Measurement characteristic error evaluation method for complex parts of helicopter

Abstract

The invention belongs to the technical field of measurement and evaluation in the machining process, and relates to a measurement characteristic error evaluation method for complex parts of a helicopter. The method comprises the steps that a measurement characteristic error evaluation model is constructed, measurement characteristic error evaluation is a process of processing and calculating measurement data, measurement points of part characteristics serve as input of an evaluation process, and an evaluation result can serve as output to be compared with tolerance requirements through a certain evaluation algorithm; if the evaluation calculation result is within the tolerance range, the evaluation item is qualified; if the calculation result is out of the tolerance range, the evaluation item is unqualified; and according to the measurement characteristic error evaluation model, evaluating whether the pose and the size error of the part before machining meet the requirements or not.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of processing process measurement and evaluation, and relates to a measurement characteristic error evaluation method for complex parts of a helicopter. BACKGROUND

[0002] With the development of science and technology, the measurement of complex parts of a helicopter increasingly relies on digital means. Furthermore, how to judge the error of the measurement characteristic under the current state according to the MBD model to prepare for the compensation processing in the subsequent in-machine measurement process has become an important research content in digital detection. The previous implementation method is to transmit the measurement result to the upper computer through the machine tool communication, and then the upper computer processes and calculates, and then the calculation result is transmitted back to the machine tool. This process undergoes twice information transmission, and often needs manual operation, which seriously affects the detection efficiency. SUMMARY

[0003] The technical problem to be solved by the application is that the method uses the CATIA secondary development tool to design an algorithm to realize the error evaluation of the measurement characteristic of the complex part of the helicopter in the CATIA V5 environment. The process is directly realized on the machine tool, and the computing power of the machine tool controller is utilized, so that the process complexity is greatly reduced and the machining efficiency of the machine tool is improved.

[0004] The technical scheme of the application is A measurement characteristic error evaluation method for complex parts of a helicopter is provided, comprising: A measurement feature error evaluation model is constructed. The measurement feature error evaluation is a process of processing and calculating measurement data. The measurement points of the part features are taken as the input of the evaluation process. Through a certain evaluation algorithm, the evaluation result can be taken as the output and compared with the tolerance requirement. If the calculation result is within the tolerance range, the evaluation item is qualified; if the calculation result is outside the tolerance range, the evaluation item is unqualified; According to the measurement feature error evaluation model, whether the part pose and size error before processing meet the requirements is evaluated.

[0005] Further, the measurement feature error evaluation model includes an in-machine measurement evaluation process model. The measurement points are taken as the input of the in-machine measurement evaluation process model, and an evaluation algorithm is used to output the evaluation result, so as to facilitate the comparison of the evaluation result with the tolerance requirement.

[0006] Further, the measurement feature error evaluation model further includes an in-machine measurement evaluation information model. The in-machine measurement evaluation information model includes measurement point attribute information, evaluation items and test items. The measurement point attribute information includes a measurement point identifier, a position coordinate, a normal vector, a tool axis vector and a touch speed. The evaluation item includes an evaluation identifier, an evaluation type, an evaluation method, an evaluation point, and a numerical control system; The inspection item includes an inspection item number, an inspection item type, a theoretical value, an upper and lower deviation, and a reference.

[0007] Further, the evaluation algorithm includes: Constructing an auxiliary coordinate system; Based on the auxiliary coordinate system, a plane-to-plane distance evaluation, a cylindrical diameter evaluation, a distance evaluation between cylinders, a measurement angle evaluation, and a measurement pose evaluation are performed.

[0008] Further, the process of the plane-to-plane distance evaluation is to select measurement points on two planes respectively for fitting, and to calculate the distance according to the two fitted planes. The specific evaluation method is as follows: Step 1: Select 3 non-collinear measurement points on the same plane 、 、 , then the formulas of two vectors and are as follows: ; ; Step 2: Solve the plane normal vector: Let the normal vector of the plane be , and the normal vector of the plane is obtained by the vector product of and : ; Step 3: Solve the plane equation: Let the plane equation be as follows:

[0009] According to the plane normal vector solved in Step 2 , the parameters abc of the plane equation are as follows: ; Bring into the plane equation to obtain the parameters of the plane equation: ; Step 4: After obtaining the first plane equation, the distances of 3 points on another plane to the plane are solved, and the average value is obtained. Let the coordinates of a point on another plane be , then the distance of the point to the plane D is as follows: .

[0010] Furthermore, a method for evaluating the diameter of a cylinder involves fitting multiple points to a circular feature and then calculating its diameter. This method utilizes two-dimensional measurement points to fit a planar circle and calculate its diameter. The specific method is as follows: Step 1: First, calculate the cylinder axis based on the measuring points on the same floor: Given three measuring points of the cylinder... , and Then we obtain vectors in the same plane. and Then the axis of the cylinder That is, the axis vector of the cylinder is and The vector product; Step 2: Construct an auxiliary coordinate system with the Z-axis as its direction. ; Step 3: Set the data points Convert to coordinate system coordinates in , will the measuring point and By substituting the coordinates into the least squares method to fit the circle formula, the radius of the circle can be obtained.

[0011] Furthermore, the data point set Convert to coordinate system coordinates in , will the measuring point and By substituting the coordinates into the least squares method to fit the circle formula, the radius of the circle can be obtained, including: In two-dimensional space, the coordinates of the center of the circle ,radius The fundamental equation of a circle is: Or: ; in:

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[0014] Point set The distance formula with the center of the circle is brought in, and an optimized intermediate quantity m, n, p, q, r of the least square fitting is obtained by solving the extreme value. m and n are the scaling of the variance, in which m is the sum of squares of deviations of the x coordinate, reflecting the dispersion degree of the x direction, and n is the sum of squares of deviations of the y coordinate, reflecting the dispersion degree of the y direction. p is the scaling of the covariance, reflecting the linear correlation of x and y. q and r are the correction terms of the third moment, used to fit the nonlinear characteristics of the circle. q is related to the skewness of the x direction and the coupling effect of xy2, and r is related to the skewness of the y direction and the coupling effect of x2y. The results are as follows:

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[0022] According to the solved parameters The radius of the cylinder is calculated R .

[0023] Further, the evaluation of the distance between the cylinders is realized by calculating the distance between the axes of the cylinders fitted by the measuring points. The distance between the axes of the cylinders is equivalent to the distance from the axis to the axis . and are the centers of the circles fitted by different sections of the same cylinder, is the center of the circle fitted by the section of another cylinder; The specific method is as follows: First, solve the angle between ; . Then the distance between the two axes is .

[0024] Further, the evaluation of the measuring angle is to calculate the angle between two measuring features, including the following three types: (1) The angle between planes: the angle between the normal vectors of the two planes is complementary to the angle between the planes; (2) Evaluate the angle between two cylinders, which is equal to the angle between the two cylinder axes; (3) Evaluate the angle between a plane and a cylinder, which is equal to the complementary angle of the angle between the normal vector of the plane and the cylinder axis.

[0025] Further, the measurement pose evaluation is used for part pose alignment before processing, and whether the actual installation position of the part is the theoretically planned position is evaluated by operating the data of the measured points; the pose evaluation includes judging whether the part has axial deviation or rotation around the coordinate axis relative to the workpiece coordinate system.

[0026] The beneficial effects of the present application are: The method establishes an error evaluation system based on measurement characteristics, and the data of online detection are operated and processed by a computer to complete the evaluation of the measurement characteristics (size, tolerance, etc.) of the complex part of the helicopter. In the CATIA V5 environment, the CAA (Component Application Architecture) tool provided by CATIA is used for secondary development of functions, and its feasibility is verified in actual projects. The method proposes an error evaluation process and algorithm for complex part measurement, continues to plan the evaluation scheme of the key process of the procedure based on the measurement point planning and serves as the output of the numerical control program, and the numerical control program can be executed by driving the machine tool to evaluate whether the part pose and dimensional error before processing meet the requirements. In this process, the degree of human participation is reduced, the efficiency of the numerical control machine tool is improved, and the process error is controlled, thereby improving the machining precision. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 A schematic diagram of the in-machine measurement evaluation process model.

[0028] Figure 2 A schematic diagram of the in-machine measurement evaluation information model.

[0029] Figure 3 A flowchart for creating evaluation information.

[0030] Figure 4 A principle diagram for cylinder diameter evaluation.

[0031] Figure 5 A diagram for cylinder axis to cylinder axis distance evaluation.

[0032] Figure 6 A principle diagram for B angle evaluation. DETAILED DESCRIPTION

[0033] The present application will be further described in detail below in combination with the accompanying drawings.

[0034] CAA provides a large number of interfaces for MBD model information acquisition and for operating various hierarchical elements, including document hierarchy (such as CATIDocument), product hierarchy (such as CATIProduct), topology hierarchy (such as CATCell), geometry hierarchy (such as CATPoint), etc. In addition, a large number of interfaces (such as CATISpecObject) are provided for operating node information of the structure tree. The method solutions in this section are all implemented by obtaining these interfaces or defining new interfaces.

[0035] Step 1: Constructing the measurement feature error evaluation model The measurement feature error evaluation for complex helicopter parts is a process of processing and calculating measurement data. The measurement points of the part features are taken as the input of the evaluation process, and through a certain evaluation algorithm, the evaluation results can be taken as the output and compared with the tolerance requirements. If the calculation result is within the tolerance range, the evaluation item is qualified; if the calculation result is outside the tolerance range, the evaluation item is unqualified. The evaluation process model is as shown in Figure 1 .

[0036] Further, an object-oriented method is used to construct the in-machine measurement evaluation information model, as shown in Figure 2 . The inspection item is abstracted as a class, and its six types of attributes are explained as follows: (1) Evaluation type: For the measurement process, according to the calculation ability of the numerical control system, the evaluation plan is divided into two types, namely, the size and part pose evaluation that can be read and calculated in the numerical control system, and the complex point output evaluation that cannot be directly calculated by the numerical control system and needs to output the measurement report to the computer for fitting. The size and part pose evaluation can be used for subsequent error compensation planning; the complex point output evaluation is for shape and position tolerance requirements such as flatness, roundness, straightness, etc. The machine will output a measurement report after executing the program. For different evaluation types, the evaluation item class method is divided into size and pose evaluation algorithm and complex point output method.

[0037] (2) Evaluation method: The evaluation method is for size and part pose evaluation type. It includes distance, angle, diameter or radius, coordinate axis evaluation and rotary axis evaluation, etc.

[0038] (3) Evaluation point: This attribute is to specify the measurement point sequence number in the evaluation program. When writing the evaluation program, the corresponding measurement point variable is generated according to the measurement point sequence number. When the machine executes the program, it will execute the evaluation process as shown in Figure 1 to realize the evaluation of machining precision. Therefore, as shown in Figure 2 , to support the calculation of the evaluation item, the evaluation item class needs to be associated with the measurement point class.

[0039] (4) Numerical control system: Different numerical control systems will be different when calling parameters, such as Siemens system can store measurement points or variables involved in operation through custom array, while Frank system must use the parameters defined in the system (# parameters) to store the measurement point or operation variable information according to the variable type represented by the # value.

[0040] (5) Evaluation identifier: Evaluation identifier is used for subsequent compensation planning evaluation information, and the evaluation result is saved in the evaluation identifier. As described above, the state of machine tool evaluation error is to compare the evaluation calculation result with the tolerance, so the inspection item class needs to be associated in the evaluation information model, and the theoretical value and upper and lower deviation attributes in this class can be used for error evaluation.

[0041] The process of creating the above evaluation information is shown in Figure 3 , which saves the numerical control system and inspection item as attributes by selecting them. Because simple feature evaluation is mostly oriented to size tolerance and part pose evaluation, the measurement point identifier involved in evaluation can be saved directly; while complex point output type is to use point output for subsequent geometric and position tolerance evaluation, so in addition to saving the measurement point identifier, the measurement point involved in the tolerance reference also needs to be saved.

[0042] Step 2: Error evaluation algorithm application According to the actual situation of part measurement, process measurement is mainly used to control the size error of the part and adjust the part pose, so this method mainly studies the size tolerance and part pose evaluation. By executing the evaluation algorithm, on the one hand, it can judge the quality state of the processed part, and the unqualified part can be processed for subsequent compensation; on the other hand, it can also judge whether the part installation position is accurate according to the calculation result, and correct the coordinate system according to the deviation of the part pose.

[0043] (1) Construct auxiliary coordinate system In the feature evaluation algorithm, an auxiliary coordinate system with a known vector as the Z-axis direction is often needed for space size calculation. Because the above known conditions can construct countless coordinate systems, this paper only introduces the construction method of one coordinate system: Step 1: Construct an arbitrary vector perpendicular to the known vector as the X-axis direction in space. There are countless vectors perpendicular to a vector in space, so only one of them is selected. First define the vector , then the X-axis vector is solved as formula (1.1): (1.1) If the value of vector Dir1 is not​ Then For X axis, otherwise the vector Recalculate.

[0044] Step2: Find the Y axis direction according to the known X axis and Z axis direction According to the geometric meaning of the vector product, the result of the vector product can obtain the vector perpendicular to the plane composed of two vectors, so the Y axis vector The solving method is as formula (1.2): (1.2) Step3: Construct auxiliary coordinate system according to coordinate origin Because coordinate transformation is only related to the direction of auxiliary coordinate system and the evaluation of space size involves the relative position relationship of measuring points or geometric shapes, the origin is selected as , and the coordinate axis vector obtained by combining Step1 and Step2 can obtain the auxiliary coordinate system .

[0045] (2) Plane to plane distance evaluation The process of plane to plane distance evaluation is to select measuring points on two planes respectively for fitting, and calculate the distance according to the two fitted planes, and the specific evaluation method is as follows: Step1: Select 3 non-collinear measuring points on the same plane , , , then the formula of two vectors and is as follows: (1.3) (1.4) Step2: Solve the plane normal vector. Let the normal vector of the plane be Because the vectors and are two non-parallel vectors in the plane, the normal vector of the plane can be obtained by the vector product of and : (1.5) Step3: Solve the plane equation.

[0046] Let the plane equation be as follows: (1.6) According to the plane normal vector solved in Step2, the parameters of the equation are as follows: (1.7) Substitute into the equation to obtain the parameter : (1.8) Step 4: After obtaining the first plane equation, the distance from the other plane to the three points is calculated and the average value is obtained. Let the coordinates of a point on the other plane be , then the distance from the point to the plane is as follows: (1.9) (3) Cylinder diameter evaluation The method of cylinder diameter evaluation is to fit multiple points into a circle feature and then calculate its diameter. Since the cylinder points are layered planning, this paper proposes to convert three-dimensional points into points in the same plane, and use two-dimensional points to fit the plane circle and calculate its diameter, as shown in Figure 4 .

[0047] The diameter evaluation method is as follows: Step 1: First, calculate the cylinder axis according to the points on the same layer. Given three cylinder points , and , then the vectors in the same plane are and , then the axis of the cylinder is , that is, the axis vector of the cylinder is the vector product of and .

[0048] Step 2: Construct an auxiliary coordinate system with the axis direction as the Z axis .

[0049] Step 3: Convert the data point set into coordinates in the coordinate system , and bring the and coordinates of the points into the least square fitting circle formula to obtain the radius of the circle.

[0050] In two-dimensional space, the center coordinates of the circle are , and the radius is The basic equation of the circle is: (1.10) or: (1.11) Where: ​(1.12) (1.13) (1.14) Put the point set into the distance formula (1.8) of the center of the circle, and by solving the extreme value, the following results can be obtained (1.15) (1.16) (1.17) (1.18) (1.19) (1.20) (1.21) (1.22) Put the solved parameters into formula (1.14) to solve the radius of the cylinder.

[0051] (4) Distance evaluation between cylinders The evaluation of the distance between the cylinders is realized by calculating the distance between the axes of the cylinders fitted by the measuring points, and the evaluation principle is shown in , Figure 5 , , and are the centers of the circular sections fitted by the cylinders. The distance between the axes of the cylinders is equivalent to the distance from to the axis . First, solve the angle between and : (1.23) Then the distance between the two axes is : (1.24) (5) Angle evaluation The angle evaluation is to calculate the angle between two measuring features, mainly including the following three types: (1) The angle between planes: the angle between the normal vectors of the two planes is complementary. (2) The angle between cylinders: the angle is equal to the angle between the axes of the two cylinders. (3) The angle between a plane and a cylinder: the angle is equal to the complementary angle of the angle between the normal vector of the plane and the axis of the cylinder. Therefore, the angle can be evaluated by calculating the angle between the corresponding vectors of different features.

[0052] (6) Measurement of pose evaluation This evaluation item is used for part pose alignment before machining. By calculating the data from measured points, it evaluates whether the actual installation position of the part matches the theoretically planned position. Pose evaluation includes determining whether there is axial offset or rotation about the coordinate axis of the part relative to the workpiece coordinate system.

[0053] Figure 6 The diagram illustrates the principle for evaluating the rotation axis angle B. For example... Figure 6 When planning on the left, select theoretical measurement points with the same Z value. and measuring points The actual measurement results are as follows Figure 6 As shown on the right, if the measured point and exist The coordinates in are respectively and The deviation angle of the machine tool's rotating axis As shown in equation (1.25): (1.25) if This indicates that the part's orientation is correct. If so, it means that the rotation axis of the part is not aligned.

[0054] Compared to evaluating the offset of a rotation axis, evaluating the coordinate position of a part can be achieved directly by comparing the measured coordinates with the theoretical coordinates. Since the evaluation of the part's coordinate pose is performed before machining, theoretical measurement points of machined features or datum features are generally selected as the evaluation objects.

Claims

1. A method for evaluating errors of measurement characteristics for complex parts of a helicopter, characterized in that, The application relates to a measurement feature error evaluation model, a measurement feature error evaluation model is a process of processing and calculating measurement data, measurement points of a part feature are taken as input of the evaluation process, an evaluation result is taken as output through a certain evaluation algorithm, if the evaluation result is within a tolerance range, the evaluation item is qualified; if the evaluation result is out of the tolerance range, the evaluation item is unqualified; According to the measurement feature error evaluation model, whether the part pose and size error before processing meet the requirements are evaluated. The measurement feature error evaluation model comprises an in-machine measurement evaluation process model; 2. The method of claim 1, wherein, Measurement points are taken as input of the in-machine measurement evaluation process model, an evaluation algorithm is adopted to output an evaluation result, so that the evaluation result can be compared with a tolerance requirement. The measurement feature error evaluation model further comprises an in-machine measurement evaluation information model; 3. The method of claim 2, wherein, The in-machine measurement evaluation information model comprises measurement point attribute information, an evaluation item and a test item; The measurement point attribute information comprises a measurement point identifier, position coordinates, a normal vector, a tool axis vector and a touch speed; The evaluation item comprises an evaluation identifier, an evaluation type, an evaluation mode, an evaluation point and a numerical control system; The test item comprises a test item number, a test item type, a theoretical value, an upper and lower deviation and a reference. The evaluation algorithm comprises:

4. The method of claim 2, wherein, An auxiliary coordinate system is constructed; Based on the auxiliary coordinate system, plane-to-plane distance evaluation, cylindrical diameter evaluation, distance evaluation between cylinders, measurement angle evaluation and measurement pose evaluation are carried out. The plane-to-plane distance evaluation process is to select measurement points on two planes for fitting respectively, and to calculate the distance according to the two fitted planes, and the specific evaluation method is as follows:

5. The method of claim 4, wherein, Step 3: solving the plane equation: Step 1: Select 3 non-collinear points on the same plane , , , then get two vectors and The formula is as follows: ； ； Step 2: Solve the plane normal vector: Let the normal vector of the plane be , the normal vector of the plane is obtained by the vector product of and : ； The cylindrical diameter evaluation method is to fit multiple points into a circle feature and then calculate the diameter, two-dimensional measurement points are used to fit a plane circle and calculate the diameter, and the specific method is as follows: Let the plane equation be as follows: The plane normal vector according to Step 2 The parameters abc of the plane equation are as follows: ； Substitute into the plane equation to obtain the parameters of the plane equation Substitute into the plane equation to obtain the parameters of the plane equation is: ； Step4: After getting the first plane equation, find the distance from the other 3 points on the other plane to the first plane, and find the average value; set the coordinates of a point on the other plane as Then the distance from the point to the plane is D As follows: 。 6. The method of claim 4, wherein, Wherein: Step 1: First, calculate the cylindrical axis according to the measuring points of the same layer: given three measuring points of a cylinder , and , then get the vectors and in the same plane, then the axis of the cylinder , that is, the axis vector of the cylinder is the vector product of the vectors and ; Step 2: Construct an auxiliary coordinate system with the axis direction as the Z axis through the axis Z ; Step 3: Set the data points Convert to coordinate system coordinates in , will the measuring point and By substituting the coordinates into the least squares method to fit the circle formula, the radius of the circle can be obtained.

7. The method of claim 6, wherein, Transforming the set of data points into coordinates in a coordinate system and and and plugging the coordinates of the data points into the least squares circle fitting formula, the radius of the circle is obtained, comprising: In two-dimensional space, the center coordinates , radius The basic equation of a circle is: or is: ; The result is as follows: The point set The distance formula is brought into the center of the circle, and an optimized intermediate quantity m, n, p, q, r of the least square fitting is obtained by solving the extreme value; m, n are the scaling of the variance, in which m is the sum of squares of deviations of x coordinates, reflecting the dispersion degree of x direction, and n is the sum of squares of deviations of y coordinates, reflecting the dispersion degree of y direction; p is the scaling of the covariance, reflecting the linear correlation of x and y; q, r are the correction terms of the third moment, used for fitting the nonlinear characteristics of the circle, q is associated with the skewness of x direction and the coupling effect of xy2, and r is associated with the skewness of y direction and the coupling effect of x2y. The specific method is as follows: According to the solved parameters Computing the cylinder radius R .

8. The method of claim 4, wherein, The evaluation of the distance between the cylinders is achieved by calculating the distance between the axes of the cylinders fitted to the measuring points, equating the distance of the cylinder axes to the distance to the axis of the other cylinder; and the center of the circle fitted to the same cylinder section, the center of the circle fitted to the section of the other cylinder; The measurement angle evaluation is to calculate the angle between two measurement features, including the following three types: First, solve With The angle ; then the two axis distance .

9. The method of claim 4, wherein, (1) evaluating the angle between planes: the included angle between the normal vectors of the two planes is complementary; (2) evaluating the angle between cylinders: the angle is equal to the angle between the two cylinder axes; (3) evaluating the angle between a plane and a cylinder: the angle is equal to the complementary angle of the angle between the normal vector of the plane and the cylinder axis. The measurement pose evaluation is used for part pose alignment before processing, the actual installation position of a part is evaluated through operation on the data of the measured points whether the actual installation position is the theoretical planned position; the pose evaluation comprises judging whether the part exists axial deviation or rotation around the coordinate axis relative to the workpiece coordinate system.

10. The method of claim 4, wherein, ​

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