Dual Head Scanner for Moving Web Thickness Measurement
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Solution Overview
Problem
In papermaking, measuring the thickness of flexible continuous webs is challenging due to the susceptibility of non-contacting optical methods to errors caused by sheet motion, and conventional contacting methods risk marking or tearing the sheet, requiring a non-marking, sub-micron accurate measurement apparatus that stabilizes the sheet effectively.
Innovation Solution
A dual mounting head scanner system with an air clamp and vacuum assembly holds the web in contact with a measurement surface, using an optical sensor to measure the distance to the web's upper surface and a displacement sensor to measure from the lower head to a reference surface, calculating the web's thickness as the difference between these distances while maintaining thermal isolation between sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If non-contacting optical measurement methods are used, then the sheet is not marked or torn, but the measurements are extremely susceptible to errors caused by sheet motion
Solution Approach 1:
An air bearing is introduced as an intermediary between the optical sensor and the moving web. The air bearing creates a stable, non-contacting measurement interface that eliminates errors caused by sheet motion while maintaining non-contacting measurement conditions. The air bearing acts as a mediator that provides both physical stability for accurate measurement and prevents direct contact that would mark or tear the sheet.
Solution Approach 2:
The patent replaces conventional mechanical contacting measurement systems with an optical measurement system supported by an air bearing. This substitution eliminates mechanical contact forces that could damage delicate sheets while the air bearing provides the necessary stabilization for accurate optical thickness measurements.
2Measurement precision
If the sheet is stabilized for accurate measurement, then measurement precision improves, but the system complexity increases due to air clamps and vacuum assembly
Solution Approach 1:
The patent employs pneumatic principles through the air bearing and vacuum assembly to stabilize the moving web during measurement. The air bearing uses a thin film of air to provide non-contact support, while the vacuum assembly creates controlled suction to maintain web position. These pneumatic mechanisms provide effective stabilization without requiring complex mechanical clamping or physical contact systems.
3Device complexity
If conventional contacting measurement methods are used, then the measurement system is simpler, but the sheet may be marked or torn
Solution Approach 1:
The patent replaces mechanical contacting measurement systems with an optical measurement system. This substitution eliminates the direct mechanical contact between the measurement probe and the sheet, thereby preventing marking or tearing while maintaining measurement capability through optical means supported by an air bearing.
Solution Approach 2:
The air bearing serves as an intermediary that enables non-contacting measurement without requiring complex mechanical protection systems. It provides a stable measurement interface that allows optical sensors to measure sheet thickness accurately without physical contact, thus avoiding sheet damage.
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 system provides accurate, continuous thickness measurements by stabilizing the web with air clamps and vacuum channels, reducing thermal interactions and ensuring consistent measurements even at high speeds, thus addressing the instability and error issues of previous methods.
Implementation Method 1
suction forces generated by vacuum channels that are configured adjacent the measurement surface flatten the contour of the web and holds the web in physical contact against the measurement surface
Implementation Method 2
an optical sensor located in the upper head measures the distance between the optical sensor and the upper surface of the web while a displacement sensor located in the lower head measures the distance
Implementation Method 3
An air clamp and vacuum source assembly maneuvers the moving web into physical contact with a measurement surface
Data Source
AI summary
Dual mounting head scanner system measures the thickness of a flexible continuous moving web such as paper by employing an optical senor positioned in the upper head to determine the distance between the optical sensor and the upper surface of the paper while a displacement sensor positioned in the lower head determines the distance between the displacement sensor, which includes an RF coil, and a reference surface on the upper head. An air clamp and vacuum source assembly on the operative surface of the lower head maintains the moving web in physical contact with a measurement surface that is incorporated in the operative surface. The optical sensor directs incident radiation onto the web at the measurement surface. Thermal isolation of the two sensors eliminates thermal interactions.