Design and Development of a Novel Soft Inflatable Multi-Filament Actuator

Soft Artificial Muscles (SAMs) are a type of soft actuator designed to contract and expand in a manner similar to natural muscles. These actuators play a crucial role in enabling flexible and adaptable movement in soft robots, which are often inspired by biological organisms. SAMs consist of a soft inflatable component that generates expansion when pressurized, and a braided sleeve that acts as a strain-limiting component, directing the contraction motion of the actuator. SAMs have a wide range of applications, including healthcare, wearable technology, and robotics. However, a key challenge lies in optimizing the performance of SAMs, as there has been limited progress in improving the design of the soft components. Specifically, advancements in the geometry and structures used could lead to improve strength and responsiveness during actuation.
This research addresses these challenges by introducing a novel approach to SAM development, inspired by the biomechanical efficiency of human muscles. A multi-filament SAM design (Model-1), along with two comparative models, was developed and evaluated through rigorous experimental testing. Model-1 introduces a circular bundle comprised of multiple soft filaments, representing the innovative soft actuator proposed in this research. Model-2 features a single cylindrical soft body containing an equivalent number of small cylindrical cavities as Model-1. Lastly, Model-3 features a single cylindrical soft body with a simple lone cavity, resembling the traditional structure found in McKibben muscles. The methodology involved the implementation of fabrication techniques to produce consistent and reliable SAM models. These models were subjected to detailed block force and displacement tests. Model-2 consistently generated the highest force output, with an 8% higher force than Model-1 and 35% higher force than Model-3. However, displacement tests did not reveal a significant effect of changing the SAM model on displacement performance. In terms of response to pressure, Model-1 demonstrated higher actuation speed, outperforming Model-2 by 25% and Model-3 by 35%. These results highlight the significant impact that improvements in the design of the soft components can have on enhancing the force generation and response to pressure performance of SAMs.
A case study confirmed the real-world potential of SAMs in dynamic systems, aligning with the results from main tests. Finally, preliminary Finite Element (FE) simulations were used to predict the behaviour of SAM models, providing an initial framework for future improvement.