Performance and Applications of Inertia Based Positioning Drives: Q-Motion

Size matters in miniaturization and automation – smaller is usually better. Traditional electromagnetic motors have limitations when it comes to shrinking dimensions while maintaining high efficiency and accuracy of motion with minimized energy consumption. Piezo ceramic inertia motors can fill this gap. The Q-Motion dubbed miniature direct drives can be employed in linear positioners, rotary stages, goniometer cradles, and even 6-axis parallel positioners. In addition to inertia motors, there are many other types of piezo motors, including ultrasonic drives and high-force piezo-walk drives.

Q-motion piezo inertia motors are extremely small. They allow the design of nanometer-precision mechanisms with scaled-down dimensions that were unthinkable a few years ago – ideal for integration into miniaturized instrumentation.

Stick-slip motors are especially cost-effective and can provide nanometer precision motion if required. They provide the best force/size ratio for smallest dimensions.

Working Principle

A piezoelectric ceramic actuator is preloaded against a moving runner. Controlled by a drive signal with a quasi saw-tooth shape, the actuator expands slowly and contracts rapidly (or in the opposite direction). During the slow expansion, the runner sticks to the coupling element and moves along, while during the rapid contraction, the coupling element slips along the runner, which basically stays in place.

Two different versions were developed optimized either for miniature size, moderate force or compact size and higher force.

1. Tangential Inertia Drive Motor

Very Small Dimensions
Simple Mechanics
To 2 N Holding Force

Watch Stick-Slip Working Principle Video

2. Mini-Rod Inertia Drive Motor

Mini-rod stick-slip principle, watch animation

Mini-Rod piezo inertia drives are based on an actuator moving a small rod – or moving along the rod if the rod is fixed. These motors are more powerful than the tangential drives, with up to 10N pushing/holding force. They can be integrated into linear actuators and linear positioning stages, however the principle does not apply to rotary stages.

The operating principle is shown in the animation.

Actuators based on the Mini-Rod drive: N-422 OEM version (left) and N-412 integrated actuator (right) (Image: PI) Learn more

The Q-545 linear positioning stage is based on the mini-rod drive principle. Vacuum version shown left, standard version shown right, 1” travel range. Encoder resolution to 1nm is available. (Image: PI) Learn more

An application of the Q-545.140 closed-loop servo linear stages in high resolution interferometry used for quantum information processing is described in this paper “Temporal-mode-selective optical Ramsey interferometry via cascaded frequency conversion” that deals with storage and retrieval of quantum information, written by Dileep V. Reddy and Michael G. Raymer, Oregon Center for Molecular, Optical and Quantum Science and Department of Physics, University of Oregon, Eugene, Oregon USA.

The nanopositioning stages used provide an encoder-based position read-out precision of 1nm.

The schematic above shows the setup of the two-stage, TM-selective optical Ramsey interferometer and the position of the Q-545.140 linear piezo motor stages that move the signal- and register-mirrors (s-mirror, r-mirror). Credit: https://arxiv.org/pdf/1710.06736 — The schematic above shows the setup of the two-stage, TM-selective optical Ramsey interferometer and the position of the Q-545.140 linear piezo motor stages that move the signal- and register-mirrors (s-mirror, r-mirror). Credit: arxiv.org/pdf/1710.06736 Learn more

Train of 6nm steps executed with Q-545 closed-loop stage, measured with laser interferometer at 5kHz sampling rate. The highest encoder resolution is 1nm. This type of resolution allows applications in high resolution microscopy. The LPS-45, a predecessor of the Q-545, was used for nanometer precise accurate positioning of the Fresnel Zone Plate along the optical axis of a compact stand-alone EUV microscope. (Image: PI) Learn more

Multi-axis combination of X-Z linear stage (Q-545), with high-speed U-628 ultrasonic miniature rotary stage. (Image: PI)

During the stick phase, the runner is moved in the defined direction.

During the slip phase, the runner does not move. The so-called back-stepping effect leads to a small backward motion during the acceleration phase of the piezo actuator.

The typical feed- motion per full cycle is 300 nm to 1 µm. It depends on the actuator type and force acting on the actuator.

The actuator can be controlled to any position within its range with sub-nm resolution by changing the drive voltage (analog mode).

(left) XY combinations mount directly without adapters. A Z-bracket is available for vertical applications.
(right) XYZ motion with combination of Q-521 stages, 12mm and 32mm travel – watch video

Self-Locking at Rest

As with most piezo motors, Q-Motion inertia drives are self-locking at rest. There is no power consumption, no heat dissipation, no position dither.

Velocity Control

Back-stepping Effect

Between each stick and slip cycle, a miniscule position shift called the back-stepping effect can be noticed. This effect is inseparably connected with the inertia drive principle and its relevance depends on the application.

Q-522.140 with E-871.1A1 controller • Operation Frequency 20 kHz • Data sample rate: 133 kHz • Time base: 0.3 milliseconds, which corresponds to 6 full stick-slip cycles

At a data sample rate of 133 kHz, a backstepping effect is too small to be noticed! Consequentially, we state that the backstepping effect does not influence the constancy and smoothness of velocity. However, there are other factors that directly influence the velocity.

Constancy of Velocity at a Microscopic Level

With the entry level E-871.1A1 motion controller, the selected velocity is reached by adjusting the operating frequency. Adjusting the frequency means that the voltage profile of a single step remains constant with pauses in between. The E-873 controller offers more sophisticated velocity control.

Simplified control voltage profile for different operating frequencies

Other Piezo Motor Drives

Force vs. velocity of different piezoelectric motors

Comparison of Different Piezo Motors

Lifetime

Lifetime is affected by load, duty cycle, environmental conditions (humidity, vacuum), etc., based on wear motion ranges of >20km are feasible.

Operation Recommendation

Duty Cycles

Ideal applications demand:

Duty cycles below 50 %
Continuous operating time <10 sec (2x back and forth across the complete travel range)

Product Overview

Linear Stages

Rotary Stages

6-Axis Parallel Positioners

In addition to linear and rotary positioners, linear stages can be combined to 6-axis parallel arrangements.

Q-821 6-axis miniature parallel positioner based on Q-521 linear stages compared to ball pen. • 80x80x48 mm³ • 1 nm sensor resolution

Q-845 6-axis vacuum positioner based on Q-545 linear stages

Motion Controllers

The E-873 3-channel motion controller features:

Broadband encoder input
Macro programmable for stand-alone functionality
Data recorder
Nonvolatile EEPROM for macros and parameters
Digital I/O ports (TTL)
ID chip support
Interfaces: TCP/IP and USB
Optional digital joystick for manual operation a single channnel version is available as the E-871

The E-870 driver features include:

For PIShift and PiezoMike Piezo Inertia Drives
Ideal for OEM Applications
One to Four Actuators, Serial Control (through demultiplexing)
With Digital USB interface
Host Software LabVIEW Driver Included

Download Technical Note for E-872 OEM Driver Learn more

Features of the E-872.01 and E-472.02 OEM driver include:

Step-Direction Input Signal
E-872.01: Full Step Modus
E-872.02: Micro Step Modus
Cost Effective

The E-873 Macro programmable specifications include:

Data Recorder
Digital I/ O Ports (TTL)
ID Chip Support
Interfaces: USB, RS-232 and TCP/ IP
Joystick Input for Manual Operation
Velocity Control
Compatible Sub-D Connectors for Q-Motion Stages
Optionally Available with Metal-Sheet Housing for OEM Applications

Vacuum and Nonmagnetic Operation

High-Vacuum to 10-6 hPa

Standard and unprepared Q-Motion stages can be used in ambient conditions and for vacuum up to 10-6 hPa. For vacuum operation, the C-815.VF vacuum feedthrough is available.

On the air side, the following cables will be available for connecting the feedthrough with the controller E-873 (plus adapter cable for E-871, which is included in the delivery of the stage):

These air-side cables also work for the feedthrough for UHV.

Ultrahigh Vacuum to 10-9 hPa

Ultrahigh vacuum models are also available.

Nonmagnetic Operation

PI is currently evaluating ceramic bearings for nonmagnetic stage designs. Nonmagnetic operation is of interest in the environment of electron beam imaging such as lithography or microscopy.

Tests in High Magnetic Fields

The KIT (Karlsruhe Institute of Technology) has performed tests in high magnetic fields of 9.4 Tesla (T). The stage (not operating) was not attracted by the magnetic field and was not magnetized.

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