1,056 research outputs found
On Grasp Quality Measures: Grasp Robustness and Contact Force Distribution in Underactuated and Compliant Robotic Hands
The availability of grasp quality measures is fundamental for grasp planning and control, and also to drive designers in the definition and optimization of robotic hands. This work investigates on grasp robustness and quality indexes that can be applied to power grasps with underactuated and compliant hands. When dealing with such types of hands, there is the need of an evaluation method that takes into account the forces that can be actually controlled by the hand, depending on its actuation system. In this paper, we study the potential contact robustness and the potential grasp robustness (PCR, PGR) indexes. They both consider main grasp properties: contact points, friction coefficient, etc., but also hand degrees of freedom and consequently, the directions of controllable contact forces. The PCR comes directly from the classical grasp theory and can be easily evaluated, but often leads to too conservative solutions, particularly when the grasp has many contacts. The PGR is more complex and computationally heavier, but gives a more realistic, even if still conservative, estimation of the overall grasp robustness, also in power grasps. We evaluated the indexes for various simulated grasps, performed with underactuated and compliant hands, and we analyzed their variations with respect to the main grasp parameters
Simulation of degraded wheel/rail adhesion conditions on a railway roller rig for the evaluation of the effect of wheel/roller contact on control performance
Development and implementation of a differential elastic wheel–rail contact model for multibody applications
A methodology to evaluate contact areas and indentations of human fingertips based on 3D techniques for haptic purposes
This paper presents a methodology to study the contact of human fingers with surfaces based on 3D techniques. This method helps to investigate the fingertip mechanical properties which are crucial for designing haptic interfaces. The dependence of the fingertip deformation on the applied forces is obtained both with theoretical and experimental approaches. The experimental procedure is based on digital measurements by 3D optical scanners to reconstruct the geometry of the fingertip impression and on force measurements by an instrumented plate. Results highlight the force-displacement trend and can be validated with a Finite Element Model (FEM), with data from literature or with measurements at a force-strain gauge. Gross contact areas, radii and work of adhesion are also detected, and results are compared with contact models available in literature.
• A sensorized plate with a thin force sensitive resistor and a dough material layer is used to measure the contact force corresponding to a specific digital imprint.
• 3D indentation maps are obtained and evaluated by comparing the 3D scan model of fingertips during imprinting with the digital model of the undeformed fingers and of the imprints.
• Force-displacement results can be validated by comparison with a developed FEM, a force-displacement gauge or literature outcomes
Modeling Compliant Grasps Exploiting Environmental Constraints
In this paper we present a mathematical framework to describe the interaction between compliant hands and environmental constraints during grasping tasks. In the proposed model, we considered compliance at wrist, joint and contact level. We modeled the general case in which the hand is in contact with the object and the surrounding environment. All the other contact cases can be derived from the proposed system of equations. We performed several numerical simulation using the SynGrasp Matlab Toolbox to prove the consistency of the proposed model. We tested different combinations of compliance as well as different reference inputs for the hand/arm system considered. This work has to be intended as a tool for compliant hand designer since it allows to tune compliance at different levels before the real hand realization. Furthermore, the same framework can be used for compliant hand simulation in order to study the interaction with the environmental constrains and to plan complex manipulation tasks
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