  Magnetically-anchored surgical devices have recently gained attention in
abdominal surgery, with the use of magnets to anchor surgical devices onto the
insufflated abdominal wall. These anchors have been used to secure passive and
active devices, where active device such as robotic manipulators produce
motions that would excite the dynamics of the non-rigid abdominal wall. Hence,
there is a need to investigate the mechanical dynamics of the abdominal wall
tissue in insufflated state, combined with magnetic anchoring, specifically its
response to mechanical excitations and the expected disturbances to the
operation of the anchored devices. In this paper, loading and unloading tests
are performed on a corresponding porcine specimen for dynamics identification.
The experiment setup was constructed to emulate the insufflated state of the
abdomen with the magnetically anchored mechanism. The tissue responses during
unloading are captured and approximated with a general numerical model, which
is in turn used for the dynamic analysis of the tissue using Bode plot. The
results showed that in such stretched and compressed state, the steady state
displacement of the tissue is approximately zero. The maximum transient error
was found to be 1mm in displacement using a high magnetic anchoring force.
Significant attenuation of the disturbances due to the high stiffness and
damping of the abdominal wall, was observed from 100rad/s in the frequency
response. If a robotic manipulator was attached to the anchoring device, the
typical operating frequency of movements would still produce unattenuated
disturbances. It is expected that some error compensation through suitable
control strategies is required. These outcomes establish the basis for the
controller design and the design specification of the active
magnetically-anchored surgical devices for minimal disturbance impact onto the
abdominal wall tissue.
