains inside the heater roller to complete the work of attaching the lamp cartridge  27 . 
     FIG.  9  and FIG. 10 show a more practically preferable embodiment having a construction obtained by modifying the above-mentioned construction. Here, the key difference is that the second lamp holder  29  as part of the lamp cartridge  27  engages in a depressed portion  59   b  provided in the inner peripheral portion of a through hole  59   a  of the housing  59 . The depressed portion  59   b  forms the lamp holder means in the present invention, and the lamp cartridge  27  is restricted in its movement in the axial direction as the second lamp holder  29  becomes engaged in the depressed portion  59   b.    
     In the case of the construction shown in FIG.  9  and FIG. 10, when the lamp cartridge  27  is to be pulled out of the heating roller  14 , an operator comes to the rear side (the side where the second lamp holder  29  exists) of the printer and inserts a cylindrical member  64 , which serves as a lamp protective member, through a through hole  59   a  formed in a housing  59 , as shown in FIG.  10 . The operator then pushes in the cylindrical member  64  until the inner front end peripheral surface of the cylindrical member  64  is held by the tapered surface  30  provided in the first lamp holder  28 . 
     As the cylindrical member  64  is inserted in the state described above, the front end of the cylindrical member  64  picks up the second lamp holder  29  and disengages it from the depressed portion  59   b , so as to release the positional restriction of the lamp cartridge  27  against movement in the axial direction caused by the depressed portion  59   b.    
     As described above, according to the present invention, since the fixing lamps are protected by the lamp protective member when the fixing lamps are attached to and removed from the heating roller, the attaching and removing of the fixing lamps can be performed efficiently and safely. 
     Further, since the fixing lamps attached inside the heating roller are held at the correct position inside the heating roller without displacement, the range of the heating region in the axial direction of the heating roller becomes stable, and, accordingly, any fixing deficiency caused by over heating or insufficient heating can be reduced.