Roll Changer Cascade Control with Adaptive Current Pre-Compensation
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Solution Overview
Problem
Existing roll changer control systems for web printing presses face inaccuracies due to unknown roll density, leading to overshooting and reduced control quality when accelerating rolls to target peripheral speeds.
Innovation Solution
A method using a current pre-control value offset by a preset density, which is adapted based on actual current values from the current control, to determine the input variable for the cascade control loop, ensuring precise control and avoiding overshoots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a cascade control circuit with preset density is used to control roll acceleration, then the control structure is simple and easy to implement, but the control precision deteriorates due to unknown actual roll density causing overshooting
Solution Approach 1:
The patent implements feedback by continuously measuring the actual current drawn by the motor during acceleration and using this measured value to update the pre-control variable. This closed-loop feedback mechanism allows the system to adapt to the actual roll density without requiring direct density measurement, thereby improving speed control precision while maintaining implementation simplicity.
Solution Approach 2:
The system uses the motor's own current consumption during acceleration as an indicator of the roll's actual density. By monitoring this self-generated signal and using it to adjust the pre-control variable, the system achieves adaptive control without external sensors or complex measurements, resolving the contradiction between simplicity and precision.
2Speed
If the pre-control variable is based on preset density calculations, then the control response is fast, but the accuracy deteriorates due to density variations between different rolls
Solution Approach 1:
The system exploits the motor current as a self-service indicator that naturally reflects the actual roll density during acceleration. This eliminates the need for separate density measurement devices while maintaining fast response, as the current data is already available from the motor control system during the acceleration process.
Solution Approach 2:
The patent dynamically changes the pre-control variable parameter based on measured current values during acceleration. Instead of using a fixed preset density value, the system adjusts this parameter in real-time according to the actual roll being accelerated, thereby maintaining fast response while improving accuracy across different roll densities.
3Manufacturing precision
If the current pre-control value is adapted to follow the actual current value, then the control precision is improved by avoiding overshoots, but the device complexity increases due to additional adaptation logic
Solution Approach 1:
The adaptation mechanism uses simple feedback comparison between the pre-control variable and the normalized actual current value. When they differ, the pre-control variable is updated to match the measured value. This straightforward feedback loop improves precision without introducing complex control logic, as it builds upon the existing cascade control structure.
Solution Approach 2:
The patent uses the motor current as an intermediary parameter that bridges the gap between the control system and the physical roll properties. By adapting the pre-control variable through this intermediary (current) rather than directly measuring density, the system achieves higher precision while keeping the control logic relatively simple and integrated with existing motor control infrastructure.
Data Source
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Figure 2
AI summary
Method for controlling a roll changer, with a cascade control loop (14) consisting of a current control (15) and a speed control (16) superimposed on the current control for controlling the speed of a motor (13) driving a printing material roll (10) and thus for controlling the peripheral speed of the printing material roll.the web speed of a substrate web (12) to be unwound from the substrate roll, wherein the speed control (16) outputs an output variable (22) depending on a speed setpoint (19) and a speed actual value (20), which is combined with at least one feedforward variable (24) to determine an input variable (23) for the current control (15), wherein the feedforward variable (24) is a current feedforward value determined depending on a preset density of the substrate roll; and wherein the feedforward variable is adjusted depending on an actual current value (25) provided by the current control (15) such that the current feedforward value used as feedforward variable (24) follows the actual current value (25). (Fig. 1).