Alternating Illumination Source Switching for Symbology Reader Flicker

Solution Overview

Problem

Existing symbology readers that switch between multiple illumination sources to mitigate specular reflection and improve illumination on curved surfaces suffer from a noticeable blinking effect due to illumination frequencies below the human eye's flicker fusion threshold.

Innovation Solution

The method involves activating a first illumination source during the exposure period of a frame and a second illumination source during the non-exposure period of the same frame, and then reversing this activation pattern in subsequent frames. This technique effectively increases the illumination frequency for each source from 30 to 60 Hz, eliminating the blinking effect.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If illumination sources are switched at 30 Hz to mitigate specular reflection and improve illumination coverage, then the ability to read symbologies from different angles is improved, but the human eye detects blinking because the frequency is below the flicker fusion threshold

Engineering Contradiction:

Improveillumination coverageVSAvoidblinking effect

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The illumination sources are activated in alternating frames at a frequency that synchronizes with the camera's exposure rate. By activating each illumination source during specific frames and keeping it off during others, the system creates a periodic illumination pattern that matches the camera's frame rate, eliminating visible flicker while maintaining the ability to capture symbologies from different angles.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system pre-determines which illumination sources to activate based on the camera's exposure schedule. Before capturing each frame, the controller activates the appropriate illumination source in advance, ensuring that illumination is present only when needed for image capture and not during non-exposure periods, thereby preventing visible blinking.

Inventive Principle:

Principle #10Preliminary action

2Object-affected harmful factors

If illumination sources are activated during every frame to eliminate blinking, then the flicker fusion threshold is exceeded and blinking is eliminated, but the ability to mitigate specular reflection through selective illumination is reduced

Engineering Contradiction:

Improveblinking effectVSAvoidspecular reflection mitigation

Core Design Contradiction:

Object-affected harmful factorsVSAdaptability or versatility

Solution Approach 1:

The illumination sources are activated in alternating frames at a frequency that synchronizes with the camera's exposure rate. By activating each illumination source during specific frames and keeping it off during others, the system creates a periodic illumination pattern that matches the camera's frame rate, eliminating visible flicker while maintaining the ability to capture symbologies from different angles.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

Instead of activating all illumination sources continuously, the system activates only the necessary illumination source for each specific frame based on the camera's exposure schedule. This partial activation approach provides sufficient illumination for image capture while avoiding the blinking effect that would result from continuous or improperly timed activation.

Inventive Principle:

Principle #16Partial or excessive action

3Illumination intensity

If multiple illumination sources are used to illuminate curved surfaces evenly, then illumination uniformity is improved, but the complexity of coordinating illumination timing increases

Engineering Contradiction:

Improveillumination uniformityVSAvoidillumination coordination

Core Design Contradiction:

Illumination intensityVSDevice complexity

Solution Approach 1:

The controller merges the illumination control with the camera's exposure timing system. By synchronizing illumination activation with the camera's predetermined exposure schedule, the system combines two separate timing functions into one coordinated operation, reducing the overall complexity of coordinating multiple illumination sources while maintaining even illumination on curved surfaces.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The illumination sources are activated in alternating frames at a frequency that synchronizes with the camera's exposure rate. By activating each illumination source during specific frames and keeping it off during others, the system creates a periodic illumination pattern that matches the camera's frame rate, eliminating visible flicker while maintaining the ability to capture symbologies from different angles.

Inventive Principle:

Principle #19Periodic action

Data Source

PatentUS12217123B2Flicker mitigation for multiple interspersed illumination systems

Publication Date: 2025.02.04 ZEBRA TECHNOLOGIES CORP

AI summary

A method of activating an illumination assembly within a symbology reader is provided, the illumination assembly having a first illumination source and a second illumination source, the symbology reader having an imaging sensor configured to operate at a predetermined framerate where each frame includes an exposure period over which the imaging sensor is active to capture image data and a non-exposure period over which the imaging sensor is not active to capture image data, the method comprising: during a first frame, activating the first illumination source during at least a portion of the respective exposure period and activating the second illumination source over at least a portion of the respective non-exposure period; and during a second frame, activating the second illumination source during at least a portion of the respective exposure period and activating the first illumination source over at least a portion of the respective non-exposure period.