Autonomous transportation and deployment with aerial robots for search and rescue missions
Journal of Field Robotics
It is generally accepted that systems composed of multiple aerial robots with autonomous cooperation capabilities can assist responders in many search and rescue (SAR) scenarios. In most of the previous research work, the aerial robots are mainly considered as platforms for environmental sensing and have not been used to assist victims. In this paper, outdoors field experiments of transportation and accurate deployment of loads, with single/multiple autonomous aerial vehicles are presented.
... is a novel feature that opens the possibility to use aerial robots to assist victims during the rescue phase operations. The accuracy in the deployment location is a critical issue in SAR scenarios where injured people may have very limited mobility. The presented system is composed of up to three small size helicopters and features the cooperative sensing, using several different sensor types. The system supports several forms of cooperative actuation as well, ranging from the cooperative deployment of small sensors/objects to the coupled transportation of slung loads. Within this paper the complete system is described, outlining the used hardware and software framework, as well as the used approaches for modeling and control. Additionally, the results of several flight field experiments are presented, including the description of the worldwide first successful autonomous load transportation experiment, using three coupled small size helicopters (conducted in December 2007). During these experiments strong steady winds and wind gusts were present. Various solutions and lessons learned from the design and operation of the system are also provided. In anticipation of the results presented in this paper it is stated, that the transportation and accurate deployment of loads, with single/multiple autonomous aerial vehicles, have been successfully demonstrated in outdoors field experiments. As it has been mentioned above, this is a novel feature that opens the possibility to use aerial robots to assist victims during the rescue phase operations. For instance, it could be possible to command such a transportation system to deploy medical kits, oxygen masks, satellite phones, etc. in places very close to the victims. The accuracy in the deployment location is a critical issue in SAR scenarios where injured people may have very limited mobility. The system can be very useful in flooding disaster scenarios where hundreds of people are isolated on the roofs of their houses. The joint transportation of a load by several ground robots has been an active subject of research and development for many years. The coordinated control of the motion of the vehicles needs to consider the involved forces. Thus, each robot could be controlled around a common compliance center attached to the transported object. Assuming that each robot holds the object firmly, the trajectories of all robots determine the trajectory of the object. Both centralized and decentralized compliant motion control algorithms have been proposed, including the consideration of non-holonomic constraints (Kosuge and Sato, 1999) . The method has been implemented in an experimental system composed of three tracked mobile robots, equipped with a force sensor. In (Sugar and Kumar, 1998) the decentralized control of cooperating mobile manipulators is studied, whereat a designated lead robot is responsible for task planning. The control of each robot is decomposed (mechanically decoupled) into the control of the gross trajectory and the control of the grasp. The excessive forces due to robot positioning errors and odometry errors are accommodated by the compliant arms. In (Borenstein, 2000) the Omnimate system, which uses a compliant linkage platform between two differential drive mobile robots, is presented. In (Huntsberger et al., 2004) the distributed coordinated control of two rovers, carrying a 2.5 meters long mockup of a photovoltaic tent, is presented and demonstrated as an example of the CAMPOUT behavior-based control architecture. The single-lift configuration, whereat a long rope couples one helicopter and one load, is the only configuration commercially utilized for the transportation of slung loads. Several textbooks, see for example (Wagtendonk, 2006) , provide information about the correct attachment of the slung loads and important safety procedures. However, the manual maneuvering of a helicopter with an attached slung load is very difficult and requires a skillful and experienced pilot. In particular the active damping of load oscillations is a difficult task, which most pilots avoid. Instead the pilots stabilize only the helicopter and wait for the load oscillation to die down. To support manual piloted slung load operations the iMAR GmbH and the German Aerospace Center DLR developed the "iSLD-IVC" (iMAR Slung Load Damping based on inertial stabilized vision control) system,