JPH07333085A - Inspection device of bolt clamping force - Google Patents

Abstract

PURPOSE:To provide an inspection device which can precisely inspect bolt clamping force by utilizing the fact that the resonance frequency changes according to the tension of a bolt. CONSTITUTION:A probe 1 is provided with an excitation coil 6 which is provided around a head part 18 of a bolt 3 or around a space part 5 for accepting the other edge part 19, a ring-shaped first permanent magnet 7 which is provided at the outer periphery of the excitation coil and is magnetized in the radius direction, a first permanent magnet 7 which is provided at the outer periphery of the excitation coil and is magnetized in the radius direction, and a ring- shaped second permanent magnet 8 which is magnetized in axial direction so that the magnet 8 is provided at the deep part of the space part while opposing the head part or the other edge part of the bolt and the magnetic pole at the side facing the bolt is in opposite magnetic pole as compared with the magnetic pole inside the magnet. Further, the title item is also provided with a vibration detector 9 for detecting the vertical vibration of the bolt via a vibration transfer rod 10 which is penetrated through the center hole of the second permanent magnet and whose tip is in contact with the bolt.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting bolt tightening force, and more specifically, it is possible to loosen or crack a bolt by simply contacting the head or the other end of the bolt with a nut. The present invention relates to a bolt tightening force inspection device for inspecting the existence of a bolt.

[0002]

2. Description of the Related Art Conventionally, a bolt is inserted through a mounting hole formed through two members, and a nut is screwed to the other end to tighten the two members. Although it is measured by a meter, this measured value does not necessarily indicate the true tightening force (tension of the bolt) because it also changes depending on the frictional force between the nut and the bolt and the washer. Further, the true tightening force differs between when the bolt is tightened slowly and when the bolt is tightened by utilizing the inertial force at a certain rotation speed. Therefore, even if the torque is tightened with a desired tightening force, there is a large variation in the true tightening force. If this variation is within the allowable range, there is no problem, but if a sufficient tightening force is not obtained, a serious problem may occur. Also, even if a sufficient tightening force is obtained at the beginning of tightening and assembly, it may loosen over time due to stress or vibration acting on the members. I can't say. In addition, the bolt may be broken.

Therefore, it is necessary to diagnose loosening or breaking of the bolt by some method, and a percussion method has already been considered, and has been used for many attempts and practical applications. In this percussion method, the head or the other end of the bolt is hit with a hammer or the like, and the looseness or breakage of the tightening is diagnosed based on the chattering state of vibration caused by the hit. However, this method still has a problem in spreading it on site due to the skill of the operator and the complexity of vibration analysis. Moreover, the error is so large that it is difficult to determine even if the tightening force is loosened to about half.

Although many methods for measuring the tightening force of other bolts have already been tried at the laboratory level such as using ultrasonic waves, each method has advantages and disadvantages, and the direct tightening of bolts is simple. Nothing can measure force. for that reason,
It is desired to provide a detection device that can easily detect the true tightening force of a bolt in a tightened state.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 5-346420, an exciting coil for applying electromagnetic vibration to the head or the other end of the tightened bolt and a hollow portion of the exciting coil are provided. The probe is composed of a vibration detector that detects the longitudinal vibration of the bolt through a vibration transmission rod that is pierced and has its tip in contact with the head or the other end of the bolt, and the frequency of the excitation coil is continuously and repeatedly changed. The control device includes an excitation circuit that supplies an excitation current to apply longitudinal vibration to the bolt, and a resonance detection circuit that detects the resonance state of the bolt based on the vibration signal of the vibration detector. There is proposed a bolt tightening diagnosis device which determines whether the tightening force is good or bad and whether or not there is a crack.

[0006]

However, the bolt tightening diagnosis device described in the above publication does not have a holding structure for mounting the probe on the head or the other end of the bolt, and therefore, the probe is not provided. It is necessary to hold it by holding it by hand with the tip of the bolt against the head or the other end of the bolt, and due to camera shake or reaction of the magnetic field created by the excitation coil, unexpected vibration or displacement of the probe may occur, resulting in accurate diagnosis. There was a fear of hindrance. Moreover, the longitudinal vibration of the bolt applied by the excitation coil is weak, and therefore the problem that the ratio of the signal (S) to the noise (N) (S / N ratio) is small remains. Further, vibrations in modes other than the fundamental vibration may appear strongly, which may cause a large error.

Therefore, in view of the above situation, the present invention is to solve the problem by quantitatively measuring the resonance frequency because the resonance frequency changes due to the tension of the bolt in the tightened state. In a bolt tightening force inspection device that inspects bolts for looseness, breakage, and cracks, a holding structure for increasing the S / N ratio and attaching the probe to the head or the other end of the bolt is provided. The purpose of the present invention is to provide a bolt tightening force inspection device which is provided and which greatly increases the vibration of the basic mode to significantly improve the sensitivity and accuracy of the tightening force inspection, and which enables highly accurate inspection.

[0008]

In order to solve the above-mentioned problems, the present invention comprises a probe and a control device, wherein the probe is arranged around a space part for receiving the head part or the other end part of a bolt. Then, an excitation coil for applying electromagnetic vibration to the bolt, a ring-shaped first permanent magnet disposed on the outer circumference of the excitation coil and magnetized in the radial direction, and the head of the bolt in the inner part of the space. Alternatively, the ring-shaped second permanent magnet is axially magnetized so as to be coaxially arranged so as to face the other end, and the magnetic pole on the side facing the bolt is opposite to the magnetic pole on the inner side of the first permanent magnet. A magnet and a vibration detector that detects longitudinal vibration of the bolt through a vibration transmission rod that penetrates the center hole of the second permanent magnet and has its tip in contact with the head or the other end of the bolt. The control device is configured such that the excitation coil has a continuous frequency. It is equipped with an excitation circuit that supplies an exciting current that changes back to apply longitudinal vibration to the bolt, and a resonance detection circuit that detects the resonance state of the bolt based on the vibration signal of the vibration detector. It is attached to the head or the other end of the bolt in the state, the excitation current is supplied from the control device to the excitation coil to give longitudinal vibration to the bolt, and the resonance frequency of the bolt changes depending on the tightening force. A control device analyzes the vibration signal detected by the vibration detector of the probe and measures the bolt tightening force from the resonance frequency to construct a bolt tightening force inspection device.

As the control device, the excitation circuit is provided with a voltage-controlled oscillator whose frequency changes according to voltage. The control voltage is changed to supply an excitation current to the excitation coil of the probe, and the resonance detection circuit is controlled by the voltage. Is equipped with a peak detector that detects the occurrence of resonance vibration and a sampling and holding device that detects the voltage corresponding to the frequency, and displays the voltage value detected by the sampling and holding device or displays the voltage as the standard tightening force for bolts. It is a preferred embodiment that the display device is provided with a percentage display based on.

[0010]

The bolt tightening force inspection device of the present invention having the above contents utilizes the fact that the vertical natural frequency (resonance frequency) of the bolt changes depending on the tightening force (tension). By measuring the resonance frequency, the true tightening force is directly measured to check the bolt for looseness and cracks.The resonance frequency also changes depending on the length of the bolt. When broken, the resonance frequency of the bolt changes greatly, so that the broken bolt can be inspected. Here, the resonance frequency of the bolt is
Decrease in tensile force, that is, 10% decrease due to loosening,
On the other hand, it is possible to discriminate it because the effective length decreases greatly due to the breakage, and thus it significantly increases.

In the probe according to the present invention, an excitation coil is provided around a space for receiving the head portion or the other end portion of the bolt, the excitation coil for applying electromagnetic vibration to the bolt, and the outer circumference of the excitation coil. And a ring-shaped first permanent magnet that is magnetized in the radial direction, and a side that is coaxially arranged in the inner part of the space facing the head or the other end of the bolt and faces the bolt. Is provided with a ring-shaped second permanent magnet that is magnetized in the axial direction so that the magnetic pole is an inner magnetic pole of the first permanent magnet and a reverse magnetic pole. When mounted on the other end, if the head of the bolt or the other end is received in the space of the probe, the probe is strongly attached to the bolt or the member tightened by the bolt by the attractive force of the first permanent magnet and the second permanent magnet. It is sucked and held, and the first permanent Bias magnetic field is generated in the magnet and the head or the other end of the bolt by magnetic field generated by the second permanent magnet,
By the action of this bias magnetic field and the eddy current induced in the head portion or the other end portion of the bolt by the varying magnetic field generated by the exciting coil, it is possible to extremely efficiently generate strong longitudinal vibration in the bolt. Then, the vibration detector detects the vertical vibration generated in the bolt, and the resonance detection circuit detects the change in the resonance frequency of the bolt based on the vibration signal, and the tightening force of the bolt is determined from the change in the resonance frequency. To measure.

[0012]

The present invention will be described in more detail with reference to the embodiments shown in the accompanying drawings. The bolt tightening force inspection device of the present invention applies electromagnetic vibration to a bolt, supplies a probe 1 for detecting the vibration, and an exciting current to the probe 1, and analyzes the detected vibration signal. And a control circuit 2 for FIG. 1 shows a cross-sectional view of a state in which the probe 1 is attached to the bolt 3, and FIG. 2 shows a conceptual diagram when actually measuring the looseness of the bolt 3.

In the probe 1 shown in FIG. 1, a hollow case 4 made of a non-magnetic material is provided with a space 5 having a circular cross section, and an excitation coil 6 is arranged on the outer periphery of the space 5. A ring-shaped first permanent magnet 7 magnetized in the radial direction is arranged on the outer circumference of the exciting coil 6, and the magnetic pole on the side facing the space portion 5 is located at the back of the space portion 5 at the first permanent magnet. Magnet 7
A ring-shaped second permanent magnet 8 magnetized in the axial direction so as to be a magnetic pole opposite to the inner magnetic pole is provided, and a vibration detector 9 composed of a ceramic vibration sensor is freely movable in and out of the case 4. The vibration transmitting rod 10 having the base end linked to the vibration detector 9 is inserted into the central hole 11 of the second permanent magnet 8 so that its tip projects into the space 5 and Vibration transmission rod 10 between the vibration detector 9 and
Is a structure in which a spring body 12 made of a compression coil spring or the like that is elastically biased in a protruding direction is arranged. In this embodiment, the inner surface side of the first permanent magnet 7 is the N pole, the outer surface side is the S pole, the side of the second permanent magnet 8 facing the space 5 is the S pole, and the side facing the vibration detector 9 is the S pole. Although it is an N pole, the above-mentioned N pole and S pole may have an inverse relationship. Here, the vibration transmission rod 1
If the tip of 0 is needle-shaped, the tip can directly contact the bolt even if the bolt 3 is painted. Although not shown, a cable for supplying the excitation current I ₀ to the excitation coil 6 and for extracting the vibration signal V ₀ detected by the vibration detector 9 is connected to the case 4.

Here, the bolt 3 is usually tightened as shown in FIG. That is, the shaft portion 17 of the bolt 3 is inserted into the mounting holes 15 and 16 formed through the two members 13 and 14 made of a ferromagnetic material such as a steel plate, and the head portion 18 and the other end portion 19 of the shaft portion 17 are screwed together. The two members 13, 14 are tightened with the nut 20. A washer 21 is appropriately interposed between the head 18 and the nut 20 and the members 13 and 14.

In this tightened state, a tensile force is constantly acting on the shaft portion 17 of the bolt 3. Therefore, the probe 1
When the head portion 18 or the other end portion 19 of the bolt 3 is received in the space portion 5, the tip of the case 4 is brought into contact with the surface of the member 13 by the attractive force of the magnetic field created by the first permanent magnet 7 and the second permanent magnet 8. The vibration transmitting rod 10 is sucked and held in a contact state, and at the same time, the vibration transmitting rod 10 is brought into contact with the head portion 18 or the other end portion 19 of the bolt 3 and is pushed against the elastic force of the spring body 12. In this state, the tip end of the vibration transmission rod 10 reliably and constantly contacts the center of the bolt 3 under a constant condition, and a constant elastic force also acts as a bias on the vibration detector 9. In the probe 1, the size of the space 5 is determined so that the portion other than the vibration transmission rod 10 does not come into contact with the bolt 3.
In addition, the magnetic field lines emitted from the N pole inside the first permanent magnet 7 pass through the inside of the head portion 18 of the bolt 3 and the head portion 1 of the second permanent magnet 8.
The S pole on the side facing 8 is reached. These permanent magnets 7, 8
The magnetic field created by is always acting as a bias magnetic field.

Then, an exciting current I _{0 is} applied to the exciting coil 6.
Is supplied, an axial magnetic field is generated in the head portion 18 of the bolt 3, and an eddy current flows so as to cancel the magnetic field. The eddy current and the Lorentz force by the magnetic field cause the shaft portion 17 of the bolt 3 to flow.
Vertical vibration is generated in the shaft 17, and the vertical vibration of the shaft 17 is transmitted to the vibration transmission rod 1
The vibration signal is detected by the vibration detector 9 via 0, and the vibration signal V ₀ is input to the control circuit 2 described later. At this time, the vibration detector 9 detects the induction caused by the excitation of the excitation coil 6 and the longitudinal vibration of the shaft portion 17, but the control circuit 2 is devised so that only the longitudinal vibration of the shaft portion 17 can be taken out. Has been done.

Next, the control circuit 2 will be described with reference to FIGS. 3 and 4. The control circuit 2 supplies an exciting current I ₀ whose frequency continuously repeats to the exciting coil 6 to give a longitudinal vibration to the bolt 3, and a vibration detector 9
And a resonance detection circuit for detecting the resonance state of the bolt 3 based on the vibration signal V ₀ .

First, the excitation circuit will be described. The excitation circuit is a very low frequency oscillator 22 that generates a ramp-shaped (serrated) control voltage V ₁ with a repetition period (T) of about 1 second.
And a voltage controlled oscillator (VCO) 23, which is controlled by its continuously changing control voltage V ₁ and generates a current whose frequency continuously changes. More specifically, the counter 24 counts the number of times the sine wave voltage V ₂ generated by the voltage controlled oscillator 23 changes continuously.
The count signal V ₃ of high level (H) and low level (L) at the instants corresponding to only 5 or 10 out of 100 times are generated. The open / close control of the analog switch 25 is performed by the counting signal V ₃ , and the sine wave voltage V
Pass ₂ only at high level. The excitation voltage wave V _{4 that} has passed through the analog switch 25 is intermittent as shown in FIG. 4 (d). That is, the excitation voltage wave V ₄ is
It is an intermittent wave with only 5/50 or 10/50 wave numbers.
In this embodiment, the excitation voltage wave V ₄ is amplified by the bias correction amplifier 26 in the previous stage and then amplified by the current amplifier 27 to generate the excitation current I ₀ . Of course,
This excitation current I _{0 is} also an intermittent wave, and the excitation voltage wave V
_The waveform is similar to ₄ . Here, the bias correction amplifier 26 also controls the bias voltage. This Baice voltage gives a bias current, which will be described later, and enables application to non-ferrous metals.

The operation of the excitation circuit will be briefly described below.
The voltage controlled oscillator 23 whose frequency can be changed by the control voltage V ₁ of the ultra low frequency oscillator 22 causes 10 kHz to 10 kHz.
A 0 kHz variable sine wave voltage V ₂ is generated, and at the same time, the oscillating wave is applied to the counter 24 to generate 5/50 or 10/50 times pulses (count signal V ₃ ), and the pulse is applied to the analog switch 25. The excitation voltage wave V ₄ of 5/50 or 10/50 times is output to the next stage. Then, it passes through a bias correction amplifier 26 for appropriately applying a direct current, and then a current amplifier 27 supplies an exciting current I ₀ of 0.5 A to 2 A (peak value) to the exciting coil 6. This exciting current I ₀ gives electromagnetic vibration to the bolt 3 by the exciting coil 6, and the exciting current I ₀ is intermittently given as described above to make the resonance characteristic remarkable and the exciting current I 0. _{Even if 0} is increased, heat generation can be suppressed to a small level.

The excitation coil 6 is placed in non-contact with the head portion 18 or the other end portion 19 of the bolt 3 (the bobbin 5 is in contact therewith), and electromagnetic vibrations corresponding to the excitation current I ₀ are applied to the shaft portion of the bolt 3. 1
Give to 7. The vibration of the bolt 3 is transmitted to the vibration detector 9 through the vibration transmission rod 10 that is in contact with the head 18 or the other end 19 of the bolt 3 through the center of the bobbin 5 around which the excitation coil 6 is wound. It is detected by the vibration detector 9. Then, the vibration signal V ₀ detected by the vibration detector 9
Is input to the resonance detection circuit of the control circuit 2.

Next, the above resonance detection circuit will be described.
It The resonance detection circuit operates when the bolt 3 reaches the resonance point.
The control voltage V₁Also detects the instantaneous value of
Of. Specifically, the vibration signal detected by the vibration detector 9
Issue V₀Is amplified by the amplifier 28 and given to the detector 29.
It As it is, the excitation current wave I₀Since the induction of
In order to remove this, the vibration amplification signal V of the amplifier 28_FiveTo
Excitation current I is passed through analog switch 30.₀Is supplied
The signal is removed while the signal is being supplied to the detector 29.
Of. Opening and closing control of this analog switch 30
Counting signal V output from the counter 24₃The phase inverter
Gate signal with high and low levels inverted through 31
Issue V₆To generate the gate signal V₆Because I will do it in
It That is, by passing the analog switch 30,
Vibration amplification signal V shown in (e)_FiveFrom excitation current I₀by
The induction is removed and the vibration output signal V shown in Fig. 4 (g)₇Is inspected
It is supplied to the wave filter 29. And this detector 2
Detection voltage signal V output from 9 ₈To the smoother 32
The smoothing device 32 detects the detected voltage signal V₈Smoothing
Amplitude signal V approximately proportional to the amplitude of vibration₉To get Inspection
Wave, amplitude signal V after smoothing₉Has a large amplitude at the resonance point.
The peak value (maximum value) with the peak detector 33.
Sampling pulse when the peak value is detected
V_TenGenerate. Finally, the ultra low frequency oscillator 22
Control voltage V₁And sampling pulse V_TenIs entered
Sampling pulse V_TenBut
Control voltage V at the moment of occurrence₁And sample this
It is held and input to the display device 35 as the output signal Vr. This
In the display 35, the output signal Vr is displayed as it is at the resonance point.
Control voltage V corresponding to wave number₁Instantaneous value or standard of bolt
As a percentage based on the tightening force, analog or digital
Display like a rule. Furthermore, the display 35 and sound generator are used together
And the tone of the tone or threshold that is proportional to the output signal Vr in the sound generator
Generates sound only when the output signal Vr is above or below the value
It is also preferable.

Since the value displayed on the display 35 corresponds to the resonance frequency of the bolt 3, the value corresponding to the tightened state of the bolt 3 is displayed. As mentioned above,
Since the resonance frequency changes depending on the tension of the shaft portion 17 of the bolt 3, it is most suitable for finding a loose bolt 3 among many bolts 3, ... is there. When the bolt 3 is loose, the resonance frequency shifts so as to decrease, so that the tightening condition can be determined, and when the bolt 3 is broken, the resonance frequency (output signal Vr) increases. It can be easily identified because it deviates greatly.

Next, a concrete example of the peak detector 33 is shown in FIG.
It will be described based on 5. Peak detector 33 of the present embodiment
Gives a signal (remote switch) to start measurement and amplitude
Signal V ₉Analogly stores the peak value of
When the same peak value is reached again, this is judged as the resonance point.
Specifically, the amplitude signal V of the smoother 32.₉To
A changeover switch 36 for changing over in two directions and a changeover switch
Analog memory circuit 3 connected to contact a of switch 36
7 and the output V of the analog memory circuit 37_AAnd b contact
Output V of the b-contact when switched_B(Amplitude signal V₉
It is itself. ) And pulse (sampling
Pulse V_Ten) Generating a comparator 38
It The changeover switch 36 resets the control circuit 2.
Interlocked with the switch, normally the a contact is closed,
Issue V₉Is stored in analog memory circuit 37 in an analog manner
Output to the negative terminal of the comparator 38_AIs always input
There is. And a few seconds when the reset switch is activated
Only during the period, the b contact of the selector switch 36 is closed and the comparator 3
Output V to the positive terminal of 8_BIs entered. Analog memory
Amplitude signal V stored in circuit 37₉The peak value of
By the cycle, it has decreased slightly (1-2%), so next time
One of the peak values of exceeds. Therefore, compare this point
Sampling pulse V detected by comparator 38_TenCause
It

More specifically, the analog memory circuit 37 has two operational amplifiers 39,
40 in series and a diode 41 in the middle,
The voltage corresponding to the peak value of the amplitude signal V ₉ is stored in the capacitor 42 arranged on the forward side of the diode 41.

The sampling pulse V ₁₀ from the peak detector 33 is input to the sampling hold 34. As shown in FIG. 5, the sampling hold 34 includes a transistor 43 that is switched by the sampling pulse V ₁₀ and a transistor 43 that is switched by the sampling pulse V ₁₀ .
The photocoupler 44 is a bidirectional analog FET output type controlled by the following, and a capacitor 45 connected in parallel to one output terminal of the photocoupler 44. The sampling pulse V ₁₀ is input to the base of the transistor 43 via the resistor 46, the collector of the transistor 43 is connected to the cathode of the photocoupler 44, and the anode of the photocoupler 44 is connected to the power supply so that a desired current can be supplied. ing. The drain of the photocoupler 44 is supplied with the control voltage V ₁ from the ultra low frequency oscillator 22, and the source is connected with the capacitor 45 and the display 35. Then, the transistor 43 conducts only while the sampling pulse V ₁₀ is input, a current flows through the light emitting diode to emit light, and the FET conducts accordingly, and the control voltage V ₁ of the ultra low frequency oscillator 22 The capacitor 45 is charged and held at the instantaneous value. In other words, if the input impedance of the display 35 is high, the drop in the voltage stored in the capacitor 45 can be ignored, and the voltage is supplied to the display 35 as the output signal Vr. Of course, before the next measurement, the reset switch is operated to discharge the capacitor 45 to the initial state.

Finally, the use of the device of the present invention will be briefly described. Inspect the tightening force of bolts that are already in practical use on bridges, etc., and identify the one with weaker tightening force compared to the one that holds many normal tightening forces, or break ( It is most suitable for detecting a small number of bolts that are cracked and have a reduced tightening force. At this time, it is sufficient to find out the one showing an abnormal value in all the inspections, and therefore the inspection time per one is sufficient if it is about 3 to 5 seconds, which is extremely quick. Moreover, since the excitation coil 6 that gives electromagnetic vibration does not have to be in contact with the bolt 3, it is not necessary to remove the coating of the bolt 3, and if the tip of the vibration transmission rod 10 is also needle-shaped, this also affects the coating. There is no.

[0027]

According to the bolt tightening force inspection device of the present invention as described above, the resonance frequency of the bolt is measured by utilizing the fact that the longitudinal resonance frequency of the bolt changes depending on the tightening force. With this, you can directly measure the true tightening force and inspect for the presence of loose bolts and cracks in the bolt.The resonance frequency also changes depending on the length of the bolt and if the bolt breaks in the middle. In addition, since the resonance frequency changes greatly, the breakage of the bolt can be inspected. A space is formed at the tip of the probe for receiving the head of the bolt or the other end, and an excitation coil for applying electromagnetic vibration to the bolt is arranged around the space and an outer periphery of the excitation coil. A ring-shaped first magnet that is installed and magnetized in the radial direction
And a permanent magnet, and a ring-shaped first magnet magnetized in the axial direction so that the magnetic pole on the side facing the bolt is the reverse magnetic pole to the inner magnetic pole of the first permanent magnet in the inner part of the space. (2) By disposing the permanent magnet, when the probe is mounted on the head or the other end of the tightened bolt, the attraction force of the permanent magnet can surely attract and hold the bolt regardless of the direction. In addition, the bias magnetic field created by the first permanent magnet and the second permanent magnet and the variable magnetic field created by the exciting coil can cause strong longitudinal vibration to the bolt extremely efficiently, thereby increasing the S / N ratio and tightening. The sensitivity and accuracy of the force inspection are significantly improved, and therefore, it is possible to perform a highly accurate inspection for the tightening force of the bolt.

[Brief description of drawings]

FIG. 1 is a simplified cross-sectional view showing a state of inspecting a tightening force of a bolt in a tightened state.

FIG. 2 is an explanatory cross-sectional view showing a relationship between a main part of a probe and a head part of a bolt.

FIG. 3 is a simplified block diagram of a control circuit.

FIG. 4 is a time chart showing signal waveforms of various parts of the control circuit.
(A) is the control voltage V ₁, (B) is the sine wave voltage V
₂, (C) is the counting signal V₃, (D) are excitation voltage waves V_Four,
(e) is the vibration amplification signal V_Five, (F) is the gate signal V₆, (G)
Is the vibration output signal V₇, (H) is the detected voltage signal V₈, (I)
Amplitude signal V₉, (J) are sampling pulses V_TenThat
Is showing.

FIG. 5 is a simplified circuit diagram showing a specific example of a peak detector and sampling hold.

[Explanation of symbols]

 1 Probe 2 Control Circuit 3 Bolt 4 Case 5 Space 6 Excitation Coil 7 First Permanent Magnet 8 Second Permanent Magnet 9 Vibration Detector 10 Vibration Transmission Rod 11 Center Hole 12 Spring Body 13, 14 Member 17 Shaft 18 Head 19 Other end 20 Nut 22 Ultra-low frequency oscillator 23 Voltage controlled oscillator 25 Analog switch 26 Bias correction amplifier 27 Current amplifier 28 Amplifier 29 Detector 30 Analog switch 31 Phase inverter 32 Smoother 33 Peak detector 34 Sampling hold 35 Indicator

Claims (2)

[Claims] 1. A probe and a control device, wherein the probe is arranged around a space portion for receiving the head portion or the other end portion of the bolt, and an exciting coil for applying electromagnetic vibration to the bolt, A ring-shaped first permanent magnet that is disposed on the outer circumference of the excitation coil and is magnetized in the radial direction, and is coaxially disposed in the inner part of the space so as to face the head or the other end of the bolt. A ring-shaped second permanent magnet axially magnetized so that the magnetic pole on the side facing the second magnetic pole is a magnetic pole opposite to the magnetic pole on the inner side of the first permanent magnet, and the center hole of the second permanent magnet is penetrated and the tip is provided. And a vibration detector that detects longitudinal vibration of the bolt through a vibration transmission rod that is in contact with the head or the other end of the bolt, wherein the control device has a continuous frequency in the excitation coil. The longitudinal vibration is applied to the bolt by supplying the exciting current that changes repeatedly Excitation circuit and a resonance detection circuit for detecting the resonance state of the bolt based on the vibration signal of the vibration detector, the probe is attached to the head or the other end of the bolt in the tightened state, The control device supplies the vibration signal detected by the vibration detector of the probe by utilizing the fact that the control device supplies the excitation current to the excitation coil to apply the longitudinal vibration to the bolt, and the resonance frequency of the bolt changes according to the tightening force. The bolt tightening force inspection device is characterized in that the bolt tightening force is measured from the resonance frequency by analyzing the above. 2. The control device includes a voltage-controlled oscillator, the frequency of which is changed by a voltage of the excitation circuit, the control voltage is changed to supply an excitation current to an excitation coil of the probe, and the resonance detection circuit is a bolt. Is equipped with a peak detector that detects the occurrence of resonance vibration and a sampling and holding device that detects the voltage corresponding to the frequency, and displays the voltage value detected by the sampling and holding device or displays the voltage as the standard tightening force for bolts. The bolt tightening force inspection device according to claim 1, further comprising an indicator that displays a percentage based on the above.