Abstract:
A retroreflector or simple reflector assembly mounted to a road, the assembly comprising a lens having a rear surface, a shell having an outer surface, the lens mounted on the outer surface of the shell, and a reflective or retroreflective sheeting disposed between the rear surface of the lens and the outer surface of the shell thereby allowing light entering the lens from vehicle headlights to reflect efficiently back to the driver of an automotive vehicle where light is emitted from the vehicle headlights. The outer surface of the shell includes a recess adapted to accept the lens, wherein the lens sits within the recess of the outer surface of the shell. The sheeting lines the recess and is disposed between the lens and the recess of the outer surface of the shell.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of U.S. Provisional Patent Application Ser. No. 61/288,687 filed Dec. 21, 2009, which is incorporated herein by reference 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to road markers. In particular, the invention relates to a road marker having a increased reflective or retroreflective characteristics due to reflective sheeting behind a lens mounted on the road marker. 
       BACKGROUND OF THE INVENTION 
       [0003]    It is known to make lenses for use in items such as reflective or retroreflective road markers which have flat surfaces on one side of the lens and a plurality of shapes such as cube corners on the opposite side. Cube corners are typically plated with vacuum depositions of aluminum or another material having high reflective properties in order to perform specular reflection to provide good reflectivity. It is also known to use a glass sheet in the front of the front surface of the lens to protect an acrylic lens from abrasion when tires pass over the surface of the lens. However, such lenses are expensive to produce. The plating process is time consuming, and it is difficult to control the quality of the plating process. 
       SUMMARY OF THE INVENTION 
       [0004]    A road marker assembly mounted to a road enabling a driver to better see road divisions, the road marker assembly comprising a lens having a rear surface, a shell having an outer surface, the lens mounted on the outer surface of the shell, and a reflective or retroreflective sheeting layer disposed between the rear surface of the lens and the outer surface of the shell thereby allowing light entering the lens from vehicle headlights to reflect efficiently near back to the originating light emitted from the vehicle headlights. The outer surface of the shell includes a recess adapted to accept the lens, wherein the lens sits within the recess of the outer surface of the shell. The reflective layer lines the recess and is disposed between the lens and the recess of the outer surface of the shell. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a perspective view of the road marker having a cutaway portion showing the sheeting; 
           [0006]      FIG. 2  is a close up view of the area shown in  FIG. 1  illustrating the positioning of the sheeting between the lens and the shell; 
           [0007]      FIG. 3  is an exploded perspective view of a portion of the lens contacting the sheeting; 
           [0008]      FIG. 4  is a diagram illustrating rays of light entering the lens and bouncing back to the viewer at predetermined angles; 
           [0009]      FIG. 5  is a cross-sectional view of an alternative embodiment showing an increased sloping angle of the lens resting within the shell; and 
           [0010]      FIG. 6  is a perspective view of an alternative embodiment showing the multiple lenses configured horizontally. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0011]    A novel lens arrangement for reflective articles such as road markers is disclosed. The lens  12  has a planar outer surface  22  and one or more inner surfaces ( 24 ,  26 ) which are covered with a retroreflective or simply reflective sheeting material  30  The lens  12  has a planar outer surface  22  and one or more inner surfaces ( 24 ,  26 ) which are covered with the sheeting material  30 . The outer surface  22  and rear surfaces  24 ,  26  are angled with respect to each other to form a prism and provide a desired angle of incidence on the sheeting  30 . Let it be understood that the sheeting  30  may have either reflective or retroreflective characteristics, this description should not serve to limit claim coverage to either reflective or retroreflective characteristics. This description should clearly serve to cover both use of a reflective or retroflective sheeting  30 . 
         [0012]    The road marker  10  has lenses  12  with inner surfaces covered with the sheeting  30  and a shell  16  having a longitudinal trapezoidal cross section. The shell  16  has a top  18  surface between a pair of stepped angled surfaces  28  formed to the lenses. The lenses  12  are secured to the shell  16  with an acceptable adhesive. Furthermore, the lenses  12  are secured to the reflective retroreflective sheeting  30  by an adhesive, and the sheeting  30  attaches to the shell  16  by means of an adhesive. The adhesives used should be suitable so as to not disrupt or compromise the specific refractive index of the lens  12 . It should be further understood that certain sheetings  30  have built in pressure sensitive adhesive enabling the requirement of having a suitable refractive index adhesive to assure continuity of light ray thru interfaces. 
         [0013]    The lenses  12  are formed of glass or suitable plastic such as acrylic. Each lens has a planar outer surface  22  and planar rear surfaces  24 ,  26 . A first rear surface  26  is angled at an angle θ R  with respect to the outer surface  22  of the lens  12 . The rear surfaces  24 ,  26  are covered by the sheeting  30  such as Diamond Grade Translucent Reflective Sheeting produced by 3M Corporation. The shell  16  further includes an inner surface defining a cavity  40  wherein the cavity  40  is filled with a potting material to improve overall strength of the road marker. 
         [0014]    An alternative embodiment of the lens  112  has a plurality of stepped portions as shown in  FIG. 5 . The stepped pattern is formed to minimize the thickness of lens  112 . The shell  116  is modified to accommodate the lens  112 . In this embodiment, the lens  112  is a one piece construction. A reflective or retroreflective sheeting  130  is disposed behind a first rear surface  126  and a second rear surface  124 . The shell  116  further includes an inner surface defining a cavity  140  wherein the cavity  140  is filled with a potting material to improve overall strength of the road marker. Because of the limitations of the plastic injection molding process it is desirable to keep the maximum thickness “T” of the lens to less than 0.150″. 
         [0015]    As shown in  FIG. 4 , light rays  50  from an approaching vehicle contacts the outer surface  22  of the lens  12  at an angle of incidence θ 1 . Light rays  50  passing through the outer surface  22  of the lens  12  are bent to an angle θ 2  which is a function of the refractive index of the material from which the lens is produced. The relationship between the angle of incidence θ 1  and angle of refraction θ 2  may be expressed according to Snell&#39;s Law as N 1  sin θ 1 =N 2  sin θ 2  where N 1  is refractive index of the material from where the light is coming and N 2  is the refractive index of the material which light passes through. For example, the refractive index for air is N 1 =1.003 and the refractive index N 2  of acrylic plastic is 1.5. Using this formula, the angle θ L  of lens  12  to road surface and the angle θ R  of the first rear surface  26  to the outer surface  22  of the lens  12  may be selected so that light rays  50  passing through the outer surface  22  of the lens  12  to contact the first rear surface  26  of the lens  12  at a predetermined desired angle θ 3 . In some cases θ 3  may be 90 degrees or may be offset from 90 degrees to interact with the reflective or retroreflective sheeting  30  material in a particular fashion. Incident light  52  is light lost and not reflected back to a user&#39;s viewing angle. 
         [0016]    The sheeting  30  has the ability to redirect light rays  50  incident upon a surface of the sheeting  30  towards its originating source, such as a vehicle. There are many types of reflective or retroreflective sheeting  30  including crystal beads, cube corners, tetrahedral cube corners, pyramid cube corners, canted cube corners, etc. The sheeting  30  generally incorporates a structured surface including at least one array of reflective elements to enhance the visibility of an object. By orientating the optics of a cube corner, the sheeting  30  may be designed to exhibit optimal performance at a specific orientation. This may be accomplished by forming cube corner elements of the sheeting  30  such that their optical axes are canted relative to an axis perpendicular to the base plane and the sheeting. Additionally, gripping members  32  are provided on the shell  16  to ease install of the road marker  10 . 
         [0017]    U.S. Pat. No. 4,588,258 discloses sheeting  30  which employs optics having canted cube corner elements which form opposing matched pairs. The sheeting  30  exhibits a primary plane of improved retroreflective performance at high entrance angles identified as the X plane and a second plane of improved retroreflective performance identified as the Y plane. The axes can be canted in either a backward negative direction or a forward positive direction. Thus when reflective sheeting is applied to a lens such as the lens of a road marker, it is desirable to direct the light through the lens to the surface of the sheeting  30  at a desired angle which will result in the light being reflected back from the sheeting  30  to maximize reflectivity. 
         [0018]    The amount of light reflected depends on the entrance angle θ 3  or angle of incidence. Thus for a −4 degree entrance angle θ 3 , the amount of light reflected is greater than for a +30 degree entrance angle. The amount of light reflected varies with the divergence angle or observation angle. Thus it is desirable to orientate the surface of the reflective material with respect to the reflective property of the material. As shown in  FIG. 4 , the angle of the rear surface θ R  is selected with respect to the light passing through the lens not only to maximize the reflectivety by selecting but also return light to the driver at a desired angle to the outer surface of the lens. Incident light  52  from the vehicle will contact the lens at θ 1  with respect to normal width of the lens surface. Light is then refracted at θ 2  according to Snells law. Then, θ R  is selected to position the inner surface of the lens at the desired θ 3  to maximize the properties of the material. Using a prism-like lens and the sheeting  30 , the angle of the lens outer surface to the road surface θ L  may be 30 degrees which is less than the conventional angle of 35 degrees. This results in a “softer” slope to the front and rear surfaces of the shell thereby making it easier for a tire to pass over the road marker, providing a softer, lower, jolt when the tire impacts the road marker. 
         [0019]    An alternative embodiment of the road marker  210  is depicted in  FIG. 6  having six lenses  212  mounted on the shell  216 . The lens  212  includes an outer surface  222  and rear surface  224 ,  226 . The outer surface  222  of the lenses  212  is angled with respect to the rear surface  226  of the lens  212  to maximize efficiency of a sheeting  230  by allowing light entering the lens  212  from vehicle headlights to reflect efficiently back to the originating light emitted from the vehicle headlights. The lens  212  is mounted to each of the angled surfaces  228  of the shell  216 . In yet another alternative embodiment, the lens  212  is a solid one piece construction lens (versus a plurality  212  lenses) extending horizontally on the angled surface  228  of the shell  216 . The lens  212  rests within the cavity  240  having a bottom wall  242  and a back wall  244 . The rear surface  224  of the lens  212  abuts the bottom wall  242  of the cavity  240 , wherein the sheeting  230  is disposed between the bottom wall  242  and the rear surface  224 . The rear surface  226  of the lens  212  abuts the back wall  244  of the cavity  240 . The lens  212  is secured within the cavity  240 , wherein the sheeting  230  is disposed between the back wall  242  and the rear surface  226 . 
         [0020]    Thus is disclosed a novel lens for an article such as a road marker which provides excellent retroreflectivity and may be produced inexpensively. The invention is not restricted to the illustrative examples and embodiments described above. The embodiments are not intended as limitations on the scope of the invention. Methods, apparatus, compositions, and the like described herein are exemplary and not intended as limitations on the scope of the invention. Changes therein and other uses will occur to those skilled in the art. The scope of the invention is defined by the scope of the claims.