A strain gauge adhesive curing stress compensation process

Abstract

The application discloses a strain gauge bonding and curing stress compensation process, which comprises the following steps: loading a strain gauge body on a shrinkage compensation device through a shape memory alloy wire; pasting the strain gauge body on a target object through an adhesive layer and applying a vertical pressing force; when it is detected that the adhesive layer enters a gel point, heating the shape memory alloy wire to above a phase transition temperature, so that the shape memory alloy wire is shrunk by phase transition, and a horizontal outward pulling force opposite to a curing shrinkage direction of the adhesive is generated; collecting a feedback signal of the shape memory alloy wire, comparing the feedback signal with a preset target value, and adjusting a heating power in real time; when the feedback signal reaches the preset target value and is stable, determining that the curing is completed, separating the shape memory alloy wire and removing the shrinkage compensation device. Through the phase transition shrinkage of the shape memory alloy wire, the adhesive curing shrinkage stress is actively offset, and closed-loop control is performed correspondingly, so that the installation stress in the strain gauge mounting process is effectively eliminated, and the strain gauge mounting quality is improved.

Description

Technical Field

[0001] This invention relates to the field of strain gauge technology, and in particular to a strain gauge bonding and curing stress compensation process. Background Technology

[0002] A strain gauge is a sensing element based on the strain effect. When a conductor or semiconductor material undergoes mechanical deformation under external force, its resistance changes accordingly. This change in resistance is measured by a specialized instrument and converted into a strain value at the measuring point. Strain gauges are widely used in the manufacturing of products such as aerospace mechanical strength testing, electrical equipment, civil engineering, building construction, and weighing sensors.

[0003] In the manufacturing process of products such as load cells and electronic scales, strain gauges are typically bonded to the strain zone surface of elastic elements using adhesives. During installation, adhesive is first applied to the mounting surface of the elastic element, then the strain gauge is attached to the mounting surface, and the adhesive is cured by heating or other methods. During the curing process, a vertical clamping force is usually applied to the strain gauge to ensure a tight bond between the strain gauge and the surface of the elastic element.

[0004] However, the adhesive undergoes volume shrinkage during curing. Since the strain gauge is fixed to the surface of the elastic element by the adhesive, the curing shrinkage of the adhesive generates a shrinkage stress in the in-plane direction, causing the strain gauge to deform. This deformation stress does not originate from the actual strain of the elastic element, but rather is an additional stress introduced during installation (i.e., installation stress). This stress will be superimposed on the actual strain signal generated by the elastic element during subsequent use, leading to a significant error in the measurement results.

[0005] To address the aforementioned issues, existing technologies have proposed several solutions, such as adding a substrate between the strain gauge and the elastic element for isolation, adding fillers to the adhesive to reduce shrinkage, or eliminating residual stress through a post-curing process. However, these solutions are all passive responses or remedial measures and cannot actively counteract the generation of shrinkage stress during the critical curing window of the adhesive.

[0006] Therefore, there is currently a lack of a method in the technology that can offset the adhesive curing shrinkage stress in real time and dynamically during the strain gauge mounting process, and continuously verify the compensation effect during the curing process. Summary of the Invention

[0007] In view of the aforementioned deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a strain gauge bonding and curing stress compensation process, which aims to actively offset the adhesive curing shrinkage stress and eliminate installation stress during the strain gauge mounting process, thereby ensuring the mounting quality and subsequent measurement accuracy.

[0008] To achieve the above objectives, the present invention discloses a strain gauge bonding and curing stress compensation process, the process comprising: Step S1: The strain gauge body to be attached is loaded onto the shrinkage compensation device using a shape memory alloy wire; wherein, the strain gauge body includes a substrate and a sensitive grid disposed on the substrate, the bottom surface of the substrate is provided with an adhesive layer, the shrinkage compensation device includes a compensation ring and a heating element, the outer side of the strain gauge body is connected to the inner side of the compensation ring through the shape memory alloy wire, thereby loading the strain gauge body inside the compensation ring, the heating element is disposed on the compensation ring, and the heating element is used to heat the shape memory alloy wire; Step S2: Attach the strain gauge body to a preset position on the target object using the adhesive layer, and apply a vertical clamping force to the strain gauge body to ensure that the strain gauge body is tightly attached to the target object. Step S3: When the adhesive layer is detected to have entered the gel point, the heating element is activated to heat the shape memory alloy wire to above its phase transition temperature, causing the shape memory alloy wire to undergo phase transition shrinkage and generate a horizontal outward pulling force opposite to the curing shrinkage direction of the adhesive layer, so as to counteract the curing shrinkage stress of the adhesive layer. Step S4: During the process of the shape memory alloy wire generating a horizontal outward pulling force, the feedback signal of the shape memory alloy wire is collected; based on the comparison result of the feedback signal and the preset target value, the heating power of the heating element is adjusted in real time. Step S5: When the feedback signal reaches the preset target value and remains stable, it is determined that the adhesive layer has been cured, and the heating element is turned off; the shape memory alloy wire is separated from the strain gauge body, and the shrinkage compensation device is removed to complete the attachment of the strain gauge body.

[0009] Optionally, the feedback signal in step S4 is the resistance value of the shape memory alloy wire; the resistance value of the shape memory alloy wire is acquired in real time through a resistance measurement circuit, and its resistance change rate is calculated. The resistance change rate is the change range of the real-time resistance value relative to the initial resistance value at room temperature; the preset target value is the target resistance change amount.

[0010] Optionally, step S4, which involves adjusting the heating power of the heating element in real time based on the comparison result between the feedback signal and the preset target value, includes: The resistance change rate is compared with the target resistance change in real time; When the rate of change of resistance is less than the target change of resistance, the heating current of the heating element is increased; When the rate of change of resistance is greater than the target change of resistance, the heating current of the heating element is reduced; An alarm signal is issued when the deviation between the resistance change rate and the target resistance change exceeds a preset threshold for an extended period.

[0011] Optionally, the shape memory alloy wire is made of a material whose resistance is not sensitive to temperature changes, and whose absolute value of temperature coefficient of resistance is less than the absolute value of strain-resistivity, so that the resistance change of the shape memory alloy wire caused by temperature rise during heating phase transformation is less than 10% of the resistance change caused by phase transformation contraction.

[0012] Optionally, the two ends of the shape memory alloy wire are fixedly connected to the inner side of the compensation ring and the outer side of the strain gauge substrate by welding, respectively; in step S5, the welding connection points at both ends of the shape memory alloy wire are cut off by laser cutting, thereby separating the shape memory alloy wire from the strain gauge body.

[0013] Optionally, the number of shape memory alloy wires is 2 to 6, and they are evenly arranged around the periphery of the strain gauge body.

[0014] Optionally, the detection method for the adhesive layer entering the gel point in step S3 specifically includes: A pair of detection electrodes are disposed on the strain gauge substrate, and the detection electrodes are in contact with the adhesive layer; the resistance value of the adhesive layer is measured in real time through the detection electrodes, and when the rate of change of the resistance value shows a sudden inflection point, it is determined that the adhesive layer has entered the gel point.

[0015] Optionally, the shape memory alloy wire is multiple, and each shape memory alloy wire is provided with an independent resistance measurement circuit; step S4 further includes: Feedback signals from each of the shape memory alloy wires are collected separately, and the deviation value between each feedback signal is calculated; when the deviation value exceeds a preset consistency threshold, an alarm signal is issued.

[0016] Optionally, the compensation ring is further provided with an ambient temperature sensor; step S4 also includes: The ambient temperature is collected in real time by the ambient temperature sensor, and the feedback signal of the collected shape memory alloy wire is temperature compensated and corrected according to the ambient temperature to compensate for the influence of changes in ambient temperature on the feedback signal.

[0017] Optionally, the top of the compensation ring is provided with a pressure surface. The vertical clamping force in step S2 is applied to the pressure surface of the compensation ring through a clamping fixture and transmitted to the strain gauge body by the compensation ring. The compensation ring also serves as a fixing reference for the shape memory alloy wire and a force transmission component for vertical pressure.

[0018] The beneficial effects of this invention are as follows: 1. This invention actively counteracts the curing shrinkage stress of the adhesive by utilizing the phase change shrinkage of the shape memory alloy wire to generate an outward horizontal tensile force in the opposite direction during the curing shrinkage of the adhesive. This ensures that the strain gauge body does not bear in-plane tensile force throughout the curing process, thus completely eliminating the installation stress caused by adhesive curing shrinkage in traditional mounting processes. Compared with the passive or post-hoc solutions in existing technologies, such as adding substrate isolation, adding fillers to reduce shrinkage rate, or post-curing to eliminate residual stress, this invention actively intervenes at the root of stress generation, fundamentally avoiding the interference of installation stress on subsequent measurement results. 2. This invention achieves closed-loop control of sensing-compensation-verification by real-time acquisition of the resistance value of the shape memory alloy wire as a feedback signal and real-time comparison with a preset target value. When the resistance change rate deviates from the target value, the system automatically increases or decreases the heating current for adjustment; when the deviation continues to exceed the threshold, an alarm signal is issued. This mechanism solves the defect in existing technologies where shape memory alloys are only used as open-loop clamping tools and cannot verify whether the compensation effect is adequate, ensuring that the compensation force is accurately matched with the actual shrinkage force of the adhesive and avoiding the risk of insufficient or excessive compensation. 3. This invention further enhances the practicality and reliability of the solution through the synergistic effect of multiple subordinate technical features: independent monitoring and consistency judgment of multiple shape memory alloy wires ensure uniform tensile force distribution; an ambient temperature sensor performs temperature compensation correction on the feedback signal, eliminating the impact of ambient temperature fluctuations on control accuracy; the resistance method accurately detects the gel point, ensuring that the compensation force is activated at the optimal time; the compensation ring simultaneously serves as a fixed reference for the shape memory alloy wires and a force transmission component for vertical pressure application, making the structure reusable and easy to operate. 4. This invention only adds a detachable shrinkage compensation device to the traditional strain gauge mounting process, without changing the strain gauge body structure, increasing product thickness, or introducing additional stress transmission media. The shape memory alloy wires are connected by welding and then separated by laser cutting. After removing the compensation device, the strain gauge operates independently, exhibiting good compatibility with existing production processes and making it suitable for mass production and application in products such as weighing sensors and electronic scales.

[0019] In summary, the present invention effectively solves the technical problem in the prior art that it is impossible to offset the curing shrinkage stress of the adhesive in real time and dynamically and to perform closed-loop verification during the strain gauge mounting process, thus significantly improving the mounting quality and measurement accuracy of the strain gauge. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of a strain gauge bonding and curing stress compensation process provided in a specific embodiment of the present invention; Figure 2 This is a schematic diagram of the connection structure between the shrinkage compensation device and the strain gauge body provided in a specific embodiment of the present invention. Detailed Implementation

[0021] This invention discloses a strain gauge bonding and curing stress compensation process. Those skilled in the art can refer to the content of this document and appropriately modify the technical details to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0022] This invention provides a strain gauge bonding and curing stress compensation process, such as... Figure 1 As shown, the process includes: Step S1: The strain gauge body to be attached is loaded onto the shrinkage compensation device using shape memory alloy wire.

[0023] The strain gauge body includes a substrate and a sensitive grid disposed on the substrate. An adhesive layer is provided on the bottom surface of the substrate. The shrinkage compensation device includes a compensation ring and a heating element. The outer side of the strain gauge body is connected to the inner side of the compensation ring through a shape memory alloy wire, so that the strain gauge body is loaded inside the compensation ring. The heating element is disposed on the compensation ring and is used to heat the shape memory alloy wire.

[0024] It should be noted that, in this embodiment, the strain gauge body to be attached is first loaded onto the shrinkage compensation device using a shape memory alloy wire. The strain gauge body includes a substrate and a sensitive grid disposed on the substrate, with an adhesive layer for attachment on the bottom surface of the substrate. The shrinkage compensation device includes a compensation ring and a heating element. The strain gauge body is located inside the compensation ring, and its outer side is connected to the inner side of the compensation ring via the shape memory alloy wire. The heating element is disposed on the compensation ring and is used to heat the shape memory alloy wire. Through the above loading method, one end of the shape memory alloy wire is fixed to the inner side of the compensation ring, and the other end is fixed to the outer side of the strain gauge substrate, so that the shrinkage force generated by the shape memory alloy wire during subsequent heating can directly act on the strain gauge substrate.

[0025] Step S2: Attach the strain gauge body to the preset position of the target object using the adhesive layer, and apply a vertical clamping force to the strain gauge body to make the strain gauge body fit tightly against the target object.

[0026] It should be noted that the strain gauge body, mounted in the shrinkage compensation device, is adhered to a predetermined position on the target object via an adhesive layer on the bottom surface of the substrate. The target object can be the elastic body of a load cell, the elastic element of an electronic scale, or other structural components requiring strain gauge mounting. After adhesion, a vertical clamping force is applied to the strain gauge body to ensure tight adhesion between the strain gauge body and the target object surface. This clamping force is the same as the pressure applied in traditional mounting processes, ensuring uniform spread of the adhesive layer and expelling air bubbles, thus guaranteeing good strain transfer efficiency between the strain gauge body and the target object.

[0027] In this specific embodiment, the vertical clamping force in step S2 is applied to the pressure surface of the compensation ring through the clamping fixture and transmitted to the strain gauge body by the compensation ring; the compensation ring also serves as the fixing reference for the shape memory alloy wire and the force transmission component for vertical pressure.

[0028] It should be noted that when applying the vertical clamping force in step S2, the clamping fixture acts directly on the pressure surface of the compensation ring, and the clamping force is transmitted from the compensation ring to the strain gauge body located inside it. Thus, the compensation ring simultaneously performs a dual function: firstly, it serves as a fixed reference for the shape memory alloy wire, providing stable anchoring for the wire's contraction; secondly, it acts as a force transmission component for vertical pressure application, uniformly transmitting the force from the clamping fixture to the strain gauge body. This reusable structural design eliminates the need for separate pressure pads or pressure heads, simplifying the device structure, reducing operational steps, and ensuring uniform pressure application.

[0029] Step S3: When the adhesive layer is detected to have entered the gel point, the heating element is activated to heat the shape memory alloy wire to above its phase transition temperature, causing the shape memory alloy wire to undergo phase transition shrinkage and generate a horizontal outward pulling force opposite to the direction of adhesive layer curing shrinkage, so as to counteract the curing shrinkage stress of the adhesive layer.

[0030] It should be noted that the adhesive undergoes a gel point from its liquid state to complete curing, which is the critical moment when the adhesive loses its fluidity and begins to establish initial structural strength. In this embodiment, when the adhesive layer is detected to have reached the gel point, the heating element is immediately activated to heat the shape memory alloy wire. After being heated above its phase transition temperature, the shape memory alloy wire undergoes phase transition contraction, generating a horizontal outward tensile force. The direction of this tensile force is opposite to the direction of adhesive curing contraction—the adhesive curing contraction generates an inward pulling force, pulling the strain gauge body towards the center; the phase transition contraction of the shape memory alloy wire generates an outward pulling force, pulling the strain gauge substrate outward. The two opposing forces cancel each other out at the strain gauge body. If heating is activated before the gel point, the adhesive is still in a liquid state, and the tensile force of the shape memory alloy wire may cause displacement of the strain gauge body; if heating is activated too late after the gel point, the adhesive has already cured and contracted, and installation stress has already formed. Therefore, activating compensation at this critical moment of the gel point can both prevent slippage during the liquid state and cancel out the shrinkage stress at the same time.

[0031] It is worth mentioning that the gel point refers to the point in time during the curing process of the adhesive layer where its storage modulus equals its loss modulus. At this point, the adhesive layer changes from a liquid state dominated by viscous flow to a gel state dominated by elastic deformation. Macroscopically, this is manifested as the adhesive layer losing its fluidity to the surface of the object being tested and beginning to build up preliminary shear strength.

[0032] In this specific embodiment, the detection method for the adhesive layer entering the gel point in step S3 specifically includes: A pair of detection electrodes are placed on the strain gauge substrate, and the detection electrodes are in contact with the adhesive layer. The resistance value of the adhesive layer is measured in real time through the detection electrodes. When the rate of change of the resistance value shows a sudden inflection point, it is determined that the adhesive layer has entered the gel point.

[0033] It should be noted that the detection method for the adhesive layer entering the gel point is the resistance method. Specifically, a pair of detection electrodes are placed on the strain gauge substrate, and these electrodes are in contact with the adhesive layer. Because the adhesive has high ion mobility and low resistance in its liquid state, as the curing reaction proceeds, the adhesive gradually crosslinks to form a three-dimensional network structure, the ion mobility decreases, and the resistance increases. Near the gel point, the rate of change of resistance exhibits a clear abrupt inflection point—that is, the resistance changes from a slow change to a rapid change or from a rapid change to a point of stabilization. By measuring the resistance of the adhesive layer in real time and monitoring its rate of change using the detection electrodes, when this rate of change reaches an abrupt inflection point, it can be determined that the adhesive layer has entered the gel point. This detection method requires no additional equipment; the detection electrodes can be directly integrated into the strain gauge substrate, resulting in low cost, fast response, and the ability to accurately capture the optimal compensation initiation time at the gel point.

[0034] Step S4: During the process of generating a horizontal outward pulling force in the shape memory alloy wire, the feedback signal of the shape memory alloy wire is collected; based on the comparison result between the feedback signal and the preset target value, the heating power of the heating element is adjusted in real time.

[0035] It should be noted that during the process of the shape memory alloy wire generating a horizontal outward tensile force, feedback signals from the shape memory alloy wire are continuously collected and compared in real time with a preset target value. The heating power of the heating element is dynamically adjusted based on the comparison results. If the feedback signal does not reach the preset target value, it indicates that the shrinkage of the shape memory alloy wire is insufficient, the generated tensile force is too small, and it fails to completely offset the curing shrinkage stress of the adhesive. In this case, the heating power is increased to further shrink the shape memory alloy wire through phase transformation. If the feedback signal exceeds the preset target value, it indicates that the shrinkage of the shape memory alloy wire is too large, the generated tensile force is too large, and there may be a risk of overcompensation. In this case, the heating power is reduced to decrease the tensile force. Through the above real-time feedback adjustment, the shrinkage force of the shape memory alloy wire is always dynamically balanced with the actual curing shrinkage force of the adhesive. This closed-loop control mechanism ensures the accuracy of compensation and avoids the shortcomings of traditional open-loop schemes that only compensate without verification.

[0036] In this specific embodiment, the feedback signal in step S4 is the resistance value of the shape memory alloy wire; the resistance value of the shape memory alloy wire is collected in real time by the resistance measurement circuit, and its resistance change rate is calculated. The resistance change rate is the change range of the real-time resistance value relative to the initial resistance value at room temperature; the preset target value is the target resistance change amount.

[0037] It should be noted that because the resistivity of shape memory alloys changes with the crystal structure during phase transformation—martensite and austenite phases have different resistivities—the resistance change of the shape memory alloy wire can directly reflect the degree of phase transformation shrinkage. Specifically, the resistance value of the shape memory alloy wire is acquired in real time through a resistance measurement circuit, and its resistance change rate is calculated, that is, the change in real-time resistance value relative to the initial resistance value at room temperature. Accordingly, a preset target value is set as the target resistance change. This target resistance change is determined in advance through a curing shrinkage rate calibration test on the same batch of adhesive, representing the resistance change corresponding to the amount of shrinkage of the shape memory alloy wire required to completely offset the curing shrinkage stress of the adhesive. By monitoring whether the resistance change rate reaches the target resistance change, it is possible to accurately determine whether the compensation is adequate.

[0038] Furthermore, in step S4, the heating power of the heating element is adjusted in real time based on the comparison result between the feedback signal and the preset target value, including: The rate of change of resistance is compared with the target change of resistance in real time; When the rate of change of resistance is less than the target change of resistance, increase the heating current of the heating element; When the rate of change of resistance is greater than the target change of resistance, reduce the heating current of the heating element; An alarm signal is issued when the deviation between the rate of change of resistance and the target change of resistance continues to exceed a preset threshold.

[0039] It should be noted that the above closed-loop control is executed as follows: the real-time measured rate of change of resistance is continuously compared with a predetermined target rate of change of resistance. When the rate of change of resistance is less than the target rate of change of resistance, it indicates that the phase change shrinkage of the shape memory alloy wire is insufficient, and the outward pulling force it generates has not completely offset the curing shrinkage stress of the adhesive. At this time, the heating current of the heating element is increased to further heat the shape memory alloy wire and generate more phase change shrinkage. When the rate of change of resistance is greater than the target rate of change of resistance, it indicates that the phase change shrinkage of the shape memory alloy wire is excessive, and the outward pulling force it generates has exceeded the curing shrinkage stress of the adhesive. At this time, the heating current of the heating element is reduced to prevent overcompensation from causing new additional stress. When the deviation between the rate of change of resistance and the target rate of change of resistance continuously exceeds a preset threshold, it indicates that the compensation process is abnormal (possibly caused by batch differences in adhesive, changes in ambient temperature, performance deviations of the shape memory alloy wire, etc.). At this time, an alarm signal is issued to prompt the operator to check.

[0040] Furthermore, the shape memory alloy wire is made of a material whose resistance is not sensitive to temperature changes. The absolute value of its temperature coefficient of resistance is less than the absolute value of its strain-resistivity coefficient, so that the resistance change of the shape memory alloy wire caused by temperature rise during heating phase transformation is less than 10% of the resistance change caused by phase transformation contraction.

[0041] It should be noted that the shape memory alloy wire is made of a material whose resistance is insensitive to temperature changes. Specifically, the absolute value of the temperature coefficient of resistance of the selected shape memory alloy wire is less than the absolute value of its strain-resistivity coefficient. This means that when the temperature rises, the resistance change of the shape memory alloy wire mainly originates from the lattice structure change caused by the phase transition (i.e., phase transition contraction), rather than from the effect of the temperature rise itself on the carrier mobility. Through this material selection, the resistance change caused by temperature rise is controlled to be less than 10% of the resistance change caused by phase transition contraction. This characteristic significantly improves the signal-to-noise ratio of the feedback signal, enabling the signal acquired by the resistance measurement circuit to accurately reflect the degree of phase transition contraction of the shape memory alloy wire, unaffected by significant interference from ambient temperature fluctuations, thereby ensuring the accuracy and reliability of closed-loop control.

[0042] In this specific embodiment, there are multiple shape memory alloy wires, and each shape memory alloy wire is provided with an independent resistance measurement circuit; step S4 also includes: Feedback signals from each shape memory alloy wire are collected separately, and the deviation between each feedback signal is calculated. When the deviation exceeds the preset consistency threshold, an alarm signal is issued.

[0043] It should be noted that when multiple shape memory alloy (SME) wires are used, each SME wire has an independent resistance measurement circuit. During the compensation process, feedback signals from each SME wire are collected separately, and the deviation between these signals is calculated. If the resistance change rate of one SME wire deviates significantly from that of the other wires, it indicates that the wire may have problems such as poor welding, localized overheating, or uneven stress. When the deviation exceeds a preset consistency threshold, the system issues an alarm signal. This independent monitoring mechanism ensures separate control over the working status of each SME wire, preventing the overall compensation effect from being affected by the failure of individual wires.

[0044] In this specific embodiment, the compensation ring is also equipped with an ambient temperature sensor; step S4 further includes: The ambient temperature is collected in real time by an ambient temperature sensor, and the feedback signal of the collected shape memory alloy wire is temperature compensated and corrected according to the ambient temperature to compensate for the influence of changes in ambient temperature on the feedback signal.

[0045] It should be noted that during the compensation process, the ambient temperature is collected in real time by the ambient temperature sensor. Since the resistance of the shape memory alloy wire changes slightly due to the ambient temperature (despite the selection of a material with a low temperature coefficient of resistance), temperature compensation correction is performed on the feedback signal of the shape memory alloy wire based on the collected ambient temperature. Specifically, the change in resistance caused by the change in ambient temperature is calculated based on the difference between the ambient temperature and the room temperature reference temperature, and this portion is subtracted from the total collected resistance change, thereby eliminating the influence of ambient temperature changes on the feedback signal. This temperature compensation mechanism further improves the accuracy of closed-loop control, making this process applicable to production environments in different seasons and regions.

[0046] Step S5: When the feedback signal reaches the preset target value and remains stable, it is determined that the adhesive layer has been cured and the heating element is turned off; the shape memory alloy wire is separated from the strain gauge body and the shrinkage compensation device is removed to complete the installation of the strain gauge body.

[0047] It should be noted that once the feedback signal reaches the preset target value and remains stable, the adhesive layer is considered to have cured completely. At this point, the adhesive has developed sufficient structural strength and no longer generates significant shrinkage stress, thus completing the compensation task of the shape memory alloy wire. The heating element is then turned off, the shape memory alloy wire is separated from the strain gauge body, and the entire shrinkage compensation device is removed. After separation, the strain gauge body is independently bonded to the surface of the target object, and there is no installation stress within it caused by the shrinkage of the cured adhesive. At this point, the installation of the strain gauge body is complete, and the installed strain gauge is ready for subsequent use.

[0048] In this specific embodiment, the two ends of the shape memory alloy wire are fixedly connected to the inner side of the compensation ring and the outer side of the strain gauge substrate by welding, respectively; in step S5, the welding connection points at both ends of the shape memory alloy wire are cut off by laser cutting, thereby separating the shape memory alloy wire from the strain gauge body.

[0049] It should be noted that the two ends of the shape memory alloy wire are fixedly connected to the inner side of the compensation ring and the outer side of the strain gauge substrate by welding, respectively. Welding offers advantages such as high connection strength, low contact resistance, and resistance to loosening during heating, ensuring that the contractile force generated by the shape memory alloy wire is reliably transmitted to the strain gauge substrate. Correspondingly, in the separation step after curing, the welded joints at both ends of the shape memory alloy wire are severed by laser cutting. Laser cutting offers advantages such as high precision, a small heat-affected zone, and non-contact with the workpiece, enabling clean and efficient separation of the shape memory alloy wire from the strain gauge body without causing mechanical impact or thermal damage. After separation, only very small welding residue remains on the outer side of the strain gauge substrate, which does not affect the normal use of the strain gauge.

[0050] In this specific embodiment, the number of shape memory alloy wires is 2 to 6, which are evenly arranged around the periphery of the strain gauge body.

[0051] It should be noted that the number of shape memory alloy wires is 2 to 6, evenly arranged circumferentially around the strain gauge body. Using multiple shape memory alloy wires ensures that the shrinkage force is evenly distributed circumferentially on the strain gauge substrate, preventing slight rotation or displacement of the strain gauge body during curing due to unilateral stress. The evenly distributed tension also ensures that the adhesive is subjected to a symmetrical stress field during curing, resulting in more uniform curing shrinkage and further improving the mounting quality. The specific number can be selected according to the size of the strain gauge and the shrinkage rate of the adhesive—2 or 3 wires can be used for small strain gauges, and 4 or 6 wires can be used for larger strain gauges.

[0052] In a specific application, the connection structure between the shrinkage compensation device and the strain gauge body can be as follows: Figure 2 As shown, Figure 2In the diagram, 201 is the sensitive grid, 202 is the substrate, 203 is the adhesive layer, 204 is the compensation ring, 205 is the shape memory alloy wire, 206 is the heating element, and 207 is the target object. The blue arrow represents the vertical clamping force, the red arrow represents the solidification shrinkage stress generated by the solidification shrinkage of the adhesive layer, and the green arrow represents the horizontal outward pulling force generated by the phase transformation shrinkage of the shape memory alloy wire.

[0053] In practice, the operator first loads the strain gauge body to be applied into the compensation ring of the shrinkage compensation device using multiple shape memory alloy wires. Then, the strain gauge body, along with the shrinkage compensation device, is placed at the preset application position on the target object, ensuring the adhesive layer contacts the object's surface and applies vertical pressure. During adhesive curing, a resistance measurement circuit continuously monitors the adhesive layer's resistance to determine the gel point. When the gel point is reached, the system automatically activates the heating element to heat the shape memory alloy wires, simultaneously collecting the resistance value of each wire as a feedback signal. The control module compares the feedback signal with a pre-calibrated target value in real time, dynamically adjusting the heating power to precisely match the shrinkage force of each wire with the adhesive's curing shrinkage force. Throughout this process, an ambient temperature sensor continuously monitors the ambient temperature and compensates for any errors in the feedback signal. Once the feedback signals from all shape memory alloy wires stabilize near the target value, the system determines curing is complete and shuts off the heating element. Finally, the welding points of the shape memory alloy wires are cut using laser cutting, the shrinkage compensation device is removed, and the strain gauge application is complete. Throughout the process, operators do not need to rely on experience to judge the timing and amount of compensation; all control is completed automatically by the system.

[0054] This invention actively counteracts the curing shrinkage stress of the adhesive by utilizing the phase transformation shrinkage of shape memory alloy wires to generate an outward horizontal tensile force in the opposite direction during the adhesive curing shrinkage process. This ensures that the strain gauge body does not experience in-plane tensile forces throughout the curing process, thereby completely eliminating the installation stress caused by adhesive curing shrinkage in traditional mounting processes. Compared to existing technologies that passively address or remedy the issue by adding substrate isolation, adding fillers to reduce shrinkage, or post-curing to eliminate residual stress, this invention actively intervenes at the source of stress, fundamentally avoiding the interference of installation stress on subsequent measurement results.

[0055] This invention achieves closed-loop control of sensing, compensation, and verification by real-time acquisition of the resistance value of shape memory alloy wire as a feedback signal and comparing it with a preset target value. When the resistance change rate deviates from the target value, the system automatically increases or decreases the heating current; when the deviation continuously exceeds a threshold, an alarm signal is issued. This mechanism solves the problem in existing technologies where shape memory alloys are only used as open-loop clamping tools and the compensation effect cannot be verified. It ensures that the compensation force is precisely matched with the actual shrinkage force of the adhesive, avoiding the risk of insufficient or excessive compensation.

[0056] The embodiments of the present invention further enhance the practicality and reliability of the solution through the synergistic effect of multiple subordinate technical features: independent monitoring and consistency judgment of multiple shape memory alloy wires ensure uniform distribution of tension; the ambient temperature sensor performs temperature compensation correction on the feedback signal to eliminate the influence of ambient temperature fluctuations on control accuracy; the resistance method accurately detects the gel point to ensure that the compensation force is activated at the optimal time; the compensation ring serves as both a fixed reference for the shape memory alloy wire and a force transmission component for vertical pressure application, making the structure reusable and easy to operate.

[0057] This invention adds a detachable shrinkage compensation device to the traditional strain gauge mounting process without altering the strain gauge structure, increasing product thickness, or introducing additional stress transfer media. The shape memory alloy wires are connected by welding and then separated by laser cutting. After removing the compensation device, the strain gauge operates independently. It exhibits good compatibility with existing manufacturing processes and is suitable for mass production of products such as weighing sensors and electronic scales.

[0058] In summary, the embodiments of the present invention effectively solve the technical problem in the prior art that it is impossible to offset the curing shrinkage stress of the adhesive in real time and dynamically and to perform closed-loop verification during the strain gauge mounting process, thus significantly improving the mounting quality and measurement accuracy of the strain gauge.

[0059] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0060] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0061] The above are merely preferred embodiments of the present invention and are 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 are included within the scope of protection of the present invention.

Claims

1. A strain gauge bonding and curing stress compensation process, characterized in that, The process includes: Step S1: The strain gauge body to be attached is loaded onto the shrinkage compensation device using a shape memory alloy wire; wherein, the strain gauge body includes a substrate and a sensitive grid disposed on the substrate, the bottom surface of the substrate is provided with an adhesive layer, the shrinkage compensation device includes a compensation ring and a heating element, the outer side of the strain gauge body is connected to the inner side of the compensation ring through the shape memory alloy wire, thereby loading the strain gauge body inside the compensation ring, the heating element is disposed on the compensation ring, and the heating element is used to heat the shape memory alloy wire; Step S2: Attach the strain gauge body to a preset position on the target object using the adhesive layer, and apply a vertical clamping force to the strain gauge body to ensure that the strain gauge body is tightly attached to the target object. Step S3: When the adhesive layer is detected to have entered the gel point, the heating element is activated to heat the shape memory alloy wire to above its phase transition temperature, causing the shape memory alloy wire to undergo phase transition shrinkage and generate a horizontal outward pulling force opposite to the curing shrinkage direction of the adhesive layer, so as to counteract the curing shrinkage stress of the adhesive layer. Step S4: During the process of the shape memory alloy wire generating a horizontal outward pulling force, the feedback signal of the shape memory alloy wire is collected; based on the comparison result of the feedback signal and the preset target value, the heating power of the heating element is adjusted in real time. Step S5: When the feedback signal reaches the preset target value and remains stable, it is determined that the adhesive layer has been cured, and the heating element is turned off; the shape memory alloy wire is separated from the strain gauge body, and the shrinkage compensation device is removed to complete the attachment of the strain gauge body.

2. The strain gauge bonding and curing stress compensation process according to claim 1, characterized in that, The feedback signal in step S4 is the resistance value of the shape memory alloy wire; the resistance value of the shape memory alloy wire is collected in real time by the resistance measurement circuit, and its resistance change rate is calculated. The resistance change rate is the change of the real-time resistance value relative to the initial resistance value at room temperature; the preset target value is the target resistance change amount.

3. The strain gauge bonding and curing stress compensation process according to claim 2, characterized in that, In step S4, adjusting the heating power of the heating element in real time based on the comparison result between the feedback signal and the preset target value includes: The resistance change rate is compared with the target resistance change in real time; When the rate of change of resistance is less than the target change of resistance, the heating current of the heating element is increased; When the rate of change of resistance is greater than the target change of resistance, the heating current of the heating element is reduced; An alarm signal is issued when the deviation between the resistance change rate and the target resistance change exceeds a preset threshold for an extended period.

4. The strain gauge bonding and curing stress compensation process according to claim 2, characterized in that, The shape memory alloy wire is made of a material whose resistance is not sensitive to temperature changes. The absolute value of its temperature coefficient of resistance is less than the absolute value of its strain-resistivity coefficient, so that the resistance change of the shape memory alloy wire caused by temperature rise during heating phase transformation is less than 10% of the resistance change caused by phase transformation contraction.

5. The strain gauge bonding and curing stress compensation process according to claim 1, characterized in that, The two ends of the shape memory alloy wire are fixedly connected to the inner side of the compensation ring and the outer side of the strain gauge substrate by welding, respectively; in step S5, the welding connection points at both ends of the shape memory alloy wire are cut off by laser cutting, thereby separating the shape memory alloy wire from the strain gauge body.

6. The strain gauge bonding and curing stress compensation process according to claim 1, characterized in that, The number of shape memory alloy wires is 2 to 6, and they are evenly arranged around the periphery of the strain gauge body.

7. The strain gauge bonding and curing stress compensation process according to claim 1, characterized in that, The detection method for the adhesive layer entering the gel point in step S3 specifically includes: A pair of detection electrodes are disposed on the strain gauge substrate, and the detection electrodes are in contact with the adhesive layer; the resistance value of the adhesive layer is measured in real time through the detection electrodes, and when the rate of change of the resistance value shows a sudden inflection point, it is determined that the adhesive layer has entered the gel point.

8. The strain gauge bonding and curing stress compensation process according to claim 1, characterized in that, The shape memory alloy wire is composed of multiple wires, and each of the shape memory alloy wires is equipped with an independent resistance measurement circuit. Step S4 also includes: Feedback signals from each of the shape memory alloy wires are collected separately, and the deviation between each feedback signal is calculated. An alarm signal is issued when the deviation value exceeds a preset consistency threshold.

9. The strain gauge bonding and curing stress compensation process according to claim 1, characterized in that, The compensation ring is also equipped with an ambient temperature sensor; step S4 further includes: The ambient temperature is collected in real time by the ambient temperature sensor, and the feedback signal of the collected shape memory alloy wire is temperature compensated and corrected according to the ambient temperature to compensate for the influence of changes in ambient temperature on the feedback signal.

10. The strain gauge bonding and curing stress compensation process according to claim 1, characterized in that, The top of the compensation ring is provided with a pressure surface. In step S2, the vertical clamping force is applied to the pressure surface of the compensation ring through a clamping fixture and transmitted to the strain gauge body by the compensation ring. The compensation ring also serves as a fixing reference for the shape memory alloy wire and a force transmission component for vertical pressure.

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