Page 119 - Flexible Robotics in Medicine

Modular origami joint operator to create bendable motions with multiple radii 105

The evaluation of endoscopic MIS systems is currently based on different characteristics such
as the size of the articulation (i.e., external diameter) to reduce the size of incisions, the
number of DOFs, and their amplitude and the radius of curvature to characterize the ability of
the articulation to navigate while avoiding organs and torque [10]. Devices relevant to the
procedure of transoral tracheotomy (TT), as such, will be evaluated according to similar
characteristics with less emphasis on the size of the articulation as the device will be inserted
through the mouth. The joints, having two DOFs, can be approximated to have properties
between that of a perpendicular rolling sliding joint and a flexure joint.

The method of articulation of commercially used MIS instruments can be classified into
cable-driven articulations and cable-driven articulations with pulleys and pivot joints [10].
In some devices, these joints and articulations are actuated by localized motors or shape
memory alloys. However, these have the problems of miniaturization and electrical
compatibility for use in vivo. As a solution, deported actuation or delocalized actuation is
widely used. These include rigid and flexible transmissions, mechanical cables with single
compact joints, distributed articulations (multiple pairs of cables to bend in different
directions independently), and fluidic actuation [10].
Current implementations of a rigid transmission going through a curving structure such as an
endoscope body imply the manufacturing of complex mechanical parts of small dimensions.
These have problems such as assembly, high friction, and thus increased risk of the system
and reduced serializability. For example, Intuitive Surgical has patented a transmission
achieved by a slider-linkage system going through a finger-like multijoint structure. In this
system, one DOF bending mechanism with 6 90-degree amplitude is composed of three
joints, one set of two linkages for drive and restraint, and a superelastic shaft [10].
Another notable device property of Intuitive Surgical is the Da-Vinci surgical system,
which makes use of rigid pivot joints to stabilize the mechanism. Although capable, the
Da-Vinci surgical system has not been fully adopted for transoral surgical procedures.

Although the use of origami in surgical manipulators is novel, the capabilities of origami
have been studied and implemented in other manipulators such as the origami twisted
tower, which is actuated by cables [11,12]. The restraints and DOFs of such manipulators
are attributed to their folding patterns and can be programmed to fit various situations. The
MOJO prototype is such a manipulator with an origami universal joint to achieve the
function of performing TT.

The MOJO prototype adds a new possibility to the growing range of endoscopic procedures.

5.2 Design and prototyping

Fig. 5.1 is an in vivo schematic showing a MOJO performing its desired function in a bent
conformation, needling between the second and third tracheal disks. MOJO has a modular