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Papers by Noah Cowan

2006 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2006

... Miniature Snake-Like Surgical Robots Robert J. Webster III, ∗ Allison M. Okamura, and Noah J.... more ... Miniature Snake-Like Surgical Robots Robert J. Webster III, ∗ Allison M. Okamura, and Noah J. Cowan Department of Mechanical Engineering The Johns Hopkins University Baltimore, Maryland 21218-2681 ∗ Corresponding Author: robert.webster@jhu.edu ...

Proceedings of the 2005 IEEE International Conference on Robotics and Automation, 2005

Feedback from antennae -long, flexible tactile sensors -enables cockroaches and other arthropods ... more Feedback from antennae -long, flexible tactile sensors -enables cockroaches and other arthropods to rapidly maneuver through poorly lit and cluttered environments. Inspired by their performance, we created a wall-following controller for a dynamic wheeled robot using tactile antenna feedback. We show this controller is stable for a wide range of control gains and robot system parameters. To test the controller, we constructed a two-link antenna that uses potentiometers and capacitive contact sensors. Experiments based on the prototype demonstrate that our controller robustly tracks unexpected corners ranging from −60 • to +90 • .

Lecture Notes in Control and Information Sciences, 2006

The Lateral Leg Spring model (LLS) was developed by Schmitt and Holmes to model the horizontal-pl... more The Lateral Leg Spring model (LLS) was developed by Schmitt and Holmes to model the horizontal-plane dynamics of a running cockroach. The model captures several salient features of real insect locomotion, and demonstrates that horizontal plane locomotion can be passively stabilized by a well-tuned mechanical system, thus requiring minimal neural reflexes. We propose two enhancements to the LLS model. First, we derive the dynamical equations for a more flexible placement of the center of pressure (COP), which enables the model to capture the phase relationship between the body orientation and center-of-mass (COM) heading in a simpler manner than previously possible. Second, we propose a reduced LLS "plant model" and biologically inspired control law that enables the model to follow along a virtual wall, much like antenna-based wall following in cockroaches.

Proceedings of the 2005 IEEE International Conference on Robotics and Automation, 2005

Fine needles facilitate diagnosis and therapy because they enable minimally invasive surgical int... more Fine needles facilitate diagnosis and therapy because they enable minimally invasive surgical interventions. This paper formulates the problem of steering a very flexible needle through firm tissue as a nonholonomic kinematics problem, and demonstrates how planning can be accomplished using diffusion-based motion planning on the Euclidean group, SE(3). In the present formulation, the tissue is treated as isotropic and no obstacles are present. The bevel tip of the needle is treated as a nonholonomic constraint that can be viewed as a 3D extension of the standard kinematic cart or unicycle. A deterministic model is used as the starting point, and reachability criteria are established. A stochastic differential equation and its corresponding Fokker-Planck equation are derived. The Euler-Maruyama method is used to generate the ensemble of reachable states of the needle tip. Inverse kinematics methods developed previously for hyperredundant and binary manipulators that use this probability density information are applied to generate needle tip paths that reach the desired targets.

Proceedings of the 39th IEEE Conference on Decision and Control (Cat. No.00CH37187), 2000

Visual servo controllers in the literature rarely achieve provably large domains of attraction, a... more Visual servo controllers in the literature rarely achieve provably large domains of attraction, and seldom address two important sensor limitations: (i) susceptibility to self-occlusions and (ii) finite field of view (FOV). In this paper, we tackle the problem of global, occlusion-free visual servoing of a fully actuated rigid body by recourse to navigation functions on a compact manifold which encode these restrictions as control obstacles. For occlusion free rigid body servoing, the manifold of interest is the "visible" set of rigid body configurations, that is, those for which the feature points are within the field of view and unoccluded by the body. For a set of coplanar feature points on one face of a convex polyhedron, we show that a slightly conservative subset of the visible set has a simple topology ammenable to analytical construction of a navigation function. We construct the controller via a closed form coordinate transformation from our problem domain into the topological model space and conclude with simulation results.

The Journal of experimental biology, Jan 15, 2014

The integration of information from dynamic sensory structures operating on a moving body is a ch... more The integration of information from dynamic sensory structures operating on a moving body is a challenge for locomoting animals and engineers seeking to design agile robots. As a tactile sensor is a physical linkage mediating mechanical interactions between body and environment, mechanical tuning of the sensor is critical for effective control. We determined the open-loop dynamics of a tactile sensor, specifically the antenna of the American cockroach, Periplaneta americana, an animal that escapes predators by using its antennae during rapid closed-loop tactilely mediated course control. Geometrical measurements and static bending experiments revealed an exponentially decreasing flexural stiffness (EI) from base to tip. Quasi-static experiments with a physical model support the hypothesis that a proximodistally decreasing EI can simplify control by increasing preview distance and allowing effective mapping to a putative control variable--body-to-wall distance--compared with an anten...

2007 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2007

It may come as no surprise that a simple "planar unicycle" (or ... more It may come as no surprise that a simple "planar unicycle" (or "skate") model can successfully follow a wall at high speed under PD-control. What would be surprising is that such a simple control mechanism may underly the control of one of Nature's fastest terrestrial insects, the American cockroach. For this paper, we implemented the same controller (up to scale)

Springer Tracts in Advanced Robotics, 2005

Inspired by nature's effective use of tactile feedback for rapid maneuvering, we designed a passi... more Inspired by nature's effective use of tactile feedback for rapid maneuvering, we designed a passive, highly compliant tactile sensor for Sprawlette, a hexapedal running robot. To bridge the gap between biology and design, we took initial steps toward understanding how the cockroach, Periplaneta americana, uses antenna feedback to control its orientation during a rapid wall following behavior. First, we developed a simple template model for antenna-based wall following. Second, we collected initial cockroach data that supports the idea that the rate of convergence to the wall or "tactile flow" is being used, in part, for controlling body orientation. Based on these steps, we designed and calibrated a prototype tactile sensor to measure Sprawlette's angle and distance relative to a straight wall, and employed a simple bio-inspired control law that can stabilize the template dynamics. Finally, we integrated the sensor and controller on Sprawlette and showed empirically that stabilizing Sprawlette during wall following does indeed require tactile flow, as predicted. Sensorized, compliant antenna Hexapedal Running Robot, Sprawlette 2.5cm

Springer Tracts in Advanced Robotics, 2003

This paper presents a global diffeomorphism from a suitably defined "visible set&quo... more This paper presents a global diffeomorphism from a suitably defined "visible set" of rigid body configurations ù a subset of SE(3) ù to an imagespace. The mapping between the visible set and the image-space is given by the projection of a set of features of a specially designed visual target. The target is a sphere marked with a feature point

International Conference on Robotics and Automation, 1999

We describe a hybrid planar image-based servo al- gorithm which, for a simplied planar convex rig... more We describe a hybrid planar image-based servo al- gorithm which, for a simplied planar convex rigid body, converges to a static goal for all initial condi- tions within the workspace of the camera. This is achieved using the sequential composition of a palette of continuous image based controllers. Each sub- controller, based on a specied set of collinear feature points,

Uncertainty in Artificial Intelligence, 2003

The task of estimating the gradient of a func- tion in the presence of noise is central to severa... more The task of estimating the gradient of a func- tion in the presence of noise is central to several forms of reinforcement learning, in- cluding policy search methods. We present two techniques for reducing gradient estima- tion errors in the presence of observable in- put noise applied to the control signal. The first method extends the idea of a reinforce-

Lecture Notes in Control and Information Sciences, 2010

... John P. Swensen and Noah J. Cowan Department of Mechanical Engineering, Johns Hopkins Univers... more ... John P. Swensen and Noah J. Cowan Department of Mechanical Engineering, Johns Hopkins University, 3400 North Charles Street ... 24 JP Swensen, V. Kallem, and NJ Cowan ... To aid the reader in understanding the basics of KBVS, we describe the details of the algorithm in a ...

2008 2nd IEEE RAS & EMBS International Conference on Biomedical Robotics and Biomechatronics, 2008

Flexible, tip-steerable needles promise to enhance physicians' abilities to accurately reach targ... more Flexible, tip-steerable needles promise to enhance physicians' abilities to accurately reach targets and maneuver inside the human body while minimizing patient trauma. Here, we present a functional needle steering system that integrates two components: (1) a patient-specific 2D preand intra-operative planner that finds an achievable route to a target within a planar slice of tissue (Stochastic Motion Roadmap), and (2) a low-level image-guided feedback controller that keeps the needle tip within that slice. The planner generates a sequence of circular arcs that can be realized by interleaving pure insertions with 180° rotations of the needle shaft. This preplanned sequence is updated in realtime at regular intervals. Concurrently, the low-level image-based controller servos the needle to remain close to the desired plane between plan updates. Both planner and controller are predicated on a previously developed kinematic nonholonomic model of bevel-tip needle steering. We use slighly different needles here that have a small bend near the tip, so we extend the model to account for discontinuities of the tip position caused by 180° rotations. Further, during large rotations of the needle base, we maintain the desired tip angle by compensating for torsional compliance in the needle shaft, neglected in previous needle steering work. By integrating planning, control, and torsion compensation, we demonstrate both accurate targeting and obstacle avoidance.

2007 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2007

Lie group symmetry in a mechanical system can lead to a dimensional reduction in its dynamical eq... more Lie group symmetry in a mechanical system can lead to a dimensional reduction in its dynamical equations. Typically, the symmetries that one exploits are intrinsic to the mechanical system at hand, e.g. invariance of the system's Lagrangian to some group of motions. In the present work we consider symmetries that arise from an extrinsic control task, rather than the intrinsic structure of configuration space, constraints, or system dynamics. We illustrate this technique with several examples. In the examples, the reduction enables us to design essentially global feedback controllers on the reduced systems.

Proceedings 2007 IEEE International Conference on Robotics and Automation, 2007

Physicians perform percutaneous therapies in many diagnostic and therapeutic procedures. Image gu... more Physicians perform percutaneous therapies in many diagnostic and therapeutic procedures. Image guidance promises to improve targeting accuracy and broaden the scope of needle interventions. In this paper, we consider the possibility of automating the guidance of a flexible bevel-tip needle as it is inserted into human tissue. We build upon a previously proposed nonholonomic kinematic model to develop a nonlinear observer-based controller. As a first step for control, we show that flexible needles can be automatically controlled to remain within a planar slice of tissue as they are inserted by a physician; our approach keeps the physician in the loop to control insertion speed. In the proposed controller, the distance of the needle tip position from the plane of interest is used as a feedback signal. Numerical simulations demonstrate the stability and robustness of the controller in the face of parametric uncertainty. We also present results from pilot physical experiments with phantom tissue under stereo image guidance.

2008 IEEE International Conference on Robotics and Automation, 2008

Active cannulas are remotely actuated thin continuum robots with the potential to traverse narrow... more Active cannulas are remotely actuated thin continuum robots with the potential to traverse narrow and winding environments without relying on "guiding" environmental reaction forces. These features seem ideal for procedures requiring passage through narrow openings to access air-filled cavities (e.g. surgery in the throat and lung). Composed of telescoping concentric pre-curved elastic tubes, an active cannula is actuated at its base by translation and axial rotation of component tubes. Using minimum energy principles and Lie Group theory, we present a framework for the kinematics of multi-link active cannulas. This framework permits testing of the hypothesis that overall cannula shape locally minimizes stored elastic energy. We evaluate in particular whether the torsional energy in the long, straight transmission between actuators and the curved sections is important. Including torsion in the kinematic model enables us to analytically predict experimentally observed bifurcation in the energy landscape. Independent calibration procedures based on bifurcation and tip and feature positions enable model parameter identification, producing results near ranges expected from tube material properties and geometry. Experimental results validate the kinematic framework and demonstrate the importance of modeling torsional effects in order to describe bifurcation and accurately predict active cannula shape.

Springer Tracts in Advanced Robotics, 2009

We present an algorithm for SLAM on planar graphs. We assume that a robot moves from node to node... more We present an algorithm for SLAM on planar graphs. We assume that a robot moves from node to node on the graph using odometry to measure the distance between consecutive landmark observations. At each node, the robot follows a branch chosen at random, without reporting which branch it follows. A low-level process detects (with some uncertainty) the presence of landmarks, such as corners, branches, and bumps, but only triggers a binary flag for landmark detection (i.e., the robot is oblivious to the details or "appearance" of the landmark). Under uncertainties of the robot's odometry, landmark detection, and the current landmark position of the robot, we present an E-M-based SLAM algorithm for two cases: (1) known, arbitrary topology with unknown edge lengths and (2) unknown topology, but restricted to "elementary" 1-and 2-cycle graphs. In the latter case, the algorithm (flexibly and reversibly) closes loops and allows for dynamic environments (adding and deleting nodes).

2007 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2007

Traditionally, visual servoing is separated into tracking and control subsystems. This separation... more Traditionally, visual servoing is separated into tracking and control subsystems. This separation, though convenient, is not necessarily well justified. When tracking and control strategies are designed independently, it is not clear how to optimize them to achieve a certain task. In this work, we propose a framework in which spatial sampling kernels -borrowed from the tracking and registration literatureare used to design feedback controllers for visual servoing. The use of spatial sampling kernels provides natural hooks for Lyapunov theory, thus unifying tracking and control and providing a framework for optimizing a particular servoing task.

Springer Tracts in Advanced Robotics, 2009

Active cannulas, so named because of their potential medical applications, are a new class of con... more Active cannulas, so named because of their potential medical applications, are a new class of continuum robots consisting of precurved, telescoping, elastic tubes. As individual component tubes are actuated at the base relative to one another, an active cannula changes shape to minimize stored elastic energy. For the first time, we derive the differential kinematics of a general n tube active cannula while accounting for torsional compliance, which can strongly affect the accuracy of robot tip pose prediction. Our derivation makes several explicit assumptions that have never been vetted for a robotic task, so we experimentally validate the Jacobian using a three-link prototype in a simple stereo visual servoing scheme. Our visual servoing experiments validate the Jacobian and also demonstrate the feasibility of using active cannulas under image guidance-a key step toward realizing their potential to reach dexterously through small, winding environments, which is of particular importance in medical applications.

2006 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2006

... Miniature Snake-Like Surgical Robots Robert J. Webster III, ∗ Allison M. Okamura, and Noah J.... more ... Miniature Snake-Like Surgical Robots Robert J. Webster III, ∗ Allison M. Okamura, and Noah J. Cowan Department of Mechanical Engineering The Johns Hopkins University Baltimore, Maryland 21218-2681 ∗ Corresponding Author: robert.webster@jhu.edu ...

Proceedings of the 2005 IEEE International Conference on Robotics and Automation, 2005

Feedback from antennae -long, flexible tactile sensors -enables cockroaches and other arthropods ... more Feedback from antennae -long, flexible tactile sensors -enables cockroaches and other arthropods to rapidly maneuver through poorly lit and cluttered environments. Inspired by their performance, we created a wall-following controller for a dynamic wheeled robot using tactile antenna feedback. We show this controller is stable for a wide range of control gains and robot system parameters. To test the controller, we constructed a two-link antenna that uses potentiometers and capacitive contact sensors. Experiments based on the prototype demonstrate that our controller robustly tracks unexpected corners ranging from −60 • to +90 • .

Lecture Notes in Control and Information Sciences, 2006

The Lateral Leg Spring model (LLS) was developed by Schmitt and Holmes to model the horizontal-pl... more The Lateral Leg Spring model (LLS) was developed by Schmitt and Holmes to model the horizontal-plane dynamics of a running cockroach. The model captures several salient features of real insect locomotion, and demonstrates that horizontal plane locomotion can be passively stabilized by a well-tuned mechanical system, thus requiring minimal neural reflexes. We propose two enhancements to the LLS model. First, we derive the dynamical equations for a more flexible placement of the center of pressure (COP), which enables the model to capture the phase relationship between the body orientation and center-of-mass (COM) heading in a simpler manner than previously possible. Second, we propose a reduced LLS "plant model" and biologically inspired control law that enables the model to follow along a virtual wall, much like antenna-based wall following in cockroaches.

Proceedings of the 2005 IEEE International Conference on Robotics and Automation, 2005

Fine needles facilitate diagnosis and therapy because they enable minimally invasive surgical int... more Fine needles facilitate diagnosis and therapy because they enable minimally invasive surgical interventions. This paper formulates the problem of steering a very flexible needle through firm tissue as a nonholonomic kinematics problem, and demonstrates how planning can be accomplished using diffusion-based motion planning on the Euclidean group, SE(3). In the present formulation, the tissue is treated as isotropic and no obstacles are present. The bevel tip of the needle is treated as a nonholonomic constraint that can be viewed as a 3D extension of the standard kinematic cart or unicycle. A deterministic model is used as the starting point, and reachability criteria are established. A stochastic differential equation and its corresponding Fokker-Planck equation are derived. The Euler-Maruyama method is used to generate the ensemble of reachable states of the needle tip. Inverse kinematics methods developed previously for hyperredundant and binary manipulators that use this probability density information are applied to generate needle tip paths that reach the desired targets.

Proceedings of the 39th IEEE Conference on Decision and Control (Cat. No.00CH37187), 2000

Visual servo controllers in the literature rarely achieve provably large domains of attraction, a... more Visual servo controllers in the literature rarely achieve provably large domains of attraction, and seldom address two important sensor limitations: (i) susceptibility to self-occlusions and (ii) finite field of view (FOV). In this paper, we tackle the problem of global, occlusion-free visual servoing of a fully actuated rigid body by recourse to navigation functions on a compact manifold which encode these restrictions as control obstacles. For occlusion free rigid body servoing, the manifold of interest is the "visible" set of rigid body configurations, that is, those for which the feature points are within the field of view and unoccluded by the body. For a set of coplanar feature points on one face of a convex polyhedron, we show that a slightly conservative subset of the visible set has a simple topology ammenable to analytical construction of a navigation function. We construct the controller via a closed form coordinate transformation from our problem domain into the topological model space and conclude with simulation results.

The Journal of experimental biology, Jan 15, 2014

The integration of information from dynamic sensory structures operating on a moving body is a ch... more The integration of information from dynamic sensory structures operating on a moving body is a challenge for locomoting animals and engineers seeking to design agile robots. As a tactile sensor is a physical linkage mediating mechanical interactions between body and environment, mechanical tuning of the sensor is critical for effective control. We determined the open-loop dynamics of a tactile sensor, specifically the antenna of the American cockroach, Periplaneta americana, an animal that escapes predators by using its antennae during rapid closed-loop tactilely mediated course control. Geometrical measurements and static bending experiments revealed an exponentially decreasing flexural stiffness (EI) from base to tip. Quasi-static experiments with a physical model support the hypothesis that a proximodistally decreasing EI can simplify control by increasing preview distance and allowing effective mapping to a putative control variable--body-to-wall distance--compared with an anten...

2007 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2007

It may come as no surprise that a simple "planar unicycle" (or ... more It may come as no surprise that a simple "planar unicycle" (or "skate") model can successfully follow a wall at high speed under PD-control. What would be surprising is that such a simple control mechanism may underly the control of one of Nature's fastest terrestrial insects, the American cockroach. For this paper, we implemented the same controller (up to scale)

Springer Tracts in Advanced Robotics, 2005

Inspired by nature's effective use of tactile feedback for rapid maneuvering, we designed a passi... more Inspired by nature's effective use of tactile feedback for rapid maneuvering, we designed a passive, highly compliant tactile sensor for Sprawlette, a hexapedal running robot. To bridge the gap between biology and design, we took initial steps toward understanding how the cockroach, Periplaneta americana, uses antenna feedback to control its orientation during a rapid wall following behavior. First, we developed a simple template model for antenna-based wall following. Second, we collected initial cockroach data that supports the idea that the rate of convergence to the wall or "tactile flow" is being used, in part, for controlling body orientation. Based on these steps, we designed and calibrated a prototype tactile sensor to measure Sprawlette's angle and distance relative to a straight wall, and employed a simple bio-inspired control law that can stabilize the template dynamics. Finally, we integrated the sensor and controller on Sprawlette and showed empirically that stabilizing Sprawlette during wall following does indeed require tactile flow, as predicted. Sensorized, compliant antenna Hexapedal Running Robot, Sprawlette 2.5cm

Springer Tracts in Advanced Robotics, 2003

This paper presents a global diffeomorphism from a suitably defined "visible set&quo... more This paper presents a global diffeomorphism from a suitably defined "visible set" of rigid body configurations ù a subset of SE(3) ù to an imagespace. The mapping between the visible set and the image-space is given by the projection of a set of features of a specially designed visual target. The target is a sphere marked with a feature point

International Conference on Robotics and Automation, 1999

We describe a hybrid planar image-based servo al- gorithm which, for a simplied planar convex rig... more We describe a hybrid planar image-based servo al- gorithm which, for a simplied planar convex rigid body, converges to a static goal for all initial condi- tions within the workspace of the camera. This is achieved using the sequential composition of a palette of continuous image based controllers. Each sub- controller, based on a specied set of collinear feature points,

Uncertainty in Artificial Intelligence, 2003

The task of estimating the gradient of a func- tion in the presence of noise is central to severa... more The task of estimating the gradient of a func- tion in the presence of noise is central to several forms of reinforcement learning, in- cluding policy search methods. We present two techniques for reducing gradient estima- tion errors in the presence of observable in- put noise applied to the control signal. The first method extends the idea of a reinforce-

Lecture Notes in Control and Information Sciences, 2010

... John P. Swensen and Noah J. Cowan Department of Mechanical Engineering, Johns Hopkins Univers... more ... John P. Swensen and Noah J. Cowan Department of Mechanical Engineering, Johns Hopkins University, 3400 North Charles Street ... 24 JP Swensen, V. Kallem, and NJ Cowan ... To aid the reader in understanding the basics of KBVS, we describe the details of the algorithm in a ...

2008 2nd IEEE RAS & EMBS International Conference on Biomedical Robotics and Biomechatronics, 2008

Flexible, tip-steerable needles promise to enhance physicians' abilities to accurately reach targ... more Flexible, tip-steerable needles promise to enhance physicians' abilities to accurately reach targets and maneuver inside the human body while minimizing patient trauma. Here, we present a functional needle steering system that integrates two components: (1) a patient-specific 2D preand intra-operative planner that finds an achievable route to a target within a planar slice of tissue (Stochastic Motion Roadmap), and (2) a low-level image-guided feedback controller that keeps the needle tip within that slice. The planner generates a sequence of circular arcs that can be realized by interleaving pure insertions with 180° rotations of the needle shaft. This preplanned sequence is updated in realtime at regular intervals. Concurrently, the low-level image-based controller servos the needle to remain close to the desired plane between plan updates. Both planner and controller are predicated on a previously developed kinematic nonholonomic model of bevel-tip needle steering. We use slighly different needles here that have a small bend near the tip, so we extend the model to account for discontinuities of the tip position caused by 180° rotations. Further, during large rotations of the needle base, we maintain the desired tip angle by compensating for torsional compliance in the needle shaft, neglected in previous needle steering work. By integrating planning, control, and torsion compensation, we demonstrate both accurate targeting and obstacle avoidance.

2007 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2007

Lie group symmetry in a mechanical system can lead to a dimensional reduction in its dynamical eq... more Lie group symmetry in a mechanical system can lead to a dimensional reduction in its dynamical equations. Typically, the symmetries that one exploits are intrinsic to the mechanical system at hand, e.g. invariance of the system's Lagrangian to some group of motions. In the present work we consider symmetries that arise from an extrinsic control task, rather than the intrinsic structure of configuration space, constraints, or system dynamics. We illustrate this technique with several examples. In the examples, the reduction enables us to design essentially global feedback controllers on the reduced systems.

Proceedings 2007 IEEE International Conference on Robotics and Automation, 2007

Physicians perform percutaneous therapies in many diagnostic and therapeutic procedures. Image gu... more Physicians perform percutaneous therapies in many diagnostic and therapeutic procedures. Image guidance promises to improve targeting accuracy and broaden the scope of needle interventions. In this paper, we consider the possibility of automating the guidance of a flexible bevel-tip needle as it is inserted into human tissue. We build upon a previously proposed nonholonomic kinematic model to develop a nonlinear observer-based controller. As a first step for control, we show that flexible needles can be automatically controlled to remain within a planar slice of tissue as they are inserted by a physician; our approach keeps the physician in the loop to control insertion speed. In the proposed controller, the distance of the needle tip position from the plane of interest is used as a feedback signal. Numerical simulations demonstrate the stability and robustness of the controller in the face of parametric uncertainty. We also present results from pilot physical experiments with phantom tissue under stereo image guidance.

2008 IEEE International Conference on Robotics and Automation, 2008

Active cannulas are remotely actuated thin continuum robots with the potential to traverse narrow... more Active cannulas are remotely actuated thin continuum robots with the potential to traverse narrow and winding environments without relying on "guiding" environmental reaction forces. These features seem ideal for procedures requiring passage through narrow openings to access air-filled cavities (e.g. surgery in the throat and lung). Composed of telescoping concentric pre-curved elastic tubes, an active cannula is actuated at its base by translation and axial rotation of component tubes. Using minimum energy principles and Lie Group theory, we present a framework for the kinematics of multi-link active cannulas. This framework permits testing of the hypothesis that overall cannula shape locally minimizes stored elastic energy. We evaluate in particular whether the torsional energy in the long, straight transmission between actuators and the curved sections is important. Including torsion in the kinematic model enables us to analytically predict experimentally observed bifurcation in the energy landscape. Independent calibration procedures based on bifurcation and tip and feature positions enable model parameter identification, producing results near ranges expected from tube material properties and geometry. Experimental results validate the kinematic framework and demonstrate the importance of modeling torsional effects in order to describe bifurcation and accurately predict active cannula shape.

Springer Tracts in Advanced Robotics, 2009

We present an algorithm for SLAM on planar graphs. We assume that a robot moves from node to node... more We present an algorithm for SLAM on planar graphs. We assume that a robot moves from node to node on the graph using odometry to measure the distance between consecutive landmark observations. At each node, the robot follows a branch chosen at random, without reporting which branch it follows. A low-level process detects (with some uncertainty) the presence of landmarks, such as corners, branches, and bumps, but only triggers a binary flag for landmark detection (i.e., the robot is oblivious to the details or "appearance" of the landmark). Under uncertainties of the robot's odometry, landmark detection, and the current landmark position of the robot, we present an E-M-based SLAM algorithm for two cases: (1) known, arbitrary topology with unknown edge lengths and (2) unknown topology, but restricted to "elementary" 1-and 2-cycle graphs. In the latter case, the algorithm (flexibly and reversibly) closes loops and allows for dynamic environments (adding and deleting nodes).

2007 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2007

Traditionally, visual servoing is separated into tracking and control subsystems. This separation... more Traditionally, visual servoing is separated into tracking and control subsystems. This separation, though convenient, is not necessarily well justified. When tracking and control strategies are designed independently, it is not clear how to optimize them to achieve a certain task. In this work, we propose a framework in which spatial sampling kernels -borrowed from the tracking and registration literatureare used to design feedback controllers for visual servoing. The use of spatial sampling kernels provides natural hooks for Lyapunov theory, thus unifying tracking and control and providing a framework for optimizing a particular servoing task.

Springer Tracts in Advanced Robotics, 2009

Active cannulas, so named because of their potential medical applications, are a new class of con... more Active cannulas, so named because of their potential medical applications, are a new class of continuum robots consisting of precurved, telescoping, elastic tubes. As individual component tubes are actuated at the base relative to one another, an active cannula changes shape to minimize stored elastic energy. For the first time, we derive the differential kinematics of a general n tube active cannula while accounting for torsional compliance, which can strongly affect the accuracy of robot tip pose prediction. Our derivation makes several explicit assumptions that have never been vetted for a robotic task, so we experimentally validate the Jacobian using a three-link prototype in a simple stereo visual servoing scheme. Our visual servoing experiments validate the Jacobian and also demonstrate the feasibility of using active cannulas under image guidance-a key step toward realizing their potential to reach dexterously through small, winding environments, which is of particular importance in medical applications.