Heating Unit Thermostat Insulation for Fixing Reliability

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Solution Overview

Problem

In fixing devices for electrophotographic image forming apparatuses, the energization interrupting member, which is in contact with the back surface of the heater, experiences early heat transfer, leading to insufficient temperature for the heater and belt, potentially causing faulty fixing during the initial stages of operation.

Innovation Solution

A heating unit is designed with a heat-insulating member between the thermostat and the heater, where the thermostat has a heat-sensitive surface with lower conductivity than the heat-insulating member, and a heat conductive member to uniformize temperature, preventing early heat radiation to the energization interrupting member.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the energization interrupting member is in contact with the back surface of the heater, then the safety function is improved, but the temperature of the heater and belt becomes insufficient at the early fixing stage

Engineering Contradiction:

Improvesafety functionVSAvoidtemperature of heater and belt

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

A heat-insulating member is introduced as an intermediary between the heater and the energization interrupting member. This mediator blocks the direct heat transfer path, preventing the thermostat from absorbing excessive heat during early fixing operations while maintaining its safety monitoring function.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The contact interface between the heater and thermostat is segmented by introducing the heat-insulating member. This segmentation separates the thermal pathways, allowing the thermostat to remain thermally isolated during normal operation while still detecting abnormal temperature increases.

Inventive Principle:

Principle #1Segmentation

2Speed

If the thermostat is in direct contact with the heater, then the temperature detection responsiveness is improved, but heat is transferred to the thermostat too early causing faulty fixing

Engineering Contradiction:

Improvetemperature detection responsivenessVSAvoidfixing quality

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The heat-insulating member acts as a thermal mediator that selectively blocks heat flow to the thermostat during normal heating operations, preventing premature temperature detection and ensuring proper fixing quality.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The thermal conductivity parameter is modified by introducing the heat-insulating member with lower thermal conductivity between the heater and thermostat, changing the heat transfer characteristics to prevent early heat absorption while maintaining safety functionality.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If no heat-insulating member is used, then the device complexity is reduced, but heat radiation to the energization interrupting member causes insufficient heating

Engineering Contradiction:

Improvestructure simplicityVSAvoidheating temperature

Core Design Contradiction:

Device complexityVSTemperature

Solution Approach 1:

A heat-insulating member is introduced as a simple intermediary component between the heater and thermostat. This single addition effectively blocks harmful heat radiation without significantly increasing overall device complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent employs composite material construction by combining the heat-insulating member with the existing heater and thermostat components, creating a composite thermal management system that prevents heat transfer while maintaining structural integrity.

Inventive Principle:

Principle #40Composite materials

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 radiation to the energization interrupting member, ensuring it reaches a sufficient high temperature, thereby preventing faulty fixing at the early fixing stage and maintaining uniform temperature distribution across the heater.

Implementation Method 1

a heat-insulating member disposed between the thermostat and the heater, the heat-insulating member having a heat conductivity less than that of a material constituting the heat sensitive surface

Methodology Applied

Scientific EffectThermal Insulation: Thermal Insulation

Implementation Method 2

a heater including a substrate and a resistance heating element provided on the substrate

Methodology Applied

Scientific EffectJoule Heating: Joule Heating

Data Source

PatentUS11803144B2Heating unit

Publication Date: 2023.10.31 BROTHER KOGYO KK

AI summary

A heating unit includes a heater including a substrate and a resistance heating element provided on the substrate, an endless belt configured to rotate around the heater, a thermostat configured to interrupt energization to the resistance heating element when the heater is abnormally increased in temperature, the thermostat having a heat sensitive surface and a heat-insulating member disposed between the thermostat and the heater. The heat-insulating member has a heat conductivity less than that of a material constituting the heat sensitive surface. The heat sensitive surface of the thermostat is in contact with the heat-insulating member.