airmuscl.txt

                  Air Muscle Article

                                      
     The air muscle is a new type of device that achieves
linear motion with the application of pressurized air. Like
a human muscle it contracts when activated. You may
think, well, this is nothing new, pneumatic cylinders have
been around for decades and can do the same thing.
But the low cost, ease of use, and effectiveness of the
air muscle far exceeds standard pneumatic cylinders. Its
ease of use allows it to be quickly adapted by robotists
and hobbyists for immediate use.

     In some ways, the air muscle is similar to Nitinol wire.
Mainly in its ability to to contract when activated. A quick
comparison yields these results: Nitinol wire only contracts
7% of its length. The air muscle contracts 25% of its length.
Nitinol wire is a power hog. It consumes large amounts of
electric current to function. While its response time may be
quick, its cycle (heating-cooling-heating) time is quite slow.
The air muscle operates off of air pressure.

     While efficiency is lost using electric power to compress
air can be stored. Its response and cycle time is very fast.
strength and overall power comparison are difficult. The
small air muscle can lift 6.5 pounds, much more than
standard Nitinol wire. Nitinol wire is weaker, but only because
the wire diameter (.006) is so small. Thick gauge Nitinol wire
(not made and would be very expensive) would have
hundreds of pounds (if not thousands of pounds) of
contractive force.

     We will build two manually operated air muscle demo devices.
We will than interface the device to the computer. When I first
encountered the air muscle, I thought a pneumatic system would be
to much of a hassle to build, regardless of how innovative the
product is. I was wrong the pneumatic system can be put together
for about $20.00.

     To control the air muscle via the IBM parallel port adds
another $25.00 to the cost.

     Advantages of the Air Muscle Lightweight- Six-inch air muscle
with 18" of 5/32 diameter air tubing, weighs approximately 1"
(about 25% of its length, ends not enclusive).

     Powerful - Has lift approximately 6.5 lbs. @ 42 psi.

     Pliable- Soft pliable construction, able to be bent around
curves and still function properly..

     Uses

     The air muscle lends itself to robotics and automation.
In some cases, it can replace servos and DC motors.
Its unique properties, lightweight, strong, and pliable
can be capitalized in many applications and used to
improve existing pneumatic designs.

     In a nutshell, the air muscle may be used in many
applications that require linear or contractive motion.
In many cases, pneumatic cylinders can be replaced.

     How the Air Muscle Works

     The air muscle looks like a long tube constructed
out of black plastic mesh. Inside of it is a soft rubber tube.
Metal clips are fastened to each end. The plastic mesh
is formed into loops on each end, tucked into end secured
by the metal clips. The loops are used for fastening the
air muscle to devices. When the air muscle is pressurized, the
soft inner tube expands.The inner tube pushes against the
black plastic mesh which also expands.As the plastic mesh
expands, it shortens its response to the expansion. This
causes the overall length of the air muscle to contract.

     To operate properly, it is important that the air muscle
be in a stretched or pulled out position when it's deactivated
or in a resting state. If not, there will not be any movement
or contraction when it is activated (see Figure 1). When air
pressure is applied, the muscle contracts.

  Components of the Air Muscle System

     Figure 2 illustrates the components needed to use the
air muscle.

Item 1-The air muscle itself (of course).

Item 2- Three-way air valve. The three-way air valve allows
one to manually operate the air muscle (see Figure 3)

Item 3- A bottle top adapter, with a pressure release valve
(set around 60 psi) . The bottle top adapter allows one to
use a standard plastic PET soda bottle for air storage.

Item 4- PET soda bottle (used for air storage). A plastic
soda bottle can hold 50 psi easily. I have static tested plastic
PET bottles to 100 psi. NEVER USE ANY TYPE OF GLASS
BOTTLE FOR AIR STORAGE! A slight fracture in a glass
bottle, or dropping it accidentally, may cause the bottle to
suddenly explode sending tiny glass fragments all over.
Plastic PET bottles elongate when over-pressurized

Item 5- Foot pump adapter.

Item 6- Foot Pump. Simple foot pump with air pressure gauge
can charge air storage up to 100 psi. Because of the low
volume of the PET bottles, air storage is brought up to 50 psi
with three or four strokes of the air pump. The air muscle!

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