IEEE Robotics & Automation Magazine - September 2023 - 95

overcome the limitations of both borescopes and continuum
robots, here, we propose a modular design at their intersection,
with both active tendon-driven and passively flexible
segments. The main elements of the novel design, including
the actuation and control interface, are described, and the system
is demonstrated in scenarios for aerospace assets, nuclear
installations, and robot-assisted surgery.
INTRODUCTION
Inspection, maintenance, and repair are critical to achieve
safety and reliability in capital-intensive infrastructures,
such as aircraft, power plants, and telecommunication
networks. However, these operations
often involve narrow, complex environments
with no direct access. For example, the components
within a gas turbine can only be accessed
through narrow channels, such as borescope
ports and a reach of several meters [1], [2]. Similarly,
the key components of a power generator
(e.g., stator core) can only be inspected through
narrow passages over a significant reach [3]. By
providing remote visual feedback and with a
cross section that can be as small as 4 mm,
borescopes are currently the state-of-the-art
solution for in situ inspection in these environments.
This technology, however, has significant
limitations: first, the single degree of
freedom (DoF) that controls tip bending is not
sufficient to intervene on a defect; further, the
difficulty in positioning the borescope camera
with respect to the inspection target leads to a
low defect detection rate [4]; finally, only a
skilled operator can manually drive the borescope
through a cluttered environment and,
even then, the procedure is slow and hindered
by the lack of control over the tool's shape.
Thus, if damage is detected, components might
need to be disassembled and repaired separately,
leading to long downtimes.
For these reasons, maintenance robots have
been proposed to perform these inspections,
aiming at a significant increase in safety and
efficiency by enabling teleoperation, automated
detection, and in situ repair. Since conventional
industrial robots cannot navigate the intricate
geometries of aeroengines, power plants, and similar
environments, snake-like continuum robots have been
developed for these applications. By routing tendons through
slender, flexible bodies, continuum robots can achieve full
control over their shape by pulling and releasing these tendons,
which act like antagonistic muscles, from the base
of the robot, deployed outside the inspection environment
[5], [6], [7]. In the last decade, tendon-driven continuum
robots have been demonstrated in real-case scenarios, such
as laser operations [8] and coating repair [9] in aeroengines;
the exploration and inspection of unknown cluttered environments
for nuclear decommissioning [10], [11]; and also
robotic surgery [12], [13].
When compared to borescopes, the main advantage of continuum
robots manifests in shape control, which enables intervention
and significantly improves navigation. However, the
length of a continuum robot is not as scalable as in borescopes
due to the intrinsic limitation of tendon-driven designs: each
independent segment of a continuum robot requires three or
more cables for 2 DoF [14]. Therefore, longer robots require
many cables routed through their bodies, increasing their
cross section. Similarly, fluid-driven, concentric needle, and
other continuum robot architectures encounter equivalent barriers
to scalability due to the additional space required to drive
each active segment. This link between mobility and size constrains
length, and this constraint is further worsened by low
stiffness, resulting in high deflections under small payloads
[15]. Furthermore, both endoscopes and continuum robots
currently require skilled operators.
Here, we present a near-industrialized continuum robot
for remote applications (COBRA) at the intersection of borescope
and continuum robot technologies, overcoming the key
inherent weaknesses of both. As reported in the " Design "
section, this new design employs both tendon-driven and passive
segments to achieve high dexterity at a long reach (more
than 5 m) while maintaining a cross-section diameter of fewer
than 9 mm. Control over the passive segments is achieved
with an external mechanism that controls the axial translation
and rotation of the robot at the entrance of the target environment,
emulating the manual action of a borescope operator.
The active segment is controlled by an actuation unit that
pulls and releases the tendons through rotary motors. A userfriendly
interface, described in the " Control " section, enables
easy motion control through a joystick. As outlined in the
" Demonstration " section, COBRA has been tested in industrial
scenarios, including an aeroengine compressor and pipes
representing a nuclear power installation. The flexibility of
the novel system is also highlighted by a medical application,
with a specific end effector (EE) designed for throat surgery.
These demonstrations highlight how COBRA improves borescope
and continuum technologies by merging the advantages
of both.
DESIGN
As shown in Figure 1, COBRA is divided into five subsystems:
■ Continuum robot: This has three tendon-driven active sections,
with 2 bending DoF each, and passive segments,
which are compliant and bend passively under external
loads. The hollow body contains an inner channel for the
connections required by the EE (e.g., signal, power, and
fluid pressure).
■ Compact and truly portable actuation pack: This drives
the active segments of the continuum robots by actuating
tendons through pulleys connected to rotary motors.
■ Miniaturized twist-and-feed mechanism: This mimics the
behavior of a borescope operator, and drives the passive
body of the robot through a rotary and linear stage, twisting
SEPTEMBER 2023 IEEE ROBOTICS & AUTOMATION MAGAZINE
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IEEE Robotics & Automation Magazine - September 2023

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