Heater Resistivity Gradient for Uniform Heat Distribution
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Solution Overview
Problem
Heat generation distribution unevenness in heaters used in image forming apparatuses occurs due to varying voltage applied to heat generation resistive members, leading to non-sheet feeding portion temperature increases and potential damage or hot offset issues.
Innovation Solution
A heater design with heat generation blocks where resistive members at end portions have higher resistivity values than those at the center, and adjusted intervals and line widths to ensure even heat generation distribution, addressing voltage drop effects and resistivity variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat generation resistive members are arranged in parallel between two conductive members in one heat generation block, then the total resistance can be adjusted to a usable range, but voltage drop in conductive members causes uneven heat generation distribution
Solution Approach 1:
The patent applies local quality by making the resistivity values of heat generation resistive members position-dependent. Specifically, resistive members at end portions of the heat generation block are assigned higher resistivity values than those at the center portion. This compensates for the voltage drop occurring in the conductive members, ensuring that end portions (which receive lower voltage) generate more heat, while center portions (which receive higher voltage) generate less heat, thereby achieving uniform heat generation distribution throughout the block.
2Temperature
If PTC heat generation resistive members are used to suppress non-sheet feeding portion temperature increase, then temperature control in non-sheet feeding portions is improved, but heat generation unevenness occurs within heat generation blocks
Solution Approach 1:
The patent combines PTC material properties with local quality principles. Each heat generation resistive member is made of PTC material, and their resistivity values are locally adjusted based on position. End portion resistive members have higher base resistivity values than center portion members. When temperature increases in non-sheet feeding portions, all PTC members increase their resistivity, but the pre-established resistivity gradient ensures uniform heat generation distribution is maintained even as temperatures rise.
Solution Approach 2:
The patent utilizes parameter changes by exploiting the positive temperature coefficient (PTC) characteristic of the resistive members. As temperature increases, the resistivity of PTC materials increases, which automatically reduces current flow and heat generation in overheated regions. This self-regulating mechanism, combined with the position-dependent resistivity design, effectively suppresses non-sheet feeding portion temperature increase while maintaining heat generation uniformity.
3Ease of manufacture
If heat generation resistive members have uniform resistivity values, then manufacturing is simplified, but voltage drop effects cause center portions to generate less heat than end portions
Solution Approach 1:
The patent resolves this contradiction by implementing local quality through position-dependent resistivity values. While this requires more complex manufacturing than uniform resistivity members, the patent provides specific guidance on achieving this: end portion resistive members are designed with higher resistivity values than center portion members. This controlled variation in resistivity across different locations compensates for the voltage drop in conductive members, achieving uniform heat generation. The manufacturing complexity is managed through systematic design rules rather than arbitrary variations.
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 design effectively suppresses heat generation unevenness along the heater's longitudinal direction, preventing non-sheet feeding portion temperature increases and improving overall heat distribution, thereby reducing the risk of apparatus damage and hot offset.
Implementation Method 1
heat generation resistive members having a positive temperature coefficient of resistance... current flows in the heat generation resistive members... amount of heat generated by a heat generation resistive member is proportional to the square of an applied voltage
Implementation Method 2
a positive temperature coefficient of resistance, which is a characteristic in which as the temperature increases, the resistance increases, is referred to as PTC
Data Source
AI summary
The image heating apparatus includes a heater that achieves even heat-generation distribution and suppression of a non-sheet feeding portion temperature increase when an image is printed on a sheet whose size is smaller than a maximum size for the apparatus, and an endless belt, wherein plural heat-generation resistive members having positive temperature coefficients are connected in parallel are provided between first and second conductive members provided along a longitudinal direction of a substrate; plural heat-generation blocks including the plural heat-generation resistive members connected in parallel, are arranged in series along the longitudinal direction; and in the plural heat-generation resistive members included in one of the heat-generation blocks, a heat-generation resistive member arranged at an end portion in the longitudinal direction has a resistivity value higher than that of a heat generation resistive member arranged at a center in the longitudinal direction, or an interval between heat generation resistive members is larger in the end portion.