CA1113440A - Retroreflector - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A multi-sided retroreflective body is disclosed having at least two retroreflective substantially planar faces adapted to intercept light that is to be retrore-flected. Each face has a predetermined angular relation-ship with the other and each contains a plurality of light-reflecting units and each unit comprises three mutually perpendicular surfaces. Each of said at least two retroreflective faces is tilted in the same general direction about a lower portion angularly away from a vertical plane and is angularly related in a horizontal plane with respect to another vertical plane disposed substantially at right angles to the direction of said light to define said angular relationship. All four of said angles are so interrelated as to make said at least two retroreflective faces substantially optically equivalent, such that light passing through said another vertical plane is retroreflected by both of said two retroreflective faces in return paths substantially parallel to that of the intercepted light.

Description

~ 3~

This application is a division of Canadian ~pp1 iC?~' Ot7, 288,403 filed October li, 1977.
This invention rclates to a retrorefleetor which may be ~I.sed wherever licJht refleetion is desi-ed. ~ leading applieation of the retrorefleetor is as a retro-refleetive element of a roadmarker to provide direetional guidance, and therefore it is deseribed with respeet to this use.

Roadmarkers are mounted on the surfaee of a roadway, sueh as along its eenter line or shoulders, to delineate paths or lanes for traffie, or at interseetions to define stopping lines or eross-lanes for traffie, both vehieular and pedestrian. Markers of this type are mounted in spaeed apart relation and serve to guide trafic in followinc3 or traversing a roadway, or in following ~
eurve or grade in the roadway. Partieularly to assist a driver of a vehiele at night, these mar~ers have light refleetors whieh eateh and return ineident beams of light from vehiele headlights baek toward the souree of the light. Sinee automobiles of recent vintac3e hav~
quite powerful headlights, the use of roadmarkers has beeome more widespread. Roadmarkers contribute to traffic - ` safety such as when roads are wet from rain. Under eertain eonditions, such as fog, roadmarkers ean be the on'y means of orienting a driver to a ehanc~in~ direction of a rGad.
~any forms of lic~ht reflectors have been suc3c3e~ted.
They usually suffer from one or more limitations, SUCII as reflcetinc~ too small a proportion of ineidcnt lic~l~t ~hile an approac}~in~ vehicle is st-i)l at an appreei~b]e c~is~anc~
As a result, Leflectillg l~larke~-s are of~en llOriC~ 00 c) late by a driver to be of substantial help.
Further, in order to avoid making a roadmarker an obstruction on the road, the marker preferably is designed to protrude only a slight amount from the road. This requirement augments problems of light reflection. Plain ceramic or plastic markers have been used, but they tend only to scatter the light. Light scattering is self-defeating in that it is accompanied by loss of intensity of the reflected light which materially reduces the effectiveness of the marker.
An effective reflecting system is a well known triple mirror reflex reflecting principle, and which is referred to in the art as a cube-corner structure. While a cube-corner structure provides satisfactory performance as to light striking perpendicularly against an array or strip of cube-corners, that is, generally parallel j to the axes of the cube-corners, this performance falls off rapidly as incident light enters at angles away from the normal to the surface of the cube-corner array.
According to the present invention there is provided a multi-sided retroreflective body having at least two retroreflective substantially planar faces adapted to intercept light that is to be retroreflected, each face having a predetermined angular relationship with the other and each containing a plurality of light-reflecting units, each unit comprising ~hree mutually perpendicular surfaces, each of said at least two retroreflective faces being tilted in the same general direction about a lower portion angularly away from a vertical plane and being angularly related in a horizontal plane with respect to another vertica] plane disposed substantially at right angles to the direction of said light to define said angular c~
relàtionship, all four of said angles being so inter-related as to make said at least two retroreflective faces substantially optically equivalent, such that light passing through said another vertical plane is retro-reflected by both of said two retroreflective faces in return paths substantially parallel to that of the inter-cepted light.
In one form, the retroreflector comprises a body having at least two and preferably three retroreflective, substantially planar faces adapted to intercept light that is to be retroreflected. The faces are angularly related to different vertical planes as well as to each other in a - horizontal plane. In particular, each reflective face is tilted in the same general direction about a lower portion angularly away from its vertical plane and form an acute I angle in a horizontal plane with respect to another ; vertical plane that is disposed substantially at right angles to the path of the incident light. ~11 four of the angles involved are so interrelated as to make the planar faces substantially equivalent, such that light retrore-flected by all of the substantially planax faces is retro-reflected in paths substantially parallel to that of the incident light.
In a preferred form, a retroreflectiv~ substantially planar ~ace may comprise a light-transmitting layer, formed ~or example from a light-transmitting organic polymeric resinous material, having a plurality of light-re~lecting units The light-transmitting layer may be in the form of a sheet having front and back, opposed, substantially parallel faces, the front face being the substantially planar face referred to and defining a light-refracting surface. The bacK face of the sheet contains Cj ~ii3~

the plurality of light-reflecting units formed directly into the back face. The reflecting units, themselves, may comprise three mutually perpendicular surfaces, such as a cube corner or a trihedral angle of a rectangular parallelepiped. In either case, the reflecting units are preferably coated with metal to aid in their reflecting function.
The angular relationship between the substantially planar faces of a present retroreflector can be mathe-matically expressed for ideal conditions for two or more contiguous, cooperating faces.
In the accompanying drawings:
Figure 1 is a perspective view of a roadmarker containing in sheet form a retroreflective element of the present embodiment;
j Figure 2 is a cross-section of Figure 1 on the line ,; 2~2;
¦ Figure 3 is a greatly enlarged, fragmentary view of ¦ the retroreflective sheet of Figure 2,and illustrates light-reflecting units in stepped rows or tiers;
Figure 4 is a view of Figure 3 on the plane of the line 4-4, Figure 5 is a view similar to Figure 3 and shows the retroreflective route a beam of light may take with that embodiment;
Figure 6 is a greatly enlarged, fragmentary view, similar to Figure 3, of a modified form of the present retroreflector;
Figure 7 is a view of Figure 6 on the plane of line 3~ 7-7; and Figure 8 is a view similar to Figure 6 and shows the retroreflective route a beam of light may take with that embodiment.

Figures 9, 10 and ~ ~e~n, front and side elevational views, respectively, of a roadmarker embodying one form of the present invention having two cooperating retroreflective, substantially planar surfaces.
Figures 12 and 13 are views of Figure 9 on the plane of the lines 12-12 and 13-13, respectively;
Figures 14, 15 and 16 are plan, front and side elevational views, respectively, of a roadmarker embodying another form of the present invention having two sets of three cooperating retroreflective, substantially planar surfaces;
Figures 17 and 18 are views of Figure 14 on the planes of the lines 17-17 and 18-18;
Figure 19 is a cross-section of Figure 14 on the line 19-19.
Referring to the drawings and initially to the embodiment of Figures 1 throuyh 5, a roadmarker comprises a generally truncated pyramidal body 10 having cut-away portions 11 at two opposite sides to form a slope 12 (Figure 2) and adjoining sidewalls 13 at each opposite side in which retroreflective elements 14 of the present invention are seated. The body 11 and retroreflective element 14 may be fabricated from any suitable material, such as a ceramic or synthetic resinous plastic material, although the retroreflective element must be sufficiently clear to trallslllit li(3ht. ~ody 11 may be suitably mo1ded from any known ceramic, glazed and pigmented if desired to impart color, or from any other durable, weather resistant material. The retroreflective element 14 may also be fabri~ated from any durable, lic;ht-transmitting, weather-resistant material, such as glass,-but preferably is made from synthetic resins such as polycarbonates and especially from the acrylates like polymethacryIate and polymetllyllllethacrylate resills. Retror~flective element 14 may be tinted, if desired, to reflect red, yellow or other light, especially if used in a roadmar~er.
Referriny more particularly to the retroreflecti.ve element of Figures 1 through 5, this component is in the form of a sheet havin~ front and back, opposed, sub-stantially parallel faces indicated at 15 and 16, . respecti.vely. Front face 15 is substantially smooth and defines a light-refracting surface. Back face 16 has a plurali.ty of li.ght-reflcctin~ units general.lv represented at 17 which prefcrably are forrned diIectly i~to the back face by a suitable mold, forming dies, or the like from an original planar faceindicated by the broken, imaginary line 18 in Figure 3, such that preferab~y the outer corncrs o~ the units 17 arc coplanar wi.t~ linc 18 as illustrated. Here and elsewhere in the drawing, it will be apprcciated that the light reflecting units are shown greatly oversi~e to facilitatc their illustration an~
descri~tion.
To aid in their ref].ecting function, lic~ht-reflectinc~ units 17 may be coated wi.til metal or metc~ .ed in a manner known in thc art to form a metalli.c la~er 19 (~ic3UrC 2). ~luminum ;..S thc prcfc-rc~d metal for this purpose. ~n adhesive 20 Iills the vo]ume J>etween slo~e ~i3'~

12 of the roadmarker and light-reflecting units 17 to secure the retroreflective element 14 in place in cut-away portions 11. A wide variety of adhesives may be used for this purpose such as natural adhesives like glue, bitumen, etc., or resinous adhesives like epoxy, polyester or polyurethane resins. Indeed, the same adhesives can be used to secure roadmar~er 10 to a surface of a road, although catalyzed thermosettiny adhesives are preferred for this purpose.
~onsidering no~ in greater detail the retro-reflective element itself, it will be apparent that the element can be used alone in sheet form as illustrated by Figures 3, 4 and 5, or as part of any support, such as a roac~arker, sign, or the like, from which retro-reflection of light is desired. In order to provide the improved retroreflection of the present invention, tlle retroreflective sheet must be anyled with resp~ci to approachiny incident pencils or beams of light. The light itself may be traveling in any direction and in any plane. To relate the relaiivc position of the retroreflective sheet 14 to approaching light which is yenerally considered to travel in straight lines, the retroreflective sheet of the presellt invention should he disposed in an anyled position such that a normai, that is a.line perpendicular to the sheet, is at an angle or about 5 to about 85, and preferahly from about 30 to about 85, from an incident bearll o~ light. ~CCOld-inyly, if line 21 in ~ic,u-e 3 repr~sel-ts a norillal t~ r~_ J

front facc 15 of the retroreflective sheet, the sheet is in position to rcceive and retroreflect light approaching the sheet within the angle A which represents an angle of about 5 to about 85 from li.ne 21.
In practice, the retrorefl~ctor is usually positioned to receive and retroreflect light traveling generally in a horizontal plane, s~ch as in a road sign or a roadmarker. While the above described angulation is important and paramount in all forms of the present invention, as a further i.ndication of the angulation involved and ~hen the retroreflector is used to intercept horizontally traveling light, the anyle B sheet 14 makes with the horizontal may be within the range of about 5 to about 60~. When the retroreflector lS part of a road-marker the angle B sheet 14 makes with the horizontal may be within the range of about 15 to about 45, since a roadmarker is normally lower in elevation with respect to the approaching light. However, these angulations are secondary to the angulation described in the proceeding paragraph which controls in all cases.
The back face 16 of retroreflective sheet 14 com-prises light--reflecting units generally repres~nted at 17 in the embodiment of Figure 3, which, in order to achieve the improved efficiency of retroreflection afforded by the present invention, cover an appreciable area of the back face and preferably are cocxtensivc with that fa-c.
The resulting array of light-reflecting units provides a more evell distribution of light reflectioll with lit je or no blind spots. The array of all the 1ight reflecting ~i 3~

units forms a multifaceted reflecting surface which totally retroreflects light in a particular direction.
In a preferred form, the array of light-reflecting units are stacked to form a series of steps or rows 22 of units which extend transversely across back face 16.
As shown in Figure 3, when the retroreflectlve sheet is in use and angled as previously described, rows 22 are laterally spaced from one another due to their generally vertical disposition. It is, therefore, not merely a matter of stacking rows 22 atop one another; rather, they must be laterally offset with respect to each other as shown. While size is not critical, light-reflecting units 17 have been shown oversized in the drawing for purposes of illustration. In one embodiment, each row was about 1/16 inch in height and the rows were spaced laterally (or horizontally as viewed in Figure 3) about 1/16 inch.
The embodiment of Figures 3, 4 and 5 illustrate the preferred form of light-reflecting units, while the embodiment of Figures 6, 7 and 8 represents a modified form. The light-reflecting units of both embodiments may generally be considered to comprise units of three mutually perpendicular surfaces defininq a trihedral angle of a rectangular parallelepiped, just as though a corner of a rectangular parallelepiped was pressed against the back face of the retroreflective sheet while it was deformable in order to form the unit. In the preferred practice, such a corner penetrates into the sheet until the remote edges of the two vertically disposed sides 4~

of the rectangular parallelepiped reach the back face of shcet.
If a polyhedron is a solid bounded by planes, and a prism is a polyhedron o~ ~hich two faces are congruent polygons in parallel ~lancs, and the other faces are parallelograms having two of their sides in the two parallel planes, a parallelepiped may be broadly defincd as a prism whose ~ases are ~arallelograms. i~
ri~ht parallelepiped, then, is a parallelepi~ed with edges perp^ndicular to the bascs. ~s used here and in the claims, the term "rectangular parallelepiped" means a-ri~ht parallelepiped ~ ose bases are rectangles.
Of the three surfaccs oL the light reilccting units of all illustrated çmobodiments,one surface is horizon-tally disposed when the retroreflectoris in the an~lcd position of about 5 to about 85~ from an incident beam of light, and the other two of the surfaces are vertically disposed and intersect each other in a direction toward the rear face of the retroreflecto- to form an intersection line. ~s used here and in the claims, the term "horizontally disposed" is taKen to mean generally horizontal, that is, more horizontal than vertical, and not an exact, true horizont~l direction.
Similarly, as used here and in the claims, the term "vertically disposed" is takcn to mean qenerally vertical, that is, more vertical than ho-izontal and not an exact, true vertical direction.
~ OI example, in the cln~odimcn'; of 11a~1r~s 3, ~ 2n~

ffi3~

at least somc of the light-reflecting units 17 comprise thre~ mutually perpendicular surfaces dcfining a tri-hedral an~lc of a rectangular parallelepiped as described.
One surface 23 is horizontally disposed when retro-reflective sheet 14 is in the described, operationalj angled position, and two surfaces 24 and 25 are vertically disposed ancl intersect each other in a direction ~oward back face 16 to form an inte-section line or péak 30. A
light-reflecting unit 17 ls so positioned with respect to front face i5 that a body diagonal of a rectangular parall--elepiped as illustrated in phantom at 28 in Figures 4 and 5,is preferably substantially parallel to and at least within an angle of about 15 of incident light reLracted by face 15. The bod~ diagonal is a straight line drawn from the trihedral angle formed by surfaces 23, 24 and 25 to the opposite trihedral angle of the rectangular parallelepiped.
While the light-reflecting units of any embodiment may be spaced from one another along a ~iven row and rows may likewise be spaced from one another, it is pre~erred that the liyht-reflecting units adjoin one another in a row without spacing therebetween and that consecutive rows be contic;uous to each other without spacins therebetween to avoid possible blind spots in the retroreflection. ~'here the units within a row have no spacing therebetween, the vertically dis~osed surfaces, such as surfaces 24 and 25 of the en~odiment of Fic~ures 3, 4 and 5, intersect vertically dis"ose~ suracc, o~

adjoining light relecting units 17 in a direction towards front face 15 to form a second intersection line or depres-sion 26. This line 26 is not only substantially parallel to the first mentioned intersection line 30 but, in the embod-Lment of Figures 3, 4 and 5, is substantially aligned witll an intersection line 30 at the peak of an adjacent lower row 22.
Figure 5 illustrates the retroreflective route of an isolated beam of li~ht represented at 31 for the embod-iment of Figure 3. The beam is first refracted by front face 15 and dixected toward light-reflecting units 17. Upon striking any on~ of the three contiguous faces 23, 24 or 25 (shown as first striking a horizontally disposed surface 23 in Figure 5~, be~n 31 is reflected in turn by the three faces and returned substantially parallel to its incident direction. In a special case, if sheet 14 is adapted to receive horizontally directed light and makes an angle B
with the horizon, surface 23 is a square, surfaces 24 and 25 are identical rectangles, each row 22 has a vertical height H in inches (Figure 5~, the overall horizontal length of two reflecting units o two adjacent rows is L in inches, and sheet 14 has an index of refraction of light n, in the ideal situation these values have su~stantially the relation:

COs B = n COs ~ an ~ hen these valuec are cxactly met, ~he pa.h of bea~.

31 of light in Figure 5 within the retroreflective sheet 14 is exactIy parallel to the body diagonal 28 of the rectangular parallelepiped. However, it will be apparent that deviations from one or more of these values may be taken without losing the advantaqes of the present invention.
Figures 6, 7 and 8 illustrate a modified form of the invention. This form differs from that of Figures 3, 4 and 5 principally in that the rows of light-reflec~ing units are spaced farther apart in a horizontal dlrection as viewed in Figure 6, so that a land or continuous plane is formed between adjacent rows which extends transversely across the back of the retroreflective sheet.
More particularlyr the retroreflecting sheet 32 of Figure 6 is positioned in use, like the embodiment of Figures 3, 4 and 5, at an angle of about 5 to about 85~ and ~referably from about 30 to about 85 from an incident beam of light. Sheet 32 has frcnt and back, opposed, substantially parallel faces shown at 33 and 34, respectively, back 34 being formed along the plane of the line bearing this reference number. Front face 33 is substantially smooth and defines a light-refracting sur-face, while back face 34 has a plurality of light-refracting units formed into that face and generally represented at 35. Rows 36 of units 35 are formed into the back face and extend transversely across the back of sheet 32. At least some of the reflecting units comprise three mutually perpendicular surfaces defining a trihedral angle ~13~

of a r~ctangular parallelepiped as previously des~ribed.
One surface 37 is hori~ontally disposed when sheel: 3 is in the angled position, and the other two surfaces 38 and 39 are vertically disposed and intersect each other in a direction away from front face 33 to form an inter-section line or peak 43. In this case, however, the hori-zontally disposed sur~aces 37 of each unit are continuous with respect to each other in a given row (Yigure 7), so that a land or continuous plane indicated at 42 is form~d.
The vertically disposed surfaces 38 and 39 of at least some of the light-reflecting units 35 can be spaced apart, but preferably they intersect vertically disposed surfaces of adjoining light-reflecting units 37 in a direc-tion towards front face 32 to form a second intersection line or depression 41 that is substantially parallel to the first mentioned intersection line or peak 43. As shown especially in Figure 6, the second intersection line or depression 41 of one row 36 is spaced laterally of the first mentioned intersection l.ine or peak 43 of an adjacent, hiaher row.
Figure 8 illustrates the retroreflectiYe route of an isolated be~m of light represented at 45 for the embodi-ment of Figures 6 and 7. Thc beam is first refracted by front face 33 and directed toward light-reflecting units 35. ~pon striking any one of the three contiguous, mutually perpendi-cular surfaces 37, 38 or 39 ~sho~rn as first striking a horizontally disposed surface 37), beam 45 is re lected in turn by the three surfaces and returned substantially parallel to its incident direction. In a 3~

special case, if the retrore~lective sheet 32 fc.~.n an angle B with the horizontal, each row 36 has a vt -~ical height ~1 in inches (Figure 8), ~he horizontal length of each reflecting unit is D in inches, and the overall hori~ontal length of two reflecting units of two adjacent ro~s 36 is S in inches, in the ideal situation these values have substantially the relation:

tan B = H
S-D

When these values are exactly met, the retro-reflcctive path of the beam of light 45 is exactly paralle]. to the incident ~eam o~ liyht 45, if the retro-reflective sheet 32 lS disposccl so as to receive the incident bcam of light within angle ~ as descri.bed for Figure 3. However, it will be appreciated that deviations from one or moreof these values may be taken without losing advanta~es of the present invention.
Neither light-l-eflecti.ve units 17 nor 35 have re-entrant surfaces and therefore are easily molded.
pro~ection of the array of units 17 or 35, that is, of just the units alone, forms a like array of hexagons filling the projection plane. Accordingly, tools for forming molds to shape the reflecting surfaces can be made from pins of hexa~onal cross-section having thr~e mutually perpendicular planar faces machined on the end of each pin. At least in the en~odirnent of Figure 3, these pl.ln-.l faces arc mutually perpendicular to _ '~cdy dia~onal 2~ of a rectangular parallelepipea which is parallel to the lateral edges of such pins under the ideal situation where diagonal 28 is exactly parallel to the refracted incident light.
It will be apparent that light-reflecting units 17 and 35 can, if desired, be metallized to aid in their reflecting function as described in connection with Figure 2. In Figures 3 through 8, this metallization has not been shown to facilitate illustration of the structure of the light-reflecting units.
Increased durability for roadmarkers can be obtained by eliminating sharp edges and corners. In order to accomplish this without sacrificing optical performance, all faces of the roadmarker which intercept li~3ht, as from oncoming headlights, must be as maximally retroreflective as feasible. A further desideratum is that the same tooling be used for forming all reLlective faces in order to reduce expenses and speed production. This can be accomplished by arranging the retroreflective surfaces itl such a way that an angle between a normal to the surface and an incident ray of light is the samefor each surface.
The present retroreflective body satisfies these conditions by rendering the associated, substantially planar faces optically equivalent. As used here and in the claims, the term "optically equivalent" and forms thereof are taken to mean that the faces receive and redirect incident light in return paths that are sub-stantially parallel to that of the intercepted light.

The ~hysical structures of the various embodiments of the drawing are first described; then the inter-related angulation of the reflecting surfaces inter se;
and finally the structures and retroreflection operation of the reflecting elements themselves.
The em~odiment of Figures 9 through 13 represents a roadmarker generally represented at 110 in form of a truncated pyramid of hexagonal cross-section of which two contiguous, substantlally planar faces 111 and 112 comprise retroreflective elements. The retroreflection of the embodiment of Fiqure 9 is unidirectional, that is, it is designed to receive and retroreflect light coming from one general direction, namely, in the general direction of arrow 113 so that faces 111 and 112 intercept the light. The body of roadmarker 110 may be fabricated from any suitable durable, weather-resistant material, such as ceramic, c31ass, or synthetic resinous plastic material. Such material may be glazed or pic~mented, if desired, to impart colors.
The retroreflective faces 111 and 112 may be present in the form of sheets or wafers suitably adhered in place onto the roadmarker, as by natural or synthetic adhesives, or in matching recesses designed to receive the sheets. The retroreflective elements defining faces 111 or 112 may also be fabricated from any durable, light-transmitting, weather-resistant material, such as qlass. But preferably such elements arc made from synt}lctic resins such as polycarbonates and especially -" ~,$i~

from the acrylates like polymethacrylate and poly-Methylmethacrylate resins. The retroreflective elements may ~e tinted, if desired, to reflect red, yellow or other light, especially if used in a roadmarker. Possible structures of the retroreflective faces 111 and 112 are hereinafter more fully described collectively in connection with the embodiment of Figures 14 through 19.
If desired, the embodiment of Figure 9 can be bi-directional, that is, receive and retroreflect light coming from either or both of two opposite directions.
In this case, opposed faces 114 and 115 are also optically equivalent, substantially planar retroreflective faces like faces 111 and 112.
Each of retroreflective faces 111 and 112 have an angular relationship with a different vertical plane and with respect to each other in a horizontal plane.
l~ace 111 is tilted about a lower portion angularly away from a vertical ~lan~ ]16 through an angle Al (Figure 13).
Similarly face 112 is tilted about a lower portion angularly away from a vertical plane 117 through an angle ~2 (Figure 12). Face 111 makes an acute angle Bl in a horizontal plane (Figure 9) with a second vertical plane 118 which is substantially at right angles to the direction of the approaching light as indicated by arrow 113.
~ ace 112 likewise makes an acute angle B2 in a horizontal plane with the second vertical plane 118. The four indicated angles are interrelated so as to make faces 111 and 112 optically equivalent as described.

v Althougll in the embodiment of Figures 9 through 13, angle Al equals angle A2 and angle Bl equals angle B2, this is not essential. These angles can substantially deviate from one another in value as long as the optical equiv-alents of faces 111 and 112 is maintained. As a rule, angle ~1 and angle A2 normally lie within the range of about 40 to about 75~.
If a retroreflector is made with _ reflective surfaces and all of these surfaces are to be formed with the same tooling and to retroreflect light in the same gelleral direction, then the angular relation can be expressed by the fol]owing equation, using the angles of Figures 9, 12 and 13:

1 1 A2 x Cos 2 This equation represents ideal conditions. Sub-stantial deviation in any value for any angle can occur without departing from the advantages of the invention.
For example, one or more of the angles of the equation may have a value lying within ~ 10~. of the value expressed by the equation.
Figures 14 through 19 ill~strate a preferred embodiment of the present multi-sided retroreflector.
roadmarker generally represented at 120 is in the form of a truncated pyramid of octagonal cross-section of which six substantially planar faces 121, 122, 123, 124, 125 and 126 contain retroreflective elements. Faces 121, 122 ancl 123 cooperate Witil one another to form one 1~ ~3~
set of retroreflective faces, while 124, 125 and 126 cooperate to define another set of retroreflective elements. In this manner, roadmarker 120 can receive and return incidental llght approaching the roadmarker from either or both of two opposite directions.
Roadmarker 120 can be fabricated from the same materials described for roadmarker 110. Figure 19 ill-ustrates an alternative construction in which an outer, one-piece shell 127 of a light-transmitting synthetic resin of the type previously disclosed is filled or potted with a relatively rigid filler material in the form of a solid core 128 The core completely fills the interior of shell 127 and contacts its inner surfaces.
Core 128 which may be of any solid, weather-resistant material, such as glass, ceramics, synthetic resins, particularly thermosetting resins, reinforces the shell and provides a solid, rugged structure to withstand forces applied to roadmarker 120 as by tires of vehicular traffic.
The inside surfaces of shell 127 forming faces 121 through 126 have light-reflecting units hereinafter more fully described. In this instance, an adhesive between shell 127 and core 128 is not usually employed, the mat:erial of core 128 providing its own adhesion to the shell.
The retroreflective operation of faces 124, 125 and 126 is the same as that of faces 121, 122 and 123 and, therefore, only the latter set of faces is described in detail. The embodiment of E'igure 14 is a special case of that of Figure 9 in which there is a frontal sub-stantially planar face and two other substantially planar faces laterally and rearwardly disposed from thefrontal face. These faces also have an angular relation both from a vertical plane and with respect to each other. In particular, face 122 is tilted about a lower portion away from a vertical plane 30 through an angle X ~Fiqure 16), the plane being adapted to be disposed substantially at right angles to the approaching direction of incident light. ~ach of faces 121 and 123 is similarly tilted about a lower portion away from vertical planes 131 and 132 through angles Y1 and Y2 respectively. Face 121 makes an acute angle Zl in a horizontal plane with vertical plane 130, and face 123 makes an acute anc31e Z2 in a horizontal plane with vertical plane 130 (Figure 14).
g , Yl, Y2, Zl,and Z2 are interrelated so as to make faces 121, 122 and 123 optically equivalent as herein defined. In a ~referred and special case (which is not essential to the invention), angle Yl equals angle Y2 and angle Zl equals angle Z2 In this arrangement and representing ideal conditions, the relationship among such angles is represented by the equation:

Cos X = Cos Y x Cos Z
All faces 121, 122, and 123 can retroreflect light in the same general direction and can be made with the same tooling, even though there is substantial deviation in any value for any angle from this equation, without departing from the advantages of the invention. For example, one or m~reof said angles may have a valuelying ~ithin + 10% of the value stated in the equation, a1though deviations exceeding even this value are permissi~le in one or more angles as long as the optical equivalence of faces 121, 122, and 123 is maintained.
As a rule, and as a basis for a starting calculation, angle A normally lies within the range of about 40~ to about 75.
Considering next the structure, itself, of the retroreflective, substantially planar faces, the follow-ing applies for any of the faces of any of the embodiments, whether it be for face 111, 112, 121, 122, 123, 124, 125, or 126. In keeping with the advantage of the present invention that the same orming tool to be used to form all retroreflective faces and yet achieve rctroreflection in substantially the same direction from those same faces, it is preferred although not essential that the retroreflective faces have a plurality of light-reflecting units comprising three mutually perpendicular surfaces. Conveniently, the retroreflective element comprises a layer or sheet having such light-reflecting units formed in its back side or face.
Light-reflecting units of three mutually perpen-dicular surfaces may include those in which the three surfaces define a ~rihedral angle of a rectallgular parallelepiped or such light-reflecting units may comprise cu~e-corners.

'3 The ligllt-reflecting units in the form of strips, wafers, films, sheets, and the like of the same construction as the slanting sides of shell 127 in Figure 19 can be used to form faces 111 and 1-12 of the em~odiment of Figure 9 and the ~aces 121, 123, 124, 125 and 126 of the embodiment of Figure 14.
The light-reflecting units of any substantially planar retroreflective faceof the present retro-reflector may comprise cube-corners as in a cube-corner array. The term "cube corner" is an art recognized term and refers to a well known triple mirror reflecting principle. If three reflecting surfaces are arranged at right angles to each other and intersect at a common point, they form the inside corner of a cube. A beam of light incident on such a cube-corner is reflected from surface to surface and then back along the same general direction taken by the arriving light beam. Such a construction may also be termed a central triple reflector.
Each cube-corner has an axis and the axes of all the cube-corners are generally parallel to one another.
Although such axes are preferably parallel to each other, this does not mean that the axes must be normal to a front face as herein defined or to an array of cube-corners.
Although the foregoing describes several embodiments of the present invention, it is understood that the invention may be practiced in still other forms within the scope of the following claims.

Claims (21)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A multi-sided retroreflective body having at least two retroreflective substantially planar faces adapted to intercept light that is to be retroreflected, each face having a predetermined angular relationship with the other and each containing a plurality of light-reflecting units, each unit comprising three mutually perpendicular surfaces, each of said at least two retroreflective faces being tilted in the same general direction about a lower portion angularly away from a vertical plane and being angularly related in a horizontal plane with respect to another vertical plane disposed substantially at right angles to the direction of said light to define said angular relationship, all four of said angles being so interrelated as to make said at least two retroreflective faces substantially optically equivalent, such that light passing through said another vertical plane is retro-reflected by both of said two retroreflective faces in return paths substantially parallel to that of the inter-cepted light.

2. The retroreflective body of claim 1 in which said body is a roadmarker.

3. The retroreflective body of claim 1 in which at least one of said substantially planar faces comprises a light-transmitting layer having said plurality of light-reflecting units.

4. The retroreflective body of claim 1 in which said planar faces are tilted away from said vertical planes through angles A1 and A2, respectively, and said faces make acute angles B1 and B2, respectively, in a horizontal plane with said another vertical plane, said angles having substantially a relationship established by the equation;
Cos A1 X Cos B1 = Cos A2 X Cos B2

5. The retroreflective body of claim 1 in which the three mutually perpendicular surfaces of said light re-flecting units define cube-corners, and said cube corners are oriented such that an axis passing through a cube corner makes an acute angle with a planar face.

6. The retroreflective body of claim 1 in which the three mutually perpendicular surfaces of said light re-flecting units define trihedral angles of a rectangular parallelepiped, and said surfaces are positioned with respect to a planar face that the body diagonal of a rectangular parallelepiped is within an angle of about 15° to incident light refracted by said planar face.

7. The retroreflective body of claim 1 in which said planar faces are tilted away from said vertical planes through angles A1 and A2, respectively, and said faces make acute angles B1 and B2, respectively, in a horizontal plane with said another vertical plane, said angles having a relationship established by the equation:
Cos A1 X Cos B1 = Cos A2 X Cos B2 one or more of said angles having a value lying within ? 10% of the value required by said equation.

8. The retroreflective body of claim 7 in which each of said angles A1, and A2 is within the range of about 40°
to about 75°.

9. The retroreflective body of claim 1 in which at least one of said substantially planar faces includes a retroreflective element comprising a light-transmitting sheet having front and back, opposed, substantially parallel faces, the front face being said substantially planar face and defining a light-refracting surface, the back face of the sheet having said plurality of light-reflecting units.

10. The retroreflective body of claim 9 in which the exposed areas of at least some of said light reflecting units are coated with metal to aid in their reflecting function.

11. The retroreflective body of claim 9 in which said sheet comprises a light-transmitting organic polymeric resinous material.

12. The retroreflective body of claim 9 in which said light-reflecting units includes rows of said units extend-ing transversely across said back face and formed over an appreciable area of said face.

13. The retroreflective body of claim 12 in which said rows are contiguous to each other without spacing there-between.

14. The retroreflective body of claim 12 in which said light-reflecting units of each row adjoin one another without spacing therebetween.

15. A multi-sided retroreflective body having at least three retroreflective, substantially planar, cooperating faces adapted to intercept light that is to be retro-reflected;
a. said faces including a first face and second and third faces laterally and rearwardly disposed from said first face, and first, second, and third faces having a predetermined angular relationship with respect to each other;
b. each face having a plurality of light-reflecting units, each unit comprising three mutually perpen-dicular surfaces;

c. said first face being tilted about a lower portion away from a first vertical plane through an angle X
having a value within the range of about 40° to about 75°, said first vertical plane being adapted to be disposed substantially at right angles to the approaching direction of said light, each of said second and third faces being tilted about a lower portion away from second and third vertical planes, respectively, through an angle Y, and each of second and third faces making an acute angle Z in a horizontal plane with said first vertical plane; and d. said angles having a predetermined relationship established by the equation:
Cos X = Cos Y x Cos Z
one or more of said angles having a value lying within ? 10% of the value required by said equation to make said three planar faces substantially optically equivalent, such that light passing through said first vertical plane is simultaneously maximally retroreflected by all three of said planar faces and directed in return paths substan-tially parallel to that of the intercepted light.

16. The retroreflective body of claim 15 in which said substantially planar faces have retroreflective elements, each element comprising said light-transmitting layer provided with a plurality of light-reflecting units.

17. The retroreflective body of claim 15 in which at least one of said substantially planar faces includes a retroreflective element comprising a light-transmitting sheet having front and back, opposed, substantially parallel faces, the front face being said substantially planar face and defining a light-refracting surface, the back face of the sheet having said plurality of light-reflecting units.

18. The retroreflective body of claim 15 in which said three mutually perpendicular surfaces of the light re-flecting units define cube corners, and said cube corners are oriented such that an axis passing through a cube corner makes an acute angle with a planar face.

19. The retroreflective body of claim 15 in which said three mutually perpendicular surfaces of the light re-flecting units define trihedral angles of a rectangular parallelepiped, and said surfaces are positioned with respect to a planar face that the body diagonal of a rectangular parallelepiped is within an angle of about 15° to incident light refracted by said planar face.

20. The retroreflective body of claim 15 in which said angles X, Y, and Z have substantially a relationship established by the equation:
Cos X = Cos Y x Cos Z

21. The retroreflective body of claim 15 in which said light-reflecting units have the same construction for all of said three faces.