Page 56 - Concise Encyclopedia of Robotics

Capacitive Proximity Sensor
Metal plates
Dielectric
foam

Robot
Oscillator ADC
controller
Capacitive pressure sensor

A capacitive pressure sensor can be fooled by massive conducting or
semiconducting objects in its vicinity. If such a mass comes near the
transducer, the capacitance changes, even if direct contact is not made.
This phenomenon is known as body capacitance. When the effect must be
avoided, an elastomer can be used for pressure sensing. For proximity
sensing, however, the phenomenon can be useful.
See also CAPACITIVE PROXIMITY SENSOR, ELASTOMER, and PRESSURE SENSING.

CAPACITIVE PROXIMITY SENSOR
A capacitive proximity sensor takes advantage of the mutual capacitance
that occurs between or among objects near each other.
A capacitive proximity sensor uses a radio-frequency (RF) oscillator,
a frequency detector,and a metal plate connected into the oscillator circuit,
as shown in the diagram. The oscillator is designed so a change in the
capacitance of the plate, with respect to the environment, causes the fre-
quency to change. This change is sensed by the frequency detector,
which sends a signal to the apparatus that controls the robot. In this
way, if the system is properly designed, a robot can avoid bumping into
things. In some detectors, the induced capacitance causes the oscillation
to stop altogether.

