The present invention relates generally to railway safety, and more particularly to such in railroad track circuits.
The track circuit is an important tool in railway operations. With the advancement of high-speed trains and heavy freight trains, the function of the track circuit is increasingly important to safe and efficient railway operations.
Current track circuits use electrical wiring to connect the two tracks in a railway section to a voltage supplied by a battery. The tracks in the section are insolated from the other sections of tracks by a set of isolation pads to minimize current leakage. A resistor, an open/close switch, one Green signal light, and one Red signal light are typically also connected to the circuit formed in this manner. The wheels and axles of trains passing through the railway section of the track circuit then act as a shunt (short), thus operating the track circuit.
Accordingly, the track circuit is designed principally as a series circuit. When a train enters the isolated section of rails its wheels and axles place a shunt (short) on the track circuit. This creates a low resistance current path from one rail to the other, changing the series circuit to a parallel circuit with intentional current paths through the relay coil as well as through the train wheels and axles.
In
The above discussion has covered theoretical track circuit operation. In practice, however, the effects of operational and environmental dynamics need to be taken into account to understand actual track circuit operation.
As can be seen in
The seemingly straightforward matter of adjusting a track circuit for operation is, unfortunately, complicated by environmental factors. When good railroad ties are supported in good crushed stone the complete isolated rails section should be dry and the resistance to current flow from one rail to the other rail should be very high. This condition is known as “maximum ballast resistance” and is ideal for good track circuit operation. Conversely, when the ballast present is wet or contains substances such as salt or minerals that conduct electricity easily, current can flow or leak from one rail to the other rail. This condition is termed “minimum ballast resistance” and it produces a ballast leakage current that is high. The total current drain from the battery during normal conditions therefore adds up to current through each ballast resistance and through the relay coils.
When the ballast resistance decreases significantly, the theoretical series circuit of the track circuit effectively, undesirably becomes a parallel circuit. When this happens, the relay can be robbed of enough current that it become de-energized, or fails to pick up again after it has been de-energized by the passage of a train.
Track circuits thus can be a very dynamic and unpredictable, and a mechanism to attempt to deal with this is also shown in
It follows from the above that the conventional track circuit has many drawbacks. It has very poor durability—the failure rate is very high and it has to be repaired or replaced at frequent intervals. It also is not accurate. It produces many false alarms, which cause accidents or unnecessarily stop trains and significantly increase railway operational costs. It also quite often fails to produce a signal when a train does pass by, which seriously affects railroad safety. It can not detect the direction of train movement. And it cannot provide information about the weight of an approaching train, which is often important to local railway, police, and emergency personnel.
Accordingly, it is an object of the present invention to provide an improved railroad track circuit.
Briefly, one preferred embodiment of the present invention is a fiber optic track circuit having a light source, a fiber Bragg grating (FBG) unit, and a receiver all connected by optical fiber. The FBG unit is mountable on a portion of a railway system directly effected by the weight of a passing train. The light source provides a light beam via the optical fiber to the FBG unit, which receives the light beam and provides a reflected beam via the optical fiber to the receiver. The receiver then provides a receiver signal based on the reflected beam. And a processor then determines, based on pre-set criteria and the receiver signal, whether to communicate and what to communicate as a track circuit signal to an external device.
Briefly, another preferred embodiment of the present invention is a process for determining information about a train passing through a railway system. A light beam is conveyed to a fiber Bragg grating (FBG) unit mounted on a portion of the railway system that is directly effected by the weight of the passing train. A reflected beam is then produces at the FBG unit based on the light beam. This reflected beam is then conveyed to a receiver, that produces a receiver signal based on the reflected beam. Finally, the receiver signal is processed based on pre-set criteria to obtain the information.
And briefly, another preferred embodiment of the present invention is a system for determining information about a train passing through a railway system. A Bragg means for reflecting a particular light wavelength based on the Bragg effect is provided, wherein the Bragg means is mountable on a portion of the railway system that is directly effected by the weight of the passing train. A producing means for producing a receiver signal based on the particular light wavelength then operates, and means for processing the receiver signal based on pre-set criteria to obtain the information then operates as well. To facilitate this, means for conveying a light beam to the Bragg means, for conveying the particular light wavelength to the producing means, and for conveying the receiver signal to the means for processing is employed.
These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as illustrated in the figures of the drawings.
The purposes and advantages of the present invention will be apparent from the following detailed description in conjunction with the appended figures of drawings in which:
a-b are simplified schematics depicting the structure and operation of a fiber Bragg grating (FBG) unit that can be used in the fiber optic track circuit, wherein
In the various figures of the drawings, like references are used to denote like or similar elements or steps.
A preferred embodiment of the present invention is fiber optic track circuit. As illustrated in the various drawings herein, and particularly in the view of
Installation of the fiber optic track circuit 10 on just one track 12 is adequate, but
Turning briefly also to
This FBG unit 14 includes a FBG zone 16 that is optically connected to or integral with optical fiber 18. The FBG unit 14 also includes mounting blocks 20 that hold the optical fiber 18 at opposite ends of the FBG zone 16. It is these mounting blocks 20 that are physically attached to the web of a railway track 12.
The FBG zone 16 is made to respond highly to a particular light wavelength and to be insensitive to other light wavelengths. A light source 22 (e.g., tunable laser, light emitting diode (LED), amplified spontaneous emission (ASE), or other broadband source) is provided (
As shown in
With reference again primarily to
Since the optical signals (light beams 24, 24a, 24b) can all be transmitted very long distances through the optical fiber 18 without losing the finesse of the signal-to-noise ratio, there is no need for electricity at the location or locations where the FBG units 14 are installed. The light source 22, a receiver 26 for detecting the reflected beam 24a, and a microprocessor 28 can all therefore be placed some distance away from the FBG units 14.
In
The external systems 36 can include, without limitation, traditional Red/Green railway warning lights, railway station control room systems, and public safety systems. For instance, since the inventive fiber optic track circuit 10 can be used to determine both the weight and the speed of a passing train, it can easily be configured to automatically provide a warning to train engineers, railway station personnel, and civil authorities. Unlike prior art systems, however, the warnings from the inventive fiber optic track circuit 10 can be much more informative. For instance, they can report if a train is moving too fast, is too heavy, or if train is detected with a particular combination of both speed and weight that is hazardous.
Traditional, electric track circuits are particularly subject to damage by a powerful force of nature, lightning. The inherent conductive nature of railway rails and the typically long paths that electrical wiring to and from track switches must travel puts conventional electrical track circuits and their control systems at great risk. A lightning strike some distance up or down a railway line can thus disable a track circuit. Lightning strikes anywhere along the electrical wiring path can also induce electrical noise into the system that triggers false reports or even burns out track circuit or control system components. The inventive fiber optic track circuit 10 is not at risk from lightning, unless it strikes so directly and powerfully that heat or explosive force physically damages the fiber optic track circuit 10. Similarly, the fiber optic track circuit 10 does not but its control system 30 or other systems at risk because its substantial elements are not conductive and thus cannot convey electricity to where it can cause damage.
In summary, the fiber optic track circuit 10 provides considerable benefits. No electricity is required at the actual installation site. There accordingly is no need for a battery at such sites, and no (electrical) isolation between sections of track 12 are needed at such site. This not only saves on direct installation costs, it also reduces the installation and maintenance times needed, thus allowing more frequent scheduling of trains on the effected lines. There is also no signal-to-noise degradation during bad weather, from snow, rain, or salt, etc., and there is no concern about shorting the circuit during railway track maintenance, system calibration, or any accident creating an electrically conductive path between the railway tracks.
The fiber optic track circuit 10 is accurate and reliable. It can easily be set to not produce false alarms, since it will respond only to the presence of the appreciable weight of a passing train. The fiber optic track circuit 10 is also durable. Fiber optic type sensors in other applications are known for their long operating life time, unless they are purposely damaged by humans or natural disasters.
The fiber optic track circuit 10 can also easily provide directionality, speed determination, and acceleration measurement. With two units, determining direction can be as simple as seeing which fiber optic track circuit 10 is actuated first. Since the position of each fiber optic track circuit 10 is fixed, measuring the amount of time for a train to travel from one to the other permits speed calculation. Further, if three or more fiber optic track circuits 10 are mounted at known positions, the acceleration of a train can also be calculated. All of this additional information is often important information, since it can permit railway personnel and other appropriate authorities to insure more efficient and safe railroad operations.
With its weight detection capability, the fiber optic track circuit 10 can measure the weight of a passing train. This in combination with directionality, speed, and acceleration provides even more potential benefit. For example, to infer whether a particular train is a passenger or freight train, and to ensure that weight limits, weight and speed limits, or weight and acceleration limits are not exceeded. This also can be important information for railway and local emergency personnel.
In addition, the fiber optic track circuit 10 permits much more information to be integrated. For example, it permits improved collision avoidance. Since all of the speed, weight, direction, etc., of all of the trains on the various track sections can now be better identified and monitored, the probability of train collisions can be greatly reduced.
FBG's are sensitive to temperature, but this can be used intentionally and quite beneficially by the inventive fiber optic track circuit 10. By letting temperature affect the FBG units 14, railway personnel can be informed in real time if an installed location has an abrupt temperature change or is experiencing an extreme temperature. In some locations in the world such a change can be indicative of flood waters crossing or ice freezing over tracks, potentially presenting a sever hazard to trains. In general, abnormally low or abnormally high temperatures are also a serious cause of derailments. Temperatures in some places, such as desert regions, can range daily by as much as 75° F. (25° C.). Large numbers of such cycles can cause tracks to work loose from ties and for other railway structure to subtly degrade. The fiber optic track circuit 10 permits aggregating data about this and employing it to improve railway safety and to conduct preemptive inspection and maintenance in ways not previously practical.
Alternately, if FBG sensitivity to temperature is a disadvantage in a particular application, it can be compensated for. The FBG units 14 that are used can be an athermal type (such as the fiber optic sensor offered by Fibera, Inc. of Santa Clara, Calif.), or the control system 30 can measure ambient temperature and adjust the data it works with as needed. Or both stressed and un-stressed FBG units 14 can be employed (literally alongside one another if desired). The reflected beam 24a of a stressed FBG unit 14 (i.e., one stressed train weight or some other direct physical influence) can then be differentially processed with the reflected beam 24a from a non-stressed FBG unit 14 (i.e., one stressed only by indirect physical influences, like ambient temperature). Still better, both athermal and normal FBG units 14 can be employed together at the same location, to provide yet more information.
While various embodiments have been described above, it should be understood that they have been presented by way of example only, and that the breadth and scope of the invention should not be limited by any of the above described exemplary embodiments, but should instead be defined only in accordance with the following claims and their equivalents.
This application claims the benefit of U.S. Provisional Application No. 60/594,094, filed 10 Mar. 2005 and hereby incorporated by reference in its entirety.
Number | Date | Country | |
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60594094 | Mar 2005 | US |