Thermal Image Pseudocalibration for Welding Cooling Rate Measurement
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Solution Overview
Problem
Current methods for determining the cooling rate of a substrate during a heating process, such as welding, using thermal cameras are cumbersome and unreliable due to the need for precise calibration, which is time-consuming and affected by varying emissivity of the material.
Innovation Solution
A method that uses a single thermal image to determine the cooling rate by identifying pixel sets with known temperatures and pixel distances, applying pseudocalibration techniques to an uncalibrated thermal camera, without requiring knowledge of the actual speed of the substrate relative to the heat tool.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermal camera is properly calibrated to identify precise correspondence between pixel intensity and temperature, then measurement precision is improved, but device complexity and time consumption increase due to the cumbersome calibration process
Solution Approach 1:
The system performs self-calibration by using the weld bead geometry and known material properties (melting point, solidus temperature) to automatically determine the relationship between pixel intensity and temperature without requiring external calibration equipment or manual intervention. The calibration data is extracted directly from the thermal image of the welding process itself.
Solution Approach 2:
The patent changes the approach from requiring precise absolute temperature calibration to using relative temperature differences and known phase change temperatures (melting point, solidus temperature) as reference points. This allows the system to work with uncalibrated cameras by leveraging material-specific thermal parameters rather than requiring general camera calibration.
2Measurement precision
If a thermal camera is properly calibrated, then measurement precision is improved, but loss of time increases due to the time-consuming calibration process
Solution Approach 1:
The system performs calibration actions during the actual welding process rather than requiring separate pre-calibration steps. By capturing thermal images during welding and using the weld bead's phase change temperatures as reference points, the calibration is accomplished simultaneously with the manufacturing process, eliminating idle calibration time.
Solution Approach 2:
The system calibrates itself automatically using information from the welding process itself, eliminating the need for operator intervention or separate calibration procedures. The calibration is extracted from the thermal image data and material properties during normal operation.
3Measurement precision
If traditional calibration methods are used, then measurement precision is improved, but reliability decreases due to varying emissivity of materials affecting calibration accuracy
Solution Approach 1:
The patent shifts from relying on emissivity calibration to using known phase change temperatures (melting point, solidus temperature) as fixed reference points. These temperature thresholds are material properties that do not depend on emissivity, allowing accurate temperature determination without needing to know or calibrate the emissivity of the workpiece material.
Solution Approach 2:
The patent uses the weld bead's phase change temperatures as an intermediary reference that bridges the gap between pixel intensity and actual temperature. Instead of directly calibrating the camera to the workpiece material (which requires knowing emissivity), the system uses the known thermal properties of the material at phase change points as a reliable intermediate reference.
4Measurement precision
If pixel speed and geometric calculations are required for cooling rate determination, then measurement precision is improved, but device complexity and ease of operation worsen
Solution Approach 1:
The system automatically extracts all necessary parameters (pixel distances, temperature values, cooling rates) directly from the thermal image and known material properties without requiring operator input for speed or geometry calculations. The processing system performs all calculations autonomously based on the captured image data.
Solution Approach 2:
The patent changes from requiring multiple input parameters (actual speed, geometric calculations) to using only image-based parameters (pixel distances, pixel intensities) combined with known material properties. This simplifies the input requirements while maintaining measurement accuracy through direct pixel-to-temperature correspondence established via pseudocalibration.
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
Enables accurate determination of the cooling rate independently of substrate speed, eliminating the need for precise camera calibration and geometric calculations, thus simplifying the process and improving reliability.
Implementation Method 1
The response of a thermal camera is due to the actual temperature of the material being imaged
Data Source
AI summary
A method for measuring a cooling rate of molten material uses a single thermal image of a heating process having a known pixel speed, and identifies a first pixel set having a first known temperature, a second pixel set having a second known temperature and a pixel distance between the first pixel set and the second pixel set. The method uses the first temperature, the second temperature, the known pixel speed and the pixel distance to determine the cooling rate. By detecting, in an uncalibrated thermal image of a heating process using a material, areas having specific states (specifically in the molten state and in the solidified state), and knowing the actual temperature in the solidified state (because of the known physical properties of that type of material), it is possible to determine the emissivity of the material in the solid state.