CN111780911B - Ultrasonic sensor for measuring bolt axial force - Google Patents
Ultrasonic sensor for measuring bolt axial force Download PDFInfo
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- CN111780911B CN111780911B CN202010674820.4A CN202010674820A CN111780911B CN 111780911 B CN111780911 B CN 111780911B CN 202010674820 A CN202010674820 A CN 202010674820A CN 111780911 B CN111780911 B CN 111780911B
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- bolt
- test piece
- axial force
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- plate
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/24—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for determining value of torque or twisting moment for tightening a nut or other member which is similarly stressed
- G01L5/246—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for determining value of torque or twisting moment for tightening a nut or other member which is similarly stressed using acoustic waves
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- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- General Physics & Mathematics (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
- Force Measurement Appropriate To Specific Purposes (AREA)
Abstract
The invention discloses an ultrasonic sensor for measuring bolt axial force, belongs to the field of sensors, and aims to solve the problem of low ultrasonic measurement precision by adopting a coupling agent. The ultrasonic sensor for measuring the axial force of the bolt comprises a metal pole plate, a medium layer, a liquid film and a tested bolt test piece; the metal polar plate and the medium layer are arranged on the upper surface of the tested bolt test piece in parallel, and the lower surface of the metal polar plate is fixed on the upper surface of the medium layer; and the liquid film is coated on the lower surface of the medium layer and the upper surface of the tested bolt test piece. The method is characterized in that a tested piece is made to be a polar plate of a capacitor, and mechanical vibration is directly caused on the surface of the test piece by the action of electrostatic force between the polar plates of the capacitor, so that the method is different from a method of transmitting the vibration of a sensor to the test piece by using a coupling agent in the conventional ultrasonic technology. Thus, the ultrasonic wave is present only inside the test piece, and the sound velocity can be measured with high accuracy.
Description
Technical Field
The invention belongs to the field of sensors, and relates to a sensor structure for measuring bolt axial force.
Background
The bolt is an extremely important part in an industrial field and is one of the weakest links of the safety of industrial equipment. The axial force measurement of the bolt is an important means for ensuring the health and long-term service of industrial equipment. At present, the axial force measurement of the bolt mainly depends on an ultrasonic method. The basic principle of measurement is the acoustoelastic effect, i.e. the influence of stress on the speed of sound. However, the acoustoelastic effect is a weak effect, and the sound velocity changes little (the relative change rate is less than one thousandth) under the action of stress. This requires that the measuring apparatus be capable of measuring the speed of sound with high accuracy.
At present, all main ultrasonic means need a couplant, equipment inevitably takes account of the thickness of the couplant when measuring sound velocity, so that the precision of a measuring result is low, and the precision requirement of measuring the axial force of a bolt by adopting an acoustic elastic effect cannot be met.
Disclosure of Invention
The invention aims to solve the problem of low ultrasonic measurement precision of a couplant, and provides an ultrasonic sensor for measuring the axial force of a bolt.
The invention relates to an ultrasonic sensor for measuring the axial force of a bolt, which comprises a metal polar plate 4, a medium layer 5, a liquid film 6 and a tested bolt test piece 7; the metal polar plate 4 and the dielectric layer 5 are arranged on the upper surface of the tested bolt test piece 7 in parallel, and the lower surface of the metal polar plate 4 is fixed on the upper surface of the dielectric layer 5; and the liquid film 6 is coated on the lower surface of the medium layer 5 and the upper surface of the tested bolt test piece 7.
Preferably, the metal pole plate 4 is a one-piece flat plate, or is formed by sleeving an inner ring flat plate 401 and an outer ring flat plate 402.
Preferably, the metal plate 4 is a circle or a regular N-polygon, and N is a natural number equal to or greater than 3.
Preferably, the metal pole plate 4 is used as a positive pole, and the tested bolt test piece 7 is used as a negative pole, so that the sensor is connected into the testing equipment.
Preferably, when the metal pole plate 4 is a whole flat plate, the testing device comprises a receiver 1, an excitation device 2 and a duplexer 3, a square wave excitation signal sent by the excitation device 2 is sent to the metal pole plate 4 through the duplexer 3 and is transmitted to a tested bolt test piece 7, and ultrasonic waves excited on the surface of the tested bolt test piece 7 are transmitted back to the receiver 1, so that the measurement of the axial force of the bolt is completed.
Preferably, when the metal pole plate 4 is in an inner and outer ring sleeved structure, the testing device comprises a receiver 1 and an excitation device 2, a square wave excitation signal sent by the excitation device 2 is transmitted to the tested bolt test piece 7, and ultrasonic waves excited on the surface of the tested bolt test piece 7 are transmitted back to the receiver 1, so that the measurement of the bolt axial force is completed.
Preferably, the metal plate 4 is at least one of gold, silver, copper and aluminum; the metal plate 4 has a thickness of 1 μm to 10 mm.
Preferably, the relative dielectric constant of the material of the dielectric layer 5 is greater than or equal to 100;
the main component of the material of the dielectric layer 5 is at least one of barium titanate, iron-doped strontium titanate and calcium copper carbonate;
the thickness of the dielectric layer 5 is 1 micrometer to 10 millimeters.
Preferably, the material of the liquid film 6 is pure water or an aqueous solution with a water mass fraction of more than 50%.
Preferably, the metal plate 4 and the dielectric layer 5 are tightly combined by a plating process.
The invention has the beneficial effects that: the invention discloses an ultrasonic sensor for measuring bolt axial force, which comprises a metal polar plate, a dielectric layer, a liquid film and a measured metal test piece. The sensor has the capability of directly exciting and receiving ultrasonic waves on the surface of a tested metal test piece, can measure the sound velocity stably and reliably with high precision, and provides a new ultrasonic solution for the axial force measurement of the bolt.
Drawings
FIG. 1 is a schematic structural diagram of an ultrasonic sensor according to an embodiment;
FIG. 2 is a schematic structural view of an ultrasonic sensor according to a second embodiment;
fig. 3 and 4 are two receive circuit topologies cooperating with a receiver to make measurements of an ultrasonic sensor.
Detailed Description
The following detailed description of the embodiments of the present invention will be provided with reference to the drawings and examples, so that how to apply the technical means to solve the technical problems and achieve the technical effects can be fully understood and implemented. It should be noted that, as long as there is no conflict, the embodiments and the features of the embodiments of the present invention may be combined with each other, and the technical solutions formed are within the scope of the present invention.
The core idea of the invention is as follows:
the method is characterized in that a tested piece is made to be a polar plate of a capacitor, and mechanical vibration is directly caused on the surface of the test piece by the action of electrostatic force between the polar plates of the capacitor, so that the method is different from a method of transmitting the vibration of a sensor to the test piece by using a coupling agent in the conventional ultrasonic technology. Thus, the ultrasonic wave is present only inside the test piece, and the sound velocity can be measured with high accuracy.
First embodiment, the present embodiment is described below with reference to fig. 1, and the ultrasonic sensor for measuring the axial force of a bolt according to the present embodiment includes a metal plate 4, a dielectric layer 5, a liquid film 6, and a bolt test piece 7 to be measured; the metal polar plate 4 and the dielectric layer 5 are arranged on the upper surface of the tested bolt test piece 7 in parallel, and the lower surface of the metal polar plate 4 is fixed on the upper surface of the dielectric layer 5; and the liquid film 6 is coated on the lower surface of the medium layer 5 and the upper surface of the tested bolt test piece 7.
The tested bolt test piece 7 is at zero potential. The metal polar plate 4 is used as a conductor to guide the spatial distribution of an electric field; the dielectric layer 5 plays a role in transmitting an electric field to the tested bolt test piece 7; the liquid film 6 plays a role in removing air and improving the strength of electric field transmitted to the tested bolt test piece 7; the metal pole plate 4, the dielectric layer 5, the liquid film 6 and the tested bolt test piece 7 form a complete capacitor which is connected into the external excitation equipment 2 and the receiver 1.
When alternating current is conducted between the metal pole plate 4 and the tested bolt test piece 7, the surface of the tested bolt test piece 7 can periodically gather and release charges; the variable charge quantity Q (t) generates a frequency-doubled electrostatic force F (t) in the variable electric field E (t), according to Coulomb's law
F(t)＝E(t)Q(t)
The electrostatic force acting on the electric charge elastically deforms due to the action inside and between atoms, induces mechanical vibration, and forms a wave in the bolt specimen 7 to be tested. The direction of the electrostatic force is vertical to the surface of the tested bolt test piece 7, so that longitudinal waves can be generated. When the frequency of the alternating current reaches the ultrasonic frequency range, the generated mechanical wave is the ultrasonic wave. The above is the basic principle of generating ultrasonic waves.
When the sound wave is reflected to the surface of the tested bolt test piece 7, the capacitance C of the capacitor is caused by the change of the distance between the capacitor plates due to the vibration of mass points in the vertical direction eq(t) is changed periodically. At this time, the capacitor is electrified with direct current, the voltage U at two ends of the capacitor is kept stable, and then according to the formula:
Q(t)＝Ceq(t)U
it can be known that the change of the charge quantity Q (t) between the capacitor plates generates an alternating current to represent an ultrasonic signal. And receiving the alternating current signal in a certain mode, namely completing the receiving process of the ultrasonic wave. The proposed receiving circuit topology is shown in fig. 3, where C1 is the sensor equivalent capacitance.
Furthermore, the ultrasound signal may also be received by:
a large resistor R1 is connected in series to the capacitor loop, so that the time constant of the loop is much larger than the frequency of the ultrasonic signal, and it can be considered that the charge amount of the capacitor remains unchanged during the receiving process, according to the formula:
it is known that an alternating voltage signal is generated across the capacitor, also characterizing the ultrasonic signal. The receiving circuit topology of this receiving mode is shown in fig. 4.
The first embodiment is as follows: an ultrasonic sensor for measuring the axial force of a bolt comprises a metal pole plate 4, a medium layer 5, a liquid film 6 and a tested bolt test piece 7.
In the embodiment, the metal polar plate 4 is a circle with the radius of 10mm, the thickness of the metal polar plate is 2mm, and the metal polar plate is made of pure copper; the dielectric layer 5 is barium titanate ceramic, the thickness is 0.15mm, and the dielectric constant is about 25000; the metal polar plate 4 and the dielectric layer 5 are tightly combined together through a vacuum coating process; the liquid film 6 is pure water; the relative dielectric constant of the pure water is 81, the pure water is far larger than other common liquids, and the pure water is non-toxic and harmless, so that the effect of removing air between the dielectric layer 5 and the tested bolt test piece 7 is achieved, the equivalent capacitance C1 of the sensor can be greatly increased, the electrostatic force is increased, and the excitation intensity of ultrasonic waves is increased.
The embodiment provides a transmitting-receiving integrated ultrasonic sensor, and when the sensor is connected with a measuring device, a duplexer 3 is required to be connected to ensure that an excitation device 2 and a receiver 1 can work normally. The structure schematic diagram of the measuring device is shown in fig. 1, wherein the peak-to-peak value of the excitation voltage of the excitation equipment 2 is 600V, square wave and excitation frequency is 2 MHz; the receiver 1 adopts the receiving topology shown in fig. 4, the dc bias voltage is 100V, and R1 takes 500k Ω.
Example two: the difference from the first embodiment is that the present embodiment adopts a structure of two concentric circular metal plates for exciting and receiving ultrasonic waves, respectively, so as to achieve the effects of replacing a duplexer and simplifying a measuring device. The remaining design remains consistent with the embodiments.
Although the embodiments of the present invention have been described above, the above descriptions are only for the convenience of understanding the present invention, and are not intended to limit the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (8)
1. An ultrasonic sensor for measuring bolt axial force is characterized by comprising a metal pole plate (4), a medium layer (5), a liquid film (6) and a tested bolt test piece (7); the metal polar plate (4) and the dielectric layer (5) are arranged on the upper surface of the tested bolt test piece (7) in parallel, and the lower surface of the metal polar plate (4) is fixed on the upper surface of the dielectric layer (5); the liquid film (6) is coated on the lower surface of the medium layer (5) and the upper surface of the tested bolt test piece (7); connecting the sensor into a test device by taking the metal polar plate (4) as a positive pole and the tested bolt test piece (7) as a negative pole;
the metal polar plate (4) is a whole flat plate or is formed by sleeving an inner ring flat plate (401) and an outer ring flat plate (402).
2. The ultrasonic sensor for measuring the axial force of the bolt as claimed in claim 1, wherein the metal plate (4) is circular or regular N-sided polygon, and N is a natural number greater than or equal to 3.
3. The ultrasonic sensor for measuring the bolt axial force is characterized in that when the metal pole plate (4) is a whole flat plate, the testing device comprises a receiver (1), an excitation device (2) and a duplexer (3), a square wave excitation signal sent by the excitation device (2) is sent to the metal pole plate (4) through the duplexer (3) and is transmitted to a tested bolt test piece (7), ultrasonic waves excited on the surface of the tested bolt test piece (7) are transmitted back to the receiver (1), and the measurement of the bolt axial force is completed.
4. The ultrasonic sensor for measuring the bolt axial force is characterized in that when the metal pole plate (4) is of an inner ring and outer ring sleeved structure, the testing device comprises a receiver (1) and an excitation device (2), a square wave excitation signal emitted by the excitation device (2) is transmitted to a tested bolt test piece (7), and ultrasonic waves excited on the surface of the tested bolt test piece (7) are transmitted back to the receiver (1) to complete measurement of the bolt axial force.
5. The ultrasonic sensor for bolt axial force measurement according to claim 1, wherein the metal plate (4) is at least one of gold, silver, copper and aluminum; the thickness of the metal polar plate (4) is 1 micrometer to 10 millimeters.
6. The ultrasonic sensor for bolt axial force measurement according to claim 1, wherein the relative dielectric constant of the material of the dielectric layer (5) is greater than or equal to 100;
the main component of the material of the dielectric layer (5) is at least one of barium titanate, iron-doped strontium titanate and copper calcium carbonate;
the thickness of the dielectric layer (5) is 1 micrometer to 10 millimeters.
7. An ultrasonic sensor for bolt axial force measurement according to claim 1, characterized in that the material of the liquid film (6) is pure water or an aqueous solution with a water mass fraction of more than 50%.
8. The ultrasonic sensor for measuring the axial force of the bolt as recited in claim 1, wherein the metal pole plate (4) and the dielectric layer (5) are tightly combined by a coating process.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010674820.4A CN111780911B (en) | 2020-07-14 | 2020-07-14 | Ultrasonic sensor for measuring bolt axial force |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010674820.4A CN111780911B (en) | 2020-07-14 | 2020-07-14 | Ultrasonic sensor for measuring bolt axial force |
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| CN111780911A CN111780911A (en) | 2020-10-16 |
| CN111780911B true CN111780911B (en) | 2022-05-24 |
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| CN113405718B (en) * | 2021-05-20 | 2022-11-11 | 华东理工大学 | Ultrasonic probe for online measurement of high-temperature bolt axial force |
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