Factors influencing the force control during precision grip

Westling, G.; Johansson, Roland S.

doi:10.1007/bf00238156

Cited by 889 publications

(477 citation statements)

References 8 publications

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“…2, during the static phase before the preparatory responses, the ratio between the grip force and the load force exceeded the minimum ratio required to prevent slips and provided a fairly constant safety margin (cf. Westling and Johansson 1984). This ratio increased during the preparatory grip force increase.…”

Section: Sudden Load Increase Produced By the Subjectmentioning

confidence: 79%

“…These subjects all habitually used high safety margins while just holding the grip apparatus still in air, i.e. the safety margin was 40-50% of the employed grip force (for inter-individual variation in safety margin see Westling and Johansson 1984).…”

Section: Sudden Load Increase Produced By the Subjectmentioning

confidence: 99%

“…While lifting and holding objects using the precision grip between the tips of the fingers and the thumb, the balance between the grip force and the load force (vertical lifting force) is accurately controlled (Johansson and Westling 1984b;Westling and Johansson 1984). Primarily, there is a programmed parallel change in the grip force and the load force.…”

Section: Introductionmentioning

confidence: 99%

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Programmed and triggered actions to rapid load changes during precision grip

1988

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Summary.A test object (grip apparatus) was held at its upper part using a precision grip. Small balls were dropped into a target cup at the bottom of the apparatus. The grip force, the load force (vertical lifting force) and the vertical movement were measured. Electromyographic activity (e.m.g.) was recorded from four antagonist pairs of hand/arm muscles primarily influencing the grip force or the load force. The balls were dropped either by the subject during a bimanual task, or unexpectedly by the experimenter. When the subject dropped the ball, preparatory actions occurred before the rapid increase in the vertical load caused by the impact. These actions appeared ca. 150 ms prior to the impact and involved a grip force increase and a lifting movement of the grip apparatus. The e.m.g, activity increased in all eight of the hand and arm muscles, indicating a general stiffening of the hand/arm system prior to the impact. Furthermore, the preparatory actions were programmed adequately for the size of the load force step at the impact, i.e. an adequate safety margin to prevent slips was preserved during the critical period of the impact. Thus, variations in this step caused by changes in (i) the weight of ball, (ii) the weight of the grip apparatus and (iii) the length of the drop were adequately taken into account during the programming of these actions. In addition, the frictional condition between the skin and the grip surface was also taken into account. The relevant sensory information apparently was obtained during the handling of the ball and the grip apparatus prior to the drop. There were also task-related automatic muscle responses triggered by the impact.These responses, which also served to stiffen the hand/arm system, were most pronounced during unexpected load changes, but they appeared too late to prevent slips. However, if no overall slip occurred, Offprint requests to: R.S. Johansson (address see above) the triggered responses were functional in the sense that they helped to quickly restore the safety margin and the vertical position of the object.

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Section: Sudden Load Increase Produced By the Subjectmentioning

confidence: 79%

Section: Sudden Load Increase Produced By the Subjectmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Programmed and triggered actions to rapid load changes during precision grip

1988

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“…However, the majority of the studies have focused only on two-digit "pinch" grasps (e.g., Westling and Johansson 1984;Johansson et al 1999), forces normal to the surface of contact (e.g., Zatsiorsky et al 2002a), and static tasks (e.g., Li et al 1998;Li 2002). For those studies that employed prismatic grasps -the type of grasp used when holding a glass filled with liquid -the grasped objects were maintained in a vertical position (e.g., Li 2002;Zatsiorsky et al 2002a).…”

Section: Introductionmentioning

confidence: 99%

Prehension synergies during nonvertical grasping, I: experimental observations

2004

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The mechanical complexities of rotating an object through the gravity field present a formidable challenge to the human central nervous system (CNS). The current study documents the finger force patterns selected by the CNS when performing one-, two-, and four-finger grasping while holding an object statically at various orientations with respect to vertical. Numerous mechanically "unnecessary" behaviors were observed. These included: nonzero tangential forces for horizontal handle orientations, large internal forces (i.e., those in excess of equilibrium requirements) for all orientations, and safety margins between 50 and 90%. Additionally, none of the investigated measures were constant across orientations or could be represented as a simple trigonometric function of orientation. Nonetheless, all measures varied in systematic (and sometimes symmetric) ways with orientation. The results suggest that the CNS selects force patterns that are based on mechanical principles but also that are not simply related to object orientation. This study is complemented by a second paper that provides an in-depth analysis of the mechanics of nonvertical grasping and accounts for many of the observed results with numerical optimization (see Part II -current issue).Together, the papers demonstrate that the CNS is likely to utilize optimization processes when controlling prehensile actions.

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“…It depends mainly on the object weight and the friction coefficient. From literature, we know that the correlation of the static grip force with the object weight is approximately linear [14]. Also, the correlation of the maximum grip force with the inverse coefficient of friction μ is approximately linear with a safety margin F safety [15].…”

Section: Design Criteriamentioning

confidence: 99%

An MR-Compatible Haptic Interface With Seven Degrees of Freedom

Kühne

Eschelbach

Aghaeifar

et al. 2018

IEEE/ASME Trans. Mechatron.

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Abstract-Functional magnetic resonance imaging (fMRI) is a powerful tool for neuroscience. It allows the visualization of active areas in the human brain. Combining this method with haptic interfaces allows one to conduct human motor control studies with an opportunity for standardized experimental conditions. However, only a small number of specialized MR-compatible haptic interfaces exist that were mostly built around specific research questions. The devices are designed for pure translational, rotational, or grasping movements. In this work, we present a novel MR-compatible haptic interface with seven degrees of freedom (DoF), which allows for both translations and rotations in three DoF each, as well as a two-finger precision grasp. The presented haptic interface is the first one with these capabilities and is designed as a universal tool for human motor control studies involving fMRI. It allows for the switching of the paradigm to reprogramming rather than redesigning when moving on to a new research question. We introduce its kinematics and control, along with results of MR compatibility tests and a preliminary fMRI study, showing the applicability of the device.

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Factors influencing the force control during precision grip

Cited by 889 publications

References 8 publications

Programmed and triggered actions to rapid load changes during precision grip

Programmed and triggered actions to rapid load changes during precision grip

Prehension synergies during nonvertical grasping, I: experimental observations

An MR-Compatible Haptic Interface With Seven Degrees of Freedom

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