Conveyer belt "wander" auto-correction?

wrote:


Look for "spreader rollers" or "banana rollers" in your favorite search tool.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
DaveC wrote:

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).
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
DaveC wrote:

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
["Followup-To:" header set to sci.electronics.design.] Phil Hobbs wrote:

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
snipped-for-privacy@bogusdomain.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

use (slightly) barrel shaped rollers.
Bye. Jasen
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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 ,
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
us:

Neither is a solution.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
snipped-for-privacy@bogusdomain.net
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.