Magnetic inspection device and conforming article determination method thereof

Abstract

To suppress wrong determination of a conforming article as a non-conforming article.SOLUTION: A magnetic inspection device allows an AC current to flow to a reference coil and an inspection coil, and determines whether a component to be inspected is a conforming article or not on the basis of a change in a value of current flowing through the inspection coil when a component to be inspected is allowed to enter a magnetic field generated around the inspection coil in a state in which a component confirmed to be a conforming article that satisfies a predetermined condition is allowed to enter a magnetic field generated around the reference coil. The magnetic inspection device comprises a conforming article range storage section for storing a conforming article range on an xy plane in which an inspection index should exist when a component to be inspected is a confirming article and a conforming article determination section for determining that the component to be inspected is a conforming article when x coordinates showing a real section and y coordinates showing an imaginary section corresponding to a difference between a value of current flowing through the reference coil and a value of current flowing through the inspection coil are set as inspection indexes.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a magnetic inspection device and a method for determining non-defective products using the same. [Background technology]

[0002] Conventionally, for example, when inspecting induction-hardened bolts (to check whether induction hardening has been performed properly), the induction-hardened bolts are cut and their internal hardness is measured to determine whether they are good products (induction hardening has been performed properly) or defective products (induction hardening has not been performed properly) on a lot-by-lot basis, but from the perspective of quality assurance, non-destructive 100% inspection is desirable. Therefore, the inventor of the present invention attempted to develop a magnetic inspection device that is capable of 100% inspection by non-destructive inspection (see, for example, Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Hisanori Usui, Tatsuya Shikata, Daisuke Ito, "Nitto Technical Report No. 77," published by Nitto Seiko Co., Ltd., July 1, 2017, pp. 6-9 Summary of the Invention [Problem to be solved by the invention]

[0004] In the magnetic inspection device of Patent Document 1, as shown in FIG. 1(a), two circumferentially wound inspection solenoid coils C1 and C2 (hereinafter referred to as inspection coils C1 and C2) are connected in series and arranged coaxially. When an AC current is applied to the two inspection coils C1 and C2, a magnetic field H0 is generated around the coils. When a workpiece W to be inspected enters between the two inspection coils C1 and C2, as shown in FIG. 1(b), the AC magnetic field generates eddy currents on the workpiece surface in the opposite direction to the AC current, which in turn generates a magnetic field H1 in the workpiece W. This magnetic field H1 generates an induced current, which changes the current flowing through the coils C1 and C2. If the workpiece W has a different structure, differences in magnetic permeability and electrical conductivity occur, causing changes in the current flowing through the inspection coils C1 and C2. Therefore, by comparing the changes in the amplitude and phase of this current, it is possible to distinguish between heat treatment conditions and materials with different structures.

[0005] The magnetic inspection device of Patent Document 1 uses a circuit as shown in Figure 2. A sine wave of a constant frequency is applied to the inspection coils C1 and C2 and the reference coils Ct1 and Ct2, and an inspection is performed using a signal synchronized with this phase. If the measurement value (hereinafter referred to as the detection signal) output from the inspection coils C1 and C2 and captured by the A / D converter is Asin(ωt+φ), and the measurement value (hereinafter referred to as the reference signal) output from the reference coils Ct1 and Ct2 and captured by the A / D converter is Bsin(ωt), the x-coordinate of the inspection indicator used for pass / fail judgment is expressed by equation (1), and the y-coordinate is expressed by equation (2).

[0006]

number

[0007]

number

[0008] That is, the x-coordinate of the inspection index indicates the real part, ABcos(φ) / 2, and the y-coordinate indicates the imaginary part, ABsin(φ) / 2. Note that Bcos(ωt) in equation (2) is a signal generated by advancing the phase by 90° based on the reference signal, Bsin(ωt).

[0009] It is known that the characteristics of electronic components used in amplifiers included in circuits such as that shown in Figure 2 change due to the influence of ambient temperature and board temperature. If the characteristics of electronic components change with temperature, the measurement values ​​input into the A / D converter will differ even when the same test workpiece is inspected, making accurate inspection impossible. Therefore, the magnetic inspection device of Patent Document 1 uses a circuit equipped with solenoid coils Ct1 and Ct2 for temperature compensation (hereinafter referred to as reference coils Ct1 and Ct2) in addition to inspection coils C1 and C2 through which the test workpiece W to be inspected is inserted, as shown in Figure 2. A good test workpiece W0 is always inserted between the reference coils Ct1 and Ct2, and temperature compensation is performed based on the acquired measurement values.

[0010] The x-coordinate expressed in equation (1) and the y-coordinate expressed in equation (2) change due to the influence of the workpiece being inspected and its temperature, whereas the z-value expressed in equation (3) is calculated using only the signal from the reference coil into which the good workpiece W0 has been inserted, and therefore changes due to the influence of temperature only. By dividing the x-coordinate and y-coordinate, which are influenced by the workpiece being inspected and its temperature, by z, which is influenced only by temperature, the x-coordinate and y-coordinate of the inspection index, which suppresses the influence of temperature, are calculated, and this inspection index is ultimately used to determine whether the workpiece is good or bad.

[0011]

number

[0012] First, when performing non-defective product inspections using the magnetic inspection device of Patent Document 1, teaching is required to determine the non-defective product range. The non-defective product range is determined based on a preset tolerance by calculating the average value and standard deviation from the inspection indices obtained by inspecting a predetermined number of non-defective workpieces. Figure 3(a) shows the inspection screen displayed on the touch panel of the magnetic inspection device. The inspection screen displays a coordinate plane with the x-axis as the horizontal axis and the y-axis as the vertical axis, and the inspection indices obtained by inspecting a predetermined number of non-defective workpieces are plotted on the screen. Figure 3(b) shows the non-defective product range, with the standard deviation calculated for each of the x- and y-coordinates of the plotted inspection indices. The non-defective product range is shown as a rectangular area (hereinafter sometimes referred to as a "3σ rectangle") within the 3σ range (±3σ range).

[0013] However, there is an area (the area surrounded by a dotted line in FIG. 3(b)) on the periphery of the non-defective range shown in FIG. 3(b) where no plots exist. For example, if the inspection indices x and y of an inspected workpiece are plotted inside the non-defective range shown in FIG. 3(b), the inspected workpiece will be judged to be a non-defective product. However, if the non-defective range is set larger than necessary, it is possible that the inspected workpiece will be erroneously judged to be a non-defective product, even though it is actually a defective product. Therefore, it is preferable that the non-defective range set based on the inspection indices x and y obtained by inspecting non-defective works includes many of the plots of a predetermined number of non-defective works, and that there be as few areas as possible where no plots exist inside the non-defective range.

[0014] Therefore, an object of the present invention is to provide a magnetic inspection device and a method for determining conformance that can appropriately set a conformance range based on inspection indices x and y obtained by inspecting a conformance workpiece. [Means for solving the problem]

[0015] That is, the magnetic inspection device according to the present invention is a magnetic inspection device that determines whether a component to be inspected is a non-defective component based on a change in the current value flowing through the inspection coil when a component that has been confirmed to be a non-defective component and that satisfies predetermined conditions is placed in the magnetic field generated around the reference coil and the component to be inspected is placed in the magnetic field generated around the inspection coil, and in this state, when the inspection indexes are the x-coordinate indicating the real part and the y-coordinate indicating the imaginary part corresponding to the difference between the current value flowing through the reference coil and the current value flowing through the inspection coil, the inspection coil is configured to detect the presence or absence of an inspection indicator in the inspection coil; and the inspection coil is configured to detect the presence or absence of an inspection indicator in the inspection coil; the inspection coil is configured to detect the presence or absence of an inspection indicator in the inspection coil; and the inspection coil is configured to detect the presence or absence of an inspection indicator in the inspection coil;

[0016] The method for determining whether a component to be inspected is a conforming component for a magnetic inspection device according to the present invention is a conforming component determination method in which an AC current is passed through a reference coil and an inspection coil, and a component that has been confirmed to be a conforming component and satisfies a predetermined condition is placed in the magnetic field generated around the reference coil. In this state, the component to be inspected is placed in the magnetic field generated around the inspection coil, and based on a change in the current value flowing through the inspection coil, the method determines whether the component to be inspected is a conforming component. When the x-coordinate indicating the real part and the y-coordinate indicating the imaginary part corresponding to the difference between the current value flowing through the reference coil and the current value flowing through the inspection coil are used as inspection indices, The method comprises a pass-quality range setting step of setting a pass-quality range on the xy plane where the inspection indicator should be if the part is pass-quality; an inspection indicator derivation step of causing the part to enter a magnetic field generated around the inspection coil and deriving an inspection indicator for the part to be inspected; and a pass-quality determination step of determining that the part to be inspected is pass-quality if the inspection indicator derived by the inspection indicator derivation step is within the pass-quality range set by the pass-quality range setting step, wherein the pass-quality range set by the pass-quality range setting step is an elliptical range set on the xy plane.

[0017] This allows the pass-through range, which is set based on the inspection index obtained by inspecting a predetermined number of pass-through workpieces, to include many of the plots of the predetermined number of pass-through workpieces, while minimizing the area within the pass-through range where no plots exist, thereby preventing a defective workpiece from being mistakenly determined to be pass-through based on the inspection index obtained by inspecting the defective workpiece.

[0018] In the magnetic inspection device according to the present invention, it is preferable that the non-defective range stored in the non-defective range storage unit is the range of a probability ellipse on an xy plane.

[0019] In the method for determining non-defective products for a magnetic inspection device according to the present invention, it is preferable that the non-defective product range set in the non-defective product range setting step is the range of a probability ellipse on an xy plane.

[0020] This allows the pass-through range, which is set based on the inspection index obtained by inspecting a predetermined number of pass-through workpieces, to include most of the plots of the predetermined number of pass-through workpieces, and to avoid including many areas within the pass-through range where no plots exist, thereby more reliably preventing a defective workpiece from being erroneously determined to be pass-through based on the inspection index obtained by inspecting the defective workpiece.

[0021] In the magnetic inspection device according to the present invention, it is preferable that the correlation coefficient between the x coordinate and the y coordinate, which are the inspection indexes, is −0.4 or less or 0.4 or more.

[0022] In the method for determining non-defective products using a magnetic inspection device according to the present invention, it is preferable that the correlation coefficient between the x coordinate and the y coordinate, which are the inspection index, is −0.4 or less or 0.4 or more.

[0023] As a result, when the correlation coefficient between the x-coordinate and y-coordinate, which are the inspection indicators, is below -0.4 or above 0.4, the non-defective range can be set to the range of a probability ellipse on the xy plane, thereby more effectively preventing the defective work from being mistakenly determined to be non-defective. [Effects of the Invention]

[0024] As described above, according to the present invention, it is possible to prevent a defective workpiece from being mistakenly determined to be a non-defective product. [Brief explanation of the drawings]

[0025] [Figure 1] 1(a) and 1(b) are diagrams for explaining a non-defective product determination method for a magnetic inspection device 1 according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing a circuit used in the magnetic inspection device 1 according to the embodiment of the present invention. [Figure 3] FIG. 3(a) shows an inspection screen on which inspection indices obtained by inspecting non-defective workpieces are plotted, and FIG. 3(b) shows an inspection screen on which the non-defective range is displayed. [Figure 4] 1 is a control block diagram of a magnetic inspection device 1 according to an embodiment of the present invention. [Figure 5] 3 is a flowchart showing the steps of a non-defective product determination method for the magnetic inspection device 1 according to the embodiment of the present invention. [Figure 6] 10 is an example of an examination screen on which a plurality of examination indices are plotted. [Figure 7] FIG. 7 is a partial enlarged view of FIG. 6. [Figure 8] The graph shows various values ​​obtained based on the inspection index of a good workpiece that has been properly induction hardened. [Figure 9] The graph shows various values ​​determined based on the inspection index of a good workpiece that has been properly tempered. [Figure 10] 10 is an example of an examination screen on which a plurality of examination indices are plotted. [Figure 11] The figures show various values ​​determined based on the inspection index of a non-defective workpiece without through holes. [Figure 12] 10 is an example of an examination screen on which a plurality of examination indices are plotted. [Figure 13] 10 shows various values ​​obtained based on the inspection index of a defective product in which a through hole is formed. DETAILED DESCRIPTION OF THE INVENTION

[0026] A magnetic inspection device 1 and its method for determining pass / fail products according to an embodiment of the present invention will be described below with reference to the drawings. The method for determining pass / fail products, the circuit used, the inspection screen on which the inspection index is plotted, etc. in the magnetic inspection device 1 of this embodiment are the same as those explained with reference to Figures 1 to 3, and the present invention differs from the prior art mainly in the method for setting the pass / fail range.

[0027] Fig. 4 is a control block diagram of the magnetic inspection device 1 of this embodiment. As shown in Fig. 4, the control unit 50 of the magnetic inspection device 1 is composed of, for example, a microcomputer, and includes a CPU, a ROM storing a program for controlling the operation of the magnetic inspection device 1, and a RAM for temporarily storing data used when executing the program. The operation of the magnetic inspection device 1 is controlled by this control unit 50. An inspection screen 55 is connected to the control unit 50.

[0028] The control unit 50 has a non-defective range storage unit 51, an inspection index derivation unit 52, and a non-defective determination unit 53. An inspection screen 55 is connected to the control unit 50.

[0029] The non-defective range storage unit 51 calculates the average value and standard deviation from the inspection index obtained by inspecting a predetermined number of non-defective works, and stores the non-defective range determined based on a preset tolerance.

[0030] The inspection index derivation unit 52 includes the circuit shown in Fig. 2, and derives an inspection index for a plurality of inspection works W when the plurality of inspection works are placed one by one between the inspection coils C1 and C2. The magnetic inspection device 1 is configured so that the plurality of inspection works are automatically placed one by one between the inspection coils C1 and C2. At this time, a non-defective work W0 is placed between the reference coils Ct1 and Ct2. The current values ​​supplied to the reference coils Ct1 and Ct2 and the inspection coils C1 and C2 are both 860 mA.

[0031] The non-defective product determination unit 53 determines the inspection work W as a non-defective product if the inspection index for the inspection work W is within the non-defective product range, and determines the inspection work W as a defective product if the inspection index for the inspection work W is outside the non-defective product range.

[0032] First, the procedure of the method for determining non-defective products by the magnetic inspection device 1 will be described with reference to Fig. 5. Fig. 5 is a flowchart showing the procedure of the method for determining non-defective products by the magnetic inspection device 1 of this embodiment.

[0033] <Step S1> In step S1, teaching is performed for a predetermined number of non-defective workpieces. Specifically, a predetermined number of non-defective workpieces that have been confirmed to be non-defective are inspected, and inspection indices are obtained and plotted on the inspection screen.

[0034] <Step S2> In step S2, a non-defective range is set based on the inspection index for the predetermined number of non-defective workpieces obtained in step S1, and the non-defective range is displayed on the inspection screen. The method for setting the non-defective range will be explained in detail later.

[0035] <Step S3> In step S3, each workpiece is inspected to obtain inspection indices, which are plotted on the inspection screen.

[0036] <Step S4> In step S4, it is determined whether the inspection index of the inspection workpiece is within the non-defective range. If the inspection index of the inspection workpiece is within the non-defective range, proceed to step S5. If the inspection index of the inspection workpiece is not within the non-defective range, proceed to step S6.

[0037] <Step S5> In step S5, the inspected workpiece for which the inspection index was obtained in step S3 is determined to be a non-defective product.

[0038] <Step S6> In step S6, the inspection workpiece for which the inspection index was obtained in step S3 is determined to be a defective product.

[0039] The method for setting the acceptable range will be described in detail below.

[0040] (First non-defective product judgment example) Fig. 6 is an example of an inspection screen on which multiple inspection indices are plotted, and inspection indices for workpieces that have been induction hardened and inspection indices for workpieces that have been tempered are plotted. The pass / fail judgment method described with reference to Fig. 6 is a judgment method for inspecting a workpiece that has been induction hardened to judge whether or not the induction hardening has been properly performed, and for inspecting a workpiece that has been tempered to judge whether or not the tempering has been properly performed.

[0041] The inspection screen shown in Figure 6 plots inspection indices obtained by inspecting a predetermined number (e.g., 800 pieces) of good-quality workpieces that have been properly subjected to induction hardening, and inspection indices obtained by inspecting a predetermined number (e.g., 800 pieces) of good-quality workpieces that have been properly subjected to tempering. FIG. 7 is a partial enlargement of FIG. 6, showing an enlarged area where the inspection indexes of good workpieces that have been properly subjected to induction hardening are plotted, and an enlarged area where the inspection indexes of good workpieces that have been properly subjected to tempering are plotted.

[0042] (About induction hardening treatment) FIG. 7 shows three non-defective ranges A1, A2, and A3 that are set based on the inspection index for non-defective workpieces that have been properly induction hardened.

[0043] The non-defective range A1 is a rectangular range (hereinafter sometimes referred to as a "3σ rectangle") set based on the range of the 3σ zone determined based on the inspection indexes of a predetermined number of non-defective workpieces. The horizontal length of the non-defective range A1 is the length of the 3σ zone determined for the inspection index x, and the vertical length of the non-defective range A1 is the length of the 3σ zone determined for the inspection index y.

[0044] The non-defective range A2 is an elliptical range (hereinafter sometimes referred to as a "standard ellipse") illustrated so as to contact the four sides of the rectangular non-defective range A1. The major axis of the elliptical shape representing the non-defective range A2 is parallel to the y-axis, and the minor axis of the elliptical shape is parallel to the x-axis.

[0045] The non-defective range A3 is the range of a probability ellipse (hereinafter sometimes referred to as a "probability ellipse") determined based on the inspection indices of a predetermined number of non-defective workpieces. The major axis of the ellipse representing the non-defective range A3 is inclined relative to the x-axis, and the minor axis of the ellipse is inclined relative to the y-axis. The non-defective range A3 shown in Figure 7 is the range of the probability ellipse corresponding to a 99.7% probability that the inspection indices of non-defective workpieces will be plotted within it.

[0046] The non-defective ranges A1, A2, and A3 set based on the inspection indexes for a predetermined number of non-defective workpieces shown in FIG. 7 will be compared and examined.

[0047] (Regarding the non-defective range A1) A predetermined number of plots, except for a1 plots, are inside the non-defective range A1, and there are areas to the left, right, and bottom of the upper end of the non-defective range A1 where there are almost no plots. Therefore, if an inspection is performed with the non-defective range A1 set, there is a relatively high possibility that the inspection indicator for a defective product will be erroneously plotted inside the non-defective range A1.

[0048] (Regarding the non-defective range A2) A predetermined number of plots, except for a2 (where a2>a1) plots, are inside the non-defective range A2, and there is an area at the bottom of the non-defective range A2 where there are almost no plots. However, the area in the non-defective range A2 where there are almost no plots is significantly smaller than that in the non-defective range A1, and when inspection is performed with the non-defective range A2 set, the possibility that the inspection indicator for a defective product will be erroneously plotted inside the non-defective range A2 is significantly reduced.

[0049] (Regarding the non-defective range A3) A predetermined number of plots are inside the good product range A3, excluding a3 (where a3 < a1) plots, and there is an area with almost no plots at the lower end of the good product range A1. However, the area with almost no plots in the good product range A3 is significantly smaller than that in the good product range A1. When inspection is performed with the good product range A3 set, the possibility that the inspection index of defective products is erroneously plotted inside the good product range A3 is significantly reduced.

[0050] (Regarding the tempering process) FIG. 7 shows three good product ranges B1, B2, and B3 set based on the inspection indexes of good workpieces for which the tempering process has been properly performed.

[0051] The good product range B1 is a rectangular range (hereinafter sometimes referred to as a "3σ rectangle") set based on the range of the 3σ area obtained based on the inspection indexes of a predetermined number of good workpieces. The horizontal length of the good product range B1 is the length of the 3σ area obtained for the inspection index x, and the vertical length of the good product range B1 is the length of the 3σ area obtained for the inspection index y.

[0052] The good product range B2 is an elliptical range (hereinafter sometimes referred to as a "standard ellipse") shown so as to contact the four sides showing the rectangular good product range B1. The major axis of the elliptical shape showing the good product range B2 is parallel to the y-axis, and the minor axis of the elliptical shape is parallel to the x-axis.

[0053] The good product range B3 is a range of a probability ellipse (hereinafter sometimes referred to as a "probability ellipse") obtained based on the inspection indexes of a predetermined number of good workpieces. The major axis of the elliptical shape showing the good product range B3 is inclined with respect to the x-axis, and the minor axis of the elliptical shape is inclined with respect to the y-axis. The good product range B3 shown in FIG. 7 is a range of a probability ellipse corresponding to a probability of 99.7% that the inspection indexes of good workpieces are plotted inside it.

[0054] Compare and examine the good product ranges B1, B2, and B3 set based on the inspection indexes of the predetermined number of good workpieces shown in FIG. 7.

[0055] (Regarding the acceptable range B1) A predetermined number of plots are inside the acceptable range B1, excluding b1 plots. There are areas with almost no plots on the left side, right side, and lower end of the upper end of the acceptable range B1. Therefore, when the inspection is performed with the acceptable range B1 set, there is a relatively high possibility that the inspection index of defective products will be erroneously plotted inside the acceptable range B1.

[0056] (Regarding the acceptable range B2) A predetermined number of plots are inside the acceptable range B2, excluding b2 (where b2 > b1) plots. There is an area with almost no plots on the right side of the lower end of the acceptable range B2. However, the area with almost no plots in the acceptable range B2 is significantly smaller compared to the acceptable range B1. When the inspection is performed with the acceptable range B2 set, the possibility that the inspection index of defective products will be erroneously plotted inside the acceptable range B2 is significantly reduced.

[0057] (Regarding the acceptable range B3) A predetermined number of plots are inside the acceptable range B3, excluding b3 (where b3 < b1) plots. There is an area with almost no plots on the lower end of the acceptable range B3. However, the area with almost no plots in the acceptable range B3 is significantly smaller compared to the acceptable range B1. When the inspection is performed with the acceptable range B3 set, the possibility that the inspection index of defective products will be erroneously plotted inside the acceptable range B3 is significantly reduced.

[0058] FIG. 8 shows the total number, average value, variance, covariance, major axis, minor axis, and rotation angle of the probability ellipse of the x - coordinates and y - coordinates obtained based on the inspection index of a good workpiece in which the high - frequency quenching process was properly performed, and also shows the correlation coefficient between the x - coordinate and the y - coordinate. The correlation coefficient between the x - coordinate and the y - coordinate for the high - frequency quenching process is 0.167.

[0059] Similarly, Figure 9 shows the total number, average value, variance, covariance, major axis, minor axis, and rotation angle of the x and y coordinates obtained based on the inspection index of a non-defective workpiece that has been properly tempered, as well as the correlation coefficient between the x and y coordinates. The correlation coefficient between the x and y coordinates for the tempering treatment is 0.268.

[0060] It is generally known that there is a correlation between the x and y coordinates when the correlation coefficient between the x and y coordinates is -0.4 or less or 0.4 or more. The inventors of the present invention have found that when the correlation coefficient between the x and y coordinates is -0.4 or less or 0.4 or more, it is preferable to set the non-defective range to the range of a probability ellipse calculated based on the inspection indexes of a predetermined number of non-defective workpieces.

[0061] The correlation coefficient between the x and y coordinates for induction hardening is 0.167, and the correlation coefficient between the x and y coordinates for tempering is 0.268, meaning that the correlation coefficient between the x and y coordinates is neither less than -0.4 nor more than 0.4. Therefore, for induction hardening and tempering, the effect of setting the non-defective range to the range of the probability ellipse determined based on the inspection indexes of a predetermined number of non-defective workpieces is small.

[0062] In Figure 7, the non-defective ranges A1, A2, and A3 for induction hardening and the non-defective ranges B1, B2, and B3 for tempering are set so that they do not overlap on the inspection screen, making it possible to distinguish between non-defective workpieces that have been properly induction hardened and non-defective workpieces that have been properly tempered.

[0063] (2nd non-defective product judgment example) Fig. 10 is an example of an inspection screen on which multiple inspection indices are plotted, for example, inspection indices for a cylindrically shaped non-defective workpiece are plotted. The non-defective determination method described based on Fig. 10 is a determination method for inspecting a cylindrically shaped workpiece to determine whether it is a non-defective workpiece without a through hole.

[0064] The inspection screen shown in Figure 10 plots inspection indices obtained by inspecting a predetermined number (e.g., 94) of good-quality workpieces without through holes, and illustrates three good-quality ranges C1, C2, and C3 that have been set based on the inspection indices for good-quality workpieces without through holes.

[0065] The non-defective range C1 is a rectangular range set based on the range of the 3σ zone determined based on the inspection indexes of a predetermined number of non-defective workpieces. The horizontal length of the non-defective range C1 is the length of the 3σ zone determined for the inspection index x, and the vertical length of the non-defective range C1 is the length of the 3σ zone determined for the inspection index y.

[0066] The non-defective range C2 is an elliptical range illustrated so as to contact the four sides of the rectangular non-defective range C1. The long axis of the elliptical shape representing the non-defective range C2 is parallel to the x-axis, and the short axis of the elliptical shape is parallel to the y-axis.

[0067] The non-defective range C3 is the range of a probability ellipse determined based on the inspection indexes of a predetermined number of non-defective workpieces. The major axis of the ellipse representing the non-defective range C3 is inclined relative to the x-axis, and the minor axis of the ellipse is inclined relative to the y-axis. The non-defective range C3 shown in Figure 10 is the range of the probability ellipse corresponding to a 99.7% probability that the inspection indexes of non-defective workpieces will be plotted within it.

[0068] The non-defective ranges C1, C2, and C3 set based on the inspection indexes for a predetermined number of non-defective workpieces shown in FIG. 10 will be compared and examined.

[0069] (Regarding the non-defective range C1) All of the predetermined number of plots are inside the non-defective range C1, and there are areas to the left of the upper end and to the right of the lower end of the non-defective range C1 where there are almost no plots. Therefore, if an inspection is performed with the non-defective range C1 set, there is a relatively high possibility that the inspection indicator for a defective product will be erroneously plotted inside the non-defective range C1.

[0070] (Regarding the non-defective range C2) All of the predetermined number of plots are inside the non-defective range C2, and there is an area with almost no plots at the bottom end of the non-defective range CA2. However, the area with almost no plots in the non-defective range C2 is significantly smaller than that in the non-defective range C1. If an inspection is performed with the non-defective range C2 set, the possibility that the inspection indicator for a defective product will be erroneously plotted inside the non-defective range C2 is significantly reduced.

[0071] (Regarding the non-defective range C3) All of the predetermined number of plots are inside the non-defective range C3, and there are areas with almost no plots at the upper and lower ends of the non-defective range C3. However, the areas with almost no plots in the non-defective range C3 are significantly smaller than those in the non-defective ranges C1 and C2, and when inspection is performed with the non-defective range C3 set, the possibility that the inspection indicator for a defective product will be erroneously plotted inside the non-defective range C3 is significantly reduced.

[0072] Figure 10 shows the total number, average value, variance, covariance, major axis, minor axis, and rotation angle of the x and y coordinates obtained based on the inspection index of a non-defective workpiece without through holes, as well as the correlation coefficient between the x and y coordinates. The correlation coefficient between the x and y coordinates for a non-defective workpiece without through holes is 0.748.

[0073] As described above, the inventors of the present invention have discovered that when the correlation coefficient between the x coordinate and the y coordinate is −0.4 or less or 0.4 or more, it is preferable to set the non-defective range as the range of a probability ellipse obtained based on the inspection indexes of a predetermined number of non-defective works.

[0074] For a non-defective workpiece without a through hole, the correlation coefficient between the x coordinate and the y coordinate is 0.748, so the correlation coefficient between the x coordinate and the y coordinate is -0.4 or less or 0.4 or more. Therefore, for a non-defective workpiece without a through hole, it is very effective to set the non-defective range to the range of a probability ellipse obtained based on the inspection indexes of a predetermined number of non-defective workpieces.

[0075] In FIG. 12, inspection indices are plotted for an inspection workpiece having a cylindrical workpiece with a 2 mm through-hole formed therein, with non-defective ranges C1, C2, and C3 set.

[0076] FIG. 12 shows three defective product ranges T1, T2, and T3 that are set based on the inspection index for a defective inspection workpiece in which a 2 mm through hole is formed in a cylindrical workpiece.

[0077] The defective product range T1 is a rectangular range set based on the range of the 3σ zone determined based on the inspection indexes of multiple defective workpieces. The horizontal length of the defective product range T1 is the length of the 3σ zone determined for inspection index x, and the vertical length of the defective product range T1 is the length of the 3σ zone determined for inspection index y.

[0078] The defective product area T2 is an elliptical area shown in contact with the four sides of the rectangular defective product area T1. The major axis of the elliptical shape representing the defective product area T2 is parallel to the x-axis, and the minor axis of the elliptical shape is parallel to the y-axis.

[0079] The defective product range T3 is the range of a probability ellipse determined based on the inspection indicators of multiple defective workpieces. The major axis of the ellipse representing the defective product range T3 is inclined relative to the x-axis, and the minor axis of the ellipse is inclined relative to the y-axis. The defective product range T3 shown in Figure 11 is the range of the probability ellipse corresponding to a 99.7% probability that the inspection indicators of defective workpieces will be plotted within it.

[0080] For the defective product ranges T1, T2, and T3 shown in FIG. 12, all the plots of the inspection indicators for multiple defective workpieces are inside.

[0081] Figure 13 shows the total number, average value, variance, covariance, major axis, minor axis, and rotation angle of the x and y coordinates obtained based on the inspection index of a defective workpiece having a 2 mm through-hole formed in a cylindrical workpiece, as well as the correlation coefficient between the x and y coordinates. The correlation coefficient between the x and y coordinates for the defective workpiece having a 2 mm through-hole formed in a cylindrical workpiece is -0.693.

[0082] 12, the non-defective ranges C1 and C2 without through holes and the defective ranges T1 and T2 of a cylindrical workpiece with a 2 mm through hole partially overlap on the inspection screen. Therefore, if defective workpieces are inspected with the non-defective ranges C1 and C2 without through holes set, there is a possibility that some of the defective workpieces will be mistakenly determined to be non-defective.

[0083] 12, the non-defective range C3 with no through-holes and the defective range T3 for a cylindrical workpiece with a 2 mm through-hole are set so that they do not overlap on the inspection screen. Therefore, when a defective workpiece is inspected with the non-defective range C3 with no through-holes set, it is possible to distinguish the defective workpiece from the non-defective workpiece.

[0084] The method for determining the above-mentioned probability ellipse will now be described.

[0085] First, the variance-covariance matrix, variance, and covariance are calculated from the non-defective product index.

[0086] (variance-covariance matrix)

[0087]

number

[0088] (dispersion)

[0089]

number

[0090]

number

[0091] (covariance)

[0092]

number

[0093] Subsequently, the coordinate axes are transformed by finding the eigenvalues ​​and eigenvectors of the variance-covariance matrix.

[0094] (eigenvalue)

[0095]

number

[0096]

number

[0097] (eigenvector)

[0098]

number

[0099]

number

[0100] (variance-covariance matrix after coordinate axis transformation)

[0101]

number

[0102] (density ellipse)

[0103]

number

[0104] If the probability ellipse is (Equation 13), the probability P and c that the distribution exists outside the ellipse are given by the property that the bivariate probability density function follows a chi-squared distribution with two degrees of freedom. 2 The relationship is as shown in Table 1.

[0105] (Chi-square distribution table)

[0106] [Table 1]

[0107] For example, if we consider an area where the non-defective index is included in the non-defective range with a probability of 99%, then c 2 =9.210.

[0108] From (Equation 14), which is the standard form of an ellipse obtained by transforming (Equation 13),

[0109]

number

[0110] The major axis a and minor axis b of the probability ellipse can be calculated using (Equation 15) and (Equation 16).

[0111]

number

[0112]

number

[0113] The rotation angle θ of the probability ellipse can be calculated from the eigenvector t1 using (Equation 17) and (Equation 18).

[0114]

number

[0115]

number

[0116] From the above, the probability ellipse showing the range of non-defective products is x , O y When the center of gravity is (O x ,O y ), the major axis is (Equation 19), the minor axis is (Equation 20), and the slope is θ.

[0117]

number

[0118]

number

[0119] As described above, the magnetic inspection device 1 of this embodiment is a magnetic inspection device that determines whether a component to be inspected is a non-defective or not based on a change in the current value flowing through the inspection coil when a component that has been confirmed to be a non-defective and that satisfies predetermined conditions is placed in the magnetic field generated around the reference coil and the component to be inspected is placed in the magnetic field generated around the inspection coil, and the magnetic inspection device 1 determines whether the component to be inspected is a non-defective or not based on a change in the current value flowing through the inspection coil. is an inspection index, the system is equipped with a pass-quality range storage unit 51 that stores the pass-quality range on the xy plane where the inspection index should be if the part being inspected is a pass-quality part, an inspection index derivation unit 52 that derives the inspection index for the part being inspected by causing the part being inspected to enter a magnetic field generated around the inspection coil, and a pass-quality determination unit 53 that determines the part being inspected to be a pass-quality part if the inspection index derived by the inspection index derivation unit 52 is within the pass-quality range stored in the pass-quality range storage unit 51, where the pass-quality range stored in the pass-quality range storage unit 51 is an elliptical range set on the xy plane.

[0120] The method for determining whether a component to be inspected is a conforming component by the magnetic inspection device 1 of this embodiment, in which an AC current is passed through the reference coils Ct1, Ct2 and the inspection coils C1, C2, and a component that has been confirmed to be a conforming component that satisfies predetermined conditions is placed in the magnetic field generated around the reference coil. In this state, the component to be inspected is placed in the magnetic field generated around the inspection coil, and based on the change in the current value flowing through the inspection coil, the method determines whether the component to be inspected is a conforming component. The method uses the x-coordinate indicating the real part and the y-coordinate indicating the imaginary part corresponding to the difference between the current value flowing through the reference coils Ct1, Ct2 and the current value flowing through the inspection coils C1, C2 as inspection indices. In this case, the method includes a pass-quality range setting step of setting a pass-quality range on the xy plane where the inspection index should be if the part to be inspected is a pass-quality part; an inspection index derivation step of causing the part to be inspected to enter a magnetic field generated around the inspection coil and deriving an inspection index for the part to be inspected; and a pass-quality determination step of determining that the part to be inspected is a pass-quality part if the inspection index derived in the inspection index derivation step is within the pass-quality range set in the pass-quality range setting step, where the pass-quality range set in the pass-quality range setting step is an elliptical range set on the xy plane.

[0121] This allows the pass-through range, which is set based on the inspection index obtained by inspecting a predetermined number of pass-through workpieces, to include many of the plots of the predetermined number of pass-through workpieces, while minimizing the area within the pass-through range where no plots exist, thereby preventing a defective workpiece from being mistakenly determined to be pass-through based on the inspection index obtained by inspecting the defective workpiece.

[0122] In the magnetic inspection device 1 of this embodiment, the non-defective range stored in the non-defective range storage unit 51 is the range of a probability ellipse on the xy plane.

[0123] In the non-defective product determination method for the magnetic inspection device 1 of this embodiment, the non-defective product range set in the non-defective product range setting step is the range of a probability ellipse on the xy plane.

[0124] This allows the pass-through range, which is set based on the inspection index obtained by inspecting a predetermined number of pass-through workpieces, to include most of the plots of the predetermined number of pass-through workpieces, and to avoid including many areas within the pass-through range where no plots exist, thereby more reliably preventing a defective workpiece from being erroneously determined to be pass-through based on the inspection index obtained by inspecting the defective workpiece.

[0125] In the magnetic inspection device 1 of this embodiment, the correlation coefficient between the x coordinate and the y coordinate, which are the inspection indexes, is −0.4 or less or 0.4 or more.

[0126] In the non-defective product determination method of the magnetic inspection device 1 of this embodiment, the correlation coefficient between the x coordinate and the y coordinate, which is the inspection index, is −0.4 or less or 0.4 or more.

[0127] As a result, when the correlation coefficient between the x-coordinate and y-coordinate, which are the inspection indicators, is below -0.4 or above 0.4, the non-defective range can be set to the range of a probability ellipse on the xy plane, thereby more effectively preventing the defective work from being mistakenly determined to be non-defective.

[0128] Although the embodiment of the present invention has been described above, the configuration of the embodiment is not limited to the above, and various modifications are possible.

[0129] For example, in the above embodiment, the cases of determining whether a workpiece has been properly induction hardened, whether a workpiece has been properly tempered, and whether a workpiece is a good-quality workpiece without through holes have been described, but the present invention is not limited to these. The present invention is applicable to a magnetic inspection device that performs a pass / fail judgment to determine whether a part to be inspected (inspection workpiece) is a good-quality part after teaching using a part (good-quality workpiece) that has been confirmed to be a good-quality part that meets predetermined conditions to set a pass / fail range. In the present invention, the "predetermined conditions" of a "good-quality part that meets predetermined conditions" may be any content.

[0130] In the above embodiment, for example, when the non-defective range A3 is defined as the range of a probability ellipse, the range of the probability ellipse is set to correspond to a 99.7% probability that the inspection index of a non-defective workpiece will be plotted inside it, but this is not limited to this. In the present invention, when the non-defective range is defined as the range of a probability ellipse, the probability that the inspection index of a non-defective workpiece will be plotted inside it may be set arbitrarily.

[0131] Other configurations can also be modified in various ways without departing from the spirit of the present invention. [Explanation of symbols]

[0132] 1. Magnetic inspection device 51 Good product range memory section 52 Inspection index derivation part 53 Good product judgment department C1, C2 Inspection solenoid coil (inspection coil) Ct1, Ct2 Reference solenoid coil (reference coil)

Claims

1. A magnetic inspection device that determines whether a component to be inspected is a non-defective component based on a change in the value of the current flowing through the inspection coil when a component that has been confirmed to be a non-defective component that satisfies predetermined conditions is placed in a magnetic field generated around the reference coil and the component to be inspected is placed in the magnetic field generated around the inspection coil, the device comprising: a non-defective range storage unit that stores a non-defective range on an x-y plane in which the inspection indicator should be located when the component to be inspected is a non-defective product, where the x-coordinate indicates a real part and the y-coordinate indicates an imaginary part corresponding to the difference between the current value flowing through the reference coil and the current value flowing through the inspection coil are used as inspection indicators; an inspection index derivation unit that causes the component to enter a magnetic field generated around the inspection coil and derives an inspection index for the component; a pass / fail determination unit that determines that the part being inspected is a pass / fail product when the inspection index derived by the inspection index derivation unit is within the pass / fail range stored in the pass / fail range storage unit, A magnetic inspection device characterized in that the non-defective range stored in the non-defective range storage unit is an elliptical range set on an xy plane.

2. 2. The magnetic inspection device according to claim 1, wherein the non-defective range stored in the non-defective range storage unit is a range of a probability ellipse on an xy plane.

3. 3. The magnetic inspection device according to claim 1, wherein a correlation coefficient between the x coordinate and the y coordinate, which are the inspection indexes, is equal to or less than −0.4 or equal to or greater than 0.

4.

4. A method for determining whether a component to be inspected is a non-defective component for a magnetic inspection device, in which an AC current is passed through a reference coil and an inspection coil, and a component that has been confirmed to be a non-defective component that satisfies predetermined conditions is placed in a magnetic field generated around the reference coil, and then the component to be inspected is placed in the magnetic field generated around the inspection coil, based on a change in the value of the current flowing through the inspection coil; a non-defective range setting step of setting a non-defective range on an x-y plane within which the inspection indicator should be located when the component to be inspected is a non-defective product, where the x-coordinate indicates a real part and the y-coordinate indicates an imaginary part corresponding to the difference between the current value flowing in the reference coil and the current value flowing in the inspection coil are used as inspection indicators; an inspection index deriving step of deriving an inspection index for the component to be inspected by causing the component to enter a magnetic field generated around the inspection coil; a pass / fail determination step of determining that the part being inspected is a pass / fail product when the inspection index derived in the inspection index derivation step is within the pass / fail range set in the pass / fail range setting step, The method for determining non-defective products for a magnetic inspection device, wherein the non-defective product range set in the non-defective product range setting step is an elliptical range set on an xy plane.

5. 5. The method for determining non-defective products for a magnetic inspection device according to claim 4, wherein the non-defective product range stored in the non-defective product range storage unit is a range of a probability ellipse on an xy plane.

6. 6. The method for determining non-defective products for a magnetic inspection device according to claim 4, wherein a correlation coefficient between the x coordinate and the y coordinate, which are the inspection indexes, is not more than -0.4 or not less than 0.4.

Images