Biomimetic soft hand combined with variable stiffness and friction

Purpose The aim of this paper is to investigate the use of soft flexible fingers with variable stiffness and friction (VSF) as an effective solution for soft-robot in-hand manipulation. Design/methodology/approach The proposed VSF structure comprises a plastic bag, jamming layers, a low-friction surface and a high-friction surface. By controlling the pressure within the plastic bag, the VSF structure facilitates the transition between high friction with low stiffness and low friction with high stiffness. Through the integration of VSF joints, a five-fingered robotic hand was developed to enable in-hand manipulation. This system successfully demonstrated bottle-rotation experiments without requiring grip release. Findings The experimental results reveal that a single joint equipped with the VSF structure exhibits a 22.35% increase in stiffness under 10 kPa pressure and a 200 g load, as well as a maximum 46.51% variation in friction force at 40 kPa positive pressure. These findings demonstrate the VSF structure’s capability to achieve VSF. By integrating this structure into soft robotic hands, dexterous two-finger gripping and in-hand manipulation with a five-finger hand can be realized. Originality/value In this study, the authors developed a VSF structure that is actuated by positive pressure and integrates both VSF capabilities. Furthermore, the authors incorporated this VSF structure into a five-fingered robotic hand, enabling it to manipulate objects by changing contact surfaces, eliminating the need for the soft hand to rotate objects by grasping and placing. This advantage makes it suitable for manipulating objects in confined spaces, with potential applications in mechanical assembly and logistics sorting.