Inspection of assembly parts and tool surfaces based on geometric measurement still states an increasing and essential part in quality management. Suited measurement techniques thereto should be, above all, flexible and fast in order to keep up with the production process. Large area analysis of topographies nowadays can be realised by commercially available fringe projection systems which carry a satisfying and sufficient accuracy. However, these systems reach their limits for assemblies with a high geometric complexity, because of shading effects in the area of measurement. Within the...
When a fluid flowing through an elastic vessel is subjected to a sudden change in pressure gradient, pressure pulses will propagate through the fluid. Velocity of these pulse waves (PWV) can be determined by simultaneous detection of wall distension on two separate points on the vessel wall, along its trajectory. PWV depends on wall stiffness, and under certain circumstances, wall stiffness can be calculated from the propagation velocity. In vivo detection of arterial PWV can have applications in cardiovascular risk management. Stiffness of large arteries has a very good predictive value for...
In a joint national project with industrial partners in the sectors of sensor technology, mechanical engineering and plastic film production, the Fraunhofer Institute for Laser Technology (ILT) has developed a novel optical sensor to monitor the production of plastic films based on interferometric measurements with low coherent radiation. This technique of Optical Coherence Tomography (OCT) is an imaging method generating high-resolution tomography scans. The sensor measures the thicknesses of single layers in multilayer films allowing for the first time inline process monitoring and...
This paper reports on the optical displacement sensors of a semi-optical system for measurements of roundness deviations of steel rings (~ 72.5 mm) during gas quenching. They are based on the extrinsic intensity modulation principle. The measurement system was developed within the scope of the Collaborative Research Centre SFB 570 of the German Research Foundation for investigation on the distortion of steel workpieces. Due to its capability for in-process measurements, this system also enables to compensate distortion effects. It is applied in a gas nozzle field specially designed for...
In this contribution some conceptual considerations regarding the implementation of optical sensors for process control will be given. Therefore first a classification of monitoring systems related to the level of process integration is made. In a second step there will be a description of relevant features for the characterization of the process state. Furthermore there a description of factors resulting from the machining process that have possibly an impact upon the measurement result is given. As an exemplary implementation of an optical sensor near the machining process a concept for a...
We present a non-incremental interferometric measurement system for in-process monitoring of the dynamic behaviour of high-speed rotors, which is essential for improving safety and energy efficiency of motors and turbo machines, such as aircraft engines. The measurement system is based on the novel laser Doppler distance sensor which exhibits the unique feature that its measurement uncertainty of some microns is independent of the velocity of the device under test. This allows precise measurements of rotor deformations and blade vibrations even at high rotor speed. By aligning three sensors...
For in-process shape monitoring of rotating objects such as workpieces in a turning machine, contactless and compact sensors with high temporal resolution as well as high precision are necessary. For this purpose, we developed a miniaturized and robust non-incremental fiberoptic distance sensor with dimensions of only 30 × 40 × 90 mm³, which can be attached to the mount of a turning tool and therefore allows precise in-process 3D shape measurements of turning parts. In this contribution we present the design of the miniaturized sensor supported by optical simulations as well as in-process...
Optical profilometry enables new dimensions of sensitivity in order to detect surface properties such as roughness and planeness of reflecting materials. For this purpose we developed an optical profilometer based on high-sensitivity heterodyne interferometry where a measurement beam is scanned over the surface of the device under test (DUT). With this measurement setup we are able to measure surfaces with approximately 5 nanometer accuracy. For scanning we developed a beam actuation system and a DUT actuation system with a lateral sensitivity of about 15µm.
Comparative profile measurements of a testspecimen with a diameter of 150 mm and a peak-to-valley height of 50 µm carried out by an ultra-precise coordinate measuring machine (Panasonic UA3P) and a highly accurate scanning interferometric multi-sensor instrument (ETMS) are presented. The instruments and their principles are described. Although the measurement principles of the instruments are different, the measurements agree within the claimed uncertainties. The rms-difference of the measurement results is less than 20 nm.
At the Physikalisch-Technische Bundesanstalt (PTB), a new Deflectometric Flatness Reference (DFR) for measuring the topography of flat or slightly curved optical surfaces has recently been installed. With existing deflectometric procedures like the direct or difference mode, the spot size of the angle measuring system (autocollimator) is the limiting factor for the lateral resolution. To reduce the spot size of the scanning beam, an additional measurement option, called Exact Autocollimation Deflectometric Scanning (EADS) is implemented. The surface under test is tilted at each measuring...