Biomedical Engineering Reference
In-Depth Information
1.4 Tactile Sensing
Tactile sensing can be defined as a form of sensing that can measure given properties
of an object through physical contact between the sensory organ and the object. Tactile
sensors, therefore, are used for measuring the parameters of a contact between the sensor
and an object, and so are able to detect and measure the spatial distribution of forces on
any given sensory area, including slip and touch sensing.
Slip, in effect, is the measurement and detection of the movement of an object relative
to the sensor. Touch sensing can be correlated with the detection and measurement of a
contact force at a specified point. The spectrum of stimuli that can be covered by tactile
sensing ranges from providing information about the status of contact, such as presence
or absence of an object in contact with the sensor, to a thorough mapping or imaging of
the tactile state and the object surface texture [15].
There are two determining factors in the design of tactile sensors: the first is the type of
application and the second is the type of object to be contacted [16]. For example, unlike
hard objects, when the tactile sensor is targeted toward soft objects (e.g., most biological
tissues), more complexities arise and there is a need for more sophisticated designs. In
general, tactile sensors can be divided into the following categories: mechanical (binary
touch mechanism), capacitive, magnetic, optical, piezoelectric, piezoresistive, and silicon-
based (MEMS or micro-electro-mechanical systems).
One of the most interesting and relatively new application areas for the tactile sensor is
in robotics, MIS, and MIRS [17]. Providing touch to a robot allows it to manipulate deli-
cate objects and to assess their shape, hardness, and texture. Some of these robots, which
are already being used in medical surgery, possess haptic capabilities to 'feel' organs
and tissues and then transmit this information to the surgeon via an instrument - patient
interface, thus replacing the human sense of touch.
1.5 Force Sensing
Force sensing is a basic and necessary capability of tactile sensors that has been investi-
gated for a long time. Nowadays, force sensors of advanced design, for both concentrated
and distributed force/pressure measurement, are available. The majority of tactile sensors
work on piezoelectric, piezoresistive, and capacitive techniques, or a combination of these
properties [16, 18 - 20].
1.6 Force Position
The capability of finding the position of an applied load is believed to be very useful
in MIS procedures. A homogeneous soft object compressed between two jaws of a MIS
grasper experiences a smooth distributed load. However, as shown in Chapter 4, the pres-
ence of an embedded lump in a grasped soft object appears as a point load superimposed
on the distributed background load. Therefore, one of the immediate and most interesting
applications of force position sensitivity, as shown in this topic, is in locating any hidden
features in a bulky soft object. Nevertheless, the application of force position sensitivity
is not only limited to lump detection.
