Fixing Device Curie Temperature Magnetic Shielding
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Solution Overview
Problem
The existing fixing devices in image forming apparatuses face temperature variations in the axial direction of the fixing rotary body, leading to inconsistent toner image gloss on large recording media due to uneven heat distribution, which existing solutions like magnetic flux shields and self-temperature control systems either degrade heat generation efficiency or complicate the device configuration.
Innovation Solution
Incorporating a temperature sensitive magnetic body with a Curie temperature-adjusted composition in the heat generation layer, paired with a non-magnetic degausser and a holder configuration that maintains the degausser's efficiency and reduces overheating, creates selective heating and non-heating regions to ensure consistent heat distribution across the fixing rotary body.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a magnetic flux shield is interposed between the exciting coil and the fixing rotary body, then temperature variation of the fixing rotary body is eliminated, but heat generation efficiency of the heat generator is degraded
Solution Approach 1:
The patent introduces a temperature-sensitive magnetic body with a Curie temperature of 150-250°C that selectively shields magnetic flux only in regions where temperature exceeds the threshold. This creates local quality differentiation: areas above the Curie temperature automatically receive reduced magnetic flux (and thus reduced heating), while areas below the threshold maintain normal heating efficiency. This resolves the contradiction by making the shielding effect conditional and spatially differentiated rather than uniform.
2Temperature
If a movable magnetic flux shield is used to adjust magnetic flux distribution, then temperature variation is eliminated, but device complexity increases
Solution Approach 1:
The temperature-sensitive magnetic body automatically adjusts its magnetic shielding properties based on its own temperature state. When heated above the Curie temperature, it loses magnetic properties and stops shielding flux; when cooled below the threshold, it regains magnetic properties and resumes shielding. This self-regulating mechanism eliminates the need for external control systems, actuators, or complex mechanical structures, thereby resolving the contradiction between temperature uniformity and device complexity.
3Speed
If the heat generation layer is made thin for quick heating, then warming up speed is improved, but temperature variation in axial direction increases
Solution Approach 1:
The temperature-sensitive magnetic body acts as an intermediary between the exciting coil and the thin heat generation layer. It modulates the magnetic flux distribution to compensate for the inherent temperature non-uniformity caused by the thin layer structure. By selectively reducing flux to overheating regions (lateral ends) while maintaining flux to underheating regions (central portions), it enables the thin heat generation layer to achieve both quick warming and temperature uniformity.
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 maintains efficient heat generation and degaussing while preventing overheating, ensuring consistent toner image quality and reducing the device's size and complexity by eliminating the need for movable magnetic flux shields.
Implementation Method 1
the heat generation layer generates heat by the magnetic flux from the exciting coil
Implementation Method 2
The temperature sensitive magnetic body obtains and loses magnetism at a temperature defined by a Curie temperature by composition adjustment
Implementation Method 3
a magnetic flux from the exciting coil penetrates the metal plate, allowing the metal plate to generate a repulsive magnetic flux that offsets the magnetic flux from the exciting coil
Data Source
AI summary
A fixing device includes an exciting coil and a heat generator disposed opposite the exciting coil. The heat generator includes a heat generation layer disposed opposite the exciting coil to generate heat by a magnetic flux from the exciting coil and a temperature sensitive magnetic body disposed opposite the exciting coil via the heat generation layer to obtain and lose magnetism at a temperature defined by a Curie temperature by composition adjustment to selectively create a heating region and a non-heating region of the heat generation layer. A degausser is disposed opposite the heat generator and made of a non-magnetic material having an electrical resistivity smaller than that of the temperature sensitive magnetic body. A holder contacting and supporting the degausser is disposed inboard from a lateral edge of the degausser and outboard from a lateral end of the exciting coil in a longitudinal direction of the degausser.