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Kinematic Optimization of a Robotic Joint With Continuously Variable Transmission Ratio

[+] Author Affiliations
Martin Grenier, Clément Gosselin

Universitè Laval, Québec, QC, Canada

Paper No. DETC2011-48443, pp. 513-521; 9 pages
  • ASME 2011 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference
  • Volume 6: 35th Mechanisms and Robotics Conference, Parts A and B
  • Washington, DC, USA, August 28–31, 2011
  • Conference Sponsors: Design Engineering Division and Computers and Information in Engineering Division
  • ISBN: 978-0-7918-5483-9
  • Copyright © 2011 by ASME


The range of possible tasks achievable by robots highly depends on the selection of motors and transmissions. For example, variable ratio transmissions surpass single ratio transmissions because they can modify the torque-speed parameters of the actuator and, therefore, maintain the optimal power output state from the motor. Consequently, the use of variable ratio transmissions may expand a robot’s achievable tasks. A robotic joint with continuously variable transmission ratio is presented in this paper. This new type of transmission joint may be used in serial or parallel robots. The transmission consists of a doubly actuated two-degree-of-freedom five-bar parallel mechanism. The main actuator is located at the input revolute joint. The variation of the ratio is achieved with the adjustment actuator located at a second revolute joint. Such a transmission, based on a linkage, may have unde-sired ratio variations for a constant adjustement joint position. Therefore, two different optimization methods are presented to determine the best geometric parameters in order to minimize the undesired ratio variation while maximizing the possible transmission ratio range. The performance indices are either optimal for the entire range or only for the maximum and minimum ratios available. A simulation is presented with the best parameters obtained with the optimization based on the maximum and minimum ratios. Results show a transmission ratio ranging from 0.9:1 to 4.5:1 with a minimal amplification of 3.9:1. The transmission ratio may vary continuously within the working boundaries. The output range of motion may be adapted to a serial robot joint.

Copyright © 2011 by ASME



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