Patent ID: 6504121
Filing Date: 2003-01-07
Classification: H01H

Abstract:
A keyboard switch comprising:a contact sheet having contact pattern means formed thereon; a base disposed on said contact sheet and having an opening formed therethrough and a pair of first journal bearing portions and a pair of second journal bearing portions formed along two opposed side edges of said opening and projecting oppositely from said base sheet, said first bearing portions having a generally trapezoidal contour in cross-section and said second bearing portions having a generally semi-circular contour in cross-section; a pantograph mechanism comprising a U-shaped first link having opposed legs and a second link including a frame portion embraced between said opposed legs of the first link, both links being disposed on said base, said opposed legs having first stud shafts protruding outwardly therefrom at their forward ends and away from each other, said first stud shafts being rotatably and movably supported in the pair of said first bearing portions, said frame portion of said second link having second stud shafts extending outwardly therefrom at the base end portion thereof, said second stud shafts being inserted and rotatably supported in a pair of said second bearing portions, said frame portion of said second link having third stud shafts extending inwardly toward each other therefrom adjacent the end thereof opposite from said base end portion, one of the inside surfaces of said opposed legs and the opposed outside surfaces of said frame portion opposing said corresponding inside surfaces of the legs having bosses protruding therefrom, said bosses being engaged in shaft receiving holes formed in the other of the inside surfaces of said opposed legs and the opposed outside surfaces of said frame portion, respectively, said first and second links being connected together for pivotal movement to form said pantograph mechanism; a keytop disposed on said pantograph mechanism and rotatably supporting said U-shaped first link and rotatably and slidably supporting said pair of third stud shafts; a resilient actuating member extending through said frame portion and interposed between said keytop and said contact membrane sheet and adapted to turn said contact patterns of the contact sheet on when the keytop is pressed down toward said contact sheet and to return the keytop to its original position when the downward pressure on the keytop is released; and a leg dislodgement preventing means comprising projection means formed on one of the inner sides of said opposed legs and the opposed outer sides of said frame portion and depression means for accommodating said projection means formed in the other of the inner sides of said opposed legs and the opposed outer sides of said frame portion, one of said projection means and the depression means being formed with tapered surfaces, wherein with said keytop in its unactuated position, said tapered surfaces and edges of the other of the projection means and the depression means are in contact with or very close to each other, and said tapered surfaces and said edges are forced into contact with each other when said keytop is moved from its unactuated position further away from said contact sheet.