Soft contact grasping and orientation control of a rigid object using multibond graph

Soft contact manipulation of an object involves grasping, sliding, displacement and orientation control. The developed bond graph model for the soft contact is applied to achieve the grasping of a cylindrical disc, an elliptical disc and a square block between two vertical soft pads. The developed contact algorithm is applied to determine contacting nodes at the interfaces at each instant for different geometries. One pad is constrained to be fixed while the required grasping force is applied to the other pad by a proportional derivative controller. The time taken to attain a steady grasping posture for all three cases is studied and compared. The model determines the contacting nodes and contacting forces at the interfaces during transient state and steady state of grasping. For same initial grasping posture, the number of contacting nodes increases with time in transient state in case of cylindrical disc while decreases during grasping of elliptical disc and remains constant for the square block. The patterns of deformed layers of the soft materials are also found to be different for different geometries. The model is further applied to control the orientation of a cylindrical disc while rolling it between the two horizontal pads. A feedback Proportional-Integral-Derivative controller measures the instantaneous orientation of the disc and applies the required horizontal force on the upper pad for the desired orientation control. The model calculates the required instantaneous contact forces to be applied for orientation control. The discussed contact algorithm and bond graph model are validated by simulation.