Design of a Bio-Inspired Stiffness Controllable Continuum Robot for Object Grasping and Moving

Continuum robots (CRs) possess better compliance than rigid manipulators. However, existing CRs suffer from difficulties in manipulating objects for the conflicting needs of high stiffness and flexibility. This letter proposes an elephant trunk-inspired CR for grasping and moving objects. The CR features a deformation mechanism based on coupling rigid discs and flexible elastic rods and a stiffness modulation mechanism (SMM) with a force amplification function. The SMM decouples the CR's stiffness adjustment from bending motion, achieving flexible control capabilities. The SMM uses a stiffness coding strategy (SCS) to adjust stiffness according to task requirements to improve grasp performance while maintaining flexibility. We established the robot's kinematics, friction, and coiling models, designed a control method to coil around and move objects, and simulated the robot's end position-pose space and object size-pose space. We designed a robot prototype and conducted various experiments. Results showed that the robot achieved free movement in randomly generated configurations, coiled around and moved various objects with a path deviation of less than 8.5%, increased stiffness to 206%, and increased grasp force by 31%, demonstrating its potential in real applications.