A method for identifying geometric errors of rotary axes of five-axis machine tools based on machining tests

Abstract

A five-axis machine tool rotary axis geometric error identification method based on machining testing includes: 1. Design of a feature workpiece; 2. Machining of the feature workpiece: machining two identical arc surfaces and two identical rectangular grooves on the same side of the workpiece; 3. On-machine measurement of the workpiece: after machining the feature workpiece, the machine tool is cooled to room temperature, and the data of each arc surface and each rectangular groove of the workpiece at room temperature is measured using the machine tool's on-machine measurement system; 4. Identification of the machine tool rotary axis geometric error: processing the data detected in step 3 to obtain three position error models and three direction error models, thereby identifying the position-independent geometric error of the rotary axis. The present invention has a simple identification mode and high identification efficiency, thereby improving the machining accuracy of the five-axis CNC machine tool.

Description

Technical Field

[0001] The invention belongs to the technical field of machining accuracy of numerically controlled machine tools, and relates to a method for identifying geometric errors of a rotating axis of a five-axis machine tool based on machining tests. Background Art

[0002] With the continuous development and progress of the manufacturing industry, five-axis machine tools, as the "industrial mother machine" of modern manufacturing, have the advantages of high productivity and flexibility, and are widely used in the aerospace field.

[0003] Compared to traditional three-axis machine tools, five-axis machine tools have two additional rotational axes. These two additional rotational axes involve a greater number of interdependent error elements, significantly increasing the corresponding technical challenges. Among these errors, position-independent geometric errors (PIGEs) are caused by component assembly issues, load variations, and thermal drift during machine tool production.

[0004] Current research on PIGEs for rotary axes relies primarily on expensive measurement equipment, such as optical displacement sensors and ballbars. While these methods offer high accuracy, they are complex and expensive to prepare, require a certain level of operator experience, and fail to consider the actual machining conditions of machine tools. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for identifying the geometric errors of the rotary axes of five-axis machine tools based on machining tests. This method identifies and compensates for the geometric errors of the coupled five-axis machine tools' rotary axes based on a characteristic workpiece. During machining and measurement of each surface of the characteristic workpiece, the tool and probe travel paths are consistent. The geometric parameters of the finished workpiece are obtained through in-machine measurement, and workpiece self-calibration is used to eliminate the influence of linear axis errors on rotary axis errors.

[0006] The geometric error identification method of the five-axis machine tool rotary axis based on machining test includes the following steps:

[0007] 1. Design of feature workpiece: Design a feature workpiece of a certain size, with the main body being a cube, and cut out two arc surfaces of the same size and two rectangular slots of the same size;

[0008] 2. Machining of feature workpieces: With all axes of the machine tool stationary and the B and C axes at 0°, the workpiece is mounted on the worktable and the linear axes X, Y, and Z are adjusted to their initial positions. Two identical circular surfaces and two identical rectangular grooves on the same side are machined on the workpiece. During the cutting process of each pair of circular surfaces and pair of rectangular grooves, the linear axes move along the same trajectory.

[0009] 3. On-machine measurement of the workpiece: After the feature workpiece is machined, the machine tool is cooled to room temperature. The on-machine measurement system of the machine tool is used to measure the data of each arc surface and each rectangular slot of the workpiece at room temperature. The rotating axes B and C are returned to 0° and kept stationary. The X, Y, and Z axes are used to measure the fitting center lines of the two arc surfaces and the fitting straight lines in the length direction of the same machined surface in the two rectangular slots.

[0010] 4. Identification of geometric errors of machine tool rotary axes

[0011] First, the data obtained from the detection in step three is processed to obtain three position error models and three direction error models; then, a rotation transformation is performed on the obtained error models, and the rotation angles of the B-axis and the C-axis are substituted into the error models; when the B-axis and the C-axis are both 0°, three geometric errors of the rotation axis of the arc surface under machine measurement that are independent of position, and the remaining two geometric errors of the rotation axis of the rectangular slot under machine measurement that are independent of position are obtained, thereby completing the identification of the geometric error of the rotation axis.

[0012] The beneficial effects of the present invention compared to the prior art are:

[0013] The present invention identifies and compensates for the geometric errors of the coupled five-axis machine tool's rotating axes based on the design of the characteristic workpiece, designs two processing modes, adopts the workpiece self-calibration method, and correctly sets the machine tool coordinate system, so that the identified errors can be complete but not redundant. The machine tool's on-machine measurement system is used to measure the features under the two processing modes (circular surface and rectangular groove), and the geometric errors of the dual rotating axes are identified in combination with the analytical method. During the processing of the workpiece, the processing trajectories of the linear axes set in the two processing modes are kept consistent to avoid the influence of linear axis related errors. Thereby achieving the purpose of improving the overall processing accuracy of the five-axis CNC machine tool. Not only is the geometric error of the machine tool's rotating axis identified while excluding the influence of the linear axis error, but the cost is greatly saved. The designed identification mode is simpler and has high identification efficiency, which fundamentally improves the processing accuracy of the five-axis CNC machine tool.

[0014] Compared with traditional methods, the present invention focuses on the identification of PIGEs in the past, which focused on measuring machine tool errors using measuring instruments such as dual ballbars (DBBs), optical displacement sensors, and R-tests. However, these measuring instruments are expensive and complex to prepare in advance, require certain experience from the operator, and do not consider the actual processing conditions of the machine tool, making them unsuitable for most machine tool users. Currently, some researchers use cutting tests to identify the PIGEs of rotary axes, but they can identify the PIGEs of two rotary axes at the same time, and the identified errors are complete but not redundant, and can exclude the influence of linear axis errors on rotary axis errors. Furthermore, there is currently no simple and quick identification method.

[0015] The method designed by this invention for identifying errors using workpiece features is low-cost and not only solves the problem of improving machine tool accuracy for general machine tool users, but also avoids the interference of linear axis errors during the identification process. The obtained results are closer to the actual working conditions of the machine tool, which is of great significance for improving the compensation efficiency and machining accuracy of five-axis CNC machine tools. The purpose of this invention is to achieve simple and rapid identification of PIGEs of rotary axes at low cost and without the need for specific and complex measurement settings.

[0016] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments: BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart of the geometric error identification method of the five-axis machine tool rotary axis based on machining test of the present invention;

[0018] Figure 2 It is the isometric view of the feature workpiece;

[0019] Figure 3 The workpiece size drawing;

[0020] Figure 4 Schematic diagram of the simplified geometric errors required for the B-axis and C-axis;

[0021] Figure 5 Schematic diagram of the geometric errors to be identified for the B-axis and C-axis;

[0022] Figure 6 Name and mark the workpiece processing surface;

[0023] Figure 7 The probe trajectory and measuring point distribution diagram on the machining surfaces U1 and U2 of the finished workpiece;

[0024] Figure 8 The figure is a schematic diagram of the fitting of the measuring points on the machining surfaces U1 and U2 of the finished workpiece;

[0025] Figure 9 This is an example diagram of the geometric error of the finished workpiece after machining the arc surface;

[0026] Figure 10 This is an example diagram of the geometric error of the finished workpiece after machining a rectangular groove. DETAILED DESCRIPTION

[0027] The embodiments of the technical solution of the present invention will be described in detail below with reference to the accompanying drawings. Unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0028] like Figure 1As shown in FIG, the geometric error identification method of the five-axis machine tool rotary axis based on machining test includes the following steps:

[0029] 1. Design of feature workpiece: Design a feature workpiece of a certain size, with the main body being a cube, and cut out two arc surfaces of the same size and two rectangular slots of the same size, such as Figure 2 As shown;

[0030] 2. Machining of feature workpieces: With all axes of the machine tool stationary and the B and C axes at 0°, the workpiece is mounted on the worktable and the linear axes X, Y, and Z are adjusted to their initial positions. Two identical circular surfaces and two identical rectangular grooves on the same side are machined on the workpiece. During the cutting process of each pair of circular surfaces and pair of rectangular grooves, the linear axes move along the same trajectory.

[0031] 3. On-machine measurement of workpieces: After the feature workpiece is machined, the machine tool is cooled to room temperature. The on-machine measurement system of the machine tool is used to measure the data of each arc surface and each rectangular slot of the workpiece at room temperature. The rotating axes B and C are returned to 0° and kept stationary. The X, Y, and Z axes are used to measure the fitting center lines of the two arc surfaces and the fitting straight lines in the length direction of the same machined surface in the two rectangular slots.

[0032] 4. Identification of geometric errors of machine tool rotary axes

[0033] First, the data obtained from the detection in step three is processed to obtain three position error models and three direction error models; then, a rotation transformation is performed on the obtained error models, and the rotation angles of the B-axis and the C-axis are substituted into the error models; when the B-axis and the C-axis are both 0°, three geometric errors of the rotation axis of the arc surface under machine measurement that are independent of position, and the remaining two geometric errors of the rotation axis of the rectangular slot under machine measurement that are independent of position are obtained, thereby completing the identification of the geometric error of the rotation axis.

[0034] The specific processing steps are as follows:

[0035] For example, the blank size is 100×100×100mm 3 The main body of the cubic workpiece is a cubic block. Two arc surfaces of the same size and diameter of φ106 are cut out. The center lines of the circles theoretically coincide with the center of the cube. Figure 2 、 Figure 3 、 Figure 5 and Figure 6 As shown;

[0036] Place the blank on the machine table and clamp it. Input the pre-written program and optimized process parameters into the CNC panel of the five-axis CNC machine. Adjust the B and C axes of the machine to 0°, and adjust the X, Y, and Z axes to an initial position.

[0037] Using the movement of the X-axis, Y-axis and Z-axis, a circular arc surface with a diameter of φ106 and a depth of 35mm is machined by a vertical milling cutter as a reference surface, and then the three linear axes X, Y and Z axes return to their initial positions.

[0038] Further, combined with Figure 4 and Figure 5 Description: The arc surface processing process of step 2 is as follows: Step 1, the initial position of the workpiece is at the center position of the C-axis. When the rotating axes B and C are both 0°, the linear axes X, Y and Z are used to move and the vertical milling cutter processes an arc surface of a certain diameter as the measurement reference surface under this processing mode. After the measurement reference surface is cut, the linear axes X, Y and Z return to the initial position; Step 2, the B-axis remains stationary, and the C-axis is rotated to 90°. The linear axis is used to perform a second cutting with the same travel trajectory as in step 1 to process an arc surface of the same size as in step 1.

[0039] For example: Figure 3 As shown in the figure, the initial position of the workpiece is at the center of the C-axis. When the machine tool's rotary axes B and C are both at 0°, the vertical milling cutter uses the motion of the linear axes X, Y, and Z to machine a Φ106 arc surface as the measurement reference surface in this machining mode. After the measurement reference surface is cut, the three linear axes return to the initial position P0. This machining process is recorded as step 1. Then, the rotary axis B remains stationary, the C-axis is rotated to 90°, and the linear axes are used to perform a second cut using the same travel trajectory as step 1, also machining a Φ106 arc surface. This machining process is recorded as step 2. Therefore, the center lines corresponding to the two arc surfaces machined in steps 1 and 2 theoretically coincide.

[0040] Furthermore, the rectangular groove machining process in step 2 is as follows: Step 1-1, first return the rotary axis B and C axis to 0°, and the linear axes X, Y, and Z axes to their initial positions. Then, the rotary axis C axis remains stationary, and the B axis is rotated to 90°. Using the movement of the linear axes X, Y, and Z axes, a rectangular groove of a certain size is machined with the upright milling cutter, which serves as the measurement reference surface in this machining mode. After the cutting is completed, the linear axes X, Y, and Z return to their initial positions. Step 1-2, then the rotary axis B axis remains stationary, and the C axis is rotated to 90°. A second cutting is performed using the same linear axis travel trajectory as in step 2, to machine a rectangular groove of the same size as in step 1). For example, a rectangular groove with a depth of 70mm and a width and thickness of 20mm is machined.

[0041] For example, combined with Figure 3Instructions: First, return the machine tool's rotary axis B and C axis to 0°, and the linear axes X, Y, and Z axes to their initial position P0. Then, keep the machine tool's rotary axis C axis stationary, rotate the B axis to 90°, and use the movement of the linear axis to machine a size such as Figure 3 The rectangular groove shown is used as the measurement reference surface in this processing mode. After cutting is completed, the three linear axes return to the initial position P0. This processing process is recorded as step 1-1. Subsequently, the rotary axis B axis remains stationary, and the C axis is rotated to 90°. The second cutting is performed using the same linear axis travel trajectory as in step 3 to process a rectangular groove with dimensions as shown in FIG. Figure 5 As shown, the processing process is recorded as step 1-2. Therefore, the size and direction of the bottom surface and side surface corresponding to the two rectangular grooves processed in steps 1-1 and 1-2 are theoretically the same.

[0042] In processing modes 1 and 2, the processing trajectories of the linear axes set in the modes remain consistent to avoid the influence of linear axis related errors.

[0043] When measuring on the machine, the four machining surfaces of the finished workpiece are measured with U i (i=0,1,2,3) for naming, such as Figure 6 As shown in the figure, U represents the machining surface of the workpiece, and i is used to distinguish different machining surfaces. When the B-axis and C-axis of the machine tool are both 0°, the reference surface machined in step 1 is recorded as U0. Similarly, the arc surface and rectangular surface machined in step 2, step 1-1 and step 1-2 are recorded as U1, U2 and U3 respectively.

[0044] Furthermore, in the on-machine measurement of step three, the measurement strategy for the arc surface is: return the rotating axes B and C to 0° and keep them stationary, perform on-machine measurement on the processed arc surface, select N groups of measuring points, in the first group of measuring points, the Z axis of the machine tool remains stationary, only the X and Y axes move to different measurement positions, in the second to N groups of measuring points, the movement distance of the Z axis is uniform, and in the measurement process of each group of measuring points, the movement trajectory of the X and Y axes is the same as that of the first group of measurements; the measurement strategy for the rectangular slot is to measure with the rotating axes B and C axes both at 0°, and perform on-machine measurement on the processed side surface.

[0045] Specifically: Figure 6 In the example, the center lines corresponding to the workpiece's machining surfaces U0 and U1 theoretically coincide, and the size and orientation of the bottom and side surfaces corresponding to machining surfaces U2 and U3, respectively, are theoretically identical. Therefore, in the measurement plan, the measurement data of machining surfaces U0 and U2 serves as a reference for other measurements in machining modes 1 and 2, respectively. The data for the workpiece's machining surfaces U0, U1, U2, and U3 are all measured with both the B and C axes at 0°.

[0046] The measurement strategy for machining arc surfaces takes the measurement solution on the machining surface U1 of the finished workpiece as an example. Figure 7 As shown, the B- and C-axes are both returned to 0° and held stationary, and then the machine surface U1 is measured on-machine using a touch-trigger probe. In the first set of measurement points, the machine's Z axis remains stationary, while the X and Y axes move to different measurement positions. In the second through fifth sets of measurement points, the Z axis moves uniformly, and the X and Y axis movement paths during each measurement are identical to those in the first set. Similarly, with the B- and C-axes both at 0°, the machine surface U0 is measured on-machine using a touch-trigger probe.

[0047] The measurement strategy for machining rectangular grooves takes the measurement scheme on the machining surface U2 of the finished workpiece as an example. The measurement of the machining surface U2 is also measured with both the B axis and the C axis at 0°. The machining surface U2 is measured on the machine using a contact trigger probe, as shown in the following example: Figure 7 Similarly, the rotation axes B and C are both at 0° and remain stationary, and the machining surface U3 is measured on-machine using a contact trigger probe.

[0048] In the measurement plan, the measuring points are arranged based on the principle that the center lines corresponding to the measuring points on the processing surfaces U0 and U1 theoretically coincide, and the straight lines fitted by the measuring points on the processing surfaces U2 and U3 coincide during the processing process, and then on-machine measurement is performed.

[0049] For example: Figure 8 As shown, the whole finished workpiece has a total of (2×5×3+2×12) measuring points. The measuring points of the machining surface U0 and U1 are fitted with the center line, and the symbol N is used. i,j,m 、S k,i and L i (i=0,1;j=1,2,3,4,5;k=1,2,3,4,5;m=1,2,3) respectively name the measuring points, the center points of each group of measuring points, and the center line of each group of center points, where N, S and L respectively represent the measuring points, the center points of each group of measuring points, and the center line of each group of center points after fitting. i and j are used to distinguish different machining surfaces and different numbers of measuring point groups on the machining surface, respectively. k represents the number of center points after fitting, and m represents the number of measuring points in each group. Therefore, the machining surface measuring points are recorded as N i,j,m , the center of the circle fitted by each set of measurement points is recorded as S k,i , the center line of each set of circle center points is recorded as L i .exist Figure 8 In the figure, taking the measuring points on the machining surface U1 of the finished workpiece as an example, there are 5 groups of measuring points in total, each group has 3 measuring points, which are respectively denoted as N 1,1,1 …N 1,5,3 , the circle center points corresponding to the five groups of measuring points are obtained based on the principle of determining the circle center by three points, and are recorded as S 1,1…S 5,1 , and then the five center points are fitted by the least square method, and the best fitting center line is recorded as L1. Similarly, the measurement point data on the machining surface U0 of the finished workpiece are processed and analyzed, and the five center points can be obtained and recorded as S 1,0 …S 5,0 , and a center line is marked as L0. Fit the straight line to the measuring points of the machining surface U2 and U3, and use the symbol X m,i and Y i (m=1,2,3…12;i=2,3;) respectively name the measuring points and the fitted straight line, where X and Y represent the measuring points and the fitted straight line respectively, and i and m are used to distinguish different machining surfaces and different measuring points on the machining surface respectively. Therefore, the machining surface measuring point is recorded as X m,i , the straight line passing through the measuring points is recorded as Y i .exist Figure 8 In the figure, taking the measuring points on the machining surface U2 of the finished workpiece as an example, there are 12 measuring points in total, which are denoted as X 1,2 …X 12,2 , the 12 measuring points are fitted by the least square method, and the best fitting straight line is recorded as Y2. Similarly, the measuring point data on the machining surface U3 of the finished workpiece are processed and analyzed, and the 12 measuring points can be obtained and recorded as X 1,3 …X 12,3 , and the best fitting straight line is recorded as Y3.

[0050] Before introducing the geometric error identification of dual rotary axes of machine tools, Figure 4 Schematic diagram of the simplified geometric errors required for the B-axis and C-axis; Figure 5 Schematic diagram of the geometric errors to be identified for the B-axis and C-axis;

[0051] Table 1 Position-independent geometric errors (PIGEs) of the rotation axis

[0052] symbol name <![CDATA[E XOB ]]> Linear error of the B-axis in the X-axis direction <![CDATA[E AOC ]]> Angular error of the C-axis around the X-axis <![CDATA[E BOC ]]> Angular error of the C-axis around the Y-axis <![CDATA[E AOB ]]> Angular error of the B-axis around the X-axis <![CDATA[E COB ]]> Angular error of the B-axis around the Z-axis

[0053] This solution uses the ISO230-1:2012 method to correctly set the machine tool coordinate system, which can ensure that the five PIGEs of the dual rotary axes identified by this solution are complete and non-redundant. k,i and the fitted center line L i , and find the best fitting straight line Y by the least squares method i To identify PIGEs with two rotation axes.

[0054] In order to identify the PIGEs of the rotary axis, the finished workpiece is measured on the machine based on the above-mentioned on-machine measurement strategy. Figure 9 and Figure 10As shown in the figure, the geometric error of the rotating axis can be obtained by combining the data obtained from the on-machine measurement with the kinematic relationship of the geometric error of the finished workpiece.

[0055] The kinematic relationship of the geometric error of the finished workpiece is shown in formula (2);

[0056] In step 4, the data obtained in step 3 are processed to obtain three position error models and three direction error models:

[0057]

[0058] Among them, P X It indicates the position error in the X direction of the actual cutting point of the tool cutting the workpiece relative to the ideal cutting point.

[0059] P Y It indicates the position error in the Y direction of the actual cutting point of the tool relative to the ideal cutting point when cutting the workpiece. Z It indicates the position error in the Z direction of the actual cutting point of the tool cutting the workpiece relative to the ideal cutting point. X It indicates the directional error in the X direction of the actual cutting point of the tool cutting the workpiece relative to the ideal cutting point. Y It indicates the position error in the Y direction of the actual cutting point of the tool cutting the workpiece relative to the ideal cutting point. Z It represents the position error in the Z direction of the actual cutting point of the tool cutting the workpiece relative to the ideal cutting point. x, y and z represent the movement of the machine tool's linear axes X, Y and Z during machining and measurement, respectively. b and c represent the angles of rotation of the machine tool's B and C axes during machining and measurement, respectively.

[0060] The geometric errors of the rotation axes are shown in Table 1. From the geometric shape of the finished workpiece, the five PIGEs related to the rotation axes B and C in Table 1 can be identified. Two machining modes (machining arc surface and machining rectangular groove) are designed to identify these five PIGEs. The machining surfaces U0 and U2 are used as the measurement references for the identification scheme. The geometric errors E of the rotation axes B and C can be identified through the arc surface machining mode. BOC 、E XOB and E COB ; The geometric error E of the rotation axis B axis and C axis can be identified through the rectangular groove processing mode AOB and E AOC .

[0061] In the arc surface machining mode, the geometric error of the finished workpiece is as follows Figure 9As shown in Figure 1, with S1,0 as the reference point, the center points S1,1 and S1,0 theoretically coincide. However, due to the influence of geometric errors, linear deviations and angular deviations occur in the X, Y, and Z directions. The kinematic relationship of the geometric error of the finished workpiece can be derived by combining Equation (2):

[0062] In order to correspond to the measurement point data in different workpiece coordinate systems, it is necessary to make a rotation transformation on the spatial error model. W T T is the HTM matrix of the workpiece relative to the machine tool. Substituting the rotation angles of the B-axis and C-axis into equation (2), the relationship between the linear displacement, angular error and geometric error of the arc surface under machine measurement can be obtained as follows:

[0063]

[0064] Among them, x, y and z represent the movement of the machine tool's linear axis X-axis, Y-axis and Z-axis during processing and measurement, respectively. It indicates the difference between the measured distance and the theoretical distance in the X-axis direction of the center line of the other arc surface fitting relative to the center line of the arc surface fitting, with the center line of one arc surface as the reference. It indicates the difference between the measured distance and the theoretical distance in the Y-axis direction of the center line of the other arc surface fitting relative to the center line of the arc surface fitting, with the center line of one arc surface as the reference. It indicates the difference between the measured distance and the theoretical distance in the Z-axis direction of the center line of the other arc surface fitting relative to the center line of the arc surface fitting, with the center line of one arc surface as the reference. Indicates the angular deviation of the center line of one arc surface fitting relative to the center line of the arc surface fitting in the X-axis direction in the YZ plane, with the center line of one arc surface fitting as the reference. Indicates the angular deviation of the center line of one arc surface fitting relative to the center line of the arc surface fitting in the Y-axis direction, with the center line of one arc surface fitting as the reference in the XZ plane. Indicates the angular deviation of the center line of one arc surface fitting relative to the center line of the arc surface fitting in the Z-axis direction, with the center line of one arc surface fitting as the reference in the XY plane. E AOB Indicates the angular error of the B-axis around the X-axis, E COB Indicates the angular error of the B-axis around the Z-axis, E AOC Indicates the angular error of the C-axis around the X-axis, E XOB Indicates the linear error of the B-axis in the X-axis direction, E BOC Indicates the angular error of the C-axis around the Y-axis.

[0065] Get the geometric error E of the rotation axis B and C axis BOC 、E XOB and E COB The identification equation is shown in formula (4):

[0066]

[0067] The linear offset in formula (3) and It can be obtained by fitting the measured distance between two points. Figure 9 As shown in (a), on the XY and YZ planes, S 1,0 As the reference point, S 1,1 Relative to S 1,0 The measured distances on the X, Y and Z axes are |S 1,1 -S 1,0 | X 、|S 1,1 -S 1,0 | Y and |S 1,1 -S 1,0 | Z ; and so on, with S 2,0 …S 5,0 As the reference point, the measured distances on the X, Y and Z axes are |S 2,1 -S 2,0 | X …|S 5,1 -S 5,0 | X 、|S 2,1 -S 2,0 | Y …|S 5,1 -S 5,0 | Y and |S 2,1 -S 2,0 | Z …|S 5,1 -S 5,0 | Z ; The best fitting distances on the X, Y, and Z axes can be obtained by the least squares method, denoted as |L1-L0| X 、|L1-L0| Y and |L1-L0| Z .

[0068] The angle deviation in formula (3) and It can be obtained by measuring the angle formed by the two center lines fitted by the center points. Figure 9 As shown in (c), on the YZ plane, with L0 as the reference, the angle deviation of L1 relative to L0 in the X direction is ∠<L1|L0>YZ , similarly, if Figure 9 (a) and Figure 9 In (b), in the XY plane and XZ plane, the angular deviation of L1 relative to L0 in the Z and Y directions is ∠<L1|L0> XY and ∠<L1|L0> XZ ;

[0069] Among them, x, y and z represent the movement of the X-axis, Y-axis and Z-axis of the machine tool during processing and measurement, respectively.

[0070] ∠<L1|L0> YZ Indicates that on the YZ plane, with the center line L0 of one arc surface fitting as the reference, the angle deviation of the center line L1 of the other arc surface fitting relative to the center line L0 of the one fitting in the X-axis direction, ∠<L1|L0> XY Indicates the angular deviation of the center line L1 of the arc surface fitting relative to the center line L0 of the arc surface fitting on the XZ plane in the Y-axis direction, with L0 as the reference, |L1-L0| X Indicates the best fitting distance on the X-axis of the center line L0 of one arc surface fitting relative to the center line L0 of the other arc surface fitting, |L1-L0| Y It indicates the fitting distance on the Y axis of the center line L0 of one arc surface fitting relative to the center line L0 of the other arc surface fitting, with the center line L1 of the other arc surface fitting as the reference.

[0071] In the rectangular slot machining mode, the geometric error of the finished workpiece is as follows Figure 10 As shown. Figure 10 As shown in (a), the measured points are fitted according to the least squares method to obtain the best fitting lines Y2 and Y3, which are projected onto the same YZ plane and recorded as Y2' and Y3' respectively. Taking the projection line Y2' as the reference, Y2' and Y3' are theoretically parallel, but due to the influence of geometric errors, they produce angular deviations in the X-axis direction. The kinematic relationship of the geometric error of the finished workpiece can be derived by combining formula (2). The relationship between the linear displacement, angular error and geometric error of the rectangular slot under machine measurement is:

[0072]

[0073] Angle deviation in equation (5) It can be obtained based on the angle between the two projection lines. Figure 10As shown in (b), the projection lines Y2' and Y3' projected on the YZ plane are translated to the center of the plane so that they intersect. With the projection line Y2' as the reference, the angle deviation of the projection line Y3' relative to Y2' in the X direction is ∠<Y3'|Y2'> YZ ;

[0074] Among them, x, y and z represent the movement of the machine tool's linear axis X-axis, Y-axis and Z-axis during processing and measurement, respectively. It represents the difference between the measured distance and the theoretical distance in the X-axis direction of the straight line fitted to the other rectangular surface relative to the straight line fitted to the one rectangular surface, with the straight line fitted to one rectangular surface as the reference. It indicates the difference between the measured distance and the theoretical distance in the Y-axis direction of the straight line fitted to the other rectangular surface relative to the straight line fitted to the one rectangular surface, with the straight line fitted to one rectangular surface as the reference. It indicates the difference between the measured distance and the theoretical distance in the Z-axis direction of the straight line fitted to the other rectangular surface relative to the straight line fitted to the one rectangular surface, with the straight line fitted to one rectangular surface as the reference. It represents the angle formed by the two projection lines when the two fitting lines are projected onto the YZ plane. It represents the angle between the two projection lines when the two fitting lines are projected onto the XZ plane. It represents the angle between the two projection lines when the two fitted lines are projected onto the XY plane.

[0075] The geometric error E of the rotation axis B and C axis can be obtained AOB The identification equation is shown in formula (6);

[0076] E AOB =∠<Y3'|Y2'> YZ (6)

[0077] Among them, ∠<Y3'|Y2'> YZ It means that the projection lines Y2' and Y3' of the two fitted straight lines on the YZ plane are translated to the center of the plane so that they intersect. With the projection line Y2' as the reference, the angle deviation of the projection line Y3' relative to Y2' in the X direction;

[0078] The obtained geometric error E AOB Substitution The geometric error E of the rotation axis B and C axis can be obtained AOC ;

[0079] E AOC =∠<L1|L0> YZ -∠<Y3'|Y2'> YZ (7).

[0080] Therefore, the above five PIGEs of the machine tool's rotary axes B and C can be identified from the machining errors of the finished workpiece.

[0081] Example

[0082] This experiment was conducted on a five-axis CNC machine tool, model JDEGR150, to perform cutting of a feature workpiece to verify the effectiveness of the proposed five-axis machine tool rotary axis geometric error identification method based on machining test. The machine tool spindle was preheated for 30 minutes before machining, and an oily cutting fluid was used during the machining process. The tool used was a 10mm diameter carbide flat-bottom milling cutter, and the on-machine measurement system used a Marposs VOP40 probe with a probe diameter of 2mm and a repeatability of 2μm. The length, width, and height of the probe were 100×100×100mm. 3 A cubic aluminum alloy blank is punched on the bottom surface and fixed on the workbench of a five-axis machine tool through a hoisting process. The pre-written program and optimized process parameters are input into the CNC panel to perform milling processing on the feature workpiece.

[0083] After the workpiece is processed, the machine tool is cooled to room temperature, and then the finished workpiece is measured on the machine by the machine tool's measurement system. The on-machine measurements of the four processing surfaces are directly carried out in succession to reduce the influence of heat on the measurement results. A total of 54 measurement point data are obtained, which are recorded as N 0,1,1 …N 1,5,3 , X 1,2 …X 12,3 ; Process the obtained data and combine the two designed pattern recognition to obtain E BOC 、E XOB 、E COB 、E AOB and E AOC , as shown in Table 2.

[0084] Table 2 Identification results of PIGEs

[0085] symbol Error value <![CDATA[E BOC ]]> 0.0001rad <![CDATA[E XOB ]]> 0.091mm <![CDATA[E COB ]]> 0.00018rad <![CDATA[E AOB ]]> 0.00012rad <![CDATA[E AOC ]]> -0.00004rad

[0086] Finally, the machine tool error compensation was performed and verified through cutting experiments, and the compensation rate reached 80.2%.

[0087] The present invention has been disclosed above with reference to preferred embodiments, but this is not intended to limit the present invention. Any person skilled in the art who, without departing from the scope of the technical solution of the present invention, can make slight changes or modifications to the above-disclosed structures and technical contents to produce equivalent embodiments with equivalent changes, all of which still fall within the scope of the technical solution of the present invention.

Claims

1. A method for identifying geometric errors of the rotary axis of a five-axis machine tool based on machining tests, characterized by: The method comprises the following steps:

1. Design of feature workpiece: Design a feature workpiece of a certain size, with the main body being a cube, and cut out two arc surfaces of the same size and two rectangular slots of the same size; 2. Machining of feature workpieces: With all axes of the machine tool stationary and the B and C axes at 0°, the workpiece is mounted on the worktable and the linear axes X, Y, and Z are adjusted to their initial positions. Two identical circular surfaces and two identical rectangular grooves on the same side are machined on the workpiece. During the cutting process of each pair of circular surfaces and pair of rectangular grooves, the linear axes move along the same trajectory.

3. On-machine measurement of the workpiece: After the feature workpiece is machined, the machine tool is cooled to room temperature. The on-machine measurement system of the machine tool is used to measure the data of each arc surface and each rectangular slot of the workpiece at room temperature. The rotating axes B and C are returned to 0° and kept stationary. The X, Y, and Z axes are used to measure the fitting center lines of the two arc surfaces and the fitting straight lines in the length direction of the same machined surface in the two rectangular slots.

4. Identification of geometric errors of machine tool rotary axes First, the data obtained from the third step is processed to obtain three position error models and three direction error models. Then, a rotation transformation is performed on the error models, and the rotation angles of the B-axis and the C-axis are substituted into the error models. The three position-independent geometric errors of the rotation axis based on the arc surface under machine measurement are obtained when the B-axis and the C-axis are both 0°. Geometric error E of the rotation axis B and C BOC 、E XOB and E COB The identification equation is shown in formula (4): Among them, x, y and z represent the movement of the X-axis, Y-axis and Z-axis of the machine tool during processing and measurement respectively. ∠<L1|L0> YZ Indicates that on the YZ plane, with the center line L0 of one arc surface fitting as the reference, the angle deviation of the center line L1 of the other arc surface fitting relative to the center line L0 of the one fitting in the X-axis direction, ∠<L1|L0> XY Indicates the angular deviation of the center line L1 of the arc surface fitting relative to the center line L0 of the arc surface fitting on the XZ plane in the Y-axis direction, with L0 as the reference, |L1-L0| X Indicates the best fitting distance on the X-axis of the center line L0 of one arc surface fitting relative to the center line L0 of the other arc surface fitting, |L1-L0| Y Indicates the fitting distance on the Y axis of the center line L0 of one arc surface fitting relative to the center line L0 of the other arc surface fitting, E COB Indicates the angular error of the B-axis around the Z-axis, E XOB Indicates the linear error of the B-axis in the X-axis direction, E BOC Indicates the angular error of the C-axis around the Y-axis; And the remaining two geometric errors that are independent of position of the rotating axis based on the rectangular slot under machine measurement, Geometric error E of the rotation axis B and C AOB The identification equation is shown in formula (6); AND AOB =∠<Y'3|Y'2> YZ (6) Among them, ∠<Y'3|Y'2> YZ Indicates that the projection lines Y'2 and Y'3 of the two fitted straight lines on the YZ plane are translated to the center of the plane so that they intersect. With the projection line Y'2 as the reference, the angle deviation of the projection line Y'3 relative to Y'2 in the X direction; The obtained geometric error E AOB Substitution The geometric error E of the rotation axis B and C axis can be obtained AOC ; AND AOC =∠<L1|L0> YZ -∠<Y'3|Y'2> YZ (7) E AOB Indicates the angular error of the B-axis around the X-axis, E AOC Indicates the angular error of the C-axis around the X-axis; Complete the identification of the geometric error of the rotating axis.

2. The method for identifying geometric errors of a five-axis machine tool's rotary axis based on machining tests according to claim 1, characterized in that: The arc surface processing process of step 2 is as follows: Step 1, the initial position of the workpiece is at the center position of the C-axis. When the rotation axes B and C are both at 0°, the linear axes X, Y and Z are used to move and the vertical milling cutter processes an arc surface of a certain diameter as the measurement reference surface in this processing mode. After the measurement reference surface is cut, the linear axes X, Y and Z return to the initial position; Step 2, the B-axis remains stationary, and the C-axis is rotated to 90°. The linear axis uses the same travel trajectory as in step 1 to perform a second cutting to process an arc surface of the same size as in step 1.

3. The method for identifying geometric errors of a five-axis machine tool's rotary axis based on machining tests according to claim 1, characterized in that: The rectangular groove processing process of step 2 is as follows: step 1-1, first return the rotary axis B axis and C axis to 0°, and the linear axes X, Y and Z axes to their initial positions, then keep the rotary axis C axis stationary, rotate the B axis to 90°, and use the movement of the linear axes X, Y and Z axes to process a rectangular groove of a certain size by the upright milling cutter as the measurement reference surface under this processing mode. After the cutting is completed, the linear axes X, Y and Z return to their initial positions; step 1-2, then keep the rotary axis B axis stationary, rotate the C axis to 90°, and use the same linear axis travel trajectory as step 2 to perform a second cutting to process a rectangular groove of the same size as step 1).

4. The method for identifying geometric errors of a five-axis machine tool's rotary axis based on machining tests according to claim 1, characterized in that: In the on-machine measurement of step three, the measurement strategy for the arc surface is: return the rotating axes B and C to 0° and keep them stationary, perform on-machine measurement on the processed arc surface, select N groups of measuring points, in the first group of measuring points, the Z axis of the machine tool remains stationary, only the X and Y axes move to different measurement positions, in the second to N groups of measuring points, the movement distance of the Z axis is uniform, and in the process of measuring each group of measuring points, the movement trajectory of the X and Y axes is the same as that of the first group of measurements; the measurement strategy for the rectangular slot is to measure with the rotating axes B and C axes both at 0°, and perform on-machine measurement on the processed side surface.

5. The method for identifying geometric errors of a five-axis machine tool's rotary axis based on machining tests according to claim 1, characterized in that: In step 4, the data obtained in step 3 are processed to obtain three position error models and three direction error models: Among them, P X It indicates the position error of the actual cutting point of the tool cutting the workpiece relative to the ideal cutting point in the X direction, P Y It indicates the position error in the Y direction of the actual cutting point of the tool relative to the ideal cutting point when cutting the workpiece. Z It indicates the position error in the Z direction of the actual cutting point of the tool cutting the workpiece relative to the ideal cutting point. X It indicates the directional error in the X direction of the actual cutting point of the tool cutting the workpiece relative to the ideal cutting point. Y It indicates the position error in the Y direction of the actual cutting point of the tool cutting the workpiece relative to the ideal cutting point. Z It represents the position error in the Z direction of the actual cutting point of the tool cutting the workpiece relative to the ideal cutting point. x, y and z represent the movement of the machine tool's linear axes X, Y and Z during machining and measurement, respectively. b and c represent the angles of rotation of the machine tool's B and C axes during machining and measurement, respectively.

6. The method for identifying geometric errors of a five-axis machine tool's rotary axis based on machining tests according to claim 1, characterized in that: In step 4, the relationship between the linear displacement, angular error, and geometric error of the arc surface under machine measurement is as follows: Among them, x, y and z represent the movement of the machine tool's linear axis X-axis, Y-axis and Z-axis during processing and measurement, respectively. It indicates the difference between the measured distance and the theoretical distance in the X-axis direction of the center line of the other arc surface fitting relative to the center line of the arc surface fitting, with the center line of one arc surface as the reference. It indicates the difference between the measured distance and the theoretical distance in the Y-axis direction of the center line of the other arc surface fitting relative to the center line of the arc surface fitting, with the center line of one arc surface as the reference. It indicates the difference between the measured distance and the theoretical distance in the Z-axis direction of the center line of the other arc surface fitting relative to the center line of the arc surface fitting, with the center line of one arc surface as the reference. Indicates the angular deviation of the center line of one arc surface fitting relative to the center line of the arc surface fitting in the X-axis direction in the YZ plane, with the center line of one arc surface fitting as the reference. Indicates the angular deviation of the center line of one arc surface fitting relative to the center line of the arc surface fitting in the Y-axis direction, with the center line of one arc surface fitting as the reference in the XZ plane. Indicates the angular deviation of the center line of one arc surface fitting relative to the center line of the arc surface fitting in the Z-axis direction, with the center line of the other arc surface fitting as the reference in the XY plane.

7. The method for identifying geometric errors of a five-axis machine tool's rotary axis based on machining tests according to claim 1 or 6, characterized in that: In step 4, the relationship between the linear displacement, angular error, and geometric error based on the rectangular slot under machine measurement is: Among them, x, y and z represent the movement of the machine tool's linear axis X-axis, Y-axis and Z-axis during processing and measurement, respectively. It represents the difference between the measured distance and the theoretical distance in the X-axis direction of the straight line fitted to the other rectangular surface relative to the straight line fitted to the one rectangular surface, with the straight line fitted to one rectangular surface as the reference. It indicates the difference between the measured distance and the theoretical distance in the Y-axis direction of the straight line fitted to the other rectangular surface relative to the straight line fitted to the one rectangular surface, with the straight line fitted to one rectangular surface as the reference. It indicates the difference between the measured distance and the theoretical distance in the Z-axis direction of the straight line fitted to the other rectangular surface relative to the straight line fitted to the one rectangular surface, with the straight line fitted to one rectangular surface as the reference. It represents the angle formed by the two projection lines when the two fitting lines are projected onto the YZ plane. It represents the angle between the two projection lines when the two fitting lines are projected onto the XZ plane. It represents the angle between two fitted straight lines projected onto the XY plane.

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