Inhomogeneous Deformations of Thermoplastics for Physically Adaptive Soft Matter Robots

In recent years robotics researchers have started using soft materials to build robots inspired from simple organisms, plants and animals which demonstrate impressive physical and behavioural adaptations originating from their soft and deformable body structures. Unlike rigid materials used in conventional robots, soft materials such as polymers and gels are continuum and visco-elastic mediums which can exhibit large deformations in many directions. Usage of these materials enables robotic systems to perform adaptive interactions with uncertain and unstructured environments during various tasks such as locomotion, manipulation and inspection. In biology, many important functions emerge from the formation of well-defined structures as a result of symmetry breaking in the cellular scale. In symmetry breaking, the non-uniform distribution of initiating stimuli around the soft and deformable cells contributes to the generation of asymmetric body forms. These asymmetric formations play important roles in the development of physical adaptations which are essential for survival. The contracting motion of muscle fibres (cell motility), growth and morphogenesis (cell division), healing (cell fusion) and specialisation of neuron axons (cell polarity) are several examples to the adaptive functions based on symmetry breaking. The mechanisms, conditions and physics of the formation asymmetric forms which lead to adaptive functions are well established and investigated in biology. However, there has been no clear theory and systematic investigation so far to discuss how deformation of soft continuum structures can be used for the emergence of physical and behavioural adaptations in autonomous robotic systems. This dissertation proposes a systematic investigation on the utilisation of inhomogeneous deformations of soft materials for the generation of physical and behavioural adaptations on robotic platforms. Inhomogeneous deformations take place in a non-uniform manner throughout a continuum body which can result in generating asymmetric forms similar to examples in biology. Soft materials present similarities to the collective behaviours of highly distributed neighbouring cells due to their molecular structure and physical properties under the influence of various stimuli. Especially thermoplastics provide suitable conditions to exhibit inhomogeneous deformations through the application of thermal and mechanical stimuli combinations. Therefore, this dissertation proposes different mechanisms to generate asymmetric forms by inducing inhomogeneous deformations on thermoplastic materials. These asymmetric forms can be used for the generation of sensing and motion functions which are crucial in an autonomous system to exhibit physical and behavioural adaptations. The conceptual discussion on physical adaptation is realised with four case studies which demonstrate the three contributions of this dissertation: regulation of plasticity for structural adaptation, differential stiffness for the emergence of motions, and sensing of soft deformations using adjustable morphology. The case studies present robotic platforms which demonstrate sensing of deformations on robot’s own body, sensing of softness and temperature of unknown objects in the environment, locomotion in free space by fabricating draglines, and adaptive manipulation with anthropomorphic and compliant joint designs. Regulation of plasticity for structural adaptation is used commonly in all of the case studies where thermoplastic materials are moulded into asymmetric forms with mechanisms that firstly regulate their plasticity via heat induction and secondly deform those using mechanical stimuli. The emergence of motion from the differential stiffness is observed in the dragline forming mobile robot and the robotic