Polygonal Mirror Surface Identification via Variable Slit Width

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Solution Overview

Problem

Existing image forming apparatuses face challenges in accurately identifying the reflecting surfaces of a rotatable polygonal mirror due to manufacturing and assembly inaccuracies, leading to deviations in scanning positions and increased costs from complex manufacturing steps and additional components required for correction.

Innovation Solution

An image forming apparatus with a rotatable polygonal mirror, a detecting portion, and a slit configured to regulate the light beam, where the slit has varying widths in the main and sub-scan directions, allowing a controller to identify one reflecting surface as a reference based on detected signals, simplifying the identification process without increasing the number of parts.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If cutting accuracy is improved to eliminate face inclination and scanning position deviations, then scanning precision is improved, but processing cost increases

Engineering Contradiction:

Improvescanning position accuracyVSAvoidprocessing cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent replaces the mechanical solution of improving cutting accuracy with an optical detection system. A light beam is used to detect the actual position and orientation of reflecting surfaces, and this detection information is fed back to the control unit to calculate correction values, substituting precision mechanical manufacturing with optical-mechanical detection and computational correction.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent implements a feedback mechanism where the detection unit measures the actual positions of reflecting surfaces, and the control unit uses this information to calculate correction values that are applied to compensate for deviations. This closed-loop feedback system allows the system to adapt to manufacturing variations without requiring higher manufacturing precision.

Inventive Principle:

Principle #23Feedback

2Difficulty of detecting and measuring

If magnets and Hall elements are added to identify reflecting surfaces, then surface identification capability is improved, but device complexity and manufacturing cost increase

Engineering Contradiction:

Improvereflecting surface identification capabilityVSAvoidnumber of parts

Core Design Contradiction:

Difficulty of detecting and measuringVSDevice complexity

Solution Approach 1:

The patent replaces the magnetic field-based detection system (magnets and Hall elements) with an optical detection system using light beams. The light beam method detects reflecting surface positions through optical reflection principles, eliminating the need for magnetic components and reducing device complexity while maintaining identification capability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Adaptability or versatility

If the number of BD signals and FG signals are not in a prime relationship, then rotation control flexibility is improved, but reflecting surface identification becomes impossible

Engineering Contradiction:

Improverotation control flexibilityVSAvoidreflecting surface identification capability

Core Design Contradiction:

Adaptability or versatilityVSDifficulty of detecting and measuring

Solution Approach 1:

The patent uses the light beam detection unit to directly measure the positions of reflecting surfaces and feeds this information back to the control unit. This feedback mechanism allows the system to identify reflecting surfaces regardless of the numerical relationship between BD and FG signals, as the identification is based on direct optical measurement rather than signal correlation.

Inventive Principle:

Principle #23Feedback

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 enables simple and accurate identification of the reflecting surface, correcting deviations in scanning positions and reducing manufacturing complexity and costs, while maintaining efficient image formation.

Implementation Method 1

a slit provided between the rotatable polygonal mirror and the detecting portion and configured to regulate the light beam toward the detecting portion

Methodology Applied

Scientific EffectLight beam regulation through slit: Filter (optical)

Implementation Method 2

a rotatable polygonal mirror configured to deflect the light beam emitted from a light source

Methodology Applied

Scientific EffectLight reflection: Reflection

Data Source

PatentUS9971273B2Image forming apparatus

Publication Date: 2018.05.15 CANON KK

AI summary

An image forming apparatus includes an optical scanning unit including a rotatable polygonal mirror, a detecting portion, and a slit; and a controller. The slit includes a first portion where a slit width is a first width with respect to a main scan direction and a second portion, different in position from the first portion with respect to a sub-scan direction, where the slit width is a second width different from the first width with respect to the main scan direction. The controller identifies one of reflecting surfaces of the rotatable polygonal mirror as a reference surface on the basis of a plurality of detected signals acquired by detecting a plurality of light beams which are deflected by the respective reflecting surfaces and which pass through the slit.