# Conveyer belt "wander" auto-correction?

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

1. ### jasenGuest

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. ### MooseFETGuest

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. ### PalindromeGuest

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 GriseGuest

The first hit here gives a good explanation, if a little wordy:

Cheers!
Rich

5. ### LionelGuest

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. ### LionelGuest

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

7. ### LionelGuest

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

8. ### [email protected]Guest

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. ### [email protected]Guest

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. ### [email protected]Guest

It is an arc and it is less than a couple degrees across the entire
face.

11. ### [email protected]Guest

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. ### [email protected]Guest

Neither is a solution.

13. ### PalindromeGuest

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. ### [email protected]Guest

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. ### MooseFETGuest

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. ### DaveCGuest

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. ### DaveCGuest

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.