Displacement Detection via Dual Diffraction Grating Tilt Compensation
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Solution Overview
Problem
Conventional displacement detection apparatuses face limitations in precision, speed, and stability due to mechanical constraints and sensitivity issues when measuring displacements in the height direction, especially when the surface is tilted or has a gradient.
Innovation Solution
A displacement detection apparatus utilizing a transmission-type diffraction grating system that divides and diffracts light to cancel changes in optical path length and wavelength, allowing for high-precision and high-speed measurements by using a semiconductor laser with controlled coherence and temperature stabilization, and a second diffraction grating to correct optical path changes caused by tilting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a mechanical actuator is used to move the objective lens vertically, then the displacement detection can be performed, but the mechanical response frequency is restricted and the measurement speed is limited
Solution Approach 1:
The patent replaces the mechanical actuator system with an optical interference measurement system. Instead of mechanically moving the objective lens to measure displacement, the invention uses light interference patterns to detect surface displacement contactlessly, thereby eliminating mechanical response limitations and enabling high-speed measurements.
Solution Approach 2:
The patent introduces light as an intermediary to transfer measurement information. By using light waves to carry displacement information through interference patterns, the system avoids direct mechanical contact and the associated speed limitations, achieving both high measurement speed and stability.
2Measurement precision
If the beam diameter is reduced to increase accuracy, then the measurement precision improves, but the measurement range decreases
Solution Approach 1:
The patent transitions from one-dimensional positional measurement to two-dimensional interference pattern analysis. By measuring displacement through the analysis of interference fringe patterns rather than direct beam position, the system achieves high precision while maintaining a larger measurement range, as the interference pattern provides丰富的 measurement information across the entire beam area.
3Ease of operation
If a laser beam is used to measure displacement, then the measurement can be performed contactlessly, but the sensitivity is low and resolution decreases when measurement range is extended
Solution Approach 1:
The patent utilizes the phase transition concept in optical interference, where small physical displacements cause large phase changes in light waves. This phase modulation effect amplifies the measurement signal, enabling high-resolution displacement detection while maintaining contactless operation and extending the measurement range.
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 precise and stable displacement measurement in the height direction with reduced noise and interference, even when the surface is tilted, without the need for mechanical actuators, thus expanding the use conditions and maintaining accuracy across varying environmental conditions.
Implementation Method 1
a first diffraction grating, which diffracts the first light flux divided by the light flux dividing portion
Implementation Method 2
a light receiving portion, which receives interference light obtained by coupling the first light flux and the second light flux
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
To provide a displacement detection apparatus capable of detecting a displacement in the height direction of a member to be measured, with a high precision, and also capable of performing a high-speed and stable measurement. A first light flux L1 serving as object light is caused to enter a member to be measured 5, and reflected light thereof is caused to enter again the member to be measured 5 after being diffracted by a first diffraction grating 7. Then, the second-time reflected light of the first light flux L1 by the member to be measured 5 is diffracted by a second diffraction grating 9. By diffracting the first light flux L1 by the second diffraction grating 9, a change of the optical path length caused by tilting of the member to be measured 5 is cancelled.