Page 189 - Flexible Robotics in Medicine

176 Chapter 7

requirement of anchoring the tendons, the 3 mm diameter springs could not accommodate
three such anchors in its circumference. Each lashing on a compression spring for a single
anchor occupies approximately half the circumference of the spring. Furthermore, the
lashing on the tendons occupied all the spaces inside the compression spring, leaving
insufficient spacing for the actuation mechanisms for the surgical equipment to be
integrated into the spring backbone. Thus the square lashing technique was dropped.

We then considered knotting techniques to create tendon guides. Using a clove hitch knot, a
knot prominently used in the lashing technique, we anchored the aluminum wire to the
compression spring and followed up with a loop to create a guide gap for the tendons. We
then created another clove hitch knot again on the circumference of the spring to secure the
loop. Although this technique was superior to the lashing technique in occupying a lesser
area within the circumference of the compression spring, the loop created by the aluminum
wire underwent constant alternating lateral force, causing the loop (that anchors the tendons)
to break over time due to the weak ductility property of the material, causing a
reliability issue.

7.3.2.2 Guiding technique

To create the guides, soldering was used to minimize the lashing space required in the
lashing technique. The loop made of aluminum wire was soldered to the circumference of
the spring (Fig. 7.4). Although the problem of space constraints in the lashing technique
was addressed using this method, the aluminum loop wire still faced ductility issues due to

Figure 7.4
Soldering aluminum wire to the circumference of spring.