Model-Based Control of Soft Robots: A Survey of the State of the Art and Open Challenges

From a functional standpoint, classic robots are not at all similar to biological systems. If compared with rigid robots, animals' bodies look overly redundant, imprecise, and weak. Nevertheless, animals can still perform a vast range of activities with unmatched effectiveness. Many studies in biomechanics have pointed to the elastic and compliant nature of the musculoskeletal system as a fundamental ingredient explaining this gap. Thus, to reach performance comparable to nature, elastic elements have been introduced in rigid-bodied robots, leading to articulated soft robotics [1] (see 'Summary'). In continuum soft robotics, this concept is brought to an extreme. Here, softness is not concentrated at the joint level but instead distributed across the whole structure. As a result, soft robots (henceforth, omitting the adjective continuum) are entirely made of continuously deformable elements. This design solution aims to bring robots closer to invertebrate animals and the soft appendices of vertebrate animals (for example, an elephant's trunk and the tail of a monkey). Several soft robotic hardware platforms have been proposed with increasingly higher reliability and functionalities. In this process, considerable attention has been devoted to the technological side of the problem, leading to a large assortment of hardware solutions. In turn, this abundance opened up the challenge of developing effective control strategies that can manage the soft body and exploit its embodied intelligence.