Transfer Power Supply Voltage Control for Image Defect Suppression
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Solution Overview
Problem
High-speed printing in electrophotographic image forming apparatuses leads to reduced time for non-image portions at the trailing end of recording materials, making it challenging to suppress separation electric-discharge and resulting in image defects like 'memory' due to insufficient reduction in transfer voltage, which can cause charging unevenness and density unevenness in images.
Innovation Solution
An image forming apparatus with a transfer power supply system that includes a transformer, switching portion, and rectifier circuit, where capacitors are configured to superimpose voltages and control the transfer voltage by adjusting capacitance values to rapidly reduce voltage while minimizing ripple, thereby preventing undershoot and maintaining image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the conveyance speed of the recording material is increased to improve printing speed, then productivity is improved, but the time period for the non-image portion at the trailing end to pass through the transfer nip portion is reduced, making it difficult to suppress separation electric-discharge and causing charging unevenness and image defects
Solution Approach 1:
The transfer voltage is reduced in advance before the non-image portion at the trailing end reaches the transfer nip portion. The controller detects the trailing edge position and提前 reduces the transfer voltage from the normal transfer voltage (e.g., +2000V) to a reduced voltage (e.g., +500V or lower) to prevent separation electric-discharge before it occurs, thereby maintaining image quality even at high printing speeds
Solution Approach 2:
The transfer voltage is dynamically adjusted based on the position of the recording material. The system transitions from a static transfer voltage to a dynamic voltage control system that changes voltage levels according to whether the image portion or non-image trailing end is passing through the transfer nip, allowing both high-speed operation and prevention of charging unevenness
2Reliability
If the transfer voltage is reduced to suppress separation electric-discharge and prevent memory defects, then image quality is improved, but the transfer efficiency may be reduced
Solution Approach 1:
The transfer voltage is applied periodically with different voltage levels at different time periods. During the image transfer period, normal high voltage is applied for efficient transfer. During the trailing end period, reduced voltage is applied to prevent discharge. This periodic voltage modulation maintains overall transfer efficiency while preventing defects
Solution Approach 2:
Different voltage levels are applied to different spatial regions of the transfer process. The image portion receives normal transfer voltage for efficient transfer, while the trailing end portion receives reduced voltage to prevent discharge. This localized voltage control optimizes both transfer efficiency and image quality in different regions
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 effectively suppresses the occurrence of 'memory' and other image defects by ensuring a rapid and controlled reduction in transfer voltage, maintaining image quality and preventing density unevenness, even at high printing speeds.
Implementation Method 1
a first rectifier circuit portion configured to rectify and amplify an AC voltage generated in the secondary coil of the first transformer by the switching operation of the first switching portion
Implementation Method 2
a first transformer including a primary coil and a secondary coil; a first switching portion configured to perform a switching operation of a current flowing through the primary coil
Implementation Method 3
the plurality of capacitors include a predetermined capacitor to be charged by a half-wave rectified voltage of the AC voltage generated in the secondary coil of the first transformer and a capacitor to be charged by a voltage higher than the half-wave rectified voltage
Implementation Method 4
a first switching portion configured to perform a switching operation of a current flowing through the primary coil based on a drive signal; and a first rectifier circuit portion configured to rectify and amplify an AC voltage generated in the secondary coil
Data Source
AI summary
An image forming apparatus includes a controller and a transfer power supply portion configured to output a transfer voltage to a transfer portion so as to transfer a toner image onto a recording material. The transfer power supply portion superimposes a voltage output from a first power supply portion and a voltage output from a second power supply portion to output a superimposed voltage to the transfer portion. The first power supply portion includes a transformer including a primary coil and a secondary coil, and a rectifier circuit portion. The rectifier circuit portion includes a plurality of diodes and a plurality of capacitors. A capacitance of a predetermined capacitor to be charged by a half-wave rectified voltage of an AC voltage generated in the secondary coil is larger than a capacitance of a capacitor to be charged by a voltage higher than the half-wave rectified voltage.