BACKGROUND TO THE INVENTION In order to warn the visually impaired of danger areas such as stairways or to simply indentify a particular route or direction it is known to fix raised markers along walkways.

These devices are called tactile indicators. The shape and configuration of the indicators are to a large extent set out by Australian Standards 1428. 4. With one version the indicator head is circular, approximately 35 mm in- diameter, 5 mm in height and has inclined or bevelled sides at about 45 degrees. Known indicators may also include a flange extending down from the underside of the head to anchor the devices in place. The indicator heads are designed to a size and shape which is readily sensed by the visually impaired using the foot or a cane while at the same time presenting only a minimum of interference to other pedestrian traffic. One current method of installing flanged indicators involves cutting parallel channels in the walkway surface to receive the flanges at the regulation centre-to-centre spacing of 50 mm. Such method however requires the use of an adhesive to obtain the necessary bond between the flange and the walls of the channel. Existing flanges may include protruding lugs, ribs or ledges etc. which can engage the walls of the channel to hold the flange in place temporarily until the adhesive sets and/or to improve the grip of said adhesive. It has been found in practice however that they do not provide sufficient anchoring effect alone to retain the indicator in place during use. Also the existing protrusions have ~virtually no tolerance for the unavoidable variations in the width of the channel caused by blade wear. This often results in the protrusions either completely failing to make wall contact or being so tight as to inhibit the insertion of the flange. Moreover the adhesive itself has disadvantages. It can only be applied when the channel is dry which for outside walkways reduces available workdays.

It also deteriorates over time, hampers the replacement of damaged indicators, is labour intensive and adds to the material cost of the installation.

SUMMARY OF THE INVENTION It is therefore an object of this invention to ameliorate the aforementioned disadvantages and accordingly a tactile indicator for the visually impaired is disclosed, said indicator having at least one marker head which in a position of use protrudes above a walkway surface and a flange directed downwardly from the underside of said marker head into an installation channel cut in said walkway surface, wherein a series of projections extend laterally out from the sides of said flange to produce an adhesive-free interference grip on the walls of said channel, said projections each having a rounded bulbous base surmounted by a nipple-like protuberance and said projections being at horizontally offset positions arranged across the sides of said flange.

Preferably said projections are arranged in lines which slant across the sides of the flange in opposite directions to form an inverted V.

It is further preferred that said series of protrusions are positioned directly below the centre of said marker head.

It is further preferred that said nipple-like protuberance is centrally positioned on said base.

BRIEF DESCRIPTION OF THE DRAWINGS One currently preferred embodiment of the invention will now be described with reference to the attached drawings in which:- figures 1 and 2 show perspective views from the top and underside of a set of flanged tactile indicators according to this concept, figure 3 is an enlarged perspective view of the flange projections under one marker head, and figure 4 is a cross-sectional view of a tactile indicator when fitted in place on a walkway.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to figure 1 there is a set of spaced apart circular indicator heads 1 which are linked by a common flange 2 connecting between the undersides. Although five indicator heads are shown in figure 1 the invention is not limited to any particular number. The indicators are installed by fitting the flange into a channel cut into an existing walkway surface. Typically a plurality of parallel channels are preferably cut at 50 mm centres across the installation area. Each channel is then fitted with the indicators by pushing the flange 2 down into it until the undersides 3 of the heads abut the surface of the walkway.

By virtue of the preset length of flange between adjacent indicator heads the required centre-to-centre spacing of 50 mm is automatically obtained. The indentations 4 preferably formed along the bottom edge of the flange allow it to flex in accordance with undulations in the walkway surface.

In accordance with this invention as shown in figures 2 and 3 the flange sides have a series of projections 5 arranged in an offset pattern along lines which slant across the height of said flange. With this particular embodiment as shown in figure 3 there are two lines which slant in opposite directions to form an inverted V formation. Each projection includes a rounded bulbous base portion 6 which is surmounted by a centrally disposed nipple-like protuberance 7 of reduced cross-section. The lateral extent of these projections to each side of the flange is chosen such that when the flange is pushed into an installation channel of median width the nipples chafe against the walls thereof to provide a tight mechanical grip without the use of adhesive. Although the invention is not restricted to any specific dimensions with the described embodiment the channel 8 as shown in figure 4 may be cut to a median width of about 4.5 mm and have a depth of between 8 to 15 mm below the walkway surface 8A depending upon the wear condition of the cutting blade. The preferred width for the flange 2 may be about 2.5 mm with the projections extending out to each side about 1 mm for each base 6 plus about. 6 mm for each nipple 7. As the flange is pushed into the channel the nipples chafe or abrade along individual vertical paths down the walls 9 of said channel and operate to mechanically hold the indicator heads 1 in place. By virtue of the offset arrangement of the projections each nipple creates its own path which maximises the grip it exerts on the wall. For those channels which due to blade wear are narrower (say down to 4. 0 mm) the nipples can abrade or break off completely so that the flanges can still be pushed down into the channels without undue force being required. In this case the base portions 6 directly engage and grip the walls 9. This novel shape for the projections thus enables a strong mechanical grip to be obtained over a wider range of channel widths without excessive insertion force being required.

With softer surfaces such as asphalt for example the nipples have been found to gouge out individual grooves in the channel walls as they are pressed down which further increases their holding abitity.

It is also preferred as shown in figure 2 that each set of projections is located directly under a marker head. This allows the flange at these points to be driven squarely into the channel by tapping on the flat topped marker head.

It will thus be appreciated that this invention at least in the form of the embodiment disclosed provides a novel and useful improvement in tactile indicators. Clearly however the example described is only the currently preferred form of the invention and a wide variety of modifications may be made which would be apparent to a person skilled in the art. For example the shape and dimensions of the flange and marker heads as well as the number and arrangement of the projections may be changed according to design preference.

Also while it is currently preferred to injection mould the indicator heads and flange as one piece from polyurethane the invention extends to the use of any other suitable material.

Expressions such as"down","bottom","below","above"and "horizontally"refer to the tactile indicator of this invention in one position of use as illustrated and are not to be read as necessarily limiting.