Patent Publication Number: US-2023152747-A1

Title: Driving transmission device, driving device and image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application is based on and claims the benefit of priority from Japanese patent application No. 2021-185205 filed on Nov. 12, 2021, which is incorporated by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates to a driving transmission device, a driving device and an image forming apparatus. 
     A driving unit in which a fixing pin is provided in a pair of supporting parts, and an idle gear is rotatably supported by the fixing pin is disclosed. A D-cut portion is formed at one end portion of the fixing pin, and the D-cut portion is fixed to one supporting part in a non-rotatable manner. The other end portion of the fixing pin is fitted in a hole opened in the other supporting part. 
     When the driving unit as described above is assembled, a lubricant such as a grease is often applied to the contact area between the fixing pin and the hole of the supporting part. Depending on a type of the lubricant and a material of the supporting part, the lubricant applied area may be deteriorated. On the other hand, when the driving unit is used, since the fixing pin and the supporting part continue to receive a load such as a vibration caused by the rotation of the idle gear, a phenomenon (a creep deformation) in which the distortion of the fixing pin and the supporting part increases with the lapse of time occurs. When the creep deformation occurs on the area deteriorated by the applying of the lubricant, a crack (a chemical crack) may occur on the area. 
     SUMMARY 
     In accordance with an aspect of the present disclosure, a driving transmission device includes a storage part, a fixing pin and a supporting part. The storage part houses a gear and has a through hole formed corresponding to the gear. The fixing pin rotatably supports the gear. To the supporting part, the fixing pin is fixed in a state where a tip end portion of the fixing pin is inserted into the through hole. A hole side chamfered portion in which a corner is notched is formed at an outside opening edge portion of the through hole. A shaft side chamfered portion in which a corner is notched is formed at the tip end portion of the fixing pin. In a state where the fixing pin is inserted into the through hole, a lubricant is applied to a contact area between the fixing pin and the through hole. A hole side boundary portion which is a boundary between an inner circumferential surface of the through hole and the hole side chamfered portion is in contact with an outer circumferential surface of the fixing pin. A shaft side boundary portion which is a boundary between an outer circumferential surface of the fixing pin and the shaft side chamfered portion faces the hole side chamfered portion with a gap. 
     In accordance with an aspect of the present disclosure, a driving device includes a driving source for driving a driven object; and the driving transmission device which transmits a driving force of the driving source to the driven object. 
     In accordance with an aspect of the present disclosure, an image forming apparatus includes the driving device. 
     The above and other objects, features, and advantages of the present disclosure will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present disclosure is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a front view schematically showing an inner structure of an image forming apparatus according to one embodiment of the present disclosure. 
         FIG.  2    is a perspective view showing a driving device according to the embodiment of the present disclosure. 
         FIG.  3    is a disassembled perspective view showing the driving device according to the embodiment of the present disclosure. 
         FIG.  4    is a perspective view showing a first cover and the others of a driving transmission device according to the embodiment of the present disclosure. 
         FIG.  5    is a perspective view showing a second cover and the others of the driving transmission device according to the embodiment of the present disclosure. 
         FIG.  6    is a perspective view showing the driving device according to the embodiment of the present disclosure. 
         FIG.  7    is a sectional view taken along the line VII-VII of  FIG.  6   . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, with reference to the attached drawings, an embodiment of the present disclosure will be described. The reference numerals Fr, Rr, L, R, U, and D in the drawings indicate the front, rear, left, right, upper and lower. Although the terms used herein refer to the direction and the position, these terms are used for convenience of explanation and do not limit the technical scope of the present disclosure. 
     With reference to  FIG.  1   , an image forming apparatus  1  according to one embodiment will be described.  FIG.  1    is a front view schematically showing the inside of the image forming apparatus  1 . 
     The image forming apparatus  1  is a printer which forms an image by transferring a toner image formed by an electrophotographic method to a sheet (not shown). As shown in  FIG.  1   , the image forming apparatus  1  includes an apparatus main body  2  constituting a substantially rectangular parallelepiped appearance. In the lower portion of the apparatus main body  2 , a sheet feeding cassette  3  in which the sheet is stored is detachably provided, for example. On the upper surface of the apparatus main body  2 , a sheet discharge tray  4  is provided. In the upper portion of the inside of the apparatus main body  2 , a toner container  5  in which a toner (a developer) for replenishment is contained is detachably attached. The sheet as an example of the medium is not limited to a paper sheet, but may be a resin sheet or the like. 
     Inside the apparatus main body  2 , a conveyance path  6  and an inversion conveyance path  7  which serve as a path along which the sheet is conveyed are formed. The conveyance path  6  is formed in a substantially S-shape from the front lower portion to the rear upper portion of the apparatus main body  2 , and is a path along which the sheet is conveyed from the sheet feeding cassette  3  to the sheet discharge tray  4 . The inversion conveyance path  7  branches downward from the downstream side portion of the conveyance path  6 , extends forward, and merges with the upstream side portion of the conveyance path  6 . The inversion conveyance path  7  is a path along which the sheet is turned upside down and conveyed again to an image forming device  11  (to be described later). In this specification, the term “upstream and downstream” refers to “upstream and downstream” in the conveying direction of the sheet (the medium). 
     The image forming apparatus  1  includes a sheet feeding device  10 , the image forming device  11 , a fixing device  12 , and a conveying device  13 . The sheet feeding device  10  is provided at the upstream end of the conveyance path  6 , the image forming device  11  is provided at an intermediate portion of the conveyance path  6 , and the fixing device  12  is provided at a downstream side portion of the conveyance path  6 . The conveying device  13  is provided in suitable positions on the conveyance path  6  and the inversion conveyance path  7 . 
     &lt;Sheet Feeding Device&gt; The sheet feeding device  10  includes a pickup roller  10 A and a sheet feeding rollers pair  10 B. The pickup roller  10 A takes out the uppermost sheet from the sheet bundle stored in the sheet feeding cassette  3 . The sheet feeding rollers pair  10 B separates the sheets taken out by the pickup roller  10 A one by one and conveys it toward the downstream side. 
     &lt;Imaging Forming Device&gt; The image forming device  11  includes a photosensitive drum  14 , a charging device  15 , a developing device  16 , a transferring roller  17  and an optical scanning device  18 . The photosensitive drum  14  is formed into a substantially cylindrical shape long in the left-and-right direction, and is driven by a motor (not shown) to be rotated around an axis. The charging device  15 , the developing device  16 , and the transferring roller  17  are arranged around the photosensitive drum  14  in the order of the image forming process. The transferring roller  17  is brought into contact with the photosensitive drum  14  from below to form a transferring nip. The optical scanning device  18  is provided above the photosensitive drum  14 , and emits scanning light toward the surface of the photosensitive drum  14 . 
     &lt;Fixing Device&gt; The fixing device  12  includes a fixing belt  12 A and a pressuring roller  12 B. The fixing belt  12 A and the pressuring roller  12 B are formed into a substantially cylindrical shape long in the left-and-right direction, and are rotatably supported by a case (not shown). Inside the fixing belt  12 A, a heater (not shown) for heating the fixing belt  12 A is provided. The pressuring roller  12 B is pressed against the fixing belt  12 A from below to form a fixing nip. The pressuring roller  12 B is driven by a motor (not shown) to be rotated around an axis, and the fixing belt  12 A rotates following the pressuring roller  12 B. 
     &lt;Conveying Device&gt; The conveying device  13  includes a feeding roller  20 A, a registration rollers pair  20 B, a conveying rollers pair  20 C, a discharging rollers pair  20 D, two double-sided conveying rollers pairs  20 E, and a driving device  21  (see  FIG.  2   ). The feeding roller  20 A, the registration rollers pair  20 B, the conveying rollers pair  20 C, and the sheet discharging rollers pair  20 D are disposed on the upstream side portion of the conveyance path  6 , and the two double-sided conveying rollers pairs  20 E are disposed on the inversion conveyance path  7 . The driving device  21  drives the feeding roller  20 A and the others described above to be rotated. 
     The feeding roller  20 A is disposed on the downstream side of the sheet feeding rollers pair  10 B, and conveys the sheet passed the sheet feeding rollers pair  10 B. The registration rollers pair  20 B is disposed between the feeding roller  20 A and the transferring roller  17 , and temporality stops the conveyed sheet to correct the inclination (the skew) of the sheet. The conveying rollers pair  20 C is disposed on the downstream side of the fixing device  12 , and conveys the sheet passed the fixing nip. The discharging rollers pair  20 D is disposed on the downstream end of the conveyance path  6 , and discharges the sheet passed the conveying rollers pair  20 C to the discharge tray  4 . The discharging rollers pair  20 D switches back the sheet in which an image is formed on the front face, and then sends it to the inversion conveyance path  7 . The two double-sided conveying rollers pairs  20 E convey the sheet sent by the discharging rollers pair  20 D. The inversion conveyance path  7  is merged with the conveyance path  6  between the feeding roller  20 A and the registration rollers pair  20 B. 
     The driving device  21  is supported by an internal frame (not shown) of the apparatus main body  2 , and drives the feeding roller  20 A and one or both rollers of each rollers pair  20 B to  20 E to rotate them around their axes. Further, the driving device  21  drives the developing roller  20 F stored in the developing device  16  to rotate it around an axis. The feeding roller  20 A, the rollers pairs  20 B to  20 E, and the developing roller  20 F are examples of the driven object, and other members other than those may be driven by the driving device  21 . In the following description, the feeding roller  20 A, the rollers pairs  20 B to  20 E, and the developing roller  20 F are collectively referred to as the “driven roller  20 ” for convenience of explanation. 
     [Image Forming Process] The operation of the image forming apparatus  1  will be described. A controller (not shown) executes image forming processing (control) based on image data inputted from an external terminal as follows. 
     The charging device  15  charges the surface of the photosensitive drum  14 . The optical scanning device  18  exposes the photosensitive drum  14  and forms an electrostatic latent image corresponding to the image data on the surface of the photosensitive drum  14 . The developing device  16  develops the electrostatic latent image on the photosensitive drum  14  to a toner image by using the toner supplied from the toner container  5 . 
     The sheet feeding device  10  separates the sheets in the sheet feeding cassette  3  one by one and feeds it to the conveyance path  6 . The registration rollers pair  20 B sends the skew corrected sheet toward the transferring nip at a predetermined timing. The transferring roller  17  transfers the toner image on the photosensitive drum  14  to the surface of the sheet passing through the transferring nip. The fixing device  12  thermally fixes the toner image on the sheet by passing the sheet between the fixing belt  12 A and the pressuring roller  12 B which are rotated around their axes (the fixing nip). In the case of one-sided printing, the sheet discharging rollers pair  20 D discharges the sheet on which the toner image is fixed to the sheet discharge tray  4 . 
     In the case of double-sided printing, the sheet discharging rollers pair  20 D switches back the sheet, and sends it to the inversion conveyance path  7 . The two double-sided conveying rollers pairs  20 E convey the sheet along the inversion conveyance path  7 , and the sheet enters the conveyance path  6  again from the inversion conveyance path  7 . Then, an image is also formed on the back surface of the sheet by the same procedure as in the above-described single-sided printing, and the double-sided printed sheet is discharged to the sheet discharge tray  4 . 
     [Driving Device] Next, with reference to  FIG.  2    to  FIG.  6   , the driving device  21  will be described in detail.  FIG.  2    is a perspective view showing the driving device  21 .  FIG.  3    is a disassembled perspective view showing the driving device  21 .  FIG.  4    is a perspective view showing a first cover member  30  and the others of the driving transmission device  23 .  FIG.  5    is a perspective view showing a second cover member  40  and the others of the driving transmission device  23 .  FIG.  6    is a perspective view showing the driving device  21  (its left side portion). 
     As shown in  FIG.  2    and  FIG.  3   , the driving device  21  includes a driving motor  22  and a driving transmission device  23 . 
     &lt;Driving Motor&gt; The driving motor  22  as an example of the driving source is a stepping motor capable of positioning control, for example. The driving motor  22  generates a driving force for driving the driven roller  20 . 
     &lt;Driving Transmission Device&gt;The driving transmission device  23  has a function of transmitting the driving force of the driving motor  22  to the driven roller  20 . The driving transmission device  23  includes a storage part  24  and a supporting part  25 . 
     (Storage Part) The storage part  24  is a case in which a plurality of gears  27  and a plurality of clutches  28  are stored. As shown in  FIG.  3   , the adjacently disposed gears  27  are meshed with each other to form a gear train. One gear  27  is meshed with a driving gear (not shown) fixed the driving shaft  26  of the driving motor  22 , and transmits the rotating force to other gears  27 . Each clutch  28  has a gear portion (not shown) meshed with one of the plurality of gears  27  and a clutch shaft (not shown) which transmits the driving force to one of the driven rollers  20 . Each clutch  28  is controlled by the controller and has a function of being switched into an ON state where the rotating driving force applied from the gear  27  is transmitted to the clutch shaft and into an OFF state where the transmission of the rotating driving force to the clutch shaft is blocked. The detailed description of the meshing relation of the respective gears  27  and the detailed description of the connection relation between the respective clutches  28  and the respective driven rollers  20  will be omitted. 
     The storage part  24  is made of synthetic resin (polycarbonate resin, acrylonitrile-butadiene-styrene synthetic resin, or the like), for example, and is formed into a substantially rectangular parallelepiped shape having a thin thickness in the left-and-right direction (see  FIG.  2   ). The storage part  24  has a first cover member  30  constituting the right side portion of the storage part  24  and a second cover member  40  constituting the left side portion of the storage part  24 . The first cover member  30  and the second cover member  40  face each other across a space in which the gear train is stored. 
     (First Cover Member) As shown in  FIG.  3    and  FIG.  4   , the first cover member  30  is formed into a tray shape with almost the left side thereof opened. A plurality of engagement holes  34  are opened in the outer peripheral portion of the first cover member  30  (see  FIG.  4   ).  FIG.  4    shows only a part of the plurality of engagement holes  34 . 
     The first cover member  30  has a first opening part  31 , a plurality of first through holes  32 , and a plurality of clutch storage portions  33 . The first opening part  31  is a hole into which the driving shaft  26  of the driving motor  22  is inserted. The plurality of first through holes  32  are circular holes formed corresponding to the plurality of gears  27 . A fixing pin  53  (described later) which supports the gear  27  rotatably is inserted into each of the first through holes  32 . The diameter (the inner diameter) of the first through hole  32  is set larger than the outer diameter of the fixing pin  53 , and the fixing pin  53  penetrates the first through hole  32  with play. Each of the clutch storage portions  33  is a recess in which the clutch  28  is fitted. 
     (Second Cover Member) As shown in  FIG.  3   ,  FIG.  5   , and  FIG.  6   , the second cover member  40  is formed into a tray shape with almost the right side opened. A plurality of engagement portions  44  protruding rightward are formed on the outer peripheral portion of the second cover member  40  (see  FIG.  5   ). Each engagement portion  44  is engaged with the engagement hole  34  of the first cover member  30 , so that the first cover member  30  and the second cover member  40  are coupled to each other to form the space in which the gear train is stored. 
     As shown in  FIG.  5    and  FIG.  6   , the second cover member  40  has a second opening part  41 , a plurality of second through holes  42 , and a plurality of gear storage portions  43 . The second opening part  41  is a bearing in which the driving shaft  26  of the driving motor  22  is rotatably supported. The plurality of second through holes  42  are holes formed corresponding to the plurality of gears  27 . The tip end portion of the fixing pin  53  penetrating through the first through hole  32  is inserted into each second through hole  42 . The diameter (the inner diameter) of the second through hole  42  is set slightly larger than the outer diameter of the fixing pin  53 , and the tip end portion of the fixing pin  53  is fitted into the first through hole  32  with almost no play. Each gear storage portion  43  is a recess in which the clutch shaft of the clutch  28  is rotatably supported and the gear portion of the clutch  28  is stored. In  FIG.  6   , a part of the plurality of second through holes  42  is hidden by an external gear. 
     (Supporting Part) As shown in  FIG.  3   , the supporting part  25  is made of metal (iron, stainless steel, aluminum alloy, or the like), for example, and formed into a flat plate shape. A supporting opening  51  into which the driving shaft  26  of the driving motor  22  is penetrated is opened in the supporting part  25 . The driving shaft  26  is inserted into the supporting opening  51  from the right to the left, and the driving motor  22  is screwed and fixed to the right surface of the supporting part  25 . A plurality of free insertion holes  52  through which screws (not shown) are passed are opened in the supporting part  25 , and a plurality of screw holes  35  are formed in the first cover member  30  at positions corresponding to the plurality of free insertion holes  52  (see  FIG.  4   ). 
     (Fixing Pin) As shown in  FIG.  3   , a plurality of fixing pins  53  are fixed to the supporting part  25  at positions corresponding to the plurality of gears  27  (the first and second through holes  32 ,  42 ). Each of the fixing pins  53  is made of metal (iron, stainless steel, aluminum alloy, or the like), for example, and formed into a substantially cylindrical shape, and is fixed to the left surface of the supporting part  25  by caulking. Each of the fixing pins  53  extends rightward from the left surface of the supporting part  25 . Each of the fixing pins  53  rotatably supports the gear  27  in a state where it penetrates the storage part  24  and its tip end portion is inserted into each of the second through holes  42 . The fixing method of the fixing pin  53  to the supporting part  25  may be screw fastening or welding. 
     Here, a case where the driving device  21  is assembled will be briefly described. The supporting part  25  to which the driving motor  22  is fixed is disposed on the right side of the storage part  24 , and the driving shaft  26  passes through the first opening part  31  of the first cover member  30  from the right to the left (see  FIG.  4   ), and is inserted into the second opening part  41  of the second cover member  40  (see  FIG.  6   ). Each of the fixing pins  53  is inserted into the first through hole  32  of the first cover member  30  from the right side to the left side (see  FIG.  4   ), penetrates the axial center portion of the gear  27 , and is inserted into the second through hole  42  of the second cover member  40  (see  FIG.  6   ). In this state, the driving gear of the driving motor  22  is meshed with one gear  27 , and each gear  27  is rotatably supported on the circumferential surface of the fixing pin  53 . The screw penetrating each free insertion hole  52  of the supporting part  25  is screwed into the screw hole  35  of the first cover member  30 , so that the supporting part  25  is fixed to the first cover member  30 . The supporting part  25  may be fixed to the apparatus main body  2  in place of the storage part  24  (not shown). 
     Next, the operation of the driving device  21  will be briefly described. The driving motor  22  is driven under the control of the controller. The rotating driving force of the driving motor  22  is transmitted to the driven roller  20  through the plurality of gears  27  (gear train). When the respective clutches  28  are controlled by the controller to be switched to the ON state or the OFF state, only the selected driven roller  20  can be rotated (or stopped). 
     When the driving device  21  (or the driving transmission device  23 ) is assembled, a lubricant (for example, a lubricating oil containing polyα-olefin as a main component) is applied to the tip end portion of each of the fixing pins  53  in order to smoothly fit the plurality of fixing pins  53  into the plurality of second through holes  42 . Therefore, in a state where the fixing pin  53  is inserted into the second through hole  42 , the lubricant is provided in the contact area P between the fixing pin  53  and the second through hole  42  (the inner circumferential surface  47  of the second through hole  42 ). In general, since the synthetic resin is more likely to be deteriorated due to the adhesion of the lubricant than the metal, in the second cover member  40  made of the synthetic resin, the inner circumferential surface  47  of the second through hole  42 , which is applied with the lubricant, may be deteriorated. 
     On the other hand, when the driving device  21  is operated (used), each of the fixing pins  53  and the storage part  24  continues to receive a load such as vibration caused by the rotation of the driving motor  22  and each of the gears  27 , and then a phenomenon (a creep deformation) in which the distortion of the fixing pins  53  and the storage part  24  increases with the lapse of time. If the creep deformation occurs in the area deteriorated by the applying of the lubricant (the inner circumferential surface  47  of the second through hole  42 ), there is a concern that a crack (a chemical crack) may occur in the area. Therefore, in the driving device  21  (the driving transmission device  23 ) according to the present embodiment, each of the second through holes  42  and each of the fixing pins  53  is provided with a configuration for suppressing the occurrence of chemical cracks. The following description focuses one fixing pin  53  and one second through hole  42  for convenience of explanation. 
     With reference to  FIG.  7   , the configuration for suppressing the occurrence of chemical crack will be described.  FIG.  7    is a sectional view (and partially enlarged view) taken along the VII-VII line in  FIG.  6   . 
     &lt;Opening Edge of Second Through Hole&gt; The opening edge of the second through hole  42  is formed in a tapered shape so as to widen toward both sides in the left-and-right direction. More specifically, a guide chamfered portion  45  in which a corner is linearly notched is formed at the opening edge of the second through hole  42 , on an inner side of the second cover member  40  (on a side of the space in which the gear train is stored). That is, the guide chamfered portion  45  is a so-called C-chamfering. A hole side chamfered portion  46  in which a corner is notched in an arc shape is formed at the opening edge of the second through hole  42 , on an outer side of the second cover member  40 . That is, the hole side chamfered portion  46  is a so-called R-chamfering. Between the guide chamfered portion  45  and the hole side chamfered portion  46 , an inner circumferential surface  47  having substantially the same inner diameter is formed in the left-and-right direction. 
     &lt;Tip End Portion of Fixing Pin &gt; The tip end portion of the fixing pin  53  is formed in a tapered shape so as to narrow toward the tip end (the left side). Specifically, a shaft side chamfered portion  56  in which a corner is linearly notched is formed at the tip end potion of the fixing pin  53 . That is, the shaft side chamfered portion  56  is a so-called C-chamfering. The outer circumferential surface  57  of the fixing pin  53 , excluding the shaft side chamfered portion  56 , has substantially the same outer diameter in the left-and-right direction. 
     When the tip end portion of the fixing pin  53  is inserted into the second through hole  42 , if the axial center of the fixing pin  53  is slightly shifted from the axial center of the second through hole  42 , a part of the shaft side chamfered portion  56  of the fixing pin  53  comes into contact with a part of the guide chamfered portion  45  of the second through hole  42 . The tip end portion of the fixing pin  53  (the shaft side chamfered portion  56 ) smoothly slides on the guide chamfered portion  45  toward the axis of the second through hole  42  due to the effect of the applied lubricant. As a result, the axial centers of the fixing pin  53  and the second through hole  42  substantially coincide with each other, so that the tip end portion of the fixing pin  53  is inserted into (fitted into) the second through hole  42 . 
     In the state where the tip end portion of the fixing pin  53  is inserted (fitted) into the second through hole  42 , the lubricant is provided between the outer circumferential surface  57  of the fixing pin  53  and the inner circumferential surface  47  of the second through hole  42  (the contact area P). The tip end surface of the fixing pin  53  penetrate the second through hole  42 , and protrudes slightly outward from the outer surface of the second cover member  40 . 
     A hole side boundary portion  48 , which is a boundary between the inner circumferential surface  47  of the second through hole  42  and the hole side chamfered portion  46 , is in contact with the outer circumferential surface  57  of the fixing pin  53 . That is, in  FIG.  7   , the inner circumferential surface  47  of the second through hole  42  and the hole side boundary portion  48  are in contact with the straight portion of the fixing pin  53 . The term “contact” herein means not only direct contact but also contact via the lubricant. 
     A shaft side boundary portion  58 , which is a boundary between the outer circumferential surface  57  of the fixing pin  53  and the shaft side chamfered portion  56 , faces the hole side chamfered portion  46  with a gap M 1 . That is, the shaft side boundary portion  58  does not come into contact with the inner circumferential surface  47  of the second through hole  42  or the hole side chamfered portion  46 . 
     A distance M 2  between the hole side boundary portion  48  and the shaft side boundary portion  58  is set in a range of not less than a half the radius (the radius of R-chamfering) of the hole side chamfered portion  46  and not more than the radius. In the present embodiment, as an example, the radius of the hole side chamfered portion  46  is 0.5 mm, and the distance M 2  between the hole side boundary portion  48  and the shaft side boundary portion  58  is set to 0.3 mm. The upper limit of the radius of the hole side chamfered portion  46  may be less than the wall thickness of the second cover member  40  excluding the guide chamfered portion  45 . 
     The driving device  21  (the driving transmission device  23 ) according to the embodiment described above is configured such that the hole side boundary portion  48  is in contact with the outer circumferential surface  57  of the fixing pin  53 , and the shaft side boundary portion  58  is not in contact with the hole side chamfered portion  46 . According to this configuration, only the outer circumferential surface  57  of the fixing pin  53  comes into surface contact with the inner circumferential surface  47  of the second through hole  42 , so that the fixing pin  53  can be securely held by the inner circumferential surface  47  of the second through hole  42 . Further, even if the fixing pin  53  and the storage part  24  (the second cover member  40 ) are creep-deformed, the shaft side boundary portion  58  of the fixing pin  53  does not interfere with the inner circumferential surface  47  of the second through hole  42  and the hole side chamfered portion  46 . As a result, a local stress concentration is prevented at the contact area P between the tip end portion of the fixing pin  53  and the inner circumferential surface  47  of the second through hole  42  where the lubricant is applied, so that a chemical crack in the contact area P can be suppressed. 
     In the driving device  21  (the driving transmission device  23 ) according to the present embodiment, in a state where the fixing pin  53  is inserted into the second through hole  42 , the hole side boundary portion  48  is provided at a position recessed by the predetermined distance M 2  from the shaft side boundary portion  58 . Thus, the interference between the shaft side boundary portion  58  and the hole side chamfered portion  46  is appropriately prevented, so that the chemical crack at the contact area P between the fixing pin  53  and the second through hole  42  can be effectively prevented. 
     In the driving device  21  (the driving transmission device  23 ) according to the present embodiment, the hole side chamfered portion  46  is an R-chamfering and the shaft side chamfered portion  56  is a C-chamfering, but the present disclosure is not limited thereto. At least one of the hole side chamfered portion  46  and the shaft side chamfered portion  56  may be cut out in an arc shape, and for example, both the hole side chamfered portion  46  and the shaft side chamfered portion  56  may be C-chamfered or R-chamfered (not shown). For example, in the case where the hole side boundary portion  48  is C-chamfered, the distance M 2  between the hole side boundary portion  48  and the shaft side boundary portion  58  may be set to in a range equal to or greater than the half the distance from the outer surface of the second cover member  40  to the hole side boundary portion  48  and less than the distance (not shown). Further, for example, by making the shaft side chamfered portion  56  R-chamfered, even if the tip end portion of the fixing pin  53  interferes with the edges of the first and second through holes  32 ,  42  when the fixing pin  53  is inserted into the first and second through holes  32 ,  42 , the tip end portion of the fixing pin  53  can be suppressed from being crushed. Further, although the guide chamfered portion  45  is C-chamfered, it may be R-chamfered or chamfering may be omitted (not shown). The angle of the C-chamfering can be set to any angle. 
     The driving device  21  (the driving transmission device  23 ) according to the present embodiment is provided with the plurality of gears  27 , the plurality of clutches  28 , the plurality of fixing pins  53 , and the like, but it is not limited thereto, and at least one gear  27  or the like may be provided. The clutch  28  may be omitted if it is not necessary (not shown). 
     Further, in the driving device  21  (the driving transmission device  23 ) according to the present embodiment, the storage part  24  includes the first cover member  30  and the second cover member  40  which can be divided in the left-and-right direction, but the present disclosure is not limited thereto. For example, the storage part  24  may be configured to be divisible in the upper-and-lower direction or may be integrally molded (not shown). For example, the storage part  24  may be divided into three or more parts (not shown). 
     Although the image forming apparatus  1  according to the present embodiment is a monochrome printer, the present disclosure may be applied to a color printer, a copying machine, a facsimile machine or a multifunction machine, for example. 
     It should be noted that the description of the above-described embodiment shows one aspect of the driving transmission device, the driving device and the image forming apparatus according to the present disclosure, and the technical scope of the present disclosure is not limited to the above-described embodiment. The present disclosure may be varied, substituted, or modified to the extent that it does not depart from the spirit of the technical idea, and the claims include all embodiments that may be included within the scope of the technical idea.