JP2003270061A - Method and device for detecting stress - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for detecting stress by which stresses applied to an object to be detected can be detected always stably without coming into contact with the object even when the ambient temperature of the object changes. <P>SOLUTION: The device generates an eddy current on the surface of an object to be detected having such a characteristic that its electrical resistance value is changed by a strain caused in the surface of the object by a stress by generating lines of magnetic force, so that the lines may be made incident almost vertically to the surface of the object by means of a detection coil. The detection coil is provided near the surface of the object in a state where the coil does not come into contact with the surface and composed of a magnetic core and a coil. Since the eddy current varies depending upon the electrical resistance value of the object, the eddy current also changes when a strain is applied to the surface of the object. The stress applied to the object is detected by detecting the change of the eddy current as the change of the induced voltage or impedance of the coil. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stress detecting method and a stress detecting device for non-contact detecting a stress applied to a rotating shaft or a flat plate from the outside.

[0002]

2. Description of the Related Art Conventionally, for example, in order to detect a stress (torque) applied to a rotating shaft, a groove is formed on the surface around the shaft in the directions of + 45 ° and −45 ° with respect to the center line of the magnetic shaft. A magnetic anisotropy is provided to change the magnetic permeability due to the magnetostriction effect resulting from applying stress to the shaft.
Or two coils to detect, or
Decrease the diameter of a part of the shaft to weaken the rigidity to make the amount of twist due to stress manifest, and detect the twist angle on both sides of the part with a small shaft diameter, or pre-exist magnetic anisotropy on the surface of the shaft There is a method in which a magnetic thin piece is attached and a change in magnetic permeability due to the magnetostriction effect is detected by a detection coil, or a strain gauge is attached to the surface of a shaft and a signal is taken out by a slip ring.

[0003]

In the method utilizing the magnetostriction effect, the magnetic permeability also changes with temperature, so that the stress signal also changes when the ambient temperature changes. As a means to correct the influence of temperature, the stress signal due to positive and negative strains is differentially detected to eliminate the influence of temperature. However, the change in permeability due to temperature is larger than the change due to stress, so it is not sufficient. Absent.
In addition, the strain gauge method has good stability against temperature, but since the slip ring is used, the contact of the slip ring may deteriorate when the shaft rotates at high speed, and the stress signal may become unstable. Is limited.

Therefore, the present invention provides a stress detecting method and a stress detecting apparatus which can detect stress in a non-contact manner with respect to an object to be detected and which can always perform stable stress detection against changes in ambient temperature. The purpose is to

[0005]

According to the stress detecting method of the present invention, the longitudinal direction of the end face is parallel to the stress generating direction of the conductive object to be detected by the force applied from the outside. By arranging one end faces of a plate-shaped core having coils wound around the respective ends so as to face each other at a predetermined interval, and energizing each coil wound around the core with an AC signal, Generate an eddy current on the surface of the object to be detected,
By processing the signal output from each coil by this bias, the change in the eddy current signal accompanying the eddy current generated on the surface of the detected object obtained from the coil is applied to the detected object. It is characterized by detecting stress.

Further, according to the stress detecting device of the present invention, one end face of the conductive object is arranged such that the longitudinal direction of the end surface is parallel to the stress generating direction of the object due to an external force. Are plate-shaped cores arranged facing each other at a predetermined interval, two coils wound around each end of the core, and the coils to be detected are energized by an AC signal to detect the detected object. Coil energizing means for generating an eddy current on the surface of the object, and by processing signals output from the coils by the energizing of the coil energizing means, the object to be detected obtained from the coil is processed. Signal processing means for detecting the stress applied to the object to be detected from the change of the eddy current signal due to the eddy current generated on the surface.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, the first embodiment will be described. FIG. 1 schematically shows the configuration of the stress detection device according to the first embodiment. In FIG. 1, reference numeral 1 denotes a conductive flat plate as a conductive object to be detected, and a plate-shaped magnetic core 2 is arranged substantially perpendicular to one surface of the flat plate 1. In this case, the magnetic core 2
When a force F is applied to the flat plate 1 from the outside, one end face has a predetermined interval so that the longitudinal direction of the end face becomes parallel to the direction in which the tensile strain (tensile stress) 3 generated in the flat plate 1 occurs. Are arranged facing each other. In addition, 4 is compressive strain (compressive stress)
And occurs with tensile strain 3. The coil 5 is wound around one end of the magnetic core 2, and the coil 6 is wound around the other end.

In such a structure, when a force F is applied to the flat plate 1 from the outside, a tensile strain 3 is generated in the X axis direction and a compressive strain 4 is generated in the Y axis direction. When an alternating current is applied to the coils 5 and 6 wound around the magnetic core 2 having a rectangular flat cross section,
The magnetic force line 7 generated from the coil 5 penetrates the flat plate 1 from the end face of the magnetic core 2, but an eddy current 8 is generated on the surface of the flat plate 1 in the direction of canceling the magnetic force line 7 due to the alternating current. This eddy current 8
Flows in the vicinity of the bundle of magnetic force lines 7, so that the path has a flat shape, and the long axis of the path is in the same X-axis direction as the tensile strain 3.

Therefore, the length of the path of the eddy current 8 is dominant in the X-axis direction, and the eddy current 8 is affected by the change in resistance value due to the tensile strain 3. When the eddy current 8 is generated, the eddy current 8
The magnetic force lines are generated by, and the change in the generated magnetic force lines changes the impedance of the coil 5.

Although the flat plate 7 is entirely made of a conductor,
For example, the same effect can be obtained even if a conductive resistance film is formed on the surface of a plate-shaped insulator.

FIG. 2 schematically shows a signal processing circuit for processing the output signals of the coils 5 and 6. In FIG. 2, the bridge circuit 15 is composed of the coils 5 and 6, the fixed resistors 11 and 12, and the variable resistors 13 and 14. The variable resistors 13 and 14 are variable resistors for adjusting the balance of the bridge circuit 15.

The AC oscillation circuit 16 generates an AC signal for energizing the bridge circuit 15. The output signal is amplified by the amplifier 17 and then applied to the slider of the variable resistor 13. . The differential amplifier 18 includes a bridge circuit 15
Differentially amplify the output of and output the output to the phase detection circuit 19. In the bridge circuit 15, the variable resistor 1 is arranged so that the output amplitude of the differential amplifier 18 becomes as small as possible.
Adjust 3 and 14.

The output signal of the AC oscillating circuit 16 is set to a phase sensitive to the eddy current signal by the phase setting circuit 20 and then sent to the phase detection circuit 19. The phase detection circuit 19 detects and rectifies the output signal of the differential amplifier 18 based on the phase set by the phase setting circuit 20. That is, the phase detection circuit 19 selectively amplifies a change in the eddy current signal from the output signal of the differential amplifier 18. The low-pass filter circuit 21 removes high-frequency components from the signal detected and rectified by the phase detection circuit 19 and outputs a stress detection signal.

Although FIG. 2 shows a method of detecting a signal from the impedance change of the coils 5 and 6, secondary windings are provided to the coils 5 and 6, respectively.
By inputting the output signal of the next winding to the input of the differential amplifier 18 shown in FIG. 2, the change signal of the eddy current can be similarly obtained and the stress signal can be detected.

Next, a second embodiment will be described. FIG. 3 schematically shows the configuration of the stress detecting device according to the second embodiment. In FIG. 3, reference numeral 31 denotes a conductive flat plate as a conductive object to be detected.
The plate-shaped first magnetic core 32 is arranged substantially perpendicular to the one surface. In this case, the first magnetic core 32 has one end face so that the longitudinal direction of the end face becomes parallel to the direction of the tensile strain 33 generated in the flat plate 31 when the force F is applied to the flat plate 31 from the outside. Are arranged opposite to each other with a predetermined interval. A first coil 34 is wound around the first magnetic core 32.

Further, a plate-shaped second magnetic core 35 is arranged substantially perpendicular to one surface of the flat plate 31. In this case, the second magnetic core 35 causes the compressive strain 3 generated in the flat plate 31 when the force F is applied to the flat plate 31 from the outside.
One of the end faces is disposed so as to face each other at a predetermined interval so that the longitudinal direction of the end faces is parallel to the direction of occurrence of 6. A second coil 37 is wound around the second magnetic core 35.

In such a structure, when a force F is applied to the flat plate 31 from the outside, a tensile strain 33 is generated in the X axis direction and a compressive strain 36 is generated in the Y axis direction. When an alternating current is applied to the first coil 34 wound around the first magnetic core 32 having a rectangular flat cross section, the magnetic force lines 38 generated from the first coil 34 are the end faces of the first magnetic core 32. Although it penetrates through the flat plate 31, the eddy current 39 is generated on the surface of the flat plate 31 in the direction of canceling the magnetic force lines 38 due to the alternating current. This eddy current 39 is
Since the magnetic flux flows around the bundle of magnetic force lines 38, the path is flat, and the major axis of the path is in the same X-axis direction as the tensile strain 33.

Therefore, the path length of the eddy current 39 is X
The axial direction becomes dominant, and the eddy current 39 is affected by the resistance value change due to the tensile strain 33. When the eddy current 39 is generated,
The magnetic force lines are generated by the eddy current 39, and the change of the generated magnetic force lines changes the impedance of the first coil 34.

In the second magnetic core 35, since the long axis of the rectangular end face is aligned with the Y axis, the path of the eddy current 41 generated by the magnetic force line 40 generated from the second coil 37 is the Y axis of the compressive strain 36. The direction becomes dominant, and the eddy current 41 is affected by the resistance value change due to the compression strain 36. When the eddy current 41 is generated, a magnetic force line is generated by the eddy current 41, and the change in the generated magnetic force line becomes a change in the impedance of the second coil 37.

Although the flat plate 31 is entirely made of a conductive material, the same effect can be obtained even if a conductive resistance film is formed on the surface of a plate-shaped insulating material.

FIG. 4 schematically shows a signal processing circuit for processing the output signals of the first coil 34 and the second coil 37. This signal processing circuit is the same as the signal processing circuit shown in FIG. 2, except that the coils 5 and 6 are the first and second coils 3.
4 and 37 are different, and the other points are the same, so the description thereof will be omitted.

In FIG. 4, the first coil 34 and the second coil 34
Although the method of detecting a signal from the impedance change of the coil 37 has been described, the first coil 34, the second coil 37
By applying a secondary winding to each of the above and inputting the output signal of each secondary winding to the input of the differential amplifier 18 of FIG. 4, it is possible to similarly obtain the eddy current change signal.
The stress signal can be detected.

Next, a third embodiment will be described. 5 and 6 schematically show the configuration of the stress detection device according to the third embodiment. In FIGS. 5 and 6, reference numeral 51 denotes a rotating conductive shaft as a conductive object to be detected, and a plate-shaped first shaft is provided with respect to the surface of the shaft 51.
Magnetic cores 52 are arranged substantially vertically. In this case, the first magnetic core 52 has one end face so that the longitudinal direction of the end face becomes parallel to the direction in which the tensile strain 53 generated in the shaft 51 occurs when the torque T is applied to the shaft 51 from the outside. Are arranged opposite to each other with a predetermined interval. That is, the first magnetic core 52 is arranged such that the longitudinal direction of the end face facing the surface of the shaft 51 is substantially +45 degrees with respect to the center line of the shaft 51. First magnetic core 5
A first coil 54 is wound around the wire 2.

Further, a plate-shaped second magnetic core 55 is arranged substantially perpendicularly to the surface of the shaft 51 on the side opposed to the first magnetic core 52. In this case, the second magnetic core 55 has one end face so that the longitudinal direction of the end face becomes parallel to the direction in which the compressive strain 56 generated in the shaft 51 occurs when the torque T is applied to the shaft 51 from the outside. Are arranged opposite to each other with a predetermined interval. That is, the second magnetic core 5
5 indicates that the longitudinal direction of the end face opposite to the surface of the shaft 51 is the shaft 5
It is arranged at an angle of approximately -45 degrees with respect to the center line of 1. The second coil 5 is attached to the second magnetic core 55.
7 is wound.

In such a structure, when torque T is applied to the shaft 51 from the outside, tensile strain 53 is generated in the longitudinal direction of the first magnetic core 52 and compressive strain 56 is generated in the longitudinal direction of the second magnetic core 55. . When an alternating current is applied to the first coil 54 wound around the first magnetic core 52 having a rectangular flat cross section, the magnetic lines of force generated from the first coil 54 are generated from the end face of the first magnetic core 52. Proceed to the surface of shaft 51,
Due to the alternating current, an eddy current is generated on the surface of the shaft 51 in a direction of canceling the magnetic force lines. Since this eddy current flows around the bundle of magnetic force lines, its path is flat, and the major axis of the path is in the same direction as the tensile strain 53 is generated.

Therefore, the length of the path of the eddy current is dominated by the direction in which the tensile strain 53 is generated, and the eddy current is the tensile strain 5
It is affected by the change in resistance value due to 3. When an eddy current is generated, a magnetic force line is generated by the eddy current, and the change in the generated magnetic force line changes the impedance of the first coil 54.

In the second magnetic core 55, since the long axis of the rectangular end face is aligned with the direction in which the compressive strain 56 is generated, the path of the eddy current generated by the magnetic force lines generated from the second coil 57 is the compressive strain 56. The generation direction becomes dominant, and the eddy current is affected by the change in resistance value due to the compression strain 56. When an eddy current is generated, a magnetic force line is generated by the eddy current, and the change in the generated magnetic force line becomes a change in the impedance of the second coil 57.

Although the shaft 51 is entirely made of a conductor,
For example, the same effect can be obtained by forming a conductive resistance film on the surface of a round bar-shaped insulator.

FIG. 7 schematically shows a signal processing circuit for processing the output signals of the first coil 54 and the second coil 57. This signal processing circuit is the same as the signal processing circuit shown in FIG. 2, except that the coils 5 and 6 are the first and second coils 5.
4 and 57 are different, and the other points are the same, so the description will be omitted.

In FIG. 7, the first coil 54 and the second coil 54
Although the method of detecting a signal from the impedance change of the coil 57 has been described, the first coil 54, the second coil 57
A secondary eddy current change signal can be obtained in the same manner by applying a secondary winding to each of the above and inputting the output signal of each secondary winding to the input of the differential amplifier 18 of FIG.
The torque signal can be detected.

As described above, in order to make the magnetic field lines incident on the shaft surface substantially perpendicularly to the shaft having the characteristic that the electric resistance value changes due to the distortion of the shaft surface caused by the torque (stress), the non-contact is made near the shaft surface. A magnetic field line is generated by a detection coil including a magnetic core and a coil provided by contact, and an eddy current is generated on the surface of the shaft. Since the eddy current changes depending on the electric resistance value of the shaft, the eddy current also changes when strain is applied. The torque signal (stress signal) can be detected by detecting the change in the eddy current as the change in the induced voltage or impedance of the coil.

The strain on the shaft surface caused by the torque is, for example, tensile strain in the + 45 ° direction with respect to the shaft center and compressive strain opposite to the −45 ° direction. Therefore, to know the change in electrical resistance due to strain from the eddy current,
The end face of the magnetic core is flattened and its longitudinal direction is aligned with the strain direction. The path of the eddy current generated by the magnetic lines of force generated from the magnetic core is also flat. Since the path of this eddy current becomes longer in the direction in which strain occurs, the amount of eddy current is approximately proportional to the electrical resistance value changed by strain, and if the change in eddy current is detected, the change in strain can be detected. As a result, the shaft torque (stress) can be detected without contact.

A conductive material such as metal, for example, a copper-nickel alloy or nichrome has a small change in electric resistance with temperature. By forming a thin film on the shaft surface by a thin film generation method such as ion sputtering using a conductive material with a small change in electric resistance, stable strain detection can be performed by applying alternating magnetic field lines of relatively high frequency. Become. In order to obtain a more stable signal, the linear expansion coefficient of the thin film may be set to a value that is the same as or close to that of the shaft material.

In addition, when the shaft rotates, if the gap between the facing surface of the magnetic core and the shaft surface changes due to rotational shake of the shaft or the like, the lines of magnetic force reaching the shaft change, the eddy current also changes, and the torque signal changes. fluctuate. As a means for eliminating the influence of this shaft shake, two detection coils are made to face each other with the center of the shaft sandwiched therebetween, one of which detects a tensile strain signal and the other of which detects a compression strain signal. Install in the same direction. By taking the difference between the output signals of these two detection coils, the influence of shaft shake is eliminated.

[0035]

As described above in detail, according to the present invention, the stress can be detected in a non-contact manner with respect to the object to be detected and the ambient temperature can be detected by setting the conductor resistance sensitive to strain as the object of detection. It is possible to provide a stress detection method and a stress detection device that can always perform stable stress detection against changes.

[Brief description of drawings]

FIG. 1 is a schematic diagram schematically showing the configuration of a stress detection device according to a first embodiment of the present invention.

FIG. 2 is a block diagram schematically showing the configuration of the signal processing circuit according to the first embodiment.

FIG. 3 is a schematic diagram schematically showing a configuration of a stress detection device according to a second embodiment of the present invention.

FIG. 4 is a block diagram schematically showing the configuration of a signal processing circuit according to the second embodiment.

FIG. 5 is a schematic diagram schematically showing the configuration of a stress detection device according to a third embodiment of the present invention.

FIG. 6 is a side view seen from the direction of arrow AA in FIG.

FIG. 7 is a block diagram schematically showing the configuration of a signal processing circuit according to the third embodiment.

[Explanation of symbols]

1, 31 ... Flat plate (object to be detected), 2 ... Magnetic core, 3, 3
3, 53 ... Tensile strain (tensile stress), 4, 36, 56 ...
Compressive strain (compressive stress), 5, 6 ... Coil, 7, 38, 40
... Magnetic force lines, 8, 39, 41 ... Eddy current, F ... Force (stress),
11, 12 ... Fixed resistor, 13, 14 ... Variable resistor, 1
5 ... Bridge circuit, 16 ... AC oscillation circuit, 17 ... Amplifier, 18 ... Differential amplifier, 19 ... Phase detection circuit, 20 ... Phase setting circuit, 21 ... Filter circuit, 32, 52 ... First magnetic core, 34, 54 ... 1st coil, 35, 55 ... 2nd magnetic core, 37, 57 ... 2nd coil, T ... Torque (stress).

Claims (8)

[Claims] 1. A coil is wound around each end of a conductive object so that the longitudinal direction of the end face is parallel to the stress generation direction of the object due to a force applied from the outside. Eddy currents are applied to the surface of the object to be detected by arranging one end surface of a plate-shaped core so as to face each other with a predetermined interval and energizing each coil wound around the core with an AC signal. By generating and processing the signal output from each coil by this urging, the change in the eddy current signal due to the eddy current generated on the surface of the detected object obtained from the coil causes a change in the detected object. A stress detection method, characterized in that the applied stress is detected. 2. A plate on which a first coil is wound so that a longitudinal direction of an end face of a conductive object to be detected is parallel to a tensile stress generation direction of the object to be detected by a force applied from the outside. The one end faces of the first core having the shape of a ring are arranged to face each other with a predetermined interval, and the longitudinal direction of the end faces is different from that of the object in the compressive stress generation direction of the object due to a force applied from the outside. One end surfaces of a plate-shaped second core around which the second coil is wound are arranged so as to be parallel to each other with a predetermined interval therebetween, and the first and second coils are supplied with an AC signal. By urging, an eddy current is generated on the surface of the object to be detected, and by processing the signals output from the first and second coils by this urging, the first and second coils are processed. Eddy current signal resulting from eddy current generated on the surface of the object to be detected obtained from the coil The stress applied to the object to be detected is detected from the change in the stress detection method. 3. The stress detecting method according to claim 1, wherein the conductive object to be detected is a rotating shaft. 4. The stress detecting method according to claim 1, wherein the conductive object to be detected is a flat plate. 5. One end face is opposed to a conductive object to be detected with a predetermined interval so that the longitudinal direction of the end surface is parallel to the stress generation direction of the object to be detected by a force applied from the outside. A plate-shaped core is provided, two coils are wound around each end of the core, and an eddy current is applied to the surface of the object to be detected by energizing each coil with an AC signal. By processing the signal output from each coil by the biasing of the coil biasing means to generate an eddy current generated on the surface of the detected object obtained from the coil. And a signal processing means for detecting the stress applied to the object to be detected from the change of the eddy current signal. 6. One end face has a predetermined interval relative to a conductive object to be detected so that the longitudinal direction of the end surface is parallel to the tensile stress generation direction of the object to be detected by a force applied from the outside. A plate-shaped first core disposed in a facing direction, a first coil wound around the first core, and a compressive stress generated in the detected object by an external force applied to the detected object. A plate-shaped second core in which one of the end faces is disposed so as to face each other so that the longitudinal direction of the end faces are parallel to each other, and the second core wound around the second core. A coil, a coil urging means for generating an eddy current on the surface of the object to be detected by urging the first and second coils with an alternating current signal, and the coil urging means for urging the eddy current. By processing the signals output from the first and second coils, the first and second coils are processed. Signal processing means for detecting the stress applied to the object to be detected from the change of the eddy current signal resulting from the eddy current generated on the surface of the object to be detected, which is obtained from the coil; apparatus. 7. The stress detecting device according to claim 5, wherein the conductive object to be detected is a rotating shaft. 8. The stress detecting device according to claim 5, wherein the conductive object to be detected is a flat plate.