Energetically Passive Multi-Degree-of-Freedom Hydraulic Human Power Amplifier with Assistive Dynamics

Sangyoon Lee, Perry Y. Li, Fredrik Eskilsson

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


This paper develops a control approach for a multi-degree-of-freedom (DoF) hydraulic human power amplifier (HHPA) which is a tool with which a human interacts physically. The control objective is to use the hydraulic actuators to amplify the human force while ensuring that the closed-loop system is energetically passive with respect to a scaled human and environment input power, so as to enhance the safety and coupling stability. A multi-DoF virtual velocity coordination approach is used to recast the force control problem as one of coordination between the velocities of fictitious inertia and of the HHPA. To aid the human to perform specific tasks, additional passive assistance dynamics are incorporated to include a passive velocity field controller (PVFC) for path guidance, and an artificial potential field for obstacle avoidance (OA). Control of the hydraulic actuators is defined by a passivity-based controller that considers the natural energy storage of the hydraulic actuators to fully account for the nonlinear pressure dynamics. The controllers specify the required flows which are then satisfied by either a servo-valve or an energy efficient hydraulic transformer. Experimental results demonstrate good control performance and effective task assistance.

Original languageEnglish (US)
Article number8697085
Pages (from-to)1296-1308
Number of pages13
JournalIEEE Transactions on Control Systems Technology
Issue number4
StatePublished - Jul 2020

Bibliographical note

Funding Information:
Manuscript received January 31, 2019; accepted March 31, 2019. Date of publication April 23, 2019; date of current version June 11, 2020. Manuscript received in final form April 3, 2019. This work was supported by the National Science Foundation through the Center for Compact and Efficient Fluid Power (CCEFP) under Grant EEC-05040834. Recommended by Associate Editor A. Serrani. (Corresponding author: Perry Y. Li.) S. Lee was with the Center for Compact and Efficient Fluid Power, Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455 USA. He is now with LG Electronics, Seoul 07336, South Korea (e-mail: sylee@umn.edu).

Publisher Copyright:
© 1993-2012 IEEE.


  • Energetic passivity
  • exoskeleton
  • human power augmentation
  • hydraulic transformer
  • natural energy storage
  • obstacle avoidance (OA)
  • passive decomposition
  • passive velocity field control (PVFC)


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