JPH03125988A - Detection level setting for metal detecting machine - Google Patents

Abstract

PURPOSE:To eliminate the need for the preparation of a sample by detecting metal material using a regular object to be inspected having the metal material to set values of 1/2-2/3 of peak levels of detection signals obtained in a receiving coil as metal detection level. CONSTITUTION:An object W to be inspected having metal material M is applied to a metal detecting machine MD and a detection level obtained in a receiving coil 3b is set as LM. A value 1/2-2/3 times as large as the level LM is set as detection criterion level Lth. With such an arrangement, there is no need for preparing a sample for setting a detection level as in the past and hence, the setting of detection level is accomplished simply by feeding an acceptable project. This allows the setting of a detection level easily regardless of the shape, type and dimension of the object W to be inspected or the metal material M attached thereto thereby achieving quick judgment of the quality of a diversifying object to be inspected.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention detects whether or not a regular metal object, such as soup containing aluminum foil in instant noodles, is contained in an object to be inspected that is being conveyed by a conveyor or the like. The present invention relates to a method of setting a detection level of a metal detector for detection.

[Conventional technology]

First, an overview of a conventionally used metal detector will be explained with reference to FIG. In this figure, 1 is an oscillator, 2 is a transmitting coil connected to the oscillator 1, and 3a
, 3b are receiving coils arranged opposite to this transmitting coil 2;
They are placed in an alternating magnetic field and arranged so that the lines of magnetic force are equally interlinked. 4a and 4b are the receiving coils 3a
, 3b induced voltage 1. 2 shows a volume for adjusting the phase and amplitude of the signal 2, and is normally set so that el-ez=o by adjusting the volumes 4a and 4b. 5 is an amplifier that amplifies the differential induced voltage Mi, -62; 6
a and 6b are synchronous detectors that detect ferrous and nonferrous metals, respectively; 7a;

7b is an analog filter of about 2 to 20Hz, 8a, 8
b is a discrimination circuit. Note that 9a and 9b are first . A second phase shifter is shown. Further, er and ag will be described later with reference to FIG.

In a metal detector having such a configuration, an object to be inspected W passes between the transmitting coil 2 and receiving coils 3a and 3b, and when metal is mixed in the object to be inspected, the type of metal (ferrous or non-ferrous) is detected. ) generates a detection signal in the discrimination circuits 8a and 8b.

To explain this point using the vector diagrams in FIGS. 5(a) and 5(b), normally the induced voltages e+, e* of the receiving coils 3a, 3b
1-6 only on the input side of the amplifier 5. =O, but when the inspected object W containing iron passes from the direction of the arrow, first, as shown in Fig. 5(a),
The induced voltage 61 of the receiving coil 3a increases to 6'1, and then the induced voltage 2 of the receiving coil 3b increases to 6'2.

Therefore, r−8m=e. , is input to the synchronous detector 6a, and is detected by only the same phase synchronous detection signal supplied to the synchronous detector 6a.

On the other hand, when the inspected object W containing non-ferrous metal (stainless steel, aluminum, etc.) passes through, an eddy current flows in the non-ferrous metal under the influence of the alternating current magnetic field of the oscillator 1. Then, due to the influence of this eddy current, the induced voltages er,
The phase of e* will change.

That is, as shown in FIG. 5(b), the receiving coil 3a
When the phase of the induced voltage changes to 6''1, the differential induced voltage e''zez = 6°, as shown in the figure, becomes approximately 90°.
° Occurs at out-of-phase points. So, look at this differential induced voltage. Non-ferrous metals can be detected by phase detection in the synchronous detector 6b to which the synchronous detection signal shown by 3 is supplied.

The key point of the above-mentioned metal detector is to detect whether metal as a foreign substance is mixed into the object W to be inspected. Therefore, foreign metals are usually detected so that even minute ones can be detected The level is set. That is, for example, when detecting whether foreign metals are mixed in packed miso, it is necessary to detect even minute foreign metals. Therefore, the conventional method of setting the detection level is to pass a good product with no foreign metals mixed in, and to
A slight induced voltage is detected. Therefore, as shown in Figure 6,
This induced voltage is defined as the non-defective product detection level L1, and the metal detection level L2 is 2 to 3 times the non-defective product detection level L1.
When an output exceeding this metal detection level L is obtained, it is determined that foreign metal is mixed in.

[Problems to be Solved by the Invention] On the other hand, when a metal object must be provided as the object W to be inspected, that is, as shown in FIG. A deoxidizing agent 11 is contained, and since this deoxidizing agent 11 is an oxide of iron, when it is passed through a metal detector, it is detected as metal contamination. Similarly,
When the powdered soup 21 containing aluminum foil is placed inside the ramen bag 20 as shown in Fig. 3(b), Fig. 3(c)
As in the case where the candy bag 30 contains a vinyl sticker 31 containing aluminum foil, or as shown in FIG. 3(d), the candy container 40 has a toy 41 made of metal attached. Furthermore, if metal is detected, which indicates a good product, the metal is not a foreign object, and the product is considered good if the output exceeds the detection level.

In this case, the method of setting the detection level is to cut the metal object (e.g., an aluminum bag) that you want to detect and cut it into pieces of ~% size and feed it into the metal detector, and set the metal detection level as shown in Figure 7. L3 is determined, and a non-defective product detection level L4 is set at 2 to 3 times the detection level Ls. As described above, there is a problem in that it is troublesome to cut the metal object into small pieces to prepare the sample, and it is difficult to prepare the sample especially when the metal object is non-uniform.

The present invention was made in order to solve the above-mentioned problems, and an object of the present invention is to provide a detection level setting method that does not require preparing a sample.

[Means for solving the problem 1 A detection level setting method for a metal detector according to the present invention is as follows:
Detect metal objects using a regular object to be inspected that is equipped with metal objects, detect the peak level of the detection signal obtained in the receiving coil at that time, and set the value of ~% of this peak level as the metal detection level. This is what you set.

[Effect]

In this invention, since a non-defective product is passed through a metal detector and the detection level is set based on the detection signal at that time, there is no need to prepare a sample.

〔Example〕

FIG. 1 is a diagram for explaining the detection level setting method of the present invention.

First, the object to be inspected W equipped with the metal object M is placed on the metal detector MD.
, and the detection level obtained at the receiving coil 3b is defined as LM. Then, a value multiplied by % of this detection level L is set as the detection judgment level L th.

The detection level shown in FIG. 2 is the detection judgment level Lth.

It goes without saying that the signal obtained by the receiving coil 3b described in the above embodiment includes the case where the signal is passed through an amplifier or an attenuator.

[Effect of the invention 1] As explained in detail above, the present invention detects a metal object using a regular object to be inspected equipped with a metal object, and measures the peak level of the detection signal obtained at the receiving coil at that time. Since the value of ~% of this peak level is set as the detection judgment level, there is no need to prepare a sample to set the detection level as in the past, and detection can be easily performed by simply flowing a good product. You can set the level. therefore,
The shape of the object to be inspected or the metal object attached to it.

Type 9 Even if the dimensions change, the detection level can be easily set.
It has the advantage of being able to quickly determine the quality of the increasingly diverse objects to be inspected.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of the present invention, and FIG.
The figure shows the relationship between each detection level obtained in Figure 1,
Figures 3 (a) to (d) are diagrams showing various objects to be inspected;
The figure is a block diagram showing an example of a metal detector, Figure 5 (a)
, (b) are block diagrams for explaining the detection operation of FIG. 4, and FIGS. 6 and 7 are diagrams showing the relationship between each detection level for explaining the conventional detection level setting method. In the figure, 1 is an oscillator, 2 is a transmitting coil, and 3a. 3b is a receiving coil, 4a, 4b are volumes, 5 is an amplifier, 6a, 6b are synchronous detectors, 7a, 7b are analog filters, 8a, 8b are discrimination circuits, 9a, 9b are first... The second phase shifter, L&l, is a detection level or a detection judgment level. Figure 1 Figure 2 Figure 3 Figure Figure Figure (a) (b)

Claims (1)

[Claims] A test object having a metal object is passed between a transmitting coil that generates an alternating magnetic field and a receiving coil that receives this alternating magnetic field, and a discrimination circuit discriminates the magnitude of a detection signal obtained from the receiving coil. When setting the detection level of a metal detector that detects the presence of a metal object, detect the metal object using a regular object to be inspected that is equipped with the metal object, and at that time, detect the metal object obtained by the receiving coil. The peak level of the detection signal is detected, and 1/2 to 2/3 of this peak level is detected.
A detection level setting method for a metal detector, characterized in that a value of is set as a metal detection level.