JP5747265B2 - Strain gauge - Google Patents

Description

  The present invention relates to a strain gauge for measuring strain or stress of an object.

  In order to maintain and manage a structure such as a bridge, it has been conventionally performed to measure strain or stress of an object such as a steel material included in the structure.

  For this type of measurement, a strain gauge or a strain gauge including a strain sensor has been generally used (see, for example, Patent Documents 1, 2, and 3). The strain gauge is usually bonded to an object measurement location with an adhesive. Moreover, a strain gauge is normally fixed to the measurement location of an object with fastening members, such as a volt | bolt.

JP 2000-55608 A JP 2009-237805 A JP 2011-180065 A

  Conventional measurement using a strain gauge that adheres to an object or a strain gauge that is fixed to the object with a fastening member such as a bolt has the following disadvantages.

  That is, when the strain gauge is bonded to the object, it is usually necessary to remove the surface of the object at the measurement location and polish it before bonding the strain gauge to the object. In addition, when the strain gauge is fixed to the object with a fastening member such as a bolt, generally, before the strain gauge is fixed to the object, it is necessary to perform a machining operation such as drilling around the measurement point of the object.

  For this reason, it takes time for installation work of the strain gauge accompanying such processing work or installation work of the strain gauge. In particular, when performing multipoint measurement, a large number of man-hours are required for installation work of a large number of strain gauges or strain gauges.

  In addition, since the object to be measured is subjected to processing operations such as polishing and drilling, the object is damaged, and the behavioral characteristics of the object (such as deformation characteristics due to stress) change from the original state. There is also a fear.

  Furthermore, strain gauges bonded to objects cannot be reused. In addition, when a crack or breakage of an object occurs at a measurement location where a strain gauge is bonded or a measurement location where a strain gauge is fixed, the strain gauge or strain gauge is often damaged. . For this reason, it is easy to raise the cost of measurement.

  The present invention has been made in view of such a background, and when measuring strain or stress of an object including a magnetic material such as steel, a strain gauge for the measurement is easily installed at a measurement location of the object. An object of the present invention is to provide a strain gauge capable of reducing the measurement cost.

  In order to achieve the above object, the strain gauge of the present invention is a strain gauge for measuring strain or stress generated in an object including a magnetic material, on which a first magnet is mounted, and the measurement location of the object The first member fixed to the object by the magnetic force acting between the object and the first magnet, and the second magnet are mounted, and are parallel to the first member at the measurement location of the object. A second member fixed to the object by a magnetic force acting between the object and the second magnet, and the first member and the second member fixed to a measurement location of the object The first member fixed to the object is mounted on either the first member or the second member so that the magnetic fields generated by the first magnet and the second magnet act, respectively. Before the relative displacement with the second member Characterized in that it comprises a magnetic field sensing element for generating an output corresponding to changes in a magnetic field (the first invention).

  According to the first invention, when measuring strain or stress generated in the object (an object including a magnetic material such as a steel material), the first member and the second member are respectively mounted on the first magnet. , And is fixed to the object by a magnetic force acting between the second magnet and the object. For this reason, the first member and the second member are not required to be subjected to processing such as polishing or drilling, and thus the object or the anticorrosion layer of the surface thereof is not damaged. Can be easily installed in a short time.

  After the first member and the second member are installed at the measurement location of the object, if a distortion of the object occurs at the measurement location, a relative displacement between the first member and the second member respectively fixed to the object occurs. . This relative displacement changes the positional relationship of the first magnet or the second magnet with respect to the magnetic field detection element, so that the total magnetic field (first magnet) acting on the magnetic field detection element from the first magnet and the second magnet. And the combined magnetic field of the magnetic fields generated by the second magnets at the arrangement positions of the magnetic field detection elements respectively change. As a result, the output of the magnetic field detection element changes.

  Therefore, the output of the magnetic field detection element changes according to the strain of the object at the measurement location. Based on the output of the magnetic field detection element, the strain generated in the object or the stress corresponding to the strain is applied. It can be measured.

  In this case, the first member and the second member are fixed to the object by magnetic force and are separate members separated from each other. Therefore, the object is between the first member and the second member. Even if a crack or break due to the strain of the first member occurs, the first member and the second member are not damaged.

  In addition, since the first member and the second member are each fixed to the object by magnetic force, after the measurement is completed, only the force against the magnetic force is applied to the first member and the second member. It can be removed from the object without damaging the object, the anticorrosion layer on the surface, or the first member and the second member. And the 1st member and 2nd member which were removed from the object can be reused as it is without trouble.

  Therefore, according to the first invention, in measuring strain or stress of an object including a magnetic material such as steel, a strain gauge for the measurement can be easily installed at the measurement location of the object, and the measurement cost The cost can be reduced.

  In the first aspect of the invention, the magnetic field detecting element is an initial initial state in which the first member and the second member are fixed to a measurement location of the object in a predetermined positional relationship determined in advance. It is preferable that the magnetic field generated by the second magnet is mounted on one of the first member and the second member so as to be arranged at positions where they cancel each other (second invention).

  Alternatively, in the initial initial state in which the first member and the second member are fixed at a predetermined measurement position of the object in a predetermined positional relationship, the first magnet and the second magnet respectively A third magnet that generates a magnetic field that cancels a combined magnetic field generated at the arrangement position at the arrangement position of the magnetic field detection element is mounted on at least one of the first member and the second member. Preferred (third invention).

  According to the second aspect of the invention, in the initial state, the magnetic fields generated by the first magnet and the second magnet at the arrangement positions of the magnetic field detection elements cancel each other, so the mutual positions of the first member and the second member In a situation where the relationship is kept constant at or near the initial state, each of the first magnet and the second magnet is generated due to a change in ambient temperature around the first member and the second member. Even if the magnetic field changes, the total magnetic field (the combined magnetic field of the magnetic field by the first magnet and the magnetic field by the second magnet) at the arrangement position of the magnetic field detecting element can be kept constant or substantially constant.

  For this reason, it becomes possible to prevent or suppress fluctuations in the output of the magnetic field detection element due to changes in the environmental temperature. As a result, the reliability of the measurement of the distortion | strain or stress of an object based on the output of a magnetic field detection element can be improved.

  According to the third aspect of the invention, in the initial state, the combined magnetic field generated by the first magnet and the second magnet at the arrangement position of the magnetic field detection element, and the arrangement of the magnetic field detection element by the third magnet Since the magnetic fields generated at the positions cancel each other, in the situation where the mutual positional relationship between the first member and the second member is kept constant in the initial state or a state close thereto, the first member and the second member Even if the magnetic field generated by each of the first magnet, the second magnet, and the third magnet changes due to the change in the ambient temperature around the magnetic field, the total magnetic field (first magnet) at the position where the magnetic field detection element is arranged (The combined magnetic field of the magnetic field by the second magnet and the magnetic field by the third magnet) can be kept constant or substantially constant.

  For this reason, similarly to the second invention, it is possible to prevent or suppress fluctuations in the output of the magnetic field detection element due to changes in the environmental temperature. As a result, the reliability of the measurement of the distortion | strain or stress of an object based on the output of a magnetic field detection element can be improved.

The perspective view which shows the structure of the strain gauge of embodiment of this invention. The graph which shows the output characteristic of the strain gauge of embodiment.

  An embodiment of the present invention will be described below with reference to FIGS. The object W to be measured for strain or stress by the strain gauge 1 of the present embodiment is an object made of a magnetic material such as steel, or an object made of a material sufficiently containing the magnetic material (in other words, An object capable of attracting an arbitrary magnet by a magnetic force).

  As shown in FIG. 1, the strain gauge 1 includes a housing-like first member 2 and a second member as two members fixed to the surface of the measurement location of the object W when measuring the strain or stress of the object W. A member 3 is provided.

  A first magnet 4 and a second magnet 5 are mounted on the first member 2 and the second member 3, respectively. Further, one of the first member 2 and the second member 3, for example, the first member 2, is further mounted with a third magnet 6 and a Hall element 7 as a magnetic field detection element.

  The first magnet 4 generates a magnetic field around it, and at the same time, generates a magnetic force between the first member 2 and the object W as a force (attraction) for fixing the first member 2 to the object W by the magnetic field. Magnet. In the present embodiment, the first magnet 4 is housed inside the first member 2 and fixed to the first member 2 at a position near the bottom surface (contact surface to the object W) of the first member 2. .

  Further, the second magnet 5 generates a magnetic field around it, and at the same time, generates a magnetic force between the second member 3 and the object W, which is a force (attraction) for fixing the second member 3 to the object W by the magnetic field. It is a magnet for generating. In the present embodiment, the second magnet 5 is housed inside the second member 3 and fixed to the second member 3 at a position near the bottom surface (contact surface to the object W) of the second member 3. .

  As described above, the first member 2 and the second member 3 on which the first magnet 4 and the second magnet 5 are respectively mounted are as shown in FIG. Are arranged in parallel in the measurement direction with a predetermined positional relationship at a predetermined interval. And in this arrangement | positioning state (henceforth an initial arrangement | positioning state), the 1st member 2 and the 2nd member 3 act between the 1st magnet 4 and the 2nd magnet 5, and the object W which are mounted in each. It is fixed (adsorbed) to the object W by the magnetic force (attraction).

  The hall element 7 outputs a signal (voltage signal) corresponding to the strength and direction (polarity) of the magnetic field (the magnetic field generated by the first magnet 4, the second magnet 5, and the third magnet 6) at its arrangement position. In this embodiment, the magnetic field detection element is attached to the outer surface of the side surface portion of the first member 2 facing the second member 3 and is fixed to the first member 2.

  The hall element 7 is electrically connected to a cable 8 led out from the first member 2, and an output signal of the hall element 7 is output to the outside via the cable 8. The first member 2 may be mounted with a circuit such as an amplifier that amplifies the output signal of the Hall element 7.

  The third magnet 6 is a magnet for adjusting the strength of the total magnetic field acting on the arrangement position of the Hall element 7 in a state where the first member 2 and the second member 3 are installed at the measurement location of the object W. The third magnet 6 generates a combined magnetic field generated by the first magnet 4 and the second magnet 5 at the arrangement position of the Hall element 7 in the initial arrangement state of the first member 2 and the second member 3. The first member 2 is accommodated in the first member 2 so as to generate a magnetic field to be canceled (a magnetic field in which the strength of the total magnetic field with the combined magnetic field is zero or substantially zero) at the arrangement position of the Hall element 7, It is fixed to one member 2.

  That is, by appropriately setting the position or posture of the third magnet 6 in the first member 2 or the size, shape, intensity of the generated magnetic field, etc. of the third magnet 6, In the initial arrangement state of the two members 3, the intensity of the total magnetic field generated at the arrangement position of the Hall element 7 by the first magnet 4, the second magnet 5, and the third magnet 6 becomes zero or almost zero. ing.

  Here, the first magnet 4, the second magnet 5, and the third magnet 6 have the same temperature characteristics, and the strength of the magnetic field generated by each of them is the ambient temperature around the first member 2 and the second member 3. It increases and decreases with almost the same characteristics with respect to the change of.

  For this reason, the mutual positional relationship between the first member 2 and the second member 3 is kept constant in the initial arrangement state or a state close thereto (and eventually the first magnet 4, the second magnet 5, and the second member 3). In the situation where the mutual positional relationship of the three magnets 6 is kept constant), even if the environmental temperature changes, the first magnet 4, the second magnet 5, and the third magnet 6 are disposed at the positions where the Hall elements 7 are disposed. The strength of the total magnetic field formed by synthesizing the magnetic fields generated is kept constant.

  In the present embodiment, the shape and size of each magnet 4, 5, 6 or the mutual positional relationship between each magnet 4, 5, 6 and Hall element 7 in the initial arrangement state is appropriately set. Thus, the relative displacement from the initial arrangement state between the first member 2 and the second member 3 is the interval direction of the first member 2 and the second member 3 (the direction of the arrow Y in FIG. 1). In this case, the strength of the total magnetic field generated at the arrangement position of the Hall element 7 by the first magnet 4, the second magnet 5, and the third magnet 6 changes with a relatively high sensitivity.

  Next, the measurement process by the strain gauge 1 of this embodiment is demonstrated.

  In measuring the strain or stress of the object W, first, the first member 2 and the second member 3 of the strain gauge 1 are arranged at the measurement location of the object W in the initial arrangement state. At this time, the first member 2 and the second member 3 are fixed to the object W by a magnetic force (attractive force) acting between the first magnet 4 and the second magnet 5 mounted on the first member 2 and the object W, respectively.

  For this reason, the first member 2 and the second member 2 of the strain gauge 1 can be easily and quickly measured at the measurement location of the object W without requiring the object W to be subjected to processing such as polishing or drilling in advance. Two members 3 can be installed.

  In the initial state where the first member 2 and the second member 3 of the strain gauge 1 are installed at the measurement location of the object W as described above (the state in which the strain of the object W is not generated), that is, the first member 2 and In the initial arrangement state of the second member 3, the strength of the total magnetic field generated at the arrangement position of the Hall element 7 by the first magnet 4, the second magnet 5, and the third magnet 6 is zero (or almost zero). . For this reason, the magnitude (voltage level) of the output signal of the Hall element 7 becomes zero level. Therefore, in a state where the object W is not distorted, the magnitude of the output signal of the Hall element 7 is zero as shown in the graph of FIG.

  Even when the object W is not distorted, if the ambient temperature around the first member 2 and the second member 3 changes, each of the first magnet 4, the second magnet 5, and the third magnet 6 becomes a Hall element. The intensity of the magnetic field generated at the arrangement position 7 changes. However, as described above, as long as the positional relationship between the first member 2 and the second member 3 is kept constant, each of the first magnet 4, the second magnet 5, and the third magnet 6 is the Hall element 7. The strength of the total magnetic field formed by synthesizing the magnetic fields generated at the arrangement positions of the positions is kept almost constant by canceling out changes due to the environmental temperature.

  For this reason, in the state where the distortion of the object W does not occur, the magnitude of the output signal of the Hall element 7 is maintained at the zero level (or almost zero level) even if the environmental temperature changes.

  When the distortion of the object W occurs after the first member 2 and the second member 3 are installed, a relative displacement between the first member 2 and the second member 3 occurs along with the distortion, and as a result, the first magnet. 4. The mutual positional relationship between the second magnet 5 and the third magnet 6 changes from the initial arrangement state. For example, distortion occurs in the object W in the direction indicated by the arrow Y in FIG. 1, and the interval between the first member 2 and the second member 3 changes.

  At this time, the intensity of the total magnetic field generated at the arrangement position of the Hall element 7 changes, and the magnitude of the output signal of the Hall element 7 changes from zero level accordingly.

  In this case, the amount of change in the strength of the total magnetic field generated at the position where the Hall element 7 is disposed increases as the strain of the object W increases. In addition, the direction of the total magnetic field generated at the position where the Hall element 7 is arranged includes the case where the strain is a strain in the direction of expansion of the interval between the first member 2 and the second member 3, and the reduction of the interval. In the case of directional strain, the directions are opposite to each other. For this reason, the magnitude and polarity of the output signal of the Hall element 7 change according to the strain of the object W, for example, as shown in the graph of FIG.

  Therefore, based on the output signal of the Hall element 7, it is possible to measure the distortion generated at the measurement location of the object W. Furthermore, the stress generated at the measurement location of the object W can also be measured from the measurement value of the strain.

  In the state where the distortion of the object W occurs, the state in which the distortion is kept constant, and the mutual positional relationship between the first member 2 and the second member 3 is kept constant. As in the case where the distortion of the object W does not occur, the output signal of the Hall element 7 is kept substantially constant even when the environmental temperature changes.

  As described above, according to the strain gauge 1 of the present embodiment, the first member 2 and the second member 3 can be fixed to the object W by the magnetic force of the first magnet 4 and the second magnet 5 mounted on each, The object W is not required to be subjected to processing such as polishing or drilling, and the object W and the anticorrosion layer on the surface thereof are not damaged, and the strain gauge 1 can be easily and quickly attached to the object W to be measured. The strain or stress generated in the object W in the original behavior state of the object W can be measured based on the output signal of the Hall element 7.

  In addition, even if the third magnet 6 is additionally mounted on the first member 2 and the positional relationship between the first member 2 and the second member 3 is kept constant, the environmental temperature changes. The strength of the total magnetic field generated at the arrangement position of the Hall element 7 is kept substantially constant, so that the object W can be detected based on the output signal of the Hall element 7 regardless of the environmental temperature change. Strain or stress can be measured with high reliability.

  In the embodiment described above, the third magnet 6 is mounted only on the first member 2 so that the total magnetic field generated at the arrangement position of the Hall element 7 does not change according to the environmental temperature. However, instead of the first member 2, the third magnet may be mounted only on the second member 3, or the third magnet may be mounted on both the first member 2 and the second member 3. .

  Alternatively, by appropriately setting the arrangement position of the Hall element 7 in the first member 2 (or the second member 3) without mounting the third magnet on both the first member 2 and the second member 3. The strength of the total magnetic field generated at the arrangement position of the Hall element 7 by the first magnet 4 and the second magnet 5 may be kept substantially constant regardless of the environmental temperature. In this case, the third magnet 6 is not necessary.

  Moreover, although the said embodiment demonstrated as an example the case where the distortion | strain which arises in the space | interval direction of the 1st member 2 and the 2nd member 3, or the stress corresponding to this was measured, it mounts in the 1st member 2 and the 2nd member 3. By appropriately setting the size, shape, mounting position, or orientation of each magnet to be performed, or the mounting position of the Hall element with respect to the first member 2 or the second member 3, the first member 2 and the second member The sensitivity of the change in the strength of the total magnetic field acting on the Hall element 7 with respect to the distortion of the object W in the direction orthogonal to the interval direction of the members 3 (direction orthogonal to the arrow Y in FIG. 1) is increased. You may make it measure the distortion | strain corresponding to the distortion | strain of the object W in the direction orthogonal to the space | interval direction of the 1st member 2 and the 2nd member 3, or this.

  Moreover, in the said embodiment, although the Hall element 7 was used as a magnetic field detection element, you may use magnetic field detection elements other than a Hall element.

  DESCRIPTION OF SYMBOLS 1 ... Strain meter, 2 ... 1st member, 3 ... 2nd member, 4 ... 1st magnet, 5 ... 2nd magnet, 6 ... 3rd magnet, 7 ... Hall element (magnetic field detection element)

Claims (3)

A strain gauge for measuring strain or stress generated in an object including a magnetic material,
A first member mounted with a first magnet and fixed to the object by a magnetic force acting between the object and the first magnet at a measurement point of the object;
A second magnet is mounted, and is arranged in parallel with the first member at a measurement location of the object and fixed to the object by a magnetic force acting between the object and the second magnet. Members,
In a state where the first member and the second member are fixed to the measurement location of the object, any one of the first member and the second member so that the magnetic fields generated by the first magnet and the second magnet act, respectively. A magnetic field detection element mounted on either side and generating an output corresponding to a change in the magnetic field due to a relative displacement between the first member and the second member fixed to the object. Characteristic strain gauge. The strain gauge according to claim 1,
The magnetic field detection element is generated by the first magnet and the second magnet, respectively, in an initial initial state in which the first member and the second member are fixed to a measurement location of the object in a predetermined positional relationship. The strain gauge is mounted on one of the first member and the second member so that the magnetic fields to be canceled are arranged at positions where they cancel each other. The strain gauge according to claim 1,
In the initial initial state in which the first member and the second member are fixed at a measurement location of the object in a predetermined positional relationship determined in advance, the arrangement positions of the magnetic field detection elements by the first magnet and the second magnet, respectively. A third magnet that generates a magnetic field that cancels the combined magnetic field generated at the position where the magnetic field detection element is disposed is mounted on at least one of the first member and the second member. Strain gauge.

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