JP2000002601A - Stress measurement method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To accurately measure a stress acting on an object to be measured. In a method of measuring a stress of an object to be measured by using a magnetostrictive sensor, an output waveform of an electromotive force when the magnetostrictive sensor is rotated and induced near the object to be measured is expressed by an equation (1). _s, B _s, determine the C _s, a _s and, dimensionless by the B _s by using a function indicating the relationship between the value to be used for dimensionless and parameter a, magnetostrictive sensors stress and dimensionless a function representing the relationship between the electromotive force of, based on the dimensionless B _s, measures the stress of the object to be measured. V = A + B · COS [2 · (θ−C)] (1) Here, V is a rectified value of the AC electromotive force induced in the magnetostrictive sensor, and θ is the open end of the two U-shaped yokes. This is the angle between the bisector of the angle formed by the connected straight lines and the reference axis of the device under test, and A, B, and C are parameters.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a stress acting on an object using a magnetostrictive sensor.

[0002]

2. Description of the Related Art Generally, ferromagnetic materials such as steel materials are
When magnetized, the length expands and contracts in that direction (magnetostriction effect).
Conversely, when stress is applied to the device under test, the magnetic properties of the device under test change (the opposite effect of the magnetostrictive effect).

Conventionally, there has been used a method of measuring a stress acting on an object to be measured by utilizing an inverse effect of the magnetostriction effect. In particular, JP-A-62-121325,
JP-A-1-135338, JP-A-7-11027
The technology disclosed in Japanese Patent Application Publication No. 0-2005 / 0105 and the like makes it possible to non-destructively measure stress applied to a steel structure or a mechanical component relatively easily by utilizing magnetic anisotropy caused by an inverse effect of the magnetostrictive effect. Is effective in

[0004] The above method is based on the following principle. FIG. 14 is a perspective view showing an example of arrangement of magnetostrictive sensors in a stress measurement method using magnetic anisotropy.

In the magnetostrictive sensor 1, a U-shaped exciting yoke 3 wound with an exciting coil 2 and a U-shaped detecting yoke 5 wound with a detecting coil 4 are mutually centered in a yoke saddle portion. Are arranged so as to be orthogonal to each other.

The exciting coil 2 is provided with an AC power supply 7 for passing an AC current to excite the DUT 6 which is a magnetic material. Further, the detection coil 4 is provided with a voltmeter 8 for measuring the induced electromotive force and detecting the magnetic flux flowing through the DUT 6. FIG.
Arrows indicate the direction of the magnetic flux.

Now, it is assumed that a tensile stress σ _X acts on the object 6 in the X direction. The permeability of the X direction of the object 6 at this time is mu _X. Further, the permeability of the object 6 in the X direction and the Y direction perpendicular to the mu _Y.

In this case, the magnetic permeability μ _X , μ _Y has a relationship represented by the following equation (1), ie, magnetic anisotropy, due to the inverse effect of the magnetostriction effect due to the stress σ _X. μ _X > μ _Y (2) The openings of both yokes 3 and 4 of the magnetostrictive sensor 1 are brought close to the DUT 6 in which such magnetic anisotropy is generated. When an object to be measured is excited by applying an AC current to the exciting coil 2 wound around the exciting yoke 3 by the AC power supply 7, most of the magnetic flux emitted from one opening end 3 a of the exciting yoke 3 is directly It goes to the other open end 3b of the exciting yoke 3.

However, the object 6 has a tensile stress σ _X
As a result, magnetic anisotropy as shown in equation (2) is generated.
Part of the magnetic flux passes through the detection yoke 5 and the excitation yoke 3
To the open end 3b.

For this reason, the voltmeter 8 attached to the detecting coil 4 wound around the detecting yoke 5 has the following (3)
The electromotive force shown in the equation is induced, and this electromotive force is output. _{V = M 0 · (μ X} -μ Y) · COS [2 · (θ-π / 4)] ... (3) where, V is is a rectification value of the AC electromotive force induced in the detection coil 4 . M ₀ is a value determined by the excitation conditions, the coil, the magnetic characteristics of the device under test 6, and the like. Further, COS [2 · (θ−π / 4)] is a cosine function,
θ is the angle between the straight line connecting one open end 5a and the other open end 5b of the detection yoke 5 and the X-axis.

Further, since the difference in magnetic permeability (μ _X -μ _Y ) is proportional to the difference in stress (σ _X -σ _Y ), the equation (3) can be rewritten as the following equation (4). V = M · (σ _X −σ _Y ) · COS [2 · (θ−π / 4)] (4) Here, M is determined by excitation conditions, coil conditions, magnetic characteristics of the DUT 6, and the like. It is a value determined.

Therefore, by measuring the voltage V and using the equation (4), the difference between the stresses acting on the object 6 can be determined. Since the case where the stress acts in the X direction is shown here, the stress can be obtained from this stress difference.

FIG. 15 is a diagram showing the relationship between the stress of the DUT 6 and the output V of the magnetostrictive sensor 1. As shown in this FIG. 15, the output V of the stress and the magnetostriction sensor has an approximately linear relationship in a predetermined linear range T _1.

Accordingly, the coefficient M of the equation (4)
Referred to as "magnetostrictive sensitivity") can be defined as a predetermined in the linear range T ₁ constant. Therefore, this predetermined linear range T
The magnetostriction sensitivity M in ₁ can be defined by regressing the characteristics of FIG. 15 on a straight line by a statistical method such as least squares approximation.

However, the magnetostrictive sensitivity M changes depending on the distance between the magnetostrictive sensor 1 and the object 6 (hereinafter referred to as "lift-off"). Generally, the DUT 6
The steel structures and mechanical parts are coated with a coating or the like for corrosion protection, but the thickness of the coating is not strict and varies.

For this reason, it is difficult to strictly define the lift-off at the time of measurement. In addition, even if such anticorrosion measures are not taken, measurement is automated,
When non-contact measurement is performed at high speed, it is difficult to strictly define the lift-off.

Japanese Patent Application Laid-Open No. 9-257598 discloses a method of detecting and using a lift-off by the magnetostrictive sensor 1 and the object 6 to prevent the influence of the lift-off.

In this stress measuring method, first, FIG.
The relationship between the lift-off and the parameter A as shown in FIG. Here, FIG. 16A is a conceptual diagram showing a state of change of the lift-off voltage _VL with respect to the lift-off.

FIG. 16B is a diagram showing a specific example in a case where SM490 is applied as the DUT 6. Next, in this stress measurement method, the relationship between lift-off and magnetostriction sensitivity M as shown in FIG. 17 is obtained.

Then, the relationship between the parameter A and the magnetostriction sensitivity M shown in FIG. 18 is obtained from the obtained FIG. 16 and FIG. Therefore, when measuring the stress acting on the DUT 6, the parameter A is measured first.

Next, using the measured parameter A and FIG. 18 obtained above, the magnetostriction sensitivity M in which the influence of the lift-off is corrected is obtained. Then, the measured magnetostrictive sensor output V and magnetostrictive sensitivity M are substituted into equation (4),
Stress is required.

[0022]

However, in the above-described conventional stress measurement method, the output characteristic of the magnetostrictive sensor generated by the stress is treated as linear as shown in FIG. In the case where the output characteristics of the magnetostrictive sensor 1 are nonlinear in the non-linear ranges T ₂ and T ₃ in the case where the stress state 6 is large or small, the magnetostrictive sensitivity used for the evaluation is larger than the actual magnetostrictive sensitivity, and the stress is consequently smaller. Will be required.

In this case, even if the stress actually acting on the structure or the mechanical component is at a dangerous level, it may be determined that the measured stress does not reach the dangerous level. That is, when the stress acting on the structure or the mechanical component is evaluated from the viewpoint of safety against destruction, a dangerous result is obtained.

As a countermeasure against such a problem, for example, when approximating the output characteristics of the magnetostrictive sensor 1 with respect to stress as shown in FIG. 15, it is considered to approximate to a higher-order polynomial in consideration of its nonlinearity. Can be

However, in this case, the mathematical processing of the correction for the lift-off described above becomes very complicated and practically difficult. The present invention has been made in view of the above situation, and provides a stress measurement method that considers the non-linearity of the electromotive force of a magnetostrictive sensor with respect to stress and that corrects output characteristics of the magnetostrictive sensor with respect to lift-off. The purpose is to:

[0026]

In order to achieve the above object, the present invention takes the following measures. The present invention uses a magnetostrictive sensor in which a U-shaped yoke wound with an exciting coil and a U-shaped yoke wound with a detection coil are arranged so as to be orthogonal to each other at the center of the yoke saddle. And a method for measuring a stress acting on an object to be measured.

The present invention will be described in detail. First, the open ends of the two U-shaped yokes are brought closer to the object to be measured. Next, an alternating current is passed through the exciting coil to rotate the magnetostrictive sensor. Thus, the output waveform of the electromotive force induced in the detection coil is expressed by the following equation (1), and the values A _s , B _s , and C _s of the parameters A, B, and C are obtained. Then, by using the function indicating the parameter values A _s, the relationship between the value to be used for dimensionless and parameter A, the dimensionless parameter value B _s. Then, a dimensionless parameter value B _s, based on the function representing the relationship between the stress and the electromotive force of the dimensionless magnetostrictive sensor to measure the stress applied to the DUT.

V = A + B · COS [2 (θ−C)] (1) V: rectified value of AC electromotive force induced by the magnetostrictive sensor θ: straight line connecting the open ends of both U-shaped yokes A, B, and C: parameters formed by the bisector of the angle formed by the reference axis of the device under test and the reference axis of the device under test Here, the function used in the above is set in advance based on the result of a calibration test. . The function used in the present invention is set in advance based on the result of a calibration test.

By measuring the stress by the above method,
The stress can be easily and accurately measured without being affected by the non-linear characteristic of the magnetostrictive sensor for an arbitrary lift-off.

[0030]

Embodiments of the present invention will be described below with reference to the drawings. In the stress measurement method according to the present embodiment, a calibration test is performed in advance to collect data, the data is analyzed, and a function specifying process for specifying approximate functions φ and ρ required for stress measurement is performed. . Then, a stress measurement process for measuring the stress acting on the object to be measured is performed using the approximate functions φ and ρ.

In the following, the same components as those in FIGS. 14 to 18 described above are denoted by the same reference numerals, and description thereof will be omitted. First, the function specifying process will be described.

FIG. 1 is a flowchart showing the flow of the function specifying process. In this process, first, a calibration test piece manufactured from a material of the same type or the same standard as the measured object is prepared (s1).

FIG. 2 is a top view showing an example of the calibration test piece. The calibration test piece 9 is provided with strain gauges 10a and 10b for detecting a load stress during the test. Also, the installation position 11 of the magnetostrictive sensor 1
Is specified. Further, here, the longitudinal direction of the calibration test piece 9 is the X direction, the width direction is the Y direction, and an angle between the X direction and the X direction is θ.

Next, in the function specifying process, the calibration test piece 9 is set in the load applying device (s2). This load application device is a device that applies a load that becomes a stress to the calibration test piece 9. As this load applying device, for example, a four-point bending test device capable of applying both tensile stress and compressive stress to the calibration test piece 9 is used.

Next, the magnetostrictive sensor 1 is arranged on the sensor installation position 11 of the calibration test piece 9 with an arbitrary lift-off (s3). In this way, by lifting the magnetostrictive sensor 1 from the calibration test piece 9 and ensuring lift-off, the axis of the magnetostrictive sensor 1 is used as a rotation axis, and this rotation axis can be rotated substantially parallel to the normal line of the calibration test piece 9. .

Next, the calibration test piece 9 is
Is applied in the X direction (s4). Next, the axis of the magnetostrictive sensor 1 is set as the rotation axis, and the magnetostriction sensor 1 is rotated by the rotation mechanism so that the rotation axis is parallel to the normal line of the calibration test piece 9 (s5).

FIG. 3 is a conceptual diagram showing a rotation mechanism for rotating the magnetostrictive sensor 1. The magnetostrictive sensor 1 is rotatably provided in a housing 13 of the rotation mechanism 12 via a pinion gear 14 and a ring gear 15. Also,
In the housing 13, a DC servo motor 16 having an encoder is provided. C ring 17 is DC
It has the function of maintaining the rotational position of the magnetostrictive sensor 1 by the servo motor 16. The ball bearing 18 has an operation of smoothly rotating the magnetostrictive sensor 1 by the DC servo motor 16. Further, the ring spacer 19 is arranged between the magnetostrictive sensor 1 and the calibration test piece 9 or the object to be measured, and has a function of securing a certain degree of lift-off. By ensuring the lift-off by the ring spacer 19 in this way, it is possible to prevent the electromotive force of the magnetostrictive sensor 1 from being saturated when the lift-off becomes extremely small.

Next, in the function specifying process, the rotation angle θ
Each time, the output value V of the electromotive force of the magnetostrictive sensor 1 induced in the detection coil 4 of the magnetostrictive sensor 1 is measured (s6). FIG.
FIG. 5 is a diagram showing a change in magnetostrictive sensor output V with respect to rotation angle θ.

As shown in FIG. 4, the change of the electromotive force V detected by rotating the magnetostrictive sensor 1 is similar to that of the equation (1). V = A + B · COS [2 · (θ−C)] (1) where V is an integer value of the AC electromotive force induced in the detection coil 4, and θ is a straight line connecting the open ends of both yokes. The bisector of the angle formed is the angle formed by the reference direction of the calibration test piece 9. Further, COS [2 · (θ−C)] is a cosine function. A, B, and C are parameters.

Therefore, in the function specifying process, the change of the magnetostrictive sensor output V with respect to the rotation angle θ is approximated by the equation (1) (s7). Here, the parameter B determined by approximation is a voltage value corresponding to the main stress difference applied to the calibration test piece 9, that is, a main stress equivalent voltage value. Further, the main direction of the stress applied to the calibration test piece 9 can be specified from the parameters B and C.

The determined parameters A, B, and C are held in relation to the current lift-off and stress. Next, the parameter B, and using the C, (5) below, the magnetostrictive sensor output V _a is obtained in the (X-direction in this case) the main direction of stress (s8). That is, this V
a is the main stress direction component of the magnetostrictive sensor output V.

V _a = B · COS (2C) (5) By applying the equation (5), a sign is given to the parameter B indicating the voltage corresponding to the main stress difference. .

Next, the load stress of the calibration test piece 9 at the time of measuring the electromotive force Va is obtained by the strain gauge (s9). The above-mentioned parameters A, B, C, and process for obtaining the principal stress direction component V _a magnetostrictive sensor output V is
It is sequentially executed while changing an arbitrary stress applied to the calibration test piece 9 at an appropriate pitch. Thus, the main stress direction component V _a magnetostrictive sensor output V is determined for various stresses (s10).

FIG. 5 is a diagram showing _a change in the main stress direction component Va of the magnetostrictive sensor output V when the stress is changed. Further, in the lift-off of the current, when measuring a principal stress direction component V _a magnetostrictive sensor output V for a sufficient number of stress changes the lift-off of the current to another state (s11).

[0045] Then, the parameter A for the new lift-off after the change, B, C are measured while changing the stress in the same manner as the above processing, thereby the main stress direction component V _a magnetostrictive sensor output V for each lift The relationship of the applied stress is determined (s12).

[0046] Figure 6 is a diagram showing the relationship between the main stress direction component V _a and the load stress of the magnetostrictive sensor output V at various lift-off. Here, FIG. 6 (a), the three lift L ₁ ~L _3, shows changes in the main stress direction component V _a magnetostrictive sensor output in the case of changing stresses (calibration curve for each lift) It is a conceptual diagram.

FIG. 6B shows a specific change when SM490 having a thickness of 20 mm is used as the calibration test piece 9. In FIG. 6B, the lift-off is 1.0
mm, 1.5 mm, and 2.0 mm.

Normally, considering the adverse effect of the magnetostriction effect, when the stress acting on the calibration test piece 9 is zero, the amplitude B of the output waveform of the electromotive force V obtained by rotating the magnetostrictive sensor 1 is also obtained. to become zero, the main stress direction component V _a of the electromotive force V is considered to be zero.

However, in FIG. 6, the applied stress is + Δ
When the X, the main stress direction component V _a magnetostrictive sensor output V is zero. That is, FIG. 6 shows that the residual stress of the calibration test piece 9 is -ΔX.

[0050] Thus, in this function a particular process, the main stress direction component V _a and the stress of the magnetostrictive sensor output V (=
sigma _X - [sigma] _Y) of characteristics (calibration curve) by shifting in the negative direction of the amount corresponding stress residual stress, the principal stress direction component V _a magnetostrictive sensor output V for the absolute stress (absolute stress)
Is required (s13).

[0051] Figure 7 is a diagram showing the relationship between the main stress direction component V _a and the absolute stress of the magnetostrictive sensor output V, are shown for the three lift L ₁ ~L _3. Here, with reference to FIG. 8, the main stress direction component V _a magnetostrictive sensor output V, and the characteristics of the absolute stress will be described. In FIG. 8 illustrates only characteristic of the case in the one lift-off L ₁ in order to simplify the description.

As the stress σ _max in FIG. 8, an existing stress level such as a yield stress or a design allowable stress of the material to be measured is used. Characteristics of the main stress direction component V _a magnetostrictive sensor output V for the absolute stress, magnetostrictive sensors 1
Is symmetrical about the origin at the point of origin. That is, when the absolute values of the absolute stresses are equal and the signs are different,
The main stress direction component V _a magnetostrictive sensor output V also has an absolute value equal signs are different relations. For example, the absolute stress σ _max
The main stress direction component V _a magnetostrictive sensor output with respect to the V _max
When a is a principal stress direction component V _a magnetostrictive sensor output V for the absolute stress - [sigma] _max becomes -V _max.

[0053] Similarly, if the principal stress direction component _{V a} magnetostrictive sensor output V in an absolute stress σ ₁ ~σ ₃ is _V 1 ~V ₃ is magnetostrictive sensor output V in an absolute stress -σ ₁ ~σ ₃ the main stress direction component V _a of becomes -V ₁ ~-V _3.

Next, in the function specifying process characteristics of the main stress direction component V _a magnetostrictive sensor output V for the absolute stress is dimensionless (normalized) by the V _max (s
14).

FIG. 9 is a graph showing the characteristic of the dimensionless magnetostrictive sensor output P with respect to the absolute stress. P _max in the FIG. _{9, P 3 ~P 1, -P} 1 ~P 3, -P max
Is a dimensionless value of the main stress direction components V _max , V _{3 to} V ₁ , −V ₁ to −V ₃ , and −V _max of the magnetostrictive sensor output V shown in FIG. ) To (13).

P _max = V _max / V _max (6) P ₃ = V ₃ / V _max (7) P ₂ = V ₂ / V _max (8) P ₁ = V ₁ / V _max (9) _{) -P 1 = (- V 1} ) / V max ... (10) -P 2 = (- V 2) / V max ... (11) -P 3 = (- V 3) / V max ... (12) - P _max = (− V _max ) / V _max (13) Unlike the case of FIG. 8, the characteristic of the dimensionless magnetostrictive sensor output P shown in FIG. 9 is unique regardless of the lift-off of the magnetostrictive sensor 1. Is defined as

Next, the x-axis and y-axis in FIG. 9 showing the relationship between the dimensionless magnetostrictive sensor output P and the absolute stress are exchanged, and FIG. 10 is obtained (s15). Here, FIG. 10A shows that the dimensionless magnetostrictive sensor output P is x
It is a conceptual diagram which made an axis | shaft an absolute stress and made a y-axis.

On the other hand, FIG. 10B shows a specific change when the SM490 having a thickness of 20 mm is used as the calibration test piece 9. That is, FIG.
Characteristics of (b) (lift-off is 1.0 mm, 1.5 mm,
(In the case of 2.0 mm), is made dimensionless, and the x-axis and the y-axis are interchanged.

Next, the relationship between the dimensionless magnetostrictive sensor output P and the absolute stress shown in FIG. 10 is approximated by a higher-order polynomial, and an approximate function φ is defined (s16). By the above processing, the approximate function φ for obtaining the stress from the dimensionless magnetostrictive sensor output P is obtained.

[0060] Subsequently, in the processing for obtaining an approximate function ρ is a characteristic of the principal stress direction component V _a magnetostrictive sensor output V for the absolute stress of FIG. 7 indicated above and describes the contact of FIG. 8 sigma _max from a, V _max of each lift-off is determined (s17).

[0061] Figure 11 is a conceptual diagram showing a state of the V _max for each lift-off. The relationship between V _max for each parameter A and a lift-off determined by the previously determined (s1
8).

[0062] Figure 12 is a diagram showing a relationship between the absolute value of this parameter A and lift-off for each of the V _max. here,
FIG. 12A shows a conceptual diagram, and FIG.
Shows a specific example in a case where SM490 having a thickness of 20 mm is used as the calibration test piece 9.

Next, the characteristic of the absolute value of V _max with respect to the lift-off voltage shown in FIG. 12 is approximated by an appropriate equation, and an approximate function ρ is defined (s20). Using this approximation function ρ, V at any lift-off
It is possible to estimate max.

Then, the obtained approximation functions φ and ρ are stored in a database as output characteristics of the magnetostrictive sensor 1 (s2
1). As described above, in the function specifying process, the approximation function ρ for _obtaining the value V _max to be used for non-dimensionalization from the parameter A and the approximation function φ for obtaining stress from the non-dimensionalized magnetostrictive sensor output are used. Is required.

Next, a description will be given of a stress measurement process for actually obtaining the stress of the object to be measured by using the approximate function ρ and the approximate function φ. FIG. 13 is a flowchart showing the flow of the stress measurement process.

First, at an arbitrary observation point S of the object to be measured, the magnetostrictive sensor 1 is rotated (t1), and the output waveform of the electromotive force V obtained by this rotation is approximated by the equation (5), and the parameters A and B are obtained. , C are obtained (t2).

Here, the obtained parameter A,
B, C, respectively A _s, B _s, and a C _s. At this time, as shown in (14) below, parameters A and approximation function indicating the relationship between V _max [rho, the value of the determined parameter A A _s is substituted, V at the observation point S
is a _max (V _{max) s} is required (t3).

(V _max ) _s = ρ (A _s ) (14) Next, using the following equation (15), B _s and (V _max ) _s , the dimensionless magnetostriction at the observation point S is obtained. Sensor output P
_s is obtained (t4).

P _s = B _s / (V _max ) _s (15) Next, as shown in the following equation (16), an approximate function φ for obtaining the absolute stress from the dimensionless magnetostrictive sensor output P is obtained. ,
The obtained magnetostrictive sensor P _s is substituted, an absolute stress difference (σ ₁ −σ ₂ ) _s at the observation point S is obtained, and a stress is measured based on this stress difference (t5).

(Σ ₁ −σ ₂ ) _s = φ (P _s ) (16) The stress direction in which the absolute stress difference (σ ₁ −σ ₂ ) _s is obtained is indicated by C _s .

Therefore, the stress (σ _x −σ _y ) _s of the component in the main stress direction of the object to be measured can be obtained by the following equation (17). (Σ _x −σ _y ) _s = (σ ₁ −σ ₂ ) _s · COS (2C _s ) (17) As described above, in the stress measurement method according to the present embodiment, first, the function identification processing is performed. , Parameter A
V _max the determined approximate function [rho, and the approximate function φ for obtaining the dimensionless stress from the magnetostrictive sensor output P has is determined from.

Then, by the stress measurement process, the stress is obtained from the characteristics of the magnetostrictive sensor output obtained by rotating the magnetostrictive sensor 1, the parameters A, B, and C, and the approximate functions φ and ρ.

When the above method is applied, the stress can be easily and accurately measured for an arbitrary lift-off without being affected by the non-linear characteristic generated in the electromotive force output of the magnetostrictive sensor.

In the present embodiment, SM490 used as a specific example of the calibration test piece has carbon of 0.20% by weight or less, silicon of 0.55% by weight or less, manganese of 1.60% by weight or less, It is a steel material containing 0.035% by weight or less of phosphorus and 0.035% by weight or less of sulfur.

[0075]

As described in detail above, in the stress measuring method of the present invention, a parameter representing the output waveform of the electromotive force induced by rotating the magnetostrictive sensor is measured, and the output characteristic of the magnetostrictive sensor is dimensionless. And measure the stress.

By applying the stress measuring method of the present invention, the stress can be measured without being affected by the nonlinearity of the output characteristics of the magnetostrictive sensor and the lift-off which is the distance between the object to be measured and the magnetostrictive sensor. be able to. Therefore, stress can be measured easily and accurately.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a flow of a function specifying process according to an embodiment of the present invention.

FIG. 2 is a top view showing an example of a calibration test piece.

FIG. 3 is a conceptual diagram showing a rotation mechanism for rotating a magnetostrictive sensor.

FIG. 4 is a diagram showing a change in a magnetostrictive sensor output V with respect to a rotation angle θ.

FIG. 5 is a diagram showing _a relationship between stress and a main stress direction component Va of an electromotive force V of a magnetostrictive sensor.

FIG. 6 is a diagram showing a relationship between _a main stress direction component Va of an electromotive force V of a magnetostrictive sensor and a load stress at various lift-offs.

FIG. 7 is a diagram showing a relationship between _a main stress direction component Va of an electromotive force V of a magnetostrictive sensor and an absolute stress at various lift-offs.

FIG. 8 is a diagram showing a specific relationship between _a main stress direction component Va of an electromotive force V of a magnetostrictive sensor and an absolute stress.

FIG. 9 is a diagram showing a relationship between an absolute stress and an electromotive force P of a dimensionless magnetostrictive sensor.

FIG. 10 is a diagram showing a relationship between an absolute stress obtained by exchanging the x-axis and the y-axis and an electromotive force P of a dimensionless magnetostrictive sensor.

FIG. 11 is a conceptual diagram showing a state of V _max for each lift-off.

12 is a diagram showing the relationship between the absolute value of the value of the parameter A and V _max.

FIG. 13 is a flowchart showing a flow of a stress measurement process according to the embodiment of the present invention.

FIG. 14 is a perspective view showing an arrangement example of a magnetostrictive sensor in a stress measurement method using magnetic anisotropy.

FIG. 15 is a diagram showing the relationship between the stress of an object to be measured and the output V of a magnetostrictive sensor.

FIG. 16 is a diagram showing a relationship between lift-off and an electromotive force _VL of a lift-off detection coil.

FIG. 17 is a diagram showing a relationship between lift-off and magnetostriction sensitivity M.

FIG. 18 is a diagram showing a relationship between an electromotive force _VL of a lift-off detection coil and a magnetostriction sensitivity M.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Magnetostrictive sensor 2 ... Exciting coil 3 ... Exciting yoke 4 ... Detection coil 5 ... Detection yoke 6 ... Measurement object 7 ... AC power supply 8 ... Voltmeter 9 ... Calibration test piece 10a, 10b ... Strain gauge 11 ... Sensor installation position 12 ... Rotating mechanism 13 ... Housing 14 ... Pinion gear 15 ... Ring gear 16 ... DC servo motor 17 ... C ring 18 ... Ball bearing 19 ... Ring spacer

Claims (1)

[Claims] 1. A magnetostrictive sensor in which a U-shaped yoke wound with an exciting coil and a U-shaped yoke wound with a detection coil are arranged so as to be orthogonal to each other at the center of a yoke saddle. In the method of measuring the stress acting on the object to be measured using the method, the open end sides of the two U-shaped yokes are brought close to the object to be measured, and an AC current is applied to the exciting coil to cause the magnetostrictive sensor to move. Is rotated, and the values of As _s , B _s , and C _s that are the values of the parameters A, B, and C when the output waveform of the electromotive force induced in the detection coil is expressed by the following equation (1) are obtained, and the parameter values a _s, by using the function indicating the relationship between the value to be used for parameters a and non-dimensional, the parameter value B _s dimensionless, and parameter values B _s which is the dimensionless, Relationship between stress and electromotive force of dimensionless magnetostrictive sensor Stress measuring method, characterized in that on the basis of the functions shown, to measure the stress applied to the object to be measured. V = A + B · COS [2 · (θ−C)] (1) V: Rectified value of AC electromotive force induced by the magnetostrictive sensor θ: Angle formed by a straight line connecting the open ends of both U-shaped yokes A, B, C: parameters between the bisector of the above and the reference axis of the DUT