Kinematic and Structural Analysis of a Cable Driven Continuum Robot

Abstract

Cable-driven continuum robots (CCRs) have been the center of attention due to their ability to undergo large deformations and operate effectively in constrained and unknown environments. The high degrees of freedom that is offered by them make them suitable for applications such as minimally invasive surgery, adaptive gripping, and many other inspection-based tasks in uncertain environments. However, accurate modelling of CCRs remains challenging due to their nonlinear and large deformation behaviour and also due to the mechanical and material constraints present in the CCRs. In this thesis, a cable-driven continuum robot is analysed using two modelling approaches. A kinematic model based on a discretized four-bar linkage approximation is developed in a bottom-to-top approach to represent the cable driven structure as a series of rigid segments. The configuration of the robot is obtained by solving a constrained optimization problem using the well-known fmincon routine available in MATLAB. The optimization enforces preservation of backbone length, uses the user provided actuation cable length and other constraints. This model efficiently predicts the deformation of the robot under varying cable actuation inputs. Along with the kinematic model, a structural analysis of the robot is carried out using nonlinear finite element analysis (FEA) in SolidWorks. The model uses the properties of super-elastic Nitinol backbone, ABS disks, and steel cables, with optimized boundary conditions to simulate cable actuation and structural deformation. The FEA results provide insights into deformation characteristics and stress distribution from a material perspective, providing valuable insight. The results demonstrate that the kinematic model effectively captures the overall shape and multi-plane bending behaviour of the robot, while the FEA model provides a more mechanical representation of structural deformation. The thesis focuses on these two different methods to understand and analyse the nature of CCR’s from a mathematical and mechanical perspective. A physical three fingered CCR prototype is also currently in the fabrication process which will aid in evaluating the accuracy of both the kinematic and FEA model.