Mapping Synergies From Human to Robotic Hands With Dissimilar Kinematics: An Approach in the Object Domain

Abstract

One of the major limitations to the use of advanced robotic hands in industries is the complexity of the control system design due to the large number of motors needed to actuate their degrees of freedom. It is our belief that the development of a unified control framework for robotic hands will allow us to extend the use of these devices in many areas. Borrowing the terminology from software engineering, there is a need for middleware solutions to control the robotic hands independently from their specific kinematics and focus only on the manipulation tasks. To simplify and generalize the control of robotic hands, we take inspiration from studies in neuroscience concerning the sensorimotor organization of the human hand. These studies demonstrated that, notwithstanding the complexity of the hand, a few variables are able to account for most of the variance in the patterns of configurations and movements. The reduced set of parameters that humans effectively use to control their hands, which are known in the literature as synergies, can represent the set of words for the unified control language of robotic hands, provided that we solve the problem of mapping human hand synergies to actions of the robotic hands. In this study, we propose a mapping designed in the manipulated object domain in order to ensure a high level of generality with respect to the many dissimilar kinematics of robotic hands. The role of the object is played by a virtual sphere, whose radius and center position change dynamically, and the role of the human hand is played by a hand model referred to as ``paradigmatic hand,'' which is able to capture the idea of synergies in human hands

A static intrinsically passive controller to enhance grasp stability of object-based mapping between human and robotic hands

“…1 and let the paradigmatic hand be described by the joint variable vector q h ∈ n qh . Assume that the subspace of all configurations can be represented by a lower dimensional input vector z ∈ nz (with n z ≤ n qh ) which parametrizes the motion of the joint variables along the synergies q h = S h z being S h ∈ n qh ×nz the synergy matrix as defined in [6]. In terms of velocities one getsq h = S hż .…”

“…In the mapping algorithm proposed in [6] a set of reference points p r is chosen also on the robotic hand and a virtual sphere is thus defined in a similar way. The same motion of the two spheres is imposed, apart of a scaling factor…”

“…The variation of the sphere radius is instead related to the rest length of the connecting stiffness l i,des . By imposing l i,des = αṙ l off (11) where l off is a fixed initial offset for the connecting spring and α is used to mitigate the difference in the workspace with a similar meaning of K c (eq. (4)) for the virtual object mapping, it is possible to related the radial deformation of the sphere to the connecting force.…”

“…In [6], [7], [8], it has been described how an object-based mapping is able to reproduce movements of a human hand model, with particular emphasis on the synergistic motion of a paradigmatic hand, in different robotic hands without considering the specific kinematics. The object-based mapping is obtained considering two virtual objects, one on the human and one on robotic hand.…”

“…In this paper we will use the concept of virtual spherical object introduced in [11] as a simplified way to describe human hand motion. The basic idea, represented in Fig.…”