Calibration method for indoor laser positioning system and heterogeneous sensors of laser tracker

Abstract

The application relates to a calibration method of a heterogeneous sensor of an indoor laser positioning system and a laser tracker, which comprises the following steps: 1) designing a calibration element; 2) measuring internal parameters of the calibration element, wherein the internal parameters comprise P1 and P2; 3) placing the calibration element in a measurement field and measuring P3; 4) calculating the distance L between the centers of the spheres two by two by using P1 to obtain a total of distance redundant observation values; 5) optimizing X1 and L1 by using the distance redundant observation values and n center coordinate necessary observation values P3; 6) performing landmark point registration according to P1 and X1 to obtain a rotation matrix R and a translation vector T; and 7) calculating X2 according to the obtained rotation matrix R and translation vector T. The method only needs to arrange the calibration element in the measurement field, and the coordinate unification of the sensor of the indoor laser positioning system and the sensor of the laser tracker can be realized in the measurement field by laser tracker measurement.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electronic information technology, and relates to a coordinate calibration method, in particular to a calibration method for heterogeneous sensors of an indoor laser positioning system and a laser tracker. BACKGROUND

[0002] In large space workpiece assembly manufacturing, accurate positioning of workpieces is one of the key technologies for assembly. A single positioning system has been unable to meet the requirements of large size measurement today, therefore, as an important means for measurement in the field of large size, the unified calibration of the sensor coordinates of a laser tracker and an indoor laser positioning system is a prerequisite for calibration of the two systems.

[0003] However, the traditional method for realizing the unified calibration of the heterogeneous sensors (i.e. the target balls of the laser tracker and the photoelectric receivers of the indoor laser positioning system) of the laser tracker and the indoor laser positioning system is to use a cooperative target ball. However, the traditional method using a cooperative target ball has a high requirement for the machining process of the cooperative target ball, and inevitably produces a centering error, thereby affecting the final calibration accuracy.

[0004] In view of the above technical defects of the prior art, there is an urgent need to develop a new calibration method for the heterogeneous sensors of a laser tracker and an indoor laser positioning system. SUMMARY

[0005] In view of the problems in the prior art, the present application provides a calibration method for the heterogeneous sensors of an indoor laser positioning system and a laser tracker, which only needs to arrange a calibration element in a measurement field, and the coordinates of the sensors of the indoor laser positioning system and the sensors of the laser tracker can be unified in the measurement field by measurement of the laser tracker.

[0006] In order to achieve the above purpose, the present application provides the following technical scheme:

[0007] A calibration method for the heterogeneous sensors of an indoor laser positioning system and a laser tracker, characterized by comprising the following steps:

[0008] 1) Design a calibration element, the calibration element is provided with n target ball bases of a laser tracker and m photoelectric receivers of an indoor laser positioning system, wherein n≥4 and the n target ball bases are in a three-dimensional structure, and m≥1;

[0009] 2) Measure the internal parameters of the calibration element, the internal parameters are the center coordinates P1 of the target ball bases after the laser tracker target balls are placed thereon and the center coordinates P2 of the photoelectric receivers in the calibration element coordinate system;

[0010] 3) placing the calibration element in the measurement field, and using the laser tracker to measure the coordinates of the ball centers P3 of the laser tracker target balls after the target ball bases are placed on the laser tracker target balls in the laser tracker coordinate system;

[0011] 4) calculating the distances L between the ball centers using P1 obtained in step 2), to obtain a total of distance redundant observation values;

[0012] 5) using the distance redundant observation values and the n ball center coordinate necessary observation values P3 obtained in step 3) to form a redundant measurement, and optimizing to obtain ball center coordinate optimal observation values X1 and distance optimal observation values L1;

[0013] 6) performing landmark registration according to P1 in step 2) and X1 in step 5) to obtain a rotation matrix R and a translation vector T between the calibration element coordinate system and the laser tracker coordinate system;

[0014] 7) calculating the coordinates X2 of the optoelectronic receiver of the indoor laser positioning system in the laser tracker coordinate system according to the obtained rotation matrix R and translation vector T, thereby completing the unified calibration of the coordinates of the optoelectronic receiver of the indoor laser positioning system and the target ball of the laser tracker.

[0015] Preferably, in step 5), the ball center coordinate optimal observation values X1 and the distance optimal observation values L1 are obtained by measurement adjustment optimization.

[0016] Preferably, in step 6), when performing landmark registration on P1 and X1, the optimal rotation matrix R and translation vector T are found by least squares method.

[0017] Preferably, finding the optimal rotation matrix R and translation vector T by least squares method specifically means: minimizing the distance between the two sets of landmark measurement values after registration, that is, the expression of this distance is where n is the number of laser tracker target ball bases on the calibration element, xi is the i-th P1, and yi is the i-th X1. i i

[0018] Preferably, the coordinates X2 of the optoelectronic receiver of the indoor laser positioning system in the laser tracker coordinate system are X2 = RP2 + T.

[0019] Preferably, the calibration element is made of a material that is not sensitive to changes in environmental factors.

[0020] Preferably, the material that is not sensitive to changes in environmental factors is carbon fiber or invar.

[0021] ​​Preferably, the high-precision photogrammetry instrument is used to measure the ball center coordinates P1 and the center coordinates P2 in step 2).

[0022] Preferably, the measurement accuracy of the internal parameters in step 2) is within 10 μm.

[0023] Preferably, n = 4, m = 6, and the four target ball seats of the laser tracker are fixed at four corners, one of which should be higher than the others by more than 5 cm.

[0024] Compared with the prior art, the indoor laser positioning system and the calibration method of the heterogeneous sensors of the laser tracker of the present application have one or more of the following beneficial technical effects:

[0025] 1. The present application only needs to arrange calibration elements in the measurement field, and the coordinate unification of the sensors of the indoor laser positioning system and the sensors of the laser tracker can be realized in the measurement field by measuring with the laser tracker, thereby providing a basic guarantee for high-precision calibration of the laser tracker and the indoor positioning system.

[0026] 2. The present application avoids using cooperative target balls, reduces the influence of processing technology and centering error, and has higher calibration accuracy. DETAILED DESCRIPTION

[0027] The present application is further described below in combination with embodiments, and the content of the embodiments does not limit the protection scope of the present application.

[0028] The present application relates to a calibration method of an indoor laser positioning system and heterogeneous sensors of a laser tracker, which only needs to arrange calibration elements in a measurement field, and the coordinate unification of the sensors of the indoor laser positioning system and the sensors of the laser tracker can be realized in the measurement field by measuring with the laser tracker, thereby providing a basic guarantee for high-precision calibration of the laser tracker and the indoor positioning system.

[0029] The calibration method of the indoor laser positioning system and the heterogeneous sensors of the laser tracker of the present application comprises the following steps:

[0030] I. Designing calibration elements.

[0031] In the present application, a calibration element is first designed. The shape and size of the calibration element are not limited. However, n target ball seats of a laser tracker and m photoelectric receivers of an indoor laser positioning system are arranged on the calibration element, so that the n target ball seats of the laser tracker and the m photoelectric receivers of the indoor laser positioning system form an integral whole. Herein, n ≥ 4 and the n target ball seats form a three-dimensional structure, and m ≥ 1.

[0032] Preferably, when n=4 and m=6, the measurement accuracy and efficiency can be balanced. For convenience, the four target ball bases of the laser tracker can be fixed at the four corners, and one of them should be higher than the others by more than 5 cm to ensure that the four target ball bases form a three-dimensional structure.

[0033] II. Measuring the internal parameters of the calibration element.

[0034] In the present application, the internal parameters are the coordinates of the centers of the target balls P1 after the target ball bases are placed on the target balls of the laser tracker and the coordinates of the centers of the photoelectric receivers P2. Since the calibration element is provided with n target ball bases, n coordinates of the centers of the target balls P1 are obtained. Meanwhile, since the calibration element is provided with m photoelectric receivers, m coordinates of the centers of the photoelectric receivers P2 are obtained.

[0035] In the present application, the coordinates of the centers of the target balls P1 and the coordinates of the centers of the photoelectric receivers P2 can be measured by a high-precision photogrammetry instrument. The measurement accuracy of the internal parameters is within 10 μm, thereby ensuring the accuracy of the measurement.

[0036] In the present application, preferably, the calibration element is made of a material which is not sensitive to environmental factors.

[0037] The environmental factors can include temperature and humidity, but are not limited thereto.

[0038] More preferably, the material which is not sensitive to environmental factors can be carbon fiber or invar, but is not limited thereto.

[0039] Since the calibration element is not sensitive to environmental factors, the P1 and P2 obtained by the measurement are not changed with the change of the environmental factors, thereby avoiding the interference of the environmental factors.

[0040] III. Placing the calibration element in a measurement field and measuring the coordinates of the centers of the target ball bases P3 in the coordinate system of the laser tracker after the target ball bases are placed on the target balls of the laser tracker.

[0041] Since the calibration element is provided with n target ball bases, n coordinates of the centers of the target ball bases P3 are obtained.

[0042] IV. Calculating the distances L between the centers of the target balls by using P1 obtained in step II.

[0043] In the present application, since the calibration element is provided with n target ball bases, n coordinates of the centers of the target balls P1 are obtained, and thus the number of the distances between the centers of the target balls is n(n-1) / 2. In the present application, it is referred to as the number of the distances between the centers of the target balls. ​a distance redundant observation value.

[0044] V. constructing a redundant measurement by using the distance redundant observation value and the n spherical center coordinate essential observation value P3 obtained in step three.

[0045] In the present application, since each P3 has three coordinate values of x, y and z, a total of observation values are obtained,

[0046] optimizing the observation values to obtain the spherical center coordinate optimal observation value X1 and the distance optimal observation value L1.

[0047] In the present application, the spherical center coordinate optimal observation value X1 and the distance optimal observation value L1 can be obtained by measurement adjustment optimization.

[0048] The measurement adjustment is an existing optimization theory and is a commonly used method in surveying. It is based on redundant observation. Since there is redundant observation, contradictions will occur between observation values. The measurement adjustment distributes the contradictory values to each observation value by the least square method according to certain principles (i.e. weighting matrix) to achieve the optimization of the observation values, thereby reducing the precision of high-precision observation values and improving the precision of low-precision observation values. In the present application, L obtained by calculating the distance between each two spherical centers of P1 is a high-precision observation value, and P3 measured by the laser tracker in the measurement field is a low-precision value. A more accurate value X1 than P3 is obtained by measurement adjustment.

[0049] VI. performing a mark point registration according to P1 in step two and X1 in step five to obtain a rotation matrix R and a translation vector T between the coordinate system of the calibration element and the coordinate system of the laser tracker.

[0050] The mark point registration is also an existing theory. The least square method is used to find the optimal rotation matrix R and translation vector T so that the distance between the two sets of mark point measurement values after registration is minimized. That is, the expression of the distance is where n is the number of laser tracker bases on the calibration element, xi is the x coordinate of the i-th P1, yi is the y coordinate of the i-th P1, zi is the z coordinate of the i-th P1, xi1 is the x coordinate of the i-th X1, yi1 is the y coordinate of the i-th X1, and zi1 is the z coordinate of the i-th X1. i i

[0051] VII. calculating the coordinates X2 of the photoelectric receiver of the indoor laser positioning system in the coordinate system of the laser tracker according to the obtained rotation matrix R and translation vector T, thereby completing the unified calibration of the coordinates of the photoelectric receiver of the indoor laser positioning system and the target sphere of the laser tracker.

[0052] where the coordinates X2 of the photoelectric receiver of the indoor laser positioning system in the coordinate system of the laser tracker are equal to RP2+T.​​​​

[0053] The indoor laser positioning system and the calibration method of the heterogeneous sensor of the laser tracker of the present application, by measuring the center coordinates P1 of the ball of the target ball base after the laser tracker target ball is placed on the ball and the center coordinates P2 of the photoelectric receiver in advance, then placing it in the measurement field, using the laser tracker to measure the center coordinates P3 of the ball of the target ball base after the laser tracker target ball is placed on the ball in its own coordinate system, and further using the redundant observation value to optimize the coordinates P3 to obtain the coordinates X1, and then using the corresponding unified physical point relationship between P1 and X1 to solve the rotation matrix R and the translation vector T between the coordinate system of the calibration element and the coordinate system of the laser tracker, and finally using the relationship to calculate the coordinates X2 of the photoelectric receiver of the indoor laser positioning system in the coordinate system of the laser tracker X2=RP2+T, thereby avoiding the defects of the traditional cooperative target ball method, and reducing the machining process and the centering error.

[0054] The above embodiments of the present application are merely examples for clearly illustrating the present application, and are not intended to limit the embodiments of the present application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the embodiments cannot be exhausted. Any obvious changes or variations derived from the technical solutions of the present application are still within the protection scope of the present application.

Claims

1. A method of calibrating a heterogeneous sensor of an indoor laser positioning system and a laser tracker, the method comprising: The method comprises the following steps: 1) designing a calibration element, on which n target ball bases of a laser tracker and m photoelectric receivers of an indoor laser positioning system are arranged, wherein n≥4 and the n target ball bases are in a three-dimensional structure, and m≥1; 2) measuring internal parameters of the calibration element, which are the coordinates of the centers of the target ball bases P1 after the target balls of the laser tracker are placed on the target ball bases and the coordinates of the centers of the photoelectric receivers P2 in the coordinate system of the calibration element; 3) placing the calibration element in a measurement field, and measuring the coordinates of the centers of the target ball bases P3 after the target balls of the laser tracker are placed on the target ball bases in the coordinate system of the laser tracker by using the laser tracker; 4) Calculate the distance L between the centers of the spheres using P1 obtained in step 2) to obtain a total of distance redundant observations; 5) using the n redundant observations of the distance and the n essential observations of the center coordinates P3 obtained in step 3), a redundant measurement is formed, and the optimal observations of the center coordinates X1 and the distance L1 are obtained by optimization. 5) using the n redundant observations of the distance and the n essential observations of the center coordinates P3 obtained in step 3), a redundant measurement is formed, and the optimal observations of the center coordinates X1 and the distance L1 are obtained by optimization. 6) performing landmark point registration according to P1 in step 2) and X1 in step 5) to obtain a rotation matrix R and a translation vector T between the coordinate system of the calibration element and the coordinate system of the laser tracker; 7) calculating the coordinates X2 of the photoelectric receivers of the indoor laser positioning system in the coordinate system of the laser tracker according to the obtained rotation matrix R and translation vector T, so as to complete the unified calibration of the coordinates of the photoelectric receivers of the indoor laser positioning system and the target balls of the laser tracker.

2. The method of calibrating a hybrid sensor of an indoor laser positioning system and a laser tracker of claim 1, wherein, In step 5), the optimal observation values X1 of the coordinates of the centers of the balls and the optimal observation values L1 of the distances are obtained through measurement adjustment optimization.

3. The method of calibrating a hybrid sensor of an indoor laser positioning system and a laser tracker of claim 2, wherein, In step 6), when performing landmark point registration on P1 and X1, the optimal rotation matrix R and translation vector T are found through the least square method.

4. The method of calibrating a hybrid sensor of an indoor laser positioning system and a laser tracker of claim 3, wherein, The optimal rotation matrix R and translation vector T are found by least square method, which is to make the distance between the two sets of measured values of the mark points after registration minimum, i.e. the expression of this distance is where n is the number of target ball bases of the laser tracker on the calibration element, x i is the i-th P1, y i is the i-th X1.

5. The method of calibrating a hybrid sensor of an indoor laser positioning system and a laser tracker of claim 4, wherein, The coordinates X2 of the photoelectric receivers of the indoor laser positioning system in the coordinate system of the laser tracker are X2=RP2+T.

6. The method of calibrating a hybrid sensor of an indoor laser positioning system and a laser tracker of any of claims 1-5, wherein, The calibration element is made of a material which is not sensitive to changes in environmental factors.

7. The method of calibrating a hybrid sensor of an indoor laser positioning system and a laser tracker of claim 6, wherein, The material which is not sensitive to changes in environmental factors is carbon fiber or invar.

8. The method of calibrating a hybrid sensor of an indoor laser positioning system and a laser tracker of claim 7, wherein, In step 2), the coordinates P1 of the centers of the balls and the coordinates P2 of the centers of the photoelectric receivers are measured by using a high-precision photogrammetric instrument.

9. The method of calibrating a hybrid sensor of an indoor laser positioning system and a laser tracker of claim 8, wherein, The measurement accuracy of the internal parameters in step 2) is within 10 μm.

10. The method of calibrating a hybrid sensor of an indoor laser positioning system and a laser tracker of claim 9, wherein, n=4, m=6, and the four target ball bases of the laser tracker are fixed at four corners, wherein one of the four target ball bases should be higher than the other three by more than 5 cm.

Images