I've got a machine that must keep constant tension on a stretchy roving.
I've got a slip-clutch on the takeup spool right now, but when it slips (sliding friction being less that starting friction) it "unwinds" some of the tension in the roving before it stops slipping... so it doesn't keep the material in the right state for one of the intermediate operations.
Are there any over-torque protection clutches that maintain a constant torque from their break-free settings? I'd really rather see this thing slipping constantly than starting and stopping.
"Lloyd E. Sponenburgh" fired this volley in news:Xns9D98A76EC9F46lloydspmindspringcom@216.168.3.70:
I should have added (my current byline these days) that so far, this is a completely mechanical machine. I could do this with a servo motor takeup and a tension arm, like an old computer tape deck, but I'd like to not modify it that much. The existing clutch is co-axial on the takeup spool shaft.
Can your current clutch be run with continuous slip? I.e., can it dissipate the heat? If so, can you run your take up motor faster?
BTW - constant torque does not equal constant tension on the roving. (Cause the diameter increases as the roving is taken up.) A dancer arm would give you constant tension.
Just got back from a little vacation on the Northern California coast. No internet access.
Have you given any thought to a clutch such as used for newer automobile fans? I know the one on our old MB 300SD turns pretty hard when moved by hand, but seems to be the same resistance no matter how quickly I move it by hand.
This reminds me of the "old" days of reel to reel tape recorders. They all had such a device. The microfilm industry also had the same situation to deal with. The must have been hundreds of solutions! One of the simplest was to have the tapeup shaft vertical, driven by a more or less constant speed motor and pulley speed reduction system that went fast enough to wind up the tape/film at the smallest diameter of the spool. That shaft had an aluminum plate on it. The hub of the tape/film holder slipped over that shaft. It had a similar aluminum plate, but this one had a felt material glues to its underside. When the weight of the product was small, the torque was low. As the weigth of the product and the diameter of it on the spool increased, there was more downward pressure on the felt/alimunum interface and more torque was transmitted to the hub to pull up the product.
Other than the one described above, these takeup systems required a fair amount of maintenance and parts. Except, of course, for the electronic solutions that you alluded to.
Pete Stanaitis
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Lloyd E. Sp> I've got a machine that must keep constant tension on a stretchy roving. >
Go back even further, there are any number of mechanisms in the textile industries to keep a constant tension on a fiber while winding either on or off a bobbin, ditto on vari-speed devices. Would suggest a peek at an old mill machinery book might be in order. Archive.org or Gutenberg would be my first stops. Also the various umpty-zillion mechanism drawing books they had, mostly kinks from American Machinist and the like from the turn of the last century. Don't reinvent the wheel. Or take a look at what the humble sewing machine does with thread tension.
A powered one would probably weigh less. I used one once, analog 24V signal, relatively high current in. I'd done the dancer arm-pot thing, but this had to account for lumps, sticky stuff, etc. I ran the web over a roller mounted on load cells which gave tension directly. I think I used a 120 deg. contact. Worked a treat. When a lump of gels hit the takeup, the lessening in tension would be detected and the slip clutch would tighten up until it passed the lump.
Wow. I went back and looked at the one I used 20 yrs ago or so, it was a Magpowr C-100, about 154 lb. That was a relatively small part of the weight of the whole rig. Mine ran pretty slow, 2000 rpm max DC motor through ~3400:1 double reduction. So yeah, I didn't need water cooling.
--Ya know this sounds like a perfect opportunity to retask the film feed apparatus from an old motion picture camera. They're a dime a dozen at swap meets, too.
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