OLED Driving Current Compensation for Image Uniformity
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Solution Overview
Problem
Existing optical writing devices using OLEDs face issues with image quality due to differences in light emission efficiency over time, leading to unevenness in printed images, especially when switching between different light emission amounts and conveyance speeds, which conventional technologies struggle to accurately compensate for.
Innovation Solution
An optical writing device with a first target current value estimation unit, a first light emission control unit, a time amount estimation unit, and a second light emission control unit that adjust the driving current to match the required light emission amounts by quantizing the target current values and accounting for the increase in current requirements over time, ensuring consistent light emission across OLEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the light emission amount of OLEDs is switched between different preset light amounts, then the adaptability to different sheet conveyance speeds is improved, but the difference between actual current amount and target current amount increases, causing image unevenness
Solution Approach 1:
The patent applies preliminary action by calculating and setting the initial current amount before switching light emission amounts. The control unit calculates the initial current amount based on the relationship between the current light emission amount and the target light emission amount, and sets this calculated value as the initial current amount for the next light emission amount. This preliminary calculation ensures that when switching occurs, the OLED starts from a current value that minimizes the difference between actual and target current amounts, preventing image unevenness from the outset.
Solution Approach 2:
The patent implements feedback by continuously monitoring the light emission duration of each OLED and using this information to dynamically adjust the driving current. The control unit stores the light emission duration for each OLED, calculates the initial current amount based on this accumulated data, and updates the current amount in subsequent switching operations. This feedback mechanism ensures that the system adapts to individual OLED characteristics and maintains image quality consistency across multiple switching cycles.
2Reliability
If the driving current amount is increased step-by-step to compensate for OLED deterioration, then the light emission efficiency is maintained, but the difference between actual current amount and target current amount remains during intervals, causing image unevenness
Solution Approach 1:
The patent applies preliminary action by calculating the initial current amount before switching light emission amounts. The control unit calculates the initial current amount based on the relationship between the current light emission amount and the target light emission amount, and sets this calculated value as the initial current amount for the next light emission amount. This preliminary calculation ensures that when switching occurs, the OLED starts from a current value that minimizes the difference between actual and target current amounts, preventing image unevenness from the outset.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the driving current amount based on light emission duration and switching history. Instead of using fixed step-by-step current increases, the system calculates the initial current amount as a specific parameter setting before switching, and uses this calculated parameter to bridge the gap between different current levels. This parameter-based approach replaces the coarse step-by-step method with a more precise continuous adjustment mechanism.
3Adaptability or versatility
If the sheet conveyance speed is switched between full speed and half speed, then the device can handle different recording sheet thicknesses, but the rotation speed change of the photoreceptor drum requires light amount switching that exacerbates current amount differences
Solution Approach 1:
The patent applies preliminary action by calculating and setting the initial current amount before switching light emission amounts. The control unit calculates the initial current amount based on the relationship between the current light emission amount and the target light emission amount, and sets this calculated value as the initial current amount for the next light emission amount. This preliminary calculation ensures that when switching occurs, the OLED starts from a current value that minimizes the difference between actual and target current amounts, preventing image unevenness from the outset.
Solution Approach 2:
The patent implements feedback by continuously monitoring the light emission duration of each OLED and using this information to dynamically adjust the driving current. The control unit stores the light emission duration for each OLED, calculates the initial current amount based on this accumulated data, and updates the current amount in subsequent switching operations. This feedback mechanism ensures that the system adapts to individual OLED characteristics and maintains image quality consistency across multiple switching cycles.
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 reduces differences in light emission between OLEDs, preventing image unevenness and maintaining high image quality by accurately adjusting driving currents based on the light emission duration and temperature, thereby compensating for the decrease in light emission efficiency over time.
Implementation Method 1
a print head with a light-emitting unit including organic light-emitting diodes (hereinafter referred to as 'OLEDs')
Implementation Method 2
OLEDs are known to have a characteristic such that the longer a total duration during which an OLED has emitted light
Data Source
AI summary
An optical writing device performing optical writing with a light-emitting element, performing light amount switching, and including: a unit estimating a first value corresponding to a current amount for causing the element to emit a first light amount immediately after the switching; a unit supplying to the element, from immediately after the switching, a current amount corresponding to a first digital value acquired by quantizing the first value; a unit estimating a time amount through which a current amount for keeping the element emitting the first light amount increases from the current amount for causing the element to emit the first light amount immediately after the switching to a current amount corresponding to a second digital value greater than the first digital value by one step; and a unit supplying to the element, when the time amount elapses after the switching, the current amount corresponding to the second digital value.