Design of an active one-degree-of-freedom lower-limb exoskeleton with inertia compensation

Gabriel Aguirre-Ollinger*, J. Edward Colgate, Michael A. Peshkin, Ambarish Goswami

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

90 Scopus citations


Limited research has been done on exoskeletons to enable faster movements of the lower extremities. An exoskeleton's mechanism can actually hinder agility by adding weight, inertia and friction to the legs; compensating inertia through control is particularly difficult due to instability issues. The added inertia will reduce the natural frequency of the legs, probably leading to lower step frequency during walking. We present a control method that produces an approximate compensation of an exoskeleton's inertia. The aim is making the natural frequency of the exoskeleton-assisted leg larger than that of the unaided leg. The method uses admittance control to compensate for the weight and friction of the exoskeleton. Inertia compensation is emulated by adding a feedback loop consisting of low-pass filtered acceleration multiplied by a negative gain. This gain simulates negative inertia in the low-frequency range. We tested the controller on a statically supported, single-degree-of-freedom exoskeleton that assists swing movements of the leg. Subjects performed movement sequences, first unassisted and then using the exoskeleton, in the context of a computer-based task resembling a race. With zero inertia compensation, the steady-state frequency of the leg swing was consistently reduced. Adding inertia compensation enabled subjects to recover their normal frequency of swing.

Original languageEnglish (US)
Pages (from-to)486-499
Number of pages14
JournalInternational Journal of Robotics Research
Issue number4
StatePublished - Apr 2011


  • Exoskeleton
  • admittance control
  • lower-limb assistance
  • rehabilitation robotics

ASJC Scopus subject areas

  • Software
  • Modeling and Simulation
  • Mechanical Engineering
  • Electrical and Electronic Engineering
  • Artificial Intelligence
  • Applied Mathematics


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