JP2551796B2 - Method and device for measuring axial force of bolt - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for measuring a tensile stress or a tensile load (hereinafter referred to as an axial force) of a bolt by using ultrasonic waves.

<Problems to be solved by conventional techniques and inventions> Conventionally, when constructing bridges, overpasses, and other building structures, or when performing piping construction, bolting aggregates and flanges together has been used. Coupling is performed, and as a method of determining the axial force of a bolt, a rotation angle measuring method for measuring the rotation angle of the bolt and a torque measuring method with a torque wrench are generally adopted.

However, according to the rotation angle measurement method and the torque measurement method described above, when the bolt that has been tightened loosens, if you try to tighten it further, the friction coefficient of the bolt will change, so the measurement will be accurate. There was a problem that I could not do it.

As a method of solving such a problem, ultrasonic waves are incident from one end of the bolt, echoes are received from the other end of the bolt, the arrival time difference is obtained, and the bolt is based on the arrival time difference. The method of measuring the axial force of the bolt by calculating the elongation of the bolt is adopted.

However, according to the above-mentioned measuring method, it is necessary to measure the difference in the arrival time of the echo before tightening the bolt and after the tightening of the bolt.

<Object of the Invention> The present invention has been made in view of the above problems,
An object of the present invention is to provide a bolt axial force measuring method and device capable of measuring the axial force of a bolt with high accuracy and efficiency.

<Means for Solving Problems> A method for measuring the axial force of a bolt as a first invention for achieving the above object is to provide an ultrasonic oscillator and an ultrasonic receiver at opposite positions with a bolt in between. The ultrasonic wave is emitted from the ultrasonic oscillator to the bolt, the ultrasonic wave transmitted through the bolt is received by the ultrasonic receiver, and a measurement value corresponding to the attenuation amount of the ultrasonic wave is obtained and the measurement is performed. It is characterized in that the axial force of the bolt is obtained by applying the value to the relationship between the attenuation amount of the ultrasonic wave and the axial force which is obtained in advance.

A bolt axial force measuring device according to a second aspect of the invention includes an ultrasonic oscillator for injecting an ultrasonic wave to the bolt,
1 for drive signal to oscillate ultrasonic wave to ultrasonic oscillator
Driving signal input means for inputting a pulse, an ultrasonic receiver for receiving ultrasonic waves transmitted through the bolt, a pulse counter for counting the number of ultrasonic pulses contained in the signal received by the ultrasonic receiver, and a pulse counter An axial force calculating means for calculating the axial force of the bolt by applying the count value to the relationship between the count value and the axial force which is obtained in advance is provided.

<Operation> According to the first aspect of the invention, the ultrasonic wave is emitted from the ultrasonic oscillator to the bolt, the ultrasonic wave transmitted through the bolt is received by the ultrasonic wave receiver, and the measurement corresponding to the attenuation amount of the ultrasonic wave is performed. The value can be calculated. Then, the axial force of the bolt can be determined by applying the obtained measured value to the relationship between the attenuation amount of the ultrasonic wave and the axial force which is obtained in advance.

More specifically, the attenuation of the ultrasonic wave incident from one end of the bolt changes according to the tensile stress in the axial direction of the bolt, and the attenuation rate of the ultrasonic wave increases as the tensile stress decreases. Therefore, by obtaining a measurement value corresponding to the attenuation amount of the ultrasonic wave incident from one end of the bolt, and applying the obtained measurement value to the relationship between the attenuation amount of the ultrasonic wave and the axial force which is obtained in advance. , It is possible to obtain the axial force of the bolt.

According to the second aspect of the invention, the drive signal input means inputs a drive signal of one pulse to the ultrasonic oscillator,
The ultrasonic wave can be incident on the bolt, the ultrasonic wave transmitted through the bolt can be received by the ultrasonic receiver, and the number of pulses included in the signal received by the ultrasonic receiver can be counted by the pulse counter. More specifically, when a drive signal consisting of one pulse is input to the ultrasonic oscillator by the drive signal input means, the reception output waveform becomes a waveform composed of a plurality of pulses that are temporally close to each other. When the bolt axial stress is small, the ultrasonic attenuation rate is large, so the number of pulses included in this received waveform is relatively small.When the bolt axial stress is large, the ultrasonic attenuation rate is large. Is small, the number of pulses included in this received waveform is relatively large. Therefore, the axial force of the bolt is calculated by counting the number of pulses included in this received waveform and applying the count value of the pulse counter in the axial force calculating means to the relationship between the count value and the axial force that is obtained in advance. can do.

<Embodiment> An embodiment will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic view showing an embodiment of an apparatus for measuring the axial force of a bolt, in which a bolt (B) (used as a concept including a machine screw) is passed through a plate material (C) and a nut ( D)
, And the ultrasonic transducer (A) for ultrasonic oscillation is attached to the end surface of the bolt (B) on the head side.
The ultrasonic transducer (F) for reception is provided on the tip surface of the under neck (E) of the
Are installed respectively. Ultrasonic transducer for oscillation (A)
Obtains its ultrasonic power source from an amplifier (3).
When the amplifier (3) receives the reset signal (the reset signal is sent by pressing the reset button (15)) from the reset circuit (14), pulsed transmission power is transmitted to the ultrasonic transducer (A). Supply. The adjustment of the transmission power supply voltage is performed by the output voltage setting circuit (2) connected to the amplifier (3). A drive signal input means is constituted by the amplifier (3) and the reset circuit (14).

The reception signal of the ultrasonic transducer for reception (F) is amplified by the amplifier (1) and is supplied to the detection circuit (4) for performing envelope detection through the gate circuit (6). The gate circuit (6) opens the gate based on the reset signal from the reset circuit (14). The output of the detection circuit (4) is input to the limiter circuit (5), and the limiter circuit (5) cuts the input voltage below the reference voltage V and outputs only the waveform portion exceeding the reference voltage V. The output of the limiter circuit (5) enters the AND gate (7) together with the clock pulse output of the clock generator (13), and the output of the AND gate (7) is supplied to the counter (9). The counter (9) is started after receiving the reset signal from the reset circuit (14) and counts the number of clock pulses.
The count number thus counted is displayed by the display (11).

The output of the gate circuit (6) is also supplied to the differentiating circuit (16), and the output of this differentiating circuit (16) enters the AND gate (8) together with the output of the limiter circuit (5). Then, the output of the AND gate (8) enters the counter (10),
In this counter (10), the number of pulses included in the differentiated waveform is counted. The count number counted by the counter (10) is displayed on the display (12) and is input to the axial force calculating means (17). The axial force calculating means (17) is composed of, for example, a microcomputer, and compares the count number with data stored in a table in advance showing the relationship between the attenuation amount and the axial force, and based on the comparison result. The axial force of the bolt is calculated. The axial force thus obtained is displayed on the display (12) as required.

In the bolt axial force measuring device configured as described above, when the reset button (15) is pressed to send the reset signal from the reset circuit (14), the level set by the output voltage setting circuit (2) is output from the amplifier (3). Is supplied, the ultrasonic transducer (A) emits ultrasonic waves corresponding to the level (for example, frequency 150 kHz, pulse width 2 μsec, peak value is about 10 V converted to the output level of the amplifier (1)). . The ultrasonic wave incident on the bolt propagates in the axial direction of the bolt, and finally is received by the ultrasonic transducer (F) for reception and converted into an electric reception signal. When this received signal waveform is observed with an oscilloscope, as shown in FIG. 2, lumps (wave packets) in which individual waves are gathered and wholly become one are observed. Ultrasonic transducer (F)
The received signal is the gate circuit with the gate open (6)
The signal is supplied to the detection circuit (4) through and is detected. Of this detection output (see the broken line in FIG. 2), the portion exceeding the reference voltage V enters the AND gate (7) together with the clock pulse and is input to the counter (9). The number of pulses in the exceeded part is counted and displayed on the display (11). Therefore, the duration of the reception signal of the ultrasonic transducer (F) can be known. The number of pulses in the portion exceeding the reference voltage V is counted because if it is below the reference voltage V, it becomes difficult to distinguish between noise and pulses, and the duration of the waveform cannot be accurately determined.

At the same time, the output of the gate circuit (6) enters the counter (10) through the differentiating circuit (16) and the AND gate (8), the number of pulses of the differentiated waveform is counted, and the display (12). Displayed by. This count number corresponds to the number of times the received signal waveform of the ultrasonic transducer (F) crosses the voltage level Vo (corresponding to the average voltage level, see FIG. 2). Since the AND gate (8) is ANDed with the output of the limiter circuit (5), the number of times of crossing is limited to within the duration of the reception signal waveform of the ultrasonic transducer (F).

The count number is correlated with the attenuation rate of ultrasonic waves in the bolt, and the axial force of the bolt can be obtained by applying this to the relationship between the attenuation amount and the axial force that is obtained in advance.

Fig. 3 shows high-strength steel bolts (F8 with a neck of 80 m / m and an outer diameter of 20 m / m).
While changing the tightening force of (T), the count number obtained as described above is plotted on the horizontal axis, and the axial force obtained by the strain gauge embedded in the high-strength steel bolt is plotted on the vertical axis. It is clear that there is a relationship.

Further, when a similar measurement was performed using a bolt made of carbon steel (SS40) for general structure instead of the high strength steel bolt, a substantially linear correlation as shown in FIG. 4 was obtained.

As described above, if the axial force corresponding to the count number of the counter (10) is obtained from the gauge, the correlation is obtained in advance, and the relation is stored in the axial force calculating means (17), thereafter, Axial force calculation means for measuring the number of counts (17)
The axial force of the bolt can be calculated and the axial force can be displayed on the display (12) by comparing with the data stored in.

The method for measuring the axial force of the bolt of the present invention is not limited to the above embodiment, and for example, as the measurement value corresponding to the attenuation amount of ultrasonic waves, the duration of the received ultrasonic wave packet itself ( The one displayed on the display (11) may be obtained. Moreover, if an electromagnetic ultrasonic oscillation type is used as the ultrasonic transducer, it is possible to perform measurement while maintaining non-contact with the bolt. Various other design changes can be made without departing from the scope of the invention.

<Effects of the Invention> As described above, according to the method and apparatus for measuring the axial force of the bolt of the present invention, the axial force of the bolt is measured by obtaining the measured value corresponding to the attenuation amount of the ultrasonic waves incident on the bolt. Therefore, the measurement can be performed independently of the coefficient of friction of the bolt. In addition, the labor for measuring the echo before tightening the bolt, which is required in the conventional measuring method for receiving the echo of the ultrasonic wave incident on the bolt, is unnecessary.

Therefore, there is a unique effect that the axial force of the bolt can be accurately and efficiently performed.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of a device for measuring the axial force of a bolt, FIG. 2 is a waveform diagram of a received signal waveform obtained by an ultrasonic transducer for reception observed with an oscilloscope, FIGS. 3 and 4. FIG. 3 is a graph showing the correlation between the axial force of high-strength steel bolts and general structural carbon steel bolts and the count number. (3) ...... Amplifier constituting drive signal input means, (10) ...... Pulse counter, (14) ...... Reset circuit constituting drive signal input means, (17) ...... Axial force calculation means, (A) ...... Ultrasonic transducer as ultrasonic oscillator, (F) …… Ultrasonic transducer as ultrasonic receiver, V …… Threshold

Claims (5)

(57) [Claims] 1. An ultrasonic oscillator and an ultrasonic receiver are arranged at opposite positions sandwiching a bolt, ultrasonic waves are emitted from the ultrasonic oscillator to the bolt, and ultrasonic waves transmitted through the bolt are ultrasonic waves. The measured value corresponding to the amount of attenuation of ultrasonic waves is received by the receiver, and the measured value is applied to the relationship between the amount of ultrasonic attenuation and the axial force that is obtained in advance to determine the axial force of the bolt. A method for measuring the axial force of a bolt, characterized in that. 2. A count value of ultrasonic pulses included in a received signal as a measurement value corresponding to the attenuation amount of ultrasonic waves, by inputting one pulse of a drive signal for transmitting ultrasonic waves to the ultrasonic oscillator. The method for measuring the axial force of a bolt according to claim 1, wherein: 3. The method for measuring the axial force of a bolt according to claim 2, wherein the count value of ultrasonic pulses is obtained by extracting pulses exceeding a threshold value. 4. An ultrasonic oscillator for applying an ultrasonic wave to a bolt, a drive signal input means for inputting one pulse of a drive signal for oscillating an ultrasonic wave to the ultrasonic oscillator, and an ultrasonic wave transmitted through the bolt. The ultrasonic receiver to receive, a pulse counter that counts the number of ultrasonic pulses included in the signal received by the ultrasonic receiver, and the count value of the pulse counter, the count value and the axial force that are obtained in advance. And an axial force calculating means for calculating the axial force of the bolt by applying the relationship of 1) to the axial force of the bolt. 5. The bolt axial force measuring device according to claim 4, wherein the pulse counter counts the number of ultrasonic pulses exceeding a threshold value.