Conventional robots are typically actuated by hard actuators, while biological entities consist mostly of soft muscles. Being soft imparts a functionality of compliance, thereby greatly enhancing the range of actuation and the degrees of freedom. Here, we demonstrate a soft electromechanically-active polymer capable of an electrically-induced linear strain beyond 500% that is continuously tunable by voltage. Previous experiments on the same material have demonstrated that by harnessing and bypassing electromechanical instability, soft electroactive polymers may bi-stably switch between an actuated state and an uncharged state of about 323% linear strain. In this paper, we use theory to inspire the possibility of suppressing electromechanical instability using pre-stretch by applying a non-isotropic pre-stretch onto the membrane, so as to achieve an ultra-large actuation strain that is continuously tunable by voltage. This geometry that enables such a large magnitude of actuation is simple and highly amenable to integration in robotic systems. With an electrically-induced strain of at least two orders of magnitude larger than conventional actuators, we expect our demonstration to expand the range of application for soft actuators.
A new approach in the development of aircraft and aerospace industry is geared toward increasing use of electric systems. An electromechanical (EM) piezoelectric-based system is one of the potential technologies that can produce a compactable system with a fast response and a high power density. However, piezoelectric materials generate a small strain, of around 0.1–0.2% of the original actuator length, limiting their potential in large-scale applications. This paper reviews the potential amplification mechanisms for piezoelectric-based systems targeting aerospace applications. The concepts, structural designs, and operation conditions of each method are summarized and compared. This review aims to provide a good understanding of piezoelectric-based systems toward selecting suitable designs for potential aerospace applications and an outlook for novel designs in the near future.
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