Optimal Synthesis of Cam-Linkage Mechanisms for Precise Path Generation

[+] Author and Article Information
D. Mundo

Department of Mechanical Engineering,  University of Calabria, 87036 Arcavacata di Rende (CS), Italyd.mundo@unical.it

J. Y. Liu

Department of Power Mechanical Engineering,  National Formosa University, Huwei 63208, Taiwan, R.O.C.

H. S. Yan

Department of Mechanical Engineering,  National Cheng Kung University, Tainan 70101, Taiwan, R.O.C.

J. Mech. Des 128(6), 1253-1260 (Jan 02, 2006) (8 pages) doi:10.1115/1.2337317 History: Received June 19, 2005; Revised January 02, 2006

The paper proposes a method for the optimal synthesis of planar mechanisms, where a combination of cams and linkages is used in order to obtain a precise path generation. As a first step, based on Gruebler’s mobility criterion, a linkage mechanism is considered, with as many degrees of freedom as required by the generation task. One or more disk cams are then synthesized in order to reduce the system’s mobility and to obtain a single-input combined mechanical system. The final combined mechanism is able to guide a coupler point through any number of precision positions. A strategy for the global optimization of the synthesis process, based on evolutionary theory, is also proposed. A goal function is defined on the basis of dimensional and kinematic constraints and performance criteria, while a genetic algorithm is employed as an optimum searching procedure. An industrial application of the proposed methodology is described, where a path generation problem with time prescription is dealt with. The objective of the generation task is to guide a coupler point along a figure-eight trajectory, with a constant tangential velocity. Such a task is required by polishing machines for fiber optic connectors and similar components. A kinematic simulation of the optimal mechanism is used to validate the proposed synthesis methodology.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Four-bar linkage synthesized in Ref. 12 to generate the path of Table 1

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Figure 2

Schematic representation of the linkage selected for precise path generation (a) and required displacement of the slider (b)

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Figure 3

Representation of the combined cam-linkage mechanism generating the path of Table 1

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Figure 4

Scheme of the genetic algorithm used for the optimal synthesis of cam-linkage mechanisms

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Figure 5

Representation of the required figure-eight trajectory in Sec. 4

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Figure 6

Schematic representation of the linkage selected for the precise path generation task in Sec. 4

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Figure 7

Cam-follower mechanism driving point E: position of the follower (a) and cam profile (b)

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Figure 8

Cam-follower mechanism driving point D: position of the follower (a) and cam profile (b)

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Figure 9

Virtual prototype of the optimal cam-linkage mechanism

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Figure 10

Comparison between required and generated paths (a) and theoretical and simulated velocity curves (b)




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