JPH09127062A - Detector for flaw of conductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the detection reliability of a flaw of which size is equal to or more than a minimum length value regardless of the speed fluctuation of a material to be inspected. SOLUTION: An annular first excitation unit 4 and a second excitation unit 5 are arranged in the direction for carrying an inspection object 1. Magnetic poles formed at the positions which are opposed to each other in the carrying direction of the first excitation unit 4 and the second excitation unit 5 are made different from each other and a magnetic field in the carrying direction is generated at the position of a detection unit 6. Using a three-phase AC power supply where a frequency f changes according to a traveling speed v of the inspection object 1, magnetic field is rotated and moved in circumferential direction as f>=v/(Ls.P). The change of eddy current due to the flaw generated at the inspection object 1 is detected as the change in magnetic field by the detection unit 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flaw detection device for a conductor which can be used for detecting flaws on the surface of a steel bar or the like.

[0002]

2. Description of the Related Art For example, when detecting a surface flaw in a steel product, an inspection is generally carried out using an eddy current flaw detection method or a leakage magnetic flux flaw detection method. In the eddy current flaw detection method, an inspection object is passed through a magnetic field generated by an exciting coil, and an eddy current is caused to flow through the inspection object. Then, since the eddy current changes depending on the presence or absence of the surface flaw of the inspection object, the magnetic flux generated by the change is detected by the detection coil or the like. In the leakage magnetic flux detection method, an inspection target, which is a magnetic material, is magnetized, and leakage magnetic flux leaking outside due to a flaw of the inspection target is detected using a sensor.

Although the eddy current flaw detection method has a good detection power, it is often disturbed by a pseudo-unwanted noise signal induced by magnetic nonuniformity of the surface state of the material to be inspected. The surface flaw is inspected by the difference between the signals of both coils.

FIG. 15 shows how the most commonly used self-exciting feedthrough coil is used to inspect a material to be inspected.
Coil 4a, 4 for exciting the through-type coil 3 and detecting flaws
In b, the winding directions are opposite to each other and differential winding is performed.
When the crack 2 is present and the test material 1 passes through the penetrating coil 3 in the direction of the arrow 20, a flaw signal 21 is obtained. The detection signal of the crack 2 caused by the penetrating coil 3 is the same regardless of how long the crack 2 is in the longitudinal direction of the material to be inspected 1. This is because the difference between the signals of the coils 4a and 4b is the detection signal. This is because the signal is generated only at two points, the signal a at the front of the defect 2 and the signal b at the tail. The detection signal is also greatly affected by the flaw shapes of the front and tail portions of the crack 2, and the detection signal is high if the flaw changes rapidly in the longitudinal direction, but is low if it is gentle. There is a problem such as a decrease in force, and the detection of the crack 2 by the through-type coil 3 is limited to the flaw having a large flaw depth.

In order to eliminate such a drawback of the through type coil, a rotary probe type is considered. This is shown in FIG.
As shown in FIG. 6, the probe 5 accommodating the exciting coil and the detection coil is rotated in the circumferential direction of the cross section of the test material 1 as shown by an arrow 19, and is perpendicular to the crack 2 of the test material 1. When the probe 5 crosses a crack, the flaw signal is detected every time the probe 5 crosses the crack, and the detection power for the crack is improved.

However, in order to traverse the probe 5 with respect to the crack 2 many times, the probe 5 must be rotated at a high speed around the material 1 to be inspected. −
It is difficult to follow the test piece 1 of the bump 5, and there are many problems such as a high risk of overlooking when the crack 2 is short.

As a conventional technique for solving such a problem, for example, Japanese Patent Laid-Open Nos. 62-6162, 62-6163, 62-123352, and 62-123352 are disclosed. No. 62-145162, JP-A-62-
Japanese Patent No. 172258 and Japanese Patent Laid-Open No. 62-172259 are known.

In Japanese Patent Laid-Open No. 62-6162, a large number of detection units each composed of an exciting coil and a detecting coil are installed in the circumferential direction, and the exciting coil generates a magnetic field in the circumferential direction or the cross-sectional direction of the inspection object. By sequentially switching a large number of detection units with a switch, the entire circumference can be inspected.

Further, in JP-A-62-6163 and JP-A-62-123352, a large number of detection units each composed of an excitation coil and a detection coil are installed in the circumferential direction,
The exciting coil generates a magnetic field in the circumferential or cross-sectional direction of the inspection object, and the exciting coil is excited using three-phase alternating current so that the exciting position is sequentially rotated in the circumferential direction without using a switch. ing.

Further, in Japanese Laid-Open Patent Publication No. 62-145162, a large number of detection units arranged in the circumferential direction are mechanically separated from each other, and a gap between the detection unit and the inspection object is kept constant. There is.

In Japanese Patent Laid-Open Nos. 62-172258 and 62-172259, a magnetic field that sequentially rotates in the circumferential direction of an inspection object is generated, and a large number of sensors are arranged in the circumferential direction. Disclosed is a technique for sequentially sampling the outputs of a large number of sensors in synchronization with the rotation of the generated magnetic field.

[0012]

Although these techniques have their respective advantages, they have the following common drawbacks. For example, in Japanese Patent Laid-Open No. 62-6162, an exciting coil and a detection coil as shown in FIG. 17 are used.
Since the -123352 publication uses the excitation coil shown in FIG. 18 and the JP-A-62-145162 uses the excitation coil shown in FIG. 19, the magnetic flux from the excitation coil is in the radial direction of the material to be inspected. Occur in. On the other hand, in the conventional through-type excitation method shown in FIG. 15, magnetic flux is generated in the longitudinal (axial) direction of the material to be inspected.

By the way, it is generally said that the S / N ratio (the ratio of the flaw signal S and the base noise N, which indicates the easiness of flaw detection) in automatic flaw detection is required to be three times or more. Due to fluctuations in the gap between the detector and the inspection target, the S / N becomes better as the gap between the detector and the inspection target becomes smaller, but the actual inspection process is, for example,
Since the inspection is performed while the steel bar to be inspected is transported at high speed, the gap cannot be extremely narrowed in consideration of the material permeability.

Further, since the object to be inspected vibrates during transportation, the gap between the detector and the material to be inspected constantly fluctuates.
At this time, when the magnetic flux from the exciting coil is generated in the radial direction of the material to be inspected, the magnetic flux density is remarkably changed due to the gap change. Therefore, not only the fluctuation of the base noise is large, but also the sensitivity change of the flaw signal occurs extremely. There is a drawback that / N is significantly deteriorated.

However, as shown in FIG. 15, when the magnetic flux from the exciting coil is generated in the axial direction of the material to be inspected, the change in the magnetic flux density in the radial direction of the material to be inspected due to the gap variation is relatively small. There are advantages. Therefore, in the present invention, instead of the above-described probe rotation method, the magnetic flux in the axial direction of the material to be inspected is generated while rotating in the circumferential direction, so that the S / The first purpose is to improve the N ratio and enhance the reliability of flaw detection, and the shortest value Ls corresponding to the shortest value Ls of the length of the flaw to be detected in the axial direction z.
The second purpose is to improve the above-described defect detection reliability, and the shortest value Ls is obtained even if the moving speed v of the inspected material fluctuates.
A third object is to ensure the above-described defect detection reliability.

[0016]

SUMMARY OF THE INVENTION A conductor flaw detection apparatus according to the present invention comprises a first set of a plurality of members which surrounds an outer periphery of an inspection object (1) which moves at a speed v in a predetermined axial direction (z). Electric coil (Fig.
The first exciting means (4) having the number of poles P, in which 2 shaded lines (24 pieces) are distributed; a plurality of electric coils of the second set (in FIG. 3) surrounding the outer circumference of the inspection object (1). The second exciting means (5) with the number of poles P, which is installed at a position apart from the first exciting means (4) in the axial direction (z), in which 24 shaded areas are distributed; Magnetic flux detecting means (6, 7) installed between the first exciting means (4) and the second exciting means (5) at a position facing the surface of the inspection object (1); and First excitation means (4) and second
The magnetic field generated by the excitation means (5) of
At the (6, 7) position, the first set is oriented in the conveying direction (z) of the inspection object (1) and rotates in the circumferential direction of the inspection object (1). And 3 for the second set of electric coils
Excitation control means (11, 3) for applying an AC voltage having a frequency f of f ≧ v / (Ls · P) Ls: a set value corresponding to the flaw detection resolution in the axial direction (z) , 2A, 2B) ;. Note that the symbols and the like shown in the above parentheses are reference numerals of corresponding elements in the examples described later, but each component of the present invention is only a specific element in the examples. It is not limited.

With this structure, the magnetic flux detecting means (6,
The magnetic field in the space between the first set of exciting means (4) in which 7) is installed and the second set of exciting means (5) is dominated by the component (Bz) in the axial direction (z). . That is, the first set of excitation means
A magnetic path is formed from one magnetic pole of (4) to one magnetic pole of the second set of exciting means (5) (or vice versa). Since this magnetic path is adjacent to the surface of the inspection object (1), an eddy current flows in the surface layer of the inspection object (1) due to the magnetic flux passing through it. The direction in which the eddy current flows is determined by the direction of the magnetic flux generated by each exciting means. When the surface of the inspection object (1) has a flaw, the eddy current flows so as to bypass the flaw. The magnetic flux detecting means (6, 7) detects the magnetic flux generated by the eddy current on the inspection object. Therefore, when the eddy current changes depending on the presence / absence of a flaw on the inspection object, the eddy current is detected by the magnetic flux detecting means (6, 7) to detect the presence / absence of a flaw. First
The magnetic fields generated by the set of exciting means and the second set of exciting means are
Since the inspection object rotates in the circumferential direction, flaws at each position in the circumferential direction can be detected.

In the present invention, the flaw is detected in a state where the inspection object is excited in parallel in the conveying direction (z), but in the conventional flaw detection device, the inspection object is surrounded by its circumference. The flaw is detected in the state of being excited in the direction of the cross section or the cross section. According to the experiment, S of the signal obtained by the flaw is
The / N ratio is in a state in which the inspection object is stationary and a state in which the inspection object vibrates due to conveyance (a state in which the gap between the magnetic flux detecting means and the inspection object changes). The device of the present invention gave much better results than the conventional device. Therefore, highly reliable flaw detection is realized.

By the way, for example, an inspection object having a certain defect
(1) goes in the axial direction (z), the rotating magnetic field generated by the exciting means (4), (5) detects when crossing the flaw, so that the flaw is the exciting means (4), (5). The flaw cannot be detected because the rotating magnetic field does not cross the flaw at least once while passing through the region between the two) because the magnetic field change due to the flaw does not occur. Therefore, if the traveling speed v of the inspection object (1) is high or the length of the flaw in the axial direction (z) is short, the flaw may not be detected.

The frequency of the voltage applied to the electric coils of the exciting means (4) and (5) is f (Hz), and the number of poles of the exciting means (4) and (5) is P.
Assuming (dimensionless), when P = 1, the cycle T = 1 / f
The magnetic field makes one rotation in (sec). In this case, the moving speed of the inspection object (1) is v (m / sec), and the minimum length of the flaw to be detected.
Letting Ls (m) be (axial direction z), if T ≦ Ls / v,
A flaw with a length of Ls or more is always detected, and if T> Ls / v, detection failure may occur. If this is generalized and expressed when the number of poles P is 2 or more, if T / P ≦ Ls / v, a flaw with a length of Ls or more is always detected, and T / P>
Ls / v may cause detection failure. T =
Substituting 1 / f into this relationship gives 1 / (f · P) ≦ Ls / v. From this, if f ≧ v / (Ls · P) (1), the length greater than or equal to Ls The flaws of the saws are always detected, and the flaw detection of the length Ls or more is highly reliable.

In the present invention, the excitation control means (11, 3, 2A, 2B)
Where f ≧ v / (Ls · P) Ls: the set value corresponding to the flaw detection resolution in the axial direction (z) in the number of phases of three or more phases in the first and second electric coils Since the AC voltage of f is applied, the stability of flaw detection for a predetermined length (Ls) or more is high according to the above-mentioned principle. That is, the reliability of flaw detection is high.

Further, since the AC voltage having three or more phases is applied, the spatial harmonics are reduced and the magnetic rotation is smooth, which guarantees the flaw detection with high accuracy and high reliability.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION When the frequency fs is set according to the above equation (1) corresponding to the minimum length (Ls) to detect a flaw,
If the moving speed (reference speed) of the inspection object (1) assumed at that time is Vs, then fs ≧ Vs / (Ls · P). Here, when the velocity Vv of fs = Vv / (Ls · P) is calculated, when the moving velocity of the inspection object (1) becomes Vv or more, the higher the Vv is, the more the flaw of the minimum length (Ls) is missed. When the moving speed v of the inspection object (1) fluctuates and the fluctuation range is relatively wide, the detection reliability of the flaw of the minimum length (Ls) decreases.

Therefore, a preferred embodiment of the present invention is speed detecting means (8-10) for detecting the moving speed v of the inspection object (1);
The excitation control means (11, 3, 2A, 2B) further comprises a frequency f proportional to the speed v detected by the speed detection means (8-10).
The alternating voltage of 1 was applied to the first and second sets of electric coils. According to this, when the moving speed v of the inspection object (1) rises, the frequency f rises accordingly, and despite the fluctuation of the moving speed v, the relationship of the above formula (1) is always maintained, and the minimum No flaws in length (Ls) are detected. That is, the stability of flaw detection for a predetermined length (Ls) or more is high.
That is, the reliability of flaw detection is high.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0026]

FIG. 1 shows an embodiment of the present invention, and FIG.
II-II line cross section of FIG. 3 is shown, and the III-III line cross section is shown in FIG.
First, a description will be given with reference to FIG. Steel bar to be inspected 1
Is manufactured on a hot rolling line, and is continuously rolled while being conveyed at a high speed in its axial direction (z: longitudinal direction). In this example, on the exit side of the finish rolling process,
The flaw detection device is arranged so as to surround the passage of the steel bar 1. Since the temperature of the steel bar 1 is at the Curie point or higher at the position of the flaw detection device, the steel bar 1 is a non-magnetic material.

The main part of the flaw detection device is a three-phase AC power supply 2
A, 2B, a sine wave signal generator 3, a first excitation unit 4, a second excitation unit 5, a detection unit 6 and a detection circuit 7. In front of the flaw detection device, there is a roller 8 that comes into contact with the steel bar 1 and rotates together with the steel bar 1.
A pulse generator (rotary encoder) 9 is attached to the axis of the rotor 8.
Are combined. The pulse generator 9 generates one electric pulse Ps for each predetermined length of movement of the steel bar 1. The f / v converter 10 generates an analog voltage (a voltage representing the speed v) corresponding to the frequency of the pulse Ps (proportional to the speed v of the steel bar 1). The v / f converter 11 generates a high-frequency electric pulse (clock pulse) whose frequency is proportional to this analog voltage and supplies it to the sine wave signal generator 3. The sine wave signal generator 3 counts the clock pulses to generate a three-phase sine wave signal (three-phase AC signal) having a count value as a phase value to generate three-phase AC power supplies 2A and 2A.
Give to B.

The frequency of the clock pulse is the speed v of the steel bar 1.
The frequency of the three-phase AC signal is also proportional to the speed v of the steel bar 1.

The first exciting unit 4 is composed of an annular iron core 40 arranged so as to surround the steel bar 1 and a large number of exciting coils 47 wound around it. The exciting coil 47 is
Actually, as shown in FIG. 2, 24 coils are arranged at equal intervals in the circumferential direction. Further, since these coils are connected as shown by the dotted lines, these are 6 sets of four exciting coil groups 41, 42, 43, 44, 4 each.
It is divided into 5 and 46. That is, as shown in FIG. 4, the exciting coil groups 41, 42, 43, 44, 45 and 4
6 is + U phase, −V phase, + W of three-phase AC voltage, respectively.
It is excited by the voltage of the phase, -U phase, + V phase and -W phase.

Similarly, the second exciting unit 5 is composed of an annular iron core 50 arranged so as to surround the steel bar 1 and a large number of exciting coils 57 wound around the iron core 50. The exciting coil 57 is actually 24 coils arranged at equal intervals in the circumferential direction as shown in FIG. Further, since these coils are connected as shown by the dotted lines, these are four sets of four exciting coil groups 51, 52, 53,
It is divided into 54, 55 and 56. That is, as shown in FIG. 4, the exciting coil groups 51, 52, 53, 54, 5
5 and 56 are -U phase and + V of 3-phase AC voltage, respectively.
It is excited by the voltages of the phase, -W phase, + U phase, -V phase and + W phase.

As shown in FIG. 1, the power supplied to the first excitation unit 4 is generated by the three-phase AC power supply 2A, and the power supplied to the second excitation unit 5 is generated by the three-phase AC power supply 2B.

The three-phase AC power supplies 2A and 2B generate three-phase (U, V, W) AC power in synchronization with the three-phase AC signal output from the sine wave signal generator 3. Therefore,
The phases of the three-phase AC power output by the three-phase AC power supply 2A and the three-phase AC power output by the three-phase AC power supply 2B are synchronized with each other.

Then, as shown in FIG. 4, the first exciting unit 4 and the second exciting unit 5 are arranged in the axial direction of the steel bar 1.
The polarities of the electric powers supplied to the exciting coil groups at the positions opposite to each other are opposite to each other. That is, for example, when the magnetic pole generated by energizing the exciting coil group 41 is the S pole, the magnetic pole generated by energizing the exciting coil group 51 is the N pole. Further, when the magnetic pole generated by energizing the exciting coil group 41 is the N pole,
The magnetic pole generated by energization of the exciting coil group 51 becomes the S pole. Therefore, a magnetic field is generated in which the first excitation unit 4 and the second excitation unit 5 face each other, that is, the magnetic field extends in the axial direction of the steel bar 1.

The detection unit 6 is formed in an annular shape so as to surround the steel bar 1 and is arranged at an intermediate position between the first excitation unit 4 and the second excitation unit 5. The magnetic flux density distribution around the steel bar 1 at the position of the detection unit 6 formed by the excitation of the first excitation unit 4 and the second excitation unit 5 was calculated and obtained by computer simulation. FIG. 8 shows the result. The real part shown on the upper side of FIG. 8 and the imaginary part shown on the lower side of FIG. 8 indicate a state where the phases of the power supply waveforms are deviated from each other by 90 degrees.

Further, FIG. 9 shows the results of decomposing the magnetic flux density distribution around the steel bar 1 at the position of the detection unit 6 into components in each axial direction as the magnetic flux density at each position in the circumferential direction.
In FIG. 9, Bz, Bt, and Br represent the magnetic flux densities in the z-axis direction (longitudinal direction of the steel bar), the radial direction of the steel bar, and the circumferential direction, respectively. That is, it can be understood from FIG. 9 that the magnetic flux density at the position of the detection unit 6 is dominated by the component in the z-axis direction.

FIG. 10 shows a time transition of the magnetic flux density distribution in the z-axis direction at the position of the detection unit 6. Here, T is one cycle of the signal output from the sine wave signal generator 3.

Referring to FIG. 10, the distribution of magnetic flux density is
It can be understood that it moves in the circumferential direction with time. That is, the magnetic field formed at the position of the detection unit 6 is
Becomes a rotating magnetic field that rotates around the circumference in the circumferential direction. At some point in time, as shown in FIG. 1, one S pole and one N pole are formed on the first excitation unit 4, and one N pole and one S pole are formed on the second excitation unit 5. Is formed, the first
Between the S pole of the excitation unit and the N pole of the second excitation unit,
A large magnetic flux density is obtained at the position of the detection unit 6 between the N pole of the first excitation unit and the S pole of the second excitation unit.

Next, description will be made with reference to FIG. As described above, when the first excitation unit 4 and the second excitation unit 5 are excited, the magnetic field H in the z-axis direction is generated near the surface of the steel bar 1. Due to this magnetic field H, an eddy current i flows in the circumferential direction on the surface of the steel bar 1 which is a conductor. However, when the flaw 1a is present on the surface of the steel bar 1, the eddy current flows so as to bypass the flaw 1a, so that a component i "in the z-axis direction is generated in the eddy current in the vicinity of the flaw 1a. Causes a magnetic field H2 in the circumferential direction. When the flaw 1a does not exist, the magnetic field H2 in the circumferential direction hardly occurs. Therefore, the presence or absence of the flaw 1a can be detected by monitoring the magnetic field H2 in the circumferential direction.

FIG. 12 shows the structure of the detection unit 6.
The detection unit 6 is installed to detect the magnetic field H2 in the circumferential direction. FIG. 12 shows the appearance of the detection unit 6 with the circumferential direction developed in the vertical direction. FIG.
The VV line cross section of is shown in FIG.

Referring to FIG. 12, the detection unit 6 is z
Two rows of detection units 6 arranged in a state of being close to each other in the axial direction
It is composed of A and 6B. The detection unit 6A includes 30 coil plates 6Aa, 6Ab, 6A arranged at equal intervals in the circumferential direction.
c, 6Ad, ... The same applies to the detection unit 6B. Two of these coil plates, which are adjacent to each other in the circumferential direction, form a pair.

FIG. 6 shows the structure of the pair of coil plates 6Aa and 6Ab. Each of the coil plates 6Aa and 6Ab has a spiral coil 62 formed by a foil-shaped conductor printed on the resin substrate 61. A lead wire 63a or 63b is connected to one end on the outside of the coil 62. The inner end of the coil 62 of the coil plate 6Aa and the inner end of the coil 62 of the coil plate 6Ab are connected to the conductive wire 64.
Are connected to each other. Other coil plates 6Ac,
The same applies to 6Ad, 6Ae, 6Af, ....

The magnetic flux generated by the magnetic field H2 is generated by the coil 6
2 and the voltage is induced in the coil 62. When the flaw 1a does not exist on the surface of the steel bar at a position facing the pair of coil plates (for example, 6Aa, 6Ab), the voltages induced in the two coils 62 are almost equal, but at the position facing one of the pair of coil plates. When the flaw 1a is present on the surface of the steel bar and the flaw is not present at the other position, the voltage induced in the two coils 62 is different. Therefore, when the flaw 1a is present, the potential difference appearing between the lead lines 63a and 63b becomes large, so that the flaw 1a can be detected by monitoring the potential difference.

FIG. 7 shows the structure of the portion of the detection circuit 7 connected to the pair of coil plates 6Aa and 6Ab. Also,
FIG. 13 shows a signal example of each part of the circuit shown in FIG. FIG.
Referring to, the differential amplifier 71 amplifies the difference between the voltage SA induced by the coil of the coil plate 6Aa and the voltage SB induced by the coil of the coil plate 6Ab, and outputs it as a signal SC. The signal SC is input to the Schmitt trigger 73 and the Schmitt trigger 74 via the inverting amplifier 72. When the amplitude of the signal SC exceeds a predetermined level, the output of the Schmitt trigger 73 and / or 74 becomes the high level H. Ogate 75 is a Schmitt trigger 7
The flaw detection signal SD is generated on the basis of the signals output from 3, 74. Other coil plates (6Ac, 6Ad, 6Ae, 6
The detection circuit having the same configuration as that shown in FIG. 7 is connected to each of the pairs Af, ...

As described above, the first excitation unit 4 and the second excitation unit 4
The magnetic field H generated by the excitation of the excitation unit 5 is a rotating magnetic field, and a portion having a large magnetic flux density rotates in the circumferential direction of the steel bar 1 at a constant speed. Then, an eddy current flows in a portion of the steel bar 1 having a high magnetic flux density, and the presence or absence of a flaw is detected by using this eddy current. Therefore, as the magnetic field H rotates,
The target position for flaw detection also moves in the circumferential direction. Steel bar 1
The upper flaw 1a is detected by a pair of coil plates (for example, 6Aa, 6Ab) existing at a position facing the flaw 1a.

In this embodiment, the two rows of detectors 6A and 6B arranged in the z-axis direction are connected so that the pairs of coil plates are staggered. That is, as shown in FIG.
Regarding the detection unit 6A in the row, coil plates 6Aa and 6A
b, 6Ac · 6Ad, 6Ae · 6Af, ... Are paired, respectively, but regarding the detection unit 6B in the second row,
Coil plates 6Bb ・ 6Bc, 6Bd ・ 6Be, 6Bf ・ 6
Bg, ... form a pair, and the coil plate pair of the detection unit 6B in the second row is positioned between the coil plate pair and the coil plate pair adjacent to each other in the detection unit 6A in the first row. ing.

For example, circumferential coil plates 6Aa, 6A
Defects are detected by them in the vicinity of b, but in the vicinity of the coil plates 6Ab and 6Ac, the coil plate pair 6 is detected.
It is difficult to detect flaws by Aa · 6Ab or coil plate pair 6Ac · 6Ad. However, the coil plate 6Ab,
In the vicinity of 6Ac, the coil plate pair 6 of the detection unit 6B in the second row is
Defects can be detected by Bb · 6Bc. Therefore, the flaw can be detected at any position in the circumferential direction, and a region (dead zone) where the flaw cannot be detected does not occur.

The relationship between the frequency f of the three-phase AC signal generated by the sine wave signal generator 3 shown in FIG. 1 and the moving speed v of the steel bar 1 will be described. Re-expressing the equation (1), f ≧ v / (Ls · P) (1). In this embodiment, P = 2 and f = k.v / (2L
s), k = 1.2, the relationship between the voltage / pulse frequency conversion characteristic of the v / f converter 11 and the counter value of the sine wave signal generator 3 versus the output instantaneous value level is set.

In this embodiment, 360 clock pulses (f / v converter 1) are generated during one period T of a three-phase sine wave signal.
0 output pulse), so T = 1 / f =
From 2Ls / (k · v), clock pulse cycle dT = 2Ls
Since / (360 ・ k ・ v) and k = 1.2, dT = 2Ls / (360 ・ 1.2 ・ v) = [2 / (360 × 1.2)] ・ Ls /
and the frequency df of the clock pulse is df = v / [2 / (360 × 1.2 Ls)]. This is the v / f conversion characteristic of the v / f converter 11. When k = 1.0 satisfies the above formula (1), k = 1.
2 and a value having a margin of 0.2 (20%) are for ensuring detection of a flaw having a length Ls or more in the axial direction z (in particular, a flaw having a length Ls).

At the start of measurement, the sine wave signal generator 3 clears the clock pulse counter (U phase) and starts counting up the clock pulses, and when the count value reaches 360, clears the clock pulse counter and starts counting the clock pulses. Counting up is started again, and while repeating this, the sine wave level data corresponding to the count value (phase value) is read from the internal memory, A / D converted, and output as a U1 phase signal to the comparator 29. Also, counter (U phase)
When the count value of 120 becomes 120, the clock pulse counter (V phase) is cleared and the clock pulse count-up is started. While repeating this, the sine wave level data corresponding to the count value (phase value) is read from the internal memory. A
/ D conversion is performed and the signal is output to the comparator 29 as a V1 phase signal.
Further, when the count value of the counter (U phase) reaches 240, the clock pulse counter (W phase) is cleared and the clock pulse counting is started. By repeating this, the sine wave level data corresponding to the count value (phase value) The data is read from the internal memory, A / D converted, and output to the comparator 29 as a W1 phase signal. The peak values of the phase signals V1 to W1 are the same.

FIG. 14 shows the configuration of the three-phase AC power supply 2A shown in FIG. The configuration of the three-phase AC power supply 2B is the same as that shown in FIG. This will be described with reference to FIG. The AC power supplied from the three-phase power supply 21 is rectified by the thyristor bridge 22 and smoothed by the inductor 25 and the capacitor 26. Therefore, a DC voltage appears between the terminals of the capacitor 26. The voltage appearing across the terminals of capacitor 26 varies depending on the phase at which thyristor bridge 22 is triggered. The voltage command value Vdc applied to the phase angle calculator 24 is used for adjusting the DC voltage appearing across the terminals of the capacitor 26. The phase angle calculator 24 calculates the trigger phase angle α corresponding to the voltage command value Vdc.

The gate driver 23 includes a phase angle calculator 24.
To trigger each thyristor of the thyristor bridge 22 with the trigger phase angle α output by
Generate a trigger signal to be applied to the output terminal. That is, a zero-cross point of an AC waveform that each thyristor switches is detected, and a trigger signal is generated when a time corresponding to the phase angle α has elapsed after the zero-cross point was detected. The transistor bridge 27 switches the DC voltage appearing between the terminals of the capacitor 26 to generate three-phase AC voltages U, V, W. A signal for controlling the switching of the transistor bridge 27 is generated by the comparator 29 and applied to the base terminal of each transistor via the gate driver 28. At the input terminal of the comparator 29,
As described above, the three-phase signals U1, V1, and W1 are supplied, and the output terminal of the triangular wave generator 30 is supplied to the control terminal.

U1 and V1 and V1 and W1 respectively have a phase difference of 120 degrees. Also, the triangular wave generator 30
Outputs a triangular wave signal having a repetition frequency of 3 KHz. The comparator 29 has six analog comparators built-in, and the positive half-wave voltage and the negative half-wave voltage of the three-phase AC voltages U1, V1, and W1 are triangular wave generators which are independent analog comparators. It is compared with the triangular wave voltage output by 30, and the comparison results are output as six binary signals. These binary signals are applied to the transistor bridge 27 via the gate driver 28, and the transistor bridge 27
Three-phase AC voltages U, V, and W appear at the output of. That is, three-phase AC voltages U, V, W are formed by PWM control of turning on / off each transistor of the transistor bridge 27. It has been confirmed by experiments that the flaw detection signal (SC) in the flaw detection device of this embodiment has a very large S / N ratio. Further, even when the variation amount of the gap between the detection unit 6 and the steel bar 1 is about 1 mm, the S / N of about 2.5 for a flaw having a depth of 0.5 mm.
It was found that a ratio was obtained.

In the above embodiment, the object to be inspected is explained as a steel bar, but it is also possible to inspect with other materials as long as it is a conductor. In the embodiment, the three-phase AC power supply is used as the power supply for energizing the excitation units 4 and 5, but a multi-phase AC power supply having more than three phases may be used.

In the above embodiment, the detection unit 6 is composed of a large number of coil plates arranged in the circumferential direction.
It is possible to detect flaws by using magnetic field detectors of various conventionally known structures.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention,
The detection units 4 and 5 show vertical cross sections.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a sectional view taken along line III-III of FIG.

4 is a schematic enlarged perspective view of the excitation units 4 and 5 shown in FIG. 1, showing the energized voltage phase divisions of the electric coils of these units.

5 is an enlarged cross-sectional view of the detection unit 6 shown in FIG.

6 is an enlarged perspective view showing a pair of coil plates 6Aa and 6Ab shown in FIG. 5. FIG.

7 is an electric circuit diagram showing a detection circuit connected to the coil plates 6Aa and 6Ab shown in FIG.

8 is a vector diagram showing a magnetic flux density distribution at the position of the detection unit 6 shown in FIG.

9 is a graph showing a circumferential direction distribution of each axial component of the magnetic flux density of FIG.

10 is a graph showing a time transition of a z-direction magnetic field component Bz shown in FIG.

FIG. 11 is a perspective view showing a relationship between a magnetic field on the steel bar 1 shown in FIG. 1 and an eddy current.

FIG. 12 is a development view showing the appearance of the detection unit 6 shown in FIG.

13 is a time chart showing an electric signal of each part of the detection circuit shown in FIG.

FIG. 14 is a block diagram showing a configuration of a three-phase AC power supply 2A shown in FIG.

FIG. 15 is a perspective view showing an appearance of a detection end of one conventional flaw detection device.

FIG. 16 is a perspective view showing a scanning direction of a detection end of another conventional flaw detection device.

FIG. 17 shows an external perspective view and a plan view of a detection end of a conventional flaw detection device.

FIG. 18 shows a cross-sectional view of an electric coil connection of a conventional flaw detection device, a time chart of an energized current, and a cross-sectional view showing a current direction and a magnetic field direction.

FIG. 19 shows a cross-sectional view of a part of an excitation unit of a conventional flaw detection device and an electric circuit diagram of electric coil connection.

[Explanation of symbols]

1: Steel bar 1a: Defects 2A, 2B, 2C: 3-phase AC power supply 3: Sine wave signal generator 4: First excitation unit 5: Second excitation unit 6: Detection unit 6A, 6B: Detection unit 6Aa, 6Ab, 6Ac , 6Ad, ...: Coil plate 6Ba, 6Bb, 6Bc, 6Bd, ...: Coil plate 7: Detection circuit 8: Roller 9: Pulse generator 10f / v converter 11: v / f converter 21 : Three-phase AC power supply 22: Thyristor bridge 23, 28: Gate driver 24: Phase angle calculator 25: Inductor 26: Capacitor 27: Transistor bridge 29: Comparator 30: Triangular wave generator 40, 50: Iron core 41 to 46 , 51 to 56: Excitation coil group 47, 57: Excitation coil 61: Resin substrate 62: Coil 63a, 63
b: Lead wire 64: Conductor wire

Claims (2)

[Claims] 1. A first exciting means having a pole number P, in which a plurality of electric coils of a first set are distributed so as to surround an outer periphery of an object to be inspected which moves in a predetermined axial direction at a speed v; A plurality of electric coils of the second set are distributed around the outer circumference of the object,
A second exciting means having a number of poles of P, which is installed at a position apart from the first exciting means in the axial direction; and the inspection target between the first exciting means and the second exciting means. Magnetic flux detecting means installed at a position facing the surface of the object; and the first
The magnetic fields generated by the exciting means and the second exciting means are oriented in the conveyance direction of the inspection object at the position of the magnetic flux detection means and rotate in the circumferential direction of the inspection object. As described above, in the first and second electric coils, f ≧ v / (Ls · P), Ls, which is the set value corresponding to the flaw detection resolution in the axial direction, of three or more phases, A flaw detection device for an electric conductor, comprising: excitation control means for applying the AC voltage of. 2. A speed detecting means for detecting a moving speed v of the inspection object; further comprising: the excitation control means for generating a first set of AC voltage having a frequency f proportional to the speed v detected by the speed detecting means. And a second set of electrical coils; the flaw detection device for a conductor according to claim 1.