Displacement Detection via Dual-Beam Interference and Astigmatism
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Solution Overview
Problem
Conventional displacement detecting devices using non-contact sensors with light face challenges in achieving high accuracy due to non-linearity of focus error signals, susceptibility to surface roughness, and limitations in mechanical response frequency and heat generation, which restrict their service conditions.
Innovation Solution
A displacement detecting device that utilizes a light source split into two beams, where one beam is reflected by a fixed member and the other by the surface, generating interference light for relative position information and astigmatism for absolute position information, eliminating the need for a microfabricated scale and drive mechanism, thereby reducing heat and mechanical limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the beam diameter condensed on the surface-to-be-measured is reduced to achieve high resolution, then detection accuracy is improved, but the reflected light becomes susceptible to surface roughness and scattering, causing measurement errors
Solution Approach 1:
The patent divides the detection function into two independent systems: a non-contact sensor for measuring surface shape and a separate focus error signal system for maintaining beam focus. This segmentation allows each system to operate independently, so the non-contact sensor can use a larger beam diameter without being affected by surface roughness, while the focus error signal system ensures proper focus maintenance.
Solution Approach 2:
The patent introduces a beam splitter as an intermediary element that separates the measurement light path from the focus control light path. This allows the focus error signal to be generated independently without affecting the measurement beam, enabling the use of a larger beam diameter for measurement while maintaining focus through the intermediary focus control mechanism.
2Measurement precision
If the beam diameter is reduced to improve resolution, then detection accuracy is enhanced, but fine foreign matter on the surface is detected, preventing accurate displacement information acquisition
Solution Approach 1:
The patent segments the detection system into two independent functions: shape measurement using a non-contact sensor with a larger beam that averages out foreign matter effects, and focus control using a separate focus error signal system. This allows the measurement to be performed with a larger beam diameter that is less sensitive to foreign matter, while the focus control ensures accurate focus maintenance.
3Ease of operation
If a drive mechanism is used to move the objective lens for focus control, then focus position can be adjusted, but mechanical response frequency is limited and heat is generated
Solution Approach 1:
The patent replaces the mechanical drive mechanism with an optical solution. Instead of physically moving the objective lens using a motor or actuator, the system uses a beam splitter and focus error signal to control the focus position optically. This eliminates the mechanical response limitations and heat generation associated with drive mechanisms.
Solution Approach 2:
The patent introduces a beam splitter as an intermediary that allows the focus control function to be separated from the measurement function. This enables focus adjustment without mechanical movement of the objective lens, replacing the mechanical drive system with an optical control mechanism that has no response frequency limitations and generates no heat.
4Measurement precision
If a microfabricated scale is used for displacement detection, then position measurement can be performed, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent uses optical interference patterns to create a virtual measurement scale without requiring physical microfabricated scales. By using the interference of reference light and measurement light, the system creates measurement references optically, eliminating the need for complex microfabricated scale components and their associated manufacturing difficulties.
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 allows for accurate detection of displacement without a microfabricated scale and eliminates the need for a drive mechanism, enhancing service conditions by reducing heat and mechanical limitations, enabling more precise and stable measurements.
Implementation Method 1
a first light receiving section adapted to receive interference light of the first beam reflected by the reflecting member and the second beam reflected by the surface-to-be-measured
Implementation Method 2
an objective lens adapted to condense the second beam split by the first beam splitter on a surface-to-be-measured
Implementation Method 3
the light reflected by the surface-to-be-measured is condensed by an astigmatic optical element so that astigmatism is generated therein
Data Source
AI summary
A displacement detecting device comprises: a light source, a first beam splitter adapted to split the light emitted from the light source into a first beam and a second beam, a reflecting member adapted to reflect the first beam, an objective lens adapted to condense the second beam on a surface-to-be-measured, a first light receiving section adapted to receive interference light of the reflected first beam and the reflected second beam, a relative position information output section adapted to output relative position information in height direction of the surface-to-be-measured, a second beam splitter adapted to extract a part of the reflected second beam, an astigmatism generator adapted to generate astigmatism in the extracted second beam, a second light receiving section adapted to receive the second beam having astigmatism, and an absolute position information output section adapted to generate absolute position information in height direction of the surface-to-be-measured.