Abstract:
A method and apparatus for nondestructive testing a railroad rail is provided. The method includes locating at least one magnetic exciter adjacent to the rail, the at least one magnetic exciter includes an emitting end and a longitudinal axis extending perpendicularly through the emitting end, discharging the energy storage circuit through the at least one magnetic exciter such that only a magnetic pulse enters the rail at a location of the exciter, and controlling a shape of the magnetic pulse. The apparatus includes at least one magnetic exciter adjacent to a rail, a energy storage circuit electrically coupled to the at least one magnetic exciter the energy storage circuit is configured to supply a shaped current pulse to the at least one exciter, and a power source electrically coupled to the energy storage circuit.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to railroad rails and more particularly to methods and apparatus for inducing ultrasonic waves into railroad rails. 
     Some known rail inspection techniques include eddy current analysis wherein perturbations in an electric current induced into the rail is indicative of defects, and electromagnetic analysis, wherein perturbations in magnetic flux induced into the rail are examined to reveal anomalies. Eddy current analysis and electromagnetic analysis have range limitations that make their use more time consuming and more expensive than using ultrasonic analysis. To facilitate inspection, other known inspection techniques include ultrasonic analysis wherein reflections of sound waves induced into the rail are evaluated to locate and characterize defects. Some known ultrasonic techniques use a piezoelectric principle to induce ultrasonic waves into railroad rails. A piezoelectric transducer is held in close contact with the rail while activated to induce ultrasonic waves into the rail. The piezoelectric technique has disadvantages that limits its usefulness as a cost-effective and reliable inspection tool. For example, the piezoelectric transducer generates transverse waves which have a limited range in the rail. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a method of inducing ultrasonic waves into a railroad rail is described. The method includes locating at least one magnetic exciter adjacent to the rail, the at least one magnetic exciter includes an emitting end and a longitudinal axis extending perpendicularly through the emitting end, discharging the energy storage circuit through the at least one magnetic exciter such that only a magnetic pulse enters the rail at a location of the exciter, and controlling a shape of the magnetic pulse. 
     In another aspect of the present invention, an apparatus for inducing ultrasonic waves into a railroad rail is described. The apparatus includes at least one magnetic exciter adjacent to the rail, an energy storage circuit electrically coupled to the at least one magnetic exciter, the energy storage circuit configured to supply a shaped current pulse to the at least one exciter, and a power source electrically coupled to the energy storage circuit configured to charge the energy storage circuit with electrical energy. 
     In a further aspect, a railroad locomotive is described. The locomotive includes a platform having a first end and a second end, a propulsion system coupled to the platform for supporting and propelling the platform on a pair of rails, and a rail ultrasonic wave inducement system comprising at least one magnetic exciter, a energy storage circuit electrically coupled to the at least one magnetic exciter, and a power source electrically coupled to the energy storage circuit, the at least one magnetic exciter is coupled to the locomotive such that the at least one magnetic exciter moves in concert with the locomotive and maintains a position adjacent to a rail, the energy storage circuit is configured to supply at least one of sequential current pulses to the at least one magnetic exciter and simultaneous current pulses to the at least one magnetic exciter according to a predetermined configuration, the energy storage circuit is further configured to control a shape of the pulses. 
     In yet another aspect, a railroad vehicle is described. The vehicle includes a platform having a first end and a second end, a truck coupled to the platform for supporting the platform on a pair of rails, and a rail ultrasonic wave inducement system comprising at least one magnetic exciter, a energy storage circuit electrically coupled to the at least one magnetic exciter, and a power source electrically coupled to the energy storage circuit, the at least one magnetic exciter is coupled to the vehicle such that the at least one magnetic exciter moves in concert with the vehicle and maintains a position adjacent to a rail, the energy storage circuit is configured to supply at least one of sequential current pulses to the at least one magnetic exciter and simultaneous current pulses to the at least one magnetic exciter according to a predetermined configuration, the energy storage circuit is further configured to control a shape of the pulses. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cut away view illustrating an exemplary locomotive 
     FIG. 2 is a sectional view of a railroad rail and an ultrasonic wave inducement system. 
     FIG. 3 is a side elevational view of a rail illustrating an exemplary position of a magnetic exciter that may be used with the ultrasonic wave inducement system shown in FIG.  2 . 
     FIG. 4 is a graph illustrating exemplary ultrasonic pulses that may be obtained with the ultrasonic wave inducement system shown in FIG.  2 . 
     FIG. 5 is a sectional view of a railroad rail including an alternative embodiment an ultrasonic wave inducement system. 
     FIG. 6 is a side elevational view of a rail illustrating an alternative position of a pair of magnetic exciters that may be used with the ultrasonic wave inducement system shown in FIG.  2 . 
     FIG. 7 is a graph of exemplary ultrasonic pulses that may be obtained with the ultrasonic wave inducement system shown in FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a partial cut away view of an exemplary locomotive  10 . Locomotive  10  includes a platform  12  having a first end  14  and a second end  16 . A propulsion system  18 , or truck is coupled to platform  12  for supporting, and propelling platform  12  on a pair of rails  20 . An equipment compartment  22  and an operator cab  24  are coupled to platform  12 . An air and air brake system  26  provides compressed air to locomotive  10 , which uses the compressed air to actuate a plurality of air brakes  28  on locomotive  10  and railcars (not shown) behind it. An auxiliary alternator system  30  supplies power to all auxiliary equipment. An intra-consist communications system  32  collects, distributes, and displays consist data across all locomotives in a consist. 
     A cab signal system  34  links the wayside (not shown) to a train control system  36 . In particular, system  34  receives coded signals from a pair of rails  20  through track receivers (not shown) located on the front and rear of the locomotive. The information received is used to inform the locomotive operator of the speed limit and operating mode. A distributed power control system  38  enables remote control capability of multiple locomotive consists coupled in the train. System  38  also provides for control of tractive power in motoring and braking, as well as air brake control. 
     An engine cooling system  40  enables engine  42  and other components to reject heat to cooling water. In addition, system  40  facilitates minimizing engine thermal cycling by maintaining an optimal engine temperature throughout the load range, and facilitates preventing overheating in tunnels. An equipment ventilation system  44  provides cooling to locomotive  10  equipment. 
     A traction alternator system  46  converts mechanical power to electrical power which is then provided to propulsion system  18 . Propulsion system  18  enables locomotive  10  to move and includes at least one traction motor  48  and dynamic braking capability. In particular, propulsion system  18  receives power from traction alternator  46 , and through traction motors  48  moves locomotive  10 . Locomotive  10  systems are monitored by an on-board monitor (OBM) system  50 . OBM system  50  keeps track of incidents occurring in the systems with an incident log. 
     FIG. 2 is a cross-sectional view of a railroad rail and an ultrasonic wave inducement system  100 . System  100  includes a magnetic exciter  102 , a pulser  104 , and a power supply  106 . A rail  108  includes a rail head  110 , a rail web  112 , and a rail base  114 . Base  114  is a longitudinally extending member, a first edge of web  112  is coupled to base  114  such that web  112  extends perpendicularly therefrom. Rail head  110  is coupled to a second edge of web  112 . Magnetic exciter  102  is coupled to locomotive  10  such that exciter  102  is fixed in a position. More specifically, as locomotive  10  moves along rail  108 , a first face  116  of exciter  102  is maintained at a substantially fixed distance  118  from rail  108 , for example a distance  118  less than a diameter of first face  116 . Additionally, exciter  102  is positioned such that a longitudinal axis  120  of exciter  102  is substantially perpendicular to a rail longitudinal axis  121 . For example, longitudinal axis  120  is substantially perpendicular to longitudinal axis  121  when the angular difference between longitudinal axis  120  and longitudinal axis  121  is within the range of about 70 degrees to about 110 degrees. In an alternative embodiment, exciter  102  is coupled to a vehicle, such as a rail car or rail road service vehicle, that is not a locomotive. 
     Exciter  102  is electrically coupled to pulser  104  by cable  122 . In an exemplary embodiment, pulser  104  is electrically coupled to power supply  106  through cable  124 . In an alternative embodiment, pulser  104  and power supply  106  are included in a single equipment enclosure wherein pulser  104  and power supply  106  are electrically coupled via wiring internal to the enclosure. Power supply  106  is configured to supply alternating current (AC) electrical power to pulser  104 . In an alternative embodiment, power supply  106  supplies at least one voltage of direct current (DC) power to pulser  104 . Power supply  106  is supplied with electrical power from a convenient power source supplied from locomotive  10  or an auxiliary source independent from locomotive  10 . 
     In the exemplary embodiment, exciter  102  includes a magnetic core (not shown) that is magnetically coupled to a winding (not shown). The core is oriented such that magnetic lines of flux exit face  116  substantially parallel to face  116 , for example, at an angle of less than or equal to about twenty degrees. In an alternative embodiment, the core is oriented in exciter  102  such that magnetic lines of flux exit magnetic lines of flux substantially perpendicular to face  116 , for example when an angular difference between the magnetic lines of flux and face  116  is within the range of about 70 degrees to about 110 degrees. 
     Pulser  104  includes an energy storage circuit  126  including a capacitive reactance for storing electrical energy for supplying exciter  102 , and electronic devices for shaping an output pulse supplied to exciter  102 . In the exemplary embodiment, pulser  104  also includes a computer configured to precisely control an output pulse of pulser  104 . 
     In an alternative embodiment, exciter  102  is buried adjacent rail base  114 . In yet another embodiment exciter  102  may be located inside a hollow rail tie  115  adjacent to rail base  114 . Pulser  104  and power supply  106  are each buried proximate exciter  102 , or in a suitable enclosure nearby. In one embodiment, exciter  102  is stationary with respect to rail  108  and may be located in a cofferdam for easy maintenance access. Pulser  104  may be remotely controlled via a wireless communications device or via a track-signaling device. 
     FIG. 3 is a side elevational view of rail  108  illustrating an exemplary position of a magnetic exciter  102 . FIG. 4 is a graph  150  illustrating exemplary trace  152  of a plurality of ultrasonic pulses  154  induced into rail  108  by exciter  102 . Vertical axis  156  represents an amplitude of pulses  154  and horizontal axis  158  represents a time in which pulses  154  are traveling through rail  108  at a constant velocity with respect to each other. Longitudinal axis  120  is illustrated as the point of origin of the pulses  154  shown in FIG.  4 . 
     In operation, distance  118  is predetermined based on physical interference objects associated with rail  108 , such as bolting hardware, grounding fixtures, and switching devices and also on magnetic coupling considerations. As distance  118  between rail  108  and exciter  102  is reduced, a magnetic coupling between rail  108  and exciter  102  is facilitated to be improved. 
     Power supply  106  supplies charging power to energy storage circuit  126  internal to pulser  104 . Pulser  104  discharges energy storage circuit  126  such that a series of current waveforms of a pre-determined shape and a pre-determined frequency are generated and supplied to exciter  102  through cable  122 . The waveforms supplied to exciter  102  generate a magnetic field pulse at face  116 , which penetrates rail  108 . An interaction between the magnetic field and rail  108  generates an ultrasonic pulse  154  inside rail  108  where axis  120  passes through rail  108 . 
     After pulse  154  is induced into rail  108 , pulse  154  travels away from axis  120  at a velocity influenced by several factors including, but not limited to, the material composition of rail  108 , the temperature of rail  108 , and the amount of stress induced into rail  108 . As pulse  154  moves away from axis  120 , exciter  102  induces a subsequent pulse into rail  108 . The frequency of pulses  154  is determined by a time constant that is controlled by pulser  104 . As pulses  154  move away from axis  120  the amplitudes of pulses  154  are attenuated and their usefulness for evaluating rail  108  is diminished because pulses  154  become indistinguishable from electrical noise in detecting circuitry and ultrasonic noise in rail  108  from sources other than exciter  102 . To facilitate increasing the distance that pulses  154  travel from axis  120  before attenuating below a useful amplitude, the amplitude of pulse  154  is increased at the time it is induced into rail  108 . 
     FIG. 5 is a sectional view of a railroad rail including an alternative embodiment of an ultrasonic wave inducement system  200 . Components of system  200  that are identical to components of system  100  are identified in FIG. 5 using the same reference numerals used in FIG.  2 . Accordingly, ultrasonic wave inducement system  200  includes rail  108 , magnetic exciter  102 , pulser  104 , power supply  106 , and interconnecting cables  122  and  124 . Ultrasonic wave inducement system  200  also includes a second magnetic exciter  202  including a face  216  and a longitudinal axis  220 , and a cable  222  that electrically couples exciter  202  to pulser  104 . 
     Exciter  202  is positioned such that longitudinal axis  220  of exciter  202  is substantially coplanar with longitudinal axis  120 , for example, a vertical angular difference between axis  220  and axis  120  at least one of less than about twenty degrees and equal to twenty degrees, and both axes  220  and  120  are substantially parallel to the ground at substantially the same height above the ground. For example, a difference in height above the ground between axes  120  and  220  of less than about four inches. Longitudinal axis  220  and longitudinal axis  121  intersect at a node  224 . Longitudinal axis  120  and longitudinal axis  121  intersect at a node  226 . A lateral distance  230 , is the distance between nodes  224  and  226 . In the exemplary embodiment, distance  230  is set at zero or an integral multiple of the wavelength of a pulse  254  and a pulse  256 . In an alternative embodiment, distance  230  is set to a distance that facilitates physical installation of exciters  102  and  202  and pulser  104  controls a timing of pulses  254  and  256 . In the exemplary embodiment, exciter  202  is identical to exciter  102 . In an alternative embodiment, exciters  102  and  202  are configured differently to account for different physical interference objects that can be unique to one side of rail  108 . Pulser  104  supplies shaped current pulses to exciters  102  and  202  substantially simultaneously, for example within about twenty microseconds. In a separate mode of operation pulser  104  supplies shaped current pulses to exciters  102  and  202  sequentially. In an alternative embodiment, pulser  104  supplies shaped current pulses to exciters  102  and  202  alternately simultaneously and sequentially. 
     FIG. 6 is a side elevational view of rail  108  illustrating an alternative position of a pair of magnetic exciters  102  and  202  that may be used with the ultrasonic wave inducement system shown in FIG.  5 . FIG. 7 is a graph  250  of exemplary ultrasonic pulses  254  and  256  that may be obtained with the ultrasonic wave inducement system shown in FIG.  5 . Vertical axis  156  represents an amplitude of pulses  254  and  256 . Horizontal axis  158  represents a time, which because pulses  254  and  256  are traveling through rail  108  at a constant velocity with respect to each other, axis  158  also represents a wavelength. Longitudinal axis  120  and  220  are illustrated as the point of origin of the pulses  254  and  256 , respectively shown in FIG.  4 . 
     In operation, exciters  102  and  202  are coupled to a locomotive or railcar and move in concert with the locomotive or railcar, while their respective faces  116  and  216  are maintained a distance (not shown) away from rail  108 . The distance between rail  108  and face  116  may be different from the distance between rail  108  and face  216  due to interference objects adjacent to rail  108 . 
     Power supply  106  supplies charging power to energy storage circuit  126  internal to pulser  104 . Pulser  104  discharges energy storage circuit  126  such that a series of current waveforms of a pre-determined shape and a pre-determined frequency are generated and supplied to exciters  102  and  202  through cables  122  and  224 . The waveforms supplied to exciters  102  and  202  generate a magnetic field pulse at faces  116  and  216 , respectively, which penetrates rail  108 . An interaction between the magnetic fields and rail  108  generates an ultrasonic pulse  254  in rail  108  at axis  120  and an ultrasonic pulse  256  in rail  108  at axis  220 . In the exemplary embodiment, pulses  254  are opposite in polarity to pulses  256  due to their respective positions on opposites sides of rail  108 . In an alternate embodiment, exciter  202  is located on the same side of rail  108  as exciter  102  and pulser  104  is configured to facilitate reversing the magnetic field emitted from exciter  202  such that pulse  256  is still oriented oppositely from pulser  254 . 
     Pulses  254  and  256  are shaped by a predetermined output of pulser  104 , which is configured to discharge a plurality of shaped current pulses to exciters  102  and  202  simultaneously, sequentially and alternating between simultaneously and sequentially. Using exciter  202  in addition to exciter  102  effectively doubles the distance capability of system  200 . After pulses  254  and  256  are induced into rail  108 , they travel away from axis  120  and axis  220 , respectively at a velocity determined by several factors including a material composition of rail  108 , a temperature of rail  108 , and a stress being experienced by rail  108 . As pulse  254  moves away from axis  120 , exciter  102  induces a subsequent pulse into rail  108 , likewise, as pulse  256  moves away from axis  220 , exciter  202  induces a subsequent pulse into rail  108 . The frequency of pulses  254  and  256  are determined by a time constant controlled by pulser  104 . As pulses  254  and  256  move away from axis  120  and  220 , respectively, the amplitudes of pulses  254  and  256  are attenuated and their usefulness for evaluating rail  108  is diminished because pulses  254  and  256  become indistinguishable from electrical noise in detecting circuitry and ultrasonic noise in rail  108  from sources other than exciter  102 . Because pulse  254  is of opposite polarity from pulse  256 , a peak-to-peak difference in amplitude between pulse  254  and  256  is larger than either peak-to-neutral amplitude. In one embodiment, the peak-to-peak difference in amplitude between pulse  254  and  256  is twice the peak-to-neutral amplitude of pulse  254 . Creating a pair of pulses with opposite polarity is an alternative method of increasing the distance the pulses travel before attenuating below a useful amplitude. In an alternative embodiment exciter  102  and  202  may be located in a fixed position adjacent to rail  108 . 
     The above-described ultrasonic wave inducement systems and methods are cost-effective and highly reliable. Each system includes an exciter that induces an ultrasonic pulse into a railroad rail, a pulser that controls the exciters, and a power supply that provides the system with electrical energy. Such systems permit a long range testing technique to find rail flaws, cracks, and anomalies before they become severe problems. Thus, the ultrasonic wave inducement system facilitates testing of railroad rails in a cost-effective and reliable manner. 
     Exemplary embodiments of ultrasonic wave inducement systems are described above in detail. The systems are not limited to the specific embodiments described herein, but rather, components of each system may be utilized independently and separately from other components described herein. Each ultrasonic wave inducement system component can also be used in combination with other ultrasonic wave inducement system components. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.