Optical Astigmatism Displacement Sensor Beam Diameter Control
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Solution Overview
Problem
Existing displacement detecting devices face challenges in achieving high detection accuracy due to the non-linearity of focus error signals and the over-detection of surface roughness, leading to measurement errors from projections, recesses, and foreign particles on the measurement surface.
Innovation Solution
A displacement detecting device with a light adjustment member that adjusts the resolution and beam diameter of the output light, and regulates the incident angle of reflected light, reducing the resolving power and minimizing measurement errors caused by surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the numerical aperture of the objective lens is increased to reduce the beam diameter and achieve higher detection accuracy, then the resolution of the displacement detecting device is improved, but the device starts to over-detect surface roughness, projections, and recesses, causing measurement errors
Solution Approach 1:
The patent changes the beam diameter parameter by introducing a light adjustment member that modifies the optical path. By controlling the beam diameter to be within a specific range (0.5-2 times the wavelength of light), the system achieves optimal detection accuracy while avoiding over-detection of surface roughness. This parameter optimization resolves the contradiction between high resolution and surface roughness sensitivity.
2Measurement precision
If the beam diameter is reduced to improve detection accuracy, then the resolving power increases, but the noise component from surface roughness reflection and scattering becomes greater
Solution Approach 1:
The patent optimizes the beam diameter parameter to fall within a specific range (0.5-2 times the wavelength) where the balance between detection accuracy and noise minimization is achieved. This parameter change allows the system to maintain high measurement precision while keeping the noise component from surface roughness reflection and scattering at acceptable levels.
3Measurement precision
If the resolving power is increased to detect smaller displacements, then the detection accuracy improves, but projections and recesses on the measurement surface are output as large waveforms
Solution Approach 1:
The patent adjusts the beam diameter parameter to an optimal range that prevents the system from over-resolving surface features. By controlling the beam size, the system maintains sufficient displacement detection accuracy while avoiding the conversion of surface irregularities into large waveform signals, thus preserving useful displacement information.
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 optimal accuracy in detecting displacement and surface roughness by reducing the resolving power and preventing measurement errors from surface irregularities and foreign particles, while maintaining high linearity and stability over time.
Implementation Method 1
an objective lens that focuses output light emitted from the light source onto a measurement surface to be measured
Implementation Method 2
a light receiving element that detects displacement information on the basis of a focal length of the objective lens by using reflected light reflected by the measurement surface
Implementation Method 3
a light adjustment member that blocks a specific light component of the output light and/or the reflected light
Implementation Method 4
a linear scale that is attached to the objective lens with a link member therebetween and configured to measure an amount of displacement of the linear scale when the focal length of the objective lens is adjusted
Data Source
AI summary
A displacement detecting device includes a non-contact sensor having a light source, an objective lens focusing output light from the light source onto a measurement surface, and a light receiving element detecting displacement information based on a focal length of the objective lens by using reflected light from the measurement surface; a control unit adjusting the focal length based on the displacement information; a displacement-amount measuring unit having a linear scale attached to the objective lens with a link member therebetween and measuring an amount of displacement of the linear scale when the focal length is adjusted. A light adjustment member is disposed between the light source and the objective lens or between the objective lens and the light receiving element and has an aperture section transmitting the output and/or reflected light therethrough and a light blocking section that blocks a specific light component of the output and/or reflected light.