Collaborative robots (Cobots) are designed to allow humans to interact and work with them in close proximity. Although they are power- and force-limited compared to traditional industrial robots, residual injury risks in the event of a collision will cause Cobots to be operated at a reduced speed when humans are nearby. This compromises the ability to achieve manufacturing cycle time targets. Outlining safe zones around Cobots may allow quicker operations, but this approach poses challenges to manufacturing efficiency and leads to an increased robot footprint over a true collaborative unit. Incorporating energy-absorbing and force-limiting hardware into the Cobot structure may offer a way to ensure human safety without reducing manufacturing productivity and efficiency. Building upon such a concept, this research proposes a rotational multistable metastructure that can be incorporated in a Cobot’s joint. The metastructure consists of pre-buckled bistable beams constrained within a pair of concentric rings. These bistable elements snap through and absorb energy in consequence of applied rotational loads. In this study, modeling and analyses are performed using Euler’s elastica theory and results are used to guide the design of the metastructure, offering insight into properties such as rotation range, asymmetric bistability, and strain energy absorption. Using the geometric parameters obtained from the elastica study, numerical studies are conducted, and a modular constituent is fabricated and evaluated experimentally. While motivated by Cobot applications, it is expected that this work will serve as an important basis for a variety of engineering applications requiring energy absorption and force limitation for rotational loads.

This content is only available via PDF.
You do not currently have access to this content.