Transfer Roller Voltage Polarity Control for Sheet Separation
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Solution Overview
Problem
Existing image forming apparatuses face issues with poor separation of sheets from the image carrier and incomplete toner image density due to burrs at the leading edge of sheets during the transfer process, as existing solutions do not fully prevent sheet winding around the image carrier and fail to secure consistent toner image density.
Innovation Solution
A transfer device with a control method that adjusts the voltage applied to the transfer roller, using a specific voltage pattern to prevent sheet separation issues by controlling the electric field direction and ensuring proper toner image transfer, including applying opposite polarity voltage before the sheet enters the transfer nip to prevent discharge and switching to transfer polarity once the sheet is aligned for effective image transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transfer voltage is applied to the transfer roller to transfer toner images, then toner transfer efficiency is improved, but sheet separation reliability deteriorates when burrs are present at the leading edge
Solution Approach 1:
The patent applies a preliminary voltage (first polarity) to the transfer roller before the sheet's leading edge enters the transfer nip. This preliminary action prevents discharge at the burr location, thereby preventing the sheet from winding around the image carrier and ensuring reliable sheet separation before the main toner transfer process begins.
Solution Approach 2:
The patent employs periodic voltage application with two distinct polarities: a first polarity applied before the sheet enters the transfer nip to prevent discharge and ensure separation, and a second polarity (opposite to the first) applied when the sheet is properly positioned for toner transfer. This periodic switching resolves the contradiction between sheet separation reliability and toner transfer efficiency.
2Reliability
If voltage is applied in the predetermined area of the leading edge to prevent discharge, then sheet separation is improved, but toner image density deteriorates
Solution Approach 1:
The patent switches the voltage polarity applied to the transfer roller based on the sheet position. When the leading edge is in the predetermined area, a first polarity is applied to prevent discharge and ensure separation. When the sheet is properly positioned for transfer, the voltage switches to a second polarity (opposite polarity) that enables effective toner transfer and ensures proper image density.
Solution Approach 2:
The patent dynamically adjusts the voltage polarity applied to the transfer roller according to the sheet's position in the transfer nip. The system transitions from a static voltage application to a dynamic, position-dependent voltage control, allowing optimal voltage polarity to be applied at different stages of the transfer process to simultaneously achieve good sheet separation and toner image density.
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
Prevents poor separation of sheets from the image carrier and ensures full toner image density by managing the electric field effectively, preventing discharge and ensuring proper toner transfer, even with sheets having leading edge burrs.
Implementation Method 1
voltage (transfer voltage) having a polarity which is opposite to the polarity of toner is applied to a transfer roller T to move the toner onto the sheet S from the photoreceptor K
Implementation Method 2
electric discharge occurs in the opening which is formed at the leading edge of the sheet between the transfer belt B and the sheet S, and the edge of the sheet S in the conveyance direction is charged with the same polarity of the transfer voltage
Data Source
Figure 1
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AI summary
A transfer device includes: a transfer section for transferring a toner image on an image carrier onto a sheet passing through a nip portion which is formed between the transfer section and the image carrier; an application section for applying a voltage to the transfer section; and a control section for controlling the application section, whereon the control section controls the application section to apply a voltage having an opposite polarity to a transfer polarity to the transfer section since a leading edge of the sheet in a conveyance direction advances into the nip portion until a predetermined non image area of the sheet has passed through the nip portion, and then switch to apply a voltage having the transfer polarity from the voltage having the opposite polarity to the transfer section while a non image area of the sheet passes through the nip portion.