Image Forming Apparatus Sheet Separation via Electrostatic Control
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Solution Overview
Problem
Image forming apparatuses experience double feeding due to electrostatic adhesion between sheets, particularly in high humidity environments, where coated sheets absorb moisture and become conductive, leading to adhesion issues that conventional air separation methods cannot reliably address.
Innovation Solution
The apparatus employs a configuration with a first and second voltage applying device to manage the transfer of toner images, applying a voltage to the secondary transfer member and a driving roller with opposite polarities to control the surface potential of sheets, ensuring they do not electrostatically adhere during transfer, while maintaining the necessary potential difference for efficient toner transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If air is blown on the sheet stack portion to separate sheets, then sheet separation is improved, but double feeding still occurs due to electrostatic adhesion between sheets
Solution Approach 1:
The patent extracts the electrostatic charge from the sheet stack portion by providing a ground connection to the sheet stack portion. This removes the harmful electrostatic adhesion force that causes double feeding, while preserving the beneficial air separation effect. The ground connection extracts accumulated electrostatic charges that would otherwise cause sheets to adhere to each other during transfer.
Solution Approach 2:
The patent introduces a ground connection as an intermediary element between the sheet stack portion and the earth. This intermediary provides a path for electrostatic charges to dissipate, mediating the interaction between the sheets and preventing electrostatic adhesion. The ground connection acts as a mediator that neutralizes the harmful electrostatic forces without interfering with the air separation mechanism.
2Productivity
If sheets are kept in contact during transfer to maintain transfer efficiency, then transfer reliability is improved, but electrostatic adhesion causes double feeding
Solution Approach 1:
The patent converts the harmful electrostatic adhesion into a beneficial effect by using the same electrostatic force that causes double feeding to improve transfer efficiency. By applying voltage to the transfer roller, the patent creates controlled electrostatic attraction that ensures reliable toner transfer while the ground connection prevents uncontrolled electrostatic adhesion between sheets. The harmful electrostatic charge is transformed into a controlled, useful force.
Solution Approach 2:
The patent changes the electrical parameter of the sheet stack portion by providing a ground connection, which alters the electrostatic properties of the sheets. This parameter change reduces the surface potential of the sheets, preventing electrostatic adhesion between sheets while maintaining the necessary electrostatic conditions for efficient toner transfer. The ground connection modifies the electrical state of the system to resolve the contradiction.
3Productivity
If voltage is applied to the transfer roller to ensure toner transfer, then transfer efficiency is improved, but surface potential of sheets increases causing electrostatic adhesion
Solution Approach 1:
The patent extracts the excessive surface potential from the sheets by providing a ground connection to the sheet stack portion. This removes the harmful high surface potential that causes electrostatic adhesion between sheets, while preserving the necessary voltage applied to the transfer roller for efficient toner transfer. The ground connection extracts the harmful electrostatic charge without affecting the transfer roller's voltage application.
Solution Approach 2:
The patent segments the electrical system into two independent parts: the transfer roller with applied voltage for toner transfer, and the sheet stack portion with ground connection for charge dissipation. This segmentation allows the transfer roller to maintain high voltage for efficient transfer while the sheet stack portion maintains low surface potential to prevent adhesion. The electrical functions are separated into distinct segments that can operate independently.
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 effectively reduces the surface potential of sheets, preventing double feeding without degrading transfer efficiency, even in typical office environments with varying humidity levels, ensuring reliable operation across different conditions.
Implementation Method 1
the preceding and following sheets adhere to each other owing to an electrostatic force
Implementation Method 2
a first voltage applying device that applies a voltage to the first transfer member; and a second voltage applying device that applies a voltage having a polarity opposite to a polarity at the first voltage applying device, to the second transfer member
Data Source
AI summary
An image forming apparatus includes a main body, a sheet stack unit, an endless intermediate transfer member, a first transfer member for transferring a toner image onto the sheets conveyed from the sheet stack unit, at a nip formed between the intermediate transfer member and the first transfer member, and a second transfer member. In addition, a first voltage applying device applies a voltage to the first transfer member, a second voltage applying device applies a voltage having an opposite polarity to the second transfer member, and a controller controls the first and second voltage applying devices. In a timing when a leading edge of a first sheet reaches the nip, a trailing edge of the first sheet contacts a second sheet conveyed on the sheet stack unit, and wherein a period in which the controller causes the first voltage applying device and the second voltage applying device to apply the voltages to the first transfer member and the second transfer member, respectively, is at least from a time when secondary transfer onto the first sheet is started to a time when the trailing edge of the first sheet stops sliding on the second sheet stacked on the sheet stack portion.