Research Papers

Design of Single-Input-Single-Output Compliant Mechanisms for Practical Applications Using Selection Maps

[+] Author and Article Information
Sudarshan Hegde

Mechanical Engineering, Indian Institute of Science, Bangalore 560012, Indiahegde@mecheng.iisc.ernet.in

G. K. Ananthasuresh

Mechanical Engineering, Indian Institute of Science, Bangalore 560012, Indiasuresh@mecheng.iisc.ernet.in

J. Mech. Des 132(8), 081007 (Aug 05, 2010) (8 pages) doi:10.1115/1.4001877 History: Received October 20, 2009; Revised May 13, 2010; Online August 05, 2010; Published August 13, 2010

We present an interactive map-based technique for designing single-input-single-output compliant mechanisms that meet the requirements of practical applications. Our map juxtaposes user-specifications with the attributes of real compliant mechanisms stored in a database so that not only the practical feasibility of the specifications can be discerned quickly but also modifications can be done interactively to the existing compliant mechanisms. The practical utility of the method presented here exceeds that of shape and size optimizations because it accounts for manufacturing considerations, stress limits, and material selection. The premise for the method is the spring-leverage (SL) model, which characterizes the kinematic and elastostatic behavior of compliant mechanisms with only three SL constants. The user-specifications are met interactively using the beam-based 2D models of compliant mechanisms by changing their attributes such as: (i) overall size in two planar orthogonal directions, separately and together, (ii) uniform resizing of the in-plane widths of all the beam elements, (iii) uniform resizing of the out-of-plane thicknesses of the beam elements, and (iv) the material. We present a design software program with a graphical user interface for interactive design. A case-study that describes the design procedure in detail is also presented while additional case-studies are posted on a website.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Spring-leverage model: (a) a compliant gripper, (b) its symmetric half used in deformation analysis, and (c) its representation as a lever with geometric amplification factor n, the input-side spring stiffness kci, and the output side spring stiffness kco

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Figure 2

SL model to match the kinematic behavior: (a) a compliant gripper, (b) its symmetric half used in deformation analysis, and (c) a leveraging mechanism to revert the direction of motion from input to output in the SL model to match the output direction in the gripper

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Figure 3

The first load case used to find the input-side stiffness kci and the inherent geometric amplification factor n of the SL model

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Figure 4

The second load case used to find the output side spring stiffness kco of the SL model

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Figure 5

The variables involved in the SL model of a single-input-single-output compliant mechanism

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Figure 6

Drawing the feasible map on the selection map: (a) the points on the curve are generated for lower bounds of the specification variables but with different values of n; only the part of the curve corresponding to the positive values of kci and kco is considered and (b) the feasible map is bounded by the curves corresponding to the upper and lower specification variables and is filled with a gray color scale based on the value of n

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Figure 7

The dots represent the compliant mechanisms in the database

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Figure 8

The six parameter curves from a selected mechanism, which is the mechanism closest to the feasible map

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Figure 9

One of the curves is selected for design. Note that there is a matching of nm with ns along this curve.

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Figure 10

Redesign by using multiple parameter curves. One of the curves is selected for redesign but it does not result in matched values of nm and ns. Hence, an alternate parameter curve is pursued from within the feasible map to obtain a feasible mechanism. The red STOP sign on the second parametric curve indicates that a particular manufacturing process limit has been reached because of the change in the corresponding parameter.

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Figure 11

Redesigning a mechanism by changing its in-plane width: (a) the mechanism as it is in the database and (b) redesigned mechanism with increased width, which is limited by the tool diameter shown as a hatched circle

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Figure 12

The graphical user interface, developed using MATLAB , aids in selection and design

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Figure 13

Design problem of a compliant mechanism to amplify the motion of a piezoelectric actuator at the output

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Figure 14

The feasible map is bound by the curves representing the lower and upper bounds on specification variables

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Figure 15

The feasible map for the modified specifications shown in Table 1 with output load reduced to 10 N. The dots show the mechanisms that are closest to the feasible map.

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Figure 16

Parameter curves: (a) the six curves represent the parameter curves from the present state and (b) the zoomed-in region

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Figure 17

The stretchXY-line is followed up to a certain distance shown by green line at the end of which the change of path option is exercised

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Figure 18

Different parameter curves from the new point of design

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Figure 19

The green dot indicates that there is a matching of n values inside the feasible map

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Figure 20

The left hand side part shows the original mechanism in the database while the right hand side part shows the modified design



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