Laser Power Control in Electro-Optic Readers
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Solution Overview
Problem
Laser power output in electro-optical readers often exceeds regulatory limits due to failures in monitor photodiodes or drive transistors, posing safety risks and requiring mechanisms to deenergize the laser while ensuring performance meets safety standards.
Innovation Solution
A laser power control arrangement that uses a microcontroller to adjust a digital potentiometer during calibration to set known output powers within regulatory limits, records drive current differences, and compares these during operation to deenergize the laser if output exceeds limits, and reduces power if the motor drive fails, ensuring safe operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the laser output power is increased to enhance reading performance, then the reading capability is improved, but the safety regulatory limits are exceeded
Solution Approach 1:
The patent performs preliminary calibration before normal operation to establish safe operating parameters. The microcontroller calibrates the laser output power and stores calibration data that defines safe operating ranges, ensuring that during subsequent operation the laser remains within regulatory limits while maintaining optimal reading performance.
Solution Approach 2:
The patent implements continuous feedback monitoring using a monitor photodiode that detects laser output power in real-time. The microcontroller compares the monitored power level against calibrated safe limits and automatically adjusts the laser drive current or shuts down the laser if limits are exceeded, thus maintaining both performance and safety.
2Reliability
If the monitor photodiode fails or loses sensitivity, then the feedback control is compromised, but the laser output power may exceed regulatory limits
Solution Approach 1:
The patent performs preliminary calibration to establish expected monitor photodiode readings for known laser power levels. During operation, the microcontroller compares actual monitor readings against these calibrated expectations to detect photodiode failures or drift, and takes corrective action before unsafe power levels are reached.
Solution Approach 2:
The patent implements redundant safety mechanisms that provide a safety margin before actual harm occurs. The microcontroller monitors for photodiode failure conditions and preemptively reduces or shuts off laser power when anomalies are detected, preventing the harmful effect of uncontrolled high power output.
3Reliability
If the drive transistor fails, then the laser control is lost, but the laser output power may increase to excessive levels
Solution Approach 1:
The patent uses the monitor photodiode feedback circuit to continuously monitor laser output power and detect drive transistor failures. When the microcontroller detects that the monitor photodiode signal deviates from expected values corresponding to the drive current level, it infers transistor failure and automatically reduces or shuts off laser power to prevent excessive output.
Solution Approach 2:
The patent introduces the monitor photodiode as an intermediary sensing element that provides indirect measurement of laser power and drive circuit health. This intermediary feedback path allows the microcontroller to detect drive transistor failures and respond appropriately without direct monitoring of the transistor itself.
4Object-affected harmful factors
If the motor drive fails and the laser is deenergized, then safety is improved, but the reader performance is reduced
Solution Approach 1:
The patent dynamically adjusts laser power based on motor drive status. When motor failure is detected, the microcontroller reduces laser power to safe levels for stationary beam conditions rather than completely shutting down, allowing limited operation to continue while maintaining safety. The system transitions between different power states based on operational 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
Effectively regulates laser power to meet safety standards, preventing excessive output while maximizing reader performance by using drive current differences to account for temperature variations and motor drive failures.
Implementation Method 1
a laser beam from a laser is directed along a light path toward a target that includes the bar code symbol
Implementation Method 2
The photodetector or sensor is positioned such that it has a field of view which ensures the capture of the reflected or scattered light, and converts the latter into an electrical analog signal
Data Source
Figure 1
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Figure 3~4
AI summary
Laser power control arrangements interrupt power to a laser used in electro-optical readers upon detection of an over-power condition not conforming to preestablished regulatory standards. In one embodiment, during an operational mode, a difference between laser drive currents at two operating points is compared to a difference between laser drive currents at the same two operating points during a calibration mode. The over-power condition is recognized when the difference during the operational mode exceeds the difference during the calibration mode by a predetermined amount. In another embodiment, the laser is only energized to emit the beam at a reduced power level well below regulatory standards for staring at even if a motor drive failed.