Experimental investigation on enhancement in pure axial deformation of soft pneumatic actuator (SPA) with cap ring reinforcement

Bio-inspired soft-robots are nowadays found their place in many applications due to its flexibility, compliance and adaptivity to unstructured environment. The main intricate part of such bio-inspired soft robots are soft pneumatic actuators (SPA) which replicate or mimic the limbs and muscles. The soft actuators are pneumatically actuated and provide bending motion in most cases. However, many engineering and medical applications need axially expanding soft pneumatic actuators to deal with delicate objects. Various studies have put forward designs for SPA with axial deformation, but the majority of them have limited axial deformation, constraining motion and less overall efficacy which limit the scope of utilization. The common practice to enhance the axial deformation of SPA is by incorporating directionally customized reinforcement using fibres or by other means like yarns, fabrics, etc. These types of reinforcements are generally embedded to SPA during fabrication and may not have capability for any correction or modification later on hence lack the customization. This paper presents a novel method of radial reinforcement for the enhancement of axial deformation of SPAs with provision of customization. The present study aims to enhance and/or customize the axial deformation of SPA by incorporating external and detachable reinforcement in the form of annulus shaped cap ring. The investigation encompasses the design and attachment of four distinct cap ring geometries to SPA at different locations. Experimental results affirm that cap ring reinforcement bolster the radial stiffness, curbing lateral deformation while permitting axial deformation of soft pneumatic actuators. Out of 64 distinct configurations, the one with full reinforcement, featuring four cap rings of maximum size, yields a remarkable 169% increase in pure axial deformation compared to unreinforced cases. It is also observed that by varying the number and placement locations of cap rings the pure axial deformation can be customized. This novel insight not only propels soft pneumatic actuation technology but also heralds prospects for highly agile and versatile robotic systems which can be used in medical, prosthetics, pharmaceutical and other industries.