So DIGITS grasping system under development at the Ohio State
University is a dextrous grasping
system consisting of four three degree of freedom fingers.
The system's modular construction
allows easy reconfiguration to perform both precision
and power grasps.
A power grasp is especially of value
in unstructured environments where
only approximate information is provided
on an object's size, weight, shape, and surface
characteristics.
It is characterized by multiple points
of contact between the grasp object
and the inner surfaces of the fingers and thumb.
Because of its enveloping nature,
it maximizes the load carrying capability of a robot hand
and is highly stable.
Even with relatively straightforward open loop
torque control, the resulting power
grasp system is quite sensitive and flexible.
Using a model of digits, its weight handling capability
can be determined using linear programming optimization
techniques.
In this demonstration, the maximum weight
which can be held stably is shown by the length
of the rotating red arrow.
The arrow's direction indicates the direction of gravity,
thereby simulating a rotation of the grasp's posture.
The torques necessary to hold the weight
are shown by the outside bars.
The yellow [? trace ?] [? drum ?] represents
the region of stability for each object.
Several analytical results, such as these,
have been experimentally verified.
More than 30 pounds can be stably held
using just two fingers of digits.
However, more general experiments [INAUDIBLE]
control algorithms can be time consuming when performed
on the digit system directly.
As a result, a dynamic simulator has been developed for it.
It allows simulation of compliance,
as well as friction, slipping, rolling, and wedging effects.
The simulator is written entirely in C under X Windows
and allows for easy entry and modification
of the many and important parameters,
including external wrenches on the object.
The simulator has been used to determine dynamic weight
handling capabilities.
The heaviest weights are typically
held in a four-point contact grasp.
However, a five-point contact grasp
can be maintained if the object is first wedged into the grasp.
As previously mentioned, external torques
may be applied to the object, allowing studies
of the effects of external [INAUDIBLE]
on the grasp under simple open loop torque control.
The simulation also supports easy application
of external forces of arbitrary direction,
as well as modification of the object's specifications.
With progress and understanding enveloping power grasps,
applications can be explored in space, nuclear, undersea,
and other unstructured environments.