Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1986-10-24
1989-03-21
Miller, Stanley D.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250227, 350 9615, 341 31, G01V 904, G02B 626
Patent
active
048146005
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to electromagnetic radiation circuit elements generally of the touch-sensitive key type, particularly but not exclusively for use in conjunction with fibre-optic communication systems.
In telecommunications and in demanding process control applications, there is a trend towards the use of light instead of electrical current as the information-carrying medium. Light guides in the form of thin, flexible fibre-optic cables are expected to play an important role in future communication networks and in signal transmission in demanding environments due to their higher information capacity and their insensitivity to electromagnetic transients, as well as their potential in terms of lighter and less bulky cables.
Although the main use of fibre-optic cables will probably be to carry heavy information loads in the form of high-frequency signals there are other applications, such as military use and process control in environments with heavy electromagnetic interference, where fibre-optic communication is in practice the only possibility, and which involve manual input of information e.g. through keyboards. In such applications, a fibre-optic circuit element for manual input of information into the system may be required. The present invention is particularly concerned with such a fibre-optic circuit element, especially in the form of a so-called touch-sensitive key, although the invention may also be used with advantage in optoelectronic applications.
BACKGROUND ART
In man-machine communication there is a trend away from the use of mechanical keys and towards the use of touch-sensitive keys. Touch-sensitive keys have several advantages compared to mechanical keys; they have no moving parts and are thus not subjected to wear, they can more easily be sealed hermetically from the environment, they can be manufactured at a lower cost, and designs with touch-sensitive keys often offer aesthetically more pleasing solutions.
Several concepts for optical touch-sensitive keys are known in the prior art. In IBM Technical Disclosure Bulletin Vol. 18 No. 2 page 483 (July 1975) a fibre-optic switch is described in which the pressure of the finger deforms a foam washer in such a way that reflected light from an optical fibre is prevented from reaching a return fibre.
In Electronic Engineering, April 1981, page 51, several designs are presented in which an approaching finger either reflects or obstructs the light path from a source fibre to a detector fibre. No consideration is given in the mentioned reference to the serious problem of external light, such as from the sun, shining into the system.
None of the above prior art references, however, relates to a true touch-sensitive key in the sense that its function involves no mechanical deformation and that it is activated when and only when the finger touches the sensitive surface.
British Pat. No. 1,600,566 (corresponding to U.S. Pat. No. 4,254,333 and corresponding Patents in other countries) describes a concept for a true optical touch-sensitive key, in which also a complete separation is achieved between, on one hand, external light such as from the sun and, on the other hand, an inner radiation system operable to affect a radiation detector. Despite the fact that said inner radiation system is completely separated from the outside, it is still possible, due to the particular properties of total internal reflection, to affect this inner radiation system by touching the surface of the key. The present invention is concerned with a development of this concept which is particularly suitable for use in a fibre-optic context bearing in mind that an important requirement with a fibre-optic touch-sensitive key is that the light loss in the key should be as small as possible, so as to avoid the need for amplification in connection with the key requiring extra electronic circuitry which would be expensive and also might make the system sensitive to external electromagnetic interference.
One way of reducing light losses would be to focus
REFERENCES:
patent: 3886544 (1975-05-01), Narodny
patent: 3937952 (1976-10-01), Ripley et al.
patent: 4254333 (1981-03-01), Bergstrom
Miller Stanley D.
Roseen Richard
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