Abstract
Soft robots are a new class of systems being developed and studied by robotics scientists. These systems have a diverse range of applications including sub-sea manipulation and rehabilitative robotics. In their current state of development, the prevalent paradigm for the control architecture in these systems is a one-to-one mapping of controller outputs to actuators. In this work, we define functional blocks as the physical implementation of some discrete behaviors, which are presented as a decomposition of the behavior of the soft robot. We also use the term ‘stacking’ as the ability to combine functional blocks to create a system that is more complex and has greater capability than the sum of its parts. By stacking functional blocks a system designer can increase the range of behaviors and the overall capability of the system. As the community continues to increase the capabilities of soft systems—by stacking more and more functional blocks—we will encounter a practical limit with the number of parallelized control lines. In this paper, we review 20 soft systems reported in the literature and we observe this trend of one-to-one mapping of control outputs to functional blocks. We also observe that stacking functional blocks results in systems that are increasingly capable of a diverse range of complex motions and behaviors, leading ultimately to systems that are capable of performing useful tasks. The design heuristic that we observe is one of increased capability by stacking simple units—a classic engineering approach. As we move towards more capability in soft robotic systems, and begin to reach practical limits in control, we predict that we will require increased amounts of autonomy in the system. The field of soft robotics is in its infancy, and as we move towards realizing the potential of this technology, we will need to develop design tools and control paradigms that allow us to handle the complexity in these stacked, non-linear systems.
Highlights
Soft robotics represents a change in thinking about the dominant materials and methods of fabrication used in the manufacture of robotic systems
The steps involved in the stacking and hierarchy heuristic for the design and control of soft robots are: (1) defining the behavior and identifying the requirement for the task; (2) decomposing this behavior into a set of functions and further reducing to subfunctions the behavior has been fully described; (3) describing a functional block with the minimum behavior necessary with an associated effort and flow variable; (4) modeling the functional block to establish an empirical relationship if none already exist; and (5) stacking the functional blocks to progress to systems and behaviors
Stacking and hierarchy as an explicit method of design and control is in its infancy in the mechanical domain, and in soft robotics, and as such the perceived limitations and benefits of this method are subject to change as progress is made in the field
Summary
Soft robotics represents a change in thinking about the dominant materials and methods of fabrication used in the manufacture of robotic systems. Biomimetics 2018, 3, 16 and the current design heuristic in soft robotics is to increase the capability of the system by adding more actuators. We describe the current design approach in soft robotics—what we call ‘stacking of functional blocks’—and we discuss the limitations of this approach. As the community moves towards more capability in soft robotic systems, and we begin to reach practical limits in control, we predict that we will require increased amounts of autonomy in the system by moving from a one-to-one mapping of functional blocks to outputs from control hardware to having more functional blocks with fewer control outputs. We begin to formalize a framework, and we start to explore how we, as a community, can begin to develop tools to allow our designers to build more complex, and more useful soft robotic systems
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