Line laser on-machine measurement calibration method

Abstract

The invention discloses a line laser on-machine measurement calibration method, and aims to improve the measurement precision and efficiency of complex part processing. The method comprises the following steps that a machine tool, a spindle, a line laser sensor and a workpiece coordinate system are defined, the relation among the coordinate systems is determined, and the directions of the spindle coordinate system, the machine tool coordinate system and the workpiece coordinate system are kept consistent; obtaining a rotation matrix from a line laser sensor coordinate system to a main shaft coordinate system by solving direction vectors of an X axis, a Y axis and a Z axis of the line laser sensor coordinate system; scanning the standard ball by using a line laser sensor to obtain a series of coordinate points, solving coordinate values of the center of the standard ball under a line laser sensor coordinate system, and obtaining a translation matrix from the line laser sensor coordinate system to a workpiece coordinate system; and finally, completing calibration of line laser on-machine measurement according to the rotation matrix and the translation matrix. According to the invention, the installation pose of the line laser on-machine measurement system can be rapidly and accurately calibrated, and the precision and efficiency of line laser on-machine measurement are effectively improved.

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 technology is mainly divided into two methods: contact and non-contact. Contact measurement relies on physical contact trigger signals to determine the geometric position of the workpiece, but its measurement efficiency is relatively low due to the contact process. In contrast, non-contact measurement technologies such as line lasers acquire data by scanning the surface of the workpiece, which not only maintains measurement accuracy, but also significantly improves measurement speed and efficiency. Especially in the field of high-precision manufacturing, it has broad application prospects.

[0003] In the manufacturing field that pursues high-precision and high-efficiency processing of complex parts, real-time detection of part processing quality during the processing is particularly important. Line laser on-machine measurement technology has become one of the key technologies to ensure the accuracy and efficiency of complex part processing by virtue of its ability to provide accurate measurement data. However, the installation accuracy of the 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 state of the line laser sensor a crucial step in the on-machine measurement system. 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 to improving measurement accuracy.

[0004] Existing line laser on-machine measurement calibration methods, such as the hand-eye calibration method based on a standard ball, can measure the center of the ball by moving the standard ball, solve equations, and calibrate the rotation matrix and translation matrix at the same time. However, the position calibration accuracy is low, and this method is only suitable for multi-axis CNC machine tools that contain both translation axes and rotation axes. In order to improve the accuracy and processing efficiency of line laser on-machine measurement, it is necessary to study a line laser on-machine measurement calibration method with a wider adaptability to solve the calibration problem that existing three-axis CNC machine tools cannot provide rotation information. Summary of the invention

[0005] The present invention aims to solve the problems existing in the existing methods and provides a method for line laser on-machine measurement calibration. The installation posture of the line laser sensor can be quickly calibrated by using a plane calibration plate and a standard ball, and the accurate conversion of the line laser sensor coordinate system L to the workpiece coordinate system W can be completed, thereby improving the accuracy and efficiency of the line laser sensor on-machine 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 transformation matrix M1 from the line laser sensor coordinate system L to the spindle coordinate system S, the transformation matrix M2 from the spindle coordinate system S to the machine tool coordinate system M, and the transformation matrix M3 from the machine tool coordinate system M to the workpiece coordinate system W;

[0008] (2) Taking 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) Taking 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 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 from 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 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:

[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 line 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 is O S To the origin of the machine coordinate system O M The translation vector of .

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

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

[0020] Where, Δd x =d2-d1.

[0021] 3) Similarly, by moving the line laser sensor along the Y′ axis and Z′ axis 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 combined equations (3), (4), and (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 the machine tool in all directions and the change of the X value of the line laser sensor coordinate system L are known, and 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 line laser sensor coordinate system L include:

[0030] 1) Select any two coordinate points Q1(a1, b1) and Q2(a2, b2) from the data collected on the plane standard plate, and assume that 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′ is [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 is 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 mutually perpendicular, 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 the 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 Solve 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 main axis coordinate system S is as follows:

[0042] 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:

[0043] The center O of the standard sphere in the line laser sensor coordinate system L is taken as the origin of the workpiece coordinate system W, and 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:

[0044]

[0045] 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 center of the sphere in the line laser sensor coordinate system L.

[0046] The transformation matrix from the line laser sensor coordinate system L to the workpiece coordinate system W is:

[0047]

[0048] 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.

[0049] The benefit effect of the present invention is: the present invention provides a linear laser on-machine measurement system calibration method, which can quickly and accurately calibrate the installation posture of the linear laser on-machine measurement system, thereby improving the accuracy and efficiency of on-machine measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A flow chart for the implementation of the present invention;

[0051] Figure 2 It is a schematic diagram of the configuration of the line laser sensor and the plane calibration plate on the machine tool;

[0052] Figure 3 Schematic diagram of the principle of solving the coordinates of the center of a standard sphere. DETAILED DESCRIPTION

[0053] The principles and features of the present invention are described in detail below in conjunction with the accompanying drawings and specific implementations. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0054] As attached Figure 1 As shown, a line laser on-machine measurement calibration method includes the following steps:

[0055] (1) As attached Figure 2As shown, the plane calibration plate is placed on the machine tool workbench at any reasonable inclination angle, and the line laser sensor is vertically installed on the machine tool spindle through the tool holder. The emission direction of the line laser is approximately the same as the positive direction of the machine tool X-axis. 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, 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;

[0056] (2) Move the line laser sensor to a suitable position and effectively collect the laser line image and surface contour coordinates on the plane calibration plate. Then, drive the line laser sensor to move along the X-axis, Y-axis, and Z-axis respectively through the machine tool, and collect a total of 6 images and 6 sets of coordinate data. Then, change the inclination angle and position of the plane calibration plate, and collect 6 images and 6 sets of coordinate data again according to the same steps as above.

[0057] The 12 sets of coordinate data are fitted with a straight line using the least square method to obtain a function of x with respect to y. When y=0, the x value is obtained, as shown in Table 1.

[0058] Table 1

[0059] Based on the above information and the machine tool coordinate values, substitute into the formula and Two equations can be obtained:

[0060] 0.999409l+0.240311m+0.960804n=1 (16)

[0061] 0.997623l-0.445742m+0.635643n=1 (17)

[0062] Lianli 2 +m 2 +n 2 =1 Solving for:

[0063]

[0064] 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 equations:

[0065]

[0066] 0.999994i-0.003288j+0.001444k=0 (20)

[0067] Lianli 2 +j 2 +k 2 =1 Solving for:

[0068]

[0069] According to the formula l·u+m·ν+n·w=0 and i·u+j·ν+k·w=0, we can get two equations:

[0070] 0.999994u-0.003288v+0.001444w=0 (22)

[0071] -0.003267u-0.999891v-0.014371w=0 (23)

[0072] Lianliu 2 +v 2 +w 2 =1 Solving for:

[0073]

[0074] 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:

[0075]

[0076] 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;

[0077] As attached Figure 3 As shown, 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.

[0078] 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:

[0079]

[0080] 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:

[0081]

[0082] Through the above operations, the line laser on-machine measurement calibration is realized, and the calibration result is:

[0083]

[0084] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for calibrating a line laser on-machine measurement system, wherein the application scenario includes a multi-axis machine tool, a line laser measurement system, and a workpiece to be processed, and the line laser sensor is vertically mounted on the machine tool spindle through a tool holder; characterized in that: 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 transformation matrix M1 from the line laser sensor coordinate system L to the spindle coordinate system S, the transformation matrix M2 from the spindle coordinate system S to the machine tool coordinate system M, and the transformation matrix M3 from the machine tool coordinate system M to the workpiece coordinate system W; (2) Taking 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) Taking 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 a 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 from the line laser sensor coordinate system L to the workpiece coordinate system W is completed to realize the on-machine measurement calibration of the line laser.

2. The method for calibrating a line laser on-machine measurement system according to claim 1, characterized in that: In the 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, characterized in that: In the step (2), the specific steps of calibrating the X-axis of the line 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 measured 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 is O S To the origin of the machine coordinate system O M The translation vector of 2) Introduce a fixed calibration plane, whose equation is Ax+By+Cz+D=0. The X-axis of the laser beam of the line laser sensor is projected on the intersection point P1 on the calibration plane. Then move the line laser sensor along the X-axis by a distance of Δx to form the intersection point P2. The coordinate points obtained by the line laser sensor are (d1, 0) and (d2, 0). Substitute the coordinates of P1 and P2 into the equation of the calibration plane α, and calculate the difference to get: 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, characterized in that: In the step (2), the specific steps of calibrating the Y axis of the line 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 assume that 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′ is [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 of the Y axis of the coordinate system L in the online laser sensor coordinate system L [ijk] T According to the known conditions: direction vector [lmn] T and [ijk] T are mutually perpendicular, 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, characterized in that: In the step (2), the Z-axis direction vector of the line laser sensor coordinate system L is calibrated. 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′ can be obtained by solving the property that the three direction vectors XYZ are mutually perpendicular and are unit vectors. T .

6. The method for calibrating a line laser on-machine measurement system according to claim 1, characterized in that: In the 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, characterized in that: In the 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 center of the sphere in the line laser sensor coordinate system L.

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