Tool axis non-orthogonal five-axis machine tool rotating shaft error measurement method based on R-test

Abstract

The invention relates to an R-test-based linkage rotating shaft geometric error identification method of a tool axis non-orthogonal five-axis machine tool, and belongs to the technical field of numerical control machine tools. Secondly, an R-test is installed on a workbench, after the RTCP function is started, the measuring track is within the range of the R-test, and the stroke of each feed shaft needs to be as large as possible, R-test data is extracted, namely, the actual tool nose position error is obtained; and finally, the position-independent geometric error and the position-related geometric error of the AB rotating shaft are identified through the actual tool nose position error. According to the method, the geometric error of the linkage rotating shaft of the tool-axis non-orthogonal five-axis machine tool is quickly identified, and the method has the advantages of high efficiency, accuracy, simplicity and convenience.

Description

Technical Field

[0001] The invention belongs to the technical field of numerically controlled machine tools, and in particular relates to a method for measuring the rotation axis error of a tool axis non-orthogonal five-axis machine tool based on R-test. Background Art

[0002] The five-axis machine tool with non-orthogonal tool axis is a special machine product developed for large blade disk processing. For the five-axis machine tool with non-orthogonal tool axis, the machine tool geometric error directly affects the position of the tool tip. The machine tool geometric error is mainly affected by the linear axis and rotary axis errors. Therefore, studying the linear axis and rotary axis errors of the machine tool has practical significance for improving the machining accuracy of the machine tool.

[0003] At present, the research on the linear axis and rotary axis errors of machine tools has been very mature in the linear axis errors of three-axis machine tools, mainly measured by laser interferometers and other equipment. After compensating the linear axis, the main difficulty lies in the measurement and identification of the geometric errors of the rotary axis. In the patent application entitled "Method for detecting and identifying the geometric errors of the rotary axis of a five-axis machine tool based on ballbar measurement" (publication number: CN 118769017 A), a precision metal ball is fixed on the workbench through a magnetic base, and another precision metal ball is installed on the machine tool spindle. The rotary axis is rotated to obtain the readings of the ballbar at different installation positions; then the expression of the actual axis of the rotary axis is obtained; finally, the actual axis is compared with the ideal axis when the rotary axis rotates, and all 10 geometric errors of the rotary axis can be determined with the help of the geometric error identification formula. This method has the following shortcomings: one installation can only measure the displacement in one direction; the use of the ballbar requires at least several installations to identify all errors, and the installation error and its cumulative effect will affect the measurement and identification accuracy.

[0004] Ibaraki et al. used R-test to identify the error of rotary axes. In “Construction of an errormap of rotary axes on a five-axis machining center by static R-test”, they proposed a geometric error identification algorithm for the rotary axes of double turntables. This method takes a long time to measure, and the operation and identification algorithm are relatively complicated, and it is impossible to directly and quickly detect the geometric error of the rotary axis.

[0005] In summary, the existing technology has the disadvantages of complicated operation, low degree of automation, low efficiency, and the need to further improve accuracy. At present, there is an urgent need for an efficient, accurate and simple method for geometric error identification of the linked rotating axes of non-orthogonal five-axis machine tools with tool axes. Summary of the invention

[0006] In order to overcome the disadvantages of the above-mentioned existing technologies, the purpose of the present invention is to provide a method for measuring the rotational axis errors of a non-orthogonal five-axis machine tool with a tool axis based on the R-test, which has the advantages of high efficiency, accuracy, and simplicity.

[0007] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0008] A method for measuring the rotational axis errors of a non-orthogonal five-axis machine tool with a tool axis based on the R-test includes the following steps:

[0009] 1) Define the error terms of the rotating axes AB involved in the linkage of the non-orthogonal five-axis machine tool with a tool axis. The rotating axes have two types of errors: position-independent errors and position-dependent errors, for a total of 20 rotational axis errors;

[0010] 2) Installation and data measurement of the R-test equipment:

[0011] Place the R-test equipment on the workbench of the machining center and fix it with a fixture. Based on the R-test equipment, after turning on the RTCP function of the machine tool, use the BXZ three-axis linkage method to measure at certain angular intervals within the stroke range of the B axis, and record the N groups of data obtained;

[0012] Use the AYZ three-axis linkage method to measure at certain angular intervals within the stroke range of the A axis, and record the N groups of data obtained;

[0013] 3) Solve the position-independent geometric errors of the AB axes:

[0014] Use the N groups of data obtained by the BXZ three-axis linkage to calculate the center coordinates of the sphere in the workpiece coordinate system, and use the least squares method to perform circle fitting on the N sampling points, as shown in Equation (1),

[0015]

[0016] In formula (1), A 1 , B 1 , C 1 , D 1 are the plane equation parameters;

[0017] Project the center coordinates of the sphere obtained by fitting onto the XOZ plane along the normal vector to solve the position-independent geometric error of the B axis, as shown in Equation (2);

[0018]

[0019] Use the N groups of data obtained by the AYZ three-axis linkage to calculate the center coordinates of the sphere in the workpiece coordinate system, and refer to the calculation method of formula (1) to solve the position-independent geometric error of the A axis as shown in Equation (3);

[0020]

[0021] 4) Solution for geometric errors related to the position of the AB axis:

[0022] Based on the obtained geometric errors independent of the B-axis position, substitute them into formula (4) to solve for the geometric errors related to the B-axis position;

[0023]

[0024] In the formula:

[0025]

[0026]

[0027] X e , Y e , Z e —— Errors of the tool tip point in the three directions of XYZ;

[0028] G x , G y , G z —— G54 coordinates; b —— Rotation angle of the B axis;

[0029] Similarly, a system of linear equations for the geometric errors related to the position of the A axis is also obtained, as shown in formula (5),

[0030]

[0031] In the formula:

[0032]

[0033]

[0034] a —— Rotation angle of the A axis; RTCP x , RTCP y , RTCP z —— Distances from the control point of the A axis to the spindle end face in the three directions of XYZ; L —— Tool length.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention designs and runs a linkage trajectory, connects the R-test to a computer, synchronously collects the displacement data of the R-test, realizes the measurement of the tool tip point error of a five-axis machine tool, and solves the geometric errors independent of the position and geometric errors related to the position of the linkage rotation axis according to the measured data. The present invention is used for the geometric errors of the rotation axes of a non-orthogonal five-axis machine tool with a tool axis, and can directly and quickly obtain the measurement results, which has practical significance for the evaluation of the machining accuracy of a machining center and the future compensation direction. Brief Description of the Drawings

[0037] Figure 1 This is a simplified structural diagram of a non-orthogonal five-axis machine tool with a tool axis according to an embodiment of the present invention.

[0038] Figure 2 This is a schematic diagram of the axis alignment of the rotating axis according to an embodiment of the present invention.

[0039] Figure 3 This is the PDGES of the actual identified turntable B axis according to an embodiment of the present invention.

[0040] Figure 4 This is the PDGES of the actual identified turntable A axis according to an embodiment of the present invention. Detailed Description of the Invention

[0041] The present invention will be described in detail below with reference to the embodiments and the drawings.

[0042] A method for measuring the rotational axis error of a non-orthogonal five-axis machine tool with a tool axis based on R-test includes the following steps:

[0043] 1) Define the error terms of the rotating axes AB participating in the linkage in the non-orthogonal five-axis machine tool with a tool axis. The rotating axes have two types of geometric errors: position-independent geometric errors and position-dependent geometric errors. The position-independent geometric errors (PIGES) are specifically shown in Table 1.

[0044] Table 1 Position-independent geometric errors (PIGES) of the rotating axes AB

[0045]

[0046] The position-dependent geometric errors (PDGES) are specifically shown in Table 2.

[0047] Table 2 Position-dependent geometric errors (PDGES) of the rotating axes AB

[0048]

[0049]

[0050] A total of 20 rotational axis errors;

[0051] 2) Installation and data measurement of the R-test equipment:

[0052] As Figure 1 shown, place the R-test equipment on the workbench of the machining center and fix it with a fixture. Based on the R-test equipment, after turning on the RTCP function of the machine tool, use the BXZ three-axis linkage method to measure at a certain angle interval within the stroke range of the B axis, and record the obtained 23 groups of data, as shown in Table 3.

[0053] Table 3 Sensor data for measuring the B axis

[0054]

[0055]

[0056] Using the method of AYZ three-axis linkage, within the stroke range of the A axis, measurements are taken at certain angular intervals, and 33 sets of obtained data are recorded, as shown in Table 4.

[0057] Table 4 Sensor data for measuring the A axis

[0058]

[0059]

[0060] 3) Solution for geometric errors independent of the AB axis positions:

[0061] Using the 23 sets of data obtained from the BXZ three-axis linkage in the above table, calculate the coordinates of the center of the sphere in the workpiece coordinate system. After fitting the actual circular trajectory ( Figure 2 ), project it onto the XOZ plane, and directly calculate the PIGEs to avoid cumulative errors in multiple steps, as shown in Equation (1);

[0062]

[0063] In Equation (1), A 1 , B 1 , C 1 , D 1 are the parameters of the plane equation;

[0064] Project the coordinates of the center of the sphere obtained by fitting along the normal vector onto the XOZ plane, and solve for the geometric errors independent of the B axis position, as shown in Equation (2);

[0065]

[0066] Solve for the geometric errors independent of the B axis position at three different positions. The B-axis PIGEs and their average values at the three installation positions are shown in Table 5;

[0067] Table 5 B-axis PIGEs and average values at three installation positions

[0068]

[0069] Using the 33 sets of data obtained from the AYZ three-axis linkage, calculate the coordinates of the center of the sphere in the workpiece coordinate system. Referring to the calculation method of Equation (1), solve for the geometric errors independent of the A axis position as shown in Equation (3);

[0070]

[0071] The solution of the geometric errors independent of the A-axis position is carried out at three different positions. The A-axis PIGES and their average values at the three installation positions are shown in Table 6;

[0072] Table 6 A-axis PIGEs and average values at three installation positions

[0073]

[0074] 4) Solution of the geometric errors related to the AB-axis position:

[0075] According to the obtained geometric errors independent of the B-axis position, substitute them into formula (4) to solve the geometric errors related to the B-axis position;

[0076]

[0077] In the formula:

[0078]

[0079] X e , Y e , Z e ——Errors of the tool tip point in the three directions of XYZ;

[0080] G x , G y , G z ——G54 coordinates; b——Rotation angle of the B-axis;

[0081] Solve the 6 geometric errors related to the B-axis according to the form of solving the linear equations, as shown in Figure 3 shown, Figure 3 (a)-(f) are the measurement results of the radial movement error (EXB), axial movement error (EYB), radial movement error in the Z direction (EZB), tilting movement error around the X axis (EAB), angular positioning error (EBB) and tilting movement error around the Z axis (ECB) of the B-axis respectively. The experimental data shows that the geometric errors related to the B-axis position are all less than ±350 μm (for example, the maximum deviation of EXB is 348 μm), and the fluctuation range of the angular error is within ±60" (for example, the maximum angular deviation of EBB is -58.6"), indicating that the identification accuracy of the geometric errors related to the position by this method is significantly better than that of the traditional ball bar. Combining the average values (XOB = 70.03 μm, ZOB = 139.23 μm) and their standard deviations (XOB ≈ 38.3 μm, ZOB ≈ 16.1 μm) of the geometric errors independent of the B-axis position in Table 5, the effectiveness of the error separation is further verified

[0082] Similarly, the linear equations of the geometric errors related to the A-axis position can also be obtained, as shown in formula (5),

[0083]

[0084] Wherein:

[0085]

[0086] a——Rotation angle of axis A; RTCP x , RTCP y , RTCP z ——Distances from the control point of axis A to the spindle end face in the three directions of X, Y, and Z; L——Tool length;

[0087] In this embodiment, six position geometric related errors of axis A are solved according to the form of solving linear equations, as Figure 4 shown, Figure 4 (a)-(f) are respectively the measurement results of the axial movement error (EXA) of axis A, the radial movement error in the Y direction (EYA), the radial movement error in the Z direction (EZA), the angular positioning error (EAA), the tilting movement error around the Y axis (EBA), and the tilting movement error around the Z axis (ECA). The data shows that the maximum of the position geometric related errors of axis A is 65.1 μm (EZA), the maximum of the angular error is +28.6" (EBA), and the error curves are smooth without mutations (for example, the standard deviation of the EZA curve is only 0.7 μm). Combining the average values of the geometric errors unrelated to the position of axis A in Table 6 (YOA = 41.39 μm, ZOA = 18.86 μm) and their low standard deviations (YOA ≈ 1.8 μm, ZOA ≈ 0.9 μm), it shows that this method can effectively avoid error coupling and improve the measurement reliability.

[0088] Combined with the experimental data and charts, the advantages of this embodiment are as follows:

[0089] (1) High efficiency: As shown in Table 5 and Table 6, the geometric errors unrelated to the position (PIGEs) of axis B and axis A can be solved respectively through the measurement data under three installation positions, and the identification of the geometric errors related to the position (PDGEs) can be completed through a single joint trajectory measurement ( Figure 3 , Figure 4 ). Compared with the traditional method that requires multiple installations and adjustments with a ballbar, in this embodiment, through the design of the BXZ and AYZ three-axis joint trajectories, only 23 groups (for axis B) and 33 groups (for axis A) of data are required to cover the full-stroke error measurement, significantly shortening the measurement time (Table 3, Table 4).

[0090] (2) Accuracy: The experimental data shows that the standard deviations of the geometric errors unrelated to the position of axis B and axis A are as low as YOA ≈ 1.8 μm and ZOA ≈ 0.9 μm respectively (Table 6), indicating that the error separation effect is significant, avoiding error coupling and verifying the measurement accuracy of this method.

[0091] (3) Simplicity: This method directly utilizes the RTCP function of the machine tool and the R-test equipment ( Figure 1 ), automatically collects the tool tip error data through the linked trajectory (Tables 3 and 4), without the need for additional adjustment of sensors or multiple installations. By combining the least squares circle fitting (Equation (1)) and the linear equation solving (Equations (4) and (5)), the automatic identification of errors is achieved, reducing manual intervention. Compared with the complex static R-test algorithms proposed by Ibaraki et al., the operation process of this embodiment is simplified and can be directly applied to the on-site inspection of non-orthogonal five-axis machine tools with a tool axis.

Claims

1. A method for measuring the rotation axis error of a non-orthogonal five-axis machine tool based on R-test, characterized in that: The following steps are involved: 1) Define the error terms of the rotary axis AB involved in the linkage in the non-orthogonal five-axis machine tool with tool axis. The rotary axis has two types of position-independent geometric errors and position-dependent geometric errors, totaling 20 rotary axis errors; 2) Installation and data measurement of R-test equipment: Place the R-test device on the workbench of the machining center and fix it with a fixture. After turning on the RTCP function of the machine tool based on the R-test device, use the BXZ three-axis linkage method to measure at certain angles within the B-axis travel range and record the N sets of data obtained; Adopt the AYZ three-axis linkage method, measure at certain angle intervals within the A-axis travel range, and record the obtained N groups of data; 3) Solution of AB axis position-independent geometric error: The N sets of data obtained by the BXZ three-axis linkage are used to calculate the coordinates of the sphere center in the workpiece coordinate system, and the least squares method is used to perform circle fitting on the N sampling points, as shown in formula (1). In formula (1), A1, B1, C1, and D1 are the plane equation parameters; Project the fitted sphere center coordinates onto the XOZ plane along the normal vector and solve the position-independent geometric error of the B axis, as shown in formula (2); Using the N sets of data obtained by the AYZ three-axis linkage, the coordinates of the sphere center in the workpiece coordinate system are calculated. Referring to the calculation method of formula (1), the position-independent geometric error of the A axis is solved as shown in formula (3); 4) Solution of geometric errors related to AB axis position: According to the obtained B-axis position-independent geometric error, it is substituted into formula (4) to solve the B-axis position-dependent geometric error; Where: X e ,Y e ,Z e ——Error of tool tip in XYZ directions; G x ,G y ,G z ——G54 coordinate; b——B axis rotation angle; Similarly, the linear equations of the position-related geometric error of the A-axis are obtained, as shown in equation (5): Where: a——A-axis rotation angle; RTCP x ,RTCP y ,RTCP z ——The distance from the A-axis control point to the spindle end face in the XYZ directions; L——Tool length.

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