Transfer Bias Controller for Image Density Uniformity
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Solution Overview
Problem
Image forming apparatuses experience insufficient image density at the end portions of both smooth and uneven paper surfaces due to inadequate transfer current, particularly when using DC or superimposed transfer biases.
Innovation Solution
The apparatus switches the transfer bias between DC and superimposed transfer biases, with the end-portion voltage set higher than the body-portion voltage in DC transfer bias, and the ratio of end-portion to body-portion voltage in superimposed transfer bias adjusted to ensure sufficient image density by optimizing the control of constant current and voltage settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If DC transfer bias or superimposed transfer bias is used for transferring toner image, then sufficient toner can be transferred to the sheet surface, but insufficient image density occurs at the end portion of the sheet
Solution Approach 1:
The patent applies dynamics by making the transfer bias voltage time-dependent and position-dependent. The controller dynamically adjusts the DC voltage level based on the sheet position (end portion vs. body portion) and changes the voltage over time during the transfer process. This dynamic adjustment ensures adequate transfer current at the sheet end while maintaining proper transfer at the body portion, resolving the contradiction between uniform image density and transfer completeness.
Solution Approach 2:
The patent implements parameter changes by modifying the DC voltage parameter of the transfer bias based on sheet position and time. Specifically, the end-portion voltage is set higher than the body-portion voltage in DC transfer bias mode, and the ratio of end-portion to body-portion voltage is controlled to be smaller in superimposed transfer bias mode compared to DC transfer bias mode. These parameter adjustments ensure sufficient transfer current at the sheet end portion while maintaining overall transfer quality.
2Manufacturing precision
If superimposed transfer bias with AC component is used to reciprocate toner for concave portions, then sufficient toner transfers to uneven surfaces, but end portion image density remains insufficient
Solution Approach 1:
The patent applies local quality by implementing different voltage control strategies for different regions of the sheet. The controller distinguishes between the end portion and body portion of the sheet, applying higher end-portion voltage specifically to the end region. This localized voltage enhancement ensures that the AC reciprocating action effectively transfers toner to concave portions at the sheet end without compromising the overall transfer quality.
3Productivity
If DC transfer bias is used for smooth paper without AC reciprocating action, then transfer is efficient, but end portion still shows insufficient image density
Solution Approach 1:
The patent implements preliminary action by pre-setting the voltage profile before the sheet reaches the transfer nip. The controller prepares the higher end-portion voltage in advance based on detected sheet position, ensuring that when the sheet end enters the transfer zone, the appropriate voltage is already applied. This preliminary preparation enables efficient transfer while preventing end portion density issues.
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 configuration effectively suppresses insufficient image density at the end portions of both smooth and uneven paper surfaces by ensuring adequate transfer current and reciprocating motion of toner particles, regardless of paper type or environmental conditions.
Implementation Method 1
a transfer power supply that outputs a transfer bias for transferring a toner image on an image bearer to a recording sheet that has entered into a transfer nip formed by abutment between the image bearer and a nip forming member
Implementation Method 2
By reciprocating the toner by the AC component of the superimposed transfer bias, a sufficient amount of toner can be transferred to the concave portions on the recording sheet
Data Source
AI summary
An image forming apparatus includes a transfer power supply and a controller. The controller is configured to execute control for an end-portion voltage that is a DC voltage of a transfer bias at a time of transferring a toner image to an end portion of a recording sheet and a body-portion voltage that is a DC voltage of a transfer bias at a time of transferring a toner image to a body portion on a rear side of an end portion of a recording sheet, such that the end-portion voltage is set to be higher than the body-portion voltage in the DC transfer bias and a value obtained by dividing the end-portion voltage by the body-portion voltage in the superimposed transfer bias is set to be smaller than a value obtained by dividing the end-portion voltage by the body-portion voltage in the DC transfer bias.