A plant built by Belgian specialist machine builder, Absolem Engineering features an innovative process for separating recyclable materials. Using PC-based control from Beckhoff, a major problem has been elegantly solved − the generation of different signal sequences for the exact synchronisation of different camera systems.
Absolem Engineering’s activities include process research in the field of laser technologies, and the construction of machines in which lasers create added value. The company has put this into practice in a project for VITO, an independent Flemish research organisation in the area of cleantech and sustainable development. “VITO has developed a fascinating technology for classifying waste streams,” says technical operations manager, Herman Van Dijck. “The idea behind this is simple. The better you are able to identify each individual element, the easier it is to separate and recycle the components.”
VITO records and categorises the components of a material flow on conveyor belts using a colour camera, a 3D laser scanner, and an X-ray machine. Machine learning is used to identify individual particles in a material flow and assign various parameters such as material class, shape or texture. This creates a digital twin of each particle.
Battery sorting with a digital twin
To test the theory in practice, VITO and a battery sorting company considered how this concept could be implemented in an industrial, automated process for sorting batteries. A tender was issued to find a machine builder that could put the algorithms developed by VITO into practice, and was awarded to Absolem.
The plant was designed to distinguish and sort a total of seven different battery types based on their chemical composition. The first functional prototype of the sorting plant was delivered to the battery sorting company after 18 months. The process was as follows: A conveyor belt transported the batteries to the sorting plant. To prevent X-rays from getting out into the external environment, the batteries were routed in a tunnel via a bend to the detection and sorting area. The length of the area and the speed of the belt were dimensioned so that there was enough space and time for the 3D camera, X-ray system and colour camera to capture the batteries. In a first run, the batteries were roughly separated into the categories ‘good’ and ‘bad’. In a second sorting process using more detailed algorithms, they were then sorted into the seven categories.
Precisely synchronised through PC-based control
As Absolem’s laser technology is based on Windows, and VITO also uses a separate Windows PC to characterise the material flows, both could be easily integrated with PC-based control to create a high-performance automation solution based on TwinCAT 3. “We rely on Beckhoff for the automation of our machines, not only because of the products and technologies they offer, but also because of their employees,” says Van Dijck, as he explains the project’s biggest challenge – the timing of the three different camera systems. The reason this was so tricky was that each camera required different frequencies and cycle times for synchronisation. The first idea was to synchronise the three systems via the software in the PLC. However, the timings were so critical that this could not be implemented, even with the PLC’s shortest cycle time. Absolem therefore needed a hardware solution.
“We tried using an EtherCAT terminal that had not yet been officially released when the project started, but which met the requirements perfectly, the EL5131 EtherCAT Terminal for incremental encoders with differential or single-ended signals,” recalls Van Dijck. “What makes the EL5131 so special is the two fast digital outputs.” The outputs can be configured so that the levels change, depending on the position values of the encoder, and also several times between two PLC cycles. This results in only a minimal phase shift between the encoder position and the output signal generated for the camera.
With this solution, Absolem is able to generate and output the different clock signals for each camera at a belt speed of up to 500 mm/s. Van Dijck adds: “We received a lot of support from Product Management I/O in Germany to set all the parameters of the EtherCAT Terminals correctly.” This enabled Absolem to build a sorting plant for VITO that is ideally suited to the application of the new process. However, the success story does not end there. The company wants to learn from its experiences and further optimise the system. “Recycling, the circular economy, and sustainability are important values for us. We are pleased that we can make a contribution to a better society,” concludes Van Dijck.
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