Abstract:
A dome portion of a contact piece has a plurality of circumferentially-spaced-apart marginal portions and a plurality of dome extensions provided between the marginal portions.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a low-profile, flip-over contact piece for a tactile switch and, more particularly, to a low-profile but relatively long-stroke, flip-over contact piece for a tactile switch.  
           [0002]    A description will be given first, with reference to FIGS. 1A, 1B and  2 , of a conventional tactile switch disclosed in Japanese Utility Model Registration Gazette 4-8590. FIG. 1A is a longitudinal sectional view taken on the line passing through the center of the tactile switch, FIG. 1B is a magnified view of its principal part, and FIG. 2 is its exploded perspective view.  
           [0003]    The tactile switch, indicated generally by  20 , has a housing  11  and a cover  12 . The housing  11  of a substantially square outside shape has in its top a centrally-disposed circular hole  13  (FIG. 2) and an exposed stationary contact  31  protrusively provided on the inside bottom of the housing  11  and molded integrally therewith at the center thereof. Terminals  31 T 1  and  31 T 2  are connected to the central stationary contact  31 . On the bottom of the housing  11  there are also molded therewith peripheral stationary contacts  32  and  33  similarly exposed at peripheral portions of the hole  13  diametrically opposite across the central stationary contact  31 . Terminals  32 T and  33 T are connected to the peripheral stationary contacts  32  and  33 , respectively.  
           [0004]    Reference numeral  4  denotes generally a convex flip-over contact piece, or movable contact piece, which is formed by press working of a springy metal sheet as of phosphor bronze. The convex movable contact piece  4  has a dome or convex portion  41  which snappingly flips over when pushed, and a sharply downturned marginal portion  42  extending from the periphery of the dome portion  41  all around it. The dome portion  41  has at the top thereof an aperture  43 .  
           [0005]    The movable contact piece  4  is placed in the hole  13  of the housing  11  with the marginal edge  42  held in contact with the peripheral stationary contacts  32  and  33  exposed on the inside bottom of the housing  11 . Mounted on the convex movable contact piece  4  placed in the hole  13  is a disk-shaped push button  5 . The push button  5  has a relatively thick circular contact disk-shaped portion  51 , a flange  53  extending outwardly from its lower marginal edge, and a pair of lugs  54  protruding beyond the side edge of the flange  53  at diametrically opposite positions so as to prevent the push button  5  from turning. The lugs  54  are held in vertically slidable engagement with guide grooves  13 R cut in the inside wall of the hole  13 . Accordingly, the push button is inhibited from turning in the hole  13  but allowed to slide up and down. Protrusively provided on the underside of the push button  5  centrally thereof is a projection  52 , by which the convex movable contact piece  4  is driven at the center thereof.  
           [0006]    The switch cover  12  is put on the top of the housing  11  from above the push button  5 , with legs  12 L of the cover  12  fixedly engaged with side walls of the housing  11 . The cover  12  has a centrally disposed opening  12 B of a diameter smaller than that of the flange  53  of the push button  5  but larger than the diameter of its central disk-shaped portion  51 , and the central disk-shaped portion  51  of the push button  5  protrudes upwardly through the opening  12 B.  
           [0007]    Upon being pushed, the push button  5  applies downward force through its projection  52  to the movable contact piece  4  to resiliently deform it, and the instant the top of the dome portion  41  passes through its dead point the movable contact piece  4  quickly flips over with a click. When the movable contact piece  4  is resiliently deformed downwardly, air in the space defined by the movable contact piece  4  and the bottom of the hole  13  is discharged through the aperture  43  in the dome portion  41  at the top thereof; hence, the air will not be compressed the cause an increase in the downward force on the dome portion  41 . The central disk-shaped portion  51  of the push button  5  slightly protrudes upwardly of the switch cover  12  through its opening  12 B. The housing  11  and the cover  12  are molded as a one-piece liquid-tight structure.  
           [0008]    The lower edge of the marginal portion  42  of the convex movable contact pieces  4  is always held in contact with the peripheral stationary contacts  32  and  33 . In the normal state in which the push button  5  is not being pushed, the movable contact piece  4  keeps its convex form due to the springiness of its own and pushes up the push button  5  through the projection  52 , urging the flange  53  against the underside of the switch cover  12  and hence resiliently biasing the push button  5  upward. With the push button  5  thus resiliently biased, the movable contact piece  4  keeps out of contact with the central stationary contact  31 , and hence no electric connections are established between the central stationary contact  31  and the peripheral stationary contacts  32  and  33 , holding the switch open. That is, no electric connections are made between the terminals  31 T 1 ,  31 T 2  and the terminal  32 , or between the terminals  31 T 1 ,  31 T 2  and the terminal  33 .  
           [0009]    Upon depression of the push button  5 , the central portion  41  of the convex movable contact piece  4  is resiliently deformed downward by the projection  52  of the push button  5 , and when pressed down beyond its dead point, the central portion  41  of the contact piece  4  snappingly flips over into contact with the central area  30  of the central stationary contact  31 . As a result, electric connections are established between the central stationary contact  31  and the peripheral stationary contacts  32  and  33  via the movable contact piece  4 , and consequently, electric connections are made between the terminals  31 T 1 ,  31 T 2  and the terminals  32 T,  33 T.  
           [0010]    The outer dimensions of the tactile switch  20  now in practical use are approximately 5 mm in width, 5 mm in depth and 3 mm in thickness at the largest. In such a small tactile switch  20 , the diameter φ of the convex movable contact piece  4  is as small as 4 mm or so.  
           [0011]    In the conventional movable contact piece  4  described above, even when the actuation force applied to the convex portion  41  by the depression of the push button  5  is transmitted to the marginal portion  42  while gradually deforming the convex portion  41 , the diameter of the marginal portion  42  is hardly deformed. The reason for this is that the marginal portion  42  extends circumferentially of the lower edge of the convex portion  41  without a break. That is, the actuation force exerted on the movable contact piece  4  is not relieved by deforming the marginal portion  42  but instead it is applied solely to the convex portion  41  to cause it flip over with a click.  
           [0012]    Incidentally, an effort is under way to introduce long-stroke and tactile-response features into such a minute convex flip-over contact piece  4  whose diameter φ is about 4 mm. The long-stroke feature can be obtained by increasing the height of the convex portion  41 . To increase only the height of the convex portion  41 , with the diameter of the movable contact piece  4  limited to a predetermined value, means to increase the inclination of the convex portion  41  --this inevitably increases the structural rigidity of the convex portion  41  and requires an increase in the force necessary for it to flip over at the dead point. To exceed the increased force for the flipping-over operation of the convex portion  41 , the actuation force to be exerted on the push button  5  must be increased, giving rise to the problem of impaired operability though the stroke increases. The increase in the actuation force is particularly important when the miniature convex flip-over contact piece  4  about 4 mm in diameter φ is made long-stroke.  
         SUMMARY OF THE INVENTION  
         [0013]    It is therefore an object of the present invention to provide a low-profile but long-stroke-type, convex flip-over contact piece for a tactile switch which has as small a diameter as 4 mm or so but requires relatively small actuation force and provides good tactile response.  
           [0014]    The low-profile, flip-over contact piece according to the present invention comprises:  
           [0015]    a convex portion made from a substantially circular springy metal sheet;  
           [0016]    a plurality of circumferentially-spaced-apart marginal portions extending from the marginal edge of the convex portion in the direction opposite to the direction of convexity; and  
           [0017]    a plurality of circumferentially-spaced-apart extensions of the convex portion defined between the plurality of marginal portions. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1A is a sectional view of a conventional tactile switch;  
         [0019]    [0019]FIG. 1B is a magnified view of its principal part;  
         [0020]    [0020]FIG. 2 is its exploded perspective view;  
         [0021]    [0021]FIG. 3A a plan view illustrating an embodiment of the low-profile, flip-over contact piece according to the present invention;  
         [0022]    [0022]FIG. 3B is a sectional view taken along the line  3 B- 3 B in FIG. 3A;  
         [0023]    [0023]FIG. 3C is a sectional view taken along the line  3 C- 3 C in FIG. 3A;  
         [0024]    [0024]FIG. 3D is its perspective view;  
         [0025]    [0025]FIG. 4A is a sectional view of the contact piece of the present invention in its non-pressed state;  
         [0026]    [0026]FIG. 4B is a sectional view of the contact piece of the present invention in its pressed state; and  
         [0027]    [0027]FIG. 5 is a plan view illustrating another embodiment of the contact piece according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Referring first to FIGS. 3A to  3 B and  4 , an embodiment of the low-profile, flip-over contact piece according to the present invention will be described. The parts corresponding to those in the afore-mentioned prior art example are identified by the same reference numerals.  
         [0029]    [0029]FIGS. 3A to  3 D are explanatory of an embodiment in which the downturned marginal portion  42  is divided circumferentially thereof into two. The low-profile, convex flip-over contact piece, or movable contact piece  4  is formed by press working a highly springy metal sheet into dome or convex form and stamping the convex metal sheet into the disk shape to form the dome or convex portion  41 . This is followed by press working a pair of diametrically opposite marginal portions of the dome portion  41  downwardly (in the direction opposite to the direction of convexity of the dome portion  41 ) to form marginal portions  42   1  and  42   2 . The boundaries between the dome portion  41  and the marginal portions  42   1  and  42   2  are press worked into arcuate ridges  45 . Between the opposite ends of the marginal portions  42   1  and  42   2  are formed dome extensions  43  left unpressed downwardly. Accordingly, the extensions  43  have their top surfaces extended from the top surface of the dome portion  41  with the same radius of curvature.  
         [0030]    When the movable contact piece  4  is placed on a flat surface, the lower edges of the marginal portions  42   1  and  42   2  contact the flat surface but the dome extensions  43  remain slightly above the flat surface. Reference numeral  44  denotes a center aperture. With the illustrated structure, when pressed down at its center from above, the movable contact piece  4  is robust against a bending force acting about the direction of its diameter passing through the marginal portions  42   1  and  42   2  but is resiliently bent relatively easily by a bending force acting about the direction of its diameter passing through the extensions  43 .  
         [0031]    In this instance, upon being pressed down at its top through the push button  5 , the dome portion  41  begins to be gradually deformed intermediate between the two arcuate ridges  45 , and upon passage through the dead point, the dome portion  41  snappingly flips over along the arcuate ridges  45 . Since the contact piece  4  is formed so that the extensions  43  between the marginal portions  42   1  and  42   2  are readily bent the instant of flipping-over action of the dome portion  41 , the minimum actuation force therefor decreases, facilitating the flipping-over action accordingly.  
         [0032]    In FIG. 4A, when the contact piece  4  is pressed at its center, the dome portion  41  is bent about the line  3 B- 3 B, and as shown in FIG. 4B, the marginal portions  42   1  and  42   2  are pushed radially outwardly and the dome portion  41  is forced to spread flat. As a result, the height h 1  of each of the marginal portions  42   1  and  42   2  is reduced to h 2 . The downward stroke for depressing the push button  5  increases by the decrease in the height from h 1  to h 2 . That is, in the present invention, the downward stroke of the push button  5  for the flipping-over action of the dome portion  41  can be increased corresponding to the decrease (h 1 -h 2 ) in the height of each marginal portion  42 , as compared with the downward stroke of the push button needed in the prior art example in which the marginal portion  42  extends along the entire circumference of the lower edge of the dome portion  41 .  
         [0033]    As described above, the downward stroke of the push button  5  from the start of its depression to the flipping-over action of the dome portion  4  is equivalent to the sum of the stroke corresponding to the flipping-over action of the dome portion  41  and the stroke corresponding to the decrease in the height of the marginal portion  42 .  
         [0034]    [0034]FIG. 5 illustrates another embodiment of the low-profile, flip-over contact piece  4  according to the present invention, in which the marginal portion of the dome portion  41  is divided into three marginal portions  42   1 ,  42   2  and  42   3 .  
         [0035]    In this embodiment, too, the pressure applied to the center of the dome portion  41  pushes marginal portions  42   1 ,  42   2  and  42   3  radially outwardly. This reduces the actuation force at the time of the flipping-over action of the dome portion  41  to provide increased tactile feedback, while at the same time, reduces the heights of the marginal portions  42   1 ,  42   2  and  43   3  to increase the downward stroke of the push button accordingly.  
       EFFECT OF THE INVENTION  
       [0036]    As described above, according to the present invention, the dome portion  41  has the same construction as in the prior art example, but the downward stroke of the push button  5  can be set larger than in the prior art in anticipation of the decrease in the height of the marginal portions  42  at the time of the flipping-over action of the dome portion  41 . Further, the actuation force for the flipping-over action can be reduced accordingly. Hence, the present invention offers a miniature low-profile, flip-over contact piece which is as small as about 4 mm in diameter but requires a smaller actuation force and provides good tactile response which are difficult to achieve with the prior art.