The laser multi-coordinate measuring system has the advantages of high precision and wide measuring range and has wide application prospects in the fields of large-scale high-precision coordinate measurement. The positional relationship between the measuring equipment and the measured point is the key factor affecting the accuracy of the system. To quantify the influence of the positional relationship between the measuring equipment and the measured point on the uncertainty of coordinate measurement, the partial derivative operation of the coordinate solving formula is obtained. The coordinate of the measuring point and the mathematical model for measuring the distance from the base station to the measured point. Firstly, the mathematical model is simulated. The results of the simulation experiment show that the nonlinearity of the measurement uncertainty of the system increases significantly when the measured target point is close to the measurement plane composed of multiple stations. Finally, the simulation results are verified by experiments. When the distance between the retroreflector and the measuring plane is reduced from 1010.7 mm to 509.6 mm, the measurement deviation increases by 4 times. When the distance continues to decrease to 10.9 mm, the measurement deviation increases to 76 times before. The results show that the mentioned error model can accurately describe the relationship between the position of the measured point and the error of the measurement accuracy, and can provide theoretical support for the layout optimization method of the laser multi-coordinate measuring system.
The position error on the end of the industrial robot is an important specification for evaluating its accuracy performance. In the ISO 9283 standard, the laser trackers and the binocular vision measurement methods are recommended to calibrate the positioning error. The calibration accuracy measured by using the laser tracker method is superior to that by using the binocular vision measurement method. Thus, this paper emphasized to study how to improve the calibration accuracy of the end position error by using the binocular vision measurement system. The high precision lengths as reference are introduced to combine with a conventional binocular vision system to make a new measurement system. The system errors of the binocular vision system can be corrected. In order to verify the correction effect, taking the industrial robot as an experiment example, the experimental results show that the absolute position error on the end of the industrial robot by using the binocular vision system with reference length constraint can reduce from 0.491 mm to 0.330 mm, and the repetitive positioning error reduced from 0.116 mm to 0.023 mm. The accuracy improved by about 33% and 80% respectively. Compared with the laser tracker measurement results under the same experimental conditions, the difference between the two are 0.34 μm and 7.80 μm. It can be considered that the corrected binocular vision calibration method can achieve the same accuracy with the laser tracker. It can be widely used for high-precision calibration of industrial robots as a means of balancing economics and precision.
It is difficult for the traditional self-calibration algorithm to achieve high precision calibration when measuring over a
wide range. To overcome this shortcoming, an improved self-calibration algorithm for multilateration coordinates
measuring system is proposed. Different from the traditional self-calibration algorithm, the improved algorithm preselect
certain calibration points which is fixedly mounted on stable base, the lengths between specific points are
measured precisely by laser interference method. Then the precise lengths are taken as a part of optimization objective
function, and then the system parameters are determined by iterative computation. The effectiveness of the proposed
algorithm is verified by simulations and experiments. The results show that by using the improved algorithm, the max
error is only 8.9μm, the improved algorithm helps to improve the accuracy of the multilateration system significantly.
To measure the spatial coordinate accurately and efficiently in large size range, a manipulator automatic measurement system which based on multilateral method is developed. This system is divided into two parts: The coordinate measurement subsystem is consists of four laser tracers, and the trajectory generation subsystem is composed by a manipulator and a rail. To ensure that there is no laser beam break during the measurement process, an optimization function is constructed by using the vectors between the laser tracers measuring center and the cat's eye reflector measuring center, then an orientation automatically adjust algorithm for the reflector is proposed, with this algorithm, the laser tracers are always been able to track the reflector during the entire measurement process. Finally, the proposed algorithm is validated by taking the calibration of laser tracker for instance: the actual experiment is conducted in 5m × 3m × 3.2m range, the algorithm is used to plan the orientations of the reflector corresponding to the given 24 points automatically. After improving orientations of some minority points with adverse angles, the final results are used to control the manipulator's motion. During the actual movement, there are no beam break occurs. The result shows that the proposed algorithm help the developed system to measure the spatial coordinates over a large range with efficiency.
Large-scale laser comparator is main standard device that providing accurate, reliable and traceable measurements for high precision large-scale line and 3D measurement instruments. It mainly composed of guide rail, motion control system, environmental parameters monitoring system and displacement measurement system. In the laser comparator, the main error sources are temperature distribution, straightness of guide rail and pitch and yaw of measuring carriage. To minimize the measurement uncertainty, an equivalent common optical path scheme is proposed and implemented. Three laser interferometers are adjusted to parallel with the guide rail. The displacement in an arbitrary virtual optical path is calculated using three displacements without the knowledge of carriage orientations at start and end positions. The orientation of air floating carriage is calculated with displacements of three optical path and position of three retroreflectors which are precisely measured by Laser Tracker. A 4th laser interferometer is used in the virtual optical path as reference to verify this compensation method. This paper analyzes the effect of rail straightness on the displacement measurement. The proposed method, through experimental verification, can improve the measurement uncertainty of large-scale laser comparator.
Abbe error is the inherent systematic error in all large-scale laser comparators because the standard laser axis is not in line with measured optical axis. Any angular error of the moving platform will result in the offset from the measured optical axis to the standard laser axis. This paper describes to an algorithm which could be used to calculate the displacement of an equivalent standard laser interferometer and to eliminate an Abbe error. The algorithm could also be used to reduce the Abbe error of a large-scale laser comparator. Experimental results indicated that the uncertainty of displacement measurement due to Abbe error could be effectively reduced when the position error of the measured optical axis was taken into account.
A large-scale laser interferometric measurement standard device was designed and developed to improve the quantity transmission and calibration capabilities for linear measuring tools and large-scale high precision measurement instruments such as laser trackers, laser scanners and electronic total stations, etc. It consisted of an 80 meters granite guiding rail system, a length measuring system composed of three interferometers, a coarse-fine composite motion platform, environmental parameter (air pressure, temperature and humidity) automatic measuring system, and an image aiming system. The uncertainty of the standard device was analyzed, and a comparative experiment was made to determine the calibration capability of the built standard device. Experiment result indicated that the measurement uncertainty of this standard device to calibrate the other interferometers was better than 0.1μm + 1.0 × 10<sup>-7</sup> <i>L</i>(<i>k</i> = 2).