Robotic Hand Offers a New Grasp on Space Construction

John Ira Petty

Johnson Space Center, TX

(281) 483-5111

Release: J00-36

A robotic system aimed at giving spacewalking astronauts a hand is being
refined at NASA’s Johnson Space Center. A mechanical hand very much like
a human hand offers remarkable abilities to operate the same tools used
by people in spacesuits.

The hand, in combination with an attached arm, is capable of actions as
delicate as lifting small objects with tweezers. It is powerful enough
to lift a 21-pound weight on the Earth’s surface – giving it
considerable capabilities in a zero-G environment.

Two of the hands will be used with the Robonaut system, which also
includes two arms and swiveling head with cameras inside. The hand and
the rest of the system are likely to find a range of applications on
Earth. Among them are work in hazardous environments like some found in
nuclear power plants and petroleum refineries. Makers of prosthetics
also have expressed interest.

Designers have worked hard to make the hand function like a human’s.
Through the cooperation of local medical schools, they were able to
dissect human hands to improve their understanding of how they work.

Chris S. Lovchik and M.A. “Ron” Diftler worked together on development
of the hand, wrist and forearm. Lovchik, who works in Johnson Space
Center’s Robotics Technology Branch, did the hand design and forearm
layout. Diftler, with Lockheed Martin’s Automation and Robotics
Department in Houston, worked on the wrist and forearm packaging.

From the project’s beginning about three years ago, Lovchik and
Diftler’s objective has been to reproduce in a machine some of the
capabilities of a spacewalking astronaut, perhaps on the International
Space Station. They decided the best approach was to make the robotic
hands and arms like those of a human.

Hand rails, foot restraints, tools and other support for space-walking
astronauts are built into the station or sent up for the astronaut’s
use. The challenge was to develop a robot that could make use of them.
“The world we’ve created is a product of our (human) form,” Lovchik
said. Alternatives were to design special tools, targets and other
things for a robot, “or design a robot to function in our world. The
hand is a critical element.”

Such a hand also has advantages for operators, who can use years of
experience with their own hands in controlling the machine.

The current model of the hand has 12 individual, controlled motions, or
degrees of freedom. “You can think of it as divided into two sections,”
Lovchik said. “The first two fingers and the thumb make up the dexterous
work side.” They have three degrees of freedom – they can open and close
as well as spread apart, essentially like human fingers. The remaining
two fingers only open and close – they are used for grasping. The palm
can “cup” to help grasp tools.

“Some simplifications and compromises had to be made to create the
hand.” Lovchik said. It had to be functional enough to work with a
variety of tools and other devices. It had to be rugged enough to
survive the space environment. It had to be extremely compact, much like
a human hand, wrist and arm. To meet all the criteria some motions of
the human hand were not replicated. But designers always focused on
retaining maximum flexibility.

The hand and forearm weigh about six pounds. In the 8-inch forearm are
14 electric motors, 13 circuit boards, 12 five-element drive trains for
the fingers, two two-element drives for the wrist, 42 base-level sensors
which provide information on the position and velocity of each actuator.
Tactile sensors, which will allow the hand operator a degree of feeling,
will be added soon.

Developers believe that as the hand evolves, other applications will
emerge. The hand and the robot, together with a human operator some
distance away, may eventually have the capability to do almost anything
a human could do.

That includes adapting to a situation that might not be fully understood
before the robot is committed, Lovchik said. “You can give it a tool box
and send it out there.”