A method for measuring and identifying geometric errors of a rotary axis of a numerical control machine tool

Abstract

The present application is suitable for the field of numerical control machine tool rotating shaft error term measurement, and particularly relates to a kind of numerical control machine tool rotating shaft geometric error measurement and identification method.Actual rotating shaft line is fitted out by target ball in different positions of rotating shaft axis line respectively by revolving a circle;Then, the target ball is installed at the position deviating from the center of the rotating shaft, and the theoretical circumference diameter is identified by rotating 180 degrees;Finally, the rotating shaft rotates 360 degrees, and the theoretical circumference and the actual circumference of the rotating shaft in space movement are fitted, and then the error term is identified through the difference between the actual circle and the theoretical circle.Compared with the prior art, the present application solves the problem that the angle positioning error cannot be identified by the laser tracker in the prior art, realizes the identification of all geometric errors of the machine tool rotating shaft based on the laser tracker, and can be used for error compensation of the machine tool.

Description

TECHNICAL FIELD

[0001] The application is suitable for the field of numerical control machine tool rotating shaft error term measurement, and particularly relates to a numerical control machine tool rotating shaft geometric error measurement and identification method. BACKGROUND

[0002] In the machining process of a numerical control machine tool, the geometric error of a rotating shaft is one of the important factors affecting the machining precision. Therefore, the accurate measurement and effective identification of the geometric error of the rotating shaft are crucial for improving the machining quality and efficiency of the numerical control machine tool. In recent years, with the rapid development of laser technology, a laser tracker, as a high-precision measurement device, has shown broad application prospects in the field of numerical control machine tool error detection.

[0003] Existing rotating shaft geometric error measurement methods mainly include mechanical measurement, contact measurement and optical measurement. Although these methods can achieve error measurement to some extent, they have problems such as limited measurement precision, complex operation, strict requirements for measurement environment, etc. In addition, these methods can only measure a single error term and cannot identify the angle positioning error of the rotating shaft, making it difficult to fully reflect the overall error situation of the rotating shaft.

[0004] Therefore, there is an urgent need for a new numerical control machine tool rotating shaft geometric error measurement and identification method to solve the above problems. SUMMARY

[0005] Therefore, the present application provides a numerical control machine tool rotating shaft geometric error measurement and identification method, which solves the problem that the angle positioning error cannot be identified by a laser tracker in the prior art, realizes the identification of all geometric errors of the machine tool rotating shaft based on a laser tracker, and can be used for error compensation of the machine tool.

[0006] The measurement method comprises the following steps:

[0007] S1, measuring the rotation center line of the rotating shaft, a chuck is fixed on the rotating shaft, a target ball seat is clamped at a predetermined distance from the end face of the chuck away from the rotating shaft, and a target ball is fixed on the target ball seat; a first center point is obtained by a predetermined method;

[0008] S2, installing and fixing the target ball seat on the end face of the chuck away from the rotating shaft, obtaining a second center point by the predetermined method, determining a straight line of the first center point and the second center point in space as the actual rotation axis of the rotating shaft, determining a reference axis by a laser tracker, and determining an axis parallel to the reference axis and passing through the first center point as the theoretical axis of the rotating shaft;

[0009] S3, fixing the target ball seat at a position deviated from the rotation center line of the chuck, recording the current position of the target ball as a first position, controlling the rotation shaft to rotate 180°, recording the current position of the target ball as a second position, rotating the rotation shaft by a preset number of turns, and recording the position coordinates at the first position and the second position at each rotation, calculating the average of the position coordinates of the first position and the average of the position coordinates of the second position as a third center point and a fourth center point respectively, and taking the spatial distance between the third center point and the fourth center point as a theoretical circle diameter;

[0010] S4, rotating the rotation shaft by a preset angle interval in the clockwise direction and the counterclockwise direction respectively by 360°, recording the spatial coordinates of the target ball at each interval, calculating the actual rotation radius and the actual circle center position according to the spatial coordinates, and measuring the X-axis coordinate position of the target ball seat to calculate the X-axis coordinate of the theoretical circle center; wherein the X-axis coordinate of the theoretical circle center is the sum of the X-axis coordinate of the target ball seat and the radius of the target ball;

[0011] S5, drawing an actual circle according to the actual rotation radius, the actual circle center position and the actual rotation axis, and drawing a theoretical circle according to the theoretical axis, the X-axis coordinate of the theoretical circle center and the theoretical circle diameter;

[0012] S6, calculating the geometric error according to the difference between the actual circle and the theoretical circle.

[0013] Preferably, the size of the preset angle is 10°.

[0014] Preferably, the preset method is: rotating the rotation shaft along the rotation center line for one turn, recording the spatial position coordinates of the target ball at a preset time interval during rotation, and calculating the average of the spatial position coordinates as a center point.

[0015] Preferably, the X-axis coordinate position of the target ball seat is measured by a centering rod.

[0016] Preferably, the geometric error includes an angle error and a perpendicular error, and the center of the theoretical circle is defined as O and the center of the actual circle is defined as O', then the angle error of the rotation shaft on the Y-axis and the Z-axis satisfies the following calculation formula:

[0017]

[0018]

[0019] wherein ε yA (m) represents the angle error of the rotation shaft on the Y-axis, and ε zA(m) represents the angle error of the rotation axis in the Z axis, represents the direction vector.

[0020] Preferably, the perpendicular error of the rotation axis in the Y axis and the Z axis satisfies the following calculation formula:

[0021]

[0022]

[0023]

[0024] wherein S yA (m) represents the perpendicular error of the rotation axis in the Y axis, S zA (m) represents the perpendicular error of the rotation axis in the Z axis, represents the normal vector of the plane O'GH, G and H are any two points on the actual circular track.

[0025] Compared with the prior art, the actual rotation axis is fitted by the target ball at different positions of the rotation axis axis respectively; then the target ball is installed at a position deviating from the center of the rotation axis, and a theoretical circular diameter is identified by rotating 180°; finally, the rotation axis rotates 360°, and the theoretical circle and the actual circle of the rotation axis in space movement are fitted, and then the error term is identified through the difference between the actual circle and the theoretical circle. The problem that the angle positioning error cannot be identified by the laser tracker in the prior art is solved, the identification of all geometric errors of the machine tool rotation axis based on the laser tracker is realized, and the error compensation of the machine tool can be used. BRIEF DESCRIPTION OF DRAWINGS

[0026] The above and other aspects of the present application will become more apparent and more readily appreciated from the following detailed description, taken in conjunction with the accompanying drawings, in which:

[0027] Figure 1 is a flowchart of the measurement and identification method of the geometric error of the numerical control machine tool rotation axis provided by the embodiment of the present application;

[0028] Figure 2 is a principle schematic diagram of steps S1-S4 of the measurement and identification method of the geometric error of the numerical control machine tool rotation axis provided by the embodiment of the present application;

[0029] Figure 3 is a schematic diagram of the actual circle and the theoretical circle of the measurement and identification method of the geometric error of the numerical control machine tool rotation axis provided by the embodiment of the present application;

[0030] Figure 4 is a schematic diagram of the geometric error of the numerical control machine tool rotation axis of the measurement and identification method of the geometric error of the numerical control machine tool rotation axis provided by the embodiment of the present application;

[0031] Figure 5 is the rotation axis error identification principle diagram of the measurement and identification method of the geometric error of the rotary axis of the numerical control machine tool provided by the embodiment of the present application. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0033] Please refer to Figures 1-5 The present application provides a measurement and identification method of the geometric error of the rotary axis of the numerical control machine tool, the measurement method comprising the following steps:

[0034] S1, measuring the rotation center line of the rotary axis, the rotary axis being fixed with a chuck, a target ball seat being clamped at a preset distance from the end face of the chuck away from the rotary axis, the target ball seat being fixed with a target ball; a first center point (i.e. fitting center point 1 in the figure) is obtained by a preset method; Figure 1

[0035] In the embodiment of the present application, the preset method is: rotating the rotary axis along the rotation center line for one revolution, recording the spatial position coordinates of the target ball at preset intervals during rotation, and calculating the average value of the spatial position coordinates as the center point.

[0036] S2, installing and fixing the target ball seat on the end face of the chuck away from the rotary axis, obtaining a second center point (i.e. fitting center point 2 in the figure) by the preset method, determining a straight line passing through the first center point and the second center point in space as the actual rotation axis of the rotary axis, determining a reference axis by a laser tracker, and determining an axis parallel to the reference axis and passing through the first center point as the theoretical axis of the rotary axis; Figure 1 S3, fixing the target ball seat on the chuck at a position deviating from the rotation center line, recording the position of the target ball as a first position (0°), controlling the rotary axis to rotate 180°, recording the position of the target ball as a second position (180°), rotating the rotary axis by a preset number of revolutions, and recording the position coordinates at the first position and the second position each time, calculating the average value of the position coordinates of the first position and the average value of the position coordinates of the second position as a third center point (i.e. fitting center point 3 in the figure) and a fourth center point (i.e. fitting center point 4 in the figure) respectively;

[0037] Figure 1 Figure 1 ​​​The fitting center point 4 in the figure is used, and the spatial distance between the third center point and the fourth center point is used as the theoretical circle diameter;

[0038] S4. Rotate the rotation axis 360° clockwise and counterclockwise at intervals of a preset angle, record the spatial coordinates of the target sphere at each interval, calculate the actual rotation radius and the actual center position of the circle based on the spatial coordinates, measure the X-axis coordinate position of the target sphere seat, and thereby calculate the X-axis coordinate of the theoretical center of the circle; wherein the X-axis coordinate of the theoretical center of the circle is the sum of the X-axis coordinate of the target sphere seat and the radius of the target sphere;

[0039] In the embodiment of the present invention, the preset angle is 10°.

[0040] In the embodiment of the present invention, the X-axis coordinate position of the target ball seat is measured by a centering rod.

[0041] S5. Draw an actual circle according to the actual rotation radius, the actual circle center position, and the actual rotation axis, and draw a theoretical circle according to the theoretical axis, the X-axis coordinate of the theoretical circle center, and the theoretical circle diameter;

[0042] S6. Calculate a geometric error based on the difference between the actual circle and the theoretical circle.

[0043] In the embodiment of the present invention, Figure 3 As shown, Figure 3 Schematic diagram of the actual circle and theoretical circle of the method for measuring and distinguishing the geometric error of the rotating axis of a CNC machine tool provided by an embodiment of the present invention. The geometric error includes angular error and vertical error. The center of the theoretical circle is defined as O, the dotted line is the theoretical circle trajectory, the solid line is the actual circle trajectory, and the coordinate difference between each measuring point of the actual circle and O is the positioning error δ of the A axis. xA (m), δ yA (m), δ zA (m). The center of the actual circle is O′, and the angular errors of the rotation axis on the Y and Z axes satisfy the following calculation formula:

[0044]

[0045]

[0046] Among them, ε yA (m) represents the angular error of the rotation axis on the Y axis, ε zA (m) represents the angular error of the rotation axis in the Z axis, Represents a direction vector.

[0047] In an embodiment of the present invention, the vertical errors of the rotation axis on the Y axis and the Z axis satisfy the following calculation formula:

[0048]

[0049]

[0050]

[0051] where S yA (m) represents the perpendicular error of the rotary axis in the Y axis, S zA (m) represents the perpendicular error of the rotary axis in the Z axis, represents the normal vector of the plane O'GH, G and H are any two points on the actual circular trajectory.

[0052] It should be noted that the following terms are explained as follows:

[0053] Fitting center point: a series of points used to determine the theoretical axis, the actual axis, the theoretical circle diameter, etc.

[0054] Target ball: the laser emitted by the measuring and tracking head of the laser tracking system is reflected on the target ball installed on the measuring target and then returned to the tracking head. When the target moves, the tracking head adjusts the direction of the light beam to aim at the target. The returned light beam is received by the detection system to measure the spatial position of the target.

[0055] Cyclic measurement: that is, when measuring the target using a laser tracker, the target chuck is rotated at certain angular intervals for measurement.

[0056] Specifically, XK200A numerical control machine tool is taken as an example for geometric error measurement, the environmental temperature is 22℃, and the new 12-line method is used to identify the error items. The main technical parameters of the machine tool are shown in Table 1:

[0057] Table 1 Main technical parameters of XK200A machine tool

[0058]

[0059] The measured geometric error of the A-axis (i.e. rotary axis) is shown in Figure 4 The geometric error of the A-axis changes with the rotation angle of the A-axis, the position error δ zA (m) is greater than δ yA (m) and δ xA (m), and is smallest near 180 degrees; the angle error basically presents the trend of first increasing and then decreasing.

[0060] To verify the accuracy of the A-axis error measurement, the rotary axis geometric error cyclic identification method is used to measure the geometric error of the A-axis. This method can identify the angle positioning error item ε xA(m) and other geometric error terms. The error term identification principle is shown in Fig. 1, and the measurement steps are as follows: Figure 5

[0061] (1) The target ball is fixed at point A1 on the end face of the A-axis, and the X, Y and Z directions of the A-axis coordinate system X A Y A Z A are respectively aligned with the X, Y and Z directions of the reference coordinate system X R Y R Z R , and the X-direction distance from the reference coordinate system X R Y R Z R to the target ball is H1. The laser tracker follows the A-axis to make a circular measurement, and the measured length is (L laser1 , α) at this time, where α is the rotation angle of the A-axis.

[0062] (2) The X-axis is fed by a distance, and the position of the A-axis is changed to H2. At this time, the target ball is moved to point A2, and a circular measurement is made again. The measured length of the laser tracker is (L laser2 , α).

[0063] In the two measurements, four measurement paths of α = 0°, 90°, 180° and 270° are selected, and the solving formula is shown below. Eight equations are obtained to realize the solving of the A-axis geometric error terms δ zA (m), δ yA (m), δ xA (m), ε zA (m), ε yA (m). The calculation results are shown in Table 2. The results show that the error term values obtained by the two methods are close. Compared with the circular measurement method, the measurement method proposed in the application realizes the measurement of all geometric error terms of the A-axis of the machine tool based on the laser tracker, and provides a method reference for the geometric error measurement of the rotary axis of the numerical control machine tool.

[0064]

[0065] Table 2 Comparison of A-axis geometric errors

[0066]

[0067]

[0068] In the formula, d laser represents the X-direction distance from the laser measurement head to the reference coordinate system; Δ'(L laser , α) represents the difference between the square of the measured value of the laser tracker and the square of the ideal value; δ zA (m) represents the position error of the A-axis rotary motion in the Z direction; δ yA (m) represents the position error of the A-axis rotary motion in the Y direction; δ xA (m) represents the position error of the A-axis rotary motion in the X direction; ε zA(m) represents the angular error of the A-axis rotary motion about the Z-axis; ε yA (m) represents the angular error of the A-axis rotary motion about the Y-axis.

[0069] According to the above analysis, the size of the geometric error is related to the position of each axis motion. In order to facilitate the calculation of the comprehensive machining error of the numerical control machine tool, the geometric error is described as a polynomial varying with the position of each axis motion, and the A-axis feed amount of the machine tool is α. The geometric error fitting equation of the A-axis is as follows:

[0070]

[0071] Perpendicularity:

[0072]

[0073] In the actual machining process of the machine tool, the motion range of each axis can be determined according to the numerical control code, each geometric error term is described by a polynomial, the geometric error is substituted into the parameter error term of the error model, and the tool posture error model is established to predict the motion trajectory of the tool in the actual machining process.

[0074] It should be noted that in this article, the term "includes", "contains" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or includes elements inherent to such process, method, article or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method, article or device including the element.

[0075] The embodiments of the present application are described above in combination with the drawings, and the disclosed is only the preferred embodiments of the present application, but the present application is not limited to the above specific embodiments. The above specific embodiments are only illustrative, not restrictive, and those skilled in the art can make many equivalent changes under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims.

Claims

1. A method for measuring and identifying geometric errors of a rotating axis of a CNC machine tool, characterized in that: The measuring method comprises the following steps: S1. Measure the rotation centerline of a rotating shaft, wherein a chuck is fixed to the rotating shaft, a target ball seat is clamped at a preset distance from the end face of the chuck away from the rotating shaft, and a target ball is fixed to the target ball seat; obtain a first center point by a preset method; S2. Mounting and fixing the target ball seat on the end face of the chuck away from the rotation axis, obtaining a second center point by the preset method, taking a straight line defined in space by the first and second center points as the actual rotation axis of the rotation axis, determining a reference axis by a laser tracker, and taking an axis parallel to the reference axis and passing through the first center point as the theoretical axis of the rotation axis; S3. Fixing the target ball seat at a position of the chuck that deviates from the rotation centerline, recording the current position of the target ball as the first position, controlling the rotation axis to rotate 180°, recording the current position of the target ball as the second position, rotating the rotation axis a preset number of times, and recording the position coordinates of each rotation at the first position and the second position, calculating the average value of the position coordinates of the first position and the average value of the position coordinates of the second position, and using them as the third center point and the fourth center point, respectively, and using the spatial distance between the third center point and the fourth center point as the theoretical circle diameter; S4. Rotate the rotation axis 360° clockwise and counterclockwise at intervals of a preset angle, record the spatial coordinates of the target sphere at each interval, calculate the actual rotation radius and the actual center position of the circle based on the spatial coordinates, measure the X-axis coordinate position of the target sphere seat, and thereby calculate the X-axis coordinate of the theoretical center of the circle; wherein the X-axis coordinate of the theoretical center of the circle is the sum of the X-axis coordinate of the target sphere seat and the radius of the target sphere; S5. Draw an actual circle according to the actual rotation radius, the actual circle center position, and the actual rotation axis, and draw a theoretical circle according to the theoretical axis, the X-axis coordinate of the theoretical circle center, and the theoretical circle diameter; S6. Calculate a geometric error based on the difference between the actual circle and the theoretical circle.

2. The method for measuring and identifying geometric errors of a CNC machine tool's rotary axis according to claim 1, wherein: The preset angle is 10°.

3. The method for measuring and identifying geometric errors of a CNC machine tool's rotary axis according to claim 1, wherein: The preset method is: rotating the rotation axis along the rotation center line for one circle, recording the current spatial position coordinates of the target ball at preset time intervals during the rotation process, and calculating the average value of the spatial position coordinates as the center point.

4. The method for measuring and identifying geometric errors of a CNC machine tool's rotary axis according to claim 1, wherein: The X-axis coordinate position of the target ball seat is measured by a centering rod.

5. The method for measuring and identifying geometric errors of a CNC machine tool's rotary axis according to claim 1, wherein: The geometric error includes angular error and vertical error. The center of the theoretical circle is defined as O and the center of the actual circle is defined as O'. Then, the angular errors of the rotation axis on the Y and Z axes satisfy the following calculation formula: Among them, ε yA (m) represents the angular error of the rotation axis on the Y axis, ε zA (m) represents the angular error of the rotation axis in the Z axis, Represents a direction vector.

6. The method for measuring and identifying geometric errors of a CNC machine tool rotary axis according to claim 5, wherein: The vertical error of the rotation axis on the Y axis and the Z axis satisfies the following calculation formula: Among them, S yA (m) represents the vertical error of the rotation axis on the Y axis, S zA (m) represents the vertical error of the rotation axis on the Z axis, represents the normal vector of the plane O′GH, G and H are any two points on the actual circular trajectory.

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