how to slow down pnuematic piston near end?
how to slow down pnuematic piston near end?
(OP)
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.
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.





RE: how to slow down pnuematic piston near end?
can you add a relief valve to the actuator to limit the pressure ?
RE: how to slow down pnuematic piston near end?
For instance, your actuator moves the piston while a position sensor tracks its movement. When the piston travels to a certain point, the sensor output signal trips a relief valve. How fast you drop the pressure determines how fast the actuator slows. You would be able to set the position relief point with a simple adjustment. That's my idea. Best of luck.
Kyle
Kyle Chandler
www.chiefengineering.net
RE: how to slow down pnuematic piston near end?
-handleman, CSWP (The new, easy test)
RE: how to slow down pnuematic piston near end?
RE: how to slow down pnuematic piston near end?
RE: how to slow down pnuematic piston near end?
REPLY 1: DIFFICULT TO ACHIEVE WITH PNEUMATICS. NEEDS TO BE ELECTRICAL ACTUATOR.
Thanks for the tip. Someone built the setup for me. Is there a drop-in replacement? Can I just remove the pneumatic cylinder with an electrical cylinder? Please advise.
REPLY 2: TRACK POSITION SENSOR OUTPUT
Mine does not have a position sensor. You seem to indicate there are such products available. I will do google search. Thanks.
REPLY 3: CYLINDER DOUBLE ACTING OR SPRING RETURN?
Yes, it is double acting. I don;t quite understand spring return, but if you are asking is there is a spring that pushes the piston back, no, it's not that kind.
Thanks.
RE: how to slow down pnuematic piston near end?
Using a choke, it is possible to get a condition where the cylinder volume changes faster than the supply can fill it. This will result in a reduction in force until the air supply can "catch up". As you might imagine, it's rather difficult to get this set up to work consistently.
Most cylinders have an option for a reed switch or other sensor to detect the piston. Using such a switch, you could cut off your supply a some point, and simply vent the "supply" side of the cylinder and just let the thing coast. You could even achieve braking if you choke the vent. You might be able to make such an arrangement work for you.
RE: how to slow down pnuematic piston near end?
They typically only come with 3-6 lb springs. I really wouldn't recommend them as you'll get better life and results from a double actuating cylinder and a 3 position valve.
Cheap and dirty you could get a one way meter-out flow control and throttle it down so it acts like a cushion on extend/retract. So you're extending faster than the exhaust can escape so you compress the air to a certain extent. I'd only try this if your extended position doesn't need to be very accurate.
James Spisich
Design Engineer, CSWP
RE: how to slow down pnuematic piston near end?
Are there any flow controls involved? Normally this will be a little gizmo threaded into the cylinder ports with an adjustment knob on it. It is also possible that it uses in-line flow controls somewhere in the hose between directional valve and cylinder, or (rarely - more common in hydraulics) it may be at the directional valve manifold itself. These restrict the speed of air flow in an adjustable manner, and normally they only restrict in one direction - which should be "out". A "meter-out" arrangement will let the air slowly out of the side of the cylinder being vented and you can adjust it.
If there aren't any flow controls ... you need them. Any pneumatics supplier (Festo, SMC, Numatics, Parker etc) can provide these fittings.
Next question is the type of solenoid valve. There are several types that do different things depending on what you want to have happen when the solenoid(s) is/are turned off. "2 position single solenoid spring return" will have the cylinder return to the home position. "3 position dual solenoid center closed" will stop it dead (although the cylinder will still drift slowly due to unavoidable leakage). "Center exhaust" will basically put the cylinder in "neutral". "Detented" will hold it in the previously-left state (but the bad thing is that if the solenoid power is cut mid-travel, the cylinder keeps going to the end stop). Watch out for possible safety-related implications.
The good thing about "center exhaust" is that it puts the cylinder in a free state when de-energized. Bad thing #1 is that if the motion is vertical, it will now come crashing down by gravity. Bad thing #2 is that even if you have meter-out flow controls, the loss of pressure from both sides will slam the cylinder because there's nothing for the flow control to restrict.
There won't be a perfect solution to this involving pneumatics. Can't be done. It might be possible to be "good enough" or "better than what you've got now", but if really good control of the motion profile is needed, you will have to use either hydraulics or air-over-oil or electric servo control.
RE: how to slow down pnuematic piston near end?
You will need fast acting valves to evacuate the forward chamber quickly and your forces will be 4x as great since you will accelerate to double the average velocity in 1/2 the time.
It looks pretty manageable to me since you are talking an average velocity of 20"/sec; that means you will achieve 80"/sec with this setup or about 7'/sec. I've seen worse.
RE: how to slow down pnuematic piston near end?
I agree with all the comments regarding the lack of fine control and the "bang bang" nature of most pneumatic devices. Throttling the exhaust side with one way needle valves is better than trying to restrict the inlet as you are controlling the action of the full pressure against the piston rather than trying to prevent this pressure build up, which will happen quicker than you think!
You might care to have a look at SMC's REC Sine Cylinder, it's supposed to give a much kinder "ramped" profile, but it was relatively expensive. We also looked at their Cushion cylinders, but after dabbling with 3-way valves and reed switches, stick-slip effects and gravity was the killer so we opted for a stepper drive.
http://ww
Good luck
Trevor Clarke. (R & D) Scientific Instruments.Somerset. UK
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RE: how to slow down pnuematic piston near end?
Offshore Engineering&Design
RE: how to slow down pnuematic piston near end?
Hope it helps.
Griffy
RE: how to slow down pnuematic piston near end?
If you do try valves, flow restrictor, etc, keep everything as close to the cylinder as possible, to minimise effected volumes.
If you do use a reed switch or similar to sense the stroke, you will have to move it along the cylinder to allow for response times.
Ring SMC and get their local rep to come and have a look!
Good luck
RE: how to slow down pnuematic piston near end?
We use sprue-picking robots on moulding machines. These travel 750mm in 0.8s. Towards the end of the stroke, the solenoid is made to cycle on/off very rapidly - I would guess approx 10Hz. (Sounds like pursing your lips and blowing to make a rude noise!) Timers allow the start position of this to be set.
When in "set-up" mode, the solenoid cycles continuously to keep things slow!
But, and here's the thing - the arm is carbon composite lightweight tube with around 200g on the end.
Cheers
Harry
www.tynevalleyplastics.co.uk
RE: how to slow down pnuematic piston near end?
Griffy
RE: how to slow down pnuematic piston near end?
Also, the spring would be external and easy check for damage or replace...
-- MechEng2005
RE: how to slow down pnuematic piston near end?
as i understand it you've got a 70psi airsupply driving an actuator that's wacking into a 1kg target trying to move it 25cm and your set-up is "walking all over the place".
is this like a brillards/snooker robot ? so you can't "nail" your set-up to the ground ??
how much work are you trying to do ? what sort of friction is under the target ??
how precise is the target's final position ?
could you use an upstream reserviour, to lower and control the airsupply pressure ?
can the actuator extend 25cm ? so you can positively place the target where you want it ??
RE: how to slow down pnuematic piston near end?
For real speed control linear motor is the way to go. SMAC, http://www
RE: how to slow down pnuematic piston near end?
-b
RE: how to slow down pnuematic piston near end?
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
RE: how to slow down pnuematic piston near end?
RE: how to slow down pnuematic piston near end?
RE: how to slow down pnuematic piston near end?
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
RE: how to slow down pnuematic piston near end?
Ed Danzer
www.danzcoinc.com
www.dehyds.com
RE: how to slow down pnuematic piston near end?
Search for it, it might work well for your application.
Tudor Agapescu
www.argusengineering.net
RE: how to slow down pnuematic piston near end?
Bill
--------------------
"Why not the best?"
Jimmy Carter