Ambient Light Suppression in Moving Laser Beam Readers
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Solution Overview
Problem
Ambient light, particularly from fluorescent lamps and LEDs operated at kilohertz frequencies, interferes with the information signal in moving laser beam readers, degrading the performance of data capture devices used for electro-optically reading bar code symbols.
Innovation Solution
The implementation of a handheld moving laser beam reader with signal processing circuitry that measures ambient light signals and switches between modes of operation to either process both signals or suppress ambient light signals when they exceed a threshold, using techniques such as correlated double sampling or bandpass filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If ambient light filtering is applied to remove DC component, then constant illumination interference is reduced, but time-varying AC frequency components at kilohertz frequencies cannot be suppressed when they are close to information signal frequency
Solution Approach 1:
The patent applies periodic action by modulating the laser beam at a specific frequency (e.g., 100 kHz) and using synchronized detection to distinguish the modulated signal from ambient light. The photodetector detects the modulated return light, and the signal processing circuitry uses the known modulation frequency to filter and extract the information signal from the combined signal containing both information and ambient light components.
Solution Approach 2:
The patent replaces simple mechanical filtering approaches with electronic signal processing. Instead of using physical filters that cannot distinguish between signals of similar frequencies, the system uses electronic modulation and demodulation techniques, along with digital signal processing, to selectively extract the information signal based on its frequency characteristics rather than relying on frequency-based filtering alone.
2Adaptability or versatility
If signal processing circuitry measures ambient light and switches modes, then ambient light suppression is activated only when needed, but device complexity increases
Solution Approach 1:
The patent implements feedback by having the signal processing circuitry continuously monitor the detected signal for characteristics of ambient light interference (such as specific frequency components or signal quality metrics). When ambient light interference is detected above a threshold, the system activates enhanced suppression techniques; when interference is low, the system operates in a simpler mode, dynamically adjusting its processing based on real-time conditions.
Solution Approach 2:
The patent applies dynamics by making the signal processing approach adaptive rather than static. The system dynamically switches between different processing modes based on the measured ambient light conditions, optimizing performance for each situation while minimizing unnecessary processing complexity. This dynamic adaptation allows the system to handle varying ambient light environments effectively.
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
Effectively suppresses ambient light interference, enhancing the decoding performance of bar code symbols by distinguishing and managing ambient light signals in relation to the information signal, thereby improving reading accuracy and reliability.
Implementation Method 1
a photodetector for detecting return light reflected and/or scattered from the target and for converting the detected return light into an analog electrical information signal
Data Source
AI summary
A reader for electro-optically reading a target in the presence of ambient light to be suppressed, includes a laser for emitting a laser beam, a scan component for scanning the laser beam across the target, a photodetector for detecting return laser light from the target to generate an information signal bearing information related to the target, and for concomitantly detecting the ambient light to generate an ambient light signal, and signal processing circuitry for measuring the ambient light signal, for processing both the information signal and the ambient light signal in one mode of operation when the measured ambient light signal is below a threshold, and for suppressing the ambient light signal and for processing only the information signal in another mode of operation when the measured ambient light signal at least equals the threshold.