Laser Diode APC Control for Droop Suppression
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Solution Overview
Problem
Conventional image forming apparatuses face issues with stray light and temperature droop in laser elements, leading to increased light emission and potential image defects like fogging due to the variation in light emission amounts during auto power control (APC) processes.
Innovation Solution
An image forming apparatus with a charging unit, light irradiation unit, and adjustment unit that switches between different light emission amounts to adjust the driving current, ensuring stable light emission and preventing stray light by performing APC in specific periods, thereby maintaining desired light levels and suppressing droop effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If laser emission is stopped between APC on second light emission amount and weak emission of second light emission amount to prevent stray light, then stray light is reduced, but laser element temperature drops causing droop and increased light emission amount
Solution Approach 1:
The patent applies preliminary action by performing APC on the third light emission amount (weak emission) before the actual weak emission of the second light emission amount. This preliminary APC measurement is conducted when the laser element temperature is stable, allowing the system to calculate and store a corrected light emission amount that compensates for future droop effects. When weak emission actually occurs, the system uses this pre-calculated correction value to maintain stable light emission despite temperature changes.
2Manufacturing precision
If second light emission amount is reduced to control non-image portion potential, then image quality is improved, but droop effect becomes more significant causing excessive light emission variation
Solution Approach 1:
The patent implements feedback by using APC measurements to detect actual light emission amounts and comparing them with target values. The system calculates correction values based on the difference between measured and target light emission amounts. These correction values are then applied to subsequent light emission operations, including weak emission of the second light emission amount. This closed-loop feedback mechanism ensures that even when the second light emission amount is reduced for image quality, the actual emitted light remains stable by compensating for droop effects.
3Measurement precision
If APC is performed at multiple light emission amounts, then light emission control precision is improved, but system complexity and control time increase
Solution Approach 1:
The patent applies segmentation by dividing light emission control into distinct segments or modes: first light emission amount for initial APC, second light emission amount for image formation, and third light emission amount (weak emission) for non-image portion control. Each segment has its own APC measurement and correction value. This segmentation allows the system to handle different light emission requirements independently while maintaining overall control precision, and the correction values for each segment can be calculated and stored separately to simplify real-time control.
Data Source
AI summary
A period in which an adjustment unit adjusts a driving current such that the light irradiation unit emits a third light emission amount of light is switched to a period in which a light irradiation unit emits a second light emission amount of light, and the period in which the light irradiation unit emits the second light emission amount of light is switched to a period in which the light irradiation unit emits a first light emission amount of light.