Shadow Casting 3D Inspection for Off-Axis Mechanical Parts
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Solution Overview
Problem
Existing optoelectronic systems struggle to achieve precise 3D reconstruction of mechanical parts lacking axial symmetry or rotating off-axis, leading to incomplete and inaccurate dimensional and geometrical feature measurements due to undesired reflectance phenomena and profile discrepancies.
Innovation Solution
A method utilizing an optical shadow casting system to rotate the mechanical part, acquire two-dimensional images, extract edge points, transform them into a Cartesian reference system, and calculate spatial coordinates based on edge point variations during rotation, enabling accurate 3D reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical measuring system of the shadow casting type is used to obtain precise linear or bidimensional images, then measurement precision is improved, but the ability to obtain proper 3D reconstruction is lost for parts without axial symmetry or rotating off-axis
Solution Approach 1:
The patent transitions from obtaining only 2D images to extracting 3D spatial coordinates by analyzing the variation of detected points during rotation. The method calculates the third coordinate (depth) by evaluating how detected profile points move across multiple 2D images taken at different rotation angles, thereby adding the depth dimension to the measurement data.
Solution Approach 2:
The patent employs continuous rotation of the mechanical part through multiple angular positions, continuously acquiring 2D images at successive angles. This continuous action provides overlapping view information that enables the system to reconstruct the complete 3D surface geometry by integrating data from all rotation angles.
2Difficulty of detecting and measuring
If optoelectronic distance sensors such as laser scanners are used to obtain 3D numerical objects, then 3D reconstruction capability is improved, but measurement precision deteriorates due to disturbances from undesired reflectance phenomena
Solution Approach 1:
The patent uses 2D shadow images as an intermediary representation of the 3D object. Instead of directly measuring distances with laser scanners that suffer from reflectance issues, the system first obtains 2D projected images and then infers 3D coordinates by analyzing the geometric variation of detected points during rotation, avoiding direct optical distance measurement through reflective surfaces.
Solution Approach 2:
The patent replaces active optical distance sensing (laser scanning) with passive 2D image acquisition and geometric reconstruction. By substituting the direct optical measurement approach with a image-based geometric inference approach, the system eliminates the harmful reflectance effects that plague laser-based distance sensors.
3Measurement precision
If the mechanical part is rotated about its own symmetry axis, then proper information about the position of points is obtained, but the method cannot be applied to parts with different shapes or rotating off-axis
Solution Approach 1:
The patent develops a universal method that works for any mechanical part shape and any rotation axis configuration. By analyzing the variation of detected profile points across multiple 2D images taken at different rotation angles, the system can reconstruct 3D coordinates regardless of whether the part has axial symmetry or not, and regardless of the rotation axis orientation.
Solution Approach 2:
The patent changes the approach from assuming axial symmetry to explicitly modeling the variation of detected points as a function of rotation angle. By treating the detected point positions as parameters that vary with rotation angle and using this variation to calculate 3D coordinates, the method adapts to any part geometry and rotation configuration without requiring axial symmetry assumptions.
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 complete and accurate measurement of geometrical and dimensional features by calculating spatial coordinates, correcting for profile discrepancies and obtaining a realistic 3D model of the mechanical part.
Implementation Method 1
employ an optical measuring system of the shadow casting type including an emitter with a light source and telecentric lenses
Data Source
AI summary
A method for checking dimensions and geometrical features of a mechanical part using an optoelectronic system of the shadow casting type includes calculating the spatial coordinates of points of the surface of the part that allow a 3D reconstruction of the surface of the part, and checking the dimensions and geometrical features making use of such spatial coordinates. The spatial coordinates of the points are calculated starting from two-dimensional images and relevant profiles obtained by means of the shadow casting system while the mechanical part rotates about a rotation axis. The position of points or edges of the profiles and variation of such position are detected at predetermined heights as the rotation angle varies. On the basis of such variation, the position, with respect to a measurement plane, of points on the part to be checked which generate points of the aforementioned profile is identified and the spatial coordinates of the points of the surface are calculated.