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So DIGITS grasping system under
development at the Ohio State

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University is a
dextrous grasping

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system consisting of four three
degree of freedom fingers.

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The system's
modular construction

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allows easy reconfiguration
to perform both precision

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and power grasps.

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A power grasp is
especially of value

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in unstructured
environments where

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only approximate
information is provided

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on an object's size,
weight, shape, and surface

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characteristics.

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It is characterized
by multiple points

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of contact between
the grasp object

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and the inner surfaces
of the fingers and thumb.

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Because of its
enveloping nature,

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it maximizes the load carrying
capability of a robot hand

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and is highly stable.

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Even with relatively
straightforward open loop

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torque control,
the resulting power

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grasp system is quite
sensitive and flexible.

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Using a model of digits, its
weight handling capability

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can be determined using linear
programming optimization

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techniques.

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In this demonstration,
the maximum weight

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which can be held stably
is shown by the length

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of the rotating red arrow.

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The arrow's direction indicates
the direction of gravity,

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thereby simulating a rotation
of the grasp's posture.

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The torques necessary
to hold the weight

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are shown by the outside bars.

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The yellow [? trace ?]
[? drum ?] represents

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the region of stability
for each object.

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Several analytical
results, such as these,

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have been
experimentally verified.

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More than 30 pounds
can be stably held

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using just two
fingers of digits.

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However, more general
experiments [INAUDIBLE]

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control algorithms can be
time consuming when performed

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on the digit system directly.

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As a result, a dynamic simulator
has been developed for it.

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It allows simulation
of compliance,

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as well as friction, slipping,
rolling, and wedging effects.

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The simulator is written
entirely in C under X Windows

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and allows for easy
entry and modification

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of the many and
important parameters,

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including external
wrenches on the object.

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The simulator has been used
to determine dynamic weight

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handling capabilities.

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The heaviest weights
are typically

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held in a four-point
contact grasp.

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However, a five-point
contact grasp

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can be maintained if the object
is first wedged into the grasp.

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As previously mentioned,
external torques

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may be applied to the
object, allowing studies

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of the effects of
external [INAUDIBLE]

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on the grasp under simple
open loop torque control.

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The simulation also
supports easy application

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of external forces of
arbitrary direction,

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as well as modification of
the object's specifications.

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With progress and understanding
enveloping power grasps,

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applications can be explored
in space, nuclear, undersea,

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and other unstructured
environments.

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