# 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 case 3, we employ seven blocks. It is found that singulation of all seven blocks is hard to achieve always. Initially, the real world formation is fed to the virtual world and the direction of scattering is decided on the basis of robot's ability to generate maximum impulse in a certain direction. Along this direction, the colliding velocity of robot is updated in the virtual world by employing a feedback routine that would minimize the error to achieve the desired singulation pattern. After achieving the singulation pattern in virtual world, the direction and velocity are applied in real world to achieve desired singulation. However, in most cases, only a partial scattering can be achieved. The advantage of the initial scattering is that we can scatter the initial cluster of seven blocks into several small groups. Figure 12, shows the hybrid manipulation, after initial scattering the blocks are not completely singulated so we have used quasi-static manipulation in which Intel RealSense Depth Camera was used that has created contours among the blocks which are very near or their boundary touching each other. As shown in Figure 12c, two contours appear in this case, one between yellow and green block  
Figure 11: Pushing (**a**) Manipulator and Soma blocks in clutter (**b**) Direction of pushing in quasi-static manipulation. Figure 10: Quasi-static manipulation. and the second contour between green and red block. All the other blocks are isolated after scattering. The robot manipulator picks each isolated block having no overlapping contour starting from the block nearest to the end gripper. After removing all the isolated blocks, the manipulator performs pushing as shown by the arrows above the contours in Figure 12h. The manipulator will follow the direction of the vector created by using image segmentation technique that is closer to manipulator. In this case, the yellow block gets isolated first. After first pushing, RealSense Depth Camera SR305 (Intel, California, USA) again captures the image and robot manipulator will decide whether the blocks get isolated or still touching each other. In the second push, the green and red blocks are separated as shown in Figure 12j. The Figure 13 shows another example of the hybrid singulation, where the blocks were scattered after dynamic manipulation. All the blocks are scattered except green and red blocks and they are removed using prehensile manipulation, leaving only green and red blocks. Using the PCA based image segmentation algorithm, the direction of pushing is easily generated which is shown by green arrow in which the tail of the arrow shows the starting point and head shows the ending point of the pushing. The manipulator initially removes the isolated blocks nearest to the manipulator using the proposed quasi-static manipulation algorithm as explained in Figure 10. Accordingly, the blocks are removed by the order of blue, orange, yellow, brown, and purple. Now the manipulator will use pushing technique to isolate the red and green blocks that has formed a cluster of two blocks. Figure 12: Hybrid Singulation (**a**) Real world soma blocks: initial position (**b**) Real world soma blocks after scattering (**c**) Two contours shown in white color among red green and yellow blocks (RealSense View). (**d**) Prehensile manipulation for clearing the isolated blue block (**e**) Prehensile manipulation for clearing the isolated orange block (**f**) Prehensile manipulation for clearing the isolated brown block (**g**) Prehensile manipulation for clearing the isolated purple block (**h**) Three blocks with two overlapping contours and arrows showing the direction of pushing (**i**) After one pushing, yellow block separated (**j**) After second pushing, both green and red block get separated. Comparative Analysis between Hybrid Singulations vs. Pure Pushing and One Time Scattering Singulation  
In this section, we have provided the comparative analysis among the approaches: hybrid singulation, pure pushing and one time scattering based singulation.