Multiple Power Supply Control for Photosensitive Drum Potential Detection

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Solution Overview

Problem

Existing image forming apparatuses face challenges in accurately determining the surface potential of the photosensitive drum due to electric discharges between the charging and transfer rollers, which complicates the control of toner image density and fogging, especially when sharing a power supply circuit for generating negative and positive transfer biases.

Innovation Solution

The apparatus employs a method where a first power supply generates a first polarity voltage for the charging member and a second power supply generates a second polarity voltage for the transfer member, with a detection circuit to detect charging current, and a controller adjusts these supplies to determine the surface potential by applying a superimposed voltage during a current detection period.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a shared power supply circuit generates both negative charging bias and negative transfer bias, then device complexity is reduced, but measurement precision of surface potential deteriorates due to electric discharge interference

Engineering Contradiction:

Improvepower supply circuit structureVSAvoidsurface potential determination accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent segments the power supply operation into distinct time periods: a current detection period where only the charging bias is applied and a transfer period where the transfer bias is applied. This temporal segmentation allows the shared power supply circuit to maintain simplicity while enabling accurate surface potential measurement by isolating the detection phase from transfer operations that cause discharge interference.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements periodic action by alternating between a current detection period and a transfer period in cyclic fashion. During the current detection period, the charging bias is applied and charging current is measured to determine surface potential. During the transfer period, the transfer bias is applied for actual image transfer. This periodic switching resolves the contradiction by providing dedicated measurement time windows free from discharge interference while maintaining the simplified shared circuit architecture.

Inventive Principle:

Principle #19Periodic action

2Adaptability or versatility

If electric discharge occurs between transfer roller and photosensitive drum during charging bias application, then transfer function is maintained, but measurement precision of charging potential deteriorates

Engineering Contradiction:

Improvetransfer function capabilityVSAvoidcharging potential detection accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent segments the operational timeline into distinct phases: a current detection period where only charging bias is applied for accurate potential measurement, and a transfer period where transfer bias is applied for image transfer functionality. This temporal segmentation eliminates discharge interference during measurement while preserving transfer capabilities during the dedicated transfer period.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent performs preliminary surface potential measurement during a current detection period before applying the transfer bias. By measuring the charging potential in advance when no transfer bias is active (and thus no discharge occurs), the system obtains accurate potential data that can then be used to control the subsequent transfer operation, ensuring both measurement accuracy and transfer functionality.

Inventive Principle:

Principle #10Preliminary action

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 approach allows for accurate and efficient determination of the surface potential of the photosensitive drum, reducing electric discharges and improving toner image density control and fog reduction, while maintaining a compact power supply design.

Implementation Method 1

a detection circuit configured to detect a charging current flowing between the charging member and image bearing member

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 2

applying a superimposed voltage generated by superimposing the voltage of the first polarity and the voltage of the second polarity to the transfer member

Methodology Applied

Scientific EffectElectrical superposition: Electric Field

Implementation Method 3

a light source configured to irradiate the surface of the image bearing member with light to form an electrostatic latent image

Methodology Applied

Scientific EffectPhotoconductivity: Photoconductivity

Implementation Method 4

a developing member configured to develop the electrostatic latent image using a toner charged to a first polarity to form a toner image

Methodology Applied

Scientific EffectElectrostatic attraction: Electrostatics

Data Source

PatentUS20250244702A1Method for controlling multiple power supplies in an image forming apparatus

Publication Date: 2025.07.31 CANON KK

AI summary

A controller operates a first power supply and a second power supply in a current detection period in which a detection circuit detects a charging current, thereby applying a superimposed voltage generated by superimposing a voltage of a first polarity and a voltage of a second polarity to a transfer member. The controller determines a surface potential of an image bearing member based on the charging current detected in the current detection period.