<p>Force and power limited collaborative robots (Cobots), in theory, allow humans to interact and work in close proximity with the robots. However, in the event that a robot collides with a human, safety concerns limit the maximum pressure the robot may induce on the human. Currently, human operator safety is maintained by incorporating algorithms to detect a collision and bring the Cobot’s motors to a stop. The time required for detection and motor control limits the Cobot’s maximum operating speed and thus inhibits their ability to meet manufacturing cycle time targets. To overcome this limitation, safe zones may be outlined around Cobots to allow quicker operations when humans are absent and slower, collaborative operations when humans are present. However, this approach poses challenges to manufacturing efficiency and leads to an increased robot footprint over a true collaborative unit. The present research effort addresses these challenges by proposing a rotational multistable metastructure that absorbs energy and limits the force transmitted during impact, thereby mitigating the consequences of Cobot-human collision and enabling faster cycle times. Multistable metastructures often employ elastic elements with buckling instability to achieve desired behaviors and have been widely explored for translational displacements. A similar approach is employed here, although to achieve a global <i>rotational </i>motion, where pre-buckled bistable beams are constrained within a pair of concentric rings of the rotational joint. These bistable elements snap through and absorb energy in consequence of applied rotational load. Modeling and analyses are performed via Euler’s elastica theory that is used to guide the design of the metastructure, offering insight into the mechanical properties such as rotation range, asymmetric bistability, and strain energy absorption. Using the geometric parameters obtained with the elastica study, numerical studies are conducted and a modular constituent is fabricated and evaluated in experiments. Studies with a single layer constituent unit serve as a catalyst for designing a multi-layer rotational joint with bi-directional functionality. The results presented in this research are the first of its kind for a joint showing buckling-induced energy absorption in rotational motion. Given the fundamental nature of this effort, it is believed that this work will serve as an important basis for a variety of industrial applications.</p>

Rotational Modular Metastructures for Cobot Impact Energy Absorption

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2021/volume/85499

ASME 2021 Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2021)

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