Externally Sensorless Position and Attitude Control of a Grasped Object Using a Virtual Frame by a Triple Soft-Fingered Hand

This paper proposes a novel object manipulation method to regulate the position and attitude of a rigid object of parallelepiped with maintaining stable grasping by a triple soft-fingered hand without use of any external sensing. In the authors' previous works, “the Blind Grasping” control scheme was proposed for a pair of soft-fingered hand to accomplish dynamic object grasping without use of any external sensing. However, it has just achieved a stable object grasping, and a simultaneous object position and attitude control has not yet been treated, so far. To this end, a ternary finger in addition to a pair of fingers is introduced in order to enhance the Blind Grasping manner to “the Blind Manipulation” manner. Since the Blind Grasping control input has been designed for a pair of fingers, in this paper it is renewed to install it into the triple-fingered robotic hand. Moreover, both the virtual object position and attitude are utilized by defining a virtual frame instead of real information of the object position and attitude in order to achieve the Blind Manipulation. First, the overall dynamics, which considers rolling contact constraints between each fingertip and object surface, is derived. Second, a control signal to regulate the virtual object position and attitude without use of any external sensing, “the Blind Manipulation”, is designed. Next, the stability of the system is discussed briefly, and finally the usefulness of our proposed manipulation method is demonstrated through a numerical simulation.