Image Sensor Dirt Detection Using Duration Time Measurement
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Solution Overview
Problem
Image forming apparatuses face issues with detecting dirt on the image sensor, leading to inaccurate readings and potential false detection of sheet conveyance, which can result in suboptimal image formation and increased maintenance requests.
Innovation Solution
The apparatus includes a sheet conveying device, an image forming device, a sheet reading unit with a lamp and line sensor, a signal processing circuit, and a counting circuit that generates detection signals based on analog picture signals to determine the necessity of cleaning the sheet reading unit by measuring the duration of dirt detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the image sensor reads an original document through a transparent plate with dirt, then the amount of light received by light-receiving elements decreases, but this causes dark streaks in image data and false detection of sheet conveyance
Solution Approach 1:
The system performs preliminary detection of dirt on the transparent plate by monitoring light reception levels before actual document reading. The determiner detects dirt by comparing light reception levels during a detection phase, allowing cleaning to be performed before false sheet conveyance detection occurs, thereby preventing the harmful effect.
Solution Approach 2:
The system continuously monitors light reception levels from the image sensor and provides feedback to the determiner, which identifies dirt conditions based on this feedback. The cleaning controller then initiates cleaning operations based on the dirt detection results, creating a closed-loop system that prevents false readings.
2Measurement precision
If the apparatus frequently checks for dirt on the image sensor, then detection accuracy improves, but this increases the frequency of cleaning requests and maintenance burden
Solution Approach 1:
The system changes the monitoring parameter from continuous high-frequency checking to periodic sampling based on light reception level thresholds. The determiner samples light reception levels at specific intervals and only triggers cleaning when the level exceeds a predetermined threshold, reducing unnecessary cleaning requests while maintaining detection accuracy.
Solution Approach 2:
Instead of continuously monitoring, the system performs partial monitoring at key decision points. The determiner evaluates light reception levels only when necessary to make cleaning decisions, avoiding excessive checking while still capturing dirt conditions that would cause false sheet conveyance detection.
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 false detection of sheet conveyance and minimizes unnecessary cleaning requests, improving the accuracy of image formation and reducing maintenance burdens by distinguishing between large and small foreign substances.
Implementation Method 1
The line sensor outputs, in order of sequence of the pixels, analog picture signals corresponding to light reflected from the sheet being conveyed
Implementation Method 2
The sheet reading unit includes a lamp and a line sensor capable of reading the sheet being conveyed
Data Source
AI summary
An image forming apparatus includes a line sensor capable of reading a sheet being conveyed. A signal processing circuit generates, based on respective analog picture signals of pixels and in order of sequence of the pixels, detection signals each indicating whether or not a reflecting object has been read. A first counting circuit measures a duration time which is a time during which the detection signals maintain a level indicating that the reflecting object has been read. When the duration time reaches or exceeds a first specified time, the first counting circuit changes a level of a first detection result signal to a level indicating necessity of cleaning. A unit control circuit determines, based on the level of the first detection result signal, whether or not cleaning is necessary.