Conveyer belt "wander" auto-correction?

[DaveC]

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!).

Other suggestions?

Thanks,

 

[Palindrome]

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!).

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.

 

[Salmon Egg]

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!).

Other suggestions?

Thanks,

Offhand, you probably have to contract with a competent licensed engineer.
My gues is that the rollers and the belt were not designed with the
appropriate camber or other features that provide self-centering.

Bill
-- Fermez le Bush--about two years to go.

 

[martin griffith]

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!).

Other suggestions?

Thanks,

You could try capacative sensing, since the belts are carbon fibre,
and some sort of bridge detector


martin

 

[John Larkin]

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!).

Other suggestions?

Thanks,

The usual fix is to "crown" the rollers so that they are bigger
diameter in the middle and skinnier at the ends. Then the belt
self-centers.

John

 

[DaveC]

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.

Thanks, Sue.

This is a *larger* diameter at the center?

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

 

[Robert Baer]

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!).

Other suggestions?

Thanks,

Very simple!
The drive roller, or largest roller, should have a curve in it so
that the center is larger than the edges.
Or pick two smaller rollers, spaced "far" apart in the loop.

For a quick and dirty test, add some adhesive-backed tape onto a
roller, centered and maybe a second, more narrow tape also centered (to
get that curve).

 

[Anthony Fremont]

The usual fix is to "crown" the rollers so that they are bigger
diameter in the middle and skinnier at the ends. Then the belt
self-centers.

When I was in high school, the school had an old-fashioned type printing
press with the giant cast-iron flywheel. It had an electric motor to keep
it going, but you still controlled the speed pretty much by hand. The shop
teacher's favorite way of getting the giant leather belt to track right was
to build up the drive pully with masking tape, forming a crown. Seemed to
do a good job.

 

[John Larkin]

Thanks, Sue.

This is a *larger* diameter at the center?

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

Yes, larger in the center. If the belt tension isn't extreme, try
using some temporary bands, hvac type aluminum tape or something, to
fake a taper and see if it works. I bet you could google "tapered
roller belt" or something for tips, too. In my (limited) experience,
the taper is usually pretty significant, and sometimes just near the
ends.

I'm surprised that anybody would use a smooth roller for a belt like
this. It's guaranteed to be unstable.

Classic leather-belt-driven lathes used rollers that were very
rounded, quarter-circle almost. It was uncanny to see a belt start at
the very edge and walk right up to the crowned center.

John

 

[Palindrome]

Thanks, Sue.

This is a *larger* diameter at the center?

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

You can either put the larger diameter/lower tension at the centre or
smaller diameter/higher tension. Both will auto-correct but the latter
will tend to make the belt to bunch up in the middle, whereas the former
can tend to make things fall off the edge of the belt..

It's just a bit of maths to work out what corrective force is being
applied, knowing the difference in tension and the angle of the inclined
plane created by the taper(s).

The alternative is to install two extra free-wheeling short rollers,
tilted towards the centre and under the edges of the belt. As the belt
tries to wander towards one edge, it has to go "uphill", up the
free-wheeling roller. The advantage of this method is that you can
adjust the position and angle of the rollers to achieve the centreing
that you want and it doesn't require any modification to the existing
equipment..

 

[Phil Hobbs]

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!).

Other suggestions?

Thanks,

One common method is to flare the rollers slightly at the ends. That
way if the belt wants to ride up on the roller, there's a centering
force due to the stretching of the belt.

Failing that, something like what you propose could probably be made to
work--but I'd definitely avoid optical sensors for this if possible.
The problem is that they get dirty and stop working, which in an
automatic control situation like this would be dangerous.

Another simple method might be to have guide rollers at the edges of the
belt. Rather than encoders and motors and microcontrollers, you could
have the guide roller turn the adjustment screw via gears or a chain
drive. That way, any time the belt got far enough out of line to spin
the guide roller, it would be gradually adjusted until it didn't spin it
any more. That's sort of an integrating servo--if the gear ratio (i.e.
gain) is too high, the control loop will oscillate, and the poor thing
will bounce back and forth until it chews itself to bits.

Since the situation doesn't require too many smarts from the controller,
this would probably be easier and a good deal more reliable.

Cheers,

Phil Hobbs

 

[Rich Grise]

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.

You need your rollers crowned. I can't draw one in ASCII, but essentially,
the rollers need to be thicker in the middle. Not by much; I don't know
if there's a formula, but that's the standard way of keeping a belt
centered.

Let me know if you need some custom rollers built - that's one of the
things that the company where I sit does.

Good Luck!
Rich

 

[gavin]

Whwn i used to work for a conveyor manufacture we used to crown one quarter
of the width to create a 2mm drop from the diameter of the roller

Try this it will help

Gavin

 

[Jamie]

Thanks, Sue.

This is a *larger* diameter at the center?

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

Normally using a crown center roller would fix it how ever, since this
is a printing machine, and the belt width isn't very wide (10 mm) I
think you said?, If you want automation it can be done via using 2
simple small light weight with following groves with rollers, that have
a small spring to keep the two rollers tight on the edges of the belt.
These 2 rollers connect to an arm which is connected to a potentiometer
that will drive a simple geared head motor on the manual screw via a
regen drive..
We had a similar problem also, ours was a much wider belt but that is
what we did. In our case we use 2 pots, one on each side of the belt
that are join electronically to report a differential signal to an
air servo piston that is attached on one side of the roller assembly.
The output operates an IP value (Current 4..20 ma's), the electronics
is nothing more than a voltage comparator that generates the current signal.
normally we would use a gear head motor how ever, money was a problem
at the time and this worked out just fine.
You may find using an air cylinder and IP valve from a dancer control
board may work fine..

 

[whit3rd]

You need your rollers crowned. I can't draw one in ASCII, but essentially,
the rollers need to be thicker in the middle.

And, the important rollers are the turnaround rollers, the end ones
that the belt wraps 180 degrees around. The simple idler rollers
and the drive roller (if it's a capstan drive and doesn't turn the
belt around) can be simple cylinders.

 

[Palindrome]

And, the important rollers are the turnaround rollers, the end ones
that the belt wraps 180 degrees around. The simple idler rollers
and the drive roller (if it's a capstan drive and doesn't turn the
belt around) can be simple cylinders.

It is generally the rollers where there is a change of direction that
are important, because they can most easily translate changes in
longitudinal tension forces into lateral movement (inclined planes).

For an outward tapering roller, the belt must be capable of conforming
to some extent to the profile of the shaped roller(s) as a result of the
belt tension. Any decrease in tension, eg belt stretch, can greatly
affect lateral stability.

OTOH, for an inward tapering roller, the belt must be rigid, laterally,
or it will bunch into the centre. Belt tension variations are generally
not so critical.

The nature of the belt thus determines the roller profile needed to
self-centre.

 

[jntel]

The usual fix is to "crown" the rollers so that they are bigger
diameter in the middle and skinnier at the ends. Then the belt
self-centers.

John

Look for "spreader rollers" or "banana rollers" in your favorite search
tool.

 

[Robert Latest]

["Followup-To:" header set to sci.electronics.design.]

Another simple method might be to have guide rollers at the edges of the
belt. Rather than encoders and motors and microcontrollers, you could
have the guide roller turn the adjustment screw via gears or a chain
drive. That way, any time the belt got far enough out of line to spin
the guide roller, it would be gradually adjusted until it didn't spin it
any more.

How about a very simple electrical "middle of the road" thing? Mechanical
switches with rollers that activate a geared-down motor. One switch on
either side of the belt, each making the gear motor turn in opposite
direction from the other. Rugged, simple, and a lot cheaper than an
all-mechanical solution.

robert

 

[Robert Latest]

["Followup-To:" header set to sci.electronics.design.]

I'm surprised that anybody would use a smooth roller for a belt like
this. It's guaranteed to be unstable.

Maybe it *has* to be flat? Who knows.

robert

 

[jasen]

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?

use (slightly) barrel shaped rollers.

Bye.
Jasen