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  1. #11
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    Re: Dual OHCF Multifeeds

    the less air the better it works in general

  2. #12
    Senior Tech 250+ Posts
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    Re: Dual OHCF Multifeeds

    Quote Originally Posted by azehnali View Post
    the less air the better it works in general
    For sheet-to-sheet alignment, yeah, absolutely. Less (or none) is better.

    But for multifeeds, I think sometimes it needs a good bit of air. (But of course, sheet-to-sheet wonít be as good.)

    And thatís exactly what Iím finding. I need to do a long run test, but the air is stopping the multifeeds, but my registration is slightly worse. Not dramatically, but noticeably. I was hoping the side shift would compensate, but there is still a little more variability than when I have the air off.

    Itís just aggravating that the wimpy little feeders on the internal trays on the 570/C70 work just fine, on the exact same paper, and Iím having so much trouble with the ďhigher endĒ OHCF. haha

    Iím done for the night though. My eyes are crossing.

    Thanks for the help!

  3. #13
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    Re: Dual OHCF Multifeeds

    Just an update in case anyone is following this, or for the future...

    I'm pretty confident at this point that the culprit is the friction clutch on the Reverse roller part of the feed head... Basically, it is just too weak, and not pushing back against a multi-fed sheet enough to separate it.

    The rest of this email isn't for experienced techs, but just in case anyone isn't familiar with the basic principle of how three-roller friction feed systems work (and this is universal for all brands) here is the quick (ish) summary you didn't ask for.

    There are three rollers in the feed heads for each tray. A Nudge roller, a Feed roller and a Reverse roller. The Feed roller and Reverse roller are in contact with each other, just in front of the stack of paper, and the Nudge roller is just a couple inches further away, above the paper.

    When it is time to feed a sheet, the Nudge roller, which normally hovers OVER the paper stack not touching, is pushed by a solenoid down onto the paper stack and also rotated, causing the top sheet of the stack to be pushed forward into the nip between the Feed and Reverse roller. At this point the solenoid lifts the Nudge roller back away from the paper stack.

    Ideally, the top sheet ONLY will have been pushed into the Feed and Reverse rollers. But as we all well know, this often isn't the case. Two or more sheets may have stuck together just enough to all be pushed into the nip between the Feed and Reverse.

    The Reverse roller is actually being driven by its gears to rotate BACKWARDS against the Feed roller, not WITH it. However, there is a friction clutch which allows the Reverse roller to slip, and go WITH the Feed roller if the friction is very high. For example, if the rollers are just touching each other (like when there is no paper between them) the rubber-against-rubber is extremely high friction, so the power of the drive on the Feed roller will force the Reverse roller to roll "with" it. The friction clutch is what allows the Reverse roller to "slip" and roll with the Feed roller in this case, even though it is actually being driven to rotate against it.

    If you have a single sheet of paper pushed into the nip between the two rollers by the Nudge roller, the Feed roller above and the Reverse roller below, it will also rotate WITH the Feed roller/sheet of paper and allow the sheet to pass. The friction of Feed roller above->sheet of paper->Reverse roller below is too great, so the friction clutch allows the Reverse roller to go ahead and roll WITH the Feed roller and pass the sheet.

    However, if you have two or more sheets, when they get pushed between the Feed and Reverse rollers, the friction of the two sheets against each other is LESS than the friction the clutch requires to "slip". So instead of feeding the multi sheets through, the Reverse roller rotates against the Feed roller and basically pushes the extra sheets back. (In reality, it doesn't push them backwards, but it does HOLD them back from going forward until the next feed cycle.) If there is anything more than a single sheet between the Feed and Reverse roller, the friction clutch is supposed to be "more friction" than the friction causing the sheets to stick together, causing them to separate.

    I've frequently seen MANY sheets held back this way by a well operating Reverse roller on a particularly difficult-to-feed paper. Sometimes you can see this exposed on tray 5 (MPT) with the heavily shingled effect of the paper stack.

    These feed heads in the OHCF, the HCF, the lower trays on the 700-and-newer and 4110-and-newer are really robust, and (typically) do an excellent job at NOT multi feeding, sometimes even holding back 3, 4, 5 or 10 sheets. (Which is why I was so befuddled by the terrible performance I was getting.)

    So, to make a short story long, basically in my case, I'm pretty sure I have several feed heads (none of them are young) with friction clutches that are wearing out. Combined with a moderately difficult-to-feed paper. That is why I was having the same experience with multiple drawers, and even after replacing the entire feed head. None of them are young. The getting-older-by-the-minute friction clutches were weak enough that they basically were "giving up" and allowing the Reverse roller to slip and roll WITH the Feed roller even when there were 2 sheets between them. A stronger/newer friction clutch would have literally pushed those two sheets apart, only allowing one to go through at a time.

    It appears that the friction clutch is nearly universal across almost all of Xerox's Fuji Xerox / Fujifilm designed models... The part number is 005K06701. There is also a part numbered 005K08950, but I have seem some indication that they are interchangeable.

    I have SO MANY spare feed heads of different types from different machines, some of which were radically less-used than the ones in my OHCF, that before buying a new one, I think I'm just going to scavenge one or two. Almost all of the Fuji Xerox designed machines' feed heads use the exact same part number friction clutch, from small machines like the 7120/7220 to the B&W Phaser 5500 series to the DocuColor 250-onwards and even the Versant, 800/1000 and Iridesse... That's convenient.

    I'll report back here in a few days on the success or lack thereof.

  4. #14
    Service Manager 2,500+ Posts tsbservice's Avatar
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    Re: Dual OHCF Multifeeds

    In Konica Minolta world(same in Toshiba also) those are called torque limiters and if they fail separation(aka reverse) roller often develops flat spot which in therms lead to frequent paper jams. Honestly I almost didn't see multifeeding pages for quite a few years except the cases where paper was sitting in tray for a looong time or really bad paper but it's quite obvious from the first look in that cases.
    That said I'm not Xerox guy and if were in your shoes I also would change them together with new tyres.

    Good luck
    A tree is known by its fruit, a man by his deeds. A good deed is never lost, he who sows courtesy, reaps friendship, and he who plants kindness gathers love.

    Blessed are they who can laugh at themselves, for they shall never cease to be amused.

  5. #15
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    Re: Dual OHCF Multifeeds

    Quote Originally Posted by tsbservice View Post
    In Konica Minolta world(same in Toshiba also) those are called torque limiters and if they fail separation(aka reverse) roller often develops flat spot which in therms lead to frequent paper jams. Honestly I almost didn't see multifeeding pages for quite a few years except the cases where paper was sitting in tray for a looong time or really bad paper but it's quite obvious from the first look in that cases.
    That said I'm not Xerox guy and if were in your shoes I also would change them together with new tyres.

    Good luck
    I wonder if there is a difference after all in the way KM and Xerox drive the Reverse rollers... Maybe I opverspoke when I said pretty much all manufacturers did it the same way.

    On Xerox, if the friction clutch fails, you'd never get a flat spot, because the roller would simply free turn along with the Feed roller like a happy duck. (But also, not do its job... haha)

    I have removed the friction clutches from two of my feed heads, and they are in fact cracked along the side. Typical example of them bulging out and then failing.

    I haven't put new ones in yet. I don't have any spares of the ACTUAL part, 005K08950, though I have tons of the other friction clutch, 005K06701, which I've been told is interchangeable, but it isn't the one in the part list. I'll try it and see ASAP.

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