A method for calibrating the tilt of a Hopkinson pressure bar axis

Abstract

This patent discloses a method for calibrating the tilt of a Hopkinson pressure bar axis. The method uses a laser emitted from one end of the axis through a photometric channel, reads the laser beam imaging point detected by a CCD imaging device at the other end, obtains the x and y deviations of the light point at different Z positions in the measurement axis coordinate system, substitutes them into the axis deflection model, and ultimately calculates accurate calibration parameters. The two pipes of the photometric channel are connected by threads, and accurate calibration can be achieved by adjusting the threads to change the length of the photometric channel. The present invention can measure and solve the tilt angle problem existing in axis alignment under different accuracy requirements, and the axis tilt angle can be quickly calculated by simply measuring the coordinates of the laser imaging position. The method is simple and easy to implement in practice.

Description

Technical Field

[0001] The invention discloses a tilt calibration method for a Hopkinson pressure bar axis, belongs to the technical field of measurement and calibration, and is particularly suitable for measuring and adjusting the axis centering tilt angle of a Hopkinson pressure bar experimental device. Background Art

[0002] During mechanical assembly, many shaft-like components often experience angular misalignment during installation, such as misalignment between two shafts or between shaft holes. If shafts and other structures are not properly aligned, wear, stress concentration, and vibration may occur at the joints, affecting the proper functioning of the components. Therefore, alignment measurement and calibration of shafts and other components are essential during mechanical assembly. The Hopkinson pressure bar experimental apparatus, based on one-dimensional elastic stress wave theory, is used to determine the dynamic mechanical properties of various metals, non-metallic materials, and composite materials at varying strain rates at room and high temperatures. The apparatus consists of an operating table, a pressure bar body, and a data acquisition unit. The pressure bar body comprises an impact bar, an incident bar, a transmission bar, a support platform, an energy absorber, a high-temperature furnace, and a pneumatic device. During the experiment, the high air pressure generated by the pneumatic device propels the impact bar, which strikes the incident bar and transmits energy through the specimen to the transmission bar, and then to the energy absorber. During the experiment, the collision test of the three rods is based on the stress wave principle. The rods should ensure good alignment when colliding. If a pressure rod with poor alignment is used for collision, the accuracy of the experimental data cannot be guaranteed, and there will be large errors or even mistakes. In addition, the collision that occurs when the pressure rod is tilted and not aligned will cause stress concentration and damage the end face of the pressure rod.

[0003] At present, there are two main methods for measuring and calibrating the tilt of the pressure bar in the Hopkinson pressure bar experimental device: one is the traditional adjustment method, which uses a tool to adjust the bolts for preliminary height adjustment and alignment before the test, and then makes a preliminary judgment based on the naked eye and conducts multiple pre-impact tests to obtain the impact data for fine-tuning to adjust the pressure bar to neutrality. This method has complicated steps, is time-consuming and labor-intensive, and the results after adjustment are highly subjective and have low accuracy. Another method is to use a laser and a rangefinder to measure the deviation, such as the method described in CN202110389116.9. Although this type of method can ensure a certain accuracy and realize rapid adjustment of the experimental device, it requires measuring multiple data and has a complex structure, requires a large number of electronic equipment such as laser instruments and rangefinders, and has a high cost. The present method discloses a method for calibrating the tilt of the Hopkinson pressure bar axis, which can greatly reduce the adjustment time and steps, and does not require a large number of laser instruments, rangefinders and other equipment. The method is simple and economical, and on the basis of the original technology, it can realize measurement and adjustment based on a given axis tilt measurement accuracy. Summary of the Invention

[0004] This invention discloses a method for calibrating the tilt of a Hopkinson bar axis. The method aims to overcome the shortcomings of existing methods for centering a Hopkinson bar, simplifying the adjustment process, saving time and costs, and improving accuracy. In addition to its application in Hopkinson bar experimental setups, the method can also be used in other applications requiring the coaxial alignment of shaft components.

[0005] This method includes a laser instrument, a photometric channel and a CCD imaging device. Among them, the photometric channel consists of two parts: one side of the photometric tube A is a closed end face with a small hole in the center, and the other side is an unclosed ordinary tube surface, the outer wall of which is threaded; one side of the photometric tube B is a closed end face with a circle with a radius of r, and the other side is an unclosed ordinary tube surface, the inner wall of which is threaded. The inner wall thread of the photometric tube B can be connected to the outer wall thread of the photometric tube A. When measuring, the length of the photometric channel can be adjusted by adjusting the thread to achieve precision adjustment. The CCD imaging device is an electro-optical device that is widely used today. It can accurately measure the position of the laser point and transmit it to the computer. The principle of the present invention is: the laser instrument on one side emits a laser beam, the laser beam enters the photometric channel through the small hole of the photometric tube A, is emitted through the small circle of the photometric tube B, and is imaged on the CCD imaging device. The implementation of this process specifically includes:

[0006] i. Measurement pre-calibration:

[0007] a) Perform preliminary pre-leveling of the measuring axis to reduce the axis tilt deviation;

[0008] b) Adjust the horizontal and vertical positions of the axis to ensure that the laser beam emitted by the laser instrument can smoothly enter the photometric channel;

[0009] ii. Obtain measurement data:

[0010] a) Turn on the measuring laser instrument. The laser beam emitted by the measuring laser instrument enters the photometric channel. The laser beam passes through the photometric channel and is emitted from a small circle with a radius of r on the other side, and is imaged on the CCD imaging device.

[0011] b) a CCD imaging device records the imaging position and collects data, converts the collected data into a signal, and transmits the signal to a computer;

[0012] iii. Tilt deviation calculation:

[0013] a) After the device is debugged, define the position where the laser beam is emitted by the laser instrument as the imaging origin. With the predefined imaging origin as the reference, establish an adjustment reference coordinate system with the vertical direction as the y-axis, the horizontal direction perpendicular to the axis as the x-axis, and the horizontal direction parallel to the axis as the z-axis;

[0014] b) Read the data collected by the CCD imaging device and compare it with the predefined imaging origin; for the tilt axis, the laser beam emitted by the laser instrument forms an image on the CCD imaging device to generate a displacement vector, and the coordinate change is recorded as (Δx, Δy);

[0015] iv. Adjust deviation and verify:

[0016] a) According to the following formula, record:

[0017] X=Δx (1)

[0018] Y=Δy (2)

[0019] b) Adjust the axis installation position, adjust the horizontal direction (X) and the vertical direction (Y) so that the image point of the laser beam is located at the specified point (0, 0) of the CCD imaging device;

[0020] c) Turn on the measuring laser again and record the displacement vector (Δx, Δy) to verify whether Δx = 0 and Δy = 0. If so, it indicates that after adjusting the installation position (X, Y), the laser beam of the laser instrument is aligned with the specified position of the imaging surface of the CCD imaging device, and the calibration is completed;

[0021] v. The adjustment method to achieve the actual required accuracy is as follows:

[0022] a) Measure the length l of the photometric channel. The distance between the incident end face of the photometric channel and the target surface of the CCD imaging device is L. The actual deviation R is calculated as follows:

[0023]

[0024] b) Calculate the actual tilt angle θ as follows:

[0025]

[0026] c) Compare R, θ with the accuracy requirements Z, When R and θ do not meet the accuracy requirements, calculate the corresponding differences ΔR and Δθ, and calculate the corresponding lengths Δl1 and Δl2 to be adjusted. Take the larger value and record it as Δl, and calculate as follows:

[0027] ΔR=RZ (5)

[0028]

[0029]

[0030]

[0031] Δl=max(Δl1,Δl2) (9)

[0032] d) Adjust the thread of the photometric channel and change the length △l to adjust the axis tilt according to the actual required accuracy.

[0033] The present invention has the following advantages:

[0034] a) This method greatly simplifies the measurement and calibration steps. Compared with traditional methods, this method does not require multiple pre-collision experiments, which greatly saves time and energy and improves measurement efficiency.

[0035] b) This method only requires a laser instrument and a CCD imaging device, which reduces the number of measuring elements required for measurement and reduces the cost of the method. At the same time, it also takes into account the characteristics of rapid measurement and acquisition of accurate data.

[0036] c) This method can adjust the measurement accuracy when measuring and calibrating shaft alignment problems. It has a wider range of applications and can achieve effective measurement in some environments where measurement accuracy needs to be adjusted. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the measurement principle diagram of the present invention

[0038] Figure 2 Measurement diagram for CCD imaging device

[0039] Figure 3 Figure 1 shows the Hopkinson pressure bar experimental setup.

[0040] Figure 4 Flowchart for the measurement process

[0041] In the figure, 1. laser instrument, 31. light measuring tube A, 32. light measuring tube B, 4. CCD imaging device, 5. impact rod, 6. incident rod, 7. test piece, 8. transmission rod, 9. impact rod support, 10-13. Hopkinson rod adjustment support. DETAILED DESCRIPTION

[0042] This method is used in the Hopkinson pressure bar experimental device. Specifically, the laser instrument is fixed on the impact rod support. One of the supports on the incident rod and the transmission rod is replaced with a support with a photometric channel. The other support on the transmission rod is selected as a support equipped with a CCD imaging device. During measurement, the laser instrument emits a laser beam through the two photometric channels, and the CCD imaging device receives the laser point signal.

[0043] Based on the characteristics of the laser beam, after the device is installed and debugged, the position of the laser beam imaged on the target surface of the CCD imaging device is recorded as the initial point. If the pressure rod position shifts or tilts, the position of the laser beam on the CCD imaging device will change, which is the error caused by the pressure rod. During measurement, the position change of the image point can be recorded, such as Δx and Δy in the figure.

[0044] The following further describes a method for calibrating the tilt of a Hopkinson pressure bar axis with reference to the accompanying drawings. Of course, this embodiment is only one specific application of this method and does not represent all embodiments. This description is based on an example of a Hopkinson pressure bar experimental setup.

[0045] like Figure 1 As shown, a method for calibrating the tilt of a Hopkinson pressure bar axis comprises a laser instrument (1), a measuring axis (2), a photometric channel (3) consisting of a photometric tube A (31) and a photometric tube B (32), a CCD imaging device (4), and a plurality of support assemblies;

[0046] The outer wall of the photometric tube A (31) and the inner wall of the photometric tube B (32) are threaded and can be assembled by thread connection. During measurement, the length of the photometric channel can be adjusted by the thread to achieve precision adjustment. One side of the photometric tube A (31) is a small hole, and one side of the photometric tube B (32) is a small circle with a radius r to achieve the injection and emission of laser light.

[0047] A method for calibrating the tilt of a Hopkinson pressure bar axis:

[0048] i. Assemble the instrument and adjustment device: Fix the laser instrument (1), the photometric channel (3), and the CCD imaging device (4) to the support assembly with bolts, wherein the photometric tube A (31) is fixed to the support with bolts, and the photometric tube B (32) is connected to the photometric tube A (31) with threads. The measuring axis (2) is fixed to the measuring position by the support.

[0049] ii. Perform centering adjustment of the device:

[0050] a) Initial leveling of the measuring axis (2): initial leveling of the measuring axis (2) is achieved by adjusting the supports that fix the measuring axis (2);

[0051] b) Turn on the laser instrument (1), adjust the support where the photometric channel (3) is located, change the incident position of the laser beam emitted by the laser instrument (1), and ensure that the laser beam is smoothly emitted from the photometric tube A (31) into the photometric channel;

[0052] c) Measure the distance L between the CCD imaging device (4) and the far end of the photometric channel (3), and calculate the lengths l1 and l2 of the photometric channel (3) according to the given accuracy requirements Z and φ.

[0053]

[0054]

[0055] Compare l1 and l2, select the larger value, and adjust the length l of the photometric channel (3) to the maximum value of the two.

[0056] iii. Read the data collected by the CCD imaging device (4) and compare it with the predefined imaging origin; for the tilted measuring axis (2), the laser beam emitted by the laser instrument (1) is imaged on the CCD imaging device (4) to generate a displacement vector, which is recorded

[0057] The coordinate change is (Δx, Δy);

[0058] iv. Adjust deviation and verify:

[0059] a) According to the following formula, record:

[0060] X=Δx (12)

[0061] Y=Δy (13)

[0062] b) adjusting the installation position of the measuring axis (2), adjusting the horizontal direction amount as X and the vertical direction amount as Y, so that the image point position of the laser beam is located at the designated point (0, 0) of the CCD imaging device (4);

[0063] c) turning on the measuring laser instrument (1) again, recording the displacement vector (Δx, Δy) of this time to verify whether Δx=0, Δy=0 is satisfied. If so, it indicates that after adjusting the installation position (X, Y), the laser beam of the laser instrument (1) is aligned with the designated position of the imaging surface of the CCD imaging device (4), and the calibration is completed;

[0064] like Figure 2 The diagram shows a measurement diagram showing a deviation between the laser beam imaging point of the CCD imaging device (4) and the reference position.

[0065] like Figure 3 As shown, the present invention is used in a Hopkinson pressure bar experimental device, which includes a laser instrument (1), a photometric channel (3) composed of a photometric tube A (31) and a photometric tube B (32), a CCD imaging device (4), an impact rod (5), an incident rod (6), a test piece (7), a transmission rod (8), an impact rod support (9), and Hopkinson bar adjustment supports (10), (11), (12), and (13).

[0066] The present invention is applied to the Hopkinson pressure bar experimental device, and the steps are as follows:

[0067] (a) Assemble the device and perform preliminary leveling. Install the laser instrument (1) on the impact rod support (9), the CCD imaging device (4) on the Hopkinson rod adjustment device (13), and the photometric channel (3) on the Hopkinson rod adjustment devices (10) and (12).

[0068] (b) According to the steps of the axis tilt calibration method with adjustable accuracy, the incident rod (6) and the transmission rod (8) are measured and calibrated, and each Hopkinson adjustment device is adjusted to achieve the centering adjustment of the rod.

[0069] The centering adjustment of the Hopkinson pressure bar experimental device according to the above method is simpler, more convenient and more accurate than the traditional method. Compared with the existing technology, it does not require too many measuring instruments, is economical and can achieve precision adjustment.

Claims

1. A method for calibrating the tilt of a Hopkinson pressure bar axis, characterized by: A laser instrument and a CCD imaging device are used to measure shaft tilt. The laser instrument located on one end of the shaft emits a laser beam that is imaged on the CCD imaging device on the other side through a photometric channel installed on the shaft. The photometric channel is composed of two cylindrical pipes assembled by threads. A small hole with a radius of r is opened on the end face of the cylindrical pipe near the CCD imaging device. The center of the hole is the horizontal corresponding point of the laser beam emitted by the laser instrument end. The thread of the cylindrical pipe of the photometric channel is adjustable. By adjusting the thread, the length of the photometric channel can be changed to achieve precise adjustable measurement. The CCD imaging device is a widely used electro-optical device that can accurately measure the position of the laser point and transmit it to a computer. The implementation of this method specifically includes: i. Assemble instruments and adjustment devices: Fix the laser instrument, photometric channel, and CCD imaging device to the support assembly with bolts, wherein photometric tube A is fixed to the support with bolts, photometric tube B is connected to photometric tube A with threads, and the measuring axis is fixed in the measuring position by the support; ii. Measurement pre-calibration: a) Perform preliminary pre-leveling of the measuring axis to reduce the axis tilt deviation; b) Adjust the horizontal and vertical positions of the axis to ensure that the laser beam emitted by the laser instrument can smoothly enter the photometric channel; iii. Adjust measurement accuracy: a) Turn on the measuring laser instrument. The laser beam emitted by the measuring laser instrument enters the photometric channel. The laser beam passes through the photometric channel and is emitted from a small circle with a radius of r on the other side, and is imaged on the CCD imaging device. b) Measure the length l of the photometric channel. The distance between the incident end face of the photometric channel and the target surface of the CCD imaging device is L. The actual deviation R is calculated as follows: c) Calculate the actual tilt angle θ as follows: d) Compare R, θ with the accuracy requirements Z, When R and θ do not meet the accuracy requirements, calculate the corresponding differences △R and △θ, and calculate the corresponding lengths △l1 and △l2 to be adjusted. Take the larger value and record it as △l, and calculate as follows: △R=RZ (3) e) Adjust the thread of the photometric channel and change the length △l to adjust the axis tilt according to the actual required accuracy; iv. Obtain measurement data: a) Turn on the measuring laser instrument. The laser beam emitted by the measuring laser instrument enters the photometric channel. The laser beam passes through the photometric channel and is emitted from a small circle with a radius of r on the other side, and is imaged on the CCD imaging device. b) a CCD imaging device records the imaging position and collects data, converts the collected data into a signal, and transmits the signal to a computer; v. Tilt deviation calculation: a) After the device is debugged, define the position where the laser beam is emitted by the laser instrument as the imaging origin. With the predefined imaging origin as the reference, establish an adjustment reference coordinate system with the vertical direction as the y-axis, the horizontal direction perpendicular to the axis as the x-axis, and the horizontal direction parallel to the axis as the z-axis; b) Read the data collected by the CCD imaging device and compare it with the predefined imaging origin; for the tilt axis, the laser beam emitted by the laser instrument forms an image on the CCD imaging device to generate a displacement vector, and the coordinate change is recorded as (△x, △y); vi. Adjust deviation and verify: a) According to the following formula, record: X=△x (8) Y=△y (9) b) Adjust the axis installation position, adjust the horizontal direction (X) and the vertical direction (Y) so that the image point of the laser beam is located at the specified point (0, 0) of the CCD imaging device; c) Turn on the measuring laser again and record the displacement vector (△x, △y) to verify whether △x=0, △y=0. If satisfied, it means that after adjusting the installation position (X, Y), the laser beam of the laser instrument is aligned with the designated position of the imaging surface of the CCD imaging device, and the calibration is completed.

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