This report describes the functional requirements for organic photoconductors (OPCs) and the most important tests for assessing OPC performance.  It demonstrates that optimal OPC performance requires supplementing the common practice of print testing with quantitative instrumental methods.

Measurement methodologies are described for critical tests such as charge acceptance, photosensitivity, cyclic fatigue, and coating uniformity, surface defects and wear. The tools discussed are essential for serious developers, manufacturers, and users of OPC drums. They include a photoconducting drum test system, an OPC coating thickness gauge and a hand-held image analysis system.

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A case study of OEM and aftermarket drums illustrates how an OPC’s electrophotographic characteristics affect print quality.

This presentation describes the design, charging mechanisms and  functional requirements of charge rollers and introduces an advanced dielectric relaxation analysis (DRA) system employing electrostatic charge decay (ECD) technology to test charge rollers  and other semi-insulating EP components. It discusses the limitations of conventional measurement techniques and demonstrates the reliability and practicality of the non-contact ECD  approach for predicting charge roller performance.

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A case study of OEM and aftermarket charge rollers demonstrates  how charge transport performance affects print quality. The study  uses the DRA system to measure dielectric relaxation; a drum test  system to measure OPC voltage with the same set of rollers; and  a hand-held image analysis system to correlate the electrical    results with print quality. The study demonstrates the utility of the  DRA system for roller development, production QC, recycled component testing and problem-solving in a wide variety of applications.

Abstract – On Counter-Charges in Development Rollers for Electrophotography

The roles of counter-charges in toner charging and toner deposition processes for single-component development are studied by quantitative analyses of charge injection into and transport through the development rollers, taking into consideration the non-Ohmic nature of the semi-insulating overcoat layer of the rollers. The electrical requirements for the roller coatings, espacially as a consequence of increased printing speed, are elucidated. Based on the findings, an ideal evaluation technique for development roller performance is suggested.

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Abstract – Instrumentation for Control and Evaluation of Color Print Quality (2006)

This presentation discusses instrumented quality measurement techniques for EP color printing, based on fundamental measurement principles, international standards and print quality requirements.

EP processes, components and sub-systems are explained. EP color print quality, a complex system issue, is discussed and the many contributing factors elucidated. PQ requirements are examined in detail. Also examined is the role of human perception in perceived print quality of such critical factors as color, gloss, distinctness of image and others.

Print quality evaluation methodologies, both traditional (subjective) and advanced (objective), are contrasted. Diverse instrumented methodologies are discussed and compared. Various instrumented quality analysis systems are presented, as are applications of quantitative methods to specific factors such as line quality, line width, text quality, graininess and mottle, image noise, dot analysis, banding, background and other print quality elements. Features to look for in instrumented EP color print quality analysis systems are outlined.

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Abstract – Electrical Characterization of Rollers and Belts for High Speed Electrophotography

This presentation discusses QEA’s DRA-2000L, a reliable, practical tool for predicting component performance. Dielectric relaxation is critical to the performance of the charging, development and transfer rollers and belts used in electrophotography, and the ability to characterize the efficiency of dielectric relaxation in each device is key to predicting its performance. Clearly, device performance is best characterized by a test method that closely simulates the physics of the device processes themselves.

The resistance measurement method traditionally used to evaluate belt and roller performance has serious limitations and is not reliable enough to be practical for predicting performance. QEA’s non-contact, non-destructive DRA-2000L system uses the ECD (electrostatic charge decay) method of measuring dielectric relaxation, a significant advance over earlier techniques. This method simulates the physics of the charging, development and transfer processes, and for this reason measurements correlate very well with device performance.

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PQ Analysis

A Predictive Model for Text Quality Analysis: Case Study
Presented at IS&T’s NIP23: International Conference on Digital Printing Technologies
Anchorage, Alaska, September 16-21, 2007

Abstract: Text quality is a key aspect of overall print quality. Assessing text quality objectively and quantitatively has remained a challenge, despite our longstanding desire to reach this goal. The range of quality attributes is still seen by many as too broad and the definitions too vague and subjective. In this study, we aim to help overcome these obstacles by exploring whether key attributes exist that can be easily quantified and dependably correlated with subjective perceptions of print quality. If such attributes can be found, we believe a simple predictive model can be developed. For insight into which perceived attributes are critical and to help us select and design objective measurement algorithms, we started by conducting a subjective survey. Guided by the results, we performed quantitative stroke quality measurements and found good correlations between basic stroke properties (e.g., blurriness, stroke width and contrast) and the subjective survey results. We also found that text defects introduced complicating factors into the predictive model. This study provides the foundation for a more comprehensive future study.

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A Handheld Image Analysis Instrument for Portable and Objective Print Quality Analysis
Presented at the Imaging Conference Japan 2007
Tokyo, Japan, June 6-8, 2007

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