Force Optimization Approaches for Common Anthropomorphic Grasps

2016 ◽  
Author(s):  
Aimee Cloutier ◽  
James Yang
Keyword(s):  
Point Contact ◽  
Contact Forces ◽  
Applied Force ◽  
Linear Matrix ◽  
Human Hand ◽  
Numerical Examples ◽  
Contact Points ◽  
Force Optimization ◽  
Grasping Forces ◽  
Grasping Force

A smart choice of contact forces between robotic grasping devices and objects is important for achieving a balanced grasp. Too little applied force may cause an object to slip or be dropped, and too much applied force may cause damage to delicate objects. Prior methods of grasping force optimization in literature have mostly assumed grasp only at the fingertips but have rarely considered how the whole hand grasps more common to anthropomorphic hands affect the optimization of grasping forces. Further, although numerical examples of grasping force optimization methods are routinely provided, it is often difficult to compare the performance of separate methods when they are evaluated using different parameters, such as the type of grasping device, the object grasped, and the contact model, among other factors. This paper presents three optimization approaches (linear, nonlinear, and nonlinear with linear matrix inequality (LMI) friction constraints) which are compared for an anthropomorphic hand. Numerical examples are provided for three types of grasp commonly performed by the human hand (cylindrical grasp, tip grasp, and tripod grasp) using both soft finger contact and point contact with friction models. Contact points between the hand and the object are predetermined. Results are compared based on their accuracy, computational efficiency, and other various benefits and drawbacks unique to each method. Future work will extend the problem of grasping force optimization to include consideration for variable forces and object manipulation.

scholarly journals Grasping Force Optimization Approaches for Anthropomorphic Hands

2017 ◽  
Vol 10 (1) ◽  
Author(s):  
Aimee Cloutier ◽  
James Yang
Keyword(s):  
Computational Efficiency ◽  
Linear Method ◽  
Contact Forces ◽  
Applied Force ◽  
Contact Friction ◽  
Linear Matrix ◽  
Human Hand ◽  
Contact Points ◽  
Force Optimization ◽  
Grasping Force

An appropriate choice of contact forces for anthropomorphic robotic grasping devices is important for achieving a balanced grasp. Too little applied force may cause an object to slip or be dropped, and too much applied force may cause damage to delicate objects. Prior methods of grasping force optimization (GFO) in the literature can be difficult to compare due to variability in the parameters, such as the type of grasping device, the object grasped, and the contact model, among other factors. Additionally, methods are typically tested on a very small number of scenarios and may not be as robust in other settings. This paper presents a detailed analysis of three optimization approaches based on the literature, comparing them on the basis of accuracy and computational efficiency. Numerical examples are provided for three types of grasp commonly performed by the human hand (cylindrical grasp, tip grasp, and tripod grasp) using both soft finger (SF) contact and hard finger (HF) contact friction models. For each method and grasping example, an external force is applied to the object in eighteen different directions to provide a more complete picture of the methods' performance. Contact points between the hand and the object are predetermined (given). A comparison of the results showed that the nonlinear and linear matrix inequality (LMI) approaches perform best in terms of accuracy, while the computational efficiency of the linear method is stronger unless the number of contact points and segments becomes too large. In this case, the nonlinear method performs more quickly. Future work will extend the problem of GFO to real-time implementation, and a related work (briefly addressed here) examines the sensitivity of optimization methods to variability in the contact locations.

Examining the Robustness of Grasping Force Optimization Methods Using Uncertainty Analysis

2018 ◽  
Vol 4 (4) ◽  
Author(s):  
Aimee Cloutier ◽  
James Yang
Keyword(s):  
Center Of Mass ◽  
Linear Method ◽  
Optimization Methods ◽  
Linear Matrix ◽  
Human Hand ◽  
Nonlinear Method ◽  
Object A ◽  
Force Optimization ◽  
Grasping Force ◽  
Robotic Devices

The development of robust and adaptable methods of grasping force optimization (GFO) is an important consideration for robotic devices, especially those which are designed to interact naturally with a variety of objects. Along with considerations for the computational efficiency of such methods, it is also important to ensure that a GFO approach chooses forces which can produce a stable grasp even in the presence of uncertainty. This paper examines the robustness of three methods of GFO in the presence of variability in the contact locations and in the coefficients of friction between the hand and the object. A Monte Carlo simulation is used to determine the resulting probability of failure and sensitivity levels when variability is introduced. Two numerical examples representing two common grasps performed by the human hand are used to demonstrate the performance of the optimization methods. Additionally, the method which yields the best overall performance is also tested to determine its consistency when force is applied to the object's center of mass in different directions. The results show that both the nonlinear and linear matrix inequality (LMIs) methods of GFO produce acceptable results, whereas the linear method produces unacceptably high probabilities of failure. Further, the nonlinear method continues to produce acceptable results even when the direction of the applied force is changed. Based on these results, the nonlinear method of GFO is considered to be robust in the presence of variability in the contact locations and coefficients of friction.

scholarly journals Modelling elastic structures with strong nonlinearities with application to stick–slip friction

2014 ◽  
Vol 470 (2161) ◽  
pp. 20130593 ◽  
Author(s):  
Robert Szalai
Keyword(s):  
Point Contact ◽  
Linear Structure ◽  
Transformation Method ◽  
Friction Model ◽  
Contact Forces ◽  
Stick Slip ◽  
Lipschitz Continuous ◽  
Contact Points ◽  
Dimensional Equation ◽  
Low Dimensional

An exact transformation method is introduced that reduces the governing equations of a continuum structure coupled to strong nonlinearities to a low-dimensional equation with memory. The method is general and well suited to problems with isolated discontinuities such as friction and impact at point contact. It is assumed that the structure is composed of two parts: a continuum but linear structure and finitely many discrete but strong nonlinearities acting at various contact points of the elastic structure. The localized nonlinearities include discontinuities, e.g. the Coulomb friction law. Despite the discontinuities in the model, we demonstrate that contact forces are Lipschitz continuous in time at the onset of sticking for certain classes of structures. The general formalism is illustrated for a continuum elastic body coupled to a Coulomb-like friction model.

Analysis of Wheel/Rail Contact Geometry in Turnout Section

2009 ◽  
Author(s):  
Hiroyuki Sugiyama ◽  
Yoshimitsu Tanii ◽  
Yoshihiro Suda
Keyword(s):  
Point Contact ◽  
Numerical Procedure ◽  
Contact Geometry ◽  
Cross Sectional ◽  
Numerical Examples ◽  
Contact Points ◽  
Contact Configuration

In this investigation, a numerical procedure that can be used for the analysis of wheel/rail two-point contact geometries in turnout sections is developed. In turnout section, the tongue rail changes its shape along the track. Cross-sectional shapes of the tongue rail, therefore, need to be generated by interpolations along the rail and these profiles are used to determine the location of contact points for given location of wheelset along the track trajectory. Numerical examples of wheel/rail contact in point section are presented in order to demonstrate the use of the procedure developed in this investigation and the effect of wheel profiles on the contact configuration in turnout section is discussed.

Modulation of Grasping Forces During Object Transport

2005 ◽  
Vol 93 (1) ◽  
pp. 137-145 ◽  
Author(s):  
Michael A. Smith ◽  
John F. Soechting
Keyword(s):  
Horizontal Plane ◽  
Grip Force ◽  
Peak Velocity ◽  
Translational Motion ◽  
Contact Forces ◽  
Load Force ◽  
Directional Tuning ◽  
Grasping Forces ◽  
Grasping Force ◽  
Object Transport

Subjects held an instrumented object in a tripod grasp and moved it in the horizontal plane in various directions. The contact forces at the digits were measured and the grip force was decomposed into 2 components: a manipulating force responsible for accelerating the object and a grasping force responsible for holding the object steady. The grasping forces increased during the movement, reaching a peak near the time of peak velocity. The grasping forces also exhibited directional tuning, but this tuning was idiosyncratic for each subject. Although the overall grip forces should be modulated with acceleration, the load force did not vary during the task. Therefore the increase in the grasping force is not required to prevent slip. Rather, it is suggested that grasping force increases during translational motion to stabilize the orientation of grasped objects.

Nonlinear Manipulation Control of a Compliant Object by Dual Fingers

2005 ◽  
Vol 128 (3) ◽  
pp. 473-481 ◽  
Author(s):  
Z. Doulgeri ◽  
A. Golfakis
Keyword(s):  
Output Feedback ◽  
Feedback Linearization ◽  
Point Contact ◽  
Contact Forces ◽  
Constraint Forces ◽  
Planar Case ◽  
Grasping Force ◽  
Simulation Results ◽  
Output Transformation ◽  
Linearization Techniques

This paper refers to the control of the position and contact forces of a compliant rectangular object grasped by a pair of robot fingers for the planar case, using input-output feedback linearization techniques. Point contact with friction is assumed and the linearizing control is designed for the case of controlling the object position and grasping force and then extended to include the constraint forces and the object orientation. In the last case, an appropriate output transformation is proposed to avoid the singularity of the decoupling matrix and apply the method successfully. This work considers the planar case and provides simulation results that confirm the theoretical findings.

Analysis of Wheel/Rail Contact Geometry on Railroad Turnout Using Longitudinal Interpolation of Rail Profiles

2010 ◽  
Vol 6 (2) ◽  
Author(s):  
Hiroyuki Sugiyama ◽  
Yoshimitsu Tanii ◽  
Ryosuke Matsumura
Keyword(s):  
Point Contact ◽  
Numerical Procedure ◽  
Contact Geometry ◽  
Cross Sectional ◽  
Numerical Examples ◽  
Contact Points ◽  
The Given

In this investigation, a numerical procedure that can be used for the analysis of wheel/rail two-point contact geometries in turnout sections is developed. In turnout section, the tongue rail changes its shape along the track. Cross-sectional shapes of the tongue rail, therefore, need to be generated by interpolations along the track and these profiles are used to determine the location of contact points for the given location of wheelset. Several numerical examples are presented in order to demonstrate the use of the procedure developed in this investigation and the effect of wheel profiles on contact geometry in turnout section is discussed.

Sensing and Force-Feedback Exoskeleton Robotic (SAFER) Glove Mechanism for Hand Rehabilitation

2015 ◽  
Author(s):  
Zhou Ma ◽  
Pinhas Ben-Tzvi ◽  
Jerome Danoff
Keyword(s):  
Force Feedback ◽  
Force Sensor ◽  
Gaussian Mixture ◽  
Contact Forces ◽  
Learning System ◽  
Human Hand ◽  
Hand Rehabilitation ◽  
Mixture Regression ◽  
Grasping Force ◽  
Force Contact

This paper presents the design and application of the SAFER glove in the field of hand rehabilitation. The authors present preliminary results on a new hand grasping rehabilitation learning system that is designed to gather kinematic and force information of the human hand and to playback the motion to assist a user in common hand grasping movements, such as grasping a bottle of water. The fingertip contact forces during grasping have been measured by the SAFER Glove from 12 subjects. The measured fingertip contact forces were modeled with Gaussian Mixture Model (GMM) based on machine learning approach. The learned force distributions were then used to generate fingertip force trajectories with a Gaussian Mixture Regression (GMR) method. To demonstrate the glove’s potential to manipulate the hand, experiments with the glove fitted on a wooden hand to grasp various objects were performed. Instead of defining a grasping force, contact force trajectories were used to control the SAFER Glove to actuate/assist this hand while carrying out a learned grasping task. To prove that the hand can be driven safely by the haptic mechanism, force sensor readings placed between each finger and the mechanism have been plotted. The experimental results show the potential of the proposed system in future hand rehabilitation therapy.

A Simplified Analytical Model of Rolling/Sliding Behavior and Friction in Four-Point-Contact Ball Bearings and Screws

2017 ◽  
Author(s):  
Bo Lin ◽  
Molong Duan ◽  
Chinedum E. Okwudire ◽  
Jason S. Wou
Keyword(s):  
Analytical Model ◽  
Contact Point ◽  
Point Contact ◽  
Contact Angles ◽  
Friction Model ◽  
Contact Forces ◽  
Ball Bearings ◽  
Contact Points ◽  
Pure Rolling ◽  
Coulomb Friction Model

Four-point contact between ball and raceways is common in machine elements like ball bearings and ball screws. The ideal four-point-contact machine element is designed with pure rolling (i.e., no sliding at contact points) to minimize friction. However, this ideal may not always be achieved, leading to sliding and higher frictional forces. In this paper, a simplified analytical model for rolling/sliding behavior and friction in four-point contact is developed, based on Coulomb friction model and rigid body assumption. It is found that pure rolling is only possible when the contact-point geometry satisfies a certain relationship. When pure rolling condition fails to hold, the sliding contact point(s) can be determined analytically as a function of contact forces and contact angles. Case studies are presented to demonstrate how the proposed model could elucidate the roles of misalignments, manufacturing errors and loading conditions on rolling/sliding behavior and friction.

Three-Point Contact Study of a Wheelset and Rails

2016 ◽  
Author(s):  
Behrooz Fallahi ◽  
Chao Pan
Keyword(s):  
Coordinate System ◽  
Point Contact ◽  
Algebraic Equations ◽  
Numerical Examples ◽  
Block Matrices ◽  
Constraint Equations ◽  
Contact Points ◽  
Set Up

Three-point contact occurs in curving and transfer of a wheelset over switches and turnouts. In this study, an approach is presented that enforces three-point contact between a wheelset and a rail. This is accomplished by placing the wheelset over the track by setting the wheelset position parameters. Then, the location of all common normal are computed. Next, three common normal with shortest length are used to set up the non-penetrating constraint equations in track coordinate system. This led to nine algebraic equations whose Jacobean can be represented by block matrices. A Newton iterate based on these block matrices are used to compute the location of the three contact points. Several numerical examples are presented to verify the accuracy of the approach.

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