PATENT ABSTRACT
An image forming apparatus includes an apparatus casing installing an image formation section, an upper cover member that swingably covers and uncovers the apparatus casing, and an image reading unit supported by the apparatus casing via the upper cover member. A lock device is provided to maintain the upper cover member in a closed state. A unlock device is provided to unlock the lock device. A unlock operation section is displaced by an operator and activates the unlock device to operate when the lock device is unlocked. A unlock operation invalidating mechanism is provided to invalidate an unlock operation executed through the operation section by interrupting transmission of the displacement of the operation section to the lock device when unlock is prohibited

PATENT DESCRIPTION
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 USC §119 to Japanese Patent Application No. 2008-184750, filed on Jul. 16, 2008, the entire contents of which are herein incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an image forming apparatus, such as a copier, a facsimile, a printer, a multifunctional machine at least having two functions of these apparatuses, etc. 
         [0004]    2. Discussion of the Background Art 
         [0005]    A sheet internally ejecting type image forming apparatus, in which an image reading unit is mounted above an image printing unit at a prescribed interval, is well known. Also well known is a upper cover member that supports an image reading device and is upwardly swingable to allow accessing to the inside of the image printing section and maintenance or replacement of the consumables or the like. In such an image forming apparatus, when an operation section is regarded as a front side and the upper cover member swings around a rotational shaft arranged at the rear side of the apparatus, the front side of the apparatus is open, whereby maintenance or the like becomes convenient. Similarly, a platen cover provided to the image reading device so as to depress an original document also swings in the same direction as the upper cover member. 
         [0006]    In such an image forming apparatus, when the upper cover member is open in addition to the platen cover, the platen cover is largely open and possibly drops by its own gravity or bumps into surroundings. Because, the platen cover is integrally arranged above the upper cover. 
         [0007]    Then, the Japanese Patent Registration No. 3,644,376 proposes an image forming apparatus capable of preventing the upper cover and the platen cover from being simultaneously open using a lock device. 
         [0008]    However, usability is not excellent. Because, a handle is used to switch from locking to unlocking of the platen cover vice versa. Further, since the handle is secured to a body at the time of the locking, rigidity of parts needs be increased expecting application of a unreasonable force. 
       SUMMARY OF THE INVENTION 
       [0009]    In view of the above, it is an object of the present invention to resolve the mentioned and the other problems and provide a new and noble image forming apparatus including a cover lock device. 
         [0010]    Such a new and noble image forming apparatus includes an apparatus casing installing an image formation section, an upper cover member that swingably covers and uncovers the apparatus casing, and an image reading unit supported by the apparatus casing via the upper cover member. A lock device is provided to maintain the upper cover member in a closed state. A unlock device is provided to unlock the lock device. A unlock operation section is operated and displaced by an operator and activates the unlock device to operate when the lock device is unlocked. A unlock operation invalidating mechanism is provided to invalidate an operation of the operation section by interrupting transmission of the displacement of the operation section to the lock device when unlock is prohibited 
         [0011]    In another embodiment, the image reading unit includes an original document depressing member that swingably opens and closes an original document placing surface in the same direction as the upper cover member. The unlock operation invalidating device invalidates the operation executed through the unlock operation section when the original document depressing member is open. 
         [0012]    In yet another embodiment, the original document depressing member is configured to rise from the original document placing surface, and wherein said unlock operation invalidating mechanism invalidates the unlocking operation when the original document depressing member is rising from the original document placing surface. 
         [0013]    In yet another embodiment, the unlock operation invalidating mechanism includes a swinging member that swings between a non-unlock position where the transmission of the displacement of the unlock operation section to the lock device is interrupted and an unlock position where the transmission of the displacement is not interrupted. As wing operation member engages with the swinging member at its one end and configured to activate the swinging member. A linking member engages with the other end of the swing operation member and transfers one of the opening and rising movements of the original document depressing member to the swing operation member. The swinging member is swung by the swing operation member between the non unlock and unlock positions in accordance with a condition of the original document depressing member. 
         [0014]    In yet another embodiment, the image reading device is slidably movable by a prescribed length together with the linking member in relation to the upper cover member. The swing operation member includes a lengthy member having a length more than the prescribed length. The linking member always engages with the lengthy member wherever the image reading device is slidably moved. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]    A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
           [0016]      FIG. 1  is a schematic perspective view illustrating an exemplary image forming apparatus according to one embodiment of the present invention; 
           [0017]      FIG. 2  is a schematic vertical cross sectional view illustrating an exemplary interior structure of the image forming apparatus; 
           [0018]      FIG. 3  is a vertical cross sectional view illustrating an exemplary condition of the image forming apparatus when an upper cover is open; 
           [0019]      FIG. 4  is a perspective view illustrating an exemplary arrangement of a lock device for preventing the upper cover member from being open and a unlock device thereof; 
           [0020]      FIG. 5  is a side view illustrating an exemplary arrangement of the lock device for preventing the upper cover member from being open and the unlock device thereof; 
           [0021]      FIG. 6  is a perspective view illustrating an exemplary operation section included in the unlock device; 
           [0022]      FIG. 7  is a perspective view illustrating an exemplary condition when a depression button arranged on the operation section of the unlock device is depressed; 
           [0023]      FIG. 8  is an exploded perspective view illustrating an exemplary operation section of the unlock device; 
           [0024]      FIG. 9  is a chart illustrating an exemplary unlock and unlock restriction positions of the unlock device; 
           [0025]      FIG. 10  is a perspective view illustrating an exemplary operation section of the unlock device; 
           [0026]      FIG. 11  is a perspective view illustrating an exemplary arrangement of the unlock device; 
           [0027]      FIGS. 12A and 12B  collectively illustrate an exemplary positional relation between the platen cover and the unlock device during an opening/closing operation; 
           [0028]      FIG. 13  is a chart illustrating exemplary unlock positions of the unlock device and the lock device; 
           [0029]      FIG. 14  is a chart illustrating an exemplary arrangement of the unlock device at a unlock restriction position; 
           [0030]      FIG. 15  is a chart illustrating an exemplary scanner when viewed from its front side; 
           [0031]      FIG. 16  is a cross sectional view mainly illustrating an exemplary condition when a rail section of the scanner slides and fits into the left side drop out prevention section; 
           [0032]      FIG. 17A  is a cross sectional view illustrating the drop out prevention section preventing an image reading device from dropping out in a detaching direction when the image reading device does not slide in the support section in an initial condition; 
           [0033]      FIG. 17B  is a cross sectional view illustrating the drop out prevention section preventing an image reading device from dropping out in a detaching direction when the image reading device slides in the support section by the maximum stroke amount; 
           [0034]      FIG. 18  is a schematic view illustrating a principal part of a slide lock; 
           [0035]      FIG. 19  is a plan view illustrating exemplary left and right supporting sections partially depicting a lock linking mechanism provided therein; 
           [0036]      FIG. 20  is a cross sectional view illustrating a principal part of an exemplary slide lock provided in the other supporting section; 
           [0037]      FIGS. 21A to 21C  collectively illustrate exemplary transition of engagement of the lock member with grooves; 
           [0038]      FIG. 22  is a perspective view illustrating the lock device when the image reading device is unlocked; 
           [0039]      FIG. 23  is a perspective view illustrating the lock device when the image reading device is locked; 
           [0040]      FIG. 24  is a schematic vertical cross sectional view illustrating an exemplary operation member included in the lock device when the upper cover is closed; 
           [0041]      FIG. 25  is a schematic vertical cross sectional view illustrating the operation member of the lock device when the upper cover is open; 
           [0042]      FIG. 26  is a cross sectional view illustrating a first supporting section and an exemplary positional relation between the lock device that prevents the upper cover member from being open when a platen cover is open and a platen lock device when viewed from the front side of the apparatus; 
           [0043]      FIG. 27  is a plan view of the first supporting section of  FIG. 23 ; and 
           [0044]      FIG. 28  is a perspective view illustrating an exemplary hinge section attached to the platen cover. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0045]    Referring now to the drawings, wherein like reference numerals and marks designate identical or corresponding parts throughout several figures, in particular in  FIGS. 1 and 2 , an image printing section  2  is arranged in the middle of an apparatus body  1  of a tandem type color image forming apparatus. A sheet feeding section  20  is provided below the image printing section to feed a sheet for receiving an image formed in the image printing section  2 . An image reading device  30  is arranged above the image printing section  2 . 
         [0046]    In the image printing section  2 , plural drum type photoconductive members  3   a  to  3   d  are included as an image bearer to form different color toner images, respectively. As shown, yellow, cyan, magenta, and black toner images are formed on the surfaces of the photoconductive members  3   a  to  3   d , respectively. These photoconductive members  3   a  to  3   d  are arranged in parallel to each other at a prescribed interval. An intermediate transfer belt  4  is arranged below opposing the photoconductive members  3   a  to  3   d  as an intermediate transfer member. The intermediate transfer member can be a drum type, but an endless belt can be wound around plural supporting rollers  5  and  6  and is driven counter clockwise in the drawing. 
         [0047]    Around the photoconductive member  3 , there are provided a charge device  7  that charges the surface of the photoconductive member, an optical scanning device (LSU)  8  that emits a laser light with image information to the surface of the photoconductive member, a developing device  9  that visualizes a latent image formed on the surface of the photoconductive member  3  by means of exposure, a transfer device  10  opposing the photoconductive member  3  via the intermediate transfer belt  4 , and a cleaning device that removes and collects toner remaining on the surface of the photoconductive member  3  after the transfer process onto the intermediate transfer belt  4 . 
         [0048]    When image formation is started in the image forming apparatus, the photoconductive member  3  is driven and rotated clockwise in  FIG. 2 , and the surface of the photoconductive member  3  is charged in a prescribed polarity by the charge device  7 . Then, to the charged surface, the laser light is emitted from the optical scanning device  8  in accordance with the image information, thereby a latent image is formed on the photoconductive member  3 . The latent image is then visualized into a toner image by the developing device  9 . The toner image is then transferred onto the intermediate transfer belt  4  by the transfer device  10 . 
         [0049]    During the color image formation, all of the above-mentioned image formation operations are executed on the photoconductive members  3 , and then respective yellow to black toner images are superimposed one after another on the intermediate transfer belt  4 . Further, a secondary transfer roller  12  is arranged opposing the supporting rollers  6  via the intermediate transfer belt  4  in the image forming apparatus. 
         [0050]    In the sheet feeding section  20  arranged below the image printing section  2 , a sheet feeding tray  21  as a sheet container section for stacking sheets S such as a transfer sheet, a resin film, etc., is provided. Also provided are a sheet feeding roller  22  for launching the sheets S stacked on the sheet feeding tray  21 , a friction pad  23  serving as a separation device for separating the double feed sheets into one, and a re-conveyance path used for conveying the sheet S again during a duplex image formation or the like. 
         [0051]    The sheet S fed from the sheet feeding section  20  is launched toward a registration roller  13 , and bumps into a stopping registration roller  13  at its leading end. Thus, the sheet s is aligned. Then, the registration roller  13  starts rotating and launches the sheet S toward the secondary transfer section at a prescribed time so that the leading end of the sheets S coincides with a color toner image formed on the intermediate transfer belt  4  at the secondary transfer section in which the secondary transfer roller  12  is arranged. 
         [0052]    The sheet S receiving the non-fixed toner image at the secondary transfer section is conveyed to a fixing section  14 . When the non-fixed toner image is fixed onto the sheet S, the sheet S is ejected onto a sheet stacking section  18 a arranged on the upper surface of the apparatus body  1  via a sheet ejection section  25 . The toner sticking and remaining on the surface of the intermediate transfer belt  4  after the toner image transfer process is removed by a cleaner  15  for belt use. 
         [0053]    Even not shown, the image reading device  30  includes a platen serving as an original document placing section on which an original document is placed, a platen cover serving as an original document depressing member foe covering the platen, an automatic original document feeding device  32  integrally arranged with the platen cover  31 , and an original document scanning section (not shown) capable of reading the original documents manually set and fed by the automatic document-feeding device  32  onto the platen. 
         [0054]    Numeric number  16  denotes a control panel for operating the image reading device  30  and the image printing section  2 . The control panel  16  side serves as a front side of the image forming apparatus. A sheet ejection section  25  is arranged at the front side of the apparatus body  1 , and the sheets ejected from the sheet ejection section  25  to sheet stacking section  18   a , i.e., from front side to the rear side, when viewed from the front side. 
         [0055]    An upper cover member  18  is arranged above the apparatus body  1 . The upper surface of the upper cover member  18  is used as a sheet stacking section  18   a . The image reading device  30  is arranged above the upper cover member  18  with an appropriate interval while being supported by first and second supporting sections  50  and  51  arranged on the left and right side of the apparatus when viewed from the front side thereof. 
         [0056]    Accordingly, the sheet stacking section  18   a  is covered by the image reading device  30  to provide an internal sheet ejection type system is provided. 
         [0057]    In the internal sheet ejection type image forming apparatus, visibility at the sheet stacking section  18   a  and withdrawal of the sheets therefrom are restricted. Then, the image reading device  30  is supported by the first and second supporting sections  50  and  51  omitting the supporting section at a rear side of the upper cover member  18 . As a result, a light can enter not only from the front side but also from the rear side, thereby a light letting in performance is improved. In addition, even a lengthy sheet is used and ejected, the sheet can be stacked partially falling over the rear side of the apparatus body across the sheet stacking section  18   a.    
         [0058]    Further, to improve sheet extraction performance and visibility the image reading device  30  is slidably supported in a direction as shown by an arrow B of  FIG. 1 , and is slid toward the rear side, an interval from the sheet ejection section  25  on the apparatus body side to the image reading device  30  can be extended. Thus, a user having big hands can smoothly perform the sheet extraction operation. 
         [0059]    To the lower side surface of the upper cover member  18 , an optical scanning device  8  as a part of the image formation device is attached. Specifically, as shown in  FIG. 3 , the upper cover member  18  is attached to a fulcrum  17  arranged at the rear side of the apparatus body  1  and is upwardly openable by a handle  18   b  in a direction as shown by an arrow A. A cover lock device  60  is arranged on the apparatus body  1  to lock the upper cover member  18  when it is closed on the apparatus body  1 . 
         [0060]    As shown in  FIGS. 2 to 4 , the cover lock device  60  includes a supporting shaft  62  rotatively attached to the upper cover member  18  being horizontally extended, and plural lock claws  63  secured to both left and right sides of the supporting shaft  62 . The cover lock device  60  locks the upper cover member  18  with the apparatus body  1  when the lock claw  63  engages with an engagement section  1 A arranged on the apparatus body  1 . A bias spring  61  is arranged on the cover lock device  60  so as to always provide a rotational force to the supporting shaft  62  in a prescribed direction so that the lock claw  63  is biased and engages with the engagement section  1 A (see,  FIG. 2 ) arranged on the apparatus body  1 . When the upper cover member  18  is closed by the spring  61 , the locking is automatically achieved. 
         [0061]    The cover lock device  60  is unlocked by an unlock device  40  as shown in  FIGS. 4 and 5 . Specifically, as shown in  FIG. 3 , the upper cover member  18  is swung around the fulcrum  17  counterclockwise in  FIG. 2  and is open. Since the upper cover member  18  is open at the front side of the image forming apparatus, accessing to respective units in the image formation section from the front side and replacement and maintenance thereof can becomes easier. 
         [0062]    As shown in  FIGS. 4 and 5 , the unlock device  40  includes an operation section  41  having a depression button  42  for unlocking, and an unlock restriction device for restricting unlocking of the cover lock device  60 . Initially, the operation section  41  is described in detail. 
         [0063]    As shown in  FIGS. 4 to 8 , the depression button  42  is swingably attached to a holder at around a shaft  42 a. The holder  43  is screwed, for example, and secured to the upper cover member  18 . On the holder  43 , a spring  44  (see  FIG. 8 ) is arranged upwardly to bias and provided a rotational force to the depression button  42  around the shaft  42   a  in a direction as shown by an arrow C in  FIG. 6 . The depression button  42  thus biased by the spring in this way is held at a normal position as shown in  FIG. 6  when a protrusion section  42   b  arranged on a side surface opposite to the shaft  42   a  contacts an engagement claw  43   a  arranged on the holder  43 . When the depression button  42  is depressed, the button goes down (sinks) against the bias of the spring  44 , and is swung to a slide down the lower surface of the depression button  42  partially contacts the holder  43  as shown in  FIG. 7 . 
         [0064]    An oscillatable member  45  is attached to the depression button  42  via a pin  46  so as to rotate the supporting shaft  62  via an relay lever  64  secured to the supporting shaft so that the lock claw  63  deviates from the engagement section  1 A when the depression button  42  is depressed. The oscillatable member  45  oscillates between a non unlock position where an operation of the depression button  42  via the pin  46  is not conveyed to the cover lock device  60  as shown by a rigid line, and an unlock position that where the operation thereof is conveyed to the cover lock device  60  to unlock thereof. When the pin  46  is viewed from right above, the axis of the pin  46  forms a prescribed angle, 90 degree centigrade in this example, with that of the shaft  42   a  serving as a rotational fulcrum of the depression button  42 . 
         [0065]    A spring  47  is arranged on the oscillating member  45  to hold it at the unlock position, capable of unlocking the cover lock device  60  in response to an operation of the button  42 . Specifically, as shown in  FIGS. 11 and 13 , the oscillating member  45  is located being slightly distanced from the relay lever  64  of the cover lock device  60  at the unlock position. 
         [0066]    Thus, when a user depresses the button  42  to open the upper cover member  18 , the depression button  42  swings in a reverse direction to an arrow C around the shaft  42   a  as shown in  FIG. 7 . Then, the oscillating member  45  depresses the relay level  64  and rotates the supporting shaft  62  counterclockwise in  FIG. 4  (clockwise in  FIG. 5 ) against the bias of the spring  61 , and thereby the lock claw  63  disengages with the engagement section  1 A. At this moment, an appropriate pop up mechanism can be provided on the upper cover member  18  to slightly raise the upper cover member  18  just when the lock claw  63  disengages, so that the user can recognize unlocking. 
         [0067]    The unlock restriction device rotates and displaces the oscillating member  45  arranged between the depression button  42  and the cover lock device  60  to the non unlock position around the pin  46 , where the operation of the depression button  42  is not conveyed to the cover lock device  60 , to prohibit the upper cover member  18  from being open, when the platen cover  31  of the image reading device  30  is open. Specifically, at that time, the depression button can be depressed by a length, but is ineffective. Specifically, almost no resistance is caused when button is depressed. 
         [0068]    As shown in  FIGS. 6 and 7 , an operation pin  48  is planted on the right side surface of the oscillating member  45 . As shown in  FIG. 11 , one end  65 a of the lengthy lever  65  is swingably arranged to the upper cover member  18  via the shaft  66  almost extending from the front to rear sides of the sheet stacking section  18   a  and contacts the lower section of the operation pin  48 . As shown in  FIG. 5 , a convex section  70  is formed on the other end of the length lever  65  and upwardly protrudes and contacts the lower surface  72  of the unlock member  71 . The unlock member  71  has a prescribed thickness and is formed in a state of rectangles. The unlock member  71  is rotatively attached to the image reading device  30  around a rotational fulcrum  73  arranged on one side of a widthwise direction thereof. The image reading device  30  is slidable in a sheet ejection direction as mentioned later. The unlock member  71  is a length member longer than a sliding width of the image reading device  30  in a sliding direction. Thus, wherever the image reading device slides, a positional relation enabling the convex section  70  of the lengthy lever  65  to contact the unlock member  71  can be maintained. Further, the lengthy level  65  is generally held at a position where the operation pin  48  biased by the spring  47  contacts the one end  65   a . The convex section  70  either almost contacts or is separated from the lower surface  72  of the unlock member  71 . In this example, the convex section  70  is separated for the purpose of ease of explanation. 
         [0069]    Swinging of the unlock member  71  is restricted by a stopper, not shown, to a range between a lock position where the lower surface  72  of the unlock member  71  of  FIG. 12   a  depresses the convex section  70  and an unlock position where the lower surface  72  is separated from the convex section  70 . To the unlock member  71 , a rotational force is applied by a spring, not shown, around the rotational fulcrum  73  toward the unlock position where the convex section  70  is separated from the lower surface  72 . 
         [0070]    The unlock member  71  swings between the lock and unlock positions via a leg  76  of the operation member  75  operated by opening and closing movements of the platen cover  31  contacting the rear end of the unlock member  71 . The operation member  75  is attached to the image reading device  30  (not shown in  FIG. 10 ) and is rotatable around the fulcrum  77 . When the platen cover is open as shown by a dotted line in  FIG. 2 , the operation member  75  is free, and is held at the lock position while the leg  76  thereof contacts the unlock member  71  by means of a spring, not shown, as shown in  FIG. 12A . Specifically, the respective springs apply reverse rotational forces to the operation member  75  and the unlock member  71  to each other. However, since the spring biasing the operation member  75  exceeds that of the unlock member  71 , the unlock member  71  is held at the lock position when the operation member  75  is free. Then, when the platen cover  31  is closed, the operation member  75  swings counterclockwise around the fulcrum  77  as shown in  FIG. 12B . As a result of this swinging, the leg  76  of the operation member  75  is moved in a direction to separate from the unlock member  71 . The unlock member  71  swings clockwise around the rotational fulcrum  73  being biased by a spring force of the spring  74  and the lower surface  72  thereof separates from the convex section  70 . 
         [0071]    In this way, when the platen cover  31  is open, the unlock member  71  pushes up the convex section  70  via the lower surface  72 . The lengthy lever  65  then swings counterclockwise in  FIG. 5  (clockwise in  FIG. 11 ) around the shaft  66 . Simultaneously, one end  65   a  of the lengthy lever  65  swings the oscillating member  45  around the pin  46  in a throw up direction to the non-unlock position via the operation pin  48  as shown in  FIG. 10 . As shown by a rigid line of  FIGS. 9 and 14 , the oscillating member  45  at the non-unlock position does not contact the relay lever  64  even when the depression button  42  is depressed. Thus, depression movement of the depression button is ineffective. 
         [0072]    In this way, in the case of the non-unlock position, the depression button is not locked (not fixed) and can be depressed. However, the depression button scarcely receives a resistance at the time. As a result, a member does not need be materially strengthened expecting application of unreasonable force. 
         [0073]    Now, an exemplary sliding operation of the image-reading device is described with reference to  FIGS. 15 and 16 . In the widthwise direction of the image reading device  30 , i.e., both left and right side in a direction D perpendicular to a slide direction B of a sheet ejection direction, plural rail sections  33  and  34  are integrally formed as a slide contacting section. Respective of the rail sections  33  and  34  integrally formed with lower surfaces  33   a  and  34 a as slide contacting surfaces and protrusion sections  33   b  and  34   b . The rail section  33  includes a groove  33   c  extending in the sheet ejection direct (i.e., slide direction B of  FIG. 2 ). 
         [0074]    The image reading device  30  is slidably supported on the upper surfaces  52  (see  FIG. 4 ) serving as slide contacted surfaces formed on the respective supporting sections  50  and  51  via the lower surfaces  33   a  and  34   a  of the respective rail sections  33  and  34 , respectively. Rattling of the image reading device  30  created in a horizontal direction is suppressed by fitting two pins  55  protruding upward from the supporting section into the groove  33   c  formed in the rail section  33  of the image reading device  30  with a prescribed gap. 
         [0075]    In the supporting sections  50  and  51 , plural drop prevention sections  53  and  54  are integrally formed with the above-mentioned upper surfaces  52  at outsides thereof, respectively. 
         [0076]    By fitting the drop prevention sections  53  and  54  and into the protrusion sections  33   b  and  34   b  with a prescribed gap, drop out and rising upward of the image reading device  30  are suppressed. 
         [0077]    Otherwise, the drop out prevention sections can be formed at insides of the supporting sections  50  and  51 , while the protruding sections are formed at insides of the rails  33  and  34  of the image reading device  30 . Then, the drop out prevention sections of the supporting sections  50  and  51  fit into the protruding sections at the inside of the rails  33  and  34  with a prescribed gap, so that the same effect can be achieved. 
         [0078]    Now, an exemplary function of the drop out prevention section according to several embodiments is briefly described. In these embodiments, the drop out prevention section arranged on the supporting section at least prevents the upper unit (e.g. an image reading device  30 ) from being extracted from the supporting section. Specifically, even when a user carries the image forming apparatus by hand gripping the upper unit, the upper unit is at least not dropped out or separated from the supporting section. Further, rising and deformation does not cause breakage, cut, and functional damage on parts and members included in the entire image forming apparatus. Specifically, the drop out prevention section assures the image forming apparatus of a prescribed intensity conventionally neglected in an image forming apparatus. 
         [0079]    In this way, according to this embodiment, since the rails  33  and  34  are integrally formed with a casing of the image reading device  30 , and the lower surfaces  33   a  and  34   a  of the rails  33  and  34  slide along the upper surface  52  of the respective supporting sections  50  and  51 , a slide mechanism can be produced without additional parts at low cost. 
         [0080]    Since the drop out prevention sections  53  and  54  are integral with the supporting sections  50  and  51  collectively forming the supporting section  50 , respectively, additional parts are not needed for preventing the image reading device from being dropped out upward, thereby saving cost. 
         [0081]    Further, the drop out prevention sections  53  and  54  can be intensified to receive load at both left and right sides of the supporting sections  50  and  51 . Further, even when a force is applied to either a left or right side of the image reading device  30 , upward rising can be prevented. 
         [0082]    Otherwise, if the above-mentioned advantage or effect is not demanded by the same degree, drop out prevention sections  53  and  54  similar to those as mentioned above can be arranged on the side of the image reading device  30 , while slide contacting sections having slide contacting surfaces similar to those in the rail sections  33  and  34  can be integrally formed on the supporting sections  50  and  51 . 
         [0083]    When the drop our prevention sections are arranged both on the inside and outside of the supporting section, a space for arranging the other parts disappears. Since the supporting section needs arrangement of parts such as an open close buffering mechanism for the upper cover, etc., the drop out prevention section preferably does not take a space as far as possible. 
         [0084]    According to this embodiment, since the drop out prevention sections  53  and  54  are arranged in one of the outside and inside of the respective first and second supporting sections  50  and  51 , the drop out prevention sections do not largely take a space obtaining prescribed rigidity. 
         [0085]    As shown in  FIGS. 4 and 16 , the drop out prevention sections  53  and  54  are separated into the drop out prevention sections  53   a  and  54   a  arranged in the front side of the supporting sections  50  and  51 , and into the drop out prevention sections  53   b  and  54   b  arranged in the rear side thereof. Thus, when a force is applied to the front side of the image reading device  30 , the drop out prevention sections  53   a  and  54   a  receives the force. Where as when a force is applied to the rear side of the image reading device  30 , the drop out prevention sections  53   b  and  54   b  receives the force. As a result, the rising of the image reading device  30  can be accurately suppressed. Further, the other parts can be arranged in a space created between the drop out prevention sections separately arranged. 
         [0086]    In this embodiment, the drop out prevention sections are separated and arranged both in the front and rear sides of the supporting sections for the reason of a limited space or a mold configuration. However, the drop out prevention sections  53  and  54  can be arranged over the entire region of the supporting section. The drop out prevention sections  53  and  54  can be formed like box to increase intensity while further reinforcing with ribs or the like. Thus, intensity of the drop out prevention sections  53  and  54  can be increased, so that when a user applies an upward force to the image-reading device  30 , the drop out prevention sections  53  and  54  are not damaged or deformed at all. 
         [0087]    As mentioned above, the image reading device  30  can slide in a direction as shown by the arrow B in  FIG. 2 . Specifically,  FIG. 17A  illustrates an initial condition in which the image-reading device  30  does not slide in the support sections  50  and  51 .  FIG. 17B  illustrates a condition where the image-reading device  30  slides in the support sections  50  and  51  by the maximum stroke amount. When the image-reading device  30  is slidable, the image-reading device  30  needs be locked at plural positions not to move during usage. Thus, a lock mechanism is provided to the image reading device  30 . 
         [0088]    A lock mechanism for the image reading device  30  is arranged on the side of the supporting section  50  that slidably supports the image reading device  30 . An operation button  80  for unlocking the lock mechanism is also arranged on the side surface as shown in  FIG. 1 . 
         [0089]    As shown in  FIGS. 18 and 19 , a torsion coil spring  82  is attached to a shaft section  81  of the operation button  80  and biases the operation button  80  to the outside of the apparatus. A hook shape portion  80   a  is integrally formed with the operation button  80  and engages with a cut away section  35  formed on the image reading device  30  and prevents the image reading device from sliding (i.e., locks) when biased by the torsion coil spring  82 . As shown in  FIG. 1 , when the operation button  80  exposed to the side surface of the supporting section  50  is depressed against the bias of the torsion coil spring  82 , the engagement is released and the image reading device becomes able to slide. Plural (e.g. three) cut away sections  35  are provided on the image reading device  30 , and the image reading device  30  can be temporarily secured (i.e., locked) at the plural sections. 
         [0090]    In this embodiment, by also providing one more slide lock mechanism on the right side supporting section  51 , rattling of the image reading device  30  in the horizontal direction is decreased at the time of temporal locking. On the right side supporting section  51 , as shown in  FIG. 20 , a cylindrical lock member  90  having a corn shape head is always biased upward by a compression spring  91  and engages with a groove  36  formed on the image-reading device  30 . One end (upper end) of the compression spring  91  is engaged with a spring engagement section of the lower end section of the lock member  90 . The other end (lower end) is engaged with a spring engagement section  51 d integrally formed with the supporting section  51 . The operation button  80  of the left side supporting section  50  and the cylindrical lock member  90  are linked together using a flexible wire  92  as shown in  FIG. 19 . The right side end the side of the supporting section  51 ) of the wire  92  of  FIG. 19  is bent by 90 degree from the rear side to front side in  FIG. 19  (i.e., from the front to rear side of the sheet in  FIG. 20 ). The wire  92  then extends upwardly from the bottom and is linked with a hook engagement section in the drawing. Accordingly, by depression of the operation button  80 , two lock mechanisms can be operated linking with each other. Further, as shown in  FIG. 19 , the wire  92  is guided without relaxing by a groove, not shown, arranged on the rear side rib formed on the upper cover member  18  in the sheet stacking section  40  and a guide  57   a  included in the wire depressing member  57  attached to the rear side of the upper cover member  18 . By using the wire  92  for linking the left and right locking, lock mechanisms can readily be linked using a few parts even through a complex path. 
         [0091]    When the operation button  80  is depressed against the biases of the torsion coil and compression springs  82  and  91 , the wire  92  pulls and lowers the lock member  90 . As a result, the lock member  90  is disengaged with the groove  36  of the image-reading device  30 . At this moment, since the lock member  90  does not completely drop out from the groove  36 , the corn shaped head is still hooked by the groove  36  as shown in  FIG. 21B . In this state, when image reading device  30  is slid, since the groove  36  further pushes down the lock member  90 , the user can feel click touch. Further, since the user can also feel click touch when the lock member  90  is pushed down and engages with the lock member  90 , the use can recognize a lock position sensuously. 
         [0092]    However, when the platen cover  31  is open in the plural locations, the lock mechanism needs to move to the respective locations as the lock mechanism for continuously preventing the upper cover member  18  from being open. Then, the members from the depression button  41  to the lengthy lever  65  of a lock mechanism are arranged on the side of the upper cover member  18 , while the members from the unlock member  71  to the platen cover  31  are arranged on the side of the image reading device  30 . 
         [0093]    When the platen cover  31  is open even a little and the upper cover member  18  is then open in the image forming apparatus including the thus configured lock mechanism, the platen cover is prevented from being swung in the same direction along with the opening of the upper cover member  18  regardless of the slide stopping positions of the image-reading device  30 . 
         [0094]    To further increase such an effect, a platen lock device  100  capable of preventing a platen cover  31  from being improperly open even when the upper cover member  18  is open is preferably employed. One example of such a platen lock device  100  is herein below described. 
         [0095]    As shown in  FIGS. 22 and 23 , the platen lock device  100  includes a lock member  101  engaging with an engagement section  37  arranged on the platen cover  31  and a lock intermediate member  105  contacting the lock member  101  at an operation section  107  for moving the lock member  101 . 
         [0096]    The lock member  101  is rotatably supported by the image reading device  30  around a rotational fulcrum  102 . The lock member  101  includes a lock claw  103  engageable with the engagement section  37  at its upper side end. The lock member  101  also includes an operation piece  104  at its one side end opposite to the lock claw  103  about the rotational fulcrum  102 . 
         [0097]    The lock intermediate member  105  has a rectangular plate and is rotatably supported by the image reading device via the supporting shaft  106  attached to its one side in a lengthwise direction. The lock intermediate member  105  includes an operation pin  107  at its another side extending in the longitudinal direction contacting the operation piece  104  of the lock member  101 . The lock member  101  is biased by a spring, not shown, to cause the operation piece  104  to rotate around the rotational fulcrum  102  and contact the operation pin  107 . Thus, the operation piece  104  always contacts the operation pin  107 . 
         [0098]    The lock intermediate member  105  swings around the supporting shaft  106 , and its leading end side is seated on the cam shape portion  109  by a bias of the above-mentioned spring. As shown in  FIG. 24 , one end of the operation member  108  is rotatably attached to the apparatus body  1  via the shaft  110 , the other end being movable along the rail  112  of the apparatus body  1 . The cam shape portion  109  has substantially the same core center as the shaft  110 . 
         [0099]    When the upper cover member  18  is closed as an ordinary condition, the protrusion section of the cam shape portion  109  as shown in of  FIG. 22  contacts the lock intermediate member  105 . At this moment, the lock intermediate member  105  obliquely inclines upward about the supporting shaft  106 , while the lock claw  103  of the lock member  101  is disengaged with the engagement section  37 . Accordingly, the platen cover can freely be open. 
         [0100]    When the upper cover member  18  is upwardly open around the shaft  17  to replace a process cartridge or the like, the other end of the operation member  108  moves along the rail  112  arranged on the upper surface of the apparatus body  1  and below the region between the first and second supporting sections  50  and  51 , and whereby the operation member  108  rises as shown in  FIG. 25 . At this moment, the operation member  108  swings clockwise in  FIG. 23  around the shaft  110 , and a protrusion section of the cam shape portion  109  separates from the lock intermediate member  105  and a circular section thereof makes contact. Then, the lock intermediate member  105  swings clockwise around the supporting shaft  106 . Simultaneously, the lock member  101  is swung counterclockwise around the rotational fulcrum  102  and the lock claw  103  engages with the engagement section  37 , whereby the platen cover  31  becomes the locked condition as shown in  FIG. 21 . 
         [0101]    Thus, when the upper cover member  18  is open, the platen cover  31  of the image-reading device  30  is locked linking with such an opening operation. Accordingly, even when both of the upper cover member  18  and the platen cover  31  of the image reading device  30  are open around the rear side rotational fulcrum from the front side of the apparatus, the platen cover  31  is prevented from being open. Accordingly, a problem, such as damage, etc., of the upper cover member  18  caused by careless opening of the platen cover  31  can be resolved. 
         [0102]    Further, the platen lock device  100  is also enabled to lock the platen cover  31  all over the sliding contact position of the image-reading device  30 . Specifically, a width of the lengthwise direction of the lock intermediate member  105  is longer than a sliding contact width of the image reading device  30 . In addition, the operation member  108  is arranged at a prescribed position not deviated from the lock intermediate member  105 . Accordingly, since the lock intermediate member  105  always contacts the cam shape portion  109  of the operation member  108 , the platen lock device  100  can lock the platen cover  31  regardless of the position of the image-reading device. 
         [0103]    When the lock intermediate member  105  swings around the supporting shaft  106 , the surface of the lock intermediate member  105  is only required to swing between an upwardly inclined position as shown in  FIG. 22  and an almost horizontal position as shown in  FIG. 23 . Thus, the lock intermediate member  105  is held by a stopper, not shown, provided in the casing of the image reading device  30  at the horizontal position of  FIG. 23  not to further swinging downward. Accordingly, the lock intermediate member  105  can either contact the cam shape portion  109  of the operation member  108  or slightly separates therefrom at the almost horizontal position of  FIG. 23 . Further, since the lock intermediate member  105  does not protrude downwardly from the lower surface of the image reading device  30 , (i.e., a slide surface) when the stopper is provided as above, a problem of hardly smoothly sliding due to the protrusion can be resolved. 
         [0104]      FIG. 26  is a cross sectional view that illustrates both of a first supporting section  50  when viewed from the front side of the apparatus and an exemplary positional relation between a lock device that prevents a upper cover member  18  from being open when the platen cover  31  is open and the platen lock device  100 . 
         [0105]    Within the width of the upper cover member  18 , there are provided a convex section  70  engaging with the lower surface  72  of the unlock member  71 , a lengthy lever  65 , an operation member  108  engaging with the lock intermediate member  105 , and a cam shape portion  109  in both left and right directions. Further, the lengthy lever  65  is arranged along the surface of the sheet placing section  18   a  of the upper cover member  18  in an apparatus front and rear side direction. 
         [0106]    Whereas in the image reading device  30 , a unlock member  71  and the lower surface  72  engaging with the convex section  70 , a lock intermediate member  105  swingably engaging with the cam shape portion  109  of the operation member  108  are arranged without interfering with each other. Further, the operation member  75  is backwardly deviated from the lock claw  103  not to interfere therewith. 
         [0107]    The lock intermediate member  108  inclines clockwise as shown in the right upper portion of the drawing while contacting the cam shape portion  109  as described with reference to  FIG. 26 . As a result, the lock claw  103  deviates from an aperture of the protrusion member  37 . Specifically, the automatic document feeding device  32  can be open. 
         [0108]      FIG. 27  illustrates a plan view of the first supporting section  50  of  FIG. 26 . As apparent from  FIG. 27 , the intermediate lock member  105  and the unlock member  71  are swingably arranged in a left and right direction side by side in the leg of the image reading device  30  within the first supporting section  50 . Further, the lock member  101  and the operation member  75  position on the rear side of the apparatus body  1  in the image reading device  30  (i.e., outside of the carriage  130  in  FIG. 28 ). Further, the protrusion member  37  is arranged on the platen cover  31  as shown in  FIG. 28 , and extend to the operation member  75  and the lock member  101  when the platen cover is closed on the image reading device  30  as shown in  FIG. 25 . 
         [0109]    Thus, the protrusion member  37  includes a function of prohibiting and allowing the platen cover  31  to open by engaging and disengaging with the lock member  101  and that of prohibiting and allowing the upper cover member  18  to open by engaging and disengaging with the operation member  75 . 
         [0110]    Since the protrusion member  37  engages with the operation member  75  and a positional relation between the lower surface  72  and the convex section  70  come to a condition as shown in  FIG. 5  when the platen cover  31  is closed as shown by a rigid line in  FIG. 2 , the upper cover member  18  is allowed to be open. Further, when the upper cover member  18  is swung as shown in  FIG. 3 , since the engagement condition between the cam shape portion  109  and the lock intermediate member  105  shown in  FIG. 22  changes to that in  FIG. 23 , the platen cover  31  is prohibited to be open. 
         [0111]    Further, it is well known that the platen cover  31  is enabled to contact and separate in a up and down direction from and to a platen, not shown, to create parallel movement as a whole, so that the platen cover  31  can sufficiently depress a thick original document BO such as a book, etc., as shown in  FIG. 28 . For example, a hinge section  38  provided in the platen cover  31  fits into a hole  39  formed on the body of the image reading device  30 . When a thick original document is used, the hinge section  39  moves up and down along the hole  39 , so that the platen cover  31  floats from the platen as a whole and thereby capable of appropriately depressing the thick original document. 
         [0112]    When the platen cover  31  floats and is swung in the same direction as the upper cover member  18  is open, the platen cover  31  can drop out from the body of the image reading device  30 . 
         [0113]    Then, the unlock member  71  is held at a lock position, because the protrusion member  37  dose not contact the operation member  75  when the platen cover  31  floats and depresses the book like thick original document. Accordingly, even when the platen cover  31  floats, the upper cover member  19  can be prohibited to open as in the case when the platen cover  31  is open. 
       Advantage 
       [0114]    According to the present invention, the operation section is not secured when the original document depression member is open and the upper cover member is locked, and the unlock operation is made ineffective. Thus, rigidity of members including the operation section is not accurately needed by the image reading device can be provided at low cost. 
         [0115]    Obviously, numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.