Displacement Detection Using Dynamic Focus Positioning
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Solution Overview
Problem
Conventional displacement detecting devices face errors in measurement due to surface roughness and attached foreign matter, and temperature issues caused by light forming an image on the surface-to-be-measured.
Innovation Solution
A displacement detecting device incorporating a light source, objective lens, separation optical system, condenser, astigmatism generator, and light receiving section, where the focus error signal is set to zero by adjusting the position of optical components, preventing errors from surface roughness and foreign matter, and avoiding light image formation to prevent temperature increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the NA of the objective lens is set large to reduce the beam diameter and improve detection accuracy, then measurement precision is improved, but surface roughness and foreign matter cause scattering errors that worsen measurement reliability
Solution Approach 1:
The patent dynamically adjusts the focus position of the objective lens to be located behind the measurement surface at a predetermined distance. This dynamic positioning strategy allows the system to maintain high measurement precision while avoiding the harmful effects of light scattering from surface roughness and foreign matter, thereby ensuring measurement reliability.
Solution Approach 2:
The patent changes the key parameter of focus position from being on the surface to being behind the surface at a specific distance. By modifying this parameter, the system achieves both high precision (through appropriate beam diameter control) and high reliability (by avoiding surface scattering effects).
2Measurement precision
If light is condensed to form an image on the surface-to-be-measured to achieve precise measurement, then measurement precision is improved, but temperature of the surface rises causing measurement error and surface deterioration
Solution Approach 1:
The patent dynamically positions the focus behind the measurement surface rather than on the surface itself. This dynamic adjustment prevents light energy concentration on the surface, avoiding temperature rise while maintaining measurement precision through the controlled beam diameter at the surface location.
Solution Approach 2:
The patent introduces an intermediate focal plane behind the measurement surface as a mediator. The light focuses at this intermediate plane rather than directly on the surface, acting as a buffer that prevents direct thermal interaction between the condensed light and the measurement surface, thereby preventing temperature rise and surface deterioration.
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 reduces measurement errors caused by surface roughness and foreign matter, while preventing temperature rises, ensuring accurate displacement detection.
Implementation Method 1
an objective lens (3), the separation optical system (4) separates the optical path of the reflected light coming from the surface-to-be-measured (101) from the optical path of the outgoing light coming from the light source (2)
Implementation Method 2
the separation optical system (4) separates the optical path of the reflected light coming from the surface-to-be-measured (101) from the optical path of the outgoing light coming from the light source (2)
Implementation Method 3
a condenser (7) condenses the reflected light separated from the optical path of the outgoing light by the separation optical system
Implementation Method 4
an astigmatism generator (8) generates astigmatism to the reflected light condensed by the condenser (7)
Implementation Method 5
The light receiving section is adapted to detect the amount of the reflected light to which the astigmatism is generated by the astigmatism generator
Data Source
AI summary
In a displacement detecting device, an objective lens condenses the outgoing light coming from a light source toward a surface-to-be-measured. The optical path of the reflected light coming from the surface-to-be-measured is separated from the optical path of the outgoing light coming from the light source by a separation optical system. The reflected light passing through the separation optical system is condensed by a collimator lens and has astigmatism generated therein by an astigmatism generator, and the reflected light in such a state is incident on a light receiving section. A position information generator generates the position information of the surface-to-be-measured using a focus error signal obtained based on the amount of light detected by the light receiving section. Further, the position of the condenser, the astigmatism generator or the light receiving section in the optical axis is set so that the value of the focus error signal is equal to “0” when the focus of the outgoing light condensed by the objective lens is located on the front side or back side of the surface-to-be-measured.