# Detecting and Solving Tube Entanglement in Bin Picking Operations
## 4 Experiments
### Results
The authors speculate this is due to the algorithm giving preference to picking the non-occluded tubes first, which postpones solving entanglement issues. This property may be advantageous since the contact forces exerted by the tubes that are picked first may move the other ones in such a way that it is easier to pick them later on. Table 5 indicates how often the robot resorted to the simulator for trajectory evaluation (i.e., how often all of the tubes had occlusions) when attempting to pick a tube. It also shows how often each type of trajectory was used to move the gripper after grasping. The simulator was used much more often with Set B since the tubes' shape lead to more cases of occlusion. Most of the time, an upwards trajectory was preferred over the escape ones, which performed an additional lateral movement. Interestingly, the trajectory simulator was only used on first attempts to pick a tube. As a result, during the second attempts, there was always at least one non-occluded tube in the pile. In addition, every single second attempt at picking a tube was successful, for both Sets A and B. This evidences \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Number of tubes in the bin**} & 7 & 6 & 5 & 4 & 3 & 2 & 1 & Overall \\ \hline \multirow{2}{*}{**Set A**} & Success rate & 100\% & 95\% & 100\% & 100\% & 100\% & 100\% & 99\% \\  & Number of picked tubes & 20 & 20 & 20 & 20 & 19 & 18 & 137 \\ \hline \multirow{2}{*}{**Set B**} & Success rate & 80\% & 95\% & 100\% & 90\% & 90\% & 100\% & 100\% & 93\% \\  & Number of picked tubes & 20 & 20 & 20 & 20 & 20 & 19 & 16 & 135 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Percentages of picked tubes that were successfully placed on the first attempt. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Number of tubes in the bin**} & 7 & 6 & 5 & 4 & 3 & 2 & 1 & Overall \\ \hline \multirow{4}{*}{**Set A**} & Usage rate (upwards trajectories) & 0\% & 9.5\% & 10\% & 10\% & 5\% & 0\% & 0\% & 5\% \\  & Usage rate (escape trajectories) & 0\% & 4.8\% & 0\% & 10\% & 0\% & 0\% & 0\% & 2\% \\  & Usage rate (total) & 0\% & 14.3\% & 10\% & 20\% & 5\% & 0\% & 0\% & 7\% \\  & Number of picking attempts & 20 & 21 & 20 & 20 & 20 & 19 & 18 & 138 \\ \hline \multirow{4}{*}{**Set B**} & Usage rate (upwards trajectories) & 25\% & 10\% & 5\% & 27\% & 5\% & 0\% & 0\% & 11\% \\  & Usage rate (escape trajectories) & 4\% & 0\% & 0\% & 0\% & 27\% & 11\% & 0\% & 6\% \\  & Usage rate (total) & 29\% & 10\% & 5\% & 27\% & 32\% & 11\% & 0\% & 17\% \\  & Number of picking attempts & 24 & 21 & 20 & 22 & 22 & 19 & 16 & 144 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Percentages of picking attempts where trajectory simulation was performed and frequency of both types of trajectories on the chosen grasp. that simply dropping the grasped tube back into the bin when it is entangled is a good strategy for bin picking. Table 6 presents the success rate of the picking attempts which used the simulator. Unlike the previous tables, these rates were not presented in function of the number of tubes in the bin, as there were not enough examples for each amount. Set A had a success rate of 100% for both kinds of trajectories, which is most likely due to the PVC tubes' surface allowing them to slip and fall back into the bin much more easily. The results from Set B show a very interesting result: the success rate for the escape trajectories is significantly higher than the one for the upwards trajectories. By combining the observations from the results in Tables 5 and 6, one can conclude that it is harder to execute a useful escape trajectory than to simply lift a tube, but, when the former alternative is possible, it yields much better results. This conclusion suggests that having a wider variety of trajectories to choose from will increase this solution's overall performance. Figure 11 depicts a successful pick with an escape trajectory. In this example, neither the grasped tube nor the gripper touched any of the other tubes.