Online proceedings - EDA Publishing Association

Layout
Total dimensions
of the gripper
(length, width,
thickness)
(µm)
Minimum
width
(µm)
Maximum
width
(µm)
11-13
May 2011, Aix-en-Provence, France
TABLE 5
RESULTS OF FEM ANALYSIS FOR EACH LAYOUT
Applied
displacement
to the moving
arm a
(µm)
Equivalent
force
(µN)
Stiffness
(µN/µm)
Tip
displacement in
direction of y
(fixed arm,
moving arm)
Ux,Relative
displacement
of two tips in
direction x b
(µm)
Uy, Relative
displacement
of two tips in
direction y b
(µm)
Maximum
stress
(Mpa)
1 1000 x 127 x 20 18 40 -20 28 3.1 (106, 102) 10 -4 33.93
2 1000 x 390 x 20 20 100 -20 25 2.6 (20, 19) 10 -1 32.94
3 1000 x 70 x 20 5 30 10 5.5 0.14 (4, 42) -0.5 -38 30.95
4 1000 x 140 x 20 5 30 10 4.2 0.11 (5, 41) -6 -35 32.55
a Positive values mean tension and minus values mean compression
b Minus values mean the two arms moved away of each other
Fig. 5. Approaching
Fig. 6. Opening
Fig. 7. Closing
Fig. 8. Keeping
The gripping procedure that was explained here is divided
in four steps; approaching to the cell, opening of the jaws,
closing of the jaws and finally, keeping the cell. These steps
are shown in Fig. 5 to 8. All relative sizes are according to
the real condition. In Fig. 1 a 35 µm cell has been shown in
front of the gripper tip. This is after the process of
approaching to the cell. Fig. 6 shows the maximum opening
range of the gripper tip that can be achieved by applying 10
µm or 4.2 µN force to the moving arm. As can be seen the
opening range in this configuration is more than the other
layouts. This also can be confirmed by the stiffness numbers
of Table 5. Stiffness was calculated by dividing the amount
of forces to the received relative displacement of the gripper
tips. Fig. 7 is the returning process of the gripper to its
unloaded condition. This figure shows the jaws when 2 µm
displacement is applied to the moving arm of the gripper.
Finally, Fig. 8 shows the relax condition of the gripper
without any applied load or displacement. In this figure the
gripper keep the cell inside its tips. One of the most
advantages of this approach is increasing the contacts area
between cell membrane and gripper tip that causes less
stress on the membrane of the cell. Also in the case of a
precise manipulation it can be completely a non-contact
gripping.
IV. RESULTS AND CONCLUSION
A new approach in designing of microgrippers for
biological cells manipulation was proposed and optimized
by finite element method. By separating the actuator part of
the microgripper from gripping jaws, many existing
problems in cell manipulation were solved. This layout
assures significant benefits such as the reduction of micro
fabrication steps, time and cost of building process. By
using this approach, there is no need to dope any kind of
metal on substrates and use several mask layers in
fabrication process that is usual in all thermal actuators.
Some attempts to design an innovative configuration were
performed and herein documented, by distinguishing
advantages and disadvantages of each new layout proposed.
The main innovation was strategy of surrounding the cells
and keeping them instead of using tweezers for gripping,
which make a local contact with the cells limited to two or
few points. A finite element optimization was then
performed to improve the performance of the proposed
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