Visual Servoing for Beating Heart Surgery - Visual Servoing via Advanced Numerical Methods - page 91

With this approach, the slave robot is replacing the surgeon's hand. As a conse-
quence, the dynamic properties of the robot must be compatible with the heart sur-
face motion. Furthermore, the device must have enough intra-cavity mobilities to
let the surgeon perform comfortably a suturing gesture. No commercial system, and
even no research prototype have currently reach these severe requirements. From a
mechanical design point of view, this is still a technical challenge.
Moreover, this approach may be questionable in terms of safety. Indeed, the robot
kinetic energy constitutes a potential danger in case of control error or failure. Sev-
eral safety principles are now widely accepted in the field of medical robot design
[16]: minimizing the robot workspace, speed and acceleration is indeed a basic re-
quirement. Safety has to be taken into account at the lowest design level, i.e. for the
hardware design. One may consider that these principles are not respected in this
case.
While remaining in the framework of heart/tool synchronization, an alternate ap-
proach could be the one adopted in the Heartlander project [35]. The robot is a
miniature mobile robot directly positioned on the heart surface. It walks on the my-
ocardium thanks to legs fitted with suction cups. The motion compensation is thus
intrinsic to the system. However, the device has been designed initially to perform
needle insertion on the epicardial surface. In the context of TECAB, design of me-
chanical structures at that scale with the force and kinematic requirements is an open
problem.

6.2.2 Heart Immobilization

In this second approach, the surgical tool is not supposed to follow the heart surface.
The idea is to remain in a teleoperation scheme, with two kinds of robotized laparo-
scopic tools. The first robotic system provides the needed intra-cavity mobilities,
with a large workspace, and is teleoperated by the surgeon from a master console.
The second robotic system stabilizes locally the heart surface: it is an active sta-
bilizer that is designed to suppress the residual motion observed with conventional
mechanical stabilizers.
With such a decomposition, we can limit the bandwidth of the slave system and
in the same time minimize the workspace of the cardiac stabilizer, which means a
quasi-suppression of its potential harmful effects. The project Cardiolock [3] aims
at developing an active stabilizer compatible with MIS. Initially developed to com-
pensate for residual displacements in a single direction, the Cardiolock device is
now designed to perform a complete stabilization [4]. The required high accuracy
and high dynamics have lead to the use of compliant architectures, with piezoelec-
tric actuation. Backlash and friction are thus eliminated. High speed vision provides
an exteroceptive feedback that allows the measurement of the stabilizer residual
displacements.
In the following, the main properties of the device are introduced with the first
Cardiolock prototype. This device globally consists of two parts. A first active part
(on the left of Figure 6.2) is composed of a 1 degree of freedom (DOF) closed-loop