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Abstract:
This video tutorial demonstrates a technique ("hack") to achieve consistent alignment when manually scanning rotationally symmetrical parts using mobile fringe projection scanners like ATOS or GOM Scan1. It addresses the challenge where the inherent mobility of these scanners leads to inconsistent coordinate systems between scans, making pre-alignment to CAD unreliable for symmetrical objects and potentially obscuring recurring defects. The proposed solution involves using a fixed measurement background (e.g., a rotation table) with reference point markers and physical markings for part placement. By exporting the reference points from the initial scan and importing them as nominal data into subsequent scans, users can perform a "best fit by reference point" alignment. This transforms the later scans (including their meshes) into the coordinate system of the first scan before aligning them to the CAD model, resulting in comparable orientations and allowing for reliable identification of consistent geometric deviations or defects across multiple parts.
Scanning Symmetrical Parts Consistently: A Manual Workflow Hack
0:00:03 Introduction: Introduces a method for consistent manual scanning of symmetrical parts using mobile fringe projection sensors.
0:00:19 The Challenge: Mobile scanners (like ATOS/GOM Scan1) offer flexibility but create inconsistent coordinate systems because the orientation is set by the first scan's angle.
0:00:41 Issue with Symmetry: For symmetrical parts lacking distinct features, standard "pre-alignment" to CAD can result in different orientations for each scanned part, making recurring defects appear random.
0:01:26 Proposed Solution: Use a fixed measurement background (like a rotation table) with reference points and markings to ensure consistent part placement. Align scans using the background's points before aligning to CAD.
0:01:53 Preparing the Setup: Mark the desired position and orientation for the part on the rotation table (using tape as an example) and apply reference point markers to the table itself.
0:02:34 Performing the First Scan: Digitize the first part, capturing its geometry relative to the reference points on the fixed background.
0:02:54 Exporting Background Reference Points: Select and export the reference points detected on the background from the first scan (e.g., as an XML file) to establish a master coordinate system.
0:03:15 Simulating Subsequent Scans: Place a new, identical part using the markings on the table and perform another scan (potentially starting from a different sensor angle).
0:04:08 Demonstrating Inconsistency: Importing the CAD and performing a direct pre-alignment on both scans shows how defects can appear in different locations due to the inconsistent initial orientations.
0:04:57 Importing Master Reference Points: In the project for the second scan, import the reference points previously exported from the first scan, choosing to import them as "nominal data".
0:05:39 Aligning Scans via Background Points: Use an alignment function (e.g., "Best Fit by Reference Point") to align the current scan's background points (actual) to the imported background points (nominal). Crucially, this transformation is applied to the scanned mesh as well.
0:06:14 Achieving Initial Consistency: Export the transformed mesh from the second scan. When both the first mesh and the transformed second mesh are imported into a new project, they are already in a very similar orientation.
0:06:50 Final Consistent CAD Alignment: Performing the CAD pre-alignment now yields comparable results for both parts, clearly showing that the defect occurs in the same location.
0:07:13 Key Takeaway: Using a fixed, marked background and aligning subsequent scans to the reference points of the first scan before CAD alignment ensures comparable results and reliable defect analysis for manually scanned symmetrical parts.