Blown Film Thickness Control via Iterative Section Measurement
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Solution Overview
Problem
Current methods for controlling the thickness profile of tubular blown films are inaccurate and time-consuming, particularly when measuring individual layers of multi-layer films, as they rely on backscatter sensors or estimation techniques that require extensive scanning and rotation of the film.
Innovation Solution
A method involving the identification of longitudinal sections of the film, collapsing and re-rotating them to form different pairings, measuring physical properties, and iteratively calculating and refining estimates to determine the thickness profile of each section, allowing for precise control within predetermined limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transmission sensors are used to measure folded film thickness, then measurement accuracy improves, but the ability to measure individual layers deteriorates because two layers are always present at any location
Solution Approach 1:
The film is divided into multiple longitudinal sections (first through fourth sections) around the tubular structure. By collapsing the film to bring specific sections into alignment and measuring each pairing combination separately, the system can isolate and measure individual layers at each section while maintaining the benefits of transmission sensor accuracy.
Solution Approach 2:
The measurement approach transitions from measuring at fixed spatial positions to measuring at different angular orientations around the tubular film. By rotating or repositioning the film to create different pairings of longitudinal sections, the system extracts individual layer information from combined measurements taken at multiple dimensional orientations.
2Manufacturing precision
If repeated rotation and measurement of folded film is performed to determine individual sector thickness, then thickness profile control improves, but measurement time increases to 2-10 minutes
Solution Approach 1:
The film is pre-folded in a specific configuration that brings multiple longitudinal sections into alignment before measurement begins. This preliminary folding arrangement allows the measurement system to capture thickness data from multiple sections simultaneously or in rapid succession, eliminating the need for repeated rotation cycles during measurement.
Solution Approach 2:
Instead of continuous rotation and measurement, the system uses periodic sampling at strategically positioned fold points. By measuring at specific periodic intervals corresponding to different section pairings, the system obtains complete thickness profile data much faster than continuous rotation would allow.
3Loss of information
If least squares method is used to estimate individual sector thickness from folded film measurements, then thickness estimation becomes possible, but measurement time increases to 10-20 scans and results are merely estimates rather than accurate measurements
Solution Approach 1:
The folding configuration acts as an intermediary mechanism that physically separates and aligns specific film sections for direct measurement. Instead of using mathematical estimation to deconvolve layer thicknesses, the physical folding arrangement directly presents individual layers (or controlled combinations) to the sensor, eliminating the need for iterative mathematical reconstruction.
Data Source
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AI summary
A method is provided for measuring and controlling a cumulative physical property, such as the thickness, of a tubular blown film, wherein the tubular blown film is being extruded from a ring-shaped extruder having a plurality of film physical property controllers disposed around the ring-shaped extruder. Where the physical property is thickness, the method includes the steps of (1) collapsing the tubular film to create a two-ply web and slowly rotating the film while taking a plurality of thickness measurements across the two-ply web at various sections of the film, (2) calculating initial estimates of the thickness of each section using a first algorithm, (3) refining the initial estimates of the thicknesses of each section by successive iterations using a second algorithm, and (4) optionally adjusting at least one film physical property controller to control the final estimate of the thicknesses of each longitudinal section.