Page 326 - Sensors and Control Systems in Manufacturing

FIGURE 6.7 Advanced Sensors in Pr ecision Manufacturing 283
Integration of a
fuzzy logic sensor
in a sensing
module.

The LED cluster is made up of three representative hues of red, green,
and blue, which provide a triple bell-shaped spectral power distribu-
tion for the light source (Fig. 6.8). The light incident on the target is
reflected with varying intensities, depending on the particular target
color under analysis.
The reflected light is received by a semiconductor receiver in the
center of the LED cluster. The amount of light reflected back onto the
receiver is transduced to a voltage and converted to digital format
immediately via an analog-to-digital converter. The internal process-
ing of the converted red, green, and blue (RGB) values offers variable
sample size and averaging to compensate for signal noise (Fig. 6.8).
Ambient light is sampled between every component pulse and
immediately subtracted from the sampled signal so the effects of fac-
tory ambient light are suppressed. Thus, hooding the sensor is not
totally necessary. In an area of a very bright or high-frequency lighting,
it may be beneficial to provide some degree of hooding to at least limit
the brightness. The sensor’s electronics also employs temperature com-
pensation circuitry to stabilize readings over temperature ranges.

6.3.2 Color Theory
Color science defines color in a space, with coordinates of hue, satura-
tion, and intensity (HSI). These three general components uniquely

FIGURE 6.8 Spectra of red, blue, and green light.