Decentralized Morphological Stiffness Tunable Interface for Continuum Manipulators

Student thesis: Doctoral ThesisDoctor of Philosophy


This thesis investigates how the problem of stiffness regulation of continuum manipulators can be simplified by inspiration from morphology of biological fish scales and experimental observation of manipulator geometry deformation. Soft continuum “trunk and tentacle” manipulators have high inherent dexterity and reconfigurability and have become an attractive candidate for safe manipulation and explorations in surgical and space robotic applications recently. The passive shape adaptation and large reachable configuration space features of this class of manipulators, due to their highly deformable nature, make them a perfect choice for minimally invasive insertion of surgical tools in the confined maze-like space in many robotic surgery sites. However, achieving accuracy in precise tasks is a challenge with these highly flexible structures, for which stiffness variable designs based on jamming, smart material, antagonistic actuation and morphing structures are introduced in the recent years. After a careful review and comparative study of current methods on modeling and stiffness modulation of continuum manipulators, an analytical model is presented based on the geometry deformation of continuum manipulators and the Rivlin’s work on continuum media and adopted the Ritz and Galerkin methods to solve the dynamics of continuum manipulators based on Cosserat beam theory and principle of virtual work. Our new approach reduces model and control space dimension while preserving the accuracy. This enabled us to solve the stiffness regulation actuation and computation problems in the morphological level which highly simplifies the central control design. Two novel integrable helical interfaces inspired by the shape and special arrangement of fish scales morphology is designed using tendon driven and thermoactive low melting point actuation mechanisms. High stiffness range, very low hysteresis and easy integration to different manipulator designs are the advantages of our design compared to the previous research. An analytical model is derived based on which the performance of the design is optimized. A comparison between the presented robotic interface designs and a real fish skin suggests that natural scales may contribute in stiffness modulation of the fish body through jamming, e.g. due to external stream and steady water pressure. Finally, a novel decentralized morphological approach is implemented to regulate the regional stiffness of the continuum manipulator integrated with the designed jamming interfaces to reject configuration disturbances and modulate the task space stiffness with possible application in soft tissue palpation.
Date of Award2018
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorMatthew Howard (Supervisor) & Thrishantha Nanayakkara (Supervisor)

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