Partially Toothless Gear Mechanism for Impact-Absorbing Engagement
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Solution Overview
Problem
Conventional power transmission mechanisms in image forming apparatuses, particularly those used in fixing devices, face issues with gear tooth collision leading to damage due to the lack of elasticity in materials like polyphenylene sulfide resin, which is used for its high heat resistance but lacks impact resistance.
Innovation Solution
A power transmission mechanism featuring a partially toothless gear that rotates with a first gear movable between positions to prevent tooth collision, using a structure that absorbs impact by moving the first gear away from the partially toothless gear, thereby preventing gear tooth damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If PPS resin is used for gear material to achieve high heat resistance and dimensional stability, then heat resistance is improved, but impact resistance deteriorates due to lack of elasticity
Solution Approach 1:
The invention introduces a resilient member between the PPS gear and the partially toothless gear to absorb impact before it reaches the rigid gear teeth. This cushioning element compensates for the lack of elasticity in PPS resin, preventing tooth breakage during collision while maintaining the heat resistance benefits of the PPS material.
2Strength
If elastic material is used for gear to enable deformation and prevent tooth breakage, then impact resistance is improved, but heat resistance deteriorates
Solution Approach 1:
The invention creates a composite gear structure combining rigid PPS resin gear with a resilient member made of elastic material. This composite approach allows the PPS gear to maintain heat resistance while the resilient member provides impact absorption and elasticity, solving both requirements simultaneously.
3Device complexity
If tooth tips are designed to collide directly to simplify structure, then device complexity is reduced, but reliability deteriorates due to tooth damage
Solution Approach 1:
The resilient member acts as an intermediary element between the PPS gear and the partially toothless gear. It mediates the interaction during tooth collision, absorbing impact energy and preventing direct damage to the gear teeth, thereby improving reliability without significantly complicating the overall structure.
Data Source
AI summary
A power transmission mechanism includes a partially toothless gear in which teeth are formed only in a part of a peripheral edge portion and which is rotationally driven and a first gear having a plurality of teeth formed on a peripheral edge portion thereof, meshing with the teeth of the partially toothless gear by rotation of the partially toothless gear and being rotationally driven by the rotation of the partially toothless gear. The first gear is movable between a first position at which a tip of the plurality of teeth and a tip of the teeth of the partially toothless gear collide with each other and a second position farther from the partially toothless gear than the first position.