Patent Publication Number: US-9432534-B2

Title: Image reading apparatus and image forming apparatus

Description:
This application is a continuation of U.S. application Ser. No. 14/286,180, filed May 23, 2014, which is incorporated herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image reading apparatus and an image forming apparatus including a hinge device that supports an opening/closing member such as an automatic document feeding device, which automatically sends an original to an image reading portion, to be opened or closed with respect to the apparatus main body of the image reading apparatus or the image forming apparatus. 
     2. Description of the Related Art 
     Conventionally, in a copying machine in which an automatic document feeding device is mounted, in a case where an original is copied, the automatic document feeding device disposed to be freely opened or closed with respect to transparent glass (hereinafter, referred to as an original base plate glass) disposed on the upper face of the apparatus main body is used in a closed state. Accordingly, the automatic document feeding device sequentially conveys originals to the original base plate glass in which an image reading portion is placed one at a time, and the originals can be automatically read one by one. In addition, instead of using the automatic document feeding device, by opening the automatic document feeding device to the apparatus main body, an original may be directly placed on the original base plate glass so as to be read. 
     In the automatic document feeding device, in order to automatically convey an original, many components such as various rollers and motors are built. Accordingly, the weight of the automatic document feeding device is several kilograms to several tens of kilograms, and an opening or closing operation cannot be easily performed as it is. Thus, generally, an opening/closing mechanism called a hinge device used for decreasing an operation force is included. 
     The hinge device has a spring built therein and applies a force in a direction opening the automatic document feeding device, in other words, a direction cancelling the weight (hereinafter, referred to as a “self-weight”) of the automatic document feeding device. Accordingly, the balance between the spring and the self-weight is set such that the automatic document feeding device can be lifted with a weak force at the time of opening and can be quietly closed at the time of closing. 
     In addition, there is an automatic document feeding device that includes a shock absorber that is an impact mitigating portion such as an oil damper in the hinge device. Since the oil damper generates a resistance force against the direction in which the automatic document feeding device is closed, there is an advantage of decreasing the closing speed of the automatic document feeding device so as to reduce a shock or a sound generated in accordance with the collision thereof with the apparatus main body. Accordingly, not only the original base plate glass, a driving portion of the automatic document feeding device, and the like are protected, but also oscillation delivered to the image forming apparatus is reduced, whereby disturbances in an image at the time of forming the image can be prevented. 
     In addition, as disclosed in Japanese Patent Laid-Open No. 3-184059, in order to easily replace an original on the original base plate glass, even when the hand is separated from the open automatic document feeding device, the automatic document feeding device is set to stay at the position (hereinafter, this state will be referred to as free stop). Furthermore, in order to maintain a state in which the automatic document feeding device securely lands on the original base plate glass, balance between the spring and the self-weight is set.  FIGS. 17A and 17B  illustrate a conventional example.  FIG. 17A  is a simplified view that illustrates each opening/closing angle state, and  FIG. 17B  is a diagram that represents the “magnitude relation between the spring and the self-weight” at each opening/closing angle converted into moment. 
     For example, a state in which the ADF (automatic document feeding device) is closed with respect to the original base plate glass disposed on the reader (image reading apparatus) side is represented as 0 degrees, and a vertical state is represented as 90 degrees. At this time, in a case where the opening/closing angle is in the range of 15 degrees to 70 degrees, a state is formed in which the spring and the self-weight are balanced, and thus, when the automatic document feeding device is in the free stop state, and the hand is separated therefrom, the automatic document feeding device does not fall in accordance with the self-weight. In addition, when the automatic document feeding device is opened up to 90 degrees, a case where a handle (a knob at the time of opening or closing) is not reached by the hand at the time of closing, a case where an impact is applied to the hinge device, or the like may be caused. Thus, actually, the opening angle of the automatic document feeding device is configured to be limited up to 70 degrees. 
     Furthermore, in a case where the opening/closing angle is in the range of 0 degrees to 15 degrees, a state is configured to be formed in which the spring&lt;the self-weight, so that the automatic document feeding device falls in accordance with the self-weight. Accordingly, the automatic document feeding device is configured not to be stopped in the state in which the automatic document feeding device is about half open with respect to the original base plate glass. By configuring the spring force of the hinge device to be sufficiently weaker than the self-weight of the automatic document feeding device, the automatic document feeding device securely lands on the original base plate glass. 
     When the automatic document feeding device does not securely land on the original base plate glass but is in a half-open state, the pressing force for the original placed on the original base plate glass is lowered, and accordingly, a defective image is generated, or a paper jam occurs when the automatic document feeding device is used. Accordingly, generally, the self-weight is set to be stronger than the spring force by about 2 to 3 Kgf as a whole at the position of the handle of the automatic document feeding device, and the state in which the automatic document feeding device is approximately half-open is avoided. 
     However, in the configuration disclosed in Japanese Patent Laid-Open No. 3-184059 or illustrated in  FIGS. 17A and 17B , the state of closing the original base plate glass is assured by setting the self-weight of the automatic document feeding device to be larger than the spring force, and accordingly, a force of about 2 to 3 Kgf is necessary for opening the automatic document feeding device. Thus, there is a limit on the decrease in the opening/closing force. 
     SUMMARY OF THE INVENTION 
     It is desirable to improve the user&#39;s operability. 
     According to the present invention, there is provided an image reading apparatus including: an apparatus main body; an opening/closing portion configured to be rotatable with respect to the main body, around a hinge shaft; a biasing portion configured to apply a force to the opening/closing portion in an opening direction to generate a moment of the hinge shaft rotation higher than the moment of the hinge shaft rotation according to self-weight of the opening/closing portion, in a state in which the opening/closing portion is in a range up to a predetermined rotation angle from a closed position with respect to the apparatus main body, and to generate a moment of the hinge shaft rotation that is substantially balanced with the moment of the hinge shaft rotation according to the self-weight of the opening/closing portion, in a state in which the opening/closing portion is opened more than the predetermined rotation angle; and a holding portion configured to maintain the opening/closing portion at the closed position. 
     Further features of the present invention will become apparent from the following description of illustrative embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external view of an image forming apparatus. 
         FIG. 2  is a schematic cross-sectional view of an image reading apparatus. 
         FIG. 3  is a block diagram of the circuit configuration and an image signal controller of the image reading apparatus. 
         FIG. 4  is a control block diagram of an image processing portion. 
         FIG. 5  is a diagram that illustrates relation between the self-weight of an automatic document feeding device and a spring force of a hinge device. 
         FIG. 6  is a cross-sectional view that illustrates the configuration of a hinge device according to a first embodiment. 
         FIG. 7  is a cross-sectional view that illustrates a free stop state of the hinge device according to the first embodiment. 
         FIG. 8  is a cross-sectional view that illustrates a tip-up state of the hinge device according to the first embodiment. 
         FIG. 9A  is a diagram that illustrates the configuration of a handle portion, and  FIG. 9B  is an enlarged view of a main part of the handle portion. 
         FIGS. 10A and 10B  are diagrams that illustrate a holding portion according to the first embodiment (the configuration of a magnet). 
         FIG. 11  is a cross-sectional view that illustrates a closed state of a hinge device according to a second embodiment. 
         FIG. 12  is a cross-sectional view that illustrates an open state of the hinge device according to the second embodiment. 
         FIGS. 13A and 13B  are diagrams that illustrate a holding portion according to the second embodiment (the configuration of a latch). 
         FIGS. 14A and 14B  are cross-sectional views that illustrate the configuration of a hinge device according to a third embodiment. 
         FIG. 15  is a diagram that illustrates relation between the self-weight of the automatic document feeding device and the spring force of the hinge device at the time of moving an adjustment portion to a lower side of the axis. 
         FIG. 16  is a diagram that illustrates relation between the self-weight of the automatic document feeding device and the spring force of the hinge device at the time of moving the adjustment portion to an upper side of the axis. 
         FIGS. 17A and 17B  are diagrams that illustrate a conventional example. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, illustrative embodiments of the present invention will be described in detail with reference to the drawings. However, the dimension, the material, and the shape of each constituent component described in the following embodiments and relative arrangements and the like thereof should be appropriately changed in accordance with the configuration and various conditions of an apparatus to which the present invention is applied. Accordingly, unless otherwise specified, the scope of the present invention is not intended to be limited thereto. 
     First Embodiment 
     Hereinafter, an image forming apparatus including a hinge device according to a first embodiment will be described with reference to  FIGS. 1 to 10B . Here, as the image forming apparatus including the hinge device, a copying machine as an image forming apparatus including an automatic document feeding device configured to be opened or closed is illustrated as an example. 
       FIG. 1  is a schematic configuration diagram of the image forming apparatus including the automatic document feeding device configured to be opened or closed. 
     An image forming apparatus  1  (hereinafter, referred to as an apparatus main body) illustrated in  FIG. 1  is configured by: a main body  100  thereof; a sheet cassette  33  that is mounted below the main body  100 ; and an automatic document feeding device (opening/closing member)  2  that is mounted on the upper face of the main body  100 . 
     In the main body  100 , an image forming portion is arranged at an approximately center portion thereof, and a feed portion is located on the lower side thereof. In addition, an image reading portion including a CCD or the like is arranged in the uppermost portion of the main body. In addition, a space is arranged between the image reading portion and the image forming portion so as to form a discharge space portion  34 . 
     In the main body  100 , the image forming portion forms an image on a sheet. The image forming portion is configured as a print engine employing a conventionally known electrophotographic system and has a laser writing portion, an electrophotographic process portion, a fixing portion, and the like, which are not illustrated in the figure, built therein. The feed portion includes the sheet cassette  33  and supplies a sheet to the image forming portion. 
     The image reading portion reads image information of an original. In the image reading portion, as illustrated in  FIG. 2 , a casing frame  102  is arranged, and, on the upper face thereof, a transparent glass  101  (hereinafter, referred to as an original base plate glass) is arranged. In addition, on the lower side thereof, an image reading unit (scan unit)  103  is arranged. 
     The automatic document feeding device  2  is mounted in the casing frame  102  disposed in the upper part of the main body  100  by a hinge device (hinge mechanism) disposed on the rear side of the apparatus and is supported by the upper face of the apparatus main body to be freely rotatable so as to open or close the original base plate glass  101  disposed on the upper face of the image reading portion. In the automatic document feeding device  2 , a bundle of originals (not illustrated in the figure) set on an original base plate  31  is conveyed from the upper side to the original base plate glass  101  one at a time. Then, after the originals are read and scanned by the image reading portion, the originals are sequentially discharged to an original discharge plate  32 . 
     When a copy is made without automatic feed, or when a book, a notebook, or the like is copied, the automatic document feeding device  2  may be used as a platen. 
     Next, a schematic configuration of an image reading apparatus according to an embodiment of the present invention will be described with reference to  FIG. 2 . 
     As illustrated in  FIG. 2 , an original base plate glass  101  is an original placement portion in which an original is placed, a casing frame  102  supports the original base plate glass ( 101 ), and an image reading unit (scan unit)  103  scans the original. In addition, a belt  104  moves the image reading unit (scan unit), and a pulley  105  drives the belt, and a motor  106  rotates the pulley. 
     The image reading unit  103  is configured by: a lighting unit  108  that lights up an original; reflecting mirrors  109 ,  110 , and  111  that guide light reflected on the original; a lens  112  that performs image formation of light; a CCD  113  that performs photoelectric conversion of imaged light and reads a resultant signal; and an electrical substrate  114  that drives the CCD. These components are integrally mounted on a carriage frame  107  as scan units. 
     In such a configuration, when image information of an original is read, the image reading unit  103  scans the original using the pulley  105  and the belt  104  by rotating the motor  106  while the original placed on the original base plate glass  101  is illuminated by the lighting unit  108 . The light hitting the original diffuses from the original face, is guided to the lens  112  by the reflecting mirrors  109 ,  110 , and  111 , and is imaged by the guide lens  112 . Thereafter, the imaged light is photoelectrically converted into an electric signal by the CCD  113 , and the signal is electrically read. 
     Units  301 ,  302 , and  303  of a white reference member provide white reference data used for shading correction, and, before the image of an original is read, the image reading unit (scan unit)  103  is moved up to this position, and shading correction is made. 
     In addition, a moving original reading glass (transparent glass)  115  is arranged and is located at a reading position in a case where the automatic document feeding device  2  is mounted. An original fed from a feed portion (not illustrated in the figure) of the automatic document feeding device  2  passes through the moving original reading glass  115 , and image information of the original is read by the image reading unit  103  that stops and is positioned below the moving original reading glass  115 . Furthermore, an inclined guide  116  is a guide member used for lifting the front end of the original passing through the moving original reading glass  115  and guiding the original to the inside of the automatic document feeding device again. 
     Next, the shading correction will be described with reference to  FIGS. 2 and 4 . 
     The shading correction performed by the image reading unit (scan unit)  103  is performed, as illustrated in  FIG. 2 , as the image reading unit (scan unit)  103  moves below a shading white board  302  that is installed to be parallel with the original base plate glass  101 . 
     Then, as illustrated in  FIG. 4 , based on the acquired image data, the image processing portion  210  performs various corrections such as a sensitivity correction using an analog signal processing portion  211 . Thereafter, in the image processing portion  210 , an A/D conversion portion  212  converts the signal into a digital image signal, and various corrections are made for the digital image signal by a gain control portion  213 , a shading correction portion  214 , a tone control portion  215 , and the like. Thereafter, the image data is transferred to an image forming apparatus (not illustrated in the figure) or the like as digital data. 
     Next, a block diagram relating to the control process of the above-described apparatus will be described with reference to  FIG. 3 . 
     A CPU circuit portion  400  includes a CPU  401  and controls a reading controller  201 , an image signal controller  405 , and an external I/F  406  in accordance with the setting of an operation portion  404  based on a program stored in ROM  402 . RAM  403  is used as an area that temporarily stores control data and as a work area of a calculation process accompanied with the control process. The external I/F  406  is an interface from a computer  407  and develops print data into an image and outputs the image to the image signal controller  405 . 
     The image processing portion  410  performs an image correction process or an editing process according to the setting of the operation portion. A line memory  411  performs a mirror image process for changing the main scanning direction and the like. The image stored in the line memory  411  is output through a page memory  412 . A hard disk  413  is used as is necessary when the page sequence is changed or the like. 
     Next, the configurations of the hinge device, the holding portion, and the handle portion according to this embodiment will be described with reference to  FIGS. 5 to 10B . 
       FIG. 5  is a diagram that illustrates magnitude relation between the self-weight of the automatic document feeding device  2  and the spring force of the hinge device by using moment in a case where the hinge device according to this embodiment is used. The horizontal axis represents the rotation angle (opening/closing angle) of the automatic document feeding device  2  with respect to the original base plate glass  101 , and the vertical axis represents the moment (a biasing force or a spring force). In the figure, a dotted line represents moment according to the self-weight of the automatic document feeding device  2 , and a solid line represents moment according to the spring force of the hinge device. In a range from the closed state to a predetermined rotation angle θ 1 , the moment according to the spring force of the hinge device is configured to be higher than the moment according to the self-weight of the automatic document feeding device  2 . In a range of a rotation angle θ 2  for which the automatic document feeding device is open more than the predetermined rotation angle θ 1 , the moment according to the self-weight of the automatic document feeding device  2  and the moment according to the spring force of the hinge device are set to be balanced. Accordingly, when the automatic document feeding device  2  is open, up to the predetermined rotation angle θ 1 , the automatic document feeding device  2  can be opened with a light force, and, in a state in which the automatic document feeding device is open more than the predetermined rotation angle θ 1 , the automatic document feeding device  2  can be stopped at a position desired by a user. 
       FIG. 6  is a cross-sectional view of the hinge device  10  according to this embodiment. The automatic document feeding device  2  is covered with a cover  3  that is an exterior configuring member. The automatic document feeding device  2  is attached to the apparatus main body  1  (casing frame  102 ) through the hinge device  10  so as to be opened or closed with respect to the original base plate glass  101 . The hinge device  10  supports the automatic document feeding device  2 , which is an opening/closing member, to be opened or closed with respect to the casing frame  102  that is the main body frame of the apparatus main body  1 . 
     The hinge device  10  includes: a hinge base  14  that is a first attachment member; a hinge arm  7  that configures a second attachment member; a lift arm  4 ; and a hinge shaft  13  that is connected to the hinge base  14  so as to allow the hinge arm  7  to be rotatable with respect to the hinge base. In addition, the hinge device  10  includes a biasing portion that is expanded or contracted in accordance with the rotation angle of the automatic document feeding device with respect to the apparatus main body  1  and applies a force to the automatic document feeding device  2  in an opening direction. The biasing portion is disposed between the hinge base  14  and the hinge arm  7 . Here, the biasing portion includes a compression spring  16  that is a first elastic member and a compression spring  12  that is a second elastic member and further includes a lower spring shaft portion  6 , a lower spring holder portion  15 , a upper spring holder portion  17 , and a upper spring shaft portion  18 . 
     The hinge shaft  13  is supported by the hinge base  14  that is the first attachment member, and the hinge base  14  is fixed to the apparatus main body  1  (casing frame  102 ). In addition, since the hinge shaft  13  axially supports the hinge arm  7  configuring the second attachment member, the hinge arm  7  is rotatable with respect to the hinge base  14 . 
     In addition, since the hinge arm  7  configuring the second attachment member supports the lift arm  4  configuring the second attachment member through the lift shaft  5 , the lift arm  4  is rotatable with respect to the hinge arm  7 . While a height adjustment screw  8  is fixed to the lift arm  4 , the height adjustment screw  8  is freely movable back and forth, and the front end abuts a part of the hinge arm  7 , whereby the height of the automatic document feeding device  2  with respect to the original base plate glass  101  can be adjusted. The lift arm  4  is fixed to the automatic document feeding device  2  (cover  3 ). 
     The lift arm  4  supports the upper spring shaft portion  18 . The upper spring shaft portion  18  axially supports the upper spring holder portion  17 . The upper spring holder portion  17  holds one end portion of each one of the compression springs  12  and  16 , and the lower spring holder portion  15  is arranged on the opposing side so as to hold the other end of each one of the compression springs  12  and  16 . The lower spring holder portion  15  is axially supported by the lower spring shaft portion  6 . The lower spring shaft portion  6  is fixed to the hinge base  14 . Accordingly, a gap between the upper spring shaft portion  18  and the lower spring shaft portion  6  changes in the opening/closing operation of the automatic document feeding device  2 , and the compression springs  12  and  16  are expanded and contracted in accordance therewith. 
       FIGS. 7 and 8  are cross-sectional views of the hinge device  10  in a case where the automatic document feeding device  2  is open up to angles θ 2  and θ 1 . By opening the automatic document feeding device  2 , a gap between the lower spring shaft portion  6  and the upper spring shaft portion  18  increases, and the reaction forces of the compression springs  12  and  16  are received, whereby a gap between the upper spring holder portion  17  and the lower spring holder portion  15  increases in accordance therewith. 
     As illustrated in  FIGS. 7 and 8 , in a case where the rotation angle (opening/closing angle) is any one of θ 1  and θ 2 , both ends of the compression spring  16  that is the first elastic member are in contact with the upper spring holder portion  17  and the lower spring holder portion  15 . Accordingly, in the case where the rotation angle is any one of θ 1  and θ 2 , the compression spring  16  acts as a biasing force for applying a force to the automatic document feeding device  2  in the opening direction. 
     In contrast to this, up to the predetermined rotation angle θ 1  from the state in which the automatic document feeding device  2  is closed with respect to the apparatus main body  1 , both ends of the compression spring  12  that is the second elastic member are in contact with the upper spring holder portion  17  and the lower spring holder portion  15  (see  FIG. 8 ). However, at the rotation angle θ 2  for which a state is formed in which the automatic document feeding device is open more than the predetermined rotation angle θ 1 , only the compression spring  16  is in contact with the upper spring holder portion  17  and the lower spring holder portion  15 , and one end portion of the compression spring  12  is configured to be separated from the upper spring holder portion  17  (see  FIG. 7 ). 
     In other words, as illustrated in  FIG. 8 , up to the rotation angle θ 1  from the closed state, the compression spring  12  acts together with the compression spring  16 , and the moment of the hinge shaft rotation according to the hinge device  10  is higher than the moment according to the self-weight of the automatic document feeding device  2 . Accordingly, between the closed state of the automatic document feeding device  2  and up to the rotation angle θ 1 , the automatic document feeding device  2  is opened in accordance with the forces of the compression springs  16  and  12 . Accordingly, up to the rotation angle θ 1  from the closed state, the opening/closing force of the automatic document feeding device  2  can be reduced. 
     On the other hand, as illustrated in  FIG. 7 , at the rotation angle θ 2  for which a state is formed in which the automatic document feeding device  2  is open more than the rotation angle θ 1 , the compression spring  12  does not act, but only the compression spring  16  acts, and accordingly, a state is formed in which the moment of the hinge shaft rotation according to the hinge device  10  (compression spring  16 ) and the moment according to the self-weight of the automatic document feeding device  2  are balanced. Accordingly, in the range of the rotation angle θ 2 , the automatic document feeding device  2  can be freely stopped at a free angle. Here, the state in which the moment according to the spring force of the compression spring  16  of the hinge device and the moment according to the self-weight of the automatic document feeding device  2  are balanced not only represents a state in which the magnitudes of the moments are precisely the same but also includes the following state. In other words, a state in which a force causing the automatic document feeding device  2  to rotate in accordance with a difference between the moment according to the spring force of the compression spring  16  and the moment according to the self-weight of the automatic document feeding device  2  is less than frictional resistance relating to the rotation of the automatic document feeding device  2 , and the state in which the automatic document feeding device  2  stops unless an external force is added to the automatic document feeding device  2  is also the state in which the two moments are balanced. 
       FIGS. 9A and 9B  are diagrams in which a portion near the handle portion  50  positioned at the approximately center portion of the front face of the automatic document feeding device  2  is extracted.  FIG. 9A  is a front view of a portion near the handle portion, and  FIG. 9B  is an enlarged view of the holding portion.  FIGS. 10A and 10B  are cross-sectional views taken along line A-A represented in  FIG. 9A .  FIG. 10A  is a diagram that illustrates a state (closed state) in which the automatic document feeding device  2  is held by the holding portion with respect to the apparatus main body (casing frame  102 ), and  FIG. 10B  is a diagram that illustrates a state in which the holding portion is released. 
     The handle portion  50  is used for opening the automatic document feeding device  2  and is disposed at the approximately center portion of the front face of the automatic document feeding device  2 . The handle portion  50  includes a handle  51  that serves as a grip when a user opens or closes the automatic document feeding device  2 . The handle  51  is attached to the automatic document feeding device  2  to be rotatable with respect to the automatic document feeding device using a rotation shaft  56 . As illustrated in  FIG. 10B , the rotated handle  51  is configured to be returned to the original position (a position illustrated in  FIG. 10A ) by a return spring  57 . 
     At both ends of the handle  51 , magnets (magnet catchers)  52  and  53  that configure the holding portion are disposed. In the apparatus main body  1  (the casing frame  102 ) that is on the opposite side of the magnets  52  and  53 , magnetic bodies  54  and  55  such as metal plates that configure the holding portion are disposed. The automatic document feeding device  2  maintains the closed state with respect to the apparatus main body  1  (the casing frame  102 ) depending on a magnetic coupling force according to the magnets  52  and  53  and the magnetic bodies  54  and  55  as the holding portions. The reason for disposing the holding portions on both end sides with the handle  51  being nipped therebetween is to maintain the automatic document feeding device  2  to be parallel to the apparatus main body  1  (the casing frame  102  and the original base plate glass  101 ). Although not illustrated in the figure, by arranging a unit that adjusts the attaching positions (heights) of the magnets  52  and  53 , the parallel state can be adjusted. 
     When the automatic document feeding device  2  is opened or closed, as illustrated in  FIG. 10B , the handle  51  is pressed in the direction of the arrow B. Accordingly, the handle  51  rotates around the rotation shaft  56 , and the magnets  52  and  53  attached to the handle  51  are separated away from the magnetic bodies  54  and  55  attached to the apparatus main body  1  (the casing frame  102 ), whereby the magnetic coupling force is released. When the magnetic coupling force is released, the automatic document feeding device  2  can be lifted up to the position of the rotation angle θ 1  by using only the spring force of the hinge device  10  (the compression springs  12  and  16 ). 
     Here, the positions of the handle  51 , the holding portions  52  to  55 , and the rotation shaft  56  will be described. As described above, in order to securely maintain the automatic document feeding device  2  with respect to the apparatus main body  1  (the casing frame  102 ), a predetermined force (for example, a force of about 2 to 3 Kgf as a whole) is necessary at the position of the handle  51 . In other words, also in this embodiment, a magnetic coupling force of about 2 to 3 Kgf is necessary. In this embodiment, as illustrated in  FIGS. 10A and 10B , the magnets  52  and  53  and the magnetic bodies  54  and  55  configuring the holding portions are arranged between the handle  51  and the rotation shaft  56 , and these holding portions are arranged as close to the side of the rotation shaft  56 . Accordingly, by using the principle of leverage, the holding force (magnetic coupling force) according to the holding portions can be easily released. 
     In this embodiment, as the holding portions, while the magnets  52  and  53  are disposed on the side of the automatic document feeding device  2 , and the magnetic bodies  54  and  55  are disposed on the side of the apparatus main body  1  (the casing frame  102 ), the holding portions may be respectively arranged on opposite sides. In other words, the holding portions may have a configuration in which the magnets  52  and  53  are disposed on the side of one of the apparatus main body  1  and the automatic document feeding device  2 , the magnetic bodies  54  and  55  are disposed on the side of the other, and the automatic document feeding device is maintained to be in the closed state (position) with respect to the apparatus main body in accordance with the magnetic coupling force. 
     Here, while two magnets and two magnetic bodies have been described to be arranged on both sides of the handle  51 , the numbers of the magnets and the magnetic bodies are not limited to two. In addition, while the handle  51  has been described as being configured to be rotated using the rotation shaft  56 , the configuration is not limited thereto as long as the holding portions can be retracted. 
     In addition, in this embodiment, while the handle portion  50  is disposed on the side of the automatic document feeding device  2 , the handle portion  50  may be disposed on the side of the apparatus main body  1 , and a configuration may be employed in which the holding state according to the holding portions can be released. 
     According to this embodiment, in the range up to the predetermined rotation angle θ 1  from the closed state of the automatic document feeding device  2  with respect to the apparatus main body  1 , the moment (biasing force) of the hinge shaft rotation according to the biasing portion is higher than the moment of the hinge shaft rotation according to the self-weight of the automatic document feeding device  2 . Accordingly, the automatic document feeding device  2  that is the opening/closing member can be opened using a weak force. 
     In addition, in the range of the rotation angle θ 2  for which the automatic document feeding device  2  is open with respect to the apparatus main body  1  more than the case of the predetermined rotation angle θ 1 , the moment (biasing force) of the hinge shaft rotation according to the biasing portion and the moment of the hinge shaft rotation according to the self-weight of the automatic document feeding device  2  are balanced. Accordingly, the automatic document feeding device  2  can be freely stopped at an arbitrary position, whereby the user&#39;s operability can be improved. 
     In this embodiment, in order to maintain the balanced state, as illustrated in  FIG. 5 , the moment of the hinge shaft rotation according to the biasing portion is set to be slightly higher than the moment of the hinge shaft rotation according to the self-weight of the automatic document feeding device  2 . The reason for this is that a change in the moment due to a variation of the self-weight of the automatic document feeding device  2  has been considered. In addition, in a case where the frictional resistance occurring when the hinge device rotates is high, the moment of the hinge shaft rotation according to the biasing portion may be set to be equal to or slightly lower than the moment of the hinge shaft rotation according to the self-weight of the automatic document feeding device  2 . 
     Second Embodiment 
     Next, a hinge device and holding portions according to a second embodiment will be described with reference to  FIGS. 11 to 13 . Since configurations other than the hinge device and the holding portions are the same as those of the above-described embodiment, the same reference sign is assigned to portions having the same function and the same configuration, and description thereof will not be presented. 
       FIGS. 11 and 12  are cross-sectional views of the hinge device  81  according to this embodiment. The hinge device  81  includes first and second attachment members  83  and  84  that are connected to a rotation shaft (hinge shaft)  82  so as to be relatively freely rotatable and a compression spring  85  that is an elastic member expanding or contracting in accordance with the rotation of the first and second attachment members  83  and  84 . In addition, a cam member  86  is fixed to the second attachment member  84 . An abutting portion  87   a  of a housing  87  housing the compression spring  85  that is one end of the elastic member is brought into contact with cam faces  86   a  and  86   b  of the cam member  86  so as to slide. 
     The first attachment member  83  configuring the hinge device  81  is fastened and fixed to the automatic document feeding device  2  by a fastening portion such as a screw not illustrated in the figure and rotates around the rotation shaft  82  together with the automatic document feeding device  2 . In addition, the second attachment member  84  that is connected to the first attachment member  83  through the rotation shaft  82  is fixed to the apparatus main body  1  (the casing frame  102 ). 
     One end of the compression spring  85  that is the elastic member expanding or contracting in accordance with the rotation of the first and second attachment members  83  and  84  abuts the cam face of the cam member  86  fixed to the second attachment member  84  through the housing  87  so as to be in contact therewith and slide. In addition, the other end of the cam member  86  is locked into a shaft  83   a  fixed to the first attachment member  83  through a housing  88  so as to be fixed thereto. 
     The shape of the cam face of the cam member  86  is appropriately set in consideration of the moment according to the self-weight of the automatic document feeding device  2  around the rotation shaft  82  and a desired opening/closing operation condition such as “a specific angle at which the automatic document feeding device stops” or “a specific angle from which the automatic document feeding device falls in accordance with the self-weight”. In this embodiment, the cam face is divided into two areas including a first cam face  86   a  as a first area and a second cam face  86   b  as a second area, and the cam faces are set so as to satisfy the following opening/closing operation condition. 
     The first cam face (first area)  86   a  of the cam member  86  is in contact with the abutting portion  87   a  of the housing  87  in the range of the rotation angles 0 degrees to β 1  (corresponding to the rotation angle θ 1  of the first embodiment). This first cam face  86   a  causes the moment according to the spring force of the hinge device higher than the moment according to the self-weight of the automatic document feeding device  2  to be generated. Accordingly, when the automatic document feeding device  2  is opened, the opening operation can be performed using a weak force. 
     The second cam face (second area)  86   b  of the cam member  86  is brought into contact with the abutting portion  87   a  of the housing  87  in the range of the rotation angle β 2  for which the automatic document feeding device  2  is open more than the case of the rotation angle β 1 . This second cam face  86   b  is in a state in which the moment according to the self-weight of the automatic document feeding device  2  and the moment according to the spring force of the hinge device are balanced. Accordingly, the automatic document feeding device  2  can be stopped at a position desired by the user. 
       FIGS. 13A and 13B  illustrates the configuration of the holding portion. The configuration of the handle portion is the same as that of the first embodiment described above, and only a part that is different from that of the first embodiment will be described. First, a locking projection  61  is a hook member disposed on the side of the automatic document feeding device  2 , and a pin  63  is a hook supporting portion disposed on the side of the apparatus main body  1  (the casing frame  102 ). The locking projection  61  configuring this holding portion is fixed to the rotation shaft  62 , and a handle  51  (the same configuration as that of the first embodiment and thus is not illustrated in the figure) is additionally fixed to the rotation shaft  62 . In other words, a configuration is employed in which, similar to the first embodiment, by pressing the handle  51  in the direction of arrow B illustrated in  FIG. 10B , as illustrated in  FIG. 13B , the rotation shaft  62  and the locking projection  61  are rotated so as to release a connection with the pin  63 . When the connection is released, the automatic document feeding device  2  can be lifted using only the spring force of the hinge device up to a position of the rotation angle β 1 . Thereafter, the locking projection  61  is returned to the original position by the spring  64 . The locking projection  61  and the pin  63 , similar to the first embodiment described above, in order to hold the automatic document feeding device  2  parallel to the apparatus main body  1  (the casing frame  102  and the original base plate glass  101 ), are disposed on both sides of the handle  51  (not illustrated in the figure). 
     In this embodiment, while the locking projection  61  (hook member) is disposed on the side of the automatic document feeding device  2 , and the pin  63  (hook supporting portion) is disposed on the side of the apparatus main body  1  (the casing frame  102 ) as the holding portions, the hook member and the hook supporting portion may be respectively arranged on the opposite sides thereof. In other words, a configuration of the holding portions may be employed in which the hook member is disposed on the side of one of the apparatus main body  1  and the automatic document feeding device  2 , the hook supporting portion is disposed on the side of the other, and the automatic document feeding device is maintained to be in the closed state with respect to the apparatus main body by locking the hook member into the hook supporting portion. 
     In addition, while two locking projections  61  and two pins  63  configuring the holding portions are arranged on both sides of the handle  51 , the numbers of the locking projections and the pins are not limited thereto. 
     In the first and second embodiments, instead of a configuration in which the automatic document feeding device  2  is caused to fall in accordance with the self-weight with respect to the apparatus main body (the casing frame  102 ), the configuration is employed in which the automatic document feeding device  2  is closed by the user. Accordingly, a shock absorber used in the hinge of the conventional example, in other words, an impact mitigating portion such as an oil damper is not necessary, which can contribute to reduced costs. 
     Also in this embodiment, in the range up to the predetermined rotation angle β 1  from the closed state of the automatic document feeding device  2  with respect to the apparatus main body  1 , the moment (biasing force) of the hinge shaft rotation according to the biasing portion is higher than the moment of the hinge shaft rotation according to the self-weight of the automatic document feeding device  2 . Accordingly, the automatic document feeding device  2  that is the opening/closing member can be opened easily. 
     In addition, in the range of the rotation angle β 2  for which the automatic document feeding device  2  is open with respect to the apparatus main body  1  more than the case of the predetermined rotation angle β 1 , the moment (biasing force) of the hinge shaft rotation according to the biasing portion and the moment of the hinge shaft rotation according to the self-weight of the automatic document feeding device are balanced. Accordingly, the automatic document feeding device  2  can be freely stopped at an arbitrary position, whereby the user&#39;s operability can be improved. 
     Third Embodiment 
     Next, an adjustment portion of a hinge device according to a third embodiment will be described with reference to  FIGS. 14A to 16 . Since configurations other than the adjustment portion are the same as those of the above-described first embodiment, the same reference sign is assigned to portions having the same function and the same configuration, and description thereof will not be presented. 
     In the third embodiment, in addition to the configuration of the first embodiment described above, an adjustment portion that can adjust the position of the compression spring  12  configuring the hinge device in the expanding/contracting direction is included. Since configurations other than the adjustment portion are the same as those of the above-described first embodiment, the same reference sign is assigned to portions having the same function and the same configuration, and description thereof will not be presented. 
     In this embodiment, as illustrated in  FIGS. 14A and 14B , an adjustment portion  19  that can adjust the position (height) of a compression spring  12  in the expanding/contracting direction is disposed on the side of a lower spring holder portion  15  so as to be in contact with the compression spring (second elastic member)  12  of a hinge device  10 . As illustrated in  FIG. 14B , the adjustment portion  19  has cut screw threads on the outer circumference and can move the position of the compression spring (second elastic member)  12  in the expanding/contracting direction by using an adjustment tool (not illustrated in the figure). By changing the position of the compression spring (second elastic member)  12  in the expanding/contracting direction using the adjustment portion  19 , a distance  71  between the end portion of the compression spring (second elastic member)  12  illustrated in  FIG. 7  and the upper spring holder portion  17  changes. Accordingly, the range up to the predetermined rotation angle θ 1  in which the compression spring (second elastic member)  12  starts to act when the automatic document feeding device  2  is closed can be changed. 
     For example, when the adjustment portion  19  is caused to act in the direction of a lower spring shaft portion  6 , the compression spring  12  also moves in the direction of the lower spring shaft portion  6 . Accordingly, a distance  71  between the end portion of the compression spring  12  and a upper spring holder portion  17  increases, and therefore, as illustrated in  FIG. 15 , the compression spring  12  starts to act at a rotation angle θ 3  that is smaller than the rotation angle θ 1  (see  FIG. 5 ) before the adjustment. In this embodiment, while the distance  71  between the compression spring  12  and the upper spring holder portion  17  is increased by moving the compression spring  12  in the direction of the lower spring shaft portion  6 , the same advantage can be acquired by arranging the adjustment portion on the side of the upper spring shaft portion  18  and positioning the upper spring holder portion  17  to be far from the compression spring  12 . 
     In addition, for example, when the adjustment portion  19  is caused to act in the direction of the upper spring shaft portion  18 , the compression spring  12  also moves in the direction of the upper spring shaft portion  18 . Accordingly, the distance  71  between the end portion of the compression spring  12  and the upper spring holder portion  17  decreases, and therefore, as illustrated in  FIG. 16 , the compression spring  12  starts to act at a rotation angle θ 4  that is larger than the rotation angle θ 1  (see  FIG. 5 ) before the adjustment. In this embodiment, while the distance  71  between the compression spring  12  and the upper spring holder portion  17  is decreased by moving the compression spring  12  in the direction of the lower spring shaft portion  6 , the same advantage can be acquired by arranging the adjustment portion on the side of the upper spring shaft portion  18  and approaching the upper spring holder portion  17  to the side of the compression spring  12 . 
     As described above, by disposing the adjustment portion  19  adjusting the position of the compression spring  12  configuring the hinge device in the expanding/contracting direction, the range up to the predetermined rotation angle in which the compression spring (second elastic member)  12  starts to act when the automatic document feeding device  2  is closed can be changed. 
     In addition, in the above-described embodiments, while the hinge device of the image forming apparatus has been described as an example as the hinge device that supports the opening/closing member to be opened or closed with respect to the apparatus main body, the present invention is not limited thereto. Thus, the hinge device may be a hinge device of an image reading apparatus such as a scanner. Furthermore, in the above-described embodiments, while the copying machine has been described as an example of the image forming apparatus, the present invention is not limited thereto. For example, the image forming apparatus may be another image forming apparatus such as a facsimile device or another image forming apparatus such as a multifunction apparatus combining such functions. By applying the present invention to a hinge device of the image forming apparatus or the image reading apparatus, the same advantages can be acquired. 
     While the present invention has been described with reference to illustrative embodiments, it is to be understood that the invention is not limited to the disclosed illustrative embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2013-124897, filed Jun. 13, 2013, which is hereby incorporated by reference herein in its entirety.