Stiffness modulation for soft robot joint via lattice structure configuration design

Abstract Soft materials have been applied on the soft robots built with high deformation and compliance. Additive manufacturing (AM) technology has the ability to fabricate functional soft materials or structures. However, soft robots generally have shortages in strength to manipulate relatively heavy objects. This paper proposes a novel concept on the application of lattice structure configuration for the lightweight functional spherical joint of soft robotics with variable stiffness modulation. A novel active spherical joint driven by air pressure is mainly composed of a rigid ball and soft porous socket. The stiffness can be adjusted by changing air pressure in the soft socket. In order to obtain a high-speed response performance and large-scale linear stiffness, the socket is divided into inner and outer layers. Parametric uniform strut-based lattice structures are populated within the inner layer of the socket to guarantee the flow of air. Trimmed TPMS-based lattice structures are infilled within the outer to keep the stable external shape of the socket. The manufacturability for two lattice structure configurations is also analyzed. In order to achieve a linear variable stiffness, the type and size of lattice unit cells and the thickness of lattice struts can be changed parametrically.