Controlling the apparent inertia of passive human-interactive robots

Tom Worsnopp*, Michael Peshkin, J. Edward Colgate, Kevin Lynch

*Corresponding author for this work

Research output: Contribution to journalConference articlepeer-review

9 Scopus citations


We have been exploring the use of passive robotic mechanisms for the display of virtual surfaces. Cobots are one way of producing virtual surfaces using a passive mechanism. Unlike powered robots, the nonlinear dynamics of the passive mechanism (e.g., an arm) can be felt by the user as a spatially varying apparent inertia. This effect occurs in many passive designs, including but not limited to cobots. We explain the variable apparent inertia as the projection of the spatially-varying inertia matrix onto the direction of motion, and discuss several ways to control the apparent inertia. We explore apparent inertia in detail for the unicycle two link arm, a cobot we have developed for experiments in single-arm motor control studies and rehabilitation. Special paths ("iso-mass contours") are found for this mechanism along which the apparent inertia is constant.

Original languageEnglish (US)
Pages (from-to)1179-1184
Number of pages6
JournalProceedings - IEEE International Conference on Robotics and Automation
Issue number2
StatePublished - 2004
EventProceedings- 2004 IEEE International Conference on Robotics and Automation - New Orleans, LA, United States
Duration: Apr 26 2004May 1 2004


  • Apparent inertia
  • Cobot
  • Haptic interface
  • Inertia ellipsoid
  • Passive robot

ASJC Scopus subject areas

  • Software
  • Artificial Intelligence
  • Electrical and Electronic Engineering
  • Control and Systems Engineering


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