GB2157497A - Elastomeric dome with tactile feedback - Google Patents

Abstract

An elastomeric dome, or diaphragm (30), for an electrical switch of a keyboard, which provides improved tactile feedback and reduces teasability about the trip point. The diaphragm construction includes a plurality of members, including an upper (38) and a lower (34) truncated conical member, the upper such member having less resistance to buckling than the lower member. <IMAGE>

Description

SPECIFICATION Elastomeric Dome with Tactile Feedback This invention relates generally a electrical switches and specifically to an improved domeshaped member, sometimes referred to as a diaphragm, used in such switches for providing tactile feedback to the switch operator. More particularly, this invention relates to diaphragms of the type described which are preferably formed on a sheet of flexible, elastomeric material so that the sheet can be advantageously used in the manufacture of keyboards or keypads incorporating a plurality of electrical switches.

Dome-shaped members used to provide tactile feedback have been incorporated in a variety of switch constructions. These include single or double pole electrical contact switches as well as multiple switch embodiments such as keyboards and keypads. By way of example only, such domeshaped members may be utilized as part of a membrane switch keypad construction having multiple component layers.These layers may typically include 1) actuatable means which may be in the form of buttons, keys or include an indicia sheet containing alphanumeric characters; 2) tactile feedback means such as a flexible sheet of integrally formed jome-shaped members, each of the domes substantially centered under an appropriate alphanumeric character; 3) an electrically conductive sheet underlying the flexible sheet; 4) a spacer sheet having openings aligned with appropriate dome-shaped members; and 5) a printed circuit board, typically having electrical contacts underlying the spacer sheet.

In accordance with well-known operation, the application of force to the actuable means at the desired alphanumeric character causes the underlying dome to snap through center, thereby providing tactile feedback to the operator. The force required to cause the dome to snap through center is sometimes referred to as the "trip point". After reaching the trip point, the dome typically continues its downward movement, urging the conductive sheet through the corresponding opening in the spacer sheet until it is brought into engagement with one or more electrical contacts at predetermined positions on the underlying printed circuit board. When the conductor sheet engages the electrical contacts on the printed circuit board the switch electronically responds in an appropriate manner, i.e., the switch is actuated.As the pressure applied by the switch operator is released, the dome snaps back to its original position, thereby disengaging the contact sheet from the electrical contacts on the underlying printing circuit board.

Electrical switches with a sheet of elastomeric material having dome-shaped members to provide tactile feedback to the switch operator have been in use for many years. Nonetheless, such switches are not without certain drawbacks and deficiencies. For example, in some instances the tactile feedback provided by some dome-shaped members is not as well-defined as the operator would desire.

Similaarly, some dome-shaped members of the prior art are characterized by an inherent teasability, whereby a slight change in pressure applied to the actuatable means by the switch operator allows the dome-shaped member to "dance" back and forth about the trip point.

It is therefore an object of this invention to provide an improved diaphragm, or dome-shaped member, for use with electrical switches of the type generally described above, or for any other electrical switch application where such improved diaphragms may be desirable. It is another object of this invention to provide an improved snap action diaphragm which provides a more accented tactile feedback than that achieved by many of the prior art switches. It is also an object of the invention to provide an improved snap action diaphragm which is subject to less teasability about the trip point than such prior art switches. It is a further object of this invention to achieve the above benefits while increasing the downward distance the diaphragm moves before the trip point is reached. This distance is sometimes referred to "pretravel".

The foregoing objects, along with other features and advantages, are achieved in a diaphragm for use in an electrical switch adapted to be actuated by tactile pressure. The diaphragm comprises a base having an opening, and first, second and third members extending, respectively, up from the base above the plane of the opening. A projecting element extends downwardly from one of the members toward the opening. The first and third members are of such relative flexibility that the resistance against buckling of the first, or lower member, is greater than the resistance against buckling of the third member. Thus, upon receipt of tactile pressure for operating the switch, the first and third members store energy until the pressure is sufficient to cause the third member to snap through center before the switch is actuated.

A preferred embodiment of the invention summarized above is illustrated in the accompanying drawings wherein: Figure 1 is a schematic, sectional view of an exemplary electrical switch construction including a flexible sheet of integrally formed dome-shaped members; Figure 2 is an enlarged, sectional view of a dome-shaped member or diaphragm of the type that can be formed in a flexible sheet such as that shown in the exemplary electrical switch of Figure 1; Figure 3A is a schematic sectional view of the diaphragm shown in Figure 2 before tactile pressure is applied thereto; Figure 3B is a schematic sectional view of the diaphragm shown in Figure 2 after tactile pressure has been applied, but before an associated member has snapped through center; and Figure 3C is a schematic sectional view of the diaphragm shown in Figure 2 after the associated member has snapped through center.

Referring now to Figure 2, there is shown a schematic rendering of an electrical switch construction 10. Switch construction 10, in this exemplary embodiment, is comprised of actuatable means shown here in the form of an indicia sheet 12, tactile feedback means shown here in the form of a flexible sheet 14 having a plurality of domeshaped members 15 integrally formed therein, an electrically conductive sheet 16, a spacer sheet 18 defining a plurality of openings 19, and an underlying printed circuit board 20.

It should be understood that the switch construction 10 can take numerous alternative forms, the specific embodiment shown in Figure 1 being exemplary. Thus, push buttons, keys or other actuatable means may be substituted for the indicia sheet 12, and various other substitutions, additions and deletions may be made in connection with the other components of switch construction 10 without departing from the true scope of the invention.

In this exemplarly embodiment, indicia sheet 12 carries a plurality of alphanumeric characters, and may therefore be particularly useful as a keypad or keyboard for calculators, computers and other such devices. Flexible sheet 14, as mentioned above, includes a plurality of integrally-formed domeshaped members preferably aligned under respective alphanumeric characters on indicia sheet 12. The construction of these dome-shaped members are discussed hereinafter in connection with the description of Figure 2.

The openings 19 defined in the spacer sheet 18 are preferably aligned under respective domeshaped members 15. Thus, when the switch operator applies pressure to a selected one of the alphanumeric characters on indicia sheet 12, an underlying dome-shaped member formed in flexible sheet 14 urges a portion of conductive sheet through an underlying opening in spacer sheet 18 and into contact with circuit means such as one or more electrical contacts (not shown) located in predetermined positions on printed circuit board 20.

When this occurs, electrical means, not shown, associated with printed circuit board 20 are selectively operated, causing an electrical response indicative of the fact that the selected alphanumeric character of indicia sheet 12 has been depressed, i.e., the switch is actuated.

In order to provide improved tactile feedback to the switch operator, and to reduce the likelihood of teasability about the trip point, the dome-shaped members 15 used with flexible sheet 14 are preferably constructed as shown in Figure 2. More particularly, Figure 2 illustrates an enlarged sectional view of such a dome-shaped member or diaphragm 30. Diaphragm 30 is preferably made from elastomeric material with all of the elements integrally formed thereon. Diaphragm 30 specifically includes a base 32, in the form of a hollow disk orcylinder, defining a central opening 33. Extending upwardly from base 32, above the plane defined by opening 33, is a first member 34.

First member 34 preferably takes the shape of a hollow, truncated cone, and makes an angle 51 with base 32. Angle 51 is greater than 90 degrees, but less than 180 degrees. In this exemplary embodiment, angle 51 is approximately 145 degrees.

Extending upwardly from first member 34, above the plane defined by opening 33, is a second member 36. Second member 36 preferably takes the form of a hollow cylinder, and makes an angle 52 with first member 34. Angle 52 is greater than or equal to 90 degrees, but less than 180 degrees. In this preferred embodiment, angle 52 is approximately 115 degrees.

A third member 38 extends upwardly from seconc member 36 above the plane defined by opening 33.

Like first member 34, second member 38 preferably takes the form, at least in part, of a hollow, truncated cone. Third member 38 makes an angle 53 with second member 36, angle 53 being greater than or equal to 90 degrees, but less 180 degrees. In this preferred embodiment, angle 53 is approximately 125 degrees. Third member 38, however, has less resistance to buckling, i.e., is more likely to snap through center, than first member 34. For this reason, it is preferred that if all of the components ot diaphragm 30 are integrally formed, and therefore made from the same flexible material, third member 38 will be of somewhat thinner cross-section than first member 34.

Extending upwardly from third member 38, or alternatively, forming part of third member 38, is a fourth member 40. Fourth member 40 extends above the plane defined by opening 33 and makes an angle 54 with third member 38 which is greater than 90 degrees, but less than 180 degrees. In this preferred embodiment, angle 54 is approximately 125 degrees.

Extending substantially downwardly from one of members 34,36, 38 or 40 is a projecting element 42.

Projecting element 42 extends toward opening 33 in the hollow space defined by members 34,36 and 38.

In this preferred embodiment, fourth member 40 and projecting member 42 define an outer surface 44 adapted to accommodate a key assembly, not shown. Alternatively, the upper configuration of diaphragm 30 could be arranged to comport with an overlying indicia sheet of the type shown in Figure 1 if that form of actuation means is used in a particular switch construction.

Though diaphragm 30 can take on countless dimensional variations without departing from the scope of the invention, the preferred embodiment utilizes the following relative dimensions and radii corresponding to the small letter designations identified in Figure 2: a-.620 i-.225 q-.082 b.270 j-.082 r-.040 c-.202 k-.030 s-.050 d-.027 1-065 t-.045 e--.356 m-.015 u-.073 f-.042 n-.040 v-.015 g-.100 o-.035 w-.015 h-.265 p-.040 x No matter what actuation means are employed, and no matter what dimensional parameters are chosen, the application of tactile pressure to the actuation means causes pressure to be ultimately applied to diaphragm 30.Thus as used herein, the application of pressure should not be construed as being limited to the application of pressure directly from the switch operator to the actuation means, but also includes the application of pressure indirectly transmitted from one element or component to another.

When tactile pressure is applied to diaphragm 30, members 34 and 38 begin to store energy. These members may initially deform without buckling, i.e.

without snapping through center. When sufficient tactile pressure has been applied to diaphragm 30, however, third member 38 ultimately snaps through center while first member 34 does not. As third member 38 snaps through center, it provides tactile feedback to the operator of the switch.

The operation of diaphragm 30 during the application of tactile pressure thereto is shown by the schematic representations in Figures 3A, 3B and 3C. Thus, in Figure 3A, no tactile pressure has been applied to diaphragm 30. In figure 3B, however, tactile pressure has been applied through fourth member 40, and has been transmitted to members 34 and 38. These members absorb at least some of this energy, and perhaps deform slightly without snapping through center. This deformation is represented schematically by the altered shape of first member 34, for example. Of course, as tactile pressure is applied, projection 42 begins to descend toward opening 33 in base 32.

As additional tactile pressure is applied to diaphragm 30, third member 38 buckles, i.e., snaps through center. This is shown in Figure 3C. After third member 38 snaps through center, projection 42 descends through opening 33, while first member 34 substantially returns to its original shape. When third member 38 snaps through center, tactile feedback in substantially accented form is provided to the switch operator. Moreover, the particular construction of diaphgram 30 reduces the likelihood of teasability about the trip point of third member 38 as the diaphragm 30 is actuated.

Further, because of the relatively large distance the diaphragm 30 moves before the trip point is reached, the construction of diaphragm 30 is desirably characterized by relatively large pretravel.

Of course, when projection 42 descends through opening 33, it causes the elements of the switch construction of the type shown in Figure 1 to operate in the manner previously described. Upon removal of the tactile pressure, the components of diaphragm 30 substantially return to the positions shown in Figure 3A.

What has been described is an improved diaphragm for use in electrical switch constructions having a variety of configurations including the exemplary construction shown in Figure 1. Though the diaphragm disclosed and described herein is preferred, numerous embodiments, variations and changes which do not part from the true scope of the invention will become apparent to those skilled in the art. All such embodiments, variations and changes are intended to be covered by the appended claims.

Claims (11)

1. A diaphragm for use in an electrical switch adapted to be actuated by the application of tactile pressure comprising: a base defining an opening; a first member extending from said base above the plane of said opening at an angle greater than 90 degrees but less than 180 degrees with said base; a second member extending from said first member above the plane of said opening at an angle equal to or greater than 90 degrees but less than 180 degrees with said first member; a third member extending from said second member above the plane of said opening at an angle equal to or greater than 90 degrees but less than 180 degrees with said second member; and a projecting element extending downwardly from one of said members toward said opening; said first and third members being of such relative flexibility that the resistance against buckling of said first member is greater than the resistance against buckling of said third member whereby, upon receipt of said tactile pressure, said third member snaps through center before said switch is actuated.

2. The diaphragm defined in Claim 1 wherein said first member and said third member have the configuration of a hollow truncated cone.

3. The diaphragm defined in Claim 2 wherein said second member has the configuration of a hollow cylinder extending perpendicularly to the plane defined in said base.

4. The diaphragm defined in Claim 3, wherein said third member includes a fourth member extending from said third member above the plane of said opening at an angle greater than 90 degrees but less than 180 degrees with said third member, and wherein said projecting element extends downwardly from said fourth member.

5. The diaphragm defined in Claim 4 wherein said base, said members and said projecting elements are integrally formed.

6. The diaphragm defined in Claim 1 wherein said diaphragm is adapted for mounting above circuit means, and wherein no part of said switch is moved into engagement therewith in response to the receipt of said tactile pressure until after said third member snaps through center.

7. An electrical switch comprising: a diaphragm having a base defining an opening, a first member extending from said base above the plane of said opening at an angle greater than 90 degrees but less than 180 degrees with said base, a second member extending from said first member above the plane of said opening at an angle equal to or greater than 90 degrees but less than 180 degrees with said first member, a third member extending from said second member above the plane of said opening at an angle greater than 90 degrees but less than 180 degrees with said third member, a fourth member extending from said third member above the plane of said opening at an angle equal to or greater than 90 degrees but less than 180 degrees with said third member, and a projecting element extending from one of said members toward said opening; said first and third members being of such relative flexibility that the resistance against buckling of said first member is greater than the resistance against buckling of said third member; contact means, aligned with said opening under said base adapted to be engaged by a portion of said switch moved in response to the movement of said projecting element to actuate said switch; and actuation means containing alphanumeric indicia, disposed above said third member for receiving tactile pressure whereby, upon application of tactile pressure thereto, said first and third members store energy until said pressure is sufficient to cause said third member to snap through center before said switch is actuated.

8. The electrical switch defined in Claim 7 wherein said base, said members and said projecting element are integrally formed.

9. The electrical switch defined in Claim 7 wherein said actuation means include a plurality of alphanumeric indicia, and wherein there is provided a tactile feedback sheet containing a plurality of integrally formed diaphragms aligned, respectively, under corresponding ones of said indicia.

10. The electrical switch defined in Claim 7 wherein no part of said switch is moved into engagement with said contact means in response to the receipt of tactile pressure until after said third member snaps through center.

11. A diaphragm for use in an electrical switch substantially as described herein with reference to the accompanying drawings.