– Reliability of Q-Motion® Systems-- Author: Mark Freyer --Reliability of Q-Motion® Systems
Lifetime, Vacuum Applications, Wear

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse. 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.de, www.pi.ws

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– Reliability of Q-Motion® Systems-- Mark Freyer --Contents
1

Working Principle of a Q-Motion® Piezomotor

32

Lifetime

33

2.1

Lifetime in a Standard Environment

32.2

Lifetime in the Vacuum

32.3

Power Consumption of the Positioning Stages

4

Test Environment
3.1

In the Standard Environment

3.1.1
3.2

44

Conclusion on the Lifetime in a Standard Environment

5

In the Vacuum

3.2.1

5

Conclusion on the Lifetime in a Vacuum

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse. 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.de, www.pi.ws

6Page 2 of 6

– Reliability of Q-Motion® Systems-- Mark Freyer --1 Working Principle of a QMotion® Piezomotor
Drives for Q-Motion® positioning stages are based on theprinciple of inertia (stick-slip drives). Piezo inertia drives save
space, are inexpensive, and have relatively high holding forcesin addition to a virtually unlimited travel range. Cyclic
alternation of stiction and friction between the moving
runner and a piezoelectric actuator ensures continuous
feeding of the runner. With an operating frequency of max.
20 kHz, the drives acting directly on the runner and achievevelocities of up to 10 mm/s.
Essentially, every Q-Motion® stage uses a compact motor
consisting of a piezo actuator, a base body for the motor andthe coupling element. This element is pushed against a runnerwith defined preload, which then provides the desired driveforce.

To reduce / avoid wear and the resulting ceramic particles, avacuum-compatible grease is used that is applied to therunner. The use of grease does not have a negative influenceon the motor force to be generated but actually ensures asofter sliding phase and therefore improved controllability.
Continuous lifetime testing began 2 years ago and alreadyindicates an endurance of at least 80 km with the following
parameters:





2.2

Full travel range for linear actuators
Complete rotation for rotational axes
Load acting against the motor force; weights for linear
motion and weights for generating a torque forrotational motion.
Max. 50% duty cycle
Mounting by screwing the positioning stages to robust
bodies made of aluminum or steel.

Lifetime in the Vacuum

The use of vacuum-compatible grease is even more importantwhen the stages are operated in a vacuum.
In a standard environment, a ceramic stores water in its
structure in the same way as a sponge, which, without
lubrication, leads to light wear. After some time, a sort ofsaturation occurs, which means that the runner or thecoupling element grind against each other and the surface ispolished as a result.

Fig. 1: Schematic diagram of a Q-Motion® inertia motor

The actuator is based on a piezoelectric ceramic that iscompletely free of wear and designed for a high number ofcycles. It is displaced by an electrical control voltage(sawtooth profile), which results in forward or backward
motion of the runner.
The contact point of the coupling element and the runner
involves friction and is therefore subject to wear.

If the stage is then operated in a vacuum, the watermolecules stored in the ceramic detach themselves and thisincreases wear dramatically.
To compensate this, all friction bodies of the Q-Motion®
series are coated with a vacuum-compatible grease thatprevents the ceramic from "drying out".
Despite the use of grease, the lifetime in a vacuum is still
considerably shorter when compared to a standard
environment.

2 Lifetime
2.1

Lifetime in a Standard Environment

The lifetime is influenced mainly by the ceramic couplingelement and the ceramic runner. The friction (slip-phase)resulting from the underlying inertia principle is subject towear. However, this wear can be considerably reduced or
avoided by using suitable materials.
Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse. 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.de, www.pi.ws

Page 3 of 6

– Reliability of Q-Motion® Systems-- Mark Freyer --Durability tests in the Q-Motion® vacuum chamber indicate
an endurance of at least 1.2 km with the following
parameters:

Full travel range for linear actuators
Complete rotation for rotational axes
In some cases with a static load in both a horizontal anda vertical direction.
10% duty cycle and reduced velocity. Due to the lack of
air for cooling the piezoceramic, the duty cycle must be
reduced significantly to keep the energy input and theresulting heat generation within the limits tolerable forthe motor.

It is absolutely necessary to screw the Q-Motion® stages to asolid metal surface to allow the heat to dissipate from themotor via the metal.

2.3

Power Consumption of the Positioning
Stages3 Test Environment
3.1

In the Standard Environment

Durability tests were performed for the following stages

Q-Motion®
StagesMinimum endurance

Q-614

Approx. 1 million rotations (360°). With load,
open loop

Q-622 / Q-632

Max. 570,000 rotations (360°). With load, closedloop

Q-522

50 km, no load, closed loop

Q-521

77 km, with load, closed loop

Q-545

72 km, with load, closed loop

Durability tests were performed for the following controllers

Motorcontrollerperformance

Q-Motion® Stages~15% piezo
hysteresis andheat input

Motor controller and driver

10 W @ 20 kHz

Q-614, Q-622, Q-632

Approx. 1.5 W

E-871.1A1

10 W @ 20 kHz

Q-522, Q-521, Q-821

Approx. 1.5 W

C-885 / E-873.10C885

30 W @ 20 kHz

Q-545, Q-845

Approx. 4.5 W

E-870.1G

Stage with and without anti-creep system
The table shows the power consumption of the different QMotion® stages with respect to the individual axes. The
respective maximum values apply to an operating frequencyof 20 kHz. In this case, it is necessary to make sure that thepiezoceramic works with a hysteresis of 15 % (reactive powerproportion) and also that the electrical energy introduced
into this reactive power proportion is converted to heat.
Attention must be paid to this characteristic when operating
in a vacuum or when operating continuously in air to avoid
overheating and failure of the motor.

Q-Motion®
StagesAnti-creep system yes / noQ-522

No anti-creep system

Q-521

No anti-creep system

Q-545

With anti-creep system

All systems are in continuous operation, which means thatthe endurance of the stages also increases continuously. The
test of each individual axis is considered to be completed only
when it fails.
At the beginning of the test, guides with anti-creep systemwere not available on the market. Therefore, the guides for
the Q-522 and Q-521 were installed without anti-creep
system. This can lead to so-called cage creep during operationand standstill of the axis at an undefined point in time. The
cage must then be pushed back to the correct position
manually and the axis can then be restarted.

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse. 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.de, www.pi.ws

Page 4 of 6

– Reliability of Q-Motion® Systems-- Mark Freyer --Depending on the customer application (with high cyclenumbers), it has been possible to equip the Q-521 / Q-522
with an optional anti-creep system since the end of Q2, 2017.
The Q-545 is already equipped with an anti-creep system andis not affected by this behavior.
At the same time, the durability of the electronics will also betested during the course of the tests on the mechanics. It isparticularly important for long-term applications in OEM
projects to make a statement on both the electronics and themechanics.

Fig. 4: 3x rotation stages with static load in Z for generating a torque. 1x
linear stage with load in Z

3.1.1 Conclusion on the Lifetime in a Standard Environment
Q-Motion® systems are suitable for applications with small to
medium numbers of cycles. Before starting up the systems, it
is strongly recommended to define the duty cycles and thesystem environment together with PI.

Fig. 2: Test environment in standard surroundings

Example: If the Q-Motion® stage is to be controlled in theapplication with very small steps and a higher number ofcycles, premature wear and failure is possible. This is also true
even if the actual endurance is lower than the values
measured during the endurance tests.
In applications, in which the same part of the travel range isused continuously, it is further recommended to perform socalled lubrication runs. The positioner is moved several times
over its entire travel range to distribute the lubrication.

3.2

In the Vacuum

A specially developed vacuum chamber was used for
endurance testing.
The following positioning stages were tested in a vacuum

Fig. 3: 6x linear stages with partially static load for generating a force inthe motion direction.

Q-Motion®
StagesEndurance

Q-622.930

Min. 5870 rotations (360°). Without load.

Q-522.14U

Min. 100 cycles

Q-521.14U

Min. 1.2 km

Q-545.X4U

Min. 0.4 km

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse. 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.de, www.pi.ws

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– Reliability of Q-Motion® Systems-- Mark Freyer --The following controllers will be tested

3.2.1 Conclusion on the Lifetime in a Vacuum

Motor controller and driver

The number of cycles that have already been measured arecurrently low because of both the short testing time of 4months (as of May, 2017) and the reduced duty cycles.

C-885 / E-873.10C885

Stages with and without anti-creep system

Q-Motion®
StagesCage control yes / noQ-522.14UNo anti-creep system

Q-521.14U

No anti-creep system

Q-545.x4U

With anti-creep system

It is recommended to keep the number of cycles low andavoid continuous motion. Point-to-point motion is ideal forclassical positioning tasks.

About PI
In the past four decades, PI (Physik Instrumente) with
headquarters in Karlsruhe, Germany has become the leading
manufacturer of nanopositioning systems with accuracies in
the nanometer range. With four company sites in Germany
and eleven sales and service offices abroad, the privately
managed company operates globally.
Over 850 highly qualified employees around the world enable
the PI Group to meet almost any requirement in the field ofinnovative precision positioning technology. All key
technologies are developed in-house. This allows thecompany to control every step of the process, from design
right down to shipment: precision mechanics and electronics
as well as position sensors.
The required piezoceramic elements are manufactured by its
subsidiary PI Ceramic in Lederhose, Germany, one of theglobal leaders for piezo actuator and sensor products.
PI miCos GmbH in Eschbach near Freiburg, Germany, is aspecialist for positioning systems for ultrahigh vacuum
applications as well as parallel-kinematic positioning systems
with six degrees of freedom and custom-made designs.

Fig. 6: View in the vacuum chamber

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse. 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.de, www.pi.ws

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WP4008E Reliability of Q-Motion® Systems 08/2017 Subject to change. © Physik Instrumente (PI) GmbH & Co. KG 2017

Fig. 5: Vacuum chamber and C-885 multi-axis controller