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Handheld flexible robot with concentric tubes aiming for intraocular procedures 153

from the ground up. To achieve this, the use of conventional straight end-effectors will
have to be replaced with end-effectors capable of more excellent intraocular dexterity.

6.2 Concentric tube robots

For the purposes of this chapter, this review aims to name the fundamental design
principles behind designing an actuation mechanism for CTRs, to design a CTR capable of
being handheld.

6.2.1 Manually actuated

While the aim of this chapter is to produce a motor actuated device, the actuation
mechanism of a manual CTR is equally as relevant. One caveat of manual CTRs is that
they are designed to be used for experiments, and as such, modularity and ease of tube
replacement tend to be the focus. Steerable cannula guidance featured rotary stages
mounted on linear stages. By rotating the knobs, the motion of the cannulas can be
controlled. The inner tube stage is mounted on the outer tube stage. Thus only the inner
stage can move independently, while moving the outer tube moves both tubes. It can be
noted that the inner tube is placed behind the outer tube, this is necessary, as if the tubes
were arranged the other way, it would not be possible to grip the inner tube, which has a
smaller diameter, while still allowing for the outer tube, which has a larger diameter, to
pass through. This further implies that the inner tube will have to be of a more
extended length relative to the outer tube, or the inner tube will not be able to exceed
the outer tube.
Rotation and translation are both done by manually turning or pushing the wheel, while a
spring pin locks it in place. Like the earlier CTR, it can be observed that one of the criteria
for an actuation mechanism is that the tubes must be concentric. This implies that the
translation mechanism will have to be offset. However, its current actuation design, where
the outer tube is fixed and only the inner tube extends/rotates, may not be suitable, as the
small workspace constraints of the eyeball would require constant adjusting on the
surgeon’s part as the inner tube extends.
It is essential for a tube robot design to have modularity, compactness, usability, and
serializability [2]. This is evidenced by the tube carrier mechanism design. All tube carriers
are the same, but by changing which guide rail a carrier sits on, independent control of each
tube can be realized in a compact platform. The actuation mechanism is using the control
knobs to control both translation and rotation. However, here the translation axes are
separate. This allows for smaller overall dimensions, but more input needed to move the
device.