Louis L. Whitcomb

Design of a novel MRI compatible manipulator for image guided prostate interventions

This paper reports a novel remotely actuated manipulator for access to prostate tissue under magnetic resonance imaging guidance (APT-MRI) device, designed for use in a standard high-field MRI scanner. The device provides three-dimensional MRI guided needle placement with millimeter accuracy under physician control. Procedures enabled by this device include MRI guided needle biopsy, fiducial marker placements, and therapy delivery. Its compact size allows for use in both standard cylindrical and open configuration MRI scanners. Preliminary in vivo canine experiments and first clinical trials are reported.

Comparative experiments with a new adaptive controller for robot arms

A model-based adaptive controller and proof of its global asymptotic stability with respect to the standard rigid-body model of robot-arm dynamics are presented. Experimental data from a study of one new and several established globally asymptotically stable adaptive controllers on two very different robot arms: (1) demonstrate the superior tracking performance afforded by the model-based algorithms over conventional PD control; (2) demonstrate and compare the superior performance of adaptive model-based algorithms over their nonadaptive counterparts; (3) reconcile several previous contrasting empirical studies; and (4) examine contexts that compromise their advantage. >

A Modular Surgical Robotic System for Image Guided Percutaneous Procedures

This paper presents a robotic system for precise needle insertion under radiological guidance for surgical interventions and for delivery of therapy. It is extremely compact and is compatible with portable X-ray units and computer tomography scanners. The system presents a modular structure comprising a global positioning module, a miniature robotic module, and a radiolucent needle driver module. This system is the newest member of a growing family of modular surgical robots under development. The system may be operated stand-alone under joystick control making it readily adaptable to any operating room, or under full image guided computer control.

Underwater robotics: out of the research laboratory and into the field

The development of two new classes of commercial underwater robotic vehicles-deep diving work-class remotely operated vehicles and survey-class autonomous vehicles-is being driven by the needs of deep water oil production and deep ocean telecommunication cable operations. The paper presents a survey of the present state and future directions of commercial underwater robotics, examines principal technical challenges, and outlines new enabling technologies for commercial underwater robotic vehicles.

Adaptive force control of position/velocity controlled robots: theory and experiment

This paper addresses the problem of achieving exact dynamic force control with manipulators possessing low-level position and/or velocity controllers typically employed in industrial robot arms. Previously reported approaches and experimental results are reviewed. A new adaptive force control algorithm for velocity/position controlled robot arms in contact with surfaces of unknown linear compliance is reported. The controller provably guarantees global asymptotic convergence of force trajectory tracking errors to zero when the robot is under exact or asymptotically exact inner loop velocity control. An additional result which guarantees arbitrarily small force errors for bounded inner loop velocity tracking errors is presented. Comparative experiments show the new adaptive velocity (position) based controller and its nonadaptive counterpart to provide performance superior to that of previously reported position-based force controllers.

A miniature microsurgical instrument tip force sensor for enhanced force feedback during robot-assisted manipulation

This paper reports the development of a new miniature force sensor designed to measure contact forces at the tip of a microsurgical instrument in three dimensions, and its application to scaled force feedback using a cooperatively manipulated microsurgical assistant robot. The principal features of the sensor are its small size of 12.5 mm in diameter and 15 mm in height, a novel configuration of flexure beams and strain gauges in order to measure forces isotropically at the instrument tip 40 mm from the sensor body, and sub-mN three-axis force-sensing resolution.

Advances in Doppler-based navigation of underwater robotic vehicles

New low-cost commercially available bottom-lock Doppler sonars can augment or replace the acoustic time-of-flight navigation systems commonly employed for three-dimensional underwater robot vehicle navigation. The paper first reviews conventional techniques for underwater vehicle navigation, and describes a Doppler-based navigation system developed by the authors. Second, we identify principal limitations to the bottom-track precision of Doppler based navigation systems. Third, we analyze the effect of heading-sensor errors on Doppler bottom-track precision. Experimental results compare bottom-track error resulting from a Doppler navigation using low-precision magnetic heading sensor with bottom-track error resulting from a high-precision a ring-laser gyroscope. The experiments were conducted during a field deployment in which the new robot navigation system enabled precision acoustic and optical survey as well as minimally invasive object recovery from hydrothermal vents in the Guaymas Basin, Gulf of California at 27/spl deg/N 111.5/spl deg/W, at 2000 m depth.

Development, comparison, and preliminary experimental validation of nonlinear dynamic thruster models

This paper examines dynamical models for bladed-propeller-type marine thrusters. Previously reported thruster dynamics models are reviewed, and a simplified model is proposed. Experimental testing of both the transient and steady-state performance of a marine thruster corroborates previously reported data, validates the simplified thruster model, and raises new questions. A companion paper reports preliminary experiments in the design and testing of thrust controllers which incorporate the dynamical thruster models described in the present paper.

Experimental Results in Synchronous-Clock One-Way-Travel-Time Acoustic Navigation for Autonomous Underwater Vehicles

This paper reports recent experimental results in the development and deployment of a synchronous-clock acoustic navigation system suitable for the simultaneous navigation of multiple underwater vehicles. The goal of this work is to enable the task of navigating multiple autonomous underwater vehicles (AUVs) over length scales of O(100 km), while maintaining error tolerances commensurate with conventional long-baseline transponder-based navigation systems (i.e., O(1 m)), but without the requisite need for deploying, calibrating, and recovering seafloor anchored acoustic transponders. Our navigation system is comprised of an acoustic modem-based communication/navigation system that allows for onboard navigational data to be broadcast as a data packet by a source node, and for all passively receiving nodes to be able to decode the data packet to obtain a one-way travel time pseudo-range measurement and ephemeris data. We present results for two different field experiments using a two-node configuration consisting of a global positioning system (GPS) equipped surface ship acting as a global navigation aid to a Doppler-aided AUV. In each experiment, vehicle position was independently corroborated by other standard navigation means. Initial results for a maximum-likelihood sensor fusion framework are reported.

Diverse styles of submarine venting on the ultraslow spreading Mid-Cayman Rise

Thirty years after the first discovery of high-temperature submarine venting, the vast majority of the global mid-ocean ridge remains unexplored for hydrothermal activity. Of particular interest are the world’s ultraslow spreading ridges that were the last to be demonstrated to host high-temperature venting but may host systems particularly relevant to prebiotic chemistry and the origins of life. Here we report evidence for previously unknown, diverse, and very deep hydrothermal vents along the ∼110 km long, ultraslow spreading Mid-Cayman Rise (MCR). Our data indicate that the MCR hosts at least three discrete hydrothermal sites, each representing a different type of water-rock interaction, including both mafic and ultramafic systems and, at ∼5,000 m, the deepest known hydrothermal vent. Although submarine hydrothermal circulation, in which seawater percolates through and reacts with host lithologies, occurs on all mid-ocean ridges, the diversity of vent types identified here and their relative geographic isolation make the MCR unique in the oceans. These new sites offer prospects for an expanded range of vent-fluid compositions, varieties of abiotic organic chemical synthesis and extremophile microorganisms, and unparalleled faunal biodiversity—all in close proximity.