Sheet Deflection Control in Image Forming Apparatus
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Solution Overview
Problem
In image forming apparatuses, sheets can form loops between the transfer unit and the conveyance unit, leading to abrupt changes in force at the transfer unit, which can cause the sheet to slip and result in image defects.
Innovation Solution
The apparatus includes a detection unit to measure the deflection amount of the sheet between the transfer and fixing units, and a control unit that adjusts the conveyance speed of the sheet by the fixing unit in multiple stages to control the deflection amount, thereby preventing sheet slippage and image defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a loop detection sensor is arranged between the transfer unit and fixing unit to detect loops, then the loop amount formed on the sheet can be controlled to maintain a constant amount, but the sheet may still form loops between the conveyance unit and transfer unit, causing abrupt force changes and sheet slippage
Solution Approach 1:
The detection unit detects the loop amount formed on the sheet between the conveyance unit and transfer unit before the sheet reaches the transfer unit. Based on this detection result, the control unit preliminarily adjusts the conveyance speed of the sheet by the conveyance unit to prevent abrupt force changes and sheet slippage at the transfer unit, ensuring stable image formation.
Solution Approach 2:
The detection unit continuously detects the loop amount formed on the sheet, and the control unit uses this feedback information to dynamically adjust the conveyance speed of the sheet by the conveyance unit. This closed-loop control ensures that the sheet is conveyed at an appropriate speed to prevent slippage at the transfer unit while maintaining constant loop amount control.
2Manufacturing precision
If the conveyance speed of the sheet by the fixing unit is controlled based on loop detection, then the loop amount can be maintained constant, but the force acting on the sheet at the transfer unit changes abruptly when the trailing edge passes through the conveyance unit, causing sheet slippage
Solution Approach 1:
The detection unit detects the loop amount formed on the sheet between the conveyance unit and transfer unit before the sheet reaches the transfer unit. Based on this detection result, the control unit preliminarily adjusts the conveyance speed of the sheet by the conveyance unit to prevent abrupt force changes and sheet slippage at the transfer unit, ensuring stable image formation.
Solution Approach 2:
The detection unit detects the loop amount formed on the sheet, and the control unit applies a counter-action by adjusting the conveyance speed of the sheet by the conveyance unit to offset the harmful effect of abrupt force changes that would cause sheet slippage at the transfer unit.
3Device complexity
If a single-stage conveyance speed control is used, then the control system is simple, but it cannot effectively prevent sheet slippage when sheets with varying grammages are conveyed
Solution Approach 1:
The control unit dynamically adjusts the conveyance speed of the sheet by the conveyance unit based on the loop amount detection result. This dynamic speed adjustment allows the system to adapt to sheets with varying grammages and prevent sheet slippage at the transfer unit, improving conveyance stability without requiring a complex multi-stage control system.
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 solution effectively maintains a consistent deflection amount of the sheet, reducing the likelihood of sheet slippage at the transfer unit and minimizing image defects, while also accommodating sheets with varying grammages.
Implementation Method 1
The loop detection sensor includes a photo interrupter and an actuator that pivots when pressed by a conveyed sheet, and the photo interrupter is turned ON or OFF in response to the displacement of the actuator
Data Source
AI summary
An image forming apparatus includes a conveyance unit, a transfer unit, a fixing unit, a detection unit configured to detect a deflection amount of the sheet, and a control unit configured to control a conveyance speed of the sheet by the fixing unit based on a detection result of the detection unit. The control unit is configured to perform a mode that performs, during a time when a single sheet is being nipped by the conveyance unit, the transfer unit, and the fixing unit, a first process of controlling the conveyance speed of the sheet by the fixing unit such that the deflection amount becomes a first deflection amount, and a second process, performed after the first process, of controlling the conveyance speed of the sheet by the fixing unit such that the deflection amount becomes a second deflection amount smaller than the first deflection amount.