Putting the throttle/needle valve on the cylinder exhaust has some significant advantages. Mainly, controlling cylinder speed on the exhaust port causes your cylinder to operate at or near it's fully capable force (air pressure * cylinder area) throughout the entire stroke. If the air inlet is throttled to control speed then your cylinder will operate just above the breakaway force of the mechanicals it is attached to. If the mechanical linkages are smooth and the load fairly constant throughout the stroke, you should have acceptable operation. But, if the linkages are not good and tend to bind or if the load changes over the length of the stroke (ie. you are rotating something from vertical to horizontal) then you will have jerky motion or inconsistent speed.Using a combination speed control / exhaust muffler like this on your solenoid valve http://www.amazon.com/Norgren-MM001A260-Sintered-Control-Muffler/dp/B002095NGA will not only provide smooth operation but will attenuate the exhaust noise.
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Hello again,Oh so you are looking for position control, which means you need feedback.This would be something like a servo system, but instead of a rotating sensor you would use a linear sensor that is attached to your piston shaft. The sensor itself may be a rotational device connected to a drive arm but either way you get feedback and that goes to the control system which compares the signal to a reference and determines which side of the piston is to be driven. There's going to be some dynamics to consider as the air is compressible and also the dynamics of the system the piston is connected to (it is driving) has to be taken into account also in order to obtain stability and the desired response.If you have ever worked with a servo system you should have an idea how this works.Tying to do it without feedback may be very difficult as you would have to calibrate the whole system and then with wear and also alterations over time due to lubrication variability it would probably have to be calibrated too often to be useful. A possibility might be to overdrive the cylinder so that the pressure on both sides is always much higher than needed, but im not sure how this would work out in practice as you'd have to calibrate that anyway. Using feedback you never have to worry because the system is constantly checking itselfThe question of how much accuracy you really need comes up too.
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