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| Author | Topic: Cutter Puller encoder problem |
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hank05 Member Posts: 4 |
posted January 28, 2005 12:24 PM
  
Extrusion of Nylon tubing (ref. .235" od) w/ encoder on product, cut maintains for a period of time then scale needs re-adjusted for no apparent reason. Line speed, cut length, puller tension, etc. do not seem to be contributors??? IP: Logged |
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louis33 Senior Member Posts: 99 |
posted January 28, 2005 12:43 PM
To be clear on the question, are you saying that your part length is changing with time? IP: Logged |
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Steve H Moderator Posts: 340 |
posted January 28, 2005 12:47 PM
quote: How are you assessing these variables? Welcome to the extrusion forum BTW Steve Hodgson ------------------ If at first you don't succeed, skydiving is not for you. IP: Logged |
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zabielski Senior Member Posts: 342 |
posted January 29, 2005 07:36 AM
What is the precision of your scale? + / - what? Could simply be that your scale is out of whack. Yes, a very common item to overlook. IP: Logged |
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hank05 Member Posts: 4 |
posted January 31, 2005 08:24 AM
Puller, line speed etc., eliminated thru experiments. Length will start to vary (will "jump" .200" long) and then return to exact (puller/cutter stated tol. is =/-.030). Encoder scale has been calculated (set according to manual). Put simply it appears the encoder is "losing it's mind" for a short period (5-8 minutes) then finding it again. Is there something else to look for or try, could static electricity be a parts of this? Thanks IP: Logged |
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Tom C Moderator Posts: 457 |
posted January 31, 2005 09:00 AM
Grounding and shielding problems are often the problem on extrusion lines where electronics go "Crazy". Of course there is always the issue of static electricity with moving plastic to deal with. The static problem often gets much worse in the winter becasue of dry air. How is the encoding supplied? If it is an ink jet, the jet could be supplying a pathway for a static charge to jump from the product to the printer. Try laying some copper gauze over the product as it runs (before and after the printer) and earth ground the gauze. Also wire the printer to an isolation transformer and then wire the printer power supply and case to the same earth ground. This is not the best solution to grounding, sheilding and static problems, but it might work as a stop gap measure. You should consult an expert to guide you through your plant's needs in this area. ------------------
Tom Cunningham
Extrusion Technical Services www.ExtrusionTechnicalServices.com [This message has been edited by Tom C (edited January 31, 2005).] IP: Logged |
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louis33 Senior Member Posts: 99 |
posted January 31, 2005 09:40 AM
Nylon is one of those materials that causes more static than most when extruding. As mentioned previously, check for that static and eliminate it! Sometimes the solution is as simple as moving the cord that runs from the encoder to the cutter away from the tube as it passes through the puller/cutter. I will assume that the encoder never stops turning (that would cause longer parts) Some people tend to tighten it down against the puller belt. If that is where it is on you set-up, try loosening the lick down screw and let it rest by it's weight alone. Static in most cases will cause long and SHORT parts. Since you only have long, that may be the problem. Another possibility is cutter wear or malfunction. What kind of cutter are you using? Clutch Brake? Wrap Spring? SCR or . . . If you let us know, we may have some more ideas for you. IP: Logged |
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Paul60 Member Posts: 2 |
posted February 08, 2005 01:34 PM
If you are running the encoder on the part, this is the best way, make sure that your electrical connections to your encoder are good, move the cable around and see if you can reproduce the longer lengths while it is operating, have the encoder scoped make sure it has a consistant output. I have often found this type of problem to be bad amphenol connectors, cracked solder joints, bad cables, vibrating encoder, bouncing encoder. But also as one had said above the cutter is often the culpret, if it is a vacume operated clutch like a Goodman cutter the clutch may need a shim removed. Good luck IP: Logged |
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hank05 Member Posts: 4 |
posted February 11, 2005 04:46 PM
To shore up some info; The Dual servo cutter unit and all associated (encoder, belts, blades etc.) are new. The encoder has a light tension spring to hold it steady on the product (a proven past practice for us). I guess I have to ask (those with more experience), if all up and downstream is "true" from the encoder shouldn't I be able to punch in a number say 10.00" and measure it (within 2 seconds) and be within the quoted tolerance (+/-.030) of the equipment (not +.200")? we've done this with both rigid and soft mtl's..?? Are we expecting to much from the unit or did we buy from the wrong unit people???? IP: Logged |
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louis33 Senior Member Posts: 99 |
posted February 11, 2005 05:12 PM
You should be able to see the length change on the very next cut. And yes, +/- 0.200 is unacceptable. Perhaps an email to discuss the manufacturer if you are uncomfortable doing it on line. eldee IP: Logged |
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