A novel non-contact three-dimensional optical scanner end probe pose calibration method

Abstract

The application provides a novel non-contact three-dimensional optical scanner end probe pose calibration method, relates to the tool coordinate system calibration technical field, and specifically comprises the following steps: establishing a three-dimensional coordinate system, and distributing three taper sockets on each coordinate axis in a uniform and equal interval manner. A laser tracker is used as a measuring device to calibrate the spatial position coordinates of the nine taper sockets. The TCP position of the three-dimensional optical scanner end probe is calibrated. The TCP attitude of the three-dimensional optical scanner end probe is calibrated. The technical scheme of the application overcomes the problem that the prior art lacks a three-dimensional optical scanner end probe pose calibration method.

Description

Technical Field

[0001] The present invention relates to the technical field of tool coordinate system calibration, and in particular to a novel method for calibrating the position and posture of a probe at the end of a non-contact three-dimensional optical scanner. 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 guaranteed 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] Currently, the main methods for calibrating the coordinate system of the end probe of a multi-axis robot's 3D optical scanner, both domestically and internationally, are external datum and multi-point calibration. In the external datum method, FANUC robots use the DynaCal system for calibration, while ABB arc welding robots use the BullEyes system's automatic tool calibration method, but these rely on external datums. In the multi-point calibration method, the robot is controlled so that the tool center point (TCP) coincides with a specific spatial point multiple times in different directions, and positional constraints are used to establish equations to determine the actual position of the tool center point. The robot is then controlled to reach multiple points with specific directional relationships, which constitute the orientation of the coordinate system of the robot's 3D optical scanner's end probe.

[0004] The six-point calibration principle is the most widely used of the multi-point calibration methods. In this method, the tool center point position calibration is performed by aligning the TCP positions of the four calibration points (the first four points) to calculate the tool center point. TCP attitude calibration is performed by establishing a specific orientation and position relationship between the three calibration points (the last three points) to calculate the attitude of the 3D optical scanner's end-of-line probe coordinate system relative to the robot's end-of-line coordinate system.

[0005] Therefore, a simple and accurate new method for calibrating the probe position of 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 posture calibration method to solve the problem of lack of three-dimensional optical scanner end probe posture calibration method in the prior art.

[0007] In order to achieve the above object, the present application provides a novel non-contact three-dimensional optical scanner end probe pose calibration method, which specifically comprises the following steps:

[0008] S1, a three-dimensional coordinate system is established, and three taper holes are uniformly and equidistantly distributed along each coordinate axis.

[0009] S2, a laser tracker is used as a measuring device to calibrate the spatial position coordinates of the nine taper holes.

[0010] S3, TCP position calibration is performed on the three-dimensional optical scanner end probe.

[0011] S4, TCP attitude calibration is performed on the three-dimensional optical scanner end probe.

[0012] Further, step S1 is specifically:

[0013] A vertical column is arranged on a horizontal plane plate, the upward extending direction of the vertical column 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 plane plate, and the horizontal plane plate is located on the horizontal plane.

[0014] Further, the taper angle of each taper hole is selected in the range of 60°-120°, and the taper angle and the depth of each taper hole are the same.

[0015] Further, step S2 is specifically:

[0016] Suppose the distance from the laser tracker to a certain taper hole is l i , wherein i is the taper hole point, i=1, 2,..., 9; the position coordinates of the laser tracker itself are set as (x0, y0, z0), the position coordinates of the taper hole point are set as (xi, yi, zi), and the following equation is obtained: i i i

[0017]

[0018] Further, step S3 is specifically:

[0019] S3.1, 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 of the three-dimensional optical scanner end probe coordinate system T relative to the base coordinate system B is The transformation relationship of the three is:

[0020]

[0021] wherein, is composed of a rotation matrix and a position vector B p E0 .​​​

[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' in the robot end coordinate system, i'=1,2,...4; BpEi is the position vector of the position calibration point in 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 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 probe coordinate system; transforming formula (4) to obtain the general formula (5) of the center point of the three-dimensional optical scanner probe:

[0027]

[0028] Combined with formula (5), the difference between the second position calibration point P2 and the first position calibration point P1 is obtained:

[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 expressed as 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 expressed as 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 the third posture calibration point P6 relative to the base coordinates.

[0041] S4.3, the Y-axis axial vector Y of the probe coordinate system T of the three-dimensional optical scanner end 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 component for calibrating the end probe of a multi-degree-of-freedom non-contact three-dimensional optical scanner, comprising six conical sockets fixed on a horizontal plane, three conical sockets fixed in a vertical direction, the cone angle of each conical socket being selected in the range of 60° to 120°, and the cone angle and depth of each conical socket being the same, a vertical column, and a horizontal breadboard. The nine conical sockets are distributed according to an orthogonal coordinate system, and then a three-dimensional optical scanner is used as a measuring device to calibrate them. The device involved in the present invention has a simple structure, is easy to operate, and is highly practical; a multi-axis robot drives a three-dimensional optical scanner mounted on its end, and touches a conical 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 coordinate system of the end probe of the three-dimensional optical scanner relative to the end of the robot can be simply and accurately solved, thereby realizing 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 embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0050] Figure 1 A schematic diagram of a standard component used for calibration of the end probe 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 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 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 clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts 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-shaped pits 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-shaped pits.

[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, if Figure 1 As shown, step S1 is specifically as follows:

[0063] A vertical column 1 is set on the horizontal breadboard, and the upward extending direction of the vertical column is the Z axis of the three-dimensional coordinate system; the X axis and 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 selected to be 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 component is made of hard aluminum alloy material. The standard component includes: a vertical column with evenly distributed threaded holes machined on the surface of the vertical column and the vertical column base, and the vertical column base and the horizontal breadboard are fixedly connected using countersunk screws; three cone sockets are fixedly connected with countersunk screws at equal intervals along the three axes of the orthogonal coordinate system. 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. It is necessary to ensure 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. Finally, the robot is controlled to move the probe at the end of the three-dimensional optical scanner to touch a cone in the space from different directions, and N groups of data (N≥3) are recorded. The position transformation of the probe end point relative to the robot end point is obtained by calculation to realize TCP position calibration. On this basis, the end point of the probe at the end of the three-dimensional optical scanner is continued to be controlled to move a certain distance along any two coordinate axes. The end point of the probe at the end of the three-dimensional optical scanner only moves in this direction and has no displacement in other directions. At the same time, 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, based on the six-point calibration principle of the robot tool coordinate system, the coordinate transformation matrix of the three-dimensional optical scanner end probe coordinate system relative to the robot end is solved to realize the calibration of the three-dimensional optical scanner end probe.

[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 between the three-dimensional optical scanner end probe coordinate system T and 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 the 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 end probe 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 are 90° apart 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' in the robot end coordinate system, i'=1, 2, ... 4; B p Ei’ is 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 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 probe coordinate system; transforming formula (4) to obtain the general formula (5) of the center point of the three-dimensional optical scanner probe:

[0079]

[0080] Because the position of the probe coordinate system at the end of the three-dimensional 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 The various 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 formula (5) and make the difference to get formula (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 expressed as 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 expressed as 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 the third posture calibration point P6 relative to the base coordinates.

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

[0096] Y=Z × X(11).

[0097] Specifically, step S4 further 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 calibration of the end probe of the 3D optical scanner is realized.

[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 scope of protection 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 evenly distribute three cones along each coordinate axis; S2, using a laser tracker as a measuring device to calibrate the spatial position coordinates of the nine cones; S3, calibrate the TCP position of the probe at the end of the 3D optical scanner; S4, perform TCP posture calibration on the end probe of the 3D optical scanner; Step S1 is specifically as follows: A vertical column is set on a horizontal breadboard, and the vertical column extends upward in the direction of the Z axis of the three-dimensional coordinate system; the X axis and Y axis of the three-dimensional coordinate system are located on the horizontal breadboard; and the horizontal breadboard is located on a horizontal plane; 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 s ,y s ,z i ), then: 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 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' in the robot end coordinate system, i'=1,2,…4; B p Ei’ is 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 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 probe coordinate system; transforming formula (4) to obtain the general formula (5) of the center point of the three-dimensional optical scanner probe: Combined with formula (5), the difference between the second position calibration point P2 and the first position calibration point P1 is obtained: 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): 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 expressed as 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 expressed as 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 of the three-dimensional optical scanner end can be obtained by the right-hand rule: Y=Z×X(11); Step S4 also includes the following steps: S4.4, calculate Z = X × Y to ensure the orthogonality of the coordinate system vectors; 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 2. A novel non-contact three-dimensional optical scanner end probe position calibration method according to claim 1, 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.

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