Fixing Device Voltage Polarity Control for Sheet Electrostatic Attachment

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Solution Overview

Problem

In electrophotographic image forming apparatuses, sheets after the fixing step often become electrostatically attached due to increased charge, making them difficult to align for post-processing tasks like cutting and punching, and existing solutions fail to sufficiently neutralize both sides of the sheets.

Innovation Solution

An image forming apparatus with a fixing device that includes a fixing side member, a back side supporting member forming a fixing nip, and a voltage applying section that applies opposite polarities of voltage to both sides of the sheet to cancel out surface potentials, with detection and adjustment based on toner image coverage, sheet resistance, and printing mode.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If high voltage is applied to increase the amount of charge for better image quality and transferring, then the surface potential of the sheet is increased, but the sheets become electrostatically attached to each other

Engineering Contradiction:

Improveimage qualityVSAvoidelectrostatic attachment

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies a discharging brush to neutralize the electrostatic charge on the sheet surface after the fixing step, before the sheet is placed in the placement tray. This preliminary anti-action counteracts the harmful electrostatic attachment effect by removing the accumulated charge that causes sheets to stick together, while allowing the high voltage charging process to proceed normally for image quality improvement.

Inventive Principle:

Principle #9Preliminary anti-action

2Productivity

If the speed of sheet conveyance is increased to improve productivity, then the charging frequency is increased, but the electrostatic attachment problem worsens

Engineering Contradiction:

Improvesheet conveyance speedVSAvoidelectrostatic attachment

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The discharging brush is positioned to continuously neutralize electrostatic charge on sheets as they pass through the fixing step, ensuring that the anti-electrostatic action occurs continuously with each sheet without interruption. This continuous action maintains effectiveness regardless of how quickly sheets are being processed, allowing high-speed conveyance while preventing electrostatic attachment.

Inventive Principle:

Principle #20Continuity of useful action

3Productivity

If duplex printing frequency is increased to improve productivity, then the charging frequency is increased, but the electrostatic attachment problem worsens

Engineering Contradiction:

Improveduplex printing frequencyVSAvoidelectrostatic attachment

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The discharging brush operates continuously for each sheet undergoing duplex printing, ensuring that electrostatic charge is neutralized after each fixing step whether it's the first or second side of the sheet. This continuous neutralization action maintains effectiveness regardless of the increased frequency of duplex printing operations.

Inventive Principle:

Principle #20Continuity of useful action

4Device complexity

If only one side of the sheet is neutralized by the discharging brush, then the device complexity is reduced, but the electrostatic attachment problem cannot be sufficiently solved

Engineering Contradiction:

Improvedischarging brush configurationVSAvoidelectrostatic attachment

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The sheet itself serves as the object being neutralized by the discharging brush. The brush makes contact with the sheet surface and automatically neutralizes the electrostatic charge without requiring additional complex mechanisms such as multiple brushes, rollers, or separate neutralization systems. The simple brush design achieves effective neutralization through direct contact with the sheet surface.

Inventive Principle:

Principle #25Self-service

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 effectively prevents sheets from electrostatically attaching post-fixing, ensuring easier alignment and reducing negative impacts on post-processing by sufficiently neutralizing both sides of the sheets, improving the overall process efficiency.

Implementation Method 1

a voltage applying section that applies to both sides of the sheet passed through the fixing nip voltages opposite in polarity to surface potentials of the both sides

Methodology Applied

Scientific EffectElectrostatic neutralization: Electrostatic Discharge

Implementation Method 2

a back side supporting member that forms a fixing nip for conveying the sheet in a tightly sandwiching manner when the back side supporting member is in pressure contact with the fixing side member

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS9223260B2Image forming apparatus and fixing device

Publication Date: 2015.12.29 KONICA MINOLTA INC

AI summary

An image forming apparatus includes a fixing side member disposed at a position on a fixing surface side of a sheet on which a toner image is formed; a back side supporting member that forms a fixing nip for conveying the sheet in a tightly sandwiching manner when the back side supporting member is in pressure contact with the fixing side member; and a voltage applying section that applies to both sides of the sheet passed through the fixing nip voltages opposite in polarity to surface potentials of the both sides.