Leslie Gordon
Senior Editor
Imagine if you could have a machine
in your home that, like the
Star Trek replicator, conjures up
a cup of coffee or a hairbrush on
command. This sort of personal
manufacturing might well be close
at hand. Researchers at Cornell
University’s Computational Synthesis
Lab in Ithaca, N.Y., have
come up with a “personal fabrication
device” — about as big as a microwave
oven — anyone can purchase
for a few thousand dollars.
Better yet, the device’s open-source
firmware, application source code,
and parts list are online for those
who’d like to build or modify their
own device.
Professor Hod Lipson and graduate
student Evan Malone named
the machine they developed a “fabber”
after the “fab labs” (short for
fabrication laboratory) that Neil
Gershenfeld of the Massachusetts
Institute of Technology recently
established around the globe. He
intended the centers to spark the
creativity of ordinary folk by giving
them free access to precision
manufacturing tools not otherwise readily available, such as 3D CAD,
laser cutters, and desktop milling
machines. Gershenfeld also
hoped to eventually create what he
called a “personal fabricator” that
would make objects on-demand
from computer-generated design
specifications. What the Cornell
researchers call the Fab@Home
project has brought this idea down
to earth.
Under the hood of a
personal fabricator
First, a brief description
of the machine. A
fabber has a three-axis
gantry configuration.
Its mostly off-the-shelf
parts include shafts, limit
switches, cabling, power
supplies, sensors, linear
motors, and the like. An
acrylic housing covers
components. On the basic
model, these include a carriage,
on which mounts a printer head
with a replaceable syringe that acts
as a deposition tool and builds part
layers in the XY plane. Syringes reside
in “smart” devices that communicate
with the printer head to
indicate the material they contain
and when they are in position. A
second carriage moves the build
surface up and down.
In fabricating a part, the syringe
tool deposits a thin, continuous
bead of material, layer-by-layer
onto the build surface. Materials
can be almost any fluid or paste.
Examples are ceramics such as
gypsum plaster, metallic materials
such as solder, thermoset polymers
such as GE Silicone II, and electrically
conductive composites such as SS-26 silver-filled silicone. Part
resolution is determined by the
needle or nozzle diameter.
The fabber connects to a Windows
PC via USB. Ancillary software
imports stereolithograpy
(STL) files to generate toolpaths
for the syringe nozzle to follow,
dictates fabrication sequences,
calculates deposition rates, and
generates tool-exchange commands
(some fabbers use more
than one syringe tool). The software
also provides an onscreen
view of the printer that updates a
part fabricates.
How to print a battery
One task was to develop and print a battery of an
arbitrary shape so a robot, say, could have batteries
as legs, says Lipson. Researchers developed a
battery with zinc as the anode and air as the cathode
because of the design’s simplicity.
First came development of a zinc-powder suspension
that did not clog the syringe nozzle. Next
came designing the separation layer between the
anode and cathode. In commercial batteries, this
layer is often paper. In contrast, the layer in the
zinc-air battery is made from ceramic slurry or a
synthetic resin.
“After a few trial runs, the fabber printed a battery
about the size of a coin and with five layers of
different material in a plastic case,” says Lipson.
“In one test, the device delivered 10 milliwatts for
50 hours to a small dc motor. While not performing
as well as a commercial unit, by around a factor
of two, the battery frees users from the design
constraints imposed by conventional devices.” |
Admittedly, items the apparatus
builds look crude compared to
those made by commercial rapidprototyping
(RP) and manufacturing
machines from Object,
Z-Corp., Stratasys, and other
companies. But, unlike commercial
equipment, fabbers can build
active, functional objects such as
batteries and electroactive actuators.
Fabbers of the future might
generate such consumer items
as toys, cell phones, and electric
toothbrushes.
Simulating evolution
The idea for the fabbers grew
out of a need to quickly produce
free-form designs, says Malone.
“The Computational Lab focuses
on artificial evolution — the simulation
of evolution to solve challenging
engineering problems,
such as robot design,” he says. “The
basic idea is to take a large number
of candidate solutions to any
problem that can be generated in
a computer algorithm. Let’s say I want to make a robot
walk forward, but don’t
know how to control
the movement. So I
start by just giving the
robot, say, 30 random
commands. Then I
determine which ones
make the robot move
more forward than the
others. I combine these commands
and keep iterating cycles in a similar
fashion.”
Malone says the lab had been
using RP for a few years as a way
to make parts for robots. “Our
evolutionary searches usually produced
nonstandard shapes. For
a while, we were outsourcing the
3D printing of unusual robot morphologies.
Then, instead of having
graduate students assemble every
robot iteration with these parts,
we decided to build a machine that
could spit out complete robot after
complete robot with minor and
major variations.”
Malone first built a larger test
machine to print circuitry, actutors, and batteries. “At the time,
commercial machines only printed
one material, and you had to use
the manufacturer’s special blends,”
he says. “We took lessons learned
from the test machine and started
working on a do-it-yourself version,
the fabber. That the machine
can print almost any material, as
well as more than one material
comes from the use of the disposable,
standard syringes. And materials
with a wide range of viscosities
work because a linear motor
driving the syringe piston controls
the deposition pressure.”
As for the design side: Design
software intended for 3D printing
does not yet exist (even for commercial
equipment), says Malone.
So there is no way, for example, to
define RP material properties in
CAD. Instead, users assign properties
to the STL geometry in the
fabber software. That said, future
design software would need to
support a file format more sophisticated
than STL — one that would
let users specify multiple materials.
Malone says developers are working
on a format now.
A robot building a robot …
“One of our main goals is to
have a robot walk or wiggle out
of the machine, its electronic and mechanical parts having been
generated seamlessly in one build,
battery included. A robot building
a robot, so to speak,” adds Lipson.
“At this stage of the game, we
have demonstrated the free-form
fabrication of components such
as electromechanical relays, polymer
transistors, elastomer strain
gages, complete zinc-air batteries, artificial muscle actuators, and inductors
and electromagnets. Next
comes designing a higher-level way
to get larger sub-assemblies built.”
The big hope is that Fab@Home
will inspire more people to fabricate
integrated systems at home,
says Lipson. “Currently, users can’t
print something like an iPod. But
these kinds of objects will appear as users continue to tweak the source
code and further refine the machine’s
design. Some have added
heaters to melt powders while
others have attached a hopper for
powder use. One individual even
included a feedback mechanism so
the machine can self-correct when
it is running.”
As for today, suppose someone
has an idea for a new electric
toothbrush. “Unless
there is a way to make it
at home, the individual
would probably just let the
idea go,” says Lipson. “So
when fabber use is more
widespread, anyone could
create a design and post it
on the Web as a 99-cent
download. This scenario
might shake up manufacturing
similar to the way
the music industry got
turned on its head.”
Make contact
Computational
Synthesis Lab,
ccsl.mae.cornell.edu
Fab@Home project,
fab@home.com
An intermediate step
Fab@Home is useful because it lets a much broader range of users experiment with
unusual designs and materials,” says Terry Wohlers of Wohlers Associates, a Ft. Collins,
Colo., consultant specializing in the rapid product-development industry. “But
one potential problem with personal manufacturing in general, and not just with additive
fabrication, is that most people don’t know how to design well. An intermediate
step currently has manufacturing involving consumers, but with limited options.”
Take for example, NIKEid.com, says Wohlers. “Users can produce a pair of custom
shoes for track, football, running, or whatever,” he says. “Customers can change shoe
color, add a school mascot, and put their initials on the heel. And, there is no way to
make a crappy pair of shoes by, say, making poor design changes to the sole.”
A lot of personalized, on-demand manufacturing is increasingly Web driven, says
Wohlers. “For example, jujups.com lets users upload an image and select a picture
frame. The company then uses a commercial 3D color printer to make the image and
frame, charging around $29.”
Wohlers cites other examples including figureprints.com, where users can order
3D color prints of characters from the World of Warcraft video game, fabjectory.com,
which builds avatars from Second Life, and zazzle.com, which provides online tools
where users can add designs to objects such as T-shirts and coffee mugs. |