Cylinder position
Cylinder position
(OP)
I am trying to get ideas on how to sense when a equal acting hydraulic cylinder bottoms out on extend and retract. Do you have any ideas? I wanted to do this without limit switches.
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RE: Cylinder position
Ted
RE: Cylinder position
The MDT rod is mounted inside the cylinder.
RE: Cylinder position
RE: Cylinder position
Lets do this again.
Why? The answer makes a big differents the answers.
1. are there physical limitations? My thoughts.
2. is fun4sparkie too cheap for limit switches. In this case a MDT rod will not do. Neither will a controller to differentiate the pressure.
3. Are there safety hazzards where the one can't have electricity in the operating enveironment?
This should have been provided by fun4sparkie to keep this from being a guessing game.
RE: Cylinder position
To try and answer all questions, we have a special cylinder already ordered, we can not have a MDT rod put in at this point (we asked, they said not on this cylinder because of the lugs), we are not cheap, we don't have the alot of space to use limit switches, possibly absolutely no space on one side. Our cylinder not only moves in a linear path, but it is able to twist up to 3 degrees at anytime during its stroke. We want the machine to stop/machine operator to know when the cylinder has bottomed out on either ext/ret. positions because we could overturn at that point. I was just trying to come up with something hydraulic to control this, but if it isn't possible, then I will work something else out.
Thanks!
fun4sparkie
RE: Cylinder position
http://www.turck-usa.com/assets/B1005_F07-F08.pdf
David Baird
Sr Controls Designer
EET degree.
Journeyman Electrician.
RE: Cylinder position
http://www.encoder.com/modellce.html
Peak hydraulic pressure could not differentiate bottoming or stalled load. The same would be true with a flow indicator.
Ted
RE: Cylinder position
http:
For this to be feasible though
1) The working pressure must be lower than relief pressure so that the switches are not tripped at mid stroke.
2) In a similar manner there must not be high dynamic loads that would hit relief pressure.
3) This would not work for static state, as the pressure will probably decay enough for the switch to reopen.
4) This would not tell you when you are at 98% stroke.
5) ...others things I couldn't think of at the moment...
ISZ
RE: Cylinder position
Ed Danzer
www.danzcoinc.com
www.dehyds.com
RE: Cylinder position
RE: Cylinder position
RE: Cylinder position
Thank you all for your help!
RE: Cylinder position
This would work well with a cylinder that has Piston Ring Seals but may not be workable with Resilient Seals. Your cylinder manufacturer could advise.
These type ports are sometime installed as Air Bleed Ports in critical cylinder applications and are an option on most cylinder manufacturers price list.
Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING
RE: Cylinder position
If bottoming out the cylinder will cause cylinder failure you need a different cylinder vendor.
Ed Danzer
www.danzcoinc.com
www.dehyds.com
RE: Cylinder position
In driving some cars with power steering the relief valve does a lot of squealing at lock (maximun travel). Most people who want their cars to last will immediately stop forcing the steering wheel at that point.
Purchase the loudest relief valve you can.
RE: Cylinder position
but if there are other reasons, I'd go with limit switch externally, prox switch internally, or Temposonics installed in parallel to the motion somewhere outside of the cylinder (if you are looking for indication, not trying for closed loop control, a bit of slack motion won't matter)
kcj
RE: Cylinder position
Ted
RE: Cylinder position
RE: Cylinder position
I would use a pressure switch set near the supply pressure on the cylinder extend/retract lines. When the light is off (pressure low/switch open) the cylinder is moving, when light is on (pressure high/switch closed) the cylinder is at the end of its travel. Note that pressure low is relative and is < system pressure.
My actual system is a little more sophisticated in that I have a separate switch for each line, and I use a double pole pressure switch wired to a red light for transit and a green light for complete. In addition a pressure gauge may be observed by the operator who looks for a dip.
RE: Cylinder position
If stalling mid-stroke is not possible, then a pressure switch will work for you.
Ted
RE: Cylinder position
My particular application is 3000 psi with a 28" travel and is used to crimp and shear oilwell pipelines.
Watching for the pressure dip on a gauge is how the operators determine closure now. The system is visually inspected (exercised) for correct operation before operations begin and the pressure drops are noted and signed on a chart recorder. This provides a reasonable assumption that the system will work in the vent of an emergency.
If absolute certainty is required that a piece of iron must be at a particular position, I agree with previous posters that a position sensing sensor (micro-switch, LVDT, etc) be used.