A two-phased object orientation controller on soft finger operations

The greatest characteristic of soft-fingered manipulation is its softness and flexibility during manipulating operations. In previous works, this intrinsic property had been quantitatively explained from the viewpoint of physical and mechanical perspective that the deformation energy induced by large elastic distortion automatically has a minimum equilibrium point. Hence this report first derive equations of motion of two-fingered soft finger robotic hand on the basis of energy- based analysis, and explain that an equilibrium point on a combined energy function exists even in the case of manipulating motions by the hand. In this paper, the equilibrium point is called LMEEwC that is unfolded as local minimum of elastic energy with constraints. Next, we show that the posture control of a rigid object grasped by the minimal degrees-of-freedom hand can easily be achieved by applying a two-phased controller associated with each joint angle of the hand, which is newly proposed in this report. This control scheme is constructed by two parts: a PD controller with respect to the finger angle and an integral controller with respect to the orientation of the grasped object. The characteristics of the control method of the latter part is that the desired joint angle of the hand is produced dynamically by the integral controller with respect to the object orientation. Finally, we clarify the effectiveness of the proposed control method in the case of the soft-fingered manipulation.