JPH112624A - Detecting device of abnormal article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable reliable discrimination of the quality of an object of measurement by using a magnetic sensor in a simple constitution. SOLUTION: In a state wherein an alternating current is given to the exciting coil 13 of a magnetic sensor 12 from an exciting power source 11, an eddy current is generated in a metal product 16 inserted into the magnetic sensor 12 and therefore an impedance of a detecting coil 14 of the magnetic sensor 12 changes. A detecting circuit 17 detects an induced current of the magnetic sensor 12 as the change in the impedance and outputs it. An RMS-DC conversion circuit 19 detects an effective value of a detection signal passing a filter circuit 18. A determination circuit 23 outputs an abnormaity signal when a change level of the effective value outputted from a comparison circuit 20 is off the range of an allowable level. Thereby the metal product 16 is discriminated from a non-defective.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign object detecting device for judging the quality of an object to be measured based on a change in impedance of a coil due to an alternating magnetic field applied to the object to be measured.

[0002]

Conventionally, in nondestructive inspection of a metal object to be measured, an eddy current is generated in the object to be measured, a defect is detected from the state of the eddy current, and a defect is determined. A circuit device for discriminating a different product (defective product) is known.

For example, as shown in FIG. 3, when an alternating current is supplied from an excitation power supply 1 to an input terminal of a magnetic sensor 2, an eddy current is generated in an object (not shown) inserted in the magnetic sensor 2. The impedance of the magnetic sensor 2 changes. The impedance change due to the eddy current is detected by the detection circuit 3
Is detected by

Then, a signal corresponding to the fundamental and harmonic components of the frequency of the excitation power supply 1 output from the filter circuit 4 connected to the detection circuit 3 and the output signal of the excitation power supply 1 are used to extract amplitude information and phase information from the output signal. The output signal of the phase shifter 5 that performs discrimination is input to the synchronous detection circuit 6, and the signal of the impedance change output from the output terminal of the magnetic sensor 4 is
The change of the amplitude wave and the change of the phase wave are detected by the synchronous detection.
Each of them is converted into a DC output signal of two systems, and the CRT display / comparator means 7 uses the output signal to convert a spot value based on a Y-axis amplitude signal and a X-axis phase signal of a CRT display (not shown) into a reference value (non-defective product). Comparing with the mask limit value of ()).

When the device under test is inserted into the magnetic sensor 2, an output signal unique to the device under test is obtained from this circuit device. Since the spot output value changes in comparison, an object to be measured whose output value deviates from the mask limit allowable value of a good product can be determined to be a different product. Therefore, the determination can be made without destroying the measured object.

[0006] In addition, conventionally, a device for converting an AC amplitude value and a phase wave output signal by synchronous detection into an output signal, comparing the peak value of a Lissajous wave on a CRT display, and discriminating a different product is also similarly used. Used.

However, the magnetic sensor 2 based on the eddy current
Since it is necessary to convert the detection signal of the impedance change of the above into two types of output signals of an amplitude value and a phase value, there is a disadvantage that the configuration of the electronic circuit device becomes complicated. Also, CR
Because the T display is used to judge the acceptability, the acceptability of the device under test is not a simple task, and the pass / fail of the device under test cannot be properly determined unless a skilled technician with electronic knowledge performs it. That is the fact.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a configuration in which the quality of an object to be measured is determined using a magnetic sensor. It is to provide a device.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a magnetic sensor having a coil whose impedance changes in accordance with the magnitude of an induced eddy current generated in an object under test while an alternating magnetic field is applied to the object. A detection means for detecting an impedance change of the magnetic sensor; and an effective value conversion means for performing RMS-DC conversion of the impedance change level detected by the detection means. The effective value by the effective value conversion means is set in advance. When the measured object is out of the allowable range, a determination means for determining that the measured object is a different product is provided.

According to such a configuration, when an alternating current is applied to the magnetic sensor, an induced magnetic field is generated. Therefore, a conductive object to be measured is inserted into the induced magnetic field. Then, an eddy current is generated in the object to be measured (not only on the surface), and the impedance of the magnetic sensor changes accordingly.

In this case, when a magnetic material such as iron is located in the induction magnetic field of the magnetic sensor, the impedance of the coil of the magnetic sensor increases in proportion to the magnetic permeability, but the impedance of the nonmagnetic material such as copper or aluminum is increased. In the case, on the contrary, the impedance of the coil decreases. This is because the eddy currents act just as if they had a resistance in parallel with the coil, and this change increases at higher frequencies.

Further, if there is a flaw in the metal, the eddy current goes around the flaw portion, so that the state of the eddy current and, consequently, the impedance of the coil of the magnetic sensor changes. Further, even if the material of the metal is different or the shape is changed, the characteristics also change. However, when the object to be measured is inserted into the magnetic path of the magnetic sensor, the frequency of the excitation power supply ( In addition to a signal having the same frequency as the fundamental frequency, a frequency signal (harmonic signal) that is an odd multiple thereof can be obtained. The fundamental frequency signal is strongly affected by the shape variation of the device under test. , Cracks and the like.

In this case, the substantial change of the eddy current, although there is also a change in the phase, mostly appears as an amplitude signal of a voltage wave including a fundamental wave and a harmonic component. Therefore, by obtaining the effective value of the impedance change level of the coil detected by the detecting means by the effective value changing means, even if a waveform distortion occurs in the detection signal due to harmonics and impedance change of the magnetic sensor, etc. A change in flowing eddy current can be accurately detected.

As a result, the judging means can surely discriminate the non-defective product from the non-defective product based on whether or not the effective value obtained by the effective value changing device is out of the preset allowable range.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a prize detecting apparatus using eddy current will be described below with reference to FIGS. In FIG. 1 schematically showing the entire configuration, an excitation power supply 11 is connected to a magnetic sensor 12. The magnetic sensor 12 includes an excitation coil 13 and a detection coil 14, and a metal product (measurement object) transported by a transport device (not shown) is inserted into the magnetic sensor 12.

The excitation coil terminal 13a is directly connected to the excitation power supply 11, and the excitation coil terminal 13b is connected to the excitation power supply 11 via the coil zero balance adjusting unit 15. The excitation power supply 11 is for supplying an alternating current of a predetermined frequency to the excitation coil 13, and an alternating magnetic field is generated from the excitation coil 13 by the current supply.

Here, the detection principle of the magnetic sensor 12 will be described. As shown in FIG. 2, when the magnetic metal product 16 is inserted into the magnetic sensor 12, the alternating magnetic field from the exciting coil 13 acts intensively on the metal product 16 to generate an eddy current. Thus, the impedance of the detection coil 14 has a value corresponding to the magnetic permeability of the metal product 16 and the magnitude of the eddy current.

Accordingly, the magnetic permeability, and hence the impedance of the magnetic sensor 12, changes depending on the type or shape of the metal product 16, so that different types of metal products 16 can be used.
Can be determined. Further, when the metal product 16 has been damaged, the eddy current bypasses the damaged portion and the eddy current generation state changes, so that the damaged metal product 16 can be determined.

Now, referring to FIG.
a is connected to the detection circuit 17 (detection means), and the detection coil terminal 14b is connected to the ground line. The detection circuit 17 receives an induction current signal from the detection coil 14 and a reference signal from the coil zero balance adjustment unit 15. In this case, the coil zero balance without the metal product 16 being inserted into the magnetic sensor 12 is performed by adjusting the coil zero balance adjusting unit 15.

The difference signal between the signal of the detection coil 14 obtained from the detection circuit 17 and the signal of the coil zero balance adjusting unit 15 is subjected to an RMS-DC conversion circuit 19 ( Effective value conversion means). This RMS-DC conversion circuit 19
Outputs a square root of a value obtained by averaging the squared value of an instantaneous value of an input signal for each cycle as a DC voltage signal, and is a well-known technique and provided as an IC chip.

The DC voltage signal from the RMS-DC conversion circuit 19 and the reference signal from the work zero balance reference signal output circuit 22 are input to the comparison circuit 20 via the work zero balance adjustment unit 21. In this case, the work zero balance adjustment unit 21 is adjusted so that the output from the comparison circuit 20 becomes a predetermined value when the regular metal product 16 is positioned on the magnetic sensor 12.

The judgment circuit 23 (judgment means)
The output value from 0 is compared with the allowable range from the pass / fail reference signal output circuit 24. If the output value is out of the allowable range, an abnormal signal is output. When an abnormal signal is output from this determination circuit, the metal product 1 conveyed by the conveying device
6 are discharged by a sorting gate (not shown).

Next, the operation of the above configuration will be described. When the metal product 16 is inserted into the magnetic sensor 12 by a transport device (not shown), the impedance of the magnetic sensor 12 changes from an initial value.
, And the output level from the RMS-DC conversion circuit 19 also changes.

At this time, when the material of the metal product 16 is not a regular material, the output level from the RMS-DC conversion circuit 19 is within a predetermined level range with respect to the signal level from the work zero balance reference signal output circuit 22. The output level from the comparison circuit 20 is also within the allowable level range. Therefore, the determination circuit 23 can determine that the metal product 16 is normal.

At this time, although the detection signal from the detection circuit 17 causes a waveform distortion due to a harmonic and a change in impedance of the magnetic sensor 12, the RMS-DC conversion circuit 1
9, the effective value of the detection signal can be reliably detected without being affected by the waveform distortion.

When a different kind of metal product 16 is conveyed and inserted into the magnetic sensor 12, the impedance change of the magnetic sensor 12 is different from that of the normal metal product 16, so that the comparison circuit is accordingly changed. The output level of the output signal from the reference numeral 20 greatly fluctuates and falls outside the allowable level range of the pass / fail reference signal output circuit 24.

Then, the judgment circuit 23 judges that the metal product 16 is not normal and outputs an abnormal signal. Therefore, the abnormal signal from the judgment circuit 23 drives a selection gate (not shown) to detect the defective metal product. Eliminate product 16. Conversely, the adjustment of the work zero balance adjustment unit 21 may be set to the metal product 16 (defective product), and the selection gate may be driven by a normal product.

According to the above configuration, the detection signal from the detection circuit 17 is converted into an effective value by the RMS-DC conversion circuit 19, so that the detection signal from the detection circuit 17 generated by the harmonics of the magnetic sensor 12, impedance change, etc. Metal product 16 in a state where the influence of the distortion of the detection signal of
Of the magnetic sensor, the change of the amplitude value and the change of the phase wave are converted into two DC output signals by synchronous detection based on the signal of the impedance change of the magnetic sensor, and the CRT display / comparator is used by using the output signal. Unlike the prior art, which is determined by the means described above, it can be easily implemented with a simple configuration by using an RMS-DC conversion circuit having a known configuration.

The present invention is not limited to the above embodiment, but can be modified or expanded as follows. The work zero balance adjustment unit 21 may be included in a circuit preceding the RMS-DC conversion circuit 19, or the voltage of the work zero balance reference signal output circuit 22 may be varied. As the magnetic sensor, two sets of integrated excitation coil and detection coil are provided facing each other, and a metal product is passed between the two sets of coils in a state where an alternating magnetic field is generated by energizing the excitation coil. You may. In this case, a magnetic core may be provided in the coil to concentrate the alternating magnetic field. Further, the present invention may be applied to a probe type device that determines a non-defective product by approaching a metal product. Further, the function of each circuit may be executed by a microcomputer.

[0030]

As is apparent from the above description, according to the foreign object detecting device of the present invention, the change in the impedance of the coil of the magnetic sensor is obtained as an effective value by the effective value converting means, and the object is detected based on the effective value. Since the suitability of the measured object is determined, an excellent effect that the quality of the measured object can be reliably determined with a simple configuration is achieved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an electrical configuration according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a state of an eddy current generated in a product.

FIG. 3 is a diagram corresponding to FIG. 1 showing a conventional example.

[Explanation of symbols]

11 is an excitation power supply, 12 is a magnetic sensor, 17 is a detection circuit (detection means), 19 is an RMS-DC conversion circuit (effective value conversion means), and 23 is a judgment circuit (judgment means).

Claims (1)

[Claims] 1. A magnetic sensor having a coil whose impedance changes according to the magnitude of an induced eddy current generated in an object under application of an alternating magnetic field to the object, and an impedance change of the magnetic sensor Detecting means for detecting the impedance change level detected by the detecting means.
Effective value conversion means for performing MS-DC conversion; and determination means for determining that the device under test is a different product when the effective value of the effective value conversion means is out of a preset allowable range. A foreign object detection device characterized by the above-mentioned.