Laser Sensor Module Wavelength Modulation for Window Soiling Detection
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Solution Overview
Problem
Existing laser sensor modules struggle to reliably detect soiling on their emission windows, such as fingerprints or fine dust, which affects measurement accuracy by reducing laser light intensity and causing scattering, making it difficult to use interference or self-mixing interference for effective detection.
Innovation Solution
The laser sensor module varies the wavelength of the laser beam over a predetermined time period to generate a soiling detection signal, using a frequency range of 1 kHz to 100 MHz, with a duration of 1 us to 5 ms, to detect soiling on the emission window based on interference signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the laser sensor module uses interference or self-mixing interference to measure particle density, then measurement capability is achieved, but soiling on the emission window reduces measurement accuracy
Solution Approach 1:
The system performs soiling detection before carrying out the main measurement task. A test laser beam is emitted through the emission window and reflected back to detect soiling conditions in advance, allowing the system to determine whether the emission window is soiled before attempting particle density measurement, thus preventing inaccurate measurements
2Reliability
If a test laser beam is emitted to detect soiling, then soiling detection capability is achieved, but the detection reliability is insufficient when soiling is produced by fingerprints or fine dust
Solution Approach 1:
The system uses periodic modulation of the laser drive current to generate a modulated test laser beam. By modulating the laser at a specific frequency and detecting the reflected light at the same frequency, the system can reliably distinguish soiling-induced signal changes from background noise, significantly improving detection reliability for fine dust and fingerprint soiling
Solution Approach 2:
The system employs feedback by detecting the reflected test laser beam and comparing it with the emitted beam. The detector receives the reflected light and the evaluation unit analyzes the signal to determine whether soiling is present, creating a closed-loop feedback mechanism that enhances detection accuracy and reliability
3Ease of operation
If the laser drive current is modulated in predefined time periods to detect blocking objects, then detection capability is achieved, but the detection method is unreliable
Solution Approach 1:
The system modulates the laser drive current periodically with a specific frequency, creating a modulated test laser beam. The detector and evaluation unit are synchronized to detect signals at this modulation frequency, transforming the detection process into a frequency-selective measurement that is both simple to operate and highly reliable for detecting soiling conditions
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 method enables reliable detection of soiling, reducing the impact on measurement accuracy by providing a clear indication of window contamination, ensuring accurate particle density, fluid velocity, and distance measurements.
Implementation Method 1
a laser diode (44) configured emit a laser beam (48)
Implementation Method 2
an optical arrangement (52) configured to focus the laser beam (48) to a focus region (58)
Implementation Method 3
The detector (50) is arranged to determine an interference signal
Data Source
AI summary
A laser sensor module includes a laser diode configured emit a laser beam, an electrical driver configured to supply the laser diode with a driving current to stimulate emission of the laser beam, a detector, and an optical arrangement configured to focus the laser beam to a focus region. The laser diode is arranged to emit the laser beam through the optical arrangement to the focus region. The optical arrangement comprises an emission window. The detector is arranged to determine an interference signal. The laser sensor module comprises a soiling detection unit configured to vary a wavelength of the laser beam with a variation amplitude over a predetermined time period to provide a soiling detection signal indicative of a soiling of the emission window based on an interference signal during the wavelength variation of the laser beam.