Development

The first coordinate measuring machines were the measuring microscopes introduced in the 1920s. Around 1970, tactile machines with automatic control were developed. Also in the 1970s, Dr Siegfried Werth developed the Werth Tastauge, the first optoelectronic sensor for measuring projectors that allowed automatic probing of object points. In conjunction with NC axes, this sensor made it possible to automate optical coordinate measuring machines for the first time in 1980.

In the course of the 1990s, the measuring microscopes and measuring projectors that had dominated non-contact coordinate metrology until then were largely replaced by coordinate measuring machines with image processing methods. The main prerequisites for this were the development of modern semiconductor cameras and the introduction of PC technology with suitable software.

In 2005, the Werth TomoScope® was introduced as the first coordinate measuring machine with X-ray tomography. This technology opened up new measuring possibilities. Complex workpieces with many sizes, including internal features, can be completely measured in a short time.

In principle, all coordinate measuring machines reduce the determination of size, form and position to the determination and subsequent mathematical evaluation of the spatial coordinates of individual points. Most machines are based on Cartesian coordinate axes with linear scales. The measuring slides in the axes are mainly moved by motors. At least one sensor is attached to one of the axes, usually the vertical one (z-ram), which is used to record the measurement points on the surface of the measuring objects. What all sensors have in common is that they determine the measurement points in reference to the sensor position. The relative position between the sensor and the workpiece is varied by moving the mechanical axes of the coordinate measuring machine so that all measurement points of interest are reached one after the other.

Due to its versatility, precision and cost-effectiveness, modern coordinate metrology has often replaced single-purpose measuring machines and has achieved a very high status in quality assurance processes. The diverse functions of these machines open up numerous application possibilities for the user, but require a sound knowledge of their function and application. In the first edition of "Multisensor coordinate metrology" (Die Bibliothek der Technik, Volume 248) published in 2003, multi-sensor systems and their technical background were presented in a coherent manner for the first time. In the meantime, aspects of this technology have also been considered in other publications, although these tend to focus on tactile measurement[1, 2, 3].

Volume 352 (2nd edition, 2019) of The Library of Technology series explains the technical fundamentals of today's multi-sensor coordinate metrology. The focus is on sensors, but important aspects of device technology and application as well as accuracy and cost-effectiveness are also examined in detail.

Coordinate measuring machines with optical sensors, X-ray tomography and multi-sensor systems are used in a wide range of applications in industrial quality assurance, for which a large number of sensors are available. Both accuracy and measuring time can be optimised for the various tasks by combining application-specific sensors in the coordinate measuring machine. The range of applications extends from the sub-micrometre-precise measurement of micro-structures and optics with the 3D fiber probe to the fully automated inspection of complete vehicle assemblies with X-ray tomography.

The creation of inspection programmes is made easier, for example, by integrating information on the geometrical characteristics into the 3D CAD data (PMI – Product and Manufacturing Information). In X-ray tomography, the setting parameters can be automatically optimised using integrated simulation processes.

New processes such as the "Raster Scanning HD" mode of the image processing sensor enable coordinate metrology to be more closely integrated into Production, as many hundreds of sizes can be measured in just a few tens of seconds. In the field of X-ray tomography, powerful radiation sources combined with fast evaluation technology mean that a qualitative inspection and the complete measurement of all geometrical characteristics of complex objects can often be carried out in the production cycle. The general trend towards multi-point measurement and the optimisation of measurement uncertainty and measuring speed of machines and sensors will continue.