Biomedical Engineering Reference
In-Depth Information
2
Tactile Sensing Technologies
Tactile sensing technologies are employed wherever interactions between a contact surface
and the environment are to be measured and registered. As mentioned in Chapter 1,
development in tactile sensing technology is driven by the need to provide for an ever
increasing number of new applications and requirements, especially in the robotics and
medical fields.
2.1 Introduction
There are many physical principles that can be exploited for the development of tactile
sensors, but, because the technologies involved are very diverse, this chapter considers
only general aspects. The operation of a tactile sensor is not only a function of the sensor
structure and its characteristics, but is also dependent on the material of the object being
touched or grasped.
Much research into the design and manufacture of a variety of tactile sensors has
been reported. For instance, the development of an 8
×
8 silicon pressure tactile sen-
sor array with on-chip signal readout circuits (Figure 2.1) has been implemented by
Wen
et al
. [1]. The integrated sensor array was fabricated by using a combination of
micro-electro-mechanical systems (MEMS) and micro-electronics. The prototype device
was characterized by the pressure range of 0 - 150 kPa, in which the sensors exhibited a
linear response with a mean sensitivity of 30.1 mV kPa
-1
. Another tactile sensor chip
has been developed for measuring the distribution of forces on its surface [2]. The chip
has eight force-sensitive areas, called 'taxels,' with a pitch of 240 μm. Surface micro-
machining techniques were used to produce small cavities that work as pressure-sensitive
capacitors. To enable transduction of normal forces to the sensitive areas, the sensor chip
surface was covered with silicone rubber. The radius of the sphere, and the load working
on it, can be estimated precisely from the tactile sensor output data.
An integrated three-dimensional tactile sensor with robust MEMS structure and soft
contact surface suitable for robotic applications has been developed by Mei
et al
.[3]
(Figure 2.2).
The sensor has a maximum force range of 50 N in the vertical direction and
±
10 N in
the
x
and
y
horizontal directions. The tactile sensor includes 4
×
8 sensing cells, each
