Digital Printing Runout Error Calibration
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Solution Overview
Problem
Digital printing systems face precision issues due to 'runout' errors in rollers, leading to misregistration of ink images on substrates, which existing methods have not adequately addressed.
Innovation Solution
A digital printing system with motorized rollers and encoders that collect rotation angle signals to compute runout correction factors, synchronizing droplet ejection from print bars with these factors to compensate for roller deviations, ensuring precise image registration across different colors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a flexible moving intermediate transfer member (blanket) is used in digital printing systems, then printing capability is enabled, but runout errors in motorized rollers cause misregistration of ink images
Solution Approach 1:
The system performs preliminary measurement of the blanket's actual position and speed using monitoring rollers and encoders before the printing process. Runout correction factors are computed in advance based on these measurements, allowing the control unit to compensate for roller runout errors during normal printing operations without stopping the process.
Solution Approach 2:
The system continuously monitors the blanket's position and speed using encoders on monitoring rollers, feeding this information back to the control unit. The control unit uses this feedback to compute runout correction factors and adjust droplet ejection timing, creating a closed-loop control system that compensates for runout errors in real-time.
2Measurement precision
If encoder signals are used to monitor roller rotation, then position control is achieved, but runout errors cause periodic deviations in the signal output
Solution Approach 1:
The control unit continuously receives feedback from encoders monitoring roller rotation and compares actual blanket position against expected position. This feedback loop allows the system to detect and compensate for periodic signal deviations caused by runout, maintaining accurate position control despite encoder imperfections.
Solution Approach 2:
The system changes the control parameter from raw encoder signals to corrected position values. By computing runout correction factors and applying them to the encoder data, the system transforms inaccurate periodic signals into accurate position information, eliminating the effect of runout errors on measurement precision.
3Manufacturing precision
If droplet ejection is synchronized with blanket advancement, then image quality is improved, but roller runout causes misalignment between droplet placement and blanket position
Solution Approach 1:
The system performs preliminary computation of runout correction factors based on encoder measurements before droplet ejection occurs. These correction factors are stored and applied in advance to the timing control, ensuring that droplets are ejected at the correct positions even when roller runout would otherwise cause misalignment.
Solution Approach 2:
The control unit uses feedback from monitoring rollers to continuously adjust droplet ejection timing. By comparing actual blanket position with expected position and applying runout correction factors, the system maintains accurate registration between droplet placement and blanket advancement, compensating for runout errors in real-time.
Data Source
AI summary
Printing apparatus (20) includes a continuous blanket (24) and a set of motorized rollers (31), which advance the blanket at constant speed through an image area. Print bars (38) eject droplets of ink at respective locations onto the blanket in the image area. Monitoring rollers (42), in proximity to the locations of the print bars, contact the blanket to be rotated by blanket advancement. Each monitoring roller includes an encoder (44), which outputs a signal indicative of a rotation angle of the monitoring roller. A control unit (40) collects, during a calibration phase, the signal from the encoders over multiple rotations of the monitoring rollers, detects a deviation of the signal from the encoder relative to a clock signal having a predefined frequency, and computes runout correction factors. During an operational phase, the control unit applies the runout correction factors to synchronize the droplets ejection from the print bars.