United States Patent 3576563

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.

Scott, Harrison A. (Minneapolis, MN)
Moe, James E. (Minneapolis, MN)
Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
International Classes:
B61L5/18; (IPC1-7): G08B5/36
Field of Search:
340/380,50 (X)
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Primary Examiner:
Pitts, Harold I.
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:

9. A railroad signal as in claim 8, wherein:


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.


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.


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.


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.


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° 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.