# Design and Validation of a Camera-Based Safety System for Fenceless Robotic Work Cells
## 4 An Industrial Case Study and Experimental Verification
### Test Results and Discussion  
The entire object in the images did not fall within the monitored areas. The desired linear velocity was reached at the exact endpoint of the object, and this end part was allowed to enter the control area. The response time of a mechanism whose speed can be controlled when the robot arm enters the camera-controlled working space was measured. The system responded at various times in response to a foreign object entering the area at various speeds. This controlled speed and the system response time are shown in the graphs given in Figure 16. On the curves in these graphs, there are two marked points, which are indicated for \"Walking Speed\" (2 m/s) and \"Hand Speed\" (1.6 m/s), as specified in the standards. The plot above and below are derived from the safety systems using low and high-resolution cameras, respectively. In both plots, the performance of two different graphics cards, including NVIDIA Geforce GTX 850 M and a GTX 1050, were compared. GTX 1050 is reported to have approximately 60% higher performance than GTX 850 M according to benchmark tests. All experiments were performed at a constant illumination level of 300 lux. Figure 15: Speed controlled foreign object and controlled area in the experimental setup. It is seen that the effect of camera resolutions on the system response was high. When using a low-resolution camera, the system response was more unstable at different speed inputs, while it seemed to work more stable with a high-resolution camera. On the other hand, the graphics processor did not have a significant effect (less than 0.01 s) on the system response with the high-resolution cameras. In the system in which low-resolution cameras were used, it was observed that the high-performance graphics processor responded in an average of 10% shorter time than the lower performance one. Therefore, the proposed system yielded efficient results even in low-performance processors when 1080p resolution cameras were used. Consequently, a camera with a resolution of at least 1080p should be used for the safety system. When a safety system with optimal values was installed, the system response time was between 0.08 and 0.1 s. These values were considered sufficient for an effective operation. When graphics processors are compared, it should not be ignored that the system memory (RAM) and the hard drive are also influential. In the comparisons in this study, both computers had 16 GB RAM and 256 GB SSD drive. Another essential criterion in this study is the response times of the proposed system at various illuminance levels in the controlled area. The system was tested under various illuminance levels. illuminance is the total luminous flux incident on a surface per unit area and measured in lux. One lux is the illuminance created by a light source with an intensity of one candlelight in the center of the sphere with a radius of 1 m [32; 33]. In the experimental system established with a sensor measuring illuminance, response time measurements were made at different illuminance, and these values are presented in Figure 17.  
Figure 16: System response time versus foreign object speed as a function of camera resolution using two graphics processors. The plots above and below in Figure 17 are derived from the safety systems using low and high-resolution cameras, respectively. In both plots, the performance of two different graphics cards, including NVIDIA Geforce GTX 850 M and a GTX 1050, were compared. GTX 1050 is reported to have approximately 60% higher performance than GTX 850 M according to benchmark tests. The graphics processor did not appear to impact system response times at high illumination levels significantly. At the same time, the same experiments were carried out with cameras with two different resolutions in the graphics shown in the figure. Camera resolution appeared to have a high impact on system response at different illuminance levels. As seen from this graph, the minimum brightness of the camera to detect a foreign object was 5 lux.