Optical Sensor Threshold Calibration for Background Light Noise
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Solution Overview
Problem
Existing optical sensors, such as lidar systems, struggle with false-positive signal filtering due to varying environmental conditions, leading to inconsistent false-positive rates and unnecessary filtering of true-positive signals, as current methods rely on assumptions about noise distribution that are not always accurate.
Innovation Solution
An optical sensor system with a control and evaluation unit that generates a calibration data set during a calibration phase by simulating various background levels, allowing it to determine signal thresholds based on actual noise conditions, independent of distribution assumptions, ensuring a consistent false-positive rate regardless of environmental changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a predefined difference from the mean value is used to filter false-positive signals, then the false-positive rate can be controlled under specific conditions, but the filtering quality varies under different environmental conditions and true-positive signals may be unnecessarily filtered out
Solution Approach 1:
The patent implements dynamic adaptation of filtering parameters by continuously tracking the statistical properties (mean and standard deviation) of the measurement signals and adjusting the threshold dynamically. This allows the filter to adapt to varying environmental conditions such as changing background light levels and temperature-dependent noise, resolving the contradiction between maintaining reliable false-positive filtering and adapting to different operational environments.
Solution Approach 2:
The patent changes the filtering parameter (threshold difference) from a fixed predefined value to a dynamically calculated value based on the current statistical characteristics of the signals. By using the current mean and standard deviation to compute the threshold, the system maintains consistent false-positive filtering performance across varying environmental conditions while preserving true-positive signals.
2Reliability
If a conservative large difference from the mean is used to ensure low false-positive rate, then false-positive signals are filtered effectively, but a large number of true-positive signals are also filtered out
Solution Approach 1:
The patent dynamically adjusts the filtering threshold parameter based on the current standard deviation of the signals. Instead of using a fixed conservative threshold, the threshold is calculated as a multiple of the current standard deviation, allowing the filtering criterion to adapt to the actual signal conditions. This maintains the false-positive rate control while preserving true-positive signals that have sufficient amplitude relative to the current noise level.
Solution Approach 2:
The filtering threshold is made dynamic by continuously updating the mean and standard deviation calculations based on recent signals. This dynamic approach allows the system to distinguish between temporary fluctuations and genuine signals, maintaining reliable false-positive filtering without unnecessarily rejecting true-positive signals even under varying environmental conditions.
Data Source
Figure 1A~1B
Figure 2A~2D
Figure 3A~3C
AI summary
An optical sensor (110), in particular a lidar, of a sensor system (100) comprises a transmitting unit (112) for emitting an optical transmitted signal, a receiving unit (114) for detecting a reflected or remitted portion of the transmitted signal, and a control and evaluation unit (116). Before an operating phase of the optical sensor, the control and evaluation unit (116) receives and stores a calibration data set (170). The calibration data set (170), which is generated in a calibration phase for the control and evaluation unit (116) of the optical sensor (110), comprises a plurality of signal threshold values assigned to a respective background level, for example due to an external light source (140), which corresponds to a respective predetermined light intensity.During the operating phase of the optical sensor, the control and evaluation unit (116) further receives operational measurement signals (128) with the transmitter unit activated from the receiver unit (114) of the optical sensor (110), determines a current background level, and selects one of the signal threshold values of the calibration data set (170) based on the current background level. This enables the control and evaluation unit (116) to identify output signals derived from the operational measurement signals (126) as invalid signals if the respective output signal is smaller than the selected signal threshold value. In addition to the sensor (110), the sensor system (100) comprises a calibration device (150) that is connected to the sensor (110) during the calibration phase. The transmitter unit (112) is deactivated during the calibration phase.Instead, the receiving unit (114) is illuminated by an illumination unit (152) of the calibration device (150), which provides a plurality of predetermined light intensities. A processing unit (156) with a control module (158) of the calibration device (150) is communicatively connected to the control and evaluation unit (116) of the sensor (110).