CA2166344A1 - Optical train motion/position and collision avoidance sensor - Google Patents

Abstract

A system for detecting the presence of objects, the relative movement between a vehicle provided on a rail track and other objects such as other railway vehicles, the speed of rail vehicles or the presence of stationary obstructions. The system having a signal emission source mountable to the railway vehicle for generating an optical signal, a signal detector mountable to the railway vehicle for receiving optical signal reflected from the other objects, and a processor operatively connected to the detector for interpreting the reflected optical signal to detect the presence of and/or relative movement between the railway vehicle and the other objects. The other object may include one or more stationary markers placed wayside of the rail track, such that reflected optical signals from the wayside markers are interpreted by the processor to provide the velocity of the railway vehicle.

Description

21~634q TITLE

OPTICAL TRAIN MOTION/POSITION
AND COLLISION AVOIDANCE SENSOR
BACKGROUND OF THE INVFNTION
1. Field of the Invention This invention relates generally to the art of railway signaling and communication. More particularly, the invention relates to an apparatus and method tili7ing optical sensing and associated signal processing for detenninin~ the ground velocity of a vehicle, as well as detecting obstacles in the path of the vehicle.

2. Description of the Prior Art To assure proper operation of rail/guideway transportation systems, a majority of the industry's efforts have been focused on the extension of traditional schemes. Such traditional schemes involve knowing where all vehicles on the system are, how they are moving, and m~int~ining continl~nce communication between each vehicle and a wayside control system. Several system problems arise if vehicles are lost, or if an uninstrumented vehicle or obstruction is introduced into the system.
Typical wayside instrumentation systems for railway and transit installations interconnected the central office to wayside equipment, such as switching and .ci~nz3llin~ devices, so that traffic flow may be remotely directed. This system requires that the system have the capability of detecting the presence of railway vehicles within the controlled territory. This train detection capability is typically provided by the railway track circuit. Although there are many variations, railway -signal control systems typically use the track circuit block as the basic element of train location, and communication and control. Blocks may range in length from a few hundred feet to approximately two to five miles. Electrical signals applied to the length of track comprising a block are shunted by the rail vehicle axle. This change in signal is detected and used to indicate that a block is occupied. In addition, such track circuits also can be used to detect for broken rail, and establish communication from wayside equipment to moving rail vehicles, i.e., cab signals.
While block signals may often provide reliable indication of the vehicle's position, a limiting factor can be the length of the given block. When a vehicle crosses two adjacent 1,000 foot block sections, for example, the signal apparatus will detect the vehicle within a 2,000 foot length of track. Because train operation depends upon the conditions in front of and behind moving vehicles, such 2,000 foot vehicle indication may effect operation in over a mile of track. The safe headway between trains must be m~int~ined at a minimum distance so as to permit a high operating frequency of service. One of the ways this can be achieved is by increasing the number of individual track circuits, and decreasing the length of each track circuit. However, to obtain shortened track blocks requires a proportionally higher number of track circuit equipments and can become cost prohibitive. Such additional track circuits would require additional equipment such as track bonds, vital track interlocking, and vital logic equipment.
Figure 1 illustrates a prior art coded track circuit installed within a block 1. Typically, block 1 is electrically isolated from adjacent blocks, such as by a number 21663~4 of insulated rail joints 2A-D. A communication link between block 1 and adjacent blocks is provided by track circuit units 3 and 4, each of which has a transmitter and a receiver. Transmitter T1 of track circuit unit 3 is connected across rails 5 and 6 at a transmit end of block 1. Receiver R2 of track circuit unit 4 is connected across rails 5 and 6 at a receive end of block 1. Similarly, receiver R1 of track circuit unit 3 is connected across rails 5 and 6 at a receive end of the block immediately to the right of block 1. Transmitter T2 of track circuit unit 4 is connected across rails 5 and 6 at the transmit end of the block immediately to the left of block 1.
The coded track circuit within block 1 thus includes, in series, tr~n~mitter T1, rail 5, receiver R2 and rail 6. When block 1 is unoccupied by a railway vehicle and no state of broken rail exists, electrical current is free to flow through this serial combination. This electrical current is typically coded to carry signal information which may be used to indicate block 1 as being unoccupied and provide other control functions.
Thus, the prior art track circuit system requires a great deal of system components which can become rather expensive. Furthermore, this track block system detects the presence of another object when the track circuit is interrupted such as by the presence of a rail vehicle axle. Other objects such as boulders, cattle, etc. may not be detectable through this system. Also, the precision of the system in locating another vehicle is limited by the specific length of the block which can be anywhere from hundreds of feet to several miles. Moreover, the requirement of communication _ 21663~q between each vehicle and a wayside control system provides the possibility of communication breakdown which would jeopardize operation of the system.
Other rail vehicle signal systems do not use traditional track circuits, but instead use a "moving block" system. The moving block system uses an automated train control system in which a following train receives information such as the velocity and position of a train ahead of it. A central control function can have a dialogue with all trains on the system. The central control can know the general velocity and position of each train on the system at all times. A vital train to wayside communication system can provide position information to each train concerning the respective lead train. In some systems, the central control function also provides velocity information concerning the lead train to the respective following train. On-board calculations may then compute the speed profile to m~int~in at least a safe braking distance between itself and the lead train. The moving block system can use vital logic at the central control facility to provide the position of each train on the system, and determine which information is transmitted to each train.
Advantages of such moving block systems are the reduction of equipment associated with discrete track circuits, and the moving block system can in some instances result in reduced headways. Some of the disadvantages of such a moving block system are the reliance upon a central control facility to process the information and transmit vital information across the system to the vehicle. Failure at the central control facility may result in down time as no information will be available to trains on the system.

21663~
-A vehicle sensor and control system has been developed by Mercedes Benz for automobiles. This system called "AICC" measures the relative speed between the automobile and other automobiles on the road as opposed to measuring the absolute speed of the vehicle. The AICC is further designed to ignore roadside objects.
SUMMARY OF THE INVENTION
The invention uses an optical sensing means and associated signal processing method for detennining the ground velocity of a rail vehicle using on-board equipment. The technique and system utilize a currently available laser based range finder with additional motion sensors and optics to sweep-out a sensory arch in front of the vehicle. The optical signal sensory arch, together with signal proces~in~, determines the motion of the ground with respect to the train. The sensory arch can also be used to detect other trains and obstacles in the path of the vehicle and to recognize encoded position markers that may be installed along the vehicle's path.
In presently prcrellcd embodiments, an optical beam sc~nning device, such as a delta-ranging optical range finding device connected to processing means, is provided upon the front end (and/or rear) of a train. The optical beam sc~nning device projects an optical beam from the front of the vehicle in the direction of motion. The device is further coupled with swivelling reflective optics or a swivelling mount which sweeps the rangefinder beam through an azimuthal or sideways arc, thus sweeping out a sensory path extendin~ at a distance beyond the vehicle. The sensory arch can be fixed at an elevation angle (beaming downward) with respect to the grade on which the train 216~3A4 -is moving. In this way, the vehicle's motion with respect to the ground may be determined.
Additional sensors are optionally employed to check the validity of the range finder's output, and/or to correct for error that is induced by using the system on a railway that is either not level or is not straight. For example, a tachometer may be used to check whether the range finder output is within reasonable range with respect to the rotation of the wheels. Conversely, the rangefinder output can be used to detect or correct wheel/rail slip error during start or stop, which can induce error in the way the train motion is controlled.
The output signal from the range finder is digitized and fed into a data processing computer for the purposes of vehicle motion-parameter determin~tion and detection of obstacles in the train's path.
Wayside location markers may be utilized to aid in the train positioning and control. These markers can use variations and combinations of height and/or spacing to form a characteristic code which is recognized by the sc~nning range finder system. The markers have a geographically fixed position uniquely associated with its code, which can be used to aid in train position determination and to provide the train control system with extra data to verify the actual status of the rail system.
Although the present invention is herein described in cooperation with railway vehicles, the invention is also applicable to guideway vehicles. A guideway vehicle is a vehicle that travels upon unguided wheels and the vehicle itself is steered -by a rail. For ease of discussion, the term "rail vehicle" will refer to railway trains and guideway vehicles.
Other objects and advantages of the invention will become apparent from a description of certain presently preferred embodiments thereof shown in the drawmgs.
BI~TFF DESCRIPTION OF THE DRAWINGS

Figure 1 is a diagrammatic representation of a prior art coded track circuit.
Figure 2 is a schematic depiction of a top view of a train on a section of track having the preferred range finding system.
Figure 3 is a schematic depiction of a side elevation view of a train on a section of track having the preferred range finding system.
Figure 4 is a block diagrammatic representation of the range finding system.
Figure 5 is a schematic depiction of a train having the range finding system having obstacles in its path.
Figure 6 is a first sample waveform from the range finding device of the sensor system of Figure 5.
Figure 7 is a second sample waveform from the range finding device of the sensor system af Figure 5.
Figure 8 is a third sample waveform from the range finding device of the sensor system of Figure 5.

216~44 _, Figure 9 is a schematic depiction of a train having the range finding system traveling on a curved section of track.
DETAILED DF~CRTPTION OF THF PREFERRED EMBODIMENTS
Referring to Figures 2 and 3, a preferred embodiment of the system is shown. A rail vehicle train 12 is shown on a section of track 18. An end of the train 12 (shown in Figures 2 and 3 as a front end of the train 12, such as a locomotive or lead car) is suited with a delta-ranging optical range-finding signal emission source and detector 14. Such optical range-finding devices 14 are generally known and suitable such devices are manufactured by Laser Atlanta. The range-finding device 14 emits an optical beam (preferably in pulses) which are projected outward from the rail vehicle 12 in a given direction. The typical range of detection for such ranging devices is approximately 1,000 to 10,000 feet.
The range-finding device 14 is preferably coupled with means for sweeping the range finder beam outward of the train car. Suitable sweep means preferably include a reflective surface (such as a mirror or prism, described in more detail below) coupled to a swivelling drive (also described in more detail below). Thus a sensory path is swept out which extends at a distance beyond the vehicle 12. The range finding beam is preferably swept out as a sideward arc. The sensing arc, therefore, has a sideways or azimuthal sweep angle design~te~l "beta" (,~). The sideways scan sweep angle ,B should cover the track 18 regardless of the orientation of the vehicle 12 with respect to the curve of the track 18. Thus, if markers (discussed in 211~344 _ detail below) are used that are placed outward of the track 18, the sweep scan angle ,B is preferably wide enough to include the markers wayside.
As the vehicle 12 travels around a curved section of track 18, the angle can be slightly broader than it would be for straight section of track 18.
The sensory arc can be fixed at an elevation angle (beaming downward) with respect to the grade on which the vehicle 12 is moving. As shown in Figure 2, the elevation angle is designated "alpha" (a). If the scan length is further out in front of vehicle 12 (i.e., a smaller angle a), the sweep angle"B, can be narrower in order to sweep out the same arc section. If angle a is smaller so that the scan length L is longer, the scan sweep angle ~ need not be as wide because the sweep is linear along the ground.
Elevation angle a dictates the length from the vehicle 12 at the height of the point at which the signal is emitted to the farthest scan point, which length is denoted "1". Length I varies based upon the angle a at which the beam is cast down the length of the track 18, the height of the emission source of range-finding signal and also the flatness of the grade extending from the train 12. The actual scan length from the bottom front of the vehicle 12 along the track to the farthest scan point is denoted "L".
The angle a relates the perceived motion of the vehicle 12 with respect to the ground within the plane of the scan arc. Thus, the value of length L is derived from the value of I and is computed in the processing means 46. L may be derived from the relationship, L = I * Cos(a).

~1663~

~ L and ~l represent the change in lengths L and 1, respectively. The changes in lengths L and 1 are due primarily to the motion of the vehicle 12. As the vehicle 12 moves, the ground will move with respect to the vehicle 12 and ~L is the length that the vehicle 12 travels during a scanned time. Vehicle motion is described by L + ~L, backward or forward, where ~L = ~1 * Cos(a), and where ~L is the distance of the vehicle 12 along track 18 traveled in time ~t.
Additional sensors can be employed to check the validity of the output from the range finding system, or to correct for error that is inclllce~l by using the system of a track section that is neither level nor straight. For example, a tachometer 28 may be used to check whether the range finder output is reasonable with respect to the rotation of the rail vehicle's wheels. Conversely, the range finder output can be used to detect or correct wheel/rail slip error during start or stop, which can induce error in the way the train motion is controlled.
A pulse of light is emitted from the range-finding device 14 of the vehicle 12, directed outward to a reflection site and returns to the range-finding device 14 in a measured time. If the vehicle 12is stationery, the distances between the vehicle 12 and a reflection site are L and 1 respectively, and the values of ~L and ~1 are equal to zero. As the train 12 begins to move, there is some distance that the train 12 travels in the time that it takes for the pulsed light signal to return to the range-finding device 14, thus there is a change in the time for the signal to reflect back to the range-finding device 14, and this change in time is perceived as the change in length due to the motion of the vehicle 12. If the vehicle is moving forward, the perceived length ~16634~
-between the vehicle 12 and the reflection site is L minus ~L. When the vehicle 12 is moving in reverse, the perceived length is L plus ~L.
The system detects vehicle speed relative to stationary reflection sites (such as ground) where it is sc~nning. Sc~nning involves a focus beam directed toward reflection sites. Reflection sites can be surfaces (such as the gravel in between or around the rails, railties, existing structures present near the rails or markers placed near the rails) that will reflect the beam back to the train. During the time in which the beam is emitted to the reflection site and is reflected back, the distance to that reflection site is going to change and is ~l. The beam is sent as a series of light pulses and the detector and processor deterrnine the time of the flight of that pulse as it reflects off an object. The ~ t~nce between the detected object and the range-finding device 14 is determinable from time of flight due to the relationship of the speed of light through the gaseous medium. As the train 12 with its range-finding device 14 moves, the range-finding device 14 treats the train 12 as a fixed reference frame, thus the reflection site is detected as moving towards the train 12 at a discernable rate.
The output signal from the range finder 14 is digitized and fed into data processing means described in more detail below for the purposes of vehicle motion-parameter determination and detection of obstacles in the vehicle's path.
Referring to Figure 4, a block diagram is provided that shows the interaction of the various components of the presently prcrt;,lcd sc~nning and processing apparatus. A sc~nning drive 16 is coupled to a scan directing surface 15.
The scan directing surface 15 is preferably a mirror-type or a prism-type. When the scan directing surface lS is the mirror-type, the sc~nninp~ drive 16 is preferably a stepper motor which oscillates or reversingly rotates the scan directing mirror back and forth. The scan directing surface 15 is mounted so that the scan beam is directed downward at a constant angle. Thus, a scan beam directed off of the scan directing mirror is swept back and forth through azimuthal angle ~ and at an elevational angle a.
When the scan directing surface 15 is prism-type, the sc~nning drive 16 continuously rotates the scan directing prism. The prism is thus rotated continuously in one direction such that the range finding beam reflects off of a first surface of the prism and sweeps the beam through azimuthal angle ,~ in one direction, the beam disappears for an instant and then as the next of the three prism surfaces comes into contact with the optical beam, the beam is swept through the same direction.
A scan controller and preprocessor 17 controls the sc~nning drive 16 mounted onboard the rail vehicle. The scan controller and preprocessor 17 also controls the range-finder emission source and detector 14. The scan controller and preprocessor 17 records the angle of the scan beam and an initial time stamp, so that it is known where and when a given beam is being driven. Then, the controller and preprocessor 17 takes the signal detected at the range finder source/detector 14 and processes the signal, yielding raw scan data (indicated at 58). Raw scan data 58 includes a series of the times for scan beams to be sent and returned from a scanned surface. The raw scan data 58 is sent to a postprocessor 19. In addition to the raw scan data 58, scan-associated data (indicated at 60) is also sent to the postprocessor 19 from the scan controller and preprocessor 17. The scan-associated data 60 includes the 2166~44 -corresponding angle of the scan (derived from the angular position of the reflective surface 15 and the scan drive 16 and the time that the respective samples were taken.
A database 21 of topographic data related to the scanned surface including wayside reference points is also input into the postprocessor 19. Since L is the point where the elevation scan angle a intersects the ground and track. If the terrain is not flat, there is some change in L which is not due to the motion of the vehicle. This variation is accounted for by the topographic information.
The postprocessor 19 processes the raw scan data 58, the scan-associated data 60 and data from the topographic ~l~t~h~e and outputs several types of information: data related to the kain position (indicated at 62), data related to train motion parameters (indicated at 64), and data related to obskuction detection and classification (indicated at 66). Train motion parameters 64 include the velocity of the vehicle and vehicle acceleration. The train position information 62 places the vehicle 12 on a specified point or location on the track 18. The obstruction detection and classification data 66 is derived from higher order functions within the postprocessor 19. These higher order functions conducted by the postprocessor 19 take the raw scan data 58, scan-associated data 60 and data from the topographic database 21 and derive information regarding an obstruction on the track 18 or between rails of the track 18 or an oncoming train 22 or wayside markers 26 based on the shape of the return scan.
The kain position information 62, kain motion parameters 64 and obstruction detection and classification information 66 are then input to an automatic train conkol processor 23 (commonly known as an ATC). The automatic train control - 2166~4~

processor 23 is an equipment that has heretofore been used in the prior art to automatically control the train based upon signals received from the wayside or a central location, and assures that the train is operated under certain limits for procee~1in~ on the track. The train propulsion and brake control 25 are common controlled train functions that the automatic train control processor interfaces with onboard.
A tachometer 28 connected to a rotating portion such as a wheel or motor produces data that is preferably used as additional input to the automatic train control processor 23 to assist in a final determination of train position and motion.
Instead of or in addition to the tachometer 28, information from an onboard accelerometer (not shown) may be input to the automatic train control processor 23.
Optional communication between the train and wayside and/or central train control equipment 27 is shown in dotted lines as being connected to the automatic train control processor 23.
The rate at which pulses of the scan beam are emitted from the signal emitter/detector 14, the number of pulses and the frequency of the pulses are controlled by the control preprocessor and scan controller 17. The scan controller and preprocessor 17 and the postprocessor 19 perform two different discreet processes and preferably are but not be two different discreet stations.
Referring next to Figure 5, the sensor system is shown interacting with moving and nonmoving obstacles. Examples of signal output from the sensor system of Figure S are depicted in Figures 6-8. The waveforms of Figures 6-8 are plots of "l"

_ 2166~44 vs. "t". Figure 6 depicts a waveform for the condition where the train 12 having the range-finding device 14 and another train 22 in its path are stationary. The waveform in this example has essentially two components, the background section 34 and a portion 36 in which an obstruction (in this case the other train 22) is detected. The background portion 34 represents the farthest most scan point that the optical beam from the range-finding device 14 reaches. In this case, the waveform background portion 34 represents the ground 20 adjacent the track 18. Waveform portion 36 provides a profile of the scanned obstruction. Thus, the general size and configuration of the obstruction may be determined from waveform portion 36. Note that in Figure 6, the position of the sensed other train 22 in relation to train 12 (represented as "1") does not change with respect to time (t). Thus, it may be readily discerned from this waveform that train 22 and train 12 are not moving in relation to one another. In this case ~l is equal to zero.
Figure 7 depicts a waveform for the condition where the train 12 having the range-finding device 14 and the other train 22 in its path are moving towards one another. Again, the waveform consists of two basic portions, the waveform background 34 and the sensed portion 36 in which an object (and again in this example the object is other train 22) is detected by the optical beam of the range-finding device 14. In this example, the leading face of the waveform portions 36 have a sequentially lower value of 1. Thus, the distance between train 12 and the other train 22 is decreasing over time and the trains are moving closer together. The amount of the change in the distance l for a particular time period ~t is depicted as ~1. Thus, the 216~

distance between the train 12 and other objects is determinable through the waveforms generated by the range-finding device 14 and the rate of change of those distances is also determinable.
Figure 8 depicts the situation where the train 12 having the range-finding sensor 14 and the other train 22 in its path are moving towards one another and a fixed obstacle 24 (shown in dotted line in Figure 4) is also positioned between the two trains 12, 22. In this example, the sensed portion of the waveform 36 has two different components, a component 38 which represents the profile of train 22 and a component 40 which represents the profile of the stationary object 24. Because train 12 and train 22 are moving relative to one another, the value of the length from component 40 of the waveform is decreasing over time. The rate at which that length changes per unit time is depicted by the dashed slope line 42. Similarly, the distance between train 12 and stationary obstacle 24 is ch~n~ing over time and this change of length is depicted by dashed slope line 44. Because train 12 and train 22 are moving toward one another, the overall change in distance between the two trains over time is larger than the rate of change between the train and the stationary obstacle 24. Thus, the slope of slope line 42 is greater than the slope of slope line 44.
As the range-finding device's beam scan-plane intersects both the fixed obstacle 24 and the train 22 ahead, the sc~nnin~ range-finder's output indicates that it encounters something closer than the background reflections (i.e., the sensor readings where the scan-plane intersects the ground). The range-finder scan indicates the distance to the objects along the track 18 and forms a signal which is characteristic of ~1~63~4 the basic shape and dimension of the obstacle or obstacles ahead. The data derived from the sensor output is preferably processed by on-board equipment to detect and identify obstacles, as well as to assist in avoiding collisions.
Wayside location markers 26 may be utilized to aid in the train positioning and control. These markers 26 can use variations and combinations of height, shape and/or spacing to form a characteristic code which is recognized by the sc~nnin~ range finder system. The markers 26 preferably have a geographically fixed position uniquely associated with its code, which can be used to aid in train position determination and to provide the train control system with extra data to verify the actual status of the rail system. The advantages of the presently described wayside markers 26 include the passive nature of the markers 26. In other words, no active signal means is required for the markers 26so that expensive circuitry and tr~n.~mission apparatus is not needed and the possibility of communication failure from the markers 26 to train 12is avoided. In addition, rail system structures, such as switches or stations, may be detected to enhance the h~z~rd avoidance control aspects of the rail system.
For conducting rail system coordination and operations, position, motion and other control-related data the system produces on board may be sent to other trains and/or wayside control equipment. This data may be communicated such as by a wireless link between nearby trains and/or the wayside control equipment. There need not be any direct interaction between and among various trains. The scanned information gathered at one train may be sent off to a central processing location so that several trains may be coordinated in an overall traffic control scheme. A stored _` ~lG6344 topographical database may be provided on the train that provides the possible tracks that can be travelled upon. The system could also have a reference point, and once it scans out a reference point it knows exactly where the vehicle is on the map and can track the vehicle's movement and therefore its position along the L direction. The system does not require that information be transmitted to any central location, although this may be done. Rather, messages may be sent along the rail that tells the vehicle its allowed velocity. The collision detection system would be ~c~nnin~ for obstacles in its way and it may have an onboard algorithm that would stop the vehicle when an obstacle is sensed. The position data and collision avoidance data that is collected or produced by the invention is used in an onboard train control and can be sent to the signaling and train control system for overall control.
As depicted in Figure 9, a car employing the prere.led sc~nning system would occasionally travel along lengths of track that are curved (in this case, for example, a right hand curve). As the system scans out the arc ,B in front of the vehicle, the center of that scan arc will be to the left, potentially outside the track. In order to assure adequate collision detection, the sc~nning arc swept out by azimuthal sc~nning angle ~ must be swept over the track no matter what the degree of the curve. The center of track curvature is design~ted as "C". The angle from the center of track curvature C formed by the two lines is designated 2a, so that if the angle is bisected, two angles are formed. Line Rl extends from the center of track curvature C to the position of the train on the track. Line R2 extends from the center of track curvature C
to the intersection of scan arc ,B and the track (which is the farthest point of the track 2166~4 which is scanned at a given time). The sc~nning angle ~ is of sufficient width to include a given curved track for a length L when 1/2 ~ > a. The safe separation distance between two trains is Ds~ the minimum track radius of curvature for a track system is Rmjn and L > Ds From Figure 9, the following relationship may be derived:
sin(a) = (L/2)/Rmjn = L/2 Rmjn. It may thus be stated that sin(~B/2) is > sin(a) = L/2 Rmjn. Therefore, sin(~/2) is > Ds/2Rmjn and hence ,~ is > 2 sin ~ (Ds/2Rmjn). Thus, if a minimum value of L desired is known and the minimum curvature of the track is known, the azimuthal sc~nning angle ,B may be determined. Note that for ease of illustration, the two rails of the track are depicted as a single path.
Variations of the pler~lled embodiments are possible. For example, although the signal emission source and signal detector are preferably a single unit, as such are commercially available, the source and detector may be separate app~dluses.
Also, although the preferred means of directing the scan beam involve a reflective surface driven by a controller, any such scan directing means may be employed, including mounting the signal source/detector to a swivelling mounting.
Additional sc~nning devices 14' may be provided. For example, in Figure 3 an additional sc~nnin~ device 14' is shown mounted on the front end of a train vehicle. The sc~nning device 14' of Figure 3 is also connected to processing means and vehicle control functions, but is preferably mounted (or otherwise has the scan beam directed) at a different elevational angle a than the scan device 14. As a further alternative, an additional sc~nning device 14' (shown in Figure 3) that is also connected to processing means and vehicle control functions may be provided on the rear of the Z166~44 train vehicle (preferably the last train car) directed behind the vehicle. Additional sc~nning device 14' on the rear of the vehicle may be employed instead of or in addition to the sc~nning device 14 on the front of the vehicle.
Also, although optical signal sc~nning is preferred, other signal means such as sonar, radar or ultrasound are possible. Furthermore, although the range-finding device and scan directing means are shown as being mounted on a front end of the rail vehicle, such may additionally or alternatively be provided on the rear end of the rail vehicle to determine the presence of and the rate at which other vehicles are closing on the vehicle. Rear mounted units can also be used to detect train speed and position.
While certain presently pl~r~lled embodiments have been shown and described, it is distinctly understood that the invention is not limited thereto but may be otherwise embodied with the scope of the following claims.

Claims (7)

1. An apparatus for use on board a railway vehicle travelling over a fixed pathway, said apparatus comprising:
a signal emission source means mountable to said vehicle for generating an optical signal;
a signal detection means mountable to said vehicle for receiving said optical signal once said optical signal has reflected from at least one passive stationary marker placed at a predetermined location wayside of the fixed pathway;
A topographic database having information identifying a detected object as a unique wayside marker;
processor means operatively connected to said detection means and said topographic database for interpreting said reflected optical signal to detect a position of said vehicle along said fixed pathway; and wherein said at least one passive wayside marker is sized and configured such that physical characteristics of said at least one wayside marker provides information identifiable by said processor means.

2. The apparatus of claim 1 wherein said at least one wayside marker is a plurality of markers, each such wayside marker being spaced a selected distance from an adjacent marker, and wherein said marker spacing provides information identifiable by said processor means.

3. The apparatus of claim 2 wherein each wayside marker is sized and configured such that combinations of physical characteristics of said wayside markers and spacing between said wayside markers provides information identifiable by said processor means.

4. The apparatus of claim 1 further comprising scanning means operatively connected to said signal emission source means for sweeping said optical signal over a selected azimuthal angle.

5. The apparatus of claim 4 wherein said scanning means directing said optical signal at a selected elevational angle from said vehicle.

6. The apparatus of claim 1 wherein said signal emission source means comprises at least two signal generating devices provided on a same end of said vehicle directing respective optical signals at respective and different selected elevational angles.

7. The apparatus of claim 6 further comprising means operatively connected to said signal emission source means for sweeping said optical signals over respective azimuthal angles.