Current drones are developed with a fixed morphology that can limit their versatility and mission capabilities. There is biological evidence that adaptive morphological changes can not only extend dynamic performances, but also provide new functionalities. In this paper, we present different drones from our recent developments where folding is used as a mean of morphological adaptation. First, we show how foldable wings can enable the transition between aerial and ground locomotion or to fly in different aerodynamic conditions, advancing the development of multi-modal drones with an extended mission envelope. Secondly, we show how foldable structures allow to transport drones easily without sacrificing payload or flight endurance. Thirdly, we present a foldable frame that makes drones to withstand collisions. However, the real potential of foldable drones is often limited by the use of conventional design strategies and rigid materials, which motivates to use smart, functional materials. Lastly, we describe a dielectric elastomer based foldable actuator, and a variable stiffness fiber using low melting point alloy for drones. The foldable actuator acts as an active compliant joint with folding functionality and mechanical robustness in drones, thanks to the compliance of dielectric elastomer, a class of smart materials. We also show re-configuration of a drone enabled by the variable stiffness fiber that can transition between rigid and soft states.
We introduce a soft actuator for grippers using DEA capable of bending actuation. The actuator is also able to generate the electro-adhesion by the fringe field formed at the edges of the electrodes. The adhesion improves the holding force and ensures the conformation of the structure to the object. After the characterization of the actuator, we develop a 2-finger soft gripper capable of holding various objects. The gripper has a mass of around 1 g, and consists of a few cm long actuation parts, realizing simple open-close movement. The compliance of the gripper leads to conformation of the structure against the object surface, which is proven by successful handling of objects with different geometries such as a toothbrush, a flat paper, and a ping pong ball. The effect of the electro-adhesion is visible when the paper is held with its flat shape meaning that an adhesion force against gravity exists. Also, by the fact that the conformed structure increases the contact area, the holding force is improved while avoiding damaging the object, which is highlighted by the ability to hold a raw egg weighing around 60 g. This soft gripper, combining both actuation and electro-adhesion, illustrates the potential use of DEA for soft robotics.
Dielectric Elastomer Actuators (DEAs) are an emerging actuation technology which are inherent lightweight and
compliant in nature, enabling the development of unique and versatile devices, such as the Dielectric Elastomer
Minimum Energy Structure (DEMES). We present the development of a multisegment DEMES actuator for use in a
deployable microsatellite gripper. The satellite, called CleanSpace One, will demonstrate active debris removal (ADR) in
space using a small cost effective system. The inherent flexibility and lightweight nature of the DEMES actuator enables
space efficient storage (e.g. in a rolled configuration) of the gripper prior to deployment. Multisegment DEMES have
multiple open sections and are an effective way of amplifying bending deformation. We present the evolution of our
DEMES actuator design from initial concepts up until the final design, describing briefly the trade-offs associated with
each method. We describe the optimization of our chosen design concept and characterize this design in terms on
bending angle as a function of input voltage and gripping force. Prior to the characterization the actuator was stored and
subsequently deployed from a rolled state, a capability made possible thanks to the fabrication methodology and
materials used. A tip angle change of approximately 60° and a gripping force of 0.8 mN (for small deflections from the
actuator tip) were achieved. The prototype actuators (approximately 10 cm in length) weigh a maximum of 0.65 g and
are robust and mechanically resilient, demonstrating over 80,000 activation cycles.
Soft robotics may provide many advantages compared to traditional robotics approaches based on rigid materials, such as intrinsically safe physical human-robot interaction, efficient/stable locomotion, adaptive morphology, etc. The objective of this study is to develop a compliant structural actuator for soft a soft robot using dielectric elastomer minimum energy structures (DEMES). DEMES consist of a pre-stretched dielectric elastomer actuator (DEA) bonded to an initially planar flexible frame, which deforms into an out-of-plane shape which allows for large actuation stroke. Our initial goal is a one-dimensional bending actuator with 90 degree stroke. Along with frame shape, the actuation performance of DEMES depends on mechanical parameters such as thickness of the materials and pre-stretch of the elastomer membrane. We report here the characterization results on the effect of mechanical parameters on the actuator performance. The tested devices use a cm-size flexible-PCB (polyimide, 50 μm thickness) as the frame-material. For the DEA, PDMS (approximately 50 μm thickness) and carbon black mixed with silicone were used as membrane and electrode, respectively. The actuators were characterized by measuring the tip angle and the blocking force as functions of applied voltage. Different pre-stretch methods (uniaxial, biaxial and their ratio), and frame geometries (rectangular with different width, triangular and circular) were used. In order to compare actuators with different geometries, the same electrode area was used in all the devices. The results showed that the initial tip angle scales inversely with the frame width, the actuation stroke and the blocking force are inversely related (leading to an interesting design trade-off), using anisotropic pre-stretch increased the actuation stroke and the initial bending angle, and the circular frame shape exhibited the highest actuation performance.