Page 205 - Flexible Robotics in Medicine

192 Chapter 7

With enough pressure difference, the elastomeric membrane will enter and jam the grooves
of the spring, creating resistance against deformation by external forces (Fig. 7.18B).
Similarly, when the differential pressure is created when the spring is in a deformed state,
the jammed grooves will create resistance in the spring from returning to its original shape,
maintaining its configuration.
To test our hypothesis, we wrapped a 2.85 mm diameter spring in the silicone membrane.
Silicone was used instead of latex rubber because of its biocompatibility. Since the spring
backbone actuating the instrument make direct contact with internal tissues, the silicone
membrane can function as a dual role in ensuring the biocompatibility of our surgical robot.
One end of a fluid line is then introduced between the membranes, and the other end is
connected to a syringe. Negative pressure can be introduced by removing air from between
the layers using the syringe. Silicone rubber was used to seal the syringe and the
elastomeric membrane. Upon withdrawing the air with the syringe, we observe that the
silicone membrane did indeed compress against the spring backbone as expected. However,
using this technique, we were unable to achieve the desired stiffness. Upon the removal of
external forces, the “jammed” spring was still able to return to its original deformation.
Despite entering the grooves of the spring, the elasticity of the silicone membrane still
conferred enough elasticity for the spring to retain its inherent flexibility.

7.6.4 Remarks

Both concepts we have employed and tested have not yielded the desired stiffening and
response time. Hence, for our future direction, we can further test out the two alternatives.
First, for the thermal phase-change mechanism, we can test out the concept using solder. As
solder has a higher thermal diffusivity as compared to wax [5], we can expect a shorter
activation and inactivation response time as compared to wax. However, we will need to
conduct mechanical and cycling tests on the solder-based mechanism to ascertain its
suitability in withstanding multiple cycles of cooling and melting in our surgical robot
application. We will be attempting granular jamming for our jamming mechanism.
However, since a substantial amount of granular matter is required for successful jamming,
it is crucial to consider the weight ratio of the granular matter to the entire mass of the
instrument prototype. Additionally, methods of integrating the various stiffening
mechanisms into our prototype, as well as considerations of any possible interference with
the tendon-driven mechanism, will have to be considered.

7.7 Conclusion

We employ a master-slave architecture with a tendon-driven actuation mechanism that
allows us to achieve the desired miniaturization and functionality for the potential