10 / 44
8
Electricity
+
Control
AUGUST 2017
CONTROL SYSTEMS + AUTOMATION
round up
Why use a colour mark sensor with
RGB
technology?
What is the difference between a true colour sensor and a col-
our registration mark sensor?
True colour sensors can be taught to detect minute colour differ-
ences (for example, tell dark blue from black), while colour mark
sensors detect a grayscale change in colour. True colour sensors,
like
Banner
’s QC50, reflect light off a target using a white LED and
red, green and blue filter elements. A colour value is then assigned
to the light returning to the sensor based on the amount of light
reflecting off the target. With colour mark sensors, the sensor uses
just a LED and no filters. The sensor distinguishes the target colour
based on how it contrasts with the background colour.
Isn’t it better to use a true colour sensor rather than a colour
mark sensor?
Not always. A large number of colour sensing applications can be
done quite effectively by detecting a grayscale change in the colour
mark. In these instances, we recommend using a colour mark sen-
sor like the R58E, especially in high-speed applications. A true colour
sensor is required when sorting out targets that differ only in colour;
for example, when you need to distinguish between light blue and
dark blue. However, when distinguishing a registration mark on a
constant background, a colour mark sensor is your best choice.
What is the difference between a colour mark sensor and a
registration mark sensor?
There is no difference; these terms are synonymous.
What does 16 grayscale contrast levels specification mean?
One way to spec a colour mark sensor is to understand how many
levels of grayscale it can detect. The finer the sensor’s resolution,
the more levels can be detected. A commercial grayscale printer’s
chart is divided into 20 segments ranging from black to white, and
the shades of gray between. Many sensors are able to detect the
first 16 segments starting at white.
Does Banner’s R58E have a spec for grayscale contrast levels?
The R58E can easily meet the spec for 16 levels of grayscale. Because
of the combination of RGB LEDs, the R58E’s resolution capability far
exceeds grayscale charts. The R58E’s capability for subtle contrast
changes far surpasses the specification for 16 levels of grayscale.
Is it true that processing time for the colour mark sensor af-
fects speed?
Speed is more of an issue for a true colour sensor rather than a
colour mark sensor. The R58E from Banner can perform 10 000
actuations per second, which is very fast!
Why does Banner’s R58E colour mark sensor use the red,
green, and blue combination of LED colours?
The R58E uses this combination so that it can reliably sense virtu-
ally any registration mark/background combination. The RGB (red,
green, and blue) combination can be combined to create almost
any colour. Your computer monitor, for example, which is capable
of millions of colours, uses RGB technology. The R58E, using these
three colours, is able to determine the colour of the registration
mark and the colour of the background. The sensor will then use
the LED that provides the best contrast between the registration
mark and the background.
How do I pick the right LED colour for my application?
With the R58E, you do not need to choose an LED colour. The
R58E selects the proper LED colour automatically during the initial
TEACH function. However, when using a monochromatic colour
mark sensor, resources such as colour selection charts are used to
select the proper LED colour.
How do I switch between the different LED colours?
You don’t need to manually switch LEDs. The R58E will automati-
cally select LED colours during the TEACH function.
Can I choose the LED colours in the R58E?
No. The R58E comes with only the possibility of three LED colours:
red, green and blue.
Does having 3 LED colours affect the sensor’s response time?
No. After the initial TEACH process, the R58E’s response time is
the same as comparable registration mark sensors. The R58E has
a 50 microsecond response time, which allows 15 microsecond
repeatability.
How do I sense a registration mark on clear material?
Clear materials (e.g. a clear poly web) do not reflect light very well,
so when sensing a registration mark on a clear material, position a
reflective surface directly behind the clear material to return light to
the sensor. The registration mark will block the light from reaching
the reflective surface and will be detected by the sensor. To avoid
the shine from clear materials, you might consider mounting your
sensor at a 15° skew angle.
How can I maximise sensing in my high-sensitivity applica-
tions with the R58E?
Use the dynamic TEACH function to teach the sensor a series of
conditions on the fly. The R58E takes multiple samples of a regis-
tration mark against its background and is able to automatically set
the sensitivity at the optimum level.
Enquiries: BrandonTopham.