Abstract:
A switch actuation device for turning on and off a switch in accordance with one of movement and rotation of at least two movable members. The switch actuation device comprises a first shaft, a supporting member swingably or rotatably disposed around the first shaft in response to movement or rotation of a first one of the at least two movable members, a second shaft disposed in the supporting member. A swingable lever is supported by the second shaft with its both ends being swingable, one of said both ends including a switch actuation section activating the switch. The swingable lever swings around the second shaft in response to movement or rotation of a second one of the at least two movable members. The switch actuation section of the swingable lever activates the switch when the supporting member and the swingable lever swing at the same time in response to the movement or the rotation of the first and second one of the at least two movable members, respectively. The switch actuation section of the swingable lever includes a cam.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority pursuant to 35 USC §119 to Japanese Patent Application No. 2010-047358, filed on Mar. 4, 2010, the entire contents of which are hereby incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a switch actuation device that turns on and off a switch in accordance with movement or rotation of plural movable members, and an interlock mechanism and an image forming apparatus, such as a copier, a facsimile apparatus, a printer, etc., incorporating the switch actuation device. 
         [0004]    2. Description of the Background Art 
         [0005]    A conventional interlock mechanism includes a switch that operates in accordance with opening and closing of a wall cover constituting a housing of an electronic instrument is known. Also known is that power supply and general control are stopped when the wall cover is opened and the switch is turned off. 
         [0006]    Such an interlock mechanism is also employed in an image forming apparatus, such as a copier, a facsimile apparatus, a printer, etc. For example, an interlock mechanism is used to control a switch actuation device to turn off a switch and stop supplying power in an image forming apparatus when a part of an openably closable housing is opened during maintenance, such as removing a jammed sheet, replenishing toner, replacing a process unit with a new one, etc. When an image forming apparatus includes plural openably closable covers, plural switch actuation devices are sometimes employed corresponding thereto to maintain the image forming apparatus by opening and closing one of the plural covers. However, a number of switch actuation devices increases as a result. 
         [0007]    Japanese Patent Application Laid Open No. H05-165267 (JP-H05-165267-A) describes an image forming apparatus that includes an actuation lever that moves to an actuation position to actuate a switch in accordance with opening and closing of a first cover, and a movable lever that moves the actuation lever to the actuation position to actuate the switch in accordance with opening and closing of a second cover. Consequently, by combining the first actuation lever with the second movable lever, a power supply can be turned on and off in accordance with opening and closing of plural covers. 
         [0008]    However, in the image forming apparatus of the JP-H05-165267-A, due to fluctuation in positions or shapes of a pressing member provided on a cover to press and activate the actuation and movable levers or of the levers themselves, the switch does not operate sometimes even when the cover is closed. Otherwise, the switch is possibly damaged or deformed when the cover is closed and the actuation lever excessively presses the actuation lever simultaneously. 
         [0009]    Japanese Patent Application Laid Open No. 2008-37054 (JP-2008-37054-A) describes an interlock mechanism that employs a switch turned on when a switch actuation element is internally depressed against a bias force of a spring provided inside a switch housing. Such an interlock mechanism employs plural members to differentiate a direction in which a switch actuation element is turned on from that in which an openably closable cover moves when being closed. Owing to such a configuration of the differentiation mechanism, a force of a cover is indirectly conveyed to the switch actuation element and is not directly conveyed to the switch actuation element from the cover. Accordingly, the switch can avoid damage, even when subjected to a force more powerful than expected when the cover is closed. 
         [0010]    However, the switch is overloaded depending on fluctuation in positions of a pressing member pressing the switch actuation element and shapes thereof in the interlock mechanism of JP-2008-37054-A. 
         [0011]    As a configuration capable of obtaining stable actuation regardless of fluctuation in closing and opening and movement amounts of plural covers, Japanese Patent Application Laid-Open No. 2009-37997(JP-2009-37997-A) proposes a switch actuation device that includes a first swingable lever and a second lever pivotally supported by a support shaft provided on the first lever serving as a fulcrum at its middle portion with its one end facing the switch. The switch actuation device further includes a first actuation section that causes a second lever to swing toward a switch in accordance with opening and closing of one of two openably closable covers. Further included is a second actuation section that causes the first lever to swing in accordance with opening and closing of the other one of the two openably closable covers. Thus, when the other one of the two openably closable cover is closed, the second actuation section swings the first lever and causes the second lever to approach an actuator of a switch. Further, when one of the two openably closable covers is closed, the first actuation section makes one of swinging ends of the second lever to swing toward an actuator of a switch, and causes one of swinging ends of the second lever to press and move the actuator, and turn on the switch. With such a switch actuation device, even when amounts of opening and closing and movement fluctuate, a mutual positional relation between the first and second actuation sections and the first and second levers can be stably maintained by forming the first and second actuation sections in a cam shape. As a result, contact positions between the first and second actuation sections and the first and second levers can be substantially the same, respectively, so that a stable operation can be obtained. 
         [0012]    However, in the switch actuation device of JP-2009-37997-A, depending on and owing to fluctuation in positions and shapes of the second lever that directly contacts the switch, the switch is susceptible to being, overloaded. 
       SUMMARY OF THE PRESENT INVENTION 
       [0013]    The present invention has been made in view of the above noted and another problems and one object of the present invention is to provide a new and novel switch actuation device. Such a switch actuation device comprises a first shaft, a supporting member swingably or rotatably supported around the first shaft in response to movement or rotation of a first movable member, a second shaft disposed in the supporting member. A swingable lever is supported by the second shaft with its both ends being swingable in response to movement or rotation of a second movable member. One of these ends includes a switch actuation section activating the switch. The switch actuation section of the swingable lever activates the switch when the supporting member and the swingable lever swing at the same time in response to the movement or the rotation of the first and second movable members, respectively. The switch actuation section of the swingable lever includes a cam. 
         [0014]    In another aspect, the cam includes an arc shaped portion disposed facing the switch. 
         [0015]    In yet another aspect, a third shaft is disposed and an actuation member is swingably or rotatably supported therearound. The actuation member presses an actuation object section positioned opposite to the switch actuation section of the swingable lever. The actuation member swings or rotates in response to the movement or the rotation of the second movable member and presses the actuation object section of the swingable lever in a prescribed direction to finally activate the switch. 
         [0016]    In yet another aspect, the actuation member includes a cam at its one end pressing the actuation object section of the swingable lever. 
         [0017]    In yet another aspect, the cam includes an arc-shaped portion facing the actuation object section of the swingable lever. 
         [0018]    In yet another aspect, a first biasing member is provided to bias the swingable lever away from the switch. A second biasing member is provided to bias the actuation member away from the in a direction lever. 
         [0019]    In yet another aspect, the switch actuation section of the swingable lever presses a leading end of a lever-shaped actuator disposed in the switch. 
         [0020]    In yet another aspect, a virtual line extending through a swinging or rotational shaft center of the supporting member and that of the swingable lever is substantially orthogonal to a longitudinal axis of the lever-shaped actuator. 
         [0021]    In yet another aspect, the supporting member and the switch collectively form a single structure. 
         [0022]    In yet another aspect, the supporting member, the actuation member, and the switch collectively form a single structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    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: 
           [0024]      FIG. 1  is a perspective view illustrating an image forming apparatus that includes an exemplary switch actuation device according to one embodiment of the present invention; 
           [0025]      FIG. 2  is a perspective view illustrating the switch actuation device of  FIG. 1 ; 
           [0026]      FIG. 3  is a front view illustrating the switch actuation device of  FIG. 1 ; 
           [0027]      FIG. 4  is an exemplary micro-switch operating in the switch actuation device of  FIG. 1 ; 
           [0028]      FIG. 5  is the switch actuation device of  FIG. 1  operating when a front cover is opened; 
           [0029]      FIG. 6  is the switch actuation device of  FIG. 1  operating when a left side cover is opened; 
           [0030]      FIG. 7  is a front view of another exemplary lever; and 
           [0031]      FIG. 8  is a front view of another exemplary switch actuation device according to another embodiment of the present invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0032]    Referring now to the drawings, wherein like reference numerals and characters designate identical or corresponding parts throughout the several figures, and in particular in  FIG. 1 , an image forming apparatus  100  includes a sheet feeding section  10  having plural sheet feeding cassettes each accommodating recording medias, a sheet ejection section  20  stacking recording medias each bearing an image, and an image formation section forming an image on a recording media. The image formation section  30  is disposed between the sheet feeding section  10  and the sheet ejection section  20 . An image formed by the image formation section  30  is transferred onto a recording sheet conveyed from the sheet feeding section  10 . The recording sheet is then ejected onto the sheet ejection section  20 . 
         [0033]    Openably closable left and front side covers  41  and  42  on respective left side and front side surfaces of a housing of the image formation section  30  are swingable in directions shown by arrows A and B around their lower sections for the purposes of allowing access to the interior of the image forming apparatus  100  for replacing a developing device with a new one when a prescribed numbers of sheets has been printed and a life of a device ends, or when removing a jammed recording media during printing. Further, there are disposed plural protrusions  41   a  and  42   a  on the both left and front side covers  41  and  42  while protruding therefrom toward an inside of the housing to serve as links linked with opening and closing of the covers  41  and  42 , respectively. 
         [0034]    Specifically, the protrusion  41   a  is disposed on an inner surface of the left side cover  41  almost at a right side end thereof, whereas the protrusion  42   a  is disposed approximately centrally along one side end of the front cover  42 ; in the present embodiment, that side is the left side. Plural openings  100 A 1  and  100 A 2  are disposed on sections of the housing facing the respective protrusions  41   a  and  42   a,  in to which the protrusions  41   a  and  42   a  are inserted. 
         [0035]    The opening  100 A 1  is formed on the left side surface almost at the corner between the front and left side surfaces. The switch actuation device described later is provided in an inner space surrounded by the openings  100 A 1  and  100 A 2 . 
         [0036]    When a developing device is replaced with a new one, the left side cover  41  is opened. When a jammed recording sheet is extracted, the front cover  42  is opened. There is a section in the interior of the image forming apparatus  100  to which a high voltage is applied such as when a toner image is transferred onto a recording sheet or when a recording sheet is conveyed. For this reason, when one of the left and front covers  41  and  42  is opened, the above-described switch actuation device is activated and a power supply is turned off to shut off the high-voltage section. 
         [0037]    As shown in  FIG. 2 , the switch actuation device is viewed from an inside of the housing of the image forming apparatus  100 . As shown in  FIG. 3 , the switch actuation device is viewed without a swingable bracket  55 . As shown in  FIGS. 2 and 3 , both left and front covers  41  and  42  are closed and accordingly a switch of the switch actuation device  50  is turned on. 
         [0038]    As shown in  FIGS. 2 and 3 , the switch actuation device  50  includes a holding bracket  51  as a single structure that holds respective members. The holding bracket includes three shafts  51   a  to  51   c.  A micro-switch  52  is screwed to the shaft  51   a  by a screw  45 . An actuation member  53  is disposed against the shaft  51   b  using an E-shaped ring and is rotatable therearound. Further, a swingable bracket  55  is disposed against the shaft  51   c  as a supporting member using an E-shaped ring and is swingable therearound. 
         [0039]    The micro-switch  52  mainly includes an actuator unit that has a hinge lever  52   a  and an actuation element  52   b,  and a housing  52   c  that has a spring as a biasing member that biases an electric contact point and the actuation element  52   b  in a prescribed direction. 
         [0040]    Now, the micro-switch  52  is described in more in detail with reference to  FIG. 4  illustrating a front view thereof when the housing lies horizontally. The micro-switch  52  is a normal open type, which is electrically turned off when the hinge lever  52   a  is free from activation. The hinge lever  52   a  is produced by a flexible thin plate with its one end being disposed against the housing and with its other end being free. Further, the actuation element  52   b  is biased downward in the drawing by a spring disposed in the housing, so that the leading end thereof contacts the hinge lever  52   a  to push the hinge lever  52   a  down when the hinge lever  52   a  is free from a load. Further, the actuation element  52   b  is enabled to step back within the housing against the bias force of the spring and turns on a contact point disposed in the housing when a free end of the hinge lever  52   a  receives load and is lifted up. 
         [0041]    When the lever  57  described later swings in a direction shown by an arrow in the drawing and contacts the free end of the hinge lever  52   a,  the hinge lever  52   a  gradually rises around its fixed end as a fulcrum due to a pressing force of the lever  57 , and presses the actuation element  52   b  at the same time. Since the micro-switch  52  includes a mechanical allowance H 1 , the contact point is not immediately turned on even when the lever  57  contacts the hinge lever  52   a.  However, when the lever  57  swings beyond the mechanical allowance H 1 , the actuation element  52   b  linked with the hinge lever  52   a  turns the contact point on in the housing. Even when the lever  57  lifts the hinge lever  52   a  up from the above-described situation, respective parts of the micro-switch  52  are not overloaded as far as it stays within the appropriate operation ranged H 2 . However, when the free end of the hinge lever  52   a  is lifted up higher than the horizontal line in the drawing, the contact point maintains the turning on condition, but the hinge lever  52   a  is bent, so that the actuation element  52   b,  the inner spring, and the inner contact point are overloaded (see a range of H 3  in the drawing). 
         [0042]    Durability of the micro-switch is excellent in general. However, when the micro-switch is continuously overloaded for a long time, the hinge lever  52   a  is sometimes permanently deformed. In addition, the actuation element  52   b,  the inner spring, and the inner contact point are damaged, thereby the micro-switch is broken. To resolve such a problem, when the micro-switch  52  is activated, the lever  57  is preferably stopped so that the hinge lever  52   a  of the micro-switch  52  operates (swings?) within the appropriate operation range H 2   
         [0043]    As shown in  FIG. 2 , the actuation member  53  includes a reception surface  53   a  that contacts the protrusion  42   a  of the front cover  42 , and an engaging section  53   b  on an opposite side of the shaft  51   b  to the reception surface  53   a,  which engages one end of the spring  54 . The protrusion  42   a  inserted through the opening  100 A 2  of the housing contacts the reception surface  53   a  when the front cover  42  is closed. Thus, the actuation member  53  swings against a bias force of the spring  54  while receiving a pressing force from the protrusion  42   a.  The spring  54  is a tension spring with the other end of it being held by the spring holder  51   d  of the holder bracket  51 . Since the actuation member  53  is always biased by the spring  54  in a direction shown by an arrow C, the reception surface  53   a  swings to a vertical position when the front cover  42  is opened and the protrusion  42   a  is withdrawn as shown in  FIG. 5 . Further, the contact section  53   c  contacting the lever  57  at the end of the actuation member  53  is constituted by an arc shaped cam rotating around the shaft  51   b.  Thus, when the actuation member  53  swings receiving the pressing force from the protrusion  42   a,  the contact section  53   c  contacts the reception surface  57   a  of the lever  57  serving as an actuation object section, and causes swinging of the lever  57 . 
         [0044]    The swingable bracket  55  includes a reception surface  55   a  contacting the protrusion  41  a of the left side cover  41 . When the left side cover  41  is closed, the protrusion  41   a  is inserted through the opening  100 A 1  of the housing and contacts the reception surface  55   a  of the holder bracket  51  due to the pressing force. Further, a shaft  55   b  swingably supporting the lever  57  and a plate spring  58  that biases the lever  57  are disposed in the swingable bracket  55 . 
         [0045]    The ends of the lever  57  are swingble around the shaft  55   b  of the swingable bracket  55 . The pressing section  57   b  serving as a switch actuation section at one end of the lever  57  faces the hinge lever  52   a  of the micro-switch  52 . A left side surface of the actuation object section (i.e., a rear end) of the actuation member  53  faces the contact section  53   c  at its other end. The lever  57  includes a reception surface  57   a  serving as the actuation object section which contacts the contact section  53   c  of the actuation member  53 , a pressing section  57   b  that contacts the hinge lever  52   a  of the switch  52 , and a spring reception surface  57   c  that receives a bias from the plate spring  58 . Thus, when the contact section  53   c  of the actuation member  53  contacts the reception surface  57   a  serving as the actuation object section, the lever  57  swings due to the pressing force so that the pressing section  57   b  of the leading end approaches the hinge lever  52   a,  while the switch  52  is turned on when the hinge lever  52   a  is pressed. In this way, the lever  57  swings together with the swingable bracket  55  being held thereon, while the lever itself swings around the shaft  55   b  of the swingable bracket  55 . 
         [0046]    One end of the plate spring  58  is disposed against the swingable bracket  55  with its free end always contacting the spring reception surface  57   c  of the lever  57 . Thus, the leading end section of the lever  57  is biased in a direction to separate away from the micro-switch  52 , i.e., a direction in which the pressing section  57   b  of the lever  57  is separated from the hinge lever  52   a.    
         [0047]    In the above-described switch actuation device  50 , when the left side cover  41  is closed, the protrusion  41   a  contacts the reception surface  55   a  of the swingable bracket  55 , and accordingly, both the swingable bracket  55  and the lever  57  swing together toward the micro-switch  52 . In such a situation, since the pressing section  57   b  of the lever  57  held by the swingable bracket  55  is located at a position separated from the hinge lever  52   a  of the switch  52  due to the bias force of the plate spring  58 , the micro-switch  52  is continuously turned off as shown in  FIG. 5 . In such a situation, when the front cover  42  is further closed, the protrusion  42   a  moves in a direction shown by an arrow D in the drawing, and contacts and presses the reception surface  53   a  of the actuation member  53 . Further, the actuation member  53  swings against the bias force of the spring  54 . Then, the contact section  53   c  contacts the reception surface  57   a  of the lever  57 , and the lever  57  swings in a prescribed direction. Consequently, the pressing section  57   b  of the lever  57  presses the hinge lever  52   a  of the micro-switch  52 , thereby turning on the micro-switch  52 . In this way, when the left and front side covers  41  and  42  are closed at the same time, the micro-switch  52  is turned on, so that power can be supplied to the image forming apparatus. 
         [0048]    Now, an exemplary operation of the switch actuation device  50  when a front cover is opened is described with reference to  FIG. 5 . As shown, when the front cover  42  is opened, the protrusion  42   a  is withdrawn. Simultaneously, the actuation member  53  is drawn by the spring  54  and swings in a direction to separate away from the lever  57 . At that moment, since the lever  57  is biased by the plate spring  58  in a direction to separate away from the micro-switch  52 , the pressing section  57   b  of the lever  57  separates from the hinge lever  52   a  of the switch  52 . Consequently, even when the front cover  42  is opened while the left cover  41  is closed, the micro-switch  52  is turned off. 
         [0049]    Now, an exemplary operation of the switch actuation device  50  when the left cover is opened is described with reference to  FIG. 6 . When the left cover  41  is opened, the protrusion  41   a,  not shown, is withdrawn. Simultaneously, the pressing force applied to the pressing section  57   b  of the lever  57  via the bracket  55  by the protrusion  41   a  to press the hinge lever  52   a  of the switch  52  is released, and the lever  57  is pressed and returned by a reacting force of the hinge lever  52   a,  so that the micro-switch  52  is turned off. At this moment, since the actuation member  53  engages the reception surface  53   a  of the other end of the lever  57 , the lever  57  substantially does not swings with regard to the swinging bracket  55 , but swings in a direction to separate away from the hinge lever  52   a  together with the swinging bracket  55 . Consequently, when the left side cover  41  is opened, the micro-switch  52  is turned off even if the front cover  42  is closed. 
         [0050]    According to one embodiment of the present invention as described above with reference to  FIGS. 1 to 6 , the micro-switch  52  is turned off when one of left and front side covers is opened, and is turned off only when both are closed. 
         [0051]    Further, the switch actuation device of the above-described embodiment can achieve a stable operation regardless of fluctuation in movement amounts of the protrusions  41  a and  42   a,  which are caused by fluctuation in opening and closing amounts of the left and front side covers  41  and  42 , and that in positions and shapes of the members. 
         [0052]    Now, a situation when the front cover  42  is closed and the protrusion  42   a  stops largely passing through a prescribed position is described with reference to  FIG. 3 . In such a situation, even though a swinging amount of the actuation member  53  increases, a swinging amount of the lever  57  caused by pressing of the actuation member  53  does not fluctuate, because the contact section  53   c  contacting the lever  57  of the actuation member  53  is constituted by an arc shaped cam having a center at a shaft  51   b . Specifically, even when a closing position of the front cover  42  fluctuates, and accordingly a swinging angle of the actuation member  53  fluctuates, the swinging amount of the lever  57  substantially does not fluctuate. However , since fluctuation in cam shapes of the contact section  53   c  of the lever  53 , and that in shapes of the reception surface  57   a  of the lever  57  that contacts the actuation member  53  remain, the swinging angle of the lever  57  is hardly limited perfectly within a prescribed level. 
         [0053]    Then, the pressing section  57   b  of the leading end of the lever  57  that contacts the hinge lever  52   a  of the micro-switch  52  is constituted by an arc shaped cam having a center at a shaft  55   b  of the support bracket  55 . Consequently, even when the lever  57  excessively swings more than a prescribed angle, a pressing amount of the lever  57  pressing the hinge lever  52   a  does not largely fluctuate, and the micro-switch  52  can avoid overload. 
         [0054]    Further, since the pressing section  57   b  of the lever  57  faces a leading end of the hinge lever  52   a,  the hinge lever  57  elastically deforms, and accordingly load on the micro-switch  52  can be reduced even when a pressing-in amount increases due to fluctuation in shapes of the lever  57 . 
         [0055]    Instead of the above-described arc shaped cam of the lever  57 , a lever  59  having a cam shape as shown in  FIG. 7  can be employed. Specifically, a pressing section  59   b  of the lever  59  which contacts the hinge lever  52   a  of the micro-switch  52  does not form an arc shape having a swinging center at a shaft hole  59   a,  and an amount of pressing the hinge lever  52   a  is changed in accordance with a rotational angle of the lever  59 . Specifically, a radius starting from a rotation center of the shaft hole  59   a  ending at a leading end of the pressing section is smaller on the right side end than that on the left side end. Consequently, as the swinging angle of the lever  59  increases contacting the hinge lever  52   a,  a pressing amount gradually decreases and does not increase even when the lever  59  swings more than a supposed level in comparison with the lever  57 . 
         [0056]    Now, another embodiment of the switch actuation device  60  is described with reference to  FIG. 8 . As shown, a micro-switch  52  is disposed at a prescribed position enabling to highly likely avoid overload thereon. 
         [0057]    Specifically, a positional relation between the lever  57  and the micro-switch  52  in the switch actuation device  60  is different from that in the switch actuation device  50 . For example, the micro-switch  52  is positioned so that a virtual line extending through a center of the shaft  51   c  serving as swinging center for the swinging bracket  55  and a center of the shaft  55   b  serving as swinging center for the lever  57  orthogonally intersects with the hinge lever  52   a  of the micro-switch  52  when the protrusion  41   a  causes swinging of bracket  55 . Consequently, even when the swinging angle of the swinging bracket  55  around the shaft  51   c  fluctuates due to the fluctuation in stopping positions and shapes of the protrusion  41   a,  the pressing section  57   b  formed on the leading end of the lever  57  swingably supported by the swinging bracket  55  contacts the hinge lever  52   a,  and the fluctuation in amounts of pressing toward the hinge lever  52   a  can be suppressed to the minimum level. When the micro-switch  52  is turned on and a swinging angle of the bracket  55  is too large for the virtual line K to orthogonally intersect with the hinge lever  52   a  (making a sharp angle), the pressing section  57   b  formed on the leading end of the lever  57  moves in a direction to separate away from the hinge lever  52   a,  so that an amount of pressing toward the hinge lever  52   a  by the lever  57  decreases. Specifically, the maximum value of the pressing-in amount toward the hinge lever  52   a  is determined by a distant between centers of the shafts  51   c  and  55   b  and that between the center of the shaft  55   b  and the pressing section  57   b  of the lever  57 . Thus, as the swinging angle of the swinging bracket  55  deviates from a prescribed angle, the pressing amount decreases. 
         [0058]    Since the pressing section  57   b  of the leading end of the lever  57  is constituted by the arc shaped cam having the center at the shaft  55   b,  the pressing amount with regard to the hinge lever  52   a  substantially does not fluctuate even when the moving amount of the protrusion  42   a,  and the swinging angle of the actuation member  53  and the lever  57  fluctuate. 
         [0059]    Further, according to the switch actuation device  60 , even when the moving amount of the protrusion  41   a  and the swinging angle of the actuation member  55  fluctuate, the amount of pressing-in of the lever  57  toward the hinge lever  52   a  can be suppressed to the minimum level, and accordingly a stable operation of the micro-switch  52  can be obtained while avoiding the overload thereon. Further, even when the moving amount of the protrusion  42   a,  and the swinging angles of the actuation member  53  and the lever  57  fluctuate, the pressing amount with regard to the hinge  52  substantially does not fluctuate, and accordingly a stable operation of the micro-switch  52  can be obtained while avoiding the overload thereon. 
         [0060]    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.