Transfer Bias Generator for Uniform Toner Density
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Solution Overview
Problem
Existing image forming apparatuses face challenges in achieving uniform toner density on recording sheets with rough surfaces, as they struggle to transfer sufficient toner into recesses, leading to uneven density patterns and the appearance of white spots due to issues with toner adhesion and the reversing electric field in the secondary transfer nip.
Innovation Solution
An image forming apparatus with a transfer bias generator that adjusts the direct current (DC) and alternating current (AC) components of the transfer bias based on detected toner adhesion amounts, using a controller to optimize the peak-to-peak current and offset current values to enhance toner transfer efficiency and prevent white spots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a superimposed bias including AC voltage component is applied to transfer toner into recesses, then image density in recesses is improved, but white spots appear in the image area corresponding to recesses
Solution Approach 1:
The patent applies a superimposed bias consisting of DC and AC voltage components to the secondary transfer roller, creating a dynamic electric field that varies with time. The AC component dynamically adjusts the electric field strength to push toner particles into recesses, while the DC component maintains overall transfer direction, resolving the contradiction between filling recesses and preventing white spots
Solution Approach 2:
The patent changes the electrical parameters by superimposing AC voltage on DC bias, creating a time-varying electric field. This parameter change allows the system to adaptively control toner transfer: during AC peaks, strong electric fields force toner into recesses; during troughs, fields relax to prevent over-compression and white spot formation
2Quantity of substance
If strong electric field is applied to move toner into recesses, then toner transfer into recesses is improved, but toner adhesion to image carrier deteriorates
Solution Approach 1:
The patent employs periodic AC voltage superimposed on DC bias, creating cyclic electric field variations. During each AC cycle, the electric field periodically strengthens to drive toner into recesses, then weakens to allow toner adhesion to recover, achieving both deep recess filling and maintained adhesion through rhythmic electric field modulation
Solution Approach 2:
The superimposed bias ensures continuous toner transfer action through the combination of DC component (providing constant transfer drive) and AC component (providing periodic enhancement into recesses). This continuous composite action ensures toner is consistently transferred into recesses without interrupting the overall transfer process, maintaining both transfer quantity and adhesion
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
The solution ensures improved toner transfer into recesses, minimizing deficiencies in image density and white spots by dynamically adjusting the transfer bias components, resulting in more uniform and high-quality images on recording sheets with varying surface roughness.
Implementation Method 1
a transfer bias including a direct current component and an alternating current component is applied to the image carrier to transfer a toner image from the image carrier onto a recording medium
Implementation Method 2
a secondary transfer electric field is generated which electrostatically moves the toner image from the side of the secondary transfer opposite roller toward the side of the secondary transfer roller
Data Source
AI summary
An image forming apparatus includes a transfer bias generator including a transfer bias supply that supplies a transfer bias to a transfer nip formed between an image carrier and a first rotary body, and a controller that detects a toner adhesion amount at a predetermined region of the image carrier located immediately upstream from the transfer nip and having a predetermined length in a moving direction of the image carrier. The transfer bias generator outputs at least an alternating current component under one of constant voltage control and constant current control and changes a target output value of the alternating current component according to the toner adhesion amount detected by the controller.