JP2009031112A - Device and method for measuring quenching depth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for measuring quenching depth capable of measuring with improved accuracy quenching depth of the measuring object even when a measuring object or an environmental temperature is varied. <P>SOLUTION: An alternating current exciting signal of a first frequency is applied to a first exciting coil to generate an induced current in an measuring object 102, while a detection signal caused by the induced current is detected by a first detecting coil. An alternating current exciting signal of a second frequency is applied to a second exciting coil to generate an induced current in the measuring object 102, while a detection signal caused by the induced current is detected by a second detecting coil. An Amplitude value Y1 of the detection signal in the first detecting coil, a phase difference X1 between the alternating current exciting signal and the detection signal in the first exciting coil, an amplitude value Y2 of the detection signal in the second detecting coil, and a phase difference Xs between the alternating current exciting signal and the detection signal in the second exciting coil are calculated. A differential value D is calculated based on Y1, X1, Y2 and X2. A quenching depth L of the measuring object 102 is calculated based on the differential value D. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for measuring the depth (quenching depth) of a quenching layer formed on the surface of a part or the like made of a steel material by performing a quenching process.

Conventionally, as a method of measuring the depth of the quenching layer (quenching depth) formed on the surface of a part made of steel material by quenching, one of the parts that have been quenched in the same batch A method is known in which a part is cut and the structure of the cut surface is observed, or the distribution of Vickers hardness in the depth direction on the cut surface is measured.
However, since this method includes (1) a step of cutting a part of a part or the like that can be a product, the measurement object after cutting must be discarded after measurement, which causes a decrease in product yield. (2) The time required for the measurement is long because it is performed through a series of processes such as cutting, processing of the cut surface (polishing, etching, etc.), observation of the cut surface with an electron microscope or the like, or hardness measurement with a Vickers hardness meter, (3) It is impossible to apply to all inspections for the above reasons. (4) There is a limit to the quality assurance of all products by sampling inspection. Depending on the measurement result of the object to be measured, quenching is performed in the same batch. There are various problems such that all of the parts etc. that have been subjected to processing must be handled as defective products, which also causes a decrease in product yield.

  As a method for solving such a problem, the measurement of the quenching depth performed in a non-contact manner using a so-called eddy current sensor has been studied. For example, it is as described in Patent Document 1 and Patent Document 2.

  In the method described in Patent Document 1, an alternating magnetic field is generated by an excitation coil of an eddy current sensor inserted through a measurement object, an eddy current is generated on the surface of the measurement object by the alternating magnetic field, and the eddy current is generated. The magnitude of the induced magnetic field is detected in the form of output voltage by the detection coil of the eddy current sensor inserted in the measurement object, and the relationship between the quenching depth of the known measurement object made of the same kind of material and the output voltage and the detection The depth of the hardened layer is measured by comparing the output voltage of the coil.

In the method described in Patent Document 2, an AC voltage (AC excitation signal) having a plurality of different frequencies is applied to an excitation coil of an eddy current sensor inserted through a measurement object, and an eddy current is applied to the surface of the measurement object by the excitation coil. The magnitude of the induced magnetic field caused by the eddy current is detected as the output voltage (detection signal) of the detection coil of the eddy current sensor inserted through the measurement object, and based on the amplitude ratio between the AC excitation signal and the detection signal While measuring the distribution of the hardness of the measurement object in the depth direction, the quenching depth of the measurement object is measured based on the phase difference of the detection signal with respect to the AC excitation signal.
The method described in Patent Document 2 can simultaneously measure both the distribution in the depth direction of the hardness of the measurement object and the quenching depth in a non-contact manner, and can be applied to 100% inspection.

However, the methods described in Patent Document 1 and Patent Document 2 vary the measurement result of the quenching depth when the temperature at the time of measurement of the measurement object varies due to the variation of the lot of the measurement object or the measurement environment. Therefore, there is a problem that it is difficult to accurately measure the quenching depth.
This is because when the temperature of the measurement object fluctuates, the permeability and conductivity of the measurement object change, and as a result, the amplitude (absolute value) of the output voltage (detection signal) of the detection coil fluctuates.

When the object to be measured is a drive shaft made of a steel material subjected to induction hardening, the environmental temperature of the drive shaft manufacturing plant is about 30 in the daytime in summer (about 35 ° C) and in the early morning in winter (about 5 ° C). There is a temperature fluctuation of ℃, and there is a big temperature fluctuation day and night even on the same day.
In addition, since the drive shaft immediately after induction hardening is higher than the environmental temperature, for example, when a manufacturing factory that has been temporarily suspended resumes operation, normal operation is performed after quenching. When the time required for starting the quenching depth measurement is different, the temperature of the drive shaft at the time of the quenching depth measurement varies.

  As a method of preventing such a decrease in the measurement accuracy of the quenching depth due to temperature fluctuations, (1) the temperature of the measurement object, the measurement apparatus, and the surrounding environment is kept constant by using an air conditioner. Measure the quenching depth, (2) measure the temperature of the measurement object immediately before measuring the quenching depth, and correct the quenching depth measurement result based on the measured temperature, etc. Can be considered.

However, the method (1) has a large equipment cost, and the measurement cannot be performed until the temperature of the measurement object, the measurement apparatus, and the surrounding environment is kept constant (work efficiency is not good). Have
Moreover, since the method of said (2) measures the temperature of a measuring object in addition to the quenching depth measurement, there exists a problem that a man-hour increases. In particular, it is generally difficult to perform temperature measurement in a short time (it is necessary to maintain the measurement temperature until it reaches an equilibrium state), so the time required for measuring the quenching depth per measurement object is long. Therefore, it becomes difficult to apply to 100% inspection in the manufacturing process of the measurement object.
JP 2002-14081 A JP 2004-108873 A

  In view of the circumstances as described above, the present invention provides a quenching depth measuring apparatus and quenching capable of accurately measuring the quenching depth of a measurement object even if the temperature of the measurement object and the surrounding environment fluctuates. A depth measurement method is provided.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

That is, in claim 1,
A first excitation coil that generates an induced current in a measurement object by applying an AC excitation signal of a first frequency;
A first detection coil for detecting a detection signal caused by an induced current generated in the measurement object by the first excitation coil;
A second excitation coil that generates an induced current in the measurement object by applying an AC excitation signal of a second frequency that is higher than the first frequency;
A second detection coil for detecting a detection signal caused by an induced current generated in the measurement object by the second excitation coil;
The amplitude value Y1 of the detection signal of the first detection coil, the phase difference X1 of the AC excitation signal of the first excitation coil and the detection signal of the first detection coil, the amplitude value Y2 of the detection signal of the second detection coil, and A phase difference X2 between the AC excitation signal of the second excitation coil and the detection signal of the second detection coil is calculated, respectively, and Y1, X1, Y2, and X2 are set to the difference value D shown in the following Equation 1 and the Y1, X1. , Y2 and X2 are substituted into a relational expression to calculate the difference value D,
A quenching depth calculation unit that calculates a quenching depth L of the measurement object based on the difference value D calculated by the difference value calculation unit.

In claim 2,
The first excitation coil and the second excitation coil are the same excitation coil,
The first detection coil and the second detection coil are the same detection coil,
An AC excitation signal applying unit capable of selectively applying either the AC excitation signal of the first frequency or the AC excitation signal of the second frequency to the same excitation coil is provided.

In claim 3,
The quenching depth calculation unit
The quenching depth L of the measurement object is calculated by substituting the differential value D calculated by the differential value calculation unit into the relational expression between the quenching depth L and the differential value D shown in the following formula 2. The quenching depth measuring device according to claim 1 or 2.

In claim 4,
The quenching depth L calculated by the quenching depth calculation unit is compared with a preset allowable quenching depth range, and the quenching depth L is within the allowable quenching depth range. In this case, it is determined that the measurement object is a non-defective product with respect to the quenching depth, and when the quenching depth L is not within the allowable quenching depth range, the measurement object is inferior with respect to the quenching depth. A determination unit that determines that the product is non-defective is provided.

In claim 5,
The first frequency and the second frequency are:
It is set by the following procedures (1) to (6).
(1) An AC excitation signal having a plurality of frequencies is applied to a setting excitation coil to generate an induced current in a measurement object for setting, and a detection signal for each frequency caused by the induced current is detected by the setting detection coil. To do.
(2) Based on the detection signal for each frequency detected by the setting detection coil, the amplitude value Y of the detection signal for each frequency and the AC excitation signal applied to the setting excitation coil and the setting detection coil A phase difference X with the detected detection signal is calculated.
(3) For each of a plurality of different frequencies applied to the setting excitation coil, a vector having the amplitude value Y of the corresponding detection signal as the Y axis and the phase difference X between the corresponding AC excitation signal and the detection signal as the X axis ^Is calculated (= (X ² + Y ² ) ^0.5 ).
(4) For all combinations of selecting two frequencies from among a plurality of different frequencies applied to the setting excitation coil, calculate the difference in vector length corresponding to the two selected frequencies, and A difference value D0, which is a value obtained by dividing the vector length difference by the vector length corresponding to the higher one of the vectors corresponding to the two selected frequencies, is calculated.
(5) For each of the selected combinations of two frequencies, the difference value D0 is plotted on the horizontal axis, and the measured value of the quenching depth by the cutting method is plotted on the vertical axis. Find an approximate expression.
(6) Among the obtained linear approximation formulas by the least square method, any one whose absolute value of the correlation coefficient is equal to or greater than a predetermined threshold is adopted as a calibration curve, and two of the adopted calibration curves are used. Of the two frequencies, the lower frequency is the first frequency, and the higher frequency is the second frequency.

In claim 6,
An AC excitation signal having a first frequency is applied to the first excitation coil to generate an induced current in the measurement object, and a detection signal caused by the induced current generated in the measurement object is generated by the first excitation coil. A first excitation / detection process detected by one detection coil;
An AC excitation signal having a second frequency that is higher than the first frequency is applied to a second excitation coil to generate an induced current in the measurement object, and the measurement object is generated by the second excitation coil. A second excitation / detection step of detecting a detection signal caused by the induced current generated in the second detection coil;
The amplitude value Y1 of the detection signal of the first detection coil, the phase difference X1 of the AC excitation signal of the first excitation coil and the detection signal of the first detection coil, the amplitude value Y2 of the detection signal of the second detection coil, and A phase difference X2 between the AC excitation signal of the second excitation coil and the detection signal of the second detection coil is calculated, respectively, and the difference value D shown in Equation 1 and the Y1, X1, Y2 are expressed as Y1, X1, Y2, and X2. And a difference value calculating step of calculating the difference value D by substituting it into the relational expression with X2,
A quenching depth calculating step of calculating a quenching depth L of the measurement object based on the difference value D calculated in the difference value calculating step.

In claim 7,
The first excitation coil and the second excitation coil are the same excitation coil,
The first detection coil and the second detection coil are the same detection coil,
In the first excitation / detection step,
Applying an AC excitation signal of a first frequency to the same excitation coil;
In the second excitation / detection step,
An AC excitation signal having a second frequency is applied to the same excitation coil.

In claim 8,
In the quenching depth calculation step,
By substituting the difference value D calculated in the difference value calculation step into the relational expression between the quenching depth L and the difference value D shown in Equation 2, the quenching depth L of the measurement object is calculated. is there.

In claim 9,
The quenching depth L calculated in the quenching depth calculation step is compared with a preset allowable quenching depth range, and the quenching depth L is within the allowable quenching depth range. In this case, it is determined that the measurement object is a non-defective product with respect to the quenching depth, and when the quenching depth L is not within the allowable quenching depth range, the measurement object is inferior with respect to the quenching depth. A determination step for determining that the product is a non-defective product is provided.

In claim 10,
The first frequency and the second frequency are set by the following procedures (1) to (6).
(1) An AC excitation signal having a plurality of frequencies is applied to a setting excitation coil to generate an induced current in a measurement object for setting, and a detection signal for each frequency caused by the induced current is detected by the setting detection coil. To do.
(2) Based on the detection signal for each frequency detected by the setting detection coil, the amplitude value Y of the detection signal for each frequency and the AC excitation signal applied to the setting excitation coil and the setting detection coil A phase difference X with the detected detection signal is calculated.
(3) For each of a plurality of different frequencies applied to the setting excitation coil, a vector having the amplitude value Y of the corresponding detection signal as the Y axis and the phase difference X between the corresponding AC excitation signal and the detection signal as the X axis ^Is calculated (= (X ² + Y ² ) ^0.5 ).
(4) For all combinations of selecting two frequencies from among a plurality of different frequencies applied to the setting excitation coil, calculate the difference in vector length corresponding to the two selected frequencies, and A difference value D0, which is a value obtained by dividing the vector length difference by the vector length corresponding to the higher one of the vectors corresponding to the two selected frequencies, is calculated.
(5) For each of the selected combinations of two frequencies, the difference value D0 is plotted on the horizontal axis, and the measured value of the quenching depth by the cutting method is plotted on the vertical axis. Find an approximate expression.
(6) Among the obtained linear approximation formulas by the least square method, the one having the largest correlation coefficient is adopted as the calibration curve, and the lower one of the two frequencies related to the adopted calibration curve is the first. The higher frequency is the second frequency.

In claim 11,
A second frequency that is higher than the first frequency and the first frequency, a third frequency and a fourth frequency that is higher than the third frequency, and a fifth frequency and the first frequency An AC excitation signal generator that selectively generates a plurality of AC excitation signals having different frequencies including a sixth frequency that is higher than the fifth frequency;
An excitation coil that generates an induced current in a measurement object by applying an AC excitation signal generated by the AC excitation signal generator;
A detection coil for detecting a detection signal caused by an induced current generated in the measurement object by the excitation coil;
The amplitude value Y1 of the detection signal corresponding to the first frequency, the phase difference X1 of the AC excitation signal corresponding to the first frequency and the detection signal corresponding to the first frequency, and the detection corresponding to the second frequency The signal amplitude value Y2 and the phase difference X2 between the AC excitation signal corresponding to the second frequency and the detection signal corresponding to the second frequency are calculated, and Y1, X1, Y2 and X2 are set to the following equation (3) A difference value calculation unit that calculates the difference value Da by substituting it into the relational expression between the difference value Da shown and the Y1, X1, Y2, and X2.
By substituting the difference value Da calculated by the difference value calculation unit into the relational expression between the quenching depth La and the difference value Da shown in the following equation 4, the quenching depth La of the measurement object is calculated. A first quenching depth calculator,
When the quenching depth La calculated by the first quenching depth calculating unit is less than a preset reference quenching depth Ls, the amplitude value Y3 of the detection signal corresponding to the third frequency. , Corresponding to the AC excitation signal corresponding to the third frequency and the phase difference X3 of the detection signal corresponding to the third frequency, the amplitude value Y4 of the detection signal corresponding to the fourth frequency, and the fourth frequency. The phase difference X4 between the AC excitation signal and the detection signal corresponding to the fourth frequency is calculated, and Y3, X3, Y4 and X4 are expressed by the difference value Db shown in the following equation 5 and the Y3, X3, Y4 and X4. The difference value Db is calculated by substituting it into a relational expression, and the quenching depth is calculated by substituting the calculated difference value Db into the relational expression between the quenching depth Lb and the difference value Db shown in Equation 6 below. Lb is calculated and When the quenching depth Lb is set as the quenching depth of the measurement object, and the quenching depth La calculated by the first quenching depth calculating unit is equal to or greater than the reference quenching depth Ls , Corresponding to the amplitude value Y5 of the detection signal corresponding to the fifth frequency, the phase difference X5 of the AC excitation signal corresponding to the fifth frequency and the detection signal corresponding to the fifth frequency, and the sixth frequency. An amplitude value Y6 of the detection signal, an AC excitation signal corresponding to the sixth frequency, and a phase difference X6 of the detection signal corresponding to the sixth frequency are calculated, and Y5, X5, Y6, and X6 are set to the following equation (7). The difference value Dc is calculated by substituting the calculated difference value Dc into the relational expression between the difference value Dc and the Y5, X5, Y6, and X6. With value Dc A second hardening depth calculating unit that calculates the hardening depth Lc, to the hardening depth Lc and hardening depth of the measurement object by substituting the engagement type,
It comprises.

In claim 12,
The quenching depth of the measurement object calculated by the second quenching depth calculation unit is compared with a preset allowable quenching depth range, and the quenching depth of the measurement object is compared with the allowable quenching depth. If it is within the quenching depth range, it is determined that the measurement object is a non-defective product with respect to the quenching depth, and the quenching depth of the measurement object is not within the allowable quenching depth range. The measurement object includes a determination unit that determines that the quenching depth is defective.

In claim 13,
The first frequency, second frequency, third frequency, fourth frequency, fifth frequency and sixth frequency are:
It is set by the following procedures (a) to (h).
(A) An AC excitation signal having a plurality of frequencies is applied to the setting excitation coil to generate an induced current in the measurement object for setting, and a detection signal for each frequency caused by the induced current is detected by the setting detection coil. To do.
(B) Based on the detection signal for each frequency detected by the setting detection coil, the amplitude value Y of the detection signal for each frequency and the AC excitation signal applied to the setting excitation coil and the setting detection coil A phase difference X with the detected detection signal is calculated.
(C) For each of a plurality of different frequencies applied to the setting excitation coil, a vector with the amplitude value Y of the corresponding detection signal as the Y axis and the phase difference X between the corresponding AC excitation signal and the detection signal as the X axis ^Is calculated (= (X ² + Y ² ) ^0.5 ).
(D) For all combinations of selecting two frequencies from among a plurality of different frequencies applied to the setting excitation coil, calculate the difference in vector length corresponding to the two selected frequencies; A difference value D0, which is a value obtained by dividing the vector length difference by the vector length corresponding to the higher one of the vectors corresponding to the two selected frequencies, is calculated.
(E) The difference value D0 is plotted with respect to each of the selected two frequency combinations on the horizontal axis, and the measured value of the quenching depth by the cutting method is plotted on the vertical axis. Find an approximate expression.
(F) Among the obtained linear approximation formulas by the least square method, those whose absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value and which meet the quenching depth standard range As a calibration curve, the lower frequency of the two frequencies related to the adopted first calibration curve is the first frequency, and the higher frequency is the second frequency.
(G) Among the obtained linear approximation equations by the least square method, the absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value, and the penetration depths of the corresponding two frequency combinations are both What fits the surface side range which is the range closer to the surface of the measuring object for setting among the ranges obtained by dividing the standard range of the quenching depth into two with the reference quenching depth Ls as a boundary Adopted as the second calibration curve, of the two frequencies related to the adopted second calibration curve, the lower frequency is the third frequency and the higher frequency is the fourth frequency.
(H) Among the obtained linear approximation formulas by the least square method, the absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value, and the penetration depths of the corresponding two frequency combinations are both Among the ranges obtained by dividing the standard range of the quenching depth into two with the reference quenching depth Ls as a boundary, those that conform to the bulk-side range that is the range farther from the surface of the measurement object for setting Adopted as a third calibration curve, of the two frequencies related to the adopted third calibration curve, the lower frequency is the fifth frequency and the higher frequency is the sixth frequency.

In claim 14,
Among the plots with the difference value D0 as the horizontal axis and the measurement value of the quenching depth by the cutting method as the vertical axis, a cubic approximate expression by the least square method is obtained for the one relating to the first calibration curve, and the minimum The measured value of the quenching depth by the cutting method corresponding to the inflection point of the cubic approximate expression by the square method is the reference quenching depth Ls.

In claim 15,
A first frequency and a second frequency that is higher than the first frequency, a third frequency and a fourth frequency that is higher than the third frequency, and a fifth frequency and the first frequency. A plurality of different frequency alternating current excitation signals including a sixth frequency that is higher than the fifth frequency are applied to the excitation coil to generate an induced current in the measurement object, and the excitation coil causes the measurement object to An excitation / detection process for detecting a detection signal caused by the induced current generated by the detection coil;
The amplitude value Y1 of the detection signal corresponding to the first frequency, the phase difference X1 of the AC excitation signal corresponding to the first frequency and the detection signal corresponding to the first frequency, and the detection corresponding to the second frequency A phase difference X2 between the amplitude value Y2 of the signal and the AC excitation signal corresponding to the second frequency and the detection signal corresponding to the second frequency is calculated, and the Y1, X1, Y2 and X2 are the differences expressed by Equation 3. A difference value calculating step of calculating the difference value Da by substituting it into a relational expression of the value Da and the Y1, X1, Y2 and X2,
First, the quenching depth La of the measurement object is calculated by substituting the difference value Da calculated in the difference value calculating step into the relational expression between the quenching depth La and the difference value Da shown in Formula 4. Quenching depth calculation step,
When the quenching depth La calculated in the first quenching depth calculating step is less than the preset reference quenching depth Ls, the amplitude value Y3 of the detection signal corresponding to the third frequency. , Corresponding to the AC excitation signal corresponding to the third frequency and the phase difference X3 of the detection signal corresponding to the third frequency, the amplitude value Y4 of the detection signal corresponding to the fourth frequency, and the fourth frequency. The phase difference X4 of the AC excitation signal and the detection signal corresponding to the fourth frequency is calculated, and the relational expression between the difference value Db shown in Equation 5 and the Y3, X3, Y4 and X4 for the Y3, X3, Y4 and X4 The difference value Db is calculated by substituting into, and the quenching depth Lb is calculated by substituting the calculated difference value Db into the relational expression between the quenching depth Lb and the difference value Db shown in Equation 6. The quenching When the depth Lb is the quenching depth of the measurement object and the quenching depth La calculated in the first quenching depth calculation step is equal to or greater than the reference quenching depth Ls, The amplitude value Y5 of the detection signal corresponding to the fifth frequency, the phase difference X5 of the AC excitation signal corresponding to the fifth frequency and the detection signal corresponding to the fifth frequency, and the detection signal corresponding to the sixth frequency And the phase difference X6 between the AC excitation signal corresponding to the sixth frequency and the detection signal corresponding to the sixth frequency are calculated, and Y5, X5, Y6 and X6 are calculated as a difference value Dc shown in Equation 7. And the difference value Dc is calculated by substituting it into the relational expression between Y5, X5, Y6 and X6, and the calculated difference value Dc is the relational expression between the quenching depth Lc and the difference value Dc shown in Formula 8. Assign to In which calculating the hardening depth Lc, comprising a second hardening depth calculation step of the hardening depth Lc and hardening depth of the measurement object, the by a.

In claim 16,
The quenching depth of the measurement object calculated in the second quenching depth calculation step is compared with a preset allowable quenching depth range, and the quenching depth of the measurement object is compared with the allowable quenching depth. If it is within the quenching depth range, it is determined that the measurement object is a non-defective product with respect to the quenching depth, and the quenching depth of the measurement object is not within the allowable quenching depth range. A determination step of determining that the measurement object is defective with respect to the quenching depth is provided.

In claim 17,
The first frequency, the second frequency, the third frequency, the fourth frequency, the fifth frequency, and the sixth frequency are set by the following procedures (a) to (h). is there.
(A) An AC excitation signal having a plurality of frequencies is applied to the setting excitation coil to generate an induced current in the measurement object for setting, and a detection signal for each frequency caused by the induced current is detected by the setting detection coil. To do.
(B) Based on the detection signal for each frequency detected by the setting detection coil, the amplitude value Y of the detection signal for each frequency and the AC excitation signal applied to the setting excitation coil and the setting detection coil A phase difference X with the detected detection signal is calculated.
(C) For each of a plurality of different frequencies applied to the setting excitation coil, a vector with the amplitude value Y of the corresponding detection signal as the Y axis and the phase difference X between the corresponding AC excitation signal and the detection signal as the X axis ^Is calculated (= (X ² + Y ² ) ^0.5 ).
(D) For all combinations of selecting two frequencies from among a plurality of different frequencies applied to the setting excitation coil, calculate the difference in vector length corresponding to the two selected frequencies; A difference value D0, which is a value obtained by dividing the vector length difference by the vector length corresponding to the higher one of the vectors corresponding to the two selected frequencies, is calculated.
(E) The difference value D0 is plotted with respect to each of the selected two frequency combinations on the horizontal axis, and the measured value of the quenching depth by the cutting method is plotted on the vertical axis. Find an approximate expression.
(F) Among the obtained linear approximation formulas by the least square method, those whose absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value and which meet the quenching depth standard range As a calibration curve, the lower frequency of the two frequencies related to the adopted first calibration curve is the first frequency, and the higher frequency is the second frequency.
(G) Among the obtained linear approximation equations by the least square method, the absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value, and the penetration depths of the corresponding two frequency combinations are both What fits the surface side range which is the range closer to the surface of the measuring object for setting among the ranges obtained by dividing the standard range of the quenching depth into two with the reference quenching depth Ls as a boundary Adopted as the second calibration curve, of the two frequencies related to the adopted second calibration curve, the lower frequency is the third frequency and the higher frequency is the fourth frequency.
(H) Among the obtained linear approximation formulas by the least square method, the absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value, and the penetration depths of the corresponding two frequency combinations are both Among the ranges obtained by dividing the standard range of the quenching depth into two with the reference quenching depth Ls as a boundary, those that conform to the bulk-side range that is the range farther from the surface of the measurement object for setting Adopted as a third calibration curve, of the two frequencies related to the adopted third calibration curve, the lower frequency is the fifth frequency and the higher frequency is the sixth frequency.

In claim 18,
Among the plots with the difference value D0 as the horizontal axis and the measurement value of the quenching depth by the cutting method as the vertical axis, a cubic approximate expression by the least square method is obtained for the one relating to the first calibration curve, and the minimum The measured value of the quenching depth by the cutting method corresponding to the inflection point of the cubic approximate expression by the square method is the reference quenching depth Ls.

  The present invention has an effect that the quenching depth of the measurement object can be accurately measured even if the temperature of the measurement object or the surrounding environment fluctuates.

  Below, the apparatus structure of the quenching depth measuring apparatus 100 which is a 1st Example of the quenching depth measuring apparatus which concerns on this invention using FIG. 1 is demonstrated.

The quenching depth measuring device 100 measures the quenching depth of the measurement object 102 and mainly includes an excitation unit 110, a detection unit 120, a control device 130, and the like.
Here, the “quenching depth” is the “effective hardened layer depth” (carbon concentration) shown in “Industrial Flame Hardened and Induction Hardened Hardened Layer Depth Measurement Method (JIS G 0559)”. Is 0.45 wt% steel, the depth corresponding to the Vickers hardness is 450 Hv), but the quenching depth according to the present invention is not limited to this. And the total hardened layer depth (physical property (hardness) or chemical property from the surface of the hardened layer to the base material (matrix)) or chemical properties (JIS G 0559) The depth to the position where the difference in macro structure) cannot be distinguished ”)” or may be determined by other methods.

The measurement object 102 is made of a metal material such as a steel material, and is a part that has been previously quenched.
The measurement object 102 of the present embodiment is a drive shaft used in a driving force transmission mechanism of an automobile, and is obtained by subjecting S45C (carbon concentration: about 0.45 wt%), which is a carbon steel for machine structure, to induction hardening. However, the shape (type of component, etc.) and material of the measurement object according to the present invention are not limited to this, and widely include components made of a metal material (mainly steel material) that can be quenched.

The excitation unit 110 generates an induced current in the measurement object 102 (more precisely, on the surface and inside of the measurement object 102) by applying an alternating magnetic field to the measurement object 102.
The exciting unit 110 includes an exciting coil 111, an AC power source 112, and the like.

The exciting coil 111 is an embodiment of the first exciting coil according to the present invention and an embodiment of the second exciting coil according to the present invention. That is, the exciting coil 111 has both the function as the first exciting coil according to the present invention and the function as the second exciting coil according to the present invention.
The excitation coil 111 is a coil made of a conductor, and is measured by applying an AC excitation signal having a plurality of different frequencies (in the case of this embodiment, the frequency fn (n: integer from 1 to 8) shown in FIG. 2). An induced current (eddy current) corresponding to each frequency is generated in the object 102.
Here, “applying an AC excitation signal” refers to applying an AC voltage having a predetermined frequency and having a predetermined frequency to the excitation coil.
Terminals 111a and 111b are formed at both ends of the exciting coil 111, respectively.

  In this embodiment, as shown in FIG. 1, the AC excitation signal is applied to the excitation coil 111 with the measurement object 102 inserted in the excitation coil 111. However, the quenching depth measuring apparatus according to the present invention is configured as follows. However, the present invention is not limited to this. For example, an AC excitation signal may be applied to the excitation coil in a state in which the excitation coil is arranged at a position separated by a predetermined distance from the plate surface of the flat measurement object.

The AC power source 112 applies an AC excitation signal (AC voltage) to the excitation coil 111 by generating an AC voltage having a predetermined frequency and a predetermined amplitude. The AC power source 112 is connected to the terminals 111 a and 111 b of the exciting coil 111.
Further, the AC power source 112 can change the frequency of the AC voltage in the range of 30 Hz to 30 kHz, and the AC excitation of eight types of frequencies f1 to f8 (see FIG. 2) that falls within the range of 30 Hz to 30 kHz. A signal (AC voltage) can be selectively applied to the exciting coil 111.
The frequency range of the AC excitation signal applied to the excitation coil of the quenching depth measuring apparatus 100 of the present embodiment is 30 Hz or more and 30 kHz or less, but the present invention is not limited to this, and the frequency of the AC excitation signal is not limited thereto. This range can be appropriately selected according to the material, size, shape, etc. of the measurement object.

The detection unit 120 detects an induced voltage (detection signal) caused by an induced current generated in the measurement object 102 (more strictly, the surface and inside of the measurement object 102).
The detection unit 120 mainly includes a detection coil 121, a voltmeter 122, and the like.

The detection coil 121 is an embodiment of the first detection coil according to the present invention and an embodiment of the second detection coil according to the present invention. That is, the detection coil 121 has both the function as the first detection coil according to the present invention and the function as the second detection coil according to the present invention.
The detection coil 121 is a coil inserted through the measurement object 102 and detects a detection signal caused by an induced current generated in the measurement object 102 (more strictly, the surface and the inside of the measurement object 102). is there.
Terminals 121a and 121b are formed at both ends of the detection coil 121, respectively.
The detection coil 121 and the excitation coil 111 are arranged so that the central axes of both are substantially straight.

  In the present embodiment, as shown in FIG. 1, the detection signal is detected in a state where the measurement object 102 is inserted into the detection coil 121, but the quenching depth measuring apparatus according to the present invention is not limited to this. For example, the detection signal may be detected in a state where the detection coil is disposed at a position separated from the plate surface of the flat measurement object by a predetermined distance.

  The voltmeter 122 is connected to the terminals 121a and 121b, and converts a detection signal (inductive voltage) detected by the detection coil 121 into a predetermined digital signal.

  In this embodiment, the excitation coil 111 that is the same excitation coil that also serves as the first excitation coil and the second excitation coil and the detection coil 121 that is the same detection coil that also serves as the first detection coil and the second detection coil are provided in the same housing. The body 105, the case 105, the excitation coil 111, and the detection coil 121 are combined to form an “eddy current sensor”. However, the present invention is not limited to this, and the first excitation coil, the first detection The coil, the second excitation coil, and the second detection coil may be housed in separate housings.

The control device 130 controls the operation of the quenching depth measurement device 100 and calculates the quenching depth of the measurement object 102 based on the detection signal from the detection unit 120 (acquires the quenching depth measurement result). To do).
The control device 130 mainly includes a control unit 131, an input unit 132, a display unit 133, and the like.

  The control unit 131 can store various programs such as a frequency change program, a difference value calculation program, a quenching depth calculation program, and a determination program, which will be described later, and can develop these programs. A predetermined calculation can be performed according to a program or the like, and the result of the calculation can be stored.

The control unit 131 may actually have a configuration in which CPUs, ROMs, RAMs, HDDs, and the like are connected to each other via a bus, or may be configured by a one-chip LSI or the like.
Although the control unit 131 of this embodiment is a dedicated product, it can also be achieved by storing the above program in a commercially available personal computer or workstation.

The control unit 131 is connected to the AC power source 112, and can change the frequency and amplitude of the AC excitation signal of the AC power source 112 by transmitting a predetermined control signal to the AC power source 112.
Further, the control unit 131 is connected to the voltmeter 122 and can acquire “a detection signal (inductive voltage) detected by the detection coil 121 and further converted into a predetermined digital signal by the voltmeter 122”. .
The operation control of the quenching depth measuring apparatus 100 by the control unit 131 and the calculation of the quenching depth of the measurement object 102 based on the detection signal from the detection unit 120 will be described in detail later.

The input unit 132 is connected to the control unit 131, and inputs various information / instructions related to the measurement of the quenching depth by the quenching depth measuring apparatus 100 to the control unit 131.
Although the input unit 132 of the present embodiment is a dedicated product, the same effect can be achieved by using, for example, a commercially available keyboard, mouse, pointing device, button, switch, or the like.

The display unit 133 displays, for example, the input contents from the input unit 132 to the control unit 131, the operation status of the quenching depth measuring apparatus 100, the measurement result of the quenching depth of the measurement object 102, and the like.
The display unit 133 of the present embodiment is a dedicated product, but the same effect can be achieved by using, for example, a commercially available liquid crystal display (LCD), CRT display (Cathode Ray Tube Display), or the like. is there.

  In this embodiment, the input unit 132 and the display unit 133 are separated from each other. However, the present invention is not limited to this, and a configuration that combines a function of inputting information and a function of displaying information, such as a touch panel ( A configuration in which the input unit and the display unit are integrated may be used.

  Hereinafter, the measurement principle of the quenching depth measuring apparatus 100 will be described with reference to FIGS. 2 to 4.

FIG. 2 is a schematic diagram showing the relationship between the crystal structure (layer), hardness and magnetic permeability of the measurement object 102 that has been subjected to quenching treatment, and the distance (depth) from the surface of the measurement object 102.
As shown in FIG. 2, the crystal structure of the measurement object 102 is composed of three layers of a hardened layer 1, a boundary layer 2, and a mother layer 3 in order from the surface.

The hardened layer 1 is a layer formed in the vicinity of the surface of the measurement object 102, and is a portion having the highest cooling rate during the quenching process.
The main crystal structure of the hardened layer 1 is martensite.

The boundary layer 2 is a layer formed at a portion having a larger distance from the surface than the cured layer 1 and a cooling rate during the quenching process smaller than that of the cured layer 1.
In this embodiment, S45C, which is a material constituting the measurement object 102, is classified as medium carbon steel (carbon concentration is about 0.45 wt%), and the main crystal structure of the boundary layer 2 is troostite (troostite). ) And sorbite, a fine pearlite, a heat-affected layer, and the like.
In addition, the crystal structure which comprises a boundary layer changes with compositions of the material which comprises a measuring object, and is not limited to a present Example.
Other examples of the crystal structure that can form the boundary layer include upper bainite and lower bainite.

The mother layer 3 is a layer that is formed in a portion having a larger distance from the surface than the boundary layer 2 and a cooling rate during the quenching process smaller than that of the boundary layer 2.
In this example, S45C, which is a material constituting the measurement object 102, is classified as medium carbon steel, and the main crystal structure of the mother layer 3 is a mixed structure of pearlite and ferrite. .
In addition, the crystal structure which comprises a mother layer changes with compositions of the material which comprises a measuring object, and is not limited to a present Example.
Other examples of the crystal structure that can form the mother layer include a pearlite structure, a mixed structure of ferrite and cementite, and the like.

  As shown in FIG. 2, the hardness (Vickers hardness) of the measuring object 102 is closely related to the crystal structure.

The martensite constituting the hardened layer 1 generally has high hardness because of its small crystal grain size and high dislocation density. However, the hardness of the hardened layer 1 generally hardly changes even if the distance from the surface changes. The hardness of the hardened layer 1 of this embodiment is about 600 to 700 (Hv) in terms of Vickers hardness.
Since the fine pearlite and the heat-affected layer constituting the boundary layer 2 generally have a larger crystal grain size and a lower dislocation density than the martensite constituting the hardened layer 1, the hardness is relatively low.
Further, the hardness of the boundary layer 2 decreases as the distance from the surface increases (becomes deeper).
The mixed structure of pearlite and ferrite composing the mother layer 3 generally has a larger crystal grain size than the fine pearlite and heat-affected layer composing the boundary layer 2, so that the hardness is relatively low. However, the hardness of the mother layer 3 generally hardly changes even if the distance from the surface changes. The hardness of the mother layer 3 in this embodiment is about 300 (Hv) in terms of Vickers hardness.

  As shown in FIG. 2, the permeability of the measurement object 102 is closely related to the crystal structure. This is because, in general, the permeability of the measurement object 102 tends to decrease when the crystal grain size of the measurement object 102 decreases, and the hardness of steel materials tends to increase as the crystal grain diameter decreases. It is. Therefore, the permeability and hardness of the measurement object 102 are in a substantially inverse relationship.

The magnetic permeability of the hardened layer 1 is low and generally hardly changes even if the distance from the surface changes.
The magnetic permeability of the boundary layer 2 is relatively larger than that of the hardened layer 1, and increases as the distance from the surface increases (becomes deeper).
The permeability of the mother layer 3 is relatively larger than that of the hardened layer 1 and the boundary layer 2, and generally hardly changes even if the distance from the surface changes.

As shown in FIG. 3, with the measurement object 102 inserted into the excitation coil 111 and the detection coil 121, an AC excitation signal having a frequency fn (n: an integer from 1 to 8) (see FIG. 2) is applied to the excitation coil 111. When applied to, a magnetic field is generated around the excitation coil 111, and an induced current (eddy current) is generated on the surface and inside of the measurement object 102 (particularly, the portion surrounded by the excitation coil 111).
Then, when the magnetic flux generated by the induced current penetrates the detection coil 121, a detection signal (induction voltage) is generated in the detection coil 121.
Further, due to the skin effect, the induced current (eddy current) concentrates on the surface of the measurement object 102 as the frequency fn (n: an integer from 1 to 8) of the AC excitation signal applied to the excitation coil 111 increases. The penetration depth δ of current (eddy current) tends to be small (δ = (π × fn × μ × σ) ^−0.5 ; μ is magnetic permeability and σ is conductivity).
That is, it is possible to change the penetration depth δ of the induced current (eddy current) by changing the frequency fn of the AC excitation signal. Note that the penetration depth δ of the induced current (eddy current) corresponds to the depth from the surface of the measurement object.
Further, the phase difference X between the AC excitation signal and the detection signal has a tendency to be proportional to the depth d from the surface and inversely proportional to the penetration depth δ (X = d / δ).

As shown in FIG. 4, the detection signal has a predetermined amplitude value Y and a predetermined phase difference X with respect to the AC excitation signal.
The permeability of the measurement object 102 is correlated with (1) the amplitude value Y of the detection signal and (2) the phase difference X of the detection signal with respect to the AC excitation signal.
Therefore, detecting the detection signal corresponding to the frequency while appropriately changing the frequency fn of the AC excitation signal, and obtaining the amplitude value Y and the phase difference X of the detection signal is the depth from the surface of the measurement object 102. Corresponds to obtaining the permeability of the portion corresponding to the penetration depth of the AC excitation signal of frequency fn.

  In this way, by calculating the relationship between the frequency (and hence the penetration depth) of the AC excitation signal of the measurement object 102 and the amplitude value Y and the phase difference X of the detection signal corresponding to the frequency, the measurement object 102 is baked. It is possible to determine the insertion depth in a non-contact (non-destructive) manner.

Below, the detail of a structure of the control part 131 is demonstrated.
Functionally, the control unit 131 includes a storage unit 131a, a frequency change unit 131b, a difference value calculation unit 131c, a quenching depth calculation unit 131d, a determination unit 131e, and the like.

The storage unit 131a stores various parameters (numerical values) used in performing control, calculation, and the like by the control unit 131, a history of operation conditions, calculation results (calculation results), and the like.
The storage unit 131a is essentially a storage medium such as an HDD (Hard Disk Drive), a CD-ROM, a DVD-ROM or the like.

The frequency changing unit 131b changes the frequency of an AC voltage having a predetermined amplitude generated by the AC power source 112, and thus the frequency of an AC excitation signal (AC voltage) applied to the excitation coil 111.
Substantially, the control unit 131 performs a predetermined calculation or the like according to the frequency change program stored in the control unit 131, thereby functioning as the frequency change unit 131b.

The frequency changing unit 131b transmits a control signal to the AC power source 112.
The control signal transmitted from the frequency changing unit 131b to the AC power source 112 is a signal that indicates the frequency of the AC voltage to be generated by the AC power source 112 (in this embodiment, any one of f1 to f8). The frequency of the alternating voltage generated based on the control signal is changed (adjusted).
In the case of the present embodiment, the frequency changing unit 131b transmits to the AC power source 112 a control signal instructing to sequentially generate AC voltages having different frequencies f1 to f8 in about 1 second. The AC excitation signals of eight frequencies f1 to f8 including the “first frequency” and the “second frequency” are applied to 111 in about 1 second.

In the case of the present embodiment, an AC excitation signal having eight different frequencies is applied to the excitation coil 111 in about 1 second (the frequency changing period is about 0.125 seconds). Is not limited to this, and the number of frequencies and the period for changing the frequencies can be appropriately selected according to the properties of the measurement object.
It should be noted that it is desirable to shorten the period for changing the frequency of the AC excitation signal as much as possible within the range in which the detection signal can be detected. This is because if the frequency changing period is long, the temperature of the object to be measured fluctuates during that period, and the measurement accuracy may be reduced.
A setting method of “first frequency” and “second frequency” will be described later.

  The combination of the frequency changing unit 131b and the AC power source 112 selectively applies either the first frequency AC excitation signal or the second frequency AC excitation signal to the excitation coil 111. This corresponds to an embodiment of the AC excitation signal applying unit according to FIG.

The difference value calculation unit 131c is an embodiment of the difference value calculation unit according to the present invention, and the amplitude value Y1 of the detection signal of the detection coil 121 corresponding to the first frequency and the excitation coil 111 corresponding to the first frequency. Phase difference X1 of the detection signal of the detection coil 121 corresponding to the first frequency, the amplitude value Y2 of the detection signal of the detection coil 121 corresponding to the second frequency, and the excitation corresponding to the second frequency The difference value D is calculated based on the AC excitation signal of the coil 111 and the phase difference X2 of the detection signal of the detection coil 121 corresponding to the second frequency.
Substantially, the control unit 131 performs a predetermined calculation or the like according to the difference value calculation program stored in the control unit 131, thereby serving as the difference value calculation unit 131c.

Based on the detection signal acquired from the detection coil 121, the difference value calculation unit 131c determines the amplitude value Y1 of the detection signal of the detection coil 121 corresponding to the first frequency and the AC excitation of the excitation coil 111 corresponding to the first frequency. The phase difference X1 of the detection signal of the detection coil 121 corresponding to the signal and the first frequency, the amplitude value Y2 of the detection signal of the detection coil 121 corresponding to the second frequency, and the excitation coil 111 corresponding to the second frequency A phase difference X2 of the detection signal of the detection coil 121 corresponding to the AC excitation signal and the second frequency is calculated. The calculated Y1, X1, Y2, and X2 are appropriately stored in the storage unit 131a.
Next, the difference value calculation unit 131c substitutes the calculated Y1, X1, Y2, and X2 into the relational expression between the difference value D shown in the following Equation 1 and the Y1, X1, Y2, and X2 to obtain the difference. The value D is calculated. The calculated difference value D is appropriately stored in the storage unit 131a.

The difference value D shown in Equation 1 is the length of the vector (X1, Y1) relating to the first frequency with the amplitude value of the detection signal as the Y axis and the phase difference between the AC excitation signal and the detection signal as the X axis ((X1 ² + Y1 ² ) ^0.5 ) minus the length ((X2 ² + Y2 ² ) ^0.5 ) of the vector (X2, Y2) related to the second frequency, and further to the vector related to the second frequency It is the value divided by the length.

The vector related to the first frequency reflects the influence of the crystal structure from the surface of the measurement object 102 to the penetration depth corresponding to the first frequency and the temperature of the crystal structure.
The vector related to the second frequency reflects the influence of the crystal structure from the surface of the measurement object 102 to the penetration depth corresponding to the second frequency and the temperature of the crystal structure.
Further, since the first frequency is lower than the second frequency, the penetration depth of the induced current generated in the measurement object 102 by the AC excitation signal of the first frequency is measured by the AC excitation signal of the second frequency. The penetration depth of the induced current generated in the object 102 is larger (deep).
Therefore, by subtracting the length of the vector related to the second frequency from the length of the vector related to the first frequency, information included in common to the vector related to the first frequency and the vector related to the second frequency It is possible to cancel the information of the shallow portion from the surface of the measurement object 102 and to emphasize the information of the portion near the quenching depth, which is information closely related to the measurement of the quenching depth.
In particular, since the temperature of the measurement object 102 fluctuates due to heat conduction between the surface of the measurement object 102 and the surrounding atmosphere, a portion (surface) that is shallower than the surface (bulk) deeper than the surface of the measurement object 102. The temperature fluctuation tends to be larger in the vicinity), and the shallower part (near the surface) of the surface of the measurement object 102 contributes to the decrease in measurement accuracy due to the temperature fluctuation.
Therefore, canceling out information on a shallow portion from the surface of the measurement object 102, which is information common to the vector related to the first frequency and the vector related to the second frequency, is caused by quenching due to temperature variation of the measurement object 102. Greatly effective in suppressing a decrease in depth measurement accuracy.
In addition, by subtracting the length of the vector related to the second frequency from the vector related to the first frequency and further dividing by the length of the vector related to the second frequency, It is possible to further suppress the influence of temperature fluctuations on “information in the vicinity”.

The quenching depth calculation unit 131d is an embodiment of the quenching depth calculation unit according to the present invention, and the quenching depth of the measurement object 102 based on the difference value D calculated by the difference value calculation unit 131c. L is calculated.
Substantially, the control unit 131 performs a predetermined calculation or the like according to a quenching depth calculation program stored in the control unit 131, thereby functioning as a quenching depth calculation unit 131d.

  The storage unit 131a stores “a relational expression between the quenching depth L and the difference value D” (more precisely, a constant A and a constant B) represented by the following formula 2, and a quenching depth calculation unit: 131d calculates the quenching depth L by substituting the difference value D calculated by the difference value calculation unit 131c into the “relational expression between the quenching depth L and the difference value D”. The calculated quenching depth L is appropriately stored in the storage unit 131a.

The constant A and the constant B in Equation 2 are obtained by conducting an experiment using a reference measurement object in advance.
That is, as shown in FIG. 5, the calculated value of the difference value D in the reference measurement object is set on the horizontal axis, and the measured value of the quenching depth by the cutting method (Vickers hardness measurement or structural observation of the cut surface) is set on the vertical axis. Plot experimental data.
The slope of the straight line obtained by the least square method based on the experimental data is a constant A, and the intercept between the straight line and the vertical axis is a constant B.
Here, the “reference measurement object” is a part, etc., that has the same material, the same shape, and the same heat treatment as the measurement object.

The determination unit 131e is an embodiment of the determination unit according to the present invention, and compares the quenching depth L calculated by the quenching depth calculation unit 131d with a preset allowable quenching depth range, When the quenching depth L is within the allowable quenching depth range, it is determined that the measurement object 102 is a non-defective product with respect to the quenching depth, and the quenching depth L is within the allowable quenching depth range. When there is not, it is determined that the measuring object 102 is defective with respect to the quenching depth.
Substantially, the control unit 131 functions as the determination unit 131e by performing a predetermined calculation or the like according to a determination program stored in the control unit 131.

The “allowable quenching depth range” refers to a range that is acceptable as the quenching depth of the measurement object.
“The quenching depth is within the allowable quenching depth range” means that the quenching depth is not less than the lower limit value of the allowable quenching depth range and not more than the upper limit value of the allowable quenching depth range. Point to.
“The quenching depth is not within the allowable quenching depth range” means that the quenching depth is smaller than the lower limit value of the allowable quenching depth range or larger than the upper limit value of the allowable quenching depth range. Point to.

In the case of the present embodiment, the lower limit value and the upper limit value of the allowable quenching depth range of the measurement object 102 are stored in advance in the storage unit 131a, and the determination unit 131e performs the quenching calculated by the quenching depth calculation unit 131d. The depth L is compared with the lower limit value and the upper limit value of the allowable quenching depth range stored in the storage unit 131a.
As a result of the comparison, when the quenching depth L is within the allowable quenching depth range, the determination unit 131e determines that the measurement object 102 is a non-defective product with respect to the quenching depth.
As a result of the comparison, when the quenching depth L is not within the allowable quenching depth range, the determination unit 131e determines that the measurement object 102 is defective with respect to the quenching depth. The determination result of the measurement object 102 by the determination unit 131e is appropriately stored in the storage unit 131a.

In the following, a setting method of “first frequency” and “second frequency” will be described.
The “first frequency” and the “second frequency” are set by the following procedures (1) to (6).

(1) First, an AC excitation signal having a plurality of frequencies is applied to a setting excitation coil to generate an induced current in the measurement object for setting, and a detection signal for each frequency caused by the induced current is detected by the setting detection coil. Is detected. The operation (1) is performed for each of the plurality of setting measurement objects.
Here, the “setting exciting coil” is an exciting coil used for setting the first frequency and the second frequency. The setting excitation coil may be the same as or different from the first excitation coil, the second excitation coil, or the same excitation coil in the case where these are the same excitation coil.
“Setting object” is a measurement object used for setting the first frequency and the second frequency, and is used for the measurement of the quenching depth by the quenching depth measuring apparatus according to the present invention. The same material, the same shape, and the same heat treatment as the object to be measured.
The “setting detection coil” is a detection coil used for setting the first frequency and the second frequency. The setting detection coil may be the same as or different from the first detection coil, the second detection coil, or the same detection coil in the case where these are the same detection coil.
In the case of the present embodiment, the plurality of frequencies related to the setting of “first frequency” and “second frequency” are frequencies f1 to f8 of the AC excitation signal applied to the excitation coil 111 by the quenching depth measuring apparatus 100. And the same.

  (2) Next, based on the detection signal for each frequency detected by the setting detection coil in (1), the amplitude value Y of the detection signal for each frequency and the application to the setting excitation coil for each frequency The phase difference X between the detected AC excitation signal and the detection signal detected by the setting detection coil is calculated.

(3) Subsequently, for each of a plurality of different frequencies applied to the setting excitation coil, the amplitude value Y of the corresponding detection signal is the Y axis, and the phase difference X between the corresponding AC excitation signal and the detection signal is the X axis. ^Is calculated (= (X ² + Y ² ) ^0.5 ).
In the case of the present embodiment, the lengths of a total of eight vectors corresponding to the frequencies f1 to f8 are calculated for one measurement object for setting.

(4) Subsequently, for all combinations of selecting two frequencies from among a plurality of different frequencies applied to the setting excitation coil, the difference in vector length corresponding to the two selected frequencies is calculated. Further, a difference value D0, which is a value obtained by dividing the difference between the vector lengths by the vector length corresponding to the higher one of the vectors corresponding to the two selected frequencies, is calculated.
In the case of the present embodiment, there are a total of 28 combinations (= 8 × 7/2) for selecting two frequencies, and the same number D0 as the number of setting measurement objects is calculated for each combination.

(5) Subsequently, for each combination of the two selected frequencies, the difference value D0 is plotted on the horizontal axis, and the measured value of the quenching depth by the cutting method is plotted on the vertical axis. Find a linear approximation formula by multiplication.
Here, the measured value of the quenching depth by the cutting method of the measuring object for setting is obtained by cutting each of the plurality of measuring objects for setting after the operation of (1) and measuring the Vickers hardness of the cut surface. It is obtained by calculating based on the distribution of the values in the depth direction, or obtained by observing the cut surface.

(6) Subsequently, any one of the obtained linear approximation equations by the least square method (in the case of the present embodiment, a total of 28) is one in which the absolute value of the correlation coefficient R is equal to or greater than a predetermined threshold value. Adopted as a calibration curve, the lower one of the two frequencies related to the adopted calibration curve is defined as the first frequency and the higher frequency as the second frequency.
Here, “correlation coefficient” may be Pearson's product-moment correlation coefficient, Spearman's rank correlation coefficient, or Kendall's rank correlation coefficient. (Kendall tau rank correlation coefficient) may also be used.
The “predetermined threshold value” can be appropriately selected according to the properties of the measurement object.
In the case of the present embodiment, the Pearson product-moment correlation coefficient is used as the correlation coefficient R, the predetermined threshold value of the correlation coefficient is “0.97 (R ² ≈0.94)”, and the frequency f8 shown in FIG. Is the first frequency and the frequency f1 is the second frequency.

  Below, the measurement result of the quenching depth of the measuring object 102 by the quenching depth measuring apparatus 100 will be described with reference to FIGS. 6 to 8.

First, a unique sample number 1 to 28 is assigned to each of the 28 measurement objects 102, 102,... To be used for measurement, and the total of 28 objects are measured using the quenching depth measuring apparatus 100. The quenching depth was measured for each measurement object 102 (black circle in FIG. 8).
The temperature (surface temperature) of the 28 measurement objects 102 in total when the quenching depth is measured by the quenching depth measuring apparatus 100 is 25 ° C. for sample numbers 1 to 20 and 21 ° C. for sample number 21. , 31 ° C. for sample number 22, 41 ° C. for sample number 23, 52 ° C. for sample number 24, 21 ° C. for sample number 25, 29 ° C. for sample number 26, 38 ° C. for sample number 27 No. 28 was 47 ° C.

  Next, a total of 28 measurement objects 102, 102,... Are cut, and the distribution of Vickers hardness in the depth direction of the cut surface is measured, thereby obtaining the “quenching depth by the cutting method”. Measure (white circles in FIGS. 6 to 8).

Subsequently, one frequency (fa) is selected from the frequencies f1 to f8 of the AC excitation signal, and the amplitude value and the phase difference value (Ya and Xa) at the selected frequency are selected from the quenching depth measuring apparatus 100. The vector length ((Xa ² + Ya ² ) ^0.5 ) obtained from the storage unit 131a and based on the amplitude value and the phase difference is calculated.
Then, the relational expression between the vector length and the quenching depth obtained by the cutting method (the vector length is plotted on the horizontal axis, and the measured value of the quenching depth obtained by the cutting method is plotted on the vertical axis is obtained in advance. By substituting into a linear approximation equation by the least square method as a calibration curve), the quenching depth (white square in FIG. 6) of Comparative Example 1 was calculated.

Subsequently, two frequencies (fa and fb) are selected from the frequencies f1 to f8 of the AC excitation signal, and amplitude values and phase difference values (Ya, Xa, Yb and Xb) at the two selected frequencies are selected. Acquired from the storage unit 131a of the quenching depth measuring apparatus 100, and based on the amplitude value and the phase difference, the length of the vector of each frequency ((Xa ² + Ya ² ) ^0.5 and (Xb ² + Yb ² ) ^{0. 5} ) is calculated, and then the difference between the lengths of these two vectors ((Xa ² + Ya ² ) ^0.5 − (Xb ² + Yb ² ) ^0.5 ) is calculated.
Then, the relationship between the vector length difference and the quenching depth obtained by the cutting method (the horizontal axis represents the difference in vector length, the vertical axis represents the measured value of the quenching depth obtained by the cutting method, The quenching depth of Comparative Example 2 (black square in FIG. 7) was calculated by substituting the linear approximation formula by the least square method for the result plotted as

  As shown in FIGS. 6 to 8, the frequency of a plurality of AC excitation signals is measured in both cases where the measurement temperature is constant (sample numbers 1 to 20) and the measurement temperature changes (sample numbers 21 to 28). The quenching depth (invention) calculated based on the difference between the vector lengths at the two selected frequencies divided by the vector length on the high frequency side is the frequency of the plurality of AC excitation signals. Of the quenching depth (Comparative Example 1) calculated based on the length of the vector at one frequency selected from the above and the length of the vector at the two selected frequencies among the frequencies of the plurality of AC excitation signals. It can be seen that the difference between the quenching depth measured by the cutting method is smaller than the quenching depth calculated based on the difference (Comparative Example 2), that is, the measurement accuracy of the quenching depth is high (± 0.57m → ± 0.32mm).

As described above, the quenching depth measuring apparatus 100 is
A first excitation coil (excitation coil 111 in this embodiment) that generates an induced current in the measurement object 102 by applying an AC excitation signal of a first frequency;
A first detection coil (in the case of the present embodiment, a detection coil 121) for detecting a detection signal caused by an induced current generated in the measurement object 102 by the first excitation coil;
A second excitation coil (in this embodiment, an excitation coil 111) that generates an induced current in the measurement object 102 by applying an AC excitation signal of a second frequency that is higher than the first frequency; ,
A second detection coil (in the case of the present embodiment, a detection coil 121) for detecting a detection signal caused by an induced current generated in the measurement object 102 by the second excitation coil;
The amplitude value Y1 of the detection signal of the first detection coil, the phase difference X1 of the AC excitation signal of the first excitation coil and the detection signal of the first detection coil, the amplitude value Y2 of the detection signal of the second detection coil, and the second excitation coil The phase difference X2 between the AC excitation signal and the detection signal of the second detection coil is calculated, and the calculated Y1, X1, Y2, and X2 are the relationship between the difference value D shown in Equation 1 and Y1, X1, Y2, and X2. A difference value calculation unit 131c that calculates the difference value D by substituting it into the equation;
A quenching depth calculation unit 131d that calculates the quenching depth L of the measurement object 102 based on the difference value D calculated by the difference value calculation unit 131c;
It comprises.
With this configuration, it is possible to accurately measure the quenching depth of the measurement object 102 even if the temperature of the measurement object 102 or the surrounding environment fluctuates.

Moreover, the quenching depth measuring apparatus 100 is
The first excitation coil and the second excitation coil are the same excitation coil (excitation coil 111),
The first detection coil and the second detection coil are the same detection coil (detection coil 121),
An AC excitation signal applying unit that selectively applies either an AC excitation signal of the first frequency or an AC excitation signal of the second frequency to the same excitation coil (excitation coil 111) (in this embodiment, the frequency is changed) The unit 131b and the AC power source 112 are equivalent to this).
This configuration has the following advantages.
That is, when the first excitation coil and the second excitation coil are separate, in order to generate an induced current by AC excitation signals of different frequencies on the measurement object, (i) a predetermined application of the first excitation coil The first detection coil is disposed at a position (in the case of this embodiment, a position inserted through the measurement object 102) and the first detection coil is a predetermined detection position (in the case of this embodiment, a position inserted through the measurement object 102 and an application position) (Ii) The first excitation coil detects the detection signal by applying an AC excitation signal corresponding to the first frequency to the first excitation coil and (iii) the first excitation coil. Is retracted from the predetermined application position and the first detection coil is retracted from the predetermined detection position. (Iv) The second excitation coil is disposed at the predetermined application position and the second detection coil is detected at the predetermined position. And (v) a series of the above (i) to (v) in which an AC excitation signal corresponding to the second frequency is applied to the second excitation coil and a detection signal is detected by the second detection coil. There is a problem that there is a time lag between the application of the AC excitation signal corresponding to the first frequency and the application of the AC excitation signal corresponding to the second frequency.
If the temperature of the measurement object fluctuates during such a time lag, it causes a decrease in the measurement accuracy of the quenching depth.
On the other hand, in the quenching depth measuring apparatus 100 of the present embodiment, the first excitation coil and the second excitation coil are the same excitation coil (excitation coil 111), and the first detection coil and the second detection coil are Since it is the same detection coil (detection coil 121), it is not necessary to move the same excitation coil every time an AC excitation signal corresponding to a different frequency is applied, and an AC excitation signal corresponding to the first frequency is applied. It is possible to minimize the time lag from application to application of the AC excitation signal corresponding to the second frequency.
Therefore, it is possible to further reduce the temperature fluctuation of the measurement object during the time lag, and it is possible to suppress a decrease in the measurement accuracy of the quenching depth due to the temperature fluctuation of the measurement object.

Further, the quenching depth calculation unit 131d of the quenching depth measuring apparatus 100 is
By substituting the difference value D calculated by the difference value calculation unit 131c into the relational expression between the quenching depth L and the difference value D shown in Equation 2, the quenching depth L of the measurement object 102 is calculated. is there.
With this configuration, the quenching depth L of the measurement object 102 can be easily calculated.

Moreover, the quenching depth measuring apparatus 100 is
When the quenching depth L calculated by the quenching depth calculating unit 131d is compared with the preset allowable quenching depth range, and the quenching depth L is within the allowable quenching depth range, When the measurement object 102 is determined to be a non-defective product with respect to the quenching depth, and the quenching depth L is not within the allowable quenching depth range, the measurement object 102 is defective with respect to the quenching depth. A determination unit 131e for determination is provided.
With this configuration, it is possible to determine the quality of the quenching depth of the measurement object 102 according to a certain standard (whether the quenching depth L is within the allowable quenching depth range). is there.

Further, the first frequency and the second frequency of the quenching depth measuring apparatus 100 are:
(1) An AC excitation signal having a plurality of frequencies is applied to a setting excitation coil to generate an induced current in a measurement object for setting, and a detection signal for each frequency caused by the induced current is detected by the setting detection coil. (2) Based on the detection signal for each frequency detected by the setting detection coil, the amplitude value Y of the detection signal for each frequency and the AC excitation signal applied to the setting excitation coil and the setting detection The phase difference X with the detection signal detected by the coil is calculated. (3) For each of a plurality of different frequencies applied to the setting excitation coil, the amplitude value Y of the corresponding detection signal is set to the Y axis, and the corresponding AC the length of the vector to the phase difference X between the excitation signal and the detection signal and the X axis ^{(= (X 2 + Y 2} ) 0.5) is calculated, (4) applied different circumferential set for excitation coil For all combinations of selecting two frequencies from the number, calculate the difference in vector length corresponding to the two selected frequencies, and further convert the difference in vector length to the two selected frequencies. A difference value D0, which is a value obtained by dividing the corresponding vector by the length of the vector corresponding to the higher frequency, is calculated, and (5) the difference value D0 for each of the selected two frequency combinations is plotted on the horizontal axis, Plotting the measured values of the quenching depth by the cutting method as the vertical axis, obtaining linear approximation equations by the least square method for each of these plots, (6) Of the obtained linear approximation equations by the least square method, Any one whose absolute value of the correlation coefficient is equal to or greater than a predetermined threshold is adopted as a calibration curve, and the lower one of the two frequencies related to the adopted calibration curve is the first frequency. , The higher frequency and a second frequency, that is intended to be set by the procedure of the above (1) to (6).
By configuring in this way, it is possible to set a combination of frequencies at which the measurement accuracy of the quenching depth is highest according to the material or shape of the measurement object as the first frequency and the second frequency. Yes, and thus contributes to the improvement of the measurement accuracy of the quenching depth of the measurement object.

Below, the 1st Example of the quenching depth measuring method based on this invention is described using FIG. 9 and FIG.
The first embodiment of the quenching depth measuring method according to the present invention is a method for measuring the quenching depth of the measuring object 102 using the quenching depth measuring apparatus 100 shown in FIG. 1, and is shown in FIG. As described above, the first excitation / detection step S1100, the second excitation / detection step S1200, the difference value calculation step S1300, the quenching depth calculation step S1400, and the determination step S1500 are provided.

In the first excitation / detection step S1100, an alternating current excitation signal having a first frequency is applied to the first excitation coil (in the present embodiment, the excitation coil 111) to generate an induced current in the measurement object 102, and the first In this step, the first detection coil (in the present embodiment, the detection coil 121) detects a detection signal caused by the induced current generated in the measurement object 102 by the excitation coil.
When the first excitation / detection step S1100 is completed, the process proceeds to the second excitation / detection step S1200.

In the second excitation / detection step S1200, an AC excitation signal having a second frequency that is higher than the first frequency is applied to the second excitation coil (excitation coil 111 in this embodiment) to measure the object 102. And a detection signal caused by the induced current generated in the measurement object 102 by the second excitation coil is detected by the second detection coil (in the present embodiment, the detection coil 121).
When the second excitation / detection step S1200 is completed, the process proceeds to a difference value calculation step S1300.

The difference value calculation step S1300 includes the amplitude value Y1 of the detection signal of the first detection coil, the phase difference X1 of the AC excitation signal of the first excitation coil and the detection signal of the first detection coil, and the amplitude value Y2 of the detection signal of the second detection coil. , And the phase difference X2 between the AC excitation signal of the second excitation coil and the detection signal of the second detection coil, respectively, and the calculated values Y1, X1, Y2, and X2 are the difference values D and Y1, X1, This is a step of calculating the difference value D by substituting it into the relational expression between Y2 and X2.
When the difference value calculation step S1300 is completed, the process proceeds to the quenching depth calculation step S1400.

The quenching depth calculation step S1400 is a step of calculating the quenching depth L of the measurement object 102 based on the difference value D calculated in the difference value calculation step S1300.
When the quenching depth calculation step S1400 is completed, the process proceeds to the determination step S1500.

  The determination step S1500 compares the quenching depth L calculated in the quenching depth calculation step S1400 with a preset allowable quenching depth range, and the quenching depth L falls within the allowable quenching depth range. If the quenching depth L is not within the allowable quenching depth range, it is determined that the measurement target 102 is inferior in the quenching depth. This is a step of determining that the product is non-defective.

As described above, the first embodiment of the quenching depth measuring method according to the present invention is:
A first excitation / detection step S1100;
A second excitation / detection step S1200;
Difference value calculation step S1300;
Quenching depth calculation step S1400,
It comprises.
With this configuration, it is possible to accurately measure the quenching depth of the measurement object 102 even if the temperature of the measurement object 102 or the surrounding environment fluctuates.

  In this embodiment, when the first excitation / detection step S1100 is completed, the process proceeds to the second excitation / detection step S1200. However, the present invention is not limited to this, and the second excitation / detection is performed as shown in FIG. The same effect can be obtained by adopting a configuration that shifts to the first excitation / detection step S1100 after the step S1200 is completed (a configuration in which the order of performing the first excitation / detection step S1100 and the second excitation / detection step S1200 is reversed).

In addition, the first embodiment of the quenching depth measurement method according to the present invention,
The first excitation coil and the second excitation coil are the same excitation coil (in this embodiment, the excitation coil 111),
The first detection coil and the second detection coil are the same detection coil (in this embodiment, the detection coil 121),
In the first excitation / detection step S1100,
Apply the AC excitation signal of the first frequency to the same excitation coil,
In the second excitation / detection step S1200,
An AC excitation signal having a second frequency is applied to the same excitation coil.
With this configuration, it is possible to minimize the time lag from applying the AC excitation signal corresponding to the first frequency to applying the AC excitation signal corresponding to the second frequency.
Therefore, it is possible to further reduce the temperature fluctuation of the measurement object during the time lag, and it is possible to suppress a decrease in the measurement accuracy of the quenching depth due to the temperature fluctuation of the measurement object.

In addition, the first embodiment of the quenching depth measurement method according to the present invention,
In the quenching depth calculation step S1400,
By substituting the difference value D calculated in the difference value calculation step S1300 into the relational expression between the quenching depth L and the difference value D shown in Equation 2, the quenching depth L of the measurement object 102 is calculated. is there.
With this configuration, the quenching depth L of the measurement object 102 can be easily calculated.

In addition, the first embodiment of the quenching depth measurement method according to the present invention,
The determination step S1500 is provided.
With this configuration, it is possible to determine the quality of the quenching depth of the measurement object 102 according to a certain standard (whether the quenching depth L is within the allowable quenching depth range). is there.

Further, the first frequency and the second frequency of the first embodiment of the quenching depth measuring method according to the present invention are:
(1) An AC excitation signal having a plurality of frequencies is applied to a setting excitation coil to generate an induced current in a measurement object for setting, and a detection signal for each frequency caused by the induced current is detected by the setting detection coil. (2) Based on the detection signal for each frequency detected by the setting detection coil, the amplitude value Y of the detection signal for each frequency and the AC excitation signal applied to the setting excitation coil and the setting detection The phase difference X with the detection signal detected by the coil is calculated. (3) For each of a plurality of different frequencies applied to the setting excitation coil, the amplitude value Y of the corresponding detection signal is set to the Y axis, and the corresponding AC the length of the vector to the phase difference X between the excitation signal and the detection signal and the X axis ^{(= (X 2 + Y 2} ) 0.5) is calculated, (4) applied different circumferential set for excitation coil For all combinations of selecting two frequencies from the number, calculate the difference in vector length corresponding to the two selected frequencies, and further convert the difference in vector length to the two selected frequencies. A difference value D0, which is a value obtained by dividing the corresponding vector by the length of the vector corresponding to the higher frequency, is calculated, and (5) the difference value D0 for each of the selected two frequency combinations is plotted on the horizontal axis, Plotting the measured values of the quenching depth by the cutting method as the vertical axis, obtaining linear approximation equations by the least square method for each of these plots, (6) Of the obtained linear approximation equations by the least square method, Any one whose absolute value of the correlation coefficient is equal to or greater than a predetermined threshold is adopted as a calibration curve, and the lower one of the two frequencies related to the adopted calibration curve is the first frequency. , The higher frequency and a second frequency, that is intended to be set by the procedure of the above (1) to (6).
By configuring in this way, it is possible to set a combination of frequencies at which the measurement accuracy of the quenching depth is highest according to the material or shape of the measurement object as the first frequency and the second frequency. Yes, and thus contributes to the improvement of the measurement accuracy of the quenching depth of the measurement object.

  Below, the apparatus structure of the quenching depth measuring apparatus 200 which is the 2nd Example of the quenching depth measuring apparatus which concerns on this invention using FIG. 11 is demonstrated.

  The quenching depth measuring device 200 measures the quenching depth of the measurement object 202, and mainly includes an excitation unit 210, a detection unit 220, a control device 230, and the like.

  The measuring object 202 is made of a metal material such as a steel material, and is a part that has been previously quenched.

The excitation unit 210 generates an induced current in the measurement object 202 (more precisely, on the surface and inside of the measurement object 202) by applying an alternating magnetic field to the measurement object 202.
The exciting unit 210 includes an exciting coil 211, an AC power supply 212, and the like.

The exciting coil 211 is an embodiment of the exciting coil according to the present invention.
The exciting coil 211 is a coil made of a conductor, and an induced current (corresponding to each frequency) is applied to the measuring object 202 by applying AC excitation signals of a plurality of different frequencies (f1 to f8 in this embodiment). Eddy current).
Terminals 211a and 211b are formed at both ends of the exciting coil 211, respectively.

The AC power supply 212 applies an AC excitation signal (AC voltage) to the excitation coil 211 by generating an AC voltage having a predetermined frequency and a predetermined amplitude. The AC power supply 212 is connected to the terminals 211a and 211b of the exciting coil 211.
The AC power supply 212 can change the frequency of the AC voltage in the range of 30 Hz to 30 kHz, and a total of eight types of frequencies f1 to f8 (see FIG. 2) that are in the range of 30 Hz to 30 kHz. A signal (AC voltage) can be selectively applied to the exciting coil 211.

The detection unit 220 detects an induced voltage (detection signal) caused by an induced current generated in the measurement object 202 (more strictly, the surface and inside of the measurement object 202).
The detection unit 220 mainly includes a detection coil 221 and a voltmeter 222.

The detection coil 221 is an embodiment of the detection coil according to the present invention.
The detection coil 221 is a coil inserted into the measurement object 202 and detects a detection signal caused by an induced current generated in the measurement object 202 (more precisely, the surface and inside of the measurement object 202). is there.
Terminals 221a and 221b are formed at both ends of the detection coil 221, respectively.
The detection coil 221 and the excitation coil 211 are disposed so that the central axes of both are substantially straight.
In the present embodiment, the excitation coil 211 and the detection coil 221 are housed in a housing 205, and the combination of the excitation coil 211, the detection coil 221 and the housing 205 constitutes an eddy current sensor.

  The voltmeter 222 is connected to the terminals 221a and 221b, and converts a detection signal (inductive voltage) detected by the detection coil 221 into a predetermined digital signal.

The control device 230 controls the operation of the quenching depth measurement device 200 and calculates the quenching depth of the measurement object 202 based on the detection signal from the detection unit 220 (acquires the quenching depth measurement result). To do).
The control device 230 mainly includes a control unit 231, an input unit 232, a display unit 233, and the like.

  The control unit 231 can store various programs such as a frequency change program, a difference value calculation program, a first quenching depth calculation program, a second quenching depth calculation program, and a determination program described later. Programs and the like can be expanded, predetermined calculations can be performed according to these programs, and the results of the calculations can be stored.

The control unit 231 may actually have a configuration in which CPUs, ROMs, RAMs, HDDs, and the like are connected to each other by a bus, or may be configured by a one-chip LSI or the like.
Although the control unit 231 of this embodiment is a dedicated product, it can also be achieved by storing the above program in a commercially available personal computer or workstation.

The control unit 231 is connected to the AC power supply 212 and can change the frequency and amplitude of the AC excitation signal of the AC power supply 212 by transmitting a predetermined control signal to the AC power supply 212.
Further, the control unit 231 is connected to the voltmeter 222 and can acquire “a detection signal (inductive voltage) detected by the detection coil 221 and further converted into a predetermined digital signal by the voltmeter 222”. .
The operation control of the quenching depth measuring apparatus 200 by the control unit 231 and the calculation of the quenching depth of the measurement object 202 based on the detection signal from the detection unit 220 will be described in detail later.

  The input unit 232 is connected to the control unit 231 and inputs various information / instructions related to the measurement of the quenching depth by the quenching depth measuring apparatus 200 to the control unit 231.

  The display unit 233 displays, for example, the input contents from the input unit 232 to the control unit 231, the operating status of the quenching depth measuring apparatus 200, the measurement result of the quenching depth of the measurement target 202, and the like.

Below, the detail of a structure of the control part 231 is demonstrated.
The control unit 231 functionally includes a storage unit 231a, a frequency change unit 231b, a difference value calculation unit 231c, a first quenching depth calculation unit 231d, a second quenching depth calculation unit 231e, a determination unit 231f, and the like. To do.

The storage unit 231a stores various parameters (numerical values) used in performing control, calculation, and the like by the control unit 231, operation history, calculation results (calculation results), and the like.
The storage unit 231a is substantially composed of a storage medium such as an HDD (Hard Disk Drive), a CD-ROM, or a DVD-ROM.

The frequency changing unit 231b changes the frequency of an AC voltage having a predetermined amplitude generated by the AC power supply 212, and thus the frequency of the AC excitation signal (AC voltage) applied to the excitation coil 211.
Substantially, the control unit 231 functions as the frequency changing unit 231b by performing a predetermined calculation or the like according to the frequency changing program stored in the control unit 231.

The frequency changing unit 231b transmits a control signal to the AC power supply 212.
The control signal transmitted from the frequency changing unit 231b to the AC power supply 212 is a signal that indicates the frequency of the AC voltage (any one of f1 to f8) that the AC power supply 212 should generate, and the AC power supply 212 is generated based on the control signal. Change (adjust) the frequency of the AC voltage.
In the case of the present embodiment, the frequency changing unit 231b transmits a control signal instructing the AC power supply 212 to generate AC voltages having eight different frequencies f1 to f8 for each predetermined short period. The "first frequency", "second frequency", "third frequency", "fourth frequency", "fifth frequency" and "sixth frequency" for each predetermined short period Including eight types of alternating current excitation signals of frequencies f1 to f8 are applied.

In the case of the present embodiment, the configuration is such that AC excitation signals of eight different frequencies are applied to the exciting coil 211 in about 1 second (the frequency changing period is about 0.125 seconds). Is not limited to this, and the number of frequencies and the period for changing the frequencies can be appropriately selected according to the properties of the measurement object.
It should be noted that it is desirable to shorten the period for changing the frequency of the AC excitation signal as much as possible within the range in which the detection signal can be detected. This is because if the frequency changing period is long, the temperature of the object to be measured fluctuates during that period, and the measurement accuracy may be reduced.
A setting method of “first frequency”, “second frequency”, “third frequency”, “fourth frequency”, “fifth frequency”, and “sixth frequency” will be described later.

  The combination of the frequency changing unit 231b and the AC power supply 212 includes a first frequency AC excitation signal, a second frequency AC excitation signal, a third frequency AC excitation signal, a fourth frequency AC excitation signal, A plurality of frequencies including an AC excitation signal of the fifth frequency and an AC excitation signal of the sixth frequency are selectively generated, and corresponds to an embodiment of the AC excitation signal generation unit according to the present invention.

The difference value calculation unit 231c is an embodiment of the difference value calculation unit according to the present invention, and the amplitude value Y1 of the detection signal of the detection coil 221 corresponding to the first frequency and the excitation coil 211 corresponding to the first frequency. Phase difference X1 of the detection signal of the detection coil 221 corresponding to the first frequency, the amplitude value Y2 of the detection signal of the detection coil 221 corresponding to the second frequency, and the excitation corresponding to the second frequency The difference value Da is calculated based on the phase difference X2 between the AC excitation signal of the coil 211 and the detection signal of the detection coil 221 corresponding to the second frequency.
Substantially, the control unit 231 performs a predetermined calculation or the like according to the difference value calculation program stored in the control unit 231, thereby serving as the difference value calculation unit 231c.

Based on the detection signal acquired from the detection coil 221, the difference value calculation unit 231c determines the amplitude value Y1 of the detection signal of the detection coil 221 corresponding to the first frequency and the AC excitation of the excitation coil 211 corresponding to the first frequency. The phase difference X1 of the detection signal of the detection coil 221 corresponding to the signal and the first frequency, the amplitude value Y2 of the detection signal of the detection coil 221 corresponding to the second frequency, and the excitation coil 211 corresponding to the second frequency A phase difference X2 of the detection signal of the detection coil 221 corresponding to the AC excitation signal and the second frequency is calculated. The calculated Y1, X1, Y2, and X2 are appropriately stored in the storage unit 231a.
Next, the difference value calculation unit 231c substitutes the calculated Y1, X1, Y2, and X2 into the relational expression between the difference value Da shown in the following Equation 3 and the Y1, X1, Y2, and X2 to obtain the difference. The value Da is calculated. The calculated difference value Da is appropriately stored in the storage unit 231a.

The difference value Da shown in Equation 3 is the length of the vector (X1, Y1) related to the first frequency ((X1 ² + Y1 ² ) ^0.5 ) minus the length ((X2 ² + Y2 ² ) ^0.5 ) of the vector (X2, Y2) related to the second frequency, and further to the vector related to the second frequency It is the value divided by the length.

The vector relating to the first frequency reflects the influence of the crystal structure from the surface of the measurement object 202 to the penetration depth corresponding to the first frequency and the temperature of the crystal structure.
The vector related to the second frequency reflects the influence of the crystal structure from the surface of the measurement object 202 to the penetration depth corresponding to the second frequency and the temperature of the crystal structure.
Further, since the first frequency is lower than the second frequency, the penetration depth of the induced current generated in the measurement object 202 by the AC excitation signal of the first frequency is measured by the AC excitation signal of the second frequency. It is larger (deeper) than the penetration depth of the induced current generated in the object 202.
Therefore, by subtracting the length of the vector related to the second frequency from the length of the vector related to the first frequency, information included in both the vector related to the first frequency and the vector related to the second frequency It is possible to cancel the information of the shallow part from the surface of the measurement object 202 and to emphasize the information of the part near the quenching depth, which is information closely related to the measurement of the quenching depth.
In particular, since the temperature of the measurement object 202 varies due to heat conduction between the surface of the measurement object 202 and the surrounding atmosphere, a portion (surface) that is shallower than the surface (bulk) deeper than the surface of the measurement object 202. The temperature variation tends to be larger in the vicinity), and the shallower portion (near the surface) of the surface of the measurement object 202 contributes more to the decrease in measurement accuracy due to the temperature variation.
Therefore, canceling out information in a shallow portion from the surface of the measurement object 202, which is information common to the vector related to the first frequency and the vector related to the second frequency, is performed by quenching due to temperature fluctuation of the measurement object 202. Greatly effective in suppressing a decrease in depth measurement accuracy.
In addition, by subtracting the length of the vector related to the second frequency from the vector related to the first frequency and further dividing by the length of the vector related to the second frequency, It is possible to further suppress the influence of temperature fluctuations on “information in the vicinity”.

The first quenching depth calculation unit 231d is an embodiment of the first quenching depth calculation unit according to the present invention, and the measurement object 202 is measured based on the difference value Da calculated by the difference value calculation unit 231c. The quenching depth La is calculated.
Substantially, the control unit 231 performs a predetermined calculation or the like according to the first quenching depth calculation program stored in the control unit 231, thereby functioning as the first quenching depth calculation unit 231d.

  The storage unit 231a stores “a relational expression between the quenching depth La and the difference value Da” (more precisely, a constant Aa and a constant Ba) expressed by the following formula 4, and the first quenching depth: The calculating unit 231d calculates the quenching depth La by substituting the difference value Da calculated by the difference value calculating unit 231c into the “relational expression between the quenching depth La and the difference value Da”. The calculated quenching depth La is appropriately stored in the storage unit 231a.

The constant Aa and the constant Ba in Equation 4 are obtained by conducting an experiment using a reference measurement object in advance.
That is, as shown in FIG. 12, the calculated value of the difference value Da in the reference measurement object is on the horizontal axis, and the measured value of the quenching depth by the cutting method (Vickers hardness measurement or structure observation of the cut surface) is on the vertical axis. Plot experimental data.
The slope of the straight line obtained by the least square method based on the experimental data is a constant Aa, and the intercept between the straight line and the vertical axis is a constant Ba.

The second quenching depth calculation unit 231e is an embodiment of the second quenching depth calculation unit according to the present invention.
Substantially, the control unit 231 performs a predetermined calculation or the like according to the second quenching depth calculation program stored in the control unit 231, thereby serving as the second quenching depth calculation unit 231e.

The second quenching depth calculation unit 231e compares the quenching depth La calculated by the first quenching depth calculation unit 231d with the reference quenching depth Ls.
The reference quenching depth Ls is set in advance and stored in the storage unit 231a. A method for setting the reference quenching depth Ls will be described later.

As a result of comparing the quenching depth La and the reference quenching depth Ls, when the quenching depth La is less than the reference quenching depth Ls (when La <Ls), the second quenching depth calculation unit 231e performs a series of operations from (11) to (13) below.
(11) The second quenching depth calculation unit 231e determines the amplitude value Y3 of the detection signal corresponding to the third frequency, the AC excitation signal corresponding to the third frequency, and the level of the detection signal corresponding to the third frequency. The phase difference X3, the amplitude value Y4 of the detection signal corresponding to the fourth frequency, the AC excitation signal corresponding to the fourth frequency, and the phase difference X4 of the detection signal corresponding to the fourth frequency are calculated.
(12) The second quenching depth calculation unit 231e substitutes the calculated Y3, X3, Y4, and X4 into the relational expression between the difference value Db and Y3, X3, Y4, and X4 shown in the following equation 5. To calculate the difference value Db.
(13) The second quenching depth calculation unit 231e substitutes the calculated difference value Db into the relational expression between the quenching depth Lb and the difference value Db shown in Equation 6 below to obtain the quenching depth Lb. And the quenching depth Lb is set as the quenching depth of the measuring object 202.

The constant Ab and the constant Bb in Equation 6 are obtained by conducting an experiment using a reference measurement object in advance.
That is, as shown in FIG. 13, the calculated value of the difference value Db in the reference measurement object is taken as the horizontal axis, and the measured value of the quenching depth by the cutting method (Vickers hardness measurement or structure observation of the cut surface) is taken as the vertical axis. Plot experimental data.
The slope of the straight line obtained by the least square method based on the experimental data is a constant Ab, and the intercept between the straight line and the vertical axis is a constant Bb.

As a result of comparing the quenching depth La and the reference quenching depth Ls, when the quenching depth La is equal to or greater than the reference quenching depth Ls (when La ≧ Ls), the second quenching depth calculation unit 231e performs a series of operations from (21) to (23) below.
(21) The second quenching depth calculation unit 231e determines the amplitude value Y5 of the detection signal corresponding to the fifth frequency, the AC excitation signal corresponding to the fifth frequency, and the level of the detection signal corresponding to the fifth frequency. The phase difference X5, the amplitude value Y6 of the detection signal corresponding to the sixth frequency, the AC excitation signal corresponding to the sixth frequency, and the phase difference X6 of the detection signal corresponding to the sixth frequency are calculated.
(22) The second quenching depth calculation unit 231e substitutes the calculated Y5, X5, Y6, and X6 into the relational expression between the difference value Dc shown in the following Equation 7 and Y5, X5, Y6, and X6. To calculate the difference value Dc.
(23) The second quenching depth calculation unit 231e substitutes the calculated difference value Dc into the relational expression between the quenching depth Lc and the difference value Dc shown in the following equation 8 to obtain the quenching depth Lc. And the quenching depth Lc is set as the quenching depth of the measuring object 202.

The constant Ac and the constant Bc in Equation 8 are obtained in advance by performing an experiment using a reference measurement object.
That is, as shown in FIG. 14, the calculated value of the difference value Dc in the reference measurement object is taken as the horizontal axis, and the measured value of the quenching depth by the cutting method (Vickers hardness measurement or structural observation of the cut surface) is taken as the vertical axis. Plot experimental data.
The slope of the straight line obtained by the least square method based on the experimental data is a constant Ac, and the intercept between the straight line and the vertical axis is a constant Bc.

The determination unit 231f is an embodiment of the determination unit according to the present invention, and compares the quenching depth calculated by the second quenching depth calculation unit 231e with a preset allowable quenching depth range, When the quenching depth is within the allowable quenching depth range, it is determined that the measurement target 202 is a non-defective product with respect to the quenching depth, and the quenching depth is within the allowable quenching depth range. If not, the measurement object 202 is determined to be defective with respect to the quenching depth.
Substantially, the control unit 231 performs a predetermined calculation or the like in accordance with a determination program stored in the control unit 231 and thereby functions as the determination unit 231f.

In the case of the present embodiment, the lower limit value and the upper limit value of the allowable quenching depth range of the measurement object 202 are stored in advance in the storage unit 231a, and the determination unit 231f is calculated by the second quenching depth calculation unit 231e. The quenching depth is compared with the lower limit value and the upper limit value of the allowable quenching depth range stored in the storage unit 231a.
As a result of the comparison, when the quenching depth is within the allowable quenching depth range, the determination unit 231f determines that the measurement target 202 is a non-defective product with respect to the quenching depth.
As a result of the comparison, when the quenching depth is not within the allowable quenching depth range, the determination unit 231f determines that the measurement target 202 is defective with respect to the quenching depth. The determination result of the measurement object 202 by the determination unit 231f is appropriately stored in the storage unit 231a.

In the following, a setting method of “first frequency”, “second frequency”, “third frequency”, “fourth frequency”, “fifth frequency”, and “sixth frequency” will be described. .
“First frequency”, “Second frequency”, “Third frequency”, “Fourth frequency”, “Fifth frequency”, and “Sixth frequency” are the following (a) ( It is set by the procedure up to h).

(A) First, an AC excitation signal having a plurality of frequencies (in the case of the present embodiment, f1 to f8 shown in FIG. 2) is applied to a setting excitation coil to generate an induced current in a setting measurement object, and the setting A detection signal for each frequency caused by the induced current is detected by the detection coil.
Here, the “setting exciting coil” is an exciting coil used for setting the first frequency and the second frequency. The setting exciting coil may be the same as the exciting coil according to the present invention, or may be a different coil.
“Setting object” is a measurement object used to set the first frequency, the second frequency, the third frequency, the fourth frequency, the fifth frequency, and the sixth frequency. It is the part etc. which were the same material, the same shape, and the same heat processing as the measuring object used for the quenching depth measurement by the quenching depth measuring apparatus which concerns on invention.
The “setting detection coil” is a detection coil used for setting the first frequency, the second frequency, the third frequency, the fourth frequency, the fifth frequency, and the sixth frequency. The setting detection coil may be the same as or different from the detection coil according to the present invention.

  (B) Next, based on the detection signal for each frequency detected by the setting detection coil, the amplitude value Y of the detection signal for each frequency, the AC excitation signal applied to the setting excitation coil, and the setting detection A phase difference X with a detection signal detected by the coil is calculated.

(C) Subsequently, for each of a plurality of different frequencies applied to the setting excitation coil, the amplitude value Y of the corresponding detection signal is the Y axis, and the phase difference X between the corresponding AC excitation signal and the detection signal is the X axis. ^Is calculated (= (X ² + Y ² ) ^0.5 ).
In the case of the present embodiment, the lengths of a total of eight vectors corresponding to the frequencies f1 to f8 are calculated for one measurement object for setting.

(D) Subsequently, for all combinations in which two frequencies are selected from a plurality of different frequencies applied to the setting excitation coil, the difference in vector length corresponding to the two selected frequencies is calculated. Further, a difference value D0, which is a value obtained by dividing the difference between the vector lengths by the vector length corresponding to the higher frequency of the vectors corresponding to the two selected frequencies, is calculated.
In the case of the present embodiment, there are a total of 28 combinations (= 8 × 7/2) for selecting two frequencies, and the same number D0 as the number of setting measurement objects is calculated for each combination.

(E) Subsequently, for each of the selected combinations of two frequencies, the difference value D0 is plotted on the horizontal axis, and the measured value of the quenching depth by the cutting method is plotted on the vertical axis. Find a linear approximation formula by multiplication.
Here, the measured value of the quenching depth by the cutting method of the setting measurement object is obtained by cutting each of the plurality of setting measurement objects after the operation of (a) and measuring the Vickers hardness of the cut surface. It is obtained by calculating based on the distribution of values in the depth direction, or obtained by observing the cut surface.

(F) Subsequently, the absolute value of the correlation coefficient R is equal to or greater than a predetermined threshold among the obtained linear approximation equations by the least square method (in the case of the present embodiment, a total of 28), and The one that covers the standard range of the quenching depth is adopted as the first calibration curve, and the lower one of the two frequencies related to the adopted first calibration curve is the first frequency, The higher frequency is set as the second frequency.
Here, the “correlation coefficient” may be a Pearson product-moment correlation coefficient, a Spearman rank correlation coefficient, or a Kendall rank correlation coefficient.
The “predetermined threshold value” can be appropriately selected according to the properties of the measurement object.
The “standard range of quenching depth” refers to the range that the quenching depth of the measurement object can take. In addition, the standard range of quenching depth can be set as appropriate according to the properties and application of the measurement object, and may be the same as the “allowable quenching depth range”. May be different.
“Conforming to the quenching depth standard range” means that the penetration depth of the induced current generated in the setting excitation coil by the AC excitation signal of two frequencies corresponding to the obtained linear approximation formula by the least square method is used. These are not values that deviate from the upper limit value and the lower limit value of the standard range of the quenching depth. Therefore, the penetration depths related to the above two frequencies do not need to be the upper limit value and the lower limit value of the quenching depth standard range, respectively, and slightly deviate from the upper limit value and the lower limit value of the quenching depth standard range, respectively. It may be a value.
In the case of the present embodiment, the Pearson product-moment correlation coefficient is used as the correlation coefficient R, the predetermined threshold value of the correlation coefficient is “0.97 (R ² ≈0.94)”, and the frequency f8 shown in FIG. Is the first frequency and the frequency f1 is the second frequency.

(G) Subsequently, in the obtained linear approximation formula by the least square method, the absolute value of the correlation coefficient R is not less than a predetermined threshold value, and the penetration depth of the combination of the two corresponding frequencies Is suitable for the surface side range which is the range closer to the surface of the measuring object for setting out of the range divided into two with the standard quenching depth Ls as the boundary. Is used as the second calibration curve (see FIG. 13), and of the two frequencies related to the adopted second calibration curve, the lower frequency is the third frequency and the higher frequency is the fourth frequency. And
“Applicable to the surface side range” means that the penetration depth of the induced current generated in the setting excitation coil by the AC excitation signal of two frequencies corresponding to the obtained linear approximation formula by the least square method is the surface side. It is not a value that deviates from the upper and lower limits of the range to a degree that is not appropriate. Therefore, the penetration depths related to the two frequencies do not need to be the upper limit value and the lower limit value of the surface side range, respectively, and may be values slightly deviated from the upper limit value and the lower limit value of the surface side range, respectively.
In the present embodiment, the frequency f5 shown in FIG. 2 is the third frequency, and the frequency f2 is the fourth frequency.

(H) Subsequently, in the obtained linear approximation formula by the least square method, the absolute value of the correlation coefficient R is equal to or greater than a predetermined threshold value, and the penetration depth of the corresponding combination of two frequencies Is the one that fits the bulk side range, which is the range farther from the surface of the object to be set, out of the range divided into two with the standard quenching depth Ls as the boundary. Is adopted as the third calibration curve (see FIG. 14), and the lower frequency of the two frequencies related to the adopted third calibration curve is the fifth frequency and the higher frequency is the sixth frequency. And
“Fit to the bulk side range” means that the penetration depth of the induced current generated in the setting excitation coil by the AC excitation signal of the two frequencies corresponding to the obtained linear approximation formula by the least square method is the bulk side. It is not a value that deviates from the upper and lower limits of the range to a degree that is not appropriate. Therefore, the penetration depths related to the above two frequencies do not need to be the upper limit value and the lower limit value of the bulk side range, respectively, and may be values slightly deviated from the upper limit value and the lower limit value of the bulk side range, respectively.
In this embodiment, the frequency f7 shown in FIG. 2 is the fifth frequency, and the frequency f4 is the sixth frequency.

Hereinafter, a method for setting the “reference quenching depth Ls” in the present embodiment will be described.
In this embodiment, the “first frequency”, “second frequency”, “third frequency”, “fourth frequency”, “fifth frequency”, and “sixth frequency” described above. Among the plots obtained by (e) and (f) in the setting method of “the difference value D0 as a horizontal axis and the measured value of the quenching depth by the cutting method as the vertical axis, the one relating to the first calibration curve” (Refer to FIG. 12) ”is used to set the reference quenching depth Ls.
More specifically, a cubic approximate expression by the least square method of “the one relating to the first calibration curve among the plots in which the difference value D0 is the horizontal axis and the quenching depth measurement value by the cutting method is the vertical axis” ( 12), and the measured value of the quenching depth by the cutting method corresponding to the inflection point of the cubic approximate expression by the least square method (see the white circle in FIG. 12) is the standard quenching depth. Let Ls.
The reference quenching depth Ls according to the present invention is not limited to the one set by the above method, and may be set by another method.

As described above, the quenching depth measuring apparatus 200 is
A second frequency that is higher than the first frequency and the first frequency, a third frequency and a fourth frequency that is higher than the third frequency, and a fifth frequency and the first frequency An AC excitation signal generator that selectively generates a plurality of AC excitation signals having different frequencies including the sixth frequency that is higher than the fifth frequency (in this embodiment, the frequency changing unit 231b and the AC power supply 212 are connected). And the equivalent)
An excitation coil 211 that generates an induced current in the measurement object 202 by applying an AC excitation signal generated by the AC excitation signal generator;
A detection coil 221 for detecting a detection signal caused by an induced current generated in the measurement object 202 by the excitation coil 211;
The amplitude value Y1 of the detection signal corresponding to the first frequency, the phase difference X1 of the AC excitation signal corresponding to the first frequency and the detection signal corresponding to the first frequency, and the amplitude of the detection signal corresponding to the second frequency The phase difference X2 between the value Y2 and the AC excitation signal corresponding to the second frequency and the detection signal corresponding to the second frequency is calculated, and the calculated difference Y1, X1, Y2, and X2 is the difference value Da shown in Equation 3. And a difference value calculation unit 231c that calculates a difference value Da by substituting it into the relational expression between Y1, X1, Y2, and X2,
First, the quenching depth La of the measurement object 202 is calculated by substituting the difference value Da calculated by the difference value calculating unit 231c into the relational expression between the quenching depth La and the difference value Da shown in Equation 4. Quenching depth calculation unit 231d;
When the quenching depth La calculated by the first quenching depth calculating unit 231d is less than the preset reference quenching depth Ls, the amplitude value Y3 of the detection signal corresponding to the third frequency, A phase difference X3 of the AC excitation signal corresponding to the third frequency and a detection signal corresponding to the third frequency, an amplitude value Y4 of the detection signal corresponding to the fourth frequency, and an AC excitation signal corresponding to the fourth frequency; The phase difference X4 of the detection signal corresponding to the fourth frequency is calculated, and the calculated Y3, X3, Y4 and X4 are substituted into the relational expression between the difference value Db shown in Equation 5 and Y3, X3, Y4 and X4. Thus, the difference value Db is calculated, and the calculated difference value Db is substituted into the relational expression between the quenching depth Lb and the difference value Db shown in Equation 6 to calculate the quenching depth Lb. Measuring depth Lb When the quenching depth La of the product 202 is the quenching depth La calculated by the first quenching depth calculating unit 231d is equal to or greater than the reference quenching depth Ls, the detection corresponding to the fifth frequency is performed. The amplitude value Y5 of the signal, the AC excitation signal corresponding to the fifth frequency and the phase difference X5 of the detection signal corresponding to the fifth frequency, the amplitude value Y6 of the detection signal corresponding to the sixth frequency, and the sixth frequency The phase difference X6 between the corresponding AC excitation signal and the detection signal corresponding to the sixth frequency is calculated, and the calculated Y5, X5, Y6 and X6 are the difference values Dc and Y5, X5, Y6 and X6 shown in Equation 7 The difference value Dc is calculated by substituting into the relational expression, and the quenching depth Lc is calculated by substituting the calculated difference value Dc into the relational expression between the quenching depth Lc and the difference value Dc shown in Equation 8. Calculate and bake A second hardening depth calculating unit 231e to the depth Lc and hardening depth of the measurement object 202 placed,
It comprises.
This configuration has the following advantages.
That is, the difference value Da, the difference value Db, and the difference value Dc are all high frequencies from the length of the vector on the low frequency side where the amplitude value of the detection signal is the Y axis and the phase difference between the AC excitation signal and the detection signal is the X axis. Since the value obtained by subtracting the length of the vector on the side is further divided by the length of the vector on the high frequency side, these values are simply affected by temperature fluctuations of the measurement object 202 and the surrounding environment. Smaller than using only length.
Further, by using different calibration curves (second calibration curve and third calibration curve) in the shallow range (surface side range) and the deep range (bulk side range) with the reference quenching depth Ls as a boundary, The measurement accuracy is improved as compared with the case where the quenching depth is calculated based on a single calibration curve that covers the entire range of the penetration depth.
Therefore, the quenching depth of the measurement object 202 can be accurately measured even when the temperature of the measurement object 202 or the surrounding environment varies.

In addition, the quenching depth measuring apparatus 200 includes:
The quenching depth of the measuring object 202 calculated by the second quenching depth calculating unit 231e is compared with a preset allowable quenching depth range, and the quenching depth of the measuring object 202 is determined to be allowable quenching. When the measurement object 202 is within the depth range, it is determined that the measurement object 202 is non-defective with respect to the quenching depth, and when the quenching depth of the measurement object 202 is not within the allowable quenching depth range, the measurement object is determined. The determination part 231f which determines with the thing 202 being inferior goods regarding the quenching depth is comprised.
By configuring in this way, it is possible to determine the quality of the quenching depth of the measurement object 202 according to a certain standard (whether the quenching depth is within the allowable quenching depth range). .

Further, the first frequency, the second frequency, the third frequency, the fourth frequency, the fifth frequency, and the sixth frequency of the quenching depth measuring apparatus 200 are (a) AC excitation of a plurality of frequencies. A signal is applied to the setting excitation coil to generate an induction current in the setting measurement object, and a detection signal for each frequency caused by the induction current is detected by the setting detection coil; and (b) the setting detection coil The amplitude value Y of the detection signal for each frequency, the AC excitation signal applied to the setting excitation coil, and the detection signal detected by the setting detection coil based on the detection signal for each frequency detected by The phase difference X is calculated, and (c) the amplitude value Y of the corresponding detection signal for each of a plurality of different frequencies applied to the setting excitation coil is set to the Y axis, and the phase difference between the corresponding AC excitation signal and the detection signal. The length of the vector to the X axis ^{(= (X 2 + Y 2} ) 0.5) is calculated, and all selects the two frequencies from a plurality of different frequencies applied to the excitation coil set (d) For the combination of, calculate the difference in vector length corresponding to the two selected frequencies, and further handle the difference in vector length corresponding to the higher frequency of the vectors corresponding to the two selected frequencies The difference value D0, which is a value divided by the length of the vector to be calculated, is calculated. (E) The difference value D0 is plotted on the horizontal axis for each of the selected two frequency combinations, and the measured value of the quenching depth by the cutting method is calculated. Plotting as the vertical axis, and obtaining a linear approximation formula by the least square method for each of these plots, (f) Of the obtained linear approximation formula by the least square method, the absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value Adopt the one that meets the standard range of the quenching depth as the first calibration curve, and select the lower one of the two frequencies related to the adopted first calibration curve. The first frequency, the higher frequency is set as the second frequency, and (g) in the obtained linear approximation formula by the least square method, the absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value, In addition, the penetration depth of the combination of the two corresponding frequencies is close to the surface of the measuring object for setting in the range in which the standard range of the quenching depth is divided into two with the reference quenching depth Ls as a boundary. The one that matches the surface side range that is the one of the two ranges is adopted as the second calibration curve, and the lower frequency of the two frequencies related to the adopted second calibration curve is the third frequency, the frequency is The higher one is the fourth frequency, and (h) is determined Standard of linear approximation formula using the least square method where the absolute value of the correlation coefficient is equal to or greater than a predetermined threshold and the penetration depth of the combination of the two corresponding frequencies is the quenching depth standard. Among the ranges divided into two with the reference quenching depth Ls as the boundary, the one that fits the bulk side range that is the range farther from the surface of the measurement object for setting is adopted as the third calibration curve, The procedure from the above (a) to (h) in which the lower frequency of the two frequencies related to the adopted third calibration curve is the fifth frequency and the higher frequency is the sixth frequency. Is set by
By configuring in this way, it is possible to set a combination of frequencies that maximizes the measurement accuracy of the quenching depth as the first frequency to the sixth frequency in accordance with the material and shape of the measurement object 202. As a result, it contributes to the improvement of the measurement accuracy of the quenching depth of the measuring object 202.
In addition, although a present Example is a structure from which all the 1st frequency thru | or 6th frequency become a different frequency, this invention is not limited to this, 1st frequency is depended on the property of a measurement object and the frequency of an alternating current excitation signal. The same effect can be obtained even when the second frequency and the fourth frequency are the same frequency, and the second frequency and the fourth frequency are the same frequency.

In addition, the quenching depth measuring apparatus 200 includes:
Among the plots with the difference value D0 as the horizontal axis and the measured value of the quenching depth by the cutting method as the vertical axis, a cubic approximate expression is obtained by the least square method for the one relating to the first calibration curve, and the least square method The measured value of the quenching depth by the cutting method corresponding to the inflection point of the third-order approximate expression is the reference quenching depth Ls.
With this configuration, it is possible to set the reference quenching depth Ls according to a certain standard according to the properties of the measurement object 202.

Below, the 2nd Example of the quenching depth measuring method which concerns on this invention using FIG. 15 is described.
The second embodiment of the quenching depth measuring method according to the present invention is a method for measuring the quenching depth of the measuring object 202 using the quenching depth measuring apparatus 200 shown in FIG. 11, and is shown in FIG. As described above, an excitation / detection step S2100, a difference value calculation step S2200, a first quenching depth calculation step S2300, a second quenching depth calculation step S2400, and a determination step S2500 are provided.

The excitation / detection step S2100 includes a first frequency, a second frequency that is higher than the first frequency, a third frequency, a fourth frequency that is higher than the third frequency, and a second frequency. A plurality of AC excitation signals having different frequencies including the fifth frequency and a sixth frequency that is higher than the fifth frequency are applied to the excitation coil 211 to generate an induced current in the measurement object 202 and excitation. In this step, the detection coil 221 detects a detection signal caused by the induced current generated in the measurement object 202 by the coil 211.
When the excitation / detection step S2100 ends, the process proceeds to a difference value calculation step S2200.

In the difference value calculation step S2200, the amplitude value Y1 of the detection signal corresponding to the first frequency, the AC excitation signal corresponding to the first frequency, the phase difference X1 of the detection signal corresponding to the first frequency, and the second frequency are calculated. The amplitude value Y2 of the corresponding detection signal, the AC excitation signal corresponding to the second frequency, and the phase difference X2 of the detection signal corresponding to the second frequency are calculated, and the calculated Y1, X1, Y2, and X2 are counted. This is a step of calculating the difference value Da by substituting it into the relational expression between the difference value Da shown in 3 and Y1, X1, Y2, and X2.
When the difference value calculation step S2200 is completed, the process proceeds to the first quenching depth calculation step S2300.

In the first quenching depth calculation step S2300, the difference value Da calculated in the difference value calculation step S2200 is substituted into the relational expression between the quenching depth La and the difference value Da shown in Equation 4 to thereby calculate the measurement object 202. This is a step of calculating the quenching depth La.
When the first quenching depth calculation step S2300 is completed, the process proceeds to a second quenching depth calculation step S2400 (more precisely, a comparison step 2410 described later).

  The second quenching depth calculation step S2400 includes a comparison step S2410, a surface side difference value calculation step S2421, a surface side quenching depth calculation step S2431, a bulk side difference value calculation step S2422, and a bulk side quenching depth calculation step S2432. It comprises.

The comparison step S2410 is a step of comparing the quenching depth La calculated in the first quenching depth calculating step S2300 with a preset reference quenching depth Ls.
As a result of the comparison, when the quenching depth La is less than the reference quenching depth Ls (when La <Ls), the process proceeds to the surface side difference value calculating step S2421.
As a result of the comparison, when the quenching depth La is equal to or greater than the reference quenching depth Ls (when La ≧ Ls), the process proceeds to the bulk-side difference value calculation step S2422.

In the surface side difference value calculation step S2421, the amplitude value Y3 of the detection signal corresponding to the third frequency, the AC excitation signal corresponding to the third frequency, and the phase difference X3 of the detection signal corresponding to the third frequency, the fourth The detection signal amplitude value Y4 corresponding to the frequency and the AC excitation signal corresponding to the fourth frequency and the phase difference X4 of the detection signal corresponding to the fourth frequency are calculated, and the calculated Y3, X3, Y4 and X4 are calculated. This is a step of calculating the difference value Db by substituting it into the relational expression between the difference value Db shown in Equation 5 and Y3, X3, Y4 and X4.
When the surface side difference value calculating step S2421 is completed, the process proceeds to the surface side quenching depth calculating step S2431.

In the surface side quenching depth calculation step S2431, the quenching depth is calculated by substituting the difference value Db calculated in the surface side difference value calculating step S2421 into the relational expression between the quenching depth Lb and the difference value Db shown in Equation 6. This is a step of calculating the thickness Lb and setting the quenching depth Lb to the quenching depth of the measuring object 202.
When the surface side quenching depth calculation step S2431 is completed, the process proceeds to the determination step S2500.

The bulk-side difference value calculation step S2422 includes the detection signal amplitude value Y5 corresponding to the fifth frequency, the AC excitation signal corresponding to the fifth frequency, and the detection signal phase difference X5 corresponding to the fifth frequency, The amplitude value Y6 of the detection signal corresponding to the frequency and the AC excitation signal corresponding to the sixth frequency and the phase difference X6 of the detection signal corresponding to the sixth frequency are calculated, and the calculated Y5, X5, Y6 and X6 are calculated. This is a step of calculating the difference value Dc by substituting it into the relational expression between the difference value Dc shown in Equation 7 and Y5, X5, Y6 and X6.
When the bulk side difference value calculation step S2422 is completed, the process proceeds to the bulk side quenching depth calculation step S2432.

In the bulk side quenching depth calculation step S2432, the quenching depth is calculated by substituting the difference value Dc calculated in the bulk side difference value calculating step S2422 into the relational expression between the quenching depth Lc and the difference value Dc shown in Formula 8. This is a step of calculating the thickness Lc and setting the quenching depth Lc to the quenching depth of the measuring object 202.
When the bulk-side quenching depth calculation step S2432 is completed, the process proceeds to the determination step S2500.

  In the determination step S2500, the quenching depth of the measurement object 202 calculated in the second quenching depth calculation step S2400 is compared with a preset allowable quenching depth range, and the quenching depth of the measurement object 202 is compared. Is within the allowable quenching depth range, it is determined that the measurement object 202 is a non-defective product with respect to the quenching depth, and the quenching depth of the measurement object 202 is not within the allowable quenching depth range. This is a step of determining that the measurement object 202 is defective with respect to the quenching depth.

As described above, the second embodiment of the quenching depth measuring method according to the present invention is:
Excitation / detection step S2100,
Difference value calculation step S2200;
First quenching depth calculation step S2300;
Second quenching depth calculation step S2400,
It comprises.
With this configuration, it is possible to accurately measure the quenching depth of the measurement target 202 even if the temperature of the measurement target 202 or the surrounding environment varies.

Further, the second embodiment of the quenching depth measuring method according to the present invention is:
The determination step S2500 is provided.
By configuring in this way, it is possible to determine the quality of the quenching depth of the measurement object 202 according to a certain standard (whether the quenching depth is within the allowable quenching depth range). .

Further, the first frequency, the second frequency, the third frequency, the fourth frequency, the fifth frequency, and the sixth frequency of the second embodiment of the quenching depth measuring method according to the present invention are: a) Applying an AC excitation signal of a plurality of frequencies to the setting excitation coil to generate an induced current in the setting measurement object, and detecting a detection signal for each frequency caused by the induced current by the setting detection coil (B) Based on the detection signal for each frequency detected by the setting detection coil, the amplitude value Y of the detection signal for each frequency and the AC excitation signal applied to the setting excitation coil and the setting detection coil A phase difference X with the detected detection signal is calculated. (C) For each of a plurality of different frequencies applied to the setting excitation coil, the amplitude value Y of the corresponding detection signal is set to the Y axis, and the corresponding AC excitation signal. When The length of the vector that the phase difference X and X axes of the output signal ^{(= (X 2 + Y 2} ) 0.5) was calculated from a plurality of different frequencies applied in (d) of setting the excitation coil For all combinations that select two frequencies, calculate the vector length difference corresponding to the two selected frequencies, and further calculate the vector length difference corresponding to the two selected frequencies. The difference value D0, which is a value divided by the length of the vector corresponding to the higher one of the frequencies, is calculated. (E) The difference value D0 is plotted on the horizontal axis for each of the selected two frequency combinations. The measured values of the insertion depth are plotted as the vertical axis, and linear approximation equations by least square method are obtained for each of these plots. (F) Among the obtained linear approximation equations by the least square method, the correlation coefficient Absolute That is equal to or greater than a predetermined threshold value and that conforms to the standard range of quenching depth is adopted as the first calibration curve, and the two frequencies related to the adopted first calibration curve are Of these, the lower frequency is the first frequency and the higher frequency is the second frequency. (G) The absolute value of the correlation coefficient is greater than or equal to a predetermined threshold in the obtained linear approximation formula using the least squares method. The measurement for setting in the range in which the penetration depth of the combination of the two corresponding frequencies is divided into two with the standard quenching depth Ls as the boundary, both of which are the penetration depth of the corresponding two frequency combinations The one that matches the surface side range that is the range closer to the surface of the object is adopted as the second calibration curve, and the lower one of the two frequencies related to the adopted second calibration curve is the first. The third frequency, the higher frequency is the fourth frequency (H) Among the obtained linear approximation formulas by the least square method, the absolute value of the correlation coefficient is not less than a predetermined threshold value, and the penetration depth of the combination of the two corresponding frequencies is any Of the range divided into two with the quenching depth standard range divided by the reference quenching depth Ls, the one that conforms to the bulk side range that is the farthest from the surface of the setting object to be measured is the third. The above-mentioned (a), in which the lower frequency of the two frequencies related to the adopted third calibration curve is the fifth frequency and the higher frequency is the sixth frequency. To (h).
By configuring in this way, it is possible to set a combination of frequencies that maximizes the measurement accuracy of the quenching depth as the first frequency to the sixth frequency in accordance with the material and shape of the measurement object 202. As a result, it contributes to the improvement of the measurement accuracy of the quenching depth of the measuring object 202.

Further, the second embodiment of the quenching depth measuring method according to the present invention is:
Among the plots with the difference value D0 as the horizontal axis and the measured value of the quenching depth by the cutting method as the vertical axis, a cubic approximate expression is obtained by the least square method for the one relating to the first calibration curve, and the least square method The measured value of the quenching depth by the cutting method corresponding to the inflection point of the third-order approximation formula is used as the reference quenching depth Ls.
With this configuration, it is possible to set the reference quenching depth Ls according to a certain standard according to the properties of the measurement object 202.

The figure which shows the 1st Example of the quenching depth measuring apparatus which concerns on this invention. The figure which shows the relationship between the crystal structure of a measuring object, hardness, and magnetic permeability, and the distance from the surface. The figure which shows the measurement principle of the quenching depth measuring apparatus which concerns on this invention. The figure which shows the relationship between an alternating current excitation signal and a detection signal. The figure which shows the relationship between the difference value D and quenching depth. The figure which shows the quenching depth measurement result of the comparative example 1. The figure which shows the quenching depth measurement result of the comparative example 2. FIG. The figure which shows the quenching depth measurement result of the 1st Example of the quenching depth measuring apparatus which concerns on this invention. The flowchart which shows the 1st Example of the quenching depth measuring method which concerns on this invention. The flowchart which shows the modification of the 1st Example of the quenching depth measuring method which concerns on this invention. The figure which shows the 2nd Example of the quenching depth measuring apparatus which concerns on this invention. The figure which shows the relationship between difference value Da and quenching depth. The figure which shows the relationship between difference value Db and quenching depth. The figure which shows the relationship between the difference value Dc and the quenching depth. The flowchart which shows the 2nd Example of the quenching depth measuring method which concerns on this invention.

Explanation of symbols

100 Hardening depth measuring device (first embodiment)
102 Measurement object 111 Excitation coil (first and second excitation coils)
121 Detection coil (first and second detection coil)
131c difference value calculation unit 131d quenching depth calculation unit

Claims (18)

A first excitation coil that generates an induced current in a measurement object by applying an AC excitation signal of a first frequency;
A first detection coil for detecting a detection signal caused by an induced current generated in the measurement object by the first excitation coil;
A second excitation coil that generates an induced current in the measurement object by applying an AC excitation signal of a second frequency that is higher than the first frequency;
A second detection coil for detecting a detection signal caused by an induced current generated in the measurement object by the second excitation coil;
The amplitude value Y1 of the detection signal of the first detection coil, the phase difference X1 of the AC excitation signal of the first excitation coil and the detection signal of the first detection coil, the amplitude value Y2 of the detection signal of the second detection coil, and A phase difference X2 between the AC excitation signal of the second excitation coil and the detection signal of the second detection coil is calculated, respectively, and Y1, X1, Y2, and X2 are set to the difference value D shown in the following Equation 1 and the Y1, X1. , Y2 and X2 are substituted into a relational expression to calculate the difference value D,
A quenching depth calculation unit that calculates a quenching depth L of the measurement object based on the difference value D calculated by the difference value calculation unit;
A quenching depth measuring device comprising:

The first excitation coil and the second excitation coil are the same excitation coil,
The first detection coil and the second detection coil are the same detection coil,
The quenching according to claim 1, further comprising an AC excitation signal applying unit capable of selectively applying either the first frequency AC excitation signal or the second frequency AC excitation signal to the same excitation coil. Depth measuring device. The quenching depth calculation unit
By substituting the difference value D calculated by the difference value calculation unit into the relational expression between the quenching depth L and the difference value D shown in the following equation 2, the quenching depth L of the measurement object is calculated. The quenching depth measuring device according to claim 1 or 2.

  The quenching depth L calculated by the quenching depth calculating unit is compared with a preset allowable quenching depth range, and the quenching depth L is within the allowable quenching depth range. In this case, it is determined that the measurement object is a non-defective product with respect to the quenching depth, and when the quenching depth L is not within the allowable quenching depth range, the measurement object is not satisfactory with respect to the quenching depth. The quenching depth measuring device according to any one of claims 1 to 3, further comprising a determination unit that determines that the product is a non-defective product. The first frequency and the second frequency are:
The quenching depth measuring apparatus according to any one of claims 1 to 4, which is set by the following procedures (1) to (6).
(1) An AC excitation signal having a plurality of frequencies is applied to a setting excitation coil to generate an induced current in a measurement object for setting, and a detection signal for each frequency caused by the induced current is detected by the setting detection coil. To do.
(2) Based on the detection signal for each frequency detected by the setting detection coil, the amplitude value Y of the detection signal for each frequency and the AC excitation signal applied to the setting excitation coil and the setting detection coil A phase difference X with the detected detection signal is calculated.
(3) For each of a plurality of different frequencies applied to the setting excitation coil, a vector having the amplitude value Y of the corresponding detection signal as the Y axis and the phase difference X between the corresponding AC excitation signal and the detection signal as the X axis ^Is calculated (= (X ² + Y ² ) ^0.5 ).
(4) For all combinations of selecting two frequencies from among a plurality of different frequencies applied to the setting excitation coil, calculate the difference in vector length corresponding to the two selected frequencies, and A difference value D0, which is a value obtained by dividing the vector length difference by the vector length corresponding to the higher one of the vectors corresponding to the two selected frequencies, is calculated.
(5) For each of the selected combinations of two frequencies, the difference value D0 is plotted on the horizontal axis, and the measured value of the quenching depth by the cutting method is plotted on the vertical axis. Find an approximate expression.
(6) Among the obtained linear approximation formulas by the least square method, any one whose absolute value of the correlation coefficient is equal to or greater than a predetermined threshold is adopted as a calibration curve, and two of the adopted calibration curves are used. Of the two frequencies, the lower frequency is the first frequency, and the higher frequency is the second frequency. An AC excitation signal having a first frequency is applied to the first excitation coil to generate an induced current in the measurement object, and a detection signal caused by the induced current generated in the measurement object is generated by the first excitation coil. A first excitation / detection process detected by one detection coil;
An AC excitation signal having a second frequency that is higher than the first frequency is applied to a second excitation coil to generate an induced current in the measurement object, and the measurement object is generated by the second excitation coil. A second excitation / detection step of detecting a detection signal caused by the induced current generated in the second detection coil;
The amplitude value Y1 of the detection signal of the first detection coil, the phase difference X1 of the AC excitation signal of the first excitation coil and the detection signal of the first detection coil, the amplitude value Y2 of the detection signal of the second detection coil, and A phase difference X2 between the AC excitation signal of the second excitation coil and the detection signal of the second detection coil is calculated, respectively, and Y1, X1, Y2, and X2 are expressed as the difference value D shown in the following equation 1 and the Y1, X1. , A difference value calculating step for calculating the difference value D by substituting it into the relational expression between Y2 and X2,
A quenching depth calculating step of calculating a quenching depth L of the measurement object based on the difference value D calculated in the difference value calculating step;
A quenching depth measuring method comprising:

The first excitation coil and the second excitation coil are the same excitation coil,
The first detection coil and the second detection coil are the same detection coil,
In the first excitation / detection step,
Applying an AC excitation signal of a first frequency to the same excitation coil;
In the second excitation / detection step,
The quenching depth measurement method according to claim 6, wherein an AC excitation signal having a second frequency is applied to the same excitation coil. In the quenching depth calculation step,
By substituting the difference value D calculated in the difference value calculation step into the relational expression between the quenching depth L and the difference value D shown in Equation 2 below, the quenching depth L of the measurement object is calculated. The quenching depth measuring method according to claim 6 or 7.

  The quenching depth L calculated in the quenching depth calculation step is compared with a preset allowable quenching depth range, and the quenching depth L is within the allowable quenching depth range. In this case, it is determined that the measurement object is a non-defective product with respect to the quenching depth, and when the quenching depth L is not within the allowable quenching depth range, the measurement object is not satisfactory with respect to the quenching depth. The quenching depth measurement method according to any one of claims 6 to 8, further comprising a determination step of determining that the product is a non-defective product. The first frequency and the second frequency are:
The quenching depth measuring method according to any one of claims 6 to 9, which is set by the following procedures (1) to (6).
(1) An AC excitation signal having a plurality of frequencies is applied to a setting excitation coil to generate an induced current in a measurement object for setting, and a detection signal for each frequency caused by the induced current is detected by the setting detection coil. To do.
(2) Based on the detection signal for each frequency detected by the setting detection coil, the amplitude value Y of the detection signal for each frequency and the AC excitation signal applied to the setting excitation coil and the setting detection coil A phase difference X with the detected detection signal is calculated.
(3) For each of a plurality of different frequencies applied to the setting excitation coil, a vector having the amplitude value Y of the corresponding detection signal as the Y axis and the phase difference X between the corresponding AC excitation signal and the detection signal as the X axis ^Is calculated (= (X ² + Y ² ) ^0.5 ).
(4) For all combinations of selecting two frequencies from among a plurality of different frequencies applied to the setting excitation coil, calculate the difference in vector length corresponding to the two selected frequencies, and A difference value D0, which is a value obtained by dividing the vector length difference by the vector length corresponding to the higher one of the vectors corresponding to the two selected frequencies, is calculated.
(5) For each of the selected combinations of two frequencies, the difference value D0 is plotted on the horizontal axis, and the measured value of the quenching depth by the cutting method is plotted on the vertical axis. Find an approximate expression.
(6) Among the obtained linear approximation formulas by the least square method, the one having the largest correlation coefficient is adopted as the calibration curve, and the lower one of the two frequencies related to the adopted calibration curve is the first. The higher frequency is the second frequency. A second frequency that is higher than the first frequency and the first frequency, a third frequency and a fourth frequency that is higher than the third frequency, and a fifth frequency and the first frequency An AC excitation signal generator that selectively generates a plurality of AC excitation signals having different frequencies including a sixth frequency that is higher than the fifth frequency;
An excitation coil that generates an induced current in a measurement object by applying an AC excitation signal generated by the AC excitation signal generator;
A detection coil for detecting a detection signal caused by an induced current generated in the measurement object by the excitation coil;
The amplitude value Y1 of the detection signal corresponding to the first frequency, the phase difference X1 of the AC excitation signal corresponding to the first frequency and the detection signal corresponding to the first frequency, and the detection corresponding to the second frequency The signal amplitude value Y2 and the phase difference X2 between the AC excitation signal corresponding to the second frequency and the detection signal corresponding to the second frequency are calculated, and Y1, X1, Y2 and X2 are set to the following equation (3) A difference value calculation unit that calculates the difference value Da by substituting it into the relational expression between the difference value Da shown and the Y1, X1, Y2, and X2.
By substituting the difference value Da calculated by the difference value calculation unit into the relational expression between the quenching depth La and the difference value Da shown in the following equation 4, the quenching depth La of the measurement object is calculated. A first quenching depth calculator,
When the quenching depth La calculated by the first quenching depth calculating unit is less than a preset reference quenching depth Ls, the amplitude value Y3 of the detection signal corresponding to the third frequency. , Corresponding to the AC excitation signal corresponding to the third frequency and the phase difference X3 of the detection signal corresponding to the third frequency, the amplitude value Y4 of the detection signal corresponding to the fourth frequency, and the fourth frequency. The phase difference X4 between the AC excitation signal and the detection signal corresponding to the fourth frequency is calculated, and Y3, X3, Y4 and X4 are expressed by the difference value Db shown in the following equation 5 and the Y3, X3, Y4 and X4. The difference value Db is calculated by substituting it into a relational expression, and the quenching depth is calculated by substituting the calculated difference value Db into the relational expression between the quenching depth Lb and the difference value Db shown in Equation 6 below. Lb is calculated and When the quenching depth Lb is set as the quenching depth of the measurement object, and the quenching depth La calculated by the first quenching depth calculating unit is equal to or greater than the reference quenching depth Ls , Corresponding to the amplitude value Y5 of the detection signal corresponding to the fifth frequency, the phase difference X5 of the AC excitation signal corresponding to the fifth frequency and the detection signal corresponding to the fifth frequency, and the sixth frequency. An amplitude value Y6 of the detection signal, an AC excitation signal corresponding to the sixth frequency, and a phase difference X6 of the detection signal corresponding to the sixth frequency are calculated, and Y5, X5, Y6, and X6 are set to the following equation (7). The difference value Dc is calculated by substituting the calculated difference value Dc into the relational expression between the difference value Dc and the Y5, X5, Y6, and X6. With value Dc A second hardening depth calculating unit that calculates the hardening depth Lc, to the hardening depth Lc and hardening depth of the measurement object by substituting the engagement type,
A quenching depth measuring device comprising:

  The quenching depth of the measurement object calculated by the second quenching depth calculation unit is compared with a preset allowable quenching depth range, and the quenching depth of the measurement object is compared with the allowable quenching depth. If it is within the quenching depth range, it is determined that the measurement object is a non-defective product with respect to the quenching depth, and the quenching depth of the measurement object is not within the allowable quenching depth range. The quenching depth measurement device according to claim 11, further comprising a determination unit that determines that the measurement object is defective with respect to the quenching depth. The first frequency, second frequency, third frequency, fourth frequency, fifth frequency and sixth frequency are:
The quenching depth measuring device according to claim 11 or 12, which is set by the following procedures (a) to (h).
(A) An AC excitation signal having a plurality of frequencies is applied to the setting excitation coil to generate an induced current in the measurement object for setting, and a detection signal for each frequency caused by the induced current is detected by the setting detection coil. To do.
(B) Based on the detection signal for each frequency detected by the setting detection coil, the amplitude value Y of the detection signal for each frequency and the AC excitation signal applied to the setting excitation coil and the setting detection coil A phase difference X with the detected detection signal is calculated.
(C) For each of a plurality of different frequencies applied to the setting excitation coil, a vector with the amplitude value Y of the corresponding detection signal as the Y axis and the phase difference X between the corresponding AC excitation signal and the detection signal as the X axis ^Is calculated (= (X ² + Y ² ) ^0.5 ).
(D) For all combinations of selecting two frequencies from among a plurality of different frequencies applied to the setting excitation coil, calculate the difference in vector length corresponding to the two selected frequencies; A difference value D0, which is a value obtained by dividing the vector length difference by the vector length corresponding to the higher one of the vectors corresponding to the two selected frequencies, is calculated.
(E) The difference value D0 is plotted with respect to each of the selected two frequency combinations on the horizontal axis, and the measured value of the quenching depth by the cutting method is plotted on the vertical axis. Find an approximate expression.
(F) Among the obtained linear approximation formulas by the least square method, those whose absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value and which meet the quenching depth standard range As a calibration curve, the lower frequency of the two frequencies related to the adopted first calibration curve is the first frequency, and the higher frequency is the second frequency.
(G) Among the obtained linear approximation equations by the least square method, the absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value, and the penetration depths of the corresponding two frequency combinations are both What fits the surface side range which is the range closer to the surface of the measuring object for setting among the ranges obtained by dividing the standard range of the quenching depth into two with the reference quenching depth Ls as a boundary Adopted as the second calibration curve, of the two frequencies related to the adopted second calibration curve, the lower frequency is the third frequency and the higher frequency is the fourth frequency.
(H) Among the obtained linear approximation formulas by the least square method, the absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value, and the penetration depths of the corresponding two frequency combinations are both Among the ranges obtained by dividing the standard range of the quenching depth into two with the reference quenching depth Ls as a boundary, those that conform to the bulk-side range that is the range farther from the surface of the measurement object for setting Adopted as a third calibration curve, of the two frequencies related to the adopted third calibration curve, the lower frequency is the fifth frequency and the higher frequency is the sixth frequency.   Among the plots with the difference value D0 as the horizontal axis and the measurement value of the quenching depth by the cutting method as the vertical axis, a cubic approximate expression by the least square method is obtained for the one relating to the first calibration curve, and the minimum The quenching depth measuring device according to claim 13, wherein a measured value of a quenching depth by a cutting method corresponding to an inflection point of a cubic approximation expression by a square method is the reference quenching depth Ls. A first frequency and a second frequency that is higher than the first frequency, a third frequency and a fourth frequency that is higher than the third frequency, and a fifth frequency and the first frequency. A plurality of different frequency alternating current excitation signals including a sixth frequency that is higher than the fifth frequency are applied to the excitation coil to generate an induced current in the measurement object, and the excitation coil causes the measurement object to An excitation / detection process for detecting a detection signal caused by the induced current generated by the detection coil;
The amplitude value Y1 of the detection signal corresponding to the first frequency, the phase difference X1 of the AC excitation signal corresponding to the first frequency and the detection signal corresponding to the first frequency, and the detection corresponding to the second frequency The signal amplitude value Y2 and the phase difference X2 between the AC excitation signal corresponding to the second frequency and the detection signal corresponding to the second frequency are calculated, and Y1, X1, Y2 and X2 are set to the following equation (3) A difference value calculation step of calculating the difference value Da by substituting it into a relational expression between the difference value Da shown and the Y1, X1, Y2 and X2.
By substituting the difference value Da calculated in the difference value calculating step into the relational expression between the quenching depth La and the difference value Da shown in the following equation 4, the quenching depth La of the measurement object is calculated. First quenching depth calculation step,
When the quenching depth La calculated in the first quenching depth calculating step is less than the preset reference quenching depth Ls, the amplitude value Y3 of the detection signal corresponding to the third frequency. , Corresponding to the AC excitation signal corresponding to the third frequency and the phase difference X3 of the detection signal corresponding to the third frequency, the amplitude value Y4 of the detection signal corresponding to the fourth frequency, and the fourth frequency. The phase difference X4 between the AC excitation signal and the detection signal corresponding to the fourth frequency is calculated, and Y3, X3, Y4 and X4 are expressed by the difference value Db shown in the following equation 5 and the Y3, X3, Y4 and X4. The difference value Db is calculated by substituting it into a relational expression, and the quenching depth is calculated by substituting the calculated difference value Db into the relational expression between the quenching depth Lb and the difference value Db shown in Equation 6 below. Calculate Lb When the quenching depth Lb is set as the quenching depth of the measurement object, and the quenching depth La calculated in the first quenching depth calculating step is equal to or greater than the reference quenching depth Ls. Corresponds to the amplitude value Y5 of the detection signal corresponding to the fifth frequency, the AC excitation signal corresponding to the fifth frequency and the phase difference X5 of the detection signal corresponding to the fifth frequency, and the sixth frequency. The detection signal amplitude value Y6 and the AC excitation signal corresponding to the sixth frequency and the phase difference X6 of the detection signal corresponding to the sixth frequency are calculated, and Y5, X5, Y6 and X6 are expressed by the following equation (7). The difference value Dc is calculated by substituting it into the relational expression between the difference value Dc shown in FIG. 5 and the Y5, X5, Y6, and X6, and the calculated difference value Dc is expressed as the quenching depth Lc shown in Equation 8 below. Difference value A second hardening depth calculation step of calculating a hardening depth Lc, to the hardening depth Lc and hardening depth of the measurement object by substituting the relation of is c,
A quenching depth measuring method comprising:

  The quenching depth of the measurement object calculated in the second quenching depth calculation step is compared with a preset allowable quenching depth range, and the quenching depth of the measurement object is compared with the allowable quenching depth. If it is within the quenching depth range, it is determined that the measurement object is a non-defective product with respect to the quenching depth, and the quenching depth of the measurement object is not within the allowable quenching depth range. The quenching depth measurement method according to claim 15, further comprising a determination step of determining that the measurement object is a defective product with respect to the quenching depth. The first frequency, second frequency, third frequency, fourth frequency, fifth frequency and sixth frequency are:
The quenching depth measuring method according to claim 15 or 16, which is set by the following procedures (a) to (h).
(A) An AC excitation signal having a plurality of frequencies is applied to the setting excitation coil to generate an induced current in the measurement object for setting, and a detection signal for each frequency caused by the induced current is detected by the setting detection coil. To do.
(B) Based on the detection signal for each frequency detected by the setting detection coil, the amplitude value Y of the detection signal for each frequency and the AC excitation signal applied to the setting excitation coil and the setting detection coil A phase difference X with the detected detection signal is calculated.
(C) For each of a plurality of different frequencies applied to the setting excitation coil, a vector with the amplitude value Y of the corresponding detection signal as the Y axis and the phase difference X between the corresponding AC excitation signal and the detection signal as the X axis ^Is calculated (= (X ² + Y ² ) ^0.5 ).
(D) For all combinations of selecting two frequencies from among a plurality of different frequencies applied to the setting excitation coil, calculate the difference in vector length corresponding to the two selected frequencies; A difference value D0, which is a value obtained by dividing the vector length difference by the vector length corresponding to the higher one of the vectors corresponding to the two selected frequencies, is calculated.
(E) The difference value D0 is plotted with respect to each of the selected two frequency combinations on the horizontal axis, and the measured value of the quenching depth by the cutting method is plotted on the vertical axis. Find an approximate expression.
(F) Among the obtained linear approximation formulas by the least square method, those whose absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value and which meet the quenching depth standard range As a calibration curve, the lower frequency of the two frequencies related to the adopted first calibration curve is the first frequency, and the higher frequency is the second frequency.
(G) Among the obtained linear approximation equations by the least square method, the absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value, and the penetration depths of the corresponding two frequency combinations are both What fits the surface side range which is the range closer to the surface of the measuring object for setting among the ranges obtained by dividing the standard range of the quenching depth into two with the reference quenching depth Ls as a boundary Adopted as the second calibration curve, of the two frequencies related to the adopted second calibration curve, the lower frequency is the third frequency and the higher frequency is the fourth frequency.
(H) Among the obtained linear approximation formulas by the least square method, the absolute value of the correlation coefficient is equal to or greater than a predetermined threshold value, and the penetration depths of the corresponding two frequency combinations are both Among the ranges obtained by dividing the standard range of the quenching depth into two with the reference quenching depth Ls as a boundary, those that conform to the bulk-side range that is the range farther from the surface of the measurement object for setting Adopted as a third calibration curve, of the two frequencies related to the adopted third calibration curve, the lower frequency is the fifth frequency and the higher frequency is the sixth frequency.   Among the plots with the difference value D0 as the horizontal axis and the measurement value of the quenching depth by the cutting method as the vertical axis, a cubic approximate expression by the least square method is obtained for the one relating to the first calibration curve, and the minimum The quenching depth measurement method according to claim 17, wherein a measured value of a quenching depth by a cutting method corresponding to an inflection point of a cubic approximation expression by a square method is the reference quenching depth Ls.

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