Drive Train Elements

Gearhead

Recirculating Ball Screws

Gearheads are used between motor and drive
screw; they improve position resolution andtorque. Most models use preloaded gearheads
to eliminate backlash.

Recirculating ball screws have significantly
less friction than leadscrews because they
replace sliding friction with rolling friction.

Leadscrews
Leadscrews can provide very high resolutionsand very smooth motion. A leadscrew drive
consists of a motor-driven screw with a nut
coupled to the moving platform of the stage.
The nut can be spring-preloaded to reducebacklash. They have higher friction than recirculating ball screws so that they are self-locking;on the other hand, however, this has an effecton velocity, motor power and lifetime. Typical leadscrews have a pitch between 0.4 and
0.5 mm/revolution, up to 1 mm/revolution for
longer travel ranges.

A recirculating ball screw drive consists of a
motor-driven screw with a nut coupled to themoving platform of the stage. Balls in a closed
circuit are located between nut (ball case) anddrive screw. Backlash can be minimized by
selecting the proper ball-to-thread-diameter
ratio. Recirculating ball screws are not selflocking but very efficient and offer high velocities and long lifetime in continuous operation.
PI uses pitches of 0.5, 1 or 2 mm/revolution.

Threaded Spindle Drives
Threaded spindle drives use rolls instead ofballs as rolling bodies so that a higher load
rating, higher velocity and considerably longer
lifetime are achieved.

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Guidings and Bearings

Linear Ball Bearing

Recirculating Ball Bearings

The balls run in a brass cage and are preloadedwith regard to the hardened precision guiding
shafts. Exact tolerances between guiding andbearing are necessary for zero backlash andlow friction. Load capacity is limited.

High-precision stages are equipped with precision double linear rails. Precision assembly
allows these bearings to yield excellent resultsin terms of load capacity, lifetime, low maintenance and guiding accuracy. The moving partof the stages is supported by a total of four
preloaded linear bearings with two rows ofrecirculating balls each. They are also immune
to the cage migration as occur with crossed
roller bearings (can be an issue where small
ranges are scanned repeatedly).

Crossed Roller Bearings
In crossed roller bearings, the point contact of
the balls in ball bearings is replaced by a line
contact of the hardened rollers. Consequently,
they are considerably stiffer and need less preload so that friction is reduced and a smooth
run is possible. Crossed roller bearings arealso characterized by high guiding accuracy
and high load capacity. Permanent guiding of
the rolling body cages avoids migration of thecrossed roller bearings.

Air Bearings
An air film of a few micrometers is used as
bearing. Therefore, air bearings are frictionfree and have a tenfold better guiding accuracy than mechanical bearings. PI miCos uses
air bearings in ultra-precion, and high-velocity
stages.

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Magnetic Bearings

Flexure Guides

Magnetic levitation ensures excellent guiding
accuracy in a plane, both linear and rotational:
The passive platform levitates on a magnetic
field and is actively guided by it. Sequenceerrors are measured and compensated by very
accurate noncontact sensors. Contrary to airbearings, which are also very accurate, magnetic bearings can also be used in vacuum.

The motion of a flexure joint is based on theelastic deformation of a solid. Therefore, there is no static, rolling or sliding friction. Flexure elements have a high stiffness and load
capacity and are very insensitive to shocks
and vibrations. Flexure guides are free frommaintenance and wear. They are 100% vacuum compatible, function in a wide temperature
range and do not require any lubricants.
Flexure guides from PI have proven their worth
in nanopositioning. They guide the piezo
actuator and ensure a straight motion without
tilting or lateral offset. A solid is elastically
deformed by a device (flexure) free from staticand sliding friction – completely without rollingor sliding parts. This deformation is sufficientto guide the actuator over travel ranges fromseveral 10 to several 100 μm.

The platform levitates on a magnetic field generated byonly six planar coils in the stator

Flexure joints extend the travel range, can re-direct themotion and offer excellent guiding accuracy without
friction. The lever mechanism shown above with flexure guides transforms the actuator travel range (vertical)
to an even, straight motion (horizontal)

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|POSITIONING

Headquarters

Subsidiaries

GERMANY

USA (East) & CANADA

USA (West) & MEXICO

Physik Instrumente (PI)GmbH & Co. KG
Auf der Roemerstrasse 176228 Karlsruhe
Phone +49 721 4846-0
Fax		 +49 721 4846-1019
info@pi.ws
www.pi.ws

PI (Physik Instrumente) L.P.
Auburn, MA 01501
www.pi-usa.us

PI (Physik Instrumente) L.P.
Irvine, CA 92620
www.pi-usa.usUSA (San Francisco Bay Area)

UK & IRELAND

PI (Physik Instrumente) L.P.
Sausalito, CA 94965
www.pi-usa.us

PI (Physik Instrumente) Ltd.
Cranfield, Bedford
www.physikinstrumente.co.uk

ITALY

NETHERLANDS

Physik Instrumente (PI) S. r. l.
Bressowww.pionline.it

PI Benelux B.V.
Sint-Oedenrode
www.pi.ws/benelux

FRANCE		SPAINPI France SAS
Aix-en-Provence
www.pi.ws

Micos Iberia S.L.
Vilanova i la Geltrú
www.pimicos.es

PI miCos GmbH
Freiburger Strasse 3079427 Eschbach
Phone +49 7634 5057-0
Fax		 +49 7634 5057-99
info@pimicos.com
www.pi.ws
PI Ceramic GmbH
Lindenstrasse
07589 Lederhose
Phone +49 36604 882-0
Fax		 +49 36604 882-4109
info@piceramic.com
www.piceramic.com

JAPANPI Japan Co., Ltd.
Tokyo
www.pi-japan.jp

PI Japan Co., Ltd.
Osaka
www.pi-japan.jp

CHINA© Physik Instrumente (PI) GmbH & Co. KG
All contents, including texts, graphics, data etc., as well as their layout,
are subject to copyright and other protective laws. Any copying, modification or redistribution in whole or in parts is subject to a written
permission of PI.
Although the information in this document has been compiled withthe greatest care, errors cannot be ruled out completely. Therefore,
we cannot guarantee for the information being complete, correct andup to date. Illustrations may differ from the original and are not bind­ing. PI reserves the right to supplement or change the information
provided without prior notice.

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Shanghaiwww.pi-china.cn

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Beijing
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TEC76 Drive Train Elements 10/2017 Subject to change without notice. © Physik Instrumente (PI) GmbH & Co. KG 2017

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