Scanner Edge Detection Using Dynamic Thresholds for Thin Paper
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Solution Overview
Problem
Existing image scanning apparatuses face difficulties in accurately detecting the leading end of a document sheet due to the absence of a shadow near the leading end, and in distinguishing between light transmitted through thin paper and reflected light, leading to incorrect detection of the white edge.
Innovation Solution
The apparatus includes a document table with a white document pressing surface and an image scanner that generates image data with gradation values, using a controller to perform processes for detecting black edges, determining sheet type, and accurately detecting white edges by setting specific thresholds based on gradation values for thin and thick paper.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If light is emitted in a single direction from the light source toward the document sheet, then the trailing end can be detected by detecting the shadow, but the leading end cannot be detected because no shadow emerges near the leading end
Solution Approach 1:
The detection process is segmented into two distinct modes: shadow detection for the trailing end and white edge detection for the leading end. The controller identifies which end is which based on the presence or absence of shadows, then applies the appropriate detection method to each end independently, enabling accurate detection of both ends despite their different optical characteristics
Solution Approach 2:
Instead of trying to detect the leading end using shadow detection (which fails), the patent inverts the approach by detecting the leading end through white edge detection - identifying the boundary where the white document sheet meets the non-white background. This inverse approach successfully detects the leading end by looking for what is absent (shadow) and compensating with an alternative detection method
2Use of energy by moving object
If the document sheet has a thin thickness, then light can be transmitted through portions with few paper fibers, but this causes erroneous detection of white edge positions due to light re-transmission
Solution Approach 1:
The patent introduces a document pressing member as an intermediary element between the light source and the document sheet. This pressing member applies pressure to ensure uniform contact and consistent light blocking at the document edges, preventing light leakage that would cause erroneous white edge detection in thin documents
Solution Approach 2:
The patent dynamically adjusts the detection threshold for white edge detection based on the detected sheet type (thin or thick). For thin sheets, a higher threshold is used to distinguish true white edges from areas where light transmits through and reflects off the document holder, thereby maintaining detection accuracy across different sheet thicknesses
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 precise detection of both leading and trailing edges of a document sheet, even when light is transmitted through thin paper, by distinguishing between different gradation values and types of paper, thereby improving the accuracy of edge detection.
Implementation Method 1
when the image scanner receives reflected light from the end face onto which the light is incident
Implementation Method 2
the document sheet has a portion where a large number of paper fibers overlap each other such that a small quantity of light may be transmitted therethrough and a portion where a small number of paper fibers overlap each other such that a large quantity of light may be transmitted therethrough
Data Source
AI summary
An image scanning apparatus includes a controller configured to acquire image data by scanning a document and a particular range of a document pressing surface, detect black edge positions by detecting, from the image data, black pixels having gradation values less than a white gradation value, determine a sheet type of the document based on the gradation values of the black pixels, detect white edge positions by detecting, from the image data, white pixels having gradation values equal to or more than the white gradation value. The controller is further configured to, when the sheet type is a thin paper, detect, as the white pixels, pixels having gradation values equal to or more than a first threshold, and when the sheet type is a thick paper, detect, as the white pixels, pixels having gradation values equal to or more than a second threshold.