Laser Scanning Density Correction for Electrophotographic Apparatus

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Solution Overview

Problem

Electrophotographic image forming apparatuses without scanning lenses with fθ characteristics suffer from density unevenness due to non-constant laser beam spot movement speed, leading to varying image density across the photosensitive member.

Innovation Solution

An image forming apparatus with a photosensitive member, a scanning unit, a width correction unit, a luminance correction unit, and a density correction unit, which adjust exposure time and luminance to maintain equal latent image widths and density across the photosensitive member, despite non-constant scanning speeds.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a scanning lens with fθ characteristics is used, then the spot of the laser beam moves at a constant speed on the photosensitive member, but the size of the scanning lens becomes large and the cost increases

Engineering Contradiction:

Improvespot movement speedVSAvoidscanning lens size

Core Design Contradiction:

SpeedVSArea of stationary object

Solution Approach 1:

The patent extracts the fθ characteristics function from the scanning lens and implements it through software processing (image clock frequency adjustment) instead. This removes the need for a large scanning lens with fθ characteristics while maintaining constant spot movement speed, effectively taking out the problematic component while preserving its function.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical/optical solution (scanning lens with fθ characteristics) with an electronic/software solution (adjusting image clock frequency based on position). This substitution eliminates the need for complex optical components while achieving the same effect of constant spot movement speed.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Area of stationary object

If a scanning lens without fθ characteristics is used to reduce size and cost, then the apparatus becomes more compact and cheaper, but the spot movement speed becomes non-constant causing density unevenness

Engineering Contradiction:

Improvescanning lens sizeVSAvoidimage density uniformity

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

The patent implements a feedback mechanism where the image clock frequency is dynamically adjusted based on the position on the photosensitive member. By detecting the position and corresponding the spot movement speed to the image clock frequency, the system compensates for speed variations and maintains uniform image density across the entire surface.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent makes the image clock frequency dynamic rather than fixed. The frequency is continuously adjusted according to the spot movement speed at different positions, allowing the system to adapt to the non-constant scanning speed and maintain consistent image quality throughout the scanning area.

Inventive Principle:

Principle #15Dynamics

3Shape

If the image clock frequency is adjusted to equalize dot widths, then the dot widths become equal, but the exposure amount per unit area varies causing density unevenness

Engineering Contradiction:

Improvedot width uniformityVSAvoidimage density uniformity

Core Design Contradiction:

ShapeVSManufacturing precision

Solution Approach 1:

The patent performs preliminary adjustment of the image clock frequency before actual image formation. By pre-calculating and setting the appropriate frequency for each position based on expected spot movement speed, the system proactively compensates for speed variations, ensuring both uniform dot widths and consistent exposure amounts before the scanning actually occurs.

Inventive Principle:

Principle #10Preliminary action

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

The apparatus achieves reduced density unevenness and improved image quality by correcting exposure time and luminance based on scanning position, ensuring consistent image density across the photosensitive member.

Implementation Method 1

an optical scanning unit for forming an electrostatic latent image by exposing a photosensitive member to light

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS9665031B2Image forming apparatus that forms latent image by irradiating photosensitive member with light

Publication Date: 2017.05.30 CANON KK

AI summary

A scanning unit performs scanning over a photosensitive member with a laser beam irradiated from a light source. A width correction unit corrects exposure time. A luminance correction unit corrects luminance of the laser beam for forming latent images. A density correction unit corrects a density value of each of the pixels of the image data according to a scanning position of the laser beam on the surface of the photosensitive member.