Chromatic Confocal Sensor Scanning for Rough Surface Measurement
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Solution Overview
Problem
Current optical comparators are sensitive to surface roughness, leading to unreliable measurements, and increasing the measurement spot size introduces optical aberrations, limiting their robustness and repeatability, especially when measuring surfaces with micrometer-level roughness.
Innovation Solution
A chromatic confocal measurement device using a polychromatic light source, an axial chromatism objective lens, and a scanning system that moves the light beam along a predetermined path during integration, allowing for dynamic spatial averaging of the reflected light energy to reduce sensitivity to surface roughness and achieve repeatable measurements comparable to mechanical probes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the measurement spot size is increased to improve robustness to surface roughness, then the sensitivity to surface roughness is reduced, but optical aberrations are introduced that distort measurements
Solution Approach 1:
The patent applies a scanning system that dynamically moves the measurement spot across the surface during the integration interval, transforming a static large spot into a dynamic scanning path. This allows the system to achieve spatial averaging of surface roughness effects while maintaining a small effective interaction area at any given moment, thus avoiding optical aberrations associated with large static spots.
Solution Approach 2:
The scanning system performs preliminary movement of the light beam across the surface before the optical sensor completes its integration. This preliminary action ensures that the measurement spot has already covered the necessary area to average out surface roughness effects before the measurement is finalized, resolving the contradiction between spot size and aberration avoidance.
2Measurement precision
If a small measurement spot is used to maintain measurement precision, then optical aberrations are minimized, but the sensitivity to surface roughness increases
Solution Approach 1:
The system uses a small measurement spot that is dynamically scanned across the surface during the integration interval. This dynamic scanning allows the small spot to achieve spatial averaging of surface roughness effects without requiring a large static spot, thus maintaining measurement precision while reducing sensitivity to surface roughness.
Solution Approach 2:
The scanning system continuously moves the measurement spot across the surface throughout the integration interval, ensuring continuous spatial averaging of surface roughness effects. This continuous action allows the small spot to accumulate sufficient measurement data to reduce sensitivity to surface roughness while maintaining precision.
3Device complexity
If the light beam is stationary during integration, then the measurement is simple, but the ability to average surface roughness is limited
Solution Approach 1:
The patent introduces a scanning system that dynamically moves the light beam during the integration interval, transforming a simple static measurement into a dynamic scanning measurement. This dynamic approach enables spatial averaging of surface roughness effects, significantly improving repeatability while adding controlled complexity through the scanning mechanism.
Solution Approach 2:
The scanning system performs preliminary movement of the light beam across the surface before the optical sensor completes its integration. This preliminary action enables the system to average surface roughness effects during the measurement process, improving repeatability without requiring complex post-processing.
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 the robustness and repeatability of measurements by reducing the impact of surface roughness, enabling accurate and reliable height and orientation measurements on surfaces with micrometer-level roughness, similar to mechanical probes, while avoiding optical aberrations.
Implementation Method 1
an axial chromatism objective lens configured to apply the light beam on the surface of the sample
Implementation Method 2
an optical sensor, configured to receive a light beam reflected from the surface of the sample and measure a total energy of said reflected light beam received during an integration interval
Data Source
AI summary
The invention concerns a device (1) for the chromatic confocal measurement of a local height and/or orientation of a surface (S) of a sample comprising—a light source (2) configured to generate a polychromatic light beam (9)—a projection lens (4) comprising a lens (4) with axial chromatism configured to apply the light beam (9) to the surface (S) of the sample, —an optical sensor, configured to receive a light beam (9) reflected by the surface (S) of the sample and measure a total energy of the reflected light beam (9) received during an integration interval, —a scanning system (10), coupled to the projection lens (4) and configured to move the propagation axis of the light beam (9) relative to the projection lens (4), such that the total energy measured by the optical sensor corresponds to a dynamic spatial average of the total energy of the light beam (9) reflected by the surface (S) of the sample.