Rolling mill third octave chatter control by process damping

1. A cold-rolling mill with reduced chatter, comprising:

a mill stand having a top work roll and a bottom work roll between which a metal strip can be passed, the mill stand comprising a hydraulic cylinder mechanically coupled to provide a rolling force to the top work roll, wherein the mill stand has damping contributing to a process damping associated with using the mill stand to reduce a thickness of the metal strip at a mill speed, and wherein a reduction in the process damping is associated with an increase in the mill speed;

a piezoelectric assist coupled to the hydraulic cylinder for changing a volume of a fluid chamber of the hydraulic cylinder to introduce additional damping to the process damping; and

a controller coupled to a sensor selected from the group consisting of a pressure sensor of the hydraulic cylinder and a strip tension sensor, wherein the controller is further coupled to the piezoelectric assist for inducing changes in the volume of the fluid chamber in response to linear movement of the top work roll to introduce the additional damping in an amount sufficient to offset the reduction in the process damping and maintain the process damping at a positive amount of damping to avoid third octave chatter of the mill stand.

2. The cold-rolling mill of claim 1 , wherein the piezoelectric assist is coupled to the hydraulic cylinder for changing the volume of the fluid chamber of the hydraulic cylinder at rates at or above approximately 90 hertz.

3. The cold-rolling mill of claim 1 , wherein the sensor is the pressure sensor and the controller is operable to determine linear movement of the top work roll based on signals from the pressure sensor.

4. The cold-rolling mill of claim 1 , wherein the sensor is the strip tension sensor and the controller is operable to determine linear movement of the top work roll based on signals from the strip tension sensor.

5. The cold-rolling mill of claim 4 , wherein the strip tension sensor is at least one load cell coupled to a roller positionable proximal the mill stand.

6. The cold-rolling mill of claim 1 , wherein the controller is configured to:

calculate a pressure signal using the linear movement of the top work roll;

determine a force to apply through the piezoelectric assist using the pressure signal, wherein the force is calculated to provide the additional damping sufficient to avoid the third octave chatter of the mill stand; and

supply a control signal to the piezoelectric assist to apply the force through the piezoelectric assist.

7. The cold-rolling mill of claim 6 , wherein the controller includes a high pass filter for filtering out signals below approximately 90 hertz, and wherein the controller is further configured to filter the pressure signal through the high pass filter before determining the force to apply through the piezoelectric assist.

8. A method, comprising:

passing a metal strip between a top work roll and a bottom work roll of a mill stand having damping contributing to a process damping associated with using the mill stand to reduce a thickness of the metal strip at a mill speed, wherein a reduction in the process damping is associated with an increase in the mill speed;

applying a rolling force to the top work roll by a hydraulic cylinder;

measuring a parameter of the mill stand, wherein the parameter is a hydraulic pressure of the hydraulic cylinder or an entry tension of the metal strip;

determining vertical movement of the top work roll using the parameter; and

actuating a piezoelectric assist to change a volume of the hydraulic cylinder in response to the vertical movement of the top work roll to introduce additional damping in an amount sufficient to offset the reduction in the process damping and maintain the process damping at a positive amount of damping to avoid third octave chatter of the mill stand.

9. The method of claim 8 , further comprising determining a corrective force to apply to the top work roll based on the vertical movement of the top work roll, wherein actuating the piezoelectric assist is done based on the determined corrective force, and wherein the corrective force is calculated to provide the additional damping sufficient to avoid the third octave chatter of the mill stand.

10. The method of claim 8 , wherein actuating the piezoelectric assist is performed at a speed at or above approximately 90 hertz.

11. The method of claim 8 , wherein the parameter is the hydraulic pressure of the hydraulic cylinder.

12. The method of claim 8 , wherein the parameter is the entry tension of the strip.

13. The method of claim 8 , wherein determining the vertical movement of the top work roll comprises rejecting movements occurring below approximately 90 hertz.

14. The method of claim 8 , further comprising calculating a desired change in hydraulic fluid pressure of the hydraulic cylinder in response to the vertical movement of the top work roll, wherein actuating the piezoelectric assist is done based on the calculated desired change in hydraulic fluid pressure.

15. The method of claim 14 , wherein calculating the desired change comprises:

calculating a pressure signal using the vertical movement of the top work roll;

determining a force to apply through the piezoelectric assist using the pressure signal, wherein the force is calculated to provide the additional damping sufficient to avoid the third octave chatter of the mill stand; and

determining the desired change necessary to effect the determined force through the piezoelectric assist.

16. A method, comprising:

passing a metal strip between a top work roll and a bottom work roll of a mill stand having damping contributing to a process damping associated with using the mill stand to reduce a thickness of the metal strip at a mill speed, wherein a reduction in the process damping is associated with an increase in the mill speed;

applying a rolling force to the top work roll by a hydraulic cylinder having a volume of hydraulic fluid;

determining vertical movement of the top work roll based on a measurement of pressure of the hydraulic fluid or entry tension of the metal strip; and

supplying supplemental damping to the process damping to avoid third octave chatter of the mill stand, wherein supplying supplemental damping comprises:

determining an amount of supplemental damping sufficient to offset the reduction in the process damping and maintain the process damping at a positive amount of damping;

calculating a desired change in the pressure of the hydraulic fluid using the determined amount of supplemental damping; and

applying force to the volume of hydraulic fluid based on the calculated desired change, wherein applying force to the volume of hydraulic fluid comprises actuating a piezoelectric actuator coupled to the hydraulic cylinder.

17. The method of claim 16 , further comprising sensing the pressure of the hydraulic fluid, wherein the vertical movement is calculated based on the sensed pressure of the hydraulic fluid.

18. The method of claim 16 , further comprising sensing the entry tension of the metal strip, wherein the vertical movement is calculated based on the sensed entry tension of the metal strip.

19. The method of claim 16 , wherein determining the vertical movement of the top work roll comprises filtering out movements below approximately 90 hertz.

20. The method of claim 16 , wherein applying force to the volume of hydraulic fluid is performed at a speed at or above approximately 90 hertz.