# Vision-Based Sorting Systems for Transparent Plastic Granulate
## 3 Results and Discussion
### Sorting Results  
The classifier was tested on a prototype sorting machine. A test mixture of granules was prepared, into which clear granules and defective granules were placed. Defective granules represented 10% of the total mixture. Testing was performed with five different settings for the feeder and the conveyor. The settings are given in Table 5. The parameters are explained in Table 6. Table 7 shows the sorting results. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**TRUE**} \\ \hline \multirow{3}{*}{**PREDICTED**} & **Class** & OK & NOK \\  & OK & **150** & 0 \\  & NOK & 0 & **150** \\ \hline \multirow{3}{*}{**PREDICTED**} & \(\sum\) & 150 & 150 \\  & Precision & 100 & 100 \\ \cline{1-1}  & Recall & 100 & 100 \\ \hline \hline \end{tabular}  
OK: clean; NOK: defective.  
\end{table} 
Table 4: Confusion matrix of results for two classes. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Test Name** & **S\({}_{\text{c}}\)—Conveyor Belt Speed (m/s)** & **S\({}_{\text{f}}\)—Feeder Belt Speed (m/s)** \\ \hline Test 1 & 0.545 & 0.006 \\ Test 2 & 0.545 & 0.024 \\ Test 3 & 0.419 & 0.013 \\ Test 4 & 0.308 & 0.006 \\ Test 5 & 0.369 & 0.006 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The settings of the feeder and the conveyor when testing the sorting efficiency. Three repetitions of the test with the same sorting machine settings were made with the granule test mixture. Table 7 provides averages of the results of these three tests. The variable parameters were the speed of the conveyor and the speed of the feeder belt. The influence of how densely the granules were arranged on the conveyor was changed by adjusting these two parameters. The size of the opening on the feeder was constant. Adjusting the conveyor speed also affected how many frames per second should be captured, and in what arc the granules would fall past the air nozzles unit below the conveyor. The faster the conveyor, the faster the image processing should be. At the full speed of the conveyor, image processing took up to 100 ms. This was 10 frames per second, so the camera was fast enough for image capturing. A schematic presentation of the testing system is shown in Figure 5. The clean granules are represented by the representatives of the clean granules class. Defective granules are a mixture of all other classes. Figure 5 shows two boxes for sorted material. After sorting, Box 1 would ideally contain only clean material. Box 0 contains defective ejected granules. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Data** & **Unit** & **Equation** & **Description** & **Acquisition** \\ \hline \(t\) & s & & Sorting time & Measurement \\ \(m\_D_{1}\) & g & & Weighing of good granules in Box 1 & Measurement \\ \(S_{1}\) & piece & & Counting defect granules in Box 1 & Measurement \\ \(\lambda\) & & S\({}_{\text{G}}\)S\({}_{\text{f}}\) & Bulk density on conveyor & Calculation \\ \(S_{0}\) & piece & & Bad granules in Box 0 & Calculation \\ \(D_{1}\) & piece & & Good granules in Box 1 & Calculation \\ \(D_{0}\) & piece & & Good granules in Box 0 & Calculation \\ \(m\). & kg/h & & Sorting capacity (granular mass flow rate) & Calculation \\ \(ni\_0\) & & S\({}_{0}\)/(S\({}_{0}\) + D\({}_{0}\)) & The quality of the ejected granules & Calculation \\  & & & (percentage of defect granules in Box 0) & Calculation \\ \(ni\_1\) & & D\({}_{1}\)/(D\({}_{1}\) + S\({}_{1}\)) & Quality of separated granules (percentage & Calculation \\  & & & of good granules in Box 1) & Calculation \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Parameters’ interpretations in sorting machine testing. Figure 5: Schematic presentation of the system prototype. The feeder, conveyor and air nozzles are shown. Below are the boxes to catch the material. A “separate” box for non-defective material (Box 1) and an “ejected” box for defective material (Box 0). After examining Table 7, the following was determined:  
* Sorting speed was measured and depends exclusively on the speed of the feeder belt.