Ultrasonic probe measurement precision maintaining mechanism for bolt fastening stress measuring sleeve

Abstract

The utility model discloses a kind of ultrasonic probe measurement precision maintaining mechanisms of bolt fastening stress measurement sleeve, including transmission shaft and ultrasonic probe, ultrasonic probe is installed in installation channel by fish eye bearing, and elastic component is provided between installation channel and outer ring, the elastic component is used to make the detection end surface of ultrasonic probe have the tendency of protruding from bolt head positioning groove groove bottom. Above mechanism is used, by additionally adding elastic component, the detection end surface of ultrasonic probe is always kept with the head of being twisted bolt abutment;Meanwhile, by additionally adding fish eye bearing, the detection end surface of ultrasonic probe can also be adaptively swing adjusted with small angle according to the head of being twisted bolt, to keep very close fit with the head of bolt, and then can according to the return ultrasonic wave information of ultrasonic probe emission and collection, the current fastening stress of being twisted bolt is very accurately inverted, meet the application requirement of bolt fastening stress precision requirement very high use scene.

Description

Technical Field

[0001] This utility model relates to the field of bolt installation auxiliary tools, specifically to an ultrasonic probe measurement accuracy maintenance mechanism for a bolt fastening stress measuring sleeve. Background Technology

[0002] Bolt tightening stress is the axial force generated between the bolt and the connected parts under the tightening torque during the bolt tightening process, along the bolt axis. The control of bolt tightening stress has an important impact on the consistency of assembly performance and the stability of the overall machine performance.

[0003] Therefore, the applicant has designed a series of intelligent bolt fastening stress detection devices, such as the intelligent washer with publication number CN217002622U, the intelligent preload nut with publication number CN113380012B, and the intelligent bolt loosening detection device with publication number CN112432779B.

[0004] However, existing intelligent bolt tightening stress detection devices either can only detect bolt tightening stress separately after bolt installation, which is a two-step process. This is not only cumbersome to operate, but also inconvenient to install on automated bolt tightening devices (such as electric tightening guns); or they are used in conjunction with bolts, and while locking the workpiece, they are also permanently installed on the workpiece, resulting in high operating costs.

[0005] Furthermore, while some existing automated bolt tightening devices come with built-in bolt tightening stress detection functions, their detection accuracy is not high due to inherent design flaws, making them unsuitable for applications requiring extremely high bolt tightening stress accuracy.

[0006] Therefore, the applicant sought to design a bolt tightening stress measuring sleeve based on an ultrasonic probe, capable of real-time, high-precision monitoring of bolt tightening stress during the tightening process. However, the applicant discovered during testing that if the ultrasonic probe was simply fixedly mounted in the bolt tightening stress measuring sleeve, the probe's detection end face could not maintain constant contact with the bolt head end face when the bolt was tightened using the sleeve, resulting in extremely poor measurement accuracy. Utility Model Content

[0007] To address the technical problem that the ultrasonic probe's detection end face cannot always maintain contact with the bolt head end face when using a bolt tightening stress measuring sleeve to tighten bolts, resulting in extremely poor measurement accuracy, this utility model provides an ultrasonic probe measurement accuracy maintenance mechanism for a bolt tightening stress measuring sleeve.

[0008] The technical solution is as follows:

[0009] The first aspect of this application relates to an ultrasonic probe measurement accuracy maintenance mechanism for a bolt tightening stress measuring sleeve, comprising a drive shaft, one end of which is provided with a quick-change connection structure for connecting to the output shaft of a tightening gun, and the other end face of the drive shaft having a bolt head positioning groove coaxially recessed therein. The drive shaft has an installation channel, one end of which communicates with the bottom of the bolt head positioning groove. An ultrasonic probe is mounted in the installation channel via a fisheye bearing, the fisheye bearing comprising an inner ring fixedly fitted on the circumferential outer wall of the ultrasonic probe and an outer ring synchronously rotatably mounted on the circumferential inner wall of the main installation channel. The inner ring is capable of spherical oscillation relative to the outer ring, and the outer ring is capable of axial movement along the circumferential inner wall of the main installation channel. An elastic component is provided between the installation channel and the outer ring, the elastic component being used to make the detection end face of the ultrasonic probe tend to protrude beyond the bottom of the bolt head positioning groove.

[0010] The ultrasonic probe measurement accuracy maintenance mechanism using the above-mentioned bolt tightening stress measuring sleeve, by adding an elastic component, allows the probe's detection end face to tend to protrude beyond the bottom of the bolt head positioning groove, thus ensuring that the probe's detection end face always remains in contact with the head of the bolt being tightened. Simultaneously, by adding a fisheye bearing, the ultrasonic probe can also adaptively adjust its small-angle swing according to the end face of the bolt head, allowing the probe's detection end face to maintain an extremely tight fit with the bolt head end face. Therefore, based on the echoing ultrasonic information emitted and collected by the ultrasonic probe, the current tightening stress of the bolt being tightened can be accurately determined, meeting the application requirements of scenarios with extremely high bolt tightening stress accuracy.

[0011] In some embodiments, the end of the mounting channel that communicates with the bolt head positioning groove is enlarged to form an elastic element mounting section. Both ends of the elastic element mounting section have annular support surfaces. The elastic component includes a first compression spring and a second compression spring. The first compression spring is elastically supported on an outer ring and an annular support surface away from the bolt head positioning groove, and the second compression spring is elastically supported on an outer ring and an annular support surface near the bolt head positioning groove.

[0012] In some embodiments, the cross-section of the bolt head positioning groove is a star-shaped polygon with 12 corners.

[0013] In some embodiments, the quick-connect structure includes a quick-connect recess formed coaxially on the corresponding end face of the drive shaft. The quick-connect recess has a square cross-section. Threaded holes are provided on the two opposite sides of the quick-connect recess, and set screws that engage with the threads are installed in the threaded holes.

[0014] In some embodiments, the opening of the quick-connect sink has a chamfer that gradually increases in the direction away from the bottom of the sink.

[0015] In some embodiments, an electric slip ring is fitted in the middle of the drive shaft. The electric slip ring includes a rotor fixedly fitted on the drive shaft, a stator rotatably fitted outside the rotor, and an electric slip ring bracket fixedly mounted on the stator. A wire hole is provided on the drive shaft, through which the cable of the ultrasonic probe passes and is electrically connected to the rotor. An external wiring harness is electrically connected to the stator. Attached Figure Description

[0016] Figure 1 A schematic diagram of the bolt fastening stress measuring sleeve from one perspective;

[0017] Figure 2 A schematic diagram of the bolt fastening stress measuring sleeve from another perspective;

[0018] Figure 3 This is a schematic diagram of the installation structure of an ultrasonic probe.

[0019] Figure 4 This is a schematic diagram showing the fit between the ultrasonic probe, the fisheye bearing, and the elastic component.

[0020] Figure 5 This is a schematic diagram showing the fit between the ultrasonic probe and the fisheye bearing. Detailed Implementation

[0021] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0022] like Figures 1-5 As shown, an ultrasonic probe measurement accuracy maintenance mechanism for a bolt fastening stress measuring sleeve mainly includes a drive shaft 2 and an ultrasonic probe 3.

[0023] The drive shaft 2 has an approximately cylindrical or tubular structure. One end of the drive shaft 2 is equipped with a quick-connect structure for connecting to the output shaft of the tightening gun, thereby enabling quick and reliable connection to the output shaft of the tightening gun and synchronous rotation with it under the drive of the tightening gun's output shaft. A bolt head positioning groove 211 is coaxially recessed on the other end face of the drive shaft 2. The structure of the bolt head positioning groove 211 is adapted to the head of the bolt being tightened. In this embodiment, the cross-section of the bolt head positioning groove 211 is preferably a star-shaped polygon with 12 angles. This design allows the bolt head to be inserted into the bolt head positioning groove 211 with only a small rotation angle. That is, when the head of the bolt being tightened is inserted, it can be quickly and reliably positioned by the bolt head positioning groove 211. Therefore, rotating the drive shaft 2 can drive the bolt being tightened to rotate synchronously with it, improving work efficiency.

[0024] Please see Figures 3-5 The drive shaft 2 is provided with an installation channel 21 that is compatible with the ultrasonic probe 3. One end of the installation channel 21 is connected to the bottom of the bolt head positioning groove 211. The ultrasonic probe 3 is installed in the installation channel 21 through the fisheye bearing 5.

[0025] Specifically, the fisheye bearing 5 has a structure similar to a ball joint. The fisheye bearing 5 includes an inner ring 51 and an outer ring that is partially spherically rotated and fitted outside the inner ring 51. The inner ring 51 is fixedly fitted onto the circumferential outer wall of the ultrasonic probe 3, while the outer ring 52 is synchronously rotatably mounted on the circumferential inner wall of the main mounting channel 21 and can move axially along the circumferential inner wall of the main mounting channel 21. Simultaneously, an elastic component 4 is provided between the mounting channel 21 and the outer ring 52. This elastic component 4 is used to make the detection end face 31 of the ultrasonic probe 3 tend to protrude beyond the bottom of the bolt head positioning groove 211.

[0026] Therefore, by adding the elastic component 4, the detection end face 31 of the ultrasonic probe 3 tends to protrude from the bottom of the bolt head positioning groove 211, so that the detection end face 31 of the ultrasonic probe 3 always keeps in contact with the head of the bolt being tightened; at the same time, by adding the fisheye bearing 5, the ultrasonic probe 5 can also adaptively adjust its small-angle swing according to the end face of the head of the bolt being tightened, so that the detection end face 31 of the ultrasonic probe 3 can adaptively maintain a very tight fit with the end face of the bolt head, and thus can very accurately infer the current tightening stress of the bolt being tightened based on the returned ultrasonic information emitted and collected by the ultrasonic probe 3, meeting the application requirements of scenarios with extremely high bolt tightening stress accuracy requirements.

[0027] Specifically, based on the acoustoelastic effect, when the stress inside the bolt changes, the propagation speed of the ultrasonic wave will change accordingly. Therefore, there is a correspondence between the propagation time of the ultrasonic wave and the stress. Through this correspondence, the ultrasonic probe 3 can measure the stress of the bolt by measuring the propagation time of the ultrasonic wave in the bolt. The principle is as follows:

[0028] First, ignoring the change in medium density caused by stress state changes, we establish the longitudinal wave propagation velocity v of ultrasound under stress-free conditions. L0 And the propagation velocity of ultrasonic transverse waves under no stress v S0 The relational expression.

[0029] Bolts are typically made of metal, which is an isotropic solid medium. For an isotropic solid medium, a vector field can be expressed as the sum of a scalar gradient and a vector curl, therefore:

[0030] v=gradφ+rotψ (1)

[0031] divψ=0 (2)

[0032] In equations (1) and (2), v represents the velocity vector, φ represents the scalar potential, and ψ represents the vector potential. Separating the scalar potential and vector potential, we obtain:

[0033]

[0034] In equations (3) and (4), ρ represents the density of the bolt, and λ and μ are the second-order elastic coefficients of the bolt. Generally speaking, scalar potential and vector potential describe longitudinal and transverse waves, respectively. Therefore, under stress-free conditions, the propagation speeds of ultrasonic longitudinal and transverse waves in a metallic medium can be expressed as:

[0035]

[0036] In equations (5) and (6), v L0 and v S0 They represent the propagation speeds of ultrasonic longitudinal waves under stress-free conditions, v and v', respectively. L0 The propagation speed v of ultrasonic transverse waves under stress-free conditions S0 Depending on the direction of ultrasonic wave propagation, the acoustic elasticity equations for different propagation directions can be expressed as follows:

[0037]

[0038] In equations (7)-(10), σ represents the bolt tightening stress, ρ0 represents the bolt density under no stress, l, m, and n represent the third-order elastic coefficients of the bolt, and v LII The longitudinal wave velocity of ultrasound parallel to the direction of stress, v L⊥ v represents the longitudinal wave propagation velocity of ultrasound perpendicular to the direction of stress. SII v represents the propagation velocity of ultrasonic longitudinal and transverse waves parallel to the direction of stress. S⊥ This represents the propagation velocity of the ultrasonic transverse wave perpendicular to the direction of stress. Since ultrasonic transverse waves are shear waves, their polarization direction is perpendicular to the stress direction, but their propagation direction is not uniform. Because ultrasonic longitudinal waves parallel to the direction of stress are most sensitive to stress changes, and ultrasonic longitudinal wave transducers are more commonly used and less expensive, most time-of-flight methods use ultrasonic longitudinal waves to detect the tightening stress of bolts. Therefore, combining equations (5) and (7), ignoring the change in medium density caused by stress state changes, i.e., ρ0 = ρ, we can obtain:

[0039]

[0040] make:

[0041]

[0042] In equations (11) and (12), K a Let be the acoustic elastic coefficient of the material. As can be seen from equation (12), the acoustic elastic coefficient is only related to the second-order and third-order elastic coefficients of the material and is not affected by other factors.

[0043] Therefore, substituting equation (12) into equation (11) yields:

[0044] v Lσ =v L0 (1+K a σ) (13)

[0045] Equation (13) is the longitudinal wave propagation velocity v of ultrasound under stress-free conditions. L0 And the propagation velocity of ultrasonic transverse waves under no stress v S0 The relational expression.

[0046] Then, establish the ultrasonic transit time Δt under stress. σ The relationship between the ultrasonic transit time Δt0 under stress-free conditions.

[0047] Among them, the relationship between bolt elongation under tightening stress is established:

[0048]

[0049] In equation (14), L0 is the total length of the bolt when it is not under stress, and L σ E is the total length of the bolt under stress, and E is the elastic modulus of the bolt.

[0050] Combining equations (13) and (14), the transit time Δt of the ultrasonic wave under stress is calculated. σ The transit time Δt0 of ultrasound under stress-free conditions is expressed as:

[0051]

[0052] For metallic materials, the acoustoelastic coefficient K a The order of magnitude is extremely small, typically K within the safe stress range of the bolt. a σ << 1, therefore, equation (15) is approximately simplified to:

[0053]

[0054] Equation (17) is the formula for establishing the ultrasonic transit time Δt under stress. σ The relationship between the ultrasonic transit time Δt0 under stress-free conditions.

[0055] Finally, establish the ultrasonic transit time Δt under stress conditions. σThe relationship between the ultrasonic transit time Δt0 and the stress coefficient K under stress-free conditions for calculating the bolt fastening stress σ.

[0056] Among them, the bolt fastening stress σ in equation (17) is extracted to obtain:

[0057]

[0058] Therefore, the formula for calculating the bolt tightening stress σ is:

[0059]

[0060] In equation (19), K represents the stress coefficient, which is obtained through calibration experiments and is related to the material properties of the bolt and the geometric dimensions of the bolt.

[0061] Equation (19) is based on the ultrasonic transit time Δt under stress. σ The relationship between the ultrasonic transit time Δt0 under stress-free conditions and the stress coefficient K for calculating the bolt tightening stress σ is given. Therefore, the ultrasonic transit time Δt0 acquired by ultrasonic probe 3... σ The bolt fastening stress σ can be obtained by using the ultrasonic transit time Δt0 under no stress and the stress coefficient K obtained through calibration experiments.

[0062] Further, please see Figure 2 The installation channel 21, which connects to the bolt head positioning groove 211, has an enlarged end to form an elastic element mounting section 212. Both ends of this elastic element mounting section 212 have annular support surfaces 213. The elastic component 4 includes a first compression spring 41 and a second compression spring 42. The first compression spring 41 is elastically supported on the outer ring 52 and an annular support surface 213 away from the bolt head positioning groove 211; that is, one end of the first compression spring 41 is supported on the adjacent end face of the outer ring 52, and the other end is supported on an annular support surface 213 away from the bolt head positioning groove 211. The second compression spring 42 is elastically supported on the outer ring 52 and an annular support surface 213 near the bolt head positioning groove 211; that is, one end of the second compression spring 42 is supported on the adjacent end face of the outer ring 52, and the other end is supported on an annular support surface 213 near the bolt head positioning groove 211.

[0063] Under the action of the first compression spring 41, the ultrasonic probe 3's detection end face 31 always tends to protrude from the bottom of the bolt head positioning groove 211. When the detection end face 31 contacts the end face of the bolt head, the bolt forces the ultrasonic probe 3 to retract a small distance, increasing the elastic potential energy of the first compression spring 41. This ensures that the detection end face 31 of the ultrasonic probe 3 fits very well with the end face of the bolt head, guaranteeing the accuracy of the ultrasonic measurement. At the same time, by setting the second compression spring 42, the ultrasonic probe 3 can be impact-reducing and vibration-damping. In particular, the bolt can push the ultrasonic probe 3 back with a small thrust, which not only protects the ultrasonic probe 3 and extends its service life, but also makes it easier for the detection end face 31 of the ultrasonic probe 3 to fit perfectly with the end face of the bolt head, ensuring the accuracy of the measurement.

[0064] Among them, the two annular support surfaces 213 are the annular step surfaces at both ends of the installation channel 21.

[0065] Please see Figures 1-3 The quick-change connection structure includes a quick-connect recess 234 coaxially recessed on the corresponding end face of the drive shaft 2. The quick-connect recess 234 has a square cross-section. Threaded holes 235 are provided on the two opposite sides of the quick-connect recess 234. Each threaded hole 235 is fitted with a set screw 26 that is threaded to it. This not only ensures the quick-change connection with the output shaft of the tightening gun, but also ensures the reliability and stability of the connection through the set screws 26. That is, when the set screws 26 move axially inward by rotation, they can tighten the output shaft of the tightening gun. When the set screws 26 move axially outward by rotation, they can release the output shaft of the tightening gun.

[0066] Furthermore, the quick-connect slot 234 has a chamfer 236 at the opening that gradually increases in the direction away from the bottom of the slot, which facilitates the insertion of the output shaft of the tightening gun.

[0067] Please see Figures 1-3 An electric slip ring 6 is fitted in the middle of the drive shaft 2. The electric slip ring 6 includes a rotor 61 fixedly mounted on the drive shaft 2, a stator 62 rotatably mounted on the rotor 61, and an electric slip ring bracket (not shown) fixedly mounted on the stator 62. The stator 62 can be mounted on a tightening gun or tooling via the electric slip ring bracket, which is simple and reliable. A wire hole 27 is provided on the drive shaft 2. The cable 32 of the ultrasonic probe 3 passes through the wire hole 27 and is electrically connected to the rotor 61. An external wiring harness 7 is electrically connected to the stator 62. Since the electric slip ring 6 is an electrical connection device used to transmit power and signals in rotating equipment, it can achieve power and signal transmission under unrestricted continuous rotation. Therefore, it can avoid the problems of tangling or breakage of the wiring harness 7 and the cable 32, thereby improving the overall durability.

[0068] Finally, it should be noted that the above description is merely a preferred embodiment of the present utility model. Those skilled in the art, under the guidance of the present utility model, can make various similar representations without departing from the spirit and claims of the present utility model, and such modifications all fall within the protection scope of the present utility model.

Claims

1. An ultrasonic probe measurement accuracy maintaining mechanism of a bolt fastening stress measurement sleeve, comprising a transmission shaft, characterized in that: One end of the drive shaft is provided with a quick-change connection structure for connecting to the output shaft of the tightening gun. The other end face of the drive shaft is coaxially recessed to form a bolt head positioning groove. The drive shaft is provided with an installation channel, one end of which is connected to the bottom of the bolt head positioning groove. An ultrasonic probe is installed in the installation channel via a fisheye bearing. The fisheye bearing includes an inner ring fixedly fitted on the circumferential outer wall of the ultrasonic probe and an outer ring synchronously rotatably installed on the circumferential inner wall of the main installation channel. The inner ring can spherically swing relative to the outer ring, and the outer ring can move axially along the circumferential inner wall of the main installation channel. An elastic component is provided between the installation channel and the outer ring. This elastic component is used to make the detection end face of the ultrasonic probe tend to protrude from the bottom of the bolt head positioning groove.

2. The ultrasonic probe measurement accuracy maintaining mechanism of a bolt fastening stress measurement sleeve according to claim 1, characterized by: The installation channel is widened at one end to form an elastic element installation section. Both ends of the elastic element installation section have annular support surfaces. The elastic component includes a first compression spring and a second compression spring. The first compression spring is elastically supported on an outer ring and an annular support surface away from the bolt head positioning groove. The second compression spring is elastically supported on an outer ring and an annular support surface close to the bolt head positioning groove.

3. The ultrasonic probe measurement accuracy maintaining mechanism of a bolt fastening stress measurement sleeve according to claim 1, characterized by: The cross-section of the bolt head positioning groove is a star-shaped polygon with 12 corners.

4. The ultrasonic probe measurement accuracy maintenance mechanism for the bolt fastening stress measuring sleeve according to claim 1, characterized in that: The quick-connect structure includes a quick-connect recess formed coaxially on the corresponding end face of the drive shaft. The quick-connect recess has a square cross-section. Threaded holes are provided on the two opposite sides of the quick-connect recess, and set screws that engage with the threads are installed in the threaded holes.

5. The ultrasonic probe measurement accuracy maintenance mechanism for the bolt fastening stress measuring sleeve according to claim 4, characterized in that: The quick-connect sink has a chamfer at the opening that gradually increases in the direction away from the bottom of the sink.

6. The ultrasonic probe measurement accuracy maintenance mechanism for the bolt fastening stress measuring sleeve according to claim 1, characterized in that: An electric slip ring is fitted in the middle of the drive shaft. The electric slip ring includes a rotor fixedly fitted on the drive shaft, a stator that can rotate relative to the rotor and is fitted outside the rotor, and an electric slip ring bracket fixedly installed on the stator. A wire hole is opened on the drive shaft. The cable of the ultrasonic probe passes through the wire hole and is electrically connected to the rotor. An external wiring harness is electrically connected to the stator.

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