Research Papers

Toward the Design of a Decoupled, Two-Dimensional, Vision-Based μN Force Sensor

[+] Author and Article Information
David J. Cappelleri1

Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, NJ 07030dcappell@stevens.edu

Girish Krishnan

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109gikrishn@umich.edu

Charles Kim

Department of Mechanical Engineering, Bucknell University, Lewisburg, PA 17837charles.kim@bucknell.edu

Vijay Kumar

Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104kumar@seas.upenn.edu

Sridhar Kota

Department of Mechanical Engineering, University of Michigan, Ann Arbor, MI 48109kota@umich.edu


Corresponding author.

J. Mechanisms Robotics 2(2), 021010 (Apr 26, 2010) (9 pages) doi:10.1115/1.4001093 History: Received July 02, 2009; Revised December 16, 2009; Published April 26, 2010; Online April 26, 2010

In this paper, we present three designs for a decoupled, two-dimensional, vision-based micro-Newton (μN) force sensor for microrobotic applications. There are currently no reliable, multi-axis, commercially-available force sensors to measure forces at this scale that can be easily integrated into standard microrobotic test-beds. In our previous work, we presented a design consisting of a planar, elastic mechanism with known force-deflection characteristics. It was inspired by the designs of pre-existing micro electromechanical system suspension mechanisms. A charge-coupled device camera was used to track the deformation of the mechanism as it was used to manipulate objects in a microscale/mesoscale robotic manipulation test-bed. By observing the displacements of select points on the mechanism, the manipulation forces were estimated. In this work, we have designed a compliant mechanism with decoupled stiffness using the building block approach. By designing mechanisms with circular compliance and stiffness ellipses along with zero magnitude compliance and stiffness vectors, we are able to achieve our design requirements. Validation of this approach through the testing of macroscale prototypes and a scaled design for microrobotic applications are offered, along with a sensitivity analysis, yielding insights for microfabricating such designs.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Microrobotic test-bed

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Figure 2

2D vision-based force sensors

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Figure 3

(a) Eigen-twist and eigen-wrench parameters for a compliant DYAD building block, (b) stiffness ellipse, and (c) stiffness coupling vector (sv)

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Figure 4

The design domain for the force sensor showing the rigid probe and the workspace around it

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Figure 5

Steps in the design. (a) Step 1. Design the symmetric half: symmetric half with CoE along the horizontal. (b) Step 2. Rotate the symmetric halves and combine: (i) symmetric halves rotated by θ, (ii) addition of stiffness coupling vectors, and (iii) addition of stiffness ellipses. (c) Step 3. Include the rigid probe: adjust design to accommodate the rigid probe in between the symmetric halves.

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Figure 6

Designs for the symmetric half of mechanism with equal X- and Y-stiffnesses: (a) one building block, (b) two building blocks, and (c) multiple building blocks

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Figure 7

Modifications of the design for the two-point sensing strategy

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Figure 8

Final designs used for prototyping (a)–(c)

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Figure 9

Deformations for X and Y forces for (a) design 1, (b) design 2, and (c) design 3

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Figure 10

Scaled prototypes

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Figure 14

Sensitivity analysis for the node locations

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Figure 11

Experimental testing setup

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Figure 13

(a) Microscale design to be fabricated with PDMS. FEA deformation of the mechanism with 5 μN loads along the (b) vertical (90 deg), (c) horizontal (0 deg), and (d) diagonal (45 deg) directions.

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Figure 12

Snapshots from manipulation tests. (a) Vertical push: undeformed (left) and deformed (right) configurations. (b) Horizontal push: undeformed (left) and deformed (right) configurations.




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