Grasp stability analysis for elastic fingertips by using potential energy

Abstract

We propose a grasp stability index which takes into account the elastic deformation of fingertips. In this index, an evaluation value of grasp stability is derived as the minimum energy which causes slippage of a fingertip on a grasped object surface. Elastic potential energy of the fingertips and gravitational potential energy of the object are considered in this index. It is ensured that any fingertip does not slip on a grasped object surface if the external energy added to the object is less than the evaluation value. This index has good features as follows. (i) Contact forces corresponding to the grasping state are taken into account. (ii) It is possible to derive a condition of stable grasp including the kinetic energy of a grasped object. The effectiveness of this index is verified through several numerical examples.

Energy-based stability analysis for grasp selection with compliant multi-fingered hands

“…This section provides a brief overview of the framework proposed by Tsuji et Al. [8], and details our contribution which allows to evaluate the stability region around the equilibrium when the system is under an external disturbance.…”

“…The index of grasp stability developed by Tsuji et al [8] is based on the principle that, as the object is grasped using elastic fingertips, it is possible to construct a potential field around the stable equilibrium point. This potential field can be divided in two parts, the region around the stable equilibrium point where no fingertip slips, denoted as the "equilibrium region" and the region around this equilibrium region where at least one fingertip slips (see Fig.…”

“…An equilibrium for a grasp corresponds to the situation when the sum of all the forces and moment acting on the grasped object equals zero. When all forces and moments are derived from a potential function, an equilibrium is said stable if the first-order derivative of the alex.caldas@esme.fr [8]), concept illustration in 1D potential energy is null and the matrix of second-order partial derivatives (corresponding to stiffness matrix) is positive definite [3].…”

“…The study of the stiffness for the grasp stability also led to energetic approaches, as in Tsuji et al [8]. In their work, Tsuji et al proposed a stability index expressed as the minimal amount of energy needed to destabilize a grasp (see Fig.…”

“…This paper presents a grasp stability analysis based on a energetic approach. This approach takes in consideration the elastic deformation of the fingertips in the same way as proposed by Tsuji et al [8], but But, our approach generalizes it in integrating the whole geometry of the hand as well as the stiffness brought by the joints into the system. This approach is well suited for compliant hands, with passive or active elastic joints.…”