Sensor for distance measurement

Dear freinds

I am called for a new project which you can see a schema of it in below.
I have two pichrolls forcing a cold rolling iron plate in to a well and grab it out from the other side. It can be called a big looper. Mechanics asked me to find a way to control the level of the plate in the depth of the well. My first solution was the encoder of the both motors I told them that I will count and measure the amount of plate inside and calculate the level of the loop. But they told me it is not possible because the shape of the loop changes time to time and the plate slips in the pinch rolls because of different reasons. I do not want and can not place a sensor down in depth of the well. so I am searching for a sensor capable of measuring distances up to 50m without reflector above the well. I can not find any.

will any of the kind professional give me a clue ?

That's a tough one...50m is a long way.

I found this: http://www.acuityresearch.com/products/ar4000/index.shtml?refer=google-laser_distance

However it's only good for 54 ft. I've never worked on this type of application but have seen them. The shape of the loop changes dramatically, and frequently, so using an ultrasonic sensor or laser device might not yeild very good results.

My advice is to go back to the two encoder idea, but place them on a pinch roller traction device that would be driven by the plate as it entered and exited the well. In this situation (steel plate), the traction drive roller would be "tired" with a hardened traction surface like what Surfalloy would apply.

try keyence's optic sensors. they can reach pretty long distances.

I have not used this eye but I have had very good results with Sick eyes on other applications.

Bob O

http://www.sick.de/de/products/categories/industrial/distancesensors/en.html

Guys,

The shape of the loop is not constant. The material is always moving and from time to time the loop will close above the bottom obstructing the view to the bottom of the loop. If Prince wants to measure the length of the material in the well, looking down at the bottom of the loop from the top of the well dosnt seem like a good answer, as he wont always be able to see it....

Thanks for all the answers you did a great Help

The sick suggestion is very good. Mike is correct I must contact and talk with our mechanics regarding the matter. One of em have seen such looper in an other site. But I still don't want to lose the chance for a sensor above. The company electrical staff told me that I myself must go down the well abd take care of the installation if I want to put something down.

I will let you know as soon as they ansewered.

Elevmike is correct here. It is typical in 'pit-loop' type systems, (ie, metal slitters) to try to look down at the bottom of the loop from the top with some kind of sensor; Ultrasonics and Lasers both work very well, BUT there will be a problem as the loop 'sways' back and forth. Eventually, it will develop a sway just so that the signal is not reflected back up, which causes havoc with the control system.

If you can make the loop wide enough to always have a solid target at the bottom, you are fine, but I doubt your pit is that wide (especially with Sonics, as the beam angle gets pretty large at the distances you are talking about).

Looking UP is never a good idea, as invariably, you will get trash on the sensor in the first 3 minutes of use.

The most reliable method (and pretty inexpensive), if you don't need to vary the loop position, and can control the inflow/outflow speeds, is just to put two optical sensors bracketing the desired bottom position of the loop, with a gap of say, 0.5 to 1 meter.

If neither sensor is blocked, you must decrease outflow speed a bit (or increase inflow). If only the top sensor is blocked, set both approximately the same. If both become blocked, increase outflow speed a bit (or decrease inflow). Simple switch logic, no PID, no tuning, and very reliable.

Multiple sensors can be used if you need to vary the position, just select an appropriate pair for top/bottom.

Oh yea....
Silly me...
Just my suggestion:
place a sensor at the maximum dept the sheet can be lowered to, then place another at the minimum dept, for the plate must not rise above that limit. Perhaps this way could help in regulating the speed of both motors. But I would still place one more sensor at the top, just to detect for "overlapping" (if you get what I mean).

regards
Sherine T.

Prince,

We have many applications like this, I too work in steel plant. The sway on the strip is a problem, and if it is reflective, that too can cause a problem. Is the pit being used as a "buffer" for speed control between two parts of the process?? The idea of using encoders will not work because of the slip in the pinch rolls. We have used lasers, but are hard to set up, and are sensitive to the sway i n the strip. Can you get to the sides of the pit or are you able to lower a sensor down into the pit?? I know we have used a sensor called SCAN-O-LINE for years here. It looks across the pit, looking length wise at the strip. It's basically a light source and photoresistor setup.

Try HERE : http://www.harris-instrument.com/
or
HERE: http://www.americansensors.com, simular pricipal, but it is based on deteting the hot to cold transition.

Hope this helps

Andrew

Prince and Andrew Evenson They can include details of the application.
Either perhaps similar to the process to define the thickness of the
steel. I have to paper the subject and uses to encoder and strain-gauges.

Wild idea:

Can you measure a current difference on the takeup motor?

20 meters of steel requires xx Amps to lift.
40 meters of steel requires the 20 Amps plus the other 20 meters in Amps.

I would do an amprobe test. If you see a variable then.
Unless the uphauling motor is powerful enough to ignore the difference between 1/4 plate, 1/2 plate; or 4' wide, and 8' wide.

Maybe check the motor drive output.

Make since``?


Rod (The CNC dude)

Could you add a dancer, that would control the depth. This sounds like a common application that uses a dancer.

It may be off the mark, but could you fit a rope across the pit .Have one end fixed and the other end on a drum. when the plate enters the well the weight of the plate pulls the rope offthe drum.The rope could pass through a pulley that can be counted for distance.

rsdoran said:

Could you add a dancer, that would control the depth. This sounds like a common application that uses a dancer.

Click to expand...

Well, yes and no. It is a dancer-type application, but you are talking a large dancer.

Typically in metal-processing, you just use a big-ol'-hole-in-da-ground after the slitter, and let material feed into it. Pit depths range from a simple 3 or 4 foot sway-loop, all the way to over 100 feet. It depends on the control system, material, and plant elevation above sea-level (yah, was at one plant on the coast, they went a bit too deep. That got expensive fast)

While a dancer COULD be used, it could potentially be very very large, and expensive, and also add tensioning to the strip, which is typically not desired. Precision metal slitter lines like to have essentially no external tension on the slitter infeed and exit sides, so entry and exit loops are common.

The exit loop is usually fairly large, and acts as an accmulator before heading off to the winder sections.

Not always the case, some slitters are tight in and tight out, but it is very easy to run into huge problems with tight/tight, as if you drag the material through the slit knives, you destroy them. Ditto if you reverse (pull material backwards, or try to drive it backwards) through the slitter. One chip on a knife, and you are looking at lots and lots of bucks.

The other reason that a dancer doesn't usually apply on an exit loop, is the material may be slit into multiple strips, and they aren't always exactly the same length (depth). Often, this is a manual 'slack takeup' / 'slack payout' function for each winder, but it's simplest to just pick two points for average depth to control the loop position.

We have had some good results using a SICK DMT laser masuring device.
We are tracking some ladle carts from 10' to 100'away with good results.It can read +- 10mm at distances up to 155 meters. We have placed the laser about 20' away from the starting position of the Ladle carts, to keep them from getting dammaged. Then set the 4to20ma signal to work in the working range.Good luck
Begolfin