Abstract:
Devices, systems, and methods for imaging and measuring deflections in structures such as railroad rail are disclosed. One exemplary embodiment relates to a vision system having a high-speed, visible-light imaging camera and an evaluation unit configured for analyzing images from the camera to detect geometric variations in the structure. In a second example, additional sensors are used to identify the wheel location(s) in the same reference frame as the measurement system. In analyzing structures such as railroad track rail, the imaging camera can be coupled to a moving rail vehicle and configured for generating images of the rail as the vehicle moves along the track.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. Provisional Application 61/733,287, filed Dec. 4, 2012, and entitled “System for Imaging and Measuring Rail Deflection,” which is hereby incorporated herein by reference in its entirety. 
    
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with government support under FRA grant FR-RRD-0026-11-01-00, entitled “Measurement of Vertical Track Deflection: Testing, Demonstration &amp; Implementation.” The government has certain rights in the invention. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to analyzing deflections in structures. More specifically, the present disclosure pertains to devices, systems, and methods for imaging and measuring deflections in structures such as railroad rails. 
     BACKGROUND 
     The economic constraints of both passenger and freight railroad traffic are moving the railroad industry to higher-speed vehicles and higher axle loads. The heavy axle loads and high speeds of modern freight trains produce high track stresses leading to quicker deterioration of track conditions. As a result, the demand for better track maintenance has also increased. Fast and reliable methods are thus needed to identify and prioritize tracks in need of maintenance in order to minimize delays, avoid derailments, and reduce maintenance costs. 
     The condition and performance of railroad tracks depends on a number of different parameters. Some of the factors that can influence track quality are track modulus, internal rail defects, profile, cross-level, gage, and gage restraint. Monitoring one or more of these parameters can improve safe train operation by identifying track locations that produce poor vehicle performance or derailment potential. Track monitoring also provides information for optimizing track maintenance activities by focusing activities where maintenance is critical and by selecting more effective maintenance and repair methods. 
     Track modulus is an important factor that affects track performance and maintenance requirements. Track modulus is defined generally as the coefficient of proportionality between the rail deflection and the vertical contact pressure between the rail base and track foundation. In some cases, track modulus can be expressed as the supporting force per unit length of rail per unit rail deflection. Track modulus is a single parameter that represents the effects of all of the track components under the rail. These components include the subgrade, ballast, subballast, ties, and tie fasteners. Both the vertical deflection characteristics of the rail as well as the track components supporting the rail can affect track modulus. For example, factors such as the subgrade resilient modulus, subgrade thickness, ballast layer thickness, and fastener stiffness can affect track modulus. 
     Variations in track shape and structural integrity present hurdles in the rail industry: both low track modulus and large variations in track modulus are undesirable. Low track modulus can cause differential settlement that subsequently increases maintenance needs. Large variations in track modulus, such as those often found near bridges and crossings, can also increase dynamic loading. Increased dynamic loading reduces the life of the track components, resulting in shorter maintenance cycles. A reduction in variations in track modulus at grade (i.e. road) crossings can lead to better track performance and less track maintenance. It has also been suggested that track with a high and consistent modulus will allow for higher train speeds and therefore increase both performance and revenue. Ride quality, as indicated by vertical acceleration, is also strongly dependent on track modulus. 
     In addition to track modulus, variations in rail geometry resulting from track defects can also affect track performance. The relationship between modulus and geometry is complex. In some cases, areas of geometry variations often correlate with areas of modulus variations and vice versa. 
     Finally, track deflection is also important. Track deflection is related to the applied loads, and the track modulus (and stiffness) is also an important factor. Deflection is defined as the ratio of applied load to track stiffness. More general, it can be defined as the vertical displacement of a single point of rail from the unloaded to the fully loaded condition. 
     SUMMARY 
     The present disclosure relates generally to imaging and measuring deflections in structures such as a railroad rail. An exemplary vision system for imaging geometric variations along a railroad track comprises at least one imaging camera adapted for coupling to a moving rail vehicle located on the rail. The imaging camera configured for generating images of the shape of the rail (or an approximation of the shape) during vehicle movement along the rail; and an evaluation unit including an image processor configured for analyzing the images from the imaging camera. 
     In the exemplary methods described, the various embodiments encompass measurement systems for determining geometric relationships to identify the shape of the rail beneath the railcar&#39;s wheels. These shapes can then be used to draw conclusions about the deflection, modulus, rail curvature, stiffness and/or other parameters relevant to track quality, so as to better provide for the analysis of the structural integrity. 
     A first exemplary method for analyzing the geometric shape of a railroad track rail comprises acquiring a plurality of images from at least one imaging camera coupled to a moving rail vehicle; detecting a location of the rail within each acquired image; identifying and measuring a change in the position or shape of the rail away from an expected position or shape of the rail within each image; and determining vertical track deflection data at a plurality of different locations along the rail. This may include the use of structured light such as a line laser. 
     A second example is also presented for a different type of railcar with a different suspension system or device. In this type of rail car the wheels (i.e. axles) have a suspension system or device (i.e. springs and/or dampers) between the railcar sideframe and the wheels. This is sometimes seen in passenger railcars or locomotives. In this example, separate measurement sensors are used to identify the location of the wheels (and or axles) with respect to the sideframe or each other. Then, the rail position can also be measured relative to the sideframe to give an understanding of the rail shape. 
     While multiple embodiments are disclosed, still other embodiments will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a certain embodiment of a system for imaging and measuring deflections in a structure; 
         FIG. 2  is a perspective view of an illustrative vision system for imaging and measuring deflections in a structure; 
         FIG. 3  is another perspective view showing an illustrative implementation of a system for imaging and measuring vertical deflections along a railroad rail; 
         FIG. 4  is another perspective view showing another illustrative implementation of a system for imaging and measuring vertical deflections along a railroad rail; 
         FIG. 5  is a schematic showing exemplary laser lines against the reference plane for use in imaging and measuring the geometric shape of a rail; 
         FIG. 6  is a schematic drawing showing an exemplary embodiment of the vision system on a railcar showing the sideframe; 
         FIG. 7  is a schematic drawing showing an exemplary embodiment of the vision system on a railcar showing the sideframe reference frame; 
         FIG. 8  is a schematic drawing showing a further illustrative example of the sideframe reference frame; 
         FIG. 9  is a schematic drawing showing yet another illustrative example of the sideframe reference frame according to one embodiment; 
         FIG. 10  is a schematic drawing showing yet another illustrative example of an the sideframe reference frame alternate according to one embodiment; 
         FIG. 11  is a schematic drawing showing an exemplary embodiment of the sideframe reference frame in space, without a rail car; and 
         FIG. 12  is a schematic drawing showing an exemplary embodiment of the sideframe reference frame in space, without a rail car. 
     
    
    
     While the various embodiments disclosed and contemplated herein are amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the disclosure to the particular embodiments described. On the contrary, the various embodiments are intended to cover all modifications, equivalents, and alternatives falling within the scope of the those embodiments as defined by the appended claims. 
     DETAILED DESCRIPTION 
     The present disclosure describes devices, systems, and methods for imaging and measuring deflections in structures such as a railroad rail. In some embodiments, for example, the devices, systems, and methods can be used to detect geometric changes in the rail that can affect the calculation of vertical track modulus and/or other characteristics of the rail. Although various embodiments are described in the context of imaging and measuring rail deflections in a railroad rail, the devices, systems, and methods described herein can be used to image and measure deflections in other types of structures that are subjected to static and/or dynamic loading. 
     Two sets of exemplary embodiments are described herein. A first set relates to a system to be mounted on what is commonly called a three piece truck. Illustrative examples of these embodiments are shown in  FIGS. 1-5 . A second set of exemplary embodiments relates to a system to be used on a truck structure having a suspension system or device—and therefore significant relative movement—between the sideframe and axles. Illustrative examples of these embodiments are shown in  FIGS. 6-12 . 
     The first exemplary embodiment is shown in  FIG. 1 .  FIG. 1  is a schematic view showing certain components of an imaging and deflection measurement system  10 , also known as the “measurement system vertical.” As shown in  FIG. 1 , in certain embodiments the measurement system vertical  10  can be incorporated into a railcar  12 . In this figure, the system  10  embodiment is overlaid onto a photograph of a railcar to give the proper proportion, as shown by reference lines A and B. The measurement system apparatus  26  is depicted schematically on the railcar  12 . In addition, the two axles  14 ,  16  and wheels  18 ,  20  of the railcar are shown with the sideframe  22  affixed to the two axles  14 ,  16 . The deflected rail  24  to be measured under the weight of the train is also shown. 
       FIG. 2  shows another exemplary embodiment of an imaging and deflection measurement system  10 .  FIG. 2  depicts the measurement apparatus  26  mounted to the railcar sideframe  30 . In this embodiment, a camera  32  and laser line  34  are used to measure the height of the deflected rail  24  at a distance (shown by reference number  36 ) from the railcar wheel  38 . Overlain schematically on the present deflected rail  24  is a line showing the expected position of an undeflected rail  44 . A measurement plane  40  is schematically depicted here by way of example to show the approximate location  42  of the measurement of the height of the railcar  12 . The measurement plane shown in  FIG. 2  is not actual physical structure, but instead is included as an example to describe where and how a measurement is made, as would be readily apparent to one of skill in the art. Alternatively, other systems could be used to measure the distance between the measurement system (i.e. sensor head) and the rail such as interferometry, acoustic based measurements, and the like, as are well known in the art. 
     In this exemplary embodiment, the measurement equipment mounting (shown here by reference number  26 ) places the camera  32  above an operating dump door  46  of the rail car, which could be, for example, a hopper car. The mounting location allows the hopper car to continue to operate (be loaded and unloaded) while the measurement apparatus  26  is attached and protects the apparatus  26  from the material as it exits from the dump door  46 . As would be clear to one of skill in the art, other mounting locations are possible for other cars when separate concerns are present. 
       FIGS. 3-4  show alternate above ( FIG. 3 ) and below ( FIG. 4 ) views of certain exemplary embodiments of the measurement system  10  on the railcar  12 .  FIGS. 3-4  depict the sideframe  22 , the wheels  18 ,  20 , axels  14 ,  16 , camera  32 , line laser  34 , and measurement plane  40 . By way of example, in  FIGS. 3-4 , two rails are also depicted: one is deflected  24  and the second is the expected position of an un-deflected rail  44 . In this embodiment, the un-deflected rail  44  is substantially perfectly straight, though other embodiments can be less substantially so.  FIGS. 3-4  depict how in certain embodiments the measurement system is capable of measuring a rail intersecting the measurement plane at different locations while the train crosses the track. 
       FIG. 5  depicts a top view of a rail from the point of view of the camera or measuring device and shows an exemplary embodiment relating to the shape of the measurement plane, as it would be measured during locomotion by the measurement camera (not shown). Again, the measurement plane is pictured to describe the manner in which the rail would be “viewed” from the perspective of the measurement camera and not an actual structure.  FIG. 5  thus depicts a hypothetical view of a passing rail as would be viewed by the measurement camera. Exemplary laser lines  40 A,  40 B are shown across the rail. The first laser line  40 A is shown intersecting a deflected rail, as defined by the dashed lines at  41 A and  41 AA. An un-deflected line  40 B is also shown on the hypothetical un-deflected rail defined by the dashed lines  41 B and  41 BB. For reference, and by way of further example, the dashed lines represent the perspective difference in the rail when deflected  41 A,  41 AA and un-deflected  41 B,  41 BB. In this exemplary embodiment, therefore, the deflected rail would cause the laser line to move up  40 A, relatively, as would be viewed from the perspective of the measurement camera. The measurement camera can thus estimate the magnitude of the rail deflection as it traverses the tracks by locating the line laser in its field of view. This can be done in real time and from a moving rail car using methods similar to those described in U.S. Pat. Nos. 7,920,984, 7,403,296, 7,755,774, 7,942,058, and 7,937,246, and U.S. Published Applications 2009/0056454, 2011/0098942, 2012/0132005, 2009/0070064, 2011/0166827, and 2012/0300060, all of which are hereby incorporated herein by reference in their entireties. 
     With the knowledge of the location of the rail at the measurement plane, several rail parameters can be derived. For example, this truck structure ensures that the wheel/rail contact points are fixed relative to the measurement system. The knowledge of the two wheel/rail contact points and the rail location at the measurement point can result in the estimation of various cords and rail quality parameters as described in the above-referenced patents, publications, and papers. 
     Also, in certain embodiments, other measurements can be made with additional sensors to render further information about the shape of the rail as the rail car passes over it. By way of example, a measurement can be made 3 feet away from the wheel/rail contact point and a second measurement can be made 5 feet away, etc. As a second example, measurements can be made from both sides of the sideframe by mounting a second sensor head on the opposite side of the sideframe. 
     A second exemplary embodiment is shown in  FIG. 6 . In this and similar embodiments, the measurement system vertical would be incorporated into a railcar  50  having an alternate truck structure. Here, the truck structure features a suspension system or device  52 —such as springs and/or dampers—between the sideframe  54  and wheel axles  56 ,  58 . In  FIGS. 6-12 , this is shown schematically as springs  60 ,  62 , although other configurations are possible. It is possible in certain embodiments that the location of the wheel/rail contact points A (labeled in  FIG. 6  with reference number  64 ) and B (labeled in  FIG. 6  with reference number  68 ) are not generally known relative to the sideframe  54  because of the unknown deflection of the sideframe. 
     By way of example, three points are shown in  FIG. 6 . The first two points define the wheel/rail contact points A ( 64 ) and B ( 68 ). More specifically, a first wheel (on axle  56 ) contacts the rail at contact point A ( 64 ), while a second wheel (on axle  58 ) contacts the rail at contact point B ( 68 ). A third point is the measurement point C ( 70 ) that can be measured with a sensor system  72 . Additional points can be included either from additional wheel/rail contact points (similar to A ( 64 ) and B ( 68 ) if the railcar has more axles), or more points measured along the rail (similar to C ( 70 ), extended either proximally or distally). The measurement system  72  presented in this example measures the relative location between such points, which in this exemplary embodiment are points A ( 64 ), B ( 68 ), and C ( 70 ). In the present example, it is expressed in a common reference frame  74  attached to the sideframe  54 , labeled in  FIG. 6  with the unit vectors Xsf and Ysf. In certain exemplary embodiments, a non-Newtonian reference frame is utilized, as compared to a global reference frame such as the one defined by Xglobal and Yglobal, which is also depicted in  FIG. 6 . Any of the points mentioned may be used to define the reference frame, given that certain distances are known and others are unknown, and the calculations can be run from each reference point regardless of the particular embodiment selected. 
       FIG. 7  depicts an exemplary embodiment in which contact point A ( 64 ) is located in the sideframe reference frame  74 A given by the vector  V   A  (shown here by reference arrow D). Generally, it may be difficult to know the location of A ( 64 ) relative to the sideframe reference frame since the wheel  61  moves relative to the sideframe  54  because of the suspension  60 ,  62 . As would be apparent to one of skill in the art, various sensors could be implemented to make these measurements. In certain embodiments, the suspension restricts wheel vertical movement relative to the sideframe  54 . In such embodiments, a sensor can be employed to measure the vertical displacement of the spring  60  compared to the known displacement of the spring  60 , thereby allowing the estimation of the wheel location and the wheel/rail contact point A ( 64 ) relative to the sideframe reference frame  74 A. As depicted in  FIG. 7 , the location  V   A  is the sum of the fixed unchanging vector  V   A,ref  (shown here by reference arrow E) and the measured spring displacement  S   A  (shown here by reference arrow F). Measurement of spring displacement,  S   A , can be made with numerous sensors such as LVDTs, ultrasonic, laser based, string potentiometers, and numerous other sensors, as would be known to one of skill in the art. 
       FIG. 8  depicts an exemplary embodiment in which contact point B ( 68 ), is located in the sideframe reference frame  74 B given by the vector  V   B  (shown here by reference arrow H). Generally, it may be difficult to know the location of B ( 68 ) relative to the sideframe reference frame  74 B since the wheel  63  moves relative to the sideframe  54  because of the suspension  60 ,  62 . As discussed in relation to  FIG. 7 , various sensors could be implemented to make these measurements. In the embodiment depicted in  FIG. 8 , the location  V   B  is the sum of the fixed unchanging vector  V   B, ref  (shown here by reference arrow G) and the measured spring displacement  S   B  (shown here by reference arrow I). Again, the measurement of spring displacement,  S   A , can be made with numerous sensors such as LVDTs, ultrasonic, laser based, string potentiometers, and numerous other sensors. 
       FIG. 9  depicts an exemplary embodiment in which measurement point C ( 70 ), is located in the sideframe reference frame  74 C given by the vector  V   C . (shown here by reference arrow J). Again, as discussed above, it may be difficult to know the location of measurement point C ( 70 ) relative to the sideframe reference frame  74 C because C ( 70 ) moves relative to the sideframe because of the suspension and rail movement. Various sensors could be implemented to make this measurement such as the sensors described above, or systems used in previous applications referenced herein, or other sensors to measure  S   C  (shown here by reference arrow K). As shown here, the location  V   C  is the sum of the fixed unchanging vector  V   C, ref  (shown here by reference arrow L) and the measured spring displacement  S   C . 
       FIGS. 10-12  depict the location of all three measurements discussed in  FIGS. 7-9 — V   A ,  V   B ,  V   C —given in this exemplary sideframe reference frame  74 . As would be clear to one of skill in the art, myriad other points and other reference frames are possible. By way of example, in certain embodiments the origin of the reference frame that is used originates at either contact point A ( 64 ) or contact point B ( 68 ). While in these embodiments this would result in a different combination of the already identified vectors, it would not depart from the spirit and teachings of the present disclosure. 
     Given the knowledge of the location of these points—A ( 64 ), B ( 68 ), and C ( 70 )—various estimates of rail quality can be made. By way of example, the curvature of the rail under the weight of the railcar could be estimated and could be correlated to railstress. Other indicators of quality can also be estimated with these measurements, as has been disclosed in the incorporated references. Also, more points can be included such as additional wheel/rail contact points and/or other measurement points, as is apparent in  FIGS. 10-12 . 
     An exemplary embodiment is depicted in  FIG. 12 . In this embodiment, one track parameter that can be calculated is the relative displacement given by the parameter of rail quality called “Yrel” and defined in currently pending U.S. application Ser. No. 13/046,064, entitled “Vertical Track Modulus Trending,” which is hereby incorporated herein by reference in its entirety. 
     As would be clear to one of skill in the art, additional techniques can be used to calibrate the camera images and measurements relative to true measurements in the real world. By way of example, known objects can be placed in view along the deflected rail and the shape of the rail can be measured with other techniques such as GPS or a surveyor&#39;s system or rulers. In addition, the railcar could be moved onto a very stiff section of track, such as a slab track or track over concrete in a car shop, and the shape of the relatively straight rail could be used to establish the calibration. 
     Certain embodiments can further include determining a vertical track deflection at each location along the rail using the measurements obtained with the imaging system. According to one implementation, the measured vertical track deflection measurements can be used to further determine a track modulus associated with each measurement point along the track, which can be used to determine whether portions of the track may require maintenance. In certain embodiments, these measurements can also be used to determine whether there may have been any tampering with the rail that may require immediate servicing. The imaging system can also be used to measure the quality of the track structure, and could be used to identify other problems such as broken ties or missing bolts in the joints, or to detect the presence of foreign material on the track such as natural debris or implements left to damage the track. 
     In certain embodiments, the measurement of vertical track deflection can also be combined with other measurements of track geometry and/or track quality to produce new metrics of track quality. Other measurements that can be made include gage, cant, mid-cord offsets, end-cord offsets, measurements of longitudinal rail stress, measurements of gage restraint, measurements of vehicle track interaction or other acceleration-based measurements. 
     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present disclosure. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the various embodiments is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.