Faster Cycle Times Achieved With ‘OnTheFly’ CT

One benefit of computed tomography is that the work-piece is captured completely, including undercuts and internal geometries but historically, computed tomography has been too slow for measurements in-cycle with the manufacturing process.

For years, Werth has used real-time reconstruction in WinWerth software in parallel with image capture has been used to minimize measurement time. To move beyond this, several methods have been introduced, each with its drawback. For instance, the power level of the X-ray tubes may be increased, but this comes at a cost of lower resolution due to the larger focal spot. The exposure time can also be decreased by reducing the distance between the X-Ray source and the detector. However, doing this will increase the severity of cone beam artifacts. Directly reducing only the exposure time means that the dynamic range of the detector will not be fully utilized. Finally, it is possible to improve measurement time for a multi-cavity measurement, by measuring several work-pieces simultaneously which is achieved because the point clouds are separated automatically. This method, however, generally limits the magnification, reducing the resolution for each individual part.

The new Werth OnTheFly CT (patent pending) saves time lag due to start-stop positioning of the work-piece by continuously rotating the machine axis. In conventional interupted start-stop operation, the rotary motion is halted in order to capture each radiographic image, so that no motion blur occurs under continuous exposure. For OnTheFly CT, short exposure times are needed in order to minimize motion blur. To achieve the same measurement uncertainty as in start-stop operation, the number of rotary increments is increased. The accuracy specification according to VDI/VDE specification is not affected, despite the greatly accelerated measurement process; ensuring traceability of the measurement results with OnTheFly CT is maintained.

With the new OnTheFly process, measurement time can be reduced by up to ten times for the same quality of data. The work-piece volume is reconstructed in real time and available immediately after measurement. Alternatively, the data quality may be increased for the same measurement time. Methods such as raster and ROI (Region of Interest) tomography or higher detector resolution produce work-piece volumes of higher resolution with a better signal-to-noise ratio. The increased measurement time traditionally associated with these methods can be avoided with OnTheFly CT. The new technology opens up further areas of application for computed tomography that have strict measurement time requirements for a given data quality.

For more information: www.werthinc.com