Abstract:
To form a printer device having the framework which is connected to a plurality of frames, there are included a main frame, as a lower frame adjacent to a surface of a table, etc. on which the printer device is arranged, and a sub-frame which is separated from the main frame. The sub-frame is connected to the main frame at three points. A plurality of image formation units and a conveyer belt are supported by the sub-frame. Even if the main frame is tilted over one side or the other as a result of an external factor, such as a warped surface of the table, such unstable arrangement of the printer device has no effect on the sub-frame. Hence, the engine parts of the image formation units supported by the sub-frame can desirably function. In this structure of the printer device, positional deviation does not occur in image components to be printed, and high quality printing can be performed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a printer device which includes a lower body, and an upper body which can be opened away from and closed toward the lower body, and, more particularly, to a printer device having a connection structure for connecting a plurality of frames forming the framework of the printer device.  
           [0003]    2. Description of the Related Art  
           [0004]    Conventionally, a well-known printer device includes an image formation unit which is attachable to and detachable from the printer device, and comprises a lower body and an upper body which can be shifted upward from the lower body for the maintenance sake.  
           [0005]    [0005]FIG. 13 illustrates an outside perspective view of a conventional monochrome printer device. In the illustration, a printer device  1  comprises a roof  2 , which forms an upper body, and a lower body  3 . The roof  2  includes a paper outputting section  5  from which papers are output onto the roof  2 , and a paper outputting tray  6  for outputting papers one on top of another. The lower body  3  includes a front cover  7  which can be opened and closed in the front section of the lower body  2 , and a paper cassette  8  which is detachable from and attachable to the lower body  3 . An MPF (Multi Paper Feeder) tray  9  which can be contained in the lower body  3  is arranged on the right side of the printer device  1 . An operational display section  4  for inputting information to the printer device  1  or for displaying the state of printer device  1  is arranged on the right upper side of the printer device  1 .  
           [0006]    In such a printer device  1 , the roof  2  is opened in a direction shown with an arrow B centrically at a rotational axis A, when clearing a jam occurring in the printer device or carrying out maintenance operation. FIG. 14 shows a cross sectional view of the printer device together with the internal structure thereof. As illustrated in FIG. 14, the printer device  1  comprises: a paper cassette  8  which is detachable from and attachable to the printer device  1 ; a paper feeding roller  12  which sequentially feeds papers contained in the paper cassette  8 ; a pair of suspension rollers  13  which suspend a received paper and send the paper to an image formation section  11  at a redetermined timing, in association with a pair of paper outputting roller  18 ; a fixation unit  14  which fixes a toner image onto a paper; the pair of paper outputting rollers  18  (a driving roller  18   a  and a driven roller  18   b ) which output the paper onto which the toner image is fixed; and an operational display section  4  for performing various settings for the printer device  1  or displaying the state of the printer device  1 .  
           [0007]    In the image formation section  11 , a charger  25  uniformly charges electric charges onto the circumferential surface of a photosensitive drum  23 . A printing head  26  selectively exposes the circumferential surface of the photosensitive drum  23  based on printing data. The electric potential of a portion of the photosensitive drum  23 , whose circumferential surface is exposed, is lower than that which is charged with electricity. Hence, an electrostatic latent image is formed on the circumferential surface of the photosensitive drum  23 . A developing unit  27  transfers internally contained toner onto the low potential section of the photosensitive drum  23  through a developing roller  27   a  so as to develop the electrostatic latent image. A transfer unit  28  transfers the toner image on the photosensitive drum  23  onto a paper to be conveyed, with an electric field whose polarity is opposite to that of the toner.  
           [0008]    The photosensitive drum  23 , the charger  25 , the developing unit  27 , the transfer unit  28 , a cleaner  24 , etc. which are included in the image formation section  11  are included in the lower body  3 , while the printing head  26  is arranged on the roof  2  as the upper body.  
           [0009]    The roof  2  can be opened and closed centrically about a hinge section  15  in both directions as shown with arrows B and B′. At this time, the printing head  26  and the driven roller  18   b  are incorporated with the roof  2  so as to be opened and closed altogether. The roof  2  shown with a straight line in FIG. 14 is in the state where it is closed, while the roof  2  shown with a double dot chain line is in the state where it is opened. To keep the roof  2  opened, a body locking mechanism  16  is arranged. The locking mechanism  16  is composed of a hook  17   a  arranged on the lower body  3  and an engagement section  17   b  which is arranged on the roof  2  and engaged with the hook  17   a.    
           [0010]    The image formation section  11  mainly forms a cartridge CT as an image formation unit which is detachable from and attachable to the lower body  3 . The cartridge CT includes the first cartridge CT 1  comprising the photosensitive drum  23  and the cleaner  24 , etc, and the second cartridge CT 2  including the developing unit  27 . The cartridge CT is dividable into the cartridges CT 1  and CT 2 . In the state where the roof  2  is opened, the cartridges CT 1  and CT 2  can be detached from and attached to a predetermined installation section of the lower body  3 . If a photosensitive drum  23  is deteriorated or if toner ran out, for example, the cartridge CT 1  or CT 2  can be replaced with a new cartridge, or other expendable supplies can be provided as needed, thus achieving the machine maintenance operation of the printer device.  
           [0011]    Today, color printer devices (color image formation devices) are widely used, and various color printing methods are employed. For example, according to one technique, a plurality of developing units are arranged adjacent to the circumferential surface of one photosensitive drum, and toner images are sequentially formed on the surface of the drum (technique (I)). There is another technique (II), which employs an intermediate transcription medium in a drum-like form. A plurality of image formation units are arranged in a predetermined direction, and toner images are sequentially output on one top of another on a paper so as to form an image (what is so-called a tandem-type printing technique).  
           [0012]    In the above technique (I), it is necessary to use a large-sized photosensitive drum, and it is difficult to form an image formation section in one unit, resulting in low printing performance. In the above technique (II), because the intermediate transcription medium is used, the size of the printer device itself is formed large.  
           [0013]    It is demanded that tandem-type color printer devices with an excellent shape can perform high-speed printing. In this type of printer device, image formation units of, for example, yellow (Y), magenta (M), cyan (C), and black (K) are used. Such image formation units are articles of consumption which are to be used up, thus need to be replaced with new ones periodically.  
           [0014]    In the printer devices having the structure shown in FIGS. 13 and 14, the image formation unit is formed in the lower body  3 . In this structure, the first cartridge CT 1  and the second cartridge CT 2  are arranged in the lower body  3 . The fixation unit  14  is also arranged in the lower body  3 . In the case where the printer device  1  is arranged on a warped surface of a table, etc., a slight twist occurs in the lower body  3 . This slight twist has an effect on the image formation unit arranged in the lower body  3  and a conveyer mechanism for conveying papers. Especially, in a tandem-type color printer, it is important to adjust the printing positions of toner images of Yellow (Y), Magenta (M), Cyan (C), and Black (K). In the above-described structure, shear occurs in the printing, thus causing the printing quality to be deteriorated.  
         SUMMARY OF THE INVENTION  
         [0015]    The present invention has been made in consideration of the above problems.  
           [0016]    It is accordingly an object of the present invention to provide a printer device performing high quality printing and having a frame connection structure for desirably maintaining the functions of engine parts of image formation units, etc. without any effect of unstable arrangement of the printer device which is caused by an external factor, such as a warped surface of a table on which the printer device is placed.  
           [0017]    In order to accomplish the above object, according to an aspect of the present invention, there is provided a printer device, having framework including a plurality of framing members connected with each other, comprising: an image holding body;  
           [0018]    writing means for writing an image in accordance with an image signal onto the image holding body;  
           [0019]    image formation means for adhering a pigment to the image which is written onto the image holding body by the writing means; and  
           [0020]    paper conveyer means for conveying a paper to transcription means for transcribing the pigment, which is adhered onto the image holding body by the image formation means, onto the paper, and  
           [0021]    the plurality of framing members including  
           [0022]    a lower frame which is arranged on a lower section of the printer device and adjacent to an installation surface of the printer device, and  
           [0023]    a sub-frame which supports the image holding body and the writing means, and  
           [0024]    the sub-frame being connected with the lower frame at three connection points, and being unlikely to be twisted even if the lower frame is twisted as a result of unstable arrangement of the lower frame.  
           [0025]    In the above structure, the image holding body is a member for forming and retaining a toner image on a photosensitive drum. The writing means is means for optically writing an image from a printing head. The image formation means is developing means, such as a developing roller for forming a toner image on the surface of the image holding body. The paper conveyer means conveys papers output from a feeding cassette, etc. to the image holding body via a suspension roller. Further, the lower frame forms one of a plurality of frames, and supports the lower section of the printer device in a position adjacent to the printer. The sub-frame is separated from the upper body, and supports the image holding body and the writing means.  
           [0026]    According to the structure, the sub-frame which is separated from the lower frame is likely to desirably function without any effect of a slight twist of the upper frame. In the three-point connection structure, wherein the lower frame and the sub-frame are connected at three connection points, the sub-frame hardly gets an effect of a positional deviation of the lower section of the printer device.  
           [0027]    In the printer device having the above-described structure, the lower frame and the sub-frame are formed approximately in a rectangular shape, and  
           [0028]    the lower frame and the sub-frame are connected with each other at two connection points on a predetermined side of the rectangular shape, and the lower frame and the sub-frame are connected with each other at one point on a side facing the predetermined side of the rectangular shape.  
           [0029]    According to the above structure, the lower frame and the sub-frame are firmly connected with each other. At the same time, the position device of the lower section of the printer device hardly has an effect on the sub-frame.  
           [0030]    The sub-frame further supports the paper conveyer means.  
           [0031]    According to the above structure, the position of papers conveyed by the paper conveyer means and the position of the image holding body supported by the sub-frame are stably determined regardless of the position deviation of the lower section of the printer device.  
           [0032]    The image holding body, the wiring means and the image formation means are incorporated with each other so as to form an image formation unit; and  
           [0033]    the printer device is a tandem-type printer device including a plurality of image formation units respectively corresponding to a plurality of colors. Having applied the frame connection structure of the present invention into such a tandem-type color printer, the deviation occurring in a plurality of image components corresponding to toner colors can effectively be prevented. This results in high quality color printing.  
           [0034]    According to the above-described frame connection structure of the printer device, even if the lower section of the printer device tilts over one side, the image formation units supported by the sub-frame can stably be operated. Therefore, in this structure, no deviation should occur in image components to be printed and the image components corresponding to the toner colors, thus providing high quality color printing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]    The object and other objects and advantages of the present invention will become more apparent upon reading of the following detailed description and the accompanying drawings in which:  
         [0036]    [0036]FIG. 1 is an outside perspective view of a printer device, according to one embodiment of the present invention, which is so-called a tandem-type color printer;  
         [0037]    [0037]FIG. 2 is an outside perspective view of a state of the printer device of FIG. 1, wherein a front cover of the printer device is opened;  
         [0038]    [0038]FIG. 3 is an exemplary cross sectional view of the internal structure of the printer device;  
         [0039]    [0039]FIG. 4 is a perspective view of the frame connection structure of the printer device;  
         [0040]    [0040]FIG. 5 is a perspective view for explaining the arrangement of a plurality of frames included in the printer device;  
         [0041]    [0041]FIG. 6 is an assembly diagram for explaining the relationship between the main frame and the sub-frame of the printer device;  
         [0042]    [0042]FIG. 7 is an outside perspective view for explaining a state of the printer device, wherein an upper body is opened by a link mechanism included in the printer device;  
         [0043]    [0043]FIG. 8 is a schematic diagram of the link mechanism which is viewed from the left side surface of the printer device;  
         [0044]    [0044]FIG. 9 is a schematic diagram of the link mechanism which is viewed from the right side surface of the printer device;  
         [0045]    [0045]FIG. 10 is a schematic perspective view of the link mechanism which is taken away from the printer device;  
         [0046]    [0046]FIG. 11 is a diagram showing a driving mechanism having a link structure in the printer device;  
         [0047]    [0047]FIG. 12 is a perspective view showing the principal components of a main frame and a sub-frame in the frame connection structure of the printer device according to a modification of the present invention;  
         [0048]    [0048]FIG. 13 is a diagram showing the entire structure of a monochrome printer device as a conventional printer device; and  
         [0049]    [0049]FIG. 14 is a diagram showing the internal structure of the monochrome printer device of FIG. 13. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0050]    [0050]FIG. 1 is a diagram for explaining a frame connection structure of a printer device of this embodiment. The printer device of this embodiment is an example of a so-called tandem-type color printer for both-side printing. In the illustration, a printer device  31  is connected to a host apparatus, such as a personal computer or the like, via a non-illustrative cable.  
         [0051]    The printer device  31  comprises an upper body  32  and a lower body  33 . The upper body  32  includes an operational panel  34  and an output tray  35  for printing papers which is arranged on the surface of the upper body  32 . The operational panel  34  comprises a key operational section  34   a  including a plurality of keys, and a liquid crystal display  34   b  for displaying information which is output under the control of a non-illustrative CPU. The output tray  35  accepts output papers, on which image data is printed by later-described image formation units, which are transported by the rotation of a paper outputting roller  36 . Papers are subsequently output onto the output tray  35  one on top of another.  
         [0052]    The lower body  33  includes a conveyer unit for both-side printing, as will be explained later, and a feeding cassette  38  which are installed in the lower body  33 . After a non-illustrative lid arranged on the side surface of the printer device  31  is opened, for example, the conveyer unit can be detached from and attached to the lower body  33 . The lower body  33  includes a front cover  37  which can be opened and closed in front of the lower body  33 , and the feeding cassette  38  which are detachable from and attachable to the lower body  33 . The front cover  37  is opened, while clearing any jams occurring in the printer device  31  or during the machine maintenance.  
         [0053]    Arranged on the right-side surface of the lower body  33  are an installation section  39  for an MPF (Multi-Paper Feeder) tray and a cover  40 . FIG. 1 shows the state of the printer device  31  in which the MPF tray is not installed in the installation section  39 . The cover  40  is one prepared for checking a paper conveyer path, and is opened so as to carry out a maintenance operation for clearing a jam caused by a paper stacked somewhere inside the printer device  31 .  
         [0054]    [0054]FIG. 2 is an outside perspective view of the printer device  31  of this embodiment, and shows a state in which the front cover  37  and the cover  40  are both opened. The feeding cassette  38  is included in the most lower stage of the printer device  31 . When providing the feeding cassette  38  with paper, a knob  38   a  is pulled out, for example, thereby the feeding cassette  38  can be pulled out in an X-direction.  
         [0055]    [0055]FIG. 3 is an exemplary cross sectional view for explaining the internal structure of the printer device  31  having the so-far described appearance. In the illustration, the printer device  31  comprises an image formation section  41 , a conveyer unit  42  for both-side printing, and a paper feeding section  43 , and the like. The image formation section  41  includes four image formation units  44  to  47  along the paper conveyer path. Those image formation units  44  to  47  include units for respective colors of magenta (M), cyan (C), yellow (Y) and black (K) sequentially in a direction from the right side to the left side of the printer device  31  in the illustration. The image formation units  44  to  46  for colors of (M), (C) and (Y) are prepared for color printing with subtractive mixture of colors. The image formation unit  47  for (K) is prepared for monochrome printing.  
         [0056]    Each of the image formation units  44  to  47  includes a drum unit C 1  and a toner unit C 2 . Each of the image formation units  44  to  47  has the same structure as each other, except the color of toner in the toner unit C 2 . Hence, in this embodiment, explanations will be made to the image formation unit  46  for (Y) by way of example. The drum unit C 1  includes a photosensitive drum, a charger, and a cleaner. The toner unit C 2  includes a developing roller, a toner, etc. The circumferential surface of the photosensitive drum  50  is formed of an organic optical-conductive material, for example. A charger  51   a,  a printing head  51   b,  a developing roller  51   c,  a transcription unit  51   d,  and a cleaner  51   e  are arranged adjacent to the photosensitive drum  50 . The photosensitive drum  50  rotates in a direction as shown with an arrow (in a clockwise direction in the illustration). The circumferential surface of the photosensitive drum  50  is uniformly charged with an electric charge from the charger  51   a.  An electrostatic latent image is formed on the circumferential surface of the photosensitive drum  50  by optical writing based on printing information from the printing head  51   b,  thereby to form a toner image by the developing roller  51   c.  At this time, the toner image formed on the circumferential surface of the photosensitive drum  50  is formed with a toner of yellow (Y) contained in the image formation unit  46 . The toner image thus formed on the circumferential surface of the photosensitive drum  50  reaches the transcription unit  51   d  along with the rotation of the photosensitive drum  50 , and is transcribed onto a paper which is conveyed in accordance with a direction, shown with an arrow in the illustration, immediately blow the photosensitive drum  50 .  
         [0057]    The drum units C 1  and the toner units C 2  of the image formation units  44  to  47  are detachable from and attachable to their corresponding units. This can be done with a unit installation section  63  which is included in each of the image formation units  44  to  47 . The unit installation section  63  is formed in such a rail-like shape that its corresponding drum unit C 1  and toner unit C 2  slide approximately in an horizontal direction and are detached from and attached to the unit. The printing head  51   b  is arranged inside the unit installation section  63 .  
         [0058]    A printing paper is conveyed from the feeding cassette  38  included in the feeding section  43 , throughout a suspension roller  52 , a conveyer belt  53 , a driving roller  54  and a driven roller  54 ′. The paper conveyed from the feeding cassette  38  by the rotation of a feeding roller  55  is sent to the suspension roller  52  and further onto the conveyer belt  53  at an appropriate timing the toner image reaches the paper, and reaches the transcription unit  51   d.  The toner image is transcribed onto a paper by the transcription unit  51   d.  The paper onto which the toner image is transcribed is conveyed on the conveyer belt  53  in the arrow direction (from the right side toward the left side in the illustration), in accordance with the movement of the conveyer belt  53 . Heat fixation treatment is performed for thus conveyed paper by a fixation unit  56  which is prepared as heat fixation means.  
         [0059]    On the paper, not only the toner image of yellow (Y), but also toner images of other colors of magenta (M) and cyan (C), which are transcribed by their corresponding drum units C 1  and toner units C 2 , are transcribed, thereby to accomplish color printing based on the subtraction mixture of colors.  
         [0060]    Not only those papers conveyed from the feeding cassette  38 , but also any paper supplied from an MPF tray  39 ′ can be used. In this case, the paper supplied from the MPF tray  39 ′ is conveyed by a feeding roller  39   a,  and the printing is performed according to the above process.  
         [0061]    The fixation unit  56  comprises a heat roller  56   a,  a press roller  56   b,  and a cleaning roller  56   c.  A paper P is sandwiched between the heat roller  56   a  and the press roller  56   b  so as to be conveyed. During this time, the toner image having a plurality of colors and transcribed on the paper melts and is fixed on the paper P with heat. The cleaning roller  56   c  has a function for applying oil onto the heat roller  56   a  and a function for removing toner remaining on the heat roller  56   a.  The paper, onto which the toner image is fixed by the fixation unit  56  is conveyed upward or in a leftward direction in the illustration via a switching plate  61 .  
         [0062]    The conveyer unit  42  for both-side printing is detachable from and attachable to the printer device  31 , and installed in the printer device  31  when to perform both-side printing. The conveyer unit  42  for both-side printing includes a plurality of conveyer rollers  60   a,    60   b,    60   c,    60   d,  and  60   e.  In the case of both-side printing, the paper is once conveyed upward by the switching plate  61 . Then, when the last end of the paper reaches a conveyer roller  62 , for example, the paper is suspended, and is conveyed in the reverse direction. Under this control, the paper is conveyed in a downward direction by the switching plate  61 , which is set in the position shown with a broken line in FIG. 3. Then, the paper is sent to the paper conveyer path of the conveyer unit  42  for both-side printing, and conveyed through the conveyer rollers  60   a  to  60   e  so as to reach the suspension roller  52 . After this, the paper is sent to the transcription unit  51   d  at a timing the toner image reaches the paper, so that the toner image is transcribed onto the back surface of the paper.  
         [0063]    In FIG. 3, the position of an FR frame  65  (including the FR frames  65   a  and  65   b  arranged on the right and left sides of the printer device  31 ) is shown.  
         [0064]    In the printer device  31  of this embodiment, the upper body  32  is opened and closed in a horizontal direction with respect to the lower body  33 , so as to carry out a maintenance operation.  
         [0065]    [0065]FIG. 4 is a diagram for explaining a frame connection structure of the printer device  31  according to this embodiment. FIG. 5 is a diagram for explaining the arrangement of a plurality of frames. FIG. 6 is an assembly diagram for explaining the relationship between the main frame and the sub-frame for clear description thereof. In each of FIGS. 4, 5 and  6 , the main frame, which forms the lower frame of the printer device  31 , is denoted by the reference numeral  85 . A plurality of frames  85   a,    85   b,    85   c,    85   d,    85   e,  etc. are fixed using either technique of welding, clamping, pressure-fixing, etc.  
         [0066]    As shown in FIG. 6, the frames  85   a  and  85   b  are incorporated with each other so as to form the front frame, while the frames  85   c  and  85   d  are incorporated with each other. One ends of the respective frames  85   c  and  85   d,  as bent sections B 2  and B 3 , are fixed on a standing edge  85   e′.  A frame  86  for installing an FR frame  65   b  is fixed on the frame  85   b,  whereas a frame  90  for installing an FR frame  65   a  is fixed on the frame  85   a.  As illustrated in FIG. 6, a lower end  86   a  of the frame  86  is fixed on the frame  85   b.  One end of the FR frame  65   a  is fixed onto a bent-concave section  90   a  of the frame  90 . A lower bent section  90   b  of the frame  90  is fixed onto an upper surface of the frame  85   a.  The above fixing of the frames onto their corresponding frames are performed using either technique of welding, clamping, etc.  
         [0067]    An electric equipment box  87  installed behind the printer device contains a control circuit or a source circuit and a driving transmission mechanism, etc. of the printer device  31 . This electric equipment box  87  is fixed on the frame  85   e  which is included in the main frame  85 . A side plate  88  of the printer device  31  is also fixed on the main frame  85 . In more particular, the electric equipment box  87  is placed on the bottom surface of the frame  85   e.  An upper bent section  85   e″  of the frame  85   e  and the other end of the FR frame  65   a  are placed on a step  87   a  of the electric equipment box  87 . A lower convex section  88   a  of the side plate  88  is fixed onto an inner surface of leg  85   b′  of the frame  85   b,  while a side section  88   b  is fixed onto a side section  87   b  of the electric equipment box  87 . A bent section  86   b  of the frame  86  is fixed onto one end (front end) of the FR frame  65   b,  while the other end (distal end) of the FR frame  65   b  is fixed onto the upper surface of the electric equipment box  87 . In the above structure, the plurality of frames, except the sub-frame  89 , are incorporated with each other so as to form the lower frame of the printer device.  
         [0068]    The sub-frame  89  is fixed above the main frame  85  so as to be included in the lower frame of the printer device, in a three-point connection manner. The sub-frame  89  is formed of a frame section  89   a  and a plate section  89   b,  as seen from FIG. 6. The frame section  89   a  includes four concave sections  89   a′  in the upper section thereof. The image formation units  44  to  47  are fixed into the concave sections  89   a′,  respectively. That is, the image formation units  44  to  47  are positioned and supported by the sub-frame  89 . The above-described conveyer belt  53  is arranged on the plate section  89   b,  and fixed thereinto.  
         [0069]    In the three-point connection manner, the main frame  85  and the sub-frame  89  are connected and fixed at three points of an A 1  point, an A 2  and an A 3  shown in FIGS.  4  to  6 . The A 1  point is a point at which a bent tip  89   b′  of the plate section  89   b  is fixed onto the front surface of the main frame  85 . The A 2  point and the A 3  point are points at which the frame section  89   a  is fixed on the frame  85   e.  Particularly, the A 2  point and the A 3  point are prepared for fixing elongated sections  89   a′,  which are elongated backward from the frame section  89   a,  onto the positions denoted by broken lines A 2 ′ and A 3 ′ of the standing edge  85   e′.  As illustrated in FIG. 4, there is a certain interval, denoted by a reference mark 1 (actually several mm), between the frames  85   a,    85   b  and the plate section  89   b  of the sub-frame  89 , with due regard to a slight twist of the main frame  85 . Thus, the front section of the sub-frame  89  and the main frame  85  are slidable centrically about the A 1  point.  
         [0070]    Accordingly, in the printer device  1  of this embodiment which is in an operational state, the image formation units  44  to  47  are supported by the sub-frame  89 . The conveyer belt  53  is arranged on the side of the sub-frame  89 . The sub-frame  89  is separated from the main frame  85  forming a lower section of the printer device  31 . Hence, a slight twist of the lower section hardly has an effect on the sub-frame  89 , when the lower frame of the printer device  31  is arranged on a warped surface of a table, etc.  
         [0071]    The upper body  32  can be opened away from the lower body  33  having the above-structured link mechanism. FIG. 7 is an outside perspective view of the printer device  32 , wherein the upper body  32  is opened. As shown in FIG. 7, the upper body  32  is opened away from the lower body  33  in a horizontal direction by the link mechanism  64  included in the printer device  31 .  
         [0072]    The link mechanism  64  comprises a link frame  66 , an F arm  67 , an R arm  68 , a stay  69 , and an FR frame  65 , on both sides of the printer device  31 . One ends of the respective F arm  67  and R arm  68  are connected to and rotatively support the link frame  66  arranged on the upper body  32 . The other end of the F arm  67  is connected to an rotatively supports the FR frame  65  arranged on the lower body  33 . The other end of the R arm  68  is connected to and rotatively supports the stay  69  which is fixed on the FR frame  65 . In this structure, the upper body  32  is opened in parallel with respect to the lower body  33 , and is gradually moved backward with respect to the lower body  33 .  
         [0073]    In FIG. 7, those sections included in the link mechanism  64  only on the right side of the printer device  31  are denoted by reference numerals, for the sake of simple illustration. In the following explanations, those sections in the link mechanism on the left side of the printer device  31  are denoted by reference numerals with “a”, while those sections in the link mechanism on the right side thereof are denoted by reference numerals with “b”. Hence, in FIG. 7, the link frame is denoted by  66   b,  the F is denoted by  67   b,  the R arm is denoted by  68   b,  the stay is denoted by  69   b,  and the FR frame is denoted by  65   b,  which are included in the link mechanism on the right side of the printer device.  
         [0074]    [0074]FIGS. 8 and 9 are schematic diagrams of the link mechanism. Particularly, FIG. 8 shows a schematic diagram of the link mechanism viewed from the left side-surface thereof, and FIG. 9 is a schematic diagram of the link mechanism viewed from the right side-surface thereof. FIG. 10 is a perspective view of the link mechanism. In FIGS.  8  to  10 , the link frame  66  ( 66   a,    66   b ), the F arm  67  ( 67   a,    67   b ), the R arm  68  ( 68   a,    68   b ), the stay  69  ( 69   a,    69   b ), and the FR frame  65  ( 65   a,    65   b ) are the principal components of the link mechanism. In FIG. 10, the link frame  66  ( 66   a,    66   b ) is not illustrated.  
         [0075]    In FIGS. 8 and 9, the F arm  67  ( 67   a,    67   b ) and the R arm  68  ( 68   a,    68   b ) illustrated with straight lines are shown in their corresponding positions when the upper body  32  is opened. At this time, the upper body  32  is retained to be opened approximately in parallel with respect to the lower body  33 . The F arm  67  ( 67   a,    67   b ) and the R arm  68  ( 68   a,    68   b ) illustrated with double dot chain lines are shown in their corresponding positions when the upper body  32  is shifted back toward the lower body  33  so as to be closed.  
         [0076]    A supporting section  71  ( 71   a,    71   b ) rotatively supports the F arm  67  ( 67   a,    67   b ) and the FR frame  65  ( 65   a,    65   b ), while a supporting section  72  ( 72   a,    72   b ) rotatively supports the R arm  68  ( 68   a,    68   b ) and the stay  69  ( 69   a,    69   b ). A supporting section  77  ( 77   a,    77   b ) rotatively supports the F arm  67  ( 67   a,    67   b ) and the link frame  66  ( 66   a,    66   b ), while a supporting section  78  ( 78   a,    78   b ) rotatively supports the R arm  68  ( 68   a,    68   b ) and the link frame  66  ( 66   a,    66   b ).  
         [0077]    [0077]FIG. 11 is a diagram for explaining the driving mechanism of the link mechanism. As shown in FIG. 11, the link mechanism is symmetrical. FIG. 11 shows the driving mechanism of the link mechanism which corresponds to that shown in FIG. 8. The front side-surface of the printer device  31  is shown on the right side in the illustration of FIG. 11. As explained above, the F arm  67   a  is rotatively supported by the supporting section  71   a,  and fixed by a rotational gear  71   a′.  The R arm  68   a  is rotatively supported by the supporting section  72   a,  and fixed by a rotational gear  72   a′.  In this structure, the F arm  67   a  and the rotational gear  71   a′  rotate as a unit, and the R arm  68   a  and the rotational gear  72   a′  rotate as a unit.  
         [0078]    An intermediate pulley  73  intermediates between the rotational gears  71   a′  and  72   a′.  A gear belt  74  is built between the rotational gears  71   a′  and  72   a′  via the intermediate pulley  73 . The intermediate pulley  73  is to give a predetermined level of tension to the gear belt  74 .  
         [0079]    The rotational gear  72   a′  is engaged with a rotator  75  having a damper mechanism. This rotator  75  includes an oil damper, and has a function for controlling a sudden fall of the upper body  32  according to the law of gravitation so as to make the upper body  32  smoothly fall. The upper body  32  is released up with a spring  76  so as to be opened. One end of this spring  76  is fixed by a casing  33 ′ of the lower body  33 , and wound in a few rounds inside the rotational gear  71   a′.  The other end of the spring  76  is fixed in a hole (not illustrated) formed in the F arm  67   a.  The additional tension of the spring  76  causes the rotational gear  71   a′  to rotate in an a′-direction denoted by an arrow a′, so that the upper body  32  is released up.  
         [0080]    In more particular, when the rotational gear  71   a′  rotates in the a′-direction, the F arm  67   a  is rotated in the same direction. At the same time, the gear belt  74  rotates in an a-direction denoted by an arrow a, and the rotational gear  72   a′  rotates in an a″-direction denoted by an arrow a″, and the R arm  68   a  is rotated in the same a″-direction. The link mechanism functions by the above-described driving mechanism. Then, the F arm  67   a  and the R arm  68   a  are rotated in accordance with the rotational tracks, shown with a chain dot line in the illustration, causing the upper body  32  to be shifted up.  
         [0081]    The state, where the upper body  32  is shifted back toward the lower body  33  so as to be closed, is illustrated in FIGS.  1  to  3 . The plate section  89   b  of the sub-frame  89  is positioned below the carrier belt  53 , which is shown with a broken line in FIG. 2. In the state where the upper body  32  is shifted backward toward the lower body  33 , the image formation units  44  to  47  (drum unit C 1 , toner unit C 2 ) are engaged with the concave section  89   a′  formed in the sub-frame  89 . The main frame  85  and the sub-frame  89  are connected in the three-point connection structure. In this structure, when the printer device  31  is placed on a warped surface of a table, etc., even the main frame  85  is slightly twisted, the sub-frame  89  is not twisted. Thus, no twist should occur in the sub-frame  89 . In addition, the image formation units  44  to  47  arranged around the sub-frame  89  and the carrier belt  53  should not mechanically be deviated.  
         [0082]    In the above-described embodiment, as shown in FIGS.  4  to  6 , the main-frame  85  and the sub-frame  89  are connected with each other at the three points, A 1 , A 2  and A 3 . The explanations have been made to the case where the bent tip  89   b′  of the plate section  89   b  in the sub-frame  89  is fixed on the front surface of the main frame  85  at the point A 1 . However, the connection structure is not limited to the above.  
         [0083]    [0083]FIG. 12 is a perspective view showing the principal components of the main frame and the sub-frame in the frame connection structure of a printer device according to a modification of the present invention. FIG. 12 shows the relationship between the main frame and the sub-frame included in the printer device of the modification. In the illustration, the same reference numerals are attached to the same component parts of the printer device illustrated in FIGS.  4  to  6 . In FIG. 12, those distinctive features in the structure of the printer device from those of the structure of the printer device according to the above-described embodiment are: that a front frame  91  forming the main frame is formed in a straight shape without any unevenness; and that a bent tip  89   b″  of the plate section  89   b  in the sub-frame  89  is further bent in a horizontal direction. Legs  91   a  and  91   b  of the front frame  91  correspond to the frames  85   a  and  85   b  illustrated in FIGS.  4  to  6 . The bent tip  89   b″  is fixed on the upper surface of the front frame  91 . The installation of such component parts of the printer device are performed using a welding or clamping technique. In this structure, even a slight twist occurs in the main frame, the sub-frame  89  should not have such a slight twist.  
         [0084]    In the above-described embodiment, the main frame  85  is fixed onto the sub-frame  89  at the three positions of A 1  (A 1 ′) to A 3  in the three-point connection structure. However, the main frame  85  may be fixed onto the sub-frame  89  at any other three positions.  
         [0085]    Various embodiments and changes may be made thereonto without departing from the broad spirit and scope of the invention. The above-described embodiment is intended to illustrate the present invention, not to limit the scope of the present invention. The scope of the present invention is shown by the attached claims rather than the embodiment. Various modifications made within the meaning of an equivalent of the claims of the invention and within the claims are to be regarded to be in the scope of the present invention.  
         [0086]    This application is based on Japanese Patent Application No. 2000-24651 filed on Feb. 2, 2000, and including specification, claims, drawings and summary. The disclosure of the above Japanese Patent Application is incorporated herein by reference in its entirety.