Investigation of Micromotion Kinematics of Continuum Robots for Volumetric OCT and OCT-Guided Visual Servoing

Continuum robots (CRs) have been recently shown capable of micron-scale motion resolutions. Such motions are achieved through equilibrium modulation using
indirect actuation
for altering either internal preload forces or changing the cross-sectional stiffness along the length of a CR. Previously reported, but unexplained, turning point behavior is modeled using two approaches. An energy minimization approach is first used to explain the source of this behavior. Subsequently, a kinematic model using internal constraints in multibackbone CRs is used to replicate this turning point behavior. An approach for modeling the micromotion differential kinematics is presented using experimental data based on the solution of a system of linear matrix equations. This approach provides a closed-form approximation of the empirical micromotion kinematics and could be easily used for real-time control. A motivating application of image-based biopsy using 3-D optical coherence tomography (OCT) is envisioned and demonstrated in this article. A system integration for generating OCT volumes by sweeping a custom B-mode OCT probe is presented. Results showing high accuracy in obtaining 3-D OCT measurements are shown using a commercial OCT probe. Qualitative results using a miniature probe integrated within the robot are also shown. Finally, closed-loop visual servoing using OCT data are demonstrated for guiding a needle into an agar channel. Results of this article present what we believe is the first embodiment of a CR capable of micro and macromotion control for 3-D OCT imaging. This approach can support the development of new technologies for CRs capable of surgical intervention and micromotion for ultraprecision tasks.