A bolt pre-tightening force sensor design method based on wireless strain detection

Abstract

The present application belongs to the technical field of force measurement, and discloses a bolt pretightening force sensor design method based on wireless strain detection, which comprises the following steps: acquiring the geometric structure, connection assembly and contact boundary information of a target bolt, establishing a pretightening transmission sectional atlas, and determining a main strain candidate band in the atlas; then, multiple probe base points are arranged in the candidate band, the response characteristics of each base point are acquired through sub-loading inspection, a measurement point optimization sequence is constructed according to the characteristics, and a formal mounting area is determined; then, strain sensing components are arranged in the formal mounting area and connected to wireless collection nodes to form a sensing layout; finally, post-assembly calibration is performed on the sensing layout, joint interpretation rules between each mounting area are established based on the calibration results and written into the wireless collection nodes, and the sensor design is completed; through systematic measurement point screening and multi-position collaborative interpretation, the present application effectively separates the pretightening force signal from the interference load, and improves the measurement accuracy and consistency.

Description

Technical Field

[0001] This invention relates to the field of force measurement technology, and more specifically, to a design method for a bolt preload sensor based on wireless strain detection. Background Technology

[0002] Current mainstream sensor design methods typically rely solely on experience to select one or a few locations on the smooth section of the bolt and attach strain gauges. This lack of in-depth analysis of the complex stress state of the bolt results in the strain signal acquired by the sensor being a mixture of axial preload strain and strain from various interfering loads. This signal aliasing introduces errors when extrapolating the actual preload from the measured strain value. When the connection structure is subjected to vibration, impact, or uneven stress, this measurement error can be drastically amplified, even leading to reverse indications. This experience-based method of selecting measurement points not only fails to guarantee measurement accuracy but also causes performance discrepancies among sensors in the same batch due to variations in manual placement. This makes it difficult to reliably apply wireless strain gauge technology in critical bolt connections with high safety requirements.

[0003] In view of this, the present invention proposes a design method for a bolt preload sensor based on wireless strain detection to solve the above problems. Summary of the Invention

[0004] To overcome the aforementioned deficiencies of the prior art and to achieve the above objectives, the present invention provides the following technical solution: a design method for a bolt preload sensor based on wireless strain detection, comprising:

[0005] Step S1: Obtain the geometric structure information, connection assembly information and contact boundary information of the target bolt; establish a preload transfer segment map based on the geometric structure information, connection assembly information and contact boundary information; and determine the candidate main strain zone in the preload transfer segment map.

[0006] Step S2: Deploy multiple detection base points within the candidate main strain zone, conduct load tests on the multiple detection base points in stages, and obtain the test results; construct an optimal sequence of measurement points based on the test results, and determine the formal mounting area from the optimal sequence of measurement points;

[0007] Step S3: Set up strain sensing components in each formal mounting area and connect each strain sensing component to the wireless acquisition node to form a sensing layout corresponding to the formal mounting area.

[0008] Step S4: Perform post-assembly calibration on the sensor layout, establish joint interpretation rules between formal mounting areas based on the post-assembly calibration results, and write the joint interpretation rules into the wireless acquisition node to obtain the bolt preload sensor.

[0009] The technical effects and advantages of the bolt preload sensor design method based on wireless strain detection of the present invention are as follows:

[0010] This invention establishes a preload transfer segmentation map, meticulously dividing the bolt surface according to stress transfer characteristics. This avoids areas prone to stress concentration and local disturbances, fundamentally solving the problem of blindly selecting points based on traditional experience. After determining the candidate main strain zones, various verification methods, such as pure tension, unilateral pressure deviation, and micro-rotation disturbance, are used to screen the candidate locations one by one. The selected measuring points are sensitive to pure preload and have good suppression capabilities against interference loads, significantly reducing signal aliasing. More importantly, this invention designs three types of... The combined layout of the mounting positions is equivalent to equipping the sensor with a state recognition system, which can distinguish between different states such as preload dominance, off-center load mixing, and bending and torsion mixing in actual operation. This prevents the sensor from generating erroneous indications when the bolt connection is subjected to vibration, impact, or uneven force, unlike traditional solutions. Instead, it can identify whether the current situation is a change in actual preload force or external interference. In addition, through standardized mounting position settings, limit boundary constraints, and directional packaging processes, the problem of arbitrary placement by manual mounting is solved, ensuring the performance consistency of sensors in the same batch. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of a bolt preload sensor design method based on wireless strain detection according to the present invention. Detailed Implementation

[0012] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0013] Example 1

[0014] Please see Figure 1 As shown in the figure, this embodiment presents a design method for a bolt preload sensor based on wireless strain detection, including:

[0015] Step S1: Obtain the geometric structure information, connection assembly information and contact boundary information of the target bolt; establish a preload transfer segment map based on the geometric structure information, connection assembly information and contact boundary information; and determine the candidate main strain zone in the preload transfer segment map.

[0016] In this embodiment, the geometric structure information refers to the external dimensional parameters of the target bolt itself, including the diameter and thickness of the bolt head, the diameter and length of the smooth shank, etc.; these parameters can be directly extracted from the bolt's engineering drawings or 3D model; the connection and assembly information refers to the fitting relationship parameters between the bolt and the connected parts in the actual assembly state, including the thickness and material of the connected parts, the gap value between the bolt hole diameter and the bolt shank diameter, etc.; the contact boundary information refers to the position and contact state parameters of each interface where the bolt contacts the surrounding parts after assembly, including the boundary position of the pressure-bearing contact area between the lower surface of the bolt head and the upper surface of the connected parts, the contact start position and end position of each tooth surface in the thread pair, etc.; this information is obtained through pressure testing during the actual assembly process.

[0017] After obtaining the above three types of information, the bolt shank surface is segmented and analyzed along the bolt axis. When the bolt is subjected to preload, the force is transmitted from the bearing surface at the head to the shank, propagating axially and finally reaching the nut through the threaded joint. Along this transmission path, the stress state varies significantly at different locations. The area near the bearing surface at the head is constrained by the head stiffness, resulting in uneven stress distribution and obvious local concentration characteristics. In the area further from the head into the smooth shank segment, the stress distribution tends to be uniform, and the axial strain shows a good linear relationship with the preload. Near the thread initiation point, the stress state becomes complex again due to changes in cross-sectional shape and the thread tooth surface beginning to bear load. The stress in the tail thread segment decreases as the tooth surface is gradually unloaded. Based on the above analysis, the bolt shank surface is divided into four functional segments along the axial direction: the head-affected segment, the uniform transmission segment, the transition disturbance segment, and the tail-release segment. The head-affected segment corresponds to the shank area from the lower edge of the head fillet to the point where the head stress influence disappears. The uniform stress transfer section corresponds to the shank region between the point where the head influence disappears and a certain distance above the thread start point; this section has the most uniform axial stress distribution. The transition disturbance section corresponds to the region between the thread start point and the first complete thread tooth; in this section, the stress state changes drastically due to the transition of the cross-sectional shape from a smooth cylinder to a threaded cross-section. The tail release section corresponds to the part of the thread segment far from the clamping area; in this section, the thread surface load gradually decreases, and the axial stress approaches zero. It should be noted that the boundaries of the above four functional sections are not strict geometric lines, but transition regions determined based on the stress gradient variation characteristics in the finite element analysis results.

[0018] After axial segmentation, it is necessary to further identify local feature areas within each segment that may cause strain signal distortion. The bolt shank surface is not an ideally smooth cylindrical surface; in actual manufacturing, various local features exist, including the rounded transition area where the head connects to the shank, the cross-sectional change area where the shank diameter changes, the relief groove area in front of the thread initiation position, and surface markings such as batch numbers and inspection marks that may exist on the shank surface. These local feature areas share the common characteristic that the load-bearing path of the bolt shank undergoes a local shift at these locations; that is, the direction or cross-section of force transmission changes abruptly, causing the stress state at that location to deviate from the ideal uniaxial tensile state. In this embodiment, the reversal sensitive area refers to the location where a local load-bearing shift occurs within the aforementioned local feature areas. Specifically, when the preload is transmitted axially along the shank to the rounded transition area, due to the abrupt change in cross-sectional shape, part of the axial force is converted into a radial component, resulting in stress concentration at the root of the rounded corner. Similarly, at the relief groove location, the groove formed by the material removal abruptly reduces the load-bearing cross-section, causing the axial force to reversal on both sides of the groove. These locations where local load transfer occurs are registered as turnaround sensitive areas.

[0019] Centered on the sensitive return zone, axial clearance boundaries are formed by extending along both sides of the bolt axis, and circumferential clearance boundaries are formed by extending along both sides of the circumference. The axial and circumferential clearance boundaries are combined to form an installation clearance zone. In this embodiment, the installation clearance zone indicates that within this area, due to significant interference from local features on the stress state, the strain signal obtained by attaching strain gauges will contain a large proportion of interference components, making it unsuitable as a location for measuring preload.

[0020] Furthermore, multiple azimuth zones are divided along the circumferential direction within the uniform transfer section. Because the bearing area on the lower surface of the bolt head may have uneven contact in the circumferential direction, the stress non-uniformity in the head-affected section will extend axially downwards, leaving a certain degree of circumferential non-uniformity in the upper region of the uniform transfer section. Similarly, the stress disturbance in the transition disturbance section will extend upwards, affecting the lower region of the uniform transfer section. The azimuth zones within the uniform transfer section that fall within the projection range of the head-affected section and the transition disturbance section are registered as disturbance identification zones. In this embodiment, the projection range refers to the azimuth angle range covered by projecting the respective stress non-uniform regions of the head-affected section and the transition disturbance section axially onto the circumferential surface of the uniform transfer section. The continuous surface area within the uniform transfer section, excluding the installation avoidance zone and the disturbance identification zone, is determined as the principal strain candidate zone. The principal strain candidate zone is the area on the bolt shank surface that is most sensitive to axial preload and least affected by local feature interference and end effects; it forms the basis for subsequent deployment of detection benchmarks and determination of the formal mounting area. All the above segment information, avoidance zone information, disturbance identification zone information and main strain candidate zone information are integrated to form a pre-tightening transfer segment map. This map visualizes and annotates each functional segment and feature area on a two-dimensional plane in the form of bolt unfolded surface.

[0021] Based on the above steps, this embodiment starts from the mechanical transmission mechanism of bolts, systematically analyzes the transmission path and distribution characteristics of preload on the bolt shank, eliminates areas affected by local feature interference and end effects, and thus accurately locates candidate areas on the bolt surface that are sensitive to preload and have pure signals, solving the problem of insufficient measurement accuracy caused by selecting patch positions based on experience in traditional methods.

[0022] Step S2: Deploy multiple detection base points within the candidate main strain zone, conduct load tests on the multiple detection base points in stages, and obtain the test results; construct an optimal sequence of measurement points based on the test results, and determine the formal mounting area from the optimal sequence of measurement points;

[0023] Since the principal strain candidate zone is still a large continuous region, the strain response characteristics at different locations within this region still differ. Therefore, further screening and optimization are needed through actual experiments.

[0024] Specifically, several rows of axial probe positions and several sets of diametrically opposed probe positions are set within the main strain candidate zone to form probe base points. In this embodiment, axial probe positions refer to rows of probe points evenly spaced along the bolt axis within the length of the main strain candidate zone. The spacing between adjacent axial probe positions is determined based on the axial length of the main strain candidate zone and the required spatial resolution. Diametrically opposed probe positions refer to two probe points opposite each other along the bolt diameter direction at the same axial height, i.e., one probe point is set at each of two positions 180 degrees apart on the circumference, forming a set of diametrically opposed probe positions. The purpose of setting up diametrically opposed probe positions is to utilize the symmetry of the strain signals at diametrically opposed positions to identify and separate the effects of interfering loads such as eccentric loads and bending moments.

[0025] After all the probe points are set up, three different types of load tests are performed sequentially: the first is a pure tension test. In the pure tension test, a pure axial preload is applied to the bolt using a hydraulic tensioner or a precision torque wrench. During the application process, the load direction is kept strictly along the bolt axis to avoid introducing lateral components and bending moments. During the loading process, multiple probe points are repeatedly read, and the order of response of each probe point is recorded. In this embodiment, the order of response refers to the order in which the strain output value of each probe point begins to change identibly as the preload gradually increases. After repeating multiple loading and unloading cycles, the probe points whose order of response remains unchanged in each cycle are registered as sequentially stable points. A sequentially stable point means that there is a stable and repeatable correspondence between the strain response and the preload at that location, unaffected by minor disturbances during the loading process.

[0026] The second method is the unilateral pressure test. In the unilateral pressure test, an eccentric pressure is applied to one side of the bolt head or the surface of the connected parts to simulate the lateral load that the bolt may experience under actual working conditions. Under the eccentric load, the direction of change and the expansion of the difference between the corresponding probe points of each pair of probes are compared. In this embodiment, the direction of change refers to whether the strain output values ​​of the probe points on both sides of the pair increase or decrease in the same direction during the application of the eccentric load, or whether one side increases while the other side decreases; the expansion of the difference refers to whether the strain difference between the probe points on both sides of the pair remains within a small range or continues to expand as the eccentric load continues to be applied. Probe point pairs with consistent direction of change and limited expansion of the difference are registered as eccentric pressure withstand point pairs.

[0027] The third method is micro-rotation disturbance testing. In this test, with the preload constant, a small change in the torsional angle is applied to the bolt to simulate minor loosening or rotation that might occur in a vibration environment. During the micro-rotation, the order of fluctuations between adjacent probe points is examined. In this embodiment, the order of fluctuations refers to whether the timing and direction of the strain output values ​​at adjacent probe points remain consistent after the micro-rotation disturbance is applied. Probe points with a continuous order of fluctuations are linked together to form a stable probe point chain. A stable probe point chain means that the strain field in the region where this chain of probe points is located maintains a continuous and smooth change characteristic under micro-rotation disturbance, without signal abrupt changes caused by local stress concentration or surface defects.

[0028] The results of three tests—sequential stable points, bias tolerance point pairs, and stable base point chains—are overlaid and analyzed. Regions that simultaneously satisfy all three results are designated as priority retention areas. These priority retention areas are experimentally verified regions within the principal strain candidate band that exhibit stable preload response, tolerance to bias load disturbances, and good signal continuity. Based on these priority retention areas, the probe base points are arranged according to their spatial adjacency to generate a preferred measurement point sequence. This preferred sequence is an ordered list where each probe base point is arranged according to its spatial position on the bolt surface, with adjacent elements also being physically adjacent on the bolt surface.

[0029] From the preferred sequence of measurement points, regions with controlled axial spacing and complementary circumferential positions are selected as the formal mounting areas. In this embodiment, controlled axial spacing means that the spacing between each formal mounting area along the bolt axial direction is kept within a predetermined range. In this embodiment, the axial spacing is not less than 1.5 times the strain gauge grid length and not more than one-third of the axial length of the main strain candidate band, to avoid the mounting areas being too dense and causing mutual interference, and also to avoid the spacing being too large and causing insufficient sampling of the strain field of the rod. Complementary circumferential positions mean that the distribution of each formal mounting area along the bolt circumference can form a diametrical or uniform distribution relationship, so that the circumferential symmetry can be used to separate the interference load components during subsequent joint interpretation.

[0030] Based on the above process, this embodiment further selects the mounting position with the optimal response characteristics, overcoming the influence of practical factors such as processing errors and assembly deviations that cannot be covered by theoretical analysis. This makes the final determined formal mounting area have high repeatability and strong anti-interference under actual working conditions, solving the problem of performance dispersion of sensors in the same batch due to differences in manual mounting positions.

[0031] Step S3: Set up strain sensing components in each formal mounting area and connect each strain sensing component to the wireless acquisition node to form a sensing layout corresponding to the formal mounting area.

[0032] After determining the formal mounting areas, precise installation and wiring connections of the strain sensing components are required within each area. In traditional methods, strain gauge placement relies entirely on the operator's manual experience; deviations in mounting angle and position directly lead to deviations in the acquired signals, thus affecting the consistency of measurement results. To address this issue, this embodiment establishes a standardized multi-mounting-position configuration and a structured wiring scheme within each formal mounting area.

[0033] Three types of mounting positions are set up in each formal mounting area: main expansion mounting position, diameter calibration mounting position, and oblique identification mounting position. The main expansion mounting position is arranged along the axial direction of the target bolt, meaning the sensitive grid direction of the strain gauge is parallel to the bolt axis, used to detect the axial expansion and contraction strain of the bolt shank under preload. The diameter calibration mounting position is set opposite to the main expansion mounting position in the bolt circumferential direction, meaning they are 180 degrees apart. The strain gauges in the diameter calibration mounting position are also arranged along the bolt axis, their function being to identify and separate the strain components caused by bending moment and lateral eccentric load by comparing the signal with that of the main expansion mounting position. Under ideal pure axial preload conditions, the axial strain on both sides of the diameter should be equal; when a bending moment exists, the tensile strain on one side of the diameter increases while the compressive strain on the other side decreases, and the difference between the two reflects the magnitude of the bending moment component. The oblique identification mounting position is inclined relative to the main expansion mounting position, meaning the sensitive grid direction of the strain gauge forms a certain angle with the bolt axis. In this embodiment, the tilt angle of the oblique identification mounting position is 45 degrees. When the bolt shank is simultaneously subjected to axial force and torque, the strain in the 45-degree direction is most sensitive to torsional shear strain, which can effectively detect the existence and magnitude of the torque component.

[0034] Strain gauge carrier, compliant transition layer, and sealing layer are sequentially arranged at each mounting position. In this embodiment, the strain gauge carrier refers to the substrate material that carries the strain-sensitive grid, typically a polyimide film or epoxy resin substrate. The compliant transition layer is disposed between the strain gauge carrier and the bolt shank surface, and its function is to compensate for the curvature of the cylindrical surface of the bolt shank, so that the strain gauge carrier can fit well with the curved surface and avoid strain transfer loss caused by non-fitting the curved surface. The sealing layer is disposed on the outside of the strain gauge carrier to protect the strain gauge from the effects of environmental humidity, mechanical impact, and chemical corrosion.

[0035] Limiting boundaries are set around each mounting position to keep the installation direction and termination position of each mounting position fixed. In this embodiment, the limiting boundaries refer to positioning features pre-marked or machined on the surface of the bolt shank, including axial positioning lines and circumferential positioning points. The axial positioning lines are used to control the installation position accuracy of the strain gauge along the axial direction, and the circumferential positioning points are used to control the angular accuracy of the strain gauge in the circumferential direction. By setting the limiting boundaries, the installation position and angular deviation of each mounting position can be controlled within a predetermined tolerance range when different operators perform mounting operations at different times, thereby ensuring the consistency of sensors in the same batch. The main telescopic mounting position and the diameter calibration mounting position are connected to the same acquisition branch, and the oblique identification mounting position is connected to an independent identification branch. The same acquisition branch means that the signals of the main telescopic mounting position and the diameter calibration mounting position are transmitted to the wireless acquisition node through the same set of wires. The two are differentially or half-bridge connected by a Wheatstone bridge inside the acquisition node, so that the preload signal and bending moment signal can be directly separated at the circuit level. The independent identification branch maintains independent signal transmission for the oblique identification mounting position, allowing for independent judgment of the torsional component. Each acquisition branch connects to the wireless acquisition node via its own wiring path, which is laid along the surface of the bolt shaft and features stress-relief bends at corners to prevent the wires from being stretched and damaged during bolt tightening.

[0036] Within the wireless acquisition node, a main telescopic input, a diameter calibration input, and a diagonal identification input are configured, with each input connected to its corresponding acquisition branch. A fixed acquisition sequence is established based on this sequence, ensuring the wireless acquisition node reads each acquisition branch in the predetermined order, preventing signal correspondence errors due to timing discrepancies. The mounting position number, formal mounting area number, and circumferential orientation number associated with each input are written into a mounting position correspondence table, and the routing direction and endpoint position associated with each acquisition branch are written into an acquisition branch number table. The mounting position correspondence table and the acquisition branch number table are then checked for consistency to confirm that the signal received by each input indeed originates from its corresponding mounting position, completing the sensor layout marking.

[0037] Based on the above process, this embodiment establishes a standardized multi-mount configuration scheme and a structured wiring specification, so that the installation position, angle and wiring method of the strain gauge no longer depend on the operator's personal experience, but are rigidly constrained by the limit boundary and the correspondence of the numbers, thereby ensuring the consistency and repeatability of sensor installation, and laying the hardware foundation for subsequent joint interpretation and interference separation.

[0038] Step S4: Perform post-assembly calibration on the sensor layout, establish joint interpretation rules between formal mounting areas based on the post-assembly calibration results, and write the joint interpretation rules into the wireless acquisition node to obtain the bolt preload sensor;

[0039] After the physical installation of the sensor layout is completed, due to the unavoidable slight deviations during the pasting process, and the difference between the constraint conditions of the bolts after final assembly into the actual connection structure and the individual component inspection, it is necessary to perform post-assembly calibration of the sensor layout to determine the output characteristics of each mounting position in the actual assembly state, and based on this, establish joint interpretation rules that can accurately identify the load state in actual working conditions.

[0040] First, the connection structure between the formal mounting area and the wireless acquisition node is oriented and encapsulated. In this embodiment, oriented encapsulation refers to the protective encapsulation of the entire connection path after the strain gauge is pasted and the wires are connected, while ensuring that the encapsulation direction corresponds to the bolt installation direction. Specifically, a start-end marker and an end-end marker are set on the outside of the formal mounting area. The start-end marker corresponds to the starting connection end of the acquisition branch, that is, the connection point between the wire leading from the strain gauge and the acquisition branch; the end-end marker corresponds to the ending connection end of the acquisition branch, that is, the connection point between the acquisition branch and the input end of the wireless acquisition node. The purpose of setting the start-end marker and the end-end marker is to establish a clear signal transmission direction marker from the strain gauge to the wireless acquisition node, preventing the branch from being reversed due to operational negligence during the encapsulation process. Along the wiring path of the acquisition branch, a covering section, a corner release section, and a node lead-out section are set sequentially, so that the acquisition branch extends in segments between the formal mounting area and the wireless acquisition node. The covering section refers to the wiring segment from the strain gauge lead-out line to the curved surface of the bolt shank. This segment of wire is laid close to the bolt surface and fixed with a thin protective coating. The corner release section refers to the middle section where the conductor extends from the bolt shank surface and makes a significant turn in the routing direction. This section of the conductor has an appropriate length allowance and forms a release bend to compensate for minor deformations that may occur in the bolt under load, preventing the conductor from breaking due to tension or transferring mechanical stress to the strain gauge. The node lead-out section refers to the routing section from the end of the corner release section to the input end of the wireless acquisition node. Port positioning areas corresponding to the acquisition branch numbers are set around the periphery of the wireless acquisition node, and each acquisition branch is connected to its corresponding port positioning area in a predetermined order. After connection, the head end markings, tail end markings, and port positioning areas are checked to confirm that the signal transmission direction and port correspondence of each acquisition branch are consistent with the sensor layout markings. The check results are then recorded in the assembly record unit corresponding to the target bolt. The assembly record unit is a data record stored in the wireless acquisition node's internal or external management system, used to trace the installation parameters and check results of the sensors on each bolt.

[0041] After completing the orientation and encapsulation, three calibration operations are performed sequentially: The first is steady-state tension calibration. In steady-state tension calibration, a known pure axial preload is applied to the bolt using a standard tensioning device, and the output results of the main telescopic mounting position, the diameter-check mounting position, and the oblique identification mounting position are collected respectively. Under pure axial load, the main telescopic mounting position and the diameter-check mounting position should show synchronous and unidirectional changes, that is, their output values ​​should increase synchronously with the increase of preload and decrease synchronously with the decrease of preload. The synchronous change relationship between the two is recorded as baseline characteristics.

[0042] The second method is yaw disturbance calibration. In yaw disturbance calibration, while maintaining a certain preload, a lateral oscillation moment is applied to the bolt to simulate the bending moment and torque disturbances experienced by the bolt under actual working conditions. Under yaw disturbance, the output of the oblique identification mounting position will show fluctuations independent of the main telescopic mounting position and the diameter verification mounting position. The independent fluctuation characteristics of the oblique identification mounting position are recorded.

[0043] The third method is bias calibration. In bias calibration, an eccentric pressure is applied to the bolt head to simulate the uneven surface of the connected parts or the eccentricity of the washer caused by the eccentric load. Under the action of the eccentric load, the output of the main telescopic mounting position and the diameter calibration mounting position will show different changes, that is, one side increases while the other side decreases or the increase is different. The order of the difference and the magnitude of the difference are recorded.

[0044] Based on the results of the three calibration operations, three types of identifiers are extracted. Specifically, a diameter consistency identifier is extracted based on the synchronous change relationship between the main telescopic mounting position and the diameter-alignment calibration mounting position. The synchronous change direction of the main telescopic mounting position and the diameter-alignment calibration mounting position during steady-state tension calibration is used as the primary criterion. When both change in the same direction, the diameter consistency identifier is registered. In this embodiment, the diameter consistency identifier indicates that the current load state is dominated by axial preload, and the strain signals on both sides of the diameter are consistent. An off-center load separation identifier is extracted based on the difference in change relationship between the main telescopic mounting position and the diameter-alignment calibration mounting position. The order of difference in change between the main telescopic mounting position and the diameter-alignment calibration mounting position during off-center calibration is used as the secondary criterion. When the two show continuous separation, the off-center load separation identifier is registered. In this embodiment, the off-center load separation identifier indicates that an off-center load component has been mixed into the current load state, resulting in a continuous difference in the strain signals on both sides of the diameter. Based on the undulation relationship of the oblique identification mounting position, the bending and torsion intervention mark is extracted. The independent undulation relationship of the oblique identification mounting position in the yaw disturbance calibration is used as the supplementary judgment condition. When the oblique identification mounting position undulates first, the bending and torsion intervention mark is registered. In this embodiment, the bending and torsion intervention mark indicates that there is a bending moment or torque component in the current load state, which makes a shear strain component independent of the axial strain appear in the oblique direction.

[0045] A joint interpretation rule is established based on the combination of the first judgment condition, the second judgment condition, and the supplementary judgment condition. Specifically, the interpretation rules include the following four states: Pre-tightening dominant state: the diameter alignment mark is valid, the off-center load separation mark is invalid, and the bending and torsion intervention mark is invalid. At this time, the main telescopic mounting position and the diameter verification mounting position keep changing synchronously and in the same direction. The oblique identification mounting position has no independent fluctuations, indicating that the current load is mainly pure axial pre-tightening force. The output of the main telescopic mounting position is directly used to calculate the pre-tightening force.

[0046] Off-center load mixed in state: the diameter alignment mark is invalid, the off-center load separation mark is valid, and the bending and torsion intervention mark is invalid; at this time, the two sides of the diameter show continuous separation but no independent undulation in the oblique direction, indicating that the current load has an off-center load component but no bending and torsion component. The preload force is calculated after averaging the output of the main telescopic mounting position and the diameter verification mounting position to eliminate the off-center load effect.

[0047] Bending and torsion mixed state: the diameter consistency indicator is valid, the off-center load separation indicator is invalid, and the bending and torsion intervention indicator is valid. At this time, the diameters are consistent on both sides but there are independent fluctuations in the diagonal direction, indicating that the current load is mixed with bending and torsion components but there are no off-center load components. The preload force is calculated after the output of the diagonal identification mounting position is used to perform bending and torsion compensation on the main channel signal.

[0048] Composite disturbance state: the diameter alignment indicator is invalid, the off-center load separation indicator is valid, and the bending and torsion intervention indicator is valid; at this time, the two sides of the diameter are separated and there are independent fluctuations in the oblique direction, indicating that the current load is mixed with off-center load and bending and torsion components. The preload is calculated after the output of the three mounting positions is used for joint compensation.

[0049] The aforementioned joint interpretation rules are written into the status identification area of ​​the wireless acquisition node, and these rules are associated with the installation position identifier of the target bolt. In this embodiment, the installation position identifier refers to the number and location information of the target bolt in the connection structure. By associating the interpretation rules with the installation position, the wireless acquisition node can automatically determine the current load state based on the combined characteristics of the three acquired signals during operation, and select the corresponding interpretation rule to calculate the preload, thereby achieving adaptive measurement of the preload.

[0050] Based on the above process, this embodiment upgrades the sensor from a simple measurement mode with a single strain gauge output to an intelligent measurement mode with multi-mount collaborative sensing and multi-state autonomous identification. By utilizing the signal correlation characteristics among the main expansion mount, the diameter calibration mount, and the oblique identification mount, a joint interpretation rule covering multiple load states is established. This enables the sensor to autonomously identify the type of interference and adopt corresponding compensation strategies when encountering interference loads such as off-center loads, bending moments, or torques in actual working conditions. This significantly improves the accuracy and reliability of preload measurement under complex working conditions and solves the problem of signal aliasing causing measurement errors to be amplified sharply under vibration and shock environments in traditional methods.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A design method for a bolt preload sensor based on wireless strain detection, characterized in that, include: Step S1: Obtain the geometric structure information, connection assembly information and contact boundary information of the target bolt; establish a preload transfer segment map based on the geometric structure information, connection assembly information and contact boundary information; and determine the candidate main strain zone in the preload transfer segment map. Step S2: Set up multiple detection base points within the candidate main strain zone, conduct load tests on the multiple detection base points in stages, and obtain the test results; Based on the test results, a preferred sequence of test points is constructed, and the formal mounting area is determined from the preferred sequence of test points; Step S3: Set up strain sensing components in each formal mounting area and connect each strain sensing component to the wireless acquisition node to form a sensing layout corresponding to the formal mounting area. Step S4: Perform post-assembly calibration on the sensor layout, establish joint interpretation rules between formal mounting areas based on the post-assembly calibration results, and write the joint interpretation rules into the wireless acquisition node to obtain the bolt preload sensor.

2. The design method for a bolt preload sensor based on wireless strain detection according to claim 1, characterized in that, Based on geometric structure information, connection assembly information, and contact boundary information, a preload transfer segmentation map is established, and candidate principal strain zones are identified in the preload transfer segmentation map, including: Extract the head bearing position, shank length, thread start position, and clamping coverage of the target bolt, and divide it into a head-affected section, a uniform transmission section, a transition disturbance section, and a tail-release section along the bolt's axial direction. Identify fillet transition zones, cross-sectional change zones, tool relief groove zones, and surface marking zones around the head-affected section, uniform transmission section, transition disturbance section, and tail-release section. Register locations with localized load transfer as return sensitive zones, and form installation avoidance zones based on these return sensitive zones. Divide multiple azimuth zones along the circumference within the uniform transmission section, and register azimuth zones falling within the projection range of the head-affected section and the transition disturbance section as disturbance identification zones. Determine the continuous surface area within the uniform transmission section, excluding the installation avoidance zone and disturbance identification zone, as the principal strain candidate zone, and generate a preload transmission segmentation map.

3. The design method for a bolt preload sensor based on wireless strain detection according to claim 2, characterized in that, Step S2 includes: Several columns of axial probe positions and several sets of diameter probe positions are set within the main strain candidate zone to form probe base points. Pure tension test, unilateral pressure deviation test and micro-rotation disturbance test are performed on the probe base points in sequence, and the response order relationship, diameter difference relationship and adjacent linkage relationship of each probe base point under different test states are recorded. The probe base points with stable response order, limited diameter difference and continuous adjacent linkage relationship are determined as priority base points, and the priority base points are arranged according to spatial adjacency relationship to generate the measurement point optimization sequence. From the measurement point optimization sequence, the area with controlled axial spacing and complementary circumferential position is selected as the formal mounting area.

4. The design method for a bolt preload sensor based on wireless strain detection according to claim 3, characterized in that, Step S3 includes: Within the formal mounting area, main telescopic mounting positions, diameter calibration mounting positions, and oblique identification mounting positions are respectively set up. The main telescopic mounting positions are arranged along the axial direction of the target bolt, the diameter calibration mounting positions are arranged circumferentially opposite to the main telescopic mounting positions, and the oblique identification mounting positions are arranged at an angle relative to the main telescopic mounting positions. Strain gauge carriers, compliant transition layers, and sealing layers are sequentially installed at each mounting position, and limiting boundaries are set around each mounting position to keep the installation direction and installation termination position of each mounting position fixed. The main telescopic mounting positions and diameter calibration mounting positions are connected to the same acquisition branch, and the oblique identification mounting positions are connected to an independent identification branch. Each acquisition branch is connected to the wireless acquisition node through its own wiring path. A correspondence between acquisition branch numbers and mounting positions is established within the wireless acquisition node to form a sensing layout.

5. The design method for a bolt preload sensor based on wireless strain detection according to claim 4, characterized in that, Step S4 includes: First, the connection structure between the formal mounting area and the wireless acquisition node is oriented and encapsulated. After the oriented encapsulation is completed, steady-state tension calibration, yaw disturbance calibration, and bias calibration are performed sequentially, and the output results of the main telescopic mounting position, the diameter verification mounting position, and the oblique identification mounting position are collected respectively. Based on the synchronous change relationship between the main telescopic mounting position and the diameter verification mounting position, the diameter consistency identifier is extracted; based on the difference change relationship between the main telescopic mounting position and the diameter verification mounting position, the off-center load separation identifier is extracted; based on the fluctuation change relationship of the oblique identification mounting position, the bending and torsion intervention identifier is extracted. The diameter consistency identifier, the off-center load separation identifier, and the bending and torsion intervention identifier are combined to establish joint interpretation rules corresponding to the pre-tightening dominant state, the off-center load mixed state, the bending and torsion mixed state, and the composite disturbance state. The joint interpretation rules are written into the wireless acquisition node and associated with the installation position identifier of the target bolt.

6. The design method for a bolt preload sensor based on wireless strain detection according to claim 5, characterized in that, Locations exhibiting localized load transfer are designated as sensitive reversal zones, and installation clearance zones are established based on these sensitive reversal zones, including: The transition position of the lower edge of the head, the position of the change in shank diameter, the position of the thread entry, the position of the relief groove, and the position of the manufacturing mark are sequentially identified along the outer surface of the target bolt, and corresponding boundary registration points are established. The continuity of the surface section between adjacent boundary registration points is checked, and the section with the change in load path or the sudden change in surface morphology is identified as the return sensitive area. The axial avoidance boundary is formed by expanding along both sides of the target bolt with each return sensitive area as the center, and the circumferential avoidance boundary is formed by expanding along both sides of the circumference. The axial avoidance boundary and the circumferential avoidance boundary are combined to form the installation avoidance zone and written into the preload transfer segmentation diagram.

7. The design method for a bolt preload sensor based on wireless strain detection according to claim 6, characterized in that, The exploration benchmarks were subjected to pure tension test, unilateral pressure deviation test, and micro-rotation disturbance test in sequence. The response order, diameter difference, and adjacent linkage relationship of each exploration benchmark under different test conditions were recorded, including: In the pure tension test, multiple probe points are repeatedly read, the order of response of each probe point is recorded, and the probe points whose response order remains unchanged are registered as sequential stable points. In the unilateral bias test, the direction of change and the extent of difference between the corresponding probe base points of each pair of probe positions are compared, and the probe base point pairs with consistent direction of change and limited difference expansion are registered as bias tolerance point pairs. In the micro-perturbation test, the order of fluctuations between adjacent probe base points is examined, and probe base points with continuous order of fluctuations are connected in series to form a stable base point chain. The overlapping area of ​​sequential stable points, bias voltage withstand point pairs and stable base point chains is determined as the priority retention area, and a preferred sequence of measurement points is generated based on the priority retention area.

8. The design method for a bolt preload sensor based on wireless strain detection according to claim 7, characterized in that, Within the wireless acquisition node, a correspondence is established between the acquisition branch number and the mounting position to form a sensor layout, including: Within the wireless acquisition node, a main telescopic input terminal, a diameter calibration input terminal, and a diagonal identification input terminal are set up, and each of these terminals is connected to its corresponding acquisition branch. An acquisition sequence is established according to a fixed arrangement of these terminals, allowing the wireless acquisition node to read data from each acquisition branch in a predetermined order. The mounting position number, formal mounting area number, and circumferential orientation number associated with each input terminal are written into a mounting position correspondence table, and the routing direction and endpoint position associated with each acquisition branch are written into an acquisition branch number table. The mounting position correspondence table and the acquisition branch number table are then checked for consistency to complete the sensor layout marking.

9. The design method for a bolt preload sensor based on wireless strain detection according to claim 8, characterized in that, The system combines the radial consistency indicator, the off-center load separation indicator, and the bending-torsional intervention indicator to establish joint interpretation rules for the pre-tension dominant state, the off-center load mixed state, the bending-torsional mixed state, and the combined disturbance state, including: The synchronous change direction of the main telescopic mounting position and the diameter calibration mounting position during steady-state tension calibration is used as the primary judgment condition, and the diameter consistency mark is registered when the two change in the same direction. The order of the difference between the main telescopic mounting position and the diameter calibration mounting position during the bias voltage calibration is used as the secondary judgment condition, and the bias load separation mark is registered when the two are continuously separated. The independent undulation relationship of the mounting position in the lateral disturbance calibration is used as a supplementary judgment condition, and the bending and twisting intervention mark is registered when the undulation of the mounting position is identified first. A joint interpretation rule is established based on the combination relationship of the first judgment condition, the second judgment condition, and the supplementary judgment condition, and the joint interpretation rule is written into the status identification area of ​​the wireless acquisition node.

10. The design method for a bolt preload sensor based on wireless strain detection according to claim 9, characterized in that, Oriented encapsulation is performed on the connection structure between the formal mounting area and the wireless acquisition node, including: Set up start and end markers on the outside of the formal mounting area. The start marker corresponds to the starting connection end of the acquisition branch, and the end marker corresponds to the ending connection end of the acquisition branch. Set up mounting sections, corner release sections, and node lead-out sections along the routing path of the acquisition branch, so that the acquisition branch extends in segments between the formal mounting area and the wireless acquisition node. Set up port positioning areas corresponding to the acquisition branch numbers on the periphery of the wireless acquisition node, and connect each acquisition branch to the corresponding port positioning area in a predetermined order. After the connection is completed, check the start marker, end marker, and port positioning area, and register the check results to the assembly record unit corresponding to the target bolt.

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