# Design and Validation of a Camera-Based Safety System for Fenceless Robotic Work Cells
## 4 An Industrial Case Study and Experimental Verification  
### Design of the Experimental Setup  
All calculated values of \(\alpha\) and h provided for design constraints are given in Figure 13, which shows the heights to be placed according to different camera lens angles graphically. The graph in the figure contains two curves. One is \"Camera Height for Safety System for 2 Cameras\", and the other one is \"Camera Height for Safety System for 3 Cameras\". In the previous calculations, it is seen that the optimal camera lens angle is 57.874\({}^{\circ}\). Therefore, it was calculated that the required height for the using two cameras system is 6028 mm, and the required height for the using three cameras system is 5023 mm. For cases in which the optimal camera angle is not desired to be used, the camera heights suitable for the lens angle of the existing camera are also shown in graphs. Three cameras were needed when two cameras were not enough (i.e., the camera height is larger than 10 m). In case of the need to use three cameras, the cameras were positioned as circular and equally spaced. If three cameras were used, the total projection area and the previous solution's constraints would change. The new constraint (htan(2\(\alpha\))) should be more than 6000 mm and less than 8000 mm. A comparison between a commercial setup and the experimental one is given in Table 3. The manipulator reach, work envelope radius, maximum manipulator speed, \begin{table}
\begin{tabular}{c c} \hline \hline
**Camera Orientation Angle Deviation** & \\ (Degree) & Percentage of Similarity to Optimal Paced Camera Image \\ \hline
10\({}^{\circ}\) Decreased & 57\% \\
5\({}^{\circ}\) Decreased & 59\% \\
5\({}^{\circ}\) Increased & 51\% \\
10\({}^{\circ}\) Increased & 41\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Percentage of similarity between the images from the optimally placed camera with the image from changed camera orientation angle. Figure 13: Optimum camera height versus camera lens angle for two- and three-camera systems. alarm zone radius, and warming zone radius were compared, as well as the number of cameras, camera resolution, camera angle, graphics cards, penetrating object radius, minimum illuminance range, and minimum frame per second. An optimized solution was presented considering the limit values and variables guided by the standards. A flexible system that can adapt to fenceless work cells at different sizes with multiple 2-D cameras was proposed. A comparative verification of the machine vision system was made. Consequently, the system operates stably at the optimal setting. Figure 14 shows the experimental setup built to test the system design. Two cameras were placed at optimal height and placement angle in the experimental setup. Real-time operating conditions and the response of the system should be examined in a controlled manner. Therefore, a test system under controlled conditions was designed and installed. First, the parameters to be controlled were selected. One of the critical variables in the system is the reaction time of the robot arm for decelerating or stopping  
Figure 14: The experimental setup with two cameras and one robot. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Case** & **Industrial** & **Experimental** \\ \hline No. of Manipulators & Variable & 1 \\ Manipulator Reach (mm) & 2800 & 270 \\ Work Envelope Radius (mm) & 3000 & 300 \\ Maximum Manipulator Speed (deg/s) & 260 & 500 \\ Alarm Zone Radius (mm) & 3500 & 300 \\ Warming Zone Radius (mm) & 4000 & 350 \\ No. of Cameras & 1 & 2 \\ Camera Resolution & Undisclosed & 1280 \(\times\) 960 and 1920 \(\times\) 1080 \\ Camera Angle (degree) & 80 & 50 and 70 \\ Graphics Cards & PSEN se AU AM3 & Nvidia Geforce GTX 1050 and GTX 850 M \\ Penetrating Object Radius (mm) & Human Body & 5 \\ Minimum Illuminance Range (lux) & 300 & 120 \\ Minimum Frame per Second & Undisclosed & 23 and 28 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Specifications of a commercial example [31] and experiment setup.