Research on the Collaborative Transportation of Highly Flexible Objects Using Multibody Dynamics and Explicit Force Control

• Applicant: Professor Dr.-Ing. Peter Eberhard
• Subject Area: Automation, Mechatronics, Control Systems, Intelligent Technical Systems, Robotics
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 433183605

This project focuses on the cooperative transportation of objects using a swarm of mobile robots, where the objects may undergo large deformations. Mobile robots are already widely used for various tasks, including the transportation of rigid objects by employing a cooperative robotic swarm. However, while this is usually accomplished implicitly by controlling the robots' positions, this project emphasizes the explicit interaction between the robots and the object. By leveraging this explicit interaction, the robots can deform objects in a desired manner depending on the application. This capability enables tasks such as generating tension to transport additional loads or to maneuver through narrow passages. This introduces new challenges in distributed robotics, necessitating the development of advanced methodologies. Key challenges are the formation synthesis and the control of the robotic swarm, which must account for the dynamic behavior of the deformable object. Conventional multibody models, which describe objects with large deformations and rotations, are not suitable for real-time applications. To overcome this limitation, the project employs an identified surrogate model of the flexible object and integrates it into an optimization-based approach. The generated setpoints for both the overall movement of the swarm and the individual forces exerted by the robots will be implemented using a cascaded control approach. In this regard, the project aims to combine distributed model predictive control approaches with underlying force controllers. This cascaded control structure enables the two primary control objectives, i.e., the coordinated swarm movement and the explicit control of the interaction forces with the object, to be addressed on different time scales. As a representative case study, the project investigates the deformation and transportation of a thin membrane such that it is always and everywhere tensioned. Each mobile robot is attached to the membrane via a rope, allowing it to exert pulling forces, which can be measured using tailored force sensors. A detailed multibody simulation environment will be developed using the Absolute Nodal Coordinate Formulation to accurately model the membrane's large deformations. This simulation framework will facilitate an in-depth analysis of robot-object interactions. In parallel, hardware experiments will be conducted to validate the simulation results. This includes the development of customized mobile robots as well as the investigation and implementation of suitable methods for sensor technology, control and communication. Ultimately, the project aims to bridge the often existing gap between control theory, high-fidelity multibody simulations, and real-world hardware experiments in distributed robotics.

• DFG Programme: Research Grants
• International Connection: Finland
• Cooperation Partner: Professor Dr.-Ing. Henrik Ebel