Patent Publication Number: US-8526856-B2

Title: Image forming unit having biasing part that biases developing unit toward drum unit and image forming device including same

Description:
CROSS REFERENCE 
     The present application is related to, claims priority from and incorporates by reference Japanese patent application number 2009-014129, filed on Jan. 26, 2009. 
     TECHNICAL FIELD 
     The present invention relates to an image forming unit and an image forming device. 
     BACKGROUND 
     A conventional image forming device, for example, a printer, a photocopier, a facsimile machine, a multifunction machine, or the like, has an image forming unit. This image forming unit has a photoreceptor drum, a charge roller, a developing part, and so on. An LED head exposes the surface of the photoreceptor drum, which is uniformly charged by the charge roller, to form an electrostatic latent image. Then, the electrostatic latent image is developed by the developing part to form a toner image. The toner image is then transferred onto a sheet of paper by a transferring roller. The transferred toner image on the sheet of paper is fused by a fuser to form an image, and therefore, a printing operation is performed. 
     The developing part is located such that it contacts and pressed the photoreceptor drum. The developing part has a developing roller that operates to adhere toner onto the photoreceptor drum, a toner supplying roller that is located such that it contacts and presses the developing roller and supplies toner to the developing roller and so on. 
     When the photoreceptor drum is a first rotating body and the developing roller is a second rotating body, the first and second rotating bodies are required to uniformly contact and press each other in the shaft directions of the bodies during the course of assembling the printer. When the first and second rotating bodies are assembled in the printer, the position of the second rotating body is changed and adjusted while the pressing force is measured. Therefore, after the pressing force is adjusted, the first and second rotating bodies are assembled in the main body of the printer, i.e., the device main body. Japanese laid-open patent application publication number 2006-48018 provides an example of such a device. 
     Similarly, when the developing roller is a first rotating body and the toner supplying roller is a second rotating body, the first and second rotating bodies are required to uniformly contact and press each other in the shaft directions of the bodies. Side plates in which the size is controlled are provided on the both ends of the first and second rotating bodies, and then the first and second rotating bodies are assembled in the device main body. Japanese laid-open patent application publication number 2007-17472 provides an example of such a device. 
     However, in the conventional printer, it takes time for adjustment work when the first and second rotating bodies are uniformly contacted and pressed against each other in the shaft directions of the bodies. As a result, productivity (?) for assembling the printer was decreased. 
     Objects of the present invention are to provide an image forming unit and an image forming device in which first and second rotating bodies are easily and uniformly contacted and pressed against each other in the shaft directions of the bodies. 
     SUMMARY 
     For the purpose, an image forming unit of the present application includes a first rotating body having a first gear; a first unit that rotatably supports the first rotating body; a second rotating body having a second gear; a second unit that rotatably supports the second rotating body; and a biasing part that biases the second unit toward the first unit, wherein a drive force is generated by transmitting rotation from the first gear to the second gear in order to transmit the rotation from the first rotating body to the second rotating body, and the biasing part biases the second unit in a biasing direction substantially perpendicular to a driving direction of the drive force. 
     In this case, the biasing part biases the second unit in the approximately perpendicular direction to the direction of the drive force that is generated by transmitting rotation between the first and second gears through meshing the first and second gears. 
     Therefore, the first and second rotating bodies are easily and uniformly contacted and pressed in the shaft directions of the bodies. As a result, workability for assembling the printer is improved. 
     Also, the application discloses an image forming device including an image forming unit above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a first schematic view of a relationship between a drum gear and a developing roller gear according to a first disclosed embodiment. 
         FIG. 2  is a schematic view of a printer according to a first disclosed embodiment. 
         FIG. 3  is a perspective view of an image forming unit according to a first disclosed embodiment. 
         FIG. 4  is a first exploded perspective view of an image forming unit according to a first disclosed embodiment. 
         FIG. 5  is a second exploded perspective view of an image forming unit according to a first disclosed embodiment. 
         FIG. 6  is a sectional view of a drum unit according to a first disclosed embodiment. 
         FIG. 7  is a sectional view of main parts of an image forming unit according to a first disclosed embodiment. 
         FIG. 8  is a schematic view of a rotation transmitting system of an image forming unit according to a first disclosed embodiment. 
         FIG. 9  is a second schematic view of relationship between a drum gear and a developing roller gear according to a first disclosed embodiment. 
         FIG. 10  is a first schematic view of movement when a developing unit is attached to a drum unit according to a first disclosed embodiment. 
         FIG. 11  is a second schematic view of movement when a developing unit is attached to a drum unit according to a first disclosed embodiment. 
         FIG. 12  is a third schematic view of movement when a developing unit is attached to a drum unit according to a first disclosed embodiment. 
         FIG. 13  is a fourth schematic view of movement when a developing unit is attached to a drum unit according to a first disclosed embodiment. 
         FIG. 14  is a first schematic view of a printer according to a second disclosed embodiment. 
         FIG. 15  is a second schematic view of a printer according to a second disclosed embodiment. 
         FIG. 16  is a first exploded perspective view of an image forming unit according to a third disclosed embodiment. 
         FIG. 17  is a second exploded perspective view of an image forming unit according to a third disclosed embodiment. 
         FIG. 18  is a schematic view of relationship among a developing roller gear, a driven gear, and a toner supplying roller gear according to a third disclosed embodiment. 
         FIG. 19  is a schematic view of a rotation transmitting system of an image forming unit according to a third disclosed embodiment. 
         FIG. 20  is a schematic view of relationship between a developing roller gear and a driven gear according to a third disclosed embodiment. 
         FIG. 21  is a first exploded perspective view of an image forming unit according to a fourth disclosed embodiment. 
         FIG. 22  is a second exploded perspective view of an image forming unit according to a fourth disclosed embodiment. 
         FIG. 23  is a schematic view of relationship among a developing roller gear, a driven gear, and a toner supplying roller gear according to a fourth disclosed embodiment. 
         FIG. 24  is a schematic view of relationship between a driven gear and a toner supplying roller gear according to a fourth disclosed embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the descriptions below, the designations a and b are used with some of the reference numerals. These refer to corresponding elements on opposite sides of different parts of the disclosed device. Although various drawings only show one of two matched elements depending upon which viewing direction the drawing represents (e.g.,  FIG. 10  shows element  48   a  but not  48   b ), the matching element that is not shown in the drawings operates in a manner comparable to the matching element that is shown in the drawings. 
     A first embodiment is explained in detail below with reference to drawings. In this embodiment, a printer that is an example of an image forming device is explained. 
       FIG. 2  is a schematic view of the printer according to the first disclosed embodiment. 
     As shown in  FIG. 2 , a main body  10  of a printer  40 , e.g., a device main body  10 , includes a carrying path  25  for carrying a sheet (not shown) as a medium. Carrying rollers  26 - 29  are located in the carrying path  25 . Image forming units (ID units), Bk, Y, M, and C, that are for forming a toner image as a developer image for black, yellow, magenta, and cyan, respectively, are provided along the carrying path  25 . Each of the ID units, Bk, Y, M, and C, has a photoreceptor drum  11  as an image carrier. 
     LED heads  23 , which are exposure devices and recording heads, are provided to face the photoreceptor drums  11  and are adjacent to each of the ID units, Bk, Y, M, and C. A transferring unit  34  is provided to carry a sheet and transfer each toner image onto the sheet. The transferring unit  34  is located below each of the ID units, Bk, Y, M, and C. A belt driving unit is configured with the transferring unit  34 . 
     A fuser  35  is located at the downstream side of the ID units, Bk, Y, M, and C, in the carrying direction of the sheet and operates as a fusing device that fuses the toner image onto the sheet. 
     In each of the ID units, Bk, Y, M, and C, the photoreceptor drums  11  rotate at a certain rotation speed and are charged by the charge rollers  12  as a charging device, so that the photoreceptor drums  11  can store electric charge on the surface of the drums. When the electric charge on the surface of the drums is removed, an electrostatic latent image (not shown) is formed as a latent image on the surface of the photoreceptor drums  11 . The charge rollers  12  contact and press the photoreceptor drums  11  with a certain amount of pressing force and rotate in the opposite direction compared with the rotation direction of the photoreceptor drums  11 . 
     A developing part  36  develops the electrostatic latent image and forms the toner image. The developing part  36  is located adjacent to the photoreceptor drums  11 . The developing part  36  has, for example, a developing roller  16  operating as a developer carrier that adheres toner as developer onto the photoreceptor drum  11 , a developing blade (not shown) operating as a developer layer regulation part that regulates the toner thickness on the developing roller  16 , and a toner supplying roller  18  operating as a developer supplying part that supplies toner to the developing roller  16 . The developing roller  16  contacts and presses the photoreceptor drums  11  with a certain amount of pressing force and rotates in the opposite direction compared with the rotation direction of the photoreceptor drums  11 . The toner supplying roller  18  contacts and presses the developing roller  16  with a certain amount of pressing force and rotates in the same direction compared with the rotation direction of the developing roller  16 . The photoreceptor drums  11 , the developing roller  16 , the toner supplying roller  18  and so on configure an image forming component. 
     The photoreceptor drums  11 , the charge roller  12 , the developing part  36  and so on are contained in the main body of the ID units, Bk, Y, M, and C, i.e., an image forming unit (ID unit) main body  20 . A toner cartridge  15 , operating as a developer container that contains toner, is located above the ID unit main body  20  and is detachable from the ID unit main body  20 . 
     The transferring unit  34  has a transferring belt  21  that flexibly rotates and transferring rollers  22 , operating as transferring parts, that are located to face each of the photoreceptor drums  11 . A certain voltage is applied to the transferring belt  21  and the transferring rollers  22  through a power source (not shown). Then toner images in each color on the photoreceptor drums  11  are sequentially transferred on the sheet to overlap each other. 
     The main body  10  has a lower cover  38  and an upper cover  39 . The upper cover  39  is swingably provided with respect to the lower cover  38 , with the spindle Sh 1  serving as the center for the swing. The upper cover  39  opens and closes at the divided face A-A. A stacker  31 , in which ejected sheets are loaded, is located at the upper cover  39 . A sheet cassette  30 , operating as a medium container that stores the sheets, is provided at the edge portion of the carrying path  25  under the transferring unit  34 . A feeding part  34  that feeds the sheet is provided at the sheet cassette  30 . 
     Next, operation of the printer  40  that has the structures mentioned above is explained. 
     An electrostatic latent image is formed in each of the ID units, Bk, Y, M, and C, when the surfaces of the photoreceptor drums  11  are uniformly charged by the charge rollers  12 , and when the LED heads  23  expose the surfaces of the photoreceptor drums  11 . Next, the developing part  36  develops the electrostatic latent image to form toner images in each color. 
     A sheet that is fed by the feeding part  32  is carried to the carrying rollers  26  and  27  and is adhered to the carrying belt  21  by electrostatic effect. The sheet is carried between each of the ID units, Bk, Y, M, and C, and the transferring unit  34  by the run of the transferring belt  21 , so that a toner image in each color is transferred to overlap each other on the sheet. As a result, a color toner image is formed. The sheet is passed the fuser  35 , which fuses the color toner image, forming a color image on the sheet. The sheet is further carried by the carrying rollers  28  and  29  and is ejected in the stacker  31 . 
     The printer  40  also has an interface part (not shown) that receives print data by communicating with an external device (not shown) and a control part (not shown) that receives the print data from the interface part and controls the entire printer  40 . 
     Next, each of the ID units, Bk, Y, M, and C, is explained. Because the structures of each of the ID units, Bk, Y, M, and C, are same, the ID unit Bk is explained below by way of example. The other ID units Y, M, and C operate in a similar manner. 
       FIG. 3  is a perspective view of an image forming unit according to a first disclosed embodiment.  FIG. 4  is a first exploded perspective view of the image forming unit according to the first disclosed embodiment.  FIG. 5  is a second exploded perspective view of the image forming unit according to the first disclosed embodiment.  FIG. 6  is a sectional view of a drum unit according to the first disclosed embodiment.  FIG. 7  is a sectional view of main parts of the image forming unit according to the first disclosed embodiment. 
     As shown in these figures, the ID unit Bk has a drum unit  13  as a first unit, and a developing unit  24  as a second unit that is detachable from the drum unit  13 . The drum unit  13  has the photoreceptor drum  11 , the charge roller  12 , a cleaning blade  14 , a carrying spiral  17 , and side plates  19   a  and  19   b  that hold the above mentioned structures. The cleaning blade  14  operates as a cleaning part that scrapes remaining toner from the surface of the photoreceptor drum  11  after toner transfer. The carrying spiral  17  operates as a carrying part that carries waste toner as waste developer scraped by the cleaning blade  14 . The side plates  19   a  and  19   b  have cylindrical projection parts  41   a  and  41   b , groove parts  42   a  and  42   b , and a bias spring  43 . The cylindrical projection parts  41   a  and  41   b  operate as first engaging components and are for attaching the developing unit  24  to the drum unit  13 ; the groove parts  42   a  and  42   b  operate as third engaging components; and the bias spring  43  operates as a biasing part that biases the developing unit  24  toward the drum unit  13 . 
     The developing unit  24  has the developing roller  16 , the toner cartridge  15 , agitating parts  45   a  and  45   b  that agitate toner  33  supplied from the toner cartridge  15 , the toner supplying roller  18  that supplies the toner  33  to the developing roller  16 , the developing blade  46  that regulates the thickness of a toner layer on the developing roller  16 , and side plates  47   a  and  47   b  that hold the above mentioned structures in the both ends. The agitating parts  45   a  and  45   b  operate to agitate toner  33  supplied from the toner cartridge  15 ; the toner supplying roller  18  operates to supply the toner  33  to the developing roller  16 ; and the developing blade  46  operates to regulate the thickness of a toner layer on the developing roller  16 . The side plates  47   a  and  47   b  have cylindrical projection parts  48   a  and  48   b , operating as fourth engaging components that are for attaching the developing unit  24  to the drum unit  13  and groove parts  49   a  and  49   b , operating as third engaging components. 
     As shown in  FIGS. 3 and 4 , the photoreceptor drum  11  is rotatably supported by the side plates  19   a  and  19   b  and serves as a first rotating body. The photoreceptor drum  11  rotates when the rotation of a motor (not shown) as a drive part is transmitted to a drum gear  44 , operating as a first gear, located in one end. The developing roller  16  is rotatably supported by the side plates  47   a  and  47   b  and serves as a second rotating body. The developing roller  16  rotates when the rotation of the photoreceptor drum  11  is transmitted to a developing roller gear  37 , operating as a second gear, that meshes with the drum gear  44  and is located in one end. 
     Next, a rotation transmitting system of the ID unit Bk is explained. 
       FIG. 1  is a first schematic view of relationship between the drum gear  44  and the developing roller gear  37  according to the first disclosed embodiment.  FIG. 8  is a schematic view of the rotation transmitting system of an image forming unit according to the first disclosed embodiment.  FIG. 9  is a second schematic view of relationship between the drum gear  44  and the developing roller gear according to the first disclosed embodiment. 
     In  FIG. 8 , the reference numeral  37  represents the developing roller gear, the reference numeral  44  represents the drum gear, the reference numeral  50  represents a motor gear that is attached to an output shaft of the motor, and the reference numeral  51  represents a reduction gear that slows down the rotation speed of the motor and transmits the rotation to the drum gear  44 . 
     As shown in  FIG. 3 , when the developing unit  24  is attached to the drum unit  13 , the developing roller gear  37  meshes with the drum gear  44 , so that the developing roller  16  rotates at a certain rotation speed that has a certain speed difference compared to the rotation speed of the photoreceptor drum  11 . In  FIG. 1 , the rotation direction of the drum gear  44  is in the direction of arrow H. The rotation direction of the developing roller gear  37  is in the direction of arrow I. When the developing unit  24  is attached to the drum unit  13 , the projection parts  41   a  and  41   b  engage with the groove parts  49   a  and  49   b , respectively. As shown in  FIGS. 1 and 9 , the engagement position that indicates the position of engagement is located in the vicinity of the position where the drum gear  44  meshes with the developing gear  37 . Namely, the engagement position is located within the area Na where the outer circumference circle  37   b  of the developing roller gear  37  and the outer circumference circle  44   b  of the drum gear  44  overlap each other with the point of contact gf between the pitch circle  37   a  of the developing roller gear  37  and the pitch circle  44   a  of the drum gear  44  being the center, i.e., within the area where the developing gear  37  meshes with the drum gear  44 . 
     The projection parts  41   a  and  41   b  are in a cylindrical shape. When the direction of the mesh pressure angle in the point of contact gf between the teeth of the drum gear  44  and the developing roller gear  37  is in the direction of arrow E (i.e., the E direction), operating as a biasing direction, the groove parts  49   a  and  49   b  are U-shaped along the E direction. When the direction of the tangent line of the pitch circles  37   a  and  44   a  is the direction of line J (i.e., the J direction), and when a direction perpendicular to the E direction is the direction of line Q (i.e., the Q direction), operating as a driving direction, an angle between the J and Q directions is referred to as the mesh pressure angle α. Note that the angle D between the E and Q directions is 90 degrees. 
     The developing unit  24  is biased in the E direction by the bias spring  43  that is located in the drum unit  13 . Therefore, the developing roller  16  uniformly contacts and presses the photoreceptor drum  11  in the shaft direction of the developing roller  16 . 
     In the disclosed embodiment, the drive force P is generated in the Q direction, which is deviated from the J direction by the mesh pressure angle α with respect to the rotation of the drum gear  44 . However, when an angle between the direction E of the biasing force and the direction of the drive force P that is caused by the meshing of the drum gear  44  and the developing roller gear  37  is very different from 90° (for example, outside of a range from 85° to 95°), the drive force P is generated in one end where the drum gear  44  and the developing roller gear  37  are located and is not generated in another end of the developing roller  16 . Therefore, the operation of the disclosed embodiment is deteriorated. In such a case, the developing roller  16  will not uniformly contact and press the photoreceptor drum  11 . 
     Because the projection parts  41   a  and  41   b  are in the cylindrical shape and the groove parts  49   a  and  49   b  are U-shaped, when the projection parts  41   a  and  41   b  and the groove parts  49   a  and  49   b  are engaged, respectively, the groove parts  49   a  and  49   b  regulates the movement of the projection parts  41   a  and  41   b  in the Q direction. The groove parts  49   a  and  49   b  can therefore receive the drive force P. Because the projection parts  41   a  and  41   b  can move in the E direction along the groove parts  49   a  and  49   b , and the developing unit  24  is biased to the drum unit  13  in the E direction by the bias spring  43 , the photoreceptor drum  11  and the developing roller  16  are easily and uniformly contacted and pressed against each other in the shaft directions. 
     Next, movements of attaching the developing unit  24  to the drum unit  13  are explained. 
       FIG. 10  is a first schematic view of movement when the developing unit is attached to the drum unit according to the first disclosed embodiment.  FIG. 11  is a second schematic view of movement when the developing unit is attached to the drum unit according to the first disclosed embodiment.  FIG. 12  is a third schematic view of movement when the developing unit is attached to the drum unit according to the first disclosed embodiment.  FIG. 13  is a fourth schematic view of movement when the developing unit is attached to the drum unit according to the first disclosed embodiment. 
     As shown in  FIGS. 10-13 , when the developing unit  24  is attached to the drum unit  13 , the projection parts  41   a ,  41   b ,  48   a , and  48   b  are engaged with the groove parts  49   a ,  49   b ,  42   a , and  42   b , respectively. 
     The engagement position between the projection parts  41   a  and  41   b  and the groove parts  49   a  and  49   b  is located in the vicinity of the area where the developing gear  37  meshes with the drum gear  44 , as discussed above. The engagement positions between the projection parts  48   a ,  48   b  and the groove parts  42   a ,  42   b  are located on an opposite side from the engagement positions between the projection parts  41   a ,  41   b  and the groove parts  49   a ,  49   b  with respect to the perpendicular line that passes through the center of gravity  52  of the developing unit  24 . A main engaging part, operating as a first engaging part, is configured with the projection parts  41   a  and  41   b  and the groove parts  49   a  and  49   b . A sub-engaging part, operating as a second engaging part, is configured with the projection parts  48   a  and  48   b  and the groove parts  42   a  and  42   b.    
     As discussed above, when the direction of the mesh pressure angle in the point of contact gf between the teeth of the drum gear  44  and the developing roller gear  37  is in the E direction, the groove parts  49   a  and  49   b  are U-shaped along the E direction. The groove parts  49   a  and  49   b  regulate the movement of the projection parts  41   a  and  41   b  in the Q direction. As a result, the drive force P is negated by the groove parts  49   a  and  49   b.    
     The groove parts  42   a  and  42   b  are parallel to the groove parts  49   a  and  49   b  and are U-shaped. The projection parts  48   a  and  48   b  located at the developing unit  24  are in a cylindrical shape and have a plane surface “sa” that is elongated in a direction perpendicular to the groove parts  42   a  and  42   b . Therefore, when the projection parts  48   a  and  48   b  and the groove parts  42   a  and  42   b  are engaged, respectively, the groove parts  42   a  and  42   b  regulates the movement of the projection parts  48   a  and  48   b  in the Q direction. The groove parts  42   a  and  42   b  can receive the drive force P. Because the projection parts  48   a  and  48   b  can move in the E direction along the groove parts  42   a  and  42   b , and the developing unit  24  is biased in the E direction to the drum unit  13  by the bias spring  43 , the photoreceptor drum  11  and the developing roller  16  are easily and uniformly contacted and pressed against each other in the shaft directions. 
     When the bottom part of the groove parts  42   a  and  42   b  is defined as the bottom part  42   f , and when the space part between the bottom part  42   f  and the tip of the bias spring  43  is defined as the space part  42   g , the relationship between L 11 , which is the longest length of the projection parts  48   a  and  48   b  in the E direction, and L 12 , which is the longest length of the space parts  42   g  in the E direction, is set as L 11 &gt;L 12 . Because the relationship between L 11  and L 12  is set as discussed above, when the projection parts  48   a  and  48   b  are inserted into the groove parts  42   a  and  42   b , a biasing force F of the bias spring  43  is certainly applied to the plane surface sa. 
     With the engagements between the projection parts  41   a ,  41   b ,  48   a , and  48   b  with the groove parts  49   a ,  49   b ,  42   a , and  42   b , respectively, the developing unit  24  can be stably attached to the drum unit  13  in the E direction, which is perpendicular to the Q direction, such that the drive force P is negated. 
     When the developing unit  24  is attached to the drum unit  13 , a holder  101  is swingably provided to a post  102  to fix the developing unit  24  into the drum unit  13  as shown in  FIGS. 12 and 13 . In this case, the holders  101  are provided at the side plates  19   a  and  19   b . Because the structure of each holder  101  is same, only the holder  101  at the side plate  19   a  is described. 
     A post  104  is fixed to the holder  101 . A lock lever  105 , operating as a locking mechanism, is swingably provided to the holder  101 , with the post  104  serving as a point of support. 
     A depression part  108  is provided at a tip part  101   a  of the holder  101 . The bias spring  43  elastically surrounds the depression part  108 . An engagement part (not shown) is provided at the depression part  108 . The bias spring  43  latches the engagement part so that the bias spring  43  does not come off from the depression part  108 . A compression spring  138 , operating as a lock mechanism bias part, is located between a pressing part  105   a  of the lock lever  105  and the holder  101  so that the lock lever  105  is biased in the lock direction. 
     The post  102  is fixed to a support part  19   c  of the side plate  19   a . The holder  101  is swingably provided to the side plate  19   a  as the post  102  is a point of support. Similarly, the post  104  is fixed to the holder  101 . The lock lever  105  is swingably provided to the holder  101  as the post  104  is a point of support. 
     As shown in  FIG. 12 , in the initial state of the drum unit  13 , the holder  101  and the lock lever  105  are in the release state, and the bias spring  43  and the depression part  108  are in the elongated state. Therefore, the biasing force is not generated. When the depression part  108  is in the elongated state, the lock lever is projected parallel to the depression part  108  and the bias spring  43 . 
     The lock lever  105  has a lever m 1 , an arm m 2 , and a pressing part  105   a . The level m 1 , operating as a handle part, is projected from a hub part hu that surrounds the post  104 ; the arm m 2  is projected in the perpendicular direction to the lever m 1 ; and the pressing part  105   a  is projected in the vicinity of the hub part hu. A hook  105   b , operating as an engaging component, is formed at the tip of the arm m 2 . 
     The side plate  19   a  has a receiving part  19   k  adjacent to the groove part  42   a , a projection part  19   p  that is projected between the groove part  42   a  and the receiving part  19   k  in the upper direction, and a hook  19   q  that is formed at the tip of the projection part  19   p  as a component to be engaged. 
     After the drum unit  13  is attached to the developing unit  24 , when the holder  101  rotates in the direction of arrow A (the A direction), the tip of the bias spring  43  contacts the projection part  48   a . At this point, the projection part  48   a  is biased toward the bottom part  42   f  of the groove  42   a  by a certain biasing force F of the bias spring  43 . The arm m 2  contacts the projection part  19   p.    
     When the holder  101  further rotates in direction A, because the lock lever  105  is swingably provided to the holder  101 , the rotation of the holder  101  is regulated under the situation where the holder contacts the projection part  19   p . As a result, the depression part  108  is compressed. 
     When the holder reaches a certain position, the hook  105   b  goes into the receiving part  19   k , passing the hook  19   q . As a result, the regulation for the rotation of the lock lever  105  is released. The lock lever  105  rotates in the direction of arrow B (the B direction) by the biasing force, and then the hook  105   b  is engaged with the hook  19   q.    
     Finally, the lock lever  105  is locked while the developing unit  24  is attached to the drum unit  13 . 
     In this disclosed embodiment, the angle D is set to 90 degrees. However, when misalignment occurs, for example, at the point of contact gf where the drum gear  44  and the developing roller gear  37  are meshed, at the engagement positions between the projection parts  48   a  and  48   b  and the groove parts  42   a  and  42   b , and/or at the engagement positions between the projection parts  41   a  and  41   b  and the groove parts  49   a  and  49   b , there is a possibility that some variations for the angle D may occur. 
     Experiments in which images were formed (i.e., printed) under conditions that had several different angles D were performed to determine whether the image quality was decreased or not. The determination results are shown in Table 1 below. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Angle D (°) 
                 80 
                 82.5 
                 85 
                 87.5 
                 90 
                 92.5 
                 95 
                 97.5 
                 100 
               
               
                   
               
             
            
               
                 Jitter 
                 x 
                 Δ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 Δ 
                 x 
               
               
                 Spot 
                 x 
                 x 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
               
               
                 Blur 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 x 
                 x 
               
               
                   
               
            
           
         
       
     
     Expected factors for decreasing of the image quality due to the occurrence of the misalignment of the positions are jitter, spot, blur, and so on. Jitter is uneven image quality in the lateral direction (i.e., scan direction) and often occurs in an image with a pitch width that is equal to one tooth of a gear. When contacting and pressing status between the photoreceptor drum  11  and the developing roller  16  are not enough, spots occur because the toner  33  does not adhere on the area in which an electrostatic latent image is formed. In the experiments, there is a possibility that a spot occurs in the ends of the photoreceptor drum  11  and the developing roller  16 . When contacting and pressing status between the photoreceptor drum  11  and the developing roller  16  are excessively strong, a blur may occur in the area in which an electrostatic latent image is not formed through adhering the toner  33  on the white background part. 
     In these experiments, a certain number of sheets was printed with several different angles for D: 80°, 82.5°, 85°, 87.5°, 90°, 92.5°, 95°, 97.5°, and 100°. Whether the decrease of the image quality occurred or not was determined. An A3 size sheet that is the largest sheet applicable for a printer of the experiments was used. 25% duty printing in which some dots are uniformly pulled from the solid printing was performed. 
     If, after the certain number of sheets was printed, jitters, spots, and blurs did not occur on any of the sheets, the mark “∘” was used; if jitters, spots, and blurs occurred on all of the sheets, the mark “x” was used; and if jitters, spots, and blurs occurred on some, but not all, of the sheets, the mark “Δ” was used. 
     When the angle D was larger, a component of force of the drive force P that was based on the meshing of the drum gear  44  and the developing roller gear  37  was applied in the direction in which the pressing force between the photoreceptor drum  11  and the developing roller  16  was increased, so that the jitters and blurs occurred. When the angle D was smaller, the component of force of the drive force P that was based on the meshing of the drum gear  44  and the developing roller gear  37  was applied in the direction in which the pressing force between the photoreceptor drum  11  and the developing roller  16  was decreased, so that the jitters and spots occurred. As a result, in these experiments, it was understood that when the angle D is in the following range, 85°≦D≦95°, the jitters, spots and blurs did not occur, and the image quality was not decreased. 
     In the present disclosed embodiment, as discussed above, when the developing unit  24  is attached to the drum unit  13 , the photoreceptor drum  11  and the developing roller  16  are easily and uniformly contacted and pressed to each other in the shaft directions because of the following features: (1) the projection parts  41   a  and  41   b , and the groove parts  49   a  and  49   b  are located in the vicinity of the point of contact gf in which the drum gear  44  and the developing roller gear  37  are meshed; (2) the grooves  42   a ,  42   b ,  49   a , and  49   b  receive the drive force P that is generated through the meshing of the drum gear  44  and the developing roller gear  37 ; (3) the developing unit  24  is provided to be movable in the E direction; and (4) the developing unit  24  is biased toward the drum unit  13  by the bias spring  43 . 
     Because the position of the developing roller  16  is changed and adjusted while the pressing force between the photoreceptor drum  11  and the developing roller  16  is measured, workability for contacting and pressing between the photoreceptor drum  11  and the developing roller  16  with the uniform pressing force is improved. 
     Next, a second disclosed embodiment is explained. Structures that have the same structures as the first disclosed embodiment are assigned the same reference numerals. The effects of the first disclosed embodiment are incorporated herein for an effect based on the same structures. 
       FIG. 14  is a first schematic view of a printer according to a second disclosed embodiment.  FIG. 15  is a second schematic view of the printer according to the second disclosed embodiment. 
     The reference numeral  10  is a main body. Bk, Y, M, and C are image forming units (ID units). The reference numeral  13  is a drum unit, operating as a first unit. The reference numeral  24  is a developing unit, operating as a second unit. The reference numerals  41   b  and  48   b  are cylindrical (or mostly cylindrical) projection parts, operating as first and fourth engaging components, respectively. The reference numerals  42   b  and  49   b  are groove parts, operating as second and fourth engaging components, respectively. A main engaging part, operating as a first engaging part, is configured with the projection part  41   b  and the groove part  49   b . A sub-engaging part, operating as a second engaging part, is configured with the projection part  48   b  and the groove part  42   b.    
     A bias spring  60 , operating as a biasing part that biases the developing unit  24  toward the drum unit  13  with a certain biasing force F, is provided at an upper cover  39 . When the upper cover is closed, a lower end of the bias spring  60  contacts and presses a certain area, i.e., the vicinity of an upper end of the developing unit  24  in this disclosed embodiment, so that the developing unit  24  is pressed to the drum unit  13 . 
     A biasing direction for the developing unit  24  by the bias spring is the G direction. A direction in which the projection part  41   b  is provided to be movable with respect to the groove part  49   b  is the H direction. A direction in which the projection part  48   b  is provided to be movable with respect to the groove part  42   b  is the I direction. The G direction is parallel to the H and I directions. In the first disclosed embodiment, the G direction is perpendicular to the Q direction in which the drive force P is generated. 
     When the upper cover  39  is open, the bias spring  60  is moved with the upper cover  38  in the opening direction of the upper cover  39 , so that the bias by the bias spring  60  is released. Under the situation discussed above, the developing unit  24  is taken out in the direction opposite to the H and I directions. 
     In this disclosed embodiment, the bias spring  60  is located at the upper cover  39 . When the upper cover  39  is open, the bias by the bias spring  60  is released. Therefore, when the developing unit  24  is replaced, the detachable operation for the developing unit  24  can be simplified. 
     Next, a third disclosed embodiment is explained. Structures that have the same structures of the first and second disclosed embodiments are assigned the same reference numerals. The effects of the first and second disclosed embodiments are incorporated herein for an effect based on the same structures. 
       FIG. 16  is a first exploded perspective view of an image forming unit according to a third disclosed embodiment.  FIG. 17  is a second exploded perspective view of the image forming unit according to the third disclosed embodiment.  FIG. 18  is a schematic view of relationship among a developing roller gear, a driven gear, and a toner supplying roller gear according to the third disclosed embodiment.  FIG. 19  is a schematic view of a rotation transmitting system of the image forming unit according to the third disclosed embodiment.  FIG. 20  is a schematic view of relationship between the developing roller gear and the driven gear according to the third disclosed embodiment. 
     The reference numeral  59  is a developing roller unit, operating as a first unit. The reference numeral  63  is a toner supplying roller unit, operating as a second unit that is provided to be adjacent to the developing roller unit  59 . 
     The developing roller unit  59  has a photoreceptor drum  11 , operating as an image carrier, a developing roller  16 , operating as a first rotating body and a developer carrier, and side plates  19   a  and  19   b  that hold the above mentioned structures. 
     The toner supplying roller unit  63  has a toner supplying roller  18 , operating as a second rotating body and a developer supplying part, and side plates  47   a  and  47   b  that hold the toner supplying roller  18 . 
     The photoreceptor drum  11  is rotatably supported by the side plates  19   a  and  19   b . The photoreceptor drum  11  rotates in the K direction when the rotation of a motor (not shown), operating as a drive part, is transmitted to a drum gear  44  located in one end through a motor gear  50  and a reduction gear  51 . Similarly, the developing roller  16  is rotatably supported by the side plates  19   a  and  19   b . The developing roller  16  rotates in the L direction when the rotation of the photoreceptor drum  11  is transmitted to a developing roller gear  37 , operating as a first gear, that meshes with the drum gear  44  and is located in one end. The developing roller  16  rotates at a certain rotation speed that has a certain speed difference compared to the rotation speed of the photoreceptor drum  11 . The toner supplying roller  18  rotates in the same direction of the developing roller  16  at a certain rotation speed that has a certain speed difference compared to the rotation speed of the developing roller  16 . 
     The toner supplying roller  18  is rotatably supported by the side plates  47   a  and  47   b . The toner supplying roller  18  rotates in the R direction when the rotation of the developing roller gear  37  is transmitted to a driven gear  62 , operating as a second gear, that meshes with a toner supplying roller gear  61  and is located in one end. The driven gear  62  is rotatably supported by the side plates  19   a  and  19   b . When the toner supplying roller unit  63  is attached to the developing roller unit  59 , the driven gear  62  meshes with the toner supplying roller gear  61 . 
     Cylindrical projection parts  64   a ,  64   b ,  65   a , and  65   b , operating as first engaging components, are formed at the side plates  47   a  and  47   b . The groove parts  66   a ,  66   b ,  67   a , and  67   b , operating as second engaging components, are formed at the side plates  19   a  and  19   b . When the toner supplying roller unit  63  is attached to the developing roller unit  59 , the projection parts  64   a ,  64   b ,  65   a , and  65   b  are engaged with the groove parts  66   a ,  66   b ,  67   a , and  67   b , respectively. In this disclosed embodiment, each of the groove parts  66   a  and  67   a  and the groove parts  66   b  and  67   b  is formed as one unit, respectively. However, they can be separately formed after they are independent. 
     When the toner supplying roller unit  63  is attached to the developing roller unit  59 , the developing roller gear  37  meshes with the toner supplying roller gear  61  through the driven gear  62  as shown in  FIG. 18 . The toner supplying roller  18  rotates at a certain rotation speed that has a certain speed difference compared to the rotation speed of the developing roller  16 . 
     When the toner supplying roller unit  63  is attached to the developing roller unit  59 , the engaging positions between the projection parts  64   a  and  64   b  and the groove parts  66   a  and  66   b , respectively, are located in the vicinity of the area where the toner supplying roller gear  61  meshes with the driven gear  62  as shown in  FIGS. 18 and 20 . Namely, the engaging positions are located within the area Nb where the outer circumference circle  61   b  of the toner supplying roller gear  61  and the outer circumference circle  62   b  of the driven gear  62  overlap each other as the point of contact gg between the pitch circle  61   a  of the toner supplying roller gear  61  and the pitch circle  62   a  of the driven gear  62  is the center, i.e., within the area where the toner supplying roller gear  61  meshes with the driven gear  62 . 
     The projection parts  64   a  and  64   b  are in the cylindrical shape. When the direction of the mesh pressure angle at the point of contact gg between the teeth of the toner supplying roller gear  61  and the driven gear  62  is in the direction of arrow E′ (the E′ direction), operating as a bias direction, the groove parts  66   a  and  66   b  are U-shaped along the E′ direction. When the direction of the tangent line of the pitch circles  61   a  and  62   a  at the point of contact gg is the J′ direction, and when the Q′ direction, operating as a driving direction, is perpendicular to the E′ direction, an angle between the J′ and Q′ directions is referred to as the mesh pressure angle α′. Note that the angle D′ between the E′ and Q′ directions is 90 degrees. 
     The toner supplying roller unit  63  is biased in the E′ direction by the bias spring  43 , operating as a biasing part, that is located at the developing roller unit  59 . Therefore, the toner supplying roller  18  uniformly contacts and presses the developing roller  16  in the shaft direction of the roller. 
     The drive force P′ is generated in the Q′ direction, which deviates from the J′ direction by the mesh pressure angle α′ with respect to the rotation of the driven gear  62 . However, when an angle between the direction E of the biasing force and the direction of the drive force P is very different from 90°, the drive force P′ is generated at one end where the developing roller gear  37  and the toner supplying roller gear  61  of the developing roller  16  and the toner supplying roller  18 , respectively, are located and is not generated in another end of the roller. Therefore, the drive force P′ affects the situation in which the toner supplying roller  18  uniformly contacts and presses the developing roller  16 . 
     Because the projection parts  64   a  and  64   b  are of a cylindrical shape and the groove parts  66   a  and  66   b  are U-shaped, when the projection parts  64   a  and  64   b  and the groove parts  66   a  and  66   b  are engaged, respectively, the groove parts  66   a  and  66   b  regulates the movement of the projection parts  64   a  and  64   b  in the Q′ direction. The groove parts  66   a  and  66   b  can receive the drive force P′. Because the projection parts  64   a  and  64   b  can move in the E′ direction along the groove parts  66   a  and  66   b , and the toner supplying roller unit  63  is biased to the developing roller unit  59  in the E′ direction by the bias spring  43 , the developing roller  16  and the toner supplying roller  18  are easily and uniformly contacted and pressed each other in the shaft directions. 
     As discussed above, the engagement position between the projection parts  64   a  and  64   b  and the groove parts  66   a  and  66   b  is located in the vicinity of the area where the toner supplying roller gear  61  meshes with the driven gear  62 . The engagement position between the projection parts  65   a  and  65   b  and the groove parts  67   a  and  67   b  is located on the opposite side of the perpendicular line that passes through the center of gravity of the developing roller unit  59  with respect to the engagement position between the projection parts  64   a  and  64   b  and the groove parts  66   a  and  66   b . A main engaging part, operating as a first engaging part, is configured with the projection parts  64   a  and  64   b  and the groove parts  66   a  and  66   b . A sub-engaging part, operating as a second engaging part, is configured with the projection parts  65   a  and  65   b  and the groove parts  67   a  and  67   b.    
     As discussed above, when the direction of the mesh pressure angle in the point of contact gg between the teeth of the toner supplying roller gear  61  and the driven gear  62  is in the direction of arrow E′ (the E′ direction), the groove parts  66   a  and  66   b  are U-shaped along the E direction. The groove parts  66   a  and  66   b  regulate the movement of the projection parts  64   a  and  64   b  in the Q′ direction. As a result, the drive force P′ is negated by the groove parts  66   a  and  66   b.    
     The groove parts  67   a  and  67   b , located at the developing roller unit  59 , are integrated with the groove parts  66   a  and  66   b  and are elongated in a liner fashion. The projection parts  65   a  and  65   b , located at the toner supplying roller unit  63 , are of a cylindrical shape. Therefore, when the projection parts  65   a  and  65   b  and the groove parts  67   a  and  67   b  are engaged, respectively, the groove parts  67   a  and  67   b  regulate the movement of the projection parts  65   a  and  65   b  in the Q′ direction. The groove parts  66   a  and  66   b  can receive the drive force P′. Because the projection parts  65   a  and  65   b  can move in the E′ direction along the groove parts  66   a  and  66   b , and the toner supplying roller unit  63  is biased in the E′ direction towards the developing roller unit  59  by the bias spring  43 , the developing roller  16  and the toner supplying roller  18  are easily and uniformly contacted and press each other in the shaft directions. 
     In this disclosed embodiment, the angle D′ is set to 90 degrees. However, when misalignment occurs, for example, at the point of contact gg where the toner supplying roller gear  61  and the driven gear  62  are meshed, at the engagement positions between the projection parts  64   a  and  64   b  and the groove parts  66   a  and  66   b , and/or at the engagement positions between the projection parts  65   a  and  65   b  and the groove parts  67   a  and  67   b , there is a possibility that some variations for the angle D′ may occur. 
     Experiments in which images were formed (i.e., printed) using several different angles D′ were performed to determine whether the image quality was decreased or not at these different angles. The determination results are shown in Table 2 below. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Angle D′ (°) 
                 80 
                 82.5 
                 85 
                 87.5 
                 90 
                 92.5 
                 95 
                 97.5 
                 100 
               
               
                   
               
             
            
               
                 Jitter 
                 x 
                 Δ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 Δ 
                 x 
               
               
                 Spot 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 x 
                 x 
               
               
                 Blur 
                 x 
                 x 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
                 ∘ 
               
               
                   
               
            
           
         
       
     
     In these experiments, a certain number of sheets was printed using several different angles D′, 80°, 82.5°, 85°, 87.5°, 90°, 92.5°, 95°, 97.5°, and 100°. Each time it was determined whether the image quality decreased or not. An A3 size sheet, which is the largest sheet applicable for a printer of the experiments was used. 25% duty printing in which some dots are uniformly pulled from the solid printing was performed. 
     If, after the certain number of sheets was printed, jitters, spots, and blurs occurred on none of the sheets, the mark “∘” was used; if jitters, spots, and blurs occurred on all of the sheets, the mark “x” was used; and if jitters, spots, and blurs occurred on some, but not all, of the sheets, the mark “Δ” was used. 
     When the angle D′ was larger, a component of the drive force P′ that was based on the meshing of the toner supplying roller gear  61  and the driven gear  62  was applied in the direction in which the pressing force between the developing roller  16  and the toner supplying roller  18  was increased, so that jitters and spots occurred. When the angle D′ was smaller, the component of the drive force P′ that was based on the meshing of the toner supplying roller gear  61  and the driven gear  62  was applied in the direction in which the pressing force between the developing roller  16  and the toner supplying roller  18  was decreased, so that jitters and blurs occurred. As a result, in these experiments, it was understood that when the angle D′ is in the following range, 85°≦D′≦95°, jitters, spots and blurs did not occur, and the image quality was not decreased. 
     In the present disclosed embodiment, as discussed above, the developing roller  16  and the toner supplying roller  18  are easily and uniformly contacted and pressed to each other in the shaft direction because of the following features: (1) the projection parts  64   a  and  64   b , and the groove parts  66   a  and  66   b  are located in the vicinity of the area in which the toner supplying roller gear  61  and the driven gear  62  are meshed; (2) the grooves  66   a ,  66   b ,  67   a , and  67   b  receive the drive force P′ that is generated through the meshing of the toner supplying roller gear  61  and the driven gear  62 ; (3) the toner supplying roller unit  63  is movable in the E′ direction; and (4) the toner supplying roller unit  63  is biased toward the developing roller unit  59  by the bias spring  43 . 
     Because the position of the toner supplying roller  18  is changed and adjusted while the pressing force between the developing roller  16  and the toner supplying roller  18  is measured, workability for contacting and pressing between the developing roller  16  and the toner supplying roller  18  with the uniform pressing force is improved. 
     Next, a fourth disclosed embodiment is explained. Structures that have the same structures of the first through third disclosed embodiments are assigned the same reference numerals. The effects of the first through third disclosed embodiments are incorporated herein for an effect based on the same structures. 
       FIG. 21  is a first exploded perspective view of an image forming unit according to the fourth disclosed embodiment.  FIG. 22  is a second exploded perspective view of the image forming unit according to the fourth disclosed embodiment.  FIG. 23  is a schematic view of relationship among a developing roller gear, a driven gear, and a toner supplying roller gear according to the fourth disclosed embodiment.  FIG. 24  is a schematic view of relationship between the driven gear and the toner supplying roller gear according to the fourth disclosed embodiment. 
     Cylindrical projection parts  73   a ,  73   b ,  74   a , and  74   b , operating as first engaging components, are formed at side plates  47   a  and  47   b . Groove parts  76   a ,  76   b ,  77   a , and  77   b , operating as second engaging components, are formed at side plates  19   a  and  19   b . When the toner supplying roller unit  63 , operating as a second unit, is attached to the developing roller unit  59 , operating as a first unit, the projection parts  73   a ,  73   b ,  74   a , and  74   b  are engaged with the groove parts  76   a ,  76   b ,  77   a , and  77   b , respectively. The toner supplying roller  18  is biased toward the developing roller  16  by a bias spring  43 , operating as a biasing part. 
     When the toner supplying roller unit  63  is attached to the developing roller unit  59 , the developing roller gear  61  meshes with the developing roller gear  37  through the driven gear  62 , as shown in  FIG. 23 . In this embodiment, the developing roller gear  61  is located at the developing roller unit  59 ; the developing roller gear  37  operates as a first gear and is located at the toner supplying roller unit  63 ; and the driven gear  62  operates as a second gear and is located at the toner supplying roller unit  63 . The toner supplying roller  18 , operating as a second rotating body and as a developer supplying part, rotates at a certain rotation speed that has a certain speed difference compared to the rotation speed of the developing roller  16 , operating as a first rotating body and as a developer carrier. 
     When the toner supplying roller unit  63  is attached to the developing roller unit  59 , the engaging positions between the projection parts  73   a  and  73   b  and the groove parts  76   a  and  76   b , respectively, are located in the vicinity of the area where the driven gear  62  meshes the developing roller gear  37  as shown in  FIGS. 23 and 24 . Namely, the engaging positions are located within the area Nc where the outer circumference circle  62   b  of the driven gear  62  and the outer circumference circle  37   b  of the developing roller gear  37  overlap each other as the point of contact gh between the pitch circle  62   a  of the driven gear  62  and the pitch circle  37   a  of the developing roller gear  37  is the center, i.e., within the area where the driven gear  62  meshes with the developing roller gear  37 . 
     The projection parts  73   a  and  73   b  are in a cylindrical shape. When the direction of the mesh pressure angle in the point of contact gh between the teeth of the driven gear  62  and the developing roller gear  37  is in the direction of arrow E″ (the E″ direction), operating as a biasing direction, the groove parts  76   a  and  76   b  are U-shaped along the E″ direction. When the direction of the line tangent to the pitch circles  62   a  and  37   a  at the point of contact gh is the J″ direction, and when the direction perpendicular to the E″ direction is the Q″ direction, operating as a driving direction, an angle between the J″ and Q″ directions is referred to as the mesh pressure angle α″. Note that the angle D″ between the E″ and Q″ directions is 90 degrees. 
     The toner supplying roller unit  63  is biased in the E″ direction by the bias spring  43  that is located at the developing roller unit  59 . Therefore, the toner supplying roller  18  uniformly contacts and presses the developing roller  16  in the shaft direction of the roller. 
     The drive force P″ is generated in the Q″ direction, which deviates from the J″ direction by the mesh pressure angle α″ with respect to the rotation of the driven gear  62 . However, when an angle between the direction E of the biasing force and the direction of the drive force P is very different from 90°, the drive force P″ is generated in one end where the developing roller gear  37  and the toner supplying roller gear  61  of the developing roller  16  and the toner supplying roller  18 , respectively, are located and is not generated in another end of the roller. Therefore, the drive force P″ affects the situation in which the toner supplying roller  18  uniformly contacts and presses the developing roller  16 . 
     Because the projection parts  73   a  and  73   b  are of a cylindrical shape and the groove parts  76   a  and  76   b  are U-shaped, when the projection parts  73   a  and  73   b  and the groove parts  76   a  and  76   b  are engaged, respectively, the groove parts  76   a  and  76   b  regulate the movement of the projection parts  73   a  and  73   b  in the Q″ direction. The groove parts  76   a  and  76   b  can receive the drive force P″. Because the projection parts  73   a  and  73   b  can move in the E″ direction along the groove parts  76   a  and  76   b , and the toner supplying roller unit  63  is biased to the developing roller unit  59  in the E″ direction by the bias spring  43 , the developing roller  16  and the toner supplying roller  18  are easily and uniformly contacted and pressed against each other in the shaft directions. 
     As discussed in the third disclosed embodiment, the engagement position between the projection parts  74   a  and  74   b  and the groove parts  77   a  and  77   b  is located on an opposite side to the perpendicular line that passes through the center of gravity of the developing roller unit  59  with respect to the engagement position between the projection parts  73   a  and  73   b  and the groove parts  76   a  and  76   b . The groove parts  77   a  and  77   b  regulate the movement of the projection parts  74   a  and  74   b  in the Q″ direction. As a result, the drive force P″ is negated by the groove parts  77   a  and  77   b . A main engaging part, operating as a first engaging part, is configured with the projection parts  73   a  and  73   b  and the groove parts  76   a  and  76   b . A sub-engaging part, operating as a second engaging part, is configured with the projection parts  74   a  and  74   b  and the groove parts  77   a  and  77   b.    
     In this disclosed embodiment, the angle D″ is also set to 90 degrees. However, when misalignment occurs, for example, at the point of contact gh where the driven gear  62  and the developing roller gear  37  are meshed, at the engagement positions between the projection parts  73   a  and  73   b  and the groove parts  76   a  and  76   b , and/or at the engagement positions between the projection parts  74   a  and  74   b  and the groove parts  77   a  and  77   b , there is a possibility that some variations for the angle D″ may occur. 
     In these experiments, it was understood that when the angle D″ is in the following range, 85°≦D″≦95°, jitters, spots and blurs did not occur, and the image quality was not decreased. 
     In the present disclosed embodiment, as discussed above, the developing roller  16  and the toner supplying roller  18  are easily and uniformly contacted and pressed each other in the shaft directions because of the following features: (1) the projection parts  73   a  and  73   b , and the groove parts  76   a  and  76   b  are located in the vicinity of the area in which the driven gear  62  and the developing roller gear  37  are meshed; (2) the grooves  76   a ,  76   b ,  77   a , and  77   b  receive the drive force P″ that is generated through the meshing of the driven gear  62  and the developing roller gear  37 ; (3) the toner supplying roller unit  63  is provided to be movable in the E″ direction; and (4) the toner supplying roller unit  63  is biased toward the developing roller unit  59  by the bias spring  43 . 
     Because the position of the toner supplying roller  18  is changed and adjusted while the pressing force between the developing roller  16  and the toner supplying roller  18  is measured, workability for contacting and pressing between the developing roller  16  and the toner supplying roller  18  with the uniform pressing force is improved. 
     In the embodiments discussed above, the printer as the image forming device is explained. However, the d disclosed system is not limited to the structure discussed above and may be applicable to a copier, a facsimile machine, a multifunction peripheral (MFP), and so on. 
     The instant disclosure is provided to further explain in an enabling fashion the best modes of performing one or more embodiments. The image forming device being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the sprit and scope of the invention, and all such modifications as would be apparent to one of ordinary skill in the art are intended to be included within the scope of the following claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.