I tested a new solenoid valve that RJ gave me. It is a two way control
solenoid valve, which means it has two solenoid one it. This new
solenoid valve reacts very fast, I love that sound when it was
working–powerful.
However, besides the fast reaction, this new solenoid valve is very the
same as the old one in the sense of control–as shown in the video, the
only way that controls the pneumatic rod maintaining in
a particular position is let it vibrates in a high frequency around that
position (name this method “vibration method”).
A big problem with this system is: uncertainty. With the same input
to the pneumatic cylinder, it results different rod positions! This
shown that the system is time varying. Thus, using “vibration method” is
definitely a bad idea.
Therefore, it is necessary to change the hardware:
B and B’ are solenoid control valves. When B apply air pressure and B’
exhaust air, the rod moves forward; wen B’ apply air pressure and B
exhaust air, the rod moves backward; when both B and B’ apply air
pressure, the rod will stand still.

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