CLOSED LOOP ROLLER LEVELER

BACKGROUND OF THE DISCLOSURE

The disclosure relates to roller levelers. More particularly it relates to a roller leveler that operates in a closed loop automatic control mode.

A metal strip product is fed into a roller leveler, typically from a coil. Roller levelers use multiple work rolls to flatten the strip. The path of the strip passes between offset upper and lower work rolls, which reverse bend the strip multiple times before the strip exits the leveler.

A given roller leveler is designed to process a range of strip thicknesses and strip yield strengths. As the strip passes between the work rolls very high separating forces are generated against the work roll face, yet the work roll diameters are of necessity relatively small; this to allow the work rolls to bend and enable the rolls to be spaced close enough to properly work the strip. The work rolls are supported by flights of back-up rolls. The back-up rolls support the work rolls and prevent them from excessive bending in reaction to the separating forces. In addition, and equally important, the back-up rolls provide a means of selectively correcting out of flat conditions across the width of the strip.

Referring now to FIG. 1, a crown, or upper half 10 of a leveler 12 is shown with upper back-up rolls 14 mounted thereon. FIG. 1 illustrates seven (7) flights 16 of back-up rolls and each flight has nine (9) back-up rolls 14 mounted to it. The flights 16 of upper back-up rolls 14 are mounted against a rigid flat upper surface 18 of the upper half 10 of leveler 12.

Referring to FIG. 2, eight upper work rolls 20 are shown as a sub-assembled module 22. When installed in the leveler, the upper work rolls 20 nest against the upper back up rolls 14 of FIG. 1. This combination provides an essentially rigid mounting of the upper work rolls. The entire face of the upper work rolls is coplanar and not intended to appreciably flex as the strip imparts a distributed load across the work roll faces.

Referring to FIG. 3, the leveler crown 10 is shown with the upper back-up rolls 14 and the upper work roll module 22 mounted thereon. The upper work rolls 20 do not bend during leveling. The entire face of the upper work rolls is coplanar and not intended to appreciably flex as the strip imparts a distributed load across the work roll faces.

FIG. 4 shows a flight 23 of lower back-up rolls 24. Shown in the flight are ten (10) lower back-up rolls 24. A given flight 23 is supported on its ends by a hydraulic cylinder 28 at each end (See FIG. 5). This creates two (2) moveable supports for each flight of lower back-up rolls. Each back-up flight cylinder has a position transducer that provides position feed back to the hydraulic servo system that controls the extension of the back-up flight support cylinder.

FIG. 5 shows seven (7) flights 23 of lower back-up rolls 24 mounted in a lower half 29 of the leveler 12. Also shown are the hydraulic cylinders 28 that support and move the lower back-up roll flights. Each flight is supported by two hydraulic cylinders 28, one at each end. Each lower back-up flight can be moved independently of others, or all of the flights can be moved to identical positions simultaneously.

For the same exemplary leveler lower work rolls similar to upper work rolls 20 nest against the flights 23 of the lower back-up rolls 24.

The lower back-up roll support cylinders provide the adjustable control of the leveler work rolls. The deeper the intermesh between the upper and lower work rolls, the greater the amount of reverse bending is imparted into the strip as it passes between the work rolls. This work roll intermesh is typically referred to as “plunge”.

The deepest plunge is near the entry of the leveler with the exit plunge being essentially zero (that is the exiting vertical gap between the upper and lower work rolls is about the same as the thickness of the strip passing between them).

In the typical control of a leveler, the entry plunge is a function of strip material properties and also a function of the incoming out of flatness condition of the strip.

For a roller leveler to improve the flatness of a given strip, the strip needs to be bent sufficiently to exceed the yield strength of the strip; in other words, the strip cross section needs to be strained into the plastic region. The deeper the plunge, the tighter the bend radius imparted to the strip, which creates greater strain into the strip. Strip mechanical properties partially define the requisite bending based on the following mathematical relationship:

R=t×E/(2×NS×YS), where

- R is the desired bend radius
- E is the modulus of elasticity of the strip
- NS is the number of yield strains desired to be imparted to the strip (this relates to how far into the plastic region the strip will be strained).
- YS is the yield strength of the strip.

The only unknown is the desired number of yield strains (NS). It is common practice in the Industry to use the following empirical observations:

To take out coil set, the leveler is set for about 1.5 yield strains (NS=1.5).

To take out crossbow, the leveler is set for 4 to 5 yield strains (NS=5).

Typically, when strip is unwound from a coil, the strip will exhibit a combination of coil set and cross bow, as well as potentially additional flatness defects like edge wave and centerbuckle.

Modern leveler controls require strip data (material properties) be input to the leveler control system; the operator then adds the desired “NS” number of yield strains. The leveler control system calculates the plunge required to achieve the desired NS. This calculation is based on the geometry of the work rolls, namely the work roll diameters and work roll spacing. Different leveler suppliers use slightly different algorithms for their plunge calculations; this because a variety of assumptions are made regarding strip reaction to the plastic deformations and different degrees of mathematical complexity are used to define the equation used.

The leveler plunge positions are commanded and achieved. At this point the plunge at each back-up roll is identical, resulting in essentially flat roll faces on the lower work rolls.

The strip is fed through the leveler and the operator observes the exiting strip shape. If the strip is flat except for exiting upturn or downturn, the operator changes the desire exit plunge to compensate. In this instance the plunge of each exit flight position is identical. This can be an iterative process until the operator is satisfied.

If there is exiting edge wave or other local out of flat condition, the operator adjusts the entry plunges accordingly; however, in this case the flight positions are not same straight across the work roll face but rather each flight has a varying position relative to its neighbor. This can be an iterative process till the operator is satisfied with the flatness of the strip exiting the leveler.

The line runs and processes the strip. The operator continues to observe the flatness and may need to make lower back-up flight adjustments, occasionally, over the run of the coil. Thus, there is a need to automate the leveling process so that the quality of the flatness of the strip is not dependent on the skill of the operator while overcoming the above mounted deficiencies while providing better overall results.

SUMMARY OF THE DISCLOSURE

One embodiment of the disclosure is to automate the leveling process so that the quality of the flatness of the strip is not as dependent on the skill of a given operator. There are existing automatic closed loop control levelers but a problem with them is the sensing systems are expensive and are not capable of covering the entire range of strip thickness, strip width and yield strength that a leveler could process. Another problem is the flatness sensors are difficult to maintain requiring lengthy outages resulting in loss of production.

Another embodiment of the present disclosure is a sensing system that has the ability to measure flatness over a much wider range of strip thickness and width combinations.

Another embodiment of the disclosure is the ease of maintenance of both the force measurement and the distance measurement sensors used in the overall sensing system.

Yet another embodiment of the disclosure is self-monitoring of the load cells and automatic repositioning of the flatness measuring system to prevent overload of the force sensors. The flatness controller handles the switch over from force sensing to distance sensing based on strip parameters and does not require operator intervention.

Yet another embodiment of the disclosure is using multiple sensing technologies to properly cover the range of strip thickness and yield strength combinations. This allows the leveler to operate in an automatic closed loop mode for its entire working range. Existing systems can only operate in closed loop mode over a narrow range of a given levelers capability.

Another embodiment of the disclosure is a closed loop roller leveler system including a roller leveler; a flatness sensor; and at least one arm for raising and lowering the flatness sensor. The sensor has a plurality of sensing rollers extending across a width of the strip of material. The sensor further has at least one load cell and at least one laser sensor for detecting flatness of the strip.

Yet another embodiment of the disclosure is a method for measuring flatness levels of a strip of material comprising providing a roller leveler; providing a flatness sensor; raising and lowering the flatness sensor with a plurality of hydraulic cylinders; providing a plurality of sensing rollers extending across a width of a strip of material; providing at least one load cell and at least one laser sensor; feeding the strip of material through the roller leveler; and feeding the strip of material through the flatness sensor.

Still other aspects of the disclosure will become apparent upon a ready understanding of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a crown (upper half) of an existing leveler with the upper back up rolls mounted thereon.

FIG. 2 is a perspective view of an upper work roll sub-assembly of FIG. 1.

FIG. 3 is a perspective view of the leveler crown of FIG. 1 with the upper back up rolls and the upper work rolls mounted to it.

FIG. 4 is a perspective view of a flight of lower back up rolls of FIG. 1.

FIG. 5 is a perspective view of the lower back-up roll flights mounted in the lower half of the leveler of FIG. 1.

FIG. 6 is a perspective view of the roller leveler and a downstream flatness sensor installed in a process line in accordance with a preferred embodiment of the disclosure.

FIG. 7 is an enlarged perspective view of the flatness sensor of FIG. 6.

FIG. 8 is a side elevational view of the flatness sensor of FIG. 6 in operating position for light gauge strip or heavy gauge strip.

FIG. 9 is a cross-sectional view of a sensing roll module of FIG. 10a.

FIG. 10a is a front elevational view of multiple sensing roll modules extending across the width of the strip.

FIG. 10b is an enlarged cross-sectional view of one of the sensing roll modules.

FIG. 11 is a side elevational view of the flatness sensor of FIG. 6 in operating position for heavy gauge strip.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring to FIG. 6, a flatness sensor 40 in accordance with a preferred embodiment is shown. A roller leveler 42 has the flatness sensor 40 downstream and installed in a process line. The strip 44 is under tension as it travels in direction T and passes over the flatness sensor. At lighter gauges, the tension is enough to make the wavy strip look flat, but it will become wavy when tension is removed.

Referring now to FIG. 7, flatness sensor 40 is shown not engaged to the strip 44. Two hydraulic cylinders 46 are used to lift the flatness sensor into operating position. As shown, hydraulic cylinders 46, lift the flatness sensor straight up and down, but the mechanism can also be designed to lift the flatness sensor in a pivoting fashion. There is a plurality of sensing rollers 48 mounted across the width of the strip 44. Each sensing roller 48 is mounted on its own pivot bracket. The entire array of sensors is moved up and down by hydraulic cylinders 46.

Load cells 50 of the sensor 40 are shown as compact puck style which is the preferred type but cantilevered beam style can be used as an alternate. The flatness sensing system utilizes different sensing techniques dependent on the thickness, width, and strength of the strip.

Referring to FIG. 8, the flatness sensing system 40 is shown after the exit side of the leveler 12. For strip threading and tailout purposes, the flatness sensing system 40 can be raised or lowered into position, by the hydraulic cylinders 46 that move the sensor support beam up or down. Typically, at least two (2) hydraulic cylinders are required. There may be more than two dependent on strip width range, and reaction forces on a flatness support beam 53 (FIG. 10a). It is important that the support beam 53 have little to no vertical deflection, as this affects the accuracy of the force sensors and the distance sensors.

Hydraulic cylinders 46 are moved in a position loop control scheme. The vertical position of the flatness sensor 40 is always known, based on position transducers mounted between the flatness sensor moving frame and the fixed support structure. These position sensors serve an additional purpose as they are actively used to reposition the flatness sensor while in use.

Referring still to FIG. 8, the flatness sensor 40 is shown in operating position for light gauge strip 44. Alternatively, the sensor can be used for heavy gauge strip 45 as seen in FIG. 11.

Referring still to FIG. 8, In this position the strip 44 takes a wrap angle (approximate 5 degrees both at entry and exit of the sensing roll). Preferably the strip is at a tension value that is at least the tension required to make the strip lay flat against the sensing rolls.

Minimum tension is a calculable number dependent on how much waviness there is in the strip. For heavier gauge strips 45, there is no wrap angle between the strip 45 and the sensing rolls 48 (see FIG. 11). The hydraulic cylinders 46 lift the rolls 48 to be merely tangent to the strip and the sensing rolls act simply as passline rolls. At this time, the output of laser sensors 52 (FIG. 9) is used for flatness control.

FIG. 9 shows a sensing roll module 48 of the sensor 40 including the load cell 50 and laser sensor 52. The flatness sensor has a series of sensing rollers 48 that are individually pivotally mounted and supported by load cell transducers 50, one per sensing roll. Additionally, the flatness sensor utilizes an array of laser distance sensors 52 mounted to the sensor support beam, but not on the pivoting arm of the sensing rolls. The pivotally mounted sensing rolls produce a force reaction on the load cell. The magnitude of the force reaction is proportional to tension in the strip that is carried by that specific roller.

It is important to realize that during usage, there is no vertical movement of the sensing rolls 48 relative to each other; they behave as if it was one continuous roll face and move in unison. The pivoting roller support bracket provides multiple advantages over a straight/direct vertical motion design: Ease of maintenance, ease of calibration, and very importantly, the pivot bracket assures there are no detrimental side loads or moments applied to the load cell. The force sensing load cells are mounted independent of the roller assemblies.

Load cells 50 are known force sensing devices and they are not subject to wear from usage. Load cells have virtually no vertical movement under load. It is important for accurate measurement that there be essentially no vertical movement of adjacent rollers as vertical movement would create an error in the measurement.

FIGS. 10a and 10b shows that there are multiple roll modules 48 extending across the width of the strip including load cells 50 and laser sensors 52. The laser array 52 measures the distance between the strip and a flat horizontal line. Deviations in the distance, across the width of the strip, are indications of an out of flat condition. This is all explained in greater detail below.

Referring back to FIG. 8, force sensing rollers 48 require the strip to be partially wrapped around the circumference of the roller(s), and the strip needs to be under tension. For a given leveler, the strip width range would typically determine the number of rollers and their roll face. Typically, there will be an odd number of sensing rollers as this places one sensing roll on the centerline of the strip, which is important for accurate measurement of narrow strip such as 18″ width.

Strip out of flatness conditions such as waviness or buckles are the result of variance in length of fibers across the width of the strip. If the strip were sliced into longitudinal ribbons, zones of waviness would have longer strands than the other zones. If the strip were perfectly flat and under tension, the tension distribution would be equal across the entire width of the strip. With out of flat strip, under tension, the flatter (shorter) zones carry more tension than the wavy zones.

When the tensioned strip is partially wrapped around the sensing rollers 48, and the strip is under tension, there will be a reaction force at the load cells 50. At a given load cell 50, the magnitude of the reaction is dependent on the tension in that zone, and on the wrap angle. Zones of the strip that are wavy will have lower reaction against their roller load cells than the zones that are flat. As the leveler gets the strip close to perfect flat, the differences in tension that are being measured can be very minute, hence it is vital that each load sensing roll assembly be in a vertical position that is identical to the other sensing rolls. Variations in vertical position would affect the accuracy of measurement because the wrap angle would be slightly different from zone to zone.

The flatness control system reads the reactions at each load cell, and looks at the variance in readings. The goal of the flatness control system is to make all the load cell readings essentially equal.

There are a variety of sensors commercially available that measure strip reaction based on a wrap angle. The present disclosure shows the sensor as a grouping of discrete relatively narrow face roll assemblies 48 that are pivotally mounted. The benefit of this approach is ease of maintenance and calibration.

Typically, during usage, the sensing system will be traversed by a broad range of strip widths. Consequently, some zones of the sensing roll face will wear faster than others. Rather than replacing the entire array of sensor rolls, which is expensive, only the worn zones need to be replaced.

If a roller 48 is worn, the discrete worn roller assembly can be pivoted up out of the way of its neighbors, and the pivot hinge is then disassembled. The removed roller has its length adjustable reaction stud 51 (FIG. 9) measured for length with a typical depth gauge. The replacement roller assembly stud is adjusted to the same length, and then the replacement roll pivot bracket assembly is installed, this with minimal downtime.

If a load cell 50 becomes defective it is easily replaced by pivoting the discrete roll assembly out of the way and removing the defective load cell, then mounting a replacement load cell and lowering the pivoting roll assembly into the operating position. The length adjustable calibration stud is attached to the roll assembly so there is no need to recalibrate the assembly. The load cell array is energized and electronic offsets are established to effectively “zero” the load cells thus compensating for the weights of the roller assemblies.

The load cells 50 need to have high resolution in order to adequately sense the small differences induced by the tension variances in the strip. This means they have a limited range and need protection from overload.

Overload can occur as a result of excess strip tension. Strip tension control is outside and independent of the flatness control of the leveler. Strip tension is typically controlled by the recoiler that is rewinding the strip. To prevent damage to the flatness sensor, the flatness controller monitors the reaction at each load cell. If the reaction force at the load cell hits a trigger value, the flatness controller commands the hydraulic cylinders 46 to slightly lower the flatness sensing system, thereby reducing the wrap angle and lowering the reaction forces at the load cells. This is potentially an iterative process.

A given roller leveler has to process a wide range of strip thickness at large range of strip widths, so clearly there will be strip thickness and width combinations that the roller force flatness sensor is incapable of properly measuring.

The technique of measuring strip flatness with the above described sensing rollers is limited in its effective range. Practitioners in this field state two types of limits, one typical limit for steel strip, is about 0.08″ to 0.09″ strip thickness. Another source states the limit as a ratio of strip width to strip thickness needing to be 400 or greater. Both perspectives are concerned with the “bending” force of the strip to make it lay against. For thicker strip the bending force is a potentially dominating force that masks the desired signal of “force variation due to tension variation”.

Also of concern: as the strip thickness increases, it takes ever increasing amounts of strip tension to make the wavy strip lay flat against the force sensing rollers. The requisite amount of tension may not be available and may not be desirable as tension control is performed outside the control of the leveler. Consequently, there can be wavy portions of strip that do not contact the sensing roller at all, and there can be zones of strip that are flat and hence have a very high reaction force on those load cells. This can overload the load cells because the load cells need to have a limited range in order to have the necessary sensitivity.

The present flatness sensor disclosure overcomes this limit by utilizing two different sensing technologies. When required, based on known incoming strip parameters, the flatness controller will command the sensing system to position itself to be either a force measuring roll system, or a non-contact distance measuring system. Typically, the force sensing system becomes ineffective as strip thickness increases.

As described above, when used as a force measuring device, the flatness system positions itself to achieve an impingement on the strip that results in a known strip wrap angle on the sensing rolls.

When strip parameters dictate, the flatness sensing system will position itself such that there is no wrap angle on the sensing roll, and the sensing roll is positioned to behave as a passline roll. At this time, the laser distance sensors 52 are made active.

An array of laser distance sensors 52 are placed across the width of the strip. The number of sensors used is dependent on the maximum strip width a given leveler will process. The number of lasers used is an odd number which places one laser on the centerline of the strip width. This is important when trying to measure flatness of narrow strip widths; like 18 inches. It is not required to have the same number of lasers as there are force measuring rollers.

The lasers are mounted on a substantially rigid beam. Any vertical deflection of the beam will result in an error in the measurement. When the lasers are in use, the strip does not take a wrap angle on the force sensing rollers so there is no dynamic loading on the laser support frame.

When the laser system is in use the strip thickness is high. This means the strip strength is such that the strip tension is insufficient to pull the strip into a flat condition. The waviness of the strip will be visible and the laser distance sensors will be capable of reading the out of flatness condition. For the thinner strips, the strip tension is sufficient to flatten the strip while it is under tension (reverts to out of flat shape when tension is removed). For this reason, the force sensing roller measurement is used with the thinner strips.

Each laser 52 measures the distance from itself to the bottom surface of the strip. Variations in distance among the array of sensors is indicative of strip flatness issues. The flatness controller commands the leveler work roll positions to achieve uniform distance measurements in the array of laser sensors, thus achieving a flat strip.

In addition, the flatness control scheme also departs from the known methods of close looping a leveler. Known control schemes establish a tight correspondence between a sensing zone and the back-up roll flight that is in the same zone.

This is not necessary, as the work roll face integrates the movements of the various back-up flights. Additionally, it is not practical from a fatigue stress standpoint, to have huge differences in vertical position of adjacent back-up roll flights 23 (FIG. 5).

The flatness control scheme of the disclosure is designed to prevent premature fatigue failure of leveler work rolls, and to simplify the movements of the back-up rolls in response to the flatness sensors.

The new flatness control scheme looks at the totality of the flatness sensor outputs to assess whether the primary out of flat condition is dominated by edge wave or centerbuckle. In addition, the flatness control looks at whether the out of flatness condition is parallel to a horizontal plane. When the shape is not parallel to a horizontal plane, the flatness controller will call for an asymmetric profile for the positions of the backup rolls.

The flatness control moves all the adjustable flights in a prescribed manner that results in a smooth curvature of the work rolls, and flight to flight differences are limited to prevent fatigue stresses in the work roll. The amplitude of the variances in the flatness measurements is used to determine the degree of leveler work roll bending used in the correction move, the range is typically from 0% roll bend to 80% roll bend. At 80% work roll bend the control will deepen the overall entry plunge setting of the leveler as opposed to further increases in the position difference between adjacent flights.

The flatness control system also monitors the torque of the work roll drive motors. If the requested plunge settings approach a max limit a warning is displayed to the operator, as a signal that the leveler is at its max settings and flatness may still have not been achieved.

The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modification and alterations will occur to others upon a reading and understanding of the detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations.

CLOSED LOOP ROLLER LEVELER

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