SIOS: High-precision length measuring technique for laboratory and industry

September, 2021: Multi-beam-interferometers measure dynamic parameters simultaneously and with nanometer precision over a length up to 80 meters

Optical adjustment aids simplify the alignment process                                                                                                                                   

From medical technology to semiconductor and optics industries, as well as for calibration tasks, highest accuracy is required. Laser interferometers measure displacements with an accuracy up to 0.1 ppm and connect the macro world with the nano world through the unique property of measuring large ranges with enormous resolutions. In science as well as in many industrial fields, high-precision measuring systems are nowadays essential. However, as diverse the areas of application are, their requirements are equally varied – for example in terms of easy handling, measurement uncertainty or applications in an industrial environment. As a company that has been equipping research facilities and calibration laboratories on the domestic market and around the world for around 30 years, with the new generation of its multi-beam interferometers, SIOS Meßtechnik GmbH also ensures to deliver highly reliable performance in industrial applications as well. Thus, these devices are able to synchronously detect several degrees of freedom of a movement and can be adjusted very easily and precisely thanks to an integrated optical alignment function. In addition, SIOS optimizes and modifies interferometric systems specifically according to individual customer requirements.

“While scientific laboratories and national metrology institutes expect highest accuracy, numerous users in the high-tech industry place greatest interest on the fact that the measuring systems can be used in a flexible manner on the one hand, but also withstand harsh industrial operating conditions on the other,” says Dr. Denis Dontsov, Managing Director of SIOS Meßtechnik GmbH. „That’s why we improve our laser interferometers specifically in respect to their ability to be used in different industrial sectors, but without losing any precision.” SIOS interferometers are characterized by the fact that, thanks to their high precision of 0.1 ppm and a resolution of 5 to 20 pm over a length of – depending on the model – up to 80 m, they can measure dynamic processes very quickly and simultaneously; for example, to calibrate coordinate measuring machines. Due to the simultaneous and highly synchronized measurement value acquisition, there is no falsification of the results, even at a high object speed of up to 3 m/s. In addition, the manufacturer integrates optical adjustment aids into its measuring systems so that the correct alignment of the measuring setup can be done quickly, accurate and easily with the help of a graphical user interface. In this way, alignment-related measuring errors can be minimized, even of very short measurement ranges.

To ensure that these high-precision measurements are not adversely affected by heat input, the light sources, frequency stabilized He-Ne lasers, are always placed outside the sensor at an uncritical distance. Since the laser beam reaches the sensor head through an optical fiber, there are only optical components in the sensor head that define its functionality, but do not cause any heat. Especially in respect to applications in industrial environments, all sensors and cables are completely closed and encapsulated. This means that even potentially dirtier operating environmental conditions cannot damage the robust interferometers of the new generation.

The matching multi-beam interferometer for every application

SIOS’s single and multi-beam interferometers address a wide range of application scenarios – from calibration tasks and simultaneous displacement-angle measurements to highly stable differential measurements and vibration analyses to multi-axis system combinations in which three-dimensional processes are recorded. The basic concept of all sensor versions is represented by the compact single-beam interferometer of the SP-NG product family, whose sensor head including adjustment joint is only 133 x 91 x 54 mm – or 227 x 91 x 67 mm for long distance measurements. This is because it is a precision length measuring system in which the single measuring beam is reflected back by a tiny reflector along the same path, i.e. into itself. Thanks to this proven principle, there is a defined probing point on the target, so that alignment errors and the typical Abbe error can be compensated. The optical properties of those reflectors allow detecting and correcting such misalignments. As they are able to tilt up to ±12.5 ° without losing the measuring beam, quick and easy adjustment of the measuring set-ups are always possible. In terms of large measuring ranges or extensive calibration tasks, wireless temperature sensors or the modular SIOS precision climate measuring station LCS can also be used instead of the wired standard temperature sensors in order to record all environmental dates in an uncomplicated and effective manner.

“Based on this basic concept, the three-beam models of the SP-TR series, for example, combine three single-beam laser interferometers in one,” explains Dr. Denis Dontsov. “In this way, high-precision simultaneous displacement and angle measurements become very easy.” This is because these devices, which are only a few centimeters larger than single beam sensor heads, use only one He-Ne laser with a long-term laser frequency stability of 2·10-8 for the three measurement channels, so that three values can be synchronously measured over a length of up to 5 m with nanometer accuracy. If, in addition to the linear position and the simultaneous determination of the pitch and yaw angle, the acquisition of the horizontal and vertical straightness is also required, a calibration interferometer of the latest generation can be used, the SP-C5 series. In this four-beam interferometer, the straightness mirror is attached directly to the sensor head, so that here, too, only two components need to be aligned to each other: the sensor head and its reflector. Therefore, the device is perfectly designed for the special requirements of machine and equipment manufacturers who would otherwise have to carry out their calibrations with the help of several linear positioning axes. The accuracy of the entire system would then be affected by the interaction of the rotatory and translatory deviations. “In order to meet the demands of various industrial applications, our interferometers are each available in vacuum versions and in special versions for OEM applications, in addition to the standard version,” adds Dr. Denis Dontsov.

Compatibility of the systems allows multidimensional measurements

Several, identical or different, single and multi-beam interferometers manufactured by SIOS can be combined with each other if required, whereby it is possible to operate them with only one supply and evaluation unit. In this way, all measured values of several axes can be recorded absolute synchronously at the same time. On the one hand, the Thuringian-based interferometry specialist offers an extensive product range for a wide range of standard applications, but on the other hand, these only represent around 60 percent of the product portfolio. “Almost half of our portfolio consists of devices that have been adapted or even newly developed for specific applications of our customers,” concludes Dr. Denis Dontsov. “This is how we ensure that every customer ultimately gets exactly what they need.”

More information here.