Controling Pneumatics

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Posted by Elliot Johnson at 1/12/2001 12:45 AM EST


Student on team #218, HP Robotics Team, from Highland Park High School and Double-E Inc..


In Reply to: Controling Pneumatics
Posted by Corvallis on 1/11/2001 7:57 PM EST:



: Ok here is our problem. We need to know how we can get our pneumatics to be able to stop without fully extending or vise versa. In other words how do we control the length of the cylinder by holding down either the trigger or the thumb. As we have it now we press the button once and it extends all the way or contracts all the way. Any help would be appreciated.

There are at least two different ways I know of to slow the cylinders
down to a controllable speed.
The first (easiest & most reliable) is to put one of the little pressure
valves inline with the cylinder's feed. I'm not sure the exact name for
them, they look like little 90 degree elbows and have a screw coming
out of them, like a small water faucet. You adjust the screw until the
cylinder moves at a comfortable speed. To move it to a certain
position, just turn on the pressure switch for the cylinder until it is
where you want it and turn off the switch. The air pressure will remain
in the cylinder so it will maintain it's position. You can also use two
valves, one for each entry into the cylinder, to have different speeds
in different directions.

The other way I've read about it to use a model like PWM for
controlling motors. The solenoid valve is quickly pulsed on and off
rapidly. The pulses begin at a constant frequency (the solenoid is
turned on every x milliseconds) but the length of the pulse depends on
how fast you want the cylinder to move. The length of the pulse can
be between 0 (not moving at all) and the full period (full power).
Anywhere in between should give a proportional speed. This setup is
more complicated, but the speed isn't fixed like with the pressure
regulators. For a better description of PWM, check out this article in
the SRS newsletter:
http://www.seattlerobotics.org//enco...68hc12pwm.html

Hope that helps!
Elliot Johnson
Team 218
Double-E Inc & Highland Park High School Robotics