Variable Step Height Grating Fields for Optical Positioning
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Solution Overview
Problem
Existing optical position measuring devices face challenges in achieving accurate production of scanning plates with optimized grating fields due to complex conditions from different angles of incidence and deflection, especially when using a single wavelength of light, limiting the process window and increasing production costs.
Innovation Solution
The introduction of variable step heights in the grating fields on the scanning plate, allowing for additional design freedom and diffraction efficiency settings, which requires different etching depths but results in a larger process window and more cost-effective production, enabling operation with a single light wavelength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single wavelength of light is used for position measurement, then the device complexity is reduced and operation is simplified, but the manufacturing precision of grating fields deteriorates due to difficult control of different angles of incidence and deflection
Solution Approach 1:
The patent applies local quality by assigning different step heights to different grating fields on the scanning plate. Each grating field is optimized locally for its specific angle of incidence and deflection conditions, while the overall system maintains compatibility with single-wavelength operation. This localized optimization resolves the contradiction by allowing precise control of diffraction efficiency at each location without requiring multiple wavelengths.
Solution Approach 2:
The patent changes the physical parameter of step height (etching depth) of the grating fields to optimize their performance. By varying the step height parameter across different grating fields, the patent achieves precise control over diffraction efficiency for different light paths, thereby maintaining manufacturing precision while using a single wavelength of light.
2Measurement precision
If different etching depths are applied to different grating fields, then the diffraction efficiency and measurement signal quality are improved, but the device complexity and production effort increase
Solution Approach 1:
Different etching depths are applied to different grating fields based on their specific functional requirements and optical path characteristics. This local optimization improves measurement precision by ensuring each grating field operates at optimal diffraction efficiency, while the systematic approach to variation keeps the increased complexity manageable.
Solution Approach 2:
The patent introduces variation in the third dimension (etching depth/step height) to optimize grating field performance. By adding this dimensional parameter to the grating design, the patent achieves superior measurement precision without requiring additional grating fields or complex optical paths, thus managing the trade-off between precision and complexity.
3Measurement precision
If optimized grating fields are produced with high precision, then the measurement accuracy is improved, but the productivity and production yield decrease due to the difficult and time-consuming production process
Solution Approach 1:
By systematically varying the step height parameter across different grating fields, the patent achieves optimized measurement accuracy while creating a reproducible manufacturing process. The parameter change approach allows for standardized production methods that can be implemented across multiple units, thereby improving productivity and yield compared to custom high-precision fabrication.
Solution Approach 2:
The localized optimization of each grating field's step height creates a design that is robust to manufacturing variations. This approach maintains measurement accuracy even with normal production tolerances, thereby improving production yield without sacrificing precision.
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 enhances the production yield and cost-effectiveness of scanning plates by allowing for optimized measurement signals across all spatial directions, despite increased manufacturing complexity, and reduces sensitivity to tilting, while maintaining accuracy with a single light source.
Implementation Method 1
a splitting grating arranged on the scanning plate for splitting light into several partial beams of different orders of diffraction
Implementation Method 2
an optical grating on the scale for further splitting of the partial beams and for recombining these further split partial beams after they have been reflected back from the scanning plate
Implementation Method 3
several grating fields on the side of the scanning plate facing the material measure, which serve as diffractive optics to influence the partial beams that are further split at the material measure
Implementation Method 4
a plurality of interfering light beams
Implementation Method 5
a coupling-out grating arranged on the scanning plate for decoupling light reflected multiple times between the material measure and the scanning plate as interfering partial beams of rays
Data Source
Figure 1~2
Figure 3~5
AI summary
An optical position measuring device for three spatial directions (X, Y, Z) is disclosed, comprising a scale (M) and a scanning plate (A). The position measuring device includes a grating (Ga) arranged on the scanning plate (A) for splitting light into several partial beams (+1, 0, -1) of different diffraction orders, and an optical grating (Gm) on the scale (M) for further splitting the partial beams (+1, 0, -1) and for recombining these further split partial beams (+1, 0, -1) after their reflection from the scanning plate (A).Furthermore, the position measuring device has several grating fields (A1 - A4, B1 - B4, X1 - X4) on the side of the scanning plate (A) facing the scale (M). These grating fields act as diffractive optics for influencing the partial beams (+1, 0, -1) that are further split at the scale (M). The device also includes an output coupling grating (Gk) arranged on the scanning plate (A) for extracting light reflected multiple times between the scale (M) and the scanning plate (A) as interfering partial beams. The position measuring device is characterized by the fact that the step heights (t1, t2, t3) of the several grating fields (A1 - A4, B1 - B4, X1 - X4), which are configured as phase gratings, are variable.