Laser Power Monitoring via Threshold Compensation
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Solution Overview
Problem
Existing barcode readers face challenges in monitoring and regulating laser output power to ensure compliance with safety standards, as failures in monitor photodiodes or drive transistors can lead to increased laser output beyond regulatory limits, posing safety risks.
Innovation Solution
A method and apparatus that monitor the output power of a laser diode by sampling and compensating the driving current, using a threshold-compensated monitoring current to detect and adjust the laser power, ensuring it remains within safety limits by deenergizing the laser when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the output power of the laser is increased to enhance reading performance, then reading performance is improved, but the laser output power may exceed regulatory safety limits
Solution Approach 1:
The patent implements a feedback control system using a monitor photodiode to continuously measure the actual laser output power and compare it against safety limits. The control circuitry receives the monitor signal and adjusts the drive current to the laser diode to maintain output power within safe operating limits, preventing excessive power output while allowing maximum safe power for optimal reading performance.
Solution Approach 2:
The patent performs preliminary characterization of the laser diode to determine its threshold current and slope efficiency before operation. This pre-characterization data is stored and used by the control circuitry to calculate safe operating parameters and predict output power based on drive current, enabling preventive control before safety violations occur.
2Ease of operation
If the drive transistor fails, then the laser output power may increase to levels exceeding regulatory limits
Solution Approach 1:
The patent implements comprehensive feedback control that continuously monitors the actual laser output power via the monitor photodiode and compares it against safe limits. The control circuitry automatically adjusts the drive signal to the drive transistor to maintain power within regulatory limits, providing real-time protection against drive transistor failures or drift that could cause excessive power output.
Solution Approach 2:
The patent uses the laser diode characterization data (threshold current and slope efficiency) as an intermediary reference to verify the relationship between drive current and output power. This intermediary information allows the control circuitry to detect anomalies in drive transistor operation by comparing actual output against expected output based on characterized parameters, enabling early detection of drive transistor failures.
3Object-affected harmful factors
If the motor drive fails and the laser is deenergized, then safety is maintained, but the laser output power will not meet regulatory standards when restarted
Solution Approach 1:
The patent performs preliminary characterization of the laser diode's threshold current and slope efficiency before operation and stores this data for later use. After a motor failure and laser restart, this pre-stored characterization data enables the control circuitry to quickly recalculate safe operating parameters and re-establish compliant power levels without requiring time-consuming recalibration, ensuring regulatory compliance is restored immediately upon restart.
Solution Approach 2:
The patent implements feedback control that becomes active upon laser restart after motor failure. The monitor photodiode immediately begins measuring output power, and the control circuitry uses the characterized laser parameters to adjust the drive current, ensuring that when the laser restarts, its output power automatically complies with regulatory standards rather than operating at potentially unsafe pre-failure levels.
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 prevents excessive laser output power, maintaining compliance with safety standards and ensuring operator safety by accurately monitoring and regulating the laser diode's power output.
Implementation Method 1
a laser diode operative to emit a laser beam at a wavelength above 700 nanometers in response to a drive current
Implementation Method 2
A monitor photodiode inside the laser housing is normally operative for monitoring the raw laser output power
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A method of monitoring the output power of a laser diode in a barcode reader. The method includes sampling a threshold monitoring-current that is related the driving-current passing through the laser diode during a first time period when this current is at the lasing threshold of the laser diode. The method includes generating a threshold-compensated monitoring-current by subtracting the threshold monitoring-current from the above-threshold monitoring-current. The method includes monitoring the output power of the laser diode in the barcode reader at least partially based on the threshold-compensated monitoring-current.