Dual Encoder System for Printing Velocity Noise Compensation
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Solution Overview
Problem
Existing printing systems face challenges in accurately synchronizing the firing of ejectors in printheads with the position of substrates due to noise sources like phase-lag, roller runout, and thermal expansion, which affect the registration of marking material drops, especially in 3D printing.
Innovation Solution
A dual encoder feedback system is implemented, using a primary encoder to maintain constant velocity and a secondary encoder to compensate for high-frequency velocity variations, generating dot clock signals that activate ejectors with precise timing to ensure accurate marking material transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single encoder is used to coordinate ejector firing with substrate position, then the system structure remains simple, but registration accuracy deteriorates due to noise sources like phase-lag, roller runout, and thermal expansion
Solution Approach 1:
The single encoder function is segmented into two separate encoders: a primary encoder that generates base dot clock signals and a secondary encoder that generates correction signals. This segmentation allows each encoder to specialize in different aspects of position measurement, improving overall registration accuracy while distributing the complexity across two simpler components rather than one complex system.
Solution Approach 2:
A correction signal generated by the secondary encoder acts as an intermediary between the primary encoder's position measurements and the final ejector firing timing. This intermediary correction signal compensates for noise sources like phase-lag and roller runout, bridging the gap between imperfect measurements and accurate positioning.
2Manufacturing precision
If feed-forward corrections are applied to compensate for roller runout and thermal expansion, then some positioning errors are reduced, but they cannot fully compensate for all noise sources including phase-lag
Solution Approach 1:
The system implements feedback by using the secondary encoder to continuously monitor actual substrate position and generate real-time correction signals. Unlike open-loop feed-forward corrections, this feedback mechanism dynamically adjusts for all noise sources including phase-lag, ensuring robust compensation throughout the printing process.
Solution Approach 2:
The correction signals from the secondary encoder are prepared in advance and applied to the dot clock generation process before ejector firing occurs. This preliminary correction ensures that positioning errors are compensated proactively rather than reactively, improving both accuracy and reliability.
3Manufacturing precision
If the encoder feedback system does not account for velocity changes in the print zone, then the system operation remains simple, but registration accuracy deteriorates over long print zones
Solution Approach 1:
The system transitions from static encoder feedback to dynamic velocity compensation by introducing a second encoder that specifically measures velocity variations in the print zone. This dynamic approach allows the system to adapt to changing conditions during operation, maintaining registration accuracy across long print zones without excessive complexity.
Data Source
AI summary
A printing system includes a pair of encoders to compensate for encoder noise in the velocity of a media transport as the transport moves past a plurality of printheads. One encoder monitors a roller that positioned at a location of low thermal stress and the signal generated by this encoder is used by a controller to maintain a constant velocity for the media transport. The second encoder monitors a roller used to drive the media transport and is positioned close to the print zone opposite the printheads. The signal from the second encoder is used to identify a corrected distance between each tic in the tics generated by the second encoder and the corrected distance is used to count a firing distance for generation of a dot clock signal to activate ejectors in a printhead when a substrate has traveled the firing distance.