Online proceedings - EDA Publishing Association

Clamps
rotation
[21]
Clamps
translation
[21]
Compliant
structures
[15]
Thermal
expanded
arms
Electromagnetic
actuation
11-13
May 2011, Aix-en-Provence, France
exploit the features of the gripper surface (shape, material,
TABLE 2
MOST COMMON KINEMATIC STRATEGIES
coatings, etc.), while the last ones make use of external
Open state
Closed state
actions (forces, pressures, vibrations, etc) [20]. A list of
releasing strategies is reported in Table 4.
TABLE 3
MOST COMMON STANDARD TYPOLOGIES OF FINGERTIP SHAPES
Flat Angular carved Cylindrical carved
piezoresistive transducers or micro capacitive sensors;
however these approaches are usually limited by the low
biocompatibility of materials and the possibility to induce
electrolysis of water with related bubbles formation.
Due to the small effect of gravity force compared to the
adhesion and capillary forces in microgripping of bio-cells,
the releasing is generally problematic. Many releasing
strategies were tested in the literature and they can be
divided in passive and active strategies; the first ones
Passive releasing
Active releasing
Releasing strategy
Rough surfaces
Hydrophobic coating
Conductive coating
Vacuum environment
Fluid environment
Ionized air
Vibrations
Air pressure
Heating
Electrostatic control
Adhesion to the
substrate
Additional tools
TABLE 4
MOST COMMON PASSIVE AND ACTIVE RELEASING STRATEGIES
III. DESIGN AND FEM OPTIMIZATION
As mentioned before, different kind of problems in living
cells manipulation are related to the health of cells and
caused by the actuator part of microgrippers. Therefore, in
all kind of actuators any undesirable effect of actuator on
biological cells has to be avoided. In this paper a kind of
gripper is considered that uses external actuator approach as
its actuation method. In this approach the actuation part
completely separates from gripping jaws. It seems that it is
the first time that external actuation method is proposed for
biological cells manipulation in order to solve all kind of
problems that are related to the actuation mechanism of
microgrippers. Furthermore, the fabrication process of the
gripper can be considerably simplified by using this
approach. This separation allows using different kind of
actuators as driving part of the gripper without any
consideration to their undesired effects on cells health.
Several configurations were considered to define a shape
suitable for this application. Figures 1 to 4 show the
improvement procedure of microgripper design in this
work. For all those layouts tip of the gripper was conceived
to be proper for gripping of a cell with 35 µm diameter.
Moreover, the total length of all proposed configurations
and their out-of-plane thickness are 1 mm and 20 µm,
respectively, and was considered fixed parameters during
optimization procedure. Furthermore, the applied
displacement to the moving arm of the gripper was
considered 20 µm when it was pulled and 10 µm when it
was pushed. In all FEM analysis of the structures we
changed the geometrical parameters so that the maximum
stress did not exceed of 34 MPa. Four dimensional models
of the proposed layouts were developed and then
investigated by the finite element code ANSYS.
Description
The contact area is reduced, as the electrostatic adhesion force.
It reduces the surface tension effect.
The electrostatic forces are reduced by conductive coatings or materials with small potential difference
with the object.
It reduced the surface tension effect.
It eliminates the surface tension effect and reduces electrostatic forces.
It reduces electrostatic forces.
The acceleration imposed causes the object releasing due to inertial force.
A pressurized air flow overcomes the adhesion forces.
The temperature increasing reduces the capillary forces.
The electrostatic force is controlled by shorting the gripper electrodes or inverting the polarity.
The object adheres to the substrate due to higher adhesion forces, or gluing on the substrate, or engagement
by the substrate.
Additional tools are used to detach the object.
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