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Conveyer belt "wander" auto-correction?
|
|
|
| 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,
--
DaveC
me@bogusdomain.net
This is an invalid return address
Please reply in the news group
| |
| Palindrome 2007-04-25, 1:25 pm |
| DaveC wrote:
> 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.
--
Sue
| |
| Salmon Egg 2007-04-25, 1:25 pm |
| On 4/25/07 7:41 AM, in article
0001HW.C254B6C5017BB457F01826C8@news.sf.sbcglobal.net, "DaveC"
<me@privacy.net> wrote:
> 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 2007-04-25, 1:25 pm |
| On Wed, 25 Apr 2007 07:41:57 -0700, in sci.electronics.design DaveC
<me@privacy.net> wrote:
>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 2007-04-25, 1:25 pm |
| On Wed, 25 Apr 2007 07:41:57 -0700, DaveC <me@privacy.net> wrote:
>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
| |
|
| > 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;
--
DaveC
me@bogusdomain.net
This is an invalid return address
Please reply in the news group
| |
| Robert Baer 2007-04-25, 1:25 pm |
| DaveC wrote:
> 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 2007-04-25, 1:25 pm |
| John Larkin wrote:
> 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 2007-04-25, 1:25 pm |
| On Wed, 25 Apr 2007 08:42:04 -0700, DaveC <me@privacy.net> wrote:
>
>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 2007-04-25, 1:25 pm |
| DaveC wrote:
>
>
> 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..
--
Sue
| |
| Phil Hobbs 2007-04-25, 1:25 pm |
| DaveC wrote:
> 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 2007-04-25, 1:25 pm |
| On Wed, 25 Apr 2007 07:41:57 -0700, DaveC wrote:
> 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
| |
|
| 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
"Rich Grise" <rich@example.net> wrote in message
news:pan.2007.04.25.18.29.59.804828@example.net...
> On Wed, 25 Apr 2007 07:41:57 -0700, DaveC wrote:
>
>
> 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
>
| |
|
| DaveC wrote:
>
>
> 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..
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
| |
| whit3rd 2007-04-26, 3:25 am |
| On Apr 25, 10:29 am, Rich Grise <r...@example.net> wrote:
> On Wed, 25 Apr 2007 07:41:57 -0700, DaveC wrote:
>
>
> 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 2007-04-26, 3:25 am |
| whit3rd wrote:
> On Apr 25, 10:29 am, Rich Grise <r...@example.net> wrote:
>
>
>
>
>
> 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.
--
Sue
| |
|
|
"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:03tu231snnt8dcpp1tvlp9k9gp42b6jkta@4ax.com...
> On Wed, 25 Apr 2007 07:41:57 -0700, DaveC <me@privacy.net> wrote:
>
>
> 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 2007-04-26, 9:25 am |
| ["Followup-To:" header set to sci.electronics.design.]
Phil Hobbs wrote:
> 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 2007-04-26, 9:25 am |
| ["Followup-To:" header set to sci.electronics.design.]
John Larkin wrote:
> 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
| |
| MooseFET 2007-04-26, 9:25 am |
| On Apr 25, 7:41 am, DaveC <m...@privacy.net> wrote:
> 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.
| |
|
| On 2007-04-25, DaveC <me@privacy.net> wrote:
>
> 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
| |
|
| On 2007-04-25, DaveC <me@privacy.net> wrote:
> 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
| |
| Palindrome 2007-04-27, 1:25 pm |
| jasen wrote:
> On 2007-04-25, DaveC <me@privacy.net> wrote:
>
>
>
> 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.
--
Sue
| |
| Rich Grise 2007-04-27, 5:25 pm |
| On Fri, 27 Apr 2007 15:04:38 +0000, Palindrome wrote:
> jasen wrote:
>
> 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 2007-04-30, 3:25 am |
| On Wed, 25 Apr 2007 07:41:57 -0700, DaveC <me@privacy.net> wrote:
>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.
--
W "Some people are alive only because it is illegal to kill them."
. | ,. w ,
\|/ \|/ Perna condita delenda est
---^----^---------------------------------------------------------------
| |
| Lionel 2007-04-30, 3:25 am |
| On Wed, 25 Apr 2007 08:42:04 -0700, DaveC <me@privacy.net> wrote:
>
>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.
--
W "Some people are alive only because it is illegal to kill them."
. | ,. w ,
\|/ \|/ Perna condita delenda est
---^----^---------------------------------------------------------------
| |
| Lionel 2007-04-30, 3:25 am |
| On 26 Apr 2007 12:08:13 GMT, jasen <jasen@free.net.nz> wrote:
>On 2007-04-25, DaveC <me@privacy.net> wrote:
>
>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).
--
W "Some people are alive only because it is illegal to kill them."
. | ,. w ,
\|/ \|/ Perna condita delenda est
---^----^---------------------------------------------------------------
| |
| SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalax 2007-04-30, 1:25 pm |
| On Wed, 25 Apr 2007 07:41:57 -0700, DaveC <me@privacy.net> Gave us:
>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 2007-04-30, 1:25 pm |
| On Wed, 25 Apr 2007 15:17:12 GMT, Palindrome <me9@privacy.net> Gave us:
>DaveC wrote:
>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 2007-04-30, 1:25 pm |
| On Wed, 25 Apr 2007 08:42:04 -0700, DaveC <me@privacy.net> Gave us:
>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 2007-04-30, 1:25 pm |
| On Mon, 30 Apr 2007 16:51:11 +1000, Lionel <usenet@imagenoir.com> Gave
us:
>On 26 Apr 2007 12:08:13 GMT, jasen <jasen@free.net.nz> wrote:
>
>
>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 2007-04-30, 1:25 pm |
| On Mon, 30 Apr 2007 16:46:51 +1000, Lionel <usenet@imagenoir.com> Gave
us:
>On Wed, 25 Apr 2007 07:41:57 -0700, DaveC <me@privacy.net> wrote:
>
>
>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 2007-04-30, 1:25 pm |
| SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalaxy.org wrote:
> On Wed, 25 Apr 2007 15:17:12 GMT, Palindrome <me9@privacy.net> Gave us:
>
>
>
>
>
> 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)).
--
Sue
| |
| SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalax 2007-04-30, 1:25 pm |
| On Mon, 30 Apr 2007 09:31:44 GMT, Palindrome <me9@privacy.net> Gave us:
>SuperM@ssiveBlackHoleAtTheCenterOfTheMilkyWayGalaxy.org wrote:
>
>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 2007-04-30, 1:25 pm |
| On Apr 29, 11:46 pm, Lionel <use...@imagenoir.com> wrote:
> On Wed, 25 Apr 2007 07:41:57 -0700, DaveC <m...@privacy.net> wrote:
>
>
> 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.
| |
|
| > 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
me@bogusdomain.net
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Please reply in the news group
| |
|
| > 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.
--
DaveC
me@bogusdomain.net
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Please reply in the news group
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