Slowing down the action of a cylinder with flow control, mechanical or via software

[Randy Forgaard]

Originally Posted by kwotremb

Sounds like you have something similar to what we did this year on our robot. We had our entire mast and arm asembly rotate at a pivot point at the base that was controlled by a pnuematic cylinder. We used the flow control valves without any issues at all (basically the simple screw ones that replaced the straight or 90s that you screw onto the festo valvues). We had them pass inspection at 3 different events so I believe there should not be any issues with you using them.

That's interesting that your simple flow-control valves screwed into the exhaust on your Festo valve passed inspection at 3 events. Sounds like we may be more worried about the flow control valves than we should be. Clearly, it seems to me that flow control valves are in the spirit of the rules, since they don't store air and are entirely passive.

Originally Posted by kwotremb

We only had the 'up' part of the piston hooked up to the air. Then for down all we did is have a flow control valve on the output that we controlled to make sure the fee fall of the arm was at a rate we needed.

That's a good idea. We have been using pressurized air to send the arm down, because "at rest," the arm is straight up in the air so it doesn't naturally fall down. But there's no reason we couldn't change the stop bar so that the top of the arm is angled out slightly, so that gravity would drop the arm with no air pressure needed, and just use a flow control valve on the exhaust to reduce the speed of the drop.

Originally Posted by kwotremb

Now for you, I would think for 'up' you guys should be able to use a flow control valve on the output just as you are thinking with the down. The flow control will make sure the rate at which the air can escape is limited, or more controlled. That way when the arm is moving slowly at first, the speed is not limited at all because the air can escape as fast as air is going in the other side of the cylinder. Then when you start to get to the top the air pressure will start to build up due to the fact that it will not be able to escape fast enough and slow down the rate of the arm. Hopefully that should be enough to prevent some of the slam you are experiencing on the top.

Your description makes sense. We experimented with a flow control valve on the exhaust port for the "up" direction, but found that the arm still slammed. But I think we must not have done enough experimenting with the valve, because it makes total sense to me that we should be able to restrict the flow enough so that it won't slam, and it also won't have any impact on the speed that the arm raises since the air can escape as fast as the air is going into the other side of the cylinder, as you note above. If indeed we can legally use a flow control valve (and, from your experience at those 3 events, it appears we can), it seems like that should solve the problem nicely for us.

Originally Posted by kwotremb

Another simple way to melp out some of the slam is to put a bumper on the arm or frame where they hit, that way the slam is less violent. We were going to do this until we designed it so our cylinder maed out before we hit a hard stop.

I'm interested in your last sentence there. You mentioned you were going to install a bumper where the arm hits the frame, but you didn't need to do that because you designed the arm so the cylinder "maed out" before it hit a hard stop. I'm not sure what the means, but it sounds promising. Could you explain a little more?

And thanks very much for your detailed recommendations. It sounds like your robot uses a very similar arm mechanism to ours.