# Direction-Based Hybrid Strategy Combining Pushing and Hitting for Fast Object Singulation
## 5 Experimental Verification
Here, the desired singulation implies that all of the objects are separated enough to grasp them with a gripper without collision. Figure 12 shows the asymmetrically arranged six circular disk formation. It is found that after hitting in the virtual simulator, few circular disks are still in contact as shown in Figure 12c. After hitting along the red arrow, we require additional pushing to complete the singulation of all of the objects. The RealSense view in Figure 12e shows purple and red disks contacting each other and as a result, there is a contour between the two disks with the pushing direction arrow. The first push created a new contacting body between red and blue as shown in Figure 12f. So, again, a contour and pushing arrow appears between the two circular disks that indicate the second pushing. Figure 12g shows desired singulation. Figure 11: Six circular disks billiard formation: (**a**) initial formation of six circular disk billiard formation in real-world, (**b**) initial formation of six circular disk billiard formation in virtual-world, (**c**) desired singulation using single hitting in virtual world showing all disks are singulated, and (**d**) desired singulation using a single hit in real-world showing all disks are singulated. Figure 10: Four circular disk formation: (**a**) experimental setup, (**b**) RealSense camera view showing the direction of pushing arrow (**c**) experiment result after the first push, and (**d**) experiment result after the second push. As a result, such an asymmetric formation achieves the desired singulation using one hit and two pushes. Figure 12e shows a small contour between the red and blue disks although these disks are not in contact with each other, this was because of the lighting issue. Figure 13 shows another asymmetrically arranged six circular disk formation and the hitting direction is chosen on the basis of simultaneous impact. After hitting two circular disks, the red and blue are still contacting each other as shown in Figure 13d. Followed by additional pushing, the desired singulation is achieved as shown in Figure 13e. The result from the simulator and the result from the experiment are not always the same, as shown in Figures 11-13, because the virtual view simulations are done on the basis of estimated physical parameters. This is due to the difference between the true and the estimated values of the parameters. Especially, in our experimental setup, the friction was not uniform over the surface, while in the simulation the coefficient friction was assumed to be constant. Comparative Analysis among Initial Desired Direction-Based Hybrid Singulation and Other Random Singulation Approaches  
This section describes the comparative analysis of the three approaches: initial desired direction-based hybrid singulation approach and random hybrid singulation (direction of pushing and hitting is random), and random pure pushing approach (only pushing technique is used for singulation). To validate the effectiveness of our initial direction-based approach, we performed three experiments using six circular disks in different configurations with the initial direction-based hybrid approach, the random hybrid approach, and the random pure pushing approach and measured the time it took for complete singulation. It took the manipulator on average 4.5 s for our proposed direction-based hybrid singula  
Figure 12: Six circular disks in asymmetric formation: (**a**) experimental setup, (**b**) virtual view of six circular disks: initial asymmetric formation, (**c**) virtual view after single hit, (**d**) real view after single hit, (**e**) RealSense camera view showing a contour and pushing direction green arrow between contacting purple and red disks, (**f**) camera view after first push showing a contour and pushing direction by green arrow between contacting red and blue disks, and (**g**) camera view.