Laser Persistence Minimization in CMOS Barcode Readers
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Solution Overview
Problem
Two-dimensional barcode readers with CMOS sensors face issues due to laser persistence, where the reference laser interferes with sensed light patterns, leading to misreading of codes, as CMOS sensors lack a mechanical shutter and rely on electronic shutters.
Innovation Solution
Implementing a timing circuit that controls both the electronic shutter and the reference laser, ensuring the laser is switched off during image exposure times and delayed to be activated only after the residual exposure time, minimizing its impact on the image captured by the CMOS sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a reference laser is used to indicate position in handheld scanners, then the user can see where the image sensors are directed, but the laser beam interferes with the sensed light patterns and causes misreading of codes
Solution Approach 1:
The laser is turned off before the image sensor exposure begins and remains off during the entire exposure period. This preliminary action of deactivating the laser prevents any laser light from reaching the sensor during code capture, eliminating laser persistence artifacts while still allowing the laser to be activated afterward for user guidance.
Solution Approach 2:
The laser operates in a periodic on-off pattern synchronized with the sensor exposure cycle. The laser is activated after exposure completes, remains on for a brief period to provide user feedback, then turns off before the next exposure begins. This periodic operation ensures the laser provides guidance functionality while avoiding interference with code reading.
2Measurement precision
If a mechanical shutter is used to block laser light during exposure, then laser persistence is eliminated, but CMOS sensors typically do not use mechanical shutters and rely on electronic shutters instead
Solution Approach 1:
The patent replaces the mechanical shutter system with an electronic control approach. Instead of using a physical shutter to block laser light, the system uses electronic timing to control the laser diode's operation, turning it off during sensor exposure through electronic signals. This eliminates the need for complex mechanical moving parts while achieving the same goal of preventing laser light from reaching the sensor during exposure.
3Ease of operation
If the laser is kept on continuously to provide user guidance, then the user always sees the field of view indication, but the laser beam persists in the image sensor and interferes with light pattern sensing
Solution Approach 1:
The laser is deactivated before the sensor exposure begins, ensuring no laser light reaches the sensor during the critical imaging period. This preliminary deactivation prevents laser persistence from contaminating the captured image while still allowing the laser to be activated afterward to provide continuous user guidance during non-exposure periods.
Solution Approach 2:
The system uses the sensor's own exposure timing information to automatically control the laser's operation. The laser control circuit receives the exposure timing signal and autonomously activates or deactivates the laser at the appropriate moments, eliminating the need for external control mechanisms while ensuring proper synchronization between laser operation and sensor exposure.
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 laser persistence, enhancing the accuracy of barcode reading by preventing the reference laser from interfering with the image sensor during exposure, thus improving code recognition.
Implementation Method 1
The laser radiation is reflected off the lines and spaces and can be sensed by a light sensor
Implementation Method 2
an electronic shutter configured to expose the array of pixels for a first period of time
Implementation Method 3
a reference laser configured to indicate a position related to a field of view of the image sensor
Implementation Method 4
A problem with the use of a reference laser when using CMOS sensors is that many CMOS sensors being developed today do not typical use a mechanical shutter as is used in other types of image sensors. Instead, CMOS sensors may use an electronic shutter. Without a mechanical shutter, the reference laser beam can interfere with the sensed light patterns and therefore can lead to a misreading of the codes.
Data Source
AI summary
Systems and methods for minimizing laser persistence are provided. In one implementation, a timing circuit for controlling a barcode reader is provided. The timing circuit comprises a shutter control circuit configured to control an electronic shutter function of an image sensor and a laser control circuit configured to control the activation of a reference laser. When activated, the reference laser directs a laser beam to an approximate position of a field of view of the image sensor. The activation of the reference laser includes a delay to minimize laser persistence on an image captured by the image sensor.