Variable Focus Lens Assembly for Bar Code Readers
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Solution Overview
Problem
Existing variable focus imaging lens assemblies for bar code readers face challenges in quickly and accurately locating a reference point for the moving lens corresponding to a reference focal plane, leading to slow acquisition of decodable images and potential systematic errors due to mechanical changes over time.
Innovation Solution
A variable focus imaging lens assembly that includes a lens movable along a path of travel, a drive mechanism, and a focusing system that projects a virtual image of a light source within the field of view to determine an acceptable in-focus resolution, allowing the lens to be positioned at a reference point providing optimal image clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a variable focus lens system is used to address blurriness at working range limits, then image resolution is improved, but the complexity of locating the reference point increases and acquisition time is lost
Solution Approach 1:
The system performs preliminary calibration by projecting a virtual image of a light source to a predetermined position within the field of view that coincides with the reference focal plane. The focusing system then energizes the drive mechanism to drive the moving lens along its path of travel and analyzes successive image frames to determine when an acceptable in-focus resolution of the virtual image is achieved, thereby establishing the moving lens reference point in advance before actual bar code reading operations begin.
2Adaptability or versatility
If mechanical movement of the lens is used to adjust focus, then adaptability to different distances is improved, but reliability decreases due to mechanical changes over time
Solution Approach 1:
The focusing system continuously monitors the image frames captured by the sensor array and analyzes the resolution quality of the virtual image projected by the projection assembly. Based on this feedback, the system determines when the moving lens has achieved the acceptable in-focus resolution and establishes the reference point accordingly. This closed-loop feedback mechanism compensates for mechanical drift and ensures reliable reference point identification despite mechanical changes over time.
3Adaptability or versatility
If the lens is moved along a path of travel to find the reference point, then focusing flexibility is improved, but device complexity increases
Solution Approach 1:
The projection assembly serves as an intermediary by projecting a virtual image of a light source to a predetermined position within the field of view that coincides with the reference focal plane. This virtual image acts as a reference target that the focusing system can use to determine when the moving lens has reached the correct reference position, simplifying the overall system by providing a clear, measurable reference point without requiring complex mechanical positioning markers or additional reference structures.
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 solution enables rapid and accurate focusing of images, reducing blurriness at the limits of the working range and mitigating systematic errors, thereby enhancing the efficiency and reliability of bar code reading.
Implementation Method 1
a projection assembly projecting a virtual image of a light source to a predetermined position within the field of view and coincident with the reference focal plane
Implementation Method 2
a lens assembly focusing light from the field of view onto the sensor array
Data Source
AI summary
A variable focus imaging lens assembly (50) for an imaging-based bar code reader (10) including: a lens assembly (52) focusing light from a field of view (FV) onto a sensor array (28), the lens assembly (52) including a lens (53) movable along a path of travel; a drive mechanism (58) to drive the moving lens (53); a focusing system (60) for establishing a reference point (RP) for the moving lens (53) along the path of travel corresponding to a reference focal plane (RFP) within the field of view; and a projection assembly (62) projecting a virtual target image (64a) of a reference target light source (64) to a predetermined position (P) within the field of view and coincident with the reference focal plane (RFP), the predetermined position (P) being a known distance (D) from the lens assembly (52) along its optic axis (OA).