Abstract:
An electrophotographic recording apparatus has a lid movable to open and close relative to a body of the apparatus, the lid having an exposing unit mounted thereto. The recording apparatus comprises a collapsible mechanism and a drive mechanism (gear mechanism). The exposing unit is suspended from the collapsible mechanism. The gear mechanism is operatively connected to the lid so that when the lid is opened and closed, the gear mechanism drives the collapsible mechanism to deform selectively into the collapsed position and the expanded position, respectively. When the collapsible mechanism is at the expanded position, the exposing unit is accurately positioned relative to an image-forming unit. When the collapsible mechanism is at the collapsed position, the exposing unit is at a retracted position so that the exposing unit allows easy access to the interior of the apparatus. The gear mechanism may include a torque limiter.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to printing apparatus such as electrophotographic copying machines and electrophotographic printers, and more particularly to an electrophotographic recording apparatus having an exposing unit on a cover thereof.  
           [0003]    2. Description of the Related Art  
           [0004]    With conventional printing apparatus such as electrophotographic copying machines and electrophotographic printers, the operator opens a lid to replace an image-forming unit and/or a toner cartridge or to remove jammed paper. The lid is usually of simple construction in which the lid is opened and closed substantially in a vertical direction.  
           [0005]    Among the electrophotographic printers on the market is one in which, for example, an LED head as an exposing unit used for electrophotography is mounted on a lid. Such a printer includes four LED heads for forming yellow, magenta, cyan, and black images on corresponding image forming units.  
           [0006]    However, such a conventional electrophotographic recording apparatus having LED heads suffers from the problem that when the operator opens a lid to replace an image-forming unit and/or a toner cartridge or to remove jammed paper, the LED heads that project downward from the lid interfere with the operator&#39;s hands. In order that the LED heads do not interfere with the operator&#39;s hands, the lid should be designed to open wider.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention was made in view of the aforementioned drawbacks of the conventional apparatus.  
           [0008]    An object of the invention is to provide an electrophotographic recording apparatus in which when the user replaces a toner cartridge and/or image forming unit or removes jammed paper, an exposing unit does not obstruct the operations.  
           [0009]    An electrophotographic recording apparatus according to the invention has a lid movable to open and close relative to a body of the apparatus, the lid having an exposing unit mounted thereto. The recording apparatus comprises a collapsible mechanism and a gear mechanism. The collapsible mechanism can be selectively deformed into a collapsed position and into an expanded position. The gear mechanism drives the collapsible mechanism to deform selectively into the collapsed position and the expanded position. When the lid is opened, the collapsible mechanism causes the exposing unit to move to a retracted position. When the lid is closed, the collapsible mechanism causes the exposing unit to move to an extended position. When the lid is opened and closed, said gear mechanism operates operatively with the lid to cause the collapsible mechanism to be selectively deformed into the collapsed position and into the expanded position.  
           [0010]    The exposing unit extends longitudinally and has a first longitudinal end and a second longitudinal end. When the lid is opened, one of the first and second longitudinal ends is moved to the retracted position.  
           [0011]    The exposing unit is mounted to the collapsible mechanism through a biasing member. When the lid is closed, the collapsible mechanism is deformed into the expanded position so that the exposing unit is placed in position with respect to an image-forming unit and the biasing member urges the exposing unit against the image-forming unit.  
           [0012]    The gear mechanism may include a torque limiter.  
           [0013]    The exposing unit extends substantially parallel to an axis about which the lid pivots to open and close.  
           [0014]    The exposing unit extends in a direction substantially perpendicular to an axis about which the lid pivots to open and close.  
           [0015]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limiting the present invention, and wherein:  
         [0017]    [0017]FIG. 1 is a perspective view of a pertinent portion of an electrophotographic printer according to a first embodiment of the invention;  
         [0018]    [0018]FIG. 2 is a side view of the LED assemblies and associated structural elements of the image recording apparatus;  
         [0019]    [0019]FIG. 3 is a fragmentary front view of a pertinent portion of the first embodiment when the lid is opened;  
         [0020]    [0020]FIG. 4 is a fragmentary side view of a pertinent portion of the first embodiment when a lid is completely closed;  
         [0021]    FIGS.  5 - 8  illustrate the opening operation of the lid according to the first embodiment;  
         [0022]    FIGS.  9 - 12  illustrate the closing operation of the first embodiment;  
         [0023]    [0023]FIG. 13 is a perspective view of a pertinent portion of an electrophotographic printer according to a second embodiment; FIG. 14 is a fragmentary plan view illustrating the second embodiment;  
         [0024]    FIGS.  15 - 17  illustrate the operation of the second embodiment;  
         [0025]    [0025]FIG. 18 is a perspective view of a pertinent portion of an electrophotographic printer according to a third embodiment;  
         [0026]    [0026]FIG. 19 is a fragmentary view of a pertinent portion of the third embodiment;  
         [0027]    [0027]FIG. 20 is a side view of a pertinent portion of the third embodiment; and  
         [0028]    [0028]FIG. 21 is the bottom view of the LED head  6 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    Embodiments of the invention will be described in detail with reference to the accompanying drawings.  
         [0030]    First embodiment  
         [0031]    {Construction} 
         [0032]    Embodiments of the invention will be described with respect to an electrophotographic printer as an electrophotographic recording apparatus. The electrophotographic printer incorporates an LED head as an exposing unit.  
         [0033]    [0033]FIG. 1 is a perspective view of a pertinent portion of an electrophotographic printer according to a first embodiment of the invention.  
         [0034]    Referring to FIG. 1, an electrophotographic printer  1  has a body  2 . The lid  3  is pivotally assembled to the main frame of the body  2 . The lid  3  has a pair of supporting projections  4  on the left and right ends thereof. A sector gear  3   a  is formed on the left side of the lid  3  in one-piece construction with the lid  3  such that the sector gear  3   a  is rotatable about an axis passing through the centers of the pair of supporting projections  4 . The lid  3  has a pair of support shafts  11   a  and  11   b  that are rotatably supported by bearings, not shown, and extend parallel to each other.  
         [0035]    There are four LED assemblies  5  assembled to an inner surface of the lid  3 , the LED assemblies  5  being aligned at equal intervals. FIG. 1 shows only one of the LED assemblies  5  in the detail and three others in phantom lines. The four LED head assemblies  5  are provided because the electrophotographic printer according to the first embodiment is a color printer. If an electrophotographic printer is a monochrome printer, only one LED head assembly is required. Each of the LED head assemblies  5  includes an LED head  6 , a pair of compression springs  7 , a sub plate  8 , a pair of base inks  9   a  and  9   b , and a pair of interconnecting links  10   a  and  10   b.    
         [0036]    The base links  9   a  and  9   b  and the interconnecting links  10   a  and  10   b  have a U-shaped cross section. The base links  9   a  and  9   b  have top end portions firmly connected to front end portions of the support shafts  11   a  and  11   b , respectively. The lower end portions of the base links  9   a  and  9   b  partially enter the upper end portions of the interconnecting links  10   a  and  10   b  such that the base links are pivotally coupled to corresponding the interconnecting links by means of coupling pins  12   a  and  12   b.    
         [0037]    [0037]FIG. 2 is a side view of the LED assemblies  5  and associated structural elements of the printer. Referring to FIG. 2, the four LED head assemblies  5  are mounted to the lid  3  such that they face corresponding image-forming units  21  accurately when the lid  3  is completely closed.  
         [0038]    [0038]FIG. 3 is a fragmentary front view of a pertinent portion of the first embodiment when the lid  3  is opened.  
         [0039]    Referring to FIG. 3, the interconnecting link  10   a  is pivotal clockwise about a coupling pin  13   a  but is prevented from pivoting counterclockwise due to the fact that when the interconnecting link  10   a  pivots counterclockwise, the upper portion of the interconnecting link  10   a  abuts the lower end portion of the base link  9   a. Specifically, the interconnecting link  10   a  is prevented from further pivoting counterclockwise when the interconnecting link  10   a  pivots such that the coupling pin  12   a  is outside of a line La connecting the support shaft  11   a  and the coupling pin  13   a.    
         [0040]    The relation between the lower end portion of the base link  9   b  and the interconnecting link  10   b  is similar to that between the lower end portion of the base link  9   a  and the interconnecting link  10   a . In other words, the interconnecting link  10   b  is pivotal clockwise about a coupling pin  13   b  but is prevented from pivoting counterclockwise due to the fact that the upper portion of the interconnecting link  10   b  abuts the lower end portion of the base link  9   b . Specifically, the interconnecting link  10   b  is prevented from further pivoting counterclockwise when the interconnecting link  10   b  pivots such that the coupling pin  12   b  is outside of a line Lb connecting the support shaft  11   b  and the coupling pin  13   b.    
         [0041]    The lower end portions of the interconnecting links  10   a  and  10   b  are coupled to upward projections  8   a  and  8   b , formed on the left and right end portions of the support plate  8 , by means of the coupling pins  13   a  and  13   b , respectively. Each of the compression springs  7  has one end thereof connected to the underside of the support plate  8  and the other end thereof connected to the LED head  6 . The LED head  6  is suspended from the supporting plate  8  by means of the compression springs  7 . The LED head  6  has engagement holes  6   a  and  6   b  (FIG. 3) formed in longitudinal end portions thereof.  
         [0042]    Disposed below the respective LED heads  6  are corresponding image-forming units  21 . Each of the image-forming units  21  has pilot pins  21   a  and  21   b  that correspond to the engagement holes  6   a  and  6   b  of the LED head  6 , respectively. When the pilot pins  21   a  and  21   b  enter the engagement holes  6   a  and  6   b , respectively, the LED heads  6  are placed in position.  
         [0043]    [0043]FIG. 4 is a fragmentary side view of a pertinent portion of the first embodiment when the lid  3  is completely closed.  
         [0044]    Referring to FIGS. 1 and 4, the support shafts  11   a  and  11   b  have worm wheels  14   a  and  14   b  secured to the rear end portions of the support shafts  11   a  and  11   b . The shaft  16  is in line with the pair of supporting projections  4  formed in the lid  3  but not coupled to the supporting projections  4 . The shaft  16  is rotatably supported by bearings, not shown, provided on the lid  3 . The shaft  16  also has worm gears  17   a  and  17   b  and an idle gear  18 , which are secured to the shaft  16 . The worm gears  17   a  and  17   b  are in mesh with worm wheels  14   a  and  14   b , respectively, and the idle gear  18  is disposed close to the sector gear  3   a.    
         [0045]    Referring to FIG. 1, a main gear  19  is rotatably supported on a rear end of the body  2  near the sector gear  3   a . The main gear  19  is in mesh with a sub gear  20  rotatably supported on the body  2 . When the main gear  19  moves into meshing engagement with the sector gear  3   a , the pivotal motion of the lid  3  is transmitted from the main gear  19  to the idle gear  18 . The pivotal motion is further transmitted from the idle gear  18  to the support shaft  11   a  and  11   b  through the worm gears  17   a  and  17   b  and worm wheels  14   a  and  14   b . The sector gear  3   a  is shaped such that the sector gear  3   a  moves into meshing engagement with the main gear  19  after the lid  3  has pivoted to a certain angle from a position where the lid  3  is completely closed to a position where the lid is partially opened.  
         [0046]    {Operation of the first embodiment} 
         [0047]    {Opening operation} 
         [0048]    FIGS.  5 - 8  illustrate the opening operation of the lid according to the first embodiment.  
         [0049]    The opening operation of the lid  3  will now be described with reference to FIGS.  5 - 8 . When the lid  3  is completely closed as shown in FIG. 3, the upper end portions of the interconnecting links  10   a  and  10   b  abut the lower end portions of the base links  9   a  and  9   b , respectively, preventing the interconnecting links  10   a  and  10   b  from further pivoting. Thus, the LED head assembly  5  is firmly positioned with the aid of the urging forces of the compression springs  7 .  
         [0050]    After the operator unlocks the lid  3  by operating a locking mechanism, not shown, the operator raises the lid  3  such that the lid  3  pivots from the closed position shown in FIG. 4 in a direction shown by arrow A of FIG. 5. At this moment, the sector gear  3   a  is not in mesh with the main gear  19  yet. The pin holes  6   a  and  6   b  of the LED head  6  will move out of engagement with the pilot pins  21   a  and  21   b  of the image-forming unit  21  before the sector gear  3   a  moves into meshing engagement with the main gear  19 . When the lid  3  is further opened, the sector gear  3   a  moves into meshing engagement with the main gear  19 , so that the main gear  19  rotates clockwise as shown by arrow B in FIG. 5. Then, the rotary motion of the main gear  19  is transmitted to the idle gear  18 . The idle gear  18  then transmits the rotary motion to the support shafts  11   a  and  11   b  through the warm gears  17   a  and  17   b , respectively. As a result, the support shaft  11   a  rotates in a direction shown by arrow C (counterclockwise) in FIG. 6, and the support shaft  11   b  rotates in a direction shown by arrow D (clockwise).  
         [0051]    As the support shaft  11   a  rotates, the base link  9   a  and interconnecting link  10   a  collapse such that one is folded over the other as shown in FIG. 6. Likewise, as the support shaft  11   b  rotates, the base link  9   b  and interconnecting link  10   b  collapse such that one is folded over the other. As the base links  9   a  and  9   b  and the interconnecting links  10   a  and  10   b  collapse, the LED head assembly  5  is deformed from an expanded position toward a collapsed position.  
         [0052]    When the lid  3  has been fully opened as shown in FIG. 7, the LED assembly  5  has completely collapsed as shown in FIG. 8. The lid  3  is at its open position where the lid  3  is at an angle greater than 90 degrees with respect to its closed position and is held at the open position.  
         [0053]    Then, with the lid  3  opened, the operator replaces the toner cartridge and/or the image-forming unit or removes jammed paper. Since the LED assemblies are at their collapsed positions, the LED assemblies  5  do not interfere with the operator&#39;s hands, facilitating replacement of the toner cartridge and/or the image-forming unit or removal of the jammed paper.  
         [0054]    {Closing operation} 
         [0055]    FIGS.  9 - 12  illustrate the closing operation of the first embodiment.  
         [0056]    When the lid  3  is fully opened as shown in FIG. 7, the sector gear  3   a  is in meshing engagement with the main gear  19 . As the operator closes the lid  3  in a direction shown by arrow F as shown FIG. 9, the sequence of the aforementioned opening operation is reversed. In other words, referring to FIG. 9, the main gear  19  rotates counterclockwise shown by arrow E, and the rotary motion of the main gear  19  is transmitted to the idle gear  18  through the sub gear  20 . The rotary motion of the idle gear is then transmitted to the support shafts  11   a  and  11   b  through the worm gear gears  17   a  and  17   b  and worm wheels  14   a  and  14   b . Then, as shown in FIG. 10, the support shaft  11   a  rotates in a direction shown by arrow G (clockwise) while the support shaft  11   b  rotates in a direction shown by arrow H (counterclockwise).  
         [0057]    As shown in FIG. 11, the clockwise rotation of the support shaft  11   a  causes the base link  9   a  and interconnecting link  10   a  to gradually open from their collapsed state. The counterclockwise rotation of the support shaft  11   b  causes the base link  9   b  and the interconnecting link  10   b  to gradually open from their collapsed state. The coupling pins  12   a  and  12   b  will have moved outside of the lines La and Lb, respectively, as shown in FIG. 12, before the sector gear  3   a  moves out of meshing engagement with the main upper gear  19  as shown in FIG. 11. Thus, in FIG. 12, the upper end corners  10   a ′ and  10   b ′ of the U-shaped interconnecting links  10   a  and  10   b  abut the common parts  9   a ′ and  9   b ′ of the U-shaped base links  9   a  and  9   b , thereby preventing the interconnecting links  10   a  and  10   b  from further pivoting. At this moment, neither a compressive force nor a tensile force is exerted to the compression coil spring  7 .  
         [0058]    As the lid  3  is further closed, the sector gear  3   a  moves out of engagement with the main gear  19  but the worm gear  17   a  and  17   b  cause the interconnecting links  10   a  and  10   b  and the base links  9   a  and  9   b  to stay at their positions. Then, the pilot pins  21   a  and  21   b  enter the engagement holes  6   a  and  6   b  formed in the LED head  6 , thereby placing the LED head  6  in position above the image-forming unit  21 .  
         [0059]    When the LED head  6  is positioned above the image-forming unit  21 , the compression spring  7  starts to be compressed so that the spring  7  urges the interconnecting links  10   a  and  10   b  and the base links  9   a  and  9   b . However, the worm gears  17   a  and  17   b  prevent the base links  9   a  and  9   b  from pivoting, and the upper end corners  10   a ′ and  10   b ′ of the interconnecting links  10   a  and  10   b  abut the common parts  9   a  and  9   b  of the base links  9   a  and  9   b . Therefore, the interconnecting links  10   a  and  10   b  and the base links  9   a  and  9   b  are not collapsed but remain positioned over the image-forming unit  21  as shown in FIG. 12. Subsequently, the lid  3  is pivoted further in the closing direction so that the compression spring  7  exerts a large biasing force on the LED head  6 . After the lid  3  has been completely closed, the operator locks the lid  3  to the body  2  by operating a fastening means, not shown.  
         [0060]    The first embodiment is advantageous in that the LED head assemblies  5  do not obstruct the operator&#39;s hands and it is only necessary for the operator o open the lid  3  through a small pivotal angle because the LED head assemblies  5  collapses into a small size.  
         [0061]    Second Embodiment  
         [0062]    {Construction} 
         [0063]    [0063]FIG. 13 is a perspective view of a pertinent portion of an electrophotographic printer according to a second embodiment.  
         [0064]    [0064]FIG. 14 is a fragmentary plan view illustrating the second embodiment.  
         [0065]    Referring to FIG. 13, the rear end portions of the support shafts  11   a  and  11   b  are firmly supported by means of torque limiters  30   a  and  30   b . The torque limiters  30   a  and  30   b  each include an inner ring member and an outer ring member. When a torque smaller than a predetermined value acts on the inner and outer ring members, the inner and outer ring members rotate together. When a torque larger than the predetermined value acts on the inner and outer ring members, one ring member rotates relative to the other with a certain torque acting on them.  
         [0066]    Referring to FIG. 14, the stoppers  31   a  and  31   b  are provided on the inner surface of the lid  3  and restrict the rotation of the base links  9   a  and  9   b . The rest of the construction is the same as the first embodiment.  
         [0067]    {Operation of the second embodiment} 
         [0068]    {Opening operation} 
         [0069]    FIGS.  15 - 17  illustrate the operation of the second embodiment.  
         [0070]    The opening operation of the lid of the second embodiment will now be described with reference to FIGS.  15 - 17 .  
         [0071]    Just as in the first embodiment, when the lid  3  has been completely closed, the upper end corners  10   a ′ and  10   b ′ of the interconnecting links  10   a  and  10   b  abut the upper common parts  9   a ′ and  9   b ′ of the base links  9   a  and  9   b . Therefore, the interconnecting links  10   a  and  10   b  are prevented from pivoting and the compression springs  7  urge the LED head  6  against the image-forming unit  21  and the sector gear  3   a  has not been in meshing engagement with the main gear  19  yet.  
         [0072]    Referring to FIG. 15, when the operator opens the lid  3 , the lid  3  pivots in a direction shown by arrow I but the sector gear  3   a  is not in meshing engagement with the main gear  19  until the lid  3  opens to an angle greater than a predetermined value. Before the sector gear  3   a  moves into meshing engagement with the main gear  19 , the LED head  6  will have moved out of engagement with the pilot pins  21   a  and  21   b  of the image-forming unit  21 . When the lid  3  is further opened, the sector gear  3   a  moves into meshing engagement with the main gear  19 , so that the main gear  19  starts to rotate clockwise. The rotation of the main gear  19  is transmitted to the idle gear  18  through the sub gear  20 , and then to the support shafts  11   a  and  11   b  through the worm gears  17   a  and  17   b  and worm wheels  14   a  an  14   b . As a result, as described in the first embodiment, the base links  9   a  and  9   b  and the interconnecting links  10   a  and  10   b  collapse into a folded position, so that the LED assemblies  5  are collapsed from their expanded positions to their collapsed positions.  
         [0073]    When the lid  3  is still further opened, the upper end corners  9   a ′ and  9   b ′ of the base links  9   a  and  9   b  abut the stoppers  31   a  and  31   b  as shown in FIG. 17, and the base links and interconnecting links are not further collapses.  
         [0074]    As shown in FIG. 16, if the operator attempts to further open the lid  3  in the direction shown by arrow J, the lid  3  can be opened with the support shafts  11   a  and  11   b  not rotated. This is because the torque limiters  30   a  and  30   b  becomes operative, so that the pivotal motion of the lid  3  is transmitted to the worm gears  17   a  and  17   b  of the relay shaft  16  and not from the worm gears  17   a  and  17   b  to the worm wheels  14   a  and  14   b.    
         [0075]    When the lid  3  has been completely opened, the operator replaces the cartridge and/or the image-forming unit or removes jammed paper. At this moment, just like the first embodiment, the LED head assemblies  5  are at their collapsed positions, facilitating replacement of the cartridge and/or image-forming unit or removal of the jammed paper.  
         [0076]    {Closing operation} 
         [0077]    The closing operation of the lid  3  will now be described with reference to FIGS. 15 and 16.  
         [0078]    When the lid  3  is fully opened, the sector gear  3   a  is in mesh with the main gear  19 . When the operator starts to close the lid  3  from this position, the sequence of the aforementioned opening operation is reversed so that the base links  9   a  and  9   b  and the interconnecting links  10   a  and  10   b  gradually open from their collapsed position.  
         [0079]    Before the lid  3  is closed to the position shown in FIG. 15 where the sector gear  3   a  moves out of engagement with the main gear  19 , the coupling pins  12   a  and  12   b  will have become outside of the lines La and Lb (FIG. 12), respectively. The upper end corners  9   a ″ and  9   b ″ of the base links  9   a  and  9   b  abut the stoppers  31   a  and  31   b  to prevent the basing links  9   a  and  9   b  from pivoting.  
         [0080]    When the lid  3  has been fully opened, the interconnecting links  10   a  and  10   b  and the base links  9   a  and  9   b  are in their expanded positions as shown in FIG. 14 and the torque limiters  30   a  and  30   b  remain operative. In this situation, the torque limiters  30   a  and  30   b  operate so that the rotation of the lid  3  is not transmitted to the support shafts  11   a  and  11   b . In other words, the lid  3  can pivot further in the closing direction with the support shafts  11   a  and  11   b  not rotating. If the gear ratio is designed such that the support shafts  11   a  and  11   b  rotate a larger number of times for the same amount of pivotal motion of the lid  3 , then the interconnecting links  10   a  and  10   b  and the base links  9   a  and  9   b  operate as follows. When the lid  3  is closed from its fully opened position, the interconnecting links  10   a  and  10   b  and the base links  9   a  and  9   b  move into their fully expanded positions when the lid  3  is still wide open. When the lid  3  is opened from its fully closed position, the interconnecting links  10   a  and  10   b  and the base links  9   a  and  9   b  move into their fully collapsed positions when the lid  3  is not wide open yet.  
         [0081]    Conversely, if the gear ratio is designed such that the support shafts  11   a  and  11   b  rotate a smaller number of times for the same amount of pivotal motion of the lid  3 , then the interconnecting links  10   a  and  10   b  and the base links  9   a  and  9   b  are in their expanded positions when the lid  3  is still wide open.  
         [0082]    When the lid  3  is further pivoted in the closing direction, the sector gear  3   a  moves out of engagement with the main gear  19 . Then, the worm gears  17   a  and  17   b  hold the interconnecting links  17   a  and  17   b  and the base links  9   a  and  9   b  at their positions, and the pilot pins  21   a  and  21   b  of the image-forming unit  21  move into engagement with the engagement holes  6   a  and  6   b  formed in the LED head  6 . Thus, the LED head  6  is placed in position with respect to the image-forming unit  21 .  
         [0083]    Since the LED head  6  is positioned on the image-forming unit  21 , the compression springs  7  are compressed such that the urging forces of the compression springs  7  act on the interconnecting links  10   a  and  10   b  and the base links  9   a  and  9   b . However, the upper end corners  9   a ″ and  9   b ″ of the base links  9   a  and  9   b  abut the stoppers  31   a  and  31   b . In addition, the upper end corners  10   a ′ and  10   b ′ of the interconnecting links  10   a  and  10   b  abut the common parts  9   a ′ and  9   b ′ of the base links  9   a  and  9   b  having a U-shaped cross section. Therefore, the overall structure of the base links  9   a  and  9   b  the interconnecting links  10   a  and  10   b  is prevented from buckling, placing the LED head  6  positioned above the image-forming unit  21 . Since the interconnecting links  10   a  and  10   b  and base links  9   a  and  9   b  do not collapse, the compression springs  7  exert large urging forces on the LED head  6  so that the LED head  6  is positioned relative to the image-forming unit  21 . When the lid  3  has been completely closed, the operator locks the lid  3  to the body by means of a fastening means, not shown.  
         [0084]    As described above, the second embodiment provides the same advantages as the first embodiment. In addition, the use of the torque limiters  30   a  and  30   b  allows the lid  3  to be opened wider or to a desired position. The second embodiment has been described with respect to a case where when the lid  3  has been completely closed, the sector gear  3   a  is not in mesh with the main gear  19 . However, the mechanism may also be designed such that the sector gear  3   a  is in mesh with the main gear at all times.  
         [0085]    Third embodiment  
         [0086]    {Construction} 
         [0087]    [0087]FIG. 18 is a perspective view of a pertinent portion of an electrophotographic printer according to a third embodiment.  
         [0088]    [0088]FIG. 19 is a fragmentary view of a pertinent portion of the third embodiment.  
         [0089]    [0089]FIG. 20 is a side view of a pertinent portion of the third embodiment.  
         [0090]    The third embodiment is characterized in that a lid has supporting projections that extend perpendicular to the longitudinal direction of the LED head.  
         [0091]    Referring to FIGS.  18 - 20 , an electrophotographic printer has a lid  53  pivotally mounted to a frame  52  of the printer such that the lid  53  can be opened and closed. The lid  53  has a pair of supporting projections  54  on the left and right sides of the printer so that the lid  53  is rotatably mounted to the frame  52  by means of the supporting projections  54 . A sector gear  53   a  is formed in one-piece construction with the lid  53 , the sector gear  53   a  rotating about an axis passing through the centers of the supporting projections  54 . There are provided four LED assemblies  5  on the inner side of the lid  53 , the LED assemblies  5  being positioned such that each of the LED assemblies  5  extends in a direction perpendicular to the axis passing through the supporting projections  54 .  
         [0092]    Each of the LED assemblies  5  includes the LED head  6 , a pair of compression coil springs  7 , a support plate  8 , a base link  9 , an interconnecting link  10 , and a long link  55 . The base link  9 , interconnecting link  10 , and long link  55  have a U-shaped cross-section. The base link  9  and interconnecting link  10  are disposed on a rear side of the lid  3  (i.e., near rotational axis X). The long link  55  is disposed on a front side of the lid  3  (i.e., the side remote from the rotational axis X). The base link  9 , interconnecting link  10 , and the long link  55  cooperate to support the LED head  6 .  
         [0093]    A support shaft  11  extends parallel to the pivotal axis of the lid  53  and is rotatably mounted on the rear side of the lid  53  by means of bearings, not shown. The upper end portion of the base link  9  is fixed to the support shaft  11  so that the rotation of the support shaft  11  causes the base link  9  to pivot. The lower end portion of the base link  9  enters the upper end portion of the interconnection link  10  such that the base link  9  and the interconnecting link  10  are pivotally coupled by a coupling pin  12  to each other.  
         [0094]    As shown in FIG. 19, the interconnecting link  10  can sufficiently pivot counterclockwise with respect to the base link  9  but is prevented from rotating clockwise because the upper end corner  10 ′ of the interconnecting link  10  abuts the common parts  9 ′ of the base link  9 . The interconnecting link  10  stops pivoting at a position where the coupling pin  12  becomes outside of a line L connecting the support shaft  11  and the coupling pin  13   b . The lower end portion of the interconnecting link  10  and an upward projection  8   b  of the support plate  8  are coupled together by means of the coupling pin  13   b  such that they are pivotal to each other.  
         [0095]    The long link  55  has an upper end portion rotatably supported on a coupling pin  56  formed on the inner side of the lid  53 , and a lower end portion coupled to the projection  8   b  of the support plate  8  by means of the coupling pin  13   a . The lid  53  has opposing stoppers  53   c  and  53   d  formed on the inner surface thereof with the upper end portion of the long link  55  between the stoppers  53   c  and  53   d . The stoppers  53   c  and  53   d  restrict the motion of the long link  55  such that the long link  55  can pivot only in a limited range. The lid  53  also has a stopper  53   e  formed on the inner surface thereof, the stopper  53   e  being located at an upper left side of the base link  9  in FIG. 19.  
         [0096]    [0096]FIG. 21 is the bottom view of the LED head  6 .  
         [0097]    There are provided compression springs  7  under longitudinal ends of the support plate  8 . Each of the springs  7  has one end connected to the support plate  8  and the other end connected to the LED head  6 . In other words, the LED head  6  is suspended from the support plate  8  via the springs  7 . The LED head  6  has an engagement hole  56   a  formed in one of the longitudinal ends thereof and a U-shaped cutout  56   b  formed in the other.  
         [0098]    Referring back to FIG. 19, there are provided image-forming units  21  under the respective LED head assemblies  5 . Each of the image-forming units  21  has pilot pins  21   a  and  21   b  corresponding to the engagement hole  56   a  and the cutout  56   b  formed in the corresponding LED head  6 , respectively. The pilot pins  21   a  and  21   b  enter the engagement hole  56   a  and cutout  56   b , respectively, so that the LED head  6  is placed in position.  
         [0099]    The support shaft  11  has a gear  57  fixedly mounted to an end portion of the support shaft  11 . There is provided a relay gear  58  that rotates about an axis passing through the pair of supporting projections  54  and is in mesh with the gear  57 . The main gear  53   a  is rotatably supported on a rear side of the lid  53  where the sector gear  53   a  is formed. The main gear  19  is in mesh with the sector gear  53   a . A sub gear  60  is rotatably provided which is in mesh with both the main gear  59  and the relay gear  58 .  
         [0100]    With the aforementioned gear mechanism, the pivotal motion of the lid  53  is transmitted through the sector gear  53   a  from the main gear  59  through the sub gear  60  to the relay gear  58 . The rotation is further transmitted through the gear  57  to the support shaft  11 . As shown in FIG. 19, when the lid  53  has been completely closed, the sector gear  53   a  and the main gear  59  are not in mesh with each other.  
         [0101]    {Operation of the third embodiment} 
         [0102]    The operation of the third embodiment will now be described.  
         [0103]    When the lid  3  has been completely closed, the upper end corner  10 ′ of the interconnecting link  10  abuts a bottom part of the U-shaped base link  9  so that the interconnecting link  10  is prevented from further pivoting and the LED head assemblies  5  are fixedly placed in position. When the lid  53  has been completely closed, the sector gear  53   a  and the main gear  59  are not in mesh with each other.  
         [0104]    {Opening operation} 
         [0105]    When the user unlocks a fastening means, not shown, and opens the lid  53  from the fully closed position (FIG. 19), the lid  53  pivots. The sector gear  53   a  is not in meshing engagement with the main gear  59  until the lid  53  has pivoted beyond a predetermined angle. If the lid  53  is further opened in a direction shown by arrow K in FIG. 20 beyond the predetermined angle, then the sector gear  53   a  moves into meshing engagement with the main gear  59 , so that the main gear  59  rotates counterclockwise. The rotation of the main gear  59  is transmitted through the sub gear  60  to the relay gear  58  and further to the support shaft  11  through the gear  57 . Just like the first embodiment, the rotation of the support shaft  11  causes the base links  9  and interconnecting links  10  to collapse so that each of the LED head assemblies  5  moves from its extended position to its collapsed position.  
         [0106]    As shown in FIG. 20, as the base link  9  and interconnecting link  10  are folded one over the other, the long link  55  pivots counterclockwise slightly about the coupling pin  56  until the upper end of the long link  55  abuts the limiter  53   c.    
         [0107]    As the lid  53  is further opened, the upper portion  9 ′ of the base link  9  abuts the stopper  53   e  as shown in FIG. 20, the limiter  53   e  preventing the base link  9  and the interconnecting link  10  from further collapsing. When the LED head assembly  5  takes the position shown in FIG. 20, the collapse of one end of the LED head assembly  5  is completed. When the lid  53  is fully opened, the lid  53  can be at an angle that is greater than 90 degrees just as in the first embodiment.  
         [0108]    After the lid  53  has been opened fully, the operator replaces the toner cartridge and/or image-forming unit or removes jammed paper. Because one end of the LED head assembly  5  has collapsed, the LED head assembly  5  does not interfere with the operator&#39;s hands.  
         [0109]    {Closing operation} 
         [0110]    The closing operation of the lid  53  will be described.  
         [0111]    When the lid  53  is fully opened, the sector gear  53   a  is still in mesh engagement with the main gear  59 . As the lid  53  is closed from where it is fully opened, the rotations of the associated parts of the mechanism are reversed with respect to the opening operation of the lid  53 . In other words, the base links  9  and the interconnecting links  10  will move from their collapsed positions toward their expanded positions. The coupling pin  12  will be outside of the line L (FIG. 19) that connects the support shaft  11  and the coupling pin  13  before the sector gear  53   a  moves out of engagement with the main gear  59 . When the shaft  12  is outside of the line L, the upper end portion  9 ′ of the base link  9  abuts the stopper  53   e  and the upper end corner  10 ′ of the interconnecting link  10  abuts the common part  9 ′ of the base link  9 . Thus, the base link  9  and interconnecting link  10  are prevented from further rotating as shown in FIG. 19 where the long link  55  extends substantially perpendicular to the upper surface of the lid  53 .  
         [0112]    As the lid  53  is further closed, the sector gear  53   a  moves out of meshing engagement with the main gear  59  and the pilot pins  21   a  and  21   b  move into fitting engagement with the engagement hole  56   a  and U-shaped, respectively, thereby placing the LED head  6  in position with respect to the image-forming unit  21 .  
         [0113]    Because the LED head  6  is positioned above the image-forming unit  21 , the compression spring  7  is compressed so that the reaction force of the compression spring  7  is exerted on the interconnecting link  10 , base link  9 , and long link  55 . The interconnecting link  10 , base link  9 , and long link  55  do not buckle but hold the LED head assembly  5  in position relative to the image-forming unit  21 . The compression spring  7  exerts a large reaction force on the LED head  6 , thereby firmly positioning the LED head  6  relative to the image-forming unit  21 . When the lid  53  has been fully closed, the user locks the lid  53  to the body  2  by a fastening, not shown.  
         [0114]    The third embodiment may be applicable to a printer where a pivot pin of the lid extends perpendicular to the longitudinal dimension of the LED heads. In such a printer, as the lid is opened, the LED head assemblies are partially collapsed to facilitate the replacement of the toner cartridge.  
         [0115]    The third embodiment has been described with respect to a case where when the lid is opened, one end of the LED assembly collapses. However, the LED head assembly may be constructed such that the entire LED head assembly collapse just like the first and second embodiments.  
         [0116]    While the first to third embodiments have been described with respect to a case where all of four LED assemblies collapse, the printer may be designed such that only one or two LED head assemblies collapse. A motor can be provided on the body for driving the interconnecting link and base link to collapse, in which case, the mechanism should be designed such that the mechanism move into a collapsed position and an expanded position only when the lid is closed. In other words, the motor is energized such that the mechanism is completely collapsed before the user starts to open the lid and the mechanism starts to move into the expanded position after the lid has been fully closed.  
         [0117]    The first to third embodiments have been described with respect to a case where the LED head assemblies are mounted on the lid of the apparatus. However, the present invention can also be applied to apparatus where the LED head assemblies are provided on the inner lid assembly of the apparatus. Although, the embodiments have been described with respect to an LED head as an exposing unit, the invention may be applied to an apparatus incorporating other type of exposing unit that employs a semiconductor laser.  
         [0118]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art intended to be included within the scope of the following claims.