Patent Description:
When manufacturing sheet material, such as a metal strip or sheet metal, the material is generally subjected to cold and hot rolling which provides the material with mechanical properties; however, residual stresses are generated within the material. The release of residual stresses within the material can be achieved by means of processes of straightening, stretch leveling, tension leveling, or by means of the roll leveling in a leveling machine.

The leveling machine has work rolls between which the sheet material is moved following a winding path from the inlet to the outlet of the leveler. The work rolls are arranged in an upper row and a lower row between which the sheet material is moved. By means of rotation of the rolls and by the exerted friction, the sheet material is moved forward at a pre-established setpoint speed. The winding path the material follows through the rolls causes the fibers of the surface of the sheet material to be subjected to tensile and compression stresses, causing a plastic deformation that corrects the defects. Generally, <NUM>-<NUM>% of the material exceeds the yield strength during deformation.

The shafts of the rolls of each row of rolls are parallel to one another, but the upper row of rolls is designed with a tilt, such that the deformation induced by the rolls arranged at the inlet of the leveler is greater than that induced by the rolls arranged at the outlet, and therefore the deformation of the material gradually decreases from the inlet towards the outlet as the sheet material moves forward. Therefore, the leveling process is divided into a first part in which the rolls of the inlet of the leveler subject the sheet material to elevated deformations, and a second part in which the rolls of the outlet of the leveler eliminate the curvature that the sheet material has acquired.

The rolls of the leveler can be operated with a single drive, but given that the process is divided into the two parts in which the inlet rolls generate more stress than the outlet rolls, leveling machines formed by a first group of rolls operated by means of a first drive and a second group of rolls operated by means of a second drive which is independent of the first drive, such that each group of rolls of the leveling machine can be controlled independently are known (see for example <CIT>, <CIT>, and <CIT>).

<CIT> , on which the preamble of claims <NUM> and <NUM> is based, shows a control method of a leveling machine which comprises moving a sheet material between a first group of work rolls and a second group of work rolls following a winding path from the first group to the second group according to a setpoint speed, driving the first group of work rolls by means of a first drive, and driving the second group of work rolls by means of a second drive which is independent of the first drive.

The second drive is controlled by means of the setpoint speed and a first torsion torque value of the second drive is measured when the second drive operates at the setpoint speed. A second torsion torque value defining a relationship with the first torsion torque value is subsequently determined, and the second torsion torque value is applied on the first drive maintaining the relationship between the first and the second torsion torque value. The torsion torque value which is applied to a drive based on the torsion torque value which is measured in the other drive is thereby controlled, maintaining a constant relationship between them during the movement of the sheet material.

The invention provides a control method of a leveling machine and a leveling machine, as defined in independent claims <NUM> and <NUM>.

One aspect of the invention relates to a control method of a leveling machine which comprises:.

Another aspect of the invention relates to a leveling machine comprising:.

The invention allows to obtain in a simple manner an equitable distribution of the stresses generated by the drives of the groups of work rolls, and therefore to obtain an optimized energy consumption of the leveling machine. The two drives are controlled independently by means of a respective torque setpoint signal which is a function of an error signal obtained from the difference between the setpoint speed at which the drives are to be operated for moving the sheet material and the real speed of the drive. The control method thereby measures the real speed of the drives and compares it with the setpoint speed, and the obtained error signal is used for acting on the setpoint torque of the drive, said setpoint torque being directly proportional to the error signal. The second torque setpoint signal applied to the second drive is also a function of an additional torque gain, whereby the setpoint torque applied to the second drive which is arranged at the outlet of the leveling machine is greater than in a conventional leveling machine in which said additional torque gain is not applied.

Therefore, the first group of rolls is used for applying the force required for deforming the sheet material and eliminating residual stresses, whereas the additional torque gain applied to the second drive allows the second group of work rolls to eliminate the curvature the sheet material has acquired when passing through the first group of work rolls, and furthermore allows the second group of work rolls to pull on the sheet material, helping to remove it from the leveler, therefore preventing the first group of rolls from having to perform said pulling effort and being able to concentrate the efforts in the deformation.

These and other advantages and features of the invention will become apparent in view of the figures and detailed description of the invention.

<FIG> shows a leveling line for leveling a sheet material <NUM> comprising a leveling machine <NUM> for leveling the sheet material <NUM>. The line comprises a reel <NUM> for supplying the sheet material <NUM>, drive rolls <NUM> for driving the sheet material <NUM>, and the leveling machine <NUM> of the sheet material <NUM>. The sheet material <NUM> is supplied according to a forward movement direction A from the reel <NUM> towards the leveling machine <NUM>.

The sheet material <NUM> can be supplied in the form of a continuous strip, as shown in <FIG>, or in the form of sheet metal.

The drive rolls <NUM> are a pair of rolls between which the sheet material <NUM> is forced to pass. As shown in <FIG>, the drive rolls <NUM> are arranged upstream of the leveling machine <NUM>, although they can also be arranged downstream of the leveling machine <NUM>, or there can be two sets of drive rolls <NUM>, one upstream of the leveling machine <NUM> and another one downstream of the leveling machine <NUM>, or there may be no drive rolls <NUM> and the sheet material <NUM> is supplied directly from the reel <NUM> to the leveling machine <NUM>.

The leveling machine <NUM> comprises a first group of work rolls <NUM> and a second group of work rolls <NUM> defining a winding path for moving the sheet material <NUM> from the first group <NUM> to the second group <NUM> according to a setpoint speed V*, a first drive <NUM> for driving the first group of work rolls <NUM>, a second drive <NUM> for driving the second group of work rolls <NUM>, which is independent of the first drive <NUM>, and a controller <NUM> of the drives <NUM> and <NUM>.

The first drive <NUM> is a first motor for driving the first group of work rolls <NUM>. The second drive <NUM> is a second motor for driving the second group of rolls.

The first motor <NUM> is coupled to the shafts of the rolls of the first group of work rolls <NUM> by means of a first system of gears and first transmission rods. The second motor <NUM> is coupled to the shafts of the rolls of the second group of work rolls <NUM> by means of a second system of gears and second transmission rods. The shaft of the first motor <NUM> is connected to the first system of gears driving the first transmission rods connected to each roll of the first group of work rolls <NUM>. The shaft of the second motor <NUM> is connected to the second system of gears driving the second transmission rods connected to each roll of the second group of work rolls <NUM>. The transmission between a motor and the rolls by means of gears and transmission rods is known in leveling machines and not depicted in the figures.

As can be seen in <FIG>, the work rolls <NUM> and <NUM> are arranged in an upper row and a lower row facing one another and separated by a distance for generating the winding path through which the sheet material <NUM> is moved. Generally, the upper row has an even number n of rolls <NUM>, and the lower row <NUM> has an uneven number n+<NUM> of rolls <NUM>, nevertheless, the rows can have other configurations with a different number of rolls.

The shafts of the rolls of each row of rolls are parallel to one another, and one of the rows (generally the upper row) is tilted with respect to the other row, such that the separation between the rolls arranged at the inlet of the leveler <NUM> is less than the separation between the rolls arranged at the outlet of the leveler <NUM>. Therefore, the deformation induced by the rolls arranged at the inlet of the leveler is greater than the deformation induced by the rolls arranged at the outlet; therefore, the deformation of the sheet material <NUM> gradually decreases from the inlet towards the outlet of the leveling machine as the sheet material <NUM> moves forward.

Therefore, the leveling process is divided into two parts, the first part corresponds to the one which occurs in the first group of work rolls <NUM>, and the second part corresponds to the one which occurs in the second group of work rolls <NUM>. In the first part, the penetration exerted by the rolls <NUM> is greater, and the sheet material <NUM> develops areas of plastic deformation which increase as the sheet material <NUM> is bent between the rolls <NUM>, until reaching a maximum plasticized thickness. Due to the strong bends in this first part, a stress profile is generated in the thickness of the sheet material. For that purpose, after the first part, the penetration exerted on the sheet material <NUM> decreases until, at the outlet, the rolls <NUM> barely deform the sheet material <NUM>. The purpose of the second part is to gradually eliminate the curvature of the sheet material <NUM> and reduce the stress gradient generated in the first part.

It has experimentally been found that when the two drives <NUM> and <NUM> are operating at the same speed, the first group of work rolls <NUM> performs a greater effort than the second group of work rolls <NUM>, such that the torsion torque exerted by the first drive <NUM> of the first group of work rolls <NUM> is greater than the torsion torque exerted by the second drive <NUM> of the second group of work rolls <NUM>. To that end, the purpose of the invention is to obtain a more equitable distribution of the stresses generated by the drive <NUM>, <NUM> of each group of work rolls <NUM> and <NUM>, such that the first group <NUM> carries out its function of deforming the sheet material <NUM>, and the second group <NUM> carries out its function of eliminating the curvature, but furthermore the second group <NUM> performs an additional effort for pulling the sheet material <NUM>, helping to remove it from the leveling machine <NUM>.

The control method of the leveling machine <NUM> comprises:.

The setpoint speed V* is pre-established and is the speed at which the drives <NUM> and <NUM> are required to operate for moving the sheet material <NUM> in the forward movement direction A of the leveling line.

Speeds V1 and V2 of the first and second drives <NUM> and <NUM> can be measured with encoders coupled to the shafts of the drives, such as magnetic encoders, optical encoders, etc. Alternatively, other detection elements instead of encoders can be used for measuring the speed of the drives.

The speed V1 is the speed measured in the shaft of the first motor <NUM>. The speed V2 is the speed measured in the shaft of the second motor <NUM>.

<FIG> shows a control diagram with proportional controllers P for controlling the speed V1 and V2 of each drive <NUM> and <NUM> of the leveling machine <NUM>. The speed V of each drive is controlled by means of a torque setpoint signal T* which is a function of an error signal e(t) obtained from the difference between the setpoint speed V* and the real speed measured in the drive.

The torque setpoint signal T* of each drive <NUM> and <NUM> is directly proportional to the error signal e(t) according to the following expression: <MAT> wherein Kp is a constant.

The constant Kp is the constant characteristic of proportional controllers P, and it is the same for the two drives.

A proportional controller P is thereby used for applying the torque setpoint signal T* to each drive which is directly proportional to the error signal e(t). The very nature of the proportional controller P means that there is always an error signal e(t) that generates a torque setpoint T* with which it is possible to control the drives <NUM> and <NUM>. If a proportional integral controller PI is used for generating the torque setpoint signal based on said error signal e(t), the controller PI would tend to achieve zero error in speed (permanent regimen), such that it would not be possible to control the stresses generated by the two drives, whereby in practice the first drive <NUM> would end up performing a greater effort than the second drive <NUM>.

The speed V1 of the first drive <NUM> is controlled by means of the first torque setpoint signal T1* which is a function of the first error signal e1 according to the following expressions: <MAT> <MAT> wherein:.

The speed V2 of the second drive <NUM> is controlled by means of the second torque setpoint signal T2* which is a function of the second error signal e2 according to the following expressions: <MAT> <MAT> wherein:.

As shown in <FIG>, the method comprises controlling the speed V2 of the second drive <NUM> by means of a second additional torque setpoint signal T2** according to the following expression: <MAT> wherein:.

As shown in <FIG>, K2 is a constant which is applied to the second torque setpoint signal T2*. Said constant is determined beforehand based on the conditions of the leveling line, and chosen based on the torsion torque required to be applied to the second drive <NUM> of the second group of rolls <NUM>.

Alternatively, for applying the additional torque gain, it is possible to directly modify the constant Kp of the proportional controller P of the second drive <NUM> and obtain the second desired torque setpoint signal T2*.

An example of the control method for a time instant in which the setpoint speed V* is <NUM> rpm, the real speed V1 measured in the first drive <NUM> is <NUM> rpm, and the real speed V2 measured in the second drive <NUM> is <NUM> rpm is shown below, being <NUM> the constant Kp of the proportional controller for both drives. By applying the control method without the additional torque gain, a first torque setpoint signal T1* of <NUM> and a second torque setpoint signal T2* of <NUM> would be obtained.

In this case, the second torque setpoint signal T2* is greater than the first torque setpoint signal T1*. According to this example, an increase in torque in the second drive <NUM> with respect to the first drive <NUM> is achieved by adding the additional torque gain to the second drive <NUM>. For example, by applying a constant K2 of <NUM>, a second additional torque setpoint signal T2** of <NUM> would be obtained for the previously indicated time instant, whereby the second drive <NUM> would perform <NUM>% more torque than the first drive <NUM>, as shown below. <MAT> <MAT>.

Additionally, if an increase in torque in the first drive <NUM> is to be obtained, another additional torque gain can be applied to the first torque setpoint signal T1* in the same way that has been described for the second drive <NUM>. To that end, as shown in the example of <FIG>, the method comprises controlling the speed V1 of the first drive <NUM> by means of a first additional torque setpoint signal T1** according to the following expression: <MAT> wherein:.

Generally, K1=<NUM>; nevertheless, based on the conditions of the leveling line it may be necessary to apply the other additional torque gain to modify the torque applied to the first drive <NUM>, K1 also being a constant which is determined beforehand based on the conditions of the leveling line.

Claim 1:
Control method of a leveling machine which comprises:
- moving a sheet material (<NUM>) between a first group of work rolls (<NUM>) and a second group of work rolls (<NUM>) following a winding path from the first group (<NUM>) to the second group (<NUM>) according to a setpoint speed (V*),
- driving the first group of work rolls (<NUM>) by means of a first drive (<NUM>),
- driving the second group of work rolls (<NUM>) by means of a second drive (<NUM>), which is independent of the first drive (<NUM>), and
- measuring the speed (V1) of the first drive (<NUM>) and measuring the speed (V2) of the second drive (<NUM>),
characterized in that the method additionally comprises:
- controlling the speed (V1) of the first drive (<NUM>) by means of a first torque setpoint signal (T1*) which is a function of a first error signal (e1) obtained from the difference between the setpoint speed (V*) and the speed (V1) of the first drive (<NUM>), and
- controlling the speed (V2) of the second drive (<NUM>) by means of a second torque setpoint signal (T2*) which is a function of a second error signal (e2) obtained from the difference between the setpoint speed (V*) and the speed (V2) of the second drive (<NUM>), and is also a function of an additional torque gain.