# An INS-UWB Based Collision Avoidance System for AGV
## 4 Experiment Results  
In this section, the performance of the proposed UWB and INS based AGV collision avoidance system is tested, including the UWB and INS positioning accuracy test and the collision avoidance ability test of the AGV.  
The AGV adopted in the experiment is a Discovery \(Q2\) four omnidirectional wheel AGV, as shown in Figure 7. It is a small and multi-port AGV high reliability robot system.  
Firstly, the positioning accuracy of UWB is tested. Due to the limitations of the test site, the test ground is set as a 10 \(\times\) 10 m area. As shown in Figure 8a, the circles represent the UWB anchor nodes, and the triangle represents the sample test locations. At the test locations, the AGV collects several sets of ranging and positioning data to assess the UWB positioning accuracy. The error distribution is shown in Figure 8b. It is obvious that the test points closer to the center of the three UWB anchor nodes achieve smaller positioning error. According to the experimental results, when the UWB anchor  
Figure 6: Different collision avoidance situations.  
Figure 7: Outlook of AGV.  
nodes are far from each other, the positioning accuracy is poor. The results are meaningful for the deployment of the UWB anchor nodes and users can choose the distance of the anchor nodes according to their demanded accuracy.  
In the test, the positioning result on each test point is recorded 10 times and the average localization error is shown in Table 1. At the same time, the error distribution is shown in Figure 9.  
Figure 8: (a) UWB localization accuracy test; (b) error distribution.  
Figure 9: Map of warehouse environment.  
After UWB positioning accuracy test, the positioning of UWB and INS integration is also tested. A map of the warehouse environment is first established as shown in Figure 9. Due to the hardware limitations, three UWB anchors are used in the test environment. The AGV goes from Start point to the End point, and goes through route points A, B, C, and D to test the accuracy on the path.  
Three positioning methods including UWB, INS and INS-UWB are tested and compared. The results are shown in Figure 10.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Line 1** & 0.1226 & 0.1219 & 0.1222 & 0.1235 & 0.1226 \\ \hline
**Line 2** & 0.0871 & 0.0664 & 0.0662 & 0.0861 & 0.0765 \\ \hline
**Line 3** & 0.0773 & 0.0272 & 0.0291 & 0.0755 & 0.0528 \\ \hline
**Line 4** & 0.1017 & 0.0546 & 0.0527 & 0.1001 & 0.0773 \\ \hline
**Average** & 0.0972 & 0.0675 & 0.0676 & 0.0963 & 0.0823 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Location error in different positions  
Figure 10: (a) route comparison method; (b) error comparison of different localization methods.  
As shown in Figure 10, the positioning error of UWB is relatively stable in the whole route, which is between 10 cm and 30 cm. As the anchor nodes are closer to point B, C and D, the error in AB period is larger than that in BC and CD period, which corresponds to the result in UWB positioning error test. The error of the INS positioning is smaller in the first period and larger in the middle and last periods. The INS-UWB positioning method has the advantages of both positioning methods. The overall error is smaller than both single positioning methods and it is relatively stable, less than 15 cm, meeting the requirement for AGV positioning.  
In the AGV collision avoidance test, the AGV is instructed to across the warehouse with shelves in order to reach a destination. The collision avoidance effect is shown in Figure 11 where the black blocks are the obstacles and the red line is the final route of the AGV. According to the results, the route in the blue circles represents that the AGV has detected the obstacles and it has correctly adjusted its direction to avoid the collision. The experimental results show that the INS-UWB based AGV collision avoidance system can be used in environments with fixed obstacles.