Two-phased controller for a pair of 2-DOF soft fingertips based on the qualitative relationship between joint angles and object location

We have previously shown that hemispherical soft fingertips are at equilibrium when they are in contact with objects, suggesting that the contact force and flexibility of these soft fingertips are important for stable grasping and manipulation. Hence, by making use of these characteristics, soft fingers can manipulate objects dexterously. While our previous work has focused on pairs of 1-DOF fingers with soft fingertips, we present here a control scheme by which a pair of 2-DOF soft fingers can control a grasped object's planar location. This new control scheme consists of a proportional controller of finger joint angles and an integral controller of object location. We subsequently describe our formulation of the equations of motion of manipulations performed by a pair of 2-DOF soft fingertips. We then apply this control scheme to an experimental situation and to a simulation based on a parallel distributed virtual spring model to control the planar location of a grasped object. These findings demonstrate the validity of the proposed scheme. Finally, we show that extending the theory of the proposed controller can lead to the control of grasping forces.