Bolt axial force measuring method self-adaptive to cable length

Abstract

The invention discloses a cable length self-adaptive bolt axial force measurement method, and relates to the technical field of bolt axial force measurement, and a system comprises a target ultrasonic transducer, a measurement terminal and an upper computer, the target ultrasonic transducer comprises an ultrasonic transduction sheet used for transmitting and receiving ultrasonic waves, a temperature measuring resistor used for sensing the temperature of a target bolt to be measured, and a ceramic resonance sheet used for enhancing and amplifying ultrasonic signals; the measurement terminal performs time-sharing execution by switching the connection combination of each core wire in the target three-core cable: measuring the resistance of the target three-core cable to obtain cable length data; measuring the loop resistance including the temperature measuring resistor to obtain current bolt temperature data; the ultrasonic transduction piece is excited with low energy, and returned echo signals are collected to obtain ultrasonic data; and the upper computer obtains the current axial force value of the target to-be-measured bolt according to the cable length data, the current bolt temperature data and the ultrasonic data. By implementing the technical scheme, the effect of improving the measurement precision and efficiency is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultrasonic measurement, in particular to a bolt axial force measurement method with adaptive cable length. BACKGROUND

[0002] High-strength bolts are widely used for key connections in wind turbines, large bridges and building structures, etc. To ensure the safety of the structure, it is crucial to monitor the pre-tightening force (axial force) of these bolts accurately and for a long time. Wind power, as one of the main components of new energy, has developed rapidly in recent years. Wind farms have developed from land to sea, and single wind turbines have developed from a few hundred kilowatts to tens of megawatts, even to twenty-some megawatts. The overall trend of wind turbines is high power, long blades, and high towers. The wind turbine tower and the blade root connecting bolt are the basic components of the wind turbine and the basis for the operation of the wind turbine. During operation, the wind turbine tower and the blade root connecting bolt are often loose due to the combined effects of long-term vibration, torsion, shear, extrusion, bending and torsional loads, etc. If the fault is not discovered in time, it will cause accidents of wind turbine generators and cause huge economic losses, and in severe cases, it will also cause personal injury accidents.

[0003] For wind turbine tower and blade root connecting bolt axial force monitoring, the main technical means currently used are ultrasonic distance pre-stress principle, magnetic rotation angle principle, and line displacement end face monitoring principle. In the existing ultrasonic bolt axial force measurement technology, the cable length between the transducer and the measurement terminal needs to be measured manually on site and manually input into the system, which not only increases the on-site workload, but also introduces errors due to complex environments or human operation. At the same time, changes in bolt temperature will cause thermal expansion and contraction and changes in ultrasonic wave speed, and the existing technology is difficult to synchronously collect bolt temperature and accurately correct, resulting in axial force measurement results being disturbed by temperature and cable length factors, and the measurement accuracy and efficiency cannot meet the monitoring needs of actual engineering. SUMMARY

[0004] To solve the above technical problems, the present application provides a bolt axial force measurement method with adaptive cable length.

[0005] In a first aspect, the application provides a bolt axial force measurement method for adaptive cable length, applied to a bolt axial force measurement system, the bolt axial force measurement system comprising a target ultrasonic transducer, a measurement terminal and an upper computer, the target ultrasonic transducer comprising an ultrasonic transducer sheet for transmitting and receiving ultrasonic waves, a temperature sensing resistance for sensing the temperature of a target bolt to be measured, and a ceramic resonator sheet for ultrasonic signal enhancement and amplification; the measurement terminal is connected with the target three-core interface of the target ultrasonic transducer through a target three-core cable, and the measurement terminal performs the following steps by switching the connection combination of each core wire in the target three-core cable: measuring the resistance of the target three-core cable to obtain cable length data; measuring the loop resistance containing the temperature sensing resistance to obtain current bolt temperature data; exciting the ultrasonic transducer sheet and collecting the returned echo signal to obtain ultrasonic data; the upper computer is in communication connection with the measurement terminal, and is used for calculating the propagation time of ultrasonic waves in the target bolt to be measured according to the cable length data, the current bolt temperature data and the ultrasonic data, and obtaining the current axial force value based on the axial force calibration curve corresponding to the target bolt to be measured based on the propagation time.

[0006] By adopting the above technical solution, the target ultrasonic transducer integrates the ultrasonic transducer sheet, the temperature sensing resistance and the ceramic resonator sheet, realizes the integrated function of ultrasonic transmission / reception, temperature sensing and ultrasonic enhancement and amplification, has the core functions of ultrasonic transmission / reception and bolt temperature sensing, and is precisely matched with the target three-core cable through the target three-core interface, thereby providing a hardware basis for multi-dimensional data acquisition; the measurement terminal switches the core wire connection combination of the three-core cable to form a targeted measurement loop with the target ultrasonic transducer, and performs the cable length measurement, temperature measurement and ultrasonic data acquisition steps in time, so as to automatically obtain the cable length data, the current bolt temperature data and the ultrasonic data of the target three-core cable, thereby avoiding the workload and errors caused by manual cable length measurement; the cable length data, the current bolt temperature data and the ultrasonic data are transmitted to the upper computer, the upper computer calculates the propagation time of ultrasonic waves in the target bolt to be measured based on these data, and obtains the current axial force value of the target bolt to be measured based on the axial force calibration curve corresponding to the target bolt to be measured based on the propagation time, thereby effectively reducing the interference of temperature and cable length factors on the axial force measurement result, and achieving the effects of improving the measurement accuracy and efficiency.

[0007] Optionally, the target ultrasonic transducer is a packaging structure integrated with a ceramic resonant sheet, an ultrasonic transduction sheet and a temperature measuring resistor, the ultrasonic transduction sheet and the temperature measuring resistor are fixed on the upper surface of the ceramic resonant sheet, the lower surface of the ceramic resonant sheet is fixed on the top of the target bolt to be measured through coupling glue, the first electrode of the ultrasonic transduction sheet and one pole of the temperature measuring resistor are connected together to the first pin of the target three-core interface through a copper wire, the second electrode of the ultrasonic transduction sheet and the other pole of the temperature measuring resistor are connected together to form a negative connection point, and at the same time, the two copper wires are connected to the second pin and the third pin of the target three-core interface from the negative connection point, respectively, the lower surface of the ceramic resonant sheet is flush with the edge of the shell of the packaging structure, and the target three-core interface extends from the back of the shell of the packaging structure.

[0008] By adopting the above technical scheme, the ceramic resonant sheet, the ultrasonic transduction sheet and the temperature measuring resistor are integrated and packaged, which is convenient for installation and use; the ultrasonic transduction sheet and the temperature measuring resistor are fixed on the upper surface of the ceramic resonant sheet, and the lower surface of the ceramic resonant sheet is fixed on the top of the target bolt to be measured through coupling glue, which can effectively transmit ultrasonic signals and collect temperature; the reasonable electrode and pin connection mode, in combination with the connection of the target three-core cable and the target three-core connector, can realize the core line connection combination switching of each function; the lower surface of the ceramic resonant sheet is flush with the edge of the shell of the packaging structure, and the target three-core interface extends from the back of the shell of the packaging structure, which ensures the compactness and stability of the structure and is conducive to accurate measurement of bolt axial force and temperature.

[0009] Optionally, the thickness of the ceramic resonant sheet is 0.3mm, the working frequency of the ultrasonic transduction sheet is 2MHz, and the frequency of the ceramic resonant sheet and the ultrasonic transduction sheet is matched to realize resonance amplification.

[0010] By adopting the above technical scheme, the thickness of the ceramic resonant sheet is set to 0.3mm, the working frequency of the ultrasonic transduction sheet is set to 2MHz, and the frequency of the two is matched to realize resonance amplification, which enhances the ultrasonic signal and improves the accuracy and reliability of bolt axial force measurement.

[0011] Optionally, the target three-core cable includes a first core wire, a second core wire and a third core wire; the resistance of the target three-core cable is measured to obtain cable length data, specifically including: injecting a preset constant current to the second core wire, and measuring the current of the third core wire and the first voltage between the second core wire and the third core wire; if the current of the third core wire is equal to the preset constant current, then the first resistance value is calculated according to the first voltage and the preset constant current; the cable length data is calculated based on the first resistance value and a preset cable resistance rate, wherein the preset cable resistance rate is used to represent the resistance value of a single core unit length of the target three-core cable; the loop resistance containing the temperature measurement resistance is measured to obtain current bolt temperature data, specifically including: injecting a preset constant current to the first core wire, and measuring the second voltage between the first core wire and the second core wire; the second resistance value is calculated according to the second voltage and the preset constant current; the second resistance value is subtracted from the first resistance value to obtain the temperature measurement resistance value; the current bolt temperature data is obtained by querying the preset temperature resistance corresponding relationship table according to the temperature measurement resistance value, wherein the preset temperature resistance corresponding relationship table records the resistance value relationship corresponding to the temperature measurement resistance at different temperatures; the ultrasonic transducer sheet is excited and the returned echo signal is collected to obtain ultrasonic data, specifically including: sending an ultrasonic trigger pulse to the ultrasonic transducer sheet, so that the ultrasonic transducer sheet sends a target ultrasonic signal of a preset frequency to the target bolt to be measured; the returned ultrasonic data is collected, wherein the ultrasonic data is the reflected echo beam signal obtained by converting the ultrasonic signal reflected by the ultrasonic transducer sheet to the target bolt to be measured; the upper computer calculates the propagation time of the ultrasonic wave in the target bolt to be measured according to the cable length data, the current bolt temperature data and the ultrasonic data, and obtains the current axial force value based on the propagation time and the axial force calibration curve corresponding to the target bolt to be measured, including: calculating the total propagation time from sending the ultrasonic trigger pulse to receiving the ultrasonic data; calculating the transmission delay of the ultrasonic trigger pulse and the reflected echo beam in the target three-core cable based on the cable length data and the current bolt temperature data; calculating the propagation time of the ultrasonic wave in the target bolt to be measured according to the total propagation time and the transmission delay; calculating the current length of the target bolt to be measured according to the propagation time; obtaining the current axial force value corresponding to the current length according to the axial force calibration curve corresponding to the target bolt to be measured which is calibrated in advance.

[0012] By adopting the technical scheme, the length of the target three-core cable can be automatically acquired, accurate measurement of the target bolt temperature to be measured can be realized, and collection of ultrasonic wave data can be realized, thereby avoiding manual field measurement of the cable length and manual input of the system, reducing field workload, avoiding errors caused by complex environment or human operation, and improving the accuracy and efficiency of bolt axial force measurement; the total propagation time from sending an ultrasonic wave trigger pulse to receiving ultrasonic wave data can be accurately calculated, the transmission time delay of the ultrasonic wave trigger pulse and the reflected echo beam in the target three-core cable can be accurately calculated in combination with cable length data and current bolt temperature data, the propagation time of the ultrasonic wave in the target bolt to be measured can be obtained, the current length of the target bolt to be measured can be calculated according to the propagation time, and finally the current axial force value of the target bolt to be measured can be obtained according to the axial force calibration curve corresponding to the target bolt to be measured which is pre-calibrated, thereby reducing the interference of the cable length and temperature factors on the axial force measurement result and improving the measurement accuracy and efficiency.

[0013] Optionally, the total propagation time from sending an ultrasonic wave trigger pulse to receiving ultrasonic wave data comprises: performing digital band-pass filtering calculation on the collected ultrasonic wave data in a frequency band range of 1.45MHz-2.8MHz, and then performing Hilbert transform processing on the filtered data to obtain an ultrasonic wave reflected echo beam; calculating a sampling point serial number n of the reflected echo beam according to a starting serial number of the reflected echo beam determined by the Hilbert transform; and calculating the total propagation time Δt according to the sampling point serial number n and a preset waveform sampling period Ts t =n*Ts. Based on the cable length data and the current bolt temperature data, the transmission time delay of the ultrasonic wave trigger pulse and the reflected echo beam in the target three-core cable is calculated, which comprises: calculating the transmission time delay according to the following formula: Δt d =L / (V d ), wherein Δt d is the transmission time delay, L is the cable length data, V d is the propagation speed of the ultrasonic wave trigger pulse and the reflected echo beam in the target three-core cable which is obtained by pre-calibration and is compensated by the current bolt temperature data; the propagation time of the ultrasonic wave in the target bolt to be measured is calculated according to the total propagation time and the transmission time delay, which comprises: calculating the propagation time according to the following formula: Δt=(Δt t -Δt d ) / 2, wherein Δt represents the one-way propagation time of the ultrasonic wave in the target bolt to be measured; the current length of the target bolt to be measured is calculated according to the propagation time, which comprises: calculating the current length of the target bolt to be measured according to the following formula: L t =Δt×V u , wherein L t represents the current length, and V urepresents the propagation speed of the ultrasonic wave in the target bolt to be measured after the current bolt temperature data correction; the current axial force value corresponding to the current length is obtained according to the axial force calibration curve corresponding to the target bolt to be measured calibrated in advance, including: the current axial force value is obtained according to the following axial force calibration curve: F=k x (L t -L0), wherein F represents the current axial force value, k is the elastic coefficient of the bolt in the same batch as the target bolt to be measured obtained by calibration, L t represents the current length, and L0 represents the length of the target bolt to be measured in a natural state determined during calibration.

[0014] By adopting the above technical scheme, the collected ultrasonic wave data is subjected to digital band-pass filtering calculation in a specific frequency band range and Hilbert transform processing, which can effectively filter out interference signals and accurately obtain the ultrasonic reflection echo beam; the sample point sequence number is calculated according to the starting index of the reflection echo beam determined by the Hilbert transform, and the total propagation time is calculated in combination with the preset waveform sampling period, which can improve the accuracy of the total propagation time calculation and further improve the accuracy of the current axial force value calculation of the target bolt to be measured. In combination with the target length data of the target three-core cable and the propagation speed of the reflection echo beam in the target three-core cable after the current temperature data correction compensation, the transmission time delay of the ultrasonic trigger pulse and the reflection echo beam in the target three-core cable is accurately calculated, thereby providing a basis for subsequent accurate calculation of the ultrasonic propagation time in the target bolt to be measured and the current axial force value of the target bolt to be measured, effectively reducing the interference of the cable length and temperature factors on the axial force measurement result and improving the measurement accuracy. Multiplying the propagation speed of the ultrasonic wave in the target bolt to be measured after the current temperature data correction by the ultrasonic propagation time can accurately calculate the current length of the target bolt to be measured, thereby providing a basis for subsequent accurate calculation of the current axial force value of the target bolt to be measured, reducing the measurement error caused by temperature changes, and improving the accuracy of the bolt axial force measurement. According to the axial force calibration curve of the target bolt to be measured calibrated in advance, in combination with the elastic coefficient of the bolt in the same batch as the target bolt to be measured, the current length of the target bolt to be measured and the length in a natural state, the current axial force value of the target bolt to be measured can be accurately obtained.

[0015] Optionally, before obtaining the current axial force value according to the axial force calibration curve, the step of temperature correcting the natural state length L0 of the target bolt to be measured by using a temperature influence coefficient a is further included, specifically: the natural state length L 0T of the bolt at the actual temperature is calculated by the formula L 0T , wherein a is a temperature influence coefficient obtained by comparing the axial force calibration curves at different temperatures, T is the current temperature data of the target bolt to be measured, and T0 is the standard temperature when the above axial force calibration curve is calibrated; the corrected L 0T is substituted into the deformation and axial force relationship formula F=k x (Lt L0) to obtain the current axial force value F=k x (L t L0) to obtain the current axial force value F=k x (L 0T )。

[0016] By adopting the above technical scheme, the temperature influence coefficient can be used to correct the natural state length of the target bolt to be measured, and then the natural state length of the bolt at the actual temperature is obtained, which is substituted into the deformation and axial force relationship to obtain the current axial force value after temperature correction, thereby reducing the interference of temperature on the axial force measurement result and improving the accuracy of the axial force measurement.

[0017] Optionally, the above method further includes a system calibration step, which specifically includes: at a first preset environmental temperature, applying a plurality of different known tensions to the calibration bolt through the tension test platform, recording each tension value and the corresponding calibration bolt length, and obtaining a plurality of first calibration data, wherein the calibration bolt is of the same specification as the target bolt to be measured; at a second preset environmental temperature, applying a plurality of different known tensions to the calibration bolt through the tension test platform, recording each tension value and the corresponding calibration bolt length, and obtaining a plurality of second calibration data; fitting a first axial force calibration curve at the first preset environmental temperature based on the plurality of first calibration data, and fitting a second axial force calibration curve at the second preset environmental temperature based on the plurality of second calibration data; comparing the first axial force calibration curve and the second axial force calibration curve to calculate the temperature influence coefficient a.

[0018] By adopting the above technical scheme, a plurality of calibration data is obtained by applying different known tensions to the calibration bolt at different preset environmental temperatures, and the axial force calibration curves at different temperatures are fitted, and the temperature influence coefficient can be calculated by comparing the axial force calibration curves at different temperatures, so that the natural state length of the target bolt to be measured can be corrected, and the accuracy of the bolt axial force measurement is improved to better meet the monitoring needs of actual engineering.

[0019] Optionally, the measurement terminal includes: a channel selection module, a group of core line switching modules, and a group of three-core aviation plugs, each core line switching module is connected between an output end of the channel selection module and a corresponding three-core aviation plug, and is used to switch the connection combination of different core lines in the three-core aviation cable associated with the corresponding three-core aviation plug, the target three-core aviation plug is any one of the group of three-core aviation plugs, and each three-core aviation plug corresponds to a route of the ultrasonic transducer; the measurement terminal selects the target core line switching module from the group of core line switching modules by using the channel selection module, and the target core line switching module switches the connection combination of different core lines in the target three-core aviation cable through the target three-core aviation plug.

[0020] By adopting the technical scheme, the measurement terminal can select a target core line switching module from a group of core line switching modules by using the channel selection module, and switch the connection combination of different core lines in the target three-core cable by the target three-core jack, so as to realize the adaptation to multiple groups of ultrasonic transducers, and measure multiple target bolts at the same time, thereby improving the applicability and measurement efficiency of the bolt axial force measurement system.

[0021] Optionally, the measurement terminal further comprises an ultrasonic trigger pulse module, an ultrasonic waveform acquisition module and a resistance measurement module, wherein the measurement terminal measures the first resistance and the second resistance by using the resistance measurement module; and the measurement terminal transmits an ultrasonic trigger pulse to the ultrasonic transducer through the first core line and the second core line by using the ultrasonic trigger pulse module, and starts the ultrasonic waveform acquisition module to collect returned ultrasonic data at a preset sampling rate.

[0022] By adopting the technical scheme, the measurement terminal can accurately measure the first resistance value and the second resistance value by using the resistance measurement module, thereby providing a basis for obtaining the target length data of the target three-core cable and the current temperature data of the target bolt to be measured; and the measurement terminal transmits an ultrasonic trigger pulse to the ultrasonic transducer through the first core line and the second core line by using the ultrasonic trigger pulse module, and starts the ultrasonic waveform acquisition module to collect returned ultrasonic data at a preset sampling rate, thereby effectively collecting ultrasonic data and providing necessary data for the host computer to calculate the current axial force value of the target bolt to be measured.

[0023] To sum up, the one or more technical solutions provided in the present application have at least the following technical effects or advantages: the measurement terminal performs the cable length measurement, temperature measurement and ultrasonic data acquisition steps in time, can automatically obtain the target length data of the target three-core cable and the current temperature data of the target bolt to be measured, and avoids the workload and errors caused by manual cable length measurement; the target length data, the current temperature data and the ultrasonic data are transmitted to the host computer, and the host computer calculates the current axial force value of the target bolt to be measured based on these data, thereby effectively reducing the interference of the temperature and cable length factors on the axial force measurement result, achieving the effects of improving the measurement accuracy and efficiency; and the bolt axial force measurement can be adapted to different cable lengths. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a bolt axial force measurement method flowchart provided by an embodiment of the present application; Figure 2 is an architecture diagram of a bolt axial force measurement system provided by an embodiment of the present application; Figure 3 is an ultrasonic axial force measurement principle diagram provided by an embodiment of the present application; Figure 4A structural schematic diagram of a combined ultrasonic transducer is provided in an embodiment of the present application. Figure 5 An adaptive cable length calculation electrical principle schematic diagram is provided in an embodiment of the present application. DETAILED DESCRIPTION

[0025] In order for those skilled in the art to better understand the technical solutions in the specification, the technical solutions in the specification will be clearly and completely described below in combination with the drawings in the embodiments of the specification. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments.

[0026] In the description of the embodiments of the present application, the words such as "for example" or "for instance" are used to represent an example, illustration or description. Any embodiment or design scheme described as "for example" or "for instance" in the embodiments of the present application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. Rather, the words such as "for example" or "for instance" are intended to present the relevant concept in a specific manner.

[0027] In the description of the embodiments of the present application, the term "a plurality of" means two or more. In addition, the terms "first", "second" are used for description purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the indicated technical features. Therefore, the features defined with "first", "second" can be explicitly or implicitly included one or more features. The terms "include", "contain", "have" and their variants mean "include but are not limited to", unless otherwise specifically emphasized.

[0028] The present application provides a bolt axial force measurement method of adaptive cable length, applied to a bolt axial force measurement system, the bolt axial force measurement system comprising a target ultrasonic transducer, a measurement terminal and an upper computer, the target ultrasonic transducer comprising an ultrasonic transducer sheet for transmitting and receiving ultrasonic waves, a temperature measurement resistance for sensing the temperature of a target bolt to be measured, and a ceramic resonant sheet for ultrasonic signal enhancement and amplification; the measurement terminal is connected with the target three-core interface of the target ultrasonic transducer through a target three-core cable, and the measurement terminal performs the following steps by switching the connection combination of each core wire in the target three-core cable in time: Figure 1 , Figure 1 A bolt axial force measurement method of adaptive cable length is provided in an embodiment of the present application, comprising: Step S101, measuring the resistance of the target three-core cable to obtain cable length data; Step S102, measuring the loop resistance containing the temperature measurement resistance to obtain current bolt temperature data; Step S103, the ultrasonic transducer is excited and the returned echo signal is collected to obtain ultrasonic data; Step S104, the host computer is in communication connection with the measurement terminal, and is used for calculating the propagation time of the ultrasonic wave in the target bolt to be measured according to the cable length data, the current bolt temperature data and the ultrasonic data, and obtaining the current axial force value based on the propagation time and the axial force calibration curve corresponding to the target bolt to be measured.

[0029] Through the above steps, the target ultrasonic transducer integrates the ultrasonic transducer sheet, the temperature measurement resistance and the ceramic resonator sheet, realizes the integrated function of ultrasonic transmission / reception, temperature sensing and ultrasonic signal enhancement and amplification, has the core functions of ultrasonic transmission / reception and bolt temperature sensing, and is accurately matched with the target three-core cable through the target three-core interface, thereby providing a hardware basis for multi-dimensional data acquisition; the measurement terminal forms a targeted measurement loop with the target ultrasonic transducer through switching the core line connection combination of the three-core cable, and executes the cable length measurement, temperature measurement and ultrasonic data collection steps in time, so as to automatically obtain the cable length data, the current bolt temperature data and the ultrasonic data of the target three-core cable, thereby avoiding the workload and errors caused by manual cable length measurement. Since the ceramic resonator sheet is used, the ultrasonic transducer sheet can be excited with low energy in the ultrasonic data collection. The cable length data, the current bolt temperature data and the ultrasonic data are transmitted to the host computer, the host computer calculates the propagation time of the ultrasonic wave in the target bolt to be measured based on these data, and obtains the current axial force value of the target bolt to be measured based on the propagation time and the axial force calibration curve corresponding to the target bolt to be measured, thereby effectively reducing the interference of temperature and cable length factors on the axial force measurement result, and achieving the effects of improving the measurement accuracy and efficiency.

[0030] The framework diagram of the bolt axial force measurement system is as shown in Figure 2As shown, the embodiment provides a bolt axial force measurement method with adaptive cable length, which realizes the purpose of automatically obtaining cable length data, current bolt temperature data and ultrasonic data of the target three-core cable by measuring the cooperation of the terminal and the target ultrasonic transducer, and finally obtains the current axial force value of the target bolt to be measured according to these data by the upper computer. Relying on the core line connection combination switching technology of the three-core cable, the three major core steps of cable length measurement, bolt temperature measurement and ultrasonic data acquisition are completed in the same bolt axial force measurement system in time, and finally the precise calculation of the bolt axial force is realized in combination with multi-dimensional data. Specifically, the actual length of the target three-core cable can be calculated by the correlation between the total resistance of the second and third core lines and the cable resistivity without manual measurement; the current resistance value of the temperature measurement resistance in the target ultrasonic transducer is inversely deduced by combining the core line resistance value obtained by cable length measurement and the total resistance of the loop formed by the first and second core lines and the temperature measurement resistance, and then the real-time temperature of the target bolt to be measured is converted; the cable length data, current bolt temperature data and ultrasonic data are uploaded to the upper computer by the first and second core lines to complete ultrasonic triggering and data acquisition, the upper computer can also correct the ultrasonic wave speed in combination with the current bolt temperature data, and finally the current axial force value of the bolt is obtained by the propagation time of the ultrasonic wave in the bolt and the corresponding axial force calibration curve of the target bolt to be measured. The axial force calibration curve is the relationship between the axial force value of the bolt and the bolt length, the current length of the target bolt to be measured can be calculated according to the propagation time, and then the current axial force value of the target bolt to be measured can be obtained by querying the corresponding axial force calibration curve. In related technologies, the cable length needs to be measured manually and input into the system, which not only increases the field workload, but also easily introduces errors due to complex environment or human operation. The cable length is automatically calculated by resistance measurement in the embodiment, which eliminates the manual operation link and solves the error and efficiency pain points of manual measurement; in addition, it is difficult to synchronously collect the bolt temperature and accurately correct the influence of the ultrasonic wave speed and the thermal expansion and contraction of the bolt in related technologies. The temperature measurement resistance built-in the target ultrasonic transducer is used to realize the synchronous collection of the bolt temperature by the core line loop resistance measurement, which provides a data basis for subsequent temperature correction and solves the problem of insufficient measurement accuracy caused by temperature interference. Through the embodiment, the cable length measurement is automatically completed, the steps of manual field measurement and manual input are eliminated, the field workload is reduced, and the field execution efficiency of the bolt axial force measurement is greatly improved; on the one hand, the manual measurement error is avoided by automatically measuring the cable length, and on the other hand, the influence of the temperature and the cable length on the axial force measurement result is effectively reduced by synchronously collecting the bolt temperature and correcting the ultrasonic wave speed and the thermal expansion and contraction of the bolt according to the bolt temperature, which improves the accuracy of the axial force measurement; the cable length, temperature and ultrasonic data are collected in time relying on the core line switching of the same three-core cable, without the need for additional measurement equipment or lines, which simplifies the structure of the measurement system, improves the integration and practicality of the system, and is more suitable for long-term monitoring needs in complex engineering scenes such as wind power.The measurement method of the embodiment can adaptively measure bolt axial force of different cable lengths.

[0031] In an optional embodiment, the target ultrasonic transducer is a packaging structure integrated with a ceramic resonant sheet, an ultrasonic transducer sheet and a temperature measuring resistor. The ultrasonic transducer sheet and the temperature measuring resistor are fixed on the upper surface of the ceramic resonant sheet. The lower surface of the ceramic resonant sheet is fixed on the top of the target bolt to be measured through coupling glue. The first electrode of the ultrasonic transducer sheet and one pole of the temperature measuring resistor are connected together to the first pin of the target three-core interface through a copper wire. The second electrode of the ultrasonic transducer sheet and the other pole of the temperature measuring resistor are connected together to form a negative connection point. At the same time, two copper wires are used to connect the negative connection point to the second pin and the third pin of the target three-core interface. The lower surface of the ceramic resonant sheet is flush with the edge of the shell of the packaging structure. The target three-core interface extends from the back of the shell of the packaging structure.

[0032] In the above embodiment, as shown in Figure 4 , the ceramic resonant sheet, the ultrasonic transducer sheet and the temperature measuring resistor (such as PT1000 in Figure 4 ) are integrated and packaged, which is convenient for installation and use. The ultrasonic transducer sheet and the temperature measuring resistor are fixed on the upper surface of the ceramic resonant sheet. The lower surface of the ceramic resonant sheet is fixed on the top of the target bolt to be measured through coupling glue, which can effectively transmit ultrasonic signals and collect temperature. The reasonable electrode and pin connection mode, in combination with the connection of the target three-core cable and the target three-core connector, can realize the core line connection combination switching of each function. The lower surface of the ceramic resonant sheet is flush with the edge of the shell of the packaging structure. The target three-core interface extends from the back of the shell of the packaging structure, which ensures the compactness and stability of the structure and is conducive to accurate measurement of bolt axial force and temperature.

[0033] The target ultrasonic transducer realizes ultrasonic transmission and reception and temperature sensing functions simultaneously through integrated packaging design and multiplexing wiring of the core wire interface. Specifically, the target ultrasonic transducer adopts a packaging structure, which internally integrates a ceramic resonant sheet, an ultrasonic transducer sheet and a temperature measuring resistor. The ultrasonic transducer sheet and the temperature measuring resistor are fixed on the upper surface of the ceramic resonant sheet, and the lower surface of the ceramic resonant sheet is attached to the top of the bolt to be measured through coupling glue. The ceramic resonant sheet transmits ultrasonic signals through its acoustic properties, and the temperature measuring resistor senses the temperature of the target bolt to be measured through its thermal conductivity properties. The first electrode of the ultrasonic transducer sheet is connected to one pole of the temperature measuring resistor and connected to the first pin of the target three-core interface, corresponding to the first core wire of the target three-core cable. The second electrode of the ultrasonic transducer sheet and the other pole of the temperature measuring resistor form a common terminal and are connected to the second and third pins of the target three-core interface, respectively, corresponding to the second and third core wires of the target three-core cable. This wiring method realizes the core wire multiplexing of the target three-core interface for ultrasonic transmission and reception and temperature measurement, without the need for additional wiring. The lower surface of the ceramic resonant sheet is flush with the edge of the packaging shell, ensuring the sealing property of the attachment to the top of the bolt. The target three-core interface extends from the back of the packaging shell, facilitating the connection with the three-core cable through the aviation plug, and adapting to the space requirements of on-site installation. The ultrasonic transducer sheet, the temperature measuring resistor and the ceramic resonant sheet are integrated in the same packaging structure in the embodiment, realizing the integration of ultrasonic transmission and reception and temperature sensing, without the need for additional temperature sensors, reducing the number of hardware components and the hardware cost and installation complexity of the system. Through the wiring method of core wire interface multiplexing, the three-core cable can be used to realize the circuit connection of ultrasonic data transmission and temperature measurement simultaneously, greatly improving the core wire utilization rate. The simple wiring logic also reduces the difficulty of on-site wiring and fault troubleshooting, adapting to the wiring requirements of complex working conditions such as wind tower and offshore wind turbine.

[0034] In an optional embodiment, the thickness of the ceramic resonant sheet is 0.3 mm, the working frequency of the ultrasonic transducer sheet is 2 MHz, and the frequency of the ceramic resonant sheet and the ultrasonic transducer sheet is matched to realize resonance amplification.

[0035] In the above embodiment, the thickness of the ceramic resonant sheet is set to 0.3 mm, the working frequency of the ultrasonic transducer sheet is set to 2 MHz, and the frequencies of the two are matched to realize resonance amplification, thereby enhancing the ultrasonic signal, reducing the energy requirement of the ultrasonic trigger pulse, and improving the accuracy and reliability of the bolt axial force measurement.

[0036] The thickness of the ceramic resonant sheet is limited to 0.3mm, and the working frequency of the ultrasonic transducer sheet is set to 2MHz. The combination of the thickness and the frequency is an adaptive parameter calculated based on the acoustic characteristics (such as sound speed, natural frequency) of the ceramic material; the natural frequency of the ceramic resonant sheet is determined by factors such as thickness and material, and the 0.3mm thick ceramic resonant sheet matches the 2MHz working frequency of the ultrasonic transducer sheet. When the transducer emits a 2MHz ultrasonic signal, the ceramic resonant sheet will produce mechanical resonance, thereby resonating and amplifying the ultrasonic signal. The amplified ultrasonic signal is transmitted to the top of the bolt to be measured through the lower surface of the ceramic resonant sheet, and the resonant amplification effect reduces the energy loss of the ultrasonic wave at the contact interface between the transducer and the bolt, allowing the ultrasonic wave to propagate more efficiently within the bolt and form a clear reflection echo.

[0037] In an optional embodiment, the target three-core cable includes a first core, a second core and a third core; the resistance of the target three-core cable is measured to obtain cable length data, specifically including: injecting a preset constant current into the second core, while measuring the current of the third core and the first voltage between the second core and the third core; if the current of the third core is equal to the preset constant current, then a first resistance value is calculated according to the first voltage and the preset constant current; the cable length data is calculated based on the first resistance value and a preset cable resistance rate, wherein the preset cable resistance rate is used to represent the resistance value per unit length of a single core of the target three-core cable; the loop resistance containing the temperature measurement resistance is measured to obtain current bolt temperature data, specifically including: injecting a preset constant current into the first core, and measuring the second voltage between the first core and the second core; a second resistance value is calculated according to the second voltage and the preset constant current; the second resistance value is subtracted from the first resistance value to obtain a temperature measurement resistance value; the current bolt temperature data is obtained by querying a preset temperature-resistance correspondence table according to the temperature measurement resistance value, wherein the preset temperature-resistance correspondence table records the resistance value relationship corresponding to the temperature measurement resistance at different temperatures; the ultrasonic transducer sheet is excited and the returned echo signal is collected to obtain ultrasonic data, specifically including: sending an ultrasonic trigger pulse to the ultrasonic transducer sheet, so that the ultrasonic transducer sheet sends a target ultrasonic signal of a preset frequency to the target bolt to be measured; the returned ultrasonic data is collected, wherein the ultrasonic data is a reflected echo beam signal obtained by converting the ultrasonic signal reflected by the target bolt to be measured; the upper computer calculates the propagation time of the ultrasonic wave in the target bolt to be measured according to the cable length data, the current bolt temperature data and the ultrasonic data, and obtains the current axial force value based on the propagation time and the axial force calibration curve corresponding to the target bolt to be measured, including: calculating the total propagation time from sending the ultrasonic trigger pulse to receiving the ultrasonic data; calculating the transmission delay of the ultrasonic trigger pulse and the reflected echo beam in the target three-core cable based on the cable length data and the current bolt temperature data; calculating the propagation time of the ultrasonic wave in the target bolt to be measured according to the total propagation time and the transmission delay; calculating the current length of the target bolt to be measured according to the propagation time; obtaining the current axial force value corresponding to the current length according to the axial force calibration curve corresponding to the target bolt to be measured which is calibrated in advance.

[0038] In the above embodiment, the length of the target three-core cable can be automatically acquired, accurate measurement of the target bolt temperature to be measured is realized, and collection of ultrasonic wave data is realized, thereby avoiding manual measurement of the cable length on site and manual input of the system, reducing the workload on site, avoiding errors caused by complex environment or human operation, and improving the accuracy and efficiency of bolt axial force measurement; the total propagation time from sending an ultrasonic wave trigger pulse to receiving ultrasonic wave data can be accurately calculated, the transmission time delay of the ultrasonic wave trigger pulse and the reflected echo beam in the target three-core cable is accurately calculated in combination with cable length data and current bolt temperature data, the propagation time of the ultrasonic wave in the target bolt to be measured is obtained, the current length of the target bolt to be measured is calculated according to the propagation time, and finally the current axial force value of the target bolt to be measured is obtained according to the axial force calibration curve corresponding to the target bolt to be measured which is pre-calibrated, thereby reducing the interference of the cable length and temperature factors on the axial force measurement result and improving the measurement accuracy and efficiency.

[0039] For the cable length data, the second core and the third core in the three-core cable are taken as the exclusive loop for cable length data measurement, a preset constant current is injected into the second core, and the current data of the third core and the first voltage data between the two cores are monitored synchronously; the third core current is equal to the injected preset constant current, which is the key basis for judging that the measurement loop has no abnormality such as open circuit, short circuit and complete current transmission, if the condition is met, the total resistance of the loop composed of the second core and the third core can be accurately calculated according to Ohm's law, that is, the first resistance value; since the resistivity of the cable is an inherent property of its material, it is a preset known parameter, and the physical correlation formula of resistance and length, resistivity can be directly calculated by L=R1 / (2p), wherein p represents the resistance value of the unit length of the single core of the target three-core cable, R1 is the first resistance value, and the target length data of the target three-core cable is finally converted through the first resistance value and the preset cable resistivity. In the related art, the cable length is measured by manual field measurement, which not only has a large workload in complex working conditions such as fan towers and offshore wind farms, but also is easy to introduce errors due to measurement environment obstruction and operation negligence. The embodiment on the one hand excludes the measurement interference caused by loop failure through current consistency verification, and on the other hand, based on Ohm's law and fixed resistivity calculation, avoids subjective errors of manual measurement, makes the cable length data more accurate, and lays a reliable data foundation for correcting the propagation path in subsequent ultrasonic shaft force calculation; the step of current matching verification adds an effective verification barrier to the measurement result, which can automatically avoid invalid measurement caused by hidden problems such as poor line contact and local damage, makes the cable length measurement result more reliable, and meets the harsh needs of long-term outdoor monitoring scenes such as wind power; the whole process does not need manual intervention for calibration or auxiliary measurement, and the measurement terminal can automatically complete the whole process of current injection, data acquisition, effectiveness judgment, resistance and length conversion, further reducing the on-site operation steps, reducing the on-site operation difficulty, and improving the overall bolt shaft force measurement process continuity.

[0040] For the current bolt temperature data, based on the temperature resistance characteristic of the resistance value of the temperature measuring resistance changing with temperature, combined with Ohm's law and the obtained cable core resistance value, the precise conversion of the bolt temperature is realized by electrical measurement and data operation. The specific principle is: a temperature measuring circuit is formed by the first core, the second core and the temperature measuring resistance in the target ultrasonic transducer, the same preset constant current as in the cable length measurement is injected into the first core, and the second voltage between the first core and the second core is measured; according to Ohm's law, the measured second voltage is divided by the preset constant current to obtain the total resistance of the temperature measuring circuit, i.e. the second resistance value (including the resistance of the first and second cores and the resistance value of the temperature measuring resistance); since the total resistance of the second and third cores (the first resistance value) has been obtained in the cable length measurement step, and the core specifications of the three-core cable are consistent and the unit length resistance is the same, the total resistance of the first and second cores can be equivalent to the first resistance value, and the second resistance value is subtracted from the first resistance value to strip the interference of the core resistance and obtain the current resistance value of the temperature measuring resistance; then the temperature resistance characteristic of the temperature measuring resistance is used to pre-establish and store a preset temperature resistance corresponding relationship table (recording the one-to-one correspondence between the resistance value of the temperature measuring resistance and the temperature), and by querying the table, the current resistance value of the temperature measuring resistance is converted into the current temperature data of the target bolt to be measured. By eliminating the long cable lead resistance, which is the largest interference factor, even at the end of a long cable of hundreds of meters, the small resistance change can be accurately measured, so that the real bolt temperature is obtained, which is the premise of realizing high-precision temperature compensation; since the real bolt temperature can be obtained, the host computer can correct the propagation speed of the ultrasonic wave accurately and compensate for the length change of the bolt due to thermal expansion and cold contraction. This makes the final shaft force measurement result basically not affected by the change of environmental temperature or the working temperature of the bolt itself, ensuring the long-term stability and reliability of the monitoring data under various working conditions of the fan operation.

[0041] For the acquisition of ultrasonic data, the ultrasonic reflection principle is used to realize the transmission of ultrasonic signals inside the bolt and the acquisition of echo signals, which is the core data acquisition link of ultrasonic axial force measurement. The specific principle is as follows: the measurement terminal sends an ultrasonic trigger pulse to the target ultrasonic transducer installed at the top of the bolt to be measured through the first core wire and the second core wire. The trigger pulse serves as a start signal to drive the target ultrasonic transducer to transmit target ultrasonic signals to the target bolt to be measured at a predetermined frequency. During the propagation of the ultrasonic signals inside the target bolt to be measured, reflections occur at the end face, internal structure interface, and other positions of the bolt. The reflected ultrasonic signals are received by the target ultrasonic transducer. The target ultrasonic transducer converts the received ultrasonic physical signals (mechanical waves) into reflected echo beam signals in the form of electrical signals. The reflected echo beam signals are the ultrasonic data to be collected, which are received and stored by the measurement terminal. The host computer can use various advanced digital signal processing algorithms to accurately identify the position of the target echo from the complex echo waveform, thereby calculating the ultrasonic flight time with high precision, which is the fundamental of high-precision axial force measurement. The present embodiment uses a single-ended transducer and pulse echo technology, which means that the measurement can be completed by operating only one end of the bolt without the need to modify the bolt structure or install equipment on the other end, achieving online, in-situ, and non-destructive measurement, which is very suitable for on-site monitoring scenarios such as fan bolts that are difficult to access or structurally important.

[0042] For the acquisition of ultrasonic data, the ultrasonic reflection principle is used to realize the transmission of ultrasonic signals inside the bolt and the acquisition of echo signals, which is the core data acquisition link of ultrasonic axial force measurement. The specific principle is as follows: the measurement terminal sends an ultrasonic trigger pulse to the target ultrasonic transducer installed at the top of the bolt to be measured through the first core wire and the second core wire. The trigger pulse serves as a start signal to drive the target ultrasonic transducer to transmit target ultrasonic signals to the target bolt to be measured at a predetermined frequency. During the propagation of the ultrasonic signals inside the target bolt to be measured, reflections occur at the end face, internal structure interface, and other positions of the bolt. The reflected ultrasonic signals are received by the target ultrasonic transducer. The target ultrasonic transducer converts the received ultrasonic physical signals (mechanical waves) into reflected echo beam signals in the form of electrical signals. The reflected echo beam signals are the ultrasonic data to be collected, which are received and stored by the measurement terminal. The host computer can use various advanced digital signal processing algorithms to accurately identify the position of the target echo from the complex echo waveform, thereby calculating the ultrasonic flight time with high precision, which is the fundamental of high-precision axial force measurement. The present embodiment uses a single-ended transducer and pulse echo technology, which means that the measurement can be completed by operating only one end of the bolt without the need to modify the bolt structure or install equipment on the other end, achieving online, in-situ, and non-destructive measurement, which is very suitable for on-site monitoring scenarios such as fan bolts that are difficult to access or structurally important.

[0042] For the acquisition of ultrasonic data, the ultrasonic reflection principle is used to realize the transmission of ultrasonic signals inside the bolt and the acquisition of echo signals, which is the core data acquisition link of ultrasonic axial force measurement. The specific principle is as follows: the measurement terminal sends an ultrasonic trigger pulse to the target ultrasonic transducer installed at the top of the bolt to be measured through the first core wire and the second core wire. The trigger pulse serves as a start signal to drive the target ultrasonic transducer to transmit target ultrasonic signals to the target bolt to be measured at a predetermined frequency. During the propagation of the ultrasonic signals inside the target bolt to be measured, reflections occur at the end face, internal structure interface, and other positions of the bolt. The reflected ultrasonic signals are received by the target ultrasonic transducer. The target ultrasonic transducer converts the received ultrasonic physical signals (mechanical waves) into reflected echo beam signals in the form of electrical signals. The reflected echo beam signals are the ultrasonic data to be collected, which are received and stored by the measurement terminal. The host computer can use various advanced digital signal processing algorithms to accurately identify the position of the target echo from the complex echo waveform, thereby calculating the ultrasonic flight time with high precision, which is the fundamental of high-precision axial force measurement. The present embodiment uses a single-ended transducer and pulse echo technology, which means that the measurement can be completed by operating only one end of the bolt without the need to modify the bolt structure or install equipment on the other end, achieving online, in-situ, and non-destructive measurement, which is very suitable for on-site monitoring scenarios such as fan bolts that are difficult to access or structurally important.

[0043] In an optional embodiment, the total propagation time from sending the ultrasonic trigger pulse to receiving the ultrasonic data is calculated, including: performing digital band-pass filtering calculation on the collected ultrasonic data in the frequency band range of 1.45MHz~2.8MHz, and then performing Hilbert transform processing on the filtered data to obtain an ultrasonic reflection echo beam; determining the starting index of the reflection echo beam according to the Hilbert transform, and calculating the sample point sequence number n of the reflection echo beam; and calculating the total propagation time Δt according to the sample point sequence number n and the preset waveform sampling period Ts t =n*Ts; based on the cable length data and the current bolt temperature data, the transmission delay of the ultrasonic trigger pulse and the reflection echo beam in the target three-core cable is calculated, including: calculating the transmission delay according to the following formula: Δt d =L / (V d ), wherein Δt d is the transmission delay, L is the cable length data, V d is the propagation speed of the ultrasonic trigger pulse and the reflection echo beam in the target three-core cable obtained by pre-calibration and corrected and compensated by the current bolt temperature data; the propagation time of the ultrasonic wave in the target bolt to be measured is calculated according to the total propagation time and the transmission delay, including: calculating the propagation time according to the following formula: Δt=(Δt t -Δt d ) / 2, Δt represents the one-way propagation time of the ultrasonic wave in the target bolt to be measured; the current length of the target bolt to be measured is calculated according to the propagation time, including: calculating the current length of the target bolt to be measured by the following formula: L t =Δt×V u , wherein L t represents the current length, V u represents the propagation speed of the ultrasonic wave in the target bolt to be measured after correction by the current bolt temperature data; the current axial force value corresponding to the current length is obtained according to the pre-calibrated axial force calibration curve of the target bolt to be measured, including: obtaining the current axial force value according to the following axial force calibration curve: F=k×(L t -L0), wherein F represents the current axial force value, k is the elastic coefficient of the bolts of the same batch as the target bolt to be measured obtained by calibration, L t represents the current length, and L0 represents the length of the target bolt to be measured in a natural state determined during calibration.

[0044] In the above embodiment, the collected ultrasonic wave data is subjected to digital band-pass filtering calculation in a specific frequency band range and Hilbert transform processing, which can effectively filter out interference signals and accurately obtain the ultrasonic wave reflection echo beam; the starting index of the reflection echo beam is determined according to the Hilbert transform, and the sample point sequence number is calculated, and then the total propagation time is calculated in combination with the preset waveform sampling period, which can improve the accuracy of the total propagation time calculation and further improve the accuracy of the current axial force value calculation of the target bolt to be measured. In combination with the target length data of the target three-core cable and the propagation speed of the reflection echo beam in the target three-core cable after being compensated by the current bolt temperature data, the transmission time delay of the ultrasonic wave trigger pulse and the reflection echo beam in the target three-core cable is accurately calculated, thereby providing a basis for subsequent accurate calculation of the propagation time of the ultrasonic wave in the target bolt to be measured and the current axial force value of the target bolt to be measured, effectively reducing the interference of the cable length and temperature factors on the axial force measurement result and improving the measurement accuracy. Multiplying the propagation speed of the ultrasonic wave in the target bolt to be measured after being corrected by the current bolt temperature data by the ultrasonic wave propagation time can accurately calculate the current length of the target bolt to be measured, thereby providing a basis for subsequent accurate calculation of the current axial force value of the target bolt to be measured, reducing the measurement error caused by temperature changes, and improving the accuracy of the bolt axial force measurement. The current axial force value of the target bolt to be measured can be accurately obtained according to the axial force calibration curve of the target bolt to be measured calibrated in advance, in combination with the elastic coefficient of the same batch of bolts as the target bolt to be measured, the current length of the target bolt to be measured, and the length in the natural state.

[0045] Regarding the calculation of the total propagation time, the collected original ultrasonic wave data is subjected to digital band-pass filtering in the frequency band range of 1.45MHz~2.8MHz, which is a noise reduction and purification process. It only retains the components close to the frequency of the transmitted "preset frequency target ultrasonic wave signal" (for example, 2MHz), while trying to suppress low-frequency interference (such as power frequency noise and vibration noise) and high-frequency noise (such as circuit white noise) outside the frequency band, thereby significantly improving the signal-to-noise ratio of the echo signal; the filtered data is subjected to Hilbert transform processing, and Hilbert transform can calculate the analytic signal of an amplitude modulation signal, and then obtain the envelope line of the signal. For ultrasonic wave echo, which is a decaying oscillation signal, its envelope line is a smooth and single-peak curve. By finding the starting point or peak point of the envelope line, the arrival time of the echo can be accurately and stably determined, avoiding the problem that the zero-crossing point of the high-frequency oscillation signal is easily affected by noise interference and amplitude. According to the echo starting point determined by the Hilbert transform, the corresponding sample point sequence number n is found; according to the known preset waveform sampling period Ts (i.e. the sampling interval of ADC, such as 100 nanoseconds), the total propagation time Δt t= n*Ts. The best data obtained by experiment in this embodiment is 100MHz sampling rate, Ts=10ns. Digital band-pass filtering eliminates invalid noise signals, making ultrasonic data purer; Hilbert transform realizes accurate positioning of the starting position of the reflected echo beam, avoiding misjudgment of the starting point; combined with the clear sampling parameter conversion formula, the calculation accuracy of the total propagation time is further ensured, laying a reliable foundation for subsequent deduction of cable transmission delay and acquisition of the real propagation time of ultrasonic waves in the bolt; the whole process from filtering, transformation to time conversion is automatically completed by the system without manual intervention, improving the automation level of measurement; it also avoids the result difference brought by different equipment and different operators, improving the standardization level of the measurement method.

[0046] Regarding the calculation of the transmission delay in the target three-core cable, the target length data L obtained in the cable length measurement step is taken as the propagation distance parameter of the electrical signal in the cable; at the same time, the reference propagation speed of the electrical signal in the three-core cable is calibrated in advance through experiment, and the reference speed is corrected and compensated combined with the current bolt temperature data collected, to obtain the temperature-corrected propagation speed V d (The temperature will change the conductive properties of the cable core, and then affect the propagation speed of the electrical signal); the target length L and the corrected propagation speed V d are substituted into the above formula to calculate the transmission delay Δt d of the ultrasonic trigger pulse and the reflected echo beam in the cable. d Δt d refers to the one-way time delay generated by the transmission of the electrical signal (ultrasonic trigger pulse and reflected echo beam) in the target three-core cable. In this embodiment, the propagation speed of the electrical signal in the cable is corrected and compensated by temperature, eliminating the interference of temperature change on the speed parameter; combined with the clear quantitative formula and considering the characteristics of the electrical signal transmission, the delay calculation result is more in line with the actual situation, providing accurate data support for subsequent deduction of the delay and acquisition of the real propagation time of ultrasonic waves in the bolt; the current bolt temperature data is applied to the correction of the cable transmission delay and the propagation speed of ultrasonic waves in the bolt at the same time, realizing the double correction of temperature on the two core links of "cable transmission" and "ultrasonic propagation in the bolt" in the measurement chain, fully eliminating the interference of temperature factors on the axial force measurement, adapting to the temperature fluctuation of wind power and other engineering scenes.

[0047] Regarding the calculation of the current length of the target bolt to be measured, the propagation time Δt of ultrasonic waves in the target bolt to be measured obtained after the deduction of the cable transmission delay by the upper computer is taken as the time parameter, Δt=(Δt t -Δt d ) / 2; at the same time, according to the current bolt temperature data collected, the reference propagation speed of ultrasonic waves in the bolt material is corrected to obtain the temperature-corrected propagation speed V u, the temperature will change the elastic modulus and density of the bolt material, and then affect the ultrasonic wave velocity; the corrected propagation velocity V u is substituted into the formula L t =Δt×Vu, the current length Lt of the target bolt to be measured is directly calculated. The physical logic of the formula is that the propagation distance of ultrasonic wave in the bolt (i.e. the length of the bolt) is equal to the product of its actual propagation velocity and propagation time, which ensures the physical rationality of the length calculation. It should be noted that the propagation time in the embodiment refers to the single-pass propagation time of ultrasonic wave in the target bolt to be measured. By correcting the ultrasonic wave propagation velocity with temperature, the interference of temperature change on the wave velocity is eliminated, and the velocity parameter is more suitable for the actual working condition of the bolt; combined with the explicit physical formula for calculating the length, the error of empirical conversion is avoided, and the calculation result of the current length of the bolt can truly reflect its actual deformation state, laying a precise data foundation for subsequent axial force calculation; the temperature difference of the working environment of structures such as fans is huge (such as day and night, winter and summer), and the scheme of the embodiment ensures the output stability of the axial force measurement system in all-weather and all-season, so as to accurately judge the relaxation state of the bolt.

[0048] By pre-experiment calibration of the bolts in the same batch as the target bolt to be measured, the elastic coefficient k of the batch of bolts (reflecting the ability of the bolt to resist elastic deformation, which is a fixed constant) is obtained; at the same time, the reference length L0 of the target bolt to be measured in the natural state without axial force is determined; the current length L t of the bolt obtained by the upper computer through ultrasonic wave propagation time conversion is subtracted by the reference length L0 in the natural state, and the elastic deformation amount ΔL=L t -L0 of the bolt due to the axial force is obtained; the deformation amount and the calibrated elastic coefficient are substituted into the quantitative relationship formula F=k×(L t -L0), and the current axial force value F of the target bolt to be measured is directly calculated. In the embodiment, the axial force calibration curve of the target bolt to be measured is obtained by experiment calibration. The use of the elastic coefficient k obtained by experiment calibration greatly reduces the conversion error caused by individual manufacturing differences and complex boundary conditions, which makes the final axial force reading more truly reflect the actual load borne by the bolt, and the measurement accuracy is much higher than that of the method relying on pure theoretical parameters; the parameters in the formula are obtained by batch calibration, and the operation process is simple and easy to execute; at the same time, the linear formula is convenient for programming in the measurement system, without the need for complex algorithm development, which improves the promotion adaptability of the measurement method in different engineering scenes.

[0049] In an optional embodiment, before obtaining the current axial force value according to the axial force calibration curve, a step of temperature correction of the natural state length L0 of the target bolt to be measured by using a temperature influence coefficient a is further included, specifically: the formula L 0TL = L0 + a x (T - T0) is calculated to obtain the bolt natural state length at the actual temperature 0T Wherein, a is the temperature influence coefficient obtained by comparing the axial force calibration curves at different temperatures, T is the current temperature data of the target bolt to be measured, T0 is the standard temperature when calibrating the above axial force calibration curve; the corrected L 0T is substituted into the deformation-axial force relationship formula F = k x (L t -L0) to obtain the current axial force value after temperature correction F = k x (L t -L 0T ).

[0050] In the above embodiment, the temperature influence coefficient can be used to correct the natural state length of the target bolt to be measured, and then the bolt natural state length at the actual temperature is obtained, which is substituted into the deformation-axial force relationship formula to obtain the current axial force value after temperature correction, thereby reducing the interference of temperature on the axial force measurement result and improving the accuracy of the axial force measurement.

[0051] The embodiment is based on the thermal expansion and contraction characteristics of the bolt and the influence law of temperature on the elastic deformation reference, and the natural state length of the bolt is corrected by introducing the temperature influence coefficient, and then the axial force is calculated in combination with the deformation-axial force formula. Specifically, the temperature influence coefficient a of the target bolt to be measured (reflecting the rate of change of the bolt length with temperature) is obtained by comparing the axial force calibration curves at different temperatures in advance; at the same time, the standard temperature T0 when calibrating the above axial force calibration curve (i.e. calibrating the deformation-axial force relationship formula) is determined, and the current bolt temperature data T and the natural state length L0 at the time of calibration are collected; the above parameters are substituted into the formula L 0T =L0 + a x (T - T0) to calculate the bolt natural state length at the actual temperature L 0T . The logic of the formula is that the difference between the current temperature and the standard temperature (T-T0) is multiplied by the temperature influence coefficient a to obtain the change amount of the bolt natural state length with temperature, and then added to L0 at the time of calibration, which is the bolt reference length at the actual temperature without axial force; the corrected natural state length L 0T replaces L0 in the original formula, and is substituted into the deformation-axial force relationship formula F = k x (L t -L 0T), and finally obtain the current axial force value after eliminating the temperature interference on the reference length. On the basis of the original temperature correction of the ultrasonic wave propagation speed and cable transmission time delay, the embodiment adds temperature correction of the natural state length of the bolt, covering the temperature interference factors of the whole measurement chain of "cable transmission-ultrasonic wave propagation-bolt deformation reference", and fundamentally improves the accuracy of the axial force measurement, especially suitable for scenes such as wind power towers and offshore wind turbines with significant temperature fluctuations; the natural length is corrected based on the temperature influence coefficient α of the actual calibration of the bolt, which conforms to the actual thermal expansion and contraction characteristics of the bolt and avoids the theoretical deviation of the general thermal expansion coefficient; the corrected L 0T As a reference calculation deformation, the axial force result can better reflect the actual stress state of the bolt.

[0052] In an optional embodiment, the above method further includes a system calibration step, which specifically includes: at a first preset environmental temperature, applying a plurality of different known tensions to the calibration bolt through the tension test platform, recording each tension value and the corresponding calibration bolt length, and obtaining a plurality of first calibration data, wherein the calibration bolt is of the same specification as the target bolt to be measured; at a second preset environmental temperature, applying a plurality of different known tensions to the calibration bolt through the tension test platform, recording each tension value and the corresponding calibration bolt length, and obtaining a plurality of second calibration data; fitting a first axial force calibration curve at the first preset environmental temperature based on the plurality of first calibration data, and fitting a second axial force calibration curve at the second preset environmental temperature based on the plurality of second calibration data; comparing the first axial force calibration curve and the second axial force calibration curve to calculate the temperature influence coefficient α.

[0053] In the above embodiment, different known tensions are applied to the calibration bolt at different preset environmental temperatures to obtain a plurality of calibration data, and axial force calibration curves at different temperatures are fitted. By comparing the axial force calibration curves at different temperatures, the temperature influence coefficient can be calculated, so that the natural state length of the target bolt to be measured can be temperature corrected, and the accuracy of the bolt axial force measurement is improved, better meeting the monitoring needs of actual engineering.

[0054] A calibration bolt of the same specification as the target bolt to be measured is selected, and a plurality of different known tensions are applied to the calibration bolt using a tension test platform at a first preset environmental temperature (such as T1) and a second preset environmental temperature (such as T2) respectively; at each tension value, the corresponding length of the calibration bolt is recorded, and a plurality of first calibration data (tension-length at T1) and a plurality of second calibration data (tension-length at T2) are obtained respectively; the first calibration data is curve-fitted to obtain a first axial force calibration curve of the tension (axial force) and the length of the bolt at the T1 temperature; similarly, the second calibration data is fitted to obtain a second axial force calibration curve at the T2 temperature, and the curve directly reflects the correlation between the axial force and the length of the bolt at different temperatures; by comparing the slopes, intercepts or length differences at the same tension of the two axial force calibration curves, the temperature influence coefficient a is quantitatively calculated, which reflects the rate of change of the natural state length and deformation law of the bolt with temperature, and is a core parameter for subsequent temperature correction. The temperature influence coefficient a is obtained through the multi-temperature tension experiment of the same specification bolt, which discards the theoretical deviation of the general coefficient and makes a truly reflect the temperature characteristics of the target bolt to be measured, providing a reliable data basis for the subsequent temperature correction of the natural state length of the bolt and further improving the accuracy of the axial force measurement. The calibration curves at multiple temperatures can cover the axial force-length correlation law in different temperature scenarios, avoiding the failure problem of single-temperature calibration curves when the temperature fluctuates, so that the measurement system can still maintain stable measurement accuracy in outdoor temperature-varying scenarios such as wind power. Here, only the first preset environmental temperature and the second preset environmental temperature are taken as examples, and in actual application, more axial force calibration curves at different environmental temperatures can be obtained.

[0055] In an optional embodiment, the measurement terminal comprises a channel selection module, a group of core line switching modules, and a group of three-core jacks, each core line switching module is connected between an output end of the channel selection module and a corresponding three-core jack, and is used for switching the connection combination of different core lines in the three-core cable associated with the corresponding three-core jack, the target three-core jack is any three-core jack in the group of three-core jacks, and each three-core jack corresponds to a route of the ultrasonic transducer; the measurement terminal selects the target core line switching module from the group of core line switching modules by using the channel selection module, and the target core line switching module switches the connection combination of different core lines in the target three-core cable through the target three-core jack.

[0056] In the above embodiment, the measurement terminal can select the target core line switching module from the group of core line switching modules by using the channel selection module, and switch the connection combination of different core lines in the target three-core cable through the target three-core jack by using the target core line switching module, so as to realize the adaptation of multiple groups of ultrasonic transducers, and simultaneously measure multiple target bolts to be measured, thereby improving the applicability and measurement efficiency of the bolt axial force measurement system.

[0057] The measurement terminal integrates a channel selection module, a group of core line switching modules and a group of three-core aviation plugs, which are in a one-to-one corresponding relationship. Each core line switching module is connected between an output end of the channel selection module and a corresponding three-core aviation plug. Each three-core aviation plug is connected to an ultrasonic transducer (corresponding to a bolt to be measured) through a three-core cable. The target three-core aviation plug is any one of the three-core aviation plugs. The channel selection module serves as a core control unit and can select a certain core line switching module (such as a target core line switching module) from the group of core line switching modules according to measurement requirements, so as to accurately select a specific measurement channel of the bolt to be measured. The remaining channels are in a standby state. The selected target core line switching module switches different core line connection combinations of the target three-core aviation plug, and then performs the steps of cable length measurement, temperature measurement and ultrasonic data acquisition in time. After completing the measurement of one bolt, the channel selection module can switch to other core line switching modules to repeat the above process to sequentially measure multiple bolts. The channel selection module is used to measure multiple bolts in time, and independent measurement terminals do not need to be configured for each bolt. In the engineering scene of a fan tower, a large bridge and the like, there are hundreds or thousands of bolts to be measured. The axial force monitoring of all the bolts can be sequentially completed, the overall measurement time is greatly shortened, and the batch monitoring efficiency is improved.

[0058] In an optional embodiment, the measurement terminal further comprises an ultrasonic trigger pulse module, an ultrasonic waveform acquisition module and a resistance measurement module. The measurement terminal measures the first resistance value and the second resistance value by using the resistance measurement module. The measurement terminal transmits an ultrasonic trigger pulse to the ultrasonic transducer through the first core line and the second core line by using the ultrasonic trigger pulse module, and starts the ultrasonic waveform acquisition module to collect returned ultrasonic data at a preset sampling rate.

[0059] In the above embodiment, the measurement terminal can accurately measure the first resistance value and the second resistance value by using the resistance measurement module, which provides a basis for obtaining target length data of the target three-core cable and current temperature data of the target bolt to be measured. The measurement terminal transmits an ultrasonic trigger pulse to the ultrasonic transducer through the first core line and the second core line by using the ultrasonic trigger pulse module, and starts the ultrasonic waveform acquisition module to collect returned ultrasonic data at a preset sampling rate, which can effectively collect ultrasonic data and provide necessary data for the host computer to calculate the current axial force value of the target bolt to be measured.

[0060] The measurement terminal calls the resistance measurement module to respectively complete accurate measurement of the total resistance of the second and third core lines (first resistance value) in cable length measurement and the total resistance of the first and second core lines and the temperature measurement resistance (second resistance value) in temperature measurement, to provide basic electrical data for subsequent cable length calculation and bolt temperature conversion. Specifically, the resistance measurement module can include a constant current source and a voltage measurement unit. In addition, the measurement terminal generates and sends an ultrasonic trigger pulse to the ultrasonic transducer through the first and second core lines through the ultrasonic trigger pulse module, as an excitation signal for driving the transducer to emit ultrasonic waves; at the same time of sending the trigger pulse, the ultrasonic waveform acquisition module is started synchronously, which acquires and quantizes the reflected echo beam signal returned by the transducer according to a preset sampling rate, and finally forms digitized ultrasonic data, to complete reception and storage of the ultrasonic signal. After the measurement terminal completes switching of the core line connection combination through the core line switching module, the corresponding special function module is automatically called according to the current measurement step (cable length / temperature / ultrasonic acquisition), to realize orderly linkage and function connection between the modules.

[0061] The present application will be described below in conjunction with specific embodiments.

[0062] The present application provides a kind of self-adapting cable length and temperature change's axial force measurement method, online real-time automatic identification high-frequency cable length between ultrasonic transducer (can be referred to as transducer) and ultrasonic measurement terminal (can be referred to as measurement terminal), synchronous measurement bolt real-time temperature, to exclude the error caused by inaccurate manual measurement cable length, also reduce the workload of field, improve system usability;At the same time, due to synchronous and timely temperature measurement, bolt thermal expansion and contraction effect caused by temperature change and measurement error caused by wave speed change with temperature can also be accurately compensated, to improve the accuracy of axial force measurement.The present application includes the following key points: Firstly, the present application provides a kind of self-adapting cable length and temperature change's axial force measurement method, first designs ultrasonic and temperature measurement combination ultrasonic transducer, transducer is connected with measurement cable interface by 3 core high-frequency cable, Figure 3 It is a kind of ultrasonic axial force measurement principle schematic diagram provided by the present application, the transmission time of ultrasonic wave in bolt is determined by ultrasonic emission wave and return wave, and then the length of bolt itself (screw rod) is calculated to determine the current state of bolt.

[0063] The combined ultrasonic transducer comprises: 2Mhz frequency ultrasonic transducer and PT1000 temperature measuring resistance are tightly adhered on 0.3mm thick ceramic resonance disc by coupling glue, the positive pole of the ultrasonic transducer, the positive pole of the PT1000 and the pin 1 of the connector are connected by copper wire through welding, the negative pole of the ultrasonic transducer and the negative pole of the PT1000 are connected by copper wire, and the pin 2 and the pin 3 of the connector are connected by two copper wires from the negative pole connection point, forming a positive pole one-wire and negative pole two-parallel-wire connection mode, and the combined ultrasonic transducer is connected with an external cable through a 3-core connector (such as a 3-core high-frequency socket in Figure 4 . Figure 4 A structure diagram of the combined ultrasonic transducer is provided in the embodiment of the application, the combined parts are covered by a high-strength plastic shell, the ceramic resonance disc is flush with the edge of the shell, and the connector extends from the back of the shell, then AB glue is injected into the cavity of the shell to form the combined ultrasonic transducer.

[0064] On the other hand, an ultrasonic trigger pulse implementation module, an ultrasonic waveform acquisition module and a line resistance measurement module are designed in the combined ultrasonic measurement terminal. The ultrasonic measurement terminal is connected with an external cable through a 3-core connector. Each measurement terminal is designed with 16 connectors at most, so that 16 transducers can be connected at the same time. The ultrasonic measurement terminal switches one of the 16 connectors through a relay node, and switches different combination connection modes of the three cables in each connector through a relay node, so that the cable length measurement, bolt temperature measurement and ultrasonic time difference measurement are realized.

[0065] Furthermore, the combined ultrasonic transducer is installed on the top of the bolt for monitoring the pre-tightening force by coupling glue, then the combined ultrasonic transducer (corresponding to the target ultrasonic transducer in Figure 2 ) is connected to one of the connector interfaces of the ultrasonic measurement terminal through a 3-core high-frequency cable with a suitable length according to the space length, finally the ultrasonic measurement terminal and the host computer (or background computer) with the shaft force monitoring software are connected through an Ethernet cable, so that a complete shaft force measurement system is formed, and the system architecture is shown in Figure 2 .

[0066] The shaft force measurement method with adaptive cable length and temperature change comprises the following steps: The first step, the ultrasonic measuring terminal scans the channel with the ultrasonic transducer according to the channel number 1-16. When the ultrasonic measuring terminal scans the selected channel, the first step is to connect the internal channel core wire to the control relay (or other selection module), disconnect the No. 1 core wire of the selected channel, inject a 200uA precise constant current into the No. 2 core wire, measure the current I of the No. 3 core wire, and measure the voltage value U1 between the No. 2 core wire and the No. 3 core wire. If the current I of the No. 3 core wire is not equal to 200uA, it is reported that the cable is disconnected, otherwise, the cable resistance value R1 between the No. 2 core wire and the No. 3 core wire is calculated by R1=U1 / I, and the cable length L between the measuring terminal and the transducer is calculated by L=R1 / (2p). Figure 5 is an adaptive cable length calculation electrical principle diagram provided by the embodiment of the application, L1, L2 and L3 respectively represent the No. 1 core wire, the No. 2 core wire and the No. 3 core wire, which correspond to the first core wire, the second core wire and the third core wire respectively, Pt1000 corresponds to the temperature measuring resistor, P represents the ultrasonic transducer, DC1 and DC2 represent the direct current power supply, and K1 and K2 are used for switching the core wire combination.

[0067] The second step, after the ultrasonic measuring terminal detects that the corresponding channel is not disconnected and measures the cable length L, the internal channel core wire is connected to the control relay, the No. 3 core wire of the selected channel is disconnected, a 200uA precise constant current I is injected into the No. 1 core wire, the voltage value U2 between the No. 1 core wire and the No. 2 core wire is measured, the resistance value R2 between the No. 1 core wire and the No. 2 core wire is calculated by R=U2 / I, then R2 is subtracted from the cable resistance value R1 measured in the first step to obtain the PT1000 temperature measuring resistor value Rt (corresponding to the current resistance value), and then the current temperature T of the measured bolt is obtained by querying the Pt1000 resistor-temperature quick lookup table.

[0068] The third step, the shaft force monitoring software sends a channel shaft force measurement instruction to the ultrasonic measuring terminal through Ethernet, the ultrasonic measuring terminal receives the instruction, controls the channel selection relay to select the measured channel from the 16 channels, and controls the core wire switching relay to connect the core wire 1 and the core wire 2 of the corresponding channel to the ultrasonic trigger pulse forming and sound wave waveform acquisition module. The ultrasonic trigger pulse forming module generates and sends an ultrasonic trigger negative pulse signal with a peak value of up to 100V and a pulse width of 250us to the core wire 1 and the core wire 2 ports, and simultaneously starts the ultrasonic waveform acquisition module to collect the ultrasonic waveform data between the No. 1 core wire and the No. 2 core wire at a sampling rate of 100MHz, and protects the waveform data in the measuring terminal. Fourthly, the shaft force monitoring software sends a waveform data calling instruction to the ultrasonic measuring terminal through Ethernet after the ultrasonic measuring terminal completes the ultrasonic data collection, and the ultrasonic measuring terminal sends the collected data to the shaft force monitoring software according to the sampling sequence number in accordance with the communication protocol after receiving the instruction, and also sends the measured current temperature T of the bolt and the length L of the high-frequency cable to the shaft force monitoring software at the same time, so that the shaft force detection software system completes the shaft force measurement calculation.

[0069] The shaft force detection software system completes the bolt shaft force calculation according to the following steps: Firstly, the shaft force detection software system performs point-by-point filtering calculation on the received ultrasonic waveform data by using a digital band-pass filter with a frequency band range of 1.45MHz-2.8MHz, and then performs Hilbert transform on the filtered data to obtain an ultrasonic reflection echo beam.

[0070] Further, the shaft force detection software system calculates the reflection beam offset sequence number n according to the starting index determined by the Hilbert transform, so as to calculate the total time difference Δt of the ultrasonic wave propagation from the trigger to the return by using the waveform sampling period Ts (the waveform sampling rate is 100MHz, and the sampling period Ts=10ns) t =n*Ts, and calculates the transmission time Δt of the trigger pulse and the return wave in the high-frequency cable by using the connection cable length and the temperature data contained in the sampling data d =L / V d (wherein V d is the propagation speed of the electric wave in the connection high-frequency cable after temperature correction compensation obtained through calibration), and the accurate transmission time Δt of the ultrasonic wave in the bolt is obtained by subtracting the time in the cable from the total time Δt t =Δt*V d / 2, and then the current length L of the bolt is calculated according to the above calculation t =Δt*V u , (wherein V u is the propagation speed of the ultrasonic wave in the measured bolt after temperature correction compensation obtained through calibration).

[0071] Further, the shaft force detection software system calculates the bolt pre-tightening force F=k* (L t -L0) by using the deformation-shaft force relationship of the measured bolt obtained through calibration (wherein F is the bolt pre-tightening force, k is the elastic coefficient of the measured batch of bolts obtained through calibration, L t is the measured current bolt length, and L0 is the length of the measured batch of bolts in the natural state after temperature calibration determined during calibration).

[0072] According to the adaptive cable length and temperature change shaft force measurement method, at least the following technical effects are achieved: the combination ultrasonic transducer realizes ultrasonic triggering and echo receiving of the measured member, current real-time temperature of the measured member and connection cable length measurement function, more importantly, the 0.3mm thick ceramic resonant sheet is used to realize resonance amplification of 2MHz ultrasonic waves, thereby reducing the ultrasonic triggering energy requirement, improving the ultrasonic recognition, improving the measurement accuracy, and at the same time, due to the electrical insulation characteristics of the ceramic, the penetration of the measured body environment electromagnetic signal is blocked, and the reliability of the system is improved; the ultrasonic measurement terminal is designed to realize the connection cable length and the online real-time measurement of the measured member temperature, and the measurement and configuration workload in engineering use is avoided, and the measurement error caused by the temperature synchronous measurement is avoided, and the temperature influence is corrected synchronously, and the adaptive ability of the cable length and temperature change is realized. It has better usability, accuracy, economy, and is suitable for industrialization and popularization.

[0073] The present application does not need to preset the connection cable length, and the measurement system eliminates the transmission delay of the measurement signal in the connection cable from the source, overcomes the influence of the different lengths of the connection cable caused by the distributed arrangement of the bolts on the shaft force measurement accuracy, eliminates the material and labor waste caused by the selection of the same length of cable to ensure the consistency of the measurement data of the same group of bolts, and also eliminates the measurement error factors caused by the possible errors of the connection cable length configuration by the field engineers.

[0074] The present application also provides related embodiments of bolt shaft force calibration curves and actual measurement result examples.

[0075] Firstly, the combination ultrasonic transducer is installed on the top of the measured bolt with a coupling glue, and then the 5m length, 3-core high-frequency cable with a resistivity of p is used to connect the combination ultrasonic transducer installed on the measured bolt to the No.1 aviation plug interface of the ultrasonic measurement terminal, finally, the Ethernet cable is used to connect the ultrasonic measurement terminal and the host computer with shaft force monitoring software, and a complete shaft force measurement system is formed. At the same time, the high-frequency cable resistivity and the measured bolt channel number are set to 1 in the shaft force monitoring background software system.

[0076] Second step, consult the national standard GB / T3098.1 to determine the measured bolt yield force is about 1200KN. The measured bolt is installed on the 200-ton tension test platform through the bowl cover test tool, the test environment temperature is adjusted to 15℃, after the temperature is stable for 30 minutes, the measured bolt is stretched to the natural state, 20% yield state, 40% yield state, 60% yield state, 80% yield state and 95% yield state respectively through the tension test platform, and 6 pairs of data of the tension and the corresponding measured bolt length of each of the 6 test points are recorded, and the relationship between the axial force and the bare double length established by the 6 pairs of data is the axial force calibration curve of the bolt under the condition of 15℃; then the test environment temperature is adjusted to 25℃, after the temperature is stable for 30 minutes, the bolt is measured again to the natural state, 20% yield state, 40% yield state, 60% yield state, 80% yield state and 95% yield state respectively, and 6 pairs of data of the tension and the corresponding measured bolt length of each of the 6 test points are recorded, and the relationship between the axial force and the bare double length established by the 6 pairs of data is the axial force calibration curve of the bolt under the condition of 25℃. The two groups of calibration data marked by the test temperature are imported into the axial force monitoring background system, the background system compares the two calibration curves to obtain the influence coefficient a of the temperature on the axial force, and the system calibration is completed.

[0077] Third step, keep the environment temperature stable, change the tension force of the test platform randomly within the yield force range of the measured bolt, and observe the comparison between the axial force tested by the axial force test system and the traction force applied by the test system, and the error is less than 3%; Fourth step, keep the environment temperature stable, replace the connection cable between the ultrasonic transducer and the measurement terminal by 10m, 20m, 30m and 50m respectively, change the tension force of the test platform randomly within the yield force range of the measured bolt respectively, and observe the comparison between the axial force tested by the axial force test system and the traction force applied by the test system, and the error is less than 3%; Fifth step, connect the ultrasonic transducer and the measurement terminal with the 30m high-frequency cable, adjust the environment temperature to 10℃, 20℃ and 30℃ respectively, and after the temperature is stable for more than 30 minutes, change the tension force of the test platform randomly within the yield force range of the measured bolt respectively, and observe the comparison between the axial force tested by the axial force test system and the traction force applied by the test system, and the error is less than 3%; In the above embodiments, the description of each embodiment has its own emphasis, and the parts not described in detail in a certain embodiment can be referred to the related description of other embodiments.

[0078] The above is only an exemplary embodiment of the present disclosure, which cannot limit the scope of the present disclosure. Any equivalent changes and modifications made according to the teachings of the present disclosure are still within the scope of the present disclosure. Other embodiments of the present disclosure will be easily thought of by those skilled in the art after considering the disclosure of the specification.

[0079] This application is intended to cover any variations, uses, or adaptations of the disclosure, including what is described in the specification and / or claims, other than those variations that occur to those skilled in the art in light of the general principles of the disclosure and including variations that would be apparent to those skilled in the art and that are within the purview of the disclosure.

Claims

1. A method for measuring bolt axial force based on adaptive cable length, characterized in that, The bolt axial force measurement system includes a target ultrasonic transducer, a measurement terminal and a host computer. The target ultrasonic transducer includes an ultrasonic transducer for transmitting and receiving ultrasonic waves, a temperature measuring resistor for sensing the temperature of the target bolt, and a ceramic resonator for amplifying the ultrasonic signal. The measurement terminal is connected to the target three-core interface of the target ultrasonic transducer via a target three-core cable. The measurement terminal performs the following steps in a time-division manner by switching the connection combinations of the core wires in the target three-core cable: The resistance of the target three-core cable is measured to obtain cable length data; Measure the loop resistance including the temperature sensing resistor to obtain the current bolt temperature data; The ultrasonic transducer is excited and the returned echo signal is collected to obtain ultrasonic data; The host computer is communicatively connected to the measurement terminal and is used to calculate the propagation time of ultrasonic waves in the target bolt based on the cable length data, the current bolt temperature data, and the ultrasonic data, and to obtain the current axial force value by querying the axial force calibration curve corresponding to the target bolt based on the propagation time.

2. The method according to claim 1, characterized in that, The target ultrasonic transducer is an encapsulated structure integrating the ceramic resonator, the ultrasonic transducer, and the temperature-sensing resistor. The ultrasonic transducer and the temperature-sensing resistor are fixed to the upper surface of the ceramic resonator. The lower surface of the ceramic resonator is fixed to the top of the target bolt to be tested by coupling adhesive. The first electrode of the ultrasonic transducer and the first electrode of the temperature-sensing resistor are connected to the first pin of the target three-core interface by copper wire. The second electrode of the ultrasonic transducer and the other electrode of the temperature-sensing resistor are connected together by copper wire to form a negative connection point. At the same time, two copper wires are used to connect from the negative connection point to the second and third pins of the target three-core interface, respectively. The lower surface of the ceramic resonator is flush with the edge of the housing of the encapsulated structure, and the target three-core interface extends from the back of the housing of the encapsulated structure.

3. The method according to claim 2, characterized in that, The ceramic resonator has a thickness of 0.3 mm, the ultrasonic transducer operates at a frequency of 2 MHz, and the frequencies of the ceramic resonator and the ultrasonic transducer are matched to achieve resonant amplification.

4. The method according to claim 1, characterized in that, The target three-core cable includes a first core wire, a second core wire, and a third core wire; Measuring the resistance of the target three-core cable to obtain cable length data specifically includes: injecting a preset constant current into the second core wire, while simultaneously measuring the current in the third core wire and a first voltage between the second and third core wires; if the current in the third core wire is equal to the preset constant current, then calculating a first resistance value based on the first voltage and the preset constant current; and calculating the cable length data based on the first resistance value and a preset cable resistivity, wherein the preset cable resistivity is used to represent the resistance value per unit length of a single core of the target three-core cable. The measurement, which includes the loop resistance of the temperature-sensing resistor to obtain the current bolt temperature data, specifically includes: injecting the preset constant current into the first core wire and measuring the second voltage between the first core wire and the second core wire; calculating the second resistance value based on the second voltage and the preset constant current; subtracting the first resistance value from the second resistance value to obtain the temperature-sensing resistor value; and querying a preset temperature-resistance correspondence table based on the temperature-sensing resistor value to obtain the current bolt temperature data. The preset temperature-resistance correspondence table records the resistance value relationship of the temperature-sensing resistor at different temperatures. The process of stimulating the ultrasonic transducer and acquiring the returned echo signal to obtain ultrasonic data specifically includes: sending an ultrasonic trigger pulse to the ultrasonic transducer, causing the ultrasonic transducer to send a target ultrasonic signal of a preset frequency to the target bolt under test; and acquiring the returned ultrasonic data, wherein the ultrasonic data is a reflected beam signal obtained by converting the ultrasonic signal reflected back from the target bolt under test by the ultrasonic transducer. The host computer calculates the propagation time of ultrasonic waves in the target bolt based on the cable length data, the current bolt temperature data, and the ultrasonic data. It then queries the axial force calibration curve corresponding to the target bolt based on the propagation time to obtain the current axial force value. This includes: calculating the total propagation time from sending the ultrasonic trigger pulse to receiving the ultrasonic data; calculating the transmission delay of the ultrasonic trigger pulse and reflected echo beam in the target three-core cable based on the cable length data and the current bolt temperature data; calculating the propagation time of ultrasonic waves in the target bolt based on the total propagation time and the transmission delay; calculating the current length of the target bolt based on the propagation time; and obtaining the current axial force value corresponding to the current length based on the pre-calibrated axial force calibration curve corresponding to the target bolt.

5. The method according to claim 4, characterized in that, Calculating the total propagation time from sending the ultrasonic trigger pulse to receiving the ultrasonic data includes: performing digital bandpass filtering calculations on the acquired ultrasonic data within the 1.45MHz~2.8MHz frequency band, then performing Hilbert transform processing on the filtered data to obtain the ultrasonic reflected echo beam; calculating the sampling point number n of the reflected echo beam based on the starting index determined by the Hilbert transform; and calculating the total propagation time Δt based on the sampling point number n and the preset waveform sampling period Ts. t =n*Ts; Calculating the transmission delay of the ultrasonic trigger pulse and reflected echo beam in the target three-core cable based on the cable length data and the current bolt temperature data includes: calculating the transmission delay according to the following formula: Δt d =L / (V d ), where Δt d The transmission delay is L, the cable length is V. d The propagation speed of the ultrasonic trigger pulse and the reflected echo beam in the target three-core cable after being obtained through pre-calibration and corrected and compensated by the current bolt temperature data; The propagation time of the ultrasonic wave in the target bolt is calculated based on the total propagation time and the transmission delay, including: calculating the propagation time according to the following formula: Δt = (Δt t -Δt d ) / 2, where Δt represents the one-way propagation time of the ultrasonic wave in the target bolt to be tested; The current length of the target bolt to be tested is calculated based on the propagation time, including: calculating the current length of the target bolt to be tested using the following formula: L t =Δt×V u , where L t V represents the current length. u This indicates the propagation speed of the ultrasonic wave within the target bolt after correction using the current bolt temperature data; The current axial force value corresponding to the current length is obtained according to the pre-calibrated axial force calibration curve corresponding to the target bolt to be tested, including: obtaining the current axial force value according to the following axial force calibration curve: F=k×(L t -L0), where F represents the current axial force value, k is the elastic coefficient of bolts from the same batch as the target bolt under test, and L t L0 represents the current length, and L0 represents the length of the target bolt under test in its natural state as determined during calibration.

6. The method according to claim 5, characterized in that, Before obtaining the current axial force value according to the axial force calibration curve, the method further includes a step of temperature correction of the natural length L0 of the target bolt under test using a temperature influence coefficient α, specifically: Through formula L 0T =L0+α×(T-T0) calculates the natural state length L of the bolt at the actual temperature. 0T Where α is the temperature influence coefficient obtained by comparing the axial force calibration curves at different temperatures, T is the current bolt temperature data, and T0 is the standard temperature when calibrating the axial force calibration curve; The corrected L 0T Substituting into the relationship between deformation and axial force F=k×(L) t -L0), to obtain the current axial force value F=k×(L) after temperature correction. t -L 0T ).

7. The method according to claim 1, characterized in that, The method further includes a system calibration step, which specifically includes: Under a first preset ambient temperature, multiple different known tensile forces are applied to the calibration bolt through a tensile testing platform, and each tensile force value and the corresponding calibration bolt length are recorded to obtain multiple sets of first calibration data. The calibration bolt is of the same specification as the target bolt to be tested. Under a second preset ambient temperature, multiple different known tensile forces are applied to the calibration bolt through the tensile testing platform, and each tensile force value and the corresponding calibration bolt length are recorded to obtain multiple sets of second calibration data. A first axial force calibration curve is fitted based on the multiple sets of first calibration data at the first preset ambient temperature, and a second axial force calibration curve is fitted based on the multiple sets of second calibration data at the second preset ambient temperature. By comparing the first axial force calibration curve and the second axial force calibration curve, the temperature influence coefficient α is calculated.

8. The method according to claim 2, characterized in that, The measurement terminal includes: a channel selection module, a set of core wire switching modules and a set of three-core aviation connectors. Each core wire switching module is connected between an output terminal of the channel selection module and a corresponding three-core aviation connector, and is used to switch the connection combination of different core wires in the three-core cable associated with the corresponding three-core aviation connector. Each three-core aviation connector corresponds to an ultrasonic transducer. The measurement terminal uses the channel selection module to select the target core wire switching module from the group of core wire switching modules. The target core wire switching module switches the connection combination of different core wires in the target three-core cable through the target three-core connector.

9. The method according to claim 4, characterized in that, The measurement terminal further includes: an ultrasonic trigger pulse module, an ultrasonic waveform acquisition module, and a resistance measurement module, wherein... The measuring terminal uses the resistance measuring module to measure the first resistance value and the second resistance value; The measurement terminal uses the ultrasonic trigger pulse module to transmit the ultrasonic trigger pulse to the ultrasonic transducer through the first core wire and the second core wire, and starts the ultrasonic waveform acquisition module to acquire the returned ultrasonic data at a preset sampling rate.

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