Optical Positioning Device Dual Wavelength Talbot Effect
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Solution Overview
Problem
Existing optical position measuring devices face challenges in achieving high modulation in both incremental and absolute position measurements while maintaining a compact design and tolerance to scanning distance changes.
Innovation Solution
The use of different wavelengths for incremental and absolute position measurements, with the shortest wavelength for incremental measurement to optimize Talbot distances and a longer wavelength for absolute measurement, along with detector arrangements optimized for spectral sensitivity, allows for high modulation and tolerance in scanning distances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single wavelength is used for both incremental and absolute position measurement, then the device structure is simplified, but the scanning distance cannot be optimized for both measurement types simultaneously
Solution Approach 1:
The patent divides the position measurement function into two separate wavelength channels: a first wavelength (e.g., 633 nm) for incremental position measurement and a second wavelength (e.g., 780 nm) for absolute position measurement. This segmentation allows each wavelength to be optimized independently for its specific measurement type, with the first wavelength providing high modulation for incremental scanning and the second wavelength enabling accurate absolute positioning, thereby resolving the contradiction between structural simplicity and scanning distance optimization.
2Measurement precision
If a shorter wavelength is used for incremental position measurement, then the Talbot distance is reduced and scanning is optimized, but the signal amplitude for absolute position measurement deteriorates
Solution Approach 1:
The patent assigns a first wavelength (shorter, e.g., 633 nm) specifically for incremental position measurement where short Talbot distance is critical, and a second wavelength (longer, e.g., 780 nm) specifically for absolute position measurement where higher signal amplitude is needed. This segmentation allows the shorter wavelength to optimize incremental scanning performance without compromising absolute positioning signal strength, as each wavelength is dedicated to its optimal function.
Solution Approach 2:
The patent changes the wavelength parameter between the two measurement types: using a shorter wavelength (633 nm) for incremental measurement to reduce Talbot distance and improve scanning precision, while using a longer wavelength (780 nm) for absolute measurement to maximize signal amplitude. This parameter change resolves the contradiction by allowing each measurement type to operate at its optimal wavelength condition.
3Measurement precision
If different scanning distances are provided for incremental and absolute scanning, then both measurement types can be optimized, but the guide structure becomes complex
Solution Approach 1:
The patent employs a single grating structure that serves dual functions: it acts as the first grating for incremental position measurement when illuminated by the first wavelength, and as the second grating for absolute position measurement when illuminated by the second wavelength. This multi-functionality eliminates the need for separate guide structures for different scanning distances, as the same physical grating is used for both purposes with different wavelengths, thereby resolving the contradiction between scanning optimization and 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
This approach enables a compact and robust position measuring device with high signal amplitude and tolerance to scanning distance variations, ensuring precise and reliable measurements.
Implementation Method 1
A repetitive self-image of the first grating takes place in the Talbot planes, so that a periodic intensity distribution is generated in these Talbot planes
Implementation Method 2
the first and second detector arrangements have different spectral sensitivities
Data Source
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AI summary
The optical position measuring device according to the invention comprises a scale (1.1) with a grating (G1) for incremental measurement and an absolute marker (R1) for absolute measurement. For incremental measurement, light with a wavelength (λ1) is used that is shorter than the wavelength (λ2) of the light used for absolute measurement.