- 8 - 6 - 4 - 2 2 4 6 8 0
-200 200 400 600 0
2: Fisher projection2 3: Fisher projection3 4: Fisher projection3
0 500 -1000 -500 0 500
2: Principalcomponent2 1 : P r i
- 4 - 2 2 4 6 0
2: Principal component 2
- 4-3 - 10 4 3 2 1 - 2
2: Principal component 2
the reflectance from the metal, allowing the
system to classify them correctly. To do so,
the perClass software from PR Sys Design
(Delft, The Netherlands; www.perclass.
com) with its Matlab-based perClass Toolbox was used to analyze different trained
classifiers and thus develop an optimal solution. These included Quadratric and Mixture Gaussian classifiers, k-nearest neighbor
classifiers, Fisher discriminant analysis, and
a Random Forest method.
Before classification, however, linear dis-
criminant analysis (LDA) was applied to the
data gathered from the hyperspectral system.
LDA can be used to find a linear combination
of features that characterizes or separates two
or more classes of objects. Based on the fea-
tures extracted from the data with LDA, the
Random Forest algorithm provided the most
promising results for metallic alloy classifica-
tion (Figure 4). Such Random Forest methods
are supervised training classifiers that operate
by first building a multitude of decision trees
as the system is trained. The classifier then
determines the class that appears most often.
As the metallic alloys are deposited on the conveyor, they are identified by the 3D Ranger
camera and then classified by the hyperspectral
system. Using a controller from ABB (Zürich,
Switzerland; www.new.abb.com) synchronized
to the conveyor belt’s encoder, these particles
are tracked as they move through the system.
Software routines written in RAPID, a high-level programming language used to control
ABB industrial robots, are then used to determine the specific position of a each alloy after it
is identified by the 3D camera. “This allows the
Conveyor Tracking module of ABB software to
provide instructions to the ABB picking robots
without having to take into account the progression of the conveyor,” says Barnabé.
Object locations are converted from the 3D
In the system, two IRB 340 ABB robots are
used for sorting. While one uses a 2-fingered
gripper, another uses a bucket to slide objects
over the conveyor while avoiding other objects.
Both are interfaced to the system using a TCP
connection between the acquisition computer
and each robot controller.
At the end of the conveyor, pneumatic
ejection devices are also used to sort material
and metallic alloys. To identify optimal picking points for the robot, a custom algorithm
is used while constrained Delaunay and A*
algorithms are used for path finding.
In this case, software routines in the ABB
Controller and the PLC controlling the air
blowers store the instructions received from
the processing computer, and perform the
actions when object is in range. A video of the
systems in operation can be found at: http://
bit.ly/VSD-SCRAP. While at present, the
system uses VNIR and SWIR cameras to capture image data, Barnabé and his colleagues
are currently integrating other types of sensors
for more advanced classification.
While the current system uses 3D and
spectral cameras, Barnabé and his colleagues are integrating X-Ray transmission
(XRT) sensors and Laser Induced Breakdown Spectroscopy (LIBS) sensors to assess
the best sensor combination for different
products and applications. While the XRT
will be used to find, for instance, steel bolts
inside aluminium scrap, the LIBS sensor
will detect the composition of different aluminium or stainless-steel alloys.
Figure 4: Based on the features extracted from the data with LDA, the Random Forest algorithm
provided the most promising results for metallic alloy classification.
For more on 3D and non-visible imaging, embedded and mobile vision
systems, and deep learning software
Figure 3: To properly light the metallic parts as they move along the conveyor at speed, a high-level of illumination was required and an extruded elliptical reflector consisting of an array of
Halogen lamps was used to produce a concentrated linear beam of light.