1. A key assembly for actuating a device, comprising: a housing; a keystem mounted on the housing to be movable through a stroke between a normally extended position and a depressed position, the keystem having a pair of elongated channels therein, each channel having a lower end defining a stop shoulder; an actuator mounted on the housing to be movable through a stroke between a normally retracted position and an extended position, the actuator having a pair of arms extending therefrom over opposite sides of the keystem, each arm having an inwardly extending portion fitting into a respective channel to form a lost-motion connection which captively retains the actuator on the keystem; first resilient means disposed between the keystem and actuator for urging the actuator away from the keystem; and second resilient means disposed between the housing and keystem for urging the keystem toward the normally extended position; the keystem and first resilient means being operative to move the actuator toward the extended position when the keystem is moved toward the depressed position, the arm portions being movable in the keystem channels to permit the keystem stroke to exceed the actuator stroke, the arm portions abutting the channel stop shoulders to drive the actuator to the retracted position when the keystem is returned to the normally extended position.

4. A key assembly for actuating a diaphragm switch, comprising: a hollow housing having a lower end adapted for mounting on the switch; a keystem slidably mounted in and extending from an upper end of the housing, the keystem being movable between a normally extended position and a depressed position; a first spring disposed between the keystem and housing for urging the keystem toward the extended position, the first spring exerting an increasing restoring force opposing an actuating force exerted on the keystem to move the keystem from the normally extended position toward the depressed position; a resilient means interposed between the keystem and housing for modifying the total force opposing the actuating force by first increasing the total force and then decreasing the total force as the keystem is moved through an intermediate portion of full downstroke travel toward the depressed position; an actuator slidably mounted in the housing and having a lower end movable into operative contact with the switch when the housing is mounted on the switch, the actuator having a coupling means extending therefrom in captive engagement with the keystem, the coupling means providing a lost-motion connection which forces the actuator away from the switch into a retracted position when the keystem is in the normally extended position while permitting limited downstroke motion of the keystem toward the depressed position without requiring equal motion of the actuator; and a second spring disposed between the keystem and actuator to urge the keystem and actuator apart, the second spring providing a resilient connection between the keystem and actuator such that an increasing restoring force exerted by the second spring during the keystem downstroke is effective to urge the actuator away from the keystem into actuating contact with the switch, the second spring permitting overtravel movement of the keystem beyond a position adequate to obtain switch actuation, while maintaining a restoring force against the actuator to hold the switch in an actuated position during overtravel movement and until the keystem is permitted to move back toward the extended position.

11. A key assembly comprising: a diaphragm switch having an actuating surface which is movable to effect switch actuation; a hollow housing having an undersurface disposed adjacent the switch actuating surface; a clamping means securing the switch and housing together; a keystem slidably mounted in and extending from an upper end of the housing, the keystem being movable toward and away from the switch actuating surface between a depressed position and a normally extended position, the keystem having a pair of side surfaces defining channels which are elongated in the direction of keystem motion, each channel having a stop shoulder at a lower end thereof; a first coil spring disposed between the keystem and housing for urging the keystem toward the extended position; an actuator slidably mounted in the housing between the keystem and switch actuating surface, the actuator having a pair of arms secured to and extending therefrom over the keystem side surfaces in captive engagement of the keystem, the arms having inwardly extending ends slidably fitted in the keystem channels and abutting the stop shoulders to limit separation of the keystem and actuator, the arms thereby forming a lost-motion connection which pulls the actuator in a direction away from the switch actuating surface into a retracted position when the keystem is in the normally extended position while permitting limited downstroke keystem motion toward the depressed position without requiring equal motion of the actuator; and a second spring disposed between the keystem and actuator to urge the keystem and actuator apart, the second spring providing a resilient connection between the keystem and actuator such that an increasing restoring force exerted by the second spring during a keystem downstroke toward the depressed position is effective to urge the actuator away from the keystem against the switch actuating surface to effect switch actuation, the second spring permitting overtravel movement of the keystem beyond a position adequate to obtain switch operation, while maintaining a restoring force against the actuator to hold the switch in an actuated position during overtravel movement and until the keystem is permitted to move back toward the extended position.