Stepped Rolling Strip Tension Control With Dancer Roller Positioning
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Solution Overview
Problem
Existing methods for controlling strip tension in step-rolling metal strips are unstable and ineffective in maintaining constant tension during rapid changes in roll gap size and resulting thickness differences, due to the high mass inertia of take-up reels and indeterminate position control of roller units.
Innovation Solution
Regulating the decoiler speed to a constant desired speed and using position control of the roller unit in the strip storage device to compensate for rapid changes in thickness, with the take-up reel maintaining a predetermined nominal strip tension and the roller unit adjusting its position to fix target positions, thereby stabilizing strip tension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the winding reel is used to regulate discharge-side strip tension, then constant strip tension is maintained at low rolling speeds, but the system cannot compensate for rapid changes in thickness due to high moment of inertia
Solution Approach 1:
The control system is divided into two independent control loops: an outer loop using the winding reel for average tension control, and an inner loop using the dancer roller for rapid tension fluctuations. This segmentation allows each component to operate within its optimal response characteristics.
Solution Approach 2:
The dancer roller is introduced as a dynamic element with low moment of inertia that can rapidly adjust to compensate for quick thickness variations. This dynamic component works in conjunction with the more inertial winding reel to provide both stability and responsiveness.
2Reliability
If the dancer roller is force-controlled to maintain desired belt tension, then tension control is achieved, but the roller unit position becomes indeterminate leading to instabilities
Solution Approach 1:
A position feedback system is implemented for the dancer roller, where the actual position is continuously measured and fed back to the controller. This closed-loop position control eliminates the indeterminacy inherent in force-only control and prevents oscillations.
Solution Approach 2:
The dancer roller serves dual functions: it maintains strip tension through force control while simultaneously providing stable position reference through position control. This multi-functionality resolves the contradiction between tension control and position stability.
3Reliability
If the winding reel regulates strip tension, then sufficient tension control is achieved at low speeds, but the system becomes unsuitable for rapid roll gap changes due to excessive moment of inertia
Solution Approach 1:
The control system is divided into two independent control loops: an outer loop using the winding reel for average tension control, and an inner loop using the dancer roller for rapid tension fluctuations. This segmentation allows each component to operate within its optimal response characteristics.
Solution Approach 2:
The dancer roller is introduced as a dynamic element with low moment of inertia that can rapidly adjust to compensate for quick thickness variations. This dynamic component works in conjunction with the more inertial winding reel to provide both stability and responsiveness.
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 ensures constant strip tension on the outlet side even with dynamic changes in roll gap and thickness, preventing temporary instabilities and maintaining stability with lower mass inertia of the roller unit compared to the take-up reel.
Implementation Method 1
a position control of the roller unit in the exit-side strip accumulator is superimposed on the aforementioned control of the strip tension using the winding reel
Implementation Method 2
the tape accumulator, particularly during operation, possibly also in conjunction with the take-up reel, can be considered a spring-mass system which, when operating near its resonant frequency, tends to oscillate uncontrollably
Implementation Method 3
The at least one roller unit in the outgoing belt storage, which is, for example, a dancer roller, is force-controlled so that a desired belt tension is present
Data Source
Figure 1~3
AI summary
The invention relates to a method for operating a roll stand for stepped rolling of a metal strip (200). According to the method the metal strip (200) is firstly introduced on the infeed side into a roll stand (100) and there undergoes stepped rolling. An upstream and a downstream portion (220, 210) of the metal strip are thus created and have a different thickness from one another. The difference in thickness is Ahi. After the roll stand, the stepped-rolled metal strip passes firstly through an outfeed-side strip store before it is wound into a coil with the aid of a winding reel. The outfeed-side reel is regulated to a constant strip tension. In order to be able to keep the outfeed-side strip tension sufficiently constant even in the event of rapid changes to the size of the rolling gap and resultant rapid changes in thickness in the rolled metal strip, according to the invention, the regulation of the strip tension with the aid of the winding reel is complemented by position regulation for a roller unit in the outfeed-side strip store.