Generative Design Procedure for Embedding Specified Planar Behavior in Modular Soft Pneumatic Actuators.

A modular actuator construction consisting of smaller articulating units in series was designed to construct soft pneumatic actuators. These units are constructed to have a preferential bending direction using Mold Star 15 and Smooth-Sil 950 silicone. By changing the orientation of each unit, a different deformed actuator shape can be achieved. A design tool was developed where a genetic algorithm was coupled with a nonlinear finite element solver. This design tool optimizes the design using the genetic information available in the initial population over multiple generations and presents a candidate design that best resembles a desired profile specified as the objective function. A two-dimensional reduced order model was developed that reduces the time for each function evaluation from ≈20 min for a three-dimensional (3D) numerical analysis to ≈45 s. The design tool was tasked to solve design targets ranging from sine and cosine functions of various amplitudes to final actuator tip positions. In each case, the inflated actuator resembled the desired profile. Selected physical actuators were cast and tested. 3D scanning was used to capture the inflated shape and compared it to the numerical solution. A quantitative comparison showed a maximum average deviation of <2.5% of the uninflated actuator length between the physical and numerical models. The proposed design tool proved successful in designing shape matching actuators with close agreement to physical models.

Soft Pneumatic Actuator with Bimodal Bending Response Using a Single Pressure Source.

Deformation behavior of soft pneumatic actuators (SPAs) can mechanically be preprogrammed into their architecture during design. To date, the majority of SPAs rely on a unimodal bending design. This paper develops a method of including a bimodal design into the deformed state by means of a bilinear material that replaces the conventional strain limiter. With a simple increase in pneumatic pressure, it is possible to have distinctly different deformation directions in one actuator. While inflating at low pressures, the actuator has a preferential deformation direction. As the pressure continues to increase, this preferential deformation direction changes due to a change in the stiffness of the strain limiter. An example of this behavior is demonstrated by an actuator that initially bends in one direction, but then gradually changes direction in plane as the pressure continues to increase. Three different physical actuators were manufactured, tested, and correlated with preliminary numerical models. The physical and numerical models exhibited the desired bimodal behavior, although at different pressures. Furthermore, it was possible to alter the pressure at which this transition occurs by changing the crimp ratio of the embedded bilinear material.