JP3500966B2 - Stress measurement method and method for specifying approximate function - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Generally, ferromagnets such as steel materials are
When magnetized, the length expands and contracts in that direction (magnetostriction effect).
On the contrary, when a stress acts on the object to be measured, the magnetic property of the object to be measured changes (an inverse effect of the magnetostrictive effect).

Conventionally, there has been used a method of measuring the stress acting on the object to be measured by utilizing the inverse effect of the magnetostrictive effect. In particular, JP-A-62-121325,
Japanese Utility Model Laid-Open No. 1-135338 and Japanese Patent Laid-Open No. 7-11027.
In the technique disclosed in Japanese Patent Publication No. 0, etc., the stress applied to a steel structure or a mechanical part can be relatively easily measured nondestructively by utilizing the magnetic anisotropy caused by the inverse effect of the magnetostrictive effect. Is effective in.

The above method is based on the following principle. FIG. 14 is a perspective view showing an arrangement example of magnetostrictive sensors in a stress measuring method utilizing magnetic anisotropy.

In the magnetostrictive sensor 1, a U-shaped exciting yoke 3 around which an exciting coil 2 is wound and a U-shaped detecting yoke 5 around which a detecting coil 4 is wound are located at the center of the yoke saddle. Are arranged so as to be orthogonal to each other.

The excitation coil 2 is provided with an AC power supply 7 for applying 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. In addition, FIG.
The arrow indicates the direction of magnetic flux.

It is now assumed that a tensile stress σ _X acts on the DUT 6 in the X direction. The magnetic permeability in the X direction of the DUT 6 at this time is μ _X. Further, the magnetic permeability of the DUT 6 in the Y direction perpendicular to the X direction is μ _Y.

In this case, the magnetic permeabilities μ _X and μ _Y have the relationship of the following equation (1), that is, magnetic anisotropy, due to the inverse effect of the magnetostrictive effect due to the stress σ _X. μ _X > μ _Y (1) Bring the opening side of both yokes 3 and 4 of the magnetostrictive sensor 1 closer to the DUT 6 in the state where such magnetic anisotropy occurs, and When an object to be measured is excited by passing an alternating current from the alternating current power supply 7 to the exciting coil 2 wound around the exciting yoke 3 of No. 1, most of the magnetic flux emitted from one opening end 3a of the exciting yoke 3 is directly generated. It goes to the other open end 3b of the exciting yoke 3.

However, the tensile stress σ _X is applied to the DUT 6.
Due to the magnetic anisotropy as shown in equation (1),
Part of the magnetic flux passes through the detecting yoke 5 and the exciting yoke 3
To the open end 3b of the.

Therefore, 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 formula is induced, and this electromotive force is output. V = M ₀ · (μ _X −μ _Y ) · COS [2 · (θ−π / 4)] (2) where V is the rectified value of the AC electromotive force induced in the detection coil 4. . M ₀ is a value determined by the excitation condition, the coil, the magnetic characteristics of the DUT 6, and the like. Further, COS [2 · (θ−π / 4)] is a cosine function,
θ is an angle formed by the X-axis and a straight line connecting one opening end 5a of the detection yoke 5 and the other opening end 5b.

Furthermore, the difference in magnetic permeability (mu _X - [mu] _Y) is proportional to the difference in stress (sigma _X - [sigma] _Y), (2) formula can be rewritten to (3) below. V = M * ([sigma] _X- [sigma] _Y ) * COS [2 * ([theta]-[pi] / 4)] (3) where M depends on the excitation condition, the coil condition, the magnetic characteristics of the DUT 6, and the like. It is a fixed value.

Therefore, by measuring the voltage V and using the equation (3), the difference in stress acting on the DUT 6 can be obtained. Further, 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 FIG. 15, the stress and the output V of the magnetostrictive sensor have a substantially linear relationship in a predetermined linear range T ₁ .

Therefore, the coefficient M of the equation (3) (hereinafter,
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 linearly regressing the characteristics of FIG. 15 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 DUT 6 (hereinafter referred to as "lift-off"). Generally, the DUT 6
The steel structures, machine parts, and the like, which have been described above, are coated for corrosion protection, but the thickness of this coating is not exact and varies.

Therefore, it is difficult to precisely specify the lift-off during measurement. In addition, even if such anti-corrosion measures are not taken, the measurement is automated,
When performing non-contact measurement at high speed, it is difficult to precisely specify lift-off.

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

In this stress measuring method, first, as shown in FIG.
Lift-off and lift-off detection coil 9 as shown in FIG.
The relationship of the electromotive force V _L (hereinafter, referred to as “lift-off voltage”) is calculated.

Here, FIG. 17A is a conceptual diagram showing a state of change of the lift-off voltage V _L with respect to lift-off. In addition, FIG. 17B shows an SM 49 as the DUT 6.
It is a figure which shows the specific example when 0 is applied.

Next, in this stress measuring method, the relationship between lift-off and magnetostriction sensitivity M as shown in FIG. 18 is obtained.
Then, from the obtained FIGS. 17 and 18, the relationship between the lift-off voltage V _L and the magnetostriction sensitivity M shown in FIG. 19 is obtained.

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

[0022]

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

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

As a measure 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 it to a higher-order polynomial in consideration of its nonlinearity. To be

However, in this case, the mathematical processing for the above-mentioned lift-off correction becomes very complicated, which makes it practically difficult. The present invention has been made in view of the above circumstances, and provides a stress measuring method that considers the non-linearity of the electromotive force of the magnetostrictive sensor with respect to stress and realizes the correction of the output characteristic of the magnetostrictive sensor with respect to lift-off. The purpose is to

[0026]

The present invention has taken the following means in order to achieve the above object. According to the present invention, a U-shaped yoke around which an exciting coil and a lift-off detection coil are wound and a U-shaped yoke around which a detecting coil is wound are arranged so as to be orthogonal to each other at the center of the yoke saddle portion. The present invention relates to a method for measuring a stress acting on an object to be measured using the magnetostrictive sensor.

The present invention will be described in detail. First, the open end sides 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. Further, at this time, the voltage value corresponding to the stress is obtained based on the output waveform of the electromotive force induced in the detection coil.
Next, the electromotive force induced in the lift-off detection coil,
The voltage value corresponding to the stress is made dimensionless by using a function indicating the relationship between the electromotive force of the lift-off detection coil and the value used for making it dimensionless. Then, based on a voltage value corresponding to the non-dimensionalized stress and a function indicating the relationship between the stress and the electromotive force of the non-dimensionalized magnetostrictive sensor, the stress acting on the DUT is measured. To do.

In the present invention, for example, as the voltage value corresponding to the stress, 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.

V = A + B · COS [2 · (θ−C)] ( 4 ) V: Rectification value of AC electromotive force induced in the magnetostrictive sensor θ: Straight line connecting the open ends of both U-shaped yokes The angle A, B, C formed by the bisector of the angle formed by the object and the reference axis of the object to be measured: The function used in the present invention is set in advance based on the result of the calibration test. .

By measuring the stress by the above method,
The stress can be easily and accurately measured without being affected by the nonlinear characteristic of the magnetostrictive sensor with respect to arbitrary lift-off.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the stress measuring method according to the present embodiment, a calibration test is executed in advance to collect data, and this data is analyzed to execute a function specifying process for specifying approximate functions φ and Ψ required for stress measurement. . Then, a stress measurement process for measuring the stress acting on the object to be measured is executed using the approximation functions φ and Ψ.

In the following description, the same parts as those in FIGS. 14 to 19 described above are designated by the same reference numerals and the description thereof will be omitted. First, the function specifying process will be described.

FIG. 1 is a flow chart showing the flow of this 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 this calibration test piece. Strain gauges 11a and 11b are attached to the calibration test piece 10 so as to detect the load stress during the test. Also, the lift-off detection coil 9
The installation position 12 of the magnetostrictive sensor 1 having 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 formed with 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 applying device is a device for applying a load that becomes a stress to the calibration test piece 10. As the load applying device, for example, a four-point bending load applying 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 in a state having an arbitrary lift-off (s3). By thus floating the magnetostrictive sensor 1 from the calibration test piece 10 and ensuring lift-off, the axis of the magnetostrictive sensor 1 serves as a rotation axis, and this rotation axis can rotate substantially parallel to the normal line of the calibration test piece 10. .

Next, the calibration test piece 1 is loaded by the load applying device.
0 is loaded with an arbitrary stress in the X direction (s4), and the lift-off voltage V _L in the state having the arbitrary lift-off is measured by the magnetostrictive sensor 1 (s5). The lift-off voltage V _L thus obtained is held in association with the lift-off value.

Next, the axis of the magnetostrictive sensor 1 is used 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 rotating mechanism (s6).
FIG. 3 is a conceptual diagram showing a rotation mechanism that rotates the magnetostrictive sensor 1.

In the housing 14 of the rotating mechanism 13, the magnetostrictive sensor 1 is rotatably provided via a pinion gear 15 and a ring gear 16. In addition, a DC servo motor 17 having an encoder is provided in the housing 14. The C ring 18 has a function of maintaining the rotational position of the magnetostrictive sensor 1 by the DC servo motor 17. The ball bearing 19 has a function of smoothly rotating the magnetostrictive sensor 1 by the DC servo motor 17. Further, the ring spacer 20 is arranged between the magnetostrictive sensor 1 and the calibration test piece 10 or the object to be measured, and has a function of ensuring a certain degree of lift-off. By thus ensuring the lift-off by the ring spacer 20, it becomes 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
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 every time (s7). Figure 4
FIG. 6 is a diagram showing a change in magnetostrictive sensor output V with respect to a rotation angle θ.

As shown in FIG. 4, the change in the electromotive force V detected by rotating the magnetostrictive sensor 1 is similar to that of the equation ( 4 ). V = A + B · COS [2 · (θ−C)] ( 4 ) where V is the rectified value of the AC electromotive force induced in the detection coil 4, and θ is the straight line connecting the open ends of both yokes. The bisector of the angle formed by is the angle formed by the reference direction of the calibration test piece 10. COS [2 · (θ−C)] is a cosine function. Further, A, B and C are parameters.

Therefore, in the function specifying process, the change in the magnetostrictive sensor output V with respect to the rotation angle θ is approximated by the equation ( 4 ) (s8). Here, the parameter B determined by approximation is a voltage value corresponding to the principal stress difference acting on the calibration test piece 10, that is, a principal stress equivalent voltage value. Further, the main directions of the stress acting on the calibration test piece 10 can be specified from the parameters B and C.

The defined parameters B and C are held in association with the current liftoff and stress. next,
Using these parameters B and C, the magnetostrictive sensor output V _a in the main stress direction (here, the X direction) is calculated by the following equation (5) (s9). That is, this Va
Is the principal stress direction component of the magnetostrictive sensor output V.

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

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 changes in the principal stress direction component V _a 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).

Then, the parameters B and C for the new lift-off after the change are measured while changing the stress in the same manner as the above-mentioned processing, whereby the main stress direction component V _a of the magnetostrictive sensor output V and the load stress at each lift-off are measured. Is required (s13).

FIG. 6 is a diagram showing the relationship between the principal stress direction component V _a of the magnetostrictive sensor output V and the load stress at various lift-offs. Here, FIG. 6A shows a change (calibration curve for each lift-off) of the main stress direction component V _a of the magnetostrictive sensor output when the stress is changed in the three types of lift-offs L _{1 to} L ₃ . It is a conceptual diagram.

FIG. 6 (b) shows a specific change when the 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 inverse effect of the magnetostrictive 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 magnetostrictive sensor 1 is also 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 load stress is + Δ.
When the X, the main stress direction component V _a magnetostrictive sensor output V is zero. That is, it is understood from FIG. 6 that the residual stress of the calibration test piece 10 is −ΔX.

Therefore, in this function specifying process, the principal stress direction component V _a of the magnetostrictive sensor output V and the stress (=
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).

FIG. 7 is a diagram showing the relationship between the principal stress direction component V _a of the magnetostrictive sensor output V and the absolute stress, which is shown for three types of lift-offs L _{1 to} 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. Note that, in FIG. 8, only the characteristics in the case of one lift-off L ₁ are illustrated in order to simplify the description.

As the stress σ _max in FIG. 8, an actual stress level such as yield stress of the material of the object to be measured or design allowable stress is used. Characteristics of the main stress direction component V _a magnetostrictive sensor output V for the absolute stress, magnetostrictive sensors 1
Due to the operation principle of, the point becomes symmetrical at the origin. That is, when the absolute values of absolute stress are equal and the signs are different,
The principal stress direction component V _{a of the} magnetostrictive sensor output V also has a relationship in which the absolute value is the same and the sign is different. 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 principal stress direction component V _{a of the above} is −V ₁ to −V ₃ .

Next, in this function specifying process, the characteristic of the principal stress direction component V _a of the magnetostrictive sensor output V with respect to the absolute stress is dimensionlessized (normalized) by V _max (s
15).

FIG. 9 is a diagram showing characteristics of the dimensionless magnetostrictive sensor output P with respect to absolute stress. P _max , P _{3 to} P ₁ , -P ₁ to -P ₃ , and -P _max in this FIG.
Is a dimensionless value of the principal 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) The characteristic of the dimensionless magnetostrictive sensor output P shown in FIG. 9 is unique regardless of lift-off of the magnetostrictive sensor 1 unlike the case of FIG. Is defined in.

Next, the x-axis and the y-axis of FIG. 9 showing the relationship between the dimensionless magnetostrictive sensor output P and the absolute stress are exchanged to obtain FIG. 10 (s16). Here, in FIG. 10A, the dimensionless magnetostrictive sensor output P is represented by x.
It is a conceptual diagram which made the absolute stress the 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 10. That is, FIG.
Characteristics of (b) (lift-off is 1.0 mm, 1.5 mm,
(In the case of 2.0 mm) is shifted to make it dimensionless and the x-axis and the y-axis are exchanged.

Next, the relationship between the dimensionless magnetostrictive sensor output P and the absolute stress shown in FIG. 10 is approximated by a high-order polynomial to define an approximate function φ (s17). Through the above processing, the approximate function φ for obtaining the stress is obtained from the dimensionless magnetostrictive sensor output P.

Subsequently, in the processing for obtaining the approximate function Ψ, the characteristic of the principal stress direction component V _a of the magnetostrictive sensor output V with respect to the absolute stress shown in FIG. 7 and σ _max described in FIG. From this, V _max for each lift-off is obtained (s18).

FIG. 11 is a conceptual diagram showing the state of V _max at each lift-off. Further, the relationship between the lift-off voltage measured for each lift-off and the V _max calculated for each lift-off is calculated (s19).

FIG. 12 is a diagram showing the relationship between the lift-off voltage and the absolute value of V _max for each lift-off. Here, FIG. 12A shows a conceptual diagram.
(B) is an 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 the approximate function Ψ is defined by this (s20). Using this approximation function Ψ, V at any liftoff
It is possible to estimate max.

The obtained approximation functions φ and Ψ are stored in the database as the output characteristics of the magnetostrictive sensor 1 (s2).
1). As described above, in the function specifying process, the approximate function Ψ for _obtaining the value V _max used for the dimensionlessization from the lift-off and the approximate function φ for obtaining the stress from the dimensionless magnetostrictive sensor output are obtained. Desired.

Next, the stress measuring process for actually obtaining the stress of the object to be measured using the approximate function Ψ and the approximate function φ will be described. FIG. 13 is a flowchart showing the flow of this 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 to the equation ( 4 ) to obtain parameters B and C. Is calculated (t2), and the magnetostrictive sensor 1
The lift-off voltage VL is measured by (t3).

Here, the obtained parameters B and C
Are B _s and C _s , respectively. In addition, 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
_The measured lift-off voltage L _s is substituted into the approximate function Ψ indicating the relationship of _max , and V _max (V _max ) _s at the observation point S is obtained (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 required (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 calculated magnetostrictive sensor P _s is substituted, the absolute stress difference (σ ₁ −σ ₂ ) _s at the observation point S is calculated, and the stress is measured by this stress difference (t6).

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

Therefore, the stress difference (σ _x −σ _y ) _s of the principal stress direction component of the object to be measured 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 measuring method according to the present embodiment, first, the function specifying process is performed. , Approximate function Ψ for obtaining V _max from the lift-off, and approximate function φ for obtaining stress from the dimensionless magnetostrictive sensor output P are obtained.

Then, the stress is obtained from the characteristic 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 the stress measuring process.

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

The SM490 used as a specific example of the calibration test piece in the present embodiment has carbon of 0.20 wt% or less, silicon of 0.55 wt% or less, manganese of 1.60 wt% or less, 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 detail, in the stress measuring method of the present invention, the voltage value corresponding to the stress is obtained based on the output waveform of the electromotive force induced in the detecting coil by rotating the 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 the above stress measuring method, the stress can be measured without being affected by the nonlinearity of the output characteristic of the magnetostrictive sensor and the lift-off which is the distance between the DUT and the magnetostrictive sensor. You can Therefore, the stress can be measured easily and accurately.

[Brief description of 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 rotating mechanism that rotates a magnetostrictive sensor.

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

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

FIG. 6 is a diagram showing a relationship between _a principal stress direction component V _{a of} an electromotive force V of a magnetostrictive sensor in various lift-offs and a load stress.

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

FIG. 8 is a diagram showing a specific relationship between _a principal stress direction component V _{a 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 the relationship between the absolute stress with the x-axis and the y-axis swapped and the electromotive force P of the dimensionless magnetostrictive sensor.

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

FIG. 12 is a diagram showing a relationship between a lift-off voltage and an absolute value of V _max for each lift-off.

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

FIG. 14 is a perspective view showing an arrangement example of magnetostrictive sensors in a stress measuring method utilizing magnetic anisotropy.

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

FIG. 16 is a perspective view showing an excitation yoke including a lift-off detection coil.

FIG. 17 is a diagram showing a relationship between lift-off and electromotive force V _L 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 the relationship between the electromotive force V _L of the lift-off detection coil and the magnetostriction sensitivity M.

[Explanation of symbols]

1 ... Magnetostrictive sensor 2 ... Excitation coil 3 ... Excitation yoke 4 ... Detection coil 5 ... Detection yoke 6 ... DUT 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 (3)

(57) [Claims] And 1. A of U-shaped wound with excitation coils and Li off-off detecting coil yokes, the U-shaped wound with the detecting coil and a yoke, perpendicular in the central portion of the yoke saddle mutually In the method of measuring the stress acting on the object to be measured using the magnetostrictive sensor arranged as described above, the opening end sides of the U-shaped yokes are separated by a lift-off to approach the object to be measured. Electromotive force V induced in the detection coil when an alternating current is passed through the excitation coil to rotate the magnetostrictive sensor
Connect the output waveform of the above to the open ends of the U-shaped yokes.
The bisector of the angle formed by the straight line and the reference axis of the DUT
The angle formed by is defined as θ and V = A + B ・ COS [2 ・
(Θ−C)], the parameter values B _s and C _s of the respective parameters B and C are obtained, and the electromotive force L _s induced in the lift-off detection coil is used to calculate the electromotive force of the lift-off detection coil. wherein for each V _L and a lift-off on the basis of the approximate function previously stored showing the relationship between the main stress direction component V _max of the electromotive force of the magnetostrictive sensor [psi (V _L) = V _max for the allowable stress of the object to be measured, the The main stress direction component (V _max ) _s = Ψ (L _s ) of the electromotive force of the magnetostrictive sensor with respect to the allowable stress of the measured object is obtained, and the main stress direction component (V _max ) _s of the obtained electromotive force is used to calculate The parameter value B _s is normalized, and the stress difference (σ ₁ −σ ₂ ) and the value P obtained by the normalization are used by using P _s (= B _s / (V _max ) _s ) obtained by the normalization. Pre-stored approximation function φ (P) =
Based on (σ ₁ −σ ₂ ), stress difference (σ ₁ −σ ₂ ) _s = φ
(P _s ) is obtained, and the stress acting on the measured object is obtained by using the obtained stress difference (σ ₁ −σ ₂ ) _s and the parameter value C _s. Method. 2. An excitation coil and a U-shaped yoke around which a lift-off detection coil for measuring a lift-off voltage is wound, and a U-shaped yoke around which a detection coil is wound are connected to each other in the yoke saddle portion. Using a magnetostrictive sensor arranged so as to be orthogonal in the central portion, the open end sides of the U-shaped yokes are brought close to the object to be measured, and an alternating current is passed through the exciting coil to move the object to be measured. A method for identifying an approximate function used for exciting, measuring an electromotive force induced in the detection coil, and measuring a stress acting on the DUT, which has an arbitrary lift-off from a calibration test piece. In this state, the magnetostrictive sensor is arranged, an arbitrary stress is applied to the calibration test piece, a lift-off voltage is measured by the magnetostrictive sensor with respect to the arbitrary lift-off, and the magnetostrictive sensor is rotated to perform the detection. The waveform of the electromotive force output V of the magnetostrictive sensor induced in use coils, forming an open end of said two U-shaped yoke
Bisector of the angle formed by the straight line and the reference axis of the DUT
The angle formed by and is defined as θ, and the values of the parameters B and C in the case of being represented by the first formula are obtained. From the values of the parameters B and C and the second formula, the main electromotive force V of the magnetostrictive sensor is calculated. The stress direction component V _a is obtained, the characteristics of the arbitrary stress for the arbitrary lift-off and the main stress direction component V _a of the electromotive force V are shifted by the amount of residual stress, and the absolute stress for the arbitrary lift-off is obtained. It determined the characteristics of the principal stress direction component V _a of the electromotive force V, and the main stress direction component V _a of the electromotive force V by the main stress direction component V _max of the electromotive force V for allowable stress sigma _max of the object to be measured Approximate function φ for dividing the dimensionless electromotive force output P with respect to absolute stress to obtain the characteristic of the dimensionless electromotive force output P and approximating this characteristic to obtain the stress from the dimensionless electromotive force output of the magnetostrictive sensor. As well as the above From the main stress direction component V _a of the electromotive force V for the absolute stress for each lift, seeking principal stress direction component V _max of the electromotive force V corresponding to the allowable stress sigma _max for each of the optional lift-off, the arbitrary how to identify the absolute value of the lift-off voltage and V _max for each lift-off from the relationship between, the approximation function and obtains the approximation function Ψ for obtaining a V _max from liftoff voltage measured by the magnetostrictive sensor. V = A + B · COS [ 2 · (θ-C)] ... first equation _{V a = B · COS (2C} ) ... second equation 3. A stress measuring method using an approximate function obtained by the method for identifying an approximate function according to claim 2, wherein the magnetostriction measured by rotating the magnetostrictive sensor at an observation point of the object to be measured. When the waveform of the electromotive force of the sensor is expressed by the first equation, the values B _s and C _s of the parameters B and C are obtained, the lift-off voltage L _s is measured by the magnetostrictive sensor, and the lift-off voltage is added to the approximate function Ψ. L _s is substituted,
(V _max ) _s , which is the value of V _{max at} the observation point, is calculated, and the dimensionless magnetostrictive sensor output P _s at the observation point is calculated from the B _s , the (V _max ) _s, and the third equation. determined, by substituting the P _s in the approximate function φ the absolute stress difference (σ ₁ -σ _{2) s} of the observation point, the absolute stress difference (sigma ₁ - [sigma]
₂ ) Based on _s , C _s, and the fourth equation, the stress difference (σ _x −σ _y ) _s of the principal stress direction component of the measured object is calculated, and the stress acting on the measured object is calculated. A stress measuring method characterized by the above. P _s = B _s / (V _max ) _s 3rd expression (σ _x −σ _y ) _s = (σ ₁ −σ ₂ ) _s · COS (2C _s ) ... 4th expression