Design Considerations and Redundancy Resolution for Variable Geometry Continuum Robots

Current multi-backbone continuum robots are limited to a constant cross-sectional diameter. This paper proposes a design alternative that overcomes this limitation. The ability to change the diameter of a continuum robot expands the repertoire of kinematic redundancy and enables kinematic parameter adaptation to optimize performance. A continuum robot design based on the angulated scissor mechanism is presented along with its position analysis. An exploration of admissible design parameter values for a given continuum robot segment with a desired maximum curvature while maintaining an open bore along its center is also carried out. A design presenting how this mechanism can be incorporated into a continuum robot is shown and a strategy for minimizing joint forces and avoiding joint limits is formulated as a gradient descent redundancy resolution problem in a simulation case study. The simulation results show that varying the diameter can significantly reduce joint forces while preserving the workspace and avoiding joint limits. This work is a first step towards continuum robots with situational awareness that will use their sensing capabilities to adapt their structure in order to optimize task execution performance.