Biomedical Engineering Reference
In-Depth Information
Reflecti
ve surface
Combined optical receiver and source
Spring steel
Figure 2.6
Reflective touch sensor
Op
tica
l receiver
Op
tical source
De
formable tube
Figure 2.7
Optical sensor shielded by deformable tube
Touch and tactile optical sensors have been developed using a range of optical technolo-
gies. The force sensitivity in the optical sensor is determined by a spring or elastomer.
For instance, in the schematic sensor shown in Figure 2.6, the distance between the
reflector and the plane of the source and the detector is the variable. The intensity of the
received light is a function of distance, and hence the applied force. The U-shaped spring
is manufactured from spring steel, leading to an overall compact design. This sensor has
been successfully used in an anthropomorphic end effector. To prevent crosstalk from
external sources, the sensor can be constructed around a deformable tube, resulting in a
highly compact sensor. A schematic of an optical sensor covered by a deformable tube is
shown in Figure 2.7.
2.6 MEMS-Based Sensors
MEMS is the technology of very small mechanical devices driven by electricity; it merges
at the nanoscale into nanoelectromechanical systems (NEMS) and nanotechnology.
MEMS are made up of components between 1 and 100 μm in size (i.e., 0.001 - 0.1
mm) and MEMS devices generally range in size from 20 μm to a millimeter. They
usually consist of a central unit that processes data, the microprocessor, and several
components that interact with the outside, such as micro-sensors, to detect temperature,
chemical, or magnetic changes, as well as one or more micro-actuators. At these size
scales, the standard constructs of classical physics are not always useful. Because of the
large surface-area to volume ratio of MEMS, surface effects such as electrostatics and
wetting dominate volume effects such as inertia or thermal mass. At the beginning of the
1970s, the producers used engraved substrate plates to produce pressure sensors. At the
