Inspection method of test object and inspection device therefor

Abstract

To provide an inspection method of test objects enabling highly precise quality determination of a test object, and inspection method therefor.SOLUTION: An inspection method of test objects includes: directly exciting a test object with a magnetic field generated by applying alternating currents of different frequencies and directly detecting vibration of the test object; and determining a resonant frequency of the detected vibration and comparing the determined resonant frequency with a known normal resonant frequency to determine whether the test object is acceptable or unacceptable.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an inspection method and an inspection device for an object to be inspected. [Background technology]

[0002] An object inspection method and device have been proposed (Patent Document 1), which involves transmitting vibrations of gradually varying frequency to excite an object to be inspected, while simultaneously detecting the vibrations of the object to be inspected, determining the natural frequency of the object to be inspected from the detected vibrations, and comparing the determined natural frequency of the object to a known normal natural frequency to determine whether the object to be inspected is good or bad. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-307510 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the object inspection method and device described in Patent Document 1 excites the object to be inspected by transmitting vibrations generated by the electromagnetic force of the excitation coil to the object to be inspected via an object to be inspected holder made of ferrite, which is a magnetic material (paragraph

[0018] ), and therefore there are limits to the accuracy with which the object to be inspected can be determined to be good or bad.

[0005] The present invention has been made in view of the above circumstances, and has as its object to provide an inspection method and an inspection apparatus for inspecting an object to be inspected that can improve the accuracy of determining whether an object to be inspected is good or bad. [Means for solving the problem]

[0006] The method for inspecting an object to be inspected according to the present invention is characterized in that the object to be inspected is directly excited by a magnetic field generated by applying alternating currents of different frequencies, and the vibration of the object to be inspected is directly detected, and the resonant frequency of the detected vibration is determined, and the determined resonant frequency is compared with a known normal resonant frequency, thereby determining whether the object to be inspected is good or bad.

[0007] The inspection device for an object to be inspected according to the present invention is characterized by comprising an excitation unit that directly excites the object to be inspected by a magnetic field generated by applying alternating currents of different frequencies, a control unit that supplies the alternating currents of different frequencies to the excitation unit, a vibration detection unit that directly detects vibrations of the object to be inspected together with the excitation, and a judgment unit that determines the quality of the object to be inspected by determining the resonant frequency of the detected vibration and comparing the determined resonant frequency with a known normal resonant frequency. [Effects of the Invention]

[0008] The present invention provides an inspection method and an inspection apparatus for inspecting an object to be inspected that can improve the accuracy of determining whether an object to be inspected is good or bad. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a conceptual side view illustrating a configuration of an inspection device for explaining an inspection method and an inspection device for an object to be inspected according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional conceptual diagram of the inspection device of FIG. 1 taken along line AA. [Figure 3] FIG. 3 is a cross-sectional conceptual diagram in which the inspection device shown in FIG. 2 is disassembled into individual components. [Figure 4] 10 is a graph illustrating the conditions for applying a magnetic field to generate a magnetic field by applying alternating currents of different frequencies to an object under test 5 in an example of the present invention. [Figure 5]This is a graph showing the results (first time) of comparing the resonance frequencies of steel material in which cracking has been confirmed and steel material in which cracking has not been confirmed (uncracked) using the inspection method and inspection device for the inspected object in an embodiment of the present invention. [Figure 6] This is a graph showing the results (second time) of comparing the resonance frequencies of steel material in which cracking has been confirmed and steel material in which cracking has not been confirmed (uncracked) using the inspection method and inspection device for the inspected object in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Fig. 1 is a schematic side view illustrating the configuration of an inspection device for explaining an inspection method and an inspection device for an object to be inspected according to the present embodiment. Fig. 2 is a schematic cross-sectional view of the inspection device of Fig. 1 taken along line AA.

[0011] In this embodiment, the inspection method for an object under test involves controlling an excitation unit 10 (specifically, an AC excitation coil 2 and a pair of magnets 3, 3) as shown in FIG. 1 by a control unit 20 (specifically, a resistor (1 Ω), a function generator 20a, a bipolar power supply 20b, and a digital multimeter 20c) to apply AC currents of different frequencies to generate magnetic fields, which directly excite an object under test 5 (specifically, an object under test 5 located within the inner surface region 2a of the AC excitation coil 2 and between the pair of magnets 3, 3 arranged opposite each other along the axis C). Simultaneously, a vibration detection unit 30 (specifically, an acceleration sensor 30a and a ceramic terminal 30b) directly detects the vibration of the excited object under test 5. A judging unit 40 (specifically, an isolation amplifier 40a, a memory high-coder 40b, and a processing circuit 40c) determines the resonant frequency of the detected vibration and compares the determined resonant frequency with a known normal resonant frequency to judge whether the object under test 5 is good or bad.

[0012] Here, "directly exciting" means exciting the object under test 5 itself, rather than exciting something other than the object under test 5, such as the object under test holder. Also, here, "directly detecting" means detecting vibrations of the object under test 5 by bringing the ceramic terminal 30b of the vibration detection unit 30 itself into contact with the object under test 5 without an intervening object or the like.

[0013] As described above, the inspection method for the object under test according to this embodiment "directly excites" and "directly detects," i.e., the object under test 5 itself is excited to vibrate, and the vibration is further detected by the ceramic terminal 30b itself, so there is no decrease in accuracy due to the presence of other intervening objects. Therefore, it is possible to improve the accuracy of the pass / fail judgment of the object under test 5. Furthermore, since it is possible to improve the accuracy of the pass / fail judgment, it is effective as a quality confirmation method for the object under test 5. The pass / fail judgment can be suitably applied to whether or not the object 5 to be inspected has flaws such as scratches or cracks.

[0014] The excitation is preferably performed directly on the entire object under test 5 by the magnetic field. This makes it possible to detect vibrations throughout the entire object 5 under inspection, making it possible to determine whether scratches, cracks, or other imperfections are present throughout the entire object 5 under inspection. This is therefore a more effective method for checking the quality of the object 5 under inspection. Here, "directly subjecting the entire test object 5 to the magnetic field" means that the entire test object 5 is placed within the inner surface region 2a of the AC excitation coil 2 and between a pair of magnets 3, 3 arranged opposite each other in the direction of the axis C.

[0015] The material and shape of the test object 5 are not particularly limited as long as it can be directly excited by a magnetic field generated by applying alternating currents of different frequencies. The object 5 to be inspected is made of steel. If the test object 5 is made of steel, it can be directly excited by a magnetic field generated by applying alternating currents of different frequencies, and the quality of the test object 5 can be reliably determined based on the resonant frequency of the detected vibration.

[0016] Next, an inspection device for an object to be inspected according to this embodiment will be described with reference to Figures 1 and 2. Note that explanations of parts that overlap with the inspection method for an object to be inspected described above will be omitted as appropriate. The inspection device 1 for the object to be inspected in this embodiment comprises an excitation unit 10 that directly excites the object to be inspected 5 by a magnetic field generated by applying alternating currents of different frequencies, a control unit 20 that supplies alternating currents of different frequencies to the excitation unit 10 (specifically, the AC excitation coil 2), a vibration detection unit 30 that directly detects the vibration of the object to be inspected 5 together with the excitation by the excitation unit 10, and a judgment unit 40 that determines whether the object to be inspected 5 is good or bad by determining the resonant frequency of the vibration detected by the vibration detection unit 30 and comparing the determined resonant frequency with a known normal resonant frequency.

[0017] As described above, the inspection device 1 for an object under test according to this embodiment "directly excites" and "directly detects," i.e., excites the object under test 5 itself to vibrate, and further detects the vibration with the ceramic terminal 30b itself, so there is no decrease in accuracy due to the presence of other intervening objects. Therefore, it is possible to improve the accuracy of determining whether the object under test 5 is good or bad. Furthermore, because it is possible to improve the accuracy of determining whether the object under test 5 is good or bad, it is effective as a quality confirmation device for the object under test 5.

[0018] The excitation is preferably performed directly on the entire object under test 5 by the magnetic field. This makes it possible to detect vibrations in the entire object 5 under inspection, making it possible to judge whether scratches, cracks, or other imperfections are present in the entire object 5 under inspection. This makes it more effective as a quality confirmation device for the object 5 under inspection.

[0019] The inspection method and inspection device for an object to be inspected according to this embodiment will be described in more detail with reference to Figures 1, 2 and 3. Figure 3 is a cross-sectional conceptual diagram in which the inspection device shown in Figure 2 is disassembled into individual components. The excitation unit 10 includes an AC excitation coil 2 and a pair of magnets 3, 3. The AC excitation coil 2 has an axis C and an inner surface area 2a on the inner surface of which the object under test 5 can be placed. The AC excitation coil 2 is configured, for example, in a cylindrical shape with a copper wire wound around it. The AC excitation coil 2 is connected to a control unit 20, and AC currents of different frequencies are supplied from the control unit 20.

[0020] The pair of magnets 3, 3 face each other in the direction of the axis C of the AC excitation coil 2, are arranged so as to sandwich the AC excitation coil 2 from the direction of the axis C, and have inner surface regions 3a, 3a on their inner surfaces. More specifically, the pair of magnets 3, 3 have an axis C that is coaxial with the axis C of the AC excitation coil 2, face each other in the direction of the axis C, are arranged so as to sandwich the AC excitation coil 2 from the direction of the axis C, and have inner surface regions 3a, 3a on their inner surfaces. The pair of magnets 3, 3 are formed, for example, by ring-shaped permanent magnets. Each of the pair of ring-shaped magnets 3, 3 has an inner half 3a1, 3a1 (on the AC excitation coil 2 side) in the direction of the axis C as an N pole, and an outer half 3a2, 3a2 (outside the AC excitation coil 2) in the direction of the axis C as an S pole. In other words, the AC excitation coil 2 is disposed between the inner half 3a1, 3a1 of the pair of magnets 3, 3 in the direction of the axis C.

[0021] The object under test 5 is placed between the inner surface region 2a of the AC excitation coil 2 and the pair of magnets 3, 3 arranged opposite to each other in the direction of the axis C. Here, "between the pair of magnets 3, 3 arranged opposite to each other in the direction of the axis C" means, more specifically, between the upper surface Ts of the lower magnet 3 and the lower surface Bs of the upper magnet 3 of the pair of magnets 3, 3 in the direction of the axis C, as shown in FIG.

[0022] The space between the pair of magnets 3, 3 arranged opposite to each other in the direction of the axis C is preferably above the upper surface Ts of the lower magnet 3 of the pair of magnets 3, 3 and below the lower surface Bs of the upper magnet 3 in the direction of the axis C. That is, the object under test 5 is preferably arranged between the upper surface Ts and the lower surface Bs in the direction of the axis C, with a certain distance (e.g., 3 cm) between the lower surface 5a of the object under test 5 and the upper surface Ts of the lower magnet 3, and a certain distance (e.g., 3 cm) between the upper surface 5b of the object under test 5 and the lower surface Bs of the upper magnet 3 in the direction of the axis C. By arranging the pair of magnets 3, 3 at a certain distance from the axis C of the test object 5 in this manner, it is possible to prevent the test object 5 from coming into contact with the pair of magnets 3, 3 when it vibrates.

[0023] The control unit 20 is connected to the AC excitation coil 2 and supplies AC currents of different frequencies to the AC excitation coil 2. The control unit 20 includes a function generator 20a that generates and outputs an arbitrary pulse waveform, a bipolar power supply 20b that is connected to the function generator 20a and one end 2E1 and the other end 2E2 of the AC excitation coil 2 and amplifies the voltage of the output pulse from the function generator 20a to supply a voltage between one end 2E1 and the other end 2E2 of the AC excitation coil 2, and a digital multimeter 20c that is connected between the bipolar power supply 20b and the AC excitation coil 2 and measures changes over time in the AC current flowing through the AC excitation coil 2.

[0024] The vibration detection unit 30 includes an acceleration sensor 30a and a ceramic terminal 30b having one end connected to the acceleration sensor 30a and the other end in direct contact with the device under test 5. More specifically, the ceramic terminal 30b is arranged to have an axis C coaxial with the AC excitation coil 2 (preferably including the device under test 5 and the pair of magnets 3, 3), one end connected to the acceleration sensor 30a, and the other end in direct contact with the device under test 5. The acceleration sensor 30a may also be arranged to have an axis C coaxial with the AC excitation coil 2 (preferably including the device under test 5, the pair of magnets 3, 3, and the ceramic terminal 30b).

[0025] The judgment unit 40 includes an isolation amplifier 40a connected to the acceleration sensor 30a, which filters the frequencies of the detected vibrations (signals) to only the frequencies of interest and transmits the filtered signals; a memory hi-corder 40b connected to the isolation amplifier 40a, which records the waveforms of the corresponding shapes based on the signals transmitted from the isolation amplifier 40a; and a processing circuit 40c connected to the memory hi-corder 40b, which determines the resonant frequency of the detected vibrations based on the waveforms recorded by the memory hi-corder 40b and compares the determined resonant frequency with a known normal resonant frequency to judge the quality of the test object 5. The processing circuit 40c preferably judges whether the test object 5 is good or bad by comparing the obtained resonance frequency with a known normal resonance frequency, and if there is a difference, it is judged as "bad," and if there is no difference, it is judged as "good."

[0026] When determining whether an object under test 5 is good or bad using the inspection device 1 according to this embodiment, as shown in FIG. 3, the object under test 5 is placed on the inner surface area 2a of the AC excitation coil 2 with its axis C aligned coaxially with the axis C of the AC excitation coil 2, and then a pair of magnets 3, 3 is placed so that their axes C are aligned coaxially with the axes C of the AC excitation coil 2 and the object under test 5, and so that the AC excitation coil 2 is sandwiched between them in the direction of the axis C, and further, the ceramic terminal of the vibration detection unit 30 is aligned coaxially with the axis C of the object under test 5 on the inner surface area 3a on one side of the pair of magnets 3, 3. 30b is inserted and brought into direct contact with the object under test 5, and AC currents of different frequencies are supplied and applied from the control unit 20 to the AC excitation coil 2 of the excitation unit 10, and the magnetic field generated by the supplied AC currents of different frequencies in the AC excitation coil 2 directly excites the object under test 5, causing it to vibrate, and the vibration is directly detected by the vibration detection unit 30, and the resonant frequency of the detected vibration is determined by the judgment unit 40, and the determined resonant frequency is compared with a known normal resonant frequency to judge whether the object under test 5 is good or bad.

[0027] As shown in FIG. 3 , in the inspection device 1 according to this embodiment, a lower insulating member 7a and an upper insulating member 7b are disposed between the AC excitation coil 2 and the pair of magnets 3, 3 in the direction of the axis C, so that their axes C are coaxial with the axis C of the AC excitation coil 2 and the pair of magnets 3, 3. The lower insulating member 7a and the upper insulating member 7b each have inner surface regions 7aa and 7bb. A terminal insulating member 30c is provided around the ceramic terminal 30b of the vibration detection unit 30. That is, when the ceramic terminal 30b of the vibration detection unit 30 is inserted into the inner surface region 3a on one side of the pair of magnets 3, 3 and the tip of the ceramic terminal 30b is brought into direct contact with the device under test 5, the inner surface region 3a on one side and the inner surface region 7bb of the upper insulating member 7b have a gap that allows the terminal insulating member 30c around the ceramic terminal 30b of the vibration detection unit 30 to pass through.

[0028] More specifically, to arrange the pair of magnets 3, 3 and the object under test 5 at a certain distance in the direction of the axis C, a lower insulating member 7a is arranged between the lower surface 5a of the object under test 5 and the upper surface Ts of the lower magnet 3 in the direction of the axis C, and an upper insulating member 7b is arranged between the upper surface 5b of the object under test 5 and the lower surface Bs of the upper magnet 3 in the direction of the axis C, as shown in Figure 1.

[0029] In addition, the upper surface Ts of the lower magnet 3 and the lower surface 5a of the test object 5 are arranged at a certain distance in the direction of the axis C, and in order to directly excite the entire test object 5 by a magnetic field generated by applying alternating currents of different frequencies, an insulating support member 5c for the test object 5, which has an axis C coaxial with the test object 5 (preferably including the AC excitation coil 2 and a pair of magnets 3, 3) and passes through the inner surface region 7aa of the lower insulating member 7a and the inner surface region 3a of the lower magnet 3, is arranged on the lower surface 5a side of the test object 5. As a result, the inspection method and inspection device for the object to be inspected according to this embodiment can achieve high accuracy in determining whether the object to be inspected 5 is good or bad, and also has the effect of preventing the object to be inspected 5 from coming into contact with the pair of magnets 3, 3 when it vibrates.

[0030] The lower insulating member 7a is arranged between the lower surface 5a of the test object 5 and the upper surface Ts of the lower magnet 3 in the direction of the axis C, and is composed of a ring-shaped body having an axis C coaxial with the AC excitation coil 2 and the pair of magnets 3, 3, and an inner surface area 7aa on the inner side through which the test object 5 and the test object insulating support member 5c that supports the test object 5 pass. The upper insulating member 7b is arranged between the upper surface 5b of the test object 5 and the lower surface Bs of the upper magnet 3 in the direction of the axis C, has the axis C coaxial with the AC excitation coil 2 and the pair of magnets 3, 3, and is composed of a ring-shaped body having an inner surface area 7bb on the inner side through which the ceramic terminal 30b and the terminal portion insulating member 30c supporting the ceramic terminal 30b pass.

[0031] Furthermore, in the inspection device 1 according to this embodiment, an insulating support member 5c for the object under test is arranged at the other end (lower surface 5a of the object under test 5) opposite to one end (upper surface 5b of the object under test 5) with which the ceramic terminal 30b of the object under test 5 comes into direct contact, so as to have an axis C coaxial with the axis C of the object under test 5. By adjusting the height of this insulating support member 5c for the object under test 5, the object under test 5 can be placed in the inner surface region 2a of the AC excitation coil 2. In other words, the inner surface region 3a of the lower magnet 3 and the inner surface region 7aa of the lower insulating member 7a have a gap that allows the insulating support member 5c for the object under test arranged at the other end (lower surface 5a of the object under test 5) to pass through.

[0032] Furthermore, as shown in FIGS. 1 to 3, in the inspection device 1 according to this embodiment, the axis C of the AC excitation coil 2 is in the vertical direction, and the AC excitation coil 2, lower insulating member 7a, upper insulating member 7b and pair of magnets 3, 3 are stacked in the vertical direction (direction of axis C), and the object under test 5 is inserted into the inner surface area 2a of the AC excitation coil 2, and in the case where the ceramic terminal 30b of the vibration detection unit 30 is inserted from above (inner surface area 3a of the upper magnet 3a), a base (insulating member) 8 may be provided further below the lower magnet 3. [Example]

[0033] Using an induction-hardened steel material (material: SCM4400, dimensions: diameter 30 mm × total length 70 mm) as the test object 5, the inspection device 1 shown in Figures 1 to 3 was used. By supplying alternating currents of different frequencies from the control unit 20 to the excitation unit 10, the test object 5 was directly excited by the magnetic field generated by applying alternating currents of different frequencies in the excitation unit 10, and the vibrations generated by this were directly detected by the vibration detection unit 30.

[0034] FIG. 4 is a graph illustrating the conditions for applying magnetic field when AC currents of different frequencies are applied to the test object 5 to generate a magnetic field in an embodiment of the present invention. As shown in Figure 4, the applied magnetic field conditions were frequency f = 900 to 1400 [Hz] (20 Hz intervals), current value I = 1.0 [A], and sinusoidal AC. The evaluation was based on the V p-p Do it by value.

[0035] The vibration of the test object 5 was directly detected by the determination unit 40, and the resonant frequency of the detected vibration was calculated, and the calculated resonant frequency was compared with a known normal resonant frequency. The above test was performed twice. The above comparison was carried out by preparing steel material in which cracking was confirmed and steel material in which cracking was not confirmed (uncracked) as the specimen 5. The resonance frequency of the steel material in which cracking was not confirmed (uncracked) was taken as the normal resonance frequency.

[0036] Fig. 5 is a graph showing the results (first time) of comparing the resonance frequencies of steel material in which quench cracks have been confirmed and steel material in which quench cracks have not been confirmed (uncracked) using the inspection method and inspection device for an object to be inspected according to an embodiment of the present invention. Fig. 6 is a graph showing the results (second time) of comparing the resonance frequencies of steel material in which quench cracks have been confirmed and steel material in which quench cracks have not been confirmed (uncracked) using the inspection method and inspection device for an object to be inspected according to an embodiment of the present invention.

[0037] As shown in Figures 5 and 6, by comparing steel material with confirmed cracks and steel material without confirmed cracks (uncracked), it was confirmed that a difference in resonance frequency occurred (first time: 60 Hz, second time: 40 Hz). If this difference occurs, the inspected object 5 is judged as "fail", and if this difference does not occur, the inspected object 5 is judged as "pass", and the pass / fail can be determined. [Explanation of symbols]

[0038] 1. Inspection device for inspected object 2 AC excitation coil 3. Magnets 5. Test subject 10 Excitation section 20 Control Unit 30 Vibration detection unit 40 Judgment section

Claims

1. A method for inspecting an object to be inspected, which directly excites the object to be inspected by a magnetic field generated by applying alternating currents of different frequencies, directly detects the vibration of the object to be inspected, determines the resonance frequency of the detected vibration, and compares the determined resonance frequency with a known normal resonance frequency, thereby determining whether the object to be inspected is good or bad.

2. 2. The method for inspecting an object under test according to claim 1, wherein the excitation is performed directly on the entire object under test by the magnetic field.

3. an excitation unit that directly excites the object under test by applying alternating currents of different frequencies to generate magnetic fields; a control unit that supplies the alternating currents having different frequencies to the excitation unit; a vibration detection unit that directly detects vibration of the test object together with the excitation; and a judgment unit that determines whether the object under test is good or bad by determining a resonance frequency of the detected vibration and comparing the determined resonance frequency with a known normal resonance frequency.

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