GB2437544A

GB2437544A - Inspection device for optically complex surfaces

Info

Publication number: GB2437544A
Application number: GB0608525A
Authority: GB
Inventors: Gary M Holloway
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-04-28
Filing date: 2006-04-28
Publication date: 2007-10-31
Also published as: WO2007125340A1; GB0608525D0

Abstract

An inspection device for use with optically complex surfaces such as carbon fibre composite materials used for e.g. air plane bodies, aeroplane fuselages, or boats is disclosed. The device uses light sources (602) to illuminate a diffuser (604) that illuminates the surface under test (610), especially to reveal the presence of cracks, roughness, or areas of the composite material surface where there are voids between bands of fibre material. The diffuse surface has a high diffuse reflectivity to specular reflectivity ratio. The diffuser has curved portions that have a constant radius of curvature as well as a flat piece of material in between.

Description

Document: 1165126

INSPECTION DEVICE FOR OPTICALLY COMPLEX SURFACES

The present invention relates to a device and method for inspecting an optically complex surface, and a system for inspecting carbon fibre composite structures. The device, system and method may also be used for inspecting optically simple surfaces.

An optically complex surface is a surface that does not conform to classical optical theories, and which caimot be defined simply in terms of properties as refractive index, specular reflectivity and diffuse reflectivity. The appearance of such a surface under different lighting conditions may be difficult to predict, difficult to control, or both.

An example of a material with an optically complex surface is carbon fibre composite.

Carbon fibre composite consists of strands of carbon fibres bonded together with a matrix of adhesive, creating a material with relatively high strength but relatively low weight. For this reason carbon fibre composites are widely used in industry. In the commercial aerospace industry, for example, aircraft are now designed with key structural portions fabricated from carbon fibre composites.

One theory which explains why carbon fibre composite material has an optically complex surface is illustrated in Figure 1. In the figure, a carbon fibre 102 is shown, including a number of reflective elements 104. Some light rays 106 may miss the fibre or the elements 104 entirely, or may be absorbed or refracted. Other light rays 108 may strike the reflective elements 104 and be reflected back. Other light rays 110 may strike a reflective element, but be reflected internally within the carbon fibre, and then emerge some distance down the fibre after striking another element. The optical complexity of the surface is exacerbated by the anisotropic nature of the carbon fibres, and the overall effect is that a carbon fibre composite surface viewed from one angle may appear completely light absorbent (black), and from another angle marginally different to the first angle it may be saturated in glare.

During experimentation, for example, there was not found to be any arrangement of a light source (sharp or diffuse) and viewing position, relative to the surface of a carbon fibre composite, that allowed surface details of the composite to be inspected without either large amounts of glare or near-total light absorbency (jet-black appearance).

Despite such difficulties there is a pressing need to develop inspection devices for optically complex surfaces, for example because any undetected cracks or defects in carbon fibre composite aircraft structures can lead to disastrous failure of the aircraft.

Figure 2 illustrates the construction process of a carbon fibre composite structure (such as might be used for an aircraft fuselage, for example). Carbon fibre strips (bundles of resin-impregnated carbon fibre filaments, also known as tows) 202, 204, 206 are laid down across the whole of the structure in by a carbon fibre placement machine. Strips are laid side-by-side until the entire structure is covered, and then the process repeats with the strips being laid down at a different orientation. A bonding matrix' material holds the strips in place, and the criss-crossing of strips in different layers builds up tensile strength in all directions in the surface. There may be some gaps between strips, which may mean that when a top layer of strips 202 is laid down, the previous layer of strips 204 may be exposed in places. In some cases the placement errors can be such that even the next layer of strips 206 and yet further layers may be exposed. Particularly large gaps or gaps spanning multiple layers can create weak points in the structure, and these gaps must be identified and repaired, either during fabrication or during maintenance.

Figures 3A and 3B illustrate the formation of a carbon fibre composite structure with a large gap between strips. The top layer of strips includes a first strip 302 and a second strip 304, and a third strip 306 of the layer below is visible in the gap between the first and second strips 302, 304. The surface profile 308 of the structure includes a valley' 310 where the second layer is exposed.

Because the properties of the carbon fibre composite surface make it difficult to image the surface consistently, a structured lighting' approach may be considered for inspecting carbon fibre composites and other optically complex surfaces.

Figures 4A and 4B illustrate a structured lighting approach as it might be applied to inspect carbon fibre composites. In such a system, the carbon fibre composite surface 402 is illuminated by an oblique light source 404, striking the surface 402 at an angle and thereby casting a shadow 406 on the surface. The surface 402 can then be imaged from a viewing angle different to the illumination angle to obtain an image 410.

Because the observer and illumination are disposed at different angles relative to the surface, the shadow 412 cast by the illumination can be seen in the image 410. From this shadow the contour of the surface, and hence the location of gaps between the carbon fibre strips (and other defects), can be determined. In this kind of scheme, a high level of illumination may be chosen so as deliberately to wash out' any surface features and colourations that might otherwise be interpreted as a shadow (and therefore a defect). In a structured lighting system, a sharp, clearly defined light source such as a laser or halogen bulb is used in order to produce clearly defined shadows.

The scheme shown in Figures 4A and 4B has only limited use, however, as it only locates one side of the gap between carbon fibre strips. To locate both sides of the gap, a scheme such as that shown in Figures 5A and 5B may be used. In this scheme, the composite surface 502 is illuminated with a first light source 504 from one angle and a second light source 506 from an opposing angle. The same viewing angle 508 is used as before. There is then case a first shadow 510 on one side of the gap and a second shadow 512 on the other side of the gap. In an image 514 taken from the viewpoint 508 there may then be visible the first shadow region 516 and the second shadow region 518, from which the size of the gap may be determined. This scheme suffers from several problems, however. The glare caused by one light can cause the shadow from the other light to become saturated or unclear, for example. The light bloom from the glare can also shrink or distort areas in shadow, which may cause smaller defects to remain hidden. The conventional structured lighting approach would be to increase the power of the lighting in order to define the shadow areas more clearly, but the effectiveness of this approach will always be limited by the optically complex characteristics of the carbon fibre composite material. For example, as the light levels are intensified, the glare and light bloom effects will also increase, potentially leading to less clearly defined features.

There is therefore a need for an inspection device that may improve on any above-mentioned scheme for inspecting optically complex surfaces.

Accordingly, in a first aspect of the invention there is provided a device for inspecting an optically complex surface, comprising: a light source; light directing means operable to direct the light to illuminate the optically complex surface, wherein the illumination is non-directional; and detection means for detecting light incident from the optically complex surface.

The term light' as used herein may include ultraviolet, visible, near-infrared and infrared electromagnetic radiation, and may in particular include light having a wavelength between (but not limited to) approximately 100 nm and 2,000 rim, or more particularly between 750 nm and 1,000 nm. It will be appreciated that other wavelengths of light which achieve a useful result in conjunction with the method and apparatus features disclosed herein may also be considered to fall within the scope of the present invention. The term non-directional light' may include light with no dominant directional component (in contrast, for example, to a structured lighting scheme in which a number of discrete light sources provide illumination). The term non-directional light' may also be considered to cover the illumination of a surface in which, for substantially any point on the surface, each ray of light arrives with a substantially random incident direction.

During the course of experimentation it was discovered that providing non-directional illumination at an optically complex surface (such as a carbon fibre composite material, for example), by means of a light source and light directing means, allowed surface detail to be viewed relatively clearly without introducing artefacts such as glare or black-out. This finding ran contrary to expectation, because conventional methods such as structured lighting generally emphasise the need for stronger, more clearly defined (in other words, directional) lighting in order to highlight surface contours more effectively.

In addition, the present invention can allow a more complete inspection of an optically complex surface, because it allows the viewing of more details (including visible sub-surface features) than methods such as structured lighting, which are limited to the analysis of contours (since the glare of optically complex surfaces can wash out' other surface details).

To improve the quality of the non-directional light, the light directing means may include a diffuse surface (which may be formed by a surface treatment such as abrasion to roughen the surface, or applying a coating of diffuse material), and the device may be arranged such that the diffuse surface is illuminated by the light source. Preferably the diffuse surface has a high diffuse reflectivity relative to its specular reflectivity (and preferably a high absolute diffuse reflectivity and a low, preferably substantially zero, absolute specular reflectivity). The diffuse surface may alternatively or additionally be defined by the characteristic that, of light reflected from the diffuse surface, at least 50%, 60%, 70%, 80%, 90%, 95%, 98%, 99% or more is reflected by scattering (instead of reflection). This characteristic may be true in particular for the light (and wavelengths thereof) emitted by the light source.

The device may be arranged such that, in use, the light source is at least partly shielded from the optically complex surface, to avoid light being emitted directly from the light source to the surface (which would introduce a strong directional element to the surface illumination).

The light source preferably emits light in a wide angle beam, which can improve the scattering effect. The term beam' should not be construed as limiting the angle of the light emission; the term wide angle beam' may for example include a light emission spanning more than (say) 15, 30, 60, 90, 135 or even 180 degrees (that is, an ultra-wide angle beam covering more than a hemisphere), for example. By contrast, a laser beam and other highly focussed light beams may be considered narrow angle', for example.

In addition, the light source may be arranged such that, in use, the beam is angled away from the optically complex surface. The term angled away' may be considered to mean that, in use, the centre (not necessarily the entirety) of the beam is angled in any direction having a normal component (relative to the optically complex surface) which is directed away from the optically complex surface. This can again reduce the amount of directional (or structured) light illuminating the optically complex surface.

The light source may be a diffuse light emitter. The term diffuse light emitter' may include emitters which are essentially area or volumetric light sources, as opposed to substantially point or thin filament sources of light. The term may also include light sources with an inherent scattering or light softening element.

In one embodiment of the invention the light source is a near-infrared light emitter. The light emitted by the near-infrared light emitter may be between 650 nm and 1,200 nm in wavelength, and may more specifically be between 750 nm and 1,000 nm in wavelength. Near infra-red light was found to have improved diffusion characteristics in carbon fibre composites (and other materials) compared to white' light, resulting for example in less glare and light bloom effects.

Consequently, the detection means may include a near-infrared (or infrared) light pass filter. In more detail, the filter may be operable such that the majority of light transmitted by the filter is between 650 nm and 1,200 nm in wavelength, and may more specifically be between 750 nm and 1,000 nm in wavelength. This can help to reduce detection errors and noise problems caused by ambient light (that is, light not generated by the light source) striking the detection means. This feature is beneficial in relation to the near-infrared emitter because ambient light (especially indoors) typically does not contain a large amount of near-infrared light.

The light directing means may include a substantially flat portion which, in use, is arranged substantially parallel to the optically complex surface. There may alternatively be provided a flat portion arranged perpendicular to a viewing direction of the detecting means, if applicable (for example the flat portion may be arranged perpendicular to the centre of a field of view of a camera element). As is described in more detail below, the flat portion is understood to scatter light from the optically complex surface back to the surface, thereby improving the quality and quantity of the non-directional illumination.

The substantially flat portion may include an opening through which the detection means is arranged to detect light. The detection means may itself protrude through the opening. This can allow a compact design of the device, and maximise the diffusing area around the surface.

The light directing means may further comprise at least one curved portion adjacent the substantially flat portion, and the device may be arranged such that the or each curved portion is illuminated by the light source. The curved portion can enhance the diffusive effect, essentially by de-focusing the light from the light source. The or each curved portion may have a substantially constant radius of curvature, and the radius of curvature and the width of the flat portion may have a ratio of between 0.2 and 0.4, between 0.25 and 0.3, or more particularly between 0.27 and 0.28.

If the light source comprises at least one light emitter, the or each emitter may be arranged such that the distance between the tip of a light-emitting portion of the or each emitter and the plane of the flat portion is between 15 mm and 40 mm, between 20 mm and 30 mm, or more particularly between 24 mm and 27 mm. Additionally or alternatively, the or each emitter may be arranged at a distance of between 50 mm and mm, 60 mm and 85 mm, or more particularly between 75 mm and 80 mm from a centre line of the flat portion.

If the light source comprises two light source portions, the light source portions may be disposed at respective opposite sides of the detection means. This can provide more even illumination of the optically complex surface.

If each light source includes a plurality of light emitters, each plurality of light emitters may be arranged in a respective linear arrangement. The arrangement may be a substantially straight line, for example, or may be curved. Additionally or alternatively the light source may comprise a plurality of light emitters arranged in a plurality of clusters.

The device as aforesaid may be suitable for attachment in a defined orientation to a further device (such as a carbon fibre placement machine) that outputs materials (such as carbon fibre strips) having an optically complex surface and a defined grain direction.

In this case, the light source may comprise a plurality of light emitters arranged substantially parallel to the grain direction and on either side of the optically complex surface to be inspected. This can improve the inspection results.

The light directing means may be formed from a resilient portion (such as a sheet of metal) having a defined width and a substantially constant cross-section across its width.

In another embodiment, the light source is a visible light emitter. The light source may emit light with a single wavelength or a range of wavelengths in the visible light spectrum (between approximately 400 nm and 700 nm), and may include a substantially white' light source. The light source may include one or more LEDs, halogen or tungsten bulbs or other light producing elements. In this embodiment, means for reducing ambient light in the vicinity of the optically complex surface and the device may be provided.

The light source preferably includes a diffuser. The light source may be of a light box' type, essentially equivalent to an area or volumetric light source (as opposed to a point light source). Mylar (RTM) material may be incorporated into the light source to enhance the diffusive properties of the light source.

The detection means may comprise an imaging apparatus, such as a camera, and a CCD camera in particular. The device may alternatively detect a (single) level of incident light at any one time, and/or may be operated on a scanning basis. The device may include optical focussing elements.

The device may also further comprise defect identification means for processing an output of the detection means, and outputting an alarm signal if the processing identifies a defect. This can allow an automated defect detection system to be provided.

In another aspect of the invention there is provided a device for inspecting an optically complex surface, comprising: a light source; a first diffuser; a second diffuser; and detection means for detecting light incident from the optically complex surface; the device being arranged such that the first diffuser scatters light from the light source to illuminate the second diffuser, and the second diffuser scatters light from the first diffuser to illuminate the optically complex surface.

In a further aspect of the invention there is provided a system for processing carbon fibre composite material, comprising: apparatus for outputting a portion of carbon fibre composite material; a device as aforesaid, operatively connected to the apparatus, and further comprising means for outputting a signal representing an image of the portion of carbon fibre composite material; and defect detection means for processing the signal output by the inspection device to determine whether a defect is present in the carbon fibre composite material.

Another aspect of the invention provides a method of inspecting an optically complex surface, comprising: directing light from a light source to the optically complex surface to illuminate the optically complex surface, wherein the illumination is non-directional; and detecting light incident from the optically complex surface.

In accordance with equivalent apparatus features, the step of directing the light may include illuminating a diffuse surface with the light source. The method may further comprise illuminating the optically complex surface with near-infrared light. The step of detecting light may further comprise filtering the light with a near-infrared (or infrared) pass filter. The step of directing light may include illuminating a curved surface. The method may further comprise illuminating a diffuser element with at least two light sources.

The method may be used with a device (such as a carbon fibre placement machine) that outputs materials (such as carbon fibre strips) having an optically complex surface and a defined grain direction, in which case the method may further comprise providing a row of light sources substantially parallel to the grain direction and on either side of the optically complex surface to be inspected. The method may further comprise passing light from the light source through a diffuser element. The method may also further comprise processing an output generated during the step of detecting, and outputting an alarm signal if a defect is identified.

In another aspect of the invention there is provided a method of inspecting an optically complex surface, comprising: illuminating a first diffuser with a light source; illuminating a second diffuser with light scattered from the first diffuser; illuminating the optically complex surface with light scattered from the second diffuser; and detecting light incident from the optically complex surface.

In a further aspect of the invention there is provided a method of inspecting a carbon fibre composite surface, comprising: illuminating the surface with non-directional light; and detecting light incident from the surface.

Although each aspect and various features of the present invention have been defined hereinabove independently, it will be appreciated that, where appropriate, each aspect can be used in any combination with any other aspect(s) or features of the invention. In particular, method features may be combined, where appropriate, with apparatus features, and vice versa.

Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is an illustration of the optically complex properties of carbon fibre composites; Figure 2 is an illustration of the process of forming a carbon fibre composite structure; Figures 3A and 3B are illustrations of a gap formed in the surface of a carbon fibre composite structure during manufacture; Figures 4A and 4B are illustrations of the application of a conventional structured lighting technique to identify the edge of the gap of Figures 3A and 3B; Figures 5A and 5B are illustrations of a further application of a conventional structured lighting technique to identify the edge of the gap of Figures 3A and 3B; Figures 6A and 6B are schematic diagrams illustrating in overview an inspection device according to a first embodiment of the invention; Figure 7 is a perspective view of the device of Figures 6A and 6B; Figure 8 is a front view of the device of Figures 6A and 6B, showing certain dimensions of the device; Figure 9 is a side view of the device of Figures 6A and 6B, showing certain dimensions of the device; Figure 10 is a side and front view of the device of Figures 6A and 6B, as attached to a carbon fibre composite placement machine; Figures 11 A and 11 B are schematic diagrams illustrating in overview an inspection device according to a second embodiment of the invention; Figure 12 is a perspective view of the device of Figures 1 1A and 1 1B; Figure 13 is a processed image based on the output of the device of Figures 6A and 6B; and Figure 14 is an enlargement of a portion of the image of Figure 13.

A first embodiment will now be described with reference to Figures 6A and 6B.

In Figures 6A and 6B, an inspection device 600 according to the first embodiment is illustrated schematically, the device comprising a set of near-infrared light emitters 602 mounted on two rows either side of the centre of the device 600, a diffuser element 604, a CCD camera 606, and a near-infrared pass filter 608. In Figure 6A the inspection device 600 is shown positioned over a surface 610, such as the surface of a carbon fibre composite structure. The portion 612 of the surface within the field of view of the camera is also shown.

The diffuser element 604 is formed from a sheet of metal that has its edges bent into shape to form the curved portions adjacent to the near-infrared light emitters 602.

During manufacture of the device 600 the surface of the sheet forming the inner part of the element is treated to impart the necessary diffuse optical qualities. This may be by abrading the surface to create a surface roughness, by coating the surface with an appropriate agent, or by physically attaching a separate sheet of diffuse material to the element (such as a sheet of matte white paper). The diffuser element 604 may alternatively be formed from a plastic or other suitable resilient material, in which case no surface treatment may be required to create the necessary optical properties.

Once the diffuser element 604 is formed, the inner surface of the diffuser element has the desired optical properties that its diffuse reflectivity (the proportion of incident light which is scattered by the surface) is relatively high and its specular reflectivity (the proportion of incident light which is reflected in a mirror-like reflection) is relatively low. The scattering effect of the diffuser is thus maximised in part by its curved shape (which in effect defocuses the near-infrared light beam), and in part by the optical properties of the diffuser's inner surface.

Because of the geometry of the inspection device, the near-infrared light emitters are also shielded from the surface, essentially preventing light travelling directly from the emitters to the surface (thus preventing the addition of a strong directional component to the surface illumination).

Super High-Power GaAIAs OD 100 (sold by the OptoDiode Corporation) near-infrared emitters were used as the near-infrared light source 602. These emitters have an ultra-wide angle beam (greater than 180 degrees) and produce a relatively diffuse light.

Narrow beam near-infrared emitters, such as near-infrared lasers, were found to be less effective but may be possible to use in conjunction with further diffuser elements.

A Basler A202K digital camera was used as the CCD camera 606. Other cameras andlor imaging systems may be used but may require some adjustment to the dimensions and components specified herein. As may be expected, better results may generally be achieved by using higher quality lenses and/or higher density sensor arrays.

In use, the inspection device should be placed between approximately 50 mm and 150 mm of the optically complex surface. Different distances were found to produce different effective image sizes, but a spacing of about 110 mm in particular was found to yield acceptable results. Different spacings may be appropriate, however, with different imaging systems, lenses, and so on.

When the inspection device is spaced from the optically complex surface approximately within the limits mentioned above, a further diffusive effect is believed to occur. At such distances, light scattered back from the optically complex surface is believed to be rediffused by the flat portion of the diffuser element in sufficient quantity to contribute to the illumination of the surface. Thus both the flat and the curved portions of the diffuser element are believed to assist in providing sufficient quantity and quality of non-directional illumination of the optically complex surface that effective imaging of it can take place.

The use of the near-infrared pass filter 608 improves the operation of the device 600 by eliminating ambient light in the visible spectrum. Additionally, near-infrared wavelengths of light were found to have beneficial characteristics compared to visible wavelengths of light in the inspection of carbon fibre composite surfaces. In particular, carbon fibre composite surfaces were found to scatter more of the near-infrared light and (specularly) reflect less compared to visible light. It was believed that the relatively longer wavelength of near-infrared light causes it to interact less with small reflective elements in the carbon fibre composite structure.

Figure 7 is a perspective view illustrating the inspection device in aconfiguration suitable for attachment to a robotic arm or to a carbon fibre placement machine, for example. In Figure 7 can again be seen the device 700, one of the near-infrared light emitters 702, the diffuser element 704, the CCD camera 706 and the near-infrared pass filter 708.

Figure 8 is a front view of the inspection device, and Figure 9 is a side view of the inspection device, both figures showing certain dimensions of the device which were found by experimentation to produce acceptable results with carbon fibre composite surfaces (although the figures shown are not necessarily to scale).

The effectiveness of the device 600 was found to vary considerably in response to relatively minor variations in the device dimensions, so precise measurement may be required during manufacture. Minor adjustments to the device may also need to be made in-situ, for example to compensate for inaccuracies and tolerances during manufacture of the device. In particular, the dimensions (A-B) and E (as shown) need careful attention. If any of these dimensions are modified, adjustments to other dimensions may also need to be made (by a process of trial and error). Further adjustments may need to be made to the dimensions of the device if different components to those specified here are used.

Figure 10 is a front and side view of the inspection device in a configuration suitable for attachment to a carbon fibre composite placement machine, such as the Cincinnati Viper 1200 machine (shown in part). The device can of course be attached to different fibre placement and other machines with suitable adjustment and rigging.

Figures hA and 1 lB are schematic diagrams illustrating in overview an inspection device according to a second embodiment of the invention. In this second embodiment, an inspection device 1100 comprises diffuse white light sources 1102, a diffuser element 1104 and a CCD camera 1106. The optically complex surface 1108 (such as a carbon fibre composite) is shown, as is the field of view 1110 of the camera.

The device 1100 of the second embodiment is much more sensitive to ambient light than the device 600 of the first embodiment, and normally will not function other than in controlled conditions. For this reason the device 1100 is less suited for in-situ inspection work, but may still provide useful results in manufacturing tasks. The device 1100 has an additional advantage compared to the device 600 of the first embodiment in that it can record colour information, due to the visible light wavelengths being used.

As noted, the light sources 1102 are essentially white light' sources, but coloured andlor single wavelength light sources (such as diffused sodium lamps, for example) may also be used. By experimentation the white light inspection device 1100 was found to function better without the curved portions of the diffuser element 604 of the near-infrared embodiment (but with the additional diffusion of the light source).

Figure 12 is a perspective view of the device of Figures 1 1A and 1 lB. A head component 1202 and one of the lighting components 1204 of the inspection device are shown. The lighting component 1204 includes a diffuser 1206 constructed from a white light source and a sheet of highly scattering Mylar (RTM) material. The inspection device head 1202 includes a diffuser element 1208 and a CCD camera 1210. Whilst shown separately, the inspection device head 1202 and lighting components 1204 are mounted on the same rig. Alternatively the inspection device head 1202 and lighting components 1204 may be provided in the same unit.

Figure 13 is a processed image based on the output of the inspection device according to the first embodiment. The image shows the surface of a carbon fibre composite structure, and clearly shows a first, top layer of carbon fibre strips running up and down the page, under which a second layer of fibre strips runs in a left-right direction. The image was taken of a the surface of an aircraft nose cone, and the surface details can be perceived despite the fact that the surface is geometrically complex (convex).

Figure 14 is an enlargement of a portion of the image of Figure 13, showing a third layer 1400 of carbon fibre strips arranged in a diagonal direction, underlying both the first and second layers. This hole in the first and second layers of strips represents a potential weak point in the structure which requires attention (for example so that the hole can be repaired).

As noted, some processing of the image has taken place in order to enhance the edges and improve the image intensity levels. However, the image is suitable for further processing, which can be carried out automatically, to perform functions such as edge detection and anomaly detection. Accordingly, automatic inspection systems may be conceived that employ an inspection device as described herein automatically to detect faults in a carbon fibre composite or other type of structure (either during manufacture or during in-situ testing). Such a system could output an alarm signal, for example, when the automatic image processing detects a defect.

The inspection device has been described above with reference in particular to carbon fibre composite materials. The device may of course be used to inspect or otherwise image or test other materials, such as ceramic matrix, glass matrix, metal matrix, metals, glasses and other composite and non-composite materials which display optically complex characteristics, for example. The device may also be used to inspect optically simple surfaces as well, such as wood, lacquered surfaces, plastics, and so on.

It will be appreciated that the principles described above may be applied with different shapes and arrangements of the diffuser element and light sources, for example. In particular, any different shapes and arrangements in which the optically complex surface is illuminated by redirecting light off a diffuse surface and/or any different shapes and arrangements in which light reflected from the optically complex surface is re-diffused back towards the surface may achieve a beneficial result.

Many arrangements may also be considered which include a light source, first diffuser and second diffuser, whereby a surface to be inspected is illuminated by light scattered from the second diffuser, which in turn is illuminated by light scattered from the first diffuser, which in turn is illuminated by light incident from the light source. This can provide a sufficient quality of non-directional illumination.

The inspection device may also conceivably be adapted, where necessary, to operate with light of wavelengths other than those discussed in detail herein. Improvements in imaging technology, for example, may permit the use of longer wavelength light than is currently contemplated.

Modifications such as these that lie within the spirit and scope of the present invention will be apparent to a skilled person in the art.

Claims

CLAIMS

1. A device for inspecting an optically complex surface, comprising: a light source; light directing means operable to direct the light to illuminate the optically complex surface, wherein the illumination is non-directional; and detection means for detecting light incident from the optically complex surface.

2. A device according to Claim 1, wherein the light directing means includes a diffuse surface, and the device is arranged such that the diffuse surface is illuminated by the light source.

3. A device according to Claim 2, wherein the diffuse surface has a high diffuse reflectivity relative to its specular reflectivity.

4. A device according to any preceding claim, wherein the device is arranged such that, in use, the light source is at least partly shielded from the optically complex surface.

5. A device according to any preceding claim, wherein the light source emits light in a wide angle beam.

6. A device according to Claim 5, wherein the light source is arranged such that, in use, the beam is angled away from the optically complex surface.

7. A device according to any preceding claim, wherein the light source is a diffuse light emitter.

8. A device according to any preceding claim, wherein the light source is a near-infrared light emitter.

9. A device according to Claim 8, wherein the detection means includes a near-infrared light pass filter.

10. A device according to any preceding claim, wherein the light directing means includes a substantially flat portion which, in use, is arranged substantially parallel to the optically complex surface.

11. A device according to Claim 10, wherein the substantially flat portion includes an opening, and the detection means is arranged to detect light passing through the opening.

12. A device according to Claim 10, wherein the light directing means further comprises at least one curved portion adjacent the substantially flat portion, and the device is arranged such that the or each curved portion is illuminated by the light source.

13. A device according to Claim 12, wherein the or each curved portion has a substantially constant radius of curvature.

14. A device according to Claim 13, wherein the radius of curvature and the width of the flat portion have a ratio of between 0.2 and 0.4, between 0.25 and 0.3, or more particularly between 0.27 and 0.28.

15. A device according to any one of Claims 13 or 14, the light source comprising at least one light emitter, and wherein the or each emitter is arranged such that the distance between the tip of a light-emitting portion of the or each emitter and the plane of the flat portion is between 15 mm and 40 mm, between 20 mm and 30 mm, or more particularly between 24 mm and 27 mm.

16. A device according to any one of Claims 13 to 15, the light source comprising at least one light emitter, and wherein the or each emitter is arranged at a distance of between 50 mm and 100 mm, 60 mm and 85 mm, or more particularly between 75 mm and 80 mm from a centre line of the flat portion.

17. A device according to any preceding claim, wherein the light source comprises two light source portions, and the light source portions are disposed at respective opposite sides of the detection means.

18. A device according to Claim 17, wherein each light source includes a plurality of light emitters, and each plurality of light emitters is arranged in a respective linear arrangement.

19. A device according to any preceding claim, suitable for attachment in a defined orientation to a further device that outputs materials having an optically complex surface and a defined grain direction, wherein the light source comprises a plurality of light emitters arranged substantially parallel to the grain direction and on either side of the optically complex surface to be inspected.

20. A device according to any preceding claim, wherein the light directing means is formed from a resilient portion having a defined width and a substantially constant cross-section across its width.

21. A device according to any one of Claims ito 7 or 10, wherein the light source is a visible light emitter.

22. A device according to any preceding claim, wherein the light source includes a diffuser.

23. A device according to any preceding claim, wherein the detection means comprises an imaging apparatus.

24. A device according to any preceding claim, further comprising defect identification means for processing an output of the detection means, and outputting an alarm signal if the processing identifies a defect.

25. A device for inspecting an optically complex surface, comprising: a light source; a first diffuser; a second diffuser; and detection means for detecting light incident from the optically complex surface; wherein the device is arranged such that the first diffuser scatters light from the light source to illuminate the second diffuser, and the second diffuser scatters light from the first diffuser to illuminate the optically complex surface.

26. A system for processing carbon fibre composite material, comprising: apparatus for outputting a portion of carbon fibre composite material; a device as claimed in any one of Claims 1 to 25, operatively connected to the apparatus, and further comprising means for outputting a signal representing an image of the portion of carbon fibre composite material; and defect detection means for processing the signal output by the inspection device to determine whether a defect is present in the carbon fibre composite material.

27. A method of inspecting an optically complex surface, comprising: directing light from a light source to the optically complex surface to illuminate the optically complex surface, wherein the illumination is non-directional; and detecting light incident from the optically complex surface.

28. A method according to Claim 1, wherein the step of directing the light includes illuminating a diffuse surface with the light source.

29. A method according to Claim 27 or 28, further comprising illuminating the optically complex surface with near-infrared light.

30. A method according to Claim 29, wherein the step of detecting light further comprises filtering the light with a near- infrared pass filter.

31. A method according to any one of Claims 27 to 30, wherein the step of directing light includes illuminating a curved surface.

32. A method according to any one of Claims 27 to 31, further comprising illuminating a diffuser element with at least two light sources.

33. A method according to any one of Claims 27 to 32 for use with a device that outputs materials having an optically complex surface and a defined grain direction, the method further comprising providing a row of light sources substantially parallel to the grain direction and on either side of the optically complex surface to be inspected.

34. A method according to any one of claims 27 to 33, further comprising passing light from the light source through a diffuser element.

35. A method according to any one of claims 27 to 34, further comprising processing an output generated during the step of detecting, and outputting an alarm signal if a defect is identified.

36. A method of inspecting an optically complex surface, comprising: illuminating a first diffuser with a light source; illuminating a second diffuser with light scattered from the first diffuser; illuminating the optically complex surface with light scattered from the second diffuser; and detecting light incident from the optically complex surface.

37. A method of inspecting a carbon fibre composite surface, comprising: illuminating the surface with non-directional light; and detecting light incident from the surface.