Key switch assembly having momentary closed interval

Claim 1

A key switch assembly of the type comprising a panel-like support, a pair of spaced-apart switch contacts on the support at a switch site, a frame on the support proximate to the switch site, the frame comprising a column extending normally of the support and having a fixed end and a free end, a plunger on the column which is normally maintained in an extended position relative to the support by a biasing spring, the plunger being movable towards the support to a depressed position, and a switch closing lever pivotally mounted on the frame which is movable in response to movement of the plunger and which is effective electrically to connect the switch contacts to each other, the key switch assembly being characterized in that: the switch closing lever is a bell crank having a pivotal axis, a switch closing arm, and a cam follower arm, the pivotal axis being adjacent to the switch site and extending parallel to the plane of the panel-like support, the switch closing arm extending from the pivotal axis towards the switch site and having a free end which is proximate to, but normally spaced from, the switch contacts, the camming arm extending from the pivotal axis beside the plunger and having a free end which is spaced from the pivotal axis, the camming arm having a cam follower portion, the plunger having a stiffly flexible camming rod extending from the upper end thereof towards the inner end, the camming rod having a camming portion which is angularly spaced from the cam follower portion of the camming arm, relative to the axis of the plunger, and which moves past the cam follower portion during movement of the plunger to the depressed position, and a cam deflector on the frame proximate to the cam follower portion of the camming arm, the cam deflector having a deflecting surface which is engaged by the camming portion of the camming rod when the plunger is moved to the depressed position, the deflecting surface causing flexing of the camming rod laterally towards the cam follower portion of the camming arm with resulting engagement of the cam follower portion by the camming portion of the camming rod and arcuate movement of the bell crank whereby the free end of the switch closing arm is moved towards the switch contacts and causes closing of the switch, the deflecting surface being of limited extent whereby the camming rod returns to its normal position when the camming portion moves past the deflecting portion with resulting movement of the free end of the switch closing arm away from the switch contacts and opening of the switch whereby the switch contacts are electrically connected to each other only during a beief interval during movement of the plunger from the extended position to the depressed position.