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Research Papers

On the Dual-Rod Slider Rocker Mechanism and Its Applications to Tristate Rigid Active Docking

[+] Author and Article Information
Paul M. Moubarak

e-mail: paul4@gwu.edu

Pinhas Ben-Tzvi

e-mail: bentzvi@gwu.edu
Robotics and Mechatronics Laboratory,
The George Washington University,
Washington, DC 20052

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the Journal of Mechanisms and Robotics. Manuscript received May 3, 2012; final manuscript received November 25, 2012; published online January 24, 2013. Assoc. Editor: Anupam Saxena.

J. Mechanisms Robotics 5(1), 011010 (Jan 24, 2013) (10 pages) Paper No: JMR-12-1054; doi: 10.1115/1.4023178 History: Received May 03, 2012; Revised November 25, 2012

The dual-rod slider rocker mechanism is equivalent to two traditional single-rod sliders that share a common rocker, where the sliders translate along two opposite directions. Unlike a single-rod system, the dual-rod mechanism is unique, in the sense that the two sliders do not translate the same distance for the same rocker rotation. In this paper, an optimal kinematic and dynamic analysis of the dual-rod slider rocker mechanism is presented. This analysis is supplemented by an application to modular robotic coupling, in which the mechanism is employed by a torque recirculation scheme to enable three independent modes of operation via a single motor. Simulation, finite element analysis, and experimental results validate the kinematic properties of this mechanism, the rigidity of the proposed docking interface, and its three modes of operation. We conclude that the compactness of the dual-rod mechanism, and its unique kinematic properties, exhibits a broad industrial value for applications where size and weight are a critical design constraint, such as space and mobile robotics.

Copyright © 2013 by ASME
Topics: Mechanisms , Torque , Engines
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References

Figures

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Fig. 1

Isometric schematic and corresponding kinematic diagram of the dual-rod slider rocker mechanism

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Fig. 2

Kinematics of the dual-rod slider rocker mechanism

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Fig. 3

Meshed solution space of the optimal problem in (14)

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Fig. 4

Free body diagram of the dual-rod slider rocker mechanism

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Fig. 5

Displacements of top slider (y), bottom slider (y′), combined stroke (y − y′), and relative translation offset plotted versus time

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Fig. 6

Velocity profiles of the top and bottom sliders, and relative velocity difference, plotted as a function of time for h′

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Fig. 7

Acceleration profiles of the top and bottom sliders, plotted as a function of time for c

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Fig. 8

Schematic of the coupling interface showing the docking shaft and the dual-rod slider rocker mechanism

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Fig. 9

Exploded schematic view of the tristate docking interface, its three modes of operation, and a proof-of-concept prototype shown connected to a small mobile robot (Central Motor: 50 W, 35 N m max. torque, Selection Motor: 15 W, 12 N m max. torque)

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Fig. 10

Transmission schematic of the tristate docking interface

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Fig. 11

Three modes of operation of the docking interface, and the active revolute joint in the clamp mode: (a) Drive Mode, (b) Neutral Mode, (c) Clamp mode

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Fig. 12

Comparison of experimental and simulated optimal displacement of the two sliders of the dual-rod mechanism in the ascending and descending strokes. Note the conformity of the two datasets, and the ability of the two sliders to simultaneously reach the terminal boundary conditions in both cases (i.e., e = 0 at both Open BC and Close BC).

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Fig. 13

Width comparison of the C-Mech with (a) dual-rod slider rocker mechanism and (b) lead screw mechanism

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Fig. 14

Finite elements analysis of the dual-rod slider rocker mechanism in the clamp mode. (a) Clamp separation gap at a torque of 23 N m without pins. (b) No separation with pins, and load propagation toward the rails (input torque 45 N m).

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Fig. 15

Rocker torque as a function of the torque applied on the active joint in the clamp mode. (a) No pins, note the separation at 24 N m, (b) with pins.

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