JPS63210690A - Detection of metallic foreign matter - Google Patents

Abstract

PURPOSE:To achieve a higher detection sensitivity of a metal foreign matter, by using air core coils as excitation coil and detection coil to ensure a better frequency characteristic of a detection coil at a high frequency area. CONSTITUTION:An excitation coil 3 is wound at a almost center position of a non-conductive and non-magnetic insulated pipe 2. Two detection coils 4 and 5 are wound on both sides of an excitation coil 2 at a position separated at an equal distance from the excitation coil 3. A high frequency current is applied to the excitation coil 3 with a control circuit 22 to detect the presence of a fine metal foreign matter mixed in an insulating member 25 passing through the insulated pipe 2 by an electromotive force induced in the detection coils 3 and 4 and an electromagnetic valve 16 is driven to remove a foreign matter mixed portion. This enables the shifting of frequency characteristic of the detection coils to a high frequency area while allowing increase in the number of turns of the detection coils thereby achieving a higher detection sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention particularly relates to a method for detecting metallic foreign matter, which detects fine metal mixed into a non-magnetic and non-conductive insulating member at high intensity.

(Prior Art) Polyethylene is generally used as an insulating member for high-voltage electric cables, but fine metal foreign matter may get mixed into the polyethylene during its manufacturing and transportation processes. If such metal foreign matter gets mixed into the insulating layer of the cable, there is a risk of causing a serious cable accident called puncture. In particular, as electric cables are becoming increasingly high-voltage, there is an increasing demand for removing metal foreign matter mixed into insulating members.

Conventionally, when detecting minute pieces of metal, such as copper or aluminum, mixed into the insulating member covering the core wire in the manufacturing process of the electric cable, as shown in FIG. A pair of E-type cores 30 and 31 are arranged to form a magnetic circuit, and an excitation coil 32 is placed in the center 30a of one core 30, and a first and second coil is placed in both sides 31b and 31c of the other core 31, respectively. Detection coil 33.3
4 is wound to form a detector 35, and a predetermined high-frequency excitation current is applied to the excitation coil 32 to generate a high-frequency magnetic field.
The object to be inspected, that is, the insulating member, is passed between these opposing cores 30, 31 perpendicular to the direction of the magnetic field, and the change in the magnetic field at this time is calculated as the difference in the output voltage of each detection coil 32, 33. This is to detect metal foreign matter that may be mixed into the insulating member.

When adjusting the balance between the output voltages of the two detection coils 33 and 34, the detector 35 used in this detection method adjusts the position of unillustrated iron blocks (liners) placed on both sides of each core 30 and 31. and each detection coil 33
．． Adjustment is made so that the difference between the output voltages of 34 becomes O.

(Problem to be Solved by the Invention) However, in the above detector, a magnetic circuit is formed by ferromagnetic cores 30 and 31 in order to strengthen the magnetic field, but it is difficult to use such a ferromagnetic core. Then, the inductance of the detection coils 33, 34 increases rapidly, and as a result, the frequency response characteristics of each of these detection coils 33, 34 deteriorate significantly. That is, the frequency response range shifts significantly to a lower frequency range. In order to improve the frequency characteristics of such detection coils, the number of turns of each detection coil 33.34 may be reduced;
If the number of turns is reduced, there is a problem that detection sensitivity decreases.

In particular, when inspecting extremely fine metal foreign objects, it is necessary to increase the frequency of the excitation current used, and for this purpose it is necessary to extend the frequency response characteristics of the coil to a high frequency range. The reason is that the metallic foreign object is regarded as one microcoil, and the characteristic frequency fe of this microcoil can be approximately determined by the following equation.

f c-5066/σμr d2 Here, σ represents the electrical conductivity of the foreign metal object, μ represents the relative magnetic permeability of the foreign metal object, and d represents the diameter of the foreign metal object. However, the metal foreign object is assumed to be a sphere with a diameter d.

As is clear from the above equation, the characteristic frequency fc is inversely proportional to the square of the diameter of the metal foreign object. Therefore, in order to detect a small diameter metal foreign object, that is, an extremely fine metal foreign object, the characteristic frequency fc of the detection coil must be It is essential to keep the response range as high as possible.

However, as described above, when a core is used in a magnetic circuit, the frequency characteristics of the detection coil shift to a low frequency range, resulting in low detection sensitivity and difficulty in detecting minute metals.

In addition, the conventional detector described above causes minute changes due to temperature changes or vibrations in the iron block, and even such a minute change causes the output balance of the detection coil to collapse, so it is necessary to adjust the balance of the detector. It is necessary to perform this on a regular basis, for example, every day. However, such balance adjustment is time-consuming and extremely troublesome to perform every day, and there are problems such as a decrease in work efficiency.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a method for detecting metal foreign matter that has extremely high detection sensitivity and is capable of detecting fine metals.

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, in the middle of a transfer passage for transferring an insulating member formed of a non-magnetic and non-conductive member, the passage is surrounded. An excitation coil and two detection coils are arranged equidistantly on both sides of the excitation coil, and a high-frequency current is applied to the excitation coil, and the electromotive force induced in the two detection coils causes the inside of the passage to be The apparatus detects metal foreign matter that may be mixed into the moving insulating member.

(Function) By using air-core coils for the excitation coil and the detection coil, the frequency characteristics of the detection coil are improved in the high frequency range, and detection sensitivity is improved accordingly, making it possible to detect minute metals mixed into insulating materials. is made possible.

(Example) An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a detector applied to the metal foreign object detection method of the present invention, and the detector l includes a non-conductive and non-magnetic insulated pipe 2, an excitation coil 3 wound around the insulated pipe 2, and a detection coil. 4.5, the excitation coil 3 is wound approximately at the center of the insulating pipe 2, and the two detection coils 4
．． 5 is wound on both sides of the excitation coil 2 at positions equidistant from the excitation coil 3. That is, the excitation coil 3 is arranged at an intermediate position between the detection coils 4 and 5.

The excitation coil 3 and each detection coil 4.5 are air-core coils. Therefore, the inductance of the detection coil 4.5 is reduced, the frequency characteristics are significantly improved, it becomes possible to move to a high frequency range, and the number of turns can be significantly increased.

Since no core is used in the magnetic circuit of each coil, the magnetic flux density generated by the excitation coil 2 is low, but by increasing the number of turns of the detection coil 4.5, the decrease in sensitivity due to the decrease in magnetic flux density can be compensated for. It can be supplemented. Also,
Since no core is used in the magnetic circuit, the temperature characteristics are greatly improved and are extremely good. Furthermore, since the excitation coil 3 and the detection coil 4.5 are simply wound around the insulated pipe 2, it is easy to adjust the balance of the output voltage of each detection coil 4.5. This eliminates the need for subsequent adjustments and makes handling easier.

The excitation coil 3 is connected to an excitation circuit 6, and each detection coil 4
．． 5 is connected to a signal processing circuit 7. The excitation circuit 6 includes a high frequency oscillation circuit, and applies a high frequency current to the excitation coil 3 to excite the excitation coil 3. The signal processing circuit 7 includes, for example, a differential amplifier, and outputs a voltage according to the difference in induced electromotive force between the two detection coils 4 and 5.

Incidentally, Table 1 shows the experimental results of the detector 1 of the present invention and the detector 35 using the conventional core shown in FIG.

Here, the inner diameter of the insulating vibrator 2 of the detector L is 2°I, the number of turns of the excitation coil 3 is 100, the number of turns of each detection coil 4.50 is 1000, and the frequency of the excitation current of the excitation coil 3 is 500kHz. The number of turns of the excitation coil 32 of the detector 35 is 20, the number of turns of each detection coil 33 and 34 is 42, and the frequency of the excitation current of the excitation coil 32 is 300 kHz.

Further, a copper ball is used as the sample (metallic foreign object) 9 to be detected, and the sample 9 is allowed to fall naturally and pass through the detector 1.35. And the diameter D- of this sample 9
The output voltage (mV) of each detector 1.35 when changing the
).

Table 1 The results of this experiment revealed the following.

(1) For large diameter samples, the output voltages of detectors 1 and 35 are approximately the same. That is, the detection sensitivity at this time is approximately the same for both.

(2) The output of the conventional detection B35 is proportional to about the 4.7th power of the diameter of the sample. That is, the output voltage E is E"D"
' Represented by '.

(3) On the other hand, the output of the detector l of the present invention is proportional to about the 2.6th power of the diameter of the copper ball. That is, the output voltage E is E
OCD customer - Represented by 6.

(4) The detector 35 has a diameter of 0.16n+ for the sample 9.
Although it is undetectable below m, the detector 1 of the present invention can detect it, and when the diameter of the sample 9 is 0.16 m+w, it is about 125 a+V, and when it is 0.1 mo+, it is about 37 mV.

Therefore, it is clear that when the diameter of the sample 9 is smaller than 0.5 an, the detection sensitivity of the detector 1 of the present invention is extremely higher than that of the conventional detector 35.

FIG. 2 shows an example of a detection apparatus for carrying out the method of detecting metal foreign matter mixed into an insulating member through the detector 1 shown in FIG. The metal foreign object detection device 10 includes a frame 11, a damper 12, a shade 13, a sorting box 14, a packet 5, and a solenoid valve 1 that drives the S-packet 15.
6 and the metal detector 1. Damper 12
is for storing the object to be inspected, for example, the insulating member 25, and is placed above the pedestal 11, the bottom of which is reduced in diameter to form a substantially conical shape, and the upper end of the chute 13 is connected to the hole in the center. This chute 13 is hung down and opens with its lower end facing the center of the upper end of the sorting box 14. This shoot 1
3 is formed of a non-conductive and non-magnetic member,
The detector l is kept free from electrical and magnetic influences.

The sorting box 14 is arranged approximately at the center of the lower position 11a of the pedestal 11 and below the damper 12, and has an open upper end 14a, and a lower end formed into two discharge ports 14b and 14C, one of which is a discharge port. The discharge port 14b is designated as a discharge port for non-defective products, and the other discharge port 14C is designated as a discharge port for defective products. The non-defective product outlet 14b is connected, for example, to a transfer path for the electrical cable coating process, and the defective product outlet 14C is connected to a waste product collection container (both not shown).

The packet 15 is housed in the center of the sorting box 14, with its upper portion being pivotably supported by a shaft 16, and the upper end 15a is a cylinder having a slightly larger diameter than the lower end 15b. This packet 15 always opens with its upper end 15a facing the lower end of the chute 13 regardless of the swinging position, and when it swings to one side shown by the solid line, its lower end 15b opens to the non-defective discharge port 14b, and the second
When they are swung to the other side indicated by the dotted chain line, they are opened facing the respective defective product discharge ports 14C.

The electromagnetic valve 17 swings the packet 15 and is connected to the rotating wheel 16 of the packet 15 via the iron 18 .

When the electromagnetic valve 17 is deenergized, it holds the packet 15 at the position shown by the solid line and communicates the lower end 15b of the packet 15 with the non-defective discharge port 14b, and when it is energized, it swings to the position shown by the two-dot chain line and the lower end 15b is communicated with the defective product discharge port 14c.

The detector 1 is placed approximately in the center of the pedestal 11 via a shield case 20, and the shield case 2° is placed on the center portion 11a via a vibration isolating member such as a spring 21. This detector 1 is constructed in the same manner as the detector shown in FIG. By fitting this insulated pipe 2 onto the chute 13,
The filling efficiency of each coil 3 to 5 is improved. An excitation coil 3 and a detection coil 4 are wound around this insulated pipe 2.
5 are connected to the control circuit 22, respectively.

The control circuit 22 is an excitation circuit that applies a high-frequency current to the excitation coil 2, and detects the presence or absence of minute metal foreign matter that is mixed into the insulating member 25 passing through the insulating pipe 2 by the electromotive force induced in each detection coil 3.4. and a signal processing circuit (both not shown) that outputs an open drive signal S for a predetermined time T after a predetermined time Td from the time of detection when a metal foreign object is detected, and the signal processing circuit outputs an open drive signal S for a predetermined time T. S is applied to the electromagnetic valve 17 to drive the electromagnetic valve 1G.

The certain time period Td is the time from the position where the metal foreign matter to be mixed into the insulating member 25 is detected, that is, from the detector 1 to the lower end of the shade 13. The predetermined time T is determined by the height of the container 1 from the packet 15, etc.
5, which is the time for removing only the portion that contains the metal foreign matter, and is determined by the detection time of the metal foreign matter, the flow rate of the insulating member 25, and the like. This time T is generally extremely short.

A method for detecting metal foreign matter mixed into an insulating member will be described below.

The insulating member 25 thrown into the damper 12 flows down the chute 13 due to its own weight and becomes a packet 15. Detector 1
When no metal foreign matter is detected in the insulating member 25, the output of each detection coil 4.5 is in a balanced state, the control circuit 22 does not output the drive signal S, the solenoid valve 16 is in a deenergized state, and the packet 15 is held at the position shown by the solid line. As a result, the insulating member 25 flows down inside the chute 13 and flows into the packet 15, and the lower end 15b of the packet 15
from there to the non-defective discharge port 14b and transferred to the above-mentioned coating process.

Now, when the detector 1 detects a metal foreign substance mixed into the insulating member 25 at time t, the control circuit 22 outputs the open drive signal S for a predetermined time T after the predetermined time Td from the time t. do. During the time Ta2 until this drive signal S is output, the one-color edge member 25, which does not contain metal foreign matter flowing down the chute 13 from the detector 1 to the lower end of the chute 13, reaches the non-defective discharge port 14b. be guided. Then, after a time Td from the time t, the portion of the insulating member 25 into which foreign matter is mixed reaches the lower end of the chute 13. At this time, the solenoid valve 16 is energized for a predetermined time T, and the packet 1
5 is swung to the position shown by the two-dot chain line, and the lower end 15b is opened facing the defective product discharge port 14c. As a result, the portion of the insulating member 25 into which the metal foreign matter is mixed is guided to the defective product outlet 14C via the packet 15.

After the predetermined time T, when the electromagnetic valve 17 is deenergized, the packet 15 is swung again to the position shown by the solid line, the lower end 15b is opened facing the non-defective discharge port 14b, and the packet flows down the chute 13 and the packet is The insulating member 25 flowing into the insulating member 15 is guided to the non-defective discharge port 14a. In this way, the insulating member 25
Only the portion of the metal contaminant that contains the metal foreign matter is removed.

Although this embodiment describes the case of detecting fine metal parts mixed into an insulating member covering an electric cable, the detection is not limited to this. Of course, the present invention can be applied to the detection of fine metals.

(Effects of the Invention) As described above, according to the present invention, an excitation coil is provided in the middle of a transfer passage for transferring a kfiM member formed of a non-magnetic and non-conductive member, surrounding the passage.
Two detection coils are placed equidistantly on both sides of the excitation coil, a high frequency current is applied to the excitation coil, and the electromotive force induced in the two detection coils causes the insulating member to move within the passage. Since the metal foreign matter that can be mixed in is detected, the frequency characteristics of the detection coils can be moved to a high frequency range, and the number of turns of each of these detection coils can be significantly increased. can be made significantly higher than in the past, and as a result, it becomes possible to detect extremely fine metal foreign matter that may be mixed into the insulating member. Furthermore, by using air-core coils for each of the coils, it is possible to significantly improve the temperature characteristics, and if the balance of the detection coils is adjusted at the time of manufacture, it is no longer necessary, making handling easier. It has excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of a detector applied to the method for detecting metal foreign objects according to the present invention, and FIG. The figure shown in FIG. 3 is a diagram showing a conventional metal foreign object detector. DESCRIPTION OF SYMBOLS 1...Detector, 2...Insulating pipe, 3...Excitation coil, 4.5...Detection coil, 6...Signal processing circuit, 7...Excitation circuit, 9...Sample , 10... Detection device, 11... Frame, 12... Damper, 13...
・Chute, 14... Sorting box, 15... Packet, 16... Solenoid valve, 22... Control circuit, 25...
...Insulating material. Figure 1 Figure 3

Claims (1)

[Claims] In the middle of a transfer path for transferring an insulating member made of a non-magnetic and non-conductive member, an excitation coil and two detection coils are arranged at equal distances on both sides of the excitation coil, surrounding the transfer path. A method for detecting metallic foreign objects, characterized in that a high frequency current is applied to the excitation coil, and metallic foreign objects mixed into the insulating member moving in the passage are detected by electromotive force induced in the two detection coils. .