7th Conference on Industrial Computed Tomography, Leuven, Belgium (iCT 2017)

www.iCT2017.org

Coordinate Measuring Machines with X-Ray Tomography Sensors – Measuring Completely and Precisely Without Contact

Tristan Schubert1

1Werth Messtechnik GmbH, Siemensstrasse 19, 35394 Giessen, Germany, mail@werth.de

Methods, Applications and Measurement Uncertainty for Computed Tomography Werth Messtechnik GmbH is a manufacturer of multisensor coordinate measuring machines, currently providing over ten different sensors in the areas of optics, computed tomography, and multisensor systems. This allows different workpieces to be measured completely on a single machine. The company was founded in the 1950s, and in 2005 launched X-ray tomography (CT) in a coordinate measuring machine with optional multisensor systems onto the market. A major innovation at the time was the use of WinWerth® measuring software for the entire measurement process. From capture of radiographic images, to workpiece surface capture with subvoxel precision, to output of the dimensions in a report, traceability of the results was guaranteed then as it is now. This also eliminates any influence by the operator on the measurement results. Customers have increased their requirements for CT in measurement technology. At the beginning, the focus was on speeding up the first article inspection process for purely plastic components with many inspection features (e.g., cell phone housing, see Figure 1). Today Werth coordinate measuring machines with CT are widespread in many industries. Besides the automotive industry, fields such as medical technology, micro-mechanics, optics, and aerospace industry result in a growing market.

Figure 1: First article inspection of a plastic workpiece with many inspection features in the TomoScope® 200 in the year 2005 The diversity resulting from these industries means that new hardware and software are continually being introduced. Today, micro-focus tubes with cathode voltages of 225 kV, 240 kV, or even up to 300 kV are used in order to apply tomography to assemblies made of several materials and very dense workpieces with high radiographic lengths. With the help of transmission targets, focal point sizes in the micron range can be produced even at these high voltages. Using a combination of such X-ray sources and high-resolution X-ray detectors, which can have up to 16 megapixel resolution, Werth can meet the need for better and better detectability even of small details. By supplementing this hardware with intelligent software functions, such as the Multi-Spectra-Tomography function in WinWerth®, artifacts from tomography of metal and plastic components are reduced to the point that measurements through different materials are possible (see Figure 2).

7th Conference on Industrial Computed Tomography, Leuven, Belgium (iCT 2017)

www.iCT2017.org

Figure 2: Results of Multi-Spectra-Tomography of an assembled plug connector

With the introduction of VDI directive 2617, Page 13, it became much easier to compare the specifications of machines from different manufacturers. Today, Werth Messtechnik is the first and probably the only company that calibrates coordinate measuring machines with CT sensor systems to the DAkkS standard. Determination of measurement uncertainty on customer parts taking into consideration various aspects such as workpiece material, operator, environmental conditions, and/or evaluation strategy is routine at Werth. In addition to the demand for higher resolution and lower measurement uncertainty, increasing the measurement speed is always important. In order to measure results faster and more efficiently, Werth has integrated an automatic pallet changer in its CT machines. This means that even in unmanned shifts workpieces of the same or different types can be loaded by the machine's axes and measurements can be performed. On the software side, for example, the WinWerth® tomography function OnTheFly CT has been developed. With this function, the rotary axis of the machine rotates continually without stopping to capture the radiographic images during the tomographic scan. At the same time, the voxel volume is reconstructed in real time. This means that a tomographic measurement including surface definition, which took just under an hour in 2005, can now be performed in one minute.