[PSUBS-MAILIST] Pneumatic Manipulator

[Stephen Fordyce via Personal_Submersibles]

Hi Alan,
I've done a little with pneumatic cylinders and I think it will be very
difficult to achieve any kind of accurate positioning. Pneumatic is fine if
you only need a cylinder to be fully extended or retracted (as is used for
industrial automation) but anything mid way is likely to need a complicated
feedback/control system.

Even considering as a perfect system, if you have varying force/load, to
avoid movement you must have an equally varying pressure in the cylinder.
Increasing pressure in the cylinder doesn't help because you then need to
increase pressure in the opposite side and then the tendency to resist a
disturbing force is not much different anyway. (And if using a single rod
cylinder, the pressures in each end need to be different to achieve the
same force due to area of the piston) Throw in real world considerations of
static friction and dynamic friction and it's harder again to reach and
hold a desired position.

I'm a bit surprised you haven't already ordered a cheap pneumatic cylinder
for some concept testing :).  That should give you a feel pretty quickly if
it's doable or not.

Cheers,
Steve Fordyce

On 17 Mar 2018 7:27 am, "Alan via Personal_Submersibles" <
personal_submersibles at psubs.org> wrote:

> Have thought a lot about pneumatic manipulators.
> Hank has commented several times that they are too "spongy".
> If you had pressure relief valves or similar in the system set at something
> like 30 psi, so there was always a minimum of 30 psi either side of the
> piston;
> would this make it a lot less "spongey".
> You would now need to put an extra 30psi in to get the same force.
> It would mean more air, but it is not likely you would be using the
> manipulator
> every dive, & it would be a small quantity compared with blowing a ballast
> tank.
> Has this been done before?
> Cheers Alan
>
>
>
> Sent from my iPad
>
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