Shadow Moiré Surface Flatness Measurement on Moving Samples
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Solution Overview
Problem
Conventional shadow moiré techniques are inadequate for measuring surface flatness of continuously moving samples due to the need for stationary support structures, which can introduce flaws and are costly and inefficient.
Innovation Solution
A system that uses a conveyor to continuously move samples beneath a grating at a non-zero angle, capturing shadow moiré fringe patterns with a camera, and processes images using phase-sensitive analysis to determine surface flatness without requiring high-precision motion systems or stopping the sample, employing algorithms like the Carré algorithm for phase calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional shadow moiré techniques use stationary support structures to measure surface flatness, then measurement precision is improved, but productivity decreases and device complexity increases
Solution Approach 1:
The patent transforms the stationary measurement system into a dynamic one by allowing continuous sample movement on a conveyor belt. The grating and camera remain stationary while the sample moves through the measurement zone, enabling real-time flatness measurement without stopping production. This dynamic approach resolves the contradiction by maintaining measurement capability while eliminating the need for stationary support structures that halt productivity.
Solution Approach 2:
The patent replaces complex mechanical motion systems with a simple conveyor belt mechanism. Instead of using high-precision mechanical stages to move the grating or camera, the system uses a basic conveyor to transport samples continuously. This substitution dramatically reduces device complexity while maintaining measurement functionality, resolving the contradiction between measurement precision and device complexity.
2Measurement precision
If conventional shadow moiré techniques require stopping the sample for measurement, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent implements continuous measurement by allowing samples to move uninterrupted through the measurement zone. The conveyor belt maintains constant motion while the camera captures flatness data at regular intervals, eliminating the need to stop the production line. This continuous action approach resolves the contradiction by maintaining both measurement precision and production continuity, eliminating time loss.
Solution Approach 2:
The system performs measurement actions in advance of quality decision points by continuously monitoring samples as they pass through the measurement zone. The conveyor system is positioned upstream in the production process, allowing flatness measurements to be taken before samples reach subsequent manufacturing steps, enabling early detection and rejection of defective parts without disrupting production flow.
3Measurement precision
If conventional shadow moiré techniques use high-precision motion systems to achieve phase steps, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces complex high-precision mechanical motion systems with a simple conveyor belt and stationary grating-camera assembly. The conveyor provides adequate transport functionality without requiring precision control, while the phase step measurement is achieved through the optical interference pattern itself rather than precise mechanical positioning. This substitution dramatically reduces device complexity and cost while maintaining sufficient measurement precision.
Solution Approach 2:
The system uses the natural movement of the conveyor belt to provide the necessary sample displacement for phase step measurement. Instead of requiring an external precision motion system to move the grating or camera, the moving sample itself provides the reference frame change needed for measurement. The optical system automatically captures the phase information as samples pass by, making the system self-sufficient and eliminating complex motion control requirements.
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
Enables efficient and cost-effective measurement of surface flatness for continuously moving samples, reducing production line disruptions and improving product quality by eliminating the need for expensive motion systems and allowing real-time monitoring.
Implementation Method 1
The light source illuminates the grating and the sample at an oblique angle of incidence. The light projects a shadow of the grating (i.e., a shadow of the opaque lines of the grating, referred to herein as a 'shadow grating') onto the sample.
Implementation Method 2
Shadow moiré is based on the geometric interference of a shadow grating projected on the sample surface and a real grating on a flat reference surface. When a printed circuit board is viewed through a grating and a shadow of the grating is cast upon the surface of the printed circuit board, the shadow and the grating can interact to create a shadow moiré fringe pattern that is indicative of the warpage of the surface of the printed circuit board.
Implementation Method 3
The camera captures one or more images of the grating, the sample, and the shadow grating.
Data Source
AI summary
Measurement of sample surface flatness of a continuously moving sample. A conveyor continuously conveys a sample beneath a grating disposed at a non-zero angle with respect to the plane of conveyance. The relative distance between the sample and the angled grating changes with the horizontal translation of the sample. A camera disposed above the sample and the grating captures, at constant time intervals, a sequence of images, each image comprising a shadow moiré fringe pattern that is indicative of the sample's surface flatness. The continuous change in relative distance between the sample and the grating introduces a known or unknown phase step between the shadow moiré fringe patterns of each successive image. A computer associated with the camera processes the images to determine phase values of pixels at, and the relative height of the sample surface at, selected pixel locations of the sample.