Static single-arm force generation with kinematic constraints

Peng Pan, Michael A. Peshkin, J. Edward Colgate, Kevin M. Lynch*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


Smooth, frictionless, kinematic constraints on the motion of a grasped object reduce the motion freedoms at the hand, but add force freedoms, that is, force directions that do not affect the motion of the object. We are studying how subjects make use of these force freedoms in static and dynamic manipulation tasks. In this study, subjects were asked to use their right hand to hold stationary a manipulandum being pulled with constant force along a low-friction linear rail. To accomplish this task, subjects had to apply an equal and opposite force along the rail, but subjects were free to apply a force against the constraint, orthogonal to the pulling force. Although constraint forces increase the magnitude of the total force vector at the hand and have no effect on the task, we found that subjects applied significant constraint forces in a consistent manner dependent on the arm and constraint configurations. We show that these results can be interpreted in terms of an objective function describing how subjects choose a particular hand force from an infinite set of hand forces that accomplish the task. Without assuming any particular form for the objective function, the data show that its level sets are convex and scale invariant (i.e., the level set shapes are independent of the hand-force magnitude). We derive the level sets, or "isocost" contours, of subjects' objective functions directly from the experimental data.

Original languageEnglish (US)
Pages (from-to)2752-2765
Number of pages14
JournalJournal of neurophysiology
Issue number5
StatePublished - May 2005

ASJC Scopus subject areas

  • Neuroscience(all)
  • Physiology


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