Optical Position Measurement Using Integrated Polarization Gratings
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Solution Overview
Problem
Existing optical position measuring devices require additional polarization-optical components in the scanning beam path, which pose challenges in compact design, mechanical stability, and signal quality under changing scanning conditions.
Innovation Solution
An optical position measuring device that utilizes a polarization grating integrated into the scanning beam path to generate phase-shifted scanning signals without separate polarization-optical components, ensuring consistent polarization effects regardless of scanning conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate polarization-optical components (lambda/4 plates, polarizers) are inserted into the scanning beam path, then polarization-optical generation of phase-shifted sampling signals is achieved, but device complexity increases and installation volume requirements increase
Solution Approach 1:
The patent combines the polarization-optical function with the grating function by designing the grating itself to have polarization-dependent diffraction properties. The grating structure includes anisotropic elements or specific orientation patterns that cause different diffraction orders to have different polarization states, eliminating the need for separate lambda/4 plates and polarizers while achieving the same phase-shifted sampling signal generation.
Solution Approach 2:
The grating is designed to perform multiple functions simultaneously: it acts as both the scanning grating for beam splitting and as the polarization-optical element for generating phase-shifted signals. The grating structure incorporates polarization-dependent characteristics, making it a multi-functional component that replaces both the grating and separate polarization-optical components.
2Measurement precision
If additional polarization-optical components are arranged in the scanning beam path, then polarization-optical generation of sampling signals is achieved, but mechanical stability requirements increase and drift-free mounting is required
Solution Approach 1:
By merging the polarization-optical function into the grating structure itself, the patent eliminates the need for separate components that would require stable mounting. The polarization-dependent properties are inherent in the grating's physical structure, which is typically rigid and stable, thereby maintaining signal phase shift stability without requiring additional mounting precision.
3Measurement precision
If separate polarization-optical components are used in the scanning beam path, then polarization-optical generation is achieved, but the installation volume increases and compact design becomes difficult
Solution Approach 1:
The patent integrates the polarization-optical generation function directly into the grating structure, eliminating the need for separate lambda/4 plates, polarizers, and associated mounting structures. This integration significantly reduces the overall installation volume while maintaining the capability to generate phase-shifted sampling signals through polarization-optical effects.
4Measurement precision
If polarization-optical components are added to the scanning beam path, then sampling signal generation is achieved, but the flatness and parallelism requirements of support structures increase
Solution Approach 1:
The patent eliminates the need for separate polarization-optical components that would require precision-mounted support structures. Instead, the polarization-dependent diffraction properties are built into the grating itself, which typically has well-controlled manufacturing precision for its geometric features, thereby reducing the additional flatness and parallelism requirements that would otherwise be needed for separate optical components.
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 a compact design and stable signal quality by eliminating the need for additional components and reducing limitations on scanning principles, while maintaining consistent polarization states across varying sampling distances.
Implementation Method 1
the polarization grating is designed such that, regardless of position, diffraction orders with different polarization states result on the grating
Implementation Method 2
the polarization grating exhibits periodically arranged grating structures both along the measurement direction and orthogonally to the measurement direction
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
The present invention relates to an optical position measuring device for detecting the relative position of two objects moving relative to each other along at least one measuring direction, which are connected to a first grating and a second grating. In this device, a beam of illumination emitted by a light source is split at one grating into at least two partial beams; these partial beams undergo different polarization-optical effects during the subsequent scanning beam paths. After the differently polarized partial beams are recombined at a grating, several phase-shifted, displacement-dependent scanning signals can be generated from the resulting signal beam in a detection unit.No separate polarizing optical components are arranged in the scanning beam paths of the partial beams between splitting and recombination; at least one of the gratings traversed serves as a polarizing grating to generate the different polarizing optical effects on the partial beams. The polarizing grating is designed such that diffraction orders with different polarization states result at each point of incidence on the grating (Fig. 6a).