Hot Strip Mill Looper Control Inertia Compensation
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Solution Overview
Problem
In hot strip mills, looper instability due to inertia causes delays in height changes of looper rolls, leading to reduced controller sensitivity and suboptimal tension control, especially when handling heavy gauge and wide products.
Innovation Solution
A method that calculates a desired speed trim for upstream rollers and estimates the looper's inertia to determine the necessary torque to overcome inertia, allowing for precise control of looper height and tension without reducing controller gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the speed of upstream rollers is controlled to increase or decrease the length of strip in an inter-stand section, then the length of strip can be adjusted, but the height of the looper roll will not change instantaneously due to inertia, causing delay and looper instability
Solution Approach 1:
The controller calculates and applies a preliminary torque to the looper arm in advance of the actual height change requirement. This preliminary action accounts for the inertia of the looper, ensuring that the torque is sufficient to overcome the inertial resistance and achieve the desired height change without delay or instability.
Solution Approach 2:
The system uses feedback from the measured angle of the looper arm to continuously monitor the actual position and adjust the torque applied by the looper motor. This closed-loop control ensures that the looper height changes accurately and stabilizes quickly, compensating for inertial effects.
2Stability of the object's composition
If the gain of the controller for upstream rollers is set at a lower level to avoid looper instability, then stability is maintained, but the controller has reduced sensitivity to disturbances in operating conditions
Solution Approach 1:
The controller dynamically adjusts the torque parameter based on the measured looper arm angle and the calculated inertia effects. By changing the torque parameter in real-time according to the actual system state, the controller maintains high sensitivity to disturbances while ensuring stability through proper torque management.
3Device complexity
If the torque applied by the looper motor is kept constant, then the control system is simple, but the strip tension changes when the height of the looper roll changes due to disturbed mass flow
Solution Approach 1:
The control system transitions from a static constant torque approach to a dynamic torque control approach. The torque applied by the looper motor is continuously adjusted based on the measured looper arm angle and the calculated inertia, allowing the system to maintain constant strip tension even when the looper height changes due to mass flow disturbances.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances controller sensitivity and stability, enabling faster correction of tension and height changes during disturbances, maintaining constant strip tension and reducing looper instability.
Implementation Method 1
each looper has an associated looper motor which applies a torque to the looper arm. This torque is transmitted, via the looper arm, to the looper roll, which then applies a force to the strip as a result of the torque
Implementation Method 2
the height of a looper roll will not change instantaneously. This is due to the inertia of the looper and the looper motor
Data Source
AI summary
The present invention provides a method of controlling the height of a looper in an inter-stand section of a hot strip mill that overcomes the problem of looper instability due to looper inertia without the need for the controller of upstream rollers to have a reduced gain. The inter-stand section of the hot strip mill comprises a pair of upstream rollers driven by a main motor and a looper driven by a looper motor. The method comprises the steps of: calculating a desired speed trim to be applied by the main motor; estimating the inertia of the looper; calculating a torque necessary to overcome the inertia of the looper from the speed trim, the estimated inertia of the looper and a sensitivity calculated from the geometry of the looper; and controlling the main motor to apply the speed trim to the upstream rollers and controlling the looper motor to apply the calculated torque to the looper.