Abstract: The soft actuator is characterized by high safety, flexibility, and adaptability. It is capable of both active and passive deformations. This paper presents a discrete degree of freedom (DOF) method for soft actuators to reveal DOF characteristics.The method draws on the superposition mechanism of the deformation characteristics of the sarcomere in the skeletalmuscles of living organisms. Firstly, the multi-DOF deformation characteristics of the soft actuator are discretized intosuperimposed combinations of single-DOF micro-units. Then, the soft actuator was determined to contain deformationcharacteristics such as extension-contraction, bending, and twisting. Eighteen types of micro-units with basic deformation characteristics were obtained depending on the axis and orientation. Further, the mapping relationship between thecombination of micro-units and the motion characteristics of the soft actuator based on the GF set theory was established.Finally, an active–passive DOF co-structured soft actuator (APCSA) was developed. The graphical approach analyzes theexperimental results, and it can be concluded that active and passive DOFs can coexist in the composite deformation ofthe soft actuator.

Key words: Soft actuator, Active and passive DOF characteristics, Active and passive motion characteristics, Microunits, ')">Soft actuator, Active and passive DOF characteristics, Active and passive motion characteristics, Microunits, , G_F Set')">G_F Set