Tactile metrology

What are the differences between the sensors for tactile measurement?

In principle a differentiation is made between switching and measuring systems. The former are in principle based on the electro-mechanical principle. Here a trigger signal is sent to the coordinate measuring machine as soon as the stylus tip makes contact with the measurement object, for example a component. The coordinates from the measuring machine produce a measurement point.

Measuring sensors are state-of-the-art. These sensors have distance measuring systems, for example inductive sensors in all three axes. If the stylus tip makes contact with a test piece, the tip is deflected in one direction by the test piece. The magnitude of this deflection is determined via the distance measuring systems. The coordinates from the sensor are then superimposed on the coordinates from the coordinate measuring machine such that a measurement point can be calculated.

Is it necessary for the stylus to withdraw and make contact again at every measurement point?

No, this action is not necessary with our modern coordinate measuring machines. Today it is standard that the stylus moves tangentially over the surface of the measurement object. In this way not only are various measurement points acquired quickly, the surface of the item inspected can be acquired along the entire path covered by the sensor

Is it possible to combine tactile and optical measurement methods?

Yes, this combination is possible without problems. Our multisensor coordinate measuring machine combines the advantages of both measurement methods. For example, with the aid of optical metrology an analysis without contact with the surface of an item inspected can be undertaken that is supplemented by the tactile sensor, for instance at difficult to access points on complex structures that remain closed to the white-light sensors. Here the measurement results are depicted in a common coordinate system which permits the common evaluation of all data. However it is important to note: although tactile sensors can supplement optical sensors, they can never improve their accuracy. The measurement result does not therefore become any more precise.

What are the advantages of tactile metrology?

For many measuring tasks, tactile measurement is still the first choice - and that for good reason.

Tactile metrology - maximum precision

With their highly precise styli, our coordinate measuring machines are able to undertake measurements with accuracies in the range of one thousandth of a millimetre. This is significantly more accurate than optical measurement methods with depiction accuracies in the range of "only" hundredths of a millimetre. As such tactile metrology is suitable above all for the inspection of workpieces on which only the smallest manufacturing tolerances are acceptable and the deviations during the measurement must be correspondingly low.

Analysis of reflective surfaces without pretreatment

Items with a reflective, high gloss or transparent surface can still be a challenge for optical sensors. This is not the case for tactile metrology. Tactile metrology can provide precise results on demanding surfaces without the need for pretreatment with a scanning spray or other work steps. It is also possible to measure areas of a workpiece that are closed to optical sensors due to their position.

What are the disadvantages of tactile metrology?

Tactile measurements are excellently suited to the determination of numerous features on an item inspected, however they also have disadvantages compared to optical measurement methods. Weighing up these advantages and disadvantages can be a demanding task. Thanks to our extensive experience with a very wide range of materials, surface geometries, etc. we can provide you with extensive advice on this topic. In this way you receive the measuring service that best meets your requirements..

Meeting the highest requirements take time

The biggest advantage of tactile methods is their precision, however this precision also has its price. Sampling a large number of individual measurement points takes time. This situation means comprehensive quality control in series production is still a challenge. Nevertheless, if an accuracy in the micron range is required in these areas, checks on random samples can be an alternative or the check can be restricted to fewer measurement points.

Contact is essential

Unlike optical methods, with tactile sensors it is necessary for the stylus to make contact with the measurement object. This action can be a problem on very delicate surfaces. In such a situation, the benefits and risks of a tactile measurement must be carefully considered. Thanks to our highly accurate 3D scanners, increasingly we can switch to optical measuring instruments in such cases.