Stability Analysis of 2-D Object Grasping by a Pair of Robot Fingers with Soft and Hemispherical Ends

Abstract

It is said that “human hand” is an agent of the brain. This might attract attention from many prominent robot engineers and researchers who eventually attempted to design multi-fingered robot hands that mimic human hands. In the history of development of multi-fingered robot hands (see the literature [1] ∼ [5]), a variety of sophisticated robot hands designed and make are indeed reported. However, most of them have not yet been used widely in practice such as assembly tasks and other automation lines in place of human hands. The most important reason of this must be owing to the high cost of manufacturing such multi-fingered hands with many joints together with expensive sensing devices such as tactile and/or force sensors, which can not redeem human potentials of flexibility and versatility in execution of a variety of tasks. In fact, multi-fingered robot hands were used only in open-loop control (see [2]) and the importance of sensory feedback was not discussed in the literature until around the year of 2000 (see [12]). This paper firstly introduces a mathematical model of full dynamics of planar but vertical motion a rigid object grasped by a pair of two and three d.o.f fingers with soft and deformable tips whose shape is hemispherical. The behavior of the soft finger tips is lumped-parameterized by assuming that the soft material is distributively composed of massless springs with spring constant k (stiffness constant per unit area) and dampers in parallel.