Conveyer belt "wander" auto-correction?

[jasen]

Thanks, Sue.

This is a *larger* diameter at the center?

seems kind of counter intuitive doesn't it but that's how I recall it
being done.

Where might I find more information re. how much taper to apply? This is not
a situation for trial-and-error (c;

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

 

[MooseFET]

A coating machine in a print shop utilizes a 1-meter-wide, 10-foot-long
conveyer. The belt for this part of the machine is 1cm (approx) mesh of what
appears to be carbon fiber. Drive is via 200mm rollers at either end of the
conveyer section.

The belt, as do all such mechanisms, doesn't want to stay centered and
constantly wanders to one edge or the other. The operator must observe the
location of the belt and manually adjust one of the roller's parallel-ism(?)
via a knob-and-screw for this purpose. Of course, this isn't a perfect
solution and the belt has many times wandered too far and frayed the edges
which necessitates replacement far more frequently than should be required.

How best to automate this process? I've seen high-speed belt sanders (1-meter
width) that have a solenoid that "jogs" one of the rollers when an optical
sensor is tripped which "jumps" the belt sideways, but this belt is traveling
at high speed and is much shorter in length than the conveyer belt, so the
conveyer will not benefit from the same solution, I think.

Motor drive of the adjustment screw with optical sensors at the edges of the
belt's limit? I see a microcontroller project in my future. Seems to call for
some fuzzy logic or such, so that the controller can "learn" where the center
is and apply just enough adjustment to limit its travel to the extremes...
(more easily said than done, by a factor of a few orders of magnitude!).

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.

 

[Palindrome]

seems kind of counter intuitive doesn't it but that's how I recall it
being done.

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.

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.

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.

 

[Rich Grise]

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.

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

Cheers!
Rich

 

[Lionel]

A coating machine in a print shop utilizes a 1-meter-wide, 10-foot-long
conveyer. The belt for this part of the machine is 1cm (approx) mesh of what
appears to be carbon fiber. Drive is via 200mm rollers at either end of the
conveyer section.

The belt, as do all such mechanisms, doesn't want to stay centered and
constantly wanders to one edge or the other. The operator must observe the
location of the belt and manually adjust one of the roller's parallel-ism(?)
via a knob-and-screw for this purpose. Of course, this isn't a perfect
solution and the belt has many times wandered too far and frayed the edges
which necessitates replacement far more frequently than should be required.

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.

 

[Lionel]

Thanks, Sue.

This is a *larger* diameter at the center?

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

 

[Lionel]

seems kind of counter intuitive doesn't it but that's how I recall it
being done.

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

 

[SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalax]

How best to automate this process?

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.

 

[SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalax]

Machine the rollers to put a very small taper into the centre. Slightly
increase the tension at the centre line of the belt. The belt will then
auto align itself onto the centre line and self-correct any tendency to
wander off.

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.

 

[SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalax]

Where might I find more information re. how much taper to apply? This is not
a situation for trial-and-error (c;
--

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

 

[SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalax]

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

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.

 

[SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalax]

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.

Neither is a solution.

 

[Palindrome]

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.

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)).

 

[SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalax]

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)).

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.

 

[MooseFET]

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.

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.

 

[DaveC]

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.

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,

 

[DaveC]

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.

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.