Abstract— We derive a local minimum of an elastic potential energy due to the deformation of a hemispherical soft fingertip, and propose a quasi-static manipulation algorithm using the local minimum of the potential energy by means of two rotational fingers, on which the soft fingertips are mounted. In this model, a geometrical constraint between the grasped object and two fingertips, which includes the deformation of the fingertip, is derived. Using the constraint and the local minimum of the potential energy, we newly propose a numerical algorithm in the quasi-static manipulation. Finally, we conclude that the existence of the local minimum allows us to stably grasp an object in soft fingered manipulation.