BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein:
FIG. 1 is a side view of a conventional metal dome;
FIG. 2 is a side view of an embodiment of the present invention; and
FIG. 3 is a side view of an embodiment of the present invention, showing the action of the key button structure.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 2, a key button structure of an embodiment of the present invention is provided for a dome membrane switch 20. The dome membrane switch 20 includes at least a conductive layer 21 and a metal dome 22. The conductive layer 21 has electrical conducting pad 211. The metal dome 22 covers the electrical contact 211 and is formed by punching a metal plate to assume an embossed cap. The top surface of the metal dome 22 has a height h, such that in normal state the metal dome 22 keeps the height h from the electrical conducting pad 211 without touching the conducting pad. An effective pressing area A, an allowable pressing area B, and a permanent deformation point C are defined from center to outer on the top surface of the metal dome 22 (as shown in FIG. 1). When the effective pressing area A of the metal dome 22 is pressed, the metal dome 22 is deformed downward and the inner side of the top surface touches the electrical conducting pad 211. After force that makes the metal dome 22 deformed is absent, the metal dome 22 recovers due to the resilience. However, if the area outside the effective pressing area A is pressed, the metal dome 22 is permanently deformed and cannot recover when force is absent.
However, the key button structure of the embodiment of the present invention includes a button cap 11 and a button stem 12. The button cap 11 and button stem 12 are made of plastic material and formed by injection molding. The button cap 11 can be formed in any type of configuration according to the electronic device (not shown) in practice and is exposed outside the surface of the electronic device for users to press. The button stem 12 is extended from the bottom of the button cap 11, and has an outer diameter smaller than the outer diameter of the effective pressing area A. The surface of the tip end surface of the button stem 12 is in the shape of a spherical camber 121.
Referring to FIG. 3 together, the button cap 11 of the key button structure is disposed above the metal dome 22. The button stem 12 is extended from the button cap 11 and toward the effective pressing area A of the metal dome 22 and the tip end thereof is spaced from the metal dome 22. When the button cap 11 is pressed downward, the button cap 11 moves the button stem 12 to press against the metal dome 22. The spherical camber 121 of the button stem 12 is in point contact with the metal dome 22, such that the button stem 12, when presses the metal dome 22, is in contact within the effective pressing area A of the metal dome 22, and further the metal dome 22 is deformed downward to make the inner side of the metal dome 22 touch the electrical conducting pad 211. Thus, the conductive layer 21 triggers a corresponding signal at once. After force pressing the button cap 11 is absent, the button cap 11 returns to the normal position (through the resilient structure on the button cap 11 or resilient elements installed in the button cap 11, not shown). Then, the metal dome 22 can resiliently recover to the normal state (as shown in FIG. 2).
Since the surface of the tip end of the button stem 12 is formed in the shape of the spherical camber 121, so that the button stem 12 is in point contact with the metal dome 22. Although slight dimension or assembling error exist, the button stem 12 can still be in contact within and press the effective pressing area A to prevent the metal dome 22 from being permanently deformed and damaged.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
Patent Application
20080035463
