Patent Publication Number: US-6911914-B2

Title: Method and apparatus for detecting hot rail car surfaces

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application is a continuation-in-part of U.S. application Ser. No. 10/063,218, filed Mar. 29, 2002, now abandoned, which application is herein incorporated by reference. 
    
    
     BACKGROUND OF INVENTION 
     This invention relates generally to the field of detecting excessively hot rail car surfaces and more specifically to the use of rank filters to process infrared signals emitted by rail car surfaces. 
     While the present disclosure emphasizes application of the present invention to detection of hot rail car wheel bearings, it will be obvious to one of ordinary skill in the art that the present invention is equally applicable to the detection of other hot rail car surfaces such as, by way of example but not limitation, rail car wheels. 
     Malfunctioning rail car wheel bearings radiate heat due to friction. To detect such overheated bearings, in an attempt to warn the operator and stop the train prior to complete bearing failure and potential train derailment, railroads have developed and deployed wayside hot bearing detectors (HBDs). Typical HBDs utilize pyroelectric infrared sensors for detecting heat profiles of the rail car wheel bearings as the rail cars roll past the sensor. As well as being pyroelectric, however, these sensor devices may often also be piezoelectric; that is, electrical outputs produced by these devices depend not only on the heat sensed, but also on sensed sound and vibration. The electrical noise pulses induced by undesirable piezoelectric effects are known as “microphonic artifacts”. 
     In some instances, microphonic artifacts present magnitudes similar to those of hot bearings. As conventional HBDs rely mainly on signal magnitudes for detection, microphonics and other phenomena can induce false alarms that result in stopping a train unnecessarily. Such false stops cost the railroad significant time and money. 
     While the signal magnitudes of microphonic artifacts are comparable to the signal magnitudes produced by truly hot bearings, the microphonic artifacts tend to present themselves as substantially sharper “spikes.” An opportunity exists, therefore, to reduce HBD sensitivity to microphonic artifacts through improved signal processing. 
     SUMMARY OF INVENTION 
     The opportunities described above are addressed, in one embodiment of the present invention, by an apparatus for detecting a hot rail car surface comprising: an infrared sensor for acquiring an infrared signal from a rail car surface of a rail car and transducing the infrared signal into an electrical signal; a rank filter for filtering the electrical signal to produce a filtered array; a first peak detector for detecting a maximum filtered value of the filtered array; and a first comparator for comparing the maximum filtered value to a detection threshold to produce a filtered alarm signal. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  illustrates a block diagram of an apparatus for detecting a hot rail car surface in accordance with one embodiment of the present invention; and 
         FIG. 2  illustrates filtered array and unfiltered array signals in accordance with the embodiment illustrated in FIG.  1 . 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with one embodiment of the present invention,  FIG. 1  illustrates a block diagram of an apparatus  100  for detecting a hot rail car surface comprising an infrared sensor  110 , a rank filter  140 , a first peak detector  150 , and a first comparator  160 . In operation, infrared sensor  110  acquires an infrared signal from a rail car surface  120  of a rail car  130  and transduces the infrared signal into an electrical signal  115 . Rank filter  140  filters electrical signal  115  to produce a filtered array  145 . 
     The process of filtering using rank filter  140  comprises: incorporating a new sample of electrical signal  115  into a data buffer; discarding the oldest sample in the data buffer; finding a rank value of the data buffer; and storing the rank value in filtered array  145 . The length of the data buffer is referred to as the “filter length.” The “rank” of the filter is a quantity between 0 and 1 and defines the fraction of the data buffer containing values smaller than the rank value. For example, if the rank equals 0.5, then the rank filter finds the median value of the data buffer; if the rank equals 0.8, then the rank filter finds the 80th percentile value (i.e., the smallest value greater than 80 percent of all the values); if the rank equals 0, then the rank filter finds the minimum value; and if the rank equals 1, then the rank filter finds the maximum value. 
     Filtered array  145  is passed to peak detector  150  wherein a maximum filtered value  155  is detected, and first comparator  160  compares maximum filtered value  155  to a detection threshold  165  to produce a filtered alarm signal useful for alerting a train operator of an incipient failure of rail car surface  120 . 
     Infrared sensor  110  comprises any electrical or electronic device capable of converting infrared electromagnetic radiation to electrical signals; examples of infrared sensor  110  include, without limitation, photodiodes, phototransistors, photomultiplier tubes, and vidicon tubes. Rail car  130  comprises any vehicle capable of traveling on railroad tracks; examples of rail car  130  include, without limitation, box cars, ore cars, flat cars, tank cars, and locomotives. Rail car surface  120  comprises any surface of rail car  130  visible from a wayside; examples of rail car surface  120  include, without limitation, wheel bearing surfaces and wheel surfaces. Rank filter  140 , first peak detector  150 , and first comparator  160  comprise any electrical or electronic devices capable of performing the indicated operations; examples of rank filter  140 , first peak detector  150 , and first comparator  160  include, without limitation: analog electronic processors comprising, for example, operational amplifiers, sample and hold circuits, peak hold circuits, analog comparators, analog computation modules, and any combination thereof; and digital electronic processors comprising, for example, single chip digital signal processors (DSPs), microprocessors, microcomputers, microcontrollers, small-, medium-, and large-scale integrated circuits, programmable logical arrays, programmable gate arrays, and any combination thereof. 
     In another embodiment in accordance with the embodiment illustrated in  FIG. 1 , apparatus  100  further comprises a wireless transceiver  170  and a filter parameter calculator  190 . In operation, wireless transceiver  170  acquires rail car surface characteristics transmitted by a wireless tag  180  mounted on rail car  130 . As a function of the rail car surface characteristics, filter parameter calculator  190  calculates a filter length and a rank of rank filter  140 . 
     By incorporating knowledge of the particular rail car surface under observation, better performance of rank filter  140  may be realized. For example, rank filter  140  passes signal pulses having widths longer than the product of the rank and the filter length; pulses narrower than the product of the rank and the filter length are rejected. A truly hot bearing produces a hot bearing signal pulse whose width is a function of bearing geometry and of the known geometry of infrared sensor  110 . With knowledge of the bearing geometry, for example, communicated by wireless tag  180 , the expected width of the hot bearing signal pulse can be calculated, and the filter length and rank of rank filter  140  can be tailored to pass the hot bearing signal pulse while rejecting narrower pulses due to microphonic artifact. 
     Wireless transceiver  170  and wireless tag  180  comprise any devices capable of wireless communication; examples of wireless transceiver  170  and wireless tag  180  include, without limitation: electromagnetic receivers and transmitters operating at, for example, radio, infrared, or optical frequencies; commercially available receivers and transmitters known as “Automatic Equipment Identification” (AEI); as well as mechanical receivers and transmitters such as, for example, microphones and loudspeakers. 
     In still another embodiment in accordance with the embodiment illustrated in  FIG. 1 , apparatus  100  further comprises an unfiltered signal buffer  200 , a second peak detector  210 , a second comparator  220 , and an alarm comparator  230 . In operation, unfiltered signal buffer  200  buffers samples of electrical signal  115  to produce an unfiltered array  205 . Second peak detector  210  detects a maximum unfiltered value  215 , which second comparator  220  compares to detection threshold  165  to produce an unfiltered alarm signal. A censored false alarm signal results when alarm comparator  230  compares the unfiltered alarm signal to the filtered alarm signal. A difference between the unfiltered alarm signal and the filtered alarm signal indicates that rank filter  140  has successfully prevented a false alarm. Knowledge that a false alarm would have otherwise occurred can be used as an indicator that apparatus  100  may be operating in a degraded mode. 
     In yet another embodiment in accordance with the embodiment illustrated in  FIG. 1 , the censored false alarm signal comprises a binary signal having a true value when the unfiltered alarm signal differs from the filtered alarm signal and a false value otherwise, and apparatus  100  further comprises a counter  240 . Counter  240  counts the false values (i.e., the number of censored false alarms) to produce a censored alarm count. While the existence of censored false alarms is indicative of degraded behavior, the censored false alarm count is further indicative of the duration and severity of the degradation. 
     In again another embodiment in accordance with the embodiment illustrated in  FIG. 1 , apparatus  100  further comprises a failure isolator  250 . Failure isolator  250  diagnoses a failure mode from the censored false alarm count. By accumulating a censored false alarm count time history, failure isolator  250  may employ statistical hypothesis testing techniques to identify (i.e., isolate) which among a group of previously identified failure modes is most likely to have occurred. 
     Unfiltered signal buffer  200 , second peak detector  210 , second comparator  220 , alarm comparator  230 , counter  240 , and failure isolator  250  comprise any electrical or electronic devices capable of performing the indicated operations; examples of unfiltered signal buffer  200 , second peak detector  210 , second comparator  220 , alarm comparator  230 , counter  240 , and failure isolator  250  include, without limitation: analog electronic processors comprising, for example, operational amplifiers, sample and hold circuits, peak hold circuits, analog comparators, analog computation modules, and any combination thereof; and digital electronic processors comprising, for example, single chip digital signal processors (DSPs), microprocessors, microcomputers, microcontrollers, small-, medium-, and large-scale integrated circuits, programmable logical arrays, programmable gate arrays, and any combination thereof. 
     In accordance with the embodiment illustrated in  FIG. 1 ,  FIG. 2  illustrates filtered array  145  and unfiltered array  205  as may be generated during operation. Unfiltered array  205  suffers a microphonic artifact placing maximum unfiltered value  215  clearly above detection threshold  165 . In contrast, the microphonic artifact has been removed in filtered array  145 . Maximum filtered value  155  thus stays well below detection threshold  165 , and a false alarm is avoided. 
     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.