Design and fabrication of devices based on Dielectric Elastomer technology for Soft Robotics applications: from materials handling to the Slowbots project

With a view to confirm that dielectric elastomer actuators (DEAs) are one the promising enabling actuation technology for soft robots, this thesis presents the design and fabrication of functional soft robotic devices based on Hydrostically Coupled DEAs (HC-DEAs) with real-world applications. We first propose a soft, compact and light weight platform based on the HC-DEA technology to respond to the need of some areas of the industrial field of systems which can transport/sort delicate objects. This platform, specifically designed to enable the rolling of round objects, consists of an array of HC-DEAs. Experiments on the electromechanical performances on the single HC-DEA are performed and presented. Experimental tests on the proposed platform demonstrate its effectiveness to roll round objects (different in weight and dimensions) when its surface is deformed according to a predetermined pattern of actuation. As example, a 10 mm diameter PVC pipe section and weight of 50 gr, can be transported from one end to the other of the platform at an average speed of around 10 mm/s. In the same context of the previous work, we next present an upgrading design of an existing push-pull Hydrostatically Coupled Dielectric Elastomer Actuator. Its main distinguishing design characteristic is the segmented electrodes which stand as four independent elements on the active membrane. An adequate sequence of activation of the electrodes can generate not only an out of plane motion (push-pull behaviour) but also in plane motion actuation resulting in a multi degree of freedom soft actuator with a roto-translational kinematics. Thanks to its ability to exert both normal and tangential thrusts in any direction in a plane, the novel multi degree of freedom (multi-DoF) HC-DEA enables a variety of possible applications in the field of soft manipulation. In particular, with this thesis intends to demonstrate the possibility of using it as a building block of a modular soft platform aimed at handling delicate objects. Moreover, since each actuator of the platform can be independently controlled by an electric signal, the result could be an easily reprogrammable and reconfigurable soft surface composed by a plane matrix of actuators allowing for both round and flat objects handling. Experimental results demonstrated just two multi-DoF actuation modules, whit a proper actuation cycles of the electrodes, are able to transport a flat object in both translational and rotational directions. Results prove that a Petri dish with a weight of 8 gr and a diameter of 90 mm can be transported in both translational and rotational directions. Specifically, following the application of 3.5 kV as driving voltage, the actuators induced a horizontal translation of the Petri Dish of 3 mm for each actuation cycle and a rotation of about 2.25° for each actuation cycle. Finally, as steps towards to these "soft robotic organisms" this thesis proposes some design concepts with the concrete aim to develop the Slowbots: slow, sustainable, biodegradable and autonomous robots made by soft components. Specifically, it is presented here the fabrication and the electro-mechanical characterisation of pectin based hydrogels with potential application in Slowbots. The hydrogels were fabricated using a solvent casting method dispersing various concentrations of pectin in deionized water and using a CaCl2 solution as crosslinking agent. The electro-mechanical investigation of the hydrogels suggested that due to their low values of apparent elastic modulus (46.45  37.76 kPa) and due to their good conductivity (1.83 S/m is the maximum value recorded) they can be employed as soft conductors for Dielectric Elastomer Actuators on which Slowbots could rely for their locomotive tasks. Moreover, since we found that an increase of temperature in pectin crosslinked matrix can cause an increase of their ionic conductivity, these hydrogels could be used as conductive interface for exteroceptive sensors in order to trigger the activation of the Slowbots on the base of the part of the day, as really happen in organisms in nature. Lastly, pectin hydrogels seem suitable to use in supercapacitors, also called ultracapacitors, to allow the robots to storage energy from the environment and thus to accomplish a set of tasks completely free from tethers.