Fixing Roller Speed Control for Jam Detection in Printers
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Solution Overview
Problem
In image forming apparatuses, the increased sheet feeding speed and larger driving motors lead to longer trailing ends being pulled into the fixing device during jams, making it difficult to detect the sheet remaining in the fixing nip, especially when the jam occurs inside the device and the sheet winds around the fixing roller, as the leading end does not reach downstream detection means.
Innovation Solution
The apparatus includes a controller that adjusts the rotational speed of the fixing roller based on the sheet length and width, allowing for detection of sheets by sensors positioned upstream of the nip, and stops the roller upon jam detection, thereby reducing the sheet's movement and improving detection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the sheet feeding speed in the fixing device is increased to improve productivity, then the printing speed is improved, but the trailing end portion of the sheet is pulled farther into the fixing device during jam occurrence, making detection difficult
Solution Approach 1:
The patent positions the sheet detection sensor upstream of the fixing nip, before the sheet enters the fixing device. This preliminary detection position allows the system to detect the trailing end of the sheet before it is pulled deep into the fixing device by high-speed rotation, enabling timely jam detection even at increased feeding speeds
Solution Approach 2:
The system uses the upstream sensor to provide feedback about sheet presence and position to the control unit, which then adjusts the fixing roller rotation accordingly. This feedback mechanism allows the system to respond to sheet position changes in real-time, preventing the trailing end from being pulled too far into the device
2Productivity
If a larger driving motor is used to increase sheet feeding speed, then productivity is improved, but the motor's higher inertia causes it to rotate longer after stop instruction, pulling the sheet farther into the fixing device
Solution Approach 1:
The patent applies preliminary braking action to the fixing roller motor when jam is detected or when the sheet trailing end approaches the fixing nip. This preliminary anti-action counteracts the motor's inertia before it can cause excessive sheet pull-in, allowing the use of larger motors for high-speed operation without the detrimental inertia effects
Solution Approach 2:
The upstream sensor provides continuous feedback about sheet position, allowing the control unit to monitor when the trailing end is approaching the fixing device. This feedback triggers timely motor braking to counteract inertia effects
3Productivity
If the sheet feeding speed is increased, then productivity is improved, but the trailing end portion of the sheet is pulled into the fixing device, making it difficult to detect by upstream sensors
Solution Approach 1:
The patent positions the detection sensor upstream of the fixing nip to detect the trailing end of the sheet before it enters the fixing device. This preliminary detection approach captures the trailing end position early in its travel, making it detectable even at high feeding speeds where the trailing end would otherwise be pulled deep into the device before detection could occur
Data Source
AI summary
An image forming apparatus includes an image forming portion, first and second rotatable members, a jam detecting portion, a detector, and a controller. When a sheet to be fed to a nip is a first sheet having a first length and a first width, the controller causes the first rotatable member rotating at a first speed to feed the first sheet. When the sheet is a second sheet having is a second length shorter than the first length and having the first width, the controller causes the first rotatable member rotating at a second speed slower than the first speed to feed the second sheet. The controller stops rotation of the first rotatable member in response to detection of the occurrence of a jam by the jam detecting portion.