A barrel bore parameter measuring device and method

Abstract

The application discloses a barrel bore parameter measuring device and method, which realizes automatic detection of the size of the whole inner cavity of a workpiece. The barrel bore parameter measuring device comprises a rack, a back plate and a reference platform arranged on the rack; a three-jaw positioning table arranged on the reference platform and used for clamping and fixing a barrel; a linear module arranged on the back plate and used for realizing a lifting function; a rotating module arranged on the linear module and used for realizing a rotating function; and a snap gauge arranged on the rotating module, wherein a zero point sensor is arranged on the upper portion of the snap gauge, the snap gauge is provided with a fixed measuring arm and a moving measuring arm, a fixed measuring head is arranged at the tail end of the fixed measuring arm, and a moving measuring head is arranged at the tail end of the moving measuring arm; the linear module drives the rotating module and the snap gauge to vertically move up and down, so as to measure different depth positions of the inner cavity of the barrel; and the rotating module drives the snap gauge to rotate, so as to measure different angle positions of the inner cavity.

Description

Technical Field

[0001] This invention relates to the field of measurement technology, and in particular to a device and method for measuring parameters inside a barrel. Background Technology

[0002] The machining quality of the bore of a small-caliber barrel directly affects the projectile's initial velocity, accuracy, impact attitude, and barrel life. Therefore, high-precision internal diameter measuring instruments are needed to accurately measure the inner diameter dimensions of each cone and the coaxiality of each cone. Currently, the use of traditional measuring tools is inefficient and inaccurate. Dozens of measuring tools exist before and after chrome plating, resulting in significant tool wear. Go / no-go gauges provide a semi-quantitative analysis of the barrel's inner diameter based on the passage of a standard cylinder within the test tube, lacking data support and leaving the actual bore condition unclear. This makes it difficult for technicians to troubleshoot and accurately assess the problem. The use of numerous rigid measuring tools increases the workload for inspectors. The current inspection process involves 100% inspection by personnel. The tubes to be inspected are sent to an inspection table, where inspectors use various chamber measuring tools to check each one. This only allows for conformity assessment, without actual measured values, making the inspection data untraceable and unable to provide precise guidance for part machining and adjustment. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a device and method for measuring the internal parameters of a barrel, so as to realize the automated detection of all internal dimensions of the workpiece.

[0004] The objective of this invention is achieved as follows:

[0005] A barrel bore parameter measuring device, comprising:

[0006] The frame is equipped with a backplate and a reference platform.

[0007] A three-jaw positioning stage set on the reference platform is used to clamp and fix the body tube;

[0008] The linear module mounted on the back panel is used to achieve the lifting function;

[0009] A rotary module is installed on the linear module to enable rotation.

[0010] A caliper is mounted on a rotating module. The caliper has a zero-point sensor on its upper part. The caliper has a fixed measuring arm and a moving measuring arm. The fixed measuring arm has a fixed probe at its end, and the moving measuring arm has a moving probe at its end.

[0011] The linear module drives the rotary module and caliper to perform vertical lifting and lowering movements to measure different depth positions inside the tube. The rotary module drives the caliper to rotate to measure different angular positions inside the tube.

[0012] Preferably, the reference platform and back plate are made of marble platform, the linear module and rotary module are both high-precision modules, the linear module, rotary module and caliper are controlled by PLC, and the linear module achieves full closed-loop control through servo motor in conjunction with motor encoder and external grating ruler.

[0013] Preferably, the zero-point sensor, the fixed probe of the caliper, and the moving probe are all contact sensors.

[0014] Preferably, the dimensions of the measuring device and the coordinates of each sensor are calibrated.

[0015] A measurement method based on a barrel bore parameter measuring device,

[0016] set up:

[0017] MN end face is the end face where the lowest point of the tube is located, point B is the moving probe of the caliper, point C is the fixed probe of the caliper, point O is the rotation center of the moving probe arm of the caliper, point D is the intersection of the perpendicular line drawn through point B and the fixed probe arm OC, and α is the angle between the moving probe arm OB and the fixed probe arm OC.

[0018] Measurement method:

[0019] Release the caliper, and it will automatically open, allowing the caliper's moving probe to contact the inner wall of the tube. The caliper moves upward, and as it encounters different inner diameters during this upward movement, the displacement of the caliper's opening will change accordingly. The moving probe of the caliper collects real-time data, thus obtaining a generatrix. Rotate the caliper and collect data again. After obtaining multiple sets of inner cavity generatrixes from this caliper, take a point on each generatrix on the same cross section and fit it into a circle. By taking n points on several sets of generatrixes, n circles can be obtained. The inner cavity shape of the tube can be fitted using these circles.

[0020] The method for calculating the cross-section circle includes the following steps:

[0021] 1) Fix the tube vertically on the three-jaw chuck. The linear module drives the rotary module and the caliper to descend until the zero-point sensor contacts the upper end face of the tube. Perform zero-point positioning, that is, calibrate the distance L0 between the zero point P and the end face of the tube MN. Assume that when the linear module is at the zero point, point O coincides with point P. At this time, the fixed probe and the moving probe of the caliper are located below the lowest point of the inner cavity to be measured in the tube.

[0022] 2) Let the section at point A be the measured inner diameter circle at a distance L1 from the end face of the tube MN. Measure the inner diameter at point A and calculate the caliper feed depth H = L0 - CO - L1. After feeding according to the calculated value of H, release the caliper's moving arm and rotate it around point O until the caliper's moving probe contacts the inner wall. At this time, the section at point B does not coincide with the measured section, and the distance between the two sections is CD. The current return value of the caliper is BC = K1. The calculation process for CD is as follows:

[0023] CD = OC - OD (1)

[0024] OD=OBcosα (2)

[0025] K1=2OCsin(α / 2) (3)

[0026] We can obtain the following from formulas (1), (2), and (3):

[0027] CD=OC-OBcos[2arcsin(K1 / 2*OC)]=OC(1-cos[2arcsin(K1 / 2*OC)]) (4)

[0028] 3) After calculating the CD value, compensation ΔH1=CD is applied to the feed direction. After compensation, since the measured inner wall is not cylindrical and the inner diameter increases along the depth feed direction, the caliper return value becomes K2. The angle α between the moving probe OB and the fixed probe OC of the caliper increases, making the actual compensation of the moving probe of the caliper in the depth feed direction less than ΔH1. At this time, the section where point B is located is close to but does not coincide with the section being measured, and the caliper return value is K2.

[0029] 4) Perform secondary compensation, and calculate the compensation value ΔH2 as follows:

[0030] ΔH2=OC(1-cos[2arcsin(K2 / 2*OC)])-OC(1- cos[2arcsin(K1 / 2*OC)])

[0031] Simplifying, we get:

[0032] ΔH2=OC*{cos[2arcsin(K1 / 2*OC)] - cos[2arcsin(K2 / 2*OC)]} (5)

[0033] 5) Repeat step 4 until the actual feed depth of the caliper moving probe is approximately equal to H within the allowable range, that is, the section where point B is located approximately coincides with the section being measured;

[0034] 6) Start data acquisition. By aligning the compensation OC with the data acquisition rotation axis, the caliper returns at equal intervals as it rotates along the axis OC and is recorded as (β1, K1), (β2, K2), (β3, K3), where βi is the acquisition angle and Ki is the acquired caliper return value. During the rotation, the change in the caliper return value K will cause the distance between the probe B section and the measured section to change. Therefore, depth feed compensation is performed in real time before each data acquisition.

[0035] 7) Establish a coordinate system for the recorded data, with the intersection of the data acquisition rotation axis and the measured circular cross section as the origin. The X-axis passes through point A1 of the acquisition record, and point J corresponds to the center of the measured inner diameter.

[0036] 8) Substitute the coordinates of point Ai into the general equation of a circle (x-x0). 2 +(y-y0) 2 =(d / 2) 2 In this process, solving the system of equations yields the diameter of the circle containing points A1(x1, y1), A2(x2, y2), and A3(x3, y3).

[0037] Using the above algorithm, the cross-sectional dimensions at various points along the axial direction of the barrel are obtained, and the coaxiality between the conical surfaces of the barrel is calculated. By combining the data of several cross-sectional circles through the algorithm, the actual contour dimensions of the inner cavity of the barrel are obtained.

[0038] Preferably, the short conical surface inside the tube is a straight line, as follows:

[0039] 1) Filtering: Perform smoothing filtering on the data to remove abrupt changes and outliers;

[0040] 2) Differentiation: Calculate the central difference of the smoothed data, i.e., calculate the rate of change for each data point;

[0041] 3) Data segmentation: The collected data is segmented, with one segment containing the taper detection area;

[0042] 4) Line detection: In the taper detection area, by limiting the angle conditions of the line, the line detection is performed to obtain the line in the taper area; for the remaining data segments, the line is directly fitted to obtain the line, and the intersection point of the corresponding line is calculated.

[0043] Preferably, in step 8 of the cross-sectional circle calculation method, the average value of multiple diameters is obtained by increasing the number of sampling points at different locations.

[0044] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0045] 1. The measuring device provided by this invention is suitable for detecting the geometric parameters of the inner bore of small-diameter barrels with a diameter of φ5mm-φ20mm. Its measuring range is 100mm-600mm for hollow workpieces, and its measurement accuracy can reach ±0.005mm, with a repeatability accuracy of 0.002mm. It has a simple structure and low cost.

[0046] 2. This invention uses a linear module to drive a contact sensor (hereinafter referred to as a caliper) to move up and down, and the caliper can rotate. It is used to measure the generatrices at different angles of the inner cavity. The measuring probe measures three generatrices on the inner surface of the bore, and the inner cavity contour is fitted to calculate the size of the pipe being measured.

[0047] 3. This invention solves the problem of the lack of a reference for the product being tested by pre-calibrating the system dimensions and the coordinates of each sensor (i.e., loading hollow workpieces only requires quickly fixing the outer side of the tube with a three-jaw chuck for initial positioning, without the need to fix the inner reference surface).

[0048] 4. This invention consists of five parts: a frame, a marble platform, a motion module, a workpiece fixing plate, and a caliper. Through the coordinated operation of these parts, the invention can automatically detect all internal dimensions of the workpiece.

[0049] 5. The measurement objective of this invention is to measure the location of the virtual intersection of each pair of adjacent straight lines on the vertical cross section along the diameter direction of the product, and to calculate the diameter of the virtual intersection on the cross section and the coaxiality of each conical surface relative to the reference. The system needs to perform automated one-stop detection and display the calculation results intuitively. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the external shape of the present invention;

[0051] Figure 2 This is a schematic diagram of the caliper mounting structure;

[0052] Figure 3 This is a schematic diagram of a caliper probe.

[0053] Figure 4 This is a schematic diagram of the data collection points;

[0054] Figure 5a , Figure 5b This is a schematic diagram of the cross-section circle algorithm;

[0055] Figure 6 This is a schematic diagram of the algorithm;

[0056] Figure 7 A schematic diagram showing the intersection point of a straight line on a conical surface;

[0057] Figure 8 This is a schematic diagram of data fitting.

[0058] Figure 9 This is a diagram illustrating data determination.

[0059] Figure Labels

[0060] In the attached drawings, 1 is a dust-proof cover, 2 is a display, 3 is an adjustable Furniture wheel, 4 is a cabinet, 5 is a grating scale, 6 is a linear module, 7 is a reference platform (marble), 8 is a caliper, 9 is a three-jaw positioning table, 10 is a zero-point sensor, 11 is an inner conical surface, 12 is a fixed probe of the caliper, 13 is a single measurement point of the zero-point sensor, 14 is a single measurement bus of the inner cavity sensor, 15 is a three-measurement fitting surface of the zero-point sensor, 16 is three bus lines of the inner cavity sensor fitting the inner cavity contour, 17 is unqualified coaxiality, and 18 is unqualified inner diameter. Specific implementation mode

[0061] See Figures 1-3 , which is a device for measuring the parameters of the inner bore of a gun barrel.

[0062] Scheme overview

[0063] To ensure the installation accuracy and structural stability of the system, the reference platform and the backplane of the system are built by a 000-level marble platform. A three-jaw positioning table is installed on the platform for quickly fixing the workpiece. A high-precision linear module is installed on the backplane marble, and with the cooperation of a servo motor, an encoder, and a grating scale, full-closed-loop control is achieved, and the coordinates of each axial point can be accurately measured. The linear module drives the contact sensor (hereinafter referred to as the caliper) to move up and down, and the caliper can rotate to measure the bus lines at different angles of the inner cavity.

[0064] This scheme solves the problem of the lack of a reference for the measured product itself by pre-calibrating the system size and the coordinates of each sensor (that is, when loading the product, only the outer side of the tube needs to be quickly fixed with a three-jaw chuck for initial positioning, and there is no need to fix the inner reference surface).

[0065] Figure 1 This is the three-dimensional structure schematic diagram of the system provided by this scheme. The whole equipment adopts a vertical design, the display can be adjusted up and down, and the human-machine interaction of the equipment is carried out through buttons and a touch screen, which is convenient and efficient.

[0066] The system includes a complete set of detection tooling, positioning fixtures, control systems, and detection software, which can automatically measure all the inner cavity dimensions in the workpiece drawing, judge the detection results in real time, and output them to the software interface for intuitive display. It can be compatible with workpieces with an inner diameter of φ5mm - φ20mm and a length of 100mm - 600mm, and there is no need to replace the probe and fixture when changing the production. During detection, manual loading and unloading are adopted, the equipment automatically clamps and positions, and starts the detection with one key. The system automatically judges qualified or unqualified, and at the same time displays, saves, and exports the measurement results. The measurement method can be dynamic and static, and a bus line diagram of the inner bore of the tube (exported in CAD format) can be drawn for later analysis.

[0067] System composition

[0068] The system mainly consists of five parts: a frame, a marble platform, a motion module, a workpiece fixing plate (three-jaw positioning stage), and a caliper. The motion module, workpiece fixing plate, and caliper components are all commercially available equipment. The caliper is a single-point internal measuring caliper with a zero-point sensor at its top. It has a fixed measuring arm and a moving measuring arm. The fixed measuring arm has a fixed probe at its end, and the moving measuring arm has a moving probe at its end. The fixed measuring arm extends vertically downwards, and the moving measuring arm elastically opens during operation, ensuring the moving probe always contacts the inner wall of the workpiece. Through the coordinated operation of these parts, the system automates the inspection of all internal dimensions of the workpiece.

[0069] 1. Rack section

[0070] The frame is constructed from cold-rolled steel, using 304 and 6061 alloy materials, providing overall support and ensuring the structure's robustness, durability, stability, and reliability. The frame integrates a control console; the system's display is mounted on the right side of the equipment, showing images, detection values, results, and other parameters. A touchscreen is installed on the equipment casing for equipment control and displaying relevant system parameters.

[0071] 2 motion modules

[0072] The motion module consists of a linear module and a rotary module, mounted on a marble backplate. A PLC is used as the main controller to drive the servo motors, and a motor encoder and external optical scale are used to achieve a fully closed-loop control system, enabling high-precision automated operation of the equipment. The linear module drives the caliper gauges in vertical lifting motion, collecting values ​​from various positions on the workpiece, and using specialized software algorithms to perform full-dimensional inspection of the workpiece's internal cavity.

[0073] The rotating module drives the caliper to rotate at a constant speed. After measuring one generatrix of the workpiece, the rotating module drives the caliper to rotate by a certain angle and collects a different generatrix again. The software interface then calculates and outputs the results.

[0074] 3. Workpiece clamping and positioning fixtures

[0075] The reference section of the workpiece to be tested is the rifling section, and all coaxiality must be based on this. However, positioning the rifling section is relatively difficult. Therefore, this solution establishes all coordinate systems on the equipment itself. The product only needs to be coarsely positioned under the guidance of a three-jaw chuck. The three-jaw chuck is compatible with diameters from φ5mm to φ50mm and is compatible with the products being tested. Figure 1 ,2 is a schematic diagram of the three-dimensional structure of this part:

[0076] 4 Zero-point positioning

[0077] After positioning the product on the three-jaw chuck, click "Measure". The precision linear module moves downward until the contact displacement sensor contacts the end face of the product. At this point, the caliper is below the lowest point of the inner cavity to be measured, and the system records the position of the product end face.

[0078] 5 Data Acquisition Card Specifications

[0079] After the zero point position is recorded, the caliper naturally opens and fits tightly against the inner wall. At the same time, the sensor begins to collect dimensions, and the grating ruler on the precision linear module records the axial position. After one acquisition is completed, the caliper exits the inner cavity, and the precision rotating component drives the caliper to rotate by several angles. Then, the end face zero point positioning and inner diameter measurement are performed again. After repeating this process three times, the system automatically fits or calculates the end face position, inner cavity contour and intersection inner diameter, as well as the coaxiality of each conical surface.

[0080] Measurement methods

[0081] 1 Measurement Principle

[0082] This method uses a three-point method to measure the inner diameter, based on the general equation of a circle: (x-x0)²+(y-y0)²=(d / 2). 2 It can be seen that by determining the coordinates of any three points on the circle, the center and radius of the circle can be determined.

[0083] Insert the caliper into the product and release it, so that the moving caliper contacts the inner wall. During the upward movement, the displacement of the caliper changes as it encounters different inner diameters. The sensor collects real-time data, thus obtaining a busbar.

[0084] Rotate the caliper and collect data again. After obtaining multiple sets of internal cavity generatrices from this caliper, take a point on each generatrice at the same cross-section to fit a circle. By taking n points from several sets of generatrices, n circles can be obtained. These circles can then be used to fit the shape of the workpiece's internal cavity. (See Figure 5.)

[0085] The calculation of the cross-section circle is briefly described below:

[0086] The system algorithm calculates the distance OAi from the sampled point to the rotation axis of the caliper, such as... Figure 5a As shown, three points are randomly selected as needed and substituted into the circle equation to solve for the inner diameter. If points are taken continuously at equal intervals and their coordinates are decomposed, the result is plotted in the coordinate system for all points, as shown below. Figure 5b As shown.

[0087] 2. Detailed Calculation

[0088] like Figure 6As shown, let the section where point A is located be the inner diameter of the measured circle at a distance L1 from the end face of MN, point B be the moving probe of the caliper, point C be the fixed probe of the caliper, point O be the rotation center of the moving probe arm of the caliper, point D be the intersection of the perpendicular line drawn through point B and the fixed probe arm OC, and α be the angle between the moving probe arm OB and the fixed probe arm OC.

[0089] 1) After the measuring mechanism and product support mechanism are installed, the distance between the positioning baffle at one end of the product MN and the zero point P of the depth feed mechanism needs to be calibrated, that is, the distance L0 between the depth feed zero point and the end face of the product MN is calibrated. It is assumed that when the depth feed mechanism is at the zero point, point O and point P coincide.

[0090] 2) Measure the inner diameter at point A, calculate the caliper gauge feed depth H = L0 - CO - L1, feed according to the calculated value of H, release the caliper gauge and rotate the measuring arm around point O until the probe B contacts the inner wall. Figure 6 As shown, the section where probe B is located does not coincide with the section being measured. The distance between the two sections is CD. The current return value of the caliper is BC = K1. The calculation process of CD is as follows:

[0091] CD = OC - OD (1)

[0092] OD=OBcosα (2)

[0093] K1=2OCsin(α / 2) (3)

[0094] From formulas (1), (2), and (3), we can obtain:

[0095] CD=OC-OBcos[2arcsin(K1 / 2*OC)]=OC(1-cos[2arcsin(K1 / 2*OC)]) (4)

[0096] Among them, OC and OB are equal to the caliper structure parameters, and K1 is the current return value of the caliper.

[0097] 3) After calculating the specific value of CD, the feed direction is compensated by ΔH1=CD. After compensation, since the inner wall being measured is not cylindrical and the inner diameter increases along the depth feed direction, the caliper return value becomes K2. The angle α between the moving probe OB and the fixed probe OC of the caliper increases, making the actual compensation of the moving probe in the depth feed direction less than ΔH1. At this time, the section where the probe B is located is close to but does not coincide with the section being measured. At this time, the caliper return value is K2.

[0098] 4) Perform secondary compensation, and calculate the compensation value ΔH2 as follows:

[0099] ΔH2=OC(1-cos[2arcsin(K2 / 2*OC)])-OC(1- cos[2arcsin(K1 / 2*OC)])

[0100] Simplifying, we get:

[0101] ΔH2=OC*{cos[2arcsin(K1 / 2*OC)] - cos[2arcsin(K2 / 2*OC)]} (5)

[0102] 5) Repeat step 4 until the actual feed depth of probe B is approximately equal to H within the allowable range, that is, the cross section where probe B is located approximately coincides with the cross section being measured. The entire compensation process is automatically calculated and executed by the system.

[0103] 6) Start data acquisition. By aligning the compensation OC with the data acquisition rotation axis, the caliper returns at equal intervals as it rotates along the axis OC and is recorded as (β1, K1), (β2, K2), (β3, K3), where βi is the acquisition angle and Ki is the acquired caliper return value. During the rotation, the change in the caliper return value K will cause a change in the distance between the section where the probe B is located and the section being measured. Therefore, depth feed compensation is performed in real time before each data acquisition.

[0104] 7) Establish a coordinate system for the recorded data, with the intersection of the data acquisition rotation axis and the measured circular cross-section as the origin. The X-axis passes through point A1 of the acquisition record, such as... Figure 5b As shown, point J corresponds to Figure 5a The center of the inner diameter being measured.

[0105] 8) Establish a coordinate system for the recorded data, with the intersection of the data acquisition rotation axis and the measured circular cross-section as the origin. The X-axis passes through point A1 of the acquisition record, such as... Figure 5b As shown, point J corresponds to Figure 5a Find the center of the inner diameter to be measured; substitute the coordinates of point Ai into the general equation of a circle (x-x0)² + (y-y0)² = (d / 2)², and solve the system of equations to obtain the diameter of the circle containing points A1(x1, y1), A2(x2, y2), and A3(x3, y3). Alternatively, by increasing the number of points taken at different locations, the average of multiple diameters can be obtained.

[0106] This system can use the above algorithm to obtain the dimensions of each cross section of the product and automatically calculate the coaxiality between each conical surface of the product.

[0107] 3. Short conical surface with straight line

[0108] Some conical surfaces within the part's internal cavity are very short, resulting in short, irregularly positioned straight lines. If the conventional method of taking lines at fixed locations and finding their intersections is used, the line positions may be incorrect, leading to significant discrepancies between the final detection results and the actual results. Therefore, this solution incorporates a new algorithm to address this issue, as detailed below:

[0109] 1) Filtering: Smooth the data and remove abrupt changes and outliers.

[0110] 2) Differentiation: Calculate the central difference of the smoothed data, i.e., calculate the rate of change of each data point.

[0111] 3) Data partitioning: such as Figure 7 In step 2, the change rate graphs for data segments A and B show very small values ​​close to zero, allowing for accurate segmentation of the collected data into three segments (A, B, and C), with segment C representing the taper detection area.

[0112] 4) Line detection: In segment C, by limiting the angle conditions of the lines, line detection can be performed to obtain the lines in the taper region; for the data in segments A and B, line fitting is directly performed to obtain the lines, and the intersection points of the corresponding lines are calculated for subsequent calculations.

[0113] 4 Data Output

[0114] After the system collects all the data, it can automatically calculate the relevant dimensions of the circle containing each cross-section along the generatrix based on the above calculation principle. By combining the data of several cross-section circles through the algorithm, the actual contour dimensions of the product's inner cavity can be obtained.

[0115] Once all the actual dimensions of the above products are obtained, the inspection data can be exported for convenient data analysis. Inspection data can be generated individually for each workpiece, using color to distinguish between qualified, unqualified, and critical edge categories. The inspection system should have printing capabilities, a USB interface, and output data for researchers' reference. See the table below:

[0116]

[0117] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A measurement method based on a barrel bore parameter measuring device, characterized in that: The measuring device includes: The frame is equipped with a backplate and a reference platform. A three-jaw positioning stage set on the reference platform is used to clamp and fix the body tube; The linear module mounted on the back panel is used to achieve the lifting function; A rotary module is installed on the linear module to enable rotation. A caliper is mounted on a rotating module. The caliper has a zero-point sensor on its upper part. The caliper has a fixed measuring arm and a moving measuring arm. The fixed measuring arm has a fixed probe at its end, and the moving measuring arm has a moving probe at its end. The linear module drives the rotary module and the caliper to perform vertical lifting and lowering movements to measure different depth positions inside the tube. The rotary module drives the caliper to rotate to measure different angular positions inside the tube. The measurement method is as follows: set up: MN end face is the end face where the lowest point of the tube is located, point B is the moving probe of the caliper, point C is the fixed probe of the caliper, point O is the rotation center of the moving probe arm of the caliper, point D is the intersection of the perpendicular line drawn through point B and the fixed probe arm OC, and α is the angle between the moving probe arm OB and the fixed probe arm OC. Measurement method: Release the caliper, and it will automatically open, allowing the caliper's moving probe to contact the inner wall of the tube. The caliper moves upward, and as it encounters different inner diameters during this upward movement, the displacement of the caliper's opening will also change accordingly. The caliper's moving probe collects real-time data, thus obtaining a generatrix. Rotate the caliper and collect data again. After obtaining multiple sets of inner cavity generatrixes from this caliper, take a point on each generatrix on the same cross section and fit it into a circle. By taking n points on several sets of generatrixes, n circles can be obtained. The inner cavity shape of the tube can be fitted using these circles. The method for calculating the cross-section circle includes the following steps: 1) Fix the tube vertically on the three-jaw chuck. The linear module drives the rotary module and the caliper to descend until the zero-point sensor contacts the upper end face of the tube. Perform zero-point positioning, that is, calibrate the distance L0 between the zero point P and the end face of the tube MN. Assume that when the linear module is at the zero point, point O coincides with point P. At this time, the fixed probe and the moving probe of the caliper are located below the lowest point of the inner cavity to be measured in the tube. 2) Let the section at point A be the measured inner diameter circle at a distance L1 from the end face of the tube MN. Measure the inner diameter at point A and calculate the caliper feed depth H = L0 - CO - L1. After feeding according to the calculated value of H, release the caliper's moving arm and rotate it around point O until the caliper's moving probe contacts the inner wall. At this time, the section at point B does not coincide with the measured section, and the distance between the two sections is CD. The current return value of the caliper is BC = K1. The calculation process for CD is as follows: CD = OC - OD (1) OD=OBcosα (2) K1=2OCsin(α / 2) (3) We can obtain the following from formulas (1), (2), and (3): CD=OC-OBcos[2arcsin(K1 / 2*OC)]=OC(1-cos[2arcsin(K1 / 2*OC)]) (4) 3) After calculating the CD value, compensation ΔH1=CD is applied to the feed direction. After compensation, since the measured inner wall is not cylindrical and the inner diameter increases along the depth feed direction, the caliper return value becomes K2. The angle α between the moving probe OB and the fixed probe OC of the caliper increases, making the actual compensation of the moving probe of the caliper in the depth feed direction less than ΔH1. At this time, the section where point B is located is close to but does not coincide with the section being measured, and the caliper return value is K2. 4) Perform secondary compensation, and calculate the compensation value ΔH2 as follows: ΔH2=OC(1-cos[2arcsin(K2 / 2*OC)])-OC(1- cos[2arcsin(K1 / 2*OC)]) Simplifying, we get: ΔH2=OC*{cos[2arcsin(K1 / 2*OC)] - cos[2arcsin(K2 / 2*OC)]} (5) 5) Repeat step 4 until the actual feed depth of the caliper moving probe is approximately equal to H within the allowable range, that is, the section where point B is located approximately coincides with the section being measured; 6) Start data acquisition. By aligning the compensation OC with the data acquisition rotation axis, the caliper returns at equal intervals as it rotates along the axis OC and is recorded as (β1, K1), (β2, K2), (β3, K3), where βi is the acquisition angle and Ki is the acquired caliper return value. During the rotation, the change in the caliper return value K will cause the distance between the probe B section and the measured section to change. Therefore, depth feed compensation is performed in real time before each data acquisition. 7) Establish a coordinate system for the recorded data, with the intersection of the data acquisition rotation axis and the measured circular cross section as the origin. The X-axis passes through point A1 of the acquisition record, and point J corresponds to the center of the measured inner diameter. 8) Substitute the coordinates of point Ai into the general equation of a circle (x-x0). 2 +(y-y0) 2 =(d / 2) 2 In this process, solving the system of equations yields the diameter of the circle containing points A1(x1, y1), A2(x2, y2), and A3(x3, y3). Using the above algorithm, the cross-sectional dimensions at various points along the axial direction of the barrel are obtained, and the coaxiality between the conical surfaces of the barrel is calculated. By combining the data of several cross-sectional circles through the algorithm, the actual contour dimensions of the inner cavity of the barrel are obtained.

2. The measurement method according to claim 1, characterized in that, The short conical surface inside the barrel is taken as a straight line, as follows: 1) Filtering: Perform smoothing filtering on the data to remove abrupt changes and outliers; 2) Differentiation: Calculate the central difference of the smoothed data, i.e., calculate the rate of change for each data point; 3) Data segmentation: The collected data is segmented, with one segment containing the taper detection area; 4) Line detection: In the taper detection area, by limiting the angle conditions of the line, the line detection is performed to obtain the line in the taper area; for the remaining data segments, the line is directly fitted to obtain the line, and the intersection point of the corresponding line is calculated.

3. The measurement method according to claim 1, characterized in that, In step 8 of the cross-sectional circle calculation method, the average value of multiple diameters is obtained by increasing the number of sampling points at different locations.

4. The measurement method according to claim 1, characterized in that: The reference platform and back plate are made of marble platform. The linear module and rotary module are both high-precision modules. The linear module, rotary module and caliper are controlled by PLC. The linear module achieves full closed-loop control through servo motor, motor encoder and external grating ruler.

5. The measurement method according to claim 1, characterized in that: Zero-point sensors, fixed probes of calipers, and moving probes are all contact sensors.

6. The measurement method according to claim 1, characterized in that: The dimensions of the measuring device and the coordinates of each sensor have been calibrated.

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