Note: Descriptions are shown in the official language in which they were submitted.
6832
This invention relates to a retroreflector which may
be used wherever light reflection is desired. A leading
application of the retroreflector is as a retro-
reflective element of a roadmarker to provide directional
guidance, and therefore it is described with respect to
this use.
Roadmarkers are mounted on the surface of a roadway,
such as along its center line or shoulders, to delineate
paths or lanes for traffic, or at intersections to define
stopping lines or cross-lanes for traffic, both vehicular
and pedestrian. Markers of this type are mounted in
spaced apart relation and serve to guide traffic in
following or traversing a roadway, or in following a
curve or grade in the roadway. Particularly to assist a
driver of a vehicle at night, these markers have light
reflectors which catch and return incident beams of
light from vehicle headlights back toward the source
of the light. Since automobiles of recent vintage have
quite powerful headlights, the use of roadmarkers has
become more widespread. Roadmarkers contribute to traffic
safety such as when roads are wet from rain. Under certain
conditions, such as fog, roadmarkers can be the only means
of orienting a driver to a changing direction of a road.
Many forms of light reflectors have been suggested.
They usually suffer from one or more limitations, such as
reflecting too small a proportion of incident light while
an approaching vehicle is still at an appreciable distance.
~; ~ As a result, reflecting markers are often noticed too
-2-
:.
., ` ~ ~
6~33~:
late by a driver to be of substantia] 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.
Plainceramic 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 acube-corner structure. While
a cube-corner structure provides satisfactory performance
as to light striking perpendicularly against an array r
or strip of cube-corners, that is, generally parallel
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.
A principal object of the present invention is to
provide a retroreflector of relatively simple design which
provides efficient retroreflectivity and represents an
improvement over the known cube-corner structure in that
better retroreflectivity is obtained for incident light t
implnging on the retroreflector at wider angles of
incidcnce. In the present retroreflector, the entering
beams of incident light can be reflected sequentially
from three mutual]y per~endicular surfaces which are so
1$~6~332
arranged that little or no light is lost.
~ nother object of the present invention is to
provide a multi-sided retroreflector of re]ative]y simple
design which is durable and yet provides efficient
retroreflectivity.
~ ccording to the present invention, there is provided
a retroreflector comprising a light-transmitting sheet
adapted in use to be disposed in an angled position such
that a normal to the sheet is at an angle of about 5 to
about 85 from an incident beam of light, said sheet
havlng front and back, opposed, substantially parallel
faces, the front face being substantially smooth and
defining a light-refracting surface, and the back face
having a plurality of light-reflecting units, at least
some reflecting units comprising three mutually perpen-
- dicular surfaces defining a trihedral angle of a
.
rectangular parallelepiped and positioned with respect to
said front face that the body diagonal pf the rectangular
parallelepiped is within an angle of about 15 to
incident light refracted by said front face.
~ccording to another feature of the present in-
- vention, the retroreflector is incorporated into a
multi-sided body having at least two retroreflective
substantially planar faces adapted to intercept light
that is to be retroreflected, each of said two
reflectiv~ faces being tilted in the samc general
direction about a lower portion angularly away from a
vertical plane and being angularly relateA in a horizon-
tal plane with respect to another vertical planc
4--
; ' .
3~
disposed substantially at right angles to the direction
of said light, all four of said angles being so inter-
related so as to make said reflective faces substantially
optically equivalent, such that light retroreflected by
said at least two reflective faces is directed in return
paths substantially parallel to that of the intercepted
light.
In the accompanying drawings:
Figure 1 is a perspective view of a roadmarker
10 containing in sheet form a retroreflective element of the
present invention;
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 S is a view similar to Figure 3 and shows the
20 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
7-7; and
Figure 8 is a vlew similar to E'igure 6 and shows the
retroreflective route a beam of light may take with that
emobidment. r
.
S83
Figures 9, 10 and 11 are plan, 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 through 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 transmit light. Body 11 may be suitably
molded 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
-6-
32
.
also be fabricated from any durable, light-transmitting,
weather-resistant material, such as glass, but preferably
is made from synthetic resins such as polycarbonates and
especially from the acrylates like polymethacrylate and
polymethylmethacrylate resins. Re-trorcflective element
14 may be tinted, if desired~ to reflect red, yellow or
other light, especially if used in a roadmarker.
- Referring more particularly to the retroreflective
element of Figures 1 thxough 5, this component is in the
form of a sheet havlng front and back, opposed, sub-
stantially parallel faces indicated at 15 and 16,
respectively. Front face lS is substantiall~r smooth and
- defines a ]ight-refracting suxLace. Back face 16 has a
plurality of light-reflecting units genera]ly represented
at 17 which preferably are formed directly into 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
corners of the units 17 are coplanar with line 18 as
- 20 illustrated. Here and elsewhere in the drawing, it will
~e appreciated that the light reflecting units are shown
! greatly oversize to facilitate their illustration an~
description.
To aid in their reflecting fw~ction, light-
reflecting units 17 may be coated with metal or metalized
in a manner known in the art to for~ a metallic layer l9
(Figure 2). Aluminum is the preferred metal for this
purpose. An adhesive 20 fills the volume between slope
--7--
3?~
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 SUCIl 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 roadmarker 10 to a
surface o a road, although catalyzed thermosetting
adhesives are preferred for this purpose.
Considering now 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 roadmarker, 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 angled with respect
to approaching incident pencils or beams of light. The
~.
light itself may be traveling in any direction and in
2~ any plane. To relate the relative position of the
retroreflective sheet 14 to approaching light which is
generally considered to travel in straight lines, the
retroreflective sheet of the present invention should be
.
~ ` ` disposed in an angled position such that a normal, that
' . .
~` is a line perpendicular to the sheet, is at an angle of
~- about 5 to about 85, and preferably from about 30
: to about 85, from an incident beam of light. ~ccord-
ingly, if line 21 in Figu e 3 represents a normal to the
- , :
,
3~:
.
front face lS of the retroreflective sheet, the sheet is
in position to receive and retroreflect light approaching
the sheet within the angle ~ which represents an angle of
about 5 to about 85 from line 21.
In practice, the retroreflector is usually
positioned to receive and retroreflect light traveling
generally in a horizontal plane, such 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 indication of the angulation
involved and when the retroreflector is used to intercept
horizontally traveling light, the angle B sheet 14 makes
with the horizontal may be within the range of about 5
to about 60. When the retroreflector is 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 unita~ generally represented 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 coextensive with that face.
The resulting array of light-reflecting units provides a
more even distribution of light reflection with little or
no blind spots. The array of all the light reflecting
.
~Q~6832
units forms a multifaceted reflecting surface which
totally retroreflects light in a particular direction.
In a preferred formr 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 retroreflective sheet is
.in use and angled as previously described, rows 22 are
laterally spaced from one another due to thei~r 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 lS~ not critical~ ght-reflectlng units
17 have been shown oversized in the drawing for purposes
of~lllustratlon. In one embodiment, each row was about
1/16~:inch in height:~a~nd the;~rows were~spaced laterally
(or:~ho~rizontally~as~vlewed~in~;Flgure 3) about~ 1/16 inch.
The embodlment~of~:FIgures~3, 9 and 5 lllustrate the
preferred~f~orm~;o2 11ght-reflecting~units, while the
embodiment~o:f~Figures~6,;~7~and 8~represents a modlfied
20~; -form..~The llght-reflecting~unlta of both~embodiments
`may~génerally~be~considered to comprise units of three
` ~ ually~perpendicular~surfaces~defining a trihedral
angle~of~a~:rectangular~paral:lelèpiped, just as though a
co~rner~of~a~rectangular~paralle~l~epiped was pressed against
the~baGk:;.~face~of;the~retroreflective sheet while it was
deformàble in order:to~:form the unit. In the preferred
pra~`tice,~ s:uch:a~corneI~penetrates lnto the~sheet until
the~remo`te~edges of the two~vertically disposed sides
1~4~32
.
of the rectangular parallelepiped reach the back face of
sheet.
If a polyhedron is a solid bounded by planes, and a
prism lS a polyhedron of which two faces are congruent
polygons in parallel planes, and the other faces are
parallelograms having two of their sides in the two
parallel planes, a parallelepiped may be broadly
defined as a prism whose bases are parallelograms. A
right parallelepiped, then, is a paxallelepiped with
edges perpendicular to the bases. As used here and in
the claims, the term "rectangular parallelepiped" means
a right parallelepiped whose bases are rectangles.
Of the three surfaces of the light reflecting units
of all illustrated emobodiments,one surface is horizon-
tally disposed when the retroreflectoris in the angled
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 retroreflector to
form an intersection line. As 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 horizontal direction.
Similarly, as used here and in the clai~s, the term
"vertically d~sposed" is taken to mean generally
vertical, that is, more vertical than horizontal and not
an exact, true vertical direction.
For example, in the embodiment of Plgures 3, ~ and 5,
.
6~3~
at least some of the li.ght-reflecting units 17 comprise
three mutually perpendicular surfaces defining a tri-
hedral angle of a rectangular parallelepiped as described.
One surface 23 is horizontally disposed when retro-
-reflective sheet 14 is in the described, operational~
angled position, and two surfaces 24 and 25 are vertically
disposed and intersect each other in a direction toward
back face 16 to form an intersection line or peak 30- A
light-reflecting unit 17 ls so-posit.ioned with respect to
~ront face 15 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 refracted
by face 15. The body 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 given row and
rows may likewise be spaced from one another, it is
, preferred that the light-reflecting unlts adjoin one
another in a row without spacing therebetween and that
consecutive rows be contiguous to each other wlthout
.
spacing therebetween to avoid possible blind spots in the
retroreflection. Where the units within a row have no
: ~ spacing therebetween, the vertically disposed surfaces,
such as surfaces 24 and 25 of the embodiment of Figures
- 3,.4 and 5, intersect vertically disposed surfaces of
. -12-
,
~ ', .
lQ~S~32
adjoining lightorelecting units 17 in a direction towards
front ~ace 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-
iment of Figures 3, 4 and 5, is substantially aligned with
an intersection line 30 at the peak of an adjacent lower row
22.
Fi~ure 5 illustrates the retroreflective route of
an isolated beam of liyht represented at 31 for the embod-
iment of Figure 3. The beam is first refracted by front
face 15 and directed toward light-reflecting units 17. Upon
striking any one o~ the three contiguous faces 23, 24 or 25
(shown as first striking a horizontally disposed surface 23
in Fi~ure 5~, beam 31 is reflected in turn by ~he three
faces ~nd returned substantially parallel to its incident
direction. In a special case, if sheet 14 is adapted to
rec~ive 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 S~, the overall hori~ontal length of two
re~lecting units of 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 substantially the re~ation:
cos B = n cos ~ n~l ~ ~
When these values are exactly met, ~he path of beam
' .
- 13 -
.,
1096832
31 of light in Figure 5 within the retroreflective sheet
14 is exactly 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'advantages 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-reflecting
units are spaced farther apart in a horizontal direction 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 particularly', the retro~reflecting 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
8~5 and preferably from about 30 to about 85 from an
incident beam of~light. Sheet 32 has front and back,
opposed,~ substant1ally parallel faces shown at 33 and 34,
20~respectlvély,~back 34 being formed along the plane of the
line bearing~this reference numb~ir. Front face 33 is
substantlally smooth and defines a~light-refracting sur-
aae,~while~back face 34 has a plurality of llght-
refracting~unit~s ,formed into that face and generally
represented at 35.~ Rows 36 of units 35 are formed into the
~s~ back~fa'ce~;and extend transversely across the back of sheet
32. At least some of the reflecting units comprise three
mutua~lly~perpendicular surfaces deflning a trihedral angle
,' ' '~ '
lQ~6~33~
of a rectan~ular parallelepiped as previously described.
One surface 37 is hori ontally disposed when sheet 32
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 t~is case, however, the hori-
æontally disposed sur~aces 37 o~ each unit are continuous
~ith respect to each other in a given row (Figure.7), so
that a land or continuous plane indicated at 42 is formed.
The ~ertically disposed surfaces 38 and 39 of at
least some of the light~reflecting units 35 can be spaced
apartl but pre~erably they intersect ~ertically disposed
surfaces of adjoining light-reflecting units 37 in a direc-
.. . .
tion towards front face 32 to form a second intersection
line or depxession 41 that.is su~stantially 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 line or peak 43 of an adjacent, higher
row.
Figure 8 illustrates the retrore~lective route of
an isolated beam of light represented at 4~ for the embodi-
ment of Figures 6 and 7. The beam is first refracted by ~ront
face 33 and directed toward light-reflecting units 35. Upon
striking any one of the three contiguous, mutually perpendi-
culax surfaces 37, 38 or 39 ~shown as first striking a
horizontall~ disposed surface 37), beam 45 is re~lected in
turn by the three surfaces and returned substantially
parallel to its incident direction. In a
. - 15 -
3Z
special case, if the retroreflective sheet 32 forms an
angle B with the horizontal, each row 36 has a v~r~ical
height ~l in inches (Figure 8), the horizontal length of
each reflecting unit is D in inches, and the overall
horizontal length of two reflecting units of two
adjacent rows 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-
reflective path of the beam of light 45 is exactly
parallel to the incident beam of liyht 45, if the retro-
-reflective sheet 32 is disposed so as to receive the
incident beam of light within angle A as described for
Figure 3. However, it will be appreciated that
; deviations from one or moreof these values may be
taken without losing advantages of the present invention.
~ .
Neither light-reflective units 17 nor 35 have re-
entrant surfaces and therefore are easily molded. A
pro3ection 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 hexagonal cross-section having three
mutually perpendicular planar faces machined on the end
of each pin. At least in the embodiment of Figure 3,
these plandr faces are mutually perpendicular to a body
diagonal 28 o~ a rectangular parallelepiped which is
-16-
3~
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.
10Increased 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
light, as from oncoming headlights, must be as maximally
retroreflective as feasible. A further desideratum
is that the same tooling be used for forming all
reflective faces in order to reduce expenses and speed
production. This can be accomplished by arranging the
- retroreflective surfaces in 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.
-17-
S83Z
The physical 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 embodiment 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, substantially planar faces 111 and 112
comprise retroreflective elements. The retroreflection
of the embodiment of Figure 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, glass, or synthetic resinous plastic
material. Such material may be glazed or pigmented, 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 lll or 112 may also be fabricated from any durable,
light-transmitting, weather-resistant material, such as
glass. But preferably such elements are made from
synthetic resins such as polycarbonates and especially
-18-
. . ~
6~32
from the acrylates like polymethacrylate and poly-
methylmethacrylate resins. The retroreflective elements
may be 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 o~ two opposite directions.
In this case, opposed faces I14 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 wlth respect to each other in a horizontal plane.
Face 111 is tilted about a lower portion angularly away
from a vertical plane 116 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 A2 (Figure 12). Face 111 makes an acute angle B] 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.
Face 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.
19
l~q6~32
Although 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 Al and angle A2 normally lie within the range of
about 40 to about 75.
If a retroreflector is made with n reflective
surfaces and all of these surfaces are to be formed
with the same tooling and to retroreflect light in
the same general direction, then the angular relation can
be expressed by the following equation, using the
angles of Figures 9, 12 and 13:
,
1 1 2 2
Thls 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 illustrate a preferred
,
embodiment of the present multi-sided retroreflector.
A 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 and 123 cooperate with one another to form one
-20-
.
` lQq6832
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 light 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 alternatlve construction in which an outer,
one-plece 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,
part1cularly 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
20~ ~126 have 1ight-reflectlng units hereinafter more fully
described. In this instance, an adhesive between shell
127~and~core 128 is not usually employed, the material
of core~12~8 provlding lts own adhesion to the shell.
; T~e retroreflective operation of faces 124, 125 and
126~1s 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 Figure 14 is a special case
of that of Figure 9 in which there is a frontal sub-
a~tlally~planar face~ and two other substantlally
.''' '" ' ' ' ' ' ' .
1~6~32
planar faces laterally and rearwardly disposed from the
frontal 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 (Figure 16), the plane being adapted to be
disposed substantially at right angles to the approaching
direction of incident light. Each of faces 121 and 123
is similarly tilted about a lower portion away from
vertical planes 131 and 132 through angles Yl and Y2
respectively. Face 121 makes an acute angle Zl in a
horizontal plane with vertical plane 130, and face 123
makes an acute angle 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 preferred 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 substantlal deviation
in any value for any angle from this equation, without
departing from the advantages of the invention. For
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example, one or meLeof said angles may have a valuelying within + 10~ of the value stated in the equation,
although deviations exceeding even this value are
permissible 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 forming tool to
- be used to form all retroreflective faces and yet
achieve retroreflection 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 trihedral angle of a rectangular
parallelepiped or such light-reflecting units may
comprise cube-corners.
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The light-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 112 of the
embodiment of Figure 9 and the faces 121, 123, 124, 125
and 126 of the embodiment of Flgure 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 reflécting 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 arrivins 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.
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