Passive autonomy: hygromorphic rotational actuators

Abstract

Inspired by phenomena in the plant world, a meteoro-sensitive rotational actuator is developed. The design uses a hygro-active shell, whose water-based swelling is restricted at selective locations to form a helicoid structure. The influence of geometrical parameters on the performance is investigated using a numerical analysis of various geometries, by looking at resulting rotation and torque during this rotation. Prototypes are built of five key geometries in the design space, to validate the simulations and to investigate the behaviour of the design experimentally. These prototypes are submerged in water to investigate their deformation, after which they are placed in a torsion machine to investigate the torque during rotation. The experiments result in similar rotations and torques as the simulations. The designed Hygromorphic Rotational Actuator is capable of passively rotating its own structure, thereby expanding the possibilities of engineers and designers when designing passive autonomous systems.

Reversible shape morphing of a neutrally stable shell by untethered local activation of embedded Ni-Ti wires

“…Stimuli-responsive materials have properties which can significantly be changed and controlled by applying certain stimuli (Hu et al, 2012; Oliver et al, 2016; Schwartz, 2008) such as humidity (Joosten et al, 2020; Liu et al, 2021), temperature (Bil et al, 2013; Rodrigue et al, 2015a, 2015b), light (Palagi et al, 2016; Wani et al, 2017), acidity (pH) (Nadgorny et al, 2018) and electric (Bilgen and Friswell, 2014; Chen et al, 2019) or magnetic fields (Diller et al, 2014; Xu et al, 2019). These materials create many novel opportunities in a wide range of disciplines: from medical devices that open in the body to release drugs (Guan et al, 2007; Okwuosa et al, 2017) to sensors (Truby et al, 2019) and novel miniature robots (Zeng et al, 2018).…”