Encoder Runout Correction via Hybrid Distance-Time Clocks
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Solution Overview
Problem
In printing devices, particularly for 3D printing, accurately registering drops in the process direction and ensuring drops from separated printheads are printed at the required absolute location is challenging due to sinusoidal runout errors caused by non-coaxial encoder spacing, which is difficult to correct with long test patterns.
Innovation Solution
The solution involves using measured time between encoder tics to generate runout correction tables, calculating the positions of media transport as a function of angular position, and implementing a hybrid approach with a primary distance clock and a secondary time-driven clock to correct for encoder runout, ensuring accurate dot clock spacing and location without drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If long test patterns (20m) are printed to generate runout correction tables, then encoder runout correction accuracy is improved, but device complexity and operational difficulty increase due to the inability to print such long patterns in cut-sheet or 3D printing systems
Solution Approach 1:
The patent divides the encoder runout measurement process into multiple segments by using multiple shorter test patterns instead of requiring one extremely long test pattern. Each segment contributes to building the complete runout correction table, making the process feasible for cut-sheet and 3D printing systems that cannot handle 20m continuous patterns.
Solution Approach 2:
The patent transitions from a spatial approach (printing one extremely long linear pattern) to a temporal approach (accumulating measurements over multiple revolutions and patterns). By integrating measurements over time and multiple cycles, the system achieves the same correction accuracy without requiring excessive linear space.
2Manufacturing precision
If encoder runout is not corrected, then device complexity remains low, but manufacturing precision deteriorates due to sinusoidal runout errors causing inaccurate drop placement
Solution Approach 1:
The patent performs preliminary measurement and characterization of encoder runout errors during system setup or calibration phases. By pre-measuring the sinusoidal runout characteristics and storing correction data in lookup tables, the system eliminates the need for complex real-time correction calculations during actual printing operations, maintaining low operational complexity while achieving high precision.
Solution Approach 2:
The patent introduces intermediary correction tables that store pre-calculated runout compensation data. These tables act as a mediator between the simple encoder measurements and the precise drop placement requirements, translating raw encoder positions into corrected positioning commands without requiring complex real-time computation.
3Measurement precision
If a single distance clock is used, then device complexity is low, but measurement precision deteriorates due to accumulation of errors over distance
Solution Approach 1:
The patent segments the distance measurement function into two separate clock systems: a primary distance clock for integer encoder counts and a secondary time-driven clock for fractional distances. This segmentation allows each clock to operate within its optimal precision range, with the distance clock handling coarse positioning and the time clock handling fine positioning, thereby eliminating error accumulation while maintaining manageable complexity.
Solution Approach 2:
The patent implements a dynamic switching mechanism between the two clock systems. The system automatically transitions from the distance clock to the time clock when fractional positioning is needed, creating a flexible hybrid timing system that adapts to different positioning requirements and maintains high precision throughout the entire measurement range.
Data Source
AI summary
Methods, Apparatus, Devices and Systems herein load a firing distance into a distance counter of a printing device. The firing distance is the distance from the current position of a printhead of the printing device to a marking location on a substrate and the distance is calculated based on an angular encoder operatively associated with a roller used to transport a marking media to the printhead for marking. These devices and methods count the firing distance in angular distance increments as a function of the encoder angular position to correct for encoder roller runout using the distance counter, based on relative movement of the substrate and printhead. When the distance counter reaches the last discrete distance increment corrected for encoder roller runout of the firing distance, these devices and methods load the fractional remaining distance of the firing distance into a time counter of the printing device. Then, the fractional remaining distance is counted using velocity-based distance increments at regular time intervals using the time counter. When the time counter reaches the last velocity-based calculated distance increment of the fractional remaining distance, the marking material is transferred from the printhead to the substrate.