Doctor of Philosophy
School of Mechanical, Materials and Mechatronic Engineering
Zhou, Hao, Modelling, Design Optimisation and Experimental Evaluation of Propulsion Concepts for in-body Robotic Systems, Doctor of Philosophy thesis, School of Mechanical, Materials and Mechatronic Engineering, University of Wollongong, 2014. http://ro.uow.edu.au/theses/4164
Applications of miniaturised robots in medicine have created significant opportunities for minimally invasive medicine. As a pioneer in such a field, wireless capsule endoscope (WCE) has brought significant advantages to the diagnosis of the gastrointestinal (GI) diseases, especially the symptoms in the small bowel to which a conventional endoscope is hard to reach. However, current commercial capsules depend on the natural peristalsis to move, which makes site-specific diagnosis and intervention less effective, limiting WCE’s prospect to a large degree. Therefore, substantial research is being dedicated to the active locomotion of WCEs, which is crucial for further therapeutic functionalities such as drug delivery and biopsy.
This thesis reports on designing, optimising, fabricating, and testing locomotion mechanisms for a spiral-type robotic WCE for operation within the GI tract, especially in the small intestine, in a safe and reliable manner. The whole locomotion system functions by coupling a capsule robot containing a magnetic element via an external electromagnetic system.
A three-axes circular Helmholtz coils has been employed to generate a rotating magnetic field to wirelessly provide actuation to the robotic capsule. By altering the frequency and amplitude of the electric current, this electromagnetic system is able to control the rotation speed and direction (in three dimensions) of the capsule.
Biomechanical and biotribological properties of a real intestine were experimentally investigated in order to obtain a sound understanding of the working environment of the robotic capsule. Our findings demonstrate that the intestine’s biomechanical and biotribological properties are coupled, suggesting that the sliding friction is strongly related to the internal friction of the intestinal tissue. Sliding friction experiments were also conducted with bar-shaped solid samples to determine the sliding friction between the samples and the small intestine.
Finite element analysis (FEA) has been used to optimise the geometry of a capsule robot assembled with spirals, like a screw assembled on its cylindrical surface. The computational fluid dynamics (CFD) has been employed to investigate the interaction between the capsule and a mucus film rather than the intestinal wall. The CFD predictions agree well with the corresponding experiments in which the spiral-type capsules (i.e. the capsule robot with spiral traction elements) were actuated by the external electromagnetic system. The FEA is extended to take the deformation and viscoelasticity of the intestine into account in order to realistically predict the propulsion performance of the capsule robot, evaluated experimentally. The close correspondence between experimental and numerical results from the FEA has encouraged us to use the FEA as a tool to evaluate the performance of different helical structures and consequently, undertake the design and optimization of the traction topology of a spiral-type capsule robot.
Most literature in this field shows qualitative results on the mechanical and dynamic behaviors of a spiral-type robotic WCE moving inside a model GI tract, rather than testing in a real small intestine. Very little was reported on the theoretical and experimental evaluation of various spiral-type capsule robots. In this thesis, significant efforts have been made to provide substantial experimental data for quantitatively analysing the performance of different traction topologies of the robotic capsule, including the resistive torque, tractive force, locomotion ability and locomotion efficiency, through in vitro experiments with real porcine small intestines. It is revealed that the optimisation of such a robotic capsule is a compromise among propulsion velocity, stability, efficiency, and safety as well. From this point of view, an optimised traction topology was identified and recommended from the performance evaluation based on the experimental data. By these findings, a significant step has been taken towards a functional robotic capsule with a swallowable size, and the development of a powerful therapeutical WCE eventually.