Thomas Gumpert’s research while affiliated with German Aerospace Center (DLR) and other places

Humans exhibit a particular compliant behavior in interactions with their environment. Facilitated by fast physical reasoning, humans are able to rapidly alter their compliance, enhancing robustness and safety in active environments. Transferring these capabilities to robotics is of utmost importance particularly as major space agencies begin investigating the potential of cooperative robotic teams in space. In this scenario, robots in orbit or on planetary surfaces are meant to support astronauts in exploration, maintenance, and habitat building to reduce costs and risks of space missions. A major challenge for interactive robot teams is establishing the capability to act in and interact with dynamic environments. Analogous to humans, the robot should be not only particularly compliant in case of unexpected collisions with other systems but also able to cooperatively handle objects requiring accurate pose estimation and fast trajectory planning. Here, we show that these challenges can be attenuated through an enhancement of active robot compliance introducing a virtual plastic first-order impedance component. We present how elasto-plastic compliance can be realized via energy-based detection of active environments and how evasive motions can be enabled through adaptive plastic compliance. Two space teleoperation experiments using different robotic assets confirm the potential of the method to enhance robustness in interaction with articulated objects and facilitate robot cooperation. An experiment in a health care facility presents how the same method analogously solidifies robotic interactions in human-robot shared environments by giving the robot a subordinate role.

Logistics and service operations involving parcel preparation, delivery, and unpacking from a supply point to a user’s home could be carried out completely by robots in the near future, taking advantage of the capabilities of the different robot morphologies for the logistics, outdoor, and domestic environments. The use of robots for parcel delivery can contribute to the goals of sustainability and reduced emissions by exploiting their different locomotion modalities (wheeled, legged, and aerial). This article reports the development and results obtained from the first robotics hackathon celebrated as part of the European Robotics and Artificial Intelligence Network involving eight robotic platforms in three domains: 1) an industrial robotic arm for parcel preparation at the supply point, 2) a Centauro robot, a dual-arm aerial manipulator, and a wheeled-legged quadruped for parcel transportation, and 3) two humanoid robots and two commercial mobile manipulators for parcel delivery and unpacking in domestic scenarios. The article describes the joint operation and the evaluation scenario, the features and capabilities of the robots, particularly those involved in the realization of the tasks, and the lessons learned.

Robotics is vital to the continued development toward Lunar and Martian exploration, in-situ resource utilization, and surface infrastructure construction. Large-scale extra-terrestrial missions will require teams of robots with different, complementary capabilities, together with a powerful, intuitive user interface for effective commanding. We introduce Surface Avatar, the newest ISS-to-Earth telerobotic experiment series, to be conducted in 2022-2024. Spearheaded by DLR, together with ESA, Surface Avatar builds on expertise on commanding robots with different levels of autonomy from our past telerobotic experiments: Kontur-2, Haptics, Interact, SUPVIS Justin, and Analog-1. A team of four heterogeneous robots in a multi-site analog environment at DLR are at the command of a crew member on the ISS. The team has a humanoid robot for dexterous object handling, construction and maintenance; a rover for long traverses and sample acquisition; a quadrupedal robot for scouting and exploring difficult terrains; and a lander with robotic arm for component delivery and sample stowage. The crew's command terminal is multimodal, with an intuitive graphical user interface, 3-DOF joystick, and 7-DOF input device with force-feedback. The autonomy of any robot can be scaled up and down depending on the task and the astronaut's preference: acting as an avatar of the crew in haptically-coupled telepresence, or receiving task-level commands like an intelligent co-worker. Through crew performing collaborative tasks in exploration and construction scenarios, we hope to gain insight into how to optimally command robots in a future space mission. This paper presents findings from the first preliminary session in June 2022, and discusses the way forward in the planned experiment sessions.

Incorporating realistic actuator dynamics in robotic simulations is key to a successful simulation-to-reality transfer. But real actuation chains are often complex and impossible to model with analytical methods alone. Although it is feasible to reverse-engineer the actuator dynamics from hardware measurements, this requires the completed robotic system to be already available. To enable the inclusion of realistic actuator dynamics in robot models also during the design phase or for initial controller tuning, this work presents an alternative hands-on approach for actuator characterization. Based on actuator measurements taken independently of the overall system integration, a model expression for the actuator is derived. This can be added to the simulation of any robotic system. To showcase this concept, we present the workflow for a robotic leg with a Series Elastic Actuation chain. We create a simulation of the leg incorporating the derived actuator model and show its validity through comparison with analogous hardware. The observed motor and link dynamics of both cases show close correspondence without increasing the needed computation times with respect to a simulation without actuation. Thus, the proposed method offers a promising approach to include realistic actuator dynamics during the design and development process of robotic applications.

To control highly-dynamic compliant motions such as running or hopping, vertebrates rely on reflexes and Central Pattern Generators (CPGs) as core strategies. However, decoding how much each strategy contributes to the control and how they are adjusted under different conditions is still a major challenge. To help solve this question, the present paper provides a comprehensive comparison of reflexes, CPGs and a commonly used combination of the two applied to a biomimetic robot. It leverages recent findings indicating that in mammals both control principles act within a low-dimensional control submanifold. This substantially reduces the search space of parameters and enables the quantifiable comparison of the different control strategies. The chosen metrics are motion stability and energy efficiency, both key aspects for the evolution of the central nervous system. We find that neither for stability nor energy efficiency it is favorable to apply the state-of-the-art approach of a continuously feedback-adapted CPG. In both aspects, a pure reflex is more effective, but the pure CPG allows easy signal alteration when needed. Additionally, the hardware experiments clearly show that the shape of a control signal has a strong influence on energy efficiency, while previous research usually only focused on frequency alignment. Both findings suggest that currently used methods to combine the advantages of reflexes and CPGs can be improved. In future research, possible combinations of the control strategies should be reconsidered, specifically including the modulation of the control signal's shape. For this endeavor, the presented setup provides a valuable benchmark framework to enable the quantitative comparison of different bioinspired control principles.

This paper addresses walking and balancing in rough terrain for legged locomotion in planetary exploration as an alternative to the commonly used wheeled locomotion. In contrast to the latter, where active balancing is not necessary, legged locomotion requires constant effort to keep the main body stabilized during motion. While common quadrupedal robots require to carefully plan motions through torque control and force distribution, this paper presents an approach where elastic elements in the drive train function as an intrinsic balancing component that allows to ignore inaccuracies in the locomotion pattern and passively accommodate for terrain unevenness. The approach proposes a static walking gait algorithm, which is formulated for a general quadrupedal robot, and a hardware foot design to support the locomotion pattern. The method is experimentally tested on an elastically actuated quadrupedal robot.

The Compliant Assistance and Exploration SpAce Robot (CAESAR) is DLR's consistent continuation in the development of force/torque controlled robot systems. The basis is DLR’s world-famous light-weight robot technology (LWR III) which was successfully transferred to KUKA, one of the world’s leading suppliers of robotics. CAESAR is the space qualified equivalent to the current service robot systems for manufacturing and human-robot cooperation. It is designed for a variety of on-orbit services e.g. assembly, maintenance, repair, and debris removal in LEO/GEO. The dexterity and diversity of CAESAR will push the performance of space robotics to the next level in a comparable way as the current intelligent and sensor based service robots changed robotics on earth.