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SHADOW AIR MUSCLE MOUNTING CONSIDERATIONS |
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Air
quality
Because of the construction of the muscles, they will
suffer if oil is allowed into them. Prevent this by properly
filtering the incoming air.
Bedding In
Because the muscles are made of rubber, there is an initial
period in which the rubber `beds in'. The first few times
it is used, it will stretch by a small percentage. Also,
as the muscle becomes warm in use, it will stretch slightly.
Chafing
Because of the braiding, if muscles are allowed to chafe
against hard or pointed objects, over time the braiding
will distort, and the muscle will balloon through the
braiding and eventually burst. Prevent this by ensuring
that the muscles are free to move.
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Environmental
conditions
We do not recommend that standard muscles be use in
ambient conditions exceeding the 0-50°C range. Muscles
can be washed with water or mild soap, but harsh detergents
are not recommended.
Puncture
The lightweight construction of the muscle means that
it is vulnerable to sharp objects. We are currently
investigating armouring techniques for muscles. Note,
however, that muscles do not necessarily suffer catastrophic
failure. In the event of a puncture, the muscle will
often leak air noisily, whilst continuing to function
at lower efficiency.
Pressure
The muscles are rated for use up to 6 bar (90psi) when
under load. If the muscle is not loaded, i.e. is not
under tension, then it should not be taken above 2 bar
(30 psi).
MOUNTING
POSITIONS
The muscle is best used to move a lever. Its simplest
configuration is when attached with a return spring
on opposite sides of a pivot point. Simple installations
often manage with elastic bands as return springs!
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The
muscle is used to raise the lever; the elastic band
acts to return it. Note that the muscle is used for
the motion that requires greater force: the return for
the lever is gravity-assisted. This is a common characteristic
of simple muscle designs: the muscle is used to provide
the power stroke.
The muscle operates with great strength in the first
part of its contraction, but exerts less force as it
contracts further. A trade-off can be used between stroke
length and force: in the case of the lever above, mounting
the muscle closer to the pivot point increases the motion
of the end of the arm, but reduces the weight that can
be raised
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Conversely,
mounting the muscle further away from the pivot point
increases the load that can be raised, but decreases the
length of the stroke |
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The
actual attachment of the muscle can be done in several
ways. The smallest sizes of muscles have loops at the
ends, and these can be simply mounted over bolts or
hooks on the machine. If the device is carefully made,
and the muscle motion required is known exactly, then
mounting bolts can be placed in the body, and the muscle
end-loops placed over them.
This technique, shown at the right end of the muscle
requires the mounting points to be exact; however, it
allows for simple replacement of a muscle at the end
of its life: the muscle need only be slipped over the
bolt, and another placed there.
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The
alternative technique, shown at the left end of the
muscle above, is to use a cable-tie, wire or string
to attach the muscle. This can then be adjusted to
produce the optimal tension in the muscle. This is
great for prototyping with muscles: the system can
be constructed very quickly, and the necessary muscle
adjustment discovered.
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The
larger sizes of muscles exert considerably greater forces,
and so are not suited to a simple attachment technique
like this. Instead, our current designs come with screw-thread
ends. These are designed for a firmer anchoring, whether
directly bolted to the frame, or attached using high-strength
ropes
Caution: When using muscles to supply
large forces (at high pressure, or muscles of large
diameter), use appropriately specified fittings.
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Adjusting
the muscle attachment
Because
of the motion of the muscle, it is necessary to carefully
adjust the system for best results.
When
the muscle is at rest, it should not be limp, but rather
taut. This ensures that as the muscle is filled, it
begins to move as soon as possible.
As
the muscle fills, it contracts. Careful placement of
the muscle end about the pivot can make significant
differences to the range of motion available.
Once
the maximum load on the muscle is known, and the pressure
at which it is to be driven is known, then the muscle
can be adjusted so that the contraction that the muscle
provides is fully utilised in the motion of the pivot.
If the muscle cannot be made to reach its full expected
contraction, then increasing the pressure slightly,
or moving the muscle closer to the pivot, will often
help; however, the pressure limits of the muscles must
be respected
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Measuring
the distance from the mounting point of the muscle when
the lever is down and the distance when the lever is up
gives the amount of contraction the muscle is expected
to produce. Then, this can be compared with the load on
the system to predict the pressure required.
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