Design and control of a variable stiffness actuator based on adjustable moment arm

Byeong Sang Kim, Jae Bok Song

Research output: Contribution to journalArticlepeer-review

108 Citations (Scopus)


For tasks that require robot-environment interaction, stiffness control is important to ensure stable contact motion and collision safety. The variable stiffness approach has been used to address this type of control. We propose a hybrid variable stiffness actuator (HVSA), which is a variable stiffness unit design. The proposed HVSA is composed of a hybrid control module based on an adjustable moment-arm mechanism, and a drive module with two motors. By controlling the relative motion of gears in the hybrid control module, position and stiffness of a joint can be simultaneously controlled. The HVSA provides a wide range of joint stiffness due to the nonlinearity provided by the adjustable moment arm. Furthermore, the rigid mode, which behaves as a conventional stiff joint, can be implemented to improve positioning accuracy when a robot handles a heavy object. In this paper, the mechanical design features and related analysis are explained. We show that the HVSA can provide a wide range of stiffness and rapid responses according to changes in the stiffness of a joint under varying loads by experiments. The effectiveness of the rigid mode is verified by some experiments on position tracking under high-load conditions.

Original languageEnglish
Article number6209442
Pages (from-to)1145-1151
Number of pages7
JournalIEEE Transactions on Robotics
Issue number5
Publication statusPublished - 2012

Bibliographical note

Funding Information:
Manuscript received July 13, 2011; revised February 29, 2012; accepted May 7, 2012. Date of publication June 1, 2012; date of current version September 28, 2012. This paper was recommended for publication by Associate Editor L. Villani and Editor B. J. Nelson upon evaluation of the reviewers’ comments. This work was supported by the Human Resources Development Program for Convergence Robot Specialists (Ministry of Knowledge Economy of Korea) and by the National Research Foundation of Korea (NRF) (No. 2012-0000792).


  • Adjustable moment arm
  • compliant joint
  • lever mechanism
  • variable stiffness actuator (VSA)

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Computer Science Applications
  • Electrical and Electronic Engineering


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