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Tendon routing and anchoring for cableriven single-t surgical manipulators 191

7.6.3 Layer jamming mechanism

The layer jamming mechanism takes advantage of the friction-induced by negative air
pressure between layers. In Ref. [13], the manipulator is then wrapped by an elastomeric
membrane made of latex rubber. The outer and inner diameter of the prototype presented in
Ref. [13] is 22 and 15 mm, respectively. At this dimension, they can manufacture the flaps
by cutting Mylar sheets via laser cutting. However, we are unable to employ the same
manufacturing method to suit our smaller dimensions, where the outer dimension shall be
less than 3 mm. Hence, we hypothesize that upon the introduction of a pressure difference
across the elastomeric membrane, the membrane would compress and enter the grooves of
the spring backbone, effectively “jamming” the spring.
Before introducing negative pressure between elastomeric membranes, no pressure difference
exists between the inside and outside of the elastomeric membrane. Hence, no external force
is exerted on the flexible helical spring backbone and hence can distort easily under load, as
can be seen from Fig. 7.18A. When negative air pressure is introduced, differential air
pressure between the atmospheric air pressure and the internal pressure between the
membranes will cause the elastomeric membranes to deflate and compress upon the spring.

Figure 7.18
(A) No pressure difference between inside and outside of the membrane. (B) The introduction of
negative pressure inside the membrane creates a pressure difference between the inside and
outside of the membrane, causing the membranes to compress against the sides of the and
springs and enter the grooves.