Pre-tightening force applying method of sandwich type piezoelectric transducer

Abstract

The invention relates to a pre-tightening force applying method of a sandwich type piezoelectric transducer, which comprises the following steps: step 1, preparation before measurement: connecting ultrasonic measurement equipment to the end surface of a bolt for detecting the sound time difference of the bolt; step 2, acquiring a linear relation graph of the axial drawing force and the sound time difference; step 3, carrying out data calibration on the pretightening force and the axial drawing force; and step 4, processing the sandwich type piezoelectric transducer: before the bolt is screwed, connecting ultrasonic measurement equipment to the end face of the bolt, and then when the bolt is screwed, acquiring the sound time difference of the bolt in real time by the ultrasonic measurement equipment, and synchronously converting the sound time difference into a pre-tightening force numerical value according to the sound time difference and displaying the pre-tightening force numerical value by the ultrasonic measurement equipment. The method has the beneficial effects that the detection of a pre-tightening force parameter is changed from a low-precision parameter torque T to a high-precision parameter sound time difference, and the piezoelectric ceramic pre-tightening force application error of the transducer is greatly reduced, so that the transducer is stable in performance and high in consistency after being assembled.

Description

Technical Field

[0001] This invention relates to a method for testing medical components, and in particular to a method for applying preload to a sandwich piezoelectric transducer. Background Technology

[0002] In sandwich piezoelectric transducers, the preload applied to the piezoelectric ceramic directly affects the transducer's performance. Current sandwich piezoelectric transducer assembly involves tightening the piezoelectric ceramic by applying torque to preload bolts, i.e., using the torque method to fasten the bolts and thus compress the piezoelectric ceramic. However, regardless of whether the preload bolts used in the piezoelectric transducer assembly are non-standard or custom-made, the designed preload force is often not achieved. The main reason is that the torque method has a high error in applying preload force to the bolts, typically around ±25%. Therefore, it is difficult to confirm whether the designed preload force has been achieved after tightening, leading to performance differences after transducer assembly, ultimately wasting materials and costs.

[0003] Specifically, firstly, the formula for calculating the preload applied to the bolt using the torque method is:

[0004]

[0005] Where T is the preload torque in N / m, F is the axial preload of the bolt, D is the nominal diameter of the bolt, and K is the torque coefficient; however, there are many factors that affect the torque coefficient K, mainly: ① thread accuracy and roughness;

[0006] ② Bolt material and surface treatment method; ③ Bolt thread fit accuracy; ④ Bolt clamping distance; ⑤ Bolt thread lubrication method and lubricant. Due to the discreteness of the torque coefficient, even under the same torque, the final bolt preload is discrete.

[0007] Secondly, the indirectness of torque and preload means that torque and preload are not directly related. When a torque wrench applies torque to a bolt, part of the rotational kinetic energy is converted into frictional heat between the bolt head and the support surface and between the threads, and another part is converted into displacement through the threads, i.e., the bolt's tensile energy. Bolt tension will generate preload. The thread friction coefficient and the end face friction coefficient will both affect the bolt preload.

[0008] In summary, the torque method for applying preload to bolts exhibits significant dispersion and low accuracy.

[0009] Currently, there are few known methods for applying preload to piezoelectric ceramics. Only a few patents describe this process, such as CN108871830A and CN113441940A; however, CN108871830A only discloses a testing platform and has no practical commercial application. The methods described in CN113441940A require the design of complex devices for processing, resulting in low testing efficiency and high testing costs. Summary of the Invention

[0010] The purpose of this invention is to provide a method for applying preload to a sandwich piezoelectric transducer. This method uses ultrasonic measurement of bolt elongation to accurately and easily determine the bolt preload, greatly improving the accuracy and consistency of the bolt preload, thereby achieving stable assembly performance of the piezoelectric transducer.

[0011] This invention is achieved through the following technical solution: a method for applying preload to a sandwich-type piezoelectric transducer, comprising the following steps:

[0012] Step 1, Preparation before measurement: Connect an ultrasonic measuring device to the end face of the bolt to detect the acoustic time difference of the bolt;

[0013] Step 2, obtain the linear relationship between axial tensile force and acoustic time difference: Prepare multiple sets of bolts of the same batch number and specification, apply multiple sets of axial tensile forces of the same length to each set of bolts using a universal testing machine, and simultaneously measure the acoustic time difference under the corresponding axial tensile force using an ultrasonic probe to obtain multiple sets of linear relationship between axial tensile force and acoustic time difference.

[0014] Step 3, perform data calibration of preload and axial tensile force: Based on the linear relationship between multiple sets of axial tensile force and acoustic time difference, the relationship between bolt acoustic time difference and preload is obtained by fitting. The accuracy of the values ​​of preload and axial tensile force is then verified to achieve data calibration.

[0015] Step 4, process the sandwich piezoelectric transducer: Before tightening the bolt, connect an ultrasonic measuring device to the bolt end face. Then, while tightening the bolt, the ultrasonic measuring device will collect the acoustic time difference of the bolt in real time, and convert it into a preload value and display it according to the acoustic time difference. Stop when the required preload is reached. After confirming that there are no abnormalities in the appearance, the next assembly step can be carried out.

[0016] Compared with previous technologies, the beneficial effects of the present invention are as follows:

[0017] 1. It changes the detection of preload parameters from low-precision parameter torque T to high-precision parameter acoustic time difference. This greatly reduces the error in applying the preload force to the piezoelectric ceramic of the transducer, resulting in stable performance and high consistency of the transducer after assembly.

[0018] 2. Due to the reduced error, the damage to piezoelectric ceramics and material waste caused by excessive error are greatly reduced. Attached Figure Description

[0019] Figure 1 This is a diagram showing the state of the bolt being stretched during the tightening process.

[0020] Figure 2 This is a diagram showing the state of the bolt being stretched during the tightening process. Figure 3 This is a diagram showing the state where the ultrasonic signal takes longer to travel through the bolt as it is stretched. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings:

[0022] A method for applying preload to a sandwich-type piezoelectric transducer includes the following steps:

[0023] Step 1, Preparation before measurement: Connect an ultrasonic measuring device to the end face of the bolt to detect the acoustic time difference of the bolt;

[0024] The ultrasonic measuring equipment here includes an ultrasonic probe and a testing unit, which are electrically connected to each other. The ultrasonic probe is connected to the end face of the bolt. It should be noted that a piezoelectric ceramic plate needs to be attached to the end face of the bolt before connecting the ultrasonic probe. The ultrasonic probe and the piezoelectric ceramic plate together form an ultrasonic transducer, which will continuously emit an electrical signal. The ultrasonic probe here is generally a probe type.

[0025] Step 2, obtain the linear relationship between axial tensile force and acoustic time difference: Prepare multiple sets of bolts of the same batch number and specification, apply multiple sets of axial tensile forces of the same length to each set of bolts using a universal testing machine, and simultaneously measure the acoustic time difference under the corresponding axial tensile force using an ultrasonic probe to obtain multiple sets of linear relationship between axial tensile force and acoustic time difference.

[0026] After obtaining multiple sets of linear relationship graphs between axial tensile force and acoustic transit time, these graphs are imported into ultrasonic probe measurement software. After software fitting, the ultrasonic measuring equipment can directly measure the acoustic transit time and preload of the bolts. By comparing the preload value from the ultrasonic measuring software with the axial tensile force value from the universal testing machine, reverse confirmation and accuracy verification can be performed. Once confirmed to be correct, the data calibration is completed. It should be emphasized that the premise of accurate data calibration is that the bolts in this batch are of the same specification, material, and batch number. Considering the same batch number, the material can generally be the same, so in practice, only the same batch number and specification are considered.

[0027] In step 2, the conversion relationship between axial tensile force and acoustic transit time is as follows: The relationship between axial tensile force and acoustic transit time is obtained by linear fitting using software. Since each set of axial tensile force and acoustic transit time relationship graphs is linear, and the axial tensile force data is assumed to be accurate while the acoustic transit time data has errors, the least squares method is the simplest and most efficient. The specific calculation steps for fitting the straight line using the least squares method are as follows: Set F as the axial tensile force and T as the acoustic transit time under that tensile force.

[0028] By collecting n data points ( , ), and calculate the following summation terms: where, The sum of all F coordinates; :all The sum of coordinates; :all The sum of products; The sum of the squares of all F coordinates;

[0029] Next, calculate the slope k.

[0030]

[0031] Simultaneously calculate the intercept b.

[0032]

[0033] Since the acoustic time difference T is also 0 when the bolt axial tensile force F is 0, the intercept b = 0; substituting the slope k and intercept b into the linear equation... The fitted straight line equation is obtained.

[0034] .

[0035] Step 3, perform data calibration of preload and axial tensile force: Based on the linear relationship between multiple sets of axial tensile force and acoustic time difference, the relationship between bolt acoustic time difference and preload is obtained by fitting. The accuracy of the values ​​of preload and axial tensile force is then verified to achieve data calibration.

[0036] In step 3, the relationship between bolt sound time difference and preload is as follows: In the free state, the bolt has no internal preload; however, in the tightened state, due to the preload, the bolt undergoes deformation and stretching, with the deformation amount being... Then the preload F and the deformation amount The following mathematical relationship exists between them:

[0037] ;

[0038] Where F is the bolt preload, E is the elastic modulus, and S is the equivalent cross-sectional area. L is the bolt elongation, and L is the clamping length, which is the distance from the bottom surface of the bolt head to the clamping surface.

[0039] Deformation The harmonic time difference also satisfies the following relationship:

[0040] ;

[0041] In the bolt's free state, the time difference between transmitting and receiving electrical signals is: With the bolt tightened, the time difference between transmitting and receiving electrical signals is... The speed at which ultrasound propagates inside the bolt is V.

[0042] Step 4, process the sandwich piezoelectric transducer: Before tightening the bolt, connect an ultrasonic measuring device to the bolt end face. Then, while tightening the bolt, the ultrasonic measuring device will collect the acoustic time difference of the bolt in real time, and convert it into a preload value and display it according to the acoustic time difference. Stop when the required preload is reached. After confirming that there are no abnormalities in the appearance, the next assembly step can be carried out.

[0043] By using ultrasonic detection, combined with the ultrasonic probe to detect the acoustic time difference and convert the acoustic time difference into preload, it is possible to intuitively and in real time check whether the designed preload has been reached during assembly. Compared with the existing method of using a torque wrench or a fixed torque wrench to read the torque and apply preload, the ultrasonic measurement method for applying preload greatly improves the accuracy, with the preload error within 3%.

[0044] The ultrasonic detection method described above can be widely used in the application of preload on piezoelectric ceramics in the field of transducer assembly.

[0045] Finally, it should be noted that the above description is only 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 method for applying preload to a sandwich-type piezoelectric transducer, characterized in that: Includes the following steps: Step 1, Preparation before measurement: Connect an ultrasonic measuring device to the end face of the bolt to detect the acoustic time difference of the bolt; Step 2, obtain the linear relationship between axial tensile force and acoustic time difference: Prepare multiple sets of bolts of the same batch number and specification, apply multiple sets of axial tensile forces of the same length to each set of bolts using a universal testing machine, and simultaneously measure the acoustic time difference under the corresponding axial tensile force using an ultrasonic probe to obtain multiple sets of linear relationship between axial tensile force and acoustic time difference. Step 3, perform data calibration of preload and axial tensile force: Based on the linear relationship between multiple sets of axial tensile force and acoustic time difference, the relationship between bolt acoustic time difference and preload is obtained by fitting. The accuracy of the values ​​of preload and axial tensile force is then verified to achieve data calibration. Step 4, process the sandwich piezoelectric transducer: Before tightening the bolt, connect an ultrasonic measuring device to the bolt end face. Then, while tightening the bolt, the ultrasonic measuring device will collect the acoustic time difference of the bolt in real time, and convert it into a preload value and display it according to the acoustic time difference. Stop when the required preload is reached. After confirming that there are no abnormalities in the appearance, the next assembly step can be carried out.

2. The method for applying preload to a sandwich-type piezoelectric transducer according to claim 1, characterized in that: In step 2, the conversion relationship between axial tensile force and acoustic transit time is as follows: The relationship between axial tensile force and acoustic transit time is obtained by linear fitting using software. Since the relationship between each set of axial tensile force and acoustic transit time is linear, the least squares method is used to fit the straight line. F is set as axial tensile force, and T is the acoustic transit time under that tensile force. By collecting n data points ( , ), and calculate the following summation terms: where, The sum of all F coordinates; :all The sum of coordinates; :all The sum of products; The sum of the squares of all F coordinates; Next, calculate the slope k. Simultaneously calculate the intercept b. Since the acoustic time difference T is also 0 when the bolt axial tensile force F is 0, the intercept b = 0; substituting the slope k and intercept b into the linear equation... The fitted straight line equation is obtained. 。 3. The method for applying preload to a sandwich-type piezoelectric transducer according to claim 1, characterized in that: In step 3, the relationship between bolt sound time difference and preload is as follows: In the free state, the bolt has no internal preload; however, in the tightened state, due to the preload, the bolt undergoes deformation and stretching, with the deformation amount being... Then the preload F and the deformation amount The following mathematical relationship exists between them: ； Where F is the bolt preload, E is the elastic modulus, and S is the equivalent cross-sectional area. L is the bolt elongation, and L is the clamping length, which is the distance from the bottom surface of the bolt head to the clamping surface. Deformation The harmonic time difference also satisfies the following relationship: ； When the bolt is in its free state, the time difference between transmitting and receiving electrical signals is: With the bolt tightened, the time difference between transmitting and receiving electrical signals is... The speed at which ultrasound propagates inside the bolt is V.

4. The method for applying preload to a sandwich-type piezoelectric transducer according to claim 1, characterized in that: The ultrasonic measuring equipment includes an ultrasonic probe and a testing unit, which are electrically connected to each other.

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