This paper presents a new class of thin, dexterous continuum robots, which we call active cannulas due to their potential medical applications. An active cannula is composed of telescoping, concentric, precurved superelastic tubes that can be axially translated and rotated at the base relative to one another. Active cannulas derive bending not from tendon wires or other external mechanisms but from elastic tube interaction in the backbone itself, permitting high dexterity and small size, and dexterity improves with miniaturization. They are designed to traverse narrow and winding environments without relying on ldquoguidingrdquo environmental reaction forces. These features seem ideal for a variety of applications where a very thin robot with tentacle-like dexterity is needed. In this paper, we apply beam mechanics to obtain a kinematic model of active cannula shape and describe design tools that result from the modeling process. After deriving general equations, we apply them to a simple three-link active cannula. Experimental results illustrate the importance of including torsional effects and the ability of our model to predict energy bifurcation and active cannula shape.

Mechanics of Precurved-Tube Continuum Robots

This paper reports some recent analysis and modeling results obtained while developing a tele-robotic system for minimally invasive surgery of the throat. One of the main enabling components of this system is a Distal Dexterity Unit that implements a novel design using a flexible multi-backbone snake-like unit with actuation redundancy and push-pull actuation. The design of this snake-like unit is compared to other alternative designs that use a single flexible-backbone and wire-actuation. A unified kinematic and virtual work model is used to perform this comparison between a multi-backbone snake like unit with an equal-diameter snake-like unit using a single flexible backbone and wire actuation. The comparison is presented for several actuation redundancy resolutions that minimize the load on the flexible backbones. The results show that the multi-backbone design is superior to the alternative wire-actuated designs using a single flexible backbone. The advantages manifest in smaller required actuation forces on the backbones and, as a result, a reduced risk of buckling of the backbones and enhanced potential downsize scalability.

/pdf/snake-like-units-using-flexible-backbones-and-actuation-2py7qh8oyj.pdf

Snake-Like Units Using Flexible Backbones and Actuation Redundancy for Enhanced Miniaturization

This paper describes a spatial-motion-constraints-generation approach for a human-machine collaborative surgical-assistant system from registered computer tomography models. We extend constrained optimization formulation incorporating task goals, anatomy-based constraints, "no fly zones," etc. We use a fast potential-collision-constraint-detection method based on a 3-D surface model and covariance tree data structure. These boundary constraints, along with task behaviors and joint limits, serve as constraint conditions for constrained robot control. We are able to follow a complex path inside a human skull, phantom represented by a surface model composed of 99 000 vertices and 182 000 triangles in real time. Our approach enables real-time task-based control of a surgical robot in a precise interactive minimally invasive surgery task. We illustrate our approach based on two example tasks which are analogous to the procedures in endoscopic sinus surgery, and analyze the user's performance on both teleoperation and cooperative control for one of the example tasks. The experimental results show that a robotic assistant employing our approach on spatial motion constraints can assist the user in skilled manipulation tasks, while maintaining desired properties. Our approach is equally applicable to teleoperative and cooperative controlled robots

/pdf/spatial-motion-constraints-using-virtual-fixtures-generated-41kkvbodk9.pdf

Spatial Motion Constraints Using Virtual Fixtures Generated by Anatomy

Minimally invasive surgery (MIS) is an increasingly important approach in many specialties, where robots are poised to play an important role in displacing the limits set to such techniques through increased precision and dexterity. However, the potential of robotically assisted minimally invasive surgery (RMIS) is still far from being fully exploited because of the newness of the approach. One of the best immediate solutions to remedy this discrepancy is through a more efficient preparation of the intervention. This paper presents a two-step strategy to optimize the most critical settings of an RMIS intervention, namely, the port placement (incision sites for minimally invasive access) and the pose of the robot (initial configuration of stationary joints). The first step relies on a patient-dependent modeling of the intervention by the surgeon that is transformed into an optimization problem where criteria such as visibility and dexterity serve as a cost function. The second one, referred to as the pose planning problem, aims at guaranteeing a collision-free operation of the robot throughout the intervention, by properly assigning stationary extra flexibility at the beginning of the intervention, under the constraint of ensuring the fixed positions of the minimally invasive port access.

Optimal planning for minimally invasive surgical robots

In this paper we develop a new framework for path planning of flexible needles with bevel tips. Based on a stochastic model of needle steering, the probability density function for the needle-tip pose is approximated as a Gaussian. The means and covariances are estimated using an error propagation algorithm which has second-order accuracy. Then we adapt the path-of-probability (POP) algorithm to path planning of flexible needles with bevel tips. We demonstrate how our planning algorithm can be used for feedback control of flexible needles. We also derive a closed-form solution for the port placement problem for finding good insertion locations for flexible needles in the case when there are no obstacles. Furthermore, we propose a new method using reference splines with the POP algorithm to solve the path planning problem for flexible needles in more general cases that include obstacles.

/pdf/the-path-of-probability-algorithm-for-steering-and-feedback-47zfp2j2gp.pdf

The Path-of-probability Algorithm for Steering and Feedback Control of Flexible Needles

Properly selected port sites for robot-assisted coronary artery bypass graft (CABG) improve the efficiency and quality of these procedures. In clinical practice, surgeons select port locations using external anatomic landmarks to estimate a patient's internal anatomy. This paper proposes an automated approach to port selection based on a preoperative image of the patient, thus avoiding the need to estimate internal anatomy. Using this image as input, port sites are chosen from a grid of surgeon-approved options by defining a performance measure for each possible port triad. This measure seeks to minimize the weighted squared deviation of the instrument and endoscope angles from their optimal orientations at each internal surgical site. This performance measure proves insensitive to perturbations in both its weighting factors and moderate intraoperative displacements of the patient's internal anatomy. A validation study of this port site selection algorithm was also performed. Six cardiac surgeons dissected model vessels using the port triad selected by this algorithm with performance compared to dissection using a surgeon-selected port triad and a port triad template described by Tabaie et al., 1999. With the algorithm-selected ports, dissection speed increased by up to 43% (p = 0.046) with less overall vessel trauma. Thus, this algorithmic approach to port site selection has important clinical implications for robot-assisted CABG which warrant further investigation.

/pdf/port-placement-planning-in-robot-assisted-coronary-artery-52o509dbwq.pdf

Port placement planning in robot-assisted coronary artery bypass

A computer-based algorithm has been developed which uses preoperative images to provide a surgeon with a list of feasible port triplets ranked according to tool dexterity and endoscopic view quality at each surgical site involved in a procedure. A computer simulation allows the surgeon to select from among the proposed port locations. The procedure selected for the development of the system consists of a coronary artery bypass graft (CABG). In this procedure, the interior mammary artery (IMA) is mobilized from the interior chest wall, and one end is attached to the coronary arteries to provide a new blood supply for the heart. Approximately 10-20 cm is dissected free, using blunt dissection and a harmonic scalpel or electrocautery. At present, the port placement system is being evaluated in clinical trials.

/pdf/dexterity-optimization-by-port-placement-in-robot-assisted-1ja51n59oc.pdf

Dexterity optimization by port placement in robot-assisted minimally invasive surgery

A computer-based algorithm is being developed which, using preoperative images, provides the surgeon with a list of feasible port triplets ranked according to tool dexterity and endoscope view quality at each surgical site involved in a procedure. Computer simulation will allow the surgeon to select from among the proposed port locations. The procedure selected for the development of the system consists of left internal mammary artery (LIMA) take-down and bypass grafting. Human trials will begin within a month. Data collected from these trials will be used to validate the system.

/pdf/optimal-port-placement-in-robot-assisted-coronary-artery-2yb3vpu0ql.pdf

Optimal Port Placement in Robot-Assisted Coronary Artery Bypass Grafting

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Papers

Port placement planning in robot-assisted coronary artery bypass

Dexterity optimization by port placement in robot-assisted minimally invasive surgery

Optimal Port Placement in Robot-Assisted Coronary Artery Bypass Grafting