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Hi
I did some 'research' in this area about three years ago for the control of
a pneumatic robot arm. It was quite simple positional control ie position
the piston at any point in the cylinders stroke and hold it there. The
controller was just a PC and in the end I used SMC (a pneumatic company)
pneumatics cylinders which I thought had higher stiction than some other
cylinders (alledgedly ;-)), but the key was a fast acting proportional
pressure or flow flow regulation valve (these were supplied by SMC and ASCO
Joucamatic, although I guess other pneumatics companies like Festo do them
now also). These valves were controlled with a 0 - 10V analogue input that
was proportional to the pressure or flowrate out of the valve. These valves
had a full scale response time of approx 1- 2ms and the controller was
sampling at just faster than this rate. Slightly differently from other
pneumatic control efforts I only controlled the pressure into one side of
the cylinder and used gravity to drive the cylinder in the other direction.
The system was pretty accurate (about ±1mm) and repeatable. I think only
controlling from one side may have made it easier rather than having two
valves fighting each other. I used a very simple feedback PID algorithm to
control the whole thing.
So I guess you could use Lego cylinders, but the valves are another matter.
I t would be nice if Lego did a few more pneumatic components - a pump, some
simple electric solenoids valves rather than the manual ones we have at
present. I know you can build these things, but I bet the Lego ones would be
smaller and neater.
Mike
> Whoa. Not entirely correct. You can do accurate positioning with
> pneumatics, it's just harder to do than with hydraulics, because you have to
> take air compressiblity and seal "stiction" into account if you want to hit
> an arbitrary position that's in the middle of your cylinder's travel.
> OK. That said, LEGO(R) pneumatic parts aren't ideal for accurate
> positioning : (
>
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