Seeing Clear Poly

[Zetor]

Hello Everyone,

I am working on a machine that bags a product. The process is to blow the bag up, extend some fingers to hold the bag, and then push the product into it. My problem is I have to know if a bag is present on the fingers and this is tough because the poly is CLEAR. I have tried several different photo-eyes and even a banner ultrasound unit. So far the best I have come up with is a cutler hammer 6" perfect prox. Right now I am missing about one in 35-50 bags. The line manager is not too happy with this. He wants one in a couple thousand missed. (LOL) Does anyone have any experience in sensing clear poly? Any thoughts would be greatly appreciated.

Thanks

Jeff

 

[rsdoran]

Sick makes a variety of Clear Material Reflex sensors:
http://www.sickusa.com/live/master/...74,14875,14876,14877,14878,14879,14880&P=3777

May want to look at contrast sensors too.

 

[dale1627]

Are you trying to use a through beam or reflective? With poly I've had good luck with using a polarized reflective eye and a reflector.

 

[jrwb4gbm]

Could you use a retractable arm with a sensitive mechanical limit switch mounted on it? Maybe you could build a pressure plate on the holding fingers that would require the bag to depress it. Sometimes mechanical devices work where electrical sensing fails.

Just some ideas ,good luck.

 

[akreel]

He wants one in a couple thousand missed. (LOL)

Ask him if he's willing to pay for 99.9% accuracy. That might change his tune.

I've never tried sensing clear plastic, but I have some thoughts for you to consider:

1) You might be able to see through the plastic, but does it pass infrared, radar, and ultrasonic? I like the ultrasonic idea that was suggested earlier.

2) Is the plastic diffuse? That might disrupt an opposed beam sensor enough to trigger it. Be careful: retroflective sensors might bounce back off the plastic, which is why Dale suggested a polarized beam. Can you shoot through at an angle to increase the effect of the plastic?

AK

 

[msinclair]

You can try something like the AB ClearSight 9000.

 

[dale1627]

Our poly applications is for overhead projection sheets. The poly is crystal clear. I use a polarized reflective eye from automation direct and along with the reflector, install them at an angle to the poly sheet as it runs through a slitter/perforator. I use the eye for batching sheets and have not had any problems at all with it. We have done checks on our batches by comparing the weights to our batch counts and come up dead on everytime. So to me that proves reliability. I am using an Automation Direct CXP-AN-1A Polarized Reflective eye that costs $38.00

 

[Blimey]

Seeing clear Poly:

A polarized retro reflective eye works well, probably the visible light spectrum. If the sensor you pick has a fixed range of operation, place the sensor towards the far limit. Example: If your sensor has a working range of 2" - 4" place the sensor towards the 4" distance if possible. This can make the sensor more sensitive to the presence of clear poly.

 

[David_Emmerich]

Hi Group...Banner also makes a "Clear Plastic Detector" that I have used with very good results on PET bottles...I have also used a UV source that makes the target material 'Glow' purple, and then sensed it with a selenium 'photo-cell' like you may have had in the flame detector in older boiler controls... this was the most accurate for PET 'cause PET is almost opaque to UV,ie it absorbs almot 90% of the UV, but is transparent to visible and IR light...I have one of those little UV light sources at home...but here I am in Fl...I think it was made by Sick, and it included both a small,shortwave UV lamp and a 'floresence' detector...runs on 24VDC...

David

 

[Terry Woods]

Use a bifurcated, analog Photo-eye. I'm pretty sure Banner has one.

The idea is to monitor the analog signal difference between bag not-present and bag present.

There WILL be a decided difference.

This will give you your "...one in a couple thousand..." if not one in several thousand.

You should be able to create a "window" that is highly effective.

If you have an HMI on the system you can provide a sensitivity adjustment to the operators.

If ambient conditions (humidity, temperature, etc...) change then the operators can make the necessary change to the "window".

As time goes on and you hear about particular trends in the performance of the photo-eye you can build-in certain automatic adjustments... maybe...

 

[Zetor]

I would like to thank everyone for the quick responses, and suggestions. I have already ordered the Automation Direct CXP-AN-1A this morning. I am also waiting on a response from our Banner supplier in FT. Smith on the bifurcated, analog Photo-eye from Banner. I believe at this point I could order one of everything just to try and see what works best on this application. We have also discussed going mechanical, but that could possible run into adjustment and wear problems.

Thanks again

Jeff

 

[Pierre]

OK, here we go!

I have done this not long ago.

I can detect glass, poly. or lexan with this real cheap photoeye...

And the winner is : SICK model # WL2000-B5300S01

With the sensitivity adjustment it works great.

Get the 3M polarized tape (yellow)

 

[eastkodakguy]

forget the others

get a tritronics photoeye, I have done testing using pretty much all of the above and none compare to the tritronics eye

 

[dandrade]

Brazilian solution

Poly clear!??! Refers to the check bottom of bag !!!?

The strong option and recicled: Sensor of diaphragm, capable of comutation when negative->positive pressure. When to bag full all volume will have a strike of air, and the diaphragm is shoved.

It can do manually: 01 pipe/tube, with top/cap, film of latex (or plastic) and a simple circuit of ray of light (LED + transistor) positioned for when to "sense film" is shoved.(interrupt ray)

The workers of manufactures of bags, did and employ up to date with years.When it tore film, possessed change cap

If the company have environmental certification is high advisable

(Sorry guys, it one solution)

 

[M. Eisenhauer]

the most common solution

Bread baggers in bakeries have this same problem.

the most common is a plastic wand on the end of a switch that will
make contact when the bag is filled with air. If the bag is gone the switch wont make and the machine will park. a safety will also be needed so the machine will turn off when fixing the problem or if the wand is hit the machine wont start right away thinking it found a bag.