JP2010216804A - Fastening body for detecting axial force, fastening body unit, and system for monitoring axial force - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fastening body for detecting an axial force and also a system for monitoring the axial force which enable the simple monitoring of a fastening axial force of the fastener, inclusive of a bolt or the like, in a relatively inexpensive manner. <P>SOLUTION: A fastening body unit 1 is constituted by fitting a pin type load cell 20, a transmitter substrate 30 and an IC tag 50 to a bolt 10 for detecting the axial force. A receiving unit supplies electric power to the bolt 10 for detecting the axial force, by using a wireless power supply technique, while in the transmitter substrate 30, a strain signal is measured by using the received electric power and is sent to the receiving unit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an axial force detection fastening body, a fastening body unit, and an axial force monitoring system that detect and manage an axial force of a fastening body including a bolt.

Fastening bodies such as bolts and rivets are widely used in various vehicles, aircraft, industrial and machine tools.
If this fastening body is used, the object can be held in a tightened state. For example, when components are tightened with bolts and nuts, the fastened body is tightened with the bolts and nuts and receives a compressive force, and the bolt is held in a state where an axial force is generated in the pulling direction.

However, even if the fastened body is firmly fastened with the fastening body, the fastening body loosens over time due to, for example, a daily operation in which a machine to which the fastening body is attached is operated, and the axial force is reduced.
The looseness of the fastening body leads to a lowering of the fastening function, and also causes fatigue breakage and part dropout.

Therefore, the management of monitoring the looseness of the fastening body over time and retightening with a torque wrench or spanner as necessary is performed.
As a method of monitoring looseness of a fastening body, conventionally, a mark is attached to a bolt and the position of the mark is visually inspected. A torque check is visually performed by using a hammer. A common method is to check for slack by listening and listening to the ear and experience and intuition.

On the other hand, a technique for measuring an axial force by an instrument using a mechanical method, an electrical method, or an optical method is also known.
As an electrical method, (1) as shown in Patent Document 1, there is a method using an electric resistance wire strain (strain) gauge, which has been developed because it can be easily measured in the field. (2) There is also a method of measuring with ultrasonic waves as disclosed in Patent Document 2.

  (1) In the method using a strain gauge, first, the strain gauge is directly attached to the bolt body with an adhesive, or the strain gauge is inserted into a narrow hole formed in the center of the bolt and hardened with an adhesive. A measuring bridge is formed with a strain gauge. Then, this bolt is applied to a tensile testing machine to give a tensile load, and the strain output at this time is read using a static strain meter or a dynamic strain meter to calibrate the tensile load (axial force) -strain output.

Then, after actually tightening using calibrated bolts, the strain output is measured with a dynamic strain meter, and the axial force is calculated based on the data corresponding to the tensile load (axial force) strain output obtained during calibration. calculate.
(2) In the method of measuring an axial force with ultrasonic waves, an ultrasonic wave emission terminal is applied to one end of the bolt, and an ultrasonic beam is emitted from the terminal in the length direction of the bolt. The emitted ultrasonic beam is reflected at the other end of the bolt and returns to the original launch terminal. Therefore, this required time is measured before (t1) and after (t2) the tightening, and the difference (Δ By multiplying the speed of sound by half of t) (since there is a round trip), the bolt elongation is accurately measured. Then, the measured amount of elongation of the bolt is converted into an axial force.
JP 2005-140653 A JP 2006-308342 A

By measuring the strain of the fastening body using the device as described above, it is possible to monitor the loosening of the fastening body over time during daily operation without depending on experience or intuition. And the accident resulting from loosening of a fastening body can be prevented by monitoring loosening of a fastening body on a daily basis.
However, in the case of the measurement method using the strain gauge of (1), it is necessary to perform calibration after attaching the strain gauge to each fastening body, which takes time.

When measuring with the ultrasonic wave of (2), it is necessary to bring the ultrasonic probe into contact with each fastening body to be measured, and the apparatus cost also increases.
With this background, the present invention is a relatively inexpensive device that can easily monitor the loosening of the tightening axial force of a fastening body such as a bolt and can easily detect the axial force. An object is to provide a fastening body and an axial force monitoring system.

In order to achieve the above object, in the present invention, a pin-type load cell for detecting the axial force of the fastening body is embedded in a long fastening body such as a bolt to constitute an axial force detection fastening body. The direction in which the load cell is embedded is preferably matched with the axial direction of the fastening body.
The pin type load cell can be configured by fixing a strain gauge to a strain generating body, and it is preferable to join this in a hole opened in a fastening body.

A silicon semiconductor or a metal thin film is preferably used as the strain gauge resistor.
In the above-mentioned axial force detection fastening body, a bridge circuit incorporating a strain gauge, an A / D converter for digitally converting an analog output from the bridge circuit, and a strain signal transmitting unit for wirelessly transmitting the digitally converted strain signal Is preferably provided.

The axial force detection fastening body is provided with a power receiving unit that receives power supplied wirelessly via electromagnetic waves, and with the power received by the power receiving unit, a bridge circuit, an A / D converter, and a distortion signal transmission It is preferable to drive the part.
An axial force monitoring system is configured by the above-described axial force detection fastening body and a strain signal receiver that receives a strain signal transmitted from the strain signal transmission unit at a position away from the axial force detection fastening body. be able to.

At this time, it is preferable to install a transmitting unit that transmits the electromagnetic wave supplied to the power receiving unit in the distortion signal receiving unit.
In the axial force monitoring system, the distortion signal transmission unit transmits a distortion signal by load-modulating the electromagnetic wave supplied to the power reception unit, and the signal reception unit demodulates the distortion signal from the modulated electromagnetic wave. preferable.

A fastening body unit may be configured by the above-described axial force detection fastening body and an IC tag that records management information related to the axial force detection fastening body. This management information includes an individual identification code, a tightening date and time, a tightening axial force, and the like.
At this time, the IC tag is preferably fixed to the axial force detection fastening body.
Axial force monitoring between the fastening unit, a distortion signal receiver that receives a distortion signal transmitted from a distortion signal transmission unit, and a reception unit that has an IC tag reader / writer that transmits and receives management information to and from an IC tag A system can also be configured.

According to the fastening body for detecting an axial force of the present invention, the pin type load cell embedded in the fastening body can convert the axial force of the fastening body into a voltage or the like and output the voltage. Therefore, based on the output from the load cell. Thus, the axial force of the fastening body can be measured. In particular, if the direction in which the load cell is embedded matches the axial direction of the fastening body, the axial force can be accurately detected by the load cell.
Therefore, the looseness of the fastening body can be monitored by measuring the axial force of the fastening body over time. Compared with the hammering method, the measurement can be easily performed in a short time without relying on experience and intuition, and the reliability is remarkably improved.

  In addition, the strain gauge is not directly attached to the fastening member for detecting the axial force as in the prior art (1), but a pin-type load cell is embedded in the fastening member, so that the load cell is calibrated alone. If the strain output-elongation relationship is obtained, the relationship between the axial force of the fastening body and the strain output can be calculated by multiplying the conversion magnification. That is, the axial force-strain output of the fastening body can be calculated without performing calibration after the load cell is embedded in the fastening body.

Since the cross-sectional area of the load cell is much smaller than the cross-sectional area of the fastening body, the tensile force at the time of calibration can be small. Therefore, when calibrated with a load cell, the tensile tester used is also relatively small and clean.
Further, since one type of load cell can be used for various types and sizes of fastening bodies, the labor required for the calibration work can be simplified and the cost required for calibration can be reduced.

Furthermore, the process of embedding the load cell in the hole of the fastening body is easier than the process of directly embedding the strain gauge in the hole of the fastening body. Therefore, the occurrence of defective products in the embedding process is suppressed, and the axial force measurement quality of the embedded bolt is stabilized.
The pin type load cell used in the present invention can be easily formed by fixing a strain gauge to a strain generating body. When this load cell is joined in the hole established in the fastening body, the strain body is stretched by being pulled in the axial direction as the fastening body is stretched by the axial force, and is fixed to the strain body. The strain gauge is also deformed together with the strain generating body, and the resistance value changes. Therefore, the axial force of the fastening body can be measured by taking out the change in resistance value of the strain gauge as an electrical signal.

If a silicon semiconductor is used as the strain gauge resistor, a high gauge factor can be obtained, and therefore measurement can be performed with high sensitivity without amplifying the output. On the other hand, if a metal thin film is used as a strain gauge resistor, a stable output can be obtained with a low gauge factor.
If the above-described fastening body for detecting an axial force is provided with an A / D converter for digitally converting an analog output from a strain gauge and a strain signal transmitting means for wirelessly transmitting a strain signal that has been digitally converted, strain signal transmission By receiving the strain signal transmitted from the means, it is possible to detect the axial force of the fastening member for detecting the axial force.

That is, an axial force monitoring system is configured by the axial force detection fastening body and a strain signal receiver that receives a strain signal transmitted from the strain signal transmission unit at a position away from the axial force detection fastening body. can do.
Therefore, it is possible to take out a distortion signal wirelessly at a remote location without drawing the wiring from the fastening member for detecting the axial force. Thereby, the burden of the maintenance inspection work of a fastening body can be reduced.

The axial force detection fastening body is provided with a power receiving unit that receives power supplied wirelessly via electromagnetic waves, and the power received by the power receiving unit is used to generate a bridge circuit, an A / D converter, a distortion By driving the signal transmission unit, it is possible to transmit a distortion signal without mounting a power source battery on the axial force detection fastening body. Therefore, the axial force detection fastening body can be realized in a small size.
In the above axial force monitoring system, if the transmitter for transmitting the electromagnetic wave supplied to the power receiver is installed in the distortion signal receiver, the power receiver and the transmitter are in the same place, so the transmitter from the transmitter The power receiving unit is suitable for receiving a distortion signal while wirelessly supplying power to the force detection fastening body.

In the axial force monitoring system, the distortion signal transmission unit transmits a distortion signal by load-modulating the electromagnetic wave supplied to the power reception unit, and the signal reception unit demodulates the distortion signal from the modulated electromagnetic wave, The distortion signal can be easily and stably transmitted from the distortion signal transmission unit to the signal reception unit.
If a fastening body unit is composed of the above-described axial force detection fastening body and an IC tag that records management information related to the axial force detection fastening body, the management information recorded on the IC tag by the IC tag reader / writer Can be read and management information can be written to the IC tag.

Accordingly, individual identification information of the fastening member for detecting the axial force can be easily obtained, and an inspection record can be left.
If the IC tag is fixed to the axial force detection fastening body, the management information can be easily read from the IC tag when a strain signal is received from the axial force detection fastening body.
Axial force monitoring between the fastening unit, a distortion signal receiver that receives a distortion signal transmitted from a distortion signal transmission unit, and a reception unit that has an IC tag reader / writer that transmits and receives management information to and from an IC tag If the system is configured, transmission / reception of distortion signals and transmission / reception of management information can be easily performed between units.

1 and 2 are diagrams showing a configuration of a fastening body unit according to an embodiment of the present invention.
The fastening unit 1 is configured by mounting a pin type load cell 20, a transmitter board 30, and an IC tag 50 on an axial force detection bolt 10.
FIG. 3 is a block diagram showing a configuration of an axial force monitoring system using the fastening body unit 1.

The fastening unit 1 and the receiving unit 100 that transmits and receives data constitute an axial force monitoring system. That is, the receiving unit 100 sends power to the axial force detection bolt 10 using wireless power supply technology, and the transmitter board 30 measures the distortion signal using the received power, send.

As a wireless power supply method, in the following, an inductive coupling method in which electric power is transmitted by a change in magnetic flux passing between coil antennas is used, but an electromagnetic back diffusion coupling method, a close contact type, or the like can also be adopted.
1. Configuration of Fastening Body Unit 1-1 Axial Force Detection Bolt 10
The axial force detection bolt 10 includes a shaft portion 11 and a head portion 12, and a thread 13 is formed on the outer peripheral surface of the shaft portion 11. Examples of the material of the bolt 10 include metals such as stainless steel and iron, plastics such as polycarbonate and phenol resin, alloys, and ceramics. The shaft portion 11 and the head portion 12 may be formed of the same material, or may be formed of different materials (for example, the shaft portion 11 is formed of iron and the head portion 12 is formed of plastic).

The bolt 10 is paired with the nut 2 and fastens and holds the fastened body 3. In the fastened state, a compression force is applied to the body 3 to be fastened, and a tensile axial force P having a magnitude corresponding to the compression force is applied to the shaft portion 11.
An insertion hole 14 is formed in the bolt 10 from the head 12 along the central axis, and a pin type load cell 20 for detecting the axial force of the bolt 10 is embedded in the insertion hole 14.

When the load cell 20 is embedded in this manner, the direction thereof coincides with the axial direction of the shaft portion 11, so that the axial force can be accurately detected by the load cell 20.
The process of embedding the load cell 20 in the insertion hole 14 of the bolt 10 is easier than the process of embedding a strain gauge directly in the hole of the bolt 10. Therefore, it is possible to suppress the occurrence of defective products in this embedding process and to stabilize the quality of axial force measurement.

A transmitter board 30 for transmitting a distortion signal is attached to the pin type load cell 20.
A concave portion 15 is formed in the head 12 of the bolt 10, and the transmitter board 30 is fitted in the concave portion 15.
The opening of the recess 15 is covered with a cap 40, and an IC tag 50 for recording management information of the bolt 10 is embedded in the cap 40.

1-2 Installation of Pin Type Load Cell 20 and Transmitter Board 30 The pin type load cell 20 is a strain gauge type load cell, and can measure the magnitude of an applied load and output it as an electrical signal.
The load cell 20 is configured by bonding a strain gauge 22 to a columnar or plate-shaped strain body 21. Cylindrical joining end portions 21 a and 21 b joined to the inner wall of the insertion hole 14 are formed at both ends of the strain generating body 21, and the joining end portions 21 a and 21 b have a diameter substantially equal to the inner diameter of the insertion hole 14. And firmly joined to the inner wall of the insertion hole 14 with an adhesive or the like.

The strain generating body 21 is an elastic body made of an aluminum alloy or a steel material, and includes a gauge attaching portion 21c to which the strain gauge 22 is attached, and joint end portions 21a and 21b formed at both ends thereof. The joining end portions 21a and 21b and the strain gauge forming portion are desirably integrally formed of the same material, but may be manufactured separately and joined with an adhesive or the like.
The joining end portions 21a and 21b are set to a diameter substantially equal to the diameter of the insertion hole 14 and are firmly joined to the inner wall of the insertion hole.

For example, the diameter of the insertion hole 14 is 3 mm, and the diameters of the joining end portions 21a and 21b are 2.9 mm.
At the time of assembly, the load cell 20 equipped with the transmitter substrate 30 is inserted into the insertion hole 14, and the outer peripheral portions of the joining end portions 21 a and 21 b are firmly joined to the inner wall of the insertion hole 14 with an adhesive. Then, the cap 40 is attached to the head 12 so as to cover the recess 15.

When the fastened body 3 is tightened with the bolt 10 and the nut 2, the shaft portion 11 expands according to the tightening axial force P, and the strain generating body 21 and the strain gauge 22 are also deformed to change their resistance values. Therefore, the axial force can be measured by taking out the change in resistance value of the strain gauge 22 as an electrical signal.
The resistance value change is converted into a voltage signal by a bridge circuit and taken out as a digital signal by an A / D converter.

This will be described in detail in “3. Detection of axial force of bolt 10 by load cell 20”.
Here, as shown in FIG. 2, the transmitter substrate 30 is embedded in the concave portion 15 of the head 12, but the transmitter substrate 30 may be affixed on the outer surface of the head 12.
When the head 12 is made of metal, the antenna portion (antenna coil 35) of the transmitter board 30 can be arranged outside the head 12 or arranged so as to surround the head 12. preferable.

As for the form in which the IC tag 50 is attached to the bolt 10, the IC tag 50 is embedded in the cap 40 in the example shown in FIG. 2, but the IC tag 50 may be attached or embedded at an appropriate site near the bolt. For example, you may attach to the washer used with the volt | bolt 10 and a set.
1-3 Transmitter board 30
The transmitter substrate 30 is joined to the joining end portion 21b of the strain generating body 21, and is connected to the strain gauge 22 by wiring.

The transmitter board 30 is provided with a reception circuit 31, a constant voltage circuit 32, an A / D converter 33, a transmission circuit 34, an antenna coil 35, a bridge circuit 36, and the like.
The reception circuit 31 rectifies the alternating voltage generated by the antenna coil 35 in an alternating electromagnetic field into a direct current, supplies the direct current to the constant voltage circuit 32, and also drives the A / D converter 33 and the transmission circuit 34. Electric power is supplied as a working voltage.

The constant voltage circuit 32 supplies a constant bridge voltage E between the input terminals A and C of the bridge circuit 36.
In order to stably output a resistance change of the strain gauge 22 as a voltage from the bridge circuit 36, it is important to keep the bridge voltage E constant. As the constant voltage circuit 32, it is preferable to use a shunt regulator provided with a shunt resistor whose resistance value changes as the coupling coefficient K changes.

The details will be described in 3-3 “Voltage Supply to Bridge Circuit 36”.
The A / D converter 33 converts the output voltage at the output terminal (between BD) of the bridge circuit 36 into a digital signal. Since this signal has a corresponding relationship with the strain (axial force) applied to the bolt, it is referred to as “strain data (distortion signal)”.
The transmission circuit 34 sends the distortion data (digital signal) generated by the A / D converter 33 to the distortion signal reception circuit 102 of the reception unit 100.

This data transmission will be described in detail in “4. Data transfer between transmitter board 30 and receiving unit 100”.
1-4 IC tag 50
The power supply circuit 51 rectifies the AC voltage generated by the antenna coil 52 in an AC electromagnetic field into DC and supplies it to the memory circuit 53, and performs data transmission / reception with the IC tag reader / writer 110.

Data transmission from the power supply circuit 51 to the IC tag reader / writer 110 is performed using a load modulation method that modulates the carrier wave, and data transmission from the IC tag reader / writer 110 to the power supply circuit 51 is also performed using a method that modulates the carrier wave. As a result, data can be stably transmitted wirelessly.
The memory circuit 53 is driven by a DC voltage supplied from the power supply circuit 51 and is used for management data (mainly data unique to the bolt 10 and used for management from the memory. For example, an individual identification code of the bolt 10 and a part to be used The initial axial force value, the assembly date and time, the axial force of the bolt 10 measured in the past) are read out and transmitted to the IC tag reader / writer 110, or the management data transmitted from the IC tag reader / writer 110 is received and stored in the memory. Write to.

2. Configuration of Receiving Unit 100 The power transmission circuit 101 generates high-frequency AC electromagnetic waves from the antenna coil 106. The frequency is, for example, 13.56 MHz.
The distortion signal receiving circuit 102 receives and demodulates a distortion signal transmitted using this electromagnetic wave as a carrier wave, and generates distortion data. Considering the possibility of variation in the distortion data obtained here, it is preferable that the distortion signal receiving circuit 102 repeatedly generates distortion data and performs an averaging process.

The axial force conversion circuit 103 converts the distortion data demodulated by the distortion signal receiving circuit 102 into axial force data.
This conversion can be easily performed by creating and storing a correspondence table between strain data values and axial force values in advance for the bolt 10 and referring to the correspondence table.
The comparison unit 104 reads the axial force data calculated by the axial force conversion circuit 103 and evaluation data (for example, data indicating an appropriate range of axial force prepared in advance, or the IC tag reader / writer 110 reads from the IC tag 50). Individual data).

The display unit 105 displays the axial force data calculated by the axial force conversion circuit 103, the evaluation result evaluated by the comparison unit 104, and the like on the screen.
Similarly to the power transmission circuit 101, the IC tag reader / writer 110 generates high-frequency AC electromagnetic waves from the antenna coil to supply power to the IC tag 50, and uses the axial force data calculated by the axial force conversion circuit 103 as a power source. It transmits to the circuit 51, transmits management data to the power supply circuit 51 as necessary, and receives axial force data and management data sent from the power supply circuit 51.

3. Detection of the axial force of the bolt 10 by the load cell 20 The strain gauge 22 is configured by laminating a resistor 24 and a protective coating 25 on a base 23, and an adhesive on the circumferential surface or a plane of the gauge attaching portion 21c of the strain generating body 21. 26 is adhered. As the resistor, it is preferable to use a metal semiconductor or a silicon semiconductor doped with impurities in silicon.

3-1 Using a Metal Thin Film as a Resistor When the bolt 10 is tightened, the shaft portion 11 expands according to the tightening axial force P (L → L + ΔL). Since the joining end portions 21a and 21b of the load cell 20 are firmly joined to the shaft portion 11, as the shaft portion 11 expands, the gauge sticking portion 21c of the strain generating body 21 is also pulled in the axial direction. (L → l + Δl). Further, the strain gauge 22 attached to the strain generating body 21 is also deformed.

The resistance value R of the resistor 24 in the strain gauge 22 is expressed as R = ρL / A. Further, when a tension is applied to the resistor and its length l increases (l → l + Δl), the cross-sectional area decreases, so that the resistance value R increases (R → R + ΔR).
L: Length of resistor A: Cross-sectional area of resistor ρ: Intrinsic resistivity of resistor The ratio (gauge factor G) between mechanical strain and resistance change of strain gauge resistor is G = (ΔR / R) / (ΔL / L).

A general metal has a Poisson's ratio σ as small as about 0.3 to 0.6, and a gauge factor G is about 1.6 to 2.2. The gauge factor G of the metal thin film used for the strain gauge is also about 2 at room temperature, and changes slightly depending on the use temperature.
Although the resistance change of the strain gauge is very small, the resistance change can be converted into a voltage change (strain-voltage conversion) by using a Wheatstone bridge circuit as follows.

As shown in FIG. 3, the bridge circuit 36 has four resistors connected to each other and has terminals A, B, C, and D at the four connection portions, and one of two opposing terminals ( The bridge voltage E is applied to the terminal A-C), and the output voltage e is detected from the other (terminal B-D).
The resistance value between A and B is R1, the resistance value between B and C is R2, the resistance value between C and D is R3, and the resistance value between D and A is R4. The relationship between the bridge voltage E and the output voltage e output between the terminals B-C is
e = E (R1R3-R2R4) / (R1 + R2) (R3 + R4).

In such a Wheatstone bridge circuit, a gauge resistor is used for one or more of the four resistors.
For example, in the one active gauge method, a gauge resistor is inserted between terminals A and B shown in the figure.
In this case, the output characteristics from the bridge circuit are
Δe = (1/4) GEΔε (Expression 1)
The mechanical strain change Δε and the bridge output voltage change Δe are proportional to each other. For example, if the gauge factor G = 2.0 and the bridge voltage E = 4V, Δe = 2Δε.

  In the 4-active gauge method, as shown in FIG. 5, four strain gauges Rg1, Rg2, Rg3, and Rg4 are attached to a columnar or plate-like strain generating body 21 (gauge attaching portion 21c). That is, the strain gauge Rg1 and the strain gauge Rg3 are pasted at positions symmetrical to each other with respect to the central axis of the strain generating body 21 in a direction along the central axis. The strain gauge Rg2 and the strain gauge Rg4 are attached in positions perpendicular to the central axis at positions symmetrical to the central axis of the strain generating body 21.

The four Rg1, Rg2, Rg3, and Rg4 are connected so as to be incorporated as resistors R1, R2, R3, and R4 of the bridge circuit 36.
When a metal thin film resistor is used, the output characteristic from the bridge circuit 36 is
Δe = E (1 + σ) GΔε / 2 (Expression 2)
(Σ: Poisson's ratio of the metal thin film) The mechanical strain change Δε and the bridge output voltage change Δe are proportional to each other.

According to the four-active gauge method, the voltage change due to the bending strain of the strain generating body 21 is canceled, and only the voltage change due to the tensile and compressive strain can be detected, and temperature compensation is also performed.
Note that since the gauge factor of the metal thin film is small, the output change Δe from the bridge circuit is also small. Therefore, it is desirable to amplify the output voltage e with a DC amplifier and then perform A / D conversion with the A / D converter 33.

3-2 Using a Semiconductor as a Resistor When a semiconductor is used as a resistor, it is basically the same as the metal thin film described above, but the resistance change of the resistor is mainly due to the piezoelectric resistance effect of the semiconductor. That is, some semiconductors have an extremely large resistance change rate Δρ / ρ due to strain compared to metal due to this piezoresistive effect, and the gauge factor G in this case is G = (Δρ / ρ) / ( ΔL / L). In addition, as a mechanism for generating a piezoresistive effect in a semiconductor, an explanation is made based on a change in an isoenergy surface due to strain of a multi-valley semiconductor.

Specific examples of the semiconductor material used for the semiconductor strain gauge include Si, Ge, InSb, and the like. These materials exhibit a unique gauge factor depending on the conduction type (p-type, n-type) and the crystal direction.
For example, a Si semiconductor exhibits the following gauge factor, and the gauge factor has a large absolute value (see “Electrical and Electronic Materials (Kyoritsu Shuppan)”).

p-type, crystal direction (100) gauge factor G = 10
p-type, crystal direction (111) gauge factor G = 177
n-type, crystal direction (100) gauge factor G = −132
n-type, crystal direction (111) gauge factor G = -13
If a semiconductor having a large absolute value of the gauge factor is used, the sensitivity is about 50 to 100 times that of a strain gauge using a metal thin film resistor, and the output voltage change Δe of the bridge circuit caused by the strain of the strain gauge. Is about several tens of mV.

Therefore, the A / D converter 33 can perform A / D conversion without amplifying the output voltage Δe from the bridge circuit.
When forming a load cell with a semiconductor strain gauge, the strain body itself may be formed of a silicon wafer, and a gauge portion formed by impurity doping may be formed on the silicon wafer, in addition to a mode in which the strain gauge is attached to the strain body.

  For example, a semiconductor resistor layer is formed by doping impurities on a silicon wafer while patterning by a masking method, and a bridge circuit can be formed by drawing a wiring pattern on the silicon wafer. In the case of the method, one gauge is formed, and in the case of the 4-active gauge method, four gauges are formed. The dimensions of each gauge are, for example, 0.3 mm long and 0.1 mm wide.

By cutting this silicon wafer, a portion corresponding to the gauge sticking portion 21c of the strain generating body can be formed. The cut-out dimensions may be appropriately determined within a range that can be inserted into the insertion hole 14 in consideration of ensuring the balance with the joining end portions 21a and 21b and the joining strength. For example, the width is about 2.5 mm and the length is 15 mm to 30 mm.
If members corresponding to the joining end portions 21a and 21b are joined, a load cell made of a silicon wafer incorporating a strain gauge and a bridge circuit can be formed.

By this manufacturing method, a load cell having a resistance value of 120Ω and a gauge factor of 100 can be manufactured.
3-3 Voltage Supply to Terminal AC of Bridge Circuit 36 In the transmitter board 30, a small battery may be mounted as the power supply voltage of the bridge circuit 36, but in the present embodiment, wirelessly from the receiving unit 100. A passive type is adopted in which the transmitter board 30 receives the supplied power and supplies it to the bridge circuit 36 and the like.

A mechanism for supplying a constant voltage to the terminals A to C of the bridge circuit 36 will be described with reference to FIG. The passive driving method is described in detail in “RFID Handbook (Nikkan Kogyo Shimbun)”.
The power transmission circuit 101 is inductively coupled to the antenna coil 106 of the power transmission circuit 101 and the antenna coil 35 of the transmission board 30 at a position close to the transmitter board 30.

When the high-frequency voltage (13.56 MHz) is generated by the AC power supply in the power supply transmission circuit 101, the high-frequency voltage is received by the receiving circuit 31 through the antenna coil 106 and the antenna coil 35 that are inductively coupled. .
A constant voltage circuit 32 is interposed between the receiving circuit 31 and the terminal AC of the bridge circuit 36.

The constant voltage circuit 32 shown in FIG. 4 is a shunt regulator having a relatively simple configuration, and includes a rectifier and a circuit for supplying a voltage generated by the Zener diode ZD to the base of an npn transistor whose emitter is grounded. Is provided.
The high frequency received by the receiving circuit 31 is rectified by the rectifier in the constant voltage circuit 32, and the voltage applied between the terminals A and C is stabilized by the Zener diode ZD and the transistor.

FIG. 6 is a diagram illustrating the relationship between the coupling coefficient K between the antenna coil 106 and the antenna coil 35 and the voltage input between the input terminals A and C of the bridge circuit 36. As shown in the figure, when the antenna coils are inductively coupled and the coupling coefficient K is more than a certain level, a constant voltage Vz is applied between the input terminals AC.
This voltage is also used as a driving power source for the A / D converter 33 and the modulator 34a.

As described above, the transmitter board 30 is supplied with a bridge voltage or the like without mounting a battery.
3-4 Creating a correspondence table to be stored in the axial force conversion circuit 103 (calibration)
FIG. 7 is a chart showing an example of the correspondence between the strain data Δe and the axial force value P.
Basically, as shown in the above formulas 1 and 2, the strain data Δe and Δε are proportional to each other, and Δε corresponds to the elongation Δl of the strain generating body 21, and this Δl is almost equal to the axial force P of the bolt 10. Since it is proportional, the strain data (Δe) and the axial force P of the bolt 10 are approximately proportional as shown in FIG.

Actually, the relationship between the axial force P of the bolt 10 and the strain data Δe varies depending on the bolt 10 to which the load cell 20 is attached. It is preferable to create a correspondence table between the strain data value Δe and the axial force value P for each bolt 10.
Such a calibration can be performed by measuring strain data (Δe) while variously changing a tensile load (axial force of the bolt 10) by applying a tensile tester after mounting the load cell 20 and the transmitter substrate 30. However, before each load cell 20 is attached to the bolt 10, the measurement can be performed by a tensile test to perform calibration.

Since the cross-sectional area of the load cell 20 is much smaller than the cross-sectional area of the bolt 10, if the load cell 20 is calibrated, the tensile force at the time of calibration can be small. Therefore, the tensile tester used for calibration can be small.
A factor that causes variations in the strain voltage characteristics for each bolt 10 is considered to be variations in the characteristics of the load cell 20 before being attached to each bolt 10. For example, a strain gauge 22 is attached to the strain generating body 21. Variations in the load cell 20 tend to vary between the tensile force of the load cell 20 and the strain data change Δe due to variations in the attachment, but the relationship between the tensile force applied to the load cell 20 and the axial force P of the bolt 10 does not vary much.

  Therefore, the conversion multiple of the tensile force applied to the load cell 20 and the axial force P of the bolt 10 is obtained in advance by measuring and calibrating each load cell 20 using a tensile tester (changes in tensile force and strain data). (If a correspondence table with Δe is created), even if the calibration is not performed after the load cell 20 is attached to each bolt 10, the correspondence table between the tensile force applied to the individually created load cell 20 and the change Δe of strain data, and the load cell By multiplying the conversion force between the tensile force applied to 20 and the axial force P of the bolt 10, a correspondence table between the strain data value Δe and the axial force value P can be created for each bolt 10.

  As described above, for each bolt 10, a correspondence table between the strain data value Δe and the axial force value P is created, and an individual identification code of each bolt 10 is attached and stored in the axial force conversion circuit 103. When the axial force of the bolt 10 is to be measured, the axial force conversion circuit 103 refers to the correspondence table to which the individual identification code of the bolt 10 is attached from the stored correspondence table. The axial force data can be calculated from the distortion data demodulated by the receiving circuit 102.

4). Data transfer between transmitter board 30 and receiver unit 100 Data transmission / reception between receiver unit 100 and transmitter board 30 and data transmission between IC tag reader / writer 110 and IC tag 50 are performed using RFID tags. This is performed using a commonly used digital modulation method.
In the RFID tag, methods such as ASK (amplitude shift keying), FSK (frequency shift keying), and PSK (phase shift keying) are used. Among them, the ASK method is a method of changing the amplitude of a sine wave based on a digital signal, is easy to demodulate, and is often used for short-distance communication such as an RFID tag. This digital modulation method is also applied to this embodiment.

In order to prevent collision (anti-collision) between the data transmission / reception between the receiving unit 100 and the transmitter board 30 and the data transmission / reception between the IC tag reader / writer 110 and the IC tag 50, the frequency of the subcarrier is set separately. It is preferable to operate in time division.
As an example of data transmission / reception, a mechanism for transmitting distortion data from the transmission circuit 34 to the distortion signal reception circuit 102 will be described with reference to FIG.

As described above, the power transmission circuit 101 of the receiving unit 100 transmits an alternating current electromagnetic wave at the frequency ft (13.56 MHz).
The transmission circuit 34 of the transmitter substrate 30 includes a modulator 34a.
The modulator 34a divides the clock signal having the frequency ft (13.56 MHz) received by the receiving circuit 31 into 1/64 to generate a subcarrier having the frequency fs (212 kHz). Further, the generated subcarrier is ASK modulated based on the distortion data (digital signal) generated by the A / D converter 33.

In the receiving circuit 31, the FET is turned on and off based on the subcarrier thus subjected to ASK modulation. As the FET is turned ON / OFF, the state is switched between the state in which the load is incorporated in the reception circuit 31 and the state in which the load is not (the load of the reception circuit 31 varies), so the original frequency ft (13.56 MHz) The electromagnetic wave is load-modulated.
In this way, when the electromagnetic wave having the operating frequency ft is load-modulated with the subcarrier of the frequency fs, the wave of the frequency ft and the wave of the frequency fs are multiplied, and thus the wave of the frequency (ft + fs) and the frequency (ft−fs). Waves are formed. That is, sidebands (sidebands) are symmetrically formed on both sides around the frequency ft, the frequency of the upper sideband is (ft + fs), and the frequency of the lower sideband is (ft−fs). .

The distortion signal receiving circuit 102 extracts distortion data (digital signal) from one of these two sidebands. In the example shown in FIG. 4, the distortion signal receiving circuit 102 removes the operating carrier wave component from the received electromagnetic wave by the band-pass filter 102a to extract only the upper sideband, and finally the distortion data ( Digital signal).
5). Use Form of Axial Force Monitoring System If the axial force measuring bolt 10 is attached to a vehicle or the like as described below using the axial force monitoring system described above, the receiving unit 100 is placed at a position close to the bolt 10. The axial force of the bolt 10 can be measured in a non-contact manner and displayed on the display unit 105.

When assembling a vehicle in a factory, when many bolts of the same type are used to fasten parts of the vehicle, the axial force measurement bolt 10 may be used for all of them, but only a part of the axial force measurement The axial force may be measured in a sample manner using the bolts 10 for use.
The receiving unit 100 is installed at the site where the bolt 10 for measuring the axial force is fastened. Then, the tightening axial force data of the bolt 10 properly tightened is measured at the time of assembling the vehicle. This axial force data is calculated by the axial force conversion circuit 103, sent from the axial force conversion circuit 103 of the receiving unit 100 to the IC tag 50 via the IC tag reader / writer 110, and recorded in the memory circuit 53.

In addition to the axial force data, the IC tag reader / writer 110 also sends management data such as the individual identification code of the bolt 10, the part to be used, the date and time of assembly to the memory circuit 53 from the IC tag reader / writer 110. To be recorded.
After the vehicle is shipped from the factory, the receiving unit 100 is installed in a place where it is known that the vehicle over the user is temporarily parked and stopped, for example, a gas station.

Then, when the vehicle is parked and stopped temporarily, the receiving unit 100 can be used to check the axial force of the bolt 10 at that time without contacting the bolt 10.
As a result of checking, if it is determined that the bolt 10 is loose, then the bolt 10 is tightened, and if there is a bolt of the same type as the bolt 10, it is tightened. Then, the axial force value of the tightened bolt 10 and the tightening date and time are written in the IC tag 50 to update the recorded content.

When the bolt 10 is removed and lost or broken, it is replaced with a new bolt 10 and data such as a new axial force is recorded on the IC tag 50.
7). Effects of the axial force monitoring system of this embodiment Since it is not so easy to manually check the axial force of the bolts used for daily operation like hammering, so far abnormal phenomena have occurred. The axial force drop in daily operation was not sufficiently monitored without checking the axial force of the bolts, but if the axial force monitoring system according to this embodiment is used, the bolt is not used for daily operation. Since it is possible to easily check the axial force of the bolt that is being used, it is possible to sufficiently monitor the decrease in the axial force.

Moreover, if the axial force monitoring system of this embodiment is used, since it does not depend on experience and intuition like hammering, reliability is also improved significantly.
Moreover, the measurement result can be recorded on an IC tag or the like attached to the fastening body.
In addition to measuring the axial force at that time, solid recognition such as bolt position and bolt size recorded on the IC tag, proper tightening date, proper axial force (tightening force) at that time, etc. New information can be obtained by simultaneously reading and comparing information from the IC tag. For example, the relationship between the position of the bolt and the degree of reduction in the axial force can be examined to determine whether or not there is a tendency for the axial force to decrease depending on the place to be fastened.

Such fine axial force management can prevent accidents caused by loose bolts.
In the axial force monitoring system of this embodiment, if the receiving unit 100 is made lightweight and portable, it is easy to mount the receiving unit 100 on a train or an aircraft. Therefore, bolts 10 are attached to trains and airplanes, and when the vehicle is parked or inspected, the bolts 10 are checked with the receiving unit 100 installed to check for loose bolts at each part. can do.

In the fastening body unit 1 of the present embodiment, since the load cell 20 is embedded in the insertion hole 14 of the bolt 10, the embedding operation is easier compared to the case where the strain gauge is directly embedded in the insertion hole of the bolt 10.
Further, the fastening body unit 1 can be calibrated by embedding the same type of load cell 20 in various types and sizes of bolts 10. By doing so, the labor required for the calibration work can be simplified and the cost required for the calibration can be reduced.

  INDUSTRIAL APPLICABILITY The present invention can be used for monitoring the axial force of a fastening body that holds a fastened body, such as a bolt or a rivet, in a fastened state.

It is an exploded view which shows the structure of the fastening body unit concerning embodiment. It is a figure which shows the structure of the fastening body unit concerning embodiment. It is a block diagram which shows the structure of the axial force monitoring system concerning embodiment. In the axial force monitoring system concerning an embodiment, it is a figure explaining the mechanism which supplies constant voltage to the terminal of a bridge circuit, and the mechanism which transmits distortion data. It is a figure explaining the method of measuring distortion by 4 active gauge method. It is a figure which shows the relationship between the coupling coefficient K of an antenna coil, and the voltage input into a bridge circuit. 6 is a chart showing an example of a correspondence relationship between strain data Δe and an axial force value P.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fastening body unit 10 Bolt for axial force detection 11 Shaft part 12 Head 14 Insertion hole 15 Recess 20 Pin type load cell 21 Strain body 22 Strain gauge 24 Resistor 30 Transmitter board 31 Reception circuit 32 Constant voltage circuit 33 A / D Converter 34 Transmission circuit 35 Antenna coil 36 Bridge circuit 50 IC tag 51 Power supply circuit 52 Antenna coil 53 Memory circuit 100 Reception unit 101 Power supply transmission circuit 102 Strain signal reception circuit 106 Antenna coil 110 IC tag reader / writer

Claims (11)

To the long fastening body that fastens and holds the fastened body,
A fastening body for detecting an axial force, characterized in that a pin-type load cell for detecting the axial force of the fastening body is embedded. The load cell is
A strain gauge is fixed to the strain generating body.
The axial force detection fastening body according to claim 1, wherein the fastening body is joined in a hole formed in the fastening body. The strain gauge is
3. The axial force detection fastening body according to claim 2, wherein a resistor made of a silicon semiconductor or a metal thin film resistor is used.   A bridge circuit incorporating the strain gauge, an A / D converter that digitally converts an analog output from the bridge circuit, and a strain signal transmitter that wirelessly transmits the digitally converted strain signal. Item 4. The fastening member for detecting axial force according to any one of Items 1 to 3. The axial force detection fastening body is:
A power receiving unit that receives power supplied wirelessly via electromagnetic waves,
With the power received by the power receiver,
The axial force detection fastening body according to claim 4, wherein the bridge circuit, the A / D converter, and the distortion signal transmission unit are driven. A fastening body for detecting an axial force according to claim 4 or 5,
A fastening body unit including an IC tag that records management information related to the axial force detection fastening body.   The fastening body unit according to claim 6, wherein the IC tag is fixed to the fastening body for detecting the axial force. A fastening body for detecting an axial force according to claim 4 or 5,
An axial force monitoring system comprising a distortion signal receiver that receives a distortion signal transmitted from the distortion signal transmission unit at a position away from the axial force detection fastening body. In the distortion signal receiving unit,
The axial force monitoring system according to claim 8, further comprising a transmitter that transmits an electromagnetic wave to be supplied to the power receiver. The distortion signal transmitter is
Transmitting a distortion signal by load-modulating the electromagnetic wave supplied to the power receiver,
The axial force monitoring system according to claim 8, wherein the signal receiving unit demodulates a distortion signal from the modulated electromagnetic wave. The fastening body unit according to claim 6 or 7,
An axial force comprising: a distortion signal receiver that receives a distortion signal transmitted from the distortion signal transmission unit; and a reception unit having an IC tag reader / writer that transmits and receives management information to and from the IC tag. Monitoring system.

Images