Method for measuring length of variable-diameter pipe

Abstract

The invention discloses a method for measuring the length of a variable-diameter pipe, the variable-diameter pipe comprises a large-hole section, a transition section and a small-hole section which are communicated in sequence, and the method is characterized by comprising the following steps: S1, positioning an auxiliary tool; s2, measuring the length of the base; s3, calculating an intermediate distance; s4, calculating the maximum offset; and S5, determining the length to be measured. According to the method, the relative reference is determined through positioning of the auxiliary tool, the problem that the reference is fuzzy in traditional measurement is avoided, the offset error of the transition section is eliminated through double guarantee of positioning reference and tolerance compensation in combination with geometric compensation calculation, the measurement error is greatly reduced, the precision of the measurement result is high, and the industrial-grade precision requirement can be met; high-precision professional equipment is not needed, the measurement process is simple and easy to understand and can be completed by one person, and the auxiliary tool is simple in structure, low in manufacturing cost and easy to popularize and apply on a large scale.

Description

Technical Field

[0001] This invention relates to the field of pipe size inspection technology, and more specifically, to a method for measuring the length of variable diameter pipes. Background Technology

[0002] In fields such as machinery manufacturing, petrochemicals, and aerospace, reducing pipes (i.e., pipes with different inner diameters in different sections connected by transition sections) are widely used, such as guide pipes and reducing conveying pipes. The length from the start of the transition section to the end of the orifice (denoted as L1) of such pipes is a critical dimension. The accuracy of this dimension directly affects the assembly precision of the pipe with other components and the realization of its functions (such as fluid flow rate and guiding accuracy).

[0003] In existing measurement methods, conventional measuring tools such as rulers and tape measures are usually used to directly measure L1. However, there is a core defect: the transition section of the variable diameter pipe is a conical surface (without obvious steps), which makes it impossible to accurately locate the "starting position of the transition section" (the junction between the large hole section and the transition section). The measurement starting point of conventional measuring tools is prone to deviate from the true starting position, thus generating measurement errors. In addition, the machining tolerance of the transition section angle (denoted as X) will further amplify this error, causing the measurement results to fail to meet industrial technical requirements.

[0004] Therefore, it is necessary to provide a method for measuring the length of variable diameter pipes to solve the above-mentioned technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for measuring the length of variable diameter pipes to solve the above-mentioned technical problems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for measuring the length of a variable-diameter pipe, the variable-diameter pipe comprising a large-hole section, a transition section, and a small-hole section connected in sequence, characterized by comprising the following steps: S1, Auxiliary tooling positioning The head of the auxiliary tooling is inserted into the end face of the large hole section of the reducing pipe along its axial direction until the head of the auxiliary tooling contacts and locks into the transition section, thus completing the tooling positioning. S2, Basic Length Measurement Using a linear measuring tool, the total length L of the variable diameter pipe and the insertion depth L3 of the auxiliary tooling are measured respectively. S3, Calculation of intermediate distance Subtracting the insertion depth L3 of the auxiliary tooling from the total length L of the reducing pipe yields the distance from the head of the auxiliary tooling to the end face of the small hole section of the reducing pipe, which is the intermediate distance L2. S4, Maximum Offset Calculation Based on the geometric relationship between the inner diameter of the large hole section, the angle of the transition section, and the outer diameter of the head of the auxiliary tooling, the offset LX of the locking position of the auxiliary tooling from the starting position of the transition section can be calculated. The maximum offset LX is then taken. max ; S5. Determine the length to be measured. The intermediate distance L2 in S3 and the maximum offset LX in S4 are compared. max The length L1 to be measured is obtained by adding the two values, which is the distance from the starting position of the transition section to the end face of the small hole section.

[0007] Furthermore, the inner diameter of the large hole section is B, where B = φB ± ΔB, and ΔB is the tolerance value of φB; the inner diameter of the small hole section is C, where C = φC ± ΔC, and ΔC is the tolerance value of φC, and φC < φB; the transition section is an inner diameter gradually changing section with a conical inner wall, and the angle of the transition section is X, where X = X° ± ΔX, and ΔX is the tolerance value of X°.

[0008] Furthermore, the auxiliary tooling includes a connecting rod and a probe that are coaxially fixedly connected. The probe has a cylindrical structure and an outer diameter of D, where D = φD ± ΔD, ΔD is the tolerance value of φD, and φC < φD < φB.

[0009] Furthermore, the LX max The calculation formula is: LX max = (B max -D min ) / 2*tan(X min ) Among them, B max The maximum inner diameter of the large-diameter section is B. max =φB+ΔB; D min The minimum outer diameter of the probe is D. min =φD-ΔD; X min The minimum angle of the transition segment, i.e., X min =X°-ΔX.

[0010] Furthermore, the outer diameter of the connecting rod of the auxiliary tooling is E, and E≤φD / 2, and the length of the connecting rod is N, and N≥L.

[0011] Furthermore, in S2, the linear measuring tool uses a tape measure or laser rangefinder with a minimum graduation value ≤1mm when measuring the total length L of the variable diameter pipe, and a steel ruler with an accuracy of 0.5mm when measuring the insertion depth L3 of the auxiliary tool.

[0012] Furthermore, the difference between φB and φD ranges from 0.1mm to 0.5mm, i.e., φB-φD∈[0.1,0.5].

[0013] Furthermore, the transition angle X ranges from 5° to 30°. When the transition angle X exceeds this range, LX is maintained by adjusting the difference between φD and φB. max The validity of the calculation.

[0014] Furthermore, the surface roughness Ra of the probe is ≤1.6μm, and the end face of the probe is flat and perpendicular to the axis of the connecting rod.

[0015] Furthermore, the probe of the auxiliary tooling is made of wear-resistant metal material, and the connecting rod of the auxiliary tooling is made of lightweight rigid material.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: Reliable accuracy: The relative reference is determined by auxiliary tooling positioning, avoiding the problem of reference ambiguity in traditional measurement. That is, it overcomes the problem of ambiguity in the starting position of the transition section in traditional methods and avoids the core error of the measurement starting point deviating from the true position. With the dual guarantee of "positioning reference + tolerance compensation" and combined with geometric compensation calculation to eliminate the offset error of the transition section, the measurement error is greatly reduced, the measurement result is highly accurate and can meet the industrial-grade accuracy requirements. Easy to operate: Only common measuring tools (steel ruler, tape measure) and auxiliary fixtures are needed. No high-precision professional equipment is required. One person can complete the measurement operation. The measurement process is simple and easy to understand. The training cost is low. It is suitable for on-site batch testing scenarios. Low cost: The auxiliary tooling has a simple structure, readily available materials, low manufacturing cost, and a long service life, making it easy to promote and apply on a large scale. High versatility: By adjusting the probe diameter, it can be adapted to reducer pipes with different large hole diameters; the transition section angle is applicable within the range of 5°~30°, which is suitable for the testing needs of most industrial reducer pipes. Attached Figure Description

[0017] Figure 1 This is a cross-sectional view of the variable diameter pipe of the present invention; Figure 2 This is a schematic diagram of the auxiliary tooling of the present invention; Figure 3 This is a schematic diagram of the auxiliary tooling of the present invention in the measurement state; Figure 4 for Figure 3 Enlarged structural diagram at point A in the middle; Figure 5 This is a schematic diagram of the measurement steps of the present invention.

[0018] Explanation of the labels in the diagram: 1. Reducing pipe; 101. Large orifice section; 102. Transition section; 103. Small orifice section; 2. Auxiliary tooling; 201. Connecting rod; 202. Probe; L, total length; L1, length to be measured; L2, intermediate distance; L3, insertion depth; LX, offset; B. Inner diameter of the large hole section; C. Inner diameter of the small hole section; D. Outer diameter of the probe; E. Outer diameter of the connecting rod; N. Length of the connecting rod; X. Angle of the transition section. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1-5 A method for measuring the length of a variable-diameter pipe, wherein the variable-diameter pipe 1 includes a large-hole section 101, a transition section 102, and a small-hole section 103 connected in sequence, characterized by comprising the following steps: S1, Auxiliary tooling positioning The head of the auxiliary tooling 2 is inserted into the end face of the large hole section 101 of the reducing pipe 1 along its axial direction until the head of the auxiliary tooling 2 contacts and locks into the transition section 102, thus completing the tooling positioning. By utilizing the gradual change in the inner diameter of the transition section 102, the head of the auxiliary tooling 2 cannot be extended further, thus establishing a relative measurement reference. S2, Basic Length Measurement Using a linear measuring tool, the total length L (the straight-line distance from the end face of the large hole section 101 to the end face of the small hole section 103) of the reducing pipe 1 and the insertion depth L3 (the distance from the head of the auxiliary tool 2 to the end face of the large hole section 101) of the auxiliary tool 2 were measured respectively. S3, Calculation of intermediate distance Subtracting the insertion depth L3 of the auxiliary tooling 2 from the total length L of the reducing pipe 1, the distance from the head of the auxiliary tooling 2 to the end face of the small hole section 103 of the reducing pipe 1 can be obtained, which is the intermediate distance L2. The distance L2 from the head stop position of the auxiliary tooling 2 to the end face of the small hole section 103 is derived by using the formula L2 = L-L3 (at this time, L2 needs to compensate for the offset to obtain the length to be measured L1). S4, Maximum Offset Calculation Based on the geometric relationship between the inner diameter of the large hole section 101, the angle of the transition section 102, and the outer diameter of the head of the auxiliary tooling 2, the offset LX of the locking position of the auxiliary tooling 2 from the starting position of the transition section 102 can be calculated. At this time, the maximum offset LX is taken. max ; The key is to consider the limit values ​​of the tolerances of each parameter to ensure that the compensation amount covers the worst case. S5. Determine the length to be measured. Compare the intermediate distance L2 in S3 with the maximum offset LX in S4. max The length L1 to be measured is obtained by adding the two lengths, which is the distance from the starting position of the transition section 102 to the end face of the small hole section 103. Using the formula L1 = L2 + LX max The measured length L1 from the starting position of transition segment 102 to the end face of small hole segment 103 is obtained (logic: the maximum offset LX is superimposed on the intermediate distance L2). max (This compensates for the deviation between the positioning reference and the actual starting position).

[0021] This solution addresses the pain point of the transition section 102 having no obvious step at its starting position and being unable to be directly positioned by using "auxiliary tooling 2 locking positioning". Then, through the combined logic of "basic measurement + geometric compensation", it eliminates the measurement errors caused by the gradual characteristics and machining tolerances of the transition section 102, and finally achieves accurate measurement.

[0022] Addressing the core pain point: Completely overcome the problem of ambiguous positioning of the starting position of the transition segment 102 in traditional methods, and avoid the core error of the measurement starting point deviating from the true position.

[0023] Controllable accuracy: Through the dual guarantee of "positioning benchmark + tolerance compensation", the measurement error is greatly reduced, the measurement result is highly accurate and can meet the industrial-grade accuracy requirements, without relying on high-precision testing equipment.

[0024] Easy to operate: Only conventional linear measurement tools and auxiliary fixtures are needed for measurement. The process is clear and easy to understand, and the operation is simple. It can be completed by a single person and is suitable for batch testing scenarios on site.

[0025] Rigorous logic: Every step from positioning to calculation is based on geometric relationships and tolerance analysis to ensure the reliability and consistency of measurement results and avoid misjudgment of product qualification.

[0026] Furthermore, the inner diameter of the large hole section 101 is B, B=φB±ΔB, where ΔB is the tolerance value of φB; the inner diameter of the small hole section 103 is C, C=φC±ΔC, where ΔC is the tolerance value of φC, and φC<φB; the transition section 102 is a section with a gradually changing inner diameter and a conical inner wall, and the angle of the transition section 102 is X, X=X°±ΔX, where ΔX is the tolerance value of X°.

[0027] Establish a unified parameter standard to provide a clear geometric basis for the design of subsequent auxiliary tooling 2 and the calculation of offset LX (all calculations must be based on this parameter system). Avoid measurement logic confusion caused by ambiguous definitions of the structural parameters of the reducing pipe 1, and ensure that the measurement benchmark is consistent for different users and different batches of reducing pipe 1.

[0028] Define the tolerance range for each critical dimension, which will be the maximum offset LX subsequently determined. max The calculation (taking the limit value of the parameter) provides the preconditions and ensures the integrity of the compensation calculation.

[0029] For further details, please refer to [link / reference]. Figure 2-4 The auxiliary tooling 2 includes a connecting rod 201 and a probe 202 that are coaxially fixedly connected. The probe 202 has a cylindrical structure and an outer diameter of D, where D = φD ± ΔD, ΔD is the tolerance value of φD, and φC < φD < φB.

[0030] The probe 202 can slide smoothly in the large hole section 101. When the probe 202 enters the transition section 102, because the inner diameter of the transition section 102 gradually changes from B to C (C < D), the probe 202 will contact and get stuck with the inner wall of the transition section 102 (and cannot continue to extend). At this time, the auxiliary tooling 2 is fixed in position, realizing "stepless positioning". The coaxial design of the connecting rod 201 and the probe 202 ensures that the probe 202 is consistent with the axis of the variable diameter pipe 1, avoiding positioning offset.

[0031] The precise switching between "sliding and locking" is achieved through size adaptation, eliminating the need for manual judgment of the starting position of the transition section 102 and reducing human error; the auxiliary tooling 2 consists only of the connecting rod 201 and the probe 202, which has low manufacturing cost, is easy to process, and is suitable for large-scale promotion and use.

[0032] In addition, by adjusting the outer diameter D of the probe 202, it can be adapted to reduce the diameter of pipes 1 with different inner diameter specifications, eliminating the need to design auxiliary tooling 2 separately for each type of pipe, thus expanding its applicability and reducing costs.

[0033] Furthermore, LX max The calculation formula is: LX max = (B max -D min ) / 2*tan(X min ) Among them, B max The maximum inner diameter of the large hole section 101 is B. max =φB+ΔB; D min The minimum outer diameter of probe 202 is D. min =φD-ΔD; X minThe minimum angle of transition segment 102, i.e., X min =X°-ΔX.

[0034] Specific calculation logic: It can be derived through geometric relationships: Establish a right triangle model: one right-angled side is the difference between the inner diameter of the large hole section 101 and the outer diameter of the probe 202, i.e. (BD) / 2, the other right-angled side is the offset LX, the hypotenuse of the triangle is the generatrix of the inner wall of the transition section 102, and the angle between the two right-angled sides is the angle X of the transition section 102. From the trigonometric function relations, we get: LX = (BD) / 2 * tan(X); Considering the tolerances of each parameter (maximum tolerance of B, minimum tolerance of D, minimum tolerance of X), calculate the maximum offset LX. max (Ensure that the compensated L1 is the maximum value. If the maximum value of L1 meets the technical tolerance, then the actual L1 must be qualified.) Therefore, LX can be obtained. max = (B max -D min ) / 2*tan(X min ); Among them, B max =φB+ΔB,D min =φD-ΔD,X min =X°-ΔX; The final length to be measured is L1 = L2 + LX max .

[0035] Based on the limit tolerances of each parameter, calculate the maximum offset LX in the worst case. max "To ensure that L1 after compensation is the upper limit (actual L1 ≤ calculated value, to avoid misjudgment of qualification).

[0036] The blurred offset LX caused by the gradual transition of transition segment 102 is converted into a precise mathematical value, completely eliminating the accuracy loss caused by "estimated offset"; the maximum offset LX is calculated by taking the parameter limit value. max If the calculated L1 meets the technical tolerance, then the actual L1 will definitely be within the tolerance range, avoiding the situation of "false non-conformity" or "false conformity". Based on trigonometric functions and tolerance analysis, the formula derivation is unambiguous, and the calculation results of different users are consistent, ensuring the repeatability of the measurement method.

[0037] Furthermore, the outer diameter of the connecting rod 201 of the auxiliary tooling 2 is E, and E≤φD / 2, to avoid the outer diameter of the connecting rod 201 being too large and rubbing or interfering with the inner wall of the reducing pipe 1, and to ensure that the auxiliary tooling 2 extends smoothly along the axis without affecting the accuracy of the probe's locking position; The length of the connecting rod 201 is N, and N≥L, which ensures that the auxiliary tooling 2 can be fully inserted into the reducing pipe 1, so that the tail of the auxiliary tooling 2 can be exposed on the end face of the large hole section 101, which is convenient for the measuring tool to read data and for hand operation.

[0038] Furthermore, in S2, when measuring the total length L of the variable diameter pipe 1, the linear measuring tool uses a tape measure or laser rangefinder with a minimum graduation value of ≤1mm. When measuring the insertion depth L3 of the auxiliary tooling 2, a steel ruler with an accuracy of 0.5mm is used. L3 is a key basic data, and the accuracy requirement is higher than L, to ensure the calculation accuracy of the intermediate distance L2.

[0039] There is no need to use high-precision testing equipment (such as coordinate measuring machines). Conventional measuring tools can meet the requirements, reducing testing costs. Measuring tapes and steel rulers are readily available tools on site, requiring no professional operation training, and are suitable for batch testing scenarios.

[0040] Furthermore, the difference between φB and φD ranges from 0.1mm to 0.5mm, i.e., φB-φD∈[0.1,0.5].

[0041] With this design, if the difference is too small (<0.1mm), the probe 202 will be obstructed from sliding in the large hole section 101 (easily stuck due to small impurities or processing errors); if the difference is too large (>0.5mm), the probe 202 will enter the transition section 102 too deep before getting stuck, increasing the offset LX and amplifying the calculation error, or it may directly pass through the transition section 102 and fail to form a stuck state.

[0042] The locking position is close to the starting position of the transition section 102, the offset LX is smaller, the error amplification effect in the calculation process is weakened, and the measurement accuracy of L1 is further improved; it can be achieved without special processing technology, reducing tooling manufacturing costs.

[0043] Furthermore, the value range of the angle X of the transition section 102 is 5°~30°. This range covers the design of the transition section 102 of most variable diameter pipes 1 in the fields of machinery manufacturing and petrochemicals (if the angle is too small (<5°), the transition section 102 is too long; if the angle is too large (>30°), the transition section 102 is too short). When the angle X of transition segment 102 exceeds this range, maintain LX by adjusting the difference between φD and φB (increase the difference appropriately if the angle is too small, and decrease the difference appropriately if the angle is too large). max The calculation validity (ensuring the probe's locking position is reasonable and the offset can be accurately calculated). It can avoid LX errors due to angles exceeding the range. max Calculate distortion to ensure the rigor and accuracy of the measurement method.

[0044] Furthermore, the surface roughness Ra of the probe 202 is ≤1.6μm. This design reduces the friction coefficient between the probe 202 and the inner wall of the variable diameter pipe 1, ensuring that the probe 202 slides smoothly in the large hole section 101 and avoiding jamming or positioning deviation caused by surface roughness. The end face of the probe 202 is flat and perpendicular to the axis of the connecting rod 201. This design ensures that the contact between the probe 202 and the inner wall of the transition section 102 is a surface contact (rather than a point contact or line contact), making the locking position more stable. Furthermore, the contact point is perpendicular to the axis, avoiding positioning deviation.

[0045] Furthermore, the probe 202 of the auxiliary tooling 2 is made of wear-resistant metal material, such as 45# steel or stainless steel. The probe 202 needs to repeatedly contact and rub with the transition section 102. Wear-resistant material can prevent dimensional wear after long-term use and ensure the accuracy and stability of φD. The connecting rod 201 of the auxiliary tooling 2 is made of lightweight rigid material, such as aluminum alloy or engineering plastic. The lightweight material makes it easy for the operator to hold, reach in and push the auxiliary tooling 2, while the rigid material can prevent the connecting rod 201 from bending and deforming, ensuring that the axis of the auxiliary tooling 2 is consistent with the axis of the variable diameter pipe 1, without affecting the positioning accuracy.

[0046] The core idea of ​​this invention is to determine the relative measurement reference by utilizing the "locking characteristics between the probe 202 and the transition section 102", and then calculate the maximum offset LX of the probe 202 from the true starting position through geometric relationships. max The measured values ​​are compensated to obtain the accurate L1.

[0047] The following provides specific parameter examples for each data point, used to calculate the length L1 to be measured: 1. Implementation parameters Transformer pipe 1 (a guide pipe of a certain specification): Inner diameter B of large hole section 101 = 35 ± 0.1 mm (φB = 35, ΔB = 0.1 mm), angle X of transition section 102 = 15° ± 2° (X° = 15°, ΔX = 2°), inner diameter C of small hole section 103 = 30 mm (φC = 30, no need for precise measurement), total length L of reducer pipe 1 (actual measured value) = 1000 mm; Auxiliary fixture 2: outer diameter of probe 202 D=34.7±0.1mm (φD=34.7, ΔD=0.1mm), outer diameter of connecting rod 201 E=10mm, length of connecting rod 201 N=1200mm (≥L=1000mm), probe 202 is made of 45# steel, surface roughness Ra=1.6μm; Measuring tools: a steel ruler with an accuracy of 0.5 mm and a measuring tape with a minimum division of 1 mm; 2. Implementation Steps Positioning of auxiliary tooling 2: Insert the probe end 202 of auxiliary tooling 2 into the large hole section 101 and push it along the axis until the probe 202 is stuck with the inner wall of the transition section 102, and stop pushing. Basic length measurement: Use a steel ruler to measure the insertion depth of auxiliary tool 2, L3 = 500.2 mm; use a tape measure to measure the total length of reducing pipe 1, L = 1000.0 mm; Calculate the distance L2 from the stop position of probe end 202 to the end face of the small hole section 103 of the reducing pipe 1: L2 = L - L3 = 1000.0 mm - 500.2 mm = 499.8 mm; Calculate the maximum offset LX max : Derivation parameter: B max =φB+ΔB=35mm+0.1mm=35.1mm; D min =φD-ΔD=34.7mm-0.1mm=34.6mm; X min =X°-ΔX=15°-2°=13°; Substitute into the formula: LX max = (B max -D min ) / 2*tan(X min )=(35.1mm-34.6mm) / 2*tan(13°)≈0.5mm / (2*0.2309)≈1.08mm; Calculate L1: L1 = L2 + LX max =499.8mm + 1.08mm = 500.88mm, that is, the measured length L1 of the reducing pipe 1 is 500.88mm.

[0048] 3. Qualification assessment; If the technical requirement for L1 of the reducing pipe 1 is 500±2mm, then the measured L1=500.88mm is within the tolerance range and is judged to be qualified; since LX max The actual offset is L1 ≤ 500.88mm, so there is no need to worry about the actual value exceeding the upper limit, ensuring reliable test results. Conversely, if the measurement result exceeds the tolerance range, the pipe needs to be reworked or judged as a non-conforming product.

[0049] 4. Precautions Before measurement, the integrity of auxiliary tooling 2 must be checked to ensure that the probe 202 is free from wear and deformation, the connecting rod 021 is not bent, and the connection is firm. During the measurement process, the reducing pipe 1 must be placed stably to avoid tilting or shaking of the reducing pipe 1, which may cause measurement errors. Measuring tools such as steel rulers and tape measures must be calibrated regularly to ensure measurement accuracy.

[0050] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method of measuring the length of a variable diameter pipe, the variable diameter pipe (1) comprising a large bore section (101), a transition section (102) and a small bore section (103) in communication in that order, characterized in that, It comprises the following steps: S1, auxiliary tool positioning The head of the auxiliary tool (2) is inserted into the large hole section (101) of the variable diameter pipe (1) along the axial direction until the head of the auxiliary tool (2) contacts and stops at the transition section (102), and the tool positioning is completed; S2, basic length measurement Linear measurement tools are used to measure the total length L of the variable diameter pipe (1) and the insertion depth L3 of the auxiliary tool (2) respectively; S3, intermediate distance calculation The total length L of the variable diameter pipe (1) is subtracted by the insertion depth L3 of the auxiliary tool (2), and the distance from the head stop position of the auxiliary tool (2) to the end face of the small hole section (103) of the variable diameter pipe (1) is obtained, that is, the intermediate distance L2; S4, maximum offset calculation Based on the geometric relationship among the inner diameter of the large hole section (101), the angle of the transition section (102), and the outer diameter of the head of the auxiliary tool (2), the offset amount LX of the locking position of the auxiliary tool (2) from the starting position of the transition section (102) can be obtained through calculation, and the maximum offset amount LX is taken at this time max ; S5, determine the length to be measured The intermediate distance L2 in the S3 is compared with the maximum offset LX in the S4 max The sum is the length L1 to be measured, i.e. the distance from the start of the transition section (102) to the end face of the bore section (103).

2. A method of measuring the length of a variable diameter pipe according to claim 1, wherein, The large hole section (101) has an inner diameter B, B=φB±ΔB, where ΔB is the tolerance value of φB, the small hole section (103) has an inner diameter C, C=φC±ΔC, where ΔC is the tolerance value of φC, and φC<φB, the transition section (102) is an inner diameter gradually changing section with a conical inner wall, the transition section (102) has an angle X, X=X°±ΔX, where ΔX is the tolerance value of X°.

3. A method of measuring the length of a variable diameter pipe according to claim 2, wherein, The auxiliary tool (2) comprises a connecting rod (201) and a measuring head (202) fixedly connected coaxially, the measuring head (202) is a cylindrical structure, the outer diameter of the measuring head (202) is D, D=φD±ΔD, where ΔD is the tolerance value of φD, and φC<φD<φB.

4. A method of measuring the length of a variable diameter pipe according to claim 3, wherein, The LX max The calculation formula is: LX max = (B max -D min ) / 2 * tan(X min ) where B max is the maximum inner diameter of the large bore section (101), i.e. B max = φB + ΔB; D min D = the minimum outer diameter of the probe (202) min = φD - ΔD; X min The minimum angle for the transition section (102), i.e. X min = X° - ΔX.

5. A method of measuring the length of a variable diameter pipe according to claim 3, wherein, The outer diameter of the connecting rod (201) of the auxiliary tool (2) is E, and E≤φD / 2, the length of the connecting rod (201) is N, and N≥L.

6. The method of variable pipe length measurement according to claim 1, wherein, In the S2, the linear measurement tool uses a tape measure with a minimum graduation value ≤1mm or a laser range finder when measuring the total length L of the variable diameter pipe (1), and a steel ruler with an accuracy of 0.5mm when measuring the insertion depth L3 of the auxiliary tool (2).

7. A method of measuring the length of a variable diameter pipe according to claim 4, wherein, The difference between φB and φD is in the range of 0.1mm~0.5mm, that is, φB-φD∈[0.1,0.5].

8. A method of measuring the length of a variable diameter pipe according to claim 6, wherein, The transition section (102) angle X is in the range of 5°-30°, when the transition section (102) angle X exceeds this range, by adjusting the difference between φD and φB, the calculation effectiveness of LX max is maintained.

9. The method of variable pipe length measurement according to claim 1, wherein, The surface roughness Ra of the measuring head (202) is ≤1.6μm, and the end face of the measuring head (202) is a plane perpendicular to the axis of the connecting rod (201).

10. The method of variable pipe length measurement according to claim 1, wherein, The measuring head (202) of the auxiliary tool (2) is made of wear-resistant metal material, and the connecting rod (201) of the auxiliary tool (2) is made of lightweight rigid material.

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