Complex curved surface part feeding track generation method based on virtual tool contact

Abstract

The invention discloses a method for generating a feeding track of a complex curved surface part based on a virtual tool contact. According to the method, the local geometric features of the virtual cutter contact are extracted, and the geometric features of the two adjacent cutter contacts are comprehensively considered to complete the solution of the actual cutter contact; on the basis of the maximum linear approximation error in the set step length, whether the generated feeding track meets the machining precision requirement or not is judged by constructing a linear approximation error band; and after the cutter contacts which do not meet the precision requirement are biased for a certain distance in the cutter feeding reverse direction, self-adaptive correction of the adjacent cutter contacts is achieved, and it is ensured that the cutter path is located between error bands so as to meet the approximation error requirement. According to the method, the influence of the local single geometric feature on the increase of the approximation error can be effectively reduced, the quantitative control of the approximation error in the step length is realized, the machining precision of the feeding path is improved, and reliable technical support is provided for the high-precision machining of the complex curved surface part.

Description

Technical Field

[0001] The invention belongs to the technical field of high-precision and high-efficiency milling processing of complex curved surface parts and a tool path generation method, in particular to a tool path generation method for complex curved surface parts based on virtual tool contacts. Background Art

[0002] The key to the machining accuracy and efficiency of complex surfaces lies in the quality of machining path planning, and the calculation of tool step length, as the basis of machining path planning, plays a vital role in the machining of complex surface parts. The tool step length refers to the distance between two adjacent tool contacts on the same tool trajectory. For complex surfaces, no matter what machining method is used, the tool interpolation movement is used to approximate the machined surface, which will inevitably lead to machining errors. To this end, while generating the tool trajectory, the tool step length must be strictly controlled to ensure that the interpolation between different tool positions is sufficiently accurate. However, the existing step length calculation method only uses the local geometric features at the position of a single tool contact point on the tool trajectory as the calculation basis for the tool step length, generates the local trajectory approximation curve, and ignores the geometric features of adjacent tool contacts. Therefore, the linearized approximation error within the step length is often greater than the set value, resulting in the difficulty in meeting the machining accuracy requirements of complex surface parts. Therefore, it is urgent to propose a new tool step length calculation method to achieve quantitative control of the error within the step length, thereby breaking through the bottleneck of high-precision machining technology for complex surface parts.

[0003] The fixed step length method is the simplest method, in which the tool maintains a fixed step length throughout the entire machining process. The advantages are simple calculation and easy implementation. However, this method may lead to an unbalanced cutting load during the machining process, resulting in uneven tool wear and poor machining surface quality. The maximum cutting force method determines the step length of the tool based on the cutting force during the machining process. This can keep the cutting force balanced during the machining process, thereby increasing the life of the tool. However, this method requires real-time monitoring of the cutting force and needs to be adjusted under different machining conditions, making it more complicated to implement. The adaptive method dynamically adjusts the step length according to the actual cutting conditions of the tool during the machining process to maintain a balanced cutting load, and reduces the step length when necessary to improve the surface quality. The adaptive method can adapt to different machining conditions, but requires more complex algorithms and control system support.

[0004] In general, no method is absolutely superior, and each method has its applicable scenarios and limitations. The selection of an appropriate method for calculating the step length depends on the shape, material, machining accuracy requirements of the machined parts, and the available control system and algorithm support. Usually, in practical applications, it is necessary to conduct experiments and adjustments according to specific circumstances, and it is necessary to propose a method for generating tool paths for complex surface parts by calculating the step length. Summary of the invention

[0005] In view of the defects of the prior art, the present invention proposes a method for generating tool paths for complex curved surface parts based on virtual tool contacts. Based on the maximum linearized approximation error within the set step length, the present invention solves and obtains the local geometric features near adjacent tool contacts, and comprehensively considers the geometric features of two adjacent tool contacts to complete the solution of the actual tool contacts; by constructing a linear approximation error band, adaptive correction of adjacent tool contacts is achieved, ensuring that the tool path is located between the error bands to meet the approximation error requirements, effectively improving the machining accuracy of complex curved surfaces, and providing reliable technical support for high-precision machining of complex curved surfaces.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] 1. A method for generating tool path for complex surface parts based on virtual tool contact points

[0008] 1) A curve in a complex surface is selected as the tool path curve, and then the parameterized curve is obtained after the tool path curve is parameterized. The initial point and the end point of the tool path curve are used as the starting point and the end point of the tool path respectively, and the starting point of the tool path is used as the initial tool contact point. The error band of the parameterized curve is constructed based on the maximum approximation error;

[0009] 2) Calculate the virtual knife contact point of the current knife contact point;

[0010] 3) Determine the actual knife contact point of the current knife contact point according to the virtual knife contact point;

[0011] 4) Using the error band of the parameterized curve, the actual knife contact point of the current knife contact point is adaptively corrected so that the corrected actual knife contact point meets the accuracy requirement, and the optimal actual knife contact point is obtained as the next knife contact point;

[0012] 5) Repeat 2)-4) to generate the optimal actual tool contact point corresponding to each tool contact point in turn, until the distance between the final tool contact point and the end point of the tool path is less than the preset accuracy, obtain all the tool contact points and generate the tool path.

[0013] In the above 1), the maximum linear approximation error ε is offset in the z direction of the parameterized curve. max After measuring the distance, the error band of the parameterized curve is formed.

[0014] The 2) is specifically:

[0015] 2.1) Calculate the tool step length L along the tangent direction of the current tool contact point s (t i ), the calculation formula is as follows:

[0016]

[0017] Among them, ε r (ti ) is the linear approximation error within the step length of the current tool contact point, ρ(t i ) is the curvature radius of the current knife contact point;

[0018] 2.2) When the current tool contact point moves along the tangent direction for a tool step length L s (t i ) is recorded as the approach point

[0019] 2.3) Calculate the approach point The Euclidean distance to all points on the parameterized curve is the distance between the approximation point and the parameterized curve. The point with the smallest Euclidean distance between them is used as the virtual knife contact point

[0020] The specific aspects of 3) are:

[0021] If the current knife contact CC i The normal radius of curvature ρ(t i ) is greater than the normal curvature radius ρ of the virtual knife contact point V (t i ), the virtual knife contact point is used as the actual knife contact point. If the current knife contact point CC i The normal radius of curvature ρ(t i ) is less than or equal to the normal curvature radius ρ of the virtual knife contact point V (t i ), the actual normal curvature is obtained by spherical interpolation, and then the actual tool step length is calculated using the actual normal curvature. When the current tool contact point moves along the tangent direction for an actual tool step length L s (t i ) is used as the approach point of the actual tool contact point Calculate the approach point of the actual knife contact The Euclidean distance to all points on the parameterized curve is the approximate point on the parameterized curve to the actual knife contact point. The point with the smallest Euclidean distance between them is taken as the actual knife contact point

[0022] In the above 3), the calculation formula for obtaining the actual normal curvature by using the spherical interpolation method is as follows:

[0023] ρ R (t i )=β·ρ(t i )+γ·ρ V (t i )

[0024]

[0025] Where β and γ are the first and second weight coefficients, respectively, || || is the Euclidean norm, and P(t i ) is the spatial coordinate of the current tool contact point, P * (t i ) is the virtual knife contact point corresponding to the approach point The spatial coordinates, P V* (t i+1 ) is the approach point of the actual knife contact The spatial coordinates of .

[0026] In 3), the formula for calculating the actual tool step length using the actual normal curvature is as follows:

[0027]

[0028] in, is the actual tool step length, ε r (t i ) is the linear approximation error within the step length of the current tool contact point, ρ(t i ) is the curvature radius of the current tool contact point.

[0029] The specific aspects of 4) are:

[0030] Determine whether there is an intersection between the tool trajectory and the error band between the current tool contact point and the actual tool contact point. If there is no intersection, the actual tool contact point meets the approximation error requirement and the actual tool contact point is used as the next tool contact point. If there is an intersection, extract all points on the parameterized curve between the current tool contact point and the actual tool contact point, where the point interval is t, offset the actual tool contact point in the direction of the current tool contact point by an interval of parameter t, obtain the offset point and use it as the new actual tool contact point, and re-determine whether there is an intersection between the tool trajectory and the error band between the current tool contact point and the new actual tool contact point, until an actual tool contact point that meets the approximation error requirement is found and used as the next tool contact point.

[0031] 2. A computer device

[0032] The computer device includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the method for generating a tool path for a complex curved surface part based on virtual tool contacts are implemented.

[0033] 3. A computer-readable storage medium

[0034] The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the method for generating a tool path for a complex curved surface part based on virtual tool contacts are implemented.

[0035] IV. A COMPUTER PROGRAM PRODUCT

[0036] The computer program product includes a computer program / instruction, which, when executed by a processor, implements the steps of the method for generating a tool path for a complex curved surface part based on virtual tool contacts.

[0037] The beneficial effects of the present invention are:

[0038] The method of the present invention realizes the solution of adjacent tool contacts by extracting the geometric features of virtual tool contacts, and comprehensively considering the geometric features of two adjacent tool contacts can effectively reduce the approximation error value and improve the accuracy of the generated tool path; based on the maximum linearized approximation error within the set step length, a linear approximation error band is constructed to judge whether the generated tool path meets the processing accuracy requirements, and a new tool contact that meets the accuracy requirements is generated by updating the offset tool contact position, and adaptive correction of adjacent tool contacts is realized to ensure that the tool path is located between the error bands to meet the approximation error requirements. This method can effectively reduce the influence of local single geometric features on increasing the approximation error, improve the probability that the tool path meets the accuracy requirements, and provide reliable technical support for high-precision processing of complex curved surface parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a flow chart of the method of the present invention;

[0040] Figure 2 Schematic diagram of approximation error within step length;

[0041] Figure 3 is ρ(t i )≤ρ V (t i ) when the tool step length is calculated;

[0042] Figure 4 is ρ(t i )>ρ V (t i ) when the tool step length is calculated;

[0043] Figure 5 Generate schematic diagrams for tool paths. DETAILED DESCRIPTION

[0044] The specific implementation method will be described in detail here in combination with the technical solution and the accompanying drawings.

[0045] like Figure 1 As shown, the present invention proposes a method for generating a tool path for a complex curved surface part based on a virtual tool contact point, comprising the following steps:

[0046] 1) A curve in the complex surface is selected as the tool trajectory curve, and then the parameterized curve is obtained after the tool trajectory curve is parameterized. The initial point and the end point of the tool trajectory curve are used as the starting point and the end point of the tool trajectory respectively, and the starting point of the tool trajectory is used as the initial tool contact point. The error band of the parameterized curve is constructed based on the maximum approximation error;

[0047] 1) Specifically:

[0048] The complex surface is represented as S(u,v)=(x(u,v),y(u,v),z(u,v)), and a curve in the complex surface is selected as the tool path curve. After the tool path curve is parameterized, a parameterized curve is obtained, which is recorded as ξ(t). Its geometric space coordinates are P(t i )(x(t i ),y(t i ),z(t i )), where CC o is the initial point of the tool path curve, and its spatial coordinate is P o (x(t o ),y(t o ),z(t o )), CC e is the end point of the tool path curve, and its spatial coordinate is P e (x(t e ),y(t e ),z(t e )).

[0049] A knife contact CC on the parameterized curve i The normal curvature radius along the tool path is ρ(t i ), the calculation formula is as follows:

[0050]

[0051] Among them, d u , d v are the differentials in the u and v directions respectively, || is the absolute value, E, F, G are the three first-class basic quantities of complex surfaces, L, M, N are the three second-class basic quantities of complex surfaces, and the expressions are as follows:

[0052] E=S u ·S u F=S u ·S v G=S v ·S v

[0053] L=S uu n M=Suv ·n N=S vv ·n

[0054] Among them, S u , S v is the first-order partial derivative of the complex surface S(u,v) in the u direction and the v direction, S uu , S uv , S vv are the three second-order partial derivatives of the complex surface S(u,v), and n is the normal vector of the complex surface S(u,v).

[0055] To ensure that the linearization approximation error ε between two adjacent knife contacts is less than the set value ε of the maximum linearization approximation error within the step size max , respectively biased ± the maximum linearization approximation error ε in the z direction of the parameterized curve max After measuring the distance, the error band of the parameterized curve is formed.

[0056] In this embodiment, a three-dimensional model of a complex curved surface part to be processed is established with the aid of Solidworks software and exported to an IGES file format. The IGES toolbox in MATLAB software is used to read the content of the IGES file. The parameterized sampling points in the u and v directions are set to 500 to discretize the geometric shape of the complex curved surface to be processed and store the three-dimensional coordinate matrix of the geometric configuration of the complex curved surface.

[0057] In this example, a ball-end milling cutter with a tool radius of 4mm is selected, and the maximum linear approximation error between adjacent tool contacts is set to 0.02mm. From the initial coordinate point as the first tool contact point, the next tool contact point is generated by solving the problem until the trajectory curve is processed. The mark for judging the completion of the trajectory curve is that the straight-line distance between the last two adjacent tool contacts is less than 0.01mm. The tool trajectory curve error band is constructed, that is, the tool trajectory curve is offset by a distance of ±0.02mm in the z direction.

[0058] 2) Calculate the virtual knife contact point of the current knife contact point;

[0059] 2) Specifically:

[0060] 2.1) Calculate the tool step length L along the tangent direction of the current tool contact point s (t i ), the calculation formula is as follows:

[0061]

[0062] Among them, ε r (t i ) is the linear approximation error within the step length of the current tool contact point, ρ(t i) is the curvature radius of the current tool contact point, which is obtained by fitting the discrete points of the trajectory curve through MATLAB software; Figure 2 (a) is a schematic diagram of the tool step length of adjacent tool contacts in the present invention, Figure 2 (b) is a schematic diagram of the traditional method for solving the tool step length.

[0063] 2.2) When the current tool contact point moves along the tangent direction for a tool step length L s (t i ) is recorded as the approach point Its spatial coordinates P * (t i ) can be calculated by the following formula:

[0064]

[0065] Among them, P(t i ) is the spatial coordinate of the current knife contact point, || || is the Euclidean norm;

[0066] 2.3) Calculate the approach point The Euclidean distance to all points on the parameterized curve is the distance between the approximation point and the parameterized curve. The point with the smallest Euclidean distance between them is used as the virtual knife contact point The formula is as follows:

[0067] d P,ξ (P i * )=min{||P i * -ξ(t)||},i=1,2,…,m

[0068] Where m represents the number of knife contact points on the trajectory curve, and ξ(t) represents the set of all parameter points on the parameterized curve.

[0069] Based on the virtual knife contact point obtained in step 2 The normal curvature of the virtual knife contact point along the trajectory curve is calculated to be ρ V (t i ). When considering the local geometric features of adjacent knife contacts, the current knife contact CC is involved. i The normal curvature radius ρ(t i ) and virtual knife contact Normal curvature radius ρ V (t i ) size relationship.

[0070] 3) Determine the actual knife contact point of the current knife contact point according to the virtual knife contact point;

[0071] 3) Specifically:

[0072] like Figure 4 As shown, if the current knife contact CC i The normal radius of curvature ρ(t i ) is greater than the normal curvature radius ρ of the virtual knife contact point V (t i ), the virtual knife contact point is used as the actual knife contact point, such as Figure 3 As shown, if the current knife contact CC i The normal radius of curvature ρ(t i ) is less than or equal to the normal curvature radius ρ of the virtual knife contact point V (t i ), the actual normal curvature is obtained by spherical interpolation, and then the actual tool step length is calculated using the actual normal curvature. When the current tool contact point moves along the tangent direction for an actual tool step length L s (t i ) is used as the approach point of the actual tool contact point Calculate the approach point of the actual knife contact The Euclidean distance to all points on the parameterized curve is the approximate point on the parameterized curve to the actual knife contact point. The point with the smallest Euclidean distance between them is taken as the actual knife contact point

[0073] Among them, the calculation formula for obtaining the actual normal curvature by using the spherical interpolation method is as follows:

[0074] ρ R (t i )=β·ρ(t i )+γ·ρ V (t i )

[0075]

[0076] Where β and γ are the first and second weight coefficients, respectively, || || is the Euclidean norm, and P(t i ) is the spatial coordinate of the current tool contact point, P * (t i ) is the approach point of the virtual knife contact point The spatial coordinates, P V* (t i+1 ) is the approach point of the actual knife contact The spatial coordinates of .

[0077] The formula for calculating the actual tool step length using the actual normal curvature is as follows:

[0078]

[0079] in, is the actual tool step length, ε r (ti ) is the linear approximation error within the step length of the current tool contact point, ρ(t i ) is the curvature radius of the current tool contact point.

[0080] Two adjacent contacts CC i Dot and The interpolation line segment between the two points is guaranteed to be within the error band, that is, the approximation error ε between the two knife contacts meets the accuracy requirements and does not need to be corrected. It is determined as the actual knife contact point next to the initial knife contact point. If there is an intersection between the interpolation line segment between the two adjacent knife contacts and the error band, it is considered that the approximation error ε between the two knife contacts is greater than the set value ε max , the actual knife contact point needs to be corrected.

[0081] 4) Using the error band of the parameterized curve, the actual knife contact point of the current knife contact point is adaptively corrected so that the corrected actual knife contact point meets the accuracy requirement, and the optimal actual knife contact point is obtained as the next knife contact point;

[0082] 4) Specifically:

[0083] Determine whether there is an intersection between the tool trajectory and the error band between the current tool contact point and the actual tool contact point. If there is no intersection, the actual tool contact point meets the approximation error requirement and the actual tool contact point is used as the next tool contact point. If there is an intersection, extract all points on the parameterized curve between the current tool contact point and the actual tool contact point, where the point interval is t, t = 1 / 500, offset the actual tool contact point in the direction of the current tool contact point by an interval of parameter t, obtain the offset point and use it as the new actual tool contact point, re-determine whether there is an intersection between the tool trajectory and the error band between the current tool contact point and the new actual tool contact point, until an actual tool contact point that meets the approximation error requirement is found and used as the next tool contact point.

[0084] 5) Repeat 2)-4) to generate the optimal actual tool contact point corresponding to each tool contact point in turn, until the distance between the final tool contact point and the end point of the tool path is less than the preset accuracy, obtain all the tool contact points and generate the tool path. In this embodiment, the distance between the final tool contact point and the end point of the tool path is less than 0.01mm, which means that the tool path generation of the trajectory curve is fully realized. The specific tool path is as follows Figure 5 shown.

[0085] It can be seen from the tool path actually generated that the tool path generated by the method of the present invention can ensure the accuracy requirement and improve the processing quality of complex curved surface parts.

[0086] The above embodiments are only used to illustrate the design ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, any equivalent changes or modifications made based on the principles and design ideas disclosed by the present invention are within the protection scope of the present invention.

Claims

1. A method for generating tool path of complex surface parts based on virtual tool contact, characterized in that: The following steps are involved: 1) A curve in a complex surface is selected as the tool path curve, and then the parameterized curve is obtained after the tool path curve is parameterized. The initial point and the end point of the tool path curve are used as the starting point and the end point of the tool path respectively, and the starting point of the tool path is used as the initial tool contact point. The error band of the parameterized curve is constructed based on the maximum approximation error; 2) Calculate the virtual knife contact point of the current knife contact point; 3) Determine the actual knife contact point of the current knife contact point according to the virtual knife contact point; 4) Using the error band of the parameterized curve, the actual knife contact point of the current knife contact point is adaptively corrected so that the corrected actual knife contact point meets the accuracy requirement, and the optimal actual knife contact point is obtained as the next knife contact point; 5) Repeat 2)-4) to generate the optimal actual tool contact point corresponding to each tool contact point in turn, until the distance between the final tool contact point and the end point of the tool path is less than the preset accuracy, obtain all the tool contact points and generate the tool path.

2. The method for generating tool path of complex curved surface parts based on virtual tool contact points according to claim 1 is characterized in that: In the above 1), the maximum linear approximation error ε is offset in the z direction of the parameterized curve. max After measuring the distance, the error band of the parameterized curve is formed.

3. The method for generating tool path of complex curved surface parts based on virtual tool contact points according to claim 1 is characterized in that: The 2) is specifically: 2.1) Calculate the tool step length L along the tangent direction of the current tool contact point s (t i ), the calculation formula is as follows: Among them, ε r (t i ) is the linear approximation error within the step length of the current tool contact point, ρ(t i ) is the curvature radius of the current knife contact point; 2.2) When the current tool contact point moves along the tangent direction for a tool step length L s (t i ) is recorded as the approach point 2.3) Calculate the approach point The Euclidean distance to all points on the parameterized curve is the distance between the approximation point and the parameterized curve. The point with the smallest Euclidean distance between them is used as the virtual knife contact point 4. The method for generating tool path of complex curved surface parts based on virtual tool contact points according to claim 1 is characterized in that: The specific aspects of 3) are: If the current knife contact CC i The normal radius of curvature ρ(t i ) is greater than the normal curvature radius ρ of the virtual knife contact point V (t i ), the virtual knife contact point is used as the actual knife contact point. If the current knife contact point CC i The normal radius of curvature ρ(t i ) is less than or equal to the normal curvature radius ρ of the virtual knife contact point V (t i ), the actual normal curvature is obtained by spherical interpolation, and then the actual tool step length is calculated using the actual normal curvature. When the current tool contact point moves along the tangent direction for an actual tool step length L s (t i ) is used as the approach point of the actual tool contact point Calculate the approach point of the actual knife contact The Euclidean distance to all points on the parameterized curve is the approximate point on the parameterized curve to the actual knife contact point. The point with the smallest Euclidean distance between them is taken as the actual knife contact point 5. The method for generating tool path of complex curved surface parts based on virtual tool contact points according to claim 4 is characterized in that: In the above 3), the calculation formula for obtaining the actual normal curvature by using the spherical interpolation method is as follows: r R (t i )=β·ρ(t i )+g·r V (t i ) Where β and γ are the first and second weight coefficients, respectively, || || is the Euclidean norm, and P(t i ) is the spatial coordinate of the current tool contact point, P * (t i ) is the virtual knife contact point corresponding to the approach point The spatial coordinates of V* (t i+1 ) is the approach point of the actual knife contact The spatial coordinates of .

6. The method for generating tool path of complex curved surface parts based on virtual tool contact points according to claim 4 is characterized in that: In 3), the formula for calculating the actual tool step length using the actual normal curvature is as follows: in, is the actual tool step length, ε r (t i ) is the linear approximation error within the step length of the current tool contact point, ρ(t i ) is the curvature radius of the current tool contact point.

7. The method for generating tool path of complex curved surface parts based on virtual tool contact points according to claim 1 is characterized in that: The specific aspects of 4) are: Determine whether there is an intersection between the tool trajectory and the error band between the current tool contact point and the actual tool contact point. If there is no intersection, the actual tool contact point meets the approximation error requirement and the actual tool contact point is used as the next tool contact point. If there is an intersection, extract all points on the parameterized curve between the current tool contact point and the actual tool contact point, where the point interval is t, offset the actual tool contact point in the direction of the current tool contact point by an interval of parameter t, obtain the offset point and use it as the new actual tool contact point, and re-determine whether there is an intersection between the tool trajectory and the error band between the current tool contact point and the new actual tool contact point, until an actual tool contact point that meets the approximation error requirement is found and used as the next tool contact point.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 7 are implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

10. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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