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Title:
A SYSTEM COMPRISING A TRANSPARENT OR TRANSLUCENT MEMBER
Document Type and Number:
WIPO Patent Application WO/2017/137111
Kind Code:
A1
Abstract:
A member system comprising a member (101) and a primary light source (106). The member comprises a first surface (103), and a first cavity (102) is provided in the member, such that the first cavity forms a hole in the first surface, the hole being surrounded by the first surface and the sides of the first cavity comprising surfaces of the member. The primary light source is arranged so that light therefrom passes into the member through a side of the first cavity, the light then travelling within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times.

Inventors:
TOMAR, Ashutosh (Jaguar Land Rover, Patents Department W/1/073Abbey Road,Whitley, Coventry Warwickshire CV3 4LF, CV3 4LF, GB)
YOUDAN, Paul (Jaguar Land Rover, Patents Department W/1/073Abbey Road,Whitley, Coventry Warwickshire CV3 4LF, CV3 4LF, GB)
Application Number:
EP2016/080051
Publication Date:
August 17, 2017
Filing Date:
December 07, 2016
Export Citation:
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Assignee:
JAGUAR LAND ROVER LIMITED (Abbey Road, Whitley, Coventry Warwickshire CV3 4LF, CV3 4LF, GB)
International Classes:
F21V8/00; B60S1/02; G02B6/00; H05B3/00; H05B3/84
Domestic Patent References:
WO2005003047A12005-01-13
WO2015121372A12015-08-20
Foreign References:
US20110273874A12011-11-10
CA2944272A12015-10-29
DE102014006532A12015-11-05
JP2008185531A2008-08-14
Attorney, Agent or Firm:
CHANG, Seon-Hee (Jaguar Land Rover, Patents Department W/1/073Abbey Road,Whitley, Coventry Warwickshire CV3 4LF, CV3 4LF, GB)
Download PDF:
Claims:
CLAIMS

1 . A system comprising a transparent or translucent member and a primary light source, wherein the member comprises a first surface, and wherein a first cavity is provided in the member, such that the first cavity forms a hole in the first surface and the hole is surrounded by the first surface, at least a first side of the first cavity comprising a surface of the member,

the primary light source being arranged so that light therefrom passes into the member through said at least first side of the first cavity, the light then travelling within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times.

2. A system according to claim 1 , wherein the primary light source is located at least partially within the first cavity.

3. A system according to claim 2, wherein the primary light source is attached to a plug which is substantially the same size and shape as the first cavity, such that the plug fills the first cavity when the primary light source is in a desired position on the member.

4. A system according to any preceding claim, wherein the cavity has a substantially circular cross section.

5. A system according to claim 3, wherein the cavity has one-fold rotational symmetry.

6. A system according to any preceding claim, wherein the member comprises a plurality of layers.

7. A system according to claim 6, wherein the first surface lies between two layers of the member.

8. A system according to any preceding claim, wherein the primary light source is a laser. 9. A system according to any preceding claim, further comprising a secondary light source, wherein a second cavity is provided in the member, such that the second cavity forms a hole in the first surface and the hole is surrounded by the first surface, at least a first side of the second cavity comprising a surface of the member,

the secondary light source being arranged so that light therefrom passes into the member through said at least first side of the second cavity, the light then travelling within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times.

10. An apparatus comprising a plug and a primary light source, suitable for use in a system according to claim 3 or any of claims 4 to 9 as depending through claim 3.

1 1 . A method of manufacturing a system comprising a transparent or translucent member and a primary light source, the method comprising:

creating a first cavity in the transparent or translucent member comprising a first surface, such that the first cavity forms a hole in the first surface and the hole is surrounded by the first surface, at least a first side of the first cavity comprising a surface of the member; and

arranging the primary light source so that light therefrom passes into the member through said at least first side of the first cavity, the light then travelling within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times.

12. A method according to claim 1 1 , wherein creating the first cavity in the member comprises forming a hole in the first surface.

13. A method according to claim 12, wherein the method further comprises:

drilling a hole through the first surface with a drill bit, the drill bit comprising a grinding surface, the grinding surface extending over at least a first region and a second region of the drill bit, wherein the first region has a first average radius, and the second region has a second average radius which is greater than the first average radius, and wherein the grinding surface is smoother in the second region than in the first region.

14. A drill bit for forming a cavity in a transparent or translucent member, the drill bit comprising a grinding surface, the grinding surface extending over at least a first region and a second region of the drill bit, wherein the first region has a first average radius, and the second region has a second average radius which is greater than the first average radius,

and wherein the grinding surface is smoother in the second region than in the first region.

15. A method of heating a transparent or translucent member and a primary light source, the member comprising a first surface, and wherein a first cavity is provided in the member, such that the first cavity forms a hole in the first surface and the hole is surrounded by the first surface, at least a first side of the first cavity comprising a surface of the member, the primary light source being arranged so that light therefrom passes into the member through said at least first side of the first cavity, the method comprising:

passing light from the primary light source into the member through said first side of the first cavity, such that the light then travels within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times,

wherein at least some of the light from the primary light source is absorbed by the member as the light from the primary light source passes through the member.

16. A method for determining a condition of a transparent or translucent member, the member comprising a first surface, and wherein a first cavity is provided in the member, such that the first cavity forms a hole in the first surface and the hole is surrounded by the first surface, at least a first side of the first cavity comprising a surface of the member, the method comprising:

passing light from a primary light source into the member through a side of the first cavity, such that the light then travels within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times;

detecting light from the primary source with a first sensor suitable for detecting radiation from the primary light source; and

determining the condition of the member by comparing the sensed light level with a first expected sensed light level.

17. A method according to claim 16, further comprising creating a record of a fault if the sensed light level is not the expected sensed light level.

18. A vehicle comprising a system according to any of claims 1 to 9.

19. A vehicle according to claim 18, the vehicle further comprising a control unit configured to carry out the method of any of claims 15 to 17.

20. A member, a system, a method or a vehicle constructed and/or arranged substantially as described herein with reference to one or more of the accompanying drawings.

Description:
A System Comprising a Transparent or Translucent Member

TECHNICAL FIELD

The present disclosure relates to a member system, a method of manufacturing a member system, a method of heating a member and a method of determining the condition of a member.

BACKGROUND

Vehicle windowpanes, such as windscreens, and mirrors, are frequently subject to "fogging" and ice formation. Fogging occurs when small water droplets form on the surface of the windowpane or mirror and disrupt the passage of light at that surface, creating a "fog". When ice forms this can also disrupt the passage of light. Both conditions therefore reduce the ability of the driver and other occupants of the vehicle to see the outside world. Therefore any fog or ice should ideally be removed, particularly from the windscreen, rear window and rear view mirrors of a vehicle, before the vehicle is driven.

Windowpanes and mirrors are also subject to flaws such as cracks, which can be caused by the impact of small objects when the vehicle is driven. Small flaws may not be visible to the driver without a close inspection, but they represent a weak spot in the windowpane or mirror, and may spread if subject to further stress. Therefore it is often desirable to detect flaws so that they can be assessed and repaired as quickly as possible.

Therefore it is desirable to fit windowpanes and mirrors in vehicles with components which will detect and counter fogging and ice, and which will at least detect flaws. However, fitting such systems is difficult. The space around a windowpane or mirror on a vehicle is limited, and windowpanes and mirrors themselves are made of materials, in particular glass, which may be brittle and sensitive to miss-handling.

Therefore a system which can be fitted easily is desirable.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a system comprising a transparent or translucent member and a primary light source, a method of manufacturing the system, a method of heating a transparent or translucent member, a method of determining the condition of a transparent or translucent member, a controller and a vehicle as claimed in the appended claims. According to an aspect of the invention there is provided a system comprising a transparent or translucent member and a primary light source. The member comprises a first surface, and a first cavity is provided in the member, such that the first cavity forms a hole in the first surface and the hole is surrounded by the first surface, at least a first side of the first cavity comprising a surface of the member. The primary light source being arranged so that light therefrom passes into the member through said at least first side of the first cavity, the light then travelling within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times. In this way the system provides a way of passing light into the member. The light passed into the member can be used, for example, to heat or monitor the member in ways laid out in greater detail below.

The hole formed by the cavity in the first surface is surrounded by the first surface, such that the hole is a self-contained break in that surface. The cavity may extend through the member such that the first cavity also forms a further hole on a further surface of the member.

Typically, the material of the member is chosen to provide a predefined absorption rate for photons of a frequency produced by the primary light source.

It may be that more than half of the light from the primary light source is absorbed by the member as the light passes through the member. It may be that 90 percent of the light from the primary light source is absorbed by the member as the light passes through the member. It may be that substantially all of the light from the primary light source is absorbed by the member as the light passes through the member.

Typically light from the primary light source propagates through the member in a direction substantially parallel with the plane of the member. It may be that the frequency of the light and absorption properties of the glass cooperate so that substantially all the light is absorbed before the primary light source reaches a surface opposed to the side of the cavity.

Typically, the first surface is substantially parallel to the plane of the member. In total internal reflection, a ray of light travelling through a first medium reaches a boundary with a second medium and the ray is refracted such that it remains within the first medium. One such boundary is a surface of the member. Provided that the angle of incidence is great enough, and that the refractive index of the first medium is greater than the refractive index of the second medium, then the ray is refracted such that it remains within the first medium as dictated by the principle of total internal reflection. The member typically comprises glass. Alternatively or additionally, the member may comprise plastic or any other material or composite of materials. Typically the member is substantially transparent, for example to light with a frequency in the spectrum visible to the human eye. The member may be a windowpane, such as a windshield or a window in a door. Alternatively, the member may form part of a mirror.

The member may be doped with impurities in order to adjust the light absorption characteristics of the member. For example, the member may comprise quantities of Iron Oxide (Fe 2 0 3 ) or Lead Oxide (PbO). The member may be doped with nanoparticles. The light may undergo total internal reflection from a plurality of surfaces within the member. For example, the light may undergo total internal reflection from the first surface and then a second surface. The light may then undergo total internal reflection from the first surface again. One or more surfaces within the member may be treated to become mirrors, so that they will more easily reflect light. One or more surfaces within the member may be shaped such that the surfaces reflect the light and retain it within the member. For example, an end of the member distal to a light source such as the primary light source may be provided with a shape such that light from the light source is reflected back towards the light source through the member. As such, the member may comprise a prism. Typically, the majority of photons produced by the primary light source undergo total internal reflection a plurality of times. It may be that 95%, 99%, or substantially all of the photons produced by a light source undergo total internal reflection a plurality of times.

Typically the majority of the photons produced by the primary light source have a frequency which is not visible to the human eye. It may be that the majority of the photons produced by the primary light source have a frequency which is lower than the range of frequencies visible to the human eye. It may be that the majority of the photons produced by the primary light source have a frequency in the infrared spectrum. Since infrared radiation is not visible to the human eye, the light will not then obscure the view through the member. It may be that the majority of the photons produced by the primary light source have a frequency between 300 and 1200 nanometres. It may be that the majority of the photons produced by the primary light source have a frequency of 300, 800 or 1200 nanometres. It may be that the majority of the photons produced by the primary light source have a frequency which is higher than the range of frequencies visible to the human eye. It may be that the majority of the photons produced by the primary light source have a frequency in the microwave spectrum. It may be that the primary light source has a power level between 1 .2 and 1 .6 watts. It may be that the primary light source has a power level of 1 .2 or 1 .6 watts. It may be that the light source is capable of producing light at a plurality of power levels, for example 800 milliwatts and 2 watts. Where this is the case, the primary light source may change the power level when moving between modes. The primary light source may operate at a first power level, for example 800 milliwatts, when detecting flaws in a member, and operate at a second power level, for example 2 watts, when heating the member. Typically, the second power level will be higher than the first power level. Alternatively, a similar effect may be achieved by using a plurality of lasers, each of which operates at a different power level, in the same cavity. It may be that the light source produces light in a beam. The beam may be directed into the member as a beam. Also, the light from the light source may be passed through optical equipment such as a prism or lens in order to shape, focus or spread the light before it enters the member. It may be that the light source produces photons of variable frequency. It may be that the light source produces light of variable intensity.

It may be that the system comprises at least a first sensor suitable for detecting radiation from the primary light source.

Typically, the primary light source is located at least partially within the first cavity. It may be that the primary light source is located completely within the first cavity.

It may be that the primary light source is attached to a plug which is substantially the same size and shape as the first cavity, such that the plug fills the first cavity when the primary light source is in position on the member. Typically, the plug will comprise a transparent material in order to allow the passage of light from the primary light source. The plug may be chosen to have similar optical properties to the windscreen, in order to reduce reflection and refraction at the boundary between the plug and the surface of the first cavity.

The plug may be a polymer such as a plastic or elastomer. The plug may be resilient. Where the plug is resilient, it may be larger than the cavity, such that once the plug is pushed into the cavity the plug will expand and push against the walls of the cavity, securing the plug in place.

The plug may be formed by placing the primary light source in the desired position on or near the cavity, and then injecting a filling agent into the cavity such that the filling agent fills the cavity and secures the primary light source in the desired position.

The plug may comprise a plurality of light sources. Where multiple light sources are used, each light source will typically be directed in a substantially different direction. It may be that the plug contains a heating light source which is intended to heat the windowpane as well as a detecting light source which is intended for use in detecting flaws in the windowpane.

The plug may comprise an aerial such as an induction coil which is connected to the light source. In this way, the light source can send and receive signals and be powered wirelessly.

It may be that the cavity has a substantially circular cross section. In particular the cavity may have a circular cross section on a plane substantially parallel to the first surface. The cavity may be cylindrical. Alternatively, the cavity may have a cross section which is elliptical, square, triangular or any other desired shape.

It may be that a cross section of the cavity has one-fold rotational symmetry. Where a pre- shaped plug is used, this will ensure that the plug only fits in the cavity in one orientation, ensuring that the primary light source is oriented in the right direction.

Typically, the member comprises a plurality of layers. It may be that the first surface lies between two layers of the member. Where this is the case, an outer layer or layers or the member may enclose the cavity such that when the system is assembled the primary light source is sealed within the member.

Typically, the primary light source is a laser. It may be that the primary light source is a maser. It may be that the primary light source is a fluorescent lamp. It may be that the primary light source is a cold cathode fluorescent lamp, such as a focussed cold cathode fluorescent lamp. It may be that the primary light source is an LED or any other suitable light source. It may be that the primary light source comprises a scanning light source, wherein the scanning light source can emit light in more than one direction. Typically, the scanning light source will be able to emit light in a range of directions that lie within the member. It may be that the system further comprises a secondary light source. A second cavity is then provided in the member, such that the second cavity forms a hole in the first surface and the hole is surrounded by the first surface, at least a first side of the second cavity comprising surfaces of the member. The secondary light source is arranged so that light therefrom passes into the member through said first side of the second cavity, the light then travelling within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times.

Alternatively, the second cavity may form a hole in a second surface of the member, the secondary light source still being arranged so that light therefrom passes into the member through a side of the second cavity, the light then travelling within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times.

The system may be provided with a plurality of cavities and light sources arranged in this way, as many as is desired.

The secondary and subsequent light sources may have any of the features described above with reference to the primary light source. According to another aspect of the invention, there is provided an apparatus comprising a plug and a primary light source, suitable for use in a system as described above.

According to another aspect of the invention, there is provided a method of manufacturing a system comprising a transparent or translucent member and a primary light source. The method comprises:

creating a cavity in the transparent or translucent member comprising a first surface, such that the first cavity forms a hole in the first surface and the hole is surrounded by the first surface, at least a first side of the first cavity comprising a surface of the member; and arranging the primary light source so that light therefrom passes into the member through said at least first side of the first cavity, the light then travelling within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times. It may be that creating the first cavity in the member comprises forming a hole in the first surface. It may be that creating a cavity in the member comprises drilling a hole through the first surface.

It may be that the method further comprises drilling a hole through the first surface with a drill bit, the drill bit comprising a grinding surface, the grinding surface extending over at least a first region and a second region of the drill bit, wherein the first region has a first average radius, and the second region has a second average radius which is greater than the first average radius, and wherein the grinding surface is smoother in the second region than in the first region.

According to a further aspect of the invention, there is provided a drill bit for drilling a cavity in a transparent or translucent member, the drill bit comprising a grinding surface, the grinding surface extending over at least a first region and a second region of the drill bit, wherein the first region has a first average radius, and the second region has a second average radius which is greater than the first average radius,

and wherein the grinding surface is smoother in the second region than in the first region

The grinding surface comprises a surface suitable for grinding and may be formed from indentations cut or cast into the surface of the drill bit. Alternatively, the grinding surface may be formed by adhering abrasive particles to the grinding surface, or may make use of a grinding paste. The grinding surface may comprise a burr.

The drill bit may comprise more than two regions. If so, the regions will be arranged in order of greatest average radius to least, and from roughest surface to smoothest. It may be that the drill bit is substantially conical. It may be that the smoothness of the grinding surface varies smoothly over the length of the drill bit. For example, the smoothness of the grinding surface may be proportional to the radius of the drill bit. The smoothness of the grinding surface may be proportional to the curvature of the drill bit.

The drill bit may be substantially hollow. Where the drill bit is hollow, it may comprise an opening, a cutting surface being provided around the opening so that a plug of material may be drilled out of the member using the drill bit, hence forming the cavity. According to a further aspect of the invention, there is provided a method of heating a transparent or translucent member and a primary light source, the member comprising a first surface, and wherein a first cavity is provided in the member, such that the first cavity forms a hole in the first surface and the hole is surrounded by the first surface, at least a first side of the first cavity comprising a surface of the member, the primary light source being arranged so that light therefrom passes into the member through said at least first side of the first cavity, the method comprising:

passing light from the primary light source into the member through said first side of the first cavity, such that the light then travels within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times,

wherein at least some of the light from the primary light source is absorbed by the member as the light from the primary light source passes through the member.

According to a further aspect of the invention, there is provided a method for determining a condition of a transparent or translucent member, the member comprising a first surface, and wherein a first cavity is provided in the member, such that the first cavity forms a hole in the first surface and the hole is surrounded by the first surface, at least a first side of the first cavity comprising a surface of the member, the method comprising:

passing light from a primary light source into the member through a side of the first cavity, such that the light then travels within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times;

detecting light from the primary source with a first sensor suitable for detecting radiation from the primary light source; and

determining the condition of the member by comparing the sensed light level with a first expected sensed light level.

Chips, cracks and other flaws in the member may alter the transmission of light through the member. Similarly, water, dust, dirt or any other accretion on the member may also alter the transmission of light through the member. Therefore both may be detected by comparing the sensed light level with an expected sensed light level. The first expected sensed light level may comprise an expected sensed light level for an intact and clean member. The invention may further comprise comparing the sensed light level with a second expected sensed light level. The second expected sensed light level may comprise an expected sensed light level for a member which has been damaged, covered in dirt, covered in dust, rained on, or otherwise altered. The method may further comprise providing a member cleaning device and activating the member cleaning device if the sensed light level is not the first expected sensed light level. The member cleaning device may comprise a windscreen wiper, a water jet or any other suitable device. The method may further comprise providing a member cleaning device and activating the member cleaning device if the sensed light level is a second expected sensed light level.

The method may comprise detecting light from the primary light source with a sensor a plurality of times and comparing the plurality of detected light levels with an expected pattern of sensed light levels.

It may be that the method for determining the condition of a member further comprises creating a record of a fault if the sensed light level is not the expected sensed light level. In accordance with a further aspect of the present invention there is provided a method for detecting a flaw in a transparent or translucent member, the member comprising a first surface, and wherein a first cavity is provided in the member, such that the first cavity forms a hole in the first surface and the hole is surrounded by the first surface, at least a first side of the first cavity comprising a surface of the member, the method comprising:

passing light from a primary light source into the member through a side of the first cavity, such that the light then travels within the member until it has undergone total internal reflection from one or more surfaces of the member a plurality of times;

detecting light from the primary light source with a first sensor suitable for detecting radiation from the primary light source;

comparing the sensed light level with an expected sensed light level; and

creating a record of a fault if the sensed light level is not the expected sensed light level.

It may be that the method for detecting a flaw in a member further comprises altering the behaviour of the primary or secondary light source if the sensed light level is not the expected sensed light level. Typically, altering the behaviour of the primary or secondary light source comprises disabling the first or second light source. Alternatively, altering the behaviour of the primary or secondary light source may comprise reducing the function of the light source. For example, in the case of a scanning light source which can emit light in more than one direction, altering the behaviour of the light source may comprise preventing the light source from emitting light in a particular direction or set of directions. Typically, a member comprises multiple layers, for example two layers of glass surrounding a layer of polyvinyl butyral (PVB). It may be that light from the primary light source is restricted to a single layer of the member. For example, it may be that the light from the primary light source is arranged to pass through a layer of the member in order to heat that layer up most effectively, and so help to prevent fogging on the outer surface of that layer, for example. It may be that light from the primary light source passes through multiple layers of the windscreen.

Altering the behaviour of the primary light source may comprise preventing the light source from emitting light in a particular layer of the member. It may be that altering the behaviour of the primary light source comprises preventing the light source from emitting light in a particular direction or set of directions in a particular layer. For example, if a first glass layer of a member has been damaged, light from the primary light source may be contained within a PVB layer, a second glass layer, or both, in order to avoid the light being scattered by the damage in the first layer.

Where a light source in an embodiment produces a beam, it may be that altering the behaviour of the primary or secondary light source comprises changing the beam shape or beam width.

Where the primary light source is a scanning light source, the method of detecting a flaw in a member may further comprise:

detecting light from the primary light source with a sensor while the primary light source is emitting light in a first direction;

comparing the sensed light level at the sensor with an expected sensed light level; and

creating a record of a fault if the sensed light level is not the expected sensed light level,

wherein the record of the fault is associated with a region of the member, the region depending upon the first direction

It may be that the system comprises a plurality of scanning light sources. Where this is the case, the method may further comprise triangulating a location from the directions associated with the record of a fault detected by more than one scanning light source. Where the light source produces photons of variable frequency, it may be that a method for determining the condition of a member or detecting a flaw as described above also comprises:

detecting the temperature of the member; and

varying the frequency of the photons according to the temperature of the member.

Where the light source produces light of variable intensity, it may be that a method for determining the condition of a member or detecting a flaw as described above also comprises:

detecting the temperature of the member; and

varying the intensity of the light according to the temperature of the member.

According to a still further aspect of the invention, there is provided a vehicle comprising a system as described above. It may be that the vehicle further comprises a control unit configured to carry out a method of heating a member or determining the condition of a member as described above.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. For example, features described in connection with one aspect or embodiment are applicable to all aspects or embodiments, except where such features are incompatible. BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a first member;

Figure 2 shows the first member when provided with a primary light source;

Figure 3 shows the passage of light through the first member;

Figures 4 and 5 show details of the first member in use;

Figures 6, 7, 8, 9 and 10 show second, third, fourth fifth sixth members respectively;

Figure 1 1 shows a drill for use in cutting a cavity in a member. DETAILED DESCRIPTION

Figure 1 shows a first member 101 for use in a vehicle according to one embodiment of the invention. Figure 1 further shows a cross section through that first member 101 . The first member 101 comprises a first cavity 102, which extends through the member between a first surface 103 and a second surface 104. The first cavity 102 is made by drilling a hole through the first member 101 . An inner surface, side 105, of the first cavity is then polished to provide a smooth optical surface.

Once the first cavity 102 has been drilled in the first member 101 , a primary light source 106 is fitted as illustrated in Figure 2. The primary light source 106 comprises an infra-red laser which is contained within a plug the same size and shape as the first cavity 102. The plug is fitted in the first cavity 102, and the infra-red laser emits a beam of light 107 towards the side 105 of the first cavity 102. The plug is arranged so as not to obstruct the passage of light from the infra-red laser to the side of the first cavity. This is done by providing space within the plug which comprises a material which is optically transparent to light for the primary light source. In an alternative embodiment, the plug may be constructed at least partially from a material chosen to be transparent to the infra-red laser light. The beam of light 107 therefore passes through the plug and through the side of the first cavity 102, into the first member 101 .

Figure 3 illustrates what happens to the beam of light once it enters the first member 101 . The beam of light 107 approaches the second surface 104. The material of the member is chosen to have a higher refractive index than the atmosphere surrounding the member, such that when the first beam of light 107 hits the surface 104 if will undergo refraction. The angle at which the light hits the surface 104 is chosen such that the first beam of light undergoes total internal reflection, and is reflected towards the first surface 103. At the first surface 103, the beam of light 107 again undergoes total internal reflection. In this way, the beam bounces back and forth between the two surfaces 103, 104, as it propagates through the first member 101 .

The infrared laser in the primary light source 106 is a scanning laser, which can emit the beam of light 107 in a range of directions. Figure 4 illustrates how the beam of light 107 moves across the first member 101 .

As the beam travels through the first glass sheet, photons in the beam of light 107 are absorbed by the member, and so energy is absorbed from the beam by the member. Therefore the energy of the first member 101 increases, raising the temperature of the member. When the temperature is raised enough, any ice on the outside of the first member 101 will melt, and any water droplets will tend to evaporate, clearing both ice and fog from the first member 101 .

Since the primary light source comprises an infrared laser, the beam of light 107 is not visible to the driver of the vehicle. Due to the absorption of the photons, the beam of light 107 attenuates as it passes through the first member 101 . The rate of attenuation depends upon the optical properties of the materials which comprise the first member 101 , as well as the frequency of the beam of light 107. The first member 101 can be doped with various impurities to adjust the absorption rate of the beam of light 107 without adversely affecting visibility for the driver. The member and the frequency of the beam of light 107 is chosen so that the intensity of the beam of light 107 approaches nothing as the beam of light 107 approaches the distal end 108 of the first member 101 . In this way, the amount of energy lost in photons escaping through the distal end of the member is minimised. As the laser light hits the side of the first cavity 105, it may be refracted owing to differences in the optical properties of the first member 101 and the material of the plug. Figure 5 illustrates this refraction, with the beam of light 107 hitting the first cavity 105, and then spreading outwards due to the curved, concave surface of the first cavity 105. In use, this may be desirable to the user, since spreading the beam of light gives more widely distributed absorption, and hence more even heating to the first member 101 .

Figure 6 shows a second member 201 . The second member 201 comprises three layers, two glass layers enclosing a middle layer 209 comprised of a laminate material. As illustrated, the middle layer 209 extends beyond the two glass layers. A first cavity 202 extends through the middle layer 209 between a first surface 203 and a second surface 204. Again, an inner surface of the first cavity is polished to provide a smooth optical surface.

A primary light source can be fitted into the second member 201 in the same manner as described above for the first member 101 , by placing an infra-red laser inside the first cavity 202 of the middle layer 209. Laser light may then propagate through the middle layer 209 in the same way that it propagated through the single layer of the member 201 . Heating the middle layer 209 will also cause the surrounding glass layers to heat up, as heat is conducted from the middle layer 209 to the glass layers. In this way, the outer surfaces of the second member 201 are heated, clearing any ice or fog.

In an alternative embodiment, the glass layers may enclose the cavity in the laminate layer, such that the primary light source is contained within the glass of the member. Figure 7 illustrates an alternative location for the infra-red laser. The primary light source 306 is located outside the cavity in a third member 301 , which is in all other respects similar to the first member 101 . However, the primary light source 306 is arranged so that the third light beam 307 is directed into the cavity and towards the wall of the cavity, so that it will pass into the third member 301 and heat it in the same way as the first member 101 .

Figure 8 shows a fourth member 401 , which comprises a primary light source 406 similar to the one found in the first member. The fourth member 401 further comprises a sensor array 410, located around the edges of the member. The sensor array is designed to detect light produced by the primary light source 406. The light sensors and the primary light source 406 are communicably connected to a control unit 41 1 .

In use, the primary light source 406 produces a fourth beam of light 407 which propagates through the member to the light sensors 410. In contrast to the first beam of light 106 described in reference to figure 1 above, the frequency of the fourth beam of light 407 is chosen so that the intensity of the fourth beam of light 407 is greater than zero as it approaches the sensor array 410. The sensor array can therefore detect the fourth beam of light 410.

In the event that the fourth member 401 develops a flaw, such as a crack, this may impede the transmission of a beam of light. As such, the intensity of light detected by the sensor array 410 will drop when the fourth beam of light is directed towards the crack. The control unit 41 1 , which is communicably connected to the sensor array 410, can detect this change from the expected intensity of light detected by the sensor array 410. The control unit 41 1 then records a fault, recording the angle a of the scanning laser at which the fault was detected. This indicates which region of the member the fault occupies. Therefore, when the vehicle is serviced, the engineer performing the service can access the record of the fault and determine which region of the member they should inspect. Detecting a flaw early may allow it to be repaired more easily than would be the case if the flaw was only detected once it became more obvious.

The control unit 41 1 can also be configured to provide information to the driver of the car, so that the driver knows that they should have their member checked in the event of a fault. This could be of use to the driver since flaws in a member may not be obvious to the naked eye, but any flaws may still contribute to a weakening of the glass sheet. The sensor array 410 may comprise a plurality of sensors placed around the edges of the member. Alternatively, the sensor array may comprise a single sensor which is either large enough to cover the edges of the member or is provided with mirrors, prisms or similar to focus laser light arriving at the edges of the member onto the sensor.

The shape described by a light beam in a member according to the invention can be altered by altering the shape of the cavity and by moving the centre of rotation of the light beam with respect to the cavity. Figure 9 illustrates an example of this. A cavity 502 in a fifth member 501 is provided with a primary light source 506. The primary light source produces beams of light 507 which can be redirected by a moveable mirror which is incorporated into the primary light source 506. The beams of light 507 effectively rotate about an origin point which is forward of the centre of the cylindrical cavity 502. As such, refraction at the edges of the cavity 502 causes the light beams to tend to bend upwards in relation to the orientation of the illustration. This effect can be adjusted by moving the laser to provide the degree alteration in the shape of the lasers transmitted that is required. This can be useful, for example, in focusing the heating effects of a laser on those areas of the member directly in front of a driver. The light from the primary light source 506, or any other light source described above, can be directed as required by the provision of a mirror or prism. Such mirrors or prisms may be mobile and motorized, or fixed, as required.

Any of the members above may be adapted to a plurality of cavities and a plurality of light sources. Where several light sources are used, shaping the distribution of the light from each light source as discussed above with reference to Figure 9 may be used to reduce the overlap in regions covered by each light source.

Figure 10 shows a sixth member 601 . The sixth member 601 comprises a cavity similar to the other members described above, but the cavity in sixth member 601 is shaped so as to accept a spherical plug 612. The spherical plug 612 is made from an elastic material such that it can be compressed and pushed into position in the sixth member 601 . Once in position, the spherical plug 612 will expand into the space cut for it in the sixth member 601 , and hence remain in position during use. The spherical plug 612 contains a primary light source 606 which is mounted on a set of gears 614 which interface with the inner surface of the spherical plug 612 such that the primary light source 606 can be turned to point in any desired direction. The spherical plug 612 also comprises an inductive coil 613 which is electrically connected to the primary light source 606. In use, another inductive coil is used to immerse the spherical plug in a suitable electromagnetic field, providing power and operating instructions to the primary light source 606 and the gears 614 through the inductive coil 613. Figure 1 1 shows a drill 715 which comprises a drill bit. The drill bit comprises a first region 716, and a second region 717, the second region being divided up into three sub-regions 717a, 717b and 717c. The first region 716 and second region 717 are provided with a coating of abrasive particles such that they can cut and polish a member such as the ones described above. The first region 716 comprises a hollow cutting head, which in turn comprises a cutting surface on the forward face of the drill bit, the forward face being the part of the drill bit which first contacts the member in use, such that the cutting head will cut a circular cavity into the member quickly. The first region 716 further comprises a grinding surface, formed at least in part by the abrasive particles, which grinds on the surface of the cavity as the drill bit is used. The first region 716 further incorporates a duct, not shown, through which a lubricant, an abrasive paste or both can be pumped during the drilling process, as required. An abrasive paste helps to grind down the member, while a lubricant helps the drill to turn.

The first sub-region 717a comprises a rough grinding surface in order to widen the cavity. However the burr on the first sub-region 717a is smoother than the burr on the first region 716, in order to provide a more controlled, smoother grind. The second sub-region 717b comprises still smaller particles in order to provide a still smoother grinding surface such that the member is ground in a still more controlled and smoother fashion. The third sub-region 717c comprises smaller particles than the second sub-region, in order to provide a smoother finish, polishing the surface of the cavity, and hence providing a good optical surface.

The rate of change of the radius of the drill varies along its axis of rotation, such that a cross section of the drill which contains the axis of rotation has curved outer walls. The rate of change of the radius decreases along the axis from the first region 716. Hence the radius of the drill changes faster in the first sub region 717a than in the second sub region 717b, and the radius of the drill changes faster in the second sub region 717b than in the third sub region 717c. As such, the amount of material being removed by the grinding surface is matched to the ability of the surface to remove it; the surface is rougher where the rate of change of the radius is greatest.

As such, the drill 715 is a single axis, single pass tool. The changes to the feed rate and bit speed are minimised by changing the angle and roughness of the grinding surfaces. This helps to reduce required tool changes in use, thus saving time and cost.

The members described above may be fitted to a vehicle. For example, they may form the front or rear windscreens of a vehicle, or the side windows.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.