Displacement Detection via Optical Interference and Segmentation
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Solution Overview
Problem
Conventional displacement detecting devices face limitations in measuring high-speed vibrations due to mechanical response frequency restrictions and are prone to errors from foreign substances and slight shape changes, limiting their application.
Innovation Solution
A displacement detecting device using a light source, light-beam splitting section, reflection/transmission section, phase plates, transmission-type diffraction grating, and light-beam combining section to measure displacement without a conventional driving mechanism, allowing for high accuracy and stability by equalizing optical path lengths and minimizing the impact of environmental changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional actuator using magnet and coil is used to vertically move the objective lens, then the displacement can be detected with high accuracy, but the mechanical response frequency is restricted by the structure or weight of the actuator
Solution Approach 1:
The patent replaces the mechanical actuator system with an optical interferometric measurement system. Instead of mechanically moving the objective lens to track surface vibrations, the system uses interference patterns of light to detect displacement, eliminating mechanical response limitations and enabling measurement of high-speed vibrations.
Solution Approach 2:
The patent introduces an optical field as an intermediary between the measured object and the detection system. By using light interference patterns as the measurement medium, the system achieves high-speed response without mechanical constraints, as the optical field can respond instantaneously to surface vibrations.
2Measurement precision
If the beam diameter is reduced to approximately 2 μm to achieve detection accuracy of several nanometers, then measurement precision is improved, but the measurement is affected by foreign substances on the object or slight shape changes
Solution Approach 1:
The patent divides the measurement beam into multiple paths (reference beam and measurement beam) that traverse different optical paths. By comparing interference patterns from these segmented paths, the system can distinguish between actual displacement signals and noise from foreign substances or shape changes, improving reliability while maintaining precision.
Solution Approach 2:
The interferometric system provides real-time feedback through interference pattern analysis, allowing the system to detect and compensate for measurement errors caused by foreign substances or shape changes. The phase information from interference patterns enables continuous monitoring and correction of measurement deviations.
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
The device achieves high-accuracy, fast, and stable measurements without the need for mechanical driving, reducing errors from environmental factors and enabling narrower measurement areas with improved sensitivity.
Implementation Method 1
a first light beam LA... and a second light beam LB... are combined by the light-beam combining section 19 to thereby become interference light
Implementation Method 2
The diffraction grating 5 diffracts the first light beam LA reflected by the surface to be measured
Data Source
AI summary
A displacement detecting device includes a light source that performs irradiation with light, a light-beam splitting section, a reflection/transmission section, a phase plate, a transmission-type diffraction grating, a light-beam combining section, a light-receiving section, and a relative position information output unit. The reflection/transmission section transmits or reflects a first light beam, and causes the beam to enter a member to be measured. Furthermore, the reflection/transmission section guides the first light beam to a specific position of the member to be measured in the case where the member to be measured is in a reference position. Moreover, an optical path of the first light beam reflected by the member to be measured again overlaps with an optical path of the first light beam reflected at a specific position of the member to be measured.