Thermal Camera Vignetting Correction for Powder Bed Fusion
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Solution Overview
Problem
Thermal cameras used in powder bed fusion apparatuses suffer from thermal vignetting distortions, leading to artificial temperature profiles and compromised control over the manufacturing process, particularly near the layer surface boundary, where temperatures appear artificially depressed, affecting object quality and build process reliability.
Innovation Solution
A method involving a moveable temperature reference at a steady state temperature, which is moved through the field of view of the thermal camera to record thermal images, identify affected pixels, construct a thermal map, and generate a correction matrix to correct for thermal vignetting distortions, ensuring accurate temperature control and image representation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermal camera is used to monitor temperature in powder bed fusion apparatus, then temperature control capability is improved, but thermal vignetting distortion causes artificial temperature profiles that compromise measurement precision
Solution Approach 1:
The patent applies parameter changes by modifying the thermal image data through a correction matrix that adjusts temperature values based on the detected vignetting pattern. The correction matrix contains calibration factors that transform the distorted temperature measurements into accurate representations of the actual surface temperature distribution.
Solution Approach 2:
The system implements feedback by using the thermal camera to monitor temperature, comparing the measured temperature profile against the known uniform temperature of the reference surface, detecting the vignetting distortion pattern, and then applying corrective transformations to subsequent measurements to compensate for the identified distortion.
2Measurement precision
If external calibration is performed for thermal vignetting, then measurement precision is improved, but device complexity increases due to recalibration requirements after camera position shifts
Solution Approach 1:
The system performs self-calibration by automatically detecting the vignetting distortion pattern using a uniformly heated reference surface and generating the correction matrix without requiring operator intervention. This self-service calibration can be repeated in-situ to update the correction matrix, eliminating the need for complex external calibration procedures and manual recalibration after position shifts.
Solution Approach 2:
The patent applies preliminary action by performing the calibration procedure beforehand to establish the correction matrix before actual temperature monitoring begins. The correction matrix is prepared in advance and can be stored for reuse, eliminating the need for repeated calibration operations during normal operation.
3Measurement precision
If frequent recalibration is performed to maintain accuracy, then measurement precision is improved, but productivity decreases due to operator intervention and build throughput impact
Solution Approach 1:
The system performs self-calibration automatically using a uniformly heated reference surface and image processing algorithms to generate the correction matrix without requiring operator intervention. This eliminates downtime associated with manual calibration and maintains build throughput while ensuring measurement accuracy.
Solution Approach 2:
The uniformly heated reference surface serves multiple functions: it acts as a calibration target for detecting vignetting distortion, provides a known uniform temperature reference, and can be integrated into the existing apparatus structure. This multi-functional approach eliminates the need for separate calibration equipment and procedures.
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 method effectively corrects thermal image distortions in-situ, allowing for precise temperature control and improved object quality by applying the correction matrix to subsequent measurements, reducing the need for frequent recalibration and minimizing operator intervention.
Implementation Method 1
a thermal camera... configured to monitor the temperature of the layer surface
Data Source
AI summary
A method for correcting thermal image distortion in a thermal camera in an apparatus for the layer-by-layer manufacture of three-dimensional objects, the thermal camera comprising a plurality of sensor pixels arranged along a first direction; the method comprising the steps of: (a) causing a temperature reference to be at a first steady state temperature; (b) moving the temperature reference at the first steady state temperature through a plurality of positions along the first direction through the field of view of the thermal camera; (c) recording a plurality of thermal images with the thermal camera while moving the temperature reference during step (b), each thermal image corresponding to one of the plurality of positions and comprising the detected temperature of the temperature reference as detected by at least one pixel of the plurality of sensor pixels; (d) identifying the at least one pixel that detected the temperature of the temperature reference within a respective thermal image at the corresponding one of the plurality of positions; (e) constructing a thermal map from the identified pixels representing the detected temperature of the temperature reference at the plurality of positions; (f) generating a correction matrix for the identified pixels based on comparison between the thermal map and the first steady state temperature; and (g) applying the correction matrix to subsequent measurements of the thermal camera. A controller and an apparatus for the layer-by-layer manufacture of three-dimensional objects comprising the controller to carry out the method are also provided.