GB2295687A

GB2295687A - Manually operable optical switch with encoded shutter

Info

Publication number: GB2295687A
Application number: GB9424276A
Authority: GB
Inventors: David Ernest Biddlecombe
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1994-12-01
Filing date: 1994-12-01
Publication date: 1996-06-05
Also published as: GB9424276D0

Abstract

A manually operable optical switch has a light transmitting path extending between input and output light conduits and means for interrupting the light transmitting path in response to activation of the switch. The latter means comprise an encoded shutter 22, having areas with differing light transmitting, reflecting or refracting properties, and means 24, 26, 28, for moving the shutter 22 relative to the light transmitting path 18 with substantially uniform velocity during manual operation of the switch to produce on the output conduit a serially encoded optical signal indicative of the activated switch. <IMAGE>

Description

Manually Operable Optical Switches The present invention relates to vehicle wiring and seeks to allow a plurality of manually operable switches to communicate with a control circuit to activate a plurality of associated electrical devices, such as motors and lights, while using a minimum number of signal conductors.

The wiring in modern motor vehicles is becoming increasingly complex. Several multiplex strategies exist that enable a group of functions (signal transmitters and signal receivers) to communicate over a multiplex bus, usually consisting of two differential signal wires, a power supply and a ground line. While these systems can offer a significant reduction in wiring they suffer from one potential disadvantage. In order to implement the multiplex system, a number of functions must be grouped into a module which then acts as one end of the multiplex link. If there is not a sufficient number of functions to justify the use of such a module, for example on grounds of cost, then multiplexing is not a viable solution, in particular having regard to the cost of a multiplex module incorporating a circuit board, power supply and a microprocessor and a communication chip.

This invention seeks to allow a plurality of switches to communicate with a control module using a single fibre optical cable.

Optical switches have been used that are associated with a plurality of fibres each acting to interrupt the passage of light along a predetermined combination of fibres to allow the activated switch to be identified. For example, optical keyboards can be produced in this way with each switch generating a binary code indicative of the key that has been depressed.

Such optical switches are not well suited for use in a motor vehicle because of the cost of the optical cable having multiple strands required to carry such binary data in parallel.

Other optical communication systems have been proposed that use electrical switches to produce modulated light, the activated switch being discernible by means of its unique code. Here the cost of the light modulating unit adds to the cost of system implementation.

The aim of the present invention is to provide a low cost switch that can allow a plurality of similar switches to communicate with a control module using a single fibre and a single source of continuous light.

According to the present invention, there is provided a manually operable optical switch having a light transmitting path extending between input and output light conduits and means for interrupting the light transmitting path in response to activation of the switch, the latter means comprising an encoded shutter, having areas with differing light transmitting, reflecting or refracting properties, and means for moving the shutter relative to the light transmitting path with substantially uniform velocity during manual operation of the switch to produce on the output conduit a serially encoded optical signal indicative of the activated switch.

Preferably, the shutter is connected to an over centre toggle mechanism operated by the activation of the switch, the toggle mechanism ensuring that the entire coded area of the shutter traverses the light transmitting path with uniform velocity during depression or release of the switch.

The shutter may be a linear shutter movable along a straight path relative to the light transmitting path or it may be formed as a disk or a sector of a disk that is mounted for pivotal movement past the light transmitting path.

The pattern of areas on the shutter may be based on a bar code. As is well known, such a code can be read in both directions of scanning and is tolerant of variations in scanning speed.

It is possible for the shutter to have either one or two stable end positions. If it has only one stable end position, then it will traverse the light transmitting path twice in opposite directions with each switch activation and comparison between the codes generated in the opposite directions of travel can be used to eliminate false readings.

If the shutter has two stable end positions, then the code may be asymmetrical so that the direction of movement of the shutter can be determined by decoding of the optical signal.

It is important that the shutter should always park in a position in which the light transmitting path is not obstructed. This allows a plurality of switches to be connected in series with one another and it is important to ensure that only one switch is operated at any one time. To this end, it is possible to provide a single housing with several switches that are mechanically interlinked in such a manner that depression of any one switch inhibits depression of the remaining switches.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of an optical switching unit comprising three switches connected in series with one another using a single optical fibre, and Figure 2 is a perspective partially cut-away view of a switch element.

In Figure 1, a light source 10, represented as a light emitting diode is connected to a receiving module 20, forming part of a control unit, by means of a single optical fibre 18 passing serially through three consecutive switches 12, 14 and 16. The term light is used herein to include radiation outside the visible spectrum, such as infra red and ultraviolet, and the source 10 may be a coherent light source (laser) if desired.

Each of the switches 12, 14 and 16 may be constructed as shown in Figure 2, of a housing within which there is movably mounted a shutter 22 carrying a bar code. The actuating button 26 of the switch acts on an over-centre cam mechanism or toggle 28 that also includes a return spring 24 and serves to move the shutter a fixed distance at substantially uniform speed with each actuation of the button 26.

As the shutter moves in the transmitting light path of the optical fibre 18, it modulates the intensity of the transmitted light to produce a serial code representative of the switch. The modulation of the light transmitted by the fibre 18 acts on a photo detector in the module 20 to produce a serially encoded signal that is stored in a buffer and used by the module in the control of the load associated with the activated switch.

The three switches 12, 14 and 16 are mounted in a common housing and have an interlock that prevents the simultaneous operation of more than one switch.

As an alternative to the linearly displaceable shutter 22 shown in the Figure 2, an arcuate disk carrying radial code markings may be pivoted in the housing for movement through the light transmitting path of the optical fibre.

It is not essential that the shutter have opaque and transparent areas, it is only important that in some position light should be able to pass through the switch and at others that the light should be obstructed. Such obstruction may be effected by reflection or refraction.

It is important that the shutter should not obstruct the optical path of the fibre in its end position as it would otherwise interfere with the operation of the other switches. It is possible, furthermore, by ensuring that the individual code bars are narrower than the transmitting path, to ensure that some light will always pass through the switch even if it fails in a blocking position, thereby allowing the other switches to continue operation. In this connection, an AGC control in the module 20 will compensate for the attenuation of the light by the faulty switch. Such construction is also advantageous in that it allows immediate detection of a fault in the system as under no normal operating conditions, even if one of the switched fails, should there be no light reaching the module 20.

An advantage of having a constantly illuminated fibre at each switch is that the light used for switching may also serve as illumination for the switches. This can be effected by bleeding part of the light transmitted along the fibre either through the shutter or at a branching point near the switch. For example, a collar surrounding the input conduit near the shutter will tend to glow because of spilled light that does not reach the output conduit. Such a construction makes for very simple assembly in that a single optical fibre serves not only to carry the switching signals but also the switch illumination.

The code markings may be symmetrical or asymmetrical.

If the switch has a spring return and always parks in the same end position, then the code bars will traverse the light path of the optical fibre twice during each switch operation and comparison of the two generated codes may be used to detect errors. The codes may themselves also have error detection and correction bits.

If the switch is an ON-OFF switch with two stable end positions, then by resorting to an asymmetrical code it is possible to determine the direction in which the switch has moved.

Claims

1. A manually operable optical switch having a light transmitting path extending between input and output light conduits and means for interrupting the light transmitting path in response to activation of the switch, the latter means comprising an encoded shutter, having areas with differing light transmitting, reflecting or refracting properties, and means for moving the shutter relative to the light transmitting path with substantially uniform velocity during manual operation of the switch to produce on the output conduit a serially encoded optical signal indicative of the activated switch.

2. A switch as claimed in claim 1, wherein the shutter is connected to an over centre toggle mechanism operated by the activation of the switch, the toggle mechanism ensuring that the entire coded area of the shutter traverses the light transmitting path with uniform velocity during depression or release of the switch.

3. A switch as claimed in claim 1 or 2, wherein the shutter is a linear shutter movable along a straight path relative to the light transmitting path.

4. A switch as claimed in claim 1 or 2, wherein the shutter is a disk or a sector of a disk that is mounted for pivotal movement past the light transmitting path.

5. A switch as claimed in any preceding claim, wherein the pattern of areas on the shutter are based on a bar code.

6. A switch as claimed in any preceding claim, wherein shutter has only one stable end position and traverses the transmitting light path once in each direction during each actuation of the switch.

7. A switch as claimed in any of claims 1 to 5, wherein the shutter has two stable end positions.

8. A switch as claimed in claim 7, wherein the code bars on the shutter are asymmetrical so that the direction of movement of the shutter may be determined.

9. A switch as claimed in any preceding claim, wherein the areas that obstruct the transmitting light path are all narrower than the transmitting light path whereby the light is attenuated but not totally obscured by any part of the shutter.

10. A switch unit having a plurality of switches as claimed in any preceding claim mounted in a common housing, wherein a mechanical interlock is provided to prevent simultaneous actuation of more than one switch.

11. A manually operable optical switch constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.