Web hole detection...

My area is centered around cutting splicing and winding rubber sheet stock. Our stock is wound with a web between the layers. This web material can become torn and frayed. We have photo eyes that look at the edges of the web and shut off the winders if a tear is detected, but we have nothing to detect holes. The webs are in basically three different widths: 11", 16", and 40". The web material is a light colered fabric...some kind of nylon I think. The web is a variety of colors from white to pink to dark green and stained with black from the rubber.

I've been asked to do a better job of hole detection. I have found light curtains (STI valuscan) and camera systems that will do the job. I was wondering if there are other devices out there that I haven't considered that may work in these applications. Cost is always a concern. I will have to install a device on each of about 30 winding stations, and mounting space can be a concern as well.

Any input will be appreciated.

?? Vacumm ???

Could you slide the web over a open box and pull a vacuum and monitor for the loss of vacuum?

Cognex makes a camera that is fairly inexpensive and should work well in that application.

Okie,

I can point you to a light curtain that is about 6 ft. wide and cost about $600.00. If necessary you could stagger two or more to bridge a wider sheet. The speed of the sheet, and the size of the holes might also be issues. For better resolution the light curtain can run diagnoally across the sheet.

you can also check out Bannerengineering.com for a-gage mini arrays

How about these guys...

Try http://www.harris-instrument.com/. We use the Scan-A-Line products to detect weld punch marks. Might be too costly, but take a look..

Andrew

I am fond of the vision systems. In many cases arent that expensive and can be used for multiple purposes...ie in this case the holes, web breaks and any other factors involved like registration, color quality,....list goes on.

Just make sure you put enough money in the budget for proper lighting. Without good lighting (proper angle, no shadows, enough to eliminate problems from background light, etc) a vision system is a pain.

dash said:

Just make sure you put enough money in the budget for proper lighting. Without good lighting (proper angle, no shadows, enough to eliminate problems from background light, etc) a vision system is a pain.

Click to expand...

dash is right on with that. Areas that large (11" to 40") will require quite an investment in proper lighting. And lighting is everything in a vision app.

Partial Retraction.

History; Okie sent me a PM and I shot him back some links for light curtain. However...after thinking about it, it dawned on me that the light curtain scans in such a manner to make it more effective in looking for the presents of an obstacle, not the lack of one.

If you need to detect very small holes in your webbing, what you may need is a non-scanning light curtain whereas every sensor will detect a signal from all transmitters, and all transmitters and sensors will be always on. Light curtains work by switching on transmitter A, and then reading Sensor A, then doing the same with B, and so on. One set at a time. This allow them to detect objects, by creating "pseudo-beams" between specific sensor and transmitters, but limits the ability for finding small holes.

What you really need is to detect any scattered light coming from and led in the transmitter. Call the manufactures and ask for tech support or engineering. Explain the application and ask them if there is some simple way to disable the scan so that all transmitters and sensors are on all the time, so that any sensor can detect a signal from any transmitter. This would provide full coverage and detect very small holes. Given the fact that you have 30 applications, they may accommodate you. This may be as simple as adding a jumper on the controller..

Then again, what's the tolerance? what size hole is going to be a reject? If a 1/2" dia hole is within tolerance, then you should get by with the standard light curtains.

Andrew Evenson said:

Try http://www.harris-instrument.com/. We use the Scan-A-Line products to detect weld punch marks. Might be too costly, but take a look..

Andrew

Click to expand...

After looking at the link provided by Andrew, I would think that this is the way to go. They have specifications about what size holes they will detect & it is a product designed around your specific requirements. I checked with some other engineers I work with & they are familiar with this product line. It seems to be well known for this type of defect detection.

Darren

In different applications in my area we have Harris Instruments (North American Controls) Scan-a-line for measuring stock widths. We have DVT camera systems for the same purpose in other applications. We also have a Keyence camera system that is currently not in use. The scan-a-line is overkill for this web hole detection, and i think the DVT products are too. I am currently deciding between an STI valuscan, and a Banner PresencePLUS P4 vision system. The vacuum box idea is very interesting, but wouldn't work here due to the porosity of our webs. A third option is to simply add more diffuse photoeyes. I have had to deal with lighting and camera systems and understand that "lighting is everything" with vision. I want something that I can set up and forget about. I will need about 14 of the wide sensors (40" wide web) and about 14 of the narrow ones (11-16" width). And due to space limitations, they are probably going to be very different systems. I will probably use a light curtion or multiple photoeyes in the narrow application and possibly vision for the wide one.

Thanks for all your feedback. I get more unbiased information here than anywhere else I look. And fast too!

Paul C.