JPS58153135A - Device for detecting axial tension of bolt - Google Patents

Abstract

PURPOSE:To detect the axial tension of the bolt readily and accurately, by winding exciting coils and magnetic flux detecting coils at a plurality of points on the central part and peripheral part of the head of the bolt, whose bolt tightening axial tension is to be detected, and selectively exciting the exciting coils. CONSTITUTION:A magnetic sensor 1 detects the magnetic property of a member to be measured. A power source 2 excites the sensor 1. A loss computing part 3 converts the output of the magnetic sensor 1. An axial tension display part 4 computes the bolt tightening axial tension from the output of said computing part 3 and displays the computed result. The magnetic sensor 1 is formed by the combination of seven U shaped iron cores 1a, 1b...1g. The exciting coils 1a1-1g1 and the magnetic flux detecting coils 1a2-1g2 are wound around the U shaped iron cores 1a-1g, respectively. Any one pair of said coils 1a1-1g1 and 1a2-1g2 is selected by linked switches 1h and 1i and switched and connected to the power source part 2 and the loss computing part 3.

Description

DETAILED DESCRIPTION OF THE INVENTION (11111!) The present invention relates to a bolt axial force detection device capable of magnetically and non-destructively detecting the tightening axial force of a bolt made of a magnetic material.

[Technical background of the invention]

In order to ensure the reliability of structures integrated using bolts, it is important to set the ultimate tightening force of the bolt and apply that value correctly. A magnetic axial force meter was developed as a device to detect force in a notebook.With this magnetic axial force meter, bolt tightening axial force can be detected simply by applying the axial force detection probe to the joint of a bolt that has been tightened, so it can be used on-site. It is multi-layered. The principle of this magnetic axial force needle is that the compressive stress applied to the bolt surface I11#L is approximately proportional to the bolt tightening axial force within the elastic IIs, and furthermore, the relationship between this compressive stress, that is, compressive strain, and magnetic properties. In other words, bolt tightening is - Iron loss value W4 detected by probe
Since there is a good correlation between the pressure and strain,
This characteristic is utilized. Therefore, we prepared calibration characteristics for the relationship between bolt axial force and iron loss variation in advance, and based on these results, we wrapped the primary and secondary coils around a U-shaped magnetic core around the bolt head that was tightened on site. A magnetic circuit is constructed by applying a probe, and the amount of change in iron loss is determined from the iron loss value at this time, and based on this value, the bolt axial force is measured.

[Problems with background value technique]

Therefore, there is a drawback in that the initial iron loss value must be recorded for each bolt before tightening the pigeonhole port, which measures the axial force using the current magnetic axial force needle.

[Purpose of the invention]

The present invention was made in view of the above circumstances, and its purpose is to provide a device that can detect the axial force of a tightened bolt without knowing the material properties of the bolt under non-axial force, that is, the magnetic properties. It's about doing.

[Summary of the invention]

That is, the present invention arranges a magnetic cell Vf made of an iron core wrapped with an excitation coil and a magnetic flux detection coil at multiple points in the center and peripheral parts of the bolt head where bolt tightening axial force is to be detected, and An iron loss value proportional to the bolt tightening minus axial force is obtained from the average value of the coil detection values, and this is displayed as the bolt tightening axial force.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration, which includes a magnetic sensor f1 for detecting the magnetic properties of a member to be measured, and a power supply section 2 for exciting this magnetic sensor 1. A loss calculating section 1 converts the output of the magnetic sensor 1, and an axial force indicating section 4 calculates the axial force for port tightening from the output of the calculating section 3 and indicates the calculated result. In addition, the magnetic sensor 1 has a center of 1 m, Ib, and Ic on one UjII#.
,Id,1m,11. These U-shaped iron cores 11 to 11 are formed by attaching the P.G. ~IM
m and one magnetic flux detection coil! ~11 It is covered with snow. Furthermore, these excitation coils 1hata, ~Ill, and magnetic flux detection coils 1m1 to l11m are connected to a changeover switch 1h1.
One set is selected and connected to the power supply section 2 and the loss calculation section 3 by the sound.

Chapter Sa! In order to detect the axial force when tightening a bolt, a shows a state in which the magnetic sensor f1 in Fig. 1 is lowered from the surface layer of the bolt head, and the member to be measured and the magnetic sensor 1 form a magnetic wA*. FIG. In the figure, φ indicates the direction in which magnetic flux flows.

FIG. 3 shows a sectional view taken along the line A in FIG. 2, and shows the arrangement of the U-shaped cores 111b...1g when a magnetic circuit is formed by applying the magnetic sensor f1 to the bolt head surface 5. This is what is shown. That is, around one U-shaped core, the other six U-shaped cores Jb, , Ic...1g are arranged at equal intervals.

By the way, as shown in Fig. 4, the diameter of the bolt shaft is r.
If the diameter of the head is rl, the stress distribution on the surface of the bolt head when tightening the bolt for this diameter ratio r[4° is C: as shown in Fig. 5.Therefore, the magnetic sensor 1 is shown in Fig. 3. If a magnetic circuit is formed by axially symmetrical islands on the surface of the port head as shown, the average stress value σm of the magnetic circuit bolt head of 1 m of U-shaped core and the U-shaped core ib.

IC... Average stress value σ of the bolt head of 1 liter magnetic circuit
The value is different for a. And this dark stress difference is (
1m-σB ) +e= l 1, but since the stress distribution on the surface layer of the bolt head is proportional within the elastic range, this stress i! 1 gN is proportional to the port tightening shaft force.

Therefore, the central U-shaped core 1m and the peripheral υ-shaped core 1b~1
Since the iron loss value detected by g is also detected as a value relative to the stress distribution, the loss calculation section 3 calculates the iron loss value fil W x, and the axial force indicating section 4 calculates the bolt axial force. If the bolt axial force is converted into and displayed, the bolt axial force can be detected without prior knowledge of the previous initial iron loss value No. for bolt tightening as in the conventional method. Therefore, magnetic sensor? 1 places a Ujll iron core 1a in the center and six U-shaped iron cores 1b around it.
~1 g are arranged at equal intervals and applied to the surface layer of the bolt head so as to be axially symmetrical. In calculating the iron loss value WX that is proportional to the bolt tightening ζ-axis force, the iron loss value Wm detected in the central U-shaped core 1 m and each of the detected U-shaped cores 1b to 1 m around the center The difference from the average value W1 of iron loss values is calculated. Therefore, when measuring bolt tightening test axial force, the order of bolts - magnetic sensor f on surface 5 is
Detection errors due to the method of application of item 1 and detection errors due to differences in characteristics around the bolt head are averaged out, and the bolt tightening axial force can be detected extremely stably and accurately.

The excitation coils 111 to Jg, t of each U-shaped core 11 to Ig are automatically switched, and a part of the output from each magnetic flux detection coil la, to Jll is fed back to determine the measurement conditions, that is, individual The detected magnetic flux severity of the glue-shaped core 1 to IM should be made constant, and the loss calculation unit 3 should be operated in conjunction with the power supply unit 2, and the U-shaped core 1
Equipped with a memory device 11 etc. for the iron loss value WIII detected in step a and each iron loss value detected in U-shaped cores 1b to 1g, the average value Wa of the iron loss values detected in U-shaped cores 1b to 1g is calculated. ,
What is necessary is to calculate the iron loss value Wx that is proportional to the bolt tightening axial force.

In addition, in the above example, the iron loss value was used as the magnetic property corresponding to the bolt tightening axial force, but it is of course possible to obtain the bolt tightening material axial force with the same original strength by using coercive force. .

Although seven U-shaped cores are used as the core configuration of the magnetic sensor 1, this number can be determined as appropriate.

〔Effect of the invention〕

As explained above, according to the present invention, the axial force of a bolt tightening material can be detected magnetically, non-destructively, and easily without prior knowledge of the characteristics when there is no bolt axial force, and the detected values at multiple points can be averaged. Since this process is carried out, it is possible to provide an extremely reliable bolt axial force detection device.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 shows a state in which the magnetic sensor shown in Fig. 1 is applied to the surface layer of the bolt head to form a magnetic circuit. 4 is a diagram showing an example of the bolt, and FIG. 5 is a diagram showing the stress distribution in the front pigtail portion of the bolt when the bolt is fastened. DESCRIPTION OF SYMBOLS 1... Magnetic sensor, 2... Power supply part, 3... Loss calculation part, 4... Axial force indication part, 11-Ig... U-shaped iron core, No, ~1g,... Excitation Coil, 111~1g■・
...Magnetic flux detection coil, 1h, 1m...selector switch,
5...Bolt order table*. Applicant's agent Patent attorney Takehiko Suzue Figure 1) Figure II2

Claims (1)

[Claims] In a device that determines the stress distribution on the surface of the bolt, which occurs in proportion to the bolt axial force, from changes in the magnetic properties of the bolt, and detects the bolt tightening axial force from this stress distribution,
A magnetic sensor consisting of a flexible iron core wrapped with excitation coils and magnetic flux detection coils is placed at multiple points in the center and periphery of the bolt head, and the excitation coil of seven magnetic coils is selectively excited. Calculate the iron loss value proportional to the bolt tightening q-axis force from the electric current #i part, the detected value of the magnetic flux detection coil in the center of the magnetic sensor, and the flat value of the detected value of each magnetic flux detection coil in the peripheral part. A bolt axial force detection device comprising: an axial force indicating section that calculates and displays a bolt tightening female axial force from the output of a loss calculation section obtained.