Metal deforming – With use of control means energized in response to activator... – Metal deforming by use of roller or roller-like tool element
Reexamination Certificate
1999-12-27
2001-07-24
Tolan, Ed (Department: 3725)
Metal deforming
With use of control means energized in response to activator...
Metal deforming by use of roller or roller-like tool element
C072S010300, C072S011800
Reexamination Certificate
active
06263714
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to rolling systems for reducing thickness of a sheet material and more particularly, to a periodic gauge deviation compensation system.
BACKGROUND OF THE INVENTION
When a strip of sheet material, such as metal, web or film, must be reduced in gauge or thickness, the material is normally processed by a rolling mill. The rolling mill passes the material strip between rolling cylindrical surfaces under pressure. Ideally, the rolling mill produces a coil of sheet at a thinner and constant gauge.
A typical single stand rolling mill feeds the material from an unwind reel to a rewind reel. The material strip is passed between work rolls that are acted upon by backup rolls. A force is applied to at least one of the backup rolls. Typically, the work rolls, backup rolls and unwind and rewind reels are not perfectly cylindrical due to a number of reasons including temperature effects, wear, and mechanical inconsistencies. As a result, periodic deviations are impressed on the metal throughout the course of rolling. In addition, cyclical perturbations may have been impressed on the material sheets due to earlier processing. Periodic or cyclical perturbations in the gauge are obviously undesirable. Indeed, they constitute the most significant component of material thickness deviation in modern rolling mills. These thickness deviations are an important concern in the production of sheet, web, and film materials such as paper, plastic and metal.
The frequencies of the cyclical perturbations are a function of the rotation frequencies and associated harmonics of the mechanical components used in the rolling process. Typically, the disturbances vary at high frequencies relative to the frequency response of conventional gauge controls. This makes it difficult to eliminate their effects with standard control techniques employing measured thickness. One known solution samples exit thickness of the sheet at fixed angular intervals based on a signal read from an encoder mounted on the roll's axis. This technique synchronizes sampling to the angular displacement of the roll, insuring that the phase relationship between disturbance, measurement, and controls remains fixed. For each rotation of the roll, the fast Fourier transform of the sample signal is computed to determine the phase and magnitude of gauge disturbances at frequencies which are integral multiples of the roll revolution rate. These frequencies are set and only these frequencies are tracked. From this information, an output to control the roll separating force or work roll gap is computed to correct the eccentricity disturbance. However, such a solution requires the mounting and continued adjustment of encoders on the rolls. These systems also ignore cyclical perturbations of incoming material. Also, this solution does not correct for slippage or extrusion occurring in the process which then results in phase shifts. This can cause the rolling mill to actually add to the problem, rather than correct the problem.
The present invention is intended to solve one or more of the problems discussed above in a novel and simple manner.
SUMMARY OF THE INVENTION
In accordance with the invention, there is provided a rolling mill control system that removes or eliminates cyclical disturbances from a sheet or web by applying digital signal processing techniques to identify instantaneous and long term values of frequencies, magnitudes and phase angles of the disturbances. This system does not require the use of angular position encoders on the target rolls. Instead, the control scheme is based on material speed through the mill. The information about cyclical disturbances is processed to develop a set of compensating control signals which, when applied to process actuators, significantly attenuate or eliminate disturbances from the delivered product.
Broadly, a control system is provided for a rolling mill that feeds sheet material from an unwind reel to a rewind reel, passing it between a pair of work rolls. The control system includes a speed sensor for sensing speed of the sheet material. A force controller controls force exerted on the sheet material by the work rolls. A tension controller controls tension on the reels. A programmed controller is operatively connected to the speed sensor, the force controller and the tension controller, and stores information representing cyclical deviations in thickness of the sheet material and controls the force controller and the tension controller using the stored information and the sensed speed.
It is a feature of the invention that the force controller is operated to correct for work gap deviations caused by disturbances occurring in the current material pass. The force and tension controllers are operated to correct for deviations in incoming material.
It is another feature of the invention that a thickness gauge is connected to the programmed controller for sensing thickness of sheet material and the programmed controller generates the stored information responsive to the sensed thickness. The programmed controller uses a time series of the sensed thickness to detect the cyclical deviations.
It is a further feature of the invention that the programmed controller detects frequency, magnitude and phase changes in the cyclical deviations and adjusts control of the force controller and the tension controller responsive to detected frequency, magnitude and phase changes.
Further features and advantages of the invention will be readily apparent from the specification and from the drawings.
REFERENCES:
patent: 3763677 (1973-10-01), Mannaka et al.
patent: 3869891 (1975-03-01), Higham
patent: 3869892 (1975-03-01), Higham et al.
patent: 4428054 (1984-01-01), Aizawa et al.
patent: 4905491 (1990-03-01), Starke et al.
patent: 5101650 (1992-04-01), Fapiano
Johnson A. J.
Johnson James
Knapp David
Telepro, Inc.
Tolan Ed
Wood Phillips VanSanten Clark & Mortimer
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