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Contrast sensors distinguish the received light beams on the basis of their degrees
of intensity, which depend on the color or material of the detected surfaces. A
typical application of these sensors is the detection of colored registration marks
used in packaging machines to synchronize the folding, cutting and welding phases.
In presence of colored surfaces, the contrast is highlighted using a LED with colored
light emission, typically a selectable red, green or blue LED. The white light emission
allows to detect very slight contrasts in similar materials and colors.
A slot sensor, also known as fork sensor, is based on a particularmodel of the through
beam sensor, where emitter and receiver are placed opposite to each other on the
internal sides of an “U-shaped” housing. Any target passing through the internal
slot interrupts the beam and is detected. The most typical slot sensor applications
are hole/teeth detection on wheels, label detection on thin supports, and control of
edge and continuity of sheets of labels or tapes. The emission is generally infrared
or red light in order to detect colored registration marks on translucent films.
Luminescence sensors emit invisible ultraviolet light, which is reflected at a higher
wavelength (minor energy) on the fluorescent and phosphorescent surface, shifting
into the visible light spectrum.
The ultraviolet emission is modulated and the visible light reception is synchronized.
The maximum immunity against external interferences, like reflections caused by very
shiny surfaces, is obtained and fluorescent targets, invisible to the human eye, can be
detected. Luminescence sensors are used in several industrial fields to detect items
containing phosphorous such as labels on glass or mirrors, fluorescent marks marked
on tiles, fluorescent glues on paper, cutting and sewing guides, as well as fluorescent
paints or lubricants.
CONTRAST
Slot/fork
LUMINESCENCE
PHOTOELECTRIC SENSORS
