Patent Publication Number: US-8112011-B2

Title: Image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of prior U.S. application Ser. No. 11/692,494, filed Mar. 28, 2007, which claims the benefit of Japanese Patent Application No. 2006-090953 filed on Mar. 29, 2006 in the Japanese Patent Office, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention relates to an image forming apparatus. The present invention is especially effective for image forming apparatus for electrophotography, such as a laser printer, copier, and the like. 
     Image forming apparatus generally includes a control board having a control circuit, and a power substrate which supplies electric power to the control board and others. 
     For example, in some type of image forming apparatus, a control board and a high-voltage board are disposed next to each other above a placement tray. A power supply substrate is disposed below the control board and the high-voltage board. 
     Moreover, the control board and the power supply substrate are connected by a cable so as to supply electric power from the power supply substrate to the control board. 
     SUMMARY 
     However, in the above-described configuration, if the cable is disposed adjacent to the high-voltage board having a high-voltage circuit, there is a possibility that the cable is influenced by noise from the high-voltage board. 
     If the noise influence from the high-voltage board remains in control signals generated by the control circuit, the quality of an image, formed on a recording medium, is likely to be reduced. 
     One aspect of the present invention provides a technique to inhibit a cable, which supplies electric power from a power supply substrate to a control board, from being influenced by such noise. 
     In one aspect of the present invention, an image forming apparatus may include a placement tray, an image forming unit, a drive unit, a control board, a power supply substrate, a high-voltage board, and low-voltage power supply harnesses. The placement tray holds a recording sheet thereon. The image forming unit forms an image on the recording sheet. The drive unit supplies driving force to the image forming unit. The control board controls the drive unit. The power supply substrate supplies electric power to the control board. The high-voltage board is disposed in one side of the placement tray. In the high-voltage board, voltage is generated higher than voltage in the power supply substrate. The low-voltage power supply harnesses are disposed in another side of the placement tray so as to supply electric power from the power supply substrate to the control board. 
     Therefore, in this aspect of the present invention, the placement tray interposes between the low-voltage power supply harnesses and the high-voltage board so as to separate the low-voltage power supply harnesses and the high-voltage board. 
     As a result, the influence of high voltage, generated in the high-voltage board, to the low-voltage power supply harnesses may be reduced, as compared to a case wherein the low-voltage power supply harnesses and the high-voltage board are both disposed in one side of the placement tray. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described below, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a sectional side view showing a schematic structure of a laser printer according to an embodiment of the present invention; 
         FIG. 2  is a perspective view showing the laser printer wherein a housing and a paper feed tray of the printer are removed therefrom; 
         FIG. 3  is a view on arrow A in  FIG. 2  showing the schematic structure of the laser printer according to the embodiment; 
         FIG. 4  is a side view showing the left side of the printer shown in  FIG. 3 ; 
         FIG. 5  is a side view showing the right side of the printer shown in  FIG. 3  wherein the paper feed tray is removed; 
         FIG. 6  is a right side perspective view showing a positional relation between a frame and a high-voltage power supply board for a charger of the printer according to the embodiment; 
         FIG. 7  is a left side perspective view showing a positional relation between the frame and a drive unit control board of the printer according to the embodiment; and 
         FIG. 8  is a perspective view showing a connection of the respective boards of the printer according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following describes a laser printer to which the image forming apparatus according to the present invention is adopted. 
     It is to be noted that a paper feed tray  21  is diagrammatically shown in  FIG. 1 , and that a portion thereof projecting outside of the housing  3  is not shown in the figure. It is also to be noted that a drive unit  110  (see  FIG. 7 ) is not shown in  FIG. 4 . 
     1. Overall Structure of Laser Printer 
     Referring to  FIG. 1 , a laser printer  1  according to the present embodiment includes a housing  3 , formed approximately in a box shape (a cubical shape). In the top surface side of the housing  3 , a paper discharge tray  5  is disposed for placing paper, OHP sheets, and so on (to be simply referred to as paper) discharged from the housing  3  after printing. 
     The paper discharge tray  5  is constituted with a tilted surface  5 A, declined from the top surface of the housing  3  toward the rear side. In the rear end side of the tilted surface  5 A, a discharge unit  7  is provided. Paper, on which printing has been performed, is discharged to the discharge unit  7 . 
     Inside of the housing  3 , a frame  100  (see  FIG. 2 ), made of metal, resin, or the like, is disposed. Process cartridges  70  and a fixation unit  80 , to be described later, are attachably/detachably installed within the frame  100  disposed inside of the housing  3 . 
     2. Internal Structure of Laser Printer 
     As shown in  FIG. 1 , the laser printer  1  includes an image forming unit  10  and a feeder unit  20 . The image forming unit  10  forms an image on paper. The feeder unit  20  supplies paper to the image forming unit  10 . 
     The laser printer  1  further includes a conveyance mechanism  30  and a duplex printing unit  90 . The conveyance mechanism  30  conveys paper to four process cartridges  70 K,  70 Y,  70 M, and  70 C constituting the image forming unit  10 . The duplex printing unit  90  reconveys paper, on which printing (image formation) has been performed, to the image forming unit  10 . 
     2.1 Feeder Unit and Conveyance Mechanism 
     As shown in  FIG. 1 , the feeder unit  20  includes a paper feed tray  21 , a paper feed roller  23 . The paper feed tray  21  is stored in the bottom side of the housing  3 . The paper feed roller  23  is disposed above the front portion of the paper feed tray  21 , and feeds (conveys) paper, placed on the paper feed tray  21 , to the image forming unit  10 . 
     The paper feed tray  21  is installed in the body of the laser printer  1  in an attachable/detachable manner. An installation opening  22  (see  FIG. 3 ) is provided in the lower portion of the front surface of the body of the laser printer  1  so as to install the paper feed tray  21  therefrom. 
     The conveyance mechanism  30  includes a driving roller  31 , a driven roller  32 , and a conveyance belt  33 . The driving roller  31  is rotated corresponding to the operation of the image forming unit  10 . The driven roller  32  rotatably disposed in a position away from the driving roller  31 . The conveyance belt  33  runs between the driving roller  31  and the driven roller  32 . 
     When the conveyance belt  33  is rotated while carrying paper thereon, the paper, fed from the paper feed tray  21 , is conveyed sequentially to the four process cartridges  70 K,  70 Y,  70 M, and  70 C. 
     The conveyance mechanism  30  further includes a belt cleaner  34 . The belt cleaner  34  removes toner adhered to the conveyance belt  33 . 
     2.2 Image Forming Unit 
     The image forming unit  10  includes a scanner unit  60 , the process cartridges  70 , and the fixation unit  80 . 
     The image forming unit  10  according to the present embodiment is capable of color printing, and is so-called a tandem type direct printing unit. In the present embodiment, from the upstream side of the paper conveyance direction, the four process cartridges  70 K,  70 Y,  70 M, and  70 C, respectively corresponding to the four colors of toner (developer); black, yellow, magenta, and cyan, are aligned in series along the paper conveyance direction. 
     The four process cartridges  70 K,  70 Y,  70 M, and  70 C are different from one another only in the way that the colors of toner contained therein are different, but otherwise configured the same. Therefore, the four process cartridges  70 K,  70 Y,  70 M, and  70 C are generically referred to as the process cartridges  70 . 
     2.2.1. Scanner Unit 
     The scanner unit  60  is disposed in the upper portion inside of the housing  3 , and forms latent images on the surfaces of photoreceptor drums  71  respectively provided to the four process cartridges  70 K,  70 Y,  70 M, and  70 C. Specifically, the scanner unit  60  includes a laser beam source, a polygon mirror, a fθ lens, and reflection mirrors (not shown in the figure). 
     A laser beam LB, emitted from the laser beam source based on image data, is deflected by the polygon mirror, and passes through the fθ lens. The path of the beam is returned by the reflection mirror, and then further turned downward by the reflection mirror. The laser beam LB is emitted on the surfaces of the photoreceptor drums  71 , and latent images are formed. 
     2.2.2. Process Cartridges 
     As described above, the four process cartridges  70 K,  70 Y,  70 M, and  70 C are different from one another only in the way that the colors of toner contained therein are different, but otherwise configured the same. The following takes the process cartridge  70 C as an example and describes the structure thereof. 
     The process cartridge  70  is attachably/detachably disposed below the scanner unit  60  in the housing  3 . The process cartridge  70  includes a photoreceptor drum  71 , a charger  72 , and a process casing  75 . The process casing  75  stores a development cartridge  74  and so on. 
     A transfer roller  73  is disposed in the opposite side to the photoreceptor drum  71  across the conveyance belt  33 , and rotatably supported by the frame  100 . 
     The photoreceptor drum  71  holds an image to be transferred to paper. The charger  72  electrically charges the surface of the photoreceptor drum  71 . 
     In the present embodiment, a scorotron charger is used as the charger  72 . This type of charger positively charges the surface of the photoreceptor drum  71  in an approximately uniform manner by conducting corona discharge from a charging wire made of tungsten and the like. 
     The transfer roller  73  is disposed so as to face the photoreceptor drum  71 , and rotated corresponding to the rotation of the photoreceptor drum  71 . When paper passes in vicinity of the photoreceptor drum  71 , the transfer roller  73  applies electric charge (negative electric charge in the present embodiment), which is opposite to the electric charge charged on the photoreceptor drum  71 , to the paper from the opposite side of the printing surface. The transfer roller  73  thereby transfers toner, adhered to the surface of the photoreceptor drum  71 , on to the printing surface of the paper. 
     The development cartridge  74  includes a toner storage container  74 A, a toner supply roller  74 B, a development roller  74 C, and a layer thickness restriction blade  74 D. The toner storage container  74 A stores toner. The toner supply roller  74 B supplies toner to the photoreceptor drum  71 . 
     The toner, stored in the toner storage container  74 A, is supplied toward the development roller  74 C by the rotation of the toner supply roller  74 B. The toner supplied toward the development roller  74 C is held on the surface of the development roller  74 C, and adjusted by the layer thickness restriction blade  74 D so that the thickness of the toner held on the surface of the development roller  74 C becomes a constant (uniform) predetermined thickness. Then, the toner is supplied to the surface of the photoreceptor drum  71  exposed to laser beam LB by the scanner unit  60 . 
     2.2.3. Fixation Unit 
     The fixation unit  80  is disposed in the downstream side of the photoreceptor drum  71  in the paper conveyance direction. The fixation unit  80  fixes toner, transferred on to paper, by heating and melting the toner. The fixation unit  80  is attached to the frame  100  in an attachable/detachable manner. 
     Specifically, the fixation unit  80  includes a heat roller  81  and a pressure roller  82 . The heat roller  81  is disposed so as to face the printing surface of paper, and applies conveyance force to paper while heating toner. The pressure roller  82  is disposed on the other side of paper opposite to the heat roller  81 , and presses paper toward the heating roller  81 . 
     2.2.4. General Description of Image Forming Operation 
     As the photoreceptor drum  71  is rotated, the surface thereof is positively charged in a uniform manner by the charger  72 , and exposed to high-speed scanning of laser beam LB emitted from the scanner unit  60 . Consequently, on the surface of the photoreceptor drum  71 , a latent image based on image date is formed corresponding to an image to be formed on paper. 
     Subsequently, as the development roller  74 C is rotated, toner, held on the development roller  74 C and been positively charged, is supplied to the latent image formed on the surface of the photoreceptor drum  71  when the toner faces and contacts the photoreceptor drum  71 . That is, the toner is supplied to an exposed portion of the surface of the photoreceptor drum  71 , which is positively charged in a uniform manner. In the exposed portion, electric potential has become low due to exposure to the laser beam LB. The latent image on the photoreceptor drum  71  thereby becomes visualized, and a toner image by reversal development is held on the surface of the photoreceptor drum  71 . 
     Subsequently, the toner image, held on the surface of the photoreceptor drum  71 , is transferred on to paper by transfer bias applied to the transfer roller  73 . The paper, to which the toner image is transferred, is conveyed to the fixation unit  80 , and heated. The toner, transferred as the toner image, is fixed on the paper, and then, image formation is completed. 
     2.3. Duplex Printing Unit 
     The duplex printing unit  90  reconveys paper, on which printing (image formation) has been performed, to the image forming unit  10 , while the surface of the paper is reversed, so that images can be printed on both sides of the paper. The duplex printing unit  90  is disposed below the paper feed tray  21 . 
     The duplex printing unit  90  includes a guide member  91  which guides paper so as to inhibit paper, conveyed to the duplex printing unit  90  in duplex printing, from hitting the bottom portion of the paper feed tray  21 . 
     In single-side printing, paper fed from the paper feed tray  21  to the image forming unit  10  goes through the image forming operation wherein an image is formed on one printing surface. Then, conveyance of the paper is directed upward due to a discharge chute (not shown). The paper is discharged from the discharge unit  7  to the paper discharge tray  5  (see the dashed double-dotted line). 
     In the duplex printing, paper fed from the paper feed tray  21  to the image forming unit  10  goes through the image forming operation wherein an image is formed on one printing surface, and is conveyed toward the discharge unit  7 . When the trailing end of the paper in the conveyance direction reaches the discharge roller  9 , disposed in vicinity of the discharge unit  7 , the rotation of the discharge roller  9  is reversed. The paper, wherein an image is formed on one of the printing surfaces, is conveyed toward the duplex printing unit  90 , and then to the image forming unit  10  once again (see the bold dashed line). 
     2.4. Frame 
     As shown in  FIG. 2 , the frame  100  includes a first side-frame  101 , a second side-frame  102 , and a bottom frame  103 . The first and the second side-frames  101 ,  102  are disposed so as to face each other in the horizontal direction. The bottom frame  103  is disposed in the bottom portion of the laser printer  1 , and connects the bottom portions of the first and the second frames  101 ,  102 . 
     The frame  100  according to the present embodiment is made of resin, such as PC, ABS, polymer alloy, and the like, having a good mechanical strength. 
     In the present embodiment, the bottom frame  103  connects the first and the second side-frames  101 ,  102  in the vicinity of the installation opening  22  in the attachment/detachment direction of the paper feed tray  21  (in the front-to-rear direction of the laser printer  1  in the present embodiment). 
     The first and the second side-frames  101 ,  102  are formed approximately in a plate shape so as to extend in the vertical direction (in the up-and-down direction). The outer peripheries of the first and the second side-frames  101 ,  102  are respectively provided with projected walls (ribs)  104  so as to improve the mechanical strength of the frames  101 ,  102 . 
     As shown in  FIG. 2 , a low-voltage power supply circuit substrate  123  and a high-voltage power source board  125  for the charger  72 , which will be described later, are attached to the first side-frame  101 . To the second side-frame  102 , a main control board  121  and a drive unit control board  122 , which will be described later, are attached as shown in  FIG. 7 . The surfaces of the boards  121 ,  122 ,  124 , and  125  are all disposed approximately in parallel to the side-frames  101 ,  102  so as to extend in the vertical direction. 
     Between the second side-frame  102  and the drive unit control board  122 , a drive unit  110  is disposed. The drive unit  110  supplies rotational driving force to the drive roller  31  of the conveyance mechanism  30 , the photoreceptor drums  71  of the image formation unit  10 , and so on. The drive unit  110  includes an electric motor, which generates the rotational driving force, and a teeth mechanism having a plurality of teeth which transmits the rotational driving force generated by the electric motor to the driving roller  31 , the photoreceptor drums  71 , and so on. 
     As also shown in  FIG. 8 , the main control board  121  controls respective boards, to be described later, upon receiving a print command from a computer (not shown) connected to the laser printer  1 . The drive unit control board  122  controls the drive unit  110  based on a command signal from the main control board  121 . 
     The low-voltage power supply circuit substrate  123  supplies electric power to the drive unit control board  122 . The low-voltage power supply circuit substrate  123  provides the drive unit control board  122  with two types of electric power: electric power for driving the drive unit control board  122  (8V power supply in the present embodiment) and electric power for driving the drive unit  110  (24V in the present embodiment). 
     A high-voltage power supply board  124  for the transfer roller  73  is a high-voltage board which generates high voltage (equal to or higher than 1000V in the present embodiment) to be applied to the transfer roller  73  for transfer bias. The high-voltage power supply board  124  is disposed above the paper feed tray  21 , and supported by the top surface of a support frame  106  (see  FIG. 6 ) disposed between the first and the second side-frame  101 ,  102 . 
     The high-voltage power supply board  125  for the charger  72  generates high-voltage (equal to or higher than 1000V in the present embodiment) for the charger  72 . The high-voltage power supply board  125  is supported by the first side-frame  101 . 
     In the present embodiment, a command signal (control signal) from the main control board  121  is sent to both of the high-voltage power supply boards  124 ,  125  via the drive unit control board  122 . Therefore, both of the high-voltage power supply boards  124 ,  125  are controlled and operated electrically in conjunction with the drive unit control board  122 . 
     Electric power is supplied from the low-voltage power supply circuit substrate  123  to the high-voltage power supply board  125  and to the drive unit control board  122 . The electric power is further supplied from the drive unit control board  122  to the high-voltage power supply board  124  and to the main control board  121 . 
     The drive unit control board  122  and the main control board  121  are connected by a power line L 2  (see  FIG. 4 ). The drive unit control board  122  supplies the electric power to the main control board  121  through the power line L 2 . 
     The drive unit control board  122  and the main control board  121  are also connected by a signal line L 1  (see  FIG. 4 ). The main control board  121  outputs a control signal for controlling the drive unit control board  122  to the drive unit control board  122  through the signal line L 1 . 
     As shown in  FIGS. 5 and 6 , the high-voltage power supply boards  124 ,  125  are disposed above the paper feed tray  21 . Low-voltage power supply harnesses  126 ,  127 , which supply electric power from the low-voltage power supply circuit substrate  123  to the drive unit control board  122 , are disposed below the paper feed tray  21 . 
     The low-voltage power supply harness  126  is used so as to supply electric power for driving the drive unit control board  122 . The low-voltage power supply harness  127  is used so as to supply electric power for driving the driving unit  110 . 
     As shown in  FIG. 8 , a harness  128  connects the high-voltage power supply board  124  and the drive unit control board  122 . A harness  129  connects the high-voltage power supply board  125  and the drive unit control board  122 . 
     The drive unit control board  122  outputs a control signal for controlling the high-voltage power supply board  124  to the high-voltage power supply board  124  through the harness  128 , and outputs a control signal for controlling the high-voltage power supply board  125  to the high-voltage power supply board  125  through the harness  129 . 
     As shown in  FIG. 8 , the low-voltage power supply harnesses  126 ,  127  are disposed along the top surface of the bottom frame  103  so as to extend between the first side-frame  101  (in the right side in  FIG. 8 ) and the second side-frame  102  (in the left side in  FIG. 8 ) in the lowest portion of the body of the laser printer  1 . 
     The low-voltage power supply harnesses  126 ,  127  are protected by a protection cover  105  which covers the low-voltage power supply harnesses  126 ,  127  with the bottom frame  103  so as to sandwich the harnesses  126 ,  127  therebetween. 
     In the present embodiment, the protection cover  105  is made of resin or metal, and attached to the bottom frame  103  by an elastically deformable locking member or an attachable/detachable mechanical fixing member, such as a screw. 
     3. Feature of Laser Printer in Present Embodiment 
     In the present embodiment, the high-voltage power supply boards  124 ,  125  are disposed in the top side of the paper feed tray  21  and the low-voltage power supply harnesses  126 ,  127  are disposed in the bottom side of the paper feed tray  21 . In other words, the paper feed tray  21  interposes between the low-voltage electric harnesses  126 ,  127  and the high-voltage power supply boards  124 ,  125 . 
     Therefore, the low-voltage electric harnesses  126 ,  127  can be insulated from the high-voltage power supply boards  124 ,  125 . As a result, the low-voltage power supply harnesses  126 ,  127  can be inhibited from being influenced by high voltage, as compared to a ease, for example, wherein the low-voltage power supply harnesses  128 ,  127  are disposed together with a high-voltage board, such as the high-voltage power supply board  124 , in one side of the paper feed tray  21 . 
     If the low-voltage power supply harnesses  126 ,  127  are disposed in the bottom side of the bottom frame  103 , extra assembling processes are required for attaching the harnesses  126 ,  127  because the harnesses  126 ,  127  are disposed in the rear side of the bottom frame  103  and cannot be directly seen. The laser printer  1  needs to be reversed in the up-and-down direction in order to attach the low-voltage power supply harnesses  126 ,  127 . 
     On the other hand, in the present embodiment, the low-voltage power source harnesses  126 ,  127  are disposed on the top side of the bottom frame  103 , and can be directly seen through the installation opening  22 . 
     Therefore, the laser printer  1  does not have to be reversed in the up-and-down direction in order to attach the harnesses  126 ,  127 . As a result, the number of assembling processes and the manufacturing cost of the laser printer  1  can be reduced. 
     Moreover, since the low-voltage electric harnesses  126 ,  127  are disposed in the vicinity of the installation opening  22 , assembling personnel can attach the harnesses  126 ,  127  to the bottom frame  103  from the installation opening  22 . 
     As compared to a case wherein the low-voltage power supply harnesses  126 ,  127  are disposed in the rear side away from the installation opening  22 , the harnesses  126 ,  127  can be more easily disposed. Therefore, the number of assembling processes of the laser printer  1  can be reduced. 
     In the present embodiment, the bottom frame  103  is disposed toward the installation opening  22  in the body of the laser printer  1 . Thus, when the low-voltage power supply harnesses  126 ,  127  are disposed along the frame  100 , the harnesses  126 ,  127  are consequently disposed in the vicinity of the installation opening  22 . In case the bottom frame  103  is formed in a plate shape extending approximately in the entire area in the insertion direction, the harnesses  126 ,  127  should be preferably disposed in a portion of the plate-shaped bottom frame  103  in the vicinity of the installation opening  22 . 
     In the present embodiment, due to the protection cover  105  being provided for covering the low-voltage power supply harnesses  126 , the endurance period of the harnesses  126 ,  127  can be inhibited from being short  127 , which otherwise may be caused by the paper feed tray  21  and the harnesses  126 ,  127  being in friction and being abraded. 
     Furthermore, in the present embodiment, the first and the second side-frames  101 ,  102  are formed approximately in a plate shape so as to extend in the vertical direction. The surfaces of the low-voltage power supply circuit substrate  123  and the high-voltage power supply board  125  are attached to the first side-frame  101  so as to be in parallel to the first side-frame  101 . The surfaces of the drive unit control board  122  and the main control board  121  are attached to the second side-frame  102  so as to be approximately in parallel to the second side-frame  102 . Therefore, as compared to a case wherein all the boards  121 ,  122 , and  125  and substrate  123  are disposed so as to extend in the horizontal direction, the size of the laser printer  1  in the horizontal direction can be reduced. 
     Still furthermore, in the present embodiment, the duplex print unit  90  is disposed in the lowest portion of the body of the laser printer  1  so as to effectively use the dead space, created in the lowest portion of the laser printer  1 , and the bottom frame  103 , and to dispose the low-voltage power source harnesses  126 ,  127 . Therefore, the low-voltage power source harnesses  126 ,  127  can be inhibited from being influenced by high voltage, such as from the high-voltage electric board  124  and the like, without making major changes in the structure of the laser printer  1 . 
     Other Embodiment 
     In the above-described embodiment, the drive unit control board  122  is attached to the second side-frame  102  such that the drive unit  110  interposes therebetween. However, the present invention is not limited to the above structure. The drive unit control board  122  may be directly attached to the second side-frame  102 . 
     Moreover, in the above-described embodiment, the high-voltage power supply boards  124 ,  125  are disposed above the paper feed tray  21  whereas the low-voltage power supply harnesses  126 ,  127  are disposed below the paper feed tray  21 . The present invention is characterized in disposing the high-voltage power supply boards  124 ,  125  in one side of the paper feed tray  21 , and the low-voltage power supply harnesses  126 ,  127  in another side. Therefore, the high-voltage power supply board may be, for example, disposed in the right side of the paper feed tray  21 , and the low-voltage power supply harnesses  126 ,  127  may be disposed in the left side. 
     In addition, in the above-described embodiment, the low-voltage power source harnesses  126 ,  127  are disposed in the top side of the bottom frame  103 . However, the present invention is not limited to the above structure. The low-voltage power supply harnesses  126 ,  127  may be disposed in the bottom side of the bottom frame  103 . 
     Moreover, in the above-described embodiment, the protection cover  105  is provided. However, the present invention is not limited to the above structure. A groove, for example, may be provided to the bottom frame  103 , instead of the protection cover  105 , so as to lay the low-voltage power source harnesses  126 ,  127  in the groove. 
     Furthermore, in the above-described embodiment, the present invention is applied to the laser printer  1  including the duplex print unit  90 . However, application of the present invention is not limited to the above application. 
     Although specific embodiments have been illustrated and described herein, it is to be understood that the above description is intended to be illustrative, and not restrictive. Combinations of the above embodiments and other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention includes any other applications in which the above structures are used. Accordingly, the scope of the invention should only be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.