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

101 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


  • 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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