The Introduction And Analysis Of A Novel Soft Actuator For A Soft Continuum Robot Arm

Abstract

In this research, a novel pneumatic soft actuator for continuum robot arm has been designed, partially modeled and manufactured. The actuator is consisting of a single tube made of silicone rubber, some elastic rings around the tube that partially divide the tube into different sections and shape-memory alloy (SMA) springs that connects the rings to each other. By increasing pressure inside the tube, the tube starts inflating in a nonuniform manner due to the existence of the rings on the surface of the tube and the nonlinear behavior of the silicone rubber. By activating SMA springs on the surface of different sections of the tube, the inflated region on the tube will be controlled. The actuator has been manufactured and tested individually. To manufacture the tube, the commercial Eco-flex 030 epoxy has been used and been molded using commercially available Bic pens as a mold. The change in the behavior of the silicone rubber tube after adding each element to the tube has been studied to monitor the change in the nonlinear behavior of the tube. The SAM springs have been made by training nitinol wires from the Flexinol company into springform. The SMA springs properties have been calculated to match the required property of the system. The behavior of the resulted actuator has been studied both during actuation and deactivation of the SMA springs. To model the behavior of the actuator, the properties of silicon rubber has been extracted by conducting required mechanical tests. Later, by fitting the results to different hyperplastic models the behavior of Eco-flex 030 has been modeled. To choose the best model, the behavior of the silicone rubber tube trough changing in pressure has been simulated using Ansys. The material model with closest results to the actual experimental model have been chosen. Due to the nonlinearity of the silicone rubber, the volume-pressure change inside the tube exhibits instability in the related function which is the result of both the material property and the geometry of the system. This will result in instability and failure of the solver. Therefore, the comparison between the different models was made by comparing the instability pressure. The presented actuator has the advantage of needing less number of air supplies to have the same degree of freedom compared to the conventional pneumatic actuators, thanks to utilizing the instability of silicone rubber.