Walk-assist robot: A novel approach to gain selection of a braking controller using differential flatness

Chun Hsu Ko, Kuu-Young Young, Yi Che Huang, Sunil K. Agrawal

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


With increasing populations of the elderly in our society, robot technology will play an important role in providing functional mobility to humans. From the perspective of human safety, it is desirable that controllers for walk-assist robots be dissipative, i.e., the energy is supplied from the human to the walker, while the controller modulates this energy. The simplest form of a dissipating controller is a brake, where resistive torques are applied to the wheels proportional to their speeds. The fundamental question that we ask in this brief is how to modulate these proportional gains over time for the two wheels so that the walker can perform point-to-point motions. The unique contribution of this brief is a novel way in which the theory of differential flatness is used to plan the trajectory of these braking gains. Since the user input forces are not known a priori , the trajectory of the braking gain is computed iteratively during the motion. Simulation and experimental results show that the walk-assist robot, along with the structure of this proposed control scheme, can guide the user to reach the goal.

Original languageEnglish
Article number6410005
Pages (from-to)2299-2305
Number of pages7
JournalIEEE Transactions on Control Systems Technology
Issue number6
StatePublished - 15 Jan 2013


  • Differential flatness
  • guidance
  • passive control
  • trajectory planning
  • walk-assist robot


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