Measurement: optical or tactile

Trends in metrology: faster, more accurate, fully integrated

The trend in the industrial manufacturing and development sector is clearly moving towards speed, accuracy and automation. The demands when it comes to quality control are growing with the optimization of processes and the setting of ambitious tolerances.

And the question quickly arises: Which measuring technique is the right one for us? Although the choice is great, the first thing to decide is: Optical or tactile measurement?

Which properties are you looking for in a measuring system?

Fast

Time is money – and this applies to manufacturing, too. The goal is short cycle times and high-quality results. Optical sensors take the prize here with high scanning rates and short inspection times. When it comes to roughness measurements that require very high point densities, fionec’s fiber-optic distance measuring systems work up to ten times faster than comparable tactile stylus profilometers. The results are consistent with the provisions of the applicable DIN EN ISO standards.

► Optical

High precision

The accuracy and resolution of styluses is generally in the micrometer range. In the case of styluses that measure even more precisely, elastic effects (“stick slip”) that can limit the degree of precision have to be taken into account, however.

Interferometric measuring systems produce measurements in the lower nanometer range. A precondition for this is that surfaces are clean and of adequate finish quality (Ra ≤ 2, Rz ≤ 10). Moreover, the measuring principle used in fionec’s systems delivers absolute values.

► Optical / interferometric

DIN compliant

Time-tested DIN Standards are available for the computation of roughness parameters in particular. The measured values are thus comparable and metrologically traceable. Although the standardization of optical roughness measurement is still in its infancy, sensor technology manufacturers have long oriented themselves towards the standards for tactile roughness measurement. fionec’s fiber-optic measuring systems deliver comparable roughness values in accordance with DIN EN ISO 4287, 11562, 13565 and 16610.

► Tactile and optical are comparable

Flexible / compatible

Because tactile styluses have been on the market for a long time, there is a large selection to choose from. There are suitable tactile measuring devices and integration solutions available for most measuring tasks. But the optical measuring technology market is growing continuously and there are suitable solutions available.
The fiber-optic measuring system from fionec offers an interesting alternative for applications where the measuring setup allows very little room for the sensor. The miniaturized probes (starting from Ø 50 µm) are very lightweight (approximately 2 g) and are simple to retrofit to a wide range of precision machinery. It isn’t generally necessary to adapt the precision design. The probe and connector cable are made from flexible glass fibers. This means that the probe and evaluation unit can be located at nearly any distance from one another. A variety of data interfaces allow for seamless data communication.

► For standard measuring tasks: conventional tactile or optical sensors
► For integration into precision machinery or complex measurement setups: miniature fiber-optic sensors

Inexpensive

Tactile measuring systems are usually cheaper than fiber-optic sensors. As such, they are often the best choice for standard measuring tasks. But specific problems require special solutions. The speed of optical systems, the ability to retrofit them to existing machinery and the high level of integration and automation they allow often make up for the higher initial costs, however.

► Tactile in most cases, but optical for special measuring tasks

Point-measuring / areal-measuring

Both traditional styluses and fionec’s fiber-optic sensors are point-measuring devices. Depending on the measuring point density, the technology can also be used to perform scans of surfaces. The recorded values can be used to create 3D models. At up to 20,000 measurement values per second, fionec’s fiber-optic technology is capable of performing this job with significantly shorter inspection cycles than conventional tactile styluses.

► Tactile and optical comparable, but optical significantly faster

Compact

Components and inspection spaces are becoming ever more compact which means the measuring technology has to be as small as possible too. fionec has developed a special micro-probe based on optical fibers that can be miniaturized down to a diameter of just 50 µm.

► Miniature fiber-optic sensor technology

Contactless

Components with delicate surfaces or high-quality finishes can often only be inspected contactlessly. Optical sensor technology, which works completely non-destructively, is ideally suited for this purpose. As such, 100-percent inspections of delicate workpieces can be performed, if required. Another benefit: unlike styluses, optical probe heads are not subject to wear either.

► Optical		 Trend toward multi-sensor technology

Due to the increasing complexity of test specimens and measuring tasks, optical and tactile methods are increasingly being combined into one measuring system. This reduces setup times and expands the range of possible metrological applications. The ability to gather a range of different parameters in a single measuring operation meets the desire for fast, fully automated, near-line inspections.