Multi-sensor tomography – two-tube measuring system now also with sub-microfocus tube

The sub-microfocus tube increases the resolution of the two-tube measuring system by an order of magnitude, a resolution of less than one micrometer is achieved. The 300 kV microfocus tube enables the measurement of large or dense workpieces with resolutions in the range of a few micrometers. This makes the machine suitable for applications with widely varying resolution requirements and for different workpiece sizes and materials. Almost all computed tomography measurement tasks can now be solved with a single machine. By combining it with region-of-interest computed tomography (ROI-CT), several small details on comparatively large workpieces can also be measured (patent). For this purpose, the overview CT is measured with the microfocus tube, the ROI with the submicrofocus tube in higher magnifcation.

Powerful duo

The microfocus tube achieves voltages up to 300 kV at a maximum power of 80 W and focal spot sizes of a few micrometers. The transmission target enables such small focal spot sizes even at maximum power. Thus, large or dense workpieces can be measured with high resolution and speed

The submicrofocus tube has a maximum voltage of 160 kV and up to 50 W power. With an additional focusing unit, it achieves a smallest focal spot size of 0.5 µm. The characteristic given for a CT machine is often the resolution in the radiographic image, which

usually does not correspond to the resolution in the volume, or only a voxel size is given, which can be chosen to be almost any small by calculation. Neither is a measurement of what structure size is actually resolved. With the Werth submicrofocus tube, the resolution in the radiographic image is 0.5 µm

The effective resolution of a CT coordinate measuring machine results mainly from the combined effect (convolution) of the resolution functions of the focal spot, rotary axis and detector, taking the magnification into account. Therefore, the machine is also equipped with a highly accurate rotary axis whose radial run-out errors are less than 0.2 µm. Thus, the practical volume structure resolution of the two-tube measuring system with submicrofocus tube is about 1 µm. Applications of the submicrofocus tube include measurements of filter materials, like fiber structure, the measurement of particle penetration depth with color-coded display, and the measurement of corresponding particle sizes

Requirements

Even a drift of less than one micrometer leads to a signifcant loss of resolution. Therefore, capturing and correcting the drift during the tomography scan is necessary. Werth has many years of experience in this feld through its highly accurate multi-sensor coordinate measuring machines. For the sub-microfocus tube, the procedure for drift detection during tomography scan was optimized and a new procedure for reverification test of the volume structure resolution was developed. In this way, it was possible to prove that the theoretically achievable resolution is actually attained and that influences such as drift are negligible according to the correction.
A two-tube measuring system can be installed in the TomoScope® L, XL and XL NC machines. Other sensors such as the Chromatic Focus Point Sensor for optical measurements can be added, for example, to quickly capture measurement points on the workpiece in designated areas or for roughness measurements.

Application examples

With a two-tube measuring machine, it is possible to solve measuring tasks with widely varying resolution requirements as well as different workpiece sizes and materials. For plastic injection molding with fiber composites, the geometrical characteristics can be measured with the microfocus tube, fiber orientation, -length and -diameter with the submicrofocus tube. For die-cast workpieces, analysis for pores, voids or cracks is ideal. Further applications can be found in research and development, for example.