Modeling, Analysis, Force Sensing and Control of Continuum Robots for Minimally Invasive Surgery

This dissertation describes design, modeling and application of continuum robotics for surgical applications, specifically parallel continuum robots (PCRs) and concentric tube manipulators (CTMs). The introduction of robotics into surgical applications has allowed for a greater degree of precision, less invasive access to more remote surgical sites, and user-intuitive interfaces with enhanced vision systems. The most recent developments have been in the space of continuum robots, whose exible structure create an inherent safety factor when in contact with fragile tissues. The design challenges that exist involve balancing size and strength of the manipulators, controlling the manipulators over long transmission pathways, and incorporating force sensing and feedback from the manipulators to the user. Contributions presented in this work include: (1) prototyping, design, force sensing, and force control investigations of PCRs, and (2) prototyping of a concentric tube manipulator for use in a standard colonoscope. A general kinetostatic model is presented for PCRs along with identification of multiple physical constraints encountered in design and construction. Design considerations and manipulator capabilities are examined in the form of matrix metrics and ellipsoid representations. Finally, force sensing and control are explored and experimental results are provided showing the accuracy of force estimates based on actuation force measurements and control capabilities. An overview of the design requirements, manipulator construction, analysis and experimental results are provided for a CTM used as a tool manipulator in a traditional colonoscope. Currently, tools used in colonoscopic procedures are straight and exit the front of the scope with 1 DOF of operation (jaws of a grasper, tightening of a loop, etc.). This research shows that with a CTM deployed, the dexterity of these tools can be increased dramatically, increasing accuracy of tool operation, ease of use and safety of the overall procedure. The prototype investigated in this work allows for multiple tools to be used during a single procedure. Experimental results show the feasibility and advantages of the newly-designed manipulators

Design of flexure-based motion stages for mechatronic systems via FACT

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 191-195).The aim of this thesis is to generate the knowledge required to (i) synthesize serial flexure systems and (ii) optimally place actuators using a comprehensive library of geometric shapes called freedom, actuation, and constraint spaces. These geometric shapes guide designers through the creative process of concept generation without compromising engineering rigor. Each shape rapidly conveys the mathematics of screw theory, projective geometry, and constraint-based design by visually depicting regions where constraints and actuators may be placed for synthesizing optimal flexure concepts. In this way, designers may consider every flexure concept that satisfies the desired functional requirements before selecting the final design. FACT was created to improve the design processes for small-scale flexure systems and precision machines. For instance, there is a need to create multi-axis nanopositioners for emerging three-dimensional nano-scale research/manufacturing. Through this work the following contributions were made: (1) the fifty freedom and constraint space types were found that may be used to synthesize both parallel and serial flexure concepts, (2) intermediate freedom spaces were created that help designers stack conjugated flexure elements to avoid or utilize underconstraint, (3) a twist-wrench stiffness matrix was created to model the elastomechanic behavior of flexure systems, (4) the twenty-six actuation spaces were found that help guide designers in placing actuators that minimize motion errors, and (5) a theory was created that determines the force and displacement actuator outputs for accessing a desired DOF once actuators have been placed. A serially conjugated lead screw flexure was designed using the FACT design process and a parallel flexure system was built to validate the theory of actuation described in this thesis.by Jonathan Brigham Hopkins.Ph.D

Design of a high-speed, meso-scale nanopositioners driven by electromagnetic actuators

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 218-230).The purpose of this thesis is to generate the design and fabrication knowledge that is required to engineer high-speed, six-axis, meso-scale nanopositioners that are driven by electromagnetic actuators. When compared to macro-scale nanopositioners, meso-scale nanopositioners enable a combination of greater bandwidth, improved thermal stability, portability, and capacity for massively parallel operation. Meso-scale nanopositioners are envisioned to impact emerging applications in data storage and nanomanufacturing, which will benefit from low-cost, portable, multi-axis nanopositioners that may position samples with nanometer-level precision at bandwidth of 100s of Hz and over a working envelope greater than 10x10x10 micrometers3 This thesis forms the foundation of design and fabrication knowledge required to engineer mesoscale systems to meet these needs.The design combines a planar silicon flexure bearing and unique moving-coil microactuators that employ millimeter-scale permanent magnets and stacked, planar-spiral micro-coils. The new moving-coil actuator outperforms previous coil designs as it enables orthogonal and linear force capability in two axes while minimizing parasitic forces. The system performance was modeled in the structural, thermal, electrical, and magnetic domains with analytical and finite-element techniques. A new method was created to model the three-dimensional permanent magnet fields of finite magnet arrays. The models were used to optimize the actuator coil and flexure geometry in order to achieve the desired motions, stiffness, and operating temperature, and to reduce thermal error motions.A new microfabrication process and design-for-manufacturing rules were generated to integrate multilayer actuator coils and silicon flexure bearings. The process combines electroplating for the copper coils, a silicon dioxide interlayer dielectric, and deep reactive-ion etching for the silicon flexures and alignment features.(cont.) Microfabrication experiments were used to formulate coil geometry design rules that minimized the delamination and cracking of the materials that comprise the coil structure. Experiments were also used to measure the previously-unreported breakdown strength of the unannealed, PECVD silicon dioxide interlayer dielectric. The results of this research were used to design and fabricate a meso-scale nanopositioner system. The nanopositioner was measured to have a range of motion of 10 micrometers in the lateral directions, a range of 2 micrometers in the out-of-plane direction, an angular range of 0.5 degrees, and a first mode resonant frequency at 900 Hz. Open-loop calibration has been shown to minimize parasitic in-plane motion to less than 100 nm over the range of motion.by Dariusz S. Golda.Ph.D

Design of parallel flexure systems via Freedom and Constraint Topologies (FACT)

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 391-393).The aim of this thesis was to generate the knowledge required to represent the possible freedom topologies (motions of a mechanism) and the possible constraint topologies (flexural elements that guide the mechanism) in a form that designers can use to design parallel flexure systems. The framework that links these topologies enables designers to create three-dimensional, multi-axis flexure systems by using "Freedom and Constraint Topologies" (FACT). FACT embodies every possible design solution for parallel flexure systems. This information enables designers to consider every possible design and then select the design that is best suited for a specific application. FACT was created to improve the design processes for small-scale flexure systems and precision machines. For instance, there is a need to create multi-axis nanopositioners for emerging three-dimensional nano-scale research/manufacturing.(cont.) Through this work the following contributions were made: (1) twenty six unique matching pairs of freedom and constraint spaces were identified; (2) it was proven that these spaces embody all possible solutions; (3) a design process was created to guide a designer from design requirements, to freedom spaces, to constraint spaces, to mechanism designs; (4) a sub-process was created to guide designers in the selection of redundant constraints that help satisfy stiffness and symmetry requirements without altering the mechanism's kinematics; (5) mathematical expressions were created to represent the freedom and constraint spaces in a form that enables computers to identify and manipulate them. In this thesis, three case studies are provided to demonstrate the FACT design process for mechanisms of varying complexity: (1) a compliant spherical ball joint, (2) a compliant probe for a five axis STM, and (3) a compliant rotary flexure are designed. The second case study demonstrates the sub-process for selecting redundant constraints.by Jonathan Brigham Hopkins.S.M