CN112325804A - Robot assembly error detection method based on laser tracker - Google Patents
Robot assembly error detection method based on laser tracker Download PDFInfo
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- CN112325804A CN112325804A CN202011196745.1A CN202011196745A CN112325804A CN 112325804 A CN112325804 A CN 112325804A CN 202011196745 A CN202011196745 A CN 202011196745A CN 112325804 A CN112325804 A CN 112325804A
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- assembly error
- laser tracker
- included angle
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/26—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes
Abstract
A robot assembly error detection method based on a laser tracker comprises the following steps: fixing a target ball of a laser instrument at the tail end of the robot, performing single motion on all axes of the robot in sequence, performing single motion on each axis for N times, wherein N is more than or equal to 3, acquiring position coordinates of the center of the target ball by using a laser tracker to obtain point groups P1-Pm of all the axes, and m is the number of the axes of the robot; wherein, before each axis of the robot is single-acting, the robot is controlled to return to the same preset position; respectively obtaining rotation planes alpha 1-alpham of all the shafts through fitting according to the point groups P1-Pm; calculating the included angle between the rotating planes of every two adjacent shafts of the robot; and calculating the difference between the calculated included angle between the rotating planes of each two adjacent shafts and the design value of the included angle of the corresponding two adjacent shafts, and taking the difference result as the assembly error of the two adjacent shafts of the robot. The invention can detect the assembly error between every two adjacent shafts of the robot.
Description
Technical Field
The present invention relates to robotics.
Background
The position precision of the industrial robot comprises two indexes of position repeatability and position accuracy, the position repeatability is related to the return difference and the friction force of a transmission chain (a gear, a synchronous belt and a speed reducer), generally can reach about 0.05mm, and can meet most application occasions. The position accuracy is generally related to machining errors (length and angle deviation), assembly errors, reduction ratio errors and zero position errors of mechanical arm parts, the length errors, the reduction ratio errors and the zero position errors can be compensated through a robot calibration technology (Dynacal wire pulling equipment and a laser tracker), and the position accuracy is remarkably improved to 0.2-1 mm. However, the existing calibration method cannot compensate the angular deviation and the assembly error (mainly the angular deviation of each axis) of the mechanical arm part, and when the angular deviation (the perpendicularity and the parallelism) of the mechanical arm and other parts and the angular deviation of each axis caused by assembly are large, the existing calibration method cannot effectively improve the position accuracy.
Disclosure of Invention
The invention aims to provide a robot assembly error detection method based on a laser tracker, which can detect the assembly error between every two adjacent shafts of a robot.
The robot assembly error detection method based on the laser tracker comprises the following steps:
fixing a target ball of a laser instrument at the tail end of the robot, performing single motion on all axes of the robot in sequence, performing single motion on each axis for N times, wherein N is more than or equal to 3, acquiring position coordinates of the center of the target ball by using a laser tracker to obtain point groups P1-Pm of all the axes, and m is the number of the axes of the robot; wherein, before each axis of the robot is single-acting, the robot is controlled to return to the same preset position;
respectively obtaining rotation planes alpha 1-alpham of all the shafts through fitting according to the point groups P1-Pm;
calculating the included angle between the rotating planes of every two adjacent shafts of the robot;
and calculating the difference between the calculated included angle between the rotating planes of each two adjacent shafts and the design value of the included angle of the corresponding two adjacent shafts, and taking the difference result as the assembly error of the two adjacent shafts of the robot.
The invention has at least the following advantages:
when the position accuracy of the robot is not up to the standard after calibration, the method provided by the invention can detect whether the axis angle deviation between every two adjacent shafts of the robot is within an allowable range, if the axis angle deviation exceeds the allowable range, the problem of assembly or part machining error can be further analyzed, and the problem can be solved by reassembling corresponding joints or replacing related parts.
Drawings
Fig. 1 shows a flow chart of a robot assembly error detection method according to an embodiment of the present invention.
Fig. 2 shows a system hardware diagram for implementing the robot assembly error detection method according to the embodiment of the present invention.
Detailed Description
Fig. 1 shows a flow chart of a robot assembly error detection method according to an embodiment of the present invention. As shown in fig. 1, a method for detecting assembly errors of a robot based on a laser tracker according to an embodiment of the present invention includes the following steps:
fixing a target ball of a laser instrument at the tail end of the robot, performing single motion on all axes of the robot in sequence, performing single motion on each axis for N times, wherein N is more than or equal to 3, acquiring position coordinates of the center of the target ball by using a laser tracker to obtain point groups P1-Pm of all the axes, and m is the number of the axes of the robot; wherein, before each axis of the robot is single-acting, the robot is controlled to return to the same preset position;
respectively obtaining rotation planes alpha 1-alpham of all the shafts through fitting according to the point groups P1-Pm;
calculating the included angle between the rotating planes of every two adjacent shafts of the robot;
and calculating the difference between the calculated included angle between the rotating planes of each two adjacent shafts and the design value of the included angle of the corresponding two adjacent shafts, and taking the difference result as the assembly error of the two adjacent shafts of the robot.
Fig. 2 shows a system hardware schematic diagram implementing the robot assembly error detection method of the embodiment of the present invention, in which a six-axis industrial robot 1 and a laser tracker 2 are shown. The working principle of the robot assembly error detection method based on the laser tracker of the embodiment of the invention is described in detail below by taking a universal six-axis robot as an example, and the method comprises the following steps:
a. control the robot 1 to return to the initial position (normally to zero for the robot)Position), fix the laser instrument target ball at the end of robot 1, rotate a shaft N of robot 1 alone, N is greater than or equal to 3, the other five shafts do not rotate, once rotate the position coordinate of record target ball centre of sphere, record N points altogether, obtain a point group P1 on the rotation plane of one shaft, P1 ═ is (x 1 ═ isi，yi，zi)，i＝0、1、…N-1。
The angle of each rotation of a shaft may be the same (for example, 10 °), or may be different, which is not limited in the present invention.
b. After the first-axis collection is finished, the robot 1 is controlled to return to the initial position, the two axes of the robot are independently rotated for N times, the position coordinates of the sphere center of the target ball are recorded every time the robot is rotated, N points are recorded in total, and a point group P2 on the two-axis rotation plane is obtained.
The number of rotations of the two shafts may be the same as or different from the number of rotations of the one shaft.
c. Similarly, point groups P3 and P4.. P6 of N independent rotations of three shafts to six shafts are collected in sequence, and the robot is controlled to return to the initial position when each shaft is singly moved, so that the axes of adjacent joints are ensured to have a determined position relation (parallel or vertical).
d. The plane α 1, α 2.. α 6 of rotation of each axis is obtained by fitting through the set of points P1, P2.. P6.
e. And calculating the angle of each two adjacent joint axes, namely, the included angle between the first axis and the second axis is equal to the included angle between the alpha 1 plane and the alpha 2 plane, the included angle between the second axis and the third axis is equal to the included angle between the alpha 2 plane and the alpha 3 plane, and the angles of the other adjacent axes are analogized.
There are many specific implementation methods for steps d and e, one of them is that the supporting software (for example, SA software) of the laser tracker has the function of fitting planes through multiple points, and can determine the included angle between the planes. And secondly, fitting a plane by a least square method, and calculating the normal vector included angle of the plane to obtain the included angle of the plane.
In this embodiment, the rotation plane of each axis of the robot is obtained by least square fitting, and the algorithm is as follows:
the general expression of the plane equation is: ax + By + Cz + D is 0
When C ≠ 0, the above formula can be converted into:
the abbreviation is: a is0x+a1y+a2Wherein
For space n (n ≧ 3) points (x)i,yi,zi) N-1, fitting the plane to minimize the point-to-plane distance, and making the equation
To minimize S, it should be satisfied
Namely, it is
To obtain
The above system of linear equations is simplified to AX ═ B and X ═ a0a1a2]T
Least square method for solving X ═ (A)TA)-1ATB
So far, the plane fitting is completed, and the fitting plane is a0x+a1y-z+a2＝0
The included angle between the two planes is calculated as follows: and setting the equation of the plane of rotation of the adjacent shafts obtained by fitting as follows:
the normal vector of the plane is then:
n1＝(a0,a1,a2),n2＝(b0,b1,b2)
the included angle of the plane is:
f. and comparing the actually measured included angle between the axes of every two adjacent joints with the designed included angle value between the two corresponding adjacent shafts in the assembly drawing for difference, and analyzing whether the assembly error is within an allowable range.
For example, in fig. 2, the design value of the axial angle between the first axis and the second axis of the robot 1 in the zero position is 90 °, if the actual measurement value is 89.95 °, the assembly error is 0.05 °, and if the allowable error is 0.02 °, the assembly error between the first axis and the second axis is large. Similarly, assembly errors between two and three axes, between three and four axes, between four and five axes, and between five and six axes can also be analyzed.
According to the method for detecting the robot assembly error based on the laser tracker, the reason that the accuracy of the robot is still poor after calibration can be analyzed, and reference is provided for improving the assembly accuracy of the robot.
Claims (5)
1. A robot assembly error detection method based on a laser tracker is characterized by comprising the following steps:
fixing a target ball of a laser instrument at the tail end of the robot, performing single motion on all axes of the robot in sequence, performing single motion on each axis for N times, wherein N is more than or equal to 3, acquiring position coordinates of the center of the target ball by using a laser tracker to obtain point groups P1-Pm of all the axes, and m is the number of the axes of the robot; wherein, before each axis of the robot is single-acting, the robot is controlled to return to the same preset position;
respectively obtaining rotation planes alpha 1-alpham of all the shafts through fitting according to the point groups P1-Pm;
calculating the included angle between the rotating planes of every two adjacent shafts of the robot;
and calculating the difference between the calculated included angle between the rotating planes of each two adjacent shafts and the design value of the included angle of the corresponding two adjacent shafts, and taking the difference result as the assembly error of the two adjacent shafts of the robot.
2. The method for detecting the assembly error of the robot based on the laser tracker as claimed in claim 1, wherein the rotation planes α 1- α m of all the axes are obtained by fitting with the matching software of the laser tracker, and the included angle between the rotation planes of every two adjacent axes of the robot is calculated.
3. The laser tracker-based robot assembly error detection method of claim 1, wherein the rotation planes of the axes of the robot are obtained by least square fitting, and the angle between the rotation planes of each adjacent two axes is obtained by calculating the angle between normal vectors of the rotation planes of each adjacent two axes.
4. The laser tracker based robot assembly error detection method of claim 1, wherein said predetermined position is a zero position of the robot.
5. The laser tracker-based robot assembly error detection method of claim 4, wherein said robot is a six-axis industrial robot, and m is 6.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113714334A (en) * | 2021-08-17 | 2021-11-30 | 山东磐金钢管制造有限公司 | Method for calibrating center line of straightening machine based on laser tracker |
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| JP2020066083A (en) * | 2018-10-24 | 2020-04-30 | 国立大学法人広島大学 | Motion accuracy measuring method and position correction method for robot |
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| JPH11167005A (en) * | 1997-12-05 | 1999-06-22 | Matsushita Electric Works Ltd | Multilens for infrared sensor |
| CN106338990A (en) * | 2016-08-12 | 2017-01-18 | 杭州亿恒科技有限公司 | Industrial robot DH parameter calibration and zero position calibration method based on laser tracker |
| CN109773774A (en) * | 2017-11-14 | 2019-05-21 | 合肥欣奕华智能机器有限公司 | A kind of scaling method of robot and positioner position orientation relation |
| CN109048876A (en) * | 2018-07-03 | 2018-12-21 | 上海新时达电气股份有限公司 | A kind of robot calibration method based on laser tracker |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113714334A (en) * | 2021-08-17 | 2021-11-30 | 山东磐金钢管制造有限公司 | Method for calibrating center line of straightening machine based on laser tracker |
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