Bi-Component Silicone 3D Printing with Dynamic Mix Ratio Modification for Soft Robotic Actuators

Pneumatically operated soft actuators are increasingly researched due to their fabrication simplicity, actuation capabilities, and low production cost. Depending on the Soft Pneumatic Actuator (SPA) objective, its design can be modified to reach new bending angles or increase its actuation strength. However, increasing the abilities of Soft Pneumatic Actuators (SPAs) requires increasing the complexity of their air cavities or using multiple materials with different mechanical stiffness. Both solutions complexify the fabrication of SPAs, reducing their primary benefits of manufacturing simplicity and low production cost. This paper presents a novel additive manufacturing fabrication process incorporating multiple mechanical stiffnesses using a single bi-component soft material. This process aims to integrate multiple bending angles with multi-channel SPAs without increasing their manufacturing complexity. Our process uses a dynamic modification of the bi-component silicone mix ratio to generate the desired mechanical properties of the material. Modifying the mix ratio allows us to control the material's cure time and mechanical properties, such as its final stiffness. We found that using a single 30 shore-A bi-component silicone, we could achieve several stiffness values with different reticulation times and levels of stickiness. Using these shore ranges and our fabrication process, we built several SPAs. We explored how the printing orientation of the SPAs modifies its bending actuation using our fabrication process to illustrate the capabilities of our approach.