Rolling Mill Stand Controller

Hydraulic cylinders for changing the work roll gap are located in either the top or bottom of the mill stand. The HGC control performs closed loop position and pressure regulation of the gap cylinders, depending on the operating mode selected.

HGC Reference Generation

During the mill setup sequence, preset position and roll separating force references are received from an external Level 2 mill setup system or from an operator data entry interface. During rolling, reference modifiers for position and force are received from the Level 2 controls. These modifiers include the average and differential position/force offsets for automatic gauge control (AGC), interstand tension control (ITC), and automatic flatness control (AFC). Operator manual references for average and differential offsets are added at Level 1.

Additional reference position and force offsets are received from an external roll eccentricity compensation (ECC) system. Due to the update speed required for ECC (1 millisecond scan), the ECC reference offsets may be acquired through hardwired analog inputs.

HGC Position and Force Regulation

Independent position or force regulation loops are implemented for the operator and drive side cylinders, depending on HGC operating mode. A supervisory differential position or force loop maintains the desired offset between the operator and drive sides, correcting errors caused by differences in dynamic response between the sides. If excessive differential force is detected, the HGC control is placed in Fault mode and further movement is prohibited. When position regulation mode is active, force regulation is suspended and vice-versa. A bumpless transition mechanism between position and force modes is provided.

Position feedback is provided by Sony Magnescale transducers. Each cylinder is typically fitted with two position transducers, one on the inside and one on the outside of the cylinder, each with separate signal conditioners. If there is no transducer fault, the inside and outside transducer signals are averaged for each cylinder to produce the position feedback value. If one of the transducers is faulted, the other is used alone. If both transducers are faulted, the HGC control is placed in the Fault mode and further movement is prohibited.

HGC Operating Modes

The HGC operating mode is generally selected automatically by the state of the mill stand. The mill operator does not typically select the operating mode. The Fault Mode is entered on intial system startup.

• Position Mode - closed-loop position regulation
• Force Mode - closed-loop force regulation
• Velocity Mode - fixed velocity reference to servos (cylinders retract at fixed rate; used when HGC Stop is selected)
• Vent Mode - full open reference to servo valves (dump all hydraulic pressure)
• Fault Mode - null reference to servo valves (hold cylinders at current position)

Hydraulic cylinders acting on the work roll chocks provide positive and negative roll bending. Depending on the mill stand configuration, intermediate rolls with associated bending cylinders acting on their chocks may also be installed. The bending cylinders also provide the roll balancing forces required to maintain a gap between the work rolls when there is no separating force. The WRB/IRB control performs closed loop pressure regulation of the bending cylinders.

WRB/IRB Reference Generation

During the mill setup sequence, preset pressure references for the bending cylinders are received from the Level 2 mill setup system or from an operator data entry interface. During rolling, a reference modifier for each bending system is received from the Level 2 automatic sheet flatness control (AFC). The operator manual reference offsets are added at Level 1.

Fixed roll balancing references are applied when there is no roll force on the stand. There may be several such references, depending on whether the roll stack is being balanced, raised, or lowered. In addition, there is a fixed bending reference applied during the mill gap calibration sequence.

WRB/IRB Pressure Regulation

In pressure regulation mode, a single pressure regulation loop is generally implemented for each roll bending system. However, depending on the mechanical roll stack configuration, independent operator and drive side regulation loops may be implemented.

WRB/IRB Operating Modes

The WRB/IRB operating mode is generally selected automatically by the state of the mill stand. The mill operator does not typically select the operating mode. The Fault Mode is entered on intial system startup.

• Pressure Mode - closed-loop pressure regulation
  • (Reference = preset + Level 2 offset + operator offset)
• Calibration Mode - closed-loop pressure regulation
  • (Reference = fixed gap calibration reference)
  • Automatically entered during the mill gap calibration sequence
• Balance Mode - closed-loop pressure regulation
  • (Reference = fixed balance reference)
  • Automatically entered when there is no roll force on the stand
• Roll Change Mode - closed-loop pressure regulation
  • (Reference = fixed roll change reference)
  • Entered when the stand is placed in roll change state
• Fault Mode - null reference to servo valves (hold cylinders at current pressure)

Balancing cylinders act on the backup roll chocks to balance the weight of the rolls and to allow them to be raised or lowered as necessary. The BRB control performs closed loop pressure regulation of the balancing cylinders.

BRB Reference Generation

During the mill setup sequence, a preset pressure reference for the BRB cylinders is received from the Level 2 mill setup system or from an operator data entry interface. No reference modifiers are required.

Additional fixed balancing references are generated at Level 1. These depend on whether the top backup roll is being raised or lowered during roll changing. In addition, there is a fixed balancing reference applied during the mill gap calibration sequence.

BRB Pressure Regulation

In pressure regulation mode, a single pressure regulation loop is implemented for all active cylinders in the backup roll balancing system.

BRB Operating Modes

The BRB operating mode is generally selected automatically by the state of the mill stand. Except for "Raise" and "Lower", the mill operator does not typically select the operating mode. The Fault Mode is entered on initial system startup.

• Balance Mode - closed-loop pressure regulation
  • (Reference = balance preset)
• Calibration Mode - closed-loop pressure regulation
  • (Reference = fixed gap calibration reference)
  • Automatically entered during the mill gap calibration sequence
• Raise Mode - closed-loop pressure regulation
  • (Reference = fixed roll raise reference)
  • Bottom roll cylinders (if applicable) are vented
  • Entered when "Backup Raise" is selected with the stand in roll change state
• Lower Mode - vent all piston side cylinder pressure
  • Used to lower the top backup rolls onto the roll changing rig
  • Entered when "Backup Lower" is selected with the stand in roll change state
• Stop Mode - vent all piston side cylinder pressure
  • Pressurize rod side to retract all cylinders (if applicable)
• Fault Mode - null reference to servo valves (hold cylinders at current pressure)