Image Forming Apparatus Transfer Unit Constant-Current Control
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Solution Overview
Problem
Existing image forming apparatuses face challenges in achieving stable transfer performance, particularly with low-resistance recording media, as they tend to experience leakage of transfer current and fluctuations in the transfer electric field due to changes in impedance during the transfer process.
Innovation Solution
The apparatus incorporates a constant-current controller that maintains a constant transfer current to the transfer region, utilizing a contact unit with lower resistance values than the transfer member, and switches the transfer member to a non-grounded state when using low-resistance media, ensuring a stable transfer electric field across the entire surface of the recording medium.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transfer electric field is generated using a transfer power source with conventional grounding, then transfer current flows to the transfer region, but current leakage occurs and transfer electric field stability deteriorates when using low-resistance recording media
Solution Approach 1:
The patent segments the grounding function by introducing a dedicated contact unit separate from the transfer member. The contact unit is configured to contact the recording medium specifically for grounding purposes, while the transfer member maintains its transfer function. This segmentation prevents the transfer member from becoming a current leakage path while still providing necessary grounding through the contact unit.
Solution Approach 2:
The contact unit acts as an intermediary between the recording medium and ground. It provides a controlled grounding path that prevents direct current leakage through the transfer member. The contact unit mediates the electrical connection, ensuring that low-resistance media are properly grounded without causing harmful current leakage that would destabilize the transfer electric field.
2Reliability
If the transfer member is grounded to ensure current path, then current flows through the transfer member, but impedance changes during transfer process cause transfer electric field fluctuations
Solution Approach 1:
The patent separates the grounding function from the transfer member by introducing a dedicated contact unit. This segmentation allows the transfer member to maintain stable impedance for transfer operations while the contact unit provides the grounding path. The transfer member is not directly grounded, preventing impedance fluctuations from affecting the transfer electric field stability.
Solution Approach 2:
The contact unit serves as an intermediary that provides grounding without directly connecting the transfer member to ground. This intermediary approach maintains stable impedance in the transfer region while still providing the necessary current path through the contact unit, preventing transfer electric field fluctuations.
3Productivity
If conventional transfer control is used, then transfer voltage is applied from transfer power source, but transfer current fluctuates when recording medium resistance varies
Solution Approach 1:
The patent implements constant-current control that provides feedback on the actual transfer current flowing through the transfer region. The transfer power source adjusts its output based on this feedback to maintain a predetermined constant current level, regardless of variations in recording medium resistance. This feedback mechanism ensures stable transfer current and consistent transfer performance.
Solution Approach 2:
The patent changes the control parameter from constant voltage to constant current. By controlling the transfer current to remain constant rather than applying constant voltage, the system adapts to varying recording medium resistance values. This parameter change ensures that transfer current stability is maintained across different media types, improving both reliability and consistency.
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 approach stabilizes the transfer electric field and prevents current leakage, resulting in improved image transfer quality and consistency, especially with low-resistance recording media like metallic sheets, by ensuring a constant transfer current and appropriate grounding conditions.
Implementation Method 1
generates a transfer electric field in a transfer region between the image retaining unit and the transfer member so as to electrostatically transfer the image retained by the image retaining unit onto the recording medium
Implementation Method 2
The contact unit is provided at an upstream side and a downstream side of the transfer region in a transport direction of the recording medium and comes into contact with the recording medium while the recording medium passes through the transfer region, so as to function as an electrode leading to a ground
Implementation Method 3
The constant-current controller performs constant-current control on a transfer current to be fed to the transfer region by using a transfer voltage applied from a transfer power source in a condition in which the recording medium is a low-resistance recording medium having a predetermined resistance value or lower or having an electrically-conductive layer along a medium base surface
Data Source
AI summary
An image forming apparatus includes a transfer unit, a contact unit, and a constant-current controller. The transfer unit nips a recording medium using an image retaining unit and a transfer member and generates a transfer electric field in a transfer region therebetween so as to electrostatically transfer the image onto the recording medium. The contact unit is provided upstream and downstream of the transfer region in a recording-medium transport direction and comes into contact with the recording medium while the recording medium passes through the transfer region, so as to function as an electrode leading to a ground. The constant-current controller performs constant-current control on a transfer current to be fed to the transfer region by using a transfer voltage when the recording medium is a low-resistance recording medium having a predetermined resistance value or lower or having an electrically-conductive layer along a medium base surface.