Grasp Stiffness Matrix for Soft Finger Contact Model in Robotic Applications

2000 ◽  
Author(s):  
Abdul Ghafoor ◽  
Jian S. Dai ◽  
Joseph Duffy
Keyword(s):  
Stiffness Matrix ◽  
Contact Stiffness ◽  
Point Contact ◽  
Point Contacts ◽  
Rigid Object ◽  
Equivalent Point ◽  
Line Spring Model ◽  
On Line ◽  
Soft Finger

Abstract This paper proposes a practical and analytical model for soft finger grasp. It presents a contact stiffness matrix by applying congruence transformation and mapping stiffnesses from a line spring model onto translational and rotational stiffnesses. The contact that is realised in this paper is in the form of a patch contact with evenly distributed finite number of equivalent point contacts. An analytical approach is hence proposed based on line springs and screw representation of the frictional elastic point contacts that provides a direct correlation between the equivalent point contact and soft finger contact of a rigid object and gives a procedure to complete the analysis. The grasp achieved with the analysis provides both translational and rotational restraint. The approach and its use for finite manipulation are supported by a case study.

Stiffness Modeling of the Soft-Finger Contact in Robotic Grasping

2004 ◽  
Vol 126 (4) ◽  
pp. 646-656 ◽  
Author(s):  
Abdul Ghafoor ◽  
Jian S. Dai ◽  
Joseph Duffy
Keyword(s):  
Stiffness Matrix ◽  
Screw Theory ◽  
Contact Stiffness ◽  
Point Contact ◽  
Elastic Model ◽  
Point Contacts ◽  
Stiffness Analysis ◽  
Stiffness Properties ◽  
Congruence Transformation ◽  
Soft Finger

This paper investigates the soft-finger contact by presenting the contact with a set of line springs based on screw theory, reveals the rotational effects, and identifies the stiffness properties of the contact. An elastic model of a soft-finger contact is proposed and a generalized contact stiffness matrix is developed by applying the congruence transformation and by introducing stiffness mapping of the line springs in translational directions and rotational axes. The effective stiffnesses along these directions and axes are hence obtained and the rotational stiffnesses are revealed. This helps create a screw representation of a six-dimensional soft-finger contact and produce an approach of analyzing and synthesizing a robotic grasp without resorting to the point contact representation. The correlation between the rotational stiffness, the number of equivalent point contacts and the number of equivalent contours is given and the stiffness synthesis is presented with both modular and direct approaches. The grasp thus achieved from the stiffness analysis contributes to both translational and rotational restraint and the stiffness matrix so developed is proven to be symmetric and positive definite. Case studies are presented with a two-soft-finger grasp and a three-soft-finger grasp. The grasps are analyzed with a general stiffness matrix which is used to control the fine displacements of a grasped object by changing the preload on the contact.

Torsional Stiffnesses of the Soft Contact of a Soft-Robotic-Finger

2004 ◽  
Author(s):  
Abdul Ghafoor ◽  
Jian S. Dai
Keyword(s):  
Contact Stiffness ◽  
Torsional Stiffness ◽  
Soft Contact ◽  
Stiffness Coefficients ◽  
Contact Points ◽  
Contour Representation ◽  
Stiffness Characteristics ◽  
Elastic Elements ◽  
Soft Finger

This paper investigates the equivalent contour representation of the soft contact, proposes torsional stiffness coefficients relating the contact contour to a soft-robotic-finger contact and develops the finite elastic elements of the soft finger. The contact is modeled between a grasped object and a soft fingertip as a number of contours with a set of equivalent elastic contact points arranged on each contour. The stiffness matrix model is presented and related to the torsional stiffness coefficients. The paper further reveals the effect of the robotic finger stiffness on the stiffness coefficients by modeling the finger with a finite number of elastic elements arranged serially. The couples which arise from the elastic elements give translational and torsional stiffness characteristics of the soft contact. This presents a way of measuring soft contact stiffness. In particular, the torsional stiffness is investigated with its variance with the contours. A case study is presented at the end.

New advances in automatic selection of eligible surface elements for grasping and fixturing

Robotica ◽  
2009 ◽  
Vol 28 (3) ◽  
pp. 341-348 ◽  
Author(s):  
Y. Zheng ◽  
W.-H. Qian
Keyword(s):  
General Condition ◽  
Point Contact ◽  
Point Contacts ◽  
Object Surface ◽  
Quantitative Criterion ◽  
Grasp Planning ◽  
Line Segments ◽  
Force Closure ◽  
Soft Finger ◽  
Selection Of

SUMMARYMany object surfaces involve a number of pieces, expressed by different equations. Previous methods of optimal grasp planning can hardly cope with such cases. Ding et al. solve this problem by characterizing the object surface with convex facets and discrete points, then selecting the eligible ones for force-closure, and finally seeking the optimal contact positions on the selected elements. So far, however, no point contact with friction (PCwF) but only frictionless point contacts (FPC) can be used on the facets, while soft finger contacts (SFC) are excluded at all. In this paper, to the above two surface elements we add line segments. Moreover, the limitations on the contact types are completely removed. A general condition and a quantitative criterion of eligibility are presented, followed by a heuristic algorithm and an iterative algorithm for finding the better eligible elements. Three common examples show: the new advances make the formerly tough problems smoothly solvable.

On-line Tropical Epidemiology -A Case-Study from The Gambia

1987 ◽  
Vol 26 (02) ◽  
pp. 73-76 ◽  
Author(s):  
Kathryn Rowan ◽  
P. Byass ◽  
R. W. Snow
Keyword(s):  
Data Collection ◽  
Field Trial ◽  
Error Rates ◽  
Database Management System ◽  
Bed Nets ◽  
Completion Rates ◽  
On Line ◽  
Access To Data ◽  
Rapid Processing

SummaryThis paper reports on a computerised approach to the management of an epidemiological field trial, which aimed at determining the effects of insecticide-impregnated bed nets on the incidence of malaria in children. The development of a data system satisfying the requirements of the project and its implementation using a database management system are discussed. The advantages of this method of management in terms of rapid processing of and access to data from the study are described, together with the completion rates and error rates observed in data collection.

RECYCLED WATER RISK PERCEPTION - A COMPARISON OF TWO CASE STUDIES

2007 ◽  
Vol 2 (4) ◽  
Author(s):  
A. Hurlimann
Keyword(s):  
Risk Perception ◽  
Case Studies ◽  
Perceived Risk ◽  
Capital City ◽  
Recycled Water ◽  
Urban Centre ◽  
On Line ◽  
Line Survey ◽  
Water Uses

This paper reports results from a study comparing perceived risk associated with various recycled water uses in two Australian locations, both in the state of Victoria: the capital city Melbourne, and Bendigo a regional urban centre. Both locations are experiencing ‘drought’, but Bendigo is experiencing this in a more acute manner. A case study is used in each location. Both case studies involve future use of recycled water in new commercial buildings. An on-line survey was used to measure attitudes to recycled water of the future occupants of both buildings. The study found perceived risk associated with 11 uses of recycled water increased as the use became increasingly personal. Interestingly, no difference in perceived risk associated with 11 uses of recycled water was found between locations. Prior experience (use) of recycled water was found to be a significant and positive factor in reducing risk perception. Various attitudinal variables were found to be significant influences on perceived risk. Results indicate that reducing perceived risk of recycled water use may increase satisfaction with its use.

scholarly journals DOLARS, a Distributed On-Line Activity Recognition System by Means of Heterogeneous Sensors in Real-Life Deployments—A Case Study in the Smart Lab of The University of Almería

Sensors ◽  
2021 ◽  
Vol 21 (2) ◽  
pp. 405
Author(s):  
Marcos Lupión ◽  
Javier Medina-Quero ◽  
Juan F. Sanjuan ◽  
Pilar M. Ortigosa
Keyword(s):  
Real Time ◽  
Activity Recognition ◽  
Real Life ◽  
Recognition System ◽  
Machine Learning Algorithms ◽  
Sensor Data ◽  
Heterogeneous Sensors ◽  
On Line ◽  
The University

Activity Recognition (AR) is an active research topic focused on detecting human actions and behaviours in smart environments. In this work, we present the on-line activity recognition platform DOLARS (Distributed On-line Activity Recognition System) where data from heterogeneous sensors are evaluated in real time, including binary, wearable and location sensors. Different descriptors and metrics from the heterogeneous sensor data are integrated in a common feature vector whose extraction is developed by a sliding window approach under real-time conditions. DOLARS provides a distributed architecture where: (i) stages for processing data in AR are deployed in distributed nodes, (ii) temporal cache modules compute metrics which aggregate sensor data for computing feature vectors in an efficient way; (iii) publish-subscribe models are integrated both to spread data from sensors and orchestrate the nodes (communication and replication) for computing AR and (iv) machine learning algorithms are used to classify and recognize the activities. A successful case study of daily activities recognition developed in the Smart Lab of The University of Almería (UAL) is presented in this paper. Results present an encouraging performance in recognition of sequences of activities and show the need for distributed architectures to achieve real time recognition.

scholarly journals Electromigration-induced directional steps towards the formation of single atomic Ag contacts

2020 ◽  
Vol 11 ◽  
pp. 680-687
Author(s):  
Atasi Chatterjee ◽  
Christoph Tegenkamp ◽  
Herbert Pfnür
Keyword(s):  
Fourier Transforms ◽  
Single Point ◽  
Point Contact ◽  
Single Atom ◽  
Point Contacts ◽  
Cross Sectional ◽  
Shell Effects ◽  
Theoretical Approaches ◽  
Average Grain Size ◽  
Thinning Process

Even though there have been many experimental attempts and theoretical approaches to understand the process of electromigration (EM), it has not been quantitatively understood for ultrathin structures and at grain boundaries. Nevertheless, we showed recently that it can be used reliably for the formation of single atomic point contacts after careful pre-structuring of the initial Ag nanostructures. The process of formation of nanocontacts by EM down to a single-atom point contact was investigated for ultrathin (5 nm) Ag structures at 100 K by measuring the conductance as a function of the time during EM. In this paper, we compare the process of thinning by EM of structures with constrictions below the average grain size of Ag layers (15 nm) with that of structures with much larger initial constrictions of around 150 nm having multiple grains at the centre constriction prior to the formation of a point contact. Even though clear morphological differences exist between both types of structures, quantized conductance plateaus showing the formation of single point contacts have been observed for both. Here we put emphasis on the thinning process by EM, just before a point contact is formed. To understand this thinning process, the semi-classical regime before the contact reaches the quantum regime was analyzed in detail. For this purpose, we used experimental conductance histograms in the range between 2G 0 and 15G 0 and their corresponding Fourier transforms (FTs). The FT analysis of the conductance histograms exhibits a clear preference for thinning along the [100] direction. Using well-established models, both atom-by-atom steps and ranges of stability, presumably caused by electronic shell effects, can be discriminated. Although the directional motion of atoms during EM leads to specific properties such as the instabilities mentioned, similarities to mechanically opened contacts with respect to cross-sectional stability were found.

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