Abstract:
An image forming apparatus includes: a photosensitive drum; a developing unit; a casing; and a supporting member. The developing unit includes a developing agent bearing member. The developing agent bearing member has an axis extending in an axial direction and defines a first side and a second side opposite to the first side in the axial direction. The casing is configured to support the photosensitive drum and the developing unit. The casing has a sidewall at a position corresponding to the first side. The developing unit is detachable from and attachable to the casing along the axial direction. The supporting member is configured to guide a movement of the developing unit in the axial direction and protrudes outward from the sidewall.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 13/796,476 filed Mar. 12, 2013 which claims priority from Japanese Patent Application No. 2012-124413 filed May 31, 2012. The entire contents of the above-noted applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an image forming apparatus including a developing unit detachably mountable in a casing thereof. 
     BACKGROUND 
     There is conventionally known an image forming apparatus provided with a main casing, an intermediate transfer belt, a plurality of process units disposed below the intermediate transfer belt, and a drawer supporting the plurality of process units and drawable from the main casing. In this configuration, the process units each integrally include a photosensitive drum and a developing unit having a developing roller for supplying toner to the photosensitive drum and a toner chamber, and can each be replaced with new one by drawing the drawer from the main casing. 
     SUMMARY 
     In general, the photosensitive drum is replaced with new one at a frequency lower than a frequency of toner replacement (i.e., replacement of the developing unit). Therefore, also in the above-mentioned configuration, the developing unit is desired to be replaced without removing the photosensitive drum from the main casing. 
     In order to achieve this, a configuration may be possible in which the developing roller (developing unit) is slightly separated from the photosensitive drum, and then the developing unit is drawn in an axial direction of the developing roller. In this case, however, there is a possibility that the developing unit slightly moves in a direction perpendicular to the axial direction of the developing roller while the developing unit is drawn in the axial direction, which causes the developing roller and the photosensitive drum to slidingly contact with each other, thereby damaging the photosensitive drum. 
     In view of the foregoing, it is an object of the present invention to provide an image forming apparatus capable of suppressing interference between the developing agent bearing member and the photosensitive drum when the developing unit is moved in the axial direction. 
     In order to attain the above and other objects, the present invention provides an image forming apparatus that may include: a photosensitive drum; a developing unit; a casing; and a supporting member. The developing unit may include a developing agent bearing member. The developing agent bearing member may have an axis extending in an axial direction and define a first side and a second side opposite to the first side in the axial direction. The casing may be configured to support the photosensitive drum and the developing unit. The casing may have a sidewall at a position corresponding to the first side. The developing unit may be detachable from and attachable to the casing along the axial direction. The supporting member may be configured to guide a movement of the developing unit in the axial direction and protrude outward from the sidewall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings; 
         FIG. 1  is a cross-sectional view of a color printer according to one embodiment of the present invention; 
         FIG. 2  is a partial cross-sectional view of the color printer according to the embodiment, showing a state in which a photosensitive member unit is drawn outward of a main casing; 
         FIG. 3  is a perspective view of the photosensitive member unit in a state where a developing unit is at a proximity position; 
         FIG. 4A  is a cross-sectional view of the photosensitive member unit in the state where the developing unit is at the proximity position; 
         FIG. 4B  is a partial side view of the photosensitive member unit in the state where the developing unit is at the proximity position; 
         FIG. 5  is a perspective view of the photosensitive member unit in a state where the developing unit is at a separated position; 
         FIG. 6A  is a cross-sectional view of the photosensitive member unit in the state where the developing unit is at the separated position; 
         FIG. 6B  is a partial side view of the photosensitive member unit in the state where the developing unit is at the separated position; 
         FIG. 7  is a perspective view of the photosensitive member unit in a state where the developing unit is at a pivoted position; 
         FIG. 8A  is a cross-sectional view of the photosensitive member unit in the state where the developing unit is at the pivoted position; 
         FIG. 8B  is a partial side view of the photosensitive member unit in the state where the developing unit is at the pivoted position; 
         FIG. 9  is a perspective view of the photosensitive member unit in a state where one of the developing unit is drawn out in an axial direction from the pivoted position; 
         FIGS. 10A and 10B  are views for illustrating a structure of a moving assembly, in which  FIG. 10A  shows the moving assembly in the state where the developing unit is at the proximity position; and  FIG. 10B  shows the moving assembly in the state where the developing unit is at the separated position; and 
         FIGS. 11A and 11B  are schematic perspective views for illustrating how the developing unit is detached, in which  FIG. 11A  shows a state where the color printer is installed in a narrow shelf; and  FIG. 11B  shows a state where the developing unit is detached from a drawer casing that has been drawn from the main casing. 
     
    
    
     DETAILED DESCRIPTION 
     A color printer as an image forming apparatus according to one embodiment of the present invention will be described with reference to  FIGS. 1 through 11B . Throughout the specification, the terms “upward”, “downward”, “upper”, “lower”, “above”, “below”, “beneath”, “right”, “left”, “front”, “rear” and the like will be used assuming that the color printer  1  is disposed in an orientation in which it is intended to be used. More specifically, in  FIG. 1  a left side and a right side are a front side and a rear side, respectively. Further, in  FIG. 1  a near side and a far side are a right side and a left side, respectively. Further, in  FIG. 1 , a top side and a bottom side are a top side and a bottom side, respectively. 
     Referring to  FIG. 1 , the color printer  1  includes a main casing  10 , and within the main casing  10 , further includes a sheet supply unit  30 , a scanner unit  40 , a photosensitive member unit  50 , a transfer unit  60 , and a fixing unit  70 . 
     A discharge tray  11  onto which a sheet S discharged from the main casing  10  is placed is provided at an upper portion of the main casing  10 . Further, a front cover  13  is supported to a front wall of the main casing  10 . The front wall of the main casing  10  is formed with an opening  12  through which the photosensitive member unit  50  is drawn outside the main casing  10 . The front cover  13  is pivotally movable between an open position for opening the opening  12  and a closed position for closing the opening  12 . 
     The sheet supply unit  30  is provided at a lower portion of the main casing  10 , and includes a sheet supply tray  31  and a sheet supplying mechanism  32 . The sheet supply tray  31  is adapted to accommodate the sheets S therein. The sheet supplying mechanism  32  is adapted to convey the sheets S from the sheet supply tray  31  to a transfer position (a portion between an intermediate transfer belt  63  and a secondary transfer roller  65 ). The sheets S accommodated in the sheet supply tray  31  are separately conveyed one by one by the sheet supplying mechanism  32  to the transfer position. 
     The scanner unit  40  is disposed above the sheet supply tray  31 , and includes a laser beam emitting portion, a polygon mirror, a lens, and a reflection mirror (which are not illustrated). A laser beam emitted from the scanner unit  40  passes through each path denoted by a chain double-dashed line to be irradiated onto a surface of each photosensitive drum  51  inside the photosensitive member unit  50  with high-speed scanning. 
     The photosensitive member unit  50  is disposed above the scanner unit  40 . The photosensitive member unit  50  is supported to the main casing  10  and movable (drawable) in a frontward/rearward direction. More specifically, the photosensitive member unit  50  is movable through the opening  12  of the main casing  10  between an inside position (position illustrated in  FIG. 1 ) at which the photosensitive member unit  50  is positioned inside the main casing  10  and an outside position (position illustrated in  FIG. 2 ) at which the photosensitive member unit  50  is positioned outside the main casing  10 . 
     It should be noted that, when the photosensitive member unit  50  is at the outside position as shown in  FIG. 2 , the photosensitive member unit  50  is still partly attached to the main casing  10 . However, the photosensitive member unit  50  may be entirely detached from the main casing  10  when the photosensitive member unit  50  is at the outside position. 
     The photosensitive member unit  50  includes four photosensitive drums  51 , four developing units  52 , and a drawer casing  80 . Details of the drawer casing  80  will be described later. 
     The photosensitive drums  51  are arranged spaced apart from each other in the frontward/rearward direction and are each rotatably supported to left and right side walls  81  of the drawer casing  80 , as illustrated in  FIG. 3 . Each photosensitive drum  51  has a surface to be charged by a charging roller  53 , as illustrated in  FIG. 1 . 
     The developing units  52  are each detachably supported to the drawer casing  80 , and each include a developing roller  52 A (developing agent bearing member), a toner supply roller  52 B, a layer thickness regulating blade  52 C, and a toner chamber  52 D. The developing roller  52 A has an axis extending in the rightward/leftward direction (axial direction). 
     The transfer unit  60  is disposed above the photosensitive member unit  50 , and includes a drive roller  61 , a driven roller  62 , the endless intermediate transfer belt  63 , and four primary transfer rollers  64 , and the secondary transfer roller  65 . The intermediate transfer belt  63  is stretched around the drive roller  61  and the driven roller  62 . The four primary transfer rollers are disposed opposite to the four photosensitive drums  51 , respectively, with the intermediate transfer belt  63  interposed therebetween. The secondary transfer roller  65  is disposed opposite to the drive roller  61  with the intermediate transfer belt  63  interposed therebetween. 
     In the photosensitive member unit  50  and the transfer unit  60  described above, after the surface of the photosensitive drum  51  is uniformly charged by the charging roller  53 , the surface is exposed to the laser beam emitted from the scanner unit  40 , whereby an electrostatic latent image based on image data is formed on the surface. The toner accommodated in the toner chamber  52 D is supplied, through the toner supply roller  52 B, to the developing roller  52 A to be carried on a surface thereof in a form of a thin toner layer having a uniform thickness by the layer thickness regulating blade  52 C. 
     The toner carried on the surface of the developing roller  52 A is supplied to the electrostatic latent image formed on the surface of the photosensitive drum  51 . As a result, a visible toner image corresponding to the electrostatic latent image is formed on the surface of the photosensitive drum  51 . Toner images of different colors formed on the respective photosensitive drums  51  are sequentially transferred onto the intermediate transfer belt  63  in an overlapping manner. Then, the sheet S conveyed from the sheet supply unit  30  passes through the transfer position between the intermediate transfer belt  63  and the secondary transfer roller  65 , whereby the toner images on the intermediate transfer belt  63  are transferred onto the sheet S as one toner image. 
     The fixing unit  70  is disposed above and rearward of the transfer unit  60 , and includes a heat roller  71  and a pressure roller  72 . The pressure roller  72  is disposed in confrontation with the heat roller  71  and adapted to press the heat roller  71 . In the fixing unit  70 , while the sheet S onto which the toner image has been transferred passes between the heat roller  71  and the pressure roller  72 , the toner image is thermally fixed onto the sheet S. The sheet S discharged from the fixing unit  70  is discharged outside the main casing  10  by a discharge roller  73  to be placed onto the discharge tray  11 . 
     &lt;Structure of Drawer Casing  80 &gt; 
     As illustrated in  FIG. 3 , the drawer casing  80  has left and right side walls  81 , a front wall  82  connecting front ends of the side walls  81 , and a rear wall  83  connecting rear ends of the side walls  81 . Hereinafter, the side wall  81  on the left side will be referred to as the left side wall  81 L, and the side wall  81  on the right side will be referred to as the right side wall  81 R, when it is necessary to distinguish between the two. 
     The right side wall  81 R is formed with four openings  81 A through which the four developing units  52  are individually drawn diagonally below and rightward. The four openings  81 A are arranged spaced apart from each other in the frontward/rearward direction. A holding portion  82 A is provided at the front wall  82 . The holding portion  82 A is adapted to be held by a user when the user draws the drawer  80  from the main casing  10 . 
     Further, the drawer casing  80  includes eight moving assemblies  90 , four of which are provided outside the left side wall  81 L and the remaining four are outside the right side wall  81 R (see  FIG. 4A ), and four supporting members  100  which are provided in the drawer casing  80 . Each moving assembly  90  is adapted to move the developing roller  52 A in proximity to (in contact with) the photosensitive drum  51  and away from the photosensitive drum  51 . Each supporting member  100  is adapted to pivotally move the developing unit  52 , which has been moved away from the photosensitive drum  51  by the moving assemblies  90 , in a direction away from the photosensitive drum  51 . The supporting member  100  has a left end portion at which a pivot shaft  101  is provided. 
     The moving assemblies  90  and the supporting members  100  having the above-described configurations allow the developing unit  52  to be moved to a proximity position as illustrated in  FIGS. 3, 4A and 4B , a separated position as illustrated in  FIGS. 5, 6A and 6B , and a pivoted position as illustrated in  FIGS. 7, 8A and 8B . 
     More specifically, the proximity position is a position of the developing unit  52  at which the developing roller  52 A is brought into proximity to (into contact with) the photosensitive drum  51 . At this proximity position, the developing unit  52  is pressed against the photosensitive drum  51  by the corresponding right and left moving assemblies  90  while being supported thereby. In this state, the developing unit  52  is spaced away from the corresponding supporting member  100 . 
     When the developing unit  52  is at the proximity position, the developing operation can be performed. In case of contact development, the developing roller  52  is in contact with the photosensitive drum  51  when the developing unit  52  is at the proximity position. In case of non-contact development, the developing roller  52  is not in contact with but in proximity to the photosensitive drum  51  when the developing unit  52  is at the proximity position. 
     The separated position is a position of the developing unit  52  at which the developing roller  52 A is spaced apart from the photosensitive drum  51  while a parallel positional relationship therebetween is maintained. At the separated position, the developing roller  52 A is positioned farther from the photosensitive drum  51  than at the proximity position. At this separated position, the supported state of the developing unit  52  by the corresponding right and left moving assemblies  90  is released, and the developing unit  52  is supported by the corresponding supporting member  100 . 
     The pivoted position is a position of the developing unit  52  at which the developing roller  52 A is pivotally moved about the pivot shaft  101  from the separated position in the direction away from the photosensitive drum  51 . The developing unit  52 , being supported by the supporting member  100  and pivotally moved from the separated position to the pivoted position to be set at the pivoted position, can be drawn (detached) from the drawer casing  80  along the axial direction of the developing roller  52 A (in a diagonally rightward and downward direction), as illustrated in  FIG. 9 . 
     Thus, by pivotally moving the developing unit  52  from the separated position to the pivoted position, the developing roller  52 A at the pivoted position can be distanced from the photosensitive drum  51  greater than at the separated position, so that the developing roller  52 A can be prevented from interfering with the photosensitive drum  51  when the developing unit  52  is moved in the axial direction. 
     More specifically, as illustrated in  FIGS. 3, 4A and 4B , the supporting member  100  is formed in an elongated shape extending in the rightward/leftward direction. The pivot shaft  101  provided at the left end portion of the supporting member  100  is pivotally movably supported to the drawer casing  80 . Hence, the supporting member  100  can be pivotally moved between the separated position and the pivoted position together with the developing unit  52  while supporting the developing unit  52 . 
     Further, the developing unit  52  is moved to the pivoted position by pivotally moving the supporting member  100 , so that the developing unit  52  can be moved by an operation on one end portion of the supporting member  100  in the axial direction, which is easier than a case where the supporting member  100  is slidingly moved parallel to the photosensitive drum  51 . 
     Further, the supporting member  100  is configured so as to guide the movement of the developing unit  52  in the axial direction. For example, as the guide structure, there can be exemplified a structure in which a convex portion and a concave portion that can be slidably engaged with each other in the axial direction are formed in an upper surface of the supporting member  100  and a lower surface of the developing unit  52 , respectively. 
     As a result, the developing unit  52  can be drawn while being guided by the supporting member  100 , so that the developing unit  52  can be prevented from interfering with the drawer casing  80 . 
     The supporting member  100  has a right end portion protruding through an opening  81 A of the drawer casing  80 . This configuration allows a user to easily grip the supporting member  100 , enhancing operability of the supporting member  100 . Further, with such a configuration, the developing unit  52  can be drawn to the nearer side with respect to the user, facilitating taking-out of the developing unit  52  from the drawer casing  80 . 
     The supporting member  100  is configured to be supported to the drawer casing  80  at the separated position in such a manner that a shallow concave portion formed in the right end portion of the supporting member  100  is engaged with a low convex portion formed in the right side wall  81 R of the drawer casing  80 . 
     The supporting member  100  is disposed below the developing unit  52  (i.e. on an opposite side of the developing roller  52 A with respect to the toner chamber  52 D: see  FIG. 1 ), whereas, as illustrated in  FIGS. 3 and 10A , the moving assembly  90  is disposed on the developing roller  52 A side. Thus, the moving assembly  90  and the supporting member  100  are distanced from each other, so that interference therebetween can be prevented. 
     Further, with this configuration, in a state where the supporting member  100  is pivotally moved to set the developing unit  52  at the pivoted position, the developing unit  52  can be drawn from the drawer casing  80  without interfere with the moving assembly  90 . 
     Specifically, the moving assembly  90  includes a cam member  91 , a gear member  92 , and a coil spring  93 . 
     The cam member  91  is formed in a generally sector shape and mounted to the drawer casing  80  through the gear member  92  so as to be pivotally movable with respect to the drawer casing  80  and the gear member  92 . 
     The cam member  91  has, on its front side (downstream side of the cam member  91  in a pivotally moving direction of the cam member  91  in a state where the cam member  91  presses the developing unit  52  toward the proximity position), a cam surface  91 A. The cam surface  91 A is adapted to abut against the developing unit  52  to press the developing unit  52  in a direction from the separated position to the proximity position. 
     More specifically, at the proximity position illustrated in  FIG. 10A , the cam surface  91 A is configured to abut against a bearing portion  521  that supports a rotation shaft of the developing roller  52 A from a diagonally lower-front side thereof. 
     Further, the cam member  91  has, on its rear side (upstream side of the cam member  91  in the pivotally moving direction of the cam member  91  in the state where the cam member  91  presses the developing units  52  toward the proximity position), an urged surface  91 B. 
     The coil spring  93  is provided between the urged surface  91 B of the cam member  91  and the gear member  92 . The cam member  91  is urged in the clockwise direction in  FIG. 10A  by the coil spring  93 . Thus, at the proximity position, the developing roller  52 A is pressed against the photosensitive drum  51  by the urging force of the coil spring  93 . 
     The gear member  92  has a hollow configuration so as to accommodate the cam member  91 . The gear member  92  is pivotally movably provided at the drawer casing  80 . The gear member  92  has a gear tooth portion  92 A at a part of an outer peripheral surface thereof and a V-shaped notch  92 B at the remaining part of the outer peripheral surface thereof. An intermediate gear  110  rotatably provided at the drawer casing  80  meshingly engages with the gear tooth portion  92 A. To the intermediate gear  110 , a clockwise or counterclockwise rotary drive force is transmitted as needed from a motor controlled by a control device (not illustrated) provided in the main casing  10 . 
     Specifically, for example, when a print mode is switched from a color mode to a monochromatic mode, a rotary drive force in one of the clockwise direction and the counterclockwise direction is transmitted to the intermediate gears  110  corresponding to the colors other than black, causing the corresponding gear members  92  to pivotally move counterclockwise from a state illustrated in  FIG. 10A  to a state illustrated in  FIG. 10B . As a result, the supported state of the developing unit  52  by the cam members  91  is released, and the developing unit  52  is moved downward by its own weight (or by receiving pressure from end faces B 2  (described later) of the gear members  92 ) to the separated position. 
     On the other hand, when the print mode is switched from the monochromatic mode to the color mode, a rotary drive force in the remaining one of the clockwise direction and the counterclockwise direction is transmitted to the intermediate gears  110  corresponding to the colors other than black, causing the corresponding gear members  92  to pivotally move clockwise from the state illustrated in  FIG. 10B  to the state illustrated in  FIG. 10A . As a result, the developing unit  52  is pressed upward to the proximity position by the cam members  91  pivotally moving together with the gear members  92 . 
     The bearing portion  521  of the developing unit  52  is disposed within the notch  92 B. The notch  92 B is defined by an end face B 1  and the end face B 2  of the gear member  92 . In the state illustrated in  FIG. 10A , the end face B 1  is positioned frontward of the end face B 2 . At the proximity position illustrated in  FIG. 10A , the cam surface  91 A protrudes diagonally above and rearward from the end face B 1  to abut against the bearing portion  521 . 
     Further, at the separated position illustrated in  FIG. 10B , the end face B 2  abuts against the bearing portion  521  from a diagonally upper-rear side thereof. As a result, the bearing portion  521  is pressed by the end face B 2  diagonally downward and frontward, thereby allowing the developing unit  52  to be moved reliably from the proximity position to the separated position. 
     As illustrated in  FIG. 10B , in a state where the developing unit  52  is at the separated position, the notch  92 B faces the opening  81 A formed in the drawer casing  80 . This eliminates the need to pivotally move the developing unit  52  from the separated position at a greater angle than, for example, in a configuration not including the notch in order for the developing unit  52  to be drawn from the drawer casing  80  without interference with the moving assembly  90 , allowing a size reduction of the entire apparatus. 
     Further, in the state where the developing unit  52  is at the separated position, the moving assembly  90  has a portion overlapping the developing unit  52  as viewed in the rightward/leftward direction (axial direction). This allows a user to understand that the developing unit  52  at the separated position cannot be drawn from the drawer casing  80  in the axial direction due to presence of the moving assembly  90 , thereby prompting the user to pivotally move the developing unit  52  to the pivoted position, which can reliably prevent interference between the developing roller  52 A and the photosensitive drum  51 . 
     In the thus configured color printer  1 , the developing unit  52  can be reliably replaced with new one even when the printer  1  is installed in a narrow shelf  200  as illustrated in  FIG. 11A . More specifically, when the developing unit  52  is to be replaced with new one, the user initially opens the front cover  13  as illustrated in  FIG. 11B . 
     At this time, the developing units  52  in the color printer  1  are all at the separated positions. The following can be considered as a method for allowing the developing units  52  to be moved to the separated positions at the opening of the front cover  13 : the moving assembly  90  is configured to operate in conjunction with the pivotal movement (opening movement) of the front cover  13 ; or a sensor detecting the opening of the front cover  13  is provided and, based on a signal from the sensor, a control device controls a motor (or the moving assembly  90 ) such that each developing unit  52  is moved to the separated position. 
     After opening the front cover  13 , the user draws the drawer casing  80  up to outside the shelf  200 . Thus, in a state where the drawer casing  80  has been drawn, the openings  81 A of the drawer casing  80  come out of a side wall of the shelf  200 , allowing the developing units  52  to be attached to and detached from the drawer casing  80  through the openings  81 A. 
     Thereafter, the user pushes down the right end portion of the supporting member  100  (not illustrated in  FIG. 11B ), whereby the developing unit  52  to be replaced can be drawn diagonally rightward and downward from the drawer casing  80  through the opening  81 A. 
     In the case of a structure other than the drawer type in which the developing unit is drawn from the main casing through an opening formed in a side wall of the main casing, when the apparatus is installed in such a narrow shelf, the developing unit cannot be drawn in the rightward/leftward direction due to existence of the left and right side walls of the shelf, so that the drawer type of the present embodiment is especially effective when the apparatus is installed in the narrow shelf. 
     In the above-described embodiment, the following advantageous effects can be obtained in addition to those described above. 
     The moving assembly  90  is configured to be pivotally movable, so that a structure can be simplified more than in a configuration in which the moving assembly is configured to be, e.g., linearly movable. 
     Drawing-out of the drawer casing  80  allows drawing-out of the plurality of photosensitive drums  51  to a position outside the main casing  10  where replacement can be easily made, so that efficiency of the replacement work of the photosensitive drum  51  can be enhanced more than in a structure other than the drawer type in which the plurality of photosensitive drums are supported to the main casing. 
     The moving assembly  90  is provided at the drawer casing  80 , so that positioning accuracy of the drawer casing  80  with respect to the main casing  10  need not be enhanced as compared to a configuration in which the moving assembly is provided at the main casing, thereby simplifying the structure. 
     Further, when the drawer casing  80  is drawn from the main casing  10 , the moving assembly  90  and the drawer casing  80  are unlikely to interfere with each other. 
     Further, various modifications are conceivable. 
     Although the drawer casing  80  is exemplified as a claimed casing in the above-described embodiment, the present invention is not limited to this. For example, the casing may be the main casing. That is, a configuration may be possible in which the supporting member and the moving assembly are provided at the main casing, and the developing unit is drawn from the main casing through an opening formed in the main casing. 
     Although the moving assembly  90  and the supporting member  100  are formed as separate members in the above-described embodiment, the present invention is not limited to this. For example, the moving assembly and the supporting member may be formed as one combined member. 
     More specifically, for example, the supporting member  100  in the above-described embodiment may be made movable also in a direction pressing the developing roller against the photosensitive drum. That is, the supporting member may be configured to exert also the function of the moving assembly. 
     Although the present invention is applied to the color printer  1 , the present invention is not limited to this. The present invention may be applied to another type of an image forming apparatus, such as a monochromatic printer, a monochromatic copier, or a monochromatic multifunction machine. 
     While the present 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 present invention.