Toward Active Cannulas:

Proceedings of the 2006 IEEE/RSJ International Conference on Intelligent Robots and Systems October 9 - 15, 2006, Beijing, China

Toward Active Cannulas: 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

Abstract— We have developed a new class of continuously flexible snake-like robots, called active cannulas, that consist of several telescoping pre-curved superelastic tubes. The devices derive bending actuation not from tendon wires or other external mechanisms, but from elastic energy stored in the backbone itself. This allows active cannulas to have a small diameter and a high degree ofdexterity, which should enable them to navigate through complex anatomy to sites inaccessible by current surgical robotic devices. Active cannulas may also enhance patient safety because their inherent compliance mitigates potential trauma from inadvertent tool-tissue collision. A consequence of our design is that dexterity improves with miniaturization. A kinematic description of active cannulashape requires a model of the elastic interaction of telescoping pre-curved flexible tubes, and we derive a two“link” beam mechanics-based model. Experiments using curved nitinol tubes and wires validate the model.

I. I NTRODUCTION While the minimally invasive surgery (MIS) revolution has profoundly improved a variety of surgical interventions, many diseases lack viable MIS alternatives becauseinstruments cannot reach them. This is often due to entry pathways being very small or requiring navigation of challenging 3D geometry. Dexterity must also be maintained after reaching the surgical site to allow surgery to proceed. These constraints render such confined surgical sites off-limits to current commercial surgical robots, as well as manual MIS instruments. New MIS tools are needed that areboth smaller and more dexterous than existing devices. We propose a new type of “snake-like” miniature flexible active cannula that derives bending actuation not from tendon wires or other external mechanisms, but from elastic energy stored in the backbone itself. Differing from traditional MIS tools, which are essentially rigid cylindrical rods (possibly with wrists at the end), active cannulasare sufficiently flexible and shapable to navigate through bends such as those found when traversing the natural orifices, lumens, and other anatomical spaces of the human body. The active cannula design is particularly advantageous because dexterity improves with miniaturization. Moreover, inherent (and also somewhat tunable) compliance makes active cannulas safer than existing MIS tools. Ifinadvertent tissue contact along the shaft occurs, the device will bend rather than damage the tissue. We envision our active cannulas as a family of both hand-held and robotic devices tailored to meet various clinical needs. A fully robotic

version could be used as a new kind of slave robot in a telesurgical system like those commercially available today. Active cannulas are relevant for a wide rangeof challenging surgical applications. For example, the least invasive treatments for tumors or other disease at the base of the skull are performed endoscopically through the nose, and are very difficult because of the winding passages and small openings involved. Two specific surgical sites that cannot be reached using straight tools are the areas behind the carotid arteries (near the base of theeye), and the frontal sinus cavities (one must reach around the bone behind the bridge of the nose) [3]. Other potential active cannula applications include throat surgery [18], transgastric surgery, and fetal surgery, all of which require require dexterity after tool shafts travel long distances and/or are constrained by tissue. II. R ELATED W ORK Hand-held laparoscopic MIS tools generally...