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.

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.

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 The influence of visual and haptic material information on early grasping force

2019 ◽  
Vol 6 (3) ◽  
pp. 181563 ◽  
Author(s):  
Wouter M. Bergmann Tiest ◽  
Astrid M. L. Kappers
Keyword(s):  
Coefficient Of Friction ◽  
Visual Information ◽  
Early Phase ◽  
Grip Force ◽  
Load Force ◽  
Vertical Acceleration ◽  
Haptic Information ◽  
The Coefficient Of Friction ◽  
Grasping Force ◽  
Lift Off

In this paper, we assess the importance of visual and haptic information about materials for scaling the grasping force when picking up an object. We asked 12 participants to pick up and lift objects with six different textures, either blindfolded or with visual information present. We measured the grip force and estimated the load force from the object’s weight and vertical acceleration. The coefficient of friction of the materials was measured separately. Already at an early phase in the grasp (before lift-off), the grip force correlated highly with the textures’ static coefficient of friction. However, no strong influence on the presence of visual information was found. We conclude that the main mechanism for modulation of grip force in the early phase of grasping is the real-time sensation of the texture’s friction.

scholarly journals Design and Calibration of a Force/Tactile Sensor for Dexterous Manipulation

Sensors ◽  
2019 ◽  
Vol 19 (4) ◽  
pp. 966 ◽  
Author(s):  
Marco Costanzo ◽  
Giuseppe De Maria ◽  
Ciro Natale ◽  
Salvatore Pirozzi
Keyword(s):  
Experimental Validation ◽  
Sensory System ◽  
Tactile Sensor ◽  
Contact Forces ◽  
Dexterous Manipulation ◽  
Soft Contact ◽  
Grasping Force ◽  
Sense Of Touch ◽  
Human Sense ◽  
Robotic Applications

This paper presents the design and calibration of a new force/tactile sensor for robotic applications. The sensor is suitably designed to provide the robotic grasping device with a sensory system mimicking the human sense of touch, namely, a device sensitive to contact forces, object slip and object geometry. This type of perception information is of paramount importance not only in dexterous manipulation but even in simple grasping tasks, especially when objects are fragile, such that only a minimum amount of grasping force can be applied to hold the object without damaging it. Moreover, sensing only forces and not moments can be very limiting to securely grasp an object when it is grasped far from its center of gravity. Therefore, the perception of torsional moments is a key requirement of the designed sensor. Furthermore, the sensor is also the mechanical interface between the gripper and the manipulated object, therefore its design should consider also the requirements for a correct holding of the object. The most relevant of such requirements is the necessity to hold a torsional moment, therefore a soft distributed contact is necessary. The presence of a soft contact poses a number of challenges in the calibration of the sensor, and that is another contribution of this work. Experimental validation is provided in real grasping tasks with two sensors mounted on an industrial gripper.

Effects of local and core body temperature on grip force modulation during movement-induced load force fluctuations

2008 ◽  
Vol 103 (1) ◽  
pp. 59-69 ◽  
Author(s):  
Stephen S. Cheung ◽  
Luke F. Reynolds ◽  
Mark A. B. Macdonald ◽  
Constance L. Tweedie ◽  
Robin L. Urquhart ◽  
...  
Keyword(s):  
Body Temperature ◽  
Grip Force ◽  
Core Body Temperature ◽  
Load Force ◽  
Force Fluctuations ◽  
Force Modulation ◽  
Core Body

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.

Contact force analysis on two-fingered robot grasping

2020 ◽  
pp. 146441932096402
Author(s):  
Jiun-Ru Chen ◽  
Wei-En Chen ◽  
CH Liu ◽  
Yin-Tien Wang ◽  
CB Lin ◽  
...  
Keyword(s):  
Kinetic Analysis ◽  
Contact Force ◽  
Numerical Procedure ◽  
Spherical Body ◽  
Solution Procedure ◽  
The Body ◽  
Contact Forces ◽  
Grasping Forces ◽  
Robot Grasping ◽  
Force Displacement

A procedure for inverse kinetic analysis on two hard fingers grasping a hard sphere is proposed in this study. Contact forces may be found for given linear and angular accelerations of a spherical body. Elastic force-displacement relations predicted by Hertz contact theory are used to remove the indeterminancy produced by rigid body modelling. Two types of inverse kinetic analysis may be dealt with. Firstly, as the fingers impose a given tightening displacement on the body, and carry it to move with known accelerations, corresponding grasping forces may be determined by a numerical procedure. In this procedure one contact force may be chosen as the principal unknown, and all other contact forces are expressed in terms of this force. The numerical procedure is hence very efficient since it deals with a problem with only one unknown. The solution procedure eliminates slipping thus only nonslip solutions, if they exist, are found. Secondly, when the body is moving with known accelerations, if the grasping direction of the two fingers is also known, then the minimum tightening displacement required for non-sliding grasping may be obtained in closed form. In short, the proposed technique deals with a grasping system that has accelerations, and in this study the authors show that indeterminancy may be used to reduce the complexity of the problem.

Variable and intermittent grip force control in response to differing load force dynamics

2018 ◽  
Vol 237 (3) ◽  
pp. 687-703 ◽  
Author(s):  
Francis M. Grover ◽  
Patrick Nalepka ◽  
Paula L. Silva ◽  
Tamara Lorenz ◽  
Michael A. Riley
Keyword(s):  
Force Control ◽  
Grip Force ◽  
Load Force ◽  
Force Dynamics ◽  
Grip Force Control

Wrist Action Affects Precision Grip Force

1997 ◽  
Vol 78 (1) ◽  
pp. 271-280 ◽  
Author(s):  
Mary M. Werremeyer ◽  
Kelly J. Cole
Keyword(s):  
Grip Force ◽  
Precision Grip ◽  
Load Force ◽  
Myoelectric Activity ◽  
Resistive Load ◽  
Wrist Flexion ◽  
Wrist Extension ◽  
Hand Muscles ◽  
Force Pulse ◽  
Grasp Stability

Werremeyer, Mary M. and Kelly J. Cole. Wrist action affects precision grip force. J. Neurophysiol. 78: 271–280, 1997. When moving objects with a precision grip, fingertip forces normal to the object surface (grip force) change in parallel with forces tangential to the object (load force). We investigated whether voluntary wrist actions can affect grip force independent of load force, because the extrinsic finger muscles cross the wrist. Grip force increased with wrist angular speed during wrist motion in the horizontal plane, and was much larger than the increased tangential load at the fingertips or the reaction forces from linear acceleration of the test object. During wrist flexion the index finger muscles in the hand and forearm increased myoelectric activity; during wrist extension this myoelectric activity increased little, or decreased for some subjects. The grip force maxima coincided with wrist acceleration maxima, and grip force remained elevated when subjects held the wrist in extreme flexion or extension. Likewise, during isometric wrist actions the grip force increased even though the fingertip loads remained constant. A grip force “pulse” developed that increased with wrist force rate, followed by a static grip force while the wrist force was sustained. Subjects could not suppress the grip force pulse when provided visual feedback of their grip force. We conclude that the extrinsic hand muscles can be recruited to assist the intended wrist action, yielding higher grip-load ratios than those employed with the wrist at rest. This added drive to hand muscles overcame any loss in muscle force while the extrinsic finger flexors shortened during wrist flexion motion. During wrist extension motion grip force increases apparently occurred from eccentric contraction of the extrinsic finger flexors. The coactivation of hand closing muscles with other wrist muscles also may result in part from a general motor facilitation, because grip force increased during isometric knee extension. However, these increases were related weakly to the knee force. The observed muscle coactivation, from all sources, may contribute to grasp stability. For example, when transporting grasped objects, upper limb accelerations simultaneously produce inertial torques at the wrist that must be resisted, and inertial loads at the fingertips from the object that must be offset by increased grip force. The muscle coactivation described here would cause similarly timed pulses in the wrist force and grip force. However, grip-load coupling from this mechanism would not contribute much to grasp stability when small wrist forces are required, such as for slow movements or when the object's total resistive load is small.

Activity of Ventroposterior Thalamus Neurons During Rotation and Translation in the Horizontal Plane in the Alert Squirrel Monkey

2008 ◽  
Vol 99 (5) ◽  
pp. 2533-2545 ◽  
Author(s):  
Vladimir Marlinski ◽  
Robert A. McCrea
Keyword(s):  
Horizontal Plane ◽  
Peak Velocity ◽  
Discharge Rate ◽  
Stimulus Frequency ◽  
Squirrel Monkeys ◽  
Response Amplitude ◽  
Whole Body ◽  
Power Functions ◽  
Stimulus Velocity ◽  
Rotational Response

The firing behavior of 107 vestibular-sensitive neurons in the ventroposterior thalamus was studied in two alert squirrel monkeys during whole body rotation and translation in the horizontal plane. Vestibular-sensitive neurons were distributed primarily along the anterior and posterior borders of ventroposterior nuclei; three clusters of these neurons could be distinguished based on their location and inputs. Eighty-four neurons responded to rotation; 66 (78%) of them responded to rotation only and 18 (22%) to both rotation and translation. Forty-one neurons were sensitive to linear translation; 23 (56%) of them responded to translation only. The population rotational response to 0.5-Hz sinusoids with a peak velocity of 40°/s showed a gain of 0.23 ± 0.15 spike·s−1·deg−1·s−1 and phase lagging behind the angular velocity by −9.3 ± 34.1°. Although rotational response amplitude increased with the stimulus velocity across the range 4–100°/s, the rotational sensitivity decreased with and was inversely proportional to the stimulus velocity. The rotational response amplitude and sensitivity increased with the stimulus frequency across the range 0.2–4.0 Hz. The population response to sinusoidal translation at 0.5 Hz and 0.1 g amplitude had a gain of 111.3 ± 53.7 spikes·s−1· g−1 and lagged behind stimulus acceleration by −71.9 ± 42.6°. Translational sensitivity decreased as acceleration increased and this was inversely proportional to the square root of the acceleration. Results of this study imply that changes in the discharge rate of vestibular-sensitive thalamic neurons can be approximated using power functions of the angular and linear velocity of spatial motion.

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