Abstract:
A push button switch is utilized in an input unit of a thin electronic apparatus is provided. A link member assembled in X-shape for supporting a key top capable of moving vertically. A base slidably supports a lower latched shaft of a first frame of the link member. The base pivotably supports a lower latched shaft of a second frame of the link member. A driving spring impels the lower latched shaft of the first frame in the central direction of the link member, and elastically deforms downwardly by a horizontal movement of the lower latched shaft to operate a switch member. An operating spring is pressed by the lower latched shaft to deform horizontally and elastically.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a push button switch used for an input unit of an electronic apparatus such as a thin notebook-type personal computer.  
         BACKGROUND OF THE INVENTION  
         [0002]    A conventional push button switch will be explained with referring to FIG. 14 through FIG. 17.  
           [0003]    [0003]FIG. 14 is a plan view of the conventional push button switch, FIG. 15 is a sectional view of the switch, FIG. 16 is an apparent perspective view of a link member of the switch, and FIG. 17 is a sectional view of the switch during a pressing operation. Key top  1  made of resin has cylindrical stem  1 A on the lower surface of the center of the key top and a pair of engaging parts  1 B at both sides on the lower surface. As shown in FIG. 16, resin-made frame  2  having substantially a square U-shape has a pair of parallel arms  2 C 1 ,  2 C 2  which include cylindrical spindles  2 A,  2 B 1  ( 2 B 2 ) at both ends, respectively, and spindle  2 A for coupling one end of the arm  2 C 1  to that of the arm  2 C 2 . Substantially central parts of arms  2 C 1 ,  2 C 2  of frame  2  have cylindrical shafts  2 D 1 ,  2 D 2 , respectively. Resin-made frame  3  having substantially a square U-shape similarly has a pair of parallel arms  3 C 1 ,  3 C 2  which include cylindrical spindles  3 A,  3 B 1  ( 3 B 2 ) at both ends, respectively, and spindle  3 A for coupling one end of the arm  3 C 1  to that of the arm  3 C 2 . Substantially central parts of arms  3 C 1 ,  3 C 2  of frame  3  have long holes  3 D 1 ,  3 D 2 , respectively. Shafts  2 D 1 ,  2 D 2  of frame  2  are pivotably and slidably supported by long holes  3 D 1 ,  3 D 2  in frame  3 . Frames  2 ,  3  are coupled to each other in an X-shape in side view to form a link member  4 .  
           [0004]    Spindles  2 B 1 ,  2 B 2  and spindles  3 B 1 ,  3 B 2  in the upper parts of link member  4  are pivotably held on respective pairs of engaging parts  1 B disposed at both sides on key top  1 .  
           [0005]    Spindles  2 A,  3 A in the lower parts of link member  4  are pivotably and slidably held between each pair of engaging recesses  5 B disposed at both sides on resin-made case  5  and switch member  6  under the case. Switch member  6  includes a flexible upper sheet, a movable contact on the lower surface of the upper sheet, a lower sheet, a fixed contact on the upper surface of the lower sheet, and a spacer interposed between both sheets. Therefore, the movable contact faces to the fixed contact. The movable contact and fixed contact touch with each other by pressing switch member  6  with projection  7 A on a lower surface of the central part of substantially conical dome part  7 . Dome part  7  is made of elastic material such as rubber and placed over the upper surface of switch member  6 .  
           [0006]    Case  5  includes, at the center, guide hole  5 A for engaging and supporting stem  1 A of key top  1  and dome part  7 , and engaging recesses  5 B at both sides on guide hole  5 A. Metal substrate  8  reinforces the lower surface of switch member  6 .  
           [0007]    An operation of a push button switch having such a structure will be described. When key top  1  has the upper surface pressed down with a finger, link member  4  held by engaging parts  1 B pivots on cylindrical spindles  2 B 1 ,  2 B 2  and  3 B 1 ,  3 B 2 . Spindles  2 A,  3 A which are pivotably and slidably held between case  5  and switch member  6  pivot and slide along recesses  5 B.  
           [0008]    Frames  2 ,  3  of link member  4  are supported with cylindrical shafts  2 D 1 ,  2 D 2  in the substantially central parts of arm  2 C 1 ,  2 C 2  and long holes  3 D 1 ,  3 D 2  in the substantially central parts of arm  3 C 1 ,  3 C 2 , and are interlocked. When key top  1  is pressed and operated, therefore, key top  1  is pressed down with keeping a substantially horizontal attitude as shown in FIG. 17. Key top  1  pushes and bends dome part  7 , and thus, projection  7 A on the lower surface of dome part  7  presses switch member  6  to turn on the switch to generate a predetermined signal.  
           [0009]    When a pressing force applied to key top  1  is subsequently removed, dome part  7  returns to an original shape due to the elastic restoring force and press back link member  4  and key top  1 , and thus the original state shown in FIG. 15 is provided.  
           [0010]    Although having a good operability, the conventional push button switch includes tall dome part  7  between key top  1  and switch member  6 . Additionally, guide hole  5 A for positioning dome part  7  and key top  1  makes the switch entirely high and not easily applicable to a recent thin electronic apparatus.  
         SUMMARY OF THE INVENTION  
         [0011]    A thin push button switch easily applied to a thin electronic apparatus is provided.  
           [0012]    The switch includes the following elements:  
           [0013]    (a) A vertically-movable key top including first and second holding parts;  
           [0014]    (b) A first frame having a first end pivotably held by the first holding part, and a second end;  
           [0015]    (c) A second frame having a first end pivotably and slidably held by the second holding part, and a second end. A substantially central part of the frame is pivotably coupled to the first frame in an X-shape through a coupling part at a substantially central part of the first frame;  
           [0016]    (d) A substantially plate-like base including a first support part for pivotably and horizontally-slidably supporting the second end of the first frame, and a second support part for pivotably supporting the second end of the second frame;  
           [0017]    (e) An operating spring disposed between the base and the key top, and elastically deformed outward by the second end of the first frame;  
           [0018]    (f) A driving spring for elastically contacting with the second end of the first frame from the lower side and for impelling the second end of the first frame inward. The spring has a tapered part pushed by the second end of the first frame; and  
           [0019]    (g) A switch member disposed under the driving spring. The member includes switch contacts pressed and operated by the driving spring.  
           [0020]    Another push button switch includes the following elements:  
           [0021]    (a) A vertically-movable key top including first and second holding parts;  
           [0022]    (b) A first frame having a first end pivotably held by the first holding part, and a second end;  
           [0023]    (c) A second frame having a first end pivotably and slidably held by the second holding part, and a second end. A substantially central part of the frame is pivotably coupled to the first frame in an X-shape through a coupling part at a substantially central part of the first frame;  
           [0024]    (d) A third frame having a first end pivotably held by the first holding part coaxially at the coupling part;  
           [0025]    (e) A plate-like base including a first support part for pivotably and horizontally-slidably supporting the second end of the first frame and the second end of the third frame, and a second support part for pivotably supporting the second end of the second frame;  
           [0026]    (f) An operating spring disposed between the base and the key top, elastically deformed outward by the second end of the first frame;  
           [0027]    (g) A driving spring elastically contacting with the second end of the third frame from the lower side for impelling the second end of the third frame inward. The spring has a tapered part pushed inward by the second end of the third frame; and  
           [0028]    (h) A switch member including switch contacts disposed under the driving spring and pressed and operated by the driving spring.  
           [0029]    A thin push button switch can be obtained in which a pressing operation force can be adjusted by changing the pressure of the operating spring. The push button switch including a downsized operating spring has a small projected area. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]    [0030]FIG. 1 is a sectional view of a push button switch in accordance with exemplary embodiment 1 of the present invention.  
         [0031]    [0031]FIG. 2 is a plan view of the switch except for a key top in accordance with embodiment 1.  
         [0032]    [0032]FIG. 3 is an exploded perspective view of the switch in accordance with embodiment 1.  
         [0033]    [0033]FIG. 4 is an exploded perspective view of a link member of the switch in accordance with embodiment 1.  
         [0034]    [0034]FIG. 5 is an apparent perspective view of a sheet member of the switch in accordance with embodiment 1.  
         [0035]    [0035]FIG. 6A is a sectional view of the switch in accordance with embodiment 1 during a pressing operation.  
         [0036]    [0036]FIG. 6B is a plan view of the switch except for the key top in accordance with embodiment 1.  
         [0037]    [0037]FIG. 7A is a sectional view of a push button switch in accordance with exemplary embodiment 2 of the present invention.  
         [0038]    [0038]FIG. 7B is a plan view of the switch except for a key top in accordance with embodiment 2.  
         [0039]    [0039]FIG. 8A is a sectional view of the switch in accordance with embodiment 2 during a sinking down period.  
         [0040]    [0040]FIG. 8B is a plan view of the switch except for the key top in accordance with embodiment 2.  
         [0041]    [0041]FIG. 9A is a sectional view of a push button switch in accordance with exemplary embodiment 3 of the present invention.  
         [0042]    [0042]FIG. 9B is a plan view of the switch except for a key top in accordance with embodiment 3.  
         [0043]    [0043]FIG. 10 is an apparent perspective view of a link member of the switch in accordance with embodiment 3.  
         [0044]    [0044]FIG. 11 is an exploded perspective view of the link member of the switch in accordance with embodiment 3.  
         [0045]    [0045]FIG. 12A is a sectional view of the switch in accordance with embodiment 3 during a pressing operation.  
         [0046]    [0046]FIG. 12B is a plan view of the switch except for the key top in accordance with embodiment 3.  
         [0047]    [0047]FIG. 13A is a sectional view of a switch in accordance with exemplary embodiment 4 during a sinking down period.  
         [0048]    [0048]FIG. 13B is a plan view of the switch except for the key top in accordance with embodiment 4.  
         [0049]    [0049]FIG. 14 is a plan view of a conventional push button switch.  
         [0050]    [0050]FIG. 15 is a sectional view of the conventional switch.  
         [0051]    [0051]FIG. 16 is an apparent perspective view of a link member of the conventional switch.  
         [0052]    [0052]FIG. 17 is a sectional view of the conventional switch during a pressing operation. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0053]    (Embodiment 1)  
         [0054]    [0054]FIG. 1 is a sectional view of a push button switch in accordance with exemplary embodiment 1 of the present invention, FIG. 2 is a plan view of the switch except for a key top, FIG. 3 is an exploded perspective view thereof, and FIG. 4 is an exploded perspective view of a link member as an important part thereof.  
         [0055]    In FIG. 1 through FIG. 3, resin-made key top  11  of which upper surface is a pressing operation surface has pair of first holding parts  12  and pair of second holding parts  13  on its lower surface, and is held vertically movably by link member  14  engaged with them. Link member  14 , as shown in FIG. 3 and FIG. 4, comprises first frame  15  in a substantially quadrangle plate shape and second frame  16  in a substantially square U shape that are both made of resin. Circular projections  15 A on both side surfaces of the intermediate part of first frame  15  are pivotably engaged and coupled with circular holes  16 A in the intermediate part of both-side arms of second frame  16 , and frames  15 ,  16  are assembled in an X shape in side view.  
         [0056]    As shown in FIG. 1, upper latched shafts  15 B on both surfaces of the upper end of first frame  15  are pivotably held by first holding parts  12  of key top  11 . The both ends of lower latched shaft  15 C in a circular shaft shape at the lower end of frame  15  are sandwiched between pair of first support parts  18  of base  17  in a lower part and the upper surface of spring plate  20  under the first support parts  18 , and are supported pivotably, slidably, vertically un-movably.  
         [0057]    Upper latched shafts  16 B on both surfaces of the upper end of second frame  6  are pivotably and slidably held by second holding parts  13  of key top  11 . Lower latched shafts  16 C on the both sides of the lower end of second frame  16  are pivotably sandwiched between pair of second support parts  19  of base  17  and the upper surface of spring plate  20 .  
         [0058]    Base  17  is made of a metal plate, and includes pair of first support parts  18  and pair of second support parts  19  that are respectively formed by punching and bending the metal plate. Positions of first support parts  18  and second support parts  19  are thus accurate, and the push button switch has high rigidity on the whole. Particularly, first support parts  18  can have a rib as necessary to improve the rigidity.  
         [0059]    Spring plate  20  is made of a thin elastic metal plate, and comprises spring support part  21 A unitarily formed by punching and bending the thin metal plate, operating spring  21  extending from support part  21 A, and stoppers  22 . Support part  21 A and spring  21  project over base  17 , are held in a state in which stoppers  22  apply a predetermined initial pressure to them, and face to lower tip  15 D of the outside of lower latched shaft  15 C of first frame  15 . Initial pressure of operating spring  21  held by stoppers  22  allows adjustment of an operation force of the push button switch.  
         [0060]    Additionally, spring plate  20  unitarily comprises driving spring  23  as a cantilever plate spring under first frame  15 . Tapered part  23 A bent upwardly at the tip of spring  23  presses a central part of lower latched shaft  15 C at the lower end of first frame  15  to energize it toward the center of link member  14 . Link member  14  is thus held in a state in which it is raised, namely key top  11  is pushed up. In this state, lower tip  15 D of first frame  15  does not contact with operating spring  21 , and is separated from spring  21  by a slight distance. Spring support part  21 A of operating spring  21  lies outside tapered part  23 A at the tip of driving spring  23 .  
         [0061]    Spring plate  20  is piled on switch member  24 . Switch member  24  comprises a flexible upper sheet, a movable contact on the lower surface of the upper sheet, a lower sheet, a fixed contact on the upper surface of the upper sheet, and a spacer interposed between both sheets. The movable contact and the fixed contact provide opposite switch contacts  24 A facing to each other to form a membrane switch. Opposite switch contacts  24 A lie directly underneath the root of tapered part  23 A of driving spring  23 . Switch member  24  is piled on metallic substrate  25  for improving rigidity of the push button switch to stabilize an operation. FIG. 5 is an apparent perspective view of sheet member  26  formed by piling base  17 , spring plate  20 , and switch member  24  on metallic substrate  25 .  
         [0062]    Since the push button switch thus comprises a sheet member integrally formed with various members, number of members for structuring the push button switch is reduced, the switch is easily assembled, and positional relations of various members can be correctly managed.  
         [0063]    A motion of the push button switch with such a structure in accordance with embodiment 1 during a pressing operation will be described with reference to a sectional view during the pressing operation shown in FIG. 6A and a plan view of the switch except for key top shown in FIG. 6B.  
         [0064]    When a pressing operation surface of key top  11  is pushed down from the state shown in FIG. 1 in the arrow direction shown in FIG. 6A, first frame  15  and second frame  16  pivot on engaging parts between circular projections  15 A of first frame  15  and circular holes  16 A of second frame  16 , and link member  14  starts to be folded.  
         [0065]    At this time, upper latched shafts  15 B of first frame  15  are pivotably supported by first holding parts  12  of key top  11 , and do not move. Lower latched shafts  16 C of second frame  16  are also pivotably supported by second support parts  19  of base  17 , and do not move. Lower latched shaft  15 C of first frame  15  move outwardly, extendedly in first support parts  18  of base  17 . Upper latched shafts  16 B of second frame  16  are move outwardly, extendedly in second holding parts  13  of key top  11 . The central part of lower latched shaft  15 C at the lower end of first frame  15  is first moved in the direction for slightly raising tapered part  23 A of driving spring  23  by a slight pressing force, and therefore, lower tip  15 D of first frame  15  bumps against operating spring  21  applied with an initial pressure. Then, as shown in FIG. 6B, lower tip  15 D presses and elastically deforms operating spring  21 , and operating spring  21  generates an operating force of key top  11 , namely the push button switch. The central part of lower latched shaft  15 C at the lower end of first frame  15  presses tapered part  23 A of driving spring  23  by the slight pressing force, and then, with a large force, presses and elastically deforms operating spring  21  applied with the initial pressure. Therefore, the push button switch feels soft during the pressing operation.  
         [0066]    In accordance with the movement discussed above, the central part of lower latched shaft  15 C at the lower end of first frame  15  further raises tapered part  23 A of driving spring  23  to elastically deform and press down driving spring  23 . Driving spring  23  then pushes opposite switch contacts  24 A of switch member  24  lying directly underneath the root of tapered part  23 A to establish a short circuit.  
         [0067]    When key top  11  is further pressed down after that, a plate-like arm of driving spring  23  elastically deforms, first frame  15  finally overlaps on second frame  16  and link member  14  is perfectly folded as shown in FIG. 6A.  
         [0068]    When a pressing force applied to key top  11  is removed, an elastic restoring force between operating spring  21  and driving spring  23  raises link member  14  to the original state shown in FIG. 1, and returns key top  11  to the predetermined position.  
         [0069]    When both first frame  15  and second frame  16  forming link member  14  are made of resin, the push button switch can be lightened. The push button switch is therefore advantageous when many push button switches, such as input switches of a personal computer especially requiring compactness and lightness, are used in parallel.  
         [0070]    First frame  15  that rubs with and bends tapered part  23 A of driving spring  23  when the push button switch is pressed is made of an abrasion resistant material such as a metal material formed by die-casting metal such as aluminum or press-working a metal plate. The push button switch is thus provided which is somewhat heavy, but has less degradation due to abrasion of first frame  15  and a long service life.  
         [0071]    (Embodiment 2)  
         [0072]    Same elements used in embodiment 1 are denoted with the same reference numbers and are not described in detail.  
         [0073]    [0073]FIG. 7A is a sectional view of a push button switch in accordance with exemplary embodiment 2 of the present invention, and FIG. 7B is a plan view of the switch except for a key top.  
         [0074]    So as to thinly fold an electronic apparatus utilizing the push button switch during its non-use, key top  11  in the push button switch in accordance with this embodiment can be sunk down during the non-use to reduce height and to be stored in the electronic apparatus. A basic structure of this switch comprises spring plate  27  transversely slidably disposed between base  17  and switch member  24 , instead of spring plate  20  in the switch in embodiment 1.  
         [0075]    Spring plate  27  is made of a thin elastic metal plate, and includes operating spring  28  unitarily formed by punching and bending it, stopper  29  for applying an initial pressure to this, and driving spring  30 , similarly to spring plate  20  in the switch in embodiment 1. Projections  27 A projecting to the upper part of base  17  are unitarily on the both sides of driving spring  30 .  
         [0076]    Next, an operation of sinking down the push button switch with such a structure in embodiment 2 will be illustrated with reference to a sectional view of the switch during the sinking down period shown in FIG. 8A and a plan view of the switch except for the key top shown in FIG. 8B.  
         [0077]    When spring plate  27  are slid from a state shown in FIG. 7A and FIG. 7B in the direction of arrows shown in FIG. 7A and FIG. 7B, operating spring  28 , stopper  29 , and driving spring  30  similarly slide in the arrow direction. Operating spring  28  thus slides in a state in which stopper  29  applies an initial pressure to lower latched shaft  15 C at the lower end of first frame  5 , and an energizing force to link member  14  by tapered part  30 A of driving spring  30  disappears. When spring plate  27  further slides in the arrow direction, projections  27 A on the both sides of driving spring  30  abuts on lower latched shaft  15 C of first frame  15  to shift lower latched shaft  15 C in the arrow direction.  
         [0078]    Link member  14 , accompanying this, pivots on an engaging part between circular projection  15 A of first frame  15  and circular hole  16 A in second frame  16  and is folded similarly to the pressing operation period, and key top  11  sinks down to a position shown in FIG. 8A. In this state, a raising force is not applied to link member  14 , link member  14  is stabilized in the folded state since lower latched shaft  15 C of first frame  15  abuts on projections  27 A of spring plate  27 , and key top  11  is kept to be sunk down. Since tapered part  30 A of driving spring  30  has slid right, a pressing force is not applied to opposite contacts  24 A of switch member  24 .  
         [0079]    When spring plate  27  slides from this state in the opposite direction of the arrows, projections  27 A of spring plate  27  separates from lower latched shaft  15 C of first frame  15  of link member  14 . Tapered part  30 A of driving spring  30  then abuts on lower latched shaft  15 C of first frame  15  from its downside to slide lower latched shaft  15 C left.  
         [0080]    Link member  14 , accompanying this, rises and presses up key top  11 , and the push button switch returns to the original state in FIG. 7A and FIG. 7B. At this time, operating spring  28  smoothly returns to a position shown in FIG. 7A and FIG. 7B in a state in which stopper  29  applies the initial pressure to lower latched shaft  15 C, namely a position a predetermined clearance away from lower tip  15 D of first frame  15 .  
         [0081]    A motion during a pressing operation of the push button switch in embodiment 2 is same as in embodiment 1, and thus is not described. In the push button switch in accordance with embodiment 2, spring plate  27  thereof can slide in a predetermined direction simultaneously when the electronic apparatus utilizing this is folded during its non-use. The push button switch can be thus stored lower by a stroke of key top  11 .  
         [0082]    (Embodiment 3)  
         [0083]    Same elements used in embodiment 1 are denoted with the same reference numbers and are not described in detail.  
         [0084]    [0084]FIG. 9A is a sectional view of a push button switch in accordance with exemplary embodiment 3 of the present invention, and FIG. 9B is a plan view of the switch except for a key top.  
         [0085]    The push button switch in accordance with embodiment 3 has a smaller projecting area and a same basic structure as in embodiment 1. The switch further comprises resin-made third frame  33  in the central crossing part of resin-made first frame  32  and second frame  16  that form link member  31 , as well as elements in embodiment 1.  
         [0086]    [0086]FIG. 10 is an apparent perspective view of the link member, and FIG. 11 is an exploded perspective view of the link member. As shown in the drawings, link member  31  comprises first frame  32  in a substantially quadrangle plate shape and second frame  16  in a substantially square U shape. Circular projections  32 A on both surfaces in an intermediate part of first frame  32  are engaged with circular holes  16 A in an intermediate part of arms on both sides of second frame  16 , and first frame  32  and second frame  16  are pivotably coupled to each other and assembled in an X shape in side view. This is similar to embodiment 1.  
         [0087]    In embodiment 3, first frame  32  further comprises coupling shaft  32 B disposed in a U-shaped cutout part formed in its center, concentrically with circular projections  32 A. A joint part  33 A with a narrow opening in the upper part of third frame  33  is engaged with coupling shaft  32 B, so that third frame  33  is rotatably combined with it.  
         [0088]    As shown in FIG. 9A and FIG. 9B, upper latched shafts  32 C on both sides of the upper end of first frame  32  is pivotably held by first holding part  12  of key top  11 . Lower latched shafts  32 D on both sides of the lower end of first frame  32  are sandwiched between pair of first support parts  35  unitarily formed in metallic base  34  in a lower part and spring plate  37  below them, and are supported pivotably, slidably, and vertically non-movably. This is similar to embodiment 1.  
         [0089]    Driving shaft  33 B is formed at the lower end of third frame  33 , and the both sides thereof are disposed inside lower latched shafts  32 D of first frame  32 , so that driving shaft  33 B is supported pivotably, slidably, and vertically non-movably between first support parts  35  and spring plate  37 .  
         [0090]    Upper latched shafts  16 B on both sides of the upper end of second frame  16  are pivotably and slidably held by second holding parts  13  of key top  11 . Lower latched shafts  16 C on both sides of the lower end of second frame  16  are sandwiched between pair of support parts  36  of base  34  and spring plate  37 , and are rotatably supported. This is similar to embodiment 1.  
         [0091]    Spring plate  37  is made of a thin elastic metal plate, and operating spring  38  formed unitarily with the plate, as a plate spring extended from spring support part  38 A, projects over base  34 . Spring  38  is held in a state in which stopper  39  formed unitarily with spring plate  37  applies a predetermined initial pressure to it, and faces to lower tips  32 E outside lower latched shafts  32 D of first frame  32 . This is similar to embodiment 1.  
         [0092]    Tapered part  40 A bent upward at the tip of a driving spring  40  formed unitarily with spring plate  37  presses driving shaft  33 B at the lower end of third frame  33 , energizes link member  31  in the central direction to raise link member  31 , and presses up key top  11 .  
         [0093]    In this state, lower tips  32 E of first frame  32  do not contact with operating spring  38  and has a slight clearance. Switch member  24  is disposed on the lower surface of spring plate  37  so that opposite switch contacts  24 A lie directly underneath the root of tapered part  40 A of driving spring  40 , and substrate  25  is further disposed on the lower surface of switch member  24 . Spring support part  38 A of operating spring  38  lies outside tapered part  40 A at the tip of driving spring  40 . This is similar to embodiment 1.  
         [0094]    Next, a motion during a pressing operation of the push button switch with such a structure in accordance with embodiment 3 will be described. FIG. 12A is a sectional view of the switch during the pressing operation, and FIG. 12B is a plan view of the switch except for the key top.  
         [0095]    When key top  11  is pressed in the push button switch in accordance with embodiment 3, lower tips  32 E of first frame  32  of link member  31  press operating spring  38 . Driving shaft  33 B of third frame  3  presses tapered part  40 A of driving spring  40  to operate switch member  24 . Operations other than this operation are same as in embodiment 1, and thus are not described in detail.  
         [0096]    In the push button switch in accordance with embodiment 3, third frame  33  supported by base  34  inside lower latched shafts  32 D of first frame  32  allows a position at which tapered part  40 A of driving spring  40  elastically contacts with and energizes the lower end of link member  31  to be on the central side of the switch than the lower end of first frame  32 . Spring support part  38 A of operating spring  38  is therefore shifted to the central side of the switch. Accordingly, a projection area of entire operating spring  38  including spring support part  38 A, namely a projection area of the push button switch, can be reduced.  
         [0097]    (Embodiment 4)  
         [0098]    A push button switch in accordance with embodiment 4 comprises a spring plate slidable between base  34  and switch member  24  similarly to the case in embodiment 2. Spring plate unitarily comprises a projection projecting over base  34 .  
         [0099]    [0099]FIG. 13A is a sectional view of the switch during a sinking down period, and FIG. 13B is a plan view of the switch except for the key top. When spring plate  41  is slid in the arrow direction as shown in the drawings, operating spring  42 , stopper  43 , and driving spring  44  also slide in the arrow direction. Operating spring  42  thus slides in a state in which stopper  43  applies an initial pressure to it, and an energizing force to driving shaft  33 B of third frame  33 , namely link member  31 , by tapered part  44 A of driving spring  44  disappears. When spring plate  41  further slides in the arrow direction, projections  45  on the both sides of driving spring  44  abut on driving shaft  33 B of third frame  33  to shift it right. Link member  31 , accompanying this, pivots on an engaging part between circular projection  32 A of first frame  32  and circular hole  16 A in second frame  16  and is folded similarly to the pressing operation period. Key top  11  therefore sinks down to a position shown in FIG. 13A, opposite switch contacts  24 A of switch member  24  is kept to be stabilized without pressing force.  
         [0100]    When spring plate  41  slides from this state in the opposite direction of the arrows, link member  31  rises and presses up key top  11  to return the push button switch to the original state.  
         [0101]    In the push button switch in accordance with embodiment 4, spring plate  41  thereof can slide in a predetermined direction simultaneously when the electronic apparatus utilizing the switch is folded during its non-use. The switch can be thus stored lower by a pressing stroke of key top  11 .  
         [0102]    Additionally, in the push button switch in accordance with embodiment 3 or embodiment 4, third frame  33  rubs with and bends tapered part  40 A ( 44 A) of driving spring  40  ( 44 ) when the push button switch is pressed, and is made of an abrasion resistant material such as metal material formed by die-casting of aluminum. The push button switch is thus provided which is somewhat heavy, but has less degradation due to abrasion of third frame  33  and a long service life.