Lately been thinking about how to implement feedback to a controller
for a machine that is either feeding wire/rope or a flexible flat,
wide material like plastic wrap or foam (even sheet metal) to a take
up reel. Enough material would be visible on its way to the take up
reel for an inspector to see any defects.
The material will break or stretch if a disturbance to the plant
causes too much tension on the mat'l and the takeup reel drive would
need to be slowed down until the plant is back up to speed, so
consider a optimum amount of sag (maybe not perceptible in the case
of wire/rope ) as the material is on its way to the take up reel.
Naturally, as the amount of material on the takeup reel increases,
the sag/tension will decrease/increase unless the take up reel is
In either case, I'm thinking the machine output could be represented
as a supply reel feeding material at a constant linear rate. Just
Case 1, wire.rope:
I was thinking that the displacement of a tension idler (placed near
the material output would indicate the tension of the material.
Either a straight line from the idler to the take up could
approximate that component of the idler force vector, or the wire
tension/sag (caternary) equation could be used in the
analysis/derivation of the transfer function. The rate of change of
force on the idler would indicate the speed difference between
supply and take up.
Case 2, flat material:
In this case I thought that a few opto detectors above and below the
"optimum" sag point could detect the increase or decrease in sag and
the rate of change of sag would indicate the speed difference
between the supply and takeup reels,
i.e., in either case, the linear velocity coming off the machine
minus the linear rate that the take up reel is *trying* to take it
Typical disturbances would be, say, the machine encountering
resistance in trying to get the material out, or the take up reel
being out of round causing a cumulative decrease in sag.
Are these sensor arrangements prctical? I've never seen this done
before so I have no clue how it might really be done in industry.
Any suggestions as to why this isn't practical or what would work
better would be appreciated.
18 years ago