string feed detection

Z

Thread Starter

Zdenko A.

In our process we feed synthetic string ( heavy thread ) into rubber extrusion. String feed speed is 120 ft/min. We are seeking easy to load (T < 5s), inexpensive sensor ( evice) to confirm string feed. Do you know of any contraption designed for this application?
 
K
We have basically the same issue in the food industry with a string we place in our re-closeable packages. What we do is as follows...

Two nip rollers (one steel and the other one rubber) running at the correct speed in feet per minute pull thread into a fixture. Two other nip rollers pull thread out of the fixture at the same rate. What we do is create a loop of thread inside the fixture. A metal puck rides inside the loop. The height that the puck rides above the bottom of the fixture is a product of the size of the thread loop that was created. As long as the thread continues to feed properly the loop never changes. If the thread breaks... the loop disappears and the puck falls to the bottom of the fixture. A proximity switch watches for the puck position. Works quite well. A DC
drive slaved to the line drives the two sets of nip rollers.

Hope this helps you.

Best Regards... Rick Kelly

Chief Electrical Technician
Natural Cuts
Cheese Operations
Kraft Canada
(613) 537-8069 V
(613) 537-8057 F
[email protected]
http://trondata.on.ca
 
M

Michael Griffin

At 10:05 21/12/00 -0500, Zdenko A. wrote:
<clip> In our process we feed synthetic string ( heavy thread ) into rubber
> extrusion. String feed speed is 120 ft/min. We are seeking easy to load (T
> < 5s), inexpensive sensor ( evice) to confirm string feed. Do you know of
> any contraption designed for this application?
<clip>
In a somewhat similar application (involving wire) we use a flag on one of the existing feed pulleys which acts as an idler (driven by wire motion only) It activates an inductive proximity sensor. The PLC detects
changes of state of the proximity sensor well enough to know the wire is moving even though it can't accurately count the revolutions of the pulley (it will miss some transitions). This is used to determine if the wire is broken (no change when there should be), or was not cut (changes occur when they shouldn't).
If the pulley is rotating too fast to detect (assuming you have a suitable pulley in the system) or the feature you are detecting is too narrow for a conventional PLC input to detect, then there are simple solutions to that which we can discuss if you wish.


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Michael Griffin
London, Ont. Canada
[email protected]
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T

Tim Beckwith, CMP Engineering, Ottawa, C

Eltex makes a sensor used in the weaving industry to detect broken weft (woven strands) during the weaving process. I believe the sensor uses a piezo-electric device which generates a voltage as long as the string is moving through a ceramic eyelet. An interface circuit converts this to a logic level for PLC input.
 
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