Chromatic Range Sensor Low Reflectivity Measurement
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Solution Overview
Problem
Current chromatic range sensing systems face limitations when measuring workpieces with low reflectivity, as they can lead to detector pixel saturation, preventing accurate distance measurement due to insufficient signal strength, and are restricted by maximum exposure times to avoid saturation.
Innovation Solution
A method is introduced to operate chromatic range sensing systems at a lower sampling rate, allowing for a longer self-saturating exposure time that causes detector pixels to saturate, but still enables valid wavelength peak detection within a subset of the measurement range, excluding saturated areas, and provides user interface indications for height measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If exposure time is increased to boost signal from low reflectivity surfaces, then measurement sensitivity is improved, but detector pixel saturation occurs preventing valid wavelength peak detection
Solution Approach 1:
The system dynamically adjusts the exposure time based on the detected signal intensity. For low reflectivity surfaces, the system automatically increases exposure time within safe limits to boost signal strength, while for high reflectivity surfaces it reduces exposure time to prevent saturation. This dynamic adaptation resolves the contradiction between needing long exposure for sensitivity and short exposure to avoid saturation.
Solution Approach 2:
The system changes the exposure time parameter adaptively based on surface reflectivity characteristics. By monitoring signal intensity and adjusting the exposure time parameter accordingly, the system optimizes measurement sensitivity for low reflectivity surfaces while maintaining reliability by preventing detector saturation through parameter adaptation.
2Illumination intensity
If maximum exposure time is used to measure low reflectivity surfaces, then signal strength is improved, but measurement range is reduced due to saturation at certain distances
Solution Approach 1:
The system dynamically adjusts exposure time based on both signal strength requirements and measured distance. For low reflectivity surfaces at closer distances where saturation risk exists, the system uses moderate exposure times. For surfaces at distances where saturation is less likely, longer exposure times are permitted, thus maintaining full measurement range while optimizing signal strength where needed.
Solution Approach 2:
The exposure time parameter is adaptively changed based on real-time measurement conditions including signal strength and distance. This parameter adaptation allows the system to extend measurement range by using shorter exposure times when saturation risk is high, while maximizing signal strength through longer exposure times when conditions permit, effectively resolving the contradiction between signal strength and measurement range.
3Measurement precision
If exposure time is extended beyond saturation threshold to improve signal, then measurement capability for low reflectivity surfaces is enhanced, but valid measurement positions are lost in saturated regions
Solution Approach 1:
The system uses feedback from detector signal intensity to determine appropriate exposure time. By continuously monitoring whether pixels are approaching saturation thresholds, the system adjusts exposure time to maintain signal strength for low reflectivity surfaces while preventing saturation that would eliminate valid measurement positions. This feedback mechanism ensures measurement capability is enhanced without sacrificing measurement area.
Solution Approach 2:
The exposure time parameter is adaptively changed based on real-time detector response and signal characteristics. The system modifies this parameter to optimize measurement capability for challenging low reflectivity surfaces while maintaining a sufficient margin below saturation thresholds to preserve valid measurement positions across the measurement area.
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
This approach allows for reliable distance measurements on low reflectivity workpieces by extending the measurement range and sampling rates, enabling accurate height determination even with saturated pixels, thus overcoming the limitations of conventional systems.
Implementation Method 1
an optical element having axial chromatic aberration, also referred to as axial or longitudinal chromatic dispersion, may be used to focus a broadband light source such that the axial distance to the focus varies with the wavelength
Implementation Method 2
A spectrometer type detector measures the signal level for each wavelength, in order to determine the surface height
Data Source
AI summary
A method is provided for operating a chromatic range sensor (CRS) system, which may comprise a chromatic point sensor (CPS) system including an optical pen, to measure a low reflectivity surface. The CRS system may include a high sensitivity measurement mode in which it uses an unconventional low sampling rate or “long” self-saturating exposure time, to measure the low reflectivity surface. The “long” self-saturating exposure time may cause one or more detector pixels to self-saturate to at least a saturation threshold level, which prevents them from indicating a valid wavelength peak. Such pixels may define an invalid peak portion of a nominal total measurement range. The CRS may still detect a valid wavelength peak or height measurement, when the surface is located in a valid subset of the nominal total measurement range of the CRS system determined such that it excludes the invalid peak portion.