With Spiral (Helical) Tomography, the measuring object is moved screw-like along the rotary axis as it rotates. This has the benefit that all parts of the measuring object are irradiated horizontally from the source to the detector at least once. Due to the principle, no cone beam or ring artifacts occur, and the systematic measurement errors are correspondingly lower.
The fast image acquisition by OnTheFly CT (patent pending) and the use of large detectors with small distances between X-ray source and detector shorten the measurement time. For a large aspect ratio of length to diameter, e.g., for long workpieces or fixtures with multiple stacked workpieces, measurement time is less than with Raster Tomography. An additional Cone Beam Artifact Correction (patent) is not necessary and this often reduces the evaluation time.
With conventional Cone Beam CT, systematic measurement errors occur as the cone angle increases. With the Werth software correction methods, these measurement errors are reduced to a few micrometers. By penetrating all parts of the measuring object horizontally, exact reconstruction is possible with Helical CT, so that cone beam artifacts and the need for corresponding correction methods are eliminated by this operating principle.
One application example for Helical Tomography are endoscope nozzles. These are millimeter-sized metal workpieces with several dozen spray holes. Spray hole diameters in the two-digit micrometer range require high resolution and therefore the use of transmission sources. With tolerances in the range of 10 µm, measurement errors should not exceed 1 µm to 2 µm. In addition, the use of a transmission source enables high-resolution measurements at high measuring speed, since much smaller focal spots are usually available for the same power compared to reﬂection tubes.