Subscribe Button 1

Helical Tomography Optimizes Measurement Accuracy

With Spiral (Helical) Tomography, from Werth Messtechnik GmbH, the measured object is moved screw-like along the machine rotary axis as it rotates. This has the benefit that all parts of the measured object are irradiated horizontally from the source to the detector at least once. Due to this principle, no cone beam or ring artifacts occur, and the systematic measurement errors are correspondingly lower.

Volume section of a dental implant from measurement with Spiral Tomography (top) and conventional Cone Beam Tomography (bottom)

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, such as 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 microns. 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.

Endoscope nozzles with injection hole diameters of around 100 µm can be measured in the production cycle using the new computed tomography  measurement method

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.

Due to a small distance between the X-ray source and a large detector, a large part of the radiation energy is used at the same time. Multi-object measurements with up to fifteen workpieces in one measurement process are possible. Thus, cycle times of about 10 minutes can be achieved. The user’s tasks in close-to-production worker self-inspection are limited to loading the machine and selecting the measuring program.

Fountain pens are another application example for Helical Tomography. Thin-walled lamellae under the nib suck in the ink by capillary action. Due to artifacts that occur, the lamellae cannot be easily measured with conventional Cone Beam CT. With Helical CT, they can now be made visible and measurable. Helical CT allows the measurement of internal geometries with correspondingly tight tolerances.

For more information: