Medical endoscopes have not fundamentally changed over the last 40 years. Mechanical cables, that are used to control current scopes, can cause several major issues such as low precision, lack of sensoric feedback and, due to the purely mechanical control, unfeasible integration into cyber-medical systems. To address these limitations, we aim to use shape memory actuators instead of mechanical cables to navigate the endoscope camera head through the bowel lumen by computer-aided control. In compact environments, shape memory alloy actuator-based devices are challenging to design due to for example of overheating with slower actuating times and risks of adjacent tissue burns. To examine whether active cooling needs to be embedded, an efficient modelling approach is desired to optimize the design of prototypes, before complex manufacturing is established. In addition to the complex thermo-electro-mechanical coupling, the model needs to be able to handle complex dynamic operating regimes and therefore a lumped model is necessary to further parametrize and optimize the design.We propose a combined simulation approach, where at first in the thermo-electro-mechanical domain, a finite element model is created for the non-symmetric cross-section of a feasible design. Then, the results are mapped to a reduced analytical thermo-dynamic description where the influence of dimensional and material parameters are describable in reference to the finite element model. In a second step, these equations and parameters are implemented into a network description enabling efficient parameter studies to improve the design and optimize the application. Within the combined network model, additional features are implemented, which for example describe the phase-change behavior of the shape memory alloy actuator based on the applied current and pre-stress. Here, a length change behavior and the Youngs Modulus is implemented, which based on the mechanical response behavior of the design, now allows to describe the resulting bending angle of the camera head. &nbsp;With our proposed modeling approach, a fast but detailed description can be established, which focuses on the optimization of dimensional and material parameters and additionally can solve efficiently complex dynamic operating regimes. Thus, prior to the establishment of any complex manufacturing of prototypes and test benches, we successfully developed an optimized design and enable the development a virtual control system for future work.

Combined Finite Element and Network Model of Embedded Shape Memory Alloy Actuators for Endoscopic Tools With an Efficient Dynamic Thermo-Electro-Mechanical Design Process

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2021/volume/85499

ASME 2021 Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2021)

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