Pre-exposure Light Control for Transfer Ghost Suppression
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Solution Overview
Problem
The DC charging method for electrophotographic image forming apparatuses suffers from non-uniform surface potential of photosensitive members, leading to transfer ghost and charging lateral stripe issues, particularly in tandem-type systems where secondary color toner images are formed, resulting in image density non-uniformity and defects.
Innovation Solution
The apparatus includes a movable intermediary transfer member with multiple image forming units, where the third unit uses a charging roller supplied with DC voltage and a pre-exposure member to expose the photosensitive member downstream of the transfer portion, allowing for adjustable exposure amounts and pre-exposure light quantities to optimize toner transfer and reduce ghosting and lateral stripe defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If DC charging method is used to charge the photosensitive member, then the lifetime of the photosensitive member is extended and running cost is reduced, but the surface potential uniformity deteriorates leading to transfer ghost and charging lateral stripe defects
Solution Approach 1:
The patent applies pre-exposure light irradiation to the photosensitive member before the charging process. This preliminary action equalizes the surface potential across the photosensitive member, preventing the formation of transfer ghosts and charging lateral stripes while maintaining the benefits of DC charging method.
Solution Approach 2:
The patent changes the physical state of the photosensitive member by irradiating it with light of specific wavelength ranges (blue region 450-495nm, green region 495-560nm, or yellow-green region 560-590nm). This parameter change in light exposure modifies the surface potential distribution, enabling uniform charging with DC voltage.
2Manufacturing precision
If pre-exposure light quantity is increased to suppress transfer ghost, then the surface potential uniformity is improved, but charging lateral stripe defects become more conspicuous
Solution Approach 1:
The patent optimizes the pre-exposure light quantity within specific ranges (0.1-10 Lux·sec, preferably 0.5-5 Lux·sec) and controls the spectral composition (blue, green, or yellow-green regions). This parameter optimization achieves surface potential equalization without causing excessive photoconductive effects that would lead to charging lateral stripes.
Solution Approach 2:
The patent applies a controlled, partial pre-exposure action rather than excessive light irradiation. By limiting the light quantity to specific ranges, it achieves sufficient surface potential equalization to suppress transfer ghosts while avoiding the excessive photoconductive effects that cause charging lateral stripe defects.
3Manufacturing precision
If secondary color toner image amount is increased for full-color image forming, then the image quality is improved, but transfer ghost becomes more conspicuous in downstream image forming portions
Solution Approach 1:
The patent applies pre-exposure light irradiation to equalize the surface potential before charging occurs in downstream image forming portions. This preliminary action prevents the accumulation of potential differences caused by secondary color toner images, thereby suppressing transfer ghost while maintaining full-color image quality.
Solution Approach 2:
The pre-exposure light acts as an intermediary mechanism between the secondary color toner image formation and the subsequent charging process. It mediates the surface potential distribution, allowing high-quality full-color images to be formed without generating transfer ghost in downstream portions.
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 transfer ghost and charging lateral stripe defects while maintaining image quality by adjusting toner amounts and pre-exposure light levels, allowing for simple operational settings to address specific image forming conditions.
Implementation Method 1
a charging roller configured to electrically charge the third photosensitive member at a charging portion and configured to be supplied with only a DC voltage
Implementation Method 2
the pre-exposure member is disposed downstream of the transfer portion and upstream of the charging portion with respect to a rotational direction of the third photosensitive member and is configured to expose the third photosensitive member to light with a predetermined pre-exposure amount
Implementation Method 3
a voltage source configured to apply a voltage to the transfer member to form an electric field for transferring the third toner image from the third photosensitive member onto the intermediary transfer member at the transfer portion
Data Source
AI summary
An image forming apparatus includes an intermediary transfer member, image forming units, a voltage source, an executing portion, a setting portion, and a selecting portion configured to select a first mode or a second mode. In the first mode, each of exposure amounts of first and second exposure members is set so that a maximum toner amount per unit area during execution of an image forming operation is a first amount per unit area and a pre-exposure amount is set at a first pre-exposure amount. In the second mode, each of the exposure amounts is set so that the maximum toner amount per unit area is a second amount per unit area smaller than the first amount per unit area, and the pre-exposure amount is set at a second pre-exposure amount larger than the first pre-exposure amount.