Nonrigid Plastic Inspection Fundamentals Using Free State Scanning Methods
Optical free state scanning paired with virtual clamping eliminates physical fixture costs while revealing true residual stress warp in nonrigid plastics.
Photogrammetry Target Frame
Meaning
Optical coordinate measurement fixtures utilize highly visible reference points at known coordinates to calibrate and stitch multiple camera angles together. A photogrammetry target frame establishes a localized three-dimensional coordinate system for capturing complex geometries. This equipment is measured against calibrated laser trackers or coordinate measuring machines to verify the baseline distance between targets.
It is used during the initial setup of large-scale industrial scans.
Dimensional Accuracy
The rigid structure of the photogrammetry target frame ensures that the reference points do not shift during temperature changes or handling. Using carbon fiber or invar tubing minimizes thermal expansion and contraction in non-controlled factory environments. This mechanical stability is critical for achieving sub-millimeter scan accuracy on large aerospace or automotive structures where environmental conditions fluctuate.
The frame must remain isolated from any external mechanical forces.
Scanning Process
Cameras capture the target positions from multiple directions, allowing the software to compute the exact position of the camera in space. These reference points allow the scanning software to align dense point clouds with high precision. Without this structured reference, cumulative errors would cause the scan to warp or drift.
System Limit
Vibration or physical impact can deform the frame and ruin the calibration. If a photogrammetry target frame is bumped during a scan, the entire dataset becomes invalid and must be discarded. Operators must re-verify the calibration of the frame if any displacement is suspected.