Dynamic object manipulation using a multi-fingered hand-arm system: Enhancement of a grasping capability using relative attitude constraints of fingers

In this paper, an enhancement of a dynamic object grasping and manipulation method, which has been proposed by us previously, is presented. This enhancement makes it possible to grasp more various shaped objects which could not have been grasped by our previous method. In our previous method, a force/torque equilibrium condition to satisfy stable object grasping has been realized by only using grasping forces normal to an object surfaces. It is because each fingertip is soft and hemispheric and then rolling constraints arise during movement, and these phenomena cannot be stopped while existing the rolling constraint forces. Therefore, satisfying the dynamic force/torque equilibrium condition depends not only on a configuration of the multi-fingered hand system, but also on the shape of the grasped object. In this paper, a class of satisfying the force/torque equilibrium condition is expanded by generating counter tangential forces to suspend the rolling motion of each fingertip. In order to generate the counter tangential force, a relative attitude constraint between each finger is introduced. Firstly, a rolling constraint between each fingertip and object surface is given. Then, a relative attitude constraint control signal to generate constantly-produced tangential forces is designed. Finally, it is demonstrated through numerical simulations that the proposed control method accomplishes to grasp arbitrary shaped polyhedral objects and regulate its position and attitude, simultaneously.