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Internal forces during object manipulation.
Fan Gao1, Mark L Latash, Vladimir M Zatsiorsky
1Biomechanics Laboratory, Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA.
Experimental Brain Research
|May 25, 2005
Summary
Human grasping involves coupled internal and manipulation forces, unlike robotic systems. This study reveals how thumb and virtual finger forces synchronize or oppose during various arm movements, impacting grip strategies.
Area of Science:
- Biomechanics
- Human motor control
- Robotics
Background:
- Robotic manipulators achieve independent control of internal and manipulation forces.
- It remains unclear if human grasping exhibits similar force decoupling or employs specific strategies.
Purpose of the Study:
- To investigate the coupling between internal and manipulation forces during human arm movements.
- To identify grasping strategies employed by human subjects under varying conditions.
Main Methods:
- Six subjects performed cyclic arm movements with a customized handle under six different orientation and movement combinations.
- Handle weight and movement frequency were systematically varied.
- Force analysis was conducted at the thumb-virtual finger (VF) level, examining internal force and moment.
Main Results:
- During parallel manipulations, thumb-VF forces were coupled and in-phase with manipulation forces.
- During orthogonal manipulations, thumb-VF forces were coupled but out-of-phase, resembling an inverted 'V'.
- A novel observation of internal moments being counterbalanced by tangential forces was noted.
Conclusions:
- Human grasping demonstrates a coupling between internal grip forces and manipulation forces, contrary to robotic decoupling.
- Grasping strategies vary with movement direction and orientation, suggesting task-specific synergies.
- The findings have implications for understanding human grasping synergies and informing robotic grip control.