Laser Diode Power Control for Barcode Reading Interference
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Solution Overview
Problem
Laser beam readers face interference from ambient light, particularly from fluorescent lamps and LEDs operated at kilohertz frequencies, which can degrade the decoding of bar code symbols, and there is a need to monitor the output power of the laser beam to prevent exceeding safety limits.
Innovation Solution
An apparatus with a laser diode emitting an adjustable output power beam, a monitor photodiode, and signal processing circuitry that adjusts the output power to enhance the signal-to-noise ratio by increasing the power level temporarily when reading close-in targets while ensuring the power does not exceed safety limits, using dual power monitors to check the output power levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the laser output power is increased to enhance the signal-to-noise ratio and mitigate ambient light interference, then the reading performance is improved, but the safety risk increases due to potential exceeding of safety limits
Solution Approach 1:
The patent employs a feedback mechanism where the actual laser output power is continuously monitored and compared against the calculated safe maximum power level. The controller adjusts the laser drive current based on this feedback to ensure the output power remains within safe limits while maximizing reading performance. This closed-loop control resolves the contradiction by dynamically balancing performance improvement with safety constraints.
Solution Approach 2:
The patent dynamically changes the laser output power parameter based on reading conditions. The controller calculates a safe maximum power level considering ambient light interference levels and adjusts the laser drive current accordingly. This allows the system to operate at higher powers when needed for performance while automatically reducing power when safety limits are approached, resolving the contradiction between performance and safety.
2Measurement precision
If the output power is increased temporarily for close-in targets to improve signal-to-noise ratio, then the reading accuracy is enhanced, but the risk of exceeding safety limits increases
Solution Approach 1:
The patent implements periodic power adjustment where the laser output power is temporarily increased only during close-in target reading operations and returned to normal levels afterward. The controller determines when temporary power increase is needed based on target distance and ambient light conditions, applies the elevated power only for the duration of the close-in reading, then reduces power again. This periodic action allows high accuracy when needed while minimizing overall exposure and safety risks.
3Reliability
If the laser power is elevated to overcome ambient light interference from fluorescent lamps and LEDs, then the signal-to-noise ratio is improved, but the safety monitoring complexity increases
Solution Approach 1:
The patent implements a self-service power monitoring system where the controller itself performs the safety monitoring function using existing system components. The controller calculates the safe maximum power level based on ambient light measurements and automatically compares the actual output power against this limit, adjusting the laser drive current as needed. This eliminates the need for separate complex monitoring hardware while ensuring safety compliance.
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 solution effectively mitigates ambient light interference, enhancing the reading performance by increasing the signal-to-noise ratio without exceeding safety limits, ensuring safe operation by monitoring the output power levels during elevated power usage.
Implementation Method 1
a laser for emitting a laser beam having an output power
Implementation Method 2
a monitor photodiode for monitoring the output power of the laser beam
Implementation Method 3
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 target is read in the presence of interference light. A photodetector generates an output signal composed of an information signal and an interference light signal. A rangefinder determines the distance of the target in a range of working distances. A controller adjusts a scan angle of a scan drive to a narrow value and adjusts an output power of a laser diode to a low power level when the target is determined to be far out in the range. The controller adjusts the scan angle to a wide value and adjusts the output power to a high power level when the target is determined to be close in the range. Signal processing circuitry processes the output signal with the information signal having a greater magnitude than that of the interference signal due to the high power level to mitigate the presence of the interference light. A power safety arrangement including dual power monitors checks the output power of the laser beam.