A thin-walled vacuum actuator (ThinVAc) and the development of multi-filament actuators for soft robotic applications

Abstract

Most contemporary soft actuators tend to have a large cross-sectional area that prevents easy integration with wearable devices. Therefore, soft actuators ideal for wearable device integration should be capable of being mounted in a small amount of space, conforming to human body contours with minimal obstruction, and delivering adequate force to move the human body. Hence, in developing assistive devices ranging from orthosis to prosthesis, there is a need for low-profile, thin, lightweight, soft actuators with a high force-to-weight ratio. In this paper, the authors present a novel, thin-walled, lightweight, contractile, soft actuator (ThinVAc) that delivers a high force-to-weight ratio. First, the authors present the design, fabrication, and performance characterization of the ThinVAc. Second, a scalable, multi-filament actuator design is presented by combining multiple thin-walled actuators, including design, fabrication, and performance characterization. Next, the paper presents numerical models to describe the proposed actuator's contractile and blocked force performance, and predict the blocked force performance of the multi-filament actuator combinations. The lightweight ThinVAc (weighing about 1 g) presents a maximum contraction ratio of 60 % at no load condition, a maximum isometric blocked force of 5.2 N, and a force-to-weight ratio of 477. An 18 g multi-filament actuator made by bundling 15, 100 mm ThinVAcs can produce a maximum blocked force of 54 N at a force-to-weight ratio of 291.