Patent Publication Number: US-6714751-B2

Title: Connecting pin for process cartridge, and process cartridge

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a process cartridge detachably mountable to an electrophotographic image forming apparatus. This invention further relates to a connecting pin for pivotally connecting two frames in the construction of the process cartridge. 
     The electrophotographic image forming apparatus forms an image on a recording medium by the use of the electrophotographic image forming process. Examples of the image forming apparatus include electrophotographic copiers, electrophotographic printers (such as laser beam printers and LED printers), facsimile apparatuses and word processors. 
     Also, the process cartridge may refer to charging means, developing means or cleaning means and an electrophotographic photosensitive drum integrally made into a cartridge which is made detachably mountable to the main body of the image forming apparatus. Alternatively, the process cartridge may refer to at least one of charging means, developing means and cleaning means and an electrophotographic photosensitive drum integrally made into a cartridge which is made detachably mountable to the main body of the image forming apparatus. Further alternatively, the process cartridge may refer to at least developing means and an electrophotographic photosensitive drum integrally made into a cartridge which is made detachably mountable to the main body of the image forming apparatus. 
     2. Description of the Related Art 
     In an image forming apparatus using the electrophotographic image forming process, there has heretofore been adopted a process cartridge into which an electrophotographic photosensitive member and process means for acting the electrophotographic photosensitive member are integrally made and which is made detachably mountable to the main body of the image forming apparatus. According to the process cartridge system, the maintenance of the apparatus can be done by a user himself without resort to a serviceman and therefore, the usability of the apparatus is markedly improved. 
     As a typical construction of such a process cartridge, there is one in which two frames are connected together. For example, a cleaning frame supporting a photosensitive drum, a charger and a cleaning device, and a frame comprising a developing frame supporting developing means and a toner frame having a toner chamber, the developing frame and the toner frame being joined together, are connected together for rotation about a fulcrum. The two frames are biased about the fulcrum by a resilient member such as a spring to thereby determine the relative position of the photosensitive drum and the developing means. The functional merits of adopting the above-described construction include many merits such as the optimization of the pressure force of a developing roller against the photosensitive drum, and the maintenance of the interval between the surface of the photosensitive drum and the surface of the developing roller, as well as the ease of the molding of the frames by the division into two, and the ease of assembly. 
     The present invention is a further development of the aforedescribed conventional art. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a connecting pin improved in connecting strength, and a process cartridge using the connecting pin. 
     It is another object of the present invention to provide a connecting pin difficult to pull out, and a process cartridge using the connecting pin. 
     It is another object of the present invention to provide a connecting pin improved in the reliability of connection, and a process cartridge using the connecting pin. 
     It is another object of the present invention to provide a connecting pin and a process cartridge practically using an improvement in pull-out strength, and particularly providing an improvement in strength to endure (i.e., not slipping out) vibration or shock applied thereto in the physical distribution process. 
     It is another object of the present invention to provide the connecting pin for a process cartridge and a process cartridge which enable stringent quality control such as periodical sampling inspection of the surface roughness and force-fit strength of the connecting pin so that a predetermined force-fit strength may be secured to be saved. 
     It is another object of the present invention to provide the connecting pin for a process cartridge which is formed of a metallic hollow material and a portion of which is formed with such a restraining portion that the trailing end thereof juts outwardly with the leading end thereof with respect to the direction of insertion as a bending proximal base by bending, and a process cartridge. 
     It is another object of the present invention to provide a process cartridge having a first frame supporting an electrophotographic photosensitive drum, a second frame supporting developing means, and a connecting pin which is formed of a metallic hollow material and a portion of which is formed with such a restraining portion that the trailing end thereof juts outwardly with the leading end thereof with respect to the direction of insertion as a bending proximal base by bending, and which pivotally fits the first frame and the second frame to each other. 
     These and other objects, features and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-sectional view of the main body of an image forming apparatus according to an embodiment of the present invention. 
     FIG. 2 is a pictorial perspective view of the main body of the image forming apparatus according to the embodiment of the present invention. 
     FIG. 3 is a longitudinal cross-sectional view of a process cartridge according to an embodiment of the present invention. 
     FIG. 4 is a perspective view showing a cleaning unit according to an embodiment of the present invention. 
     FIG. 5 is a perspective view showing a developing unit according to an embodiment of the present invention. 
     FIG. 6 is a longitudinal cross-sectional view showing the construction of the connecting portion of the frames of the process cartridge. 
     FIG. 7 is a horizontal cross-sectional view showing a frame connecting portion according to the conventional art. 
     FIG. 8 is a perspective view showing a connecting pin according to Embodiment 1 of the present invention. 
     FIG. 9 is a horizontal cross-sectional view showing a frame connecting portion according to Embodiment 1 of the present invention. 
     FIG. 10 is a perspective view showing the process of manufacturing the connecting pin according to Embodiment 1 of the present invention. 
     FIG. 11 is a side view showing the detailed shape of the connecting pin according to Embodiment 1 of the present invention. 
     FIG. 12 is a side view showing the detailed shape of the connecting pin according to Embodiment 1 of the present invention. 
     FIG. 13 is a perspective view showing another aspect of the connecting pin according to Embodiment 1 of the present invention. 
     FIG. 14 is a perspective view showing another aspect of the connecting pin according to Embodiment 1 of the present invention. 
     FIG. 15 is a horizontal cross-sectional view showing a frame connecting portion according to Embodiment 2 of the present invention. 
     FIG. 16 is a horizontal cross-sectional view showing another aspect of the frame connecting portion according to Embodiment 2 of the present invention. 
     FIG. 17 is a perspective view showing a connecting pin according to Embodiment 3 of the present invention. 
     FIG. 18 is a horizontal cross-sectional view showing a frame connecting portion according to Embodiment 3 of the present invention. 
     FIG. 19 is a perspective view showing another aspect of the connecting pin according to Embodiment 3 of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Some preferred embodiments of the present invention will hereinafter be described in detail with reference to the accompanying drawings. In the following description, the widthwise direction of a process cartridge B is a direction in which the process cartridge B is mounted to and dismounted from a main body  14  of an apparatus, and aligned with a transporting direction of a recording medium. Also, the lengthwise direction of the process cartridge B is a direction intersecting with (substantially orthogonal to) the direction in which the process cartridge B is mounted to and dismounted from the main body  14  of the apparatus, and is parallel to the surface of the recording medium and is a direction intersecting with (substantially orthogonal to) the transporting direction of the recording medium. Also, the right or left with respect to the process cartridge is the right or left as viewed from above the recording medium with respect to the transporting direction of the recording medium. 
     FIG. 1 is an illustration of the construction of an electrophotographic image forming apparatus (laser beam printer) to which an embodiment of the present invention is applied, and FIG. 2 is a pictorial perspective view thereof. FIGS. 3 to  6  are drawings regarding a process cartridge to which the embodiment of the present invention is applied. Also, in the following description, the upper surface of the process cartridge B is a top surface thereof in a state in which the process cartridge B is mounted to the main body  14  of the apparatus, and the lower surface thereof is a bottom surface thereof in the above-described state. 
     Electrophotographic Image Forming Apparatus A and Process Cartridge B 
     The laser beam printer A as the electrophotographic image forming apparatus to which the embodiment of the present invention is applied will first be described with reference to FIGS. 1 and 2. FIG. 3 shows a side cross-sectional view of the process cartridge B. 
     The laser beam printer A, as shown in FIG. 1, forms an image on a recording medium (such as recording paper, OHP sheet or cloth) by the electrophotographic image forming process. It forms a toner image on a drum-shaped electrophotographic photosensitive member (hereinafter referred to as the photosensitive drum). More particularly, charging is effected on the photosensitive drum  7  by charging means  8 , and then a laser beam modulated in accordance with image information is applied from optical means  1  to the photosensitive drum  7  to thereby form a latent image conforming to the image information on the photosensitive drum  7 . The latent image is then developed by developing means  9  to thereby form a toner image. In synchronism with the formation of the toner image, a recording medium  2  set in a feed cassette  3   a  is reversed and transported by a pickup roller  3   b , pairs of transporting rollers  3   c  and  3   d  and a pair of registration rollers  3   e . Then, the toner image formed on the photosensitive drum  7  of the process cartridge B is transferred to the recording medium  2  by a voltage being applied to a transferring roller  4  as transferring means. Thereafter, the recording medium  2  to which the toner image has been transferred is transported to fixing means  5  by a transportation guide  3   f . The fixing means  5  has a driving roller  5   c  and a fixing roller  5   b  containing a heater  5   a  therein. The fixing means applies heat and pressure to the passing recording medium  2  to thereby fix the transferred toner image. The recording medium  2  is then transported by pairs of delivery rollers  3   g ,  3   h  and  3   i , and is delivered onto a delivery tray  6  through a surface reverse path  3   j . The delivery tray  6  is provided on the upper surface of the main body  14  of the image forming apparatus A. A swingable flapper  3   k  can be operated to deliver the recording medium  2  by a pair of delivery rollers  3   m  without the intermediation of the surface reverse path  3   j . In the present embodiment, the pickup roller  3   b , the pairs of transporting rollers  3   c  and  3   d , the pair of registration rollers  3   e , the transportation guide  3   f , the pairs of delivery rollers  3   g ,  3   h  and  3   i  and the pair of delivery rollers  3   m  together constitute transporting means  3 . 
     On the other hand, in the process cartridge B, as shown in FIGS. 1 and 3, the photosensitive drum  7  is rotated and the surface thereof is uniformly charged by the application of a voltage to the charging roller  8  which is charging means. Then, the laser beam from the optical system  1  modulated in accordance with the image information is applied to the photosensitive drum  7  through an exposure opening portion  1   e  to thereby form a latent image. The latent image is developed by the developing means  9  by the use of a toner. That is, the charging roller  8  is provided in contact with the photosensitive drum  7 , and effects charging on the photosensitive drum  7 . The charging roller  8  is driven to rotate by the photosensitive drum  7 . Also, the developing means  9  supplies the toner to the developing area of the photosensitive drum  7  to thereby develop the latent image formed on the photosensitive drum  7 . The optical system  1  has a laser diode  1   a , a polygon mirror  1   b , a lens  1   c  and a reflecting mirror  1   d.    
     The developing means  9  feeds the toner in a toner container  11 A to a developing roller  9   c  by the rotation of a toner feeding member  9   b . The developing roller  9   c  containing a stationary magnet therein is rotated and also a toner layer in which triboelectrification charges have been induced by a developing blade  9   d  is formed on the surface of the developing roller  9   c , and the toner is supplied to the developing area of the photosensitive drum  7 . The toner is then shifted to the photosensitive drum  7  in conformity with the latent image to thereby form a toner image and visualize the image. The developing blade  9   d  regulates the amount of toner on the peripheral surface of the developing roller  9   c  and also induces triboelectrification charges in the toner. Also, a toner agitating member  9   e  for circulating the toner in a developing chamber is rotatably mounted in the vicinity of the developing roller  9   c.    
     A voltage opposite in polarity to the toner image is applied to the transferring roller  4  to thereby transfer the toner image formed on the photosensitive drum  7  to the recording medium  2 , whereafter any residual toner on the photosensitive drum  7  is removed by cleaning means  10 . The cleaning means  10  scrapes off the residual toner on the photosensitive drum  7  by a cleaning blade  10   a  provided in abutting relationship with the photosensitive drum  7  and collects the removed toner into a removed toner reservoir  10   b.    
     When an opening-closing member  35  provided on a right and upper portion of the main body  14  of the apparatus shown in FIG. 1 is opened around the hinge  35   a  thereof as a fulcrum, it is seen that guide rails (not shown) are provided obliquely from right and upper positions to left and lower positions on the right and left sides of the right and upper portion of the main body  14  of the apparatus. On the other hand, as shown in FIG. 4, round guides  13   m  to be fitted into positioning grooves formed at the terminal ends of the guide rails and long ridge-shaped posture-determining guides  13   n  integral with or separate from the round guides  13   m  and to be fitted into the guide rails are provided at the right and left ends on the axis of the photosensitive drum  7  of the process cartridge B, and the round guides  13   m  and the posture-determining guides  13   n  are inserted into the aforementioned guide rails to thereby mount the process cartridge B to the main body  14  of the apparatus. To detach the process cartridge B from the main body  14  of the apparatus, the process cartridge can be detached out of the main body  14  of the apparatus by pulling the process cartridge up from left direction below toward the right up direction, conversely what has been described above. 
     The mounting or dismounting of the process cartridge B is effected by putting a hand on the protruding threads  11   c  of the recess  17  of an upper frame  11   a  and the protruding threads  11   c  of a lower frame  11   b . A toner frame  11  comprises the upper frame  11   a  and the lower frame  11   b  made integral with each other by being welded together on a joint surface U. 
     Frame Construction of the Process Cartridge 
     The process cartridge B according to the present embodiment is such that a developing unit D comprising the toner frame  11  having the toner container (toner containing portion)  11 A containing the toner therein and a developing frame  12  holding the developing means  9  such as the developing roller  9   c , the toner frame  11  and the developing frame  12  being joined together by welding at locations  701   a  and  701   b , and a cleaning unit C comprising the cleaning means  10  such as the cleaning blade  10   a  and the charging roller  8  attached to a cleaning frame  13  are rotatably connected together with connecting pins  22  as a fulcrum. As shown in FIG. 6, a compression coil spring  23  is compressedly provided with its opposite end portions inserted in a spring receiving portion  13   b  of the cleaning frame  13  and a bar-shaped spring-retainer  12   a  of the developing frame  12 , whereby the cleaning frame  13  and the developing frame  12  are biased counter-clockwisely and clockwisely, respectively, about a hole  20  to thereby bring the photosensitive drum  7  and spacer rollers  9   i  on the opposite ends of the developing roller  9   c  into pressure contact with one another. 
     Method of Connecting the Cleaning Frame and the Developing Frame Together 
     FIGS. 4,  5 ,  6  and  7  show a method of connecting the cleaning unit C and the developing unit D together. FIG. 4 shows the cleaning frame  13  which is a first frame and the connecting pins  22 . As shown in FIGS. 5 and 6, arm portions  19  protrude toward the cleaning frame  13  at the lengthwise opposite ends of the developing frame  12 , which is a second frame. Hanging holes  20  are formed coaxially with each other at the distal ends of the two arm portions  19  of the developing frame  12 . A hole  13   eo  is formed in the lengthwise outer plate  13   a  of the cleaning frame  13 , and a hole  13   ei  is formed in an inner plate  13   f  spaced apart from the outer plate  13   a  by a little greater distance than a size of the width of the arm portions  19  on the inner side of the outer plate  13   a . The holes  13   eo  and  13   ei  are on a lengthwise straight line and are parallel to the photosensitive drum  7 . The diameter of the hole  13   eo  is slightly larger than or substantially equal to the diameter of the hole  13   ei.    
     To connect the cleaning frame  13  and the developing frame  12  together, the arm portions  19  of the developing frame  12  are inserted between the outer plates  13   a  and the inner plates  13   f  of the cleaning frame  13  and positioning is effected so that the supporting hole portions  13   e  ( 13   ei ,  13   eo ) and the hanging holes  20  of the developing frame  12  may be disposed substantially coaxially with each other, thereafter the connecting pins  22  are force-fitted from the opposite outer sides of the cleaning frame  13 . The outer diameter portion of the connecting pin  22  and the inner diameter of the supporting hole  13   ei  of the cleaning frame  13  are in tight fit relationship, and the outer diameter portion of the connecting pin  22  and the inner diameter of the supporting hole  13   eo , and the outer diameter portion of the connecting pin  22  and the hanging holes  20  of the developing frame  12  are in running fit relationship and therefore, after the connecting pins  22  are force-fitted into the supporting holes  13   ei  to thereby complete the assembly, the cleaning frame  13  is supported for rotation about the connecting pins  22 , which on the other hand, are restrained relative to the cleaning frame  13  with a strength that can endure a predetermined or greater pull-out load. 
     FIG. 7 is a cross-sectional view showing the details of the connecting construction by a conventional connecting pin. The connecting pin  22  is a cylindrical solid pin made of steel such as stainless steel, or a nonferrous metal such as aluminum or brass, and manufactured by cutting, grinding or cold forming and has an outer diameter d 1 . In FIG. 7, a direction of insertion of the connecting pin  22  is indicated by the arrow “a”, and the state shown in FIG. 7 is an assembly-completed state. That is, the connecting pin  22  is inserted from the outer side toward the inner side of the cleaning frame  13 . In the example of the conventional art, the outer diameter d 1  of the connecting pin  22  is d 1 =φ3.0 mm (tolerance: maximum 0 mm, minimum −0.020 mm), and the inner diameters of the holes  13   ei ,  13   eo  and the hanging holes  20  are φ3.0 mm (tolerance: maximum −0.030 mm, minimum −0.060 mm), φ3.05 mm (tolerance: maximum +0.050 mm, minimum 0 mm), and φ3.0 mm (JIS D 10 , tolerance: maximum +0.060 mm, minimum +0.020 mm), respectively. As the result, the connecting pin  22  is tight-fitted in the hole  13   ei  of the cleaning frame  13  and is restrained by the force-fit, the hanging hole  20  of the developing frame  12  is running-fitted relative to the connecting pin  22  and thus, the developing frame  12  is rotatably connected with the connecting pin  22  as a rotation axis. 
     Now, if in the conventional construction as described above, the connecting pin  22  should slip out of one of the holes  13   eo  and  13   ei  of the cleaning frame  13 , the connecting pin  22  will become a cantilever and the pressure contact between the photosensitive drum  7  and the developing roller  9   c  at the opposite ends thereof will become unstable, and a desired electrostatic latent image or visible image cannot be obtained and as the result, a desired image cannot be obtained. Furthermore, if the connecting pin  22  slips out of the hanging hole  20  of the developing frame  12 , the cleaning frame  13  and the developing frame  12  will separate from each other and will become incapable of performing their function as an image forming apparatus. 
     Accordingly, in order to avoid the inconvenience as noted above, heretofore the outer diameter of the connecting pin  22  and the inner diameter of the hole  13   ei  have been strictly controlled to thereby always secure a predetermined force-fit strength so that the force-fit of the connecting pin  22  into the hole  13   ei  of the cleaning frame  13  may not be released. 
     The predetermined force-fit strength referred to here is, for example, the strength to endure (i.e., not slipping out) vibration or shock applied in the physical distribution process after the process cartridge has been shipped. That is, in the physical distribution process, vibration or shock greater than during image formation or during the user&#39;s handling is applied the process cartridge and therefore, the physical distribution process is a more severe condition for the slipping-out of the connecting pin  22 . Accordingly, sufficient slipping-out preventing strength is necessary to endure without slipping out the vibration or shock occurring in the physical distribution process. 
     The present invention has as its object to secure a sufficient slip-out preventing strength of the connecting pin  22  relative to the holes  13   eo  and  13   ei  of the cleaning frame  13  without performing the severe control as described above. 
     Embodiment 1 
     In order to achieve the above object, a connecting pin  24  as shown in FIG. 8 is used as Embodiment 1 of the present invention. The connecting pin  24  shown in FIG. 8 is of a cylindrical shape (hereinafter referred to as the hollow pin) and formed with a restraining portion  24   a  by cutting, raising, and bending so that the leading end of the restraining portion  24   a  in the direction indicated by the arrow “a” which is the direction of insertion is made the bending proximal base, and the trailing end of the restraining portion  24   a  in the direction indicated by the arrow “a” juts outwardly. FIG. 9 is a cross-sectional view showing the details of a connecting construction incorporating the hollow pin  24  therein. The hollow pin  24  is made of steel such as stainless steel or a nonferrous metal such as aluminum or brass having a plate thickness of the order of 0.2 mm-0.4 mm, and the restraining portion  24   a  serves as a snap fit. That is, in FIG. 9, when the hollow pin  24  is inserted in the order of a first hole  13   eo , a hanging hole  20  (a third hole) and a second hole  13   ei  in the direction indicated by the arrow “a”, the restraining portion  24   a  is inserted from the bending proximal base side and therefore is resiliently inwardly flexed by the hole  13   eo  and inserted into the hole  13   eo , and the flexure is released when the restraining portion  24   a  has passed through the hole  13   ei . The restraining portion  24   a  released from flexure collides against the inner plate  13   f  of the cleaning frame  13  when the hollow pin  24  is about to slip out in the direction opposite to the direction indicated by the arrow “a”, but cannot be inwardly flexed because the colliding portion is not the bending proximal base. Accordingly, the hollow pin  24  can be inserted into the holes  13   eo ,  20  and  13   ei  in the direction indicated by the arrow “a”, but once the hollow pin  24  is inserted, the hollow pin  24  cannot slip out in the direction opposite to the direction indicated by the arrow “a”. 
     However, after the hollow pin  24  has been inserted until the flexure of the restraining portion  24   a  is released, when such a force that the hollow pin  24  is further pushed in the direction indicated by the arrow “a” is applied to the hollow pin  24 , the restraining portion  24   a  cannot block the further insertion of the hollow pin  24 . That is, when the hollow pin  24  receives a force in a direction in which the hollow pin  24  is further pushed in the direction indicated by the arrow “a” from the state of FIG. 9, the trailing portion of the hollow pin  24  will slip off the hole  13   eo . So, in the present invention, a rib  13   h  is provided on the cleaning frame  13 . The rib  13   h  is disposed at a location against which the leading portion of the hollow pin  24  collides before the trailing portion of the hollow pin  24  slips off the hole  13   eo , and therefore can prevent the trailing portion of the hollow pin  24  from slipping off the hole  13   eo.    
     Accordingly, when such a force that the hollow pin  24  slips out in a direction opposite to the direction indicated by the arrow “a” acts due to vibration or shock applied in the physical distribution process, the restraining portion  24   a  collides against the inner plate  13   f , and when such a force that the hollow pin  24  is pushed in the direction indicated by the arrow “a” acts, the leading portion of the hollow pin  24  collides against the rib  13   h  and therefore the hollow pin  24  can be prevented from slipping off the holes  13   ei  and  13   eo.    
     While in the above-described embodiment, mention has been made of an example in which the rib  13   h  is provided on the cleaning frame  13  to prevent the trailing portion of the hollow pin  24  from slipping off the hole  13   eo  when the hollow pin  24  receives a force in such a direction that it is further pushed in the direction indicated by the arrow “a” from the state of FIG. 9, this is not restrictive, but for example, the rib may be replaced by the end surface of the cleaning blade  10   a  of the cleaning means, and in short, any means that collides against the leading portion of the hollow pin  24  will do. That is, the means for preventing the hollow pin  24  from slipping off is not restricted to the rib  13   h  integral with the cleaning frame  13  which is a first frame, the cleaning blade  10   a  or a cleaning blade supporting plate, but may be any regulating member for regulating the amount of inward insertion of the hollow pin  24 . 
     The hollow pin  24  will be described in detail here. FIG. 10 shows an example of the manufacture of the hollow pin  24  shown in FIGS. 8 and 9. First, as shown in FIG. 10, a metal plate formed of steel such as stainless steel or a nonferrous metal such as aluminum or brass has its configuration blanked out into a rectangular shape by press working and portions thereof also are blanked out into a U-shape except for a proximal base of a restraining portion  24   a  to thereby form restraining portions  24   a , and then the metal plate is bent in the direction indicated by the arrow “b” to thereby work it into a substantially cylindrical shape as shown in FIG.  11 . The reason why the metal plate is made into the substantially cylindrical shape is that since there is somewhat so-called spring back with which the metal plate tends to be restored to its original shape after it has been bent, the edges of the metal plate do not come into close contact with each other, but a slit  24   b  is formed. Also, FIG. 11 is a side view of the hollow pin  24  as viewed from its trailing portion side, but since the aforementioned spring back is liable to become greater in the bent edges, the bent edges are liable to jut out as shown in FIG.  11 . That is, the bent edges desired to be bent into a cylindrical shape as indicated by broken lines in FIG. 11 somewhat return outwardly as depicted by solid lines due to the spring back. When the bent edges jut out as shown in FIG. 11, there is the possibility that the corners of the edges and the inner wall of the hanging hole  20  of the developing frame  12  may be caught thereby and the hollow pin  24  and the developing frame  12  may become incapable of smoothly rotating. So, in the present invention, as shown in FIG. 12, with portions  24   h  in which the spring back substantially begins to appear as bent portions, bent edges  24   i  are designed to be bent inwardly of broken lines. If this is done, the corners of the bent edges  24   i  do not gall the inner wall of the hanging hole  20  and therefore, smooth rotation can be secured. 
     Letting it be said for caution&#39;s sake, if a seamless tube as shown in FIG. 14, which will be described later, is worked so as to be provided with a restraining portion  24   a , as well as the general cylindrical shapes including Embodiment 2 and Embodiment 3, which will hereinafter be described, are defined as “a tubular shape having a circular cross-section”, the hollow pin  24  having the slit  24   b  and the bent edges  24   i  further inwardly bent from the bent portions  24   h  may strictly not be said to be of a cylindrical shape, but yet may suitably be referred to as having a cylindrical shape when it is viewed, and the expression “a plate material bent into a cylindrical shape” is easy to understand in describing the aforementioned example of the pin&#39;s manufacture and therefore, herein, for the sake of convenience, the hollow pin as shown in FIGS. 8,  11 , and  12 , which is provided with the slit  24   b  and the inwardly bent edges  24   i , and further, hollow pins  24  shown in FIGS. 13,  17  and  19 , which will be described later, are also referred to as having a cylindrical shape. 
     Also, the hollow pin  24  formed with the slit  24   b  as described above has the following advantage. In the method of manufacturing the hollow pin  24  by bending a metal plate as shown in FIG. 10, there is the spring back phenomenon as previously described and therefore, the accuracy of the configurational dimension d 2  of the hollow pin  24  is very difficult to provide. That is, the accuracy is difficult to provide because the amount of spring back is delicately changed by the unevenness of the plate thickness and the strength characteristic of the metal plate (the unevenness referred to herein means the unevenness within the tolerance). More particularly, it is very difficult to mass produce the pins with a stable mating-tolerance like the outer diameter d 1 =φ3.0 of the connecting pin  22  (tolerance: maximum 0, minimum −0.020), and if it is possible at all, the yield will be bad and an increase in cost will result. According to the applicant&#39;s estimate, it is presumed that when the configurational dimension d 2  of the hollow pin  24  is nominally φ3.0 mm, the tolerance which can be stably mass produced is 0.15 mm both at maximum and minimum and the order of 0.3 mm is suitable as the tolerance range. However, if as previously described, the inner diameter of the hanging holes  20  of the developing frame  12  is φ3.0 mm (JIS D10 tolerance: maximum +0.060 mm, minimum +0.020 mm) and the configurational dimension d 2  of the hollow pin  24  is d 2 =φ3.0±0.15 mm (tolerance: maximum +0.15 mm, minimum −0.15 mm), the hanging hole  20  and the hollow pins  24  become tight-fitted and the developing frame  12  become incapable of rotating smoothly and may prevent spacer rollers  9   i  at the opposite ends of the developing roller  9   c  from being urged against the photosensitive drum  7 . So, if the configurational dimension d 2  of the hollow pin  24  is φ3.0 (tolerance: maximum 0 mm, minimum −0.30 mm), the hanging holes  20  and the hollow pins  24  will not become tight-fitted, but yet in this case, as compared with the connecting pin  22 , the play or slop of the hollow pins  24  relative to the hanging holes  20  may become great, and for the spacer rollers  9   i  at the right and left ends to be urged in a well balanced manner against the photosensitive drum  7 , it is not preferable that the play or slop become great. Describing this in detail, there will be no problem if the play or slop, when the hanging holes  20  at the right and left ends and the hollow pins  24  are fitted together, is within the range of the play or slop caused by the tolerance of the connecting pin  22  and the tolerance of the hanging holes  20 , but as previously described, the tolerance of the connecting pins  22  is (maximum 0 mm, minimum −0.020 mm), whereas the tolerance of the hollow pins  24  is (maximum 0 mm, minimum −0.30 mm) and therefore, the play or slop when the hanging holes  20  and the hollow pins  24  are fitted together may become great as compared with that when the connecting pins  22  and the hanging holes  20  are fitted together. Particularly, if the play or slop of one of the hanging holes  20  and one of the hollow pins  24  become a minimum within the tolerance range (when the tolerance of the inner diameter of the hanging hole  20  has become a minimum and the configurational tolerance of the hollow pin  24  has become a maximum) and the play or slop of the other hanging hole  20  and the other hollow pin  24  becomes a maximum within the tolerance range (when the tolerance of the inner diameter of the hanging hole  20  has become a maximum and the configurational tolerance of the hollow pin  24  has become a minimum), the degree of parallelism between the generatrices of the developing roller  9   c  and the photosensitive drum  7  will deviate and the pressure contact of the spacer roller  9   i  at the right and left ends with the photosensitive drum  7  will become unbalanced, and in the worse case, a desired image may become unobtainable. 
     However, it will be possible to elastically change the outer diameter of the hollow pin  24  if it is provided with the slit  24   b  as previously described. That is, if the hollow pin  24  is inserted into a hole having an inner diameter somewhat smaller than the outer diameter of the hollow pin  24 , the hollow pin  24  will flex in a direction in which the width of the slit  24   b  becomes narrower, that is, so that the outer diameter thereof may become smaller and thus, the outer diameter will be restrained by the inner diameter of the hole. In other words, by the utilization of the springiness of the hollow pin  24 , it is easily possible to match the outer diameter thereof with the inner diameter of the hole into which the pin is inserted. 
     Let me try to apply this way of thinking to the aforedescribed holes  13   ei ,  13   eo  and hanging hole  20 . First, the inner diameter of the holes  13   ei  and  13   eo  is made equal to the outer diameter of the connecting pin  22 , i.e., φ3.0 mm (tolerance: maximum 0 mm, minimum −0.020 mm), and the outer diameter of the hollow pins  24  is made into φ3.0 mm (tolerance: maximum +0.30 mm, minimum 0 mm). If this is done, from the viewpoint of tolerance, the outer diameter of the hollow pin  24  necessarily becomes equal to or larger than the inner diameter of the holes  13   ei  and  13   eo . If substantially in this tolerance relation, the hollow pin  24  is inserted into the holes  13   ei  and  13   eo , in almost all cases the hollow pin  24  flexes in a direction in which the width of the slit  24   b  becomes narrower, and the outer diameter thereof is restrained by the inner diameter of the holes  13   ei  and  13   eo . Of course, there is rarely a case where the outer diameter of the hollow pin  24  and the inner diameter of the holes  13   ei  and  13   eo  become equal to each other, but it is just when both of the outer diameter of the hollow pin  24  and the inner diameter of the holes  13   ei  and  13   eo  are φ3.0 mm and therefore, it is within the range of the inner diameter tolerance (maximum 0 mm, minimum −0.20 mm) of both of the holes  13   ei  and  13   eo . Accordingly, in the state in which the hollow pin  24  is inserted in the holes  13   ei  and  13   eo , the outer diameter tolerance of the hollow pin  24  can secure the same (maximum 0 mm, minimum +0.020 mm) range as the tolerance of the holes  13   ei  and  13   eo . Thus, even if the outer diameter of the hollow pin  24  is mass producable at φ3.0 mm (tolerance: maximum +0.30 mm, minimum 0 mm), if the inner diameters of the holes  13   ei  and  13   eo  are made equal to the outer diameter of the connecting pin  22 , i.e., φ3.0 mm (tolerance: maximum 0 mm, minimum −0.020 mm), the tolerance of the hollow pin  24  in its inserted state can be made the same as that of the connecting pin  22  and therefore, the play or slop of the hollow pin  24  and the hanging hole  20  can be easily made the same as the play or slop of the connecting pin  22  and the hanging hole  20  without any increase in cost. Also, the hollow pin  24  as it is substantially inserted in the holes  13   ei  and  13   eo  flexes in the direction in which the width of the slit  24   b  becomes narrower and therefore, there can be obtained the effect that by the reaction force thereof, they are firmly connected together and are, as it were, force-fitted together and the slip-out strength thereof is increased. 
     If as shown in FIG. 13, a tapered leading portion  24   f  is provided at the leading portion of the hollow pin  24  by bending or drawing, it will be easy to insert the hollow pin  24  into the holes  13   ei  and  13   eo . This is because particularly when as described above, the hollow pin  24  is to be force-fitted into the holes  13   ei  and  13   eo , the tapered leading portion  24   f  serves as a guide and besides, the outer diameter of the hollow pin  24  gradually flexes along the taper. 
     Also, while in the above-described embodiment, there has been shown an example in which the hollow pin  24  is formed with the slit  24   b , the slit  24   b  is not always necessary, but use may be made of a hollow pin having no slit as shown in FIG.  14 . The hollow pin  24  shown in FIG. 14 is a so-called seamless tube worked so as to have a restraining portion  24   a , and unlike the aforedescribed hollow pin  24  formed with the slit, it cannot be expected to have the effect of regulating its outer diameter dimension by the utilization of resiliency when it is inserted into the holes  13   ei  and  13   eo , but yet the seamless tube has its outer diameter tolerance formed with high accuracy and therefore, it is not necessary to regulate the outer diameter dimension by the utilization of resiliency. 
     Also, while as an example of the manufacture of the hollow pin  24  formed with a slit, there has been shown an example in which the metal plate as shown in FIG. 10 is bent in the direction indicated by the arrow “b” and made into a substantially cylindrical shape, such a manufacturing method is not always restrictive, and for example, the hollow pin may be manufactured by applying the working of forming a slit in the seamless tube shown in FIG.  14 . 
     Embodiment 2 
     A description will now be provided of Embodiment 2 shown in FIG.  15 . The difference between Embodiment 2 of FIG.  15  and Embodiment 1 shown in FIG. 9 is that instead of the rib  13   h  provided on the cleaning frame  13  for preventing the trailing portion of the hollow pin  24  from slipping off the first hole  13   eo , the second hole  13   ei  in the inner plate  13   f  is made into not a through-hole but a blind hole having its inner end closed to thereby prevent the trailing portion of the hollow pin  24  from slipping off the hole  13   eo.    
     In FIG. 15, the outer diameter dimension of the hollow pin  24  and the inner diameter dimensions of the second hole  13   ei , the first hole  13   eo  and the hanging hole  20  are the same as the dimensional relation shown in Embodiment 1, and the hole  13   ei  in the inner plate  13   f  is not a through-hole but a hole having closed its end opposite to the end through which the hollow pin  24  is inserted. A counterbore portion  20   a , having an inner diameter larger than the dimension of the restraining portion when the flexure of the restraining portion  24   a  of the hollow pin  24  is released, is provided around the hanging hole  20  formed in the arm portion  19  of the developing frame  12 , so as to surround the restraining portion  24   a . In other words, the restraining portion  24   a  is located in an area surrounded by the inner plate  13   f  and the counterbore portion  20   a . By doing this, even if a force acts that would cause the hollow pin  24  to slip out in a direction opposite to the direction indicated by the arrow “a”, the restraining portion  24   a  collides against the seat surface of the counterbore portion  20   a , and even if a force acts that would cause the hollow pin  24  to be pushed in the direction indicated by the arrow “a”, the hollow pin  24  can be prevented from slipping off because the hole  13   ei  is closed. As a method of closing the hole  13   ei , the inner side of the inner plate  13   f  may be made into a convex shape as shown in FIG.  16 . If this is done, the fit length of the hollow pin  24  and the hole  13   ei , like that in FIG. 9, can be secured by an amount corresponding to the thickness of the inner plate  13   f . The counterbore portion  20   a  is not restricted to the inner plate  13   f  side of the arm portion  19  as shown in FIGS. 15 and 16, but may be provided on the outer plate  13   a  side (not shown). As a matter of course, in this case, the restraining portion  24   a  is located in an area surrounded by the outer plate  13   a  and the counterbore portion  20   a , and when a force acts that would cause the hollow pin  24  to slip out in the direction opposite to the direction indicated by the arrow “a” acts, the restraining portion  24   a  collides against the inner side of the outer plate  13   a . Also, it is unnecessary that the hole  13   ei  have completely closed its end opposite to the end through which the hollow pin  24  is inserted, as shown in FIGS. 15 and 16, and that end may have an aperture smaller than the outer diameter of the hollow pin  24 . For example, the hole  13   ei  may be a stepped hole having an aperture on the outer end surface side of the inner plate  13   f  and an inner aperture having an inner diameter smaller than the inner diameter of the outer aperture. In short, it will suffice if the leading portion of the hollow pin  24  does not go out of the hole  13   ei . However, if the leading portion of the hollow pin  24  has the tapered leading portion  24   f  as shown in FIG. 13, a tip end of the tapered leading portion  24   f  may be shot out of the hole  13   ei.    
     Embodiment 3 
     A hollow pin shown in FIG. 17 will now be described. The hollow pin  24  shown in FIG. 17 comprises a small-diametered portion  24   c  having the same outer diameter as the outer diameter d 2  of the hollow pin  24  shown in FIGS. 8 and 14, a large-diametered portion  24   d  having an outer diameter d 3  larger than that of the small-diametered portion  24   c  formed by drawing or the like, and a tapered portion  24   e  connecting the small-diametered portion  24   c  and the large-diametered portion  24   d  together. FIG. 18 shows a state in which this hollow pin  24  is incorporated. In FIG. 18, the inner diameters of the hole  13   ei  and the hanging hole  20  and the outer diameter of the small-diametered portion  24   c  are equal to those in Embodiment 1, that is, φ3.0 mm (tolerance: maximum 0 mm, minimum −0.020 mm), φ3.0 mm (JIS D10 tolerance: maximum +0.060 mm, minimum +0.020 mm) and φ3.0 mm (tolerance: maximum +0.30 mm, minimum 0 mm), respectively. The inner diameter of the hole  13   eo  and the outer diameter of the large-diametered portion  24   d  are φ3.5 mm (tolerance: maximum 0 mm, minimum −0.020 mm) and φ3.5 mm (tolerance: maximum +0.30 mm, minimum 0 mm), respectively. As is apparent from FIG. 17, in this embodiment, the outer diameter of the trailing portion of the hollow pin  24  is made larger than the inner diameter of the hanging hole  20  in order to prevent the trailing portion of the hollow pin  24  from slipping off the hole  13   eo . That is, even if a force acts that would cause the hollow pin  24  to be pushed in the direction indicated by the arrow “a” from the state of FIG. 18 , the tapered portion  24   e  strikes against the end portion of the hanging hole  20  and the hollow pin  24  is not pushed in. When a force acts that would cause the hollow pin  24  slip out in the direction opposite to the direction indicated by the arrow “a”, the restraining portion  24   a  collides against the inner plate  13   f  as in Embodiment 1. Such a hollow pin having a large-diametered portion and a small-diametered portion can be introduced as a substitute for a connecting pin having a plurality of outer diameters described in Japanese Patent Application Laid-Open No. 11-15354 without the design of the cleaning frame  13  and the developing frame  12  being changed. 
     While in FIG. 18, a description has been provided of a case where the small-diametered portion  24   c  is fitted into the hole  13   ei  and the hanging hole  20  and the large-diametered portion  24   d  is fitted into the hole  13   eo , the large diametered portion  24   d  may be long enough to be fitted into the hanging hole  20 , and the small-diametered portion  24   c  may be fitted into the hole  13   ei  and the large-diametered portion  24   d  may be fitted into the hanging hole  20  and the hole  13   eo . In this case, the inner diameter of the hanging hole  20  may suitably be φ3.5 mm (JIS D10 tolerance: maximum +0.078 mm, minimum +0.030 mm). 
     Also, FIG. 19 shows a hollow pin  24  provided with a bent portion  24   g  in the trailing portion thereof, instead of the large-diametered portion  24   d . The bent portion  24   g  is bent radially outwardly of the hollow pin  24 . The bent portion  24   g  is bent perpendicularly or substantially perpendicularly to the direction of insertion of the hollow pin  24  into the holes  13   eo ,  13   ei  and the hanging hole  20 . This is for preventing the trailing portion of the hollow pin  24  from slipping off the hole  13   eo  by the bent portion  24   g  striking against the outer plate  13   a  of the cleaning frame  13 . If such a bent portion  24   g  is provided, it is not necessary to provide the rib  13   h  of FIG. 9, or to make the hole  13   ei  into a blind hole as shown in FIG. 15, or to make the inner diameters of the hole  13   eo  and the hole  13   ei  different from each other as shown in FIG.  18  and therefore, it is possible to introduce the hollow pin into an existing product using the conventional art shown in FIG. 7 without changing the design of the cleaning frame  13  and the developing frame  12 . 
     While in the above-described embodiments, the shapes of the hollow pin have been shown by way of example in FIGS. 8,  13 ,  14 ,  17  and  19 , the present invention is not restricted to those shapes. That is, for example, the purpose of the tapered leading portion  24   f  shown in FIG. 13 is to facilitate the insertion of the hollow pin and therefore, the leading portion of each of the hollow pins of FIGS. 14,  17  and  19  may be tapered, and each of the hollow pins of FIGS. 13,  17  and  19  may be manufactured by working the seamless tube as shown in FIG.  14 . Also, while the number of the restraining portions  24   a  has been shown as two, it may be one or three or more. Also, the plate thickness, outer diameter dimension and tolerance of the hollow pin, the inner diameter dimensions and tolerances of the holes  13   ei  and  13   eo  of the cleaning frame  13 , and the inner diameter dimension and tolerance of the hanging hole  20  of the developing frame  12  are not restricted to the numerical values in the above-described embodiments. In addition, the shape of the hollow pin need not always be a cylindrical shape, but may be a polygon having a triangular or square cross-section, or a semicircular shape. 
     According to the aforedescribed embodiments, as functional advantages, there could be realized an improvement in pull-out yield strength, and particularly an improvement in strength to endure (i.e., not slipping out) vibration or shock applied in the physical distribution process. Also, as advantages in terms of quality control, the periodic sampling inspection of the surface roughness of the connecting pin and the force-fit strength thereof to the first frame, and stringent control necessary so that a predetermined force-fit strength may be secured are not necessary. 
     As described above, according to the present invention, reliable connection can be ensured. 
     While the invention has been described with reference to the structure disclosed herein, it is not confirmed to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.