Andrew T. Conn

Swimming like algae: biomimetic soft artificial cilia

Cilia are used effectively in a wide variety of biological systems from fluid transport to thrust generation. Here, we present the design and implementation of artificial cilia, based on a biomimetic planar actuator using soft-smart materials. This actuator is modelled on the cilia movement of the alga Volvox, and represents the cilium as a piecewise constant-curvature robotic actuator that enables the subsequent direct translation of natural articulation into a multi-segment ionic polymer metal composite actuator. It is demonstrated how the combination of optimal segmentation pattern and biologically derived per-segment driving signals reproduce natural ciliary motion. The amenability of the artificial cilia to scaling is also demonstrated through the comparison of the Reynolds number achieved with that of natural cilia.

Active-elastic bistable minimum energy structures

The design of structures that combine the principles of minimum energy and bistable mechanisms is presented. A minimum energy configuration is achieved by the interaction of one or more elastic elements and two strips of stretched elastomer, which also operate as dielectric actuators. The system has two equilibrium states, and the actuators are used to trigger the switch from one state to the other. An analytical model, based on the approach of energy minimization, was implemented to assist the design of the geometrical parameters. A prototype shows bistability and is able to switch equilibrium state varying its bending angle from −40° to 40°.

Bistable minimum energy structures (BiMES) for binary robotics

Bistable minimum energy structures (BiMES) are devices derived from the union of the concepts of dielectric elastomer minimum energy structures and bistable systems. This article presents this novel approach to active, elastic and bistable structures. BiMES are based on dielectric elastomer actuators (DEAs), which act as antagonists and provide the actuation for switching between the two equilibrium positions. A central elastic beam is the backbone of the structure and is buckled into the minimum energy configurations by the action of the two DEAs. The theory and the model of the device are presented, and also its fabrication process. BiMES are considered as fundamental units for more complex structures, which are presented and fabricated as proof of concept. Two different ways of combining the multiple units are proposed: a parallel configuration, to make a simple gripper, and a serial configuration, to generate a binary device. The possibility of using the bistable system as a continuous bender actuator, by modulating the actuation voltage of the two DEAs, was also investigated.

WormTIP: An Invertebrate Inspired Active Tactile Imaging Pneumostat

WormTIP is a novel lightweight self-actuating exploratory sensor, using a pneumostatic vessel and a dielectric elastomeric actuator DEA to create an active sensory tip capable of object shape determination as part of a flexible soft robot. Utilising the coupling of a static fluid vessel, the DEA is paired with a sensory membrane with internal papillae mimicking the internal morphology found in the fingertip. The sensory membrane is extended onto an object, conforming to its surface. Experimental results are presented which show the detection of shapes using particle velocimetry and papillae density analysis. These are preliminary results which show the potential of the WormTIP, which is the focus of ongoing work. The device is aimed for use as a self-contained palpating sensor, or as an attachment to a bio-inspired robotic worm forming a self-contained exploratory vehicle with the device acting as the sensory appendage or proboscis.

Euglenoid-inspired Giant Shape Change for Highly Deformable Soft Robots

Nature has exploited softness and compliance in many different forms, from large cephalopods to microbial bacteria and algae. In all these cases, large body deformations are used for both object manipulation and locomotion. The great potential of soft robotics is to capture and replicate these capabilities in controllable robotic form. This letter presents the design of a bioinspired actuator capable of achieving a large volumetric change. Inspired by the changes in body shape seen in the euglena Eutreptiella spirogyra during its characteristic locomotion, a novel soft pneumatic actuator has been designed that exploits the hyperelastic properties of elastomers. We call this the hyperelastic bellows (HEB) actuator. The result is a structure that works under both positive and negative pressure to achieve euglenoid-like multimodal actuation. Axial expansion of 450% and a radial expansion of 80% have been observed, along with a volumetric change of 300 times. Furthermore, the design of a segmented robot with multiple chambers is presented, which demonstrates several of the characteristic shapes adopted by the euglenoid in its locomotion cycle. This letter shows the potential of this new soft actuation mechanism to realise biomimetic soft robotics with giant shape changes.

Elastic Actuation for Legged Locomotion

The inherent elasticity of dielectric elastomer actuators (DEAs) gives this technology great potential in energy efficient locomotion applications. In this work, a modular double cone DEA is developed with reduced manufacturing and maintenance time costs. This actuator can lift 45 g of mass (5 times its own weight) while producing a stroke of 10.4 mm (23.6% its height). The contribution of the elastic energy stored in antagonistic DEA membranes to the mechanical work output is experimentally investigated by adding delay into the DEA driving voltage. Increasing the delay time in actuation voltage and hence reducing the duty cycle is found to increase the amount of elastic energy being recovered but an upper limit is also noticed. The DEA is then applied to a three-segment leg that is able to move up and down by 17.9 mm (9% its initial height), which demonstrates the feasibility of utilizing this DEA design in legged locomotion.