Machine tool rotary table error measurement method based on trigger probe

Abstract

The present application belongs to the technical field of error measurement of numerical control machine tool, and discloses a machine tool rotary table error measurement method based on a trigger type probe. Firstly, the geometric error elements and kinematics of the rotary table are analyzed, and a geometric error model of the rotary table is established; then, a contact type probe and a standard ball are combined to determine an error measurement mode, the center coordinates of the standard ball are calculated by using the probe readings at different rotary angles of the rotary table, and the three-direction displacement deviations of the center of the standard ball are calculated at different rotary angles of the rotary table according to the measurement mode; finally, the center coordinates of the ball and the three-direction displacement deviations calculated by measurement are combined with the geometric error model to identify all the 20 geometric errors of the rotary table of the five-axis numerical control machine tool. The error measurement method proposed in the present application can effectively separate the geometric errors irrelevant to the rotary shaft position and the geometric errors relevant to the rotary shaft position, has low requirements for the installation precision of the measurement tool, simple measurement mode, and full error items.

Description

Technical Field

[0001] This invention belongs to the field of CNC machine tool error measurement technology, and relates to a method for measuring the error of a machine tool rotary table based on a trigger probe. Background Technology

[0002] In CNC machine tool machining, the geometric errors of each motion axis are a crucial factor affecting machining accuracy. In addition to three linear axes, a rotary table five-axis machine tool also incorporates two rotary axes. Currently, methods for measuring the geometric errors of linear axes are relatively mature, but efficient and comprehensive methods for measuring the geometric errors of rotary axes still need improvement.

[0003] In the patent "A Universal Method for Identifying Geometric Errors of Rotary Axes in Five-Axis CNC Machine Tools" (application number 201410096074.X), based on the geometric error model of the CNC machine tool, different ballbar measurement modes are set to identify 16 geometric errors of the two rotary axes of the five-axis CNC machine tool. In the patent "A Method for Identifying Geometric Errors of the Swing Axis of a Five-Axis CNC Machine Tool Based on RTCP" (application number 201610045130.6), the positional error of the ball head fixture center is combined with the geometric error model of the rotary axis to establish a set of geometric error identification equations for the ball head fixture center with respect to the rotary axis. By repeatedly adjusting the geometric offset parameters of the ball head fixture center, 12 position-related geometric errors of the two rotary axes are identified.

[0004] Analysis of the current research reveals that commonly used machine tool rotary table geometric error measurement tools, such as ballbars, R-test devices, and contact probes, each have the following advantages and disadvantages:

[0005] Ballbar-based measurement methods are relatively mature and universal, but ballbars can only measure displacement deviation in one direction at a time. In actual measurement, the instrument's installation position needs constant adjustment, significantly reducing measurement efficiency. R-test-based methods can simultaneously detect three-dimensional composite displacement deviation, offering relatively high measurement efficiency. However, mature R-test products are currently scarce and expensive, and these devices require RTCP functionality on the machine tool, limiting their use to five-axis machine tools. Trigger-type probes, as a cheaper and more readily available device, although limited to discrete measurements, have lower requirements for installation accuracy and simpler measurement modes compared to ballbars. Compared to R-test devices, probes do not require multi-axis linkage, and there are no geometric constraints between the probe and the target, effectively increasing the flexibility of probe motion trajectory programming and avoiding the risk of measurement system damage due to incorrect motion trajectories. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for measuring the geometric error of a rotary table that is efficient, low-cost, and comprehensive in terms of measurement items. This method uses a combination of a trigger probe and a standard ball to measure 20 geometric errors of two rotating axes, and the measurement mode is simple.

[0007] The technical solution of the present invention:

[0008] A method for measuring the error of a machine tool rotary table based on a trigger probe includes the following steps:

[0009] Step 1: Geometric error elements and kinematic analysis of the pendulum table;

[0010] Determine the rotary axis type of the rotary table of a five-axis CNC machine tool. For rotary axis A and rotary axis C, establish the transformation matrix that introduces position-dependent errors and position-independent errors of the rotary axis. The actual transformation matrix from the workpiece coordinate system to the machine tool coordinate system under geometric error conditions, for rotation axes A and C, ;in, This is the transformation matrix from the X-axis coordinate system to the Y-axis coordinate system. Let A be the position-independent error matrix of the rotation axis. Let A be the position-related error matrix of the rotation axis. Let A be the transformation matrix from the rotation axis coordinate system to the X-axis coordinate system. Let C be the position-independent error matrix of the rotation axis. Let C be the position-related error matrix of the rotation axis. Let be the transformation matrix from the C-axis rotation coordinate system to the A-axis rotation coordinate system. Let be the transformation matrix from the workpiece coordinate system to the C-axis rotation coordinate system; the ideal transformation matrix from the workpiece coordinate system to the machine tool coordinate system under the condition of no geometric error is . The difference between the coordinates P of the center of a standard sphere on the rotary table of a five-axis CNC machine tool and the actual situation is: .

[0011] Step 2: Determine the error measurement mode and obtain the coordinates of the measurement point;

[0012] In the machine tool coordinate system, the probe is mounted on the spindle tool holder, and the standard ball is mounted on the rotary table of the five-axis CNC machine tool away from the center of the rotation axis. The probe is brought close to the surface of the standard ball on the rotary table of the five-axis CNC machine tool from different directions. The coordinates of the center of the standard ball are determined by measuring at least 4 points on the surface of the standard ball.

[0013] Based on the transformation matrix determined in step 1, plan the number and location of measurement points for the center coordinates of the standard sphere;

[0014] Step 2.1, Planning of measurement points for position-independent error of rotary axis C: Keep rotary axis A at zero position, and the installation height of the standard ball's center from the rotary axis surface of the five-axis CNC machine tool's rotary table is... Measure the initial coordinates of the center of the standard sphere. Control the rotation of axis C to measure the center coordinates of the standard sphere n times at equal intervals within the range of 0~360°;

[0015] Step 2.2, Planning of measurement points for the position-related error of the C-axis: After completing step 2.1, adjust the A-axis and C-axis to zero, and adjust the initial installation position of the standard ball twice to ensure they are in the correct positions. and Repeat step 2.1 to obtain the center coordinates of the standard sphere at three different initial positions with respect to the rotation axis C.

[0016] Step 2.3, Planning of measurement points for position-independent errors of rotation axis A: Keep rotation axis C at zero position, and the installation height of the standard ball's center from the rotation axis surface of the five-axis CNC machine tool's rotary table is... Measure the initial coordinates of the center of the standard sphere. Control the rotation of axis A to measure the center coordinates of the standard sphere m times at equal intervals within the range of -30° to 90°;

[0017] Step 2.4, Planning of measurement points for position-related errors: After completing step 2.3, adjust the A and C rotation axes to zero, and adjust the initial installation position of the standard ball twice to ensure that it is in the correct position. and Repeat step 2.3 to obtain the center coordinates of the standard sphere at three different initial positions with respect to the rotation axis A.

[0018] Step 3: Calculate the geometric error of the pendulum table.

[0019] Calculate the position-independent errors of rotation axes C and A: The measurement results of the standard sphere's center coordinates from step 2 are processed as follows: The center coordinates of the standard sphere obtained in steps 2.1 and 2.3 are respectively fitted to a three-dimensional discrete space circle. The least squares method is used to solve for the center coordinates of the fitted circles of rotation axes A and C and the normal vector of the plane containing them. The equation of the plane containing the fitted circle of the standard sphere's center coordinates obtained in step 2.1 is then obtained. The coordinates of the center of the fitted circle are The equation of the plane containing the fitted circle of the standard sphere obtained in step 2.3 is: The coordinates of the center of the fitted circle are Then, combined with the installation height of the standard ball's center distance from the rotation axis of the five-axis CNC machine tool's rotary table... The calculation yielded:

[0020] A. Rotation axis position-independent error:

[0021] C. Rotation axis position-independent error: ;

[0022] in, This represents the actual displacement deviation between the axis of rotation A and the Y direction. This represents the actual displacement deviation between the axis of rotation A and the Z direction. This represents the angular deviation between the actual axis of rotation A and the Y-direction. This represents the angular deviation between the actual axis of rotation A and the Z-direction. This represents the actual displacement deviation between the axis of rotation C and the X direction. This represents the actual displacement deviation between the axis of rotation C and the Y direction. This represents the angular deviation between the actual C-axis rotation axis and the X-direction. The actual angular deviation between the axis of rotation of the C-axis and the Y-direction is given, while the X, Y, and Z directions are all within the machine tool coordinate system.

[0023] Calculate the positional correlation error between rotation axis C and rotation axis A: keeping rotation axis A at zero, then the transformation matrix... and All are set as identity matrices; keeping the C rotation axis at zero, the transformation matrix is... and All are set as identity matrices; using the center coordinates of the standard sphere in the workpiece coordinate system obtained in steps 2.2 and 2.4, respectively, the ideal coordinate values ​​under each rotation angle of the C-axis and the A-axis are calculated when the standard sphere is in different installation positions; here, the rotation angle of the C-axis corresponds to the angle of rotation of the C-axis when the center coordinates of the standard sphere are measured at equal intervals in step 2.1, and the rotation angle of the A-axis corresponds to the angle of rotation of the A-axis when the center coordinates of the standard sphere are measured at equal intervals in step 2.3; assuming that the ideal coordinate value corresponding to the first rotation angle of the center coordinates of the standard sphere in each group is consistent with the measured value, then the ideal coordinate values ​​of the center coordinates of the standard sphere under each subsequent rotation angle are based on the actual transformation matrix in step 1. We obtain the difference between the ideal and actual coordinates of the center P of the standard sphere obtained in step 1. The calculation methods yielded results regarding the rotation axis C at the initial installation position. , , Error equations at time, combined with the error equations, yield the system of error identification equations related to the position of rotating axis C: AE=B; rotating axis A at its initial installation position. , , By solving the error equations simultaneously, we obtain the system of equations for identifying the position-related errors of the A rotation axis: CF=D, where...

[0024]

[0025]

[0026]

[0027] in, The angle of rotation of axis C corresponds to the angle of rotation of axis A when the center coordinates of the standard sphere are measured at equal intervals in step 2.1. The positional deviation of axis C in the X, Y, and Z directions is... , , The angular deviations of the C-axis of rotation around the X, Y, and Z directions are: , , The positional deviations of rotation axis A in the X, Y, and Z directions are: , , The angular deviations of axis A around the X, Y, and Z directions are: , , , The difference from the ideal coordinates is , , , The difference from the ideal coordinates is , , , The difference from the ideal coordinates is , , , The difference from the ideal coordinates is , , , The difference from the ideal coordinates is , , , The difference from the ideal coordinates is , , .

[0028] For each measured angle of the C-axis of rotation And A rotation axis for each measurement angle In the following cases, it is necessary to solve the six position-related errors using the above-mentioned position-related error identification equation system;

[0029] The solution results E and F of the system of equations include the calculated position-independent errors of rotation axes C and A, and the position-dependent errors of rotation axes C and A to be determined. Finally, the two error components need to be separated, the position-independent errors of rotation axes C and A removed, and the six position-dependent errors of rotation axis C obtained. The six positional errors related to the rotation axis A .

[0030] The beneficial effects of this invention are:

[0031] (1) No additional measuring device is required; the side probe and standard ball are sufficient to complete all measurement tasks. This invention utilizes the side probe built into the machine tool, using only the standard ball as the sole external reference to achieve the entire measurement process. No laser interferometer, multi-axis measuring device, or centering fixture is needed, nor are any additional clamps required. The overall hardware requires no additional components and is low in cost. It can be directly used for machine tool factory testing and rapid on-site retesting, and is easy to deploy.

[0032] (2) The measurement mode is insensitive to the installation status, and the overall process is robust, simple, and has high repeatability. This invention is based on the solution of the sphere center coordinates and displacement deviation, without relying on strict alignment or optical alignment. It has good robustness to errors in probe installation and standard sphere clamping, and can maintain measurement stability under normal installation conditions. Compared with traditional optical solutions with high alignment requirements, it is easier to implement and has higher field consistency.

[0033] (3) It can identify all 20 geometric errors of the pendulum stage in the same measurement process, achieving complete coverage and effective separation of error terms. By constructing a complete geometric error model of the pendulum stage and combining the center of the sphere and displacement deviation data under multi-angle poses, this invention can solve all 20 errors, including PIGE and PDGE, at once. This overcomes the limitations of existing technologies that have insufficient identification of terms or cannot separate the two types of errors, providing sufficient data support for subsequent error compensation and accuracy optimization. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the AC rotary table type five-axis machine tool.

[0035] Figure 2 Flowchart for identifying geometric errors of the rotating pendulum stage.

[0036] Figure 3The diagram shows the distribution of measurement points for the geometric error of the pendulum table; where a is the distribution of the initial installation position of the standard ball when measuring the positional error of the C rotation axis, b is the fitted circle trajectory of the ball center of the C rotation axis, and c is the fitted circle trajectory of the ball center of the A rotation axis.

[0037] Figure 4 The diagram illustrates the principle of identifying the position-independent error of the C-axis rotation of the rotary table. Here, 'a' represents the initial position of the center of the standard sphere when measuring the position-independent error of the C-axis rotation, and 'b' represents the principle of obtaining the position-independent error of the C-axis rotation by combining the installation height 'h' of the standard sphere's center distance from the rotation axis surface of the five-axis CNC machine tool rotary table.

[0038] Figure 5 Let be the position-related error of the C rotation axis, where a is the actual angular deviation of the C rotation axis around the X, Y, and Z directions, and b is the position deviation of the C rotation axis in the X, Y, and Z directions.

[0039] Figure 6 Let be the positional error of rotation axis A. Here, 'a' represents the actual angular deviation of rotation axis A around the X, Y, and Z directions, and 'b' represents the positional deviation of rotation axis A in the X, Y, and Z directions.

[0040] In the diagram: 1-Machine bed; 2-Y translation axis; 3-X translation axis; 4-A rotary axis; 5-C rotary axis; 6-Z translation axis; 7-Spindle tool holder; 8-Standard ball; 9-Probe. Detailed Implementation

[0041] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0042] Example

[0043] Before measuring the error of the machine tool's rotary table, a laser interferometer is needed to measure and compensate for the geometric error of the translational axis in advance. The geometric error of the translational axis is pre-compensated, meaning it is set to zero during the measurement process.

[0044] Step 1: Geometric error elements and kinematic analysis of the pendulum table;

[0045] Figure 1 This is a schematic diagram of an AC rotary table type five-axis machine tool, including an X translation axis 3, a Y translation axis 2, a Z translation axis 6, an A rotary axis 4, and a C rotary axis 5. The C rotary axis 5 is rotatably mounted on the A rotary axis 4, the A rotary axis 4 is rotatably mounted on the X translation axis 3, the X translation axis 3 is mounted on the Y translation axis 2, and the Y translation axis 2 is mounted on the machine tool bed 1.

[0046] There are eight types of position-independent errors of the pendulum table caused by installation errors, specifically:

[0047] Actual displacement deviation of the axis of rotation A from the Y direction The actual displacement deviation between the axis of rotation A and the Z direction The actual angular deviation between the axis of rotation A and the Y direction The actual angular deviation between the axis of rotation A and the Z direction The actual displacement deviation between the axis of rotation C and the X direction. The actual displacement deviation between the axis of rotation C and the Y direction The actual angular deviation between the axis of rotation C and the X direction The actual angular deviation between the axis of rotation C and the Y direction ;

[0048] There are 12 errors related to the position of the rotary table caused by manufacturing defects and wear of key machine tool components. These are as follows:

[0049] The positional deviations of rotation axis A in the X, Y, and Z directions are: , , The angular deviations of axis A around the X, Y, and Z directions are: , , ;

[0050] The positional deviations of the C-axis of rotation in the X, Y, and Z directions are: , , The angular deviations of the C-axis of rotation around the X, Y, and Z directions are: , , ;

[0051] The positional relationship between any two axes of a machine tool can be described by a homogeneous transformation matrix containing three displacement parameters and three rotational parameters. The AC rotary axis machine tool kinematic chain starts from the machine tool bed 1 and is divided into two: the tool kinematic chain and the workpiece kinematic chain. The tool kinematic chain is from the machine tool bed → Z-axis → tool, and the workpiece kinematic chain is from the machine tool bed → Y-axis → X-axis → A rotary axis → C rotary axis.

[0052] Based on the machine tool kinematic chain, the position coordinates of a point in the workpiece coordinate system can be transformed to the machine tool mechanical coordinate system using the following transformation matrix;

[0053] Ideally ;

[0054] in, , These are the transformation matrices from the X-axis coordinate system to the Y-axis coordinate system and from the Y-axis coordinate system to the machine tool mechanical coordinate system, respectively. Let A be the transformation matrix from the rotation axis coordinate system to the X-axis coordinate system. Let be the transformation matrix from the C-axis rotation coordinate system to the A-axis rotation coordinate system; ideally, for the coordinates P of the center of the standard sphere 8 in the workpiece coordinate system, since the workpiece coordinate system coincides with the C-axis rotation coordinate system, we have . It is a fourth-order identity matrix.

[0055] In the case of actual geometric errors of the rotary table, the actual transformation matrix from the workpiece coordinate system to the machine tool coordinate system. ;

[0056] in, Let A be the position-independent error matrix of the rotation axis. , Let A be the position-related error matrix of the rotation axis. , Let C be the position-independent error matrix of the rotation axis. , Let C be the position-related error matrix of the rotation axis. ;

[0057] The difference between the coordinates P of the center of the standard ball 8 on the pendulum table under ideal and actual conditions is:

[0058] ;

[0059] Step 2: Determine the error measurement mode and obtain the coordinates of the measurement point;

[0060] like Figure 3 As shown, the probe 9 is mounted on the spindle tool holder 7, and the standard ball 8 is mounted on the rotary table away from the center of the rotation axis. The probe 9 approaches and touches the surface of the standard ball 8 on the rotary table from different directions. The coordinates returned by the probe 9 after touching the standard ball 8 are the coordinates of the probe's center point. The coordinates of the ball's center can be determined by measuring at least four points on the surface of the standard ball 8.

[0061] Based on the transformation matrix determined in step 1, plan the number and location of measurement points for the center coordinates of the standard sphere;

[0062] Step 2.1, Planning of measurement points for position-independent error of rotary axis C: Keep rotary axis A at zero position, and the installation height of the standard ball's center from the rotary axis surface of the five-axis CNC machine tool's rotary table is... =150mm, measuring the initial coordinates of the center of the standard sphere. Control the rotation of axis C to measure the center coordinates of a standard sphere 18 times at equal intervals within the range of 0 to 360°. , n=1,2,…,18.

[0063] Step 2.2, Planning of measurement points for the position-related error of the C-axis: After completing step 2.1, adjust the A-axis and C-axis to zero, and adjust the initial installation position of the standard ball twice to ensure they are in the correct positions. and Repeat step 2.1 to obtain the center coordinates of the standard sphere at three different initial positions with respect to the rotation axis C.

[0064] Step 2.3, Planning of measurement points for position-independent errors of rotation axis A: Keep rotation axis C at zero position, and the installation height of the standard ball's center from the rotation axis surface of the five-axis CNC machine tool's rotary table is... =150mm, measuring the initial coordinates of the center of the standard sphere. Control the rotation of axis A to measure the center coordinates of a standard sphere 10 times at equal intervals within the range of -30° to 90°. , m=1,2,…,10.

[0065] Step 2.4, Planning of measurement points for position-related errors: After completing step 2.3, adjust the A and C rotation axes to zero, and adjust the initial installation position of the standard ball twice to ensure that it is in the correct position. and Repeat step 2.3 to obtain the coordinates of the center of the standard sphere at three different initial positions about the rotation axis A;

[0066] Step 3: Calculate the geometric error of the pendulum table;

[0067] First, calculate the position-independent error of rotation axis C. For example... Figure 4 As shown, when rotation axis C rotates alone, the trajectory of the center of the standard sphere on it is ideally a circular trajectory, and the coordinates of the center are the average line of the rotation axis of C. However, due to the influence of the position-independent error of rotation axis C, the coordinates of the center have positional offsets in the X and Y directions, and the normal vector of the circular trajectory plane passing through the center has a perpendicularity deviation with the X and Y directions. The coordinates of each point of the center of the standard sphere obtained in step 2.1 are... For n=1,2,…,18, perform circle fitting in a three-dimensional discrete point space. The equation of the plane containing the fitted circle is as follows: ;

[0068] Rewritten as a matrix equation: ;

[0069] in The coordinates of the center points of the standard sphere obtained in step 2.1. n=1,2,…,18 To fit the normal vector of the plane containing the circle, .

[0070] The normal vector of the plane containing the fitted circle is obtained using the least squares method: ;

[0071] Assuming that the coordinates of all measurement points (i.e., the center of the standard sphere) lie on the fitted circle, then the perpendicular bisector of the line connecting any two measurement points must pass through the center of the circle. Let's take two measurement points as... and ,vector center ,Pass and midpoint Vector connected to the center of the circle .

[0072] have It can be simplified to ;

[0073] in, ;

[0074] Considering all measurement points, we have:

[0075] ;

[0076] abbreviated as ;

[0077] in, n=1,2,…,18, n=1,2,…,18;

[0078] In addition, the center The plane containing the fitted circle must satisfy the equation of that plane: ,Right now Solve the above optimization problem under these constraints. The least-squares solution for the center coordinates is obtained:

[0079] ;

[0080] Center coordinates The normal vector of the plane containing the fitted circle Due to the installation height of the standard ball's center from the rotation axis of the pendulum table Given this information, the displacement and angular deviations of the axis of rotation C can be calculated.

[0081] Based on the above, the equation of the plane containing the fitted circle is obtained. :

[0082] like Figure 4 As shown, the equation of the projected line in the XZ plane slope This is the angular deviation between the actual C-axis rotation axis and the X-direction: ;

[0083] Actual displacement deviation of the C-axis rotation axis from the X direction: ;

[0084] Equation of the projection line in the YZ plane slope This is the angular deviation between the actual C-axis rotation axis and the Y-direction: ;

[0085] Actual displacement deviation of the C-axis rotation axis from the X direction: ;

[0086] The four position-independent errors of the C rotation axis are obtained: ;

[0087] Next, calculate the positional error related to rotation axis C. Keeping rotation axis A at zero, the transformation matrix... and All are set as identity matrices. Using the coordinates of the center of the standard sphere in the workpiece coordinate system obtained in step 2.2, the ideal coordinate values ​​of each rotation angle of the C-axis are calculated when the standard sphere is in different installation positions.

[0088] Based on the difference between the coordinates P of the center of the standard sphere under ideal and actual conditions The calculation method yields the standard sphere in its initial installation position. Error equation at time:

[0089] ;

[0090] Convert to matrix form:

[0091] ;

[0092] in, This corresponds to the angle of rotation of axis C when measuring the center coordinates of the standard sphere at equal intervals in step 2.1. Assuming that the ideal coordinate value corresponding to the first rotation angle of the center coordinates of each set of standard spheres is consistent with the measured value, then the ideal coordinate values ​​of the center coordinates of the standard spheres at each subsequent rotation angle are based on the ideal transformation matrix in step 1. get. The difference from the ideal coordinates is , The difference from the ideal coordinates is , The difference from the ideal coordinates is .

[0093] Then establish the standard ball in the initial installation position as described in step 2.2. , The error equations at time are combined to obtain the system of equations for identifying the position-related errors of the C rotation axis: AE = B;

[0094] in,

[0095] ;

[0096] ;

[0097] .

[0098] The above nine equations form an overdetermined system of equations. According to the existence relation of solutions to the system, the condition for the existence of a unique solution is that the rank of the coefficient matrix A and the rank of the augmented matrix [AB] are both equal to 6. Therefore, the simplified equation is:

[0099] ;

[0100] ;

[0101] .

[0102] For each measured angle of the C-axis of rotation In the following cases, the six position-related errors need to be solved using the aforementioned system of position-related error identification equations. It is important to note that the solution E of the linear equation system includes both the previously calculated position-independent error of the C rotation axis and the position-related error of the C rotation axis to be determined. Finally, these two error components must be separated, and the position-independent error of the C rotation axis must be removed to obtain the six position-related errors of the C rotation axis. The solution results are as follows Figure 5 As shown.

[0103] Then, calculate the position-independent error of rotation axis A. For example... Figure 3 As shown, rotation axis A cannot rotate a full circle, but the trajectory of the center of the standard sphere on it should ideally be an arc. The coordinates of the center of the circle on which the arc is located pass through the average line of the rotation center of rotation axis A. However, due to the influence of the position-independent error of rotation axis A, the coordinates of the center have positional offsets in the Y and Z directions, and the normal vector of the trajectory plane passing through the center of the circle has a perpendicularity deviation from the Y and Z directions.

[0104] Referring to the three-dimensional discrete point space circle fitting method used to calculate the position-independent error of rotation axis C, the coordinate data of the standard sphere's center from step 2.3 are substituted into the data. For m = 1, 2, ..., 10, use the least squares method to find the coordinates of the center of the fitted circle. and the normal vector of the plane containing the fitted circle The equation of the plane containing the fitted circle is obtained: .

[0105] The equation of the plane containing the fitted circle obtained above ;

[0106] Equation of the projection line in the XY plane slope The actual angular deviation between the axis of rotation A and the X direction is: ;

[0107] Actual displacement deviation of the axis of rotation A from the X direction: ;

[0108] Equation of the projection line in the XZ plane slope The actual angular deviation between the axis of rotation A and the Y direction is: ;

[0109] Actual displacement deviation of the axis of rotation A from the X direction: ;

[0110] The four position-independent errors of rotation axis A are obtained: ;

[0111] Finally, calculate the positional error of rotation axis A. Keeping rotation axis C at zero, the transformation matrix... and All are set as identity matrices. Using the coordinates of the center of the standard sphere in the workpiece coordinate system obtained in step 2.4, the ideal coordinate values ​​of each rotation angle of the C-axis are calculated when the standard sphere is in different installation positions.

[0112] Based on the difference between the coordinates P of the center of the standard sphere under ideal and actual conditions The calculation method yields the standard sphere in its initial installation position. Error equation at time:

[0113] ;

[0114] Convert to matrix form:

[0115] ;

[0116] in, This corresponds to the angle of rotation of axis A when measuring the center coordinates of the standard sphere at equal intervals in step 2.3. Assuming that the ideal coordinate value corresponding to the first rotation angle of the center coordinates of each group of standard spheres is consistent with the measured value, then the ideal coordinate values ​​of the center coordinates of the standard spheres at each subsequent rotation angle are based on the ideal transformation matrix in step 1. get. The difference from the ideal coordinates is , , , The difference from the ideal coordinates is , , , The difference from the ideal coordinates is , , .

[0117] Then, establish the standard ball in the initial installation position as described in step 2.4. , The error equations at time are combined to obtain the system of error identification equations related to the position of rotation axis A: CF=D;

[0118] in,

[0119] ;

[0120] ;

[0121] ;

[0122] For each measured angle of rotation axis A In the following cases, the six position-related errors need to be solved using the aforementioned system of position-related error identification equations. It is important to note that the solution F of the linear equation system includes both the previously calculated position-independent error of the A-axis and the position-related error of the A-axis to be determined. Finally, these two error components must be separated, and the position-independent error of the A-axis must be removed to obtain the six position-related errors of the A-axis. The solution results are as follows Figure 6 As shown.

[0123] This embodiment ultimately yields 20 geometric errors for the AC rotary table five-axis machine tool, including 8 position-independent errors and 12 position-dependent errors.

[0124] In the description of this invention, it should be noted that the terms "upper", "lower", "front", "back", "left", "right", etc., are only used to describe the relative relationship of the directions and are based on the state shown in the accompanying drawings. They should not be construed as limiting the invention.

[0125] It should be understood that those skilled in the art can make various modifications and improvements without departing from the spirit and scope of the present invention, and all such modifications and improvements should be considered within the scope of protection of the present invention.

Claims

1. A method for measuring the error of a machine tool rotary table based on a trigger-type probe, characterized in that, Includes the following steps: Step 1: Geometric error elements and kinematic analysis of the pendulum table; Step 2: Determine the error measurement mode and obtain the coordinates of the measurement point; In the machine tool coordinate system, the probe is mounted on the spindle tool holder, and the standard ball is mounted on the rotary table of the five-axis CNC machine tool away from the center of the rotation axis. The probe is brought close to the surface of the standard ball on the rotary table of the five-axis CNC machine tool from different directions. The coordinates of the center of the standard ball are determined by measuring at least 4 points on the surface of the standard ball. The specific implementation process of step 2 is as follows: Based on the transformation matrix determined in step 1, plan the number and location of measurement points for the center coordinates of the standard sphere; Step 2.1, Planning of measurement points for position-independent error of rotary axis C: Keep rotary axis A at zero position, and the installation height of the standard ball's center from the rotary axis surface of the five-axis CNC machine tool's rotary table is... Measure the initial coordinates of the center of the standard sphere. Control the rotation of axis C to measure the center coordinates of the standard sphere n times at equal intervals within the range of 0~360°; Step 2.2, Planning of measurement points for the position-related error of the C-axis: After completing step 2.1, adjust the A-axis and C-axis to zero, and adjust the initial installation position of the standard ball twice to ensure they are in the correct positions. and Repeat step 2.1 to obtain the center coordinates of the standard sphere at three different initial positions with respect to the rotation axis C. Step 2.3, Planning of measurement points for position-independent errors of rotation axis A: Keep rotation axis C at zero position, and the installation height of the standard ball's center from the rotation axis surface of the five-axis CNC machine tool's rotary table is... Measure the initial coordinates of the center of the standard sphere. Control the rotation of axis A to measure the center coordinates of the standard sphere m times at equal intervals within the range of -30° to 90°; Step 2.4, Planning of measurement points for position-related errors: After completing step 2.3, adjust the A and C rotation axes to zero, and adjust the initial installation position of the standard ball twice to ensure that it is in the correct position. and Repeat step 2.3 to obtain the coordinates of the center of the standard sphere at three different initial positions about the rotation axis A; Step 3: Calculate the geometric error of the pendulum table; In step 3, the specific calculation of the positional errors of rotation axis C and rotation axis A is as follows: If rotation axis A is kept at zero, then the transformation matrix is... and All are set as identity matrices; keeping the C rotation axis at zero, the transformation matrix is... and All are set as identity matrices; Using the center coordinates of the standard sphere in the workpiece coordinate system obtained in steps 2.2 and 2.4, calculate the ideal coordinate values ​​under each rotation angle of the C-axis and the A-axis when the standard sphere is in different installation positions. Here, the rotation angle of the C-axis corresponds to the angle of rotation of the C-axis when the center coordinates of the standard sphere are measured at equal intervals in step 2.1, and the rotation angle of the A-axis corresponds to the angle of rotation of the A-axis when the center coordinates of the standard sphere are measured at equal intervals in step 2.

3. Assuming that the ideal coordinate value corresponding to the first rotation angle of the center coordinates of the standard sphere in each group is consistent with the measured value, the ideal coordinate values ​​of the center coordinates of the standard sphere at each subsequent rotation angle are based on the actual transformation matrix in step 1. We obtain the difference between the ideal and actual coordinates of the center P of the standard sphere obtained in step 1. The calculation methods yielded results regarding the rotation axis C at the initial installation position. , , Error equations at time, combined with the error equations, yield the system of error identification equations related to the position of rotating axis C: AE=B; rotating axis A at its initial installation position. , , By solving the error equations simultaneously, we obtain the system of equations for identifying the position-related errors of the A rotation axis: CF=D, where... in, The angle of rotation of axis C corresponds to the angle of rotation of axis A when the center coordinates of the standard sphere are measured at equal intervals in step 2.

1. The positional deviation of axis C in the X, Y, and Z directions is... , , The angular deviations of the C-axis of rotation around the X, Y, and Z directions are: , , The positional deviations of rotation axis A in the X, Y, and Z directions are: , , The angular deviations of axis A around the X, Y, and Z directions are: , , , The difference from the ideal coordinates is , , , The difference from the ideal coordinates is , , , The difference from the ideal coordinates is , , , The difference from the ideal coordinates is , , , The difference from the ideal coordinates is , , , The difference from the ideal coordinates is , , .

2. The machine tool rotary table error measurement method based on a trigger-type probe according to claim 1, characterized in that, The specific implementation process of step 1 is as follows: Determine the rotary axis type of the rotary table of a five-axis CNC machine tool. For rotary axis A and rotary axis C, establish the transformation matrix that introduces position-dependent errors and position-independent errors of the rotary axis. The actual transformation matrix from the workpiece coordinate system to the machine tool coordinate system under geometric error conditions, for rotation axes A and C, ;in, This is the transformation matrix from the X-axis coordinate system to the Y-axis coordinate system. Let A be the position-independent error matrix of the rotation axis. Let A be the position-related error matrix of the rotation axis. Let A be the transformation matrix from the rotation axis coordinate system to the X-axis coordinate system. Let C be the position-independent error matrix of the rotation axis. Let C be the position-related error matrix of the rotation axis. Let be the transformation matrix from the C-axis rotation coordinate system to the A-axis rotation coordinate system. The transformation matrix from the workpiece coordinate system to the C-axis rotation coordinate system is given by: [Mathematical matrix to be inserted here]. The ideal transformation matrix from the workpiece coordinate system to the machine tool coordinate system under the condition of no geometric error is: [Mathematical matrix to be inserted here]. The difference between the coordinates P of the center of a standard sphere on the rotary table of a five-axis CNC machine tool and the actual situation is: .

3. The machine tool rotary table error measurement method based on a trigger-type probe according to claim 1, characterized in that, In step 3, the specific details regarding the calculation of the position-independent error of rotation axis C and rotation axis A are as follows: The measurement results of the center coordinates of the standard sphere obtained in step 2 are processed as follows: The center coordinates of the standard sphere obtained in steps 2.1 and 2.3 are respectively fitted to a three-dimensional discrete space circle. The least squares method is used to solve for the center coordinates of the fitted circles along rotation axes A and C, and the normal vector of the plane containing them. The equation of the plane containing the fitted circle of the standard sphere obtained in step 2.1 is then obtained. The coordinates of the center of the fitted circle are The equation of the plane containing the fitted circle of the standard sphere obtained in step 2.3 is: The coordinates of the center of the fitted circle are Then, combined with the installation height of the standard ball's center distance from the rotation axis of the five-axis CNC machine tool's rotary table... The calculation yielded: A. Rotation axis position-independent error: C. Rotation axis position-independent error: ; in, This represents the actual displacement deviation between the axis of rotation A and the Y direction. This represents the actual displacement deviation between the axis of rotation A and the Z direction. This represents the angular deviation between the actual axis of rotation A and the Y-direction. This represents the angular deviation between the actual axis of rotation A and the Z-direction. This represents the actual displacement deviation between the axis of rotation C and the X direction. This represents the actual displacement deviation between the axis of rotation C and the Y direction. This represents the angular deviation between the actual C-axis rotation axis and the X-direction. The actual angular deviation between the axis of rotation of the C-axis and the Y-direction is given, while the X, Y, and Z directions are all within the machine tool coordinate system.

4. The machine tool rotary table error measurement method based on a trigger-type probe according to claim 1 or 3, characterized in that, For each measured angle of the C-axis of rotation And A rotation axis for each measurement angle In the following cases, it is necessary to solve the six position-related errors using the above-mentioned position-related error identification equation system; The solution results E and F of the system of equations include the calculated position-independent errors of rotation axes C and A, and the position-dependent errors of rotation axes C and A to be determined. Finally, the two error components need to be separated, the position-independent errors of rotation axes C and A removed, and the six position-dependent errors of rotation axis C obtained. The six positional errors related to the rotation axis A .

Images