Robots Interacting with Humans and Unknown Worlds: Pushing the Boundaries of Nonlinear Control

Abstract

Robots are not only machines that are supposed to relieve humans from dangerous or routine work – they are a scientific endeavour pursued to better understand human motion and intelligence in a synthetizing way, by using the system analytic tools of engineering and computer science. As such, robots, in particular humanoid robots, became complex mechatronic systems, having highly coupled multibody kinematics, being high-dimensional, sometimes exceeding hundred degrees of freedom actuated by electro-mechanical drives. They can include highly nonlinear concentrated or distributed visco-elastic elements, be under-actuated, and be exposed to large closed-loop time delay during teleoperation. Furthermore, robots are supposed to closely interact with their human users or to operate in remote, unknown worlds – in both cases, robustness is a central issue, as precise mathematical models of the interaction cannot be expected. In view of these challenges, robotics became a prime application and a major driver for modern nonlinear control. In this talk I will present how energy-based nonlinear control concepts evolved to match the robot design evolution from fixed manipulator arms to machines having humanoid kinematics and physical properties matching ever closer the biological performance. Controlling motion at low energetic cost, both from mechanical and computational point of view, certainly constitutes one of the major locomotion challenges in biology and robotics. In our research, we demonstrate that robots can be designed and controlled to walk efficiently by exploiting resonance body effects, increasing the performance compared to rigid body designs. To do so, however, legged robots need to achieve limit cycle motions of the highly coupled, non-linear body dynamics. This led us to the research of the still not very well understood theory of nonlinear system intrinsic modal oscillation control. I will present recent results in this direction from my ERC Advanced Grant project M-Runners. Finally, putting the human in the centre of robot development also means going beyond the pure field of engineering and interacting with biosciences. I will particularly highlight in this regard the interplay of biomechanics and neuroscience with advanced robot design and control. Humans can also directly benefit from this research through the development of better human-machine interfaces, robotized medical procedures, and prosthetic and rehabilitation devices which will further reduce the barriers between humans and robots in the future.