Transfer Bias Control for Uniform Image Density
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Solution Overview
Problem
In image forming apparatuses using the electrophotographic method, the electrical resistance variation at the leading end of the recording sheet causes insufficient transfer bias, leading to reduced image density on the leading end side due to the absence of toner, resulting in an uneven transfer process.
Innovation Solution
The implementation of a superimposed transfer bias with a direct current (DC) and alternating current (AC) component, where the AC component cyclically alternates between transfer-directional and opposite-directional biases, and a controller adjusts the ratio of these components to ensure adequate bias transfer across the recording sheet, particularly at the leading end.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a constant transfer bias is applied to the transfer portion, then the transfer process is simple, but the image density becomes insufficient at the leading end where electrical resistance is high
Solution Approach 1:
The transfer bias is changed from a constant value to a time-varying waveform that includes both DC and AC components. The AC component dynamically adjusts the bias strength during different phases of the transfer process, allowing higher bias at the leading end when resistance is high, and lower bias at the trailing end where resistance decreases, thereby achieving uniform image density across the entire recording sheet.
Solution Approach 2:
The transfer bias parameter is modified by superimposing an AC waveform on the DC bias level. This creates a time-dependent bias that varies throughout the transfer cycle, enabling the system to adapt to the changing electrical resistance conditions along the recording sheet path without requiring complex multi-level control circuits.
2Manufacturing precision
If the transfer bias is increased to compensate for high electrical resistance at the leading end, then image density at the leading end improves, but the transfer process becomes uneven and may cause issues at the trailing end
Solution Approach 1:
The AC component of the transfer bias operates in a periodic manner, cycling through positive and negative phases. This periodic variation allows the system to provide enhanced bias strength during specific phases when needed (such as at the leading end with high resistance) while automatically reducing bias during other phases to prevent over-transfer at the trailing end, maintaining overall transfer uniformity.
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 ensures consistent and improved image density across the recording sheet by maintaining a sufficient transfer bias, even at the leading end, where electrical resistance is high, thereby preventing reductions in image quality.
Implementation Method 1
a transfer bias power source that outputs a transfer bias to transfer the toner image from the image bearer to a recording medium at the transfer portion
Data Source
AI summary
An image forming apparatus includes an image bearer, a transfer device contacting the image bearer to form a transfer portion, a transfer bias power source, and a controller. A ratio of a time period of application of the opposite-directional bias to a total time period of one cycle of the AC component of the superimposed bias is greater than 50%. A ratio of a value of the DC component of the superimposed bias output within a region ranging from a leading end of the recording medium to a predetermined length to a value of the DC component of the superimposed bias output outside the region is greater than a ratio of a value of the AC component of the superimposed bias output within the region to a value of the AC component of the superimposed bias output outside the region.