Patent Publication Number: US-6909866-B2

Title: Drive system for an Image forming appartus which transmits a drive force to a photosensitive drum of a process cartridge

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
   This application claims priority under 35 USC 119 to Japanese Patent Application No. 2002-143547 filed in the Japanese Patent Office (JPO) on May 17, 2002, the entire disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a drive system which transmits a drive force to a photosensitive drum of a process cartridge detachably mountable to an image forming apparatus. The present invention also relates to an image forming apparatus which includes the process cartridge. 
   2. Description of the Related Art 
   In image forming apparatuses such as a printer, a facsimile machine, and a copying machine, a photosensitive drum is charged uniformly by a charging unit. An exposing unit selectively exposes the photosensitive drum according to image information scanned by an image reading unit or received facsimile data. Then, electrostatic latent image is formed on the photosensitive drum. A developing unit forms a toner image on the electrostatic latent image. A transfer unit transfers the toner image onto a paper fed from a paper feeding unit, and the image is recorded on the paper. 
   A conventional process cartridge integrally includes a photosensitive drum, a charging unit, a developing unit, and a cleaning unit. The process cartridge is detachably mountable to the image forming apparatus. The process cartridge includes the photosensitive drum, and at least one of the charging unit, the developing unit, or the cleaning unit. 
   An electro-photographic typed image forming apparatus, which uses an electro-photographic image forming process, includes a photosensitive drum, and a process unit which is actable to the photosensitive drum. In the electro-photographic typed image forming apparatus, a process cartridge is used as a unit which is detachably mountable to the image forming apparatus. By using the process cartridge, it is not necessary for a user to depend on a service worker, and the user can carry out the maintenance of the machine. As a result, operationality is improved. For example, even when the amount of toner remaining in the process cartridge becomes low, or when there is a failure in the photosensitive drum, if the process cartridge is replaced with a new cartridge, the image forming apparatus can be recovered to a normal state. 
   A drive system for the photosensitive drum in the process cartridge type is desirable to have a structure in which the process cartridge can be easily detachably mounted to the image forming apparatus, and a drive force is transmitted accurately to the photosensitive drum. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention, a process cartridge can be detachably mounted to an image forming apparatus which includes a drive source and a gear. The gear is rotated by the drive source, and includes a coupling protrusion on a radial line. The process cartridge includes a photosensitive drum, a process unit which acts upon the photosensitive drum, and a coupling hole which is provided at an end part of a radial direction of the photosensitive drum. When a cover member (which forms an outer wall) of the image forming apparatus is closed, the coupling protrusion and the coupling hole are fit together. Then, the photosensitive drum, which is provided inside the image forming apparatus, is rotated by the drive source via the coupling protrusion and the coupling hole. Accordingly, the photosensitive drum is prevented from rotating eccentrically, and the quality of recorded image can be maintained. In addition, an unnatural force is not applied to a joined part between a drive force supplying shaft of a drive output gear and drive force receiving shaft of the photosensitive drum. 
   According to a second aspect of the present invention, the drive system includes a member which slides the gear of the image forming apparatus when the cover member is opened or closed. When the cover member is opened, the drive force supplying shaft and the drive force receiving shaft are released from the fit state, and the process cartridge can be removed from the image forming apparatus. When the cover member is closed, the coupling hole of the photosensitive drum and the coupling protrusion of the gear are fit together, and the photosensitive drum can be rotated by the drive source. 
   According to a third aspect of the present invention, a joining face is formed on the coupling protrusion of the gear. In addition, a joining face is formed on the coupling hole which is provided at the end part of the radial direction of the photosensitive drum. The joining surfaces are fit together, and the drive force from the drive source can be transmitted. The gear is a helical gear. To release the coupling protrusion of the gear and the coupling hole of the photosensitive drum from the fit state, the helical gear is slid in a direction to separate from the drive force receiving shaft. Then, the helical gear rotates in a direction opposite to the direction to transmit the drive force according to a mesh with the gear which transmits the drive force from the drive source to the helical gear. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic perspective view showing an outer configuration of an image recording unit  2  according to an embodiment of the present invention. 
       FIG. 2  is a perspective view showing a state in which a front side of a scanner unit  3  is swung upward. 
       FIG. 3  is a perspective view showing a state in which a top cover  8  is opened. 
       FIG. 4  is a perspective view showing a state in which a process cartridge  9  is pulled out. 
       FIG. 5  is a perspective view showing a work to eliminate a paper jam. 
       FIG. 6A  is an enlarged partial cross-sectional view of an end part of a drive force receiving shaft of the process cartridge  9 .  FIG. 6B  is an enlarged perspective view showing a detailed configuration of a coupling part  25   a.    
       FIG. 7  is a side view of a drive unit  12 . 
       FIG. 8  is a plan view of a fuser drive output part  15 . 
       FIG. 9  is a cross-sectional view taken on line A—A of  FIG. 7  under a state in which the process cartridge  9  is inserted. 
       FIG. 10  is an enlarged perspective view showing a detailed configuration of a coupling part  24   a.    
       FIG. 11  is a cross-sectional view showing a state in which an axis line O of a slide gear is slanting to be joined together with the drive force receiving shaft of the process cartridge  9 . 
       FIG. 12  is a cross-sectional view showing a configuration in which a gap C is provided to a second bearing  42 . 
       FIG. 13  is a cross-sectional view showing a state in which the axis line O of the slide gear is slanting to be joined together with the drive force receiving shaft of the process cartridge  9 . 
       FIG. 14  is a perspective view showing a configuration of a pushing cam  26  which slides the slide gear. 
       FIG. 15  is a cross-sectional view showing a configuration of the pushing cam  26  which slides the slide gear. 
       FIG. 16  is a perspective view showing a state in which the pushing cam  26  pushes to slide the slide gear. 
       FIG. 17  is a cross-sectional view showing a state in which the pushing cam  26  pushes to slide the slide gear. 
       FIG. 18  is a side view showing a configuration of a cam mechanism  27  which links the top cover  8  and a swing arm  19 . 
       FIG. 19  is a side view showing a state in which the top cover  8  is opened and the swing arm  19  is swung downward. 
       FIG. 20  is a side view showing a state in which the swing arm  19  is swung downward and locked. 
       FIG. 21  is a side view showing a state in which the top cover  8  is closed and a lever  29  is returned to an original position. 
       FIG. 22  is a side view showing a state in which the lever  29  is swung. 
       FIG. 23  is a side view showing a state in which the top cover  8  is closed and the swing arm  19  is swung upward. 
       FIG. 24  is a perspective view showing a method to mount a drive unit  12  to the image recording unit  2 . 
       FIG. 25  is a perspective view showing a method to mount the drive unit  12  to the image recording unit  2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An image forming apparatus according to an embodiment of the present invention will be described specifically with reference to the drawings. 
   (Overall Configuration) 
     FIG. 1  is a perspective view showing an outer appearance of a copy and facsimile composite machine which includes the image forming apparatus of the present embodiment. As shown in the drawing, in the copy and facsimile composite machine, an image recording unit  2  is provided above a paper feeding unit  1 . In addition, a scanner unit  3  is provided above the image recording unit  2 . A recorded paper discharge tray is provided in a space formed between the image recording unit  2  and the scanner unit  3 . 
   The paper feeding unit  1  includes a plurality of paper feeding cassettes  10 , and a paper conveyance path. Each of the paper feeding cassettes  10  accommodates paper of a size different from the size accommodated in other paper feeding cassettes  10 . In accordance with an input from an operation part  4  of the scanner unit  3 , a paper of a requested size is fed from either one of the paper feeding cassettes  10 , and the paper is fed to the image recording unit  2 . 
   The scanner unit  3  can scan image of an original in the following ways. In case of a book or the like set on a reading frame  6 , a scanner (not shown in the drawing) such as a Charge-Coupled Device (CCD) that is provided inside the reading frame  6 , scans the book or the like. In case of sheet documents to be fed by an automatic document feeder (ADF) that is provided on a document cover  7 , the scanner is brought to a prescribed position, and reads the image of the fed sheet document continuously. 
   As it is widely known, a paper conveyance path is formed inside the image recording unit  2  for conveying the paper fed from the paper feeding unit  1 . A conveyance roller, a photosensitive drum, a transfer unit, and a fuser or the like are provided along the paper conveyance path. The conveyance roller feeds the paper. The photosensitive drum and the transfer unit record an image on the paper. The fuser fixes on the paper, the toner image transferred onto the paper as a permanent image. 
   In the image recording unit  2 , after the photosensitive drum is charged uniformly by a charging device, an exposure is carried out selectively by an exposing device according to image information read by the scanner unit  3 , or the facsimile received information. Then, electrostatic latent image is formed on the photosensitive drum. A developing device supplies toner to the electrostatic latent image, and the toner image is formed. A transfer device transfers the toner image onto the paper fed from the paper feeding unit  1 . The paper is further conveyed, and a fusing device fuses the toner by heat to fix the toner image onto the paper. Then, the paper is conveyed to the paper discharge tray  5 . When there are plural pages of originals or facsimile received information, the above process is repeated, and the paper recorded with the image is discharged to the paper discharge tray  5  one after the other. 
   The photosensitive drum, and a process device such as the charging device or the exposing device which acts upon the photosensitive drum, the developing device, and a toner container, are formed integrally to the process cartridge. The process cartridge is detachably mountable to the image recording unit  2 . This configuration is adopted for a convenience of when carrying out maintenance to the image recording unit  2 . 
   FIG.  2  through  FIG. 5  show a procedure to eliminate a paper jam in the paper conveyance path of the image recording unit  2 . As shown in  FIG. 2 , a lever  6   a  is provided on a front-lower side of the reading frame  6 . When the user pulls the lever  6   a , a locked state of the scanner unit  3  with respect to the image recording unit  2  is released, and the scanner unit  3  can be swung upward with a fulcrum as a center. By swinging a front side of the scanner unit  3  upward with a rear side of the image forming apparatus as the fulcrum, an upper part of the image recording unit  2  can be opened. Then, the top cover  8  of the image recording unit  2  is exposed. The top cover  8  is a part of the discharge tray  5  where the recorded paper is discharged. The top cover  8  can be opened and closed from the front side with an inner side (rear side of the image forming apparatus) supported pivotally. When the top cover  8  is opened, an opening for the process cartridge is opened. Then, as shown in  FIG. 3 , the process cartridge  9 , the fuser  11  or the like which are provided inside the image recording unit  2  are exposed to the outside. The process cartridge  9  is detachably mountable in a vertical direction. As shown in  FIG. 4 , the process cartridge  9  can be removed from the image recording unit  2  by picking up a gripper  9   a . The gripper  9   a  is formed on the upper surface of the process cartridge  9 . By removing the process cartridge  9 , the paper conveyance path is exposed. Then, as shown in  FIG. 5 , the paper which had caused a paper jam in the conveyance path can be removed completely. As described above, the process cartridge  9  can be easily attached and detached by the user without using tools such as a driver. 
   (Configuration of Drive Input Shaft of Process Cartridge) 
   As shown in  FIG. 6A , a photosensitive drum  39  is stored in the process cartridge  9 . The photosensitive drum  39  can rotate with a drive force receiving shaft as an axis. One end of the drive force receiving shaft is protruding from a side of the process cartridge  9 . A coupling part  25   a  is formed on an end section of the drive force receiving shaft of the protruding side. A circular guide  40  is provided integrally or separately on a side surface of the process cartridge  9  to surround a side peripheral surface of the protrusion of the drive force receiving shaft. As shown in  FIG. 6B , the coupling part  25   a  includes a column-shaped core part  25   b , drive force receiving surfaces  25   c , and slanting surfaces  25   d . The core part  25   b  is formed at a shaft center of the helical gear  240 . Two drive force receiving surfaces  25   c  are formed in a radial direction from the core part  25   b  such that to be symmetrical with the core part  25   b  as the center. Each of the slanting surfaces  25   d  is formed to be slanting from a tip end of one of the drive force receiving surfaces  25   c  toward a base end of the other drive force receiving surface  25   c  in a counterclockwise direction. The rotational drive force in the counterclockwise direction input to the coupling part  25   a  is transferred to the drive force receiving shaft via the core part  25   b , and the photosensitive drum  39  is rotated. 
   (Drive Unit) 
   As shown in  FIG. 5 , a drive unit  12  is fixed on a side of a position where the processing cartridge  9  is set. The drive unit  12  transfers the drive force from the image forming apparatus to the process cartridge  9  and the fuser  11 . Next, the drive unit  12  will be described in details. 
     FIG. 7  is a side view showing the entire drive unit  12 . As shown in the drawing, the drive unit  12  includes a frame body  13  as a frame formed from sheet metal. A motor  14  which is a drive source is fixed in a cantilever on one side of the frame body  13 . Moreover, a train of gears (shown with dashed lines in the drawing) which transfer power of the motor  14  are supported inside the frame body  13 . Furthermore, two drive output parts, a fuser drive output part  15  and a cartridge drive output part  16 , are provided on the frame body  13 . The drive force of the motor  14  is transmitted constantly to the two drive output parts  15 ,  16  via the train of gears. 
   (Fuser Drive Output Part) 
   As shown in  FIG. 7 , the fuser drive output part  15  transmits the drive force transmitted from the motor  14  via the train of gears to a fuser drive input gear  17 . The fuser drive output part  15  can mesh with or separate from the fuser drive input gear  17 . In addition, the fuser drive output part  15  transmits or cuts off the drive force.  FIG. 8  is a cross-sectional plan view showing a configuration of the fuser drive output part  15  of the drive unit  12 . As shown in the drawing, the fuser drive output part  15  is supported by the frame body  13 . The fuser drive output part  15  includes a sun gear  18 , a swing arm  19 , and a planet gear  20 . The sun gear  18  is connected to the motor  14  via the train of gears. The swing arm  19  is pivotally supported by the frame body  13  such that the swing arm  19  can swing with a shaft center the same as the shaft center of the planet gear  18  as the center. The planet gear  20  is supported by the swing arm  19 , and is meshed with the sun gear  18  at all times. 
   The sun gear  18  can be rotated by a sun gear shaft  21  which is built over the frame body  13 . The swing arm  19  is formed by bending sheet metal into a shape of a horseshoe in a plan view. Both end parts of the swing arm  19  will be referred to as swing base parts  19   a . The swing base parts  19   a  are pivotally supported by the sun gear shaft  21 . Three small protrusions  23  are formed on an outer surface of each of the swing base parts  19   a  respectively. Each of the protrusions  23  has a domelike roundness. A summit of the protrusion  23  contacts against an inner surface of the frame body  13 . Accordingly, a contacting area of the frame body  13  and the swing arm  19  is narrowed, and a friction of when the swing arm  19  swings is reduced. In addition, the swing arm  19  can be swung smoothly, and noise is prevented from generating. Moreover, work for secondary processing such as deburring can be eliminated, and the manufacturing cost can be reduced. 
   A planet gear shaft  22  is provided in parallel to the sun gear shaft  21  inside the swing arm  19 . The planet gear  20  is provided around the planet gear shaft  22 , and the planet gear  20  can rotate by being meshed with the sun gear  18 . The swing arm  19  swings with the sun gear shaft  21  as the axis. Therefore, a distance between the sun gear shaft  21  and the planet gear shaft  22  is constant also when the swing arm  19  swings. The sun gear  18  and the planet gear  20  are maintained under the meshed state also when the swing arm  19  swings. 
   Further, in the present embodiment, the protrusions  23  are provided on the outer surface of the swing arm  19 . However, the present invention is not limited to this example, and the same effect can be obtained even when the protrusions  23  are provided on an inner surface of the frame body  13 . Therefore, the protrusions  23  can be provided to either the frame body  13  or the swing arm  19  at a part of a surface where the frame body  13  and the swing arm  19  are facing with one another. 
   In addition, the shape of the protrusions  23  is not limited to the shape disclosed in the present embodiment. The shape of the protrusions  23  can be in other shapes which can reduce the area where the frame body  13  and the swing arm  19  contact against one another. The protrusions  23  are preferable to be formed convexly. Moreover, as shown in the present embodiment, it is especially preferable to form the protrusions  23  in a domelike shape such that the frame body  13  and the swing arm  19  contact against one another on a point. Furthermore, in the present embodiment, the protrusions  23  are formed in three parts. However, the protrusion  23  can be formed in four parts or more. 
   As shown in  FIG. 7 , the swing arm  19  formed as described above can swing vertically with the sun gear shaft  21  as the axis. When the swing arm  19  swings upward, the planet gear  20  meshes with the fuser drive input gear  17 , and the drive force from the motor  14  can be transmitted to the fuser drive input gear  17  via the sun gear  18  and the planet gear  20 . Meanwhile, when the swing arm  19  swings downward, the planet gear  20  and the fuser drive input gear  17  are released from the meshed state, and the drive force from the motor  14  to the fuser drive input gear  17  is cut off. 
   (Cartridge Drive Output Part) 
   As shown in  FIG. 7 , the cartridge drive output part  16  is provided at a position adjacent to the fuser drive output part  15  above the frame body  13 . A slide gear is supported rotatable on the cartridge drive output part  16 . The drive force from the motor  14  can be transferred constantly via the train of gears. In addition, a guide cover  43  covers a side of the cartridge drive output part  16 . A guide groove  43   a  is formed on the cartridge cover  43  for guiding the circular guide  40  when setting the process cartridge  9 . A drive force supplying shaft  242  having a projection  242   a  of the slide gear is protruding from a lower end part of the guide groove  43   a . The guide groove  43   a  controls a direction in which the process cartridge  9  is inserted to the image forming apparatus. In addition, the drive force receiving shaft of the process cartridge  9  is positioned at approximately same position as the drive force supplying shaft  242  having a projection  242   a  of the slide gear. 
     FIG. 9  is a cross-sectional view taken on line A—A in FIG.  7 .  FIG. 9  shows a state in which the process cartridge  9  is inserted and the top cover  8  is opened. The slide gear is a helical gear formed integrally with shafts. That is, the drive force supplying shaft  241  is protruding to the opposite side of the guide cover  43  from the shaft center of the helical gear  240 , and the drive force supplying shaft  242  having a projection  242   a  is protruding to the guide cover  43  side. The drive force supplying shaft  241  is supported rotatable by a first bearing  41  that is provided at a rear side (left side shown in the drawing) of the frame body  13 . The drive force supplying shaft  242  having a projection  242   a  is supported rotatable by a second bearing  42  that is formed on the guide cover  43 . Moreover, the first bearing  41  and the second bearing  42  are so-called sliding bearings. The drive force supplying shafts  241 ,  242  are supported slidable in a radial direction. The slide gear is urged in a direction toward the second bearing  42  by an compression spring  38  which is provided between the slide gear and the first bearing  41 . By the sliding movement of the slide gear in the axial direction, the drive force from the slide gear is transferred to or cut off from the drive force receiving shaft of the process cartridge  9 . In addition, by adopting the helical gear  240  for the slide gear, the slide gear can be rotated smoothly, and unevenness in the rotation of the photosensitive drum is controlled. 
   A coupling part  24   a  is formed at an end part of the drive force supplying shaft  242  having a projection  242   a  of the slide gear. The coupling part  24   a  can be joined with or separated from the coupling part  25   a  of the process cartridge  9 . As shown in  FIG. 10 , the coupling part  24   a  includes a core receptor which is formed at the shaft center of the slide gear. The core receptor can be joined with the core part  25   b  of the coupling part  25   a . In addition, to be symmetrical with the shaft center as the center, two drive force supplying surfaces  24   c  are formed in a radial direction from the shaft center. Slanting surfaces  24   d  are formed in a slanting state from a tip end of one of the drive force supplying surfaces  24   c  toward a base end of the other drive force supplying surface  24   c  in a counterclockwise direction. 
   The coupling part  24   a  formed as described above can be joined with the coupling part  25   a  of the process cartridge  9  to transmit the drive force from the slide gear to the drive force receiving shaft. In detail, when the coupling part  24   a  of the slide gear and the coupling part  25   a  of the drive force receiving shaft of the process cartridge  9  are joined, the drive force supplying surface  24   c  of the coupling part  24   a  and the drive force receiving surface  25   c  of the coupling part  25   a  contact against one another. Accompanying the rotation of the slide gear, the drive force supplying surface  24   c  rotates while pushing the drive force receiving surface  25   c  of the drive force receiving shaft, and the drive force is transmitted to the drive force receiving shaft. By contacting the drive force supplying surface  24   c  and the drive force receiving surface  25   c  against one another as surfaces approximately perpendicular to the axial direction, in other words, to the rotational direction, a torque can be increased. As a result, load applied to the coupling parts  24   a ,  25   a  can be reduced, and the durability can be improved. 
   Moreover, the slanting surfaces  24   d  of the coupling part  24   a  and the slanting surfaces  25   d  of the coupling part  25   a  can contribute for the coupling part  24   a  and the coupling part  25   a  to be joined and separated smoothly. In detail, when the drive force is transferred, the drive force supplying surface  24   c  of the coupling part  24   a  and the drive force receiving surface  25   c  of the coupling part  25   a  are joined such that the surfaces contact against one another. However, the shaft center of the slide gear and the shaft center of the drive force receiving shaft are not necessarily located at a preferable position at all times. Therefore, when the coupling part  24   a  rotates accompanying the rotation of the slide gear, and the coupling part  24   a  reaches a position where the coupling part  24   a  can be joined with the coupling part  25   a  of the drive force receiving shaft, the coupling part  24   a  and the coupling part  25   a  are joined by the urging force of the compression spring  38 . However, until reaching the position where the coupling part  24   a  can be joined with the coupling part  25   a , an end surface of the coupling part  24   a  of the slide gear contacts against the slanting surface  25   d  of the coupling part  25   a  of the drive force receiving shaft, and slides over the slanting surface  25   d  accompanying the rotation of the slide gear to be guided to a position where the drive force supplying surface  24   c  and the drive force receiving surface  25   c  are engaged. 
   As described above, by provided the slanting surfaces  24   d  to the coupling part  24   a  and the slanting surfaces  25   d  to the coupling part  25   a , the sliding movement of the slide gear is controlled until the slide gear urged by the compression spring  38  rotates to the position where the coupling part  24   a  can be joined with the coupling part  25   a . The slide gear does not slide all of sudden at the position where the coupling part  24   a  can be joined with the coupling part  25   a . The slide gear is guided to the position where the coupling part  24   a  can be joined with the coupling part  25   a , while sliding gradually along the slanting surfaces  24   d ,  25   d  accompanying the rotation of the slide gear. Accordingly, the coupling parts  24   a ,  25   b  or the like can be prevented from being damaged by buffering shock that generate when the slide gear slides. 
   A diameter of a shaft hole of the first bearing  41  is formed slightly larger than a diameter of the drive force supplying shaft  241  of the slide gear. Therefore, a prescribed gap C is maintained between the first bearing  41  and the drive force supplying shaft  241 . That is, the first bearing  41  only supports the drive force supplying shaft  241  softly, and does not position the drive force supplying shaft  241  strictly. Therefore, the slide gear is positioned mainly by the drive force supplying shaft  242  having a projection  242   a  and the second bearing  42 . The slide gear is not positioned strictly by the first bearing  41  and the drive force supplying shaft  241 . Thus, the axis line O of the slide gear can be slightly rotated eccentrically. Here, the gap C to be secured between the first bearing  41  and the drive force supplying shaft  241  is slightly larger than a gap that is generally provided for the bearing to support the shaft rotatable. For example, it is preferable to secure a gap which can permit the axis line O of the slide gear  24  to slant from a standard position (horizontal position) by an angle of eccentricity which is approximately tan−1 ({fraction (1/100)}) (approximately 0.573 degrees). Moreover, it is preferable for a size of the gap C to be approximately {fraction (5/100)} of the diameter of the drive force supplying shaft  241 . 
   As described above, a prescribed gap C is formed between the first bearing  41  and the drive force supplying shaft  241 , and the slide gear is supported by permitting the axis line O to rotate eccentrically. As a result, a displacement between the axis line O of the slide gear and an axis line P of the drive force receiving shaft of the process cartridge  9  as shown in  FIG. 8  can be absorbed by a space permitting the slide gear to rotate eccentrically. Generally, the axis line O of the slide gear and the axis line P of the drive force receiving shaft of the process cartridge  9  are designed to be located on the same axis line. However, there are many cases when the axis line O of the slide gear is displaced from the axis line P of the drive force receiving shaft due to mistake of when assembling the drive unit  12  or the process cartridge  9 . When the slide gear and the drive force receiving shaft are connected under a state in which the slide gear is displaced from the drive force receiving shaft, the coupling parts  24   a ,  25   a  can be damaged by unnatural force being applied to the coupling parts  24   a ,  25   a . In addition, the photosensitive drum  39  can be caused to rotate eccentrically, and the recording image quality can be deteriorated. 
   However, for example, as shown in  FIG. 9 , even in the case the axis line P of the drive force receiving shaft of the process cartridge  9  is slanting by an angle α from the standard position of the axis line O of the slide gear, since the slide gear  24  is permitted to rotate eccentrically by the gap C provided to the first bearing  41 , when the coupling part  24   a  of the slide gear and the coupling part  25   a  of the drive force receiving shaft are joined, the slide gear is positioned by the joined part and the second bearing  42 . Then, the axis line O of the slide gear also rotates eccentrically by the angle α. Accordingly, as shown in  FIG. 11 , the displacement between the axis line O of the slide gear and the axis line P of the drive force receiving shaft is solved. As a result, the coupling part  24   a  of the slide gear and the coupling part  25   a  of the drive force receiving shaft can be joined accurately. In addition, the photosensitive drum  39  can be prevented from being rotated eccentrically, and the coupling parts  24   a ,  25   a  can be prevented from being damaged due to unnatural joining of the coupling parts  24 ,  25   a.    
   Further, according to the present embodiment, the circular guide  40  of the process cartridge  9  is positioned by the guide groove  43   a  provided on the guide cover  43  of the drive unit  12 . Since the position of the slide gear and the position of the drive force receiving shaft can be corresponded easily, the slide gear is positioned by the second bearing  42 , and the gap C is provided to the first bearing  41 . However, for example, as shown in  FIG. 12 , under a structure in which the circular guide  40  of the process cartridge  9  is positioned by the main body, the displacement between the slide gear and the drive force receiving shaft is prone to generate due to mistake in the assembling of the main body and the drive unit  12 . 
   Therefore, there are cases when it is preferable to provide the gap C to the second bearing  42 . That is, as shown in the drawing, the gap C is not provided to the first bearing  41 , and the slide gear is position strictly by the first bearing  41 . The gap C is provided to the second bearing  42 , and a space is provided for the axis line O of the slide gear to rotate eccentrically. Accordingly, as shown in  FIG. 13 , the angle of eccentricity α formed by the joined coupling parts  24   a ,  25   a  is permitted by the gap C of the second bearing  42  with the first bearing  41  as the fulcrum. As a result, as shown in  FIG. 9 , the angle of eccentricity which can be permitted by the gap C can be enlarged than when the angle of eccentricity α is permitted by the gap C of the first bearing  41  with the second bearing  42  as the fulcrum. 
   Further, the determination for whether to provide the gap C to the first bearing  41  or to the second bearing  42  can be made in accordance with the above-described difference in the positioning of the process cartridge  9 . In addition, the determination can be made in accordance with length of the drive force supplying shafts  241 ,  242 , or relationship between the position of the first bearing  41  and the second bearing  42 . 
   (Linkage Configuration of Both Output Parts) 
   Next, linkage configuration of the fuser drive output part  15  and the cartridge drive output part  16  will be described. The swing arm  19  of the fuser drive output part  15  and the slide gear of the cartridge drive output part  16  are linked by a cam mechanism to be described later on. When the drive force is not transmitted from the fuser drive output part  15  to the fuser drive input gear  17 , the drive force is not transmitted from the cartridge drive output part  16  to the drive force receiving shaft. 
   The cam mechanism will be described in details with reference to the drawings. As shown in  FIG. 6A ,  FIG. 6B , and  FIG. 14 , a pin  37  is protruding from a free end surface of the swing arm  19  of the fuser drive output part  15 . A pushing cam  26  is provided in proximity to the free end surface of the swing arm  19 . In addition, the pushing cam  26  is provided in an upright state with a lower end pivotally supported such that the pushing cam  26  can contact against or separate from the side of the helical gear  240  of the slide gear. As shown in  FIG. 14 , a cam groove  26   a  is formed on the pushing cam  26 . The cam groove  26   a  is long lengthwise, and has a shape like a dogleg. The pin  37  is inserted in the cam groove  26   a.    
   Meanwhile, as shown in  FIG. 15 , a circular reinforcement rib  240   a  is formed in a peripheral direction on the side of the helical gear  240 . The pushing cam  26  can contact against the reinforcement rib  240   a . The reinforcement rib  240   a  prevents the pushing cam  30  from being damaged by contacting against a tooth part of the helical gear  240  when the pushing cam  30  contacts against the slide gear. In addition, the reinforcement rib  240   a  prevents the slide gear from being rotated unevenly due to imperfect meshing. Further, the shape of the reinforcement rib  240   a  is not limited in particular. However, the reinforcement rib  240   a  is preferable to have a trapezoid semicircular shape in the cross-section. 
   FIG.  14  and  FIG. 15  show a state in which the fuser drive output part  15  is transmitting the drive force to the fuser drive input gear  17 , and the cartridge drive output part  16  is transmitting the drive force to the drive force receiving shaft of the process cartridge  9 . Under this state, as shown in  FIG. 14 , the swing arm  19  of the fuser drive output part  15  swings upward, the planet gear  20  (not shown in the drawing) meshes with the fuser drive input gear  17  to transmit the drive force from the motor  14 . Under a state in which the swing arm  19  is swung upward, the pin  37  is located in proximity to the uppermost end of the cam groove  26   a  of the pushing cam  26 . As shown with a double dashed line in  FIG. 15 , the pin  37  is located away from the slide gear. Therefore, the slide gear slides to the process cartridge  9  side by the urging force of the compression spring  38 , and as described above, the slide gear is linked to the drive force receiving shaft of the process cartridge  9  to transmit the drive force. 
   Meanwhile, FIG.  16  and  FIG. 17  show a state in which the drive force is not transmitted from the fuser drive output part  15  to the fuser drive input gear  17 , and the drive force is not transmitted from the cartridge drive output part  16  to the drive force receiving shaft of the process cartridge  9 . As shown in  FIG. 16 , the swing arm  19  is Swung downward by the pushing surface  19   b  of the swing arm  19  being pushed by a cam  30  to be described later on. Accordingly, the planet gear  20  (not shown in the drawing) and the fuser drive input gear  17  are separated, and the drive force from the motor  14  is cut off from being transmitted. Moreover, when the swing arm  19  swings downward, the pin  37  that is provided on the free end surface of the swing arm  19  also moves downward. In addition, the pushing cam  26  is inclined to the direction of the slide gear. Accordingly, as shown in  FIG. 17 , the pushing cam  26  contacts against the reinforcement rib  240   a  of the slide gear, and the slide gear is pushed to the direction of the first bearing  41  against the urging force of the compression spring  38 . When the slide gear is slid to the direction of the first bearing  41 , the slide gear is separated from the drive force receiving shaft of the process cartridge  9 , and the drive force is cut off from being transmitted to the drive force receiving shaft. 
   Here, the slide gear is formed by the helical gear  240 . Therefore, as shown in  FIG. 16 , when sliding toward the direction of the first bearing  41 , the slide gear rotates slightly to a direction opposite to the rotational direction (counterclockwise direction in  FIG. 16 ) along the mesh between the slide gear and the train of gears (not shown in the drawing) which are meshed at all times to transmit the drive force from the motor  14 . As described above, the slide gear separates from the drive force receiving shaft while the drive force supplying surface  24   c  of the coupling part  24   a  of the slide gear rotates in a direction to separate from the drive force receiving surface  25   c  of the coupling part  25   a  of the drive force receiving shaft. Therefore, the coupling part  24   a  of the slide gear can be separated smoothly from the coupling part  25   a  of the drive force receiving shaft. Moreover, in the coupling part  24   a , the slanting surface  24   d  is formed between the drive force supplying surfaces  24   c , and in the coupling part  25   a , the slanting surface  25   d  is formed between the drive force receiving surfaces  25   c . Therefore, a reverse rotation of the slide gear is not disturbed. 
   Further, when the pushing force of the cam  30  to swing the swing arm  19  downward is released, the slide gear slides toward a direction of the second bearing  42  by the urging force of the compression spring  38 . As a result, the pushing cam  26  is pushed backward to uprise, and an upward force is applied to the pin  37  by a cam function of the cam groove  26   a  of the pushing cam  26 , and the swing arm  19  swings upward. As described above, the compression spring  38  also functions as a return spring to push back the downward swing of the swing arm  19 . Therefore, when the cam  30  does not push the swing arm  19  downward, the swing arm  19  swings upward, and the drive force is transmitted to the fuser drive input gear  17 . 
   (Configuration to Transmit/Cut Off Drive Force According to Opened or Closed State of Top Cover) 
   Next, the cam mechanism  27  which links the top cover  8  and the swing arm  19  of the fuser drive output part  15  will be described. By linking the swing arm  19  to the top cover  8  via the cam mechanism  27  to be described below, when the top cover  8  is opened, the swing arm  19  is pushed by the cam  30  and swung downward. When the swing arm  19  is swung downward, the drive force is prevented from being transmitted between the fuser drive output part  15  and the fuser drive input gear  17 . In addition, the drive force is prevented from being transmitted between the cartridge drive output part  16  and the drive force receiving shaft of the process cartridge  9 . Accordingly, as shown in FIG.  4  and  FIG. 5 , the setting and removing of the process cartridge  9 , and the eliminating of the paper jam can be carried out easily. Meanwhile, when the top cover  8  is closed, the pushing by the cam  30  is released, and as described above, the swing arm  19  swings upward to become capable of transmitting the drive force to the fuser drive input gear  17 . In addition, the slide gear becomes capable of transmitting the drive force to the drive force receiving shaft of the process cartridge  9 . 
     FIG. 18  is a side view showing a configuration of the cam mechanism  27 . The cam mechanism  27  is provided between the drive unit  12  and the top cover  8  which is pivotally supported by the support shaft  44  to be openable or closable. In detail, the cam mechanism  27  includes a lever  29  and the cam  30 . The lever  29  includes a hook part  29   a  which can join with the pin  28  provided on the top cover  8 . The cam  30  is provided at a lower end of the lever  29 . 
   The pin  28  of the top cover  8  is protruding laterally from proximity of a lower end of a bracket  8   a  which is dropping from a ceiling surface of the top cover  8  (side facing toward an inner side of the image recording unit  2 ). The pin  28  moves when the top cover  8  is opened or closed. Moreover, the lever  29  is provided such that longitudinal direction of the lever  28  becomes vertical direction. A hook part  29   a  is formed in an upper part of the lever  29 . A long hole  29   b  is formed in approximately a center part of the lever  29 . A concave part  29   d  is formed at an edge of the center part of the lever  29 . 
   The apparatus front side of the upper end of the lever  29  is shaped hook-like to form the hook part  29   a . Meanwhile, an opening part  29   e  is formed at the apparatus back side with an upper part opened. Furthermore, at the apparatus back side, a slanting part  35  is formed approximately opposing against the hook part  29   a , slanting downward toward the apparatus front side. The hook part  29   a  can be joined with the pin  28  of the top cover  8 . Meanwhile, the pin  28  can pass through the opening part  29   e . That is, when the top cover  8  is opened, the pin  28  is joined with the hook part  29   a  to pull the lever  29  upward. Then, when the lever  29  is slanted down to the apparatus front side, the pin  28  passes through the opening part  29   e , and the link between the top cover  8  and the lever  29  is released. Meanwhile, when closing the top cover  8 , the pin  28  contacts against the slanting part  35  to push down the lever  29  to the apparatus back side. 
   A support pin  33 , which is provided to the image recording unit  2 , is inserted through the long hole  29   b  that is formed in proximity to the center of the lever  29 . The support pin  33  supports the lever  29 . The long hole  29   b  is formed in a vertical direction. A free part  29   c  is formed at the lower end of the long hole  29   b . The free part  29   c  is slanting toward the apparatus back side, and has a wide width. Therefore, the lever  29  can move vertically along the long hole  29   b  and the shape of the free part  29   c . Moreover, when the support pin  33  is inserted into the free part  29   c , the lever  29  can swing with the linked part with the cam  30  as approximately the center. 
   Two tension springs  31 ,  32  are provided between the lever  29  and the image recording unit  2  main body. The lever  29  is urged to the apparatus front side by the first tension spring  31 , and approximately downward by the second tension spring  32 . The lever  29  urged to the apparatus front side by the first tension spring  31  contacts against a stopper  34  provided to the image recording unit  2  at the edge part of the lever  29 . As a result, the movement of the lever  29  toward the apparatus front side is controlled. Furthermore, when the lever  29  is urged approximately downward by the second tension spring  32 , the support pin  33  is contacted against the upper end of the long hole  29   b . Moreover, under a state in which the support pin  33  is located at the lower end of the free part  29   c , the stopper  34  moves into the concave part  29   d  to slant the lever  29 . Further, the concave part  29   d  is formed on an edge of the lever  29 . 
   The cam  30  is approximately isosceles triangle shaped. Approximately the center of the lower part of the cam  30  is pivotally supported directly above the swing arm  19  of the fuser drive output part  15 . An edge of the cam  30  at the apparatus inner side is pivotally connected to the lever  29 . By the vertical movement of the lever  29 , the cam  30  moves like a seesaw. As described above, the other end of the cam  30  pushes down the pushing surface of the swing arm  19 . 
   Next, a movement of the cam mechanism  27  will be described. First, under a state in which the top cover  8  is closed, as shown in  FIG. 18 , the pin  28  which is provided to the top cover  8  is located inside the hook part  29   a  of the lever  29 . The lever  29  is urged to the apparatus front side by the first tension spring  31  to contact against the stopper  34 . Then, the lever  29  is urged approximately downward by the second tension spring  32 , and the support pin  33  is contacted against the upper end of the long hole  29   b . At this time, the lever  29  is pulling the connected part between the lever  29  and the cam  30  downward, and the cam  30  is not contacting against the pressing surface  19   b  of the swing arm  19 . Therefore, as described above, the swing arm  19  swings upward by a force which the compression spring  38  (not shown in the drawing) urges the slide gear. Then, the planet gear  20  and the fuser drive input gear  17  are meshed, and the drive force from the motor  14  (not shown in the drawing) can be transmitted to the fuser  11  (not shown in the drawing) via the fuser drive input gear  17 . Moreover, the slide gear joins with the drive force receiving shaft (not shown in the drawing) of the process cartridge  9 , and the, drive force of the motor  14  can be transmitted to the process cartridge  9 . 
   From this state, when the top cover  8  is pulled upward to be opened, as shown in  FIG. 19 , the pin  28  joins with the hook part  29   a  of the lever  29 . The hook part  29   a  is pulled upward by following the movement of the top cover  8 , and the lever  29  transfers upward while guided by the long hole  29   b  and the support pin  33 . When the lever  29  transfers upward, the cam  30  which is pivotally connected to the lower end of the lever  29  is also pulled upward, and the cam  30  moves like a seesaw to descend the other end. The other end pushes up the pushing surface  19   b  of the swing arm  19 , and the swing arm  19  is swung downward. Accordingly, the planet gear  20  and the fuser drive force input gear  17  are separated, and the drive force is cut off from being transmitted to the fuser drive force input gear  17 . Moreover, as described above, accompanying the downward swing of the swing arm  19 , the pushing cam  37  slides the slide gear, and the slide gear and the drive force receiving shaft of the process cartridge  9  are released from the joined state. 
   Furthermore, accompanying the upward movement of the top cover  8 , the lever  29  also moves upward, and the concave part  29   d  formed at an edge of the lever  29  reaches the position facing the stopper  34 .  FIG. 19  shows a state directly before the stopper  34  enters into the concave part  29   d . Subsequently, the lever  29  is slanted down to the apparatus front side by the urging force of the first tension spring  31  with the connected part between the lever  29  and the cam  30  as approximately the center. Then, as shown in  FIG. 20 , the stopper  34  enters into the concave part  29   d , and the downward slanting movement of the lever  29  is completed. Moreover, when the stopper  34  enters into the concave part  29   d , the vertical movement of the lever  29  is locked. Accompanying this, the cam  30  is also locked under a state in which the cam  30  is pushing the swing arm  19  downward. 
   Meanwhile, by the lever  29  being slanted down, the hook part  29   a  and the pin  28  are released from the joined state, and the pin  28  is located at the opening part  29   e . Accordingly, when the top cover  8  is further pulled upward, the pin  28  passes through the opening part  29   e , and the pin  28  can be detached from the inner side of the hook part  29   a . As a result, the connection between the top cover  8  and the lever  29  is released, and the top cover  8  can be opened widely to its limit. Therefore, the process cartridge  9  can be set or removed easily, and the paper jam can be eliminated easily. 
   Next, an operation of when closing the top cover  8  will be described. As shown in  FIG. 21 , when the top cover  8  is pulled downward from a state in which the top cover  8  is opened in proximity to its limit, the pin  28  enters into the inner side of the hook part  29   a  from the opening part  29   e  of the lever  29 . Then, the pin  28  contacts against the slanting part  35 . When the top cover  8  is further pushed downward, as shown in  FIG. 22 , the pin  28  pushes the slanting part  35  to the apparatus back side while sliding over the slanting part  35 . The lever  29  swings to the apparatus back side against the urging force of the first tension spring  31 , with the connection between the lever  29  and the cam  30  as approximately the center. Accordingly, the concave part  29   e  at the edge of the lever  29  departs from the stopper  34 , and the lever  29  and the stopper  34  are released from the joined state. 
     FIG. 22  shows a state directly before the joined state is released. Subsequently, the lever  29  which is released from the joined state with the stopper  34  transfers downward while guided by the long hole  29   b  and the support pin  33  by following the urging force of the second tension spring  32 . Then, as shown in  FIG. 23 , the support pin  33  is contacted against the upper end of the long hole  29   b . Accompanying the descend of the lever  29 , the connected part between the lever  29  and the cam  30  is pulled down, and the cam  30  moves like a seesaw to elevate the other end. Accordingly, the pushing movement of the swing arm  19  is released. Then, as described above, the swing arm  19  swings upward, and the drive force can be transmitted to the fuser drive input gear  17 . In addition, the slide gear can transmit the drive force to the drive force receiving shaft of the process cartridge  9 . 
   As described above, the swing arm  19  is swung by the cam mechanism  27  when the top cover  8  is opened or closed. Under a state in which the top cover  8  is opened, the drive force is cut off from being transmitted to the fuser drive input gear  17  and the drive force receiving shaft of the process cartridge  9 . As a result, the process cartridge  9  can be set or removed easily. In addition, since the fuser  11  can be rotated freely, the maintenance such as elimination of the paper jam can be carried out easily. Meanwhile, under a state in which the top cover  8  is closed, the drive force can be transmitted to the fuser  11  and the process cartridge  9 . 
   Moreover, when opening and closing the top cover  8 , the top cover  8  and the lever  29  are linked only under a state in which the pin  28  provided to the top cover  8  is joined with the hook part  29   a  of the lever  29 . When the top cover  8  is completely closed or opened, the pin  28  and the hook part  29   a  are not joined, and the linked state is released. Accordingly, no force is applied to the pin  28  and the hook part  29   a  which link the top cover  8  and the lever  29 , other than when opening an closing the top cover  8 . Therefore, the pin  28  and the hook part  29   a  are not required to have strong strength. Thus, it is not necessary to use a strong and expensive material for the pin  28  and the hook part  29   a . In addition, it is not necessary to provide a reinforcement member, and a cost can be reduced. 
   (Configuration to Attach Drive Unit to Image Forming Apparatus) 
   FIG.  24  and  FIG. 25  are perspective views showing a method to attach the drive unit  12  to the image recording unit  2 . As described above, the motor  14  is fixed in a cantilever on the drive unit  12 . The motor  14  is generally heavy load, and for many cases, the motor  14  is occupying a greater part of the total weight of the drive unit  12 . Therefore, a center of gravity of the drive unit  12  is slanted, and the drive unit  12  is not balanced. Thus, it is difficult for the drive unit  12  to maintain an upright state. However, it is necessary to attach the drive unit  12  to the main body under an upright state. As a result, there is difficulty in attaching the drive unit  12  to the image recording unit  2 . 
   In consideration to the above-described circumstance, a through hole  46  is formed on a main body frame  45  of the image recording unit  2  for setting the motor  14 . The main body frame  45  is formed from sheet metal. Plate shaped guides  47  are provided around the through hole  46 , specifically at both sides and lower side of the through hole  46 . The guides  47  are protruding toward the inner side of the apparatus to guide the sides and the lower surface of the motor  14 . When attaching the drive unit  12 , first, as shown in  FIG. 24 , the motor  14  is inserted though the through hole  46  from the outer side of the main body frame  45 . Then, as shown in  FIG. 25 , the motor  14  is placed on the guide  47  of the lower surface such that the weight of the motor  14  is accepted by the main body frame  45 . Accordingly, the drive unit  12  can be maintained under upright state easily. 
   Moreover, from a state shown in  FIG. 25 , the frame body  13  of the drive unit  12  is attached to the main body frame  45  by sliding the motor  14  along the guides  47 . Then, the drive unit  12  is fixed to the main body frame  45  by a screw (not shown in the drawing). By adopting such a simple attaching method, the attaching steps can be reduced. 
   Further, the guides  47  are formed by leaving the guide parts when stamping the through hole  46  of the main body frame  45 , and bending the guide parts toward the inner side of the image recording unit  2 . Accordingly, the parts protruding to the outside of the image forming apparatus can be reduced, and the size of the image forming apparatus can be reduced. In addition, since the direction in which the guides  47  are bent is corresponding to the direction in which the motor  14  is inserted, the motor  14  can be inserted smoothly. Furthermore, the through hole  46  is formed in square and the guides  47  are formed in tabular shape to correspond to the shape of a casing of the motor  14  which is approximately rectangular parallelepiped. 
   In the above described embodiment, the slide gear  24  is formed as the coupling protrusion and the photosensitive drum  39  is formed as the coupling hole. However, the present invention is not limited to this example, and for example, the slide gear  24  can be formed as the coupling hole and the photosensitive drum  39  can be formed as the coupling protrusion. 
   The present invention is not limited to the above-described embodiment, but includes variations or modifications within the technical concept.