Design and experiment of a novel pneumatic soft arm based on a deployable origami exoskeleton

Abstract

Soft arms have shown great application potential because of their flexibility and compliance in unstructured environments. However, soft arms made from soft materials exhibit limited cargo-loading capacity, which restricts their ability to manipulate objects. In this research, a novel soft arm was developed by coupling a rigid origami exoskeleton with soft airbags. The joint module of the soft arm was composed of a deployable origami exoskeleton and three soft airbags. The motion and load performance of the soft arm of the eight-joint module was tested. The developed soft arm withstood at least 5 kg of load during extension, contraction, and bending motions; exhibited bistable characteristics in both fully contracted and fully extended states; and achieved a bending angle of more than 240° and a contraction ratio of more than 300%. In addition, the high extension, contraction, bending, and torsional stiffnesses of the soft arm were experimentally demonstrated. A kinematic-based trajectory planning of the soft arm was performed to evaluate its error in repetitive motion. This work will provide new design ideas and methods for flexible manipulation applications of soft arms.

Key words： pneumatic soft arm; soft airbag; deployable origami exoskeleton; bistable characteristics; cargo-loading capacity

Nomenclature

F	Applied force
h	Half the height of the waterbomb origami structure
i	ith joint module
ki	Curvature of the ith joint module
K_{\text{α}}, K_{\text{β}}, K_{\text{χ}}	Stiffnesses in the fully contracted, extended, and intermediate state, respectively
M	Torque
O_i	Position of the coordinate origin of the upper platform of the ith joint module
{}^{i-1}{\mathit{p}}_i	Column vector of the ith joint module positions
r	Radius of the joint module
{}_i^{i-1}\mathit{R}	Rotation matrix of the ith joint module
si	Arc length of the ith joint module
t	Thickness of the waterbomb origami structure
{}_{i-1}^i\mathit{T}	Homogeneous matrix of the ith joint module
xi, yi, zi	X, Y, and Z coordinate values of the end of the ith joint module, respectively
Yi, Zi	Y- and Z-axis of the coordinate system at the end of the ith joint module, respectively
\alpha	Bending angle of soft arm
{\beta }_i	Rotation angle of the end of the ith joint module around Z_i
\mu	Design angle of the origami pattern
\lambda	Folding angle of the waterbomb origami structure
\varphi	Displacement of soft arm
{\phi }_i	Deflection angle of the ith joint module
{\chi }_i	Rotation angle of the end of the ith joint module around Yi
{\delta }_i	Rotation angle of the end of the ith joint module around Xi

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant Nos. 51975566, 61821005, and U1908214) and the Key Research Program of Frontier Sciences, CAS, China (Grant No. ZDBS-LY-JSC011).

Conflict of Interest

The authors declare that they have no conflict of interest.

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