Fixing Device Nip Forming Unit Asymmetric Protrusion
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Solution Overview
Problem
Conventional fixing devices experience issues with image unevenness and conveying failures, particularly with smooth-surfaced recording sheets, due to insufficient friction and pressure distribution across the nip forming unit, leading to slipping and rotation stoppage of the fixing belt.
Innovation Solution
The fixing device incorporates a nip forming unit with a center contact surface protrusion less than the bent amount in a no-load state, ensuring a curved contact surface when pressed, which increases nip pressure at non-sheet passing portions and maintains sufficient friction across the fixing belt, preventing slipping and rotation stoppage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the center of the contact surface of the nip forming unit protrudes toward the pressing roller by a bent amount in no-load state, then the contact surface becomes flat when bent, solving deviation between end and center in main-scanning direction, but the nip pressure at non-sheet passing portions decreases, causing insufficient friction and belt slippage
Solution Approach 1:
The patent applies local quality by creating different protrusion amounts at different locations of the contact surface. Specifically, the center portion protrudes by a first amount while the end portions protrude by a second amount that is less than the first amount. This localized differentiation ensures that when the nip forming unit bends under pressure, both the center and end portions maintain appropriate contact with the pressing roller, preventing both surface deviation and pressure loss at non-sheet passing portions.
2Ease of manufacture
If the friction between recording sheet and pressing roller decreases due to smooth surface, then the rotational driving force transmitted to fixing belt decreases, causing belt slippage and conveying failure
Solution Approach 1:
The patent applies preliminary action by pre-configuring the contact surface with specific protrusion amounts at the center and end portions before the recording sheet is conveyed. This pre-configuration ensures that when the smooth recording sheet passes through, the nip forming unit is already positioned to maintain adequate nip pressure at non-sheet passing portions, thereby ensuring sufficient friction and reliable conveying even with smooth-surfaced sheets.
3Device complexity
If the nip width is narrowed at the center compared to the end in main-scanning direction, then the contact surface becomes uneven, causing image unevenness and conveying failure
Solution Approach 1:
The patent applies asymmetry by intentionally designing the contact surface with different protrusion amounts at the center versus the end portions. The center protrudes by a first amount while the ends protrude by a smaller second amount. This asymmetric design compensates for the bending deformation that occurs during operation, ensuring uniform nip width across the main-scanning direction despite the structurally simple nip forming unit.
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 enhances frictional force transmission and prevents image defects and conveying failures, even with smooth-surfaced sheets, by maintaining stable belt rotation and uniform pressure distribution across the nip forming unit.
Implementation Method 1
The driving force is transmitted to the fixing belt by the friction against the pressing roller
Implementation Method 2
a heating unit that heats the fixing belt; a pipe-like metallic heat conductor disposed so as to face an inner peripheral surface of a fixing belt
Implementation Method 3
the center of the contact surface of the nip forming unit in the main-scanning direction protrudes toward the pressing roller by a bent amount
Data Source
AI summary
A fixing device may include an endless fixing member; a heater inside the fixing member; and a nip forming unit configured to form a nip through which a recording sheet is conveyed, the nip forming unit including a supporting member and a contact member supported by the supporting member, the supporting member including at least one contact surface and the contact member including a plurality of protrusions protruding towards the supporting member such that two or more of the plurality of protrusions are configured to contact one of the at least one contact surface of the supporting member, each of the plurality of protrusions having a height associated there with such that the height of the plurality of protrusions increases in a direction from ends of the contact member towards a center of the contact member.