Knitted Pneumatic Actuators for Soft Robotics: Influence of Material and Geometric Parameters

Owing to the growing demand for textile-based wearable soft robots for construction of exosuits and rehabilitation gloves, a detailed investigation of different types of constructing materials and geometric properties of knitted pneumatic actuators is required to achieve desired functioning. This study did comparative analysis among different seamless pneumatic actuators which were constructed by knitting yarns of different materials. The actuators featured pleats on the top layer and were shaped like tubes. We selected Viscose Polyester Nylon (VPN), Acrylic, and Polyester-punched Lycra for the top layers and low-melt Nylon yarn for the bottom layers. To assess their performance, actuators were designed with three length sizes, two widths, and three course ratios. Bending angle and distal tip force were measured on a customized test rig developed for this study. It was observed that actuators made of acrylic yarn with a 3:1 course ratio achieved the desired bending angle of 160° at just 31 kPa internal air pressure, an improved result than those developed in previous studies. These acrylic yarn actuators were also easier to knit compared to the other materials selected. While other actuators required higher internal pressure to achieve the bending angle of 160º, only a wider width (3.2 cm) produced a desired bending angle and a higher tip force (4.3 N at 32 kPa). This study highlights that the interplay of constructing materials and the geometry of pneumatic actuators significantly alters their input and output, allowing for tailored performance across different human hand/finger sizes and specific applications.