Propeller blade section thickness measuring method

Abstract

The invention discloses a propeller blade section thickness measuring method, and relates to the technical field of ships, and the method comprises the steps: carrying out the measurement on a blade surface of a propeller through a pitch gauge according to Sitaf and r, measuring a vertical distance Xf, calculating the coordinates of a point corresponding to the blade surface on a two-dimensional section through a point searching method according to the coordinates of a measuring point of the blade surface of a cylindrical coordinate system, and calculating the thickness of the blade surface. Through the distribution of the section, the point coordinates and the standard thickness t corresponding to the blade back on the two-dimensional section are calculated, then through a blade curved surface equation, two-dimensional data are converted into theoretical three-dimensional coordinates of blade back measuring points, the propeller is turned over by 180 degrees, the pitch gauge can make contact with the propeller blade back, the vertical distance is obtained through measurement, and the blade back measuring precision is improved. The measurement coordinates of the blade surface and the blade back can be measured according to the process, the actual thickness is calculated according to the measurement coordinates, the actual thickness can be compared with the standard thickness, the manufacturing tolerance is calculated, and whether the propeller manufacturing specification is met or not is judged. And the measurement precision and reliability are improved.

Description

Technical Field

[0001] The invention relates to the technical field of ships, and in particular to a method for measuring the thickness of a propeller blade section. Background Art

[0002] Marine propellers are the mainstream propulsion devices in modern ship propulsion. They absorb the shaft torque from the main engine and drive the propeller to rotate in the water, causing a pressure difference between the propeller blades and the back of the blades, forming a propulsion force to push the ship to sail in the water. At present, the domestic high-performance marine propeller design capabilities are becoming more and more perfect, but from the product perspective, there is still room for improvement in the processing and manufacturing capabilities of marine propellers.

[0003] For large-diameter marine propellers (propeller diameter greater than or equal to 6.0m), programmed cutting is mainly carried out by five-axis CNC machine tools. The advantage is high processing precision, and the disadvantage is high cost. It usually requires the propeller manufacturer to have sufficient funds for the project to be undertaken or a sufficient number of propellers to spread the cost.

[0004] For small-diameter marine propellers (propeller diameter less than 6.0m), the cost of mold opening is high because the funds for such projects are relatively tight and the number of propellers is small, usually 2 to 4 sets. Therefore, for such marine propellers, propeller processing manufacturers will use the method of selecting blade control points for precision control and manually polishing the blade surface for processing. The advantages of this method are fast processing speed and low cost, and the disadvantages are that the blade surface cannot fully meet the design requirements, the smoothness of the blade surface cannot meet sufficient continuity, and it has high requirements on the technical level of workers.

[0005] From the perspective of the hydrodynamic performance of marine propellers, the thickness of the propeller blade section will affect its propulsion efficiency in the water. If it is too thick, it may cause a large pressure resistance of the blade section, causing the propeller torque to increase and reduce the propulsion efficiency; if it is too thin, it may cause the fluid to flow separation, change the pressure distribution on the blade surface and the back of the blade, cause the propeller thrust to decrease, and reduce the propulsion efficiency. Therefore, the thickness of the manufactured propeller has an important impact on whether the actual propeller performance can reach the expected design performance. Therefore, the thickness needs to be tested during the processing and inspection of the propeller to determine whether it meets the national specifications and standards in the industry.

[0006] The measurement method proposed in this patent is proposed for the small diameter marine propeller as mentioned above. At present, domestic propeller manufacturers usually use the manual caliper method to measure the thickness during the propeller processing and inspection process.

[0007] The specific method is as follows: There are two surfaces on the propeller, namely the blade surface and the blade back. According to the drawings and data, locate the measuring point on the blade surface, and clamp one end of the caliper on the measuring point on the propeller blade surface. According to experience, clamp the other end of the caliper on the propeller blade back. After clamping, gently remove the caliper, and use a ruler to measure the distance between the two ends of the caliper, which is used as the propeller blade section thickness of the measuring point.

[0008] The existing propeller blade section thickness measurement described above has many disadvantages, which are summarized as follows: First: the measurement efficiency is low. For a propeller, the number of measuring points ≥ the number of blades · the number of blade sections on each blade (radial) · the number of measuring points on each blade section (chordwise). For example, for a 4-blade propeller, the blade sections are 0.4r, 0.5r, 0.6r, 0.7r, 0.8r, 0.9r, 0.95r (r refers to the relative blade height, which = the height of the blade section in the radial direction / blade radius). There are more than 3 measuring points on each blade section. The sampling method is adopted. For example, 2 blade sections are sampled for each blade, then the number of measuring points = 4·2·3=24. Each measuring point needs to go through the processes of caliper clamping, removal, caliper measurement, data recording and specification review calculation. It takes 120 minutes if it takes 5 minutes. If it fails to pass the inspection standard, it still needs to be re-measured.

[0009] Second: Large measurement errors. The existing technical solution uses manual calipers + ruler measurement, which causes large measurement errors for two reasons: First, the calipers on site are highly worn and updated slowly, such as large wear on the outside of the caliper and small wear on the inside, and the contact position between the caliper and the blade is between the inside and the outside, which results in errors; second, the measurement ruler is usually not suitable for vernier calipers, and the measurement is done with a ruler, which is not accurate enough, usually 0.5mm or above.

[0010] Third: poor reliability. Reliability refers to the fact that the thickness measured by this method cannot effectively guarantee repeatability, just like when one person measures and reads again or multiple people measure, it cannot effectively guarantee that the measurement result has high repeatability, that is, the reliability of the measurement result is poor. There are two main reasons for the low reliability: First, the caliper is heavy. When the caliper is gently moved out of the leaf surface by hand, the hand will shake due to the force, which is imperceptible and may cause changes in the measured value, resulting in poor reliability; second, a ruler is used for measurement and reading. Since the minimum unit of the ruler is 1mm, the minimum accuracy of manual reading is 0.5mm, and the caliper has the above-mentioned measurement error phenomenon, resulting in poor reliability. Summary of the invention

[0011] The present invention provides a method for measuring the thickness of a propeller blade section. The method controls the measuring radius and angle according to a high-precision instrument, has repeatability, and performs back calculation according to a mathematical equation, so the measuring point at the back of the blade is also guaranteed to be unique and has high reliability.

[0012] According to one aspect of the present disclosure, a method for measuring the thickness of a propeller blade section is provided, wherein the propeller blade section is a blade section generated by the intersection of a rotation trajectory of a pitch gauge with a propeller shaft as the rotation center and the propeller, and the method comprises: Set the rotation angle Sita_f and measurement radius r when measuring with the pitch gauge. The pitch gauge measures the vertical distance X_f at different rotation angles Sita_f under the fixed measurement radius r, and obtains the cylindrical coordinates of the blade surface measurement point (X_f, Sita_f, r). Calculate the x value in the coordinates (x, Yf) of the two-dimensional leaf section of the leaf surface measurement point (X_f, Sita_f, r) by the point-finding method; According to the known leaf section profile value distribution and coordinate x value, calculate the Yf in the coordinate (x, Yf) of the measuring point on the leaf surface of the two-dimensional leaf section and the Yb in the coordinate (x, Yb) of the measuring point on the back of the leaf on the two-dimensional section; the leaf section profile value distribution includes the Yf value and Yb value corresponding to different x values ​​under the radius r; subtract Yb from Yf to get the standard thickness t; According to the coordinate expression formula of x, Yf, Yb and the blade section arch surface, the coordinates in the rectangular coordinate system (x_3d, y_3d, z_3d) are obtained; Convert the coordinates (x_3d, y_3d, z_3d) into cylindrical coordinates to obtain the theoretical cylindrical coordinates of the blade back measuring point (X_b, Sita_b, r); According to Sita_b and r, the vertical distance x_test in the cylindrical coordinates (X_test, Sita_b, r) of the blade back measuring point is measured by the pitch gauge; The measured thickness T is calculated based on the measured coordinates of the leaf surface measuring point (X_f, Sita_f, r) and the measured coordinates of the leaf back measuring point (X_test, Sita_b, r).

[0013] In a possible implementation, the x value in the coordinates (x, Yf) of the two-dimensional leaf section of the leaf surface measurement point (X_f, Sita_f, r) is calculated by a point finding method, including: When the pitch gauge rotates a known angle dSita from the guide edge to the measuring point, the length of the arc is dSita / 360·6.28·r, which is equal to the arc length Lf between the guide edge and the measuring point on the back of the blade on the two-dimensional blade section, that is, Lf is a known quantity, and the coordinate origin of the two-dimensional blade section is at the guide edge tangent point; Design a discrete array of horizontal coordinates ; According to the cubic spline interpolation method, construct the interpolation function F(x); Substitute the horizontal coordinate discrete array as a variable into the F(x) discrete array to obtain the vertical coordinate discrete array ; The horizontal coordinate discrete array and the vertical coordinate discrete array can obtain n+1 points. The point coordinates are marked as ; in, ; ; When Lf(i) is approximately equal to the known quantity Lf, determine the value of x in the coordinates (x, Yf) .

[0014] In a possible implementation, the method further includes: Obtaining the design parameters of the propeller blade, the design parameters include: pitch gauge measurement radius r, propeller blade section chord length C, measurement point pitch P, rear skew, and longitudinal rake; According to the coordinate expression formula of x, Yf, Yb and the blade section arch surface, the coordinates in the rectangular coordinate system (x_3d, y_3d, z_3d) are obtained, including the calculation of s, f, t: (1) f=0.5·Yb+0.5·Yf (2) t = Yb-Yf (3) (4) (5) Among them, s is the dimensionless chord length, t is the standard thickness, f is the longitudinal distance from the midpoint of the thickness to the horizontal axis of the section, and C is the chord length of the blade section, which is a known quantity; The blade section arch surface coordinate expression formula includes: (6) (7) (8) (9) in, For vertical rake, is the side bevel angle, is the pitch angle, is the polar coordinate azimuth, the trim is positive when it is towards the stern and the skew is negative when it is towards the leading edge.

[0015] In a possible implementation, a manufacturing tolerance is obtained according to the standard thickness t and the measured thickness T, and whether the propeller blade thickness is qualified is determined according to the manufacturing tolerance.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The propeller blade section thickness measurement method of the disclosed embodiment has the following beneficial effects: First, the measurement efficiency is high. The patent uses a pitch gauge to completely replace the manual caliper measurement method. By rotating the pitch gauge, the blade surface and the back of the blade are dotted to obtain the three-dimensional coordinates. The efficiency of this measurement is significantly improved. It only needs to input the three-dimensional coordinates of the two surfaces into the measurement method based on the above method. The actual thickness can be automatically calculated and compared with the standard thickness, the manufacturing tolerance is calculated, and it is determined whether the specification is met.

[0017] Second, the reliability and calculation accuracy are high. This patent uses a professional marine pitch gauge, which uses a probe to measure data according to the measurement angle and displays it electronically with an accuracy of 0.001mm. Then, according to the standard parameters of the drawing, the measurement angle of the blade back is calculated through calculus and the blade surface equation, and the high-precision marine pitch gauge is used again to obtain the three-dimensional coordinates of the blade back measurement point and automatically calculate the thickness. The measurement method of this patent controls the measurement radius and angle based on high-precision instruments, has repeatability, and is reversed based on mathematical equations, so the measurement point at the blade back is also guaranteed to be unique, so the reliability is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram showing a marine pitch gauge for measuring a propeller blade according to an embodiment of the present disclosure is shown.

[0019] Figure 2 A schematic diagram showing the measurement process of a blade section measured by a pitch gauge according to an embodiment of the present disclosure is shown.

[0020] Figure 3 A schematic diagram of the arched surface of a propeller blade section according to an embodiment of the present disclosure is shown.

[0021] Figure 4 A schematic diagram showing the use of a caliper measurement method to measure blade thickness according to an embodiment of the present disclosure is shown.

[0022] Figure 5 A schematic diagram showing a propeller blade arch curved surface unfolded into a plane according to an embodiment of the present disclosure.

[0023] Figure 6 An expanded view of a propeller cut off by a cylinder with a radius of r according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0024] Various exemplary embodiments, features and aspects of the present disclosure will be described in detail below with reference to the accompanying drawings. The same reference numerals in the accompanying drawings represent elements with the same or similar functions. Although various aspects of the embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless otherwise specified.

[0025] The word “exemplary” is used exclusively herein to mean “serving as an example, example, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0026] In addition, in order to better illustrate the present disclosure, numerous specific details are given in the following specific embodiments. It should be understood by those skilled in the art that the present disclosure can also be implemented without certain specific details. In some examples, methods, means, components and circuits well known to those skilled in the art are not described in detail in order to highlight the subject matter of the present disclosure.

[0027] The technical solution disclosed in the present invention completely abandons the manual caliper + ruler measurement method, and adopts the marine pitch gauge + point-finding algorithm method (the former is a measuring tool, and the latter is a measuring algorithm, which is combined into a patented thickness measurement method) to accurately measure the thickness.

[0028] Here, let's first introduce the measuring instrument pitch gauge: The marine pitch gauge is a tool used to measure the pitch of ship propellers. Using the pitch gauge, each blade is based on the reference line, and the pitch of each measuring point on each radius is measured at 5° or 10° from the leading edge and the trailing edge. Figure 1 It can be seen that the pitch gauge is a measuring mechanism based on a cylindrical coordinate system with its origin at the propeller axis. By adjusting the rotation angle sita and measuring the radius r, the probe needle is moved vertically to the propeller blade surface and the vertical distance z is measured to obtain the three-dimensional cylindrical coordinates (r, z, sita) of the measuring point, which can be displayed on a digital instrument.

[0029] Take a single blade as an example: the propeller is divided into two surfaces, the blade surface and the blade back. During the measurement process, a marine pitch gauge is usually used to measure the propeller blade surface measurement point data.

[0030] as follows Figure 2 As shown in the figure, this figure is a top view of the propeller blade surface. The pitch gauge uses the propeller center as the rotation center, a certain propeller blade section (such as the relative radius 0.7r) as the rotation radius, and the intersection trajectory with the propeller in the top view is the blade section. The red line of the propeller is the rotation trajectory measured by the pitch gauge, the purple line is the blade reference line (blade centerline), the leftmost green line is the following edge boundary angle, and the rightmost green line is the leading edge boundary angle. The intersection of each green line and the red line between the two is the measurement point position formed every 5 degrees of rotation.

[0031] According to the blade section generated by the intersection of the pitch gauge rotation trajectory and the propeller, we extract the blade section as shown in the figure below. It can be seen that it is a curved surface with an arch surface (non-plane, such as Figure 3 As shown in Figure 1.1, the pitch gauge is a track formed on the propeller blade surface, and its measuring point is Figure 4Measurement point on the middle left leaf surface (red), Figure 4 The black horizontal line is a hypothetical ray that can penetrate the blade vertically, and its intersection point on the back of the blade is Figure 4 The green point on the right, but its actual thickness measurement point should be Figure 4 According to the measurement, the line connecting the red dot on the left and the red dot on the right has a lateral difference, which explains why the caliper measurement method has a large error phenomenon.

[0032] If Figure 3 The three-dimensional arch surface is unfolded into a plane as follows Figure 5 As shown, the right side is the guide edge, the left side is the trailing edge, the horizontal direction is the chord direction, and the vertical direction is the longitudinal direction. The upper side is the back of the blade, the lower side is the blade surface, and the two red straight lines are the axis center lines. The red point on the lower blade surface is the measuring point of the pitch gauge on the blade surface, and its distance to the center line is Yf, and the length of the curve to the rightmost point is Lf. The point on the back of the blade corresponding to its thickness is the upper blue point, and its distance to the center line is Yb, and the length of the curve to the rightmost point is Lb. The horizontal distance between the two points and the rightmost point is x.

[0033] Now let's introduce the point-finding method for thickness measurement: Taking a certain leaf section radius and a certain measuring point angle as an example, the three-dimensional coordinates X, Sita and r (leaf section radius) in the cylindrical coordinate system can be measured using the pitch track. The corresponding section parameters under the leaf section radius r are: initial longitudinal inclination X R , the side inclination angle, pitch angle, and chord length can be found from the drawings.

[0034] The process of the thickness measurement method of this patent is as follows: Use a pitch gauge to measure on the propeller blade surface according to Sita_f and r, measure the vertical distance X_f, and calculate the corresponding point coordinates (x, Yf) of the blade surface on the two-dimensional section according to the blade surface measurement point coordinates (X_f, Sita_f, r) in the cylindrical coordinate system by the point finding method. Through the distribution of the section (the blade section profile value distribution is known on the drawing, but the measurement point and the profile value distribution point cannot be one-to-one corresponding, and the point finding method must be used to solve; The blade profile value distribution includes: when the section radius r is fixed, the discrete value list of x, Yf and Yb), calculate the point coordinates (x, Yb) and standard thickness t corresponding to the blade back on the two-dimensional section, and then convert the two-dimensional data into the theoretical three-dimensional coordinates (X_b, Sita_b, r) of the blade back measurement point through the blade surface equation, turn the propeller 180 degrees so that the pitch gauge can contact the propeller blade back, and measure according to Sita_b and r to get X_b_test. According to this process, the measurement coordinates (X_f, Sita_f, r) and (X_b_test, Sita_b, r) at the blade surface and blade back can be measured, and the actual thickness (the length of the line segment connecting the two points in three-dimensional space) can be calculated based on the measured coordinates, and can be compared with the standard thickness, the manufacturing tolerance can be calculated, and it can be determined whether the propeller manufacturing and processing specifications are met.

[0035] According to one aspect of the present disclosure, a method for measuring the thickness of a propeller blade section is provided, wherein the propeller blade section is a blade section generated by the intersection of a rotation trajectory of a pitch gauge with a propeller shaft as the rotation center and the propeller, and the method comprises: Set the rotation angle Sita_f and measurement radius r when measuring with the pitch gauge. The pitch gauge measures the vertical distance X_f at different rotation angles Sita_f under the fixed measurement radius r, and obtains the cylindrical coordinates of the blade surface measurement point (X_f, Sita_f, r). Calculate the x value in the coordinates (x, Yf) of the two-dimensional leaf section of the leaf surface measurement point (X_f, Sita_f, r) by the point-finding method; According to the known leaf section profile value distribution and coordinate x value, calculate the Yf in the coordinate (x, Yf) of the measuring point on the leaf surface of the two-dimensional leaf section and the Yb in the coordinate (x, Yb) of the measuring point on the back of the leaf on the two-dimensional section; the leaf section profile value distribution includes the Yf value and Yb value corresponding to different x values ​​under the radius r; subtract Yb from Yf to get the standard thickness t; According to the coordinate expression formula of x, Yf, Yb and the blade section arch surface, the coordinates in the rectangular coordinate system (x_3d, y_3d, z_3d) are obtained; Convert the coordinates (x_3d, y_3d, z_3d) into cylindrical coordinates to obtain the theoretical cylindrical coordinates of the blade back measuring point (X_b, Sita_b, r); According to Sita_b and r, the vertical distance x_test in the cylindrical coordinates (X_test, Sita_b, r) of the blade back measuring point is measured by the pitch gauge; The measured thickness T is calculated based on the measured coordinates of the leaf surface measuring point (X_f, Sita_f, r) and the measured coordinates of the leaf back measuring point (X_test, Sita_b, r).

[0036] In a possible implementation, the x value in the coordinates (x, Yf) of the two-dimensional leaf section of the leaf surface measurement point (X_f, Sita_f, r) is calculated by a point finding method, including: When the pitch gauge rotates a known angle dSita from the guide edge to the measuring point, the length of the arc is dSita / 360·6.28·r, which is equal to the arc length Lf between the guide edge and the measuring point on the back of the blade on the two-dimensional blade section, that is, Lf is a known quantity, and the coordinate origin of the two-dimensional blade section is at the guide edge tangent point; Design a discrete array of horizontal coordinates ; According to the cubic spline interpolation method, construct the interpolation function F(x); Substitute the horizontal coordinate discrete array as a variable into the F(x) discrete array to obtain the vertical coordinate discrete array ; The horizontal coordinate discrete array and the vertical coordinate discrete array can obtain n+1 points. The point coordinates are marked as ; in, ; ; When Lf(i) is approximately equal to the known quantity Lf, determine the value of x in the coordinates (x, Yf) .

[0037] In a possible implementation, the method further includes: Obtaining the design parameters of the propeller blade, the design parameters include: pitch gauge measurement radius r, propeller blade section chord length C, measurement point pitch P, rear skew, and longitudinal rake; According to the coordinate expression formula of x, Yf, Yb and the blade section arch surface, the coordinates in the rectangular coordinate system (x_3d, y_3d, z_3d) are obtained, including the calculation of s, f, t: (1) f=0.5·Yb+0.5·Yf (2) t = Yb-Yf (3) (4) (5) Among them, s is the dimensionless chord length, t is the standard thickness, f is the longitudinal distance from the midpoint of the thickness to the horizontal axis of the section, and C is the chord length of the blade section, which is a known quantity; The blade section arch surface coordinate expression formula includes: (6) (7) (8) (9) in, For vertical rake, is the side bevel angle, is the pitch angle, is the polar coordinate azimuth, the trim is positive when it is towards the stern and the skew is negative when it is towards the leading edge.

[0038] In a possible implementation, a manufacturing tolerance is obtained according to the standard thickness t and the measured thickness T, and whether the propeller blade thickness is qualified is determined according to the manufacturing tolerance.

[0039] The embodiments of the present disclosure have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for measuring the thickness of a propeller blade section, characterized in that: The propeller blade section is a blade section generated by the intersection of the rotation trajectory of the pitch gauge with the propeller shaft as the rotation center and the propeller. The method comprises: Set the rotation angle Sita_f and measurement radius r when measuring with the pitch gauge. The pitch gauge measures the vertical distance X_f at different rotation angles Sita_f under the fixed measurement radius r, and obtains the cylindrical coordinates of the blade surface measurement point (X_f, Sita_f, r). Calculate the x value in the coordinates (x, Yf) of the two-dimensional leaf section of the leaf surface measurement point (X_f, Sita_f, r) by the point-finding method; According to the known leaf section profile value distribution and coordinate x value, calculate the Yf in the coordinate (x, Yf) of the measuring point on the leaf surface of the two-dimensional leaf section and the Yb in the coordinate (x, Yb) of the measuring point on the back of the leaf on the two-dimensional section; the leaf section profile value distribution includes the Yf value and Yb value corresponding to different x values ​​under the radius r; subtract Yb from Yf to get the standard thickness t; According to the coordinate expression formula of x, Yf, Yb and the blade section arch surface, the coordinates in the rectangular coordinate system (x_3d, y_3d, z_3d) are obtained; Convert the coordinates (x_3d, y_3d, z_3d) into cylindrical coordinates to obtain the theoretical cylindrical coordinates of the blade back measuring point (X_b, Sita_b, r); According to Sita_b and r, the vertical distance x_test in the cylindrical coordinates (X_test, Sita_b, r) of the blade back measuring point is measured by the pitch gauge; The measured thickness T is calculated based on the measured coordinates of the leaf surface measuring point (X_f, Sita_f, r) and the measured coordinates of the leaf back measuring point (X_test, Sita_b, r).

2. A method for measuring the thickness of a propeller blade section according to claim 1, characterized in that: The x value in the coordinates (x, Yf) of the two-dimensional leaf section of the leaf surface measurement point (X_f, Sita_f, r) is calculated by the point finding method, including: When the pitch gauge rotates a known angle dSita from the guide edge to the measuring point, the length of the arc is dSita / 360·6.28·r, which is equal to the arc length Lf between the guide edge and the measuring point on the back of the blade on the two-dimensional blade section, that is, Lf is a known quantity, and the coordinate origin of the two-dimensional blade section is at the guide edge tangent point; Design a discrete array of horizontal coordinates ; According to the cubic spline interpolation method, construct the interpolation function F(x); Substitute the horizontal coordinate discrete array as a variable into the F(x) discrete array to obtain the vertical coordinate discrete array ; The horizontal coordinate discrete array and the vertical coordinate discrete array can obtain n+1 points. The point coordinates are marked as ; in, ; ； When Lf(i) is approximately equal to the known quantity Lf, determine the value of x in the coordinates (x, Yf) .

3. A method for measuring the thickness of a propeller blade section according to claim 1, characterized in that: The method further comprises: Obtaining the design parameters of the propeller blade, the design parameters include: pitch gauge measurement radius r, propeller blade section chord length C, measurement point pitch P, rear skew, and longitudinal rake; According to the coordinate expression formula of x, Yf, Yb and the blade section arch surface, the coordinates in the rectangular coordinate system (x_3d, y_3d, z_3d) are obtained, including the calculation of s, f, t: （1） f=0.5·Yb+0.5·Yf (2) t = Yb-Yf (3) （4） （5） Among them, s is the dimensionless chord length, t is the standard thickness, f is the longitudinal distance from the midpoint of the thickness to the horizontal axis of the section, and C is the chord length of the blade section, which is a known quantity; The blade section arch surface coordinate expression formula includes: （6） （7） （8） （9） in, For vertical rake, is the side bevel angle, is the pitch angle, is the polar coordinate azimuth, the trim is positive when it is towards the stern and the skew is negative when it is towards the leading edge.

4. A method for measuring the thickness of a propeller blade section according to claim 1, characterized in that: The manufacturing tolerance is obtained based on the standard thickness t and the measured thickness T, and whether the propeller blade thickness is qualified is determined based on the manufacturing tolerance.

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