Claims
- 1. A keymat for use with a substrate or board having electrically conductive contact areas or surfaces thereon, wherein the keymat comprises a membrane of resiliently deformable material having at least one integrally formed dome key whose top surface constitutes a touch button joined to the membrane by a frusto-conical wall, and whose bottom surface has an electrically conductive contact area or surface thereon for contacting an underlying conductive surface on a substrate, for thus defining an electrical switch, and wherein:
- (a) the membrane and at least the periphery of the touch button are relatively thick and the wall is relatively thin so that deformation during the keystroke is localized in the wall;
- (b) the length of the wall is approximately equal to the keystroke; and
- (c) the junction between the wall and the membrane is located at a distance less than the keystroke below the junction between the wall and the touch button so that on depression of the touch button the wall deflects from its initial upstanding attitude through a dead-center condition and then suddenly collapses to provide a tactile feedback.
- 2. A keypad according to claim 1, wherein the junction between the wall and the membrane is located at a distance greater than the keystroke above the lower surface of the membrane.
- 3. A keypad according to claim 1, wherein the ratio of the thickness of the membrane to the thickness of the wall is from about 4:1 to about 10:1.
- 4. A keypad according to claim 3, wherein the ratio of the thickness of the membrane to the thickness of the wall is about 7:1.
- 5. A keypad according to claim 1, wherein the wall is directed at from 25.degree. to 60.degree. to the membrane when the key is undeflected.
- 6. A keypad according to claim 5, wherein the wall is directed at about 45.degree. to the membrane when the key is undeflected.
- 7. A keypad according to claim 6, wherein the wall joins the membrane flush with its top surface and the membrane is at least 1.5 mm thick.
- 8. A keypad according to claim 7, wherein the the key stroke is about 0.7 mm to 2 mm.
- 9. A keypad according to claim 8, wherein the keystroke is about 1.3-1.4 mm.
- 10. A keypad according to claim 1, wherein the touch button is of low profile.
- 11. A keypad according to claim 10, wherein the maximum thickness of the touch button is less than half its width and the distance between the top surface of the touch button and the lower face of the membrane is less than three times the thickness of the membrane the thickness of the touch button being such that it does not substantially flex during the keystroke.
- 12. A keypad according to claim 11, wherein the undersurface of the touch button is disposed no higher than the top surface of the membrane when the touch button is undeflected.
- 13. A keypad according to claim 12, wherein the wall joins the touch button at least partway up the touch button.
- 14. A keypad according to claim 1, wherein the touch button presents a continuous curved lower face having a conductive surface that occupies most of its width, the radius of curvature of the conductive face being selected in relation to the length, the angle, the height of the wall junction with the membrane and the touch button size and travel so that when the keypad is placed in area contact with the substrate the conductive surface makes area contact with the conductive surface on the substrate over the full range of angles to which the touch button tilts when finger pressure is asymmetric.
- 15. A keypad according to claim 14, wherein the material of the membrane is transluscent in thin sections and the touch button presents a continuous top face and is formed with a cavity opening from its underside and defining an annular lower face, the cavity being spanned by an integral web that is thin enough to be transluscent and that defines portions of said top face.
- 16. A keypad according to claim 15, wherein the periphery of the touch button is formed with an upstanding wall inturned at its end to retain a disk of light-transmitting rigid material.
- 17. A keypad according to claim 16, wherein the touch button presents a convex conductive lower face.
- 18. A keypad according to claim 1, wherein the touch button is circular in plan.
- 19. A keypad according to claim 1, wherein the touch button is oval in plan.
- 20. A keypad according to claim 1, wherein the touch button is square in plan with radiused corners.
- 21. A keypad according to claim 1, wherein the touch button is rectangular in plan with radiused corners.
- 22. A keypad according to claim 1, wherein the touch button is polygonal in plan with radiused corners.
- 23. A two-component switch comprising a keymat arranged as a cover on a substrate or board having electrically conductive contact areas or surfaces thereon, and wherein the keymat comprises a membrane of resiliently deformable material having at least one integrally formed dome key whose top surface constitutes a touch button joined to the membrane by a frusto-conical wall, and whose bottom surface has an electrically conductive contact area or surface thereon for contacting the underlying conductive surface on the substrate, thus defining an electrical switch, and wherein:
- (a) the membrane and at least the periphery of the touch button are relatively thick and the wall is relatively thin so that deformation during the keystroke is localized in the wall;
- (b) the length of the wall is approximately equal to the keystroke; and
- (c) the junction between the wall and the membrane is located at a distance less than the keystroke below the junction between the wall and the touch button so that on depression of the touch button the wall deflects from its initial upstanding attitude through a dead-center condition and then suddenly collapses to provide a tactile feedback.
- 24. A switch according to claim 23, wherein the keypad membrane is formed with self-aligning retainer means engaging behind the substrate to hold the membrane in face to face contact with the substrate and in a predetermined position relative thereto, said retainer means tensioning the membrane and comprising a peripheral lip on the membrane into which the edges of the substrate locate.
- 25. A switch according to claim 19, wherein the retaining means further comprises studs projecting from the concealed face of the membrane that locate via through holes in the substrate.
- 26. A switch according to claim 20, wherein the conductive formations on the substrate are an array of interdigitated contact fingers defining a contact area under the touch button, and the underside of the touch button is conductive.
- 27. A switch according to claim 26, wherein there are a multiplicity of touch buttons, each individually colored or marked for identification.
- 28. A keypad for an electrical switch, in which the keypad is adapted to overlie a substrate having at least one electrically conductive contact area thereon, said keypad comprising a membrane of resiliently deformable material having at least one frusto-conical dome-shaped key molded therein so that its top surface constitutes a touch button, the touch button being connected to the membrane by a dome wall, the thickness and angle of the or of each dome wall relative to the touch button and the membrane being such that irrespective of the angle to which the touch button tilts when depressed, the wall gives way to give a change in tactile sensation without substantially deforming the surrounding membrane or touch button, the thickness of the membrane being greater than the distance the button tilts or travels before the respective dome wall inverts, and said key having electrically conductive means on a bottom surface thereof for contact with a contact area on a substrate.
- 29. A keypad as claimed in claim 28, wherein the touch button is of a thickness such that the touch button does not substantially flex when depressed at least until after the change in tactile sensation.
- 30. A keypad according to claim 24, wherein the membrane and touch button are of substantially the same thickness and the undersurface of the touch button is conductive and convex and is disposed no higher than the line of the top surface of the membrane.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 8402974 |
Feb 1984 |
GBX |
|
FIELD OF THE INVENTION
This application is a continuation-in-part of U.S. application Ser. No. 07/000897, filed Jan. 6, 1987, now abandoned, which in turn is a continuation-in-part of U.S. application Ser. No. 783927, now U.S. pat. No. 4,634,818.
The present invention relates to a keypad for an electrical switch and to a switch using such a keypad that may be used, e.g. for the input of data to an electronic device such as a digital device.
The cost of digital data processing circuitry has fallen spectacularly since computers began to be mass produced and this cost reduction has exerted a corresponding downward pressure on the cost of peripherals such as keyboards.
A conventional typewriter-type keyboard has moving keys controlling individual switches, but is relatively expensive to make. A membrane keyboard such as has been fitted to the Sinclair ZX 81 microcomputer enables substantial cost reductions to be made but provides no tactile feedback to the user as to whether depression of a key has provided a registrable signal. In other low cost computers such as that fitted to the Sinclair Spectrum the keys are formed integrally with a molded rubber membrane. But the rubber sheet has to be overlaid by an apertured cover plate or bezel and the keys are used to close contacts in a membrane-type grid supported by a backing plate which is still relatively complex. Keyboards using silicone rubber sheets bearing conductive pads resiliently supported in contact elements formed in the sheets that directly close circuits between conductors on an underlying circuit board are sold by Maag Technic AG and provide a snap action and hence a degree of user tactile feedback. But again the silicone sheet is concealed within the keyboard structure and is intended to be used with separate typewriter- or calculator-style keys working in a guiding bezel. The key may either itself project through the bezel or a plastics keytop placed over the key may project through the bezel.
German OLS 3218404 describes a keypad with raised dome keys but little information is given about the effective design of the dome walls. Membrane switches are also described by Ed. Connolly in Electronic Design, Volume 30, Sept. 30, 1982 at pages 183-192.
It is an object of the invention to provide an improved keypad for an electrical switch enabling a keyboard or other device of simplified construction using essentially only two interfitting parts--one being the keypad--which is of attractive low profile appearance and provides a tactile response to key depression.
Broadly stated the invention provides a keypad for an electrical switch comprising a membrane of resiliently deformable material having an integrally formed dome key whose top surface constitutes a touch button joined to the membrane by a frusto-conical wall, wherein:
(a) the membrane and at least the periphery of the touch button are relatively thick and the wall is relatively thin so that deformation during the key stroke is localised in the wall;
(b) the length of the wall is approximately equal to the keystroke; and
(c) the junction between the wall and the membrane is located at a distance less than the keystroke below the junction between the wall and the key so that the wall passes overcenter during the keystroke resulting in a change in tactile sensation.
With the arrangement just described the wall exhibits a true overcenter action, i.e. the junction between the wall and the button passes from above to below the junction between the wall and the membrane resulting in a sharp and noticeable difference in tactile sensation.
The invention also provides a two component switch wherein a keypad as aforesaid is in face to face contact with a contact surface, the top face of the keypad providing an outer face for the switch without the need for an alignment bezel.
The invention further provides a keypad for an electrical switch consisting of a membrane of resiliently deformable material having at least one frusto-conical dome-shaped key molded therein so that its top surface constitutes a touch button, the thickness and angle of the or each dome side wall relative to the touch button and the membrane being such that irrespective of the angle to which the touch button tilts when depressed the unsupported wall gives way to give a change in tactile sensation without substantially deforming the surrounding membrane, the thickness of the membrane being greater than the distance the button tilts or travels before the respective side wall gives way.
The junction between the wall and the membrane is desirably located at a distance greater than the keystroke above the lower surface of the membrane and the distance should be such that the wall is not significantly tensioned before the keystroke is complete.
The relative thicknesses of the wall and the membrane have to be selected in relation to the structure and material of the keypad so that deformation during the keystroke is localised in the wall and neither the key nor the surrounding membrane distorts perceptibly to the user. The ratio of the thickness of the membrane to the thickness of the wall is therefore desirably from about 4:1 to about 10:1; most usually about 7:1. The wall may be directed at an angle of from 25.degree. to 60.degree. to the membrane when the touch button is undeflected depending upon the tactility required, with angles of about 45.degree. being preferred.
The touch button may in plan be circular or oval but preferably polygonal with radiused corners, square or rectangular keys being the most common. The polygonal key shape has been found to retain tactility well under asymmetric finger pressure, the wall part that travels furthest collasping overcenter all along its length and the opposite wall part acting as a hinge with the intervening wall parts exhibiting intermediate behavior.
US Referenced Citations (15)
Foreign Referenced Citations (5)
| Number |
Date |
Country |
| 123184 |
Oct 1984 |
EPX |
| 2540011 |
Mar 1976 |
DEX |
| 3218404 |
Nov 1983 |
DEX |
| 871287 |
Apr 1942 |
FRX |
| 2082840A |
Mar 1982 |
GBX |
Non-Patent Literature Citations (1)
| Entry |
| Electronic Design; Ed Connolly; "Focus on Membrane Switches: Simple, Colorful, and Reliable"; vol. 30, Sep. 1982, pp. 183-192. |
Continuation in Parts (2)
|
Number |
Date |
Country |
| Parent |
897 |
Jan 1987 |
|
| Parent |
783927 |
Sep 1985 |
|
Patent Grant
4839474
