Abstract:
An image forming apparatus includes an image carrier unit, a unit containing portion, a plurality of driving units, a plurality of driving source, and a phase change matching unit. The image carrier unit integrally has a plurality of image carriers that respectively carries images, and respectively has rotational shafts. The unit containing portion removably contains the image carrier unit. Each of the driving units includes at least one driving gear, and transmits driving force by the driving gear to the rotational shaft of one of the image carriers that corresponds thereto. The plurality of driving source applies the driving force to the driving gears of the driving units. The phase change matching unit matches phase changes in the driving gears of the driving units when no image is formed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Japanese Patent Application No. 2006-50366 filed Feb. 27, 2006 in the Japan Patent Office, the disclosure of which is incorporated herein by reference.  
       BACKGROUND  
       [0002]     The present invention relates to an image forming apparatus including: an image carrier unit integrally having a plurality of image carriers, which respectively carries an image; and a unit containing portion which removably contains the image carrier unit. The present invention also relates to a technique associated with the image forming apparatus.  
         [0003]     Conventional laser color printers are generally provided with a plurality of photoreceptor drums for carrying images corresponding to the respective colors in one direction.  
         [0004]     In addition, some conventional laser color printers are provided with a plurality of drive motors corresponding to the respective photoreceptor drums rotatably secured to the bodies of the printers, so that the driving force of each drive motor can be individually transmitted to each of the photoreceptor drums, and thus, can drive all of the photoreceptor drums stably with a sufficient driving force.  
         [0005]     In such laser color printers, a drum gear for transmitting a driving force to a photoreceptor drum is connected to each of the photoreceptor drums, and a plurality of body gears which receive a driving force from the drive motors are engaged with the respective drum gears.  
         [0006]     The drum gears and the body gears are formed in such a manner that the center of each circle works as the center of rotation. However, in a precise sense, the center of rotation slightly deviates from the center of the circles. Therefore, the displacement rate on the outer circumference of the gears at the time of rotation (the displacement amount on the outer circumference per unit time) is not constant.  
         [0007]     When images, carried by respective the photoreceptor drums, are sequentially superposed on a sheet of paper conveyed in the above-described laser printer, the respective images are misaligned due to the dislocation of the center of gear rotation. A solution is required so as to inhibit misalignment of images carried by the photoreceptor drums.  
         [0008]     For this purpose, in the above-described laser printer, a phase reference point is predetermined for the respective gears based on the dislocation of the rotational center, and the phase differences between the adjacent drum gears and between the adjacent body gears are set so as to be respectively constant.  
       SUMMARY  
       [0009]     In the above-described laser color printers, the photoreceptor drums are secured to the bodies of the laser color printers, and this results in a problem such that in some cases, the maintenance work becomes difficult.  
         [0010]     Therefore, a configuration is considered in this laser color printers wherein a plurality of photoreceptor drums are integrated as one unit, and configured so as to he removable from the body of the laser color printer,  
         [0011]     In this case, there is a possibility that the drum gears and the body gears may interfere with each other when the photoreceptor drums are removed or a user accidentally touches a photoreceptor drum, a drum gear or a body gear after the photoreceptor drums are removed, and thus, these gears may rotate, and make the phase differences between the adjacent drum gears or between the adjacent body gears out of predetermined phase differences.  
         [0012]     For this reason, in one aspect of the present invention, a technique is preferably provided wherein a plurality of image carriers integrated in a removable manner can be stably driven by a plurality of driving sources, and wherein phase differences between the adjacent gears for driving the image carriers can be inhibited from becoming out of predetermined phase differences.  
         [0013]     In one aspect of the present invention, an image forming apparatus includes an image carrier unit, a unit containing portion, a plurality of driving units, a plurality of driving source, and a phase change matching unit. The image carrier unit integrally has a plurality of image carriers that respectively carries images, and respectively has rotational shafts. The unit containing portion removably contains the image carrier unit. Each of the driving units includes at least one driving gear, and transmits driving force by the driving gear to the rotational shaft of one of the image carriers that corresponds thereto. The plurality of driving source applies the driving force to the driving gears of the driving units. The phase change matching unit matches phase changes in the driving gears of the driving units when no image is formed.  
         [0014]     In this image forming apparatus, all the phase changes between the driving gears match, when no image is formed. Therefore, phase differences between the adjacent driving gears may be inhibited from becoming out of predetermined phase differences.  
         [0015]     In another aspect of the present invention, an image carrier unit includes a plurality of image carriers, a housing, a plurality of first gears, and a phase change matching unit. The plurality of image carriers respectively carries images, and has rotational shafts. The housing integrally supports the plurality of image carriers. The plurality of first gears is respectively connected to the rotational shafts. The phase change matching unit matches phase changes of all the first gears.  
         [0016]     In this image carrier unit, all the phase changes between the first gears match. Therefore, the phase differences between the adjacent first gears may be inhibited from becoming out of the predetermined phase differences. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The invention will now be described below, by way of example, with reference to the accompanying drawings, in which:  
         [0018]      FIG. 1  is a perspective view showing an exterior appearance of a printer according to a first embodiment of the present invention;  
         [0019]      FIG. 2  is a perspective view showing the exterior appearance of the printer and an image forming unit in which the image forming unit is removed outside of the printer.  
         [0020]      FIG. 3  is a perspective view showing an exterior appearance of a drum unit from which all development cartridges are removed;  
         [0021]      FIG. 4  is a cross sectional view showing an internal structure of the printer in which the image forming unit is installed;  
         [0022]      FIG. 5  is a schematic view showing a structure of a drive mechanism for driving various parts of the image forming unit as installed in a body frame of the printer;  
         [0023]      FIG. 6  is a schematic view showing a structure of a drive mechanism in a printer according to a second embodiment of the present invention;  
         [0024]      FIG. 7  is a perspective view showing the drive mechanism according to the second embodiment;  
         [0025]      FIG. 8  is a schematic view showing a structure of a drive mechanism in a printer according to a third embodiment of the present invention;  
         [0026]      FIG. 9  is a schematic view showing a structure of a drive mechanism in a printer according to a fourth embodiment of the present invention; and  
         [0027]      FIG. 10  is a schematic view showing a structure of a drive mechanism in a printer according to a fifth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     First Embodiment  
       [0000]     &lt;External Structure of Printer  100  in First Embodiment&gt; 
         [0028]     In the following, when the disposition order of a plurality of constituents is indicated, the start point of the order is set in the front side of a printer  100 . That is, the constituent disposed in the most front side of the printer  100  is referred to as the first one among the plurality of constituents.  
         [0029]     As shown in  FIG. 1 , a body  110  of the printer  100  includes a body casing  111  and a body frame  112  contained inside of the body casing  111 .  
         [0030]     The body casing  111  is made of synthetic resin, and formed approximately in a rectangular parallelepiped shape. On a top surface  111 A of the body casing  111 , a paper discharge tray  111 B is formed. The paper discharge tray  111 B is downwardly inclined from the front side of the body casing  111  toward the rear side thereof. A paper discharge opening  111 C is disposed in an upper portion of the body casing  111  above the rear end portion of the paper discharge tray  1113 . Paper is discharged through the paper discharge opening  111 C on to the paper discharge tray  111 B.  
         [0031]     In a front side of the body casing  111 , a front opening  111 D is formed. A front cover  111 E is disposed in an openable/closable manner for closing the front opening  111 D. The lower end of the front cover  111 E is supported by the body casing  111 .  
         [0032]     The body frame  112  is configured so as to support various members provided for an image forming operation inside of the body  110 . Driving sources and driving force transmission mechanisms are disposed inside of the body frame  112  for rotating and driving the various members.  
         [0033]     The left inner wall and the right inner wall of the body frame  112  are respectively provided with upper side guide rails  112 A and lower side guide rails  112 B. More specifically, the respective upper side guide rails  112 A are disposed approximately horizontally from the front side of the printer  100  toward the rear side thereof, while the respective lower side guide rails  112 H are disposed approximately parallel to the upper side guide rails  112 A. Guide grooves  112 C are formed approximately horizontally between the upper side guide rails  112 A and the lower side guide rails  112 B.  
         [0034]     In the body frame  112 , an image forming unit  120  is installed such that the image forming unit  120  can be removed in a direction (shown with Arrow S in the figure) from the rear side of the printer  100  toward the front side thereof. In other words, the rear side of the printer  100  corresponds to the upstream side of the removal direction of the image forming unit  120 , and the front side of the printer  100  corresponds to the downstream side of the removal direction.  
         [0000]     &lt;External Structure of Image Forming Unit  120 &gt; 
         [0035]     As shown in  FIG. 2 , the image forming unit  120  includes a drum unit  130 , and four development cartridges  140 .  
         [0036]     The drum unit  130  includes a frame forming approximately a quadrangular plane with a front beam  131 , a left supporting plate  132 , a right supporting plate  133 , and a rear beam  134 .  
         [0037]     More specifically, the front beam  131  and the rear beam  134 , respectively provided in the front end side and in the rear end side of the drum unit  130 , are disposed in parallel to each other. To the left and right ends of the respective front beam  131  and the rear beam  134 , the left supporting plate  132  and the right supporting plate  133  are connected. In the inner side of the left supporting plate  132 , four left plates  135  are aligned along the left supporting plate  132 . In the inner side of the right supporting plate  133 , four right plates  186  are aligned along the right supporting plates  133 .  
         [0038]     Between the left plates  135  and the right plates  136 , the above-described development cartridges  140  are aligned from the front side of the drum unit  130  toward the rear side thereof. The development cartridges  140  are respectively supported by the left plates  135  and the right plates  136  in an attachable/detachable manner.  
         [0039]     In the drum unit  130 , flange portions  132 A and  133 A which are engaged with the above-described guide grooves  112 C are formed on the upper end portions of the left side supporting plate  132  and the right side supporting plate  133 , respectively. That is, the drum unit  180  is guided along the guide grooves  112 C in the forward and backward directions of the body frame  112  by engagement of these flange portions  132 A and  133 A with the guide grooves  112 C.  
         [0040]     The drum unit  130  is provided with a front handle  131 A in the front surface of the front beam  131 . The drum unit  130  can be easily removed from the body frame  112  by a user pulling the front handle  131 A toward the front side of the body frame  112 .  
         [0041]     The drum unit  130  is also provided with a rear handle  134 A in the upper end portion of the rear beam  134 . The drum unit  130  can be easily carried by a user holding the front handle  181 A and the rear handle  184 A.  
         [0042]     As shown in  FIG. 3 , the left supporting plate  132  of the drum unit  130  is provided with four coupling insertion holes  132 B along the disposition direction of the development cartridges  140  such that the respective coupling insertion holes  132 B face the respective development cartridges  140 . Each of the left plates  135  is provided with a coupling exposure hole  135 B in a position so that the coupling exposure hole  135 B faces the coupling insertion hole  132 B.  
         [0043]     The coupling insertions holes  132 B and the coupling exposure holes  135 B are provided for inserting driving shafts (not shown) disposed within the body frame  112  so as to apply driving force to coupling receiving gears (not shown) disposed in the development cartridges  140 .  
         [0044]     On the respective inner walls of the left plates  135  and the right plates  136 , guide grooves  135 A,  136 A are formed for guiding the development cartridges  140  in the up-and-down direction.  
         [0045]     In the bottom portion of the drum unit  130 , four drum portions  150  are disposed along the disposition direction of the development cartridges  140  (only first three drum portions  150  from the front side are shown in  FIG. 3 ).  
         [0000]     &lt;Internal Structure of Printer  100 &gt; 
         [0046]     As shown in  FIG. 4 , in the body  110  of the printer  100 , the image forming unit  120  is disposed in the center portion thereof, and the paper discharge unit  193  is disposed behind the image forming unit  120 .  
         [0047]     The body  110  further includes a scanner unit  160 , a transfer unit  170 , and a feeder unit  180 . The scanner unit  160  is disposed above the image forming unit  120 . The transfer unit  170  is disposed below the image forming unit  120 . The feeder unit  180  is disposed below the transfer unit  170 .  
         [0000]     &lt;&lt;Structure of Feeder Unit  180 &gt;&gt; 
         [0048]     The feeder unit  180  includes a feeder case  181 , a feed roller  183 , a separation roller  184 , a separation pad  185 , and a paper dust removal roller  187 .  
         [0049]     The feeder case  181  is formed in such a manner that sheets of paper P can be stacked inside thereof. In the feeder case  181 , a paper pressing plate  182  is disposed. A rear end portion  182 A of the paper pressing plate  182  is rotatably supported inside of the feeder case  181 . That is, in the feeder case  181 , a front end portion  182 B of the paper pressing plate  182  is swayed approximately in the up-and-down direction in the figure.  
         [0050]     The feed roller  183  is made of synthetic rubber. The feed roller  183  is rotatably supported above the front end portion  182 B of the paper pressing plate  182  by the body frame  112 . The feed roller  183  is driven so as to rotate in the counterclockwise direction in the figure, and conveys a sheet of paper P, stacked on the top inside of the feeder case  181 , toward the front side of the feed roller  183 .  
         [0051]     The separation roller  184  is made of synthetic rubber in the same manner as the feed roller  183 . The separation roller  184  is rotatably supported by the body frame  112  in the front side of the feed roller  183 . The separation roller  184  is driven so as to rotate in the same direction as the feed roller  183 , and conveys the sheet of paper P toward the front side thereof.  
         [0052]     The separation pad  185  is disposed so as to face the separation roller  184 . A separation surface  185 A of the separation pad  185  facing the separation roller  184  is made of a material having a high friction coefficient, such as synthetic rubber, felt, and so on. Below the separation pad  186 , a separation pad biasing spring  186  is disposed. By the separation pad biasing spring  188  biasing the separation pad  185  toward the separation roller  184 , the separation roller  184  and the separation pad  185  are pressed against each other.  
         [0053]     The paper dust removal roller  187  removes paper dust adhered to the sheet of paper P. The paper dust removal roller  187  is disposed above and in the front side of the separation roller  184  so as to face a pinch roller  188 , and rotatably supported by the body frame  112 .  
         [0000]     &lt;&lt;Structure of Image Forming Unit  120 &gt;&gt; 
         [0054]     In the image forming unit  120 , the four development cartridges  140  ( 140 Y,  140 M,  140 C, and  140 K) are aligned from the front side of the printer  100  toward the rear side thereof. Beneath the development cartridges  140 , the four drum portions  150  are aligned from the front side of the printer  100  toward the rear side thereof, so as to face the development cartridges  140 .  
         [0055]     The four development cartridges  140 Y,  140 M,  140 C, and  140 K respectively contain a toner (a developer) in a color different from one another, such as yellow, magenta, cyan, and black. Although the development cartridges  140 Y,  140 M,  140 C, and  140 K contain toners of different colors, the structures thereof are exactly the same.  
         [0056]     More specifically, the development cartridges  140  respectively contain a toner, which is a developer for developing an electrostatic latent image, in a cartridge case  141 . The development cartridges  140  respectively include an agitator  142 , a supply roller  143 , a development roller  144 , and a blade  145 .  
         [0057]     The agitator  142  stirs a toner contained in the cartridge case  141 , and is rotatably supported by the cartridge case  141 .  
         [0058]     The supply roller  143  is made of a sponge roller, and rotatably supported by the cartridge case  141 .  
         [0059]     The development roller  144  is made of a rubber roller, and rotatably supported by the cartridge case  141 .  
         [0060]     The supply roller  143  and the development roller  144  are disposed such that the supply roller  143  and the development roller  144  face each other and the periphery surfaces thereof contact with each other. The supply roller  143  is driven so as to rotate in the counterclockwise direction in the figure, and supplies an electrically-charged toner to the periphery surface of the development roller  144 .  
         [0061]     The blade  145  is disposed so as to abut on the periphery surface of the development roller  144 . The blade  145  adjusts the amount of the toner supplied on to the periphery surface of the development roller  144 , which is driven so as to rotate in the counterclockwise direction in the figure.  
         [0062]     The four drum portions  150  are configured exactly in the same manner. The drum portions  150  respectively include a photoreceptor drum  151  and a scorotron charger  152 .  
         [0063]     The photoreceptor drum  151  has a photoreceptive layer, made of a photoconductor, on the periphery surface thereof. The photoreceptor drum  161  is disposed such that the periphery surface thereof faces the periphery surface of the development roller  144  in the development cartridge  140 .  
         [0064]     The photoreceptor drum  151  is rotatable supported by the drum unit  130 , and driven so as to rotate in the clockwise direction in the figure by a drive mechanism to be described later. However, the direction of all the rotational shafts  1510  of the photoreceptor drums  151  is set to be perpendicular to the installation direction of the drum unit  130  in a horizontal plane (a direction perpendicular to the surface of the drawing). That is, all the rotational shafts  151 C are disposed in parallel to one another.  
         [0065]     The scorotron charger  152  is constituted so as to uniformly charge the periphery surface of the photoreceptor drum  151 . The scrotron charger  152  is disposed above the photoreceptor drum  151  so as to face the periphery surface of the photoreceptor drum  151 .  
         [0000]     &lt;&lt;Structure of Scanner Unit  160 &gt;&gt; 
         [0066]     The scanner unit  160  is constituted so as to emit laser beam, generated based on image data, from a laser emission portion (not shown) on to the periphery surfaces of the photoreceptor drums  151 . Also the scanner unit  160  is constituted so as to scan laser beam emitted therefrom in the width direction of the printer  100  (the direction perpendicular to the surface of  FIG. 4 ).  
         [0000]     &lt;&lt;Structure of Transfer Unit  170 &gt;&gt; 
         [0067]     The transfer unit  170  includes a belt driving roller  171 , a driven roller  172 , a conveyance belt  173 , four transfer rollers  174 , and a belt cleaner  175 .  
         [0068]     The belt driving roller  171  is disposed below and behind the drum portion  150  facing the development cartridge  140 K disposed in the most rear side among the four development cartridges  140 . The belt driving roller  171  is rotatably supported by the body frame  112 .  
         [0069]     The driven roller  172  is disposed below and in the front side of the drum portion  150  facing the development cartridge  140 Y disposed in the most front side among the four development cartridges  140 . The driven roller  172  is rotatably supported by the body frame  112 .  
         [0070]     The conveyance belt  173  is an endless belt made of a resin film, such as conductive polycarbonate or polyimide, wherein conductive particles, such as carbon, are dispersed. The conveyance belt  173  runs between the belt driving roller  171  and the driven roller  172 .  
         [0071]     The conveyance belt  173  is moved in the counterclockwise direction in the figure by the belt driving roller  171  being driven so as to rotate in the counterclockwise direction. The conveyance belt  173  conveys the sheet of paper P placed thereon along the disposition direction of the development cartridges  140 .  
         [0072]     The transfer rollers  174  are respectively disposed beneath the respective photoreceptor drums  151  so as to face the photoreceptive drums  151  of the drum portions  150  with the conveyance belt  178  in between. The transfer rollers  174  are rotatably supported by the body frame  112 , and rotated corresponding to the conveyance belt  178  moving counterclockwise.  
         [0073]     The belt cleaner  175  is disposed beneath the second transfer roller  174  among the four transfer rollers  174 .  
         [0074]     The belt cleaner  175  removes toner and paper dust adhered to the surface of the conveyance belt  173  by a pair of cleaning rollers  175 A,  175 B.  
         [0000]     &lt;&lt;Structure of Paper Discharge Unit  193 &gt;&gt; 
         [0075]     The paper discharge unit  193  includes a heat roller  193 A and a pressure roller  193 B.  
         [0076]     The heat roller  193 A is constituted with a metal cylinder, having a surface treated with a mold release process, and a halogen lamp contained in the cylinder. The heat roller  193 A is rotatably supported by the body frame  112 .  
         [0077]     The pressure roller  193 B is made of silicone rubber, and disposed so as to be pressed against the heat roller  198 A at predetermined pressure. The pressure roller  193 B is rotatably supported by the body frame  112 .  
         [0078]     In the paper discharge unit  193 , when the heat roller  193 A is driven so as to rotate in the clockwise direction in the figure, the pressure roller  193 B is correspondingly rotated in the counterclockwise direction. The sheet of paper P, conveyed from the transfer unit  170 , is fed between the heat roller  193 A and the pressure roller  193 B, and conveyed behind the rollers  193 A and  193 B. As a result, a toner on the sheet of paper P melts and adheres (is fixed) to the sheet of paper P. Then, the sheet of paper P is conveyed toward the paper discharge opening  111 C.  
         [0079]     The paper discharge unit  193  furthermore includes a conveyance roller  194  for conveying the sheet of paper P on which toner is adhered, and a pinch roller  195 . The conveyance roller  194  and the pinch roller  195  are disposed behind the heat roller  193 A and the pressure roller  193 B.  
         [0080]     The conveyance roller  194  is rotatably supported by the body frame  112 .  
         [0081]     The pinch roller  196  is disposed so as to face the conveyance roller  194 , and rotatably supported by the body frame  112 .  
         [0082]     By the conveyance roller  194  being driven so as to rotate in the clockwise direction in the figure, the pinch roller  195  is correspondingly rotated in the counterclockwise direction in the figure. As a result, the sheet of paper P is conveyed toward the paper discharge opening  111 C.  
         [0083]     The paper discharge unit  193  still further includes paper guides  196 A,  196 B disposed above the conveyance roller  194  and the pinch roller  195 , for guiding the sheet of paper P with a toner adhered thereon.  
         [0084]     The paper guides  196 A and  196 B guide the sheet of paper P, conveyed by the conveyance roller  194  and the pinch roller  195 , toward the paper discharge opening  111 C.  
         [0085]     The paper discharge unit  193  further includes a paper discharge roller  197  and a paper discharge driven roller  198  both disposed in the vicinity of the paper discharge opening  111 C.  
         [0086]     The paper discharge roller  197  and the paper discharge driven roller  198  are disposed so as to face each other in the up-and-down direction in the figure and respectively supported by the body frame  112  in a rotatable manner.  
         [0087]     By the paper discharge roller  197  being driven so as to rotate in the counterclockwise direction in the figure, the paper discharge driven roller  198  is correspondingly rotated in the clockwise direction. As a results the sheet of paper P is discharged outside of the body  110  from the paper discharge opening  111 C.  
         [0000]     &lt;&lt;Structure of Drive Mechanism&gt;&gt; 
         [0088]     As shown in  FIG. 6 , the left outer walls of respective development cartridges  140  are provided with a supply roller driving gear  143 A and a development roller driving gear  144 A. The supply roller driving gear  143 A is connected to the rotational shaft of the supply roller  143 . The development roller driving gear  144 A is connected to the rotational shaft of the development roller  144 . The respective teeth of the supply roller driving gear  143 A and the development roller driving gear  144 A are engaged with the teeth of the above-described coupling receiving gear. When driving force is applied from the above-described driving shaft to the coupling receiving gear, the supply roller driving gear  143 A and the development roller driving gear  144 A are correspondingly rotated.  
         [0089]     Inside of the drum unit  130 , four drum gears  151 A are disposed so as to be respectively connected to the rotational shafts  151 C of the photoreceptor drums  151 . Phases of the respective drum gears  151 A, which indicate rotational angles thereof, are determined with respect to reference rotational positions thereof. The reference rotational positions are set based on the locations of the rotational centers of the respective drum gears  151 A. The rotational orientations of the respective drum gears  151 A are set such that phase differences between the first and second drum gears  151 A, between the second and third drum gears  151 A, and between the third and fourth drum gears  151 A are predetermined phase differences. The predetermined phase differences may be all the same, or be partly the same, or be different from each other.  
         [0090]     The body frame  112  (not shown in  FIG. 5 ) is provided with four body gears  113  constituted with two-stage gears. The body gears  113  are disposed beneath the drum unit  130 , and rotatably supported by the body frame  112 . More specifically, the body gears  113  are disposed along the disposition direction of the drum gears  151 A. The teeth on the inner side of the body gears  113  are engaged with the teeth of the drum gears  151 A. Phases of the respective body gears  118 , which indicate rotational angles thereof are determined with respect to reference rotational positions thereof. The reference rotational positions are set based on the locations of the rotational centers of the respective body gears  113 . The rotational orientations of the respective body gears  113  are set such that phase differences between the first and second body gears  113 , between the second and third body gears  113 , and between the third and fourth body gears  113  are predetermined phase differences. The predetermined phase differences may be all the same, or be partly the same, or be different from each other.  
         [0091]     The body frame  112  is further provided with two drive motors  114 . More specifically, the drive motors  114  are respectively disposed between the first and second body gears  113 , as well as between the third and fourth body gears  113 .  
         [0092]     The teeth of a motor gear  114 A which is connected to the rotational shaft of the drive motor  114  disposed between the first and second body gears  113  are engaged with the outside teeth of these two body gears  113 . On the other hand, the teeth of a motor gear  114 A which is connected to the rotational shaft of the drive motor  114  disposed between the third and fourth body gears  118  are engaged with the outside teeth of these two body gears  113 .  
         [0093]     Below these body gears  113 , a body gear interlocking mechanism  116  is provided. The body gear interlocking mechanism  115  interlocks the second and third body gears  113 .  
         [0094]     More specifically, the body gear interlocking mechanism  115  includes an interlocking gear  115 A, a gear supporting member  115 B, and a link  115 C.  
         [0095]     The interlocking gear  115 A is provided below the portion between the second and third body gears  113  in a moveable manner in the up-and-down direction in the figure.  
         [0096]     The gear supporting member  115 B is a member in a rod form directed in the vertical direction. The upper end portion of the gear supporting member  115 B rotatably supports the interlocking gear  115 A.  
         [0097]     The link  115 C is a member in a plate form directed in the horizontal direction. The front end portion of the link  115 C is connected in the vicinity of the lower end portion of the above-described front cover  111 E. As a result, together with the operation of the front opening  111 D being opened, the link  115 C moves to the front side, and together with the operation of the front opening  111 D being closed, the link  115 C moves to the rear side.  
         [0098]     On the upper surface of the rear end portion of the link  115 C an inclined member  115 D is provided. The inclined member  115 D has a slanted surface which is upwardly inclined from the front side of the inclined member  115 D.  
         [0099]     The inclined member  115 D pushes up the connecting gear  115 A with the slanted surface making contact with the lower end portion of the gear supporting member  116 B when the link  115 C moves to the front side. As a result, the interlocking gear  115 A is pressed up to the portion between the second and third body gears  113 , and thus, the teeth of the interlocking gear  115 A are engaged with the outside teeth of these two body gears  113  (that is, these two body gears  113  are interlocked therebetween).  
         [0100]     The slanted surface of the inclined member  115 D moves away from the lower end portion of the gear supporting member  115 B when the link  115 C moves to the rear side. As a result, the interlocking gear  115 A moves down due to its own weight and away from the portion between the two body gears  113 .  
         [0000]     &lt;Effects of Printer  100 &gt; 
         [0101]     In the printer  100  according to the first embodiment, the second and third body gears  113  are interlocked therebetween by the body gear interlocking mechanism  115  when the front opening  111 D is opened and no image is formed. Thereby, all of the body gears  113  rotate in sync, when the body gears  113  rotate at the time of removal of the image forming unit  120 . That is, the phase changes of the respective body gears  113  are consistent therebetween. Accordingly, the phase differences between the adjacent body gears  113  can be inhibited from becoming out of the predetermined phase differences.  
         [0102]     On the other hand, when the front opening  111 D is closed and an image is formed, the interlock between the second and third body gears  113  is disengaged by the body gear interlocking mechanism  115 . As a result, the four photoreceptor drums  151  can be stably driven by the two drive motors  114  without the driving forces from the two drive motors  114  interfering between the respective body gears  118 .  
         [0103]     That is, in the printer  100  according to the first embodiment, the plurality of photoreceptor drums  151  removably integrated can be stably driven by the plurality of drive motors  114 , and the phase differences between the adjacent body gears  113  can be inhibited from becoming out of the predetermined phase differences when the image forming unit  120  is removed.  
         [0104]     Moreover, in the printer  100  according to the first embodiment, all of the body gears  113  can be interlocked the between in a simple structure where the interlocking gear  115 A is disposed between the second and third body gears  113 . On the other hand, the interlock between these two body gears  113  can be disengaged in a simple structure where the interlocking gear  115 A is disengaged from the portion between the second and third body gears  113 .  
         [0105]     In the printer  100  according to the first embodiment, the body gears  113  are interlocked therebetween as a user opens the front opening  111 D in order to remove the image forming unit  120  from the inside of the body frame  112 . As a result, the user can remove the image forming unit  120  immediately after opening the front opening  111 D.  
         [0106]     In the printer  100  according to the first embodiment, the interlock between the second and third body gears  113  is disengaged as a user installs the image forming unit  120  inside the body frame  112  and closes the front opening  111 D in order to form an image. As a result, the photoreceptor drums  151  can be stably driven in the printer  100  immediately after the front opening  111 D is closed.  
         [0107]     In the printer  100  according to the first embodiment, the first and second body gears  113 , which are adjacent to each other, and the third and fourth body gears  111 , which are adjacent to each other, are interlocked therebetween via the motor gears  114 A. Therefore, in the printer  100 , four photoreceptor drums  161  can be stably driven with two drive motors  114  instead of four drive motors  114 , which is the same number as that for photoreceptor drums  151 . Moreover, all of the body gears  113  can be simply interlocked by disposing an interlocking gear  115 A in the portion between the second and third body gears  113 , where the second and third body gears  113  are not engaged with the motor gear  114 A.  
       Second Embodiment  
       [0108]     A printer according to the second embodiment can be simply obtained by partially modifying the structure of the above-described printer  100  according to the first embodiment. Accordingly, the same reference numbers are used to components that are the same as in the printer  100  according to the first embodiment, and the descriptions thereof are not repeated here. The following describes only the distinctive structure.  
         [0000]     &lt;Structure of Drive Mechanism&gt; 
         [0109]     As shown in  FIGS. 6 and 7 , in the printer  200 , the above-described interlocking gear  115 A is provided above the portion between the second and third body gears  113  in a moveable manner in the up-and-down direction.  
         [0110]     In the printer  200 , the interlocking gear  115 A moves downward and interlocks between the second and third body gears  113  when the front opening  111 D is opened. On the other hand, the interlocking gear  115 A moves upward and disengages from these body gears  113  when the front opening  111 D is closed.  
         [0000]     &lt;Effects of Printer  200 &gt; 
         [0111]     In the printer  200  according to the second embodiment, the second and third body gears  113  are interlocked when the front opening  111 D is opened, and the interlock between these body gears  113  is disengaged when the front opening  111 ) is closed. Therefore, the same effects as in the above-described printer  100  according to the first embodiment can be obtained.  
       Third Embodiment  
       [0112]     A printer  300  according to the third embodiment can be simply obtained by partially modifying the structure of the above-described printer  100  according to the first embodiment. Accordingly, the same reference numbers are used to components that are the same as in the printer  100  according to the above-described first embodiment, and the descriptions thereof are not repeated here. The following describes only the distinctive structure.  
         [0000]     &lt;Structure of Drive Mechanism&gt; 
         [0113]     As shown in  FIG. 8 , in the printer  300 , the above-described drive motor  114  are provided so as to correspond to the respective body gears  113  (that is, four drive motors  114  are provided). In addition, the teeth of each motor gear  114 A are engaged with the outside teeth of the corresponding body gear  113 .  
         [0114]     In addition, the above-described interlocking gears  115 A are respectively provided below the portions between the first and second body gears  118  and between the second and third body gears  113 , as well as between the third and fourth body gears  113 , in a moveable manner in the up-and-down direction (that is, three interlocking gears  115 A are provided).  
         [0115]     In the printer  300 , three interlocking gears  115 A move upward and interlock adjacent body gears  113  when the front opening  111 D is opened. On the other hand, these interlocking gears  115 A move downward and disengage from these body gears  113  when the front opening  111 D is closed.  
         [0000]     &lt;Effects of Printer  300 &gt; 
         [0116]     In the printer  300  according to the third embodiment, adjacent body gears  113  are interlocked when the front opening  111 D is opened, and the interlock of these body gears  113  is disengaged when the front opening  111 D is closed. Therefore, the same effects as in the above-described printer  100  according to the first embodiment can be obtained.  
         [0117]     Furthermore, in the printer  300  according to the third embodiment, the respective photoreceptor drums  161  are individually driven by the respective drive motors  114 , and therefore, the driving forces of the respective drive motors  114  does not interfere with each other. Accordingly, all of the photoreceptor drums  151  can be reliably and stably driven.  
       Fourth Embodiment  
       [0118]     A printer  400  according to the fourth embodiment can be simply obtained by partially modifying the structure of the printer  100  according to the first embodiment. Accordingly, the same reference numbers are used to components that are the same as in the printer  100  according to the above-described first embodiment, and the descriptions thereof are not repeated here. The following describes only the distinctive structure.  
         [0000]     &lt;Structure of Drive Mechanism&gt; 
         [0119]     As shown in  FIG. 9 , the printer  400  includes a drum unit  230  instead of the above-described drum unit  130 .  
         [0120]     The drum unit  230  is formed by adding idle gears  151 B and the above-described interlocking gears  115 A to the drum unit  130 .  
         [0121]     More specifically, in the drum unit  230 , idle gears  151 B are respectively supported in a rotatable manner above the first drum gear  151 A on the rear side thereof, above the second drum gear  151 A on the front and rear sides thereof, above the third drum gear  151 A on the front and rear sides thereof, and above the fourth drum gear  151 A on the front side thereof (that is, six idle gears  151 B are provided). The teeth of these drum gears  151 A and the teeth of these idle gears  151 B are engaged.  
         [0122]     In the drum unit  230 , interlocking gears  116 A are provided above the respective portions between adjacent idle gears  151 B in a movable manner in the up-and-down direction (that is, three interlocking gears  115 A are provided).  
         [0123]     In the printer  400 , the interlocking gear  115 A, which is provided below the portion between the second and third body gears  113  in the above-described printer  100  according to the first embodiment, is omitted.  
         [0124]     In the printer  400 , the above-described drive motors  114  are provided so as to correspond to the respective body gears  113  (that is, four drive motors  114  are provided). The teeth of each motor gear  114 A are engaged with the outside teeth of the corresponding body gear  113 .  
         [0125]     In the printer  400 , the three interlocking gears  115 A move downward and interlock the adjacent idle gears  151 B when the front opening  111 D is opened. On the other hand, these interlocking gears  115 A move upward and disengage from these idle gears  151 B when the front opening  111 D is closed.  
         [0000]     &lt;Effects of Printer  400 &gt; 
         [0126]     In the printer  400  according to the fourth embodiment, adjacent idle gears  151 B are interlocked to each other when the front opening  111 D is opened, and as a result, all of the drum gears  151 A are interlocked. Thereby, all of the drum gears  151 A rotate in sync, when the drum gears  151 A rotate at the time of removal of the drum unit  230 . That is, the phase changes of the respective drum gears  151 A are consistent therebetween. Accordingly, the phase differences between the adjacent drum gears  151 A can be inhibited from becoming out of the predetermined phase differences.  
         [0127]     In addition, the interlock between the idle gears  151 B is disengaged when the front opening  111 D is closed, and as a result, the interlock between all of the drum gears  151 A is disengaged. Thereby, the driving forces of the respective drive motors  114  does not interfere with each other, and all of the photoreceptor drums  151  can be reliably and stably driven.  
       Fifth Embodiment  
       [0128]     A printer  500  according to the fifth embodiment can be simply obtained by partially modifying the structure of the printer  100  according to the first embodiment.  
         [0129]     Accordingly, the same reference numbers are used to components that are the same as in the printer  100  according to the first embodiment, and the descriptions thereof are not repeated here. The following describes only distinctive structure.  
         [0000]     &lt;Structure of Drive Mechanism&gt; 
         [0130]     As shown in  FIG. 10 , the printer  500  is different from the printer  100  only in that the above-described drum unit  230  is provided instead of the above-described drum unit  130 .  
         [0131]     In the printer  500 , three interlocking gears  115 A provided in the drum unit  230  move downward and interlock the adjacent idle gears  161 D, when the front opening  111 D is opened. In addition, simultaneously with this, the interlocking gear  115 A provided between the second and third body gears  113  moves upward and interlocks these body gears  113 .  
         [0132]     On the other hand, the three interlocking gears  115 A provided in the drum unit  280  move upward and disengage from the adjacent idle gears  151 B when the front opening  111 D is closed. In addition, simultaneously with this, the interlocking gear  115 A provided between the second and third body gears  113  moves downward and disengages from these body gears  113 .  
         [0000]     &lt;Effects of Printer  500 &gt; 
         [0133]     In the printer  500  according to the fifth embodiment, the adjacent idle gears  151 B are interlocked when the front opening  111 D is opened, and as a result, all of the drum gears  151 A are interlocked, and all of the body gears  113  are also interlocked.  
         [0134]     Therefore, all of the drum gears  151 A rotate in sync when the drum gears  151 A rotate at the time of removal of the drum unit  230 , and all of the body gears  113  rotate in sync when the body gears  113  rotate at the time of removal of the drum unit  230 .  
         [0135]     As a result, the phase difference between the adjacent drum gears  151 A and the phase difference between the adjacent body gears  113  can be inhibited from becoming out of the predetermined phase differences.  
         [0136]     In addition, the interlock between all of the drum gears  151 A is disengaged and the interlock between the second and third body gears  113  is also disengaged, when the front opening  111 D is closed. Therefore, the four photoreceptor drums  151  can be stably driven by the two drive motors  114 .  
         [0000]     [Variation] 
         [0137]     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.  
         [0138]     For example, all of the above-described printers  100  to  500  are constituted so as to interlock either the body gears  113  or the drum gears  151 A together with the operation of the front opening  111 D being opened and closed. However, these gears may be interlocked when electric power is supplied to the printer, and the interlock may be disengaged when the electric power supply is cut off.