Build-Surface Optical Calibration for Additive Fabrication Drift
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Solution Overview
Problem
Additive fabrication devices, such as those using selective laser sintering, face challenges in maintaining accurate optical system calibration over time due to thermal changes and physical disruptions, leading to inaccuracies in part fabrication as the alignment of the optical system can drift, and conventional calibration methods using fixed targets may not accurately reflect the alignment with the powder bed.
Innovation Solution
The implementation of an optical system calibration method that uses calibration features generated on the build surface, such as illuminated regions or partially sintered areas, which are imaged by a sensor to determine optical corrections, allowing for precise mapping between pixel coordinates and build surface coordinates, and the use of fiducial targets to account for changes in the imaging device's position and orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional calibration methods using fixed targets are used, then the calibration process is simple, but the calibration accuracy deteriorates because the fixed targets may not accurately reflect the alignment with the powder bed
Solution Approach 1:
The patent introduces calibration features (such as illuminated regions or partially sintered areas on the build surface) as an intermediary between the optical system and the powder bed. These features are generated by the optical system itself and imaged by the sensor, serving as a mediator that directly reflects the alignment relationship between the optical system and the powder bed, thereby improving calibration accuracy without requiring external fixed targets
Solution Approach 2:
The optical system calibrates itself by generating calibration features on the build surface using its own light source and imaging system. The calibration features are created by the optical system's light directing mechanism and then imaged back by the sensor to detect alignment drift. This self-service approach eliminates the need for separate fixed calibration targets while maintaining calibration accuracy
2Manufacturing precision
If the optical system operates without calibration corrections, then the operation is continuous, but the manufacturing precision deteriorates due to thermal changes and physical disruptions causing alignment drift
Solution Approach 1:
The patent implements periodic calibration by generating calibration features at regular intervals (between layers or between operations) to detect and correct alignment drift caused by thermal changes and physical disruptions. This periodic calibration maintains manufacturing precision without requiring continuous calibration, thus minimizing time loss while ensuring accuracy
Solution Approach 2:
The system performs preliminary calibration by generating calibration features before actual fabrication operations begin, and can also perform calibration between operations. This preliminary action ensures the optical system is properly aligned before manufacturing starts, preventing accuracy degradation and reducing the need for corrective re-calibration during production
3Measurement precision
If calibration features are generated on the build surface, then the calibration accuracy improves, but the device complexity increases due to additional control and imaging requirements
Solution Approach 1:
The optical system serves multiple functions: it directs light for sintering operations and simultaneously generates calibration features for alignment detection. The same light source and imaging sensor used for fabrication are utilized for calibration purposes. This multi-functionality improves alignment detection accuracy without requiring separate dedicated calibration hardware, thus managing device complexity
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 approach enables robust and accurate calibration of the optical system, ensuring precise light direction and reducing the likelihood of fabrication inaccuracies by detecting and correcting for drift during initial setup, between operations, or even during ongoing fabrication, thereby maintaining the quality of the produced parts.
Implementation Method 1
In one approach to additive fabrication, known as selective laser sintering, or 'SLS,' solid objects are created by successively forming thin layers by selectively fusing together powdered material
Implementation Method 2
an image sensor configured to receive light produced from the source material
Data Source
AI summary
Techniques are described for calibrating an optical system in an additive fabrication device using an image of the build surface within the device. These techniques allow calibration to be performed by imaging one or more calibration features generated on (or at) the build surface, which may include illuminated regions of the build surface, regions of the build surface on which solid material has been formed, and/or regions of the build surface to which energy has otherwise been directed thereby making those regions distinguishable from their surroundings. The calibration features may be produced (at least in part) by the optical system to be calibrated. The location of the calibration features within the image may be compared with the intended location of these calibration features, and corrections to the optical system determined based on any differences between the actual and intended locations.