Alignment procedure

The 2-D alignment step is carried out to relate the video and scanner coordinate system. This is done by selecting 10-15 points for each Laser head on the scan area. PSV software stores the video coordinates and the scan angles of these points on the scan area and calculates the polynomial interpolation. 2-D alignment step performed for one of the scan heads is shown in Figure 36.5(b).

Figure 36.5 (b) 2-D alignment step performed for the composite plate

Alignment procedure for 3D

In 3D alignment, coordinate system for the scan area is defined. This is done by selecting origin, point on X-axis, and point on X-Y plane on the scan area. After this step, all the three Lasers are made to coincide at other four to five points. The purpose of using these points is to back calculate the position and angle between the Laser heads by PSV software. After 3-D alignment procedure, the software is able to provide the coordinates (X, Y, and Z) of any point on the scan area with respect to the chosen coordinate system.

Geometry scan

All the scan points in the mesh grid are accessed by the three Lasers in order to estimate the surface of the test object. The three Lasers coincide at each and every scan point on the mesh grid [Figure 36.5(c)]. The accuracy of the surface estimated depends on the previous steps. This step is crucial to obtain the exact simulations of the test surface during the test.

Figure 36.5 (c) Status points on the scanned composite plate

Rectangular mesh grid of size 250 mm x 200 mm was done in ABAQUS. This grid was imported into the PSV software to define the scan area as shown in Figure 6.5(d). The grid has 356 scan points in the present case.

Figure 36.5 (d) Mesh grid with the scan points on the rectangular composite plate.

Data acquisition parameters

Data acquisition properties such as the excitation signal to be used, frequency range, parameters for the FFT analysis (number of FFT lines, bandwidth etc.), averages, windows, velocity decoder are given in this step. Time required for the complete scan depends on the number of scan points defined and FFT parameters. In the present analysis, 356 scan points were defined on the composite plate and it took about one hour to complete the scan. Response plots, mode shapes animations are visualized after the scan.