A safe robot arm with safe joints and gravity compensator

Dongeun Choi, Junho Choi, Changhyun Cho, Shinsuk Park, Sungchul Kang

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


This study presents a robot arm equipped with safe joints and multi DOFs gravity compensators. The safe joint, also referred to as "Spring- clutch", is simple passive mechanism that consist of a spring, a cam, and a joint torque sensor. When the torque applied is lower than a pre-set threshold, the Spring-clutch serves as a rigid joint between the input and output. When the applied torque exceeds the threshold, the Spring-clutch is released and is free to rotate like a revolute joint, which significantly reduces the collision force to avoid damage to the robot, as well as to humans. In addition, a compact joint torque sensor is installed in the Spring-clutch to measure the torque at the joint. Also, the analysis of energy and torque shows that the proposed mechanism can function as a gravity compensator capable of static balancing. Since joint torques vary in accordance with the pose of a manipulator (i.e., rotation angles), a Spring-clutch with a constant threshold torque cannot always guarantee the maximum collision torque in some poses of a manipulator. To overcome this limitation, a gravity compensator is adopted to eliminate the gravitational torque. In this research a bevel gravity compensator is applied which can perform static balancing completely. This paper describes the design principles and fabrication of the safety mechanisms and the robot arm.

Original languageEnglish
Pages (from-to)362-368
Number of pages7
JournalInternational Journal of Control, Automation and Systems
Issue number2
Publication statusPublished - 2013 Apr


  • Gravity compensator
  • joint torque sensor
  • safe joint mechanism
  • safe robot arm

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Computer Science Applications


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