A method for on-machine measurement calibration of line laser

Abstract

The present invention discloses a line laser on-machine measurement calibration method, which aims to improve the measurement accuracy and efficiency of complex parts processing. The present invention includes the following steps: defining the machine tool, spindle, line laser sensor and workpiece coordinate system, and determining the relationship between them, the spindle coordinate system, the machine tool coordinate system and the workpiece coordinate system are all consistent in direction; by solving the direction vectors of the X-axis, Y-axis and Z-axis of the line laser sensor coordinate system, the rotation matrix of the line laser sensor coordinate system to the spindle coordinate system is obtained; using the line laser sensor to scan the standard sphere to obtain a series of coordinate points, the coordinate value of the center of the standard sphere in the line laser sensor coordinate system is obtained, and the translation matrix of the line laser sensor coordinate system to the workpiece coordinate system is obtained; finally, according to the rotation matrix and the translation matrix, the calibration of the line laser on-machine measurement is completed. The present invention can quickly and accurately calibrate the installation posture of the line laser on-machine measurement system, effectively improving the accuracy and efficiency of the line laser on-machine measurement.

Description

Technical Field

[0001] The invention belongs to the technical field of line laser non-contact on-machine precision measurement, and in particular relates to a line laser on-machine measurement calibration method. Background Art

[0002] On-machine measurement technologies are primarily categorized into contact and non-contact methods. Contact measurement relies on physical contact trigger signals to determine the workpiece's geometric position, but due to the limitations of the contact process, its measurement efficiency is relatively low. In contrast, non-contact measurement technologies, such as line lasers, acquire data by scanning the workpiece surface. This not only maintains measurement accuracy but also significantly improves measurement speed and efficiency. This holds broad application potential, particularly in high-precision manufacturing.

[0003] In the manufacturing industry, which strives for high-precision and efficient processing of complex parts, real-time monitoring of part quality during the machining process is particularly important. Line laser on-machine measurement technology, with its ability to provide accurate measurement data, has become one of the key technologies for ensuring the accuracy and efficiency of complex part machining. However, the installation accuracy of line laser on-machine measurement equipment directly determines the accuracy of the measurement results, and the existence of installation errors makes the calibration of the position and posture of line laser sensors a crucial step in on-machine measurement systems. By accurately calibrating the line laser sensor, its installation position and posture information on the spindle of a multi-axis CNC machine tool can be determined, which is crucial for improving measurement accuracy.

[0004] Existing methods for on-machine line laser measurement calibration, such as the hand-eye calibration method based on a standard sphere, can measure the center of the sphere by moving the standard sphere, solve equations, and simultaneously calibrate the rotation and translation matrices. However, these methods suffer from low pose calibration accuracy and are only suitable for multi-axis CNC machine tools with both translation and rotation axes. To improve the accuracy and machining efficiency of on-machine line laser measurement, a more adaptable on-machine line laser measurement calibration method is needed to address the calibration problem of existing three-axis CNC machine tools, which lack rotation information. Summary of the Invention

[0005] This invention addresses the problems of existing methods and provides a method for on-machine line laser measurement calibration. Using a flat calibration plate and a standard sphere, the installation position of a line laser sensor can be quickly calibrated, accurately converting the line laser sensor coordinate system L to the workpiece coordinate system W, thereby improving the accuracy and efficiency of on-machine line laser measurement.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] (1) The line laser on-machine measurement system is defined as four interrelated coordinate systems: machine tool coordinate system M, spindle coordinate system S, workpiece coordinate system W, and line laser sensor coordinate system L. The directions of the spindle coordinate system S, machine tool coordinate system M, and workpiece coordinate system W are all consistent, and the relationship between them is determined, including the conversion matrix M1 from the line laser sensor coordinate system L to the spindle coordinate system S, the conversion matrix M2 from the spindle coordinate system S to the machine tool coordinate system M, and the conversion matrix M3 from the machine tool coordinate system M to the workpiece coordinate system W;

[0008] (2) Using the plane calibration plate as the measurement object, fit the straight line projected by the line laser on the plane calibration plate; calibrate the X-axis, Y-axis, and Z-axis direction vectors of the line laser sensor coordinate system L; solve the rotation matrix R1, that is, the rotation matrix from the line laser sensor coordinate system L to the principal axis coordinate system S;

[0009] (3) With the standard sphere as the measurement object, a series of coordinate points are obtained by scanning the standard sphere with a line laser. The radius r of the scanning circle is obtained by fitting the circle using the least squares method. According to the radius R of the standard sphere, the radius r of the scanning circle and the Pythagorean theorem, the coordinate value (x L0 ,y L0 ,z L0 ); Given the machine tool reading and the rotation matrix R1, solve the partial translation matrix T13 from the line laser sensor coordinate system L to the workpiece coordinate system W.

[0010] (4) According to the rotation matrix R1 and the translation matrix T13, the transformation of the line laser sensor coordinate system L to the workpiece coordinate system W is completed, and the line laser on-machine measurement calibration is realized.

[0011] Furthermore, in step (1), the relationship among the workpiece coordinate system W, the machine tool coordinate system M, the spindle coordinate system S and the line laser sensor coordinate system L is:

[0012] P3=M3M2M1P0 (1)

[0013] Among them, P0(x L ,y L , z L ) is the point selected in the line laser sensor coordinate system L, P3(x W ,y W , z W ) is the corresponding point in the workpiece coordinate system W, i=1, 2, 3.

[0014] Furthermore, in step (2), the specific steps of calibrating the X-axis of the laser sensor coordinate system L include:

[0015] 1) Assuming that a virtual line laser sensor coordinate system L′ is in the same direction as the spindle coordinate system S, the machine tool coordinate system M, and the workpiece coordinate system W, the unit direction vector of the X axis of the actual line laser sensor coordinate system L in the virtual line laser sensor coordinate system L′ is [lmn] T , the measurement distance of the X axis is d (the coordinate point (x i , 0), that is, d = x i ), the coordinate value of this point in the virtual line laser sensor coordinate system L′ is [ld md nd] T , then the coordinate transformation relationship of the point is:

[0016]

[0017] Among them, (x M ,y M ,z M ) is the coordinate value of point Q in the machine tool coordinate system M, T1=[x1 y1 z1] T is the origin of the line laser sensor coordinate system O L To the origin of the spindle coordinate system O S The translation vector, T2 = [x2 y2 z2] T The origin of the main axis coordinate system O S To the origin of the machine coordinate system O M The translation vector of .

[0018] 2) Introduce a fixed calibration plane with the equation Ax+By+Cz+D=0. The X-axis of the laser beam of the line laser sensor is projected onto the intersection point P1 on the calibration plane. Then, the line laser sensor is moved a distance Δx along the X-axis to form the intersection point P2. The coordinates of the points obtained by the line laser sensor are (d1, 0) and (d2, 0), respectively. Substitute the coordinates of P1 and P2 into the equation of the calibration plane α and calculate the difference to obtain:

[0019] A(lΔd x -Δx)+B(mΔd x )+C(nΔd x )=0 (3)

[0020] Where Δd x =d2-d1.

[0021] 3) Similarly, if the line laser sensor is moved along the Y′ and Z′ axes by distances Δy and Δz, respectively, the following relationship can be obtained:

[0022] A(lΔd y )+B(mΔd y -Δy)+C(nΔd y )=0 (4)

[0023] A(ld z )+B(mΔd z )+C(nΔd z -Δz)=0 (5)

[0024] 4) Solving the simultaneous equations (3)(4)(5) yields:

[0025] l(Δd x / Δx)+m(Δd y / Δy)+n(Δd z / Δz)=1 (6)

[0026] Introducing a calibration plane, we can get:

[0027]

[0028] The displacement of the line laser sensor along all directions of the machine tool and the change in the X value of the line laser sensor coordinate system L are both known. The unit direction vector [lm n] of the X axis of the line laser sensor coordinate system L in the virtual line laser sensor coordinate system L′ can be obtained. T .

[0029] Furthermore, in step (2), the specific steps of calibrating the Y axis of the laser sensor coordinate system L include:

[0030] 1) Take any two coordinate points Q1(a1, b1) and Q2(a2, b2) from the data collected on the plane standard plate, and let the unit direction vector of the Y axis of the actual line laser sensor coordinate system L in the virtual line laser sensor coordinate system L′ be [ijk] T Converting points Q1 and Q2 to the machine tool coordinate system M yields:

[0031]

[0032]

[0033] Among them, (x′ M1 ,y′ M1 ,z′ M1 ),(x′ M2 ,y′ M2 ,z′ M2 ) are the coordinate values ​​of point Q1 and point Q2 in the machine tool coordinate system M, T1=[x1′y1′z1′] T is the origin of the line laser sensor coordinate system O L To the origin of the spindle coordinate system O S The translation vector, T2 = [x′2y′2z′2] T The origin of the main axis coordinate system O S To the origin of the machine coordinate system OM The translation vector of .

[0034] 2) The distance D between coordinate points Q1 and Q2 in the online laser sensor coordinate system L and the machine tool coordinate system M L and D M The following relationship exists:

[0035]

[0036] in, and The calculation formula is as follows:

[0037]

[0038]

[0039] 4) In addition, the direction vector [lmn] T and [ijk] T are perpendicular to each other, and [ijk] T is the unit direction vector. According to formula (12), the unit direction vector [ijk] of the Y axis of the coordinate system L in the online laser sensor coordinate system L can be calculated. T .

[0040] Furthermore, in step (2), the Z-axis direction vector of the calibration line laser sensor coordinate system L can be obtained by the formula l·u+m·ν+n·w=0, i·u+j·ν+k·w=0 and u 2 +v 2 +w 2 = 1 and solve them together to obtain the unit direction vector [uvw] of the Z axis of the line laser sensor coordinate system L in the virtual line laser sensor coordinate system L′. T .

[0041] Furthermore, in step (2), the calculation formula of the rotation matrix R1 from the line laser sensor coordinate system L to the principal axis coordinate system S is as follows:

[0042]

[0043] Furthermore, in step (3), the specific steps of solving the translation matrix from the line laser sensor coordinate system L to the workpiece coordinate system W include:

[0044] The center O of the standard sphere in the line laser sensor coordinate system L is used as the origin of the workpiece coordinate system W. The partial translation matrix T13 from the line laser sensor coordinate system L to the workpiece coordinate system W is calculated using the following formula:

[0045]

[0046] Among them, T13 is the synthesis of the translation matrix T1 of the line laser sensor coordinate system L to the spindle coordinate system S and the translation matrix T3 of the machine tool coordinate system M to the workpiece coordinate system W. T13 can be expressed as a vector (a, b, c); (x L0 ,y L0 ,z L0 ) is the coordinate of the sphere center in the line laser sensor coordinate system L.

[0047] The transformation matrix from the line laser sensor coordinate system L to the workpiece coordinate system W is:

[0048]

[0049] Among them, (x2, y2, z2) is the origin of the main axis coordinate system O S To the origin of the machine coordinate system O M The translation matrix can be read directly on the machine tool.

[0050] The beneficial effects of the present invention are as follows: the present invention provides a method for calibrating a line laser on-machine measurement system, which can quickly and accurately calibrate the installation posture of the line laser on-machine measurement system, thereby improving the accuracy and efficiency of on-machine measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A flow chart for the implementation of the present invention;

[0052] Figure 2 This is a schematic diagram of the configuration of the line laser sensor and the plane calibration plate on the machine tool;

[0053] Figure 3 Schematic diagram of the principle of solving the coordinates of the center of a standard sphere. DETAILED DESCRIPTION

[0054] The principles and features of the present invention are described in detail below with reference to the accompanying drawings and specific embodiments. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0055] As attached Figure 1 As shown, a line laser on-machine measurement calibration method includes the following steps:

[0056] (1) As attached Figure 2As shown, a flat calibration plate is placed on the machine tool workbench at any reasonable inclination angle. The line laser sensor is vertically mounted on the machine tool spindle via the tool holder. The emission direction of the line laser is approximately the same as the positive direction of the machine tool's X-axis. The line laser on-machine measurement system is defined as four interrelated coordinate systems: the machine tool coordinate system M, the spindle coordinate system S, the workpiece coordinate system W, and the line laser sensor coordinate system L. The relationships between them are determined, including the conversion matrix M1 from the line laser sensor coordinate system L to the spindle coordinate system S, the conversion matrix M2 from the spindle coordinate system S to the machine tool coordinate system M, and the conversion matrix M3 from the machine tool coordinate system M to the workpiece coordinate system W.

[0057] (2) Move the line laser sensor to a suitable position and effectively capture the laser line image and surface contour coordinates on the plane calibration plate. Then, use the machine tool to drive the line laser sensor to move along the X-axis, Y-axis, and Z-axis, respectively, to capture a total of 6 images and 6 sets of coordinate data. Then, change the tilt angle and position of the plane calibration plate, and follow the same steps as above to capture 6 images and 6 sets of coordinate data again.

[0058] The 12 sets of coordinate data are fitted with a straight line using the least squares method to obtain a function of x with respect to y. When y=0, the x value is obtained, as shown in Table 1.

[0059] Table 1

[0060]

[0061]

[0062] According to the above information and the machine tool coordinate value, substitute into the formula and Two equations can be obtained:

[0063] 0.999409l+0.240311m+0.960804n=1 (16)

[0064] 0.997623l-0.445742m+0.635643n=1 (17)

[0065] Joint 2 +m 2 +n 2 =1 Solving, we can get:

[0066]

[0067] Take any two points in any set of coordinate data, such as point Q1 (132.9200, 27.0360) and point Q2 (127.2680, 2.5360), according to the formula And l·i+m·j+n·k=0, we can get two equal equations:

[0068]

[0069] 0.999994i-0.003288j+0.001444k=0 (20)

[0070] Lianli i 2 +j 2 +k 2 =1 Solving for:

[0071]

[0072] According to the formula l·u+m·ν+n·w=0 and i·u+j·ν+k·w=0, we can get two equations:

[0073] 0.999994u-0.003288v+0.001444w=0 (22)

[0074] -0.003267u-0.999891v-0.014371w=0 (23)

[0075] Lianliu 2 +v 2 +w 2 =1 and solve to get:

[0076]

[0077] After the above steps, the rotation matrix R1 from the line laser sensor coordinate system L to the principal axis coordinate system S is obtained, that is:

[0078]

[0079] Move the line laser sensor to a suitable position, scan the standard sphere to obtain a series of coordinate points and corresponding images, and use the least squares method to fit the circle to obtain the radius of the scanning circle r = 12.806381;

[0080] As attached Figure 3 As shown in the figure, according to the standard sphere radius R, the scanning circle radius r and the Pythagorean theorem, the coordinate value of the sphere center O in the online laser sensor coordinate system L is calculated (122.085332, 15.208588, 7.810225), and the sphere center O is regarded as the origin of the workpiece coordinate system W.

[0081] According to the known machine tool readings (x2, y2, z2) and the rotation matrix R1, the partial translation matrix T13 from the line laser sensor coordinate system L to the workpiece coordinate system W can be calculated, that is:

[0082]

[0083] Solving the above equations, we can obtain the partial translation matrix T13 from the line laser sensor coordinate system L to the workpiece coordinate system W:

[0084]

[0085] Through the above operations, the line laser on-machine measurement calibration is realized, and the calibration results are:

[0086]

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for calibrating a line laser on-machine measurement system, the application scenario includes a multi-axis machine tool, a line laser measurement system, and a workpiece to be processed. The line laser sensor is vertically mounted on the machine tool spindle through a tool holder; the method is characterized by: The method comprises the following steps: (1) The line laser on-machine measurement system is defined as four interrelated coordinate systems: machine tool coordinate system M, spindle coordinate system S, workpiece coordinate system W, and line laser sensor coordinate system L. The directions of the spindle coordinate system S, machine tool coordinate system M, and workpiece coordinate system W are all consistent, and the relationship between them is determined, including the conversion matrix M1 from the line laser sensor coordinate system L to the spindle coordinate system S, the conversion matrix M2 from the spindle coordinate system S to the machine tool coordinate system M, and the conversion matrix M3 from the machine tool coordinate system M to the workpiece coordinate system W; (2) Using the plane calibration plate as the measurement object, fit the straight line projected by the line laser on the plane calibration plate; calibrate the X-axis, Y-axis, and Z-axis direction vectors of the line laser sensor coordinate system L; solve the rotation matrix, that is, the rotation matrix R1 from the line laser sensor coordinate system L to the principal axis coordinate system S; (3) Using the standard sphere as the measurement object, the standard sphere is scanned by a line laser to obtain a series of coordinate points, and the radius r of the scanning circle is obtained by fitting the circle; according to the radius R of the standard sphere, the radius r of the scanning circle and the Pythagorean theorem, the coordinate value (x L0 ,y L0 ,z L0 ); Given the machine tool reading and the rotation matrix R1, solve the partial translation matrix T13 from the line laser sensor coordinate system L to the workpiece coordinate system W; (4) According to the rotation matrix R1 and the translation matrix T13, the transformation of the line laser sensor coordinate system L to the workpiece coordinate system W is completed, and the line laser on-machine measurement calibration is realized.

2. The method for calibrating a line laser on-machine measurement system according to claim 1, wherein: In step (1), the relationship between the workpiece coordinate system W, the machine tool coordinate system M, the spindle coordinate system S and the line laser sensor coordinate system L is: P3=M3M2M1P0 (1) Among them, P0(x L ,y L , z L ) is the point selected in the line laser sensor coordinate system L, P3(x W ,y W , z W ) is the corresponding point in the workpiece coordinate system W, 3. The method for calibrating a line laser on-machine measurement system according to claim 1, wherein: In step (2), the specific steps of calibrating the X-axis of the laser sensor coordinate system L include: 1) Assuming that a virtual line laser sensor coordinate system L′ is in the same direction as the spindle coordinate system S, the machine tool coordinate system M, and the workpiece coordinate system W, the unit direction vector of the X axis of the actual line laser sensor coordinate system L in the virtual line laser sensor coordinate system L′ is [lmn] T , the measurement distance of the X axis is d (the coordinate point obtained by the line laser sensor is (x i , 0), that is, d = x i ), the coordinate value of point Q in the virtual line laser sensor coordinate system L′ is [ld md nd] T , then the coordinate transformation relationship of the point is: Among them, (x M ,y M ,z M ) is the coordinate value of point Q in the machine tool coordinate system M, T1=[x1 y1 z1] T is the origin of the line laser sensor coordinate system O L To the origin of the spindle coordinate system O S The translation vector, T2 = [x2 y2 z2] T The origin of the main axis coordinate system O S To the origin of the machine coordinate system O M The translation vector of 2) Introduce a fixed calibration plane with the equation Ax+By+Cz+D=0. The X-axis of the laser beam of the line laser sensor is projected onto the intersection point P1 on the calibration plane. Then, the line laser sensor is moved a distance Δx along the X-axis to form the intersection point P2. The coordinates of the points obtained by the line laser sensor are (d1, 0) and (d2, 0), respectively. Substitute the coordinates of P1 and P2 into the equation of the calibration plane α and calculate the difference to obtain: A(lΔd x -Δx)+B(mΔd x )+C(nΔd x )=0 (3) Where Δd x =d2-d1; Similarly, move the line laser sensor along the Y′ axis and Z′ axis by distances Δy and Δz respectively, and combine with formula (3) to obtain: l(Δd x / Δx)+m(Δd y / Δy)+n(Δd z / Δz)=1 (4) 3) Similarly, introducing a calibration plane, we can get: Unit direction vector of the X-axis of the line laser sensor coordinate system L in the virtual line laser sensor coordinate system L′ [lmn] T , which can be solved using the displacement of the line laser sensor along each direction of the machine tool and the change in the X value of the line laser sensor coordinate system L.

4. The method for calibrating a line laser on-machine measurement system according to claim 1, wherein: In step (2), the specific steps of calibrating the Y axis of the laser sensor coordinate system L include: 1) Take any two coordinate points Q1(a1, b1) and Q2(a2, b2) from the data collected on the plane standard plate, and let the unit direction vector of the Y axis of the actual line laser sensor coordinate system L in the virtual line laser sensor coordinate system L′ be [ijk] T , transform points Q1 and Q2 to the machine tool coordinate system M; 2) The distance D between coordinate points Q1 and Q2 in the online laser sensor coordinate system L and the machine tool coordinate system M L and D M The following relationship exists: 3) The unit direction vector [ijk] of the Y axis of the coordinate system L in the online laser sensor coordinate system L T According to the known conditions: direction vector [lmn] T and [ijk] T are perpendicular to each other, and [ijk] T is the unit direction vector, which is calculated by combining formula (6).

5. The method for calibrating a line laser on-machine measurement system according to claim 1, wherein: In the step (2), the Z-axis direction vector of the calibration line laser sensor coordinate system L can be solved by the property that the three direction vectors XYZ are perpendicular to each other and are unit vectors to obtain the unit direction vector [uvw] of the Z-axis of the line laser sensor coordinate system L in the virtual line laser sensor coordinate system L′. T .

6. The method for calibrating a line laser on-machine measurement system according to claim 1, wherein: In step (2), the calculation formula of the rotation matrix R1 from the line laser sensor coordinate system L to the main axis coordinate system S is as follows:

7. The method for calibrating a line laser on-machine measurement system according to claim 1, wherein: In step (3), the specific steps of solving the partial translation matrix from the line laser sensor coordinate system L to the workpiece coordinate system W include: The center O of the standard sphere in the line laser sensor coordinate system L is used as the origin O of the workpiece coordinate system. W , use the following formula to calculate the partial translation matrix T13 from the line laser sensor coordinate system L to the workpiece coordinate system W: Among them, T13 is the synthesis of the translation matrix T1 of the line laser sensor coordinate system L to the spindle coordinate system S and the translation matrix T3 of the machine tool coordinate system M to the workpiece coordinate system W. T13 can be expressed as a vector (a, b, c); (x L0 ,y L0 ,z L0 ) is the coordinate of the sphere center in the line laser sensor coordinate system L.

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