GB1566654A

GB1566654A - Switches

Info

Publication number: GB1566654A
Application number: GB5021277A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1978-05-04
Filing date: 1978-05-04
Publication date: 1980-05-08

Description

(54) SWITCHES (71) We, STANDARD TELEPHONES AND CABLES LIMITED, a British Company, of 190 Strand, London W.C.2, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to switches, and in particular to a matrix type optical keyboard arrangement.

A wide variety of keyboard switch arrangements exist for such applications as data terminals, telecommunication equipment and control systems, Generally such switch arrangements include a printed circuit board on which an array of switch modules is mounted, as many as 80 switches being required in some fully comprehensive keyboards. This module printed circuit board approach, while providing a reasonably flexible solution to the problem, requires an electrical sensing element at every switch position, thus resulting in relatively high manufacturing costs.

The object of the invention is to minimise or to overcome this disadvantage.

According to one aspect of the invention there is provided an optical switch, including a flat plate having at least one straight channel formed in one of its surfaces, a flexible sheet member arranged adjacent the plate and having one or more resilient deformable portions each coinciding with a mid-channel, and means for deforming the one or more resilient portions each into the respective channel so as to obstruct a light path directed along that channel.

According to another aspect of the invention there is provided an optical switch matrix arrangement adapted to perform a switching function by the selective obstruction of a respective one or ones of a plurality of light beams, the arrangement including a flat plate in one surface of which intersecting arrays of parallel straight grooves or channels are formed, the channels providing light paths therealong, a flexible sheet member arranged adjacent the grooved surface of the plate and having a plurality of deformable regions each of which corresponds to the position of a channel intersection, and push-button means for displacing selectively the deformable regions of the sheet member into the corresponding channel intersections so as to obstruct the light path along each channel com- municating with those intersections.

An embodiment of the invention will now be described with respect to the drawings accompanying the Provisional Specification in which:- Fig. 1 shows a cut-away schematic view of the optical switch arrangement; Fig. 2 and 3 show the operation of the individual switches of the arrangement of Fig. 1; Fig. 4 is a plan view of the light guide system of the arrangement; and Fig. 5 is a block schematic of the electrical circuitry of the arrangement.

Referring to the drawings, the switch arrangement essentially comprises three portions.

The light guide system This is provided by a flat plate 11, which may be machined from a metal or may be a plastics moulding, and which has in one surface two intersecting arrays of parallel grooves 12. At each groove intersection a substantially hemispherical depression 13 is formed.

The diaphragm structure A flexible sheet 14, which may be made advantageously of a silicone rubber, is placed adjacent the plate 11 and has an array of dome portions 15 each of which corresponds to a groove intersection of the plate 11. The sheet 14 is arranged with the domes 15 aligned with hemispherical depressions 13 and facing away from the plate 11.

The operating keys The switch keys 16 are mounted in guide channels 17 formed in an upper housing member 18, which may be advantageously a plastics moulding. The position of the guide channels corresponds to the position of the flexible diaphragm and the underlying groove intersections. Thus, operation of any one key 16, deforms the corresponding diaphragm into the corresponding intersection thereby obstructing light paths provided by the grooves communicating with that intersection.

As can be seen from Fig. 2, light is passed along each groove 12 between a light emitter 20 at one end of the groove to a light receiver element 21 at the other end of the groove. In a preferred arrangement the light emitter and receiver may be provided each by a respective optical fibre 23, 24 terminated by a beam expander lens 25, 26 mounted in the groove or channel 12. The fibres 23 and 24 are coupled to a light source and a photodetector respectively. In other applications the optical system may be provided by a combination of a light emitting diode (LED) and a semiconductor photodetector diode arranged in each said groove or channel.

When a key is depressed it deflects the corresponding diaphragm into the corresponding hemispherical depression thereby obstructing the light path to the detectors in the two channels intersecting below the key. This produces a coded output from the switch arrangement, which output may be fed to logic circuitry for performing both the keyboard decoding and output coding functions.

The domes or diaphragms 15 of the sheet member 14 are designed so as to provide the required force/travel characteristic.

Thus, for example, as is indicated in Fig. 3, each dome 15 can be designed to give a "collapsing" response or a linear response according to the particular requirement.

Each dome also provides the restoring force for its corresponding key. Silicone rubber is the preferred material for the sheet member as it is able to withstand extremes of temperature and exhibits a relatively small change of stiffness over the range 20 to 70"C. It does not degrade when subjected to ozone or to many other corrosive agents and has a high fatigue resistance.

In its simplest form the keyboard arrangement uses an LED and detector in each groove or channel 12 of the plate 11.

However, if light guides or light multiplexers are used it is possible to reduce the number of LED's and detectors.

Fig. 5 is a schematic diagram of the optoelectronic system used with the keyboard assembly of Figs. 1 to 4. As shown, the kevboard is arranged similarly to a typewriter keyboard layout and has four rows of keys, providing a total of 56 in dividual switches. The LED's are arranged in groups of four and are coupled via gates G1-G5 to a microprocessor MPU. The detectors are also coupled to the microprocessor.

The microprocessor is programmed to pulse the switch matrix LED's in groups, via an ENABLE circuit El, and to examine the associated detector outputs. This is done many times during one key depression and the information is processed to provide a predetermined coded output.

Also, where necessary, the microprocessor protects against lost information key 'roll over', the simultaneous operation of two or more keys. The opto-electronic circuitry may be mounted on a circuit board fixed to the underside of the plate member 11.

WHAT WE CLAIM IS:--- 1. An optical switch, including a flat plate housing at least one straight channel in one of its surfaces, a flexible sheet member arranged adjacent the plate and having one or more resilient deformable portions each coinciding with a said channel, and means for deforming the one or more resilient portions each into the respective channel so as to obstruct a light path directed along that channel.

2. An optical switch matrix arrangement adapted to perform a switching function by the selective obstruction of a respective one or ones of a plurality of light beams, the arrangement including a flat plate in one surface of which intersecting arrays of parallel straight grooves or channels are formed, the channels providing light paths therealong, a flexible sheet member arranged adjacent the grooves surface of the plate and having a plurality of deformable regions each of which corresponds to the position of a channel intersection, and push-button means for displacing selectively the deformable regions of the sheet member into the corresponding channel intersections so as to obstruct the light path along each channel communicating with those intersections.

3. A switch matrix as claimed in claim 2, in which each said channel is provided with a light emitting diode and a photodetector, the light path being disposed therebetween.

4. A switch matrix is claimed in claim 3, in which the light emitting diodes and detectors are arranged in respective grouns, the diodes of each group being operable via a respective gate by a microprocessor.

5. A switch matrix as claimed in any one of claims 2 to 4, and in which the flexible member comprises a plastics sheet provided with domed-regions, the domes being so designed as to provide a restoring force to the push-button keys.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. channels 17 formed in an upper housing member 18, which may be advantageously a plastics moulding. The position of the guide channels corresponds to the position of the flexible diaphragm and the underlying groove intersections. Thus, operation of any one key 16, deforms the corresponding diaphragm into the corresponding intersection thereby obstructing light paths provided by the grooves communicating with that intersection. As can be seen from Fig. 2, light is passed along each groove 12 between a light emitter 20 at one end of the groove to a light receiver element 21 at the other end of the groove. In a preferred arrangement the light emitter and receiver may be provided each by a respective optical fibre 23, 24 terminated by a beam expander lens 25, 26 mounted in the groove or channel 12. The fibres 23 and 24 are coupled to a light source and a photodetector respectively. In other applications the optical system may be provided by a combination of a light emitting diode (LED) and a semiconductor photodetector diode arranged in each said groove or channel. When a key is depressed it deflects the corresponding diaphragm into the corresponding hemispherical depression thereby obstructing the light path to the detectors in the two channels intersecting below the key. This produces a coded output from the switch arrangement, which output may be fed to logic circuitry for performing both the keyboard decoding and output coding functions. The domes or diaphragms 15 of the sheet member 14 are designed so as to provide the required force/travel characteristic. Thus, for example, as is indicated in Fig. 3, each dome 15 can be designed to give a "collapsing" response or a linear response according to the particular requirement. Each dome also provides the restoring force for its corresponding key. Silicone rubber is the preferred material for the sheet member as it is able to withstand extremes of temperature and exhibits a relatively small change of stiffness over the range 20 to 70"C. It does not degrade when subjected to ozone or to many other corrosive agents and has a high fatigue resistance. In its simplest form the keyboard arrangement uses an LED and detector in each groove or channel 12 of the plate 11. However, if light guides or light multiplexers are used it is possible to reduce the number of LED's and detectors. Fig. 5 is a schematic diagram of the optoelectronic system used with the keyboard assembly of Figs. 1 to 4. As shown, the kevboard is arranged similarly to a typewriter keyboard layout and has four rows of keys, providing a total of 56 in dividual switches. The LED's are arranged in groups of four and are coupled via gates G1-G5 to a microprocessor MPU. The detectors are also coupled to the microprocessor. The microprocessor is programmed to pulse the switch matrix LED's in groups, via an ENABLE circuit El, and to examine the associated detector outputs. This is done many times during one key depression and the information is processed to provide a predetermined coded output. Also, where necessary, the microprocessor protects against lost information key 'roll over', the simultaneous operation of two or more keys. The opto-electronic circuitry may be mounted on a circuit board fixed to the underside of the plate member 11. WHAT WE CLAIM IS:---

1. An optical switch, including a flat plate housing at least one straight channel in one of its surfaces, a flexible sheet member arranged adjacent the plate and having one or more resilient deformable portions each coinciding with a said channel, and means for deforming the one or more resilient portions each into the respective channel so as to obstruct a light path directed along that channel.

6. A switch matrix as claimed in claim

5, and in which the plastics material is silicone rubber.

7. A switch matrix as claimed in claim 4, and in which the diodes and detectors together with the gates and the microprocessor are mounted on a circuit board adjacent the flat plate member.

8. An optical switch matrix substantially as described herein with reference to the drawings accompanying the Provisional Specification.

9. An optical switch embodying any novel feature described herein and/or illustrated in the drawings but not claimed in any one of the preceding claims.

10. A method of optical code switching substantially as described herein with reference to the drawings accompanying the Provisional Specification.