JP6010844B2 - Tension measurement method - Google Patents

Description

  The present invention relates to a tension measuring method for measuring a tension acting on a long magnetic body by using a stress magnetic effect of the magnetic body.

  As a device for accurately measuring the tension applied to long steel members, such as cables for suspension structures and tension members for ground anchors over a long period of time, the stress magnetic effect (magnetization caused by stress) appears in magnetic materials such as steel. A tension measuring device utilizing a changing phenomenon) has been proposed (see, for example, Patent Document 1).

  The tension measuring device of Patent Document 1 was proposed by the present applicant, and a part of a magnetic material to be measured is partially saturated asymptotically magnetized in the longitudinal direction (the region where the hysteresis ring of magnetization characteristics is closed, magnetic physics In this term, DC magnetization is performed up to the “rotational magnetization region”), the spatial magnetic field strength in the vicinity of the surface of the magnetized portion is detected, and the tension acting on the magnetic material is measured from the detected value. If this tension measuring device is used, it is possible to measure the tension at an arbitrary position of the existing long steel member, but only when starting the measurement, the measurement accuracy normally required in the low load area (measurement error is in the use area) It was found that there was a problem that it was not possible to obtain (within ± 5% of the maximum load).

As shown in FIG. 4, the measurement error at the start of the measurement described above is that when a change in stress is repeatedly applied to a magnetic body under a constant magnetic field, the change in magnetization due to the second and subsequent stress changes is reversible and has a substantially linear relationship ( This is close to the ideal stress-magnetization relationship (hereinafter referred to as the ideal magnetization curve), but the initial state before the initial stress loading is considered to be out of the ideal magnetization curve. That is,
Detection of spatial magnetic field strength at the start of measurement (when the load is applied for the first time) using the ideal magnetization curve because the magnetization state before the start of measurement (before the load is applied) deviates from the ideal magnetization curve When the tension is obtained from the value, it is estimated that the measured value greatly deviates from the actual tension.

  On the other hand, when performing the tension measurement using the tension measuring device of Patent Document 1, the applicant of the present invention is not less than the upper limit value of the working load region under the magnetic field in the saturation asymptotic magnetization range of the magnetic body before the measurement is started. A tension measurement method has been proposed that reduces the measurement error by carrying out the step of applying a load once or more and keeping the magnetization state close to an ideal magnetization curve (Patent Document 2).

JP 2009-265003 A JP 2011-95033 A

  However, in the tension measuring method proposed in Patent Document 2, if a large load is to be applied to an existing long member before starting measurement, it is necessary to use a large-scale hydraulic device or the like, which is very laborious. For this reason, it is actually difficult to apply to the tension measurement of the existing long member, and even when applying to the new long member, the magnetic material for measurement such as a short PC steel bar previously loaded at the factory It was necessary to take the method of connecting the cable to the long member currently installed at the construction site.

  Therefore, an object of the present invention is to improve measurement accuracy at the start of measurement with a simple operation in a tension measurement method using the stress magnetic effect of a magnetic material.

  In order to solve the above-described problems, the present invention provides a spatial magnetic field in the vicinity of the surface of the central portion in the longitudinal direction of the magnetization section of the magnetic material in a state where a part of the magnetic material is DC-magnetized in the longitudinal direction to the saturation asymptotic magnetization range. In the tension measurement method for detecting the strength and measuring the tension acting on the magnetic body based on the detected value, before starting the tension measurement in the magnetization section of the magnetic body, adjacent to both sides in the longitudinal direction of the magnetization section An adjacent portion magnetization step is performed in which at least one of the portions is DC magnetized to the saturation asymptotic magnetization range. According to this method, the measurement accuracy at the start of measurement can be improved only by performing a simple operation compared to the conventional method in which a large load is applied to the magnetic material before the start of measurement.

  Here, the reason why the measurement accuracy at the start of measurement is improved by DC magnetizing the adjacent portion of the magnetization section of the magnetic material before the start of measurement as described above is considered as follows.

  As shown in FIG. 5, when a magnetic material is DC magnetized to a saturation asymptotic magnetization range (quasi-saturated magnetization) by a magnetizer, a certain amount of magnetic flux density remains even after the magnetizing action by the magnetizer disappears (residual magnetization). It has been known. Therefore, it is considered that the adjacent portion of the magnetization section of the magnetic material to be measured is quasi-saturated before starting the tension measurement, so that the adjacent portion is in a residual magnetization state at the start of measurement. And, when quasi-saturated magnetization is performed only in the magnetization section as in the prior art, the magnetization characteristics of the adjacent portion become unstable due to the leakage of magnetic flux from the magnetization section, and accordingly the magnetization characteristics of the magnetization section also show unstable behavior. On the other hand, when the adjacent portion is in the residual magnetization state, the magnetization characteristic of the adjacent portion is stabilized, so that the magnetization property of the magnetization section is also stabilized, which is presumed to contribute to improvement of measurement accuracy.

  Here, in order to further improve the measurement accuracy at the start of measurement, the adjacent portion magnetization step is performed twice or more before starting the tension measurement, and on both sides of the magnetization section of the magnetic body. It is desirable that the adjacent portion be DC magnetized over at least a length of ½ or more of a magnetizer that applies a magnetic field to the magnetic material.

  When using a tension measuring device comprising a magnetizer for direct current magnetization in the magnetization section of the magnetic material and a magnetic sensor for detecting the spatial magnetic field intensity in the vicinity of the surface in the longitudinal center of the magnetization section, the adjacent section magnetization is used. As a specific implementation method of the process, a method of sliding the tension measuring device in the longitudinal direction from the magnetization section can be adopted.

  The present invention is particularly effective when the magnetic material to be subjected to tension measurement is a drawn steel wire, a stranded wire obtained by twisting a plurality of steel wires, a steel rope, or a steel rod. can do.

  As described above, the tension measuring method according to the present invention is configured so that at least one of the adjacent portions on both sides in the longitudinal direction of the magnetization section at the time of measurement of the magnetic material is measured before starting the measurement using the stress magnetic effect of the magnetic material. Since the measurement accuracy at the start of measurement is improved by quasi-saturated magnetization, it can be easily implemented compared to the conventional method in which a large load is applied to the magnetic material before the measurement is started, and a new construction is provided. The present invention can be easily applied not only to measuring the tension of a long member but also to measuring the tension of an existing long member.

Longitudinal front view schematically showing a tension measuring device used in the tension measuring method of the embodiment FIGS. 1A to 1C are explanatory diagrams of adjacent part magnetization steps using the tension measuring device of FIG. a and b are graphs showing the results of tension measurement accuracy confirmation experiments, respectively. Graph showing the relationship between stress and magnetic flux density in a constant magnetic field Graph explaining remanent magnetization generation behavior

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, a tension measuring device 1 used in the tension measuring method of this embodiment includes a cylindrical magnetizer 2 disposed so as to surround a part of a long magnetic body (measurement target material) A, and The spacer 3 inserted between the magnetizer 2 and the magnetic body A, the Hall element 4 as a magnetic sensor for detecting the spatial magnetic field intensity in the vicinity of the surface of the magnetic body A, and an amplifier for amplifying the output of the Hall element 4 5 is basically configured. The magnetizer 2 and the spacer 3 are divided into two in the circumferential direction so that the entire apparatus can be mounted at an arbitrary position of an existing member.

  The magnetizer 2 fixes four permanent magnets 7 each having a shape of a cylinder to both ends of the inner periphery of a cylindrical steel yoke 6 with an adhesive, and the outer end surfaces of the permanent magnets 7 are attached to the magnetizer 2. Covering covers 8 are attached to both end faces of the yoke 6. The permanent magnets 7 are arranged in such a posture that they are opposed to each other with different magnetic poles spaced apart in the longitudinal direction of the magnetic body A one by one in the vertical direction, and the magnetic body A is DC magnetized to a saturation asymptotic magnetization range in a short range in the longitudinal direction. Quasi-saturated magnetization).

  The spacer 3 is made of nonmagnetic polyethylene and is adhesively fixed to the inner peripheral side of each permanent magnet 7 to prevent contact between the permanent magnet 7 and the magnetic body A. A plurality of the Hall elements 4 and the amplifiers 5 are attached to positions on the outer peripheral surface facing the inner peripheral surface of the yoke 6.

  The Hall elements 4 are arranged at equal intervals in the circumferential direction near the midpoint of the pair of permanent magnets 7 on the inner peripheral side of the magnetizer 2, that is, in the vicinity of the central portion in the longitudinal direction of the magnetization section of the magnetic material A. Then, the output of each Hall element 4 is amplified by an amplifier 5 and sent to a data processing device (not shown), and the spatial magnetic field strength in the vicinity of the surface of the magnetic material A obtained as an average value thereof is determined in advance by experiments or the like. The tension acting on the magnetic body A is obtained by applying the relational expression between strength and tension.

  In the tension measuring method of this embodiment, before the measurement by the tension measuring device 1 having the above-described configuration, the tension measuring device 1 (magnetizer 2) is used to measure the longitudinal direction of the magnetization section during the measurement of the magnetic substance A. An adjacent portion magnetization step is performed in which the adjacent portions on both sides are quasi-saturated.

  Specifically, first, the tension measuring device 1 is installed in a predetermined position of the magnetic body A as shown in FIG. 2A, and then the longitudinal direction of the magnetic body A as shown in FIG. Slide to one side (left side in FIG. 2). As a result, the magnetization section that is quasi-saturated in the state of FIG. 2A becomes a residual magnetization state, and the adjacent portion on the left side of the magnetization section is quasi-saturated. Here, it is desirable that the slide amount of the tension measuring device 1 is set so that the length of the adjacent portion to be quasi-saturated is at least ½ or more of the magnetizer 2 that applies a magnetic field to the magnetic body A. FIG. 2B shows an example in which the adjacent portion is quasi-saturated magnetized over a sufficient length by sliding the tension measuring device 1 as much as its length.

  And although illustration is abbreviate | omitted, the tension | tensile_strength measuring apparatus 1 is slid to the reverse direction to FIG.2 (b), and the adjacent part on the right side of a magnetization area is quasi-saturated similarly to the adjacent part on the left side. At this time, the magnetization section and the adjacent portion on the left side are in a residual magnetization state. In this manner, the operation of quasi-saturating the adjacent portions on the left and right of the magnetization interval is repeated twice or more.

  Finally, as shown in FIG. 2 (c), the tension measuring device 1 is returned to the predetermined position at the time of wearing. As a result, the magnetization section is quasi-saturated again and the left and right adjacent portions are in a residual magnetization state. In this state, measurement by the tension measuring device 1 is started.

  Next, an experiment for confirming the measurement accuracy improvement effect of the tension measurement method of this embodiment will be described. In this experiment, a 7-strand PC steel stranded wire (JIS standard: SWPR7BN) having a standard diameter of 15.2 mm was used as a magnetic material to be measured. Then, this PC steel stranded wire is set in a tensile testing machine, and the tension measuring device 1 (outer diameter: 40 mm, length: 120 mm) of the embodiment is attached to the PC steel stranded wire, and the tension is changed while changing the load of the tensile testing machine. When the measurement with the measuring device 1 is performed and the tension measuring device 1 is slid to both sides in the longitudinal direction as described above and the adjacent portion magnetization step is performed before the measurement (Example), the adjacent portion magnetization step is not performed. When the measurement was performed (Comparative Example), the relationship between the actual tension measured with the load cell of the tensile tester and the output voltage corresponding to the measured value of the tension measuring device 1 was examined. The result is shown in FIG.

  As apparent from FIG. 3, the behavior of the output voltage of the tension measuring device 1 in the initial state and the initial stress load is the output for the second and subsequent loads in the comparative example (FIG. 3A), particularly in the low load region. In contrast to the voltage reproducible behavior, the example (FIG. 3B) is close to the behavior of the output voltage for the second and subsequent loads. This shows that a large measurement error occurs in the initial state and the initial stress load in the comparative example, but the measurement error can be greatly reduced in the example.

  Quantitatively, the measurement error of the comparative example in the initial state is about 50% (measurement error is expressed as a ratio to the maximum load in the use area, the same shall apply hereinafter), whereas in the example, it is about 10%. When a stress (60% of the standard load) that is normally introduced after installation is applied, the measurement error of the comparative example is about 10%, whereas in the example, it is about 5%. This measurement error includes variations due to hysteresis in the relationship between the load and output voltage for the second and subsequent times.

  Therefore, as in this embodiment, the tension measuring device 1 is slid before the start of measurement, and the adjacent portions on both sides in the longitudinal direction of the magnetization section are quasi-saturated, so that the accuracy that can withstand practical use from the start of the measurement. It was confirmed that tension could be measured with

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  For example, it is desirable to perform the adjacent portion magnetization step twice or more, but it may be performed only once. Moreover, although the adjacent part which carries out a quasi-saturation magnetization is desirable for the longitudinal direction both sides of a magnetization area, only one side may be sufficient. Furthermore, as a material to be measured, not only a stranded wire obtained by twisting a plurality of steel wires as in the embodiment, but also all steel wires, steel ropes, steel bars, etc. formed of a magnetic material such as a drawn wire. Includes a long member.

DESCRIPTION OF SYMBOLS 1 Tension measuring device 2 Magnetizer 3 Spacer 4 Hall element 5 Amplifier 6 Yoke 7 Permanent magnet 8 Cover A Magnetic body

Claims (5)

  In a state in which a part of the magnetic material is DC magnetized in the longitudinal direction to the saturation asymptotic magnetization range, the spatial magnetic field strength in the vicinity of the surface of the central portion in the longitudinal direction of the magnetization section of the magnetic material is detected, and based on the detected value, the magnetic material is detected. In the tension measuring method for measuring the tension acting on the magnetic material, before starting the tension measurement in the magnetization section of the magnetic material, at least one of the adjacent portions on both sides in the longitudinal direction of the magnetization section is dc to the saturation asymptotic magnetization range. The tension measuring method characterized by carrying out the adjacent part magnetization process to magnetize.   The tension measuring method according to claim 1, wherein the adjacent portion magnetization step is performed twice or more before starting the tension measurement.   3. The tension measuring method according to claim 1, wherein the adjacent portions on both sides of the magnetization section of the magnetic material are DC-magnetized over at least a length of ½ or more of a magnetizer that applies a magnetic field to the magnetic material. .   A tension measuring device comprising a magnetizer for direct current magnetization in a magnetization section of the magnetic body and a magnetic sensor for detecting a spatial magnetic field intensity in the vicinity of the surface in the longitudinal center of the magnetization section from the magnetization section of the magnetic body. The tension measuring method according to claim 1, wherein the adjacent portion magnetization step is performed by sliding in the longitudinal direction.   The tension measuring method according to any one of claims 1 to 4, wherein the magnetic body is a drawn steel wire, a stranded wire obtained by twisting a plurality of steel wires, a steel rope, or a steel rod. .

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