WO2007135375A1

WO2007135375A1 - Road stud with plastic eye

Info

Publication number: WO2007135375A1
Application number: PCT/GB2007/001807
Authority: WO
Inventors: Dave Hill
Original assignee: Industrial Rubber Plc
Priority date: 2006-05-18
Filing date: 2007-05-17
Publication date: 2007-11-29
Also published as: GB0609917D0; GB2451209A; GB0820434D0; GB2451209B; GB2438203A

Abstract

A depressible insert for a road stud includes a plastic eye comprising a corner cube reflector held in a resilient body of the insert. The insert further includes at least one resilient wiper forming part of the resilient body. The wiper serves to clean the plastic eye. The corner cube reflector is formed from a hexagonal cell pattern. The cell pattern includes at least first and second groups of cells, where the different groups of cells are configured at different orientations.

Description

ROAD STUD WITH PLASTIC EYE

Field of the Invention

The present invention relates to road studs, and in particular to a road stud with one or more plastic eyes.

Background of the Invention

Road studs are in widespread use to provide visible guidance and warnings to motorists and other road users. Such road studs typically include one or more reflectors to reflect light from vehicle headlights. The road studs help a motorist to determine his or her position on the road during hours of darkness.

There are two main types of road stud in use in the UK. The first is generally known as a "stick on", and is normally formed from a plastic unit incorporating one or more plastic reflectors (often in the form of tape). Plastic stick-on reflectors are placed on top of the surface of the road and are attached to the road by adhesive. They are relatively cheap but also have a relatively short life-time. For example, they may become detached from the road surface by passing traffic, and/or the visibility of the reflector may become reduced, for example by dirt being deposited onto the surface of the reflector.

A well-known form of plastic reflector comprises a corner-cube reflector. US 3541606 discloses plastic corner cube reflectors for a vehicle. The reflectors comprise two or more sections, where the corner cubes are aligned at differing angles to the normal of the reflector. US 5706132 discloses retroreflective sheeting involving corner cubes for use in road signs, traffic cones, etc. The corner cubes are tetrahedral and are arranged into zones, wherein the optical axes of the two zones are canted to provide different planes of enhanced reflectivity.

The other main type of road stud in use in the UK is a depressible (also sometimes referred to as a

"cat's eye"). This comprises a base unit, normally made of cast iron, which holds a resilient insert. The insert is typically made of rubber, and carries one or more glass reflectors (the "eyes"). This type of road stud is installed by drilling a hole in the road, and then bonding the road stud into location using bitumen. The inserts for depressible road studs are generally provided with one or more wiper blades. When the insert is compressed, for example because a lorry has driven over the road stud, these blades are designed to wipe across the reflectors. This helps to keep the surface of the reflectors free from dirt, and hence helps to maintain high visibility.

One example of a depressible road stud is described in GB 2263298 B. A road stud generally in accordance with this patent is sold commercially under the "Light Dome" trademark by Industrial Rubber pic, of Fareham, Hampshire. The insert described in this patent includes ducts to allow water that has collected in the base of the road stud to be applied to the wiper blades. The water helps to lubricate the wiping action of the blades on the reflectors, thereby reducing wear, as well as assisting with the overall cleaning process.

US 4854768 proposes the use of a plastic corner-cube type reflector with a depressible road stud (see also GB 2175943). The resilient insert (elastomeric core) includes a T-shaped pocket for retaining a single plastic reflector. The reflector itself comprises a flat, transparent, and very thin outer layer, made from an abrasion-resistant material such as glass. This helps to avoid the action of the wiper blades degrading the effectiveness of the underlying plastic reflector. The reflector further comprises a lens having a flat surface against the outer layer and reflector elements (such as corner-cubes) on the opposite surface. The lens is formed of plastic, such as polycarbonate. The lens is hermetically sealed to a backing member, which has a T-shape for insertion into the elastomeric core. The lens is approximately 19mm by 45mm. It is stated that the specific intensity at 0.2 degrees observation angle and 0 degrees entrance angle is five times that of a known glass eye.

The use of a glass layer to protect the plastic lens in US 4854768 significantly increases the cost and complexity of the reflector. In addition, no details are given about the design of the lens elements, and no details are provided about performance of the reflector at other (larger) entrance angles and/or other (larger) observation angles. This omission is significant since a plastic reflector for a road stud must have sufficient reflectivity to satisfy the criteria set out in British Standard BS EN 1463 (for use in the United Kingdom). In general, the reflectivity of plastic corner cube reflectors tends to decrease rapidly at higher entrance angles and higher observation angles. It therefore seems likely that the reflectivity of the road stud of US 4854768 would not satisfy the criteria of BS EN 1463 at larger entrance and observation angles.

Of course, for a stick-on plastic road stud, there is considerable flexibility in size. Accordingly, a stick-on road stud can be made larger (especially wider) to provide sufficient area to obtain the desired total reflectivity. In contrast, the size of a depressible insert is effectively fixed by the very large number of base units that are already installed into the road. It has been found very difficult to provide the required level of reflectivity from a plastic reflector within these size constraints. Consequently, the depressible road studs currently installed on roads in the UK have glass eyes.

Summary of the Invention

Accordingly, one embodiment of the invention provides a plastic eye for use with a road stud. The plastic eye comprises a plastic corner cube reflector having a front surface made of plastic. The corner cube reflector comprises a pattern of hexagonal cells, the cells being aligned substantially parallel to the surface of the reflector such that the central (diagonal) axes of the corner cubes are substantially normal to the reflector surface. The hexagonal cells are divided into first and second groups having first and second orientations respectively. The first and second orientations are configured as a mirror image of one another. Such a plastic eye avoids the need for a glass front surface while offering excellent reflectivity. For example, in one embodiment, the plastic eye has a reflectivity of at least 5 mcd.lux^"1 for an entrance angle of 15° and an observation angle of 2°, and a reflectivity of at least 50 mcd.lux^"1 for an entrance angle of 10° and an observation angle of 1°.

In one embodiment, the first and second groups of cells are separated by a central bridge, whereby all cells on one side of the bridge have the first orientation and all cells on the other side of the bridge have the second orientation. (The bridge itself need not have any physical structure, but may simply represent the boundary or border between the first and second orientations). In other embodiments, more complex configurations of the different orientations may be provided, and/or more than two different orientations may be included.

In one embodiment, the reflector surface has a generally rectangular shape with a major axis and a minor axis, and each corner cube includes a surface which is substantially parallel to the minor axis. The central bridge (if present) is substantially parallel to the minor axis. In the first orientation, the corner cube surface which is substantially parallel to the minor axis is at a first angle to the reflector surface, and in the second orientation, the corner cube surface which is substantially parallel to the minor axis is at a second angle to the reflector surface. The first and second angles are substantially equal in magnitude but opposite in sign. In use, it is expected that the major axis will be horizontal and the minor axis vertical (and light will be incident on the plastic eye from a substantially horizontal direction). The first and second groups are horizontally separated from one another and are symmetric about the vertical axis. This helps to provide good reflectivity for a range of incoming light beams.

In one embodiment, the reflector comprises at least 80 complete cells, and may comprise between 110 and 130 complete cells. Having a large number of cells such as 80 or more provides good reflectivity (for example, relatively fewer cells are impacted by being close to the edge of the plastic eye). In one embodiment, the cells have a width of less than 2.8mm, for example a width of between 2.45 and 2.3mm, in order to obtain a large number of cells within an insert that still fits into an existing base unit. (Note that this relatively small size requires very accurate machining which is comparatively expensive, but has been found to produce good reflectivity).

In one particular embodiment, the eye has dimensions of approximately 17mm by 42mm for the reflecting surface, which accommodates approximately 120 cells of width approximately 2.38mm. These dimensions are small enough to fit into an existing base unit, yet big enough to provide sufficient reflecting area to help the plastic eye satisfy the relevant reflectivity standards.

In one embodiment, the corner cube reflector is made of acrylic. It is noted that tougher and more resistant plastics are often used in the road, such as nylon, given the harsh conditions (weathering by wind, rain, etc, passing vehicles, dirt, stones, etc). However, the advantage of using acrylic for the plastic eye is that it permits more precise machining, which in turn allows smaller cells and higher reflectivity.

In one embodiment, the plastic eye further includes a backing plate with a sealed air gap between the corner cube reflector and the backing plate. The sealed air gap helps to avoid contamination of the back surface of the reflector (where reflection takes place), for example by water, dirt, etc, which can degrade reflectivity performance. In one particular embodiment, the corner cube assembly is attached to the backing plate by acoustic welding to provide the sealed air gap. (It has been found that acoustic welding provides a better seal than other forms of attachment, such as a press fit, while the use of adhesive can lead to problems with the adhesive itself contaminating the air gap).

In one embodiment, the backing plate comprises two studs for engagement in two corresponding holes in a resilient body of a reflector insert. The two studs act to hold the plastic eye in the resilient body. Providing two studs for this purpose offers significantly better retention of the plastic eye in the resilient insert. In particular, if the insert is twisted or distorted sideways, this tends to compress the insert around one of the studs, thereby holding the eye within the insert, despite any potential loosening around the other stud. In one embodiment, each stud is provided with a Hp facing away from the other stud. The lip is located at the end of the stud opposite the corner cube reflector. Each lip engages a corresponding recess in the resilient body to further assist in retaining the plastic eye in the resilient body.

Another embodiment of the invention provides a depressible insert for a road stud. The insert comprises a resilient body; a plastic eye as described above, held in the resilient body; and at least one resilient wiper forming part of the resilient body for cleaning the plastic eye.

In such an insert, it has been found that the use of a plastic eye with a flat surface changes the performance of the wiping blade(s) (compared to the wiping performance for a conventional insert with two glass eyes providing dome-like protrusions). In particular, there may be a tendency for the wiping blade(s) to apply too much or too little pressure on the surface of the eye during the wiping action. Accordingly, in one embodiment the maximum overlap between any of the wiper blades and the surface of the plastic eye to be wiped is less than lmm,' for example, the overlap may be approximately 0.5mm. This reduced overlap helps to avoid any undue distortion of the wiper blades. (Wiper blades for conventional glass eyes have a greater maximum overlap, but this maximum overlap only exists in relation to the portion of the wiper blade(s) corresponding to the maximum protrusion of the glass eyes). In another embodiment, at least three wiper blades (e.g. four wiper blades) are provided to enhance the wiping action. This set of wiper blades may all have substantially the same overlap with the surface of the plastic eye to be wiped (in contrast to existing inserts, in which the wiper blades are generally staggered).

Another embodiment of the invention provides a depressible insert for a road stud. The insert includes a resilient body and a plastic eye comprising a corner cube reflector held in the resilient body. The insert further comprises at least one resilient wiper forming part of the resilient body for cleaning the plastic eye. The corner cube reflector comprises a pattern of hexagonal cells. The cells are divided into first and second groups having first and second orientations respectively. The first and second orientations are configured such that in use the first and second groups of cells provide different horizontal distributions of reflectivity from the road stud, thereby helping the insert to meet the required reflectivity standards. (N.B. This insert may have the same preferred features as the plastic eye and/or insert described above).

The present invention also provides a road stud incorporating an insert and/or eye such as described above.

Brief Description of the Drawings Various embodiments of the invention will now be described in detail by way of example only with reference to the following drawings:

Figure 1 is a plan view of a base unit for a road stud in accordance with one embodiment of the invention;

Figure 2 is a schematic diagram of a corner cube reflector in accordance with one embodiment of the invention;

Figure 3 A is a section through a plastic eye in accordance with one embodiment of the invention;

Figure 3B is a rear view of a plastic eye in accordance with one embodiment of the invention; Figure 3C is an isometric view of a plastic eye in accordance with one embodiment of the invention;

Figure 3D is an enlarged detail of the cross-section of Figure 3 A showing more clearly the bonding of the reflector to the backplate in accordance with one embodiment of the invention;

Figure 4 is a schematic view of an insert including a plastic eye in accordance with one embodiment of the invention;

Figure 5 A is a horizontal section through the insert of Figure 4 in accordance with one embodiment of the invention;

Figure 5B is a vertical section through the insert of Figure 4 in accordance with one embodiment of the invention; Figure 6 A is a vertical section through an insert in accordance with one embodiment of the invention having a different wiper blade positioning from the embodiment of Figure 5B;

Figure 6B is a vertical section through an insert in accordance with one embodiment of the invention having a different wiper blade configuration from the embodiment of Figure 5B;

Figure 7 is a section through a plastic eye in accordance with another embodiment of the invention;

Figure 8 is a front view of a road stud with a plastic eye in accordance with another embodiment of the invention; and

Figure 9 is a side view of the road stud of Figure 8 in accordance with one embodiment of the invention.

Detailed Description Figure 1 illustrates a base unit 100 for a road stud. The base unit is designed to receive a depressible insert having one or more reflectors. The base unit 100 has a known shape, and may be made of cast iron, plastic, or any other suitable material.

Figure 1 shows a plan view of the base unit 100. For convenience of explanation, the front of the base unit (as perceived by an oncoming motorist) is indicated by the location of letter A, the rear of the base unit by the letter B, and the sides by the letters C and D. It will be appreciated nevertheless that the base unit of Figure 1 is symmetric, so that alternatively B could be considered as the front and A as the rear. This symmetry supports bi-directional operations, for example, if the road stud is to be fitted down a central line of a single carriage-way road, in which case the insert can incorporate reflectors for both directions (forwards and backwards). In other locations, such as to demarcate lanes within one carriageway of a motorway, the insert only needs to be provided with reflectors (or a reflector) facing in the forwards direction, i.e. towards oncoming traffic.

The main body of the base unit 100 includes side walls 101 and 102, front portion 106 and rear portion 107. When the base unit 100 is installed in the road, the top surface of front and rear portions 106 and 107 and also of side walls 101 and 102 protrudes slightly above the road surface. The base unit further includes a recess 110 defined between side walls 101 and 102, which is used to receive the depressible insert. Each side wall includes a pair of projections 121A, 121B, and 122A, 122B that extend into recess 110. The projections 121, 122 are used to retain the resilient insert within recess 110. The insert is sized so that when held in recess 110, it protrudes slightly above the top surface of the base unit 100. As a result, the insert is compressed by any vehicle wheel that passes directly over the road stud, thereby activating the wiper blades within the insert to clean the reflectors.

The front portion 106 of the base unit 100 is formed with a channel 116 that slopes down towards recess 110. The channel 116 helps to provide a clear line of sight to the reflector(s) located on the insert within recess 110. In addition, the channel 116 also helps rainwater to run into recess 110, where it can collect for use in cleaning and lubricating the reflector(s). The final portion of channel 116 is bifurcated by ridge 126, which helps to direct rainwater to corresponding ducts in the insert that communicate with the bottom of recess 110, where rainwater can accumulate (as described in GB 2263298). Note that the height of ridge 126 is substantially less than that of side walls 101, 102, and accordingly it has only minimal impact on the visibility of the reflector(s) provided on an insert fitted into the base unit 100. The rear portion 107 of the base unit is shaped in the same manner as the front portion 106. In particular, rear portion includes channel 117, which is bifurcated by ridge 127. It will be recognised by the skilled person that there are very many base units such as shown in Figure 1 (or of a similar size and configuration) already installed into the roads in the United Kingdom. The inserts in these installed base units are replaced as they become damaged or worn out by passing traffic, environmental conditions, and so on. Any new inserts must have a size and shape that is compatible with the base units that are already installed on the roads.

Figure 2 is a schematic diagram of a plastic corner cube reflector 200 in accordance with one embodiment of the invention. A corner cube reflector is a retroreflector, in that it returns incident light along a path substantially parallel to the path of the incident light. The corner cube reflector 200 is based on a honeycomb 205 of hexagonal cells 210A, 210B, etc formed on the back surface of the corner cube reflector 200, while the front surface of the corner cube reflector is flat. Thus incident light passes through the front surface of the corner cube reflector 200 and is reflected off the rear surface of the corner cube reflector (via total internal reflection - there is no coating on the back of corner cube reflector 200). The reflected light then passes back out through the front surface of the corner cube reflector.

Each hexagonal cell comprises three faces configured as a corner cube reflector, as explicitly shown for cells 21 IA and 21 IB (but omitted for simplicity from the remaining cells). The configuration of the corner cubes is such that the plastic is thickest (rather than thinnest) at the centre of each hexagonal cell.

The edge or frame of the corner cube reflector 200 in Figure 2 is shown by line 220. (Although Figure 2 depicts honeycomb 205 extending outside line 220, these additional cells are for ease of illustration only). The embodiment of Figure 2 comprises 122 whole cells within frame 220 to form the corner cube reflector 200. The corner cube reflector 200 also contains partial cells around the periphery - i.e. cells that are intersected by frame 220. Note that these partial cells are generally significantly less reflective than complete cells.

In one embodiment the corner cube reflector 200 is produced using the superpin electroform technology of DBM Reflex Enterprises of Quebec Canada (www.dbmreflex.com), as described for example in US 5844712. The width of each hexagonal cell is 2.38mm (prior to any shrinkage at manufacture, which might typically be of the order of 0.5%). This leads to a total width for the corner cube reflector 200 of approximately 42mm and a total height for the corner cube reflector of approximately 17mm (directions of dimensions correspond to the orientation shown in Figure 2, which also matches the orientation when installed in the road). Note that the use of relatively small cells for the corner cube reflector helps to increase overall reflectivity (one reason for this is that it reduces the proportion of partial cells within the reflector).

The corner cubes are configured such that the hexagonal cells are substantially parallel to the plane of the overall reflector. In other words, the axis through the centre of each hexagonal cell towards the (imagined) centre of the corresponding cube is substantially normal to the plane of the overall reflector. The hexagonal cells are further arranged such that they have a top and bottom edge that is parallel to the long (and, in use, horizontal) axis of the reflector. Consequently, each corner cube element contains a vertical face.

The corner cube reflector 200 is provided with a bridge, indicated schematically by line 245 in Figure 2. Note that there is no physical structure per se associated with the bridge (which might interfere with the reflectivity of the cells adjacent to the bridge). Rather the bridge represents a logical division, whereby cells on one side of the bridge 245 have one orientation, while cells on the other side of the bridge 245 have an opposite orientation. This can be seen in Figure 2, where the configuration of cell 21 IA is the mirror image of the configuration of cell 21 IB, with bridge 245 representing the line of symmetry. In particular, the vertical face of the corner cube 21 IA is directed to the right, while the vertical face of corner cube 21 IB is directed to the left.

This difference in orientation provides a different horizontal distribution of reflected light for the two portions of corner cube reflector 200 (i.e. the portion to the left of bridge 245 and the portion to the right of bridge 245). These two distributions are complementary, and help to ensure that the overall reflectivity of corner cube 200 is satisfactory across a range of angles. (Some embodiments may forego the different orientations of cells if a single orientation is found to provide satisfactory reflectivity across the relevant range of angles).

In the embodiment of the Figure 2, the cells to the left of the bridge give better reflectivity for light incident from right of centre, while the cells to the right of the bridge give better reflectivity for light incident from left of centre (this follows from the orientation of the vertical face of the corner cube in the two different orientations, and the fact that the cell pattern of Figure 2 is on the back of the reflector, as shown in Figure 3 - see below). One advantage of this configuration is that a certain portion of light incident from left of centre onto the cells on the left of the bridge is in effect obscured by the left-hand edge of the eye; in contrast, the cells on the right of the bridge are fully visible to light incident from left of centre. Conversely, the cells on the left of the bridge are fully visible to light incident from right of centre, thereby helping to maximise overall reflectivity.

Note that although the two different orientations of cells are segregated in the embodiment of Figure 2 (one to the left of bridge 245, one to the right), other embodiments may adopt different arrangements, depending on manufacturing considerations. For example, the cells of the corner cube reflector might be arranged in stripes, with alternate stripes having first and second orientations respectively.

It will be appreciated that road studs with conventional inserts generally have two glass eyes in any given direction. In contrast, corner cube reflector 200 comprises in effect only a single continuous eye (which is then logically divided into two structures by bridge 245). This allows an increased reflective area for corner cube reflector 200, and also helps to minimise the number of partial cells by reducing the ratio of perimeter to area.

In one embodiment the corner cube reflector 200 comprises acrylic. Although acrylic does not have such good wear resistance as certain other plastics such as nylon or polycarbonate, acrylic supports the provision and better definition of sharp surfaces and edges. This in turn allows better reflectivity characteristics to be obtained for the corner cube reflector.

Figures 3A-3D illustrate a plastic eye 300 in accordance with one embodiment of the invention. Figure 3 A is a section through the eye in a horizontal plane (for the normal orientation of installation); Figure 3B is a rear view (i.e. looking from the back of the reflector); Figure 3C is an isometric view; and Figure 3D is a detail of Figure 3 A to show the bonding of the eye in more detail.

The plastic eye 300 comprises the corner cube reflector 200 attached to a backing plate 320. The front surface of the reflector is flat (and made of plastic, without any further protective layer). The back surface of reflector 200 is patterned with the hexagonal cell configuration of Figure 2 (this corner cube pattern is not specifically shown in Figure 3). The backing plate includes two protruding studs 321 A, 321B, where each stud is provided with a lip 322A, 322B. The body of an insert for a road stud has holes corresponding to studs 321A, 321B. These holes are then provided with recesses for receiving lips 322A, 322B. This configuration allows studs 321A, 321B to retain plastic eye 300 within the body of an insert. The provision of two studs 321A, 321B provides improved retention for the plastic eye 300 within the insert (compared to the use of just a single stud). In particular, if the insert is distorted sideways by a passing vehicle, this will tend to loosen the insert around one stud (the stud on the side that the insert moves away from) and to compress the insert around the other stud (the stud on the side to which the insert is moved). For example, if the insert is pushed to the right, this may loosen the insert around the left-hand stud, but increase the grip on the right-hand stud. Consequently, at least one stud remains gripped tightly by the insert to retain the plastic eye 300 within the insert.

The corner cube reflector 200 includes a peripheral rim 310 that is bonded to the backing plate 320. This rim defines an air gap 315 between the hexagonal cell pattern on the back surface of the corner cube reflector 200 and the backing plate 320. In one embodiment this air gap is approximately 0.8mm across. It is important to maintain the air gap free from contamination such as by water, dirt, and so on, in order to avoid degrading the reflectivity of the corner cube reflector.

It has been found that a press or interference fit for corner cube reflector 200 to backplate 320 can lead to problems with the seal for air gap 315. It has also been found that using an adhesive to bond the corner cube reflector 200 to the backplate 320 can lead to contamination of the air gap 315 by the adhesive. Accordingly, in one embodiment the corner cube reflector 200 is provided with a V-bead 311 along rim 310 of height approximately 0.6mm and angle approximately 60° for acoustic bonding the corner cube reflector 200 to the backplate 320 (see Figure 3D). During acoustic welding, this V-bead melts to securely bond the corner cube reflector 200 to the backplate 320 to prevent contamination of air gap 315. The resulting seal is robust enough to survive the effects of weathering, passing vehicles, and so on.

Table 1 sets out the formal reflectivity requirements for a plastic reflector in accordance with BS EN 1463. Table 1 also lists the observed reflectivity results from a plastic eye 300. The tests are performed at six different entrance angles -15, -10, -5, +5, +10 and +15 degrees. This angle represents the difference between an incident beam and a normal to the plastic eye (300) (the normal is perpendicular to the plane of Figure 2). This angle is measured in the horizontal plane (i.e. left-right in Figure 2, where negative angles are to the left, and positive angles to the right). The angle of incidence in the vertical plane is fixed at 0 degrees (i.e. it is assumed that the incident light beam is horizontal for a plastic reflector having a vertical face). The observation angle is likewise measured in a horizontal plane (left-right in the context of Figure 2) and corresponds to the path of the observed reflected light. This angle is measured away from the path of incidence towards the normal. The minimum and observed reflectivity are given in millicandela per lux, corresponding in effect to the reflected luminosity as a proportion of the incident luminosity on the reflector. The two figures given for the observed reflectivity reflect the two different entrance angles - i.e. there is an observed reflectivity of 13 mcd.lux^"1 for an entrance angle of -15° and an observed reflectivity of 17 mcd.lux^"1 for an entrance angle of +15°'

Table 1

It can be seen that a plastic eye in accordance with the present invention provides excellent levels of reflectivity that clearly satisfy the minimum reflectivity values of the relevant standard. However, it should be noted that these measurements were performed on a new sample. Some margin is required to allow for degradation during use in the road (the plastic eye must still pass the minimum requirements of Table 1 after a test period in the road). It is also noted that there is some asymmetry in reflectivity performance between the left and right measurements. This may indicate a slight discrepancy between the two different orientations of the cells (which might, for example, arise from the original flow direction of plastic injection into the mould when making the plastic eye).

It will be appreciated that the values in Table 1 relate to a white light reflector. If a coloured reflector is used; then the observed reflectivity and the specified minimum reflectivity are lower. A coloured plastic eye can be obtained by using suitably coloured plastic for the body of the reflector 200 (instead of the transparent plastic used for a white light reflector). (It may also be possible to impart a small amount of colouration to the reflector by having a coloured backing plate 320, rather than a neutral colour for the backing plate).

Figure 4 shows a plastic eye 300 positioned in an insert 400 in accordance with one embodiment of the invention. The view of Figure 4 is from the front of the insert, in other words as seen by an approaching vehicle (it will be appreciated that in practice the bottom portions of insert 400 are obscured from approaching vehicles by being sunk into the base unit). In general insert 400 has a largely conventional shape, including ducts 412 as previously mentioned for facilitating the passage of water onto the surface of the plastic eye during the wiping action when the insert 400 is depressed. However, the external aperture 410 for receiving the plastic eye is increased a little (compared to certain known inserts with glass eyes) in order to accommodate the slightly larger size of the plastic eye 300.

Figure 5A is a section through an insert 400 including a plastic eye 300 in accordance within one embodiment of the invention (the section is horizontal for the normal orientation of the insert 400). The insert comprises a rubber body 401 which has a pair of holes 421 A, 42 IB facing in each direction. Each pair of holes accommodates a corresponding pair of studs 321A, 321B for a plastic eye 300. (It will be appreciated that the insert shown in Figure 5A includes a plastic eye 300 facing in one direction but no plastic eye is fitted to face in the opposite direction). As previously mentioned, each hole 42 IA, 42 IB incorporates a recess 422A, 422B at the rear of the hole. The recess receives a lip 322A, 322B from the corresponding stud 321A, 321B and acts to firmly retain the plastic eye 300 within the rubber body 401.

Figure 5B is a vertical section through the insert 400 of Figure 5 A from front to back (again assuming a normal orientation for the insert). Figure 5B shows the wiper blades 440 (omitted from Figure 5A) that are used to keep the external surface of the reflector 200 free from dirt and debris. The embodiment of Figure 5B has two wiper blades 440A and 440B. Note that wiper blade 440A is set marginally forward of the surface of reflector 200 when in the rest position shown in Figure 5B. However, when the insert 400 is depressed by a passing vehicle, wiper blade is forced inwards to engage reflector 200 (which is forced downwards).

In some embodiments, the wiping action on the flat surface of the plastic eye has been found to be somewhat less effective than for a conventional insert with two glass eyes. Thus if there is too small an overlap between the surface of the plastic eye and the edge of the wiper blades, the wiper blades may have a tendency to skid or flip over the surface of the plastic eye, which does not provide such a reliable cleaning action. On the other hand, if there is too large an overlap between the surface of the plastic eye and the edge of the wiper blades, the resistance of the wiper blades may be too strong for proper wiping.

(In contrast to the flat surface of plastic eye 300, a conventional glass eye has a hemi-spherical protruding surface. Consequently, the resistance of the glass eyes to the wiper blades decreases with blade depth. In particular, the glass eyes are widest at the bottom of the domes, corresponding to the edges of the wiper blades, reducing to zero width at the top of the domes, corresponding to a deeper portion of the wiper blades. This gradual increase in resistance with depth, plus the gap between the two eyes, allows the wiper blades to deform relatively easily over the surfaces of the glass eyes, while at the same time maintaining a good pressure for wiping on the surfaces of the glass eyes). Figures 6A and 6B illustrate two embodiments for improving the wiping performance in comparison with the embodiment shown in Figure 5B. In the embodiment of Figure 6A, the overlap of the wiper blades 440 and the surface of the reflector 200 has been reduced. In particular, the maximum overlap for the lower blade 440B is now only approximately 0.5mm, compared with an overlap of approximately 1.5mm in Figure 5B. This can be achieved either by making holes 421 deeper, so that the plastic eye 300 sits further into the body 401 of the insert, and/or by adjusting the overall dimensions of the wiper 440. The reduced overlap makes it easier for the wiper blade 440B to flex over the flat surface of the reflector 200. (In contrast, a greater overlap can be better tolerated for a conventional glass eye, since the maximum overlap only exists at the top surface of the dome for such a glass eye).

Reducing the overlap between the wiper blades 440 and the surface of the plastic reflector 200 decreases the force needed to perform a wiping action. This reduced force makes it easier for the wiping action to occur, but can make the wiping action less effective at removing dirt. Thus in the embodiment of Figure 6B, four wiping blades 440A, 440B, 440C and 440D are provided. The increased number of wiping blades for this embodiment helps to compensate for the reduced overlap between the blades and the surface of the reflector. For example, even if one blade slips or slides over a particular portion of the surface of the plastic eye, it is likely that one of the other blades will wipe this portion of the surface properly.

Figure 7 illustrates a plastic reflector 700 in accordance with another embodiment of the invention. This reflector is substantially the same as the reflector 300 of Figures 3A-3D, except that the backing member 720 is just a flat plate (without any protruding suds). Plastic reflector 700 may be used, for example, in the road stud 900 shown in Figures 8 and 9. Thus road stud 900 includes a flat base 910 that can be attached to the road by any appropriate method, such as adhesive, slotting into another base unit, etc. Road stud 900 also includes an upright member 915, which supports or mounts plastic reflector 700. The plastic reflector may be attached to the upright member 915 by any suitable method, such as adhesive (N .B upright member 915 may be shaped or profiled to better accommodate the plastic reflector 700). Although the road stud 900 has only a single reflector facing in single direction, it will be appreciated that in other embodiments, a road stud may have multiple reflectors, and these may be arranged to face in multiple directions - e.g. front and back, on both faces of upright member 915.

A road stud such as described above has now undergone road testing in the UK. Preliminary indications are very positive that the plastic reflector is going to meet the criteria of BS EN 1463, even after a period of use in the road. Indeed, it has been found that if anything, such use appears to have improved the reflectivity performance. The reasons for this are not fully understood, but one possibility might be that very minor abrasions on the front surface of the reflector help to disperse light within the reflector.

In conclusion, although a variety of embodiments have been described herein, these are provided by way of example only, and many variations and modifications on such embodiments will be apparent to the skilled person and fall within the scope of the present invention, which is defined by the appended claims and their equivalents.

Claims

1. A plastic eye for use with a road stud, the plastic eye comprising a plastic corner cube reflector having a front surface made of plastic, wherein the corner cube reflector comprises a pattern of hexagonal cells, said cells being aligned substantially parallel to the surface of the reflector such that the central axes of said corner cubes are substantially normal to the reflector surface, wherein said hexagonal cells are divided into first and second groups having first and second orientations respectively, wherein the first and second orientations are configured as a mirror image of one another.

2. The plastic eye of claim 1, wherein said first and second groups of cells are separated by a central bridge.

3. The plastic eye of claim 1 or 2, wherein the reflector surface has a generally rectangular shape with a major axis and a minor axis, and each corner cube includes a surface which is substantially parallel to said minor axis.

4. The plastic eye of claim 3 as dependent on claim 2, wherein said central bridge is substantially parallel to said minor axis.

5. The plastic eye of claim 4, wherein in said first orientation, the corner cube surface which is substantially parallel to said minor axis is at a first angle to the reflector surface, and wherein in said second orientation, the corner cube surface which is substantially parallel to said minor axis is at a second angle to the reflector surface, wherein said first and second angles are substantially equal in magnitude but opposite in sign.

6. The plastic eye of any preceding claim, wherein said reflector comprises at least 80 complete cells.

7. The plastic eye of claim 6, wherein said reflector comprises between 110 and 130 complete cells.

8. The plastic eye of any preceding claim, wherein said cells have a width of less than 2.8mm.

9. The plastic eye of claim 8, wherein said cells have a width between 2.45 and 2.3mm.

10. The plastic eye of any preceding claim, wherein said eye has dimensions of approximately 17mm by 42mm for the reflecting surface.

11. The plastic eye of any preceding claim, wherein said corner cube reflector is made of acrylic.

12. The plastic eye of any preceding claim, wherein said plastic eye further includes a backing plate with a sealed air gap between the corner cube reflector and the backing plate.

13. The plastic eye of claim 12, wherein said corner cube assembly is attached to the backing plate by acoustic welding to provide said sealed air gap.

14. The plastic eye of claim 12 or 13, wherein the backing plate comprises two studs for engagement in two corresponding holes in a resilient body for a road stud to hold the plastic eye in the resilient body.

15. The plastic eye of claim 14, wherein each stud is provided with a lip facing away from the other stud and located at the end of the stud opposite the corner cube reflector, each lip engaging a corresponding recess in the resilient body for retaining the plastic eye in the resilient body.

16. The plastic eye of any preceding claim, wherein said plastic eye has a reflectivity of at least 5 mcd.lux^"1 for an entrance angle of 15° and an observation angle of 2°.

17. The plastic eye of any preceding claim, wherein said plastic eye has a reflectivity of at least 50 mcd.lux^"1 for an entrance angle of 10° and an observation angle of 1°.

18. A depressible insert for a road stud, said insert comprising: a resilient body; the plastic eye of any preceding claim, held in the resilient body; and at least one resilient wiper forming part of said resilient body for cleaning the plastic eye.

19. The depressible insert of claim 18, wherein the maximum overlap between any of said wiper blades and the surface of the plastic eye to be wiped is less than lmm.

20. The depressible insert of claim 19, wherein the maximum overlap between any of said wiper blades and the surface of the plastic eye to be wiped is approximately 0.5 mm.

21. The depressible insert of any of claims 18 to 20, wherein the depressible insert comprises at least three resilient wiper blades.

22. The depressible insert of claim 21 , wherein the depressible insert comprises four resilient wiper blades.

23. The depressible insert of claim 21, wherein said at least three wiper blades all have substantially the same overlap with the surface of the plastic eye to be wiped.

24. A depressible insert for a road stud, said insert comprising: a resilient body; a plastic eye comprising a corner cube reflector held in the resilient body; and at least one resilient wiper forming part of said resilient body for cleaning the plastic eye; wherein the corner cube reflector comprises a pattern of hexagonal cells, said cells being divided into first and second groups having first and second orientations respectively, and wherein the first and second orientations are configured such that in use the first and second groups of cells provide different horizontal distributions of reflectivity from the road stud.

25. A road stud including the plastic eye of any of claims 1 to 17.

26. A road stud comprising a base unit and the depressible insert of any of claims 18 to 24.

27. A plastic eye for use in a road stud substantially as described herein with reference to the accompanying drawings.

28. A depressible insert for use in a road stud substantially as described herein with reference to the accompanying drawings.

29. A road stud substantially as described herein with reference to the accompanying drawings.