Controlling the apparent inertia of passive human-interactive robots

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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Passive robotic devices may exhibit a spatially varying apparent inertia perceptible to a human user. The apparent inertia is the projection of the inertia matrix onto the instantaneous direction of motion. The spatial variation is due to the configuration dependence of the inertia matrix and relevant to many passive mechanisms, including programmable constraint machines or "cobots," which use low-power steering actuators to choose the direction of motion. We develop two techniques for controlling the apparent inertia in cobots to emulate the desired inertial properties of a virtual object or mechanism. The first is a path-limiting method, which constraints the cobot to steer along certain paths where the apparent inertia and desired inertia are equivalent. The second uses a low-power actuator to control the apparent inertia by driving the device along its direction of motion. We illustrate these ideas for a two-link cobot we have built for experiments in human motor control and rehabilitation. For the actuated control method, we show that the power actuator can be relatively low power compared to the actuators of a traditional robot performing similar tasks.

Original languageEnglish (US)
Pages (from-to)44-52
Number of pages9
JournalJournal of Dynamic Systems, Measurement and Control, Transactions of the ASME
Issue number1
StatePublished - Mar 2006


  • Apparent inertia
  • Cobot
  • Effective mass
  • Inertia ellipse
  • Passive robot

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Information Systems
  • Instrumentation
  • Mechanical Engineering
  • Computer Science Applications


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