IEEE Robotics & Automation Magazine - June 2017 - 25

The Surgical Robot Challenge, hosted by the Hamlyn
Center for Robotic Surgery at Imperial College London,
offers a unique arena to propose custom instrument designs
for the da Vinci platform. Members of the Center for Image
Guided Innovation and Therapeutic Intervention at The
Hospital for Sick Children in Toronto proposed miniature
continuum-joint instrument designs for the 2015 and 2016
competitions. This article highlights the design and implementation of these custom tools with the da Vinci Research
Kit (dVRK).
The dVRK
The dVRK is an open-source robotics platform created to promote the development of new applications and technologies
for surgical robotics [5]. The kit functions similar to a commercial da Vinci robot; through a master-slave teleoperation
framework, the surgeon controls a series of seven degrees-offreedom (7 DoF) patient-side manipulators (PSMs) via the
surgeon-console manipulators. Unlike the clinical da Vinci
robot, the dVRK's open-source software allows designers to
customize the system.
The PSM's sterile adapter provides an interface that
enables easy instrument interchangeability (Figure 1).
The sterile adapter has four disks, each with a range of
motion (RoM) of ±170°, that can be used to actuate an
attached tool. This interface allows for new custom tools
to be designed to complement the existing tool line. With
modifications to the dVRK's code, these custom tools can
be teleoperated.
Continuum Robotic
Manipulators
Continuum joints have often been
used to create miniaturized manipulators for medical device applications.
Unlike classic rigid-link joints, many
continuum mechanisms' DoF are
based on intentional elastic structural
deformation. This approach enables
joint miniaturization by removing
the need for complex assemblies [6].
Two examples include concentrictube robots and notched-tube joints,
shown in Figure 2.
Concentric tube robots are composed of precurved superelastic nitinol tubes arranged in a concentric
fashion. The robot's overall shape, tip
position, and orientation can be precisely controlled by rotating and
translating the individual tubes relative to one another. The key advantages of concentric tube robots include
their small form factor, robustness,
and ease of fabrication. This technology has been studied extensively,

and the kinematics of such systems are described in [9]
and [10].
Notched-tube compliant joints have been developed for a
variety of medical devices such as catheters, steerable needles, and miniature wrists [11]-[13]. These monolithic
structures are of interest because of the simplicity of their
fabrication and assembly. There are many variations of this
mechanism, but most of the existing designs operate by creating directional compliance in a tube by cutting notches into
it. Actuation of the joint is achieved by applying tension on a
cable routed within the tube's lumen, causing the tube to
bend. Notched-tube geometries can be broadly categorized
as symmetric or asymmetric. Symmetric notches have the
benefit of bending equally in both directions, but are limited
by fatigue. Asymmetric notches, which typically cross the
midline of the tube, bend in a single direction and can
achieve more compact bending radii because of the structure's tendency to fold into itself [14].
Designing Miniaturized Continuum
Tools for the dVRK
Our motivation was to develop instruments capable of
working through smaller incisions within smaller body
cavities and in closer proximity to other instruments.
Therefore, our design goals were to reduce the shaft diameter to 2 mm and improve the joint compactness (i.e., minimize the bend radius and joint length). Also, we aimed to
maximize the joint stiffness and maintain similar RoM
(±80° in pitch and yaw) and dexterity (3 DoF + end

Tool Base
Sterile Adapter

(a)

2
3

Instrument Wrist
and End Effector
(c)

(b)

Figure 1. The dVRK's PSM displaying 7 DoF and the tool interface: (a) the back
of the tool base, which mates with the actuation disks; (b) the sterile adapter
with four actuation disks; and (c) a tool mounted on the PSM.

June 2017

Ieee ROBOTICS & AuTOMATIOn MAGAZIne

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - June 2017