Variable Interlock Mechanism Joining Shoulder Rotation and Elbow Flexion for Body-Powered Upper Limb Prostheses

Akira Kato, Masato Hirabayashi, Masakatsu G. Fujie, Shigeki Sugano

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Citation (Scopus)


People with upper limb amputations wearing body-powered prostheses perform elbow joint flexion and opening/closing the terminal device by pulling one control cable with the contralateral shoulder. When moving the terminal device close to the mouth during eating, the socket obstructs shoulder rotation motion. In this paper, we developed the variable interlock mechanism to realize shoulder rotation and elbow flexion simultaneously by pulling only one control cable for a body-powered prosthesis. We propose a mechanism consisting of a differential bevel gear and a continuous variable transmission (CVT) unit with a conical cone and roller. With the CVT unit, the user can change the interlocking relationship without multiple steps. The number of teeth of the bevel gear, the radius of conical cone, and roller were designed to realize the interlocking motion of the inner rotation of the shoulder joint at 80° when the elbow flexion angle is 145°. We measure the terminal device trajectory and each joint angle by fixing the prosthesis with the proposed mechanism in an aluminum frame and by pulling the control cable from the top using a motion capture system. For the two conditions of the designed CVT ratio (kσ=1.00, 3.46), the measured CVT ratio becomes ki=1.04, 1.54. We confirm the interlocking motion of our mechanism, and the error between designed and measured CVT ratio can be improved by reducing the backlash of the bevel gear and the slip between the conical cone and the roller at the CVT unit.

Original languageEnglish
Title of host publication2018 World Automation Congress, WAC 2018
PublisherIEEE Computer Society
Number of pages6
ISBN (Print)9781532377914
Publication statusPublished - 2018 Aug 8
Event2018 World Automation Congress, WAC 2018 - Stevenson, United States
Duration: 2018 Jun 32018 Jun 6

Publication series

NameWorld Automation Congress Proceedings
ISSN (Print)2154-4824
ISSN (Electronic)2154-4832


Other2018 World Automation Congress, WAC 2018
Country/TerritoryUnited States


  • body-powered prosthesis
  • continuous variable transmission
  • differential gear
  • variable interlocking mechanism

ASJC Scopus subject areas

  • Control and Systems Engineering


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