Page 425 - The Mechatronics Handbook

0066_frame_C19 Page 47 Wednesday, January 9, 2002 5:17 PM

D
D

D

Printed Circuit Board
Elastomere
Protective Cover

FIGURE 19.43 Typical taxel sensor array.

Adder
Parallel Voting
redundancy system
m
n
2-d Image l Line scan

x

FIGURE 19.44 General arrangement of an intelligent sensor array system [9].

A typical tactile sensor array can consist of several sensing elements. Each element or taxel (Fig. 19.43)
is used to sense the forces present. Since tactile sensors are implemented in applications where sensitivity
providing semblance to human touch is desired, an elastomer is utilized to mimic the human skin. The
elastomer is generally a conductive material whose electrical conductivity changes locally when pressure
is applied. The sensor itself consists of three layers: a protective covering, a sheet of conductive elastomer,
and a printed circuit board. The printed circuit board consists of two rows of two “bullseyes,” each with
conductive inner and outer rings that compromise the taxels of the sensor. The outer rings are connected
together and to a column-select transistor. The inner rings are connected to diodes (D) in Fig. 19.43.
Once the column in the array is selected, the current flows through the diodes, through the elastomer,
and thence through a transistor to ground. As such, it is generally not possible to excite just one taxel
because the pressure applied causes a local deformation in neighboring taxels. This situation is called
crosstalk and is eliminated by the diodes [10].
Tactile array sensor signals are used to provide information about the contact kinematics. Several
feature parameters, such as contact location, object shape, and the pressure distribution, can be obtained.
The general layout of a sensor array system can be seen in Fig. 19.44. An example of this is a contact and
force sensing finger. This tactile finger has four contact sensors made of piezoelectric polymer strips on
the surface of the fingertip that provide dynamic contact information. A strain gage force sensor provides
static grasp force information.

©2002 CRC Press LLC