The Extension Arm Design Method Based on a Two-Bar Tension Stretchable Mechanism.

The deployable and foldable structure is a unique structural system that provides convenience in terms of transportation and expansion. Although the current deployable mast can transition between closed and extended structures, it lacks stability during movement and does not have the ability to recover on its own after contracting. Hence, improving the stability of deployable mechanisms while enabling them to self-restore has become an essential area for development. Spatial deployable mast expansion and contraction properties are essential for aerospace. In this paper, based on a two-bar and four-cable tensegrity structure, the research was conducted. A new spatially deployable mast structure with zero Poisson's ratio and self-stability, as well as self-adaptability, is proposed. In comparison to existing space deployable masts, the new deployable masts incorporate a tensegrity structure feature that enables them to recover autonomously to their initial state in a contracted state. Firstly, an innovative design based on a two-bar, four-cord tensegrity structure is conducted, which evolves into a two-bar and four-cable tensegrity structure with zero Poisson's ratio by increasing the longitudinal axis to restrict the structure's degrees of freedom and combines with the force density method to analyze the stability of the structure and derive the optimal dimensional parameters. The positive definiteness of the stiffness matrix