Patent Publication Number: US-6909864-B2

Title: Image forming apparatus configuring air passage and process cartridge for the apparatus

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image forming apparatus having a process cartridge. 
   2. Description of the Related Art 
   In an image forming apparatus of the electrophotographic system, a toner image is transferred to a sheet, and the transferred toner image is fixed to the sheet. A process cartridge in which an image carrier and a developing device are integrally formed is used as a section for forming a toner image. Usually, a thermal pressure fixing device which performs fixation by means of heat and pressure is used in fixation of a toner image. 
   As a result of miniaturization of an image forming apparatus, a process cartridge and a fixing device are place in close proximity to each other. Consequently, there is a possibility that the process cartridge receives radiant heat from the fixing device to adversely affect an image carrier and a toner. 
   Therefore, a technique has been proposed in which a shutter disposed in a process cartridge is used for forming a gap between the shutter and a main unit of the process cartridge, and a fan is disposed to produce an air flow in the gap (for example, see JP-A-2-50169 JP-A-5-224476). 
   In the above two conventional arts, a single blower fan is placed in the vicinity of a process cartridge, and the single blower fan performs both air suction and exhaust, thereby causing a problem in that the cooling efficiency is poor. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide an image forming apparatus which can solve the problem of the conventional art, and in which a process cartridge can be efficiently cooled, and also a process cartridge which is to be used in the image forming apparatus. 
   In order to attain the object, a first feature of the invention is in an image forming apparatus which comprises: a process cartridge having at least an image carrier; and a fixing device which fixes an image that is formed on a sheet by the process cartridge, to the sheet, wherein a suction fan and an exhaust fan are disposed across the process cartridge to configure an air passage which produces an air flow, between the process cartridge and the fixing device. Since the suction fan and the exhaust fan are disposed respectively on both sides across the process cartridge, an air flow for cooling the process cartridge can be efficiently produced between the process cartridge and the fixing device. Preferably, the suction fan and the exhaust fan are disposed to be opposed to the process cartridge. According to the configuration, an air flow for cooling the process cartridge can be produced more efficiently between the process cartridge and the fixing device. More preferably, the suction fan or the exhaust fan is opposed to an approximately middle portion in a longitudinal direction of the process cartridge. According to the configuration, a temperature difference in the longitudinal direction which may be caused in the case where only one end portion of the process cartridge is cooled can be reduced, and hence dispersion of changes with time in members which are used in image formation can be reduced. 
   Preferably, the process cartridge has: a process cartridge main unit; and a shutter which is disposed in the process cartridge main unit, and which opens and closes a side face of the image carrier in accordance with attachment and detachment of the process cartridge, the shutter is retracted to a position where the shutter faces the fixing device when the process cartridge is attached, and a gap is formed between the shutter and the process cartridge main unit, thereby allowing an air flow to be formed in the gap. Radiant heat from the fixing device can be blocked by the shutter, and an air flow is produced in the gap. Therefore, the process cartridge can be cooled more efficiently. 
   More preferably, air vent holes which communicate with the gap are formed in the shutter. According to the configuration, the air flow to the gap can be smoothly produced. Preferably, the shutter has a hollow structure. When the shutter is formed into a hollow structure, the heat insulating property can be enhanced, and the heat insulating effect on radiant heat from the fixing device can be enhanced. 
   The cooling due to the air flow flowing through the air passage can be applied not only to the process cartridge, but also to a power supply device, an electric circuit board, an optical writing device, and other devices. 
   Preferably, the apparatus further comprises a sheet transportation guide on an upstream side of the fixing device, and air vent openings constituting the air passage are formed in the sheet transportation guide, so that exhaust is conducted through the air vent openings. Preferably, the air vent openings have an opening area which is larger than a bore area of the exhaust fan, so that the air flows more smoothly. Preferably, the air vent openings are configured by forming at least part of the sheet transportation guide into a lattice structure, so that a large opening area can be obtained while maintaining the strength of the sheet transportation guide. 
   A second feature of the invention is in a process cartridge which is to be used in an image forming apparatus, and which comprises: a process cartridge main unit; an image carrier housed in the process cartridge main unit; and a shutter that opens and closes an image carrier exposure window formed in the process cartridge main unit, wherein air vent holes are formed in the shutter to guide an air flow between the shutter and the process cartridge main unit. Preferably, the shutter of the process cartridge has a hollow structure as described above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a section view showing an image forming apparatus which is an embodiment of the invention. 
       FIG. 2  is a perspective view showing a process cartridge which is used in the image forming apparatus of the embodiment of the invention. 
       FIG. 3  is a plan view showing a shutter which is used in the process cartridge of the embodiment of the invention. 
       FIG. 4  is an enlarged partial section view showing the shutter which is used in the process cartridge of the embodiment of the invention. 
       FIG. 5  is a perspective view as viewed from the front side showing a first duct which is used in the image forming apparatus of the embodiment of the invention. 
       FIG. 6  is a perspective view as viewed from the rear side showing the first duct which is used in the image forming apparatus of the embodiment of the invention. 
       FIG. 7  is a perspective view as viewed from the rear side showing a second duct which is used in the image forming apparatus of the embodiment of the invention. 
       FIG. 8  is a perspective view as viewed from the front side showing a state where an optical writing device, a first duct, and a second duct which are used in the image forming apparatus of the embodiment of the invention are combined with one another. 
       FIG. 9  is a perspective view as viewed from the rear side showing a state where the optical writing device, the first duct, and the second duct which are used in the image forming apparatus of the embodiment of the invention are combined with one another. 
       FIG. 10  is a front view showing a sheet transportation guide which is used in the image forming apparatus of the embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Next, an embodiment in which the invention is applied to an actual image forming apparatus will be described. 
   Referring to  FIG. 1 , an image forming apparatus  10  has an image forming apparatus main unit  12 . A discharge section  14  is disposed in an upper part of the image forming apparatus main unit  12 , and two sheet supply cassettes  16   a ,  16   b  are placed in a lower part of the image forming apparatus main unit  12 . 
   Nudger rolls  18   a ,  18   b  are placed above the vicinities of the inner ends of the sheet supply cassettes  16   a ,  16   b , respectively. Retard rolls  20   a ,  20   b  and feed rolls  22   a ,  22   b  are placed in front of the nudger rolls  18   a ,  18   b.    
   A transportation path  24  is a sheet passage elongating from the nudger roll  18   b  for the lower sheet supply cassette  16   b  to a discharge port  26 . The transportation path  24  has a portion which is in the vicinity of the rear face (the right side face in  FIG. 1 ) of the image forming apparatus main unit  12 , and which is formed substantially vertically in a range from the feed roll  22   b  for the lower sheet supply cassette  16   b  to a fixing device  28  that will be described later. In the transportation path  24 , a transferring device  32  and an image carrier  34  which will be described later are placed via a sheet transportation guide  30  on the upstream side of the fixing device  28 , and a registration roll  36  is placed on the upstream side of the transferring device  32  and the image carrier  34 . A discharge roll  38  is placed in the vicinity of the discharge port  26  of the transportation path  24 . 
   Therefore, a sheet which is selectively fed out from one of the sheet supply cassettes  16   a ,  16   b  by the nudger roll  18   a  or  18   b  is separated by the retard roll  20   a  or  20   b  and the feed roll  22   a  or  22   b , and then guided into the transportation path  24 . The sheet is temporarily stopped by the registration roll  36 , and then timely passed between the transferring device  32  and the image carrier  34  so that the toner image is transferred to the sheet. The transferred toner image is fixed by the fixing device  28 , and the sheet is then discharged to the discharge section  14  via the discharge port  26 . 
   The discharge section  14  is inclined so that the discharge port side is lower and the section is gradually raised as advancing toward the front face (the leftward direction in FIG.  1 ). The discharge section  14  is supported by the image forming apparatus main unit  12  so as to be swingable about the lower end of the section. When the discharge section  14  is upward swung to be opened, a process cartridge  44  which will be described later can be attached to and detached from the apparatus. 
   The fixing device  28  is configured by, for example, a heat roll  40  and a pressurization roll  42 . The heat roll  40  and the pressurization roll  42  pressingly contact each other to form a nip portion. When a sheet is passed through the nip portion, a toner image is fixed to the sheet. The fixing device  28  is positioned in the vicinity of the process cartridge  44 . In the embodiment, particularly, the heat roll  40  is placed so as to be opposed to the process cartridge  44 . 
   As shown also in  FIG. 2 , the process cartridge  44  has a process cartridge main unit  46 . The image carrier  34 , a charging device  48 , a developing device  50 , and a cleaning device  52  are integrally housed in the process cartridge main unit  46 . The image carrier  34  is formed by a photosensitive member or the like, and a latent image is formed on the image carrier by an optical writing device  54  which will be described later. The transferring device  32  which is configured by, for example, a transfer roll is placed so as to be opposed to the image carrier  34 . The charging device  48  is configured by, for example, a charging roll, and rotated with contacting with the image carrier  34  to uniformly charge the image carrier  34 . 
   The developing device  50  develops the latent image formed on the image carrier  34  by a toner, and has a first toner chamber  56 , a second toner chamber  58 , and a development chamber  60 . The first toner chamber  56  and the second toner chamber  58  are vertically arranged across an opening  62 . A first toner stirring and transporting member  64  is placed in the first toner chamber  56 , and second to fourth stirring and transporting members  66 ,  68 , and  70  are placed in the second toner chamber  58  to transport a toner to the development chamber  60 . The opening  62  is formed so that a scanning beam emitted from the optical writing device  54  which will be described later passes therethrough. The first toner chamber  56  and the second toner chamber  58  communicate with each other through both sides of the opening  62 , so that a toner in the first toner chamber  56  is transported into the second toner chamber  58 . A development roll  72  is placed in the development chamber  60 . The development roll  72  causes a toner image to be carried on a latent image on the image carrier  34 . 
   The cleaning device  52  has, for example, a cleaning blade  74  and a toner recovery chamber  76 , so that a toner which is scraped off by the cleaning blade  74  is recovered into the toner recovery chamber  76 . 
   The optical writing device  54  is placed in the image forming apparatus main unit  12 , and in the vicinity of the front face (in the vicinity of the right end in  FIG. 1 ) of the image forming apparatus main unit  12  so as to be parallel to the sheet supply cassettes  16   a ,  16   b . The optical writing device  54  has an optical writing device main unit  78 . A polygon unit  80  consisting of a polygon mirror and a motor for rotating the polygon mirror, a semiconductor laser (not shown), and other optical components (not shown) are housed in the optical writing device main unit  78 . The scanning beam is emitted through an emission window  82  which is formed in the optical writing device main unit  78  on the side of the process cartridge. The scanning beam then impinges on the image carrier  34  via the opening  62  of the process cartridge  44 . 
   The process cartridge  44  has a shutter  84  which opens and closes a side face of the image carrier  34  on the side of the transferring device  32 . As shown also in  FIG. 3 , the shutter  84  has: a support portion  86  which is supported swingably and movably by the process cartridge main unit  46 ; and a shield portion  88  which extends from the support portion  86 . The shutter  84  is guided by a guide (not shown) disposed in the image forming apparatus main unit  12  so as to be opened and closed in conjunction with attachment and detachment of the process cartridge  44 . Namely, when the process cartridge  44  is not attached to the apparatus, the shutter  84  is closed by an elastic member (not shown) to protect the side face portion of the image carrier  34  as shown in FIG.  2 . When the process cartridge  44  is attached to the apparatus, the shutter  84  is moved against the elastic member to a retract position where the side face portion of the image carrier  34  is exposed as shown in FIG.  1 . In the retract position, the shield portion  88  is opposed to the heat roll  40  of the fixing device  28  to block radiant heat from the heat roll  40 , thereby preventing the process cartridge  44  from being heated. 
   In the shutter  84 , a large number of air vent holes  90  are formed in parallel with the support portion  86  and in the shield portion  88  in the vicinity of the support portion. When the shutter  84  is in the retract position, a first gap  92  is formed between the shutter  84  and the process cartridge main unit  46 . The air vent holes  90  communicate with the first gap  92 . The first gap  92  constitutes part of an air passage  94  which will be described later. An air flow is produced in the first gap  92  by air which is introduced through the air vent holes  90 , to cool the process cartridge  44 . In the shutter  84 , as shown in  FIG. 4 , the shield portion  88  has a hollow structure, so that the heat insulating property of the shield portion  88  is enhanced by the air inside the shield portion  88 . 
   A suction fan  96  is placed inside the image forming apparatus main unit  12  and above the optical writing device  54 . An exhaust fan  98  is placed in approximately the middle of the rear face side of the image forming apparatus main unit  12 . Therefore, the suction fan  96  and the exhaust fan  98  are placed respectively on both sides of the process cartridge  44  so as to be opposed to each other across the process cartridge  44  in an approximately middle portion in the longitudinal direction of the process cartridge  44 . An air flow indicated by the arrows in  FIG. 1  is produced by the suction fan  96  and the exhaust fan  98 . The air passage  94  is a passage for forming the air flow. The suction fan  96  is not always required to be opposed straight to the process cartridge  44  as shown in  FIG. 1 , and may be placed at an arbitrary angle in accordance with the degree of the air flow and the portion to be cooled. For example, the fan may be placed in a direction parallel to a line perpendicular to the plane of the sheet of  FIG. 1  so as to be opposed straight to a power supply device  100  which will be described later. 
   Next, the air passage  94  will be described in detail. 
   The air passage  94  has a suction port (not shown) which is formed in a side face of the image forming apparatus main unit  12 . The suction port is connected to a first duct  102  through the power supply device  100  which is placed in parallel with the side face of the image forming apparatus main unit  12 , thereby cooling the power supply device  100 . An electric circuit board may be placed in place of the power supply device  100 , or an electric circuit board may be placed together with the power supply device  100 . 
   In the first duct  102 , as shown also in  FIG. 9 , an inlet  104  which is opposed to the power supply device  100  is formed in one end. The first duct  102  elongates from the inlet  104  to an approximately middle portion of the optical writing device  54 . As shown also in  FIGS. 5 ,  6 , and  8 , a projection  106  is formed on the front face (the left side in  FIG. 1 ) of the elongating portion. The projection  106  is opposed to the polygon unit  80  of the optical writing device  54 , so that air is introduced into the projection  106  to conduct efficient cooling particularly on the polygon unit  80 . A suction fan receiving portion  108  is formed in the rear face side (the right side in  FIG. 1 ) of the first duct  102 . The suction fan  96  is insertedly placed in the suction fan receiving portion  108 . 
   A second duct  110  is connected to the first duct  102  in the suction fan receiving portion  108  of the first duct  102 , and attached together with the first duct  102  to an upper portion of the optical writing device  54 . In the second duct  110 , as shown also in  FIG. 7 , a suction fan attachment portion  112  is disposed in approximately the middle of the front face. The suction fan  96  is attached to the suction fan attachment portion  112 . The second duct  110  has first air guide faces  114   a ,  114   b  which laterally extend from the suction fan attachment portion  112  to the respective sides. A second air guide face  116  is disposed so as to be opposed to the first air guide faces  114   a ,  114   b . Therefore, the air flow from the suction fan  96  is guided by the first air guide faces  114   a ,  114   b  and the second air guide face  116  to be spread to both the sides, and then supplied toward the process cartridge  44  with passing over the second air guide face  116 . 
   A second gap  118  is formed above the first toner chamber  56  and between the process cartridge main unit  46  and the discharge section  14 . In the discharge section  14 , a large number of air guide ribs  120  which protrude into the second gap  118  are formed in parallel with the air flow direction. Air flows to the sheet transportation guide  30  through the second gap  118  and the first gap  92 . 
   As shown in  FIG. 10 , the sheet transportation guide  30  has: a guide body  122 ; and many sheet transportation ribs  124  which protrude from the guide body  122  and elongate in parallel with the sheet transportation direction. The guide body  122  is formed into a lattice-like shape. A large number of air vent openings  126  are formed between the sheet transportation ribs  124 . The total opening area of the air vent openings  126  is larger than the bore area of the exhaust fan  98 , and hence air can smoothly flow through the air vent openings  126 . An exhaust port  128  is formed outside the exhaust fan  98  so that air is discharged through the exhaust port  128 . 
   Next, the function of the air cooling system based on the suction fan  96  and the exhaust fan  98  will be described. 
   When the suction fan  96  and the exhaust fan  98  are rotated, air is sucked trough an air suction port (not shown) which is formed in the side face of the image forming apparatus main unit  12 , and then introduced into the first duct  102  through the power supply device  100 . At this time, the sucked air absorbs heat from the power supply device  100  to cool the device. The air which is introduced into the first duct  102  is guided into the projection  106  to absorb heat from the optical writing device  54 , particularly, from the polygon unit  80 , thereby cooling the optical writing device  54 . Thereafter, the air passes through the suction fan  96  to enter the second duct  110 . In the second duct  110 , the air flow is spread to both the sides by the first air guide faces  114   a ,  114   b  and the second air guide face  116 , and then passes through an upper portion of the second duct  110  to be directed toward the process cartridge  44 . Since the second gap  118  is formed between the process cartridge  44  and the discharge section  14 , the air passes through the second gap  118 . Since the air vent holes  90  are formed in the shutter  84  and the first gap  92  is formed between the process cartridge main unit  46  of the process cartridge  44  and the shutter  84 , moreover, the air passes through the first gap  92 . The radiant heat from the fixing device  28  is blocked to some extent by the shield portion  88  of the shutter  84 . Furthermore, the heat of the process cartridge  44  is absorbed by the air flow passing through the first gap  92 , whereby the process cartridge  44  is cooled. Thereafter, the air passes through the lattice-like air vent openings  126  formed in the sheet transportation guide  30 , and then discharged to the outside of the image forming apparatus from the exhaust port  128  via the exhaust fan  98 . 
   As described above, according to the invention, a suction fan and an exhaust fan are disposed respectively on both sides across a process cartridge, and hence the process cartridge can be efficiently cooled.