Developing innovative measurement and sensor systems for open-field measurements: That is the goal of the priority program “Metrology on flying platforms” (SPP 2433). In November 2023, the priority program, which is funded by the German Research Foundation (DFG), entered its first funding period with a duration of three years.
The research focuses in particular on the space close to the ground up to an altitude of around 500 meters, where drones are used as mobile measurement platforms. Civilian drone technology has untapped potential, especially with regard to precise, quantitative measurements with specified uncertainty.
SPP 2433 focuses on four scientific priorities: the development of new measurement principles, the optimization of existing sensor concepts, the improvement of signal processing, and the comprehensive evaluation of measurement quality in relation to the resources required.
The aim is to push the current limits of drone-based measurement and create new metrological foundations. Through exchange between the individual subprojects of SPP 2433, robust and valid measurement methods are being developed.
Limitations in the measurement of large objects
A measurement system capable of measuring objects of any size—such as infrastructure or large-scale industrial components—is being developed by the Institute of Assembly Technology and Robotics (match) in cooperation with the Institute of Measurement and Automatic Control (imr) at Leibniz University Hannover in the subproject “Referenced Large-Scale Airborne Measurement System.”
For this type of measurement object, the precise acquisition of geometric measurement data is crucial in order to reliably detect aging effects or manufacturing inaccuracies, for example. To detect such errors, a high-resolution and precise sensor is required to accurately capture the geometry.
The largest coordinate measuring machines currently available, which achieve an accuracy of less than 30 µm, are capable of measuring objects with dimensions of up to 6 m x 10 m x 4 m in temperature-controlled indoor environments. However, these machines are too limited in their working space for the intended measurement objects and are also not suitable for use in uncontrolled outdoor environments. Accordingly, there is currently no measurement system capable of scanning the aforementioned measurement objects with submillimeter accuracy.
High-precision 3D measurement with a large working space
In order to be able to measure infrastructure and large-scale industrial components in the future, match and imr are developing a measuring system consisting of a drone with a high-precision sensor, a laser tracking system, and several mobile robots. The sensor, which will be mounted on the drone, is being developed, validated, and ultimately put into operation by imr. This sensor is a stripe light projection system that can extract depth information by projecting a pattern onto a surface to create a 3D point cloud of the object being measured.
However, two fundamental problems arise when surveying with a drone-based measurement system: First, the sensor only captures a limited area with each measurement, which means that large objects must be scanned in several sections. Second, a drone is a relatively unstable system that is subject to minimal movements due to environmental influences. These movements can affect the accurate localization of the drone, which can result in incorrect recorded positions. As a result, when the individual measurements are stitched together, the result is not a coherent 3D model of the objects, but rather overlaps or gaps.
In order to precisely locate the drone in space at all times, the project partners use an external laser tracking system that determines the exact position of the drone and the structured light projection system in real time. However, this tracking system requires visual contact with the drone, which can be interrupted when surveying infrastructure objects. To prevent this, the laser trackers are mounted on several mobile robots so that the tracking system can be moved around the measurement object together with the drone, thus maintaining visual contact.
In this context, match contributes its extensive expertise in the navigation of mobile robots. A path planning algorithm enables the mobile robot platforms to navigate around the measurement object without collision. An important constraint is that the laser tracking system must be connected via a fiber optic cable, which complicates path calculation because the mobile robots must not drive over the fiber optic cables to avoid damage.
In parallel, match is developing positioning algorithms for the drone and the mobile robots, ensuring that the entire measurement object can be fully surveyed. The positions of the mobile robots depend on the range of the laser tracking system, which can only locate the drone within a limited field of view. Finally, the measurement positions of the drone and the mobile robots must be coordinated so that the entire measurement object can be measured with a minimum number of repositionings.
Innovative system overcomes the limitations of traditional measurement techniques
In summary, the SPP 2433 priority program pursues innovative approaches to high-precision measurement of large-scale infrastructure and industrial components.
The measurement system, which is being developed in one of the subprojects, consists of a drone, a high-resolution sensor, and mobile robots, and has the potential to overcome the existing limitations of traditional measurement techniques and achieve sub-millimeter accuracy. The combination of advanced technologies, such as the laser tracking system and intelligent algorithms, enables efficient and precise collection of geometric data.
In the future, this technology could not only revolutionize infrastructure maintenance and inspection, but also open up new fields of application that can benefit from precise 3D data—for example, in industry or environmental research. This will help to significantly increase efficiency and safety in these areas.
