# Scattering or Pushing for Object Singulation in Cluttered Environment: Case Study with Soma Cube
## 7 Discussion  
In this paper, we have proposed the hybrid singulation combining scattering and pushing. This framework uses both prehensile as well as non-prehensile manipulation to achieve desired singulation. In the initial stage, we performed scattering based manipulation to achieve singulation of blocks in clutter. After scattering, all blocks may not be singulated. So, in the second stage, we conduct pushing. Prior to pushing, we need to remove the blocks that may collide with the blocks in clutter and hinder pushing. So, we have use prehensile manipulation to pick the isolated soma blocks. Then, we perform pushing to achieve the desired object singulation. [PERSON] et al., provided a framework for non-prehensile manipulation under clutter [19]. In this approach, they have used pushing as a non-prehensile manipulation method to manipulate objects in clutter. In this approach, they had termed some spaces as invisible or unknown because the clutter had blocked the sensors (cameras or laser scanners). However, in our approach we do not face any such spaces and our sensors are not blocked and after each push and scattering, our manipulator having RealSense Depth Camera SR305 (Intel, California, USA) takes picture and move the manipulator based on the pushing directing of the arrow generated by image segmentation technique. A framework of push-grasping in clutter is an approach for planning in clutter that is based on human strategies [1]. However, in their approach they have experienced the problem of unnecessary displacement of objects. The hybrid singulation approach proposed in our paper allows the blocks to remain in the workspace because if we rely only on scattering, we can also face the similar problem, but the hybrid approach solve the problem by using pushing once the scattering has been done and all the block remain in the workspace and there is no unnecessary displacement of objects that can create hindrance for other blocks. Figure 15: Hybrid Singulation with three different formations. (**a**) Initial formation of first case of 7 soma blocks. (**b**) Formation after scattering showing the need of single pushing and green arrow points in the direction of pushing between green and blue blocks, (**c**) green and blue blocks are singulated after single pushing, (**d**) Initial formation of second case of 7 soma blocks, (**e**) Formation after scattering showing the need of single pushing and green arrow points in the direction of pushing between yellow and red blocks, (**f**) yellow and red blocks are singulated after single pushing, (**g**) Initial formation of third case of 7 soma blocks, (**h**) Formation after scattering showing the need of single pushing and green arrow points in the direction of pushing between green and purple blocks, (**i**) green and purple blocks are singulated after single pushing. Several factors affect the time required for singulation and these are: the direction for robot scattering, appropriate light for image processing algorithm, orientation of objects, and number of objects. The direction for robot scattering was selected on the basis of the ability of the manipulator to generate impulse in certain direction. The direction of robot scattering was decided to apply the maximum impulse [15]. Appropriate light in the environment allows the image processing algorithm to adequately point out the direction of pushing. For three or four blocks formation, if the orientation/position of the blocks relative to the robot changes, the time to execute the scattering will not change too much as long as the robot can hit the blocks at the chosen point along the chosen direction. When the number of blocks are more than four, one time scattering approach cannot acheive desired singulation for all various different formations of Soma blocks. The pushing can achieve desired singulation but it is time consuming.