CLOSED LOOP ROLLER LEVELER

Abstract

A closed loop roller leveler system has a roller leveler; a flatness sensor; and at least one arm for raising and lowering the flatness sensor. The sensor includes a plurality of sensing rollers extending across a width of a strip of material. The sensor further has at least one load cell and at least one laser sensor for measuring the flatness level of the strip.

Claims

1. A closed loop roller leveler system comprising: a roller leveler; a flatness sensor; at least one arm for raising and lowering said flatness sensor; said flatness sensor comprising a plurality of sensing rollers extending across a width of an associated strip of material; said sensor further comprising at least one load cell and at least one laser sensor.

2. The closed loop leveler system of claim 1, wherein said at least one arm comprises a pair of hydraulic cylinders.

3. The closed loop leveler system of claim 2, wherein said pair of hydraulic cylinders raise and lower said plurality of sensing rollers.

4. The closed loop leveler system of claim 3, wherein each of said plurality of sensing rollers is mounted on a pivot bracket.

5. The closed loop leveler system of claim 1, wherein said flatness sensor is used to measure flatness of light gage strip.

6. The closed loop leveler system of claim 1, wherein said flatness sensor is used to measure flatness of heavy gage strip.

7. The closed loop leveler system of claim 1, wherein each of said sensing rollers are mounted on one of said load cells.

8. The closed loop leveler system of claim 1, wherein said laser sensors are mounted on a support beam.

9. The closed loop leveler system of claim 1, wherein each of said sensing rollers move up and down in unison.

10. A method for measuring flatness levels of a strip of material comprising: providing a roller leveler; providing a flatness sensor; raising and lowering said flatness sensor with a plurality of hydraulic cylinders; providing a plurality of sensing rollers extending across a width of an associated strip of material; providing at least one load cell and at least one laser sensor; feeding said strip of material through said roller leveler; and feeding said strip of material through said flatness sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 is a perspective view of a crown (upper half) of an existing leveler with the upper back up rolls mounted thereon.

[0037] FIG. 2 is a perspective view of an upper work roll sub-assembly of FIG. 1.

[0038] 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.

[0039] FIG. 4 is a perspective view of a flight of lower back up rolls of FIG. 1.

[0040] FIG. 5 is a perspective view of the lower back-up roll flights mounted in the lower half of the leveler of FIG. 1.

[0041] 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.

[0042] FIG. 7 is an enlarged perspective view of the flatness sensor of FIG. 6.

[0043] 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.

[0044] FIG. 9 is a cross-sectional view of a sensing roll module of FIG. 10a.

[0045] FIG. 10a is a front elevational view of multiple sensing roll modules extending across the width of the strip.

[0046] FIG. 10b is an enlarged cross-sectional view of one of the sensing roll modules.

[0047] 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

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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).

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.