Web Printer Encoder Synchronization for Front-Back Misalignment
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Solution Overview
Problem
The existing printing apparatuses face misalignment issues between images printed on the front and back surfaces of a web due to the decrease in ink landing position accuracy caused by the distance from the encoder to the inkjet heads, leading to color misregistration and decreased print image quality.
Innovation Solution
A printing apparatus is configured with two printers for each surface, each equipped with encoders that output pulse signals, and a controller that generates corrected pulse signals based on the difference in rotation cycles between the rollers to synchronize the print timings, reducing the misalignment between the images on the front and back surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the encoder is disposed near and upstream of the printer for the front surface side, then the control accuracy for the front surface printer is improved, but the ink landing position accuracy decreases for the back surface printer due to the distance from the encoder
Solution Approach 1:
A correction value calculation unit is introduced as an intermediary component that receives pulse signals from both encoders, calculates the difference in rotation cycles between the two rollers, and generates correction values. This intermediary processing step compensates for the distance-related accuracy loss by mathematically aligning the reference positions of both printers, thereby resolving the contradiction between front surface control accuracy and back surface image alignment accuracy.
2Device complexity
If the encoder is disposed far from the inkjet head, then the structural complexity is reduced, but the ink landing position accuracy decreases due to web stretching and shrinking effects
Solution Approach 1:
The system implements a feedback mechanism where pulse signals from both encoders are continuously monitored, the rotation cycle difference is calculated, and correction values are generated based on this feedback. This closed-loop feedback approach compensates for web stretching and shrinking effects that occur over distance, maintaining measurement precision without requiring the encoder to be positioned close to the inkjet head, thus reducing device complexity while preserving accuracy.
Data Source
AI summary
A controller: generates a first corrected pulse signal by correcting a received first pulse signal or generate a second corrected pulse signal by correcting a received second pulse signal, based on a difference value between a first rotation cycle of a first roller and a second rotation cycle of a second roller such that a difference between a first pulse cycle of the received first pulse signal and a second pulse cycle of the received second pulse signal is reduced; upon generating the first corrected pulse signal, controls first print timings in respective first print mechanisms of a first printer based on the generated first corrected pulse signal; and upon generating the second corrected pulse signal, controls second print timings in respective second print mechanisms of a second printer based on the generated second corrected pulse signal.