Submicrometer precision for lasers in space

Created by MED Engineering 2020/09/28 |

The Fraunhofer ILT has designed a laser for measuring methane concentrations, which will be used in 2021/2022 in the German-French satellite Merlin. For this purpose, we developed an assembly station with position stability in the nanometer range.

 

Putting into the right light with pinpoint accuracy

09/23/202020 | Author / Editor: Dipl.-Ing. (FH) Monika Zwettler

In order to be able to connect laser components with pinpoint accuracy, Steinmeyer Mechatronik uses a positioning system to control the air from the air bearings used. When Albert Einstein described the stimulated emission in 1916 and thus provided the theoretical basis for the laser, Steinmeyer Mechatronik was already looking back on 44 years of company history. Decades were to pass up to the construction of the first functional laser: Not until 1960 were the efforts crowned with success. Today - more than 100 years later - laser technology is one of the key technologies and industry, medicine, science and everyday life would be unthinkable without it. No matter what industry or application: the basic prerequisite for an optimal result is exact alignment or positioning.

 

Solutions for laser technology

Steinmeyer Mechatronics is an expert for high-precision positioning solutions for optical and precision mechanical systems. For laser technology, the Dresden-based company offers systems that meet the demanding tasks. In addition to the manufacture of standard products, the company's core competence includes the realization of individual special projects.

 

Laser in space

Fraunhofer's laser specialists from Aachen have designed a laser for measuring methane concentrations, which is to be used from 2021/2022 on in the German-French satellite Merlin. The laser system consists of many individual parts, which are joined together with optical soldering. The joining process offers decisive advantages for the journey into space: The connection can withstand even high shocks and vibrations up to 25 times the acceleration due to gravity.

 

Assembly station with nanometer stability

One example of the Dresden company's innovative strength is the development of an assembly station with nanometer stability for the Fraunhofer Institute for Laser Technology ILT. This institute has developed a laser for above-ground tasks. In order to connect the various components of the laser to one another with pinpoint accuracy, they must be adjusted in the beam path and fixed with submicrometer precision.

 

Fixing optical elements securely

The dual 4-axis system (XYZ-Phi) designed by Steinmeyer Mechatronik roughly positions the parts to be connected and fixes them so that nothing can move. Finally, a hexapod takes over the fine positioning in the submicrometer range before the soldering process begins.

Our task was to develop a gas-free system for aligning and holding the individual optical elements. The biggest challenge was the required position stability. Only deviations of a maximum of 50 nm were allowed.

Elger Matthes, Development and Product Management at Steinmeyer Mechatronics

 

Controlled venting of bearings for nanometer stability

The stability of a positioning system is influenced by many factors such as controlled oscillations, settlement effects, displacement of lubricant or natural frequency. For absolute standstill all these influences must be eliminated. The solution from Steinmeyer Mechatronics is as simple as it is effective: clamping - by means of air bearings. "Air bearings stand for smooth, gliding movements and extremely good run-off values," explains Matthes. The trick: the air must come out.

 

If you bleed the bearings in a controlled manner, you get an incredibly quiet system. With relatively simple methods, we achieve stability in the nanometer range.

Elger Matthes, Development and Product Management at Steinmeyer Mechatronics 

So the X and Y axes were equipped with air-bearing slides. Once the system is positioned, it is lowered by releasing the air from the vertical bearings and fixed by venting the horizontal bearings.

 

Drives for standstill

To decouple the drive from the guides, the horizontal axes are driven by toothed belts. These have no effect on the stability of the entire system. For the vertical axes a ball screw drive with stepper motor was chosen. "Thanks to its self-locking in full step, the stepper motor contributes optimally to the stability," says Matthes. "Another advantage is the high rigidity of the ball screw drive and the high efficiency for lifting loads". The rotary motion is performed by a screw turntable. In combination with a stepper motor, absolute standstill is also achieved on the fourth axis. The result: a position holding accuracy of 0.05 µm - proven with a capacitive sensor in the fully assembled system.

 

Maximum flexibility and optimum protection

For a second hexapod a second Y-beam with Z-axis and rotation axis is provided. Both Y-traverses can be moved out of the working area, thus ensuring maximum accessibility. In addition, an opening in the retaining wall facilitates access to the component from all sides.

 

Everything from one source

ike all products from Steinmeyer Mechatronik, the positioning system for the Fraunhofer ILT was developed and produced in-house. All departments work together under one roof at the Dresden location. This allows optimal use of synergies and uncomplicated implementation of specific customer requirements. Assembly was carried out in the company's own clean room. "On a clean room area of 150 m² we are able to manufacture everything from individual assemblies up to serial components. The large area allows us to operate several workstations in parallel, thus ensuring exceptional flexibility," Matthes points out and adds: "In packaging, we rely on standards to ensure that the components reach their destination in the condition in which they left our clean room."