Fixing Device Metal Stay Positioning for Eddy Current Suppression
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Solution Overview
Problem
In electrophotographic image forming apparatuses, the use of metal stays inside heating coils leads to unwanted heat generation due to eddy currents caused by concentrated magnetic flux, which reduces the design flexibility and efficiency of the fixing devices.
Innovation Solution
A fixing device with a cylindrical rotary member and a helical coil that generates an alternating magnetic field, where the metal stay is positioned outside the coil and shaped to avoid forming an electrical loop, reducing heat generation and allowing for increased design freedom and improved heating efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metal stay is disposed inside the coil to form a fixing nip portion, then the structural rigidity is improved, but heat is generated in the stay due to eddy currents caused by concentrated magnetic flux
Solution Approach 1:
The patent extracts the metal stay from the interior of the coil and repositions it to the exterior. This separation removes the stay from the harmful magnetic flux region, eliminating eddy current-induced heat generation while preserving the stay's structural function in forming the fixing nip portion.
Solution Approach 2:
The patent introduces a non-magnetic rod as an intermediary element to provide the necessary structural support and maintain the fixing nip portion geometry. This intermediary material does not interact with the magnetic flux, thereby preventing heat generation while still achieving the desired mechanical function.
2Ease of operation
If a metal stay is disposed inside the coil, then the fixing nip portion can be formed, but the heating efficiency of the coil is reduced due to energy loss from eddy currents
Solution Approach 1:
By extracting the metal stay from the coil's magnetic flux region and positioning it externally, the patent eliminates the energy loss pathway through eddy currents. This allows the coil to transfer magnetic energy to the conductive layer more efficiently, improving heating performance while the externally positioned stay continues to provide mechanical support for nip formation.
3Strength
If the stay is made of metal to ensure rigidity, then the structural strength is improved, but the stay generates heat when exposed to concentrated magnetic flux
Solution Approach 1:
The patent replaces the metal stay with a non-magnetic rod material that does not generate heat under magnetic exposure. While the specific material composition changes, the functional requirement for rigidity is maintained, and the harmful heat generation effect is eliminated by using a material that is inherently resistant to electromagnetic induction heating.
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 effectively suppresses heat generation in the metal stay, allowing for a more rigid and efficient fixing device with enhanced heating performance and reduced risk of heat-related issues.
Implementation Method 1
the coil being configured to form an alternating magnetic field to generate heat in the conductive layer by electromagnetic induction
Implementation Method 2
the core configured to guide a line of magnetic force of the alternating magnetic field
Implementation Method 3
when a stay is disposed inside a coil, eddy current occurs in the stay due to magnetic flux concentrating inside the coil, disadvantageously resulting in generation of heat in the stay
Data Source
AI summary
Disclosed is a cylindrical rotary member including a conductive layer; a coil disposed inside the rotary member, the coil including a helical portion having a helical axis that is substantially parallel to a generatrix direction of the rotary member, the coil forming an alternating magnetic field to generate heat in the conductive layer by electromagnetic induction; a core disposed inside the helical portion, the core inducing a line of magnetic force of the alternating magnetic field; a roller coming in contact with an outer surface of the rotary member to form a fixing nip portion; and a metal stay disposed inside the rotary member, in which an image on a recording material is fixed to the recording material by being heated at the fixing nip portion and the stay is disposed outside the coil and has a shape that does not form an electrical loop around the coil.