Insulating Holder for Belt Unit Creepage Distance
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Solution Overview
Problem
In image forming apparatuses, the insufficient creepage distance between the heater and the leaf spring for urging a temperature detecting element in the fixing device leads to an increase in current supplied to the heater, particularly when the diameter of the fixing film is small, making it difficult to ensure a large gap between components.
Innovation Solution
A belt unit with an insulating supporting member and an interposed portion between the leaf spring and the metal stay to provide insulation, ensuring a sufficient creepage distance and preventing excessive current flow to the heater.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the diameter of the fixing film is reduced to make the apparatus compact, then the overall size is reduced, but the creepage distance between the heater and the leaf spring becomes insufficient, causing current to increase
Solution Approach 1:
The patent introduces a third dimension (radial direction) to solve the creepage distance problem. By providing an insulating layer on the heater surface that extends radially outward, the creepage distance is increased without increasing the axial or circumferential dimensions. This allows compact apparatus design while maintaining sufficient electrical insulation between the heater and the leaf spring.
Solution Approach 2:
The insulating layer acts as an intermediary between the heater (primary circuit) and the leaf spring (secondary circuit). This intermediate insulating structure provides the necessary creepage distance to prevent current increase, while allowing the components to be positioned close together for compact design.
2Length of moving object
If the gap between the heater and the leaf spring is reduced to accommodate small diameter fixing film, then the apparatus becomes more compact, but the current supplied to the heater increases due to insufficient creepage distance
Solution Approach 1:
The insulating layer provides localized electrical insulation precisely where needed - on the heater surface facing the leaf spring. This local quality enhancement ensures sufficient creepage distance in the critical gap region while allowing the overall apparatus to remain compact. The insulation is applied only to the necessary area rather than throughout the entire heater structure.
3Reliability
If insulating structures are added to ensure sufficient creepage distance, then current increase is prevented, but the device complexity increases
Solution Approach 1:
The insulating layer is merged with the heater structure, forming an integrated assembly. The insulating layer serves dual purposes: providing the necessary creepage distance for electrical insulation and maintaining the thermal coupling between the heater and the fixing film. This merging approach prevents current increase while avoiding the need for separate, complex insulation structures.
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
The solution effectively suppresses the increase in current supplied to the heater, enhancing the reliability and efficiency of the image heating apparatus by maintaining a safe creepage distance and preventing overheating.
Implementation Method 1
a heater including a heat generating element generating heat by energization and configured to heat the endless belt in contact with an inner peripheral surface of the endless belt
Implementation Method 2
an insulating holder portion including an interposed portion interposed between an exposed portion of the leaf spring and the stay so as to provide insulation therebetween
Data Source
AI summary
A belt unit includes an endless belt including a metal layer, a nip forming member having a heater that includes a heat generating element, a metal stay that presses the nip forming member toward a rotatable member, and a temperature detecting element. A metal leaf spring urges the temperature detecting element toward the inner peripheral surface of the endless belt, and an insulating supporting member is positioned inside the stay and supports the leaf spring. A cord electrically connects with the temperature detecting element through the leaf spring, and an insulating holder portion includes an interposed portion interposed between an exposed portion of the leaf spring and the stay, so as to provide insulation therebetween, and to hold the supporting member. A creepage distance from the heat generating element to the exposed portion of the leaf spring, through the stay and the interposed portion, is 2.5 mm or more.