Page 47 from: March 2016

47March 2016

and that the maximum P/B ratio
was reached at 8 μs,’ said Owada.
The settings vary depending on the
metals to be detected.
Even a slight shift of 1 to 2 mm in
the laser focal position ‘consider-
ably affected’ the analysis accuracy.
Owada advised using a mechanism
to fit the focal position onto the
flat surface of the sample and at
the respective height of the sam-
ples running on the conveyor belt.
Detection probabilities for all the
standard samples were as high
as 100%. ‘The minimum length
of sample material for optimum
detection is 0.2 mm at 0.5 m/s belt
speed,’ Owada stated. ‘As a next
step, we are now focusing specifi-
cally on sintered tantalum from
used electronics.’

Taking on black plastics
Black plastics or multi-layered
products in the waste stream are
‘virtually unsortable’ with today’s
sorting solutions, pointed out
Christian Brandt of Germany’s
Fraunhofer Institute. Three of the
institute’s bodies have partnered
in a bid to overcome this issue. ‘As
a first step, we have developed a

frequency domain line-scan cam-
era working in the terahertz (THz)
range with frequencies below 300
GHz,’ Brandt stated.
Using mainly plastics derived from
end-of-life cars, plastic flakes on a
conveyor belt have been exposed to
a THz sensor as well as an RGB line

camera and pneumatic ejection.
The material yielded approximate-
ly 10 points measured per flake,
and a total of 35 000 during the
entire trial. This translates into a
97% precision rate in sorting ABS
and a 96% rate for polypropylene
and polyethylene.

Better performance expected
One problem encountered was that
the shape of the samples analysed
by the THz sensor alone was ‘too
coarse to allow precise ejection’,
Brandt admitted. ‘The more com-
pact the material flow, the bigger
the problem.’
Furthermore, the material may
be only partially visible at times.
‘Luckily, the data fusion of the THz
and the RGB image enabled us to
recover the shape of the objects
with high spatial resolution,’
Brandt noted. By using improved
next-generation sensors with a
‘higher dynamic range’ as well as
more different data for training
and testing, the research team
expects a ‘much better perfor-
mance’ in harder separation tasks.
A potential follow-up project
might be the more efficient sort-

ing of PVC. In the
meantime, the equip-
ment developed during
the project – dubbed
TableSort and FlexSort
– will be presented at the
upcoming IFAT trade
show as well as the K
Trade Fair, both to be
held in Germany.

‘Mechanically
articulated bridge’

‘Optical sorting systems
may appear as the logi-
cal future technology
for waste treatment, but

analysis of possible ejection con-
figurations proves that a one and
only ejection technology does not
exist,’ argued Winfrid Rauch of
Manufacture à Besançon (MaB).
While the various contemporary
machines available have their own
advantages and disadvantages, ‘a

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Munich University
conducted innovative trials
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million tonnes of paper
recycled in Germany
each year.