JPH0310055B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention utilizes the fact that when stress acts on a magnetic material, the iron loss of the magnetic material changes in relation to the stress. By inserting a washer-type magnetic sensor between the structure and tightening the bolt, the iron loss is measured with the washer-type magnetic sensor, and the measured iron loss is converted into axial force with an axial force converter.
This invention relates to a washer-type magnetic sensor used in a magnetic axial force meter that measures the axial force acting on a bolt.

[Technical Background of the Invention] Generally, in assembled structures fastened with bolts and nuts, it is necessary to appropriately manage the axial force of the bolts. Usually, the axial force of a bolt is controlled by the tightening torque when tightening the bolt using the torque method. However, with this torque method, it is difficult to control the axial force of the bolt to a predetermined value due to large variations in the coefficient of friction between the threaded surface of the bolt/nut and the contact surface between the bolt/nut and the fastened object. The disadvantage was that there was a large variation in the axial force. Therefore, recently, there is a relationship between the iron loss of magnetic materials and the tensile stress and compressive stress acting on the magnetic materials.
Taking advantage of the close relationship shown in Figure 1, the iron loss of a bolt made of magnetic material is measured, and the axial force acting on the bolt is calculated from the measured iron loss. A magnetic method of measuring is used.

FIG. 1 shows the relationship between stress acting on a magnetic material and iron loss, with tensile stress and compressive stress on the horizontal axis and iron loss on the vertical axis. As is clear from Figure 1, when compressive stress acts on a magnetic material, there is a nearly linear relationship between compressive stress and iron loss, so if you use this relationship to measure iron loss, you can achieve high accuracy. The compressive stress acting on the magnetic material can be determined.

Generally, when an assembled structure is tightened with bolts, tensile stress is applied to the shaft of the bolt in the longitudinal direction.
A compressive stress according to Poisson's ratio acts in the radial direction. Furthermore, compressive stress corresponding to the axial force of the bolt is generated in the circumferential direction and the radial direction on the surface layer of the head of the bolt. Therefore, by measuring the core loss at the center of the upper surface of the bolt head and determining its compressive stress, the axial force acting on the bolt can be determined.

Normally, in order to measure the iron loss of a bolt made of magnetic material using the above-mentioned relationship, as shown in FIG. Among them, the magnetic sensor 4 is brought into contact with the top surface of the head of the bolt 2 to measure the iron loss, and the measured iron loss is input to an axial force converter (not shown) to convert the iron loss to axial force. Then, measure the axial force of bolt 2.
The magnetic sensor 4 is constructed by winding a primary coil (excitation coil) 6 and a secondary coil (output secondary voltage coil) 7 around an iron core 5 having a substantially U-shaped cross section.The lead wire 8 of the primary coil 6 is connected to an external power source. When the lead wire 9 of the secondary coil 8 is connected to a control device (not shown) and the primary coil 6 is excited with alternating current (not shown), the magnetic flux from the iron core 5 will cause the surface layer of the head of the bolt 2 to A closed magnetic path is formed that flows in the direction of the arrow and returns to the iron core 5 again. In this case, the output secondary voltage induced in the secondary coil 7 is
The excitation current of the primary coil 6 is controlled so as to be equal to a preset setting voltage, and the magnetic flux flowing through the surface layer of the head of the bolt 2 is kept constant, so that the excitation current of the primary coil 6 and the secondary If the output secondary voltage of the coil 7 is input to an iron loss measuring device (not shown),
The core loss at the center of the top surface of the bolt 2 can be measured. If the iron loss when axial force is acting on the bolt is Wi, and the iron loss when no axial force is acting on the bolt is Wo, then the amount of change in iron loss (Wi
-Wo) is approximately proportional to the compressive stress acting on the head of bolt 2, that is, the axial force of the bolt, from the relationship shown in Figure 1. The axial force of 2 can be found.

Axial force of bolt = α (Wi−Wo) ……(1) Here, the proportionality constant α is the amount of magnetic flux, the thickness of the bolt,
It is determined by the material, type of magnetic sensor, etc., and bolts in the same lot can be considered to be substantially the same.

[Problems with the background technology] By the way, when measuring iron loss by bringing a magnetic sensor into contact with the top surface of the bolt head as described above, there are raised letters and rough finishing irregularities on the top surface of the bolt head. When a magnetic sensor is placed in contact with the top surface of a bolt head, a gap is created between the two contact points, and this gap has a large effect on the measurement accuracy of iron loss, making it impossible to accurately measure the axial force of the bolt. There were flaws.

In addition, in conventional magnetic sensors, the iron core is composed of two members, and there is a gap in the iron core itself.
As the gap changes depending on the load applied to the sensor, the detected iron loss itself also changes, so the iron loss does not have an accurate proportional relationship to the load, making it impossible to measure the axial force with high precision. There were also some drawbacks.

[Object of the Invention] The present invention was made in order to solve the problems of the conventional magnetic sensor as described above.
Another object of the present invention is to provide a washer-type magnetic sensor for use in a magnetic axial force meter that enables accurate measurement of axial force without being affected by changes in load applied during tightening.

[Summary of the Invention] The washer type magnetic sensor of the present invention is provided with a horizontal hole penetrating the inside of the core on the side surface of a ring-shaped core made of a single member having a bolt insertion hole in the center, and a primary A coil and a secondary coil are wound along the circumferential direction of an iron core.

[Embodiment of the Invention] An embodiment of the washer type magnetic sensor of the present invention is described in the third embodiment.
This will be explained in detail with reference to the drawings below.

3 and 4 show a first embodiment of the present invention. In this first embodiment, the iron core 2
0 has an opening 21 for bolt insertion in the center,
It is a ring-shaped member with smooth upper and lower surfaces, and a central opening 2 is formed from the outer surface of the ring-shaped core 20.
1, a plurality of horizontal holes 2 passing through the iron core 20
2 are provided radially. The primary coil 23 and the secondary coil 24 are wound within this radial horizontal hole 22. That is, one end of each coil 23, 24 is inserted into the horizontal hole 22a from the outer surface of the iron core 20, and after the coil tip is pulled out into the central opening 21 of the ring-shaped iron core 20, the coil tip is inserted into the adjacent horizontal hole. After pulling it out from 22b to the outer surface of the iron core 20,
The primary coil 23 and the secondary coil 24 are wound around the iron core 20 by repeating the operation of reinserting it into the center of the iron core from the adjacent horizontal hole 22c.

The number of turns of each coil 23, 24 is from several turns to several tens of turns around the iron core 20 depending on the size of the washer-type magnetic sensor.
It is drawn out to the outer surface of the iron core 20 as a lead wire. Further, on the outer surface of the iron core 20 and the inner circumferential surface of the opening 21, each coil 23, 2 exposed at this portion is provided.
It is also possible to form a groove 25 in accordance with the position 4 and allow each coil to fit within this groove 25 so that each coil protrudes largely from the side of the core and does not come into contact with the bolt. .

In the washer-type magnetic sensor of this embodiment with such a configuration, the iron core 20 is made of one piece and has no unevenness at all in the part that contacts bolts, nuts, or assembled structures, so it is difficult to measure conventional iron loss. The problem of gaps caused by embossed letters on the top of the bolt head, etc., which caused errors in installation, has been resolved, and as a result,
The measurement accuracy of the iron loss value measured by this washer-type magnetic sensor is improved, and the axial force of the bolt can be accurately measured.

Next, a second embodiment of the present invention shown in FIGS. 5 and 6 will be described.

In this second embodiment, a ring-shaped core 20 has an opening 21 for inserting a bolt in the center, and six straight horizontal holes 22 penetrate from the outer surface to the outer surface of the ring-shaped core 20.
The openings 26 of each horizontal hole are provided at different positions so that they are at the apexes of the hexagon. The primary coil 23 and the secondary coil 24 are connected to the first horizontal hole 22a.
It is inserted into the core 20 through the opening 26a of the adjacent horizontal hole, and once pulled out to the outside of the core 20 through the opening 26b of the adjacent horizontal hole.
2b. By repeating this operation, the primary coil 23 and the secondary coil 24 are
It is wrapped with.

In the second embodiment with such a configuration, the iron core 20 is made of one piece and has smooth upper and lower surfaces as in the previous embodiment, so regardless of the embossed letters etc. on the top surface of the bolt head, It has the advantage of being able to measure bolt axial force with high precision. Moreover, since the horizontal hole 22 is provided in a straight line from the outer surface to the outer surface of the ring-shaped core 20, the horizontal hole 22 is
This has the advantage that the coil can be easily inserted into the inside of the coil. Note that in this second embodiment,
The number of horizontal holes penetrated through the core is not limited to six, but may be smaller or larger as long as they are arranged in a polygonal shape as a whole.

It should be noted that the present invention is not limited to the above-mentioned embodiment. For example, as shown in FIG. This also includes those wound around a plurality of rings arranged along the circumferential direction of the ring.

[Effects of the Invention] As described above, according to the washer-type magnetic sensor of the present invention, iron loss can be measured regardless of raised letters or rough finishing unevenness on the upper surface of the bolt head.
The measurement accuracy of the axial force of the bolt of the magnetic axial force meter can be improved. Furthermore, since the entire core is made of one member and has no internal gap, the gap does not have an adverse effect on measurement unlike conventional sensors, and highly accurate axial force measurement can be carried out.

[Brief explanation of the drawing]

Figure 1 is a characteristic curve diagram showing the relationship between stress and iron loss of a magnetic material, and Figure 2 is a cross-sectional diagram illustrating a method for measuring iron loss by bringing a conventional magnetic sensor into contact with the center of the upper surface of a bolt head. , FIG. 3 is a cross-sectional view showing the first embodiment of the washer-type magnetic sensor of the present invention, FIG. 4 is a cross-sectional view taken along line A-A in FIG. 3, and FIG. 5 is a cross-sectional view of the washer-type magnetic sensor of the present invention FIG. 6 is a cross-sectional view taken along line BB in FIG. 5, and FIG. 7 is a cross-sectional view showing a third embodiment of the washer type magnetic sensor of the present invention. 1, 1'... assembled structure, 2... bolt, 3...
...nut, 4...magnetic sensor, 5...iron core, 6...
...Primary coil, 7...Secondary coil, 8, 9...Lead wire, 20...Iron core, 21...Opening, 22...
Horizontal hole, 23...primary coil, 24...secondary coil, 25...groove, 26...opening.

Claims (1)

[Claims] 1. A plurality of horizontal holes penetrating the inside of the core are provided on the side surface of a ring-shaped core made of a single member with an opening for inserting a bolt in the center, and a primary coil and a secondary coil are inserted into the horizontal holes. A washer-type magnetic sensor characterized in that the secondary coil is wound along the circumference of a ring-shaped core so that the coil is not exposed on the top and bottom surfaces of the core. 2 Multiple horizontal holes provided on the side of the iron core,
A patent in which each of the horizontal holes passes through the outer surface of the core and the opening in the center, and these horizontal holes are arranged radially with respect to the core as a whole, and each coil is wound in a meandering shape within the horizontal holes. A washer-type magnetic sensor according to claim 1. 3 Multiple horizontal holes provided on the side of the iron core,
These horizontal holes are arranged radially with respect to the core as a whole, and each coil is arranged along the circumferential direction of the core within these horizontal holes. The washer-type magnetic sensor according to claim 1, wherein the washer-type magnetic sensor is wound in a plurality of ring shapes. 4 Multiple horizontal holes provided on the side of the iron core,
The washer-type magnetic sensor according to claim 1, wherein the horizontal holes are linear and pass through the outer and outer surfaces of the iron core, respectively, and these horizontal holes are provided adjacent to the iron core in a polygonal shape. .