Research on active and passive motion characteristics of bionic soft actuators in rigid-flexible coupled single-open-chain configurations

Soft actuators possess both active and passive degrees of freedom (DOFs). This paper proposes the concept of using soft actuators to drive rigid-soft coupled single-open-chain (SOC) configurations. Research focuses on the active and passive DOF characteristics of the soft actuator within this framework. First, based on the graphical approach and generalized function set theory, the motion characteristics at the input points of the human skeletal structure and the corresponding skeletal muscle motion characteristics are analyzed. Then, the matching relationship is mapped onto the rigid-soft coupled configuration. The motion requirements at the input points of the rigid branch and the end characteristics that the soft actuator should possess are analyzed. Furthermore, based on the end characteristics of the soft actuator, the discrete element method is employed to analyze the types of micro-units constituting its deformation characteristics. Finally, an experimental setup featuring a rigid-soft coupled SOC mechanism based on pneumatic soft actuators was constructed. Results demonstrate that the soft actuator achieves active deformation during passive bending, twisting, and combined bending-twisting deformations. The influence of passive DOFs on active DOFs within specific ranges in the rigid-soft coupled composite configuration was analyzed.