Patent Publication Number: US-6222144-B1

Title: Pushbutton switch

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a pushbutton switch that can be used to detect whether a portable telephone, notebook PC, or similar miniature electronic equipment is open or closed. 
     Heretofore, switches called limit switches have widely been used as “open” and “closed” position detectors for electronic equipment. Many of the limit switches utilize the snap action of a spring contact to drive a movable contact. 
     The conventional limit switches are so complex in their contact driving mechanism that they cannot be miniaturized. Besides, because of large stroke lengths required for the switching operation of the actuator (a pushbutton), they are not suitable for use as switches to detect the open/closed position of small-sized electronic equipment such as a portable telephone or notebook PC. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a pushbutton switch that is small-sized and short in the pushbutton stroke length and hence is suitable for use as a switch to detect the open/closed position of a portable telephone or notebook PC. 
     Another object of the present invention is to provide a pushbutton switch that can be turned ON and OFF with a light force and hence is highly durable. 
     The pushbutton switch according to the present invention comprises: an insulating body molded of an insulating material and having a box-like shape consisting of a pair of opposed side panels, a pair of opposed front and rear panels and a bottom panel, said insulating body having an opening at one end, and a pair of contact pieces to be electrically connected to and disconnected from each other being embedded in the inner bottom surface of said bottom panel of said insulating body; 
     a rotary actuator rotatably held at one end in said insulating body at a position higher than said inner bottom surface and carrying at the other end a push button projecting outwardly of said insulating body; 
     a plate spring having a retaining contact piece engaged at one end with the free end of said rotary actuator and a movable contact piece for sliding at one end into or out of contact with said pair of fixed contact pieces on said inner bottom surface of said bottom panel of said insulating body, said retaining contact piece and said movable contact piece being coupled together at the other end to form a V-letter shape, and said plate spring being disposed between said rotary actuator and said inner bottom surface of said bottom panel and resiliently biasing by reaction force from said inner bottom surface the free end portion of said rotary actuator in a direction in which to project out said push button from said opening of said insulating body; and 
     a cover covering said opening of said insulating body but having a window through which said push button projects out of said insulating body. 
     According to the present invention, since the movable contact piece slides into or out of contact with the fixed contact piece on the inner bottom surface of the insulating body, it does not undergo severe elastic deformation. Accordingly, the present invention offers a pushbutton switch that permits ON-OFF control between contacts with a light force and is almost free from breakage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a pushbutton switch according to the present invention; 
     FIG. 2A is a plan view of the pushbutton switch with its metal cover  12  taken off; 
     FIG. 2B is a sectional view taken along the line  2 B— 2 B in FIG. 2A; 
     FIG. 3A is a plan view of the pushbutton switch, for explaining the state of its actuation; 
     FIG. 3B is a sectional view taken along the line  3 B— 3 B in FIG. 3A; 
     FIG. 4A is a plan view of the pushbutton switch, for explaining its ON state; 
     FIG. 4B is a sectional view taken along the line  4 B— 4 B in FIG. 4A; 
     FIG. 5A is a plan view explanatory of a rotary actuator  19  for use in the present invention; 
     FIG. 5B is its side view; 
     FIG. 6A is a plan view explanatory of a plate spring for use in the present invention; 
     FIG. 6B is its side view; 
     FIG. 7 is a plan view depicting a modified position of the fixed contact piece; and 
     FIG. 8 is a plan view showing the position of the fixed contact piece of the pushbutton switch modified to the push-off type. 
    
    
     DETAILED DESCRIPTION THE PREFERRED EMBODIMENTS 
     In FIGS. 1 through 4 there is illustrated an embodiment of the pushbutton switch according to the present invention. 
     As seen from its exploded perspective view shown in FIG. 1, the pushbutton switch of the present invention comprises: a substantially rectangular box-shaped insulating body  15 ; a plate spring  11  placed in the body  15  and bent into a V-letter shape; a rotary actuator  19 ; and a metal cover  12  that closes the upper open end of the body  15 , covers its front and rear panels  15 C and  15 D and is bent in contact with its underside. 
     FIG. 2A is a plan view of the pushbutton switch with the metal cover  12  removed. FIG. 2B is a sectional view taken along the line  2 B— 2 B in FIG. 2A, showing the state in which a push button  19 P formed integrally with the rotary actuator  19  is at its outermost position. 
     FIGS. 2A and 2B depict the state in which terminals  17 A and  18 A are electrically isolated from each other with the push button  19 P at its outermost position. FIGS. 3A and 3B depict, in correspondence with FIGS. 2A and 2B, the state in which the push button  19 P is pressed halfway into the insulating body  15 . FIGS. 4A and 4B illustrate, in correspondence with FIGS. 2A and 2B, the state in which the push button  19 P is fully pressed into the insulating body  15 . 
     The insulating body  15  is a box-like container that has a substantially rectangular bottom panel  15 F, the front and rear panels  15 C and  15 D opposed across the bottom panel  15 F, and both side panels  15 A and  15 B opposed across the bottom panel  15 F. In the formation of the insulating body  15  fixed contact pieces  17  and  18  are inserted therein and molded therewith so that they are flush with the upper surface of the bottom panel  15 F (hereinafter referred to also as the inner bottom surface of the insulating body) and that the terminals  17 A and  18 A extended from the fixed contact pieces  17  and  18  project out of the side panels  15 A and  15 B, respectively. In inner wall surfaces of the opposed side panels  15 A and  15 B of the insulating body  15  there are formed bearing recesses  15   a  and  15   b  which communicate with the upper end faces of the side panels  15 A and  15 B in close proximity to the rear panel  15 D. 
     The metal cover  12  is made of stamped sheet metal bent into the required shape. The cover  12  comprises: a substantially rectangular top panel  12 T; front and rear panels  12 C and  12 D bent downward from a pair of opposed marginal edges of the top panel  12 T; and retaining lugs  12 L which are extended from the lower marginal edges of the front and rear panels  12 C and  12 D and bent inward after the assembling of the switch. The top panel  12 T has a window  12 W which extends from its center toward the front panel  12 C and through which the push button  19 P of the rotary actuator  19  protrudes beyond the top panel  12 T. 
     The rotary actuator  19  comprises, as depicted in FIGS. 1,  5 A and  5 B, a rotary plate  19 D having at its opposite ends circular rotary shaft portions  19 S, a lever portion  19 E extended from the center of the rotary plate  19 D substantially at right angles to the surface thereof, the push button  19 P formed integrally with the lever portion  19 E on the top of its free end portion, an engaging hole  19   h  made in the underside of the free end of the push button  19 P, and an engaging projection  19 C formed integrally with the rotary plate  19 D on the underside thereof adjacent to the hole  19   h.    
     The plate spring  11  is formed by stamping a spring metal sheet into an E-letter shape as shown in FIG.  6 A and bending downward both side movable contact pieces  11 A and  11 B relative to the middle retaining contact piece  11 E so that they form substantially a V-letter shape as viewed from the direction normal to the plane of the paper in FIG.  6 B. The movable contact pieces  11 A and  11 B have at their tip movable contacts  11   a  and  11   b  which slide into or out of contact with the fixed contact pieces  17  and  18 . In this embodiment, with a view to increasing the number of points of contact with the fixed contact pieces  17  and  17 , the tip end portions of the movable contact pieces  11 A and  11 B are bifurcated to provide the movable contacts  11   a  and  11   b.  The movable contacts  11   a  and  11   b  are each formed convex with respect to the inner bottom surface  15   f  of the insulating body  15  for smooth sliding movement thereon. The base portion  11 D of the plate spring  11 , which couples the both side movable contact pieces  11 A and  11 B and the middle retaining contact piece  11 E, is bent into a circular arc of approximately 90 degrees about an axis parallel to the marginal edge of the base portion  11 D to provide increased mechanical strength in its lengthwise direction and to assure smooth sliding movement of the plate spring  11  on the inner bottom surface of the insulating body  15 . 
     The retaining contact piece  11 E has an engaging hole  11   h  made therein near its extremity and has its free end portion bent upward at right angles to form a fixing lug  11 C. The fixing lug  11  is guided into the guide hole  19   h  of the level portion  19 E of the rotary actuator  19 , then the engaging projection  19 C of the rotary actuator  19  is fitted into the engaging hole  11   h.  The opposite rotary shaft portions  19 S of the rotary plate  19 D are rotatably supported in the bearing recesses  15   a  and  15   b  formed in the both side panels  15 A and  15 B of the insulating body  15 . As a result, the retaining contact piece  11 E extends backward (toward the rear panel  15 D) at an angle to the underside of the level portion  19 E, and the movable contact pieces  11 A and  11 B extend from the base portion  11 D forwardly thereof toward the inner surface of the bottom panel  15 D. The lengths of the retaining contact piece  11 E and the movable contact pieces  11 A and  11 B are chosen to be substantially equal to, for example, the length of the lever portion  19 E. The width of the retaining contact piece  11 E is about twice larger than the widths of the movable contact pieces  11 A and  11 B. 
     When the rotary actuator  19  assembled with the plate spring  11  is mounted in the insulating body  15  with the opposite rotary shaft portions  19 S held in the bearing recesses  15   a  and  15   b,  the movable contacts  11   a  and  11   b  are pressed against the inner bottom surface  15   f  and the push button  19 P protrudes upwardly of the upper end face of the insulating body  15 . The switch is assembled by pressing the push button  19 P into the insulating body  15  against the spring force of the plate spring  11 , putting the metal cover  12  onto the insulating body  15 , letting the push button  19 P project out through the window  12 W, and bending the lugs  12 L of the metal cover  12  inwardly. 
     Depressing the push button  19 P of the switch according to the present invention, the rotary actuator  19  turns about the rotary shaft portions  19 S, causing the base portion  11 D of the plate spring  11  to move toward the rear panel  15 D. For example, letting the lengths of the level portion  19 E and the retaining contact piece  11 E be represented by L and the angle of rotation of the rotary actuator  19  from its horizontal position by φ, the maximum distance of travel, D MAX , of the base portion  11 D is given by D MAX =2L(1−cos φ). With the movement of the base portion  11 D, the movable contacts  11   a  and  11   b  also move toward the rear panel  15 D by the same distance as that of the base portion  11 D. When L is constant, a large distance of travel DMAX is obtained by increasing the angle of rotation φ. This can be achieved by increasing the height of the center of the rotary shaft portion  19 S from the inner bottom surface  15   f.    
     FIGS. 2 and 3 illustrate push-ON type switches in which electric connections are established between the terminals  17 A and  18 A by depressing the push button  19 P. To keep the fixed contact piece  18  in contact with the movable contact  11  at all times, the right-hand marginal edge of the fixed contact piece  18  is positioned nearer to the front panel  15 C than the position where the movable contact piece  11  lies when the push button  19 P is at its highest position (FIGS. 2A,  2 B), and the left-hand marginal edge of the fixed contact piece  18  is positioned near the rear panel  15 D so that the distance between the left- and right-hand marginal edges of the fixed contact piece  18  is sufficiently larger than the maximum distance of travel D MAX . The width of the fixed contact piece  17  (in the front-to-back direction) is sufficiently larger than the maximum distance of travel D MAX , and the fixed contact piece  17  is positioned apart from the front panel  15 C so that when the push button  19 P is at its highest position, the movable contacts  11   a  lie nearer to the front panel  15 C than the fixed contact piece  17  and that when the base portion  11 D is moved, for example, one half that of the maximum distance of travel D MAX  by the depression of the push button  19 P, the movable contacts  11   a  move onto the fixed contact piece  17 FIGS. 3A,  3 B). 
     In the switch according to the present invention, since the movable contact pieces  11 A and  11 B and the retaining contact piece  11 E are bent by the depression of the push button  19 P in a manner to reduce the angle θ of the V-letter shape of the plate spring  11  (FIG.  6 B), the effective length of the plate spring  11  that serves as a spring is the sum of the distance from the fixing hole  11   h  to the base portion  11 D of the retaining contact piece  11 E and the distance from the base portion  11 D to the movable contacts  11   a  and  11   b,  providing a long effective length. Accordingly, no metal fatigue is likely to occur in the spring plate  11  even after the switch is actuated repeatedly, for example, tens of thousands of times. 
     In the present invention, the plate spring  11  is incorporated into the switch with the angle θ of the V-letter shape between the retaining contact piece  11 E and the movable contact pieces  11 A and  11 B held small; the spring force of the plate spring  11  acts on the free end of the level portion  19  and the inn bottom surface  15   f  of the insulating body  15  in the direction in which to increase the angle θ of the V-letter shape, resiliently holding the push button  19 P at its outermost position. To turn ON the switch, depress the push button  19 P to bend the retaining contact piece  11 E and the movable contact pieces  11 A and  11 B in a manner to reduce the angle θ between them. The resulting increased spring reaction force mostly serves to increase the contact pressure of the movable contacts  11   a  and  11   b  with the inner bottom surface  15   f  of the insulating body  15 , but since the distance between the base portion  11 D of the plate spring  11  and the center of the rotary shaft  19 S undergoes substantially no change, the contact pressure between the base portion  11 D and the inner bottom surface  15   f  hardly change. The base portion  11 D need not be in touch with the bottom panel  15 F but may be in light touch with it. 
     As described above, the pushbutton switch according to the present invention features a structure in which the tip end portion of the one arm (the fixed contact piece  11 E) of the V-shaped plate spring  11 , which turns and biases the rotary actuator  19  in the direction in which to let the push button  19 P project out of insulating body  15 , is engaged with the free end side of the lever portion  19 E and the tips (that is, movable contacts  11   a  and  11   b ) of the other arms (the movable contact pieces  11 A and  11 B) are urged against the inner bottom surface  15   f  of the insulating body  15 , applying resilient biasing force to the rotary actuator  19  by the reaction force from the inner bottom surface  15   f.  Another structural feature resides in that the center of rotation of the rotary actuator  19  is provided near the upper end of the insulating body  15  to convert the rotation of the rotary actuator  19  to rectilinear sliding motion of the movable contact pieces  11 A and  11 B. 
     Accordingly, the movable contacts  11   a  and  11   b  also slide on the inner bottom surface  15   f.  In the illustrated example, as the push button  19 P is depressed, the movable contact pieces  11 A and  11 B slide leftward, by which the fixed contact pieces  17  and  18  embedded in the inner bottom surface  15   f  can be electrically connected to or disconnected from each other. 
     In the embodiment depicted in FIGS. 2 to  4 , when the push button  19 P is at its outermost position on the outside of the insulating body  15  as depicted in FIG. 2, the movable contacts  11   a  are held out of contact with the fixed contact piece  17  as shown. Pressing the push button  19 P into the insulating body  15 , the movable contact pieces  11 A and  11 B move leftward accordingly. As a result, the movable contacts  11   a  approach the fixed contact piece  17 ; and when the push button  19 P is pressed into the insulating body  15  to a certain level, the movable contacts  11   a  slide into contact with the fixed contact piece  17  and onto them as depicted in FIGS. 3 and 4. Thus, when the push button  19 P is pressed into the insulating body  15 , electric connections are established between the fixed contact pieces  17  and  18  via the movable contact pieces  11 A,  11 B and the retaining contact piece  11 E, making it possible to generate a contact signal across the terminals  17 A and  18 A. 
     In the embodiment of FIGS. 2 to  4 , the above the movable contacts  11   b  and the fixed contact piece  18  have been described to be in contact with each other at all times irrespective of whether and how much the push button  19  is pressed into the insulating body  15 ; however, as depicted in FIG. 7 corresponding to FIG. 2A, the right-hand marginal edge of the fixed contact piece  18  may be positioned in alignment with the right-hand marginal edge of the fixed contact piece  17  so that the movable contacts  11   b  slide onto the fixed contact piece  18  when the push button  19 P is pressed into the insulating body  15 . In this instance, there is provided between the terminals  17 A and  18 A a distance of electrical isolation that corresponds to the sum of the distance between each movable contact  11   a  and the fixed contact piece  17  and the distance between each movable contact  11   b  and the fixed contact piece  18  when the push button  19 P is at its outermost position. 
     While in the above the present invention has been described as being applied to a switch of the type that turns ON when the push button  19 P is depressed, the invention is also applicable to a switch that is turned OFF by the depression of the push button  19 P. In this case, for example, as depicted in FIG. 8 corresponding to FIG. 2A, the fixed contact piece  17  is positioned near the front panel  15 C so that it underlies the movable contacts  11 A when the push button  19 P is at its outermost position and that the movable contacts  11   a  move out of contact with the fixed contact piece  17  when the push button  19 P is depressed. The fixed contact piece  18  may be of such a shape as shown in FIG. 2 but may also be changed to a shape symmetrical to that of the fixed contact piece  17  as depicted in FIG.  8 . 
     In the above embodiments the cover  12  for covering the opening of the insulating body  15  has been described to be metal-made, but it may also be formed of synthetic resin. In such an instance, engaging protrusions need only to be provided which slightly protrude inwardly from the lower marginal edges of the front and rear panels  12 C and  12 D for engagement with external angles formed between the front and rear panels  15 C,  15 D and the bottom panel  15 F of the insulating body  15 . 
     EFFECT OF THE INVENTION 
     As described above, according to the present invention, the movable contact pieces  11 A and  11 B slide rectilinearly on the inner bottom surface  15   f  of the insulating body  15  with the rotation of the rotary actuator  19  by the depression of the push button  19 P; at this time, the push button  19 P needs only to be pressed down against the spring force of the plate spring  11  in such a manner as to reduce the angle θ between its retaining contact piece  11 E and movable contact pieces  11 A,  11 B. Hence, the switch of the present invention can be turned ON and OFF with a light force. Moreover, since the effective length of the spring is about the same as the sum of the lengths of the retaining contact piece  11 E and the movable contact pieces  11 A and  11 B, the amount of deformation of the spring per unit length can be kept small—this effectively prevents the possibility of the spring being broken by metal fatigue, making it possible to offer a highly durable pushbutton switch. 
     The pushbutton switch according to the present invention is intended for use as an “open” and “closed” position detector for small-sized electronic equipment such as a portable telephone or notebook PC, and the pushbutton has a body measuring approximately 3.8×3.0×1.8 mm, for instance. In the switch of this size, the maximum amount of travel of the movable contact pieces  11 A and  11 B is 0.4 mm when the push button  19 P is pressed down to its lowermost or innermost position. 
     It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.