Optical Reflectance Calibration for Nonlinear Detector Signals
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Solution Overview
Problem
Current optical detection systems inaccurately measure optical reflectance due to non-linear relationships between target reflectance and detector output signals, caused by multiple light paths within the chassis, leading to overestimation and underestimation of reflectance, especially for high reflectance targets, and lack flexibility in varying target distances.
Innovation Solution
A method to calibrate optical detection systems by determining a calibration factor M and height scaling factor η(z) to correct for non-linearities, using equations R = M ⋅ R R (S S - S H ) / (M ⋅ (S R - S H ) ⋅ η(z)) and R(λ) = M(λ) ⋅ R R (S S (λ) - S H (λ)) / (M(λ) ⋅ (S R (λ) - S H (λ)) ⋅ η(z)) to linearize the system response and account for varying target heights.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a linear relationship is assumed between target reflectance and detector output signal, then the system is simple to operate, but measurement precision deteriorates due to non-linear effects from multiple light paths
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements before actual reflectance measurements. The system pre-determines calibration factors (M and η(z)) by measuring signals from targets with known reflectance values. This preliminary calibration step stores correction data that compensates for non-linear effects, allowing accurate reflectance calculations during actual measurements without requiring complex real-time computations.
2Measurement precision
If the system is calibrated for a specific target distance, then measurement precision is improved for that distance, but adaptability deteriorates when target distance varies
Solution Approach 1:
The patent applies parameter changes by introducing a height scaling factor η(z) that depends on the target distance z. The calibration factor M is determined as a function of height M(z), allowing the system to adapt to different target distances. During operation, the system measures or estimates the target distance and selects or interpolates the appropriate calibration parameters, enabling accurate reflectance measurements across a range of distances rather than being limited to a single fixed distance.
3Device complexity
If multiple light paths in the chassis are not accounted for, then device complexity is reduced, but measurement precision deteriorates due to overestimation of detected intensity
Solution Approach 1:
The patent uses an intermediary approach by introducing calibration factors M and η(z) that mediate between the complex non-linear optical interactions and the simple reflectance calculation. Instead of directly modeling multiple light paths, the system uses calibration measurements with known reflectance targets to determine correction factors. These intermediary calibration factors encapsulate the effects of multiple reflections and geometric dependencies, allowing accurate measurements without requiring detailed optical path modeling.
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 method provides accurate and flexible optical reflectance measurements by compensating for non-linearities and varying target distances, ensuring consistent results across different devices and heights, enhancing measurement precision and reducing device-to-device dispersion.
Implementation Method 1
detecting light reflected from the target using the light detector
Implementation Method 2
the light detector provides an electrical output signal S S indicative of the intensity of the detected light
Data Source
Figure 1
Figure 2a
Figure 2b~3
AI summary
According to a first aspect of the present invention there is provided a method of measuring the optical reflectance R of a target using a detection system comprising a light emitter and a light detector spaced apart from one another. The method comprises illuminating the target with the light emitter, detecting light reflected from the target using the light detector, wherein the light detector provides an electrical output signal S S indicative of the intensity of the detected light, and determining the optical reflectance R of the target according to (Formula 1), where RR is the spectral reflectance of a reference standard, SR is the detector electrical output signal with the reference standard in place, SH is the detector electrical output signal with no target in front of the light emitter and light detector, and M is a calibration factor.