Andrew T Conn

Towards holonomic electro-elastomer actuators with six degrees of freedom

Functionally efficient six degree of freedom (DOF) actuators have not yet been developed in a scale-invariant and inherently compliant unified form. This has primarily been due to the use of conventional serial or parallel kinematical configurations and electromagnetic motors, pneumatics and hydraulics. Contrary to traditional technologies, utilizing electro-active elastomers enables multi-DOF actuation and holonomic operation with minimal structural complexity. Conical dielectric elastomer actuators (DEAs) are compact multi-DOF actuator?sensors that are scalable and can be entirely polymeric, making them suitable for a variety of applications including minimally invasive medical devices. In this paper, cone DEAs are developed towards integrated 6-DOF actuation with muscle-like performance from a single structure. This is achieved by demonstrating the feasibility of holonomic 6-DOF actuation and through experimental characterization of a 5-DOF prototype. The 5-DOF prototype (50?mm length, 60?mm diameter) produced rotational actuation outputs of ?21.7??and ?9.42?mN?m and linear actuation outputs of ?4.45?mm (?9.1%) and ?0.55?N. Finally, combined multi-DOF actuation is demonstrated as part of development towards scalable holonomic electro-active elastomer actuators.

Biomimetic chromatophores for camouflage and soft active surfaces.

Chromatophores are the pigment-containing cells in the skins of animals such as fish and cephalopods which have chromomorphic (colour-changing) and controllable goniochromic (iridescent-changing) properties. These animals control the optical properties of their skins for camouflage and, it is speculated, for communication. The ability to replicate these properties in soft artificial skin structures opens up new possibilities for active camouflage, thermal regulation and active photovoltaics. This paper presents the design and implementation of soft and compliant artificial chromatophores based on the cutaneous chromatophores in fish and cephalopods. We demonstrate artificial chromatophores that are actuated by electroactive polymer artificial muscles, mimicking the radially orientated muscles found in natural chromatophores. It is shown how bio-inspired chromomorphism may be achieved using both areal expansion of dielectric elastomer structures and by the hydrostatic translocation of pigmented fluid into an artificial dermal melanophore.

From Natural Flyers to the Mechanical Realization of a Flapping Wing Micro Air Vehicle

This paper presents a novel micro air vehicle (MAV) design that seeks to reproduce the unsteady aerodynamics of insects in their flight. Many prototype MAVs have been developed around the world over the last decade, with various wing configurations, e.g. fixed, rotary, flapping or hybrid. Many of these projects aim to implement the insect flight mechanics and their associated aerodynamic benefits onto a miniature flying robot. In this paper, the mechanical realization of a flapping wing MAV is described, where a novel parallel crank rocker mechanism has been designed to produce the wing flapping motion. Various potential actuators are outlined, with recommendation made for the best suited actuator for powering flight. A brief account of the development and manufacture of the MAV prototype is also given.

Advances in Autonomous Robotics

In order to perform a reaching movement towards a moving target, an autonomously learning robot must first learn several transformations, such as motion detection, coordinate transformation between the camera and the arm and the inverse model of the arm. A curious reaching robot learns them better by performing the appropriate actions so as to expedite and improve their learning speed and accuracy. We implement a model of hierarchical curiosity loops in an autonomous active learning robot, whereby each loop converges to the optimal action that maximizes the robot’s learning of the appropriate transformation. It results in the emergence of unique behaviors that ultimately lead to the capability of reaching.

Smart Radially Folding Structures

In this paper, we present novel methods for exploiting passive and active radially folding mechanisms for reactive and dynamic structures. These enable the application of radially folding structures in domains including fluidics, medical stents, and auxetic materials. A compact form of elastic deployment utilizing linkage strain energy is proposed using beam theory analysis. Elastic strain energy is also shown to produce bistable folding behavior, with two low energy states at full contraction and full expansion, and a bistable switching point at some intermediate position. Polymeric smart materials are investigated for driving active folding. These materials can be readily exploited through the features of the folding structure including its ability to resolve 1-D, 2-D, and 3-D actuation strains into a more effective single degree-of-freedom linear, areal, volumetric or rotational output. The elastic and solid-state nature of many polymeric smart materials means they can implement elastic deployment and bistability. A thermally-activated shape memory polymer is shown to fold a 4-segment structure from expanded to contracted states. Experimental testing of an 8-segment dielectric elastomer actuator prototype demonstrates that radially folding structures can resolve large biaxial planar strains generated by dielectric elastomers into a single linear or rotational output stroke.

Harnessing electromechanical membrane wrinkling for actuation

Dielectric elastomers are soft electromechanical transducers that can exhibit unstable wrinkling behavior under large electric fields. This instability can be exploited by optimizing electrode boundaries to accentuate or attenuate localized wrinkling. An analytical model is presented, which demonstrates that the critical electric field to induce wrinkling can be lowered as the electrode geometry changes from convex to concave. This allows a single dielectric elastomer membrane to generate either biaxial or uniaxial extension in specific regions. A prototype 56 μm thick membrane actuator incorporates this principle to generate an in-plane rotational output, producing an actuation stroke of 15.7°.

Soft segmented inchworm robot with dielectric elastomer muscles

Robotic devices typically utilize rigid components in order to produce precise and robust operation. Rigidity becomes a significant impediment, however, when navigating confined or constricted environments e.g. search-and-rescue, industrial pipe inspection. In such cases adaptively conformable soft structures become optimal. Dielectric elastomers (DEs) are well suited for developing such soft robots since they are inherently compliant and can produce large musclelike actuation strains. In this paper, a soft segmented inchworm robot is presented that utilizes pneumatically-coupled DE membranes to produce inchworm-like locomotion. The robot is constructed from repeated body segments, each with a simple control architecture, so that the total length can be readily adapted by adding or removing segments. Each segment consists of a soft inflatable shell (internal pressure in range of 1.0-15.9 mBar) and a pair of antagonistic DE membranes (VHB 4905). Experimental testing of a single body segment is presented and the relationship between drive voltage, pneumatic pressure and active displacement is characterized. This demonstrates that pneumatic coupling of DE membranes induces complex non-linear electro-mechanical behaviour as drive voltage and pneumatic pressure are altered. Locomotion of a two-segment inchworm robot prototype with a passive length of 80 mm is presented. Artificial setae are included on the body shell to generate anisotropic friction for locomotion. A maximum locomotion speed of 4.1 mm/s was recorded at a drive frequency of 1.5 Hz, which compares favourably to biological counterparts. Future development of the soft inchworm robot are discussed including reflexive low-level control of individual segments.

Antagonistic dielectric elastomer actuator for biologically-inspired robotics

For optimal performance, actuators designed for biologically-inspired robotics applications need to be capable of mimicking the key characteristics of natural musculoskeletal systems. These characteristics include a large output stroke, high energy density, antagonistic operation and passive compliance. The actuation properties of dielectric elastomer actuators (DEAs) make them viable for use as an artificial muscle technology. However, much like the musculoskeletal system, rigid structures are needed to couple the compliant DEA layers to a load. In this paper, a cone DEA design is developed as an antagonistic, multi-DOF actuator, viable for a variety for biologically-inspired robotics applications. The design has the advantage of maintaining pre-strain through a support structure without substantially lowering the overall mass-specific power density. Prototype cone DEAs have been fabricated with VHB 4910 acrylic elastomer and have characteristic dimensions of 49mm (strut length) and 60mm (DEA diameter). Multi-DOF kinematical outputs of the cone DEAs were measured using a custom 3D motion tracking system. Experimental tests of the prototypes demonstrate antagonistic linear (±10mm), rotational (±25°) and combined multi-DOF strokes. Overall, antagonistic cone DEAs are shown to produce a complex multi-DOF output from a mass-efficient support structure and thus are well suited for being exploited in biologically-inspired robotics.

Development of a novel Electro Active Polymer (EAP) actuator for driving the wings of flapping micro air vehicle

This paper describes the development and testing of an EAP (electroactive polymer) actuator for driving the wings of an MAV (micro air vehicle). Creating the drive system for a flapping MAV is extremely challenging because of the required combined bending/twisting of the wing during flapping. Silicone-based DEs (dielectric elastomer) were used for the actuator material. In addition, the EAP actuators were operated at resonant frequency which is an important means of producing optimal flight performance with reduced power consumption. The paper presents the optimisation of the structural and operational performance of the EAP actuator. The paper also presents the test results of the actuator driving an actual MAV wing.

The parallel crank-rocker flapping mechanism: an insect-inspired design for micro air vehicles

This paper presents a novel micro air vehicle (MAV) design that seeks to reproduce the unsteady aerodynamics of insects in their natural flight. The challenge of developing an MAV capable of hovering and maneuvering through indoor environments has led to bio-inspired flapping propulsion being considered instead of conventional fixed or rotary winged flight. Insects greatly outperform these conventional flight platforms by exploiting several unsteady aerodynamic phenomena. Therefore, reproducing insect aerodynamics by mimicking their complex wing kinematics with a miniature flying robot has significant benefits in terms of flight performance. However, insect wing kinematics are extremely complex and replicating them requires optimal design of the actuation and flapping mechanism system. A novel flapping mechanism based on parallel crank-rockers has been designed that accurately reproduces the wing kinematics employed by insects and also offers control for flight maneuvers. The mechanism has been developed into an experimental prototype with MAV scale wings (75 mm long). High-speed camera footage of the non-airborne prototype showed that its wing kinematics closely matched desired values, but that the wing beat frequency of 5.6 Hz was below the predicted value of 15 Hz. Aerodynamic testing of the prototype in hovering conditions was completed using a load cell and the mean lift force at the maximum power output was measured to be 23.8 mN.