JP4002034B2 - Foreign object detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a foreign object detector that detects the presence or absence of foreign objects such as metal pieces contained in an article to be packaged or a packaged article (hereinafter simply referred to as “article”).
[0002]
[Prior art]
A conventional foreign object detector conveys an article as a detection object in an alternating magnetic field by a conveyor, and differentially amplifies the electromotive force induced in two detection coils arranged side by side in the conveyance direction to perform phase detection. When the phase detection signal exceeds a certain determination level, it is determined that foreign matter is mixed. At this time, the set phase for phase detection is set to a value that minimizes the phase detection signal when only the article is used in order to avoid the influence of the article. The relationship between the phase and the output of the phase detection signal for an article is as shown by curve B in FIG. In this case, the set phase is the dip point d at which the phase detection signal from the article is minimized. On the other hand, the relationship between the phase of the article mixed with foreign matter and the output of the phase detection signal is shown as curve A. As can be seen, at the dip point d, which is the set phase point, the level of the signal A is higher than that of the signal B, and foreign matter can be detected by setting the determination level during this time.
[0003]
A foreign object detector that automatically sets the phase of the dip point d to a phase point used for determination (hereinafter referred to as “determination phase point”) is also known.
[0004]
However, depending on the article, the detection sensitivity of the foreign matter may not necessarily be the maximum at the dip point d, and the dip point of the signal B as shown in FIG. d may not be clear. In such a case, conventionally, a determination phase point having a large level difference between the signal A and the signal B is obtained by trial and error, or the output signal is measured by sequentially shifting the phase point, and the signal A and the signal B shown in FIG. A phase-output characteristic curve is created, and from this phase-output characteristic curve, the phase point where the level of the signal A is higher than that of the signal B and the level difference between the two signals is the largest is determined. The phase point was set.
[0005]
[Problems to be solved by the invention]
However, the conventional method for setting the determination phase point of an article whose dip point is not clear has a problem in that it takes a lot of work.
[0006]
An object of the present invention is to solve the above-described problems and to obtain a foreign object detector that can automatically detect an optimal phase point and set it as a determination phase point.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a foreign object detector according to the present invention includes a reaction signal generation circuit that passes an article in an alternating magnetic field and generates a reaction signal for the article based on the magnetic field affected by the article, and a predetermined signal The first storage means for storing the phase-output characteristic of the first test reaction signal for the foreign object or the article to which the foreign object is added, and the phase-output characteristic of the second test reaction signal for the article to which the foreign object is not added Second storage means, and an optimum phase setting means for setting a phase point where the level of the first test reaction signal is higher than that of the second test reaction signal and the level difference between the two signals is the maximum as a determination phase point; Determination means for determining the presence or absence of foreign matter from the level of the reaction signal at the judgment phase point during the foreign matter detection operation of the article.
According to the above configuration, the first test reaction signal stored in the first storage means has a higher level than the second test reaction signal stored in the second storage means, and the level difference between the two signals is maximized. By setting the phase point as a determination phase point, the presence or absence of foreign matter can be determined from the level of the reaction signal at the determination phase point when foreign matter is detected in the article.
[0008]
In a preferred embodiment of the present invention, a signal obtained from the reaction signal generation circuit when the article to which the predetermined foreign matter is added is passed through the alternating magnetic field is stored in the first storage means as a first test reaction signal. A signal obtained from the reaction signal generation circuit when the first writing means to be stored and / or the article to which the foreign matter is not added is passed through the alternating magnetic field is used as the second test reaction signal as the second test reaction signal. Second writing means for storing in the storage means is provided.
[0009]
According to the above configuration, the phase-output characteristic of the first test reaction signal is stored in the first storage unit, and the phase-output characteristic of the second test reaction signal is stored in the second storage unit. By reading the level value of the same phase point of the first test reaction signal and the second test reaction signal, the first test reaction signal is higher in level than the second test reaction signal, and the level difference between the two signals It is possible to automatically detect the phase point at which becomes the maximum.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 shows a configuration of a foreign object detector according to an embodiment of the present invention. In the figure, a foreign object detector 1 includes a reaction signal generation circuit 2 that applies an alternating magnetic field E to a conveyance path of an article P by a conveyor C and generates a reaction signal for the article P passing through the alternating magnetic field E. Yes.
[0011]
The foreign object detector further includes a phase detector 3 for outputting a phase detection signal obtained by phase detection of the reaction signal, an amplifier 4 for amplifying the phase detection signal, and detecting a phase detection signal output from the amplifier 4 as a foreign object. A first switch 5 that switches between an operation and a test that will be described later, and a second switch 6 that switches between a first phase detection signal A for an article containing a predetermined foreign object and a second phase detection signal B for an article having no foreign object during the test. The first and second storage means 7A, 7B, the first writing means 8A for storing the phase-output characteristics of the first phase detection signal A in the first storage means 7A, and the second phase detection signal B A second writing means 8B for storing the phase-output characteristics in the second storage means 7B, an optimum phase setting means 9 for automatically setting a judgment phase point serving as a judgment criterion during operation, and a set judgment phase point Detection operation at Detection phase setting unit 13 for setting the detection phase of phase detector 3, determination level setting means 12 for automatically setting the determination level, and pass / fail (foreign matter) based on the determination phase point and the determination level during operation. Determination means 10 and a display device 11 that displays various types of information.
[0012]
The reaction signal generating circuit 2 is provided at a position that receives an equal amount of magnetic flux of the magnetic field generator 22 that generates an alternating magnetic field E by passing an exciting current through the transmitting coil 21 and the alternating magnetic field E generated from the transmitting coil 21 and the transmitting coil 21. A magnetic sensor 25 formed by a pair of receiving coils 23 and 24 arranged and a differential amplifier 26 to which a voltage signal induced in the receiving coils 23 and 24 is input.
[0013]
When the article P to which the foreign matter is added passes through the alternating magnetic field E of the reaction signal generation circuit 2, the magnetic flux crossing the two receiving coils 23 and 24 of the magnetic sensor 25 becomes unbalanced and the receiving coils 23 and 24 A difference is caused in the induced voltage. The difference voltage signal is amplified by the differential amplifier 26, the amplified difference voltage signal is phase-detected by the phase detector 3, and the phase detection signal is amplified by the amplifier 4 and output to the first switch 5.
[0014]
Next, the setting operation of “determination phase point” and “determination level”, which are determination criteria for determining whether or not there is a foreign substance in the article P, according to the present embodiment will be described.
First, the first switch 5 is switched to the terminal a side, the second switch 6 is switched to the terminal a side, and an article P () in which a foreign material having a predetermined material and dimensions is added to a product such as meat or pickles for testing. The test piece) is conveyed by the conveyor C, and the phase-output characteristic of the first test reaction signal A is stored in the first storage means 7A. Next, the second switch 6 is switched to the terminal b side, the article P (test piece) to which no foreign matter is added is conveyed by the conveyor C, and the phase − of the second test reaction signal B is transferred to the second storage means 7B. Store output characteristics.
[0015]
Next, the optimum phase setting unit 9 sequentially reads out the level value of the same phase point from the first storage unit 7A and the second storage unit 7B, and the level value stored in the first storage unit 7A is the second storage unit. A phase point that is higher than the level value stored in 7B and has the maximum level difference between the two is searched, and that phase point is set as a determination phase point. At the same time, the determination level setting means 12 sets the gain of the amplifier 4 so as not to determine that foreign matter is mixed in based on a signal from the second storage means 7B containing no foreign matter.
The optimum phase setting operation will be specifically described below with reference to the flowchart of FIG.
[0016]
The optimum phase setting means 9 first resets the level of the difference signal stored in step S1 to 0, and the phase is 0 ° in S2 (the voltage phases of the transmission coil 21 and the reception coils 23 and 24 in FIG. 1 are the same). Reset to). Next, in S3 and S4, the level value of the first test reaction signal A and the level value of the second test reaction signal B having a phase of 0 ° are read from the first storage means 7A and the second storage means 7B, and both in S5. The signal level difference is calculated, and the phase and level difference are temporarily stored in S6. Next, when the phase is not 180 ° in S7, the phase point is advanced by one step (for example, 1 °) in S8 and the process returns to S3, and the level values of the first test reaction signal A and the second test reaction signal B in S3 and S4. Are read out in S5, the level difference between the two signals is calculated in S5, and the larger one compared to the stored level difference is left in S6 until the phase reaches 180 °. When it becomes, the phase of the maximum level difference stored in S6 is set to the “determination phase point”. The determination level setting means 12 sets a level value that is approximately ½ of this maximum level difference to the “determination level”.
FIG. 3 shows the determination phase points and determination levels set as described above.
[0017]
After the determination phase point and the determination level are set as described above, the actual operation for detecting the article P is started. At this time, the first switch 5 is connected to the contact b side, and the obtained reaction signal at the time of the detection operation is input to the determination means 10, the level value of the determination phase point is compared with the determination level value, and the response signal When the level value is smaller than the determination level value, the pass (no foreign matter) is judged, and when the level value is larger, the judgment (existing foreign matter) is made and displayed on the display device 11.
[0018]
According to the present embodiment, the determination phase point and the determination level are automatically set only by conveying the article with the foreign substance added and the article with no foreign substance added to the conveyor one by one. Setting work is greatly reduced.
[0019]
The determination phase point to be set is a phase point where the first test reaction signal A is higher in level than the second test reaction signal B and the level difference between the two signals is maximized, so that the determination accuracy is improved. .
[0020]
In the above-described embodiment, an article to which foreign matter is added is used to obtain the phase-output characteristics of the first test reaction signal. However, depending on the type of the article, the first test reaction signal when a test piece made only of foreign matter is flowed is used. Using the 1 test reaction signal and the second test reaction signal when a test piece made of only an article is flowed, the optimum determination phase point can be similarly obtained.
[0021]
In the embodiment, since the first and second test reaction signals are obtained by actually flowing the test piece, the determination level can be set without being affected by the difference in the output characteristics of each foreign matter detector. However, when the difference in output characteristics for each foreign matter detector can be ignored, the data of the first test reaction signal may be stored directly in the first storage means 7A in advance.
[0022]
Furthermore, in the embodiment, the foreign material is a magnetic metal such as a steel ball, but a nonmagnetic metal such as stainless steel can be applied in the same manner and the same effect can be obtained. It is also possible to test a plurality of times by changing the type of metal, store a plurality of first test reaction signals, and obtain a phase at which the most desirable output of the first test reaction signal is obtained with respect to the second test reaction signal. .
[0023]
【The invention's effect】
As described above, the foreign object detector according to the present invention stores the phase-output characteristic of the first test reaction signal for the article to which the predetermined foreign substance is added in the first storage unit, and the article to which the foreign substance is not added. The phase-output characteristic of the second test reaction signal is stored in the second storage means, and the optimum phase setting means is the same as the first test reaction signal and the second test reaction signal from the first storage means and the second storage means. Read the level value of the phase point, calculate the level difference, compare the level difference of each phase point, the first test reaction signal is higher than the second test reaction signal, and the level difference between both signals is the maximum The phase point is detected, the phase point is set as a determination phase point, and the presence / absence of foreign matter in the article during operation is determined based on the level of the reaction signal at the determination phase point. Because there is a maximum level difference Since it is set to the determination signal point phase point that is automatically detected and, together with the setting operation of the criterion is reduced, the determination accuracy is improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a foreign object detector according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a determination phase point setting procedure of an optimum phase setting unit of the present embodiment.
FIG. 3 is a phase-output characteristic diagram of a first test reaction signal and a second test reaction signal for explaining a determination level of the present embodiment.
FIG. 4 is a phase-output characteristic diagram of a first test reaction signal and a second test reaction signal showing a conventional determination phase point.
FIG. 5 is a phase-output characteristic diagram of a first test reaction signal and a second test reaction signal showing determination phase points of another conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Foreign substance detector, 2 ... Reaction signal generator circuit, 3 ... Phase detector, 4 ... Amplifier, 5 ... 1st switch, 6 ... 2nd switch, 7A ... 1st memory | storage means, 7B ... 2nd memory | storage means, 8A ... 1st writing means, 8B ... 2nd writing means, 9 ... Optimum phase setting means, 10 ... Determination means, 11 ... Display device, 12 ... Determination level setting means.

Claims (2)

A reaction signal generating circuit for passing an article through an alternating magnetic field and generating a reaction signal for the article based on a magnetic field influenced by the article;
First storage means for storing a phase-output characteristic of a first test reaction signal for a predetermined foreign object or an article to which the foreign object is added;
Second storage means for storing a phase-output characteristic of a second test reaction signal for an article to which the foreign matter is not added;
An optimum phase setting means for setting a phase point where the level of the first test reaction signal is higher than that of the second test reaction signal and the level difference between the two signals is the maximum as a determination phase point; A foreign object detector comprising: determination means for determining the presence or absence of foreign substances from the level of the reaction signal at the determination phase point. In claim 1,
First writing means for storing a signal obtained from the reaction signal generating circuit as a first test reaction signal in the first storage means when the article to which the predetermined foreign matter has been added is passed through the alternating magnetic field; and Or
A second writing means for storing a signal obtained from the reaction signal generation circuit in the second storage means as a second test reaction signal when the article to which the foreign matter is not added is passed through the alternating magnetic field; Foreign object detector.

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