Abstract:
An image forming device includes a main body having a main frame, a plurality of photosensitive members, a conveying unit that conveys a recording medium onto which images are transferred from the photosensitive members, a fixing unit that fixes the images onto the recording medium, and an attaching member that attaches both the fixing unit and an end section of the conveying unit nearest the fixing unit to the main frame.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2009-041886 filed Feb. 25, 2009. The entire content of this priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an image forming device, such as a laser printer. 
     BACKGROUND 
     There has been known a direct tandem type laser printer capable of forming color images. This type of laser printer includes a plurality of process cartridges arranged in a substantially horizontal direction, a conveying unit disposed below the process cartridges, and a fixing unit, all accommodated in a main casing having a main frame. 
     Each of the process cartridges includes a photosensitive drum on which a toner image is formed. The conveying unit includes a drive roller, a support roller, and an endless belt wound on the drive roller and the support roller. The toner image formed on each photosensitive drum is transferred onto a recording paper supported on the belt as the recording paper is conveyed by the rotation of the belt. 
     The fixing unit is disposed on a downstream side of the conveying unit in a paper conveying direction. The fixing unit includes a heat roller, a pressure roller pressing against the heat roller, and a guide member. The recording paper conveyed by the conveying unit is guided by the guide member to a nip point between the heat roller and the pressure roller, and the toner image transferred on the recording paper is fixed onto the recording paper as the recording paper passes through the nip point. 
     SUMMARY 
     It is an object of the present invention to provide an image-forming device capable of improving the precision in fixing the relative positions of a conveying unit and a fixing unit and the relative positions of the conveying unit and a guide member provided between the conveying unit and the fixing unit. 
     In order to attain the above and other objects, the present invention provides an image forming device including a main frame, a plurality of photosensitive members, a conveying unit, a fixing unit, and an attaching member. The main body has a main frame, and the plurality of photosensitive members are arrayed in the main body. The conveying unit is disposed in the main body so as to confront the plurality of photosensitive members. The conveying unit conveys a recording medium with images transferred from the photosensitive members. The fixing unit is disposed in the main body, and receives the recording medium conveyed by the conveying unit, and fixes the images onto the recording medium. The attaching member attaches both the fixing unit and an end section of the conveying unit nearest the fixing unit to the main frame. 
     According to another aspect, the present invention provides an image forming device including a main body, a plurality of photosensitive members, a conveying unit, a fixing unit, a first guide, and an attaching member. The main body has a main frame, and the plurality of photosensitive members are arrayed in the main body. The conveying unit is disposed in the main body so as to confront the plurality of photosensitive members. The conveying unit conveys a recording medium with images transferred from the photosensitive members. The fixing unit is disposed in the main body, receives the recording medium conveyed by the conveying unit, and fixes the images onto the recording medium. The first guide is disposed between the conveying unit and the fixing unit, and guides the recording medium from the conveying unit toward the fixing unit. The attaching member attaches both the first guide and an end section of the conveying unit nearest the fixing unit to the main frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is an illustrative cross-sectional right-side view of a printer according to an embodiment of the present invention; 
         FIG. 2  is a perspective view of main components accommodated in a main casing of the printer from a point diagonally rightward and frontward thereof; 
         FIG. 3  is a perspective view of a left side wall of the main casing attached with one of mounting parts from a point diagonally rightward and frontward thereof; 
         FIG. 4  is a perspective view of the mounting parts from a point diagonally frontward and rightward thereof; 
         FIG. 5  is a perspective view of the mounting parts from a point diagonally rearward and rightward thereof; 
         FIG. 6  is a perspective view of a sheet-conveying unit of the printer from a diagonally rightward and frontward thereof; 
         FIG. 7  is perspective view of a fixing unit supported in the mounting parts from a point diagonally rightward and rearward thereof; 
         FIG. 8  is a perspective view of a first guide member of the printer from a point diagonally rightward and frontward thereof; and 
         FIG. 9  is a perspective view of the first guide member attached to the mounting parts from a point diagonally rightward and rearward thereof. 
     
    
    
     DETAILED DESCRIPTION 
     An image forming device according to an embodiment of the invention will be described while referring to the accompanying drawings. The present embodiment pertains to a laser printer  1  shown in  FIG. 1 . 
     The terms “upward,” “downward,” “upper,” “lower,” “above,” “below,” “beneath,” “right,” “left,” “front,” “rear” and the like will be used throughout the description assuming that the printer  1  is disposed in an orientation in which it is intended to be used. 
     The printer  1  is a direct tandem type color printer and, as shown in  FIG. 1 , includes a main casing  2  that is substantially box-shaped and elongated in a front-to-rear direction. The main casing  2  has a front wall  2 A and a rear wall  2 B. 
     Four photosensitive drums  3  are rotatably disposed inside the main casing  2 . The photosensitive drums  3  are arranged parallel to each other, with their axes extending in a width direction (left-to-right direction) and are juxtaposed in the front-to-rear direction. The main casing  2  also accommodates four developer cartridges  6 , four Scorotron chargers  4 , and a scanning unit  7 . 
     Each developer cartridge  6  supports a developing roller  5 . The developing roller  5  is positioned adjacent to the photosensitive drum  3  and confronts the top thereof. The developer cartridges  6  are detachably mounted in the main casing  2 . Each developer cartridge  6  accommodates toner that is supplied to and carried on the outer surface of the respective developing roller  5 . Each Scorotron charger  4  is disposed in confrontation with the corresponding photosensitive drum  3 . The scanning unit  7  is disposed in the top section of the main casing  2 . 
     During image forming operations, each of the Scorotron chargers  4  uniformly charges the outer peripheral surface of the corresponding photosensitive drum  3 . Then, the outer peripheral surface of the photosensitive drum  3  is exposed by a laser beam L emitted from the scanning unit  7 . As a result, an electrostatic latent image corresponding to image data is formed on the outer peripheral surface of each photosensitive drum  3 . Subsequently, the toner carried on the developing roller  5  is selectively supplied to the electrostatic latent image on the photosensitive drum  3 . As a result, the electrostatic latent image is transformed into a visible toner image. In this manner, the toner image is formed on the photosensitive drum  3 . 
     Each of the developer cartridges  6  accommodates toner of a different color. In this embodiment, the colors of toner accommodated in the developer cartridges  6  are black, yellow, magenta, and cyan. Accordingly, the color of the toner images formed on each photosensitive drum  3  also differs according to the photosensitive drum  3 . In the following description, the four photosensitive drums  3  will be differentiated based on the color of the toner image formed thereon. Specifically, the photosensitive drums  3  include a black photosensitive drum  3 K, a yellow photosensitive drum  3 Y, a magenta photosensitive drum  3 M, and a cyan photosensitive drum  3 C arranged in this order from front to rear. 
     The printer  1  also includes, within the main casing  2 , a sheet-supply cassette  8 , a sheet-supply roller  9 , a pair of registration rollers  10 , a sheet-conveying unit  23 , and a fixing unit  13 . The sheet-conveying unit  23  includes a conveying belt  11 , a drive roller  21 , a follow roller  22 , four transfer rollers  12 , and a belt frame  24 . 
     The sheet-supply cassette  8  is disposed in a bottom section of the main casing  2  and accommodates stacked sheets S of paper. The sheets S accommodated in the sheet-supply cassette  8  have a long dimension aligned with the front-to-rear direction and a short dimension aligned with the width direction. 
     During image-forming operations, the sheet-supply roller  9  disposed above the front edge of the sheet supply cassette  8  feeds the topmost sheet S accommodated in the sheet supply cassette  8  forward. The path along which the sheet S is fed is such that the sheet S is conveyed upward while being reversed from a forward direction to a rearward direction. 
     When fed upward, the leading edge of the sheet S is interposed between the pair of registration rollers  10 . At a prescribed timing, the registration rollers  10  continue to convey the sheet S rearward onto the conveying belt  11 . 
     The conveying belt  11  is an endless belt formed of a resin material and is wider than the sheet S. The conveying belt  11  is mounted over the drive roller  21  and the follow roller  22  and pulled taut with a prescribed force. The drive roller  21  and the follow roller  22  are arranged parallel to each other and are separated in the front-to-rear direction. 
     Center axes of the drive roller  21  and the follow roller  22  extend in the width direction. The drive roller  21  is disposed on the rear side of the photosensitive drum  3 C, and the follow roller  22  is disposed on the front side of the photosensitive drum  3 K. 
     When viewed along the width direction, the conveying belt  11  has a circular shape, elongated in the front-to-rear direction and flattened on the top and bottom. The portion of the conveying belt  11  running between the top of the drive roller  21  and the top of the follow roller  22  will be referred to as an upper portion  11 A of the conveying belt  11 . The top surface of the upper portion  11 A is substantially horizontal. The four photosensitive drums  3  described above contact the top surface of the upper portion  11 A of the conveying belt  11 . 
     The four transfer rollers  12  are positioned inside the conveying belt  11 , i.e., in the area between the drive roller  21  and the follow roller  22 . The transfer rollers  12  are arranged parallel to each other and juxtaposed in the front-to-rear direction. Each transfer roller  12  confronts the bottom surface of the corresponding photosensitive drum  3 , with the upper portion  11 A of the conveying belt  11  interposed therebetween. Each of the transfer rollers  12  is applied with a transfer bias. 
     The belt frame  24  rotatably supports the drive roller  21 , the follow roller  22 , and the transfer rollers  12 . The sheet-conveying unit  23  can be mounted in and removed from the main casing  2  through the front side thereof by displacing the front wall  2 A of the main casing  2 , for example, to expose the interior of the main casing  2 . 
     As described above, the registration rollers  10  convey a sheet S to the conveying belt  11  and transfer the sheet S onto the surface of the upper portion  11 A. The conveying belt  11  is driven to circulate clockwise in  FIG. 1  by the rotation of the drive roller  21 . Accordingly, a sheet S transferred onto the upper portion  11 A is conveyed rearward. 
     At this time, toner images carried on the surfaces of the photosensitive drums  3  are transferred onto the top surface of the sheet S being conveyed on the top surface of the upper portion  11 A by the transfer bias applied to the corresponding transfer rollers  12 . The sequentially transferred images are superimposed over each other. Since the toner images carried on the photosensitive drums  3  are each of a different color, as described above, the toner images of the four colors form a color image when superimposed on the sheet S. 
     As the four toner images (color image) are transferred onto the sheet S from the four photosensitive drums  3 , the conveying belt  11  continues to convey the sheet S rearward toward the fixing unit  13  disposed on the rear side of the sheet-conveying unit  23 . 
     The fixing unit  13  can be mounted in and removed from the main casing  2  through the rear side thereof by displacing the rear wall  2 B of the main casing  2 , for example, to expose the interior of the main casing  2 . 
     The fixing unit  13  includes a fixing casing  25 , a heat roller  26 , and a pressure roller  27 . The fixing casing  25  is in a hollow box shape elongated in the width direction as shown in  FIG. 2 . The fixing casing  25  has a front surface formed with an inlet  28  and a rear surface formed with an outlet  29 . Both the inlet  28  and the outlet  29  are in fluid communication with the interior of the fixing casing  25 , and are elongated in the width direction to have an enough width to let the sheet S pass therethrough. 
     The heat roller  26  and the pressure roller  27  are disposed in the fixing casing  25  so as to be rotatable about respective center axes extending in the width direction. The peripheral surface of the heat roller  26  is covered with a fluorine resin, for example. The heat roller  26  also has a built-in halogen lamp (not shown) for heating the peripheral surface of the heat roller  26 . 
     The peripheral surface of the pressure roller  27  is covered with a silicon rubber, for example. The pressure roller  27  presses against the bottom of the heat roller  26 . The area of contact between the heat roller  26  and the pressure roller  27 , referred to as a “nip position N” herein, is positioned rearward of the inlet  28  and forward of the outlet  29 . 
     The sheet S conveyed to the fixing unit  13  enters the fixing casing  25  through the inlet  28  and passes rearward through the nip position N between the heat roller  26  and the pressure roller  27 . 
     When the sheet S passes through the nip position N, the pressure roller  27  presses the upper surface of the sheet S transferred with the toner image onto the heated outer peripheral surface of the heat roller  26 . As a result, the toner image is thermally fixed onto the upper surface of the sheet S. 
     Then, the sheet S is discharged out of the fixing casing  25  through the outlet  29 . Subsequently, the sheet S is conveyed by pairs of conveying rollers  14  disposed downstream of the fixing unit  13  along a sheet-conveying path. The conveying rollers  14  convey the sheet S along a path that guides the sheet S upward while changing from a rearward direction to a forward direction, and discharge the sheet S onto a discharge tray  15  provided on top of the main casing  2 . 
     The printer  1  further includes a first guide part  30  and a second guide part  31  within the main casing  2  at a position between the sheet-conveying unit  23  and the fixing unit  13 . As shown in  FIG. 8 , the first guide part  30  is rectangular in shape and elongated in the width direction. The dimension of the first guide part  30  in the width direction is greater than the width of the sheet S. 
     More specifically, as shown in  FIG. 1 , the first guide part  30  is disposed at a position between the sheet-conveying unit  23  and the fixing unit  13  and is slightly biased toward the sheet-conveying unit  23  side (i.e., forward, or upstream in the sheet-conveying direction). The first guide part  30  is positioned to the rear of and adjacent to the rear end of the upper portion  11 A of the conveying belt  11 . The first guide part  30  extends diagonally upward and rearward toward the inlet  28  of the fixing casing  25 . 
     The second guide part  31  is attached to the rear end of the first guide part  30 , and the dimension of the second guide part  31  in the width direction is greater than the width of the sheet S. The second guide part  31  is pivotably supported at a front end to the first guide part  30  so that a rear end can move upward and downward, i.e., in a direction perpendicular to both the width direction of the sheet S and a sheet conveying direction in which the sheet S is conveyed. The rear end of the second guide part  31  is urged upward by a spring  76  ( FIG. 9 ). The second guide part  31  extends diagonally upward and rearward from the rear end of the first guide part  30  toward the inlet  28  of the fixing casing  25 . 
     From the upper portion  11 A of the conveying belt  11 , a sheet S conveyed rearward passes sequentially over the top surfaces of the first guide part  30  and the second guide part  31  and enters the inlet  28  of the fixing unit  13 . Hence, the first guide part  30  and the second guide part  31  receive the sheet S conveyed by the sheet-conveying unit  23  and guide the sheet S to the fixing unit  13 . 
     Normally, the fixing unit  13 , and specifically the heat roller  26  and the pressure roller  27 , is configured to convey the sheet S at a slower speed than the conveying belt  11  so that the fixing unit  13  positioned downstream from the conveying belt  11  in the sheet-conveying direction does not pull the sheet S from the conveying belt  11 . The difference in the conveying speed of the fixing unit  13  and the conveying speed of the conveying belt  11  produces flexure in the sheet S between the conveying belt  11  and the fixing unit  13 . To absorb this flexure, the second guide part  31  can pivot downward against the urging force of the spring  76 , thereby preventing wrinkles from being formed in the sheet S guided by the second guide part  31  and preventing the sheet S from becoming jammed in the fixing unit  13  when the sheet S is transferred thereto. 
     As shown in  FIG. 2 , the main casing  2  includes a main frame  35 . The main frame  35  includes a pair of metal side walls  36  arranged parallel to each other and separated in the width direction. In  FIG. 2 , the right side wall  36  is depicted with a dotted line. 
     As shown in  FIG. 3 , the side walls  36  have a rectangular plate shape with a thin width dimension and a surface aligned with the front-to-rear and vertical directions. The side walls  36  are formed by pressing metal plates with a prescribed die. In this embodiment, both the left and right side walls  36  are pressed using the same die. 
     A mounting part  37  is attached to the widthwise inner surface of each side wall  36 . The mounting parts  37  are depicted with shading in  FIGS. 2 ,  3 , and other drawings. The mounting part  37  fixed to the right surface of the left side wall  36  in  FIG. 3  is a left mounting part  37 L, and the mounting part  37  fixed to the left surface of the right side wall  36  in  FIG. 2  is a right mounting part  37 R. Details of the mounting parts  37  will be described later. 
     More specifically, as shown in  FIG. 2 , the sheet-conveying unit  23 , the fixing unit  13 , the first guide part  30 , and the second guide part  31  are disposed between the side walls  36 . Hence, the left and right side walls  36  define the interior space of the main casing  2  in the width direction. 
     As shown in  FIG. 2 , the sheet-conveying unit  23  is disposed between the lower edges of the left and right side walls  36  and is elongated in the front-to-rear direction. The fixing unit  13  is disposed between the rear ends of the left and right side walls  36  and confronts the rear side of the sheet-conveying unit  23 . The first guide part  30  and the second guide part  31  are disposed between the sheet-conveying unit  23  and the fixing unit  13 , as described above, and extend between the left and right side walls  36 . 
     The sheet-conveying unit  23  has rear end parts  23 A. As will be described later, the left rear end part  23 A and the left ends of the fixing unit  13  and the first guide part  30  are mounted in the left mounting part  37 L on the left side wall  36 , and the right rear end part  23 A and the right ends of the fixing unit  13  and the first guide part  30  are mounted in the right mounting part  37 R on the right side wall  36 . 
     As shown in  FIG. 2 , the pair of right and left mounting parts  37 R and  37 L are disposed in the main casing  2  with a space therebetween in the width direction. The left mounting part  37 L is attached to a rear section on the widthwise inner surface of the left side wall  36 , and the right mounting part  37 R is attached to a rear section on the widthwise inner surface of the right side wall  36 , so that the right and left mounting parts  37 R and  37 L confront with each other in the width direction. That is, the right and left mounting parts  37 R and  37 L are disposed at substantially the same position with respect to both the vertical direction and the front-to-rear direction. 
     Although not shown in the drawings, each mounting part  37  is formed with a craw (not shown) and is fixed to the corresponding side wall  36  with the craw engaging with the side wall  36 . Alternatively, the mounting part  37  may be fixed to the side wall  36  with a fixing member, such as a screw. 
     The mounting parts  37  are formed of a synthetic resin material. Because the side walls  36  of the main frame  35  are formed of metal, as described above, the side walls  36  have a higher rigidity than the mounting parts  37 , even when the side walls  36  have been molded in the shape shown in  FIG. 3 . Hence, the main frame  35  can solidly support the mounting parts  37 . Although the left and right mounting parts  37  are formed in a block shape that is slender in the left-to-right direction and elongated vertically, the shapes of the mounting parts  37  differ from each other in minor details. 
     Specifically, the left mounting part  37 L when viewed from the right side, as shown in  FIG. 3 , is shaped substantially like the letter J. The front-to-rear dimension of the left mounting part  37 L expands toward the rear from the approximate vertical center of the left mounting part  37 L upward, and expands toward the front from the approximate vertical center downward. Two openings  39  penetrating the left mounting part  37 L in the width direction are formed in the left mounting part  37 L at positions aligned vertically. A gear or other inputting means (not shown) on the main casing  2  side for inputting a drive force into the fixing unit  13  is inserted into the top opening  39  along the width direction from the outer side thereof. Also, a gear or other inputting means (not shown) on the main casing  2  side for inputting a drive force into the sheet-conveying unit  23  is inserted into the bottom opening  39  along the width direction from the outer side thereof. 
     As shown in  FIG. 2 , the right mounting part  37 R, on the other hand, extends upward from the bottom edge thereof in substantially a vertical direction, and then extends upward along a slope to the rear. 
     As shown in  FIGS. 4 and 5 , a recessed part  38  is formed in the widthwise inner surface of each mounting part  37  (the right surface of the left mounting part  37 L and the left surface of the right mounting part  37 R) at substantially opposing positions in the lower ends thereof. The recessed parts  38  are groove-like cutout portions extending in the front-to-rear direction that are formed in the inner widthwise surfaces of the corresponding mounting parts  37  from the front edge to a midpoint in the front-to-rear direction. Hence, the front end of each recessed part  38  is open in the front endface of the corresponding mounting part  37  and exposed on the front side thereof. 
     As shown in  FIG. 5 , a first boss  40 , a first threaded hole  41 , a second boss  42 , and a second threaded hole  43  are provided on the rear endface of each mounting part  37  in order from top to bottom. The vertical positions of the first boss  40 , the first threaded hole  41 , the second boss  42 , and the second threaded hole  43  are approximately the same for both the left and right mounting parts  37 . 
     More specifically, the first boss  40  is disposed on the top end of the rear endface of each mounting part  37 , and the first threaded hole  41  is formed immediately below the first boss  40 . The second boss  42  is disposed on the rear endface of each mounting part  37  in substantially the vertical center thereof or at a position slightly lower than the vertical center, and the second threaded hole  43  is formed immediately below the second boss  42 . The first boss  40  and the second boss  42  are both cylindrically shaped and protrude rearward from the rear endface of the respective mounting part  37 . 
     As described above, the sheet-conveying unit  23 , the fixing unit  13 , and the first guide part  30  are mounted in the mounting parts  37  attached to both left and right side walls  36  (see  FIG. 2 ). Next, the manner in which the sheet-conveying unit  23 , the fixing unit  13 , and the first guide part  30  are mounted in the mounting parts  37  will be described in that order. 
     As shown in  FIG. 6 , the belt frame  24  of the sheet-conveying unit  23  is substantially plate-shaped, flattened vertically, and elongated in the front-to-rear direction. Most of the belt frame  24  is disposed inside the conveying belt  11 . However, on the left and right sides, the belt frame  24  has side frame parts  24 L and  24 R spanning the entire length of the belt frame  24  in the front-to-rear direction and protruding outward from the conveying belt  11  in the width direction. 
     A grip part  45  spans between the front ends of the left and right side frame parts  24 L and  24 R. The grip part  45  is elongated in the width direction and is positioned in front of the conveying belt  11  to oppose the front end of the conveying belt  11 , but is separated therefrom. An operator grips the grip part  45  when mounting the sheet-conveying unit  23  in the main casing  2  or removing the sheet-conveying unit  23  therefrom, as described above. 
     A front boss  47  and a rear boss  48  protrude outward in the width direction from each of the side frame parts  24 L and  24 R. The front bosses  47  are disposed on the front ends of the side frame parts  24 L and  24 R, while the rear bosses  48  are disposed on the rear ends thereof. The front bosses  47  are cylindrical in shape, for example. Each of the rear bosses  48  is integrally provided with a cylindrical body  48 A, and a rib  48 B connected to the front side of the cylindrical body  48 A and slightly elongated in the front-to-rear direction. Overall, the rear boss  48  is elongated in the front-to-rear direction. 
     When the sheet-conveying unit  23  is mounted inside the main casing  2 , as shown in  FIG. 2 , the left and right rear bosses  48  ( FIG. 6 ) on the sheet-conveying unit  23  are fitted in a rearward direction into the recessed parts  38  ( FIG. 4 ) of the mounting parts  37  on the same widthwise side. Through this operation, the rear bosses  48  are fixed to the corresponding mounting parts  37 . 
     That is, as shown in  FIG. 2 , the rear end parts  23 A of the sheet-conveying unit  23  (strictly speaking, the rear ends of the left and right side frame parts  24 L and  24 R) are mounted in the mounting parts  37 , with the left end being mounted in the left mounting part  37 L and the right end in the right mounting part  37 R. In this way, the rear end parts  23 A of the sheet-conveying unit  23  are mounted in the main casing  2  (the main frame  35 ) via the left and right mounting parts  37 L and  37 R. The front side of the sheet-conveying unit  23  is directly mounted on the left and right side walls  36  of the main frame  35 . For example, support parts (not shown) are formed on the left and right side walls  36  protruding toward each other in opposing directions, and the front portions of the side frame parts  24 L and  24 R rest on and are supported by the support parts. 
     As shown in  FIG. 2 , levers  51  (only one lever  51  is shown in  FIG. 2 ) are provided in the main casing  2 . In this embodiment, the levers  51  are supported so as to be pivotable about their bottom ends. Springs  52  are provided in the main casing  2  for urging the levers  51  to pivot rearward. The upper portions of the levers  51  urged rearward by the springs  52  press the front bosses  47  of the sheet-conveying unit  23  rearward. Consequently, the entire sheet-conveying unit  23  is urged rearward so that the left and right rear bosses  48  on the sheet-conveying unit  23  are maintained in the corresponding recessed parts  38  formed in the mounting parts  37  (i.e., the recessed parts  38  on the same widthwise side). 
     Hence, after displacing the front wall  2 A of the main casing  2  (see  FIG. 1 ) to expose the interior of the main casing  2  on the front side thereof, the operator grips the grip part  45  of the belt frame  24  and pulls the sheet-conveying unit  23  in a forward direction. At this time, the front bosses  47  move forward and are disengaged from the levers  51 , and the rear bosses  48  come out of the recessed parts  38 . By removing the sheet-conveying unit  23  from the left and right mounting parts  37  (i.e., the main casing  2 ) in this way, it is possible to perform maintenance on or replace the sheet-conveying unit  23 . 
     As shown in  FIG. 2 , the fixing unit  13  is mounted in the left and right mounting parts  37 L and  37 R from the rear side thereof and spans between the top edges of the left and right mounting parts  37 L and  37 R. 
     More specifically, as shown in  FIG. 7 , a mounting hole  54  is formed one in both widthwise ends in the upper edge of the fixing case  25  of the fixing unit  13  (only the right mounting hole  54  is shown in  FIG. 7 ). The fixing unit  13  is tentatively assembled on the left and right mounting parts  37 L and  37 R by mounting the fixing unit  13  so that the first bosses  40  formed on the mounting parts  37  are inserted through the mounting holes  54  on the same widthwise sides. 
     The mounting holes  54  are slightly elongated in the width direction so that the first bosses  40  can move slightly in the width direction when inserted into the mounting holes  54 . Hence, the position of the fixing unit  13  in the width direction can be fine-tuned after the fixing unit  13  has been tentatively assembled on the left and right mounting parts  37 L and  37 R. 
     After the fixing unit  13  has been tentatively mounted on the left and right mounting parts  37 L and  37 R, screws  55  are inserted through the fixing case  25  from the rear side thereof in regions immediately below the corresponding mounting holes  54 . The screws  55  are then screwed into the first threaded holes  41  (see  FIG. 5 ) of the corresponding mounting parts  37  (i.e., the mounting parts  37  on the same widthwise sides) to fasten the fixing unit  13  to the mounting parts  37 . 
     Through this operation, the fixing unit  13  is assembled and fastened to the left and right mounting parts  37 L and  37 R. That is, the left end of the fixing unit  13  is fastened to the left mounting part  37 L and the right end to the right mounting part  37 R. Hence, the fixing unit  13  is mounted on the main casing  2  (main frame  35 ) via the mounting parts  37 . 
     To replace or conduct maintenance on the fixing unit  13 , the operator displaces the rear wall  2 B of the main casing  2  to expose the interior of the main casing  2  on the rear side, as described above. Next, the operator removes the screws  55  and pulls the fixing unit  13  rearward, at which time the first bosses  40  come out of the corresponding mounting holes  54  in the fixing unit  13 . Consequently, the fixing unit  13  can be removed from the mounting parts  37  (and from the main casing  2 ) for maintenance or the like. 
     As shown in  FIG. 8 , the first guide part  30  is rectangular in shape and elongated in the width direction, as described above. The top surface of the first guide part  30  slopes slightly upward toward the rear side. 
     Fixing parts  65  ( 65 L and  65 R) are integrally provided on each widthwise end of the first guide part  30  for fixing the first guide part  30  to the corresponding left and right mounting parts  37 L and  37 R. The left and right fixing parts  65 L and  65 R are plate-shaped, with the thin dimension in the front-to-rear direction. The right fixing part  65 R is particularly elongated vertically. 
     A first circular hole  66  and a second circular hole  67  are formed in the left fixing part  65 L, with the first circular hole  66  positioned above the second circular hole  67 . Both the first and second circular holes  66  and  67  are circular when viewed in the front-to-rear direction and penetrate the left fixing part  65 L in the front-to-rear direction. The first circular hole  66  is larger than the second circular hole  67 . 
     A first elongated hole  68  and a second elongated hole  69  are formed in the right fixing part  65 R near the top end thereof, with the first elongated hole  68  positioned above the second elongated hole  69 . Both the first and second elongated holes  68  and  69  are elongated in the width direction when viewed along the front-to-rear direction and penetrate the right fixing part  65 R in the front-to-rear direction. The first elongated hole  68  is larger than the second elongated hole  69 . 
     An actuator  70  is mounted on the lower end of the right fixing part  65 R. The actuator  70  has a built-in solenoid (not shown) and a rotating member  71  disposed on the top thereof. The rotating member  71  can rotate about a shaft  72  extending in the front-to-rear direction. Specifically, the rotating member  71  rotates about the shaft  72  in a prescribed direction or in a direction opposite the prescribed direction, depending on whether the solenoid in the actuator  70  is excited or not excited. 
     A sensor  60  is provided one on each widthwise end of the first guide part  30 . The sensors  60  are mounted on the front end of the bottom surface of the first guide part  30 . The left and right sensors  60  confront the rear side of the sheet-conveying unit  23  (and specifically the outer surface of the conveying belt  11  on the rear end of the sheet-conveying unit  23 ; see  FIG. 1 ). 
     The printer  1  has a check mode for confirming whether toner images are properly transferred onto a sheet S conveyed on the conveying belt  11  of the sheet-conveying unit  23 . In the check mode, the printer  1  directly transfers toner images from the photosensitive drums  3  onto the conveying belt  11  of the sheet-conveying unit  23  and controls the sensors  60  to detect the toner images on the conveying belt  11 . More specifically, a control unit (not shown) provided in the main casing  2  determines whether there are any irregularities in the densities of the toner images or any problems in registration among toner images of each color when the images are actually transferred onto a sheet S based on output from the sensors  60  when the sensors  60  detect the toner images. Based on the above determinations, the printer  1  can adjust variables in the image-forming process, such as the timing at which toner images are transferred onto the sheet S. 
     As shown in  FIG. 8 , a shutter  73  is provided on the front end of the first guide part  30 . The shutter  73  is slightly longer in the width direction than the first guide part  30  (the portion of the first guide part  30  excluding the left and right fixing parts  65 ). The shutter  73  can move between open and closed positions on the front side of the left and right sensors  60  for respectively exposing or covering the sensors  60 . 
     Specifically, the shutter  73  is rotatably supported on both widthwise ends by the first guide part  30  and can rotate about an axis extending in the width direction. A protrusion  74  is integrally provided on the right end of the shutter  73 . The protrusion  74  protrudes rightward from the shutter  73  and contacts the rotating member  71  of the actuator  70  described above. With this construction, when the rotating member  71  rotates as described above, the rotating member  71  pushes against the protrusion  74 , causing the shutter  73  to rotate. 
     When rotated diagonally downward and forward, as shown in  FIG. 8 , the shutter  73  is positioned below the left and right sensors  60 . Consequently, the sensors  60  are exposed on the front side, and no objects are present between the sensors  60  and the sheet-conveying unit  23  (the outer surface of the conveying belt  11  on the rear end of the  23 ; see  FIG. 1 ). At this time, the sensors  60  can detect toner images transferred onto the conveying belt  11  of the sheet-conveying unit  23  when the printer  1  is in the check mode described above. 
     However, when the shutter  73  is rotated upward from the state shown in  FIG. 8 , the shutter  73  covers and protects the sensors  60  from the front side thereof. Thus, the shutter  73  can prevent contaminants or the like from becoming deposited on the sensors  60  during an image-forming operation. 
     Plates  78  are provided in the first guide part  30 , and specifically beneath the top surface of the first guide part  30 , with one on either widthwise end. The plates  78  are electrically grounded via springs  79  (see  FIG. 9 ) to eliminate static electricity from the first guide part  30 . 
     As described above, the second guide part  31 , which is rectangular and elongated in the width direction, is mounted on the rear edge of the first guide part  30  so that the second guide part  31  and the first guide part  30  form a single unit. The first guide part  30  supports the front edge of the second guide part  31  on both widthwise ends thereof (see also  FIG. 9 ). Accordingly, the second guide part  31  can pivot freely about its front edge so that the rear edge moves vertically, as described above. 
     As shown in  FIG. 9 , a protruding part  75  is provided on the rear edge of the first guide part  30  at a position in the widthwise center thereof. The protruding part  75  protrudes rearward below the second guide part  31 . The spring  76  is disposed on the top surface of the protruding part  75  and extends upward therefrom. The spring  76  pushes upward against a rear edge portion of the second guide part  31 , urging the rear edge of the second guide part  31  to pivot upward about its front edge. 
     The first guide part  30  having this construction is mounted on the left and right mounting parts  37 L and  37 R from the rear side thereof and spans between the lower ends of the mounting parts  37 . 
     Specifically, the first guide part  30  is mounted on the mounting parts  37  so that the second boss  42  of the left mounting part  37 L is inserted rearward through the first circular hole  66  formed in the left fixing part  65 L of the first guide part  30 , and the second boss  42  of the right mounting part  37 R is inserted rearward through the first elongated hole  68  formed in the right fixing part  65 R of the first guide part  30 . When inserted into the first elongated hole  68 , the second boss  42  on the right mounting part  37 R can move slightly in the longitudinal direction of the first elongated hole  68  (the width direction). Hence, the second bosses  42  on both the left and right mounting parts  37 L and  37 R can be inserted through the corresponding first circular hole  66  and first elongated hole  68 , even when there is a small error in the gap between the left and right second bosses  42  (i.e., the gap between the left and right mounting parts  37 L and  37 R). 
     In this way, the first guide part  30  is tentatively mounted on the left and right mounting parts  37 L and  37 R. At this time, the second circular hole  67  on the left fixing part  65 L is aligned with the second threaded hole  43  formed in the left mounting part  37 L from the rear side thereof, while the second elongated hole  69  formed in the right fixing part  65 R is aligned with the second threaded hole  43  formed in the right mounting part  37 R from the rear side thereof. Next, a screw  77  is inserted in a forward direction through the second circular hole  67  formed in the left fixing part  65 L and screwed into the second threaded hole  43  formed in the left mounting part  37 L, and another screw  77  is inserted in a forward direction through the second elongated hole  69  formed in the right fixing part  65 R and screwed into the second threaded hole  43  formed in the right mounting part  37 R. 
     This operation completes the process for mounting the first guide part  30  on the left and right mounting parts  37 L and  37 R. In other words, the left end (left fixing part  65 L) of the first guide part  30  is mounted on the left mounting part  37 L, and the right end (right fixing part  65 R) is mounted on the right mounting part  37 R. Accordingly, the first guide part  30  is mounted on the main casing  2  (main frame  35 ) via the left and right mounting parts  37 L and  37 R (see  FIG. 2 ). 
     To remove the first guide part  30  from the main casing  2 , the operator displaces the rear wall  2 B on the main casing  2  (see  FIG. 1 ) to expose the interior of the main casing  2  on the rear side thereof, and subsequently removes the screws  77  and pulls the first guide part  30  rearward. At this time, the second boss  42  of the left mounting part  37 L is disengaged from the first circular hole  66  of the left fixing part  65 L of the first guide part  30 , and the second boss  42  of the right mounting part  37 R is disengaged from the first elongated hole  68  of the right fixing part  65 R of the first guide part  30 . By disengaging the second bosses  42  from the holes  66  and  68  in this way, it is possible to detach the first guide part  30  from the mounting parts  37 , i.e., from the main casing  2 . Thus, it is possible to perform maintenance on the first guide part  30  and the second guide part  31 . 
     Alternatively, the fixing unit  13  and the first guide part  30  may be premounted on the left and right mounting parts  37 L and  37 R. In this state, the mounting parts  37  may be mounted in the main frame  35 , as shown in  FIG. 2 . Thereafter, the sheet-conveying unit  23  may be mounted in the recessed parts  38  of the mounting parts  37  and supported on the support parts (not shown) of the side walls  36 . In order to perform maintenance or the like, the fixing unit  13  and the first guide part  30  are removed together with the mounting parts  37  from the main frame  35 . 
     In the printer  1  having the above construction, the mounting parts  37  are mounted in the main frame  35  of the main casing  2 , and the rear end parts  23 A of the sheet-conveying unit  23  and the ends of the fixing unit  13  and the first guide part  30  are all mounted in the same mounting parts  37  on the same widthwise sides. This configuration assures that the sheet-conveying unit  23  (specifically, the rear end parts  23 A), the fixing unit  13 , and the first guide part  30  can be positioned relative to each other with greater precision than when these components are mounted in separate mounting parts. 
     Hence, the present invention improves the precision in positioning the fixing unit  13  and the first guide part  30  relative to the sheet-conveying unit  23 , which functions to convey sheets S. Any offset that occurs in the relative positions of the fixing unit  13  and the first guide part  30  based on the sheet-conveying unit  23  reduces the precision in which the sheet-conveying unit  23 , the fixing unit  13 , and the first guide part  30  convey the sheets S. This reduction in precision may lead to sheets S passing through the nip position N between the heat roller  26  and the pressure roller  27  in an improper state, for example, producing wrinkles in the sheet S or creating other problems. 
     However, the structure of the above-described embodiment improves the precision of positioning the fixing unit  13  and the first guide part  30  based on the sheet-conveying unit  23 . Hence, the first guide part  30  (including the second guide part  31 ) can guide the sheets S conveyed by the sheet-conveying unit  23  to the fixing unit  13  with great precision, enabling the fixing unit  13  to fix toner images on sheets S conveyed therethrough with great precision. 
     Because at least the rear end parts  23 A of the sheet-conveying unit  23  (parts of the sheet-conveying unit  23  adjacent to the fixing unit  13  and the first guide part  30 ) are mounted on the same mounting parts  37  as the fixing unit  13  and the first guide part  30  in the above-described embodiment, the sheet-conveying unit  23  can convey sheets S to the fixing unit  13  with great precision. 
     As described above, the mounting parts  37  position all of the components that function to perform all operations from conveyance of the sheet S after toner images are transferred thereto to fixing of the toner images on the sheet S (i.e., the sheet-conveying unit  23 , the fixing unit  13 , and the first guide part  30 ). 
     Because this construction improves the precision in relative positioning of the sheet-conveying unit  23  and the first guide part  30 , the relative positioning of the sensors  60  mounted on the first guide part  30  to the sheet-conveying unit  23  is also improved (see  FIG. 1 ). Accordingly, the sensors  60  can detect toner images transferred onto the conveying belt  11  with greater precision. 
     Further, forming both side walls  36  using the same die to press the plates can equalize the error when molding each side wall  36 , thereby reducing error in mounting the mounting parts  37  on the side walls  36 . Accordingly, this method reduces the error in mounting the sheet-conveying unit  23 , the fixing unit  13 , and the first guide part  30  on the mounting parts  37  for both widthwise sides thereof. As a result, the present invention improves the precision in fixing the relative positions of the sheet-conveying unit  23 , the fixing unit  13 , and the first guide part  30  across the entire width thereof. 
     Further, by forming the mounting parts  37  of a synthetic resin material, the mounting parts  37  can easily be shaped to facilitate mounting of the sheet-conveying unit  23 , the fixing unit  13 , and the first guide part  30 . 
     Further, mounting each widthwise end of the sheet-conveying unit  23 , the fixing unit  13 , and the first guide part  30  in a mounting part  37  provided on the same widthwise side improves the precision is positioning the sheet-conveying unit  23 , the fixing unit  13 , and the first guide part  30  relative to one another across the entire width thereof. 
     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. 
     For example, in the above-described embodiment, each widthwise end of the sheet-conveying unit  23 , the fixing unit  13 , and the first guide part  30  is mounted in a mounting part  37  disposed on the same widthwise side. However, it is possible to mount only one widthwise end of each of the sheet-conveying unit  23 , the fixing unit  13 , and the first guide part  30  in a mounting part  37  disposed on the same widthwise side thereof. In this case, the left ends of the sheet-conveying unit  23 , the fixing unit  13 , and the first guide part  30  can be mounted in the left mounting part  37 L, for example, while the right ends of the same components are directly mounted in the main frame  35  (i.e., the right side wall  36 ). 
     Further, while the second guide part  31  is provided on the first guide part  30  in the above-described embodiment, the second guide part  31  may be provided on the fixing unit  13  (the fixing case  25 ) instead of the first guide part  30 .