Flexible Intermediate Transfer Member Stretch Compensation
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Solution Overview
Problem
In digital printing systems using an intermediate transfer member, the longitudinal stretching of the ITM causes variations in inter-droplet spacing of ink images, leading to inconsistencies when images are transferred from the ITM to a substrate.
Innovation Solution
A method is disclosed that involves measuring the local velocity of the ITM under print bars, determining a time-interval-specific stretch factor based on the stretched length and a fixed physical distance, and controlling the ink deposition parameter, such as droplet spacing, to compensate for the stretching of the ITM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the downstream drive roller imparts a higher velocity to the belt than the upstream drive roller, then the belt remains taut in the image forming station, but the belt becomes stretched longitudinally causing variation in inter-droplet spacing
Solution Approach 1:
The system dynamically adjusts the ink droplet ejection timing based on real-time velocity measurements of the intermediate transfer member. The controller modifies the ejection timing of the first and second inkjet devices to compensate for the stretching effect, ensuring consistent inter-droplet spacing despite the varying belt velocity and tension conditions
Solution Approach 2:
The system employs velocity sensors to continuously monitor the local velocity of the intermediate transfer member at the image forming station. This feedback information is used by the controller to calculate the actual stretched length and adjust the ink droplet ejection timing accordingly, creating a closed-loop control system that maintains printing precision
2Stability of the object's composition
If the belt is stretched between upstream and downstream drive rollers, then the belt remains taut during image formation, but the stretch factor at the impression station differs from the stretch factor at the image-forming station
Solution Approach 1:
The system measures the velocity of the intermediate transfer member at specific locations (under the print bars) to determine the local stretch factor at the image forming station. This localized measurement approach allows the system to account for variations in stretching at different positions along the belt path, enabling precise compensation for the specific conditions at the image forming station
Solution Approach 2:
The controller calculates the stretched length and determines the appropriate ink droplet ejection timing before the actual printing occurs. By pre-calculating the compensation based on measured velocity data, the system prepares the correct ejection parameters in advance, ensuring that the ink droplets are deposited at the correct intervals despite the stretching conditions
Data Source
AI summary
Methods for printing using printing systems comprising a flexible intermediate transfer member (ITM) disposed around a plurality of guide rollers at which encoders are installed, and an image-forming station at which ink images are formed by droplet deposition by print bars onto the ITM, can include measuring a local velocity of the ITM under one of the print bars, determining a stretch factor for a portion of the ITM based on a relationship between an estimated stretched length fixed physical distance between print bars, controlling an ink deposition parameter according to the stretch factor so as to compensate for stretching of the reference portion of the ITM.