Single-Head Absolute Position Detection Using Multiplexed Interference Light
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Solution Overview
Problem
Existing detection devices for determining absolute positions on scales with diffraction gratings require multiple displacement detecting units, making them large and unable to accurately determine positions when the grating pitch is expressed by a second or higher-order polynomial.
Innovation Solution
A detection device with a single head that uses multiplexed light from diffracted beams at specific points on a diffraction grating with varying grating interval lengths, allowing for accurate absolute position detection by analyzing differences in phase information across distinct regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple displacement detecting units (heads) are used to determine absolute position, then the accuracy of absolute position detection is improved, but the size of the detection device increases
Solution Approach 1:
The patent combines multiple detection functions into a single head by using a diffraction grating with multiple regions having different grating interval lengths. The single head receives multiplexed light containing phase information from multiple regions simultaneously, eliminating the need for multiple separate displacement detecting units while maintaining absolute position detection capability.
Solution Approach 2:
The diffraction grating is designed with multi-functionality by incorporating multiple regions with different grating interval lengths within a single structure. This allows one grating to perform the function that previously required multiple separate gratings and detection units, enabling absolute position detection with a single head.
2Length of stationary object
If the grating pitch is expressed by a second or higher-order polynomial, then the detection range is expanded, but it becomes impossible to determine a single position based on phase information difference
Solution Approach 1:
The patent applies local quality by creating different grating interval lengths in different regions of the diffraction grating. Each region has a specific grating pitch characteristic (different polynomial orders), allowing the system to handle various detection ranges while maintaining unique position determination capability through the combination of regional differences.
Solution Approach 2:
The patent changes the grating pitch parameter across different regions of the diffraction grating, expressing it by different polynomial orders. This parameter variation allows the system to expand detection range while maintaining the ability to determine single absolute positions by analyzing the unique phase information patterns from each region.
3Measurement precision
If more displacement detecting units (heads) are added to handle polynomial grating pitches, then the accuracy of absolute position determination is improved, but the device complexity increases
Solution Approach 1:
The patent merges multiple detection functions into a single head by integrating multiple diffraction regions with different grating interval lengths into one diffraction grating structure. The single head receives and processes multiplexed light containing phase information from all regions simultaneously, reducing device complexity while maintaining high accuracy.
Solution Approach 2:
The patent transitions from using multiple separate heads in one dimension to using multiple regions within a single grating in another dimension (spatial arrangement on the grating surface). This dimensional change allows the system to maintain detection accuracy while reducing the number of discrete detection units.
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 and accurate detection of absolute positions on scales using a single head, overcoming the limitations of multiple unit devices and polynomial grating pitches, while maintaining reliability and efficiency.
Implementation Method 1
diffracted light obtained by causing light from the light source to enter first two points residing on a diffraction grating
Implementation Method 2
multiplexed light (interference light) of diffracted light
Data Source
AI summary
In order to provide a small detection device capable of detecting an accurate absolute position with a single head, there is provided a detection device including a head including a light source and a detecting unit configured to receive multiplexed light (interference light) of diffracted light obtained by causing light from the light source to enter first two points residing on ax diffraction grating and being separated from each other by a known distance and diffracted light obtained by causing the light from the light source to enter second two points residing on the diffraction grating, being separated from each other by a known distance, and including at least one point being different from the first two points, wherein the diffraction grating includes a first region between the first two points separated from each other by the known distance and a second region between the second two points separated from each other by the known distance, the first and second regions having at least partially different grating interval lengths, and an absolute position on the diffraction grating is detected based on the multiplexed light (interference light) received by the detecting unit.