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Bending permits soft arms to access a workspace that is not colinear with the initial arm axis; the size and shape of this space depends on the characteristics of the soft arm. Soft bending actuators and arms have developed for specific applications, but not characterized for the general relationship between design variables and performance. This paper defines a class of soft bending arms based on its design, considering the arm as a system constructed from many contracting actuators organized into segments. A modular segment design is presented, and seven variants of this design were constructed and tested for bend radius, bend direction, lateral stiffness and contraction. The variants isolate system parameters, in this case, arm radius and number of actuators within a given segment, to quantify how these parameters affect performance. A trade-off was found between lateral stiffness and bend radius, which can be controlled by altering the arm radius or the number of actuators. Bend direction was found to be coupled to both bend radius and arm load. Finally, a three-segment arm following a bio-inspired design is presented to demonstrate how the experimental results apply to soft robot system design.
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A generalizable equilibrium model for bending soft arms with longitudinal actuators
Current models of bending in soft arms are formulated in terms of experimentally determined, arm-specific parameters, which cannot evaluate fundamental differences in soft robot arm design. Existing models are successful at improving control of individual arms but do not give insight into how the structure of the arm affects the arm’s capabilities. For example, omnidirectional soft robot arms most frequently have three parallel actuators, but may have four or more, while common biological arms, including octopuses, have tens of distinct longitudinal muscle bundles. This article presents a quasi-static analytical model of soft arms bent with longitudinal actuators, based on equilibrium principles and assuming an unknown neutral axis location. The model is presented as a generalizable framework and specifically implemented for an arm with [Formula: see text] fluid-driven actuators, a subset of which are pressurized to induce a bend with a certain curvature and direction. The presented implementation is validated experimentally using planar (2D) and spatial (3D) bends. The planar model is used to initially estimate pressure for a closed-loop curvature control system and to bound the accessible configurations for a rapidly-exploring random trees (RRT) motion planner. A three-segment planar arm is demonstrated to navigate along a planned trajectory through a gap in a wall. Finally, the model is used to explore how the arm morphology affects maximum curvature and directional resolution. This research analytically connects soft arm structure and actuator behavior to unloaded arm performance, and the results may be used to methodically design soft robot arms.
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- Award ID(s):
- 1734627
- PAR ID:
- 10546891
- Publisher / Repository:
- SAGE Publications
- Date Published:
- Journal Name:
- The International Journal of Robotics Research
- Volume:
- 40
- Issue:
- 1
- ISSN:
- 0278-3649
- Format(s):
- Medium: X Size: p. 148-177
- Size(s):
- p. 148-177
- Sponsoring Org:
- National Science Foundation
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