This paper presents an improvement of our previously proposed dynamic object grasping and manipulation method. This method, which utilizes a dual-fingered hand of which each soft and hemispheric fingertip owns a torsional joint, has performed novel 3-dimensional dynamic object grasping and manipulation stably without the use of any external sensing device. However, several limitation and weakness have still remained in terms of dexterity and robustness. In order to improve it, firstly a triple-fingered hand is newly introduced instead of the dual-fingered hand to perform regrasping. Next, the previously proposed stable object grasping controller is adequately modified to perform dynamic regrasping during manipulation. Additionally, the virtual object attitude controller is also modified to improve its performance. Finally, several experiments are conducted by using a prototype, and the usefulness of proposed controller is demonstrated through these results.

This paper proposes a novel object manipulation method by using a dual soft-fingered robotic hand system, in which each fingertip has a torsional joint. By using the torsional motion of the fingertips, a novel 3-dimensional dynamic object manipulation without use of any external sensing can be achieved even though the hand system has only two fingers. Firstly, our proposed system, which includes contact models between each fingertip and surfaces of an object, is modeled. A rolling contact between each fingertip and the object surfaces can be allowed because our proposed system has soft and deformable hemispheric fingertips. Moreover, a torsional contact model between each fingertip and the object surfaces is newly proposed. It is based on an assumption that the torsional motion induces an elastic strain potential. Secondly, a dynamic object manipulation control method is designed. The control signal is composed of four parts, the one is for grasping the object stably, the second one is for controlling a position of the object, the third one is for controlling an attitude of the object, and the last one is for the torsional fingertip motion. A numerical simulation based on our model is performed, and a manipulation experiment by using our developed setup is performed. The usefulness of our proposed method is demonstrated through these results.