LED Print Bar Alignment via Capacitance Sensing

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Solution Overview

Problem

LED bar-type print head systems face challenges in maintaining accurate alignment and depth of focus due to positional errors and environmental changes, leading to imaging defects, which existing methods fail to address effectively and economically.

Innovation Solution

The use of capacitance measurement systems with sensor pads to determine the position of the LED bar relative to the photoreceptor, allowing for contactless and cost-effective alignment adjustments, combined with temperature and humidity compensation to maintain optimal focus.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a lens mechanism such as a SELFOC lens is used to focus light from the LED bar on the photoreceptor, then the light can be focused on the photosensitive recording member, but the depth of focus is very small (about ±60 μm) and requires constant adjustment due to production variations and environmental changes

Engineering Contradiction:

Improvefocus accuracyVSAvoidadjustment complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical lens-based focusing system with a direct LED-to-photoreceptor imaging approach. By eliminating the SELFOC lens mechanism, the system avoids the small depth of focus problem (±60 μm) and the associated mechanical adjustment complexity. The LED bar is positioned in direct conjugate relationship with the photoreceptor surface, allowing for more tolerant alignment and eliminating the need for constant focus adjustments.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Manufacturing precision

If the depth of focus is maintained within ±60 μm tolerance, then focus accuracy is preserved, but constant adjustment is required due to production variations and environmental changes, increasing design and production cost

Engineering Contradiction:

Improvedepth of focus toleranceVSAvoidproduction cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent eliminates the mechanical lens adjustment system and replaces it with a direct imaging configuration. This substitution removes the need for constant focus adjustments and reduces sensitivity to production variations and environmental changes, thereby lowering design and production costs while maintaining adequate image quality.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the optical parameters by removing the lens mechanism entirely and using direct LED-to-photoreceptor imaging. This parameter change increases the depth of focus tolerance from ±60 μm to a much larger range, making the system more robust to manufacturing variations and environmental changes without requiring constant adjustment.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If traditional laser systems are replaced with LED bar print heads, then cost savings and reliability improvements are achieved, but alignment accuracy becomes a significant mechanical challenge

Engineering Contradiction:

Improvesystem reliabilityVSAvoidalignment measurement difficulty

Core Design Contradiction:

ReliabilityVSDifficulty of detecting and measuring

Solution Approach 1:

The patent replaces the laser-based optical system with an LED bar direct imaging system. This substitution improves reliability by eliminating laser uniformity and coherence issues, while the direct imaging geometry simplifies alignment requirements. The LED bar can be positioned in direct conjugate relationship with the photoreceptor without requiring complex optical alignment, thereby reducing alignment measurement difficulty.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This solution enables precise and automatic alignment of the LED bar with respect to the photoreceptor, improving imaging quality by maintaining the desired conjugate length and reducing production and maintenance costs associated with depth of focus corrections.

Implementation Method 1

determining a position of an LED bar with respect to a photoreceptor using capacitance measurement

Methodology Applied

Scientific EffectCapacitance measurement: Capacitance

Data Source

PatentUS9581930B2LED print bar imaging apparatus and systems useful for electrophotographic printing

Publication Date: 2017.02.28 XEROX CORP

AI summary

A print head apparatus is provided for use with a xerographic printing device having a rotating photoreceptor with a curved conductive surface. The apparatus includes an LED bar print head configured for locating adjacent the photoreceptor; a first distance sensor located on the print head at a first location, the first distance sensor being configured for measuring a first gap between the print head and the photoreceptor at the first location; and a second distance sensor located on the print head at a second location, the second location being different from the first location, the second distance sensor being configured for measuring a second gap between the print head and the photoreceptor at the second location. The print head is configured such that the sensors are arranged on the print head such that the sensors are configured to enable a measurement of angular position of the print head relative to the surface of the photoreceptor.