Workpiece Surface Depth Mapping With Focus Fitting and Aberration Correction
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Solution Overview
Problem
Conventional optical measuring instruments for workpiece surfaces can only record 2D data, requiring additional techniques for depth information, and existing Shape from Focus (SFF) methods are not suitable for industrial metrology due to low resolution and accuracy.
Innovation Solution
A method using an optical sensor to capture multiple images of a workpiece surface at varying focal planes, generating a focal image stack, fitting functions to focus values, and correcting imaging errors like astigmatism to create a high-resolution depth map.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Shape from Focus (SFF) technique is used to determine depth information, then depth mapping capability is improved, but measurement accuracy and resolution deteriorate due to optical aberrations like astigmatism
Solution Approach 1:
The patent applies preliminary action by performing astigmatism correction through function fitting before final depth map generation. The system captures multiple images at different focal planes, fits functions to the image data to correct astigmatism errors, and then generates the depth map. This preliminary correction ensures that the subsequent depth mapping operates on corrected data, resolving the contradiction between depth mapping capability and measurement accuracy.
Solution Approach 2:
The patent implements feedback by using the captured images to determine astigmatism characteristics, which then feed into the function fitting process to generate correction values. These correction values are applied to subsequent measurements. The system continuously refines the depth map by incorporating feedback from the image analysis, thereby improving both depth mapping accuracy and measurement resolution simultaneously.
2Loss of information
If multiple images at different focal planes are captured, then depth information completeness is improved, but measurement time and processing complexity increase
Solution Approach 1:
The patent applies segmentation by dividing the depth measurement process into discrete focal plane steps. Instead of capturing all possible depth information continuously, the system captures images at specific, predetermined focal planes. This segmentation allows the system to obtain sufficient depth information while limiting the total number of images captured, thereby reducing measurement time and processing complexity while maintaining depth information completeness.
Solution Approach 2:
The patent employs partial action by capturing images at a selective subset of focal planes rather than exhaustively sampling all possible depths. The function fitting process interpolates between these partial measurements to generate the complete depth map. This approach achieves sufficient depth information completeness without the excessive time and processing requirements of exhaustive sampling.
3Measurement precision
If astigmatism correction is applied through function fitting, then measurement accuracy is improved, but device complexity and computational requirements increase
Solution Approach 1:
The patent applies parameter changes by transforming the astigmatism correction problem into a function fitting task with specific parameters. The system fits mathematical functions (such as polynomial or Gaussian functions) to the image data, where the function parameters represent the astigmatism characteristics. By changing the problem representation to parameter-based function fitting, the system achieves accurate correction while maintaining manageable computational complexity through well-established fitting algorithms.
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 high reproducibility and accuracy in measuring workpiece surfaces with extended-depth-of-field images, correcting optical aberrations for precise depth mapping.
Implementation Method 1
capturing a plurality of images of an area of the workpiece surface with defined focal plane positions differing in the depth direction
Implementation Method 2
capturing a plurality of images of an area of the workpiece surface using the optical sensor
Data Source
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AI summary
The present invention relates to a computer-implemented method (40) for generating a depth map of an area of a surface of a workpiece (12), comprising the following steps: receiving (42) a focal image stack, wherein the focal image stack comprises a plurality of images of the workpiece (12), the images depicting the area of the surface of the workpiece (12) with defined focal plane positions (22) differing in a depth direction, each image of the focal image stack being assigned a focal plane position (22), each image of the focal image stack being assigned a focal plane position (22), and each image point of the images being assigned to a corresponding object point on the surface of the workpiece (12); determining (44) a focus value of each image point of each image of the focal image stack; fitting (46) a function along the depth direction (20) to the focus values of those image points of the images that are assigned to the same object point;Determining (48) a depth value of each object point on the surface of the workpiece (12) in the depth direction (20) based on an extremum of the fitted function; and generating (50) the depth map of the area of the surface of the workpiece (12) based on the determined depth values. The present invention further relates to a method (60) for measuring a surface of a workpiece (12), a measuring device for measuring a surface of a workpiece (12), and a computer program product.