how to slow down pnuematic piston near end?

[knowlittle]

BACKGROUND:
An air actuator moves an object to target in 0.5 sec. Air pressure 70-80 psi, 25 mm dia piston, travel distance 25 cm. Shock absorber (dash pot) at the end. Object 1 kg.

PROBLEM:
Too much impact at stop even with dash pot. My setup walks around.

QUESTION:
Do they make an intelligent air piston that cuts down air pressure near the end? Or can I fabricate one with electronic control? Difficult to implement?

Thanks.

 

[bvanhiel]

One suggestion I didn't see already proffered is this: put a stiff spring at the end of the stroke. The piston will have to overcome it and you should be able to tune your decelleration. Of course you'll have to switch springs to tune it, so it may not work well for different masses/speeds. You'll also have to figure out a way to mount it if you can't fasten it inside the cylinder.

-b

 

[unclesyd]

I've been checking to find out about a machine we built that incorporated a pneumatic cylinder operating in a manner the same as in your OP. This machine essentially imulated an air over oil system. These cylinders operated at a certain rate for a period of time and then were called on to have the rapid approach and then go to a slow feed rate cycle for several hundred times and then switch back to the normal rate. The stroke was a little longer than yours.
For the variable rate mode of operation we used an in house built Fluidic control system for the rate control and electro-pneumatic for the normal operation.

On another system I believe we used this system or one very similar for the rate control on a much larger system.

Enidine also has a myriad of shock absorbing system as posted above.

http://www.enidine.com/Industrial/ADA700main.html

 

[DiamondDave]

could you have a small relief valve installed on the system, perhaps a small flap non return valve that after the piston reaches a certain distance this opens and allows some presure out to slow it down? but on the return it shuts again.

 

[strokersix]

X2 what alansimpson said. Air cushion at the end of the stroke should do what you need. Think of an old tape machine teletype carriage return. Very fast with an air cushion at the end of the stroke.

 

[waross]

We used to solve similar problems y screwing a pipe plug into the exhaust port of the control valve. Drill a small hole in the plug. Experiment with different size holes.
Another backyard fix is to charge a small cylinder through a small restriction. Then use the cylinder air to operate the piston. You will have full pressure to initially accelerate the piston and then dropping pressure as the piston travels.
The best cylinder volume will probably be some fraction of the cylinder volume. You an fad it out of nipples and reducers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[EdDanzer]

To make air cylinders stiff you must meter the air coming out to control movement well. To make a smooth move you really need an S curve acceleration and deceleration curve. This requires servo valves, feedback and a controller. Pud’s suggestion is a PWM method of metering to provide an acceleration and deceleration curve. This will still require a controller, meter out control with individual valves for each port and testing to obtain acceptable results.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[argusengineering]

Did you considered using a Rodless Cylinder With Magnetic Cushioning. It has a magnetic piston & adjustable cushioning.
Search for it, it might work well for your application.

Tudor Agapescu

http://www.argusengineering.net

 

[waross]

What is your application? It is likely that someone has already solved your problem.

Bill
--------------------
"Why not the best?"
Jimmy Carter