Biomedical Engineering Reference
In-Depth Information
film, this sensor exhibits high sensitivity, a large dynamic range, a wide bandwidth with
good linearity, and a high signal-to-noise ratio [5].
Using the design demonstrated here, for a concentrated load, the entire surface of the
sensor can be used to sense the force as well as its position. This effect is very novel
compared to other reported tactile sensor arrays where the region between the two sensing
elements is essentially a dead area (no sensitivity) [16]. The magnitude of the applied
force can be obtained from the magnitude of the output from PVDF sensing elements,
and the position of the applied force can be found from the value of the slope at the point
of application of the load. This information can be displayed, or fed back to the surgeon's
finger, by means of a haptic interface.
A more sophisticated multi-functional sensor system is described below. Although this
sensor is capable of measuring the force, and the position of the force, both along the
grasper length as well as its breath, it was mainly designed to measure the softness of the
grasped object. It is shown that a wide range of soft objects, including soft tissues, can
be differentiated by this sensor. There are other features, such as lump detection which
are discussed in detail later in this chapter.
4.2 Multi-Functional MEMS
Based Tactile Sensor:
Design, Analysis, Fabrication, and Testing
This section describes the design, microfabrication, and testing of a second endoscopic
tactile sensor whose design and geometry are explained in the following subsections.
A finite element model of the sensor is also developed. To check the accuracy of the
numerical model, its deflection profile for a given load is compared with that of a closed-
form relationship. The microfabrication steps are also explained and then the experimental
results for softness sensing are compared with the results of this finite element model.
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4.2.1 Sensor Design
An illustration of the complete grasper (host device) is shown in Figure 4.13, in which
either the lower or upper jaw is equipped with an array of sensor units. Although the
number of teeth may vary in different graspers and/or applications, this modular design
y
x
Figure 4.13
The MIS grasper equipped with an array of the proposed sensor
