Method for measuring ovality of large ring

Abstract

The application provides a large ring piece ovality measuring method, comprising the steps of: calculating a step arc length and a quarter oval circumference; moving a measuring point by the step arc length in a selected direction to measure a diameter, and continuously measuring until the cumulative moving arc length reaches or exceeds the quarter oval circumference; determining the extreme value type contained in the scanning interval, and selecting the maximum point or minimum point of the diameter in the scanning interval as a candidate extreme value point; moving one-half step arc length to both sides of the candidate extreme value point, measuring three-point diameters, and obtaining a first principal axis point and a diameter by comparison; positioning a second principal axis point by moving the quarter oval circumference along the ring piece from the first principal axis point, and measuring a diameter; calculating the difference between the diameters of the first principal axis point and the second principal axis point to obtain the ovality of the ring piece. The measuring method reduces the equipment cost, improves the on-site adaptability and operation convenience under the premise of ensuring the measuring accuracy, and provides a fast, accurate and low-cost measuring scheme for large ring pieces with a diameter of 10 meters.

Description

Technical Field

[0001] This invention relates to the field of geometric accuracy measurement technology for large mechanical parts, and in particular to a method for measuring the ellipticity of large ring parts. Background Technology

[0002] Ring components are key structural parts in the aerospace rocket field. As rocket body sizes gradually increase, the required ring diameters have grown from the 3-meter level to the 5-meter level, and the next generation of launch vehicles will reach the 10-meter level. With the increase in ring size, the accuracy of ellipticity measurement becomes increasingly important.

[0003] Currently, the main ellipticity measurement techniques include the following: Contact measurement method: This method uses tools such as a measuring tape to obtain the maximum and minimum diameter values ​​of the ring through multiple sets of measurements, and then calculates the ellipticity. However, this method lacks standardized references and cannot ensure that the measurement data accurately represents the major and minor axes of the ellipse, thus failing to yield a true ellipticity result.

[0004] Non-contact measurement methods: For example, Chinese patent CN201310201516.8 discloses a non-contact measurement device for the inner and outer diameters of large-diameter ring-shaped parts, which uses a laser displacement sensor. However, this method requires auxiliary rotating fixtures, and the requirements for the matching fixtures for large ring parts are extremely high, resulting in a complex system.

[0005] Machine vision method: This method is affected by the workshop environment (such as light, vibration and dust), and the equipment is expensive and the system is complex, making it unsuitable for measuring large-sized ring parts.

[0006] In summary, contact measurement methods cannot ensure that the measured data accurately approximates the major and minor axes of the ellipse, leading to inaccurate and unreliable ellipticity calculations. Non-contact measurement and machine vision methods, on the other hand, face challenges such as expensive equipment, complex systems, and stringent environmental requirements, failing to provide a fast, accurate, and low-cost measurement solution for large ring components with diameters reaching 10 meters. Summary of the Invention

[0007] To address the aforementioned technical problems, the purpose of this invention is to provide a method for measuring the ellipticity of large ring components, aiming to reduce equipment costs and improve on-site adaptability and ease of operation while ensuring measurement accuracy.

[0008] A method for measuring the ellipticity of a large ring component includes the following steps: Parameter determination and preparation: Determine the nominal diameter and expected ellipticity of the ring, and calculate the step arc length and the circumference of a quarter ellipse; Quarter circumference scan: Starting from any point on the circumference of the ring, the measurement point is moved along the selected direction by step arc length. The diameter passing through the point is measured at each measurement point. The measurement is continued until the cumulative arc length moved reaches or exceeds one-quarter of the ellipse circumference. Extreme value type determination: Based on the trend of the measured diameter change, determine the type of extreme values ​​contained in the scanning interval; Candidate extreme point location: Select the point with the largest or smallest diameter within the scanning interval as candidate extreme points based on the extreme value type; Precise extreme point location: Taking the candidate extreme point as the center, move it to both sides by half the step arc length, measure the diameter values ​​of the three points, and determine the precise extreme point position by comparison, thus obtaining the first principal axis point and the corresponding diameter; Determining the second principal axis: Starting from the first principal axis point, move along the ring piece by a quarter of the ellipse circumference to locate the second principal axis point and measure the corresponding diameter; Calculation of ring ellipticity: Calculate the difference between the diameter corresponding to the first principal axis point and the diameter corresponding to the second principal axis point to obtain the ellipticity of the ring.

[0009] In some alternative embodiments, the step arc length is calculated using formula (1): (1) in: The step arc length is in mm. D is the nominal diameter of the ring, in mm; e represents the expected ellipticity, in mm.

[0010] In some optional embodiments, the derivation of formula (1) satisfies the following mathematical model: The diameter error near the extreme point is ≤ 1mm, where Δθ is the step angle.

[0011] In some alternative embodiments, the circumference of the quarter ellipse is calculated using formula (2): (2) in: The circumference of one-quarter of the ellipse is expressed in mm. D is the nominal diameter of the ring, in mm.

[0012] In some optional embodiments, the extreme value type determination step specifically involves: If the diameter of the measurement point continues to increase, the scanning interval will contain the extreme points of the major axis; If the diameter of the measurement point continues to decrease, the scanning interval will contain the extreme points of the minor axis.

[0013] In some optional embodiments, the step of locating candidate extreme points specifically involves: If the scan interval contains extreme points along the major axis, then the point with the largest diameter is selected as the candidate extreme point. If the scan interval contains extreme points along the minor axis, then the point with the smallest diameter is selected as the candidate extreme point.

[0014] In some optional embodiments, the step of precise extreme point localization includes: If the scan interval contains extreme points of the major axis, then the candidate extreme point and the point with the largest diameter among the points on both sides are selected as the extreme points of the major axis. If the scan interval contains extreme points of the minor axis, then the candidate extreme point and the point with the smallest diameter among the points on both sides are selected as the extreme point of the minor axis.

[0015] In some optional embodiments, the method for measuring the ellipticity of large ring components further includes verifying the rationality of the step arc length, specifically: When the scanning interval contains extreme points along the major axis, if the candidate extreme point is also an extreme point along the major axis, the selected step arc length is reasonable; if the candidate extreme point is not an extreme point along the major axis, and the difference between the diameter corresponding to the candidate extreme point and the maximum diameter is less than or equal to 1 mm, the selected step arc length is reasonable; if the candidate extreme point is not an extreme point along the major axis, and the difference between the diameter corresponding to the candidate extreme point and the maximum diameter is greater than 1 mm, the selected step arc length is unreasonable. When the scanning interval contains extreme points of the minor axis, if the candidate extreme point is an extreme point of the minor axis, the selected step arc length is reasonable; if the candidate extreme point is not an extreme point of the minor axis, and the difference between the diameter corresponding to the candidate extreme point and the minimum diameter is less than or equal to 1 mm, the selected step arc length is reasonable; if the candidate extreme point is not an extreme point of the minor axis, and the difference between the diameter corresponding to the candidate extreme point and the minimum diameter is greater than 1 mm, the selected step arc length is unreasonable.

[0016] In some optional embodiments, if the selected step arc length is unreasonable, the step arc length is halved, and the steps of quarter-circumference scanning, extreme value type judgment, candidate extreme value point location and precise extreme value point location are repeated until the selected step arc length is reasonable.

[0017] In some alternative embodiments, the diameter is measured using a contact measuring tool.

[0018] Compared with the prior art, the method for measuring the ellipticity of large ring components provided in this invention has at least the following technical problems: The method for measuring the ellipticity of a large ring component involves the following steps: First, determine the nominal diameter and expected ellipticity of the ring component, and calculate the step arc length and quarter-ellipse circumference. Next, using any point on the circumference of the ring component as the starting measurement point, move along a selected direction at the step arc length, recording the diameter of each measurement point until the cumulative arc length reached or exceeded the quarter-ellipse circumference. Based on this, determine the type of extreme values ​​within the scanning interval according to the trend of diameter changes, and select the point with the largest or smallest diameter as a candidate extreme value point. Subsequently, using the candidate extreme value point as the center, move to both sides by half the step arc length, measuring the diameter values ​​of these three points. By comparison, determine the precise location of the extreme value point, thus obtaining the first principal axis point and its corresponding diameter. Next, starting from the first principal axis point, move along the ring component a distance of quarter-ellipse circumference to locate the second principal axis point, and measure the diameter of this point. Through this series of steps, the major axis extreme point, major axis diameter, minor axis extreme point, and minor axis diameter can be accurately obtained, and the ellipticity of the ring component can be finally calculated. This method is based on the geometric properties of an ellipse, utilizing the principle that a quarter of the circumference must contain an extreme point. Combined with a rigorous formula for step arc length, it ensures measurement accuracy. A three-point extreme point positioning method is used to precisely determine the location of the extreme point, and the position of the other principal axis is determined by the perpendicular relationship between the major and minor axes. Simultaneously, a simple contact measuring tool (such as a measuring tape) is used for diameter measurement, enabling precise measurement of the ellipticity of large ring components. Compared to traditional contact measurement methods, this invention has a more rigorous theoretical foundation, thus ensuring measurement accuracy. Compared to non-contact measurement methods, this invention does not require complex equipment and algorithms, thereby reducing equipment costs, improving on-site adaptability and ease of operation, and providing a fast, accurate, and low-cost measurement solution for large ring components with diameters up to 10 meters. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of a method for measuring the ellipticity of a large ring component in one embodiment of the present invention. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly set on the other component; when a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to the other component.

[0023] It should be noted that the structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which this application can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size should still fall within the scope of the technical content disclosed in this application, provided that they do not affect the effects and purposes that this application can produce.

[0024] Ring components are key structural parts in the aerospace rocket field. As rocket body sizes gradually increase, the required ring diameters have grown from the 3-meter level to the 5-meter level, and the next generation of launch vehicles will reach the 10-meter level. With the increase in ring size, the accuracy of ellipticity measurement becomes increasingly important.

[0025] Currently, the main ellipticity measurement techniques include the following: Contact measurement method: This method uses tools such as a measuring tape to obtain the maximum and minimum diameter values ​​of the ring through multiple sets of measurements, and then calculates the ellipticity. However, this method lacks standardized references and cannot ensure that the measurement data accurately represents the major and minor axes of the ellipse, thus failing to yield a true ellipticity result.

[0026] Non-contact measurement methods: For example, Chinese patent CN201310201516.8 discloses a non-contact measurement device for the inner and outer diameters of large-diameter ring-shaped parts, which uses a laser displacement sensor. However, this method requires auxiliary rotating fixtures, and the requirements for the matching fixtures for large ring parts are extremely high, resulting in a complex system.

[0027] Machine vision method: This method is affected by the workshop environment (such as light, vibration and dust), and the equipment is expensive and the system is complex, making it unsuitable for measuring large-sized ring parts.

[0028] In summary, contact measurement methods cannot ensure that the measured data accurately approximates the major and minor axes of the ellipse, leading to inaccurate and unreliable ellipticity calculations. Non-contact measurement and machine vision methods, on the other hand, face challenges such as expensive equipment, complex systems, and stringent environmental requirements, failing to provide a fast, accurate, and low-cost measurement solution for large ring components with diameters reaching 10 meters.

[0029] Therefore, please refer to the appendix. Figure 1 As shown, an embodiment of the present invention provides a method for measuring the ellipticity of a large ring, comprising the following steps: S1. Parameter determination and preparation: Determine the nominal diameter and expected ellipticity of the ring, and calculate the step arc length and the circumference of a quarter ellipse; S2, Quarter circumference scan: Starting measurement point is any point on the circumference of the ring. Move the measurement point along the selected direction by step arc length, at each measurement point Measure the diameter passing through this point Continue measuring until the cumulative arc length reaches or exceeds one-quarter of the ellipse's circumference; among which, For the i-th measurement point, This is the measured diameter value passing through the i-th measurement point; S3. Extreme value type judgment: Determine the extreme value type contained in the scanning interval based on the trend of the measured diameter change; S4. Candidate extreme point location: Select the point with the largest or smallest diameter within the scanning interval as the candidate extreme point according to the type of extreme value. S5. Precise extreme point location: Taking the candidate extreme point as the center, move half the step arc length to both sides, measure the diameter values ​​of the three points, and determine the precise extreme point position by comparison, thus obtaining the first principal axis point and the corresponding diameter. S6. Determining the second principal axis: Starting from the first principal axis point, move along the ring piece by a quarter of the ellipse circumference to locate the second principal axis point, and measure the second principal axis point and its corresponding diameter; S7. Calculation of ring ellipticity: Calculate the difference between the diameter corresponding to the first principal axis point and the diameter corresponding to the second principal axis point to obtain the ring ellipticity.

[0030] Specifically, the formula for calculating ellipticity is as follows:

[0031] in, Ellipticity ， This is the measured diameter value corresponding to the extreme point of the major axis. This represents the diameter measurement corresponding to the extreme point of the minor axis. To further clarify, if the first principal axis point is an extreme point of the major axis, then the second principal axis point corresponds to an extreme point of the minor axis; conversely, if the first principal axis point is an extreme point of the minor axis, then the second principal axis point corresponds to an extreme point of the major axis.

[0032] This invention provides a method for measuring the ellipticity of a large ring component, implemented through the following steps: First, determine the nominal diameter and expected ellipticity of the ring component, and calculate the step arc length and one-quarter ellipse circumference. Next, using any point on the circumference of the ring component as the starting measurement point, move along a selected direction at the step arc length, recording the diameter of each measurement point until the cumulative arc length moved reaches or exceeds one-quarter ellipse circumference. Based on this, determine the extreme value type within the scanning interval according to the trend of diameter changes, and select the point with the largest or smallest diameter as a candidate extreme value point. Subsequently, using the candidate extreme value point as the center, move to both sides by half the step arc length, measuring the diameter values ​​of these three points. By comparison, determine the precise extreme value point position, thereby obtaining the first principal axis point and its corresponding diameter. Next, starting from the first principal axis point, move along the ring component a distance of one-quarter ellipse circumference to locate the second principal axis point, and measure the diameter of this point. Through this series of steps, the major axis extreme point, major axis diameter, minor axis extreme point, and minor axis diameter can be accurately obtained, and the ellipticity of the ring component can be finally calculated. This method is based on the geometric properties of an ellipse, utilizing the principle that a quarter of the circumference must contain an extreme point. Combined with a rigorous formula for step arc length, it ensures measurement accuracy. A three-point extreme point positioning method is used to precisely determine the location of the extreme point, and the position of the other principal axis is determined by the perpendicular relationship between the major and minor axes. Simultaneously, a simple contact measuring tool (such as a measuring tape) is used for diameter measurement, enabling precise measurement of the ellipticity of large ring components. Compared to traditional contact measurement methods, this invention has a more rigorous theoretical foundation, thus ensuring measurement accuracy. Compared to non-contact measurement methods, this invention does not require complex equipment and algorithms, thereby reducing equipment costs, improving on-site adaptability and ease of operation, and providing a fast, accurate, and low-cost measurement solution for large ring components with diameters up to 10 meters.

[0033] To ensure that the measurement error of the extreme point diameter is controlled within 1mm, a mathematical model is established based on the geometric properties of an ellipse: Diameter error near extreme points ≤ 1mm, where Δθ is the step angle. Where 'e' is the diameter error and 'e' is the ellipticity; Solving for: The formula is derived based on the arc length formula ΔL = (D / 2)·Δθ. .

[0034] It should be further explained that the step arc length is calculated using formula (1): (1) in: The step arc length is in mm. D is the nominal diameter of the ring, in mm; e represents the expected ellipticity, in mm.

[0035] The step arc length is calculated using formula (1), which can effectively control the diameter measurement error caused by discrete sampling near the extreme point, so that the diameter measurement error is kept within an acceptable range and the error does not exceed 1mm.

[0036] In some alternative embodiments, the circumference of the quarter ellipse is calculated using formula (2): (2) in: The circumference of one-quarter of the ellipse is expressed in mm. D is the nominal diameter of the ring, in mm. Formula (2) is derived based on the approximate formula for the circumference of an ellipse and its symmetry characteristics.

[0037] In some optional embodiments, the extreme value type determination step specifically involves: if the diameter of the measurement point... As the diameter increases, the scanning interval will contain the extreme points of the major axis; if the diameter of the measurement point... If the value is continuously reduced, the scan interval will contain the extreme points of the minor axis.

[0038] In some optional embodiments, the step of locating candidate extrema points specifically involves: if the scanning interval contains extrema points along the major axis, then the point with the largest diameter is selected as the candidate extrema point; if the scanning interval contains extrema points along the minor axis, then the point with the smallest diameter is selected as the candidate extrema point.

[0039] In some optional embodiments, in the step of precise extreme point location: if the scanning interval contains an extreme point of the major axis, then the candidate extreme point and the point with the largest diameter among the two points on both sides are selected as the extreme point of the major axis; if the scanning interval contains an extreme point of the minor axis, then the candidate extreme point and the point with the smallest diameter among the two points on both sides are selected as the extreme point of the minor axis.

[0040] In some optional embodiments, the method for measuring the ellipticity of large ring components further includes verifying the rationality of the step arc length. Specifically, when the scanning interval contains an extreme point of the major axis, if the candidate extreme point is an extreme point of the major axis, then the selected step arc length is reasonable; if the candidate extreme point is not an extreme point of the major axis, and the difference between the diameter corresponding to the candidate extreme point and the maximum diameter is less than or equal to 1 mm, then the selected step arc length is reasonable; if the candidate extreme point is not an extreme point of the major axis, and the difference between the diameter corresponding to the candidate extreme point and the maximum diameter is less than or equal to 1 mm, then the selected step arc length is reasonable. If the difference in diameter is greater than 1 mm, the selected step arc length is unreasonable. When the scanning interval contains an extreme point of the minor axis, if the candidate extreme point is an extreme point of the minor axis, the selected step arc length is reasonable. If the candidate extreme point is not an extreme point of the minor axis, and the difference between the diameter corresponding to the candidate extreme point and the minimum diameter is less than or equal to 1 mm, the selected step arc length is reasonable. If the candidate extreme point is not an extreme point of the minor axis, and the difference between the diameter corresponding to the candidate extreme point and the minimum diameter is greater than 1 mm, the selected step arc length is unreasonable.

[0041] In some optional embodiments, if the selected step arc length is unreasonable, the step arc length is halved, and the steps of quarter-circumference scanning, extreme value type judgment, candidate extreme value point location and precise extreme value point location are repeated until the selected step arc length is reasonable, that is, the condition for verifying the reasonableness of the step arc length is met.

[0042] The diameter is measured using a contact measuring tool. Optional, but not limited to, a measuring tape.

[0043] The following detailed description of the ellipticity measurement method for rocket body rings with a diameter of 10 meters is illustrated with a specific embodiment.

[0044] The nominal diameter of the ring is D = 10000.0 mm, the expected ellipticity is e = 10.0 mm, and the step arc length is ΔL = ≈3162.3 mm, ≈0.8×10000.0 = 8000.0 mm.

[0045] The measurement point is any point on the circumference of the ring. The measurement was performed in a clockwise direction, and the measurement data is as follows: Starting measurement point Corresponding diameter measurement value = 10001.5 mm, first measurement point (That is, moving the starting measurement point clockwise with a step arc length of 3162.3 mm) = 10003.8 mm, compared to Increase; second measurement point (That is, moving the first measuring point clockwise with a step arc length of 3162.3 mm) = 10005.3 mm, compared to Increase; third measurement point (That is, moving the second measuring point clockwise with a step arc length of 3162.3 mm) Corresponding = 10004.7 mm, compared to The value decreases. The cumulative movement of 9486.9 mm > 8000.0 mm; therefore, the extreme point containing the major axis within the scanning interval is determined.

[0046] The second measurement point As candidate extreme points The diameter measurement corresponding to 1581.2 mm on the left is 10004.6 mm. The corresponding diameter measurement is 10005.3 mm. The diameter measurement corresponding to 1581.2 mm on the right is 10004.5 mm, therefore the first principal axis point is determined, which is the extreme point of the major axis. for Corresponding diameter measurement value =10005.3 mm.

[0047] From the extreme point of the major axis Starting from the beginning, move 8000.0 mm along the ring and measure the diameter corresponding to the extreme point of the minor axis. = 9996.2 mm. Ellipticity calculation: = 10005.3 - 9996.2 = 9.1 mm.

[0048] The above description is merely an embodiment of the present invention. It should be noted that those skilled in the art can make improvements without departing from the inventive concept of the present invention, but these improvements all fall within the protection scope of the present invention.

Claims

1. A method for measuring the ellipticity of a large ring component, characterized in that, Includes the following steps: Parameter determination and preparation: Determine the nominal diameter and expected ellipticity of the ring, and calculate the step arc length and the circumference of a quarter ellipse; Quarter-circumference scan: The measurement starting point is any point on the circumference of the ring. Move the measurement point along the selected direction by step arc length, at each measurement point Measure the diameter passing through this point Continue measuring until the cumulative arc length reaches or exceeds one-quarter of the ellipse's circumference; Extreme value type determination: Based on the trend of the measured diameter change, determine the type of extreme values ​​contained in the scanning interval; Candidate extreme point location: Select the point with the largest or smallest diameter within the scanning interval as candidate extreme points based on the extreme value type; Precise extreme point location: Taking the candidate extreme point as the center, move it to both sides by half the step arc length, measure the diameter values ​​of the three points, and determine the precise extreme point position by comparison, thus obtaining the first principal axis point and the corresponding diameter; Determining the second principal axis: Starting from the first principal axis point, move along the ring piece by a quarter of the ellipse circumference to locate the second principal axis point and measure the corresponding diameter; Calculation of ring ellipticity: Calculate the difference between the diameter corresponding to the first principal axis point and the diameter corresponding to the second principal axis point to obtain the ellipticity of the ring.

2. The method for measuring the ellipticity of large ring components according to claim 1, characterized in that, The step arc length is calculated using formula (1): （1）； in: The step arc length is in mm. D is the nominal diameter of the ring, in mm; e represents the expected ellipticity, in mm.

3. The method for measuring the ellipticity of large ring components according to claim 2, characterized in that, The derivation of formula (1) satisfies the following mathematical model: Diameter error near extreme points ≤ 1mm, where Δθ is the step angle.

4. The method for measuring the ellipticity of large ring components according to claim 1, characterized in that, The circumference of the quarter ellipse is calculated using formula (2): （2）； in: The circumference of one-quarter of the ellipse is expressed in mm. D is the nominal diameter of the ring, in mm.

5. The method for measuring the ellipticity of large ring components according to claim 1, characterized in that, The extreme value type determination step is specifically as follows: If the diameter of the measuring point As the value increases, the scanning interval will contain the extreme points of the major axis; If the diameter of the measuring point If the value is continuously reduced, the scan interval will contain the extreme points of the minor axis.

6. The method for measuring the ellipticity of large ring components according to claim 5, characterized in that, The specific steps for locating candidate extreme points are as follows: If the scan interval contains extreme points along the major axis, then the point with the largest diameter is selected as the candidate extreme point. If the scan interval contains extreme points along the minor axis, then the point with the smallest diameter is selected as the candidate extreme point.

7. The method for measuring the ellipticity of large ring components according to claim 6, characterized in that, In the precise extreme point location step: If the scan interval contains extreme points of the major axis, then the candidate extreme point and the point with the largest diameter among the points on both sides are selected as the extreme points of the major axis. If the scan interval contains extreme points of the minor axis, then the candidate extreme point and the point with the smallest diameter among the points on both sides are selected as the extreme point of the minor axis.

8. The method for measuring the ellipticity of large ring components according to claim 7, characterized in that, This also includes verifying the rationality of the step arc length, specifically: When the scanning interval contains extreme points along the major axis, if the candidate extreme point is also an extreme point along the major axis, the selected step arc length is reasonable; if the candidate extreme point is not an extreme point along the major axis, and the difference between the diameter corresponding to the candidate extreme point and the maximum diameter is less than or equal to 1 mm, the selected step arc length is reasonable; if the candidate extreme point is not an extreme point along the major axis, and the difference between the diameter corresponding to the candidate extreme point and the maximum diameter is greater than 1 mm, the selected step arc length is unreasonable. When the scanning interval contains extreme points of the minor axis, if the candidate extreme point is an extreme point of the minor axis, the selected step arc length is reasonable; if the candidate extreme point is not an extreme point of the minor axis, and the difference between the diameter corresponding to the candidate extreme point and the minimum diameter is less than or equal to 1 mm, the selected step arc length is reasonable; if the candidate extreme point is not an extreme point of the minor axis, and the difference between the diameter corresponding to the candidate extreme point and the minimum diameter is greater than 1 mm, the selected step arc length is unreasonable.

9. The method for measuring the ellipticity of large ring components according to claim 8, characterized in that, If the selected step arc length is unreasonable, halve the step arc length and repeat the steps of quarter-circumference scanning, extreme value type judgment, candidate extreme value point location and precise extreme value point location until the selected step arc length is reasonable.

10. The method for measuring the ellipticity of large ring components according to claim 1, characterized in that, The diameter is measured using a contact measuring tool.

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