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Virtual crumpling

New computer program calculates uncertainty of 3D measurements


[es]A procedure developed at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig will now be subjected to practical testing: In a project implemented in cooperation with industry, the "virtual coordinate measuring machine" will be tried and tested. Equipped with a novel software, coordinate measuring machines are permitted to do something other measuring instruments are forbidden to do: they may influence the object and even deform it in a specific way - but only virtually. During this process, together with the measurement proper, exact data regarding the uncertainty of measurement of the device in question are obtained. Industry is most interested in the novel procedure.

When a motor unit is measured in the car industry, a coordinate measuring machine frequently goes into action. It is capable of checking even complicated three-dimensional objects - for example for defective workmanship. If possible, the measuring instrument itself should not cause any defects. But as it is impossible to fabricate measuring instruments free from defects, there is only one way out: The uncertainty of measurement of the device must be accurately determined. With most measuring instruments this is no problem but with coordinate measuring machines this has up to now been so complicated that most users have done without. Now this procedure is radically simplified: With the new software developed at the PTB, a coordinate measuring machine calculates its own uncertainty already during the measurement proper.

With its measuring head the machine first scans the surface of the object, for example a cylinder, and then calculates the space coordinates. This yields a cloud consisting of individual points the program joins to form a virtual object (in the example: a cylinder). At the same time the software starts simulating potential disturbances so that the virtual cylinder is multiply crumpled, and calculates from this the uncertainty of measurement.

To try this novel software in practice, the PTB now has combined its efforts with several partners from industry: with two manufacturers and eight users of coordinate measuring machines. In the middle of next year, the users - among them two big car manufacturers - will have gathered enough experience to be accredited by the Deutscher Kalibrierdienst (DKD) for this area. They then can use the DKD Calibration Certificate to demonstrate for each workpiece: We know that the measuring instruments we use make mistakes - but now we can assess the magnitude this mistake may have.

Further information can be obtained from:Dr. Heinrich Schwenke, telephone: (05 31) 592-5320,E-Mail: heinrich.schwenke@ptb.deLaboratory "Coordinate measuring machines"Physikalisch-Technische Bundesanstalt (PTB)