Thickness Measuring Device Using Multi-Wavelength Interferometry
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Solution Overview
Problem
Existing thickness measurement technologies face challenges in achieving high accuracy, particularly for thin metal foils used in capacitors or accumulators, due to sensitivity to environmental fluctuations and limitations in interferometric methods.
Innovation Solution
A thickness measuring device using multi-wavelength interferometry with thermal insulation and a constant air supply to minimize refractive index variations and thermal expansions, allowing for absolute thickness measurement without calibration, and employing a method to calculate thickness from effective phase differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional interferometric methods are used for thickness measurement, then measurement capability is provided, but measurement precision deteriorates due to sensitivity to environmental fluctuations
Solution Approach 1:
The patent introduces a reference beam path that travels through the same environmental conditions as the measurement beam path. This reference beam serves as an intermediary that captures environmental fluctuations (temperature, pressure, humidity changes affecting refractive index), allowing these fluctuations to be measured and compensated for in the final thickness calculation, thereby maintaining measurement precision despite environmental variations
Solution Approach 2:
The patent changes the measurement approach from direct absolute thickness measurement to measuring effective phase differences. By forming differences between interferometric distance measurements (with and without workpiece) and calculating effective phase, the system transforms the measurement parameters to eliminate common environmental influences, improving measurement precision while maintaining reliability under environmental fluctuations
2Measurement precision
If multi-wavelength interferometry is implemented, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent employs a single light source that emits multiple wavelengths simultaneously, making this one component perform the function of multiple separate wavelength sources. This multi-functional approach achieves the precision benefits of multi-wavelength interferometry while avoiding the complexity of multiple independent laser sources and their respective control systems
Solution Approach 2:
The patent combines multiple wavelength measurements into a unified interferometric system where a single light source provides multiple wavelengths that are processed through the same optical path. By merging the measurement functions into one integrated system rather than using separate interferometers for each wavelength, the device achieves high precision while minimizing structural complexity
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
The solution provides low measurement uncertainty and increased robustness by compensating for refractive index fluctuations and thermal changes, enabling precise thickness measurement of thin workpieces in varying environments.
Implementation Method 1
a first interferometer (26) which has a light source (28) and forms a first light beam (34) from a first source light beam (32) emitted by the light source (28), a second interferometer (48) which forms a second light beam (54) from a second source light beam (52) emitted by the light source (28)
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a thickness-measuring device (16) for measuring a thickness of flat workpieces, in particular films (14), comprising (a) a first arm (20) and a second arm (22), which form an intermediate space (24) therebetween for the insertion of the workpiece, (b) a first interferometer (26) for emitting a first light beam (34) onto the workpiece (14) and sensing a first phase (Φo) between the first light beam (34) and a first return light beam (40) reflected by the workpiece (14), (c) a second interferometer (48) for emitting a second light beam (54) onto the workpiece (14) and sensing a second phase (Φυ) between the second light beam (54) and a second return light beam (58) reflected by the workpiece (14), (d) a third interferometer (62) for forming a third light beam (64) from one arm (20) to the other arm (22) at a distance from the workpiece (14) and sensing a control phase (Φko) and (e) an evaluation device for determining the thickness of the workpiece (14) from interferometer data from the interferometers (26, 48, 62). According to the invention, the evaluation device is designed to automatically determine an effective phase (Φeff) from the phases (Φo, Φυ, Φko) and determining the thickness (lx) from the effective phase (Φeff).