Biomedical Engineering Reference
In-Depth Information
5
Bulk Softness Measurement Using
a Smart Endoscopic Grasper
5.1 Introduction
This chapter investigates the characteristics of the dynamic load that occurs when an
object is grasped. In the realm of minimally invasive surgery (MIS) graspers, information
about the amplitude, waveform, and frequency content of the load transferred to a soft
object is important when performing experimental tests. In addition, the response of all
smart endoscopic graspers (those equipped with tactile sensors) depends on the behavior
and softness of the grasped object [1, 2].
A majority of studies on tactile applications are dedicated to force and pressure sensors
[3, 4], although a couple of researchers have investigated and introduced tactile sensors
capable of softness sensing, tailored for the measurement of local distribution of stress
within the grasper [5, 6]. In Chapter 4, two endoscopic sensors were described that were
capable of measuring distributed force or softness locally (along the grasper length) in
order to detect foreign objects hidden in bulk soft tissue. These simple, smart sensorized
graspers are also useful in obtaining information with regard to the interaction between
soft objects and the sensor itself. The objective of this research is to obtain a profile of
the repercussions of this phenomenon in finite element analysis, as well as the results of
experiments using smart endoscopic graspers [7]. A simple, smart laparoscopic grasper is
also presented and tested in order to determine the bulk softness of a grasped object by
measuring the grasper jaw angle and the force applied.
5.2 Problem Definition
After an endoscopic tactile sensor is manufactured, we need to apply dynamic forces in an
experimental test in order to characterize and calibrate the sensorized graspers. Although
we have attempted to apply forces that are similar to those that grasper will actually
encounter
in situ
, the initial problem will be to identify the constituent aspects of these
force profiles. Because the amplitude and profile of the force depends, to some extent,
on the geometry of the endoscopic grasper itself, we concentrated our attention on the
influence that the object has on the grasper - object interaction in a typical MIS grasper. In
