Five-axis machine tool rotary axis geometric error detection and identification method based on ball-bar measurement

Abstract

The present application relates to a kind of five-axis machine tool rotation axis geometric error detection and identification method based on ball bar measurement, comprising: establishing five-axis machine tool geometric error model;Determine the axis of rotation of two points, and respectively determine the installation position of ball bar X direction, Y direction, Z direction at the two points;Get the reading of ball bar at different installation positions when rotation axis rotates;According to the two groups of readings of ball bar and the coordinates of fixed ball when ball bar X direction, Y direction, Z direction is installed, 3 three-dimensional spherical surfaces are established respectively, the intersection point is a point on the axis of rotation, the axis expression of rotation axis is determined by two different space points;Compare actual axis and ideal axis when rotation axis rotates, determine all 10 geometric errors of rotation axis by means of corresponding geometric error identification formula.The present application is suitable for different types of five-axis machine tool rotation axis error detection scene, only need rotation axis to participate in rotation when measuring, principle is correct, convenient and simple, measurement is convenient, identification efficiency and identification precision are high.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of geometric error measurement, and particularly relates to a method for detecting and identifying geometric errors of a rotating shaft of a five-axis machine tool based on a ball bar measurement. BACKGROUND

[0002] In the field of modern manufacturing, five-axis machine tools play an important role. Compared with three-axis machine tools, five-axis machine tools have higher machining efficiency and more extensive machining capabilities, but also introduce multiple geometric errors of rotating shafts, which adversely affect the machining accuracy of the machine tool. The error elements of the rotating shafts are more difficult to detect and identify than the error elements of the linear shafts, thus bringing many difficulties to the error compensation of the five-axis machine tool.

[0003] However, the existing methods for detecting and identifying geometric errors of rotating shafts still have defects in terms of operational simplicity and directness of identification target: some measurement methods adopt a linear shaft linkage mode, which is complex to operate and introduces linear shaft error terms, which is not conducive to improving the error identification accuracy. The above problems seriously restrict the operability and efficiency of the identification of geometric errors of the rotating shafts, affect the further geometric error compensation of the machine tool, and indirectly cause the bottleneck problem that the geometric quality of parts cannot be improved in the manufacturing process, threatening the market competitiveness and long-term development of products and enterprises. SUMMARY

[0004] The present application aims to overcome the deficiencies of the prior art and provide a method for detecting and identifying geometric errors of a rotating shaft of a five-axis machine tool based on a ball bar measurement. First, the installation position of the ball bar is determined according to the type of the rotating shaft of the machine tool. Second, the rotating shaft is rotated to obtain readings of the ball bar at different installation positions. Third, the expression of the actual axis of the rotating shaft is obtained. Finally, the actual axis and the ideal axis of the rotating shaft during rotation are compared, and all 10 geometric errors of the rotating shaft can be determined by using the geometric error identification formula. This method does not require the participation of linear shafts in linkage and has no principle errors, thus improving the operability and overall efficiency of the detection process while ensuring the identification accuracy.

[0005] The present application solves its technical problem by the following technical solution:

[0006] A method for detecting and identifying geometric errors of a rotating shaft of a five-axis machine tool based on a ball bar measurement, the steps of the method being:

[0007] S1, establishing a geometric error model of the five-axis machine tool based on the screw theory;

[0008] S2, determining two points on the axis of the rotating shaft according to the type and position of the rotating shaft of the machine tool, and determining the installation positions of the ball bar in X, Y and Z directions at the two points, respectively;

[0009] S3, according to the influence of the geometric error of the rotating shaft on the precision of the machine tool, readings of the ball bar at different installation positions when the rotating shaft rotates are obtained;

[0010] S4, according to the two groups of readings of the ball bar and the coordinates of the fixed ball when the ball bar is installed in the X direction, the Y direction and the Z direction, three spatial spherical surfaces are respectively established, and the intersection point is a point on the axis of the rotating shaft, and the axis expression of the rotating shaft is determined by two different spatial points;

[0011] S5, the actual axis and the ideal axis when the rotating shaft rotates are compared, and all 10 geometric errors of the rotating shaft are determined by means of the corresponding geometric error identification formula.

[0012] Moreover, the S1 fully considers whether the actual movement direction of each axis of the machine tool is the same as the direction of the right-hand coordinate system, and if the directions are different, the error matrix corresponding to the axis is changed into the inverse matrix of the error matrix.

[0013] Moreover, the S2 is specifically:

[0014] S21, the type of the rotating shaft of the machine tool is determined, and the rotating coordinate system of the rotating shaft to be measured is set according to the structure of the machine tool and the structure of the rotating shaft;

[0015] S22, two groups of measurement positions of the ball bar in the corresponding rotating shaft coordinate system are determined, including the position of the center ball of the ball bar and the placement direction of the ball bar, and specifically as follows:

[0016] In the first group of measurements, the center ball t of the ball bar is installed at h1 on the X axis of the rotating shaft coordinate system, and the coordinates are (h1, 0, 0), and the tool side ball s is clamped at the spindle end, and the ball bar is placed along the X axis, Y axis and Z axis direction respectively, and the coordinates of the tool side ball s are (h1+L, 0, 0), (h1, L, 0) and (h1, 0, L) respectively.

[0017] In the second group of measurements, the center ball t of the ball bar is installed at h2 on the X axis of the rotating shaft coordinate system, and the coordinates are (h2, 0, 0), and the tool side ball s is clamped at the spindle end, and the ball bar is placed along the X axis, Y axis and Z axis direction respectively, and the coordinates of the tool side ball s are (h2+L, 0, 0), (h2, L, 0) and (h2, 0, L) respectively.

[0018] Moreover, the S3 is specifically: in the first group of measurements, the readings of the ball bar placed along the X axis, Y axis and Z axis direction are respectively recorded as L1, L2 and L3; in the second group of measurements, the readings of the ball bar placed along the X axis, Y axis and Z axis direction are respectively recorded as L4, L5 and L6.

[0019] Moreover, the S4 is specifically:

[0020] The first group of measurements, according to the coordinates (h1+L, 0, 0), (h1, L, 0), (h1, 0, L) of the tool-side ball s, the length L of the ball bar and the corresponding readings L1, L2, L3 of the ball bar, three spatial spherical surfaces are respectively established, and the intersection point of the three spatial spherical surfaces is a point D1 on the axis of the rotation axis, and the coordinates of the point D1 are represented as (x1, y1, z1);

[0021] The second group of measurements, according to the coordinates (h2+L, 0, 0), (h2, L, 0), (h2, 0, L) of the tool-side ball s, the length L of the ball bar and the corresponding readings L4, L5, L6 of the ball bar, three spatial spherical surfaces are respectively established, and the intersection point of the three spatial spherical surfaces is a point D2 on the axis of the rotation axis, and the coordinates of the point D2 are represented as (x2, y2, z2);

[0022] The line l connecting the t-ball coordinate points (h1, 0, 0) and (h2, 0, 0) of the ball bar at two different installation heights is the ideal axis of the rotation axis, and the actual axis l' of the rotation axis when rotating is obtained by connecting the two different spatial points D1 and D2.

[0023] Moreover, the S5 specifically comprises:

[0024] S51, comparing the actual axis l' of the rotation axis with the ideal axis l, the deviation of the actual axis of the rotation axis in the X-axis, Y-axis and Z-axis directions at the coordinate origin is the linear error term ε xa , ε ya , ε za in the rotation axis position related error term.

[0025] S52, comparing the deviation angle of the actual axis l' of the rotation axis relative to the ideal axis l in the XOZ and XOY planes is the rotation error term ε ya , ε za around the Y-axis and the Z-axis in the rotation axis position related error term.

[0026] S53, in the first group of measurements, the ball bar is placed along the Y-axis direction, and the vector of the center ball t pointing to the tool-side ball s in the workpiece coordinate system can be obtained by subtracting the coordinates of the two in the workpiece coordinate system, or can be obtained by rotating the vector of the point D1 on the actual axis of the rotation axis in the global coordinate system pointing to the ball s around the X-axis, and the rotation error term ε xa around the X-axis in the rotation axis position related error term can be obtained by combining the two.

[0027] S54, the rotation axis position independent error term is regarded as a part of the position related error term, and the position related error term value of the rotation axis when the rotation angle is 0 is the rotation axis position independent error value, and the measured position related error term is respectively subtracted by the value when the rotation angle is 0, so as to obtain the rotation axis position related error term, and thus the 10 geometric error terms of the rotation axis can be identified.

[0028] The advantages and beneficial effects of the present application are:

[0029] 1、The method of the present application is simple to operate: only the rotating shaft to be measured needs to be rotated, and no linear shaft is involved in linkage;

[0030] 2、The identification of the present application is direct, and the data of the ball bar instrument measured only contains the error term caused by the rotating shaft, without the linear shaft error term introduced by the linear shaft linkage;

[0031] 3、The present application has wide applicability, and the method is applicable to machine tools of different structures;

[0032] 4、The present application promotes the technological progress of the manufacturing industry, and the application of the present application improves the precision, safety and efficiency of the detection and identification of the geometric error of the rotating shaft, and has guiding significance for the identification and compensation of the geometric error of the machine tool. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is the installation position diagram of the ball bar instrument of the present application;

[0034] Figure 2 is a schematic diagram of position-related error identification of the present application. DETAILED DESCRIPTION

[0035] The present application will be further described below through specific embodiments, and the following embodiments are only descriptive and not limiting, and cannot limit the protection scope of the present application.

[0036] The embodiment of the present application discloses a five-axis machine tool rotating shaft geometric error detection and identification method based on ball bar measurement, and the ball bar instrument installation position is as shown in Figure 1 During the rotating shaft geometric error identification process, the method is divided into three links of ball bar instrument installation, ball bar instrument data reading during rotating shaft rotation and rotating shaft geometric error identification.

[0037] Specifically, the five-axis machine tool rotating shaft geometric error detection and identification method provided by the embodiment includes the following steps:

[0038] (1) Establishing a five-axis machine tool geometric error model

[0039] Taking A-axis measurement and identification as an example, the A-axis motion matrix can be expressed as

[0040] Among them:

[0041]

[0042] (2) Determine the installation position of the ball bar instrument

[0043] As shown in Figure 1As shown, in the first set of measurements, the central ball t of the ballbar is installed at position h1 on the X-axis of the rotation axis coordinate system, with coordinates (h1, 0, 0). The tool side ball s is clamped at the spindle end. The ballbar is placed along the X-axis, Y-axis, and Z-axis directions, respectively. The coordinates of the tool side ball s are (h1+L, 0, 0), (h1, L, 0), and (h1, 0, L), respectively.

[0044] In the second set of measurements, the central ball t of the ballbar is installed at h2 on the X-axis of the rotation axis coordinate system, with coordinates (h2,0,0). The tool side ball s is clamped at the spindle end. The ballbar is placed along the X-axis, Y-axis, and Z-axis respectively, so the coordinates of the tool side ball s are (h2+L,0,0), (h2,L,0), and (h2,0,L).

[0045] (3) Determine the axis expression of rotation of the axis of rotation from the bar reading and the coordinates of the fixed ball.

[0046] The first set of measurements establishes three spatial spheres based on the coordinates (h1+L,0,0), (h1,L,0), and (h1,0,L) of the tool side ball s (fixed ball), the length L of the ball bar itself, and the corresponding readings L1, L2, and L3 of the ball bar. The intersection of these spheres is a point D1 on the axis of rotation, with coordinates (x1,y1,z1).

[0047] The second set of measurements establishes three spatial spheres based on the coordinates (h2+L,0,0), (h2,L,0), and (h2,0,L) of the tool side ball s (fixed ball), the length L of the ball bar itself, and the corresponding readings L4, L5, and L6 of the ball bar. The intersection of these spheres is a point D2 on the axis of rotation, with coordinates (x2,y2,z2).

[0048] The actual axis l' of the rotation axis is obtained from two points in space.

[0049] (4) Identify 10 geometric errors of the rotating axis

[0050] like Figure 2 As shown, where ε xa ε ya δ za These represent the displacement error terms in the X, Y, and Z directions respectively when the A-axis rotates, ε xa ε ya ε za These represent the angular errors caused by rotation around the X, Y, and Z axes when the A-axis rotates.

[0051] The average X-coordinate of points D1 and D2 on the axis of rotation The average X-coordinate of the two sets of central spheres t Then the position-related term error

[0052] We can obtain:

[0053]

[0054] Find the x-coordinate of line l' when its value is δ. xa At that time, the Y-coordinate value of the straight line is the position-related term error δ. ya The Z-coordinate value of the straight line is the position-related term error δ. za .

[0055] The equation of a line given two points in space can be expressed as:

[0056]

[0057] The vector pointing from D1 to D2 The position-related term error ε is (x2-x1, y2-y1, z2-z1). za For vectors Projection on the XOY plane The angle between (x2-x1, y2-y1, 0) and the positive X-axis; position-related term error ε ya For vectors Projection on the XOZ plane The angle between (x2-x1,0,z2-z1) and the positive X-axis. ε za and ε ya The sign of a denoted is determined by the right-hand rule.

[0058] From the formula for calculating the angle between spatial vectors, we get:

[0059]

[0060] In the first set of measurements, the ball bar is placed in the Y-axis. The initial position of ball t in the workpiece coordinate system is (h1,0,0), and the initial position of ball s in the workpiece coordinate system is (h1,L,0). The ball is rotated along the A-axis by an angle θ. a back.

[0061] The coordinates of the tool ball s in the workpiece coordinate system are:

[0062] The coordinates of the workpiece sphere t in the workpiece coordinate system are:

[0063] The vector pointing from the workpiece sphere t to the tool sphere s in the workpiece coordinate system is:

[0064]

[0065] The vector pointing from the workpiece sphere t to the tool sphere s in the workpiece coordinate system is represented as:

[0066]

[0067] Two expression methods are combined and simplified as:

[0068]

[0069] Where θ a ≠0, π, 2π. When θ a =0, 2π, ε xa =0; when π, The value of the error term at an angle can be interpolated from the error values at adjacent angles, which are denoted as

[0070]

[0071] Where i represents the corresponding position number during data collection.

[0072] Therefore, the position-related error ε xa is expressed as:

[0073]

[0074] For the A-axis, the position-independent error δ yoa , δ zoa represent the position error terms generated by the A-axis in the Y and Z directions, respectively, and the position-independent error S boa , S coa represent the direction error terms of the A-axis on the B and C axes, respectively. The position-independent error δ yoa is considered as part of the position-related error δ ya , and δ zoa is considered as part of δ za . The perpendicularity error S boa is considered as part of the rotation angle error δ ya , and S coa is considered as part of the rotation angle error ε za .

[0075] When the rotation angle of the A-axis is 0, the rotation angle errors ε ya and ε za are 0, and the position errors δ ya and δ za are also 0. Therefore, the comprehensive rotation angle error ε ya identified at the rotation angle of 0 is the perpendicularity error S boa , the comprehensive rotation angle error ε za is the perpendicularity error S coa , and the comprehensive position error term error δ ya is the position-independent error δ yoa, the position dependent error term error δ za is the position independent error term error δ zoa . Thereby the rotational axis 10 term geometric error is identified.

[0076] Although embodiments of the present application and figures are disclosed for illustrative purposes, it will be understood by those skilled in the art that various alterations, modifications and changes can be made therein without departing from the spirit and scope of the present application and the appended claims, therefore, the scope of the present application is not limited to the embodiments and figures disclosed.

Claims

1. A method for detecting and identifying the geometric error of the rotary axes of a five-axis machine tool based on ball bar measurement, characterized in that: The steps of the method are: S1, establishing a five-axis machine tool geometric error model based on the screw theory; S2, determining two points on the rotating shaft axis according to the type and position of the machine tool rotating shaft, and determining the installation positions of the ball bar X, Y and Z directions at the two points; S3, obtaining the readings of the ball bar at different installation positions when the rotating shaft rotates according to the influence of the rotating shaft geometric error on the machine tool accuracy; S4, establishing three spatial spherical surfaces according to the two sets of readings of the ball bar and the coordinates of the fixed ball when the ball bar X, Y and Z directions are installed, and the intersection point is a certain point on the rotating shaft axis, and the axis expression of the rotating shaft is determined by two different spatial points; S5, comparing the actual axis with the ideal axis when the rotating shaft rotates, and determining all 10 geometric errors of the rotating shaft by means of the corresponding geometric error identification formula; S51, compare the actual axis of rotation with the ideal axis The deviation of the actual axis of rotation at the coordinate origin in the X-axis, Y-axis, and Z-axis directions is the linear error term in the rotation axis position-related error ; S52, compare the actual axis of rotation with respect to the ideal axis The deflection angle in the XOZ, XOY plane is the rotation term error around the Y axis, around the Z axis in the rotation axis position related term error ; S53, the first group of measurements, the ball bar is placed along the Y-axis direction, and the vector of the center ball t pointing to the tool side ball s in the workpiece coordinate system can be obtained by subtracting the coordinates of the two in the workpiece coordinate system, or by the point on the actual axis of the rotating shaft in the global coordinate system The vector pointing to the ball s is obtained by rotating around the X-axis, and the rotation term error around the X-axis in the rotation axis position related term error can be obtained by combining the two ; S54, considering the rotating shaft position independent error as part of the position dependent error, the position dependent error value of the rotating shaft when the rotating angle is 0 is the rotating shaft position independent error value, and the measured position dependent error is reduced by the value when the rotating angle is 0, which is the rotating shaft position dependent error, thereby identifying the 10 geometric errors of the rotating shaft.

2. The method according to claim 1, wherein the method is characterized in that: The S1 fully considers whether the actual movement direction of each shaft of the machine tool is the same as the direction of the right-hand coordinate system, and if the directions are different, the error matrix corresponding to the shaft is changed to the inverse matrix of the error matrix.

3. The geometric error detection and identification method of the rotary axes of a 5-axis machine tool based on ball-bar measurement according to claim 1, characterized in that: The S2 is specifically: S21, determining the type of the machine tool rotating shaft, setting the rotating coordinate system of the rotating shaft to be measured according to the machine tool structure and the rotating shaft structure; S22, determining two sets of measurement positions of the ball bar under the corresponding rotating shaft coordinate system, including the position of the ball bar center ball and the placement direction of the ball bar, which is specifically as follows: In the first group of measurements, the center ball t of the ball bar is installed on the X axis of the rotary axis coordinate system , and the coordinates are , the tool side ball s is clamped at the spindle end, and the ball bar is placed along the X axis, Y axis, and Z axis directions, respectively, so the coordinates of the tool side ball s are , , ; In the second group of measurements, the center ball t of the ball bar is installed on the X axis of the rotary axis coordinate system , and the coordinates are , the tool side ball s is clamped at the spindle end, and the ball bar is placed along the X axis, Y axis, and Z axis directions respectively, and the coordinates of the tool side ball s are , , .

4. The geometric error detection and identification method of the rotary axes of a 5-axis machine tool based on ball-bar measurement according to claim 1, characterized in that: The S3 is specifically: in the first group of measurements, the readings of the club instrument placed along the X axis, Y axis and Z axis are respectively recorded as , , ; in the second group of measurements, the readings of the club instrument placed along the X axis, Y axis and Z axis are respectively recorded as , , .

5. The geometric error detection and identification method of the rotary axes of a 5-axis machine tool based on ball-bar measurement according to claim 1, characterized in that: The S4 is specifically: The first group of measurements, according to the coordinates of the tool side ball s , , , the length of the ball instrument L and the corresponding reading of the ball instrument , , Three spatial spherical surfaces are respectively established, and the intersection point of the three spatial spherical surfaces is a point on the axis of the rotation axis , and the coordinates of the point are recorded as ; Second set of measurements, coordinates of the tool-side sphere s , , , the length of the club itself L and the reading of the club , , Three spatial spheres are established respectively, and the intersection of the three spheres is a point on the axis of the rotation axis , and the coordinates of the point are recorded as ; T-ball coordinate points of a ball tee at two different mounting heights for a ball tee meter and a line the ideal axis of rotation is obtained from two different points in space and a line the actual axis of rotation is obtained from the rotation of the ideal axis

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