MINIATURE COMPLIANT GRIPPERS WITH VISION BASED FORCE

SENSING

BY

SIDDHARTH KASHYAP

MT10CDM002

OBJECTIVE

INTRODUCTION

DESIGN AND ANALYSIS OF GRIPPER

MESOSCALE PROTOTYPING

MICROMANIPULATION

VALIDATION AND TESTING

CONCLUSION

REFERENCES

OBJECTIVE

Develop cost effective miniature grippers. Capability to manipulate biological objects. Force estimation using a new technology. Ability to vary stiffness of gripper.

INTRODUCTION

What is biological cell manipulation ? Types of techniques.

NON-CONTACT TYPE

CONTACT TYPE

Cell trapping using radiation pressure of the lasers

Optoelectrostatic rotation

Magnetic twisting cytometry

Magnetic tweezers

NON-CONTACT TYPE

Micro grippers

Micro capillary

CONTACT TYPE

DESIGN OF GRIPPER

Two approach have been used to arrive at the two different types of grippers.

1) Intuitive design approach 2) Topology optimization approach

INTUITIVE DESIGN

The initial design was conceived intuitively. Finite element model created and checked in

MATLAB. Gripper was modeled in Solid Works. Stress concentration and deformation patterns

were analyzed in COMSOL MultiPhysics, For analysis purposes, one of the gripper jaws was

considered fixed to calculate the overall jaw displacement. After several iterations, an improved gripper design was selected on the basis of

-Mechanical efficiency -Stiffness of mechanism -Stress concentration.

TOPOLOGY OPTIMIZED GRIPPER DESIGN

The statement of the topology optimization is-

Where,

MSE :- Mutual strain energy numerically equal to the output displacement

SE :- Strain energy which is measure of stiffness

K :- Stiffness matrix of the FEM

U,V :- Displacements for actual loading

F :- Actual applied load

Fd :- Unit dummy load

Ai :- Areas of cross-section of frame elements

V* :- Allowed volume of material to be used

MESOSCALE PROTOTYPING OF THE GRIPPERS

Wire Cut EDM

Photolithography

Vacuum Casting For PDMS

W-EDM METHOD

The material used for manufacturing by w-edm was spring steel.

The dimension of the gripper to be manufactured was 11mm x 11mm x 0.5mm

It was possible to achieve dimensional tolerance of ±20 μm.

PHOTOLITHOGRAPHY METHOD

This technique was used to manufacture thick gripper.

The process involves following steps: 1) It involves use of two conjugate dry film

photo masks; a spring steel sheet. 2) Spring steel sheet is coated with

photoresist. 3) Sheet is placed between the masks to get

UV exposure on both sides. 4) Both sides are etched simultaneously to

decrease the undercut

FABRICATION USING VACUUM CASTING-

This method we use polydimethylxsiloxane (PDMS) as the gripper material because of certain advantages

Steps involved under this method are as follows: 1) The molds were cut out of 2mm thick spring

steel sheet using w-edm method. 2) Molds were properly attached on the substrate. 3) PDMS gel and 10% binder mixed and poured in

the molds after degassing in a vacuum chain. 4) PDMS was cured in an oven at 100 EC for 6-7

hours. 5) Minimum 2mm thickness kept to avoid self

weight sagging of gripper.

MICROMANIPULATION

Micromanipulation Setup - It includes an inverted microscope of

Olympus and two XYZ stages. - Two rigid metal tubes were used to

suspend the gripper. - The movement of tubes was controlled

using a joystick. Experiments The experiments were conducted on various

biological entities and several motions such as roll, stretch, move, pick etc were performed.

Spherical zebra fish egg cell (0.7mm dia).

Ellipsoidal drosophila embryos (0.2mm wide and 0.5mm long).

Yeast ball (dia< 1mm).

Hibiscus pollen (0.1mm dia).

FORCE SENSING VALIDATION

The basis for the criterion is the sensitivity matrix of the estimated forces with respect to measured displacements. In order to get the correct sensitivity matrix, spurious forces have to be suppressed.

To avoid extensive computation, forces were applied in a sequence at desired locations (labeled as locations B)

A set of displacement vectors at measured locations (labeled these locations M).

When force sensing was done on zebra fish egg cell similar points were taken and various forces were computed using the CCD camera.

Computed forces on zebra fish egg cell-

CONCLUSION

Grippers presented can grasp and manipulate biological objects smaller than 1 mm in diameter and immersed in aqueous medium.

Two variants were designed intuitively, while the second type was designed using topology optimization.

The experimental setup and how we grasped and manipulated zebra fish egg cells, drosophila embryos, yeast balls, and grains of pollen have been described.

Forces applied were estimated.

REFERENCES

Miniature compliant grippers with vision based force sensing by Annem Narayana Reddy, Nandan Maheshwari, Deepak Kumar Sahu, and G. K. Ananthasuresh.

T. N. Bruican,M. J. Smyth, H. A. Crissman, G. C. Salzman, C. C. Stewart, and J. C.Martin, “Automated single-cell manipulation and sorting by light trapping,” Appl. Opt., vol. 26, pp. 5311–5316, 1987.

M. Nishioka, S. Katsura, K. Hirano, and A. Mizuno, “Evaluation of cell characteristics by step-wise orientational rotation using opto electrostatic micromanipulation,” IEEE Trans. Ind. Appl., vol. 33, no. 5, pp. 1381–1388, Sep/Oct. 1997.

K. J. van Vliet, G. Bao, and S. Suresh, “The biomechanics toolbox: Experimental approaches for living cells and biomolecules,” Acta Mater., vol. 51, pp. 5881–5905, 2003.

A. Yeung and E. Evans, “Cortical shell-liquid core model for passive flow of liquid-like spherical cells into micropipettes,” Biophys. J., vol. 56, pp. 139–149, 1989.

H.-Y. Chan and W. J. Li, “Design and fabrication of a micro thermal actuator for cellular grasping,” Acta Mech. Sin., vol. 20, no. 2, pp. 132–139, 2004.

N. Chronis and L. P. Lee, “Electrothermally activated SU-8 microgripper for single cell manipulation in solution,” J. Microelectromech. Syst., vol. 14, no. 4, pp. 857–863, 2005.

F. H. C. Crick and A. F. W. Hughes, “The physical properties of the cytoplasm: A study by the means of the magnetic particle method,” Exp.Cell Res., vol. 1, pp. 37–80, 1950.

K. Kim, X. Liu, Y. Zhang, and Y. Sun, “Nanonewton force-controlled manipulation of biological cells using a monolithic MEMS microgripper with two-axis force feedback,” J. Micromech. Microeng., vol. 18, no. 5, pp. 1–8, 2008.

M. Puig-de-Morales, M. Grabulosa, J. Alcaraz, J. Mullol, G. N. Maksym, J. J. Fredberg, and D. Navajas, “Measurement of cell microrheology by magnetic twisting cytometry with frequency domain demodulation,” J. Appl. Physiol., vol. 91, pp. 1152–1159, 2001

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