Dome shaped switch member

Abstract

A dome shaped element which is used as a switch member in a keyboard switch assembly consists of a hollow, geometric solid having an open circular base with a plurality of planar side walls extending from the base. The side walls are joined by an arcuate surface and arcuate feet members join segments of the arcuate surface to the adjacent side walls. The feet are bent angularly to the plane of the arcuate surface.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to conductive, snap-acting or spring type, dome shaped elements which are used as switch members in a keyboard switch assembly.

Keyboard switch assemblies, particularly those used in currently available miniature electronic calculators, generally include a set of appropriately symbolized pushbutton keyboard members having numeric characters or mathematical function representations imprinted on them. These characters and mathematical functions are generated by manual depression of the pushbutton to establish electrical contact with circuit elements. Conductive, generally hemispherical (i.e. a portion of a hemisphere), snap-acting or spring type dome elements which act as switch members are generally positioned beneath the pushbutton members. Depression of the pushbutton deflects a portion of the dome element member and conpletes the electrical circuit. When the pushbutton is released, the dome element snaps back from its deflected position to its normal position thereby breaking the electrical contact.

Such dome shaped elements which are used as switch members in electronic calculators are described in U.S. Pat. No. 3,806,673 for "Pushbutton Keyboard Switch Assembly with Improved Disc Spring Contact and Printed Circuit Structure", which issued Apr. 23, 1974.

One of the problems associated with these dome shaped switch members has been the manufacture of large quantities of the dome elements having uniform characteristics such as consistent trip and release forces -- the trip force being the force needed to depress the dome and the release force being the minimum force necessary to snap the dome from its deflected position to its normal position. This problem has been particularly acute with respect to the lightweight, small diameter dome shaped switch members, such as those having a trip force of 3 to 7 ounces and being 0.35 to 0.5 inches (9.0 to 12.7 mm) in diameter.

When it was attempted to manufacture large numbers of the generally hemispherical dome elements, it was found that these domes could not be produced in large numbers with uniform trip and release force characteristics. Further, it was found that the generally hemispherical dome elements would not snap well on a flat surface so that it became necessary to emboss dimples on a printed circuit board so as to raise the dome members on one side approximately 0.005 inches to 0.007 inches (0.13 mm to 0.18 mm) to achieve a crisp snap action. This was unsatisfactory because the embossing was expensive and it was difficult to achieve a uniform embossing height.

Another attempted solution to the problem of manufacturing large numbers of these dome elements having uniform characteristics was the manufacture of the modified dome member described in U.S. Pat. No. 3,751,612 for "Snap Action Capacitive Type Switch", which issued Aug. 7, 1973 and which is referred to here as the "delta dome". However, specialized tooling is required to manufacture the delta dome described in that patent, so that the production of large numbers of such dome elements would be expensive.

SUMMARY OF THE INVENTION

The dome shaped switch member of this invention, which overcomes the above-mentioned difficulties, is in the form of a hollow geometric solid having an open circular base with a plurality of planar side walls extending from the base at equal angles to the base toward each other. The planar side walls of the dome are joined by an arcuate surface. Three feet which are bent angularly to the general plane of the arcuate surface join the arcuate portion of the dome to the adjacent planar side walls.

The dome element of this invention has made possible the manufacture of large quantities of domes having uniform trip and release force characteristics.

The dome switch member of this invention also permits the use of thinner materials in the manufacture of the domes without experiencing the bi-stable condition (no returning spring action) previously encountered when thinner materials were used in generally hemispherical domes. The use of thinner dome thicknesses from 0.002 inches to 0.005 inches (0.05 mm to 0.13 mm) permits a reduction in the dome trip force characteristic which is desirable in certain applications.

The edge bend or feet which are formed on the dome arcuate surface raise the arcuate surface of the dome allowing it to snap on a flat surface. Also, the snap action of the dome element of this invention is much crisper than was encountered with previously used generally hemispherical domes.

The primary advantage obtained by the dome element of this invention is a simplification of the tooling necessary to produce the dome element from the more complex and expensive tooling which is required to manufacture the dome element described in U.S. Pat. No. 3,751,612, referred to above. The delta dome element described in that patent is substantially similar to the dome element of this invention with the exception that the delta dome element has an open polygonal base whereas the base of the dome element of this invention is circular. In order to produce the delta dome element, it is necessary to modify existing circular die buttons and it is also necessary for there to be close tolerances between the modified die buttons and the die punch. In manufacturing the dome element of the present invention, standard circular die buttons may be used in conjunction with a cylindrical die punch.

Structural features and the complete nature of the dome of this invention will become apparent from the ensuing specification and the appended claims in which the invention is defined, particularly when taken in conjunction with the accompanying illustrative drawings which set forth the preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of the face of the punch which is used to make the dome of this invention;

FIG. 2 is a transverse section of the punch illustrated in FIG. 1, taken along the line 2--2;

FIG. 3 is a perspective view of the dome of this invention;

FIG. 4 is a plan view of the dome illustrated in FIG. 3; and

FIG. 5 is a cross-sectional view of the dome illustrated in FIG. 3 taken along the line 5--5.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, the punch 10 which is used in making the dome element 12 illustrated in FIG. 3 may be formed of a cylindrical rod with one end machined to a spherical surface 14 having a radius R. A circular chamfer 16 is formed at the periphery of the spherical radius and the punch 10 is machined to the cross section shown in FIG. 1, by forming flat surfaces 18 which intersect with the spherical surface 14 and the outer cylindrical surface 20 of the punch 10.

The dome element 12 is made in the same manner as the delta dome described in U.S. Pat. No. 3,751,612 except that a standard circular die button is used in conjunction with the punch 10 described above in manufacturing the dome element 12.

The dome element 12 includes three feet 22 which are bent angularly to the general plane spherical surface 24 of the dome element. These feet bridge a tip of the spherical surface 24 and the outer portion of adjacent flats 26, forming three reinforced zones about which the general plane of the dome element may buckle to its snap-over position by application of a force to its upper surface. The deflected plane of the dome element returns to its normal position upon removal of the buckling force.

To better enable those skilled in the art to practice the invention without experimentation, the following dimensions and specifications of a preferred embodiment of the dome element 12 are set forth below, as follows:

R = 2.000 inches (50.8 mm)

A = 0.500 inch (12.7 mm)

B = 36.degree.

c = 0.015 inch (0.38 mm)

D = 0.018 inch (.46 mm)

E = 10.degree.

f = 0.028 inch (.71 mm)

G = 120.degree.

Trip Force = 170 grams

Release Force (minimum) = 50 grams

Material: stainless steel, No. 302, full hard, 0.0040 inches (.1 mm) thick.

While the preferred embodiment of various aspects of the invention has been shown in the drawings and described with particularity above, it is to be understood that this disclosure is for the purpose of illustration only and that various changes in the angles and dimensions of the dome shaped switch member described above may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

Claims

What is claimed is:

1. A dome element for use as a switch member, said dome element comprising an open circular base, a plurality of planar side walls, each of said planar side walls extending from a segment of said open circular base at equal angles thereto, an arcuate surface interconnecting said side walls and a plurality of arcuate corners angled downwardly from a tip of said arcuate surface, each of said arcuate corners interconnecting said tip of said arcuate surface with an adjacent pair of said planar side walls.

2. The dome element recited in claim 1, said arcuate surface being spherical.