Sheet Registration via Offset Rotational Skew Control
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Solution Overview
Problem
Existing media handling systems, particularly in printing systems, face challenges in accurately registering the leading edge of a sheet due to skew and lateral misalignment, which can lead to errors in image and color registration, and the current methods introduce errors in leading edge arrival time at the registration datum.
Innovation Solution
A system with first and second nip assemblies and sheet leading edge sensors, where a controller imparts a rotational skew velocity to the sheet, with the skew velocity center of rotation offset laterally from the leading edge, allowing for precise registration by adjusting the sheet driving velocities of the nip assemblies based on sensor offset distances and lateral positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If separate drive rollers are used to correct skew mispositioning, then sheet skew correction is improved, but leading edge arrival time registration accuracy deteriorates
Solution Approach 1:
The patent introduces a lateral dimension offset for the center of rotation relative to the sheet leading edge. By positioning the center of rotation laterally offset from the leading edge center, the system creates a three-dimensional registration approach that simultaneously addresses skew correction and leading edge arrival time accuracy, resolving the contradiction between these two functions.
Solution Approach 2:
The patent employs asymmetric positioning of the center of rotation relative to the sheet leading edge. Instead of symmetric alignment, the center of rotation is deliberately offset laterally, creating an asymmetric configuration that enables simultaneous skew correction and accurate leading edge registration by differentiating the rotational action from the leading edge position.
2Loss of time
If sheet velocity is varied to deliver sheet at target time, then delivery timing is improved, but sheet position accuracy deteriorates
Solution Approach 1:
The patent segments the velocity control into two independent components: process direction velocity for timing control and lateral velocity for position control. This segmentation allows the system to adjust delivery timing through process direction speed variations while maintaining position accuracy through separate lateral positioning, eliminating the trade-off between timing and position.
Solution Approach 2:
The patent adds a lateral dimension to the velocity control system. By introducing lateral velocity control independent of process direction velocity, the system can adjust delivery timing through process speed while maintaining position accuracy through lateral adjustments, resolving the contradiction between timing and position control.
3Difficulty of detecting and measuring
If leading edge sensors are positioned to detect arrival, then detection capability is improved, but skew measurement accuracy deteriorates
Solution Approach 1:
The patent positions the leading edge sensor asymmetrically relative to the center of rotation, specifically offset laterally. This asymmetric positioning allows the sensor to accurately detect leading edge arrival while the offset configuration enables separate measurement of skew through the relationship between sensor detection and rotation center position.
Solution Approach 2:
The patent introduces the center of rotation as an intermediary reference point that mediates between sensor detection and skew measurement. The center of rotation serves as a geometric reference that allows the system to differentiate between leading edge arrival detection and skew angle measurement, improving both detection capability and measurement precision.
Data Source
AI summary
Accurate sheet leading edge registration system and method including a first and second nip assembly, a first sheet leading edge sensor and a controller. The first and second nip assemblies being spaced apart from one another. The first sheet leading edge sensor capable of detecting an arrival of a leading edge of a sheet at a point in the process direction. The arrival being associated with engagement of the first and second nip assemblies with the sheet. The controller capable of imparting a rotational skew velocity to the sheet using the first and second nip assemblies. A center of rotation of the skew velocity being offset laterally from a center of the sheet leading edge and being coincident with a lateral position of a virtual point, the virtual point lateral position being offset from a lateral position of the first sheet leading edge sensor.