Polygon Mirror Wheel Barcode Scanner Jitter Reduction
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Solution Overview
Problem
Barcode readers with motor-driven rotating polygon mirror wheels suffer from measurement reliability issues due to jitter in trigger signals caused by surface quality variations and mechanical tolerances, leading to incorrect barcode detection, especially when partial information from multiple scans needs to be combined.
Innovation Solution
A barcode reader design that ensures the same sequence of scans is always evaluated by assigning a marking to a specific mirror surface using a marking assignment element, ensuring consistent starting points for all devices in a series, thereby eliminating systematic measurement value fluctuations and increasing detection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If trigger signals are generated from receiving element signals for each mirror surface, then scan start times can be determined, but jitter occurs due to surface quality variations and mechanical tolerances
Solution Approach 1:
A marking element is introduced as an intermediary feature on the polygon mirror wheel to provide a consistent reference point. The marking element with its specific geometric pattern (such as a slot or notch) serves as a mediator between the mechanical rotation and the signal generation system, enabling precise identification of a fixed reference position without being affected by mirror surface variations or mechanical tolerances.
Solution Approach 2:
The marking element creates a distinct optical signature that can be detected by the receiving element. The geometric pattern of the marking (such as a slot or notch) produces a characteristic signal pattern that is easily distinguishable from the regular mirror surface reflections, allowing for reliable identification of the reference position through optical detection.
2Measurement precision
If the same mirror surface is used for trigger signal generation, then systematic jitter can be eliminated, but the scanning area coverage is reduced
Solution Approach 1:
The polygon mirror wheel is segmented into multiple functional zones: marking elements are positioned on specific mirror surfaces to serve as reference points, while other mirror surfaces continue to perform the scanning function. This segmentation allows the system to maintain both precise timing references and comprehensive scanning coverage by distributing different functions across different segments of the same component.
Solution Approach 2:
The solution moves from a two-dimensional scanning plane to a three-dimensional spatial arrangement by positioning marking elements at specific angular positions on the rotating mirror wheel. This adds a temporal dimension to the spatial arrangement, allowing the system to reference time-based position information while maintaining full scanning area coverage through the rotational movement of the marked mirrors.
3Reliability
If barcode information is composed from partial information of multiple scans, then detection reliability improves, but jitter in start times makes composition difficult or impossible
Solution Approach 1:
The marking element provides a preliminary reference point that is detected before the actual barcode scanning begins. By establishing this reference position in advance, the system can accurately determine the start time of each scan and create a consistent time baseline, which is then used to properly align and compose partial barcode information from multiple scans even when jitter occurs during the scanning process.
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 significantly enhances the reliability of barcode detection by maintaining a consistent sequence of scans and calibrating received signals, reducing jitter and improving the accuracy of combining partial information from multiple scans.
Implementation Method 1
a deflection unit for periodically deflecting the transmitted light beams within a scanning area. The deflection unit is formed by a motor-driven, rotating polygon mirror wheel with several identical mirror surfaces
Implementation Method 2
the transmitted light beams are directed from the deflection unit during each period directly to a receiving element arrangement arranged outside the scanning area, from whose output signals a trigger signal is derived
Data Source
Figure 1
Figure 1a~1c
Figure 2
AI summary
The barcode reader (1) comprises an evaluation unit (9) for evaluating received signals of a receiver (6). A deflection unit is provided for periodic deflection of transmitted light beams (3) in a scanning area. The transmitted light beams are guided during scanning period through a mirror surface (11) of a motor-driven polygon mirror wheel (10). A marking assignment element is provided for assigning a marking, where a marking signal for mirror surface is generated by detecting the marking by a sensor element, by which the received signals of the scans of the mirror surfaces are referenced.