Low tension cascade mill speed control by current measurement with temperature compensation

A method of controlling the motor speeds between adjacent mill stands of a continuous rolling mill to reduce tractive forces in a rolled material including the steps of:

• measuring a first value of current I.sub.N (t1) drawn by a mill stand motor N at time t1 when there is no tractive force in the rolled material;
• measuring a first temperature TEMP1 at the surface of the rolled material while positioned at stand N and corresponding to the time t1 when said first value of current is measured;
• measuring a second value of current I.sub.N (t2) drawn by said mill stand motor N at time t2 when there is a tractive force in the rolled material;
• measuring a second temperature TEMP2 at the surface of the rolled material while positioned at stand N and corresponding to the time t2 when said second value of current is measured;
• generating a correction factor S.sub.N of the form:
• S.sub.N =I.sub.N (t1)-I.sub.N (t2)+K.sub.T (TEMP1-TEMP2)I.sub.N (t1)
• where
• S.sub.N =tension current between two successive rolling stands N, N+1;
• I.sub.N (t1)=the current drawn by the motor of stand N for a no tension condition at time t1;
• I.sub.N (t2)=the current drawn by the motor of stand N for a tension condition at time t2;
• K.sub.T =a proportionality constant relating a change in temperature to a change in current for a motor of rolling stand N;
• TEMP(t1)=the temperature of the surface of said workpiece at the location of stand N at time t1;
• and
• TEMP(t2)=the temperature of the surface of said workpiece at the location of stand N at time t2;
• and correcting one of the said mill stand motor speeds in a direction tending to null S.sub.N.

A method of controlling the motor speeds between adjacent mill stands of a continuous rolling mill to reduce tractive forces in a rolled material including the steps of:

• measuring a first value of current I.sub.N (t1) drawn by a mill stand motor N at time t1 when there is no tractive force in the rolled material;
• measuring a second value of current I.sub.N (t2) drawn by said mill stand motor N at time t2 when there is a tractive force in the rolled material;
• generating a current correction profile which has values of correction current different from an average current due to temperature variations in the rolled material, said profile comprising at least two values I.sub.1 (t1), I.sub.1 (t2) corresponding to the times said first and second values of current are measured;
• and
• generating a correction factor S.sub.N of the form:
• ##EQU6## where S.sub.N =tension current between two successive rolling stands N, N+1;
• I.sub.N (t1)=the current drawn by the motor of stand N for a no tension condition at time t1;
• I.sub.N (t2)=the current drawn by the motor of stand N for a tension condition at time t2;
• I.sub.1 (t)=current of stand 1 at time t;
• OFFSET(N)=time between stand 1 and stand N;
• and correcting the speed of said mill stand motor N in a direction tending to null S.sub.N.

A cascade speed controller for a plurality of rolling mill stands of a continuous rolling mill having a closed loop motor speed controller associated with each stand, wherein each closed loop motor speed controller controls the actual speed of a motor of an associated rolling mill stand to follow a speed reference signal, said cascade speed controller comprising:

• means for measuring the current drawn by each motor and for generating actual current signals indicative of the measured currents;
• means for measuring the temperature at the surface of a workpiece rolled in said rolling mill and for generating a temperature signal indicative of the measured temperature;
• means for storing a plurality of temperature values comprising a temperature profile of said temperature signal and representing the surface temperature of the workpiece as a function of time and position for a predetermined interval and length, said predetermined interval and length corresponding to substantially the time and length of the workpiece required to travel between one of the plurality of rolling stands and the next of the plurality of rolling stands;
• means for generating an associated reference speed signal for each of said motor speed controllers;
• means for generating an associated individual correction signal for each stand as a function of a no tension current measurement, a plurality of tension current measurements, and temperature values from said stored temperature profile corresponding to said tension and no tension current measurements;
• means for modifying each reference speed signal by said associated individual correction signal;
• and
• means for combining said individual correction signals such that any individual correction signal associated with a rolling stand and the individual correction signal for the subsequent rolling stand.

A cascade speed controller for a plurality of rolling mill stands of a continuous rolling mill having a closed loop motor speed controller associated with each stand, each closed loop motor speed controller modifying the actual speed of a motor of an associated rolling stand to follow a speed reference signal, said cascade speed controller comprising:

• means for measuring the current drawn by each motor and for generating actual current signals indicative of the measured currents;
• means for measuring the temperature at the surface of a workpiece rolled in said rolling mill and for generating a temperature signal indicative of the measured temperature;
• means for storing a plurality of temperature values comprising a temperature profile of said temperature signal and representing the surface temperature of the workpiece as a function of time and position for a predetermined interval and length, said predetermined interval and length corresponding to substantially the time and length of the workpiece required to travel between one of the plurality of rolling stands and the next of the plurality of rolling stands;
• means for generating a reference speed signal for each of said motor speed controllers in sequence wherein each reference speed signal is generated as a function of a no tension current measurement, a plurality of tension current measurements, and temperature values from said stored temperature profile corresponding to said tension and no tension current measurements, said reference speed signals reducing tension between adjacent mill stands by setting a no tension speed ratio;
• and
• means for adjusting the speed ratio between adjacent stands to said no tension speed ratio based upon a speed adjustment to one of said adjacent stands caused by reducing tension between one of said adjacent stands and another stand in said sequence.