Geometry acquisition using light
For the last month I’ve been working on my final year project (Diplomarbeit) which consists of a measurement integration for high precision forged crankshafts. The institute I’m working at has bought a shaft measurement system. The system from Hommelwerke (Jena) uses the principle of light projection and - using focused light-rays - can detect geometrical variations quite well. For this purpose, the part that’s being measured is shone above and it’s contour is detected by a camera at the other side.
The first image shows a test object. Looking at it using the silhouette method provided by Hommelwerke the system has the ability to see most geometry elements (second image). The object can be rotated around the z-axis (top-down) to provide more data for the geometry reconstruction.
The projection system has a flaw though which is, it can’t detect or measure concave elements. That’s why the existing system has to be extended by a geometry acquisition system using structured (mostly striped) light. Using different angles for light-projection and camera system, the relief of a given system can be detected and any variations in geometry can be measured.
Using the course of the projected stripes (which usually variate in thickness to avoid stripe-mixing) the system can calculate the resulting geometry. Again, to fully capture all geometry elements, the test object should be rotated around the z-axis. Additionally the projection system should be translated along the y-axis (perpendicular to the stripe direction) each time the test object is rotated.
For that purpose a four-way positioning system has to be constructed that will hold the additional sensor (light source and camera) and bring it up to the object (i.e. crank shaft).
..to be continued..
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