TECHNICAL FIELD

Tms invention relates to illumination apparatus for a microfiche reaαer.

BACKGROUND ART

I; s often αesireα to use microi icne reaαers in situations wnere tnere is a risk 01 fire or expiosion αue to voxatile suostances, eg in tne paint snop of a motor manui acturer or situations within tne petrocftemicai inαustry. In orαer to use a microi icne r aαer in bucn c ήάiarαous situation, it nas oeen necessary to provide the lignt source of the reader in an expiosion proof container and tnis has to be certified as meeting tne appropriate standards, f or instance as set by the British Approvals Service for Electrical Equipment n Flammable Atmospheres (BASEEFA). This is both expensive amα time consuming and the end result is usually a heavy ana ^■ cumbersome piece oi equipment. In addition, there are different levels of BASEEFA approval f or electrical equipment according to the type of hazardous situation under consideration.

Tne 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.

DISCLOSURE OF INVENTION

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 remote light source to the reader, a first optical system for focussing light from tne iignt source into the input end of the fibre optic cable and a second optical system for receiving light from the output enα of tne fibre optic cabie and directing it towards a microfiche holder within the reaαer.

Pret ^' erreα features of the invention will De apparent from the following αescπption ana from the subsidiary claims of the specification.

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BRIEF DESCRIPTION OF DRAWINGS

The invention will now be further described, merely by way of example, with reference to the accompanying αrawings, in which:

Figure i is a schematic diagram illustrating apparatus according to an embodiment of the invention;

Figure 2 is a diagram showing detail of tne output end of a fibre optic cable used in the apparatus shown in Figure i;

Figure 3 shows a side ana end view showing further detail of part of the apparatus shown in Figure 2; and

Figures 4A, B and C show a perspective view, a partial siαe view ana a sectional plan view, respectively, of a light source for use with the apparatus snown in Figure i .

BEST MODE OF CARRYING OUT THE INVENTION

The apparatus shown in Figure i comprises a light source i 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 tne fibre optic cable 1 towards a microfiche 4 (see Fig 2) held within the reader. A cross-section of the fibre option cable 2 is shown in an inset in Figure 1.

As shown in Figure 4, the light source comprises a lamp 1, for example a 13.8 volt, 30 Watt or 75 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 αown transformer 5 of suitable ratio ana capacity. An air cooling fan 6 is also provideα to prevent overheating of the light source. These components are mounted within a casing 7, for instance made from mild steel sheeting, with ventilation louvres 7A in the side thereof. An on-off switch 8 is provided on one end of the casing 7.

One end of the fibre optic cable 2 is mounteα within tne casing 7 and the lamp i and cable 2 are positioned so 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. Typical dimensions of the casing 7 are shown in Figure 4 in millimetres.

In an alternative arrangement (not shown) a lamp which produces a collimated beam of lignt may De useα togetner witn a converging lens for focussing the beam into tne input enα of the fibre optic cable 2.

The fibre optic cable 2 comprises a ounαie of optical fiDres, eg of 100 micron αiameter, and has an effective optical diameter of 3mm. The cable 2 has a plastics sneathing 2A and may be supplied in different lengths, e.g. 3m, 5m or 10m. Both ends of the cable 2 are terminated in a conventional plastics or brass ferrule i l 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 αiameter 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 (e.g. 10mm) to illuminate fully the film gate of the microfiche reader. The lens 3 thus provides an image of tne end of the fibre optic cable sufficiently large to illuminate fully the film gate of the microfiche reader. In the arrangement shown, the lens 3 is positioned approximately 10mm from the end of the fibre optic cable 2 to achieve this.

Figure 3 snows a more detailed view of tne lens holder 12 togetner witn typical dimensions of its component parts. The lens holder 12 comprises a neck portion i2A in which the enα of tne fibre optic cable is mounted, a

DOdy portion 12B in which the lens 3 is mounted and a flange 12C for mounting the holder within the microfiche reader. Different arrangements may De used to enable the lens holder 12 to be mounted in different types of microfiche reader. Typical dimensions of the lens holder 12 are shown in Figure 3 in millimetres.

With the apparatus αescribed aoove, it is possible to use a microfiche reader in a hazardous environment without incurring the risks innerent in using electrical equipment in such an environment. The light source 1 hbuseα within tne casing 7 can oe positioned remote from the microfiche reaαer outside the hazarαous area. The light is tnus generated m a safe area and transmitted by tne fibre optic cable 2 into the hazardous area. This can be simply achieved by passing tne fibre optic caoie 2 through a small hole in a wall separating the hazardous area from tne sate area ana sealing the hoxe around the f ibre 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 is 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 tne lens holder 1 described above or a mounting suitable for receiving the lens holder 12.

It is important tnat suff icient light is transmitted oy the fiDre optic cable to illuminate the microficne in a satisfactory manner. To illuminate tne 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. Also, due to the divergence of the light it emits, much of the light output is wasted. The use of lenses with sucn a large fibre optic cable is also undesirable as tnis adds to tne expense anc 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 αiameter. It is found that the arrangement ^• described above provides a oeam 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 ana 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 lamp 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.

INDUSTRIAL APPLICABILITY

The apparatus can oe manufactured ana usea with microfiche reaaers in situations where it is desirable to position the light source remote from the reaoer.