JPS6344161B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an eddy current track displacement measuring method and apparatus.

Measuring gauge deviations on railway tracks is done by measuring the inner surface of the rail by detecting the deviation between the center of the track and the center of the rail, but these measurements are usually carried out by an inspection vehicle running on the rail. Therefore, it is desirable to measure without contacting the rail.
On the other hand, since this measurement information is extremely important for track maintenance management, high reliability is desired.

Conventionally, these measurement methods include (1) a direct method of measuring directly with a gauge scale or the like, (2) an optical measurement method, and (3) an eddy current measurement method. Although the direct method (1) allows highly accurate measurements, it is practically impossible to measure the entire trajectory using this method, and the measurement takes too much time.

In method (2), if dust, rain, etc. adhere to the measurement surface of the track, or if there are inclusions that obstruct the optical path, the accuracy will be extremely reduced and become unstable. If there is, the function will be completely lost.
In particular, the light path is seriously obstructed by snow and the like thrown up by the wind generated while the inspection vehicle is running at high speed. In the eddy current method (3), the detection coil is placed opposite the rail, and the high frequency magnetic flux generated by passing a high frequency current (resonant current) through the detection coil causes the coil inductance and eddy current to be generated within the rail. Since the equivalent loss of the coil due to current loss is a function of the distance between the detection coil and the rail, the distance is detected by measuring the impedance of the detection coil. This method does not cause the problems seen with optical methods, and has a simple and robust structure.
It has many advantages, such as being relatively inexpensive to manufacture and economical to maintain.

In the conventional eddy current measurement method, circular sensing coils 1 and 2 as shown in FIGS. 1 and 2 or rectangular sensing coils 4 and 5 as shown in FIGS. It is attached to the underside of the vehicle body of the inspection vehicle so as to face the rail at a symmetrical position centering on the longitudinal center line 31, and a resonant current is applied to each detection coil to determine the impedance of each of detection coils 1, 2, 4, and 5. is converted into a DC voltage, and the displacement of the center position of the differential voltage rail between the detection coils 1 and 2 or between the detection coils 4 and 5 is measured.

The biggest drawback of these conventional methods is that the width including the pair of detection coils 1, 2 or 4, 5 is regulated within the width of the wheels for safety reasons of the inspection vehicle. On the other hand, it is inevitable that the distance for measuring the amount of displacement will be short due to restrictions on the size of the pair of sensing coils arranged symmetrically. The distance sensing ability of a sensing coil is determined by the pattern of effective magnetic flux, not simply the area of the coil, so the sensing coil can be changed from the circular one shown in Figures 1 and 2 to the one shown in Figures 3 and 4. Even if the area is increased by using a rectangular shape, it is not only impossible to increase the measurement distance of the displacement amount, but also because the detection sensitivity of the detection coil increases in proportion to the measurement distance. It responds unnecessarily sensitively to vertical vibrations, changes in wheel diameter, etc., and becomes a major hindrance in measuring the amount of rail displacement.

The present invention aims to solve the above-mentioned problems existing in the conventional eddy current measuring method and to provide a more advanced measuring device of this type.

The present invention will be explained in detail with reference to FIGS. 5 to 10. In the present invention, equilateral triangular coils 6 and 7 as shown in FIG. 5 are used as the detection coils mounted on the inspection vehicle.

When the rail 3 is installed in the normal position, one corner of each of the equilateral triangular coils 6 and 7 intersects the longitudinal center line 31 of the rail 3, and
Measurements are made so that they face the rail at a predetermined distance symmetrically with respect to the center line 31, and the distance between the outer sides of the sides facing each of the above corners is larger than the width of the rail tread. A total of two pairs are installed, one pair at the bottom of each side in the longitudinal direction of the car. The sensing characteristics of the equilateral triangular coils 6 and 7 with respect to the amount of rail displacement are expressed by the following equation.

S=K1/√3l ² where S is the rail displacement sensitivity, K is the coefficient, and l is the rail displacement amount.

On the other hand, the strength of the magnetic field is inversely proportional to the square of the measurement distance. Since the equilateral triangular coil has a characteristic including a square term, it is possible to obtain high linearity of the output voltage corresponding to the amount of rail displacement compared to the conventional method.
From the above two points, the embodiment in which the equilateral triangular coils 6 and 7 are arranged as shown in FIG. It can be detected with clear linearity. That is, according to the inventor's experiments, in the conventional method shown in FIGS. 1 to 4, the gap between the rail tread and the detection coil is 18.
Where the displacement could only be detected within ±20mm of the span of the rail in the left and right direction,
In the above embodiment, it has been found that the gap can be clearly detected within a range of approximately 30 mm and the span within a range of approximately ±27 mm.

Figure 7 shows some of the experimental results, a
b is the relationship between the output voltage of the triangular coils 6 and 7 and the rail displacement when the distance between the detection coil and the rail tread is 30 mm and the displacement of the rail center position is ±30 mm, and b is the relationship between the detection coil and the rail tread. The output voltage of the rectangular coil when the distance between the rails is 18 mm and the displacement amount of the rail center position is ±20 mm, and c indicates the output voltage of the circular coil.

On the other hand, when the distance between the rail tread and the detection coil changes, the rail distance detection sensitivity changes. 8th
The figure shows the left and right displacement outputs centered on the rail center line, where a and a' are the displacement outputs when the distance between the rail tread and the detection coil is the reference distance, and n and n' are greater than the reference distance. m and m' indicate the displacement output when the distance is separated, and m and m' indicate the displacement output when the distance is smaller than the reference distance. When the distance between the detection coil and the rail tread is larger than the reference distance, the detection sensitivity of the rail displacement amount by the detection coil decreases, and when it is small, the detection sensitivity increases.

Furthermore, even if the amount of left-right displacement of the rail is the same and the distance between the detection coil and the rail tread is set constant, the output voltage of the detection coil will be affected by vibration transmitted from the wheels or after a long period of time. Changes depending on rail wear.

Figure 9 shows an example of this, where a indicates the output voltage when the reference distance is reached, g indicates the output voltage when the distance is greater than the reference distance, and r indicates the output voltage when the distance is smaller than the reference distance. Even if the amount of horizontal displacement of the rail by the detection coil is the same, the output voltage changes as described above as the distance between the detection coil and the rail tread changes.

Therefore, the inventor of the present invention discovered that the distance between the detection coil and the rail tread surface is proportional to the sum of the displacement output voltages of a pair of detection coils, and that in the present invention, the equilateral triangular detection coils are arranged as described above. It has been found that since a voltage is used, it can be expressed as a linear voltage as shown as d, e, and f in FIG. In Figure 8, d=(n+n')1/2, e=(a
+a′)1/2, f=(m+m′)1/2.

Therefore, in the present invention, when a signal other than e in FIG. 8, for example d or f, is received, it is corrected to the e signal, and the displacement voltages m and n are corrected so as to have the reference setting characteristic a. By doing this, even if the distance between the detection coil and the rail tread changes, the amount of displacement at the center of the rail can be continuously measured with high precision and within a safety margin, without using a separate sensor to measure the distance. It is possible.

An example of the correction calculation mechanism is shown in FIG. A resonant frequency is applied to the detection coils 6 and 7 from an oscillator (not shown). The impedances of the detection coils 6 and 7 are amplified by amplifiers 8 and 9, respectively, and then converted to DC voltage or DC current by converters 8' and 9',
The signal is applied to the arithmetic circuit 10. The calculation circuit 10 calculates the difference voltage and average voltage of the DC voltage. Then, the average voltage is applied to a comparator 11 having a memory. The comparator 11 compares the average voltage with the reference voltage e stored in the memory, and if there is a difference between them, the difference voltage is given to the arithmetic circuit and the average voltage is used as the compensation voltage. , the difference voltage is calculated and corrected.

According to the present invention, the rail center position can be accurately detected between wider spans and gaps than conventional methods without being affected by changes in the distance between the detection coil and the rail tread. Therefore, the effect of contributing to track maintenance is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a conventional eddy current detection coil for rail displacement measurement, FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1, and FIG. 3 is a plan view showing another conventional detection coil. 4 is a sectional view taken along line B-B in FIG. 3, FIG. 5 is a plan view showing an embodiment of the present invention, FIG. 6 is a sectional view taken along line C-C in FIG. 5, and FIG. 7 is a sectional view taken along line C--C in FIG. Fig. 8 is a diagram for comparing the outputs of the triangular detection coil and conventional rectangular detection coils and circular detection coils. A diagram showing an example of the output corresponding to displacement and the relationship between it and the distance between the rail tread surface and the detection coil. Figure 9 is a diagram showing the difference between the left and right displacement outputs in Figure 8. Figure 10 is a diagram showing the difference between the left and right displacement outputs in Figure 8. FIG. 3 is a circuit diagram showing an example of an output voltage correction mechanism according to the present invention. 3...Rail, 6,7...Detection coil, 31...Rail longitudinal direction center line.

Claims (1)

[Claims] 1 Two equilateral triangular detection coils are arranged so that one corner intersects the longitudinal center line of the rail in its normal position and faces the rail symmetrically with respect to the center line at a predetermined distance. and,
The distance between the outer sides of the opposite sides of each of the above corners is set to be larger than the width of the rail tread, and one pair is installed at the bottom of both sides in the longitudinal direction of the measuring car, in total, two pairs are attached to each of the above pairs. an oscillator that sends a resonant frequency to the detection coil of the sensor; a converter that converts the output impedance of each of the pair of detection coils into a DC voltage or DC current via an amplifier; The comparator is equipped with an arithmetic circuit that calculates a differential voltage and an average voltage, and a comparator that has a memory that stores a reference voltage, and the comparator obtains the voltage by comparing the average voltage input from the arithmetic circuit with the reference voltage that it stores. The differential voltage input from the comparator is set to be output to the arithmetic circuit, and the arithmetic circuit calculates and corrects the differential voltage input from the comparator using the average voltage as a compensation voltage to calculate the displacement of the center position of the rail. An eddy current track displacement measuring device consisting of a device configured to measure.