Piezoelectric unidirectional force measuring device and method based on structural strain

Abstract

A piezoelectric one-way force measuring device and method based on structural strain belong to the field of structural mechanics measurement and piezoelectric sensing technology, and are suitable for non-invasive measurement of one-way bearing capacity of large-scale non-destructive key components. The piezoelectric one-way force measuring device is composed of an attached piezoelectric strain sensor, a measured member and a standard calibration block. The sensor is attached to the surface of the measured member through a single pre-tightening bolt, and a Y0 cut type piezoelectric quartz wafer is used as a sensitive element inside. The strain-charge conversion is realized by using the shear piezoelectric effect. The method completes the traceable calibration through the standard calibration block and the standard force source, establishes the quantitative relationship between the force value and the charge, and converts the output charge of the sensor to obtain the axial bearing capacity of the measured member during real-time measurement. The present application only needs to drill a small diameter threaded hole on the surface of the measured member, and completely retains its mechanical properties. The measurement precision is high, the range coverage is wide, the installation is convenient, the impact load and the alternating load can be accurately measured, and the long-term stable monitoring demand of the industrial field can be met.

Description

Technical Field

[0001] This invention belongs to the field of structural mechanics measurement and piezoelectric sensing technology, and relates to a piezoelectric unidirectional force measurement device and method based on structural strain. It is applicable to non-invasive high-precision measurement of unidirectional load-bearing capacity of large, indestructible key components such as hydraulic press columns, ship propulsion shafts, wind turbine tower flanges, and heavy machinery load-bearing beams. Background Technology

[0002] In the fields of heavy industrial equipment, energy equipment, and aerospace, numerous critical load-bearing components bear enormous axial loads. Real-time monitoring of their load-bearing capacity is a core means of ensuring safe equipment operation and preventing catastrophic accidents. Currently, the mainstream method for measuring the unidirectional load-bearing capacity of large components is the series force sensor method, which involves cutting off the component being measured and connecting a large number of force sensors in series in the load-bearing chain to directly measure the transmitted force value. Although this method has high measurement accuracy, it has a fatal flaw: the cutting operation permanently destroys the structural integrity of the component being measured, resulting in a significant decrease in its load-bearing capacity. This makes it unsuitable for indestructible critical core components. Furthermore, the installation and maintenance of series sensors require production shutdown and disassembly, which is costly and time-consuming.

[0003] Existing non-invasive measurement methods mainly employ digital image displacement measurement and fiber optic grating surface attachment methods, calculating the load-bearing capacity by measuring the surface strain of the component. Chinese invention patent "A Digital Image Correlation Strain Measurement System and Method Based on Metalens" (CN119123990A) proposes a single-camera three-dimensional digital image correlation (3D-DIC) strain measurement scheme. This scheme simultaneously images the same test area using different optical lenses, acquiring the three-dimensional morphology, displacement, and deformation measurements of the object under test, making it suitable for strain measurement in small areas. While this method achieves non-contact three-dimensional strain measurement and has high system integration, the digital image correlation method relies on the speckle quality of the measured surface. Oil and dust in industrial environments can easily contaminate the speckle pattern, leading to measurement failure. Furthermore, the operating wavelength of the metalens is limited, requiring the use of filters for white light imaging. Additionally, existing metalenses have a relatively small imaging field of view, making it difficult to cover the measurement needs of large-sized load-bearing components in heavy equipment. The Chinese invention patent "A Non-Invasive Monitoring Device for the Health Status of a Prestressed Steel Cable System" (CN115585848A) uses a fiber optic grating strain sensor to convert the tension of the steel cable into axial stress. The fiber optic grating strain sensor can detect changes in the reflected wavelength to measure the tension change of the steel cable. When the steel cable is subjected to tension, the sleeve can withstand the tension of the steel cable and transmit the strain of the steel cable. The fiber optic grating strain sensor is arranged at the detection point of the sleeve to detect the strain change of the sleeve. However, the grating wavelength drift is affected by both strain and temperature (cross-sensitivity), and the strain measurement accuracy is about 1μm. In addition, an additional temperature reference grating or a dual-parameter demodulation scheme is required, increasing the system complexity and cost.

[0004] Therefore, there is an urgent need to develop a device and method for measuring the unidirectional load-bearing capacity of large, non-destructible components that is non-destructive to the structure being measured, easy to install, highly accurate, and has strong anti-interference capabilities. Summary of the Invention

[0005] Existing methods for measuring the unidirectional load-bearing capacity of large components suffer from drawbacks such as damage to structural integrity, low measurement accuracy, poor anti-interference capability, and insufficient measurement range, failing to meet the long-term stable monitoring requirements of critical, non-destructible components in industrial settings. This invention provides a piezoelectric unidirectional force measurement device and method based on structural strain. It measures the axial strain on the surface of the tested component using an attached piezoelectric sensing structure, and then calculates the unidirectional load-bearing capacity, all without damaging the main structure of the tested component.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A piezoelectric unidirectional force measuring device based on structural strain is disclosed. The device includes an attached piezoelectric strain sensor, a signal processing unit, and a data processing unit. When used in conjunction with the device, it is mounted on the surface of the workpiece being measured, which has an M6 threaded hole. The attached piezoelectric strain sensor is attached to the surface of the workpiece via its built-in pre-tightening structure, forming a fixed connection. When the workpiece is subjected to a single axial force and deforms, the structural deformation is measured by two Y0-type piezoelectric quartz crystal groups on the attached piezoelectric strain sensor and converted into an electric charge signal. This signal is sequentially transmitted to the signal processing unit for amplification and conditioning, and the data processing unit performs calculations. The surface strain is converted using a pre-calibrated sensor sensitivity, and the axial load-bearing capacity of the workpiece is further calculated. Specifically: The attached piezoelectric strain sensor includes a sensor substrate, two sets of identical Y0-type piezoelectric quartz crystals, contact bosses, a sensor sealing plate, preload bolts, preload washers, signal wires, and a sealing interface. The sensor substrate is made of high-strength alloy steel after heat treatment and has a rectangular parallelepiped structure, placed horizontally along its length. A through-hole with a diameter of 6mm to 8mm is machined at the center of the sensor substrate's thickness direction. This hole allows the preload bolt to pass through, achieving a tight connection between the attached piezoelectric strain sensor and the M6 ​​threaded hole on the surface of the measured workpiece. A tapered preload washer is fitted onto the preload bolt. A tapered countersunk hole is machined at the end of the preload through-hole facing the head of the preload bolt. The top opening diameter of the countersunk hole is larger than the bottom diameter of the through-hole, smoothly transitioning along a 45° conical surface to the preload through-hole. This countersunk hole is used to contact the bottom of the tapered preload washer, achieving automatic centering of the preload force and ensuring that the preload force of the preload bolt is evenly applied to the sensor substrate. The lower surface of the sensor substrate is machined with an upward-facing rectangular groove. A ring wall structure is retained in the center of the groove along the axis of the pre-tightening through hole. This ring wall structure isolates the pre-tightening bolt from the internal space of the groove, and is coaxial with the pre-tightening through hole. Two mounting bosses are symmetrically arranged on the inner surface of the groove along its length, positioned on either side of the ring wall structure. These bosses are used to bond and fix the Y0-type piezoelectric quartz crystal assembly, which serves as the sensing element. The bottom of the Y0-type piezoelectric quartz crystal assembly is mounted to the sensor sealing plate via contact bosses and passes through the sensor sealing plate. The horizontal distance between the centers of the two mounting bosses is the measuring point distance of the attached piezoelectric strain sensor, denoted as . 2l ,in l This refers to the distance from the center of a single mounting boss to the center of the pre-tightening through-hole in the sensor substrate. 2l It can be adjusted according to different measurement range requirements. At the same time, the side wall of the sensor substrate is machined with M5 threaded through holes along the length direction for installing and fixing the sealing interface. The sealing interface is connected to the Y0 type piezoelectric quartz crystal group through the signal wire for transmitting the induced charge signal. The sealing interface can achieve the sealing protection of the cavity and isolate external environmental interference while ensuring the stable transmission of internal signals to the outside.

[0007] Furthermore, each Y0-type piezoelectric quartz crystal assembly includes multiple electrode plates and Y0-type piezoelectric quartz crystal wafers. The planar shapes of the electrode plates and Y0-type piezoelectric quartz crystal wafers are all octagonal, and their external dimensions are matched. The Y0-type piezoelectric quartz crystal assembly adopts a multi-layer alternating stacked structure, consisting of two Y0-type piezoelectric quartz crystal wafers arranged in opposite polarization directions and three electrode plates tightly bonded together with conductive adhesive. An electrode plate is tightly attached to the middle position and the upper and lower outer edges of the two Y0-type piezoelectric quartz crystal wafers. The electrode plate located in the middle is the signal output electrode, which is connected to the sealed interface through a signal wire to transmit the induced charge signal. The upper and lower outer electrode plates are all grounding electrodes, uniformly grounded to shield against external electromagnetic interference. Two sets of Y0-type piezoelectric quartz crystals are symmetrically bonded to the mounting bosses on both sides of the sensor substrate. In the left crystal set, the negative polarizations of the two Y0-type piezoelectric quartz crystals are close to the central electrode, and the positive polarizations are close to the upper and lower outer electrodes. In the right crystal set, the positive polarizations of the two Y0-type piezoelectric quartz crystals are close to the central electrode, and the negative polarizations are close to the upper and lower outer electrodes, resulting in opposite shear sensitivity directions for the two sets of crystals. When the measured object deforms, causing relative shear displacement between the two contact bosses, the induced charges generated by the two sets of Y0-type piezoelectric quartz crystals have the same polarity and can be superimposed and output in the same direction. The signal output terminals of the two sets of Y0-type piezoelectric quartz crystals are connected in parallel via signal wires and then transmitted to an external signal processing unit through a sealed interface.

[0008] Furthermore, the electrode plates in the Y0-type piezoelectric quartz crystal assembly are made of highly conductive copper or silver foil material with a thickness of 0.05 mm to 0.1 mm, and the surface is plated with a silver layer to improve conductivity and oxidation resistance. The Y0-type piezoelectric quartz crystal achieves force-electric signal conversion based on the thickness shear piezoelectric effect, and has inherent characteristics of high sensitivity, good temperature stability, and small long-term zero-point drift. Its shear piezoelectric coefficient... =4.6pC / N.

[0009] Furthermore, the contact boss is made of hard alloy and has an overall stepped cylindrical structure, consisting of a large-diameter end and a small-diameter end. The large-diameter end of the contact boss is glued to the Y0 type piezoelectric quartz crystal assembly, and its diameter is larger than the circumcircle of the Y0 type piezoelectric quartz crystal assembly, with a single-sided dimension 0.5mm to 1mm larger. This design ensures that the contact boss fully compacts the Y0 type piezoelectric quartz crystal assembly during the pre-tightening process of the attached piezoelectric strain sensor, avoiding measurement errors caused by local stress concentration. The small-diameter end of the contact boss extends beyond the sensor sealing plate and contacts the surface of the measured object after pre-tightening installation. The surface roughness of both ends of the contact boss is controlled to Ra≤0.8μm, and the flatness is controlled to ≤0.01mm. This ensures that under the pre-tightening force of the pre-tightening bolts, the sensor substrate, the Y0 piezoelectric quartz crystal assembly, and the contact boss are tightly pressed together, while the contact boss is in close contact with the surface of the measured object, achieving stable and uniform strain transmission.

[0010] Furthermore, the sensor sealing plate is made of 304 stainless steel and has an overall open rectangular plate structure. Three through holes are machined on the sensor sealing plate: a first through hole in the center, and second and third through holes symmetrically located on either side of the first through hole. The first through hole is coaxially aligned with the pre-tightening through hole of the sensor substrate and its size is larger than the outer diameter of the pre-tightening bolt. The second and third through holes are coaxially aligned with two contact bosses, and their diameters are larger than the cross-sectional dimensions of the small-diameter end of the contact bosses, ensuring that the bosses can extend freely without contacting or interfering with the housing. The sensor sealing plate is bonded to the bottom of the sensor substrate with epoxy resin adhesive, forming a sealed mounting cavity. This cavity protects the internal Y0-type piezoelectric quartz crystal assembly and signal wires from corrosion by dust, oil, and moisture in the external environment. A gap of 0.5mm to 1mm is left between the sensor sealing plate and the contact bosses, ensuring no contact between them and preventing the sensor sealing plate from participating in strain transmission and interfering with the accuracy of the measurement signal. After the attached piezoelectric strain sensor is assembled with the sensor substrate, Y0 type piezoelectric quartz crystal assembly, contact boss and sensor sealing plate in sequence, the small diameter end of the contact boss faces downward and the height of the sensor sealing plate is 0.5mm to 1mm.

[0011] Furthermore, the pre-tightening bolt is an 8.8 grade high-strength bolt, which can provide sufficient pre-tightening force to ensure a reliable connection between the sensor and the measured object. The pre-tightening bolt passes sequentially through the pre-tightening washer, the first through hole of the sensor sealing plate, and the pre-tightening through hole of the sensor base, and is finally screwed into the pre-machined M6 threaded hole on the surface of the measured object. The head of the pre-tightening bolt adopts an internal hexagonal design, which facilitates precise control of the pre-tightening torque using a torque wrench.

[0012] Furthermore, the pre-tightening shim is a double-conical shim, symmetrical at both ends with a taper of 45°, placed between the head of the pre-tightening bolt and the conical countersunk hole of the sensor substrate. The pre-tightening shim can evenly distribute the pre-tightening force on both sides of the sensor substrate, and then evenly transfer it to the two sets of Y0-type piezoelectric quartz crystals, effectively avoiding localized stress concentration. Simultaneously, the conical shim can also rely on friction with the substrate to restrict bolt loosening, ensuring that the sensor maintains a stable pre-tightened state during long-term use.

[0013] Furthermore, the signal wire is a thin-diameter wire with a shielding layer, arranged inside the sealed cavity. One end of the signal wire is connected to the intermediate signal electrode plate of the Y0 type piezoelectric quartz crystal assembly, and the other end is connected to the sealed interface, used to realize the transmission of induced charge signals.

[0014] Furthermore, the sealing interface is a sealing connector, which is fixed to the M5 threaded through hole on the side wall of the sensor substrate by threaded engagement. A rubber sealing ring is provided on the mating surface between the interface and the M5 threaded through hole to achieve sealing protection of the sealing cavity. The external end of the sealing interface is used to connect to external signal cables, which can ensure the stable output of internal charge signals while preventing external moisture and dust from entering the sensor, thus ensuring the long-term working stability of internal sensitive elements such as the Y0 type piezoelectric quartz crystal group.

[0015] The signal processing unit is a charge amplifier, used to convert the high-impedance charge signal output by the attached piezoelectric strain sensor into a low-impedance voltage signal and perform gain amplification, making it a general industrial testing device.

[0016] The data processing unit is a computer equipped with a data acquisition module, used to realize signal acquisition, calibration coefficient calculation and display and storage of force value results, and is a general industrial testing device.

[0017] The measured component is a unidirectional axially loaded structural member, which is the object of measurement for this device. This includes, but is not limited to, large, indestructible, critical load-bearing components such as hydraulic press columns, ship propulsion shafts, wind turbine tower flanges, and heavy machinery load-bearing beams. Its measured area has a defined elastic modulus and cross-sectional area, capable of converting the axial static load and alternating vibration load into uniform surface axial strain, providing strain input for the attached piezoelectric strain sensor. The measured surface of the component is pre-machined with M6 threaded holes matching the specifications of the pre-tightening bolts. The threaded hole depth is 14mm to 20mm, ensuring the structural strength and pre-tightening reliability of the pre-tightening bolt connection. The mounting surface around the threaded hole is ground and cleaned, with a flatness ≤0.02mm / m and a surface roughness not exceeding Ra≤1.6μm, allowing for close contact with the working surface of the contact boss. This ensures that the surface strain of the measured component can be uniformly and losslessly transmitted to the Y0-type piezoelectric quartz crystal assembly inside the sensor through the contact interface.

[0018] A piezoelectric uniaxial force measurement method based on structural strain, implemented using the aforementioned piezoelectric uniaxial force measurement device, includes the following steps: Step 1: Calibrate the attached piezoelectric strain sensor. Calibration is performed using a combination of a standard calibration block and a standard force source to establish a quantitative correspondence between the standard force value and the sensor's output charge. This yields the sensitivity coefficient and performance indicators of the attached piezoelectric strain sensor, ensuring accurate and reliable measurements. Specifically: Step 1.1: Design the standard calibration block; Design cross-sectional area A standard calibration block with a uniform cross-section is used. The standard calibration block is made of a stable material with a known elastic modulus. The overall structure is a cuboid with a uniform cross-section, consisting of a fixed lower section and a working upper section. The length, width, and height of the working section are as follows: , , ,length ≥150mm, ensuring a sufficiently large uniform strain zone within the working section to fully accommodate the installation of the attached piezoelectric strain sensor, with the sensor installation position located within the uniform strain zone. An M6 threaded hole is pre-machined at the center of the working section height for mounting the attached piezoelectric strain sensor.

[0019] Meanwhile, the surface flatness of the working section of the standard calibration block is controlled to ≤0.02mm / m, the surface roughness Ra≤1.6μm, and the perpendicularity of both end faces to the axis is ≤0.02mm, ensuring no eccentric bending moment is generated during loading and uniform strain in the working section. The cross-sectional area of ​​the fixed section is more than twice that of the middle working section, and through holes are evenly distributed around the perimeter for fixing the standard calibration block. According to Hooke's law of axial tension and compression, the standard calibration block is subjected to a standard force value... Uniform strain generated under action Satisfying the formula: (1) in, The elastic modulus of the standard calibration block material.

[0020] According to the applied standard force value The range and the cross-sectional area of ​​the standard calibration block are Determine the strain generated by the standard calibration block This ensures that the value is greater than the strain generated by the measured part under actual force, and guarantees that the strain range of the standard calibration block covers the strain range of the measured part.

[0021] Step 1.2: Calibrate the attached piezoelectric strain sensor.

[0022] The attached piezoelectric strain gauge to be calibrated is fixed to the center of the working section of the standard calibration block using the same installation method as in actual use, using the same pre-tightening bolts and pre-tightening washers, and applying the same pre-tightening torque. The standard calibration block with the attached piezoelectric strain gauge installed is then fixed onto a metrologically calibrated standard force source. The standard force source is a large-range calibration stage that can provide stable and accurate axial tensile and compressive forces.

[0023] A standard force value is applied using a stepped loading method, covering the full strain range of the standard calibration block, with at least five uniformly distributed loading gradients. After each gradient is applied, the load is held for 3 to 5 seconds to allow the charge signal to stabilize. The signal processing unit then conditions the charge signal, and the data processing unit collects and records the output charge value. After each loading gradient, the load is unloaded to zero. This loading and unloading cycle is repeated three times, recording complete loading and unloading data for each cycle. The full-scale output of the attached piezoelectric strain sensor represents the applied force value. Output at maximum.

[0024] Step 1.3: Calculate the performance indicators of the attached piezoelectric strain sensor.

[0025] Based on the average data from the three calibration cycles in step 1.2, the standard force value was determined using the least squares method. With output charge By performing linear fitting, the slope of the fitted line is obtained, which is the force sensitivity coefficient of the attached piezoelectric strain sensor. The unit is pC / με, as shown in formula (2): (2) The linearity error of the attached piezoelectric strain sensor is calculated based on the fitting results. The linearity error is the ratio of the maximum deviation between the fitted straight line and the average measured charge value under the same loading gradient in three cycles to the full-scale output, expressed as a percentage.

[0026] The repeatability error of the attached piezoelectric strain sensor was calculated using the range method. The repeatability error is the ratio of the maximum difference in output charge under the same loading gradient in three cycles to the full-scale output, expressed as a percentage.

[0027] Based on the above calculation results, ensure that the linearity and repeatability error of the attached piezoelectric strain sensor meet the design requirements within the calibrated strain range, where the linearity error is ≤2%FS and the repeatability error is ≤2%FS.

[0028] Step 2: Pre-process the measured part.

[0029] Drill an M6 threaded hole matching the specifications of the preload bolt at the measurement location on the workpiece. The depth of the threaded hole should be 14mm to 20mm to ensure the connection strength of the preload bolt. Sand the mounting surface around the threaded hole to ensure that the flatness of the mounting surface does not exceed 0.02mm / m and the surface roughness does not exceed Ra≤1.6μm, ensuring that the attached piezoelectric strain sensor can fit tightly against the surface of the workpiece. After sanding, clean the mounting surface with anhydrous ethanol to thoroughly remove surface oil and dust, preventing impurities from affecting the strain transfer effect.

[0030] Step 3: Install the attached piezoelectric strain sensor onto the surface of the workpiece being measured and pre-tighten it.

[0031] Align the preload through-hole of the attached piezoelectric strain sensor with the threaded hole on the surface of the workpiece being measured. Then, place a preload washer between the head of the preload bolt and the sensor sealing plate. Use a torque wrench to tighten the preload bolt, and preload evenly based on the preload torque, which ranges from 10 N·m to 12 N·m. After preloading, ensure that the two contact bosses are in tight contact with the surface of the workpiece without any gaps.

[0032] Step 4: Real-time measurement and force calculation; When the measured part is subjected to an axial load, its surface will generate an axial strain proportional to the magnitude of the load. ε The cross-sectional area of ​​the measured part is S The elastic modulus is E Axial strain ε The charge signal is transmitted to the Y0-type piezoelectric quartz crystal assembly below through two contact bosses, and is proportional to the strain due to shear deformation. Q Then, based on the sensitivity of the attached piezoelectric strain sensor in step 1.3... The uniaxial bearing capacity borne by the measured component is calculated by converting its cross-sectional dimensions and elastic modulus parameters. F : (3) In summary, the piezoelectric unidirectional force measurement device and method based on structural strain proposed in this invention achieves non-invasive force measurement through surface-attached installation. By combining a symmetrical differential architecture of two sets of reverse-polarized piezoelectric crystal groups with a rigid friction force transmission structure, it has the advantages of high measurement accuracy, good long-term stability, and wide dynamic response. It effectively solves the defects of traditional solutions such as large structural damage, poor environmental adaptability, and limited frequency response. It can be widely adapted to the load-bearing capacity monitoring needs of large key load-bearing components in fields such as hydraulic equipment, wind power, and shipbuilding.

[0033] The beneficial effects of this invention are: (1) Non-invasive measurement, preserving the structural load-bearing capacity. The present invention adopts a non-invasive measurement method, which only requires machining a small threaded hole with a diameter of 6mm and a depth of 14mm on the surface of the measured part. There is no need to cut off or modify the measured part, and the original mechanical properties and load-bearing capacity are completely preserved. It is particularly suitable for measuring the load-bearing capacity of critical core components that cannot be destroyed.

[0034] (2) Symmetrical differential sensing structure, which combines high precision and long-term stability. The present invention adopts two sets of reverse polarized Y0 type piezoelectric quartz crystal groups for symmetrical parallel output. The reverse series connection of the two crystal crystals in the crystal group can cancel common mode interference such as normal load and temperature fluctuation. The bolt pre-tightening makes the contact boss and the measured object fit tightly. The rigid friction force transmission replaces the adhesive layer, eliminates creep aging error, and the connection state is stable for a long time. The measurement linearity and repeatability are excellent.

[0035] (3) High rigidity force transmission design, covering a wide range of dynamic measurements. This invention uses a high rigidity piezoelectric quartz crystal as the sensitive core, combined with a hard alloy contact boss and bolt fastening connection structure. The overall structure has a high natural frequency and fast response speed. The tightly fitting contact interface ensures that the strain transmission is lag-free and attenuated, and can accurately reproduce quasi-static loads, alternating loads and impact loads. The natural frequency is not less than 5kHz, which meets the wide range monitoring requirements of equipment transient conditions and vibration states. Attached Figure Description

[0036] Figure 1 The flowchart shows a piezoelectric uniaxial force measurement method based on structural strain. Figure 2 The composition of the measuring device and the attached piezoelectric strain sensor; Figure 3 for Figure 2 The mid-mounted piezoelectric strain sensor is connected to the measured object. Figure 2 Enlarged section view (within the dashed box); Figure 4 Exploded view, assembly view and cross-sectional view of the internal structure of the attached piezoelectric strain sensor; (a) Exploded view of the internal structure of the attached piezoelectric strain sensor; (b) Assembly view of the attached piezoelectric strain sensor; (c) Cross-sectional view of the attached piezoelectric strain sensor; Figure 5 This is a parallel output mode for Y0 type piezoelectric crystal groups; Figure 6 This is a connection diagram between the attached piezoelectric strain sensor and the standard calibration block. Figure 7 The following are simulation diagrams of the attached piezoelectric strain sensor and the standard calibration block under a pre-tightened state of 10kN: (a) Simulation diagram of the attached piezoelectric strain sensor under pre-tightened installation; (b) Deformation cloud diagram of attached piezoelectric strain sensor 1 after pre-tightening; (c) Deformation cloud diagram of Y0 type piezoelectric quartz crystal group after pre-tightening; (d) Charge change of Y0 type piezoelectric quartz crystal group 1-2. Figure 8 For the attached piezoelectric strain sensor to be pre-tightened to the standard calibration block and subjected to standard force F s=50kN state simulation diagram, (a) simulation diagram of the force of the attached piezoelectric strain sensor after pre-tightening, (b) force deformation cloud diagram of the attached piezoelectric strain sensor, (c) force deformation cloud diagram of the Y0 type piezoelectric quartz crystal group, (d) charge change of the Y0 type piezoelectric quartz crystal group after being subjected to force. Figure 9 This is a modal simulation diagram of an attached piezoelectric strain sensor.

[0037] In the diagram: 1. Attached piezoelectric strain sensor; 2. Signal processing unit; 3. Data processing unit; 4. Measured component; 5. Standard calibration block; 1-1 Sensor substrate, 1-2 Y0 type piezoelectric quartz crystal assembly, 1-3 Contact boss, 1-4 Sensor sealing plate, 1-5 Preload bolt, 1-6 Preload gasket, 1-7 Signal wire, 1-8 Sealing interface; 1-2-1 Electrode sheet; 1-2-2Y0 type piezoelectric quartz crystal. Detailed Implementation

[0038] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings and technical solutions.

[0039] This embodiment provides a piezoelectric unidirectional force measuring device based on structural strain. The piezoelectric unidirectional force measuring device includes an attached piezoelectric strain sensor 1, a signal processing unit 2, and a data processing unit 3. When used in conjunction with the device, it is installed on the surface of the workpiece 4 being measured. Figure 2 , Figure 3 As shown, the surface of the measured component 4 has an M6 threaded hole. The attached piezoelectric strain sensor 1 is attached to the surface of the measured component 4 through its built-in pre-tightening structure, forming a fixed connection with the measured component 4. When the measured component 4 is subjected to a single axial force and deforms, the structural deformation is measured by the two Y0-type piezoelectric quartz crystal groups 1-2 on the attached piezoelectric strain sensor 1 and converted into an electric charge signal. The electric charge signal is sequentially transmitted to the signal processing unit 2 for amplification and conditioning, and the data processing unit 3 for calculation. The surface strain is converted through the pre-calibrated sensor sensitivity, and the axial bearing capacity of the measured component 4 is further calculated. Specifically: The attached piezoelectric strain sensor 1 includes a sensor substrate 1-1, two sets of identical Y0-type piezoelectric quartz crystals 1-2, a contact boss 1-3, a sensor sealing plate 1-4, a preload bolt 1-5, a preload gasket 1-6, a signal wire 1-7, and a sealing interface 1-8, as shown below. Figure 4 (a) ~ Figure 4As shown in (c) above. The sensor substrate 1-1 is made of high-strength alloy steel 18Ni350 after quenching and tempering. It has a rectangular structure and is placed horizontally along its length. A through pre-tightening hole with a diameter of 7mm is machined at the center of the thickness direction of the sensor substrate 1-1 for passing through the pre-tightening bolt 1-5. A tapered pre-tightening washer 1-6 is mounted on the pre-tightening bolt 1-5. A tapered countersunk hole with a depth of 4mm is machined at the end of the pre-tightening through hole facing the head of the pre-tightening bolt 1-5. The opening diameter of the top of the countersunk hole is larger than that of the bottom through hole, with a diameter of 15mm. It smoothly transitions to the 7mm pre-tightening through hole along a 45° tapered surface for contact with the bottom of the tapered pre-tightening washer 1-6. A rectangular groove is machined upwards on the lower surface of the sensor substrate 1-1. A ring wall structure is retained in the center of the groove along the axis of the pre-tightening through hole. This ring wall structure isolates the pre-tightening bolt 1-5 from the internal space of the groove. The ring wall structure is coaxial with the pre-tightening through hole. Two mounting bosses are symmetrically arranged on the inner surface of the groove along its length, positioned on either side of the ring wall structure. These bosses are used to bond and fix the Y0-type piezoelectric quartz crystal assembly 1-2, which serves as the sensing element. The bottom of the Y0-type piezoelectric quartz crystal assembly 1-2 is mounted on the sensor sealing plate 1-4 via contact bosses 1-3, and passes through the sensor sealing plate 1-4. The horizontal distance between the centers of the two mounting bosses is the measuring point distance of the attached piezoelectric strain sensor 1, denoted as . 2l In this embodiment l The distance from the center of a single mounting boss to the center of the pre-tightening through hole 1-1 in this structure is... 2l =24mm. Meanwhile, the side wall of the sensor substrate 1-1 is machined with an M5 threaded through hole along the length direction for mounting and fixing the sealing interface 1-8. The sealing interface 1-8 is connected to the Y0 type piezoelectric quartz crystal group 1-2 through the signal wire 1-7 for transmitting the induced charge signal.

[0040] In this embodiment, each Y0-type piezoelectric quartz crystal assembly 1-2 includes multiple electrode plates 1-2-1 and Y0-type piezoelectric quartz crystal wafers 1-2-2. The planar shapes of both electrode plates 1-2-1 and Y0-type piezoelectric quartz crystal wafers 1-2-2 are octagonal, and their dimensions match each other. In this embodiment, the Y0-type piezoelectric quartz crystal assembly 1-2 adopts a five-layer alternating stacked structure. Two Y0-type piezoelectric quartz crystal wafers 1-2-2 arranged with opposite polarization directions and three electrode plates 1-2-1 are tightly bonded together with conductive adhesive. One electrode plate 1-2-1 is tightly attached to the middle position and the upper and lower outer edges of each of the two Y0-type piezoelectric quartz crystal wafers 1-2-2. The middle electrode plate 1-2-1 is the signal output electrode, connected to the sealed interface 1-8 via a signal wire 1-7 to transmit the induced charge signal. The upper and lower outer electrode plates 1-2-1 are all grounding electrodes, uniformly grounded. Figure 5As shown, two sets of Y0-type piezoelectric quartz crystal groups 1-2 are symmetrically bonded to the mounting bosses on both sides of the sensor substrate. In the left crystal group, the negative polarization electrodes of the two Y0-type piezoelectric quartz crystal pieces 1-2-2 are close to the middle electrode piece 1-2-1, and the positive polarization electrodes are close to the upper and lower outer electrode pieces 1-2-1. In the right crystal group, the positive polarization electrodes of the two Y0-type piezoelectric quartz crystal pieces 1-2-2 are close to the middle electrode piece 1-2-1, and the negative polarization electrodes are close to the upper and lower outer electrode pieces 1-2-1, making the shear sensitivity directions of the two crystal groups opposite. When the measured object deforms, causing relative shear displacement of the two contact bosses 1-3, the induced charges generated by the two sets of Y0-type piezoelectric quartz crystal groups 1-2 have the same polarity and can be superimposed and output in the same direction. The signal output terminals of the two sets of Y0-type piezoelectric quartz crystal groups 1-2 are connected in parallel through signal wires 1-7, and then transmit the charge signal to the external signal processing unit 2 through the sealed interface 1-8.

[0041] In this embodiment, the electrode sheet 1-2-1 in the Y0 type piezoelectric quartz crystal group 1-2 is made of highly conductive copper with a thickness of 0.8 mm.

[0042] In this embodiment, the contact boss 1-3 is made of F141 material and has a stepped cylindrical structure, consisting of a large-diameter end and a small-diameter end. The large-diameter end has a diameter of 12mm and a thickness of 2.2mm, while the small-diameter end has a diameter of 8mm and a thickness of 1.4mm. The large-diameter end of the contact boss 1-3 is glued to the Y0-type piezoelectric quartz crystal assembly 1-2, and its diameter is larger than the circumcircle of the Y0-type piezoelectric quartz crystal assembly 1-2, with a single-sided dimension 0.6mm larger. The small-diameter end of the contact boss 1-3 extends beyond the sensor sealing plate 1-4 and, after pre-tightening installation, contacts the surface of the measured object 4. The surface roughness of both ends of the contact boss 1-3 is controlled to Ra≤0.8μm, and the flatness is controlled to ≤0.01mm. The sensor sealing plate 1-4 is made of 304 stainless steel and has an open rectangular plate structure. The sensor sealing plate 1-4 has three through holes: a first through hole in the center, and second and third through holes symmetrically located on either side of the first through hole. The first through hole is coaxially aligned with the pre-tightening through hole of the sensor base 1-1, and its size is larger than the outer diameter of the pre-tightening bolt 1-5. The diameter of the first through hole is 7mm. The second and third through holes are coaxially aligned with the two contact bosses 1-3, respectively, and their diameters are larger than the cross-sectional dimensions of the small-diameter end of the contact bosses 1-3. The diameters of the second and third through holes are 8mm. The sensor sealing plate 1-4 is bonded to the bottom of the sensor base 1-1 with epoxy resin adhesive, forming a sealed mounting cavity. A 0.8mm gap is left between the sensor sealing plate 1-4 and the contact bosses 1-3, and there is no contact between them. After the attached piezoelectric strain sensor 1 is assembled with the sensor substrate 1-1, the Y0 type piezoelectric quartz crystal group 1-2, the contact boss 1-3 and the sensor sealing plate 1-4 in sequence, the small diameter end of the contact boss 1-3 faces downward and the height of the sensor sealing plate 1-4 is 0.5mm.

[0043] In this embodiment, the pre-tightening bolt 1-5 is an 8.8 grade high-strength bolt with a specification of M6×30 mm. The pre-tightening bolt 1-5 passes sequentially through the pre-tightening washer 1-6, the first through hole of the sensor sealing plate 1-4, and the pre-tightening through hole of the sensor base 1-1, and is finally screwed into the pre-machined M6 threaded hole on the surface of the measured component 4. The head of the pre-tightening bolt 1-5 adopts an internal hexagonal design. The pre-tightening washer 1-6 is a double-conical washer, symmetrical at both ends with a taper of 45°, placed between the head of the pre-tightening bolt 1-5 and the conical countersunk hole of the sensor base 1-1, such as... Figure 6 As shown.

[0044] In this embodiment, the signal wire 1-7 is a thin-diameter wire with a shielding layer, arranged inside the sealed cavity. One end of the signal wire 1-7 is connected to the intermediate signal electrode 1-2-1 of the Y0 type piezoelectric quartz crystal assembly 1-2, and the other end is connected to the sealing interface 1-8, used to realize the transmission of induced charge signals. The sealing interface 1-8 is a sealing connector, which is fixed to the M5 threaded through hole on the side wall of the sensor base 1-1 by threaded engagement. A rubber sealing ring is provided on the mating surface between the interface and the M5 threaded through hole to achieve sealing protection of the sealed cavity.

[0045] The signal processing unit 2 is a charge amplifier, used to convert the high-impedance charge signal output by the sensor into a low-impedance voltage signal and complete the gain amplification, and is a general industrial testing device.

[0046] The data processing unit 3 is a computer equipped with a data acquisition module, used to realize signal acquisition, calibration coefficient calculation and display and storage of force value results, and is a general industrial testing device.

[0047] The measured component 4 is a unidirectional axially loaded component, which is the object of measurement in this device. It is a square hydraulic press support column, and the cross-section of the area to be measured is a constant square interface. It can convert the axial static load and the alternating vibration load within 0-500Hz into uniform surface axial strain, providing strain input for the attached piezoelectric strain sensor 1. The natural frequency of the attached piezoelectric strain sensor 1 reaches 5459Hz, which meets the required measurement frequency range. Figure 9 As shown. The surface of the measured component 4 is pre-machined with M6 threaded holes matching the specifications of the pre-tightening bolts 1-5. The threaded hole depth is 15mm, which can ensure the structural strength and pre-tightening reliability of the pre-tightening bolt connection. The mounting surface around the threaded hole is ground and cleaned, with a flatness ≤0.02mm / m and a surface roughness not exceeding Ra≤1.6μm. It can fit tightly with the working surface of the contact bosses 1-3, ensuring that the surface strain of the measured component can be uniformly and losslessly transmitted to the Y0 type piezoelectric quartz crystal group 1-2 inside the sensor through the contact interface.

[0048] This embodiment also provides a piezoelectric unidirectional force measurement method based on structural strain, implemented using the aforementioned piezoelectric unidirectional force measurement device, as shown in the flowchart below. Figure 1 As shown, it includes the following steps: Step 1: Calibrate the attached piezoelectric strain sensor 1. Calibration is performed using a combination of standard calibration block 5 and a standard force source to establish a quantitative correspondence between the standard force value and the sensor's output charge. This yields the sensitivity coefficient and performance indicators of the attached piezoelectric strain sensor 1, ensuring accurate and reliable measurements. Specifically: Step 1.1: Design standard calibration block 5; Design cross-sectional area The standard calibration block 5 is a rectangular parallelepiped with a constant cross-section. It is made of a stable material with a known elastic modulus, and its overall structure consists of a fixed lower section and a working upper section, forming a rectangular parallelepiped with a constant cross-section. The length, width, and height of the working section are as follows: =100、 =100、 =200, ensuring that a sufficiently large uniform strain zone is formed within the working section, which can fully accommodate the installation of the attached piezoelectric strain sensor 1 and the sensor installation position is in the uniform strain zone. An M6 threaded hole is pre-machined at the center of the working section height for mounting the attached piezoelectric strain sensor 1.

[0049] Meanwhile, the surface flatness of the working section of standard calibration block 5 is controlled to ≤0.02mm / m, the surface roughness Ra≤1.6μm, and the perpendicularity of both end faces to the axis is ≤0.02mm, ensuring no eccentric bending moment is generated during loading and uniform strain in the working section. The cross-sectional area of ​​the fixed section is more than twice that of the middle working section, and through holes are evenly distributed around the perimeter for fixing the standard calibration block. According to Hooke's law of axial tension and compression, standard calibration block 5 is subjected to a standard force value... Uniform strain generated under action Satisfying the formula: (4) in, The elastic modulus of the material for standard calibration block 5.

[0050] According to the applied standard force value The range and the cross-sectional area of ​​the standard calibration block 5 are Determine the strain generated by the standard calibration block This ensures that the value is greater than the strain generated by the measured part 4 under actual force, and guarantees that the strain range of the standard calibration block 5 covers the strain range of the measured part 4.

[0051] Step 1.2: Calibrate the attached piezoelectric strain sensor 1.

[0052] The attached piezoelectric strain sensor 1 to be calibrated is fixed to the center of the working section of the standard calibration block 5 using the same installation method as in actual use. Pre-tightening bolts 1-5 and pre-tightening washers 1-6 of the same specifications are used, and a pre-tightening force of 10 kN is applied. The deformation cloud map of the attached piezoelectric strain sensor 1 after pre-tightening, the deformation cloud map of the Y0 type piezoelectric quartz crystal group 1-2, and the surface charge output of the crystal are shown below. Figure 7 (a)- Figure 7 As shown in (d), the standard calibration block 5, on which the attached piezoelectric strain sensor 1 is installed, is fixed on a standard force source that has been calibrated by metrology. The standard force source is a large-range calibration table that can provide stable and accurate axial tensile and compressive forces.

[0053] The standard force value is applied in a stepped loading manner, with the loading range covering the full strain range of the standard calibration block 5. Five uniformly distributed loading gradients of 10kN, 20kN, 30kN, 40kN, and 50kN are set. After each gradient loading is completed, the load is held for 3 to 5 seconds until the charge signal stabilizes. Then, the signal processing unit 2 completes the charge signal conditioning, and the data processing unit 3 collects and records the output charge value. The attached piezoelectric strain sensor 1 is subjected to the standard force. F s Deformation cloud diagram after 50kN, deformation cloud diagram of Y0 type piezoelectric quartz crystal group 1-2 and crystal surface charge output are as follows: Figure 8 (a)- Figure 8 As shown in (d). After each loading gradient is completed, the load is unloaded to zero. This loading and unloading cycle is repeated three times, and complete loading and unloading data is recorded for each cycle. The full-scale output of the attached piezoelectric strain sensor 1 is the loading force value. Output at maximum.

[0054] Step 1.3: Calculate the performance indicators of the attached piezoelectric strain sensor 1.

[0055] Based on the average data from the three calibration cycles in step 1.2, the standard force value was determined using the least squares method. With output charge By performing linear fitting, the slope of the fitted straight line is obtained, which is the force sensitivity coefficient of the attached piezoelectric strain sensor 1. The unit is pC / με, as shown in formula (5): (5) The linearity error of the attached piezoelectric strain sensor 1 is calculated based on the fitting results. The linearity error is the ratio of the maximum deviation between the fitted straight line and the average measured charge value under the same loading gradient in three cycles to the full-scale output, expressed as a percentage.

[0056] The repeatability error of the attached piezoelectric strain sensor 1 was calculated using the range method. The repeatability error is the ratio of the maximum difference in output charge under the same loading gradient in three cycles to the full-scale output, expressed as a percentage.

[0057] Based on the above calculation results, ensure that the linearity and repeatability error of the attached piezoelectric strain sensor 1 meet the design requirements within the calibrated strain range, wherein the linearity error is ≤2%FS and the repeatability error is ≤2%FS.

[0058] Step 2: Pre-process the measured part 4.

[0059] At the measurement location of the measured component 4, drill an M6 threaded hole matching the specifications of the preload bolts 1-5. The depth of the threaded hole is 15mm to ensure the connection strength of the preload bolts 1-5. Grind the mounting surface around the threaded hole with sandpaper to ensure that the flatness of the mounting surface does not exceed 0.02mm / m and the surface roughness does not exceed Ra≤1.6μm, ensuring that the attached piezoelectric strain sensor 1 can fit tightly against the surface of the measured component 4. After grinding, clean the mounting surface with anhydrous ethanol to thoroughly remove surface oil and dust, avoiding impurities from affecting the strain transfer effect.

[0060] Step 3: Install the attached piezoelectric strain sensor 1 onto the surface of the measured part 4 and pre-tighten it.

[0061] Align the preload through hole of the attached piezoelectric strain sensor 1 with the threaded hole on the surface of the measured part 4. Then, place the preload shim 1-6 between the head of the preload bolt 1-5 and the sensor sealing plate 1-4. Tighten the preload bolt 1-5 using a torque wrench and preload it evenly based on the preload torque of 10 N·m, applying a preload force of approximately 10 kN. After preloading, ensure that the two contact bosses 1-3 are tightly fitted to the surface of the measured part 4 without any gaps.

[0062] Step 4: Real-time measurement and force calculation; When the measured part 4 is subjected to an axial load, its surface will generate an axial strain proportional to the magnitude of the load. ε The cross-sectional area of ​​the measured part 4 is S The elastic modulus is E Axial strain ε The charge signal is transmitted to the Y0-type piezoelectric quartz crystal group 1-2 below through two contact bosses 1-3, and is proportional to the strain due to shear deformation. Q Then, based on step 1.3, the sensitivity of the attached piezoelectric strain sensor 1... The uniaxial bearing capacity borne by the measured component 4 is calculated by converting its cross-sectional dimensions and elastic modulus parameters. F : (6) The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. For example, the number of Y0 type piezoelectric quartz crystal groups 1-2 can be adjusted to 1 group or 4 groups according to the range requirements, the shape of the contact bosses 1-3 can be designed as circular or elliptical, and the pre-tightening method can adopt hydraulic pre-tightening to improve the uniformity of the pre-tightening force.

[0063] The above embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A piezoelectric unidirectional force measuring device based on structural strain, characterized in that, The piezoelectric unidirectional force measuring device includes an attached piezoelectric strain sensor (1), a signal processing unit (2) and a data processing unit (3), which are installed on the surface of the measured part (4) when used together. The surface of the measured part (4) is provided with a threaded hole. The attached piezoelectric strain sensor (1) is attached to the surface of the measured part (4) through its own pre-tightening structure, forming a fixed connection with the measured part (4); when the measured part (4) is subjected to a single axial force and deforms, it is measured by two Y0 type piezoelectric quartz crystal groups (1-2) on the attached piezoelectric strain sensor (1) and converted into an electric charge signal. The electric charge signal is transmitted to the signal processing unit (2) and the data processing unit (3) in sequence to obtain the surface strain, and then the axial bearing capacity of the measured part (4) is calculated. The attached piezoelectric strain sensor (1) includes a sensor substrate (1-1), two sets of identical Y0-type piezoelectric quartz crystals (1-2), a contact boss (1-3), a sensor sealing plate (1-4), a preload bolt (1-5), a preload gasket (1-6), a signal wire (1-7), and a sealing interface (1-8). The sensor substrate (1-1) is a cuboid structure, placed horizontally along its length. A through hole for the preload bolt (1-5) is machined at the center of its thickness direction. A tapered preload gasket (1-6) is mounted on the preload bolt (1-5). A rectangular groove is machined upward on the lower surface of the sensor substrate (1-1), with the center of the groove at the preload through hole. A ring wall structure is retained on the axis; two mounting bosses are symmetrically arranged on the inner surface of the groove along the length direction, on both sides of the ring wall structure, for mounting the Y0 type piezoelectric quartz crystal group (1-2) as a sensitive element; the Y0 type piezoelectric quartz crystal group (1-2) is mounted on the sensor sealing plate (1-4) through the contact boss (1-3), and its bottom passes through the sensor sealing plate (1-4); the horizontal distance between the centers of the two mounting bosses is the measuring point distance of the attached piezoelectric strain sensor (1); the sealing interface (1-8) is located on the side wall of the sensor base (1-1), and the sealing interface (1-8) is connected to the Y0 type piezoelectric quartz crystal group (1-2) through the signal wire (1-7) for transmitting charge signals.

2. The piezoelectric unidirectional force measuring device based on structural strain according to claim 1, characterized in that, In the attached piezoelectric strain sensor (1): The sensor substrate (1-1) is made of high-strength alloy steel after quenching and tempering. The diameter of the pre-tightening through hole is 6mm to 8mm. A tapered countersunk hole is machined at one end of the pre-tightening through hole facing the head of the pre-tightening bolt (1-5). The opening diameter of the top of the countersunk hole is larger than the diameter of the bottom through hole. It smoothly transitions to the pre-tightening through hole along the tapered surface. It is used to fit and contact the bottom of the tapered pre-tightening pad (1-6) to realize automatic centering of the pre-tightening force and ensure that the pre-tightening force of the pre-tightening bolt (1-5) can be evenly applied to the sensor substrate (1-1). The ring wall structure is used to isolate the pre-tightening bolts (1-5) from the internal space of the groove, and the ring wall structure is coaxial with the pre-tightening through hole; The distance between the measuring points is denoted as 2l ,in l The distance from the center of a single mounting boss to the center of the pre-tightening through hole in the sensor base (1-1) is adjusted according to different measurement range requirements; The sidewall of the sensor substrate (1-1) is machined with threaded through holes along its length for mounting and fixing the sealing interface (1-8).

3. The piezoelectric unidirectional force measuring device based on structural strain according to claim 2, characterized in that, In the Y0 type piezoelectric quartz crystal group (1-2): Each Y0 type piezoelectric quartz crystal group (1-2) includes multiple electrode sheets (1-2-1) and Y0 type piezoelectric quartz crystal wafers (1-2-2). The planar shapes of the electrode sheets (1-2-1) and the Y0 type piezoelectric quartz crystal wafers (1-2-2) are both octagonal and their external dimensions match each other. Furthermore, the shear sensitivity directions of the two Y0 type piezoelectric quartz crystal groups (1-2) are opposite. Each Y0-type piezoelectric quartz crystal group (1-2) adopts a multi-layer alternating stacked structure. It consists of two Y0-type piezoelectric quartz crystals (1-2-2) arranged in opposite polarization directions and three electrode plates (1-2-1) bonded together with conductive adhesive. An electrode plate (1-2-1) is closely attached to the middle position and the upper and lower outer sides of the two Y0-type piezoelectric quartz crystals (1-2-2). The middle electrode plate (1-2-1) is the signal output electrode, which is connected to the sealed interface (1-8) through the signal wire (1-7) to transmit the induced charge signal. The upper and lower outer electrode plates (1-2-1) are all grounded electrodes. When the deformation of the test piece causes the two contact bosses (1-3) to generate relative shear displacement, the induced charges generated by the two sets of Y0 type piezoelectric quartz crystal groups (1-2) have the same polarity and can be superimposed in the same direction for output; after the signal output terminals of the two sets of Y0 type piezoelectric quartz crystal groups (1-2) are connected in parallel through the signal wire (1-7), the charge signals are uniformly transmitted to the external signal processing unit (2) through the sealed interface (1-8).

4. The piezoelectric unidirectional force measuring device based on structural strain according to claim 3, characterized in that, In the Y0 type piezoelectric quartz crystal group (1-2): Two sets of Y0 type piezoelectric quartz crystal groups (1-2) are symmetrically bonded to the mounting boss. In the left Y0 type piezoelectric quartz crystal group (1-2), the polarization negative electrodes of the two Y0 type piezoelectric quartz crystal wafers (1-2-2) are close to the middle electrode (1-2-1), and the polarization positive electrodes are close to the upper and lower outer electrode wafers (1-2-1). In the right Y0 type piezoelectric quartz crystal group (1-2), the polarization positive electrodes of the two Y0 type piezoelectric quartz crystal wafers (1-2-2) are close to the middle electrode (1-2-1), and the polarization negative electrodes are close to the upper and lower outer electrode wafers (1-2-1), so that the shear sensitivity directions of the two sets of Y0 type piezoelectric quartz crystal groups (1-2) are opposite. The electrode sheet (1-2-1) is made of highly conductive copper or silver foil material with a thickness of 0.05 mm to 0.1 mm and a silver layer plated on the surface; the Y0 type piezoelectric quartz crystal (1-2-2) realizes the conversion of force and electricity signals based on the thickness shear piezoelectric effect.

5. The piezoelectric unidirectional force measuring device based on structural strain according to claim 4, characterized in that, The contact boss (1-3) is made of hard alloy and has a stepped cylindrical structure, consisting of a large-diameter end and a small-diameter end. The large-diameter end of the contact boss (1-3) is glued to the Y0 type piezoelectric quartz crystal group (1-2), and its diameter is larger than the outer circle of the Y0 type piezoelectric quartz crystal group (1-2), with a single-sided dimension larger by 0.5mm to 1mm. The small-diameter end of the contact boss (1-3) extends out of the sensor sealing plate (1-4) and contacts the surface of the measured part (4) after pre-tightening installation. The surface roughness of the two end faces of the contact boss (1-3) is controlled at Ra≤0.8μm, and the flatness is controlled at ≤0.01mm.

6. The piezoelectric unidirectional force measuring device based on structural strain according to claim 5, characterized in that, The sensor sealing plate (1-4) is made of 304 stainless steel and has three through holes machined on it: a first through hole in the middle, and a second and a third through hole symmetrically arranged on both sides of the first through hole. The first through hole is coaxially arranged with the pre-tightening through hole of the sensor base (1-1) and its size is larger than the outer diameter of the pre-tightening bolt (1-5). The second and third through holes are coaxially arranged with the two contact bosses (1-3) respectively, and their diameters are larger than the cross-sectional dimensions of the small diameter end of the contact bosses (1-3). The sensor sealing plate (1-4) is bonded and fixed to the bottom of the sensor base (1-1) to form a sealed mounting cavity. A gap of 0.5mm to 1mm is left between the sensor sealing plate (1-4) and the contact bosses (1-3), and there is no contact between the two.

7. The piezoelectric unidirectional force measuring device based on structural strain according to claim 6, characterized in that, The pre-tightening bolt (1-5) passes through the pre-tightening washer (1-6), the first through hole of the sensor sealing plate (1-4), and the pre-tightening through hole of the sensor base (1-1) in sequence, and is finally screwed into the threaded hole on the surface of the measured part (4); the pre-tightening washer (1-6) is a double conical washer with symmetrical upper and lower ends and a taper of 45°, and is placed between the head of the pre-tightening bolt (1-5) and the conical countersunk hole of the sensor base (1-1).

8. The piezoelectric unidirectional force measuring device based on structural strain according to claim 7, characterized in that, The measured component (4) is a unidirectional axial load-bearing component, selected from hydraulic press column, ship propulsion shaft system, wind turbine tower flange or heavy machinery load-bearing beam; The measured area on the surface of the measured part (4) has a defined elastic modulus and cross-sectional area, which can convert the axial static load and alternating vibration load into uniform surface axial strain, providing strain input for the attached piezoelectric strain sensor (1); the measured surface of the measured part (4) is pre-machined with threaded holes that match the specifications of the pre-tightening bolts (1-5), with a threaded hole depth of 14mm to 20mm; the mounting surface around the threaded hole is ground and cleaned, with a flatness ≤0.02mm / m and a surface roughness not exceeding Ra≤1.6μm.

9. A piezoelectric unidirectional force measurement method based on structural strain, characterized in that, Based on the piezoelectric unidirectional force measuring device according to any one of claims 1-8, the method includes the following steps: Step 1: Calibrate the attached piezoelectric strain sensor (1); use a combination of standard calibration block (5) and standard force source to calibrate, establish a quantitative correspondence between standard force value and sensor output charge, and obtain the sensitivity coefficient and performance index of the attached piezoelectric strain sensor (1). Step 2: Pre-process the measured part (4); At the measurement position of the measured part (4), a threaded hole matching the specifications of the preload bolt (1-5) is machined, and the mounting surface around the threaded hole is ground and cleaned. Step 3: Install the attached piezoelectric strain sensor (1) onto the surface of the measured part (4) and pre-tighten it; Align the pre-tightening through hole of the attached piezoelectric strain sensor (1) with the threaded hole on the surface of the measured part (4), place the pre-tightening washer (1-6) between the head of the pre-tightening bolt (1-5) and the sensor sealing plate (1-4); screw in the pre-tightening bolt (1-5) and pre-tighten it evenly based on the pre-tightening torque, the range of the pre-tightening torque is 10 N·m to 12 N·m, after pre-tightening, ensure that the two contact bosses (1-3) are tightly fitted with the surface of the measured part (4) without any gaps; Step 4: Real-time measurement and force calculation; When the measured part (4) is subjected to an axial load, its surface generates an axial strain proportional to the magnitude of the load. ε The cross-sectional area of ​​the measured part (4) is S The elastic modulus is E ; Axial strain ε The charge signal is transmitted to the Y0 type piezoelectric quartz crystal group (1-2) through two contact bosses (1-3) to generate a charge signal. Q Then, based on the sensitivity of the attached piezoelectric strain sensor (1) in step 1.3... The uniaxial bearing capacity of the measured component (4) is calculated by converting its cross-sectional dimensions and elastic modulus parameters. F : 。 10. The piezoelectric unidirectional force measurement method based on structural strain according to claim 9, characterized in that, In step 1, the calibration process is specifically as follows: Step 1.1: Design the standard calibration block (5); Design cross-sectional area The standard calibration block (5) is a rectangular prism with a constant cross-section, consisting of a fixed section at the bottom and a working section at the top; the length, width, and height of the working section are respectively... , , ,length ≥150mm, pre-machine a threaded hole at the center of the working section height, and use an attached piezoelectric strain sensor (1); The surface flatness of the working section of the standard calibration block (5) is controlled to be ≤0.02mm / m, the surface roughness Ra≤1.6μm, and the perpendicularity of the two end faces to the axis is ≤0.02mm, to ensure that no eccentric bending moment is generated during loading and the strain of the working section is uniform; the cross-sectional area of ​​the fixed section is more than twice the cross-sectional area of ​​the middle working section, and through holes are evenly distributed around the perimeter for fixing the standard calibration block; According to Hooke's law of axial tension and compression, the standard calibration block (5) is at the standard force value Uniform strain generated under action Satisfy the following formula: in, The elastic modulus of the standard calibration block (5) material; According to the applied standard force value The range and the cross-sectional area of ​​the standard calibration block (5) are Determine the strain generated by the standard calibration block This ensures that the strain range of the standard calibration block (5) is greater than the strain generated by the measured part (4) under actual force, and that the strain range of the standard calibration block (5) covers the strain range of the measured part (4). Step 1.2: Calibrate the attached piezoelectric strain sensor (1); The attached piezoelectric strain sensor (1) to be calibrated is fixed in the center of the working section of the standard calibration block (5) in the same way as in actual use, using the same pre-tightening bolts (1-5) and pre-tightening washers (1-6) and applying the same pre-tightening torque; the standard calibration block (5) on which the attached piezoelectric strain sensor (1) is mounted is fixed on the standard force source that has been calibrated by metrology. The standard force value is applied in a stepped loading manner, and the loading range is the full strain range of the standard calibration block (5). At least 5 uniformly distributed loading gradients are set. After each gradient is loaded, it is held for 3 to 5 seconds. After the charge signal stabilizes, the signal processing unit (2) completes the charge signal conditioning, and the data processing unit (3) collects and records the output charge signal. After each loading gradient is completed, it is unloaded to zero. The loading and unloading process is repeated three times, and the complete loading and unloading data is recorded each time. Among them, the full-scale output of the attached piezoelectric strain sensor (1) is the loading force value. Output at maximum; Step 1.3: Calculate the performance indicators of the attached piezoelectric strain sensor (1); Based on the average data from the three calibration cycles in step 1.2, the standard force value was determined using the least squares method. With output charge By performing linear fitting, the slope of the fitted line is obtained, which is the force sensitivity coefficient of the attached piezoelectric strain sensor (1). The unit is pC / με, as shown in the following formula: The linearity error of the attached piezoelectric strain sensor (1) is calculated based on the fitting results. The linearity error is the ratio of the maximum deviation between the fitted straight line and the average measured charge value of the three cycles of the same loading gradient to the full-scale output, expressed as a percentage. The repeatability error of the attached piezoelectric strain sensor (1) was calculated using the range method. The repeatability error is the ratio of the maximum difference in output charge under the same loading gradient in three cycles to the full-scale output, expressed as a percentage. It was ensured that the linearity and repeatability error of the attached piezoelectric strain sensor (1) met the design requirements within the calibrated strain range, where the linearity error was ≤2%FS and the repeatability error was ≤2%FS.

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