WO2002041448A1

WO2002041448A1 - Reflector for road vehicles

Info

Publication number: WO2002041448A1
Application number: PCT/GB2001/005019
Authority: WO
Inventors: Gareth Liam Harris; Adrian George Garrod
Original assignee: Roke Manor Research Limited
Priority date: 2000-10-16
Filing date: 2001-11-15
Publication date: 2002-05-23
Also published as: AU2002215104A1

Abstract

A reflector is provided, which advantageously combines the functions of an optical reflector and a radar reflector, enabling objects with a low inherent radar cross-section to be reliably detected by automotive navigation systems.

Description

REFLECTORFORROADVEHICLES

At the present time, much research effort is being put into automatic or semiautomatic navigation systems for controlling road vehicles such as private motor cars. Such systems typically incorporate sensors for detecting the presence of obstacles, such as vehicles in the path of the controlled vehicle. For example, on a highway, a vehicle in front of the controlled vehicle may be travelling relatively slowly, and the controlled vehicle will have to slow to match the speed of the leading vehicle, or would have to pass it. Similarly, in town, a stationary vehicle will have to be passed if it is parked, but the controlled vehicle would have to be brought to a stop behind it if the leading vehicle is the last vehicle in a queue of traffic.

A typical system uses a radar emitter on the controlled car to emit radar signals forwards, and the controlled car will detect any returning radar signals to determine the position and relative velocity of any object reflecting the radar signals, such as the leading vehicle discussed above. Using such a system, a typical motor car may have a radar cross section (RCS) of 10 square metres. The RCS (Radar Cross Section) of a target is the area which would intercepting that amount of power which, if scattered equally in all directions, would produce an echo at the radar source equal to that from the target.

Such automated guidance systems have hitherto ignored a potentially fatal shortcoming in that low RCS road users are unlikely to be noticed by the system. For example, cyclists, wheelchair users and pedestrians will each reflect much less radar than a motor car, and their presence in the road ahead of the controlled vehicle may be ignored. The controlled vehicle will then believe the road to be clear and the vehicle will continue to travel as normal, despite the presence of a cyclist or pedestrian in the way. Similar considerations apply to animals, pushchairs and perambulators which may find themselves in the path of the oncoming traffic.

Fig. 1 shows a face-on view of a trihedral corner reflector, such as is known for reflecting radar signals. Such reflectors are commonly used, for example, on seagoing vessels to enable their position to be tracked by radar. They are composed of three conductive sheets held in mutually perpendicular planes. The shape of a corner reflector is typically that which could be obtained by a single cut, diagonally across three adjacent faces of a cube. Such devices form effective reflectors because, as shown in Fig. 2, any radar signals entering the reflector will be reflected successively from two of the surfaces, and the angles of incidence of the reflections will add up to 90°, producing an overall

reflection turned through 180°, that is, retro-reflection.

The radar reflector is typically made of thin metal sheet, such as aluminium, which is a good reflector of radar signals.

Similar optical reflectors are known but these comprise arrays of solid transparent trihedral corners and reflection is by way of total internal reflection at two surfaces of the corner. These are very widespread and are used on motor vehicles.

US Patent 6,120,154 describes a combined optical and radar reflector for motor vehicles, using a conventional corner radar reflector whose open end is sealed with a conventional optical reflector. Because of its size and weight, the reflector described in this patent is most unsuitable for mounting on cycles, pushchairs, perambulators or wheelchairs, the clothing of pedestrians or harnesses of animals. The present invention addresses the drawbacks of the existing systems, and provides a safety device for low RCS road users, as described below, preferably comprising an array of trihedral comer reflectors mounted on the road user.

The present invention provides safety device comprising a radar reflector for mounting on a vehicle, animal, person, or a portable accessory, comprising an array of comer reflectors substantially arranged in a plane.

The present invention also provides a combined radar and optical reflector comprising at least one comer reflector having internal surfaces which are also reflective to light. In such a combined optical and radar reflector for mounting on a vehicle, animal, person, or portable accessory, an array of such comer reflectors may be substantially arranged in a plane.

Each of the comer reflectors may have a depth approximately equal to the depth of the reflector. The reflector may have an area in the plane substantially equal to the sum of the sizes of the individual comer reflectors in the plane. Each corner reflector is preferably shaped as a pyramid comprising three surfaces each comprising a right angle, the right angles meeting at an apex.

The reflector may have a radar cross section sufficient to enable reliable detection by an automotive navigation system, whereas each of the comer reflectors alone may have a radar cross section insufficient to enable such detection by such a navigation system.

The comer reflectors may be contiguous in the array.

The reflector may comprise a sheet of metal pressed into a shape comprising the array of comer reflectors. Alternatively the reflector may comprise a metallic moulding having a surface including the array of corner reflectors. Alternatively the reflector may comprise an inert substrate having a surface including the shapes of the array of comer reflectors, a radar reflective coating being applied to that surface. Alternatively, the reflector may comprise a metallic member formed by deposition of a metal vapour on an appropriately shaped former, which has been removed from the former. The reflector may further comprise an optically-opaque, radar-transparent covering over the reflective side of the reflector.

Alternatively, the combined radar and optical reflector may further comprise an optically- and radar- transparent covering over the reflective side of the reflector. Such covering may be coloured to provide coloured reflected light in response to incident white light.

Any such covering may be a planar covering retained in place over the reflective side of the reflector by a retaining means. Alternatively, it may be shaped to fill the contours of the reflective side of the reflector. In this case, the covering may be applied as a liquid which hardens in contact with the reflector. Alternatively, the covering may be is separately moulded or pressed and applied to the reflector in its solid state.

The reflector may be composed of a flexible material.

The reflector may comprise substantially non-flexible comer reflectors mounted on a flexible backing.

The reflector may further comprise attaching means for attaching the reflector to a vehicle, an animal, a pedestrian or an accessory to be carried by or on any of them.

The present invention also provides a method of increasing the likelihood of detection of a vehicle, animal or person by an automotive navigation system, comprising the steps of applying a reflector as described to the vehicle, animal, person, or an accessory to be carried by or on any of them. The present invention also provides a method of manufacturing a radar reflector for mounting on a vehicle, animal, person, or accessory^' to be carried by or on any of them, comprising forming an array of comer reflectors substantially arranged in a plane.

The present invention also provides a method of manufacturing a combined radar and optical reflector comprising applying an optically reflective surface to the interior surfaces of at least one corner reflector.

The reflector may be mechanically mounted onto the rear of a cycle, or it may be worn on the clothing of a pedestrian, a harness of an animal or mounted on an accessory such as a bag, walking stick, pushchair, perambulator or wheelchair. The above, and further, objects, characteristics and advantages of the present invention will become more apparent with reference to the following description of certain embodiments of the invention, given by way of example only, in conjunction with the accompanying drawings, wherein:

Fig. 1 shows a conventional trihedral radar reflector; Fig.2 shows signals reflected by the reflector of Fig.1 ;

Fig.3 shows a face-on view of a reflector of a reflector of the present invention;

Figs. 4-7 show cross-section of reflectors according to certain embodiments of the present invention;

Figs. 8A, 8B show face-on and cross-sectional views of a radar reflector according to an embodiment of the present invention in a protective enclosure, ready for mounting on a vehicle such as a cycle, pushchair, perambulator, wheelchair or the like; and Figs 9A, 9B show face-on and cross-sectional views of a radar reflector according to an embodiment of the invention, suitable for mounting on belts, harnesses, and the like for carrying on persons or animals. A typical automated vehicle guidance system uses 76 to 77 GHz (0.0039 metre wavelength (lambda)) radar. To produce a reflector similar to that shown in Fig.l, and having an RCS of 10 square metres, the reflector would need to have an effective area

of: sqrt(10*lambda**2/(4*pi)), that is, 0.0035 square meters, or about 6cm square.

A corner reflector of this size would have a triangular end-shape with a side of about 9cm, and be cut from a cube having sides of about 6.5cm. The reflector would have a depth of about 3cm). As can be appreciated, such a reflector would be rather inconvenient for mounting on a person or animal, and would disadvantageously occupy space on a cycle, pushchair, perambulator or wheelchair.

Furthermore, such a reflector could become soiled with mud, rendering it inefficient, and possibly ineffective, particularly if mounted over the rear wheel of a bicycle, which is a popular location for the mounting of optical reflectors. According to a first aspect of the invention, the reflector is rendered more practical for mounting on a cycle or on the person, etc. Instead of providing a single comer reflector, as shown in Figs 1-2, the first aspect of the invention provides an array of much smaller reflectors, as illustrated in Figs. 3 and 4. Since the RCS of the reflector 10 (i.e. its effectiveness), depends on its effective surface area, such an array of small reflector cells 12 may be just as effective as a single large reflector of the same effective area. However, the thickness t of the reflector will reduce according to the size of each individual reflector cell 12. This is clearly shown in Fig. 4, which is a cross-section of the reflector shown in Fig.3, taken along the line A- A'. The result is a much thinner, flatter reflector which may more easily be mounted on cycles, clothing and the like, yet which still has a sufficiently large RCS.

Fig. 3 shows one possible arrangement, suitable for use as a radar reflector for a cycle or pedestrian. The dimension of the reflector in the direction A- A' would be about 7.8 cm to achieve an effective area of 0.0035m². With such dimensions, each cell 12 would have sides 14 of length 2.25 cm, and the reflector would have a depth of about 0J cm. Different sizes and shapes of reflector could, of course, be used. The radar reflector cells do not all have to be contiguous.

A flange 16 is provided around the perimeter of the reflector of the invention. This is optional, but is useful in mechanical assembly and mounting of the reflector, as discussed below.

A second aspect of the present invention reduces the likelihood of the radar reflector becoming filled with dirt for example when mounted on a cycle.

According to this second aspect of the present invention, a layer of radar- transparent material is placed over the reflective side of the reflector. Figs 5 A and 5B illustrate alternative embodiments of the invention which incorporate this second aspect.

In Fig. 5A, a planar sheet 20 of radar transparent material is placed over the reflector 10. This sheet may be of a material such as glass; polycarbonate, acrylic, ABS, polytetrafluoroethylene resins; or other plastics material, but may be of any material which is transparent to radar signals of the appropriate frequency. The material should be weather resistant to prevent deterioration when used on a road vehicle, pedestrian etc. The sheet is preferably sealed to the reflector at its edges, for example by locally heating the flanges 16 of the reflector to melt the adjacent portion of a plastic sheet 20, and to bond with it on cooling. Alternatively, the sheet may be glued onto the flange 16.

In Fig. 5B, a layer 24 of radar-transparent material is applied to the reflector 10, but in this case, one surface 26 of the layer conforms to the contours of the reflector, while the other, outer, surface 28 of the layer is substantially planar to resist the accumulation of dirt and facilitate cleaning. The layer may be of polycarbonate, acrylic, ABS, polytetrafluoroethylene resins or other plastics material, but may be of any material which is transparent to radar signals of the appropriate frequency. The material should be weather resistant to prevent deterioration when used on a road vehicle, pedestrian etc. The layer 24 may be applied as a liquid, such as a thermoplastic or thermosetting resin, or may be moulded or stamped into shape before being combined with the reflector as with the sheet 20 of Fig. 5 A.

Such layers 20,24 perform multiple functions. Firstly, they protect the radar reflector 10 from dirt, ensuring that the comer reflector cells 12 retain full efficiency. Dirt may accumulate on the outside of the layer, but will be easy to remove due to its planar surface. The layer will reduce possible corrosion to the surface 18 of the reflector cells 12 by preventing or substantially reducing the likelihood of the ingress of water, dirt, salt etc which could otherwise cause corrosion.

In accordance with a third aspect of the present invention, the interior surfaces 18 of the radar reflector cells 12 are composed of, or coated with, a material which is reflective to both radar signals and visible light. For example, the reflector may be made of polished aluminium, or copper, possibly coated with a protective layer. Alternatively, a reflective coating such as aluminium, chromium or silver may be applied, before or after the reflector attains its final shape. This allows the reflector of the present invention to function as a radar reflector to enable the cycle, person, animal etc. to which it is attached to be detected by a vehicle navigation system, but also allows the reflector to reflect light, for example from the headlights of a motor vehicle, ensuring that the cycle, pedestrian or animal etc. can easily be seen by drivers of passing motor vehicles during the hours of darkness. This aspect of the invention provides increased road safety when used in conjunction with clothing or equipment such as walking sticks or harnesses for pedestrians and animals, or such articles as pushchairs, perambulators and wheelchairs.

In a particularly preferred embodiment, the features of the second and third aspects are used in combination, to provide a reflector which conforms to the relevant laws and regulations for use as an optical reflector, and may replace the reflectors presently used on bicycles, for example. This would avoid overloading the rear of vehicles such as bicycles with safety devices and would add the safety feature that the bicycle etc. will be easily detectable by a radar based automatic navigation system. For such applications, a sheet 20 or layer 24 such as shown in Figs. 5 A or 5B is preferably used. The material of the layer, such as polycarbonate, may preferably be coloured red, yellow, orange or amber, for example, as appropriate. The layer may be made of the same material that is currently used for making prismatic optical reflectors for road vehicles. Any plastics or glass material may be used, provided that it is transparent to visible light of the appropriate wavelength and to radar signals of the appropriate wavelength. As discussed above, the material should be weatherproof, resistant to corrosion, easy to clean and should be bonded to the radar reflector at least around its perimeter flange 16. As an alternative, a coloured coating may be applied to the surface of the reflector, and a colourless sheet 20 or layer 24 may be used.

Furthermore, the sheet 20 or layer 24 may be omitted if a coloured coating is applied to the reflector, or if coloration of the reflected light is not required. Current optical reflectors for motor vehicles have a cell side length (analogous to

14 in Fig.3) of about 3mm. That is, the reflectors are based on cubes of side 2mm. It may not be possible to reduce the cell side length 14 of the radar reflector 10 of the present invention to this size. At the edges 14 in the reflector, that is, where the various planes of each comer reflector cell 12 meet, and where the edges of adjacent reflector cells 12 meet, reflection is imperfect. By reducing the size of the cells, the proportion of the radar reflector which is occupied with these edges increases, degrading the overall efficiency of the reflector. In addition, smaller comer reflectors may be more directional. A certain degree of directionality is beneficial, in that radar signals from following vehicles are reflected back, warning of the presence of the cycle, pedestrian etc, but cycles placed on the pavement or in an adjacent traffic lane should not be detected so strongly. However, the directional characteristic should not be allowed to become so pronounced that a bicycle, etc will be ignored merely because it (or rather the reflector) is oriented in a slightly different direction from the following vehicle.

There are therefore conflicting requirements for a thin reflector, which is efficient and not overly directional.

The reflectors of the present invention may be manufactured in a variety of ways. Conventionally, large comer reflectors are constructed from a flat sheet of metal which is cut and bent into shape before being welded or otherwise fastened into the required comer shape. Such method is unlikely to be suitable for the small size comer reflector cells 12 of the reflector of the present invention.

The reflectors of the present invention may be made by pressing a sheet of thin metal, such as aluminium, between suitably shaped dies. The dies may need to have somewhat rounded edges, leading to rounded edges 14 of the reflectors, to avoid puncturing the pressed sheet. Such method would produce a reflector similar to that shown in cross-section in Fig.4.

The reflectors may be moulded. For example, liquid aluminium may be poured into a mould having a suitably shaped lower surface, to produce a solid reflector having a flat rear surface, such as is shown at 30 in Fig. 6.

In any of these types of reflector, the surface 18 may be reflective tp light, either by virtue of the materials chosen, or by the addition of a surface coating, for example in polished aluminium or chromium. The modifications shown in Figs, 5A, 5B may also be made. In an alternative method, a former corresponding to the shape of the reflector may be made of some inert material, and a conductive material such as aluminium deposited upon it, for example by physical or chemical vapour deposition. If such deposition is thick, the deposited material may then be released and a reflector such as shown in Fig 4 will be produced. Alternatively, a thin layer of conductive material may be deposited, and left on the former, and the combination may be used as a reflector. Fig. 7 shows such a combination 40. In this instance, the material of the former 42 is of little importance, and its only required properties are that its surface is capable of supporting the deposition of the material of the conductive layer 44, and is weather resistant, where necessary. In either case, the cover sheets or layers as shown in Figs 5 A or 5B, or a coloured coating, may be applied.

In similar method, the former is of a material which is transparent to the appropriate wavelengths of radar and light, but is able to withstand the conditions required for chemical of physical vapour deposition of a conductive and reflective material such as aluminium, chromium or silver. The former may be of a plastics material such as polycarbonate, or glass, coloured if required. The former is shaped as the layer 24 in Fig 5B, and a layer of the conductive material is deposited onto the former, and will conform to the shape of the former, forming a reflective surface corresponding to the reflector 10 of Fig. 5B. The former and the applied conductive layer then together form a combined optical and radar reflector.

The flange 16 illustrated in the figures is optional, but is advantageous in the mechanical assembly of the reflectors of the present invention. The flange may be of any required size, and may be of a different shape from the active radar reflective portion. For example, for aesthetic reasons, it may be desired to have the reflector appear rectangular, but to have a hexagonal functional part. This may simply be achieved by having a square cover sheet 22 or layer 24, possibly in conjunction with a rectangular flange 16

The reflectors, of whatever type, are preferably mounted within some kind of protective enclosure, or at least are provided with some means for mechanically attaching them to the desired object. Radar reflectors made by deposition of a conductive layer will most likely require mechanical protection, whereas radar reflectors made by pressing a sheet of metal may be strong enough to be left exposed. Figs. 8 A, 8B show a two-part metal mounting 51, 52 which may be secured by screws 54 or other fastenings. It may be more cost effective to use moulded plastic mounting parts, and possibly even a single moulded plastic part into which the reflector of the invention snap-fits. Fig. 9A, shows a face-on view of a reflector 90 according to the present invention. Fig. 9B shows a cross-section along line DCB - IXB of Fig. 9A. The radar reflector 92 and a cover sheet 94 are held by a resilient semi-rigid plastic moulding 95, which clamps sheet 94 and flange 16 together by action of resilient retaining lip 96 which is referenced to the rear surface of radar reflector 92 at the rear portion of moulding 95. Preferably, the surface 18 is reflective to light and radar, and the sheet 94 is transparent to light and radar. It may be coloured if required. End portions 98 enable the reflector to be attached to a belt, harness or strap for mounting the reflector on a person, animal or vehicle.

As an alternative to the use of a coloured sheet 94, a coloured coating may be applied to the reflector surface, and a colourless protective sheet 94 used. Alternatively, the protective sheet may be omitted if a coloured coating is applied to the reflector, of if no coloration of the reflected light is required.

The reflectors of the present invention preferably have an effective area of about 35 square centimetres. They preferably also have a depth of less than 1cm. Other applications could involve fixing the reflectors of the present invention to barriers, such as entry and exit control barriers for car parks, level crossing gates, or any obstacle to traffic flow which has a low inherent radar cross section.

In a different domain of application, the reflectors of the present invention may be applied to persons or objects to assist in their location by search parties.

Claims

CLA S:

1. A safety device for low RCS road users comprising: a radar reflector for mounting on a vehicle of low inherent radar cross-section, animal, person, or accessory to be carried, pushed or pulled by any of these, itself comprising: an array of comer reflectors substantially arranged in a plane.

2. A safety device according to claim 1 comprising: - a combined radar and optical reflector wherein: at least one of the comer reflectors has internal surfaces which are also reflective to light.

3. A safety device according to any preceding claim, having a radar cross section sufficient to enable reliable detection by an automotive navigation system, whereas each of the corner reflectors alone has a radar cross section insufficient to enable such detection by such a navigation system.

4. A safety device according to any preceding claim wherein each of the comer reflectors has a depth approximately equal to the depth of the reflector, and wherein the reflector has an area in the plane substantially equal to the sum of the sizes of the individual comer reflectors in the plane.

5. A safety device according to any preceding claim wherein each comer reflector is shaped as a pyramid comprising three surfaces each comprising a right angle, the right angles meeting at an apex.

6. A safety device according to any preceding claim, comprising a sheet of metal pressed into a shape comprising the array of comer reflectors.

7. A safety device according to any preceding claim, comprising a metallic moulding having a surface including the array of corner reflectors.

8. A safety device according to any of claims 1-5, comprising an inert substrate having a surface including the shapes of the array of comer reflectors, a radar reflective coating being applied to that surface.

9. A safety device according to any of claims 1-5 comprising a metallic member formed by deposition of a metal vapour on an appropriately shaped former, which has been removed from the former.

10 A safety device according to claim 2 or any claim dependent on claim 2, further comprising an optically- and radar- transparent covering over the reflective side of the reflector.

11. A safety device according to claim 10 wherein the covering is coloured to provide coloured reflected light in response to incident white light.

12. A safety device according to claim 11 wherein the colour is selected according to regulations pertaining to optical reflectors used in conjunction with vehicles, animals and/or pedestrians.

13. A safety device according to claim 11 or claim 12 wherein the colour is one of red, yellow, amber, and orange.

14. A safety device according to any of claims 10-13 wherein the covering is a planar covering retained in place over the reflective side of the reflector by a retaining means.

15. A safety device according to any of claims 10-13 wherein the covering is shaped to fill the contours of the reflective side of the reflector.

16. A safety device according to claim 15 wherein the covering is applied as a liquid and hardens in contact with the reflector.

17. A safety device according to claim 15 wherein the covering is separately moulded or pressed and is applied to the reflector in its solid state.

18. A safety device according to any of claims 10-13 wherein the covering is a coating applied to the light-reflective surface(s).

19. A safety device according to any preceding claim, composed of a flexible material.

20. A safety device according to any of claims 1-18, comprising 5 substantially non-flexible corner reflectors mounted on a flexible backing.

21. A safety device according to any preceding claim further comprising attaching means for attaching the reflector to a vehicle of low inherent radar cross- section, an animal, a pedestrian or an accessory.

10

22. A method of increasing the likelihood of detection of a vehicle, animal or person by an automotive navigation system, comprising the steps of applying a safety device according to any of claims 1-21 to the vehicle, animal or person or an accessory to be carried, pushed or pulled by one of these.

15.

23. A method of manufacturing a safety device according to any of claims 1- 21, comprising forming an array of comer reflectors substantially arranged in a plane.

24. A method according to claim 25 for manufacturing a safety device 20 comprising a combined radar and optical reflector, further comprising applying an optically reflective surface to the interior surfaces of at least one of the corner reflectors.

25. A method according to any of claims 23-24, comprising the step of pressing a sheet of metal into a shape comprising the array of corner reflectors.

26. A method according to any of claims 23-24 comprising the step of producing a metallic moulding having a surface including the array of comer reflectors.

27. A method according to any of claims 23-24 comprising the step of applying a radar reflective coating to a surface of an inert substrate, that surface including the shapes of the array of comer reflectors.

28. A method according to any of claims 23-24 comprising the steps of: - forming a metallic member by deposition of a metal vapour on an appropriately shaped former, followed by - removing the metallic member from the former.

29. A method according to any of claims 23-28 further comprising the step of applying an optically- and radar- transparent covering over the reflective side of the reflector.

30. A method according to claim 29 wherein the covering is coloured to provide coloured reflected light in response to incident white light.

31. A method according to claim 30 wherein the colour is selected according to regulations pertaining to optical reflectors used in conjunction with vehicles, animals and/or pedestrians.

32. A method according to claim 30 or claim 31 wherein the colour is one of red, yellow, amber, and orange.

33. A method according to any of claims 29-32 wherein the covering is a planar covering, and is retained in place over the reflective side of the reflector by a retaining means.

34. A method according to any of claims 29-32 wherein the covering is shaped to fill the contours of the reflective side of the reflector.

35. A method according to claim 34 wherein the covering is applied as a liquid and hardens in contact with the reflector. ■

36. A method according to claim 34 wherein the covering is separately moulded or pressed and is applied to the reflector in its solid state.

37. A method according to claim 34 wherein the covering is a coating applied to the light-reflective surface(s).

38. A method according to any of claims 23-37, further comprising the step of mounting substantially non-flexible comer reflectors onto a flexible backing.

39. A method according to any of claims 23-38 further comprising providing mounting means attached to the reflector, for attaching the reflector to a vehicle of low inherent radar cross-section, animal, person, or accessory to be carried, pushed or pulled by any of these.

40. A safety device as claimed in any of claims 1-22, having an effective area of about 35cm² and a depth of less than 1cm.

41. A safety device substantially as described and/or as illustrated in Figs. 3 et seq. of the accompanying drawings.

42. A method substantially as described and/or as illustrated in Figs. 3 et seq. of the accompanying drawings.