Optimizing Precharged Cylinders

[vamfun]

Originally Posted by Ether

Any one have simulation modeling experience and access to Simulink/Matlab (or some other modern simulation tool) ? Give the computer the right equations and let it do numerical integration.
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I took on the task a few months ago for the Vex pneumatic system (both excel and Simulink model) and later modified the excel model for FRC components. The model lacks FRC lab validation but has a few check results from Vex.

Here are some conclusions I drew from the model:
a) The Cv for the SMC and Festo are sized to keep a .75 in bore from flow limiting the valve most of the time. The larger bores push the valve into sonic conditions and limit the power to the cylinder. (I spoke of this in http://www.chiefdelphi.com/forums/sh...ad.php?t=80134)
b) Precharging a .75 and 1.06 in bore cylinders actually degrades the performance. With a 0% and 40% stroke precharge the .75 in bore energy went from 9.7 to 6 ftlbs and the 1.06 in bore went from 12.5 to 10.1 ftlbs.
c) Precarging the 1.5 in bore gave a peak near 40% stroke as expected and increased the energy output from 9.4 ftlbs to 14.2 ftlbs.
d) Precharging the 2 in bore gave a peak of 18 ft lbs between 40 and 50%. Without the precharge, it was essentially unusable.


I ran the cases under the following assumptions:
Stroke: 6 in
Pressure:60psig
Cylinder load: near 50% of max force. (eg around 10 lbs for a .75 in bore)
Two way adiabatic piston model: Exhaust chamber fights pressure chamber.
System Cv = 50% of solenoid Cv to account for piping and fitting effects.
Cv was same for input and exhaust ports. (I am a little uncomfortable with this since I suspect the exhaust port is not as restricted. If anyone has knowledge of this please chime in. I emailed SMC on this but haven't heard back).