Compliant Manipulation for Autonomous Search and Rescue Operations: developing a variable stiffness robotic arm for the SHERPA project

Autonomous robotic systems are performing an ever-increasing variety of tasks, including disaster response, and search and rescue missions. Robots can support human rescuers by expanding their capabilities and relieving them of dangerous or routine tasks. The SHERPA project envisages a mixed ground and aerial robotic team with a high degree of autonomy that helps to locate missing or injured people in a hostile alpine environment. A compliant robotic arm mounted on a mobile platform is used to service small-scale UAVs; a collaborative task that involves dexterous manipulation in an unfamiliar environment, and potentially impacts or collisions. For this reason it is equipped with Variable Stiffness Actuators (VSAs), which allow it to control its mechanical end effector stiffness, and to interact with the environment in a passively compliant way. This thesis presents the design and control of this novel manipulator and its components, its integration with the other agents of the SHERPA team, and experimental validation of the mission.
A core component of this compliantly actuated system are a number of VSAs, which allow safe and dexterous interaction with the environment. The analysis of their design focuses on modeling the internal energy flows and optimization of their mechanical energy storage elements. The arm’s actuation topology and its effect on the achievable workspace compliance are investigated, and a thorough mathematical framework for solving associated control problems introduced. The mechatronic design of the robotic arm and its components is presented, including its kinematics, the design of several differentially coupled joints, and a custom gripper, developed to latch into an interface mounted on the UAV to ensure robust grasping under misalignment. The arm has been successfully integrated with the rest of the SHERPA team through a control and delegation framework which allows the agents to autonomously plan and execute complex missions. The completion of the arms main task of replacing a landed UAVs battery is used to demonstrate the systems capabilities, and underlines the role such automated systems can play in supporting and improving search and rescue operations.