Mechanical Programming of Soft Actuators by Varying Fiber Angle

Abstract

In this work we investigate the influence of fiber angle on the deformation of fiber-reinforced soft fluidic actuators. We demonstrate that, by simply varying the fiber angle, we can tune the actuators to achieve a wide range of motions, including axial extension, radial expansion, and twisting. We investigate the relationship between fiber angle and actuator deformation by performing finite element simulations for actuators with a range of different fiber angles, and we verify the simulation results by experimentally characterizing the actuators. By combining actuator segments in series, we can achieve combinations of motions tailored to specific tasks. We demonstrate this by using the results of simulations of separate actuators to design a segmented wormlike soft robot capable of propelling itself through a tube and performing an orientation-specific peg insertion task at the end of the tube. Understanding the relationship between fiber angle and motion of these soft fluidic actuators enables rapid exploration of the design space, opening the door to the iteration of exciting soft robot concepts such as flexible and compliant endoscopes, pipe inspection devices, and assembly line robots.

Automatic design of fiber-reinforced soft actuators for trajectory matching

“…To realize actuators capable of replicating complex motions, we use segments consisting of a cylindrical elastomeric tube surrounded by fibers arranged in a helical pattern at a characteristic fiber angle α ( Fig. 2A) (23,24), because it has been shown that by varying the fiber angle and materials used, these segments can be easily tuned to achieve a wide range of motions (17)(18)(19)(20)(21). When the elastomeric tube is of uniform stiffness, the segment undergoes some combination of Significance Fluid-powered elastomeric soft robots have been shown to be able to generate complex output motion using a simple control input such as pressurization of a working fluid.…”

“…Previous work has explored the design space of fiber-reinforced actuators capable of extending, expanding, and twisting using FE analysis (20) and kinematics and kinetostatics modeling (17)(18)(19). Although these existing analytical models provide great insight into the behavior of fiber-reinforced actuators, they are restricted to exactly two sets of fibers (a set of fibers being fibers arranged at the same angle).…”

“…Furthermore, to simplify the fabrication procedure, we impose a minimum fiber angle of 5 • . Also, we prescribe a maximum allowed fiber angle of 50 • , because above this angle, the radial expansion of the actuators becomes significant (20). Note that for a finger, bending occurs at discrete joints, but for the actuator, it will of course take place over some finite length.…”

“…Although their inherent compliance, easy fabrication, and ability to achieve complex output motions from simple inputs have made soft robots very popular (10,11), there is growing recognition that the development of methods for efficiently designing actuators for particular functions is essential to the advancement of the field. To this end, some research groups have begun focusing their efforts on modeling and characterizing soft actuators (12)(13)(14)(15)(16)(17)(18)(19)(20). In particular, significant progress has been made on solving the forward kinematics problem (16)(17)(18)(19) and even on using dynamic modeling to perform motion planning (14).…”

“…Here, we focus on fiber-reinforced actuators (17)(18)(19)(20)(21), and given a particular trajectory, we find the optimal design parameters for an actuator that will replicate that trajectory upon pressurization. To achieve this goal, we first use a nonlinear elasticity approach to derive analytical models that provide a relationship between the actuator design parameters (geometry and material properties) and the actuator deformation as a function of pressure for each motion type of interest (extending, expanding, twisting, and bending).…”