High-precision comparison measurement method and system for five-axis machine tool in-machine measurement

Abstract

The application provides a high-precision comparison measurement method and system for in-machine measurement of a five-axis machine tool, comprising: obtaining surface point data of a workpiece, and taking the workpiece with the obtained surface point data as a standard piece; symmetrically clamping the standard piece and a workpiece to be tested on a rotary table of the machine tool, ensuring that the positions of the standard piece and the workpiece to be tested are the same after being rotated by 180 degrees; measuring the surface of the workpiece to be tested according to a set measurement path; rotating the C shaft of the machine tool by 180 degrees to make the positions of the standard piece and the workpiece to be tested the same, and measuring the surface of the workpiece to be tested; using the surface point data of the standard piece obtained by a coordinate measuring machine and the in-machine measurement point data of the standard piece to calibrate the surface of the standard piece, and eliminating the machining error of the surface; and calculating the error between the workpiece to be tested and the calibrated standard piece to obtain the surface error. The application does not need additional machine tool system error detection and compensation, is simple to operate, efficient, and has significant cost-effectiveness.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of on-machine measurement technology, in particular, to a high-precision comparison measurement method and system for on-machine measurement of a five-axis machine tool. BACKGROUND

[0002] On-machine measurement (OMM) by installing a trigger probe has greatly improved production efficiency and accuracy. In-situ measurement of parts can avoid re-clamping positioning errors, while also providing timely feedback required for precision machining processes. Therefore, compared with off-line measurement, this is a more promising method to shorten the production cycle and improve product quality. However, there comes with it the new challenge of ensuring the accuracy of on-machine measurement results. The geometric and thermal errors of the machine tool are the main error sources that significantly affect the accuracy of on-machine measurement. Usually, the measurement accuracy is an order of magnitude higher than the machining accuracy, which seriously restricts the ability and credibility of on-machine measurement.

[0003] In order to achieve accurate process control within the workshop at a lower cost, various methods and measurement tools have been proposed to address these errors. Error identification and compensation are common means to address these errors, and the geometric and thermal errors of the machine tool are mainly measured by R-test equipment, ball bar, optical measurement equipment, etc. In addition, mechanical processing measurement during actual machining is also a method, which measures the workpiece being processed by devices such as dial indicators or coordinate measuring machines, so as to quantitatively evaluate the impact of machine tool errors on the geometric shape of the workpiece. The errors of the measurement system also have a significant impact on the measurement results, among which the pre-travel error and radius error of the trigger probe are important parts. Currently, the standard ball calibration method is widely used to address these errors. In addition, dynamic errors, random errors, and repeatability of the machine tool are also factors that affect the quality of on-machine measurement. However, most of these methods can usually only address one type of error, making it difficult to consider multiple errors comprehensively.

[0004] After literature retrieval of the prior art, it is found that the invention patent with publication number CN115979170A discloses a straight tooth surface gear parameter on-machine measurement and error compensation method. The method can obtain the probe delay error, probe measurement error and measurement coordinate error during measurement by combining the optimal scheme of the spiral measurement path, and establish a probe error model based on the measurement principle. Finally, through the calibration process, the overall error is obtained, so as to obtain the accurate measurement point coordinates after compensation. However, the method mainly focuses on the probe error, the compensation method is not comprehensive enough, and it is only suitable for straight tooth surface gear parameters, lacking of universality. The invention patent with publication number CN107220213A discloses a five-axis numerical control machine tool online measurement and analysis method. The method analyzes the error sources of the five-axis numerical control machine tool in detail, eliminates the error factors and deduces the related specific model. This method eliminates the error and constructs the model, and then uses the correction method for error correction, so as to improve the measurement accuracy, but the efficiency is low. SUMMARY

[0005] In view of the defects in the prior art, the present application provides a high-precision comparison measurement method and system for on-machine measurement of a five-axis machine tool.

[0006] According to the high-precision comparison measurement method and system for on-machine measurement of a five-axis machine tool provided by the present application, the scheme is as follows:

[0007] In a first aspect, a high-precision comparison measurement method for on-machine measurement of a five-axis machine tool is provided, which comprises:

[0008] Step S1: obtaining surface point data of a workpiece by using a coordinate measuring machine (CMM), and taking the workpiece with the obtained surface point data as a standard piece;

[0009] Step S2: symmetrically clamping the standard piece and the workpiece to be tested on the rotary table of the machine tool, so as to ensure that the positions of the standard piece and the workpiece are the same after rotating 180°;

[0010] Step S3: measuring the surface of the workpiece to be tested according to the set measurement path;

[0011] Step S4: rotating the C-axis of the machine tool by 180° to make the positions of the standard piece and the workpiece the same, and then measuring the surface of the workpiece to be tested by using the same measurement path as step S3;

[0012] Step S5: using the surface point data of the standard piece obtained by the coordinate measuring machine and the on-machine measurement point data of the standard piece obtained in step S4 to calibrate the surface of the standard piece to eliminate the machining error of the surface thereof;

[0013] Step S6: Calculate the error between the test workpiece and the calibration standard, and the surface error obtained is the accurate measurement result after eliminating the error of the in-machine measurement system.

[0014] Preferably, the step S1 comprises measuring the point data of the standard by a coordinate measuring machine, and the measurement process must be consistent with the subsequent in-machine measurement process, i.e., the distribution of the measured points is consistent.

[0015] Preferably, in the step S2, the measurement errors of the two measurements are ensured to be the same, and the two workpieces, i.e., the standard and the test workpiece, are symmetrically clamped, i.e., after the C-axis is rotated by 180°, the position of the standard must be the same as the position of the test workpiece before rotation, so as to ensure that the paths of the two measurements are the same.

[0016] The process of recognizing and eliminating the rotation of the workpiece by 180° itself introduces the geometric error of the C-axis rotation axis:

[0017] The geometric error of the C-axis includes three angle errors and three displacement errors, which represent the deviation between the reference coordinate system and the actual coordinate system and is denoted as GE c =[ε x ε y ε z δ x δ y δ z T According to the active frame principle, the geometric error can be regarded as the rotation of the active frame at the origin of the static frame around the X-axis, Y-axis, and Z-axis by angles ε x , ε y , and ε z , and the translation in the X, Y, and Z directions by δ x , δ y , and δ z , and is expressed as:

[0018]

[0019] According to the method of the homogeneous transformation matrix HTM, the C-axis kinematics transformation model considering the geometric error is obtained, and the position of a point is calculated as follows:

[0020]

[0021] and the ideal position P ideal,1 ' of the point without the geometric error is calculated as:

[0022] P' ideal,1 =R(C)R'(C) -1 P'1

[0023] Finally, by inversely calculating the measured point data by using the above formula, the C-axis error can be successfully eliminated.​

[0024] Where C represents the angular change between two measurements of the C-axis; P1 represents the ideal position before rotation; P'1 represents the measurement point of the OMM system; and R represents the rotation matrix without geometric errors.

[0025] Preferably, the machine tool needs to be fully preheated when measuring the workpiece in step S3.

[0026] Preferably, a test block is used to measure the geometric error of the rotating shaft. The measurement of the geometric error is performed directly on the workpiece. The corner point on the workpiece is selected as the reference point. Different surfaces are measured as measurement references. The required measurement points are obtained through the intersection of the three surfaces. To reduce random errors, six points are measured on each surface in a uniform layout. Finally, the least squares method is used to fit the plane to obtain accurate measurement results.

[0027] Preferably, in step S5, the processing error is evaluated by using a point-to-surface function, discrete detection points are used to replace the actual surface, and surface reconstruction is performed. Typically, the B-spline surface fitting method is used for surface reconstruction.

[0028] B-spline surfaces are defined by p-degree in the u direction and q-degree in the v direction:

[0029]

[0030] Where P(u,v) is formed by... u and v A point C on a defined surface i,j Indicates control points, n and m They represent u and v Number of control points in the direction, N i,p (u) and N j,q (v) is an unrational B-spline basis function;

[0031] Reconstruct the surface of the standard part using a formula, and calculate the error between the measured points of the test piece obtained from the OMM system and the surface using the following formula:

[0032]

[0033] Where i represents the number of measurement points; e i This refers to the machining error of the specimen, excluding the measurement error of the OMM system; d e,i This represents the distance from the measurement point of the OMM system to the calibrated surface of the standard part; p ot,i q represents the measurement point of the OMM system; e,i This indicates that the measurement points of the OMM system are mapped to the corresponding points on the surface of the calibrated standard part; denote the corresponding direction vectors.

[0034] Preferably, the step S5 calibrating the standard part comprises:

[0035] The coordinate measuring machine measurement point P c {p c,i The B-spline surface fitting method is used to reconstruct the surface, and the coordinate measuring machine surface is obtained, marked as S c (u,v), which is regarded as the standard part surface containing only machining errors. The error and its coordinate components are calculated by the following formula:

[0036]

[0037] In the formula: p i denotes the OMM measurement point of the standard part; q i denotes the OMM measurement point of the standard part mapped onto the standard part CMM measurement point, located on the surface normal; denote the corresponding direction vectors; δ x,i , δ y,i , δ z,i are the x, y, and z direction components, respectively; d p,i denotes the system error not containing machining errors;

[0038] The error not containing any machining error is superimposed on the design surface, marked as S d (u,v), the distance from the design surface is determined and the corresponding point is found, and the corresponding point is determined by the formula:

[0039]

[0040] In the formula, q' i denotes the corresponding point located on the surface normal; denotes the point q i on the CMM surface to the distance of the design surface; denotes the corresponding direction vector;

[0041] The error is superimposed on the point q' i :

[0042]

[0043] Expressed in coordinate components as:

[0044]

[0045] In the formula, q r,i denotes the coordinates of the point on the calibrated standard part surface; q x,r,i denotes the x coordinate value of the point on the calibrated standard part surface; q y,r,iy coordinate value of the point on the calibrated standard part surface; q z,r,i z coordinate value of the point on the calibrated standard part surface; q' x,i x coordinate value of the corresponding point on the theoretical surface; q' y,i y coordinate value of the corresponding point on the theoretical surface; q' z,i z coordinate value of the corresponding point on the theoretical surface; δ x,i component of the measurement error in the x direction without any machining error; δ y,i component of the measurement error in the y direction without any machining error; δ z,i component of the measurement error in the z direction without any machining error; the surface is reconstructed using the calibration points.

[0046] In a second aspect, a high-precision comparison measurement system for in-machine measurement of a five-axis machine tool is provided, and the system comprises:

[0047] Module M1: obtaining surface point data of a workpiece by a coordinate measuring machine (CMM), and taking the workpiece with the obtained surface point data as a standard part;

[0048] Module M2: symmetrically clamping the standard part and the workpiece to be tested on a rotary table of a machine tool, so as to ensure that the positions of the standard part and the workpiece are the same after being rotated by 180°;

[0049] Module M3: measuring the surface of the workpiece to be tested according to a set measurement path;

[0050] Module M4: rotating the C-axis of the machine tool by 180°, so that the positions of the standard part and the workpiece are the same, and then measuring the surface of the workpiece to be tested by using the same measurement path as that in module M3;

[0051] Module M5: calibrating the surface of the standard part by using the surface point data of the standard part obtained by the CMM and the in-machine measurement point data of the standard part obtained in module M4, so as to eliminate machining errors of the surface of the standard part;

[0052] Module M6: calculating errors between the workpiece to be tested and the calibrated standard part, so as to obtain a precise measurement result after eliminating errors of the in-machine measurement system.

[0053] Preferably, the module M1 comprises: measuring point data of the standard part by a three-coordinate measuring machine, and the measurement process must be consistent with the subsequent in-machine measurement process, that is, the distribution of the measured points is consistent;

[0054] In the module M2, the measurement errors of two measurements are ensured to be the same, the two workpiece centers of the standard part and the workpiece to be tested are symmetrically clamped, that is, after the C-axis is rotated by 180°, the position of the standard part must be the same as the position of the workpiece to be tested before rotation, so as to ensure that the paths of two measurements are the same;

[0055] The process of identifying and eliminating the workpiece rotation by 180° itself introduces the geometric error of the C-axis rotation axis:

[0056] The geometric error of the C-axis includes three angle errors and three displacement errors, which represent the deviation between the reference coordinate system and the actual coordinate system and is denoted as GE c =[ε x ε y ε z δ x δ y δ z ] T According to the active frame principle, the geometric error can be regarded as the active frame rotating angles ε x 、ε y 、ε z around the X-axis, Y-axis and Z-axis respectively at the origin of the static frame, and translating δ x 、δ y 、δ z in the X, Y and Z directions, which can be expressed as:

[0057]

[0058] According to the method of homogeneous transformation matrix HTM, the C-axis kinematics transformation model considering the geometric error is obtained, and the position of any point is calculated as follows:

[0059]

[0060] And the ideal position P ideal,1 ' of the ideal position of the point if it does not contain the geometric error is calculated as:

[0061] P' ideal,1 =R(C)R'(C) -1 P'1

[0062] Finally, the C-axis error can be successfully eliminated by inversely calculating the measured point position data through the above formula;

[0063] Wherein, C represents the angle change between the two measurements of the C-axis; P1 represents the ideal position before rotation; P'1 represents the measured point of the OMM system; R represents the rotation matrix without geometric error.

[0064] In the module M3, the workpiece is measured, and the machine tool needs to be fully preheated;

[0065] The test block is used to measure the geometric error of the rotating shaft. The geometric error is directly measured on the workpiece. The angular point on the workpiece is selected as a reference point. Different surfaces are selected as measurement references. The intersection of the three surfaces is used to obtain the required measurement point. In order to reduce random error, six points on each surface are measured. The uniform layout method is used. Finally, the least square method is used to fit the plane to obtain accurate measurement results.

[0066] The machining error is evaluated by using a point-to-surface function in the module M5. A discrete detection point is used instead of an actual surface, and surface reconstruction is performed. The B-spline surface fitting method is usually used for surface reconstruction.

[0067] The B-spline surface is defined by p degrees in the u direction and q degrees in the v direction:

[0068]

[0069] Where P(u, v) is a point on the surface determined by u and v, C i,j represents a control point, and n and m represent the number of control points in the u and v directions, respectively, N i,p (u) and N j,q (v) are non-rational B-spline basis functions.

[0070] The standard part surface is reconstructed by the formula. The error between the measurement points of the test part obtained by the OMM system and the surface is calculated according to the following formula, i.e.

[0071]

[0072] Where i represents the number of measurement points; e i is the machining error of the test part excluding the measurement error of the OMM system; d e,i represents the distance from the measurement point of the OMM system to the calibrated standard part surface; p ot,i represents the measurement point of the OMM system; q e,i represents the corresponding point on the calibrated standard part surface to which the measurement point of the OMM system is mapped. represents the corresponding direction vector.

[0073] The module M5 calibrates the standard part, which includes:

[0074] The coordinate measuring machine measurement point P c {p c,i}(i = 1, 2,...) is reconstructed by the B-spline surface fitting method to obtain the coordinate measuring machine surface, which is marked as S c (u, v). It is considered as a standard part surface containing only machining error. The error and its coordinate components are calculated by the following formula:

[0075]

[0076] where p i is the OMM measurement point of the standard part; q i is the corresponding point on the surface normal of the standard part CMM measurement point; is the corresponding direction vector; δ x,i , δ y,i , δ z,i are the x, y, z direction components respectively; d p,i is the systematic error not including the machining error;

[0077] The error not including any machining error is superimposed on the design surface, which is marked as S d (u, v), the distance to the design surface is determined and the corresponding point is found, which is determined by the formula:

[0078]

[0079] where q' i is the corresponding point on the surface normal of the standard part CMM measurement point; is the point q i on the CMM surface; is the distance to the design surface;

[0080] The error is superimposed on the point q' i :

[0081]

[0082] which is expressed in coordinate components as:

[0083]

[0084] where q r,i is the coordinate of the point on the calibrated standard part surface; q x,r,i is the x coordinate value of the point on the calibrated standard part surface; q y,r,i is the y coordinate value of the point on the calibrated standard part surface; q z,r,i is the z coordinate value of the point on the calibrated standard part surface; q' x,i is the x coordinate value of the corresponding point on the theoretical surface; q' y,i is the y coordinate value of the corresponding point on the theoretical surface; q' z,i is the z coordinate value of the corresponding point on the theoretical surface; δ x,i is the component of the measurement error in the x direction not including any machining error; δ y,i is the component of the measurement error in the y direction not including any machining error; δ z,irepresents the component of the measurement error in the z direction that does not contain any processing errors; the surface is reconstructed using the calibration points.

[0085] In a third aspect, a computer readable storage medium storing a computer program is provided, the computer program, when executed by a processor, implements the steps in the high-precision comparison measurement method of in-machine measurement of a five-axis machine tool.

[0086] Compared with the prior art, the present application has the following beneficial effects:

[0087] 1、 The present application is designed according to a five-axis numerical control machine tool with a rotary shaft turntable, so the present application is suitable for in-machine measurement of all five-axis machine tools with rotary shaft turntables, and can be popularized to all five-axis machine tools.

[0088] 2、 The method provided by the present application makes the system errors of two workpieces during measurement the same to a great extent, and can measure the workpieces by using a comparison measurement method, thereby reducing the influence of system errors such as machine tool geometric errors and probe errors on the measurement results.

[0089] 3、 The method does not need additional machine tool system error detection and compensation, is simple and convenient to operate, efficient, and has significant cost-effectiveness.

[0090] Other beneficial effects of the present application will be described in the specific embodiments by introducing specific technical features and technical solutions, and those skilled in the art should be able to understand the beneficial technical effects brought by the technical features and technical solutions through the introduction of the technical features and technical solutions. BRIEF DESCRIPTION OF DRAWINGS

[0091] Other features, objects and advantages of the present application will become more apparent through reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0092] Figure 1 It is a schematic diagram of the overall process of the present application;

[0093] Figure 2 It is a schematic diagram of comparison measurement workpiece clamping;

[0094] Figure 3 It is a schematic diagram of in-machine measurement measurement path;

[0095] Figure 4 It is a "standard part" calibration schematic diagram. DETAILED DESCRIPTION

[0096] The application will be described in detail below with specific examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the application. These are within the scope of protection of the application.

[0097] The embodiment of the application provides a high-precision comparison measurement method for in-machine measurement of a five-axis machine tool, as shown in Figure 1 The step specifically comprises the following steps:

[0098] Step S1: obtaining surface point data of a workpiece by using a coordinate measuring machine (CMM), and taking the workpiece with the obtained surface point data as a standard piece;

[0099] Step S2: symmetrically clamping the standard piece and a workpiece to be tested on a rotary table of a machine tool, so that the position of the standard piece is the same as that of the workpiece to be tested after rotating 180 degrees;

[0100] Step S3: measuring the surface of the workpiece to be tested according to a set measurement path;

[0101] Step S4: rotating the C-axis of the machine tool by 180 degrees to make the position of the standard piece the same as that of the workpiece to be tested, and then measuring the surface of the workpiece to be tested by using the same measurement path as that in step S3;

[0102] Step S5: calibrating the surface of the standard piece by using the surface point data of the standard piece obtained by the CMM and the in-machine measurement point data of the standard piece obtained in step S4, so as to eliminate the machining error of the surface of the standard piece;

[0103] Step S6: calculating the error between the workpiece to be tested and the calibrated standard piece, and obtaining the surface error as the accurate measurement result after eliminating the in-machine measurement system error.

[0104] In step S1, the point data of the standard piece is measured by using a three-coordinate measuring machine, and the measurement process must be consistent with the subsequent in-machine measurement process, that is, the distribution of the measurement points is consistent.

[0105] In step S2, the measurement errors of the two measurements are ensured to be the same, and the two workpieces, that is, the standard piece and the workpiece to be tested, are symmetrically clamped, that is, after the C-axis is rotated by 180 degrees, the position of the standard piece must be the same as that of the workpiece to be tested before rotation, so as to ensure that the paths of the two measurements are the same.

[0106] The process of identifying and eliminating the rotation of the workpiece by 180 degrees itself introduces the geometric error of the C-axis rotation axis:

[0107] The geometric error of the C-axis includes three angle errors and three displacement errors, and represents the deviation between the reference coordinate system and the actual coordinate system, denoted as GE c = [ε x ε y ε z δ x δ y δ z T According to the active frame principle, the geometric error is regarded as an active frame rotating around the X-axis, Y-axis and Z-axis at the origin of the stationary frame by angles ε x , ε y , ε z , and translating in the X, Y and Z directions by δ x , δ y , δ z , and expressed as:

[0108]

[0109] According to the method of the homogeneous transformation matrix HTM, the geometric error of the C-axis kinematics transformation model is considered, and the position of a point is calculated as follows:

[0110]

[0111] The ideal position P ideal,1 ' of the ideal position of the point without containing the geometric error is calculated as:

[0112] P' ideal,1 = R(C)R'(C) -1 P'1

[0113] Finally, the measured point position data is inversely calculated by the above formula, and the C-axis error can be successfully eliminated.

[0114] Wherein, C represents the angle change between the two measurements of the C-axis; P1 represents the ideal position before rotation; P'1 represents the measured point of the OMM system; R represents the rotation matrix without containing the geometric error.

[0115] In step S3, the workpiece is measured, and the machine tool needs to be fully preheated.

[0116] The geometric error of the rotating shaft is measured by using a test block. The measurement of the geometric error is directly performed on the workpiece. The corner point on the workpiece is selected as the reference point. Different surfaces are selected as the measurement reference to obtain the required measurement point through the intersection of the three surfaces. In order to reduce random errors, six points on each surface are measured in a uniform layout. Finally, the least squares method is used to fit a plane to obtain accurate measurement results.

[0117] ​In step S5, the machining error is evaluated by using a point-to-surface function, using discrete detection points to replace the actual surface, and performing surface reconstruction, usually using a B-spline surface fitting method to perform surface reconstruction;

[0118] A B-spline surface is defined by p degrees in the u direction and q degrees in the v direction:

[0119]

[0120] Where P(u, v) is a point on the surface determined by u and v, C i,j represents the control points, and n and m represent the number of control points in the u and v directions, respectively, N i,p (u) and N j,q (v) are non-rational B-spline basis functions;

[0121] The standard part surface is reconstructed using the formula, and the error between the measurement points of the test part obtained by the OMM system and the surface is calculated according to the following formula, i.e.

[0122]

[0123] Where i represents the number of measurement points; e i is the machining error of the test part excluding the measurement error of the OMM system; d e,i represents the distance from the measurement point of the OMM system to the calibrated standard part surface; p ot,i represents the measurement point of the OMM system; q e,i represents the corresponding point on the calibrated standard part surface to which the measurement point of the OMM system is mapped; represents the corresponding direction vector.

[0124] Step S5 calibrates the standard part, including:

[0125] The coordinate measuring machine measurement point P c {p c,i}(i = 1, 2, …) is reconstructed into a surface using a B-spline surface fitting method, obtaining a coordinate measuring machine surface, marked as S c (u, v), which is considered as a standard part surface containing only machining error, and the error and its coordinate components are calculated by the following formula:

[0126]

[0127] Where: p i represents the OMM measurement point of the standard part; q i represents the OMM measurement point of the standard part mapped onto the standard part CMM measurement point, located on the surface normal; represents the corresponding direction vector; δ x,i , δ y,i , δz,i are the components in x, y, z directions respectively; d p,i denotes the systematic error without machining error;

[0128] The error without any machining error is superimposed on the design surface, which is marked as S d (u, v), the distance to the design surface is determined and the corresponding point is found, and the corresponding point is determined by the formula:

[0129]

[0130] where q' i denotes the corresponding point on the normal of the surface; denotes the point q on the CMM surface i to the design surface; denotes the corresponding direction vector;

[0131] The error is superimposed on the point q' i :

[0132]

[0133] is expressed as the coordinate components:

[0134]

[0135] where q r,i denotes the coordinates of the point on the calibrated standard part surface; q x,r,i denotes the x coordinate value of the point on the calibrated standard part surface; q y,r,i denotes the y coordinate value of the point on the calibrated standard part surface; q z,r,i denotes the z coordinate value of the point on the calibrated standard part surface; q' x,i denotes the x coordinate value of the corresponding point on the theoretical surface; q' y,i denotes the y coordinate value of the corresponding point on the theoretical surface; q' z,i denotes the z coordinate value of the corresponding point on the theoretical surface; δ x,i denotes the component of the measurement error without any machining error in the x direction; δ y,i denotes the component of the measurement error without any machining error in the y direction; δ z,i denotes the component of the measurement error without any machining error in the z direction; the surface is reconstructed using the calibration points.

[0136] The application also provides a high-precision comparison measurement system for five-axis machine tool on-machine measurement, which can be realized by performing the flow steps of the high-precision comparison measurement method for five-axis machine tool on-machine measurement, that is, the high-precision comparison measurement method for five-axis machine tool on-machine measurement can be understood as the preferred embodiment of the high-precision comparison measurement system for five-axis machine tool on-machine measurement by those skilled in the art. The system specifically includes the following contents:

[0137] Module M1: obtaining surface point data of a workpiece by using a coordinate measuring machine (CMM), and taking the workpiece with the obtained surface point data as a standard piece;

[0138] Module M2: symmetrically clamping the standard piece and the workpiece to be tested on a rotary table of a machine tool, so as to ensure that the positions of the standard piece and the workpiece are the same after being rotated by 180°;

[0139] Module M3: measuring the surface of the workpiece to be tested according to a set measurement path;

[0140] Module M4: rotating the C-axis of the machine tool by 180°, so that the positions of the standard piece and the workpiece are the same, and then measuring the surface of the workpiece to be tested by using the same measurement path as that of module M3;

[0141] Module M5: calibrating the surface of the standard piece by using the surface point data of the standard piece obtained by the coordinate measuring machine and the on-machine measurement point data of the standard piece obtained in module M4, so as to eliminate the machining error of the surface thereof;

[0142] Module M6: calculating the error between the workpiece to be tested and the calibrated standard piece, and obtaining the surface error as the accurate measurement result after eliminating the on-machine measurement system error.

[0143] In the module M1, the point data of the standard piece is measured by a three-coordinate measuring machine, and the measurement process must be consistent with the subsequent on-machine measurement process, that is, the distribution of the measured points is consistent;

[0144] In the module M2, the measurement errors of the two measurements are ensured to be the same, and the two workpieces, that is, the standard piece and the workpiece to be tested, are symmetrically clamped, that is, after the C-axis is rotated by 180°, the position of the standard piece must be the same as that of the workpiece to be tested before rotation, so as to ensure that the paths of the two measurements are the same;

[0145] The process of recognizing and eliminating the rotation of the workpiece by 180° itself introduces the geometric error of the C-axis rotation axis:

[0146] The geometric error of the C-axis includes three angle errors and three displacement errors, and the deviation between the reference coordinate system and the actual coordinate system is denoted as GE c =[ε x ε y εz δ x δ y δ z ] T According to the activity frame principle, the geometric error can be regarded as the rotation of the activity frame at the origin of the static frame around the X axis, Y axis and Z axis by angles ε x , ε y , ε z , and the translation in the X, Y and Z directions by δ x , δ y , δ z , and is expressed as:

[0147]

[0148] According to the method of the homogeneous transformation matrix HTM, the C-axis kinematics transformation model considering the geometric error is obtained, and the position of a point is calculated by the following method:

[0149]

[0150] and the ideal position P ideal,1 ' of the ideal position of the point without containing the geometric error is calculated:

[0151] P' ideal,1 =R(C)R'(C) -1 P'1

[0152] Finally, the C-axis error can be successfully eliminated by inversely calculating the measured point position data through the above formula;

[0153] Wherein, C represents the angle change between the two measurements of the C-axis; P1 represents the ideal position before rotation; P'1 represents the measured point of the OMM system; R represents the rotation matrix without containing the geometric error.

[0154] When the workpiece is measured in the module M3, the machine tool needs to be fully preheated;

[0155] The test block is used to measure the geometric error of the rotating shaft, and the measurement of the geometric error is directly performed on the workpiece. The corner point on the workpiece is selected as the reference point, different surfaces are selected as the measurement reference, and the intersection of the three surfaces is used to obtain the required measurement point. In order to reduce random error, six points on each surface are measured, and a uniform layout method is used. Finally, the least square method is used to fit the plane to obtain accurate measurement results.

[0156] In the module M5, the point-to-surface function is used to evaluate the machining error, the discrete detection points are used to replace the actual surface, and the surface reconstruction is performed. The B-spline surface fitting method is usually used for surface reconstruction.

[0157] A B-spline surface is defined by p degrees in the u direction and q degrees in the v direction:

[0158]

[0159] where P(u,v) is a point on the surface determined by u and v, C i,j represents the control points, n and m represent the number of control points in the u and v directions, respectively, N i,p (u) and N j,q (v) are non-rational B-spline basis functions;

[0160] The standard part surface is reconstructed by the formula, and the error between the test part measurement points obtained by the OMM system and the surface is calculated according to the following formula, i.e.

[0161]

[0162] where i represents the number of measurement points; e i is the machining error of the test part not containing the measurement error of the OMM system; d e,i represents the distance from the measurement point of the OMM system to the calibrated standard part surface; p ot,i represents the measurement point of the OMM system; q e,i represents the corresponding point of the measurement point of the OMM system mapped onto the calibrated standard part surface; represents the corresponding directional vector.

[0163] The module M5 calibrates the standard part, which includes:

[0164] The coordinate measuring machine measurement point P c {p c,i}(i=1, 2, …) is reconstructed by the B-spline surface fitting method to obtain the coordinate measuring machine surface, which is marked as S c (u,v), which is regarded as the standard part surface containing only machining error, and the error and its coordinate components are calculated by the following formula:

[0165]

[0166] where p i represents the OMM measurement point of the standard part; q i represents the OMM measurement point of the standard part mapped onto the standard part CMM measurement point, which is located on the surface normal; represents the corresponding directional vector; δ x,i , δ y,i , δ z,i are the x, y, and z directional components, respectively; d p,i represents the system error not containing machining error;

[0167] The error not containing any processing error is superimposed on the design surface, and the design surface is marked as S d (u, v), the distance from the design surface is determined and the corresponding point is found, and the corresponding point is determined by the formula:

[0168]

[0169] wherein q' i represents the corresponding point located on the normal of the curved surface; represents the point q on the surface of the CMM i to the distance of the design curved surface; represents the corresponding direction vector;

[0170] The error is superimposed on the point q' i :

[0171]

[0172] is expressed as coordinate components:

[0173]

[0174] wherein q r,i represents the coordinate of the point on the calibrated standard part curved surface; q x,r,i represents the x coordinate value of the point on the calibrated standard part curved surface; q y,r,i represents the y coordinate value of the point on the calibrated standard part curved surface; q z,r,i represents the z coordinate value of the point on the calibrated standard part curved surface; q' x,i represents the x coordinate value of the corresponding point on the theoretical curved surface; q' y,i represents the y coordinate value of the corresponding point on the theoretical curved surface; q' z,i represents the z coordinate value of the corresponding point on the theoretical curved surface; δ x,i represents the component of the measurement error in the x direction not containing any processing error; δ y,i represents the component of the measurement error in the y direction not containing any processing error; δ z,i represents the component of the measurement error in the z direction not containing any processing error; the surface is reconstructed using the calibration points.

[0175] Specifically, the implementation process of the present application is as follows:

[0176] Step 1: Before measurement, select a workpiece that has obtained surface point data as a "standard part".

[0177] Step 2: The "standard part" and the workpiece to be tested are symmetrically clamped on the rotary table of the machine tool, and it is ensured that after rotating 180°, the position of the "standard part" is the same as that of the test workpiece. In this way, when the measurements of steps 3 and 4 are performed, the measurement errors in the two measurement processes are approximately the same.

[0178] Step 3: Measure the surface of the test workpiece according to the planned measurement path, refer to Figure 2 .

[0179] Step 4: Rotate the C-axis of the machine tool by 180°, so that the position of the "standard part" is the same as that of the test workpiece, and then measure the surface of the test workpiece using the same measurement path as in Step 3, refer to Figure 2 .

[0180] Step 5: Use the "standard part" surface point data obtained by the coordinate measuring machine and the "standard part" in-machine measurement point data obtained in Step 4 to calibrate the "standard part" surface to eliminate the machining error of its surface.

[0181] Step 6: Calculate the error between the test workpiece and the calibrated "standard part". The resulting surface error is the accurate measurement result after eliminating the in-machine measurement error, thus achieving high-precision measurement.

[0182] In Step 1, the point data of the "standard part" is measured using a three-coordinate measuring machine. This measurement process must be as consistent as possible with the subsequent in-machine measurement process, that is, the distribution of measurement points for both measurements must be consistent.

[0183] In Step 1, in order to ensure that the system errors of the two measurements are the same, the two workpieces are symmetrically clamped in this example, as shown in Figure 2 . Even after the C-axis is rotated by 180°, the position of the "standard part" must be the same as that of the test workpiece before rotation. In theory, as long as the paths of the two measurements are the same, the system errors can remain consistent. However, it needs to be considered that the process of rotating by 180° itself will introduce geometric errors of the C-axis. Therefore, identification and elimination of C-axis geometric errors are also needed in this part.

[0184] P' ideal,1 = R(C) R'(C) -1 P'1

[0185] After completing the identification of C-axis geometric errors, the C-axis errors can be eliminated by inversely calculating the measured point data using the above formula.

[0186] When measuring the workpiece in Step 3, the machine tool is required to be fully preheated to prevent the change of thermal errors during the preheating process from adversely affecting the comparison results.

[0187] In Step 3, the distribution of measurement points can be uniform, and the planning of the measurement path follows Figure 3The principle is shown. It is noted that the present example adopts a "3+2" axis measurement strategy, aiming to avoid interference in the measurement process and reduce errors in the in-machine measurement through vertical measurement. Under this strategy, the workpiece is measured using five-axis linkage, although the geometric errors of the five axes are introduced, but they can be eliminated through the method in the present patent.

[0188] In step 4, the measurement process of the "standard part" is consistent with the measurement process of the test part. After measuring the test part, the C-axis of the machine tool is manually rotated 180°, the workpiece coordinate system is zeroed, and then the measurement is re-performed. In order to ensure that the time interval between measuring the "standard part" and measuring the test part is small, so as to prevent the cooling of the machine tool from having a greater impact on thermal error.

[0189] The calibration method of the "standard part" mentioned in step 5 needs attention. The three-coordinate measuring machine (CMM) is regarded as an accurate measurement means, which can approximately restore the machining error of the "standard part". However, in reality, it is impossible to completely eliminate the error by correcting the "standard part" or by comparing the measurements. Figure 4 The calibration process of the "standard part" is shown, in which the reconstructed surface of the coordinate measuring machine measurement point is regarded as the "standard part" surface containing only machining error. The error and its coordinate components can be calculated by the following formula:

[0190]

[0191] In the formula: q i is located on the surface normal; δ x,i , δ y,i , δ z,i are the components in x, y, z directions respectively; d p,i represents the form error not containing machining error.

[0192] In addition, the coordinate measuring machine points calculated in the previous step are used to determine the distance from the design surface and find the corresponding point. The corresponding point is determined by the formula:

[0193]

[0194] In the formula: q' i represents the corresponding point located on the surface normal.

[0195] The error is superimposed on the point q' i :

[0196]

[0197] In the formula, the calibration point of the "standard part" does not have machining error. In addition, the surface is reconstructed using the calibration point.

[0198] The error is calculated using the calibrated reconstructed surface obtained in step 5, and the error between the measurement points of the test piece obtained by the OMM and the surface is calculated according to the following formula, i.e.

[0199]

[0200] wherein i represents the number of measurement points, e i is the machining error of the test piece without the measurement error of the OMM system.

[0201] Next, the present application is described in more detail.

[0202] In the present application, a B-C double-turntable five-axis machine tool and an equal-ratio reduced S-shaped test piece are selected to illustrate the key part of the present application, including three main aspects:

[0203] P1 workpiece clamping and rotation axis geometric error identification and elimination:

[0204] To ensure that the system errors of the two measurements are the same, it is necessary to ensure that the two workpieces are installed symmetrically relative to the center, as Figure 2 shown. After the C-axis is rotated by 180°, the position of the "standard piece" must be the same as that of the test workpiece before rotation. In theory, as long as the paths of the two measurements are the same, the system error can remain unchanged. However, it needs to be noted that the rotation process will introduce additional geometric errors of the C-axis rotation axis. The geometric error caused by 180° rotation will not only cause the position of the test piece to deviate, but also affect the geometric error independent of the position. Therefore, in this part, we will determine and eliminate the geometric error of the C-axis. The geometric error of the C-axis includes 3 angle errors (unit: degree) and 3 displacement errors (unit: millimeter), which represent the deviation between the reference coordinate system and the actual coordinate system, denoted as GE c = [ε x ε y ε z δ x δ y δ z T According to the active frame principle, the geometric error can be expressed as an active frame rotating angles ε x , ε y , ε z around the X-axis, Y-axis, and Z-axis at the origin of the stationary frame, respectively, and translating δ x , δ y , δ z in the X, Y, and Z directions, respectively, which can be expressed as:

[0205]

[0206] ​According to the method of homogeneous transformation matrix (HTM), the position of a point can be calculated by the following formula:

[0207]

[0208] And the ideal position P of the point without geometric error can be calculated ideal,1 :

[0209] P' ideal,1 =R(C)R'(C) -1 P'1

[0210] Finally, the C-axis error can be successfully eliminated by the above formula for the measured point data.

[0211] Where C represents the angle change between the two measurements of the C-axis, and is also the rotation angle of the C-axis when measuring using the "3+2" strategy. The geometric error has been accurately identified before elimination. The present application uses a test block to measure the geometric error of the rotating shaft, which is efficient and practical. In order to avoid introducing additional measurement steps, the measurement of the geometric error is directly on the workpiece. We choose the corner point on the workpiece as the reference point, but due to the existence of error and the limitation of measurement conditions, it is not feasible to directly measure the corner point of the workpiece. Therefore, we measure different surfaces as measurement references, and obtain the required measurement points through the intersection of three surfaces. In order to reduce random error, six points on each surface are measured in a uniform layout. Finally, we use the least squares method to fit the plane to obtain accurate measurement results.

[0212] P2 comparison algorithm:

[0213] The main idea of the comparison measurement is to evaluate the machining error by using the point-to-surface function, and referring to the "standard part" surface calibrated in P3. In order to achieve this goal, discrete detection points are used instead of the actual surface, and surface reconstruction is carried out. The current research usually uses B-spline surface fitting method for surface reconstruction. The B-spline surface is defined by p degrees in the u direction and q degrees in the v direction,

[0214]

[0215] Where P(u,v) is a point on the surface determined by u and v, C i,j represents the control point, n and m represent the number of control points in the u and v directions respectively, N i,p (u) and N j,q (v) are non-rational B-spline basis functions. The "standard part" surface is reconstructed by the formula, and the surface calculated in P3 is marked as S r(u, v). Then the error of the test piece measurement points from the OMM to the surface is calculated according to the following equation:

[0216]

[0217] where i represents the number of measurement points, e i is the machining error of the test piece without the measurement error of the OMM system.

[0218] Correction of the "standard piece" P3:

[0219] In order to eliminate the influence of the system error in the on-machine measurement system on the measurement results by comparison measurement, the "standard piece" must have the accurate size and shape required by the theoretical design model, but it is impractical to achieve this in the machining process. Therefore, it is necessary to calibrate the machining error of the "standard piece" by using other higher-precision measurement means. If the machining error of the on-machine measurement points can be eliminated by calibration, the "standard piece" will only be affected by the on-machine measurement system error at the measurement points in the on-machine measurement system. The present application aims to regard the coordinate measuring machine as a reliable measurement form which can reproduce the machining error of the "standard piece". However, in practice, this is only an approximate method. By calibrating the "standard piece", although the influence of the machining error can be significantly reduced, it cannot be completely eliminated. The only solution is to pursue higher machining precision.

[0220] Figure 4 The calibration process of the "standard piece" is shown. p1 is the OMM measurement point. The coordinate measuring machine measurement points P c {p c,i The surface is reconstructed by the B-spline surface fitting method, and the coordinate measuring machine surface is obtained, marked as S c (u, v). It is regarded as the surface of the "standard piece" containing only machining error. The error and its coordinate components can be calculated by the following equation:

[0221]

[0222] where q i is located on the surface normal; δ x,i , δ y,i , δ z,i are the components in the x, y, z directions respectively; d p,i represents the system error without machining error.

[0223] In addition, it is necessary to superimpose the error without any machining error on the design surface, which is marked as S d (u, v). However, it is not directly feasible to determine the theoretical points that need to be superimposed on the design surface. Therefore, it is necessary to use the points qi to determine the distance from the design surface and find the corresponding point. The corresponding point is determined using the formula:

[0224]

[0225] where q' = q + e i represents the corresponding point located on the normal of the curved surface.

[0226] The error is superimposed on the point q' i :

[0227]

[0228] in terms of coordinate components:

[0229]

[0230] where the calibration points of the "standard part" do not have machining errors. In addition, the surface is reconstructed using the calibration points, and the error is calculated using the comparison method specified by P2.

[0231] The embodiment of the present application provides a high-precision comparison measurement method and system for in-machine measurement of a five-axis machine tool. The five-axis numerical control machine tool with a rotary shaft turntable is designed, so that the present application is suitable for in-machine measurement of all five-axis machine tools with rotary shaft turntables, and can be extended to all five-axis machine tools. This method largely makes the system errors of two workpieces during measurement the same, and can measure the workpieces by using the comparison measurement method, thereby reducing the influence of machine tool geometric error, probe error and other system errors on the measurement result. Most importantly, the present application does not need additional machine tool system error detection and compensation, is simple to operate, efficient, and has significant cost-effectiveness.

[0232] Those skilled in the art know that, in addition to implementing the system and each device, module and unit thereof provided by the present application in the form of pure computer readable program code, the system and each device, module and unit thereof provided by the present application can also be implemented in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers and embedded microcontrollers by logically programming the method steps to achieve the same functions. Therefore, the system and each device, module and unit thereof provided by the present application can be considered as a hardware component, and the devices, modules and units included therein for achieving various functions can also be considered as structures within the hardware component; the devices, modules and units for achieving various functions can also be considered as both software modules for implementing methods and structures within hardware components.

[0233] 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 at will without conflict.

Claims

1. A high-precision alignment measurement method of a five-axis machine tool in-machine measurement, characterized by, The method comprises the following steps: Step S1: obtaining surface point data of a workpiece by using a coordinate measuring machine, and taking the workpiece with the obtained surface point data as a standard workpiece; Step S2: symmetrically clamping the standard workpiece and the workpiece to be tested on a rotary table of a machine tool, so that the position of the standard workpiece is the same as that of the workpiece to be tested after the rotary table is rotated by 180 degrees; Step S3: measuring the surface of the workpiece to be tested according to a set measurement path; Step S4: rotating the C-axis of the machine tool by 180 degrees so that the position of the standard workpiece is the same as that of the workpiece to be tested, and then measuring the surface of the standard workpiece by using the same measurement path as that in step S3; Step S5: calibrating the surface of the standard workpiece by using the surface point data of the standard workpiece obtained by the coordinate measuring machine and the in-machine measurement point data of the standard workpiece obtained in step S4, so as to eliminate the machining error of the surface of the standard workpiece; Step S6: calculating the error between the workpiece to be tested and the calibrated standard workpiece, and obtaining the surface error as the accurate measurement result after eliminating the in-machine measurement system error; In step S5, the machining error is evaluated by using a point-to-surface function, discrete detection points are used to replace the actual surface, surface reconstruction is performed, and a B-spline surface fitting method is used for surface reconstruction; The B-spline surface is defined by p degrees in the u direction and q degrees in the v direction: where P(u, v) is a point on the surface determined by u and v, C i,j denotes the control points, n and m denote the number of control points in the u and v directions, respectively, N i,p (u) and N j,q (v) are non-rational B-spline basis functions. The standard workpiece surface is reconstructed by using a formula, and the error between the measurement point of the workpiece to be tested obtained by the OMM system and the surface is calculated according to the following formula: where i represents the number of measuring points; e i is the processing error of the test piece not containing the OMM system measurement error; d e,i represents the distance from the measuring point of the OMM system to the calibrated standard piece surface; p ot,i represents the measuring point of the OMM system; q e,i represents the corresponding point on the calibrated standard piece surface to which the measuring point of the OMM system is mapped; represents the corresponding direction vector; The step S5 of calibrating the standard workpiece comprises: The coordinate measuring machine measurement point P c {p c,i} are fitted by B-spline surface fitting method to obtain the coordinate measuring machine surface, marked as S c (u, v), which is regarded as the standard part surface containing only machining errors. The error and its coordinate components are calculated by the following formula: where: p i q represents the OMM measurement point of the standard part; q i represents the mapping of the OMM measurement point of the standard part onto the CMM measurement point of the standard part, lying on the surface normal; represents the corresponding direction vector; δ x,i , δ y,i , δ z,i are the components in the x, y, z directions, respectively; d p,i represents the systematic error not including machining error; The error, which does not include any processing errors, is superimposed on the design surface, which is marked S d (u, v), determine the distance to the design surface and find the corresponding point, which is determined using the formula: where q' i denotes the corresponding point on the surface normal; denotes the point q on the CMM surface i distance to the design surface; denotes the corresponding direction vector; adding the error to the point q' i : wherein q r,i represents the coordinates of the point on the calibrated standard part surface.

2. The high-precision alignment measurement method of five-axis machine tools in-machine measurement according to claim 1, characterized in that, The step S1 comprises: measuring the point data of the standard workpiece by using a three-coordinate measuring machine, and the measurement process must be consistent with the subsequent in-machine measurement process, that is, the distribution of the measurement points is consistent.

3. The high-precision alignment measurement method of in-machine measurement of a five-axis machine tool according to claim 1, characterized in that, In step S2, the measurement error of the two measurements is ensured to be the same, and the two workpieces are symmetrically clamped, that is, the position of the standard workpiece must be the same as that of the workpiece to be tested after the C-axis is rotated by 180 degrees, so that the measurement paths of the two measurements are the same; The process of identifying and eliminating the workpiece rotation by 180 degrees itself introduces the geometric error of the C-axis rotation axis: The geometric errors of the C-axis include three angle errors and three displacement errors, representing the deviation between the reference coordinate system and the actual coordinate system, denoted as GE c = [ε x ε y ε z δ x δ y δ z ] T According to the active frame principle, the geometric errors are regarded as the rotation of the active frame around the X-axis, Y-axis and Z-axis at the origin of the stationary frame by angles ε x , ε y , ε z , and the translation in the X, Y and Z directions by δ x , δ y , δ z , expressed as: According to the method of the homogeneous transformation matrix HTM, the C-axis kinematics transformation model considering the geometric error is obtained, and the position of an arbitrary point is calculated by the following formula: and the ideal position P of the point not containing geometric error is calculated ideal,1 ideal position: P' ideal,1 = R(C)R'(C) -1 P'1 Finally, the point data measured by the above formula is inversely calculated, and the C-axis error can be successfully eliminated. Wherein, C represents the angle change between the two measurements of the C-axis; P1 represents the ideal position before rotation; P'1 represents the measurement point of the OMM system; R represents the rotation matrix without geometric error.

4. The high-precision alignment measurement method of in-machine measurement of a five-axis machine tool according to claim 1, characterized in that, In step S3, the machine tool needs to be fully preheated when the workpiece is measured.

5. The high-precision alignment measurement method of in-machine measurement of a five-axis machine tool according to claim 1, characterized in that, The geometric error of the rotation axis is measured by using a test block, the measurement of the geometric error is directly performed on the workpiece, an angular point on the workpiece is selected as a reference point, different surfaces are selected as measurement references, and the required measurement points are obtained through the intersection of the three surfaces. In order to reduce random errors, six points on each surface are measured, and a uniform layout is adopted. Finally, a least square method is used to fit a plane to obtain accurate measurement results.

6. The high-precision alignment measurement method of in-machine measurement of a five-axis machine tool according to claim 1, characterized in that, In step S5: The coordinate components are represented as: wherein q x,r,i represents the x coordinate value of the point on the calibrated standard part surface; q y,r,i represents the y coordinate value of the point on the calibrated standard part surface; q z,r,i represents the z coordinate value of the point on the calibrated standard part surface; q' x,i represents the x coordinate value of the corresponding point on the theoretical surface; q' y,i represents the y coordinate value of the corresponding point on the theoretical surface; q' z,i represents the z coordinate value of the corresponding point on the theoretical surface; δ x,i represents the component of the measurement error in the x direction not containing any machining error; δ y,i represents the component of the measurement error in the y direction not containing any machining error; δ z,i represents the component of the measurement error in the z direction not containing any machining error; the surface is reconstructed using the calibration points.

7. A high-precision alignment measurement system for in-machine measurement of a five-axis machine tool, characterized in that The method comprises the following steps: Module M1: Obtain surface point data of the workpiece by using a coordinate measuring machine, and take the workpiece with the obtained surface point data as a standard piece; Module M2: Symmetrically clamp the standard piece and the workpiece to be tested on a rotary table of a machine tool, so as to ensure that the position of the standard piece is the same as that of the workpiece to be tested after rotating 180°; Module M3: Measure the surface of the workpiece to be tested according to a set measurement path; Module M4: Rotate the C-axis of the machine tool by 180°, so that the position of the standard piece is the same as that of the workpiece to be tested, and then measure the surface of the standard piece by using the same measurement path as that in module M3; Module M5: Calibrate the surface of the standard piece by using the surface point data of the standard piece obtained by the coordinate measuring machine and the in-machine measurement point data of the standard piece obtained in module M4, so as to eliminate the machining error of the surface of the standard piece; Module M6: Calculate the error between the workpiece to be tested and the calibrated standard piece, and obtain the surface error as the accurate measurement result after eliminating the in-machine measurement system error; In module M5, the machining error is evaluated by using a point-to-surface function, discrete detection points are used to replace the actual surface, surface reconstruction is performed, and a B-spline surface fitting method is used for surface reconstruction; The B-spline surface is defined by p degrees in the u direction and q degrees in the v direction: where P(u, v) is a point on the surface determined by u and v, C i,j denotes the control points, n and m denote the number of control points in the u and v directions, respectively, N i,p (u) and N j,q (v) are non-rational B-spline basis functions. The standard piece surface is reconstructed by using a formula, and the error between the measurement point of the workpiece to be tested obtained by the OMM system and the surface is calculated according to the following formula: where i represents the number of measuring points; e i is the processing error of the test piece not containing the OMM system measurement error; d e,i represents the distance from the measuring point of the OMM system to the calibrated standard piece surface; p ot,i represents the measuring point of the OMM system; q e,i represents the corresponding point on the calibrated standard piece surface to which the measuring point of the OMM system is mapped; represents the corresponding direction vector; The module M5 for calibrating the standard piece includes: The coordinate measuring machine measurement point P c {p c,i}(i = 1, 2,...) are reconstructed by B-spline surface fitting method to obtain the coordinate measuring machine surface, marked as S c (u, v), which is regarded as a standard part surface containing only machining errors, and the error and its coordinate components are calculated by the following formula: where: p i q represents the OMM measurement point of the master part; q i represents the mapping of the OMM measurement point of the master part onto the CMM measurement point of the master part, lying on the surface normal; represents the corresponding direction vector; δ x,i , δ y,i , δ z,i are the components in the x, y, z directions, respectively; d p,i represents the systematic error not including machining error; The error, which does not include any processing errors, is superimposed on the design surface, which is marked S d (u, v), the distance from the design surface is determined and the corresponding point is found, which is determined using the formula: where q' = q + q i represents the corresponding point on the surface normal; represents the point q on the CMM surface i distance to the design surface; represents the corresponding direction vector; adding the error to the point q' i : wherein q r,i represents the coordinates of the point on the calibrated standard part surface.

8. The high-precision alignment measurement system for in-machine measurement of a five-axis machine tool according to claim 7, characterized in that, The module M1 includes: measuring the point data of the standard piece by using a three-coordinate measuring machine, and the measurement process must be consistent with the subsequent in-machine measurement process, that is, the distribution of the measurement points is consistent; In module M2, the measurement error of the two measurements is ensured to be the same, and the two workpieces, the standard piece and the workpiece to be tested, are symmetrically clamped, that is, after the C-axis is rotated by 180°, the position of the standard piece must be the same as that of the workpiece to be tested before rotation, so as to ensure that the measurement paths of the two measurements are the same; The process of rotating the workpiece by 180° itself introduces the geometric error of the C-axis rotation axis: The geometric errors of the C-axis include three angle errors and three displacement errors, representing the deviation between the reference coordinate system and the actual coordinate system, denoted as GE c = [ε x ε y ε z δ x δ y δ z ] T According to the active frame principle, the geometric errors are regarded as the rotation of the active frame around the X-axis, Y-axis and Z-axis at the origin of the stationary frame by angles ε x , ε y , ε z , and the translation in the X, Y and Z directions by δ x , δ y , δ z , and expressed as: According to the method of the homogeneous transformation matrix HTM, the C-axis kinematics transformation model considering the geometric error is obtained, and the position of an arbitrary point is calculated by the following method: and the ideal position P of the point not containing geometric error is calculated ideal,1 ideal position: P' ideal,1 = R(C)R'(C) -1 P'1 Finally, the point data measured by the above formula is inversely calculated, and the C-axis error can be successfully eliminated; Wherein, C represents the angle change between the two measurements of the C-axis; P1 represents the ideal position before rotation; P'1 represents the measurement point of the OMM system; R represents the rotation matrix without geometric error; In module M3, the machine tool needs to be fully preheated when measuring the workpiece; A test block is used to measure the geometric error of the rotation axis, the measurement of the geometric error is directly performed on the workpiece, an angular point on the workpiece is selected as a reference point, different surfaces are measured as measurement references, and the required measurement points are obtained through the intersection of the three surfaces, in order to reduce random errors, six points on each surface are measured, and a uniform layout is adopted, finally, a least square method is used to fit a plane to obtain an accurate measurement result; In module M5, it is expressed by coordinate components as follows: wherein q x,r,i represents the x coordinate value of a point on the calibrated standard part surface; q y,r,i represents the y coordinate value of a point on the calibrated standard part surface; q z,r,i represents the z coordinate value of a point on the calibrated standard part surface; q x,i represents the x coordinate value of the corresponding point on the theoretical surface; q y,i represents the y coordinate value of the corresponding point on the theoretical surface; q z,i represents the z coordinate value of the corresponding point on the theoretical surface; δ x,i represents the component of the measurement error in the x direction not including any machining error; δ y,i represents the component of the measurement error in the y direction not including any machining error; δ z,i represents the component of the measurement error in the z direction not including any machining error; the surface is reconstructed using the calibration points.

9. A computer readable storage medium storing a computer program, characterized in that, The computer program, when executed by a processor, implements the steps of the high-precision alignment measurement method of the in-machine measurement of the five-axis machine tool according to any one of claims 1 to 6.

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