Light-powered self-excited bouncing of a liquid crystal elastomer ball

Abstract

Light-powered self-excited motions of liquid crystal elastomers (LCEs) have great application prospects in the fields of actuators, soft robots, medical devices and micro-nano devices, and are capable of collecting energy directly from the environment to maintain its own motion without complex controller and additional battery. In this paper, a new light-powered self-excited bouncing system made up of LCE is originally established, and the self-excited bouncing is studied theoretically based on the well-established dynamic LCE model and Hertz contact theory. Numerical calculation shows that the LCE ball can develop into two motion modes: static mode and bouncing mode. The feedback mechanism of the bouncing mode is elucidated to be expansion-in-contact mechanism, of which the coupling of expansion and contact process enables light energy input from the environment to compensate for damping dissipation of the system. The phase diagrams and triggering conditions for provoking self-excited bouncing are quantitatively described for different system parameters. The results show that self-excited bouncing can be regulated by the system parameters, such as light illumination zone, gravitational acceleration, light intensity, equivalent modulus, contraction coefficient and damping coefficient. In addition, the system parameters have important effects on the amplitude and frequency of the self-excited bouncing of the LCE ball. It is expected that the study may provide some instructive suggestions for the design and motion control of active jumping machines.