Controlling force variations during soft-tissue grasping

2009 ◽  
Vol 223 (6) ◽  
pp. 749-753 ◽  
Author(s):  
T Alja'afreh
Keyword(s):  
Soft Tissue ◽  
Basis Set ◽  
Grasping Forces ◽  
Grasp Stability ◽  
Grasping Force ◽  
Frictional Forces ◽  
Major Criterion ◽  
Model Independent ◽  
Limited Basis ◽  
Tissue Relaxation

This paper develops a mechatronic grasper that can be used to investigate a preliminary experiment of a simple model-independent approach to control soft-tissue grasping based on, first, measurement of the total tangential grasp force and, second, discrimination of relaxation and frictional forces by imposing a limited basis set of grasper motions. The main motivation for this work is that tissue grasping is an important component of surgical procedures. However, there is a major criterion which should be achieved: maintaining grasp stability while avoiding damage due to excessive grip force. Thus, the automation of grasping force control requires a controller to apply grasping forces just sufficient to maintain grasp stability. This task is complicated by the serially connected dynamics of grasp friction and tissue relaxation.

Microgripper-Embedded Fluid Fingertip-Enhancing Positioning and Holding Abilities for Versatile Grasping

2017 ◽  
Vol 9 (6) ◽  
Author(s):  
Toshihiro Nishimura ◽  
Yoshinori Fujihira ◽  
Tetsuyou Watanabe
Keyword(s):  
Position Control ◽  
Layer Structure ◽  
Outer Part ◽  
Robotic Hand ◽  
Mechanical Constraints ◽  
Grasping Forces ◽  
Geometrical Constraints ◽  
Grasping Force ◽  
Object Shapes ◽  
Contact Position

This paper presents a novel fingertip system with a two-layer structure for robotic hands. The outer part of the structure consists of a rubber bag filled with fluid, called the “fluid fingertip,” while the inner part consists of a rigid link mechanism called a “microgripper.” The fingertip thus is a rigid/fluid hybrid system. The fluid fingertip is effective for grasping delicate objects, that is, it can decrease the impulsive force upon contact, and absorb uncertainties in object shapes and contact force. However, it can only apply a small grasping force such that holding a heavy object with a robotic hand with fluid fingertips is difficult. Additionally, contact uncertainties including inaccuracies in the contact position control cannot be avoided. In contrast, rigid fingertips can apply considerable grasping forces and thus grasp heavy objects effectively, although this makes delicate grasping difficult. To maintain the benefits of the fluid fingertip while overcoming its disadvantages, the present study examines passively operable microgripper-embedded fluid fingertips. Our goal is to use the gripper to enhance the positioning accuracy and increase the grasping force by adding geometrical constraints to the existing mechanical constraints. Grasping tests showed that the gripper with the developed fingertips can grasp a wide variety of objects, both fragile and heavy.

Two-Dimensional Team Lifting Prediction With Different Box Weights

2020 ◽  
Author(s):  
Asif Arefeen ◽  
Yujiang Xiang
Keyword(s):  
Joint Angle ◽  
Inverse Dynamics ◽  
Reaction Force ◽  
Optimization Method ◽  
Two Dimensional ◽  
Dynamics Modeling ◽  
Floating Base ◽  
Grasping Forces ◽  
Design Variables ◽  
Grasping Force

Abstract A novel multibody dynamics modeling method is proposed for two-dimensional (2D) team lifting prediction. The box itself is modeled as a floating-base rigid body in Denavit-Hartenberg representation. The interactions between humans and box are modeled as a set of grasping forces which are treated as unknowns (design variables) in the optimization formulation. An inverse-dynamics-based optimization method is used to simulate the team lifting motion where the dynamic effort of two humans is minimized subjected to physical and task-based constraints. The design variables are control points of cubic B-splines of joint angle profiles of two humans and the box, and the grasping forces between humans and the box. Two numerical examples are successfully simulated with different box weights (20 Kg and 30 Kg, respectively). The humans’ joint angle, torque, ground reaction force, and grasping force profiles are reported. The joint angle profiles are validated with the experimental data.

Multidigit Control of Contact Forces During Transport of Handheld Objects

2007 ◽  
Vol 98 (2) ◽  
pp. 851-860 ◽  
Author(s):  
Sara A. Winges ◽  
John F. Soechting ◽  
Martha Flanders
Keyword(s):  
Contact Force ◽  
Muscle Activity ◽  
Center Of Mass ◽  
Contact Forces ◽  
Load Force ◽  
Emg Activity ◽  
Experimental Conditions ◽  
Contact Plane ◽  
Grasping Forces ◽  
Grasp Stability

When an object is lifted vertically, the normal force increases and decreases in tandem with tangential (load) force to safely avoid slips. For horizontal object transport, horizontal forces at the contact surfaces can be decomposed into manipulation forces (producing acceleration/deceleration) and grasping forces. Although the grasping forces must satisfy equilibrium constraints, it is not clear what determines their modulation across time, nor the extent to which they result from active muscle contraction or mechanical interactions of the digits with the moving object. Grasping force was found to increase in an experimental condition where the center of mass was below the contact plane, compared with when it was in the contact plane. This increase may be aimed at stabilizing object orientation during translation. In another experimental condition, more complex moments were introduced by allowing the low center of mass to swing around a pivot point. Electromyographic (EMG) activity recorded from several intrinsic and extrinsic hand muscles failed to reveal active feedback regulation of contact force in this situation. Instead, in all experimental conditions, EMG data revealed a strategy of feedforward stiffness modulation. Multiple regression analysis revealed that muscle activity at remote digits (e.g., the index and ring fingers) was highly correlated with the contact force measured at another digit (e.g., the thumb). The data suggest that to maintain grasp stability during horizontal translation, predictable as well as somewhat unpredictable inertial forces are compensated for by controlling the stiffness of the hand through cocontraction and modulation of hand muscle activity.

Limited-Basis-Set Hartree-Fock Theory of NiF64−

1969 ◽  
Vol 180 (2) ◽  
pp. 385-395 ◽  
Author(s):  
H. M. Gladney ◽  
A. Veillard
Keyword(s):  
Basis Set ◽  
Hartree Fock ◽  
Limited Basis

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.

Verrucous Hyperplasia

2006 ◽  
Vol 96 (4) ◽  
pp. 348-350 ◽  
Author(s):  
Mark Anthony Rosales ◽  
Billy R. Martin ◽  
David G. Armstrong ◽  
Brent P. Nixon ◽  
H. Ryan Hall
Keyword(s):  
High Risk ◽  
Soft Tissue ◽  
External Compression ◽  
Verrucous Hyperplasia ◽  
Affected Tissue ◽  
Frictional Forces

Although verrucous hyperplasia may be common in high-risk insensitive feet, the literature contains little discussion on this topic. Treatment of verrucous hyperplasia is aimed primarily at reducing the causative forces. In cases that result from edema, external compression has proved to be adequate. If verrucous hyperplasia on the foot results from frictional forces, then shoe modifications with proper fit, accommodative liners, or fillers in the case of amputation are necessary. In recalcitrant cases, excision of the affected tissue with local soft-tissue or graft coverage has been successful. We describe a 56-year-old man with verrucous hyperplasia. (J Am Podiatr Med Assoc 96(4): 348–350, 2006)

Bond Functions and Core Correlation Energy Contributions To HeBe Potential

1998 ◽  
Vol 09 (07) ◽  
pp. 1041-1054
Author(s):  
A. S. Shalabi ◽  
E. M. Nour ◽  
W. S. Abdel Halim
Keyword(s):  
Correlation Energy ◽  
Basis Set ◽  
Energy Potential ◽  
Core Correlation ◽  
Energy Lowering ◽  
Empirical Scheme ◽  
Exchange Repulsion ◽  
Bond Functions ◽  
Well Depth ◽  
Limited Basis

An empirical scheme for implementation of bond functions in heteronuclear diatomics is suggested and applied to HeBe using universal even-tempered functions. The effects of bond functions and core-correlation energy on the interaction potential of HeBe calculated at the uncorrelated (SCF) and correlated (MBPT and CC) levels are examined. The results confirm that an accuracy of sub μ Hartree level can be obtained using even-tempered functions with s-, p-, and d- symmetry and that bond functions of size {4s2p} for He and {6s3p} for Be recovers 100% of energy lowering obtained from the addition of 10d atom-centered functions to He and 13d atom centred functions to Be. The various treatments of the electron correlation, conclude that the system is interacting weakly with a well depth from 14.5–24.7 μE h at a separation near 9.1a0 compared with 20.7–25.5 μE h previously reported with a rather limited basis set. The most reliable well depth corrected for BSSE (19.0 μE h ) was obtained at the CC-SD(T)level at separation of 8.71a0 taking into account the effects of bond functions and core correlation energy. Potential energy curves at the CC-SD(T) valence and CC-SD(T) valence + core correlation levels are analyzed in analytical forms in terms of exchange repulsion, induction and dispersion components.

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.

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