Patent ID: 6538641
Filing Date: 2003-03-25
Classification: H01H

Abstract:
A key switch device including:a key top provided at its underside with a first engagement portion and a second engagement portion; a third engagement portion corresponding to the first engagement portion, and a fourth engagement portion corresponding to the second engagement portion, both of which are arranged below the key top; a first link member provided with an upper end portion which is rotatably engaged in the first engagement portion and a lower end portion which is slidably engaged in the third engagement portion; a second link member provided with an upper end portion which is rotatably engaged in the second engagement portion and a lower end portion which is slidably engaged in the fourth engagement portion; an urging member for urging the first link member and the second link member in a direction to allow them to come close to each other; and a switching member for conducting a switching operation in association with vertical movement of the key top, the key switch device being designed to be symmetric with respect to a perpendicular line passing through a midpoint between the first engagement portion and the second engagement portion, wherein the upper end portion of the first link member is allowed to rotate about a predetermined rotation point in the first engagement portion, and the lower end portion of the first link member is allowed to slide outwardly from a predetermined slide starting point in the third engagement portion, an urging force of the urging member is exerted on the first link member at a predetermined acting point in the first link member, a depressing load applied to the key top when the key top is depressed is defined by a function expressed by: a distance between the rotation point and the slide starting point; a distance between the rotation point and the acting point; an angle between a line segment extending from the rotation point to the slide starting point, and the direction along which the lower end portion of the first link member in the third engagement portion is allowed to slide; and various characteristic values of the urging member; and a curve of the depressing load defined by the function takes a shape of an upward projecting curve having a maximum point, and a key clicking function is performed based on a difference in loads between the maximum point and a point from which the depressing load starts to increase after the switching operation is conducted by the switching member.