# Scattering or Pushing for Object Singulation in Cluttered Environment: Case Study with Soma Cube
## 4 Parameter Estimation and Simulator Based Dynamic Manipulation
### Hybrid Singulation
In order to validate the effectiveness of the hybrid singulation, we conducted experimentation with three, four, and full seven block formations; seven experiments were conducted for each case. For three and four blocks formation, one time scattering can achieve singulation and it takes 0.5 s to perform one time scattering. With the increase in the number of blocks, one time scattering approach cannot singulate Soma blocks for all different formations. In case of seven blocks formation for seven different formations only one time we achieve successful singulation out of seven experiments using one time scattering approach. Pure pushing approach can singulate blocks however, it is time consuming. Hybrid approach is the most effective since it utilizes both pushing and scattering together and achieve singulation in less time as shown in Table 1. We have measured the time for all cases. In case of hybrid singulation for seven blocks, the average task completion time was 6.7 s and in case of pure pushing it was 30.2 s. The standard deviation and coefficient of variation for pure pushing were 2.69 and 8.88, respectively. The standard deviation and coefficient of variation for hybrid approach were 2.13 and 31.84 respectively. It is observed that hybrid approach has less standard deviation but that coefficient of variation is larger. That implies that pure pushing is more consistent in terms of task completion time, though it took more time for singulation of seven objects. Figure 13: Hybrid Singulation. (**a**) After initial scattering, two blocks in a cluttered group and other isolated blocks are shown. (**b**)–(**e**) Each of the separated blocks are removed by prehensible manipulation. (**f**) Purple block is removed, and pushing direction between red and green blocks is shown. (**g**) After pushing, red and green blocks are separated. In Figure 14a it took manipulator 10 pushing to completely singulate all the blocks, similarly in Figure 14b,c it took seven pushing to completely singulate all the blocks. In case of Figure 15 we have used same formations as used in pure pushing cases and tried to singulate them using hybrid approach and in all the three cases it took single pushing after initial single scattering to singulate all the blocks. Hybrid singulation approach comprises of one scattering and one pushing on average. In case of pure pushing, it takes on average seven pushing to perform complete singulation. That is why pure pushing technique takes more time. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Formations**} & **7 Block** & **7 Block** \\  & **(Pure Pushing)** & **Hybrid Approach** \\ \hline
**Number of Experiment** & 5 & 5 \\ \hline
**Success/Fail** & 5/0 & 5/0 \\ \hline
**Average Time (sec)** & 30.28 & 6.71 \\ \hline
**Standard Deviation** & 2.69 & 2.13 \\ \hline
**Coefficient of Variation (CV)\%** & 8.88 & 31.84 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison between pure pushing and hybrid singulation. Figure 14: Pure Pushing with three different formations and green arrow showing direction of pushing. (**a**) Initial formation for first case to final singulation takes 10 pushing. (**b**) Initial formation for the second case to final singulation takes 7 pushing. (**c**) Initial formation for the third case to final singulation takes 7 pushing.