Fraunhofer IZM
Navigation systems for unmanned drones
Particularly lightweight drones with a high payload are required for photogrammetric surveying of industrial buildings and terrain topographies or as cargo drones in the logistics sector. Fraunhofer IZM has developed a special navigation unit for this purpose.
The navigation unit (IMU) enables photogrammetric surveying from the air using unmanned drones.
© angkhan/stock.adobe.comThe aim of the 'IMUcompact' research project was to develop a measurement unit for the precise positioning of autonomous drone systems. The system's Inertial Measurement Unit (IMU for short) is essentially based on three gyroscope axes and three acceleration sensors, which enable centimeter-accurate positioning for navigation and terrain surveying without a GPS signal.
Compact gyroscopes with low resolution are found in all smartphones and smartwatches today, for example to ensure the orientation of the screen or the camera. Although these so-called MEMS1 gyroscopes are also small and lightweight, they are too susceptible to environmental influences such as temperature, humidity and electromagnetic fields for use in drones. IMU systems with higher resolution have so far not been profitable for industry or business due to their size and cost.
The interferometric fiber optic miniature gyroscope (IFOG) developed at the Fraunhofer Institute for Reliability and Microintegration (IZM) enables a higher level of detail and can be combined with a wide variety of carrier drones due to its compactness and low weight. As this form of gyroscope contains no moving parts and is electromagnetically insensitive, it is far better suited for use in unmanned drones than conventional MEMS alternatives. 1 MEMS gyroscope stands for microelectromechanical system gyroscope and refers to conventional measuring systems based on a vibrating silicon structure.
Innovative assembly method for miniaturization
With a newly developed mounting method, the electronic and optical components of the IMU can be arranged in such a way that a high degree of miniaturization is achieved without compromising on accuracy. Conventional IMUs only have a resolution in the range of 25 to 30 cm. The gyroscope developed at Fraunhofer IZM now allows an absolute accuracy of less than 10 cm. The special arrangement of the measuring components on a 3D-printed optical bench also enables high mechanical strength for industrial applications with very low weight. In addition, an application-specific circuit board was developed that is very robust and compact at the same time thanks to its design.
Photogrammetric measurements from the air
One of the first practical applications of the new IMU is photogrammetry with unmanned aerial vehicles (UAVs). Photogrammetry is the measurement and determination of physical objects using a combination of 2D images and 3D measurement methods such as LIDAR. In this case, the weight of the IMU must not exceed 1 kg and the entire measuring system including IMU, LIDAR, cameras, data logger PC and power supply via batteries must weigh less than 5 kg. Possible applications for drone-based photogrammetry include the automated surveying of factory buildings, the technical monitoring of offshore wind turbines or automated stocktaking in agriculture and livestock farming. Drone-based photogrammetry can also make an important contribution to damage assessment in disaster areas, especially when large areas are affected by unexpected environmental events. Providers of online map services also use photogrammetric methods to create digital 3D map material, although this often requires the cost-intensive use of aircraft or gyrocopters with appropriate measurement technology.
Partnership between research and business
"As experts in the assembly and connection technology of optical fibers, Fraunhofer IZM was able to develop a demonstrator together with project partners in which the IMU was combined with a GPS system and a powerful integrated circuit to create a complete, integrated solution. This prototype is now to be optimized in a further step in order to further advance the civilian use of autonomous drone systems," project manager Dr. Alethea Vanessa Zamora Gómez and developer Christian Janeczka summarize the end of the project with satisfaction. It is also conceivable that the system could be used in other carrier systems such as ships, aerospace and autonomous vehicles, as well as in AI-based logistics networks that enable a higher degree of automation.
In addition to Fraunhofer IZM, the project partners for IMUcompact were the companies IGI - Ingenieur-Gesellschaft für Interfaces, Intranav and Milan Geoservice as an associated partner. The project was funded by the Federal Ministry of Education and Research for a period of five years until March 2023.
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