JP3140105B2 - Electromagnetic induction type inspection equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection apparatus using electromagnetic induction for detecting an abnormality of an inspection object by a change in the electromagnetic induction, and more particularly to a food, a pharmaceutical tablet, a synthetic resin product, a workpiece, and the like. The present invention relates to an inspection apparatus in which an object to be inspected is placed in a magnetic field generated by an exciting coil, and a foreign substance or the like mixed in the object to be inspected due to a change in electromagnetic induction caused by the object.

[0002]

2. Description of the Related Art When an object is placed in an alternating magnetic field, the magnetic flux changes, and the inductance of a coil placed in the same magnetic field changes. This inductance changes in proportion to factors such as the permittivity, magnetic permeability, size, and position in the magnetic field of the object in the magnetic field. If some of these known factors are kept constant and the object is placed in a magnetic field, other unknown factors can be accurately recognized. Many electromagnetic induction inspection apparatuses having a nondestructive inspection function such as identification of a specimen and recognition of the presence or absence of a substance using this principle have been proposed.

FIG. 10 shows a typical example of such a conventional inspection apparatus.
According to the configuration described above, there is a configuration in which an electromagnetic coil 1 that generates a magnetic field by applying an alternating current is interposed on one side of a bridge circuit 2. In this inspection device, when the coil 1 is in a steady state, the electromagnetic coil 1 excited by the AC power supply 3 and the inductor L on the corresponding side have the same inductance, and the resistances R1 and R2 on the other two sides are the same. To maintain equilibrium. That is, in a balanced state, the output Vout from the differential amplifier 4 that takes the differential voltage between the output points a and b of the bridge circuit 2 becomes theoretically zero.

However, when the object S enters the magnetic field (magnetic flux f) formed by the electromagnetic coil 1, the self-induced inductance of the electromagnetic coil 1 changes. As a result, the balance between the inductor L and the electromagnetic coil 1 in the bridge circuit 2 breaks down, causing a potential difference between the output points a and b, and an output Vout corresponding to the induction coefficient of the object S is obtained. If the change in the output Vout due to this is converted into data in advance, it is possible to recognize the material and size of the object S, as well as the speed of moving in the magnetic field. Further, a foreign substance mixed in a known sample can be easily detected. In this case, a predetermined reference object is set to face the inductor L, and the reference object and the test object are set so as to exhibit a balanced steady state when a normal test object approaches the electromagnetic coil 1. I have.

Further, there has been proposed an inspection apparatus using mutual inductance as shown in FIG. This conventional device comprises an exciting coil (primary coil) 6 excited by an AC power supply 5, a pair of detection coils (secondary coils) 7a and 7b receiving an magnetic flux of the exciting coil 6 to generate an electromotive force, and a differential amplifier 8 Consists of The detection coils 7a and 7b are wound in opposite directions and connected in series in a differential manner, and receive a magnetic flux f of the excitation coil 6 in a steady state to cancel the electromotive force. That is, in the steady state, the detection coils 7a, 7b
Differential voltage at output points a and b (output Vout of differential amplifier 8)
Is theoretically zero.

In this inspection apparatus, usually, an inspection path 9 is formed between the excitation coil 6 and the detection coils 7a and 7b, and the object S is made to pass therethrough. When the object S cuts off the magnetic flux f from the excitation coil 6, the number of magnetic flux linkages applied to the detection coils 7a and 7b changes, and the respective electromotive forces of the detection coils 7a and 7b become unbalanced, and the differential output Vout becomes appear. This makes it possible to detect the material and size of the object S, a defect of the workpiece, and the like.

[0007]

As apparent from the configuration of the above-mentioned conventional apparatus, in this type of electromagnetic induction inspection apparatus, the unbalanced state of the induced inductance in a balanced circuit including an induction coil is detected as a differential voltage. Therefore, in order to improve the detection accuracy, it is necessary to detect a change in the electromotive force due to the interlinkage of the magnetic flux with the sample with high sensitivity.

However, in the former self-inductance type inspection apparatus, the rate of change of the self-inductance (the difference from the inductance at the time of change with respect to the base inductance) is extremely small, and the test object has a sufficiently large dielectric constant. However, detection cannot be performed unless a large magnetic field change is caused, such as a ferromagnetic material. That is, the detection sensitivity is extremely low, and it cannot be applied to an inspection object having a small inductance change rate such as identification of a material of the inspection object or detection of a nonmetal.

On the other hand, the latter mutual inductance type electromagnetic induction type inspection apparatus has an inspection path 9 between the excitation coil (primary coil) 6 and the detection coils (secondary coils) 7a, 7b, and the detection coil 7a, Since the induction efficiency of 7b is inversely proportional to the size of the inspection path 9 (the distance d from the excitation coil to the detection coil), there is a limit in increasing the distance between the excitation coil and the detection coil (inspection path). In other words, the size of the object to be inspected is limited, and it is impossible to inspect a substantially large object even though the size of the apparatus is increased due to the necessity of the inspection path 9. In addition, when the excitation performance of the excitation coil 6 is increased and the inspection path 9 is widened, the resolution decreases,
A minute change cannot be detected.

Another disadvantage is that a mutual inductance type inspection device is inevitably included. For example, as shown in FIG. 11, the inductance of the detection coil 7a changes when the sample S is present in the vicinity of the detection coil 7a at the time of the test and changes the magnetic flux linked to the detection coil 7a. The inductance of the detection coil 7b, which should be the inductance, also changes more or less. That is,
The object S cancels the electromotive force of the detection coil 7a, which changes simultaneously with the electromotive force of the detection coil 7b. This canceling action of the electromotive force changes in a complicated manner depending on the relative position of the sample S to the coil, and the expected electromotive force change amount sometimes causes a detection error that cannot be ignored.

As described above, in the conventional electromagnetic induction type inspection apparatus, the size of the inspection object is limited, and the accuracy of detecting a minute object such as a foreign substance mixed in food or a defect of a workpiece is inferior. There is a drawback in that it cannot respond to delicate inspections such as material identification of inspection objects.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the conventional apparatus.
High sensitivity for all inspection objects regardless of dielectric or magnetic
An object of the present invention is to provide an electromagnetic induction type inspection device capable of performing inspection and detection with high accuracy. Another object of the present invention is to detect not only the presence or absence of inspection objects such as foods, pharmaceutical tablets, synthetic resin products, and workpieces, but also foreign objects or defects contained in those inspection objects with high resolution, and Another object of the present invention is to provide a high-performance electromagnetic induction type inspection apparatus that can cope with miniaturization regardless of the size of an object to be inspected.

[0013]

To achieve the above object, the electromagnetic induction device according to the present invention employs the following means.

A magnetic substance and a non-magnetic substance are inspected, a) an AC power supply for outputting an AC current, b) an excitation coil which forms a magnetic field by being excited by the application of the AC current, and A detection coil unit comprising at least one induction coil for generating an electromotive force by electromagnetic induction, and integrally forming the induction coil so as to be coaxially wound closely on the outer peripheral surface or the inner peripheral surface of the excitation coil; c) a portion to be inspected, which is selectably provided at one of a position facing one end and an inner hollow hole of the detection coil portion; and d) a detection circuit for detecting a change in a magnetic field due to the object to be inspected from an output of the induction coil. The detection circuit, the detection circuit, a balanced circuit in which an inductor having the same configuration as the detection coil unit is connected in series to the detection coil unit, and an amplifier that amplifies the output from the balanced circuit, The amplification A determination circuit for determining an object to be inspected from the output of the device.

[0015]

The induction coil interlinks with the magnetic flux of the magnetic field of the exciting coil to induce electromotive force, and the inductance corresponding to the number of magnetic flux interlinkage that changes when the object to be inspected is placed in the magnetic field formed by the exciting coil. Change. The detection circuit is composed of a balance circuit, an amplifier, and a determination circuit having an inductor of the same configuration as the detection coil unit, and amplifies a change in inductance of the induction coil.
By making the determination, the amount of change in the inductance can be easily grasped.

By disposing the induction coil on the outer peripheral surface or the inner peripheral surface of the excitation coil, a detection coil unit in which the induction coil and the excitation coil are coaxially integrated is formed. At this time, electromagnetic induction of the induction coil by the AC magnetic field of the excitation coil reduces the leakage magnetic flux by increasing the integration ratio between the induction coil and the excitation coil, thereby causing mutual inductance with high efficiency. In addition, since the portion to be inspected can be selected from either the internal hollow hole or a position facing one end, the configuration of the detecting unit in the inspection device can be reduced as necessary, and the size of the object to be inspected can be reduced. Does not impose any restrictions. Other objects and features of the present invention will become apparent from the following detailed description with reference to the accompanying drawings.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a first embodiment of the present invention, an electromagnetic induction type inspection apparatus schematically shown in FIG. 1 forms an AC power supply 11 for outputting an alternating current and a change in electromagnetic induction facing an object to be inspected. And a detection circuit 15 for determining an aspect of the inspection object from an output from the detection coil unit 13.

The detection coil unit 13 is provided with an excitation coil 13a which is excited by receiving an AC current from the AC power supply 11 to form an AC magnetic field (magnetic flux f), and a part of one end of the outer peripheral surface of the excitation coil 13a. Closely coaxially wound excitation coil 13a
And an induction coil 13b that outputs an electromotive force by electromagnetic induction by the AC magnetic field. The excitation coil 13a on the primary side and the induction coil 13b on the secondary side are integrated, and the induction coil 13b is linked to all of the excitation magnetic flux f generated by the excitation coil 13a. Occurs, and a large AC electromotive force is output. Therefore, as shown in the drawing, when the inspection object S is placed so as to link the magnetic flux f generated by the excitation coil 13a, the inductance of the induction coil 13b changes. This change in inductance depends on factors such as the size and material of the inspection object S. Induction coil 13 in a steady state where test object S does not exist in the magnetic field generated by exciting coil 13a
By determining the difference between the inductance of the test object S and the inductance when the test object S is present in the same magnetic field, not only the existence or size of the test object S but also its material,
Further, the presence of a foreign substance mixed in the inspection object S can be accurately identified.

As shown in FIG. 2, the detection coil unit 13 forms an exciting coil 13a by winding a conductive wire around a bobbin 16 in multiple layers, and forms an electromagnetic shielding layer 17 such as aluminum foil on the outer peripheral surface of the exciting coil 13a. And the insulating sheet 18 are wound in layers, and a conductive wire is wound multiple times around the outer peripheral surface of the insulating sheet 18 to form the induction coil 13b. When used as the detection coil unit 13, the bobbin 16
May be removed. However, the method and components for manufacturing the detection coil section basically composed of the excitation coil and the induction coil are not particularly limited thereto, and it goes without saying that the detection coil section can be manufactured by various methods.

[0020]

The detection circuit 15 detects the output Vo of the induction coil 13b.
It has the function of identifying changes in ut. In the first embodiment shown in FIG. 3, the detection circuit 15 includes a balance circuit 22, an amplifier 24, and a determination circuit 25.

In the balance circuit 22, the inductance of the induction coil 13b in the steady state is balanced with the real part L, and the inductor connected in series with the real part L is defined as the imaginary part -L. The method of configuring the inductance -L is the same as that of the balancing circuit 22 shown in FIG.
3, a balanced inductor section 23 having substantially the same structure is connected in series with the detection coil section 13. That is, the balanced inductor section 2
3 is composed of an excitation coil 23a having the same configuration as the excitation coil 13a of the detection coil unit 13, and an induction coil 23b having the same configuration as the induction coil 13b of the detection coil unit 13 except for the winding direction.

In the above inspection apparatus, the excitation coils 13a,
When the induction coil 23a is excited by the common AC power supply 11 and the induction coils 13b and 23b are electromagnetically induced, an equal amount of electromotive force is generated in each coil, but the winding directions of the induction coils 13b and 23b are opposite. The inductance has the opposite sign. That is, as long as the detection coil unit 13 is in a steady state, the electromotive forces generated in the induction coils 13b and 23b cancel each other out, and the differential output becomes substantially zero. However, when the inspection object S is present in the magnetic field of the excitation coil 13a in the detection coil unit 13, the inductances of the induction coils 13b and 23b become unbalanced, and a differential output Vout appears. Thereby, a subtle change in the inspection object can be detected.
This differential output Vout is output to the amplifier 24. This facilitates the determination by the determination circuit 25. Further, if the reference of the differential output is set in the determination circuit 25, the standard inspection of the inspection object can be easily performed.

By using the above-described embodiment, it is possible to easily detect a foreign substance mixed in the inspection object or a minute abnormality such as a defect inside the workpiece. That is,
As shown in FIG. 4, the reference product Sref is permanently provided in the magnetic field of the balanced inductor section 23, and the test object S is placed in the magnetic field of the detection coil section 13. At this time, if the reference product Sref and the inspection object S are in the same steady state, that is, if the inspection object S has no abnormality such as entry of foreign matter, the induction coil 13
Since b and 23b maintain balance, the differential output Vout becomes substantially zero. However, when the foreign matter e exists inside the inspection object S, the induction balance of the induction coils 13b and 23b is broken, and a differential output Vout appears, whereby the presence of the foreign matter e can be recognized. Needless to say, the reference product Sref and the inspection object S need to be located at the same relative position with respect to the balanced inductor section 23 and the detection coil section 13, respectively.

When the inspection object S is a metal workpiece, for example, as shown in FIG.
By arranging the reference product Sref and the inspection object S of the detection coil unit 13 facing each other, the presence or absence of a defect c such as a crack in the inspection object S can be reliably detected with high resolution. When the inspection object S is a metal and the inspection object is a defect in a spot welded portion, the entire inspection object S is magnetized by the magnetic field formed by the exciting coil 13a, but is affected by an eddy current generated by the defect c. The mutual inductance of the induction coil 13b changes. As described above, the present invention is effective in various nondestructive inspections, for example, it is possible to effectively detect even a defect such as a crack or a pinhole in a welded portion of a metal that is difficult to be detected by visual inspection to the extent of the defect.

In the evaluation experiment, 30 conductors were attached to a synthetic resin bobbin 2.0 cm long, 5.2 cm inside diameter and 5 mm thick.
The coils are wound 0 times to form the exciting coils 13a and 23a, respectively.
Furthermore, the conductor is wound 300 times on the induction coil 13.
The detection coil unit 13 and the balanced inductor unit 23 were formed by respectively forming the components b and 23b, and an alternating current having a frequency of 0.2 to 1 kHz and a voltage of 15 V was applied to the excitation coils 13a and 23a. In this case, the inductance of the excitation coils 13a and 23a was 5.8 mH, and that of the induction coils 13b and 23b was 6.5 mH. 20mm diagonal distance with this inspection device
Was inspected as the inspection object S, it was found that the
A minute crack having a length of 1 mm and a length of 3 mm was detected.

In the above embodiment, the induction coil 13b is wound around a part of one end of the outer peripheral surface of the primary excitation coil 13a of the detection coil unit 13. However, the excitation coil and the induction coil are coaxial. Any configuration may be adopted as long as a part is brought into contact and integrated. Hereinafter, a modified example of the detection coil unit will be described.

The detection coil unit 33 shown in FIG.
An induction coil 33b is provided substantially at the center in the length direction of the outer peripheral surface of 3a. This configuration has reversibility such that the same mutual inductance characteristics can be obtained at both ends of the exciting coil 33a. Here, the inspection object S is connected to the exciting coil 33a.
Is arranged to face one end (the upper end in the figure) of the above, but the object to be inspected is passed or dropped by using the internal hollow hole 34 of the cylindrical excitation coil 33a as an inspection path, and the inductance change at that time is measured. It may be.

In the detection coil unit 43 shown in FIG. 7, an induction coil 43b is provided inside the excitation coil 43a by closely coaxial winding. According to this configuration, the induction coil 43b
Is built in the exciting coil 43a, so that the size of the detection coil unit can be reduced, and the size of the entire inspection apparatus can be reduced.

FIG. 8 shows a detection coil unit 63 provided with a pair of induction coils 63b on the outer peripheral surface of the excitation coil 63a. Alternatively, as shown in FIG. 9, a pair of induction coils 73b wound in the opposite direction and connected in series may be housed inside the excitation coil 73a to form the detection coil unit 73. In either embodiment, a differential circuit can be configured by itself by winding both induction coils in opposite directions and connecting them in series. In the evaluation experiment, a conducting wire was wound 1000 times around a synthetic resin bobbin having a length of 15 cm, an inner diameter of 3 cm, and a thickness of 1 mm to form an exciting coil 63a.
The detection coil section 63 is formed by winding both turns to form both induction coils 63b.
An alternating current of 1 kHz and a voltage of 15 V was applied. in this case,
The inductances of the excitation coil and the induction coil are 10
It was 0 mH. An iron ball having a diameter of 0.1 mm was detected by this inspection device.

As described above, the shapes of the exciting coil and the induction coil constituting the detecting coil unit can be variously modified, and the present invention is not particularly limited to the illustrated embodiment. For example, the induction coil in any of the above-described embodiments also has a smaller cross-sectional area than the excitation coil. On the contrary, the induction coil may be larger, and may be set as appropriate according to design factors such as the winding state of the conductor and the flux linkage conditions. do it.

Further, the object to be inspected arranged in the detection coil section is opposed to any one end in the axial direction of the exciting coil so as to be close to the end, so that the efficiency of magnetic flux linkage can be increased, thereby increasing the detection sensitivity. However, the position of the test object is not particularly limited, and the test object may be placed at any position as long as the magnetic flux formed by the exciting coil can reach. For example, the inspection object may be passed or dropped using the internal hollow hole of the cylindrical excitation coil as a passage.

[0033]

As described above, the electromagnetic induction type detection device of the present invention comprises a detection coil portion composed of an excitation coil and an induction coil which are coaxially and closely integrated, and is adapted to generate a magnetic field formed by the excitation coil. A change in the mutual inductance of the induction coil due to a certain test object is reduced and the leakage magnetic flux is detected efficiently. This makes it possible not only to determine the presence or material of various objects irrespective of dielectrics, magnetic materials, conductors / non-conductors, metals / non-metals such as foods, pharmaceutical tablets, synthetic resin products, and workpieces, but also Even a minute change in magnetic flux due to a minute foreign matter or a defect included in the inspection object can be inspected and detected with high resolution and high sensitivity and high accuracy.

In addition, since the portion to be inspected outside the detection coil can be selected, various inspections can be performed regardless of the size of the object to be inspected. In addition, since the excitation coil and the induction coil are integrated, the device can be used. The size can be freely changed, and the size can be easily reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a first embodiment of an electromagnetic induction type inspection apparatus according to the present invention.

FIG. 2 is a half sectional side view showing a configuration of a detection coil unit in FIG.

FIG. 3 is a schematic configuration diagram showing a first embodiment.

FIG. 4 is an explanatory view showing an example of application of inspection by the inspection device of FIG. 3;

FIG. 5 is an explanatory view showing another example of application of the inspection by the inspection device of FIG. 3;

FIG. 6 is a schematic view showing a second embodiment.

FIG. 7 is a schematic view showing a third embodiment.

FIG. 8 is a schematic view showing a fourth embodiment.

FIG. 9 is a schematic view showing a fifth embodiment.

FIG. 10 is a schematic explanatory view showing an example of a conventional electromagnetic induction type inspection apparatus.

FIG. 11 is a schematic explanatory view showing another example of a conventional electromagnetic induction type inspection apparatus.

[Explanation of symbols]

11 ... AC power supply, 15 ... Detection circuit, S ... Test object, f ...
Magnetic field, 13, 33, 43, 63, 73: detection coil unit 13a, 33a, 43a, 63a, 73a: excitation coil, 13b, 33b, 43b, 63b, 73b: induction coil.

Claims (1)

(57) [Claims] 1. An inspection apparatus comprising: a magnetic material and a non-magnetic material; a) an AC power supply for outputting an AC current; b) an excitation coil for exciting and forming a magnetic field by applying an AC current; A detection coil unit comprising at least one induction coil for generating electromotive force by electromagnetic induction by excitation, wherein the induction coil is closely coaxially wound around an outer peripheral surface or an inner peripheral surface of the excitation coil and integrally formed. C) a part to be inspected which is selectively provided at one of positions facing the inner hollow hole of the detection coil part and one end; and d) detection for detecting a change in a magnetic field due to the object to be inspected from an output of the induction coil. A detection circuit comprising: a detection circuit; a balanced circuit in which an inductor having the same configuration as the detection coil unit is connected in series to the detection coil unit; and an amplifier for amplifying an output from the balanced circuit. And the increase A determination circuit test objects from the output of the vessel, in construction the electromagnetic induction type inspection device.