Dynamic gage averaging and length determining device and method for continuous sheet material

Method and apparatus for dynamically determining average gage of continuous sheet material passing about a work roll for subsequent winding or coiling upon a take-up reel. The apparatus includes pulse tachometers for both the work roll, of known diameter, as well as the take-up reel. A comparison of the angular velocity of both the work roll and take-up reel results in a precise velocity ratio for a given period of time. The ratio, when taken in conjunction with the revolutions of the take-up reel, is then used within a digital logic apparatus for determining the change in coil diameter for the given time period, thereby resulting in the average gage of the continuous sheet material wound upon the take-up reel for that given time period. Strip length may also be calculated by the same apparatus.

BACKGROUND OF THE INVENTION 
The area of cold mill production has, for some time, required on-line 
gaging equipment that responds quickly and gives accurate results. This 
requirement has been heightened recently by attempts at cost reduction and 
economic cold mill production programs. Steel producers have found one 
area (cold mill production) in which "extra" give-aways to the customer 
can be alleviated or merely reduced, resulting in surprising cost 
reduction and increased mill production efficiency. These "give-aways", 
which are basically extra product sent to the customer in order to insure 
he gets at least what he has ordered, are predicated upon an uncertainty 
in footage of product or product weight and/or product gage. If the mill 
operator could find a more exact way of determining these parameters, 
there could be a reduction in the amount of steel product with confidence 
that the customer will not be "short-changed". 
Since the first gaging devices were installed within cold reduction mills 
to the present sophisticated radiation absorption devices (such as X-rays 
and Accuray gages) on-line instantaneous gaging has been desired. 
Operating experience has shown, however, that the new equipment, like the 
old equipment, can be subject to gross and costly errors due to instrument 
drift and equipment malfunctioning. In response to this basic defect, some 
method of checking average product gage has been necessary. Current 
practice in this regard continues to be the "Wrap Check Average Gage 
Method". 
The present "Wrap Check Average Gage Method" of checking the accuracy of 
the on-line cold mill gaging equipment is accomplished manually on solely 
a random basis. This task is performed by inserting markers into the side 
wall of a coil being rolled with a known number of wraps between the 
markers. After the coil has been completely rolled, the distance between 
the markers is measured and divided by the number of wraps between the 
markers. This method, while cumbersome, is accurate if care is taken in 
inserting the markers, measuring the distance therebetween, and 
calculating the end result. This method, however, does have major 
disadvantages, i.e. (1) gage results are not available until the coil 
being "tested" has been completely rolled; (2) the results obtained 
represent only the average gage for that portion of the coil lying between 
the two markers inserted in the coil; (3) the results can be no better 
than the measurements taken to calculate the average gage--the factor of 
human error; and (4) the method is extremely hazardous to the operator 
inasmuch as he must open the safety enclosure surrounding the moving coil 
to insert the markers. 
It should be apparent that the present manual calculation method leaves 
much to be desired. Additionally, there would appear to be some degree of 
dissatisfaction with the modern expensive gaging systems which are subject 
to drift and slippage errors. The present dynamic gage-averaging method 
and apparatus is a successful attempt to fill this void. 
SUMMARY OF THE INVENTION 
The present invention is addressed to an on-line dynamic gage averaging 
device which gives an acurate and incremental average gage of the sheet 
material throughout the entire length of a coil during processing. The 
apparatus does not require operator assistance, calibration or the 
changing of ranges regardless of the gage being produced. 
The underlying basis of the present method and apparatus is the "stopping" 
of the recoiling action for an instant in time to permit the automatic 
measurement of the coil diameter. While this is not physically possible, 
it may be accomplished in effect by looking at the instantaneous velocity 
ratio between the work roll and the take-up reel or mandrel. This, of 
course, presumes that the angular velocities of the work roll and the 
take-up reel may be accurately measured. By using pulse tachometers, one 
for each reel, this can easily be accomplished. Once the instantaneous 
velocity ratio has been derived for a given time instant, it is multiplied 
by the work roll diameter (which had been previously factored into a 
digital logic apparatus) to yield the instantaneous diameter of the coil 
on the take-up reel for that given instant of time. This process may be 
repeated, and is repeated constantly, for any number of "instants of 
time". As a result, the average gage may be calculated continuously for 
the sheet material existing any two coil diameters between any two given 
time instants. 
To achieve the continuous gage averaging ability just discussed, two pulse 
tachometers, two high speed counters, and a programmable digital logic 
apparatus are employed. One each of the pulse tachometers (1000 pulses per 
revolution) and counters are associated with the work roll and take-up 
reel. The pulses coming from the work roll are counted for a period of 
time equal to 1,000 pulses received by the take-up reel counter or one 
revolution of the take-up reel. This process in effect divides the pulses 
counted from the work roll by 1,000 for each revolution of the take-up 
reel and provides the ratio between the work roll velocity and the take-up 
reel for that instant of time. By reading a ratio counter and wrap counter 
simultaneously, a starting and stopping pair of data points are acquired. 
These data points are employed to calculate the change in the coil 
diameter between the stopping point and the starting point. The number of 
wraps between these diameters is then made by subtracting the first wrap 
count from the second wrap count. As a result, all of the required 
information necessary for calculating average sheet material gage is 
acquired while the coil remains in a dynamic or rotating state. 
It is therefore a primary object and feature of the present invention to 
provide a method and apparatus for calculating the average gage of a 
continuous strip of sheet material for a given time period while the strip 
is constantly moving. 
It is a general object and feature of the present invention to provide a 
dynamic gage averaging device and method which provides a continuous gage 
readout for a moving strip of continuous sheet material and which also 
provides precise footage counter as an adjunct thereto. 
It is another general object and feature of the present invention to 
provide a dynamic gage averaging and footage determining method and 
apparatus which provides a continuous readout for a moving strip of 
continuous sheet material and which provides for the cancellation of 
errors due to slippage and the like of the work roll with respect to the 
moving sheet material. 
It is yet another object and feature of the present invention to provide an 
inexpensive and easily maintained dynamic gage averaging and footage 
counting device and method for calculating both gage and footage of a 
continuously moving strip of sheet material. 
Other objects and features of the invention will, in part, be obvious and 
will, in part, become apparent as the following description proceeds. The 
features of novelty which characterize the invention will be pointed out 
with particularity in the claims annexed to and forming part of the 
specification.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, there is shown a schematic representation of a 
five-stand cold reduction mill 10. The cold reduction mill 10 generally 
includes a first stand 12, a second stand 14, a third stand 16, a fourth 
stand 18 and a final or fifth stand 20. Each of the individual stands, for 
example stand 20, is composed of an upper back-up roll 22, a lower back-up 
roll 24, a first work roll 26 and a second work roll 28. As indicated in 
FIG. 1, the strip 30 to be cold reduced is passed between each of the sets 
of work rolls, each performing another step in the reduction of the strip 
to its finally gaged size just before it is wound upon a take-up reel or 
mandrel 32. The strip 30 is moved through the five-stand cold mill 10 in a 
direction indicated by arrow 34 and is wound upon the take-up reel or 
mandrel 32 in the direction of the arrow 36. 
Each of the five stands 12, 14, 16, 18 and 20 has an associated on-line 
gage which is an indication of the separation of the work rolls in each of 
the five stands. As noted previously, these gages, for the most part, are 
relatively accurate but are subject to drift and error thereby resulting 
in off-gage products. Inasmuch as the customer requires specific gage 
tolerances, any sheet material produced must be within the tolerances set 
or is considered off-gage and non-acceptable. Therefore, even if the gages 
associated with each of the five stands indicates a specific gage being 
produced by that stand, there is the distinct possibility for some reason 
that the gage actually being produced by that stand is different from the 
gage indication. In order to preclude the complete running of off-gage 
product on a relatively long coil, and in order to provide an independent 
check of the gage of the product being produced, an independent on-line 
dynamic gage averaging apparatus and method according to the present 
invention is provided. 
Looking to FIG. 2, there is shown a schematic flow diagram indicating the 
individual elements of the appartus and the steps to be performed in the 
practice of the method according to the present invention. Associated with 
the take-up reel 32 and the last stand work roll 26 are two pulse 
tachometers 38 and 40, respectively. The pulse tachometers 38 and 40 have 
an out-put of 1,000 pulses per revolution of the associated roll. 
Consequently, during one full revolution of the take-up reel or the work 
roll, its associated pulse tachometer will produce an out-put of 1,000 
pules. A high speed wrap counter 42 is operative to receive the in-put 
from pulse tachometer 38 and to count the number of 1,000 pulses and 
translate that information into the number of full revolutions or wraps of 
the take-up reel. A high speed ratio counter 44 is associated with the 
pulse tachometer 40. The high speed ratio counter 44 is operative to 
receive the pulse out-put of the pulse tachometer 40 as well as the pulse 
out-put of the pulse tachometer 38. The pulse coming from the work roll 
pulse tachometer are counted for a period of time equal to 1,000 pulses 
into the in-put channel of the ratio counter. Simultaneously, the ratio 
counter is operative to count the number of pulses from the tachometer 40 
during the period of time it takes to receive the 1,000 pulses into the 
control channel of the ratio counter. This in effect divides the pulses 
counted from the work roll by 1,000 for each revolution of the take-up 
reel and provides the necessary ratio between the work roll velocity and 
the take-up reel velocity for that instant of time. By reading the ratio 
counter and wrap counter simultaneously, a starting and stopping pair of 
data points are acquired. These data pairs are fed directly into a 
programmable digital logic counter 46 which performs the necessary 
mathematical calculations for determining the diameter difference between 
the stopping and starting points. The programmable calculator 46 also 
functions to calculate the number of wraps between these two diameters by 
subtracting the first wrap count from the second wrap count. With this 
information in-put into the calculator 46, all of the necessary parameters 
to calculate average gage are present. 
The digital logic apparatus employed within the present invention may be 
any one of a variety of commonly available types and serves to accumulate 
the necessary parameter in-puts (from the counter primarily) for the 
calculation of dynamic average gage and strip length. The calculator then 
makes the appropriate mathematical comparisons for subsequent print-out as 
gage and length as well as total coil weight and outside diameter. All of 
these read-outs are not only desirable, but necessary for the proper 
manufacture of each coil by the producer as well as identification by the 
customer. 
Any number of different calculators, both simple and complex can be used 
for the above-noted calculations. These range from the "desk-top" 
calculator to the sophisticated microprocessor, the latter being the type 
of calculator employed in the preferred embodiment of the present 
invention. Whatever the specific apparatus used, there remain several 
given formulas which must be solved for each instant of time that such 
calculations are made. As previously noted, the high speed ratio counter 
44 is operative to provide an out-put signal to the programmable digital 
logic calculator which, in ratio form, reflects the relative angular 
velocities of the take-up reel 32 to the work roll 26. It is this ratio R 
which, when taken in conjunction with the known work roll diameter 
D.sub.W, provides the diameter of the coil on the take-up reel at the 
instant of time such ratio is obtained. Specifically, 
EQU R(ratio).times.D.sub.W =D.sub.C (diameter of coil on take-up reel at time.) 
The diameter of the coil D.sub.C accordingly can be read continuously any 
number of times during the coiling of the strip product. By taking two 
coil diameters, (a starting diameter D.sub.S and a stopping diameter 
D.sub.E) the average gage of the product therebetween may be determined 
according to the following formula: 
EQU G(average gage)=(D.sub.E -D.sub.S /2N) 
where N is the number of wraps of coil within the two diameters. One side 
benefit of the data in-put to the microprocessor 46 is that the length of 
the strip lying within the two diameters may be calculated as follows: 
EQU L(length)=(.pi./24)N(D.sub.S +D.sub.E), 
or 
EQU L=0.1309N(D.sub.S +D.sub.E). 
if reliable signals are provided which can be used to accurately indicate 
these "starting" and "stopping" diameters, the error in footage 
measurement, for instance, is less than .+-.0.1%. 
The necessity for acquiring a constant read-out of average gage, coil 
length, coil weight and diameter, to be displayed on a display console 50, 
associated with the microprocessor 46, is achieved in the following 
manner: The two pulse tachometers begin their 1,000 pulse per revolution 
out-puts at the commencement of the sheet material being wound upon the 
take-up reel 32. Both the high speed wrap counter 42 as well as the high 
speed ratio counter 44 begin counting wraps and the angular velocity 
ratio, respectively, at the start of coil winding. The digital logic 
calculator or microprocessor 46 is adapted to receive the out-put signals 
from the two counters immediately. However, for purposes of minimizing 
errors and getting the system "on track", the first eight wraps, while 
counted, are discounted for the most part in any precise calculation of 
subsequent average gage. Average gage is made from any given number of 
wraps which is constantly updated as coiling progresses. For instance, in 
the preferred embodiment of the present invention, the gage sampling is 
done for a given number equal to fifty (50) wraps. In effect, any read-out 
of gage average on the display console 50 is based upon this sampling of 
fifty wraps which is constantly updated with each new wrap added to the 
coil. As each new wrap is added, for gage average sampling purposes, the 
"first" wrap is dropped. Accordingly, a "new" sampling of a different 
fifty wraps is made constantly with each additional wrap made to the coil. 
This procedure serves two very specific purposes. Specifically, errors in 
slippage of the sheet material about the work roll are minimized because 
of the large sampling number. Any slippage (within reason, of course) in 
the work roll-sheet material interface is infinitesimal considering the 
large gage sample constantly being considered. Additionally, the use of a 
large sampling which is constantly updated provides a very accurate 
average gaging system which is insulated from other possible errors such 
as timing, etc. which might affect other less tolerant and less accurate 
systems. In short, the procedure just outlined is tolerant of small errors 
which would cause very detrimental errors in other gage averaging 
apparatus and methods. 
The dynamic gage averaging apparatus and method of the present invention 
provides an inexpensive and most easily maintained system for accurately 
computing the average gage (and footage) of a continuous sheet product to 
be wound upon a take-up reel while the product is being wound. The current 
system is independent of the other mill gaging equipment and provides a 
constant and accurate check on this equipment. The present system not only 
does not require calibration, but eliminates the current safety hazards 
associated with present calculation methods. In conclusion, the present 
on-line dynamic gage averaging device is an accurate and continuous way of 
obtaining average gage and coil length as the coil is being wound. By 
using this information correctly, the amount of off-gage produce being 
produced may be drastically reduced, thereby alleviating the expensive and 
wasteful production of product not within the tolerances required by the 
customer. 
While certain changes may be made in the above-noted method and apparatus, 
without departing from the scope of the invention herein involved, it is 
intended that all matter contained in the above description, or shown in 
the accompanying drawings, shall be interpreted as illustrative and not in 
a limiting sense.