After decades of intensive research, it seems that we are getting 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 opinion is not only shared by many robotics researchers but also by the 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 than today’s industrial robots. Rich sensory information, lightweight design, and soft-robotic features are required to reach the expected performance and safety during interaction with humans or in unknown environments. In this article, we will present and compare two approaches for reaching the aforementioned soft-robotic features. The first one is the mature technology of torque-controlled lightweight robots (LWRs) developed during the past decade at the German Aerospace Center (DLR) (arms, hands, a humanoid upper body, and a crawler). Several products resulted from this research and are currently being commercialized through cooperations with different industrial partners (DLR-KUKA LWR, DLR-HIT-Schunk hand, DLRBrainlab medical robot). The second technology, still a topic of worldwide ongoing research, is variable compliance actuation that implements the soft-robotic features mainly in hardware. We start by reviewing the main design and control ideas of actively controlled compliant systems using the DLR arms, hands, and the humanoid manipulator Justin as examples. We take these robots as a performance reference, which we are currently trying to outperform with new variable stiffness actuators. This leads us to the motivation of the variable stiffness actuator design. We 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 are presented finally.
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