JP6178364B2 - Nondestructive inspection coil sensor and nondestructive inspection apparatus provided with the same - Google Patents

Description

  The present invention relates to a nondestructive inspection coil sensor and a nondestructive inspection apparatus including the same, and more particularly, a coil for continuously performing nondestructive inspection from a metal outermost surface to a predetermined depth using a high-frequency alternating magnetic field. The present invention relates to a sensor and a nondestructive inspection apparatus including the sensor.

  In recent years, a high frequency alternating magnetic field generated by a coil is applied to a metal surface to generate a demagnetizing field (eddy current magnetic field), which is collected and analyzed to check for the presence of minute flaws, void / quenching, hardness, etc. Nondestructive inspection methods for performing evaluation are widespread. For example, Japanese Patent Application Laid-Open No. 2006-10665 discloses an eddy current flaw detection method that enables inspection from a metal surface to a deep region of about 40 mm by combining coils with opposite polarities. Has been proposed.

  On the other hand, the evaluation of the metal outermost surface (0 to 10 μm) has recently been regarded as important, and it has been widely performed to increase the strength by performing surface treatment of metal products by shot peening treatment or the like. . In view of this, a nondestructive inspection method for inspecting the residual stress with high accuracy using a coil sensor (coil probe) for the properties of the outermost surface of the steel material subjected to shot peening has been proposed in Japanese Patent Application Laid-Open No. 2008-2973. Yes.

  The eddy current flowing in the vicinity of the metal surface by the high frequency alternating magnetic field generated by the exciting coil is derived by the mask well electromagnetic equation, and the penetration depth of the eddy current is expressed by the following equation (1). That is, as the excitation frequency f (conductivity σ, magnetic permeability μ property of the inspection object) increases, the skin effect of the eddy current becomes more prominent and the eddy current flows in a region near the surface of the inspection object. Therefore, when inspecting to a deep region (500 to 100 μm), a frequency of about several tens KHz to 200 KHz is required, and when inspecting a shallow region (up to 5 to 100 μm) including the outermost surface, a frequency of about 200 KHz to 20 MHz is required. Become.

  And also in the surface inspection of the present iron products and iron-based alloy products, it is preferable that in addition to the inspection region of about several tens KHz to about 200 KHz, continuous inspection can be performed without having a resonance point in a wide range from about 200 KHz to about 20 MHz. However, there is currently no coil sensor capable of supplying a sufficient excitation current in each region while covering such a wide frequency range with one excitation coil.

  That is, in the coil wound with the conductive wire, the impedance of the inductance L is ωL = 2πfL, and is proportional to the frequency at that time. Therefore, if 10Ω at 10 MHz is 0.01Ω at 10 KHz, it is 10V at 10 MHz. When a voltage of 1 is applied, a current of 1 A is obtained according to Ohm's law, whereas at 10 kHz of 10 KHz, a current of 1000 A flows and the coil is burnt.

  Therefore, when performing nondestructive inspection from the conventional inspection area to the outermost surface area, create multiple types of exciting coils for each frequency area, and perform stepwise inspection while exchanging them according to each area. The current situation is. However, preparing and preparing several types of exciting coils for a single metal specimen not only increases the size of the device and increases the cost, but also allows for inspection time by performing multiple replacements and switching. (Tact time) is excessively required.

JP 2006-10665 A JP 2008-2773 A

  The present invention is intended to solve the above-described problems, and for a nondestructive inspection using a coil sensor, a single excitation coil can continuously and quickly inspect a wide area from the outermost surface to a predetermined depth. The challenge is to do so.

  Therefore, the present invention includes an exciting coil formed by winding a predetermined conductive wire around a holding body, and generates an alternating magnetic field by flowing an alternating current of a predetermined frequency through the conductive wire, and has a depth corresponding to the frequency level. In the nondestructive inspection coil sensor for inspecting the property of the inspection area in the inspection object while generating a demagnetizing field on the inspection object in the inspection area and detecting this by the detection means, the conductive wire is: A plurality of small-diameter small conductive wires are bundled together while being electrically insulated from each other on the outer peripheral side to form one large-diameter large conductive wire, and both end sides thereof are separated into individual small conductive wires to form a predetermined The connection state switching means is connected to each other, and the connection state of all or part of the small conductive wires constituting the large conductive line by the connection state switching means is a series, parallel, or combination of series and parallel. Switching between , And it is capable of changing the impedance of the entire excitation coil to a size adapted to the inspection area as a target, and shall be characterized in that.

  In this way, the conductive wires constituting the coil are bundled in a state where a plurality of small conductive wires are insulated from each other, and the plurality of the conductive wires are individually connected to the connection state switching means at the both ends. The impedance of the entire exciting coil can be changed by switching the mutual connection state of the small conductive wires between series, parallel, and a combination of series and parallel. A wide range of areas can be inspected continuously and quickly while changing according to the inspection area targeted for the thickness.

  Further, in this nondestructive inspection coil sensor, the connection state switching means is a digital switch, and the plurality of small conductive lines constituting the large conductive line are all in a series state, all in parallel. It is possible to switch the connection state between a state, a state in which a plurality of parallels are in series, a state in which parallel and series are combined, a state including these connection states, and a state including those not connected to them. If it is characterized, extremely diverse impedances can be realized with a single exciting coil, and inspection of extremely various depth regions can be carried out continuously and rapidly.

  Furthermore, in the coil sensor for nondestructive inspection described above, the large conductive wire is formed by a composite twist obtained by bundling a plurality of small conductive wires made of a collective twist of conductive strands into one. If it is characterized, the overall flexibility is excellent and the winding property to a holding body such as a bobbin is good, and the flexibility and operability of each small conductive wire are also excellent. Connection to the connection state switching means is also easy.

  In this case, the small conductive wire is a litz wire formed by twisting a plurality of conductive wires made of enamel wires, and the large conductive wire is a bundle of six or more litz wires. As a result, the increase in AC resistance due to high frequency is small, and it is easy to suppress the temperature rise of the coil, and it is easy to achieve miniaturization and high efficiency of the device.

  And the nondestructive inspection coil sensor, the AC power supply, the frequency adjusting means for adjusting the frequency of the AC power supplied from the AC power supply and outputting it to the nondestructive inspection coil sensor, and the nondestructive inspection Determination means for determining and outputting the property of the inspection object in the inspection area based on the data detected by the coil sensor detection means, and switching the connection state between the small conductive wires by the connection state switching means However, by changing the impedance of the entire excitation coil, it is possible to continuously inspect different depth regions. While using the apparatus, it is possible to continuously inspect a wide range of inspection areas on various inspection objects without requiring labor.

  According to the present invention in which the entire impedance is changed while switching the connection state between the conductive wires of the coil as a bundle of a plurality of small conductive wires, even with a single excitation coil, a predetermined depth from the outermost surface can be obtained. A wide range of areas can be inspected continuously and quickly.

It is a block diagram of the coil sensor for nondestructive inspection as embodiment in this invention. (A) is the elements on larger scale which show the detail of the terminal side of the conductive wire of the coil sensor for nondestructive inspection of Drawing 1, (B) is an expanded sectional view which meets an AA line of (A). It is a schematic diagram for demonstrating the connection state by the combination of the small conductive wire which comprises the conductive wire of the coil sensor for nondestructive inspection of FIG. (A) is a schematic diagram when all of the small conductive wires in FIG. 3 are connected in series, (B) is a schematic diagram when all of the small conductive wires in FIG. 3 are connected in parallel, (C) is It is a schematic diagram at the time of connecting in parallel what connected three of the small conductive wires of FIG. It is the schematic diagram which showed the small electrically conductive line of FIG. 3 with the impedance equivalent circuit. (A)-(D) are schematic diagrams which show the example of the connection method of the small conductive wire of FIG. FIGS. 6A and 6B illustrate an example of a method for connecting small conductive lines in FIG. 5, and FIG. 6E is a schematic diagram illustrating a partially open state and FIG. It is a graph which shows the state of resonance frequency and Q value in the case of a partial short of Drawing 7 (F). It is a photograph which shows the air core type coil sensor provided with the coil probe which served as the detection coil and exciting coil by this invention. The left is a plane photograph showing a coil probe that serves as both a detection coil and an exciting coil of a coil sensor for a planar specimen according to the present invention, and the right is a photograph showing a state during measurement of the coil sensor. The right is a photograph showing a state in which a round bar slice specimen is measured by an excitation coil and a detection coil that constitute a coil probe by a coil sensor for a flat specimen according to the present invention, and the left is a photograph of the round bar slice specimen. It is a plane photograph. The left is a plane photograph of the E-core type coil probe for the planar specimen coil sensor according to the present invention, and the right is a bottom photograph in which the detection coil is visible. It is a longitudinal cross-sectional view for demonstrating the structure of the coil probe of FIG. It is a circuit diagram which shows an example of the impedance measurement means of the nondestructive inspection apparatus as embodiment in this invention.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows the configuration of a nondestructive inspection coil sensor 10A according to the present embodiment. This nondestructive inspection coil sensor 10A includes an air-core coil probe 11 formed by winding a conductive wire 110 around a bobbin 13, and a connection state switching means 12 to which both ends of the conductive wire 110 are connected, and is cylindrical. By applying an alternating magnetic field of a predetermined frequency to the surface of the inspection object 50 inserted through the center of the coil probe 11 to generate a demagnetizing field, and detecting this by the coil probe 11 also serving as a means for detecting the demagnetizing field. In the region from the outermost surface of the inspection object 50 to a predetermined depth, the inspection apparatus main body side (not shown) evaluates the properties of the inspection object 50 according to items such as the presence or absence of minute scratches, the presence or absence of voids and quenching, and hardness. It comes to let you.

  FIG. 2A is an enlarged view of the configuration of the end side connected to the connection state switching means 12 side of the conductive wire 110 of the coil sensor for nondestructive inspection 10A described above. The conductive wire 110 is composed of six small-diameter small conductive wires 110a, 110b, 110c, 110d, 110e, and 110f, which are bundled in a state where the outer peripheral sides are electrically insulated from each other. And both end sides thereof are connected to the connection state switching means 12 in a state of being separated into individual small conductive lines.

  FIG. 2 (B) shows an enlarged cross-sectional view along the line AA in FIG. 2 (A), and this conductive wire 110 is a small conductive wire made of a collective twist of conductive wires made of copper wire or the like. 110a, 110b, 110c, 110d, 110e, and 110f are formed by a composite twist obtained by bundling them into one, so that the overall flexibility is excellent and the winding property to the bobbin 13 is good. In addition, the small conductive wires 110a, 110b, 110c, 110d, 110e, and 110f are also excellent in flexibility and operability, so that the connection to the connection state switching means 12 is also excellent. .

  The conductive wire 110 is preferably a litz wire formed by twisting a plurality of conductive wires made of enameled wire. In this embodiment, 2UEW 6/38 / 0.1 (2 type polyurethane insulated copper wire) This assumes a litz wire of 6 small twisted conductive wires bundled with 38 wires of φ0.1 mm. By using such a litz wire, the increase in resistance due to the high-frequency alternating current can be suppressed to a relatively small value, so that the temperature rise of the coil probe 11 can be easily suppressed, and the device can be made smaller and more efficient. It will be easy.

  FIG. 3 schematically shows the connection state of the six small conductive wires by the connection state switching means 12 for changing the impedance of the exciting coil by the coil probe 11, for example, as shown in FIG. If the impedance is 6Z in series, the impedance is 1 / 6Z in all parallel states as shown in FIG. 4 (B), and two sets of three in series are parallel as shown in FIG. 4 (C). In the series-parallel state, the impedance is 2 / 3Z.

  FIG. 5 shows an equivalent circuit of the impedance assuming that the impedance for each connection state of the six small conductive wires constituting the conductive wire (large conductive wire) 110 of the coil probe 11 is actually obtained. Specifically, the conductive wire 110 is unraveled and divided into six small conductive wires, and one impedance is set as Z0, and connection is made while being aware of the start and end of winding (R: DC resistance) , Ls: self-inductance, Lm mutual inductance).

  And, as a combination when connecting the six small conductive lines using the connection state switching means 12, an extremely large number of patterns are assumed, but FIGS. 6A to 6D are standard connection examples. The impedance can be calculated by the following formula.

As described above, the maximum impedance value Z = 6Z _{0 is obtained in} the case of six in series, and when there is a detection coil apart from the excitation coil, a current flows through this, so it is necessary to consider the mutual impedance value. is there. In addition, as shown in FIG. 7, the impedance value may fluctuate by leaving unused ones of the six small conductive wires as they are or by short-circuiting (shorting the beginning and end of winding). It is known that when an unused one is short-circuited as shown in FIG. 7F, the resonance frequency and the Q value tend to decrease as shown in the graph of FIG.

  Next, actual modes of the coil probe corresponding to the form of the object to be inspected and the coil sensor for nondestructive inspection having the coil probe will be described. The photograph in FIG. 9 is an actual production of the nondestructive inspection coil sensor 10A provided with the coil probe 11 described above, and is suitable for nondestructive inspection of a rod-shaped inspection object. In this embodiment of the photograph, a manual insertion / extraction method is employed as the connection state switching means.

  The left photograph of FIG. 10 shows a coil probe for a planar specimen, and the right photograph shows a coil sensor for nondestructive inspection provided with this coil probe and a digital switch type connection state switching means. The detection signal from the coil probe detection means is transmitted to the main body (not shown) of the nondestructive inspection apparatus.

  In addition to the nondestructive inspection coil sensor, the nondestructive inspection apparatus adjusts the frequency of the AC power supply and the AC power supplied from the AC power supply and outputs the frequency to the nondestructive inspection coil sensor. Based on the data detected by the detecting means of the coil sensor for nondestructive inspection, the impedance measuring means for measuring the impedance for each combination of the adjusting means, the small conductive wire, and the property of the inspection object in the inspection area And determining means for outputting.

  The photograph in FIG. 11 shows a coil probe suitable for a flat specimen, in particular, a round bar slice specimen, and has a system in which an inspection object is sandwiched between an exciting coil and a detection coil facing each other. . The photograph in FIG. 12 is a top-mounted E-core type coil probe for a planar specimen, but a detection coil is arranged on the lower surface side of the excitation coil as shown in the right photograph in FIG. The nondestructive inspection is performed in the state shown in the longitudinal sectional view of FIG.

  As described above, the coil sensor for nondestructive inspection according to the present invention has a simple configuration of a coil probe made of a single exciting coil, from the outermost surface of the inspection object to a predetermined depth without requiring excessive cost and labor. The non-destructive inspection apparatus provided with the coil sensor for non-destructive inspection is the same.

  FIG. 14 shows an example of the impedance measurement circuit of the nondestructive inspection apparatus according to the present invention. The present invention is characterized in that an alternating current having a wide range of frequencies (for example, 40 kHz to 10 MHz) is continuously used. However, as means for measuring the impedance of the coil by the combination of the connection of the small conductive wires, The IV method for measuring as a complex quantity (vector) is suitable.

  The measurement principle of the IV method is based on the fact that the coil impedance Zx is voltage divided by current, and measures the current flowing in the device under test (coil) and the voltage across the device terminal and calculates the value from that value. Thus, the impedance is obtained. Further, by adopting the impedance measurement circuit shown in FIG. 14 as means for carrying out such 1-V method, even when measuring up to a frequency level of several MHz, the stray capacitance, parasitic capacitance, While minimizing the effects of wiring inductance, wiring resistance, etc., the impedance can be easily measured accurately.

  Then, the output V1 (current signal) and V2 (voltage signal) are rectified and smoothed and taken into a control unit having a microcomputer (not shown) to perform predetermined calculations to obtain the impedance Zx and the inductance Lx. It has become. In addition, a well-known thing can be utilized for the digital switch which is a connection state switching means for switching the connection state of the end part side in a plurality of small conductive lines.

  As described above, with respect to nondestructive inspection using a coil sensor, a wide area from the outermost surface to a predetermined depth can be continuously and rapidly inspected with a single exciting coil according to the present invention.

  10A coil sensor for nondestructive inspection, 11 coil probe, 12 connection state switching means, 13 bobbin, 50 inspected object, 110 conductive wire, 110a, 110b, 110c, 110d, 110e, 110f small conductive wire

Claims (5)

An excitation coil is formed by winding a predetermined conductive wire around a holding body, and an inspection is performed in an inspection region having a depth corresponding to the frequency level while generating an alternating magnetic field by passing an alternating current of a predetermined frequency through the conductive wire. In the coil sensor for nondestructive inspection for inspecting the property of the inspection area in the inspection object while generating a demagnetizing field in the object and detecting the demagnetizing field by a detecting means,
The conductive wire is formed by bundling a plurality of small-diameter small conductive wires while being electrically insulated from each other on the outer peripheral side to form one large-diameter large conductive wire. Mutual connection state in all or a part of the small conductive lines separated into the small conductive lines and connected to predetermined connection state switching means, respectively, and constituting the large conductive line by the connection state switching means By switching between series, parallel, and combination of series and parallel, the impedance of the entire exciting coil can be changed to a size suitable for the intended inspection area. Coil sensor for destructive inspection.   The connection state switching means is a digital switch, and the plurality of small conductive lines constituting the large conductive line are all in a series state, in a parallel state, in a state in which a plurality of parallels are in series, The connection state can be switched between a state in which parallel and series are combined, a state including these connection states, and a state including those not connected to them. Coil sensor for nondestructive inspection.   3. The large conductive wire is formed by a composite twist in which a plurality of the small conductive wires made of a collective twist of conductive wires are bundled and twisted into one. The coil sensor for nondestructive inspection described in 1.   The small conductive wire is a litz wire formed by twisting a plurality of conductive wires made of enamel wires, and the large conductive wire is a bundle of six or more litz wires. Item 4. The coil sensor for nondestructive inspection according to Item 3.   The nondestructive inspection coil sensor according to claim 1, 2, 3, or 4, an AC power supply, and a frequency that is adjusted to output a frequency of the AC power supplied from the AC power supply to the nondestructive inspection coil sensor. An adjustment unit, and a determination unit that determines and outputs the property of the inspection object in the inspection area based on data detected by the detection unit of the coil sensor for nondestructive inspection, and the connection state switching unit A nondestructive inspection apparatus characterized in that inspection of different depth regions can be continuously performed by changing the impedance of the entire exciting coil while switching the connection state of the small conductive wires.