When NASA Langley Research Center hired Honeybee Robotics
Spacecraft Mechanisms Corp. to develop a totally mechanical tool changer, the
requirements were anything but simple. For starters, the tool changer was to be
designed for the end of what Langley's Lunar Surface Manipulation System (LSMS)
team describes as a robot that could unload landers. After the landers are
unloaded, the tool changer must also be able to mate with tools to perform
various science experiments.
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In essence, this robot could be likened to a crane but with more
dexterity. And on top of all the other requirements, this dexterous crane had
to be able to work remotely so that it could be used on an unmanned mission
without human interaction.
Design Scope
To start, NASA gave Honeybee a project envelope - a
footprint to stay within - that included all the requirements for load ratings
and misalignment allowances.
Lee Carlson, a systems engineer who was part of the Honeybee
team, describes the project from a design perspective: "The crane might be
sitting on the lander deck or on the lunar surface and then be driven quite a
distance away from the tool to be mated to. This required designing for large
misalignment allowances - and that was our first design challenge. We had to
design the device so that the end of the crane and target tool could be
misaligned by as much as a couple inches in any direction with up to 20 degrees
angular misalignment when attempting a mate."
Other requirements included having the tool changer be capable of carrying about 1,000 lb. And since this
was a lunar project, it has to be tolerant to moon dust. These two design
criteria required special seals to protect large roller bearings.
The original assignment called
for "dumb" tools requiring no power. The crane would do all the work. Tools
would range from a forklift attachment, a shovel or scoop for acquiring surface
samples or digging, or even a bucket for lifting human passengers.
The Scope Expands
Then NASA decided it wanted the capability of attaching
an electronic or electromechanical tool to the end of the crane. Now the tool
changer would also have to provide an electrical connection. Solving this
problem fell to Carlson.
"The contract was expanded to add an electrical connector to the
existing mechanical connector, which meant that we had to have a power source
on the crane itself. However, space to accommodate an electrical connector had
not been accounted for because it was not a part of the original contract and
the budget did not allow for starting from scratch.
Carlson had to work within the
constraints of the current design because NASA did not want a redesign of the
whole tool changer. They just wanted to add an electrical connector to it
without increasing the current envelope. With only about 2½ x 4 inch of free
space to incorporate the male side of the new autonomous connector (the
connector has to mate itself to a female connector mounted on the tool), the
task before Carlson was not an easy one.
To compensate for the new
requirement, Honeybee designed both the male and female sides of the connector.
The female side had to be inexpensive and easy to create because each tool
would have to have its own female connector versus a single male connector
attached to the crane.
The male connector has all the
moving parts. It is cylindrical and populated with 11 1/16-inch diameter
aluminum pins plated with gold over nickel configured in a standard MIL/Spec
pattern. The connector rides on compact slides - miniature guides made by NB
Corp. The top faces of the two glides face each other and Honeybee's components
reside in between the two glides supporting the connector. This configuration
reduces the moment loads on the slides.
"We use a total of six slides
within the space - three on each side," says Carlson. "The slides ride on each
other in the manner of drawer slides stacked to extend the distance they can
open a drawer. Our configuration achieves an extension of the movement equal,
approximately, to the length of three slides. So instead of a half-inch stroke,
we could get an inch-and-a-half stroke within a very, very small footprint. Low
mass, low load and very low profile were all required for this application."
Larry Hansen is general sales manager
- director at NB Corp. of America
For more information, go to www.nbcorporation.com.
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