# Scattering or Pushing for Object Singulation in Cluttered Environment: Case Study with Soma Cube
## 4 Parameter Estimation and Simulator Based Dynamic Manipulation
### Simulator-Based Dynamic Manipulation  
Control singulation can be performed, without disturbing the real-world environment, by using a virtual world simulator. Since singulation is an irreversible process, so iterative singulations for the same scenario is not possible in real world experiment. Contrarily, virtual world simulator would allow us to perform iterative singulations for the same scenario. In order to perform the control iterative singulation in virtual world simulator, the initial configurations of pile of objects would be scanned from real world environment by using camera and initial positions and physical properties' information of each object will be given in virtual world simulator. Finally, iterative control singulation would be performed in virtual world. Once the desired singulation is achieved in the virtual world at specific colliding velocity, the same velocity would be given to the robot manipulator in real world to perform the singulation  
In this paper, virtual world simulations have been done using a physics engine: a commercially available multi-body simulation software called \"Daful\", which is made by Virtual-motion Co. [18]. These virtual world simulations have been performed by integrating the estimated physical properties such as mass ratios, coefficient of restitution and coefficient of frictions to perform the control singulation of objects. Control singulation implies to achieve the desired minimum distance among objects. The objective is to achieve the minimum distance among objects so that it is enough to grasping them by gripper. The colliding velocity of robot and direction of collision is updated in virtual world by employing a feedback routine that would minimize the error to achieve the desired singulation pattern [15]. The error is calculated by comparing the minimum distance of objects in each iteration in virtual world with the minimum desired distance among objects. Once, the minimum distance among object is achieved in virtual world, the same velocities information is used in real world to perform the object singulation. However, for large pile of objects such as for case of seven objects, it is not always possible to achieve the desired minimum distance among objects within predefined workspace. In those cases, the velocity of the manipulator is continuously increased, until the blocks leave the predefined workspace. That maximum threshold velocity is applied in real world to perform the singulation. The blocks, which remained in contact even after scattering, are singulated by using the pushing technique without using the virtual world simulator.  
Figure 5: Coefficients of friction and restitution.  
In case 1, we employ three, four, and seven blocks formation. What will be done in the experiment is that the robot scatters all blocks by hitting the initial formation. There are three parameters when conducting scattering: the position of the collision, the direction of collision, and the velocity, which are being updated by feedback routine. We can conduct scattering in the virtual world same as the real world since we already identified all parameters of blocks and environment. Real world orientation of the soma block formation will be fed to virtual world using the camera attached with manipulator and scattering is performed in virtual world until it will create separation among blocks. These parameters form virtual world are then fed to real world to perform singulation. Figures 6-8 demonstrate the successful singulation by just one time scattering and prehensile manipulation to move the blocks to other places.