U.S. patent number 3,576,563 [Application Number 04/730,482] was granted by the patent office on 1971-04-27 for railroad signal having light piping from source mounted an exterior of reflector cone.
This patent grant is currently assigned to Railroad Accessories Corporation. Invention is credited to James E. Moe, Harrison A. Scott.
United States Patent |
3,576,563 |
Scott , et al. |
April 27, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
RAILROAD SIGNAL HAVING LIGHT PIPING FROM SOURCE MOUNTED AN EXTERIOR
OF REFLECTOR CONE
Abstract
A railroad signal has separate light sources for each of the
separate colors employed, such as red, yellow, and green or other
standard colors. The light sources are located away from the
external lens of the signal unit, and are housed deep within the
metal casing in order to protect them from vandalism. Yet no
mechanical motion at the light source is required to switch the
signal from one color to another; instead the switching is done
electrically by means of relays in the conventional control
circuitry which select one of the alternative light sources for
energization. The light from all three lamps, red, yellow and
green, is brought together by fiber optic bundles so that it
emerges through a single external lens in an unusually bright,
concentrated beam which is aimed down the right of way. A sighting
tube is provided, as is test apparatus for adjusting the sighting
tube to achieve precise alignment of the signal relative to the
direction of the railroad track.
Inventors: |
Scott; Harrison A.
(Minneapolis, MN), Moe; James E. (Minneapolis, MN) |
Assignee: |
Railroad Accessories
Corporation (Minneapolis, MN)
|
Family
ID: |
24935539 |
Appl.
No.: |
04/730,482 |
Filed: |
May 20, 1968 |
Current U.S.
Class: |
385/115;
246/473.3 |
Current CPC
Class: |
B61L
5/1827 (20130101) |
Current International
Class: |
B61L
5/00 (20060101); B61L 5/18 (20060101); G08b
005/36 () |
Field of
Search: |
;340/380,50 (X)/ |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pitts; Harold I.
Claims
We claim:
1. A high-efficiency railroad signal comprising a plurality of
sources of light beams of different colors, means providing a
common axis egress from said railroad signal for said
different-colored beams, and a light pipe including branches having
entrance ends positioned for capturing respective different-colored
light beams and combining into a common trunk having an exit end
positioned to direct all of said different-colored light beams to
said common egress, said light pipe being a fiber optic bundle
comprising a plurality of discrete light-conducting fibers of a
first material individually coated with a second material of a
differing refractive index to produce total internal refraction at
the interface between the materials, a different group of fibers
originating from said common trunk and diverging therefrom to form
each of said branches.
2. A high-efficiency railroad signal as in claim 1, wherein the
fibers in each branch are continuous and uninterrupted by
reflective end faces over their entire length from the entrance end
of each branch to the exit end of said common trunk whereby to
achieve maximum light transmissivity.
3. A high-efficiency railroad signal as in claim 2, wherein the
fibers from each of said branches are distributed over said exit
end of said common trunk whereby to achieve substantial homogeneity
of the signal beam regardless of color.
4. A railroad signal comprising a housing formed with an opening to
allow a light beam to exit therefrom, a supporting cone having an
opening at its apex and an opening at its base, said cone being
mounted with said base in surrounding relationship to the opening
in said housing, a lens mounted over said opening and cooperating
with said cone substantially to enclose the interior thereof, at
least one light source supported on the exterior of said supporting
cone, and a light pipe arranged to convey light from said source to
said apex opening.
5. A railroad signal as in claim 4, including means for focusing
the light from said source upon the adjacent light pipe end.
6. The railroad 5, defined in claim 5 wherein said light-focusing
means include an ellipsoidally shaped reflector and a light source
positioned substantially at a first focus of the ellipsoidal
reflector, with the input end of said light pipe being positioned
at a second focus of the ellipsoidal reflector.
7. The railroad signal defined in claim 6, wherein the light pipe
is formed with a plurality of tributary input branches converging
to form a common output end, and with a corresponding plurality of
different-colored light sources and associated focusing means each
optically aligned with the input end of one of said tributary input
branches.
8. A railroad signal comprising:
A. a plurality of light sources;
B. means for focusing the light from said sources so as to provide
a minimum size image of each light source;
C. respective different color filter means interposed between each
source and its image;
D. corresponding plurality of branch fiber optic bundles each
having an input end cylindrically encased in a relatively rigid
material positioned so said image falls upon said cylindrical input
end;
E. means engaging said rigid material to secure said branch bundles
in place in relation to said images;
F. said branch bundles being continuous and converging into a
common trunk bundle;
G. said trunk bundle terminating in an output end for delivering
light from each of said sources;
H. means for collimating the light delivered by said trunk bundle
end;
I. said trunk bundle end being cylindrically encased in a
relatively rigid material;
J. means engaging said rigid casing to secure said trunk bundle end
in position relative to said collimating means.
9. A railroad signal as in claim 8, wherein:
A. said branch bundles curve from said light sources to the place
where they combine into said trunk bundle; and
B. a flexible protective coating covers said fiber optics between
said rigid casings to permit flexing of said branch bundles for
ease of installation in said railroad signal.
Description
FIELD OF THE INVENTION
This invention is particularly concerned with signals for railroad
use, and generally relates to traffic signals or any application
requiring the display of colored indications.
THE PRIOR ART
Multicolor traffic control signals are employed for the control of
both road and rail traffic. By convention, a red signal indicates
stop, a yellow signal indicates caution, and a green signal allows
the traffic to proceed. In certain instances, another color such as
blue or lunar white may be required for a particular signaling
function.
Such traffic control signals suffer from a number of problems,
particularly in the railroad field. Railroad trains often include a
large number of cars traveling at substantial speeds, and therefore
develop such great momentum that they are very difficult to stop
quickly when the need arises. In order to give the railroad
engineer maximum warning of the need for stopping or slowing down,
it is essential that railroad signals be extremely bright, and
oriented in precise alignment with the track direction, so that
they can be seen from great distances.
One approach to the problem is represented by the "doublet" systems
and other multiple-lens systems incorporating separate light
sources for each of the colors employed, and selecting among them
by means of electrical switching techniques. However, without
additional refinement, this approach requires the use of separate
lenses and optical systems for each of the signal colors. Such
redundancy unnecessarily increases the cost of the signal,
introduces space interference problems, and in addition requires
considerable effort for a technician to adjust the signal so that
all of the optical systems are aligned properly with the railroad
track, in order to be seen for great distances down the track.
Furthermore, such doublet systems must not employ reflectors,
because a beam from a vehicle headlight, the sun, or other
extraneous illumination may enter the device and be reflected down
the right of way to give a "phantom" indication to the approaching
locomotive engineer, resulting in a false signal aspect. Because a
reflector cannot be used, a nonreflecting background is required
behind each signal light, greatly reducing the usable illumination
from the lamp.
Another approach to the problem has been to provide a single light
source and a single lens system, and to change the color of the
signal by interposing different color filters between the light
source and the lens system by mechanical means, electromagnetically
operated.
The principal disadvantage of a system of this type is that its
mechanism employs precisely machined and precisely adjusted parts,
due to the small electromagnetic force available; therefore the
assembly cannot be fabricated in a rough and rugged manner. The
moving parts of this system are highly vulnerable to jamming. This
disadvantage is further accentuated when it is considered that in
practical operating circumstances this precise mechanism is usually
placed in a most inaccessible position for inspection, maintenance
and adjustment-- for example, at the top of a high signal mast--
and in locations subject to all natural elements and to
vandalism.
In the current state-of-the-art devices, it is often necessary to
progress successively through an undesired color display to achieve
the desired color display. In many cases this transition displays a
signal indication which may cause unnecessary and even undesirable
responsive action by the engineer of the approaching train,
producing the danger of damage to equipment and injury to
personnel.
In addition, equipment of this kind is extremely expensive to
produce due to the precision required in its manufacture.
A proposal to combine a plurality of light sources into a single
optical system for greater economy is seen in Peter, U.S. Pat. No.
2,589,569, in which the light from three different light sources is
combined by means of a "light pipe" material, so as to converge in
a single optical system. However, the light pipe material suggested
in the Peter patent is conventional plastic such as polymerized
methyl methacrilate, commonly known by various trademarks such as
Lucite, Plexiglass, or, as referred to in the Peter patent,
Perspex. By whatever name it is known, this material, although well
suited for various light-conducting applications where light
intensity is not a serious problem, is subject to a very serious
defect which makes it totally unacceptable in the present
environment. Specifically, the material suggested in the Peter
patent conducts light by means of internal reflection with an
efficiency of approximately 50 percent per reflection. The light
travels through the plastic pipe in a series of bounces. With each
bounce approximately 50 percent of the light is lost by refraction
at the surface of the plastic material, and escapes from the light
pipe, while only the remaining 50 percent is internally reflected
to continue traveling through the light pipe. When the total number
of internal reflections which occur in a device of the type
exemplified by the Peter patent is taken into account, it is
realized that the device suffers several consecutive 50 percent
losses. Therefore, as a practical result overall light
transmissivity of the system illustrated in the Peter patent is
only about 5 to 10 percent. For this reason, practical experience
has shown that the Peter system is completely unsatisfactory for
railroad signal use, and until the present invention, no operating
railroad signal had ever been made and successfully used which
combined a plurality of separate light sources into a single
optical system.
The successive 50 percent transmission losses suffered by the
system of the Peter patent would in themselves be enough to prevent
the Peter device from being a practical solution for railroad
signals. To make matters worse, however, the Peter device suffers
from another very serious problem. It utilizes in its tributary
light pipes only a very small solid angle of the illumination
produced by its lamps, with no suggestion of techniques which might
be used to increase the light flux entering the light conductor.
The total light flux loss through the entire Peter system is so
serious as to render it impracticable.
Other problems that the prior art has encountered are also obviated
by the railroad signal of this invention. In recent years railroad
rolling stock and other equipment has been subject to a great deal
of vandalism. Not only the windows of the cars, but also the
external optical components of railroad signals have been targets
for boys throwing rocks and even in some instances using air guns
or rifles. When such vandals are on target, a lamp located just
behind the external lens of the railroad signal can be hit by a
bullet passing through the lens, completely disabling the signal.
This can have serious consequences for railroad traffic.
Accordingly there is a need for a railroad signal in which the
light sources can be located deep within the protective metal
housing of the signal, away from the line of fire of the vandal's
weapons, so that they cannot be destroyed. Then the signal will
continue to function to some extent even if the external lens is
destroyed.
SUMMARY AND OBJECTS OF THE INVENTION
This invention aims to provide a railroad signal of very high
efficiency and generally improved design. More specifically, an
objective of this invention is to provide a railroad signal of such
high efficiency that it will produce an adequate and acceptable
signal indication. At the same time, it is also an object of this
invention to achieve this result without the use of any mechanical
moving parts. The object is to change signal colors entirely by
means of electrical switching. However, it is an objective to
accomplish this without the use of separate optical systems. To
state the matter another way, this invention for the first time
provides a plurality of different colors, operating through a
common optical system, without an objectionable loss of light flux
through the system.
Another specific object of the invention is to provide a railroad
signal having a high efficiency light-piping system, with no
interfaces whatsoever interposed in the path of the signal
light.
It is also an object of this invention to provide a railroad signal
in which the light sources are in a protected location within the
housing, so that they are not vulnerable to vandalism. Another
objective is to provide a railroad signal which will function at
least to some extent in the event of the destruction of the
external optical components of the signal.
The invention achieves these objectives by providing an optical
system for conducting light from the individual signal sources to a
common optical outlet by means of fiber optics. Fiber optics are
bundles of individual light-conducting fibers, each fiber within
the bundle being individually coated with a material which causes
the walls of the individual fibers to achieve substantially total
internal reflection as the light is guided through the fiber. Thus,
there is no light loss due to partial refraction at the surface
each time the light is turned back into the interior of the fiber.
In addition, the main trunk bundle is easily separated into a
plurality of individual bundles without the need for any interfaces
interposed across the path of the signal light.
The present invention for the first time provides a railroad signal
constructed with the light sources located deep within the confines
of the metal housing of the signal, where they are protected from
vandalism, yet the light produced by these sources is piped with
very high efficiency, to a common optical outlet. The result is the
very first railroad signal of this type which is intense enough to
be practical for actual railroad applications.
In addition, this construction obviates the necessity for a
plurality of individual optical outlets for the signal light, thus
effecting economies in the construction, installation, and
alignment of the railroad signal.
There is also no need for moving parts and electromagnetic
actuators to move filters back and forth, because this is done
electrically by switching from one light source to another.
Finally, the use of a common optical system for all colors eases
the problems of the installer or service man who must align the
railroad signal with the track direction with great precision.
The invention may take various particular forms, and is broad
enough to encompass whatever is within the spirit or scope of the
claims appearing at the end of this patent. However, in order to
facilitate a detailed description, reference will be made to the
particular embodiment illustrated in the following drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a front elevational view of the railroad signal in
accordance with this invention, mounted upon a supporting post;
FIG. 2 is a sectional view of the same railroad signal taken along
the lines 2-2 of FIG. 3;
FIG. 3 is a rear view of the signal of the previous FIGS., with the
rear casing cover removed to reveal details of the interior
construction;
FIG. 4 is a side elevational view, with parts sectioned, of the
fiber optic light pipe of the railroad signal of the previous
FIGS.,
FIGS. 5, 6, 7 and 8 are sectional views of the fiber optic light
pipe of FIG. 4 taken along the lines 5-5, 6-6, 7-7, and 8-8 thereof
respectively;
FIG. 9 is a perspective view, partially schematic, of a test
facility in accordance with additional aspects of this
invention;
FIG. 10 is a side elevational view of the sighting tube of the
railroad signal of this invention;
FIG. 11 is a side elevational view, with parts removed, of the
light source and part of the optics of the railroad signal of this
invention; and
FIG. 12 is a sectional view, taken along the lines 12-12 of the
light source of FIG. 11.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows the entire railroad signal 20 which is mounted beside
a railroad track upon a supporting post 22 by means of U-bolts 24
cooperating with a triangular bracket 26. A cable 28 carrying power
and signal lines comes up through the interior of the supporting
post 22 and emerges therefrom, entering the railroad signal 20
through a supporting hub 30 which is integral with the triangular
bracket 26. The signal 20 is rotatable upon the hub 30 in order to
permit alignment with the track direction.
The signal is enclosed within a protective metal housing 32. In the
front view of FIG. 1 it is seen that the front wall of the housing
32 has a light-emitting port which is covered by a substantially
circular collimating lens 34 of the Fresnel variety, which may be
molded of glass or of an impact-resistant plastic material such as
"Tenite" butyrate. The lens 34 may be designed to provide any
desired divergence or spread of the collimated beam in any desired
direction by such means as the ribbed center portion thereof shown
in FIGS. 1 and 2, or other superimposed ribbing or deflectors. A
plurality of bolts 36 secure the retaining ring 50 of the
collimating lens 34 to the front wall of the housing 32.
As the lens 34 provides a bright, highly visible and enticing
target for vandals, it is vulnerable to rocks, pellets and rifle
bullets. In prior art railroad signals there were one or more such
lenses on each railroad signal with the light bulbs or mechanism
mounted immediately behind the lens in optical relationship
therewith. Accordingly, a rifle bullet fired at the apparent source
of light, i.e. the lens, would destroy the light bulb or mechanism
as well, and could thereby put the railroad signal entirely out of
commission or cause it to display a false signal indication.
One additional feature, which is visible in the front view of FIG.
1, is the front end of an alignment sight 38 which is used for
orienting the railroad signal 20 precisely parallel to the railroad
track so that its light can be seen from great distances as the
train approaches.
At the top of the metal housing 32 are a pair of ears 40 which
support the hinges 42 of a rear cover 44 cooperating with the
housing 32 to provide a protective shell for the railroad signal
20. The rear cover 44 may be opened by means of the hinges 42 to
expose the internal components of the railroad signal 20 for
servicing when necessary. At other times, a bolt 46 serves to keep
the rear cover 44 closed.
The bolts 36 pass through a flange of a metal cone 52. This cone
serves a variety of purposes. It is the basic support for a
plurality of light bulbs 54, 55, and 57 and color filters 68, one
for each color generated by the railroad signal 20. Any required
number of colors may be similarly provided by the signal units of
the invention, limited only by space requirements. In the following
discussion, three units will be described, for simplicity of
description. The cone 52 also serves to support the transmitting
end of a fiber optic bundle 56 which is inserted into a cylindrical
opening at the narrow end of the cone and clamped in place by a
setscrew 58. It will be appreciated that with this arrangement, if
a rifle bullet pierces the collimating lens 34 and enters the
interior of the cone 52, it will most likely spend its force
harmlessly against the interior of the metal cone, and will not be
able to do harm to the lamps or any part of the fiber optic bundle
situated externally of the protective cone 52. Even without the
lens 34, the output end of the light pipe 56 would be a reasonably
effective light source visible to an engineer some distance down
the track.
The cone 52 also serves to absorb and avoid reflection of
extraneous light, and to exclude extraneous light from the aperture
of lens 34, and to exclude extraneous light from the aperture of
lens 34, and to provide a contrasting background for the
observation of the illuminated output end of fiber bundle 56 if
lens 34 should be destroyed by vandalism.
FIGS. 2 and 3 show the manner in which the light bulbs 54, 55 and
57 are mounted upon the cone 52. Each of the light bulbs is
supported within an electrical socket 64 which in turn is mounted
upon a metal bracket 66 attached to the outer surface of the metal
cone 52 for firm support and good heat conduction. The light from
each bulb, e.g. the bulb 54, passes through a colored filter such
as filter 68 which determines the color of the signal light. In a
typical signal, light bulb 54 would have a red filter, light bulb
55 would have a yellow filter, and light bulb 57 would have a green
filter. Opposite the filter, each of the brackets 66 has a hollow
cylindrical extension 70 into which is inserted the input end of a
branch of the fiber optic bundle 56. Additionally, this bracket
extension 70 serves as a heat sink conducting heat produced by lamp
54 away from an input and ferrule 74 of fiber bundle 56.
Specifically, the fiber optic bundle is divided into branches 72,
80 and 82, each of which includes approximately one-third of the
total number of fibers in the bundle 56. The input end of branch
fiber optic bundle 72, banded with the protective metal ferrule 74,
is inserted into the interior of the cylindrical extension 70 and
held in place there by a setscrew 76. In similar fashion, the other
branch fiber optic bundles 80 and 82 are inserted and clamped in
the cylindrical extensions 70 of the supporting brackets 66 of the
other signal lamps 55 and 57. A shrink-fit plastic sleeve 84
surrounds the fiber optic bundle 56 at the point where it separates
into the three branch bundles 72, 80 and 82.
Before turning our attention from FIGS. 2 and 3, it should be noted
in passing that a terminal block 90 is mounted in the lower
interior of the housing 32 to provide convenient electrical
connections at the termination of the cable 28. There is also a
bank of resistors 92 in the lower section of the housing 32 which
are adjustable by means of slides 94 to control the voltage applied
to the signal lamps 54, 55 and 57.
FIGS. 4 through 8 are enlarged views of the fiber optic bundle 56,
and its branches 72, 80, and 82. Light from one of the three bulbs,
e.g. light bulb 54, enters one of the branch fiber optic bundles,
e.g. the branch 72, at the end where it is bound by the metal
ferrule 74, and continues on down the light pipe formed by each
branch bundle until all three branches are joined into one trunk
fiber optic bundle 56 comprising a uniform intermixture and
distribution of all the fibers from the three branches across the
entire cross section of trunk bundle 56, in order to spread the
light from each bulb 54 uniformly across the entire output end area
of bundle 56. The light then continues through the trunk bundle 56
until it emerges from the end of the bundle which is clamped in the
cylindrical opening of the cone 52. Thus, the termination of the
fiber optic bundle 56 constitutes the source of a light beam 100
which emerges from the fiber optic bundle 56 with a spread of about
60.degree. as shown in FIG. 2. This light beam 100 is then
collimated by the plastic lens 34 to provide a collimated beam 102
projecting forward from the signal 20 and far down the track where
it is visible at great distances to the engineer of an approaching
train. It is essential that this light beam 100 have the same axis
and distribution pattern regardless of the selection of color
supplied by bulb 54, 55 or 57, and this is assured by the
intermixture and distribution of all fibers from each branch bundle
72, 80 and 82 across the cross section of trunk bundle 56.
The entire fiber optic assembly is a unit specially fabricated in
the form illustrated, including the metal ferrule 74 at the end of
each branch bundle 72, 80 and 82. Behind the metal ferrules the
branch bundles are protected by flexible plastic sleeves 103 and
further on by the shrink-fit sleeve 84 where the three branch
bundles come together. Beyond that point, a metal protective sleeve
104 is provided to prevent damage to the fiber optic bundle 56.
The flexible sleeves 103 provide protection for the branch bundles
72, 80 and 82, yet permit them to be flexed so as to assume the
curved configuration required (see FIG. 3) for connection to the
three different cylindrical extensions 70 during construction of
the signal 20.
Within the protective confines of the metal sleeve 104, the
individual fibers of each of the branch bundles 72, 80 and 82
become intermixed in a uniform fashion between sections 6-6 and 8-8
shown in FIG. 4. This uniform intermixture means that the light
beam which emerges from the end of the bundle 56 is substantially
the same, except for color, regardless of which one of the three
branch bundles is the source of the light at any given time.
The properties of the fiber optic bundle 56 are such that it has an
extremely high light transmissivity, because it does not lose any
light laterally at the interface of the core and coating of the
fibers during refraction. This is because of the individual coating
on the outside surface of each fiber, which causes nearly total
internal refraction at the interface, so that the fibers act as
highly efficient light guides.
In addition, along the entire fiber optic light path, from the
input end of the branch bundles 72, 80 and 82 to the output end of
the trunk bundle 56, there is no transverse interface which the
light rays must cross, hence no scatter or reflection losses occur,
as in the structure of the Peter patent.
It will also be appreciated that the structure of the Peter patent
results in delivery of the light from each of the branch light
pipes to only one lateral portion of the trunk pipe, with the
result that the beam which emerges from the delivery end of the
combined pipe is not homogeneously distributed over the end face of
the trunk pipe. In contrast, the structure of the present invention
guarantees far greater homogeneity, since the individual fibers
which make up any one branch light pipe 72, 80 or 82 are
distributed uniformly over the trunk bundle 56.
FIGS. 11 and 12 are closeup views of the light bulb, e.g. bulb 54,
showing the filament 110, and ellipsoidal reflector surface 112 at
the rear, and an annularly shaped segment of a spherical reflector
surface 114 at the front of the bulb surrounding a transparent
window 116. The filament 110 is substantially at one focus of the
ellipsoidal surface 112, while the entrance end of the branch fiber
optic light pipe 72 is at the other focus. Therefore, the light
originating from the filament 110 and initially striking the rear
reflector 112, passes through the window 116 and is focused at a
point inside the entrance end of the branch light pipe 72. The
filament 110 is also substantially at the center of the spherical
front reflector surface 114, so that light originating from the
filament and initially striking the front reflector is reflected
back to the point of origin in the other direction, eventually
reaching the reflector 112 and then being focused in the manner
described above. Light originating from the filament 110 and
proceeding directly forwardly passes directly through the window
116. Light rays having all these various paths of course pass
through the colored filter 68 on their way to the light pipe branch
72. As shown in FIG. 2, color filter 68 is preferably tilted
slightly to avoid direct and return reflections from filter 68 to
ellipsoidal reflector 112.
It will be understood that ellipsoidal reflector 112 with filament
110 at its first focus and the input end of branch fiber bundle 72
at its second focus may be incorporated in other forms of lamp
envelopes or lamp assemblies, or that a conventional condenser lens
system may be used with reduced efficiency.
FIG. 10 shows the alignment sight 38 for the railroad signal 20,
together with the bracket for mounting and adjusting the sight
within the casing 32. A technician can look through the alignment
sight 38 and far down the track so as to determine the point toward
which the signal beam is directed.
FIG. 9 illustrates apparatus according to this invention for
determining that the sight 38 is aligned properly with respect to
the axis of the beam of signal 20. Several feet in front of the
signal lens 34 is placed a target board 130 which has four
photocells 132 at the corners thereof and a target 134 at the
center. At the factory, the light beam of the signal is directed at
the target board 130, and the signal is turned until the beam hits
the center of the target 134. Fine adjustments are made until the
electrical response from all four photocells 132 is equal. This
condition can be determined by a sensitive electrical instrument
such as a Wheatstone bridge having the four photocells 132 in the
respective bridge arms. Such equality indicates that the beam of
signal 20 is pointed directly toward the center of the target.
The signal 20 is then fixed in that position, and the alignment
sight 38 is loosened and aligned with a secondary target 136
provided at the right-hand side of the target board 130. It is then
assured that the sight is properly positioned with respect to the
signal beam. The alignment sight 38 can then be used to align the
signal 20 with the railroad track during installation by sighting
down the tube 38.
It will now be appreciated that in addition to having provided the
first workable high-efficiency railroad signal employing the light
pipe principle, with all the advantages of relative immunity to
vandalism, ruggedness, economy, and lightweight, the present
invention provides apparatus for precisely aligning the sight
within the railroad signal unit. Then the sight can be used for
aligning the signal beam with the track so that its high light
output can be used for maximum effect and will be visible at great
distances down the track.
While the objects of the invention are efficiently achieved by the
preferred forms of the invention described in the foregoing
specification, the invention also includes changes and variations
falling within and between the definitions of the following
claims.
* * * * *