Research Papers

Variable Radius Drum Mechanisms

[+] Author and Article Information
Stefano Seriani

Department of Engineering and Architecture,
University of Trieste,
via A. Valerio 10,
Trieste 34127, Italy
e-mail: stefano.seriani@phd.units.it

Paolo Gallina

Department of Engineering and Architecture,
University of Trieste,
via A. Valerio 10,
Trieste 34127, Italy
e-mail: pgallina@units.it

1Corresponding author.

Manuscript received March 22, 2015; final manuscript received October 19, 2015; published online November 24, 2015. Assoc. Editor: Leila Notash.

J. Mechanisms Robotics 8(2), 021016 (Nov 24, 2015) (9 pages) Paper No: JMR-15-1069; doi: 10.1115/1.4031951 History: Received March 22, 2015; Revised October 19, 2015; Accepted October 21, 2015

This paper presents the concept of variable radius drum mechanisms (VRDMs). A drum, or spool, consists of a spindle with flanges, around which a cable is wound. The cylindrical surface of an ordinary spool has a constant radius. In a variable radius drum (VRD), the radius of the spool varies along its profile. Properties of such devices are discussed, as well as the kinematic analysis and synthesis. The main contribution of the work is the theory of the VRD synthesis problem, rooted in a closed-form analytical solution. In order to highlight the benefits of VRDMs, two applications are presented and analyzed as examples. The first example consists of a mechanism which can support and guide a load along a horizontal linear path. The second example shows a solution to improve the locomotion of a legged robot. Finally, a prototype is made on the basis of the first case scenario and its performance is evaluated and discussed, showing a remarkable accuracy, with a deviation from the nominal trajectory of less than 1%.

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Fig. 2

Geometric parameters associated to the VRD

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Fig. 3

Geometric parameters associated to the VRD in case of a nonpointlike idler pulley and cable with a thickness of 2f

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Fig. 4

Sketch of a VRDM for horizontal motion

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Fig. 5

Kinematics configurations for the VRDM at different α values: (a) initial condition: α = 0, (b) α = 0.622, (c) α = 3.135, and (d) α = 5.649

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Fig. 7

Schema of the joint referring to the locomotion system of a robotic cat

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Fig. 8

A set of kinematic configurations of the VRDM: (a) initial configuration: r3 = 0.02 m, α = −1.888 rad; (b) r3 = 0.02 m, α = 1.528 rad; (c) r3 = 0.02 m, α = 3.608 rad; and (d) r3 = 0.01 m; α = −4.023 rad

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Fig. 9

Experimental setup (measures in millimeter). The figure shows the front and top views of the prototype. The VRD is shown in the middle, along with the CRD. The frame is aligned horizontally. The end-effector is suspended 500 mm below the frame and is to move parallel to the frame, toward the right-hand direction.

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Fig. 10

A set of pictures of the experimental setup and prototype. In the upper-left corner, the VRD and CRD assemblies are shown; on the right and below, the whole assembly is visible.

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Fig. 11

Experimental results




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