Design and Analysis of Soft Hybrid-Driven Manipulator with Variable Stiffness and Multiple Motion Patterns

Soft manipulators offer the advantages of safety and adaptability. However, due to insufficient stiffness and single motion mode limitations, existing soft manipulators usually exhibit low load capacity and small working space. To address this problem, we propose a novel soft hybrid-driven manipulator with continuous stiffness control capability and multiple motion patterns (omnidirectional bending and extension). Furthermore, we develop kinematic and stiffness models based on the constant curvature assumption. The soft robot consists of a soft bellows actuator and inextensible rigid skeletons, which exhibit a high extension ratio and low drive pressure. With the antagonistic actuation of tendon-pulling and air-pushing, the robot can achieve independent control over stiffness and position in three-dimensional space. The performance associated with the designed soft hybrid-driven manipulator is experimentally verified. The robot can achieve an elongation of 198% and a maximum bending angle of up to 240°. The robot can also increase stiffness by increasing internal air pressure to resist deformation caused by external loads. Additionally, tracking experiments with various trajectories in space verify the accuracy of the kinematic model, which indicates that the soft manipulator can stabilize motion within a broad workspace.