Electricity: circuit makers and breakers – Multiple circuit control – Multiple switch
Patent
1985-09-26
1987-01-06
Scott, J. R.
Electricity: circuit makers and breakers
Multiple circuit control
Multiple switch
200159B, H01H 1370
Patent
active
046348182
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a switch for an electrical or electronic device that may be incorporated into a keypad for the input of data to a digital device.
BACKGROUND TO THE INVENTION
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 2X 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 moulded 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 bezel.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a switch for a keyboard or other device of simplified construction using essentially only two interfitting parts but which nevertheless is of attractive appearance and provides a tactile response to effective key depression.
Broadly stated the invention provides an electrical switch comprising a contact surface and a combined cover and membrane of resiliently deformable material positioned against the contact surface so that an otherwise unsupported integral touch pad raised from the surrounding membrane by a thin angled wall flexes under finger pressure through an over-centre position to press its convex underside against the contact surface to close the switch, wherein the membrane surrounding the wall is at least 1.5 mm thick and the wall length and underside curvature are selected in relation to the touch pad size and travel so that the underside makes face to face contact with the contact layer over the full range of angles to which the touch pad tilts when the finger pressure is asymmetric.
The invention further provides a keyboard comprising a contact surface and a combined cover and membrane of resiliently deformable material positioned against the contact surface so that otherwise unsupported integral touch pads disposed in an array and each raised from the surrounding membrane by a thin angled wall flex through an over-centre position to press respective convex undersides against the contact surfaces to close respective switches, the membrane between the touch pads being at least 1.5 mm thick and the wall length and underside curvature being selected in relation to the touch pad size and travel so that the underside makes face to face contact with the contact layer over the full range of angles to which the touch pad tilts when the finger pressure is asymmetric.
German OLS. No. 3218404 describes a key mat with raised keys connected to the mat by a hinge but no attention has been paid to the possibility that pressure on one key might affect other keys or disturb the flatness of the surrounding membrane. The invention therefore further provides a low profile switch or keypad assembly having one or more touch pads formed integrally with and raised from a surrounding membrane of resiliently deformable material by a wall of a thickness and angle relative to the membrane enabling the wall to flex under finger pressure on the or each p
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Electronic Design; Ed Connolly; "Focus on Membrane Switches: Simple, Colorful, and Reliable"; vol. 30, Sep., 1982, pp. 183-192.
Hayes-Pankhurst Richard P.
Smith Brian D.
NPM International
Scott J. R.
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