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Research Papers: Mechanisms and Robotics

Evaluation and Design of Displacement-Amplifying Compliant Mechanisms for Sensor Applications

[+] Author and Article Information
Girish Krishnan

Mechanical Engineering, Indian Institute of Science, Bangalore 560 012, Indiagirish@mecheng.iisc.ernet.in

G. K. Ananthasuresh

Mechanical Engineering, Indian Institute of Science, Bangalore 560 012, Indiasuresh@mecheng.iisc.ernet.in

An external load could be the suspension added to the output side to make the sensing point to move on a straight line, the electrostatic force when capacitive sensing is used, or the force to be sensed. It may be something else.

J. Mech. Des 130(10), 102304 (Sep 09, 2008) (9 pages) doi:10.1115/1.2965599 History: Received May 30, 2007; Revised May 17, 2008; Published September 09, 2008

Displacement-amplifying compliant mechanisms (DaCMs) reported in literature are widely used for actuator applications. This paper considers them for sensor applications that rely on displacement measurement, and proposes methods to evaluate and design such mechanisms. The motivation of this work is to increase the sensitivity of a micromachined capacitive accelerometer and a minute mechanical force sensor using DaCMs. A lumped spring-mass-lever (SML) model, which effectively captures the effects of appending a DaCM to a sensor, is introduced. This model is a generalization of the ubiquitously used spring-mass model for the case of an elastic body that has two points of interest—an input and an output. The SML model is shown to be useful in not only evaluating the suitability of an existing DaCM for a new application but also for designing a new DaCM. With the help of this model, we compare a number of DaCMs from literature and identify those that nearly meet the primary problem specifications. To obtain improved designs that also meet the secondary specifications, topology and size-optimization methods are used. For the two applications considered in this paper, we obtain a few new DaCM topologies, which are added to the catalog of DaCMs for future use. The spring-mass-lever model, the evaluation and design methods, and the catalog of DaCMs presented here are useful in other sensor and actuator applications.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) A high-sensitivity micromachined accelerometer (20) and (b) a mechanical force sensor used for vision-based force-sensing of cells

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Figure 2

(a) A generic sensor based on an elastic structure and (b) its usual spring-mass model

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Figure 3

(a) A DaCM with a sensor on its input side and an external load on the output side and (b) a spring-mass-lever model for an inverting DaCM

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Figure 4

Finite element simulations that are required to determine input and output side stiffnesses of a DaCM: (a) Load case 1: for determining kci and (b) load case 2: for determining kco

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Figure 5

Performance of DaCMs M1–M9 based on the six criteria of comparison. The units of ẑ1 (unloaded output displacement) are m/N, of stress are in MPa, while others are dimensionless. Cross-axis stiffness shown is the lateral-axis stiffness divided by the stiffness in the desired direction. Frequencies are normalized by dividing with 500Hz.

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Figure 6

(a) Force applied and the output displacement for the objective function and the cross-axis constraint, (b) ground structure used for optimization along with the applied load, (c) optimized topology, and (d) deformed configuration of the optimized topology

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Figure 7

Optimized mechanism in conjunction with a proof-mass and suspensions

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Figure 8

Topology of a DaCM: (a) Ground structure made of grillages and (b) optimized topology

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Figure 9

Shape and size-optimization of the DaCM. (a) Skeletal topology from topology optimization. This is the interpreted flexible part of the topology solution shown in. (b) Final mechanism from shape and size-optimization.

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Figure 10

Catalog of DaCMs selected from literature (M1–M6)

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Figure 11

Catalog of DaCMs selected from literature (M7–M9)

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Figure 12

New DaCMs added to the catalog (M10–M12)

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