To obtain an image of a gear surface, the gear is set up to rotate on its axis while a laser beam moves linearly across the width of the gear as it spins. Figure 1 shows an experimental setup for a simple timing gear. Gears with different tooth geometries may require scanning by more than one laser beam simultaneously to get a detailed surface profile. 

Figure 1. Experimental setup for scanning a gear

An image of the surface profile of the gear surface is shown in Figure 2. Color variations represent differences in height of the teeth relative to a  circumferential surface on the gear.

Figure 2. Wrap around view of the gear teeth of the gear of Figure 1

A more detailed view of the gear teeth can be obtained by graphing a linear cross section of a segment of the gear. These cross sections can be obtained for any scanned location on the gear surface without retaking any measurements. A scan over a 14 teeth is shown in Figure 3.

Figure 3. Cross sectional graph of several gear teeth

While it may appear that the signal is noisy, when a 3D image of the teeth are graphed it can be seen that the variations are ridges that run along the teeth (Figure 4). They are therefore real surface features, since if they were noise the locations of the peaks would tend to be random.

Figure 4. 3D representation of gear teeth for the gear shown in Figure 1

The gear tooth data can also be displayed in a polar graph, which is shown in 

Figure 5.

Figure 5. Polar representation of data from the gear of Figure 1