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Research Papers

How to Choose From a Synthesized Set of Path-Generating Mechanisms

[+] Author and Article Information
Sujitkumar V. Naik

 Indian Institute of Technology, Kanpur 208016, Indiasujitkvn@gmail.com

Anupam Saxena1

 Indian Institute of Technology, Kanpur 208016, Indiaanupams@iitk.ac.in

Ashok Kumar Rai

Sr. Software Engineer Aon Hewitt, Techbolevard Tower A, Sector 127, Noida 201304, Indiarai284@gmail.com

B. V. S. Nagendra Reddy

 Indian Institute of Technology, Kanpur 208016, Indiabvsnagendrareddy@gmail.com

1

Corresponding author.

J. Mech. Des 133(9), 091009 (Sep 15, 2011) (11 pages) doi:10.1115/1.4004608 History: Received September 15, 2010; Revised June 16, 2011; Accepted July 18, 2011; Published September 15, 2011; Online September 15, 2011

Partially compliant mechanisms inherit the attributes of fully compliant and rigid-body linkages and offer simpler, compact design alternatives to accomplish complex kinematic tasks such as tracing large nonsmooth paths. This paper describes qualitative and quantitative criteria that can be employed to select the linkage configuration. The proposed criteria are categorized as general or specific. General criteria pertain to often-used kinematic attributes whereas specific criteria address the application at hand. The veracity and viability of each mechanism are evaluated with respect to compactness, design simplicity, static and dynamic failure, number of rigid-body joints, relative ease of fabrication, and other relevant criteria. Three decision-making techniques, namely, Pugh decision matrix, analytic hierarchy process, and a variant of the Pugh decision matrix are used to perform the evaluation. An example of a displacement-delimited gripper with a prescribed large nonsmooth path is used to illustrate linkage selection.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Comparison between the Synthesis methods: (a) Sequential Synthesis Method by Pucheta and Cardona. The initial graph specified by the user has four links (vertices 1–4) connected by revolute pairs (edges R) and a prismatic pair (edge P). A search is executed through the atlases that contain graphs of mechanisms consisting of revolute joints and one prismatic joint only. No other atlas is searched. Candidate mechanisms are selected based on the occurrence of the initial graph in the atlas. (b) Concurrent synthesis with the Unified procedure by Rai A user prescribes only the design space, a monotonic input and the path to be traced. The design domain is represented as a grid superstructure. Each edge can be present or absent. If present, it can represent a deforming member with fixed ends or a rigid member with hinged ends. The link geometry comprising in-plane widths, out-of-plane thickness, end nodes, and slopes (only for deforming members) is evolved iteratively so that the prescribed kinematic goal is attained.

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Figure 2

Illustration of counting of links and joints in partially and fully compliant linkages. Rigid and flexible links are shown in black (dark) and red (gray), respectively. Hinges are shown as white circles. Triangles and square represent fixed displacement and no change-of-slope boundary conditions, respectively. (a) links 2, 3, 11, and 6, 7, 9 form two units of flexible members; (b) links 2, 3, 10, and 7 and 8 form two units of flexible members; (c) links 1–8 form a single unit of flexible links.

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Figure 3

Illustration of presence of redundant degrees-of-freedom in a partially compliant linkage

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Figure 4

Presence of a discontinuity in a flexible unit (Node 2)

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Figure 5

Schematic diagram for the design of the displacement-delimited gripper

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Figure 6

(a-f) Synthesized solutions for the displacement-delimited gripper selected for comparison and the respective prototypes fabricated using Teflon; (g) shows the magnified prescribed path for all solutions in (a-f) in green (light gray), and traced path in blue (dark gray).

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Figure 7

(a-e) Quasi-static, large deformation stress analysis of M1–M5 in Figs. 6a6e using ABAQUS ®. (a) Force: 82 N–Stress (1.7 × 10−8 –21.35 MPa), (b) force: 40 N–stress (8.6 × 10−6 –19.41 MPa), (c) force: 65 N–stress (2.9 × 10−8 –38.71 MPa), (d) force: 35 N–stress (6.1 × 10−7 –35.66 MPa), (e) force: 35 N–stress (3.187 × 10−9 –21.77 MPa).

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Figure 8

Bottom left: Fatigue testing machine, top left: guide way, top right: eccentric mounted on a motor, bottom right: enlarged view of the counter circuit

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