Novel non-contact three-dimensional optical scanner tail end probe rod pose calibration method

Abstract

The invention provides a novel non-contact three-dimensional optical scanner tail end probe rod pose calibration method, and relates to the technical field of tool coordinate system calibration, and the method specifically comprises the following steps: building a three-dimensional coordinate system, and uniformly distributing three conical pits at equal intervals along each coordinate axis; and a laser tracker is used as measuring equipment to calibrate the spatial position coordinates of the nine conical nests. And carrying out TCP position calibration on the probe rod at the tail end of the three-dimensional optical scanner And carrying out TCP attitude calibration on the probe rod at the tail end of the three-dimensional optical scanner According to the technical scheme, the problem that in the prior art, a three-dimensional optical scanner tail end probe rod pose calibration method is lacked is solved.

Description

Technical Field

[0001] The invention relates to the technical field of tool coordinate system calibration, and in particular to a novel non-contact three-dimensional optical scanner end probe rod position and posture calibration method. Background Art

[0002] Multi-axis robots can perform complex trajectory tasks such as welding, spraying, handling and inspection. In order to complete these complex tasks, the end of the multi-axis robot needs to be equipped with corresponding tools, such as welding guns, ball-end probes and optical probes. Therefore, it is crucial to accurately obtain the position and posture of the tools in the robot's end coordinate system. In addition, the optical probe is an indispensable tool for completing the precision measurement of deep holes with a large aspect ratio. In order to avoid collision between the probe and the workpiece during the measurement process, the robot's trajectory accuracy needs to be ensured by an accurate three-dimensional optical scanner end probe coordinate system TCF. Therefore, it is of great significance to establish a standard part for the calibration of the three-dimensional optical scanner end probe.

[0003] At present, there are mainly external reference method and multi-point calibration method for the calibration of the probe coordinate system of the end of the multi-axis robot 3D optical scanner at home and abroad. In the external reference method, FANUC robots use the DynaCal system for calibration, and ABB arc welding robots use the BullEyes system tool automatic calibration method, but these rely on external references. In the multi-point calibration method, the robot is controlled to make the tool center point TCP coincide with a specific spatial point multiple times in different directions, and the position constraint relationship is used to establish an equation to obtain the actual position of the tool center point. Then, the robot is controlled to reach multiple points with a specific direction relationship, which constitutes the direction of the probe coordinate system of the robot's 3D optical scanner.

[0004] The six-point calibration principle is the most widely used in the multi-point calibration method. In this method, the position calibration of the tool center point is to make the TCP positions of the four calibration points (the first four points) coincide, so as to calculate the tool center point. The TCP attitude calibration is to make the three calibration points (the last three) have a special direction and position relationship, so as to calculate the attitude of the probe coordinate system at the end of the three-dimensional optical scanner relative to the coordinate system of the robot end.

[0005] Therefore, a simple and accurate new method for calibrating the position and posture of the probe at the end of a non-contact three-dimensional optical scanner is needed. Summary of the invention

[0006] The main purpose of the present invention is to provide a novel non-contact three-dimensional optical scanner end probe rod position and posture calibration method to solve the problem of lack of three-dimensional optical scanner end probe rod position and posture calibration method in the prior art.

[0007] To achieve the above object, the present invention provides a novel non-contact three-dimensional optical scanner end probe position calibration method, which specifically includes the following steps:

[0008] S1, establish a three-dimensional coordinate system, and distribute three cone sockets evenly and equidistantly along each coordinate axis.

[0009] S2, using a laser tracker as a measuring device to calibrate the spatial position coordinates of the nine cone sockets.

[0010] S3, calibrate the TCP position of the probe at the end of the 3D optical scanner.

[0011] S4, perform TCP posture calibration on the end probe of the 3D optical scanner.

[0012] Furthermore, step S1 is specifically as follows:

[0013] A vertical column is arranged on the horizontal breadboard, and the direction in which the vertical column extends upward is the Z axis of the three-dimensional coordinate system; the X axis and the Y axis of the three-dimensional coordinate system are located on the horizontal breadboard; and the horizontal breadboard is located on a horizontal plane.

[0014] Furthermore, the cone angle of each cone dimple is selected in the range of 60° to 120°, and the cone angle and depth of each cone dimple are the same.

[0015] Furthermore, step S2 is specifically as follows:

[0016] Assume that the distance from the laser tracker to a cone is l i , where i is the cone nest point, i = 1, 2, ... 9; let the laser tracker's own position coordinates be (x0, y0, z0), and the cone nest point coordinates be (x i ,y i , z i ), then:

[0017]

[0018] Furthermore, step S3 is specifically as follows:

[0019] S3.1, the transformation relationship between the probe coordinate system T at the end of the 3D optical scanner and the robot coordinate system E at the end is: The transformation relationship between the probe coordinate system T at the end of the three-dimensional optical scanner and the base coordinate system B is: The conversion relationship between the three is:

[0020]

[0021] in, By rotation matrix and position vector B p E0 composition:

[0022]

[0023] is the transformation matrix from the robot end coordinate system E to the base coordinate system B.

[0024] S3.2, expand equation (2) to obtain equation (4):

[0025]

[0026] in, is the rotation matrix of the position calibration point i' of the robot's terminal coordinate system, i'=1,2,...4; BpEi is the position vector of the position calibration point of the robot's terminal coordinate system; is the rotation matrix of the probe at the end of the 3D optical scanner; E p T is the position vector of the probe rod at the end of the three-dimensional optical scanner; is the rotation matrix of the end of the probe coordinate system at the end of the 3D optical scanner; B p T is the position vector of the end of the three-dimensional optical scanner end probe coordinate system; transforming equation (4) to obtain the general equation (5) of the center point of the three-dimensional optical scanner end probe:

[0027]

[0028] Combined with formula (5), the second position calibration point P2 is subtracted from the first position calibration point P1 to obtain:

[0029]

[0030] According to formula (6), the relationship between all position calibration points is obtained:

[0031]

[0032] S3.3, Gaussian elimination method is used to obtain the TCP position of the end probe of the 3D optical scanner ( E p Tx , E p Ty , E p Tz ), as shown in formula (8):

[0033]

[0034] Furthermore, step S4 is specifically as follows:

[0035] S4.1, the X-axis axial vector X of the probe coordinate system T at the end of the three-dimensional optical scanner is as shown in formula (9):

[0036]

[0037] in,( B p 5Ex , B p 5Ey , B p 5Ez ) represents the position of the second posture calibration point P5 relative to the base coordinates.

[0038] S4.2, the Z-axis axial vector Z of the probe coordinate system T at the end of the three-dimensional optical scanner is as shown in formula (10):

[0039]

[0040] in, B p 5E The position of the second posture calibration point P5 relative to the base coordinates; B p 4E The position of the first posture calibration point P4 relative to the base coordinates; B p 6E The position of point P6 relative to the base coordinates is marked for the third posture.

[0041] S4.3, the Y-axis axial vector Y of the probe coordinate system T at the end of the three-dimensional optical scanner can be obtained by the right-hand rule:

[0042] Y=Z×X (11).

[0043] Furthermore, step S4 further includes the following steps:

[0044] S4.4, calculate Z = X × Y;

[0045] S4.5, normalize the axial vectors of the three coordinate axes to obtain the posture of the probe coordinate system T at the end of the three-dimensional optical scanner relative to the base coordinate system B Left multiplication Obtain the attitude matrix of the probe coordinate system at the end of the 3D optical scanner

[0046]

[0047] The present invention has the following beneficial effects:

[0048] The present invention discloses a standard part for calibrating the end probe of a multi-degree-of-freedom non-contact three-dimensional optical scanner, including six cone sockets fixed on a horizontal plane, three cone sockets fixed in a vertical direction, the cone angle of each cone socket is selected in the range of 60° to 120°, and the cone angle and depth of each cone socket are the same, a vertical column, and a horizontal breadboard. The nine cone sockets are distributed according to an orthogonal coordinate system, and then the three-dimensional optical scanner is used as a measuring device to calibrate them. The device involved in the present invention has a simple structure, convenient operation, and strong practicality; a multi-axis robot drives a three-dimensional optical scanner mounted on its end, and touches a cone socket in the space from different directions to provide multiple accurate spatial calibration points for the end probe of the three-dimensional optical scanner. In conjunction with the six-point calibration principle of the coordinate system of the end probe of the robot three-dimensional optical scanner, the coordinate conversion matrix of the end probe of the three-dimensional optical scanner relative to the end of the robot can be simply and accurately solved, so as to realize the calibration of the end probe of the three-dimensional optical scanner. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the specific implementation or the prior art description. Obviously, the drawings described below are some implementations of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0050] Figure 1 A schematic diagram of a standard part used for calibration of a probe rod at the end of a multi-degree-of-freedom non-contact three-dimensional optical scanner in the present invention is shown.

[0051] Figure 2 A schematic diagram showing the relative positions of the robot and the end probe of the three-dimensional optical scanner in the present invention is shown.

[0052] Figure 3 A schematic diagram of four position calibration points of the end probe rod of the three-dimensional optical scanner in the present invention is shown.

[0053] Figure 4 A schematic diagram of three attitude calibration points of the end probe of the three-dimensional optical scanner in the present invention is shown.

[0054] The reference numerals of the above-mentioned drawings are:

[0055] 1. Vertical column; 2. Conical socket; 3. Horizontal breadboard; 4. End probe of 3D optical scanner; 5. Robot. DETAILED DESCRIPTION

[0056] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] like Figure 1 A novel non-contact three-dimensional optical scanner end probe position calibration method is shown, which specifically includes the following steps:

[0058] S1, establish a three-dimensional coordinate system, and distribute three cone sockets evenly and equidistantly along each coordinate axis.

[0059] S2, using a laser tracker as a measuring device to calibrate the spatial position coordinates of the nine cone sockets.

[0060] S3, calibrate the TCP position of the probe at the end of the 3D optical scanner.

[0061] S4, perform TCP posture calibration on the end probe of the 3D optical scanner.

[0062] Specifically, Figure 1 As shown, step S1 is specifically as follows:

[0063] A vertical column 1 is arranged on the horizontal breadboard, and the direction in which the vertical column extends upward is the Z axis of the three-dimensional coordinate system; the X axis and the Y axis of the three-dimensional coordinate system are located on the horizontal breadboard 3; and the horizontal breadboard is located on a horizontal plane.

[0064] Specifically, the cone angle of each cone socket 2 is in the range of 60° to 120°, the spacing between the two cone sockets on each coordinate axis is ≥125mm, and the cone angle and depth of each cone socket are the same. First, a standard part is made of hard aluminum alloy material, which includes: a vertical column, evenly distributed threaded holes are processed on the surface of the vertical column and the base of the vertical column, and the vertical column base and the horizontal breadboard are fixedly connected by countersunk screws; three cone sockets are fixedly connected by countersunk screws at equal intervals along the three axis directions of the orthogonal coordinate system, and the cone angle and depth of each cone socket are the same. The purpose of the cone socket is to locate the position and posture of the end probe 4 of the multi-degree-of-freedom non-contact three-dimensional optical scanner, and it must be ensured that each cone socket has a good conicity.

[0065] Specifically, step S2 is as follows:

[0066] The laser tracker is used as a measuring device to calibrate the spatial coordinates of the nine cones. During the entire measurement process, the cone position must remain unchanged. Assume that the distance from the laser tracker to a cone is l i, where i is the cone nest point, i = 1, 2, ... 9; let the laser tracker's own position coordinates be (x0, y0, z0), and the cone nest point coordinates be (x i ,y i , z i ), then:

[0067]

[0068] A three-dimensional optical scanner is mounted on the end of a multi-axis robot, and finally the robot is controlled to move the probe at the end of the three-dimensional optical scanner to touch a cone socket in the space from different directions, and N groups of data (N≥3) are recorded; the position transformation of the end point of the probe rod relative to the end point of the robot is obtained by calculation to realize TCP position calibration; on this basis, the end point of the probe rod at the end of the three-dimensional optical scanner is continued to be controlled to move a certain distance along any two coordinate axis directions respectively, and the end point of the probe rod at the end of the three-dimensional optical scanner only moves in this direction, and there is no displacement in other directions, and the initial posture is fixed and remains unchanged; the posture transformation of TCF relative to the robot end coordinate system is obtained by calculation.

[0069] In summary, according to the six-point calibration principle of the robot tool coordinate system, the coordinate transformation matrix of the probe rod coordinate system at the end of the three-dimensional optical scanner relative to the end of the robot is solved to realize the calibration of the probe rod at the end of the three-dimensional optical scanner.

[0070] Specifically, step S3 is as follows:

[0071] S3.1, such as Figure 2 As shown, B is the base coordinate system of the robot 5; E is the robot end coordinate system; T is the three-dimensional optical scanner end probe coordinate system, and the transformation relationship of the three-dimensional optical scanner end probe coordinate system T relative to the robot end coordinate system E is: The transformation relationship between the probe coordinate system T at the end of the three-dimensional optical scanner and the base coordinate system B is: The conversion relationship between the three is:

[0072]

[0073] in, By rotation matrix and position vector B p E0 composition:

[0074]

[0075] is the transformation matrix from the robot end coordinate system E to the base coordinate system B.

[0076] S3.2, using the four-point calibration method TCP, such as Figure 3As shown, the four position calibration points of the probe rod at the end of the three-dimensional optical scanner are calibrated, namely: the first position calibration point P1, the second position calibration point P2, the third position calibration point P3, and the fourth position calibration point P4. The four position calibration points differ by 90° and cannot be on the same plane. Expanding equation (2) yields equation (4):

[0077]

[0078] in, is the rotation matrix of the position calibration point i' of the robot end coordinate system, i'=1, 2, ... 4; B p Ei’ The position vector of the position calibration point of the robot end coordinate system; is the rotation matrix of the probe at the end of the 3D optical scanner; E p T is the position vector of the probe rod at the end of the three-dimensional optical scanner; is the rotation matrix of the end of the probe coordinate system at the end of the 3D optical scanner; B p T is the position vector of the end of the three-dimensional optical scanner end probe coordinate system; transforming equation (4) to obtain the general equation (5) of the center point of the three-dimensional optical scanner end probe:

[0079]

[0080] Because the position of the probe coordinate system at the end of the 3D optical scanner in the base coordinate system remains unchanged under the four different postures, that is, B p Ei is a fixed value; E p T All parameters remain unchanged and are also fixed values.

[0081] Will Figure 3 Substitute the second position calibration point P2 and the first position calibration point P1 at the calibration point into equation (5) and make a difference to obtain equation (6):

[0082]

[0083] According to formula (6), the relationship between all position calibration points is obtained:

[0084]

[0085] S3.3, Gaussian elimination method is used to obtain the TCP position of the end probe of the 3D optical scanner ( E p Tx , E p Ty , E p Tz), as shown in formula (8):

[0086]

[0087] Specifically, after completing the TCP position calibration, the TCP posture is calibrated in the Z-axis and X-axis directions. This process keeps the posture of the TCF unchanged. Figure 4 As shown, the fourth position calibration point P4 is used as the first posture calibration point P4, and the robot moves at least 125 mm along the +X axis direction as the second posture calibration point P5; then the robot returns to the first posture calibration point P4, and then moves at least 125 mm along the +Z direction as the third posture calibration point P6.

[0088] Step S4 is specifically as follows:

[0089] S4.1, the X-axis axial vector X of the probe coordinate system T at the end of the three-dimensional optical scanner is as shown in formula (9):

[0090]

[0091] in,( B p 5Ex , B p 5Ey , B p 5Ez ) represents the position of the second posture calibration point P5 relative to the base coordinates.

[0092] S4.2, the Z-axis axial vector Z of the probe coordinate system T at the end of the three-dimensional optical scanner is as shown in formula (10):

[0093]

[0094] in, B p 5E The position of the second posture calibration point P5 relative to the base coordinates; B p 4E The position of the first posture calibration point P4 relative to the base coordinates; B p 6E The position of point P6 relative to the base coordinates is marked for the third posture.

[0095] S4.3, the Y-axis axial vector Y of the probe coordinate system T at the end of the three-dimensional optical scanner can be obtained by the right-hand rule:

[0096] Y=Z×X(11).

[0097] Specifically, step S4 also includes the following steps:

[0098] S4.4, calculate Z=X×Y; to ensure the orthogonality of the coordinate system vectors.

[0099] S4.5, normalize the axial vectors of the three coordinate axes to obtain the posture of the probe coordinate system T at the end of the three-dimensional optical scanner relative to the base coordinate system B Left multiplication Obtain the attitude matrix of the probe coordinate system at the end of the 3D optical scanner

[0100]

[0101] The rotation matrix of the end probe of the 3D optical scanner is solved and the end probe of the 3D optical scanner is calibrated.

[0102] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A novel non-contact three-dimensional optical scanner end probe position calibration method, characterized in that: The specific steps include: S1, establish a three-dimensional coordinate system, and distribute three cones evenly and equidistantly along each coordinate axis; S2, using a laser tracker as a measuring device to calibrate the spatial position coordinates of the nine cone sockets; S3, calibrating the TCP position of the probe at the end of the three-dimensional optical scanner; S4, perform TCP posture calibration on the end probe of the 3D optical scanner.

2. According to the novel non-contact three-dimensional optical scanner end probe rod position calibration method of claim 1, it is characterized in that: Step S1 is specifically as follows: A vertical column is arranged on the horizontal breadboard, and the direction in which the vertical column extends upward is the Z axis of the three-dimensional coordinate system; the X axis and the Y axis of the three-dimensional coordinate system are located on the horizontal breadboard; and the horizontal breadboard is located on a horizontal plane.

3. According to the novel non-contact three-dimensional optical scanner end probe rod position calibration method of claim 2, it is characterized in that: The cone angle of each cone dimple is selected in the range of 60° to 120°, and the cone angle and depth of each cone dimple are the same.

4. According to the novel non-contact three-dimensional optical scanner end probe rod position calibration method of claim 1, it is characterized in that: Step S2 is specifically as follows: Assume that the distance from the laser tracker to a cone is l i , where i is the cone nest point, i = 1, 2, ... 9; let the laser tracker's own position coordinates be (x0, y0, z0), and the cone nest point coordinates be (x i ,y i ,z i ), then:

5. According to the novel non-contact three-dimensional optical scanner end probe rod position calibration method of claim 1, it is characterized in that: Step S3 is specifically as follows: S3.1, the transformation relationship between the probe coordinate system T at the end of the 3D optical scanner and the robot coordinate system E at the end is: The transformation relationship between the probe coordinate system T at the end of the three-dimensional optical scanner and the base coordinate system B is: The conversion relationship between the three is: in, By the rotation matrix and position vector B p E0 composition: is the transformation matrix from the robot end coordinate system E to the base coordinate system B; S3.2, expand equation (2) to obtain equation (4): in, is the rotation matrix of the position calibration point i, of the robot end coordinate system, i,=1,2,…4; The position vector of the position calibration point of the robot end coordinate system; is the rotation matrix of the probe at the end of the 3D optical scanner; E p T is the position vector of the probe rod at the end of the three-dimensional optical scanner; is the rotation matrix of the end of the probe coordinate system at the end of the 3D optical scanner; B p T is the position vector of the end of the three-dimensional optical scanner end probe coordinate system; transforming equation (4) to obtain the general equation (5) of the center point of the three-dimensional optical scanner end probe: Combined with formula (5), the second position calibration point P2 is subtracted from the first position calibration point P1 to obtain: According to formula (6), the relationship between all position calibration points is obtained: S3.3, Gaussian elimination method is used to obtain the TCP position of the end probe of the 3D optical scanner ( E p Tx , E p Ty , E p Tz ), as shown in formula (8):

6. According to the novel non-contact three-dimensional optical scanner end probe rod position calibration method of claim 1, it is characterized in that: Step S4 is specifically as follows: S4.1, the X-axis axial vector X of the probe coordinate system T at the end of the three-dimensional optical scanner is as shown in formula (9): in,( B p 5Ex , B p 5Ey , B p 5Ez ) represents the position of the second posture calibration point P5 relative to the base coordinates; S4.2, the Z-axis axial vector Z of the probe coordinate system T at the end of the three-dimensional optical scanner is as shown in formula (10): in, B p 5E The position of the second posture calibration point P5 relative to the base coordinates; B p 4E The position of the first posture calibration point P4 relative to the base coordinates; B p 6E The position of the third posture calibration point P6 relative to the base coordinates; S4.3, the Y-axis axial vector Y of the probe coordinate system T at the end of the three-dimensional optical scanner can be obtained by the right-hand rule: Y=Z×X (11).

7. A novel non-contact three-dimensional optical scanner end probe position calibration method according to claim 6, characterized in that: Step S4 also includes the following steps: S4.4, calculate Z = X × Y; S4.5, normalize the axial vectors of the three coordinate axes to obtain the posture of the probe coordinate system T at the end of the three-dimensional optical scanner relative to the base coordinate system B Left multiplication Obtain the attitude matrix of the probe coordinate system at the end of the 3D optical scanner

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