Fixing Unit Voltage Application Circuit for Electrostatic Offset
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Solution Overview
Problem
High-speed print output in image forming apparatuses leads to increased electrostatic charge on pressure rollers, causing image defects like electrostatic offset, and attempts to mitigate this through conductive layers can result in electrical breakdown of the fixing film.
Innovation Solution
A fixing unit with a tubular film and a heater having a metal substrate, insulating layer, and heating element, where a voltage application circuit applies a voltage of the same or opposite polarity to the substrate or pressing member to reduce electrostatic offset without causing electrical breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conductive layer is provided to the fixing film and a bias voltage is applied to cancel charge-up of the pressure roller, then electrostatic offset is reduced, but electrical breakdown of the fixing film surface layer occurs
Solution Approach 1:
The patent introduces an intermediary voltage application circuit that applies voltage to the pressure roller core metal through a conductive elastic member, rather than directly to the fixing film. This intermediary approach allows charge cancellation without causing electrical breakdown of the fixing film surface layer.
Solution Approach 2:
The patent replaces the direct electrical connection approach (conductive layer on fixing film) with a mechanical contact approach (conductive elastic member contacting the pressure roller core metal). This substitution eliminates the risk of electrical breakdown while maintaining the charge cancellation function.
2Productivity
If print output speed is increased, then productivity is improved, but charge-up of the pressure roller increases causing electrostatic offset
Solution Approach 1:
The patent implements a feedback mechanism where a voltage application circuit continuously monitors and counteracts the charge-up on the pressure roller. By applying a compensating voltage based on the friction-induced charge, the system maintains image quality even at high print speeds where charge-up would normally increase.
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
Effectively reduces electrostatic offset while preventing electrical breakdown of the fixing film, even with high-resistance recording materials, by forming an electric field in the fixing nip portion without supplying current between the film and pressure roller.
Implementation Method 1
a heating element arranged on the insulating layer and configured to generate heat when electric current flows therethrough
Implementation Method 2
a voltage application circuit configured to apply a voltage of a same polarity as a normal charging polarity of the toner to the substrate
Implementation Method 3
a surface of a pressure roller is charged-up by friction between the recording material and the pressure roller
Data Source
AI summary
A fixing unit includes a film with a tubular shape, a nip forming unit including a heater and configured to be in sliding contact with an inner surface of the film. The heater includes a substrate made of metal. The fixing unit further includes a power supply connector electrically connected to the power supply electrode so that the power supply connector is connected to the heating element at a first end portion of the substrate in a longitudinal direction of the heater, and a pressing member opposed to the nip forming unit. The fixing unit further includes a voltage application circuit configured to apply a voltage of a same polarity as a normal charging polarity of the toner to the substrate, the voltage application circuit being connected to the substrate at a second end portion of the substrate opposite to the first end portion in the longitudinal direction.