Laser Barcode Reader Ambient Light Rejection via Dynamic Scan Angle and Filter Bandwidth
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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 solution involves a handheld moving laser beam reader with a controller that measures ambient light signals and adjusts the scan angle and filter bandwidth to reject interfering frequencies, ensuring the information signal is not impeded by ambient light. This is achieved by deenergizing the laser for short intervals during scans and using a filter with an adjustable bandwidth to isolate the ambient light signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a filter with fixed bandwidth is used to remove ambient light, then ambient light interference is reduced, but the information signal may be attenuated when frequencies are close
Solution Approach 1:
The patent applies dynamics by making the filter bandwidth adjustable rather than fixed. The controller dynamically adapts the filter bandwidth based on detected ambient light conditions, allowing the system to optimize between rejecting ambient light and preserving the information signal. This dynamic adjustment resolves the contradiction by enabling the filter to be wide enough to pass the information signal while still blocking ambient light frequencies.
Solution Approach 2:
The patent changes the parameter of filter bandwidth dynamically. By varying the bandwidth parameter according to the detected ambient light frequency and intensity, the system can adapt to different lighting conditions. When ambient light is strong, the bandwidth is adjusted to maintain signal passage; when ambient light frequencies are well-separated, the bandwidth is reduced to enhance rejection, thus resolving the contradiction between signal preservation and interference rejection.
2Productivity
If the scan angle is reduced to increase scan frequency, then reading speed improves, but ambient light interference increases when frequencies are close
Solution Approach 1:
The patent applies dynamics by making the scan angle adjustable during operation. The controller dynamically modifies the scan angle based on detected ambient light conditions and symbol characteristics. When ambient light interference is detected at high scan frequencies, the system increases the scan angle to reduce scan frequency, thereby moving the information signal frequency away from ambient light frequencies and reducing interference while maintaining reading capability.
Solution Approach 2:
The patent changes the scan angle parameter dynamically to control the information signal frequency. By adjusting the scan angle, the system can shift the frequency of the information signal away from problematic ambient light frequencies. This parameter change allows the system to maintain high reading speed when possible while reducing ambient light interference when frequencies overlap, resolving the contradiction between productivity and interference rejection.
3Reliability
If the filter bandwidth is increased to pass the information signal, then signal detection improves, but ambient light interference increases
Solution Approach 1:
The patent applies dynamics by making the filter bandwidth adaptive rather than fixed. The controller continuously monitors the detected signal and dynamically adjusts the filter bandwidth to be the minimum necessary to pass the information signal while maximizing ambient light rejection. This dynamic adaptation resolves the contradiction by preventing excessive bandwidth that would allow ambient light through while ensuring sufficient bandwidth for signal detection.
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 effectively reduces interference from ambient light, enhancing the decoding accuracy of bar code symbols by adjusting the scan angle and filter settings to isolate the information signal from ambient light signals, thereby improving reader performance.
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
Implementation Method 2
a laser for emitting a laser beam, a focusing lens assembly for focusing the laser beam to form a beam spot
Data Source
AI summary
A reader for electro-optically reading a target in the presence of ambient light to be rejected, includes a laser for emitting a laser beam, a scan component for scanning the laser beam over a scan angle across the target, a photodetector for generating an output signal by detecting return laser light from the target to generate an information signal bearing information related to the target, and by concomitantly detecting the ambient light to generate an ambient light signal, and signal processing circuitry for measuring the ambient light signal to determine a threshold, for processing the output signal by passing the output signal through a filter having a bandwidth, and for rejecting the ambient light signal from the output signal by adjusting the scan angle and/or the bandwidth when the ambient light signal exceeds the threshold.