Speed independent system for obtaining preselected numbers of samples from object moving along fixed path

A speed independent system is used for obtaining a preselected number of samples from an object moving along a fixed path, such as a railroad train passing through a sensing zone along the section of track. The sensing zone is defined by a pair of wheel sensors. Upstream of the sensing zone a third sensor is positioned. The distance between the third sensor and the closer of the pair of sensors comprises a reference distance which is the length of the sensing zone multiplied by a known multiple. The time for the train to pass through the reference distance is obtained and then divided by a divisor comprising the product of the known multiple and the desired number of samples to obtain a single interval. During the time the train passes through the sensing zone consecutive intervals are counted off to obtain the desired number of samples.

BACKGROUND OF THE INVENTION 
The present invention relates to moving equipment, such as railroads and 
the like, and in particular to a system for obtaining a preselected number 
of data samples from the moving equipment while passing through a selected 
portion of its path of travel independent of the speed of travel. 
Railroads are commonly provided with various types of scanning devices 
along their track sites which extract information from passing railroad 
cars. One such scanning device may, for example, be a hot bearing detector 
such as that disclosed in U.S. Pat. No. 3,545,005 and marketed by the 
Servo Corporation of America of Hicksville, New York under the trade name 
HOT BOX DETECTIVE. As each wheel of the train enters a scanning zone, an 
infrared scanner generates a waveform indicative of the temperature of the 
bearing for that wheel. Information can be obtained from the waveform as 
to whether the bearing is operating properly or not. Such scanning systems 
have heretofore been real time analog systems. However, with the 
increasing use of microprocessors, it is desirable to obtain such 
information in a discrete form for subsequent processing. To this end, it 
is necessary to obtain discrete information from the scanner as the wheel 
passes through the scanning zone. The problem in obtaining such discrete 
information is that the equipment has no way of knowning at what speed the 
train will pass through the scanning zone and hence the rate at which data 
is extracted from the scanner must be totally independent of train speed. 
In view of the above, it is a principal object of the present invention to 
provide a system for obtaining a preselected number of samples from a 
scanner viewing an object moving through a scanning zone independent of 
the speed at which the object moves through the zone. 
A further object is to provide such a system which utilizes available 
components and would be readily compatible with existing equipment. 
A still further object is to provide such a system which, in addition to 
being independent of the speed of the moving object is also independent of 
the direction of the moving object. 
Still further objects and advantages will become apparent from the 
following description of the present invention. 
SUMMARY OF THE INVENTION 
The above and other objects and advantages are attained in accordance with 
the present invention by providing along the path of motion of a railroad 
car or the like first and second sensors to determine when the car enters 
and leaves a sensing zone. Upstream of the sensing zone a third sensor is 
positioned. The distance between the third sensor and the closer of the 
first and second sensors comprises a reference distance which is the 
length of the sensing zone multiplied by a known multiple. Preferably the 
multiple is also the same number as the number of samples required while 
the car is within the sensing zone. 
The time the car takes to traverse the reference distance is used to start 
and stop a first counter which counts pulses generated by a clock. When 
the first counter stops (i.e., when the car traverses the reference 
distance and reaches the sensing zone) a second, ring-around counter is 
set by the first counter to the count reached by the first counter divided 
by the product of the known factor and the number of samples required. 
Each time the second counter reaches zero a pulse is triggered and the 
second counter returns to its initial setting and resumes counting down. 
As a result, as the car passes through the sensing zone, the time it takes 
to pass through the sensing zone will be divided into the required number 
of samples, regardless of the speed of the car. 
The foregoing is independent of speed but assumes that the speed of the car 
remains constant from the time the car starts to traverse the 
predetermined distance until the car leaves the sensing zone. 
For bi-directional capabilities, a fourth sensor may be positioned 
downstream of the sensing zone. The tripping of either the third or fourth 
sensor triggers the first counter. A determination of whether the third or 
fourth sensor was in fact triggered determines the direction of the car.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference is now made to the drawings and to FIG. 1 in particular wherein 
the present invention is shown as being utilized along a section of 
railroad track. In accordance with the present invention, a section of 
track 10 is shown having a pair of wheel sensors 12 and 14 positioned 
along the track to define a sensing zone the length of which is equal to a 
distance "x." An infrared hot bearing detector 16 such as that disclosed 
in the previously mentioned U.S. Pat. No. 3,545,005 is positioned along 
the track to scan each bearing of a railroad car as the car passes through 
the sensing zone. The wheel sensors which are of conventional design and 
are commercially available, serve to generate a signal each time a 
railroad car wheel passes over it. 
In accordance with the present invention a third wheel sensor 18 is 
positioned upstream of the sensing zone. The distance from wheel sensor 18 
to wheel sensor 12, the closer of wheel sensors 12 and 14, comprises a 
reference distance which is a known multiple "y" of the distance "x" 
between sensors 12 and 14 (i.e., the length of the reference distance is 
x.multidot.y). A fourth wheel sensor 20 is positioned the same distance 
from wheel sensor 14 that wheel sensor 18 is from wheel sensor 12. Thus, 
if a train moves in the direction indicated by the arrow wheel sensor 18 
will trigger a first signal, followed by signals triggered by wheel 
sensors 12, 14 and 20 in that order. During the time period starting with 
the triggering of counter 32 by wheel sensor 12 and ending with the 
triggering of wheel sensor 14 by a particular wheel, the bearing of that 
wheel will be scanned by scanner 16. 
As stated, the principal object of the present invention is to enable the 
scanner 16 to sample each wheel bearing a fixed number of times as it 
passes from sensor 12 to sensor 14 regardless of the speed at which the 
train is moving. To this end, the circuitry depicted in FIG. 2 is 
utilized. 
As shown in FIG. 2, as a train wheel passes each of the sensors 18, 12, 14 
and 20 along the track a signal is generated. The signals from the sensors 
are fed to a threshold detection and latch circuit 22 which first serves 
to insure that each sensor signal exceeds a fixed threshold value, 
selected to eliminate extraneous noise and misreadings caused by animals 
crossing the track, vandalism, and the like. Circuit 22 also performs the 
necessary time latching functions as required. The output of circuit 22 is 
fed to a gate 24 along with the output pulses of a 1 MHz pulse generator. 
Circuit 22 maintains gate 24 in an "on" state from the time the wheel 
passes sensor 18 until it reaches sensor 12 and thereafter turns the gate 
"off". The output of gate 24 is fed to a counter 28 and accordingly 
counter 28 counts the number of clock pulses from the time the wheel 
passes sensor 18 until it passes sensor 12. The output of counter 28 is 
fed to a divider 30 the divisor of which comprises N.multidot.y the 
product of (a) the number of samples required ("N") and (b) the multiple 
of the sensing zone by which the reference distance exceeds the sensing 
zone ("y"). The output of divider 30 which comprises a single interval of 
time is used to set a ring-around down counter 32. Counter 32 serves to 
count down to zero from the number set by divider 30 with each advance 
pulse from clock pulse generator 26. Thus, each time counter 32 reaches 
zero another time interval has elapsed. Counter 32 is turned on when 
sensor 12 is triggered and counter 32 is turned off when sensor 14 is 
triggered and thus counts down clock pulses when the wheel under 
observation is within the sensing zone. Each time counter 32 reaches zero 
it automatically re-sets to the number determined by the divided output of 
counter 28. 
The output of counter 32 is gated through gate 34 with the clock pulse 
generator 26 so that each time counter 32 reaches zero a sample control 
pulse is generated. During the time it takes for the wheel to pass from 
sensor 12 to sensor 14, N control pulses will be generated equi-spaced in 
time. This follows from the following mathematics: 
______________________________________ 
Output of counter 32 = 
##STR1## 
where 
##STR2## 
##STR3## 
D = divisor of divider 30 = y .multidot. N 
N = number of samples required 
y = 
##STR4## 
but 
##STR5## 
##STR6## 
where 
v = velocity of wheel, and 
##STR7## 
therefore 
##STR8## 
##STR9## 
but 
##STR10## 
##STR11## 
therefore 
##STR12## 
______________________________________ 
From the above, it can be seen that as long as the velocity of the wheel 
remains constant during the period from which it passes through the 
reference distance until it passes through the sensing zone the output of 
counter 32 will equal the time required to travel the distance between 
sensors 12 and 14 divided by the desired number of samples independent of 
the velocity of the train. 
The above description was prepared for a train travelling in the direction 
indicated in FIG. 1. If the train were travelling in the opposite 
direction, sensor 18 would be replaced by sensor 20 and sensors 12 and 14 
would be reversed for all purposes. 
In a successful practice of this invention, sensors 12 and 14 were placed 
27 inches apart while sensor 18 was spaced 72 feet from sensor 12 and 
sensor 20 was spaced 72 feet from sensor 14. As a result, the multiple y, 
was equal to 32. The desired number of samples was also 32 so that divider 
30 was set to divide by 32.multidot.32 or 1024. 
Thus, in accordance with the above, the aforementioned objects are 
effectively attained.