Print Medium Position Detection Using Differential Light Sensors
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Solution Overview
Problem
Existing printing apparatuses face challenges in accurately detecting the position of a print medium due to fluctuations in signal values caused by the posture and environmental factors such as external light in the conveyance path.
Innovation Solution
A printing apparatus is equipped with a position detection unit comprising a light emitting unit and two light receiving units, which generate a differential signal output to enhance detection accuracy by canceling out the influence of environmental factors, allowing precise detection of the print medium's position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a light emitting element and a light receiving element are used to detect the print medium, then the print medium can be detected, but the signal value of the light receiving element fluctuates due to print medium posture and external light, reducing detection accuracy
Solution Approach 1:
The single light receiving element is segmented into two separate light receiving elements (first light receiving element and second light receiving element). Each element detects light at different positions, and their signals are differentially processed to eliminate common-mode noise from external light and posture variations, thereby improving both detection accuracy and signal stability.
Solution Approach 2:
The system implements feedback by continuously monitoring the difference signal between the two light receiving elements and using this information to accurately determine print medium position. The differential signal provides real-time feedback that compensates for environmental fluctuations, maintaining reliable detection despite changing conditions.
2Loss of information
If the light receiving element detects reflected light in the conveyance path, then the print medium position can be detected, but external light and environment cause signal fluctuations
Solution Approach 1:
The second light receiving element acts as an intermediary reference that detects the same external light conditions as the first element. By comparing the two signals differentially, the system uses this intermediary measurement to cancel out the harmful effect of external light, preserving accurate print medium position detection.
Solution Approach 2:
The system converts the harmful effect of external light into a useful reference signal. The external light that would normally cause noise is now detected by both light receiving elements, and their differential measurement transforms this harmful interference into a cancelable common-mode signal, improving detection accuracy.
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 solution improves the detection accuracy of the print medium's position, enabling precise ink discharge up to the end of the medium without overspill, and facilitates efficient intermittent conveyance and scanning printing.
Implementation Method 1
the light emitting element emits light to the conveyance path of a print medium, and the light receiving element detects reflected light
Data Source
Figure 1
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Figure 4A~4B
AI summary
A printing apparatus, comprising a printing unit, a conveyance unit and a position detection unit, the position detection unit including a light emitting unit configured to emit light to a conveyance path of a print medium, a first light receiving unit configured to detect reflected light from the conveyance path, and a second light receiving unit configured to detect reflected light from the conveyance path, the first and the second light receiving units being arranged side by side with other in a direction crossing a conveyance direction of a print medium, and a position of a print medium in a direction crossing the conveyance direction is specified based on a difference signal between signals of the first and the second light receiving units.