Patent Application
20120248261
Railroad grade crossings (sometimes referred to in the U.K. as level crossings) are locations at which railroad tracks intersect roads. Avoiding collisions between people, trains and automobiles at grade crossings has always been a matter of great concern in the railroad industry.
Warning systems have been developed to warn people and cars of an approaching train at a grade crossing. These warning systems typically include lights, bells and one or more gate arms (e.g., the familiar black and white striped wooden or fiberglass arms often found at highway grade crossings) that block the road and/or sidewalks when a train is approaching the crossing. The lights, bells and gate arms of these warning systems are typically controlled by a controller. Most controllers in use in the U.S. today utilize an input from a grade crossing predictor circuit to determine when to activate the warning system. A crossing predictor circuit is an electronic device which is connected to the rails of a railroad track and is configured to detect the presence of an approaching train, determine its speed and distance from a crossing, and use this information to generate a constant warning time signal for control of a crossing warning device. Other techniques for providing an input to a controller include laser-based systems for detecting a train and determining its distance and speed.
These known systems share a common characteristic: they are independent of any active signal from a train. In other words, these systems detect a train but do not rely on the train to generate any control signals.
Another characteristic of these known systems is that, although they are highly reliable, they are not perfect and have been known to malfunction on occasion. Such a malfunction can take the form of a warning system activating (e.g., a gate staying in a lowered position) when no train is approaching and, more dangerously, a warning system failing to activate (e.g., a gate staying in the raised position) when a train is approaching.
A more recent development in train safety has been the use of positive train control, or PTC, systems onboard locomotives. These systems are designed to prevent collisions between trains, to enforce speed restrictions, and to perform other safety-related functions. Although these systems vary widely in their implementation, many of them share common characteristics such as a positioning systems and map databases that allow a locomotive to determine its position relative to a track system and communications system that allow the locomotive to communicate with devices located off of the train.
It is known in the art to utilize such locomotive PTC systems as a means to ensure that a train does not pass a grade crossing when a warning system is malfunctioning. The leading patent in this area is U.S. Pat. No. 6,996,461 to Kane et al. In Kane's system, a train approaching a grade crossing transmits an interrogation signal to a wayside device such as a grade crossing controller prior to reaching the grade crossing, and does not go through the crossing if a response indicating that the warning system has been properly activated has been received. Note that Kane's system does not trigger activation of the crossing warning system or control it in any way; rather, Kane's system only interrogates the wayside warning system to determine if it has activated prior to the train passing the crossing.
Another system, described in U.S. Pat. No. 5,620,155 to Michalek, discloses an system located onboard a locomotive that can send a signal to a wayside warning system to activate the wayside warning system. Michalek's system, however, operates by sending an activation signal to the warning system when the train is at a predetermined distance from the crossing. This is wasteful as such a scheme will cause the warning system to activate in advance of when necessary for a slow moving train (it being understood that the predetermined distance must be sufficiently spaced apart from the crossing to allow for a train traveling at the highest allowable speed). This drawback might be tolerable for rural crossings with warning devices consisting of only flashing lights as cars may be able to pull up to the tracks, determine the distance of the train, and proceed through the crossing if the train is still far away (although this is still wasteful as the car is forced to slow down or stop needlessly). However, such a system is far less tolerable for crossings with gates that prevent cars from going through the crossing when the warning system is active.
In the following detailed description, a plurality of specific details, such as time periods and types of communications systems, are set forth in order to provide a thorough understanding of the preferred embodiments discussed below. The details discussed in connection with the preferred embodiments should not be understood to limit the present inventions. Furthermore, for ease of understanding, certain method steps are delineated as separate steps; however, these steps should not be construed as necessarily distinct nor order dependent in their performance.
A hardware block diagram of a system 100 for controlling a grade crossing warning system according to one embodiment is illustrated in
The onboard equipment 101 is controlled by a processor 110. The processor 110 may be a microprocessor, a microcontroller, a programmable logic array, fabricated from discrete logic, or may be realized using any other devices or methods known in the art. As used herein, the terms “processor,” “computer” or the like should be understood to refer to one device or a plurality of devices. Thus, a statement that a processor or computer performs a step or series of steps should be understood to mean that one or more processors or computers performs the step or series of steps. The processor 110 is programmed to perform the functions described below. The processor is connected to a GPS receiver 114, from which it receives messages including the location of the train. In some embodiments, the messages may further include a time, a heading, and a speed. The GPS receiver 114 may be, e.g., a commercially available RF receiver utilizing a SiRFstar III chipset. As illustrated in
The processor 110 is also connected to a track database 112. The track database 112 is used by the processor 110 to translate position reports in latitude/longitude from the GPS receiver 114 to positions on the track (often expressed in terms of miles relative to some fixed position on the track, in the manner of mileposts but with greater precision). The track database 140 preferably includes a non-volatile memory such as a hard disk, flash memory, CD-ROM or other storage device, on which track data is stored. Other types of memory, including volatile memory, may also be used. In preferred embodiments, the track data comprises latitude and longitude coordinates for a plurality of points corresponding to different locations on the track in a manner well known in the art. The points are not necessarily uniformly spaced. In some embodiments, the points are more closely spaced where the track is curved and less closely spaced where the track is straight. The route or path between points in the database can be described as a vector, and the processor may determine the train's position along the track by determining the point on the vector that is closest to the position reported by the GPS receiver as described in U.S. Pat. Pub. No. 20090043435, the contents of which are hereby incorporated herein by reference.
The processor 110 is also connected to a wayside transceiver 116. The wayside transceiver 116 may be any device capable of communicating with a wayside device. In some embodiments, the wayside transceiver 116 is an RF transceiver, such as the 220 MHz radios currently available from MeteorComm. The wayside transceiver 116 is connected to an antenna as shown in
A brake interface 118 and alarm interface 120 are also connected to the processor 110. The brake interface may be of any type known in the art, and may configured to send a digital message to the braking system, or may be configured to generate an analog signal connected to a P2A valve to initiate an emergency or penalty brake operation. Similarly, the alarm interface 120 may be configured to interact with a simple alarm, such as generating an analog signal to drive a light or bell directly or via a relay, or may be configured to output a digital signal (e.g., a USB or RS-232C signal) to drive an operator display. The processor 110 uses the alarm interface 120 to warn the operator under certain conditions to be discussed further below. The brake interface 118 and the alarm interface 120 may be realized using discrete logic or by any other means depending on the systems with which they must interface.
As shown in
As shown in
The processing performed by the processor 110 in one embodiment of the invention will now be discussed with reference to the flowchart 300 of
If a new crossing is in range at step 304, the processor 110 attempts to establish a communication session with the wayside interface unit 152 at the crossing by transmitting a “session request” message at step 306. Preferably, the session request message is addressed to the specific wayside interface unit 152 identified in step 304 (as will be discussed in further detail below, there may be multiple wayside interface units within the threshold range of the train, and possibly even multiple wayside interface units being controlled by the train at any one time). If the wayside interface unit 152 fails to establish a communications session by responding to the session request message with an acknowledgement (ACK) message, or the ACK message is not received for some other reason, at step 308, the processor 110 assumes that there is a malfunction at proceeds under malfunction conditions at step 310. The train may proceed under malfunction conditions in a number of ways. For example, in some embodiments, the processor may ensure that the train comes to a complete stop prior to reaching the crossing, and then allow the train to proceed through the crossing at a low speed. Alternatively, the processor 110 may allow the train to proceed through the crossing at a low speed without coming to a complete stop. Those of skill in the art will recognize that other procedures are also possible, and all are within the scope of the invention.
If a communications session is established at step 308, the crossing is added to a list of active crossings at step 312, preferably in distance order starting with the nearest crossing. Once the crossing is added to the active list at step 312, or if no new crossings were in range at step 304, the processor 110 calculates an estimated arrival time for the crossing at the top of the list at step 314. The estimated arrival time (i.e., the estimated time at which the train will arrive at the crossing) is calculated based at least in part on the train speed and the distance between the current train position and the location of the crossing retrieved from the track database 112 (those of skill will recognize that more refined estimates could include a current acceleration of the train). The arrival time calculated in step 314 is compared to an arrival time threshold at step 316. The arrival time threshold is based on two values: a desired constant warning time (which is the desired time period prior to the train's arrival at the crossing that the wayside warning system 150 will activate, typically on the order of 30-40 seconds) plus a buffer time (typically on the order of ten seconds) which will be used by the wayside interface unit to start a timer as explained further below. The constant warning time may be a constant, or may be retrieved from the track database 112 in systems in which the desired constant warning time varies by crossing. In yet other embodiments, the wayside equipment 102 may be configured to inform the train of the desired constant warning time, such as in the ACK message transmitted in response to the session request message.
If the arrival time threshold has not been met at step 316, a maintain session message is sent to the wayside interface unit 152 at step 320. If the arrival time threshold has been met at step 316, an “activate after expiration” message will be sent at step 318. The activate after expiration message includes a timeout time discussed above, which will be used by the wayside interface unit 152 to set a timer. The timeout time is the difference between the desired constant warning time and the calculated arrival time. If the arrival time is exactly equal to the arrival time threshold, the timeout time in the activate after expiration message will be equal to the buffer time discussed above. If the arrival time is less than the threshold, the timeout time will necessarily be less than the buffer time and may be zero (signifying that the train has already passed the point at which the warning system 150 should have been activated). It should be understood that the process of
After sending either the maintain session message at step 320 or the activate after expiration message at step 318, the processor 110 determines if the a responsive acknowledgement message is received from the wayside interface unit 152 at step 322. If the acknowledgement message is not received, or an acknowledgement indicating a malfunction or other non-satisfactory status is received, at step 322, the processor 110 ensures that the train proceeds under malfunction conditions at step 310 as described above. If an ACK message is received at step 322, the train's speed and position are updated (e.g., by checking the database and/or querying the GPS receiver 114) at step 324. Next, the processor determines whether additional active crossings are on the list at step 326. If so, step 314 is repeated for the next crossing on the list; otherwise, the process begins again at step 302.
Once the timer is set (or reset in the event that the same train had previously sent an activate after expiration message) at step 406, or cleared at step 407, the status of the wayside equipment 102 is checked at step 408 and an ACK message including the status is transmitted at step 410. Step 402 is then repeated when the next message is received. It should be understood that the expiration of one of the timers discussed above will result in the activation of the warning system 150 by the wayside interface unit 152. For example, the wayside interface unit may be configured such that the expiration of a timer generates an interrupt, and an interrupt service routine in the wayside interface unit 152 then triggers an output that activates the wayside warning system 150. Alternatively, this functionality may be implemented as a polled function rather than an interrupt-drive function. In yet other embodiments, the timers may be implemented in hardware forming part of the warning system 150, and wayside interface unit 152 may write values to the hardware timers and activate, reset and deactivate the timers as discussed above. In this way, if the wayside interface unit 152 fails after initiating a timer, the timer will continue counting down and activate the warning system 150. Still other arrangement may be used in other embodiments.
The discussion of
In the embodiments discussed above, the “activate after expiration” message includes an express time period (referred to as the timeout) after which the crossing should activate. Including the time expressly in the message provides for the ability to change the time to account for train accelerations and declerations as discussed above. However, in other embodiments, the time period can be implied. For example, in a railway system in which the constant warning time is the same for all crossings (say, 30 seconds), the activate after expiration message may not expressly include any time period, and the wayside equipment may treat the message as including an implied timeout period (in other words, the message type itself indicates the timeout period). In such a system, the “activate after expiration” message need only be sent and acknowledged once. In this embodiment, the train may not have a mechanism to accelerate the activation of the warning system to accommodate any train acceleration so the constant warning and timeout periods must be chosen with this in mind, and likewise the train may not have a mechanism to delay a previously-started timer at the wayside unit to account for decelerations of the train. In yet other embodiments, such a provision could be realized by providing for a reset message to be sent from the train when a change in the timeout value is desirable due to a train acceleration or deceleration.
The above discussion illustrates how equipment onboard a locomotive can control the activation of wayside grade crossing equipment. This function is typically performed by wayside constant warning time predictor equipment as discussed above. This equipment is costly, both in terms of initial installation cost and maintenance. Thus, in some situations, the equipment discussed in
In the discussion of
An exemplary sequence in a hypothetical situation in which a train approaches three closely spaced crossings is illustrated in Table 1 below:
The foregoing examples are provided merely for the purpose of explanation and are in no way to be construed as limiting. While reference to various embodiments is made, the words used herein are words of description and illustration, rather than words of limitation. Further, although reference to particular means, materials, and embodiments are shown, there is no limitation to the particulars disclosed herein. Rather, the embodiments extend to all functionally equivalent structures, methods, and uses, such as are within the scope of the appended claims.
The purpose of the Abstract is to enable the patent office and the public generally, and especially the scientists, engineers and practitioners in the art who are not familiar with patent or legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The Abstract is not intended to be limiting as to the scope of the present inventions in any way.
