In the automotive industry, volume gauging is an important application in engine development. Each cylinder in an engine block has to be measured for correct combustion volume. While CAD data can be used to determine nominal volume, compliance testing requires the acquisition of a large number of measurement points, their connection by line or curve approximation, and finally computation of the displacement volume.
Tactile and Traditional Methods of Volume Gauging
Tactile coordinate measuring machines (e.g., CMMs) can accomplish volume gauging with a high degree of accuracy, but this method requires a tremendous amount of time. Compared to tactile methods, traditional methods using liquid, gas or acoustics are much simpler and still remain in wide use.
The Advantage of Optical Methods: Structured Light
Optical methods based on structured light (fringe projection) offer a 3D scanning method that is non-contact and area based. This means scanning is significantly faster (seconds, not hours) and the 3D data produced is of much higher data density representing a more accurate shape of the part.
A structured light 3D snapshot sensor projects a line pattern onto the cylinder head of an engine block. The line pattern is recorded by a camera from an optimal angle, yielding information on the cylinder’s surface topology calculated from the deformation of the projected lines.
There is a significant advantage to using this inspection method. Namely, when blue LED stripes with smooth value gradients are projected and moved across the engine block in close steps, the analysis of these values allows for a magnitude better position resolution than the single point measurement typical of classical triangulation methods.
Stripe pattern projection provides coordinate resolution down to 1/50 of the projected stripe width. This means the cylinder head can be fully inspected with the acquisition of just a few dozen images with slightly shifted stripe positions (phases), which can be accomplished in just a few seconds.
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