Static characteristics of a biomimetic robot module driven by water hydraulic artificial muscles resisted with helical spring

Soft modular biomimetic robots, driven by flexible actuators, are extensively used in various fields due to their excellent flexibility, environmental adaptability, and isomorphism. However, existing flexible modules typically possess no more than two degrees of freedom for structural limitations. This paper proposes a biomimetic robot module supported by a spring and actuated by water hydraulic artificial muscles (WHAMs). Combining the mechanical properties of WHAMs and spring, the static model of the soft module was established by force balance method. Moreover, the contraction force coefficient and contraction ratio coefficient of WHAMs were identified through the static characteristics test. The rod length coefficient and stress coefficient of the spring were also identified through the spring bending test. The errors between the experimental results and the model are analyzed and discussed, uncovering the main reasons. The influence of spring pre-compression, spring elasticity coefficient, initial working pressure of WHAM, and the installation distance of WHAM on the motion space of module were analyzed and discussed. This work serves as a guide for the structural design of flexible modules to meet specific requirements and lays the foundation for future research on integrated flexible biomimetic robots driven by WHAMs. [Display omitted] •Mechanical modeling of spring subjected to simultaneous axial load and bending moment.•Mechanical modeling of unidirectional deflection of modules based on symmetric variation of working pressure of WHAMs.•The effect of relevant factors on module movement is analyzed.