GB2244816A

GB2244816A - Illumination apparatus for a microfiche reader

Info

Publication number: GB2244816A
Application number: GB9008167A
Authority: GB
Inventors: Charles James Forbes Taylor
Original assignee: MICROPHAX Ltd
Current assignee: MICROPHAX Ltd
Priority date: 1990-04-10
Filing date: 1990-04-10
Publication date: 1991-12-11
Also published as: WO1991015803A1; GB9008167D0

Abstract

The apparatus comprises a light source (1) for positioning remote from the reader (not shown); a fibre optic cable (2) for transmitting light from the remote light source (1) to the reader, a first optical system for focussing light from the light source into the input end of the fibre optic cable and a second optical system (3) for receiving light from the output end of the fibre optic cable (2) and directing it towards a microfiche holder within the reader. The first and second optical systems are such as to optimise the light intensity transmitted to the microfiche reader and the fibre optic cable (2) is preferably of smaller diameter than the area to be illuminated. The apparatus is suitable for use in situations in which the microfiche reader is positioned in a hazardous area so the light source can be positioned within a safe area with the fibre optic cable (2) arranged to transmit light from the light source to the reader.

Description

ILLUMINATION APPARATUS FOR A MICROFICHE READER This invention relates to illumination apparatus for a microfiche reader.

It is often desired to use microfiche readers in situations where there is a risk of fire or explosion due to volatile substances, eg in the paint shop of a motor manufacturer or situations within the petrochemical industry. In order to use a microfiche reader in such a hazardous situation, it has been necessary to provide the light source of the reader in an explosion proof container and this has to be certified as meeting the appropriate standards set by the British Approvals Service for Electrical Equipment in Flammable Atmospheres (BASEEFA). This is both expensive amd time consuming and the end result is usually a heavy and cumbersome piece of equipment. In addition, there are different levels of BASEEFA approval for electrical equipment according to the type of hazardous situation under consideration.

The term microfiche reader used herein is to be understood to include devices suitable for reading information held on microfiches, microfilm or any other similar microform medium.

According to the present invention there is provided illumination apparatus for a microfiche reader comprising a light source for positioning remote from the reader; a fibre optic cable for transmitting light from the light source to the reader, a first optical system for focussing light from the light source into the input end of the fibre optic cable and a second optical system for receiving light from the output end of the fibre optic cable and directing it towards a microfiche holder within the reader.

Preferred features of the invention will be apparent from the following description and from the subsidiary claims of the specification.

The invention will now be further described, merely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram illustrating apparatus according to an embodiment of the invention; Figure 2 is a diagram showing detail of the output end of a fibre optic cable used in the apparatus shown in Figure 1; Figure 3 shows further detail of part of the apparatus shown in Figure 2; and Figures 4A, B and C show perspective, side and sectional views respectivedly of a light source for use with the apparatus shown in Figure 1.

The apparatus shown in Figure 1 comprises a light source 1 which may be positioned remote from the microfiche reader (not shown) and which includes an optical system for focussing light emitted thereby, a fibre optic cable 2 for receiving light from the light source 1 and transmitting the light to the reader and a further optical system 3 for directing light from the fibre optic cable 1 towards a microfiche 4 (see Fig 2) held within the reader.

As shown in Figure 4, the light source comprises a lamp 1, for example a 13.8 volt, 30 Watt quartz halogen micrographic pre-focussed bulb as conventionally used in a microfiche reader. This has an aperture of about 50 mm and a focal length of about 350 mm. The lamp 1 is powered from the mains supply via a step down transformer 5 of suitable ratio and capacity.

A cooling fan 6 is also provided to prevent overheating of the light source.

These components are mounted within a casing 7, for instance made from mild steel sheeting. An on-off switch 8 is provided on the outside of the casing 7.

One end of the fibre optic cable 2 is mounted within the casing 7 and the lamp 1 and cable 2 are positioned 60 as to ensure that the main beam from the lamp is focussed to just fill the focussing aperture, or inlet end, of the fibre optic cable 2. The fibre optic cable 2 is locked in position with respect to the lamp 1 by a boss 9 and locking screw 10 provided in. the side of the casing 7.

In an alternative arrangement (not shown) a lamp which produces a collimated beam of light may be used together with a converging lens for focussing the beam into the input end of the fibre optic cable 2.

The fibre optic cable 2 comprises a bundle of optical fibres, eg of 100 micron diameter, and has an effective optical diameter of 3mm. The cable 2 has a plastics sheathing and typically has a length of about 4m. Both ends of the cable 2 are terminated in a conventional plastics or brass ferrule 11 and the ends of the glass fibres are polished. Fibre optic cables of other diameters can be used, with appropriate adjustment of the other components as described below.

As shown in Figure 2, the output end of the fibre optic cable 2 is mounted within a lens holder 12 which may be fitted within a microfiche reader in place of its conventional light source. The lens holder 12 also provides a mounting for a single, biconvex lens 3 of polished glass with a diameter of about 19mm and a focal length of about 16mm. The lens 3 is arranged to receive light from the fibre optic cable 2 and to focus it into a well collimated beam of light of sufficient diameter to illuminate fully the film gate of the microfiche reader. The lens 3 thus provides an image of the end of the fibre optic cable of sufficient diameter to illuminate fully the film gate of the microfiche reader. In the arrangement shown, the lens 3 is positioned approximately lOmm from the end of the fibre optic cable 2 to achieve this.

Figure 3 shows a more detailed view of the lens holder 12 together with typical dimensions of its component parts. The lens holder 12 comprises a neck portion 12A in which the end of the fibre optic cable is mounted, a body portion 12B in which the lens 3 is mounted -and a flange 12C for mounting the holder within the microfiche reader.

With the apparatus described above, it is possible to use a microfiche reader in a hazardous environment without incurring the risks inherent in using electrical equipment in such an environment. The light source 1 housed within the casing 7 can be positioned remote from the microfiche reader outside the hazardous area. The light is thus generated in a safe area and transmitted by the fibre optic cable 2 into the hazardous area.

This can be simply achieved by passing the fibre optic cable 2 through a small hole in a wall separating the hazardous area from the safe area and sealing the hole around the fibre optic cable 2 as appropriate. The fibre optic cable 2 is simply plugged into the light source casing 7 at one end and into the lens holder 12 in the microfiche reader at the other end.

An additional advantage is that not only is the light source outside the hazardous area but no wires, electrical connections or switches need to be provided in the hazardous area (unlike the conventional explosion proof light sources) since no electrical power is brought into the hazardous area.

Also, there is no heat generation within the hazardous area. The apparatus is thus intrinsically safe and does not require certification by the BASEEFA.

The fibre optical cable is preferably provided with a protective shield or armoured to prevent it from being damaged.

The microfiche reader used with the apparatus may be entirely conventional but with its light source removed and replaced by the lens holder 12 described above or a mounting suitable for receiving the lens holder 12.

It is important that sufficient light is transmitted by the fibre optic cable to illuminate the microfiche in a satisfactory manner. To illuminate the full frame of a conventional microfiche, it is necessary to provide a beam of light having a diameter of at least 9mm and for the light to be of sufficient uniformity and strength across the beam to produce a bright image. At first, it might be thought that this is best provided by a relatively large fibre optic cable of the appropriate diameter to form the required beam. However, it is found that a large fibre optic cable, eg 9mm in diameter or larger, is not satisfactory as not only is this very expensive but the light output tends to be speckled and not very uniform and, due to the divergence of light it emits, much of the light output is wasted. The use of lenses with such a large fibre optic cable is also undesirable as this adds to the expense and complexity of the system.

Instead, a relatively small diameter optical fibre should be used, eg one quarter to one half the diameter of the beam of light required, in conjunction with a simple optical system to produce a beam of light of the required diameter. It is found that the arrangement described above provides a beam of light of sufficient uniformity and strength to satisfy the British standard (4191/1976) for the illumination of microform readers.

The smaller diameter fibre optic cable is also much less expensive and the optical sytem need comprise only a pre-focussed bulb and a single lens as described above.

The arrangement of the lamp 1, optical fibre cable 2 and lens 3 should be such as to optimise the light intensity transmitted to the microfiche reader. For this reason, a pre-focussed lamp, or a lamp provided with a suitable reflector and used with a converging lens, is preferred so that substantially all the light output from the lemp is focussed into the input end of the fibre optic cable. Careful positioning of the cable with respect to the lamp or the lens is required to minimise light loss at this stage.

At the output end of the fibre optic cable, the diverging light emitted by the cable is focussed into a collimated beam of appropriate diameter to avoid any light loss and to maximise the light intensity across the film gate of the microfiche reader.

Clearly, the components of the system can be varied to some extent so long as they are arranged to make optimum use of the light available. However, as indicated above, it is preferable to use a relatively small diameter fibre optic cable, to keep down the expense and because it is found that by focussing light into the cable and then focussing it again into a collimated beam, the uniformity of the light intensity across the beam is improved.

A further advantage of using a relatively small diameter fibre optic cable is that it can be bent around smaller radius bends and so is easier to fit into a microfiche reader and orientated in the appropriate direction within the confines of the reader's casing.

Claims

1. Illumination apparatus for a microfiche reader comprising a light source for positioning remote from the reader; a fibre optic cable for transmitting light from the light source to the reader, a first optical system for focussing light from the light source into the input end of the fibre optic cable and a second optical system for receiving light from the output end of the fibre optic cable and directing it towards a microfiche holder within the reader.

2. Apparatus as claimed in claim 1 in which the first optical system is arranged to receive substantially all the light emitted by the light source and to focus it into the input end of the fibre optic cable.

3. Apparatus as claimed in claim 1 or 2 in which the light source and first optical system comprise a focussed light bulb.

4. Apparatus as claimed in claims 1, 2 or 3 in which the light source is mounted in a unit with a transformer and a cooling fan.

5. Apparatus as claimed in any preceding claim in which the effective optical diameter of the fibre optic cable is one quarter to one half of the diameter of the area to be illuminated.

6. Apparatus as claimed in claim 5 in which the effective optical diameter of the fibre optic cable is 3 mm and the diameter of the area to be illuminated is 9 mm.

7. Apparatus as claimed in any preceding claim in which the second optical system comprises a converging lens arranged to focus light emitted from the output end of the fibre optic ca.ble into a collimated beam of the required diamater.

8. Apparatus as claimed in claim 7 which comprises a lens holder in which the output end of the fibre optic cable and the converging lens are mounted.

9. Apparatus as claimed in claim 8 in combination with a microfiche reader with the lens holder fitted in the reader in place of its conventional light source.

10. Apparatus as claimed in claim 9 in which the microfiche reader is positioned within a hazardous area and the light source positioned within a safe area with the fibre optic cable arranged to transmit light from the light source in the safe area to the microfiche reader in the hazardous area.

11. Apparatus as claimed in any preceding claim in which the fibre optic cable is provided with a protective shield or armoured to prevent it from being damaged.

12. Illumination apparatus for a microfiche reader substantially as hereinbefore described with reference to the accompanying drawings.