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Conveyer belt "wander" auto-correction?

Discussion in 'Electronic Design' started by DaveC, Apr 25, 2007.

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  1. jasen

    jasen Guest

    seems kind of counter intuitive doesn't it :) but that's how I recall it
    being done.
    sure it is! apply some packing tape to the centre of both rollers and see
    how it goes, if good have a permanent fix done.

    Bye.
    Jasen
     
  2. MooseFET

    MooseFET Guest

    Others have suggested the crowned roller.

    Take a look at how the web is kept centered in the presses. The same
    methods should work for the belt. It involves adding an extra roller
    or two to the path so that

    You can also use a split roller to do the job. This means that you
    have to add torque between the sections of the roller to push one part
    of the belt forwards with respect to the other. This can be made to
    work on a mechanically "automatic" manner much like the crowned
    roller.
     
  3. Palindrome

    Palindrome Guest

    Think of two independent belts, one each side of the centre line. They
    would both tend to move away from the centre and run off the edge of the
    rollers.

    Now tie the two belts together. As one tries to run off, it pulls the
    other towards the centre. Which creates a restorative force, as that
    belt's tension increases due to the increased running length.
    The self-centreing mechanism does rely on the tension in one section of
    the width of the belt being able to change wrt the other. If the tension
    across the belt is always uniform (belt is very stiff laterally) then no
    corrective force is created. Similarly, if the belt is not under
    tension, no corrective force is created. Also, if the running length
    does not increase (eg a mid roller, not an end roller) then no
    corrective force is generated.
     
  4. Rich Grise

    Rich Grise Guest

    The first hit here gives a good explanation, if a little wordy:
    http://www.google.com/search?q=crowned+rollers

    Cheers!
    Rich
     
  5. Lionel

    Lionel Guest

    Two solutions:

    * A spring-arm on either side of the belt as it approaches the roller,
    with a sleeve on each arm to prevent friction on the belt.

    * Profile the rollers.
     
  6. Lionel

    Lionel Guest

    IIRC, it depends on the belt & roller material, also on whether the
    roller is powered, or an idler.
     
  7. Lionel

    Lionel Guest

    Again, IIRC, it's a convex profile for elastic belts (eg; leather,
    neoprene), & concave for other materials (eg; chain,
    fibre-reinforced).
     

  8. Have a roller tube made that is concave in shape. That tube goes at
    one end, and the adjustment end is the other. Then, the taughtness of
    the belt is what keeps it in the center of the "fall zone" of the
    concave roller.
     

  9. Or, just the opposite by placing a "dip" in the center, the belts edges
    are kept within the ends of the roller.

    Some cases concave works, and some cases convex works. That roller
    goes at one end, and the adjusting roller goes at the other. It may or
    may not already have an arced (convex) face. The overall taughtness of
    the belt is also a factor.
     
  10. It is an arc and it is less than a couple degrees across the entire
    face.
     
  11. Go away, troll. Your grasp of mechanical engineering is on par with
    your level of maturity in your behavior in usenet, and you have proven
    that to be nil.
     

  12. Neither is a solution.
     
  13. Palindrome

    Palindrome Guest

    There are two different mechanisms that can be at work. One is the
    "inclined plane". The other is "longitudinal displacement", caused by
    part of the belt having a longer path (ie over the larger roller
    diameter(s)).
     

  14. There is one more. The belt flexes, and then rebounds from the flexure.
    The taughtness of the belt in its center on the domed set up creates a
    line of tension down the length of the conveyor. The perpendicularity
    of the other end (the adjustment face/roller) with respect to that line
    of tension, is what keeps things centered. The less taught sides are
    where the entire "system" looks for a symmetry in the forces that would
    shove the belt end off the edge of a roller.

    The goods being placed on the belt also become a factor.

    So, the tension is really one of the most important factors for making
    the domed roller have enough "affect" to exert continuous control.
     
  15. MooseFET

    MooseFET Guest

    You could put small rollers on the arms that do this. You really
    don't want to add a drag to the one side. The added drag will work
    against the effect of the arm. This method requires that the belt in
    question be somewhat springy. I don't think the OP stated how springy
    it is.
     
  16. DaveC

    DaveC Guest

    Have a roller tube made that is concave in shape. That tube goes at
    Great explanation and suggestion. Thanks.

    Which brings up a question: does a concave or convex roller work best at the
    drive (no adjustment) or idler (adjustment) end? Or would it matter where
    either is placed?

    Thanks,
     
  17. DaveC

    DaveC Guest

    Others have suggested the crowned roller.
    OP here...

    Crowned looks like the best option. Splitting the roller requires additional
    support and bearings. We regularly have rollers reground by a specialty
    service, and I will ask them about doing this to the (rubber) drive and idler
    rollers. (Would having both rollers crowned be better? Or is one sufficient?)

    Second, as someone suggested here, will consider the inclined rollers added
    in the belt's path at the extreme ends of the belt's width to encourage
    centering.

    FYI, it's a sheet-fed operation, not continuous web printing (and,
    specifically, this machine is a sheet-fed coater). Light weight product on
    the belt (less than a few pounds over the entire length of the belt at low
    speed). Belt is mesh carbon fiber. Seems somewhat springy, overall, but the
    material, per se, isn't flexible.

    Thanks to all for your suggestions.
     
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