Patent Publication Number: US-10310437-B2

Title: Drum unit and image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application is based on and claims the benefit of priority from Japanese patent application No. 2017-099829 filed on May 19, 2017, which is incorporated by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates to a drum unit including a photosensitive drum and an image forming apparatus including the drum unit. 
     In a conventional electrographic image forming apparatus, an electrostatic latent image is formed on a surface of a charged photosensitive drum, and then the electrostatic latent image is developed by a toner to form a toner image. When the surface of the photosensitive drum is charged as described above, a discharge product may adhere on the surface of the photosensitive drum. If the discharge product absorbs moisture, an electrical resistance of the surface of the photosensitive drum is lowered, and failure called as an image flow may occur. 
     In order to avoid the occurrence of the image flow, a configuration to heat the photosensitive drum by a heater and to evaporate the moisture adhered on the surface of the photosensitive drum is well known. When such a configuration is applied, in order to heat the photosensitive drum intensively, the heater is preferably installed inside the photosensitive drum. 
     For example, conventionally, a drum heater, which includes a heating coil arranged on an insulation sheet, is rolled, and the rolled drum heater is inserted in an inside of the photosensitive drum. Flanges are forcefully inserted in both ends of the photosensitive drum, and a terminal for supplying electrical power to the drum heater is mounted on one of the flanges. An electrode always comes into contact with a circumferential face of an electrode plate coupled to the terminal, and the electrical coupling is kept during the rotation of the photosensitive drum. 
     SUMMARY 
     In accordance with an aspect of the present disclosure, a drum unit includes a photosensitive drum and a heater. The photosensitive drum rotates around a rotation axis extending along a rotation axis direction. The heater is installed inside the photosensitive drum and heats the photosensitive drum. The heater includes a heater substrate and a plurality of resistance elements. The heater substrate extends along the rotation axis direction. The plurality of resistance elements are aligned in the rotation axis direction and are mounted on the heater substrate. 
     In accordance with an aspect of the present disclosure, an image forming apparatus includes the drum unit and an apparatus main body to which the drum unit is attached. 
     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 schematic view showing an image forming apparatus according to an embodiment of the present disclosure. 
         FIG. 2  is a perspective view showing a drum unit according to the embodiment of the present disclosure. 
         FIG. 3  is a sectional view showing the drum unit according to the embodiment of the present disclosure. 
         FIG. 4  is a perspective view showing a heater and a pair of wires according to the embodiment of the present disclosure. 
         FIG. 5  is a perspective view showing a heater cover, a supporter, a cap, a metal plate and the pair of wires according to the embodiment of the present disclosure. 
         FIG. 6  is a perspective view showing the heater, the supporter, the metal plate and the pair of wires according to the embodiment of the present disclosure. 
         FIG. 7  is a sectional view showing the supporter and its peripheral portion according to the embodiment of the present disclosure. 
         FIG. 8  is a disassembled perspective view showing a front portion of the drum unit according to the embodiment of the present disclosure. 
         FIG. 9  is a perspective view showing the front portion of the drum unit according to the embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, with reference to the attached drawings, an image forming apparatus  1  according to one embodiment of the present disclosure will be described. Arrows Fr, Rr, L, R, U and Lo shown in each figure respectively indicate a front side, a rear side, a left side, a right side, an upper side and a lower side of the image forming apparatus  1 . 
     First, an entire structure of the image forming apparatus  1  will be described. The image forming apparatus  1  is a multifunctional peripheral including multi functions, such as a printing function, a copying function and a facsimile function, for example. 
     As shown in  FIG. 1 , the image forming apparatus  1  includes a box-shaped apparatus main body  2 . On an upper end portion of the apparatus main body  2 , an image reading device  3  configured to read an image of a document is provided. In an upper portion of the apparatus main body  2 , an ejected sheet tray  4  is provided below the image reading device  3 . In the upper portion of the apparatus main body  2 , four toner containers  5  are provided below the ejected sheet tray  4 . The four toner containers  5  respectively store a yellow toner, a magenta toner, a cyan toner and a black toner. 
     In an approximate center portion of the apparatus main body  2 , an intermediate transferring belt  6  is stored below the four toner containers  5 . In the approximate center portion of the apparatus main body  2 , four image forming parts  7  are stored below the intermediate transferring belt  6 . The four image forming parts  7  respectively correspond to the yellow toner, the magenta toner, the cyan toner and the black toner. Each of the image forming parts  7  includes a photosensitive drum  8 , a charging device  9 , a developing device  10 , a primary transferring roller  11  and a cleaning device  12 . Between the primary transferring roller  11  and the photosensitive drum  8 , the intermediate transferring belt  6  is interposed, and a primary transferring nip N 1  is formed between the intermediate transferring belt  6  and the photosensitive drum  8 . 
     In a lower portion of the apparatus main body  2 , an exposing device  13  is stored below the four image forming parts  7 . In a lower end portion of the apparatus main body  2 , a sheet feeding cassette  14  is stored below the exposing device  13 . The sheet feeding cassette  14  stores a sheet S (an example of a recording medium). 
     In a right side portion of the apparatus main body  2 , a conveying path P for the sheet S is provided so as to extend from the sheet feeding cassette  14  to the ejected sheet tray  4 . At an upstream portion of the conveying path P, a sheet feeding part  15  is provided. At a middle portion of the conveying path P, a secondary transferring roller  16  is provided. Between the secondary transferring roller  16  and the intermediate transferring belt  6 , a secondary transferring nip N 2  is formed. At a downstream portion of the conveying path P, a fixing device  17  is provided. 
     Next, an operation of the image forming apparatus  1  having the above configuration will be described. 
     When the image forming apparatus  1  is directed to start printing, first, the charging device  9  charges a surface of the photosensitive drum  8 . Next, laser light (refer to a dotted line in  FIG. 1 ) emitted from the exposing device  13  forms an electrostatic latent image on the surface of the photosensitive drum  8 . Then, the developing device  10  supplies the toner to the photosensitive drum  8 , the electrostatic latent image formed on the surface of the photosensitive drum  8  is developed, and a toner image is carried on the photosensitive drum  8 . The toner image is primarily transferred on a surface of the intermediate transferring belt  6  at the primary transferring nip N 1 . The above operation is performed at each image forming part  7  to form a full color toner image on the intermediate transferring belt  6 . The toner remained on the photosensitive drum  8  is removed by the cleaning device  12 . 
     On the other hand, the sheet S fed from the sheet feeding cassette  14  by the sheet feeding part  15  is conveyed to a downstream side along the conveying path P and enters the secondary transferring nip N 2 . At the secondary transferring nip N 2 , the full color toner image formed on the intermediate transferring belt  6  is secondarily transferred on the sheet S. The sheet S on which the toner image is secondarily transferred is conveyed to the downstream side along the conveying path P and enters the fixing device  17 . The fixing device  17  fixes the toner image on the sheet S. The sheet S on which the toner image is fixed is ejected on the ejected sheet tray  4 . 
     The image forming apparatus  1  according to the present embodiment includes a drum unit  20  detachably attached to the apparatus main body  2 . Hereinafter, the drum unit  20  will be described. An arrow O shown in each figures after  FIG. 2  indicates an outside in the front-and-rear direction of the drum unit  20 , and an arrow I shown in each figure after  FIG. 2  indicates an inside in the front-and-rear direction of the drum unit  20 . 
     With reference to  FIG. 2  and  FIG. 3 , the drum unit  20  includes a unit main body  21 , the photosensitive drum  8  arranged at an upper portion in the unit main body  21 , the charging device  9  arranged at a lower side of the photosensitive drum  8 , the cleaning device  12  arranged at a right side of the photosensitive drum  8 , a heater  22  and a heater cover  23  installed inside the photosensitive drum  8 , a front side flange  24  and a supporter  25  and a cap  26  and a metal plate  27  which are arranged at a front end side of the photosensitive drum  8 , a rear side flange  28  arranged at a rear end side of the photosensitive drum  8 , a connector  29  fixed to a front end portion of the unit main body  21 , a main body cover  30  covering a front side of the unit man body  21  and a pair of wires  31  connecting the heater  22  to the connector  29 . 
     The unit main body  21  of the drum unit  20  is formed in a box-like shape with a part of an upper face and a left face opened. At a front portion of the unit main body  21 , a frame  33  is provided. At an upper portion of the frame  33 , a supporting hole  34  is provided. 
     The photosensitive drum  8  of the drum unit  20  is formed in a cylindrical shape extending along the front-and-rear direction. The photosensitive drum  8  is rotatable around a rotation axis X extending along the front-and-rear direction. That is, the front-and-rear direction is a rotation axis direction of the photosensitive drum  8 . 
     The photosensitive drum  8  has a diameter of 40 mm or smaller, for example. The photosensitive drum  8  includes a blank tube  36  and a photosensitive layer  37  covering an outer circumference of the blank tube  36 . The blank tube  36  is made of metal, such as aluminum and stainless steel. The photosensitive layer  37  is made of amorphous silicon. That is, the photosensitive drum  8  is formed by an amorphous silicon photoreceptor. 
     The charging device  9  of the drum unit  20  includes a charging roller  39  arranged at the lower side of the photosensitive drum  8  and a cleaning roller  40  arranged at the lower side of the charging roller  39 . The charging roller  39  and the cleaning roller  40  extend along the front-and-rear direction. The charging roller  39  comes into contact with the surface of the photosensitive drum  8 , and is rotated by following the rotation of the photosensitive drum  8  so as to charge the surface of the photosensitive drum  8  uniformly. The cleaning roller  40  comes into contact with an outer circumferential face of the charging roller  39 , and is rotated by following the rotation of the charging roller  39  so as to clean the outer circumferential face of the charging roller  39 . 
     The cleaning device  12  of the drum unit  20  includes a blade  42 . The blade  42  extends along the front-and-rear direction. The blade  42  comes into contact with the surface of the photosensitive drum  8 , and cleans the surface of the photosensitive drum  8  as the photosensitive drum  8  is rotated. 
     With reference to  FIG. 3  and  FIG. 4 , the heater  22  of the drum unit  20  includes a heater substrate  44  and a plurality of resistance elements  45  mounted on the heater substrate  44 . The heater substrate  44  is formed in a flat plate shape extending along the front-and-rear direction. The plurality of resistance elements  45  are made of resistance chips. The plurality of resistance elements  45  are aligned in the front-and-rear direction. 
     With reference to  FIG. 3  and  FIG. 5 , the heater cover  23  of the drum unit  20  includes a main body part  47  and a closing part  48  closing a rear end portion of the main body part  47 . The main body part  47  is formed in a cylindrical shape with the rotation axis X as a center, and extends along the front-and-rear direction. The main body part  47  covers an outer circumference of the heater  22 . The main body part  47  includes a plurality of communication holes  49  through which an inside of the heater cover  23  and an outside of the heater cover  23  communicate with each other. The plurality of communication holes  49  are each formed in a shape elongated in the front-and-rear direction. The plurality of communication holes  49  are provided at intervals in the front-and-rear direction and a circumferential direction. The closing part  48  covers a rear side of the heater  22 . 
     With reference to  FIG. 3 , the front side flange  24  of the drum unit  20  is formed in an annular shape with the rotation axis X as a center. An outer circumferential portion of the front side flange  24  is attached to a front end portion (an end portion at the outside in the front-and-rear direction) of the photosensitive drum  8 . Thereby, the front side flange  24  is rotatable integrally with the photosensitive drum  8 . At an inner circumferential portion of the front side flange  24 , a through hole  50  is provided. 
     The supporter  25  of the drum unit  20  is formed in a tubular shape with the rotation axis X as a center, and extends along the front-and-rear direction. The supporter  25  penetrates through the supporting hole  34  of the frame  33 . Thereby, the supporter  25  is supported by the frame  33 . The supporter  25  penetrates through the through hole  50  of the front side flange  24 . Thereby, the supporter  25  rotatably supports the front side flange  24 . 
     With reference to  FIG. 6  and  FIG. 7 , on a rear end portion (an end portion at the inside in the front-and-rear direction) of an outer circumferential face of the supporter  25 , an annular fitting groove  52  is provided. Into the fitting groove  52 , a front end portion (an end portion at the outside in the front-and-rear direction) of the main body part  47  of the heater cover  23  is fitted. Thereby, the supporter  25  supports the heater cover  23  in a cantilever manner. At a rear end portion (an end portion at the inside in the front-and-rear direction) of the supporter  25 , a pair of split grooves  53  are provided at both left and right sides of the fitting groove  52 . Into the pair of split grooves  53 , a front end portion (an end portion at the outside in the front-and-rear direction) of the heater substrate  44  of the heater  22  is inserted. Thereby, the supporter  25  supports the heater  22  in a cantilever manner. At a front end portion (an end portion at the outside in the front-and-rear direction) of the supporter  25 , a slit  54  extending along the front-and-rear direction is formed. 
     With reference to  FIG. 7 , the cap  26  of the drum unit  20  is attached to the front end portion (the end portion at the outside in the front-and-rear direction) of the supporter  25 , and closes a front end portion of the supporter  25 . A part of the cap  26  is inserted into the supporter  25 . 
     With reference to  FIG. 5  to  FIG. 7 , the metal plate  27  of the drum unit  20  is formed in a flat plate shape. The metal plate  27  is provided along a plane perpendicular to the front-and-rear direction. At a left upper portion of the metal plate  27 , a fixing hole  56  is provided. Through the fixing hole  56 , the supporter  25  penetrates. The metal plate  27  is fixed to the supporter  25  by caulking or welding at a peripheral of the fixing hole  56 , and is integrated with the supporter  25 . To a right upper portion of the metal plate  27 , a pin  57  is fixed. With reference to  FIG. 8  and  FIG. 9 , the metal plate  27  is fixed to the frame  33  by a plurality of screws  58 . 
     With reference to  FIG. 3 , the rear side flange  28  of the drum unit  20  is formed in an annular shape with the rotation axis X as a center. An outer circumferential portion of the rear side flange  28  is attached to a rear end portion (an end portion at the outside in the front-and-rear direction) of the photosensitive drum  8 . Thereby, the rear side flange  28  is rotatable integrally with the photosensitive drum  8 . At an inner circumferential portion of the rear side flange  28 , a coupling hole  60  is provided. Into the coupling hole  60 , a driving joint  61  provided at the apparatus main body  2  is inserted. Thereby, the rear side flange  28  is coupled to the driving joint  61 , and the rear side flange  28 , the photosensitive drum  8  and the front side flange  24  are rotated around the rotation axis X by following the rotation of the driving joint  61 . 
     The connector  29  of the drum unit  20  is arranged outside the photosensitive drum  8 . The connector  29  includes a connector substrate  63  and a unit side terminal  64  fixed to a rear face of the connector substrate  63 . The unit side terminal  64  is connected to a main body side terminal  65  provided at the apparatus main body  2 . 
     A lower portion of the main body cover  30  of the drum unit  20  covers a front side of the connector  29 . An upper portion of the main body cover  30  covers a front side of the metal plate  27 . Ata left upper portion of the main body cover  30 , an exposing hole  67  is provided. Through the exposing hole  67 , the supporter  25  penetrates. Thereby, the front end portion of the supporter  25  and the cap  26  are exposed to an outside of the drum unit  20 . 
     With reference to  FIG. 4 , one end portions of the pair of wires  31  of the drum unit  20  are connected to the heater substrate  44  of the heater  22 . With reference to  FIG. 7 , the pair of wires  31  pass through an inside of the supporter  25 . The pair of wires  31  pass through the slit  54  of the supporter  25  at the rear side (the inside in the front-and-rear direction) of the cap  26 , and is pulled out to an outside of the supporter  25 . With reference to  FIG. 9 , the other end portions of the pair of wires  31  are connected to the connector substrate  63  of the connector  29 . 
     Next, an example of an assembling work of the drum unit  20  will be described. 
     When the drum unit  20  is assembled, first, as shown by an arrow A in  FIG. 6 , a worker inserts the front end portion of the heater substrate  44  of the heater  22  into the pair of split grooves  53  of the supporter  25 . Thereby, the heater  22  is fixed to the supporter  25 . Next, as shown by an arrow B in  FIG. 5 , the worker fits the front end portion of the main body part  47  of the heater cover  23  into the fitting groove  52  of the supporter  25 . Thereby, the heater cover  23  is fixed to the supporter  25 . Then, as shown by an arrow C in  FIG. 5 , the worker attaches the cap  26  to the front end portion of the supporter  25 . 
     Next, as shown by an arrow D in  FIG. 8 , the worker makes the supporter  25  penetrate through the supporting hole  34  of the frame  33  while inserting the heater  22  and the heater cover  23  into the photosensitive drum  8 . Then, as shown in  FIG. 9 , the worker fixes the metal plate  27  to the frame  33  by the plurality of screws  58 . Then, the worker connects the pair of wires  31  to the connector substrate  63  of the connector  29 . Finally, as shown in  FIG. 2 , the worker fixes the main body cover  30  to the unit main body  21 . Thereby, the assembling work of the drum unit  20  is finished. 
     By the way, when the surface of the photosensitive drum  8  is charged by the charging roller  39  at performing the image forming operation, a discharge product may adhere on the surface of the photosensitive drum  8 . If the discharge product absorbs moisture, an electric resistance of the surface of the photosensitive drum  8  is lowered, and failure called as image flow may occur. 
     Then, when the image forming apparatus  1  is used under a high humidity environment, electric power is supplied to the heater  22  through the main body side terminal  65 , the connector  29  and the pair of wires  31  from a power source (not shown) provided at the apparatus main body  2 . When the electric power is supplied to the heater  22  is powered, the plurality of resistance elements  45  provided at the heater  22  are heated to heat the photosensitive drum  8 . Thereby, it becomes possible to vaporize the moisture adhered on the surface of the photosensitive drum  8  and to prevent the discharge product from absorbing the moisture. Accordingly, it becomes possible to prevent the occurrence of the above described image flow. 
     By the way, when the photosensitive drum  8  is heated by the heater  22  as described above, the heater  22  may be arranged at the outside of the photosensitive drum  8 . Specifically, the heater  22  provided in the sheet feeding cassette  14  may be used to heat the photosensitive drum  8 , or the heater  22  may be arranged at the lower side of the charging device  9  of the drum unit  20 . 
     However, recently, in view of lowering the heating temperature of the toner in the fixing device  17  and preventing the power consumption of the image forming apparatus  1 , the toner is developed to have a lower melting temperature. If the configuration in which the heater  22  is arranged at the outside of the photosensitive drum  8  as described above is applied, the heater  22  heats the developing device  10  arranged near the photosensitive drum  8  in addition to the photosensitive drum  8 , and the low melting point toner stored in the developing device  10  may be affected. 
     In the present embodiment, the heater  22  is installed inside the photosensitive drum  8 . By applying such a configuration, it becomes possible to prevent the developing device  10  from being heated and to heat the photosensitive drum  8  intensively. Therefore, if the low melting point toner is used, it becomes possible to prevent thermal deterioration of the toner. 
     By the way, if the configuration in which the heater  22  is installed inside the photosensitive drum  8  is applied, the heater  22  with a heating coil may be rolled, and then the rolled heater  22  may be inserted in the inside of the photosensitive drum  8 . 
     However, recently, the tandem type image forming apparatus  1  capable of outputting a color image becomes major. As a result, the photosensitive drum  8  is developed to have a small diameter. If the configuration in which the heater  22  with the heating coil is rolled and then the rolled heater  22  is inserted into the inside of the photosensitive drum  8  is applied, because a large space for inserting the heater  22  is required, if a small diameter photosensitive drum  8  (for example, the photosensitive drum  8  having a diameter of 40 mm or smaller) is used, the heater  22  may not be inserted inside the photosensitive drum  8 . 
     In the present embodiment, the heater  22  including the heater substrate  44  extending along the front-and-rear direction and the plurality of resistance elements  45  mounted on the heater substrate  44  is installed inside the photosensitive drum  8 . By applying such a configuration, it becomes possible to install the heater  22  inside the photosensitive drum  8  having a small diameter. 
     As described above, in the present embodiment, regardless of a size of the diameter of the photosensitive drum  8 , it becomes possible to install the heater  22  inside the photosensitive drum  8  by a simple structure and to heat the photosensitive drum  8  intensively without heating any mechanism (for example, the developing device  10 ) arranged near the photosensitive drum  8  unnecessarily. 
     Additionally, the heater  22  is supported by the supporter  25  penetrating through the front side flange  24 . By applying such a configuration, it becomes possible to use the supporter  25  in common for supporting the front side flange  24  rotatably and for supporting the heater  22 , and it becomes possible to support the heater  22  by a simple structure. 
     Additionally, the supporter  25  is formed in a tubular shape, and the pair of wires  31  pass through the inside of the supporter  25 . By applying such a configuration, it becomes possible to use the supporter  25  as a guide member for the pair of wires  31 , and it becomes possible to guide the pair of wires  31  by a simple structure. 
     Additionally, the pair of wires  31  pass through the slit  54  of the supporter  25  at the rear side (the inside in the front-and-rear direction) of the cap  26 , and then are pulled out to the outside of the supporter  25 . By applying such a configuration, it becomes possible to prevent the pair of wires  31  from being fallen from the supporter  25  accidentally. 
     Additionally, the heater  22  is supported by the supporter  25  in a cantilever manner. By applying such a configuration, it becomes possible to utilize a space formed near the rear end portion of the photosensitive drum  8  as an arrangement space for members (for example, the rear side flange  28  and the driving joint  61 ) to input the driving force to the photosensitive drum  8 . 
     Additionally, the metal plate  27  is fixed to the frame supporting the supporter  25 . By applying such a configuration, it becomes possible to improve a positional precision of the supporter  25  with respect to the frame  33 . 
     Additionally, the photosensitive drum  8  is formed by an amorphous silicon photoreceptor. By applying such a configuration, compared with a case where the photosensitive drum  8  is formed by an organic photoreceptor, it becomes possible to prevent an abrasion of the photosensitive drum  8  and to prolong the lifetime of the photosensitive drum  8 . On the other hand, in a case where the photosensitive drum  8  is formed by an amorphous silicon photoreceptor, compared with a case where the photosensitive drum  8  is formed by an organic photoreceptor, because the photosensitive drum  8  is hardly scraped, the moisture adhered on the surface of the photosensitive drum  8  is hardly removed and the image flow easily occurs. Then, heating the photosensitive drum  8  by using the above heater  22  provides a merit preventing the occurrence of the image flow. 
     Additionally, the image forming apparatus  1  includes the above described drum unit  20  and the apparatus main body  2  to which the drum unit  20  is attached. By applying such a configuration, it becomes possible to prevent the occurrence of the image flow and to improve an image quality of an output image. 
     In the present embodiment, the heater  22  is supported by one supporter  25  in a cantilever manner. On the other hand, in another embodiment, the heater  22  may be supported by two supporters  25  from its both sides. 
     In the present embodiment, the heater  22  is installed inside the photosensitive drum  8  having a diameter of 40 mm or smaller. On the other hand, in another embodiment, the heater  22  may be installed inside the photosensitive drum  8  having a diameter exceeding 40 mm. 
     In the present embodiment, the image forming apparatus  1  is a multifunctional peripheral. In another embodiment, the image forming apparatus  1  may be a printer, a copying machine and a facsimile. 
     While the present disclosure has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present disclosure.