RESUMEN
Precision measurement methods and technologies for large-scale three-dimensional coordinates are in high demand in advanced equipment manufacturing. The multi-station triangulation network represented by the rotary-laser scanning measurement system has the advantages of having high precision, having multitask parallel measurement capability, and having a high degree of automation. It is widely used in the docking of large components, quality control of key points, and collaborative positioning of production equipment. Nevertheless, due to the limitations in the measurement principle, the positioning accuracy along the depth direction is notably lower when compared to other directions. This difference becomes more pronounced with increasing distance. This paper proposes a method to address this issue by integrating a distance measurement station into the network. A novel, to the best of our knowledge, cooperative target, coupled with a high-dynamic beam guidance mechanism, is designed to achieve fast absolute distance measurement to the target. The weighted fusion of the distance and angle observations effectively enhances the measurement accuracy while preserving the advantages of highly automated measurement. Additionally, we introduce a joint calibration method for extrinsic parameters of multi-type stations. High-precision absolute distances are utilized to establish optical scale bars, complemented by the incorporation of physical scale bars, thereby obviating the necessity for using external reference instruments such as laser trackers. Finally, a series of experimental verifications demonstrate the effectiveness of calibration and measurement methods. The root mean square error of all measured points drop to 42.6% of that the triangulation method measures.
RESUMEN
Precisely and efficiently measuring three-dimensional coordinates of key points on large-scale components in the manufacturing process of aircraft and ships is critically essential. This study presents a multi-target automatic positioning method based on rapid angle and distance measurement in parallel. The measurement processes for angles and distances are decoupled and, when executed simultaneously, aims to enhance the measurement efficiency and automation compared with conventional metrology systems. A cooperative target is devised to realize the rotary-laser scanning angle measurement and absolute distance measurement in parallel. The method of multi-target rough positioning based on rotary-laser scanning and then the precise coordinate measurement method introducing absolute distance constraint are detailed. Especially for the distance measurement, we propose a method to determine the internal zero length and compensate for the distance error caused by mirror offset. A real-site experiment is implemented to verify the method's feasibility and demonstrate that the 3D coordinate measurement accuracy is better than 0.17 mm compared with laser tracker.
RESUMEN
In this paper, we discuss two aspects concerning terrestrial laser scanners (TLSs) - error model calibration and performance evaluation. Error model calibration is the process of determining parameters of an error model to improve the accuracy of TLSs. Performance evaluation refers to a series of tests to determine if a TLS meets specifications provided by the manufacturer. Both procedures can be accomplished using a network of stationary targets whose locations are known from a prior calibration using another method/instrument. This paper explores the question of whether the network (i.e., target locations) must be calibrated using an instrument of higher accuracy such as a laser tracker (LT) or whether the TLS under study is itself suitable for network calibration. Regardless of whether an LT or a TLS is used, the calibration is performed from target measurements made from multiple locations of the instrument to average out systematic errors and reduce the uncertainties in target coordinates. Such multi-position measurements on stationary targets is referred to as the network method. We provide guidance on when the TLS is sufficient for network calibration and when an LT may be necessary for performance evaluation purposes.
RESUMEN
In the measurement process of photoelectric scanning measurement network, the laser surface edge area has lower measurement accuracy than the middle area due to the geometrical distortions of the laser surface of the transmitter. This paper presents a sub-regional calibration method that can accomplish error compensation for the measurement system. Unlike the camera sub-regional calibration, the regional division and identification of the laser surface are more difficult. In this paper, the pitch angle in the transmitter coordinate frame of the spatial point was used as the basis for the division and identification of the laser surface. In the calibration process, the laser surface of the transmitter was divided into different regions and each region was calibrated independently, so that an intrinsic parameters database containing the intrinsic parameters of different regions could be established. Based on the database, the region identification and error compensation algorithm were designed, and comparison experiments were carried out. With the novel calibration method, the measurement accuracy of the system had an obvious upgrade, especially at the edges of the laser surface within a certain measurement area, which could enlarge the effective measurement area of the transmitter and would broaden and deepen the application fields of photoelectric scanning measurement network.