JP4657154B2 - Electromagnetic induction type inspection method and electromagnetic induction type inspection device - Google Patents

Description

  The present invention relates to an electromagnetic induction inspection method and an electromagnetic induction inspection apparatus that detect a change in magnetic flux caused by an article to be inspected passing through a magnetic field and inspect the quality of the article based on the detection result.

  When an article is placed in or passed through an AC magnetic field, the magnetic flux changes due to the article in the AC magnetic field, and the value of the electromotive voltage (induced voltage) induced in the coil placed in the AC magnetic field changes. . Many electromagnetic induction type article inspection apparatuses (electromagnetic induction type inspection apparatuses) using such a phenomenon have been proposed (see Patent Documents 1 to 5). An electromagnetic induction inspection device detects an abnormality in the shape or material of an article, metal mixed in the article, scratches on the article surface, etc. by inspecting the article based on a detection signal representing an induced voltage in a coil. ing.

  FIG. 5 is a block diagram showing the basic configuration of such an electromagnetic induction type inspection apparatus 21. The excitation coil 22a is applied with a high frequency voltage of a predetermined frequency (excitation frequency) by the excitation circuit unit 23 to generate a magnetic field. The detection coil 22b generates an induced voltage corresponding to a change in magnetic flux caused by an article to be inspected (hereinafter referred to as a workpiece) passing through the magnetic field generated by the excitation coil 22a, and the detection unit 24 is generated in the detection coil 22b. An analog signal (detection signal) corresponding to the induced voltage is output.

  The phase detection unit 25 uses the detection signal output from the detection unit 24 to perform phase detection in synchronization with an analog signal (AC voltage signal) corresponding to the AC voltage of the excitation circuit unit 23, and inspects the signal after phase detection To the unit 26. The inspection unit 26 inspects the workpiece based on the output signal from the phase detection unit 25.

For example, when using a magnetic sensor in which the detection coil 22b is disposed inside the excitation coil 22a and the detection coil 22b and the excitation coil 22a are integrated coaxially, all of the excitation magnetic flux generated by the excitation coil 22a is used. Since the detection coil 22b is linked to each other, mutual inductance occurs in the detection coil 22b with extremely high efficiency, and a large induced voltage is generated. Then, when sequentially inspecting a plurality of workpieces, each workpiece to be inspected is passed through the inside of the detection coil 22b one by one, and according to the peak value or bottom value of the output signal from the phase detector 25 that is passing through Then, the inspection unit 26 inspects the quality of the workpiece.
Japanese Patent No. 3140105 JP-A-6-201653 JP-A-60-78378 JP 59-138946 A Japanese Patent No. 3625911

  In the electromagnetic induction type inspection apparatus 21 having such a configuration, a change in output characteristics in the excitation circuit unit 23 and a change in detection characteristics in the detection unit 24 occur due to a change in ambient temperature. The result also fluctuates, so that an accurate result cannot be obtained, and there is a problem that an erroneous determination of the quality of the work occurs.

  In the magnetic metal detector disclosed in Patent Document 5, erroneous detection of the position of a passing article due to a temperature change or the like is prevented by a difference signal between a plurality of coils. However, since a plurality of coils are used, there is a problem that the configuration becomes complicated and the cost is increased.

  The present invention has been made in view of such circumstances, and even with a simple and low-cost configuration, the effects of fluctuations in excitation output characteristics and detection characteristics due to changes in ambient temperature and the like are reduced, and the article It is an object of the present invention to provide an electromagnetic induction type inspection method and an electromagnetic induction type inspection device capable of performing an accurate pass / fail inspection.

The electromagnetic induction type inspection method according to the present invention generates a magnetic field by applying an alternating voltage to an excitation coil, and a change in magnetic flux caused by passing an article to be inspected that is intermittently sent through the generated magnetic field is detected by a detection coil. In the electromagnetic induction type inspection method of detecting and inspecting the quality of the inspected article according to the detection result obtained, upstream and downstream in the transport direction with respect to the excitation coil and the detection coil in the vicinity of the transport path of the inspected article A detector that detects the passage of the inspected article that is installed detects the timing at which one inspected article passes, and a detection signal that indicates a change in the magnetic flux detected within the detected inspected article passage time interval. A difference between a maximum value and a minimum value is obtained, and the quality of the inspected article is inspected based on a comparison result between the obtained difference and a predetermined standard.

The electromagnetic induction type inspection apparatus according to the present invention generates a magnetic field by applying an alternating voltage to an exciting coil, and a detection coil detects a change in magnetic flux caused by passing an article to be inspected that is sent intermittently in the generated magnetic field. In an electromagnetic induction type inspection apparatus that detects and checks the quality of the inspected article according to the detection result obtained, upstream and downstream in the transport direction with respect to the excitation coil and the detection coil in the vicinity of the transport path of the inspected article A detecting means for detecting a timing at which one inspected article is installed , and a maximum of a detection signal indicating a change in the magnetic flux detected by the detection coil within an inspected article passage time interval detected by the detecting means; And a difference detecting means for obtaining a difference between the value and the minimum value, and an inspection means for inspecting the quality of the article to be inspected based on a comparison result between the obtained difference and a predetermined reference.

  In the present invention, the maximum value of the detection signal representing the induction voltage of the detection coil within the detected article passing time interval is detected by detecting the timing at which the article to be inspected passes through the excitation coil / detection coil. A difference from the minimum value is obtained, and the quality of the article is inspected by comparing the obtained difference with a predetermined standard. The maximum value of the detection signal corresponds to the timing at which the article passes through the center position of the excitation coil / detection coil, and the minimum value of the detection signal corresponds to the timing at which the article has passed through the excitation coil / detection coil.

  Excitation output characteristics and detection characteristics vary according to the ambient temperature change, but the same fluctuation occurs at the timing when the article passes through the center position and the timing when the article finishes passing. By seeking, these fluctuations are offset. Therefore, the influence of these fluctuations can be reduced by inspecting the quality of the article based on the difference between the maximum value and the minimum value of the detection signal. As a result, an accurate quality inspection result of the article can be obtained even if the ambient temperature changes.

In addition, since the influence of the temperature change can be prevented with one set of excitation coil / detection coil, it can be realized with a small and low-cost configuration.
In the electromagnetic induction type inspection apparatus according to the present invention, the difference detecting means includes a maximum value Asin of the sin component and a maximum value Acos of the cos component, a minimum value Bsin of the sin component, and a minimum value Bcos of the cos component of the detection signal. The difference x = Asin−Bsin and y = Acos−Bcos are calculated, and the inspection means determines whether the inspected article is good based on whether the calculated (x, y) falls within a predetermined elliptical area. It is characterized by having comprised so that it may test | inspect.

In the present invention, the timing at which one article to be inspected passes through the alternating magnetic field is detected, and the difference between the maximum value and the minimum value of the detection signal indicating the change in magnetic flux detected within the detected inspected article passage time interval is determined. Since the quality of the article to be inspected is inspected based on the obtained difference and the comparison result with the predetermined standard, it is possible to reduce the influence of ambient temperature change even in a small and low-cost configuration. can both if it is possible to always obtain a correct quality results regardless of the temperature environment, the installed detector in the conveying direction upstream and downstream with respect to the excitation coil and the detection coil in the transport path proximal of the test article (detection Means) to detect the timing at which the article to be inspected passes, so it is confirmed whether or not two or more inspected articles are present in the excitation coil and the detection coil within the inspected article passage time. Because you can It is possible to improve the reliability of the inspection.

  Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof. Note that the present invention is not limited to the following embodiments.

  FIG. 1 is a configuration diagram showing an example of an electromagnetic induction inspection apparatus 1 according to the present invention. In FIG. 1, reference numeral 10 denotes a conveyance path in which an article to be inspected (workpiece W to be inspected) is intermittently conveyed in the arrow direction (vertical direction in FIG. 1). 1 is provided. The electromagnetic induction type inspection apparatus 1 includes a magnetic sensor 2, an excitation circuit unit 3, a detection unit 4, a phase detection unit 5, an inspection unit 6, a display unit 7, a first passage detector 8, a second And a passage detector 9.

  The magnetic sensor 2 includes an excitation coil 2a that generates an alternating magnetic field and a detection coil 2b that generates an induced voltage corresponding to a change in magnetic flux. The excitation coil 2a and the detection coil 2b carry the axial direction of the coils 2a and 2b. In the longitudinal direction (conveying direction) of the path 10, they are arranged concentrically at substantially the same position in the longitudinal direction so as to surround the conveying path 10 with the excitation coil 2 a outside and the detection coil 2 b inside.

  The excitation coil 2a is applied with a high frequency voltage by the excitation circuit unit 3 to generate an alternating magnetic field. The workpiece W to be inspected passes through the alternating magnetic field generated by the exciting coil 2a by passing through the inside of the detection coil 2b. The detection coil 2b generates an induced voltage corresponding to a change in magnetic flux caused by the work W to be inspected passing through the AC magnetic field generated by the excitation coil 2a. The generated induced voltage is input to the detection unit 4.

  The excitation circuit unit 3 applies a high-frequency voltage having an excitation frequency to the excitation coil 2a to generate an AC magnetic field, and an analog signal corresponding to the high-frequency voltage applied to the excitation coil 2a is used as an AC voltage signal for the phase detection unit 5 Output to. The detection unit 4 outputs a signal corresponding to the induced voltage input from the detection coil 2b as a detection signal to the phase detection unit 5.

  The phase detector 5 that receives the AC voltage signal from the excitation circuit 3 and the detection signal from the detector 4 extracts only the frequency component of the AC voltage signal from the detection signal, and sends the extracted signal to the inspection unit 6. Output.

  The first passage detector 8 that detects the passage of the workpiece W to be inspected is provided in the vicinity of the transport path 10 on the downstream side in the transport direction with respect to the magnetic sensor 2. Further, the second passage detector 9 that detects the passage of the workpiece W to be inspected is provided on the upstream side in the transport direction with respect to the magnetic sensor 2 in the vicinity of the transport path 10. Each of the first passage detector 8 and the second passage detector 9 outputs a detection signal indicating the presence or absence (timing) of the passage of the workpiece W to be inspected to the inspection unit 6.

  FIG. 2A is a diagram illustrating a detection signal of the first passage detector 8, and the level increases at the timing when passage of the workpiece W to be inspected is detected. FIG. 2B is a diagram showing an output signal from the phase detection unit 5 to the inspection unit 6 and is shown in synchronization with FIG. Since the workpiece W to be inspected is intermittently conveyed on the conveyance path 10, the time between the adjacent high levels in FIG. 2A represents the time during which one workpiece W passes (work passage time). . Within this workpiece passage time, the output signal of the phase detector 5 is initially at a low level as shown in FIG. 2B, but increases monotonically when the workpiece W to be inspected passes through the magnetic sensor 2. After that, it exhibits a monotonically decreasing level change and then returns to the first low level.

  The inspection unit 6 has a maximum value (maximum level) A and a minimum value (minimum level) in the output signal (detection signal) as shown in FIG. 2B within the workpiece passage time corresponding to one workpiece W to be inspected. B is obtained, and the difference between the obtained maximum value A and minimum value B is calculated. Then, the inspection unit 6 compares the calculated difference with a predetermined reference (predetermined region or predetermined threshold) stored in advance in the internal memory 6a, and determines whether the inspection workpiece W is acceptable based on the comparison result. inspect.

  The inspection result of quality on the workpiece W to be inspected is output from the inspection unit 6 to the display unit 7, and the display unit 7 displays the inspection result on a liquid crystal screen or the like.

  Next, the operation of the electromagnetic induction inspection apparatus 1 having such a configuration will be described. FIG. 3 is a flowchart showing the procedure of the electromagnetic induction type inspection method according to the present invention (the operation procedure of the inspection unit 6). The memory 6a of the inspection unit 6 stores in advance information on a predetermined elliptical area (x, y) as shown in FIG. 4 as a predetermined reference for determining the quality of the workpiece W to be inspected.

  The excitation circuit unit 3 applies a high frequency voltage to the excitation coil 2a to generate an alternating magnetic field. Then, a plurality of workpieces W to be inspected are intermittently conveyed one by one along the conveyance path 10 in the arrow direction. Each of the workpieces W to be inspected passes through the alternating magnetic field generated by the exciting coil 2a by passing through the inside of the detection coil 2b. In the detection coil 2b, an induced voltage is generated according to a change in magnetic flux caused by the work W to be inspected passing through the AC magnetic field generated by the exciting coil 2a.

  The generated induced voltage is input to the detection unit 4, and a detection signal corresponding to the induced voltage is output from the detection unit 4 to the phase detection unit 5. In the phase detection unit 5, only the frequency component of the excitation current (AC voltage signal) is extracted from the input detection signal according to the AC voltage signal from the excitation circuit unit 3, and the extracted signal is sent to the inspection unit 6. Is output.

  On the other hand, detection signals indicating the presence / absence (timing) of the passage of the workpiece W to be inspected are output from the first passage detector 8 and the second passage detector 9 to the inspection unit 6. The inspection unit 6 can know the workpiece passage time for each workpiece W based on the detection signal of the first passage detector 8. Then, the inspection unit 6 determines pass / fail of each workpiece W to be inspected based on the output signal from the phase detection unit 5 within the workpiece passage time.

  The quality determination process for each workpiece W to be inspected will be described in detail with reference to the flowchart of FIG.

  The inspection unit 6 determines whether or not a signal indicating the passage of the workpiece W to be inspected (high level in FIG. 2A) is input from the first passage detector 8 (step S1). When the signal is not input (S1: NO), the inspection unit 6 determines the maximum value (specifically, the maximum value Asin of the sin component and the maximum value Acos of the cos component) and the minimum value in the output signal from the phase detection unit 5 ( Specifically, the minimum value Bsin of the sin component and the minimum value Bcos of the cos component) are detected (step S2), and the operation returns to S1. When a signal indicating the passage of the workpiece W to be inspected (high level in FIG. 2A) is input (S1: YES), the inspection unit 6 determines the detected maximum value and minimum value (step S3). In this way, the inspection unit 6 can obtain the maximum value and the minimum value of the output signal (detection signal) from the phase detection unit 5 within the workpiece passage time for each workpiece W to be inspected. At this time, the detection signal in the first passage detector 8 contributes to the determination of the determination timing of the maximum value and the minimum value.

  Next, the inspection unit 6 calculates the difference between the maximum value and the minimum value, specifically, x = Asin−Bsin, y = Acos−Bcos (step S4). Then, the inspection unit 6 determines whether or not the calculated (x, y) falls within a predetermined elliptical region R (see FIG. 4) stored in the memory 6a (step S5).

  When entering the predetermined elliptical area (S5: YES), the inspection unit 6 determines that the workpiece W to be inspected is a non-defective product and outputs the determination result to the display unit 7 (step S6). On the other hand, when it does not fall within the predetermined elliptical area (S5: NO), the inspection unit 6 determines that the workpiece W to be inspected is a defective product and outputs the determination result to the display unit 7 (step S7). .

  The inspection unit 6 clears the acquired maximum value and minimum value (step S8), the operation returns, and the same operation procedure is executed for the next workpiece W to be inspected.

  As the ambient temperature changes, the output voltage of the excitation circuit unit 3, the resistance of the detection coil 2b, etc. fluctuate, and the output signal (detection signal) from the phase detection unit 5 also fluctuates. The same applies when the workpiece W passes through the magnetic sensor 2 and when the workpiece W does not exist in the magnetic sensor 2. Therefore, as described above, by obtaining the difference between the maximum value and the minimum value of the output signal (detection signal) from the phase detection unit 5 within the workpiece passage time, the influence of such variation due to temperature change can be obtained. Can be small. Since the quality of the workpiece W to be inspected is determined based on this difference, an accurate quality determination result can be obtained without being affected by the temperature change, and each of the objects to be tested can be obtained without depending on the temperature environment. The inspection workpiece W can always be correctly inspected. Moreover, since the prevention of the influence of such a temperature change can be realized by one magnetic sensor 2, the structure is not increased in size and the cost is not increased.

  By the way, the detection signal from the second passage detector 9 is combined with the detection signal from the first passage detector 8, and two or more workpieces W to be inspected exist in the magnetic sensor 2 within the workpiece passage time. This is necessary for confirming whether or not the inspection has been performed, and the reliability of the inspection can be improved.

  In the example described above, the case where a two-dimensional predetermined region is used as the predetermined reference has been described. However, the difference between the maximum value and the minimum value is compared with a predetermined threshold, and the quality of the workpiece W to be inspected is inspected based on the comparison result. You may make it do.

  If a moving average between the detection result of the minimum value until the previous time and the minimum value detected this time is obtained, sudden effects such as noise can be avoided. Also, comparing the moving average of the minimum value up to the previous time and the minimum value detected this time, if there is a difference of more than a predetermined value, if it is determined that the detected value is abnormal due to noise, False detection can be prevented.

It is a block diagram which shows an example of the electromagnetic induction type inspection apparatus by this invention. It is a figure which shows the detection signal of a 1st passage detector, and the output signal of a phase detection part. It is a flowchart which shows the procedure (operation | movement procedure of a test | inspection part) of the electromagnetic induction type inspection method by this invention. It is a figure which shows an example of the predetermined area | region (predetermined reference | standard) for determining the quality of the to-be-inspected workpiece | work W. It is a block diagram which shows the basic composition of an electromagnetic induction type inspection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electromagnetic induction type inspection apparatus 2 Magnetic sensor 2a Excitation coil 2b Detection coil 3 Excitation circuit part
4 detection unit 5 phase detection unit 6 inspection unit 7 display unit 8 first passage detector 9 second passage detector 10 transport path W work to be inspected

Claims (3)

A magnetic field is generated by applying an alternating voltage to the excitation coil, and a change in magnetic flux due to the passage of an article to be inspected that is intermittently sent through the generated magnetic field is detected by the detection coil, and according to the obtained detection result, In the electromagnetic induction type inspection method for inspecting the quality of the inspected article,
The timing at which one inspection article passes is detected by a detector that detects the passage of the inspection article upstream and downstream of the excitation coil and the detection coil in the vicinity of the conveyance path of the inspection article. A difference between a maximum value and a minimum value of the detection signal indicating a change in the magnetic flux detected and detected within the detected article passage time interval is obtained, and the difference is determined based on a comparison result between the obtained difference and a predetermined reference. An electromagnetic induction inspection method characterized by inspecting the quality of an inspection article. A magnetic field is generated by applying an alternating voltage to the excitation coil, and a change in magnetic flux due to the passage of an article to be inspected that is intermittently sent through the generated magnetic field is detected by the detection coil, and according to the obtained detection result, In an electromagnetic induction type inspection device that inspects the quality of an article to be inspected,
A detection means that is installed upstream and downstream in the conveyance direction with respect to the excitation coil and the detection coil in the vicinity of the conveyance path of the article to be inspected;
A difference detection means for obtaining a difference between a maximum value and a minimum value of a detection signal indicating a change in the magnetic flux detected by the detection coil within an inspection article passage time interval detected by the detection means;
An electromagnetic induction type inspection apparatus comprising: inspection means for inspecting the quality of the inspected article based on a comparison result between the obtained difference and a predetermined reference. The difference detection means is a difference between the maximum value Asin of the sine component and the maximum value Cos of the cos component and the minimum value Bsin of the sine component and the minimum value Bcos of the cos component x = Asin−Bsin, y = Acos−Bcos is calculated, and the inspection means is configured to inspect the quality of the inspected article based on whether or not the calculated (x, y) falls within a predetermined elliptical area. The electromagnetic induction type inspection apparatus according to claim 2.

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