Chromatic Confocal Optical System for Surface Topography Measurement
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Solution Overview
Problem
Existing optical measuring devices face challenges in accurately determining the surface topography of objects due to issues with chromatic aberration, shading effects, and limited resolution, which affect the precision and distortion of measurements.
Innovation Solution
A chromatic confocal measuring device is designed with a light source emitting multiple wavelengths, utilizing a first splitting optical element and a lens system with significant longitudinal chromatic aberration, combined with detection imaging optics and a confocal aperture to improve focusing accuracy and suppress defocused light, allowing for precise measurement of surface topography without distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a lens system with significant longitudinal chromatic aberration is used, then the focal points of different wavelengths are formed at different locations along a line segment, enabling measurement of surface topography, but the image quality and resolution deteriorate due to chromatic aberration
Solution Approach 1:
The optical system is segmented into separate illumination imaging optics and detection imaging optics, with each optimized for its specific function. The illumination optics use a lens system with significant longitudinal chromatic aberration to create wavelength-dependent focal points, while the detection optics use a lens system with minimal chromatic aberration to maintain high image quality when detecting reflected light.
Solution Approach 2:
Different parts of the optical system are given different optical qualities suited to their specific functions. The illumination imaging optics employ a lens system with strong chromatic aberration characteristics to achieve the required focal point separation, while the detection imaging optics use an apochromatic or corrected lens system to preserve image quality during detection.
2Measurement precision
If the angle of incidence is increased to reduce shadowing effects, then the measurement range and coverage are improved, but vignetting effects increase and reduce light intensity at the edges
Solution Approach 1:
The system uses asymmetric optical paths for illumination and detection, with the illumination imaging optics positioned to achieve steep angles of incidence that minimize shadowing, while the detection imaging optics are configured to capture the reflected light efficiently despite the asymmetric illumination geometry.
Solution Approach 2:
The patent transitions from a single optical axis configuration to a multi-dimensional optical arrangement where illumination and detection occur along different paths and angles, allowing simultaneous achievement of steep incidence angles and adequate light collection without vignetting limitations.
3Device complexity
If illumination imaging optics and detection imaging optics are combined in a single system, then the device structure is simplified, but the performance and resolution are compromised due to mutual interference
Solution Approach 1:
The optical system is divided into two independent subsystems: illumination imaging optics and detection imaging optics. This segmentation allows each subsystem to be optimized for its specific function without compromise, while maintaining a relatively compact overall structure through careful spatial arrangement.
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 solution enhances measurement precision by reducing shading effects and distortion, providing a higher signal-to-noise ratio and allowing for direct determination of surface topography in a Cartesian coordinate system with improved luminous efficacy and resolution.
Implementation Method 1
The first splitter optical element splits the light depending on the wavelength; that is, light of different wavelengths, which is incident on the splitter optical element at the same angle, exits the splitter optical element at different angles. In the case of a prism, this is due to dispersion
Implementation Method 2
in the case of a grating, the first or a higher diffraction order (positive or negative diffraction orders) is used as the output light, which is spectrally split
Implementation Method 3
The first lens system is characterized by the fact that its effective focal length differs significantly for different wavelengths. This property is also known as longitudinal chromatic aberration. The light is focused by the illumination imaging optics, whereby focusing points, in particular focal points or focal lines, of different wavelengths are formed at different locations
Implementation Method 4
The second confocal aperture has the effect of suppressing light of wavelengths that hit the measurement object in a defocused manner and are therefore not accurately focused back onto the second confocal aperture, thereby reducing the background and improving the signal/noise ratio
Implementation Method 5
The detection imaging optic is designed to receive light reflected from the object from a direction different from the direction from which the illumination light strikes the object and to image the focal points of all wavelengths used onto a second confocal aperture
Data Source
Figure 1~2
Figure 3a
Figure 3b
AI summary
The invention relates to a measuring apparatus comprising a light source (1) which emits light at a plurality of wavelengths and has in particular a continuous spectrum. The measuring apparatus comprises a first confocal aperture (2), through which light from the light source (1) passes, and an illumination image-forming optical system (BA) having a first splitting optical element which is in the form of a prism or grating. The illumination image-forming optical system (BA) is designed such that the light enters the first splitting optical element (4) in a collimated manner. The illumination image-forming optical system (BA) comprises a first lens system (5) having at least one first lens which is spatially separated from the first splitting optical element (4), wherein the effective focal length (ƒ(λ)) of the first lens system (5) significantly differs for different wavelengths (A), and wherein the illumination image-forming optical system (BA) is designed such that focal points of different wavelengths are formed at different locations along a line segment. The measuring apparatus is configured to measure an object (30) which intersects the line segment (41) and reflects at least some of the light.