A rotary shaft position related error measurement device and identification method for a double-turntable five-axis numerical control machine tool

Abstract

The application belongs to the technical field of error measurement, and discloses a rotary shaft position related error measurement device and identification method for a double-rotary-table five-axis numerical control machine tool, which comprises an R-test measurement unit, a first standard ball, a second standard ball, a standard ball tool clamp, a connecting rod, a first supporting rod, a second supporting rod and two magnetic bases. The R-test measurement unit comprises a micro-ohmmeter clamp and three micro-ohmmeters, wherein the three micro-ohmmeters are fixed on the micro-ohmmeter clamp; the first standard ball and the second standard ball are fixed on the two ends of the connecting rod; the connecting rod is connected with the first supporting rod and the second supporting rod through two standard ball tool clamps; the first supporting rod and the second supporting rod are fixed on the two magnetic bases respectively, and the two magnetic bases are fixed on a horizontal rotary table; the length of the first supporting rod is greater than that of the second supporting rod, and the first standard ball is arranged at the end of the first supporting rod. The application avoids the clamping error introduced by multiple installations and solves the problem of high difficulty in full-geometric-error identification.

Description

Technical Field

[0001] This invention belongs to the field of error measurement technology, and more specifically, relates to a device and method for measuring and identifying the position-related errors of the rotary axis of a dual-rotary-table five-axis CNC machine tool. Background Technology

[0002] A dual-rotary-table five-axis CNC machine tool includes two rotary axes and three linear axes. The rotary axes function to adjust the workpiece posture during the machining process to adapt to the machining of various complex curved surfaces, giving five-axis machining advantages such as high cutting rate and short machining time. However, due to the precision of the machining and assembly of the machine tool components, more geometric error terms are introduced during actual machining. This causes changes in the position of the tool center point in the workpiece coordinate system after the RTCP linkage function is enabled, ultimately leading to a reduction in the surface quality of the machined parts and affecting the quality and performance of the machined products. Typically, the errors of the rotary axes in all six degrees of freedom in space cannot be directly obtained through inspection tools. Indirect identification based on error models, using inspection data as a basis, becomes the main method for analyzing the geometric errors of the rotary axes.

[0003] Currently, there are two main identification methods: identification based on the precision of the machined specimen and identification based on testing instruments. The precision identification method based on the machined specimen primarily involves pre-compensating for translational axis errors. It utilizes a five-axis CNC machine to machine specimens with specific geometric features, and then uses a coordinate measuring machine to detect the deviation between the position of the feature points on the test specimen and their actual position, as well as the machine tool's geometric error model, to identify the geometric error terms of the rotary axis. Classic test specimens include square stepped parts, NAS979 truncated cone parts, and "S"-shaped specimens. However, specimen machining usually reflects the overall performance of the machine tool and is difficult to effectively identify the various geometric error terms of the rotary axis. The geometric error identification method based on testing instruments mainly uses specific instruments, combined with standard parts and specially made tooling fixtures, to obtain direct error detection information. This direct information, combined with the machine tool's geometric error model, is used to identify the various geometric errors of the rotary axis. Commonly used testing instruments include laser interferometers, ballbars, and R-test instruments. This detection method has the advantages of high detection accuracy and good efficiency, but it usually faces difficulties such as complicated tooling design, the need for multiple installations of testing equipment to introduce clamping errors, and the difficulty in identifying all geometric errors. Summary of the Invention

[0004] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a measuring device and identification method for the position-related errors of the rotary axes of a dual-rotary-table five-axis CNC machine tool. The purpose is to provide a measuring device capable of measuring 12 position-related errors of the two rotary axes of a dual-rotary-table machine tool, avoiding the problems of clamping errors introduced by multiple installations and the difficulty in identifying all geometric errors.

[0005] To achieve the above objectives, according to one aspect of the present invention, a device for measuring the position correlation error of the rotary axis of a dual-rotary-table five-axis CNC machine tool is provided, comprising an R-test measuring unit, a first standard ball, a second standard ball, a standard ball tooling fixture, a connecting rod, a first support rod, a second support rod, and two magnetic bases. The R-test measuring unit includes a dial indicator fixture and three dial indicators, wherein: the three dial indicators are fixed on the dial indicator fixture, and the dial indicator fixture is fixed on the CNC machine tool spindle; the first standard ball and the second standard ball are fixed at both ends of the connecting rod; the connecting rod is connected to the first support rod and the second support rod respectively through the two standard ball tooling fixtures; the first support rod and the second support rod are respectively fixed on the two magnetic bases, and the two magnetic bases are fixed on the horizontal rotary table; the length of the first support rod is greater than that of the second support rod, and the first standard ball is disposed at the end of the first support rod.

[0006] Preferably, the three dial indicators are evenly distributed around the periphery of the dial indicator fixture.

[0007] Preferably, the three dial indicators are movably connected to the periphery of the dial indicator fixture.

[0008] Preferably, the flat probes of the three dial indicators are tangent to the first or second standard sphere.

[0009] Preferably, the first and second standard spheres have the same diameter.

[0010] According to another aspect of the present invention, a method for identifying the rotary axis position correlation error measurement device of the above-mentioned dual rotary table five-axis CNC machine tool is provided, comprising: S1: driving the spindle to move the R-test measurement unit until the readings of the three dial gauges are the same, and determining the corresponding position at this time as the measurement zero point; S2: driving the spindle again to move the R-test measurement unit in the x, y and z directions with a fixed step size, obtaining the readings of the three dial gauges at each point, constructing the analytical solution relationship between the dial gauge readings and the center coordinates of the first and second standard spheres, and converting the readings to the measurement coordinates of the R-test measurement unit. Under the standard system; S3: Connect the three dial indicators to the first and second standard spheres in sequence, and drive the spindle to obtain the original data at different positions; S4: Based on the analytical solution relationship, convert the original data into the coordinate changes of the center of the first and second standard spheres at different positions of the turntable to obtain the target data; S5: Establish the correlation between the center coordinate deviation of the first or second standard sphere and the position-related error by combining the kinematic model of the five-axis machine tool with the properties of the position-related error term of the turntable, and identify the target data as the six position-related errors of each turntable.

[0011] Preferably, the analytical solution relationship is obtained by constructing the tangent constraint between the centers of the first and second standard spheres and the dial indicator based on the point-to-plane distance formula.

[0012] Preferably, the analytical solution relation is:

[0013]

[0014] Where x, y, z are the coordinates of the center of the first or second standard sphere in the dial indicator coordinate system, θ is the tilt angle between the dial indicator and the mounting base plane, l, m, n are the distances from the center of the bottom surface of the three dial indicators to the center of the dial indicator probe, R is the radius of the circumscribed circle of the bottom surface of the dial indicator, and r is the radius of the first or second standard sphere.

[0015] Preferably, step S3 specifically includes: S31: When measuring the C-axis error, return the A-axis to zero, tangent the three dial indicator probes to the first standard ball, adjust the spindle so that the readings of the three dial indicators are the same, regard this position as the zero point, and record the actual coordinates of the machine tool at this time; S32: Rotate the C-axis in preset angle steps and obtain the dial indicator data for each rotation; S33: Adjust the dial indicator probes to be tangent to the second standard ball 7, repeat steps S31 and S32 to obtain the first dataset; When measuring the A-axis error, return the C-axis to zero, repeat steps S31 to S33 to obtain the second dataset, both the first and second datasets are original data.

[0016] Preferably, steps S3 to S5 are repeated to obtain the average value of the position-related error.

[0017] In summary, compared with the prior art, the present invention provides a device and method for measuring and identifying the position correlation error of a rotary axis in a five-axis CNC machine tool with a dual rotary table, which has the following advantages:

[0018] 1. This application designs a complete set of auxiliary tooling fixtures, which avoids multiple clamping during the testing process, thereby avoiding the introduction of more clamping errors. It can achieve 12 position-related errors of the two rotary axes of a dual rotary table machine tool without disassembling the tools. The testing process is simple and efficient, avoids clamping errors introduced by multiple installations, and solves the problem of the difficulty in identifying all geometric errors.

[0019] 2. The R-test measurement unit of this application is made of three dial indicators and corresponding tooling fixtures, which is low in cost, uses readily available raw materials, has strong applicability, and is easy to use in industrial applications.

[0020] 3. During the identification process, based on the position adjustment of the dial indicator and the first and second standard spheres, as well as the transformation relationship between the coordinate systems, the identification of six position-related errors of each turntable can be achieved without disassembling or assembling parts, thus avoiding clamping errors. At the same time, the identification of 12 position-related errors can be achieved. Attached Figure Description

[0021] Figure 1 This application embodiment describes a device for measuring the position correlation error of the rotary axis of a five-axis CNC machine tool with a dual rotary table.

[0022] Figure 2 This is a schematic diagram of the rotation of axis A and axis C in an embodiment of this application;

[0023] Figure 3 This is a flowchart illustrating the error measurement and identification process of an embodiment of this application;

[0024] Figure 4 This is a schematic diagram of the identification process in an embodiment of this application. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0026] The first aspect of this application provides a device for measuring the position correlation error of the rotary axis of a dual-rotary-table five-axis CNC machine tool, such as... Figure 1 As shown, the measuring device includes an R-test measuring unit, a first standard ball 3, a second standard ball 7, a standard ball tooling fixture 5, a connecting rod 6, a first support rod 8, a second support rod 9, and two magnetic bases 4. The R-test measuring unit includes a dial indicator fixture 1 and three dial indicators 2.

[0027] Dial indicator fixture 1 is fixed to the spindle of a CNC machine tool, and three dial indicators 2 are fixed to dial indicator fixture 1. Preferably, the three dial indicators 2 are evenly distributed around the periphery of dial indicator fixture 1, and the flat probes of the three dial indicators 2 can all rotate, thereby allowing adjustment of the tangency between the flat probes of the dial indicators 2 and the first standard ball 3 and the second standard ball 7. The dial indicators 2 are preferably Bluetooth dial indicators.

[0028] The first standard ball 3 and the second standard ball 7 are fixed at both ends of the connecting rod 6. The connecting rod 6 is connected to the first support rod 8 and the second support rod 9 respectively through two standard ball tooling fixtures 5. The first support rod 8 and the second support rod 9 are fixed on two magnetic seats 4 respectively, and the two magnetic seats 4 are fixed on the horizontal turntable.

[0029] The length of the first support rod 8 is greater than the length of the second support rod 9. The first standard ball 3 is fixed at the end closer to the first support rod 8, and the second standard ball 7 is fixed at the end closer to the second support rod 9.

[0030] This application, in another aspect, provides an identification method based on the aforementioned dual-rotary-table five-axis CNC machine tool rotary axis position correlation error measurement device, combined with... Figure 3 The method includes the following steps S1 to S5.

[0031] S1: Drive the spindle to move the R-test measuring unit until the readings of the three dial gauges (2) are the same, and determine that the corresponding position at this time is the measurement zero position.

[0032] By rotating the handwheel, the main shaft is driven to move the R-test measuring unit until the three dial gauges read the same at a certain position, which is the zero point of the measurement.

[0033] S2: Drive the spindle again to move the R-test measurement unit in the x, y and z directions with a fixed step size, obtain the readings of three dial gauges 2 at each point, construct the analytical solution relationship between the readings of dial gauge 2 and the coordinates of the center of the first standard sphere 3 and the second standard sphere 7, and convert the readings to the measurement coordinate system of the R-test measurement unit.

[0034] Move the handwheel in fixed steps in the X, Y, and Z directions, and record the readings of the three dial gauges 2 at each point. Establish the analytical solution relationship between the center coordinates of the dial gauge 2 and the first standard sphere 3 and the second standard sphere 7, and convert the dial gauge readings to the measurement coordinate system of the R-test measurement unit.

[0035] In this embodiment, the spindle is moved in 0.02mm increments along the X, Y, and Z directions of the machine tool coordinate system using a handwheel, within a measurement range of ±0.2mm. The dial indicator data at each point is recorded as l. 1i ,l 2i ,l 3i For i = 1, 2, ..., n, the distance l used for calculation can be obtained by combining the dial indicator readings with the dial indicator's own structural data. i ,m i ,n i ,i=1,2...n.

[0036] The data collected in the above steps are converted to the standard spherical coordinate system. Based on the design principle of the contact R-test, a suitable measurement coordinate system is established. Utilizing the constraint relationship between the center of the standard sphere and the tangency of the probe, the following three equations can be written according to the point-to-plane distance formula:

[0037]

[0038] Where r is the radius of the first or second standard sphere, R is the radius of the circumcircle of the bottom surface of the dial indicator, the lengths of the dial indicator are l, m, n (distances from the starting point to the center point of the contact surface, which can be calculated from the readings), θ is the angle between the dial indicator and the plane of the mounting base, and x, y, z are the coordinates of the center of the first or second standard sphere in the dial indicator coordinate system. The final analytical solution is as follows:

[0039]

[0040] S3: The three dial indicators 2 are sequentially tangent to the first standard ball 3 and the second standard ball 7, and the main shaft is driven to obtain the raw data at different positions, combined with... Figure 2 .

[0041] S31: When measuring the C-axis error, return the A-axis to zero, tangent the three dial indicator probes to the first standard ball 3, adjust the spindle so that the readings of the three dial indicators are the same, regard this position as the zero point, and record the actual coordinates of the machine tool at this time.

[0042] When measuring the C-axis error, keep the A-axis at zero and find zero. Place the probes of the three dial indicators tangent to the first standard ball, adjust the spindle so that the readings of the three dial indicators are the same, take this position as the zero point, and record the actual coordinates of the machine tool at this time.

[0043] S32: Rotate the C-axis in preset angle steps to obtain the dial indicator data for each rotation;

[0044] Rotate the C-axis from 0° to 360° in 30° increments and enable the RTCP function. Hold each measurement point for 2 seconds until the data stabilizes, then transmit the dial indicator data to the host computer.

[0045] S33: Adjust the dial indicator probe to be tangent to the second standard ball 7, and repeat steps S31 and S32 to obtain the first dataset.

[0046] Adjust the R-test measurement unit position to be tangent to the second standard sphere, and repeat the zeroing process in step S31 and the measurement process in S32. When measuring the A-axis error, return the C-axis to zero and repeat steps S31 to S33. Similar to measuring the C-axis, when measuring the raw error data of the A-axis, keep the C-axis at zero and rotate the A-axis from -90° to 90° in 15° steps. Turn on the RTCP function and measure the data of the second standard sphere respectively to obtain the second dataset. The first dataset and the second dataset are the raw data.

[0047] Repeat the above steps, measuring 3 to 5 times, and take the average value.

[0048] S4: Based on the analytical solution relationship, the original data is converted into the coordinate changes of the center of the first standard ball 3 and the second standard ball 7 at different positions of the turntable to obtain the target data.

[0049] By analyzing and solving the above relationships, the raw data collected in step S3 is converted into the changes in the center coordinates of the sphere at different positions of the turntable, thus obtaining the target data.

[0050] S5: By combining the kinematic model of the five-axis machine tool with the properties of the position-related error terms of the rotary table, establish the correlation between the center coordinate deviation of the sphere and the position-related error. Based on the correlation, identify the target data into six position-related errors for each rotary table.

[0051] By using the geometric error relationship model of a five-axis machine tool and combining the properties of the position-related error terms of the rotary table, a mathematical relationship is established between the coordinate deviation of the center of the first and second standard spheres and the position-related error terms, thus identifying the target data as six position-related errors for each rotary table.

[0052] S51: Record the offset vectors of the first and second rotary axes of the machine tool displayed in the CNC system, denoted as L. acx L acy L acz L mcx L mcy L mcz Based on the initial position, actual machine tool coordinates, and tool length, the initial center positions O of the first and second standard spheres in the machine tool coordinate system can be obtained. h (O hx O hy O hz ) and O l (O lx O ly O lz ).

[0053] S52: At the position-related error identification point, step S4 above obtains the positional variation of the first and second standard spheres relative to the ideal position in the X, Y, and Z directions. The ideal position is the position of the sphere's center when no error exists. Based on this, combined with the machine tool's geometric error relationship model, the following set of geometric error identification equations about the C-axis can be obtained:

[0054] C i e i =Δ i i = 1, 2, ..., n

[0055] in:

[0056]

[0057] Among them, ei =[δ c (x) δ c (y) δ c (z) θ c (x) θ c (y) θ c (z)] T The geometric error term of the C-axis at the detection point is Δ. i =[Δx 1i Δy 1i Δz 1i Δx 2i Δy 2i Δz 3i ] T H represents the sphere center error value at the detection point along the C-axis. h H represents the height offset of the first standard sphere and the C-axis error analysis coordinate system. l R represents the height offset of the second standard sphere relative to the C-axis error analysis coordinate system. h Let R be the radius of rotation of the first standard sphere. l Let C be the radius of rotation of the second standard sphere. i Let δ be the error identification matrix. c (x), δ c (y), δ c (z) represents the position error term, θ c (x), θ c (y), θ c (z) represents the angle error term, Δx 1i Δy 1i Δz 1i The deviation of the center of the first standard sphere is Δx. 2i Δy 2i Δz 3i This represents the deviation of the center of the second standard ball.

[0058] We can solve for e i =C i -1 ·Δ i This refers to the C-axis position correlation error.

[0059] S53: Similar to step S52, the original error data of the A-axis and the identification equation set can be obtained:

[0060] A i e i =Δ i i = 1, 2, ..., n

[0061] in:

[0062]

[0063] Ai Error identification matrix

[0064] We can solve for e i =A i -1 ·Δ i This allows us to obtain the positional error of the A-axis.

[0065] In a further optimized scheme, steps S3 to S5 above can be repeated multiple times, and the average value of the position-related error identification results can be taken.

[0066] This application effectively separates and identifies comprehensive measurement error values, conveniently obtaining all 12 position-related error values ​​of a dual-axis five-axis machine tool, which can be used for machine tool accuracy evaluation and error compensation. The R-test measurement unit of this application is simple to manufacture, low in cost, and highly applicable.

[0067] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for identifying rotational axis position correlation errors in a dual-rotary-table five-axis CNC machine tool, characterized in that, Based on the rotary axis position correlation error measurement device of a five-axis CNC machine tool with dual rotary table, the measurement device includes an R-test measurement unit, a first standard ball (3), a second standard ball (7), a standard ball tooling fixture (5), a connecting rod (6), a first support rod (8), a second support rod (9), and two magnetic seats (4). The R-test measurement unit includes a dial indicator fixture (1) and three dial indicators (2), wherein: Three dial indicators (2) are fixed on the dial indicator fixture (1), which is fixed on the spindle of the CNC machine tool; The first standard ball (3) and the second standard ball (7) are fixed at both ends of the connecting rod (6); The connecting rod (6) is connected to the first support rod (8) and the second support rod (9) respectively through two standard ball tooling fixtures (5); The first support rod (8) and the second support rod (9) are respectively fixed on two magnetic bases (4), which are used to fix the rod on the horizontal turntable. The length of the first support rod (8) is greater than that of the second support rod (9), and the first standard ball (3) is disposed at the end of the first support rod (8); Identification methods include: S1: Drive the spindle to move the R-test measuring unit until the readings of the three dial gauges (2) are the same, and determine that the corresponding position at this time is the measurement zero position; S2: Drive the main shaft again to move the R-test measurement unit in the x, y and z directions with a fixed step size, obtain the readings of the three dial gauges (2) at each point, construct the analytical solution relationship between the readings of the dial gauges (2) and the coordinates of the center of the first standard sphere (3) and the second standard sphere (7), and convert the readings to the measurement coordinate system of the R-test measurement unit; S3: The three dial gauges (2) are sequentially tangent to the first standard ball (3) and the second standard ball (7), and the main shaft is driven to move to obtain the original data at different positions; S4: Based on the analytical solution relationship, the original data is converted into the coordinate changes of the center of the first standard ball (3) and the second standard ball (7) at different positions of the turntable to obtain the target data; S5: By combining the kinematic model of the five-axis machine tool with the properties of the position-related error terms of the rotary table, establish the correlation between the center coordinate deviation of the first or second standard ball and the position-related error. Based on the correlation, identify the target data into six position-related errors for each rotary table. In step S2, the analytical solution relationship is obtained by constructing the tangent constraint between the center of the first standard sphere (3) and the second standard sphere (7) and the dial gauge (2) based on the distance formula from point to plane; The analytical solution relationship is as follows: in, Let be the coordinates of the center of the first or second standard sphere in the dial indicator coordinate system. The tilt angle between the dial indicator and the mounting base plane. R is the distance from the center of the bottom surface of the three dial indicators to the center of the dial indicator probe, R is the radius of the circumscribed circle of the bottom surface of the dial indicator, and r is the radius of the first or second standard sphere.

2. The identification method according to claim 1, characterized in that, The three dial gauges (2) are evenly distributed around the dial gauge fixture (1).

3. The identification method according to claim 1 or 2, characterized in that, The three dial gauges (2) are movably connected to the periphery of the dial gauge fixture (1).

4. The identification method according to claim 1 or 2, characterized in that, The flat probes of the three dial gauges (2) are tangent to the first standard sphere (3) or the second standard sphere (7).

5. The identification method according to claim 1, characterized in that, The first standard ball (3) and the second standard ball (7) have the same diameter.

6. The identification method according to claim 1, characterized in that, Step S3 specifically includes: S31: When measuring the C-axis error, return the A-axis to zero, tangent the three dial indicator probes to the first standard ball (3), adjust the spindle so that the readings of the three dial indicators are the same, regard this position as the zero point, and record the actual coordinates of the machine tool at this time; S32: Rotate the C-axis in preset angle steps to obtain the dial indicator data for each rotation; S33: Adjust the dial indicator probe to be tangent to the second standard ball (7), repeat steps S31 and S32 to obtain the first dataset; When measuring the A-axis error, return the C-axis to zero and repeat steps S31~S33 to obtain the second dataset. Both the first and second datasets are the original data.

7. The identification method according to claim 1, characterized in that, It also includes repeating steps S3 to S5 to obtain the average value of the position-related error.

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