A Compliant Manipulator for Confined Space Tissue Diagnostics: Kinematic and Force Analyses and Initial Characterization Experiments

Minimally invasive procedures employ continuum manipulators, however internal human anatomy presents challenges relating to size, dexterity, and workspace for these manipulators. This manuscript presents modeling, kinematic analysis, prototyping, and characterization of a micro-robotic manipulator for transurethral palpation of bladder tissue. The proposed micro-robot consists of two subsystems: a tendon-driven continuum segment with an elastic tube encompassing each joint for compliance and structural integrity, and a hyper-spherical joint ensuring higher dexterity and manipulability with a comprehensive actuation and modeling approach. The forward kinematics follow the Denavit-Hartenberg formulation. A developed differential Jacobian inverse kinematics formulation prevents motion singularities for desired poses while operating in the confined space. The simulated kinematic results confirm the dexterity and reach of the proposed micro-robot. A strain energy quasi-static model is developed for a single continuum module. The model is evaluated for tension-bend angle relationships as function of tube material and geometry, and joint length. Limited functionality continuum modules (4mm outside diameter) with four different joint lengths, (3, 6, 9, 12) mm, are prototyped for tension-bend angle characterization using a computer vision outfitted experimental setup. An equivalent shear modulus relationship for the elastic tube for selected joint length values and bend angles is developed using experimental results. The tension-bend angle response is nonlinear and function of tube properties, joint geometry, and their interactions. The comparison of the experimental and quasi-static model results shows high fidelity for use in predicting the robot continuum segment behavior.