Frequency Comb Absolute Length Measurement
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Solution Overview
Problem
Absolute length measurement systems are either very complex or less accurate compared to relative measuring systems, which are simpler and more accurate, posing a challenge in achieving high measurement accuracy with a straightforward construction.
Innovation Solution
A method involving a femtosecond laser to generate a frequency comb, filtering specific comb lines to create two beams with a non-zero frequency offset, allowing them to interfere and generate a beat signal from which the absolute length can be calculated, using a minimal number of components for a robust and accurate measurement system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If absolute length measurement systems use traditional methods (multi-wavelength interferometers with multiple light sources), then measurement accuracy can be achieved, but device complexity increases significantly
Solution Approach 1:
The patent combines multiple comb line filtering operations into a single frequency comb source. By filtering every nth and every mth comb line from one frequency comb, the system generates multiple wavelengths from a single source, eliminating the need for multiple coordinated laser sources and significantly reducing device complexity while maintaining measurement accuracy
Solution Approach 2:
The frequency comb source serves multiple functions simultaneously: it provides the coherent light source, generates multiple wavelengths through comb line filtering, and enables both absolute and relative measurements. This multi-functionality reduces the number of components needed and simplifies the overall system architecture
2Measurement precision
If absolute length measurement systems use traditional methods, then measurement capability is provided, but the number of components increases making the system less robust
Solution Approach 1:
The patent merges multiple light sources into a single frequency comb source, reducing the number of components that can fail. By deriving all measurement wavelengths from one stable frequency comb, the system improves reliability while maintaining the capability for precise absolute length measurement
Solution Approach 2:
The system changes the operational parameters of a single frequency comb source by selectively filtering different comb lines (every nth and every mth line) to generate the required wavelengths. This parameter-based approach replaces the need for multiple physical sources, thereby improving system robustness
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 approach enables high measurement accuracy comparable to relative systems with a simple structure, suitable for applications like coordinate measuring machines and machine tools, achieving previously unattainable precision with fewer components and a robust design.
Implementation Method 1
generating a frequency comb, which can be described as consisting of a plurality of equidistant comb lines
Implementation Method 2
allowing the first beam and the second beam to interfere so that at least one beat signal is created
Implementation Method 3
the first and second beams interfere on it, so that at least one beat signal is generated
Data Source
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AI summary
Method for measuring length, in particular absolute length measurement, comprising the steps of: (a) generating a frequency comb which can be described as consisting of a plurality of equidistant comb lines, then (b) filtering out each nth comb line from the frequency comb so that a first beam (S1) is produced, and (c) filtering out each mth comb line from the frequency comb so that a second beam (S2) is produced, (d) generating a non-zero frequency offset (ΔfAOM) between the two beams (S1, S2), (e) sending at least a part S1M of at least one of the beams (S1) onto a measuring section, then (f) interfering the first beam and the second beam so that at least one beat signal is produced, and (g) calculating the absolute length from the at least one beat signal.