Fixing Device Heater Asymmetry for Thermal Stress
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Solution Overview
Problem
Conventional fixing devices for electrophotographic image forming apparatuses face issues with unintended energization interruption due to abnormal temperature rises, leading to decreased fixing property and glossiness of output images, and potential heater breakage from thermal stress, especially when the heater upstream end protrudes beyond the fixing nip.
Innovation Solution
A fixing device with a heater having a symmetric heat generating pattern and a thermo-sensitive member positioned downstream of the heater's center line with respect to the recording material feeding direction, ensuring controlled temperature and reduced thermal stress by maintaining the thermo-sensitive member below the normal usable temperature during normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the heater upstream end protrudes outward from the fixing nip to reduce thermal capacity and shorten first-print-out time, then the heating response speed improves, but the thermo-sensitive member temperature exceeds normal usable temperature causing unintended energization interruption
Solution Approach 1:
The patent positions the thermo-sensitive member asymmetrically downstream of the heater center line rather than at the center, creating a temperature gradient exploitation strategy where the downstream position experiences lower temperature than the upstream protruding end, allowing the sensor to remain below normal usable temperature while the heater still achieves rapid heating
2Loss of time
If the heater upstream end protrudes outward from the fixing nip, then the thermal capacity is reduced and first-print-out time is shortened, but the fixing film temperature decreases reducing fixing property and image glossiness
Solution Approach 1:
The patent applies local quality by creating different temperature zones within the heater system - the upstream protruding end achieves high temperature for rapid heating response, while the downstream region where the thermo-sensitive member is positioned maintains lower temperature to prevent sensor activation, allowing both rapid heating and proper fixing properties to coexist
3Volume of stationary object
If the heater upstream end protrudes outward from the fixing nip, then the thermal capacity is reduced, but the difference in thermal stress in the ceramic substrate causes breakage or crack in the heater
Solution Approach 1:
The patent employs beforehand cushioning by strategically positioning the thermo-sensitive member downstream to detect temperature changes before they cause excessive thermal stress accumulation, enabling early intervention through energization control to prevent heater breakage or cracking
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 allows for higher fixing film temperatures, enhancing the fixing property and image glossiness while preventing unintended energization interruptions and heater breakage by maintaining the thermo-sensitive member within a safe temperature range.
Implementation Method 1
a heater as a heating member including a heat generating resistor on a ceramic substrate
Implementation Method 2
a thermo-sensitive member (thermo-switch, temperature fuse or the like) for interrupting energization to a heat generating resistor
Implementation Method 3
the recording material carrying an unfixed toner image is heated at a press-contact portion formed by pressing the pressing roller against the fixing film toward the heater
Data Source
AI summary
A fixing device for fixing a toner image on a recording material includes: a cylindrical film; a plate-like heater contacting an inner surface of the film; a roller for forming a nip in cooperation with the heater through the film; and a thermo-sensitive member for detecting the temperature of the heater to interrupt electric power supply to the heater when the temperature of the heater reaches an abnormal temperature. The heater has a heat generating pattern symmetric with respect to a center line thereof extending in a direction perpendicular to a recording material feeding direction. The thermo-sensitive member is provided in a side which is opposite from a surface of the heater contacting the inner surface of the film and which is downstream of the center line of the heater with respect to the recording material feeding direction.