Page 484 - Flexible Robotics in Medicine

478 Chapter 21

that is inserted in the endoscopic manipulator working channel, a distal controllable
compression spring connected to the said tension spring, and a biopsy forceps. The insertion
portion comprises of the three latter components. The proximal control uses a ball and
socket mechanism to transmit omnidirectional control to the distal spring. This control
method is intuitive and easy to master. The insertion portion is of smaller diameter
(3 5 mm) to prevent irritation when inserted into the patient’s open channel. The
compression spring is connected to four driven metal cables at the distal end. These four
cables transmit motion from the proximal control to the distal actuation spring (Fig. 21.1).
The cables used in the design are metal cables since it can exert both push and pull force,
secure and nonelastic so that it can transmit precise movement. Moreover, compression
spring exerts counter-moment and hence stabilizes the system. The compression spring
portion can also detach from the distal end to reach the target lesion. The forceps are like a
conventional biopsy forceps with hollow cups to hold the lesion and is controlled by a
metal cable capable of push and pull. The whole system, especially the insertion portion,
has minimal and straightforward components, which is easy to manufacture and scale down
(Table 21.1). Thus this design meets the input criteria: small, so anesthesia is unnecessary,
omnidirectional, stable, and able to detach from the distal end to increase precision.
Our prototype is to be inserted into the working channel of the existing endoscopic
manipulators to improve the actuation process during the biopsy. The unique flexible
property of our prototype enables surgeons to manipulate the forceps attached in narrow
and intricate regions of the nasal cavities, to perform biopsies with ease. Since bending
mechanisms of the various endoscopic manipulators are similar, OmniFlex can translate
into other endoscopic surgeries.
There are two broad categories of endoscopic manipulators: rigid and flexible. Rigid
endoscopic manipulators usually consist of different segments linked together in a
serpentine structure. This type of endoscopic manipulators has limited degrees of freedom
and is tough to operate. Hence, it is very demanding and depends highly on the skillset of
the surgeons. On the other hand, flexible endoscopic manipulators allow a greater DOF
[6,18,19,21]. Complex and curved regions can be reached with a flexible distal end.
Furthermore, if the prototype is omnidirectional, surgeons will not have to turn and rotate

Table 21.1: Design rationale from acceptance criteria.
Acceptance criteria Prototype verification Chosen design
High DOF Omnidirectional Four driving cables, ball, and socket control
Small size to prevent Insertion portion: 3 Simple components, ease of manufacture, and
the use of anesthesia and 4.5 mm downscale
Ease of use One-hand operation Shape-lock ability, intuitive ball, and socket control
High precision Predictable, accurate Compression spring with adequate elastic
control to actuation modulusMetal driving cables: nonelastic to transmit
exact movement