WHITEPAPER – Piezo Linear Drives for Laser Technology
Steffen Arnold

Piezo Linear Drives for Laser Technology
Automatic Mirror Positioning in Vacuum and in Inaccessible Places

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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 – Piezo Linear Drives for Laser Technology
Steffen Arnold

Lasers are versatile tools with a wide range ofThe Liop-Tec GmbH has shown by way of a good

applications. For example, in material processing theyexampleare nowadays as indispensable as they are in medical

indispensable for laser technology, can be automatedtechnology or in material and environmental research.

optimally adapted to the application.

howthepositioningoftip/tilt

mirrors,

Everywhere the principle is the same: Tip/tilt mirrors
ensure correct guidance of the laser beam.
This

makes

them

importantcomponents,

which,

however, have to be positioned accurately, in order toachieve the desired result. Here manual setting is mostly
still the state of the art. But manual adjustment is notalways possible, for example, when tilt/tip mirrors areused in a vacuum or are mounted in inaccessible places
where they have to be preset before start-up orreadjusted. This is where piezo-based linear drives canprovide a solution: These space-saving and low-cost
microdrives work with a positioning accuracy down to thenanometer range and – when installed in a mirror mount– replace the manually actuated micrometer screws.

Fig. 2 The mirror mounts are now also being offeredwith piezo drives instead of micrometer screws (Image:Liop-Tec)
The company offers standard and customized mirror
mounts (Fig. 1), which can now optionally also beequipped with piezo drives instead of manual micrometerscrews (Fig. 2).
"In collaboration with Physik Instrumente (PI), we have
Fig. 1 Customized mirror mount for large optics.
These mechanical systems can also be automated with
PiezoMike drives (Image: Liop-Tec)developed piezo-based linear actuators to seriesproduction level and, in doing so, adjusted the screw andnut to the requirements of the drive principle.

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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 – Piezo Linear Drives for Laser Technology
Steffen Arnold

The PiezoMike drives from PI have been integrated
successfully into the mirror mount concept of our Star
series," explains Patrick Incorvaia, Sales Manager at
Liop-Tec (Fig. 3).

Operating Principle and Adjustment
Piezo-based inertia drives utilize the stick-slip effect forfine steps with step sizes of just a few micrometers. In
the first part of the motion cycle, the actuator expands
slowly taking along the moving rod (stick effect).
In the second part of the motion cycle, the actuator
contracts so rapidly that it slides along the moved rod,which cannot follow this rapid motion due to its inertia,
and thus remains in the same position (slip effect). The
electric control is easy; its output signal is similar to a
saw-tooth voltage. The drives are small, which makes
them suitable for many application areas.
Typical fields of application for this drive principle can befound not only in laser technology, but also range fromsolder

Fig. 3 Patrick Incorvaia, Sales Manager at Liop-Tec(Image: Liop-Tec)

tippositioning

toshutterandmembrane

adjustments in micromanipulation.

The piezomotors based on the inertia principle areoperated at a frequency of up to 2 kHz. The PiezoMikelinear actuator achieves forces of up to several 10 N, canbe easily integrated into a wide range of applications andare also suitable for vacuum applications (Fig. 4) "We
are particularly proud of being able to offer mirror mounts
for high- and ultra-vacuum that are adjustable fromoutside with extremely high precision," continues Patrick
Incorvaia. "The outstanding collaboration with PI has
brought us a good step forward." The manual positioning
screw is simply exchanged for a PiezoMike.

Fig. 5 Piezo-based inertia drives utilize the stick-slip
effect for fine steps with step sizes of just a few
micrometers (Image: PI)
The operating principle of the inertia drive has been
adapted to the requirements of the application by thedevelopment

partners

PIandLiop-Tec(Fig.

5):

In this case, the stick effect does not take along amoving rod but causes a screw to rotate.
Fig. 4 PiezoMike linear actuator: Minimumdimensions, high force and stable positioning undervacuum conditions (Image: PI)

The claw, which grasps around the screw, opens withthe expansion of the actuator and causes the screw toslightly turn.
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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 – Piezo Linear Drives for Laser Technology
Steffen Arnold

Once the maximum expansion of the actuator has been

Furthermore, their life expectancy of more than one

reached, the actuator contracts quickly and the claw

billion steps is quite impressive. Converted, this would

moves back to its initial position, but does not take alongcorrespond to a working range of 20 m or to 100 hours of

the screw, which due to its inertial mass, remains in its

continuous operation. This is more than sufficient given

position (slip effect). This step cycle is repeated, causing

the small travel ranges of a few micrometers, the shortthe screw to continue its rotation until the desired

control times and the comparably rare motions.

position is reached. The motion sequence works, ofcourse, also in the opposite direction. "Nevertheless, it
has been a lengthy process to find out the optimum
material parameters for the slip effect, which required alot of know-how in the manufacture of the screw and nut.
Theimplementationalso

requiredvery

stringent

tolerance and surface quality requirements for themechanical components," says Patrick Incorvaia.

Control and Fine Adjustment
The E-870 driver (Fig. 6), specifically tuned to therequirements

oflinear

actuators,

controls

theactuatorOne driver can serially control a unit with up to
four channels, keeping investment costs low. For fineadjustment, the piezo linear motors inserted into themirror mounts can also be operated in analog mode:

Thanks to their compact dimensions, the inertia drives

Here, the "stick phase" is more or less stopped in thecan be integrated in a space-saving manner.In addition,

last positioning phase and the piezo actuator is operated

these drives also have other advantages.

within the rising edge of the piezo actuator voltage andnot in full-step mode. In this way, a positioning resolutionof 5 nm can be achieved. The driver behaves then like apiezo voltage amplifier.
The development of high-precision PiezoMike drives will
be pursued. Patrick Incorvaia is already looking forward
to the continued collaboration with PI: "High-speed,
noiseless direct drives (Fig. 7) and position-regulated
variants currently in preparation should make our mirror
mounts even more flexible in the future."

Fig. 6 The E-870 driver (Figure 6), specifically tuned
to the requirements of linear actuators, controls theactuator. One driver can serially control a unit with up to
four channels, keeping investment costs low (Image: PI)
The piezo solution is not only much smaller than any
motor-driven micrometer screw available on the market,
but the PiezoMike linear actuator also works with a very
high resolution. Step widths of approx. 20 mm can hardly
be achieved using traditional stepper motor drives.
In doing so, the piezo-based linear drive develops a feed
force of 22 N, works at a maximum speed of 3 mm/min
and is designed for travel ranges from 7.5 mm to 26 mm.

Fig. 7 Rod drive with piezoelectric stick-slip drive. Thedrive principle can be modified, depending on theapplication (Image: PI)

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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 – Piezo Linear Drives for Laser Technology
Steffen Arnold

The required piezoceramic elements are manufactured

Authorby our subsidiary PI Ceramic in Lederhose, Germany,
one of the global leaders for piezo actuator and sensor
products. PI miCos GmbH in Eschbach near Freiburg,
Germany, is a specialist for positioning systems forultrahigh vacuum applications as well as parallelkinematic positioning systems with six degrees of
freedom and custom-made designs.

Steffen Arnold Head of "Marketing and Products" atPhysik Instrumente (PI) GmbH & Co. KG

About Liop-Tec
The

LIOP-TEC

Radevormwald

GmbHwithitsnearCologne,headquarters
Germany,inPI headquarters in Karlsruhe, Germany: More than 350
employees work on high-resolution drive systems andpositioning systems

wasestablished in 2012 by Dr. Jürgen Lindener-Roenneke
and Privatdozent Dr. Michael Gutmann. Both can build
on more than two decades of experience in laser
technology. It should not come as a surprise, then, thatthe newly established company has an excellent
reputation in the area of innovative laser technology andoptomechanical components. Today the company's
focus is on custom laser applications, especially in thearea of molecular science, material and environmentalscience, general science and medical technology.

About PI (Physik Instrumente)
In the past four decades, PI (Physik Instrumente) with
headquarters in Karlsruhe, Germany has become theleading manufacturer of nanopositioning systems withaccuracies in the nanometer range.
With four company sites in Germany and ten sales andservice offices abroad, the privately managed company
operates globally. Over 700 highly qualified employees
around the world enable the PI Group to meet almost
any requirement in the field of innovative precision
positioningtechnology.

Allkeytechnologies

aredeveloped in-house. This allows the company to control
every step of the process, from design right down toshipment: precision mechanics and electronics as wellas position sensors.
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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