WHITEPAPER – Mechanical System Approaches Limit of Technical Feasibility
Dipl.-Phys. Birgit Schulze

Tailor-Made Positioning Solution for Analytical Methods
Performed on a Beamline
Mechanical System Approaches Limit of Technical Feasibility

Page 1 of 6
Physik Instrumente (PI) GmbH & Co. KG_Auf der Roemerstrasse 1_76228 Karlsruhe, Germany
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WHITEPAPER – Mechanical System Approaches Limit of Technical Feasibility
Dipl.-Phys. Birgit Schulze

Nowadays X-ray and tomographic methods help detect

In the nanotomography hutch, X-ray optics for three-very fine structures inside objects. For spatial resolutions

dimensional

down to 100 nanometers, diffractive X-ray optics are

100 nm are used, that consist of up to many hundreds ofavailable today. However, various challenges have to bediffractive lenses, which were developed at the Instituteovercome to obtain a three-dimensional image withofvolume resolution in this range. It is a major challenge toGermany. The setup also includes microscopy optics forachieve the extremely high mechanical accuracy andvisible light, used for further magnification of the X-ray

stability required for the alignment of the optics andmicrographs and their transfer to a camera.

micrographs

MicrostructurewithTechnology

resolutions

(KIT)

at

aroundKarlsruhe,samples in the X-ray beam and for the entire

temperature or vibrations could degrade the desired

The Instruments Must Meet HighStandards

resolution. This is why the improvement of the X-ray

With the aim to carry out as many different experiments

optics must always go hand in hand with the mechanicalas possible, the HZG provides two different X-ray optics

perfection of the entire setup. If specialists work closely

configurations: An imaging setup, in which the sample istogether, considerable progress can be made as shown

positioned in front of the objective optics (Fig. 2), and aby the example described below.

cone-beam setup, in which the sample is placed in theexperimentalsetup.

Evenminutechangesindiverging beam behind the optics.
In both cases, high mechanical stability and precision
positioning are essential in order to obtain micrographsof high quality. This is why the instruments used for theexperiments at the P05 beamline must meet very highstandards.
However, thanks to the close cooperation of the clientswith the engineers and developers from PI (PhysikInstrumente), this complex task could be solved in apractice-orientedmanner.

Fig. 1 At the X-ray light source PETRA III at the DESY
research center (German Electron Synchrotron) in
Hamburg, the Helmholtz-Zentrum Geesthacht - Centerfor Materials and Coastal Research (HZG) - operates theImaging Beamline P05 (image: PI / HZG)At the X-ray light source PETRA III at the DESY
research center (German Electron Synchrotron) in
Hamburg, Germany, the Helmholtz-Zentrum Geesthacht- Center for Materials and Coastal Research (HZG)
operates the Imaging Beamline P05, which includes twoexperimental hutches, one for nanotomography (Fig. 1)
and one for microtomography. Each name designates
the attainable (spatial) resolution.

Fig. 2 Different X-ray optics configurations are possible:
The one shown here is an imaging setup in which thesample is positioned in front of the optics (image: HZG)

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Physik Instrumente (PI) GmbH & Co. KG_Auf der Roemerstrasse 1_76228 Karlsruhe, GermanyTel. +49 721 4846-0, Fax +49 721 4846-1019 Email info@pi.ws, www.pi.ws

WHITEPAPER – Mechanical System Approaches Limit of Technical Feasibility
Dipl.-Phys. Birgit Schulze

After all, this company has valuable know-how and manyyears

ofexperienceespecially inthe"Beamline

Instrumentation" field of application.
The aim of the team of specialists, coordinated byPI miCos, is to develop application-specific solutions that
go beyond offering individual components and include
systemintegrationaswellasthecompleteinstrumentation.
On the Beamline P05, they once again demonstrated
these capabilities. A particular challenge was how toconfigure the control, which was based on an industrialcontroller. The challenge consisted in controlling almost
50 axes independently of one another while ensuringcollision protection. The entire system was finallyFig. 3 The substructure, which weighs several tons, ismounted on air bearings. This allows the entire system
to be moved out of the X-ray beam with minimal effort,
while maintaining a stable position as soon as the air
flow is switched off. The picture shows the assembly inthe parking position outside the beam (image: PI / HZG)

integrated into the TANGO interface customary forbeamlines.

Complex Sequences during Sample
Positioning

The Base: Granite Platform
Supported by Air Bearings

The basis of sample positioning is a horizontal

To minimize the effect of vibrations and securely fasten

beam. It has a travel range of 20 mm, can be subjected

the individual components and stabilize them, relative toto a load of 300 kg and works with a repeatability of

one another, a granite base 6.8 m in length forms the30 nm.

basis of the instrument. Another four moving graniteWhat drives this high-precision positioning unit are

platforms driven by linear motors are arranged on thisstepper motors combined with high-resolution opticalbase on air bearings.

linear encoders. When driven accordingly, this allows

This makes it possible to position all components withclosed-loop step sizes of a few nanometers. The

high speed and precision: The sample stage, the X-ray

precision crossed roller guides and ball screws used also

optics, and the detector. The substructure itself, which

contribute to the high positioning accuracy.

positioning unit which moves the sample stage into theweighs several tons, is also mounted on air bearings.
This allows the entire assembly to be moved out of theX-ray beam with minimal effort when the second
experimental station is to be used, while maintaining astable position as soon as the air flow is switched off(Fig. 3).
A particular challenge was the construction of thesample stage, since it had to be mechanically stable in
the range below 100 nm, in order to achieve the required
spatial resolution. To this end, several positioning
systems have to work hand in hand with maximum
precision, to ensure that always the same volume
element is investigated when the sample is rotating.

Fig. 4 The Z lifting stage performs the height adjustment,
tilt correction, and orthogonal alignment, relative to thebeam (image: PI / HZG)
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Physik Instrumente (PI) GmbH & Co. KG_Auf der Roemerstrasse 1_76228 Karlsruhe, Germany
Tel. +49 721 4846-0, Fax +49 721 4846-1019 Email info@pi.ws, www.pi.ws

WHITEPAPER – Mechanical System Approaches Limit of Technical Feasibility
Dipl.-Phys. Birgit SchulzeThis displacement unit is equipped with three lifting
elements which perform the height adjustment, tilt
correction, and orthogonal alignment, relative to thebeam(Fig.

4).

Itisbasedonthreeidentical,

symmetrically arranged, and position-controlled stepper
motors, combined with worm gears and spindle drives.

Parallel Kinematics for the Sample
Holder and the Optics
The actual sample holder is located in the aperture of therotation stage on the moving platform of a six-axis
parallel kinematic machine (Fig. 6).

Mounted on this Z stage is an air-bearing supported

The SpaceFAB clearly makes work easier for therotation stage (Fig. 5).

researchers, since the small samples - only a few 10 to
100 micrometers in size - plus the holder can initially be
inserted into the stage with low precision.
They can then be aligned automatically using softwarecommands. Thus, no additional mechanical components
are required for correct alignment.
The samples are positioned with six degrees of freedom.
Essential features are the freely selectable pivot point of
the parallel-kinematic system and its high stiffness.
A six-axis parallel-kinematic machine of this type is also
usedFig. 5 Mounted on the combined tilt and Z stage is an
air-bearing supported rotation stage. It rotates at avelocity of up to 36 °/s and works with flatness deviationsof less than 100 nm at a resolution of 0.5 µrad (image: PI/ HZG)

for

thepositioning

nanotomography,

which

micrographs

resolutions

withofallows

theoptics.

In

three-dimensional

below

100 nm,thismachine is used to align compound refractive lenses(CRL) in the beam with high precision.

In developing this stage, the designers had to go push
the limits of technical feasibility: What was required wasa really "pure" rotary motion of the sample with minimal
wobble, radial runout or eccentricity.
Only in this case can sharp pictures over 360 degrees bemade which all refer to the same volume element andcan all be clearly assigned when reconstructing thepicture. This is why the rotation stage, which rotates at avelocity of 36°/s, works with flatness deviations of lessthan 100 nm at a resolution of 0.5 µrad. The air bearing
does not produce any friction, which over time would
lead to a deterioration of these values.

Fig. 6 The actual sample holder is located in the apertureof the rotation stage on the moving platform of a six-axis
parallel kinematics (image: PI / HZG)

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Physik Instrumente (PI) GmbH & Co. KG_Auf der Roemerstrasse 1_76228 Karlsruhe, Germany
Tel. +49 721 4846-0, Fax +49 721 4846-1019 Email info@pi.ws, www.pi.ws

WHITEPAPER – Mechanical System Approaches Limit of Technical Feasibility
Dipl.-Phys. Birgit Schulze

A wide range of areas, from industrial research toThe SpaceFAB principle is based on three XY stages

materials science and examination of bones in biology,

that jointly position a platform using three struts ofcan benefit from the investigation results obtained byconstant length and a suitable joint configuration (Fig. 7).

means of these high-resolution tomographic methods on
the Imaging Beamline P05.
The positioning solutions tailor-made by the "Beamline

It is the principle of choice in particular when long
distances have to be covered in the X and Y directionsora

low-profile

designisrequired.

Instrumentation" specialists, used to align the small
samples and optical components with high precision,
make an important contribution.

Parallel-Kinematic Positioning
Systems
PI's parallel-kinematic positioning systems offer a seriesof advantages over serially stacked assemblies, such asa lower moving mass, resulting in improved dynamics,
less space required in combination with higher stiffness.
Thus, for motions with six degrees of freedom, either thestrut length of the Hexapods can be changed - or in theSpaceFABs mentioned in the text - the angle can beFig. 7 Assembly principle of a SpaceFAB: The principle
is based on three XY stages that jointly position aplatform using three struts of constant length and asuitable joint configuration (image: PI)varied if the strut length is constant.

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Physik Instrumente (PI) GmbH & Co. KG_Auf der Roemerstrasse 1_76228 Karlsruhe, Germany
Tel. +49 721 4846-0, Fax +49 721 4846-1019 Email info@pi.ws, www.pi.ws

WHITEPAPER – Mechanical System Approaches Limit of Technical Feasibility
Dipl.-Phys. Birgit Schulze

Author

The PI Group in Brief
Over the last four decades, PI (Physik Instrumente) with
headquarters in Karlsruhe, Germany, has developed into
the leading manufacturer of positioning systems withaccuracies in the range of only a few nanometers.
With four company sites in Germany and ten sales andservice offices abroad, the privately managed company
operates globally. More than 700 highly qualified
employees all over the world enable the PI Group to
fulfill almost any requirement from the area of innovative
precision positioning technology.

Dipl.-Phys. Birgit Schulze, Product Manager at Physik
Instrumente (PI) GmbH & Co. KG

the company to control every step of the process, fromdesign right down to shipment: precision mechanics andHelmholtz-Zentrum Geesthacht Center for Materials and Coastal
Research - in BriefTheHelmholtz-ZentrumGeesthacht–Centerelectronics as well as position sensors. The required
piezoceramicforHelmholtz Association of German Research Centers, thelargest German Scientific Organization, in charge of thedevelopment and operation of German and internationallarge-scale research installations. This interdisciplinary
research center was established in 1956. Until Octoberit

operatedunder

thenameofelements

aredevelopment

workatthebyourGKSS-

the global leaders for piezo actuator and sensor
products.
The PI miCos GmbH in Eschbach near Freiburg,
Germany, is a specialist for positioning systems forultrahigh vacuum applications and parallel-kinematic
positioning systems with six degrees of freedom andcustom-made designs.

Forschungszentrum Geesthacht GmbH. The researchandmanufactured

subsidiary PI Ceramic in Lederhose, Germany, one ofMaterials and Coastal Research – is part of the2010,

All key technologies are developed in-house. This allows

Helmholtz-Zentrum

Geesthacht is organized in the research divisions of theHelmholtz Association in different programs, one ofwhich is materials research. Synchrotron radiation andneutrons allow researchers to carry out non-destructive
investigations on materials and biological systems and toproduce three-dimensional images in high quality. To
this end, the Helmholtz-Zentrum Geesthacht operates
test installations both at DESY in Hamburg at thePETRA III storage ring and at the FRM-II research
reactor in Garching near Munich.

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Physik Instrumente (PI) GmbH & Co. KG_Auf der Roemerstrasse 1_76228 Karlsruhe, Germany
Tel. +49 721 4846-0, Fax +49 721 4846-1019 Email info@pi.ws, www.pi.ws