Laser Printer Dot Clock Controller for Color Plane Alignment
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Solution Overview
Problem
Inline color laser printers face challenges in aligning color planes due to misregistration, skew, and mismatched sizes of laser scanning units, leading to print quality degradation and artifacts, with existing calibration methods being expensive or visible in the printed output.
Innovation Solution
A controller system using a master clock and frequency dividers to generate dot clock signals, allowing precise control of dot boundaries and alignment, and compensating for angular velocity variations in the mirror, enabling accurate and efficient alignment of color planes without complex mechanical adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If four laser scanning units are used to expose each of the four CYMK color planes in a single pass, then printing speed is improved, but alignment precision of color planes deteriorates
Solution Approach 1:
The system uses feedback from a sensor that detects the actual position of each color plane as it is printed. This feedback information is used to dynamically adjust the timing and positioning of subsequent color planes, compensating for variations in laser scanning unit positions and maintaining precise alignment despite the high-speed single-pass printing process
Solution Approach 2:
The system dynamically changes the timing parameters (dot clock signals) for each laser scanning unit based on detected alignment variations. By adjusting the frequency and phase of dot clock signals for each color plane, the system compensates for positional variations and maintains precise color alignment during high-speed printing
2Manufacturing precision
If the position of each laser scanning unit is adjusted mechanically to improve alignment, then alignment precision is improved, but device complexity and cost increase
Solution Approach 1:
The system replaces complex mechanical adjustment mechanisms with an electronic control system. Instead of physically moving laser scanning units to achieve alignment, the system uses electronic timing adjustments via dot clock signals and feedback control to achieve precise alignment, thereby reducing mechanical complexity while maintaining or improving alignment precision
3Manufacturing precision
If dot deletions or insertions are used to compensate for scan line differences, then alignment precision is improved, but visible artifacts are introduced in the printed output
Solution Approach 1:
Instead of deleting or inserting dots, the system changes the timing parameters of the dot clock signals to precisely control dot placement. By adjusting the frequency and phase of the dot clock, the system achieves alignment compensation through continuous parameter variation rather than discrete dot deletions or insertions, thereby avoiding visible artifacts while maintaining alignment precision
Data Source
AI summary
Laser printers are plagued with an assortment of alignment issues. In color laser printers the issues are exacerbated. Variations in distance from the mirror to the drum can lines in different color planes to vary in size. Variations in angles in the facets of the mirror can cause alignment issues between lines. Even lack of synchronization between the dot clock and start of line indication can cause misalignment between rows. In addition, a cosine distortion occurs due to the non-constant linear velocity of the laser scan of a single line. A very high speed master clock can drive the laser scanning unit. By using a very high speed clock, the control circuitry has the resolution to compensate for many of these distortion types, by appropriately counting clock cycles and indicating such to the laser modulator.