Sensor for distance measurement

[john paley]

This will sound ourageous, but here goes. How about a spring loaded table below the loop that springs against the loop. The spring should just barely overcome the weight of the table. As the loop rises and falls, so the table does. Just read the position of the table and hence the loop. This could be done with a linear pot, yo yo pot, or distance sensor, as the surface of the table will be consistent. The table could have a teflon top, or even a convex shaped top or something to prevent scratches to the loop. It's kind of a poor man's dancer.

 

[kirso]

Forgive my ignorance but what is a "dancer" ?

 

[Mickey]

Kirso,
Google took me here


http://www.google.com/search?hl=en&lr=&q=type+2+dancer+position+regulator&btnG=Search

 

[Eric Nelson]

Forgive my ignorance but what is a "dancer" ?

A dancer could be what is depicted in THIS post, but I think in this context it would be something more like what I circled in this picture:

[attachment]

beerchug

-Eric

 

[elevmike]

Eric,

If I had to choose...it would be the second from the left....

 

[jdbrandt]

dancer... slitter

I did this application in aluminum, for a pit slitter, with a
pit about 50 feet deep.

There were 26 one-inch wide strips feeding into the pit.

The strips came back up, and fed under an air bladder
tension device.

What we did was to pull one of the 26 strips tighter than the
rest, up to nearly level with the feed rolls.

THEN we put a dancer on the one tight strip, and modulated
the pressure in the air bladder nip to maintain rewind
tension.

Now, if this is a full width sheet, the way Reliance did it
for that (back in the day) was with 5 sensors.
HIGH-HIGH (increase unwind speed)
HIGH
MID
LOW
LOW-LOW (decrease unwind speed)

I know you don't want to go down in the pit, but this is
the way to do this.

And, you might want to cross-angle the sensors, and use
polarized sensors, in case the metal is reflective.

 

[Prince]

Hello everybody

Thanks for the ideas. Here I am trying to talk more about the real application.

I have used sensors for dancers and loopers for rolling mills but this application is much more. This system is used to accomulate the plate it is used for a pipe line and gives the system ability to continue the job While the coils are being changed.
when the coil is reaching the end the first pinch roll moves faster and fill the accomulator(well). then when the coil finishes and the operators are changing the coil. the end of the plate is clamped and stopped waiting to be welded to next coil while the system is still working with the plate been accomulated in the well.

hope this would be helpful. and thanks again about your comments

 

[Eric Nelson]

Hooray, more info...

I still like your original idea. I don't see why you can't accurately measure how much loop you have based on linear travel - linear travel out. You said that the material can slip in the pinch rollers, so instead use external encoders with measuring wheels, friction driven off the material.

Since this is strictly an accumulator, you're not really trying to maintain a constant loop level. The loop will only drop down deep during splicing.

I'd still have a distance sensor looking down. Use it to directly control the loop when it's near the top. At some preset distance, zero out two encoders and use distance in - distance out to keep track of the loop the rest of the way down. When the loop returns to the top, let the distance sensor take over again.

beerchug

-Eric

 

[elevmike]

Ahh. Haa!

Erics, post goes back to my orgional suggestion in post 2, but a little more clear..

The encoders would be driven by an independent "idler" traction wheel. (not connected to the slipping drive rollers). If done properly and with a hardened traction surface on the friction roller, there wont be any slippage on the encoder drive mechenisem. This would give you the exact amount of material in the accumulator pit.

 

[john paley]

Oh, is an accumulator. Still, the looping principle is the same--until it's time to empty, or fill, the accumulator. When you empty it, you have to make sure it's never really empty--just almost.

The encoders would be driven by an independent "idler" traction wheel. (not connected to the slipping drive rollers). If done properly and with a hardened traction surface on the friction roller, there wont be any slippage on the encoder drive mechenisem. This would give you the exact amount of material in the accumulator pit.

But, you know, without a sensor of some type, you're never really sure how much material you,ve got. Especially over time. Try it out. I have. I put counters with encoders on the unwind and rewind of the same machine and reset on the same knife cut pulse--they never, never agreed. True story. The only explanation is that the material was changed in some way in between.

Uh oh! I posted this before I read Eric's post, sheesh. The combination of the counter sensor sounds neat. The sensor could periodically re-start the counters to keep them more accurate.

 

[MarkTTU]

Overflow Hopper

Along the same lines...

I need a way to measure how much seed cotton is in an overflow hopper. The overflow bin is a metal box about that can be up to 30' high depending on the particular cotton gin.

Here's a link to a little more info on overflow hoppers:
http://www.lummus.com/tech_conveyor_dist.pdf

I'm concerned about using a laser system because of dust accumulation. Cotton gins are incredibly dusty places, even NEMA 4X doesn't keep all the dust out of our enclosures.

In the past several (6-10) photo switches were put in the hopper to give a rough idea of fill level, but now I really need to use the hopper level as an analog PV.

 

[TRACY H]

Ok

Mark we use these and have had good luck with them. They may not
detect as for as you nned though? Looks like 20 feet max
http://www.am.pepperl-fuchs.com/pdf/fa/documents/sc04-290.pdf

:site:

 

[elevmike]

What about an ultra-sonic level sensor?

LOL, I didnt notice Tracy's post.

 

[Rich1955]

I have one ?, does the material have resistance, if so can it be measured over distance.

 

[Mtn_Bkng_Dave]

Now, if this is a full width sheet, the way Reliance did it
for that (back in the day) was with 5 sensors.
HIGH-HIGH (increase unwind speed)
HIGH
MID
LOW
LOW-LOW (decrease unwind speed)

I used this method on a coil shear that cut roll stock into plate a few months back and it worked great.

It was a little different in the fact that the infeed was continuous and the outfeed indexed thru the sheer. It was feeding at about 300fpm with a 6ft pit.

I would highly recommend this method as opposed to laser (reflectivity variances) or ultrasonic (noise interference).

Dave