GB2120780A - Switch - Google Patents

Abstract

A switch comprises a pair of relatively movable switch components 21, 23 and an optical fibre system 15, 17, 22 which defines a light path when the switch is in a closed position and which when the switch is in the open position is prevented from conducting light. There may only be two optical fibres one in each switch component. The switch components may be plastic mouldings, removeable from members to which they are attached such as a door and door frame. Each moulding may have a number of optical fibres defining alternative channels 32, 33. A switch system for a series of fluid flow control valves, each with a stem having a light transmitting window has optical fibres defining a light path from an emitter to a receiver via the windows and arranged so that light can travel only when all the valves are in a predetermined mode. <IMAGE>

Description

SPECIFICATION Switch This invention relates to switches and one object is to provide a novel kind of switch operating in response to relative movement of two components, for example in response to the opening or closing of a door, or a safety guard on a machine, or to opening or closing movement of a steam valve stem so that a usable signal will be obtainable when such an action occurs.

According to the present invention, a switch comprises two switch components which are relatively movable between a closed position and an open position, and at least two lengths of optical fibre having respective ends which, when the switch components are in the closed position, are in close proximity so allowing the passage of light from one length to the other, and which, when the switch components are in open position are so arranged that the passage of light from one length to the other is prevented. There can be a small gap between the facing ends in the one switch position, perhaps as small as a few thousandths of an inch, but perhaps as great as a few millimetres depending upon the size of the fibre, the intensity of the light available, and the surrounding circumstances. It is also possible that in the one switch position the two ends come into contact with each other.

Although the end faces of the two lengths of fibre may be oblique to the respective fibre axes, it is thought that in almost all practical cases the end faces will be perpendicular to the fibre axes.

One application of the invention is to give an indication whether a door is open or closed, and then the two lengths may be respectively in the door and the door frame.

In general there will be an emitter of light at one end of one length, and a detector at the other end of the other length which detector will only receive light from the source when the switch is in the position which will be called in this specification "the closed position". It may be that the source of light will be infra-red, or other radiation with some characteristic, and the detector will be sensitive to that characteristic, so as not to be responsive to ambient light entering the length of fibre when the switch is open.

When the switch is applied to a door or a gate it may well be desirable for neither of the emitter and the detector be mounted in the movable door, and accordingly the switch may be a double switch. One part of the switch might be between a length of optical fibre from the emitter to the door frame, and one end of a length of fibre in the door, and the other part might then be between the other end of the length of fibre in the door and a length of fibre leading to the detector.

Optical fibre can of course be bent to suit the space available, and the length of fibre in the door might be bent through a right angle so that the exposed ends are respectively in the back and the top of the door while the operating fibre ends are in the adjacent parts of the frame, or again the length of fibre in the door could make a 'U' turn to provide communication between two lengths of fibre side by side in the door frame, one leading to the emitter and one to the detector.

The lengths of fibre can conveniently be embodied in plastics mouldings or other pieces which can be easily fixed to the door or door frame. Such a moulding might be formed with a number of alternative channels in any one of which the fibre can be fitted, so that there could be a number of different dispositions available if the doors needed to be coded.

It is of course possible to have a number of switches in series between the emitter and the detector, so that if any one of them is opened the detector will know and can give a signal which can be used for switching off a machine, or isolating a power supply, or giving a warning signal perhaps.

The plastics pieces mentioned above could be permanently fitted to the door and door frame or other relatively movable component, but they could also be separate items to be temporarily fixed to the door and door frame when for example a maintenance engineer was working on a machine within a guard containing the door.

In another application of the invention the switch could be applied to give an indication whether a steam valve was, or was not open.

If the valve had a valve stem which was turned through 90 to open or close the valve, then the stem could have a hole through which light could pass between the ends of the two lengths of optical fibre, one on either side of the stem. Then the detector could give a direct indication whether the valve was open or closed. If there were a number of valves and it was important to know if any one was closed, then the light could pass through holes in the various stems, one after another, so that the detector would only receive light from the emitter when all the valves were open. Of course the interconnecting optical fibre can be curved as required between the different switch positions.

Thus according to another aspect of the present invention, there is provided a switch system for a series of fluid flow control valves comprising a series of valves, each having a valve stem with a light transmitting window, and a system of optical fibres defining a light path between an emitter and a receiver so arranged that when the valves are all in a predetermined mode, light can travel from the emitter to the receiver via the optical fibres and the light transmitting windows.

The invention may be carried into practice in various ways, and two embodiments will now be described by way of example, with reference to the accompanying drawings, in which Figure 1 is a diagram showing switches used in a protective system involving a couple of doors; Figure 2 is a schematic detail of the switches on one of the doors, and Figure 3 is a schematic diagram of another application of the invention.

A machine operates within a guard having two access doors, shown at 11 and 1 2 in Fig.

1, and it is important for the power supply to be removed from the machine if either door is opened, so that the machine cannot operate when anyone is working on it.

Accodingly, each of the doors is fitted with a double switch, according to the invention, and shown in more detail in Fig. 2. The two switches are connected in series between a light emitter 1 3 and a light detector 14. The light, could for example be frequently modulated infra-red radiation, and is supplied from the emitter to the detector by way of a first length of optical fibre 1 5 to the first switch 16, then through a second length of optical fibre 1 7 to the second switch 1 8 and finally through a third length of optical fibre 1 9 to the detector 14.If both switches are closed, the detector will receive radiation from the emitter, and can give a signal allowing the power supply to be available for the machine, but if either door is opened, then its corresponding switch 16 or 18 will be opened, light will be lost from the detector 14 and the output of the detector can be arranged to disconnect the power supply.

Each of the switches 1 6 and 18 is as shown in more detail in Fig. 2, and consists of the ends of the fibres 1 5 and 1 7 (or 1 7 and 19) embodied in a plastics link piece 21 together with an inter-linking length of fibre 22 embodied in a moulded plastics corner key 23.The pieces 23 and 21 are fixed temporarily or permanently to the door and the frame respectively, so that when the door is closed, light from the fibre 1 5 passes through the end of the fibre 1 5 across the gap 25 and into the end 26 of the fibre 22, and then similarly passes across the gap 27 between the corner key 23 and the link piece 21 into the fibre 1 7. The ends of the fibres might be about a millimetre apart, and they will be parallel with each other, and perpendicular to the axes of the fibres.

Fig. 2 shows how each of the pieces 21, 23 is moulded with a number of alternative channels 32, 33 any one of which can be used with the fibre such as 1 6. That enables a method of coding to be used according to which the positions of the fibres in different switches on different doors will not be the same. It is indeed possible to cause the fibre 16 to branch to have components along two of the channels co-operating with two channels in the corner key, and many different combinations can be provided.

The idea of the corner key with a particular "combination" means that if the two pieces 21 in the door frame have their fibres 1 6 and 1 7 in particular positions, then it can be arranged that there is only one key with its fibre lengths 22 in a corresponding position so that particular key must be fixed to the corner of the door before the switch can be connected into circuit. They can be removed by someone working in an area protected by the door preventing the power being supplied to the area even if the door is inadvertently closed behind the worker.

The optical switching system may use TTL compatible components (5 volts) to be suitable for intrinsically safe systems operating at under 8 volts and 8 milli-amps. No power travels along the optical fibres, so that use is possible in wet areas.

Fig. 3 shows another application of the invention in a petro-chemical refinery, where three valves are indicated at 34, 35 and 36.

Each is operated by a motor 37, 38 or 39, but it is important that only one of the three valves can be closed at any one time. Accordingly, the valve stem for each of the valves includes a hole 41 and when all the valves are open, light is passed from the emitter 1 3 to the detector 14 by way of a number of lengths of optical fibre 42 and the holes 41 in the valve stems. The fibres are fixed to terminate on either side of the hole when the valve is open.

The output of the detector 14 operates a relay 43 for energising a solenoid 44. The power supply from 45 to any of the motors is by way of a three position switch 46 which can be positioned so that one motor at a time can be energised. In the position shown in Fig. 3, the motor 38 can be energised when its switch 47 is closed.

The requirement is that neither of the other valves 34 and 36 is to be capable of being closed until the valve 35 is open, and the solenoid 44 prevents operation of the three position switch 46 until when the valve 35 is open, the detector receives a signal from the emitter and energises the relay so that the solenoid 44 operates a detent 51 and then the switch 46 can be moved so that the power supply can be connected to either of the motors 37 and 39.

This is just another example of many which will occur to the reader of the way in which the relative position of two movable components can be arranged to give a signal by way of the optical fibre switch which can automatically provide a safety or other control.

Claims (9)

1. A switch comprising two switch compo nents which are relatively movable between a closed position and an open position, and at least two lengths of optical fibre having respective ends which, when the switch components are in the closed position, are in close proximity so allowing the passage of light from one length to the other, and which, when the switch components are in open position are so arranged that the passage of light from one length to the other is prevented.

2. A switch as claimed in Claim 1 in which ends of the optical fibres have faces which are parallel to each other and perpendicular to the fibre axes.

3. A switch as claimed in Claim 1 or Claim 1 in which one length of optical fibre is located in or on a door and the other length of optical fibre is located in or on a corresponding door frame.

4. A switch as claimed in any preceding claim in the form of a double switch comprising two lengths of optical fibre in one of the switch components and a third length of optical fibre in the other switch component, the third length of optical fibre being arranged to form a light conductive path between the first two lengths of optical fibre when the two switch components are in the closed position.

5. A switch as claimed in any preceding claim in which one of the switch components is associated with a door and the other switch component is associated with a corresponding door frame.

6. A switch as claimed in any preceding claim in which at least one of the switch components is a plastics moulding which is removable from any member to which it is attached.

7. A switch as claimed in Claim 6 in which the or each moulding includes a number of optical fibres defined in a corresponding number of alternative light channels.

8. A switch system for a series of fluid flow control valves comprising a series of valves, each having a valve stem with a light transmitting window, and a system of optical fibres defining a light path between an emitter and a receiver so arranged that when the valves are all in a predetermined mode, light can travel from the emitter to the receiver via the optical fibres and the light transmitting windows.

9. A switch constructed and arranged substantially as herein specifically described with reference to and as shown in Figs. 1 and 2 or Fig. 3 of the accompanying drawings.