Linear Array Calibration Using Hybrid Dark and Light Response Measurements
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Solution Overview
Problem
Image sensor arrays in printer/scanner devices require initial calibration and ongoing calibration due to variations in photosensor chips and light sources, which degrade over time and with temperature changes, necessitating a method for absolute calibration that can account for these factors.
Innovation Solution
A hybrid calibration method using a calibration strip and printable media, where the calibration strip provides absolute feedback to modify the calibration of the linear array, allowing it to function as a spectrophotometer even without a full-length calibration strip, by measuring dark and light responses, applying offsets, and calculating gains to correct sensor responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a full-length calibration strip is used for absolute calibration, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The calibration process is segmented into two parts: a calibration sensor chip that views the calibration standard for absolute reference, and imaging sensor chips that view the calibration piece for relative calibration. This segmentation allows absolute calibration capability without requiring a full-length calibration strip across all sensor chips, thereby reducing hardware complexity while maintaining measurement precision.
Solution Approach 2:
The calibration sensor chip acts as an intermediary that obtains absolute reference measurements from the calibration standard and uses this information to correct the measurements from imaging sensor chips. This intermediary approach enables absolute calibration without requiring direct access to the calibration standard by all imaging sensors, simplifying the overall system design.
2Reliability
If calibration is performed frequently to account for degradation, then reliability is improved, but loss of time increases
Solution Approach 1:
The system performs preliminary characterization during manufacturing to establish initial gain and offset values for each sensor chip. This preliminary action creates a baseline that reduces the need for frequent full recalibrations, allowing the system to maintain reliability over time with minimal calibration intervention.
Solution Approach 2:
The calibration sensor chip continuously provides feedback on the absolute reference level, allowing the system to detect drift and degradation. This feedback mechanism enables targeted recalibration only when necessary, balancing reliability maintenance with minimal time loss.
3Productivity
If multiple sensor chips are used in the linear array, then productivity is improved, but manufacturing precision becomes more difficult to maintain
Solution Approach 1:
Each sensor chip is treated with local quality adjustments through individual gain and offset calibration factors. This allows each chip to be optimized for its specific characteristics while working together as part of the overall linear array, enabling high productivity with varied manufacturing precision across chips.
Solution Approach 2:
The system applies parameter changes in the form of calibration factors (gains and offsets) to each sensor chip to compensate for manufacturing variations. These parameter adjustments enable the array to function as a unified high-productivity system despite variations in individual chip performance.
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 method enables absolute calibration of linear arrays, ensuring accurate imaging across the lifespan of the device by accounting for temperature variations and degradation, allowing for efficient operation without the need for complex hardware or additional mechanisms.
Implementation Method 1
Image sensor arrays typically comprise a linear array of photosensors which raster scan an image bearing surface or document and convert the microscopic image areas viewed by each photosensor to image signal charges
Data Source
AI summary
A method of balancing responses of a plurality of sensor chips arranged generally in a linear array comprising: exposing the plurality of sensor chips to an absence of illumination; measuring a dark response of each photosensor of a plurality of photosensors; positioning a calibration piece within a field of view of the plurality of sensor chips other than a calibration sensor chip; illuminating a calibration standard and the calibration piece with a light source; measuring a light response of each photosensor of the plurality of photosensors; applying an offset to the light response of each photosensor of the plurality of photosensors by subtracting the dark response of each photosensor of the plurality of photosensors to obtain an offset light response for each photosensor of the plurality of photosensors; calculating a mean offset light response for each sensor chip of the plurality of sensor chips by averaging the offset light response for each photosensor of the plurality of photosensors in each sensor chip of the plurality of sensor chips; calculating a modified light response for each photosensor of the plurality of photosensors by modifying the offset light response for each photosensor of the plurality of photosensors based on the mean offset light response of the sensor chip comprising the respective photosensor, the mean offset light response of the calibration sensor chip, an initial mean offset light response of the sensor chip comprising the respective photosensor, and an initial mean offset light response of the calibration sensor chip; and, applying a first gain to the offset light response of each photosensor of the plurality of photosensors based on the modified light response of each respective photosensor to obtain a corrected light response of each photosensor of the plurality of photosensors.