Completely lost about Pneumatics

[brianaong]

My team's programming this year has been jumbled up; from trying to switch to Java at the beginning of the season, reverting back to LabView two weeks ago, having our head programmer drop out, and having a completely new programming team (consisting of two new members), we're clueless. So far we've been able to worm our way with programming the drive and our pulley system but we stuck at pneumatics.

Would it be possible for someone to help explain everything about pneumatics in layman's terms? (And if it's not too much, help with the actually programming.) We don't really have a set and consistent programming mentor so any help would be appreciated to the fullest.

We're using two cylinders and a double solenoid. Our cylinders are mounted outwards from each other with an arm on the end of each. We plan for the robot to clamp on the sides of the totes/bins by releasing the air. We want to be able to control how much air is released from the cylinders because the arms, in theory, should adjust to the width of both of the bins and all sides of the totes.

Thank you!

[Mark McLeod]

See if these help any:

Pneumatics Step-By-Step (for the roboRIO Controller)
Pneumatics For Newbies

[Alan Anderson]

Originally Posted by brianaong

We plan for the robot to clamp on the sides of the totes/bins by releasing the air. We want to be able to control how much air is released from the cylinders...

Normal pneumatic cylinders "want" to be either extended or retracted. Doing any sort of in-between control is not simple, and it takes a lot of careful design to make it work well.

How much pressure do you need the arms to squeeze the totes with? If you choose the size of the cylinder appropriately, you can apply the right amount of pressure no matter how big the thing between the arms is.

[VacioArconte]

Hi!

I'd like to preface my statement by saying that I am definitely not a pneumatics expert.

That being said, the main thing to know about pneumatics is that they are usually two-position actuators. This is mainly a result of the lack of precision involved in pneumatics. Teams often have small leaks in their systems, but ignore them because the main idea with pneumatics is the difference in pressure. This means that it is incredibly difficult to give the correct amount of pressurized air to the cylinder to make it stay at one point.

You can try the Dart Actuators http://dartactuators.com/ which will provide you with some accuracy.

Best of luck to you, hopefully I helped a little bit.

TL;DR Pneumatics are 2-position actuators, if you want more positions go to linear actuators like DART.

[Skyehawk]

There has been a misconception about pneumatics for teams that don't regularly use them. I would like to stress, pneumatics and hydraulics are NOT the same thing. Hydraulics and pneumatics both operate with fluid flow, however the main difference is the type of the fluid, the pneumatics operate with air, therefor a gas; while hydraulics operate with a liquid, it is very difficult to compress a liquid, gas on the other hand will fill their container( just one of the properties of gasses).
If you're still interested in trying to achieve position control with a pneumatic cylinder take a look through THIS thread.
(sorry for spelling out the differences between hydraulics and pneumatics, It's just important to understand.)


One other option, (I don't know if variable pressure regulators are legal in pneumatic systems) try using a variable pressure regulator, you may be able to slowly increase/decrease the pressure in the system and measure the current height of your lift mechanism with a sensor and adjust via sensor input. Just an idea.

[GeeTwo]

Originally Posted by brianaong

We want to be able to control how much air is released from the cylinders because the arms, in theory, should adjust to the width of both of the bins and all sides of the totes.

If I'm reading this correctly, this is one of the few cases where it is easy to get pneumatic cylinders to stop halfway.

Just dump all of the air on the other side - if the tote is between the arms of the cylinders, and unless the cylinders can exert enough force to deform or brake the totes, the arms will stop shortly after meeting the ends of the tote, and hold it with a steady pressure. The grabber is "self-adjusting".

[Skyehawk]

Originally Posted by brianaong

We want to be able to control how much air is released from the cylinders because the arms, in theory, should adjust to the width of both of the bins and all sides of the totes.

I'm sorry, I over analyzed this. The default pneumatics system will do this, if you want it to self adjust to the width of the container or tote this will happen with a single or a double solenoid setup.

Basically there will be pressure applied to one side or the other of the pneumatics (one of the solenoids will be open) the other solenoid is exhausting it's pressure to allow for a pressure differential in the system, this is what allows for extension or retraction of the piston. There will always be one side of the pneumatics in the "Exhaust" state, when your actuator comes into contact with something it will exert force until equilibrium is reached, there is no need to do anything with the exhausted air. Just set up your pneumatics like you see on test boards, robots, etc. and this system will work for you.

[Alan Anderson]

Originally Posted by GeeTwo

Just dump all of the air on the other side...

i.e., use the pneumatic cylinder and solenoid valve exactly as they are designed to work.