JPS6131423B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a probe used in an eddy current flaw detection method using a probe-shaped coil, and particularly to a probe that enables quantitative evaluation of a defect to be detected regardless of its direction.

In the eddy current flaw detection method using a probe-shaped coil, the test material is scanned by moving the test material and the probe-shaped coil relative to each other, and local fluctuation points in the electromagnetic coupling state between the coil and the test material are detected. This is a method of detecting it as a defect.

Now, as this coil, generally a rectangular coil is often used. This is because the rectangular coil has a high ability to detect defects in a specific direction.The rectangular coil RC shown in Figure 5 and the circular coil shown in Figure 6
Focusing on the electromagnetic coupling between CC (equal area) and defect F, the former has a higher proportion of defects within the effective magnetic field generation range of the coil (approximately proportional to its surrounding area). This is also explained by the phenomenon that the higher this ratio, the greater the change in coil impedance, and the higher the detection ability.

However, in the case of a rectangular coil, the generated magnetic field is not isotropic with respect to the center of the coil axis, and therefore, even for the same defect, the output will differ depending on the scanning angle of the coil. That is, the output is controlled by the scanning direction of the coil or the relative movement direction between the coil and the object to be inspected. Therefore, even if the direction of the defect is constant, if there are defects in various directions, there is a problem in that it is not possible to quantitatively evaluate the defect (depth, etc.) based on the output signal of the coil.

Therefore, a method has been proposed in which a rectangular coil is rotated around its center while scanning to solve the adverse effect of directivity, but this method requires a slip ring, a rotating transformer, etc. as a mechanism to extract signals from the rotating body. Therefore, there is a problem that the detection head including the coil becomes complicated and large, and there is also the problem that maintenance to maintain the precision of the rotating part is troublesome.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an eddy current flaw detection probe that enables quantitative evaluation of defects simply by performing linear scanning.

The eddy current flaw detection probe according to the present invention includes a plurality of rectangular detection coils parallel to the flaw detection surface of the test object, and the plurality of detection coils are rotatably provided around an axis perpendicular to the flaw detection surface, It is characterized in that the rotational positions are fixed so as to form different angles with respect to the scanning direction. Note that the term "rectangle" as used herein includes a rectangle in a broad sense, that is, a square.

First, the principle by which defects in various directions can be quantitatively evaluated by flaw detection using the probe of the present invention will be explained.

FIG. 1 is a schematic diagram showing the planar layout of the probe of the present invention at a certain point in time. The coils (that is, those to be regarded as detection coils) 11 to 17 each have a rectangular shape in plan view, and more specifically, three coil units having a planar dimension of 10 mm x 10 mm are arranged in a row in one direction. They are arranged in a rectangular shape of 10 mm x 30 mm. The coils are arranged in a fan shape on the same circumference, spaced apart by 15 degrees. That is, one short side of each coil is placed on the center side of this circle, and the other side is placed on the distal side, and the seven coils are arranged so that the pitch between the coil centers is 15 degrees.
The coils are arranged radially in the order of 12...17, and each coil output is synthesized by placing the end of coil 11 at the beginning of coil 12, the end of coil 12 at the beginning of coil 13, etc. Connect in series so that the beginning of winding of coil 11 and coil 1
The end of volume 7 is connected to the bridge. This probe is used so that the longitudinal direction of the intermediate coil 14 is the scanning direction (indicated by an open arrow).

FIG. 2 shows actual measurement results of the output characteristics of the above-mentioned coils 11 to 17 alone. The coil is used as a detection coil (pickup coil) of the mutual induction coil, and the size of the artificial defect is 10mm deep and 10mm wide.
The angle θ between the scanning direction of the coil and the longitudinal direction of the artificial defect F and the normalized output are calculated when the length is 0.3 mm and the length is 100 mm. According to this, the directivity of the detection ability of the coil as described above is clear, but when flaw detection is performed using the probe of the present invention, such directivity is canceled out. This is because the angle in the longitudinal direction of each coil with respect to the scanning direction differs from one another, and if there is a defect in the angle that causes the output of a certain coil to be a low value, the output of other coils acts to compensate for this. It is.

FIG. 3 shows the composite normalized output of all the coils using a chain double-dashed line, where α is the angle between the scanning direction of the probe shown in FIG. 1 and the longitudinal direction of the defect F. In the figure, the solid lines marked with ... indicate the individual outputs of each coil 11, 12...17, and as is clear from the layout, each output has a phase difference of 15 degrees, and the composite output is The characteristics are shown by the envelope line of each coil output. Therefore, according to the present invention, a stable output value can be obtained regardless of the direction of the defect. Note that the composite output shown in Figure 3 has a slightly low value near 0° (or 180°), but this is because the probe shown in Figure 1 has a maximum longitudinal angle of the coil with respect to the scanning direction. (Coils 11, 17) are 45 degrees, and by adding coils of 60 degrees, 75 degrees, and 90 degrees, it is possible to obtain a flat composite output characteristic over all angles. Of course.

In the above example, each coil was connected in series, but each coil was connected to a separate bridge,
Composite processing may be performed by combining the unbalanced currents of each bridge.

FIG. 4 is a schematic plan view showing the structure of the probe according to the present invention. This probe is capable of changing the relative angular relationship between a plurality of detection coils, in other words, the coil angle with respect to the scanning direction.
The following motor, gear group, coil, etc. are arranged in a bottomless case 30 that is installed at the lower end of a support member (not shown) so as to face the flaw detection surface of the test object located further below. Each coil is housed so as to face the object to be inspected at an appropriate distance.

31 is a gear directly connected to the output shaft of the motor 32, and the rotating shaft (motor output shaft) is vertical. 33 and 34 are gears of the same specification and mesh with each other, gear 33 meshes with gear 31, and gear 3
The gears are positioned so that the lines connecting the center of the rotation axis of No. 3 and the center of each rotation axis of the gears 31 and 34 are orthogonal to each other. Each of the rotating shafts of these gears 33 and 34 has a smaller diameter gear 3 with the same specifications.
5 and 36 are coaxially attached to each other.

A gear 37 is mounted so that the center of the rotation axis is located on the extension of the line segment on the gear 33 side connecting the centers of the rotation axes of the gears 31 and 33, and this gear 37 meshes with the gear 35. There is. On the other hand, on a straight line that is parallel to the line segment and passes through the rotation axes of gears 34 and 36, there is a gear 3 having the same specifications as gear 37.
8 is attached so as to mesh with the gear 36.

Coils 24 and 22 are attached to the lower surfaces of these gears 37 and 38, respectively. Further, a coil 23 is attached between the gears 37 and 38. This coil 23, unlike the other coils, is fixedly attached to the case 30.

Gears 39 and 40 with the same specifications are the gears 33 and 34.
These gears 39, 40 are arranged so as to mesh with each other.
Coils 25 and 21 are attached to the lower surface of each. The centers of the coils 21 to 25 or the rotation centers of the gears 37 to 70 are on the same circumference, and 15
Even if the gears are rotated in conjunction with each other, the relative positional relationship of the coil centers will not change, and as shown in the figure, in the initial state, each coil 21 to 25 The longitudinal directions of the two are parallel to each other. Further, the number of teeth of gears 33 and 34 is N ₃ , the number of teeth of gears 35 and 36 is N ₅ , gear 37,
When the number of teeth on gear 38 is N ₇ and the number of teeth on gears 39 and 40 is N ₉ , the number of teeth is determined to satisfy the following relationship: 2N ₅ /N ₇ = N ₃ /N ₉ (1) . This probe is used by aligning the scanning direction indicated by the white arrow with the longitudinal direction of the central fixed coil 23, but the angle β of the longitudinal direction of the other coils with respect to this scanning direction is determined by rotating the motor 32 by an appropriate amount. By rotating each gear in a predetermined direction, the number of teeth can be changed arbitrarily, and by determining the number of teeth as shown in equation (1), the outer coil 21 can be changed as shown by the two-dot chain line in FIG. , 25 angle to the inner coil 22, 2
The angle β can be automatically set to twice the angle β of 4, that is, 2β. Therefore, when using this probe, flaw detection can be performed by changing the angle β as appropriate depending on the nature of the defect. For example, if the target is only defects perpendicular to the scanning direction, β = 0°, and if defects in various directions are to be detected, β = 30 to 45°. This is desirable in terms of increasing detection sensitivity and avoiding the influence of the direction of the defect.

As described above, in the case of the present invention, the various directivity problems of the coil can be solved and the probe can be made non-directional, so the depth of the defect can be evaluated regardless of the scanning direction and the direction of the defect. be able to. Since the angle of the coil can be set according to the object being tested, the best sensitivity can be obtained.
Furthermore, since there is no need to rotate the coil as in the conventional case (the probe of the present invention shown in Fig. 4 does not require rotation during inspection), the structure of the detection head is not complicated and maintenance is not troublesome. It has excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining the principle of the present invention, FIG. 2 is an output characteristic diagram of the coil alone, FIG. 3 is a composite output characteristic diagram, and FIG. 4 is a schematic plan view of the probe according to the present invention. FIG. 5 and FIG. 6 are explanatory diagrams of directivity. 11, 12...17, 21, 22...Coil, 3
1, 33, 34...39, 40...gear.

Claims (1)

[Claims] 1. It is equipped with multiple rectangular detection coils parallel to the flaw detection surface of the test object, and the multiple detection coils are provided so as to be rotatable around an axis perpendicular to the flaw detection surface. An eddy current flaw detection probe characterized in that the rotational position is fixed so as to form an angle.