JP2000002600A - Method for measuring stress - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid influence of a nonlinearity of an output characteristic of a magnetostriction sensor and a distance between an object to be measured and the magnetostriction sensor by making a voltage value corresponding to a stress dimensionless and measuring the stress based on the stress-corresponding voltage value with no dimension. SOLUTION: In measuring a stress acting to an object to be measured by a magnetostriction sensor having a yoke to which an excitation coil 2 and a lift-off detection coil 9 are wound and a yoke orthogonal to the yoke 3 to which a detection coil is wound, a voltage value corresponding to the stress is obtained on the basis of a waveform of an electromotive force induced to the detection coil when the magnetostriction sensor rotates. The obtained voltage value is made dimension less with the use of an electromotive force induced to the lift-off detection coil 9 and a function set beforehand by a calibration test or the like which represents a relationship between the electromotive force at the lift-off detection coil 9 and a value utilized for the dimensionless making. The stress acting to the object to be measured is obtained on the basis of the dimensionless value and a preliminarily set function showing a relationship between the stress and a dimensionless electromotive force of the magnetostriction sensor without dimension.

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 (1) 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 (1) occurs,
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 detection coil 4 wound around the detection yoke 5 has the following (2)
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)] ... (2) 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 expression (2) can be rewritten into the following expression (3). V = M · (σ _X −σ _Y ) · COS [2 · (θ−π / 4)] (3) where 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 (3), 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.

Therefore, the coefficient M of the equation (3)
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.

In order to prevent the influence of such lift-off, as shown in FIG. 16, the stress is measured using a magnetostrictive sensor 1 in which an exciting yoke 3 and a lift-off detecting coil 9 different from the exciting coil 2 are wound. JP-A-62-1
No. 21325 and Japanese Utility Model Application No. 63-33647.

In this stress measuring method, first, FIG.
Lift-off and lift-off detecting coil 9 as shown in FIG.
Electromotive force V _L (hereinafter referred to as "lift-off voltage") relationship is required.

FIG. 17A is a conceptual diagram showing a state of change of the lift-off voltage _VL with respect to the lift-off. FIG. 17 (b) shows the measured object 6 as SM49.
It is a figure showing a specific example at the time of applying 0.

Next, in this stress measuring method, a relationship between lift-off and magnetostriction sensitivity M is obtained as shown in FIG.
Then, the relationship between the lift-off voltage _VL and the magnetostriction sensitivity M shown in FIG. 19 is obtained from the obtained FIG. 17 and FIG.

Therefore, when measuring the stress acting on the object 6 to be measured, first, the lift-off voltage _VL is measured. Next, using the measured lift-off voltage _VL and FIG. 19 obtained above, the magnetostriction sensitivity M in which the influence of the lift-off is corrected is obtained. Then, the measured output V of the magnetostrictive sensor and the measured magnetostrictive sensitivity M are substituted into the equation (3), and the stress is obtained.

[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. In the present invention, a U-shaped yoke wound with an exciting coil and a lift-off detection 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. The present invention relates to a method for measuring a stress acting on an object to be measured by using a magnetostrictive sensor.

The present invention will be described in detail. First, the open ends of both U-shaped yokes are brought close to the object to be measured. next,
An alternating current is passed through the exciting coil to rotate the magnetostrictive sensor. At this time, a voltage value corresponding to the stress is obtained based on the output waveform of the electromotive force induced in the detection coil.
Next, an electromotive force induced in the lift-off detection coil,
Using a function indicating the relationship between the electromotive force of the lift-off detection coil and the value used for dimensionlessization, the voltage value corresponding to the stress is dimensionlessized. Then, the stress acting on the object is measured based on a voltage value corresponding to the dimensionless stress and a function indicating the relationship between the stress and the electromotive force of the dimensionless magnetostrictive sensor. I do.

In the present invention, for example, the parameter B when the output waveform of the electromotive force induced in the detection coil is expressed by the following equation (4) is applied to the voltage value corresponding to the stress.

V = A + B · COS [2 · (θ−C)] (1) V: Rectified value of AC electromotive force induced in the magnetostrictive sensor θ: Straight line connecting the open ends of both U-shaped yokes A, B, and C: parameters between the bisector of the angle formed by the reference axis of the DUT and the reference axis of the DUT The function used in the present invention is set in advance based on the results 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.

[0031]

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 executed in advance to collect data, and the data is analyzed to execute a function specifying process for specifying the approximate functions φ and Ψ necessary for the stress measurement. . Then, a stress measurement process for measuring the stress acting on the object to be measured is performed using the approximate functions φ and Ψ.

In the following, the same components as those in FIGS. 14 to 19 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 10 is provided with strain gauges 11a and 11b for detecting a load stress during the test. The lift-off detection coil 9
The installation position 12 of the magnetostrictive sensor 1 having the following is designated. Further, here, the longitudinal direction of the calibration test piece 10 is the X direction, the width direction is the Y direction, and the angle between the X direction and the X direction is θ.

Next, in the function specifying process, the calibration test piece 10 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 10. As the 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 10 is used.

Next, the magnetostrictive sensor 1 is placed on the sensor installation position 12 of the calibration test piece 10 with an arbitrary lift-off (s3). By lifting the magnetostrictive sensor 1 from the calibration test piece 10 to secure lift-off in this way, the axis of the magnetostrictive sensor 1 can be used as a rotation axis, and this rotation axis can be rotated substantially parallel to the normal line of the calibration test piece 10. .

Next, the calibration test piece 1 was
0 is applied with an arbitrary stress in the X direction (s4), and the lift-off voltage _VL in a state having this arbitrary lift-off is measured by the magnetostrictive sensor 1 (s5). The obtained lift-off voltage V _L is held in association with the lift-off value.

Next, the axis of the magnetostrictive sensor 1 is set as a rotation axis, and the rotation axis is parallel to the normal line of the calibration test piece 10.
The magnetostrictive sensor 1 is rotated by the rotation mechanism (s6).
FIG. 3 is a conceptual diagram illustrating a rotation mechanism that rotates the magnetostrictive sensor 1.

The magnetostrictive sensor 1 is rotatably provided in a housing 14 of the rotating mechanism 13 via a pinion gear 15 and a ring gear 16. In the housing 14, a DC servomotor 17 having an encoder is provided. The C ring 18 has an operation of maintaining the rotational position of the magnetostrictive sensor 1 by the DC servo motor 17. The ball bearing 19 has an operation of smoothly rotating the magnetostrictive sensor 1 by the DC servo motor 17. Further, the ring spacer 20 is disposed between the magnetostrictive sensor 1 and the calibration test piece 10 or the object to be measured, and has a function of securing a certain degree of lift-off. By securing the lift-off by the ring spacer 20 in this manner, 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 (s7). 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 by the angle is the angle formed by the reference direction of the calibration test piece 10. 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) (s8). Here, the parameter B determined by approximation is a voltage value corresponding to the main stress difference applied to the calibration test piece 10, that is, a voltage value corresponding to the main stress. Further, the main direction of the stress applied to the calibration test piece 10 can be specified from the parameters B and C.

The determined parameters B and C are held in relation to the current lift-off and stress. next,
This parameter B, and using the C, (5) below, the magnetostrictive sensor output V _a is obtained in the main direction of stress (X-direction in this case) (s9). That is, this Va
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 10 at the time of measuring the electromotive force Va is obtained by a strain gauge (s10). Process of obtaining the principal stress direction component V _a magnetostrictive sensor output V as described above is sequentially performed while changing any stress to be applied to the calibration test piece 10 at a suitable pitch. Thus, the main stress direction component V _a magnetostrictive sensor output V is determined for various stresses (s11).

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 for a sufficient number of stress changes the lift-off of the current to another state (s12).

[0047] Then, the parameter B for the new lift-off after the change, C is measured while varying 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 load stress Is obtained (s13).

[0048] 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 10. In FIG. 6B, the lift-off is 1.
The case of 0 mm, 1.5 mm, and 2.0 mm is illustrated.

Usually, considering the adverse effect of the magnetostriction effect, when the stress acting on the calibration test piece 10 is zero, the amplitude B of the output waveform of the electromotive force V obtained by rotating the magnetostriction 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, it can be seen from FIG. 6 that the residual stress of the calibration test piece 10 is −ΔX.

[0052] 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 (s14).

[0053] 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, a level of an existing stress such as a yield stress or a design allowable stress of a 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.

[0055] 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
15).

FIG. 9 is a diagram 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 (s16). 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. 10 (b) shows a specific change when SM490 having a thickness of 20 mm is used as the calibration test piece 10. 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 (s17). By the above processing, the approximate function φ for obtaining the stress from the dimensionless magnetostrictive sensor output P is obtained.

[0062] Subsequently, in the processing for obtaining an approximate function Ψ has a characteristic in the main 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 (s18).

[0063] Figure 11 is a conceptual diagram showing a state of the V _max for each lift-off. Also, the lift-off voltage for each lift-off measured in the previous relationship V _max for each determined liftoff is determined (s19).

[0064] Figure 12 is a diagram showing a relationship between the absolute value of the liftoff voltage for each lift-off and V _max. Here, FIG. 12A shows a conceptual diagram, and FIG.
(B) shows a SM4 having a thickness of 20 mm as the calibration test piece 10.
A specific example when 90 is used is shown.

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 Ψ is defined (s20). Using this approximation function Ψ, V at any lift-off
It is possible to estimate max.

Then, the obtained approximation functions φ and 化 are compiled into a database as output characteristics of the magnetostrictive sensor 1 (s2).
1). As described above, in the function specifying process, the approximate function 求 め る for _obtaining the value V _max used for dimensionlessization from lift-off and the approximate function φ for obtaining stress from the dimensionless magnetostrictive sensor output are: Desired.

Next, a description will be given of a stress measurement process for actually obtaining the stress of the measured object by using the approximate function Ψ 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 B and C are obtained. (T2), and the magnetostrictive sensor 1
The lift-off voltage VL is measured (t3).

Here, the obtained parameters B, C
Are B _s and C _s , respectively. Further, the measured lift-off voltage V _L is assumed to be L _s. At this time, as shown in the following equation (14), the lift-off voltages L and V
approximation function indicating the relationship _max [psi, and the measured lift-off voltage L _s is substituted, is V _max at the observation point S (V _{max) s} is determined (t4).

(V _max ) _s = Ψ (L _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 (t5).

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 (t6).

(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 .

Accordingly, the stress difference (σ _x −σ _y ) _s of the component in the main stress direction of the measured object is 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. , An approximate function を for obtaining V _max from lift-off, and an approximate function φ for obtaining stress from the dimensionless magnetostrictive sensor output P.

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 lift-off electromotive force, and the approximate functions φ and Ψ.

By applying this method, the stress can be easily and accurately measured for any lift-off without being affected by the non-linear characteristics 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 a carbon content 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.

[0077]

As described above, in the stress measuring method of the present invention, a voltage value corresponding to a stress is obtained based on an output waveform of an electromotive force induced in a detecting coil by rotating a magnetostrictive sensor. The stress equivalent voltage value is made dimensionless, and the stress is measured based on the dimensionless stress equivalent voltage value.

By applying this stress measurement method, 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. Can be. 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 liftoff voltage for each lift 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 perspective view showing an excitation yoke provided with a lift-off detection coil.

FIG. 17 is a diagram showing a relationship between lift-off and an electromotive force _VL of a lift-off detection coil.

FIG. 18 is a diagram showing a relationship between lift-off and magnetostriction sensitivity M.

FIG. 19 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 ... Lift-off detection coil 10 ... Calibration test piece 11a 11b Strain gauge 12 Sensor installation position 13 Rotation mechanism 14 Housing 15 Pinion gear 16 Ring gear 17 DC servo motor 18 C ring 19 Ball bearing 20 Ring spacer

Claims (1)

[Claims] 1. A U-shaped yoke wound with an exciting coil and a lift-off detection 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. A method for measuring stress acting on an object to be measured using a magnetostrictive sensor comprising: a step of bringing an open end of the two U-shaped yokes close to the object to be measured; Based on the output waveform of the electromotive force induced in the detection coil when flowing and rotating the magnetostrictive sensor, a voltage value corresponding to the stress is determined, the electromotive force induced in the lift-off detection coil, Using a function indicating the relationship between the electromotive force of the lift-off detection coil and the value used for dimensionless, the voltage value corresponding to the stress is dimensionless, and the voltage value corresponding to the dimensionless stress is used. And stress and dimensionless Has been based on the function representing the relationship between the electromotive force of the magnetostrictive sensor, the stress measurement method characterized by measuring a stress which is applied to the object to be measured.