Intelligent curved surface sampling point planning method and system based on real-time interaction

Abstract

The application provides a kind of intelligent curved surface sampling point planning method and system based on real-time interaction, first by establishing shared folder etc. Real-time interactive communication between machine tool numerical control system and personal computer is realized, then the initial sampling point and its in-machine measurement program planned are transmitted to machine tool by real-time interactive communication, after machine tool measurement is completed, measurement result is transmitted to computer in real time to be used for the planning of next sampling point, that is, according to all measured point data, one point is planned each time, one point is measured, then new point is planned again according to new measurement result, the above process is repeated until the sampling requirement is met. According to two sampling criteria, the area with larger machining deviation, i.e. the defect area, is automatically identified, and more sampling points are distributed in the defect area, which reduces the reconstruction deviation and improves the reconstruction accuracy of the actual curved surface by the replacement curved surface.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of complex curved surface detection sampling, in particular to an intelligent curved surface sampling point planning method and system based on real-time interaction. BACKGROUND

[0002] Complex curved surface parts are widely used in aerospace, automobile, shipbuilding, mold and other industrial fields due to their superior geometric and mechanical properties. The free curved surface profile precision will directly affect the working performance of the parts. Trigger type probes are widely used for detection and evaluation of workpiece machining quality, but their working mode is point-by-point measurement, i.e. only one point can be measured at a time. In order to realize high-precision detection of complex curved surfaces and reduce reconstruction error, a large number of sampling points need to be measured point by point, which greatly affects the measurement efficiency. Some scholars have proposed various sampling point planning algorithms by adjusting and optimizing the distribution of sampling points to reduce the number of measurement points as much as possible without affecting the measurement accuracy to improve the measurement efficiency, such as the Chinese patent "Adaptive Sampling Method Based on Machining Error Model and Hammersley Sequence" with the application number CN201711383515.4 and the Chinese patent "Intelligent Geometric Sampling Method Based on Three-coordinate Free Curved Surface" with the application number CN201710454589.6.

[0003] However, the existing sampling point planning methods are all based on the information of the design curved surface, such as the size of the curved surface, the geometric curvature, the sampling density, etc., and the goal is also to reduce the sampling deviation. However, the actual machined curved surface inevitably has some deviation from the design curved surface. The existing sampling point planning methods do not take this information into account, resulting in fewer sampling points distributed in areas with large deviations, which cannot accurately reconstruct the actual curved surface and affects the detection accuracy. Therefore, a sampling point planning method that can consider the information of the actual curved surface is needed, which can automatically identify areas with large deviations and intelligently increase the sampling points at the corresponding positions to more accurately reconstruct the actual curved surface and reduce the reconstruction error. SUMMARY

[0004] In view of the defects in the prior art, the present application aims to provide an intelligent curved surface sampling point planning method and system based on real-time interaction.

[0005] The intelligent curved surface sampling point planning method based on real-time interaction provided by the present application comprises the following steps:

[0006] Step S1: Establish a shared folder between the machine tool numerical control system and the personal computer for real-time interactive communication;

[0007] Step S2: when reconstructing the actual surface by using B-spline surface fitting of the measured points, the initial sampling points and their corresponding measurement procedures are generated on the computer according to the design surface and are transmitted to the machine tool through the shared folder for on-machine measurement to obtain the measurement results of the initial sampling points;

[0008] Step S3: according to the measurement results of the initial sampling points, a substitute surface of the actual surface is reconstructed by using B-spline surface fitting, the next sampling point is automatically calculated based on the comparison between the substitute surface and the design surface and the two sampling criteria, the new sampling point and its measurement procedure are transmitted to the machine tool for measurement, and then the new measurement point data and all the measured data are used to reconstruct the next substitute surface, and the new sampling point is generated again, and the above process is iterated until the sampling requirement is met.

[0009] Among them, the first sampling criterion is to select the position P1 with the maximum deviation e1 between the substitute surface and the design surface as the next sampling point; the second sampling criterion is that the change e2 of the substitute surface between the adjacent two iterations is less than e 2m in the circular region with the new measurement point as the center and R as the radius.

[0010] Preferably, the step S1 comprises: firstly linking the personal computer and the machine tool numerical control system by using the TCP / IP protocol, then establishing a folder in the numerical control system, and sharing it to the personal computer through TCP / IP, and the sampling points, their measurement procedures and measurement data are transmitted in real time through the shared folder.

[0011] Preferably, the step S2 comprises: according to the design surface, the initial measurement points are determined by using the uniform sampling method, and the calculation formula is:

[0012]

[0013] Among them, (x i , y i ) is the horizontal and vertical coordinates of the sampling point; (x0, y0) is the coordinate of the corner point of the design surface; L and W are the length and width of the design surface; N x , N y are the number of points set in the length and width directions;

[0014] The number of initial sampling points is related to the order of subsequent B-spline surface fitting. If the order of B-spline surface fitting is 3x3, the initial sampling points should be at least 4x4.

[0015] Preferably, the step S3 comprises: according to the measurement results returned by the shared folder, a substitute surface of the actual surface is reconstructed by using B-spline surface fitting, and the definition of B-spline surface fitting is:

[0016]

[0017] wherein P(u,v) is a point on the B-spline surface, determined by parameters u,v; C i, is the control point of the surface; n,m are the number of control points in u,v direction respectively; N i, (u), N j, (v) are the base functions of the B-spline surface.

[0018] Preferably, the deviation ε1 refers to the distance between the substitute surface and the design surface, the machining error d1 refers to the deviation distance between the actual surface and the design surface, and the reconstruction error d2 refers to the deviation distance between the substitute surface and the actual surface, and the relationship among them is:

[0019] ε1=d1-d2

[0020] wherein the substitute surface and the design surface are both known, thus ε1 is directly calculated; the machining error d1 is constant after the surface machining is completed, with the increase of the number of sampling points, the substitute surface tends to the actual surface more and more, and the reconstruction error d2 gradually decreases, if the reconstruction error d2 is completely eliminated, the machining error d1 is directly determined by ε1;

[0021] According to the sampling criterion one, the position with the maximum deviation ε1 is selected as the next sampling point and is sent to the machine tool for measurement, the measurement result and all the measured points are fitted to generate a new substitute surface, and then the next sampling point is determined similarly, when the position with the maximum deviation ε1 is just the position with the zero reconstruction error, the newly added sampling point does not change the substitute surface, thus the position is repeatedly sampled and measured, leading to the sampling algorithm falling into a dead loop, thus the change amount of the deviation ε1 of the substitute surface generated by two adjacent iterations is defined as ε2:

[0022] ε2=ε1-ε1 ′ |=(d1-d2)-(d1-d2 ′ )=|d2-d2 ′ |

[0023] According to the local support of the B-spline surface, when the new sampling point is added, the change amount of the reconstruction error in the vicinity of the sampling point is very small, indicating that the region can be well fitted by the substitute surface, and the region does not need to add the sampling point, the region is quantified as a circular region with the newly added sampling point as the center and R as the radius, and by changing the size of R, the reconstruction accuracy and the number of sampling points in different regions are balanced.

[0024] The intelligent curved surface sampling point planning system based on real-time interaction provided by the application comprises:

[0025] Module M1: a shared folder is established between the machine tool numerical control system and the personal computer for real-time interactive communication;

[0026] Module M2: when reconstructing the actual surface by fitting the measured points with B-spline surface, the initial sampling points and their corresponding measurement procedures are generated on the computer according to the design surface and transmitted to the machine tool through the shared folder for on-machine measurement to obtain the measurement results of the initial sampling points;

[0027] Module M3: according to the measurement results of the initial sampling points, a substitute surface of the actual surface is reconstructed by fitting with B-spline surface, the next sampling point is automatically calculated based on the comparison between the substitute surface and the design surface and the two sampling criteria, after the new sampling point and its measurement procedure are transmitted to the machine tool for measurement, the new measurement point data and all the measured data are used to reconstruct the next substitute surface, and then the new sampling point is generated again, and the above process is iterated until the sampling requirement is met;

[0028] The first sampling criterion is to select the position P1 with the maximum deviation ε1 between the substitute surface and the design surface as the next sampling point; the second sampling criterion is that the change amount ε2 of the substitute surface in the circular region with the new measurement point as the center and the radius R is less than ε 2m The sampling point is not increased in the region.

[0029] Preferably, the module M1 comprises: firstly linking the personal computer and the machine tool numerical control system by using the TCP / IP protocol, then establishing a folder in the numerical control system and sharing it to the personal computer through TCP / IP, and realizing real-time interactive transmission of the sampling points, their measurement procedures and measurement data through the shared folder.

[0030] Preferably, the module M2 comprises: determining the initial measurement points distributed uniformly according to the design surface by using the uniform sampling method, and the calculation formula is:

[0031]

[0032] Wherein, (x i , y i ) is the horizontal and vertical coordinates of the sampling point; (x0, y0) is the coordinate of the corner point of the design surface; L and W are the length and width of the design surface; N x , N y are the number of points set in the length and width directions;

[0033] The number of initial sampling points is related to the order of the subsequent fitted B-spline surface, if the order of the B-spline surface is 3x3, the initial sampling points should be at least 4x4.

[0034] Preferably, the module M3 comprises: according to the measurement results returned by the shared folder, a substitute surface of the actual surface is reconstructed by fitting with B-spline surface, and the definition of the B-spline surface is:

[0035]

[0036] Wherein, P(u,v) is a point on the B-spline surface, determined by parameters u, v; C i, is the control point of the surface; n, m are the number of control points in u, v direction respectively; N i, (u), N j, (v) is the base function of the B-spline surface.

[0037] Preferably, the deviation ε1 refers to the distance between the substitute surface and the design surface, the machining error d1 refers to the deviation distance between the actual surface and the design surface, and the reconstruction error d2 refers to the deviation distance between the substitute surface and the actual surface, and the relationship among them is:

[0038] ε1=d1-d2

[0039] Wherein, the substitute surface and the design surface are both known, so that ε1 is directly calculated; the machining error d1 is constant after the surface machining is completed, with the increase of the number of sampling points, the substitute surface tends to the actual surface more and more, and the reconstruction error d2 gradually decreases, if the reconstruction error d2 is completely eliminated, the machining error d1 is directly determined by ε1;

[0040] According to the sampling criterion one, the position with the maximum deviation ε1 is selected as the next sampling point and is sent to the machine tool for measurement, the measurement result and all the measured points are fitted to generate a new substitute surface, and then the next sampling point is determined similarly, when the position with the maximum deviation ε1 is just the reconstruction error zero, the newly added sampling point does not change the substitute surface, so that the position is repeatedly sampled and measured, resulting in that the sampling algorithm falls into a dead loop, therefore, the change amount of the deviation ε1 of the substitute surface generated by two adjacent iterations is defined as ε2:

[0041] ε2=ε1-ε1 ′ |=(d1-d2)-(d1-d2 ′ )=|d2-d2 ′ |

[0042] According to the local support of the B-spline surface, when the new sampling point is added, the reconstruction error change amount near the sampling point is very small, which indicates that the region can be well fitted by the substitute surface, and the region does not need to add the sampling point, the region is quantified as a circular region with the new sampling point as the center and the radius R, and by changing the size of R, the reconstruction accuracy and the number of sampling points in different regions are balanced.

[0043] Compared with the prior art, the present application has the following beneficial effects:

[0044] The present application ensures that the sampling points and their measurement results can be immediately used for new sampling point planning through real-time interaction with the machine tool, that is, the actual surface is also used for sampling point planning; two new sampling criteria are proposed to optimize the distribution of sampling points, intelligently distribute relatively more sampling points in places with large deviations, and improve the reconstruction accuracy of the actual surface; by changing the sampling algorithm setting parameters, the density of the sampling point distribution at the defect can be adjusted to balance the measurement efficiency and accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0045] Other features, objects, and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments with reference to the attached drawings:

[0046] Figure 1 A flowchart of the intelligent surface sampling point planning method based on real-time interaction provided by the embodiments of the present application is shown in FIG. 1.

[0047] Figure 2 (a) and (b) in FIG. 1 are schematic diagrams illustrating the sampling criteria provided by the embodiments of the present application. DETAILED DESCRIPTION

[0048] The present application will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that, for those skilled in the art, without departing from the concept of the present application, a number of changes and improvements can be made. These all belong to the protection scope of the present application.

[0049] Example 1:

[0050] As Figure 1 A flowchart of the intelligent surface sampling point planning method based on real-time interaction provided by the embodiments of the present application is shown in FIG. 1, which includes the following steps:

[0051] S1, Real-time interactive communication between the machine tool numerical control system and the personal computer is established. Taking a shared folder as an example, based on the TCP / IP protocol, a shared folder is established in the numerical control system and the personal computer respectively, and any change in the folder will be updated in real time at both ends. Therefore, through real-time interaction, the sampling points and their measurement programs, actual measurement data can be quickly and real-time transmitted between the numerical control system and the computer, which is the premise and basis for the subsequent sampling point planning method.

[0052] S2, Planning and measurement of a small number of initial sampling points. When fitting the measurement points with B-spline surfaces to reconstruct the actual surface, there are certain requirements for the number of initial measurements, therefore, according to the design surface, a small number of uniformly distributed initial sampling points and their corresponding measurement programs are generated on the computer side and transmitted to the machine tool for on-machine measurement through the shared folder established in S1.

[0053] S3. Intelligent Planning of Subsequent Sampling Points. Based on the measurement results of the initial sampling points in S2, a substitute surface for the actual surface can be reconstructed using B-spline surface fitting. By comparing the substitute surface with the design surface, the next sampling point can be automatically calculated based on the two proposed sampling criteria. After the new sampling point and its measurement program are transmitted to the machine tool to complete the measurement, the new measurement point data and all previously measured data are used to reconstruct the next substitute surface, thereby generating new sampling points again. This process iterates until the sampling requirements are met. The first sampling criterion is to select the position P1 with the largest deviation ε1 between the substitute surface and the design surface as the next sampling point; the second sampling criterion is that within a circular area with the new measurement point as the center and a radius of R, the change ε2 of the substitute surface between two adjacent iterations is less than ε. 2m No more sampling points will be added within the designated area.

[0054] Specifically, step S1 includes: first, connecting the personal computer and the machine tool CNC system using the TCP / IP protocol; then, creating a folder in the CNC system and sharing it to the personal computer via TCP / IP. Sampling points, their measurement programs, and measurement data can then be transmitted interactively in real time through the shared folder.

[0055] Specifically, step S2 includes: determining a small number of uniformly distributed initial measurement points based on the designed surface using a uniform sampling method, the calculation formula of which is:

[0056]

[0057] Among them, (x i y i 0 represents the x and y coordinates of the sampling point; (x0, y0) represents the coordinates of the corner point of the designed surface; L and W represent the length and width of the designed surface; N x N y The number of points set in the length and width directions.

[0058] The number of initial sampling points is related to the order of the subsequent fitted B-spline surface. If the order of the B-spline surface is 3×3, the initial sampling points should be at least 4×4.

[0059] Specifically, step S3 includes: based on the measurement results returned by the shared folder, a substitute surface for the actual surface can be reconstructed using B-spline surface fitting. The definition of a B-spline surface is:

[0060]

[0061] Where P(u,v) are points on the B-spline surface, determined by parameters u and v; C i, These are the control points of the surface; n and m are the number of control points in the u and v directions, respectively; N i,(u), N j, (v) is a basis function of the B-spline surface.

[0062] As Figure 2 shown, the deviation e1 refers to the distance between the substitute surface and the design surface, the machining error d1 refers to the deviation distance between the actual surface and the design surface, and the reconstruction error d2 refers to the deviation distance between the substitute surface and the actual surface. The relationship among them is:

[0063] e1 = d1 - d2

[0064] Where the substitute surface and the design surface are known, and thus e1 can be directly calculated. The actual surface is unknown, and thus d1 and d2 cannot be directly calculated. The machining error d1 is constant after the surface is machined. As the number of sampling points increases, the substitute surface becomes more and more close to the actual surface, and the reconstruction error d2 gradually decreases. Obviously, if the reconstruction error d2 is completely eliminated, the machining error d1 can be directly determined by e1. However, unless all the points on the actual surface are measured, there will always be a certain reconstruction error, that is, the reconstruction error can only be reduced by various sampling point planning methods, but cannot be completely eliminated.

[0065] According to the first sampling criterion, the position with the maximum deviation e1 is selected as the next sampling point and sent to the machine tool for measurement. The measurement result and all the measured points are used to generate a new substitute surface, and then the next sampling point is determined in a similar manner. However, this iterative process may fall into a dead loop, that is, when the position with the maximum deviation e1 happens to have a reconstruction error of zero, the newly added sampling point will not change the substitute surface, and thus the position will be repeatedly sampled and measured, causing the sampling algorithm to fall into a dead loop, as shown in Figure 2 To avoid this situation, the change amount of the deviation e1 of the substitute surface generated by adjacent two iterations is defined as e2:

[0066] e2 = e1 - e1 ′ | = (d1 - d2) - (d1 - d2 ′ ) = |d2 - d2 ′ |

[0067] Since the machining error d1 is constant, e2 essentially reflects the change amount of the reconstruction error of the substitute surface in adjacent two iterations. According to the local support property of the B-spline surface, when a new sampling point is added, if the change amount of the reconstruction error in the vicinity of the sampling point is small, it indicates that the region can be well expressed by the substitute surface, and thus the region does not need to add a sampling point. The region is quantified as a circular region with the newly added sampling point as the center and R as the radius. Therefore, the second sampling criterion essentially aims to exclude the regions with good fitting effect, reduce unnecessary sampling points, and avoid the dead loop problem that may be caused by using only the first criterion.

[0068] The size of the radius R directly affects the number of sampling points in the defect area by the second criterion. The smaller R is, the more sampling points are in the defect, and the smaller the reconstruction error in the defect is. However, if R is too small, most of the sampling points will be distributed in the defect, and the number of sampling points in other areas will be too small, resulting in a larger reconstruction error in other areas. Therefore, the total number of sampling points may need to be increased to ensure the reconstruction accuracy. Therefore, by changing the size of R, the reconstruction accuracy and the number of sampling points in different areas can be balanced. It is recommended that R be set to 1-2 mm.

[0069] The technical solution provided by the present application has the following advantages: 1. Through real-time interaction with the machine tool, actual measurement data is used for fitting the replacement surface, that is, the information of the actual surface is used for planning the sampling points; 2. According to the two sampling criteria, the area with larger machining deviation, i.e. the defect area, is automatically identified, and more sampling points are distributed in the defect area, reducing the reconstruction deviation and improving the reconstruction accuracy of the replacement surface to the actual surface; 3. By adjusting the value of the parameter R, different reconstruction accuracy requirements can be met. The smaller R is, the more sampling points are in the defect area, and the smaller the reconstruction error is.

[0070] Example 2:

[0071] The present application also provides an intelligent curved surface sampling point planning system based on real-time interaction. The intelligent curved surface sampling point planning system based on real-time interaction can be realized by executing the process steps of the intelligent curved surface sampling point planning method based on real-time interaction. That is, those skilled in the art can understand the intelligent curved surface sampling point planning method based on real-time interaction as the preferred implementation of the intelligent curved surface sampling point planning system based on real-time interaction.

[0072] According to the application, the intelligent real-time interaction-based sampling point planning system for curved surface comprises the following modules: module M1: a shared folder is established between a machine tool numerical control system and a personal computer for real-time interaction; module M2: when a B-spline curved surface is used to fit and reconstruct a measured point to form an actual curved surface, initial sampling points and corresponding measurement programs are generated on the computer according to a design curved surface, and are transmitted to the machine tool through the shared folder for in-machine measurement to obtain measurement results of the initial sampling points; module M3: according to the measurement results of the initial sampling points, a B-spline curved surface is used to fit and reconstruct a substitute curved surface of an actual curved surface, the substitute curved surface is compared with the design curved surface, and the next sampling point is automatically calculated based on two sampling criteria; after the new sampling point and its measurement program are transmitted to the machine tool for measurement, the new measurement point data and all the measured data are used to reconstruct the next substitute curved surface, and then new sampling points are generated again, and the above process is iterated until the sampling requirement is met; the first sampling criterion is that the position P1 with the maximum deviation e1 between the substitute curved surface and the design curved surface is selected as the next sampling point; the second sampling criterion is that the sampling point is not increased in a circular region with the new measurement point as the center and a radius R, and the variation e2 of the substitute curved surface of the adjacent two iterations is less than e 2m .

[0073] The module M1 comprises the following steps: first, the personal computer and the machine tool numerical control system are linked by using a TCP / IP protocol; then, a folder is established in the numerical control system, and is shared to the personal computer by using the TCP / IP; and the sampling points, the measurement programs and the measurement data are transmitted in real time by using the shared folder.

[0074] The module M2 comprises the following steps: according to the design curved surface, the initial measurement points are determined by using the uniform sampling method, and the calculation formula is as follows:

[0075]

[0076] wherein (x i , y i ) are the horizontal and vertical coordinates of the sampling point; (x0, y0) are the corner coordinates of the design curved surface; L and W are the length and width of the design curved surface; N x and N y are the number of points set in the length and width directions; the number of the initial sampling points is related to the order of the subsequent fitted B-spline curved surface; if the order of the B-spline curved surface is 3x3, the initial sampling points should be at least 4x4.

[0077] The module M3 comprises the following steps: according to the measurement results returned by the shared folder, a B-spline curved surface is used to fit and reconstruct a substitute curved surface of an actual curved surface, and the definition of the B-spline curved surface is as follows:

[0078]

[0079] Where P(u, v) is a point on the B-spline surface, determined by parameters u, v; C i, is the control point of the surface; n, m are the number of control points in u, v direction respectively; N i, (u), N j, (v) are the basis functions of the B-spline surface.

[0080] The deviation ε1 refers to the distance between the substitute surface and the design surface, the machining error d1 refers to the deviation distance between the actual surface and the design surface, and the reconstruction error d2 refers to the deviation distance between the substitute surface and the actual surface. The relationship among them is:

[0081] ε1 = d1 - d2

[0082] Where the substitute surface and the design surface are both known, so ε1 is directly calculated; the machining error d1 is constant after the surface is machined, and as the number of sampling points increases, the substitute surface tends to the actual surface, and the reconstruction error d2 gradually decreases. If the reconstruction error d2 is completely eliminated, the machining error d1 is directly determined by ε1.

[0083] According to the first sampling criterion, the position with the maximum deviation ε1 is selected as the next sampling point and sent to the machine tool for measurement. The measurement result and all measured points are fitted again to generate a new substitute surface, and the next sampling point is determined in the same way. When the position with the maximum deviation ε1 is exactly the reconstruction error of zero, the newly added sampling point will not change the substitute surface, so this position will be repeatedly sampled and measured, causing the sampling algorithm to fall into a dead loop. Therefore, the change amount of the deviation ε1 of the substitute surface generated by two adjacent iterations is defined as ε2:

[0084] ε2 = ε1 - ε1 ′ | = (d1 - d2) - (d1 - d2 ′ ) = |d2 - d2 ′ |

[0085] According to the local support of the B-spline surface, when a new sampling point is added, the reconstruction error change in the vicinity of the sampling point is very small, indicating that this area can be well fitted by the substitute surface. This area does not need to add sampling points, and the area is quantified as a circular area with the new sampling point as the center and R as the radius. By changing the size of R, the reconstruction accuracy and the number of sampling points in different areas are balanced.

[0086] Those skilled in the art know that, in addition to implementing the system, device and each module thereof provided by the present application in the form of pure computer readable program code, the same program can also be implemented in the form of logic gate, switch, special integrated circuit, programmable logic controller and embedded microcontroller, etc. by logically programming the method steps. Therefore, the system, device and each module thereof provided by the present application can be considered as a hardware component, and the modules included therein for implementing various programs can also be considered as structures in the hardware component; the modules for implementing various functions can also be considered as both software programs for implementing methods and structures in the hardware component.

[0087] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily without conflict.

Claims

1. A real-time interaction based intelligent curved surface sampling point planning method, characterized in that, The method comprises the following steps: Step S1: a shared folder is established between the machine tool numerical control system and the personal computer for real-time interactive communication; Step S2: when the B-spline surface fitting measurement points are used to reconstruct an actual surface, initial sampling points and corresponding measurement programs are generated on the computer according to the design surface, and are transmitted to the machine tool through the shared folder for on-machine measurement to obtain the measurement results of the initial sampling points; Step S3: a substitute surface of the actual surface is reconstructed by using the B-spline surface fitting according to the measurement results of the initial sampling points, the next sampling point is automatically calculated by comparing the substitute surface with the design surface based on two sampling criteria, the new sampling point and the measurement program thereof are transmitted to the machine tool for measurement, and then the new measurement point data and all the measured data are used to reconstruct the next substitute surface, and the new sampling point is generated again, and the above process is iterated until the sampling requirement is met; One of the sampling criteria is the deviation between the selected alternative surface and the designed surface. Largest position Selected as the next sampling point; sampling criterion two is to use the newly added measurement point as the center of a circle with a radius of... Within the circular region, the change in the alternative surface between two adjacent iterations Less than No more sampling points will be added within the area; The step S2 comprises the following steps: initial measurement points are determined by using the uniform sampling method according to the design surface, and the calculation formula is as follows: wherein, is the horizontal and vertical coordinates of the sampling points; is the coordinates of the corner points of the design surface; , is the length and width of the design surface; , is the number of points set in the length and width direction; The number of initial sampling points is related to the order of the subsequent fitted B-spline surface. If the order of the B-spline surface is , the initial sampling points should be at least .

2. The real-time interaction based intelligent curved surface sampling point planning method according to claim 1, characterized in that, The step S1 comprises the following steps: the personal computer and the machine tool numerical control system are linked by using the TCP / IP protocol, then a folder is established in the numerical control system, and is shared to the personal computer through the TCP / IP, and the sampling points, the measurement programs and the measurement data are transmitted in real time through the shared folder.

3. The real-time interaction based intelligent curved surface sampling point planning method according to claim 1, characterized in that, The step S3 comprises the following steps: a substitute surface of the actual surface is reconstructed by using the B-spline surface fitting according to the measurement results returned by the shared folder, and the definition of the B-spline surface is as follows: wherein is a point on the B-spline surface determined by parameters , ; is a control point of the surface; , are the number of , direction control points, respectively; is a basis function of the B-spline surface.

4. The real-time interaction based intelligent curved surface sampling point planning method according to claim 1, characterized in that, deviation distance between the substitute surface and the design surface, machining error deviation distance between the actual surface and the design surface, reconstruction error deviation distance between the substitute surface and the actual surface, the relationship among the three is: Where both the approximating surface and the design surface are known, thus the machining error is directly calculated; the reconstruction error is directly calculated; the machining error is directly calculated; the machining error is directly calculated; the machining error is directly calculated; the machining error According to the sampling criterion one, the deviation The position with the largest deviation is selected as the next sampling point and sent to the machine tool for measurement. The measurement result and all the measured points are fitted again to generate a new replacement surface, and then the next sampling point is determined similarly. When the deviation When the position with the largest deviation exactly reconstructs the error to zero, the newly added sampling point will not change the replacement surface, so this position will be repeatedly sampled and measured, causing the sampling algorithm to fall into a dead loop. Therefore, the change amount of the deviation between the replacement surfaces generated by two adjacent iterations is defined as ​ According to the local support of B-spline surface, when a new sampling point is added, if the change of reconstruction error near the new sampling point is very small, it means that the region can be well fitted by the alternative surface, and the region does not need to add a new sampling point. The region is quantified as a circular region with the new sampling point as the center and the radius of By changing the size of , the reconstruction accuracy and the number of sampling points in different regions are balanced.

5. A real-time interaction based intelligent curved surface sampling point planning system, characterized in that, The method comprises the following steps: Module M1: a shared folder is established between the machine tool numerical control system and the personal computer for real-time interactive communication; Module M2: when the B-spline surface fitting measurement points are used to reconstruct an actual surface, initial sampling points and corresponding measurement programs are generated on the computer according to the design surface, and are transmitted to the machine tool through the shared folder for on-machine measurement to obtain the measurement results of the initial sampling points; Module M3: a substitute surface of the actual surface is reconstructed by using the B-spline surface fitting according to the measurement results of the initial sampling points, the next sampling point is automatically calculated by comparing the substitute surface with the design surface based on two sampling criteria, the new sampling point and the measurement program thereof are transmitted to the machine tool for measurement, and then the new measurement point data and all the measured data are used to reconstruct the next substitute surface, and the new sampling point is generated again, and the above process is iterated until the sampling requirement is met; One of the sampling criteria is the deviation between the selected alternative surface and the designed surface. Largest position Selected as the next sampling point; sampling criterion two is to use the newly added measurement point as the center of a circle with a radius of... Within the circular region, the change in the alternative surface between two adjacent iterations Less than No more sampling points will be added within the area; The module M2 comprises the following steps: initial measurement points are determined by using the uniform sampling method according to the design surface, and the calculation formula is as follows: wherein, is the horizontal and vertical coordinates of the sampling points; is the coordinates of the corner points of the design surface; , is the length and width of the design surface; , is the number of points set in the length and width direction; The number of initial sampling points is related to the order of the subsequent fitted B-spline surface. If the order of the B-spline surface is , the initial sampling points should be at least .

6. The real-time interaction based intelligent curved surface sampling point planning system according to claim 5, characterized in that, The module M1 comprises the following steps: the personal computer and the machine tool numerical control system are linked by using the TCP / IP protocol, then a folder is established in the numerical control system, and is shared to the personal computer through the TCP / IP, and the sampling points, the measurement programs and the measurement data are transmitted in real time through the shared folder.

7. The real-time interaction based intelligent curved surface sampling point planning system according to claim 5, wherein, The module M3 comprises the following steps: a substitute surface of the actual surface is reconstructed by using the B-spline surface fitting according to the measurement results returned by the shared folder, and the definition of the B-spline surface is as follows: wherein is a point on the B-spline surface determined by parameters , ; is a control point of the surface; , are the number of , direction control points, respectively; is a basis function of the B-spline surface.

8. The real-time interaction based intelligent curved surface sampling point planning system according to claim 5, wherein, deviation distance between the substitute surface and the design surface, machining error deviation distance between the actual surface and the design surface, reconstruction error deviation distance between the substitute surface and the actual surface, the relationship among the three is: where both the replacement surface and the design surface are known, and the machining error is directly calculated and is constant after the surface machining is completed, and as the number of sampling points increases, the replacement surface increasingly tends to the actual surface, and the reconstruction error gradually decreases, and if the reconstruction error is completely eliminated, the machining error is directly determined . According to the sampling criterion one, the deviation The position with the largest deviation is selected as the next sampling point and sent to the machine tool for measurement. The measurement result and all the measured points are fitted again to generate a new replacement surface, and then the next sampling point is determined similarly. When the deviation The newly added sampling point does not change the replacement surface when the position with the largest deviation exactly reconstructs the error to zero. Therefore, the position is repeatedly sampled and measured, which leads to a dead loop of the sampling algorithm. Therefore, the change of the deviation between the replacement surfaces generated by two adjacent iterations is defined as : According to the local support of B-spline surface, when a new sampling point is added, if the change of reconstruction error near the new sampling point is very small, it means that the region can be well fitted by the alternative surface, and the region does not need to add a new sampling point. The region is quantified as a circular region with the new sampling point as the center and the radius of By changing the size of , the reconstruction accuracy and the number of sampling points in different regions are balanced.

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