summary
Environmental vibration is common in engineering sites such as wind tunnels, vibration tables, and impact tests. Vibration can cause camera and support to shake, resulting in overall image shift. This directly introduces errors in displacement and strain calculations, causing DIC speckle tracking to fail.
Complete DIC camera vibration suppression requires the cooperation of hardware structure vibration reduction and software algorithm compensation: the hardware reduces vibration transmission through structure and materials; the software uses rigid stationary markers within the field of view to perform real-time correction of image drift through dynamic positioning.
I. Applicable Scenarios
Wind tunnel test : High-speed airflow impacts the cavity and support, causing continuous low-frequency shaking of the camera, which is a very typical vibration condition in the DIC field;
Vibration table and impact test environment : Ground vibration is transmitted to the DIC bracket through the base, and the camera shakes along with the environment.
Long-distance, wide-field-of-view DIC test : At long test distances, even slight vibrations of the support bracket will be magnified in the image, causing a noticeable image shift;
Modification-type field tests : It is not possible to carry out large-scale vibration reduction modifications on the test bench foundation, and environmental vibration cannot be eliminated at its source. It is necessary to rely on algorithms for error compensation.
II. Hardware vibration damping operation
Hardware vibration reduction is the foundation of the entire vibration suppression solution, prioritizing the reduction of vibration at its source from transmission to the camera.
1. DIC camera body vibration damping design: A vibration damping and buffer structure is added at the connection between the camera and the bracket to cut off the direct transmission path of vibration and reduce the transmission of high-frequency vibration to the camera body;
2. Bracket Material Selection: High-strength aluminum alloy or carbon fiber should be the preferred material for camera mounting brackets. High-modulus materials can improve the overall rigidity of the bracket and reduce the risk of deformation and resonance under stress.
3. Assembly and reinforcement: During installation, tighten the bracket base and each connecting joint to eliminate assembly gaps; fix the base to a foundation component with higher rigidity as much as possible, and avoid installing it on thin-walled or easily vibrating plates;
When conditions permit, the DIC support should be separated from the vibration source test bench to avoid direct coupling and transmission of vibration.
III. Software Dynamic Positioning Calibration Operation
When hardware vibration reduction cannot completely eliminate vibration, software dynamic positioning function can be enabled for drift compensation.
1. Within the camera's field of view, select a completely rigid and stationary area that will not deform or displace throughout the entire experiment;
2. Paste high-contrast markers in the rigid area; these markers will serve as reference points for image drift.
3. Enable the dynamic positioning calibration function in the DIC software;
4. During the test run, the software continuously tracks the changes in the image coordinates of the rigid, stationary marker points;
5. Based on the offset detected by the marker points, the entire image is corrected in real time to offset the image drift error caused by camera shake.
IV. Key Points of Practical Operation
1. Hardware vibration reduction is the primary method, while software dynamic positioning is only used as an error compensation method and cannot completely replace hardware vibration reduction; when the vibration amplitude is too large, relying solely on algorithm compensation will still produce a large error.
2. Rigid reference markers must be affixed to components such as the testing machine frame and cavity walls that will not undergo displacement or deformation;
3. The markers should be distributed as widely as possible, and not concentrated in a local area of the image. Multiple reference points can improve the stability of the correction algorithm.
4. If abnormal measurement results are found, first check whether the bracket connection is loose. Do not rely on software compensation to cover up hardware installation problems.
5. If the reference marker is obstructed during the test, the dynamic positioning correction will fail. When setting up the points, the obstruction range of the sample movement should be avoided.
V. Summary
The DIC camera vibration suppression employs a combination of hardware and software solutions. On the hardware side, vibration input is reduced through camera vibration isolation structures and high-strength aluminum alloy/carbon fiber high-rigidity brackets; on the software side, dynamic positioning is enabled using on-site rigid stationary markers to compensate for image drift in real time.
This combined DIC measurement solution can effectively address camera shake issues in complex environments such as wind tunnels and vibration tables, ensuring the accuracy of DIC displacement and strain data.
