Modular Joints for Soft Robots

Traditional rigid robotic limbs inadequately address the mass, flexibility and actuation requirements needed to build effective space-faring robots capable of achieving complex tasks safely onboard space craft and in uncertain extraterrestrial environments. The underlying structure of these limbs, a series of single degree of freedom joints, is a primary contributor to many of the short comings of these existing technologies. To overcome this, we have designed a robotic limb with high degree-of-freedom cable driven joints which draw inspiration from human shoulder and hip joints. These robotic joints are designed as tensegrity structures, soft structures with discontinuous stiff compression elements suspended in a web of continuous elastic tension elements. Tensegrity structures are inherently compliant, have excellent structural mass efficiency, and are highly parallel structures. By using this structural design paradigm, we can incorporate these desirable traits into a soft robotic joint which is capable of smooth continuous high degree of freedom motion across a single joint. We use the term soft to describe omnidirectional compliance across the robotic joint. We have identified one promising topology capable of producing a large uniform set of combined rotations and have optimized its geometry to maximize the number of possible configurations. We have created several analytic and numerical simulations of the joint’s dynamics. We have tested different control approaches to evaluate their performance while also enabling system requirements to be estimated for the physical prototype. We have completed an initial prototype and gathered results from real-world experiments. We have also worked to implement the joint within the context of a robotic limb to further demonstrate its effectiveness.