Soft robotics: From Torque Feedback Controlled Lightweight Robots to Intrinsically Compliant Systems

After decades of intensive research, it seems that we get closer to the time when robots will finally leave the cages of industrial robotic workcells and start working in the vicinity of and together with humans. This is not only believed by robotics researchers, but meanwhile also by leading automotive and IT companies, and of course by some clear-sighted industrial robot manufacturers. Several technologies required for this new kind of robots reached the necessary level of performance, e.g. computing power, communication technologies, sensors, and electronics integration. However, it is clear that these human friendly robots will look very different from today’s industrial robots. Rich sensory information, light-weight design and soft robotics features are required in order to reach the expected performance and safety during interaction with unknown environments or with humans. In this paper we will present and compare two approaches for reaching the aforementioned soft robotics features. The first one is the meanwhile mature technology of torque controlled light-weight robots developed during the past decade at DLR (arms, hands, a humanoid upper body, a crawler). Several products resulted from this research and are currently being commercialized through cooperations with different industrial partners (DLR-KUKA Lightweight Robot, DLR-HIT-Schunk Hand, DLR-Brainlab-KUKA medical robot). The second technology, still a topic of worldwide ongoing research, is variable compliance actuation which implements the soft robotics features mainly in hardware. We will start by reviewing the main design and control ideas of actively controlled compliant systems using as examples the DLR arms, hands, and the humanoid manipulator Justin. We are taking these robots as a performance reference, which we are currently trying to outperform with new variable stiffness actuators. This will lead us to the motivation of the variable stiffness actuator design. We will present the main design ideas and our first results with the new actuator prototypes. Some experimental examples providing first validation of the performance and safety gain of this design approach finally will be presented.